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

In situ infrared (FTIR) spectrometry has demonstrated that more CO2 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 photostabilities in as little as 3 h. This study focuses on clarifying the mechanism of this rapid CO2 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 CO2 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 COZ 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 COZ measurements, films are pre-exposed to UVA, to generate carbonyl groups. In addition, more COZ is evolved from both PE and PP films if they are pre-exposed. (C) 2007 Elsevier Ltd. All rights reserved.