Preparation and application of durable and efficient flame retardants: phosphorus-nitrogen-boron synergistic effect, flame retardant properties, combustion behavior and mechanical properties

The durability of flame-retardant cotton fabrics has been widely valued. A reactive P/N/B spiro compound in this work, diethanolamine borate methylene phosphonium ammonium salt (DMAPS), was prepared, which could endow cotton fabrics with excellent flame retardance at low concentration. The limiting oxygen index (LOI) of the fabrics treated with 100 g/L DMAPS was increased to 31.6%, and the char length was reduced to 5.9 cm. Continuing to increase concentration of DMAPS, the LOI value could reach about 42.9%. The cone calorimetric test results showed that the peak heat release rate of DMAPS treated cotton fabrics was only 15 kW/m2, which was about 92% lower than that of the untreated, and the total heat release rate (THR) was also decreased from 5.0 to 0.9 MJ/m2, which decreased by 82% compared with untreated cotton fabrics. The analysis of char residue showed that the polyphosphoric acid formed during the pyrolysis of DMAPS accelerated the formation of the char, while the carbide boron structure remained in the char, stabilizing the char layer, so that the char residue could still maintain the original warp and weft structure of the fabrics. In addition, the treated samples still had fire resistance and self-extinguishing behavior after 10 washing cycles. This study provides a possibility for the preparation of durable flame-retardant cotton fabrics.Graphical abstractAn efficient and durable phosphorus-nitrogen-boron synergistic flame retardant for cotton was prepared and applied.