Improving Interfacial Properties Of Carbon/Epoxy Composites Produced By Resin Transfer Moulding

As an advanced technology used to fabricate high performance fiber reinforced polymer based composites, resin transfer molding (RTM) process has been extensively applied in aircraft, aerospace and communication industries for its outstanding advantages, including low cost, high molding speed, high efficiency, stable quality, simple processing technology and environment friendliness, especially in the aspects of high performance resin matrix composites with high specific strength and high specific modulus. But it is a truth that interfacial adhesion between the fiber and the matrix is poor because of the characters of RTM processing and carbon fibers. Mechanical properties are influenced by the degree of adhesion between the fibers and matrices. As carbon fiber is inert, untreated carbon fiber-reinforced composites exhibit weak fiber/matrix bonding. For these reasons, it is very important to research the influence of fiber surface modification on interfacial properties of composites produced by RTM.In this paper, a resin system suitable for RTM was studied which was prepared by using E-51 to modify TDE-85 epoxy/imidazole. A chemorheological model of the resin was developed based on the dual-Arrhenius equation. It is indicated that the predicted viscosity values of the established model are in good agreement with the experimental ones and the processing window of the resin system can be well determined for the process based on the developed model. The untreated and treated carbon fibers are characterized by X-ray photoelectron spectroscopy (XPS), atomic force microscopy (AFM) and dynamic contact angle analyzer (DCA) to analyze the surface properties of carbon fibers and interfacial properties of composites. The results indicate that an O2 plasma treatment has increased the carbonyl functional group and the surface roughness, and improved the wettability of carbon fibers, so that the interfacial adhesion between fibers and matrix is enhanced. The effect of plasma treatment on interlaminar shear strength (ILSS) and flexural strength of 2D braided fabric composites and unidirectional CF/epoxy composites is studied and the best performance is attained after a plasma treatment at 300W for 3 min. It is found that plasma treatment can significantly improve interface adhesion of composites. Experimental results for 2D braided fabric /epoxy composites exhibit an increase of 16.72% and 28.80% on the ILSS and flexural strength, respectively, when compare to the untreated samples. The ILSS of unidirectional CF/epoxy composites increase by 20.46% when compare to the untreated samples.