An efficient and durable DOPO/H3PO4-based flame retardant for cotton fabric

In this study, a novel high-efficiency and durable flame retardant DOPO–ammonium phosphate (DOPO–AP) was synthesized and applied for cotton fabric by a facile process. Nuclear magnetic resonance (NMR 1H, 13C, 31P) spectroscopy confirmed the molecular structure of DOPO–AP. Flame retardancy of the treated cotton was studied by limiting oxygen index (LOI), vertical combustion, scanning electron microscopy and cone calorimetry test. It was found that for the DOPO–AP dose of 300 g/L, the LOI value increased from 18% obtained for pure cotton to 40.2% for treated cotton, and after 50 laundering cycles, the LOI value was still maintained at 26.4%. The treated cotton showed no afterburning and smoldering phenomenon before and after the washing of the fabric in multiple laundering cycles. Additionally, the residual carbon fraction increased from 1.23% of pure cotton to 15.99% of treated cotton, effectively prolonging the ignition time of the treated cotton, and reducing the heat release rate and total heat release. Flame retardant mechanism was investigated by thermogravimetric (TG) and thermogravimetry–infrared (TG–IR) analysis. The whiteness and mechanical properties of treated cotton were well-maintained, indicating that DOPO–AP treated cotton has potential for use in textile and other industries to reduce the likelihood of fire-related accidents.