ORIGINAL PAPER

Aromatic/Aliphatic Polyester Blends

A. C. Quental • F. P. de Carvalho • M. L. Rezende •

D. S. Rosa • M. I. Felisberti

Published online: 23 April 2010

� Springer Science+Business Media, LLC 2010

Abstract Blends of poly(3-hydroxybutyrate) (PHB) and

poly(ethylene terephthalate-co-1,4-cyclohexenedimethanol

terephthalate) (PETG) were prepared in a batch mixer and

in a twin screw extruder and characterized by differential

scanning calorimetry (DSC), dynamic mechanical analysis

(DMA), field emission scanning electron microscopy (FE

SEM), flexural tests, biodegradation tests in soil compost

and in an enzymatic medium. The torque data showed that

the addition of PETG to PHB improved its processability.

DSC, DMA and FE SEM showed that the polymers are

immiscible with morphology dependent on the processing

conditions. A fine dispersion of PETG in the PHB matrix

was observed for extruded and injection molded blends.

Flexural modulus for blends was higher for blends in

comparison with PHB, while the impact resistance of

blends containing 20 wt% and 30 wt% of PETG is com-

parable to the value for PHB. PHB is biodegradable, while

PETG did not degrade either in simulated soil or in the

a-amylase medium. On the other hand, the PHB phase of

the blends degrades under these aging conditions. Thus, the

addition of PETG to PHB results in advantage such as

improving of processability and Young0s modulus without

significant changes in the impact resistance while keeping

the biodegradability of PHB.

Keywords Blends � Biodegradability � PHB � PETG �Processing

Introduction

In general, commercially available biodegradable polymers

are either expensive or present poor physical properties,

compared with conventional thermoplastics like polyeth-

ylene and poly(ethylene terephthalate). Poly(3-hydroxy-

butyrate), PHB, is one of more interesting biodegradable

polymers because it is obtained by bacterial fermentation

from renewable resources [1–3]. However, PHB presents

some drawbacks like thermal instability at temperatures

close to its melting point and a relatively low impact

resistance. PHB molar mass decreases proportionately with

some processing parameters like time and temperature. In

spite of its narrow processing window PHB with high

molar mass can be processed like other thermoplastics if

adequate processing parameters are used [4, 5].

Two efforts, among others, have been used to change

PHB properties: biosynthesis and blending. Since blends

are a cheaper and faster method to improve polymer

properties than synthesis, blends have often been used to

improve mechanical properties and processability of PHB.

A variety of polymers having different chemical, physical

and mechanical characteristics, biodegradable and non-

biodegradable, amorphous or crystalline have been blended

with PHB and its copolymers [5–9].

Complete biodegradable PHB blends have been

obtained with poly(ethylene glycol) (PEG) [10], polyoxy-

ethylene (PEO) [11–14], polycaprolactone (PCL) [15, 16],

A. C. Quental � F. P. de Carvalho � M. I. Felisberti (&)

Instituto de Quımica, Universidade Estadual de Campinas,

UNICAMP, P.O. Box 6154, Campinas, SP 13083-900, Brazil

e-mail: misabel@iqm.unicamp.br

M. L. Rezende � D. S. Rosa

Programa de Pos Graduacao em Engenharia e Ciencias dos

Materiais, Universidade Sao Francisco, Rua Alexandre

Rodrigues Barbosa, 45, Centro, Itatiba, SP CEP 13251-900,

Brazil

D. S. Rosa

e-mail: derval.rosa@ufabc.edu.br

123

J Polym Environ (2010) 18:308–317

DOI 10.1007/s10924-010-0183-2

polydioxanone (PDS) [17], poly(lactic acid) (PLA) [18,

19], cellulose [20] and cellulose derivatives [21–24],

among others. Partially biodegradable blends have been

formed with poly(epichlorohydrin) (PECH) [25–27],

poly(vinyl acetate) (PVAc) [28–30], poly(vinyl chloride)

(PVC) [31], poly(methyl methacrylate) (PMMA) [32–35],

poly(ethylene-co-vinyl acetate) (EVA) [36], poly(vinyl

phenol) (PVPh) [37, 38], terpolymer of acrylonitrile-g-

(ethylene-co-propylene-co-diene)-g-styrene (AES) [39],

polyethylene [40].

