Influence of the exposure parameters on the mechanism of photooxidation of polypropylene

Samples of polypropylene were exposed to artificial accelerated photoageing in various conditions of light intensity. The aged samples were analyzed by FTIR techniques coupled with chemical derivatization to determine the degradation structures resulting from UV exposure. Chemical titrations of the hydroperoxides and determinations of the oxygen consumption were carried out to quantify the formation of the oxidation photoproducts. As expected, our results showed that modifying the exposure parameters induced notable changes of the kinetics of the reactions. These changes led also to some modifications of the relative concentrations of the various oxidation photoproducts, particularly those of the carbonylated products including esters and carboxylic acids. This light intensity dependent behaviour permitted the proposal of a mechanism to account for the formation of the final photoproducts resulting from the hydroperoxides. Our results indicated two possible mechanisms of decomposition of the hydroperoxides, whose relative importance is dependent on the light intensity. (C) 1999 Elsevier Science Ltd. All rights reserved.