Dyeing of water swollen, solvent exchanged cotton with anionic dyes from dimethylformamide-trichloroethylene solvent mixtures

Attempts have been made to study the equilibrium adsorption at 40°C of three acid dyes having the same structure but a varying number of sulphonic acid groups on water swollen, solvent exchanged cotton from different ratios of dimethylfor mamide-trichloroethylene solvent mixtures. The equilibrium adsorption of the dyes in general increased with decrease in dye solubility in the solvent mixture and increase in the number of sulphonic acid groups in the dye molecule. To understand the dyeing mechanism, the adsorption isotherms were plotted and interpreted in terms of distribution of dye between the dye bath and the solvent closely associated with the fiber, followed by Langmuir adsorption on cotton. The affinity values were cal culated using the Langmuir equation and were consistent over a wide range of dye concentrations. The dye affinity increased with the increase in trichloroethylene con tent in the solvent mixture and with the increase in sulphonic acid groups in the dye molecule.