Thermal stability of gamma irradiated ethylene-propylene-diene monomer/divinyl benzene systems

The improvement in thermal resistance of ethylene-propylene-diene monomer (EPDM) by exposure to γ-radiation (137Cs source) in the presence of divinyl benzene was studied. Several divinyl benzene (DVB) proportions in the polymer were selected (5, 8, 12, 20, and 30%) to prove the influence of unsaturation level on the radiation crosslinking of the elastomer. Irradiation at different total doses (7.6, 14.4, 25.2, 35.5, 70.1 and 92.5 kGy, dose rate of 0.4 kGy/h) was performed. Thermal stability of γ-radiation-modified ethylene-propylene-diene monomer/divinyl benzene systems was evaluated by means of oxidation resistance according to the oxygen uptake procedure. Kinetic characteristics, oxidation induction time and oxidation rate in the propagation step, were calculated from the dependencies of oxygen uptake on degradation time at different irradiation doses. A low dose of around 90 kGy is enough to attain high stability. At this dose the oxidation induction times for EPDM/DVB specimens are 1.7, 2.4 and 2.8 times longer than the OIT of control films. Based on these data a mechanism of radiation crosslinking is proposed.