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.