Preparation of waterborne polyurethane with high surface activity for regulating the interfacial properties of carbon fiber/polyamide 6 composite

The poor wetting and spreading performances of waterborne polyurethane dispersion (WPUD) on carbon fiber (CF) surface limited its application in regulating the interfacial properties of CF reinforced polyamide 6 (PA6) composites. Unlike previous studies, this work diversified into improving the film-forming property of WPUD on CF surface. Two novel WPUD sizing agents named WPUD-Y1 and WPUD-F1 were synthesized by introducing block polyether and organic fluorine into the molecular chain. Results showed that surface energies of the elaborately designed WPUD-Y1 (35.5 mN/m) and WPUD-F1 (32.7 mN/m) were significantly lower than that of ordinary WPUD (40~55 mN/m). Especially, both sizings formed a complete and uniform film on CF surface. Interfacial shear strength (IFSS) analysis from micro-droplet test showed that sizing relieved the thermal residual stress at composite interphase by over 40%, at the cost of reducing its interfacial strength by 20%. More importantly, although sizing had not enhanced interfacial adhesion, the IFSS values between the sized CF and PA6 were still 20% higher than the maximum interlaminar shear strength (ILSS) values reported in literatures.