Preparation And Tribological Behavior Of Multi-scale Nano-MnO₂/Carbon Fabric Reinforced Resin Friction Materials

With the rapid development of rail transit,wet transmission/brake system has an urgent need for carbon fabric reinforced phenolic resin composites（CFRP）.However,low surface energy of carbon fiber（CF）and poor interface between fiber and resin become the obstacles to improve the performance of these composites.In this paper,in order to improve the interface bonding strength and then improve the mechanical and tribological properties of CFRP,carbon fiber/manganese dioxide nanosheets（CF-MnO₂）multiscale reinforcement have been designed and fabricated out.On the basis of that,γ-aminopropyl triethoxy silane（APS）and melamine（MA）is covalently bonded on the surface of CF-MnO₂ by molecular graft crosslinkingtechnology,respectively,therefore,successfully constructing CF-MnO₂-APS and CF-MnO₂-MA hierarchical reinforcements.The morphology and structure,composition and wettability of different reinforcements are characterized to study and explore the mechanism for which to improve the mechanical and tribological properties of composites.MnO₂ nanosheets were successfully grown on carbon fibers by one-step hydrothermal method to produce CF-MnO₂ hybrids reinforced.The effect of reaction temperature on morphology and structure of MnO₂ nanosheets was studied systematically.The results show that when the reaction temperature is125°C,MnO₂ nanosheets uniformly distributed on the surface of CF with relatively large pore size,which is in favor of the full impregnation of resin.The growth of MnO₂ nanosheets not only increase the surface roughness of fibers,but also can achieve a strong mechanical interlocking with the resin matrix,and further results in an improvement of 16.3%and 30.2%in the flexural strength and tensile strength of the composite.Meanwhile,friction behavior of composite was significantly improved,together with a 38.7%reduction in wear rate compared with that of raw carbon fiber reinforced composite.Chemical grafting was used to introduce APS onto CF-MnO₂ surface.After hydrolysis,one end of the APS is transferring from silyl group to silicon hydroxyl group,and then combines with the rich hydroxyl groups on MnO₂nanosheets surfaces via chemical bonds through condensation.Besides,the amino group at the other end of APS binds resin matrix by chemical crosslinking.Accordingly,the synergetic effects of mechanical interlocking and chemical bonding at interface are achieved and then the interfacial bonding strength of the composites is improved remarkably.The results show that the flexural and tensile strength of CF-MnO₂-APS reinforced composites increased by 46.9%and31.7%,respectively,compared with that of raw carbon fiber reinforced composite.Besides,the tribological properties of the composites were significantly improved,the friction coefficient is not only maintained at a high and stable state,but also the wear rate decreased by 17.3%.Polyaminomelamine dendrimers were successfully grafted onto the surface of CF-MnO₂ by chemical grafting.It not only achieved the synergetic enhancement of mechanical interlocking and chemical crosslinking between carbon fiber and resin matrix,but also improved the carbon fiber surface energy with the introduction of polar amino molecules and the wettability between carbon fiber and resin matrix.Furthermore,the interfacial bonding of the composites can be improved significantly.The experiment results show that the flexural and tensile strength of the composite CFRP-MnO₂-MA increased by24.1%and 14.5%,respectively.And the wear rate is reduced by about 29.6%.