Influence of microcrystalline cellulose fiber (MCCF) on the morphology of poly(3-hydroxybutyrate) (PHB)

Biopolymer composites were prepared from poly(3-hydroxybutyrate) (PHB)/microcrystalline cellulose fiber (MCCF)/plastiziers/poly(vinyl acetate) by melt extrusion. The morphology, crystal structure, and non-isothermal crystallization of these composites were investigated by polarized optical microscopy (POM), differential scanning calorimetry, Fourier transform infrared spectrometer, and wide-angle X-ray diffraction. The results of DSC indicate that the addition of small amount of MCCF improved the crystallization rate. Non-isothermal crystallization shows that the composites 1 and 2 have lower crystallization half time (t _{0 .5}) than that of pure PHB. Higher MCCF contents in PHB (composite 4) lead to a decrease in the crystallization rate. POM micrographs show that the MCCF were well dispersed in the PHB matrix and served as a nucleating agent with a strong change in PHB morphology. Increasing the isothermal crystallization temperature above 120 °C, leads to the formation of banded spherulites with large regular band spacing. Decreasing the isothermal crystallization temperature below 100 °C produces more and small spherulites.     

Nonisothermal crystallization and melting behavior of poly(3-hydroxybutyrate) and maleated poly(3-hydroxybutyrate)

Nonisothermal crystallization and melting behavior of poly(3-hydroxybutyrate) (PHB) and maleated PHB were investigated by differential scanning calorimetry using various cooling rates. The results show that the crystallization behavior of maleated PHB from the melt greatly depends on cooling rates and its degree of grafting. With the increase in cooling rate, the crystallization process for PHB and maleated PHB begins at lower temperature. For maleated PHB, the introduction of maleic anhydride group hinders its crystallization, causing crystallization and nucleation rates to decrease, and crystallite size distribution becomes wider. The Avrami analysis, modified by Jeziorny, was used to describe the nonisothermal crystallization of PHB and maleated PHB. Double melting peaks for maleated PHB were observed, which was caused by recrystallization during the heating process.     

Isothermal crystallisation kinetics of poly(3-hydroxybutyrate) using step-scan DSC

The crystallisation kinetics, melting behaviour and morphology, of bacterial poly(3-hydoxybutyrate) (PHB) have been investigated by using differential scanning calorimetry (DSC), step-scan DSC (SDSC), wide angle X-ray diffraction (WAXRD) and hot stage polarised optical microscopy (HSPOM). DSC imparted isothermal crystallisation thermal history. The subsequent melting behaviour revealed that all PHB materials experienced secondary crystallisation during heating and the extent of secondary crystallisation varied depending on the crystallisation temperature. PHB samples were found to exhibit double melting behaviour due to melting of SDSC scan-induced secondary crystals, while considerable secondary crystallisation or annealing took place under the modulated heating conditions. The overall melting behaviour was rationalised in terms of recrystallisation and/or annealing of crystals. Interestingly, the PHB materials analysed by SDSC showed a broad exotherm before the melting peak in the non-reversing curve and a multiple melting peak reversing curve, verifying that the melting-recrystallisation and remelting process was operative. HSOM studies supported the conclusions from DSC that the radial growth rate of the PHB spherulites was significantly varied upon the crystallisation conditions. One form of crystals was shown by WAXRD from isothermally crystallised PHB.     

Miscibility and crystallization behavior of poly(3‐hydroxybutyrate‐co‐3‐hydroxyhexanoate) and methoxy poly(ethylene glycol) blends

