Web viewThe most considered active initiator for the L-lactide ring-opening polymerization is...

A class seminar on

USE OF POLY (LACTIC ACID) AS PACKAGING MATERIAL FOR

DAIRY INDUSTRY

By

Sushil Koirala

B Tech 4th year

Department of Food Technology

Pokhara Bigyan Tatha Prabidhi Campus

Institute of Science and Technology

Tribhuvan University, Nepal

2015

Sushil koirala[PLA in dairy industries],sushilbandhu.wordpress.com

Use of poly (lactic acid) as packaging material for dairy industry

A class seminar submitted to Department of food Technology,Pokhara Bigyan

Tatha Prabidhi Campus,Tribhuvan University.

Sushil Koirala


Pokhara Bigyan Tatha Prabidhi Campus,Pokhara

Institute of Science and Technology

Tribhuvan University, Nepal

April, 2015

ii


Tribhuvan University

Institute of Science and technology


Pokhara Bigyan Tatha Prabidhi Campus

Approval LetterThis class seminar entitled Use of Poly (Lactic Acid) as Packaging material for Dairy

Industry presented by Sushil Koirala has been accepted as the partial fulfillment of the

requirement for the B.Tech. Degree in Food Technology.

Seminar Committee

1. Campus Chief…………………………………………………….

Mr.Hari Prasad Khanal, Campus Chief

2. Convenor………………………………………………………….

Mr Ramesh Baral , Lecturer PBPC

3. Commentator……………………………………………………………….

Mr.Prakash Timalsina, Senior Technical Officer at Sujal Dairy and Lecturer, PBPC

Mr.Abhishek Khadka, Lecturer (PBPC) and UNYSAN member.

Date of Submission: 24th Chaitra, 2071

iii


Table of Contents

Approval Letter..............................................................................................................iii

Table of Contents...........................................................................................................iv

List of figures.................................................................................................................v

List of plates..................................................................................................................vi

List of Abbreviations.....................................................................................................vii

1. Introduction...............................................................................................................1

1.1 General Introduction.......................................................................................................1

1.2. Commercial viability of PLA..........................................................................................2

1.3 Use of Polylactic acid as a packaging material in dairy industry.....................................3

1.4 Statement of the problem.................................................................................................3

1.5 Objectives of the seminar.................................................................................................4

1.5.1 General objectives.........................................................................................................................4

1.5.2 Specific Objectives.........................................................................................................................4

1.6 Significance of the seminar..............................................................................................5

1.7 Limitations of the work...................................................................................................5

2. Literature review........................................................................................................6

2.1 Poly (Lactic Acid)............................................................................................................6

2.2 Synthesis and Production of Poly (lactic Acid)................................................................7

2.2.2 Lactic acid from Dairy Industry..................................................................................................9

2.2.3 Lactide and PLA production......................................................................................................10

2.2.4 Ring Opening Polymerization....................................................................................................10

2.2.5 Environmental Aspects...............................................................................................................11

2.2.6 Energy requirement in relation to production of PLA.............................................................12

2.3 PLA processing technologies for food applications........................................................12

2.3.1 Extrusion......................................................................................................................................13

iv


2.3.2 Injection molding........................................................................................................................13

2.3.3 Thermoforming...........................................................................................................................13

2.4 General Properties of PLA............................................................................................13

2.4.1 Thermal stability of PLA............................................................................................................13

2.4.2 PLA properties............................................................................................................................14

2.4.3 Barrier properties of PLA..........................................................................................................14

2.4.4 Studies on migration from PLA.................................................................................................14

2.4.5 PLA modifications.......................................................................................................................15

2.4.6 Biodegradability nature of PLA.................................................................................................15

2.5 Application of PLA........................................................................................................15

2.5.1 Reference to Dairy Industry.......................................................................................................17

2.6 Quality control of PLA..................................................................................................17

