Oxidation of polyethylene under irradiation at low temperature and low dose rate. Part II. Low temperature thermal oxidation

Abstract This paper deals with the kinetic modelling of unstabilised polyethylene thermal oxidation, particular attention being paid to the domain of low temperatures, typically below 80 °C. Experimental data show that the temperature dependence of the induction time t i and the steady state rate of oxygen absorption r S display a discontinuity at 80 °C. A model based on the hypothesis that this discontinuity concerns only the PO 2 bimolecular combination processes and is essentially explained by the competition between terminating and non-terminating PO 2  + PO 2 reactions, was proposed. With pertinent values of the Arrhenius parameters of the elementary reactions under consideration, the model fits well the experimental data (in the 40–200 °C temperature range) and is consistent with previously analysed results of radiochemical ageing. According to this model, 35–40% of the bimolecular PO 2 combinations would not be terminating at 45 °C and this proportion would increase with the temperature. Concerning terminations, the relative fraction of coupling processes, leading to peroxide bridges, would decrease relatively to the disproportionation processes when the temperature increases.