Oxidative resistance of high-density polyethylene geomembranes

摘要

Data are reported from oven aging in air for more than 13 years (!) and from water immersion tests for 6 years at 80℃ on various high-density polyethylene geomembranes (GM) used in landfill lining. The mechanical properties and oxidative induction times (OIT) of the samples were monitored during the long-term testing. Aging behavior in hot air is different from that in hot water. During oven aging a slow, exponential decrease of OIT is observed. Even after 13.6 years there is no indication of an oxidative degradation of the mechanical properties. During immersion in water a strong reduction in OIT occurs within the first year, after which time the curve levels off. Oxidation starts when very low OIT-values are reached after about 5 years at which time the mechanical strength rapidly falls to values below the yield point. We conclude from these data that the service life of HDPE GM's is essentially determined by the slow loss of stabilizers due to migration. The oxidation starts only after the depletion of antioxidants and then quickly leads to brittleness of the sample. However, no complete oxidative deterioration has been observed to date. We estimate by the van't Hoff rule that under normal ambient conditions many centuries will have to pass before the functional mechanical properties of state-of-the-art stabilized HDPE bulk material will be reduced below acceptable limits by oxidative degradation.