Sustainable lignosulfonate-modified PA6.6 fabrics to improve durable flame retardancy, hydrophilicity and mechanical performance

Creating durable flame retardancy, enhanced mechanical performance, and hydrophilic polyamide 6.6 (PA6.6) textiles via cost-effectiveness from sustainable renewable sources is a considerable challenge. This study introduces a pretreatment process involving the application of sodium lignosulfonate (LS) to the surface of PA6.6 fabrics, thereby enhancing their hydrophilic and flame-retardant properties. Subsequently, a layer-by-layer (LbL) nanocoating treatment is employed, utilizing renewable polyelectrolytes—chitosan (CS), LS, and poly (sodium phosphate) (PSP)—to create 8-bilayer (BL) and 4-quarda layer (QL) structures that further improve the hydrophilicity and durable flame resistance of PA6.6 fabrics. The combined LS-modified and LbL coatings notably increased the limiting oxygen index (LOI) values from 19.5 % to 22.5 %, eliminated melt dripping, and secured a V-1 rating in the vertical burning (UL-94) tests. Moreover, the treated fabrics exhibited a 43 % reduction in the peak heat release rate (PHRR) and a lower fire growth rate (FGR) of 0.84 W/g·s, with a significant increase in char yield% in both air and nitrogen (N₂) atmospheres. A cross-linked network structure is responsible for the superior hydrophilicity, enhanced tensile strength, and fabric softening properties. The self-crosslinking of sulfur-containing radicals with amide units ensures an anti-dripping performance that can withstand up to 30 home laundering cycles, demonstrating remarkable washing durability. However, a convincing approach has been developed for sustainable and high-performance materials for the textile industry, and a simple LbL technique using renewable polyelectrolytes that have traditionally been utilized in water treatment and food processing has been developed.