2.7 Pros and Cons of using PLA as Packaging material in Dairy industry.........................17

2.7.1 Pros...............................................................................................................................................17

2.7.2 Cons..............................................................................................................................................18

3. Conclusions..............................................................................................................20

REFERENCES............................................................................................................21

APPENDICES...........................................................................................................................................25

v


List of Tables

Table 1: Physical properties of Lactic Acid.........................................................................................8

vi


List of figures

Fig 2.1. Polymerization routes to Poly (lactic Acid) showing the formation of lactide and

PLA........................................................................................................................................7

Fig 2.2 General routes of PLA production showing direct polycondensation and ring

opening polymerization..........................................................................................................8

Fig 2.3: Stereo isomers of Lactic acid....................................................................................9

Fig 2.4 Greenhouse gas emissions (kg/ton) for production of various polymers. ..............11

Fig 2.5 Showing the energy requirement comparison of various packaging materials.......12

Fig 2.6: Some commercial PLA products............................................................................16

v


List of plates

Plate 1 Showing general process of PLA yoghurt cup manufacture from corn................................17

Plate 2 showing PLA cup..................................................................................................................19

vi


List of Abbreviations

Abbreviation Full form

PLA Poly (Lactic Acid)

PET Poly Ethylene Terapthalate

PE Poly Ethylene

PP Poly Propylene

GRAS Generally Recognized As Safe

BOD Biological Oxygen Demand

LDPE Low Density Poly Ethylene

DP Direct Polycondensation

ROP Ring Opening Polymerization

OPS Oxially Poly Styrene

LLDPE Linear Low Density Polyethylene

WVTR Water Vapour Transimission Rate

GC Gas Chromatography

FI Flame Ionization

PBPC Pokhara Bigyan Tatha Prabidhi Campus

UNYSAN United Nations Youth And Students Association

vii


1. Introduction

1.1 General Introduction

Poly (lactic Acid) (PLA) is the first commodity polymer produced from annually

renewable resources like corn starch and beet roots. Some of the environmental benefits of

PLA, such as low energy to produce and reduced green house gas production, are

presented and opportunities for the future . PLA was discovered in 1932 by Carothers (at

DuPont) . PLA is a rigid thermoplastic polymer that can be semi crystalline or totally

amorphous, depending on the stereo purity of the polymer backbone. L-lactic acid (2-

hydroxy prop ionic acid) is the natural and most common form of the acid, but D-lactic

acid can also be produced by microorganisms or through racemization and this “impurity”

acts much like co monomers in other polymers such as polyethylene terephthalate (PET) or

polyethylene (PE) .

PLA is a unique polymer that in many ways behaves like PET, but also performs a lot like

polypropylene (PP), a polyolefin. Ultimately it may be the polymer with the broadest range

of applications because of its ability to be stress crystallized, thermally crystallized, impact

modified, filled, copolymerized, and processed in most polymer processing equipment. It

can be formed into transparent films, fibers, or injection molded into blow moldable

preforms for bottles, like PET. PLA also has excellent organoleptic characteristics and is

excellent for food contact and related packaging applications. In spite of this unique

combination of characteristics, the commercial viability has historically been limited by

high production costs (greater than $2/lb). It is one of the few polymers that can be easily

modified by using a controlled mixture of L-or D-isomers to yield high molecular weight

crystalline or amorphous that can be used for food contact and are generally recognized as

safe (GRAS) .

The biggest advantage that puts Polylactic acid way in front of other biodegradable and

non-biodegradable materials is its biodegradability and biocompatibility. In 2008,

worldwide plastics production was around 245 million metric tons which can’t be degraded

.


