Polylactic Acid: PLA Biopolymer Technology and Applications

Polylactic Acid

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Polylactic AcidPLA Biopolymer Technology and Applications

Lee Tin SinAbdul Razak Rahmat

Wan Azian Wan Abdul Rahman

AMSTERDAM � BOSTON � HEIDELBERG � LONDONNEW YORK � OXFORD � PARIS � SAN DIEGO

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Contents

1 Overview of Poly(lactic Acid) 11.1 Background to Biodegradable Polymers 11.2 Market Potential of Biodegradable Polymers

and PLA 131.3 General Properties and Applications of PLA 33

1.3.1 PLA for Domestic Applications 331.3.2 PLA and Copolymers for Biomedical

Applications 431.4 Environmental Profile of PLA 571.5 Ecoprofile of PLA in Mass Production 581.6 Environmental Impact of PLA at the

Post-Consumer Stage 631.7 Conclusion 67References 67

2 Synthesis and Production of Poly(lactic Acid) 712.1 Introduction 712.2 Lactic Acid Production 72

2.2.1 Laboratory Scale Production of Lactic Acid 852.3 Lactide and Poly(lactic Acid) Production 86

2.3.1 Review of Lactide Production Technology 882.3.2 Polymerization and Copolymerization of

Lactide 942.3.3 Lactide Copolymer 972.3.4 Quality Control 992.3.5 Quantification of Residual Lactide in PLA 1002.3.6 Quantification of D-Lactic Acid Content

in PLA 1032.4 Conclusion 105References 105

v

3 Thermal Properties of Poly(lactic Acid) 1093.1 Introduction 1093.2 Thermal Transition and Crystallization of PLA 1123.3 Thermal Decomposition 1233.4 Heat Capacity, Thermal Conductivity and

Pressure�Volume�Temperature of PLA 1313.5 Conclusion 138References 139

4 Chemical Properties of Poly(lactic Acid) 1434.1 Introduction 1434.2 Stereochemistry of Poly(lactic Acid) 1464.3 Analytical Technique of PLA 154

4.3.1 Nuclear Magnetic Resonance Spectroscopy 1544.3.2 Infrared Spectroscopy 157

4.4 Solubility and Barrier Properties of PLA 1624.4.1 Solubility of Polylactic Acid 1634.4.2 Permeability of Polylactic Acid 164

4.5 Conclusion 172References 172

5 Mechanical Properties of Poly(lactic Acid) 1775.1 Introduction 1775.2 Effect of Crystallinity and Molecular Weight

on Mechanical Properties of PLA 1795.3 Effect of Modifier/Plasticizer on PLA 1825.4 Polymer Blends of PLA 191

5.4.1 Poly(lactic Acid) and PolycaprolactoneBlend 192

5.4.2 Blends of Polylactide with Degradable orPartially Degradable Polymers 198

5.4.3 Blends of Polylactide andPolyhydroxyalkanoates 202

5.4.4 PLA Blends with Nondegradable Polymers 2075.5 Conclusion 215References 215

vi CONTENTS

6 Rheological Properties of Poly(lactic Acid) 2216.1 Introduction 2216.2 Rheological Properties of Poly(lactic Acid) 2226.3 Effects of Molecular Weight 2266.4 Effects of Branching 2306.5 Extensional Viscosity 2326.6 Solution Viscosity of PLA 2336.7 Rheological Properties of Polymer Blends 233

6.7.1 PLA/PBAT Blend 2356.7.2 Blend with Layered Silicate

Nanocomposites 2376.7.3 PLA/Polystyrene Blend 239


7 Degradation and Stability of Poly(lactic Acid) 2477.1 Introduction 2477.2 Factors Affecting PLA Degradation 2487.3 Hydrolytic and Enzymatic Degradation of PLA 2557.4 Environmental Degradation of PLA 2657.5 Thermal Degradation of PLA 2787.6 Flame Resistance of PLA 2887.7 Conclusion 295References 295

8 Applications of Poly(lactic Acid) 3018.1 Introduction 3018.2 Poly(lactic Acid) for Domestic Applications 3028.3 Poly(lactic Acid) for Engineering and

Agricultural Applications 3178.4 Poly(lactic Acid) for Biomedical Applications 3178.5 Conclusion 317References 326

Index 329

viiCONTENTS

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1 Overview of Poly(lactic Acid)

Chapter Outline1.1 Background to Biodegradable Polymers 11.2 Market Potential of Biodegradable Polymers and PLA 131.3 General Properties and Applications of PLA 33

1.3.1 PLA for Domestic Applications 331.3.2 PLA and Copolymers for Biomedical

Applications 431.4 Environmental Profile of PLA 571.5 Ecoprofile of PLA in Mass Production 581.6 Environmental Impact of PLA at the Post-Consumer

Stage 631.7 Conclusion 67References 67

1.1 Background to Biodegradable Polymers

People have been using polymers for thousands of years.In ancient times natural plant gum was used to adhere pieces ofwood in house building. When the ancients started to explore theoceans, natural plant gum was applied as a waterproof coating toboats. At that time people did not know the extent to which poly-mers could be put to use, so their use was limited to very specificapplications. Of course, the ancients depended on plant-derivedpolymers. No modifications were made to their formulation, norwere polymers synthesized to improve applications.

Natural rubber has been known about since 1495, whenChristopher Columbus landed on the island of Haiti and sawpeople playing with an elastic ball. At that time rubber latexwas harvested from the rubber tree Hevea brasiliensis as asticky lump, which had limited applications. However, by 1844Charles Goodyear discovered and patented a method to sulfur

1Polylactic Acid. DOI: http://dx.doi.org/10.1016/B978-1-4377-4459-0.00001-9

© 2012 Elsevier Inc. All rights reserved.

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vulcanize rubber, and since then it has been widely used in thetire industry.

The first synthetic polymer was invented by Leo HendrikBaekeland in 1907. This was a thermosetting phenol-formaldehyderesin called Bakelite. In recent decades, the rapid developmentof polymers has made a large contribution to technology withthe invention of a highly effective catalytic polymerizationprocess. Because commodity polymers � polyethylene, polypro-pylene, polystyrene and poly(vinyl chloride) (PVC) � can beproduced so cheaply, their use has been exploited for the massproduction of disposable packaging. Thus, around the world,polymer pollution has become a serious issue. These petroleum-derived commodity synthetic polymers require hundreds ofyears to fully degrade into harmless soil components. This,together with the reducing reserves of crude oil, is encouragingresearch into the development of renewable sources of rawmaterials for polymers. Figure 1.1 shows the general trend ofpolymer development globally.

Although steps have been taken to educate people about theenvironmental impact caused by the exploitation of plastics,these materials continue to represent the largest proportion of

Natural polymers(amber, shellac, tar, latex...)

Synthetic polymers(PE, PP, PS, PVC, rayon...)

Polymers blending with biomass(lignocellulosic, starch, straw...)

Biodegradablepolymers

Renewable source of rawmaterials

Non-renewable source ofraw materials

Poly (vinyl alcohol)PolycaprolactonesPolyanhydrideAliphatic co-polyesterAromatic co-polyesters

Poly (lactic acid)PolyhydroxybutyratePolyhydroxyvalerateCellulose acetate

Ancient

Present

Tim

e a

sc

en

din

g

Figure 1.1 Trends in polymer development.

2 POLYLACTIC ACID

domestic waste. Conventional plastic waste takes a very longtime to be broken down into harmless substances comparedwith organic material. For instance, a telephone top-up cardtakes over 100 years to naturally degrade, while an apple corerequires just 3 months to be naturally transformed into organicfertilizer. Due to the better degradability of biomass overconventional plastics, polymer�biomass blends were the firststep in providing alternatives to help reduce plastic waste pro-blems. Generally, abundant biomass such as lignocellulosicsand starches are blended with synthetic polymers. These poly-mer compounds are partially degradable by microorganisms.However, after the biomass portion has been consumed, theleftover polymer skeleton will still cause harmful effects to theenvironment.

These days, the focus is on developing environmentallyfriendly polymers. These polymers are naturally degradablewhen disposed in the environment. The carbon footprint of pro-duction of these polymers is monitored to ensure sustainableenvironmental protection.

Biodegradable polymers can be divided into two categories �petroleum-derived and microorganism-derived biodegradablepolymers (see Figure 1.1). The petroleum-derived biodegradablepolymers, such as poly(vinyl alcohol) (PVOH), use ethylene toproduce vinyl acetate for polymerization of poly(vinyl acetate)and is further hydrolyzed into PVOH. The production costof this polymer is very sensitive to the fluctuation of crude oilprices and it is not environmental friendly, due to the emissionof greenhouse gases during production. However, microorgan-ism-derived biodegradable polymers utilize the bio-activityof bacteria to convert plant products, such as starch, into thestarting product for polymerization. Poly(lactic acid), alsoknown as polylactide (PLA), is the subject of this book, and isproduced in this way, utilizing the activity of microorganisms.Polyhydroxylalkanoate is also the product of bacterial fermenta-tion. These polymers use renewable feedstock, and the productionprocess possesses carbon credit.

There are also some polymer products on the market calledoxo-biodegradable plastics. These so-called ‘biodegradable’

31: OVERVIEW OF POLY(LACTIC ACID)

plastics have caused controversy, and disputes with environ-mentalists. Oxo-biodegradable plastics are actually degradedusing a controlled catalyst to kick-start a chain-scissioningreaction to attack the polymer macromolecules. This catalystis made of series of active organo transition metals, which areadded to the polymer. When oxo-biodegradable polymers areexposed to ultra-violet light and free oxygen attacks, the chain-scissioning reaction occurs extensively, finally reducing theplastic to carbon dioxide. In the market, the oxo-degradationadditives are mostly added to polyethylene and polypropylene.The additives are present in very small amounts (,1%) andare highly effective. Nevertheless, controversy has also arisenabout these types of ‘eco-friendly’ plastics because they arestill derived from petroleum-based products and the degrada-tion still generates carbon dioxide, which is against the princi-ple of carbon credit products. In the short term, these plasticsmay help to reduce the burden on landfill. However, the useof these oxo-biodegradable materials also causes other environ-mental problems. The most serious of these is that the plasticstake time to be fully degraded into carbon dioxide. During theearly breakdown process, fragmentation of the plastic causespollution to the soil, and this can be accidentally consumedby organisms living off the soil. Again, this has shown that afully biodegradable polymer with carbon credit is crucial fora sustainable future.

Prior to a more detailed discussion of PLA, several biode-gradable polymers will now be examined and compared withPLA, to determine the reasons for which PLA is the most pop-ular among the biodegradable polymers nowadays. PVOH andPLA are the most widely produced biodegradable polymers,while other biodegradable polymers, such as polycaprolactoneand polyhydroxylbutylarate, are produced in small quantitiesat the laboratory scale or at pilot plants. In 2006 the world pro-duction of PVOH reached over 1 million metric tons (MT) perannum. However, PVOH is a petrochemical-type biodegradablepolymer. The major markets for PVOH are textile sizing agents,coatings and adhesives. Only a limited amount of PVOH ismade for packaging applications. The main reason for this is the

4 POLYLACTIC ACID

hydrophilic behavior of PVOH. Prolonged environmental expo-sure causes PVOH to absorb moisture extensively. There arehydrolyzed and partially hydrolyzed forms of PVOH. Both typesof PVOH are soluble in water, and the solubility temperatureof hydrolyzed PVOH is higher. The major producer of PVOHis Kuraray, in the United States, which has nearly 16% of theworld’s production. China is still the country that producesthe most PVOH; it accounts for 45% of the global output.

In the early 1800s PLA was discovered when Pelouze con-densed lactic acid through a distillation process of water to formlow-molecular-weight PLA. This is the early polycondensationprocess of lactic acid to produce low-molecular-weight PLAand lactide. Lactide is a pre-polymer or an intermediate prod-uct used for the transformation to high-molecular-weight PLA.This polycondensation process merely produces low yieldand low purity PLA. Almost a century later, DuPont scientistWallace Carothers found that the heating of lactide in a vac-uum produced PLA. Again, for high purity PLA this processis not feasible on an industrial scale due to the high costof purification, which limits it to the production of medicalgrade products, such as sutures, implants and drug carriers.The ambitious company Cargill has been involved in theresearch and development of PLA production technology since1987, and first set up a pilot plant in 1992. Later on, in 1997,Cargill and Dow Chemical formed a joint venture namedCargill Dow Polymer LLC to further commercialize PLA.Their efforts have been fruitful, with the introduction of pro-ducts branded as Ingeot. As part of this joint venture, Cargillhas made efforts to improve the hardening time for productsmade of PLA, while Dow has focused on the manufacture ofPLA (Economic Assessment Office, 2007). Generally, PLA’smonomer, lactic acid, can be obtained from the fermentationof dextrose by bacteria; dextrose is derived from plant starch.Thus, PLA is a polymer made from renewable sources, andhas the potential to reduce our dependence on conventionalplastics made from fossil-based resources. In recent years, PLAresearch has developed tremendously, with many inventions andpublications globally (see Figures 1.2 and 1.3).


In addition to PVOH and PLA, there are some other biode-gradable polymers on the market; these are listed in Table 1.1.These polymers are only produced on a small scale, primarilyfor biological applications, but also for exploration of commer-cial potential. Most of the biodegradable polymers are in thepolyesters group. Biodegradable polymers can be derived fromrenewable and non-renewable sources (see Figure 1.4). Useful

Data source from Web of Science

Year

1000

1950

1966

1967

1971

1972

1973

1974

1975

1976

1977

1978

1979

1980

1981

1982

1983

1984

1985

1986

1987

1988

1989

1990

1991

1992

1993

1994

1995

1996

1997

1998

1999

2000

2001

2002

2003

2004

2005

2006

2007

2008

2009

800

600

400

200

0

Pu

blicati

on

s

Figure 1.2 Research publication about PLA 1950�2009.

0

5000

USPO WIPO EPO JPO UKPO

10000

15000

20000

25000

30000

35000

4000038722

19891

6105

2209 386

Num

ber

of P

aten

t

Data Source from Scopus asper 3rd Dec 2010

Figure 1.3 Number of patents published about PLA (USPO5UnitedStates Patent Office, WIPO5World Intellectual Property Organization,EPO5European Patent Office, JPO5 Japanese Patent Office,UKPO5United Kingdom Patent Office).

6 POLYLACTIC ACID

Table 1.1 Some Common Biodegradable Polymers on the Market

Polymer Chemical Composition Producer Applications Biodegradability

ε-Polycaprolactone(PCL) (CH3)5C C

O

n

DURECT

Corporation:

Lactels

Ethicon:

Monocryls �suture;

.12 months

Daicel Chemical

Industry:

Celgreens

Capronors �contraceptive

implant

Union Carbide

Corporation:

TONEs

Agrotec: Agrothanes�paint and metal

protection film

Solvay Group:

CAPAs

Purac: Purasorbs

PC 12

Polyglycolide or

polyglycolic acid

(PGA)CH2O C

O

n

Purac: Purasorbs

PG 20

Dolphin:

Petcryls � sutures;

.3 months

Teleflex Incorporated Bondeks � sutures

Kureha Corporation Dexont S � sutures

DemeTechs � sutures

Table 1.1 Some Common Biodegradable Polymers on the Market—cont’d

Polymer Chemical Composition Producer Applications Biodegradability

Polyhydroxyalkanoate:

polyhydroxybutyrate

(PHB) and

polyhydroxylvalerate

(PHBV)

CHCH3

CH2O CO

n

CHCH2

CH2O CO

n

CH3

(PHB)

(PHV)

Metabolix/ADM

(Telles): MireltCompost bags 3�12 months

Ningbo Tianan

Biologic Material:

Enmatt

Consumer packaging

Copersucar:

Biocycles

Agriculture/

horticulture film

Biomer: Biomers

Rubbermaids,

Calphalons,

PaperMates

BioTuftEcoGent

Polydioxanone (PDO)

CH2 CH2O CH2O CO

n

Ethticon DemeTechs sutures ,7 months

Samyang Duracryls sutures

D-Teks sutures

Surgeasys sutures

Ethicons PDS� II

sutures

OrthoSorbs pin

Cellulose acetate O

O

O

O

CH3

H3CCH3

CH3

O

HOHO

n

O

O

OO O

OO

Celanese Cigarette filters ,24 months

(depends on

acetate content)

Rhodia Textiles

Spectacle frames

Film media

Wound dressings �ADAPTICt

Biocetas: toothbrush

biodegradable polymers are not limited to neat polymers, but alsoinclude copolymers (polymerization of different monomers), thelatter having improved biodegradability and structural properties.Polycaprolactone (PCL), polyglycolic acid (PGA) and polydioxa-none (PDO) are common biodegradable materials for sutures,pins and drug carrier implants. Generally, PGA and PDO arepreferable to PCL in biomedical applications because PCL takeslonger to be resorbed in vivo. A clinical study of the PCL-basedimplantable biodegradable contraceptive Capronors, containinglevonorgestrel, remains intact during the first year of use and isfinally degraded and absorbed by the body (Darney et al., 1989)after two years.

Polyhydroxybutyrate (PHB) and poly-3-hydroxybutyrate-co-valerate (PHBV) both belong to the polyhydroxyalkanoates (PHA),

Biodegradable Polyester

AromaticAliphatic

PLA PCL PHA

PHB PHV PHH PBAT PRMATPBSA

PHB/PHHPHB/PHV

AAC – Aliphatic-Aromatic CopolyestersPBAT – Poly(Butylene Adipate/Terephthalate)PET – Poly(Ethylene Terephthalate)PBS – Poly(Butylene Succinate)PBSA – Poly(Butylene Succinate/Adipate)PCL – PolyCapro LactonePLA – Poly(Lactic Acid)PHB – Poly(Hydroxy Butyrate)PHH – Poly(Hydroxy Hexanoate)PHV – Poly(Hydroxy Valerate)PTMAT – Poly(TetraMethylene Adipate/Terephthalate)

PBS Modified PET AAC

Renewable

Non-Renewable

Figure 1.4 Biodegradable polyester family.

10 POLYLACTIC ACID

that are also being developed using biological fermentation ofdextrose. A joint venture between Metabolix and ADM, underthe name of Tellest, has produced PHB with trade nameMirelt. Their PHB compost bags take 6�12 months to be natu-rally degraded. Sanford, the international stationary manufac-turer, uses PHB in their famous PaperMates product range.PHB is not easily degraded under normal condition of usage orstorage, even in a humid environment. However, when aPaperMates pen made of PHB is buried in soil and compost thepen decomposes in nearly a year.

Cellulose acetate is commonly used for cigarette filters,textiles, spectacle frames and film media. Since the early partof the 20th century, cellulose acetate has been a very impor-tant base material for the photographic film industry. Overthe decades, the application of cellulose acetate has changed.Nowadays, a modified cellulose acetate has been producedthat is suitable for injection molding to produce biodegradableplastic articles. Some ranges of sunglasses marketed by LouisVuitton are made of cellulose acetate. This material comesin a wide variety of colors and textures and has the abilityto be adjusted easily, but it tends to become brittle with age.A knitted cellulose acetate fabric treated with a specially for-mulated petrolatum emulsion is used as a wound dressing � ithelps to protect the wound and prevents the dressing fromadhering. Prolonged exposure of cellulose acetate to moisture,heat or acids reduces the acetyl (CH3C) groups attached to thecellulose. The degradation process causes the release of aceticacid; this is known as ‘vinegar syndrome’. This is why whencellulose acetate film is stored under hot and humid condi-tions there is a release of saturation acetic acid resulting insmelt. The release of acetic acid further attacks the polymerchain and deteriorates the cellulose. A study of cellulose ace-tate reported by Buchanan et al. (1993) showed that celluloseacetate was biodegraded in a wastewater treatment assay byapproximately 70% in 27 days to cellulose diacetate; the rateof degradation also depended on the degree of substitutionof acetate. A high degree of substitution of acetate requireslonger exposure.


As can be seen, most of the biodegradable polymers men-tioned belong to the polyester group (see Figure 1.4). This isdue to the ester-containing covalent bond with a reactive polarnature. It can be broken down easily by the hydrolysis reaction.The biodegradable polyesters can be divided into aliphatic andaromatic groups, with members of each group being derivedfrom renewable and non-renewable sources. PLA and PHA areboth aliphatic polyesters from renewable agricultural sources,while PCL and PBS/PBSA are aliphatic polyesters producedfrom non-renewable feedstock. Most of the PCL on the marketis used in biomedical applications. PBS/PBSA as marketedby Showa Denko, under tradename Bionollet, is supplied forJapanese local government programs for packing domesticsolid waste before collection. Generally, all the aromatic polye-sters are produced from petroleum. Some consider the petro-leum-based biodegradable polymers to be more viable thanbio-based biodegradable polymers. The reason is that the man-ufacture of bio-based polymers has led to competition betweenfood supply and plastic production, and this continues to be anissue as many people in the third world are still living withfood shortage. However, this view should not be an obstacleto the development of bio-based polymers, because a smallstep in this direction has the potential to lead to a giant leap inreducing our dependence on fossil resources.

BASF has introduced their aliphatic-aromatic copolyesters(AAC) product under the name Ecoflexs. This material iswidely used to produce compostable packaging and films.According to the BASF’s corporate website, annual produc-tion of Ecoflexs has risen to 60,000 MT to keep up with thedemand for biodegradable plastics, which is growing at a rateof 20% per year. At the same time, BASF also produces ablend of polyester and PLA � a product called Ecovios. Thishigh-melt-strength polyester�PLA can be directly processedon conventionally blown film lines without the incorporationof additives. Moreover, Ecovios has extraordinary puncture-and tear-resistance and weldability. Another company, Eastman,has also produced AAC, with the tradename Eastar Bios. EastarBios has a highly linear structure, while Ecoflexs contains

12 POLYLACTIC ACID

long-chain branching. Late in 2004, the Eastar Bios AACtechnology was sold to Novamont S.p.A. Eastar Bios is mar-keted in two different grades: Eastar Bios GP is mainly forextrusion, coating and cast film applications; Eastar Bios Ultrais marketed for use in blown films. A study reported by BASF(2009) shows that the AAC of Ecoflexs has comparable biode-gradability to cellulose biomass, which is 90% degraded in180 days as per CEN EN 13432. This has shown that a petro-leum-based biodegradable polymer can be as good as a naturalmaterial in terms of degradability.

The conventional polyethylene terephthalate (PET) takeshundreds of year to naturally degrade. However, the situtationis different with PET with appropriate modification, such asco-monomer ether, amide or aliphatic monomer. The irregularweak linkages promote biodegradation through hydrolysis. Theweaker linkages are further susceptible to enzymatic attack onthe ether and amide bonds (Leaversuch, 2002). Such modifiedPET materials include polybutylene adipate/terephthalate (PBAT)and polytetramethylene adiphate/terephthalate (PTMAT). DuPonthas commercialized Biomaxs PTT 1100 with a plastic meltingpoint of 195�C for high service-temperature applications. Thisproduct is suitable for use as fast-food disposable packaging forhot food and drink. In general, the development of biodegradablepolymers is still in the preliminary stages and it is anticipatedthat this will expand in the near future.

1.2 Market Potential of BiodegradablePolymers and PLA

Plastics manufacturing is the major industry worldwide.Every year, billions of tons of virgin and recycled plastics areproduced. The world production of plastics has increased160 times in a little less than 60 years, from 1.5 million tonsin 1950 up to 245 million tons in 2008. Figure 1.5 shows thatthe production of polymers has increased year on year, with theexception of 2008, which showed a reduction in plastic produc-tion due to the global financial crisis. The demand for plastics


soon recovered with the rebound of the world economy. This isevidenced by the fact that the giant global producers DowChemical, ExxonMobil Chemical, and BASF showed double-digitgains in sales and volumes (Plastics Today, 2010). Dow ChemicalCompany reported sales were up 15% in all geographic areas inthe fourth quarter of 2010. This was contributed to by the highgrowth in the automotive industry and the need for elastomermaterials for the increased demand for vehicles worldwide. BASFreported an increase in sales by 26% in the first quarter of 2010due to substantial volume gains from the automotive and electri-cal/electronic sectors. Sales of the giant chemical companyExxonMobil rose 38%, or US$6.3 billion, in the first quarter of2010 due to the larger chemical margins, with a large portion con-tributed by its plastic business.

Overall, the worldwide demand for plastic is forecast to be45 kg per capita by 2015 (PlasticsEurope, 2009). The plasticsmarket is still a big cake to be shared among the existingplayers, and newcomers will also have the opportunity to gain amarket share. From research data provided by the global

Mtonne

300

250

200

150

100

50

01950 1960 1970 1980 1990 2000

2008: 2452002: 200

1989: 100

2008: 60

Europe

World

1976: 50

1950: 1.5

Figure 1.5 World plastics from 1950 to 2008 (adapted from PlasticsEurope, 2009, with permission).

14 POLYLACTIC ACID

management consulting company Accenture (2008), the highestgrowth in polymer consumption belongs to the electrical/elec-tronics sector. The highly sophisticated electrical/electronic pro-ducts on the market, such as smart phones, computers andentertainment appliances, require durable and lightweight parts,which make polymers crucial for use in their design. A varietyof plastic products, both liquid and solid, including packaging,toys, containers and stationery, remains the sector with the high-est polymer consumption, with forecasts reaching 78,361 thou-sand MT per annum (see Table 1.2).

These figures provide strong evidence that the demand forplastic products will grow further in future. However, the major-ity of polymers on the market are petroleum-based products.Although the current price of crude oil has returned to an afford-able level since the price hike to US$147 per barrel in July 2008,

Table 1.2 World Polymer Consumption

Market Sector 2006(ThousandMT)

2016(ThousandMT)

2006�2016CompoundAnnual GrowthRate (%)

Food 42,025 71,774 5.5

Textiles 32,176 51,630 4.8

Furniture 13.687 22,993 5.3

Printing 780 1,220 4.6

Plastic products 43,500 78,361 6.1

Fabricated metals 1,519 2,259 4.0

Machinery 2,397 3.658 4.3

Electrical/electronic 13,810 25,499 6.3

Other transportation 9,330 16,181 5.7

Vehicles & parts 10,746 15.625 3.8

Other equipment 3,852 6,334 5.1

Other manufacturing 21,238 33,569 4.7

Construction 45,886 72,919 4.7

Total 240,947 402,022 5.3

Data: Accenture, 2008.


the price of many petroleum commodity products, especiallypolymers, has reached a historical high. Today, many believethat another petroleum price hike is very likely to happen in thenext decade, due to the limited crude oil reserves. Continualexploitation of these natural resources has also caused seriousglobal warming. Thus, the search for alternative sources of energyand non-petroleum based products is crucial for a sustainableeconomy and environment.

As mentioned previously, biodegradable polymers can bederived from both petroleum and renewable sources. Bothtypes of biodegradable polymers have attracted attention in theindustry. Petroleum-based biodegradable polymers may help toovercome the accumulation of non-degradable plastic waste.However, renewable biodegradable polymers not only possessbiodegradability, but the polymers are also derived from sus-tainable sources with environmental credit.

Many countries have imposed regulations to reduce or ban theuse of non-degradable plastics for environmental protection. Forinstance, China, the largest polymer-consuming country with apopulation of 1.3 billion, has banned the usage of plastic bags.Major supermarkets do not provide free plastic bags to their cus-tomers. These actions have helped to save at least 37 millionbarrels of oil per year. In Europe, several regulations have drivenforward organic waste management to help reduce soil/waterpoisoning and the release of greenhouse gases. Recycling of bio-waste is the first measure to reduce the generation of methane (agreenhouse gas) from landfills. Directive 1999/21/EC on theLandfill of Waste requires European Union members to reducethe amount of biodegradable waste to 35% of 1995 levels by2016. The second measure is to increase the usage ofcompostable organic materials, so that they become useful inhelping to enrich the soil. This can help replace the lost carbonfrom the soil as emphasized in Directive 2008/98/EC on waste(Waste Framework Directive). Following the introduction ofDirective 94/62/EC on Packaging and Packaging Waste, whichimposed requirements for plastic and packaging waste, plasticand packaging waste should now fulfill the European standardEN 13432, with these materials to be declared as

16 POLYLACTIC ACID

compostable prior to being marketed to the public (EuropeanBioplastics, 2009).

Ireland was one of the first countries to introduce a plasticbag levy. Ireland’s Department of Environment, Heritage andLocal Government introduced a charge of 15 cents on plasticbags in 2002. This move had an immediate effect, reducing theusage of plastic bags from 328 to 21 bags per capita. After thisencouraging outcome, the Irish Government increased the levy to22 cents, further reducing the usage of plastic bags (IDEHLG,2007). Although biodegradable plastic bags degrade more quicklythan standard ones, the Irish Government did not distinguishbetween the two in their laws. However, reusable plastic bagssold in the shops are exempt from the levy, with the conditionthat they should not be sold for less than 70 cents.

Because the use of plastic bags is not entirely avoidable inmodern life, the production of reusable plastic bags made of acompostable material is recommended, so that disposal will notburden the environment. As people have become more awareabout using compostable packaging, many companies havetried to make their products at least appear to have such pack-aging. Consequently, various types of ‘eco-packaging’ are avail-able in the market. Such eco-plastic products need to undergo aseries of tests to verify their biodegradability and compostability.In the European Union, compostable packaging must fulfill therequirements of EN 13432, while other countries have their ownstandard to be met in order to allow the use of a compostable logo(see Table 1.3).

The production of biodegradable polymers has increasedtremendously over the past few decades. In an overview of theproducts and market of bio-based plastics by Shen et al. (2009)known as PRO-BIP 2009, the global output of bio-based plasticswas 360,000 MT in 2007. This represents only 0.3% of the totalamount of plastic produced worldwide. However, the productionof bio-based plastics has grown rapidly, at a rate of 38% annuallybetween 2003 and 2007 (Shen et al, 2009). Shen et al. (2009)have predicted that bio-based plastic production will increaseto 3.45 million MT in 2020, and will be primarily made up ofstarch plastics (1.3 million MT), PLA (800,000 MT), bio-based


Table 1.3 Certification of Compostable Plasticfor Different Countries

Certificating Body Standard ofReference

Australia Bioplastics

Association

(Australia)

EN 13432: 2000

www.bioplastics.org.au

Association for

Organics Recycling

(UK)

EN 13432: 2000

www.organics-

recycling.org.uk

Polish Packaging

Research and

Development Centre

(Poland)

EN 13432: 2000

www.cobro.org.pl/en

DIN Certco

(Germany)

EN 13432: 2000

www.dincertco.de/en/

Keurmerkinstituut

(Netherlands)

EN 13432: 2000

www.keurmerk.nl

Vincotte (Belgium) EN 13432: 2000

www.okcompost.be

Jatelaito-syhdistys

(Finland)

EN 13432: 2000

www.jly.fi

Certiquality/CIC

(Italy)

EN 13432: 2000

www.compostabile.com

18 POLYLACTIC ACID

http://www.bioplastics.org.au

http://www.organics-recycling.org.uk

http://www.organics-recycling.org.uk

http://www.cobro.org.pl/en

http://www.dincertco.de/en/

http://www.keurmerk.nl

http://www.okcompost.be

http://www.jly.fi

http://www.compostabile.com

polyethylene (600,000 MT) and PHA (400,000 MT). Bio-basedpolyethylene is the produced from the feedstock of ethylene,which is based on the dehydration of bio-ethanol from sugarfermentation. A large number of bio-based projects have beenstarted in the United States, Europe and Japan, and then produc-tion has been transferred to other parts of the world.

Based on the information from Shen et al. (2009), the produc-tion output for different types of biodegradable polymer in 2009is summarized in Figure 1.6. Cellulose-based polymers representthe largest proportion of biodegradable polymers globally.Cellulose polymers are mainly used in the manufacture of fiber

Table 1.3 Certification of Compostable Plasticfor Different Countries—cont’d

Certificating Body Standard ofReference

Biodegradable Products

Institute (USA)

ASTM D 6400-04

www.bpiworld.org

Bureau de

normalisation du

Quebec (Canada)

BNQ 9011-

911/2007

www.bnq.qc.ca

Japan BioPlastics

Association

(Japan)

Green Plastic

Certification

System

www.jbpaweb.net


http://www.bpiworld.org

http://www.bnq.qc.ca

http://www.jbpaweb.net

for textiles, bedding, cushions, filters, etc. Most of the celluloseis harvested from cotton and chemically treated or modified tosuit the end use. Starch-based polymers relate to starch�polymerblends and thermoplastic starch. Companies such as NovamontS.p.A, Plantic DuPont and Cereplast blend starch with othersynthetic polymers to improve the processability and mechanicalproperties of the starch alone. Normally, blending of starch witha biodegradable polymer such as PCL, PLA and PHB is prefera-ble, to ensure the resulting blends are fully biodegradable. Somestarch-based polymer producers also blend starch with polyole-fin. These starch�polymer blends are partially degradable, withstarch initiating the degradation. However, the leftover polymerskeleton can still cause harmful effects to the environment.

PLA, PHA and other biodegradable polymers contributed to14% of the world production in 2009. PLA is the most widelyproduced of the renewable biodegradable polymers. Currently,most of the renewable biodegradable polymers are still in thedeveloping stages. PLA represents a large portion of the marketbecause of the maturity of its technology for mass production.Technologists prefer PLA due to its renewable feedstock forcarbon credit. The establishment of downstream processing and

PLA5%

Starch Based6%

Others (PBS, PBT, PCL, PBAT etc.)7%

Cellulose based80%

PIIA2%

Figure 1.6 World production of renewable biodegradable plasticsin 2009.

20 POLYLACTIC ACID

the market by renowned producers, especially NatureWorks,have also contributed to the expansion of PLA production in arange of countries. In the coming decade, the production ofPLA may overtake the sum of other biodegradable polymers,such as PBS, PBT, PCL, PBAT, etc. (see Figure 1.7). Futuremass production and market competition will also assist thedevelopment of economically viable technology to offer cheaperproducts. Investors are likely to favor bulk production PLA withits known profitability and long-term low-cost feedstock fromagricultural sources. Moreover, the development of starch-basedand other bio-plastics will also increase demand for PLA. Thisis because fully biodegradable starch blended with PLA helpsto improve the properties of the weaker starch structure itself.Similarly, BASF’s aliphatic-aromatic copolyester Ecovios is

1400

Starch Based

PLA

PHA

Others

1200

1000

800

Met

ric T

on

600

400

200

02003 2007 2009 2013

Year

2020

Figure 1.7 World production of renewable biodegradable polymersin 2003 to 2020 (projected).


blended with PLA for better processability and flexibility ofthe end product.

Figure 1.8 shows the average prices of biodegradable plasticsand conventional commodity plastics in 2009. The price ofPLA is the lowest of the biodegradable polymers. The nearestcompeting biodegradable polymer is PVOH, which is producedby hydrolysis of polyvinyl acetate from petroleum sources.PLA and PVOH are very unlike to compete directly in thebiodegradable polymer industry due to their respective charac-teristics. PVOH possesses hydrophilic properties, and is usedas a sizing agent, adhesive and paper coating. Only a limitedamount of PVOH is used for the manufacture of packagingfilm for food. PVOH tends to be soluble in water at 90�C.In contrast, PLA is hydrophobic, and has the potential to beused as a substitute for some of the existing polyolefin polymers.The starch-based plastics have a higher price compared to PLA;this can be attributed to the technological processing of starch,which is remarkably complex. Starch needs to be blended withother polymers, such as PP and PLA, and, consequently, thisleads to higher costs and extra processing on melt blending of

6.00

5.00

4.00

3.00

2.00

Avera

ge p

rice (

Eu

ro/k

g)

1.00

0.00

PLA

Starc

h Bas

ed

Cellulo

se

PHBVPHB

PBTPBS

HDPE PP PSPVC

PVOH PCPET

EVA

4.00

5.00

3.50

1.90

3.40

2.50

3.50

1.20 1.101.40

1.00

2.10

3.70

1.501.60

Figure 1.8 Average prices of polymers in 2009.

22 POLYLACTIC ACID

starch with PP or PLA. Although cellulose is the biodegradableplastic most produced, its price remains higher due to its spe-cialty application. The ability of cellulose to be injection moldedis also limited. Extra treatment and modification of cellulose iscrucial for processability using injection molding.

From the direct comparison in Figure 1.8, PLA is thenearest competitor to the commodity polymers PE, PP, PS,PET and EVA. At the same time, the price of PLA is muchless than PC. The potential of PLA to substitute PC is great,especially in the fabrication of electric/electronic casings.Fujitsu has introduced a laptop casing made of PC and PLA.This PC�PLA laptop casing has a 14.8% lower carbon oxideemission compared to conventional PC�ABS casing. Overall,the PLA resin price is relatively high compared to commodityplastic. However, increasing production efficiency and a com-petitive marketplace are likely to provide better prices in thenear future.

Although PLA was first synthesized in the early 1800s, thedevelopment of PLA has taken long time to reach productionviability. In the early stages of commercialization, the PLAproduced was limited to use in biomedical devices, because thecost of synthesis was expensive and was not mass-produced.Direct polycondensation requires critical process control inorder to achieve high-molecular-weight PLA. In the 1990s, themarket for PLA started to expand, with the first pilot plantbeing set up in 1992 by Cargill, using the indirect polymeriza-tion of lactide monomer for a higher production yield of PLA.In 1997, the Cargill and Dow Chemical joint venture foundedthe company NatureWorks with their preliminary commercialproducts coming to market under the name Ingeot. A plantwas built at Blair, in the United States, costing US$300 millionin 2002. Later, in 2007, Dow Chemical sold its 50% stake inNatureWorks to Japan’s Teijin. Teijin has been very committedto developing green plastic technologies to expand theirexisting polymer resins range. During the recent economicdownturn, Teijin underwent restructuring, and transferred its50% ownership to Cargill (Teijin 2009; NatureWorks, 2009a).Teijin is now focusing in the development of their PLA product


BIOFRONTt, a heat-resistant type of PLA plastic for substitu-tion of PET. BIOFRONTt has 40�C higher melting tempera-ture than existing poly-L-lactic acid. Teijin’s BIOFRONTthas been produced in collaboration with Mazda, to develop acar-seat fabric made of 100% bio-based fibers (Teijin, 2007).More recently, Teijin has announced the co-development ofa PLA compound with Panasonic Electric Works; MBA900Hhas superior moldability, and 1000 MT are set to be producedin 2012. Since the withdrawal of Teijin, NatureWorks has beenwholly owned by Cargill. In a March 2009 corporate pressrelease, NatureWorks announced that the company is assessingplans for a new production plant for Ingeot (NatureWorks,2009b). Ingeot is used by hundreds of leading brands andretailers in the United States, Europe, and Asia (see Table 1.4).

Purac, currently the world’s largest lactic acid producer, oper-ates a lactic acid plant in Thailand with an annual output of100,000 MT in 2007. This entire plant has the capacity of200,000 MT annually in the future. Currently, Purac supplies over60% of lactic acid globally from its operation facilities located inthe Netherlands, Spain, Brazil and the United States. Purac hasbeen manufacturing PLA and PLA copolymers for biomedicalapplications such as sutures, pins, screws and tissue scaffoldingmaterials. In planning for further business expansion and with thematurity of the PLA market, Purac has decided to utilize itsproduction of lactic acid for PLA manufacture. With its existinghigh-volume production of lactic acid, Purac has the opportunityto convert lactic acid into L-lactide and D-lactide under the brandname PURALACTt. Purac has invested EUR45 million to pro-duce 75,000 MT of PLA at its lactide plant in Thailand. Recentlyon February 2012, Purac announced the plant has completed andis currently undergoing commissioning. Several batches of lactidehave been produced and ready to be delivery to customers.

Purac in the Netherlands and Sulzer Chemtech AG inSwitzerland have joined forces to produce PLA foam. Synbra,a company in Etten-Leur, Netherlands, has been engaged toset up the PLA foam technology for Purac�Sulzer, expandingtheir product range, which includes a green polymer foam

24 POLYLACTIC ACID

Table 1.4 Examples of PLA Product Applications

Company Area ofApplication

MarketProducts

CL Chemical

Fibers

Spunbond fabrics Medical

applications,

shopping bags

and landscape

textiles

Dyne-a-Pak Foam meat trays Dyne-a-Pak

Naturet tray

Bodin (France) Foam tray Tray for meat,

fish and

cheese

CDS srl Food serviceware Cutlery

Cargo

Cosmetics

Casings Casings for

cosmetics


Table 1.4 Examples of PLA Product Applications—cont’d


MarketProducts

DS Technical

Nonwoven

Exhibition grade

carpeting

Ecopunchs

carpets

Sant’Anna,

Swangold,

Cool Change,

Good Water,

Primo Water

Bottles Bottle for juice

and still water

Natures

Organics

PLA bottles Shampoo bottle

in Australia

Naturally Iowa EarthFirsts shrink

sleeve label

Bottles for

debuted

Yogurt 7.0

Priori Cosmestic

packaging

CoffeeBerrys

26 POLYLACTIC ACID



MarketProducts

Frito-Lay Packing bags SunChipss

InnoWare

Plastics

Deep hinged trays

and lids

ECO

OctaViewtand ECO

ExpressionstAhlastrom Nonwoven fabric Tea bags

Telecom Italia

and MID

product

design studio

Telecommunication

casing

Cordless

telephone

Carrefour

Belgium

Film Clear film over

wrap for tray




MarketProducts

Kik & Boo Fiber Soft toys filled

with PLA

fiber

Stilolinea Stationery Pen

DDCLAB USA Fabric Slim fit’s mean

shirt and

trousers

Pacific Coast

Feather

Company

Fiberfill Comforter,

pillow

Method Fibers cloth Sweeper cloths

omopt

28 POLYLACTIC ACID



MarketProducts

Valor Brands Fiber Diapers �Natural

Choicet

Kimberly-Clark Fiber Huggiess Pure

& Natural

diapers

Fujitsu Computer casing FMV-BIBLO

notebook

Toyota Automotive Toyota

Eco-Plastic �spare tire

cover and

floor mat

Bioserie Electronics cover iPhone cover


called BioFoams (see Figure 1.9). Synbra has been in theStyrofoam manufacturing line for more than 70 years. Theexpandable PLA of Synbra utilizes the lactide produced byPurac’s lactide facility in Spain. Purac’s Spanish plant willhave the production capacity of 10 million lb per year in thenear future once it is fully commissioned. In September 2010,Purac entered into collaboration with Arkema to develophigh-purity functional block copolymers, containing PLA seg-ments, using the Purac’s lactide. The output of the develop-ment is an improvement on the current lactide polymerizationprocess with the absence of metal residues, which ensuressafe medical and consumer goods packaging. In addition,Purac is also collaborating with Toyobo, a Japanese film,fiber and biotechnology firm, to make an amorphous andbiodegradable PLA product for the European market underthe brand name Vyloecols. Unlike the production technologyused by Purac�Sulzer, Vyloecols developed by Purac�Toyobo

(a)

(b)

Figure 1.9 (a) Sulzer’s 23 kg/hr pilot plant in Switzerland usingPurac’s new lactide monomer; (b) Purac’s 75,000 MT/year lactidemonomer plant operating in Thailand from 2011.

30 POLYLACTIC ACID

is a patented amorphous PLA for application as coatings oradhesives for packaging films and materials.

Purac is also active in PLA production in the EuropeanUnion, with Galactic and Total Petrochemicals. They estab-lished a 50/50 joint venture � Futerro � in September 2007 todevelop PLA technology. The preliminary project was to con-struct a demonstration plant with a 1500 MT PLA productioncapacity; this pilot unit cost $15 million. The Galactic produc-tion site is located at Escanaffles, Belgium. The monomer,lactide, is obtained from fermenting sugar beet. Another jointventure, known as Pyramid Bioplastics Guben GmbH, is alsoplanning to construct and operate a plant for the productionof PLA, this time in Guben, eastern Germany. The company isa partnership between Pyramid Technologies Ltd, of Zug inSwitzerland, and the German company Bioplastics GmbH,of Guben. The first construction plant will have a 60,000 MTcapacity of PLA per annum by 2012. A pilot-plant scale pro-ducer, Hycail, used to produce a small quantity of PLA beforeit was sold to Tate & Lyle in 2006. This plant was shut downtwo years later.

In Asia many companies have been established to explorePLA technology. Japan is the first country to be involved inthe research and development of PLA. China then followed,as the market for PLA started to grow. Although Japan wasinvolved in PLA technology earlier than other Asian countries,some of the large ambitious companies halted production dueto high production costs, lack of availability of raw materialsand an immature market to accept such premium plastics witha higher price. Shizmadu initially operated a pilot plant to pro-duce small commercial quantities of PLA. Since then, produc-tion has ceased and the technology sold to the Toyota MotorCorporation. Toyota increased production to 1000 MT per year,mainly for automotive applications. In 2008, the plant wassold to Teijin, and now Teijin is expanding production for itsBIOFRONTt products. The company plans to increase theproductivity of BIOFRONTt to 5000 MT per year in 2011.Unitika Ltd, a 120-year-old textile company has marketedPLA products under the Teramacs brand. Teramacs resin can


be processed using a wide range of plastic technologies, includ-ing injection, extrusion, blow, foam and emulsion. The Koreancompany Toray has launched a full-scale commercialization ofEcodeart PLA films and sheets. Ecodeart possesses heat andimpact resistance as well as flexibility and high transparencyequivalent to petroleum-based plastic films.

Since 2007 many projects have been announced in China.However, many of these have seen a lack of further development

Table 1.5 Polylactic Acid Resin Producers

Producer Capacity(MT/year)

Location

NatureWorks 140,000 Nebraska, United

States

Purac�Sulzer

Chemtech�Synbra

Technology

5,000 Netherlands

Galactic�Total

Petrochemicals: Futerro

1,500 Belgium

Zhejiang Hisun Biomaterial 5,000 Zhejiang, China

Shanghai Tongjieliang

BioMaterial

300 Shanghai, China

Mitsui Chemical �LACEAs

No data Japan

Unitika�Terramac 5000 Japan

Nantong Jiuding

Biological Engineering

1,000 Jiangsu, China

Piaoan Group 10,000

(in planning)

Henan, China

Purac�Toyobo No data Japan

Toray Industries 5,000 Kyungsangbuk-do,

South Korea

Pyramid Bioplastics

Guben GmBH

60,000 (in

planning)

Guben, Germany

Teijin Limited 1200 Matsuyama, Ehime

Prefecture, Japan

32 POLYLACTIC ACID

(Jem et al., 2010). Zhejiang Hisun Biomaterial was the firstcompany in China to produce PLA on a commercial scale,with an annual production of 5000 MT per year. Other compa-nies had smaller plants at the time: Shanghai TongjieliangBioMaterial had a pilot plant producing 300 MT per year PLA,and Nantong Jiuding Biological Engineering had a larger facil-ity that could produce up to 1000 MT per year. At the end of2009, Nantong Jiuding Biological Engineering secured fundingof US$1.4 million from the National Development ReformCommission to expand its PLA project (CCM International,2010). This was followed by an expansion project, involvinga total investment of US$19 million, to boost production to20,000 MT per year. Henan Piaoan Group, a medical equip-ment and supplies manufacturer has purchased the patentedPLA technology of Japan’s Hitachi Plant Technologies Ltd.The Henan Piaoan plant is expected to produce 10,000 MTof PLA annually. Most of the PLA produced in China is forexport rather than internal use, because the biodegradable mar-ket in China is still in its infancy and there is a lack of localregulation on biodegradable polymer use for environmentalprotection.

A list of PLA resin producers worldwide is given inTable 1.5.

1.3 General Properties and Applicationsof PLA

1.3.1 PLA for Domestic Applications

NatureWorks is the largest PLA producer in the world. Theirproduct range includes injection molding, extrusion, blowmolding, thermoforming, films and fiber applications. Ingeot,NatureWorks’ PLA resin, is produced at a rate of 140,000 MTper year from a facility located in Nebraska, USA. The companyhas 19 worldwide distribution points from which to sell andpromote their products. NatureWorks has initiated a co-brandingpartnership program for better market positioning of Ingeot.


Currently there are over 900 companies involved in this partner-ship program, which has successfully strengthened the Ingeotbrand worldwide.

Tables 1.6�1.8 give a summary of the properties ofIngeot. As with commodity plastics such as polyethylene andpolypropylene, the selection of Ingeot is made according tothe processing technique as well as the end use of the product.According to Patrick Gruber, Chief Technology Officer atNatureWorks, and colleagues (Drumright et al., 2000), thevariety grades of PLA are formulated using the principle ofstereochemical purity, molecular weight and the incorporationof additive packages. Manipulation of the stereochemicalcomposition of PLA has a significant effect on the meltingpoint, rate of crystallization and ultimately the extent ofcrystallization (Drumright et al., 2000). Pure PLA either fullyin L or D stereochemistry has a melting point of 180�C anda glass transition temperature at 60�C (Nijenhuis et al., 1991).Copolymerization of D-lactide or meso-lactide affects thestereochemical purity. The crystallinity of PLA is totallydestroyed after the incorporation of 15% meso-lactide orD-lactide in PLLA. The copolymerization of L and D stereo-chemistry induce the formation of an amorphous structure inthe resulting polymer. Nevertheless, the higher melting pointof the resulting polymer is preferable to avoid heat deflectionof the PLA-formed article, typically in hot food serviceware.Purac claim that through the manipulation of the stereo com-plex and stereo block of lactide during the copolymerizationprocess the melting temperature can effectively be increasedto 230�C, which is almost as good as polystyrene (meltingpoint of polystyrene is about 240�C). In spite of that, it isimportant that the rheological properties of the resultingpolymer suit the processing technology. PLA is typical ofaliphatic polyesters, having relatively poor strength andlacking in shear sensitivity. The introduction of branching inPLA makes it possible to able to obtain a longer chain of theresulting polymer for better entanglement, which can result ina better melt strength for blow film application (Henton et al.,2005). However, the details of such modifications are rarely

34 POLYLACTIC ACID

Table 1.6 NatureWorks PLA Grades for Thermoform and Injection Molding

Grade 2003D 3001D 3051D 3251D 3801X

Specific gravity 1.24a 1.24a 1.25a 1.24a 1.33a

Melt index (g/10 min) 5�7b�

10�30b# 10�25b�

70�85b�

8b#

Tensile strength at break

(MPa)

53c � � � �

Tensile yield Strength

(MPa)

60c 48e 48e 48e 25.9e

Tensile modulus (MPa) 3500c � � � 2980e

Tensile elongation (%) 6c 2.5e 2.5e 2.5e 8.1e

Notched Izod impact (J/m) 12.81d 0.16d 0.16e 0.16e 144d

Flexural strength (MPa) � 83f 83f 83f 44f

Flexural modulus (MPa) � 3828f 3828f � 2850f

Crystalline melt

temperature (�C)� � 150�165g � 160�170g

Glass transition

temperature (�C)� � 55�65h � 45h

Applications General

extrusion for

thermoform

production of

food

Injection

molding

applications

for clear

cutlery,

Injection

molding

applications

with the

requirement

Injection

molding

applications

with higher

melt flow

Injection

molding for

high-heat and

high-impact

applications.

Table 1.6 NatureWorks PLA Grades for Thermoform and Injection Molding—cont’d

Grade 2003D 3001D 3051D 3251D 3801X

packaging,

dairy

containers,

food

serviceware,

transparent

containers,

hinged ware

and cold drink

cups

cups, plates,

etc. with

heat

deflection

temperature

,55�C

for clarity

and heat

deflection

temperature

,55�C

capability.

High gloss,

UV-

resistance

and stiffness

More rapid

crystallization

kinetics for

shorter cycle

time.

Application at

heat deflection

temperatures

65�140�Cwithout food

contact

a5ASTM D792; b� 5ASTM D1238 (210�C/2.16 kg); b#5ASTM D1238 (190�C/2.16 kg); c5ASTM D882; d5ASTM

D256; e5ASTM D638; f5ASTM D790; g5ASTM D3418; h5ASTM D3417; i5ASTM D1505; j5ASTM D1922;

k5ASTM D1434; m5ASTM E96; n5ASTM D1003; p5ASTM D3418.

Data: NatureWorks.

Table 1.7 NatureWorks PLA Grades for Films and Bottles

Grade 4043D 4060D 7001D 7032D

Density (g/cm3) 1.24i 1.24i 1.24a 1.24a

Melt index (g/10 min) � � 5�15b�

5�15b�

Tensile strength MD (kpsi) 16c � � �TD (kpsi) 21c � � �

Tensile modulus MD (kpsi) 480c � � �TD (kpsi) 560c � � �

Elongation at

break

MD (%) 160c � � �TD (%) 100c � � �

Elmendorf tear MD (g/mil or g/25 μm) 15j � � �TD (g/mil or g/25 μm) 13j � � �

Transmission

rate

Oxygen (cc-mil/m2/24 h

atm or cm3 25 μm/m2/

24 h atm)

550k 550k 550k 550k

Carbon dioxide (cc-mil/

m2/24 h atm or cm3

25 μm/m2/24 h atm)

3000k 330k 3000k 3000k

Water vapor (g-mil/m2/

24 h atm or g 25 μm/

m2/24 h atm)

325m 325m 325m 325m

Optical

characteristics

Haze (%) 2.1n 2n � �Gloss (20�) 90n 90n � �

Table 1.7 NatureWorks PLA Grades for Films and Bottles—cont’d

Grade 4043D 4060D 7001D 7032D

Thermal

characteristics

Melting point (�C) 135n � 145�155p 160p

Glass transition

temperature (�C)� 52�58p 52�58h 55�60h

Seal initiation

temperature (�C)� 80q � �

Application Biaxial oriented

film application.

Excellent

optics, twist and

deadfold.

Barrier to

flavor, grease

and superior oil

resistance

For heat seal

layer in

coextruded

oriented

films.

Excellent

heat seal

and hot tack

Injection stretch

blow molded

bottles.

Potential for

fresh dairy,

edible oil,

fresh water

and liquid

hygiene

products

Injection stretch

blow molded

bottles. Ideal

for

applications

requiring heat

setting �fruit juices,

sports drinks,

jams, jellies

a5ASTM D792; b� 5ASTM D1238 (210�C/2.16 kg); b#5ASTM D1238 (190�C/2.16 kg); c5ASTM D882; d5ASTM

D256; e5ASTM D638; f5ASTM D790; g5ASTM D3418; h5ASTM D3417; i5ASTM D1505; j5ASTM D1922;

k5ASTM D1434; m5ASTM E96; n5ASTM D1003; p5ASTM D3418.

Data: NatureWorks.

Table 1.8 NatureWorks PLA Grades for Fiber Application

Grade 5051X 6060D 6201D 6202D 6204D 6251D 6302D 6550D 6400D 6751D

Specific gravity 1.24a 1.24a 1.24a 1.24a 1.24a 1.24a 1.24a 1.24a 1.24a 1.24a

Melt Index

(g/10 min)

� 10b�

15�30b�

15�30b�

15�30b�

70�85b�

20b�

65b�

4�8� 15b�

Crystalline melt

temperature (�C)

145�155g 125�135g 160�170g 160�170g 160�170g 160�170g 125�135g 145�160g 160�170g 150�160g

Glass Transition

Temperature (�C)

55�65h 55�60h 55�60h 55�60h 55�65h 55�60h 55�60h 55�60h 55�60h 55�60h

Denier per filament .1.5 .4 .0.5 .0.5 .0.5 1�2 .4 � 10�20 .1.5

Tenacity (g/d) 2.5�4.0r 3.5r 2.5�5.0r 2.5�5.0r 2.5�5.0r � 3.5r � 2.0�2.4r 2.5�4.0r

Elongation (%) 10�70r 50r 10�70r 10�70r 10�70r � 50r � 10�70r 10�70r

Modulus (g/d) 20�40r � 30�40r 30�40r 30�40r � � � � 20�40r

Hot Air

Shrinkage (%)

,8s � 5�15s ,8y 5�15y � � � � 8

Table 1.8 NatureWorks PLA Grades for Fiber Application—cont’d

Grade 5051X 6060D 6201D 6202D 6204D 6251D 6302D 6550D 6400D 6751D

Application Non-woven

spunlace

wipes

Low melt

binder

polymer in a

sheath-core

configuration.

Good for

thermal

bonded

non-wovens

Woven and

knitted

100%

continuous

filament

apparel,

intimate

staple blend

fabrics,

including

blends with

cotton,

wool, or

other

fibers; for

home

furnishings

and civil

engineering

applications

Fiberfill,

non-wovens,

agricultural

woven and

no-woven

fabrics,

articles for

household

disposal

Woven and

knitted

100%

continuous

filament

apparel,

intimate

staple blend

fabrics,

including

blends with

cotton,

wool, or

other fibers;

for home

furnishings

and civil

engineering

applications

Suitable for

wipes,

geotextiles,

hospital

garments,

absorbent

pad liners

and

personal

hygiene

products,

agricultural/

horticultural

products

Low melt

binder

polymer in a

sheath-core

configuration.

Good for

thermal

bonded non-

wovens

For extrusion

into

spunbond

non-wovens

using

conventional

bi-component

PET

spunbond

equipment,

where

filament

velocities

.4000 m/min

For bulk

continuous

filament,

tufted

carpet-

loop/cut

pile, broad

loom

carpet and

carpet

mats

Suitable for

non-

woven

(spunlace

wipes)

and multi

filament

twine

a5ASTM D792; b� 5ASTM D1238 (210�C/2.16 kg); b#5ASTM D1238 (190�C/2.16 kg); c5ASTM D882; d5ASTM D256; e5ASTM D638; f5ASTM D790; g5ASTM D3418; h5ASTM D3417;

i5ASTM D1505; j5ASTM D1922; k5ASTM D1434; m5ASTM E96; n5ASTM D1003; p5ASTM D3418.

Data: NatureWorks.

disclosed by the manufacturers. Further details of researchwork on the rheological properties of PLA are discussed inChapter 2.

Unitika Limited and FKuR Kunststoff GmBH havemarketed their products based on NatureWorks’ Ingeot underthe tradenames of Bio-Flexs and Terramacs, respectively.Although both of the manufacturers have stressed theirproducts are based on Ingeot, some modifications or additiveshave been incorporated into the product to improve theoriginal properties of the PLA. It can be seen fromTables 1.9�1.11 that the heat distortion/deflection temperatureof the Terramacs series is higher than that for Ingeot.A higher heat distortion/deflection temperature is crucialfor certain products, particularly food serviceware for hotfood and drink. Bio-Flexs (see Table 1.12) also has differentproperties to Ingeot, after converting the unit of analysis. Theimprovements to PLA made by other manufacturers are consid-ered to be positive moves to enable PLA to fulfill a wide rangeof market needs. In its series of Terramacs products Unitikahas also included a foam and emulsion of PLA. The foam PLAis targeted to replace Stryrofoam, while reducing environmentalpollution. The emulsion grade of PLA is suitable as a coatingagent. Similarly, Toyobo’s PLA under the tradename ofVyloecols is mainly produced for use as a general-purpose coat-ing agent (see Table 1.13).

