Study On Grafting Treatment Of Carbon Fiber

Carbon fiber has the characteristics of high strength,high modulus,etc.It is one of the common reinforcing fibers for the preparation of high-strength composite materials.In order to facilitate transportation,carbon fibers are coated on the surface with epoxy sizing agent,which is not conducive to the oxidation and grafting of the carbon fiber surface;the compatibility with the resin matrix is??poor,and the interface is not firm.Therefore,the surface modification of carbon fiber has a very important significance.This article discusses the cleaning of carbon fiber surface slurries under supercritical CO₂;nitric acid oxidation of carbon fibers;oxidation of carbon fibers after grafting ethylenediamine,through weight loss,monofilament strength and interfacial shear strength tests,SEM,Raman Spectral analysis,photoelectron spectroscopy analysis,and atomic force microscopy characterization methods have reached the following conclusions:1.Effect of supercritical CO₂ fluid on the cleaning of epoxy resin sizing agent on carbon fiber surface:The optimum process conditions for supercritical CO₂ cleaning of carbon fiber surface slurry were analyzed through the weight loss rate of carbon fiber and the surface morphology of the SEM fiber.The carbon fiber monofilament strength was measured by a fiber strength meter and Weibull function was used for fitting analysis.The average monofilament strength of the carbon fiber treated under the optimum cleaning process conditions was 4.71GPa,which was a decrease of2.89%compared with the original carbon fiber tensile strength of 4.85GPa.The supercritical cleaning method has a small loss of carbon fiber strength and maintains it near the original filament strength.The average surface roughness of carbon fiber atomic force microscopy is 9.23 nm.Compared with the uncleaned carbon fiber,the roughness decreases;fitting by Raman spectroscopy And the integral intensity analysis:the supercritical CO₂ optimal cleaning process treatment carbon fiber integrated intensity ratio of 2.52,and the untreated carbon fiber strength ratio increased by 2.02%,indicating that the disordered carbon structure has increased;Photoelectron spectroscopy analysis:the best cleaning of supercritical CO₂ The content of carboxyl and ester groups on the surface of the treated carbon fiber was almost zero,indicating that the slurry on the fiber surface had been cleaned.Therefore,under the optimum cleaning process conditions of supercritical CO₂,the treated carbon fiber can effectively clean the carbon fiber surface slurry,and the strength loss of the carbon fiber is small,which is a cleaning method that has little effect on the strength structure of the carbon fiber body.2.The effect of nitric acid solution oxidation on the surface and strength of carbon fiber:The optimum oxidation condition of carbon fiber was set to 70°C for 4 h by scanning electron microscopy.Through fiber monofilament strength test analysis,the carbon fiber monofilament strength is 4.52GPa,and the strength of the carbon fiber monofilament after cleaning is reduced by 4.03%.Nitric acid oxidation carbon fiber can affect the carbon fiber strength and reduce the strength;through the surface roughness analysis of the fiber through the atomic force microscope,The carbon fiber surface has a mean square roughness of 43.2 nm,an arithmetic mean roughness of35.6 nm,and an improved roughness of the carbon fiber after cleaning.The nitric acid solution oxidizes and erodes the surface of the carbon fiber,and increases the surface roughness.The Raman spectrum fitting to the surface of the carbon fiber is fitted.Calculating the integral intensity ratio analysis,the carbon fiber Raman R?ID/IG?value increased to 2.83,indicating that the disordered carbon structure of the fiber increases after treatment,and the effect of surface etching increases the grain boundary activity;the photoelectron spectroscopy peaks are proposed Together,the oxygen-containing functional groups on the surface of carbon fibers increase,the carboxyl groups and ester groups increase to 14.08%and 7.08%,respectively,and a certain amount of oxygen-containing functional groups such as carboxyl groups or hydroxyl groups have been formed on the surface of the fibers.Therefore,the use of nitric acid solution can etch the carbon fiber surface,increase the surface roughness,and increase the surface oxygen-containing reactive functional groups.3.Effect of ethylenediamine grafting on fiber strength and interface of CF/epoxy composites:The results of fiber surface morphology analysis by scanning electron microscopy show that the best experimental conditions for the grafting of ethylenediamine on carbon fiber surface is 70°C 5h.By analyzing the monofilament strength of the grafted carbon fiber,the strength of the monofilament of the grafted ethylenediamine carbon fiber is 4.92GPa,which is 8.85%higher than that of the carbon fiber monofilament after oxidation.The grafted ethylenediamine could repair the surface of the fiber.Oxidation causes defects and improves the tensile properties of monofilaments.Raman spectroscopy shows that the carbon fiber Raman R?ID/IG?value is reduced to 2.41,and the disordered carbon structure of the grafted carbon fibers is reduced;the carbon fiber surface is obtained by photoelectron spectroscopy.The carboxyl content was reduced from 14.08%of the oxidized carbon fiber to 2.09%.Ethylenediamine was grafted onto the surface of the fiber through the reaction,and the carboxyl content was reduced.Through the analysis of the fracture surface of the composite material by scanning electron microscopy and interlaminar shear strength,the fracture surface of the grafted carbon fiber composite material is uniform,the gap between the fiber and the matrix is??small,and the interfacial properties are enhanced.The interlaminar shear strength of the grafted carbon fiber is 56.32GPa.The interlaminar shear strength of the carbon fiber treated by the branch increased by36.5%,and the interfacial properties of the carbon fiber composite grafted with ethylenediamine increased.