Molecular Engineering of Hybrid Functional Waterborne Polyurethane Coatings: Synergistic Effects on Interfacial Enhancement of Carbon Fibers

Waterborne polyurethanes (WPUs) have emerged as the preferred alternative to conventional sizing coatings such as epoxy resins and solvent-borne polyurethanes for carbon fibers (CF), owing to their superior environmental compatibility and cost efficiency. However, WPUs typically exhibit poor mechanical properties, low thermal stability, and inadequate adhesion. To overcome the limitations of the coatings, it is essential to design WPUs through molecular optimization, co-monomer compounding, and incorporation of functional segments. A polyetheramine diol (PHBA-D1000) was synthesized via a Schiff base reaction between Jeffamine D1000 and 4-hydroxybenzaldehyde (PHBA) and was employed as the soft segments. Subsequently, a silane coupling agent (BASE) featuring a bisimine structure was prepared using ethylene glycol, trichlorosilane, and ethanol as the backbone components. Finally, N, N ′-di-sec-butyl-4, 4’-methylenedianiline and BASE were utilized as chain extenders to construct molecular architectures incorporating dynamically reversible imines, π-conjugated stacking, ether linkages, biphenyls, polyureas, carbamates, siloxane functionalities, and Si–O–Si cross-linking networks within PWPUs. The synergistic effects between polar groups and rigid chains contribute to enhanced thermal stability (T10% of 331.2 °C), tensile strength (36.4 MPa), elastic modulus (14.2 MPa), adhesion (21.9 kPa), water, and chemical resistance in PWPUs. Additionally, sizing CFs with PWPU coatings enhanced the interfacial adhesion, chemical activity, and wettability of the fibers. Specifically, the surface energy of PWPU-CF reached 59.7 mN/m, representing increases of 68.2% compared to unsized CF. Similarly, PWPUs demonstrate the ability to repair defects and improve surface roughness at CF interfaces. PWPU exhibits excellent functional properties, demonstrating significant potential for development and research in CFs and their composites. It can meet the application requirements of aerospace, new energy vehicles, rail transit, chemical equipment, and building materials, etc.