Effect of lignin particles as a nucleating agent on crystallization of poly(3‐hydroxybutyrate)

The effect of lignin fine powder, as a new kind of nucleating agent, on the crystallization process of poly(3‐hydroxybutyrate) (PHB) was studied. The kinetics of both isothermal and nonisothermal crystallization processes from the melt for both pure PHB and PHB/lignin blend was studied by means of differential scanning calorimetry. Lignin shortened the crystallization half‐time t_1/2 for isothermal crystallization. The activation energy ΔE for PHB/lignin and pure PHB in the isothermal crystallization process was ?237.40 and ?131.22 kJ/mol, respectively, clearly indicating that the crystallization of the PHB/lignin blend was more favorable than that of pure PHB from a thermodynamic perspective. At the same time, according to polarized optical microscopy, the rate of spherulitic growth from the melt increased with the addition of lignin, which is ascribed to the reduction of surface fold energy σ_e, that is, σ_e is 59.2 × 10^?3 and 41.6 × 10^?3 J m^?2 for pure PHB and PHB/lignin, respectively. Polarized optical microscopy also showed that the spherulites found in PHB with lignin were smaller in size and greater in number than those found in pure PHB. The wide‐angle X‐ray diffraction indicated that an addition of lignin caused no change in the crystal structure and degree of crystallinity. These results indicated that lignin is a good nucleating agent for the crystallization of PHB. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 94: 2466–2474, 2004     

Thermogravimetric analysis of poly(3‐hydroxybutyrate) and poly(3‐hydroxybutyrate‐co‐3‐hydroxyvalerate)

The thermal degradation of poly(3‐hydroxybutyrate) (PHB) and poly(3‐hydroxybutyrate‐co‐3‐hydroxyvalerate) [P(HB‐HV)] was studied using thermogravimetry (TG). In the thermal degradation of PHB, the temperature at the onset of weight loss (T_o) was derived by T_o = 0.97B + 259, where B represents the heating rate (°C/min). The temperature at which the weight loss rate was maximum (T_p) was T_p = 1.07B + 273, and the final temperature (T_f) at which degradation was completed was T_f = 1.10B + 280. The percentage of the weight loss at temperature T_p (C_p) was 69 ± 1% whereas the percentage of the weight loss at temperature T_f (C_f) was 96 ± 1%. In the thermal degradation of P(HB‐HV) (7:3), T_o = 0.98B + 262, T_p = 1.00B + 278, and T_f = 1.12B + 285. The values of C_p and C_f were 62 ± 7 and 93 ± 1%, respectively. The derivative thermogravimetric (DTG) curves of PHB confirmed only one weight loss step change because the polymer mainly consisted of the HB monomer only. The DTG curves of P(HB‐HV), however, suggested multiple weight loss step changes; this was probably due to the different evaporation rates of the two monomers. The incorporation of 10 and 30 mol % of the HV component into the polyester increased the various thermal temperatures (T_o, T_p, andT_f) by 7–12°C (measured at B = 20°C/min). © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 80: 2237–2244, 2001     

Fast crystallization of poly(3‐hydroxybutyrate) and poly(3‐hydroxybutyrate‐co‐3‐hydroxyvalerate) with talc and boron nitride as nucleating agents

The crystallization behavior of poly(3‐hydroxybutyrate) (PHB) and poly(3‐hydroxybutyrate‐co‐3‐hydroxyvalerate) (PHBV) induced by two kinds of nucleating agents, boron nitride (BN) and talc, was investigated by differential scanning calorimetry, polarized optical microscopy and X‐ray diffraction. Both BN and talc have good nucleating ability in the crystallization of PHB and PHBV. From these results, combined with molecular weight measurement by gel permeation chromatography, the mechanism of nucleation by BN and talc in the crystallization of PHB and PHBV has been proposed. BN acts as a nucleating agent itself and initiates nucleation in the crystallization of PHB and PHBV. Talc acts in a different way. It reacts as a chemical reagent with the molten chains of PHB/PHBV, while the reaction product acts as the true nucleating agent, which lowers the crystallization barriers of PHB and PHBV. ¹H NMR spectroscopy provides evidence for the reaction between PHB and talc and supports the proposed nucleation mechanism. Copyright © 2005 Society of Chemical Industry     

