Antioxidant depletion in high-density polyethylene pipes exposed to synthetic leachate and air

Abstract

ABSTRACT: Antioxidant depletion rates are reported for samples of one particular high-density polyethylene pipe when immersed in air and a synthetic municipal solid waste leachate, obtained by measuring the oxidative induction time (OIT) at temperatures of 22°C, 40°C, 70°C and 85°C with time. Of the factors examined, the rate of antioxidant depletion was affected most by the ageing temperature, with much faster depletion occurring at higher temperatures. Antioxidant depletion was faster when immersed in the synthetic leachate rather than in air, and faster for the thin pipe examined compared with a thick pipe. No significant difference in antioxidant depletion was found whether the pipe was deflected with a 10% reduction in vertical outside pipe diameter or not deflected. Predictions of the time to deplete antioxidants are then made from Arrhenius extrapolations of the reported data. It is estimated that depletion of antioxidants may take from as long as 600 years at 10°C to as little as 20 years at 50°C when exposed to air, and may reduce to 160 years at 10°C or 10 years at 50°C if exposed to the synthetic leachate. These results are applicable for the particular pipe, antioxidant formulation and conditions examined.