Poly(3‐hydroxybutyrate‐co‐3‐hydroxyhexanoate) (PHB‐HHx) and methoxy poly(ethylene glycol) (MPEG) blends were prepared using melt blending. The single glass transition temperature, T_g, between the T_gs of the two components and the negative χ value indicated that PHB‐HHx and MPEG formed miscible blends over the range of compositions studied. The Gordon–Taylor equation proved that there was an interaction between PHB‐HHx and MPEG in their blends. FTIR supported the presence of hydrogen bonding between the hydroxyl group of MPEG and the carbonyl group of PHB‐HHx. The spherulitic morphology and isothermal crystallization behavior of the miscible PHB‐HHx/MPEG blends were investigated at two crystallization temperatures (70 and 40 °C). At 70 °C, melting MPEG acted as a noncrystalline diluent that reduced the crystallization rate of the blends, while insoluble MPEG particles acted as a nucleating agent at 40 °C, enhancing the crystallization rate of the blends. However, no interspherulitic phase separation was observed at the two crystallization temperatures. The constant value of the Avrami exponent demonstrated that MPEG did not affect the three‐dimensional spherulitic growth mechanism of PHB‐HHx crystals in the blends, although the MPEG phase, such as the melting state or insoluble state, influenced the crystallization rate of the blends. © 2006 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 44: 2852–2863, 2006     

The melting behaviour of poly(3-hydroxybutyrate) by DSC. Reproducibility study

This work is concerned with the melting behaviour and accuracy of differential scanning calorimeter (DSC) analyses of poly(3-hydroxybutyrate) (PHB), a semi-crystalline thermoplastic polymer completely biodegradable and biocompatible, and obtained from renewable resources. Melting parameters of PHB were determined for the first fusion event applying standard experimental procedures for thermal analysis, using heating rates ranging between 1 °C/min and 20 °C/min. The analyses of DSC energy flow scans showed a complex melting peak that may be resolved into three elementary peaks having different intensities at different melting temperatures. Peak temperatures depend on heating rate, while the total crystallinity detected was independent of the rate. A study of 24 DSC runs showed good temperature reproducibility (±0.5 °C), but poor reproducibility of mass crystallinity (±10%).     

Crystallization behaviors of poly(3-hydroxybutyrate) and poly(l-lactic acid) in their immiscible and miscible blends

By adjusting the molecular weight of the poly(l-lactic acid) (PLLA) component in poly(3-hydroxybutyrate) (PHB)/PLLA blends, we investigated the crystallization behaviors of the two components in their immiscible and miscible 50:50 blends by real time infrared (IR) spectroscopy. In the immiscible PHB/PLLA blend, the stepwise crystallization of PHB and PLLA was realized at different crystallization temperatures. PLLA crystallizes first at a higher temperature (120 degrees C). Its crystallization mechanism from the immiscible PHB/PLLA melt is not affected by the presence of the PHB component, while its crystallization rate is substantially depressed. Subsequently, in the presence of crystallized PLLA, the isothermal melt-crystallization of PHB takes place at a lower temperature (90 degrees C). It is interesting to find that there are two growth stages for PHB. At the early stage of the growth period, the Avrami exponent is 5.0, which is unusually high, while in the late stage, it is 2.5, which is very close to the reported value (n approximately 2.5) for the neat PHB system. In contrast to the stepwise crystallization of PHB and PLLA in the immiscible blends, the almost simultaneous crystallization of PHB and PLLA in the miscible 50:50 blend was observed at the same crystallization temperature (110 degrees C). Detailed dynamic analysis by IR spectroscopy has disclosed that, even in such apparently simultaneous crystallization, the crystallization of PLLA actually occurs faster than that of PHB. It has been found that, both in the immiscible and miscible blends, the crystallization dynamics of PHB are heavily affected by the presence of crystallized PLLA.     

Thermal behavior of the maleic anhydride modified poly(3-hydroxybutyrate)

Poly(3-hydroxybutyrate), PHB has been structurally modified through reaction with maleic anhydride, MA. Transesterification reaction was carried out fixing the PHB and MA and besides time and temperature the concentration of the triethylamine (used as catalyst) was changed. Glass transition, melting and crystallization temperature obtained from DSC curves and thermal degradation temperatures obtained from TG traces were used to evaluate the influence of the reaction conditions on the modification of PHB according to factorial design. On the base of the results the optimum conditions are to perform the PHB modification reaction with MA reaction at 110°C for 1 h with 5% v/v triethylamine.     