The kinetics of the thermal decomposition of poly(3‐hydroxybutyrate) and maleated poly(3‐hydroxybutyrate)

The thermal decomposition mechanism of maleated poly(3‐hydroxybutyrate) (PHB) was investigated by FTIR and ¹H NMR. The results of experiments showed that the random chain scission of maleated PHB obeyed the six‐membered ring ester decomposition process. The thermal decomposition behavior of PHB and maleated PHB with different graft degree were studied by thermogravimetry (TGA) using various heating‐up rates. The thermal stability of maleated PHB was evidently better than that of PHB. With increase in graft degree, the thermal decomposition temperature of maleated PHB gradually increased and then declined. Activation energy E_a as a kinetic parameter of thermal decomposition was estimated by the Flynn‐Wall‐Ozawa and Kissinger methods, respectively. It could be seen that approximately equal values of activation energy were obtained by both methods. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 84: 1789–1796, 2002; DOI 10.1002/app.10463     

Carbon dioxide sorption and diffusion in poly(3‐hydroxybutyrate) and poly(3‐hydroxybutyrate‐CO‐3‐hydroxyvalerate)

CO₂ sorption and diffusion in poly(3‐hydroxybutyrate) and three poly(3‐hydroxybutyrate‐co‐3‐hydroxyvalerate) copolymers were investigated gravimetrically at temperatures from 25° to 50°C and pressures up to 1 atm. The sorption behavior proved to be linear for all the copolymers studied. An additional set of measurements performed in a pressure decay apparatus at 35°C showed that the linearity could be extrapolated to pressures up to 25 atm. The sorption results obtained from both techniques were in good agreement. The poly(3‐hydroxybutyrate‐co‐3‐hydroxyvalerate) sorption kinetics were increasingly non‐Fickian at the higher temperatures, thus preventing the calculation of diffusion coefficients above 35°C. Interestingly, this was not the case for poly(3‐hydroxybutyrate), and diffusion coefficients and permeabilities could be calculated at all of the investigated temperatures. The 35°C permeabilities were fairly low, which is attributed to the high degree of crystallinity of this polyester family. Finally, the poly(3‐hydroxybutyrate) barrier properties against CO₂ are successfully compared with those of some selected common thermoplastics. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 71: 2391–2399, 1999     

Water transport properties in poly(3‐hydroxybutyrate) and poly(3‐hydroxybutyrate‐co‐3‐hydroxyvalerate) biopolymers

Water sorption and diffusion have been investigated in poly(3‐hydroxybutyrate) (PHB) and three poly(3‐hydroxybutyrate‐co‐3‐hydroxyvalerate) copolymers [P(HB‐HV)] by means of a Cahn electromicrobalance. Permeability of these samples have been determined using a gravimetric permeation cell. Two experimental setups were used for the gravimetric sorption measurements, under dynamic and static conditions, respectively. The differences observed in the results obtained using these techniques are discussed. The sorption measurements have evidenced the tendency of water molecules to form aggregates or clusters in the polymer. In addition, the static sorption method revealed the potential of PHB and P(HB‐HV) to undergo molecular relaxations, eventually leading to a partial desorption of the previously sorbed water after an induction period. The clustering effect was adequately described by the polycondensation model. On the other hand, the interpretation of the diffusivity in terms of mobility coefficients has revealed a competition between a plasticization effect and clustering. As a whole, water transport properties in PHB and its copolymers can be considered to be very close in magnitude to those of common thermoplastics such as PVC and PET. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 73: 455–468, 1999     

Synthesis and characterization of maleated poly(3‐hydroxybutyrate)

