Influence of the exposure parameters on the mechanism of photooxidation ofpolypropylene

Samples of polypropylene were exposed to artificial accelerated photoageing in various conditions of light intensity. The aged samples were analyzed b y FTIR techniques coupled with chemical derivatization to determine the deg radation structures resulting from UV exposure. Chemical titrations of the hydroperoxides and determinations of the oxygen consumption were carried ou t to quantify the formation of the oxidation photoproducts. As expected, ou r results showed that modifying the exposure parameters induced notable cha nges of the kinetics of the reactions. These changes led also to some modif ications of the relative concentrations of the various oxidation photoprodu cts, particularly those of the carbonylated products including esters and c arboxylic acids. This light intensity dependent behaviour permitted the pro posal of a mechanism to account for the formation of the final photoproduct s resulting from the hydroperoxides. Our results indicated two possible mec hanisms of decomposition of the hydroperoxides, whose relative importance i s dependent on the light intensity. (C) 1999 Elsevier Science Ltd. All righ ts reserved.