RADIATION-INDUCED DEGRADATION OF POLY(3-HYDROXYBUTYRATE) AND THE COPOLYMER POLY(3-HYDROXYBUTYRATE-CO-3-HYDROXYVALERATE)

Poly(3-hydroxybutyrate) {P(3HB)} and the copolymer poly(3-hydroxybutyrate-co-3-hydroxyvalerate) {P(3HB-co-3HV)} were irradiated with gamma-rays at 25 degrees C in air and in vacuum. Melting points (T-m) and glass-transition temperatures (T-g) were measured by differential scanning calorimetry. Number-average molecular weights (($) over bar M(n)) were analyzed by gel permeation chromatography. No significant differences were observed between T-m values of P(3HB) and P(3HB-co-3HV) irradiated in air and in vacuum, which decreased almost linearly with increasing irradiation dose. The ($) over bar M(n) values of both samples decreased sharply with increasing dose, reflecting typical random chain scission. The decrease in ($) over bar M(n) of the sample irradiated in vacuum was smaller than that irradiated in air with the same dose, implying the occurrence of crosslinking. The T-g values for both polymers irradiated in vacuum remained almost unchanged over a wide dose range, while those irradiated in air decreased as the irradiation dose increased. Both the T-m and T-g of samples irradiated in air were inversely proportional to ($) over bar M(n). Biodegradability was clearly promoted with decreasing molecular weight.