The Structure And Properties Of Ultra-high Molecular Weight Polyethylene Fibers With Enhanced Abrasion Resistance

Ultra-high molecular weight polyethylene(UHMWPE)fibers have the highest specific strength among 3 kinds of high-performance fibers.Due to the performances of good weather resistance,chemical resistance,low temperature resistance,excellent abrasion resistance,bending resistance,cutting resistance,impact resistance,low electrical conductivity and etc.,UHMWPE fibers have been widely used in the fields of aerospace,defense and military,marine engineering,fishery breeding,sports and etc.The national defense industry has occupied the main consuming market of UHMWPE fibers for a long time.But the consumption of UHMWPE fibers gradually increased in civil and industrial fields in recent years because of expanding application of UHMWPE fibers.Notably,the consumptions share of UHMWPE fibers that were used in ropes has been higher than 30%.When UHMWPE ropes rub with high hardness materials such as metal and non-metallic ceramic particles,there is a sanding phenomenon that occurs on the ropes surface because of their low surface hardness,poor molecular interforce and uneven stress applied on every filament.Which greatly influence the service life of UHMWPE ropes.It's necessary to modify UHMWPE fibers to improve their abrasion resistance.The defects in UHMWPE fiber when the UHMWPE fibers were modified using the method of blending modification or chemical surface modification,much defects will be introduced into UHMWPE fibers.According to the theory of high strength high modulus fiber models,the tensile strength of UHMWPE fiber greatly decreases as the defects content increases.However,the smaller diameter of commercial UHMWPE fibers restricts the added content of modifier in UHMWPE fibers,thus the abrasion resistance of fibers cannot be improved by improving the added content of modifier.Hence,how to balance the relationship between fiber's abrasion resistance and tensile strength has become an urgent problem nowadays.Based on above analysis,large diameter high strength UHMWPE fibers are much suitable for preparing high strength ropes,thus these fibers were prepared using high concentration gel spinning with optimized spinning technology.Based on the UHMWPE fibers prepared with high concentration gel spinning,the correlation between the fiber's structure and their abrasion resistance was investigated to analyze the reasons of their poor abrasion resistance.With the help of scanning electronic microscope(SEM),the evolution process of UHMWPE fiber abrasion fracture was observed and several characteristics about abrasion procedure of UHMWPE fibers were summarized.According to the characteristics of UHMWPE fibers abrasion fracture,a series of modification solutions were proposed to improve the abrasion resistance of UHMWPE fibers.Firstly,the wear resistance of the UHMWPE fiber was enhanced by modified graphite oxide(m-GO)because m-GO was beneficial to the formation of smooth transfer film in the process of friction.Secondly,the UHMWPE fiber was treated by?-aminopropyl triethoxysilane(?-ATPS)and graphite oxide(GO)to construct a layer on the surface of the UHMWPE fiber.The abrasion resistance performance of UHMWPE fiber was significantly enhanced.Finally,according to the poor molecular interforce and the advantage of abrasion resistance layer,the UHMWPE fiber was treated by dibenzoyl peroxide(BPO)and vinyltrimethoxysilane(VTMS)to achieve crosslinking modification.Finally,a layer of fluoride coating with low friction coefficient was generated on the surface of the crosslinking UHMWPE fiber after it was treated by 1H,1H,2H,2H-perfluorodecyltriethoxysilane(PFDTES).The results and analysis of this thesis provide a guideline to prepare UHMWPE fiber with high tensile strength and excellent abrasion resistance.The main research contents and conclusions of this thesis were summarized as follow.(1)The preparation and structural performance of high titre UHMWPE fibersBased on the optimized wet technology of UHMWPE gel spinning,the UHMWPE fibers were prepared using different concentration UHMWPE suspension.The results indicated that UHMWPE gel fiber with high concentration of gel-spun solution although had low solvent separation ratio,had high UHMWPE content that greatly decreases the consumption of extractant and decreased the production cost.In the process of extracting and drying,the UHMWPE gel fibers had axis shrinkage and transverse shrinkage due to the continue interface variation of UHMWPE gel fibers and regular stacking of UHMWPE chains under interface stress.By limiting the axial shrinkage of UHMWPE gel fiber in the process of extracting and drying,the structure of the obtained UHMWPE extracted fiber was conducive to the draw stress dispersion in the hot stretch.It is easy to prepare high tensile strength UHMWPE fiber by this treatment.The UHMWPE monofilament prepared by high concentration gel-spun solution has high titre(>32 dtex).When the concentration of gel spinning solution increased by 2%,the tensile strength of UHMWPE fiber only decreased by 1?2 c N·dtex^-1.The decrease range of tensile strength was relatively small.The obtained UHMWPE fibers were conducive to the preparation of UHMWPE rope and had potential value for industrialization and application.