Structural Evolution of UHMWPE Fibers during Poststretching with Distinct Initial Structures

By adopting a homemade extension apparatus and wide-angle X-ray diffraction(WAXD)technique,the structural evolutions of the extracted ultra-high molecular weight polyethylene(UHMWPE)fibers with different spinning draw ratios were investigated during the poststretching process.Molecular chains oriented along the axis quickly at the early stage of drawing,which is quite different from the situation of drawing with solvents.The crystal regions,which have not melted at higher temperature,show stronger rigidity in the absence of solvents.Rigid characteristics show faster response to the external field.Also,the surface morphologies of fibers after poststretching are characterized by scanning electron microscopy(SEM).The lamellae stack disordered before stretching,but arranged in order along the draw direction when the draw ratios were larger than 1.

Dissolving of Ultra‑high Molecular Weight Polyethylene Assisted Through Supercritical Carbon Dioxide to Enhance the Mechanical Properties of Fibers

The molecular weight of ultra-high molecular weight polyethylene(UHMWPE)fbers is severely decreased compared with raw materials due to high temperature and strong shearing in the dissolving process.In this study,we reported a novel method to assist the dissolving of UHMWPE in parafn oil without severe degradation in order to improve the tensile strength of resultant fbers.UHMWPE fbers with relatively high molecular weight and more excellent disentanglement efect were prepared by gel-spinning with UHMWPE suspension treated with supercritical carbon dioxide(SC-CO_(2)).The dynamic thermomechanical,mechanical and crystalline properties of UHMWPE extracted fbers and drawn fbers were researched comprehensively.UHMWPE extracted fbers obtained after SC-CO_(2) treatment display a higher molecular weight.More importantly,it is clear that the disentanglement of UHMWPE gel fbers gained by processing SC-CO_(2) has been signifcantly promoted compared with that without SC-CO_(2) treatment from dynamic thermomechanical and rheological results,which could also be demonstrated from the cross-sectional morphology of UHMWPE extracted fbers.Furthermore,the tensile strength of UHMWPE fbers prepared through SC-CO_(2) treating is able to attain 30.11 cN/dtex,increased by 10.3%in comparison to UHMWPE fbers gained without assistance of SC-CO_(2).Beyond that,the thermal behavior and crystallization performance of UHMWPE extracted fbers and drawn fbers acquired by way of SC-CO_(2) treatment have also been enhanced.