Antioxidant-stabilizer depletion of 4 HDPE geomembranes with high HP-OIT in MSW leachate

The antioxidant-stabilizer depletion of four 1.5-mm HDPE geomembranes from the same manufacturer each with a different resin and additive package is examined in air and a synthetic municipal solid waste leachate at a range of temperatures (40-95°C) for 7.5 years. Two were formulated for high-temperatures and used polyethylene of raised temperature resistance (PE-RT) resins while two used more conventional HDPE geomembrane formulations. The depletion of protective antioxidants and stabilizers was monitored using standard and high-pressure oxidative induction time (OIT) tests and the notably different depletion times for both OIT tests implied they were detecting different groups of AO-S. Although both PE-RT GMBs showed significantly slower AO-S depletion at 85°C in air compared to the conventional PE GMBs, only one PE-RT GMB maintained this status in 85°C leachate, highlighting the limitation of air aging tests (and importance of fluid immersion tests). The importance of running immersion tests long enough to reveal the residual HP-OIT value is stressed. The roles of stabilizer mobility and solubility in polyethylene and their suspected involvement in residual HP-OIT behavior is also illustrated.