Graft copolymerization of maleic anhydride (MA) onto poly(3‐hydroxybutyrate) (PHB) was carried out by use of benzoyl peroxide as initiator. The effects of various polymerization conditions on graft degree were investigated, including solvents, monomer and initiator concentrations, reaction temperature, and time. The monomer and initiator concentrations played an important role in graft copolymerization, and graft degree could be controlled in the range from 0.2 to 0.85% by changing the reaction conditions. The crystallization behavior and the thermal stability of PHB and maleated PHB were studied by DSC, WAXD, optical microscopy, and TGA. The results showed that, after grafting MA, the crystallization behavior of PHB was obviously changed. The cold crystallization temperature from the glass state increased, the crystallization temperature from the melted state decreased, and the growth rate of spherulite decreased. With the increase in graft degree, the banding texture of spherulites became more distinct and orderly. Moreover, the thermal stability of maleated PHB was obviously improved, compared with that of pure PHB. Its thermal decomposition temperature was enhanced by about 20°C. In addition, the introduction of the MA group promoted the biodegradability of PHB. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 88: 659–668, 2003     

Tailoring the surface architecture of poly(3‐hydroxybutyrate‐co‐4‐hydroxybutyrate) scaffolds

This study was designed to determine whether the surface modifications of the various poly(3‐hydroxybutyrate‐co‐4‐hydroxybutyrate) [P(3HB‐co‐4HB)] copolymer scaffolds fabricated would enhance mouse fibroblast cells (L929) attachment and proliferation. The P(3HB‐co‐4HB) copolymer with a wide range of 4HB monomer composition (16–91 mol %) was synthesized by a local isolate Cupriavidus sp. USMAA1020 by employing the modified two‐stage cultivation and by varying the concentrations of 4HB precursors, namely γ‐butyrolactone and 1,4‐butanediol. Five different processing techniques were used in fabricating the P(3HB‐co‐4HB) copolymer scaffolds such as solvent casting, salt‐leaching, enzyme degradation, combining salt‐leaching with enzyme degradation, and electrospinning. The increase in 4HB composition lowered melting temperatures (T_m) but increased elongation to break. P(3HB‐co‐91 mol % 4HB) exhibited a melting point of 46°C and elongation to break of 380%. The atomic force analysis showed an increase in the average surface roughness as the 4HB monomer composition increased. The mouse fibroblasts (L929) cell attachment was found to increase with high 4HB monomer composition in copolymer scaffolds. These results illustrate the importance of a detailed characterization of surface architecture of scaffolds to provoke specific cellular responses. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012     

Blending and characterizations of microbial poly(3‐hydroxybutyrate) with dendrimers

Blending of microbial polyester poly(3‐hydroxybutyrate) (PHB) with various dendritic polyester oligomers or dendrimers was achieved by solution casting to improve the film forming ability of PHB. Films of the blends were characterized by differential scanning calorimetry (DSC), thermogravimetric analysis (TGA), scanning electron micrograph (SEM), and Fourier transform infrared spectroscopy (FTIR). It was revealed that there were mainly two types of interactions in the blending system: the plasticizing or lubricating effect of the low melting spherical dendrimers molecules improved the polymer chain mobility through the suppression of PHB crystallization in the blends; The dendrimers also functioned as crosslinking agents or antiplasticizing agents via weak hydrogen bonding to enhance the overall intermolecular interactions which decrease the chain mobility and thus cause the increase of glass transition temperature (T_g) of PHB. TGA results concluded that incorporating the dendrimers could retard the thermal decomposition of PHB and enhanced its thermal stability accordingly. With the above blend processes, the so‐obtained PHB possessed better film forming ability and even patterned surface structures. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 102:3782–3790, 2006     

Synthesis and characterization of multi‐block copolymers containing poly [(3‐hydroxybutyrate)‐co‐(3‐hydroxyvalerate)] and poly(ethylene glycol)

Various problems, including high crystallinity, high melting temperature, poor thermal stability, hydrophobicity and brittleness, have impeded many practical applications of poly[(3‐hydroxybutyrate)‐co‐(3‐hydroxyvalerate)] (PHBV) as an environmentally friendly material and biomedical material. In the work reported here, multi‐block copolymers containing PHBV and poly(ethylene glycol) (PHBV‐b‐PEG) were synthesized with telechelic hydroxylated PHBV as a hard and hydrophobic segment, PEG as a soft and hydrophilic segment and 1,6‐hexamethylene diisocyanate as a coupling reagent to solve the problems mentioned above. PHBV and PEG blocks in PHBV‐b‐PEG formed separate crystalline phases with lower crystallinity levels and lower melting temperatures than those of phases formed in the precursors. The crystallite dimensions of the two blocks in PHBV‐b‐PEG were smaller than those of the corresponding precursors. Compared to values for the original PHBV, the maximum decomposition temperature of the PHBV block in PHBV‐b‐PEG was 16.0 °C higher and the water contact angle was 9° lower. In addition, the elongation at break was 2.8% for a pure PHBV fiber but 20.9% for a PHBV/PHBV‐b‐PEG fiber with a PHBV‐b‐PEG content of 30%. PHBV‐b‐PEGs can overcome some of the disadvantages of pure PHBV; it is possible that PHBV might be a good candidate for the formulation of environmentally friendly materials and biomedical materials. Copyright © 2010 Society of Chemical Industry     

