Factors Affecting Purple Shade Dyeing Due to Indirubin in Indigo Dyeing Using Fresh Leaves by Heating

Abstract

The effect of temperature and pH on the yields of indigo and indirubin from indoxyl which was generated from indoxyl acetate was examined. In the indoxyl solution of pH 9-10 at 65-85°C, a significant amount of indirubin was produced in addition to indigo. In the case of indigo dyeing using fresh leaves of Strobilanthes cusia, a kind of indigo plants, a purple shade of dye can be achieved by merely heating the dye bath. This was explained by the relatively higher pH of the juice of the plant. In this condition, a yield of indirubin was promoted by heating. The indirubin dyeing consists of two processes, the production of indirubin in the fiber and the penetration of indirubin, which has already been produced in the dye bath, into the fiber. In the case of Polygonum tinctorium, indirubin could be dyed by making a mild alkaline juice from fresh leaves and by heating.