Ageing of HDPE geomembranes in jet fuel A-1

摘要

ABSTRACT: The latest findings regarding the ageing of high-density polyethylene (HDPE)ngeomembrane (GM) exposed to jet fuel are presented. Data from std-OIT and HP-OIT tests bothnindicate that some component(s) of the antioxidant package are readily leached into the jet fuel butnonce this component is removed the OIT values remain relatively stable for up to at least 4 years.nThe std-OIT depletion rates for the readily leachable component of the antioxidant package arenestimated from the available data. Based on the jet fuel immersion test at 238C the depletion timento reach the residual standard oxidative induction time (OIT) is 1.6 years for 1.5 mm thicknconventional GM and 5.5 years for the 1.5 mm fluorinated GM. Thus fluorination had ansignificantly beneficial effect in terms of slowing antioxidant depletion. Arrhenius modelling basednon data at three temperatures (23, 9 and u0001228C) is used to predict std-OIT depletion times at antemperature (u000118C) applicable to containment of jet fuel spill at Brevoort Island in the Arctic. Thenestimated depletion time ranged from 14–24 years for 1.5 mm thick untreated GM, 22–33 yearsnfor 2 mm untreated GM, and 26–33 years for 1.5 mm fluorinated GM. For GMs with a similarncomposition, the OIT depletion rate decreased approximately with the square of GM thickness. Atn238C the depletion rate in the diffusion test was only about one-quarter of that in an immersionntest. Tensile elongation at yield increased with time of immersion in jet fuel. Tensile yieldnproperties and initial tear resistance of the GM were lower when the GM was wet with jet fuelnthan when dry. However, no significant change in dry initial tear resistance was observed. Nonsignificant change in crystallinity was observed in GM exposed to jet fuel. The immersion datansuggest that the 1.5 mm f-HDPE GM liner used to containing the hydrocarbon spill on BrevoortnIsland is likely to perform well for a period well in excess of 25 years at the average fieldntemperature (u000118C). Based on the findings from the diffusion tests with jet fuel on one side andnwater on the other (i.e. similar exposure conditions to that in the field), the time to antioxidantndepletion is likely to about four times longer than when immersed in jet fuel and so the depletionntime in the field under these conditions is projected to be in excess of 100 years. These tests willnneed to be run for a much longer period of time to allow a better estimate to be made of thendepletion rate of remaining antioxidants and service life of GM exposed to jet fuel.