In addition to converting and improving Ingeos, ZhejiangHisun Biomaterial has produced two other grades, REVOD201and REVODE101 (see Table 1.14), for injection molding andextruded sheet thermoforming applications, respectively, from itsfacility located in China. The Galactic and Total Petrochemicaljoint venture has introduced Futerros polylactide consisting ofthree grades, for thermoforming, fiber and injection moldingapplications (see Table 1.15). Other manufacturers such asMitsui, Teijin, Purac, Toray and some Chinese manufacturerslack data about their product grades. This might be due tothe manufacturer’s technology still being in the pilot stage and,therefore, yet to produce detailed specifications prior to massproduction for the market.


Table 1.9 Unitika�Terramacs PLA Grades for Injection Molding

Grade ISO BasicGradeTE-2000

HighImpactGradeTE-1030

HighImpactGradeTE-1070

Heat-ResistingGradeTE-7000



High-DurabilityGradeTE-8210

High-DurabilityGradeTE-8300

Density 1183 1.25 1.24 1.24 1.27 1.42 1.47 1.42 1.47

Melting point (�C) � 170 170 170 170 170 170 170 170

Breaking strength (MPa) 527 63 51 34 70 54 54 50 56

Tensile elongation (%) 527 4 170 .200 2 2 1 2 1

Blending strength (MPa) 178 106 77 50 110 85 98 90 104

Bending modulus (GPa) 178 4.3 2.6 1.4 4.6 7.5 9.5 6.8 9.3

Charpy impact strength:

with notch (kJ/m2)

179 1.6 2.3 5.6 2.0 2.5 2.4 4.0 2.8

Deflection temperature

under load of

0.45MPa (�C)

75 58 51 54 11- 120 140 120 140

Molding shrinkage (%) � 0.3�0.5 0.3�0.5 0.3�0.5 1.0�1.2 1.0�1.2 1.0�1.2 1.0�1.2 1.0�1.2

1.3.2 PLA and Copolymers for BiomedicalApplications

In addition to the usage of PLA for the production ofenvironmentally friendly domestic articles to substitute existing

Table 1.10 Unitika�Terramacs PLA Grades for Extrusion,Blow, and Foam Sheet

Grade ISO BasicgradeTP-4000

SoftTP-4030

FoamHV-6250H

Density 1183 1.25 1.24 1.27

Melting point (�C) � 170 170 170

Breaking strength (MPa) 527 66 50 69

Tensile elongation (%) 527 5 44 2

Bending strength (MPa) 178 108 71 111

Bending modulus (GPa) 178 4.6 2.4 4.7

Charpy impact strength:

with notch (kJ/m2)

179 1.6 2.6 1.9

Deflection temperature

under load of

0.45 MPa (�C)

75 59 52 120

Molding shrinkage (%) � 3�5 3�5 1�3

Table 1.11 Unitika�Terramacs PLA Grade for Emulsion

Grade Standard Type LAE-013N

Solids content

concentration (wt%)

50�55

pH 3.5�5.5

Particle diameter (μm) ,1

Viscosity (mPa.s) 300�500

Lowest film-foaming

temperature (�C)60�70


Table 1.12 FKuR Kunststoff GmbH PLA Specification

Grade Test

Method

Bio-Flexs

A 4100 CL

Bio-Flexs

F 1110

Bio-Flexs

F 1130

Bio-Flexs

F 2110

Bio-Flexs

F 6510

Bio-Flexs

S 5630

Bio-Flexs

S 6540

Tensile modulus

of elasticity (MPa)

ISO 527 1840 230 390 730 2600 2160 2800

Tensile strength

(MPa)

ISO 527 44 16 17 20 47 32 31

Tensile strain

at tensile

strength (%)

ISO 527 5 .300 .300 .300 4 6 5

Tensile stress at

break (MPa)

ISO 527 22 No break No break No break 23 29 28

Tensile strain

at break (%)

ISO 527 12 No break No Break No break 19 9 7

Flexural modulus

(MPa)

ISO 178 1770 215 370 680 2650 2400 2890

Flexural strain

at break (%)

ISO 178 No break No break No break No break No break No break 6

Flexural stress at

3.5 % (MPa)

ISO 178 48 6 9 17 64 46 50

Notched impact

strength (Charpy),

RT (kJ/m2)

ISO 179-

1/1 eA

3 No break No break 83 7 3 3

Impact strength

(Charpy),

RT (kJ/m2)

ISO 179-

1/1 eU

44 No break No break No break No break 51 36

Density (g/cm3) ISO 1183 1.24 1.28 1.40 1.27 1.30 1.55 1.62

Melt temperature (�C) ISO

3146-C

.155 .155 .155 145�160 150�170 140�160 110�15-

Vicat A softening

temperature (�C)ISO 306 44 68 89 78 60 105 105

Heat distortion

temperature

HDT B (�C)

ISO 75 40 n/a n/a n/a n/a 68 n/a

Melt flow rate �190�C/2.16 g

(g/10 min)

ISO 1133 10�12 2�4 2�4 3�5 2.5�4.5 10�12 8�10

Water vapor (g/m2.d) ISO 15

106-3

170 � 70 130 130 �

Oxygen

(cm3/(m2.d.bar))

ISO 15

105-2

130 � 850 1450 1.060 �

Nitrogen �25 μm film

(cm3/(m2/d/bar))

DIN

53380-2

65 � 160 230 150 �

Application Film

extrusion

Film

extrusion

Film

extrusion

Film

extrusion

Film

extrusion

Thermoforming

and injection

molding

Injection

molding

petrochemical-based plastic products, PLA is also widely usedin the biomedical field, for the production of bioresorbableimplants and devices. Most of the PLA in biomedical applica-tions is produced from L-lactic acid. The implants made ofpoly(L-lactide) can be easily degraded and resorbed by thebody through the action of enzymes. Unfortunately, the stereo-isomer D-lactic acid is not degraded by the body’s enzymes.However, prolonged hydrolysis in body fluids eventuallybreaks down the bulk of poly(D-lactide). This degradationmechanism is discussed in Chapter 2.

A considerable amount of PLA copolymer is synthesized fortissue engineering. The main objective when synthesizing suchcopolymers is to fine-tune the period of degradation fromweeks to years (Morita and Ikada, 2002). Commonly, themonomer of glycolide acid and ε-caprolactone are copolymer-ized with lactide. As can be seen from Table 1.16, when in vitroat 37�C, the mass of poly(L-lactide) is significantly increasedafter being copolymerized with glycolide and ε-caprolactone.This is very important for the fabrication of scaffolds for tissueengineering and for wound dressings. The degradation of the

Table 1.13 Toyobo PLA Specification

Grade Vyloecol BE-400 Vyloecol BE-600

Form Pellet Sheet

Molecular weight 43,000 25,000

Specific gravity

at 30�C1.26 1.24

Tg (�C) 50 30

Hydroxyl group

value KOH (mg/g)

3 11

Features and

applications

General purpose

grade, agent

for various

coatings

Anchor coating for

vapor deposition

film, anchor

coating for

printing ink

46 POLYLACTIC ACID

Table 1.14 Hisun Biomaterial PLA Specification

Grade Test Method REVODE201 REVODE101

Specific gravity GB/T1033-1986 1.256 0.05 1.256 0.05

Melt index �190�C/2.16 kg

(g/10 min)

GB/T3682-2000 10�30 2�10

Melting point (�C) GB/T19466.3-2004 137�155 140�155

Glass transition temperature

(�C)GB/T19466.2/2004 57�60 57�60

Tensile strength (MPa) GB/T1040-1992 45 50

Tensile elongation (%) GB/T1040-1992 3.0 3.0

Impact strength (kJ/m2, Izod) GB/T1040-1992 1�3 1�3

Applications For injection

molding,

including cutlery,

toys, plates, cups,

etc.

Easily processed using conventional

extrusion equipment for producing

sheet ranging between 0.2�10 mm

in thickness for thermoforming.

Suitable for dairy containers, food

serviceware, transparent food

containers and cold drink cups

Table 1.15 Futerro PLA Specification

Grade Test Method FuterroPolylactide �Extrusion Grade

FuterroPolylactide �Fiber MeltSpinning Grade

FuterroPolylactide �Injection Grade

Specific Gravity at 25�C ISO 1183 1.24 1.24 1.24

Melt Index � 190�C/2.16 kg

(g/10 min)

ISO 1133 2�4 10�15 10�30

Haze � 2 mm (%) ISO 14782 ,5 ,5 ,5

Glass transition temperature (�C) ISO 11357 52�60 52�60 52�60

Crystalline melt

temperature (�C)ISO 11357 145�175 145�175 145�175

Tensile strength at break (MPa) ISO 527 55 55 55

Tensile yield strength (MPa) ISO 527 60 60 60

Tensile modulus (MPa) ISO 527 3500 3500 3500

Tensile elongation (%) ISO 527 6.0 6.0 6.0

Notched Izod impact (kJ/m2) ISO 180 3.5 3.5 3.5

Flexural yield strength (MPa) ISO 178 90 90 90

Application For extrusion and

thermoforming

application

For extrusion into

mechanically

drawn staple

fibers or

continuous

filament.

Potential for

woven and

knitted apparel,

fabrics or

netting for civil

engineering

applications

For injection

molding

applications

with

deflection

temperatures

,55�C.

Table 1.16 Physical Properties of Synthetic Biodegradable Polymers Used as Scaffolds in Tissue Engineering(Morita and Ikada, 2002, with permission from Marcel Dekker)

Polymer Poly(glycolide)

Poly(L-lactide)

Poly(ε-caprolactone)

Copolymerof L-lactideandglycolide(10:90)

Copolymer ofL-lactide andε-caprolactone(75:25)

Copolymer of(L-lactide

Tm (�C)a 230 170 60 200 130�150 90�120

Tg (�C)b 36 56 260 40 15�30 217

Shape Fiber Fiber, sponge,

film

Fiber, sponge,

film

Fiber Fiber, sponge,

film

Fiber, sponge,

film

Tensile strength

(MPa)

890 (fiber) 900 (fiber) 10�80 (fiber) 850 (fiber) 500 (fiber) 12 (film)

Young’s

modulus

(GPa)

8.4 (fiber) 8.5 (fiber) 0.3�0.4 (fiber) 8.6 (fiber) 4.8 (fiber) 0.9 (film)

Elongation at

break (%)

30 (fiber) 25 (fiber) 20�120 (fiber) 24 (fiber) 70 (fiber) 600 (fiber)

Pwoc 2�3 months 3�5 years .5 years 10 weeks 1 year 6�8 months

Pt50d 2�3 weeks 6�12 months � 3 weeks 8�10 weeks 4�6 weeks

a5 Melting point;b5 glass transition temperature;c5 period until the polymer mass becomes zero (in saline at 37�C);d5 period until tensile strength of polymers becomes 50% (in saline at 37�C).

copolymer is designed to couple with the growth of tissue andthe loss of mass and strength of the prescribed implants.Eventually, the scaffold structure is substituted by the permanenttissue of the patient.

PLA and its copolymers can be used for a wide range ofbiomedical applications such as sutures, anchors, screws, andscaffolds, etc. They have uses in oral, orthopedic, auricular andcraniofacial augmentations in plastic surgery (see Table 1.17).Screws and anchors are produced by the injection moldingmethod, and sutures are manufactured using a fiber spinningprocess. Bioresorbable scaffolds are prepared using a range oftechniques, including phase separation, solvent evaporation,casting/salt leaching and fiber bonding to form a polymermesh. PLA copolymers are also widely used as a drug carriermedium (see Table 1.18). Such drug carriers contain activedrugs, which can be efficiently delivered to the target cells andsubsequently released at a controlled rate (Yin et al., 2010; Seoet al., 2007). One of the best known products on the market,Zoladexs, is a polylactide-co-glycolide with a formulation ofgoserelin as a controlled release drug for the treatment of breastcancer (Jain et al., 2010). Zoladexs allows the slow releaseof the drug, which inhibits the growth of cancer cells that arehormone-dependent. The US Food and Drug Administrationalso approved Zoladexs for the treatment of prostate cancer.There are couple of other PLA-copolymer-related drug deliverysystem widely available on the market.

Purac is the main global company actively involved in pro-ducing biomedical and drug delivery grade PLA and copoly-mers; it is marketed as Purasorbs. Durect Corporation alsomarkets a bioabsorbable polymer under the tradename Lactels.As can be seen from the grade specification from both manufac-turers (see Tables 1.19, 1.20 and 1.21) the PLGA copolymer isthe most widely produced grade. All grades are tested for theirintrinsic viscosities as guidance on the molecular weight of thesynthesized polymer. This is very important in biomedicalapplications, as it ensures the rate of resorption in the body. Whenthe polymer is exposed to aqueous media or tissue, the esterlinkages of the polymer react with the absorbed water through


Table 1.17 PLA in Biomedical Applications

Polymer Area of Application Products

Poly(lactide) Orthopedic surgery, oral and

maxillofacial surgery

Takiron: Osteotranst MX, Fixsorbt MX (screws,

nails, pins)

Gunze: Grandfixs, Neofixs (screws, nails, pins)

Arthrex: Bio-Tenodesiss (interference screw),

Bio-Corkscrews (suture anchor)

Conmed Linvatec: SmartScrews, SmartNails,

SmartTacks, SmartPins BioScrews

Stryker: Biosteons, Biozips (interference screw,

anchor)

Zimmer: Bio-Stataks (suture anchor), prostatic stent,

suture anchor, bone cement plug

Dermik Laboratories: Sculptras (injectable facial

restoration)

Kensey Nash: EpiGuides

Poly(D,L-lactide-co-

glycolide)

Sutures USS Sport Medicine: Polysorbt sutures

Poly (D,L-lactide-co-

glycolide) 85/15

Drug delivery Instrument Makar: Biologically Quiett

(interference screw) Staple 85/15

Poly(D,L-lactide-co-

glycolide) 82/18

Oral and maxillofacial

surgery

Biomet: ALLthreadt LactoSorbs, screws, plates, mesh,

surgical clip, pins, anchor

Poly(D,L-lactide-

co-glycolide) 10/90

General surgery Ethicon: Vicryl suture, Vicryl mesh

Sutures, periodontal surgery,

general surgery

Poly(L-lactide-co-

D,L-lactide) 98/2

Orthopedic surgery Phusilines interference screw, Sage

Poly(L-lactide-co-

D-lactide) 98/4

Oral and maxillofacial

surgery

ConMed: Bio-Mini Revos

Poly(L-lactide-co-

D,L-lactide) 50/50

Sulzer: Sysorbs screw (50/50)

Poly(L-lactide-co-

D,L-lactide) 70/30

Geistlich: ResorPins 70/30

Poly(D-lactide-co-

D,L-lactide-co-L-lactide)

Kensey Nash: Drilacs

Surgical dressing

Poly(D,L-lactide-

co-caprolactone)

Nerve Regeneration Ascension Orthopedics: Neurolacs

Polyganics: Vivosorbs

Table 1.18 List of Commercially Available PLA and Copolymer Delivery Carriers and the CorrespondingTherapeutic and its Indication (extracted from Branco and Schneider, 2009)

DeliverySystem

Material Composition Product Name Therapeutic Type of Drug: Indications

Microspheres PLA (poly(lactic acid)) Lupron Depot Leuprolide

acetate

Peptide hormone: cancer and

Alzheimer’s

PLGA (polylactide-

glycolide)

Eligard Leuprolide

acetate

Peptide hormone: cancer and

Alzheimer’s

Risperdal Consta Risperidone Peptide: schizophrenia

Trelstar LA Triptorelin

pamoate

Peptide hormone: prostate cancer

PLGA-glucose Sandostatin LAR Octreotide Peptide: anti-growth hormone

Implant PLGA Durin Leuprolide Peptide hormone: cancer and

Alzheimer’s

Zoladex Goserelin

acetate

Peptide hormone: prostate/breast

cancer

Gel PLGA Oncogel Paclitaxel Small molecule: anticancer

Table 1.19 Purac Purasorbs PLA for Medical Devices

Grade Structure InherentViscosityMidpoint (dl/g)

Purasorb PL 18 Poly(L-lactide) 1.8

Purasorb PL 24 2.4

Purasorb PL 32 3.2

Purasorb PL 38 3.8

Purasorb PL 49 4.9

Purasorb PL 65 6.5

Purasorb PD 24 Poly(D-lactide) 2.4

Purasorb PDL 45 Poly(DL-lactide) 4.5

Purasorb PLDL 8038 80/20 L-lactide/DL-lactide

copolymer

3.8

Purasorb PLDL 8058 5.8

Purasorb PLDL 7028 70/30 L-lactide/DL-lactide

copolymer

2.8



Purasorb PLD 9620 96/04 L-lactide/D-lactide

copolymer

2.0

Purasorb PLD 9655 5.5

Purasorb PLG 8523 85/15 L-lactide/glycolide

copolymer

2.3

Purasorb PLG 8531 3.1

Purasorb PLG 8560 6.0


copolymer

1.8


copolymer

5.5


copolymer

1.7

Purasorb PLC 9517 95/05 L-lactide/

caprolactone copolymer

1.7

Purasorb PLC 9538 3.8



1.6



1.5

Purasorb PDLG 8531 85/15 DL-lactide/

glycolide copolymer

3.1


glycolide copolymer

1.0


a hydrolysis reaction. Over time, the long polymer chains arebroken into shorter ones to form water-soluble fragments.Eventually, the water-soluble fragments diffuse away from theinitial polymer structure and finally hydrolyze to glycolic andlactic acid for metabolism by the liver. Generally, the rateof degradation is higher at lower molecular weights and forhigher glycolide content (Durect, 2010). The detailed process of

Table 1.20 Purac Purasorbs PLA for Drug Delivery

Grade Structure IntrinsicViscosityMidpoint (dl/g)

Purasorb PDL 02A �acid terminated

Poly (DL-lactide) 0.2

Purasorb PDL 02 0.2

Purasorb PDL 04 0.4

Purasorb PDL 05 0.5

Purasorb PDL 20 2.0


glycolide copolymer

0.2

Purasorb PDLG

7502A � acid

terminated

75/25 DL-lactide/

glycolide copolymer

0.2


glycolide copolymer

0.7


glycolide copolymer

0.2

Purasorb PDLG

5002A � acid

terminated

50/50 DL-lactide/

glycolide copolymer

0.2


glycolide copolymer

0.4

Purasorb PDLG

5004A � acid

terminated

50/50 DL-lactide/

glycolide copolymer

0.4


glycolide copolymer

1.0

56 POLYLACTIC ACID

degradation is described in Chapter 4. Overall, PLA and copoly-mers have contributed significantly to the medical industry.

1.4 Environmental Profile of PLA

PLA is produced from renewable agricultural sources, whichis why it is known for its eco-friendliness. As well as the tech-nology used by NatureWorks for mass production from corn,sugarcane is also used as the raw material for producing lacticacid. Sugarcane-based production of lactic acid has been devel-oped by Purac, with the setting up of a commercial lactic acidplant in Thailand. In general, PLA is produced using a directpolycondensation reaction and ring-opening polymerizationapproaches. The majority of commercial producers find that

Table 1.21 Durect Lactels Absorbable Polymer

Grade Chemical Name InherentViscosityMidpoint (dl/g)

B6017-1 50:50 Poly(DL-lactide-co-glycolide) 0.2



B6010-3 50:50 Poly(DL-lactide-glycolide) 0.85




B6005-1 Poly(DL-lactide) 0.40

B6005-2 Poly(DL-lactide) 0.65

B6002-2 Poly(L-lactide) 1.05



B6015-1 25:75 Poly(DL-lactide-co-

ε-caprolactone)0.8

B6016-1 80:20 Poly(DL-lactide-co-

ε-caprolactone)0.8


ring-opening polymerization is preferable for better control ofthe process and better production quality.

In the environmental credit analysis of PLA, there are twomajor aspects that need to be considered � the PLA manufactur-ing process and the post-consumer PLA product disposal.Several research projects on lifecycle analysis of PLA massproduction have been conducted in recent years. Two of thelife cycle analyses of PLA production have been undertaken byNatureWorks and Purac. The objective here is to summarizethese studies rather than directly perform life cycle analysisof PLA. More detailed information can be found in the relevantpublications (Vink et al., 2003; Vink et al., 2007; Vink et al.,2010; Groot and Boren, 2010).

1.5 Ecoprofile of PLA in Mass Production

PLA is produced from sugar fermentation by bacteria. Thesource of sugar is starch, and this currently comes mainly fromcorn and cassava. NatureWorks grows corn to produce starchas the input for their PLA production, while Purac uses cassavato produce PLA, using the Synbra�Sulzer Chemtech technol-ogy. Both technologies utilize the fermentation approach toproduce lactic acid. This is followed by transforming lacticacid into lactide and finally undergoing ring-opening polymeri-zation into PLA.

According to Vink et al. (2003), the initial technology ofNatureWorks required 54.1 MJ of fossil energy to produceevery kilogram of Ingeot PLA. Fossil energy is used forrunning the factory, transportation of corn to the wet mill,waste water treatment, etc. Although the combustion energy ofcorn residue is renewable energy, it merely contributes 34.4%of the overall energy required (82.5 MJ/kg of PLA) in theplant. Figure 1.10 shows the gross energy required to producePLA by NatureWorks’ first generation technology. Energy isrequired to operate supplies such as fertilizers and pesticidesfor growing the corn (total 3.8 MJ/kg of PLA) as well as trans-portation of the corn to the wet mill and related wastewater

58 POLYLACTIC ACID

treatment throughout the production process. All these opera-tions require an external supply of energy, because it is notpossible to self-supply using the heat of combustion of the cornresidue. Most people think that PLA is a novel environmentallyfriendly polymer. However, this usage of fossil energy stillgenerates greenhouse gases. Nevertheless, PLA is still worthyof exploration due to its fully biodegradable nature when dis-posed of in the natural environment. In fact, the biodegradabil-ity of PLA is its most important selling point in the domesticmarket.

Despite the fact that the gross fossil energy consumptionis considered high (.50% of the total energy to produce eachkilogram of PLA), when NatureWorks first-generation PLAis compared to a petrochemical polymer, PLA retains itsoutstanding production characteristics. Vink et al. (2003) com-pared ten commercially available polymers with the first gen-eration of Ingeot and found that PLA consumed the leastfossil energy (see Figure 1.11). Over the years, NatureWorkshas shown initiative by maximizing the usage of biomass aswell as wind power to reduce its dependence on fossil fuel.NatureWorks has highlighted that the advances of second-generation PLA technology manages to capture more free

PLA: gross energy electricity and fuels

PLA: gross energy operating supplies and WWT

LA: gross energy electricity and fuels

LA: gross energy operating supplies and WWT

Dextrose: gross energy electricity and fuels

Dextrose: gross energy operating supplies and WWT

Transport: gross energy used to transport corn to CWM

Corn: gross energy electricity and fuels

Corn: gross energy operating supplies (fertilizers, pesticides, ...)

Corn feedstock: renewable energy (16.3 MJ/kg corn)

12.8

0.4

14.9

11.4

8.8

0.6

0.4

1.1

3.8

0.0 5.0 10.0 15.0 20.0 25.0 30.0

28.4

Renewable energy

Fossil energy54.1 MJ/kgPLA

[MJ/kg PLA]

Figure 1.10 Energy requirement for the production of NatureWorks’first generation PLA (Vink et al., 2003). LA5 lactic acid, WWT5wastewater treatment, CWM5 corn wet mill (published with permission ofElsevier).


carbon in the air. The production of second generation PLAcan achieve a negative emission impact to protect the envi-ronment against global warming. The second generationIngeot production system in 2006 emitted 0.27 kg CO2 eq./kg PLA and used 27.2 MJ/kg PLA of fossil energy. Thisrepresents a reduction of 85% and 50% respectively whencompared to Ingeo’s 2003 eco-profile data (Vink et al.,2007). In an announcement in early 2009, NatureWorksclaimed that Ingeot production had been further improvedwith greenhouse gas emissions lowered by 36% and non-renewable energy utilization reduced by 44% compared todata from 2005. The latest Ingeot technology generates1.24 kg CO2 eq/kg of Ingeot (see Figure 1.12) and uses42 MJ of nonrenewable energy (Vink et al., 2010). At thesame time, the gross water saving for the production of PLAis encouraging compared to the majority of petrochemicalpolymers (see Figure 1.13). However, the total gross waterrequired for amorphous PET production is slightly lower

160.0

140.0

120.0

100.0

80.0

60.0

40.0

[MJ/

kg p

olym

er]

20.0

0.0Nylon 66 Nylon 6 PC HIPS GPPS LDPE PET SSP PP PE TAM PLA1 PLA Bio/WPCellophane

Fossil fuels Fossil feedstock

Figure 1.11 Fossil energy requirement for petrochemical polymersand PLA. The cross-hatched area of the bars represent the fossilenergy used as chemical feedstock (i.e., fossil resource to build thepolymer chain). The solid part of the bars represented the grossfossil energy used for the fuels and operation supplies used to drivethe production processes. PC5 polycarbonate; HIPS5 high-impactpolystyrene; GPPS5 general purpose polystyrene; LDPE5 low-density polyethylene; PET SSP5 polyethylene terephthalate,solid-state polymerization (bottle grade) PP5 polypropylene; PETAM5 polyethylene terepthalate, amorphous (fiber and film grade);PLA5PLA first generation; PLA B/WP (PLA, biomass/wind powerscenario) (adapted from Vink et al., 2003).

60 POLYLACTIC ACID

than for PLA. This is because the production of PLA usesan agricultural source, which needs water for irrigation.Furthermore, the fermentation and wastewater treatment alsorequire plenty of water. Thus, water is considered an unavoid-able input for the production of PLA.

Purac’s technology uses sugarcane as the feedstock for lacticacid production. Purac’s lactic acid facility in Thailand has been

0

10

From

cra

de to

pol

ymer

fact

ory

gate

, kg

CO

2 eq

/kg

poly

mer

9

8

7

6

5

4

3

2

1

Nylon

66

Nylon

66 PCABS

HIPS/G

PPS

PET(SSP)

PET (am

orph

ous)

LDPE PP

PVC (sus

pens

ion)

Inge

o 20

05

Inge

o 20

09

Figure 1.12 Contribution of petrochemical polymers and Ingeot PLAto global climate change (adapted from Vink et al., 2010).

160.0

140.0

120.0

100.0

80.0

60.0

40.0

[MJ/

kg p

olym

er]

20.0

0.0Nylon 66 Nylon 6 PC HIPS GPPS LDPE PET SSP PP PE TAM PLA1 PLA Bio/WPCellophane

Fossil fuels Fossil feedstock

Figure 1.13 Gross water used in the production of petrochemicalpolymers and PLA (adapted from Vink et al., 2003).


in operation since 2007. The lactic acid is scheduled for conver-sion into lactide once the new large-scale plant is ready in 2011.During the development stage, most of the lactic acid has beenexported for conversion at Purac’s lactide plant in Spain. Grootand Boren (2010) in a life cycle assessment of lactide and PLAproduction from sugarcane in Thailand reported that every ton ofPLA emits 500 kg CO2. Although alternative renewable energycan be obtained through the burning of sugarcane bagasse � inthe range of 17�95 kWh/MT of sugarcane, Groot and Boren(2010) point out that environmental credit varies, depending onthe type of byproducts, combustion technology and the mix ofenergy in application. In other words, every source of PLA has aunique eco-profile. Thus, it is of the utmost importance to developa green PLA through the careful selection of processes. The envi-ronmental impact of PLA is shown in Figure 1.14 together withthat of some of the petrochemical polymers. It is clear thatsome ecological aspects of PLA production need improvementto become greener. The most detrimental impact scores of

1.2

1

0.8

Nor

mal

ised

val

ues

0.6

0.4

0.2

0PED non-

renPED ren. ADP GWP AP EP POCP HTP Farm land

PLLA PE-HD granulate PE-LD granulate PP granulatePET granulate PS

Figure 1.14 Comparison of the most relevant ecological factorsinvolved in the production of PLLA and fossil-based derived polymers.PED5 primary renewable energy; PED non-ren5 primary non-renewable energy; GWP5 global warming potential; AP5 acidificationpotential; EP5 eutrophication potential; POCP5 photochemical ozonecreation potential; ADP5 abiotic resource depletion potential;HTP5 human toxicity potential (adapted from Groot and Borén, 2010).

62 POLYLACTIC ACID

PLA belong to the process of sugarcane cultivation and transfor-mation into sugar. In addition, the farming of sugarcane alsocontributes significantly to the eutrophication, acidification andphotochemical ozone creation due to the nitrogen emission ofammonia-based fertilizers. The combustion of agricultural resi-dues for the co-generation operation tends to release greenhousegases such as NOx, SOx and CO. Some of the related soil activ-ity by microorganism can cause emission of NOx and methaneas well. PLA is the one polymer that causes effects on farmlanddue to the continuous re-planting, resulting in soil erosion andloss of natural nutrients. As a result, precautions and environ-mental assessment need to be conducted prior to deforestationfor the farming of sugarcane.

1.6 Environmental Impact of PLA at thePost-Consumer Stage

PLA is a suitable substitute for existing petrochemical poly-mers in the manufacture of cups, containers and packaging.PLA is known to degrade well when disposed along withmunicipal waste, and so is less of a burden to the environment.Unlike petrochemical polymers such as PE, PP, PET, PCand PS, which require one hundred years to break down intoharmless substances, PLA is fully compostable and is acceptedas a green product, especially in Japan, the United States andEU countries. Several reports have been published about theeco-efficiency of PLA post-consumer, and this has been com-pared to conventional plastics. These reports have includedPLA cups (Vercalsteren et al., 2010), clamshells (Kruger et al.,2009) and wrappings (Hermann et al., 2010).

An eco-analysis was carried out comparing four types ofplastics cups � the reusable PC cup, one-way PP cup, one-wayPE-coated cardboard cup and one-way PLA cup � used atpublic events held in Flanders (Belgium). Vercalsteren et al.(2010) presented their findings in a report for the FlemishInstitute for Technological Research (VITO), which concludedthat there was no obvious indication as to which cup system


had the highest or lowest environmental impact. There is a nodecisive formula that makes it possible to use all the impactcategories � e.g. carcinogens, ecotoxicity, fossil fuels etc. � toindicate which cup system is superior (see Figure 1.15a). Forinstance, the PLA cup uses less fossil fuel than the PP cup;however, the respiratory effects caused by the inorganics of thePE-coated cardboard cup remain the highest. In other words,the size of the event also has an effect on the eco-efficiency ofthe cups. The PC cup appears to have the lowest environmentimpact when used for a small event. This is due to the reusablenature of PC, which can be washed by hand, meaning that lesswater and detergent is used in the cleaning process. However,the turnover usage of the PC cup is higher at a large event.Consequently, washing is carried out frequently, and so the PCcups wear out rapidly and require regular replacement. Althoughthe PLA cup has the highest eco-indicator points, PLA is alsolikely to be competitive in long-term applications. This isbecause PLA technology is still in its infancy and there willbe future improvements to environmental issues such as acidi-fication/eutrophication and the dependence on fossil fuels.Eco-improvement initiatives conducted by NatureWorks haveproved fruitful for the production of second generation Ingeot(PLA6), the eco-indication points for which are 20% lowerthan for the first generation PLA (PLA5) (see Figure 1.15b).NatureWorks is currently working on PLA/NG (i.e. next gen-eration Ingeot), which should be an absolutely green product,for better environmental protection.

The Institute for Energy and Environmental Research(IFEU), Heidelberg, Germany, has carried out a head-to-headcomparison of the lifecycle of clamshell packaging made ofIngeot, virgin and recycled PET. The report by Kruger et al.(2009) compared the environmental impact according to thetreatment of the respective clamshells using landfill and incin-eration approaches. Both methods are commonly used in Europeand the United States. Data from the report is summarized inTable 1.22, and shows that Ingeot has numerous advantagescompared to virgin PET. The aquatic eutrophication and acidifi-cation of Ingeot appears to be higher, mainly due to the

64 POLYLACTIC ACID

Eco-Indicator values for the use of cups on SMALL events

Eco-Indicator values for the use of cups on SMALL events - update

2008

Eco-Indicator values for the use of cups on LARGE events - update

2008

Eco-Indicator values for the use of cups on LARGE events

Exp

ressed

in

eco

-in

dic

ato

r p

oin

ts (

Pt)

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-in

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Pt)

Exp

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-in

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ato

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0.655 0.666

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Cardb

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PLA-c

up (P

LA 5

)PLA

-cup

(PLA

6)

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G)

Carcinogens

Resp. organics

Resp. inorganics

Climate change

Ozone layer

Ecotoxicity

Acidification/EutrophicationMinerals

Fossil fuels

Carcinogens

Resp. organics

Resp. inorganics

Climate change

Ozone layer

Ecotoxicity


Fossil fuels

Carcinogens

Resp. organics

Resp. inorganics

Climate change

Ozone layer

Ecotoxicity


Fossil fuels

Carcinogens

Resp. organics

Resp. inorganics

Climate change

Ozone layer

Ecotoxicity


Fossil fuels

0.518

0.581 0.626 0.609

0.5010.534

0.589

0.507

0.297

0.632

0.318

0.309

0.6550.5790.5620.610

Figure 1.15 (a) Eco-indicator values for the usage of cups at small-scale indoor and large-scale outdoor events;(b) eco-indicator values for the usage of cups at small-scale indoor and large-scale outdoor events for PLA6and PLA/NG (adapted from Vercalsteren et al., 2010).

production stage involving farming and soil activity, whichgenerate greenhouse gases. Although recycled PET seemsto be a greener product compared to PLA, recycled PET isactually made of virgin PET, thus, the upstream fabricationprocess is offset during the virgin PET calculation. It is confi-dently believed that Ingeot can yield a better ecological per-formance in recycled usages as well. However, this requires athorough analysis in the near future. In conclusion, the greenstatus of PLA is undoubted for sustainable environmentprotection.

Table 1.22 Comparison of the Ecological Aspects of Ingeot,Virgin PET (vPET) and Recycled PET (rPET) for DifferentEnd-of-Cycle Treatment Approaches under the EuropeanUnion framework

Treatment Landfill Incineration

Clamshell Ingeot vPET rPET Ingeot vPET rPET

Renewable

primary

energy (GJ)

0.53 0.02 0.02 0.52 0.01 0.02

Non-renewable

primary

Energy (GJ)

1.22 1.70 1.04 0.96 1.37 0.88

Aquatic

eutrophication,

(g PO4)

9.73 3.81 2.20 6.61 0.68 0.62

Acidification

(kg SO2)

0.52 0.34 0.20 0.49 0.33 0.19

Climate change

(kg CO2)

60.6 77.8 49.4 81.8 104 62.7

Fossil resources

(kg crude oil)

13.5 26.0 14.6 9.9 21.4 12.3

Data Extracted from Kruger et al., 2009.

66 POLYLACTIC ACID

1.7 Conclusion

PLA has been around for decades, but it is only in morerecent years that the growth in its applications has expanded rap-idly. PLA is a biodegradable polymer that possesses the poten-tial to substitute existing petroleum-based commodity polymers,to help overcome the accumulation of plastic waste in landfills.In addition to its use in general and packaging products, it alsohas biomedical applications in surgery, due to its compatibilitywith living tissue. PLA is favored because it can be mass pro-duced from agricultural sources, which are renewable, allowingsociety to reduce its dependency on petrochemicals. Continuedresearch and development has made it possible to lower green-house emissions associated with the production process. In con-clusion, PLA has got great potential and marketability as abiodegradable polymer for a sustainable future.

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Groot, W.J., Boren, T., 2010. Life cycle assessment of the manufacture

of lactide and PLA biopolymers from sugarcane in Thailand. Int.

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Henton, D.E., Gruber, P., Lunt, J., Randall, J., 2005. Polylactic acid

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70 POLYLACTIC ACID

2 Synthesis and Production ofPoly(lactic Acid)

Chapter Outline2.1 Introduction 712.2 Lactic Acid Production 72

2.2.1 Laboratory Scale Production of Lactic Acid 852.3 Lactide and Poly(lactic Acid) Production 86

2.3.1 Review of Lactide Production Technology 882.3.2 Polymerization and Copolymerization of

Lactide 942.3.3 Lactide Copolymer 972.3.4 Quality Control 992.3.5 Quantification of Residual Lactide in PLA 100

2.3.5.1 Calculations 1022.3.6 Quantification of D-Lactic Acid Content in PLA 103

2.3.6.1 Calculations 1042.4 Conclusion 105References 105

2.1 Introduction

Poly(lactic acid) (PLA) is produced from the monomer oflactic acid (LA). PLA can be produced by two well-knownprocesses � the direct polycondensation (DP) route and thering-opening polymerization (ROP) route. Although DP is sim-pler than ROP for the production of PLA, ROP can produce alow-molecular-weight brittle form of PLA. Generally, severalsubstances are involved in the production of PLA, and theserelationships have been summarized in Figure 2.1. The lacticacid for the process is obtained from the fermentation of sugar.Lactic acid is converted to lactide and eventually to PLA. It shouldbe noted that there are two different terms, ‘poly(lactic acid)’ and‘polylactide’, for the polymer of lactic acid. Both terms are used



http://dx.doi.org/10.1016/B978-1-4377-4459-0.00002-0

interchangeably; however, scientifically there is a differencebecause polylactide is produced through the ROP route whereaspoly(lactic acid) is generated using the DP route. Generallyspeaking, the term ‘poly(lactic acid)’ is widely used to mean thepolymer that is produced from lactic acid. (The explanationregarding the difference between poly(lactic acid) and polylactideis given here to help readers’ understanding.)

2.2 Lactic Acid Production

Lactic acid is the basic building block for the production ofPLA. It is chemically known as 2-hydroxy-propionic acid withchiral stereoisomers L (2) and D (1). Its physical propertiesare listed in Table 2.1. Naturally occurring lactic acid is mostlyfound in the L form, while chemically synthesized lactic acidcan be a racemic D and L mixture. Lactic acid is a biologicallystable substance and highly water soluble. Prior to the massapplication of lactic acid for the manufacture of biodegradablepolymer materials, lactic acid was widely used in industry as asolvent for metal cleaning, as a detergent, a humectant, a mor-dant, and for tanning leather. Its use as a humectant means thatit acts as a moisturizer in cosmetic and personal hygiene pro-ducts, while its use as a mordant relates to its use as an additiveduring color dying, in order to improve dye acceptance of afabric in textile manufacture. Lactic acid is also added duringthe manufacture of lacquers and inks for better absorption onthe printing surfaces. Lactic acid is also used in the food indus-try to provide a sour taste to beverages. The addition of lactic

Glucosefermentation Lactic acid

Lactide

Poly(lactic) acid

Polylactide

1

2Route 1 Direct PolycondensationRoute 2 Ring Opening Polymerization

Figure 2.1 General routes of PLA production.

72 POLYLACTIC ACID

acid in the form of kalium lactate extends the shelf life ofmeat, poultry and fish, through the ability to control pathogenicbacteria while maintaining the original flavor of the food.Many dairy products, including yogurt and cheeses, tastemildly sour due to the presence of lactic acid, which providesaddition antimicrobial action in these products.

Lactic acid and lactate are naturally present in the mamma-lian body when glycogen (a form of carbohydrate stored inmammalian cells) is anaerobically utilized by muscle to pro-duce energy (i.e. during insufficient oxygen supply). Althoughgeneration of lactic acid and lactate by the muscles duringanaerobic exercise can cause fatigue and soreness afterward,lactate has been found to be an important chemical forsustained exercising � lactate serves as a fuel produced by onemuscle to be readily consumed by another muscle. The feelingof soreness is due to the accumulation of acidic ions caused bythe glycolysis reaction.

Carl Wilhelm Scheele was the first to discover lactic acid in1780. Since then, lactic acid has been industrially producedusing the fermentation process, with the earliest technology

Table 2.1 Physical Properties of Lactic Acid

CAS Registry No. 50-21-5 (DL-lactic acid)

79-33-4 (L-lactic acid)

10326-41-7 (D-lactic acid)

Chemical formula C3H6O3

Chemical name 2-hydroxy-propanoic acid

Molecular weight 90.08

Physical appearance Aqueous solution

Taste Mildly sour

Melting point 53�CBoiling point .200�CSolubility in water (g/100 g H2O) Miscible

Dissociation constant (Ka) 1.383 1024

pKa 3.86

pH (0.1% solution, 25�C) 2.9

732: SYNTHESIS AND PRODUCTION OF POLY(LACTIC ACID)

introduced by the French scientist Fremy in 1881. Pure lacticacid has two stereoisomers (also known as enantiomers), whichare shown in Figure 2.2. These two stereoisomers are synthe-sized by different lactate dehydrogenase enzymes in livingorganisms. Currently, 85% of the lactic acid produced is con-sumed by the food-related industry, while the balance is usedfor non-food applications, such as the production of biopoly-mers, solvents, etc. (John et al., 2009).

L-lactic acid can be metabolized by enzyme action in thehuman body. However, the intake of D-lactic acid should beundertaken with caution: 100 mg/kg of body weight is the dailymaximum stipulated for adult humans, and strictly no D-lacticacid and DL-lactic acid should be present in infant food, accord-ing to the guidelines of the FAO/WHO (Deshpande, 2002).Although the human body does not produce an enzyme forD-lactic acid, a small intake is considered safe because thehigh solubility of D-lactic acid promotes hydrolysis in the bodyfluid subsequently removed by the body’s excretion system.

Most of the lactic acid produced globally is made using thefermentation process. According to a review paper on lacticacid bacteria fermentation (Reddy et al., 2008), there are about20 genera in the phylum Firmicutes that encompass lactic acidproducing bacteria; these include Lactococcus, Labctobacillus,Streptococcus, Leuconostoc, Pediococcus, Aerococcus,Carnobacterium, Enterococcus, Oenococcus, Tetragenococcus,Vagococcus andWeisella. Of the many genera that contain lactic-acid producing bacteria, Lactobacillus is the most significant,

HOO

OHL-(+)-lactic acid

Lactic acidmolecular structure

D-(–)-lactic acid

CH3H

HOO

OH

HH3COxygen CarbonHydrogen

Figure 2.2 Stereoisomers of lactic acid.

74 POLYLACTIC ACID

comprising around 80 species that produce lactic acid (Axelsson,2004). These include the species Lactobacillus amylophilus,Lactobacillus bavaricus, Lactobacillus casie, Lactobacillusmaltoromicus, and Lactobacillus salivarius. Strains ofLactobacillus delbrueckii, Lactobacillus jensenii, andLactobacillus acidophilus produce D-lactic acid and a mixture ofthe two stereoisomers concurrently (Nampoothiri et al., 2010).Some species of Lactobacillus have the ability to undergo fer-mentation using a variety of saccharines, as listed in Table 2.2.

Although the bacterial organism and the carbohydrate are theessential components in the fermentation process, the organismrequires a variety of nutrients to ensure its healthy functional-ity, including B-vitamins, amino acids, peptides, minerals, fattyacids, nucleotide bases and carbohydrates. The amounts arespecies-dependent and the source of these nutrients can be agri-cultural derivatives, such as corn steep liquor and yeast extract.Lactic acid bacteria are heterotrophic, which mean that theylack biosynthetic capabilities (Reddy et al., 2008). The additionof complex nutrients can significantly increase the cost of pro-duction. However, a higher purity lactic acid is produced.

In the lactic acid fermentation process, the lactic acid bacte-ria are grown under anaerobic conditions with low energy pro-duction. Such low-energy yield bacteria grow slowly compared

Table 2.2 The Different Saccharines Fermented by LactobacillusSpecies that Produce Lactic Acid

Lactobacillus Saccharine

Lactobacillus delbreuckii, subspecies

delbreuckii

Sucrose

Lactobacillus delbreuckii, subspecies

bulgaricus

Lactose

Lactobacillus helveticus Lactose and galactone

Lactobacillus amylovirus Starch

Lactobacillus lactis Glucose, sucrose and

galactose

Lactobacillus pentosus Sulfite waste liquor


to respiration-type microbes. Lactic acid bacteria survive wellat temperatures of between 5�45�C and mildly acidic condi-tions (pH 5.5�6.5). Reddy et al. (2008) has divided theLactobacillus genus into three groups according to fermenta-tion patterns (see Table 2.3). The products of each patternare shown in Figure 2.3. Fermentation of different types ofcarbohydrate-rich material varies the yield of lactic acid (seeTable 2.4). In addition to Lactobacillus bacteria there are othermicrobial sources � fungi such as Rhizopus oryzae also pro-duce lactic acid, but under aerobic conditions. However fer-mentation of such fungi is not favorable, due to their slowgrowth and low productivity, while the significant agitationand aeration required leads to high energy costs for long-termoperations (Jem et al., 2010). Despite the focus on using wildmicroorganisms for producing lactic acid, a few attempts have

Table 2.3 Fermentation Patterns of Lactobacillus Genera(Reddy et al., 2008)

Homofermentative Yields more than 85% lactic acid from

glucose, which is equivalent to

fermenting 1 mol of glucose to 2 mol

of lactide acid while generating a net

yield of 2 mol of ATP per molecule of

glucose metabolized. Mostly lactic

acid is produced in this process

Heterofermentative Yields a lower amount (about 50%) of

lactic acid accompanied by side

products. Every mol of glucose

generates 1 mol of lactic acid, 1 mol

of ethanol and 1 mol of carbon

dioxide. There is less growth for each

mol of glucose metabolized, as only

1 mol of ATP is produced for every

mol of glucose

Rare heterofermentative Less-well-known fermentative species,

which yield DL-lactic acid, acetic acid

and carbon dioxide

76 POLYLACTIC ACID

been made to improve L-lactic acid yield through metabolicengineering, as summarized in Table 2.5.

Most of the commercial fermentation processing of lacticacid in batches requires 3 to 6 days to complete; sugar concen-trations of between 5�10% are used (Garlotta, 2001). Manylactic acid fermentation processes have been patented over thedecades. Most of these patents are restricted in the disclosingof the fermentation process, as they also provide the lactic acidseparation technologies. In US patent 6 319 382 B1, by theinventor Norddhal (2001), whey protein is added as a nutrientsubstrate for the lactic acid bacteria and protease is added tothe fermentor to enable hydrolysis of protein to supply aminoacids during the fermentation process. In addition, the aqueous

ATP

ADP

NAD+

NAD+

NAD+

NAD+

NADH

NADH

NADH

NADH

NADH

NADH

CO2

Glucose

Glucose 6-P

Fructose 6-P 6-Phosphogluconate

Xylulose 5-PFructose 1-6-bis P

2 NAD+2 ADP2 ATPNAD+

NAD+

2 NADH

2 NAD+

2 Lactate

Homolactic metabolism

A-Lactate dehydrogenase B-Alcohol dehydrogenase

Heterolactic metabolism

Lactate Ethanol

4 ADP4 ATP

2 H2O H2O2 NADH

Glyceraldehyde 3-P—DHAP — Glyceraldehyde 3-P

Pyruvate2 Pyruvate Acetaldehyde

Acetyl -P

BAA

ATP

ATP

ADP

ADP

Figure 2.3 Metabolism of lactic acid bacteria (Reddy et al., 2008).Published with permission from Elsevier.


medium in use consists of yeast extract, K2HPO4,MgSO4.7H2O, MnSO4.2H2O, Tween

s 80, lactose and cysteinhydrochloride to ensure optimum reactivity of lactic acid bacte-ria (Norddahl, 2001; Tsao et al., 1998; Robison, 1988). Duringthe fermentation process, the pH of the aqueous slurry is moni-tored to maintain near-neutral mildly acidic conditions. Theobjective is to avoid the accumulation of lactic acid in the fer-mentative medium, which can inhibit the productivity of thebacteria. Thus, a continual addition of bases such as calciumhydroxide, sodium hydroxide or ammonia can help to convertthe generated lactic acid into a lactate salt. The lactate salt canlater be converted to lactic acid by reaction with acids.

Table 2.4 Yield of Lactic Acid Corresponding to Type ofStarchy and Cellulosic Material and to Microorganism(Nampoothiri et al., 2010) (Published with Permissionof Elsevier)

Substrate Microorganism Lactic AcidYield

Wheat and rice

bran

Lactobacillus sp. 129 g/l

Corn cob Rhizopus sp. MK-96-1196 90 g/l

Pretreated wood Lactobacillus delbrueckii 48�62 g/l

Cellulose Lactobacillus coryniformis

ssp. Subsp. torquens

0.89 g/g

Barley Lactobacillus casei NRRL

B-441

0.87�0.98 g/g

Cassava bagasse L. delbrueckii NCIM 2025,

L. casei

0.90�0.98 g/g

Wheat starch Lactococcus lactis ssp. ATCC

19435

0.77�1 g/g

Whole wheat Lactococcus lactis and

Lactobacillus delbrueckii

0.93�0.95 g/g

Potato starch Rhizopus oryzae, R. arrhizuso 0.87�0.97 g/g

Corn, rice and

wheat starches

Lactobacillus amylovorous

ATCC 33620

,0.70 g/g

Corn starch L. amylovorous NRRL B-4542 0.935 g/g

78 POLYLACTIC ACID

Table 2.5 Modification of Strains for Better Yield of L-LacticAcid (Narayanan et al., 2004)

Strain Modification

Lactobacillus

helveticus

Inactivation of D-lactate dehydrogenase

gene increases the amount of L-lactic acid

two-fold

Lactobacillus

plantarum

L-lactate dehydrogenase gene of Lactobacillus

plantarum was isolated and cloned

into Escherichia coli. This has increased

the L-lactate dehydrogenase activity 13-fold

Lactococcus

lactis

Increasing the number in lac operon that

increases the L-lacate dehydrogenase results

in slight increases in yield of lactic acid.

Operon: functioning unit of genomic material

containing a cluster of genes under the

control of a single regulatory signal or

promoter

Lac operon: an operon required for the

transport and metabolism of lactose in enteric

bacteria

Lactobacillus

johnsonii

D-lactate dehydrogenase gene was isolated and

an in vitro truncated copy of the gene was

used to inactivate the genomic copy of the

wild strain. Due to lowering L-lactate

dehydrogenase activity rerouted pyruvate to

L-lactate with an increase of byproducts such

as acetaldehyde, acetoin and diacetyl

E. coli The dehydrogenase and phosphotransacetylase

double mutants able to grow anaerobically on

glucose by lactate fermentation producing

D-lactate. An L-lactate dehydrogenase gene

is introduced, resulting in fermentation yields

of L-lactate

Rhizopus oryzae The mutant grows under limited oxygen

conditions with 5% wild type alcohol

dehydrogenase activity, which leads the

pyruvate to form lactic acid


According to Norddhal (2001), ammonia is preferable overother bases, because it has the advantage of providing a sourceof nitrogen nutrients to the bacteria. This has shown evidenceof improved growth compared to sodium hydroxide. Most pro-cesses employ calcium hydroxide to control the pH of theaqueous mixture, including in the production process utilizedby NatureWorks (Vink et al., 2010). Sulfuric acid is then addedto the lactic acid broth to recover the lactic acid, resulting inthe formation and precipitation of gypsum (i.e. calcium sulfate,CaSO4.2H2O). The gypsum is separated from the broth using afiltration method and this gypsum is a byproduct, which can besold as a construction material or a soil conditioner. It is esti-mated up to 1 ton of gypsum is produced for every ton of lacticacid yield (Garlotta, 2001).

The lactic acid broth from the fermentor needs to furtherundergo thorough separation before pure lactic acid is recov-ered. Some approaches include electrodialysis, reverse osmosis,liquid extraction, ion-exchange acidification, ion-exchangepurification, distillation, insoluble salt processes or esterifica-tion. Henton et al. (2005) have comprehensively summarizedthe lactic acid purification technologies and their respectiveadvantages and disadvantages (see Table 2.6). Although thereis no difference in recovering D-lactic acid and L-lactic acid,extreme conditions should be avoided (e.g., high temperatures),due to the high possibility of converting D-lactic acid andL-lactic acid into each other, thus forming a racemic mixture.High optical purity of L-lactic acid (.99%) is required forfood- and pharmaceutical applications in order to achieve thestringent requirements for oral intake. Selectivity of a singleoptical lactic acid is preferable for quality control, becausedifferent optical lactic acids can affect the properties of PLA,such as melting point, mechanical strength and degradability.

Currently, NatureWorks owns the largest single lacticacid production facility, with 180,000 MT produced per yearusing corn as the feedstock. The lactic acid produced byNatureWorks is mainly used for conversion to Ingeos PLA.Meanwhile, Purac is the largest lactic acid producer, andtheir products are widely used in the food, beverage and

80 POLYLACTIC ACID

Table 2.6 Lactic Acid Purification Technology (Henton et al.,2005, Published with Permission)

Technology Feature Advantage/Disadvantage

Electrodialysis Can be used to

continuously remove

lactic acid (lactate

ions) through a

membrane driven by

electrical potential

1. Does not require

acidification of

fermentation

2. Energy cost and

capital

Reverse

osmosis

Lactic acid is

continuously

removed through a

membrane

1. Higher productivity

due to ability to

maintain low-acid

level in fermentor

2. Fouling of the

membrane

3. Requires acidic pH

stable organism

Liquid

extraction

Lactic acid is

continuously

removed from the

fermentation of

acidified broth by

preferential

partitioning into a

solvent

1. Suitable for

continuous process

and provides

efficient removal

from many non-

acidic impurities

2. High cost of capital

3. Solvent loss costs

Ion exchange

(acidification)

The lactate salt is

acidified by a strong

acid ion-exchange

resin

1. Eliminates the need

to add a strong acid

to the fermentation

2. Cost of resin and

issues of resin

regeneration

Ion exchange

(purification)

Lactic acid is removed

from the aqueous

solution by

complexing with an

amino-containing resin

1. This is the solid

equivalent of

t-amine extraction

technology without

the solvent loss

issues


pharmaceutical industries, as well as for producing PLA, pri-marily for surgical applications (e.g. pins, sutures and screws).Purac is also involved in the copolymerization of lactic acidwith other monomers � glycolide, ε-caprolactone or D,L-lactic

Table 2.6 Lactic Acid Purification Technology (Henton et al.,2005, Published with Permission)—cont’d

Technology Feature Advantage/Disadvantage

2. Regeneration of the

resin

3. Cost and availability

of the resin

Distillation Lactic acid is separated

from less volatile

components by

vacuum steam

distillation

1. Lactic acid can be

steam distilled

2. Significant

purification must be

done prior to

distillation

3. Depending on

conditions, some

degradation and

oligomerization can

occur

Insoluble salt

processes

The fermentation or

purification process is

run at a concentration

that exceeds the

solubility of the

lactate salt (e.g.

CaSO4), which is

isolated and acidified

1. Simple process that

utilizes low-cost

capital

2. The crystallization

of CaSO4 occludes

impurities and

results in relatively

impure acid

Esterification Lactate esters are

prepared and the

volatile esters are

distilled

1. Distillation and

separation of esters

gives high-quality

product

2. Requires

reconversion to acid

82 POLYLACTIC ACID

acid. The company built a new lactic acid plant in Thailand,which has been operating since 2007. The plant is designed toutilize locally harvested sugarcane as the feedstock, with aninitial capacity of 100,000 MT. It is planned that the plant willbe at full operating capacity in the near future. While lacticacid is mainly produced using cheap agricultural feedstock,two companies use still use the chemical synthesis method toproduce a racemic mixture of lactic acid. These companies areMusashino, in Japan, and Sterling Chemicals Inc., in the USA.Chemical synthesis and the ordinary fermentation processesundergo different reaction paths (Narayanan et al., 2004).These are outlined below:

Chemical Synthesis Approach

(a) Addition of hydrogen cyanide

CH3CHOAcetaldehyde

1 HCNhydrogen cyanide

��!catalystCH3CHOHCN

lactonitrile

(b) Hydrolysis by H2SO4

CH3CHOHCNLactonitrile

1H2O1 1/2H2SO4sulphuric acid

��! CH3CHOHCOOHlactic acid

1 1/2ðNH4Þ2SO4ammonium salt

(c) Esterification

CH3CHOHCOOHLactic acid

1 CH3OHmethanol

��! CH3CHOHCOOCH3methyl lactate

1H2O

(d) Hydrolysis by H2O

CH3CHOHCOOCH3Methyl lactate

1H2O


1 CH3OHmethanol


Fermentation Approach

(a) Fermentation and neutralization

C6H12O6Carbohydrate

1 CaðOHÞ2calcium hydroxide

��!fermentation ð2CH3CHOHCOO2ÞCa211 2H2O

calcium lactate

(b) Hydrolysis by H2SO4

2ðCH3CHOHCOO2Þ

Calcium lactate

Ca211 H2SO4sulphuric acid

��! 2CH3CHOHCOOHlactic acid

1 CaSO4calcium sulphate

(c) Esterification

CH3CHOHCOOHLactic acid

1 CH3OHmethanol

��! CH3CHOHCOOCH3methyl lactate

1H2O

(d) Hydrolysis by H2O

CH3CHOHCOOCH3Methyl lactate

1H2O


1 CH3OHmethanol

Commercial purified lactic acids are sold at concentrationsbetween 50�80%. Typical food-grade lactic acids differ inconcentration and depend on the carbohydrates blended withthem, which are mainly added to improve taste, nutrition oras preservatives. Galacids, which is produced in food gradesby Galactic S. A., one of the major manufacturers of lacticacid in Europe, has nutritional energy data as provided inTable 2.7. Industrial lactic acid is sold in aqueous solution at80�88% purity for small scale applications such as terminatingagents for phenol formaldehyde resins, alkyd resin modifiers,solder flux, lithographic and textile printing developers, adhesive

84 POLYLACTIC ACID

formulations, electroplating and electropolishing baths or deter-gent builders.

The pharmaceutical grade of lactic acid is sold atUS$1000�1500 per ton while the industrial grades can be20% less expensive depending on the area of application. Manyof the new lactic acid production facilities in China have yet toprove their feasibility in the short term due to the maturity ofthe implementation of the high efficiency fermentation processas well as the local market demands of PLA. Nevertheless, themulti-applications of LA will maintain its market interest on along term basis.

2.2.1 Laboratory Scale Production of Lactic Acid

Fermentation is the most common approach used for the pro-duction of lactic acid. The method that is outlined here (Oharaet al., 2003) can be utilized to synthesize lactic acid in lactateform for prepolymer lactic acid production:

Box 2.1 Method for Synthesis of Lactic Acid in LactateForm

1. First, 5 L of culture medium is prepared, which con-

sists of 500 g glucose, 100 g yeast extract and 100 g

polypeptone. The medium is sterilized using an

autoclave and finally a microbe species, from one

of the flowing genera is implanted: Lactobacillus,

Streptococcus, Rhizopus, Bacillus or Leuconostoc.

Table 2.7 Nutritional Data of Galacids

Nutritional Data Concentration

Basis (per 100 g) 50% 80% 85% 88% 90%

Energy (kJ) 745�760

1196�1211

1271�1287

1317�1332

1347�1362

Total carbohydrates

(%)

49.5�50.5

79.5�80.5

84.5�85.5

87.5�88.5

89.5�90.5


Box 2.1 Method for Synthesis of Lactic Acid in LactateForm—cont’d

2. The mixture is cultured at a temperature of 37�C,with the pH maintained at 7.0 using 6 N ammo-

nia�water. The culture takes 15 hours to complete.

