The influence of gamma radiation on the molecular weight and glass transition of PLLA and HAp/PLLA nanocomposite

The influence of gamma radiation on the molecular weight and glass transition behaviour of poly-l-lactide (PLLA) and hydroxyapatite/poly-l-lactide (HAp/PLLA) nanocomposite has been studied. Since PLLA exposed to high-energy radiation in the presence of air is prone to chain scission reactions and large degradation, changes in molecular weight were obtained by gel permeation chromatography (GPC). Alterations in the glass transition behaviour were investigated by differential scanning calorimetry (DSC). The apparent activation energy (ΔH∗) for glass transition was determined on the basis of the heating rate dependence of the glass transition temperature (Tg). Our findings support the fact that chain scission is the main reason for the decrease of Tg and ΔH∗ with the absorbed dose. Furthermore, more intensive chain scission degradation of PLLA was observed in HAp/PLLA and can only be ascribed to the presence of HAp nanoparticles. Consequently, initial differences in the glass transition temperature and/or apparent activation energy of PLLA and HAp/PLLA became more pronounced with absorbed dose. This study reveals that radiation-induced changes in molecular weight and glass transition temperature occur in a predictable and fairly accurate manner. Therefore, gamma radiation can be used not only for sterilization but also for tailoring desirable end-use properties of these biomaterials.