A durable flame retardant with N−P=O(O−NH4+)2 based on amino acid for cotton fabrics

The ammonium salt of glycine phosphamide phosphoric acid (AGPP), a highly durable bio-based flame retardant with N−P=O(O−NH4+)2, was synthesized without formaldehyde for cotton fabrics (CF). It was attached to CF by forming P−O−C with cellulose. The p-π conjugation of N and P=O made N−P(=O)−O−C very stable, so P−O−C was difficult to hydrolyze even during high-intensity washing, which greatly improved the launderability of treated CF. The limiting oxygen index of 25 wt% AGPP-treated CF was 51.6%, and only dropped to 43.9% after 50 laundering cycles performed following AATCC 61–2013 3 A standard (high temperature, intense machine wash). FT-IR and XPS results showed the presence of N−P and P−O−C bonds. TG, TG-FTIR, and residual char analyses implied that AGPP changed the degradation direction of CF and showed the condensed-phase flame-retardant mechanism. SEM, XRD, and mechanical property tests showed that the morphology, crystal structure, and mechanical performance of the finished CF were well sustained.