Effects of fumed silica on the crystallization behavior and thermal properties of poly(hydroxybutyrate‐co‐hydroxyvalerate)

The effects of fumed silica on the crystallization behavior and thermal properties of poly(hydroxybutyrate‐co‐hydroxyvalerate) (PHBV) were investigated. The PHBV/silica composites were prepared by a melt‐blending method. The nonisothermal crystallization, melting process, and isothermal crystallization kinetics of PHBV and PHBV/silica composites were characterized with differential scanning calorimetry. The spherulite development and morphology were observed by polarized optical microscopy. In addition, the thermal degradation properties were determined via thermogravimetric analysis. The results indicated that the melting and crystallization kinetics of PHBV were greatly affected by fumed silica, and this was due to the effective nucleation function of silica, which enhanced the crystallization process. The thermal onset degradation temperature of PHBV increased with the addition of fumed silica. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

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.     

On the use of ball milling to develop poly(3‐hydroxybutyrate‐co‐3‐hydroxyvalerate)‐graphene nanocomposites (II)—Mechanical,barrier, and electrical properties

In this work, poly (3‐hydroxybutyrate‐co‐3‐hydroxyvalerate) (PHBV) nanocomposites containing functionalized graphene sheets (FGS) were prepared by means of high‐energy ball milling. The crystalline structure, oxygen barrier, mechanical and electrical properties, and biodegradability of the developed nanocomposites were analyzed and correlated with the amount of FGS incorporated and with their morphology, which was reported in a previous study. Addition of FGS into the PHBV matrix did not affect the crystal morphology of the material but led to somewhat enhanced crystallinity. The good dispersion and distribution of the nanofiller within the polymeric matrix, revealed in the first part of this study, was thought to be crucial for the mechanical reinforcing effect of FGS and also resulted in enhanced gas barrier properties at high relative humidity. Additionally, the conducting behavior of the nanocomposites, as interpreted by the percolation theory, displayed a very low percolation threshold set at ～0.3 vol % of FGS, while the materials exhibited an overall significantly enhanced conductivity. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 42217.     

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     

Morphology and thermal degradation studies of melt‐mixed PLA/PHBV biodegradable polymer blend nanocomposites with TiO2 as filler

The morphology and thermal stability of melt‐mixed poly(lactic acid) (PLA)/poly(hydroxybutyrate‐co‐valerate) (PHBV) blends and nanocomposites with small amounts of TiO₂ nanoparticles were investigated. PLA/PHBV at 50/50 w/w formed a co‐continuous structure, and most of the TiO₂ nanoparticles were well dispersed in the PLA phase and on the interface between PLA and PHBV, with a small number of large agglomerates in the PHBV phase. Thermogravimetric analysis (TGA) and TGA–Fourier‐transform infrared spectroscopy was used to study the thermal stability and degradation behavior of the two polymers, their blends, and nanocomposites. The thermal stability of PHBV was improved through blending with PLA, whereas that of the PLA was reduced through blending with PHBV, and the presence of TiO₂ nanoparticles seemingly improved the thermal stability of both polymers in the blend. However, the degradation kinetics results revealed that the nanoparticles could catalyze the degradation process and/or retard the volatilization of the degradation products, depending on their localization and their interaction with the polymer in question. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 42138.     

Influence of amorphous alkaline lignin on the crystallization behavior and thermal properties of bacterial polyester

Bacterial polyester poly(3‐hydroxybutyrate‐co‐3‐hydroxyvalerate) (PHBV) and alkaline lignin composites were prepared via melt processing method, and the influence of amorphous lignin on the crystallization behavior and thermal properties of PHBV were investigated. It was found that dual melting peaks appeared in DSC curves of PHBV/lignin composites, while only one single peak existed in PHBV. The non‐isothermal crystallization process analyzed by Jeziorny method suggested that lignin changed the nucleation mode of composites and hindered the crystallization rate of PHBV. Data calculated from the results of WAXD demonstrated that lignin did not change the basic crystal structure of PHBV, but decreased the average size of the lamellar stacks. POM results confirmed that the effect of lignin on the crystallization behavior of PHBV carried out in two opposite way, namely the enhanced effect of nucleation and the hindered effect of growth. Besides, the thermal stability of composites was also decreased significantly. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 41325.     

