DEGRADABILITY OF POLY(3-HYDROXYBUTYRATE) AND ITS COPOLYMER GRAFTED WITH STYRENE BY RADIATION

The thermal stability of poly(3-hydroxybutyrate) (PHB) and its copolym er P(HB-co-HV) was improved by a low degree of grafting of polystyrene . For instance, the time for 50% weight loss at 220 degrees C was 76 m in for control (ungrafted PHB) and 110min for PHB having a degree of g rafting of 9%. The glass transition temperature of a grafted PHB sampl e shifted to higher temperatures with the introduction of polystyrene chains. Enzymatic degradability of films obtained by solution casting and hot-pressed films after grafting were also compared. The enzymatic degradability of PHB and its copolymer solution-cast film was largely retarded even at a low degree of grafting (9%). This is due to the fo rmation of a PSt layer on the film surface which prevents the penetrat ion of the enzyme. Enzymatic degradation and aminolysis of the grafted polymer was faster in a film prepared by casting than by hot-pressing , due to the formation of holes, except for enzymatic degradation of t he grafted PHB. M-n of the branch chain for aminolysis is higher than that of thermal degradation. This is because some of the branch chains were degraded during thermal degradation as compared to aminolysis. H ence, it was confirmed that aminolysis is favourable for isolation of the branch polymer from main chain PHB. (C) 1998 Elsevier Science Limi ted. All rights reserved.