A biodegradable composite material based on polyhydroxybutyrate (PHB) and carnauba fibers

7/25/2019 A biodegradable composite material based on polyhydroxybutyrate (PHB) and carnauba fibers

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A biodegradable composite material based on polyhydroxybutyrate (PHB)

and carnauba fibers

J.D.D. Melo, L.F.M. Carvalho, A.M. Medeiros, C.R.O. Souto, C.A. Paskocimas

Department of Materials Engineering, Federal University of Rio Grande do Norte, Natal, RN 59078-970, Brazil

a r t i c l e i n f o

Article history:Received 21 August 2011

Received in revised form 13 January 2012

Accepted 16 January 2012

Available online 11 May 2012

Keywords:

A. Polymermatrix composites (PMCs)

B. Mechanical properties

B. Thermal properties

E. Surface treatments

a b s t r a c t

In this investigation, carnauba fibers obtained from the leaves of the carnauba palm tree were chemicallymodified and their potential for the development of a biodegradable composite was evaluated. Fiber

treatments to improve interfacial bonding were carried out by alkali, peroxide, potassium permanganate

and acetylation. Biodegradable composites were prepared using carnauba fibers and polyhydroxybuty-

rate (PHB) as matrix. Mechanical properties of the composites prepared with 10 wt.% of short carnauba

fibers were investigated and related to fiber treatment. According to the results, the tensile strength of

the composites made from peroxide treated fibers was superior to those using untreated fibers or any

other fiber treatment. SEM observations on the fracture surface of the composites suggest improved

fibermatrix adhesion after peroxide treatment. This surface modification of the fibers was found to con-

tribute to the enhancement of the mechanical properties of the composites, even though the tensile

strength of the fibers was slightly reduced. Dynamic mechanical thermal analyses suggested improve-

ment in storage modulus of the composites reinforced with carnauba fibers at higher temperatures as

compared to the neat polymer.

2012 Elsevier Ltd. All rights reserved.

1. Introduction

The growing environmental awareness and new environmental

regulations observed in recent decades have led to increasing

interest in biodegradable materials. Studies focusing on the use

of natural fibers as a replacement to man-made fibers in fiber-

reinforced composites have gained ever-increasing importance.

Besides biodegradability, natural fibers offer cost savings and

reduction in density when compared to some man-made fibers

such as glass. Thus, even though the strength of these fibers is low-

er than fiberglass, natural fiber composites have potential use in

many applications[13].

A major market for the application of plant-derived fibers as

replacement of fiberglass is the automotive industry. Currentapplications for these fibers in vehicles include door trim panels,

rear parcel shelf, damping and insulation parts, center console trim

and seat cushion parts[4]. However, the large scale production of

cellulosic fiber composites is still limited by two important issues:

compatibility with the polymer matrix and water absorption. As a

result of the incompatibility between the hydrophilic fibers and

the hydrophobic polymer matrix, the wettability of the fibers is

poor and strength of natural fiber composites is low compared to

glass fiber reinforced composites. Water absorption is also a

limiting factor since it produces swelling and reduces strength, in

addition to an increase in mass.

Natural cellulosic fibers consist primarily of cellulose, hemicel-

lulose, pectin, lignin, waxes and water soluble substances[5]. Cel-

lulose is a semicrystalline polysaccharide with large amount of

hydroxyl groups which is responsible for the hydrophilic nature

of the natural fibers. Hemicellulose is an amorphous polysaccha-

ride of lower molecular weight when compared to cellulose. Hemi-

cellulose is partly soluble in water and hygroscopic because of the

many hydroxyl and acetyl groups in its structure[6]. Pectin is also

a polysaccharide and its main function is to hold the fiber together.

Lignin is an amorphous mainly aromatic polymer and has the least

water absorption of all natural fiber components[6].

