What is Environmental Stress Cracking and ESCR?

The definition of stress cracking according to ASTM D883 is "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 polymeric material from its adjacent failure surfaces. Slow crack growth is another term commonly used to describe stress cracking. The best known type of slow crack growth is  environmental stress cracking" or ESC. These are instances involving cracking of stressed samples, generally in the presence of surface active wetting agents such as alcohols, soaps, surfactants, or others. The surface-active agents do not chemically attack the polymer nor produce any effect other than microscopically brittle-appearing fractures. In the absence of the surface-active environment, these fractures would not occur in any reasonable period of time under the same stress conditions. These cracks are generally thought to initiate at microscopic imperfections and propagate through the crystalline regions of the polymer structure. The ability of a polymer to resist slow crack growth or environmental stress cracking is known as ESCR. Different polymers exhibit varying degrees of ESCR. Some grades of HDPE have very good resistance against ESC, while some have marginal resilience.


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