Comparison of covalent and noncovalent interactions of carbon nanotubes on the crystallization behavior and thermal properties of poly(3‐hydroxybutyrate‐co‐3‐hydroxyvalerate)

In this study, multiwalled carbon nanotubes (MWCNTs) were dispersed into a poly(3‐hydroxybutyrate‐co?3‐hydroxyvalerate) (PHBV) matrix, in which PHBV was either covalently attached to the nanotubes through an esterification reaction between the carboxylic groups of functionalized MWCNTs and the hydroxyl groups of PHBV with toluene diisocyanate as a coupling agent or physically mixed to result in only noncovalent interactions. The structure, crystallization behavior, and thermal properties of the resulting nanocomposites were studied. We found that the crystallization of PHBV grafted onto the MWCNTs (PHBV‐g‐MWCNTs) was markedly hindered and exhibited an exothermic peak caused by cold crystallization, whereas the nonisothermal crystallization of PHBV was enhanced because a heterogeneous nucleation effect appeared in the PHBV/MWCNTs. Moreover, the maximum decomposition temperature of the PHBV‐g‐MWCNTs was improved by about 14.4°C compared with that of the PHBV/MWCNTs and by about 23.7°C compared with that of the original PHBV. Furthermore, the PHBV‐g‐MWCNTs exhibited the wider melt‐processing window than the PHBV/MWCNTs and original PHBV. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 130: 4299–4307, 2013     

The morphology and thermal properties of multi‐walled carbon nanotube and poly(hydroxybutyrate‐co‐hydroxyvalerate) composite

Nanocomposites based on poly(hydroxybutyrate‐co‐hydroxyvalerate) (PHBV) and multi‐walled carbon nanotubes (MWNTs) were prepared by solution processing. Ultrasonic energy was used to uniformly disperse MWNTs in solutions and to incorporate them into composites. Microscopic observation reveals that polymer‐coated MWNTs dispersed homogenously in the PHBV matrix. The thermal properties and the crystallization behavior of the composites were characterized by thermogravimetric analysis, differential scanning calorimetry and wide‐angle X‐ray diffraction, the nucleant effect of MWNTs on the crystallization of PHBV was confirmed, and carbon nanotubes were found to enhanced the thermal stability of PHBV in nitrogen. Copyright © 2004 Society of Chemical Industry     

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.     

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     

Crystallization kinetics of bacterial poly(3‐hydroxylbutyrate) copolyesters with cyanuric acid as a nucleating agent

Effects of cyanuric acid (CA) on nonisothermal and isothermal crystallization, melting behavior, and spherulitic morphology of bacterial copolyesters of poly(3‐hydroxybutyrate), i.e., poly(3‐hydroxybutyrate‐co‐3‐hydroxyvalerate) (PHBV) and poly(3‐hydroxybutyrate‐co‐3‐hydroxyhexanoate) (PHBH), have been investigated. CA has excellent acceleration effectiveness on the melt crystallization of bacterial PHB, PHBV, and PHBH, better than the nucleating agents reported in the literatures, such as boron nitride, uracil, and orotic acid. PHBV and PHBH do not crystallize upon cooling from the melt at 10°C/min, while they are able to complete crystallization under the same conditions with an addition of 1% CA, with a presence of sharp crystallization exotherm at 75–95°C. Isothermal crystallization kinetics of neat and CA‐containing PHBV and PHBH were analyzed by Avrami model. Crystallization half‐times (t_1/2) of PHBV and PHBH decrease dramatically with an addition of CA. The melting behavior of isothermally melt‐crystallized PHBV and PHBH is almost not influenced by CA. Spherulitic numbers of PHBV and PHBH increase and the spherulite sizes reduce with an incorporation of CA. Nucleation densities of PHBV and PHBH increase by 3–4 orders of magnitude with a presence of 1% CA. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013     

Characterization and thermal degradation kinetics of poly(l‐lactide) nanocomposites with carbon nanotubes

