Phytic acid and chitosan layer-by-layer coating of PET fabric shows semi-durable, non-drip fire performance. Woven 120 g/m2 PET (polyethylene terephthalate) was prepared by heating to 60°C in sodium hydroxide, then alternate layers of phytic acid and chitosan were deposited by soaking in aqueous solution, before finishing by soaking in 3-glycidyloxypropyltrimethoxysilane (GPTMS). With 2 x 20 bi-layers coating, LOI (limiting oxygen index) is increased from 19% to 34%, the textile is self-extinguishing (6.5 mm damage in vertical burn test) with no burning drips and total smoke production is reduced by more than 10%. After four washes at 50°C, LOI has decreased back to 26% and the textile is no longer self-extinguishing. The layer-by-layer coating also significantly deteriorates wearability parameters (fibre softness, air permeability).
“Durable flame retardant and anti-dripping of PET fabric using bio-based covalent crosslinking intumescent system of chitosan and phytic acid”, Y. Fang et al., Progress in Organic Coatings 183 (2023) 107785 https://doi.org/10.1016/j.porgcoat.2023.107785