Glass-transition-temperature depression in chemically crosslinked low-density polyethylene and high-density polyethylene and their blends with ethylene vinyl acetate copolymer

A reduction in the glass-transition temperature (T-g) was found for polyolefins chemically crosslinked by peroxide. This tendency, which was observed for low-density and high-density polyethylenes, was also validated for their blends with Ethylene Vinyl Acetate copolymer. It is proposed that the constrained crystallization process, as a result of a restriction imposed on the chain packing by the chemical crosslinks, results in an increasing net free volume in the amorphous phase and hence reduces T-g. The T-g depression becomes greater with increasing crosslink density, whereas at the same time, the degree of crystallinity and consequently the density of the system decreases with an increase in the peroxide content. (c) 2007 Wiley Periodicals, Inc.