Effects Of Electrophoretically Deposited Carbon Nanotubes And Graphene Oxide Coatings On Interfacial Properties Of Carbon Fiber Composite

As a new structural material,carbon fiber(CF)was developed into an important low density,high strength and modulus,outstanding heat-resistance properties reinforcement material used in the fabrication of high performance composites.However,due to the manufacturing process,the untreated carbon fiber has large surface inertia and small active specific surface area,which leads to the poor fiber–matrix interfacial adhesion and affects the carbon fiber composite material’s excellent performance into full play.As a result,extensive researches have been devoted to the surface treatment of CF,such as physical and chemical active treatment,which enhance the surface activity of CF and the interfacial strength between carbon fibers and epoxy matrix,which helps to improve the mechanical properties of CF reinforced composite.In this work,carbon nanotubes(CNTs)and graphene oxide(GO)coatings were utilized to improve the interfacial performance of carbon fiber by electrophoretic deposition(EPD)process.Special emphasis has been put on the influence of ultrasonic and acidizing during EPD process on the deposition effect of CNTs and GO.Surface functional group,surface chemical properties,surface roughness and surface morphologies of carbon fibers before and after coating were examined by Fourier transform infrared spectrometer(FTIR),X-ray photoelectron spectroscopy(XPS),atomic force microscopy(AFM)and scanning electron microscopy(SEM),respectively.Surface free energy of the fiber was characterized by dynamic contact angle analysis(DCAA).The mechanical properties and water absorption and the interlaminar shear fracture morphologies of composites were evaluated by interlaminar shear strength(ILSS),moisture absorption and SEM,the interfacial fracture mechanism was also analyzed.To improve the interfacial performance of carbon fiber(CF)and epoxy resin,carbon nanotubes(CNTs)coatings were utilized to achieve this purpose through coating onto CF by the treatment with hydrogen peroxide and concentrated nitric acid combined with electrophoretic deposition(EPD)process.The results indicated that the quality and quantity of depositing GO were increased and improved by the introduction of ultrasonic during the EPD process.The CNTs formed a thin internetwork wraps up the whole surface of carbon fibers,enhanced surface roughness and changed surface morphologies of carbon fibers.The deposition of carbon nanotubes introduced some polar groups to carbon fiber surfaces,surface wettability of carbon fibers may be significantly improved by increasing surface free energy of the fibers.The interfacial adhesion of CNTs/CF reinforced epoxy composites showed obvious enhancement of interlaminar shear strength by 58.6%,moisture absorption was is off by 61.3%,thus improves interfacial adhesion.CNTs were utilized to coat onto CF by the treatment with hydrogen peroxide and concentrated nitric acid combined with electrophoretic deposition(EPD)process.The CNTs were tightly coated and covalently attached to CF surfaces.The XPS results showed that the deposition of carbon nanotubes increased the concentration of oxygen,and introduced the C=O onto the fiber surface.CNTs deposition enhanced the surface roughness of CF and the surface morphologies of CF became more complicated,increasing in the surface free energy of carbon fiber is beneficial to improve the wettability between carbon fibers and matrix.The interfacial adhesion of CNTs/CF reinforced epoxy composites showed obvious enhancement of interlaminar shear strength by 60.2%,the primary failure mode of the composites was changed from interface failure to matrix fracture.Optimal treatment condition was obtained using the orthogonal design,which could be stated as: the concentration of the coating resin is 3%,constant voltage is 25 V,and the treatment time is 10 min.GO was prepared using modified Hummers method,results showd that the GO sheet has uniform thickness and the thickness of the sheets is under 1 nm.The fiber surfaces were roughened and the surface wettabilities were improved.Ultrasonically assisted EPD increased the thickness and uniformity of graphene oxide coatings whereas only sparse deposition formed without ultrasonic.An improvement of 55 % from 36.7 to 56.9 MPa in interlaminar shear strength confirms the remarkable improvement in the strength of the fiber/matrix the interface.GO were utilized to prepare graphene oxide/carbon fiber hybrid fiber by the treatment with hydrogen peroxide and concentrated nitric acid combined with electrophoretic deposition process.Results showed that the deposition of GO increased the concentration of C-O and O=C-O,enhanced the surface roughness and changed the surface morphologies of CF.The surface free energy of GO/CF hybrid fiber was increased from 32.72 mJ/m2 to 55.92 mJ/m2 by the increasing surface area and polar groups.The introduction of GO in the carbon fiber/epoxy resin composites results in a 55.6% enhancement in the interlaminar shear strength,measured by short beam shear tests.