Straightforward one-step solvent-free synthesis of the flame retardant for cotton with excellent efficiency and durability

A flame retardant, ammonium salt of 1-hydroxyethylidene-1,1-diphosphonic acid (AHEDPA), was synthesized by a facile one-step methodology and was proven to have achieved remarkable improved flame retardancy of cotton with exceptional durability because AHEDPA with functional groups PO^-(NH_4⁺)₂ could react with OH of cellulose to form new POC bonds characterized by Fourier transform infrared (FT-IR) spectra, which further verify that AHEDPA was chemically bound to cotton instead of as additive or mixing into polymer. Combustion behaviors of the control and treated cotton were assessed by cone calorimetry, vertical flammability and limiting oxygen index (LOI) tests. The cone calorimetry results display that the peak heat release rate (PHRR) and total heat release (THR) of cotton fabric treated by 30% AHEDPA were reduced up to 95% and 68%, respectively, compared with those of control cotton. No after-flame and after-glow phenomena for treated cotton were observed in vertical flammable test. LOI test evinces that the cotton fabric treated with 30-40 % AHEDPA could be used as a durable flame retardant fabric with a LOI value of 26.2-29.5% after 50 laundering cycles. Thermogravimetric (TG) data both in nitrogen and in air atmosphere reveal that the AHEDPA treated cotton notably increased the char yield by catalyzing dehydration of cellulose, thus protecting the underlying matrix from heat and fuel. The efficient and durable flame retardant for the AHEDPA by the one-step synthesis method has great development prospects in industrial.