A facile strategy to achieve efficient flame-retardant cotton fabric with durable and restorable fire resistance

Abstract

Novel, durably flame-retardant cotton fabrics with fascinatingly restorable fire resistance were prepared by simple grafting of phosphate and melamine, which contributed to a phosphorous-nitrogen (P/N) synergism. During the preparation process, phosphate was grafted with the hydroxyl groups of cellulose to form P-O-C bonds; subsequently, melamine reacted with the aldehyde groups of cellulose generated from phosphorylation to form P/N modified fabrics (P/N-Cotton). The P/N synergistic effect endowed cotton fabric with prominent fire resistance and durability. The Limit oxygen index (LOI) was as high as 51.1 ± 0.3% and was maintained at 32.7 ± 0.8% after 50 laundering cycles (LCs). The total heat release (THR) and peak values of heat release rate (pHRR) of P/N-Cotton were significantly reduced by 70.11% and 64.19%, respectively. Amazingly, the modified cotton fabrics exhibited restorable fire resistance once immersed into the acetic acid solution due to the ion exchange between Na+ from detergent and H+ from acetic acid. The LOI of P-Cotton and P/N-Cotton after 50 LCs can be restored to 32.4 ± 0.7% and 35.7 ± 0.7% from 20.8 ± 0.7% and 32.7 ± 0.8%, respectively. The analysis of gas-phase products and residual char demonstrated that the incorporation of phosphate and melamine facilitated cellulose fibers to convert to dense and stable graphitized carbon layers and carbon-nitrogen heterocycles, effectively protecting the fabric from decomposing to flammable gases.