Some kinetic features of the initial stage of oxidation of isotropic and oriented polypropylene

Abstract

A definition of the induction period of polyolefin oxidation is proposed. It may be regarded as the time after which the oxidation kinetics are subject to regularities peculiar to reactions involving degenerate chain branching and mutual termination of the chains. The problem of the nature of the induction period in the uninhibited oxidation of isotactic polypropylene (IPP) is discussed. Experimental data are presented to show the low initiating ability of the hydroperoxide formed in the initial stage of the oxidation reaction (in the induction period). An estimate of the isotactic polypropylene primary initiation rate of auto-oxidation at 130° has been made for two cases: the absence of quasi-stationarity in respect to radical concentrations in the induction period of oxidation. A kinetic study has been made of changes in the mechanical properties of the isotropic and oriented IPP during auto-oxidation. Experimental data have been obtained evidencing the higher initiating ability of hydroperoxide and the lower initiating ability of azoisobutyronitrile (ABN) in the oriented IPP compared with the isotropic one.