Eco-friendly and durable flame-retardant coating for cotton fabrics based on dynamic coordination of Ca2+-tannin acid

Eco-friendly durable flame-retardant coatings for cotton fabrics are urgently needed but remain a huge challenge. Here, we reported a highly durable flame-retardant coating without formaldehyde, halogen, or even phosphorus through co-coordination of biomass tannin acid (TA), tartar emetic (TE), and Ca2+. In this system, due to the dynamic replenishment of Ca2+ naturally present in tap water, the coating can maintain high durability during the long-term tap washing process. Meanwhile, Ca2+ can effectively catalyze TA and cotton fibers to form graphitized carbon residues, thereby achieving high flame retardancy. As a result, the treated cotton fabrics showed excellent durable flame retardancy. Even after 50 cycles of tap washing, the fabric can show much lower heat release and pass the horizontal flammability test, while the deionized water laundered samples largely reduced the flame retardancy due to the lack of Ca2+ supplementation. The analysis of the flame-retardant mechanism confirmed that the dense graphitized carbon layer formed in the condensed phase and abundant CO2 released in the gas phase can effectively prevent the transfer of heat and dilute the combustible gas, respectively. This work provides a new dynamic coordination strategy for the design and fabrication of flame-retardant coatings with high efficiency, environmental friendliness, and durability.