3. The culture is concentrated using 1000 g of ethanol

and refluxed for 3 hours at between 90 and 100�Cin a condenser to obtain ethyl lactate.

4. The inconsumable ammonia is separated using a

gas-washing bottle connected at the end of the con-

denser, cooling with ice-water. This ammonia

entrapping system is able to collect up to 98% of

the ammonia.

5. The remaining reaction mixture is maintained at

80�C to vaporize the 750 g of unreacted ethanol by

distillation.

6. The reaction mixture is further raised to a tempera-

ture of 120�C to remove the water.

7. After the removal of water, the reaction mixture

undergoes a distillation process at 50 mmHg at a liq-

uid temperature of 70�100�C, to yield 650 g of puri-

fied ethyl lactate for the polycondensing process.

As shown in the step 3, the ethanol is used to react with fermen-ted lactic acid via an esterification reaction to form ethyl lactate(generally known as lactate ester). The reason lactate ester is pref-erable over lactic acid for conversion into lactic acid prepolymeris because lactic acid has a corrosive nature. Therefore, synthesiz-ing PLA from lactic ester can help to reduce costs by avoiding theneed to invest in corrosive-resistant reactors and equipment. Thisrepresents significant cost reduction in the long term.

2.3 Lactide and Poly(lactic Acid) Production

Lactide is an intermediate substance in the production ofPLA via the ring-opening polymerization method. As can beseen from Figure 2.4, although both direct polycondensation

86 POLYLACTIC ACID

and ring-opening polymerization involve the step of producinglactic acid prepolymer, the polymerization through lactide for-mation can be done without the application of coupling agents.The purpose of the coupling agents is to increase the molecularweight of the PLA. In fact, the lactic acid prepolymer is low-molecular-weight PLA (Mw5 1000�5000). This low-molecular-weight PLA is unusable � it possesses weak, glassy andbrittle properties. According to Garlotta (2001), the formationof low-molecular-weight PLA for direct reaction of prepolymeris mainly used because of the lack of reactivity of the endgroups, excess water and high viscosity of the polymer meltonce polymerization completed. Ring-opening polymerizationof lactide was first performed by Carothers in the mid-1900s,and later patents relating to this technology by DuPont kick-started the mass production of PLA. Lactide molecules undergoeither anionic or cationic ring polymerization, depending onthe selection of initiator type. The formation of free radicalswith the action of initiators upon the functional groups elevatesthe propagation of chain reaction; consequently, a high-molecular-weight polymer is formed.

Directcondensationpolymerization

Polymerizationthroughlactideformation

Low molecular weight prepolymerMW = 1000–5000

CH3

CH3 CH3

CH3

HO

OHH3C

H

O

HOC

C

OHH

CH3

O

HO

O

O

O

O

O

Opoly

CH3

CH3 CH3

CH3

HO

O

O

O

OO

O

O

OH

Chain coupling agent

Ring-openingpolymerization

Azeotropic dehydration condensation

–H2O

L-Lactic acid

D-Lactic acid

CH3

CH3

CH3

CH3

OHO

O

O


Low molecular weight polymerMW > 100 000

O

O

OO

CH3

H3C

HC C

OCCH

O

O

Lactide

Opoly

O

CC

OO

Figure 2.4 Reaction paths of producing poly(lactic acid) from lacticacid. Published with permission from Elsevier.


2.3.1 Review of Lactide Production Technology

Lactide production technologies have been in use since the1930s, with the related publication by Carothers et al. (1932)about the reversible polymerization of six-membered cyclicesters. After that, lactide technology underwent a period of inac-tivity because the purity of lactide was insufficient for large-scale production. Lactide technology did well after DuPontdeveloped a purification technique. This ultimately led towardsmass-scale production by NatureWorks. This section mainlyfocuses on the mass-scale lactide production as developed byCargill�DuPont (currently known as NatureWorks) in the earlyphases, as well as some related lactide technologies.

US Patent 5 274 073, entitled ‘Continuous Process ForManufacture of A Purified Lactide’, as filed by Gruber et al.(1993), describes a method of lactide production that can besummarized into the steps shown in Figure 2.5. Initially, thecrude lactic acid is fed into an evaporator. Generally, this iscommercially produced lactic acid, consisting of 15% lacticacid with 85% water. This solution is due to the fact that thefermentation process was carried out in an aqueous medium.The evaporator is used to vaporize the water as the top product,while the remainder is the concentrated lactic acid. Lactic acidproduced by fermentation contains other impurities mixed withthe enantiomers of L- and D-lactic acid. These impurities,including carbohydrates, proteins, amino acids, salts, metal ion,aldehydes, ketones, carboxylic acids and esters of carboxylicacids, can affect the production quality of lactide, and subse-quently of PLA. Hence, on a case-by-case basis, an evaporatorcan be designed to fulfill the purity requirement. Nevertheless,a conventional evaporator, such as a multiple effects evapora-tor, a wiped film evaporator or a falling film evaporator, canprovide a basic separation to the crude lactic acid. The opera-tion of the evaporator works best at below atmospheric pres-sure, in order to reduce the consumption of heating energywhile, importantly, avoiding a racemic stereocomplex of D-lac-tide, L-lactide or meso-lactide (see Figure 2.6), which tends tocause quality issues when undergoing polymerization to form

88 POLYLACTIC ACID

polyD,L-(lactic acid). Upon exiting the evaporator, the crudelactic acid has been concentrated to over 85%.

For the next stage, the concentrated lactic acid is transferredinto a prepolymer reactor. The prepolymer reactor is actually asecond evaporator, which further removes water from the lacticacid. At the same time, the condensation polymerization takes

Side StreamSide Stream

Main

Pro

cess

Pat

hMa

in P

roce

ss P

ath

Feed crude lactic acid to an evaporator continuously

Discard or recycle removedwater, solvent of

condensation by-product

Recycle of discard removedwater, solvent or condensationby-product contaminated with

lactic acid

Remove and recycle or discardhigh boiling unreacted polymer

as liquid from lactide reactor

Remove uncondensed waterand lactide impurity as a

vapor and recycle or discard

Remove water and lactideacid impurities as a

distillate/overhead stream,recycle or discard

Remove water or solvent from crude lactic acid

Feed concentrated lactic acid to a pre-polymer reactor

Polymerize concentrated lactic acid to from a pre-polymer by removing water

Feed pre-polymer to a lactide reactor

Simultaneously feed catalyst to a lactide reactor

Remove crude lactide as a vapor from lactide reactor

Partially condense crude lactide in a condenser

Feed condensed crude lactide to a distillation system

Purify lactide in the distillation system

Remove purified lactide as a high boiling bottomsstream from the distillation system

Feed purified lactide as a liquid directly to apolymerization system

Polymerize lactide to polylactide

Figure 2.5 Process flow of lactide production.


place to form poly(lactic acid) with an optimum molecularweight of 400�2500. When lactic acid has undergone conden-sation polymerization, the alkoxy group is reacted with thehydrogen cleaved from the hydroxyl group of the nearest lacticacid molecule. So the remaining products are a long lactic acidlinkage and excess water molecules. The removal of water isimportant in order to ensure that the reaction proceeds towardthe right side of the reaction path shown in Figure 2.7. Duringthe polymerization reaction a depolymerization reaction alsotakes place due to the inherent equilibrium of the reactionscheme. The equilibrium reaction suggested by Gruber et al.(1993) is shown in Figure 2.8.

Gruber et al. (1993) assert that the prepolymer reactor canbe designed into a single system, which can facilitate both theconcentrating of the lactic acid feed while polymerizing thelactic acid into oligomer lactic acid. However, split units forevaporation and prepolymerization stages are preferable forcontrollability. The recovery of lactic acid can be done moreeffectively when the water separated from the crude lactic acidis recycled back to prevent loss of feed material. At the sametime, a high concentration of lactic acid at reduced volume inthe prepolymerization stage is helpful to shift towards polymer-ization rather than depolymerization, for a better yield of

OH

CH3

H3C

C C

OCCH

O

O

L-Lactide

OCH3

H

H3C

C C

OCCH

O

O

meso-Lactide

OCH3

H

H

C C

OCCH3C

O

O

D-Lactide

Figure 2.6 Lactide Stereocomplex. Published with permission fromElsevier.

HO C

H O

CH3

C OH OH + n–1 H2OHO C

H O

CH3

C O C

H O

CH3n–2

C O C

O

CH3

C

Figure 2.7 Condensation polymerization of lactic acid.

90 POLYLACTIC ACID

oligomer lactic acid. The oligomer lactic acid, which has alsobeen described previously as the prepolymer, is fed into thelactide reactor. Many suitable types of catalyst can be simulta-neously fed with the prepolymer stream into the reactor.Catalysts such as metal oxides, metal halides, metal dusts andorganic metal compounds derived from carboxylic acids arecommonly used. Based on the reaction scheme set out inFigure 2.8 the depolymerization reaction (as shown in the bot-tom part) immediately reaches equilibrium. The reaction is car-ried out at high temperature to enable the crude lactide tovaporize and be continuously removed from the reactor, thusshifting the reactor towards the depolymerization reaction. Thisfollows Le Chatelier’s principle that the lactide reactor yield ishigher when there is a reduced amount of lactide, in order toseek reaction equilibrium in the lactide reactor. However, theunreacted long chain of PLA, with its high boiling point,remains in the bottom of the reactor as it is purged. Such prod-uct can be recycled back into either the prepolymer reactor orthe lactide reactor. The unreacted high-molecular-weight PLAundergoes transesterification to form a shorter chain of oligo-mer, which is a source of lactide for the reactor as well. The

HO CH

CH3 CH3

C

O O

O CH C O CH C

O

CH3

O CH C OH

O

CH3

O CH C OH

O

CH3

HO CH C CO CH

O

CH3

O

CH3

n–3

O CH C

O

CH3n–4

C

O

O

CH

CH3

CH3

OO

C HC

+

Figure 2.8 Equilibrium reaction of polymerization anddepolymerization reaction of lactic acid (Gruber et al., 1993).


use of such a recycle stream is not limited to improving therecovery of valuable feed material; it also helps to improve theproduction yield and it reduces the cost of waste treatment.

As mentioned earlier, the stereocomplex composition of thelactide produced is dependent on the initial crude lactic acid

Source of pentose and/or hexose derived from starch,agricultural biomass etc.

Culture medium containing microbes for fermentation

Lactic fermentation

Addition ammonium lactate Recycling ofammonia

Esterification

Lactate esterRecycling of alcohol

Polycondensation and dealcoholization

Lactic acid prepolymer

Depolymerization and intramolecular esterification

Lactide

Polylactic acid

Ring-opening polymerization

Figure 2.9 Steps to produce poly(lactic acid) from the initialfermentation process (Ohara et al., 2003).

92 POLYLACTIC ACID

feed, the catalyst used and the processing parameters (i.e.temperature and pressure). Thus, the crude lactide vapor con-sists of a mixture of L-lactide, D-lactide and meso-lactide.Some low-volatility products, such as water, lactic acid anddimer lactic acid, are contained in this stream as well. A par-tial condenser can be used to partly condense the low-boiling-point components, such as water and lactic acid, prior toundergoing distillation. A conventional distillation column isfitted to separate the feed into three component streams. Thedistillate or overhead low-boiling components are water andlactic acid, and the other low-molecular-weight byproductsfrom the reactions of the prepolymer reactor and lactidereactor. The bottom stream consists of products with lowervolatility than lactide, such as lactic acid oligomers with morethan three repeating units. Both overhead and bottom productsare recyclable in order to achieve a higher conversion of lacticacid into lactide. Lactide is simultaneously withdrawn fromthe side stream as the third component. The purity of the lac-tide is considered acceptable at a concentration of 75%; witha higher purity of lactide it is very important to form a highquality polylactide.

Ohara et al. (2003), in US Patent 6 569 989, disclosed a moredetailed process for synthesizing lactide (see Figure 2.9). Lacticacid is polycondensed by stepwise heating at 130�C to 220�C atdifferent stages, while the pressure of each stage is reduced to5 mmHg, yielding PLA prepolymer of molecular weight1000�3500. This multi-stage process can be further defined atdifferent temperatures, where the first stage is at 135�C, the sec-ond stage 150�C, the third stage 160�C, the fourth stage 180�C,and finally the fifth stage at 200�C. A metal type of catalyst, assummarized in Table 2.8, is added during the reaction toimprove selectivity while reducing reaction time. Since bothpolymerization and depolymerization take place simultaneously,a similar catalyst is also suitable to be applied in lactide produc-tion. Hence, a metal catalyst is added with the reaction condi-tions of 200�C and pressure of 5 mmHg to produce lactide. Thecatalyst is preferably applied at 0.001�0.01 wt% with respect tothe fresh or crude lactic acid or lactide to the reactor.


2.3.2 Polymerization and Copolymerization of Lactide

Most of the processes in industry employ ring-opening poly-merization of lactide to achieve high-molecular-weight PLA.

Table 2.8 Type of Catalyst for Polymerization andDepolymerization of Lactic Acid

MetalGroup

Type Catalyst

IA Hydroxide of alkali metal Sodium hydroxide, potassium

hydroxide, lithium

hydroxide

Salt of alkali metal with

weak acid

Sodium lactate, sodium

acetate, sodium carbonate,

sodium octylate, sodium

stearate, potassium lactate,

potassium acetate,

potassium carbonate,

potassium octylate

Alkoxide of alkali metal Sodium methoxide, potassium

methoxide, sodium

ethoxide, potassium

ethoxide

IIA Calcium salt of organic

acid

Calcium acetate

IIB Zinc salt of organic acid Zinc acetate

IVA Tin powder, organic tin

type catalyst except

monobutyltin

Tin lactate, tin tartrate, tin

dicaprylate, tin dilaurylate,

tin diparmitate, tin

distearate, tin dioleate, tin

α-naphthoate, tinβ-naphthoate, tin octylate

IVB Titanium type compound

and zirconium type

compound

Tetrapropyl titanate,

zirconium isopropoxide

VA Antimony type compound Antimony trioxide

VIIA Manganese salt of organic

acid

Manganese acetate

94 POLYLACTIC ACID

Although the direct polycondensation reaction path appears to bethe simplest to polymerize monomer lactic acid, the yield ofPLA is relatively low in molecular weight (,5000) and weak inmechanical properties. Consequently, its applications are lim-ited. The ring polymerization is conducted in a solvent-basedsystem with anionic and cationic initiations. This has the advan-tages of high reactivity and selectivity as well as low racemiza-tion and impurity levels. Trifluoromethane sulfonic acid andmethyl trifluoromethane sulfonic acid are the cationic initiatorsused to polymerize lactide (Garlotta, 2001). Such cationic ring-opening polymerization is carried out at a low temperature(100�C), and the resulting PLA product is an optically purepolymer. The used of a primary alkoxide, such as potassiummethoxide, as the anionic initiator can produce a ,5% racemi-zation of PLA. Nevertheless, the anionic lactide polymerizationrequires a higher reaction temperature, typically for weakerbases such as potassium benzoate and potassium phenoxide,which initiate its reactivity at 120�C.

Although the anionic and cationic initiations as describedabove have the advantage of producing low racemization PLAat a lower temperature, the reaction process needs to be con-ducted in a solvent system in a dilute condition, in order tocontrol its reactivity and the sensitiveness for the presence ofimpurities. The anionic and cationic initiators also possess hightoxicity. These aspects narrow the application of anionic andcationic initiators in lactide polymerization. In the large-scalePLA industry, the metal catalyst approach is preferable, withits fast and high yield in lactide polymerization. The highlyeffective catalyst is merely applied at a low level (,10 ppm),which helps to ensure the safety of PLA when used in foodpackaging and in biomedical applications. Polymerization oflactide yields high-molecular-weight (.250,000) with the useof stannous octoate (commonly known as tin octoate). The cat-alytic ring-opening polymerization reaction is also applicablefor copolymerization of lactide with other monomers such asglycolide and ε-caprolactone.

Many of the catalyst systems can be used to polymerize lactide,including transition metals such as aluminum, zinc, tin and the


lanthanides. These metal oxides and complexes have differentdegrees of conversion and high racemization. Of the metal com-pounds listed in Table 2.8, tin or stannous (Sn) complexes arevery important for the bulk polymerization of lactide, especiallytin (II) bis-2-ethylhexanoic acid (also known as tin octoate). Tinoctoate is preferred due to its solubility in molten lactide; thus,it achieves a high conversion .90% with high selectivity by pro-ducing less than 1% racemization. Such high conversion reactiv-ity is favorable for good quality control in terms of mechanicaland biodegradability properties. This is important for lactic acidpolymers used for biomedical applications because only the Lenantiomer of lactic acid is consumable by the living cell due tothe lack of an enzyme in the body to consume D-lactic acid afterhydrolysis into its monomer. Meanwhile, substantial racemizationcan significantly affect crystallinity rearrangement structure com-pared to a single isomer, thus lowering the mechanical properties.

Lactide polymerization with the addition of tin octoate isproposed via the coordination�insertion mechanism, as shownin Figure 2.10 (Henton, et al., 2005). The tin catalyst initiatesthe ring-opening reaction by attacking the nearest double-bondoxygen of the lactide. The hydroxyl and nucleophilic speciessimultaneously react with the ring-opened radical and finally

O

O

O

O

O

O

O

O

OH

Sn R

O

O

O O

RSn

Sn(Oct)2 Sn(Oct)2

(Oct)2

O H

(Oct)2

R-OH

Sn(Oct)2

O

O

O

O

OO H

ORO

HROO

Figure 2.10 Coordination-insertion chain growth reaction scheme oflactide to PLA using tin octoate: R, growth of polymer chain (Hentonet al., 2005).

96 POLYLACTIC ACID

form a water molecule as a byproduct to achieve a steady state.The polymerization process produces low racemic mixture, highproductivity and high-molecular-weight PLA. The typical poly-merization conditions are: 180�210�C, at tin octoate concentra-tions of 100�1000 ppm, and 2�5 h to achieve 95% conversion.The tin octoate catalyst is also applicable for copolymerizationof caprolactone and glycolide, with the reaction scheme asshown in Figure 2.11. The residual catalyst in the above poly-merization process can cause unexpected problems in terms ofprocessing degradation, hydrolysis or toxicity. Thus, the reactiv-ity of the catalyst is deactivated with the addition of phosphoricor pyrophosphoric acid. The catalyst can also be separated byreaction with sulfuric acid by precipitation. The catalyst levels inthe PLA or its copolymer should be reduced to 10 ppm or lessto ensure the quality for end-user applications (Hartmann, 1998).

2.3.3 Lactide Copolymer

Lactide can be copolymerized with glycolide monomer toimprove the biological compatibility and good absorptiontime when implanted in living tissue. Typical applications oflactide�glycolide copolymers, such as surgical sutures, should

O

O

O

O

O

O

O

O

O

OO

O

m n

O

OO

O

Lactide Glycolide

Lactide Caprolactone

+

+

Sn(Oct)2

Sn(Oct)2

OO

OO

O

O

mn

Figure 2.11 Copolymerization of glycolide and caprolactonerespectively with lactide using tin octoate (Henton et al., 2005).


contain .80% glycolide by weight. This is because when theglycolide in the copolymer is less than 80% the crystallinity islower and so it lacks tensile strength and retention in applica-tions. Low glycolide content in a copolymer is not favorablebecause the predominance of lactide in the suture lowers therate of absorption by living tissue. The copolymerization oflactide and glycolide shares a similar process to the polymeri-zation of optically active lactide alone. Stannous octoate is alsoused as a catalyst in the copolymerization reaction, as shown inFigure 2.11. A high glycolide-content copolymer is achievablethrough a two-step reaction process. According to Okuzumiet al. (1979), the first stage involves polymerization at65�75% of optically active lactide with the remaining glyco-lide monomer. In the second stage, a high content of monomerat 80�90% glycolide is used in the copolymerization reaction.Okuzumi et al. (1979) found that if the reverse is attempted,the resulting lactide�glycolide copolymer has a low molecularweight and forms an amorphous polymer, which makes it inap-propriate for surgical sutures, which need a high strength fiber.This observation is summarized in Table 2.9.

Lactide is also copolymerized with ε-caprolactone monomerto produce biomaterials for the manufacture of surgical implantsand drug carriers. The copolymerization of lactide�caprolactonefollows a similar reaction path as lactide�glycolide. The prefer-ence is for a random copolymer comprising of 55�70 mol% oflactide and 30�45 mol% of caprolactone for application as apharmaceutical carrier (Bezwada, 1995).

Although the above-mentioned lactide�glycolide and lactide�caprolactone copolymers are suitable for making medical deviceswith excellent properties, such as high strength, stiffness andlong braking-strength retention, copolymerization of lactidewith dioxanone monomer is able to enhance the elongationproperties of lactide for toughened applications, such as absorb-able medical devices, foams for tissue scaffolds and hemostaticbarriers. The production of lactide�dioxanone copolymer isundertaken in a two-step reaction as well (see Figure 2.12).Initially, the lactide is reacted with a small amount of p-dioxanonemonomer at 100�130�C for 4�8 h. This is followed by increasing

98 POLYLACTIC ACID

the temperature to 160�190�C for 1�4 h to further copolymerizelactide with the long-chain poly(p-dioxanone) prepared in the firststep. This finally produces a high-strength, tough and elastomericbiopolymer with 30�50 mol% of lactide. The low toxicity andhigh-selectivity stannous octoate is used in the copolymerizationprocess to produce a high-molecular-weight moxanone copolymerof 60,000�150,000.

2.3.4 Quality Control

The mass-scale production of PLA is most commonly used tomake domestic consumer products, such as packaging or bottles,which come into contact with food. For these PLA productsquality control no longer limits mechanical properties, as it doesfor commodity polymers (polyethylene, polypropylene, polysty-rene, etc.). However, manufacturers need to carefully classifythe extent of lactide, and specifically D-lactic acid, in the finalproduct. NatureWorkss, as the largest producer of PLA, has setup standard testing procedures for the firms that produce items

Table 2.9 Tensile Strength of Lactide�Glycolide Copolymerwith Respect to the Composition

Wt% of Lactide�Glycolide TensileStrength(psi)3 1031st Stage

Copolymerization2nd StageCopolymerization

FinalCopolymerComposition

40/60 0 40/60 53

70/30 12/88 35/65 64

70/30 12/88 40/60 67

70/30 12/88 45/55 72

87/13 12/88 35/65 60

87/13 12/88 50/50 58

78/22 12/88 35/65 71

78/22 12/88 45/55 63

78/22 18/72 50/50 58


using their Ingeos products. These testing procedures are sum-marized below. Although these tests were developed byNatureWorkss LLC, their application is not limited, and can bewidely used throughout the PLA industry.

2.3.5 Quantification of Residual Lactide in PLA(NatureWorks LLC, 2010b)

The determination of lactide composition in PLA is con-ducted by gas chromatography (GC) using a flame ionizationdetector (FID). This GC/FID method is only able to detectresidual lactide in the range 0.1�5 wt%. Although the detec-tion range is narrow, it is still within the concentration 3 wt%of lactide monomer found in PLA at 180�C, as well as after thedevolatilization of PLA, when the concentration can furtherreduce to ,0.3 wt%. As mentioned before, the lactide mono-mer consists of three stereoisomers � L-lactide, D-lactide and

Step 1: Partial polymerization of p-dioxanone monomer

Step 2: Copolymerization of lactide, and poly(p-dioxanone) homopolymer and p-dioxanone monomer to form segmented copolymer

Lactide Poly(p-dioxanone)

Poly(p-dioxanone)

110–160 ºC forlactide copolymers

p-Dioxanone

p-Dioxanone

Catalyst

100–130 ºCO

O O

O

O O

O

O O

O

O C C C COHHH

Hm

HHO

O C C C COHHH

Hm

HHO

O C C C COHHH

Hy

p m

HHO O C C C C

OHHH

HHHOC C

OH

CH3x

O

+ +

Poly(p-dioxanone-co-lactide) segmented copolymersm>>p, and the poly(p-dioxanone) portion 70–98 wt %

Figure 2.12 Copolymerization reaction steps of lactide-dioxanonecopolymer (Bezwada, 1995).

100 POLYLACTIC ACID

meso-lactide. The GC method is only able to detect two lactidepeaks with respect to the meso-lactide and the D-lactide orL-lactide (detected in a single peak). Meso-lactide has the earli-est eluting peak, while the following eluting peak represents theco-existing D-lactide and L-lactide. The GC/FID method startswith the preparation of four solutions, namely a) internal standardstock solution, b) lactide standard stock solution, c) lactide work-ing standard solution, and d) PLA samples solution. The methodsof preparation are summarized in Table 2.10. Methylene chlorideis the solvent used to dissolve PLA and release the free lactide.

Table 2.10 General Procedures for Preparing Standard andPLA Solution Samples for GC�FID Testing to Determine thePresence of Residual Lactide

Preparation ofSolution

General Procedure

Internal standard stock

solution (IS)

Solution is prepared by adding 2,6-

dimethyl-γ-pyrone with methylene

chloride under dilute conditions

Lactide standard stock

solution (LS)

Solution is prepared by adding a high

purity L-lactide to methylene chloride

under dilute conditions

Lactide working

standard solution

(LW)

Solution is prepared by mixing

methylene chloride with IS and LS.

Small amount of acetone is added and

diluted with cyclohexane. This

solution is analyzed using GC�FID

PLA solution samples Solution is prepared to determine the

composition of lactide in the PLA

sample. First, a small known amount

of PLA is added with the IS solution

and diluted with methylene chloride as

solution #1. Solution #1 is added with

a small amount of acetone and diluted

with cyclohexane to become solution

#2. Solution #2 is filtered and

analyzed using GC�FID


The free lactide remains in the methylene chloride while excesscyclohexane is added to precipitate the PLA. Then, the super-nate solution is filtered and injected into the GC and is finallydetected by the FID. The selection of the GC injection tempera-ture is crucial � it must be 200�C to avoid the possibility ofreformed lactide due to the presence of low-molecular-weightlactic acid oligomers in the supernate.

2.3.5.1 Calculations

1. The calculation of residual lactide as below relates toa DB-17 ms capillary column (Agilent J&W), and isalso equivalent to (50%-phenyl)-methylpolysiloxane:

RRF5Peak Area of both D- and L-lactide standard

Amount ðgÞ of D- and L-lactide

� �

3Amount ðgÞ of ISPeak Area of IS

� �

2. The weight of D- and L-lactide (g) in the sample canbe determined according to the following equation:

Total D- and L- lactide ðgÞ

5Peak Area of both D- and L-lactide in sample

RRF

� �


� �(2.1)

3. The weight percentage (wt%) of total D- andL-lactide presence in the sample is calculatedusing the following equation:

wt:% D- and L- lactide in sample

5D- and L- lactide ðgÞSample weight ðgÞ

� �3 100

(2.2)

102 POLYLACTIC ACID

4. The weight of meso-lactide (g) in the sample canbe determined according to the following equation:

meso-lactide ðgÞ

5Peak Area of meso-lactide in sample

RRF

� �


� � (2.3)

5. The weight percentage (wt%) of meso-lactidepresent in the sample is calculated using the fol-lowing equation:

wt:% meso-lactide in sample

5meso-lactide ðgÞSample weight ðgÞ

� �3 100

(2.4)

6. Total both the D- and L-lactide and meso-lactideto obtain the wt% of residual lactide monomer inthe PLA.

7. The prescribed GC/FIB testing method has evalu-ated its precision of 1.9% relative standard deviationto detect lactide in PLA.

2.3.6 Quantification of D-Lactic Acid Content in PLA(NatureWork LLC, 2010a)

The evaluation of D-lactic acid presence is very important,especially if the PLA product will be in contact with food or is abiological implant. The daily allowable intake of D-lactic acid inadult humans is ,100 mg/kg and no D-lactic acid must be foundin infant food. The residual of D- and L-lactic in the PLA samplescan be detected using the chiral gas chromatography (CGC)method, together with a flame ionization detector (FID). In thismethod, the samples are initially hydrolyzed in methanolic potas-sium hydroxide and this is followed by acidification under strongacid to catalyze the esterification reaction. Then, methylene chlo-ride and water are added to the acidified solution, which separate


into a double layer � an organic layer containing methyl lactateenantionmers dissolved in methylene chloride at the bottomand the non-organic water as the top layer. The bottom organiclayer is collected and analyzed using a GC�FID system (seeTable 2.10). The procedure for preparing PLA samples for testingis shown in Box 2.2:

Box 2.2 Procedure for Preparing PLA Samples for Testing

1. PLA sample is dissolved in methanolic potassium

hydroxide solution at 65�C.2. Sulfuric acid is added to the sample solution and

heated to 65�C again.

3. Deionized water and methylene chloride are added.

4. The liquid sample is left to separate into two layers.

5. The bottom layer of the sample is drawn up and

analyze with GC�FID.

The separation of methyl lactate enantiomers is recom-mended using an Agilent J&W CycloSil-B column, which is30% hepatkis (2,3-di-O-methyl-6-O-t-butyl dimethylsilyl)-β-cyclodextrin in DB-1701� stationary phase. β-cyclodextrin issuitable for chiral separation due to the fact that its cyclicoligosaccharide units forms inclusion complexes with differentequilibrium constants with respect to methyl lactate enantiomers,leading to easy GC separation. This method has a wide detectionrange of 0.05�50% D-lactic acid in PLA.

2.3.6.1 Calculations

1. The relative percentages of D- and L-lactic acidenantiomers present in PLA is calculated as follows:

% D-lactide

5Area of methyl D-lactate peak

Area of methyl D-lactate peak1Area of methyl L-lactate peak

3100%

(2.5)

104 POLYLACTIC ACID

2. The prescribed GC�FIB testing method has anevaluated precision of ,1% relative standard devi-ation to determine D-lactic acid in PLA.

2.4 Conclusion

PLA is produced from the starting substance, lactic acid,which is derived through the fermentation of carbohydrate. Theproduction of PLA can be conducted by direct polycondensationor ring-opening lactide polymerization methods. Of the two,ring-opening lactide polymerization remains the most widelyused method, because the process has a higher yield and lowtoxicity. In addition, ring-opening lactide polymerization issuitable for lactide copolymerization with caprolactone, glycolideor dioxanone. The traces of lactide and D-lactic acid present inthe PLA are determined to avoid overdose consumption. Overall,the understanding of production and quality control of PLA arevery helpful to ensure the feasibility of PLA in the long term.

References

Axelsson, L., 2004. Lactic acid bacteria: classification and physiol-

ogy. In: Salminen, S., von Wrignht, A., Ouwehand, A. (Eds),

Lactide Acid Bacteria: Microbiological and Functional Aspects.

Marcel Dekker, New York, USA, pp. 1�66.

Bezwada, R.S., 1995. Liquid copolymers of epsilon-caprolactone and

lactide. U.S. Patent 5 442 033. U.S. Patent Office.

Bezwada, R.S., Cooper, K., 1997. High strength, melt processable,

lactide-rich, poly(lactide-co-p-dioxanone) copolymers. U.S. Patent

5 639 851, U.S. Patent Office.

Carothers, W.H., Dorough, G.L., van Natta, F.J., 1932. J. Am. Chem.

Soc. 54, 761�772.

Deshpande, S.S., 2002. Handbook of Food Toxicology. Marcel

Dekker, New York, Basel.

Garlotta, D., 2001. A literature review of poly(lactic acid). J. Polym.

Environ. 9, 63�84.


Gruber, P.R., Hall, E.S., Kolstad, J.J., Iwen, M.L., Benson, R.D.,

Borchardt, R.L., 1993. Continuous process for manufacture of a

purified lactide. U.S. Patent 5 274 073, U.S. Patent Office.

Hartmann, H. (1998). High molecular weight polylactic acid poly-

mers. In: Kaplan, D. L. (Ed.), Biopolymers from Renewable

Resources, Springer-Verlag, Berlin, pp. 367�411.

Henton, D. E., Gruber, P., Lunt, J., and Randall, J. (2005). Polylactic

acid technology. In: Mohanty, A. K., Misra, M., and Drzal, L.T.

Editors. Natural fibers, biopolymers, and biocomposites. Boca

Raton, FL. Taylor & Francis. p. 527–77.

Jem, K.J., Por, J.F.v.d., Vos, S.d., 2010. Microbial Lactic acid, its

polymer poly(lactic acid), and their industrial applications. In:

Chen, G.-Q. (Ed.), Plastics from Bacteria: Natural Functions and

Applications. Microbiology Monographs, 14, pp. 323�345.

John, R.P., Anisha, G.S., Nampoothiri, K.M., Pandey, A., 2009.

Direct lactic acid fermentation: focus on simultaneous saccharifi-

cation and lactic acid production. Biotechnol. Adv. 27,

145�152.

Nampoothiri, K.M., Nair, N.R., John, R.P., 2010. An overview of the

recent developments in polylactide (PLA) research. Bioresour.

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Narayanan, N., Roychoudhury, P.K., Srivastava, A., 2004. L (1) lac-

tic acid fermentation and its product polymerization. Electron. J.

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NatureWorks LLC, 2010b. Evaluation of %D-Lactic Acid Content of

Polylactide (PLA) Samples by Gas Chromatography (GC) Using

A Flame Ionization Detector (FID)- External Release Version.

NatureWorks LLC, 2010a. Quantification of Residual Lactide in

Polylactide (PLA) by Gas Chromotography (GC) Using a Flame

Ionization Detector (FID)- External Release Version.

Norddahl, B., 2001. Fermentative Production and Isolation of Lactic

Acid. U.S. Patent No. 6 319 382 B1, U.S. Patent Office.

Ohara, H., Ito, M., Sawa, S., 2003. Process for producing lactide and

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employed as starting material. U.S. Patent 6 569 989 B2, U.S.

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Okuzumi, Y., Mellon, A.D., Wasserman, D., 1979. Addition

Copolymers of Lactide and Glycolide and Method of Preparation.

U.S. Patent 4 157 437, U.S. Patent Office.

106 POLYLACTIC ACID

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3 Thermal Properties ofPoly(lactic Acid)

Chapter Outline3.1 Introduction 1093.2 Thermal Transition and Crystallization of PLA 1123.3 Thermal Decomposition 1233.4 Heat Capacity, Thermal Conductivity and

Pressure�Volume�Temperature of PLA 1313.5 Conclusion 138References 139

3.1 Introduction

Poly(lactic acid) (PLA) is a biodegradable hydrolyzable ali-phatic semi-crystalline polyester produced through the directcondensation reaction of its monomer, lactic acid, as the oligo-mer, and followed by a ring-opening polymerization of the cycliclactide dimer. Lactic acid optical monomers consist of L-lacticacid and D-lactic acid, as shown in Figure 3.1. From both opticalmonomers, three possible stereoforms of lactide can be formedfrom the oligomer of lactic acid; these are L-lactide, D-lactideand meso-lactide (also known as DL-lactide, see Figure 3.2).The purified L-lactide, D-lactide, meso-lactide dimers are con-verted into corresponding high-molecular-weight polyester bycatalytic ring-opening polymerization. The stereochemical com-position of the PLA has significant effects on its melting point,crystallization rate, extent of crystallization and mechanicalproperties (Drumright et al., 2000). In this chapter, the thermalproperties of PLA and PLA-based composites, including heatcapacity, thermal transition, thermal decomposition and crystal-lization, are discussed.

Thermal properties of PLA are usually determined by differ-ential scanning calorimetry (DSC), thermogravimetric analysis



http://dx.doi.org/10.1016/B978-1-4377-4459-0.00003-2

(TGA) and dynamic mechanical analysis (DMA). Crystallization,crystallinity degree and thermal properties of PLA depend on thepolymer molecular weight, polymerization conditions, thermalhistory, purity, etc. (Fambri and Migliaresi, 2010). It has beenreported by Achmad et al. (2009) that poly(L-lactide) (PLLA)and poly(D-lactide) (PDLA) are semi-crystalline polymerswith melting points of about 180�C, whereas the copolymerpoly(DL-lactide) (PDLLA) is an amorphous material with aglass transition temperature of only 50�57�C. From Table 3.1,it can be seen that different lactide isomers can significantlyaffect the molecular number (Mn), glass transition temperature(Tg), melting temperature (Tm), enthalpy and crystallization tem-perature (Tc) of PLA. It can be observed that the Tg and Tm ofPLA increases in relation to Mn regardless of whether the iso-mer type is L or D. Information about Tg is very important for

H

OH

O

HO

H3C

OH

D-lactic acidL-lactic acid

L-lactide Meso-lactide D-lactide

O

HO

H CH3

H3C

CH3

O

O

O

O

H3C

CH3

O

O

O

O

H3C

CH3

O

O

O

O

Figure 3.2 Stereoform of lactides.

OHO

OH

H

L-lactic acid D-lactic acid

CH3

OHO

OH

H3C H

Figure 3.1 Lactic acid optical monomers.

110 POLYLACTIC ACID

polymers � when the temperature is below its Tg large-scalemolecular motion is not possible because the material is essen-tially frozen, whereas if the temperature is above its Tg molecularmotion on the scale of its repeat unit (such as a single mer in apolymer) is able to take place, allowing it to be ‘soft’ or ‘rub-bery’. In other words, the Tg of a polymer is linked to its pro-cessability and service temperature. PLA with a low Tg is notsuitable for containing hot water as the material would soften andbe deformed.

However, melting and crystallization of copolymers ofPDLLA, which consist of polymerization of L-lactic and D-lacticacid, were not detectable even at high molecular weight. Thiscan be explained by the formation of an atactic structure,which can affect the microstructure rearrangement upon cooling.At the same time, the molecular weight has minimal effects onthe heat of crystallization ΔHc (0.3 J/g), as shown by comparingL isomers of Mn of 4.7 and 14.0, but the crystallization tempera-ture increased by 12�C. This indicates that longer chain PLArequires higher kinetic energy to break down intermolecularbonds, while the free energy of crystallization of polylactideremains. This shows the limits of crystallization in PLA.Nevertheless, there were less obvious trends of polydispersity(Mw/Mn) influence on the thermal properties of PLA.

Table 3.1 Effects of Isomers on the Thermal Properties of PLA(Ahmed and Varshney, 2010)

IsomerType

Mn

3 103Mw/Mn

Tg

(�C)Tm

(�C)ΔHm

(J/g)Tc

(�C)ΔHc

(J/g)

L 4.7 1.09 45.6 157.8 55.5 98.3 47.8

DL 4.3 1.90 44.7 � � � �L 7.0 1.09 67.9 159.9 58.8 108.3 48.3

DL 7.3 1.16 44.1 � � � �D 13.8 1.19 65.7 170.3 67.0 107.6 52.4

L 14.0 1.12 66.8 173.3 61.0 110.3 48.1

D 16.5 1.20 69.1 173.5 64.6 109.0 51.6

L 16.8 1.32 58.6 173.4 61.4 105.0 38.1

1113: THERMAL PROPERTIES OF POLY(LACTIC ACID)

3.2 Thermal Transition and Crystallizationof PLA

L- and D-lactic acid stereoisomers occur naturally as the pro-ducts of microorganism activity. However, L-type lactic acidis regularly found and it is also occasionally in the form of aracemic mixture. Typical D and L-forms of low-molecular-weight lactic acid can form racemic crystals when mixedtogether. This can be realized in the cyclic form of lactic acid,known as L- or D-lactides, which have a melting point of97.5�C in contrast with their racemic compound, which melts at124�C (Tsuji et al, 1991). The blending of PDLA and PLLA canform a stereocomplex with a melting point of 230�C, which isconsiderably higher than the 180�C for the respective neatPDLA and PLLA. This was demonstrated by Ikada et al. (1987)in a study using X-ray diffraction, which showed the differencesof crystalline structure in the formation of a stereocomplex ofPDLA and PLLA blending. Tsuji et al. (1991) quoted the find-ings of Sakakihara et al. (1973) that when an equimolar ratio ofoptically active polymers are blended together, the opticalcompensation of the stereopolymer occurs, leading to inactivematerials in the crystalline region or unit cell. The side-by-sidepacking of stereo complexes can be expected to form a compact,ordered structure with a high melting temperature.

PLLA is a semicrystalline polymer with a melting range ofabout 180�C and a crystallinity of about 70%. It can be pro-cessed by thermal processing such as injection-molding andextrusion. This L-type polymer shows the slowest degradationrate of all resorbable polylactides because of its high crystallin-ity (Bendix, 1998). Semicrystalline PLA has a higher shearviscosity than amorphous PLA. However, as the temperatureincreases the shear viscosity decreases for both amorphous andsemicrystalline PLA (Auras et al., 2004). Semicrystalline PLAexhibits both Tg and Tm conditions. Above Tg (i.e. .58�C)PLA is rubbery, while below Tg it becomes glassy but it is stillcapable of creeping until it is cooled to its transition tempera-ture at approximately245�C, below which it behaves as a

112 POLYLACTIC ACID

brittle polymer (Henton et al., 2005). However, PDLLA is anamorphous polymer that shows no melting but a Tg of50�60�C. Therefore, polymerization can be easily carried outin the melt, preferably in a reactor capable of processing highlyviscous media (Martin and Averous, 2001). In contrast, a stereo-complexed PLLA�PDLA blend has a melting temperature of220�230�C, higher than that of PLLA and PDLA. ThePLLA�PDLA blend also has a higher hydrolysis resistance com-pared with pure PLLA and PDLA (Yu et al., 2006).

PLLA and PDLA are crystalline polymers due to the enan-tiomeric purity of the pristine monomers and the stereoregu-larity of the polymer chains. However, PDLLA, which isnormally consists of random copolymers of L and D-lactide inequimolar amounts, remains amorphous because of its irregu-lar structure (Ahmed et al., 2009). Nevertheless, most PLA isin crystalline form because the majority of sources of lacticacid are derived from microorganism activity, which producesthe L-isomer. Auras et al. (2004) reported that depending onthe composition of the optically active L- and D,L-enantiomers,PLA can crystallize in three forms (α, β and γ). The α-structureis more stable and has a melting temperature of 185�C com-pared to the β-structure, which has a Tm of 175�C. Both D andL isomers of PLA exhibit insignificant differences in thermalproperties and DL lactides exhibit amorphous behavior at iden-tical molecular weights. In other words, the changes in micro-structure showed significant differences between the two typesDL and D or L isomers. Typical thermograms for L and DL-PLA are presented in Figure 3.3 (Ahmed and Varshney, 2011).The peaks at 171.97�C and 101.77�C (see Figure 3.3a) indicatethe melting point and crystallization of PLLA, while PDLLA isthe amorphous polymer and exhibits merely the glass transition at52.73�C (see Figure 3.3b).

Thus the Tg of PLA is dependent on both the molecularweight and the optical purity of the polymer. As reported byDorgan et al. (2005), PLA with a higher content of L-lactidehas higher Tg values than the same polymer with the sameamount of D-lactide (Dorgan et al., 2005). In general, the


relationship between Tg and molecular weight can be repre-sented by the Flory�Fox equation:

Tg5TNg 2K

Mn

(3.1)

where TNg is the Tg at the infinite molecular weight, K is a con-

stant representing the excess free volume of the end groups forpolymer chains, and Mn is the average molecular weight. Thevalues of TN

g and K are around 57�58�C and (5.5�7.3)3 104

respectively, as reported in the literature for PLLA and PDLLA(Jamshidi et al., 1988).

Lim et al. (2008) have reported that thermal history has asignificant effect on the glass transition behavior of PLA.Rapid cooling or quenching of the polymer from the melt(.500�C/min) results in a highly amorphous polymer. Thiscondition is regularly found during the injection molding pro-cess, which can contribute to shrinkage, warping or even opac-ity of the molding products. Figure 3.4 shows a typicaldifferential scanning calorimetry (DSC) analysis of the thermalbehavior of two amorphous PLAs, that is, a PDLLA(Mw5 70 kDa) sample that is intrinsically amorphous and aPLLA (Mw5 200 kDa) sample that was quenched to the amor-phous state by fast cooling at 100�C/min after melting. In both

1.5

1.0

0.5

0.0

Hea

t flo

w (

W/g

)

–0.5

–1.0

–1.580 35 40 45 50 55 60 65 70

Exo Up Exo UpTemperature (ºC) Temperature (ºC)UniversalV4.2E TA

Instruments

UniversalV4.2E TA

Instruments

100 120 140 160 180 200

+

+

+ +

+

+ +

101.77 ºC

171.97 ºC

Hea

t flo

w (

W/g

)

–0.35

–0.40

–0.45

–0.50

–0.55

(a) (b)

49.70 ºC

52.73 ºC(T)

55.78 ºC

Figure 3.3 Thermograms of (a) PLLA and (b) PDLLA (adapted fromAhmed and Varshney, 2011).

114 POLYLACTIC ACID

cases, the Tg is evident and is located at about 65�C (Fambriand Migliaresi, 2010). However, the Tm of PLA is also relatedto its optical purity. The maximum practical obtainable Tm forstereochemically pure PLA (either L or D) is around 180�Cwith enthalpy of 40�50 J/g. However, typical Tm values forPLA are in the range 130�160�C. The Tm depression effect ofmeso-lactide in polymerization can produce positive implica-tions as it can improve processability by reducing thermal andhydrolytic degradation or lead to the reverse reaction of lactideformation (Lim et al., 2008). Furthermore, the fastest rates ofcrystallization for pure PLA are found in the temperature range110�130�C (Fambri and Migliaresi, 2010). The crystallizationconditions influence the way in which PLLA crystallizes intothree different crystal forms, α, β, and γ (Vasanthan and Ly,2009). The X-ray diffraction outcomes of the stereocomplexfor blends of PDLA and PLLA revealed that its crystallinestructure differs from the homopolymer (Martin and Averous,2001).

According to Auras et al. (2004), the improvement ofcrystallinity in PLA can be done by annealing at a temperatureof 75�C to the melting point of amorphous PLA. This is

80

70

60

50

40

30

20

10

00 10

Annealing time (min)

Cry

stal

linity

(%

)

20 30 40 50 60

PLLA 40 kDaPLLA 68 kDaPLLA 85 kDaPLLA 230 kDa

Figure 3.4 Effect of annealing time on crystallinity of compressionmolded PLLA at 160�C (adapted from Migliaresi et al., 1991).


applicable for those PLA copolymers that are originally crystal-lizable, i.e. the PLA should possess good stereochemical purity.Moreover, the crystallinity of the polymers, as shown inFigure 3.5, increases with annealing time with decreasingmolecular weights (Mw), which are favorable. From the studyof Migliaresi et al. (1991), it can be asserted that slow anneal-ing can progressively promote the movement of chains for rear-rangement in the crystalline structure. At the same time, thedifferent cooling rates also induce variation in the crystal mor-phology, with the formation of regular geometry and definedspherulites at high undercooling and spherulites with irregularshape and a coarse-grained structure at lower decompositiontemperatures (Fambri and Migliaresi, 2010).

As usual, the addition of plasticizer results in a pronouncedeffect on the characteristics of a polymer. The addition of plas-ticizer can introduce flexibility to a rigid polymer while pro-cessability can be significantly improved, with lower Tm andTg. Although the introduction of an amorphous structure canreduce the Tg using the copolymerization of L- and D-lactideisomer, Kulinski and Piorkowska (2005) noted that there was adecrease of only 1�2 K of Tg for amorphous PLA compared tocrystalline PLA. Nevertheless, the Tg of the crystallized PLA issignificantly reduced from 59�C to 35�37�C after the additionof only 5% monomethyl ether polyethylene glycol as a

0 50Temperature (ºC)

100 150 200

0.0

–0.5

PDLLATg

Tc

Quenched PLLATg

TmHea

t flo

w (

W/g

)ex

o

Figure 3.5 Differential scanning calorimetry thermograms ofamorphous PLLA prepared by quenching and PDLLA (heating rate10�C/min) (adapted from Fambri and Migliaresi, 2010).

116 POLYLACTIC ACID

plasticizer, as shown in Figure 3.6. As the content of plastici-zers is increased to 10 wt%, the Tg dramatically drops to belowroom temperature for all polymers, and becomes nearly indis-tinguishable. The plasticization of PLA with PEG and mono-metyl ether of PEG effectively lowers Tg due to enhancedsegment mobility of the PLA chains caused by the presence ofplasticizers, and this increases with the increasing plasticizercontent (Kulinski and Piorkowska, 2005). Nonetheless, there isa lack of evidence that the reactivity of the monomethyl etherend group affects the Tg of the crystalline PLA � this is shownby the comparison of the curves of P550 (normal grade poly-ethylene glycol) and P600 (monomethyl ether polyethyleneglycol). This can be attributed to the fact that the PLA crystal-linity has a stronger affinity than the intermolecular interactionwith plasticizer.

PLA

0

–2

–4

PLA + 5%P 550

PLA + 5%P 600

PLA + 10%P 550

PLA + 10%P 600

0 40 80

Temperature (ºC)

Hea

t flo

w [W

/g]

120 100

Figure 3.6 DSC thermograms recorded during heating at the rate of10 K/min for crystallized PLA and PLA plasticized with 5 and 10 wt.%of P600 and P550 (adapted from Kulinski and Piorkowska, 2005).


It is obvious to suggest the use of lactide as the plasticizerfor PLA, but it tends to migrate to the material surface, causingthe surface to turn sludgy and sticky. For a long time, PLA pro-ducts suffered from an excessive loss of plasticizer and, there-fore, stiffening. Baiardo et al. (2003) compared the monomericplasticizers acetyl tri-n-butyl citrate (ATBC) and poly(ethylene-glycol) (PEG) on the thermal behavior of PLA. Baiarado et al.(2003) found the miscibility limit of ATBC to be 50 wt% whilethe miscibility of PEG in PLA decreases with high molecularweight. The miscibility of typical PEG at molecular weights,Mw5 400 and Mw5 10,000, were 30 wt% and 5 wt%, respec-tively. In other words, the plasticization efficiency of the plasti-cizer increases at lower molecular weights. Recently, otherplasticizers such as, glucose monoesters and partial fatty acidesters (Hoffman, 2002), were used to improve the flexibilityand impact-resistance of PLA.

Pilin et al. (2006) extended the study on the effect of foodgrade plasticizer in PLA, as listed in Table 3.2. The solubilityparameter δ and interaction parameter χ were used to evaluatethe extent of compatibility of the PLA and the plasticizer.When the δ of the components are close to each other or blendwith χ, 0.5, it can be considered that the mixture is miscibleand no phase separation is expected. The differential scanningcalorimetry results as shown in Table 3.3 indicate that the

Table 3.2 Solubility Parameter δ and Interaction Parameter χbetween PLA and Plasticizers (Pilin et al., 2006)

Name Mw

(g/mol)δ(MPa0.5)

χ/PLA

Poly(lactic acid (PLA) 74,000 23.1 �Poly(1,3-butanediol) (PBOH) 2100 21.3 2.3

Dibutyl sebacate 314 17.7 3.7

Acetyl glycerol monolaurate (AGM) 358 18.5 1.5

Poly(ethylene glycol) (PEG-200) 200 23.5 0

Poly(ethylene glycol) (PEG-400) 400 22.5 0.1

Poly(ethylene glycol) (PEG-1000) 1000 21.9 0.5

118 POLYLACTIC ACID

Table 3.3 Melting Temperature and Enthalpies for the Pure Component, and PLA�Plasticizers Blends (Pilinet al., 2006)

Material 100% 10% 20% 30%

Tm (�C) ΔHm (J/g) Tm (�C) ΔHm (J/g) Tm (�C) ΔHm (J/g) Tm (�C) ΔHm (J/g)

Pure PLA 154.0 0.5 � � � � � �PEG-200 � � 148.0 34.1 � � � �PEG-400 6.9 113 150.8 32.4 142.4 44.6 � �PEG-1000 39.8 149.4 153.0 32.1 150.6 38.6 149.3 41.3

PBOH 215.5 1.8 152.5 1.3 151.9 23.9 151.0 34.3

AGM 28.3 71.9 150.3 1.6 146.6 29.3 143.4 31.4

DBS 26.9 160.8 148.8 2.2 144.2 32.3 143.4 32.0

melting endotherm of PLA shifts to low temperatures for allthe plasticizers and compositions. However, the enthalpy ofmelting (ΔHm) increases for the lower molecular weight PEG,which helps to explain the macroscopic phase separationobserved for PEG-200 and PEG-400. The ability of PBOH,AGM and DBS to induce PLA crystallinity is quite low,whereas PEG promotes crystallinity to reach a value close tocrystallized PLA (55 J/g) as found by Younes and Cohn (1988).In addition, Pilin et al. (2006) reported that such a phenomenonis due to higher mobility � PEG enhances the mobility of PLAmacromolecules by increasing crystallization kinetics of thepolymers. A high molecular scale miscibility is always desir-able to achieve pronounced PLA chain mobility. Martin andAverous (2001) also found that the addition of various types ofplasticizers, such as glycerol, PEG, citrate ester, polyethyleneglycol monolaurate (M-PEG) and oligomeric lactic acid, caninduce crystallization as well as fusion in PLA (see Table 3.4).

Table 3.4 Thermal Properties of PLA with the Addition ofPlasticizers (Martin and Averous, 2001)

Material Tg

(�C)Tc

(�C)Tm

(�C)Crystallinity

(%)

Pure PLA 58 � 152 1

PLA/10% glycerol 54 114 142 24.3

PLA/20% glycerol 53 110 141 25.4

PLA/10% citrate ester 51 � 144 12

PLA/20% citrate ester 46 � 142 20

PLA/10% polyethylene glycol

monolaurate

34 94 148 22

PLA/20% polyethylene glycol

monolaurate

21 75 146 24

PLA/10% polyethylene glycol 30 82 147 26

PLA/20% polyethylene glycol 12 67 143 29

PLA/10% oligomeric lactic acid 37 108 144 21

PLA/10% oligomeric lactic acid 18 76 132 24

120 POLYLACTIC ACID

It is thought that plasticizer may promote crystallinity as aresult of enhanced chain mobility for lamellar rearrangement.

Highly stereochemically pure PLA is a semicrystalline poly-mer with a Tg of 55�C and Tm of 180�C. The variation ofmonomer types can significantly change the structural proper-ties of the PLA. For instance, poly(L-lactide-co-D,L-lactide)copolymers are commercially available up to a D,L-lactide con-tent of 30 mol% while poly(D,L-lactide-co-glycolide) copoly-mers are available up to 70% glycolide as an amorphouscompound with a Tg of 40�50�C (Bendix, 1998). The changesin the characteristics are due to the fact that the polymers con-sist of a random distribution of comonomers. The Tg of PLAcopolymers decreases in a near proportional relationship to thecontent of glycolide or ε-caprolactone comonomers, due to theintroduction of irregularity. Moreover, the presence of stereo-chemical defects in PLLA reduces Tm, rate of crystallization,and percentage crystallization of the resulting polymer(Migliaresi et al., 1991) up to a stage that approaches the char-acteristics of the comonomers. In addition, the incorporation offiber can also cause changes to the thermal transition of PLA.One of the studies conducted by Gregorova et al. (2009) foundthat the addition of 20 wt% of untreated natural fiber harvestedfrom the plant species Picea sitchensis (which is also known asthe Sitka spruce and grows in North America) causes a rise inTg to 52�54�C and the degree of crystallinity to 25.0�28.7%,with unchanged Tm compared to the pure PLA. The PLA usedpossessed a Tg of 46

�C, a Tm of 150�C and a degree of cystalli-nility of 18.2%. This effect is caused by the restricted mobilityof PLA chains in the presence of the fibers. The unchanged Tm

was also observed by Jang et al. (2007) in their study involvingthe blending of PLA and starch (see Table 3.5). The Tg and Tm

showed insignificant changes but the heat of fusion was found tobe lowered after the addition of starch. Further study with theaddition of maleic anhydride as the compatibilizer showed thatthe Tg of the PLA and the natural blend had reduced as well.Athough maleic anhydride was introduced as a compatibilizer ittends to cause a plasticizing effect. This is because maleic anhy-dride does not induce a reinforcing effect but tends to enhance the


adhesion of natural fibers and PLA for better elongation, to avoidthe formation of voids which cause premature failure whenloaded (Rahmat et al., 2009).

In a study by Jang et al. (2007), the addition of starch producedan increase in crystallinity in a PLA blend. The crystallinity ofthe PLA�starch was enhanced because starch induced nucleationeffects (see Table 3.4). When comparisons were done on thenumber and weight average molecular weights (Mn and Mw) ofdifferent PLA�starch blends and pure PLA, it was observed thatthe molecular weight had been significantly reduced � almost byhalf � when as little as 10% starch was added. This significantreduction of molecular weight is believed to be caused by thepresence of water from starch moisture initiating the hydrolysisreaction in PLA. It should be noted that the percentage crystallinityof maleic anhydride (MA)-compatibilized blends is much higherthan other blends with a similar starch content. The crystallinity ofMA-compatibilized blends increases with increasing starch content.Compatibilizing also enhances the regularity of the structural chainarrangement in the PLA�starch blend, as shown in the scanningelectron microscope (SEM) micrograph in Figure 3.7. When com-paring the morphology of the MA-compatibilized PLA�starch,

Table 3.5 Thermal Characteristics and Molecular Weight ofPLA/Starch Blends (Jang et al., 2007)

Ratio ofPLA/Starch(wt%)

MA(phr)

Tg

(�C)Tm

(�C)Crystallinity(%)

Mn Mw Mw/Mn

100/0 � 63 154 � 95000 231000 1.6

90/10 � 62 154 2 49000 125000 2.5

80/20 � 61 153 2 39000 76000 1.9

70/30 3 59 155 36 47000 86000 1.8

60/40 3 60 155 48 45000 82000 1.8

50/50 3 60 155 41 44000 84000 1.9

90/10 3 61 153 12 41000 74000 1.8

80/20 3 57 154 18 41000 77000 1.9

122 POLYLACTIC ACID

the blending system forms a continuity without edges, holes orcavities. Such crystallinity does not affect the bonding strength;thus, the heat of fusion increases, but both Tg and Tm remainunchanged due to the migration of MA into PLA during blending.

3.3 Thermal Decomposition

High-temperature decomposition of PLA has been found tobe dependent on a range of factors, such as molecular weight,crystallinity, purity, temperature, pH, presence of terminal car-boxyl or hydroxyl groups, water permeability and additivesacting catalytically, which may include enzymes, bacteria orinorganic fillers (Park and Xanthos, 2009). Celli and Scandola(1992) and Sodegard and Stold (2002) state that PLLA is sensi-tive to thermal decomposition and the thermal decompositionof PLA can be affected by the following factors:

1. hydrolysis by trace amounts of water, catalyzedby hydrolyzed monomers � lactic acids � (seeFigure 3.8);

2. zipper-like depolymerization, catalyzed by theremaining polymerization catalysts (see Figure 3.9);

Figure 3.7 SEM micrograph of PLA/starch with and without MAcompatibilizer (adapted from Jang et al., 2007).


3. oxidative, random main-chain scission;4. intermolecular transesterification to monomer and

oligomeric esters (see Figure 3.10) or intramolecu-lar transesterification resulting in the formation ofmonomer and oligomeric lactides of low molecu-lar weight.

OR

R

O

OO

OOH + HOH

O

HOOH

O

O

OO

OO

OH

OFigure 3.8 Hydrolysis of PLA with the reaction of water.

