The effect of oxygen pressure on the rate of polypropylene oxidation determined by chemiluminescence

The chemiluminescence of non stabilized polypropylene films has been studied at temperatures 130 and 140 degrees C at various concentrations of oxygen in the flow of oxidizing gas introduced above the polymer sample, Results have shown that the maximum level of chemiluminescence intensity is linearly proportional to the concentration of oxygen in the gas above the sample, i.e. to the concentration of oxygen in the polymer. A kinetic model based on a simple mechanistic scheme where the initiation of oxidation results only from hydroperoxide decomposition was proposed. Approximate analytical solutions have been found in the case when k(4)k(6)/k(5)(2)much less than 1, k(4), k(5), k(6) being the termination rate constants, for, respectively (P degrees + P degrees), (P degrees + PO(2)degrees) and (PO(2)degrees PO(2)degrees) radicals. According to this approximation, the POS concentration will be a hyperbolic function of the oxygen concentration, The experimental results may then be interpreted as: (1) in the conditions under study there is no sufficient oxygen concentration to scavenge all P degrees radicals, i.e. termination reactions involving these radicals are not negligible; (2) the results are consistent with the fact that the chemiluminescence would result directly from hydroperoxide decomposition rather than from the POS bimolecular termination reaction. (C) 1999 Elsevier Science Ltd. All rights reserved.