Miscibility and crystallization behaviors of poly(3‐hydroxybutyrate‐co‐11%‐4‐hydroxybutyrate)/Poly(3‐hydroxybutyrate‐co‐33%‐4‐hydroxybutyrate) blends

Biopolyesters poly(3‐hydroxybutyrate‐co‐4‐hydroxybutyrate) with an 11 mol % 4HB content [P(3HB‐co‐11%‐4HB)] and a 33 mol % 4HB content [P(3HB‐co‐33%‐4HB)] were blended by a solvent‐casting method. The thermal properties were investigated with differential scanning calorimetry. The single glass‐transition temperature of the blends revealed that the two components were miscible when the content of P(3HB‐co‐33%‐4HB) was less than 30% or more than 70 wt %. The blends, however, were immiscible when the P(3HB‐co‐33%‐4HB) content was between 30 and 70%. The miscibility of the blends was also confirmed by scanning electron microscopy morphology observation. In the crystallite structure study, X‐ray diffraction patterns demonstrated that the crystallites of the blends were mainly from poly(3‐hydroxybutyrate) units. With the addition of P(3HB‐co‐33%‐4HB), larger crystallites with lower crystallization degrees were induced. Isothermal crystallization was used to analyze the melting crystallization kinetics. The Avrami exponent was kept around 2; this indicated that the crystallization mode was not affected by the blending. The equilibrium melting temperature decreased from 144 to 140°C for the 80/20 and 70/30 blends P(3HB‐co‐11%‐4HB)/P(3HB‐co‐33%‐4HB). This hinted that the crystallization tendency decreased with a higher P(3HB‐co‐33%‐4HB) content. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

Study of miscibility,crystallization, mechanical properties,and thermal stability of blends of poly(3‐hydroxybutyrate) and poly(3‐hydroxybutyrate‐co‐4‐hydroxybutyrate)

Natural amorphous polymer poly(3‐hydroxybutyrate‐co‐4‐hydroxybutyrate) (P3HB4HB) containing 41 mol % of 4HB was blended with poly(3‐hydroxybutyrate) (PHB) with an aim to improve the properties of PHB. The influence of P3HB4HB contents on thermal and mechanical properties of the blends was evaluated with differential scanning calorimetry (DSC), Fourier transform infrared (FTIR) spectroscopy, stress–strain measurement and thermo gravimetric analyzer. Miscibility of PHB/P3HB4HB blends was mainly decided by the contents of P3HB4HB. When P3HB4HB exceeded 50 wt %, the two polymer phases separated and showed immiscibility. The addition of P3HB4HB did not alter the crystallinity of PHB, yet it diluted the PHB crystalline phase as revealed by DSC studies. DSC and FTIR results showed that the overall crystallinity of the blends decreased remarkably with increasing of P3HB4HB contents. Decreased glass transition temperature and crystallinity imparted desired flexibility for the blends. The ductility of the blends increased progressively with increasing of P3HB4HB content. Thus, the PHB mechanical properties can be modulated by changing the blend composition. P3HB4HB did not significantly improve the thermal stability of PHB, yet it is possible to melt process PHB without much molecular weights loss via blending it with suitable amounts of P3HB4HB. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 2007     

Morphology and properties of biodegradable and biosourced polylactide blends with poly(3‐hydroxybutyrate‐co‐4‐hydroxybutyrate)

Biodegradable polymer blends based on biosourced polymers, namely polylactide (PLA) and poly(3‐hydroxybutyrate‐co‐4‐hydroxybutyrate) (P(3HB‐co‐4HB)), were prepared by melt compounding. The effects of P(3HB‐co‐4HB) on the miscibility, phase morphology, thermal behavior, mechanical properties, and biodegradability of PLA/P(3HB‐co‐4HB) blends were investigated. The blend was an immiscible system with the P(3HB‐co‐4HB) domains evenly dispersed in the PLA matrix. However, the T_g of P(3HB‐co‐4HB) component in the blends decreased compared with neat P(3HB‐co‐4HB), which might be attributed to that the presence of the phase interface between PLA and P(3HB‐co‐4HB) resulted in enhanced chain mobility near interface. The addition of P(3HB‐co‐4HB) enhanced the cold crystallization of PLA in the blends due to the nucleation enhancement of PLA caused by the enhanced chain mobility near the phase interface between PLA and P(3HB‐co‐4HB) in the immiscible blends. With the increase in P(3HB‐co‐4HB) content, the blends showed decreased tensile strength and modulus; however, the elongation at beak was increased significantly, indicating that the inherent brittlement of PLA was improved by adding P(3HB‐co‐4HB). The interesting aspect was that the biodegradability of PLA is significantly enhanced after blends preparation. POLYM. COMPOS., 2012. © 2012 Society of Plastics Engineers     

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.     

