High‐epoxy value bio‐based epoxy emulsion reinforced interfacial properties of carbon fiber/epoxy composites

Abstract The development of new bio‐based epoxy resins and the search for new application areas have become important research directions for bio‐based epoxy resins. Using protocatechuic acid (PA) as a bio‐based raw material, brominated alkenes with different chain length were introduced into PA through substitution reaction, and then oxidized to obtain epoxy resins (PA‐EP) with different epoxy values. After that, it was introduced into epoxy resin (diglycidyl ether bisphenol A DGEBA) sizing agent to replace part of DGEBA to prepare new sizing agents. Sizing amount test and sizing CF surface morphology show that the introduction of PA‐EP with high‐epoxy value made it easier be adhered to carbon fiber (CF) surface during sizing process. Interfacial shear strength and interlaminar shear strength of composite made of sizing CF (20 wt% PA‐EP‐3) were 56.86% and 30.29% improvement against the bare CF, which was attributed to the increase in surface energy and epoxy groups after CF sizing. Therefore, PA‐EP with high‐epoxy value was applied as sizing agent for improving interface performance of CF for the first time, and this application was less affected by its low‐output problem compared to its application as a matrix resin in the field of composite manufacturing.