DEGRADATION OF POLYPROPYLENE UNDER GAMMA-IRRADIATION - PROTECTION EFFECT OF ADDITIVES

The protection mechanism of antioxidants and an antirad agent dissolve d in isotactic polypropylene (PP) irradiated under practical condition s has been investigated by the analysis of gas products and the measur ement of mechanical properties. In vacuum radiolysis, protection opera ting 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 add itive, and retardation of the film deterioration. Under oxygen atmosph ere, 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 recove red quickly after the consumption of additives at higher doses. In add ition, it was found that the reduction of H-2 evolution in the presenc e 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 experi ment by using liquid alkanes.