The purpose of this research was to study the thermal degradation kinetics of nanocomposites of poly(l ‐lactide) (PLLA) with carbon nanotubes (CNT) in order to provide further insight into their thermal stability. Nanocomposites were prepared by solvent casting with 1, 3, and 5% by weight of pristine CNT (P‐CNT) or functionalized CNT (F‐CNT), and were characterized using infrared spectroscopy, transmission electron microscopy, differential scanning calorimetry, thermogravimetric analysis, and dynamic‐mechanical‐thermal analysis. The kinetic parameters of thermal decomposition were determined employing Coats‐Redfern method to calculate the reaction order and E₂ function model to calculate the activation energy (Ea). We found no major changes in PLLA glass transition temperatures due to CNT presence, but melt‐crystallization temperature increased slightly in some composites. In general, composites consisting of 3% or 5% of F‐CNT had superior thermal stability than did pure polymer or P‐CNT composites. This improved thermal stability was revealed by slightly higher degradation and onset temperatures, and Ea obtained from kinetic analysis. In addition, 3% or 5% of F‐CNT in PLLA composites slightly enhanced the storage modulus above the glass transition. Therefore, functionalization promoted, in some extent, better morphology and dispersion of CNT into the matrix, which was responsible for improved thermal stability and thermomechanical performance of composites at higher temperatures relative to pure polymer. POLYM. ENG. SCI., 55:710–718, 2015. © 2014 Society of Plastics Engineers     

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     

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.     

Effect of poly(propylene carbonate) on the crystallization and melting behavior of poly(β‐hydroxybutyrate‐co‐β‐hydroxyvalerate)

The crystallization and melting behavior of poly(β‐hydroxybutyrate‐co‐β‐hydroxyvalerate) (PHBV) and a 30/70 (w/w) PHBV/poly(propylene carbonate) (PPC) blend was investigated with differential scanning calorimetry (DSC) and Fourier transform infrared (FTIR). The transesterification reaction between PHBV and PPC was detected in the melt‐blending process. The interaction between the two macromolecules was confirmed by means of FTIR analysis. During the crystallization process from the melt, the crystallization temperature of the PHBV/PPC blend decreased about 8°C, the melting temperature was depressed by 4°C, and the degree of crystallinity of PHBV in the blend decreased about 9.4%; this was calculated through a comparison of the DSC heating traces for the blend and pure PHBV. These results indicated that imperfect crystals of PHBV formed, crystallization was inhibited, and the crystallization ability of PHBV was weakened in the blend. The equilibrium melting temperatures of PHBV and the 30/70 PHBV/PPC blend isothermally crystallized were 187.1 and 179°C, respectively. The isothermal crystallization kinetics were also studied. The fold surface free energy of the developing crystals of PHBV isothermally crystallized from the melt decreased; however, a depression in the relative degree of crystallization, a reduction of the linear growth rate of the spherulites, and decreases in the equilibrium melting temperature and crystallization capability of PHBV were detected with the addition of PPC. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 92: 2514–2521, 2004     

Thermophysical properties of bacterial poly(3‐hydroxybutyrate): Characterized by TMA,DSC, and TMDSC

The melting, isothermal and nonisothermal crystallization behaviors of poly(3‐hydroxybutyrate) (PHB) have been studied by means of temperature modulated differential scanning calorimetry (TMDSC) and conventional DSC. Various experimental conditions including isothermal/annealing temperatures (80, 90, 100, 105, 110, 120, 130, and 140°C), cooling rates (2, 5, 10, 20, and 50°C/min) and heating rates (5, 10, 20, 30, 40, and 50°C/min) have been investigated. The lower endothermic peak (T_m1) representing the original crystals prior to DSC scan, while the higher one (T_m2) is attributed to the melting of the crystals formed by recrystallization. Thermomechanical analysis (TMA) was used to evaluate the original melting temperature (T_melt) and glass transition temperature (T_g) as comparison to DSC analysis. The multiple melting phenomenon was ascribed to the melting‐recrystallization‐remelting mechanism of the crystallites with lower thermal stability showing at T_m1. Different models (Avrami, Jeziorny‐modified‐Avrami, Liu and Mo, and Ozawa model) were utilized to describe the crystallization kinetics. It was found that Liu and Mo's analysis and Jeziorny‐modified‐Avrami model were successful to explain the nonisothermal crystallization kinetic of PHB. The activation energies were estimated in both isothermal and nonisothermal crystallization process, which were 102 and 116 kJ/mol in respective condition. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 42412.     

