Effect Of Surface Modification On Interfacial Properties Of Carbon Fiber/Epoxy Composites

Carbon fiber reinforced polymers?CFRPs?,due to their high mechanical properties;low weight and corrosion resistance have widely attracted great interests in aerospace and automotive industry.However,carbon fiber composites do fail always catastrophically at the interface between carbon fiber and matrix because of the smooth surface and chemical inertness of carbon fiber.As an important part of carbon fiber composites,the interface plays a vital role for the results mechanical properties and influences the stress propagation and fail mode of composites.When a fiber breaks in composites,loads previously carried by the broken fiber transfer to the neighboring fibers through the matrix.With the increasing of broken fiber,triggers the final failure of composites due to the formation of critical clusters.Many methods have been used to modify the surface of carbon fiber in order to introduce the mechanical interlock and chemical bonding.However,a lot of methods have been achieved at the expense of mechanical properties for base fibers and are accompanied with tedious procedures and high pollution.The aim of this article was to improve the interface adhesion of carbon fiber composites and developed a novel method to build hierarchical interface layer through enhancing the surface roughness and surface activity.The main research contents of this paper are as follows:In order to enhance interfacial properties of carbon fiber/epoxy composites,a facile and effective process was developed to fabricate three dimensional interconnected nanosheets architecture by in-situ growing Ni?OH?₂ nanosheets on carbon fibers?CFs?.Scanning electron microcopy?SEM?clearly revealed that the nanostructured Ni?OH?₂nanosheets were uniformly grown on carbon fibers which could play as nanocontainers of epoxy matrix when fracture occurred.In order to explore the mechanical interlocking of composites,EDS mapping scanning was performed to explore penetration transition layer.The interfacial shear strength?IFSS?improved up to 82.1%compared with untreated composites,the optimal interlaminar shear strength?ILSS?of composites reached up to93.9 MPa.According to the test results,it is reasonably to be considered that this new effective and low cost strategy could effectively improve the interfacial properties of CF/epoxy composites and could be a good candidate for potential large-scale industrial application.Besides,based on the different morphology of Ni?OH?₂ crystals,the influence of morphology on the interfacial properties for carbon fiber composites has been studied.According to the results,the enhancement of interfacial properties of composites was in order of nanosheets?nanorods?nanoparticles.In order to enhance the interfacial properties of carbon fiber composites,a multiscale rigid-soft dual-locked interface layer with sandwich structure was designed and fabricated in order to modify the interface between carbon fibers?CFs?and matrix by a versatile and green strategy,with water as the only solvent.Polydopamine?PDA?was chosen as a functional platform to introduce Ni?OH?₂ nanosheets self-assembling onto the CFs surface.After incorporation with a soft and amine-rich polymer,a steadier and more entangled dual-locked interface layer could be realized.The surface composition and morphology were analyzed by X-ray photoelectron spectroscopy?XPS?,Fourier transform infrared?FTIR?and scanning electron microscopy?SEM?.The interlaminar shear strength?ILSS?results indicated that the ILSS improved up to 43.4%compared with untreated CFs composites,indicating the superiority of this interfacial network.Poor interfacial interaction and damage-tolerance restrict practical application of carbon fiber?CF?composites.The brick and mortar structure meets the requirements of high strength and small crack growth behavior of composites.However,it is still a challenge to uniformly fabricate the three-dimension brick and mortar structure as an interface layer on CF surface.Herein,3D brick and mortar structure has been uniformly constructed on carbon fiber surface via in-situ growth.Ni?OH?₂ nanosheets which matched the geometry of fiber were used as the“brick”to improve the strength of resultant composites,and multifunctional polydopamine?PDA?was employed as“mortar”toward simultaneously guaranteeing the powerful bonding interactions with“brick”and complex chain entanglements,filling up this technical gap of fabrication of brick and mortar interface on carbon fiber.The synergistic effects of composites were demonstrated through interlaminar shear strength?ILSS?and flexural tests,and results indicated that the optimize ILSS and flexural performance was obtained from the composites with this superior interface,respectively,53.5%and 95.6%enhancement than the pristine CF/EP,which was attributed to the brick and mortar structure arising from stress dissipation,plastic deformation and physical and chemical entanglements.