Antioxidant Depletion Lifetime in High Density Polyethylene Geomembranes

A major issue in the use of geomembranes for waste containment is an estimate of the material's durability (i.e., its lifetime) to various aging phenomena. For high density polyethylene geomembranes, which are the focus of this study, there are three stages in assessing lifetime: depletion of antioxidants, induction time, and time to reach half-life of a relevant engineering property. This paper addresses the first stage of these three sequential processes. Twenty laboratory incubation devices were made to simulate landfill conditions. Four sets of five columns were maintained at elevated temperatures of 85, 75, 65 and 55°C. Samples were retrieved at various intervals over a 24-month incubation period. Various physical, mechanical, and chemical properties were evaluated. The depletion of antioxidants in the incubated samples was monitored using both standard and high pressure oxidative induction time tests. Arrhenius modeling was used on the data to extrapolate the antioxidant lifetime to a typical landfill site temperature of 20°C. The resulting predicted time was 200 to 215 years. Also, it should be emphasized that within this period of time the physical and mechanical properties of the incubated samples remained unchanged.