There are many chemical treatments that havebeen successfullyapplied to natural cellulosic fibers aimed at improving fiber proper-

ties and also their adhesion to polymer matrices. These include

alkaline, acetylation, permanganate and peroxide treatments,

among others [5]. Alkaline treatment with sodium hydroxide

(NaOH) also known as mercerization is oneof the most common

chemical treatments of cellulosic fibers intended to be used as rein-

forcement to polymers. This treatment has been reported as having

two main effects on the fiber: (1) it increases the surface roughness

that results in a better mechanical interlocking; and (2) it incre-

ments the amount of cellulose exposed on the fiber surface, thus

increasing the number of possible reaction sites[7,8]. Acetylation

is a well-known treatment that can reduce the hygroscopic nature

1359-8368/$ - see front matter 2012 Elsevier Ltd. All rights reserved.http://dx.doi.org/10.1016/j.compositesb.2012.04.046

Corresponding author. Tel./fax: +55 84 3342 2406.

E-mail address:[email protected](J.D.D. Melo).

Composites: Part B 43 (2012) 28272835

Contents lists available atSciVerse ScienceDirect

Composites: Part B

j o u r n a l h o m e p a g e : w w w . e l s e v i e r . c o m / l o c a t e / c o m p o s i t e s b
http://dx.doi.org/10.1016/j.compositesb.2012.04.046mailto:[email protected]://dx.doi.org/10.1016/j.compositesb.2012.04.046http://www.sciencedirect.com/science/journal/13598368http://www.elsevier.com/locate/compositesbhttp://www.elsevier.com/locate/compositesbhttp://www.sciencedirect.com/science/journal/13598368http://dx.doi.org/10.1016/j.compositesb.2012.04.046mailto:[email protected]://dx.doi.org/10.1016/j.compositesb.2012.04.046


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of natural cellulosic fibers [9] and increase the dimensional stability

of composites. In a previous study, acetylation treatment of sisal

fibers was reported to increase surface roughness and improve

the fibermatrix adhesion[10]. Fiber treatments using potassium

permanganate (KMnO4) reduce the hydrophilic nature of the fibers

[9]. In an investigation involving sisal-LDPE composites, it was

shown that the tensile properties of composites made from per-

manganate treated fibers can be significantly improved as com-pared to composites made from untreated fibers [8]. Peroxide

treatments can also decrease hydrophilicity of the cellulosic fibers

[9]and increase the tensile properties[8].

Even though natural cellulosic fibers have been successfully

used with petroleum-derived polymers, the environmental bene-

fits of natural fiber composites can be enhanced considerably if

biodegradable polymers are used. Polyhydroxybutyrate (PHB) is a

biodegradable polymer produced by bacteria from renewable raw

materials such as sugarcane[11]. PHB has been studied for many

applications ranging from construction applications[12]to nano-

particles used as drug carrier [13]. PHB and its co-polymers have

been combined with natural cellulosic fibers such as hemp

[14,15], jute[16],flax [14,1719], and bamboo[20].

In this investigation a novel biodegradable composite material

based on polyhydroxybutyrate (PHB) and carnauba fibers is pro-

posed and evaluated. Carnauba (Copernicia prunifera (Miller) H. E.

Moore) is a palm tree native to Brazil. Its main product is the car-

nauba wax which has many applications in the pharmaceutical

industry, food industry, cosmetics, electronics components, grease

and lubricants and as mold release. Alkali, peroxide, potassium

permanganate and acetylation treatments were carried out on

the carnauba fibers to improve fibermatrix compatibility.

Mechanical and thermal properties of the carnauba fibers and com-

posites prepared with PHB and 10 wt.% of fibers were investigated

and related to fiber treatment.

2. Experimental

2.1. Materials

PHB was obtained from PHB Industrial S/A BRAZIL. This poly-

mer is produced from sugarcane by microorganisms of the alcalig-

enes s.p. species [11]. Typical properties of the PHB used are:

density: 1.3 g/cm3; tensile strength: 2536 MPa; and melting

point: 165170 C.

The carnauba fibers used in this investigation (Fig. 1) were col-

lected from the State of Piau in the northeastern region of Brazil.

The typical cross-section of the fibers observed using an optical

microscope (Olympus BX60m) is shown in Fig. 2. As shown in

Fig. 2, the cross-section is irregular in shape and can be approxi-

mated to an ellipse. The chemical composition of the carnauba fi-

bers is shown inTable 1.

