In-situ analysis for melt-drawing behavior of ultra-high molecular weight polyethylene / normal molecular weight polyethylene blend films

Abstract

Blend films composed of ultrahigh molecular weight polyethylene (UHMW-PE) and normal molecular weight polyethylene (NMW-PE) with various ratios were prepared. Structural development during melt-drawing at 150 °C for these blend films were analyzed by using in-situ measurement combined with stress-strain curve and wide-angle X-ray diffraction (WAXD). With increasing NMW-PE composition, the stress value on the plateau-stress region decreases, and the slope of stress hardening due to subsequent oriented crystallization becomes gentler. Correspondingly, the in-situ measurement results clarified that blending NMW-PE restricts amorphous orientation during melt-drawing, and delays the appearance of the orthorhombic reflections. Additionally, the hexagonal crystallization, which is characteristic of melt-drawing of pure UHMW-PE, was unrecognizable for blend films. These results indicate that blending NMW-PE reduces the amount of molecular entanglements under molten state and accelerates disentanglement during melt-drawing. During cooling after such melt-drawing for blend films, arc-shaped orthorhombic reflections spreading along azimuthal direction newly appear. Morphological observation of the resultant melt-drawn films suggests that blending NMW-PE induces thin formation of the extended crystal chain (ECC), thus subsequent epitaxial crystallization of folded crystal chains (FCC) during cooling gives the homogeneous lamellae structure arranged perpendicular to drawing direction.