Construction Of Multi-scale Interfacial Phase Of Carbon Fiber Epoxy Composite And Its Construction Performance Studies

In recent years,carbon fiber(CF)composites have been increasingly demanded in aviation equipment,transportation,new energy and other fields due to their excellent strength and good corrosion resistance.In carbon fiber composites,the interface between fibers and resins plays an important role in transferring and dispersing applied loads,and the overall performance of the composite can be improved by regulating the interfacial properties.However,poor interfacial adhension derived from the low surface energy and chemically inert surface of carbon fiber makes the efficiency of reinforcement reduced.Moreover,the improvement of interfacial adhension is usually accompanied by a simultaneous decrease in toughness,which have become an obstacle to the performance enhancement of CF/epoxy composites.In this thesis,in order to optimize the interfacial properties of carbon fiber composites,UiO66-NH2 was immobilized onto carbon fiber surface by coating and in-situ growth methods.Subsequently,the multistage gradient structure UiO66-NH2/carbon nanotubes(CNTs)was constructed on the surface of carbon fiber to further improve the strength and toughness of the composites.The specific research contents and the main results are as follows:(1)The synthesized UiO66-NH2 was immobilized on the surface of carbon fiber by coating method to prepare the multi-scale reinforcement c-CF/UiO66-NH2.Firstly,the effects of glacial acetic acid addition on the morphology and the structure of UiO66-NH2 were discussed,and the optimal synthesis process of UiO66-NH2 was determined.The experimental results showed that the glacial acetic acid had a significant effect on the morphology of UiO66-NH2,and when the amount was 9 mL,the synthesized UiO66-NH2 presented the most regular morphology,which will be conducive to the optimization and performance of the interface structure of the composite.Secondly,the influence of coating fluid concentration on the properties of carbon fiber and its composites was investigated.When the coating solution concentration was 2 mg/mL,the nanoparticles on the carbon fiber surface were most uniformly distributed.Compared with CF/EP,the bending strength,interlaminar shear strength(ILSS)and impact strength of c-CF/UiO66-NH2 composites increased by 33.9%,31.4%and 16.1%,respectively,and the mechanical properties were significantly improved.(2)Ui066-NH2 was in-situ grown onto the carbon fiber surface by solvothermal method to prepare the multi-scale reinforcement i-CF/UiO66-NH2.Compared with the previous part,the distribution of UiO66-NH2 on the carbon fiber surface is more dense and uniform,and the active functional groups and surface roughness of the fiber surface are significantly improved.which could promote the chemical bonding,the physical anchoring at the interface and further improve the performance of the composites.Compared with c-CF/UiO66-NH2 epoxy composites,the mechanical properties of i-CF/UiO66-NH2 epoxy composites were improved obviously.In addition,the flame retardant properties of two composites reinforced by c-CF/UiO66-NH2 and i-CF/UiO66-NH2 were preliminarily discussed.The results of cone calorimetry test showed that the flame retardant performance of both composites was improved,among which i-CF/UiO66-NH2 was the most obvious,and its maximum heat release rate(PHRR)and maximum total heat release(THR)decreased to 291 kW/m2 and 14 MJ/m2,which was decreased to 68.5%and 38.9%of untreated carbon fiber composites.The ignition experiment was extended to 293 s,which was extended by 45.8%compared with that of untreated carbon fiber composites.(3)In order to further improve the mechanical properties of the composites,carbon fiber/carbon nanotube/UiO66-NH2 multi-sc ale composite reinforcement(CF/(CNT/UiO66-NH2))with gradient modulus was designed and prepared.The scale span of the hierarchical structure is from macroscopic material,micron to nanometer,which could not only improve the interfical bonding strength between CFs and resin,but also make the load the transfer more uniformly in the interphase and finally enhance the performance of the composites.The results showed that the addition of CNT could further enhance the mechanical properties of the composites compared with CF/UiO66-NH2.The bending strength,interlaminar shear strength and impact strength compared with the modification were increased by 64.2%,76.7%and 51.5%,respectively.