Synthesis of a phosphorus-nitrogen flame retardant endowing cotton with high whiteness and washability

Cotton is the seed fiber of the Gossypium plant (from the Malvaceae family), which is one of the most important crops worldwide and is suitable for the application in clothes, furniture, and industrial fabrics areas. Combustible cotton easily triggers fire hazard. Thus, a phosphorous-nitrogen flame retardant, ammonium salt of tris-(hydroxymethyl)-aminomethane-penta(methylphosphonic acid) (ATPMPA) was synthesized to produce fire-retardant cotton. The ATPMPA structure was characterized by nuclear magnetic resonance (H-1 NMR, C-13 NMR, and P-31 NMR) spectroscopy. ATPMPA flame-retardant cotton was prepared by phosphate esterification between ATPMPA and the -OH groups of cotton cellulose. Scanning electron microscopy verified that the surface of the treated cotton fiber was not obviously changed. The flame retardantcy of cotton was tested using the LOI, vertical burning and cone calorimetry. The results revealed that the LOIs of the control cotton and treated cotton fabrics increased from 18.4% to 40.8%. 42.4%, and 43.6% after treated with 20 wt%, 30 wt% and 40 wt% flame retardant, respectively. After 50 laundering cycles (LCs), the LOIs of the treated cotton fabrics only decreased to 26.7%, 30.8%, and 32.3%, respectively, indicating that treated cottons obtained the superior flame retardancy and excellent washing resistance. Thermogravimetry (TG) analysis showed that the charring ability of the treated cotton was markedly improved. TG-IR result of treated cotton indicated that the decomposition temperature and the amount of volatile matter produced by the flame-retardant cotton were lower than that of control cotton. The whiteness of treated cotton sustains well.