Effects of electron beam irradiation on thermal and mechanical properties of poly(lactic acid) films

The purpose of this study is to examine the effect of electron-beam (EB) radiation on biodegradable polylactic acid (PLA), and to understand radiation-induced degradation mechanisms. PLA films were irradiated between 0 and 120 kGy and physical properties were characterized by means of GPC, DSC, DMA and tensile drawing. It was shown that degradation of PLA under EB leads to a random chain scission responsible for a reduction of the molar mass. These molar mass changes affect glass transition temperature Tg, degree of crystallinity, and mechanical properties. It was found that Tg, stress and strain at break decrease with increasing irradiation dose, whereas the degree of crystallinity increases up to 45 kGy then decreases. Cross-linking Gx and chain scission Gs values of PLA revealed that chain scission reactions at lower dose predominate over cross-linking. DMA results exhibit an exothermal re-crystallization for neat and irradiated samples, which disappears with increasing heating rate. These results were confirmed by DSC measurements. Ductile-brittle transition was determined as function of EB-dose and crosshead speed. A change of physico-chemical and mechanical properties was evidenced during application of a dose of 45 kGy.