Construction Of Nano-Reinforcement On Carbon Fiber And Study Of Interfacial Properties Of Carbon Fiber/Polymer Composite

Due to the outstanding properties of carbon fiber(CF),such as low density,high stiffness,high corrosion resistance,and decent heat resistance,CF reinforced polymer(CFRP)composites have been regarded as one of the strategic materials by the national industrial development planning.Based on the different characteristics of the resin matrix,the CF reinforced thermosetting and thermoplastic resin composites have been playing their respective advantageous roles in the aviation industry,highspeed train,automobile manufacturing,and so on.In general,the interfacial bonding between CF and resin matrix is relatively weak,the development of high-performance CFRP composites still faces many challenges in improving the interfacial bonding strength.Introducing nanomaterials with excellent properties into the interface of CFRP composites has been proven as an effective means to enhance the interfacial properties.However,there are still some problems to be solved,such as complex processes,high energy consumption,and limited strengthening effect.In this study,based on the existing theories and multi-scale fiber structure design strategies,the surface modification methods of CF are designed by using different nanoparticles(metal particles,carbon nanotubes(CNT),and MXene),considering the characteristics of epoxy resin(EP)and poly(ether ether ketone)(PEEK)resin matrix.The interfacial structure of composites is optimized under mild and nondestructive conditions,leading to the improvement of the microscopic interfacial properties and the macroscopic mechanical properties of the composites.In this study,the contact angle between desized CF,EP,and PEEK resin and the probe liquids are measured.The surface energy is calculated based on acid-base theory,and the results show that the desized CF,EP,and PEEK resin all exhibit high dispersive and alkaline components.The wetting parameters between the fiber and the resin indicate that the work of adhesion between them is low,the resin is difficult to spontaneously spread on the fiber,which leads to weak interface bonding.Based on the interface theory,combined with the physicochemical properties and technological conditions of EP and PEEK matrix,a variety of sizing agent are designed.By analyzing the results of molecular dynamics simulation,wetting parameter and Hansen solubility parameter calculation,polydopamine(PDA)and polyetherimide(PEI)are selected as CF sizing agents of CF/EP and CF/PEEK composites for grafting nano-reinforcement,respectively.For the CF/EP composite,0D silver nanoparticles(Ag NPs)are deposited on the CF surface based on the super adhesion and reducibility of PDA.The surface morphology,chemical composition and surface energy of the fiber before and after modification are investigated.The results show that the fiber has a rougher surface and the wettability between the fiber and the resin is improved by the PDA nanolayer and Ag NPs.That the interfacial shear strength(IFSS),interlaminar shear strength(ILSS),flexural strength,and flexural modulus of the CF/EP composites are increased by 72.1 %,51.5 %,41.3 %,and 50.9 %,respectively,while maintaining the tensile strength of monofilament.The failure mechanism of composites changes from interface failure to cohesive failure.Moreover,using PDA as the secondary reaction platform,a simple and environment-friendly method is developed to construct CNT on CF surface.The PDA nanolayer and CNT network structure on the CF surface significantly increase the roughness of the fiber,leading to significant increments in the surface energy and polarity components,and effectively enhanced the microscopic interface properties and macroscopic mechanical properties of the CF/EP composites.For the CF/PEEK composite,a sizing agent consisting of 1D/2D MXene/CNT hybrid nanoparticles and a dual compatibilizer PEI is designed and prepared.The effects of the sizing agent on the surface morphology,chemical properties,surface structure,wettability of CF,and mechanical properties of CF/PEEK composites are systematically studied.The results show that the unique structure of CNT can provide more sites for mechanical interlocking and a large number of oxygen-containing functional groups on the MXene surface increases the polar component of the fiber surface,which helps to enhance the interaction between the fiber and the matrix.The ILSS,flexural strength,and flexural modulus of the prepared modified CF/PEEK composites are 62.8 %,74.2 %,and 63.8 % higher than those of desized CF,respectively.The wetting behavior of molten PEEK on the fiber surface is particularly important during the molding process for CF/PEEK composite.Therefore,properties such as viscosity and surface tension of molten PEEK at high temperatures are tested,and the dynamic wetting behavior of molten PEEK on the CF substrate is investigated.The classical hydrodynamics approach(HD)and molecular dynamics theories(MKT)are used to fit the wetting dynamics of molten PEEK at the solid/liquid interface.The results show that the spreading dynamics of molten PEEK is in good agreement with HD and MKT models.Based on the modified MKT theory,the activation free energy of the viscous interaction between the molten PEEK molecules is much larger than that of the interaction between the melt molecules and the solid surface,which indicates that the viscous dissipation channel plays a dominant role in the wetting process of molten PEEK.It is of great significance to optimize the preparation process of resin matrix composites.In this study,starting from the perspective of the interfacial properties between fiber and resin,CF reinforcement modified with different nanoparticles are designed and prepared using a combination of theoretical analyses,molecular dynamic simulations,and experiments,aiming at the construction of the micro-nano multiscale interfacial structures of the composites.The effects of surface treatment on CF properties and mechanical properties of the composites are systematically studied,and the microscopic enhancement mechanism of interface modification is revealed.This study explores an eco-friendly and efficient direction for the substantial improvement of macroscopic mechanical properties of CF reinforced thermoplastic and thermosetting resin matrix composites.