Interfacial and interlayer enhancement of highly hydrophilic dual-affinity waterborne polyurethane sizing agent acting on carbon fiber/epoxy resin composites

Dual-affinity waterborne polyurethane (WPU) sizing agents with different solid concentrations were designed to achieve two-stage interfacial properties of carbon fiber (CF) and epoxy resin (EP) reinforced composites. The effects of hydrophilic monomer content on the emulsion dispersion of WPU sizing agents and the thermal properties of the coating films were investigated, and the best performing component was selected as the sizing agent of CF to prepare WPU treated-CF. The analysis focuses on the changes of surface morphology and roughness, ionic group types, tensile strength of CF before and after WPU sizing, and the interfacial properties, interfacial strengthening mechanism of CF/EP composites. Compared with conventional commercial CF, the WPU treated-CF shows a 4 % increase in surface free energy and a noticeable improvement in surface roughness and morphology. The wettability, compatibility and adhesion of WPU treated-CF/EP composites were improved according to the strong polar “similarity intermiscibility” between the strong polar functional groups in WPU and EP. Most importantly, the interfacial shear properties (IFSS) of WPU treated-CF/EP composites were improved by 17.2 % and the interlaminar shear properties (ILSS) were improved by 23.8 %. The dual-affinity WPU sizing agent optimizes the practical effect of CF/EP composites for applications such as instrument components and surface coatings used in new energy vehicles, high-speed rail trains, aerospace and provides a boost to the development of new environmentally friendly high-performance chemical coatings.