Evaluation of the Durability of PE-HD Geosynthetic Barriers Using High-Pressure Autoclave Tests

To evaluate the resistance of a 2 mm thick polymeric geosynthetic barrier (GBR-P) made of high-density polyethylene (PE-HD), oxidation tests at 80 °C using high-pressure autoclaves at three different oxygen pressures were carried out. After different times, 18 different evaluations were performed on the aged test specimens of the GBR-P. The following characteristics were considered: thermoanalytical methods like oxidation induction time (OIT), crystallinity and oxidation onset temperature (OOT), viscosity measurements like melt mass-flow rate (MFR) and viscosity, mechanical properties of the short term tensile test as well as stress crack resistance methods with the notched constant tensile load (NCTL) test and the strain hardening test (SHT). The failure times extrapolated to atmospheric conditions at the test temperature of 80 °C were in the range of 450–550 days for the stress crack tests. For the analytical methods, the failure times were 620–780 days and for the tests in the short-time tensile test, the failure times were between 700 and 900 days, depending on the property. To evaluate the OIT measurements, investigations were carried out on the influence of the sampling, preparation and treatment of the OIT measurement samples. Furthermore, the influence of oxidation on the thickness of the test samples was investigated. For this purpose, test specimens with thicknesses of 1 mm, 2 mm, 4 mm and 10 mm were produced and tested with the same material. The consumption of antioxidants on the surface of the test specimens was twice as high as inside the specimens. It was shown that a wide range of parameters is suitable for representing the ageing states of a PE-HD GBR-P. With very few exceptions, it was possible to determine the time transitions up to which the properties hardly changed and from which a steep rise or steep fall occurred. The most reliable and practicable test methods for ageing tests in the study were: elongation at break in the tensile test, the strain hardening modulus, OIT and OOT.