Evaporation Induced Flame Retardant Polyelectrolyte Complex for Cotton

Cotton is one of the most used textiles due to its comfort and breathable nature, but it is extremely flammable. To reduce the flammability, a polyelectrolyte complex coating composed of polyethylenimine (PEI) and sodium hexametaphosphate (PSP) is deposited in a single step. Ammonia is used as a volatile base that evaporates to reduce the pH and induces complexation on the cotton surface. Cotton coated with a 1:2 molar ratio of PEI:PSP gains 28 wt % and reduces the total heat release by 93%, compared to neat cotton. The method of flame retardant action can be attributed to an effective intumescent coating. After five water rinses, the coated cotton maintains its flame retardant behavior, with only 7 wt % added to the textile, due to a more effective ionically cross-linked network. This study demonstrates, for the first time, an efficient and scalable evaporation induced polyelectrolyte complex coating that imparts self-extinguishing behavior to cotton and can be adapted for many other flammable materials.