Degradability of poly(3-hydroxybutyrate) and its copolymer grafted with styrene by radiation

The thermal stability of poly(3-hydroxybutyrate) (PHB) and its copolymer 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 min for control (ungrafted PHB) and 110min for PHB having a degree of grafting of 9%. The glass transition temperature of a grafted PHB sample 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 formation of a PSt layer on the film surface which prevents the penetration 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 the 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. Hence, it was confirmed that aminolysis is favourable for isolation of the branch polymer from main chain PHB. (C) 1998 Elsevier Science Limited. All rights reserved.