Kinetic modelling of radiochemical ageing of ethylene–propylene copolymers

A non-empirical kinetic model has been built for describing the general trends of radiooxidation kinetics of ethylene–propylene copolymers (EPR) at low γ dose rate and low temperature. It is derived from a radical chain oxidation mechanism composed of 30 elementary reactions: 19 relative to oxidation of methylene and methyne units plus 11 relative to their eventual cooxidation. The validity of this model has been already checked successfully elsewhere for one homopolymer: polyethylene (PE) (Khelidj et al., 2006a and Khelidj et al., 2006b; Colin et al., 2007). In the present study, it is now checked for polypropylene (PP) and a series of three EPR differing essentially by their mole fraction of ethylene (37%, 73% and 86%) and their crystallinity degree (0%, 5% and 26%). Predicted values of radiation-chemical yields are in good agreement with experimental ones published in the last half past century.