A Novel Flame Retardant for Cotton Containing Ammonium Phosphonic Acid and Phosphonate Prepared from Urea

A novel urea tetramethylene diphosphate dimethyl ammonium diphosphate (UTDDAD) flame retardant was synthesized. The structure of UTDDAD was characterized by NMR. The limiting oxygen index of 30% UTDDAD cotton fabric was 42.2% and was still 32% after 50 laundry cycles (LCs). The results showed that the UTDDAD flame retardant displays excellent flame retardancy and durability. Fourier transform infrared spectroscopy, X-ray photoelectron spectroscopy and durability test results suggested that the UTDDAD formed covalent bonds with the cellulose, while scanning electron microscopy and X-ray diffraction results showed that UTDDAD has only a slight effect on the structure of the cellulose fiber. The thermogravimetric analysis and cone calorimetry results indicated that cotton fabric treated by UTDDAD follow the condensed flame retardancy mechanism. The UTDDAD-finished cotton fabrics maintained approximately 70% of the tensile strength of the original cotton. Hence, introduction of phosphonate groups in flame retardants is an effective strategy for increasing the durability of flame retardant cotton products.