New Relaxation Phenomena in Linear Polyethylene at Cryogenic Temperatures

Abstract

The internal friction of linear high-density polyethylene (LPE) at cryogenic temperatures was investigated using an inverted free-oscillating torsion pendulum (1–3 Hz). The results show that LPE is not viscoelastically inactive below its γ peak as had been previously contended. Two new relaxation peaks, δ at 48 °K and ε at 20 °K, were observed. The characteristics of these loss maxima are identical to those of the cryogenic relaxations observed for polyethylene terephthalate and polyoxymethylene. A mechanism consisting of the motions of dislocation jogs and their interactions with specific conformational kink defects is proposed. This mechanism is consistent with all the experimental data in that it accounts for the effects of orientation and thermal histories on the relaxation strength of the δ and ε internal-friction peaks.