PLA excels from others on this aspect as when pure PLA is exposed toexcessive heat or

moisture or as a natural process over time, the polymer chains that make up the substance

begin to break down. This creates ever smaller polymer chains. The result of this process is

lactic acid, which is a naturally occurring nutrient that is also found in milk. Lactic acid is

completely biodegradable, and it poses no threat to local wildlife or water supplies. As

lactic acid breaks down in the environment, it produces carbon dioxide, water, and stable

organic matter used to form humus and topsoil . Almost all the conventional plastics such

as PE, PP, PS, and PVC are resistant to microbial attack; on the contrary aliphatic

polyesters like PLA are readily degraded by microorganisms present in the environment

1.2. Commercial viability of PLA

PLA requires 20-50% less fossil resources than comparable petroleum based plastics. With

PLA, carbon dioxide is removed from the atmosphere when growing the feedstock crop

and is returned to the earth when PLA is degraded. Since the process recycles the earth’s

carbon, PLA has the potential to reduce atmospheric CO2 levels. Disposal of PLA fits with

existing systems including the additional option of composting. Long-term, with the proper

infrastructure, PLA products could be recycled back to a monomer and into polymers. The

landmass necessary for feedstock production is minimal. Producing one billion pounds of

PLA requires less than 0.5% of the annual US corn crop. Compared to the escalating and

volatile cost of petroleum-based feed stocks, long-term PLA will eventually reap the

benefits of a more stable and lower priced feedstock. In spite of PLA’s excellent balance of

properties and environmental benefits, traditionally the commercial viability of PLA has

been limited by high production costs, more than 2$ for 0.453 kg. Until the last decade,

PLA has enjoyed little success in replacing petroleum-based plastics outside of biomedical

applications like sutures. Though development of PLA is at the early stages of

commercialization versus more traditional, petroleum-based plastic, expansion of

commercial adoption for applications like PLA bottles has been rapidly increasing as of

late .

To address the challenges of high production cost for the production of PLA, newer

methods like Melt Condensation are being studied .

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Also by using other sources of dextrose, optimizing lactic acid, production processes and

its costs, substituting electricity energy by wind and solar energy for PLA production,

optimizing PLA production processes, and increasing PLA demands, reduction of its price

can be attained.

The present PLA price is much lower than in previous years, but it is not fixed and it even

will be considerably lower in the future because, according to expert forecasts, beyond

2010 the global demand for biodegradable plastics will continue to increase by 30% each

year and PLA will take a large part of this market because of its valuable properties .

1.3 Use of Polylactic acid as a packaging material in dairy industry.

Dairy industry produces huge volumes of wastes, both solid and liquids. This waste poses

escalating disposal and pollution (high BOD) problems and represents a loss of valuable

biomass and nutrients. However despite their pollution and hazard aspects, in many cases,

dairy processing wastes have a good potential of converting into useful products of higher

value as by-product, or even as raw material for other industries. Organic acids are

examples of such valuable by-product of the fermentation of high carbohydrate containing

industrial substrates. They therefore could be utilized cheaply as substrate for

microorganisms producing intermediate volume high value organic acids like lactic acid.

Lactic acid is under increasing demand in food and for production of polylactic acid

polymers, which possess outstanding packaging applications. Wastes generated from dairy

plants may be regarded as a viable option for meeting this growing demand for lactic acid

and lactic acid has received attention for use if a wide range of applications mostly as it

acts as a monomer for the production of biodegradable PLA .

PLA with incorporated bioactive material has been effectively used for milk packaging .

1.4 Statement of the problem

According to environmental, economic, and safety challenges have provoked packaging

scientists and producers to partially substitute petrochemical-based polymers with

biodegradable ones. The figures shows the global production of plastic to stack up to 245

million metric ton ,that’s a lot of non-biodegradable petroleum based plastics. Plastics

manufacture makes up 4.6% of the annual petroleum consumption in the U.S., using

3


roughly 331 million barrels per year. None of this energy is recovered when plastics are

disposed of in landfills, and very little is recovered when plastic waste is incinerated . So

the need of the hour and focus is to shift to biodegradable biopolymers to save the world

and reduce the use of petroleum based packaging materials. Dairy industry possess

problem in LDPE and pouch packaging its low mechanical and wet strength . Also it has

problems on low temperature fragility and when stored at lower temperature LDPE

packaging material doesn’t contain to the stored temperature.

