Study On Modification Of Carbon Fiber And Preparation And Properties Of Paper-based Friction Materials

The paper-based friction material has developed into an important friction material due to the stable dynamic friction coefficient,close dynamic/static friction coefficient ratio,low wear rate,smooth bonding performance,low production cost,long service life and the advantages of protecting dual materials.Carbon fiber,as the most commonly used reinforcing body in paper-based friction materials,has the advantages of friction resistance,high temperature resistance,good corrosion resistance,good fatigue resistance and no creep,Nevertheless,the surface of carbon fiber is smooth and the bonding force between the resin matrix is poor,which affects the application of carbon fiber.The purpose of this study was to increase the surface roughness of polyacrylonitrile?PAN?carbon fiber surface by functional modification,and to improve the surface activity.The modified carbon fiber paper-based friction material with superior mechanical properties and significant tribological properties was prepared by wet papermaking method.In this paper,the effects of carbon fiber length,the impregnation concentration of polyimide resin and phenolic resin,hot-pressing temperature and pressure on the physical properties of the precursor of paper-based friction materials were systematically investigated,and the optimum preparation process was to determined to produce the precursor of carbon fiber reinforced paper-based friction materials is obtained.The results showed that when the PAN-based carbon fiber length was 6mm and the polyimide resin with a impregnation concentration of 20%,the carbon fiber reinforced paper-based friction material had the best performance at hot pressing temperature of 240?,hot pressing pressure 15MPa and hot pressing time 5min,the paper tensile index is 25.3N·m/g,and the porosity is 43.3%.In order to enhance the surface properties of the fiber and improve the friction performance of the paper,the PAN-based carbon fiber was modified by triethoxyvinylsilane?VTEO,A151?and bis-??-triethoxysilylpropyl?-tetrasulfide?TESPT,Si69?.The effects of two coupling agents on mechanical properties and friction and wear properties of carbon fiber and its paper-based friction materials were studied.The results showed that Si69 and A151 increased the fiber roughness compared with the unmodified CF,and the A151-CF surface could increase the surface energy of the 37.3%,Si69-CF by 109.4%.Compared with the untreated CF reinforced paper-based friction material samples,under the fixed speed 2000r/min and 1.0MPa braking pressure,the dynamic friction coefficient of Si69 modified CF reinforced paper-based friction material is the most stable,the dynamic/static friction coefficient ratio is 0.961,and the wear rate is 1.8×10^-8·cm^-3·J^-1,decrease by 18.2%,Si69-CF reinforced paper-based friction material has a relatively best tribological performance.In order to further enhance the friction performance of the material and reduce the wear rate,the TESPT-SiO₂ nanoparticles were first modified by SiO₂ nanoparticles,and then a gentle and simple impregnation method was used to introduce TESPT-SiO₂ nanoparticles on the surface of carbon fiber,forming a layered interface structure of carbon fiber/resin composites.The surface energy and wettability of fiber increased obviously with the increase of TESPT-SiO₂ grafting density,the surface energy?of 1.0wt%TESPT-SiO₂-CF was 103.34mN·m^-1,the polar parts of surface energy₁was 61.28 mN·m^-1,and the dispersive parts of surface energy₁⁽?9? was 42.06mN·m^-1.The ILSS and IFSS of the composites were highly dependent on the graft density of TESPT-SiO₂ on the CF.Compared with the untreated CF composites,the TESPT-SiO₂-CF composites with 1.0wt%TESPT-SiO₂ increased 35.14%and 71.25%respectively,the mechanical properties of the composites increased obviously.The tensile strength of fiber monofilament is slightly increased,the tensile strength of 1.0wt%TESPT-SiO₂-CF was 5.34GPa,which increased by 0.38GPa compared with the tensile strength of unmodified CF.In TESPT-SiO₂-CF reinforced paper-based friction materials,the surface active group,the roughness and the fiber surface activity energy of TESPT-SiO₂-CF fiber increases,and makes the CF fiber distribute more uniform,bridge each other and forms different sizes of the pores that the porosity is 41.7%,the dynamic/Static friction coefficient ratio is 0.971,specific wear rate is 1.5x10^-8cm^-3·J^-1.In this paper,the method of preparing paper-based friction materials for modified carbon fiber and the coating modification of grafted nanoparticles is better than that of coupling agent wet chemical modification.