The Molecular Design And Mechanical Study Of Interfaces Enhancement And Interface Self-healing Of Carbon Fiber/Epoxy Composites

Carbon fiber reinforced resin-based composite materials are one of the most high-profile engineering materials in the modern era,with the advantages of high strength and high modulus,strong durability,dimensional stability and lower density.However,due to the chemical inertness and low surface energy of the carbon fiber surface in the carbon fiber composite material,the interface bonding force between the carbon fiber and the resin matrix is weak.When the external force is applied,the interface of the composite material is easily destroyed first,and the load cannot be effectively transferred.To carbon fiber,it exerts its high-strength and high-modulus performance,thereby limiting the comprehensive performance of carbon fiber composite materials.In addition,the interface layer of the composite material is prone to generate micro-cracks under the action of external force,causing stress concentration effect and eventually rupture.Even if the interface layer is strengthened by other methods,the generation of microcracks cannot be avoided.After the interface is broken,it is not only difficult to find,but also unable to recover by itself.Therefore,the material performance will be significantly reduced after the interface is broken,and the service life of the composite material will be greatly affected,and the risk of material use will increase.In response to the above problems,this study uses epoxy resin as the matrix,from the two directions of reinforcing the interface strength of carbon fiber and resin matrix,and introducing interface self-healing,to design the interface molecular of the composite material to improve the interface performance of the composite material.Specifically:(1)Using six-arm epoxy monomer(EHEP)as the reaction raw material,a new ?-hydroxyl primary amine end-branch was grafted on the surface of carbon fiber by repeating the stepwise grafting and the ring-opening reaction of epoxy groups.Polyphosphazene.The branched polyphosphazene can significantly improve the chemical activity of the carbon fiber surface,and participate in the curing process of the matrix,forming a strong chemical bond between the carbon fiber and the matrix.The results of the Interfacial Shear Strength Test(IFSS)showed that the interfacial strength of carbon fibers that had undergone two grafting and ammoniation ring-opening reactions was increased by 105%.(2)The in-situ construction of poly(hexachlorocyclotriphosphazene(HCCP)-co-4,4'-diaminodiphenyl ether(ODA))layer on the surface of carbon fiber can improve the polarity and wettability of the carbon fiber surface,thereby enhancing the composite Material interface strength.However,the high cross-linking degree of the polyphosphazene layer leads to its high brittleness,which is easily broken when the load is transmitted,which affects the interface strength.In this study,the flexible segment D230 was introduced into the raw material composition of the polyphosphazene layer to regulate the chain mobility in the molecular structure of the ring-crosslinked polyphosphazene grafted on the surface of the carbon fiber,and adjust the strength and toughness of the interface of the carbon fiber composite material.Explore the effect of the polyphosphazene layer formed on the different rigid /flexible segment ratios of ODA and D230 on the IFSS value.The research results show that after the polyphosphazene layer is composed of only flexible components,the IFSS value of the carbon fiber / epoxy resin interface has no significant change compared to the IFSS value of the polyphosphazene layer composed of only rigid segment ODA in previous studies.However,as the molar ratio of the flexible segment increases,the IFSS value will increase accordingly,and when the molar ratio of ODA: D230 is 1: 3,the IFSS value may increase from 40.8 MPa to 81 MPa.(3)A modified epoxy monomer FAE with furan groups at both ends was prepared by using furfurylamine to carry out amination ring-opening reaction on commercial E51 epoxy resin.By reacting the commercial three-arm longchain curing agent T403 with maleic anhydride,a crosslinking agent MAT with 3 maleimide groups was prepared.The two compounds together form an epoxy-based sizing agent,and the two components of the sizing agent will undergo a forward / reverse Diels-Alder(DA)reaction at 70 ° C and 130 ° C,respectively,which can be used in carbon fiber / epoxy resin After the interface is damaged,the interface layer is reconstructed by DA reaction to achieve the purpose of the interface self-healing.The results of the research conducted through the cyclic IFSS test show that the IFSS value of the carbon fiber /epoxy resin interface after sizing is increased by 75.6%,and it can bring an initial healing efficiency of 93.8%,and it can still maintain 51.3% after 3healings.