Effect of initial crystallinity on the response of high-density polyethylene to high-energy radiation

Samples of each of two high-density polyethylenes with various initial degr ees of crystallinity, but otherwise identical, were exposed under a vacuum to moderate doses of gamma irradiation. The results indicate that, for othe rwise initially identical polymer samples, the dose required to reach the g el point increases with increase of the initial degree of crystallinity. Ab ove the critical dose for gelation, the gel content decreases with higher d egrees of crystallinity at equal radiation doses. The mechanical behavior o f the polymers changed progressively from ductile to brittle as the crystal linity was increased. The extensibility of originally ductile samples decre ases with increasing radiation dose. The irradiation of samples having inte rmediate behavior produces a change to ductile behavior. Mechanical behavio r is not modified substantially when brittle samples are irradiated. The in itial modulus is little altered by irradiation, while the yield stress show s a slight increase with irradiation. The mechanical properties, such as dr aw ratio at break and ultimate tensile stress, decrease with dose in ductil e samples. (C) 1999 John Wiley & Sons, Inc.