Poly(ethylene terephthalate) (PET) is a semicrystalline

polyester obtained by polycondensation of ethylene glycol

and terephthalic acid. By replacing some of the ethylene

glycol with secondary glycols, the crystallization of the

polyester can be slowed. For example, replacing a fraction

of ethylene glycol by 1,4-cyclohexanedimethanol the

poly(ethylene terephthalate-co-1,4-cyclohexanedimethanol-

terephthalate), PETG, an amorphous copolyester, is obtained

[41, 42].

PETG is not able to crystallize and offers a larger range

of processing parameters than equivalent aromatic semi-

crystalline polyesters. PETG combines good toughness

even at low temperatures with film clarity and melt

strength. While mechanical properties of the PET reduce

with annealing due to embrittlement, PETG does not

present any change in these properties [41, 42]. Since

PETG is an amorphous polymer the processing temperature

profile can be lower in comparison with the usual pro-

cessing conditions for PET. Thus, the mechanical blending

of PETG and PHB appears to be possible in the processing

window of the PHB. The mostly PHB blends described in

the literature were obtained by casting from polymer

solutions in order to avoid the thermal degradation of PHB.

The present paper investigates the miscibility and com-

patibility of PHB/PETG blends obtained by mechanical

mixture in the melted state.

Experimental

The polymers used in this study were obtained from

commercial sources. The PHB was supplied by PHB

Industrial (Serrana, Brazil) with a molar mass of

450.000 g/mol. The PETG was supplied by Eastman

Chemical Company (Kingsport, TN). It consists of a

copolymer of 1,4-cyclohexanedimethanol, ethylene glycol

and terephthalic acid with a molar ratio of approximately

1:2:3 as determined by 1H and 13C NMR [43]. Polymer

blends containing 20, 40, 50, 60 and 80 wt% of PETG were

prepared by melt mixing in a model 600 Haake Rheomix

batch mixer (Karlsruhe, Germany) equipped with roller

blades and a mixing head with a volumetric capacity of

69 cm3. The mixing conditions were 80 rpm, 180 �C and

5 min of processing time. Polymers in pellets were pre-

mixed before being fed into the mixer. The pure polymers

were also subjected to the same procedure.

Blends containing 50, 60, 70, 80 and 90 wt% of PETG

were also prepared in a co-rotating, intermeshing twin

screw APV 2000 extruder (Aylesbury, England), with four

zones under barrel temperatures of 165 �C, 175 �C, 175 �C

and 185 �C from the hopper to die, and a screw speed of

100 rpm. The polymers were dried at 80 �C for 4 h before

processing.

The crystallization, melting and glass transition tem-

peratures of the pure polymers and their blends were

determined using a DSC 2910 from TA Instruments (New

Castle, DE). The following program was used for DSC

analysis: the samples were melted at 200 �C, held iso-

thermally for 2 min, then cooled to -20 �C and heated to

200 �C again. For some experiments the second step was

modified introducing an isothermal step at 70 �C for

20 min to allow the crystallization of PHB followed by

cooling to -20 �C and heating to 200 �C (third heating

scan). The heating and cooling rates were 10 �C/min under

nitrogen atmosphere. The crystallinity of PHB was calcu-

lated from the ratio between the melting enthalpy (DHm)

determined from the second scan of the DSC analysis and

the melting enthalpy of the 100% crystalline phase (DHo)

from the literature. For PHB, DHm value of 149 J/g was

used [44]. All DSC curves shown in this work were nor-

malized with respect to sample mass and shifted from each

other to allow better visualization of the transitions.

The dynamic mechanical analysis (DMA) was con-

ducted using a Rheometric Scientific DMTA V equipment

(Piscataway, NJ). The samples obtained from the batch

mixer were compression molded in sheets with 1 mm

thickness in a Marconi 098/A hydraulic press (Piracicaba,

Brazil) under a pressure of 1.10 MPa and temperature of

180 �C for 5 min, followed by cooling in water. The mean

dimensions for the sample between the clamps in the DMA

equipment were 1 mm of thickness, 5 mm of width and

10 mm of length. The analyses were carried out in the

temperature scan mode from -50 �C to 200 �C, at a fre-

quency of 1 Hz, 0.05 of strain and a heating rate of 2 �C/min.

