A concise water-solvent synthesis of highly effective, durable, and eco-friendly flame-retardant coating on cotton fabrics.

A new halogen-free and formaldehyde-free ammonium salt of melamine hexa(methylphosphonic acid) (AMHMPA) was facilely synthesized as flame retardant (FR) material under water-solvent and low temperature condition to counter inflammable cotton fabric fire hazard. The reactive PO(NH4)2 and PO(OH)2 groups from AMHMPA reacted with cotton reactive OH groups to form POC bonds. A layer of AMHMPA was coated onto the treated-cotton surface, and a carbon skeleton was formed after combustion. The char residue percentages of the treated-cotton fabrics and untreated fabric were 38.5 and 3.6% at 600 °C, respectively. The phosphorus contents for the control, treated-cotton and burned-cotton were 0, 37.499 and 24.896%, respectively. The LOIs of cotton treated with 30-90 g/L AMHMPA reached 32.0-43.0%. After 50 laundering cycles (LCs), the LOIs still maintained 26.0-33.4%. AMHMPA-treated cotton had no cytotoxicity towards the environment and humans. These results demonstrated that AMHMPA-treated cotton exhibited eco-friendly, outstanding durability and excellent flame retardancy. TG-IR and cone calorimeter results confirmed AMHMPA condensation phase flame retardant mechanism.