1.5 Objectives of the seminar

1.5.1 General objectives

To study the use of PLA as packaging material.

To study the prospective use of PLA in dairy Industry.

1.5.2 Specific Objectives

To study the emergence and actual bottlenecks of PLA

To study the production, application, merits and demerits of PLA as packaging

material

To study the compatibility of PLA as packaging material for Dairy industry.

4


1.6 Significance of the seminar

To cognizant food technologist on the perspective supersede of it to conventional

packaging material that impose the environmental threats.

To study the potentiality of PLA on the basis of its cost and energy keeping in mind

the adoption in industry is focused on this matter.

To present Poly (Lactic Acid) as a potential alternative packaging material to dairy

industries from the waste generated by dairy industries.

To give impetus to food technologist on Packaging material in broad sense as well

with knowledge of application of PLA in dairy industry.

This entire attempt is to make a world greener and better.

1.7 Limitations of the work

No work is an easy walking like ice on the cake. There were few uphill challenges and task

that led to constraints of this study. Few of them are mentioned below

This study fails to relate the use of PLA for developing country like ours where

primary basic packaging material has still not found its place.

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2. Literature review

2.1 Poly (Lactic Acid)

Research and development of packaging materials and packaging technology have shown a

clear and irreversible trend toward “green” and active packaging. New studies on

packaging materials have emphasized the use of biobased materials. The examples include

agricultural fibers; products and byproducts from agricultural processing such as cellulose,

starch, and pectin, polymers were synthesized using renewable biobased monomers, such

as (PLA), polyhydroxybutyrate, and Ecoflex®, as well as proteins from animal tissues,

soybean flour, and corn. Those materials are biodegradable, and their final degradation

products are nontoxic and environmentally friendly .

Among these biobased monomers, PLA have caught the worlds’ attention.PLA is aliphatic

polyester, a thermoplastic, high strength, high modulus polymer that can be made from

100% renewable resources. PLA is degraded by simple hydrolysis of the ester bond and

does not require the presence enzymes to catalyze this hydrolysis .

In today’s world of green chemistry and concern for the environment, PLA has additional

drivers that make it unique in the marketplace. The starting material for the final polymer,

lactic acid, is made by a fermentation process using 100% annually renewable resources.

The polymer will also rapidly degrade in the environment and the by-products are of very

low toxicity, eventually being converted to carbon dioxide and water.

PLA can be prepared by both direct condensation of lactic acid and by the ring-opening

polymerization of the cyclic lactide dimer, as shown in Figure 2.1.

Because the condensation route is an equilibrium reaction, difficulties of removing trace

amounts of water in the late stages of polymerization generally limit the ultimate molecular

weight achievable by this approach. Most work has focused on the ring-opening

polymerization of lactide, although other approaches, such as azeotropic distillation to

drive the removal of water in the direct esterification process, have been evaluated. Cargill

Dow LLC has developed a patented, low-cost continuous process for the production of

lacticacid-basedpolymers.

6


The process combines the substantial environmental and economic benefits of synthesizing

both lactide and PLA in the melt rather than in solution and, for the first time, provides a

commercially viable biodegradable commodity polymer made from renewable resources

Fig 2.1. Polymerization routes to Poly (lactic Acid) showing the formation of lactide and PLA

2.2 Synthesis and Production of Poly (lactic Acid)

Poly (lactic acid) (PLA) is produced from the monomer of lactic acid (LA). PLA can be

produced by two well-known processes .

direct polycondensation (DP) route

And the ring-opening polymerization (ROP) route.

Although DP is simpler than ROP for the production of PLA, ROP can produce a low-

molecular-weight brittle form of PLA. Generally, several substances are involved in the

production of PLA, and these relationships have been summarized in figure 2.1. The lactic

acid for the process is obtained from the fermentation of sugar. Lactic acid is converted to

lactide and eventually to PLA. It should be noted that there are two different terms, ‘poly

(lacticacid)’and ‘polylactide’, for the polymer of lactic acid.

