Chemiluminescence study on the endurance of EVA under radiation and thermal degradation

Full text: Ethylene vinyl acetate (EVA) copolymer is a good electrical insulation material for nuclear purposes. The present investigation points out the synergistic effects of radiation and heat on the degradation of EVA. The chemiluminescence procedure at three temperatures was applied for the determination of the temporal kinetic parameters for oxidation induction, demioxidation, maximum oxidation, the rate of oxidation and values of activation energy required by the process. The co-operative factors for radiation and thermal degradation were calculated for various ageing conditions in order to evaluate the stability of EVA under hard service. The irradiation performed with accelerated electrons brings about a significant instability to oxidation due to the chemical modifications occurred in polymer backbones. A mechanism of radiation degradation is presented as the results of chemiluminescence measurements on the oxidation progress in material damage. It has been demonstrated that the applied irradiation providing the formation of free radicals is the main cause of material instability. The subsequent thermal treatment will carry on the oxidation by the stimulation of the reaction between radical intermediates and molecular oxygen that pre-exists or is diffused from the outer molecular layers into the sample bulk. The cumulative doses induce fast degradation as the result of high concentration of reactive intermediates. (authors)