Polymer alloys are a class of polymer blends where the addition of the second polymer is tailored to provide controlled morphology, and thus specific performance characteristics.

Cold Shock By Ian D. Peggs and Chris Kelsey

Low temperatures, fast-dropping temperatures, and strong winds can provide the ideal conditions for rapid crack propagation (RCP)—“shattering”—in exposed high-density polyethylene geomembranes. In the United States and Canada, winter weather patterns have become far less predictable, with “polar vortex” episodes, ice storms, and even tornado conditions followed by snow (as some areas of the US South experienced in January 2020). Where temperatures reach atypically low levels, or when regions experience rapid fluctuations in temperature with cold temps involves, some risk may be posed to high-density polyethylene geomembranes if they are in an exposed state. One threat that must be considered is rapid crack propagation, a phenomenon that can take a number of forms—many of which are dramatic—as a crack or cracks spread quickly through a polymeric material.

Core Thickness/Asperity Height

Core thickness is a measure of thickness characteristics of a geomembrane; whereas asperity height is a measure of surface roughness of a textured geomembrane.


The phenomenon that produces a network of fine cracks on the surface of a material, for example in a glaze layer. Crazing frequently precedes fracture in some glassy thermoplastic polymers. As it only takes place under tensile stress, the plane of the crazing corresponds to the stress direction.


Ductility is the measure of a material's ability to plastically deform without fracturing when placed under a tensile stress that exceeds its yield strength. High ductility indicates that a material will be more apt to deform and not break whereas low ductility indicates that a material is brittle and will fracture before deforming much under a tensile load. Ductility depends largely on a material's chemical composition, a material's crystalline structure, and the temperature at which the ductility is being measured.


The ability of an object or material to resume its normal shape after being stretched or compressed; stretchiness.

EPDM Ethylene Propylene Diene Monomer

Usage: Rubber roof; in vibrators and seals; glass-run channel; radiator; garden and appliance hose; tubing; washers; belts; electrical insulation; and speaker cone surrounds. It is also used as a medium for water resistance in high-voltage polymeric cable jointing installations, roofing membrane, geomembranes, rubber mechanical goods, plastic impact modification, thermoplastic, vulcanizates, as a motor oil additive, pond liner, electrical cable-jointing and RV roofs.


A geosynthetic material intended to contain fluids is referred to as a geomembrane or a geosynthetic liner, which is essentially impermeable when properly installed.

Hippos & Whales By Ian D. Peggs, Ph.D., P.E., P.Eng

There continue to be failures of HDPE geomembrane lining systems in waste water treatment plant (WWTP) lagoons and farm manure ponds. These geomembrane whales, which are bubbles that develop under the geomembrane, are generally caused by leakage through the liner, the inability to remove leakage, the generation of methane, and the subsequent inability to vent the methane.


High-density polyethylene is a thermoplastic polymer produced from the monomer ethylene. With a high strength-to-density ratio, HDPE is used in the production of plastic bottles, corrosion-resistant piping, geomembranes and plastic lumber.

Stress Crack

According to ASTM D883, stress cracking is defined as "an external or internal crack in a plastic caused by tensile stresses less than its short-term mechanical strength". This type of cracking typically involves brittle cracking, with little or no ductile drawing of the material from its adjacent failure surfaces.


A chemical compound or mixture of compounds formed by polymerization and consisting essentially of repeating structural units.

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