On the Nature of the Induction Stage in Polypropylene Oxidation

Abstract Propagation of fracture sites in stressed inhibitor containing polypropylene and the macrokinetics of oxidation of isotropic and oriented polypropylene films were studied. Localization of oxidation in the sites of primary initiation was considered. The induction period is given a new interpretation as the time of oxidation localized within the sites of primary high rate initiation at catalytic admixtures. The end of the induction stage is marked by the expansion of the oxidation reaction from the initiation sites and its propagation over the entire polymer. The mechanism of initiation of the kinetic chain process at this stage becomes controlled by the decomposition of hydroperoxides. An increase in induction period observed during orientation is explained by enhanced structure-related localization of the oxidation reaction within the initiation sites owing to morphological changes and by increased rigidity of the polymeric matrix.