Egg white protein-hypophosphorous acid-based fire retardant single bilayer coating assembly for cotton fabrics

The combination of egg white proteins (W) and hypophosphorous acid (HA) was used for developing a flame retardant coating for cotton fabrics by adopting the layer-by-layer assembly technique. This has resulted in a novel phosphorous-nitrogen-based assembly due to strong electrostatic interactions between W and HA. Coated cotton fabrics were characterized by using a variety of microscopic, analytical and thermal/combustion tests. Flammability properties of the fabrics were evaluated as per widely recognized standards like BS EN ISO 15025:2016 for protective clothing and ASTM D6413 for flame resistance of textiles. Coated cotton fabric showed self-extinguishing property with significant but fragile residual char structure, whereas uncoated fabric completely burnt with a little ash as residue. Thermogravimetric analysis revealed that decomposition temperature of coated fabric was lowered compared to control fabric, but char residue increased at 800 °C. Forced combustion cone calorimeter tests on the coated and uncoated fabrics showed that peak heat release rate, total heat released, and average rate of heat emission values reduced by 80%, 38%, and 40%, respectively, for coated fabrics as compared to control fabric. Even the mass loss rate value of the coated fabric has reduced significantly (from 514 g/m2.s for the uncoated fabric to 2 g/m2.s for coated fabric). Wash durability of the coated fabrics, though showed a slight reduction in flame-retardant properties as a consequence of ~ 9.7 wt% coating loss during soaking, yet there was no after-glow