Miscibility and crystallization behavior of poly(3‐hydroxyvalerate‐co‐3‐hydroxyvalerate)/ poly(propylene carbonate) blends

Blends of synthetic poly(propylene carbonate) (PPC) with a natural bacterial copolymer of 3‐hydroxybutyrate with 3‐hydroxyvalerate (PHBV) containing 8 mol % 3‐hydroxyvalerate units were prepared with a simple casting procedure. PPC was thermally stabilized by end‐capping before use. The miscibility, morphology, and crystallization behavior of the blends were investigated by differential scanning calorimetry, polarized optical microscopy, wide‐angle X‐ray diffraction (WAXD), and small‐angle X‐ray scattering (SAXS). PHBV/PPC blends showed weak miscibility in the melt, but the miscibility was very low. The effect of PPC on the crystallization of PHBV was evident. The addition of PPC decreased the rate of spherulite growth of PHBV, and with increasing PPC content in the PHBV/PPC blends, the PHBV spherulites became more and more open. However, the crystalline structure of PHBV did not change with increasing PPC in the PHBV/PPC blends, as shown from WAXD analysis. The long period obtained from SAXS showed a small increase with the addition of PPC. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 90: 4054–4060, 2003     

Miscibility and crystallization behavior of biodegradable poly(3‐hydroxybutyrate‐co‐3‐hydroxyvalerate)/phenolic blends

Poly(3‐hydroxybutyrate‐co‐3‐hydroxyvalerate) (PHBV)/phenolic blends are new miscible crystalline/amorphous polymer blends prepared via solution casting method in this work, as evidenced by the single composition dependent glass transition temperature. The measured T_gs can be well fitted by the Kwei equation with a q value of 13.6 for the PHBV/phenolic blends, indicating that the interaction between the two components is strong. The negative polymer–polymer interaction parameter, obtained from the melting depression of PHBV using the Nishi‐Wang equation, indicating the thermal miscibility of PHBV and phenolic. The spherulitic morphology and crystal structure of PHBV/phenolic blends were studied with polar optical microscopy and wide angle X‐ray diffraction compared with those of neat PHBV. It is found that the growth rates of PHBV in the blends are lower than that in neat PHBV at a given crystallization temperature, and the crystal structure of PHBV is not modified by the presence of phenolic in the PHBV/phenolic blends, but the crystallinity decrease with the increasing of phenolic. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012     

Mechanical and thermal properties of poly(butylene succinate)/poly(3‐hydroxybutyrate‐co‐3‐hydroxyvalerate) biodegradable blends

Biodegradable polymer blends of poly(butylene succinate) (PBS) and poly(3‐hydroxybutyrate‐co‐3‐hydroxyvalerate) (PHBV) were prepared with different compositions. The mechanical properties of the blends were studied through tensile testing and dynamic mechanical thermal analysis. The dependence of the elastic modulus and strength data on the blend composition was modeled on the basis of the equivalent box model. The fitting parameters indicated complete immiscibility between PBS and PHBV and a moderate adhesion level between them. The immiscibility of the parent phases was also evidenced by scanning electron observation of the prepared blends. The thermal properties of the blends were studied through differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA). The DSC results showed an enhancement of the crystallization behavior of PBS after it was blended with PHBV, whereas the thermal stability of PBS was reduced in the blends, as shown by the TGA thermograms. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 42815.     

Compatibility of poly(butadiene‐co‐acrylonitrile) with poly(L‐lactide) and poly(3‐hydroxybutyrate‐co‐3‐hydroxyvalerate)

Poly(L ‐lactide) (PLLA) and poly(3‐hydrobutyrate‐co‐3‐hydroxyvalerate) (PHBV) were blended with poly(butadiene‐co‐acrylonitrile) (NBR). Both PLLA/NBR and PHBV/NBR blends exhibited higher tensile properties as the content of acrylonitrile unit (AN) of NBR increased from 22 to 50 wt %. However, two separate glass transition temperatures (T_g) appeared in PLLA/NBR blends irrespective of the content of NBR, revealing that PLLA was incompatible with NBR. In contrast, a single T_g, which shifted along with the blend composition, was observed for PHBV/NBR50 blends. Moreover NBR50 suppressed the crystallization of PHBV, indicating that PHBV was compatible with NBR50. Decrease of both elongation modulus and stress at maximum load was less significant and increase of elongation at break was more pronounced in PHBV/NBR50 blends than in PLLA/NBR50 blends. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 92: 3508–3513, 2004     

