Fluorine-Free Waterborne Polyurethane Water-Repellent Coatings: Synthesis and Textile Applications

Water-repellent textiles have gained increasing popularity in the consumer markets. However, developing high-performance water-repellent coatings without fluorine remains challenging. In this work, we propose a practical method for obtaining water-repellent waterborne polyurethane (WPU) coatings by leveraging the synergy between polydimethylsiloxane (PDMS) and 3-(2-aminoethylamino) propyldimethoxymethylsilane (KH-602). The incorporation of PDMS imparted high hydrophobicity to the WPU chains, while KH-602 underwent hydrolysis–condensation, facilitating mild interchain cross-linked networks. The effects of the PDMS content (0–30%) and KH-602 cross-linking density (0–35%) on coating properties were investigated, with conventional cross-linker DETA serving as a control. After treatment with WPU emulsions via a straightforward pad-dry-cure process, the cotton fabrics achieved a water contact angle (WCA) of 143.1°, a spray rating of 90 points, and retained a WCA of 132.0° even after 60 abrasion cycles. Notably, water repellency showed no significant loss after 360 h of continuous weathering. The diffusion and penetration of acidic/alkaline solutions (HCl, pH 3; NaOH, pH 12), saline (0.9% NaCl), and oxidizing solution (3.0% H2O2) on the treated fabric surface were suppressed, demonstrating the coating’s chemical resistance. Additionally, the tear force of the treated fabrics increased by more than 43% (from 35.82 to 51.38 N), while air permeability was only minimally reduced. The total color difference was kept below the visual perception threshold (ΔE <1.0). This work not only develops practical fluorine-free water-repellent coatings but also offers insights for the eco-friendly production of functional textile coatings.