Influence of external and self‐emulsifying sizing agent on the properties of carbon fiber reinforced polyamide composites

Improving the interfacial adhesion is indispensable for carbon fiber (CF) reinforced polyamide (PA) composites. An external emulsion sizing agent based on epoxy resin and an anionic self‐emulsifying sizing agent by introducing p‐aminobenzoic acid (PABA) into epoxy resin and neutralizing with triethanolamine were prepared, respectively. It was found that the self‐emulsifying agent showed the benefit on reducing the hairiness of CF, which was pronouncedly decreased from 47.4 to 7.7 mg. The tensile strength of corresponding PA composite was improved from 148.3 to 186.3 MPa, while the notched impact strength was increased from 7.7 to 13.7 KN/m², compared with that of unsized CF reinforced composite. The self‐emulsifying sizing agent exhibited higher interfacial adhesion between CF and PA matrix than the external emulsion, due to the hydrogen bond between the NH group in PABA and CO group in PA. The combination of physical adsorption and chemical bond of the self‐emulsifying sizing agent resulted in the improvement of mechanical properties. POLYM. COMPOS., 40:514–522, 2019. © 2017 Society of Plastics Engineers