Molecular weight dependence on the morphological properties of polyethylene gels

Abstract

Polyethylene gels were prepared by gelation/crystallization from dilute decalin solutions using five kinds of polyethylenes with different molecular weights and degrees of branching. The decalin was allowed to evaporate from the gels under ambient condition in order to prepare dry gels. The dry gel of ultra-high molecular weight polyethylene (UHMWP) of Mw=6×106 forms a film but the other low molecular weight polyethylenes (LMWP) with molecular weight lower than 3×105 do not form a film. In order to investigate such a difference, the morphological properties of five kinds of dry gels were investigated by scanning electron microscopy, polarized microscopy, small angle light scattering, and small angle X-ray scattering. Within LMWP dry gels, observation reveals spherulitic textures whose crystal lamellae are rotated around a radial direction. In contrast, within the dry gels of UHMWP, there exists rodlike textures as assemblies of large lamellar crystals which are highly oriented with their flat faces parallel to the film surface. To assure ultradrawing up to consistently high draw ratio, a suitable number of entanglements should be formed by tie molecules which connect the crystal lamellae. © 1986 The Society of Polymer Science, Japan.