Control and development of crystallinity and morphology in poly(β‐hydroxybutyrate‐co‐β‐hydroxyvalerate)/poly(propylene carbonate) blends

Two different methodologies (reactive blending and mechanical blending) for preparing blends of poly(β‐hydroxybutyrate‐co‐β‐hydroxyvalerate) (PHBV) and poly(propylene carbonate) (PPC) were used. The miscibility, chemical structure, thermal behavior, crystallinity, morphology, and mechanical properties of the blends were investigated with Fourier transform infrared spectroscopy, differential scanning calorimetry, polarized optical microscopy, scanning electron microscopy, and tensile tests. A certain extent of hydrogen‐bonding interactions between PHBV and PPC took place in the blends. The graft copolymerization was confirmed in the reactive system. The incorporation of PPC hampered the crystallization process of PHBV and evidently altered the morphology, and the effect was enhanced in the reactive blend. The mechanical properties of PHBV could be changed by 1–2 orders of magnitude by blending modification. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 98: 1427–1436, 2005     

Effect of graft modification with poly(N‐vinylpyrrolidone) on thermal and mechanical properties of poly (3‐hydroxybutyrate‐co‐3‐hydroxyvalerate)

Poly(N‐vinylpyrrolidone) (PVP) groups were grafted onto poly(3‐hydroxybutyrate‐co‐3‐hydroxyvalerate) (PHBV) backbone to modify the properties of PHBV and synthesize a new novel biocompatible graft copolymer. The effect of graft modification with PVP on the thermal and mechanical properties of PHBV was investigated. The thermal stability of grafted PHBV was remarkably improved while the melting temperature (T_m) was almost not affected by graft modification. The isothermal crystallization behavior of samples was observed by polarized optical microscopy and the results showed that the spherulitic radial growth rates (G) of grafted PHBV at the same crystallization temperature (T_c) decreased with increasing graft yield (graft%) of samples. Analysis of isothermal crystallization kinetics showed that both the surface free energy (σ_e) and the work of chain‐folding per molecular fold (q) of grafted PHBV increased with increasing graft%, implying that the chains of grafted PHBV are less flexible than ungrafted PHBV. This conclusion was in agreement with the mechanical testing results. The Young's modulus of grafted PHBV increased while the elongation decreased with increasing graft%. The hydrophilicity of polymer films was also investigated by the water contact angle measurement and the results revealed that the hydrophilicity of grafted PHBV was enhanced. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

Blends of polylactide and poly(3‐hydroxybutyrate‐co‐3‐hydroxyvalerate) with low content of hydroxyvalerate unit: Morphology,structure, and property

The Polylactide (PLA)/poly(3‐hydroxybutyrate‐co‐3‐hydroxyvalerate) (PHBV) blends with four different weight ratios were prepared by melt mixing. PLA and PHBV in PLA/PHBV blends were immiscible while the weak interaction between PLA and PHBV existed. The PHBV domains below 2 μm were dispersed in PLA matrix uniformly. The addition of PHBV made the crystallization of PLA easier due to PHBV acting as nucleating agent. PLA spherulites in PLA/PHBV blends presented various banded structures. In addition, the crystallinity of neat PLA was lower than those of PLA/PHBV blends. With the increase of PHBV content in PLA/PHBV blends, the crystallinity of PLA/PHBV blends increased. PHBV could enhance significantly the toughness of PLA. However, with the increase of PHBV content, the yield stress (σ_y), tensile modulus (E), and the yield strain (ε_y) of PLA/PHBV blends decreased gradually. In addition, incorporation of PHBV to PLA caused a transformation from an optical transparent to an opaque system. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 42689.     

