Isothermal annealing of poly(lactide-coglycolide) (PLGA) and its effect on radiation degradation

The purpose of this study was to examine how the presence of crystals can retard electron-beam (e-beam) radiation degradation, and their effects on the thermal and morphological properties of poly(lactide-co-glycolide) (PLGA) upon e-beam irradiation. Isothermal annealing at 115 degreesC was carried out on PLGA films and the effect of different annealing times on the degree of crystallinity (DOC) of PLGA was recorded. The DOC increased with annealing time to a maximum value, and remained unchanged with further annealing. The annealed films were then e-beam irradiated at doses of 5, 10, 20 and 30 Mrad. The degradation of the films was studied by measuring the changes in their molecular weight, DOC, thermal properties and FTIR spectra. It was observed that, regardless of the DOC of the films, the molecular weight of PLGA generally decreased with increasing radiation dose, indicating that chain scission is dominant. However, the extent of degradation is less for the films with a higher DOC. The thermal properties of PLGA also decreased with increasing radiation dose. Radiation increases the DOC for films with initial crystallinity below 5% but decreases the DOC for films with initial crystallinity above 5%. Crystals in PLGA films decreased the extent of radiation degradation. (C) 2005 Society of Chemical Industry.