Molecular Engineering of Waterborne Polyurethanes via Functional Copolymerization for High-Performance Carbon Fiber Coating: Synergistic Strengthening of Wettability and Mechanical Properties

Waterborne polyurethanes (WPUs) have become the preferred alternative for researchers aiming to replace solvent/emulsion-based resins in carbon fiber (CF) coatings, owing to their superior adhesion, eco-friendliness, and cost-effectiveness. However, conventional polyester-based WPUs have often exhibited inadequate mechanical properties, thermal stability, and solvent resistance. To tackle these limitations, modified WPUs were developed by incorporating alkyl long chains, benzene π–π bond stacking, aromatic ring ether bonds, and biphenyl groups into the molecular structure through the functionalization of the polymerization system with 1,7-hexanediol, ethoxylated bisphenol A, and 1,3/1,4-bis(2-hydroxyethoxy) benzene. The inclusion of these comonomers optimized the properties of the WPUs with significant increases in thermal weight loss temperature T5% and tensile strength of 23.4% and 53.1%, respectively. The utilization of WPUs as coatings proved to be highly effective in enhancing the chemical activity, wettability, and mechanical properties of CF. The application of the coating resulted in a substantial improvement, with a 58.2% increase in the fiber surface energy and a 21.5% enhancement in the filament tensile strength, reaching values of 54.1 mN/m and 6.053 GPa, respectively. Furthermore, the WPUs exhibited the capability of rectifying defects in CF and enhancing surface roughness. Importantly, the tensile properties of WPUs-CF exceeded those of numerous established counterparts globally, highlighting a broad spectrum of potential applications.