Study on short glass fiber‐reinforced poly(3‐hydroxybutyrate‐co‐4‐hydroxybutyrate) composites

Biobased non‐fossil polyester poly(3‐hydroxybutyrate‐co‐4‐hydroxybutyrate) (P3/4HB) containing 4.0 mol % 4‐hydroxybutyrate (4HB) was melt‐mixed with short glass fibers (SGF) via a co‐rotating twin‐screw extruder. The compositing conditions, average glass fiber length and distribution, thermal, crystallization, and mechanical properties of the P3/4HB/SGF composites were investigated. Calcium stearate, two kinds of paraffin wax and modified ethylene bis‐stearamide (TAF) were investigated as lubricants for the P3/4HB/SGF composites. It revealed that TAF is the most efficient lubricant of the P3/4HB/SGF composites. Coupling agents 2,2′‐(1,3‐phenylene)bis‐2‐oxazoline (1,3‐PBO) and pyromellitic dianhydride (PMDA) were used as end‐group crosslinkers to reduce the degradation of P3/4HB and increase the mechanical properties of the P3/4HB/SGF composites. It showed that 1,3‐PBO is the efficient coupling agent. The optimum condition of the P3/4HB/SGF composites is 1.5 phr TAF, 1.0 phr 1,3‐PBO, and 30 wt % glass fiber content. And the maximum of tensile strength, tensile modulus, and impact strength of the composites is 3.7, 6.6, 1.8 times of the neat P3/4HB polymer, respectively. © 2012 Wiley Periodicals, Inc. J Appl Polym Sci, 2012     

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     

Mechanical properties,thermal stability,and crystallization kinetics of poly(3‐hydroxybutyrate‐co‐4‐hydroxybutyrate)/calcium carbonate composites

Bacterial polyester poly(3‐hydroxybutyrate‐co‐4‐hydroxybutyrate) (P3/4HB) containing 5 mol% 4HB was composited with different calcium carbonate (CaCO₃) fillers. The effect of CaCO₃ contents on thermal properties, mechanical property, and crystallization kinetics was evaluated. The thermal stability of P3/4HB was reduced by mixing with CaCO₃ particles. With increasing CaCO₃ content, the elongation at break, tensile strength, and impact strength decrease; however, elastic modulus increases. When P3/4HB with 20 mol% 4HB was added into the P3/4HB/CaCO₃ composite, the impact strength were enhanced significantly; however, the elongation at break and tensile strength were only slight to moderate improvements. However, when compared with nano‐ and light‐CaCO₃, heavy CaCO₃ had the best mechanical properties. The nonisothermal and isothermal crystallization results demonstrated that the crystallization rate of P3/4HB was reduced and the highest crystallinity was obtained for all kinds of CaCO₃ fillers at 40 phr content. POLYM. COMPOS., 2011. © 2011 Society of Plastics Engineers     

Miscibility and intermolecular hydrogen‐bonding interactions in poly(3‐hydroxybutyrate‐co‐3‐hydroxyhexanoate)/poly(4‐vinyl phenol) binary blends

The miscibility and hydrogen bonding interaction in the poly(3‐hydroxybutyrate‐co‐3‐hydroxyhexanoate)/poly(4‐vinyl phenol) [P(3HB‐co‐3HH)/PVPh] binary blends were investigated by differential scanning calorimetry (DSC) and Fourier transform infrared spectroscopy (FTIR). The DSC results indicate that P(3HB‐co‐3HH) with 20 mol % 3HH unit content is fully miscible with PVPh, and FTIR studies reveal the existence of hydrogen bonding interaction between the carbonyl groups of P(3HB‐co‐3HH) and the hydroxyl groups of PVPh. The effect of blending of PVPh on the mechanical properties of P(3HB‐co‐3HH) were studied by tensile testing. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 2007     

Preparation and characterization of biodegradable poly(3‐hydroxybutyrate‐co‐4‐hydroxybutyrate)/silica nanocomposites

