Degradation of polypropylene under gamma irradiation: protection effect of additives

摘要

The protection mechanism of antioxidants and an antirad agent dissolved in isotactic polypropylene (PP) irradiated under practical conditions has been investigated by the analysis of gas products and the measurement of mechanical properties. In vacuum radiolysis, protection operating through energy and charge-transfer processes, as observed in the model alkane liquids previously reported, results in the reduction of H_2 evolution, in proportion to the number of benzene rings in the additive, and retardation of the film deterioration. Under oxygen atmosphere, G-values of more than 50 for oxygen uptake were measured in pure PP, which is attributable to a chain reaction. Although the uptake was significantly reduced by the addition of additives, the uptake recovered quickly after the consumption of additives at higher doses. In addition, it was found that the reduction of H_2 evolution in the presence of additives decreases to nil under severe oxidation. The mechanism of the degradation of PP and the protection by additives is discussed by comparison with the results previously obtained in the model experiment by using liquid alkanes.