Synthesis And Characterization Of Novel Epoxy-modified Waterborne Polyurethanes And Their Use In Carbon Fiber Sizing

Carbon fibers sizing is one important assistant material in the industry ofcarbon fibers, which plays an important role in protecting fibers andimproving the fibers surface properties．At present, the emulsion form ofsizing agent is widely used. Although the emulsifier can increase the wettingof fibers, emulsifier is a poor bonding agent which can impact the mechanicalproperties and water absorption of end products. In this work, a novel watersoluble sizing agent with self-emulsifying and self-crosslinked ability wasprepared.Two epoxy-modified waterborne polyurethanes (EPU1and EPU2,namely EPUs) were synthesized from toluene2,4-diisocyanate (TDI),polyethylene glycol (PEG,200/400), dimethylolbutyric acid (DMBA), and2,3-epoxy-1-propanol. The chemical structures of EPUs were characterized by1H NMR and IR. The effect of various reaction conditions, such as reactiontemperature, solvent, feeding method and pH on the synthesis of the prepolymer were investigated, and the best reaction parameters was selected.The thermal properties and curing reactions of the EPUs were examined byTGA and DSC. The TGA analysis showed that EPU1appears to be morestable than EPU2, and their initial decomposition temperature are high than250℃. The DSC analysis showed that the self-crosslinked reaction betweencarboxylic acids and epoxies of EPUs can take place at over140℃Two kinds of waterborne sizing agent, namely, s-EPU1and s-EPU2wereprepared and used to size the carbon fibers. Effect of sizing agent on the fiberssurface properties and mechanical properties are analyzed, including massfraction of sizing agent, water absorption, abrasion resistance, cluster, fibersurface and interface property. Compared with epoxy emulsion sizing ands-EPU1, the property of fiber sized s-EPU2is much better, sizing amount isstable; sizing agent can develop into a complete film on the surface of carbonfiber to protect the fiber efficiently; it also can greatly reduce the amount offluff and water absorption, but enhance the abrasion resistance and cluster;moreover, some concave and convex hills on the fiber surface were observed,which increase the carbon fibers surface polarity and roughness. As a result,the interfacial shear strength of matrix and fibers was enhanced. Compared tothe unsized carbon fiber composites, the interlaminar shear strength (ILSS) ofcomposites reinforced by the s-EPU1sized carbon fiber reached75.5MPa,increased17%; composites reinforced by s-EPU2sized carbon fiber reached71.2MPa, increased12%. The first time the sizing agent s-EPU2contains well dispersed CNTs,namely, e-EPU2was prepared and used to size the carbon fibers. Effect ofe-EPU2on the electrical conductivity and interfacial adhesion in fibercomposite are analyzed. The results showed that after e-EPU2sizing treatment,the composites electrical conductivity reached17.7×102S/m; the ILSS reached66MPa.