Thermo-oxidative stability of PP waste films studied by imaging chemiluminescence

Imaging chemiluminescence (ICL) was used to study the oxidative stability of PP waste films and of unstabilised PP particles for comparison. It was found that the unstabilised particles oxidised homogeneously with no induction period, whereas stabilised PP waste films showed a considerable distribution of induction times sometimes affected by the presence of threadlike defects. Individual specimens of a population of PP films all showed a sigmoidal increase of the CL intensity after the induction period. A sequence of chemiluminescence images showed a propagating oxidation front and a perfect match of the fraction of oxidising material covered by the front and the increase in chemiluminescence intensity. The role of physical spreading in the oxidation of stabilised PP material was clearly demonstrated. On artificial recycling of these films ICL showed a significant change in the oxidative stability (residual lifetime) much earlier than FTIR (carbonyl index) and DSC (oxidation induction temperature). (C) 2001 Elsevier Science Ltd. All rights reserved.