ENVIRONMENTAL-STRESS CRACKING OF POLYETHYLENE - CRITERIA FOR LIQUID EFFICIENCY

In the reported experiments, the environmental stress cracking (ESC) of polyethylene in nonreacting, nonswelling liquids has been studied using uniaxial creep tests. For active liquids, three types of behavior have been recognized. At low stresses, ″pure″ ESC occurs; at intermediate stresses, time to failure is largely controlled by the ability of the liquid to flow into a growing crack; and at high stresses, ESC is in competition with failure by necking, and the latter prevails. The liquid does not therefore play a significant role in this last case. Nonactive liquids produce results similar to those observed in air. It is believed that this is because these liquids are unable to flow into growing cracks sufficiently quickly even at low stresses and thus the liquid does not influence failure behavior. This criterion for activity of the liquid is largely determined by the viscosity of the liquid and by the spreading coefficient of the liquid on the solid - a parameter defining the ability of the liquid to wet the solid.