Variation of size, numerical concentration and size distribution of free volume of heat shrink polyethylene prepared by electron irradiation cross-linkage with temperature probed by positron annihilation technique

Variations of free volumes of cross-linked heat shrink low density polyethylene, prepared by the electron beam irradiation, in terms of temperature are studied through the analysis of positron annihilation parameters, such as S parameter, mean lifetime, lifetime and intensity of pick-off reaction of ortho-positronium (o-Ps), and a size distribution of free volume. Recognizable differences are observed for all parameters between the unirradiated and irradiation cross-linked polyethylene. Differences of parameters are also observed for the expanded poly ethylene before and after the thermal treatments for shrinkage. Recognizable differences of free volumes as a function of temperature are not observed in all parameters between the calcium carbonate unfilled and filled heat shrink polyethylenes. (C) 1999 Elsevier Science Ltd. All rights reserved.