Methacrylamide‐substituted para‐aramid as an innovative sizing agent for improving the mechanical properties of carbon fiber/vinyl ester resin composites

Abstract Carbon fiber‐reinforced resin composites (CFRCs) utilizing vinyl ester (VE) resin as the matrix have found extensive applications in military equipment, transportation, sports and entertainment, wind power generation, and various other fields. However, the inherent inertness of the carbon fiber (CF) surfaces makes it difficult to form covalent bonds between VE resin and CFs, thereby limiting the application of CFs/VE composites. The sizing process is an effective method for the surface modification of CFs that improves the final mechanical properties of CFRCs. In this study, a novel organo‐soluble methacrylamide‐substituted para‐aramid, poly(p‐methacrylamino‐phenylene methacrylamino‐terephthalamide) (mPPTA), characterized by methacrylamide side groups attached to the phenyl moieties of its rigid‐rod‐like backbone, was used as a novel sizing agent for the surface modification of CFs in the fabrication of CFRCs via vacuum‐assisted resin infusion (VARI). CF fabrics were coated with mPPTA through solution impregnation. The CF‐matrix interfacial bonding was evaluated using a transverse fiber bundle tensile test, which indicated a 51.1% enhancement in interfacial bonding strength due to mPPTA. The application of merely 0.281 mg/cm² of mPPTA on each CF sheet resulted in significant improvements in flexural strength, flexural fracture total energy, interlaminar shear strength, and mode II interlaminar fracture toughness of the composites, with increases of 75%, 156.3%, 85.1%, and 90.1%, respectively. These enhancements surpass those reported for CFRCs modified using other sizing agents or matrix reinforcements. This method presents a new opportunity for fabricating of high‐performance VE resin‐based CFRCs using VARI. Highlights A novel methacrylamide‐substituted rigid‐rod para‐aramid (mPPTA) was synthesized. mPPTA was synthesized by reacting methacryloyl chloride with aminated PPTA. mPPTA serves as a novel sizing agent for producing VE/CF composites through VARI. mPPTA significantly enhances the mechanical properties of the VE/CF composites.