Sustainable two-step polyelectrolyte complex for flame retardant nylon-cotton fabric†

Blended nylon-cotton (NYCO) fabric is frequently used due to its unique combination of comfort and strength, but it suffers from high flammability. Flame-retardant NYCO is created by applying a simple two-step process of an eco-friendly, water-based polyelectrolyte complex consisting of egg white proteins (EWP), pectin (P), and guanidine phosphate (GP). The addition of GP to the EWP/P system facilitates charge screening of the P macromolecule, allowing a sufficient coating to form and impart flame-retardant properties to the fabric. The NYCO fabric coated with a positively charged 4% EWP solution at pH 3 and a negatively charged 1% P + 20% GP solution at pH 3 exhibits self-extinguishing behavior during vertical flame testing and retains mechanical properties similar to those of the uncoated fabric. This coating modifies the thermal degradation behavior of NYCO by promoting the formation of an intumescent charred layer that protects the fabric from further decomposition. As a result, the coated fabric shows 10.8% residue at 700 °C in air and 29.2% in nitrogen, which is significantly higher than the uncoated fabric, which retains only 2.5% residue in air and 10.4% in nitrogen. Additionally, the coated fabric releases 32.6% less heat and exhibits a 37.9% reduction in fire growth capacity. This simple and completely bio-based coating provides an effective and benign way to protect this important class of textiles from fire.