Intumescent flame-retardant cotton produced by tannic acid and sodium hydroxide

Abstract Tannins, natural phenolic compounds abundant in many plants, exhibit low thermal conductivity and low flammability and have inspired bionic approaches in the development of flame-retardant materials. Still, tannins have been used as a dyeing fixative for cotton, and their potential contribution to developing flame-retardant cotton has not yet been examined. This study shows that tannic acid with the aid of sodium ions can produce intumescent flame-retardant cotton. Treatment with tannic acid alone altered the thermal patterns of the pyrolysis and combustion of cotton and increased the char yield, but the limiting oxygen index (LOI) was not improved significantly. The addition of low concentrations of sodium hydroxide enhanced the adsorption of tannic acid onto cotton and catalyzed the decarboxylation of tannic acid and the dehydration of cotton cellulose at lower temperatures. Such modified thermal reactions as well as the formation of intumescent char led to a reduction in heat release capacity of 82% (from 278 to 51 J/g K) and an increase in the LOI by as much as 30.2% as compared with that for control cotton.