Construction And Properties Of Interfacial Phase Of Carbon Fiber/PPEK Composites

Carbon fiber（CF）reinforced thermoplastic composites（CFRTPs）have widely used in the fields of a high-tech with the advantages of low density,high strength,excellent fatigue resistance,corrosion resistance,and recyclability.However,the smooth and chemically inert CF surface,coupled with the high melt viscosity of thermoplastic,is resulting in poor wettability.Meanwhile,no chemical reaction occurs during CFRTPs curing and molding,and the chemical bond cannot be formed between CF and thermoplastic in.The low bonding strength between CF and thermoplastic result in the poor interfacial property,which seriously affects the comprehensive performance of composite.Therefore,some effective methods have been applied to the surface treatments of CF to enhance the interfacial bonding between fibers and resins.In this paper,GO and GO-SiO₂ were introduced into CF/PPEK composites as interphases by using an electrostatic adsorption method to enhance the interfacial property.（1）The electrostatic adsorption between-COO^-in GO and-N（CH₃）₃⁺in N-trimethoxysilylpropyl-N,N,N-trimethylammonium chloride（KHN⁺）was uesd to preparation of CF-GO multiscale reinforcements.FTIR,Raman,XPS and SEM showed that the electrostatic adsorption method could construct a uniform GO layer on the CF surface.The effects of KHN⁺and GO suspension concentrations on the surface morphology of CF and mechanical property of composites were explored.When the concentration of coupling agent is 4wt%and the concentration of GO suspension is 0.4wt%（CF-4KHN⁺-4GO）,GO can evenly wrap the CF and improve the surface roughness of CF（59.8 nm）.The dynamic contact angle test results showed that the surface energy of CF was significantly improved after adsorption of GO（59.09 m N/m）.GO improves the wettability between PPEK and CF and increases the surface roughness of CF,resulting in a strong mechanical meshing effect between them.Therefore,the flexural strength and interlaminar shear strength of the CF-4KHN⁺-4GO/PPEK composite was increased by 38.8%and 30.8%,respectively,compared with the Untreated CF/PPEK composite.The glass transition temperature（T_g）increased to 283^oC（2）SiO₂ treated by the anionic surfactant cetyltrimethylammonium bromide（CTAB）was adsorbed on the surface of CF-GO multiscale reinforcement to form a GO-SiO₂ interface layer.The results showed that the spherical structure of SiO₂ further improved the surface roughness of CF to enhance the mechanical locking effect.The increasement in the number of polar groups in the interfacial layer leads to increased surface energy and enhanced wettability between CF and PPEK.The abundant silanols on the surface of SiO₂ interacted with the PPEK,which strengthens the chemical bonding between molecules at the interface.The interface property of the composite were improved,the tanδdecreased to 0.33,and the glass transition temperature（T_g）increased to 285^oC.Meanwhile,the electrostatic adsorption between CF,GO and SiO₂effectively avoids the exfoliation of GO and SiO₂ under the action of external force,which improve the enhancement efficiency of the GO-SiO₂ interface layer on the interface strength.Compared with the Untreated CF/PPEK composite,the flexural strength and interlaminar shear strength of the CF-GO-SiO₂/PPEK composite were increased by 37.3%and 48.4%,respectively.The GO-SiO₂ interface layer significantly improves the hydrothermal aging resistance of CF/PPEK composite.