–OO

O O

OO O O

n

OO O O

O

O O

O O nO

O

OO

OLactide

OHO O

Unzipping reaction

Figure 3.9 Unzipping reaction upon decomposition of PLA.

O

OOH

OOO

OOO

O–O O

OO nO

O

OOH

OOO

OO

Intermolecular transesterification

O

OHO O

OO

O

H

O

OH

C = O

O

O

OOH

OHO

O

OHHO

Figure 3.10 Transesterification of PLA.

124 POLYLACTIC ACID

The decomposition temperature of PLA is normally230�260�C. Therefore, it is considered to be safe for roomtemperature applications. PLA is seldom used at elevated tem-peratures, such as the boiling point of water, because PLAtends to lose its structural properties at temperatures .60�C.Although PLA is unlikely to release toxic substances exten-sively, residues of plasticizer or oligomers still need furtherattention. PLA undergoes initial thermal decomposition attemperatures above 200�C by hydrolysis reaction followed bylactide reformation, oxidative main-chain scission, and inter-or intramolecular transesterification reaction (Jamshidi et al.,1988). Thermal decomposition can occur at 200�C withoutcatalysts, but it requires higher temperatures to induce a fasterand more prevalent reaction (Achmad et al., 2009).

Because PLA is among the polymers that are highly sensi-tive to heating, many researchers have conducted studies vary-ing the conditions of PLA. McNeil and Leiper (1985a) carriedout the degradation of PLA under isothermal conditions at sev-eral temperatures and found that the energy of activation was119 kJ/mol for the temperature range 240�270�C, where themechanism of thermal degradation was believed to initiatefrom the hydroxyl end ester. The propagation of chain cleavageoccurs to produce cyclic oligomers, lactide, acetaldehyde andcarbon monoxide, and finally at higher temperatures producesproducts such as carbon dioxide and methylketene. In a furtherstudy by McNeil and Leiper (1985b) under programmed heat-ing conditions it was observed that oligomers comprise morethan 50% of the total volatile up to 440�C, which is the temper-ature at which volatilization is complete. Carbon dioxide, acet-aldehyde, a ketene and carbon dioxide are formed in thevolatile stream as well. During the thermal decomposition, anacetylation reaction of the chain ends stabilizes the polymer bynearly 30�C. This indicates the participation of hydroxyl endgroups in PLA degradation. In addition McNeil and Leiper(1985b) added poly(methyl methacrylate) as the source of radi-cals during the thermal decomposition of PLA. The decomposi-tion of PLA increased, while the PMMA was stabilized, i.e. theyield of CO2 and oligomers from PLA dramatically increased,


and this showed that the radical reaction is one of the importantpathways for the formation of oligomer PLA on heating to ahigh temperature. PLA tends to follow the dominant reactionpathway of intramolecular transesterification of pure PLA toform cyclic oligomers, usually with residue of carbon oxidesand acetaldehyde from the fragmentation reaction. However,when the PLA samples were contaminated with residual stan-nous catalyst, i.e. the polymerization catalyst, PLA underwenta selective depolymerization step, which produced lactideexclusively (Kopinke et al., 1996). This observation was furtherverified by Cam and Marucci (1997), whose findings showedthat the residual metals can cause a drastic thermal degradativeeffect on the PLA. Of the series of metals normally used forpolymerization of PLA, i.e. tin, zinc, aluminum and iron, thedegradation reactivity of metal residues follow the sequencestannous , zinc , aluminum , iron.

The depolymerization of PLLA at a high temperatureinduces the chain-transfer intra- and inter-transesterificationand depolymerization reactions by the evident change of thespecific optical rotation number. In other words, the highcapacity of a transition metal is able to coordinate ester groupsand accelerate reactions.

A recent study by Zou et al. (2009) analyzed the composi-tion of gaseous products on the decomposition process of PLAusing TGA coupled with Fourier transform infrared spectros-copy (FTIR). As shown in Figure 3.11a, the three-dimensionaldiagram corresponding to the FTIR spectra with the heatingrate of 20�C/min, the highest intensity of the decomposition asdenoted by the highest absorbance occurs at 1060s, which isabout 370�C. The main decomposition process has completedat 800�1200s, corresponding to the temperature range282�418�C. Further investigations at the respective severedecomposition temperature of 372�C produce the FTIR spec-trum as shown in Figure 3.11b. It can be seen that there aretwo absorption peaks, at 1750 and 2747 cm21, which are attrib-uted to the CQO and OQCaH and indicate the possibility ofthe formation of carbonyl complexes. Subsequent peaks at2010 and 2930 cm21 for the CaH stretching and 1445 and

126 POLYLACTIC ACID

1380 cm21 for CaH bending bands of CH3 strongly agree thataldehyde is extensively formed during the severe degradationof PLA. In addition, the bands at 1260 and 1100 cm21 corre-spond to the CaO and at 1750 cm21 for CQO stretching ofthe carbonyl group, together with two peaks of 2930 and1380 cm21 for CaH stretching and ring skeletal vibration at930 cm21 have evidently implied the evolvement of lactide or

0.5

0.4

0.3

0.2

Y a

bsor

bran

ce u

nits

0.1

0.01500

1000500

1000

X wavenumber cm

–1

Z second s

2000

3000

(a) (b)

(c)

0.5

0.4

0.3

0.2

0.1

0.0

4000 3000 2000 1000

370 ºC

3575

Abs

orba

nce

3490

3010

2930 27

47

2364 23

2421

7921

1017

5014

4513

8013

5012

6011

00

930

Abs

orba

ncer

rel

ativ

e in

tens

ity

4000

270ºC

300ºC348ºC

372ºC

400ºC

445ºC

500ºC

O=C

O=C–HO=C–O

Cyclic

CH2 CO2CO

CH3CH

CH

3000 2000

Wavenumber/cm–1

Wavenumber/cm–1

1000

Figure 3.11 (a) FTIR spectra in 3D for the evolvement of gaseousproducts at 20�C/min (b) FTIR spectra for the gaseous products atdifferent temperatures of PLA (c) FTIR of the gaseous product of PLAheated at 372�C (adapted from Zou et al., 2009).


cyclic oligomer due to the inter-esterification and chain homol-ysis of PLA. Moreover, the thermal degradation based on chainhomolysis of PLA produced two bands located at 2364 and2324 cm21. Both bands, together with carbon monoxide peakslocated at 2179 and 2110 cm21, remain obvious up to atemperature of 445�C. This is because when the hydroxyl-end-initiated ester is subjected to a high temperature it tends toproduce carbon dioxide in addition to the production of CO2

attributed to the chain homolysis occuring at high temperatures.It should be noted that some water is still produced as abyproduct as a result of fragmentation of lactide oligomersduring the decomposition of PLA. Furthermore, the activationenergy for the thermal decomposition can be modeled with theincreasing manner in relation to the temperature. Thus, basedon the Ozawa�Flynn�Wall method and Friedman’s methods,as summarized in Table 3.6, the average activation energy fordecomposition of PLA is 177.5 and 183.6 kJ/mol.

Fan et al. (2003, 2004) revealed the influence of the differentfunctional groups of the end-capped PLLA. This included thecarboxyl, acetyl and calcium ion type of end-capped PLLAanalyzed by TGA. By comparing the carboxyl-type PLLA(PLLA-H) and calcium-ion end-capped PLLA (PLLA-Ca), theTG data showed that PLLA-H has a higher pyrolysis tempera-ture (280�370�C) over PLLA-Ca for a range of lower tempera-tures (220�360�C). Further investigation also showed that theapparent activation energies for PLLA-H and PLLA-Ca werein a range rising from 140 to 176 kJ/mol and 98 to 120 kJ/mol,respectively. The major products of pyrolysis of PLLA-H con-sisted of lactides (67%) and other cyclic oligomers, which wereregarded as the random transesterification in the main, whereasthe degradation of PLLA-Ca resulted mostly in lactide (95%),which indicated that an unzipping depolymerization processhad taken place extensively. When PLLA is treated with aceticanhydride this results in the acetylation of end hydroxyl groups(PLLA-Ac). Fan et al. (2004) found the thermal degradation ofacetylated PLLA showed a shift to a higher degradation tem-perature range (300�360�C) than that of the untreated PLLA(260�315�C) with a high stannous catalyst (Sn) residue content(437 ppm). However, at the same time the acetylation treatment

128 POLYLACTIC ACID

has a less pronounced effect when compared to the PLLA with asimilar Sn content. This effect had been reported previously inanother analysis (Nishida et al., 2003), which involved the varyingof the Sn content to determine the effects of pyrolysis of PLLA.It showed that acetalylated PLLA had about a 50�60�C higherdegradation temperature range (300�365�C) than that of PLLAcontaining 485 ppm of Sn. The activation energy of PLLA-Ac(Sn content: 74 ppm) is 140�160 kJ/mol, while neat PLLA (Sncontent: 60 ppm) is 124�163 kJ/mol (Fan et al., 2004).

As mentioned in Chapter 2, the blending of starch with PLAis an important approach in order to make cost savings while

Table 3.6 Activation Energies of PLA Obtained UsingOzawa�Flynn�Wall and Friedman’s Methods(Zou et al., 2009)

Conversion,α

Ozawa-Flynn-WallMethoda

Friedman’sMethodb

E (kJ/mol)

CorrelationCoefficient (r)

E (kJ/mol)

CorrelationCoefficient (r)

0.2 161.1 0.9985 171.9 0.9995

0.3 168.4 0.9989 173.4 0.9965

0.4 176.9 0.9993 175.6 0.9995

0.5 177.3 0.9996 181.2 0.9954

0.6 182.0 0.9997 185.4 0.9987

0.7 182.7 0.9998 190.9 0.9985

0.8 183.5 0.9998 193.9 0.9870

0.9 188.0 0.9995 196.5 0.9895

Average 177.5 183.6

aKinetic model of Ozawa�Flynn�Wall method

ln β5 lnAE

R2 lnFðαÞ2 E

RT(3.2)

bKinetic model of Friedman’s method

lndαdT

� �5 ln

A

β2 ln f ðαÞ½ �2 E

RT(3.3)

where T is the absolute temperature, β is the heating rate, E is the

activation energy, A is the pre-exponential factor (min21), α is the

conversion degree and R is the universal gas constant (8.314 J/K mol).


maintaining the biodegradability of PLA. The blending of anatural ingredient with PLA can significantly influence thecharacteristics of the PLA, including the thermal transitionstate. A recent investigation performed by Petinakis et al.(2010) blended starch and wood-flour (WF) with PLA. Theresearchers found that both starch and WF accelerated the ther-mal decomposition of PLA, and starch showed a more pro-nounced effect than WF (see Figure 3.12). When starch and

(a)

(b)

100

90

80

70

60

50

Wei

ght (

%)

Wei

ght (

%)

Temperature (ºC)

40

30

20

10

050 100 150 200 250 300 350 400 450 500 550 600

100

90

80

70

60

50

Temperature (ºC)

40

30

20

10

050 100 150 200 250 300 350 400 450 500 550

Der

ivat

ive

wei

ght (

%/º

C)

Der

ivat

ive

wei

ght (

%/º

C)

0–10

–5–15

–25

–35

–45

–55

–65200 250 300 350 400 450 500

–20–30–40–50

WF

PLA

–60200 300 400 500 600

PLA

Starch

PLA + 40%starch

PLA + 40%WF

PLA + 30%WF

PLA + 20%WF

PLA + 10%WF

WF

PLA

PLA + 30%starchPLA + 20%starch

PLA + 10%starchPLA + 50%starch

PLAStarch

Figure 3.12 (a) Thermogravimetry results of PLA/starch blends(b) Thermogravimetry results of PLA/wood-flour (WF) blends(adapted from Petinakis et al., 2010).

130 POLYLACTIC ACID

WF decompose, both materials emit oxide gases and radicals,which initiate the degradation of PLA to break down the chain.PLA blended with WF is more resistant to decomposition dueto the complex lignin structure, which acts as a hydrophobicshield protecting the PLA chains from direct attack of the vola-tiles. This observation can be further justified by the work ofTao et al. (2009) who compared PLA blended with jute andramie fibers; they found that there was a lack of significantdifference in thermal decomposition for both natural fibers (seeFigure 3.13).

3.4 Heat Capacity, Thermal Conductivity andPressure�Volume�Temperature of PLA

Heat capacity, thermal conductivity and pressure�volume�temperature (PVT) are the macroscopic characteristicsof polymers that are very important during the processingstage. Typical heat capacity determines the amount of heatrequired to bring the respective volume of PLA up to the finalprocessing temperatures. Meanwhile, thermal conductivity andPVT can affect the rate of heat transfer and compressibility,which are important in determining the shrinkage of injection-molded products.

100

80

60M

ass

frac

tion/

%

Temperature/ºC

40

20

0100 200 300 400

a

a – Neat PLAb – PLA/Ramie composite (70/30)c – PLA/Jute composite (70/30)

bc

Figure 3.13 Thermogravimetric curves of PLA and PLA-basedcomposites (adapted from Tao et al., 2009).


Heat capacity characterizes the amount of heat required tochange a substance’s temperature by a given amount. It is veryimportant to determine the preliminary amount of energyrequired to increase the temperature of a polymer up to the pro-cessing temperature. A comprehensive study on the heat capacityof PLA has been reported by Pyda et al. (2004). The data shownin Table 3.7, as disclosed by Pyda et al. (2004), is the most com-prehensive to date and includes the temperature range 5�600 K.

The thermal conductivity of PLA is summarized inTable 3.8. As can be seen, the thermal conductivity of PLAincreases almost in relation to the elevation of temperature.Thermal conductivity of a polymer has a great influence whendealing with heat removal during the cooling process for injec-tion-molded articles. Sufficient and controlled heat removalcan reduce the possibility of warping.

The PVT relationship of a polymer determines the compress-ibility of a molten polymer and defines shrinkage of the fin-ished product. This is particularly relevant to products madewith high-thickness material (.5 mm) of a complex design.When the molten polymer is cooled it has been found that fastcooling leads to the formation of an amorphous structure. Inother words, the macromolecules of the polymer are unableform a crystalline structure even though the polymer is inher-ently crystallizable. Crystalline plastics undergo significantchanges to their specific volume. This is because crystallinestructures are highly compact. When a semicrystalline polymeris injection molded in a specific closed channel, the resultantproducts tend to have some deviation of dimensions, indicatingshrinkage. Irregular shrinkage throughout a hot article can alsolead to warpage. Since PLA is a semicrystalline polymer, ther-mal processing of PLA can help to eliminate shrinkage. ThePVT information is summarized in Table 3.9 and shows thechange in specific volume in relation to temperature and pres-sure. In the injection-molding process, high pressure assists inthe compression of the PLA molten polymer during the pack-ing stage to produce high-dimensional stable output articles.Typical PVT can be modeled using the two-domain Tait PVTmodel, as shown in Table 3.10, which is extensively used in

132 POLYLACTIC ACID

Table 3.7 Measured, Theoretical and Recommended HeatCapacity of PLA (Pyda et al., 2004)

T (K) Cp (Exp) by

Adiabatic

Calorimetrya

(J/K/mol)

Cp

(Exp)b

(J/K/

mol)

Cp

(Vibrational)c

(J/K/mol)

Recommended

Experimental

Heat Capacityd

(J/K/mol) Cp

5 0.31 NA 0.46 (Solid) 0.31

6 0.60 NA 0.77 0.60

7 0.95 NA 1.17 0.95

8 1.34 NA 1.62 1.34

9 1.78 NA 2.11 1.78

10 2.25 NA 2.63 2.25

15 4.85 NA 5.30 4.85

20 7.74 NA 7.83 7.74

25 10.585 NA 10.22 10.585

30 13.15 NA 12.535 13.15

40 18.06 NA 17.04 18.06

50 22.585 NA 21.48 22.585

60 26.575 NA 25.86 26.575

70 30.455 NA 30.14 30.455

80 34.195 NA 34.27 34.195

90 37.77 NA 38.21 37.77

100 41.145 NA 41.195 41.145

110 44.40 NA 45.40 44.40

120 47.52 NA 48.66 47.52

130 50.52 NA 51.73 50.52

140 53.41 NA 54.64 53.41

150 56.2 NA 57.40 56.2

160 58.98 NA 60.05 58.98

170 61.71 NA 62.61 61.71

180 64.40 NA 65.10 61.40

190 67.08 69.76 67.54 67.08

200 69.75 68.23 69.95 69.75

210 72.43 72.27 72.34 72.35

220 75.13 74.78 74.71 74.96

230 77.87 77.15 77.08 77.51

240 80.65 79.61 79.44 80.13

250 83.50 82.10 81.81 82.80


Table 3.7 Measured, Theoretical and Recommended HeatCapacity of PLA (Pyda et al., 2004)—cont’d

T (K) Cp (Exp) by

Adiabatic

Calorimetrya

(J/K/mol)

Cp

(Exp)b

(J/K/

mol)

Cp

(Vibrational)c

(J/K/mol)

Recommended

Experimental

Heat Capacityd

(J/K/mol) Cp

260 NA 84.25 84.19 84.25

270 NA 87.11 86.57 87.11

280 NA 89.82 88.95 89.82

290 NA 92.48 91.35 92.48

298.15 NA 94.69 93.31 94.69

300 NA 95.30 93.75 95.30

310 NA 98.13 96.15 98.13

320 NA 101.59 98.55 101.59

330 NA 112.16 100.95 112.16

332.5 (Tg) NA 123.57 101.67 145.44

340 NA 144.36 103.34 (Liquid) 146.01

350 NA 144.40 105.74 146.77

360 NA 147.59 108.12 147.53

370 NA 148.24 110.49 148.29

380 NA 148.61 112.86 149.05

390 NA 149.91 115.21 149.81

400 NA 150.56 117.55 150.57

410 NA 151.62 119.87 151.33

420 NA 152.31 122.18 152.09

430 NA 152.97 124.47 152.85

440 NA 153.725 126.74 153.61

450 NA 154.29 129.00 154.37

460 NA 154.98 131.24 155.13

470 NA 155.77 133.46 155.89

480 (Tm) NA NA 135.66 156.65

490 NA NA 137.84 157.41

500 NA NA 140.01 158.17

510 NA NA 142.15 158.93

520 NA NA 144.28 159.69

530 NA NA 146.40 160.45

540 NA NA 148.49 161.21

550 NA NA 150.57 161.97

134 POLYLACTIC ACID

Table 3.7 Measured, Theoretical and Recommended HeatCapacity of PLA (Pyda et al., 2004)—cont’d

T (K) Cp (Exp) by

Adiabatic

Calorimetrya

(J/K/mol)

Cp

(Exp)b

(J/K/

mol)

Cp

(Vibrational)c

(J/K/mol)

Recommended

Experimental

Heat Capacityd

(J/K/mol) Cp

560 NA NA 152.64 162.73

570 NA NA 154.69 163.49

580 NA NA 156.72 164.25

590 NA NA 158.74 165.01

600 NA NA 160.75 165.77

NA5 not available;

a5 experimental data of heat capacity by adiabatic calorimetry in accordance with

Kulagina et al. (1982);

b5 experimental data represent an average of three runs performed on two samples

each with standard differential scanning calorimetry and temperature modulated

differential scanning calorimetry for 1.5% D isomer, 8.1% D isomer and 16.4% D

isomer PLA;

c5 the calculated heat capacity of solid PLA assuming only vibrational motion,

refer to Pyda et al. (2004) for more information;

d5 recommended experimental heat capacity for solid and liquid state of PLA.

Table 3.8 Thermal Conductivity of NatureWorks PLA GradeMAT2238

Temperature(�C)

Thermal Conductivity(W/m �C)

48.4 0.111

68.1 0.178

87.8 0.198

109.0 0.197

129.4 0.198

149.6 0.192

169.7 0.195

190.6 0.195

211.9 0.205

233 0.195


Table 3.9 Pressure�Volume�Temperature of NatureWorks PLA Grade MAT2238

Temperature(�C)

Pressure (MPa)

0 MPa 50 MPa 100 MPa 150 MPa 200 MPa

Specific Volume (cm3/g)

38.79 0.8052 0.7923 0.7825 0.7741 0.7666

50.13 0.8108 0.7957 0.7851 0.7763 0.7681

62.41 0.8180 0.8004 0.7883 0.7787 0.7698

75.25 0.8259 0.8066 0.7930 0.7819 0.7721

88.43 0.8369 0.8145 0.7997 0.7873 0.7764

102.4 0.8526 0.8264 0.8090 0.7950 0.7827

116.7 0.8638 0.8353 0.8164 0.8019 0.7887

132.0 0.8753 0.8441 0.8244 0.8086 0.7950

147.7 0.8879 0.8538 0.8329 0.8162 0.8018

163.3 0.9005 0.8635 0.8411 0.8231 0.8084

179.3 0.9142 0.8736 0.8499 0.8322 0.8158

195.3 0.9279 0.8836 0.8584 0.8388 0.8224

211.2 0.9435 0.8948 0.8661 0.8460 0.8291

230.4 0.9601 0.9078 0.8778 0.8553 0.8356

Table 3.10 PLA Coefficients for Two-Domain Tait PVT Model

Two-domain Tait PVT Model Coefficient for NatureWorksPLA MAT2238

b1s 348.15 K

b2s 9.5473 1028 K/Pa

b3s 0.000826 m3/kg

b4s 8.5033 1027 m3/kg.K

b1m 1.628003 1028 Pa

b2m 0.00622 1/K

b3m 0.000821 m3/kg 20�20

b4m 4.4693 1027 m3/kg.K

b5 2.142003 1028 Pa

b6 0.006079 1/K

b7 0 m3/kg

b8 0 1/K

b9 0 1/Pa

Melt density 1.0727 g/cm3

Solid density 1.2515 g/cm3

Where the detail of two-domain tait PVT equation is explained as

follows:

VðT ;PÞ5V0ðtÞ 12C3 ln 11P

BðTÞ

� �� 1VtðT ;PÞ (3.4)

V(T,P) is the specific volume at temperature T and pressure P

V0 is the specific volume at zero gauge pressure

T is the temperature, in K

P is the pressure, in Pa

C is a constant, 0.0894

The upper temperature region (T. Tt) can be described by the

equations:

V05 b1m 1 b2mðT 2 b5Þ (3.5)

BðTÞ5 b3m exp½2b4mðT 2 b5Þ� (3.6)

Vt(T,P)5 0

where:

b1m, b2m, b3m, b4m and b5 are data-fitted coefficients


injection-molding simulation software to predict the problemareas of molded articles.

3.5 Conclusion

Thermal aspects are important in relation to their effect onthe properties of PLA. The thermal properties and the crystallin-ity of PLA are inter-related. Importantly, the L and D stereo-chemistry has an effect on crystallization, which consequentlyaffects the melting temperature and glass transition temperatureof PLA. Copolymers and additives can be helpful, due to theimprovement in the thermal transition, giving better processabil-ity. PLA can undergo severe degradation when the temperaturereaches .200�C; this involves the generation of lactide andoxide gases. Finally, information about heat capacity, thermalconductivity and PVT are very important in helping to designprocessabable PLA, for high quality marketable products.

Table 3.10 PLA Coefficients for Two-Domain Tait PVTModel—cont’d

Two-domain Tait PVT Model Coefficient for NatureWorksPLA MAT2238

The lower temperature region (T, Tt) can be described by the

equations:

V0 5 b1s1 b2sðT 2 b5Þ (3.7)

BðTÞ5 b3s exp½2b4sðT2 b5Þ� (3.8)

VtðT ;PÞ5 b7 exp½ðb8ðT 2 b5Þ2 b9PÞ� (3.9)

where:

b1s, b2s, b3s, b4s, b5, b7, b8, and b9 are data-fitted coefficients

The dependence of Tt on pressure can be described by the

equation:

Tt(P)5 b51 b6 P

where:

b5 and b6 are data-fitted coefficients

138 POLYLACTIC ACID

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4 Chemical Properties ofPoly(lactic Acid)

Chapter Outline4.1 Introduction 1434.2 Stereochemistry of Poly(lactic Acid) 1464.3 Analytical Technique of PLA 154

4.3.1 Nuclear Magnetic Resonance Spectroscopy 1544.3.2 Infrared Spectroscopy 157

4.4 Solubility and Barrier Properties of PLA 1624.4.1 Solubility of Polylactic Acid 1634.4.2 Permeability of Polylactic Acid 164


4.1 Introduction

Poly(lactic acid) (PLA) is known to be biocompatible andbiodegradable, and it can be readily broken down by a hydrolysisreaction. PLA is derived from renewable agricultural resources,such as corn and cassava. Mass production of PLA can lead tohigh consumption of agricultural yields, which increases the farmeconomy. Moreover, the production of PLA helps to reduce CO2

emissions when used in place of conventional petroleum-basedcommodity plastics, as the agricultural activities involve signifi-cant carbon fixation.

PLA is a biodegradable polymer that has been widely studiedand is used for domestic packaging, and biomedical applications,such as resorbable sutures, surgical implants, scaffolds for tissueengineering and controlled drug-delivery devices. PLA can existas two stereoisomers, designated as D and L, or as a racemic mix-ture, designated as DL. The D and L forms are optically activewhile the DL form is optically inactive. Poly(L-lactic acid)(PLLA) and poly(D-lactic acid) (PDLA) are semicrystalline,



http://dx.doi.org/10.1016/B978-1-4377-4459-0.00004-4

while poly(DL-lactic acid) (PDLLA) is amorphous (Jain, 2000;Urayama et al., 2003).

PLA belongs to the family of aliphatic polyesters commonlymade from α�hydroxyl acids, which also includes polyglycolicacid (PGA), polycaprolactone and polydioxanone. It is one ofthe few polymers that has a stereochemical structure that canbe easily modified by polymerizing a controlled mixture ofL and D isomers to yield a high-molecular-weight and amor-phous or semicrystalline polymer. The properties of PLA can bemodified both through the variation of isomers (L/D ratio) aswell as copolymerization with other monomers, such as glyco-lide and caprolactone. PLA can also be tailored by formulationinvolving the addition of plasticizers, other biopolymers and fil-lers. The biodegradability of PLA blends means that they arewell suited for short-term packaging materials, and they also fur-ther expand PLA’s applications in the biomedical field, wherebiocompatible characteristics are essential, such as implants,sutures and drug encapsulations.

In the early days of PLA development, PLA was producedusing the polycondensation method (see Figure 4.1). This was themost direct method of synthesizing PLA but the drawback was

Directcondensationpolymerization

Polymerizationthroughlactideformation


CH3

CH3 CH3

CH3

HO

OHH3C

H

O

HOC

C

OHH

CH3

O

HO

O

O

O

O

O

Opoly

CH3

CH3 CH3

CH3

HO

O

O

O

OO

O

O

OH

Chain coupling agent

Ring-openingpolymerization

Azeotropic dehydration condensation

–H2O

L-Lactic acid

D-Lactic acid

CH3

CH3

CH3

CH3

OHO

O

O


Low molecular weight polymerMW > 100 000

O

O

OO

CH3

H3C

HC C

OCCH

O

O

Lactide

Opoly

O

CC

OO

Figure 4.1 Routes for synthesis of poly(lactic acid) (adapted fromHartmann et al., 1998).

144 POLYLACTIC ACID

the generation of excessive water and a low-molecular-weight(Mn,1000�5000 Da) product. Sometimes, a chain extendermay be needed to increase the molecular weight, but this resultsin a higher cost of production. PLA also can be produced usingthe azeotropic dehydrative condensation approach. This polymeri-zation technique yields high-molecular-weight polymers, butrequires various diacids, diols, or hydroxyl acids as well as high-level catalysts (Garlotta, 2002). All these ingredients remain asimpurities in the PLA and may initiate unwanted degradationduring subsequent processing work at elevated temperatures.

The most important method for mass production of high-molecular-weight PLA is through the ring-opening polymerizationapproach. High-molecular-weight PLA is produced from the cyclicdilactate ester (commonly known as lactide), which commonlyinvolves the action of stannous octoate as a catalyst. This mecha-nism does not generate additional water, hence, a higher molecularweight can be achieved. Polymerization of a racemic mixture ofL- and D-lactides usually leads to the synthesis of PDLLA, whichis amorphous. The utilization of stereospecific catalysts tends toproduce stereochemically pure PLA with good crystallinity. Thedegree of crystallinity and the physicomechanical properties aregreatly determined by the ratio of D to L enantiomers, which is alsopartially related to the types of catalyst used. It has been reportedthat high-quality production of PLA yields a minimum amountof unreacted lactic acid monomer, which limits the tendency oflactic acid to leach out from the PLA when using as packaging.Furthermore, the amount of leached lactic acid is very much lowercompared to the amount of lactic acid in common food ingredients(Mutsuga et al., 2008). Therefore, polymers derived from lacticacid can be good candidates for packaging applications (Iwata andDoi, 1998). PLA has been growing as an alternative packagingmaterial for niche markets. Currently, PLA is used as a food pack-aging polymer for short-shelf-life consumer products, includingcontainers, drinking cups, razors and stationery. PLA fibers are alsoused in carpet, sportswear and diapers. A number of new applica-tions have been developed in recent years, such as casing for elec-tronic devices, flooring materials, etc. The ‘green’ credentials of

1454: CHEMICAL PROPERTIES OF POLY(LACTIC ACID)

PLA means there is a sustainable future for plastic materialsglobally.

4.2 Stereochemistry of Poly(lactic Acid)

The basic ingredient of PLA is lactic acid, which is yieldedfrom bacterial fermentation or from a petrochemical source.Lactic acid is a naturally occurring substance with the standardchemical name 2-hydroxy propionic acid. It is the simplesthydroxyl acid with an asymmetric carbon atom, and has opticallyactive L(1) and D(�) isomers. Both L and D isomers are pro-duced in bacterial systems, with the L isomer more commonlyfound. Meanwhile, mammalian systems produce only the L iso-mer, which is easily assimilated by enzyme protease K. Figure 4.2shows the chemical structure of the L- and D-lactic acids.

Nowadays, lactic acid is mass produced through the bacte-rial fermentation of carbohydrates, where corn and cassava arethe main agricultural sources. There are about 20 genera inthe phylum Firmicutes that generate lactic acid; these includeLactococcus, Lactobacillus, Streptococcus, Leuconostoc,Pediococcus, Aerococcus, Carnobacterium, Enterococcus,Oenococcus, Tetragenococcus, Vagococcus and Weisella (Reddyet al., 2008). Strains of Lactobacillus delbrueckii, Lactobacillusjensenii, and Lactobacillus acidophilus produce D-lactic acidand some also produce mixtures concurrently (Nampoothiriet al., 2010). Many fermentation processes nowadays use a spe-cies of Lactobacillus that has a higher yield of lactic acid. Thesebacteria can actively produce lactic acid under broad processingconditions, including a pH of 5.4�6.4, temperatures of38�42�C, and they survive in a low oxygen concentration.Often agricultural sources of simple sugars, such as glucose and

OHO

OH

H

L-lactic acid D-lactic acid

CH3

OHO

OH

H3C H

Figure 4.2 Chemical structures of L- and D-lactic acid with a meltingpoint of 16.8�C.

146 POLYLACTIC ACID

maltose from corn or potato, sucrose from cane or beet sugar,and lactose from cheese whey are widely used for lactic acid fer-mentation. Other nutrients, such as vitamin B complex, aminoacids and nucleotides are needed to ensure functionality of thebacteria throughout the process; such a nutrient package can beprovided by a rich corn-steep liquor.

Polymerization through lactide formation is the currentmethod employed by NatureWorkss to produce high-molecular-weight PLA polymers for commercial applications. The lactideis the cyclic dimer of lactic acid, and is the intermediate productfor ring-opening polymerization of PLA. A step is taken toprepolymerize either D-lactic acid, L-lactic acid or a mixture ofthe two, to obtain intermediate lactic acid oligomers (chainsof ,1000 lactic acid repeating units) and this is followed by acatalytic reaction under lower pressure to depolymerize andobtain a mixture of lactide stereoisomers. There are three stereo-forms of lactide, the cyclic dimer of lactic acid, which is builtup from a condensation reaction of two lactic acid molecules asfollows: L-lactide (two L-lactic acid molecules), D-lactide (twoD-lactic acid molecules) and meso-lactide (an L-lactic acid anda D-lactic acid molecule) as shown in Figure 4.3. According toHartmann (1998), the formation of different percentages of thelactide isomers can be affected by the lactic acid isomer feed-stock, the temperature and the catalyst. The lactide undergoesvacuum distillation for optical purification and this is followedby bulk melt polymerization to produce high optically purePLA. Commercial manufacturers prefer bulk melt polymeriza-tion because it involves lower levels of nontoxic catalysts, such

H3C

CH3

O

O

O

O

H3C

CH3

O

O

O

O

H3C

CH3

O

O

O

O

L,L-lactide (m.p. 97 ºC) Meso or L,D-lactide (m.p. 52 ºC) D,D-lactide (m.p. 97 ºC)

Figure 4.3 Chemical structures of L,L-, meso- and D,D-lactides(m.p. is melting point).


as less-reactive metal carboxylates, oxides, and alkoxides. Thesework to assist in synthesizing a high-molecular-weight PLA.It has been observed that lactides easily undergo polymerizationin the presence of transition metals (tin, zinc, aluminum, etc.)with tin (II) and zinc having the ability to yield the purest poly-mers. Some studies have reported that these catalysts are moreeffective in lactide polymerization because of the covalentmetal�oxygen bonds and free p or d orbitals (Kricheldorf andBoettcher, 1993; Dahlman et al., 1990).

As mentioned, lactic acid is a chiral molecule possessing Land D isomers, and the composition of the lactic acid in termsof these two isomers significantly affects the characteristics ofthe PLA. This means that the stereochemistry of PLA may betailored to fit its applications. It is the stereoregularity of thebuilt-up monomers that determines PLA as a highly crystallinepolymer (Huang et al, 1998). Stereochemically pure PLA ofeither D-lactic acid or L-lactic acid can be a crystalline polymer.Amorphous materials can be made by the inclusion of relativelyhigh D or L content (.20%), whereas highly crystalline materi-als can be obtained when the D or L content is low (,2%) (Luntand Shafer, 2000). Hence, PLA can be made up of the threestereoisomers of lactide: L-lactide, D-lactide, and meso-lactide;depending on the constituents, the resulting polymer can havevarying characteristics. The stereochemical composition of thepolymer has a dramatic effect upon the melting point of thepolymer, the rate of crystallization and the ultimate extent ofcrystallization. According to Drumlight et al. (2000), PLA madefrom pure L-lactide, also called poly(L-lactide), has an equilib-rium melting point of 207�C and a glass transition temperatureof about 60�C. Commonly, high stereochemically pure PLA,either in L or D, possesses a melting point of around 180�C withan enthalpy of melting of 40�50 J/g. Subsequent introduction ofirregularity of stereochemistry in the polymer, such as by copo-lymerization of poly(L-lactide) with meso-lactide or D-lactide,can cause a significant reduction in melting point (seeFigure 4.4), rate of crystallization and extent of crystallization,but it has no effect on the glass transition temperature (Lunt,1998). From a study conducted by Kolstad (1996), it was

148 POLYLACTIC ACID

recognized that the peak melting temperature reduced in aroughly proportional manner. The crystallization half-time ofthe copolymer increased significantly for a high-meso-lactidecontent version (see Table 4.1). Higher average molecularweight causes the recrystallization time to increase several-fold.These findings were further strengthened by Huang et al. (1998),who found that spherulitic growth rates were strongly depen-dent on meso- content as well. The degree of crystallinity of thepoly(L-lactide-co-meso-lactide) copolymer exhibits a dramaticdrop with increasing D isomer content (D-isomer contributed bymeso-lactide), ranging from 40�60% for poly(L-lactide) to values,20% for copolymer with 12% meso- content (or containing6.6% D isomer), as shown in Figure 4.5. The melting point andglass transition data for selected PLA structures and blends aresummarized in Table 4.2 (Henton et al., 2005).

Pure crystal of PLA, i.e. 100% crystallinity, has the theoreti-cally enthalpy of melting (ΔHm) of 93.7 J/g as compared to theexperimental values 40�50 J/g for a polymer with 37�47%

180

170

160

150

Pea

k M

eltin

g Te

mpe

ratu

re (

°C)

140

130

120

110

1000 5

Meso-lactide, wt%

10 15 20

Figure 4.4 Peak melting temperature of poly(L-lactide-co-meso-lactide)(adapted from Kolstad, 1996).


Table 4.1 Crystallization Half-Time (Min) for Poly(L-lactide-co-meso-lactide) (Kolstad, 1996)

Temperature

(�C)0% Meso- 3% Meso- 6% Meso-

Mn5101,000

Mn5157,000

Mn588,000

Mn5 1

14,000

Mn558,000

Mn5114,000

85 14.8 � 23.9 � � �90 7.0 11.4 11.0 � � �95 4.5 � 8.1 � � �100 3.8 4.8 9.4 11.4 27.8 �105 2.9 � 8.6 � 19.6 �110 1.9 4.0 6.0 10.8 19.7 44

115 3.5 � 6.9 � 22.2 �120 4.0 5.7 8.2 11.6 � �125 5.1 � 11.5 � � �130 8.7 13.4 � � � �135 22.9 � � � � �

30 55 80ΔT

105

0.75

0.5

ϕc

0.25

0

Figure 4.5 Bulk degrees of crystallinity (ϕc) as a function of degree ofsupercooling (ΔT5Tm

o�Tx, where Tm� is the equilibrium melting point

and Tx is isothermal crystallization temperature) of poly(L-lactide-co-meso-lactide). &5 0% meso-lactide with 0.4 D-isomer content; e5 3%meso-lactide with 2.1% D-isomer content; x5 6% meso-lactide with3.4 isomer content; ƒ5 12% meso-lactide with 6.6% D-isomer content(adapted from Huang et al., 1998).

150 POLYLACTIC ACID

crystallinity (Tsuji and Ikada, 1995; Tsuji and Ikada 1996). It isimportant to note that the extent of crystallization can be variedaccording to the rate of cooling, polymerization conditions andthe presence of impurities or enantiomers. Huang et al. (1998)

Table 4.2 The Effects of Stereochemistry of PLA on MeltingPoint and Glass Transition

Structure Description Tm (�C) Tg (�C)

Isotactic

poly(L-lactide)

or poly(D-lactide)

BLLLLLLB or

BDDDDDDB170�190 55�65

Random optical

copolymers

Random level of meso- or

D-lactide in L-lactide

or D-lactic acid in

L-lactic acid

130�170 45�65

PLLA/PDLA

stereocomplex

BLLLLLLB blended

with BDDDDDDB220�230

(Ikada

et al.,

1987)

65�72

(Tsuji

and

Ikada,

1999)

PLLA/PDLA

stereoblock

complexes

BLLLLLLBDDDDDDB 205 (Yui

et al.,

1990)

40 (Ovitt

and

Coates,

1999)

Syndiotactic

poly(meso-)

PLA

BDLDLDLDLDLBAl-centered R-chiral catalyst

179 (Ovitt

and

Coates,

2000)

152 (Ovitt

and

Coates,

1999)

Heterotactic-

(disyndiotactic)

poly(meso-lactide)

BLLDDLLDDLLDDLLDDBAl-centered rac-chiral

catalyst

40 (Ovitt

and

Coates,

1999)

Adapted from Henton et al., 2005.


and Nijenhuis et al. (1991) have reported the heat of meltingcan reach a value of 100 J/g for a slow polymerization processyielding a highly crystalline stereospecific polymer.

Poly(L-lactide) can be crystallized into the α-form, β-form orγ-form, and this depends on the method of preparation and thethermal history. De Santis and Kovacs (1968) found that theconformation of the chain in the α-phase was a left-handed 107helix for the L-isomer (PLLA), whereas it was a right-handed103 for the D-isomer (PDLA) (see Figure 4.6). Both PLA chainshave an orthorhombic unit cell of dimensions a5 10.7 A,b5 6.126 A and c5 28.939 A. Based on the ratio of a and bparameters with a value of 1.737 (it is approximated to O3), itexhibits an almost hexagonal packing of helices. Hoogsten et al.(1990) suggested that the β-form of PLA was also in an ortho-rhombic unit cell, with parameters a5 10.31 A, b5 18.21 Aand c5 9.0 A, which accommodate six helices with a near-hexagonal packing (the b/a ratio is 1.76, i.e. �O3). In addition,Brizzolara et al. (1996) worked out that an orthorhombic unitcell based on a three-fold helix conformation with two parallelchains showed the existence of two distinct and interrelatedphases. PLLA in the γ-form can be recovered through the epi-taxial crystallization with two antiparallel s(3/2) helices in thepseudoorthorhombic unit cell (a5 9.95, b5 6.25, c5 8.8) exhi-biting a three-fold helix conformation. Tsuji (2002) summarizedunit cell parameters for non-blended and stereocomplex crystalsand these are given in Table 4.3.

(a) (b)

abαβ

γ

c

Figure 4.6 (a) Left-hand and right-hand helices (Morgan, 2002);(b) simple unit cell and parameters of designation.

152 POLYLACTIC ACID

Table 4.3 Unit Cell Parameters for Non-Blended PLLA and Stereocomplex Crystals

Form Space Group Chain

Orientation

No. of

Helices/

Unit Cell

Helical

Conformation

a

(nm)

b

(nm)

c

(nm)

α(degree)

β(degree)

γ(degree)

PLLA

α-formPseudo-

orthorhombic

� 2 103 1.06 0.61 2.88 90 90 90

PLLA

α-formOrthorhombic Parallel 2 103 1.05 0.61 � 90 90 90

PLLA

α-formOrthorhombic � 6 31 1.031 1.821 0.90 90 90 90

PLLA

α-formTrigonal Random up-

down

3 31 1.052 1.052 0.88 90 90 120

PLLA

α-formOrthorhombic Antiparallel 2 31 0.995 0.625 0.88 90 90 90

PLLA

α-formTriclinic Parallel 2 31 0.916 0.916 0.870 109.2 109.2 109.8

Adapted from Auras et al., 2004.

4.3 Analytical Technique of PLA

4.3.1 Nuclear Magnetic Resonance Spectroscopy

PLA is formed by ring-opening polymerization of lactide,the cyclic dimer of lactic acid. In addition to the presence ofstereoisomers of lactic acid, PLA properties are also influencedby the amount and distribution of L and D stereocenters of thepolymer chains. Nuclear magnetic resonance (NMR) spectros-copy is playing an important role in determining the stereose-quence distribution of the polymer. It is known that PLA withhigh stereoregularity can form highly crystalline polymers, i.e.isotactic PLA made up by either D-lactide or L-lactide has ahigher rate of crystallization compared to meso-lactide, which-tends to form amorphous PLA when synthesized using nonstereo-selective catalysts. NMR applies the principle that the magneticnuclei in a magnetic field absorbs and re-emits electromagneticradiation illustrating the tacticity of the structural orientation inthe polymer.

The NMR spectrum exhibits resonances of particular polymersthat possess stereosequence sensitivity. In the case of PLA,NMR spectra can distinguish the diads �LD� (or �DL�)and�LL� (or�DD�). But, the similar diads,�DD� and�LL�,or �LD� and �DL�, do not show different chemical shifts.In the stereosequence of PLA, the �DD� and �LL� producean isotactic pairwise relationship, while �LD� and �DL� havethe structure in a syndiotactic pairwise relationship. The observa-tions from NMR have shown difficulties, such as overlayingof chemical shifts, insufficient resolution and probability of stereo-sequence formation due to polymer chains remaining in a hugemacromolecule. For instance, for the stereosequence sensitivityof length n, there are 2(n21) possible combinations of pairwiserelationships to be observed in NMR spectra.

Several studies have been conducted using NMR spectro-scopy to determine the stereosequence distribution in PLA.Kricheldorf and Kreiser-Saunders (1990) has pioneered the useof methine resonance in 1H and 13C NMR spectra on varioussynthesis methods of PLA as well as the initiators/catalysts

154 POLYLACTIC ACID

involved. Meanwhile, Zell et al. (2002) has revised the tetradstereosequence assignment for the methane carbon and protonof Kricheldorf et al. (1996) (see Figure 4.7). The revised tetradstereosequence is an extension to the methine stereosequenceassignments in PLA for upgrading to hexad level and includesa method for quantifying the amount of L-, D- and meso-lac-tide in PLA.

Figure 4.8 shows the 1H and 13C solution NMR spectra ofPLA synthesized using 5% L-lactide and 95% D-lactide. Asobserved by Zell et al. (2002) in the 1H spectrum, the directintegration of the isi resonance is impossible due to the over-lapping of the isi resonance with the iii resonance. The 1H and13C resonance relationship is shown in Figure 4.9. A similarsituation can be found in the overlapping of the sis resonance

sss

sss, isi,ssi/iss

ssi/iss

ssi/iss

1H13C

(a)

(b)

sis

69.4 69.2ppm

ppm

69.0 5.25 5.20ppm

5.15

sisisi

sss

sss, isi,ssi/iss

ssi/iss

ssi/iss

1H13C

isi

69.4 69.2 69.0 5.25 5.20ppm

5.15

sis, ssi/isssis

Figure 4.7 Comparison of the (a) Kricheldorf et al. (1996) and (b) Zellet al. (2002) tetrad stereosequence assignments of the methinecarbon and proton in PLA synthesized using meso-lactide. The linesbetween peaks in the 1H and 13C NMR spectra indicate connectivityobserved in the heteronuclear correlation NMR spectra (i designatesisotactic, s designates syndiotactic).


with the iii resonance, which has caused no direct intergrada-tions of the sis resonance. Zell et al. (2002) reported that the L-stereocenters from the L-lactide had at least four D stereocentersfrom D-lactide on either side in respect to the PLA synthesizedusing 5% L-lactide and 95% D-lactide with tin octanoate as aninitiator in toluene at 70�C for 18 h.Thakur et al. (1997) also conducted a study varying the com-

position of L-, D- and meso-lactide prepared by ring-opening

1H 2.64

6.19

5.30

13C

5.25 5.20 5.15 5.10 5.05

2.94

94.42

ppm

69.4 69.2 69.0 68.8ppm

sis

iis/sii

iii

93.81sis, iii, iis/sii

isi

isi

Figure 4.8 1H and 13C solution NMR spectra of PLA synthesizedusing 5% L-lactide and 95% D-lactide (Zell et al., 2002).

. . .D D D D L L D D D D. . .

13C

1H

i s

s i s

i

Figure 4.9 Direction of central pairwise relationship of 1H and 13Cresonances (Zell et al., 2002).

156 POLYLACTIC ACID

polymerization of lactides and catalyzed by tin (II) octanoatein a 1:10,0000 catalyst:monomer ratio, at 180�C for 3 h. Therespective NMR spectra of the samples are shown inFigure 4.10. It can be observed that there is a preference forsyndiotactic addition during the polymerization process, asinferred from the stereosequence distribution in the NMRspectra.

4.3.2 Infrared Spectroscopy

Infrared (IR) spectroscopy is an analytical method to deter-mine the presence of functional groups and unveil the bonding

(a)

iss/ssi iss/ssisss isi

iss/ssi iss/ssisss isi

isi

isisiiii

iiisi/isiii

iiisi/isiii

iss/ssi

iissi/issii

iissi/issii

iss/ssisss isi

sissssss

sisss/sssis sisis

sisss/sssis

(b)

(c)

69.4 69.2 69.2 69.169.0 69.0 68.9ppm ppm

(d)

(e)

(f)

Figure 4.10 Methine resonances in the 13C NMR spectra of PLA(a) 3:3:94 (% L-lactide:% D-lactide:% meso-lactide); (b) 51.5:1.5:47;(c) 70.9:0.9:28.2; (d) 50:50:0; (e) 60:40:0; (f) 70:30:0 (adaptedfrom Thakur et al., 1997).


or interactions within the substance. The IR spectrum of apolymer is normally analyzed using the Fourier transforminfrared spectroscopy (FT-IR) method with the scans normallydone at 4000�400 cm21, with results provided in percentagetransmission or absorbance. IR spectroscopy picks up the vibra-tions of bonds and provides evidence of functional groups.Stronger bonds are generally stiffer, requiring greater forcesto stretch or compress them. Peak assignments for PLA(98% L-lactide) of IR spectra are summarized in Table 4.4.As shown in Figure 4.11, the most important indication ofPLA is the presence of aCQO carbonyl stretch at 1748 cm21

and aCQO carbonyl bending at 1225 cm21. There are threestretching bands for aCaH, denoted by 2997 cm21 for asym-metric, 2945 cm21 for symmetric and 2877 cm21. The lowestwavenumber, 2877 cm21, is assigned for the methyl aCH3,which has weaker bonding. However, when the oxygen atom isnext to CaH, the wavenumber will increase due to the electro-negativity of the atom strengthening CaH. As a result, theOQCaH is assigned the wavenumber 2997 cm21. The aOH

Table 4.4 The Infrared Spectroscopy WavenumberCorresponding to the Bonding and Functionality in PLA

Assignment Wavenumber (cm21)

aOH stretch (free) 3100

aCHastretch 2997 (asymmetric), 2946

(symmetric), 2877

aCQO carbonyl stretch 1748

�CH3 bend 1456

aCHadeformation including

symmetric and asymmetric bend

1382, 1365

aCQO bend 1225

aCaOastretch 1194, 1130, 1093

aOH bend 1047

aCH3 rocking modes 956, 921

aCaCastretch 926, 868

Adapted from Auras et al., 2004.

158 POLYLACTIC ACID

stretching band at 3571 cm21 is a broad band, which is alsocharacteristic of carboxylic acid. The aOH stretching band ofcarboxylic acid is lower than for alcohol (3300 cm21) dueto the unusually strong hydrogen bonding in carboxylic acids.The bending mode corresponds to aCQO and aOH and canbe found at 1225 cm21 and 1047 cm21, respectively. However,the band at the lower wavenumber tends to show overlapping,leading to difficulty in characterization.

Recently, Pan et al. (2011) conducted a study using theFT-IR technique to investigate the crystalline structure ofPLLA and PLLA/PDLA stereocomplex. PLA tends to formvarious crystal polymorphisms depending on the crystallizationconditions. The usual polymorph, α-form, is crystallized by thecold, melt or solution route, yielding an orthorhombic (orpseudo-orthorhombic) unit cell in a distorted 103 conformation(Aleman et al., 2001). When the α counterpart is stretched at ahigh temperature to a high drawing ratio, the PLA will trans-form into the β-form, which adopts a 31 helical conformation(Sawai et al., 2003). Another metastable α0-form is attainedfrom the stereoregular PLA melt-crystallined at a low crystalli-zation temperature Tc (,100�C), whereas the α-form is yielded

10002000

Wavenumber (cm–1)

%T

3000

CH3 O

C n)OPLA ( CH

Figure 4.11 Infrared spectrum for PLA composed of 95% L-lactide,5% meso-lactide, with average molecular weight (Mw) of 9.733 104.


at higher Tc (.120�C) (Zhang et al., 2005a). Pan et al. (2011)found that the α-form PLA showed spectral splitting (seeFigure 4.12). The α-form PLA spit into a few new peaks whencooled to 2140�C: 23006 cm21 (CH3 asymmetric stretching),2964 cm21 (CH3 symmetric stretching), 1777 and 1749 cm21

(CQO stretching), 1468 and 1443 cm21 (CH3 asymmetricbending), 1396 and 1381 cm21 (CH3 symmetric bending),1222 cm21 (CaOaC asymmetric bending and CH3 asymmetricrocking), 1144 cm21 (CH3 asymmetric rocking), and 1053 cm21

(CaCH3 bending). The α0 crystal has remarkable result com-pared to the former without exhibiting spectral splitting. Thisis because the α0 crystal has weaker interchain interactions inits crystal lattice. In other words, there is lack of lateral inter-actions between the molecular chains contained in a crystalunit cell. When a comparison was made for the blend ofPLLA/PDLA, which was in the amorphous structure,

3050

(a)

–140

140AB

S2n

d de

rivat

ive

–140

–140

–14080

80

sc

sc

sc

scsc

sc

sc

sc

sc

sc

α

αα

α

α′

α′

α′

α′ α′

α′α′αα

α′α

ααα

α′

α′

α′α′α

α

sc

sc

–140

–140

140

140

140

–140

140

–140

–140

–140

80

80T(°C)T(°C)

2880

1777

1749

1759

1458

1443 13

87

1381

1360

1222 12

13

1184

1144 11

35

1110

1092

1053

1045

957

921

90829

45

2964

299029

96

–140

–140

140

140

140

–140

140

–140

–140

–14080

80

–140

–140

140

140

140

(b) (c)

3000 2950 2900 2850 1800 1750 1500 1450 1400 1350 1250 1200 1150 1100 1050 950 900Wavenumber (cm–1)Wavenumber (cm–1)Wavenumber (cm–1)

Figure 4.12 Temperature-dependent FT-IR spectra and their secondderivatives of α0, α and amorphous (sc) forms of PLA. Intensities ofFT-IR spectra and their second derivatives in the wavenumber ranges1500�1325 and 975�890 cm21 were magnified for clarity.ABS5 absorbance (adapted from Pan et al., 2011).

160 POLYLACTIC ACID

it showed that the corresponding peak for CQO stretching isabout 10 cm21 lower, while CH3 asymmetric/symmetric stretch-ing and CH symmetric stretching is reduced by 4�6 cm21. It can,therefore, be assumed that weak hydrogen bonds form inCaHaaaaOQC in the amorphous PLA crystal (Zhang et al.,2005b).

Figure 4.13 shows the IR spectra of PLLA films annealed atroom temperatures of 80�120�C at the region of 1000�650 cm21,which were done to investigate the spectral differencesbetween semicrystalline and amorphous PLLA. The PLLAfilms annealed at higher temperatures possess higher crystal-lization due to the increase in temperature-enabled flexiblechain movement, which promotes crystallization rearrange-ment. The spectra of the annealed PLA have distinct differ-ences, with few peaks at 956, 922, 872, 848, 756, 737, 711 and695 cm21. It is obvious that the IR spectra of semicrystallineand of amorphous PLLA have distinct differences. It can beobserved that when annealed at higher temperatures, the bandsshift to higher wavenumbers. This is due to the fact that

1000

Abs

orba

nce

900

956

922

848

872756

737711 695(a)

(b)

(c)

(d)

800 700

Wavenumbers (cm–1)

Figure 4.13 Infrared spectra of neat PLLA at various annealingtemperatures in the region 1000�600 cm21: (a) room temperature25�C, (b) 80�C, (c) 110�C and (d) 140�C (Vasanthan et al., 2011).


crystallization limits the vibration of bonding. For instance,the vibration of �COOH as assigned to the band at 956 cm21

is shifted by a reduction of 5�8 cm21 when the annealingtemperature is higher. It has also been noted that the band at956 cm21 decreases in intensity (or absorbance) while the bandat 922 cm21 increases in intensity with increasing annealingtemperature. The band at 922 cm21 represents the combinationof C�C backbone and CH3 rocking mode of PLLA crystals(Zhang et al, 2005b). The bands at 872 and 848 cm21 becomeweaker as the annealing temperature increases. The bands at737 and 717 cm21 appeared as a single band in the IR spectrumand both bands split into two bands as the annealing tempera-ture exceeds 100�C. The splitting of the band can be explainedby the formation of a multiphase related to the presence ofcrystal and amorphous regions. As a result, the split is into thehigher band, which is assigned to crystal region functionality,and the lower band, which represents the functional group inthe amorphous region. The prescribed functional group of thesplitting of the band belongs to the bending/rocking mode of�CH3.

4.4 Solubility and Barrier Properties of PLA

PLA is a suitable biopolymer to replace conventional petro-chemical polymers as packaging materials. The ‘green’ charac-teristics of PLA have been ‘eye-opening’ in the food packagingindustry, as it has good barrier properties in maintaining thefreshness of food while not polluting the environment. Carefulselection of packaging material by food producers is extremelyimportant to avoid chemical and biological contamination, andthe rapid spoilage of food. Packaging materials must provide asufficient barrier against water vapor to prevent food degrada-tion or the growth of microorganisms, prevent the permeationof atmospheric gases what would initiate oxidation, and main-tain the volatile organic compounds contained in the food topreserve the aromas and flavors. Moreover, packaging shouldbe insoluble in many types of solvents to avoid the migration

162 POLYLACTIC ACID

of packaging traces into the food, which could endanger healthwhen consumed.

In general, the possibility of food contamination or poisoningfrom PLA containers used in the market is low. This is becausePLA is produced from the lactide monomer, which is origi-nated from L-lactic acid, a nontoxic component that exists nat-urally in the human body. Nevertheless, the presence of tracelevels of D-lactic acid, a minor side-product during polymeri-zation, is possible. D-lactic acid cannot be consumed by thehuman body, due to the lack of an appropriate enzyme. Thedetermination of the permeability (solubility and diffusion) ofgases, flavors and aromas in polymers is of vital importance inthe application of PLA in the food packaging industry. This isdiscussed in the next section. The method of determining levelsof D-lactic acid and lactide for safety purposes are discussed inChapter 2, and this is an important aspect of the application ofPLA as packaging material.

4.4.1 Solubility of Polylactic Acid

According to Nampoothiri et al. (2010), PLA can be dis-solved in chloroform, methylene chloride, dioxane, acetonitrile,1,1,2-trichloroethane and dichloroacetic acid. PLA can also besoluble in toluene, acetone, ethyl benzene and tetrahydrofuran(THF) when heated to boiling temperatures, but its solubility islimited at low temperatures. Generally, no PLA can be dis-solved in water, selective alcohols and alkanes. Highly crystal-line PLLA resists solvent attack of acetone, ethyl acetate andtetrahydrofuran, whereas amorphous PLA, such as the copoly-mer of poly (L,D-lactide), can be easily dissolved in variousorganic solvents, such as THF, chlorinated solvents, benzene,acetonitrile and dioxane.

The solubility of PLA depends on the crystallinity of thepolymer because a highly oriented structure increases the diffi-culty of interchain migration of solvent molecules. The princi-ple of thermodynamic criterion of solubility is based on thefree energy of mixing (ΔGM), which states that two substancesare mutually soluble if ΔGM is zero or negative. The free


energy of mixing for a solution process between a solvent anda polymer is related as: ΔGM5ΔHM2 T ΔSM, where ΔHM, T,and ΔSM are the enthalpy of mixing, absolute temperature andentropy of mixing, respectively. Normally the value of ΔSM issmall and positive. Thus, the solubility of solvents greatlydepend on the ΔHM and T. The solubility of a substance isrepresented by solubility parameter (δ), which was introducedby Hildebrand and Scott (1950), and is related to the cohesiveenergy density. Hansen and Skaarup (1967) later proposedsolubility parameters linked with polarity and the hydrogenbonding system, which was divided into three components,namely non-polar (δD), polar (δp) and hydrogen bond (δh), wherethe Hansen solubility parameter, δT5 δD1 δ1 δk. Table 4.5 andTable 4.6 summarize the solubility parameters for solvents andPLA, respectively. In order to dissolve PLA in a solvent, thesolubility parameters of the polymer and solvent should have adifference of δt,2.5 (Auras, 2007). The liquid componentscontained in food, such as water, ethanol and paraffin (as repre-sented by hexane), have greater differences of solubility para-meters than PLA; thus PLA is safe to be in contact with foodwithout the possibility of migration.

