Study On The Melt Spinning Of High Density Polyethylene Modified Ultra-high Molecular Weight Polyethylene

Ultra-high molecular weight polyethylene(UHMWPE)fibers are widely used in various applications because of their excellent performance.At present,the main industrial method for preparing high-strength and high-modulus UHMWPE fibers is gel spinning.However,the gel spinning method has the disadvantages of low yield,environmental pollution,complicated processing and high cost.Melt spinning method can overcome the above shortcomings of the gel spinning method and become the main method for producing low molecular weight polymer fibers such as polyester(PET)and polypropylene(PP).Due to the extremely long molecular chain,UHMWPE is still in the high-elastic state after melting.In the UHMWPE melt spinning processing,there would be too much pressure on the extruder and melt fracture phenomenon would occur on the as-spun filament surface,leading to the failure of the fiber preparation.The main research efforts are summarized as follows:1.According to the processing characteristics of UHMWPE/HDPE blend materials,POLYFLOW software was used to simulate the flow state of blended melt in the guide hole and micro hole of the spinneret.The strain field,velocity field and stress field of the melt under different inlet angle,different aspect ratio and different micro hole diameter were calculated.The parameters of the spinneret of the experimental platform were designed and optimized according to the simulation results.2.The microstructure of the as-spun filaments and fibers prepared with different process parameters(including the flowability of HDPE,mass ratio of UHMWPE and HDPE,formation temperature and draw ratio)was investigated.The influence mechanism of process parameters on the lamellar crystal structure of the as-spun filaments and on the microfibrillar crystal structure of fibers was analyzed.The crystal form of the as-spun filaments and fibers prepared at different process parameters was obtained.The influence of the process parameters on the mechanical properties of the fibers was disclosed.3.The orienting process that the molecular chains induced by flow shear effect and the process that folded chains grew epitaxial on the oriented chains were investigated.The evolution process that the molecular chains were stretched and the lamellar structure was destroyed,melt and reorganized of the as-spun filaments during the drawing process was revealed.The mechanism that the mechanical properties were improved as the microstructure of the fibers was optimized was analyzed.4.The difference of the microstructure and mechanical properties of the UHMWPE/HDPE blend fibers and UHMWPE fibers prepared by melt spinning was obtained.In the blending system,the enhancement effect of the shorter molecular chains of HDPE in the molecular chains orienting process of UHMWPE was revealed.The optimization function of HDPE on the crystal structure evolution of the UHMWPE/HDPE as-spun filaments and fibers was disclosed.