7


Fig 2.2 General routes of PLA production showing direct polycondensation and ring opening polymerization

2.2.1 Lactic Acid Production.

Lactic acid as we can see from above figure is a building block of PLA production. It is

chemically known as 2-hydroxy-propionic acid with chiral stereoisomer L (-) and D (+)

isomers. Its physical properties are listed in Table 1

Table 1: Physical properties of Lactic Acid

CAS Registry No. 50-21-5(DL-lactic acid)79-33-4(L-lactic acid)

Chemical Formula C3H603

Chemical Name 2-Hydroxy-Propanoic acidMolecular Weight 90.08Physical Appearance Aqueous solutionTaste Mildly sourMelting Point 53°CBoiling Point >200°CSolubility in water(g/100 g H20)

Miscible

Dissociation constant, Ka 1.38*10-4

pKa 3.86pH(0.1% solution,25*C) 2.9

Many dairy products, including yogurt and cheeses, taste mildly sour due to the presence

of lactic acid, which provides additional antimicrobial action in these products . Pure lactic

8


acid has two stereoisomer (also known as enantiomers), which are shown in Figure 2.2.

These two stereoisomers are synthesized by different lactate dehydrogenase enzymes in

living organisms. Currently, 85% of the lactic acid produced is con-sumed by the food-

related industry, while the balance is used for non-food applications, such as the

production of biopolymers, solvents, etc

Fig 2.3: Stereo isomers of Lactic acid

The lactic acid bacteria fermentation process is carried out anaerobically with low energy

production. Red dy et a l. (2008) has divided the Lactobacillus genus into three groups

according to fermentation patterns, namely heterofermentative, homofermentative and rare

heterofermentative. So the microbial fermentation process yield Lactic acid which

according to needs purification technologies like electrodialysis, reverse osmosis, liquid

extraction and ion exchange.

2.2.2 Lactic acid from Dairy Industry

Dairy industry residues comprise a large variety of different biomasses and sludges that

can be roughly categorized to agricultural wastes and food production wastes. Food

9

Sushil koirala[PLA in food industries],sushilbandhu.wordpress.com

production residues have been tested for bioconversion applications for ages, and the

variety of used materials is large. Whey and other dairy industry residues are the prominent

raw materials with respect to lactic acid production. Whey retains about 55% of total milk

nutrients, from which approximately 70% consists of lactose . Hence these lactose,

according to , Lactococcus lactis can covert lactose to lactic acid , a monomer for PLA.

2.2.3 Lactide and PLA production

Lactide is an intermediate substance in the production of PLA via the ring-opening

polymerization method which is also present in Appendix (A.1)

The purpose of the coupling agents is to increase the molecular weight of the PLA. In fact,

the lactic acid prepolymer is low- molecular-weight PLA. This low-molecular- weight

PLA is unusable- it possesses weak, glassy and brittle properties. According to , the

formation of low-molecular-weight PLA for direct reaction of prepolymer is mainly used

because of the lack of reactivity of the end groups, excess water and high viscosity of the

polymer melt once polymerization completed. Ring-opening polymerization of lactide was

first performed by Carothers in the mid-1900s, and later patents relating to this technology

by Du Pont kick- started the mass production of PLA. The general and basic steps for

lactide production include feeding the concentrated lactic acid into prepolymer reactor and

then polymerizing it. Then it is fed into lactide reactor where after processing crude lactide

is obtained in the form of vapour. Recovery is done by condensation and distillation. This

is again polymerized to form poly lactide .Now Ring opening polymerization proceeds to

produce PLA.

