Stress Cracking Behaviour of a High Density Polyethylene Geomembrane Seam Created in Sub-Zero Conditions.

High-density polyethylene (HDPE) geomembranes are used extensively in barrier systems for landfills and mining applications. Shipped as rolls these geomembranes require in-situ seaming to create a continuous barrier against liquid and gas migration. The most commonly employed seaming techniques for HDPE geomembranes include dual track wedge welding and extrusion welding, both of which subject overlapped sections of geomembrane sheet to high temperatures and molten polymer during seaming. Reports have indicated cracking failures at the heat-affected zone (HAZ) for both dual track wedge welds and extrusions welds created during sub-zero temperatures, prompting interest into the examination of a geomembrane’s susceptibility to stress cracking following cold weather seaming. Stress crack resistance (SCR) tests of one HDPE seam, in both notched and un-notched configurations, and sheet specimens are reported. The craze formation and failures times of a seam created at a sheet temperature of -27℃ for one welding speed, pressure, and welding temperature combination, as well as rapidly cooled extrudate and seam squeeze-out crystallinity tests are examined. Notched SCR results indicate little difference between -27℃ seam and sheet values while un-notched seams exhibited a significantly shorter failure time (2895 ± 64hrs) than un-notched sheet, which have yet to fail after ~8000hrs. Crystallinity results suggest that material embrittlement did not occur within the seam. Furthermore, rapid cooling, specifically in terms of material crystallinity, may actually be beneficial in hindering crystalline region growth in HDPE GMBs.