Photo-oxidation of thick isotactic polypropylene films - I. Characterisation of the heterogeneous degradation kinetics

Photo-oxidation kinetics of thick isotactic polypropylene films have been c ompared to thermal-oxidation kinetics of thin films, and noticeable differe nces have been found. The non-classical kinetic trend of the former can be described as a three step evolution: a typical induction/autoacceleration P OOH build-up at the beginning, an intermediate slower POOH content increase and, finally, a gentler POOH increase, which can be better described by qu adratic functions of the oxidation time than by a linear dependence. In add ition, a series of oscillations appearing from the beginning of the photo-o xidation are found. This kinetic heterogeneity is suggested to be related t o the progression of the oxidation to the inside of the strips. However, th e FTIR analysis of the evolution of the POOH band position in both photo an d thermal oxidation, enables the observed shape changes to be associated to kinetic stages. (C) 2000 Elsevier Science Ltd. All rights reserved.