2.2.4 Ring Opening Polymerization

Lactide purification is accomplished by vacuum-distillation of high temperatures. After the

vacuum-distillation of L-lactide, high molecular weight PLA with a controlled optical and

crystal purity is formed by ring-opening polymerization. Ring-opening polymerization of

lactide can be carried out in melt or solution by cationic, anionic, and coordination

mechanisms, depending on the initiator utilized. The most considered active initiator for

the L-lactide ring-opening polymerization is stannous octoate (bis 2-ethyl hexanoate,

10


SnOct2), which causes a low degree of racemization at high temperature. It has a low

toxicity and is accepted by FDA.

Appendix A.1 shows ring opening polymerization with stannous octaoate as an initiator

2.2.5 Environmental Aspects

One of the most positive points of PLA production in comparison with the other

hydrocarbon-based polymers is the decrease of CO2 emission. Carbon dioxide is believed

to be the most important contributor to global climate change and its warming. Because,

carbon dioxide is absorbed from air when corn is grown, use of PLA has the potential to

emit fewer greenhouse gases compared to competitive hydrocarbon-based polymers .

Fig 2.4 Greenhouse gas emissions (kg/ton) for production of various polymers. Long-term

emissions for PLA are based on utilization of biomass for the production of lactic acid .

2.2.6 Energy requirement in relation to production of PLA

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PLA as a packaging material has been seen by the world as a major drive force to combat

the challenges of global warming and climate change as it is scientifically approved by all

as 100% biodegradable packaging material. To produce PLA and use it as a packaging

material, however is a different thing altogether from industrial view point where less cost

of production is must. But to everyone’s surprise PLA requires very low energy in terms of

production .

PLA Longterm

PLA year 5PLA year 1PET amorphPPGPPSCellophaneHIPSNylon 66

Various Packaging material

150

120

90

60

30

0

Mean

Energ

y Req

uirem

ent in

KJ/K

g

5

34

57

7677879192

142

Fig 2.5 showing the energy requirement comparison of various packaging materials.

It shows PLA needs low energy input in terms of production which works tremendously in

its favor.

2.3 PLA processing technologies for food applications

2.3.1 Extrusion

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According to Jamshidi an et a l. (2010a)

The first major step in the conversion of plastic resin into films, sheets, containers and so

on, is to change the pellets from solid to liquid or molten phase in an extruder.

Recommended extrusion conditions for PLA pellets include general purpose screws with

L/D ratios from 24:1 to 30:1 and compression ratio of 2.5:1 to 3:1, melt temperature of 200

to 220 ◦C, and also smooth barrels.

2.3.2 Injection molding

Injection molding involves melting a thermoplastic by extrusion, injecting the polymer

melt into a mold, cooling the part, and finally ejecting the part. Injection mold-grade PLA

is injection molded on most conventional equipment, but there could be some torque

limitations if the screw design has a high compression ratio. Compression ratios of 2.5 to 3

should be adequate and the recommended melting temperature is 200 to 205 ◦C. Since

PLA has a lower glass transition temperature (about 58 ◦C) than PS or PET, it might take a

little longer time to set up in the mold.

2.3.3 Thermoforming

PLA sheet can be thermoformed with vacuum, compressed air/vacuum, or only

compressed air assistance. The radiant heater of the thermoforming line for PLA must be

adjusted to very low temperatures. Preheating is not absolutely necessary; however it has

the general advantage that the sheet is homogeneously preheated.

2.4 General Properties of PLA

2.4.1 Thermal stability of PLA

PLA is thermally unstable and exhibits rapid loss of molecular weight as the result of

thermal treatment at processing temperatures. The ester linkages of PLA tend to degrade

during thermal processing or under hydrolytic conditions. PLA undergoes thermal

degradation at temperatures lower than the melting point of the polymer, but the

degradation rate rapidly increases above the melting point. It has been postulated that

thermal degradation mainly occurs by random main-chain scissions. Several reactions such

13


as hydrolysis, depolymerization, and oxidative degradation are suggested to be involved in

the degradation process during thermal treatments .

