Flame retardant treatments for polyamide 66 textiles: Analysis the role of phosphorus compounds.

l Three different P-compounds were used to prepare the flame retardant coatings for PA66 textiles. l Chitosan, alginate and MMT as additives were also incorporated with the P-compounds. l Graphene phosphonic acid based coating offered a maximum LOI by 27.5% and reduction in pHRR by 45%. l Phytic acid based coating brought a substantial reduction in pHRR and increase in char yield%. l P-compound active in the condensed phase and well-supported with a physical barrier effect seemed to be well-suited for PA66. Three different phosphorus (P) compounds, namely phytic acid (PA), graphene phosphonic acid (GPA) and a DOPO derivative [3-H-P-DOPO HQ (DOH)] having a diverse origin, structure and chemical activity were used along with some naturally derived polyelectrolytes like chitosan (CS), sodium alginate (SA) and montmorillonite (MMT) in a layer-by-layer (LbL) fashion to enhance the flame retardant performance of polyamide 66 (PA66) textiles. Obtained results showed that these P-compounds, irrespective of their varied action surely played a positive role in improving the flame retardancy; though a typical P-compound was effective in modifying a specific type of flame retardant parameter. The formulation containing phytic acid particularly brought a considerable reduction in the peak heat release rate (pHRR) and a handsome increase in residue% due to its dominant activity in the condensed phase flame retardant mechanism. Meanwhile, the application of GPA further modified this condensed phase activity via providing added thermal stability to these residues and thus, a sharp increase in limiting oxygen index (LOI) value up to 27.5% and a maximum reduction in pHRR by 45% was handed. In contrast, the DOPO derivative (DOH) was quite effective in the gas phase mechanism through its radical quenching effect and offered a moderate increase in LOI values (i.e., 24.5%). Finally, it was realized that the formulation containing an engineered structure of a P-compound with graphene, basically worked in the condensed phase mechanism and well supported by thermal insulation effect available from graphene nanosheets and MMT platelets seemed to be an effective solution in escalating the fire performance of PA66 textiles. Image, graphical abstract [ABSTRACT FROM AUTHOR]