Lac Dyeing Cotton Fibers by Pretreating with Tannic Acid and Aluminum Acetate

Lac color is one of the natural dyestuffs with an anthraquinone structure and is conveniently adsorbed to protein fibers, especially wool. Although the adsorption of lac dye to cellulose fibers is extremely low, dyeing is possible by using a mordant containing metallic ion. It is possible in such a way to obtain a deep purple color by mordant dyeing if cotton fibers are pretreated with tannic acid. The adsorption of tannic acid to cotton fibers and the relationships between tannic acid and aluminum, and aluminum and lac dye in a solution were examined to clarify this effect. It was found that the adsorption of tannic acid to cotton fibers increased the binding of aluminum to the fibers and then effectively enhanced the adsorption of lac dye. Aluminum acetate and aluminum potassium sulfate being used for the mordant in the binding ratio of aluminum to tannic acid differed. The adsorption of tannic acid to cotton was of the Langmuir type below 0.5 mM and resulted in -32.0 kJ/mol of heat of adsorption.