Strain hardening modulus as a measure of environmental stress crack resistance of high density polyethylene

In this paper it is shown that the resistance to slow crack propagation in polyethylene can be predicted from a simple tensile measurement performed at 80 °C. It is shown that for different types of polyethylene homopolymers and copolymers the slope of a tensile curve above its natural draw ratio (i.e. strain hardening) correlates well with the measured stress crack resistance. The data presented in this paper confirm that the slow crack resistance in polyethylene is determined by the failure of the fibrils within the craze, which is shown to be determined by the strain hardening of a tensile curve. A material with a strong strain hardening will reduce the strain rate and consequently the time to failure will be strongly increased. Considering the fact that the slow crack resistance of polyethylene is usually assessed by tedious and time consuming testing methods performed on the notched samples in contact with specific fluids, the findings reported in this publication offer a possibility to assess the information on slow crack propagation in much simpler and faster way.