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

High-density polyethylene (HDPE) and low-density polyethylene (LDPE) were i rradiated in vacuo at 30-220 and 30-360 degrees C, respectively, with gamma -rays at doses of 10-400 kGy. Temperature dependence of cross-linking and g as evolution was investigated. It was found that cross-linking was the pred ominant process up to 300 degrees C and the gel point decreased smoothly wi th temperature. The increase of G(x) with temperature was likely attributed to the temperature effect on addition of radicals to the double bonds pres ent in the polymer. Above 300 degrees C, the gel fraction at a given dose d ecreased remarkably with temperature and turned to zero at 360 degrees C. T he molecular weight variation determined with gel permeation chromatography (GPC) indicated the enhanced degradation at 360 degrees C by radiation. G- values of H-2 increased with temperature and varied with dose. The composit ions of the C-1-C-4 hydrocarbons evolved depended on the structures of side branches. Raising the temperature favored the formation of unsaturated hyd rocarbons, and the yield of unsaturated relative to saturated hydrocarbons decreased with dose. (C) 1999 John Wiley & Sons, Inc.