Enhancing Water Resistance and Mechanical Properties of Waterborne Polyurethane Coating Films via Surface Modification of Cellulose Nanocrystals With Long‐Chain Alkyl Alcohols

ABSTRACT In the application of waterborne coatings, enhancing the water resistance and mechanical properties of coating films derived from waterborne coatings has been a critical challenge in need of urgent resolution. To tackle this issue, we propose an innovative strategy that involves surface modification of cellulose nanocrystals (CNC) using long‐chain alkyl alcohols and the preparation of polyurethane composite films with excellent hydrophobicity by compounding the modified CNC (C‐CNC) with waterborne polyurethane (WPU). Using a custom mold, we achieved surface hydrophobic functionalization. This study delves into the impact of CNC on the hydrophobic composite film, particularly focusing on its contribution to film morphology, thermal properties, and mechanical properties, significantly enhancing its hydrophobicity. Experimental results demonstrate that the mold with a rough surface constructs numerous rough and porous structures on the coating film surface, significantly enhancing its hydrophobicity. Notably, the C 28 –CNC/WPU composite film prepared using octacosanol‐modified CNC exhibits the best hydrophobicity, with a water contact angle reaching 122.80°. This strategy of preparing hydrophobic coating films through a simple and effective method not only overcomes limitations of waterborne coatings in terms of water resistance and mechanical properties but also holds significant potential for environmentally friendly coatings, offering new insights for waterborne coating development.