Auras (2007) computationally compared the solubility ofPLA, polyethylene terephthalate (PET) and polystyrene (PS)using regular solution theory (RST) for various solvents. Ascan be seen from Figure 4.14, the solubility regions of PLA, PET,and PS can be approximated by a boundary of radius B2.5δ unitfrom the value of PLA (δv5 19.01, δH5 10.01), PET (δv5 19.77,δH5 10.97) and PS (δv5 15.90, δH5 5.00). Nevertheless, thesolubility of the polymers declines when the distance of solventsis large. It can be concluded from the results that both PLAand PET have similar solubility properties, and so both can beused interchangeably.

4.4.2 Permeability of Polylactic Acid

The gas permeation properties of PLA are important whenconsidering it as a packaging material. Packaging requires lowpermeability materials, to avoid the loss of flavor, aroma or the

164 POLYLACTIC ACID

Table 4.5 Solubility Parameters of Solvents at 25�C (Hansen,2000)

Solvent Hansen Solubility Parameter,δT (J/cc)0.5 at 25�C

δda δpa δha δt

Acetone 15.0 10.4 7 19.6

Acetonitrile 15.3 18.0 6.1 24.4

Benzene 18.4 0.0 2.0 18.5

Chloroform 17.8 3.1 5.5 18.9

m-Cresol 18 5.1 12.9 22.7

Dimethyl formamide 17.4 13.7 11.3 24.9

Dimethyl suphoxide 18.4 16.4 10.0 26.6

1-4 Dioxane 19.0 1.8 7.4 20.5

1-3 Dioxolane 18.1 6.6 9.3 21.4

Ethyl acetate 15.8 5.3 7.2 18.2

Furan 17.8 1.8 5.3 18.7

Hexafluoro isopropanol 17.2 4.5 14.7 23.1

Isoamyl alcohol 15.8 5.2 13.3 21.3

Methylene dichloride 18.2 6.3 6.1 20.2

Methyl ethyl ketone 16.0 9.0 5.1 19.1

n-Methyl pyrolidone 18.0 12.3 7.2 23.0

Pyridine 19.0 8.8 5.9 31.8

Tetrahydrofuran 16.8 5.7 8.0 19.5

Toluene 18.0 1.4 2.0 18.2

Xylene 17.6 1.0 3.1 17.9

Nonsolvents

Isopropyl ether 13.7 3.9 2.3 14.4

Cyclohexane 16.5 0.0 0.2 16.5

Hexane 14.9 0.0 0.0 14.9

Ethanol 15.8 8.8 19.4 26.5

Methanol 15.1 12.3 22.3 29.6

Water 15.5 16.0 42.3 47.8

Diethyl ether 14.5 2.9 5.1 15.6


occurrence of oxidation, all of which can shorten the shelf lifeof food. Because PLA is a biodegradable material with thepotential to substitute existing plastic materials, such as PET,PS and low-density polyethylene (LDPE), it is very importantfor PLA to have as effective permeability characteristics asthese existing polymers.

Lehermeier et al. (2001) conducted a study on the gas per-meation of PLA for nitrogen, oxygen, carbon dioxide andmethane. The results are summarized in Table 4.7. The activa-tion energy of permeation (Ep) can be calculated as follows:

P5Po exp 2Ep

RT

� �(4.1)

It was observed that the permeability of PET was lower thanPLA. In other words, PET has superior barrier properties thanPLA with an L:D ratio of 96:4. Lehermeier et al. (2001) con-cluded that this is due to PET containing aromatic rings in thepolymer chain backbone, which reduces free volume and chainmobility. There is a lack of significant change with the intro-duction of branching in the PLA chains. However, crystalliza-tion can greatly improve the barrier properties. The incrementof crystallinity in biaxially orientated PLA film (L:D ratio of95:5) with 16% crystallinity caused the permeability to reduce4.5 times less than PLA film samples (with L:D of 96:4 and98:2) having 1.5% and 3% crystallinity, respectively. This is

Table 4.6 Solubility Parameters for PLA at 25�C (See Agrawalet al., 2004, for Calculation Method)

Method δd(J/cc)0.5

δp(J/cc)0.5

δh(J/cc)0.5

δt(J/cc)0.5

Intrinsic 3D viscosity 17.61 5.30 5.80 19.28

Intrinsic 1D viscosity � � � 19.16

Classical 3D geometric 16.85 9.00 4.05 19.53

Fedors group contribution � � � 21.42

Van Kreveln group

contribution

� � � 17.64

166 POLYLACTIC ACID

because crystallinity improves the compaction of structure,leading to a difficulty for gas molecules to diffuse through thefilm. A comparison of the permeation properties of 100% linearPLA possessing an L:D ratio in line with other commoditypolymers mainly for packaging are shown in Figure 4.15. Thedata is self-explanatory: PLA possesses good barrier propertiescompared to PS and LDPE. PLA has been shown to havepreferential barrier properties in relation to nitrogen, carbondioxide and methane, but slightly weaker barrier properties for

12.0015.00

14.00

13.00

12.00

11.00

10.00

9.00

8.00

7.00

OA9

TDA

NON

DTA

DBU2EH

2EB

IPL3CP

EMEIDH

ELAEGB

EMEDGM

PET

PLAIDE

IOL

DALDGN

BLA

6.00

5.00

4.0014 15 16 17 18 19

PS+

20 21 22

11.00

10.00

9.00

8.00

δh, M

Pa1/

2

δh, M

Pa1/

2

δv, MPa1/2

δv, MPa1/2

MEL

DME

PLA

PET

THD

DBE 14D

ANIBCE

FUR+ PS PXP

7.00

6.00

5.00

4.0015.00 16.00 17.00 18.00 19.00 20.00 21.00

Figure 4.14 (a) Volume-dependent cohesion parameter (δv) versusHansen hydrogen-bonding parameter (δh) for PLA. Values indicatedfor solvents with Δδ, 5 MPa1/2: FUR5 furan; EPH5 epichlorohydrin;THD5 tetrahydrofuran; 14D5 1,4-dioxane; MEL5methylal(dimethoxymethane); BCE5 bis(2-chloroethyl) ether; ANI5 anisole(methoxybenzene); DME5 di-(2-methoxyethyl) ether; DBE5 dibenzylether; PXP5 bis-(m-phenoxyphenol) ether; 3CP5 3-chloropropanol;BEA5 benzyl alcohol; CHL5 cyclohexanol; 1PL5 1-pentanol;2EB5 2-ethyl-1-butanol; DAL5 diacetone alcohol; DBU5 1,3-dimethyl-1-butanol; ELA5 ethyl lactate; BLA5 n-butyl lactate;EME5 ethylene glycol monoethyl ether; DGM5 diethylene glycolmonoethyl ethermethyl; DGE5 diethylene glycol monoethyl ether;EGB5 ethylene glycol mono-n-butyl ether; 2EH5 2-ethyl-1-hexanol;IOL5 1-octanol; 2OL5 2-octanol; DGN5 diethylene glycol monon-butyl ether; 1DE5 1-decanol; TDA5 1-tridecanol; NON5 nonyl;OA95 oleyl alcohol (adapted from Auras, 2007).


Table 4.7 Permeation Properties of PLA and PET

Gas Polymer Permeability at 25�C(310210 cm3

(STP).cm/cm2.s.cm.Hg)

Activation(kJ/mol)

Temperature DependencePermeation, PT (310210 cm3 (STP).cm/cm2.s.cm.Hg)

Nitrogen Linear PLA L:D (96:04) 1.3 11.2 PT5 109.86 e21.36X

Linear PLA L:D (98:02) �PET 0.008a 26.4b �

Oxygen Linear PLA L:D (96:04) 3.3 11.1 PT5 276.43 e21.34X


Carbon

dioxide

Linear PLA L:D (96:04) 10.2 6.1 PT5 115.67 e20.78X


Methane Linear PLA L:D (96:04) 0.9 13.0 PT5 149.95 e21.55X

Linear PLA L:D (98:02) 0.8 � �Biaxially oriented film L:

D (95:05)

0.19 � �

PET 0.004a 24.7b �

a5Michaels et al. (1963); b5 Pauly (1999); X5 1/T3 103/K.

Adapted from Lehermeier et al., 2001.

oxygen. This finding is important, in that it shows that PLAcan be utilized as a robust packaging material to substitute var-ious commodity petrochemical-based plastic films. Its goodbarrier properties, along with its biodegradability and ‘green’production, mean that PLA is a strong contender as a futurepackaging material.

Permeability to water is another important factor that needsto be considered for packaging materials. Shogren (1997) com-pared the water vapor permeability of various biodegradablepolymers, including poly(β-hydroxybutyrate-co-hydroxyvale-rate) (PHBV) containing 6, 12 and 18% valerate, poly(ε-capro-lactone) (PCL), amorphous and crystalline poly(L-lactic acid),etc. The water transmission rates for these materials as estab-lished by Shogren are presented in Table 4.8. PLA exhibitsgood water resistance in comparison to many biodegradablepolymers except PHBV. Moreover, annealing of PLA at 130�C

LDPE

Polystyrene

PLA

PET

LDPE

Polystyrene

PLA

PET 0.2

0 5 10 15 20 25 30 0.0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0

10.2

10.5

28.0 LDPE

Polystyrene

PLA

PET 0.004

1.0

2.3

4.0

LDPE

Polystyrene

PLA

PET0.008

0.0 0.5 1.0 1.5 2.0 2.5 0

O2 Permeation (× 10–10 cm3(STP)-cm/cm2-s-cm Hg)

1 2 3 4 65 7

N2 Permeation (× 10–10 cm3(STP)-cm/cm2-s-cm Hg)

CO2 Permeation (× 10–10 cm3(STP)-cm/cm2-s-cm Hg) CH4 Permeation (× 10–10 cm3(STP)-cm/cm2-s-cm Hg)

1.3

2.2

1.9 6.9

2.6

3.3

0.04

Figure 4.15 Permeation properties of 100% linear PLA having aL:D ratio of 96:04 compared to other common plastics at 30�C(adapted from Lehermeier et al., 2001).


induces the formation of a crystalline structure, which improveswater resistivity. This can be explained by the fact that crystal-lization reduces the molecular cross-sectional area for diffusionand increases the diffusion path length by imposing restraintson the mobility of the amorphous phase (Shogren, 1997).Similarly, the solubility parameters of the polymers also greatlyinfluence water vapor permeability. When the differencebetween the solubility parameter value for a polymer and wateris small, this means that the polymer favors water, thus, thetransmission rate is higher.

Siparsky et al. (1997) performed an depth investigation onthe effect of copolymerization on water transmission of PLAfilm. The ‘solution-diffusion’ model (Equation 4.2) was used to

Table 4.8 Water Vapor Transmission Rates of BiodegradablePolymer Films (Shogren, 1997)

Film Water Vapor

Transmission

Rate (g/m2/day)

Crystallinity

(%)

Solubility

Parameter

(J/cm3)1/2

T5

6�CT5

25�CT5

49�C

PHBV-6 1.8 13 124 74 21.5

PHBV-12 3.1 21 204 69 21.5

PHBV-18 3.5 26 245 62 21.4

PLA-crystalline 27 82 333 66 22.7

PLA-amorphous 54 172 1100 0 22.7

PCL 41 177 1170 67 20.8

Bionolle 59 330 2420 0 �BAK 1095 134 680 3070 0 �CAP 590 1700 5200 41 24.2

CA 1020 2920 7900 33 25.7

PHBV5 poly(β-hydroxybutyrate-co-hydroxyvalerate) with 6, 12 and 18% valerate;

PLA-cystalline5 PLA annealed at 130�C; PCL5 poly(ε-caprolactone);CA5 cellulose acetate; CAP5 cellulose acetate propionate; Bionelle5 blown film

containing an aliphatic polyester; BAK 10955 blown film containing poly(ester-

amide). Solubility parameter for water is 47.9 (J/cm3)1/2.

170 POLYLACTIC ACID

characterize the water vapor in PLA. P is the permeabilitycoefficient relates to flux, S is the solubility coefficient repre-senting the equilibrium water concentration and D is diffusioncoefficient relates to diffusivity.

Solution Diffusion Model: P5 S3D (4.2)

Table 4.9 exhibits the diffusivity of water vapor as affectedby the composition of L:D in PLA. A stereospecific isomer ofPLA has a better water vapor barrier resistance due to its

Table 4.9 Diffusion, Solubility, and Permeability Coefficients ofPLA, PCL and its Copolymers/Blends, Measured at 90% RelativeHumidity and Temperature of 20�C (Siparksy et al., 1997)

Composition Tg (�C) %

crystallinity

P

(31013)

S

(3106)

D

(3106)

50:50 L:D PLA 52 � 2200 3400 0.067

70:30 L:D PLA 50 � 2200 2200 0.10

90:10 L:D PLA 54 � 1500 2000 0.078

95:5 L:D PLA 59 � 1400 3000 0.044

100:0 L:D PLA

(quenched)

63 11 1900 4000 0.052

100:0 L:D PLA 63 39 1600 4000 0.046

100:0 L:D (annealed

15 min at 160�C)63 46 2000 4000 0.040

30% random PCL:

PLA

40 PCL,5 2900 2200 0.13

30% block PCL:

PLA

263, 47 PCL: 9 3100 3100 0.10

30% oriented PCL:

PLA

263, 43 PCL: 11 2700 2600 0.11

PCL 260 52 3200 1600 0.20

20% blend

polyethylene

glycol with PLA

48 � 5700 10900 0.052

P is in units of cm3 (STP) cm/cm2 s Pa; S is in units of cm3 (STP) cm3 Pa; D is in

unit of cm2/s.


oriented structure. Nevertheless, the crystallinity of PLAshowed a lack of influence on the permeability to water vapor.Incorporation of caprolactone monomers have a moderateeffect on the diffusivity, but the blending of polyethylene gly-col (PEG) caused a dramatic drop in water vapor resistance.The hydrophilicity of PEG, as well as the disruption of struc-ture, are factors that caused this reduction in barrier propertieswhen combined with PLA.

4.5 Conclusion

The properties of PLA are significantly influenced by thestereochemistry of its monomers. When PLA has high stereo-chemical purity, it tends to form a highly crystalline structure.Copolymerization of different lactide isomers can yield a vari-ety characteristics of PLA. The effect of isomerization in PLAcan be detected by IR and NMR spectroscopic methods. Manystudies have proven that PLA has a low solubility in a widerange of solvents/liquids, such as water, alcohol and paraffin.This indicates that PLA can be safely employed as a food pack-aging material without causing adverse health effects. In addi-tion, PLA also possesses barrier properties that are just aseffective as LDPE and PS. The ‘green’ aspect of PLA meansthat it represents a viable environmentally friendly substitutefor petrochemical-based polymers.

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176 POLYLACTIC ACID

5 Mechanical Properties ofPoly(lactic Acid)

Chapter Outline5.1 Introduction 1775.2 Effect of Crystallinity and Molecular Weight on

Mechanical Properties of PLA 1795.3 Effect of Modifier/Plasticizer on PLA 1825.4 Polymer Blends of PLA 191

5.4.1 Poly(lactic Acid) and Polycaprolactone Blend 1925.4.2 Blends of Polylactide with Degradable or

Partially Degradable Polymers 1985.4.3 Blends of Polylactide and

Polyhydroxyalkanoates 2025.4.4 PLA Blends with Nondegradable Polymers 207


5.1 Introduction

The mechanical properties of commercial poly(lactic acid)(PLA) can be varied, ranging from soft, elastic materials tostiff, high-strength materials, according to different parameters,such as crystallinity, polymer structure, molecular weight,material formulation (blends, plasticizers, composites, etc.) andorientation.Table 5.1 summarizes some of the mechanical prop-erties of PLA developed by NatureWorks LLC.

PLA, also known as polylactide (i.e. polymerization of cycliclactic acid, also called lactide), originally is a brittle materialwith lower impact strength and elongation at break, similar toanother relatively brittle polymer�polystyrene (PS). However,its tensile strength and modulus are comparable to polyethyleneterephthalate (PET). This is shown in Table 5.2 as reported byAnderson et al (2008). Poor toughness limits its usage in



http://dx.doi.org/10.1016/B978-1-4377-4459-0.00005-6

Table 5.1 Mechanical Properties of PLA from NatureWorks LLC

Properties� Ingeo™

2003DASTMMethod

Ingeo™3801X ASTMMethod

Ingeo™

8052DASTMMethod

Tensile strength, MPa (psi) 53 (7700) D882 � � � �Yield strength, MPa (psi) 60 (8700) D882 25.9 (3750) D638 48 (7000) D638

Young’s modulus, GPa

(kpsi)

3.5 (500) D882 2.9 (432) D638 � D638

Elongation at break, % 6.0 D882 8.1 D638 2.5 D638

Notched Izod Impact, J/m

(Ib.ft/in)

12.81 (0.24) D256 144 (2.7) D256 16 (0.3) D256

Flexural strength, MPa (psi) � � 44 (6400) D790 83 (12,000) D790

Flexural modulus, GPa

(kpsi)

� � 2.85 (413) D790 3.8 (555) D790

�Ingeot 2003D is a transparent general-purpose extrusion grade, specifically designed for use in fresh food packaging and food

serviceware applications. Ingeot 3801X is designed for injection molding applications that require high-heat and high-impact

performance. Ingeot 8052D is a strong and lightweight foam, suitable for packaging fresh meat and vegetables.

applications that need plastic deformation at higher stresslevels. Several modification methods have been employed toimprove PLA’s mechanical properties, especially its toughness.

5.2 Effect of Crystallinity and MolecularWeight on Mechanical Properties of PLA

From the point of view of the structure�property relation-ship, crystallinity is an important characteristic affecting themechanical properties of PLA (see Figure 5.1). Perego et al.(1996) studied the effect of molecular weight and crystallinityon the mechanical properties of poly(L-lactide) (PLLA), poly(D,L-lactide) (PDLLA) and annealed poly(L-lactide) (ann.PLLA). They reported that PLLA and PDLLA at variousmolecular weights exhibited small changes in tensile strength

Table 5.2 Comparison of PLLA with Polystyrene andPolyethylene Terephthalate

Material TensileStrength(MPa)

Young’sModulus(GPa)

Elongationat Break(%)

NotchedIzod(J/m)

Poly (L-lactide

acid) PLLA

59 3.8 4�7 26

Polystyrene

(PS)

45 3.2 3 21

Polyethylene

terephthalate

(PET)

57 2.8�4.1 300 59

CH3

O

HO

O

OH

CH3

CH3

O

OO

n

Figure 5.1 Poly(lactic acid) structure.

1795: MECHANICAL PROPERTIES OF POLY(LACTIC ACID)

that varied from 55�59 MPa for PLLA and from 40�44 MPafor PDLLA. The results are set out in Tables 5.3 and 5.4.

However, PLLA showed a better strength compared toPDLLA, as shown by PLLA IV in Table 5.4, withMw5 67,000, which had a strength of 59 MPa, while PDLLAIII, with Mw5 114,000, had a strength of 44 MPa. This isthought to be due to the stereoregularity of the polymer chains.In other words, the presence of L and D stereoisomers in thePLA affect the crystallinity and structural chain arrangement,which leads to variation in physicomechanical properties.

Table 5.5 shows the effect of annealing on the mechanicalproperties of PLLA. There is a slight increment in tensilestrength from 47 to 66 MPa within the range of molecularweights of annealed PLLA. Evidently, the crystalline fractionof this material is influenced by the increment in molecularweight, which corresponds to crystallinity. On annealing,PLLA samples present the highest tensile modulus of elasticity,with values ranging from 4000 to 4200 MPa, as compared to

Table 5.3 Mechanical Properties of Poly(L-Lactide) Specimens

Sample PLLA I PLLA II PLA III PLA IV

Molecular weight, Mw

(g/mol)

23,000 31,000 58,000 67,000

Tensile Properties

Yield strength (MPa) � 65 68 70

Tensile strength (MPa) 59 55 58 59

Young’s modulus (MPa) 3550 3550 3750 3750

Elongation at break (%) 1.5 5.5 5 7

Flexural Properties

Flexural strength (MPa) 64 97 100 106

Modulus of elasticity

(MPa)

3650 3600 3600 3650

Maximum strain (%) 2 4.2 4.1 4.7

Impact Resistance

Notched strength (J/m) 19 22 25 26

Unnotched strength (J/m) 135 175 185 195

180 POLYLACTIC ACID

Table 5.4 Mechanical Properties of Nonannealing Poly(D,L-Lactide) Specimens

Sample PDLLA I PDLLA II PDLA III

Molecular weight, Mw (g/mol) 47,500 75,000 114,000

Tensile PropertiesYield strength (MPa) 49 53 53

Tensile strength (MPa) 40 44 44

Young’s modulus (MPa) 3650 4050 3900

Elongation at break (%) 7.5 4.8 5.4

Flexural PropertiesFlexural strength (MPa) 84 86 88

Modulus of elasticity (MPa) 3500 3550 3600

Maximum strain (%) 4.8 4.1 4.2

Impact ResistanceNotched strength (J/m) 18 17 18

Unnotched strength (J/m) 135 140 150

Table 5.5 Mechanical Properties of the Annealed Poly(L-Lactide) Specimens

Sample Ann.PLLA I

Ann.PLLA I

Ann.PLLA I

Ann.PLLA IV

Molecular weight,

Mw (g/mol)

20,000 33,500 47,000 71,000

Tensile PropertiesYield strength (MPa) � 63 68 70

Tensile strength (MPa) 47 54 59 66

Young’s modulus (MPa) 4100 4100 4050 4150

Elongation at break (%) 1.3 3.3 3.5 4.0

Flexural PropertiesFlexural strength (MPa) 51 83 113 119

Modulus of elasticity

(MPa)

4200 4000 4150 4150

Maximum strain (%) 1.6 2.3 4.8 4.6

Impact ResistanceNotched strength (J/m) 32 55 70 66

Unnotched strength (J/m) 180 360 340 350


3550�3750 MPa for the nonannealed PLLA samples. Similarresults can be observed for flexural strength, where theannealed PLLA samples have higher flexural strength thanthe nonannealed PLLA and PDLA samples. The trends of theresults of tensile and flexural strength suggest that these prop-erties increase with the degree of crystallization, particularlyabove Mn5 55,000 for the annealed PLLA samples. The impactresistance varies with the molecular weight of PLLA, and it ishigher for the annealed PLLA samples, mainly due to the rigidityeffects of the crystalline domains. However, PDLLA samplesshow no variation of impact strength with molecular weights, dueto their completely amorphous nature.

5.3 Effect of Modifier/Plasticizer on PLA

PLA is a glassy polymer that has poor elongation at break(,10%). Typical biodegradable as well as non-biodegradableplasticizers have been used to lower the glass transition temper-ature, increase ductility, and improve processability (Masciaand Xanthos, 1992). Such effects have been achieved bymanipulating the molecular weight, polarity, and end groups ofthe plasticizers being added to PLA.

Lactide is an effective monomer for plasticizing PLA.By adding 17.3 wt% of lactide to PLA the elongation at breakincreases to 288%. However, it has the disadvantage of fastmigration and losses, resulting in a stiffened polymer with asludgy surface (Sinclair, 1996). Thus, high-molecular-weightplasticizers, which are unlikely to migrate, remain the choiceof researchers. Table 5.6 summarizes the mechanical propertiesof reported plasticizers used in PLA.

Jacobsen and Fritz (1999) investigated the effects ofthree different types of plasticizers on polylactide, namelypoly(ethylene glycol) (PEG1500; Mw5 1500 g/mol), glucosemonoesters, and partial fatty acid esters, to compare their char-acteristics. They observed that, in general, the addition of alltypes of plasticizers led to a decrease in the modulus of elastic-ity. The addition of 2.5 wt% was able to lower the modulus by

182 POLYLACTIC ACID

Table 5.6 Summary of Reported Mechanical Properties for Plasticized PLA

Material Plasticizer Wt% Modulus ofElasticity(GPa)

TensileStrength(MPa)


ImpactCharpy(MJ/mm2)

Reference

PLA Lactide 1.3 2.0 51.7 3 � Sinclair

(1996)17.3 0.8 15.8 288 �25.5 0.23 16.8 546 �

PLA None � 3.7 58 3 32 (unnotched) Jacobsen

and Fritz

(1999)

PLA Polyethylene

glycol (PEG),

Mw5 1500 g/mol

10 1.2 28 .40 .80 (not

break)

PLA Glucose monoester 10 2.5 38 12.5 18

PLA Partial fatty acid ester 10 3.0 45 8 21

PLA None � 2.0 � 9 � Martin and

Averous

(2001)

PLA Polyethylene glycol (PEG400),

Mw5 400 g/mol

10 1.5 � 26 �20 0.98 � 160

PLA PEG monolaurate (M-PEG),

Mw5 400 g/mol

10 1.6 � 18 �20 1.1 � 142 �

PLA Oligomeric lactic acid (OLA) 10 1.2 � 32 �20 0.74 � 200 �

Table 5.6 Summary of Reported Mechanical Properties for Plasticized PLA—cont’d





Reference

PLLA None � 58 8 � Nijenhuis

et al. (1996)PLLA Polyethylene oxide (PEO) 10 54 11 �15 35 100

20 23 500 �PLA None � � 51.7 7 � Labrecque

et al. (1997)PLA Triethyl citrate 10 � 28.1 21.3 �20 � 12.6 382 �30 � 7.2 610 �

PLA Tributyl citrate 10 � 22.4 6.2 �20 � 7.1 350

PLA Acetyl triethyl citrate 10 � 34.5 10 �20 � 9.6 320 �

PLA Acetyl tributyl citrate 10 � 17.7 2.3 �20 � 9.2 420 �

PLLA None � 2.2 57 4.5 � Yoon et al.

(1999)PLLA Poly(ethylene-co-vinyl acetate)

EVA

10 1.8 46 4.7 �50 1.3 17 10.2

90 0.64 14 209 �

PLA None � 3.3 66 1.8 � Baiardo et al.

(2003)PLA Polyethylene glycol (PEG400),

Mw5 400 g/mol

5 2.5 41.6 1.6 �10 1.2 32.5 140 �12.5 0.5 18.7 115 �15 06 19.1 88

20 0.5 15.6 71 �PLA Polyethylene glycol (PEG1.5K),

Mw5 1500 g/mol

5 2.9 52.3 3.5 �10 2.8 46.6 5 �12.5 0.7 18.5 194 �15 0.8 23.6 216 �20 0.6 21.8 235 �

PLA Polyethylene glycol (PEG10,000),

Mw5 10,000 g/mol

5 2.8 53.9 2.4 �10 2.8 48.5 2.8 �15 2.5 42.3 3.5 �20 0.7 22.1 130 �

PLA Acetyl tri-n-butyl citrate (ATBC) 5 3.2 53.4 5.1 �10 2.9 50.1 7 �12.5 0.1 17.7 218 �15 0.1 21.3 299 �20 0.1 23.1 298 �

Table 5.6 Summary of Reported Mechanical Properties for Plasticized PLA—cont’d





Reference

PLA None � 2.8 64 3.0 � Pillin et al.

(2006)PLA Polyethylene glycol (PEG200),

Mw5 200 g/mol

10 1.7 30 2.0 �20 � � � �30 � � � �


Mw5 400 g/mol

10 1.9 39 2.4 �20 0.63 16 21.2 �30 � � � �


Mw5 1000 g/mol

10 1.9 39.6 2.7 �20 0.29 21.6 200 �30 0.42 4.7 1.5 �

PLA Poly (1,3-butanediol) (PBOH),

Mw5 210 g/mol

10 2.35 6.3 3.0 �20 0.35 30.2 302.5

30 0.30 25.2 390 �PLA Dibutyl sebacate (DBS),

Mw5 314 g/mol

10 2.2 52.1 32 �20 0.03 27.1 335 �30 0.11 17.9 320 �

PLA Acetyl glycerol monolaurate

(AGM), Mw5 358 g/mol

10 2.0 39.2 2.3 �20 0.43 23.1 269 �30 0.37 18.3 333 �

PLA none � � 25.5 64 � Kulinski et al.

(2006)PLA Polypropylene glycol (PPG);

Mw5 425 g/mol

5.0 � 20.7 19 �7.5 � 17.7 107 �10.0 � 21.0 524 �12.5 � 21.0 702 �

PLA Polypropylene glycol (PPG),

Mw5 1000 g/mol

5.0 � 22.2 44 �7.5 � 22.6 329 �10.0 � 22.8 473 �12.5 � 21.6 496 �

PLA Polyethylene glycol (PEG),

Mw5 600 g/mol

5.0 � 19.3 67 �7.5 � 17.5 360 �10.0 � 18.5 427 �12.5 � 19.7 622 �

10�15%. When larger amounts of plasticizer were added (5 wt%and 10 wt%), the reduction in modulus became more pro-nounced. Similar results were observed for tensile strength,which progressively decreased with an increasing amount ofpoly(ethylene glycol) as well as glucose monoester, and therewas a linear or slight decrease with a larger partial fatty acidester content.

For the elongation at break, an increasing amount of the par-tial fatty acid ester led to lower values. This is because thefinely dispersed partial fatty acid ester acts as an activation cellfor crack formation. However, the remaining two plasticizertypes showed an opposing effect to the partial fatty acid ester,whereby the elongation at break increased in relation to theamount of plasticizer. The best plasticizer from the elongationpoint-of-view is poly(ethylene glycol), which can achieve animprovement in elongation at break of up to 180% when addedto PLA at 10 wt%.

The addition of glucose monoester or partial fatty acid esterwas unable to induce an improvement in the impact resistanceof polylactide at any concentration. In fact, they resulted in adecrease in impact strength, which was due to the disturbancecreated by the plasticizer particles in the PLA matrix restrictingthe sliding of chains to absorb shock energy. This effect is alsoobservable for low levels of poly(ethylene glycol) in PLA.Small amounts of poly(ethylene glycol) led to a decrease inimpact resistance, but with a 10 wt% concentration, the plasti-cizing effect became dominant�the impact resistance increasedso much that no break was observed.

Some authors have reported improved properties using poly-meric plasticizers. Nijenhuis et al. (1996) found elongationat break to be improved by adding high-molecular-weight poly-(ethylene oxide) (PEO) to PLLA. The effect was mostpronounced at PEO concentrations exceeding 10 wt%. Forexample, at 20 wt% of PEO the elongation at break could reachup to 500%. However, as expected, the tensile strength wasreduced, from 58 MPa for the pure PLLA to 24 MPa with 20wt% PEO. Citrate esters derived from naturally occurring citricacid were investigated as plasticizers for PLA by Labrecque

188 POLYLACTIC ACID

et al. (1997). The addition of all plasticizers decreased the ten-sile strength of PLA significantly (by B50%), even at 10 wt%concentrations, and the deterioration was larger with higherconcentrations. However, elongation at break did not show anysignificant change at the lower concentrations (,10 wt%),although it was dramatically increased at higher concentrations(.20 wt%) in all cases. The highest elongation value of 610%was observed at 30 wt% triethyl citrate, but this was accompa-nied with considerable loss of tensile strength.

Yoon et al. (1999) investigated the effect of poly(ethylene-co-vinyl acetate) (EVA) as a plasticizer in PLLA. They foundthat the elongation at break for the blend of PLLA/EVAslightly increased up to 70 wt% of EVA. However, a signifi-cant improvement in elongation at break occurred for the blendcontaining 90 wt% of EVA (209%). However, the tensilestrength and modulus of the PLLA�EVA blend dropped rap-idly, followed by a more gradual decrease, with increasingEVA content. Martin and Averous (2001) used poly(ethyleneglycol) (PEG), polyethylene glycol monolaurate, and oligo-meric lactic acid to plasticize PLA. They found that the addi-tion of these plasticizers decreased the modulus, which rangedfrom 28% to 65% according to the type and concentration ofplasticizer used. The greater reductions in modulus�of 53%and 65% were obtained at 20% of added PEG (Mw5 400 g/mol)and oligomeric lactic acid, respectively. At the same time, theelongation at break increased with higher concentrationsof plasticizer. An elongation at break as high as 200% wasobtained, indicating that the properties of PLA can be changedeasily from rigid to ductile. Baiardo et al. (2003) used acetyltri-n-butyl citrate and PEGs with different molecular weights(Mw ranging between 400�10,000 g/mol) to plasticize PLA.These researchers also observed a significant increase in elon-gation at break at the expense of strength and tensile modulus.Inspection of the elongation at break values indicated that atwo-fold change of elongation occurred with a plasticizer con-tent of 5%, but also depended on the type of plasticizeremployed. When PEG at Mw5 10,000 g/mol was used, itrequired 20 wt% to induce a large increase in elongation at


break, whereas the same change was attained by a 10 wt% con-centration of low-molecular-weight PEG (Mw5 400 g/mol).

Multiple plasticizers�low-molecular-weight triacetin (TAC)and oligomeric poly(1,3-butylene glycol adipate) (PBGA)�have also been employed to plasticize PLA, as reported by Renet al. (2006). They found that this achieved a significantimprovement in the elastic properties, but at the cost of tensilestrength. The elongation at break leveled off at plasticizer con-tent ranging from 0 to 5%, but increased dramatically at5�9%. This indicates that the blends were brittle at less than5% plasticizer content, and were ductile when the plasticizercontent was greater than 9%.

The effects of different molecular weight of polyethyl-ene glycol (PEG) (Mw ranging between 200�1000 g/mol),poly(1,3-butanediol) (PBOH), dibutyl sebacate (DBS) andacetyl glycerol monolaurate (AGM) as plasticizers in PLAwere studied by Pillin et al. (2006). The Young’s moduluswas found to decrease drastically for plasticizer contenthigher than 20 wt%. The PEGs provided lower Young’smodulus than the other plasticizers. Nevertheless, PEG atMw5 200 g/mol when blended to PLA at a content of10 wt%, or 20 wt% for PEG at Mw5 400 g/mol, and 30 wt% for PEG at Mw5 1000 g/mol�showed that there was nodeterioration in the physicomechanical properties of PLA. Athigher plasticizer content, the material becomes brittlebecause of a lack of cohesion between the separate phases.The efficiency of the plasticizer is, therefore, related to themolecular level miscibility, which is higher for PEG than forother molecules. The elongation at break increases withgreater plasticizer content, but the optimum is reached at20 wt% for PEG, whereas the optimum point for other plasti-cizers can be .20 wt%. In other words, the cohesion ofPLA blends is higher for the plasticizers PBOH, AGM andDBS than for PEG. At 20 wt%, the most efficient plasticizeris AGM, which reduces the elastic modulus values from2840 to 35 MPa. Moreover, the elongation at break is thehighest with AGM added at 10 to 20 wt%. PBOH and DBSdid yield better mechanical properties than the PEGs and the

190 POLYLACTIC ACID

obtained materials were not brittle. When a larger amount ofplasticizer (PBOH, AGM and DBS) is blended with PLA(B30 wt%), tensile modulus or elongation at break isstable in comparison to 20 wt%, when the tensile strengthis slightly reduced. In light of these results, the most effi-cient plasticized formulations are AGM, PBOH and DBS at20 to 30% according to the mechanical requirements.

Comparisons between PEG and polypropylene glycol (PPG) asa plasticizer for PLA were investigated by Kulinski et al. (2006).The advantage of using PPG is that it does not crystallize, has a lowglass transition temperature and is miscible with PLA. PLA wasplasticized with PPGs with a nominal Mw of 425 and 1000 g/mol.Pure PLA showed a tensile strength and average elongationat break of 26 MPa and 64%, respectively. The elongation atbreak of all blends exceeded that of pure PLA, beginning witha plasticizer content of 7.5 wt% and it reached a peak of500�700% for plasticizer content of 12.5 wt%. The effect wasenhanced by the higher PPG content and also by a reduction inmolecular weight of PPG. However, the deformation reflects thestrength of the blends, which is generally lower than that of purePLA, in the range of 17.5�22.8 MPa. As shown in Table 5.6,lower molecular weight of polypropylene glycol (PPG) at12.5 wt% shows the greatest promise as a plasticizing agent forpolylactide, as it gives the largest increase in elongation at breakwith the smallest decrease in tensile strength.

5.4 Polymer Blends of PLA

Polymer blending is an alternative approach to obtain newmaterials with desirable properties, and is based on commer-cially available polymers rather the design and synthesis ofcompletely new polymers. Since the 1980s, there has been arapid growth in the development of commercial polymerblends, and research in this field has continued to be intense.Blending different polymers and yet conserving their individualproperties in the final mixture is an extremely attractive andinexpensive way of obtaining new materials. When preparingthe blends, which generally involve using twin-screw extruders,


many factors must be considered in order to obtain a blend withuseful properties. The barrel temperature must be set above theglass transition temperature of the amorphous polymer compo-nents and above the melting point of the semicrystalline polymercomponents in order to manage the viscosity for obtaining opti-mum dispersion. For PLA blends, the lower limit should beabout 180�C. Polymers that require very high processing tem-peratures (.270�C) can result in thermal degradation of PLAand, thus, are not favorable candidates for PLA blends.

The desired beneficial effects induced by polymer blendingdo not always come without some negative consequences.A few issues arise when dealing with miscible blends; the mostobvious is to obtain good interfacial adhesion among the blend-ing phases, which can directly affect the morphology and, con-sequently, the physical and mechanical properties. If the addedpolymer is not very compatible with PLA, plenty of subsequentdevelopment work is necessary to improve compatibility. Poorinterfacial adhesion results in embrittlement, and the morphol-ogy of the phases can be changed extensively, depending onthe processing conditions as well as the design of the partsbeing produced. Some polymers are not biodegradable andblending them with PLA can affect its compostability. In gen-eral, PLA blends can be divided into two groups: blends withdegradable polymers and blends with non-degradable polymers.However, research work focusses on blending PLA withdegradable or renewable resource polymers, in order to main-tain the biodegradability of PLA.

5.4.1 Poly(lactic Acid) and Polycaprolactone Blend

The blend of PLA with polycaprolactone (PCL) has beenstudied extensively by many researchers. This is becausePCL exhibits rubbery characteristics with an elongation atbreak of approximately 600% (Wang et al., 1998), thus, actingas a good candidate for toughening PLA. In addition, PCL is adegradable polyester, meaning that blending with PLA canresult a totally degradable material.

192 POLYLACTIC ACID

Unfortunately, many researchers have found that blends ofPLA and PCL generally result in an improvement in elongationat break, but with a reduction of tensile strength and modulus.For instance, Hiljanen-Vainio et al. (1996) reported that modifi-cation of PLLA with 20 wt% of PCL somewhat decreased thetensile modulus, tensile strength and shear strength, but slightlyincreased the elongation at break (9.6% versus 1.6% for purePLLA). In contrast, the blending of the elastic poly(ε-caprolac-tone/L-lactide) (PCL/L-LA) copolymer with PLLA significantlyincreased the elongation at break (.100%) compared to bothpure PLLA and the binary blend. They also showed that PLAblends containing 5, 10, and 20 wt% of PCL/L-LA copolymerexhibited yield deformation. Moreover, when the amount reached30 wt% of PCL/L-LA copolymer, the blend exhibited tough rub-ber-like behavior. The initial impact strength of PLLA was verypoor, and a quadruple improvement in impact strength wasachieved with the addition of 20 wt% of PCL/L-LA copolymer.

Tsuji and Ikada (1996) investigated tensile data for PLA/PCL blend films prepared with a solution casting method usingmethylene chloride as a solvent. Although the elongation atbreak increased for the blend with 15 wt% PCL, the calculatedstandard deviation obtained was quite high (2506 200%).Wang et al. (1998) showed that the elongation at break forreactive blends of PLA/PCL using triphenyl phosphite as a cat-alyst improved significantly when compared to pure PLA atcertain compositions (PLA/PCL5 80/20 or 20/80). Theseresults indicate that reactive blending is a promising method toimprove the elongation and toughness of PLA. The elongationincreased to 127% compared to 28% for the nonreactive binaryblend. Meanwhile, Maglio et al. (1999) also found an improve-ment in the elongation at break (53% versus 2%) and thenotched Charpy impact strength (3.7 kJ/m2 versus 1.1 kJ/m2)when a PLLA�PCL�PLLA triblock copolymer was used as acompatibilizer in PLLA/PCL 70/30 wt% blends.

Broz et al. (2003) investigated the binary blends of PLA andPCL by dissolution in methylene chloride with a total polymermass fraction of 10%. They found that the elongation at breakonly increased significantly for .60 wt% PCL content, and


this could not be justified as it was accompanied by a signifi-cant loss in modulus and tensile strength. However, Tsuji et al.(2003) observed some improvements in mechanical propertieswhen a PLLA�PCL diblock copolymer was added to theirbinary PLLA/PCL blends. The addition of the copolymerimproved the tensile strength of the blends at XPLLA of0.5�0.8 and the Young’s modulus at XPLLA 0.5�0.8, whileimproving the elongation at break for all of the XPLLA values(XPLLA5weight of PLLA/(weight of PLLA and PCL)).These findings strongly suggest that PLLA�CL was misciblewith PLLA and PCL, and that the dissolved PLLA�CL inPLLA-rich and PCL-rich phases increased the compatibilitybetween both phases.

Another type of reactive blending was reported by Sembaet al. (2006) for PLA/PCL blends through the application ofdicumyl peroxide (DCP) as a crosslinker. Dicumyl peroxide(DCP) was added to this system to improve elongation at breakof the blends. The optimum blend ratio of the PLA/PCL blendwas found to be 70/30. It was observed that the value of elonga-tion at break peaked at low DCP concentrations (B0.2phr).Under tensile testing the samples showed yield point and ductilebehavior at low DCP content. The impact strength of the opti-mum composition was 2.5 times superior to neat PLA with duc-tile behavior, indicating that plastic deformation was observedat its fracture surface. This is an interesting application of a rad-ical-based crosslinking being applied to PLA blends.

Yuan et al. (1998) synthesized semi-interpenetrating polyure-thane/PLA networks. The polyurethane was prepared usingPCL diols and triols and toluene-2,4-diisocyanate. The opti-mum was found to be 5 wt% of crosslinked polyurethane net-work blended with PLA. The elongation at break increased to60% and the tensile toughness increased to 18 MJ/m3 comparedto 1.6 MJm3 for neat PLA.Grijpma et al. (1994) studied blends of PLA and a rubbery

copolymer of caprolactone (CL) and trimethylene carbonate(TMC) (poly(TMC/CL)). They reported an increase in thenotched Izod impact strength of neat PLA with the addition of20 wt% copolymer (from 40 J/m to a maximum of 520 J/m).

194 POLYLACTIC ACID

However, for homopolymer poly(TMC) and PLA blends, thecorresponding wt% of rubber phase did not improve the notchedIzod impact strength. Joziasse et al. (1998) have investigatedblends of PLA homopolymer with poly(trimethylene carbonate)(poly(TMC)) rubbery copolymers. They found that the sampleswith 21 wt% of the rubber block of poly(TMC) in PLA didnot break in an unnotched impact test. Diblock copolymersof L-lactide and caprolactone (P(LA/CL)) were also blendedwith PLA to determine their influence on the mechanicalproperties. The addition of 20 wt% of diblock copolymerimproved the unnotched impact strength of the blend from5 kJ/m2 to 50 kJ/m2.

Hasook and coworkers (2006) reported the mechanical prop-erties for PLA/PCL and an organoclay nanocomposite. It wasfound that the Young’s modulus increased with the addition oforganoclay to the PLA matrix, but decreased the strength andelongation at break. Originally, the Young’s modulus decreasedwith the addition of PCL to the PLA matrix. However, the ten-sile strengths and elongation at break of PLA/organoclay nano-composites increased with the addition of PCL. When usingPCL (Mw5 40,000 g/mol) the tensile strength was the greatestof all the PLA/clay nanocomposite blends.

Chen et al. (2003) observed that the addition of a low quantityof surfactant (i.e. copolymer of ethylene oxide and propyleneoxide) could improve the elongation at break, but other mechani-cal properties, such as tensile strength and modulus, were simul-taneously weakened. Moreover, the addition of a small amountof PLA�PCL�PLA triblock copolymer (B4 wt%) to PLA/PCL(70:30) blends improved the dispersion of PCL in PLA andenhanced the ductility of the resultant ternary blend. The elonga-tion at break increased from 2% for a PLA/PCL (70:30) blend to53% for the ternary blend (Maglio et al.,1999). This has beenproven to have been caused by the dispersion of PCL domains,which decreased from 10�15 to 3�4 μm on addition of thetriblock copolymer (4 wt%) as calculated from scanning electronmicroscope (SEM) micrographs of liquid-nitrogen-fractured sur-faces of the blend. The mechanical properties for the PLA blendswith PCL for the above studies are summarized in Table 5.7.


Table 5.7 Summary of Reported Mechanical Properties for Blends of Poly(lactic Acid) (PLA) withPolycaprolactone (PCL)

Material Blend Components Tensile

Strength (MPa)

Young’s

Modulus

(GPa)

Elongation

at Break

(%)

Impact Strength Reference

2nd Component Wt% 3rd Component Wt% Charpy

kJ/m2

Izod J/

m

PLA None � � 48 2.3 3 � � Wang et al., 1998

PLA PCL 20 � 44 0.6 28 � �PLA PCL 20 Catalyst: triphenyl phosphite, (TPP) 2 33 1.0 127 � �PLLA None � 60 1.3 5 � � Tsuji et al. (2003)

PLLA PCL 20 � 30 1.1 175 � �PLLA PCL 20 Copolymer: poly(L-lactide-co-

ε-caprolactone) (PLLA-CL)10 40 1.1 300 � �

PLA None � � � 70 1.5 10 � � Semba et al. (2006)

PLA PCL 30 � 55 1.3 20 � �PLA PCL 30 Dicumyl peroxide 0.2phr 50 1.2 160 � �PLLA None � � � 45 3.7 2.1 Hasook et al (2006)

PLLA PCL 5 � � 52 3.4 2.9 � �PLLA PCL 4.8 Organoclay 4.8 54 4.1 3.2 � �PLLA none � � � 35 3.1 3 1.8 � HiIjanen-Vainio

et al. (1996)

PLLA PCL 20 � � 31 2.1 10 � �PLLA PCL 16 Copolymer: poly(ε-caprolactone/L-

lactide) P(CL/LLA)

20 11 0.66 .100 10 �

PLLA PCL 30 � � 1.4 2 1.1 � Maglio et al.

(1999)

PLLA PCL 30 PLLA�PCL�PLLA triblock

copolymer

4 � 1.4 53 3.7 �

PLA None � � � 56.8 � � � 40 Grijpma et al.

(1994)

PLA Copolymer of

trimethylene

carbonate and

caprolactone�poly(TMC/CL)

20 � � 36.0 � � � 293-520

PLLA None � � � 34 0.020 56 � � Chen et al. (2003)

PLLA PCL 20 � 41 0.021 129 � �PLLA PCL 20 Surfactant: copolymer of

ethylene oxide and

propylene oxide

2 20 0.010 129 � �

5.4.2 Blends of Polylactide with Degradableor Partially Degradable Polymers

In addition to PCL, blends with other biodegradable/renew-able-resource-based polymers have been explored. For instance,Pezzin et al. (2003) prepared blends of PLA with poly(para-dioxanone) (PPD), also a biodegradable polyester. They foundthat by adding only 20 wt% of PPD to the PLLA phase, theblend presented higher values of Young’s modulus (1.6 GPa)and elongation at break (55%) than pure PLLA and PPD, butthe tensile strength was lower than pure PLLA. These blendswere more flexible, tough and showed neck formation duringelongation, which could be due to the plasticizing effect ofPPD. However, the mechanical properties of the other blends atcompositions of 50/50 and 80/20 (PLLA/PPD) were notimproved, as compared to pure PLLA.

Ma et al. (2006) prepared blends of PLA and poly(propylenecarbonate) (PPC), a degradable, amorphous material of ali-phatic polycarbonate at different compositions. For all types ofblend, the tensile strength and modulus decreased with increas-ing PPC content. However, the tensile toughness was improvedwith increasing amounts of PPC over pure PLA. The increasein toughness was very obvious above 40 wt% PPC. This isbecause PLA is a continuous matrix phase when blendedat ,30 wt% PPC, whereas PPC is the continuous phase at highPPC concentrations (.40 wt%). The continuous PPC phasefavors the matrix yielding, which requires more energy to breakthe materials.

Blends of PLLA with poly(tetramethylene adipate-co-tere-phthalate) (PTAT), another type of biodegradable polyester,have been prepared by solution casting from chloroform, andthe resultant mechanical properties were reported by Liu et al(2005). PLLA/PTAT blends showed interesting, nonlinear ten-sile behavior over the three compositions (75/25, 50/50 and25/75 wt% PLLA/PTAT) when investigated. The 75/25 wt%PLLA/PTAT blend had a tensile strength of 25 MPa and anelongation at break of 97%, compared to 28 MPa and 19%,respectively, for pure PLLA. However, for the 50/50 wt%

198 POLYLACTIC ACID

PLLA/PTAT blend the tensile strength and elongation at breakreduced to 7 MPa and 34%, respectively. This could be due topoor miscibility and higher phase separation in the blend.Furthermore, the 75/25 wt% PLLA/PTAT blend showed a ten-sile strength slightly better than 50% PTAT (11 MPa), althoughthe elongation at break was about fifteen times higher than thatof pure PLLA (285%). These results suggest that PLLA is hardand brittle, whereas PTAT possesses more ductility.

Jiang et al. (2006) investigated the melt blending of PLAwith poly(butylene adipate-co-terephthalate) (PBAT). PBAT isa flexible, biodegradable, aliphatic-aromatic polyester, with anelongation at break of 700%. Incorporation of PBAT content(5�20 wt%) to PLA decreased the tensile strength and modulusof the blends. Tensile strength decreased from 63 MPa for thepure PLA to 47 MPa with the addition of 20% PBAT content.A slight reduction in modulus was also observed at 20% PBATcontent (2.6 GPa) as compared to pure PLA (3.4 GPa). Theseresults are expected, because PBAT has a lower modulus andtensile strength than PLA. With the increase in PBAT contentfrom 5 to 20 wt%, the Izod impact strength improved, with thehighest toughening seen at 20 wt% PBAT loading. The elonga-tion at break was also tremendously increased with higherPBAT content; this was noticed even at 5 wt% PBAT, wherethe elongation at break reached more than 200%. With theincrease in PBAT content, the mode of failure changed frombrittle fracture for the pure PLA to ductile fracture of the blend.This has been proven by SEM micrographs of the impact-frac-tured surfaces, which show more and longer fibrils from thesurfaces with increasing PBAT content. SEM micrographs alsorevealed that a debonding-initiated shear-yielding mechanismwas involved in the toughening of the blend.

Blends of PLA with various amount of poly(ethylene/butyl-ene succinate) (Bionolles) using single-screw extruder havebeen reported by Liu et al. (1997). Bionolle is also a biodegrad-able aliphatic thermoplastic polyester. The elongation at breakfor the blend at various ratios of Bionolle was slightly higherthan for pure PLA. The highest elongation at break for theblends was 8.2% with 40 wt% Bionolle. However, the tensile


strength and modulus of the blends decreases with increasingamount of Bionolle. This is expected as the tensile strength andmodulus of Bionolle are lower than that of PLA.

The effects of blending poly(butylene succinate) (PBS) andpoly(butylene succinate co-L-lactate) (PBSL) with PLLA wasreported by Shibata et al. (2006). PBSL is a new type of PBS-based biodegradable polyester. Blending PLLA with PBS orPBSL was done by melt-mixing and subsequent injectionmolding. The tensile strength and modulus of the blends gener-ally decreased with higher amounts of PBSL or PBS, exceptfor the blend of PLLA with 1 and 5 wt% of PBS, where thevalues were higher than for neat PLLA. The authors suggestedthat this result could be attributed to the formation of finelydispersed blends in the system, as proven by field emissionscanning electron microscopy (FESEM) micrographs. All theblends showed considerably higher elongation at break over thewhole composition range compared with pure PLLA, PBSL,and PBS. As a whole, the PLLA/PBSL blends showed higherelongation at break but lower tensile strength and moduluscompared to the PLLA/PBS blends at similar percentages.

Chen and Yoon (2005) compared the effect of addinguntreated and treated organoclay, Cloisite 25A, on the mechan-ical properties of PLLA/poly(butylene succinate-co-butyleneadipate) (PBSA) composite. In this study the compositionof PLLA/PBSA was fixed at 75/25 on a weight basis becausebrittleness of PLLA was greatly ameliorated at this blendcomposition. The treated organoclay was prepared by reacting(glycidoxypropyl)trimethoxy silane (GPS) with Cloisite 25A toproduce functionalized organoclay (TFC). Nanocomposites ofPLLA/PBSA/clay were prepared by melt compounding ofPLLA and PBSA with the organoclays at 180�C. The research-ers found that the tensile modulus of the PLLA/PBSA compo-sites with C25A and TFC was higher than the binary blend ofPLLA/PBSA throughout the whole range of clay compositions.This is expected, as the clay acts as reinforcement in the com-posite. However, the elongation at break of the composite, bothwith organoclay C25A and TFC, was much lower than theblend of PLLA/PBSA. Nevertheless, the elongation at break

200 POLYLACTIC ACID

and modulus for the composite containing treated clay, TFC,was higher than the untreated clay, C25. For example, the elon-gation at break of PLLA/PBSA/C25A having 10 wt% of C25Awas 5.2%, while that of PLLA/PBSA/TFC containing the sameamount of TFC was 46%. The higher tensile modulus and elon-gation at break of PLLA/PBSA/TFC compared to those para-meters of PLLA/PBSA/C25 composite are attributed to thereduction in agglomeration observed in the former compositethan in the latter. This, consequently, contributes to a higherdegree of exfoliation and improved interaction between theepoxy group of TFC and the functional groups of PLLA/PBSA.

Similar work on blending different amounts of untreated andtreated clay with PLLA composite has also been reported byChen et al. (2005). Instead of merely blending PLLA withPBSA, as reported by Chen and Yoon (2005), Chen et al.(2005) blended PLLA and poly(butylene succinate) (PBS) withorganoclay to improve the mechanical properties of the blends.Again, the weight ratio of PLLA/PBS was fixed at 75/25, andthe same untreated organoclay, Cloisite 25A, and treated orga-noclay, TFC, was used. The tensile modulus of the PLLA/PBScomposite incorporating different amount of Cloisite 25A andTFC was higher than for the PLLA/PBS blend. For example,the modulus of the composite at 10 wt% Cloisite 25A organo-clay was 1.94 GPa whilst the blend without organoclay, was1.08 GPa. This demonstrates that the untreated and treatedclays act as a reinforcing filler on account of their high aspectratio and platelet structure. As compared to PLLA/PBS rein-forced with untreated Cloisite 25A, the tensile modulus of thePLLA/PBS with treated Cloisite 25A (i.e. TFC) shows a pro-nounced effect with increasing clay content. The modulus ofthe PLLA/PBS blend with 10 wt% of TFC was 1.99 GPa.

However, the elongation at break of the PLLA/PBS compos-ite decreased sharply as a result of adding untreated Cloisite25A. In contrast, the elongation at break of the PLLA/PBScomposite increased with TFC content, although in manycases compounding with clay reduced the elongation at break.The authors observed that the composite blends containing thetreated clay, TFC, showed an increase in necking and the


formation of a prominent fibrillar fracture surface, whereas theblends containing untreated C25A exhibited brittle fracturewithout necking. This shows that the chemical bonds betweenthe epoxy functional groups of TFC and the two polymers ofPLLA/PBS act as a compatibilizer, which, in turn, increasesinterfacial interaction. A summary of the above studies is givenin Table 5.8

5.4.3 Blends of Polylactide andPolyhydroxyalkanoates

Polyhydroxyalkanoates (PHAs) are biodegradable linearpolyesters produced in nature by a wide range of commonmicroorganisms. They are produced by bacteria to store carbonand energy. More than 150 different monomers can be com-bined with this family to produce materials with extremelydifferent properties. The best-known types of PHAs includepoly-(3-hydroxybutyrate) (PHB) homopolymer, 3-hydroxybuty-rate and 3-hydroxyvalerate (PHBV) copolymer and poly(3-hydroxybutyrate)-co-(3-hydroxyalkanote) copolymer. SincePHAs are made from natural resources, blends of PHA/PLAare likely to be totally biodegradable. A number of research-ers have reported the mechanical properties of PHA/PLAblends. Iannace and coworkers (1994) reported on a blend ofPLLA with poly(3-hydroxybutyrate-co-3 hydroxyvalerate)(PHBV) prepared by solution casting of chloroform at roomtemperature. A slight increase in the elongation at break wasobserved for the blends containing 20 and 40 wt% PHBV.However, the tensile strength and modulus of the blends werefound to decrease with higher amounts of PHBV. This wasconfirmed by the reduction in crystallinity of the PLLA phasewith increasing amounts of PHBV.

In a similar study conducted by Ferreira et al. (2002), thetensile strength of blends of PLLA with different amounts ofPHBV were lower than those achieved by Iannace et al.(1994). This was because the PLLA film obtained in this studywas porous, unlike that of Iannace et al. (1994), who obtainedonly dense films. However, the study by Ferreira et al. (2002)

202 POLYLACTIC ACID

Table 5.8 Summary of Reported Mechanical Properties for Blends of Polylactide with Degradable orPartially Degradable Polymers


Strength

(MPa)

Young’s

Modulus

(GPa)

Elongation at

Break (%)


2nd Component Wt% 3rd Component Wt% J/

cm2

Notched

Izod (kJ/m2)

PLLA None � � � 30 1.4 15 � � Pezzin et al.

(2002)

PLLA Poly(para-dioxanone) PPD 20 � � 20 1.6 55 � �PLA None � � � 59 3.2 � 2 � Ma et al. (2006)

PLA Poly(propylene carbonate)

(PPC)

15 � � 45 2.4 � 5 �

30 � � 42 2.1 � 13 �PLLA None � � � 28 � 19 � � Liu et al (2005)

PLLA Poly(tetramethylene adipate-co-

terephthalate) (PTAT)

25 � � 25 � 97 � �

50 � � 7 � 34 � �75 � � 11 � 285 � �

PLA None � � � 63 3.4 � � 2.6 Jiang et al.

(2006)

PLA Poly(butylene adipate-co-

terephthalate) (PBAT)

5 � � 58 3.0 � � 2.7

10 � � 54 2.9 � � 3.0

15 � � 51 2.8 � � 3.6

20 � � 47 2.6 � � 4.4

PLA None � � � 36 2.5 2 � � Liu et al. (1997)

PLA Poly(ethylene/butylene

succinate) (Bionolle)

20 � � 26 1.8 2.2 � �

40 � � 22 1.4 8.2 � �PLLA None � � � 63 3.0 3 � � Shibata et al.

