Study of fine structure of viscoelastic crystalline absorption in polyethylene single crystals

Abstract

Viscoelastic measurements were made on polyethylene single crystals prepared from dilute solution under isothermal crystallization conditions and on annealed crystals of the same samples. As the long period of the isothermally crystallized samples increases, both the absorption temperature and the intensity of the crystalline absorption (α_c) also increase. On the other hand, thickening of single crystals by annealing causes the intensity of the absorption to decrease, whereas the absorption temperature shifts to higher values. These findings are interpreted in terms of the introduction of defect regions into the crystalline phase by annealing. The socalled crystalline absorption is further classified into four separate mechanisms. A peak characteristic of the annealed samples (α_c) is found at the lowest temperature of the crystalline dispersion region. A second peak (α_f) is found in both the isothermally crystallized samples and the annealed ones. A third peak (α_m) appears to consist of three separate peaks and is associated with permanent structural change. A fourth peak (α_m) is measurable only in γ- irradiated crystals and is concerned with the final melting of crystals. The nature of the relaxation mechanisms of each absorption is discussed.