Non-isothermal crystallization kinetics of bacterial poly(3-hydroxybutyrate) in poly(3-hydroxybutyrate-co-butylene adipate) urethanes

Abstract

The non-isothermal melt crystallization kinetics of a series of copoly(ester–urethane)s, PUs, based on poly(3-hydroxybutyrate), PHB, and poly(butylene adipate), PBA, of different PHB content 20, 40, and 60 wt% were studied using DSC at different cooling rates. Various macrokinetic models, namely, Avrami, Tobin, Ozawa, and Mo models were applied to describe the crystallization process of PHB in the PU matrices. Avrami, Tobin, and Mo models could successfully describe the non-isothermal crystallization behavior of PHB segments in all samples, while Ozawa model provides a fair description of the non-isothermal crystallization process of PUs containing only 20 and 40 wt% PHB. The Avrami exponent was found to range from 3.6 to 4.0, while the Tobin exponent was found to range from 2.3 to 3.0. The spherulites shape and size were analyzed using polarized optical microscopy (POM). The results of kinetic parameters showed that the crystallization rate of PHB segments in the investigated PUs was increased with increasing the PHB content. The isoconversional method of Friedman was used to determine the effective activation energy of crystallization of the PUs and the Lauritzen–Hoffman parameters (Kg and U*) were calculated by applying the Vyazovkin method.