Temperature dependence of radiation effects in polyethylene: Cross-linking and gas evolution

Abstract

High-density polyethylene (HDPE) and low-density polyethylene (LDPE) were irradiated in vacuo at 30–220 and 30–360°C, respectively, with γ-rays at doses of 10–400 kGy. Temperature dependence of cross-linking and gas evolution was investigated. It was found that cross-linking was the predominant process up to 300°C and the gel point decreased smoothly with temperature. The increase of G(x) with temperature was likely attributed to the temperature effect on addition of radicals to the double bonds present in the polymer. Above 300°C, the gel fraction at a given dose decreased remarkably with temperature and turned to zero at 360°C. The molecular weight variation determined with gel permeation chromatography (GPC) indicated the enhanced degradation at 360°C by radiation. G-values of H2 increased with temperature and varied with dose. The compositions of the C1–C4 hydrocarbons evolved depended on the structures of side branches. Raising the temperature favored the formation of unsaturated hydrocarbons, and the yield of unsaturated relative to saturated hydrocarbons decreased with dose. © 1999 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 37: 1541–1548, 1999