Effect of mechanically initiated processes on kinetics of thermal oxidative degradation and the durability of oriented polypropylene subjected to a load

Abstract

A study was made of the durability of oriented isotactic PP under conditions of thermal oxidative degradation and in vacuum ( T = 130°) over a wide range of tensile stress. It was shown that under conditions of elastic deformation of samples durability is practically constant and is determined exclusively by the rate of thermal oxidative degradation of the polymer. Under a load causing creep of samples the rate of thermal oxidative degradation increases with an increase of stress as a result of the effect of thermal fluctuation rupture on initiation of oxidation. At considerable rates of deformation samples are further elongated, which results in orientation hardening and a related reduction in the rate of oxidation as a result of lower conformation mobility of continuous molecules of the amorphous phase. This results in the apperance on isothermal curves of a new section of practically constant durability, in which durability is determined exclusively by the rate of mechanical degradation.