Fully-biodegradable poly(3-hydroxybutyrate)/poly(vinyl alcohol) blend films with compositional gradient

Fully-biodegradable bacterial poly(3-hydroxybutyrate) (PHB)/chemosynthetic poly(vinyl alcohol) (PVA) blend films with compositional gradient from one surface to the other surface of the films were prepared by a dissolution-diffusion technique. Three kinds of PVA samples, high- and low-molecular weight atactic PVA and highly syndiotactic PVA (s-PVA), were used in order to investigate the effects of molecular weight and tactic structure on the generation of compositional gradient. The solution of PHB in 1,1,1,3,3,3-hexafluoro-2-propanol (HFIP), which is also a good solvent for PVA, was cast on the PVA film and then the solvent HFIP was evaporated. By selecting the optimum volume of solvent and the evaporation rate, the PHB/PVA blend film with compositional gradient was obtained. The formation of compositional gradient was confirmed by FT-IR microscopy and ATR-FT-IR analysis. The 50%/50% PHB/s-PVA blend film with a nearly ideal compositional gradient, that is, the composition of PHB (or PVA) in the film changing gradually from 100% at one surface to 0% at the other surface of the film was obtained by casting PHB/HFIP solution on to the s-PVA film. Positional dependence of the absorbance of C==O and OH stretching bands along the film thickness direction for the PHB/S-PVA cast films.     

Spontaneous thinning/thickening deformation observed for plastic blend films and some factors affecting film deformation

The fully amorphous films of highly syndiotactic poly[(R,S)‐3‐hydroxybutyrate] (s‐PHB)/atactic poly(4‐vinylphenol) (PVPh) blends show reversible thinning/thickening phenomena at 37 °C in aqueous medium. On the other hand, isotactic poly[(R)‐3‐hydroxybutyrate] (i‐PHB)/PVPh blend film, in which i‐PHB blend component was partially crystalline, did not show any thinning/thickening phenomena under the same conditions. To elucidate the factors influencing these phenomena, the structure and molecular interaction in these blends were characterized by Fourier transform infrared spectroscopy (FTIR), differential scanning calorimetry, and wide‐angle X‐ray diffraction. The FTIR spectra indicated that the ester carbonyl of PHB and the phenolic hydroxyl of PVPh formed hydrogen bonds in both the thinned and thickened s‐PHB/PVPh blend films. The blend composition, intermolecular hydrogen‐bonding interaction, crystallization behavior, miscibility, and the glass‐transition temperature of the blends affected the thinning/thickening phenomena. Some other polyesters such as poly(?‐caprolactone), poly (L‐lactic acid), atactic poly(D,L‐lactic acid), and poly(ethylene terephthalate) had no ability to exhibit thinning/thickening phenomena in water at 37 °C when they were blended with PVPh. This result implies that s‐PHB/PVPh is the rare example with the ability to show reversible thinning/thickening phenomena. © 2002 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 40: 2736–2743, 2002     

Crystallization behavior, thermal property and biodegradation of poly(3-hydroxybutyrate)/poly(ethylene glycol) grafting copolymer

The poly(3-hydroxybutyrate)(PHB)/poly(ethylene glycol)(PEG) grafting copolymer was successfully prepared by PHB and acrylate groups ended PEGM using AIBN as initiator. The crystallization behavior, thermal stability and environmental biodegradability of PHB/PEG grafting copolymers were investigated with differential scanning calorimetry (DSC), Thermogravimetric analysis (TGA), wide angle X-ray diffraction (WAXD), scanning electron microscopy (SEM), and Biodegradation test in vitro. In the results, all the grafting copolymers were found to show the X-ray diffraction arising from the PHB crystal lattice, while none of the PEG crystallized peaks could be found even though the graft percent reached 20%. This result indicated that PEG molecules were randomly grafted onto PHB chain. The thermal properties measured by DSC showed that the melting temperature(T_m) and glass transition temperature (T_g) were both shifted to lower temperature with the graft percent increasing, and this broadened the narrow processability window of PHB. According to TGA results, the thermal stability of the grafting copolymers is not changed compared to pure PHB. From the biodegradation test, it could be concluded that degradation occurred gradually from the surface to the inside and that the degradation rate could be adjusted by the PEG grafting ratio. In another words, the biodegradation profiles of PHB/PEG grafting copolymer can be controlled. These properties make PHB/PEG grafting copolymer have promising potential applications especially in agriculture fields.     