2.4.2 PLA properties

PLA has unique properties like good appearance, high mechanical strength, and low

toxicity; and good barrier properties have broadened its applications. It has low melting

point and glass transition temperature which makes PLA better for heat sealing and

thermal processing. It has high tensile modulus and flexural modulus as well

The other important property of polymers is their rate of crystallinity. Crystallinity is the

indication of amount of crystalline region in the polymer with respect to amorphous

content. Crystallinity influences many polymer properties including hardness, modulus,

tensile strength, stiffness, crease point, and melting point.

So, while selecting a polymer for a required application its crystallinity plays the foremost

role. measured the crystallinity of PLA and it was found to be high.

2.4.3 Barrier properties of PLA

One of the most important factors in food packaging polymers is their barrier or

permeability performance against transfer of gases, water vapor, and aroma molecules. The

barrier properties of PLA are remarkable and better than those of OPS. As a consequence,

PLA is suitable for packaging wide range of food. However the oxygen and gas

transmission rate has been found to be on lower side .

2.4.4 Studies on migration from PLA

Lactic acid is the lone monomer in the PLA structure and so, migrated agents are lactic

acid monomers, dimmers, and oligomers. investigated the safety of PLA as a food contact

polymer under different conditions and studied the migration of most probable species

from PLA. They concluded:

Very limited migration can be expected from PLA into foods that it contacts during

the intended conditions of use.

14


The small amount of any material that might migrate from PLA into food will be

lactic acid, or its dimers (lactoyl lactic acid and lactide) and oligomers that will be

subsequently hydrolyzed in aqueous systems to lactic acid.

Based on these findings, researchers concluded that PLA is safe and GRAS for its intended

uses in fabricating articles intended for use in contact with food. The projected intake of

lactic acid from PLA is approximately 700 times less than the estimated daily lactic acid

intake of a breast-fed infant. So, for a PLA much of the concerns about migrations of

potential dangerous materials, which exist for petrochemical-based polymers are resolved.

These results are only for pure PLA polymer and more studies are needed for its blends

and copolymers, also for all the compounds that are applied or added for improving

physical, mechanical, and barrier properties of PLA .

2.4.5 PLA modifications

As mentioned earlier because of special properties of PLA makes it a go to packaging

material. However its application has been restricted by high oxygen and moisture

permeability in comparison to other plastics like PE, PP and PET . For extending PLA

applications, the properties like impact strength or flexibility, stiffness, barrier properties,

thermal stability, and production costs must be improved. Generally, modifiers have been

studied to improve stiffness at elevated temperatures, reduce cost, or increase the

degradation rate of PLA. Some efforts of PLA modifications in the field of packaging are

presented in Appendix A.2.

2.4.6 Biodegradability nature of PLA

PLA also will not emit toxic fumes when incinerated. PLA may well break down into its

constituent parts (carbon dioxide and water) within three months in a “controlled

composting environment,” that is, an industrial composting facility heated to 140 °F and

fed a steady diet of digestive microbes .

According to , hydrolysis of ester linkage is the primary mechanism of degradation of

PLA.

2.5 Application of PLA

15


PLA has potential for use in a wide range of applications; PLA is a growing alternative as

a “green” food packaging polymer. New applications have been claimed in the field of

fresh products, where thermoformed PLA containers are used in retail markets for fruits,

vegetables, and salads. The market capacity of these products packaged in PLA is

unlimited. The major PLA application today is in packaging (nearly 70%).

