Synthetic design of waterborne polyurethane and its effect on structural properties of carbon fiber sizing agent

To improve the high-temperature resistance of epoxy-based sizing agents，waterborne polyurethane （WPU） with excellent performance is synthesized and blended with the epoxy-based sizing agent to obtain a composite sizing agent. The carbon fiber surface is then sized with this composite sizing agent. The influence of the introduction of WPU on the high-temperature resistance of the composite sizing agent is studied，and the effects of the composite sizing agent on the surface structure and properties of the carbon fiber are analyzed. The results show that WPU with uniform particle size and excellent thermal stability can be synthesized using polycarbonate diol as the raw material，and it exhibits superior wettability on the surface of carbon fibers. During the preparation of the composite sizing agent，when the mass ratio of WPU to epoxy resin （EP） is 1∶2，the composite sizing agent obtained has good particle size distribution，exhibits excellent wettability （with a contact angle of only 53.75°） on the carbon fiber surface，and possesses outstanding thermal stability with no significant mass loss up to 600 ℃. After further sizing the carbon fibers with the composite sizing agent，the oxygen-to-carbon ratio （O/C） on the fiber surface increases significantly，the fiber strength increases slightly，and the mechanical properties of the composites are significantly improved.