聚3-羟基丁酸酯薄膜结晶的ATR-FTIR研究

使用匀胶机(spincoater),通过溶液铸膜的方法,在铝箔基板上制备出具有不同厚度的聚3羟基丁酸酯(PHB)薄膜.20℃室温条件下,通过衰减全反射傅立叶红外光谱(ATRFTIR)原位观测了不同厚度薄膜的结晶过程,并通过偏光ATRFTIR对薄膜中PHB分子的取向进行了研究.ATRFTIR原位观测结果显示,PHB在薄膜中的结晶速率以及结晶度均随着薄膜厚度的减小而逐渐降低;同时,偏光ATRFTIR测试结果表明,随膜厚减小,薄膜中结晶部分的PHB分子逐渐倾向于沿垂直于基板表面方向取向,膜越薄,倾向越明显.可以认为,PHB分子与基板间的相互作用以及扩散控制结晶导致了上述现象的产生.     

Thermal memory of poly(3‐hydroxybutyrate) using temperature‐modulated differential scanning calorimetry

The influence of thermal history on morphology, melting, and crystallization behavior of bacterial poly(3‐hydroxybutyrate) (PHB) has been investigated using temperature‐modulated DSC (TMDSC), wide‐angle X‐ray diffraction (WAXRD) and polarized optical microscopy (POM). Various thermal histories were imparted by crystallization with continuous and different modulated cooling programs that involved isoscan and cool–heat segments. The subsequent melting behavior revealed that PHB experienced secondary crystallization during heating and the extent of secondary crystallization varied with the cooling treatment. PHB crystallized under slow, continuous, and moderate cooling rates were found to exhibit double melting behavior due to melting of TMDSC scan‐induced secondary crystals. PHB underwent considerable secondary crystallization/annealing that took place under modulated cooling conditions. The overall melting behavior was interpreted in terms of recrystallization and/or annealing of crystals. Interestingly, the PHB analyzed by temperature modulation programs showed a broad exotherm before the melting peak in the nonreversing heat capacity curve and a multiple melting reversing curve, verifying that the melting–recrystallization and remelting process was operative. WAXRD and POM studies supported the correlations from DSC and TMDSC results. © 2005 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 44: 70–78, 2006     

Morphological varieties and kinetic behaviors of poly(3-hydroxybutyrate) (PHB) spherulites crystallized isothermally from thin melt film

The spherulitic morphologies of poly(3-hydroxybutyrate) (PHB) crystallized isothermally from thin melt film with different crystallization temperatures were observed by means of polarized optical microscopy, optical microscopy, SEM, and atomic force microscopy techniques, and the kinetic behaviors were analyzed carefully in this work. It was found that the nonbanded spherulites could be observed at lower and higher crystallization temperatures, and the banded spherulites were formed usually at an intermediate range within experimental crystallization temperatures. The competition of the crystallization rate (v _c) and the diffusion rate (v _d) of melt molecules was employed to explain the transition of the spherulitic morphologies. It was considered that the change of the ratio of v _d and v _c would result in the transition of the spherulitic morphologies. The formation and development of the banded structure were discussed in detail. It was found that the band spacing was proportional to diffusion length of melt molecules and increased with increasing of crystallization temperature. The kinetic behaviors of PHB spherulites formed from the thin melt film with different crystallization temperatures were also discussed in this work.     

