Degradation of poly(L-lactic acid) by y-irradiation

摘要

Poly(L-lactic acid) (PLA), was irradiated with y-rays in air and in vacuum at 25℃. Melting point T_m, glass transition temperature T_g and number-average molecular weight M_n decreased with increasing irradiation dose. At low doses, T_m, T_g and M_n decreased sharply and then the rate became slower. Up to 200 kGy, PLA was predominantly degraded by random chain-scission. Above 200 kGy, recombination reactions or partial crosslinking may occur in addition to chain-scission. The degree of chain-scission G_s of irradiated PLA was calculated to be 1.97 in air and 0.83 in vacuum. The decrease in M_n, T_m and T_g of the sample in air was faster than in vacuum because of oxidative chain-scission. Biodegradation of PLA was retarded with increasing dose due to the intro- duction of crosslinking during irradiation. ESR spectroscopy showed five kinds of radicals assigned to three kinds of ESR spectra.