A theoretical model for diffusion-limited oxidation applied to oxidation profiles monitored by chemiluminescence in hydroxy-terminated polybutadiene

Imaging by chemiluminescence (CL) has been used to monitor the heterogeneous oxidation of isophorone diisocyanate cured hydroxy-terminated polybutadiene samples during thermal ageing. The system used to obtain CL images was based on a charged coupled device (CCD) camera coupled to a temperature-controlled hot-stage of a DSC apparatus, which was modified to allow use at various oxygen pressures. Oxidation profiles were obtained from the CL imaging, which showed heterogeneous CL emission. The shapes of the profiles, for various conditions of temperature and oxygen pressure, showed a good fit to a theoretical oxygen concentration profile. The latter was calculated from a simplified model which assumes that oxygen consumption is proportional to the oxygen concentration. From the fitted curves, a decrease of the oxygen diffusion coefficient was found during the oxidation, which was consistent with reduced oxygen permeability due to crosslinking of the rubber during the oxidation. (C) 2000 Society of Chemical Industry.