Study On Gel-Spinning Properties Of Ultra-High Molecular Weight Polyethylene Resin

Ultra-high molecular weight polyethylene (UHMWPE) is a kind of thermoplastic resin with linear structure and it has plenty of excellent performance. Foreign manufacturers of UHMWPE fiber hold complete technology from fiber-used resin developing to fiber processing. However, domestic UHMWPE resin and UHMWPE fiber are made from different manufacturers, and the corresponding relationships between UHMWPE resin, gel-spinning process and fiber properties are not clear. In this thesis, four kinds of UHMWPE resin (A, B, C and D) are studied in details, with measurements on their physical properties and dissolving properties. Different UHMWPE fibers are prepared by dissolving, gel-spinning, extracting, drying and ultrahigh drawing. The relationships between UHMWPE resins and fibers are investigated with varies of measurements. The results as below:The physical property of four kinds of UHMWPE resin had the following characteristics:the intrinsic viscosity was 20-26, the average particle size was from 150 to 180 microns, the 80% of particle was between 60 and 100 mesh (150-420μm), the particle size distribution width (D90-D10)/D50<1.5, the yield strength≥20MPa, tensile strength≥29MPa, elastic modulus≥690MPa and elongation at break≥290%. The SEM photos of four different resins showed that particle surface of A and C resins holded comminuted structure, and the particle surface of B and D resins was the ravine structure. Crystallizing property of four different resins was analyzed, the results showed that the crystallinity of A was the maximum, the crystallinity of D was the minimum, and the crystallinity of B and C were in the middle.The preparation of uniform UHMWPE solution was the chief task of gel-spinning. The preparation of UHMWPE solution included swelling and dissolving of UHMWPE resins. The swelling effect was judged by the optimum swelling temperature and swelling ratio of the resin. Experimental results showed that the optimum swelling temperature of four resins was all at about 134℃. With the increasing of slurry concentration, swelling ratio of UHMWPE gradually decreased. In order to meet the industrialized production, the UHMWPE concentration was chosen as 10%. The swelling effect of UHMWPE became better when prolonging the swelling time, and the swelling ratio tended to a balanced value when the swelling time reached 20 minutes. The particle size distribution and the molecular weight distribution of resins was important parameters to influence the swelling ratio. As the molecular weight of UHMWPE resin increased, the swelling ratio decreased. When the molecular weight distribution of resin was narrow, the swelling effect was good, and the UHMWPE resin could be fully swollen and dissolved when particle size distribution was small. Spinnability was a complex concept, in this thesis, spinnability was characterized by the freely broken height of UHMWPE solution after extruded from twin-screw extruder in the gel-spinning process. The results showed when the freely broken height was above 6cm, the spinnability of UHMWPEwas good.During gel-spinning process of four different resins, UHMWPE gel fiber could be produced when the solution concentration was 8wt%, the spinning temperature was 240-290℃and the screw rotating speed was 5.6r/min. After extracted and dried, UHMWPE fibers were drawn by three-step stretch process. The optimal drawing temperatures for the first-step, the second-step and the third-step were 80℃,100℃and 110℃, respectively.By means of universal tensile testing machine, DSC, WAXD, SEM, sonic velocity method, the mechanical, thermal and crystallizing properties, the morphological structure and the orientation of UHMWPE fibers were measured and analyzed. The results showed that the tensile strength and modulus of four kinds UHMWPE fibers can reach 30-32cN/dtex and 730-940cN/dtex, respectively. As the drawing ratio of fibers increased, the thermal properties and crystallinity of UHMWPE fibers increased, and the crystallinity of A fiber and D fiber were both higher than that of B fiber and C fiber. The SEM results of four gel fibers showed that the fiber surface was rough, many flakes arrange layer upon layer, fiber cross section showed entangled network structure, and the network of A fiber and D fiber were much denser than that of B fiber and C fiber. With the increasing of draw ratio, fiber orientation got better, and the orientation factor of A fiber and D fiber was higher than that of B fiber and C fiber.