(2006)

PLLA Poly(butylene succinate) (PBS) 10 � � 60 2.7 120 � �PLLA Poly(butylene succinate co-

L-lactate) (PBSL)

10 � � 55 2.5 160 � �

Table 5.8 Summary of Reported Mechanical Properties for Blends of Polylactide with Degradable orPartially Degradable Polymers—cont’d


Strength

(MPa)

Young’s

Modulus

(GPa)

Elongation at

Break (%)


2nd Component Wt% 3rd Component Wt% J/

cm2

Notched

Izod (kJ/m2)

PLLA Poly(butylene succinate-co-

butylene adipate) (PBSA)

� � � � 1.16 154 � � Chen and Yoon

(2004)

PLLA PBSA 25 Untreated Cloisite

25A organoclay

2 � 1.39 11.3 � �

5 � 1.58 10.6 � �10 � 1.75 5.2 � �

PLLA PBS 25 Treated Cloisite

25A (TFC)

2 � 1.44 69 � �

5 � 1.70 43 � �10 � 1.78 46 � �

PLLA None � � � 2.21 6.9 � � Chen et al.

(2005)

PLLA Poly(butylene succinate) (PBS) 25 � � 1.08 72 � �PLLA PBS 25 Untreated Cloisite

25A organoclay

2 � 1.36 4.4 � �

5 � 1.62 4.1 � �10 � 1.94 3.6 � �

PLLA PBS 25 Treated Cloisite

25A (TFC)

2 � 1.41 76 � �

5 � 1.62 100 � �10 � 1.99 118 � �

verified the trend of the Young’s modulus values seen for thePLLA/PHBV blends by Iannace et al. (1994).

PHB is the simplest and most common PHA. Yoon et al.(2000) have studied the effect of different types andamounts of compatibilizer on the mechanical properties of PLLA/PHB blends. PLLA and PHB (50/50 wt%) were blended inchloroform (3 wt%) and films of the PLLA/PHB blend werethen recovered by evaporating the solvent followed by dryingin a vacuum at 40�C. The compatibilizers used werePLLA�PEG�PLLA triblock copolymer, PEG�PLLA diblockcopolymer and poly(vinyl acetate) at 2 and 5 wt%. For all ofthe blends with a compatibilizer, the elongation at break and thetensile toughness for both compositions (2 and 5 wt%) wereimproved relative to the PLLA/PHB blend without compatibili-zer. However, the tensile modulus for all the blends at differentamounts of compatibilizer decreased as compared to theuncompatibilized PLLA/PHB blend. The tensile strengthresults somewhat varied with the type and composition ofthe compatibilizers. The blend prepared with 2 wt%PLLA�PEG�PLLA triblock copolymer showed the highesttensile strength (69.8 MPa), followed by 2 wt% PEG�PLLAdiblock copolymer (65.5 MPa), while the blends with 5 wt% ofdiblock and triblock copolymers and the polyvinyl acetate ascompatibilizers decreased the tensile strength compared to theuncompatibilized PLLA/PHB blend. From the view point oftensile strength, elongation at break and toughness, the blendof PLLA/PHB with 2 wt% of PLLA�PEG�PLLA triblockcopolymer was the best choice of formulation, as the mechanicalproperties were higher than those of the uncompatibilized PLLA/PHB blend, although the Young’s modulus was slightly lower.

Takagi et al. (2004) prepared blends of PLA and a biode-gradable thermoplastic known as poly(3-hydroxyalkanoate)(PHA) at different compositions. Together with PHA, PLA wasalso blended with functionalized PHA (ePHA), which con-tained 30% epoxy group in its side chains. They found that theCharpy impact strength for both blends of PLA increased withthe composition of PHA or ePHA. These results were higherthan for pure PLA. However, the tensile strength for both


blends of PLA/PHA and PLA/ePHA were lower than the purePLA at all compositions. When compared to both blends, theCharpy impact strength and the tensile strength were higherfor the PLA/ePHA blends relative to the PLA/PHA blends.This is because the ePHA, with its inserted epoxy side group,improved the compatibility of the blend.

Blends of PLA with biodegradable PHA were prepared byNoda et al (2004), using melt mixing in a single-screw extruder.The PHA used was a copolymer of poly(3-hydroxybutyrate)-co-(3-hydroxyalkanote), with the brand name Nodaxt, devel-oped by Procter and Gamble. The authors found that the additionof 10 wt% Nodaxt dramatically improved the toughness of theblend. They discovered that the tensile energy at break calcu-lated from the area under the tensile stress�strain curve was10 times higher than for the pure PLA. However, remarkablythis effect was observed only up to about 20 wt% Nodaxt. Infact, further incorporation of Nodaxt reduced the toughness ofthe blend back to the original level of pure PLA. This is becausebelow 20 wt% Nodaxt, the copolymers finely disperse in thePLA matrix as discrete domains, meaning that the PHA portionof the blend remains predominantly in a liquidlike amorphousstate, which retards crystallization. The reduced crystallinitythen provides the ductility and toughness of the blend.

Similar work on melt blending Nodaxt with PLLA wasreported by Schreck and Hillmyer (2007). The blends werecompounded using a Haake batch mixer at 190�C, 75 rpm for15 min, with Nodaxt compositions varying from 0 to 25 wt%.Instead of studying the tensile energy at break, as reported byNoda et al. (2004), Schreck and Hillmyer investigated the effectof PLLA/Nodaxt blends on Izod impact strength. Similarimprovements in toughness were observed for the blends, for upto 20 wt% Nodaxt. The highest impact strength was obtainedfor the blend with 15 wt% Nodaxt, which was 44 J/m com-pared to 22 J/m for the pure PLLA. In order to improve thebinary blend properties, Schreck and Hillmyer (2007) alsoinvestigated the effect of ternary blends of PLLA/Nodaxt andoligoNodax-b-poly(L-lactide) diblock copolymers as compatibi-lizers. The amount of oligoNodax-b-poly(L-lactide) was fixed

206 POLYLACTIC ACID

at 5 wt% in a blend of 81/14 wt% PLLA/Nodaxt. However, theaddition of 5 wt% oligoNodax-b-poly(L-lactide) did not showany improvement in toughness. This is because of poor interfa-cial adhesion at the particle/matrix interface due to low entan-glement of oligoNodax with Nodaxt, which consequentlyreduces the ability to deform and dissipate impact loads. A sum-mary of the literature on blending polylactide and PHAs is setout in Table 5.9.

5.4.4 PLA Blends with Nondegradable Polymers

Blending of PLA with nondegradable polymers has not been asextensively studied as blending with degradable or renewable-resource polymers. Nevertheless, blending PLA with commoditypolymers, in particular, can be very useful in terms of improvingprocessability, lowering costs and controlling the biodegradationrate. Kim et al. (2001) investigated the effect of blending high-molecular-weight PEO with PLLA. The blending compositionswere fixed at 60:40 wt% of PLLA/PEO. In addition to the blendof PLLA/PEO, they also added poly(vinyl acetate) (PVAc) as acompatibilizer at various concentrations (2�20 wt%). The blendswere prepared by solution and melt blending. Solution blendingwas performed in chloroform at 3 wt%, while melt blending wasprepared using a Brabender (Plasti-Corder) mixer. The research-ers found that at the same PVAc loading the tensile strength ofthe solution blend was higher than that of the melt blend.However, the elongation at break for the solution blend was lowerthan the melt blend for comparable amounts of PVAc.

In the solution blend, the addition of various amount ofPVAc slightly reduced the tensile strength and improved theelongation at break. The optimum properties were obtained at2 wt% of PVAc, where the elongation at break significantlyincreased without a drastic reduction in the tensile strength.Meanwhile, the tensile strength of the melt PEO/PLLA blendsincreased with increasing amounts of PVAc. The elongation atbreak increased up to 5 wt% and then significantly dropped atgreater amounts of PVAc. However, Kim et al. (2001) did not


Table 5.9 Mechanical Properties of Polylactide/PHA Blends


Strength

(MPa)

Young’s

Modulus

(GPa)

Elongation

at Break

(%)

Tensile

Toughness

(Nmm)

Charpy

Impact Test

(J)

Reference

2nd Component Wt% 3rd Component Wt%

PLLA None N/a � � 71 2.4 5.6 � � Iannace

et al.

(1994)

PLLA Poly(3-hydroxybutyrate-

co-3 hydroxyvalerate)

(PHBV)

20 � � 54 2.1 6.2 � �

40 39 1.5 6.7 � �PLLA None � � 30 2.0 � � � Ferreira

et al.

(2002)

PLLA PHBV 20 � � 28 1.8 � � �40 � � 22 1.6 � � �

PLLA Poly((R)-3-hydroxy-

butyrate) (PHB)

50 � � 49.6 2.7 4.4 5.9 � Yoon et al.

(1999)

PLLA PHB 50 PLLA�PEG�PLLA

triblock

copolymer

2 69.8 2.3 5.1 9.2 �

PLLA PHB 50 PLLA�PEG�PLLA

triblock

copolymer

5 38.5 1.9 5.1 7.9 �

PLLA PHB 50 PEG�PLLA diblock

copolymer

2 65.5 2.6 4.4 6.5 �

PLLA PHB 50 PEG�PLLA diblock

copolymer

5 32.7 2.1 5.9 8.3 �

PLLA PHB 50 Polyvinyl acetate 2 41.5 1.8 4.8 8.4 �

PLLA PHB 50 Polyvinyl acetate 5 43.4 2.1 4.9 6.6 �Charpy (J)

PLA None � � 55 � � � 0.052 Takagi et al.

(2004)

PLA Poly(3-hydroxy

alkanoate) (PHA)

10 � � 50 � � � 0.081

20 � � 28 � � � 0.137

30 � � 25 � � � 0.161

PLA Functionalized PHA (ePHA) 10 � � 51 � � � 0.089

20 � � 47 � � � 0.169

30 � � 37 � � � 0.260

TT (Nm)

PLA None N/a � � � � � 0.2 � Noda et al.

(2004)

PLA Poly(3-hydroxybutyrate)-

co-(3-hydroxyalkanote),

Nodaxt

10 � � � � � 1.9 �

20 � � � � � 1.4 �40 � � � � � 0.2 �

Notched Izod

(J/m)

PLLA None N/a � � � � � � 22 Schreck

and

Hillmyer

(2007)

PLLA Nodaxt 15 � � � � � 44

PLLA Nodaxt 14 OligoNodax-b-poly

(l-lactide) diblock

copolymers

5 � � � � 44

show any morphological data to verify the difference in themelt and solution blend properties.

Jin et al. (1999) investigated the effect of blending PLA withdifferent amounts of polyisoprene. They found that with theaddition of 20 wt% polyisoprene the elongation at break andtensile toughness decreased relative to the neat PLA. However,when PLA was blended with a polyisoprene/poly(vinyl acetate)graft copolymer, the elongation at break and tensile toughnessslightly improved as compared to the neat PLA.

The effects of blending PLA with organically modifiedmontmorillonite nanoclays (Cloisite 30B) and the combinationof blending PLA/Cloisite 30B and core (polybutylacrylate)�shell (polymethylmethacrylate) rubbers (Paraloid EXL2330)were reported by Li et al (2006). The MMT nanoclays are sur-face-treated by ion exchange reaction prior to modificationwith bis-(2-hydroxyethyl) methyl (hydrogenated tallow alkyl)ammonium cations. The addition of 5 wt% Cloisite 30Bimproved the modulus of the blend, but reduced the tensilestrength and elongation at break. However, the blend of PLA/Cloisite 30B (5 wt%) with Paraloid EXL2330 (20 wt%) signifi-cantly improved the impact strength (134%), increased theelongation at break (6%), gave a similar modulus and reducedthe tensile strength (28%) as compared to neat PLA.

NatureWorks, the largest manufacturer of PLA, has reportedthe use of a high-rubber-content (35�80%) impact modifier,namely Blendex 338, a terpolymer of an acrylonitrile-butadiene-styrene containing 70% butadiene rubber, to improve the impactstrength. With the addition of 20 wt% Blendex 338 to the PLAblend, an improvement on the notched Izod impact strength andthe elongation at break has been observed. The notched Izodimpact strength increased from 26.7 J/m to 518 J/m and the elon-gation at break increased from 10% to 281%. (NatureWorks,2011) also reported a toughening effect on PLA by blending itwith a polyurethane supplied by the Dow Chemical Company,namely Pellethanet 2102-75A. With the addition of 30 wt%Pellethanet 2102-75A, the notched Izod impact strengthincreased from 26.7 J/m to 769 J/m and the elongation at breakincreased significantly from 10% to 410%.

210 POLYLACTIC ACID

DuPont developed Biomaxs Strong, a petrochemical-basedimpact modifier that is designed to modify polylactide(Dupont, 2011). It is an ethylene copolymer that can improvetoughness and reduce the brittleness of PLA materials.Biomaxs Strong can reduce the brittleness of PLA at levels aslow as 2 wt%. It can also enhance impact strength, flexibilityand melt stability of PLA; these characteristics are particularlybeneficial when used in rigid applications, like cast sheets forthermoforming and injection molding. When used at the recom-mended levels of 1�5 wt%, Biomaxs Strong outperforms com-peting products in terms of improved toughness with minimalimpact on transparency. This product has good contact clarity atthe recommended levels and provides a much clearer containerthan other alternatives. By using Biomaxs Strong at the recom-mended levels, PLA’s performance attributes are enhanced andyet it still allows the material to meet compostabilityrequirements.

Anderson and Hillmyer (2004) investigated blends of PLLAwith linear low-density polyethylene (LLDPE) (PLLA/LLDPE)and high-density polyethylene (HDPE) (PLLA/HDPE). In addi-tion they also compared the effect of incorporating copolymerpoly(L-lactide)-polyethylene (PLLA-PE) with PLLA/LLDPEblends and copolymer poly(L-lactide)-poly(ethylene-alt-propyl-ene) (PEP) with PLLA/HDPE blends. The addition of 20 wt%LLDPE in PLLA drastically increased the impact strength to490 J/m, compared to 20 J/m for the neat PLLA. With the addi-tion of 5 wt% PLLA-b-PE block copolymer in the blend sys-tem, the impact values were further improved to 760 J/m. Theelongation at break has also increased to 23% and 31% respec-tively for the binary and ternary blends of PLLA, relative to4% for the neat PLLA. However, both blends of PLLA/LLDPEand its copolymer reduced the tensile strength and modulus.When comparing the blends of PLLA with LLDPE and thatwith HDPE, it was observed that the blend with HDPE, andeven with its copolymer, had lower tensile strength and modu-lus than the LLDPE blends. This is because the dispersed rub-bery phase of LLDPE imparts more adhesion with the matrix


of PLLA compared to the stiff HDPE, which improves thedegree of toughening.

A recent study by Balakrishnan et al. (2010) also focused onblending PLA with LLDPE; however, instead of addingLLDPE only, they added organophilic modified montmorillon-ite (MMT). The composition of LLDPE was fixed at 10 wt%,while the amount of MMT was varied at 2 and 4phr. Theresearchers found that with the increasing amounts of MMT inthe PLA/LLDPE blend, Young’s and the flexural modulusincreased with a sacrifice in tensile and flexural strength. Thisshows that MMT is effective in increasing the stiffness of theblend. There is transmission electron microscope (TEM) andX-ray diffraction (XRD) proof that the intergallery spacing ofMMT increases in the blend, forming an intercalated nanocom-posite system (Balakrishnan et al., 2010). The well dispersedMMT platelets contribute to the enhancement of the LLDPEtoughened PLA nanocomposite.

Jiang et al. (2007) compared the mechanical properties ofPLA nanocomposites prepared with nano-size precipitated cal-cium carbonate (NPCC) and organically modified montmoril-lonite (MMT) clay. The PLA nanocomposites were prepared bymelt blending, using a co-rotating twin-screw extruder usingdifferent amounts of NPCC and MMT (2.5, 5 and 7.5 wt%).They observed that the elongation at break for PLA improvedwith increasing levels of NPCC from 2.5 to 7.5 wt%, whereas itonly increased with the amount of MMT up to 2.5 wt%, afterwhich it decreased. The tensile strength of PLA nanocompositesdecreased with increasing levels of NPCC, whereas it increasedwith MMT up to 5 wt%. Meanwhile, the Young’s modulus wasslightly increased for PLA with increasing NPCC loading andwas significantly increased with MMT loading. The MMT wasrevealed to be intercalated by PLA, and good dispersions ofboth nanoparticles were achieved when the filler loading wasabout 5 wt%. However, with increasing amounts of nanoparti-cles, large agglomerates were observed. The authors suggestedthat the different reinforcing effects of both nanoparticles couldbe primarily attributed to the differences in microstructure andthe interactions between the nanoparticles and PLA in the

212 POLYLACTIC ACID

Table 5.10 Mechanical Properties of Blends of Polylactide with Nondegradable Polymers


Strength

(MPa)

Young’s

Modulus

(GPa)

Elongation

at Break

(%)

Tensile

Toughness

(Nmm)

Impact

Strength

(kJ/m2)

Reference


PLLA - Solution blend Kim et al.

(2001)

PLLA PEO 40 � � 28 � 70 � �PLLA PEO 40 Poly(vinyl aectate)

(PVAc)

2 29 � 110 � �

40 PVAc 5 27 � 115 � �PLLA- Melt blend

PLLA PEO 40 � 17 � � � �PLLA PEO 40 Poly(vinyl aectate)

(PVAc)

2 18 � � � �

(PVAc) 5 18 � 410 � �PLLA None � � 18.1 1.6 10.2 7.4 � Jin et al. (2000)

PLLA Polyisoprene (PI) 20 � � 6.3 1.0 2.5 �PLLA PI-g-PVAC 20 � � 14.6 1.1 14.3 18.2

PLA None � 61 1.8 6.6 � 2.2 Li et al. (2006)

PLA Cloisite 30B 5 � � 56 2.2 4.5 � 2.1

PLA Cloisite 30B 5 Paraloid EXL2330 20 44 1.8 7.0 � 5.15

J/m

PLLA None � � � 62 2.4 4 � 20 Anderson and

Hillmyer

(2004)

PLLA LLDPE 20 � � 22 1.7 23 � 490

Table 5.10 Mechanical Properties of Blends of Polylactide with Nondegradable Polymers—cont’d


Strength

(MPa)

Young’s

Modulus

(GPa)

Elongation

at Break

(%)

Tensile

Toughness

(Nmm)

Impact

Strength

(kJ/m2)

Reference


PLLA LLDPE 20 PLLA�b�PE

diblock

copolymer

5 24 1.3 31 � 760

PLLA HDPE 20 � � 42 1.7 2.9 � 12

PLLA HDPE 20 PLA�b�PEP

diblock

copolymer

5 25 1.4 13 � 64

PLA None � � � 64.5 3.5 4 � � Jiang et al.

(2007)

PLA Nano-sized precipitated

calcium carbonate

(NPCC)

2.5 � � 63 3.5 5.1 � �

PLA NPCC 5 � � 59 3.6 13 � �PLA NPCC 7.5 � � 57.5 3.7 13.5 � �PLA Montmorillonite

(MMT) clay

2.5 � � 66 4.0 12.5 � �

PLA MMT 5 � � 67 4.6 1.8 � �PLA MMT 7.5 � � 54 5.1 1.1 � �

respective nanocomposites. Table 5.10 summarizes the mechan-ical properties of polylactide/nondegradable polymer blends.

5.5 Conclusion

The mechanical properties of pure PLA can be varied bychanging the stereochemistry, crystallinity, molecular weight,etc. PLA with high stereochemical purity possesses the charac-teristic of high tensile strength and modulus, but lacks impactstrength. In contrast, the copolymer of L-lactide and D-lactideremains in an amorphous state, which has poor mechanicalproperties. Researchers tend to utilize the copolymerizationtechnique to modify the existing properties of PLA, in order towiden its applications. In addition, polymer-blending techni-ques have been used to combine the properties of PLA withthose of another polymer to achieve better impact and flexuralstrength. Generally, most of the modifications made to PLAare targeted at improving its mechanical properties while main-taining its biodegradability. It is likely that this trend in PLAdevelopment will continue for the coming decades.

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6 Rheological Properties ofPoly(lactic Acid)

Chapter Outline6.1 Introduction 2216.2 Rheological Properties of Poly(lactic Acid) 2226.3 Effects of Molecular Weight 2266.4 Effects of Branching 2306.5 Extensional Viscosity 2326.6 Solution Viscosity of PLA 2336.7 Rheological Properties of Polymer Blends 233

6.7.1 PLA/PBAT Blend 2356.7.2 Blend with Layered Silicate Nanocomposites 2376.7.3 PLA/Polystyrene Blend 239


6.1 Introduction

Rheology is defined as the study of the deformation andflow of a fluid. It is an important property of a molten poly-mer; it relates the viscosity with temperature and shear rate,and is consequently linked to the processability of a polymer.Most polymer melts are classified as shear thinning fluids,whereby at higher shear rates the polymer molecules orientand the number of entanglements between the polymer chainsdecreases. These phenomena help the polymer chains to floweasily past one another into narrow cavities during the poly-mer-forming process. The viscosity also decreases at elevatedtemperatures due to the higher kinetic energy of themolecules.

Rotational and capillary rheometers are devices that can beemployed to gain data on the shear viscosity of polymers.Rotational rheometers are primarily used for low-shear-rate



http://dx.doi.org/10.1016/B978-1-4377-4459-0.00006-8

analysis from 0.001 to B100 s21. These instruments normallyconsist of cone and plate geometry; the design of the coneangle can maintain the shear rate during the analysis. Capillaryrheometers use a pressure-driven flow and measure the pressureat the entrance to a capillary die in order to obtain the apparentrheological data of the polymer melt. This data appears asvalues for the viscosity and shear rate, which are further cor-rected using the Bagley and Weissenberg�Rabinowitsch corre-lations. Capillary rheometers are used to measure moderate tohigh shear rates, from B10 to 10,000 s21. These measurementsrequire significantly more material and time to perform thanthe rotational approach.

Poly(lactic acid) (PLA) is made into useful items using ther-mal processes, such as injection molding and extrusion.Therefore, its rheological properties, especially its shear viscos-ity, have important effects on the thermal processes, such asfilm blowing, paper coating, injection molding, sheet formingand fiber spinning. Thus, the study of rheological properties ofPLA is crucial to gain a fundamental understanding of the pro-cessability of PLA materials.

6.2 Rheological Properties ofPoly(lactic Acid)

Melt rheological properties of PLA have a profound effecton the polymer flow conditions during the processing stage. Ingeneral, the melt viscosities of high-molecular-weight PLA arein the order of 500�1000 Pa � s at shear rates of 10�50 s21.Such polymer grades are equivalent to molecular weight (Mw)B100,000 g/mol for injection molding to B300,000 g/mol forfilm cast extrusion applications (Garlotta 2001). The melts ofhigh-molecular-weight PLA behave like a pseudoplastic, non-Newtonian fluid, whereas low-molecular-weight PLA(B40,000 g/mol) shows Newtonian-like behavior at shear ratesfor typical film extrusion. Under identical processing condi-tions, semicrystalline PLA tends to possess higher shear viscos-ity than its amorphous counterpart. Moreover, as shear rates

222 POLYLACTIC ACID

increase, the viscosities of the melt reduce considerably, i.e.the polymer melt exhibits shear-thinning behavior. This phe-nomenon was revealed by Fang and Hanna (1999) who con-ducted an analysis using a tube rheometer attached to anextruder. In this study two types of PLA resins (amorphous andsemicrystalline) were analyzed at 150�C and 170�C. The vis-cosity data was calculated from the pressure profiles and thevolumetric flow rate as the functions of resin type, temperature,and shear rate. The results in Figure 6.1 show that the semi-crystalline PLA has a higher viscosity than amorphous PLA atelevated temperatures. This is due to the difference in molecu-lar structure. The molecules of semicrystalline PLA arearranged in an organized pattern, which provides stronger inter-molecular forces and a relatively large resistance to flow.Conversely, the arrangement of the molecules in amorphousPLA is random, which, in turn, exhibits less resistance to flow.In general, materials with crystalline structures have strongerphysical and mechanical properties than amorphous materials.

An increase in temperature was found to cause a reductionin the shear viscosities for both semicrystalline and amorphousPLA. It was observed that the values of viscosity at 150�C are

3700

3600

3500

3400

3300

3200

3100

3000

2900150 170

Temperature (°C)

Vis

cosi

ty (

Pa

·s)

Amorphous

Semicrystalline

Figure 6.1 Effects of resin type and temperature on PLA-meltviscosity (Fang and Hanna 1999).

2236: RHEOLOGICAL PROPERTIES OF POLY(LACTIC ACID)

significantly higher than those at 170�C. This can be explainedby the fact that the connections between the molecular chainsat high temperature become weaker, due to the higher vibra-tional amplitude of the PLA molecules, which transforms themelt to flow smoothly. Furthermore, the shear rate greatlyaffects the viscosity of PLA melt. As shown in Figure 6.2, ηreduces drastically as the shear rate increases for both types ofPLA. The relationship between η and shear rate is nonlinear,but exhibits typical non-Newtonian pseudoplastic behavior.This is mainly due to the fact that the molecular chains are bro-ken down by the strong shearing action during extrusion.

The work by Fang and Hanna (1999) also summarizes thepower law equation of both amorphous and semicrystallinePLA (see Table 6.1). The data is derived from rheology testingusing a single-screw Brabender extruder with an L/D and com-pression ratio of 20/1 and 3:1, respectively. Upon performingnonlinear regression analysis on the power law equations, itwas found that all equations have correlation coefficients (r2)greater than 0.99 and a relatively small mean square error onpower law equations. This gives further evidence that bothamorphous and semicrystalline PLA exhibit typical non-Newtonian pseudoplastic behavior. In spite of that,

8000

7000

6000

5000

4000

3000

2000

1000

00 200 400 600

Shear rate (s–1)

800 1000 1200

Vis

cosi

ty (

Pa

·s)

Amorphous

Semicrystalline

Figure 6.2 Effect of shear rate on PLA-melt viscosity (adapted fromFang and Hanna, 1999, with permission of Elsevier).

224 POLYLACTIC ACID

NatureWorks’s injection moldable grade of Ingeos in the cap-illary rheometer test has shown a good fit into the Cross-WLFviscosity model (see Table 6.2). There are seven coefficients inthe model and it is readily embedded into Moldflows softwarefor injection molding simulation (Moldflow Plastic Labs 2007).Moldflows is computer software that is widely used across theplastic injection molding industry to predict and optimize the

Table 6.1 Power-Law Equation for PLA (Fang and Hanna 1999)

PLA Temperature (�C) Equation r2

Amorphous 150 η5 649386 _γ20:8332 0.9984

Amorphous 150 η5 242038 _γ20:7097 0.9980

Semicrystalline 170 η5 609159 _γ20:8134 0.9992

Semicrystalline 170 η5 24172 _γ20:7031 0.9982

Table 6.2 Cross�WLF Model Coefficient for PLA(Moldflow Plastic Labs 2007)

Cross�WLF Model

η5ηo

11 ηo _γΓ

� ð12nÞ

where

ηo5D1exp 2A1ðT2 T� Þ

A21 ðT2 T� Þ

h iand

η is the viscosity, _γ is the shear rate, T is the temperature

T�5D21D3�P, where P is the pressure (Pa)

A25A2B1D3TP and n, Γ, D1, D2, D3, A1, A2B are

data-fitted coefficients as shown as below:

Coefficient Value

A1 20.194

A2 51.600 K

D1 3.317193 109 Pa.s

D2 373.15 K

D3 0K/Pa

n 0.2500

Γ 1.008613 105 Pa


injection molding process and assist with mold design. TheCross-WLF model can provide insight on the injection condi-tions, such as the pressure and temperature effects with themolten polymer when flowing into a narrow cavity.

6.3 Effects of Molecular Weight

The viscoelastic properties of PLA melts of varying molecu-lar weights have been measured over a range of temperatures,frequencies and shear rates, utilizing the parallel plate geome-try. A typical study was performed by Cooper-White andMackay (1999) using a Rheometrics RDSII torsional rheome-ter, with 7.9 mm stainless steel parallel plates on three com-mercial grades of PLLA with significantly different molecularweights�40,000 g/mol, 130,000 g/mol and 360,000 g/mol.Figure 6.3 shows a plot of complex viscosity (η�) as a function

106

105

104

103

102

10–2 10–1 100

Reduced frequency or shear rate (s–1)

Mw = 40,000 Da

Mw = 130,000 Daη*, η

(P

s·s

)

Mw = 360,000 Da

101 102 103

Dynamic

Steady

Figure 6.3 Effect of molecular weight on viscosity for PLLA melts at200�C (Cooper-White and Mackay 1999).

226 POLYLACTIC ACID

of frequency and molecular weight for the series of PLLApolymers when subjected to both dynamics and steady shear. Itwas observed that there was good agreement between dynamicand steady viscosity for both low Mw (40,000 g/mol) andmedium Mw (130,000 g/mol). Agreement between dynamic andsteady behavior is difficult to observe for the high molecularweight PLA (Mw5 360,000 g/mol), even at very low frequen-cies, due to notable sample edge fracture and degradation understeady shear. Newtonian-like behavior is observed for low-molecular-weight PLA, which suits the shear rates typical forthose encountered during film extrusion (B100 s21). However,this Newtonian-like behavior was noticeably shortened withincreasing molecular weight.

Viscoelastic properties of polymer melts can be character-ized by zero-shear viscosity, ηo. This parameter can be obtainedfrom dynamic experiments by determining the dynamic moduliat the limit of low frequency. Table 6.3 shows the zero-shearviscosity, ηo, and also the elastic coefficient, AG (the ratio ofthe applied stress to the change in shape of an elastic body),for all samples at 200�C.

The empirical equation relating viscosity at zero-shear rate(ηo) to molecular weight for linear amorphous polymers is usedto compare PLLA melts with those of conventional polymers.The form of this equation has been applied to the elasticitycoefficient, AG, to further quantify the effect of molecularweight on the elasticity (Cooper-White and Mackay 1999):

ηo5KðMwÞa (6.1)

Table 6.3 Molecular Weight, Zero-Shear Viscosity and ElasticCoefficient for Different Mw of PLA at 200�C

Mw (g/mol) ηo (Pa � s) AG (Pa � s2)40,000 100 0.23

130,000 6,200 840

360,000 7.03 105 7.13 107


AG5K 0ðMwÞb (6.2)

Within these equations, the constants K and K0 depend uponthe polymer type, its number molecular weight and tempera-ture. The power-law factors ‘a’ and ‘b’ can be determined bythe slope of the log viscosity and log elasticity coefficient,respectively, versus log molecular weight plots, as shown inFigure 6.4. The molecular weight exponent ‘a’ has been theo-retically predicted to have a universal value of 3.4 above Mc �the critical molecular weight of entanglements for linear flexi-ble polymers (Ferry 1980). Many systems have been shown tofollow this relationship. The dependence of the elasticity coef-ficient on molecular weight, described explicitly by the expo-nent ‘b’, has been shown experimentally to be around 7.5 formonodisperse polystyrene (Onogi et al., 1966).

From Figure 6.4, the following equations are obtained:

ηo5 ð33 10217PaUsÞðMwÞ4:0 (6.3)

10

8

6

4

2

0

–2

–43 4

log (Mw)

AG (slope = 8.0)

r2 = 0.994

η0 (slope = 4.0)

r2 = 0.996

log

(η0)

, log

(A

G)

5 6

Figure 6.4 Effect of molecular weight on zero-shear viscosity andelasticity coefficient for PLLA at 200�C (Ferry 1980).

228 POLYLACTIC ACID

AG5 ð23 10238PaUs2ÞðMwÞ8:0 (6.4)

The value for the exponent of molecular weight, with respectto zero-shear viscosity, is slightly higher than the generallyaccepted value of 3.4. The elasticity coefficient for PLLA meltsshows a higher dependence on molecular weight at a value of8.0 than that observed for monodisperse polystyrene melts.This deviation is thought to be caused by steric hindrance�aresult of excessive coil expansion produced by possible chemi-cal shift differences within and between PLLA polymer chains(including tertiary chain-to-chain interactions).

Witkze showed that the temperature effect on ηo for 15%D-lactide PLA can be described by (Witzke 1997):

ηo5 ηo;refMw

100; 000

� �aexp

Ea

R

1

TðKÞ 21

373

� �� (6.5)

where a5 3.386 0.13, the activation energy of flowEa5 190 kJ/mol, ηo,ref5 89,4006 9300 Pa � s, R is the gasconstant5 8.314 J/K mol, and T is the temperature in K. Thezero-shear viscosity, ηo can be correlated with the isomer com-position by fitting to the well-known Williams�Landel�Ferryequation (WLF) (Witzke 1997):

ηo5 ða11 a2Wmeso1 a3WL2merÞMw

100; 000

� �3:38

3 exp2C1 TðCÞ2 100

�C21 TðCÞ2 100

�( ) (6.6)

where Wmeso and WL-mer are the initial weight fractions formeso-lactide and L-lactide, respectively, a1523,000,a25242,000, a35 112,000, C15 15.66 1.6, andC25 1106 11�C; a1, a2, a3, and C1 do not have units; and T(C)is the testing temperature in �C. Equation (6.6) can be used topredict ηo of amorphous polylactides with L-monomer composi-tion higher than 50% between Tg and Tg1 100�C. The equationpredicts that ηo increases with increasing L-monomer andreduces as meso-lactide content becomes higher.


6.4 Effects of Branching

The rheological properties of PLA can be significantly modi-fied with the introduction of branching. Since the linear polymerexhibits low melt strength for certain applications, it is desirableto increase the melt strength by introducing long-chain branching.There are several ways to improve branching in PLA, such as theuse of multifunctional polymerization initiators, hydroxycyclicester initiators, multicyclic esters and crosslinking via free radicaladdition (Lehermeier and Dorgan 2001). Figure 6.5 shows theplot of complex viscosity versus frequency for commercial-gradebranched and linear PLA (Dorgan et al., 2000). These polymershave a 96:4 of L:D content and are produced by melt polymeriza-tion using stannous octoate as a catalyst. The commercial-gradebranched material is produced by further processing throughperoxide-initiated crosslinking of the linear material by reactiveextrusion. The linear material has a weight average molecularweight (Mw)5 111 kg/mol and a polydispersity of 2.1, and thebranched PLA has a weight average molecular weight (Mw)5149 kg/mol and a polydispersity of 2.9.

10000

1000

1000.0 0.1 1.0 10.0

Frequency (1/s)

Com

plex

vis

cosi

ty (

Pa

·S)

100.0 1000.0 10000.0

η0 (linear) = 3620 Pa · s

η0 (branched) = 8350 Pa · s Branched

Linear

Figure 6.5 Comparative flow curves for commercial-grade branchedand linear materials (Dorgan et al., 2000).

230 POLYLACTIC ACID

According to Figure 6.5 the branched PLA provides a higherzero-shear viscosity ηo and stronger shear thinning than the lin-ear PLA. This conclusively demonstrates that a wide spectrumof flow properties is available through simple architecturalmodification of PLA, allowing the use of this importantdegradable thermoplastic in a variety of processing operations.The deviation of ηo could be due to the effect of free volume,which leads to instability of viscosity. In view of this effect,Lehermeier and Dorgan (2000) used tris(nonylphenyl) as thestabilizer of viscosity for PLA during the thermorheologicaltime-sweep experiment of branched PLA polymers(Lehermeier and Dorgan 2000). The stabilizing effect of tris(nonylphenyl) phosphate is elucidated by using the time�temperature superposition technique. This compound greatlyfacilitated the thermorheological experiments by preventing theconfounding effect from degradation reactions.

In order to parameterize the data into a descriptive model,the combined data sets of viscosity and shear rate relationshipfor linear and linear-branched PLA are fitted to theCarreau�Yasuda model. The form of the model used is givenby (Lehermeier and Dorgan 2001):

η5C1½11ðC2 _γÞC3 �C421

C3

� (6.7)

where η is the viscosity, _γ is the shear rate, and C1, C2, C3 andC4 are material-dependent parameters. The coefficients for themodel are summarized in Table 6.4. C1 determines ηo, which

Table 6.4 Carreau�Yasuda Model Parameters for PLA

Blend (% Linear) Carreau Parameters

C1 (Pa � s) C2 (s) C3 C4

0 10,303 0.01022 0.3572 2 0.0340

20 8418 0.00664 0.3612 2 0.0731

40 6409 0.01364 0.4523 0.0523

60 5647 0.00513 0.4356 2 0.1002

80 4683 0.00450 0.4754 2 0.1108

100 3824 0.01122 0.7283 0.0889


decreases at higher linear content. C2 is the relaxation time,approximately corresponded to the reciprocal of frequency forthe onset of shear thinning, and C3 influences the shear thinning,which increases with higher linear content, i.e. branched PLAshear thinned more strongly than the linear material. Theincrease of both ηo and shear thinning with the addition ofbranching is also reported by other studies on PLA polymerswith star polymer chain architectures (Dorgan et al., 1999).

6.5 Extensional Viscosity

The study on extensional viscosities of high L-content PLA(Mw5 110,000�120,000 g/mol) shows that PLA can be drawnto large strains without breaking. The polymer also exhibitsstrain-hardening behaviors during the deformation (Paladeet al., 2001), which is an important characteristic for processingoperations such as fiber spinning, film casting, and film blow-ing. Figure 6.6 presents the plot of extensional viscosity, ηel,

107

105

103

100 101 102

Time (s)

η el (

Pa

·s)

3ηss L:D = 98:02 3ηss L:D = 96:04

T = 180 °C

L:D = 96:04

L:D = 98:02

Figure 6.6 Growth of the extensional viscosity ηel versus timemeasured at a rate of 0.1 s21. PLA samples (nominal L:D values of98:02 and 96:04 and corresponding weight-averaged molecularweights of 120,000 and 110,000 g/mol).

232 POLYLACTIC ACID

versus time data for PLA weight-averaged molecular weightsof 110,000 and 120,000 g/mol respectively, for PLA synthe-sized using stannous octoate as a catalyst. The elongationalmeasurements are performed on a Rheometrics elongationalrheometer, at a temperature of 180�C and elongation rate of0.1 s21 using rectangular samples. The most striking feature ofthe response is a strong strain hardening (the extensional vis-cosity increases by 2 orders of magnitude). This effect is mostsignificant when long chain branching is present because itintroduces very long relaxation times.

6.6 Solution Viscosity of PLA

Although solution viscosity of PLA in solvent is not directlyrelevant to the processing of molten PLA polymers, this prop-erty is often evaluated to determine the molecular weight ofresins and processed parts for quality control purposes. Therelationship between viscosity and the molecular weight ofPLA dissolved in a dilute solution is commonly modeled usingthe Mark�Houwink equation:

½η�5K3Mva (6.8)

where [η] is the intrinsic viscosity, K and a are constants, andMv is the experimental viscosity average molecular weight. TheMark�Houwink equation is dependent on the type of PLA, thesolvent used and the temperature of the solution. Table 6.5 sum-marizes the Mark�Houwink parameters for different composi-tions of PLA polymers in different solvent solutions.

6.7 Rheological Properties of Polymer Blends

The properties of PLA can be modified by polymer blendingtechniques. PLA has been blended with several synthetic andbiopolymers in order to enhance its properties and to obtainnovel materials. PLA has been blended with rubbers,thermoplastic starch (TPS), poly(butylene succinate) (PBS),poly(butylenes succinate adipate) (PBSA), poly(butylene


Table 6.5 Mark�Houwink Coefficients of PLA in SelectedSolvents

Polymer Types Equations Conditions

(1) PLLA ½η�5 5:453 1024Mv0:73 25�C in chloroform

(Perego et al.,

1996; Tsuji and

Ikada 1996)

(2) PDLLA ½η�5 1:293 1025Mv0:82 25�C in chloroform

(Doi and Fukuda

1993)

(3) PDLLA ½η�5 2:213 1024Mv0:77 25�C in chloroform

(Perego et al.,

1996; Tsuji and

Ikada 1996)

(4) Linear PLLA ½η�5 4:413 1024Mv0:72 25�C in chloroform

(Doi and Fukuda

1993)

(5) PDLLA ½η�5 2:593 1024Mv0:689 35�C in THF (Van

Dijk et al., 1983)

(6) PDLLA ½η�5 5:503 1024Mv0:639 31.1525�C in THF

(Van Dijk et al.,

1983)

(7) PDLLA

(amorphous)

½η�5 6:403 1024Mv0:68 30�C in THF (Spinu

et al., 1996)

(8) PLLA

(amorphous/

semicystalline)

½η�5 8:503 1024Mv0:66 30�C in THF (Spinu

et al., 1996)

(9) PLLA

(semicystalline)

½η�5 1:003 1023Mv0:653 30�C in THF (Spinu

et al., 1996)

(10) PDLLA ½η�5 2:273 1024Mv0:75

(one-point method)

30�C in benzene

(Gupta and

Deshmukh 1982)

Tuan-Fuoss

viscometer

(11) PDLLA ½η�5 1:583 1024Mv0:78 25�C in ethyl acetate

(Xu et al., 1996)

THF5 tetrahydrofuran.

234 POLYLACTIC ACID

adipate-co-terephthalate) (PBAT), acrilontryl�butadiene�styrene (ABS), polypropylene (PP), polyethylene (PE), polysty-rene (PS) and layered silicate to obtain materials with lowercost and improved properties.

6.7.1 PLA/PBAT Blend

The steady shear rheological behaviors of PLA/PBAT blendmelts at different blend ratios of PBAT show a typical non-Newtonian fluid (Gu et al., 2008). As shown in Figure 6.7, atlower shear rates the shear viscosities of PLA/PBAT melts arehigher than those of pure PLA melt and increase considerablywith PBAT content. The shear-thinning tendency of PLA/PBAT melts becomes stronger with increased PBAT content,so that the shear viscosities of PLA/PBAT melts are even lowerthan those of pure PLA melt at higher shear rates. The fluctua-tion of the data might be caused by the immiscible formingtwo-phase structure. In the study by Shu-Ying Gu et al. (2008)the PLA/PBAT blends were prepared by melt mixing usinga twin-screw extruder with a screw diameter of 27 mm and an

10–2 10–1 100

Shear rate (1/s)

η (P

a·s

)

101

PLA100PLA95PLA90PLA85PLA80PLA70

103

102

Figure 6.7 Steady shear viscosity of PLA and PLA/PBAT melts at170�C (PLA85 contains 85% PLA and 15% PBAT. Similar for others)(Adapted from Gu et al., 2008, published with permission of Elsevier).


L/D ratio of 42. About 0.5 wt% (weight ratio to PLA/PBAT) oftris(nonylphenyl) phosphate (TNPP) was used as a stabilizer toeliminate the degradation of PLA in the heating process. TNPPacts as a chain extender, reconnecting polymer chains that havebeen broken due to moisture and elevated temperature.

The power-law equation is used to fit the data and it shows agood result where all the equations have a correlation coeffi-cient (r2) greater than 0.99. The calculated values of n for PLAand its blend melts are presented in Table 6.6. The incorpo-ration of PBAT leads to a decrease of flow index n. The tem-perature dependence of the viscosity of polymer melts is one ofthe most important parameters in polymer flow. Within a cer-tain range of temperatures, the dependence can be expressed inthe Arrhenius form:

ηo5A expEa

RT

� �(6.9)

where ηo is the zero-shear viscosity, R is the gas constant, A isa constant and Ea is the flow activation energy. Higher Ea willlead to a melt that is more sensitive to the change in tempera-ture. The flow activation energy values (Ea) of pure PLA andPLA/PBAT melts obtained from Arrhenius fit are presented inTable 6.6. Values of Ea are calculated by using ηo data at tem-peratures of 160, 170 and 180�C. The results obey theArrhenius model very well, and it is clear that Ea tends todecrease with the incorporation of PBAT. The low dependencyof PLA/PBAT melts on temperature simplifies the selection of

Table 6.6 Rheological Characteristics of PLA and PLA/PBATMelts (Gu et al., 2008)

Characteristic PLA:PBAT

100:0 95:5 90:11 85:15 80:20 70:30

Flow index, n 0.8555 0.8298 0.7374 0.7582 0.7260 0.7304

Flow activation

energy Ea (KJ/mol)

113.02 91.34 89.01 61.99 72.53 68.89

236 POLYLACTIC ACID

processing temperatures for the blends. In other words, PLA/PBAT blends have a broad processing temperature window dueto the low viscosity sensitivity to temperature.

6.7.2 Blend with Layered Silicate Nanocomposites

The steady shear rheological behavior of pure PLA and aseries of intercalated PLA/organically modified MMT areshown in Figure 6.8 (Ray and Okamoto 2003). In the studyby Ray and Okamoto (2003) the amounts of MMT used were2 wt%, 3 wt% and 4.8 wt%�these are abbreviated as PLACN3,PLACN5, and PLACN7, respectively. The measurements wereconducted on Rheometric Dynamic Analyzer (RDAII) at175�C using 25-mm diameter cone and plate geometry with acone angle of 0.1 rad. The plot shows that the shear viscosityof the PLACNs is enhanced considerably at all shear rates withtime, and at a fixed shear rate it increases monotonically withincreasing MMT content. All the intercalated PLACNs exhibitstrong rheopexy behavior, and this behavior becomes promi-nent at a low shear rate ( _γ5 0.001 s21), while pure PLA exhi-bits a time independent viscosity at all shear rates. Atincreasing shear rates, the shear viscosity attains a plateau aftera certain time (indicated by the arrows in Figure 6.8), and thetime required to attain this plateau decreases at higher shearrates. A possible reason for this behavior may be the planaralignment of the MMT particles towards the flow directionunder shear. When shear rate is very slow ( _γ5 0.001 s21)MMT particles take a longer time to attain complete planaralignment along the flow direction, and this measurement time(1000 s) is too short to attain such alignment. For this reasonnanocomposites show strong rheopexy behavior. However,under slightly lower shear rates (0.005 s21 or 0.01 s21) thismeasurement time is enough to attain such alignment, andhence, nanocomposites show time-independent shear viscosityafter a certain time.

The shear rate dependence of viscosity for pure PLA andvarious PLACNs measured at 175�C is plotted in Figure 6.9.Pure PLA exhibits almost Newtonian behavior at all shear


rates, while the PLACNs exhibited non-Newtonian behavior.At very low shear rates, the shear viscosity of the PLACNsinitially exhibit some shear-thickening behavior, and this

104

105

104

101 102 103

Time/s

105

104

105

103

104

PLA

PLACN3

PLACN5

Vis

cosi

ty, η

/Pa

·s

Temperature = 175 °C

PLACN7

Shear rate = 0.001/sShear rate = 0.005/sShear rate = 0.01/s

Figure 6.8 Steady shear viscosity of PLA and various PLACNs as afunction of time (Ray and Okamoto 2003).

238 POLYLACTIC ACID

corresponds to the rheopexy as observed at very low shear rates(see Figure 6.8). Consequently, all PLACNs show a very strongshear-thinning behavior at all measured shear rates.Additionally, at very high shear rates, the steady shear viscosi-ties of PLACNs are comparable with that of pure PLA. Theseobservations suggest that at high shear rates the silicate layersare strongly oriented towards the flow direction, and that thepure polymer dominates shear-thinning behavior.

6.7.3 PLA/Polystyrene Blend

Hamad et al. (2010) investigated blending fossil-basedpolystyrene with PLA to improve the stiffness of the blendingwhile determining its rheological behavior at a high shearrate. The mechanical properties of PLA/polystyrene will notbe discussed in this section. However, the rheological proper-ties of the PLA/polystyrene blend was studied using aDavenport 3/80 capillary rheometer at 165, 175, 185 and195�C, and capillaries of L/R5 8, 15, 25 and 36. The blendswere prepared using a laboratory scale single-screw extruder

105

104

103

10–4 10–3 10–2

Temperature = 175 °C

γ/s–1.10–1 100 101

η /P

a·s

PLAPLACN3PLACN5PLACN7

Figure 6.9 Steady shear viscosity of PLA and various PLACNs as afunction of shear rate (Ray and Okamoto 2003).


at ratios of 30 wt%, 50 wt% and 70 wt% of polystyrene,abbreviated as PLA70, PLA50 and PLA30, respectively(Hamad et al., 2010). The flow curves of these blends areshown in Figure 6.10 for sample melts at 165�C. It can beseen that the linearity of these lines is excellent, and theyobey the power law in a certain range of shear rates. Thevalues of power-law index n, which is calculated from theslope of the fitted lines, are less than 1. This implies that thePLA/PS blend melts are pseudoplastic, similar to most ther-moplastic polymeric melts. Figure 6.11 shows the plot of trueviscosity versus true shear rate for PLA/PS blends at 165�C.PLA, PS and their blends exhibit a typical shear-thinningbehavior over the range of the studied shear rates. This behav-ior is possibly due to the arrangement of chain segments ofpolymers in the direction of applied shear stress.

The plot of true viscosity and PLA content in the blend atshear rates of 10 s21 and 100 s21 is shown in Figure 6.12. Itcan be seen that the viscosity of polystyrene is higher than thatof pure PLA, and the viscosity of the blend increases withincreasing polystyrene content. As polystyrene contentincreases, this effect is clearly observed. This phenomenon isdue to the inherent high viscosity of polystyrene. These results

100000

100000.01 0.1 1 10

Apparent shear rate (s–1)

App

aren

t she

ar s

tres

s (P

a)

PLA0PLA30PLA50PLA70PLA100

Figure 6.10 Flow curves of PLA/PS blends (165�C, L/R5 15) (Hamadet al., 2010).

240 POLYLACTIC ACID

are important because they indicate that the optimal processingconditions for shaping operations of PLA/polystyrene blendscould be quite different as compared to those for pure PLA. Byadding 30% PLA to polystyrene, the true viscosity (at_γ5 10 s21) drops by a factor of 0.7; this could be due to poorcompatibility between PLA and polystyrene.

1000000

100000

10000

100

1000

0.01 0.1 1 10

True shear rate (s–1)

True

vis

cosi

ty (

Pa

·s)

PLA0PLA30PLA50PLA70PLA100

Figure 6.11 True viscosity versus true shear rate of the blends(165�C, L/R5 15).

25000

20000

15000

10000

5000

00 10 20 30 40 50

PLA content (wt%)

True

vis

cosi

ty (

Pa

·s)

60 70 80 90 100

10

100

γ (s–1)

Figure 6.12 True viscosity versus PLA content (wt%) (165�C,L/R5 15).


The plots of true viscosity versus 1/T for PLA70 (L/R5 15)at a constant shear stress (τ) and a constant shear rate ( _γ) areshown in Figure 6.13.

The flow activation energy at constant shear stress (Eτ) andat constant shear rate (E _γ) can be obtained from the slope ofthe graphs as follows:

Eτ 5Rdlogηrd 1

T

� !

τ

(6.10)

E _γ 5Rdlogηrd 1

T

� !

_γ

(6.11)

The values of Eτ and E _γ for PLA70 are listed in Table 6.7.It can be observed from both tests at constant shear stress

and constant shear rate that the melt viscosity is reciprocal oftemperature. The melt viscosity is relatively related to thestructure and free volume, whereby the increase in temperaturemight result in the enhancement of free volume and theimprovement of chain mobility. Thus, viscosity graduallydecreased exponentially with rising temperature. It is wellknown that the value of flow activation energy reflects the tem-perature-sensitivity of viscosity; so, higher Eτ or E _γ leads tohigher sensitivity of the blends to temperature. It can be seenfrom the values of Eτ and E _γ that Eτ increases with increasing

10000

1000

100

102.1 2.15 2.2 2.25 2.3

1/T × 10+3 (K–1)(a)

True

vis

cosi

ty (

Pa

·s) 2.13

τ × 10–4 (Pa)

2.983.894.73

10000

1000

1002.1 2.15 2.2 2.25 2.3

1/T × 10+3 (K–1)(b)

True

vis

cosi

ty (

Pa

·s) 9.71

γ (s–1)

20.7631.554.21

Figure 6.13 True viscosity versus 1/T of PLA70 at a constant(a) shear stress and (b) shear rate (L/R5 15).

242 POLYLACTIC ACID

shear stress, while E _γ reduces with the increasing of shear rate.

Also, it can be seen that Eτ.E _γ andE _γEτ

� , 1, which confirms

that PLA70 is a pseudoplastic material (Han 2007).

6.8 Conclusion

The rheological properties of amorphous and semicrystallineforms of PLA have a significant influence on processability.Although different types of PLA and blends have been studied,many results have indicated that PLA maintains non-Newtonianpseudoplastic behavior when subjected to high-shear conditions.Several models have been developed to represent the rheologicalbehavior of PLA and its blends. Such models are important forpredicting processing behavior and unveiling the molecularinteractions under shear effects. Because of the growth of PLAapplications, it is thought that modification of the rheologicalproperties and processability of PLA will enhance the develop-ment of polymer production technology in the future.

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poly(lactides). Effect of molecular weight and temperature on the

viscoelasticity of poly(l-lactic acid). J. Polym. Sci. Part B:Polym.

Phys. 37, 1803�1814.

Table 6.7 Values of Flow Activation Energy for PLA70 Blend ata Constant Shear Stress and a Constant Shear Rate

Shear Stress,τ 3 1024 Pa

Eτ (KJ/mol) Shear Rate,_γ (s21)

E _γ (KJ/mol)

2.13 108.9 9.71 54.04

2.98 111.4 20.76 52.71

3.89 119.8 31.5 51.96

4.73 126.04 54.21 50.21


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Onogi, S., Kato, H., Ueki, S., Ibaragi, T., 1966. J. Polym. Sci: Part C

15, 481�494.

244 POLYLACTIC ACID

Palade, L.-I., Lehermeier, H.J., Dorgan, J.R., 2001. Melt rheology of

high content poly(lactic acid). Macromolecules 34, 1384�1390.

Perego, G., Cella, G.D., Bastioli, C., 1996. Effect of molecular

weight and crystallinity on poly(lactic acid) mechanical properties.

Polymer 59, 37�43.

Ray, S.S., Okamoto, M., 2003. New polylactide/layered silicate nano-

composites, 6a melt rheology and foam processing. Macromol.

Mater. Eng. 288, 936�944.

Spinu, M., Jackson, C., Keating, M.Y., Gardner, K.H., 1996.

Material design in poly(lactic acid) systems: block copolymers,

star homo- and copolymers, and stereocomplexes. J. Macromol.

Sci. A 33, 1497�1530.

Tsuji, H., Ikada, Y., 1996. Blends of isotactic and atactic poly(lac-

tide)s. 2. Molecular-weight effects of atactic component on crys-

tallization and morphology of equimolar blends from the melt.

Polymer 37, 595�602.

Van Dijk, J.A.P.P., Smit, J.A.M., Kohn, F.E., Feijen, J., 1983.

Characterization of poly(d,l-lactic acid) by gel permeation chroma-

tography. J. Polym. Sci. Polym. Chem. 21, 197�208.

Witzke, D.R., 1997. Introduction to properties, engineering, and pro-

spects of polylactide polymers, PhD thesis, Michigan State

University, East Lansing, MI.

Xu, K., Kozluca, A., Denkbas, E.B., Piskin, E., 1996. Synthesis and

characterization of PDLLA homopolymers with different molecu-

lar weights. J. Appl. Polym. Sci. 59, 561�563.


7 Degradation and Stability ofPoly(lactic Acid)

Chapter Outline7.1 Introduction 2477.2 Factors Affecting PLA Degradation 2487.3 Hydrolytic and Enzymatic Degradation of PLA 2557.4 Environmental Degradation of PLA 2657.5 Thermal Degradation of PLA 2787.6 Flame Resistance of PLA 2887.7 Conclusion 295References 295

7.1 Introduction

As discussed in Chapter 6, poly(lactic acid) or polylactide(PLA) is known for its environmental credit, being consider-ably ‘greener’ than commodity plastics such as polyethylene,polypropylene, polystyrene and poly(ethylene vinyl acetate) forpackaging applications. Although several aliphatic polyesters,including polycaprolactone (PCL), polyhydroxyalkanoates(PHA) and poly(butylene succinate) (PBS), are also biodegrad-able, PLA has the advantage of being produced by lactic acidfermentation from sugar, enabling mass production. While PCLand PBS are also biodegradable polymers, both are producedfrom petrochemical sources. This further underlines the advan-tage of PLA, the production of which has lower greenhousegas emissions. However, PHA still requires further develop-ment in order to improve its production for better yield.

Understanding the biodegradability and biodegradation ofPLA is crucial for the plastic industry in order to meet the currentstrict environmental regulations. Furthermore, PLA and its copo-lymers have been used for medical applications for decades, andso evaluation and control of its biodegradation in the living body

247Polylactic Acid. DOI: http://dx.doi.org/10.1016/B978-1-4377-4459-0.00007-X


http://dx.doi.org/10.1016/B978-1-4377-4459-0.00007-X

has been essential. Currently, most of the PLA on the market issynthesized through ring-opening polymerization of lactide,which is the cyclic dimer of lactic acid. Lactic acid possesses Dand L stereoisomers, and the stereoisomer make up has a signifi-cant influence on the mechanical properties and the biodegrad-ability of the resulting PLA. The L-form of lactic acid isnaturally produced from the fermentation action of microorgan-isms. D-lactic acid is occasionally produced in small amounts bysome bacterial species. Chemical synthesis substantially contri-butes to PLA production. Since D-lactic acid does not occur innature in significant quantities, the ability of cells and microor-ganisms to metabolize this form is nonexistent or very low. Mostdegradation of D-lactic acid is through the hydrolysis reaction, toconvert it into simple molecules. After polymerization, the steor-eoforms of PLA � poly(L-lactide) (L-PLA), poly(D-lactide) (D-PLA) and poly(DL-lactide) (DL-PLA) have shown differences inmelting points and crystallinity, depending on the isomer compo-sition of the PLA. In the development of PLA for biomedicalpurposes, the manipulation of average molecular weight (Mw)plays an important role in controlling the erosion of PLA. Theaddition of the D-lactide isomer can also help to reduce PLAdegradability in body fluids and tissues. This is due to the factthat mammals do not produce a suitable enzyme to act on D-lac-tic acid. Consequently, the hydrolysis reaction is believed to takepart in reducing D-lactic acid before assimilation by the liver.Although PLA has been known about and used for decades, theinformation about its degradation and consumption by microor-ganisms and living tissue has remained limited (Tokiwa andCalabia, 2006). This chapter aims to review the degradation ofPLA through the action of microorganisms, enzymes and in liv-ing tissues, and via thermal-irradiation and fire.

7.2 Factors Affecting PLA Degradation

The degradation of polymers occurs mainly as a result ofattack by external elements. This is because polymer chains arehighly stable and seldom undergo autocatalysis. Although

248 POLYLACTIC ACID

PLA is produced from the lactic acid produced by an organicprocess (fermentation of sugars by bacteria), its conversionto PLA results in significant changes to the biological andchemical degradation mechanism. PLA is unable to be directlybroken down and consumed by living cells as effectively aslactic acid itself. The stereochemistry, crystallinity and molecu-lar weight are the main factors that influence the biodegrada-tion behavior of PLA.

First, several terms need to be clarified to enable a betterunderstanding of the degradation mechanism. The definitions ofthese terms are summarized in Table 7.1. It is important to dif-ferentiate between the ‘biodegradation’ that occurs in the envi-ronment and that which occurs in living tissue. This is becausebiodegradation in the environment is initiated by the action ofmicroorganisms, whereas biodegradation in tissue relates to thedegradation process that happens in vivo or in vitro in responseto enzymes and the components in cells or body fluids. PLA is abiopolymer that has found application in both the domestic andbiomedical fields. It can be used as a packaging material as wellas for sutures and implants for surgery.

