Effect of hydrophilic-hydrophobic ratio in self-emulsifying amphiphilic epoxy sizing agent on interfacial properties of carbon fibre/epoxy composites

Abstract

More and more attention has been paid to the synthesis and characterization of self-emulsifying sizing agents without organic solvent due to the demand of environment-friendless. Herein, self-emulsifying amphiphilic epoxy sizing agents with different hydrophilic-hydrophobic ratios were synthesized and used to enhance interfacial adhesion between carbon fibre (CF) and epoxy resin (EP). The effects of hydrophilic-hydrophobic ratio on the characteristics of sizing agent emulsion, the wettability and morphology of sized CFs, the monofilament CF tensile strength and the interfacial shear strength (IFSS) of CF/EP were investigated. The results showed that the emulsions were mono-dispersed nanospheres and the particle size was increased with the hydrophobic groups increasing. High thermal stability with negligible weight loss unless well above 300℃ was obtained for all the emulsions. The sized CFs by the emulsions of high hydrophobic ratio (9:1 and 19:1) exhibited more favorable wettability. The CF surface defects were healed and the roughness was reduced mildly by sizing treatment. The IFSS showed a growing trend with the hydrophobic groups increasing and was significantly enhanced by 96 % as the hydrophilic-hydrophobic ratio was 19:1. The improvement of IFSS benefited mainly from the strong interphase due to the excellent film-forming property, favorable wettability and mechanical interlocking.