Dielectric relaxation analysis of biopolymer poly(3‐hydroxybutyrate)

Poly(3‐hydroxybutyrate), PHB, is a widely distributed carbon storage polymer among prokaryotes including Rhizobium. Capacities of Rhizobium etli R13 to produce the bioplastic during growth on media with different carbon sources appeared to be specific carbon‐source. In fed batch fermentation, R. etli R13 resulted in cell dry weight 6.2 g/L and PHB 51.4%. Gas chromatography‐mass spectrometry and gel permeation chromatography analysis revealed that PHB produced from R. etli R13 was solely composed of 3‐hydroxybutyric acid and the molecular mass of the purified PHB was 3.4 × 10⁵ Da with polydispersity 1.47. Dielectric relaxation of PHB has been studied in the temperature and frequency ranges 300–440 K and 10 kHz–4 MHz, respectively. A clear dielectric α and ρ‐relaxation processes are observed in these studied ranges of temperature and frequency. The first process is due to the dipole relaxation in the crystalline phase of PHB. The second one is due to the space‐charge formation or Maxwell‐Wagner‐polarization. The α‐relaxation process has been investigated by semiempirical Havriliak‐Negami relaxation function. The activation energy (E_a) and the relaxation time (τ₀) are calculated using the Arrhenius equation. The dielectric relaxation strength (Δε) is strongly temperature dependent. The calculated values of E_a for ac conductivity, ln(σ), of PHB provide information about the presence of electronic conduction. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

Dielectric relaxation spectroscopy of poly[(R)‐3‐hydroxybutyrate] (PHB) during crystallization

The dielectric response of poly [(R)‐3‐hydroxybutyrate] (PHB) was investigated as a function of time after quenching a film from the melt to a crystallization temperature of 20 °C. In the frequency range investigated (20 to 10⁶ Hz) a relaxation maximum was observed–attributable to the glass transition–which could be analysed by the Havriliak–Negami relation. Changes in the complex dielectric constant were monitored both during spherulite growth (primary crystallization) and subsequently during a period of progressive crystallization (secondary crystallization) at room temperature. The relaxation strength changed only slightly during primary crystallization and its peak position remained at a constant frequency. Subsequently a continuous decrease in relaxation strength occurred, indicating considerable changes in molecular mobility after spherulite growth had been completed. The results provide further evidence that molecular mobility in the amorphous regions decreases significantly with time, and that this would be the reason why PHB shows embrittlement on ageing at room temperature. Copyright © 2004 Society of Chemical Industry     

Influence of the rubbery phase on the crystallinity and thermomechanical properties of poly(3‐hydroxybutyrate)/elastomer blends

Poly(3‐hydroxybutyrate) (PHB) is a very promising biopolymer. In order to improve its processability and decrease its brittleness, PHB/elastomer blends can be prepared. In the work reported, the effect of the addition of a rubbery phase, i.e. ethylene–propylene–diene terpolymer (EPDM) or poly(vinyl butyral) (PVB), on the properties of PHB was studied. The effects of rubber type and of changing the PHB/elastomer blend processing method on the crystallinity and physical properties of the blends were also investigated. For blends based on PHB, the main role of EPDM is its nucleating effect evidenced by a decrease of crystallization temperature and an increase of crystallinity with increasing EPDM content regardless of the processing route. While EPDM has a weak effect on PHB glass transition temperature, PVB induces a marked decrease of this temperature thank to its plasticizer that swells the PHB amorphous phase. A promising solution to improve the mechanical properties of PHB seems to be the melt‐processing of PHB with both plasticizer and EPDM. In fact, the plasticizer is more efficient than the elastomer in decreasing the PHB glass transition temperature and, because of the nucleating effect of EPDM, the decrease of the PHB modulus due to the plasticizer can be counterbalanced. Copyright © 2010 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     

