Enhanced flame retardancy of cotton fabrics with a novel intumescent flame-retardant finishing system

Imidazole spirocyclic phosphoramidate (ISPA) has been synthesized through one-step reaction between spiralphosphodicholor (SPDPC) and imidazole. The optimal flame-retardant finishing for cotton fabrics process was designed by orthogonal experiment L25 (54) and the finished cotton fabrics with different formulas of aqueous solution containing ISPA, phosphoric acid, and cyanuric acid were prepared. The limiting oxygen index (LOI) to characterize the minimum amount of oxygen needed to sustain a candle like flame revealed that this novel intumescent SPDPC flame system exhibited an excellent flame retardant efficiency on the cotton fabric finished with the optimal formula possessing a high LOI value of 36.6 %. The cotton fabric was investigated by vertical flame test revealing a combustion characteristic of the lowest damaged length (64 mm) without continuing burning and no smoldering. The flame-retardant cotton fabric showed an acceptable decreased tensile strength by 13.3 % and enhanced excellent thermal stability compared with pure cotton fabric. Cone calorimeter test revealed a reduced heat release rate by 57 % and a decreased total heat rate by 60 % for the flame-retardant cotton fabric compared with pure cotton fabric. Scanning electron microscopy (SEM) indicated a solid and tough residue for the burned flame-retardant cotton fabric as compared with the very loose and brittle residue of the burned pure cotton fabric.