Post-irradiation degradation of polypropylene: comparison of hindered aromatic phenol and amine as gamma-stabilizer: Pt. 1

Post-irradiation stability of 60Co-γ-ray irradiated isotactic polypropylene (PP) has been studied at 25 and 50 kGy. The effectiveness of 2,6-di-tert-butyl-p-cresol (BHT) and polymerized 2,2,4-trimethyl-1,2-dihydroquinoline (TMQ) at various concentrations is compared. The variation of crystallinity, carbonyl and hydroxyl index, mechanical properties, of stabilized and unstabilized PP was followed for 6 months after irradiation. Although the percentage of crystallinity of the unstabilized samples increased upon irradiation, for all stabilized ones not only the initial value was retained but remained constant and lower to that of the unstabilized samples during storage. Tensile strength and bend strength was also retained. The extent of chain scission has been followed by measuring the change in apparent viscosity (μa) and flowability parameters, (K) and (n), using power law equations. Although both types of stabilizers were highly effective, the amine type imparts more stability at a longer time after irradiation as the corresponding nitroxyl and hydroxyl amine groups are formed. (author)