Thermal properties of blends of poly(hydroxybutyrate‐co‐hydroxyvalerate) and poly(styrene‐co‐acrylonitrile)

Thermal properties of blends of poly(hydroxybutyrate‐co‐hydroxyvalerate) (PHBV) and poly(styrene‐co‐acrylonitrile) (SAN) prepared by solution casting were investigated by differential scanning calorimetry. In the study of PHBV‐SAN blends by differential scanning calorimetry, glass transition temperature and melting point of PHBV in the PHBV‐SAN blends were almost unchanged compared with those of the pure PHBV. This result indicates that the blends of PHBV and SAN are immiscible. However, crystallization temperature of the PHBV in the blends decreased approximately 9–15°. From the results of the Avrami analysis of PHBV in the PHBV‐SAN blends, crystallization rate constant of PHBV in the PHBV‐SAN blends decreased compared with that of the pure PHBV. From the above results, it is suggested that the nucleation of PHBV in the blends is suppressed by the addition of SAN. From the measured crystallization half time and degree of supercooling, interfacial free energy for the formation of heterogeneous nuclei of PHBV in the PHBV‐SAN blends was calculated and found to be 2360 (mN/m)³ for the pure PHBV and 2920–3120 (mN/m)³ for the blends. The values of interfacial free energy indicate that heterogeneity of PHBV in the PHBV‐SAN blends is deactivated by the SAN. This result is consistent with the results of crystallization temperature and crystallization rate constant of PHBV in the PHBV‐SAN blends. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 77: 673–679, 2000     

Biopolymer nanocomposites based on poly(hydroxybutyrate‐co‐hydroxyvalerate) reinforced by a non‐ionic organoclay

In this study, a nanocomposite based on a biodegradable polymer poly(hydroxybutyrate‐co‐hydroxyvalerate) (PHBV) reinforced by triethylene glycol mono‐n‐decyl ether (C₁₀E₃) non‐ionic organoclay (C₁₀E₃‐Mt) was prepared. The morphology and the thermal and mechanical properties of PHBV/C₁₀E₃‐Mt were compared with those of PHBV nanocomposites prepared using commercial organically modified montmorillonite Cloisite^® 30B (OMt) and raw montmorillonite (Mt). Nanocomposites with 3 wt% nanoparticles were obtained by melt processing. The high level of dispersion with improved interfacial interactions between OMt and polymer led to an increase in the thermal stability and modulus of PHBV. However, this nanocomposite presented a lower strain before fracture, typical of brittle behavior. The transmission electron microscopy and wide angle X‐ray diffraction results revealed a significant increase in the interlayer spacing of clay for the PHBV/C₁₀E₃‐Mt nanocomposite, which was favored by the wide expansion of the platelets of the starting non‐ionic organoclay. This characteristic of C₁₀E₃‐Mt, together with its hydrophobic behavior, allowed its easy incorporation in the PHBV matrix, thus improving the processing and maintaining a high modulus with increased material toughness. © 2014 Society of Chemical Industry     

Crystallization and melting behavior of partially miscible six‐armed poly(l‐lactic acid)/poly(3‐hydroxybutyrate‐co‐3‐hydroxyvalerate) blends

The crystallization kinetics and spherulitic morphology of six‐armed poly(L‐lactic acid) (6a‐PLLA)/poly(3‐hydroxybutyrate‐co?3‐hydroxyvalerate) (PHBV) crystalline/crystalline partially miscible blends were investigated with differential scanning calorimetry and polarized optical microscopy in this study. Avrami analysis was used to describe the isothermal crystallization process of the neat polymers and their blends. The results suggest that blending had a complex influence on the crystallization rate of the two components during the isothermal crystallization process. Also, the crystallization mechanism of these blends was different from that of the neat polymers. The melting behavior of these blends was also studied after crystallization at various crystallization temperatures. The crystallization of PHBV at 125°C was difficult, so no melting peaks were found. However, it was interesting to find a weak melting peak, which arose from the PHBV component for the 20/80 6a‐PLLA/PHBV blend after crystallization at 125°C, and it is discussed in detail. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 42548.     

