Chain‐scission and yellowing in high impact polystyrene

Different grades of impact‐modified polystyrene were studied by viscometry, tensile impact test and colour change upon exposure to polychromatic irradiation at 55°C in air. The samples underwent extensive reduction in intrinsic viscosity [η] and tensile impact strength, and yellowed upon polychromatic irradiation (λ ≥ 290 nm). Chain‐scission during photo‐oxidative degradation was also studied under conditions where evolution of volatiles was negligible. Tristimulus values were calculated for unirradiated and irradiated samples. The rate of oxidative degradation was maximum in the sample possessing higher unsaturation content.