Dielectric investigation of cold crystallization of poly(3-hydroxybutyrate)

Crystallization of microbial polyhydroxyalkanoates: A review

Polyhydroxyalkanoates (PHAs), produced by the microbial fermentation, is a promising green polymer and has attracted much attention due to its excellent biocompatibility, complete biodegradability, and non-cytotoxicity. The physical properties of PHAs are closely related to their chemical and crystalline structure. Therefore, deep understanding and regulating the structure and crystallization of PHAs are the key factors to improve the performance of PHAs. This review first provides a brief overview of the development history, chemical structure, and basic properties of PHAs. Then, the crystal structure, crystal morphology, kinetics theories and crystallization behavior of nucleation-induced PHAs are systematically summarized to provide a theoretical foundation for improving PHAs crystallization rate and physical properties. In the end, the outlook on the crystallization and application prospects of PHAs is also addressed.

Effect of WS₂ Inorganic Nanotubes on Isothermal Crystallization Behavior and Kinetics of Poly(3-Hydroxybutyrate-co-3-hydroxyvalerate)

Nanocomposites of poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBV) and tungsten disulfide inorganic nanotubes (INT-WS₂) were prepared by blending in solution, and the effects of INT-WS₂ on the isothermal crystallization behavior and kinetics of PHBV were investigated for the first time. The isothermal crystallization process was studied in detail using various techniques, with emphasis on the role of INT-WS₂ concentration. Differential scanning calorimetry (DSC) and polarized optical microscopy (POM) showed that, in the nucleation-controlled regime, crystallization rates of PHBV in the nanocomposites are influenced by the INT-WS₂ loading. Our results demonstrated that low loadings of INT-WS₂ (0.1⁻1.0 wt %) increased the crystallization rates of PHBV, reducing the fold surface free energy by up to 24%. This is ascribed to the high nucleation efficiency of INT-WS₂ on the crystallization of PHBV. These observations facilitate a deeper understanding of the structure-property relationships in PHBV biopolymer nanocomposites and are useful for their practical applications.

Physico-chemical properties of polyhydroxyalkanoate produced by mixed-culture nitrogen-fixing bacteria

Ultra-high molecular weight polyhydroxyalkanoates (PHAs) with low polydispersity index (PDI = 1.3) were produced in a novel, pilot scale application of mixed cultures of nitrogen-fixing bacteria. The number average molecular weight (M (n)) of the poly(3-hydroxybutyrate) (P(3HB)) and poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (P(3HB-co-3HV)) was determined to be 2.4 x 10(6) and 2.5 x 10(6) g mol(-1), respectively. Using two types of carbon sources, biomass contents of the P(3HB) and P(3HB-co-3HV) were 18% and 30% (PHA in dry biomass), respectively. The extracted polymers were analysed for their physical properties using analytical techniques such as nuclear magnetic resonance (NMR) spectroscopy, differential scanning calorimetry (DSC) and gel permeation chromatography (GPC). NMR confirmed the formation of homopolymer and copolymer. DSC showed a single melting endotherm peak for both polymers, with enthalpies that indicated crystallinity indices of 44% and 37% for P(3HB) and P(3HB-co-3HV), respectively. GPC showed a sharp unimodal trace for both polymers, reflecting the homogeneity of the polymer chains. The work described here emphasises the potential of mixed colony nitrogen-fixing bacteria cultures for producing biodegradable polymers which have properties that are very similar to those from their pure-culture counterparts and therefore making a more economically viable route for obtaining biopolyesters.