The effect of different doses of γ-irradiation on the mechanical and
relaxation properties of High Density Polyethylene (HDPE) and Low Density
Polyethylene (LDPE) were studied. It was found that HDPE is more susceptible
than LDPE to the influence of radiation. Recognizable differences are observed
for all parameters between the unirradiated and irradiated cross-linked
polyethylene. Existence of a relaxation mechanism within the first 200 s is
reported. The shear modulus for all samples is also obtained and discussed.
These data are used to calculate the strain energy density using the equation
proposed by Blatz et al (1974 Trans. Soc. Rheol. 18 145-61), based on the
n-measure of Sethe. It was found that the n-measure is still a material constant
for both types and independent of γ-irradiation dose.