Oriented crystalline structure in melt-drawn ultrahigh-molecular-weight polyethylene induced by entanglement networks

In this study, we focused on the unique structure with oblique periodicity formed by the melt-drawing of metallocene-catalyzed ultrahigh-molecular-weight polyethylene (UHMW-PE) to clarify the relationship between tight entanglements that cannot be disentangled during melt-drawing and the formation of the periodic structure. In situ X-ray measurements during the heating of the melt-drawn UHMW-PE film revealed that the disappearance of the characteristic oblique streaks that appeared tilted from the drawing direction and the orthorhombic-to-hexagonal phase transition occurred simultaneously, suggesting that the change in the tension state of extended-chain crystals due to the orthorhombic-to-hexagonal phase transition and the disappearance of order in the structure resulting in oblique streaks are related behaviors. This indicates the presence of the network structure including oriented amorphous chains in which molecular chains are fixed by tight entanglements in metallocene-catalyzed UHMW-PE melt-drawn film.