Application of chitosan and DOPO derivatives in fire protection of polyamide 66 textiles: Towards a combined gas phase and condensed phase activity

Abstract A DOPO-based phosphorus compound (DOPA) was synthesized and applied onto the pure and chitosan (CS) modified polyamide 66 (PA66) fabric surfaces via a simple pad-dry-cure method to improve the flame retardant properties of the same. The pure and chitosan modified fabric samples treated with DOPA at different content % degraded in a different way as the char residue formation and releasing of volatile and non-volatile gas species were dissimilar which are evident from the thermogravimatric and thermogravimetric-gas chromatography-mass spectroscopy test analysis. Obtained results also showed that no dripping occurred in the vertical burning test and a sharp increase in LOI values was noticed for all the treated fabric samples. CS modified PA66 fabric sample treated with a 10 wt % of DOPA exhibited a greater reduction in pHRR by 40% and showed superior flame retardant performance compared to the only DOPA treated pure fabric sample. The superb flame retardant properties of CS modified fabrics were due to the co-presence of DOPA and CS; where a synchronized gas phase and a condensed phase flame retardant mechanism was realized as DOPA showed a quenching effect in a gas phase mechanism and simultaneously, catalyzed the charring of CS in a condensed phase activity which was also justified from the TG-GC-MS analysis, TGA and FTIR analysis of char residues. However, this kind of facile application showed poor wash durability and deteriorated the physical properties of the fabric materials specifically treated with a higher DOPA content.