Influence of water hardness on acid dyeing with silk

Abstract

In this paper, the effect of water hardness, expressed in CaCO3 equivalent, on the dyeing silk with acid dye under acid, alkaline and isoelectric point dyeing conditions was studied by zeta potential method. Under acidic condition and in the presence of calcium ion, the positive zeta potential of silk was found to decrease with a reduction in the dye adsorption. Such a phenomenon might be due to the presence of cation which increased the dyeing potential barrier at the interface between fibre and dye solution. This would result in a higher resistance of dye anions passing through the interface. Under alkaline condition, the zeta potential on silk was negative and resulted in a strong potential barrier for the dye anions. The presence of calcium ion would result in a decrease in the absolute value of zeta potential of silk fibre with an overall increase in dye absorption. Under isoelectric point, the zeta potential of silk fibre was found to be near zero and dye adsorption was not influenced by the cations. These results showed that calcium ion could produce strong electrolytic effect on dyeing even under very low concentrations.