Biodegradable poly(3‐hydroxybutyrate‐co‐4‐hydroxybutyrate) [P(3HB‐co‐4HB)]/silica nanocomposites were prepared by melt compounding. The effects of silica on the morphology, crystallization, thermal stability, mechanical properties, and biodegradability of P(3HB‐co‐4HB) were investigated. The nanoparticles showed a fine and homogeneous dispersion in the P(3HB‐co‐4HB) matrix for silica contents below 5 wt%, whereas some aggregates were detected with further increasing silica content. The addition of silica enhanced the crystallization of P(3HB‐co‐4HB) in the nanocomposites due to the heterogeneous nucleation effect of silica. However, the crystal structure of P(3HB‐co‐4HB) was not modified in the presence of silica. The thermal stability of P(3HB‐co‐4HB) was enhanced by the incorporation of silica. Silica was an effective reinforcing agent for P(3HB‐co‐4HB), and the modulus and tensile strength of the nanocomposites increased, whereas the elongation at break decreased with increasing silica loading. The exciting aspect of this work was that the rate of enzymatic degradation of P(3HB‐co‐4HB) was enhanced significantly after nanocomposites preparation. POLYM. ENG. SCI., 2012. © 2011 Society of Plastics Engineers     

Effect of nucleation agents on the crystallization of poly(3‐hydroxybutyrate‐co‐4‐hydroxybutyrate) (P3/4HB)

Boron nitride (BN), talc, hydroxyapatite (HA), and zinc stearate (ZnSt) were investigated as nucleation agents (NA) for nonfossil‐based poly(3‐hydroxybutyrate‐co‐4‐hydroxybutyrate) (P3/4HB) plastics. Nonisothermal crystallization behaviors of the P3/4HB/NA blends were examined by DSC. It revealed that BN is the most efficient nucleation agent to promote the crystallization rate, however, but not the crystallization degree. The lasting crystallization of P3/4HB was also removed. The nucleation effect was strengthened with increase of BN content up to 1% and then slackened deeply when further BN was added. Isothermal crystallization analysis revealed that the addition of nucleation agent BN does not alter the crystal growth mode of P3/4HB, with maintaining the Avrami parameter n value around 2.40. Talc did enhance the crystallization of P3/4HB with however milder crystal growth rate. HA and ZnSt did not promote, but depressed the crystallization of P3/4HB plastics. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

Mechanical and thermal properties of poly(vinyl chloride)/α‐methyl‐styrene‐acrylonitrile blends prepared by melt extrusion

In this article, we have examined the physical and mechanical properties of poly(vinyl chloride) (PVC)/α‐methyl‐styrene‐acrylonitrile (αMSAN; 31 wt % AN concentrations) blends with different blend ratios. And, we also examined the effect of the molecular weights of PVC on the miscibility and material properties of the blends prepared by melt extrusion blending. Our results showed that the PVC/αMSAN blends have good processing properties and good miscibility over all blend ratios because of the strong interaction between PVC and αMSAN. And, the blends showed enhanced mechanical and thermal properties. In addition, high molecular weight PVC showed reasonable processability when melt blended with αMSAN, which resulted in enhanced mechanical and physical properties. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Blends of bacterial poly[(R)‐3‐hydroxybutyrate] with oligo[(R,S)‐3‐hydroxybutyrate]‐diol

The miscibility, melting and crystallization behaviour of poly[(R)‐3‐hydroxybutyrate], PHB, and oligo[(R,S)‐3‐hydroxybutyrate]‐diol, oligo‐HB, blends have been investigated by differential scanning calorimetry: thermograms of blends containing up to 60 wt% oligo‐HB showed behaviour characteristic of single‐phase amorphous glasses with a composition dependent glass transition, T_g, and a depression in the equilibrium melting temperature of PHB. The negative value of the interaction parameter, determined from the equilibrium melting depression, confirms miscibility between blend components. In parallel studies, glass transition relaxations of different melt‐crystallized polymer blends containing 0–20 wt% oligo‐HB were dielectrically investigated between ?70 °C and 120 °C in the 100 Hz to 50 kHz range. The results revealed the existence of a single α‐relaxation process for blends, indicating the miscibility between amorphous fractions of PHB and oligo‐HB. © 2002 Society of Chemical Industry     

Miscibility and crystallization kinetics of poly(3‐hydroxybutyrate‐co‐3‐hydroxyvalerate)/ poly(methyl methacrylate) blends