Generally, the degradation of a polymer is inherently influ-enced by the chemical bonding. The low reactivity backbone ofa polymer is barely attacked by external elements. This is obvi-ous for polymers free of electronegative elements, especiallyoxygen, as they can remain unchanged for longer becausethey are unlikely to be hydrolyzed. Gopferich (1996), in hisreview paper, compared some of the hydrolyzable polymers ofpoly(anhydrides), poly(ortho esters) and poly(esters) (seeTable 7.2). He found that the oxygen-bearing backbone ofpoly(anhydrides) and poly(ortho esters) was the most reactiveto undergo hydrolysis. PLA belongs to the group of polyesters,and requires a longer time to reach its half-life of hydrolysis.This is due to steric effects: the voluminous alkyl group hindersthe attack of water (Gopferich, 1996). Poly(vinyl alcohol)(PVOH) is another type of hydrolyzable polymer. PVOH hasa higher rate of hydrolysis in the presence of hydroxylgroups (aOH) as the pendant can easily form hydrogen bonds.Although PLA is a polar polymer like PVOH, it acts as a

2497: DEGRADATION AND STABILITY OF POLY(LACTIC ACID)

Table 7.1 Definitions of Common Biological Terms Relating toBiopolymers

Biodegradables1

(environment)

Polymers that can be broken down through

the action of aerobic microorganisms to

CO2, water and mineral salts

(mineralization). In the absence of

oxygen, microorganism-driven

degradation of these polymers produces

CO2, methane, mineral salts and new

biomass

Biodegradables2

(in vivo)

Polymers that can be broken down in vivo

through the action of macromolecular

degradation. Biological elements in the

body attack the polymer system/implant.

However, there is a lack of data about the

elimination of fragmented

macromolecules from the body. Body

fluids may transport the fragments from

the original site for elimination from the

body after hydrolysis

Bioresorbables2 Polymers that can be fully eliminated from

the body. These polymer implants undergo

bulk degradation and are resorbed in vivo

and then naturally metabolized. Such

bioresorbable polymers do not cause side

effects

Bioerodibles2 Similar to bioresorbables. However, with

these polymers the focus is on surface

breakdown in vivo

Bioabsorbables2 These polymers can be dissolved in body

fluids with minimal change to their

original molecular weight. These polymers

are mainly used as slow water-soluble

implants

1Summarized term from British Standard Institutions BS EN 13432 (2005);2summarized term from Woodruff and Hutmacher (2010).

250 POLYLACTIC ACID

hydrophobic polymer, with a lack of moisture-sensitive behav-ior. Prolonged exposure of PLA to water is needed in order toinitiate the hydrolysis process in relation to microorganisms ortissue/organ assimilation.

Copolymer compositions also affect polymer degradation.Table 7.3 shows the approximate degradation times for neatpolymers and their derived copolymers. One of the main rea-sons for the change in degradation kinetics of a copolymer isthat the additional monomer affects the crystallinity andreduces the steric effects (Hiemenz, 1984). The rate of chaincleavage has been found to be accelerated with increasingglycolide portion. Conversely, however, copolymerization of

Table 7.2 Half-Lives for Degradation ofHydrolyzable Polymers (Dependent onMolecular Weight)

Polymer Half-Life

Poly(anhydrides)1 0.1 h

Poly(ortho esters)1 4 h

Poly(vinyl alcohol)2 23 h

Poly(esters)1 3.3 yr

1Gopferich (1996);2Yamaoka et al. (1995).

Table 7.3 Degradation Time of Biopolymers and TheirCopolymers

Polymer System Approximation ofDegradationTime (Months)

Polylactide 6�12

Polyglycolide .24

Polycaprolactone .24

Poly(D,L-lactide-co-glycolide) 5�6

Poly(L-lactide-co-D,L-lactide) 12�16

Poly(D,L-lactide-co-caprolactone) .24


L-lactide with D,L-lactide increases the degradation time. Thisis due to the oligomer D-lactic acid, which is unlikely to benaturally degraded by the body’s enzymes. This approach helpsto prolong the functionality of PLA implants in the humanbody. PCL, a biopolymer consumable by bacteria and fungi butnot by mammalian bodies due to the lack of suitable enzymes(Vert, 2009), is polymerized with lactide to yield a copolymerwith a prolonged degradation time. This biopolymer undergoeshydrolytic degradation in the early stage, and proceeds to sur-face and bulk degradation pathways. Manipulation of copoly-mer composition is very important in the development ofdesirable media for controlled release drugs in body (Gopferichet al., 1995).

Molecular weight and crystallization are important factorsaffecting the degradation of polymers. Research on PLA (Tsujiand Miyauchi, 2001; Zhou et al., 2010; Itavaara et al., 2002;Sodergard and Nasman, 1994) has shown that the crystallinepart of PLA is more resistant to degradation than the amor-phous portion. Tsuji and Miyauchi (2001) found that even theamorphous regions that exist between the crystalline regionshave good hydrolysis resistance compared to the fully amor-phous regions of amorphous PLA. Hydrolysis is the prelimi-nary stage for both microorganism-based and enzymaticdegradation, because the cleavage of macromolecules providesa larger surface area for further effective reactions. Typicalcrystallization of the polymer depends on the composition ofthe copolymer as well. The glycolide in poly(lactide-co-glyco-lide) decreases the crystallinity of this copolymer, because thedifferent molecular size of the monomer prevents the rear-rangement of chains in a compact crystal structure. Gilding andReed (1979) found that poly(lactide-co-glycolide) that con-tained 25�65 mol% of glycolide remained amorphous,although both neat polylactide and polyglycolide have about35�55% crystallinity (see Figure 7.1). An amorphous type ofcopolymer is desired for use as a drug delivery carrier, wheresimultaneous mass loss can promote good dispersion ofactive agents. In the case of sutures or physical implants, wheremechanical strength is desired, the composition of glycolide

252 POLYLACTIC ACID

should be reduced for better physical performance over time(Gilding and Reed, 1979).

As already mentioned, in addition to crystallinity, molecularweight plays an important role in the degradation of PLA. Infact, most of the pharmaceutical/medical grades of PLA are cate-gorized according to their intrinsic viscosity, which is an indirectmethod of determining molecular weight. Measurement of intrin-sic viscosity is easier for quality control purposes than the use ofchromatography, because the latter is more expensive and timeconsuming. Nevertheless, intrinsic viscosity measurement shouldbe used with caution of accuracy when dealing with sensitiveproducts. Researchers have observed that high-molecular-weightpolyesters are degraded at slower rate (Saha and Tsuji, 2006;Burkersroda et al., 2001). This is due to the fact that the high-molecular-weight molecules have greater entanglement, whichmeans that they resist hydrolysis for chain cleavage. The oligo-mers from the initial surface degradation tend to form an inter-mediate medium and this is metabolized by living cells andmicroorganisms (Tokiwa and Calabia, 2006).

Water uptake and acidity are also the important factorsinfluencing the degradation of biopolymers. Normally, wateruptake is related to hydrolytic degradation, where the watermolecules react to fragment the polymer; this is also knownas reverse polycondensation (Sodergard et al., 1996). The

50

40

30

Per

cent

age

crys

talli

nity

20

10

0 20 40 60Mole % glycolide units in copolymer

80 100

Figure 7.1 Percentage of crystallinities for glycolide/lactide copolymeras a function of composition determined by X-ray and differentialscanning calorimetry measurements (adapted from Gilding and Reed,1979).


water-uptake-induced hydrolysis process is an important mech-anism that ensures the functionality of biopolymers in biologi-cal systems and their degradation by microorganisms. Theextent of water uptake depends on the morphology, molecularweight, purity, shape of the specimen and the processing his-tory of the polymer. For instance, a crystal structure can reducethe ability of water permeation. This can be achieved via copo-lymerization or the quenching process of the polymer. Wateruptake of aliphatic polyesters leads to the splitting of esterbonds; subsequently, the oligomers can be assimilated by livingcells. Acidity controls the rate of reaction of ester splittingthrough catalysis (Vert et al., 1991). By comparing poly(glyco-lic acid) and poly(lactide-co-glycolide) sutures, Chu (1982) dis-covered that the breaking strength of an entire suture dependson pH, especially at high and low pH values. Under acidic andbasic conditions, the ion exchange can be effectively taken partto promote a stable condition when chain cleavage occurs.

The in vivo degradation mechanisms according toHutmacher (2001) are illustrated in Figure 7.2 for typicalresorbable polymers such as PLA. Initially, the hydration

Hydration

100%

50%

0%

0 6 9

Mass loss

Molecular weight loss

Number of months

12 18

HydrationDegradation

DegradationMass loss

ResorptionMetabolization

Metabolization

Figure 7.2 Degradation stages of resorbable polyester-types ofpolymer (adapted from Hutmacher, 2001).

254 POLYLACTIC ACID

process occurs over the first 0�6 months, during which massloss occurs while the molecular weight remains unchanged.Excess water is required to penetrate the higher molecular-weight structure to initiate the hydrolysis reaction with the esterbonds. After prolonged accumulation of water in the polymer,the ester bonds are cleaved, generating water-soluble mono-mer-oligomers. Lactic acid monomers are formed, causinghydration degradation during the 6�9 month period. Suchmonomers diffuse into the body fluids, leading to significantmass loss. The cleaved monomers and oligomers are furthertransferred to the liver to be metabolized. During this stage, thelactic acid in the body fluids is subjected to enzymatic degrada-tion, but this is only limited to L-lactic acid as the body doesnot produce a D-lactic acid enzyme. Thus, D-lactic acid needsa longer period of time to undergo hydrolytic degradation,being finally reduced to carbon dioxide and water before beingeliminated from the body. From the curve it can be seen thatthe final mass loss of the entire bioresorble polymer occurs bythe ninth month, with the molecular weight gradually beingreduced. This is in agreement with what we know about therate of the hydrolytic process, which is slow, the polymer beingfragmented only after prolonged immersion in water or bodyfluids.

7.3 Hydrolytic and Enzymatic Degradationof PLA

Hydrolysis, also known as hydrolytic degradation, is themajor degradation mechanism of PLA. It is an autocatalyticprocess yielding carboxylic acid, i.e. the lactic acid helps tocatalyze the hydrolysis process. This has been observed in astudy, where a thick sample was immersed in a buffer of pH7.4 at 37�C; bulk hydrolysis occurred at a higher rate than thesurface hydrolysis (Henton et al., 2005). This can be explainedby the fact that the surface of the thick PLA sample was incontact with the buffer and the lactic acid generated from thehydrolysis of PLA end group at the surface could easily


diffuse, and the exterior pH was maintained at pH 7.4.However, the interior of the PLA sample cleaved at a higherrate because the acid produced had a lower rate of diffusion tothe buffer medium; thus, the accumulation of lactic acid fromthe cleaved PLA end groups induced the autocatalytic reaction.This hydrolytic degradation mechanism is illustrated inFigure 7.3, where a hollow sample is formed during degrada-tion, due to the misconception that degradation initiates fromthe outer layer.

The study of PLA hydrolysis has been performed in aqueousmedia, such as phosphate-buffered solutions or water, at 37�Cto simulate its degradation in body fluids at the appropriatetemperature. Studies have also been done at higher tempera-tures, in acidic solutions, alkaline solutions or buffered solu-tions, with the addition of enzymes, in order to determine thehydrolytic effects of PLA under severe and accelerated condi-tions (Tsuji et al., 2004). When hydrolysis of crystallizedPLLA was carried out at temperatures below its melting point,it was found that the amorphous region suffered substantial

(a)

Degradationproducts

Deg

ree

of

Deg

rada

tion

time

(b) (c)

degr

adat

ion

Figure 7.3 Degradation modes for biopolymers under: (a) surfaceerosion, (b) bulk degradation, and (c) bulk degradation withautocatalysis (adapted from Woodruff and Hutmacher, 2010).

256 POLYLACTIC ACID

losses regardless of the hydrolysis media and it maintained acrystalline chain.

Tsuji (2002) conducted an investigation into the hydrolysisof an amorphous form of PLA, to determine the effects ofL-lactide content, tacticity and enantiomeric polymer blends.In this work four samples were prepared�poly(D,L-lactide),poly(L-lactide), poly(D-lactide) film and the blend sample ofpoly(L-lactide) and poly(D-lactide). The results are summa-rized in Table 7.4, which also covers a complementary studythat explored the effects of hydrolysis in terms of molecularweight and its distribution, glass transition temperature, crystal-lization temperature, melting temperature and mechanicalproperties.

Tsuji (2002) found that the copolymer of poly(D,L-lactide)showed significant weight losses compare to the homopolymer�either poly(D-lactide) or poly(L-lactide)�as indicated byFigure 7.4. When both poly(D-lactide) and poly(L-lactide) areblended together, the weight losses due to hydrolysis are notsignificant. The weight losses of the copolymer of poly(D,L-lactide) is mainly caused by the effect of the molecular rear-rangement, which disrupts the crystalline compact structure inrelation to molecular tacticity. The poly(D-lactide), poly(L-lactide)and the blend of poly(D-lactide) and poly(L-lactide) are com-prised totally of isotactic structures. In contrast, poly(DL-lactide)consists of a predominantly isotactic sequence with minor atacticsequences. Consequently, water molecules can easily migrate inbetween the disordered helical conformation of the DL chainsand interact effectively with the inside of the sample to promoteautocatalysis. Although blending of stereocomplex homopoly-mers can affect the structural rearrangement of the polymer chain,the weight of the polymer remains unchanged for 24 months.This indicates that the neat homopolymer possesses strong struc-tural properties, preventing hydrolysis from occurring, while thewater-soluble oligomers formed in between the blending regionsare believed to become trapped in the strongly interacted structure(Tsuji, 2002).

Although the weights of PLA films do not show significantlosses over time, the average molecular weight, Mn, changes


Table 7.4 Characteristics of Amorphous-Made PLA FilmsBefore and After Hydrolysis in Phosphate-Buffered Solution(pH 7.4) at 37�C for 16 Hours (D,L Copolymer Film) or 24 Hours(L, D, and L/D Blend Film) (Tsuji, 2002)

Properties Form of PLA BeforeHydrolysis

AfterHydrolysis

Mn/105 (g/mol) D,L copolymer 3.7 0.02

L homopolymer 5.4 0.23D homopolymer 4.4 0.15L-D blend 4.4 0.38

Mw/Mn D,L copolymer 2.0 6.3L homopolymer 2.2 2.9D homopolymer 1.9 3.5L-D blend 2.1 2.1

Glass transitiontemperature,Tg (

�C)

D,L copolymer 54 �a

L homopolymer 68 65D homopolymer 68 62L-D blend 69 68

Crystallizationtemperature,Tc (

�C)

D,L copolymer � �L homopolymer 109 87D homopolymer 112 85L-D blend 101 91

Homo-crystallinemeltingtemperature,Tm,H (�C)

D,L copolymer � �L homopolymer 177 173D homopolymer 178 171L-D blend 177 175

Stereo-complexmeltingtemperature,Ts,H (�C)

D,L copolymer � �L homopolymer � �D homopolymer � �L-D blend 222 229

Tensile strength(kg/mm2)

D,L copolymer 4.0 0.0L homopolymer 4.8 1.4D homopolymer 5.2 0.3L-D blend 4.2 1.5

Young’s modulus(kg/mm2)

D,L copolymer 184 0L homopolymer 183 99D homopolymer 209 34L-D blend 155 132

Elongation atbreak (%)

D,L Copolymer 21.0 0.0L homopolymer 6.5 0.8D homopolymer 5.3 0.2L-D blend 14.5 1.2

258 POLYLACTIC ACID

100

80

60

40

20

00 4 8 12

Hydrolysis time/months

Rem

aini

ng w

eigh

t/%

16 20 24

Figure 7.4 Remaining weight of copolymer poly(D,L-lactide) e,homopolymer poly(L-lactide) K, homopolymer poly(D-lactide) ’ andhomopolymers blend of poly(L-lactide) and poly(D-lactide) x as afunction of hydrolysis time (adapted from Tsuji, 2002).

40 60 80 100 120 140Temperature (°C)

(a)

160 180 200 40 60

60

40

20120

600

1440

End

o. ←

→ E

xo.

End

o. ←

→ E

xo.

0 (min)0 (min)160 °C

ΔHcc peak

120 °C

80 100 120 140Temperature (°C)

(b)

160 180 200

Figure 7.5 Differential scanning calorimetry thermograms of PLLA at:(a) 120�C and (b) 160�C (adapted from Tsuji et al., 2008).


significantly over time, as shown in Figure 7.5. The copolymerof poly(D,L-lactide) shows the greatest change over a 16-month period, while the homopolymer and its blends reducegradually. This provides evidence that the copolymer has aweaker structure, which allows water molecules to migratefreely while inducing an autocatalysis reaction, resulting in theaccumulation of catalytic oligomers formed by hydrolysis. Thehomopolymer, on the other hand, has a strong migration-lower-ing structure and this causes the hydrolysis reaction to proceedin a moderate manner. The rate of hydrolysis of the PLA canbe represented using the following equation with the k coeffi-cients as summarized in Table 7.5:

ln Mnðt2Þ5 ln Mnðt1Þ2 kt (7.1)

where, Mn(t2), Mn(t1) are the average molecular weight Mn athydrolysis times of t2 and t1.

Moreover, according to the data in Table 7.4, the tempera-ture values of glass transition (Tg), crystallization (Tc), andmelting for homo-crystallites (Tm,H) and stereocomplex crystal-lites (Tm,S) were reduced after undergoing the hydrolysis pro-cess. Poly(L-lactide), poly(D-lactide) and blends of bothconsisting of the homopolymer, upon crystallization formhomo-crystallites, while the copolymer poly(D,L-lactide) formsstereocomplex crystallites. This indicates that the hydrolysis isa chain cleavage process, which reduces the molecule weightof the polymer and results in oligomers, which reduce the for-mation of crystallites. It has been found that the Tg, Tc, and Tm,H

values of the poly(L-lactide) and poly(D-lactide) blend are higher

Table 7.5 Rate of Hydrolysis of PLLA, PDLA, PDLLA andBlends

Polymer Value k � See Eq (7.1)

Homopolymer poly(L-lactide) 3.493 10�3 day�1

Homopolymer poly(D-lactide) 3.883 10�3 day�1

Copolymer poly(D,L-lactide) 7.223 10�3 day�1

Blending of homopolymers 2.963 10�3 day�1

260 POLYLACTIC ACID

than the rest. This is in agreement with the molecular weight ofMn and the molecular weight distribution Mw/Mn remainsunchanged after 24 months of hydrolysis. It is shown that theblending of poly(L-lactide) and poly(D-lactide) has markedlystrong interactions, which retard the occurrence of hydrolysis.This phenomenon was observed by Tsuji (2000), who foundthat well-stereocomplexed D and L blends of polylactide canpromote a three-dimensional network structure in the amor-phous region. These findings are relevant to the biomedicalapplications of PLA in relation to controlling the degradationof implants. It is known that D-lactic acid cannot be brokendown by enzymes in the body, while the existence of tacticitycontributes to the unusually strong interactions in copolymerpoly(D,L-lactide), which retards the hydrolysis degradationequally.

Tsuji et al. (2008) further extended their study on the hydro-lysis of PLA at elevated temperatures. The thermal propertiesof hydrolytically degraded poly(L-lactide) under different con-ditions are summarized in Table 7.6. It is clear that the PLLAexhibits cold crystallization with the presence of ΔHcc for spe-cimens degrading at temperatures above 160�C. The cold crys-tallization results from the rearrangement of the amorphousregions into a crystalline phase (Wellen and Rabello, 2005).The re-crystallization process of PLLA at high-temperaturehydrolytic degradation induces the formation of wide amorphousregions with a chain cleavage reaction. This is proven from theresults of Tsuji et al. (2008) by comparing the molecular weight,Mn, of PLLA at 120�C and 160�C in Figure 7.6. On reaching anelevated temperature, the molecules in the amorphous regiontend to rearrange into a more stable crystalline state and, thus,undergo an exothermic process.

In spite of that, hydrolytic degradation at elevated tempera-tures with increased exposure has shown a reduction of meltingtemperature (Tm) and percentage of crystallinity (Xc) of PLLA.The Tm and Xc are interrelated: the crystalline structure of thepolymer requires higher thermal exposure to induce molecularvibration (i.e. ΔHm) in order free it from the lattice. The Xc isa measure of crystallinity of a polymer, and includes cold


crystallization and enthalpy of melting following equation (7.2).The ΔHmc of PLLA with infinite sized crystals is 135 J/g, asreported by Miyata and Masuko (1998). The loss of crystallinityis due to the increase of lattice disorder due to hydrolyticdegradation.

Table 7.6 Thermal Properties of Hydrolytically DegradedPoly(L-lactide) (Tsuji et al., 2008)

DegradationConditions

Thermal Properties

Temperature(�C)

Time(Min)

Tg

(�C)Tcc

(�C)Tm

(�C)ΔHcc

(J/g)ΔHm

(J/g)Xc

(%)

� 0a 63.3 � 171.9 � 37.0 27.2

120 120 55.5 � 173.8 � 67.6 50.1

600 �b � 169.5 � 79.0 58.5

1440 �b � 167.1 � 92.0 68.1

140 60 55.0 � 174.3 � 64.7 47.9

120 44.1 � 169.9 � 66.9 49.6

210 �b � 163.8 � 65.5 48.5

150 40 53.1 � 173.9 � 62.1 46.0

80 35.8 � 171.1 � 57.4 42.5

120 �b � 164.2 � 41.4 30.7

160 20 56.2 90.4 171.4 211.6 52.4 30.2

40 54.1 91.5 165.9 214.1 56.0 31.0

60 48.2 96.4 150.4 240.8 41.2 0.3

170 10 59.3 113.3 173.0 239.4 39.9 0.4

20 55.4 97.0 168.4 250.8 51.2 0.3

40 �b 87.9 127.1 218.5 18.5 0

180 5 59.7 115.4 172.8 238.4 39.2 0.6

15 53.6 96.1 166.3 247.3 47.5 0.1

30 �b 90.4 119.3 211.6 12.0 0.3

190 5 58.0 99.4 169.4 251.4 51.7 0.2

10 56.1 98.9 169.1 247.1 47.4 0.2

20 33.4 96.6 136.4 234.8 34.9 0.1

aBefore hydrolytic degradation;bglass transition was too diffuse to estimate Tg.

262 POLYLACTIC ACID

Xc 5ðΔHcc 1ΔHmÞ

ΔHmc

3 100% (7.2)

The hydrolytic degradation of PLLA at high temperaturescauses a loss of molecular weight as well as an increase in themolecular weight distribution. This is similar to the bulk ero-sion mechanism found in PLLA. The typical sharp peak asshown in Figure 7.7 is obtained from a gel permeation chroma-tography (GPC) spectrum of PLLA after hydrolytic degrada-tion, where the wide spread of the peak indicates the largemolecular weight distribution. The hydrolyzed PLLA in

120 °C 160 °C

0 250 500 750 1000 1250 1500

105

104

103

Hydrolytic degradation time (min)0 10 20 30 40 50 60

Hydrolytic degradation time (min)

a Mn

Mn

105

104

103

Mn

a Mn

Figure 7.6 Molecular weight, Mn, in the functions of hydrolyticdegradation time at temperatures of: (a) 120�C and (b) 160�C (Tsujiet al., 2008).

2 3 4 5 6

100 (min)

100

100

80

60

40

20

00 50 100 150 200

80

60

40

Yie

ld o

f lac

tic a

cid

(%)

Yie

ld o

f lac

tic a

cid

(%)

Yield of lactic acid

20

0

2030

180 °C

0 10 20Hydrolytic degradation time (min)

Hydrolytic degradation time (min)

30 40log M

(a) (b)

Figure 7.7 (a) Gel permeation chromatography spectrum; (b)formation of lactic acid of PLLA hydrolytic degradation at atemperature of 180�C (Tsuji et al., 2008).


oligomer form, further reduces to lactic acid. The formation oflactic acid from PLLA resulting from hydrolysis increasesgradually, as shown in Figure 7.7, and the time to achieve thetotal yield of lactic acid depends on the temperature. Tsujiet al. (2008) showed that lactic acid yields exceeding 95%could be successfully attained when degradation was continuedover 4320, 510, 180 and 120 minutes, at 120, 140, 160, and180�C. The hydrolytic degradation can be calculated accordingto equation (7.1) as given in Table 7.7, assuming it to be anautocatalytic mechanism (Tsuji, 2005).

Enzymes can be added to the hydrolysis process to improvethe rate of degradation. Unlike autocatalysis, where degradationis faster in the internal parts compared to the surface, for PLAenzymatic degradation the focus is on the surface with the useof a suitable enzyme, namely proteinase K. PLA is bioassimil-able by microorganisms, including fungi and bacteria, with theaction of proteinase K (Torres et al., 1996). The properties ofproteinase K are listed in Table 7.8. This enzyme preferentiallydegrades L-lactic acid over D-lactic acid (Reeve et al., 1994).Generally, the amorphous phase of PLA is subjected to theattack of the enzyme more than the crystalline region. Reeveet al. (1994) were the first to observe this phenomenon forPLA with 8% D-lactide. MacDonald et al. (1996) found thatcopolymerization of PLA from L-lactide and meso-lactide hadweight-loss rates that were about 43% slower than those for

Table 7.7 Rate of Hydrolysis of PLLA at DifferentTemperatures

Temperature (�C) Value k � See Eq (7.1)

120 1.003 10�2 min�1

140 2.783 10�2 min�1

150 3.773 10�2 min�1

160 7.763 10�2 min�1

170 1.573 10�1 min�1

180 1.933 10�1 min�1

190 2.113 10�1 min�1

264 POLYLACTIC ACID

amorphous PLA films produced by copolymerization ofL-lactide or D-lactide, respectively. This indicates that theselectivity of proteinase K is highly sensitive to the type ofstereochemical structure, which affects crystallinity and, conse-quently, influences the degradation of PLA.

7.4 Environmental Degradation of PLA

Understanding the environmental degradation of PLA is veryimportant because more than 100,000 MT of PLA are producedannually � mainly for consumer products and packaging.Therefore, most of this PLA will be disposed in landfill sitesafter a short period of use. PLA undergoes biodegradation via

Table 7.8 Properties of Proteinase K

Feature Description

Alternative name Peptidase K, protease K

Specificity Cleaves at the carboxyl side of aliphatic,

aromatic or hydrophobic residues

Source Tritirachium album or Engydontium album

Molecular weight 28,900

Form Lyophilized form

Concentration/

activity

.20 units/mg at 35�C

Protease type Serine protease

Uses/applications Molecular biology applications to digest

unwanted proteins, such as nucleases,

from DNA or RNA preparations from

microorganisms, cultured cells, and plants

Reaction conditions 0.05�1 mg/ml proteinase K, pH 7.5�8,

often containing 0.5�1% sodium dodecyl

sulphate

Storage conditions Store at220�CInhibitors Diisopropyl fluorophosphates, phenyl

methane sulphonyl fluoride


aerobic and anaerobic pathways, and depends on the presenceof oxygen for assimilation by bacteria and fungi. Many meth-ods can be used to measure the biodegradation of biopolymers,such as the consumption of oxygen, weight losses, biogas gen-eration and carbon dioxide production.

A number of material properties can influence the biodegra-dation of PLA, including the molecular weight, stereocomplexand crystallinity. At the same time, external aspects, such asmoisture, sunlight, temperature, presence of a solvent and oxy-gen supply, can significantly affect its rate of biodegradation aswell. Massardier-Nageotte et al. (2006) conducted a study onthe aerobic and anaerobic biodegradation of commerciallyavailable plastics. The results are shown in Table 7.9. Thestarch-rich MaterBis sample had the highest mass loss underboth aerobic and anaerobic conditions, while PLA showedmass loss in aerobic conditions, but an insignificant loss ofmass in anaerobic conditions. When the MaterBis and PCLsamples were analyzed in detail it was found that that PCL hadlow biodegradability and the mass loss of the MaterBis samplewas caused predominantly by the starch. This is because starchis a natural material readily consumed by microorganisms, anddoes not need to undergo hydrolysis to cause chain cleavageinto monomers for consumption. In other words, the biodegra-dation of a polymer is not only dependent on the reactivity of

Table 7.9 Weight Losses of Biopolymers under Aerobic andAnaerobic Conditions (Massardier-Nageotte et al., 2006)

Polymer Mass Loss (%)

AerobicConditions

AnaerobicConditions

NatureWorks PLA�polylactide 39.166 10.97 Not significant

MaterBis�polycaprolactone

1 starch

52.916 11.51 44.826 0.88

Eastar Bios�poly(butadiene

adipate-co-terephthalate)

0.436 0.21 Not significant

Polycaprolactone 7.626 0.77 Not significant

266 POLYLACTIC ACID

microbes on the polymer itself, but the chemical degradation ofthe polymer may also affect the degradability prior to beingconsumed by living cells.

Further study of the percentage of biodegradation of differ-ent biopolymers for 7, 14 and 28 incubation days has beenundertaken (Massardier-Nageotte et al., 2006). The results arelisted in Table 7.10. PLA appeared to have the slowest rate ofbiodegradation among the biopolymers. Of the four types ofbiopolymer, only MaterBis was able to generate biogas, atlevels of 58.2, 113.6 and 216.4 ml biogas per gram of samplefor 7, 14 and 28 days, respectively. The researchers concludedthat the biodegradation of PLA was very slow and sufferedfrom a lack of microorganism colonization on the sample sur-face compared with the other biopolymers (see Figure 7.8).Typical data indicates that PLA is durable and can resist degra-dation for a longer time compared to other biopolymers, whilestill maintaining its biodegradable characteristics. It is veryimportant for PLA to maintain its functionality for a range ofapplications that involve long-term use, such as woven fabricsand matting. These products can be used until worn out andthen disposed of for biodegradation, when the material finallytransforms to a harmless residue in the natural environment.

This leads to the question, ‘how long does it take for PLAproducts to fully degrade?’ Kale et al. (2007) conducted a bio-degradability study on polylactide bottles in real and simulatedcomposting conditions. The study used PLA 500 ml bottlesused for packaging spring water sold by Biota of America. ThePLA bottles were fabricated by NatureWorks. The PLA was

Table 7.10 Percentage Biodegradation of Biopolymers underAerobic Conditions (Massardier-Nageotte et al., 2006)

Time (Days) PLA MaterBis Eastar Bios PCL

7 3.2 23.9 4.9 13.7

14 3.6 35.7 11.6 29.3

28 3.7 42.8 15.1 34.8


composed of 96% L-lactide with a bluetone additive, as shownin Figure 7.9. The PLA bottles were subjected to real compost-ing burial and international standard of ASTM D5338 and ISO14855-1 under controlled conditions.

Eastar bio®

Mater-Bi®

Polycaprolactone

Polylactic acid

Initial state

Initial state

Initial state 28 days in solid medium

28 days in solid medium

28 days in solid medium

28 days in solid mediumInitial state

Figure 7.8 Evolution of different biopolymers after 28 days ofincubation (adapted from Massardier-Nageotte et al., 2006).

268 POLYLACTIC ACID

When PLA bottles were buried in a compost pile made ofcow manure, wood shavings, and waste feed (i.e. the feed thatthe cows left) for 30 days, the bottles had totally decomposed bythe end of the test period. Kale et al. (2007) reported that thehigher temperature produced in the compost pile (65�C), as aresult of microbiological action and environmental heat caused adistortion of the PLA bottles in days 1 and 2. This temperatureis higher than the glass transition temperature (Tg) of PLA(60.6�C). The structure of the bottles remained tough until days6 to 9, when a powdery texture appeared on the surface andfragmentation occurred. The bottles lost their structure, and byday 15 a large portion of the bottle had composted. No visibleresidue was found by day 30. The chronology of PLA bottle bio-degradation in the compost pile is illustrated in Figure 7.10.

Further investigation of PLA biodegradation using the cumula-tive measurement respirometric (CMR) system (according toASTM D5338 and ISO 14855-1) showed that the biodegradationof PLA bottles required .30 days buried in a compost pile toachieve 80% mineralization. CMR is a system designed to yield

Figure 7.9 Bottle marketed by Biota, fabricated using NatureWorkss

PLA (Kale et al., 2007).


the percentage of carbon dioxide from the organic carbon contentof a sample. A typical setup up for a CMR system is shown inFigure 7.11. It consists of a set of bioreactors in which the air sup-ply is controlled. A pressurized air supply at 2 psi was passedthrough a 10 N sodium hydroxide (NaOH) solution to measurethe carbon dioxide in the air. The deionized water is mainly for

Day 0 Day 1 Day 2 Day 4

Day 6 Day 9 Day 15 Day 30

Figure 7.10 Biodegradation of PLA bottle in compost pile (adaptedfrom Kale et al., 2007).

10 NNaOH

Air Inlet

Dry air

RHmeter

Compost+ Vermiculite

Bioreactor 1

Set of 9 Bioreactors

Bioreactor 9

Humidified airgeneration

CO2 Trap0.25 N NaOH

solution

CO2 Trap0.25 N NaOH

solution

10 NNaOH

DeionizedWater

Figure 7.11 Setup of CMR system by Kale et al. (2007).

270 POLYLACTIC ACID

humidifying the air � the moisturized air is further mixed withdry air to achieve 50% humidity when measured using the rela-tive humidity (RH) meter. The bioreactors contain compost andvermiculite, to provide a high water-holding capacity of 300%,compared to soil’s water-holding capacity of 28�45% in sandy toclay loam soils (Grima et al., 2001). Samples are placed inthe compost. Cellulose is used as a reference material. During thetesting, microorganisms contained in the bioreactors consume thesamples and release CO2. The CO2 is entrapped in the 0.25 NNaOH solution. A small known quantity of reacted NaOH solu-tion is transferred out for acid titration (i.e. to HCl) for a certainperiod to determine the amount of CO2 generated.

The reaction scheme for titration is described in ASTMD5338 as follows. A strong mineral acid HCl is used.

During absorption of CO2 generation from biodegradation ofsamples:

NaOH1CO2 NaHCO3 (R-1)

NaHCO31NaOH Na2CO31H2O (R-2)

Titration reaction

Na2CO31HCl NaHCO31NaCl (R-3)

NaHCO31HCl NaCl1H2O1CO2 (R-4)

An indicator such as phenolphthalein is used during the titra-tion. The concentration of CO2 can be calculated according tothe equation:

CO2 ðin gramsÞ5 V 3C3 44

1000(7.3)

where, V is the volume of HCl consumed in the reaction (R-4).The percentage of mineralization is used to calculate the quan-tity of CO2 generated in the positive control, such as cellulose,and the PLA sample with the blank according to the equation:

% Mineralization5wCO22wCO2b

Wmaterialð%Cmaterial=100Þð44=12Þ3 100

(7.4)


where wCO25 total amount of CO2 generated by samples andthe positive control in grams; wCO2b5 amount of CO2 gener-ated in the blank in grams; Wmaterial5mass of the sample;%Cmaterial5 percentage of organic carbon content of the sample.

The CMR system for the biodegradation of PLA bottles andcellulose is shown in Figure 7.12. It was found that the percent-age of mineralization of PLA was low at the beginning, but itwas able to catch up until finally its level of mineralizationwas comparable with cellulose. This finding is different fromthat of Masardier-Nageotte et al. (2006), who found PLA to bea fully degradable polymer. However, further in-depth investi-gations have discovered that the degradation of PLA requiresthe action of various microorganisms to actively consume thetraces of PLA residues. The slower mineralization of PLA isessentially due to PLA requiring the hydrolysis process todegrade its macro-structure into oligomers, so that it is consum-able by microbes, finally evolving CO2.

0

0

20

40

60

80

% M

iner

aliz

atio

n

100

5 10 15 20 25 30Time, Days

35 40 45 50 55 60

Figure 7.12 Percentage of mineralization for biodegradation ofcellulose(K), and PLA bottle (x), in CMR system (adapted from Kaleet al., 2007).

272 POLYLACTIC ACID

Kale et al. (2007) also reported that the rate of biodegradationof PLA, and biopolymers in general, differs for real in-soil burialand simulated composting, as shown in CMR. Simulatedcomposting has a higher rate of biodegradation, mainly due tothe smaller sample sizes used in testing, which enhances thehydrolysis and provides a larger surface for the reaction ofmicroorganisms. In real composting conditions, the rate of bio-degradation tends to be slower due to the humidity, the compostraw materials, the types of microorganisms and the larger size ofthe disposed products. Consequently, Kale et al. (2007) con-cluded that it is essential to conduct real composting tests toensure that biopolymer products can successfully biodegrade anddecompose in commercial composting facilities and landfills.

An early study on the types of microorganisms involved inbiodegradation was carried out by Torres et al. (1996) usingthe various microorganism strains (see Table 7.11). The aimwas to screen for the microorganisms involved in the biodegra-dation of PLA and lactic-acid-containing polymers. Initially,the researchers used DL-lactic acid (DL-LA) and its oligomersto investigate the extent of filamentous fungi reactivity in 7days. Torres et al. (1996) conducted two analyses on DL-LAand oligomers separately at a concentration of 10 g/liter, andsterilization was undertaken to avoid biological contamination,which can produce faulty results. The results showed that allstrains could actively consume lactic acid and oligomers. Outof the analyzed strains, only three strains could totally utilizeDL-LA and DL-LA oligomers as the sole carbon and energysource (two strains of Fusarium moniliforme and one strain ofPenicillium roqueforti). Others strains could only partiallyassimilate the DL-lactic acid and oligomer substances. Thisindicates that lactic acids merely serve as sources of assimila-tion for selected strains. The biomass production of the strainsremained higher for Fusarium moniliforme and Penicilliumroqueforti. Yield of biomass from strain assimilation is alwaysfavorable as the source of plant nutrients.

An investigation on the different types of fungal strainsgrowing on poly(lactide-co-glycolide) found that onlyFusarium moniliforme (Fmm) grew on the specimens after a


2-month period. Figure 7.13 shows the formation of mycelia onthe surface of a specimen, which appeared in the form of swol-len or emptiness. Enlargement of the image (see arrow) showsthat the Fusarium moniliforme filaments had penetrated thespecimen to some depth. This is thought to be related to theway in which microorganisms attack the cutin of plants tocause infection (Torres et al., 1996). Cutin is the structuralcomponent of the plant cuticle. It is a polyester composed ofω-hydroxy-C16 and C18 fatty acids, dihydroxy-C16 acid, 18-hydroxy-9,10-epoxy-C18 acid and 9,10,18-trihydroxy-C18 acid.

Table 7.11 Composition of PLA and Dry Biomass after 7 Days inCulture Media with Different Types of Filamentous Fungi

Strain Final Amount (g/liter)

Lactic Acid with: Biomass with:

DL-LA Oligomers DL-LA Oligomers

Aspergillus awamori

Aa 20

7.8 7.8 0.1 0.4

Aspergillus awamori

NRRL 3112

8.6 7.6 0.1 0.3

Aspergillus foetidus 3.3 5.6 0.7 1.4

Aspergillus nidulans 4.8 5.6 0.9 0.9

Aspergillus niger CH4 7.8 7.7 0.1 0.5

Aspergillus niger An 10 3.1 5.9 0.7 2.0

Aspergillus oryzae 3.3 7.4 0.2 1.3

Fusarium moniliforme

Fmm

0.0 0.0 2.8 3.1

Fusarium moniliforme

Fm1

0.0 0.0 2.6 2.9

Penicillium roqueforti 0.0 0.0 0.9 2.8

Penicillium sp. 6.1 7.7 0.1 0.7

Rhizopus oligosporus 7.5 7.5 0.1 0.4

Trichoderma harzianum 2.2 7.8 0.1 1.8

Trichoderma sp. 3.6 5.5 1.0 0.3

Control 9.2 8.2 0.0 0.0

274 POLYLACTIC ACID

This insoluble polymer constitutes a major physical barrier thathelps to protect plants from penetration by pathogenic fungi.Pathogenic fungi produce an extracellular cutinase when grownon cutin as the sole source of carbon (Kolattukudy et al.,1987). Since PLAGA copolymer is also a type of polyester, thedegradation mechanism is similar. The degradation starts withabiotic degradation, which causes the transformation of PLAinto its oligomers and the attachment of strain filaments ontothe PLGA. This leads to the conclusion that PLAGA is bioassi-milable polymer. A very similar observation was made whenPLA was buried in natural soil for a 2-month period.Filamentous fungi also grew on and penetrated the polymermass, as shown in Figure 7.14.

Rudeekit et al. (2008) conducted a biodegradation test ofPLA under wastewater treatment, landfill, composting plantand controlled composting conditions (see Table 7.12). Theresearchers found that the PLA sheets had noticeable whitespots on the surface after a 1-month exposure to wastewatertreatment conditions and the areas affected by the white spots

Figure 7.13 Scanning electron micrographs indicating the penetrationof Fusarium moniliforme filaments into the PLAGA copolymer structureafter incubation for 2 months. Enlarged image on left side (adaptedfrom Torres et al., 1996).


Figure 7.14 Scanning electron micrograph indicating the growth offilamentous fungi at the surface of a racemic PLA plate buried for 8weeks in local natural soil and allowed to age for 8 more weeks at30�C in a hydrated environment (adapted from Torres et al., 1996).

Table 7.12 Biodegradation Conditions of PLA Tested byRudeekit et al. (2008)

Conditions Details

Wastewater

treatment

Wastewater treatment in Supanburi Province,

Thailand, for 15 months

Composting

plant

The samples were placed inside a composite pile

made of vegetable waste (32 wt%), wood chips

(17 wt%), coconut shells (17 wt%), fruit peels

(17 wt%) and old compost (17 wt%). The

compost pile was measured for the conditions

of temperature (45�70�C), moisture content

(40�55%) and pH (4�8). The composting

process was carried out for 3 months until

stabilized compost was obtained

Landfill Outdoor test with seasonal changes in landfill in

Supanburi Province, Thailand, for 15 months.

The samples were buried at a 1 m depth from

the landfill surface

276 POLYLACTIC ACID

had grown significantly larger over the testing period (seeFigure 7.15). However, the biodegradation of PLA was morerapid under composting plant conditions at high temperatureand humidity (50�60�C and relative humidity (RH) .60%).The PLA sample in sheet form became brittle and started tobreak into small pieces after testing for 8 days (seeFigure 7.16). This is because the degradation temperature ata land composting plant is higher than the glass transitiontemperature of PLA. Thus, when the temperature exceedsthe glass transition temperature this causes chain movement,enabling the penetration of water to progress the hydrolysisreaction. The importance of this mechanism is illustrated bycomparing the rate of biodegradation of the land compostingplant and wastewater treatment conditions. This shows thatregardless of the large volume of water in contact with PLA inthe wastewater treatment conditions, because the degradationtemperature is lower than the glass transition temperature the

0 month 1 month 2 months

15 months11 months6 months

Figure 7.15 Degradation of PLA samples under wastewater treatmentconditions (adapted from Rudeekit et al., 2008).


degradation rate is significantly lower than that under compost-ing plant conditions.

When the PLA sheets were buried in the landfill conditionsthey degraded more slowly than those in the composting plantconditions (see Figure 7.17). Again, this is because of the high-er temperature and humidity in the composting plant condi-tions, which help the PLA to degrade rapidly. In the landfillconditions it required 6 months for major fragmentation tooccur and 15 months for there to be some disappearance. Incontrast, PLA under composting plant conditions showed dis-appearance in merely 30 days. It is possible to conclude thatthe degradability of PLA is dependent on the hydrolysis andcleavage of ester linkages in the polymer backbone to formoligomers.

7.5 Thermal Degradation of PLA

Polymeric materials are commonly used above room temper-ature. Existing commodity polymers, such as polyethylene,polypropylene, polystyrene, polycarbonate, etc., are frequently

0 day 5 days 8 days

11 days 14 days 17 days 30 days

Figure 7.16 Degradation of PLA samples under composting plantconditions (adapted from Rudeekit et al., 2008).

278 POLYLACTIC ACID

used to fabricate cups and containers for hot food and drink,and even piping for hot water. In relation to these uses,marketable biodegradable PLA should possess a comparablethermal stability feature so that PLA is able to substitute exist-ing commodity polymers for a wide range of processing andapplications.

In the early days, thermal degradation of PLA was studiedby McNeil and Leiper (1985) using the thermogravimetrymethod. It was reported that PLA had the highest degradationat 365�C under flow of nitrogen, and the decomposition wasaccelerated under excess air due to oxidation by free oxygen.This was also observed in a recent study by Zhan et al. (2009),which involved the comparison of fire resistivity of PLA afterthe incorporation of a flame retardant (see Figure 7.18) �SPDPM was the intumescent flame retardant. PLA has a simplesingle-stage degradation, where the initial 5% mass loss occurs

0 month 1 month 2 months

15 months11 months6 months

Figure 7.17 Degradation of PLA samples under landfill conditions(adapted from Rudeekit et al., 2008).


at 325�C and finally no residue is left on heating up to 500�C.It can be observed from the Fourier transform infrared spec-troscopy (FTIR) spectrum in Figure 7.19 that PLA’s thermaldecomposition compounds contain aOH, such as H2O(3400�3600 cm�1), CO2 (2360 cm�1), aliphatic ethers(1120 cm�1), single-, double- and cyclic-bond hydrocarbons(1400�1200 cm�1) and compounds containing carbonyl groups(1760 cm21) (Wang et al., 2011). Such observations can be

100

100PLASPDPMPLA/5SPDPMPLA/15SPDPMPLA/25SPDPM

PLASPDPMPLA/5SPDPMPLA/15SPDPMPLA/25SPDPM

80

60

40

20

0

0

10

20

30

40

50

60

200 300 400Temperature (°C)

500 600 100 200 300 400Temperature (°C)

Der

iv. W

eigh

t (%

/min

)

Wei

ght (

%)

500 600

Figure 7.18 TGA and DTG curves of PLA and SPDRM intumescentflame retardant (adapted from Zhan et al., 2009).

4000 3500 3000

3575

Abs

orba

nce

2980

2740

0.8

0.6

0.4

0.2

0.0

2360

1373

1760

11201420

2500

Wavenumbers (cm−1)

2000 1500 1000 500

Figure 7.19 Infrared spectrum of pyrolysis products for PLA at themaximum decomposition rate (Wang et al., 2011).

280 POLYLACTIC ACID

found in polymers and this indicates that depolymerizationoccurs vigorously.

The thermal decomposition and stability of PLA as it relatesto processing methods has been studied by Carrasco et al.(2010). Table 7.13 provides a summary of this work: PLA-V isthe fresh supply from the manufacturer, which possessed thehighest degradation temperatures (Tn, n5 5, 50, 95, denotingthe percentage of mass losses, and p was the highest rate ofdecomposition at respective temperatures). As the PLA under-went extrusion and injection, the thermal degradation droppedslightly. This was attributed to the repetitive heating and cool-ing resulting in a minor decrease in molecular weight, causedby the presence of moisture that induces the hydrolysis reac-tion. Wang et al. (2008) found that when PLA samples wereextruded/injected, they had more chromophoric groups, i.e. thepresence of double terminal bonds, CQC and conjugates withcarbonyls CQO, which were responsible for chain scissioning,leading to the yellowish color. Further examination ofTable 7.13 shows that the annealed PLA samples had a lowerdegradation temperature. This may be due to prolonged expo-sure to elevated temperatures causing reactivity of the func-tional group within the molecules, although the annealingprocess led to crystallization as well as a slight increase in the

Table 7.13 Thermal Degradation Characteristics of PLA inRelation to Processing Method, Analyzed by TGA (Carrascoet al., 2010)

Sample T5 (�C) T50 (

�C) T95 (�C) ΔT5�95 (

�C) Tp (�C)

PLA-V 331 358 374 43 362

PLA-I 325 356 374 49 359

PLA-IA 323 353 370 47 357

PLA-EI 325 357 374 49 358

PLA-EIA 324 352 369 45 356

PLA-V5 unprocessed raw material; PLA-I5 injected; PLA-EI5 extruded

and injected; PLA-IA5 injected and annealed; PLA-EIA5 extruded,

injected and annealed.


glass transition temperature of PLA. A higher glass transitiontemperature is favorable when used for serviceware for hotfood and drinks, as this avoids the collapsing of containers dueto the softening of the polymer.

The thermal stability and the average molecular weightexhibit a linear relationship. Indeed, for 10 kDa increases in theaverage number molecular weight (Mn) (see Figure 7.20), theinitial decomposition temperature T5 elevates at the rate of2.6�C, while the T5 rises by 1.4�C when the average weightmolecular weight (Mw) increases by 10 kDa. Again, the proces-sing of PLA under heat and shear in extrusion and injectioncauses a lowering of the molecular weight; this is the main rea-son for the weakening thermal resistance of PLA. This is fur-ther supported by the determination of the polydispersity index(see Figure 7.21) by comparing PLA-EI (underwent extrusionand injection) and PLA-I (underwent injection): PLA-EI had alower initial decomposition temperature than PLA-I. In short,reprocessing of PLA and the careful selection of processingmethod is crucial to preserve the inherent properties of PLA.

332

330

PLA-VPLA-V

PLA-I PLA-IPLA-EI PLA-EI

Mn Mw

y = 0.257x + 313R2 = 0.985

y = 0.136x + 302R2 = 0.989

328

326

324

3220 60

Initi

al d

ecom

posi

tion

tem

pera

ture

(°C

)

120 180 240

Average molecular weight (kDa)

Figure 7.20 Variations of initial decomposition temperature T5 inrelation to the average molecular weight Mn and Mw for different typesof processing of PLA (adapted from Carrasco et al., 2010).

282 POLYLACTIC ACID

Photodegradation can have an important effect on the life ofa PLA product, especially those for outdoor applications.Generally, when polymers are exposed to the outdoor environ-ment they are subject to weathering effects. Ultraviolet (UV)and moisture are the main degradation agents leading to thealteration of the chemical structure, which further influencesthe mechanical response of the polymers. When PLA is sub-jected to accelerated UV ageing, the chemical structure of thepolymer changes substantially, and involves chain scission,crosslinking and intermolecular reactions to form new func-tional groups.

Belbachir et al. (2010) reported that the elugrams from gelpermeation chromatography (GPC) analysis (see Figure 7.22a)exhibited a shift of elution to higher volumes after virgin PLAwas subjected to accelerated UV irradiation. Moreover, theelugram of irradiated PLA also exhibited a broader curve com-pared to virgin PLA. This indicated that the molecular weightdistribution has been widened as a consequence of chain scis-sioning. When the dosage of UV is higher, the molecular

332

330

328

326

324

322

Initi

al d

ecom

posi

tion

tem

pera

ture

(°C

)

3.0 3.2 3.4 3.6 3.8 4.0Polydispersity index

PLA-I

PLA-EI

PLA-V

y = −9.4x + 360R2 = 0.9416

Figure 7.21 Variations of initial decomposition temperature T5 inrelation to the polydispersity index for different types of processing ofPLA (Carrasco et al., 2010).


weight starts to reduce, whereas the molecular weight distribu-tion increases (see Figure 7.22b). Free radicals are generatedduring photodegradation to attack the backbone and formlower-molecular-weight species. Ikada (1993, 1997, 1999) hassuggested that PLA follows the Norrish II mechanism, whichinvolves substantial chain cleavage and formation of CQC andOaH, as shown in Figure 7.23. When UV rays reach the back-bone of the PLA, the electronegative oxygen atoms are acti-vated to form radicals; this is known as photophysicalexcitation. The reaction further involves attack of free oxygenfrom the air and finally the chain is cleaved. Prolonged expo-sure to UV irradiation can cause loss of mechanical properties.Figure 7.22a shows the UV dosage has almost a linear relation-ship with the elastic modulus and yield stress, whereas thestress�strain at break has shown a rapid decline at higher UVdosage. This can be explained by the fact that higher UV pro-vokes chain cleavage and excessive local cavitation occurs,promoting localized weak points. When external loads areapplied to the irradiated samples, such weak points propagateand combine, impairing the entire structure.

A photosensitizer can be added to enhance the photodegrada-tion of PLA. The purpose of this is to increase the rate of degra-dation when accelerated PLA waste treatment is required. Tsujiet al. (2005) has studied the effect of N,N,N0,N0-tetramethyl-1,4-phenylenediamine (TMPD) on amorphous and crystalline PLA

10 12 14 16 18

Elution volume (ml) Emitted dose (ml/mm2)

(a) (b)

20 22 24100

120

140

160

Mol

ecul

ar w

eigh

t (10

3 g/

mol

)

Mol

ecul

ar w

eigh

t dis

trib

utio

n

180

200Virgin PLAIrradiated PLA

220

0 20 40 60 80 100

3

2

1

Figure 7.22 (a) GPC elugrams of virgin and irradiated PLA after beingsubjected to a dose of 91.2 mJ/mm2 UV irradiation.

284 POLYLACTIC ACID

films. When TMPD is exposed to UV irradiation it is activatedand releases free radicals, which attack the backbone; the mech-anism is similar to the Norrish II reaction. Typical results for theTMPD action in irradiated PLA are summarized in Table 7.14.

CH3

CH3

CH3

CH3

CH2

CH2

CHCH

CH

CH

CH

CHCC

C

CC

C

O

O

O

(a) (b)

(c)

hv

O

O

O

O

O

O

+ O2

OO

O

H

H

+

Figure 7.23 Norrish II mechanism for photo-oxidation of PLA: (a)backbone radical activation under UV irradiation, (b) photophysicalexcitation, and (c) oxidation and scission reactions (adapted fromBelbachir et al., 2010).

40

30

20

10

01008060

Emitted dose (mJ/mm2)40200

6000

5000

4000

3000

2000

Ela

stic

mod

ulus

(M

Pa)

Yie

ld s

tres

s (M

Pa)

1000

0

Figure 7.22a Effect of UV irradiation on the elastic modulus and yieldstress of PLA (adapted from Belbachir et al., 2010, with permission ofElsevier).


TMPD enhances the photodegradation irrespective of the crys-tallinity of PLA. This indicates that the formation of radicals areinvolved in a free reaction with the backbone, whereas hydro-lytic degradation requires water molecules to be in contact withthe amorphous structure for chain cleavage to take place (Tsujiet al., 2005).

In contrast, electron irradiation is used to improve the physi-cal and mechanical properties of PLA. Improving the structuralproperties of PLA is important, especially for the use of ther-moform PLA products at elevated temperatures. This isbecause neat PLA is very likely to soften at temperatures over60�C. The electron irradiation of PLA requires triallyl isocya-nurate (TAIC) (see Figure 7.24) as the crosslinking agent toenhance its properties. Without it electron irradiation tends todeteriorate PLA, worsening both the processing properties andfunctional qualities of PLA (Malinowski et al., 2011;Kanazawa, 2008). Figure 7.25a shows that the melt flow index(MFI) of neat PLA drops as the electron irradiation dosageincreases. MFI is the measurement of viscosity; higher MFImeans lower viscosity. A high dosage of electron irradiation

Table 7.14 Properties of PLA Film with Added TMPDPhotosensitizer at 60 h UV Irradiation (Tsuji et al., 2005)

Sample TMPD(wt%)

Mn=105 Mn=Mw TS3

(MPa)YM4

(GPa)EB5

(%)

PLA-A1 0 1.13 1.65 43.8 1.24 6.1

0.01 0.94 1.78 50.5 1.15 5.8

0.1 0.82 1.78 40.3 1.24 4.1

PLA-C2 0 1.14 1.77 50.5 1.21 5.5

0.01 0.93 1.91 31.1 1.20 3.2

0.1 0.86 1.97 28.8 1.15 3.3

1Amorphous PLA;2crystalline PLA;3tensile strength;4Young’s modulus;5elongation at break.

286 POLYLACTIC ACID

provokes chain cleavage, which leads to a reduction in molecu-lar weight of PLA at low viscosity. A different phenomenoncan be observed for the addition of TAIC. For the addition of1% TAIC, the increment of MFI is lower compared to neatPLA. This indicates that both chain cleavage and crosslinkinghappen simultaneously. According to Malinowski et al. (2011),the amount of TAIC should be less than 1% because excessiveTAIC can cause PLA to thermoset and the material cannot beextruded through a plastometer die. However, the electroncrosslinking is able to improve the glass transition (Tg) of PLA(see Figure 7.26). At 3% TAIC the maximum value of Tg canbe achieved at a dose of 60 kGy. This method of crosslinkingcan be applied in the manufacture of right films for PLA ther-moforming products when elevated temperature application isneeded.

CH2=CH−CH2−N N−CH2−CH=CH2

CH2−CH=CH2

N

O

OOC

C

C

Figure 7.24 Chemical structure of triallyl isocyanurate (TAIC).

200

150

100

MF

I [g/

10 m

in]

50

0

20

25

1T3T5T

(b)(a)

15

10

MF

I [g/

10 m

in]

5

00 10 20 40 60

Dose [kGy]

80 0 10 20 40 60

Dose [kGy]

80

Figure 7.25 (a) Melt flow index for neat PLA at different dosages ofelectron irradiation; (b) melt flow index for PLA added with TAIC with1% (1T), 3% (3T) and 5% (5T) (adapted from Malinowski et al., 2011).


7.6 Flame Resistance of PLA

When electronic and electrical appliances are subjected to anelectrical current and voltage for a prolonged period, typicalmisuse or malfunction can cause unintentional firing, such as ashort circuit event. Because the applications of PLA extend tothe housings of electrical and electronic appliances, the flam-mability of PLA is important in order to minimize fire risk. Inaddition, understanding the flammability behavior of PLA isalso helpful in designing flame retardant packaging to meet thefire safety requirements as well as maintaining its biodegrad-able features.

The flammability of plastic materials is regularly evaluatedaccording to UL-94 and the limiting oxygen index (LOI). UL-94 is the most famous standard, and is released byUnderwriters Laboratories of the United States. According tothis standard, plastics are classified by their burning character-istics and further assigned to 12 flame categories. Basically,consumer electronic products that use manufacturing enclo-sures, structural parts and insulators are classified into six rat-ings � 5VA, 5VB, V-0, V-1, V-2 and HB; the observationsduring testing are listed in Table 7.15. The ratings HF-1, HF-2,

76

75

74

73

72

71

70

69

680 10 20 40

P

3T

60 80Dose [kGy]

Tg

[g/1

0 m

in]

Figure 7.26 Glass transition temperature (Tg) for 3% TAIC PLA (3T)and neat PLA (P) at respective electron irradiation dosages (adaptedfrom Malinowski et al., 2011).

288 POLYLACTIC ACID

Table 7.15 Classification of Flammability According to UL-94

Classification Burning Rate Dripping FlameRetardant

5VA Specimen at vertical

orientation burning

stops within 60

seconds. Plaque

specimens may not

develop a hole

Not allowed LOW

5VB Specimen at vertical

orientation burning

stops within 60

seconds. Plaque

specimens may not

develop a hole

Not allowed

V0 Specimen at vertical

orientation burning

stops within 10

seconds

Allowed but

not

inflamed

HIGH


orientation burning

stops within 30

seconds

Allowed but

not

inflamed


orientation burning

stops within 30

seconds

Allowed and

inflamed

HB Horizontal specimen

burning slowly at rate

,76 mm/min for

thickness ,3 mm

Not

applicable


HBF are for low-density foam materials used in speaker grillsand sound-deadening materials and the last three ratings, VTM-0, VTM-1 and VTM-2, are assigned to very thin films.

