A general solution of the closed-loop kinetic scheme for the thermal oxidation of polypropylene

A general solution of the closed-loop kinetic scheme for the thermal oxidation of hydrocarbon polymers is presented in which no assumptions are made concerning the concentration of oxygen, the kinetic chain length, the ratio of termination rate constants or the existence of a steady-state for the concentration of radicals. The proposed model is used to simulate the thermal oxidation of unstabilized polypropylene films under ambient air at 80-150 degreesC, with reaction and diffusion parameters that result in realistic estimates of induction times, hydroperoxide concentrations and oxygen uptakes. Simulation results indicate that the oxidation of films 10-100 mum thick is likely to become oxygen-diffusion-limited before the end of the induction time for oxygen absorption, with heterogeneous degradation predominating as the process approaches stationary conditions. The model is used, among others, to identify operating conditions under which the oxidation process may be considered free of oxygen mass transfer limitations. (C) 2001 Elsevier Science Ltd. All rights reserved.