Isothermal Crystallisation Kinetics of Microbial Poly(3-hydroxybutyrate- Co-3-hydroxyhexanoate)

Polyhydroxyalkanoates (PHA), a class of microbial polyesters produced from fermentation, is of interest for scientists and environmentalists due to its wide-ranged combinations of monomers, biodegradability and biocompatibility properties. In this study, efforts were made to understand the kinetics of isothermal crystallisation of PHA containing 3 mol% of 3-hydroxyhexanoate (3HHx) co-monomer [P(3HB-co-3 mol% 3HHx)]. Avrami model is used to describe the kinetics of the isothermal crystallisation. Besides, we discuss crystallinity, equilibrium melting temperature, kinetics of isothermal crystallisation and activation energy of isothermal crystallisation of P(3HB-co-3 mol% 3HHx). The average crystallinity of P(3HB-co-3 mol% 3HHx) is found to be 42.5% when it is isothermally crystallised from 121-127 °C. Meanwhile, the equilibrium melting temperature of P(3HBco-3 mol% 3HHx) ( 0 m T ) is 183 °C, which is in good agreement to the 0 m T s of various PHA reported in the literature. Half-time of crystallisation (t0.5) increases exponentially with temperature. Correspondingly, overall rate of isothermal crystallisation (K1/n) decreases with temperature. The isotherms of crystallisation exhibit sigmoid dependence on time, and they gradually shift toward longer crystallisation times with increasing crystallisation temperature. Kinetic data are compared with data for other alkanoates and copolymers with them.