Study On The Rigidity And Flexibility Of Carbon Fiber Surface And Its Performance Of Reinforced Epoxy Resin Composite

Carbon fiber reinforced epoxy polymer composites(CFRPs)are widely used in aerospace,national defense,automotive and electronic equipment as the "king of new materials in the 21 st century" due to their advantages of light weight,high strength and corrosion resistance.Although the carbon fiber reinforced epoxy polymer composites have outstanding advantages,the carbon fiber surface is non-polar and chemically inert,and the modulus of the carbon fiber is quite different from that of the matrix,so the potential has not been fully developed.Generally,the interfacial phase between reinforcement and matrix has special properties,which plays a decisive role in the properties of composite materials.The strength and toughness of structural materials are relative.Strong interfacial bonding is conducive to stress transfer,thus improving the strength of composite materials,while weak interfacial bonding increases the interfacial toughness through the plastic deformation of the interface and the energy consumption when the composite material breaks.Therefore,how to design,construct and optimize the interface,to build a balanced and coordinated interface phase,is the urgent task of improving the strength and toughness of structural materials.In this paper,based on the control interface structure,the "flexible" polymer polyethylenimide(PEI),"rigid" polymer polydopamine(PDA)and hexagonal boron nitride(h-BN)were used to construct the interface of different rigid and flexible structures,and the influence of different rigid and flexible interfaces on the interface and mechanical properties of the composite materials was studied.(1)The "flexible" PEI and "rigid" PDA were grafted onto carbon fiber by chemical grafting method,and an "alternately rigid and flexible" structure CF-PEI-PDA with multiple gradient moduli was constructed.The experimental results show that PEI and PDA polymers can greatly improve the surface roughness and wettability of carbon fiber(CF),and further enhance the mechanical interlocking and chemical bonding between CF and epoxy polymer.Compared with unmodified CF,the interfacial shear strength(IFSS),interlaminar shear strength(ILSS),impact strength and fracture toughness increased by80.2%,23.5% and 167.2%,respectively.(2)In order to further study the effects of different rigid and flexible structures on the interface and mechanical properties of carbon fiber,a "gradually rigid and flexible" structure(CF-PDA-PEI)was constructed between "rigid" carbon fiber and "flexible" epoxy polymer(EP)by using "flexible" PEI and "rigid" PDA.Compared with the unmodified CF,the IFSS,ILSS and bending strength of the "gradually rigid and flexible" structure of CF-PDA-PEI increased by 80.1%,19.9% and 33.3%,respectively.Therefore,the strengthening effect of the "alternately rigid and flexible" structure of CF-PEI-PDA was better.(3)By chemical grafting method,"flexible" PEI and "rigid" BN were constructed between "rigid" carbon fiber and "flexible" epoxy polymer respectively to construct "gradually rigid and flexible" structure CF-BN-PEI and "alternately rigid and flexible" structure CF-PEI-BN.The experimental results show that: Compared with the unmodified CF,the IFSS,ILSS and bending strength of the "gradually rigid and flexible" CF-BN-PEI reinforced composites increased by 109.4%,27.1% and 29.8%,respectively.The IFSS,ILSS and bending strength of the alternately rigid and flexible CF-PEI-BN reinforced composites are increased by 112.1%,30.1% and 33.2%,respectively,and the enhancement effect of the "alternately rigid and flexible" CF-PEI-BN reinforced composites is better.