Chiang Mai Journal of Science

Leaves of  Indigofera tinctoria were fermented in water. During fermentation, indican in leaves decomposed completely to indoxyl and was consecutively oxidized to indigo that finally precipitated from the fermented solution.  The hybrid-race silk yarn was then dyed till equilibrium with obtained indigo reduced by Na₂S₂O₄ under alkaline condition and thermodynamics of  dyeing process was investigated. The obtained adsorption isotherm was classified as a Langmuir type.  The apparent diffusion coefficients at 33, 40 and 50^oC are 1.23x10^-12, 8.26x10^-13 and 4.26x10^-13 m²s^-1, respectively.  The heat of  adsorption and the change of  entropy are -9.43 kcalmol^-1 and 0.023 kcalmol^-1 K^-1, respectively.  In addition, the saturated dye uptake was found to be decreased when the dyeing temperature was increased. The obtained results are useful for designing appropriate dyeing equipment and conditions for dyeing silk with natural indigo.