High doses gamma radiolysis of PVC: Mechanisms of degradation

Anaerobic and aerobic radiolysis mechanisms of poly(vinyl chloride) were investigated using electron spin resonance (ESR), nuclear magnetic resonance (NMR), Fourier transform infrared spectroscopy (FTIR) and size exclusion chromatography (SEC). PVC samples have been irradiated by γ rays (60Co) at high doses (up to 4 MGy) and at room temperature. High dose anaerobic radiolysis of PVC induced several modifications in polymer. Alkyl radicals are formed, and then these radicals induced the formation of polyenic radicals. 13C NMR spectra have also shown the formation of polyenic sequences and crosslinking reactions. The modifications induced in PVC irradiated under aerobic condition are different. ESR spectra have shown that peroxyl radicals are formed. Propagating reactions from peroxyl radicals are mainly composed by β-scission reactions. These β-scission reactions involved the decrease of average molecular weight and the formation of aldehydes, acids chloride and/or carboxylic acids. From all these results, anaerobic and aerobic mechanisms of degradation by PVC radiolysis are proposed.