The limiting oxygen index (LOI) is used to determine theminimum concentration in percentage required to sustain thecombustion of the polymer. The flow of nitrogen is manipu-lated during the burning of the specimen until the oxygenreaches a critical level. The measuring standards for LOI are:BS EN ISO 4589-2 Plastics. Determination of BurningBehavior of Oxygen Index, Ambient-Temperature Test andASTM D2863-10 Standard Test Method for Measuring theMinimum Oxygen Concentration to Support Candle-LikeCombustion of Plastics (Oxygen Index). From the experimentsas reported by Reti et al. (2008) and Zhan et al. (2009), noneof the ratings match neat PLA according to the standard UL-94, due to its flammable behavior. It has a heavy dripping rat-ing. Dripping during burning is unpleasant and can cause burninjuries when it comes into contact with skin. Furthermore, theinflamed dripping can cause the further spread of the fire fromthe initial source to another area, providing both the source offire and fuel for ignition. Making PLA packaging flame retar-dant is essential in order to fulfill applications for fire safetypurposes.

Some studies propose that intumescent flame retardant tech-nology should be used for PLA. Intumescent technology is pas-sive fire protection. The inflamed polymer materials produce alight char, acting as poor conductors of heat and retarding heattransfer. As shown in Figure 7.27, the isolating carbon layerseparates the combustible material from the fire/heat sourceand oxygen using insulating foam on the surface. The charredlayer acts as physical barrier that effectively reduces the trans-fer of heat and mass between the gas and the condensedphases. Typical intumescent technology flame retardant sys-tems usually consist of acids, ammonium salts and phosphates.Reti et al. (2008) evaluated the efficiency of intumescent flameretardant systems in PLA with the use of ammonium polypho-sphate (APP) and pentaerythritol (PER). In this system, APPacts as both the acid source and the blowing agent while the

290 POLYLACTIC ACID

PER functions as the carbonization agent. APP decomposes ata high temperature, producing phosphoric acid derivatives thatact as catalysts to accelerate the decomposition of the PER toform a char. During APP decomposition, the formation of low-boiling-point acid derivatives act as the blowing agent, produc-ing nonflammable gas to expand the char layer. Nevertheless,APP and PER are petrochemical products and are nonbiode-gradable. Blending it with PLA diminishes PLA’s ‘green’ cre-dentials. Therefore, Reti et al. (2008) substituted PER forstarch and lignin as the carbonization agents. The flammabilityproperties as tested under LOI and UL-94 of the PLA blendcombinations are given in Tables 7.16 and 7.17. The data showthat PER has the highest LOI, followed by starch and lignin.

Table 7.16 UL-94 Classification of Intumescence of PLAMaterials as Observed by Reti et al. (2008)

Specimen Classification

100% PLA Not classified

60% PLA1 30% APP1 10% PER V2

60% PLA1 30% APP1 10% lignin V0

60% PLA1 30% APP1 10% starch V0

O2 Heat

Reduce smoke emission

Plastic with intumescent flame retardant

Isolating Carbon Layer

Figure 7.27 Schematic of an intumescent flame retardant in plastics.


The carbonization effect of starch and lignin as observed withthe LOI was higher than for neat PLA. In addition, accordingto UL-94 testing outcomes, the substitution of PER with starchand lignin has superior fire retardant properties. This outcomewas also found by Wang et al. (2011), who used polyurethanemicroencapsulated ammonium polyphosphate as the intumes-cent flame retardant. When 10% starch was added to PLA withan unchanged composition of flame retardant (compare PLA-2and PLA-10 in Table 7.17), the flame retardance improved dra-matically, from burning and dripping to V0 that stops burningin 10 seconds. Wang et al. (2011) also reported that LOIimproved with higher amounts of starch, indicating that a high-er concentration of oxygen is needed to sustain burning (seeFigure 7.28). This finding is favorable for PLA blending withstarch, as it possesses a flame retardant effect withoutcompromising its biodegradability. As can be seen from

Table 7.17 UL-94 Classification of Intumescence of PLAMaterials as Observed by Wang et al. (2011)

SampleCode

Composition (Wt%) Flame Retardance

PLA IFR Starch LOI (%) UL-94 Rating

PLA-1 100 0 0 20.0 Burning and

dripping


dripping

PLA-3 80 17 2.5 28.5 V1

PLA-4 80 15 5 30.0 V1

PLA-5 80 10 10 31.5 V1


dripping


dripping

PLA-8 70 30 0 33.0 V1

PLA-9 70 25 5 38.0 V0

PLA-10 70 20 10 41.0 V0

292 POLYLACTIC ACID

Figure 7.29, the residue left after burning neat PLA was small,whereas the PLA�starch tends to produce foam char, produc-ing an intumescent effect. Zhan et al. (2008) observed that theformation of char is very similar when spirocyclic pentaerythri-tol bisphosphorate disphosphoryl melamine flame retardant(SPDRM FR) is added to PLA. This observation demonstratesthat starch is capable of equivalent intumescent effects as syn-thetic flame retardants.

46

44

42

40

38

36

34

LOI (

%)

32

30

28

V1

V1

0 2 4 6Starch (wt%)

8 10

V1V1

V0

V0

PLA/10wt% MCAPP/5wt% MA/StarchPLA/15wt% MCAPP/7.5wt% MA/Starch

Burning

26

24

22

Figure 7.28 Relationship of LOI and starch content in PLA (Wanget al., 2011).

Figure 7.29 Pictures of the PLA specimens containing ammoniumpolyphosphate-starch flame retardant (APP FR) and spirocyclicpentaerythritol bisphosphorate disphosphoryl melamine flameretardant (SPDRM FR) after LOI test.


Li et al. (2009) used organically modified montmorillonite(OMMT) coupled with APP as an intumescent flame retardantfor PLA. According to these researchers and Si et al. (2007),the purpose of the OMMT is twofold: 1) the formation of car-bonaceous-silicate char building up on the polymer surface dur-ing combustion protects the polymer matrix and slows the rateof mass losses; and 2) the MMT provides an anti-drippingeffect to the firing polymer. The anti-dripping effect plays avery important role in linear polymers, such as PLA, polyethyl-ene terephthalate and poly(butylene succinate), which have lowmelt viscosities compared with branched or thermoset poly-mers. These polymers are very unfavorable on burning: theyintensify burning due to serious melt dripping. Li et al. (2009)used MMT modified with N,N-dimethyl dehydrogenated tallowquaternary ammonium chloride and APP flame retardant sys-tem to blend with PLA (see Table 7.18). This successfullyovercame the dripping of PLA. The addition of MMT in com-bination with an intumescent flame retardant is crucial becauseneither one of these additives (MMT nor the intumescent flameretardant) can independently control the dripping when PLA isin a fire. Nevertheless, APP is an effective flame retardant thathas the highest LOI, even without the incorporation of OMMT.

Table 7.18 Flammability of PLA with OMMT IntumescentFlame Retardant

Sample PLA(Wt%)

IFRa

(Wt%)OMMT(Wt%)

LOI Dripping UL-94Rating

PLA 100 � � 20.1 Yes NCb

PLA-

MMT

95 � 5 21.8 Yes NCb

PLA-IFR 80 20 � 28.7 Yes V2

PLA-

MMT-

IFR

80 15 5 27.5 No V0

aIntumescent flame retardant;bnot classified.

294 POLYLACTIC ACID

Overall, the selection of appropriate flame retardant to suppressthe flammability of PLA is important, especially when firesafety is needed.

7.7 Conclusion

PLA is a polymer derived from an agricultural source and itis biodegradable. These are features that need to be enhancedfor the diversification of PLA applications. Its biodegradabilityand biocompatibility mean that it has wide biomedical applica-tions. By manipulating the crystallinity and copolymerizationof isomers or other monomers, it is possible to influence therate of in vitro and in vivo biodegradation. Generally, degrada-tion of PLA is initiated through a hydrolysis process and this isfollowed by enzymatic or microorganism-based actions. Suchdegradation eventually leads to the fragmentation of PLA,which is ultimately transformed into harmless substances.

PLA has a low softening point, which limits its use at ele-vated temperatures. However, crosslinking, copolymerizationand recrystallization can be helpful in order to improve its ther-mal properties. Prolonged exposure to thermal and UV irradia-tion can cause severe degradation to PLA. With regard to fire,PLA is a combustible material and the selection of a flameretardant package can improve its fire resistance for electricand electronic applications. In conclusion, understanding thedegradation and stability of PLA is an important preliminarystep in the manipulation of its properties while preserving its‘green’ aspect.

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8 Applications of Poly(lactic Acid)

Chapter Outline8.1 Introduction 3018.2 Poly(lactic Acid) for Domestic Applications 3028.3 Poly(lactic Acid) for Engineering and Agricultural

Applications 3178.4 Poly(lactic Acid) for Biomedical Applications 3178.5 Conclusion 317References 326

8.1 Introduction

Poly(lactic acid) (PLA) is a biodegradable polymer that hasa variety of applications. It has been widely used in the bio-medical and pharmaceutical fields for several decades due toits biocompatibility and biodegradability in contact with mam-malian bodies. For many years, however, the application ofPLA was very limited, due to the high cost of synthesis in thelaboratory. For the most part, the direct polycondensation route(see Figure 8.1) was employed to produce PLA from lacticacid. The resultant PLA had a low molecular weight and poormechanical properties.

The properties of PLA improved tremendously with thedevelopment of production using ring-opening polymerization.This route requires an intermediate substance known as lactide.Lactide is the cyclic dimers of lactic acid, and it can be in theform of L-lactide, L,D-lactide (meso-lactide) and D-lactidestereocomplex (see Figure 8.2). Nowadays, the synthesis ofPLA rarely starts from chemically synthesized lactic acid. Thelactic acid used is yielded from the fermentation of carbohy-drates such as starch and cellulose. A large proportion isderived from the crops corn and cassava. Microorganism-basedfermentation yields mainly L-lactic acid.



http://dx.doi.org/10.1016/B978-1-4377-4459-0.00008-1

Currently, NatureWorks is largest producer of PLA fordomestic applications. NatureWorks employs lactide ring-open-ing polymerization for the mass production of 140,000 MT peryear of PLA, which is branded as Ingeot. NatureWorks’ PLAis produced mainly for biodegradable packaging, containers,clothing, fibers, etc. Purac is the major producer of PLA forthe biomedical and pharmaceutical industries.

In this section the product applications of PLA are summa-rized. The applications of PLA can be grouped into three maincategories: domestic, pharmaceutical/biomedical and engineer-ing. Products, trade names and producers have been includedwhere useful. The intention is not to advertise but rather to pro-vide supportive information and references.

8.2 Poly(lactic Acid) for DomesticApplications

Most of the PLA produced worldwide is made for domesticapplications, such as apparel, bottles, cups, food serviceware,etc. (see Table 8.1). All these PLA products are targeted to

C

CO

C

CO

H

CH3

OH

O

H3C

C

CO

C

CO

CH3

H

OH

O

H3C

C

CO

C

CO

CH3

H

OH3C

O

H

Meso-Lactide D-LactideL-Lactide

Figure 8.2 Lactide stereocomplex.

Glucosefermentation

Route 1 Direct polycondensationRoute 2 Ring opening polymerization

Lactic acid

Lactide

1

2Polylactide

Poly(lactic Acid)

Figure 8.1 General route of PLA production.

302 POLYLACTIC ACID

Table 8.1 Domestic Applications of PLA

Application Manufacturer/User (Product) Description

Apparel Mill Direct Apparel (jackets,

caps, polo shirts),

Codiceasbarre (shirts),

Gattinoni (wedding dresses), Descente

(sportswear), etc.

PLA fiber is used as a material for

making garments. According to

Natureworks (2011a), substitution of

10,000 polyester performance sports

shirts with the usage of Ingeot can

help to save fossil fuels equating to

540 gallons gas/greenhouse gas

emissions or 11,500 miles of driving a

car. Apparel made of PLA has

excellent wicking properties, and has

low moisture and odor retention. It is

hypoallergenic, eliciting no skin

irritation. For apparel, Ingeot can be

blended with a maximum of 67%

natural, cellulosic or man-made fiber

to achieve a variety of properties.

Bottles Shiseido-Urara (shampoo bottles),

Polenghi LAS (lemon

juice bottle), Sant’Anna

(mineral water bottles), etc.

PLA is know to be suitable for making

bottles. Most of the PLA grades are

suitable for application at or slightly

above room temperature. This is

because PLA bottles tend to deform at 303

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Table 8.1 Domestic Applications of PLA—cont’d


temperatures of 50�60�C(NatureWorks, 2011b), i.e. the glass

transition temperature (Tg) of PLA.

When the temperature reaches Tg, the

amorphous chain mobility of the

plastic starts to increase significantly.

The PLA material, which is glassy

and rigid at room temperature,

gradually turns mobile and rubbery

at Tg. However, PLA bottles have

excellent gloss, transparency and

clarity�equal to polyethylene

terephthalate (PET). The PLA also

has exceptional flavor and aroma

barrier properties. The substitution

of 100,000 of 32oz juice bottles can

save fossil fuels equating to 1160

gallons of greenhouse gases or a car

traveling for 23,800 miles

(Natureworks, 2011c).

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POLYLACTIC

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Cups and food

serviceware

Fabri-Kal (cold drink cups and

lids), Coca-Cola (lining of

paper hot cups), Avianca

(in-flight cold drink cups),

StalkMarket (cutlery sets), etc.

This is one of the most important

applications of PLA. PLA is used for

these applications in order to reduce

the volume of nondegradable

disposable food serviceware, such as

cups, plates, utensils and cutlery going

to landfill. Conventionally,

polystyrene and polypropylene have

been widely used for making food

serviceware due to their low cost,

light weight and acceptable properties.

PLA is a good alternative; it has

excellent gloss, clarity, printability

and rigidity. It has good barrier

properties with grease, oil and

moisture, and has the flexibility to

adapt with high production plastic

technologies, such as injection

molding and thermoforming. PLA is

also suitable for coating or lining

paper cups. The environmentally

friendly characteristics of PLA means

that it can help to save 5950 gallons

of gas/greenhouse gas emissions for

every million of cups, forks, spoons

and knives when substituting

petrochemical polymers

(Natureworks, 2011d).

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Food packaging Lindar (thermoform container),

InnoWare Plastics

(thermoform container), Carrefour

Belgium grocery bags), etc.

PLA is suitable to be used for light

weight and transparent food

packaging containers. It is highly

glossy and can be easily

printed�equal to existing materials

such as polystyrene, polyethylene

and polyethylene terephthalate.

Container lidding made from PLA is

compostable and renewable;

typical lidding applications include

yogurt pots, sandwich containers

and fresh food trays for fruits,

pastas, cheeses and other

delicatessen products. The design

solution of compostable

delicatessen lidding of

NatureWorkss PLA is

shown.

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POLYLACTIC

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The advantages of this lidding design

are: superior flavor and aroma barrier

up to 47�C, with strong resistance to

most oils and fats in contact with food

products (NatureWorks, 2011e).

The heating sealing can be done at

temperatures as low as 80�C with the

heat seal strength .1.5 lb/in. PLA has

good compatibility with many ink

formulations with a natural surface

energy of 38 dyne/cm2. Additional

treatment with both corona and flame

can further enhance surface energy to

over 50 dyne/cm2. The conversion

of 250,000 medium-sized deli

containers to PLA can save

3000 gallons of gas/greenhouse

gas emissions progressively

(NatureWorks, 2011f)

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Films Frito-Lay (SunChip), Walmart

(salad packaging), Naturally Iowa

(EarthFirsts shrink sleeve label), etc.

PLA films are made for bakery goods,

confectionery, salads, shrink wrap,

envelope windows, laminated

coatings, multi-layer performance

packaging, etc. PLA can be made into

biaxially oriented plastic film for

packaging bags. PLA plastic bags take

a few months to fully degrade when

buried in compost. The thickness of

the film affects the rate of degradation

and mass losses. PLA marketed by

NatureWorks is specially made for

processing using the blown film

equipment for low-density

polyethylene film. It can be also

processed using the oriented

polypropylene facility with minor

modifications to setting. Every year,

millions of plastic bags are disposed

of, causing white pollution to the

ground and water. The substitution of

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POLYLACTIC

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petroleum-based plastic bags for PLA

bags can make significant

environmental savings. The

replacement of 20 million medium

salad package bags can help to save

fossil fuel equal to 29,200 gallons of

greenhouse gas emissions

(NatureWorks, 2011g)

Cards for transactions Apple Store (iTunes), The Plastic Card

Shops (gift card), etc.

Transaction cards made of PLA are as

durable as polyethylene, polyvinyl

chloride (PVC) or polyethylene

terephthalate. Most of the existing

plastic cards are made for single use,

such as gift cards or prepaid topup

cards. There are millions of regular

hotel key cards, loyalty and

transaction cards produced every year.

PLA cards have good adaptability to

cope with security features and

magnetic strips. They have durable

characteristics and can be film

laminated. Water-based acrylic and

solvent-based nitrocellulose and

polyamide are the suitable inks for 309

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printing onto PLA cards. By

converting 40 million plastic cards to

PLA, this can make an environmental

saving equivalent to 20,800 gallons of

gas/greenhouse gas emissions or a car

traveling 691,700 miles

(NatureWorks, 2011h)

Rigid consumer goods Bioserie (iPod and iPad covers),

Henkel (correction roller and

stationery), NEC (Nucycle

desktop computer), Cargo

(lipstick case)

PLA is widely used as the casing for

electronic devices, cosmetics and

stationary. The rigid character of PLA

can provide protection to enclosures

for highly sensitive products, such as

electronics and cosmetics. There are a

few grades of PLA on the market

specially designed for high-impact and

heat-stable applications. PLA is readily

coupled with fibers to form composites

for exteme applications. Potential

applications for PLA composite

include computer casings with good

stiffness. PLA is very important for the

electronics industry nowadays, because

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POLYLACTIC

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the development and turnover of

electronic appliances is tremendous.

A handheld device can become

outdated because of embedded

software in a single year. Every year,

millions of mobile phone casings are

disposed. Every 1,000,000 casings

generate 6,400 gallons of greenhouse

gas emissions. Laptop cases,

disposable razors, pens, cosmetic

containers, etc. all place a burden

on landfill. Substitution of

petrochemical-based plastics with PLA

can reduce the volume of waste in

landfill sites due to the

biodegradability of PLA. Life cycle

analysis demonstrates that a desktop

computer with PLA content

(B75% plant based) offers a significant

carbon footprint reduction, lowering

CO2 emissions by around 50%

compared to the petroleum-based

polycarbonate/ABS blends

Home textiles Eco-centric (cushion), Ahlstrom

(tea bag), Natural Livings

(mattress topper), etc.

PLA can be transformed into fiber to

substitute existing PET products such

as fabrics. PLA in this form has

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equally good breathability and

comfort. It has outstanding moisture

management properties and good

thermo-regulating characteristics.

PLA fabric is easy to care for, quick

drying and requires no ironing. In a

comparison of PLA fiber with soy and

bamboo fibers to determine the

percentage of shrinkage after washing

and tumble drying following the

AATCC 135-2004 IIIA (American

Association of Textile Chemists and

Colorists, 2006), PLA fiber showed a

reduction of 2.2% in length after three

washes, while soy and bamboo fibers

reduced by 15.0% and 17.2 %,

respectively (NatureWorks, 2011i).

Although bamboo, soy and PLA are

all biodegradable and agriculturally

derived, PLA fiber tends to show

superior properties

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POLYLACTIC

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Nonwoven products GroVia (diapers), Elements Naturalss

(baby wipes), Renewable Fiber LLC

(shopping bags), etc.

Many nonwoven products can be made

from PLA instead of PET and

polypropylene. Existing synthetic

nonwoven products such as diapers,

baby wipes, sanitary pads, shopping

bags, etc. require hundreds years to

degrade after landfill burial. PLA is

favorable because it can be spun into

fibers. It has low flammability, with a

limiting oxygen index of 26, high

resilience and excellent wicking.

It has also been found that PLA fibers

exhibit 20% and 45% higher

extension than wool and cotton,

respectively (NatureWorks, 2011j).

It has been shown in tests that PLA

does not cause irritation to the

mammalian body (NatureWorks,

2011k). When 1 million diapers

are converted from PET and

polypropylene to PLA, it can help

to save fossil fuel equivalent to

1,000 gallons of gas/greenhouse gas

emissions or driving a car for

12,800 miles

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Foam trays Sealed Air (Cryovacs NatureTRAY

food tray),Dyne-a-pak Inc (Dyne-a-

pak Naturet meat foam tray), etc.

Foam trays are important in packaging,

especially for fresh food. ‘Styrofoam’

is the well-known foam tray made

from polystyrene. This type of

polystyrene is cheap but

nondegradable. Recycling of foam

trays is not a profitable business

because the collection volume is large

in order to rework it into a small

amount of dense resin. The density of

Styrofoam is 0.025 g/cm3 compared to

virgin polystyrene resin, which is

1.05 g/cm3. This means that 42 foam

trays are needed to revert to the

original dense polystyrene at similar

volume. PLA is a good replacement

because the disposed PLA foam tray

can be composted easily without

causing adverse effects to the

environment. Moreover, the

compostable nature of PLA provides

enriching nutrients when buried in soil

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POLYLACTIC

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Expanded foam Foam Fabricator, Inc

(expandable foam for cushioning)

The technology was developed by

Biopolymers Network, and the work

received the ‘Best Innovations in

Bioplastics Award’ at the annual

European Bioplastics Conference. The

technology relies on the application of

expansion agent of CO2, which is a

safer substance compared to

expandable polystyrene using pentane

as the expansion agent. The

compostability of the expanded PLA

foam provides an environmentally

friendly solution to the electrical and

electronics industry, which uses

expanded foam as a cushioning

material during shipping

Children’s toys Kik&Boo (soft toy filled with

PLA fiber)

PLA can be used to make both rigid and

soft toys for children. In one example,

the fabric of the soft toy is produced

from woven PLA fiber, while the soft

toy is filled with PLA fiber padding.

Both soft and rigid toys made of

PLA are washable and hygienic.

The production of PLA does not 315

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involve toxic petrochemicals, thus,

it reduces the exposure of the children

to toxins

Fashion products Fashion Helmet (designer helmet),

Rizieri (ladies shoes), etc.

Environmentally friendly PLA can used

to produce typical parts of the helmet.

This is only limited by the artistic

design; the outer part of the helmet is

covered with PLA-calendered cloth.

Similarly, the ladies fashion brand,

Rizieri, of Milan, Italy, has created an

innovation known as ‘Zero Impact’,

involving models of ‘handmade’

products based on PLA or Ingeos

fabric. These products have all the

delicacy of silk to the touch

316

POLYLACTIC

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substitute existing petrochemical polymers, with the advantagethat the PLA products have environmentally friendly produc-tion and are biodegradable upon disposal.

8.3 Poly(lactic Acid) for Engineering andAgricultural Applications

PLA is suitable for typical engineering applications thatimpose environmental burdens at the end of life. The rigidityof PLA can ensure good mechanical properties during applica-tions, and yet it can easily undergo biodegradation after dis-posal. The use of PLA for essential engineering parts islimited. The use of PLA is mostly focused on secondary appli-cations as listed in Table 8.2. In relation to its use in electron-ics and electrical applications, Table 8.3 sets out a comparisonof PLA and PVA-coated cables.

8.4 Poly(lactic Acid) for BiomedicalApplications

In the early days of PLA development, most of its applica-tions were in the biomedical field. PLA continues to be used inthis arena (see Table 8.4). It is widely used in scaffolds to pro-vide temporary structural support for the attachment andgrowth of tissues in surgery. It is also used as a drug carrier,containing controlled release active agents for long-term treat-ments, including for cancer.

8.5 Conclusion

PLA is a very useful polymer that has found applications ina wide range of industries. PLA is well positioned in a nichemarket because of its biodegradable and environmentallyfriendly characteristics. Its applications in the biomedical andpharmaceutical field can be traced back several decades.

3178: APPLICATIONS OF POLY(LACTIC ACID)

Table 8.2 Engineering and Agricultural Applications of PLA


Engineering materials Singoshu (Lactboards for draining plate) Drainage material is used in

construction ground works to reduce or

eliminate hydrostatic pressure while

improving the stability of the enclosed

materials. PLA drainage material has

good workability for soft ground with

sufficient permeability and tensile

strength. The favorable biodegradability

of PLA enables the drainage material to

return to nature safely. In other words,

after the consolidation period, PLA can

reduce the load on the surrounding

environment and be detoxified. The PLA

material can become impaired after

completion of the shield for excavation

and underground construction

consolidation settlement

Automotives Toyota (floor mat of Toyota Prius and

spare tire cover), Toray (fiber for car

mat), etc.

The automotive industry uses large

quantities of plastics, especially

polyethylene, polyvinyl chloride (PVC)

318

POLYLACTIC

ACID

and acrylonitrile-butadiene-styrene

(ABS), which are derived from non-

renewable petroleum sources. The levels

of recycled plastics in use are as low as

30% (by weight); the remaining are

virgin polymers. When the car is

disposed of, the percentage of plastic

recycled from it can be as low as 20%.

This means that a large volume of

automotive plastics eventually end up

polluting the environment. PLA is an

environmentally friendly material for

automotive applications. This is

particularly important for those parts

that cannot be recycled, such as car mats

and cushion fabrics. The rigidity of PLA

is an advantage for external cover

applications. Although PLA is

biodegradable, the rate of degradation is

low and requires high moisture

conditions to initiate the hydrolysis

process (the depolymerization reaction).

The involvement of microorganisms

takes part only after the

depolymerization reaction transforms the

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Table 8.2 Engineering and Agricultural Applications of PLA—cont’d


material to low-molecular-weight

oligomer lactate. Normally, this process

takes time, and this exceeds the lifetime

of the products

Building materials LG Hausys (laminated flooring and

wallpapers), Saint Maclou (carpets),

Sommer Needlepunch (Eco2punchs

carpets), etc.

Most PLA products in the construction

industry are related to flooring. Products

include carpet, laminated flooring

materials and wallpapers. PLA in this

area is aimed at substituting PVC, which

dominates as a building material. One of

the problems of PVC is that its

processing requires plasticizers, which

increases flammability. Consequently,

halogen flame retardants are added to

achieve better fire resistance. In contrast,

PLA is derived from agricultural

sources, and involves less toxic

substances during processing stage.

Most of the building materials made

of PLA can last well when well

maintained. These PLA products can be

320

POLYLACTIC

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disposed without causing serious

pollution to the environment at the

end of life

Electrical and

electronics

Fujikura (conductor cable coating),

Renesas (computer network device

casing), ABB (socket casing), etc.

The usage of PLA in the electrical industry

is still in the developing stage. PLA can

be used as the coating agent for

conductor wire. It can also be easily

formed into rigid casing for socket and

plug applications. Nakatsuka (2011)

compared PLA with polyethylene and

polyvinyl chloride (PVC) found that the

resistivity of PLA (4.33 1017 Ωcm) is

higher than polyethylene (.1016 Ωcm)

and PVC (1011 to 1014 Ωcm). The

dielectric dissipation factor of the three

polymers are PLA5 0.01%,

polyethylene5 0.01% and

PVC5 0.10%. Generally, PLA has

equally good electrical properties as

other commodity polymers used in the

electric and electronics industries.

(See Table 8.3 for a comparison of

PLA and PVC cable)

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Table 8.2 Engineering and Agricultural Applications of PLA—cont’d


Agricultural FKuR Kunststoff GmbH (Bio-Flex

mulch film), Desch Plantpak B.V.

(D-Grades Bio thermoformed flower

pot, trays and packs), BASF (Ecoflexs

mulch film)

The biodegradable characteristic of PLA is

favorable in agricultural applications.

This is because PLA can be well

composted without leaving harmful

residues in the soil. PLA mulch film can

provide soil protection, weed

management, fertilizer retention, etc.

Over time, the mulch films slowly

degrade and finally decompose when the

crops reach the harvest period. This

eliminates the need for farmers to

collect and dispose of the used mulch

film. The composted PLA mulch film

also provides soil nutrients. Flower pots

made of PLA can be buried in soil and

left there to degrade when the plant is

ready to be planted in the ground

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Table 8.3 Evaluation of PLA-Coated Cable in Comparison with PVC-Coated Cable (Nakatsuka, 2011)

Item/Cable Pure PLA Plasticized PLA with

Flexibility

600 V PVC Cable (IV)

JIS C 3307

Extrusion ’: Excellent appearance ¢: Excellent appearance �¢: Void in surface between conductor and

insulation

’: Analogous with pure

PLA

Bending £: Whitening at 10 times bending and cracking

at 4 times bending

¢: Whitening at 2 times

bending

�

’: No cracking at self-

diameter bending

Tensile ’: Strength5 59 MPa ’: Strength5 43 MPa Strength .10 MPa

£: Elongation5 12% £: Elongation5 25% Elongation .100%

Heat

deformation

J: 60�120�C5 reduction ,10% J: 60�90�C5 reduction

,10%

Thickness reduction less

than 50%

£: 120�C5 reduction 58%

Electrical J: tan δ5 0.35%, ε5 3.2 £: tan δ5 2.31 %, ε5 4.1 ρ5 53 1012 ΩcmJ: ρ5 2.73 1016 Ωcm ’: ρ5 4.63 1012 Ωcm

Dielectric

breakdown

J: 35B45 kV (0.7 mm thickness) J: 45B50 kV (0.7 mm

thickness)

Withstand voltage test

1.5 kV3 1 min

Dielectric

breakdown

with bending

£: Cracking at 4 times bending ’: 25 kV at self-diameter

bending

�

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Table 8.4 Biomedical Applications of PLA


Surgical

implants

Zimmer (Bio-stataks suture anchor and

bone cement plug), Ethicon

(Vicryl suture and Vicryl mesh) and

Sulzer (Sysorbs screw), etc.

PLA and its copolymer PLGA (polylactide-co-

glycolide) are compatible with living tissue.

However, this is limited to the L stereoisomer

of PLA because mammalian bodies only

produce an enzyme that breaks down this one.

PLA and PLGA are used to fabricate screws,

pins, scaffolds, etc., to provide a temporary

structure for the growth of tissue, eventually

breaking down after a certain period. The

purpose of copolymerizing with comonomer

glycolide is to control the rate of degradation

through the modification of crystallization.

Sometimes, L and D isomers of lactides are

copolymerized for this purpose. Although

poly(D-lactic acid) cannot be consumed by

the body’s enzymes prolonged exposure to

body fluid tends to initiate hydrolysis, which

eventually breaks down the macromolecules.

Orthopedic surgery often uses PLA and

copolymers to fabricate artificial bones and

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POLYLACTIC

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joints. PLA has been used to make

surgical sutures for decades. In short, PLA is

an important material for biomedical surgical

applications

Drug carrier Abbott (Lupron Depots for palliative

treatment of advanced prostate cancer),

AstraZeneca UK Limited (Zoladexs,

an injectable hormonal treatment for men

with certain types of prostate cancer),

Janssen Pharmaceuticals (Risperdals

Constas, for treatment of schizophrenia

and for the long-term treatment of bipolar I

disorder), etc.

Most of the PLA drug carriers on the market

are available in the copolymer form. This is

due to the fact that high purity PLA possesses

high crystallinity and takes a longer time

to degrade while releasing active drugs.

The majority of PLA drug carriers are

copolymerized with different percentages

of polyglycolic acid (PGA). Normally such

drug carriers slowly release the medication

for long-term treatments. For instance,

leuprolide acetate applied with a microsphere

delivery system of PLA and PLGA is used for

the treatment of cancer and fibroids. PLGA

(polylactide-co-glycolide) can be used in the

form of implants and gels with the

therapeutics goserelin acetate and paclitaxel

for the treatment of prostate/breast cancer,

or other anticancer drugs

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The development of PLA applications in recent years mainlyrelates to environmental concerns and the adverse effects of usingnon-degradable petrochemical-based polymers. The use of PLAhas grown well in the domestic market for general consumergoods and, importantly, in biodegradable packaging. The devel-opment of PLA is forecast to grow tremendously in the future,making the price of PLA as economical as commodity plastics,but with the added benefit of being kinder to the environment.

References

American Association of Textile Chemists and Colorists, 2006.

AATCC Test Method 135-2004 Dimensional Changes of Fabrics

after Home Laundering.

Nakatsuka, T., 2011. Polylactic acid-coated cable. Fujikura Tech.

Rev. 40, 39�45.

Natureworks, 2011a. Can a t-shirt help change the world? Available at

,http://www.natureworksllc.com/Product-and-Applications/Apparel.

aspx..

NatureWorks, 2011b. Thermal Stability of PLA Preform. Available at

,http://www.natureworksllc.com/..

NatureWorks, 2011c. Choosing a bottle to make a difference.

Available at ,http://www.natureworksllc.com/Product-and-

Applications/Bottles.aspx..

NatureWorks, 2011d. Can plastic dinnerware make a difference?

Available at ,http://www.natureworksllc.com/Product-and-

Applications/Serviceware.aspx..

NatureWorks, 2011e. Top if off with NatureWorks PLA Dairy and

Delicatessen Container Lidding Solutions. Available at ,http://

www.natureworkllc.com..

NatureWorks, 2011f. Can fresh food packaging help change any-

thing? Available at ,http://www.natureworksllc.com/Product-and-

Applications/Fresh-Food-Packaging.aspx..

NatureWorks, 2011g. Can a simple plastic film wrap really make a

difference? Available at ,http://www.natureworksllc.com/

Product-and-Applications/Films.aspx..

NatureWorks, 2011h. Can your next plastic card really make a differ-

ence? Available at ,http://www.natureworksllc.com/Product-and-

Applications/Cards.aspx..

326 POLYLACTIC ACID

http://www.natureworksllc.com/Product-and-Applications/Apparel.aspx

http://www.natureworksllc.com/Product-and-Applications/Apparel.aspx

http://www.natureworksllc.com/

http://www.natureworksllc.com/Product-and-Applications/Bottles.aspx

http://www.natureworksllc.com/Product-and-Applications/Bottles.aspx

http://www.natureworksllc.com/Product-and-Applications/Serviceware.aspx

http://www.natureworksllc.com/Product-and-Applications/Serviceware.aspx

http://www.natureworkllc.com

http://www.natureworkllc.com

http://www.natureworksllc.com/Product-and-Applications/Fresh-Food-Packaging.aspx

http://www.natureworksllc.com/Product-and-Applications/Fresh-Food-Packaging.aspx

http://www.natureworksllc.com/Product-and-Applications/Films.aspx

http://www.natureworksllc.com/Product-and-Applications/Films.aspx

http://www.natureworksllc.com/Product-and-Applications/Cards.aspx

http://www.natureworksllc.com/Product-and-Applications/Cards.aspx

NatureWorks, 2011i. IngeoTM fibers comparison with soy and bam-

boo fibers. Available at ,http://www.natureworksllc.com..

NatureWorks, 2011j. Basic fiber properties. Available at ,http://

www.natureworksllc.com..

NatureWorks, 2011k. Wipes toxicology study/ regulatory informa-

tion, access ,http://www.natureworksllc.com..

3278: APPLICATIONS OF POLY(LACTIC ACID)

http://www.natureworksllc.com




Index

AAcetyl (CH3C) groups, 11

Activation energies of PLA, 129t

Aliphatic polyesters, 34�41

Amorphous-made PLA films,

characteristics of, 258t

Analytical technique of PLA

CH symmetric stretching,

159�161

Fourier transform infrared

spectroscopy (FT-IR),

157�1591H and 13C NMR spectra,

154�156, 155f, 156f, 157f

infrared (IR) spectroscopy,

157�162

nuclear magnetic resonance

(NMR) spectroscopy,

154�157

aOH stretching band,

157�159

presence ofaCQO carbonyl,

157�159

Applications of PLA, 25t

biomedical, 43�57, 52t,

143�144, 317, 324t

domestic, 33�42, 302�317,

303t

engineering, 317, 318t

BBagley correlation, 221�222

Bakelite, 2

Bio-based polyethylene, 17�19

Biodegradability and

biodegradation of PLA

aerobic and anaerobic

biodegradation, 266�267,

266t

chemical bonding and,

249�251

copolymer compositions,

effect of, 251�252

degradation time, 251t

environmental degradation,

265�278

factors affecting, 248�255

flame resistance, 288�295

fungal strains involved in,

273�275, 274t

high-molecular-weight

polyesters, 253

hydrolytic and enzymatic

degradation, 255�265

microorganisms involved in,

273

molecular weight and

crystallization, effect of,

252�253

test under controlled

composting conditions,

275�278, 276t, 277f, 278f,

279f

thermal degradation,

278�287

using cumulative

measurement respirometric

(CMR) system, 269�272

329

Biodegradability and


(Continued)

in vivo degradation

mechanisms, 254�255

water uptake and acidity,

253�254

Biodegradable polyesters, 10f, 12

Biodegradable polymers, 3,

17�19

background, 1�13

biological applications, 6�10

common, 7t

definitions of common

biological terms, 250t

degradation modes, 256f

degradation time, 251t

evolution after 28 days, 268f

hydrolyzable polymers, 251t

market potential, 13�33

petroleum-derived, 12, 16

physical properties of

synthetic, 50t

weight losses due to

hydrolysis, 257�261, 258t,

259f, 260t, 263f

Bio-ethanol, 17�19

Bio-Flexs, 41

BioFoams, 24�31

BIOFRONTt, 23�24, 31�32

Biomaxs, 211

Biomedical applications, of

PLA, 43�57, 52t,

143�144, 317, 324t

Bionollet, 12

Bionolles, 199�200

Bionollet PTT 1100, 13

Blendex 338, 210

Blends, polymer. see polymer

blends

Brabender extruder, 224�226

Branching in PLA, 230�232

Bulk production PLA, 20�22

CCapillary rheometers, 221�222

e-caprolactone, 46�51, 80�83,

95

monomer, 98

Capronors, 6�10

Cargill Dow Polymer LLC, 5

Carothers, Wallace, 5

Carreau�Yasuda model

parameters, 231t

Cellulose acetate, 11

fabric, knitted, 11

Cellulose polymers, 19�20

C�H bending bands, 126�128

Chemical properties of PLA

copolymerization effects,

148�149

crystallinity and supercooling,

149�152, 150f

crystallization half-time,

148�152, 150t

α-form, β-form and γ-form,

152, 159�161, 160f

infrared (IR) spectroscopy,

157�162

lactide isomers, 147�148

nuclear magnetic resonance

(NMR) spectroscopy,

154�157

permeation properties,

164�172, 168t, 169f

revised tetrad stereosequence,

154�155

solubility, 163�164, 165t, 166t

‘solution-diffusion’ model,

170�171

330 INDEX

stereochemistry, 146�153

stereoregularity, 154

stereosequence distribution,

154�155

stereospecific isomer,

171�172

thermodynamic criterion of

solubility, 163�164

water vapor transmission

rates, 170t

China, PLA in, 32�33

Climate change, PLA and, 61f

Cloisite 25A, 201�202

Columbus, Christopher, 1

Commercial-grade branched

material, 230

Condensation polymerization of

lactic acid, 89�90, 90f

Copolymerization

of lactide and glycolide,

97�99

of L and D stereochemistry,

34�41

Copolymers, 24�31

Cross�WLF model coefficient,

225t

Cup system, 63�64

b-cyclodextrin, 104

DDecomposition temperature of

PLA, 123�131

Depolymerization of PLLA, 126

Development of PLA, in early

days, 144�145

Dextrose, biological

fermentation of, 10�11

Directive 94/62/EC on

Packaging and Packaging

Waste, 16�17

Directive 1999/21/EC on the

Landfill of Waste, 16�17

Directive 2008/98/EC on waste

(Waste Framework

Directive), 16�17

Distortion/deflection

temperature, impact on, 41

D-lactic acid, 74, 80�83, 88�89,

95�96, 163, 247�248,

251�252, 254�255

content in PLA, calculations,

104�105

presence, evaluation of,

103�105

D-lactide, 34�41, 92�93, 229

Domestic application, PLA for,

33�42, 302�317, 303t

Downstream processing, 20�22

Drug carrier medium, PLA as,

51, 54t

Durect Lactels, 57t

EEastar Bios, 12�13

Eastar Bios Ultra, 12�13

Ecodeart, 31�32

Eco-efficiency, of PLA post-

consumer, 63

Ecoflexs, 12�13

Eco-indication points, 63�64,

65f

Ecological aspects of PLA

production, 61�63

Eco-plastic products, 17

Ecoprofile of PLA in mass

production, 58�63

Ecovios, 12�13, 20�22

Elastic poly(e-caprolactone/

L-lactide) (PCL/L-LA)

copolymer with PLLA, 193

331INDEX

Engineering applications, PLA

for, 317, 318t

Environmental degradation of

PLA, 265�278

Environmental impact of PLA,

63�66

Environmental profile of PLA,

57�58

European standard EN 13432,

16�17

European Union, PLA in, 31

Extensional viscosities of PLA,

232�233

FFibers, PLA, 145�146

First generation PLA, 63�64

FKuR Kunststoff GmbH grade,

44t

Flame resistance of PLA,

288�295

Food packaging polymer, PLA

as, 145�146

Fossil energy requirement for

PLA, 59�61, 60f

Fremy, 73�74

Futerros, 41

Futerro specification, 48t

GGalacids, 84�85, 85t

Glycolide, 95

Glycolide-content copolymer,

97�99

Goodyear, Charles, 1

‘green’ credentials of PLA,

145�146

Green plastic technologies,

23�24

HHeat capacity of PLA, 132, 133t

High-molecular-weight PLA,

23�24, 145�146

Hisun Biomaterial PLA

specification, 47t

Hydrolisis of PLA, 124f

Hydroxycyclic ester initiators,

230

IIngeot, 5, 23�24, 34�41,

58�61, 63�66, 66t

IngeosPLA, 80�83

IR spectrum of PLA, 157�162

LLactate ester, 86

Lactels, 51�57

Lactic acid

with addition of bases,

production, 77�80

during anaerobic exercise,

production, 73

bacteria, 74�75, 75t, 77�80,

146�147

from bacteria fermentation,

74�75

broth from the fermentor, 80

chemical synthesis approach,

83

commercial purified, 84�85

condensation polymerization,

90f

evaporation and

prepolymerization stages,

90�92

and feeling of soreness, 73

fermentation process, 74�75,

77�80, 84, 146�147

332 INDEX

industrial, 84�85

laboratory scale production,

85�86

NatureWorks, 80

pharmaceutical grade, US, 85

physical properties, 73t

polylactide (PLA) from,

43�46

production, 72�85

Purac’s, 30f, 57�58, 61�63

purification technologies, 80,

81t

reaction of polymerization

and depolymerization

reaction, 90�92, 91f

sugarcane-based production,

57�58

synthesis in lactate form, 85b

water removal during

production, 89�90

yield corresponding to type of

starchy and cellulosic

material and to

microorganism, 78t

Lactide, 5

coordination-insertion chain

growth reaction scheme,

96f

Lactide copolymer, 97�99

Lactide�dioxanone copolymer,

98�99, 100f

Lactide�glycolide copolymers,

97�98

tensile strength, 99t

Lactide polymerization, 95�96

Lactide production technology,

88�93

anionic initiators used, 94�95

cationic initiators used,

94�95

mass-scale production, 88

polymerization and

copolymerization, 94�97

process flow, 89f

US Patent 5 274 073, 88�89

Lactobacillus species, 74�77,

75t, 76t

Le Chatelier’s principle, 90�92

Lignocellulosics, 2�3

Limiting oxygen index (LOI),

288�290

Linear-branched PLA, 231

L-lactic acid, 43�46, 79t,

80�83, 88�89, 251�252,

254�255

L-lactide, 74, 92�93

Long-chain poly(p-dioxanone),

98�99

Low-molecular-weight PLA,

86�87

MMark�Houwink equation, 233,

234t

Market potential of PLA, 13�33

Mass production, ecoprofile of

PLA in, 58�63

MaterBis sample, 266�267

MBA900H, 23�24

Mechanical properties of PLA

of annealed poly (D,L-lactide)

specimens, 181t

of blends of polylactide with

nondegradable polymers,

213t

crystallinity and molecular

weight, effect of, 179�182

electron irradiation and,

286�287

elongation at break, 190�191

333INDEX

Mechanical properties of PLA

(Continued)

glucose monoester or partial

fatty acid ester, effect of,

188

nanocomposites, 212�215

from NatureWorks LLC, 178t

of nonannealing poly (D,L-

lactide) specimens, 181t

oligomeric lactic acid, effect

of, 189�190

PBOH, AGM and DBS, effect

of, 190�191

PLA/organoclay

nanocomposites, 195

for PLA/PCL, 195, 196t, 198

PLA�PCL�PLA triblock

copolymer, 195

PLA/polystyrene blend,

239�240

plasticizers and modifiers,

effect of, 182�191, 183t

with polycaprolactone (PCL),

blending with, 192�197

poly(ethyleneco-vinyl acetate)

(EVA), effect of, 189�190

polyethylene glycol

monolaurate, effect of,

189�190

poly(ethylene glycol) (PEG),

effect of, 189�191

of polylactide/PHA blends,

208t

of poly(L-lactide) specimens,

180t

polymer blends, 191�215

with poly(tetramethylene

adipate-co-terephthalate)

(PTAT), 198�199

triacetin (TAC), effect of, 190

Meso-lactide, 34�41, 88�89,

156�157

Methyl trifluoromethane

sulfonic acid, 94�95

Microorganism-derived

biodegradable polymers, 3

Mineralization of PLA, 272,

272f

Mirelt, 10�11

MMT nanoclays, 210

Moldflows software, 224�226

Multicyclic esters, 230

Multifunctional polymerization

initiators, 230

NNatureWorks, PLA by, 58�61,

59f

NatureWorks grades, 35t, 37t,

39t

NMR spectrum of PLA,

154�157

N,N,N0,N0-tetramethyl-1,4-

phenylenediamine (TMPD),

284�286

Nodaxt, 206�207

OoligoNodax, 206�207

oligoNodax-b-poly(L-lactide)

diblock copolymers,

206�207

Organically modified

montmorillonite (OMMT),

294�295, 294t

Oxo-biodegradable plastics,

3�4

Oxo-biodegradable polymers,

3�4

334 INDEX

PPaperMates, 10�11

Patents published about PLA, 6f

PBS/PBSA, 12

p-dioxanone monomer, 98�99

PE-coated cardboard cup, 63�64

Pellethanet 2102-75A, 210

Permeation properties of PLA,

207�215

Petrochemical polymers and

climate change, 61f

Petroleum-derived

biodegradable polymers, 3,

12, 16

Phenol-formaldehyde resin, 2

Picea sitchensis, 121�122

PLA-copolymer-related drug

delivery system, 51�57

PLAGA copolymer, 273�275

Plastics

ban on non-degradable,

16�17

certification of compostable,

18t

degradability of, 2�3

global producers, 13�14

products, 15�16

renewable biodegradable, 20f

reusable plastic bags, 17

world production, 13�14

worldwide demand, 14�15

Plastic surgery, PLA in, 51

Polybutylene adipate/

terephthalate (PBAT), 13

Polycaprolactone (PCL), 6�10

Polydioxanone (PDO), 6�10

Poly(D-lactide)/poly(D-lactic

acid) (PDLA), 43�51,

109�112, 143�144

copolymers, 113

Poly(DL-lactide)/poly(DL-lactic

acid) (PDLLA), 109�111,

114f, 143�144

Polyethylene, 2�4

Poly (ethylene oxide) (PEO),

188�189

Polyethylene terephthalate

(PET), 13, 164

permeability, 166�169

Polyglycolic acid (PGA), 6�10

Poly(3-hydroxyalkanoate)

(PHA)/PLA blends,

205�206

Polyhydroxyalkanoates (PHA),

10�11

Poly(b-hydroxybutyrate-

co-hydroxyvalerate)

(PHBV), 169�170

Poly-3-hydroxybutyrate-

covalerate (PHBV), 10�11

Polyhydroxybutyrate (PHB),

10�11

Poly(lactic acid)/polylactide

(PLA), 3, 5

applications, 25t

arrangement of molecules of

semicrystalline, 222�223

average prices, 22�23

biodegradability, 144.

see also biodegradability

and biodegradation of PLA

biomedical applications,

43�57, 52t, 143�144, 317,

324t

bulk production, 20�22

Carreau�Yasuda model

parameters, 231t

characteristics of amorphous-

made, 258t

in China, 32�33

335INDEX

Poly(lactic acid)/polylactide

(PLA) (Continued)

and climate change, 61f

copolymers, 24�31

cross�WLF model

coefficient, 225t

cup system, 63�64

development, early days,

144�145

direct method of synthesizing,

144�145

distortion/deflection

temperature, impact on,

41

domestic application, 33�42,

302�317, 303t

downstream processing,

20�22

as a drug carrier medium, 51,

54t

eco-efficiency, post-

consumer, 63

eco-indication points, 63�64,

65f

engineering applications, 317,

318t

environmental profile of,

57�58

in the European Union, 31

family, 144

fibers, 145�146

first generation, 63�64

FKuR Kunststoff GmbH

grade, 44t

as a food packaging polymer,

145�146

fossil energy requirement,

59�61, 60f

Futerro specification, 48t

‘green’ credentials, 145�146

high-molecular-weight,

23�24, 145�146

Hisun Biomaterial

specification, 47t

impact on environment,

63�66. see also

biodegradability and


from L-lactic acid, 43�46

market potential, 13�33

mass production and

ecoprofile, 58�63

by NatureWorks, 58�61, 59f

NatureWorks grades, 35t, 37t,

39t

patents published, 6f

PLA-coated cable vs PVC-

coated cable, 323t

in plastic surgery, 51

power�law equation, 225t,

236

Purac’s product range,

24�31, 51�57

research publications

(1950�2009), 6f

routes for synthesis, 144f

second generation, 59�61

Toyobo grade, 46t

Unitika�Terramacs grade,

42t, 43t

virgin PET (vPET) vs

recycled PET (rPET),

66t

Polylactic acid resin producers,

32t

Polylactide bottles,

biodegradability study of,

267�269

in compost pile, 270f

evolution after 28 days, 268f

336 INDEX

Poly(L-lactic acid)/poly(L-lactide)

(PLLA), 109�111,

143�144

activation energy, 128�129

calcium-ion end-capped,

128�129

carboxyl-type, 128�129

depolymerization, 126

effects of pyrolysis, 128�129

functional groups of end-

capped, 128�129

IR spectra, 161�162

melting range, 112�113

PBS/PBSL blends, 200

PLLA/HDPE blends,

211�212

PLLA/LLDPE blends,

211�212

PLLA/Nodaxt blends,

206�207

PLLA/PBSA composites with

C25A and TFC, 200�201

PLLA/PBS blends, 201

PLLA�PEG�PLLA triblock

copolymer, 205

PLLA/PEO, 207�210

PLLA/PHB blends, 205

PLLA/PHBV blends,

202�205

PLLA/PTAT blends,

198�199

rate of hydrolysis, 264t

re-crystallization process, 261

stereochemical defects and

crystallization, 121�122

thermal decomposition,

123�125

thermal properties of

hydrolytically degraded,

261�264, 262t

thermograms, 114f, 259f

unit cell parameters for

non-blended, 143�144

Polymer blends, 191�215

with dicumyl peroxide (DCP),

194

elastic poly(e-caprolactone/

L-lactide) (PCL/L-LA)

copolymer with PLLA, 193

with nondegradable polymers,

207�215

PEO/PLLA blends, 207�210

PLA/Cloisite 30B blends,

210

PLA/ePHA blends, 205�206

PLA/PHA blends, 205�206

PLA/poly(butylene adipate-

co-terephthalate) (PBAT),

199

PLA/polyisoprene/poly(vinyl

acetate) blends, 210

PLLA/Nodaxt blends,

206�207

PLLA/PBS blends, 201

PLLA/PBSL blends, 200

PLLA�PCL diblock

copolymer, 193�194

PLLA�PCL�PLLA triblock

copolymer, 193

PLLA/PHB blends, 205

PLLA/PHBV, 202�205

PLLA/PHBV blends, 202

with polycaprolactone (PCL),

192�197

with poly(ethylene/butylene

succinate), 199�200

with polyhydroxyalkanoates

(PHAs), 202�207

of polylactide with

degradable or partially

337INDEX

degradable polymers,

198�202, 203t

poly(TMC/CL), 194�195

polyurethane/PLA networks,

194

with poly(vinyl acetate)

(PVAc), 207

solution and melt blending,

207

using triphenyl phosphite, 193

at XPLLA, 193�194

Polymerize lactide, 95�96

Polymers, 1

average prices, 22f

biodegradable, 3, 21f

global development, 2, 2f

oxo-biodegradable, 3�4

petroleum price and, 15�16

synthetic, 2

worldwide consumption, 15t

Polypropylene, 2�4

Polystyrene (PS), 2, 194�195

Polytetramethylene adiphate/

terephthalate (PTMAT), 13

Poly(vinyl acetate), 3

Poly(vinyl alcohol) (PVOH),

3�5, 249�251

average prices, 22�23

Poly(vinyl chloride) (PVC), 2

Potassium methoxide, 94�95

Power�law equation, 225t, 236

Prepolymer reactor, 89�92

PRO-BIP 2009, 17�19

Production of poly(lactic acid)/

polylactide (PLA),

86�105

application of coupling agents

in, 86�105

calculation of residual lactide,

102�103

catalyst used, 94t

coordination-insertion chain

growth reaction scheme of

lactide, 96f

direct polycondensation (DP)

route, 71�72

evaluation of D-lactic acid

presence, 103�105

evaporation and

prepolymerization stages,

90�92

formation of free radicals,

86�87

GC/FID method of residual

lactide quantification,

100�102, 101t

from initial fermentation

process, 92f

from lactate ester, 86

low-molecular weight, 86�87

low-molecular-weight

byproducts, 92�93

quality control, 99�100

quantification of residual

lactide in, 99�103

reaction of polymerization

and depolymerization

reaction, 90�92, 91f

ring-opening polymerization

(ROP) route, 71�72,

86�87

sample preparation for

testing, 104b

stereocomplex composition,

92�93

testing procedures, 99�100

transesterification mechanism,

90�92

US Patent 6 569 989,

92�93

338 INDEX

Proteinase K, 265t

Purac’s product range, 24�31,

51�57

PURALACTt, 24

Purasorbs, 51�57, 55t, 56t

PVC-coated cable

PLA-coated cable vs, 323t

PVT relationship of PLA,

132�138, 136t, 137t

Pyramid Bioplastics Guben

GmbH, 31

RRecycled PET (rPET)

virgin PET (vPET) vs, 66t

Recycling of biowaste, 16�17

Regular solution theory (RST),

164

Research publications about

PLA (1950�2009), 6f

Residual lactide, quantification

of, 99�103

calculations, 102�103

GC/FID method, 100�102,

101t

REVOD201, 41

REVODE101, 41

Rheological properties of PLA,

222�226

blends with layered silicate

nanocomposites, 237�239

branching effects, 230�232

extensional viscosities,

232�233

flow activation energy for

PLA70 blend, 243t

molecular weight, effect of,

226�229, 227t, 228f

non-Newtonian pseudoplastic

behavior of PLA, 224�226

of PLACNs, 237�239, 238f

PLA-melt viscosity, 223f,

224f

PLA/PBAT melts, 235�237

PLA/polystyrene blend,

239�243

of polymer blends, 233�243

shear viscosities, 222�224

solution viscosity, 233

true viscosity vs 1/T for

PLA70, 242, 242f

viscoelastic properties,

226�227

zero-shear viscosity,

227�229, 227t

Rheometric Dynamic Analyzer

(RDAII), 237

Rheometrics RDSII torsional

rheometer, 226�227

Rhizopus oryzae, 75�77

Ring-opening polymerization of

lactide, 86�87

Rotational rheometers, 221�222

Rubber, natural, 1

SScheele, Carl Wilhelm, 73�74

Second generation PLA, 59�61

Semicrystalline, arrangement of

molecules of, 222�223

Solution viscosity of PLA, 233

Stannous (Sn) complexes,

95�96

Starch-based plastics, 22�23

Starches, 2�3

Starch�polymer blends, 19�20

Stereochemistry of PLA,

146�153

Stereoisomer D-lactic acid,

43�46

339INDEX

Sulfur vulcanization, 1

Synthesis of PLA, routes for, 144f

Synthesizing PLA, direct

method of, 144�145

Synthetic polymer, 2

TTellest, 10�11

Teramacs, 31�32

Terramacs, 41

Thermal conductivity of PLA,

131�132, 135t

Thermal degradation of PLA,

278�287, 281t, 282f, 283f

Thermal properties of PLA

activation energies, 129t

annealing point, 115�116

crystallization, 111�123

degradation under isothermal

conditions, 125�126

determination, 109�111

DSC thermograms, 117f

fiber incorporation and

thermal transition, 121�122

food grade plasticizer, effects

of, 116�121, 120t

FTIR spectra, 126�128, 127f

glass transition behavior,

114�115

glass transition temperature,

112�115

heat capacity, 132, 133t

isomers, effects of, 111t

lactide and, 118

maleic anhydride (MA)-

compatibilized blends,

122�123

melting temperature and

enthalpies, 114�115, 119t,

149f

microstructure rearrangement

upon cooling, 111

molten polymer, 132�138

monomer types, impact on

structural properties,

121�122

PLA�starch blends,

122�123, 122t, 123f

pure PLA, 121�122

PVT relationship, 132�138,

136t, 137t

shear viscosity, 112�113

solubility parameters, 118t

stereocomplexed

PLLA�PDLA blend,

112�113

stereoform of lactides, 110f

thermal conductivity,

131�132, 135t

thermal decomposition,

123�131

thermogravimetry, 130f

transition temperature,

112�123

WF accelerated thermal

decomposition, 129�131

Tin octoate catalyst, 96�97

Titration reaction scheme,

271, 271

Toyobo PLA specification, 46t

Transesterification of PLA,

124f

Triallyl isocyanurate (TAIC),

286�287, 287f

Trifluoromethane sulfonic acid,

94�95

Tris(nonylphenyl), 231

Tris (nonylphenyl) phosphate,

231

Tweens80, 77�80

340 INDEX

UUL-94, 288�290, 289t, 291t,

292t

Unitika�Terramacs PLA

grade, 42t, 43t

VVinegar syndrome, 11

Virgin PET (vPET) vs recycled

PET (rPET), 66t

Vuitton, Louis, 11

Vulcanization of rubber, 1

Vyloecols, 24�31, 41

WWeissenberg�Rabinowitsch

correlation, 221�222

Williams�Landel�Ferry

equation (WLF), 229

ZZoladexs, 51

341INDEX

Polylactic Acid: PLA Biopolymer Technology and Applications

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Transcript of Polylactic Acid: PLA Biopolymer Technology and Applications