A JEOL JSM-6340F field emission scanning electron

microscope (Middleton, WI) was used to examine the

morphology of the blends. The microscope operated at a

voltage of 3 kV. Batch mixed blends, extruded blends and

injection molded specimens were analyzed. Samples were

cryogenically fractured and the fractured surfaces were

sputtered with carbon and gold in a BAL-TEC MED 020

equipment (Principality of Liechtenstein).

Flexural tests were performed according to ASTM D790

using an EMIC model DL-2000 (Sao Jose dos Pinhais,

Brazil) at a cross head speed of 5 mm/min. Izod impact

properties were evaluated using an EMIC model AIC-1

J Polym Environ (2010) 18:308–317 309

123

(Sao Jose dos Pinhais, Brazil) with a pendulum energy of

2,7 J and notched specimens, according to ASTM 256. The

flexural and impact test specimens were prepared by

injection molding in a Arburg Allrounder model 221 M

250-55 (Lossburg, Germany). All samples were condi-

tioned prior to testing for 48 h at 50% humidity and a

constant temperature of 23 �C. The testing was performed

under the same conditions. At least ten specimens were

used for each test.

Biodegradation tests were conducted in soil compost

and in an enzymatic media. For enzymatic biodegradation

tests samples were placed in a vial filled with 10 mL of

0.05 mol/L acetate buffer, pH 6.0, containing 2.7 mg of

a-amylase, according to the Corn Products protocol, to

reduce the activation energy. The vials were placed in a

water bath at 60 �C. Every 48 h the samples were removed,

washed with distilled water, wiped dry, and weighed before

being returned to the incubation media. Controls consisted

of 10 mL of acetate buffer without enzyme.

Soil compost containing 23% loamy silt, 23% organic

matter (cow manure), 23% sand and 31% distilled water

(all w/w) was used for other biodegradation tests. Calcium

hydroxide was added to obtain a soil compost of pH 11.

The samples were weighed and buried in the soil compost,

in triplicate in containers of 30 9 30 9 40 cm. The sam-

ples were buried maintaining one distance of 15 cm of the

soil surface. The biodegradability was monitored by mass

variation after specified periods in the soil compost. The

buried samples were retrieved, washed with distilled water

and dried in air before being weighed. The samples were

buried again in their respective trays after weighing.

Results and Discussion

In order to investigate processability, pure polymers and

blends were processed in a Haake Rheomix 600 batch

mixer. Batch mixers are important and useful equipment to

prepare blends at lower quantities and to provide infor-

mation about torque and temperature as a function of the

processing time. Due to the small dimensions of the mixing

chamber, torque data measured by the torque meter are

reasonably representative of the actual torque exerted on

the polymer melt and is proportional to viscosity of the

polymers [45, 46].

Lee and Han [47, 48] studied the morphology evolution

of several polymer blends in a batch mixer using differ-

ent pairs of polymers: crystalline/crystalline; amorphous/

amorphous and crystalline/amorphous. The authors intro-

duced the concept of critical flow temperature (Tcf) as the

effective plasticizing temperature of an amorphous poly-

mer. Amorphous polymers at Tg \ T \ Tcf may be regar-

ded as rubbers and at T C Tcf may be regarded as liquids

(and be considered to flow). Tcf may be considered the real

plasticization temperature of an amorphous polymer or the

equivalent melting point of a crystalline polymer. For

polystyrene and polycarbonate the following relation

between Tcf and Tg was found: Tcf & Tg ? 55 �C.

According to this equation, the mechanical processing of

PETG is possible at temperatures used to prepare PHB/

PETG blends, around 180 �C, since the glass transition

temperature of this polymer is around 80 �C.

Figure 1 shows the temperature and torque as a function

of PETG content in the blends after 5 min of mixing. The

initial temperature in the mixer chamber was 180 �C,

however the final temperature is quite different and

depends on the composition of the mixtures, as can be seen

in Fig. 1. PHB shows a torque value of 3 Nm at the end of

the processing (T = 193 �C), while PETG had a value of

14 Nm (T = 231 �C), significantly higher than PHB.

The disadvantage of processing PETG at this tempera-

ture range (180–230 �C) is its higher viscosity. Despite of

this, our results showed that it is possible to mix PETG

with PHB, which acts as a plasticizer, decreasing the vis-

cosity and, consequently, the final temperature of the PHB/

PETG blends (Fig. 1). For example, blends containing up

to 50 wt% of PHB are processed at temperatures lower

than 200 �C. Under this condition the degradation of PHB

is minimized or avoided, making PETG a good partner to

mix with PHB.

