Slow fracture in a homopolymer and copolymer of polyethylene

Abstract

The slow crack-growth behaviours of a high-density polyethylene and an ethylene-hexene copolymer with 4.5 butyl chains per 1000 carbon atoms are compared. The slow crack-growth rate in the copolymer is about 10² to 10³ times slower than for the homopolymer. The two polymers are compared with respect to their kinetics of slow crack growth, the morphology of the damage zone that grows from a notch, the stress-strain behaviour and the temperature dependence of the rate of damage. The results suggest that the major effect of the butyl branches is to decrease the rate of disentanglement which governs the process of slow crack growth.