Durable Hydrophobic Textile Coatings Enabled by <scp>PDMS</scp> /Fumed Silica‐Modified Bio‐Based Waterborne Polyurethane

ABSTRACT The development of environmentally compliant, PFAS‐free low‐surface‐energy and protective coatings has increased demand for sustainable polymer systems with tunable thermal, mechanical, and surface properties. In this study, bio‐based waterborne polyurethane‐PDMS‐fumed silica (BWPU‐PDMS‐SiO 2 ) hybrid dispersions were synthesized using renewable polyols, PDMS soft segments, and controlled silica load. FT‐IR and XRD confirmed hybrid formation without structural disruption of the polymer backbone, while XPS revealed silica‐polymer interfacial interactions that evolved with the filler content. Thermal analysis (DSC/TGA) showed that the soft‐segment glass transition remained unchanged, whereas the thermal stability improved with increasing fumed silica content, with the most pronounced enhancement observed at 3 wt%. Mechanical testing demonstrated an increase in tensile strength at the same loading, indicating that well‐dispersed silica contributes to effective network reinforcement of the polymer. Contact angle measurements revealed reduced surface energy for cast films and coated fabrics, consistent with the effects of PDMS chemistry, silica‐induced surface restructuring, and substrate microtexture. These results identify 3 wt% as the optimal fumed silica concentration that balances the dispersion, interfacial organization, and property enhancement within the hybrid matrix. This study provides a sustainable and versatile route to bio‐based, PFAS‐free polyurethane‐siloxane hybrid coatings suitable for low‐surface‐energy, fouling‐resistant and advanced surface‐engineering applications.