A novel high durability flame retardant with phosphoric acid ester groups and a reactive ammonium phosphorus acid group for cotton fabrics

A novel reactive flame retardant with two phosphoric acid ester groups and one ammonium phosphorus acid group, the ammonium salt of 2,7-bis(dimethoxyphosphoryl)-3,7-dimethyl-3-phosphonic acid (FR–LO), was synthesized. The treated cotton fabrics displayed a high flame retardancy and excellent durability because the FR–LO molecule contains two phosphoric acid ester groups without an ammonium ion that can be eliminated and decrease the flame retardancy. The cotton fabrics treated with 30% FR–LO had limiting oxygen indexes of 43.4, and 29.7 after 50 laundry cycles according to AATCC 61–2013 2A standard. Scanning electron microscope images and energy-dispersive X-ray spectroscopy showed that the treated cotton fibers retained their complete structure after combustion, and nitrogen and phosphorus were present in the treated cotton fibers. Thermogravimetric and thermogravimetric-infrared analyses showed that the treated cotton produced more carbon residue and released fewer combustible gases during thermal decomposition. Microscale combustion calorimetry showed that the heat release rate and total heat release of the treated cotton during combustion were much lower than those of pre-treated cotton. The stiffness of cotton treated with FR–LO increased, and its tensile strength decreased compared with pre-treated cotton.