2.2. Fiber treatments

The following fiber treatments were conducted: alkaline at con-

centrations of 1%, 3% and 5% (FT1%, FT3%, FT5%), acetylation (FTAc),

permanganate (FTP) and peroxide (FTPH). The fiber treatments are

summarized inFig. 3.

For the alkaline treatments, fibers were immersed in a NaOH

solution with the specified concentration (1%, 3% or 5%), at room

temperature (approx. 25C), for 3 h, 2 h, and 1 h, respectively.

The fibers were then washed thoroughly with distilled water to re-

move the excess of NaOH. After that, the fibers were oven dried at

60C for 24 h.

The acetylation and permanganate treatments were conducted

in fibers previously treated with NaOH at 1%. For the acetylation,

the dewaxed fibers were first immersed in glacial acetic acid for1 h, at a temperature of approximately 25 C. The fibers were then

washed with distilled water and air dried. The acetylation reaction

was performed with fibers soaked in acetic anhydride containing

sulfuric acid as reaction catalyst. The solution containing the fibers

was stirred for 5 min. The fibers were then washed thoroughly

with distilled water and dried at 60 C for 24 h. For the permanga-

nate treatment, the alkali treated fibers were soaked with a 0.25%

solution of KMnO4 in acetone for 3 min. This solution was then

decanted and the fibers were washed thoroughly with distilled

water and dried at 60 C for 24 h.

The peroxide treatment started with fiber purification by reflux-

ing with toluene and ethanol (2:1 v/v) for 6 h in a Soxhlet extractor,

followed by washing with distilled water. The fibers were then

dried at 30 C for 24 h. The dried fibers were then immersed for2 h in a NaOH solution at 1%, at a temperature of 55 C. After that,

the fibers were washed repeatedly with distilled water and then

dried at 30 C for 24 h. The dry fibers were soaked for 6 h in a

hydrogen peroxide 1% solution at 45 C. After that, the fibers were

oven dried at 60C for 24 h.

Fig. 1. Carnauba fibers (untreated).

Fig. 2. Typical cross-section of the carnauba fibers.

Table 1

Chemical composition of the carnauba fibers [21].

Component (%)

Cellulose 58.04 4.49

Hemicellulose 14.02 0.64

Lignin 19.03 1.02

Humidity 7.53 0.63

Ash 1.80 0.47

2828 J.D.D. Melo et al. / Composites: Part B 43 (2012) 28272835


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2.3. Fiber characterization

The morphologies of the fibers, before and after the chemical

treatments, were examined by means of a Philips XL30 ESM. Fiber

density was measured with a gas pycnometer using helium dis-

placement method (Model AccuPyc 1340; Micromeritics Co.).Tensile properties of the fibers tensile strength and Youngs

modulus were measured using a dynamic mechanical analyzer

(DMA Q 800 TA) in a tensile test mode and following recommen-

dations of ASTM C1557-03 (2008). All tests were conducted under

displacement-control with rate of straining set to 1%/min. The

length of the gage section was 20 mm. A piece paper was

epoxy-bonded at the gripping area of thefiberspecimens to prevent

gripping damage which could cause premature failure. The cross-

sectional areas of the fibers were calculated assuming an elliptical

cross-section. Cross-sectional dimensions major and minor axes

were measured using a profile projector (Mitutoyo PHA-14) at se-

ven locations along the fiber length. Twenty-five specimens were

tested for each fiber treatment.

Thermogravimetric analyses (TGA) were carried out in a TA

Instruments, model TGA 2050, to measure the thermal stability

of the fibers and of the PHB. The samples were scanned over tem-

perature ranges of 30600 C (fibers) and 30350 C (PHB), using a

heating rate of 10C/min, in a nitrogen-gas atmosphere (150 cm3/

min).

