Adsorption kinetics of lac dye on eri silk yarn

The use of natural dyes for the dyeing of naturally-derived fibres is of economic and cultural importance in many countries and there is thus ongoing research interest in this area. In the current work, the dyeing of eri silk yarn with lac dye was investigated, with both components being accessed in Thailand. While some qualitative studies of this particular dye-yarn combination have been reported, more quantitative aspects, which could give a deeper molecular understanding of the process, have not been described. The aim of the current research was thus to obtain quantitative details on the kinetics of lac dye adsorption on eri silk yarn which then might also underpin better village-based dyeing procedures. The adsorption kinetics of lac dye on village-produced yarn revealed an increase in the adsorption rate constant and diffusion coefficient with an increase in temperature owing to a diffusion kinetically controlled process. At higher temperatures, a lower affinity and less dye uptake was observed after the equilibrium state had been reached, consistent with an exothermic adsorption process. The effect of a mordant on the dyed eri silk yarn was also assessed. Different shades of colour could be obtained on the silk yarn by changing the mordant used. In addition, post-mordanting with different mordants significantly improved wash and light fastness properties.