Thermo-oxidative degradation of isotactic polypropylene film: Structural changes and its correlation with properties

Degradation of isotactic polypropylene has been studied by ageing the film samples at 70°, 80° and 90°C in air. Reactions involved in changing the molecular structure and formation of oxygenated and unsaturated groups, during thermo-oxidative degradation, are discussed. The increase in molecular weight ($\text{M}\text{?}{}_{\mathrm{v}}$) suggests molecular enlargement mainly by recombination of alkyl and alkoxy radicals which produces non-radical products. Tensile strength has been found to increase initially and then decreases with ageing time. Increase in isotacticity and density of polypropylene may be due to the cleavage of the backbone chain in the amorphous intercrystalline region, facilitating poorly ordered molecular segments into a more ordered helical form.