2.4. Prepreg preparation

The first step in the fabrication of the composites was the prep-

aration of a prepreg. PHB-carnauba fibers prepreg was prepared by

a solution mixing technique. First PHB was dissolved in chloroform

under reflux (Fig. 4) to form a solution, which was thoroughly

mixed for 15 min at 90 C. Carnauba fibers cut to 30 mm length

were then added to the solution (10 wt.%), which was mixed foradditional 15 min at 90 C. After that, the material was poured into

a mold and covered with a polyamide fabric to reduce the solvent

evaporation rate and thus minimize cracking. The material was

then removed from the mold and oven dried at 50 C for 24 h to

evaporate the solvent. Similar procedure has been described in

the literature for processing PHB-flax composites[19]. The prepreg

obtained is shown inFig. 5.

2.5. Composite processing and specimen preparation

Composite plates (250 200 2 mm) with randomly distrib-

uted fibers were prepared in a hot-press from a stack of four pre-

preg films for the total thickness of 2 mm. The prepreg stack washot-pressed at 190 C, for 2 min. Then, the composite plates were

CARNAUBA FIBERS

NaOHsolution1%, 3h

Distilled water

Drying60 C, 24h

Acetic Acid1h

Distilled water

Acetic anhydride+ H2SO4 5 min

Drying60 C, 24h

Drying60 C, 24h

KMnO4 solution0,25 %, 3 min

NaOH solution3%, 2h

Distilled water

Drying60 C, 24h

NaOH solution5%, 1h

Distilled water

Drying60 C, 24h

SoxhletExtractortoluene + ethanol

6h

Distilled water

Drying30 C, 24h

Drying60 C, 24h

NaOH solution1%, 55 C, 2h

Hydrogen peroxide1%, 45 C, 6h

Distilled water

FT1% FT3% FT5% FTPH

FTPFTAc

Fig. 3. Chemical treatments of carnauba fibers: FT1% alkaline treatment at 1%; FT3% alkaline treatment at 3%; FT5% alkaline treatment at 5%; FTAc acetylation; FTP

permanganate treatment; and FTPH peroxide treatment.

Fig. 4. Schematic of the apparatus for PHB/carnauba fiber prepreg preparation.

J.D.D. Melo et al. / Composites: Part B 43 (2012) 28272835 2829


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water cooled to room temperature. Tensile and flexural specimens

were cut using a laser cutter (Versa Laser).

2.6. Composite characterization

Tensile tests of the composites were carried out in a Shimadzu

(Autograph) universal testing machine, which has a load capacity

of 100 kN. All measurements were conducted at a temperature of

approximately 25C and following recommendations of ASTM D

638-99. A constant cross-head displacement rate of 5.0 mm/min

was used in all tests. Seven specimens were tested for each fiber

treatment. The surfaces of the tensile fractured specimens were

examined using a Philips XL30 ESM model scanning electron

microscope (SEM).

Fig. 5. PHB/carnauba fiber prepreg.

Fig. 6. SEM micrographs of carnauba fibers: (a) untreated; (b) alkaline (1%) treated; (c) alkaline (3%) treated; (d) alkaline (5%) treated; (e) acetylation treated; (f)permanganate treated; (g) peroxide treated.



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Flexural tests were conducted using a dynamic mechanical ana-

lyzer (DMA Q 800 TA) in quasi-static and also oscillatory modes.Quasi-static tests were carried out in a 3-point bending mode, with

a 20.0 mm span between the supports, using a crosshead speed of

0.5 mm/min. These tests were conducted at 25 C for the determi-

nation of the composite flexural modulus. The test procedure fol-

lowed general recommendations of ASTM D 7264-07. Oscillatory

flexural tests were carried out under sinusoidal strain-control for

the determination of the glass transition temperature and the tem-

perature dependence of storage modulus. These tests were con-

ducted following recommendations of ASTM D 5418-07.

Specimens were tested in double-cantilever mode, using strain

amplitude of 0.1%. Temperature scan measurements were per-

formed over the temperature range of 120C to +40C, with a

heating rate of 2.0C/min, and under a constant frequency of

1.0 Hz. Storage modulus (E0) and tan d were determined as a func-

tion of temperature. Five specimens were tested in each of the flex-

ural test condition.