DSC curves in Fig. 2a and b show the glass transition

region of the PHB phase determined from the second

heating scan and of the PETG phase determined from the

third heating scan, respectively, for blends prepared in the

Fig. 1 Compositional dependence of (open circle) Torque and (opentriangle) Temperature as a function of PETG content for PHB/PETG

blends

310 J Polym Environ (2010) 18:308–317

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batch mixer. PHB shows a cold crystallization during the

second heating scan at temperatures near the PETG glass

transition. Thus, the glass transition of the PETG phase in

the blends can be better observed if the PHB phase is

previously crystallized. As described in the ‘‘Experimen-

tal’’ section, the isothermal crystallization of PHB was

conducted at 70 �C for 20 min and after this the samples

were cooled to -20 �C and heated again to 200 �C (third

heating scan shown in Fig. 2b). The blends presented two

glass transitions for all blend compositions, at the same

temperatures as the pure polymers, meaning that these

blends are immiscible.

Figure 3a,b show the crystallization and melting

behavior of the PHB/PETG blends prepared in the

batch mixer, respectively, during the second heating at

10 �C/min. PHB does not crystallize during the cooling

scan at 10 �C/min (data not shown), but under heating an

endothermic peak with a maximum at 58 �C, corresponding

to cold crystallization, appears (Fig. 3a). The blends also

show cold crystallization at the same temperature range,

from 40 �C to 70 �C (Fig. 3a) followed by PHB melting at

temperatures higher than 160 �C (Fig. 3b). PHB shows a

Fig. 2 DSC curves showing the glass transition of a PHB (second

heating scan) and b PETG (third heating scan) for blends prepared in

a batch mixer. Heating rate of 10 �C/min

Fig. 3 DSC curves showing crystallization and melting for PHB/

PETG blends: a cooling, b heating. Second heating scan

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broad and asymmetric exothermic peak with a minimum at

175 �C. This peak shifts to lower temperatures as the PETG

content increases and a shoulder at lower temperature

appears. Since the blends are immiscible the shift of the

melting temperature of the PHB can be attributed to kinetics

and morphological effects. Moreover, the shift of the

melting temperature is in the range of 2–6 �C, therefore the

degradation of PHB can be considered insignificant [27].

Table 1 summarizes the crystallization (Tc), melting

(Tm), glass transition temperatures (Tg) and melting

enthalpy (DHm) obtained from DSC curves. The melt-

ing enthalpy of the PHB phase is practically independent of

the blend composition showing that PETG phase does not

influence the PHB crystallization.

Figure 4a,b show the storage and the loss moduli as a

function of temperature, respectively, for PHB, PETG and

their blends. The PHB storage modulus is practically

constant and around 4 9 109 Pa until 10 �C. At this tem-

perature a small drop is verified due to a glass transition

followed by a quite intense drop at 180 �C due to melting.

PETG is amorphous and its storage modulus presents a

quite intense drop at 80 �C due to its glass transition. The

loss modulus curves show peaks corresponding to the same

relaxation described above. PETG glass transition relaxa-

tion is observed as a quite intense peak, located in the

temperature range from 70 to 90 �C. PHB glass transition

relaxation is located in the temperature range from 0 to

30 �C and a rearrangement of the crystalline phase occurs

above 75 �C. The viscoelastic properties of PHB suffer the

influence of a physical aging process, which induces a

depression of the glass transition peak intensity [49, 50].

Table 1 Thermal behavior of PHB, PETG and their blends obtained

from DSC analysis

PHB PETG

% PETG Tc (�C) Tm (�C) Tg (�C) DHm (J/g) Tg (�C)

0 58 175 4 82 –

20 62 173 3 81 74

40 58 171 2 83 73

50 58 172 3 81 74

60 60 171 3 84 73

80 47 169 1 83 73

100 – – – – 77

Fig. 4 a Storage modulus (E0) and b loss modulus (E0 0) as a function

of temperature for PHB/PETG blends. PETG: 0 (filled square), 20

(down-pointing triangle), 40 (plus), 50 (open square), 60 (opentriangle), 80 (open circle), 100 (wt%) (closed circle)

Fig. 5 Storage modulus as a function of PETG content at 130 �C for

PHB/PETG blends

312 J Polym Environ (2010) 18:308–317

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Loss modulus curves of the blends present peaks related to

the glass transition of PHB and PETG, confirming

immiscibility over the whole composition range.

