Modification Of Carbon Fiber Surface And Study Of Its Composite Performance

Due to the advantages of high specific strength,specific stiffness and fatigue resistance,carbon fiber reinforced plastic composites have been widely used in the areas of national defense,military industry and aerospace.However,with the continuous improvement of science and technology,people have put forward higher requirements for the mechanical properties of composites,and the weak interface has become the main factor limiting the further development of composites.As the"bridge"and"bond"between carbon fiber（CF）and resin,the overall properties of composites are largely affected by the interface microstructure and bonding strength.Because of nanocarbon have advantages of excellent mechanical properties and large specific surface area,in this work,based on the design idea of multiscale structure,the purpose was to solve the dispersion of nanocarbon and improve the interfacial properties of composites.Nanocarbon were selected to modify the CF surface with different designs,at the same time,the interface compatibility and interphase structure were optimized to improve the interfacial properties of composites.The main research contents of this paper are as follows:In order to improve the wettability and mechanical interlocking between CF and epoxy resin,and accordingly improve the interfacial shear strength（IFSS）of composites,the graphene aerogel/CF multiscale reinforcement was prepared by chemical reduction self-assembly method.In addition,the preparation conditions of self-assembly process were optimized.The surface morphology,microstructure,specific surface area,tensile strength and IFSS of CF multiscale reinforcement were studied.Compared with the unsized CF,the IFSS of multiscale reinforced composites increased by 83.2%,and the interfacial failure mechanism changed from weak interface debonding to strong resin cohesion failure.In order to study the effects of the bonding types between graphene oxide（GO）and CF on the interfacial properties of polyether ether ketone（PEEK）composites,three different types of multiscale GO/CF reinforcements were prepared,namely,van der Waals forces,zwitterionic interactions and covalent bonds.According to the results of SEM images and dynamic contact angles,it was observed that GO were deposited on the CF surface uniformly,and the multiscale reinforcement combined in the form of covalent bond had the highest surface energy.The enhancement of interfacial properties of the composites was in order of covalent bonds>zwitterionic interactions>van der Waals forces.According to the similar dissolve mutually theory,thermoplastic CF sizing suitable for PEEK resin was prepared in this paper.By adjusting the proportion of copolymer monomer,a series of amino functionalized polyether ether ketone（PEEK-NH₂）that can be dissolved in organic solvents was obtained and used as the main component of sizing.The thermal performance of sizing were characterized by differential scanning calorimeter and thermal gravimetric analyzer（TGA）.Compared with PEEK,the glass transition temperature of PEEK-NH₂polymer was maximal increased 67.5°C,the highest initial decomposition temperature was decreased by 143.0°C,the carbon residue rate was maximal increased by 14.9%.Meanwhile,the sizing concentration and the proportion of amino copolymer monomer in PEEK-NH₂ were optimized and regulated.To give full play to the advantages of multiscale structure,complex sizing containing different content of GO was prepared.After being modified by 5 mg/mL GO sizing,the composites possessed the best interfacial properties.To improve the dispersion of GO in the sizing and increase the interfacial compatibility between GO and polyether sulfone（PES）resin,two amino compounds similar to the structure of PES were selected to chemically grafted to the GO surface.And the thermoplastic CF sizing suitable for PES resin was prepared.Fourier transform infrared spectroscopy and X-ray photoelectron spectroscopy showed that amino compounds had been grafted to GO surface successfully,and the stability of GO in sizing was effectively improved.TGA and dynamic contact angle results indicated that the modified CF have good thermal stability,and the thermal decomposition temperature of sizing was higher than the processing temperature range of the composites.Moreover,the surface energy of CF increased from the 34.5 mJ/m² to 55.9 mJ/m²,which was beneficial to improve the wettability between fiber and resin.After being modified by PES/GO-DDS sizing,the composites exhibited the best interfacial properties.