A representation of the autoacceleration stage of polypropylene thermooxidation in reduced coordinates

Abstract

The kinetic curves of hydroperoxide build-up and chemiluminescence emission along the thermooxidation of polypropylene have been normalised by using the co-ordinates of the autoacceleration point of inflection. It has been found that the curves thus normalised do not depend on the oxidation temperature (between 130 and 160°C) nor on the presence of stabilisers or on whether the kinetics of chemiluminescence emission or hydroperoxide build-up are considered. To find out what do these curves depend on, the spreading equation given by George and co-workers (George GA, Celina M, Lerf C, Cash G, Weddell D. Macromol Symp 1997;115;69) has been normalised with the co-ordinates of its analytical point of inflection. The normalisation of the spreading equation results in a new function which depends only on one parameter, a, which is related to the initial fraction of oxidation centres. The comparison of experimental normalised curves with the analytically normalised spreading equation is proposed as a means of further understanding the initiation and propagation of oxidation in polypropylene.