STRUCTURAL-KINETIC MODEL OF THE STRENGTH VARIATION IN ORIENTED POLYPROPYLENE DURING RADIATION-INDUCED OXIDATION IN THE PRESENCE OF INHIBITOR

The variation of strength of an oriented PP containing an antioxidant as a result of radiation-induced oxidation of a sample in air was stud ied. It was demonstrated that the strength drops at a higher rate duri ng the induction period of oxidation than upon its completion. This is related to the scission of most highly stressed tie chains (identifie d as interfibril links), ruptured directly in the course of irradiatio n, that is, during the initiation events. A decrease in polymer streng th after completion of the induction period can be related to the dest ruction of less stressed intrafibril chains at the stage of propagatio n or termination of the kinetic oxidation chains. The experimental dat a can we described within the framework of a model taking into account the mechanical and kinetic unequivalence of the tie chains belonging to various types. The model leads to the equation of first order with respect to concentrations of the tie chains of various types, which pr ovides an adequate description of the strength variation of oriented P P during the oxidative radiolysis in air. The theory agrees well with experiment. On this basis, the kinetic parameters of PP oxidation and the characteristics of decreasing polymer strength were determined.