Miscibility and properties of completely biodegradable blends of poly(propylene carbonate) and poly(butylene succinate)

Completely biodegradable blends of poly (propylene carbonate) (PPC) and poly(butylene succinate) (PBS) were melt‐prepared and then compression‐molded. The miscibilities of the two aliphatic polyesters, that is, PPC and PBS, were investigated by dynamic mechanical analysis (DMA) and scanning electron microscopy (SEM). The static mechanical properties, thermal behaviors, crystalline behavior, and melt flowability of the blends were also studied. Static tensile tests showed that the yield strength and the strength at break increased remarkably up to 30.7 and 46.3 MPa, respectively, with the incorporation of PBS. The good ductility of the blends was maintained in view of the large elongation at break. SEM observation revealed a two‐phase structure with good interfacial adhesion. The immiscibility of the two components was verified by the two independent glass‐transition temperatures obtained from DMA tests. Moreover, thermogravimetric measurements indicated that the thermal decomposition temperatures (T_?5% and T_?10%) of the PPC/PBS blends increased dramatically by 30–60°C when compared with PPC matrix. The melt flow indices of the blends showed that the introduction of PBS improved the melt flowability of the blends. The blending of PPC with PBS provided a practical way to develop completely biodegradable blends with applicable comprehensive properties. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

Crystallization and melting behavior of blends comprising poly(3‐hydroxy butyrate‐co‐3‐hydroxy valerate) and poly(ethylene oxide)

Blends of poly(3‐hydroxy butyrate‐co‐3‐hydroxy valerate) (PHBV) and poly(ethylene oxide) (PEO) were prepared by casting from chloroform solutions. Crystallization kinetics and melting behavior of blends have been studied by differential scanning calorimetry and optical polarizing microscopy. Experimental results reveal that the constituents are miscible in the amorphous state. They form separated crystal structures in the solid state. Crystallization behavior of the blends was studied under isothermal and nonisothermal conditions. Owing to the large difference in melting temperatures, the constituents crystallize consecutively in blends; however, the process is affected by the respective second component. PHBV crystallizes from the amorphous mixture of the constituents, at temperatures where the PEO remains in the molten state. PEO, on the other hand, is surrounded during its crystallization process by crystalline PHBV regions. The degree of crystallinity in the blends stays constant for PHBV and decreases slightly for PEO, with ascending PHBV content. The rate of crystallization of PHBV decreases in blends as compared to the neat polymer. The opposite behavior is observed for PEO. Nonisothermal crystallization is discussed in terms of a quasi‐isothermal approach. Qualitatively, the results show the same tendencies as under isothermal conditions. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 101: 2776–2783, 2006     

Fabrication and improved performance of poly(3‐hydroxybutyrate‐co‐3‐hydroxyvalerate) for packaging by addition of high molecular weight natural rubber

The packaging industry is searching for alternative materials to attain environmental sustainability. Poly(3‐hydroxybutyrate‐co‐3‐hydroxyvalerate (PHBV) is a semicrystalline polymer that meets this sustainability goal since it is bioderived and biodegradable. However, its brittle nature and relatively high water permeation and transmission rates make it unsuitable for packaging applications. In addition, PHBV has poor mechanical, thermal, and rheological properties above 160 °C, limiting its use in cast sheets and thermo‐formed packaging applications. To improve these properties, new blends of PHBV with high molecular weight natural rubber at 5, 10, 15, and 25% by weight were fabricated, and physico‐chemical properties of the blends were characterized. The rubber in the blends aided in the following: increased thermal stability since the complex viscosities of the blends were improved by one log over pure PHBV at 170 °C, created more uniform melting peaks attesting to improved homogeneity, decreased water permeation to a level similar to that of traditional thermoplastics; increased the elongation at break, and stabilized the Young's modulus. Therefore, these blends can potentially be used in‐place of traditional, petroleum‐based thermoplastics in cast sheets and thermoforms. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016 , 133, 43937.     