(2)The investigation on the abrasion mechanism of UHMWPE fibers with different gel-spinning concentrationBased the studies about the structure and properties of UHMWPE fiber with different concentration of gel spinning solution,the correlation between the tensile strength and abrasion resistance performance of UHMWPE fiber was investigated.The results revealed that there was high correlation between the abrasion resistance and the titre,crystallinity,melting temperature,molecular weight and sonic orientation of UHMWPE fiber.The order of correlation coefficient is crystallinity>titre>melting temperature>molecular weight>sonic orientation.Except for titre,the other structural paraments are negatively correlated with the abrasion resistance of UHMWPE fiber.The main reasons for this result lie in the facts as follow.The UHMWPE fiber with high titre had high break force and can support the loading for long time in the abrasion process.The UHMWPE fiber with high crystallinity and melting temperature is not conducive to the rapid formation of smooth transfer film on the surface of counterface,which reduce the self-lubrication effect of UHMWPE fiber.The decreasing molecular weight caused easy damage for the surface of UHMWPE fiber and simultaneously enhanced the adhesive abrasion(self-lubrication).The UHMWPE fiber with high sound velocity orientation was difficult to prevent the propagation of cracks on its surface due to poor intermolecular force and the abrasion area was expanded on the surface of UHMWPE fiber in a short time.The main abrasion mechanisms were adhesive wear,abrasive wear and fatigue wear.The abrasive wear and fatigue wear were related to the spinning solution concentration.The abrasive wear morphologies can be easily observed on the abrasion section surface of the UHMWPE fiber with low spinning solution concentration and the fatigue wear morphologies can be easily observed on the abrasion section surface of the UHMWPE fiber with high spinning solution concentration.(3)The enhanced abrasion resistance of UHMWPE fibers by modified graphite(m-GO)After oxidation treatment for graphite,the obtained GO was modified by hexadecylamine to prepare m-GO with graft ratio of 23.38%.Due to well dispersion in dichloromethane,m-GO was well dispersed in the UHMWPE suspension with the help of dichloromethane.Then,the modified UHMWPE fibers were prepared using gel spinning technology.The results indicated that m-GO shows excellent lubrication performance due to its large layer distance.Due to the excellent lubrication performance of m-GO,the smooth transfer film of modified UHMWPE fibers can be rapidly formed to reduce the wear rate.Compared with the pure UHMWPE fiber with gel-spun solution concentration of 10%,the tensile strength of the modified UHMWPE fiber was 29.98c N·dtex^-1 increasing by 4.46%when the m-GO content was 1.5%.Besides,the maximum friction number(N_f)and abrasion resistance index K(the ratio of N_f and titre)of the modified UHMWPE fiber increased by 55.46%and 28%respectively.(4)The preparation and structural performances of UHMWPE fiber coated by GOThe?-ATPS was dispersed in the UHMWPE extracted fibers using extraction modification technology and modified UHMWPE fibers were prepared after hot stretch process.Then,the GO coating was constructed using spray technology.Part of GO was grafted on the modified UHMWPE fiber surface due to the chemical reaction between GO and?-ATPS.The investigation results revealed that the UHMWPE fiber treated by high concentration of?-ATPS had high content of GO.UHMWPE fiber can be protected by GO coating in the friction behavior because the stripped GO was a part of transfer film and worked as a lubricant.When the concentration of?-ATPS was 1%and the GO suspension concentration was 5 g·L^-1,compared with the pure UHMWPE fiber with gel-spun solution concentration of 10%,the N_f and K of the modified UHMWPE fiber were more than 268.12%and 257.13%respectively.And the tensile strength of such fiber was 27.62 c N·dtex^-1,decreasing by 3.76%.(5)The preparation and structural performances of the crosslinking UHMWPE fibers coated by fluorideBy the extracting modification technology,the BPO and VTMS were dispersed in the UHMWPE extracted fiber with gel-spun solution concentration of 10%,and the crosslinking UHMWPE fibers were prepared after hot stretch process.The results indicated that the molecular interforce was enhanced by crosslinking modification,which was beneficial to transfer friction force and prevent the crack growth.When the VTMS concentration was 2%,the gel content of UHMWPE was 3.28%.Compared with the pure UHMWPE fiber with gel-spun solution concentration of 10%,the N_f and K of the above fiber increased by 189.82%and 204.04%.Interestingly,the tensile strength of such fiber decreased by only 0.52%.After grafted by fluoride coating,the coefficient of friction of crosslinking UHMWPE fibers were decreased.When the VTMS concentration and PFDTES concentration were 2%and 1%respectively,compared with pure UHMWPE fiber,the static friction coefficient and dynamic friction coefficient of modified UHMWPE fiber individually decreased by 12.41%and 11.68%.And the N_f and K of this fiber increased by 408.82%and 380.31%.The tensile strength of this fiber was 26.54 c N·dtex^-1,decreasing by 7.53%.In this thesis,the UHMWPE monofilament with high titre was prepared by high concentration gel spinning technology.Using the methods of filling modification,cross-linking modification and wear-resistant coating construction on the surface of UHMWPE fiber,the abrasion resistance of UHMWPE fiber can be significantly improved without affecting the excellent mechanical properties.