52-58jelcic NOVO.indd

The purpose of applying the high-energy γ-ionizing radiation with doses up to 100 kGy was to enable controllable change of mechanical properties of high impact polystyrene (PS-HI) and, at the same time, to investigate the possibility of using reprocessed irradiated polymeric material. Dielectric relaxation of radiation modifi ed high impact polystyrene (PS-HI) has been investigated below the polystyrene glass transition temperature (T g ) by the direct current (dc) charging/discharging transient method. Time dependence of charging/discharging current for the PS-HI has been well described by the power function of the logarithm of time. The relationship between the dc conductivity and the dielectric relaxation time (τ) has been approximated by the fractal dimension. The dc transient current method is considered to be a practical tool for analyzing the dielectric relaxation process of the radiation modifi ed PS-HI. It was also shown that yield strength and tensile strength increase while elongation at break decreases with increasing radiation dose. The specimen prepared by a post-irradiation moulding gave higher melt fl ow rate than those of specimens formed before irradiation. These results indicate that after radiation the system of PS-HI is reprocessable. It is concluded that an oxygen environment at the beginning of irradiation leads to enhanced chain scission at the expense of crosslinks via peroxide formation and causes oxidative degradation of the main polymer chain of irradiated PS-HI at a low dose. However, at higher absorbed doses the quasi-inert environment has been established and crosslinking, due to recombination of macroradicals, is dominant.