Layer double hydroxides for enhanced poly(3‐hydroxybutyrate‐co‐3‐hydroxyvalerate) crystallization

Enabling the widespread utilization of poly[(3‐hydroxybutyrate)‐co‐(3‐hydroxyvalerate)] (PHBV) is strongly associated with enhancing its crystallization kinetics. In this article, we utilize a highly surface active (one reactive group per nanometer square) anion exchanged layered‐double hydroxide (LDH) functionalized by stearic acid to probe the crystallization kinetics of PHBV. Our prior work has shown that the addition of LDH decreases the cold crystallization and induces a melt recrystallization peak in PHBV. Since the melt‐recrystallization temperature shifted to higher temperature and its corresponding enthalpy increased with increasing LDH loading, this article is focused on understanding the effect of LDH on kinetics and energetics of PHBV crystallization. Both Avrami and Lauritzen–Hoffman modeling are utilized to develop a comprehensive understanding of thermal history effects through differential scanning calorimetry and polarized optical microscopy measurements. Five concentrations by weight of LDH are used: 1, 3, 5, and 7%. The results show that the addition of LDH promoted both primary and secondary nucleation at low concentrations but additional LDH resulted in primary nucleation alone. The crystallization rate and activation energy show a significant increase, which is accompanied by a decrease in the nucleation constant, the surface energy and the work of chain folding for PHBV crystallization. © 2012 Wiley Periodicals, Inc. J Appl Polym Sci, 2013     

Crystallization and mechanical behavior of covalent functionalized carbon nanotube/poly(3‐hydroxybutyrate‐co‐3‐hydroxyvalerate) nanocomposites

To improve the dispersity of multi‐walled carbon nanotubes (MWCNTs) in poly(3‐hydroxybutyrate‐co?3‐hydroxyvalerate) (PHBV) matrix, MWCNTs functionalized with carboxyl groups, hydroxyl groups, and atactic poly (3‐hydroxybutyrate) (ataPHB) through acid oxidation, esterification reaction, and “grafting from” method, respectively, were used to fabricate nanofiller/PHBV nanocomposites. The crystallization behavior, dispersion of MWCNTs before and after functionalization in PHBV matrices, and mechanical properties of a series of nanocomposites were investigated. The differential scanning calorimetry, wide‐angle X‐ray diffraction, and polarized optical microscope results suggested that the four types of MWCNTs acted as effective heterogeneous nucleation agents, inducing an increase in the crystallization rate, crystallinity, and crystallite size. Scanning electron microscope observations demonstrated that functionalized MWCNTs showed improved dispersion comparing with MWCNTs, suggesting an enhanced interfacial interaction between PHBV and functionalized MWCNTs. Consequently, the mechanical properties of the functionalized MWCNTs/PHBV nanocomposites have been improved as evident from dynamic mechanical and static tensile tests. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 42136.     

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     

Preparation,thermal properties,and morphology of graft copolymers in reactive blends of PHBV and PPC

Chemical modification of poly(3‐hydroxybutyrate‐co‐3‐hydroxyvalerate) (PHBV) with glycidyl methacrylate (GMA) monomer, followed by reactively blending with end‐capped poly(propylene carbonate) (PPC) (50 wt%) was carried out during melt processing with dicumyl peroxide (DCP) initiation. The two kinds of graft copolymers of PHBV‐g‐GMA and PHBV‐g‐PPC were extracted with Soxhlet's apparatus, respectively. These grafting reaction mechanisms were proposed and the presence of grafting copolymers was confirmed by weight analysis, FTIR and NMR. The methyne carbon of GMA is confirmed to attach to quaternary carbon of the PHBV backbone. The epoxy groups in the copolymer of PHBV‐g‐GMA were capable to react with the carboxyl groups of end‐capped PPC, resulting in the formation of PHBV‐g‐PPC copolymer in situ. Their thermal properties and morphology were also characterized by DSC, WAXD, POM, and AFM. It revealed that after GMA grafting, the degradation of PHBV decreased and the nucleation of PHBV improved. The crystallinity degree, spherulites dimension and phase segregation between the two macromolecules decreased after PHBV grafted with PPC. POLYM. COMPOS., 2012. © 2012 Society of Plastics Engineers