THE EFFECT OF MOLECULAR-STRUCTURE AND POLYMER MORPHOLOGY ON THE FRACTURE-RESISTANCE OF HIGH-DENSITY POLYETHYLENE

The fracture resistance of a range of polyethylenes was examined. The tearing modulus, T, was used as a measure of the resistance of the polymer to crack propagation. The values of the tearing modulus were calculated from the gradient of the J-integral versus crack extension lines, J(DELTA-a). Strain rates in the range from 10(-7) s-1 to 0.1 s-1 were tested. The strain rate dependency of crack initiation and crack propagation have been correlated with the composition and morphology of the polymers. The thickness of the lamellae, side chain concentration and degree of order in the crystalline regions have been shown to influence the resistance of the polymer to crack initiation, J(c)(e). The tearing modulus appears to be influenced mainly by changes to the morphology that are due to short side chain branches.