Toward greener coating technologies: CNC-enhanced waterborne polyurethanes for robust barrier and corrosion resistance

Waterborne polyurethane (WBPU) coatings offer an eco-friendly substitute for corrosion protection, though their barrier qualities remain limited. In this work, the effect of cellulose nanocrystals (CNCs) at 0.5, 1, and 2 wt.% loadings on the physico-chemical and protective performance of WBPU nanocomposites is examined. CNCs, with high crystallinity and hydroxyl functionality, strengthen the polymer matrix via hydrogen bonding, improving network compactness and decreasing defect formation. FTIR analysis verified enhanced molecular interactions, while thermal tests (DSC, TGA) demonstrated elevated stability and crystallinity, especially at 1 wt.% CNC. Tensile strength and modulus peaked with 1 wt.% CNC, pointed optimal dispersion and stress transfer. FESEM imaging represented homogeneity at lower CNC levels, which were further corroborated by atomic force microscopy (AFM) through surface topography analysis, while Water Vapor Permeability (WVP) analysis showed reduced water vapor diffusion due to increased tortuosity. Electrochemical impedance spectroscopy (EIS) demonstrated superior long-term corrosion resistance in WBPU/1%CNC coatings, with high coating resistance, reduced capacitance, and stable impedance over 70-day immersion. Overall, CNCs—especially at 1 wt.%—function as multifunctional nanofillers, enhancing WBPU coatings in terms of durability, barrier performance, and sustainability. These nanocomposites present a promising solution for advanced protective applications in corrosive environments.