The combined effect of two major causes of polymer failure, photo-oxidative degradation and environment stress cracking (ESC), have been investigated in this paper. Polycarbonate (PC) injection molded specimens were aged for 168 hours at 50 °C in an ultraviolet (UV) weatherable chamber. Then the stress relaxation and tensile tests were carried out in the ethanol environment to examine ESC behavior of PC. The results show that the tensile yield stress and stress relaxation resistance of PC improve slightly due to photo-oxidative degradation, while the ethanol will accelerate the failure of undegraded PC. When the previous degraded specimens were tested under the presence of ethanol, the stress relaxation rate increases significantly and the surface cracks appear to be more intensive in comparison with other ones. This indicates that there is a synergistic effect between photo-oxidative degradation and environmental stress cracking for PC injection molded parts.
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