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 number-average molecular weight (($) over bar M(n)). Decrease in ($) over bar M(n) of the sample irradiated in vacuum was smaller than that irradiated in air, implying introduction of crosslinking. The T-m and T-g of samples irradiated in air were inversely proportional to ($) over bar M(n). Their biodegradability was clearly promoted with decreasing ($) over bar M(n). Radiation grafting of methyl methacrylate (MMA) or 2-hydroxyethyl methacrylate (HEMA) was carried out by in-source polymerization. Degree of grafting (X(g)) increased as irradiation dose increased and leveled off around 5 kGy. The X(g) of PHB grafted was lower than that of P(HB-HV) because of higher crystallinity of the former. Crosslinking between the grafted PMMA chains was easily formed. Biodegradability of both polymers steeply decreased by introduction of MMA grafting, while that of polymers grafted with HEMA increased at first because of improvement of wetiability then steeply decreased with increasing X(g) of HEMA.