RADIATION EFFECT ON POLYESTERS

Poly(3-hydroxybutyrate) (PHB) and its copolymer poly(3-hydroxybutyrate -3-hydroxyvalerate) [P(HB-HV)] were irradiated with gamma-rays in air or vacuum. Polymer chain scission occurred and resulted in depression of melting points (T-m), glass-transition temperatures (T-g) and numbe r-average molecular weight (($) over bar M(n)). Decrease in ($) over b ar M(n) of the sample irradiated in vacuum was smaller than that irrad iated in air, implying introduction of crosslinking. The T-m and T-g o f samples irradiated in air were inversely proportional to ($) over ba r M(n). Their biodegradability was clearly promoted with decreasing ($ ) over bar M(n). Radiation grafting of methyl methacrylate (MMA) or 2- hydroxyethyl methacrylate (HEMA) was carried out by in-source polymeri zation. Degree of grafting (X(g)) increased as irradiation dose increa sed and leveled off around 5 kGy. The X(g) of PHB grafted was lower th an that of P(HB-HV) because of higher crystallinity of the former. Cro sslinking between the grafted PMMA chains was easily formed. Biodegrad ability of both polymers steeply decreased by introduction of MMA graf ting, while that of polymers grafted with HEMA increased at first beca use of improvement of wetiability then steeply decreased with increasi ng X(g) of HEMA.