Eco-friendly synthesis of a highly efficient phosphorus flame retardant based on xylitol and application on cotton fabric

A novel formaldehyde-free and bio-based flame retardant, ammonium salt of xylitol phosphoric ester acid (ASXPEA), was synthesized under moderate and solvent-free conditions. The structure of this flame retardant was characterized by 1H nuclear magnetic resonance (NMR), 13C NMR, and 31P NMR. The FT-IR spectrum confirms that the ASXPEA flame retardant was grafted on cotton fibers through P–O–C covalent bonds. The limiting oxygen index (LOI) values of cotton treated with 7% and 10% ASXPEA flame retardant reached 41.8% and 45.2%, and their LOI values after 50 laundering cycles were maintained at 29.6% and 30.2%, respectively, with outstanding durability. Results of vertical flammability and cone calorimetry suggest that the treated cotton fabrics achieved excellent flame resistance, and high residues were obtained after combustion by thermogravimetry (TG) analysis. TG-infrared analysis indicated that the treated cotton released fewer flammable gases than the control. Scanning electron microscopy and X-ray diffraction analyses of cotton before and after treatment verified that the fiber structure of the treated cotton had sustainable mechanical properties.