Sulfonate/Carboxylate Synergistically Modified Waterborne Polyurethane Sizing Coatings with Chemical Cross-Linking and Hydrogen Bonding Effects for Improving Surface Wettability and Mechanical Performance of Carbon Fibers

Abstract

The sulfonate/carboxylate synergistically modified waterborne polyurethane (SWPU) was designed with intramolecular chemical cross-linking and hydrogen bonding interactions by introducing trihydroxy cross-linker into carboxylate WPU (CWPU) and using aliphatic diamine sulfonate as the hydrophilic post-chain extender. The particle size, viscosity, thermal stability of SWPU, as well as the surface energy, wettability, roughness, adhesion, interface functionality, compatibility, and mechanical performance of carbon fibers (CF) treated with SWPU (SWPU-CF) were improved by adjusting the ratio of carboxylate and sulfonate hydrophilic units. The complexation and dipolar effects of −COO−NH+ and polar −SO3−Na+ groups in SWPU enhanced the interaction forces and configuration regularity between molecular chains. SWPU not only repaired the defects on CF, improving the surface roughness, but also reduced the original inertness of CF while enhancing the surface chemical activity and wettability through polar groups. The surface energy and polar components of SWPU-CF reached 44.4 mN/m and 33.1 mN/m, which were increased by 1.5 times and 4.7 times, respectively, while the tensile strength of fibers improved by 24.3% (5.78 GPa) compared to untreated CF (4.65 GPa). SWPU can optimize CF filaments and fiber-resin composites for practical industrial applications, such as vibration damping devices for trains and drive shafts for energy vehicles.

Keywords: Waterborne polyurethane, Complex hydrophilic units, Carbon fibers, Surface wettability, Interface functionality, Mechanical performance