3. Results and discussion

3.1. Fiber characterization

SEM photomicrographs of the surface of untreated and treated

carnauba fibers are presented in Fig. 6. The untreated fibers

Fig. 6a have deposits of wax on the surface which was removed

by all treatments. Alkaline treatment was proven effective to re-

move waxes from the fiber surfaces (Fig. 6bd). However, theSEM micrographs suggest that part of the surface topography of

FNT FT1% FT3% FT5% FTAc FTPH FTP

0,0

0,2

0,4

0,6

0,8

1,0

1,2

1,4

1,6

Fig. 7. Density of carnauba fibers: untreated (FNT); alkaline (1%) treated (FT1%);

alkaline (3%) treated (FT3%); alkaline (5%) treated (FT5%); acetylation treated

(FTAc); peroxide treated (FTPH); permanganate treated (FTP).

0 100 200 300 400 500 600

0 50 100 150 200 250 300

0

20

40

60

80

100

0

20

40

60

80

100

FNT

FT1%

FT3%

FT5%

FTAc

FTPH

FTP

236 - 393 C

383 ~ 500 C

30 -132 C

350

(a)

(b)

Fig. 8. Thermogravimetric curves of: (a) neat PHB; and (b) carnauba fibers under

various treatments.

FNT FT(1%) FT(3%) FT(5%) FTAC FTPH FTP

0

50

100

150

200

250

0

2

4

6

8

10

12

FNT FT(1%) FT(3%) FT(5%) FTAC FTPH FTP

(a)

(b)

Fig. 9. Mechanical properties of carnauba fibers: untreated (FNT); alkaline (1%)

treated (FT1%); alkaline (3%) treated (FT3%); alkaline (5%) treated (FT5%); acetyla-tion treated (FTAc); peroxide treated (FTPH); permanganate treated (FTP).



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the fibers can be destroyed as the NaOH concentration increases.

Acetylation treatment resulted in a more preserved surface topog-

raphy (Fig. 6e), while the SEM micrographs of permanganate trea-

ted fibers shows residue attached to the fiber surface (Fig. 6f).

Among all treatments studied, peroxide treated fibers have a clea-

ner surface with rougher surface topography (Fig. 6g). This devel-

opment of a rough surface topography improves fibermatrix

interface adhesion and therefore increases mechanical properties.

This will be corroborated by the subsequent results presented.

Fiber densities ranged from 1.34 to 1.47 g/cm3 which are similar

to many other lignocellulosic fibers[3,5]. Even though fiber densitywas not significantly affected by fiber treatment, fibers treated

with NaOH (FT1%, FT3%, FT5%), permanganate (FTP) and peroxide

(FTPH) presented a small increase in density (Fig. 7). A previous

work have indicated that fiber treatments such as alkali may result

in a more compacted cellular structure, with reduced void content

and hence increased density[22].

Thermogravimetric curves (TGA) of neat PHB and carnauba fi-

bers are presented inFig. 8. The TGA curve for PHB shows a gradual

weight loss with the increasing temperature, which started at

about 220 C and entirely degrading at around 315 C, leaving a

weight residue of 2.32%. The thermal instability of PHB above

250C has been reported in previous works [20,23]. It has been

suggested that the degradation process involves chain scission

and hydrolysis which leads to a reduction in molecular weight.

The processing temperature of 190 C for the composite used in

this work is about 30 C below the initial degradation temperature

of the polymer. PHB is known to thermally degrade at tempera-

tures just above the melting temperature [19]. Thus, processing

time was reduced to a minimum, which in this case was 2 min at

190C.

The TGA curves for the carnauba fibers show a weight loss be-

tween 30 and 130 C corresponding loss of humidity and other res-

idue solvent vaporized (Fig. 8). Above this temperature, thermal

stability gradually decreases with increasing temperature andthermal decomposition takes place in two main stages. The first

stage of thermal degradation occurred over the range 240380 C

and is due to thermal depolymerization of hemicelluloses [24]

and destruction of crystalline regions [25]. The weight loss over

this temperature range was about 50%. The final stage occurs above

380C and up to 530 C and represents the final decomposition.