Morphology and thermal behavior of poly (3‐hydroxybutyrate‐co‐3‐hydroxyvalerate)/poly(butylene adipate‐co‐terephthalate)/clay nanocomposites

Biopolymers are gaining increasing interest because of decline of mineral oil reserves, increasing waste problem, and increasing consciousness of society for environmental problems. However, competitiveness of biopolymers compared with conventional plastics is still limited due to partly insufficient properties and high prices. This study investigates the influence of blending of poly(hydroxybutyrate‐co‐hydroxyvalerate) (PHBV) with poly(butylene adipate‐co‐terephthalate) (PBAT) as well as the influence of addition of functionalized montmorillonite (OMMT) to the blends on morphology and thermal behavior. Dispersion state and morphology of the nanocomposites are studied by X‐ray diffraction as well as scanning electron microscopy. Thermal stability is studied by thermogravimetric analysis and crystallization behavior is studied by differential scanning calorimetry and polarized optical microscopy. With respect to the morphology for the blends it can be seen that the immiscible biopolymers PHBV and PBAT are distributed in interlocking zones. There is a good dispersion and homogeneous distribution of OMMT within the biopolymer blends. The addition of 50% or more PBAT to PHBV as well as the insertion of OMMT enhances thermal stability of PHBV. In the blends, the addition of PBAT retards crystallization of PHBV. The OMMT acts as nucleating agent leading in total to more but less perfect crystals in the blends, and the crystallization slows further due to constraint in the movement of polymer chains. These results contribute to the understanding of the structure–properties relationship of bionanocomposite materials for packaging applications. POLYM. COMPOS., 36:2051–2058, 2015. © 2014 Society of Plastics Engineer     

Effects of l‐aspartic acid and poly(butylene succinate) on thermal stability and mechanical properties of poly(propylene carbonate)

Poly(propylene carbonate) (PPC) was modified by l ‐aspartic acid (Asp) and poly(butylene succinate) (PBS). To assess the effects of Asp and PBS on the thermal stability, mechanical properties of PPC, different PPC/Asp, PPC/PBS, and PPC/PBS/Asp blends were prepared by twin‐screw extruder. The results indicated that the thermal stability improved with the Asp content increasing from 0.5 to 5%. With trace presence of 2% Asp, the degradation temperature of PPC was greatly increased upon extruding and the Yield strength and Young's modulus increased 62 and 849 times, respectively, at 20°C. The flexibility of PPC was effectively improved by blending with PBS, the PBS has no significant effect on the thermal stability of PPC until PBS up to enough amount. Besides the Asp additive in PPC/PBS blends not only improved the thermal stability PPC, but improved the interfacial compatibility of the blend. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016 , 133, 42970.     

Crystallization behavior of partially crosslinked poly(β‐hydroxyalkonates)/poly(butylene succinate) blends

Partially crosslinked poly(β‐hydroxybutyrate‐co‐β‐hydroxyvalerate)/poly(butylene succinate) (PHBV/PBS) and poly(β‐hydroxybutyrate)/poly(butylene succinate) (PHB/PBS) blends were prepared by melt compounding with dicumyl peroxide. The effect of partial crosslinking on crystallization of the PHBV/PBS and PHB/PBS blends was investigated systematically. Differential scanning calorimetry results showed that the overall crystallization rates of both PHBV and PBS in their blends were enhanced considerably by the partial crosslinking. Similar results were also detected in the PHB/PBS blends. The polarized optical microscope observation displayed that the nuclei density of PHBV was increased while the spherulitic morphology did not change much. Conversely, the PBS spherulites turned into cloud‐like morphology after the partial crosslinking which is a result of the decrease in spherulite size, the reduction in interspherulite distance and the interconnection of fine PBS domains. Wide angle X‐ray diffraction patterns confirmed the enhancement in crystallization of the PHBV/PBS blends after the partial crosslinking without modification on crystalline forms of the PHBV and PBS components. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 41020.     

Miscibility of poly(3‐hydroxybutyrate‐co‐3‐hydroxyvalerate) with high molecular weight poly(lactic acid) blends determined by thermal analysis

An important strategy used in the polymer industry in recent years is blending two bio‐based polymers to attain desirable properties similar to traditional thermoplastics, thus increasing the application potential for bio‐based and bio‐degradable polymers. Miscibility of poly(3‐hydroxybutyrate‐co‐3‐hydroxyvalerate) (PHBV) with poly(L ‐lactic acid) (PLA) were characterized using differential scanning calorimetry (DSC), thermogravimetric analysis (TGA), and scanning electron microscopy (SEM). Three different grades of commercially available PLAs and one type of PHBV were blended in different ratios of 50/50, 60/40, 70/30, and 80/20 (PHBV/PLA) using a micro‐compounder at 175°C. The DSC and TGA analysis showed the blends were immiscible due to different stereo configuration of PLA polymer and two distinct melting temperatures. However, some compatibility between PHBV and PLA polymers was observed due to decreases in PLA's glass transition temperatures. Additionally, the blends do not show clear separation by SEM analysis, as observed in the thermal analysis. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012     

