Investigation on flame retardancy of sulfur/nitrogen-based compounds for polyamide 6 fabric through facile exhaustion route

•GAS, THU and AMS showed high FR efficiency on PA6 fabric through facile exhaustion approach.•GAS and AMS with higher sulfur valence displayed better FR efficiency than THU.•GAS, THU and AMS modification inhibited dripping action of PA6 by forming cross-linked network on PA6 surface.•GAS, THU and AMS mainly function as gas source FR functional agent. Improving the flame retardancy and anti-dripping ability of polyamide 6 (PA6) fabrics through facile textile finishing technique is of great interest. This study focused on the flame retardant (FR) modification of PA6 fabric using three sulfur/nitrogen-containing compounds with different sulfur valence through exhaustion process. We further explored and compared the thermal stability, heat release ability, FR performance and mechanism of guanidine sulfamate (GAS), thiourea (THU), ammonium sulfate (AMS) on PA6 fabric. The modified PA6 fabrics displayed self-extinguishing ability without dripping action. They also possessed the low damaged length of 8–12 cm and high LOI of about 31.0%, suggesting good flame retardancy. As a comparison, GAS and AMS with positive sulfur valence had higher FR efficiency than THU with negative sulfur valence on PA6 fabric. GAS and AMS modification also decreased the heat release of PA6 fabric by about 20.1% and 16.2%, respectively. According to the thermal stability and char residue analyses, GAS, THU and AMS mainly worked through the gas-phase FR mechanism. A condensed FR action also occurred for THU modified PA6 fabric. Besides, no obvious influence on mechanical performance of PA6 fabric was observed. [Display omitted]