The mechanical properties of all fibers tested treated and un-

treated are presented inFig. 9. Stressstrain behavior of all fibers

was rather linear up to failure. Strength and Youngs modulus of

carnauba fibers are found to be similar to the same properties of

cotton fibers, and therefore lower than other cellulosic fibers such

as jute, flax, hemp, ramie and sisal [5].

Tensile strength of treated carnauba fibers was in general lower

than that of the untreated fibers. For peroxide treated fibers, thestrength was similar to that of the untreated fibers if the standard

deviation is considered. Acetylation and permanganate treated fi-

bers presented the lowest strengths. In this case, the treatment

may have affected the cellulose which is the main responsible for

the fiber strength. Strain to failure of fibers was typically around

2% for all fiber treatments.

The Youngs modulus of chemically treated fibers was improved

by alkali and peroxide treatments. As in the case of strength, acet-

ylation and permanganate treated fibers presented the lowest

properties.

A summary of the properties of carnauba fibers is presented in

Table 2, where the same properties of other common cellulosic fi-

bers are also presented for comparison. The properties presented

for the carnauba fibers correspond to untreated and peroxide trea-ted fibers.

Table 2

Properties of carnauba fibers as compared to other natural cellulosic fibers.

Fiber Density (g/cm3) Elongation (%) Tensile strength (MPa) Youngs modulus (GPa)

Carnauba (FNT) 1.34 1.72.6 205264 8.29.2

Carnauba (FTPH) 1.44 1.72.6 148242 6.314.0

Cottona 1.51.6 3.010.0 287597 5.512.6

Jutea 1.31.46 1.51.8 393800 1030

Flaxa 1.41.5 1.23.2 3451500 27.680

Hempa 1.48 1.6 550900 70Ramiea 1.5 2.03.8 220938 44128

Sisala 1.331.5 2.014 400700 9.038.0

a Published data5.

PHB FNT FT(1%) FT(3%) FT(5%) FTAC FTPH FTP

0

5

10

15

20

25

30

PHB FNT FT1% FT3% FT5% FTAc FTPH FTP

0,0

0,5

1,0

1,5

2,0

2,5

3,0

3,5

4,0

(a)

(b)

Fig. 10. Mechanical properties of neat PHB and PHB/carnauba fiber composites

with the following fiber treatments: untreated (FNT); alkaline (1%) treated (FT1%);

alkaline (3%) treated (FT3%); alkaline (5%) treated (FT5%); acetylation treated(FTAc); peroxide treated (FTPH); permanganate treated (FTP).



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3.2. Composite characterization

The mechanical properties of the composites (tensile strength

and flexural modulus) are presented inFig. 10. The properties of

plain PHB are also presented in the same figure for comparison

purposes. According to the data presented, an increment of up to

45% was obtained when peroxide treated fibers were used as com-

pared to composites with untreated fibers. Composites with alka-

line treated fibers showed improvement in tensile strength only

when fibers were treated with NaOH 5%. In this case, the tensilestrength was improved by 24% in comparison to composites with

untreated fibers, due to an increase in the amount of cellulose ex-

posed on the fiber surface which improves fibermatrix interface

adhesion.

Considering that the tensile strength of treated carnauba fibers

was in general lower than that of the untreated fibers, the

improvement strength of the composites is due to better interface

properties. Improved fibermatrix interface adhesion was also

responsible for the enhancement of the flexural modulus of the

composites with untreated fibers (Fig. 10). As in the case

of strength, the composites with peroxide treated fibers pre-sented the highest modulus, which was similar to neat PHB. The

Fig. 11. SEM fractographs of PHB/carnauba fibers using fibers in the following conditions: (a) untreated; (b) alkaline (1%) treated; (c) alkaline (3%) treated; (d) alkaline (5%)

treated; (e) acetylation treated; (f) permanganate treated; (g) peroxide treated.



