Waterborn Epoxy Resin Sizing Agent For Carbon Fiber

Because of their excellent strength, modulus and heat resistance, carbon fibers are now utilized in a variety of applications. However, Carbon fibers have low ductility and are brittle, so they are apt to be damaged during processing which includes repeated bending and repeated frictional contact with, for example, guide rollers, thereby causing cleavage of filaments and fluff of the fibers. In the preparation of fiber-reinforced composite material, the fluff of carbon fibers impedes the compatibility thereof with a matrix resin so that the composite material fails to exhibit satisfactory mechanical properties. To cope with this problem, a method is proposed for treating carbon fibers with a sizing agent. Traditionally, acetone are usually used as the solvent for the sizing agent of carbon fiber, which could not only increase the production cost, but also cause the variation of concentration for sizing agents, environmental pollution and fire hazard due to the volatility. Without these problems, waterborne epoxy resin sizing agent adopting water as solvent or dispersed medium have attracted more and more attention.In recent years, research about waterborne epoxy resin sizing agent mainly focuses on the mixing emulsifier to prepare a waterborne epoxy resin sizing agent, though there is little research on counterpart with self-emulsifying ability through chemical modification. However, some problems occur that although the emulsifier can increase the wetting speed of fibers during the sizing process, the residual inactive emulsifier can impact the chemical resistance and hydrolytic resistance of end products, while these problems don't exist in the sizing agent with self-emulsifying ability.In this article, chemical modification method has been used to prepare the modified epoxy resin with self-emulsifying ability. Hydrophilic diethanolameine reacts with epoxy resin to form termination agent, which is neutralized by acetic acid to produce the salts. By testing conversion of epoxy group, the reaction temperature, time and proportion of reactants can be determined. Moreover, modified epoxy resin is used to form waterborne system with high solid content, and the stability, viscosity and dilutability of it are also analyzed.Waterborne epoxy resin sizing agent is obtained by diluting the solid content of waterborne system from 60% to 3%. According to the performance requirements of sizing agent, stability, viscosity, pH value, distribution of particle size and film forming properties are characterized by tests.Compared with epoxy resin/acetone sizing agent, waterborne epoxy resin sizing agent has been used to size the carbon fiber, at same time this article analyzed the effect of sizing agent on the carbon fiber, including fiber surface, abrasion resistance, breaking amount, tensile property and interface property. The result shows that the property of carbon fiber sized by waterborne epoxy resin is much better than the sizing agent of epoxy resin/Acetone:add-on size is more stable, sizing agent can develop into a lubricating, complete film around the surface of single carbon fiber, protecting the fiber efficiently; it can greatly reduce the amount of fluff and enhance the abrasion resistance, as a result, the tensile strength can be improved; it can also give full play of transmission layer, enhancing the interfacial shear strength of matrix and fibers, which can meet the needs of using carbon fiber in different kinds of finished products such as weaving and composite materials.