Studies on the alcoholysis of poly(3-hydroxybutyrate) and the synthesis of PHB-b-PLA block copolymer for the preparation of PLA/PHB-b-PLA blends

摘要

Poly(3-hydroxybutyrate) (PHB) is a particular biodegradable polyester that is mainly produced by fermentation of bacteria. Besides microbial degradation, it can also be degraded by several other methods including hydrolytic degradation, alcoholysis degradation and thermal degradation. The degraded PHB products can be used in various applications such as chain extender, plasticizer, coating and painting. In this study, a high-molecular-weight PHB was degraded by methanolysis and catalyzed by acid; and the produced PHB oligomer with one terminal hydroxyl group was used to initiate the ring-opening polymerization of lactide to produce poly(3-hydroxybutyrate)-b-poly(lactic acid) (PHB-b-PLA) block copolymer. The alcoholysis kinetics of the PHB was investigated at 80, 90, and 100 degrees C, and found to obey a pseudo-first-order reaction. The rate constants were in the range of 2.45 to 3.68x10(-4) 1/min, and the activation energy derived from the Arrhenius plot was 22.3 kJ/mol. Moreover, the molecular weight and glass transition temperature (T-g) of various PHB oligomers after degradation were all measured, and a linear plot of the T-g with the reciprocal of the molecular weight indicated a T-g of 4.3 degrees C for the PHB with infinite molecular weight. Moreover, unlike the immiscible PLA/PHB blends, the synthesized PHB-b-PLA block copolymer was miscible with the PLA, in which there was only one T-g in each of PLA/PHB-b-PLA blends. The T-g of the blend decreased with increasing the composition of PHB-b-PLA; and the T-g-composition relationship was fitted very well by both Fox's equation and Gordon-Taylor equation.