Miscibility in crystalline/amorphous blends of poly(3-hydroxybutyrate)/DGEBA

A differential scanning calorimetry (DSC) and small-angle X-ray scattering (SAXS) study of miscibility in blends of the semicrystalline polyester poly(3-hydroxybutyrate) (PHB) and amorphous monomer epoxy DGEBA (diglycidyl ether of bisphenol A) was performed. Evidence of the miscibility of PHB/DGEBA in the molten state was found from a DSC study of the dependence of glass transition temperature (T_g) as a function of the blend composition and isothermal crystallization, analyzing the melting point (T_m) as a function of blend composition. A negative value of Flory–Huggins interaction parameter χ_PD was obtained. Furthermore, the lamellar crystallinity in the blend was studied by SAXS as a function of the PHB content. Evidence of the segregation of the amorphous material out of the lamellar structure was obtained. © 2013 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys, 2013     

Melting temperature evolution of non-reorganized crystals. Poly(3-hydroxybutyrate)

In the present study the correlation between the melting behaviour of poly(3-hydroxybutyrate) (PHB) original, non-reorganized crystals and the crystallinity increase during isothermal crystallization is presented and discussed. Since the reorganization processes modify the melting curve of original crystals, it is necessary to prevent and hinder all the processes that influence and increase the lamellar thickness. PHB exhibits melting/recrystallization on heating, the occurring of lamellar thickening in the solid state being excluded. The first step of the study was the identification of the scanning rate which inhibits PHB recrystallization at sufficiently high T_c. For the extrapolated onset and peak temperatures of the main melting endotherm, which is connected to fusion of dominant lamellae, a double dependence on the crystallization time was found. The crystallization time at which T_onset and T_peak change their trends was found to correspond to the spherulite impingement time, so that the two different dependencies were put in relation with primary and secondary crystallizations respectively. The increase of both T_onset and T_peak at high crystallization times after spherulite impingement was considered an effect due to crystal superheating and an indication of a stabilization process of the crystalline phase. Such stabilization, which produces an increase of the melting temperature, is probably connected with the volume filling that occurs after spherulite impingement.     

Effect of poly(vinyl acetate) (PVAc) on thermal behavior and mechanical properties of poly(3-hydroxybutyrate)/poly(propylene carbonate) (PHB/PPC) blends

To assess the compatibility of blends of synthetic poly(propylene carbonate) (PPC), with a natural bacterial poly(3-hydroxybutyrate) (PHB), a simple casting procedure of blend was used. poly(3-hydroxybutyrate)/poly(propylene carbonate) blends are found to be incompatible according to DSC and DMA analysis. In order to improve the compatibility and mechanical properties of PHB/PPC blends, poly(vinyl acetate) (PVAc) was added as a compatibilizer. The effects of PVAc on the thermal behavior, morphology, and mechanical properties of 70PHB/30PPC blend were investigated. The results show that the melting point and the crystallization temperature of PHB in blends decrease with the increase of PVAc content in blends, the loss factor changes from two separate peaks of 70PHB/30PPC blend to one peak of 70PHB/30PPC/12PVAc blend. It is also found that adding PVAc into 70PHB/30PPC blend can decrease the size of dispersed phase from morphology analysis. The result of tensile properties shows that PVAc can increase the tensile strength and Young’s modulus of 70PHB/30PPC blend, and both the elongation at break and the tensile toughness increase significantly with PVAc added into 70PHB/30PPC.     

