Sol-gel coatings from DOPO-alkoxysilanes: Efficacy in fire protection of polyamide 66 textiles

Two different DOPO- Alkoxysilane based flame retardant compounds were synthesized and applied onto the polyamide 66 (PA66) fabric surfaces via sol-gel method to improve the thermal stability and flame retardant properties. The as prepared coatings exhibited a much higher char yield% compared to the pure PA66 and simultaneously suppressed the dripping tendency of PA66 in the vertical burning test. The fabric sample modified with 20 wt% of DOPO-APTES showed a significant reduction in the peak heat release rate (pHRR) by 36%, whereas the 20 wt% of DOPO-GPTMS treated fabric sample could manage a 20% reduction in pHRR. The supremacy of DOPO-APTES treated fabrics were due to the co-presence of P, Si, and N elements; where a DOPO structure showed a quenching effect in a vapor phase, and Si-compounds accelerated the limited charring of DOPO in a condensed phase and stabilized the char residues in a higher temperature range. Moreover, the as treated PA66 fabrics show some sort of wash durability and among them, the fabric sample treated with 20 wt% of DOPO-APTES can withstand against fierce laundering where it maintains UL-94V-1 rating even after 10 washing cycles.