The interconnection between the structural-mechanical and chemical phenomena accompanying oxidative degradation processes in oriented polypropylene

Abstract

Mechanical stresses accumulate in the surface layers of the specimen during diffusive oxidation of oriented polypropylene and these stresses, in their turn, affect the chemical mechanism. Degradation of chains in the surface layers of thick specimens occurs to a considerably greater extent than in oriented thin film oxidized under analogous conditions. The yield of hydroperoxide per mole of absorved oxygen is less by a factor of 1·6–1·8 in the thick specimens, and the yield of the number of acts of chain scission is greater by a factor of 1·8–2·6 than in the thin film oxidized under analogous conditions. The observed effects are probably connected with the occurrence of oxidation in the field of the mechanical stresses in the case of the thick specimen, a fact which leads to a more important part being played by the decomposition of the radicals R· and RO 2 · reactions which compete with the usual reaction of chain prolongation that leads to the formation of hydroperoxide.