Study On Mechanical Properties And Tribological Properties Of Non-destructive Modified Carbon Fiber Reinforced Composites

Due to its excellent properties such as low density,high specific strength and high abrasion resistance,carbon fibers reinforced resin matrix composite have become the optimal choice for new transmission/braking system materials.However,the surface of carbon fibers is almost free of active functional groups due to its graphite structure.The inert surface of carbon fibers gives rise to the poor interfacial bonding between the carbon fibers and resin matrix interface,which has become a bottleneck preventing the development of carbon fibers.The interface cannot efficiently transfer the loading from the matrix to the reinforcement,which limits the excellent performance of the fibers.It has become urgent problems to be solved that how to efficiently graft and modify the surface of carbon fibers non-destructively;how to improve the inert environment and its surface activity of the fibers surface;how to enhance the interfacial bonding performance between fibers and resin as well as how to systematically improve the composite machinery and tribological properties.In order to effectively solve the above-mentioned problems,this study used some non-destructive methods such as Diels-Alder reaction,diazotization reaction,hydrothermal growth and other grafting modification to chemically graft the surface of carbon fibers.Then,the composite materials were prepared by precasting,impregnation resin and hot pressing.By systematically studying the interfacial bonding strength,mechanical and tribological properties of composite materials,the optimal conditions of grafting modification process parameters among different wet chemical modification methods were explored,which could provide technical support for further optimizing the interfacial structure of composite materials and give full play to its excellent properties.(1)The carboxyl functional carbon fibers surface was formed by grafting methacrylic acid monomer onto carbon fibers surface.The effects of different modification temperatures on the surface morphology,structure and activity of carbon fibers were systematically analyzed by various characterization methods.The results showed that the optimum grafting temperature was 80 ℃ without damage to the fibers structure,and the carboxyl functional group content of the fiber surface increased from the original 5.16% to 19.30%.The shear strength and tensile strength of the composites were increased by 90.3% and 78.7% respectively,at the same time the wear rate decreased by 52.7%.(2)Based on the diazotization reaction to produce aniline layer,phenylacid functional groups were introduced onto the surface of carbon fibers through the nucleophilic substitution reaction,which effectively solved the problem of low chemical activity on the fibers surface.This grafting modification reaction realized the synergistic enhancement of mechanical meshing and chemical grafting,effectively avoided the phenomenon of interface debonding and fibers fracture caused by stress concentration,and significantly improved the interfacial bonding strength between fiber and resin.By comparing the mechanical properties and tribological properties of the composites before and after modification,the tensile strength and three-point bending strength were improved by 45.9% and 106.8%,respectively.The friction coefficient become higher,more stable and the wear resistance was significantly improved,and the wear rate decreased by about 53.8 %.(3)The MOF-5/carbon fibers reinforcement was designed and prepared by hydrothermal growth and chemical grafting.MOFs was treated with nitric acid to conduct in-situ growth on the carbon fibers surface containing nucleation sites,and grafted on the carbon fiber surface to grow a relatively uniform lamellar structure of MOF-5,which was effectively connected with carbon fiber by C-O-Zn bond in a new chemical bonding method.Successful grafting of MOF-5 was conducive to the improvement of carbon fibers surface activity and surface energy.As a type of interfacial connector between fibers and polymer matrix,MOF-5 can effectively avoid stress concentration and obtain composite materials with high interfacial strength.There are some modification effect verified by the test results.The tensile strength of the composite was 43.2 MPa,which increased about 130.1%;the bending strength was 75.2 MPa,which increased about 74.1%;the wear rate decreased about 59.2%;and the stability was significantly improved during continuous braking.