Controllable Construction Of Rigid-flexible Structures On Carbon Fiber Surfaces And Research On Interface Properties Of Resin Matrix Composites

Carbon fibers(CFs)reinforced polymer matrix composites are widely applied in defense aviation,sports equipment,transportation and marine due to their lightweight and high strength.Nevertheless,carbon fiber surface has a highly ordered graphite microcrystalline structure,which makes the surface of CFs smooth,chemically inert,going against carbon fiber wetting with polymer and leads to poor interfacial adhesion and mechanical properties,in addition,the modulus difference between CFs and polymer would cause stress concentration at the interface layer,resulting in weak stress transfer efficiency.Therefore,from the perspective of molecular structure design,this paper firstly grafting carbon nanotubes(CNTs,)graphene oxide(GO)to the surface of CFs through esterification,and then grafting polyamide(PA)through anionic polymerization to construct nano-polymer "rigid and flexible" structure CF-CNTs-PA,CF-GO-PA,CF-GO-CNTs-PA,CF-CNTs-GOPA,and construct multi-scale enhancement,moderate modulus and easy interface buffer layer fused with the matrix.Optimize the overall performance of CFs/epoxy composites by adjusting the structure of the interface phase.Finally,the surface element composition,microstructure,wetting property,interfacial bonding strength and mechanical properties of CFs was analyzed by a variety of testing methods.The main research content and the results were as follows:1.The chemical grafting method was used to design double “rigid-flexible” structure of CNTs and PA on the surface of the carbon fiber,forming gradient modulus intermediate layer between CF and epoxy.The elemental composition and structural changes of functionalized CFs were analyzed by a variety of test methods,and the effects of modulus intermediate layer on interfacial and mechanical properties of CFs composites were investigated.The introduced CNTS-PA interface increases the CFs surface polar functional group,micron roughness and surface energy.Compared with CFs/epoxy composites,the interfacial shear strength(IFSS),interlaminar shear strength(ILSS),flexural strength,and impact strength of CF/epoxy composites increased by 75.6%,44.1%,41.3%,and 34.6%,respectively.In addition,the interfacial failure behavior and strengthening mechanism of composites have been studied.2.The chemical grafting method was used to introduce GO sheets and PA on the surface of CFs to construct a layered reinforced "rigid and flexible" structure.forming a thicker multi-level gradient modulus interface layer between CFs and epoxy resin.The element composition and structural changes of functionalized CFs were analyzed by a variety of test methods,and the changes and interface properties of the functionalized carbon fiber composite intermediate layer were studied.The introduced GO-PA interface phase increases the polar functional groups,micron roughness and surface energy of the CFs surface.Compared with CFs/epoxy composites,the IFSS,ILSS,compressive and impact toughness of the CF-GO-PA/epoxy resin composite material increased by 76.8%,46.4%,40.7% and 37.8%,respectively.In addition,systematically elaborated the interface enhancement mechanism.3.On the basis of covalently grafting CNTs-PA and GO-PA on the surface of carbon fiber,the grafting sequence and constructed different GO-CNTs,CNTs-GO,GO-CNTs-PA and CNTs-GO-PA structure with synergistic hierarchical enhancement.Through various tests,the surface element composition and active functional groups of functionalized CFs were characterized and analyzed.XPS and Raman tests show that GO,CNTs and PA have been covalently grafted to the surface of CFs,which significantly improved the active functional groups,roughness and wettability of CFs surface.In addition,the effect of the synergistically enhanced multi-layer GO-CNTs-PA "rigid-flexible" structure on the surface micromorphology of CFs and the thickness and interfacial adhesion of the composite was also studied.Compared with CFs/epoxy composites,the IFSS,ILSS and impact strength of CF-GO-CNTs-PA reinforced epoxy resin increased by 80.9%,51.7% and 40.2%,respectively.And systematically elaborated the interface enhancement mechanism.