The analysis of storage modulus curves allows us to

predict PHB/PETG morphology. For example, PETG at

130 �C is a viscous liquid and the modulus assumes values

of 4 9 106 Pa. On the other hand, PHB at 130 �C is present

as a liquid and a crystalline phase and the modulus is still

around 109 Pa. In this case the crystalline phase is

responsible for maintaining the stiffness of PHB. The

blends are immiscible and at this temperature three phases

should coexist: PETG liquid phase, PHB liquid phase and

crystalline phase. The modulus of the blends at 130 �C

(Fig. 5) is almost constant (and near the value found for

PHB, &5 9 108 Pa) until 50 wt% of PETG suggesting that

PHB is the matrix. For blends containing 60 and 80 wt% of

PETG the modulus drops abruptly indicating that PETG is

the matrix. So, phase inversion should take place at PETG

contents between 50 wt% and 60 wt%. This conclusion

will be confirmed by microscopy images, as described

below.

The factors affecting phase dispersion and blend mor-

phology during the mixing process are: (i) temperature,

(ii) mixing time in an internal mixer or the residence time

in a twin-screw extruder, (iii) the intensity of mixing (rotor

or screw speed), (iv) blend composition, (v) viscosity ratio,

and (vi) interfacial tension [47, 48]. The mechanical pro-

cessing of PHB is not trivial because the thermal degra-

dation starts at temperatures close to melting. Thus, mixing

conditions, i.e., temperature, time and intensity of mixing

in a batch mixer and extruder have narrow possibilities,

different from other thermoplastics [51, 52]. The viscosity

ratio is one of the most important factors affecting blend

morphology. The viscosity ratio of PETG and PHB can be

considered equal to the torque ratio, that is, around 4.

Consequently the dispersion of one component in the other

Fig. 6 Field emission scanning

electron micrographs of batch

mixer PHB/PETG blends. At

PHB/PETG compositions: a 80/

20; b 60/40; c 50/50; d 40/60

and e 20/80

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should occur under high shear. Since both PETG and PHB

are polyesters, interfacial tension should not be high.

Figure 6 shows the micrographs of PHB/PETG blends

obtained in the batch mixer. The micrographs of blends

containing 20 wt% (Fig. 6a), 40 wt% (Fig. 6b) and 80 wt%

PETG (Fig. 6e) show a disperse phase in a matrix. For

blends containing 20 wt% and 40 wt% of PETG the matrix

is PHB, while for the blend containing 80 wt% of PETG the

matrix is PETG. For these blends equatorial fracture of the

disperse domains (arrows on the micrographs) as well as

entire particles can be observed. In blends containing

50 wt% and 60 wt% of PETG (Fig. 6c, d, respectively), no

Fig. 7 Field emission scanning

electron micrographs for blends

containing 10 (a and b), 20 (cand d), 30 (e and f) and 40 wt%

of PETG (g and h). Micrographs

a, c, e and g correspond to

blends prepared in a twin screw

extruder. Micrographs b, d, fand h corresponding to injection

molded blends

314 J Polym Environ (2010) 18:308–317

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spherical domains can be seen. Probably, this composition

range is close to the phase inversion and a co-continuous

morphology is developed.

Figure 7 shows the micrographs of PHB/PETG blends

obtained in the twin screw extruder (Fig. 7a,c,e and g) and

submitted to injection molding (Fig. 7b, d, f and h).

The morphology of the blends obtained in the twin

screw extruder is quite different from those with compa-

rable composition obtained in the batch mixer. Blends

obtained in the twin screw extruder show a finer dispersion

of PETG in the PHB matrix, in comparison with the same

blends after injection molding or obtained in a batch mixer.

Blends prepared by extrusion as well as blends prepared in

an internal mixer and containing 20, 40 and 80 wt% of

PETG show a relatively smooth fracture surfaces without

significant deformation of the PHB and PETG phases.

Furthermore, the debonded interfaces between PHB/PETG

are very smooth. These results indicate that very little

energy was dissipated by ductile deformation. Table 2

presents the size of dispersed domains of blends obtained

in a twin screw extruder and submitted to injection mold-

ing. The coalescence of the dispersed phases of PETG took

place during the injection molding process, increasing the

size of the PETG domains.

