Dielectric relaxations of high and low density irradiated polyethylenes

A systematic study of dielectric spectrum on a series of high and low density commercial polyethylenes has been performed. Every polyethylene was characterized by determination of molecular weight distribution, the number of functional groups: ketone, aldehyde, vinyl, vinylidene, trans-vinylene, the fraction crystalline, and the degree of branching. We have observed that both γ and α dielectric relaxations zones are formed by two overlap relaxations which have been labeled γ_II, γ_I, and α′, and α respectively, in order of increasing temperatures. The intensity of the dielectric spectrum of all polyethylene depends over and above other parameters on the number of the carbonyl groups formed as a result of irradiation. This number is different for every polyethylene even when they receive the same dose of irradiation (20 Mrad). However, the participation of carbonyl groups in the γ_I and α′ dielectric relaxations decreases with the total crystalline content of each polyethylene. The α dielectric relaxation position in the temperature axis is governed by the most probable crystallite thickness.