Synergistic effects of EB irradiation and heat on EVA electrical insulators

Radiation/thermal degradation is discussed as a successful endurance check. EVA samples were subjected to electron beam irradiation at 12, 30, 60 and 90 kGy. Heat treatment was performed in air at 120 °C for 72 h and 120 h. Chemiluminescence (CL) investigations on EVA specimens were carried out at 200, 210 and 220 °C. Several kinetic parameters such as oxidation induction time (ti), half-oxidation time (t1/2), maximum oxidation rate (voxmax), maximum time of thermal oxidation (tmax) and other chemiluminescence features were obtained from the time dependencies of the CL intensity. While the ageing factors of processed EVA samples reveal a constant value for two testing temperatures (200 and 210 °C), the co-operative factors that describe a combined (synergistic) degradation present higher than unity values, either for the oxidation rates or for the maximum CL intensity measured for all irradiation doses. They increase linearly with dose.