Effect of γ-irradiation on slow crack growth in a copolymer of polyethylene

The effect of y-irradiation on slow crack growth (SCG) in a medium density polyethylene (MDPE) was measured and compared with behavior of high density polyethylene (HDPE) and a recrystallized HDPE (RCHDPE). The three materials exhibited the same dependence on dose up to 3 Mrd. The HDPE became brittle above 50 Mrd. The resistance to SCG of MDPE and RCHDPE increased very rapidly with dose above 3 Mrd, until at 50-80 Mrd their resistance to SCG became extraordinarily high. This high resistance to SCG was accompanied by a transition from crazing to shear deformation at the root of a notch. It was found that for the same concentration, crosslinks are more effective than short chain branches for increasing resistance to SCG.