Highly durable phosphoramidate/ammonium phosphate flame retardant for cellulose textile from natural materials: phytic acid and l-lysine

Due to the depletion of oil resources and the implementation of carbon-neutral strategies, pursuit of natural material-based flame retardants with high-durability flame retardancy has become an increasingly important issue. In this work, a small molecular phosphoramidate/ammonium phosphate flame retardant for cotton fabrics was synthesized with natural materials phytic acid and l-lysine, which was characterized by phosphorous-31 nuclear magnetic resonance and Fourier-transform infrared (FTIR) spectroscopy. Limiting oxygen index (LOI), vertical combustion, cone calorimetry, and durability tests showed that the finished sample had outstanding flame retardancy and superb washing resistance. LOI of the treated fabric at a weight gain of only 17% was 50.7%, and remained at 38.3% after 50 laundering times under AATCC 61-2013 3A standard. Thermogravimetric and thermogravimetric-infrared measurements proposed that the flame retardants primarily promoted char formation of cellulose and performed a condensation phase flame-retardant mechanism. FTIR and X-ray photoelectron spectroscopy results showed that the flame retardants grafted onto cellulose by N–P(=O)–O–C covalent bonds. Surface micromorphology and energy-dispersive X-ray analyses showed that flame retardants were evenly distributed in cotton, and with little metal ions remained after washing, indicating that the stable phosphoramidate maintained its flame retardancy. The whiteness and softness retention after modification were significantly improved.