Stress Cracking and Photodegradation: TheCombination of Two Major Causes of HIPS Failure

摘要

This work investigates the effects of photodegradation on the stresscracking resistance of high impact polystyrene (HIPS). Injection moulded sampleswere exposed to the ultraviolet light for various times in the laboratory prior tosolvent contact. The bars were then stressed with several different loads in a tensiletesting machine under the presence of several types of alcohols (mostly butanol).During this period, the stress relaxation was monitored and, after unloading, theultimate properties were evaluated. Complementary tests were done by size exclu-sion chromatography, and scanning electron microscopy. The results indicated thatboth photodegradation and butanol causes significant modification in HIPS proper-ties, with reduction in mechanical properties. The previously degraded samplesshowed a higher level of stress relaxation and a greater loss in tensile strength incomparison to the undegraded ones. The synergistic action of photodegradation andstress cracking in polystyrene may be a consequence of the chemical changes causedby oxidation and the reduction in molecular sizes.