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     

Crystallization kinetics and melting behaviour of microbial poly(3‐hydroxybutyrate‐co‐3‐hydroxyhexanoate)

Isothermal and non‐isothermal crystallization kinetics of microbial poly(3‐hydroxybutyrate‐co‐3‐hydroxyhexanoate) [P(3HB‐3HHx)] was investigated by differential scanning calorimetry (DSC) and ¹³C solid‐state nuclear magnetic resonance (NMR). Avrami analysis was performed to obtain the kinetic parameters of primary crystallization. The results showed that the Avrami equation was suitable for describing the isothermal and non‐isothermal crystallization processes of P(3HB‐3HHx). The equilibrium melting temperature of P(3HB‐3HHx) and its nucleation constant of crystal growth kinetics, which were obtained by using the Hoffman–Weeks equation and the Lauritzen–Hoffmann model, were, respectively, 121.8 °C and 2.87 × 10⁵ K² when using the empirical ‘universal’ values of U* = 1500 cal mol^?1. During the heating process, the melting behaviour of P(3HB‐3HHx) for both isothermal and non‐isothermal crystallization showed multiple melting peaks, which was the result of melting recrystallization. The lower melting peak resulted from the melting of crystals formed during the corresponding crystallization process, while the higher melting peak resulted from the recrystallization that took place during the heating process. Copyright © 2005 Society of Chemical Industry     

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     

The synthesis of poly(3‐hydroxybutyrate)‐g‐poly(methylmethacrylate) brush type graft copolymers by atom transfer radical polymerization method

Brush type of poly (3‐hydroxy butyrate), PHB, copolymer synthesis has been reported. Natural PHB was chlorinated by passing chlorine gas through PHB solution in CHCl₃/CCl₄ mixture (75/25 v/v) to prepare chlorinated PHB, PHB‐Cl, with the chlorine contents varying between 2.18 and 39.8 wt %. Toluene solution of PHB‐Cl was used in the atom transfer radical polymerization (ATRP) of methyl methacrylate, MMA, in the presence of cuprous bromide (CuBr)/2,2′‐bipyridine complex as catalyst, at 90°C. This “grafting from” technique led to obtain poly (3‐hydroxybutyrate)‐g‐poly(methylmethacrylate) (PHB‐g‐PMMA) brush type graft copolymers (cylindrical brush). The polymer brushes were fractionated by fractional precipitation methods and the γ values calculated from the ratio of the volume of nonsolvent to volume of solvent of brushes were ranged between 2.8 and 9.5 depending on the molecular weight, grafting density, and side chain length of the brushes, while the γ values of PHB, PHB‐Cl, and homo‐PMMA were 2.7–3.8, 0.3–2.4, and 3.0–3.9, respectively. The fractionated brushes were characterized by gel permeation chromatography, ¹H‐NMR spectrometry, thermogravimetric analysis (TGA), and differential scanning calorimetry techniques. PHB‐g‐PMMA brush type graft copolymers showed narrower molecular weight distribution (mostly in range between 1.3 and 2.2) than the PHB‐Cl macroinitiator (1.6–3.5). PHB contents in the brushes were calculated from their TGA thermograms and found to be in range between 22 and 42 mol %. The morphologies of PHB‐g‐PMMA brushes were also studied by scanning electron microscopy. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 2007     

Crystallization of poly(1‐butene)/hydrogenated oligocyclopentadiene blends

The crystallization process of poly(1‐butene) and its blends with hydrogenated oligocyclopentadiene was analyzed in dependence on composition. Both isothermal and nonisothermal crystallization processes were studied, and the isothermal crystallization process was investigated starting from both the glass and the melt states. Results revealed that spherulite growth rate, overall crystallization rate, and morphology are strongly dependent on crystallization conditions and blend composition. Nonisothermal crystallization data were analyzed according to the theories of Ozawa and Ziabicki. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 71: 1677–1690, 1999