Figure 2.6 Some commercial PLA products

The relatively poor water vapor barrier of PLA has been shown to be a factor limiting the

shelf life of moist foods. For example, semi-hard cheese packaged in PLA lost moisture,

and surface drying was observed after 56 days due to the high WVTR of the PLA; cheese

packaged in conventional materials had a shelf life of 84 days . PLA resins can be tailor-

made for different fabrication processes and made into films, coextruded into laminates,

thermoformed and injection stretch blow molded into bottles. PLA films can be prepared

by the blown double-bubble technology or, preferably, cast tentering, the latter having very

low haze, excellent gloss and gas transmission rates desirable for consumer food

packaging. PLA films also have superior dead fold or twist retention properties, making

them suitable for twist wrap packaging. The major application to date has been as

16


food service containers. Other current uses include thermoformed packaging for bakery

products and bags for bread, fresh pasta and salads. Now that production costs are being

reduced, PLA is expected to find packaging applications in areas such as coatings for

paperboard beverage cartons, plastic film wraps for foods, blister packs and plastic

windows in cartons .

2.5.1 Reference to Dairy Industry.

One of the first commercial applications of PLA for foods was packaging of organic

yoghurt in thermoformed PLA cups

Plate 1 Showing general process of PLA yoghurt cup manufacture from corn

2.6 Quality control of PLA

The quality determination of PLA is the determination of lactide composition by gas

chromatography (GC) or flame ionization (FI) technique which measures and detects the

L-lactide, M-lactide and D-Lactide residues. The evaluation of D-lactic acid presence is

very important, especially if the PLA product will be in contact with food or is a biological

implant. The daily allowable intake of D-lactic acid in adult humans is, 100 mg/kg and no

D-lactic acid must be found in infant food

2.7 Pros and Cons of using PLA as Packaging material in Dairy industry

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2.7.1 Pros

According to

Good Ultraviolet light barrier properties.

PLA seals well at temperatures below the melting temperature.

The amount of lactic acid and its derivatives that migrate to food simulant solutions

from PLA is much lower than any of the current average dietary lactic acid intake

values

Environment friendly

Made from 100% renewable resources

Net gas emission is also lower in comparison to other packaging material.

Use of Power is also lower in comparison to other packaging material.

And according to

Due to its intrinsic high value of surface tension of 36 to 38 mN/m, PLA is easily

printable.

Moreover, trays from PLA show an excellent sealability at temperatures much

lower than required to process common polymer material

As PLA has a very good flavor and aroma barrier, it is very qualified for packing

food with a distinctive smell as e.g. cheese or goods, that require a protection of

their specific aroma, like e.g. herbs

The climatic conditions inside a PLA packaging due to the gas exchange from

inside the package to the environment, related to its pronounced permeation ability,

is beneficial for the maturing of cheese without influencing its unique taste.

Another advantage of PLA trays for packing food is its high resistance to grease

and oil.

They are resistant to microbial attack in comparison to PE, PP and PET which aids

in its biodegradability.

2.7.2 Cons

High amount of gypsum is produced as by-product which is environmental hazard

which would also increase the COD level

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Its dynamic application in food is restricted by its high oxygen and water vapor

transmission rate .

It has been observed that largest manufacture of PLA, nature works have used

genetically modified corns which are under huge scruitinity.

Though newer technologies have replaced Ring Opening Polymerization, its high

production cost is still an issue.

Plate 2 showing PLA cup

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3. Conclusions

PLA is derived from starting substance lactic acid which is derived through the

fermentation of carbohydrates. The production of PLA can be conducted by two methods

either by direct polycondensation or ring opening polymerization. Of the two, ring opening

lactide polymerization remains the most widely used method, because the process has

higher yield and low toxicity. The traces of lactide present in PLA are determined to avoid

overdose consumption.

Lactic acid is the monomer for PLA production which is present easily as by-product in

industrial sectors especially dairy from whey and cheese. It can be recovered and used

subsequently to produce PLA for yoghurt and other products so as to minimize the use of

conventional LDPE and LLDPE. It would ultimately be beneficial as it is made from

renewable material corn and is therefore biodegradable making the earth greener and better

place to live in.

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REFERENCES

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APPENDICES

A.1 –Production steps for PLA

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A.2 -- PLA modification for the use in different products.

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Web viewThe most considered active initiator for the L-lactide ring-opening polymerization is...

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