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improvement in modulus of composites with peroxide treated fi-

bers when compared to composites with untreated fibers was

about 14%. However, the lower strength of the composites when

compared to the plain PHB indicates that fibermatrix interface

adhesion still needs improvement. Further development in fiber

treatment needs to be studied.

The SEM micrographs of the fractured surfaces of the specimens

after the tensile tests are shown inFig. 11. Poor fibermatrix adhe-

sion was observed in the fracture surface of composites with un-

treated fibers (Fig. 11a). Among all specimens evaluated, the best

adhesion was verified for composites with alkaline (5%) treated

(Fig. 11d) and peroxide treated (Fig. 11g) fibers. These are also the

composites with highest tensile strength (Fig. 10). Superior interfa-

cialinteractions obtained with peroxide treatmentwas alsoreportedin a previous work published in the literature for sisal fiber-rein-

forced LDPE (low density polyethylene) composites[8]. In this case,

dicumyl peroxide and benzoyl peroxide treatments were used.

Fig. 12shows the temperature dependence of storage modulus

and tan delta of neat PHB and PHB/carnauba fiber composites with

various fiber treatments. According to the data presented, the E0

values of neat PHB and all composites decrease considerably with

increasing temperature, over the temperature range studied (120

to 40C). This is due to increased mobility of the polymer chain at

higher temperatures.

Up to the glass transition region, the storage modulus of the

neat polymer was larger than that of the composites. However,

over the glass transition region the storage modulus of neat PHB

falls sharply resulting in lower storage modulus at higher temper-atures, when compared to the fiber reinforced composites. Thus,

the addition of fibers will provide higher storage modulus at higher

temperatures, where the matrix modulus is lower. Below the Tg,

the matrix material is in the glassy state and the storage moduli

of the composites are matrix dominated. In this case, the presence

of fibers results in lower modulus.

Based on the peak of tan d, the glass transition temperature of

the neat polymer was higher than that of the composites. All fiber

reinforced composites presented a glass transition temperature ofabout 20 C, while for the neat polymer the glass transition occurs

at a temperature of about 30 C. The lower Tg of the composites

may be attributed to the presence of residual solvent entrapped

during the preparation of the prepreg. Similar behavior was de-

scribed in a previous work for polystyrene based composites rein-

forced with short sisal fibers[10].

4. Conclusions

In this research, carnauba fibers were modified by alkali, perox-

ide, potassium permanganate and acetylation treatments and used

for the development of a biodegradable composite. PHB based

composites containing 10% by weight of carnauba fibers were pre-

pared using randomly distributed fibers of 30 mm length.The mechanical properties of carnauba fibers were found to be

comparable to many other natural fibers. The fiber treatment using

hydrogen peroxide resulted in better mechanical properties than

any other treatment considered and was also found to improve

wettability. The thermal decomposition of the carnauba fibers

was found to start at about 240 C what makes them suitable for

combination with many thermoplastics.

Strength and elastic modulus of composites made from perox-

ide treated carnauba fibers randomly dispersed was superior to

those using untreated fibers or any other fiber treatment and sim-

ilar to neat PHB. Storage modulus measured by dynamic mechan-

ical analysis was lower than that of the neat PHB at temperatures

below the glass transition, but higher above the Tg.

In summary, carnauba fiber reinforced PHB biodegradable com-posite may prove as an alternative to plain PHB with cost reduction

and similar mechanical properties. The addition of these fibers to

PHB may provide a smaller reduction in modulus at higher temper-

atures, where the matrix modulus is lower. However, the lower

strength of the composites when compared to the plain PHB indi-

cates that fibermatrix interface adhesion still needs improve-

ment, which should be the subject of future work.

Acknowledgements

The authors are grateful to Eduardo Brondi of PHB Industrial S/A

BRAZIL for donating the polyhydroxybutyrate (PHB) used in this

investigation.

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Fig. 12. Storage moduli (a) and tan delta (b) of neat PHB and PHB/carnauba fiber

composites with various fiber treatments.

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A biodegradable composite material based on polyhydroxybutyrate (PHB) and carnauba fibers

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