Preparation And Structural Performance Research In High Density Polyethylene/ultra-high Molecular Weight Polyethylene Fiber

Ultra-high molecular weight polyethylene(UHMWPE)fiber has the highest tensile strength and modulus in chemical fiber,which makes it widely used in aerospace,military and other fields.However,the high melt viscosity and surface inertia of UHMWPE make it difficult to process through traditional extrusion.And it also cannot be modified by other polymers and additives.High density polyethylene(HDPE)has good mechanical properties and thermal fluidity,and it is better for integration with UHMWPE surface.Therefore,this article adopted HDPE to modify UHMWPE,and prepared HDPE/UHMWPE composite fibers through the gel spinning-ultra drawing process.The tensile test,wide angle X-ray diffraction(WAXD),small angle X-ray scattering(SAXS)and scanning electron microscope(SEM)were characterized to explores the effect of UHMWPE content,the modification methods,the cold and hot drawing process on the performance and structure of composite fibers.Firstly,HDPE/UHMWPE composite was prepared by solution blending,and gel spinning was performed.When the addition of HDPE is less than 50wt%,the fracture strength of the composite fiber reaches 17.9 cN/dtex,meets the requirements of high performance fiber.The increase of UHMWPE content is beneficial to the growth of the orthogonal crystal on(110)and(200)crystal surface,and also improves the orientation of the fibers.The SAXS test results showed that the increase of UHMWPE had no effect on the length of shish,but it had a positive effect on improving the orientation of shish.And when the content of UHMWPE increased to a certain extent,kebab structure began to gather with shish.Secondly,the bimodal HDPE/UHMWPE alloy fibers were prepared.It has higher fracture strength and better drawing effectiveness than solution blending composite fibers.Compared with the solution blending composite fibers,the HDPE/UHMWPE alloy fibers tend to form smaller and more microcrystalline structures,and it had longer shish and smaller kebab structure.The properties and structure benefits of the alloy fibers obtained by drawing were larger,which is more suitable for the gel spinning process.Finally,the research on the cold and hot drawing process of the alloy fibers revealed that a certain degree of cold drawing made the diameter of the fibers smaller,so the radial transmit of heat and mass was more even and has a promoting effect on the strength improvement of composite fibers.However,the excessive cold drawing ratio destroyed the inner crystalline structure of the fiber.Multistage hot drawing process makes the fracture strength of composite fibers increased significantly.The average length and orientation of shish have been improved after two stage hot drawing,but the secondary drawing conditions have little influence on shish.The improvement of secondary drawing temperature made the crystallization more perfect,and increased the long period and lateral dimension of kebab.The increase of secondary drawing ratio prompted the structure transformation of kebab,so its lateral dimension has decreased.