Time, Temperature, and Molecular Weight Effects in Environmental Stress Cracking

Abstract

A parametric study was made of the stress relaxation of linear polyethylene in air and a stress cracking environment, Igepal. Breaking time is shown to be a function of reduced variables of time, temperature, and molecular weight. Acreleration of tests for failure time can be achieved if the test temperature is raised, since for 0.96 density P.E. over the range of 50–110°C no mechanism change occurs. Stress relaxation measurements are shown to give results similar to the bent strip stress cracking test (ASTM D 1693-60T). This latter test can also be accelerated 80 times for 0.96 density polyethylene and 1500 times for 0.95 density polyethylene. A slight modification of the test procedure is required to obtain meaningful results. Some effects of strain, thickness, and presoaking are also reported.