Photo-oxidative degradation of mechanically stressed polyolefins

The influence of mechanical tensile stress on the photodegradation of commercial drawn polyolefin tapes has been investigated. The degradation was monitored by the time-to-break in creep experiments. Surprisingly, photodegradation had little effect on creep rates of polyethylene and only a small effect on creep rates of polyethylene-propylene copolymer (<10% ethylene content). The stress was shown to accelerate photodegradation. The extent was proportional to the applied stress for polyethylene. With copolymer, the extent was negligible below about 50% of break stress, but important above 50%. For example, with 90% of break stress applied, the time-to-break in the standard creep test was reduced by 30%. The presence of antioxidant in the copolymer was partially effective in preventing photodegradation, and the stress effect was reduced.