Environmental Stress Cracking and Crazing (ESC)

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Some polymers, when stressed, are affected by contact with certain chemical substances.
ESC describes a slow brittle failure in stressed polymers by organic substances. For example PVC exposed to certain hydrocarbon impurities mai crack and PS in contact with organic liquids, may develop crazes.
Crazed materials retain considerable strength but crazing may precede cracking.
In both ESC and crazing, damage arises from simultaneous action of a substance and environmental stress. The resistance of a polymer to ESC failure depends on structural factors; for example, PE's resistance varies with molar mass, melt flow index, crystallinity and density.
ASTM D-1693 addresses the accelerated stress cracking. A sample plaque (1.5" X 0.5"> is slit lengthwise, bent 180 deg., and placed in a holder and submerged in a surface active re-agent (for PE Igepol) at 50 deg. C.

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