Assessment of Polyethylene Geomembrane Properties after Accelerated Thermal Ageing

Abstract

Application temperatures and exposure environments are among the causes of premature antioxidant loss in polymer geomembranes. Therefore, over the long term, polymer degradation takes place which is reflected in geomembrane properties. In this work, accelerated thermal ageing of polyethylene geomembrane was carried out in a climatic chamber at 70℃ with 21% oxygen. The evolution of tensile properties, puncture resistance, and shore D hardness with exposure time was assessed. Changes in chemical and crystalline structure and melt flow index were made. According to the findings, geomembrane surface oxidation takes place in the polyethylene matrix after 9 months of exposure. This fact is confirmed by evaluating carbonyl, vinyl, and hydroxyl indexes. Uniaxial tensile properties, puncture resistance, and shore D hardness indicated slight changes after one year of exposure. While the crystallinity index, determined by XRD measurement, has shown an increase with exposure. Further, melt flow index measurements confirmed the absence of chain scission during the early exposure periods. However, for longer periods, chain scission reactions occurred and MI values increased moderately after five months of accelerated aging. All results indicated no significant bulk degradation while maintaining a certain mechanical resistance with applications under a temperature of 70℃. This temperature value is relevant in a waste storage center, but the studied geomembrane is not recommended for this case.