Predicting the depletion of antioxidants in high density polyethylene (HDPE) under sunlight using the reciprocity law

Depletion of antioxidants in HDPE subjected to sunlight exposure was studied. Sunlight radiation was simulated using a laboratory xenon light weatherometer at three irradiation levels. Oxidative induction time (OIT) test was performed on different layers along the thickness of the test coupons to establish the antioxidant depletion throughout the exposure duration. The highest drop in OIT was obtained for the surface layer facing the radiation, followed by the backside layer which was exposed to indirect radiation reflected from the wall of the weatherometer. The core section showed a slower decrease under the same exposure conditions. Furthermore, the OIT depletion rate in the surface layer increased with radiation intensity. The study proved that the sunlight degradation of the tested polyethylene can be accelerated by increasing the irradiation intensity based on the reciprocity law.