Environmentally-benign, water-based covalent polymer network for flame retardant cotton

Relatively simple flame retardant finishing technologies for cotton are greatly desired in a variety of fire-sensitive applications (e.g., transportation, workwear, etc.). Many current industrial processes take advantage of halogen-containing flame retardants or require complicated processing. This study demonstrates a simple and halogen-free flame retardant treatment for cotton, which proceeds via a spontaneous Mannich-type reaction between branched polyethylenimine (PEI) and tetrakis(hydroxymethyl)phosphonium chloride (THPC). A polymer network deposited using 5 wt% THPC and 10 wt% PEI endows cotton fabric with self-extinguishing behavior during vertical flame testing. The treated cotton maintains high flame retardancy after simulated washing. This coating promotes formation of a continuous intumescent char layer, effectively protecting the cellulose matrix from fire and inhibiting the production of flammable volatiles during pyrolysis and burning. The simplicity and efficacy of this relatively environmentally-benign treatment makes it attractive for replacing halogen-containing and more complex flame-retardant finishing processes.