Table 3 shows the flexural and impact resistance prop-

erties to PHB/PETG blends as a function of the PETG

content. The flexural modulus of the blends is higher in

comparison with the modulus of PHB and of PETG. The

modulus achieves the maximum values at PETG concen-

tration of 20 and 30 wt%. The impact strength of PHB and

blends containing 20 and 30 wt% of PETG is close and

about 5 times lower than the value found for PETG. Thus,

the addition of PETG to PHB results in material with

higher modulus and, depending on the composition, with-

out significant changes in impact resistance in relation to

pure PHB. The mechanical behavior of the PHB/PETG

blends with the composition is characteristic of mixtures

with low interfacial adhesion.

Table 2 Sizes of the dispersed phase in several blend compositions

(%) PETG Dispersed

phase

Diameter of dispersed phase (lm)

Extrusion Injection

10 PETG 0.3–1.0 2–10.0

20 PETG 0.3–1.0 2–10.0

30 PETG 0.2–1.0 2–16.0

40 PETG 0.2–2.0 1–11.0

Table 3 Tensile strength, flexural modulus and impact strength of

PHB/PETG blends

PETG

(%)

Tensile strength

(MPa)

Flexural modulus

(MPa)

Impact strength

(J/m)

0 58 ± 1 3067 ± 34 24 ± 3

10 49 ± 2 3566 ± 62 13 ± 2

20 42 ± 2 3634 ± 105 22 ± 2

30 33 ± 1 3127 ± 38 27 ± 3

40 33 ± 1 3164 ± 33 15 ± 3

100 70 ± 4 2100 ± 40 122 ± 6

Fig. 8 Aging of PHB, PETG and their blends prepared in the batch

mixer in a simulated soil and b a-amylase medium: 0 (filled square),

10 (star), 20 (down-pointing triangle), 30 (cross), 40 (plus), 50 (opensquare), 60 (open triangle), 80 (open circle), 100 wt% of PETG

(closed circle)

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Biodegradable polymers are able to degrade via enzy-

matic and hydrolytic mechanisms [53]. The extent of

polymer environmental degradation depends on the kind of

environment in which the experiment is conducted, for

example, sea and river water, compost or soil. Besides

factors such as pH, UV radiation, temperature and the

presence of specific microorganism affect the degradation

process.

Figure 8 shows the mass retention of the pure polymers

and their blends during aging in simulated soil and in

enzymatic media. PHB showed a total mass loss in simu-

lated soil after 600 days of aging. On the other hand, PETG

did not show any mass change during the test, leading to

the conclusion that PETG is inert to the attack of micro-

organism presents in the soil. However, the mass loss is

also complete for all the blends (Fig. 8a). Since the blends

present low interfacial adhesion, PHB could have degraded

and the PETG phase could have fallen out during the

washing step. The data of aging in enzymatic a-amylase

media (Fig. 8b) show a significant degradation for PHB,

followed by blends containing 60 wt%, 50 wt% and

20 wt% of PHB.

Conclusions

PETG is an amorphous aromatic polyester with a process-

ing window wider in comparison with crystalline aromatic

polyesters. This characteristic allows mixing it with PHB in

the melted state independent of the mixture method: batch

mixer or twin screw extruder. Moreover, the injection

molding parameters of PETG/PHB blends is more constant

during the injection process, in comparison with the injec-

tion molding parameters of pure PHB. The PHB/PETG

blends are immiscible throughout the entire composition

blend and their morphology depends on the composition

and the processing conditions used to prepare them.

Extrusion resulted in finer dispersions of PETG in the PHB

matrix. The fracture morphology of the samples suggests

poor interfacial adhesion. The addition of PETG to PHB

results in material with higher moduli and, depending on the

composition, without significant changes in the impact

resistance in comparison to PHB. PETG is not biodegrad-

able in simulated soil as well in enzymatic media under the

studied conditions. However, the biodegradability of the

PHB phase of the blends is maintained.

Acknowledgements The authors would like to thank FAPESP

(Proc.: 01/07841-3; no. 00/10063-0; 2004/15084-6; 2003/09926-1;

04/13723-1) for financial support, PHB Industrial and Eastman for

supplying the polymers and Profa. Dra. Carol Hollingworth Collins for

manuscript revision.

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