The miscibility and crystallization kinetics of the blends of random poly(3‐hydroxybutyrate‐co‐3‐hydroxyvalerate) [P(HB‐co‐HV)] copolymer and poly(methyl methacrylate) (PMMA) were investigated by differential scanning calorimetry (DSC) and polarized optical microscopy (POM). It was found that P(HB‐co‐HV)/PMMA blends were miscible in the melt. Thus the single glass‐transition temperature (T_g) of the blends within the whole composition range suggests that P(HB‐co‐HV) and PMMA were totally miscible for the miscible blends. The equilibrium melting point (T°_m) of P(HB‐co‐HV) in the P(HB‐co‐HV)/PMMA blends decreased with increasing PMMA. The T°_m depression supports the miscibility of the blends. With respect to the results of crystallization kinetics, it was found that both the spherulitic growth rate and the overall crystallization rate decreased with the addition of PMMA. The kinetics retardation was attributed to the decrease in P(HB‐co‐HV) molecular mobility and dilution of P(HB‐co‐HV) concentration resulting from the addition of PMMA, which has a higher T_g. According to secondary nucleation theory, the kinetics of spherulitic crystallization of P(HB‐co‐HV) in the blends was analyzed in the studied temperature range. The crystallizations of P(HB‐co‐HV) in P(HB‐co‐HV)/PMMA blends were assigned to n = 4, regime III growth process. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 91: 3595–3603, 2004     

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.     

Biodegradable blends of high molecular weight poly(ethylene oxide) with poly(3‐hydroxypropionic acid) and poly(3‐hydroxybutyric acid): a miscibility study by DSC,DMTA and NMR spectroscopy

The miscibility of high molecular weight poly(ethylene oxide) blends with poly(3‐hydroxypropionic acid) and poly(3‐hydroxybutyric acid) (P(3HB)) has been investigated by differential scanning calorimetry (DSC), dynamic mechanical thermal analysis (DMTA) and high‐resolution solid state ¹³C nuclear magnetic resonance (NMR). The DSC thermal behaviour of the blends revealed that the binary blends of poly(ethylene oxide)/poly(3‐hydroxypropionic acid) (OP blends) were miscible over the whole composition range while the miscibility of poly(ethylene oxide)/poly(3‐hydroxybutyric acid) blends (OB blends) was dependent on the blend composition. OB blends were found to be partly miscible at the middle P(3HB) contents (25 %, 50 %) and miscible at other P(3HB) contents (10 %, 75 % and 90 %). Single‐phase behaviour for OP blends and phase separation behaviour for OB blends were observed from DMTA. The results from NMR spectroscopy revealed that the two components in the OP50 blend were intimately mixed on a scale of about 35 nm, while the domain sizes in the OB blend with a P(3HB) content of 50 % were larger than about 32 nm. © 2000 Society of Chemical Industry     

Processability modifications of poly(3‐hydroxybutyrate) by plasticizing,blending, and stabilizing

Poly(3‐hydroxybutyrate) (PHB) was plasticized with dioctyl (o‐)phthalate, dioctyl sebacate, and acetyl tributyl citrate (ATBC). The thermal properties, mechanical properties, and melt flow ability were studied with differential scanning calorimetry, thermogravimetric analysis, a universal material testing machine, and a melt flow indexer. ATBC was revealed to be an efficient plasticizer, reducing the glass‐transition temperature and increasing the thermoplasticization ability of PHB. We also blended poly(3‐hydroxybutyrate‐co‐hydroxyhexanoate) (PHBHHx) and poly(3‐hydroxybutyrate‐co‐4‐hydroxybutyrate) [P(3/4HB)] with PHB, ATBC, and antioxidant 1010 to overcome the brittleness of PHB and improve the melt flow stability of the materials. PHBHHx did little to improve the thermal processing but increased the fluidity of PHB, and P(3/4HB) toned the toughness of PHB. The addition of antioxidant 1010 enhanced the thermal stabilization of PHB. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

Hydrogen bonding,miscibility, crystallization,and thermal stability in blends of biodegradable polyhydroxyalkanoates and polar small molecules of 4‐tert‐butylphenol

The hydrogen bonding, miscibility, crystallization, and thermal stability of poly(3‐hydroxybutyrate) (PHB)/4‐tert‐butylphenol (BOH) blends and poly(3‐hydroxybutyrate‐co‐3‐hydroxyhexanoate) [P(3HB‐3HHx)]/BOH blends were investigated by Fourier transform infrared (FTIR) spectroscopy, solid‐state¹³C‐NMR, differential scanning calorimetry, wide‐angle X‐ray diffraction (WAXD), and thermogravimetric analysis. The results of FTIR spectroscopy and solid‐state¹³C‐NMR show that intermolecular hydrogen bonds existed between the two components in the blends and that the interaction was caused by the carbonyl groups in the amorphous phase of both polyesters and the hydroxyl groups of BOH. With increasing BOH content, the chain mobility of both the PHB and P(3HB‐3HHx) components was improved. After the samples were quenched, the detected single glass‐transition temperatures decreased with composition, indicating that both PHB/BOH and P(3HB‐3HHx)/BOH were miscible blends in the melt. Moreover, as BOH content increased, the melting temperatures of PHB and P(3HB‐3HHx) clearly decreased, which implied that their crystallization was suppressed by the addition of BOH. Although the crystallinity of PHB and P(3HB‐3HHx) components decreased with increasing BOH content in the blends, their crystal structures were hardly affected after they were blended with BOH, which was further proven by WAXD results. In addition, the thermal stability of PHB was improved by a smaller amount of BOH.     