Reactive compatibilization of poly(l‐lactic acid)/poly(propylene carbonate) blends: Thermal,thermomechanical, and morphological properties

Poly(l ‐lactic acid) (PLLA) was blended with poly(propylene carbonate) (PPC) with various compositions by a melt‐blending process to evaluate their general properties for a potential flexible packaging field. The mechanical properties, including the tensile strength and modulus, revealed a tendency to decrease with the addition of ductile PPC; this was induced by the poor interfacial adhesion between PLLA and PPC with the cavities and clear edges and was observed through morphological observation. Reactive compatibilization was applied to improve the interfacial adhesion between PLLA and PPC, and the elongation at break was profoundly enhanced because of the improved interfacial adhesion between the two phases. The compatibilized PLLA/PPC blends showed considerable improvements in the storage modulus in the transition region with stable thermal stability; this could be a benefit for thermal processing. The addition of PPC had a great effect on the solidlike behavior and increased the elasticity of the PLLA/PPC blends. Up to 2.0 phr maleic anhydride showed a great efficiency in enhancing the dynamic storage modulus and complex viscosity of the PLLA/PPC blends. We also confirmed that it was feasible to fabricate PLLA/PPC blends with controllable barrier properties with combination of PLLA and PPC under reactive compatibilization while retaining the biodegradability. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016 , 133, 43388.     

Hydrolysis of poly(hydroxybutyrate‐co‐hydroxyvalerate) nanoparticles

Poly(hydroxybutyrate‐co‐hydroxyvalerate) (PHBV) is a natural polyester known for its biocompatibility and biodegradability. The hydrolysis of PHBV nanoparticles (90–150 nm) and microparticles (33–58 µm) was investigated. Particles were formulated from preformed polymer(s) by miniemulsification/solvent evaporation technique to obtain nanoparticles or by emulsification/solvent evaporation technique to obtain microparticles. The morphology of the nanoparticles was studied by Field Emission Gun‐Scanning Electron Microscopy (FEG‐SEM). The kinetics of PHBV degradation was followed by gel permeation chromatography. After storage of PHBV nanoparticles for 25 days at 37 °C, the M_n and M_w of PHBV was reduced up to 85 and 80%, respectively. PHBV nanoparticles stored at 4 °C presented a much lower molecular weight reduction. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013     

Thermal analysis of poly(3‐hydroxybutyrate‐co‐3‐hydroxyvalerate) irradiated under vacuum

Poly(3‐hydroxybutyrate‐co‐3‐hydroxyvalerate) (PHBV) was irradiated by ⁶⁰Co γ‐rays (doses of 50, 100 and 200 kGy) under vacuum. The thermal analysis of control and irradiated PHBV, under vacuum was carried out by thermogravimetric analysis (TGA) and differential scanning calorimetry (DSC). The tensile properties of control and irradiated PHBV were examined by using an Instron tensile testing machine. In the thermal degradation of control and irradiated PHBV, a one‐step weight loss was observed. The derivative thermogravimetric curves of control and irradiated PHBV confirmed only one weight‐loss step change. The onset degradation temperature (T_o) and the temperature of maximum weight‐loss rate (T_p) of control and irradiated PHBV were in line with the heating rate (°C min^?1). T_o and T_P of PHBV decreased with increasing radiation dose at the same heating rate. The DSC results showed that ⁶⁰Co γ‐radiation significantly affected the thermal properties of PHBV. With increasing radiation dose, the melting temperature (T_m) of PHBV shifted to a lower value, due to the decrease in crystal size. The tensile strength and fracture strain of the irradiated PHBV decreased, hence indicating an increased brittleness. Copyright © 2004 Society of Chemical Industry