Fabrication And Properties Of A Self-Emulsified Sizing Agent Based On Waterborne Epoxy Resin

With the development of rapid industrialization, carbon fiber has become an essential strategic material in national defense industry and national economy, due to excellent high temperature resistance, high specific strength and modulus. Carbon fiber, as one of the most important technology-intensive products, has been widely used in the field of astronautics, aeronautics, automobile, mechanical industry, electronics, chemical industry. However, the further application of carbon fiber is limited by its brittleness and lower elongation rate, which may cause broken filaments and fracture of monofilament, hindering the infiltration of resin matrix into carbon fiber bundles during the manufacture of fiber reinforced composites. In order to solve the above problems and improve the interfacial properties of composites, sizing agent with the thickness ranged from tens to hundreds nanometers is usually applied to the surface of carbon fibers. In this paper, a self-emulsifying sizing agent based on water-borne epoxy resin was prepared and its properties were carefully studied.We introduce epoxy groups into castor oil polyoxyethylene ether (EL-80) with strong hydrophilic property to prepare castor oil polyoxyethylene glycidyl ether (COPEGE) using chemical modification method. The effects of catalyst dosage, reaction temperature, reaction time and reactant ratio on the epoxy value were studied. Then COPEGE was grafted onto epoxy resin to obtain self-emulsifying hydrophilic polymer. The optimum experimental conditions, such as catalyst dosage, reaction temperature, reaction time and reactant radio, were determined through examining the stability of emulsion.The structure identification of two-step synthesis products were characterized by FTIR spectrum, and gel permeation chromatography (GPC). Finally, the self- emulsifying water-borne epoxy resin sizing agent with a solid content of 40% was prepared from the synthetic polymer by phase inversion techno logy. The particle size and distribution, emulsion stability, and emulsion particle microstructure of the sizing agent were then characterized. Results indicated that sizing agent has a small emulsion particle size and uniform stability without sedimentation. The viscosity value of the sizing agent was close to that of AK-8 (made in Japan) at the same solid content.The properties of two kinds of sizing agent and their effects on carbon fibers and composites were compared. The results showed that the property of carbon fiber sized by self-emulsifying water-borne epoxy resin sizing agent was slightly lower than that of the AK-8 sizing agent. However, the self-emulsifying sizing agent had a stable sizing rate, moderate viscosity, and could form a smooth and complete film on the surface of carbon fiber monofilament, which could effectively protect the carbon fiber and give full play to the role of the transition layer. Therefore, the interlaminar shear strength of the composites was significantly improved due to the strong carbon fiber/resin interface which was enhanced by the self-emulsifying sizing agent.