| Carbon fiber(CF)is used to prepare carbon fiber composites due to its excellent mechanical properties,good heat resistance and corrosion resistance,and light weight.CF composite materials are widely used in aerospace,cycling and civil applications.With the development of application,people also put forward higher requirements for its performance.However,there are still some problems in carbon fiber composite materials.Because of smooth and chemical inertness of CF,the interface between the fiber and resin matrix is poor which limit the mechanical property of composites.Even if the interface between them is well combined,the interface will still produce micro-cracks after receiving external force over loaded,which will lead to interface failure and affect the service life of the material.Therefore,it is very necessary to modify the surface of carbon fiber to improve the interfacial properties of carbon fiber and matrix resin and to further realize self-healing of the interface.In this thesis,MOF were introduced on the fiber surface to improve the interfacial properties with resin,and the mechanism of interfacial enhancement was analyzed and investigated.The interfacial self-healing behavior with MOF as platform was further studied.An interfacial self-healing system based on Diels-Alder(DA)thermoreversible dynamic chemical bonds was constructed by introducing Ui O-66-M on the surface of carbon fibers.Ui O-66-M was prepared by hydrothermal synthesis and post-synthetic modification(PSM)and uniformly distributed in the state of nanoparticles on the fiber surface.Ui O-66-M can improve the roughness of the fiber surface and improve the microscopic morphology of the fiber.The results showed that PSM did not destroy the morphology and crystal structure of MOF.Compared with the unmodified carbon fiber,the IFSS and ILSS of the modified carbon fiber were increased by 39.53% and 16.62%,respectively.Meanwhile,the interfacial self-healing behavior based on DA reaction was studied,Ui O-66-M and furfuryl glycidyl ether(FGE)which containing furan structure were added to epoxy resin.When the interface between the modified fiber and the resin system fails,the covalent bond formed by the maleimide group contained in Ui O-66-M on the fiber surface and the furan structure in the resin matrix is broken,which occurs after heating.DA reacts to bond again so that the damaged interface is repaired.The healing efficiency of the three interface self-healing were 89.96%,90.6% and 80.94%,respectively.To overcome the temperature requirement of DA reaction,Cu2(F2Azo BDC)2Dabco,which can respond to light,was introduced on the surface of carbon fiber.This MOF can not only improve the interface properties of carbon fiber,but also can be used as an external repair agent carrier to realize light-responsive self-healing.F2 Azo BDC with an azobenzene structure was synthesized,and Cu2(F2Azo BDC)2Dabco,which can undergo isomerization under530 nm and 400 nm light stimulation,was introduced on the surface of carbon fiber by hydrothermal method.Compared with the untreated carbon fiber,the modified IFSS and ILSS increased by 51.70% and 25.44%,respectively.Cu2(F2Azo BDC)2Dabco can occur cis-trans isomerzation under the irradiation upon green light and violet light,and the MOF polarities of two isomer are significantly different.Therefore,using MOF as a carrier to load healing agent can control the isomer of MOF by light to control the loading and releasing of healing agent.After the interface between the fiber and the resin droplet was damaged,the MOF loaded healing agent was trigered by violet light to release the repair agent to repair the interface.The light control can realize the precise and multiple release of the repair agent,and the repair rates are 96.31%,80.71%,75.28%.The layer-by-layer self-assembly method(Lb L)can limit the crystal formation and is beneficial to obtain a uniform MOF structure.Therefore,in order to overcome the aggregation phenomenon of MOF prepared by hydrothermal reaction on the surface of carbon fiber,Lb L was used to introduce Zn(Az DC)(4,4-BPE)0.5,which can induce by UV light,on the surface of carbon fiber.The results show that the MOF porducted by Lb Lwere uniformly distributed on the CFsurface as nanosheets.As a comparison,this MOF was also introduced on the fiber surface by a hydrothermal method.The surface energy of fibers prepared by Lb L method after 10 cycles was 38.71% higher than that of the fiber prepared by hydrothermal method,and its IFSS is 75.46 MPa.Compared with the pristine CF,it increased by 70.3%.The results of single fiber tensile strenth and IFSS show that the properties of fibers prepared by Lb L method have a better performance.The photo-responsive ligands lead to MOFs can also undergo cis-trans isomerism under the stimulation of light.Therefore,MOF can be used as a repair agent carrier,and multiple interface self-healing can be achieved by light control,and the healing efficiency were 97.01% and 81.4%,respectively. |
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