Dyeing and adsorption studies of madder (Rubia tinctorum) on wool fabrics

Abstract

In this study, the dyeing behavior of wool fabrics with madder has been studied. Three well-known types of adsorption isotherms i.e. the Nernst, Freundlich and Langmuir isotherms were used to fit the data. It was found that the adsorption isotherm of madder on wool fabrics follows Freundlich type of adsorption. The exponent α in Freundlich isotherm equation (Cf = kCsα) was obtained 0.61 corresponding to 0.5 for the direct dyes on cellulosic fibers. The effect of salt and pH on dyeing of wool samples was also investigated by the use of color characteristics measurements. The results showed that the color strength of the sample dyed at pH 4.5 was considerably higher than that of the samples dyed at pH 7 and 9. The difference between the K/S of the samples dyed at pH 7 and 9 was not significant, however, the color characteristics of the samples changed due to pH variation in dyebath. Also, addition of salt in the dyebath increased the madder adsorption. The b* value of the dyed sample did not change as a result of salt addition but the L* and a* values showed variations to some extent.