KINETIC EFFECT IN ENVIRONMENTAL-STRESS CRACKING OF POLYETHYLENE DUE TO LIQUID VISCOSITY

Results of an experimental study are presented. An interesting kinetic effect in the environmental stress cracking (E. S. C. ) of PE has been observed, in which the liquid viscosity plays an important role. E. S. C. of a low density, high melt index PE due to silicone oils has been studied using constant load creep experiments. For relatively low stresses, it has been found that the time to fracture is independent of the viscosity of the silicone oil, all other factors being approximately equal. However, at high stresses, the time to fracture increases with increasing viscosity for a given stress. This effect has been shown to be due to the relative ease with which the liquid penetrates a growing crack and thus always be at the crack front. Times to fracture for viscous liquids at high stresses are longer since crack propagation continues partially with and partially without liquid contact, fracture rate being much slower when not in the presence of the liquid.