Preparation and characterization of waterborne polyurethane coatings modified with cyclotriphosphonitrile derivative for waterproof and flame-retardant cotton fabrics

Since the main solvent of waterborne polyurethane (WPU) is water, its water resistance is poor. Additionally, the low oxygen index of WPU adhesive films limits their flame-retardant efficacy as coatings, thereby restricting their application scope. To address these limitations, this study independently modified the hydrophobicity and flame retardancy of WPU. First, a cyclophosphonitrile derivative (HCCP-6) was synthesized as a flame retardant. Flame-retardant WPU (NPWPU) was then prepared by reacting the –NH 2 group of HCCP-6 with the –NCO group of a polyurethane prepolymer, incorporating the flame-retardant properties into the WPU polymer chain via free-radical grafting. Next, hydrophobic F-SiO 2 suspensions were prepared and combined with NPWPU emulsions of varying concentrations. The mixtures were sprayed onto cotton fabrics using an airbrush to produce waterproof, flame-retardant polyurethane-coated textiles. Results demonstrated that NPWPU/F-SiO 2 -coated cotton fabrics exhibited water contact angles exceeding 150°, indicating excellent hydrophobicity. These fabrics also showed increased char residue, reduced total heat release, and suppressed smoke production. This performance stems from the synergistic flame-retardant effect of nitrogen (N) and phosphorus (P), coupled with the high-temperature resistance of SiO 2 , which promotes char formation, shields the material’s inner layers from thermal degradation, and enhances overall flame retardancy.