Effect of aging on fractional crystallization of poly(ethylene oxide) component in poly(ethylene oxide)/poly(3‐hydroxybutyrate) blends

The effect of aging on the fractional crystallization of the poly(ethylene oxide) (PEO) component in the PEO/poly(3‐hydroxybutyrate) (PHB) blend has been investigated. The partial miscibility of the PEO/PHB blends with high PEO molecular weight (M_v = 2.0 × 10⁵ g/mol) was confirmed by differential scanning calorimetry (DSC) and dynamic mechanical thermal analysis. The fractional crystallization behavior of the PEO component in the PEO/PHB blends with low PEO content (not more than 30 wt% of PEO), before and after aging under vacuum at 25 °C for 6 months, were compared by DSC, fourier transform infrared microscopic spectroscopy, small angle X‐ray diffraction, and scanning electron microscopy. It was confirmed that nearly all the PEO components remain trapped within interlamellar regions of PHB for the PEO/PHB blends before aging. Under this condition, the crystallization of PEO is basically induced by much less active heterogeneities or homogeneous nucleation at high supercoolings. While, after the same PEO/PHB samples were stored at 25 °C in vacuum for 6 months, a part of the PEO component was expelled from the interlamellar region of PHB. Under this condition, the expelled PEO forms many separate domains with bigger size and crystallizes at low supercoolings by active heterogeneous nucleation, whereas the crystallization of PEO in the interlamellar region is still mainly induced by less active heterogeneities or homogeneous nucleation at extreme supercoolings. © 2005 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 43: 2665–2676, 2005     

Melting and crystallization of poly(vinylidene fluride) under high pressure

Precise melting and crystallization temperatures of extended-chain and folded-chain crystals of form I and folded-chain crystals of form II poly(vinylidene fluoride) under high pressure have been obtained by microdifferential thermal analysis (DTA). Upon heating at pressures above 4000 kg/cm², the micro-DTA thermogram of form II crystallized from the melt at atmospheric pressure shows melting of the form II structure and the melting of the folded-chain and extended-chain crystals of form I, formed through recrystallization processes. These features were clarified by supplemental methods. The bandwidth seen in electron micrographs of the extended-chain crystal of form I obtained by crystallization under high pressure was in the range of 1500 to 2000 Å. At atmospheric pressure, the extended-chain crystal of form I melted at 207°C, approximately 17°C higher than the folded-chain crystal of form I and 31°C higher than the folded-chain crystal of form II.     

Calorimetric analysis of the multiple melting behavior of melt-crystallized poly(l-lactic acid) with a low optical purity

The polymorphous crystallization and multiple melting behavior of poly(l-lactic acid) (PLLA) with an optical purity of 92 % were investigated after isothermally crystallized from the melt state by wide-angle X-ray diffraction and differential scanning calorimetry. Owing to the low optical purity, it was found that the disordered (α′) and ordered (α) crystalline phases of PLLA were formed in the samples crystallized at lower (<95 °C) and higher (≥95 °C) temperatures, respectively. The melting behavior of PLLA is different in three regions of crystallization temperature (T _c) divided into Region I (T _c < 95 °C), Region II (95 °C ≤ T _c < 120 °C), and Region III (T _c ≥ 120 °C). In Region I, an exothermic peak was observed between the low-temperature and high-temperature endothermic peaks, which results from the solid–solid phase transition of α′-form crystal to α one. In Region II, the double-melting peaks can be mainly ascribed to the melting–recrystallization–remelting of less stable α crystals. In Region III, the single endotherm shows that the α crystals formed at higher temperatures are stable enough and melt directly without the recrystallization process during heating.     

Calorimetric study of blends of poly(butylene terephthalate) and liquid crystalline copolyester

A calorimetric study of blends of poly(ethylene terephthalate-co-p-oxybenzoate), PET/PHB, with poly(butylene terephthalate), PBT has been carried out in the form of as-spun and drawn fibres. DSC melting and crystallization results show that PBT is compatible with LCP and the crystallization of PBT decreases by the addition of LCP in the matrix. The crystallization behaviour of blend fibres is investigated as a function of temperature of crystallization. A detailed analysis of the crystallization course has been made utilizing the Avrami expression. The isothermal calorimetric measurements provide evidence of decrease of rate of crystallization of PBT on addition of the liquid crystalline component up to about 50% by weight. The values of the Avrami exponents change in the temperature range from 200° to 215°C. Dimensionality changes in crystallization could be due to LCP mesophase-transition.