Carbon dioxide evolution and carbonyl group development during photodegradation of polyethylene and polypropylene

In situ infrared (FTIR) spectrometry has demonstrated that more CO 2 is photogenerated from polypropylene (PP) than from polyethylene (PE) films. Potential applications of the method include investigation of polymer degradation mechanism and ranking of polymer photo-stabilities in as little as 3 h. This study focuses on clarifying the mechanism of this rapid CO 2 formation from PE and PP, and complementary insight was obtained from changes in the IR transmission spectra of films irradiated by UVA for hundreds of hours. A 30 min induction time observed for CO 2 photogeneration from PP, but not PE, was reflected, on a much longer time scale, in the induction time for carbonyl development in PP, but not PE. This suggests that, in PP, the CO 2 induction time is a consequence of the slow development of carbonyl groups, a hypothesis that is supported by the elimination of the PP induction time when, prior to the CO 2 measurements, films are pre-exposed to UVA, to generate carbonyl groups. In addition, more CO 2 is evolved from both PE and PP films if they are pre-exposed.