Preparation And Properties Of High Molecular Weight Polyethylene Fibers By Melt Spinning

Ultra high molecular weight polyethylene(UHMWPE)fiber which has many excellent properties such as high strength,high modulus,low density and high flexibility,is one of high-performance fibers.It has been widely used in the field of aerospace,military industry,safety protection,fishery,cord,and sports etc.UHMWPE fibers are usually prepared by gel spinning and plasticized spinning method.However,gel spinning method has some disadvantages of long process flow,high cost and environmental pollution.The residual waxy plasticzer affects mechanical properties of fiber by plasticized spinning method.The coarse fibers cannot be prepared by above two methods.It is expected that HMWPE will be melt-spun into coarse denier fibers with high strengtb in this thesis.HMWPE was blended with medium molecular weight polyethylene which was used for improving flowability of HMWPE and then the blend was melt-spun into coarse denier fiber.Their structure and properties were characterized.To increase the flowability of HMWPE,HMWPE was blended with high density PE(HDPE),low density PE(LDPE)or linear low density PE(LLDPE)respectively with a small amount of PE wax,CaSt2 and antioxidant 1010.It showed that melt fracture happened in the blend of HMWPE and LDPE or LLDPE,and it was difficult to pelletize them into chips.However,the bland of HDPE and HMWPE indicated better compatibility.Therefore,HDPE was chosen as main modifier in this thesis.FTIR,DSC,XRD,POM and melt index instrument were used to characterize structure and properties of modified HMWPE.The results showed that there was no changes in the chemical structure after modification.HMWPE was compatible with HDPE while crystallinity decreased a little.The subcrystalline size of modified HMWPE was smaller than the pure HMWPE.The melt index of modified HMWPE had a great improve which indicated that flowability increased.Melt index instrument was used to measure the rheological behavior and it turned out that non-Newtonian index increased firstly and then decreased with increased temperature while viscous flow activation energy decreased as load increased.Non-isothermal crystallization kinetics of raw and modified HMWPE could be described by Mo method while Avrami and Ozawa methods were not suitable.It showed that crystallization rate decreased due to modifier and the crystallization capability weakened because of the decreased crystallization activation energy.The modified HMWPE was made into as-spun fiber at temperature of between 265? and 275? and pressure reached 20MPa.The mechanical properties of fibers which were hot-stretched at different temperatures or stretch ratio were measured.The structure and properties of HMWPE fibers were analyzed by SEM,XRD and universal testing instrument.The results demostrated that the pure HMWPE could not be melt-spun into fibers while modified HMWPE could be melt-spun due to the increase of flowability.Fibers prepared by melt spinning had compact structure and the crystallinity of fibers was higher than modified HMWPE resin.The strength increased at first,then decreased with the increase of stretching temperature which had an optimum temperature of 100? and elongation at break decreased with increased temperature.The strength increased and elongation at break decreased with increased stretching ratio which had an optimum stretching ratio of 5.9.When stretching ratio of 5.9 and temperature of 100?,the tensile strength of HMWPE fiber could reach 9.6 cN/dtex with elongation at break of 6.8%.In general,the HMWPE coarse denier fibers were melt-spun successfully.This method had advantages of simple process,environment friendly,improvement of production efficiency and low production cost.