Constructing an interaction in plant polyphenol-modified carbon fiber with amylopectin-based waterborne polyurethane sizing agent via hydrogen bonding to improve the interfacial performance of carbon fiber/nylon 6 composites

The adhesive strength between the sizing agent and carbon fiber (CF) plays a crucial role in improving the interfacial properties of composites, while such a vital aspect has been consistently disregarded. In this study, a hyperbranched waterborne polyurethane (HWPU) sizing agent was synthesized from biogenetically raw materials including gallic acid, l-Lysine diisocyanate and amylopectin. Concurrently, hydrogen-bonded cross-linked network structures were established utilizing a botanical polyphenol tannin as coupling agent to effectively connect CF with HWPU. This meticulous process yielded CF/nylon 6 composites with improved properties and their mechanical characteristics were systematically investigated. The findings showcased a noteworthy boost in flexural strength and interlaminar shear strength (ILSS), showing enhancements of 54.6 % and 61.4 %, respectively, surpassing those of untreated CF. Furthermore, the interfacial shear strength (IFSS) test indicated a remarkable 70.3 % improvement. This approach presents a highly promising concept aimed at developing sustainable green waterborne polyurethane sizing agent and improving the interfacial performance of CF composite materials.