Relaxation Dynamics in Disentangled Ultrahigh Molecular Weight Polyethylene via Torsional Rheology

The relaxation dynamics of disentangled ultrahigh molecular weight polyethylene (UHMWPE) were analyzed by means of torsional rheology in a broad frequency and temperature range. The disentangled specimens were compression-molded at two different temperatures, solid state (125 °C) and melt state (160 °C), and the latter was compared with a melt-state-processed commercial UHMWPE specimen. Three different relaxation processes were observed, namely, α_c-, β-, and γ-relaxations, as expected for polyethylene. The relaxation strengths of the α_c- and γ-relaxations were found to be dependent on the crystallinity content, verified by means of differential scanning calorimetry. The relaxation molecular dynamics of the γ-relaxation in the solid-state-compressed disentangled sample follows a Vogel–Fulcher–Tammann–Hesse trend, suggesting a dynamic glass-to-rubber transition. The same trend is not found for the γ-relaxation of both melt-state-processed samples, thus suggesting a role of crystalline polydispersity and entanglement density in the free volume of the amorphous segments.