Dynamic Change in Entanglement State of Entangled Polyethylene Melts Induced by Cyclic Deformation

In this study, the change in the entanglement state of entangled polyethylene (PE) melts was induced by cyclic deformation, i.e., a continuous orientation–relaxation process. The change in density fluctuation during the cyclic deformation process of ultrahigh-molecular-weight linear low-density PE (UHMW-LLDPE) melts was evaluated using in situ small-angle X-ray scattering (SAXS) measurements. Significant differences in scattering anisotropy were observed between the UHMW-LLDPE films polymerized using metallocene and Ziegler catalyst systems. For the metallocene film, the density fluctuation developed gradually in the deformation direction and was maintained via orientation/relaxation during the cyclic deformation. In contrast, for the Ziegler film, which contained a large amount of loosely entangled chains with higher mobility, the density fluctuation rapidly increased and stabilized. The scattering was constantly isotropic, and the isotropic scattering was maintained throughout the cyclic deformation. Thus, cyclic deformation stabilized the molecular entanglement of entangled PE melts based on the intrinsic relaxation time of each entanglement.