Synthesis of P-N-S elemental flame-retardant waterborne polyurethane and its application in polyamide fabric

A new type of flame-retardant polyether diols containing phosphorus, nitrogen, and sulfur (SPAE) was first synthesized by using phosphoryl chloride, 2-aminobenzothiazole and ethylene glycol. The SPAE as the soft segment was then utilized to prepare a series of flame-retardant waterborne polyurethanes (SPAE-WPU) through emulsion polymerization. Subsequently, SFR-WPU as a finishing agent was coated on polyamide fabric. When the content of SPAE-WPU was 18 wt%, the coated fabric exhibited a limiting oxygen index (LOI) of 28.2 %, afterflame time of 4.6 s, afterglow time of 0 s and damaged length of 11.2 cm, respectively. After 10 washes, the coated fabric retained its good flame-retardancy and anti-dripping properties. Furthermore, the flame-retardant mechanism of SPAE-WPU was investigated using various spectral analyses, which revealed that the P, N and S elements worked together to create non-combustible gas compounds, release free radicals, and promote dehydration and carbonization, leading to synergistic flame-retardant effects in both gas- and condensed-phase.