Flame‐Retardant Waterproof Breathable Polyurethane Thin Films via Green Synthesis for Textile Applications

ABSTRACT The demand for flame‐retardant, waterproof, and breathable textiles is increasing, but achieving fire resistance in polyurethane (PU) films without compromising mechanical properties and sustainability remains challenging. Conventional PU coatings often rely on toxic solvents and non‐biodegradable flame retardants, raising safety concerns. This study develops hydrophilic, flame‐retardant PU films using 1,3‐dioxolane, a greener alternative to dimethylformamide (DMF). Two series of PU films were synthesized via condensation of polyethylene glycol (PEG 1500) and methylene diphenyl diisocyanate (MDI) with and without a crosslinker. A ternary flame‐retardant (FR) formulation of ammonium polyphosphate (APP), aluminum trihydrate (ATH), and pyromellitic dianhydride (PMDA) was incorporated to enhance flame resistance. The films were evaluated for morphology, thermal stability, flame retardancy, mechanical strength, water sorption, breathability, and waterproofness. Non‐crosslinked films achieved a VTM‐0 rating but exhibited melt drips, necessitating crosslinking for improved performance. FR additives reduced the initial degradation temperature while increasing char yield. FTIR analysis indicated in situ polyimide formation by the reaction of PMDA with isocyanate released from the degradation of PU. By integrating a green solvent and an optimized FR formulation, this study presents an eco‐friendly approach to flame‐retardant breathable coatings, advancing sustainable protective textiles for fire‐resistant applications.