Improved interfacial adhesion in carbon fiber/poly (ether ether ketone) composites with the sulfonated poly (ether ether ketone) sizing treatment

A water‐soluble sulfonated poly (ether ether ketone) (SPEEK) sizing agent is prepared and applied to improve the interfacial adhesion of carbon fiber/poly (ether ether ketone) (CF/PEEK) composites. The surface morphology, surface roughness, surface chemistries, and surface free energy of SPEEK sized CF are obtained to understand the sizing effect. The results reveal the increased surface free energy and surface roughness of SPEEK sized CF. In addition, a chemical reaction between the CF surface and sizing layer is proved based on the results of XPS, IR, and 1H NMR. The interfacial structure of CF/PEEK composites is further ascertained by AFM and the appearance of gradient interface could be verified for SPEEK sized CF/PEEK composites. The formation of the gradient interface is due to the chemical reaction between the CF and sizing agent as well as the improved compatibility between the sized CF and matrix, which benefits the improvement of interfacial adhesion. The SPEEK sizing agent was used to improve the interfacial adhesion between CF and PEEK resin based on the formation of gradient interface. The main reasons for the formation of the gradient interface are the improved interfacial compatibility between SPEEK sized CF and PEEK resin as well as the existence of the chemical reactions between CF and SPEEK sizing layer.