Performance Of Carbon Nanotube/Carbon Fiber Hierarchical Reinforcement Epoxy Composites

Carbon fibers reinforced resin composite,with designable ability of structure and excellent mechanical properties,has been used in the aerospace,aviation,ship and automobile industry and so on.Light weighting and high performance of composites has become the most important direction for high-performing advanced materials.However,the weak interface bonding performance and poor the interlaminar shear strength of composite by the chemical inertness of carbon fiber become the performance bottleneck in the further pursuing progress.To improve interfacial shear strength and interlaminar shear strength of the composite,by means of structural design of hierarchical reinforcement,carbon nanotubes/carbon fiber(CNT/CF)hierarchical reinforcement were prepared by three methods,including continuous sizing and electrophoretic deposition(EPD)with the coaxial cylindrical electrode and EPD with the parallel electrode,respectively.The orientation and surface physicochemical properties of nanotubes were designed and decorated to improve interfacial property of composites.CNTs were intrudced in the surface of CF to enhance interfacial strength of CF reinforced composites.The sizing agent was prepared by adding CNTs and epoxy into N-Methyl pyrrolidone in proportion.CFs were surface treated with the sizing agent.CNTs were amino-functionalized with polyethylenimine(PEI).PEI with branched structure with amounts of amine groups has been chemically-grafted on CNTs identified by element analysis.CNTs uniformly disperse in sizing by sterically hindered effect.CNTs were densely attached to the surface of CF after epoxy sizing containing CNTs.The average roughness of obtained hierarchical reinforcement has increased by 15.9%than that of as-received CF,which lead to realize increasing mechanical interlock of the composite interface.The dynamic contact angle results showed that the surface free energy of hierarchical reinforcement increased by 32.6%because of introducing polar group and epoxy sizing agent Therefore,the wettability between CF and epoxy improved.The micro-droplet bongding results suggest the remarkable enhancements(56.2%)were achieved in interfacial shear strength(IFSS)of hierarchical reinforcement composites by sizing.In response to further increasing the interfacial strength of CF reinforced composites by intruducing vertically aligned to CF surface.The coaxial cylindrical electric field EPD was exploited to prepare vertically aligned carbon nanotube/carbon fiber(VACNT/CF)hierarchical reinforcement conditionally.The statistical results confirmed the optimum electrophoretic deposition parameter for VACNT/CF hierarchical reinforcement is the diameter of carbon nanoscale reinforcements of110–170 mm,acetonitrile as the dispersion medium,deposition voltage of 30 V,deposition time of 20 s and dispersion concentration of the carbon nanoparticles and Mg salt of 0.01 mg/m L and 0.025 mg/m L,respectively.The tensile strength of filament increased by 4.2%compared to that of as-recieved CF which states coaxially cylindrical electric field EPD is a kind of mild meld for CNT/CF preparaion.Results of interphase properties tests demonstrated that the contact angle and the IFSS were significantly improved by 48.3%and 58.1%,respectively.The capillary of VACNTs leads the wettability of hierarchical reinforcement improved.Furthermore,the symmetrical structures of VACNTs around the CF made the stress transfer from matrix to CF more uniformly and effectively.To improve the interlaminar shear strength of CF reinforced composites,the vertically aligned CNT arrays were introduced into the surface of the CF fabric by parallel electric field EPD.The analysis of CNT suspension Zeta value used for EDP shows that it increased first and then remained steady as the growth of Mg(NO₃)₂concentrations.The susupension has best dispersed stability when Zeta value reached maximum value 45.6 e V with 0.02 mg/m L Mg(NO₃)₂.The parallel electrode was employed to prepare VACNT/CF fabric hierarchical reinforcement with deposition voltage of 120 V,deposition time of 60 s.The tensile strength of filament increased by 3.0%which shows the tensile strength of CF was saved.The specific surface area inceased to 23.2 m²/g and was about one order of magnitude higher than as-received CF fabric.The dynamic contact angle reduced to 38.08^o stated that the wettability improved dramatically because of the special directional structure of the vertical CNTs array.IFSS and the interlaminar shear strength(ILSS)of VACNT/CF fabric hierarchical reinforcement composite increased by 93.6%and 64.0%,respectively.VACNTs arrays in adjacent hierarchical reinforcement forms the embeddedness in the resin enrich regions between layers of composite laminates,which resulted in the significant increasement of composite interlaminar performance.The flexural strength of VACNT/CF fabric hierarchical reinforcement composite increased by32.7%.