Miscibility and crystallization behavior of poly(3‐hydroxybutyrate‐co‐3‐hydroxyvalerate)/poly(vinyl acetate) blends

The miscibility and crystallization behavior of poly(3‐hydroxybutyrate‐co‐3‐hydroxyvalerate) (P(HB‐co‐HV))/poly(vinyl acetate) (PVAc) blends have been investigated by differential scanning calorimetry (DSC) and polarized optical microscopy (POM). It was found that P(HB‐co‐HV)/PVAc blends were miscible in the melt over the whole compositions. Thus the blend exhibited a single glass transition temperature (T_g), which increased with increasing PVAc composition. The spherulitic morphologies of P(HB‐co‐HV)/PVAc blends indicated that the PVAc was predominantly segregated into P(HB‐co‐HV) interlamellar or interfibrillar regions during P(HB‐co‐HV) crystallization because of the volume‐filled spherulites. As to the crystallization kinetics study, it was found that the overall crystallization and crystal growth rates decreased with the addition of PVAc. The kinetics retardation was primarily attributed to the reduction of chain mobility and dilution of P(HB‐co‐HV) upon mixing with higher T_g PVAc. The overall crystallization rate was predominantly governed by the spherulitic growth rate and promoted by the samples treated with the quenched state because of the higher nucleation density. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 100: 980–988, 2006     

Thermal,mechanical, and morphological characterization studies of poly(2,6‐dimethyl‐1,4‐phenylene oxide) blends with polystyrene and brominated polystyrene

The miscibility of the binary and ternary blends of poly(2,6‐dimethyl‐1,4‐phenylene oxide), brominated polystyrene, and polystyrene was investigated using a differential scanning calorimeter. The morphology of these blends was characterized by scanning electron microscopy. These studies revealed a close relation between the blend structure and its mechanical properties. The compatibilizing effect of poly(2,6‐dimethyl‐1,4‐phenylene oxide) on the miscibility of the polystyrene/brominated polystyrene blends was examined. It was found that poly(2,6‐dimethyl‐1,4‐phenylene oxide), which was miscible with polystyrene and partially miscible with brominated polystyrene, compatibilizes these two immiscible polymers if its contention exceeds 33 wt %. Upon the addition of poly(2,6‐dimethyl‐1,4‐phenylene oxide) to the immiscible blends of polystyrene/brominated polystyrene, we observed a change in the morphology of the mixtures. An improvement in the mechanical properties was noticed. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 75: 225–231, 2000     

Studies on comonomer compositional distribution and its effect on some physical properties of bacterial poly(3‐hydroxybutyric acid‐co‐3‐hydroxypropionic acid)

Comonomer compositional distribution of bacterially synthesized poly(3‐hydroxybutyric acid‐co‐3‐hydroxypropionic acid) [P(3HB‐co‐3HP)] was investigated via solvent/non‐solvent fractionation techniques. The result indicates the presence of extremely broad comonomer compositional distribution in the original bacterial product. Furthermore, utilizing compositionally fractionated bacterial copolyesters with much narrower comonomer compositional distributions, the 3HP comonomer content‐dependence of their thermal and crystallization behavior was studied by means of differential scanning calorimeter (DSC) and polarized optical microscopy and the results compared with those of unfractionated copolyesters. It was revealed that the physical features of the fractionated copolyester P(3HB‐co‐3HP)s strongly depends on the 3HP comonomer content. In addition, to clarify the effect of the compositional distribution on the properties of the unfractionated copolyester, the miscibility between bacterial poly(3‐hydroxybutyric acid) [P(3HB)] and two fractionated P(3HB‐co‐3HP) samples with 11.3 and 14.9% 3HP was investigated for blends obtained by solvent casting techniques. The evidence of thermal analysis and spherulitic growth rates imply miscibility of the P(3HB)/3HB‐rich P(3HB‐co‐3HP) binary blends. © 1999 Society of Chemical Industry