THE KINETICS AND MECHANISM OF POLYETHYLENE PHOTOOXIDATION

The kinetics of the natural and accelerated photo-oxidation of low-den sity polyethylene (LDPE) films have been studied; different geographic al locations have been selected for the natural tests, and a range of temperatures used in the accelerated experiments in a specially built temperature-controlled ultraviolet radiation enclosure. A meaningful c orrelation between natural and accelerated weathering results was esta blished, by means of an adequate superposition of the effects of UV ra diation exposure and temperature. Reasonably detailed and accurate, lu mped-parameter, kinetic models of the photo-oxidation process have als o been developed, to interpret and predict the results of measurements of carbonyl, hydroperoxide and vinyl absorbances as functions of time and temperature; the models predict the general experimental behaviou r, and also that both the formation of hydroperoxides and carbonyl Nor rish-I reactions are important initiation steps. More complex models h ave the potential of interpreting other fine details of the degradatio n behaviour, namely the generation of other chemical species, and the chain scission and cross-linking processes which are directly related to changes in the mechanical properties.