Some Observations on the Effect of Urea on the Dyeing Behaviour of Wool at Low Temperatures

Abstract

The effect of adding urea to the dyebath on the rate of absorption of reactive and acid dyes by wool, and of acid dyes by other protein bres, has been studied. Possible modesof action of aqueous solutions of urea on wool are discussed. The observed increase in the ite of dyeing in the presence of urea is due to disaggregation of the dye in solution and reduction in dye‐protein hydrophobic interactions. The action of urea in promoting fibre swelling is also likely to be a contributory factor.

Mechanism of dye solubilization and de-aggregation by urea

“…Urea is one of the most common dye solubilizers which has been used successfully for centuries [28][29][30][31][32]. In addition to its ability to improve dye solubility in water [25,30], urea also enhances dye de-aggregation [33][34][35][36] and the swelling of the fibres in water [32,33,[37][38][39]. Furthermore, low dye solubility leads to self-aggregation in water, which becomes more prominent as the concentration of the dye increases [34,40,41].…”

Synthesis of acid dyes containing polyetheramine moieties and their low‐temperature dyeing properties on wool fiber

“…Another way to realize the low‐temperature dyeing of wool is to use auxiliaries. Urea, thiourea and related compounds, multilamellar liposomes, redox systems, reverse micellar systems, benzyl alcohol, and nonionic surfactants have been investigated for low‐temperature wool dyeing . Until now, the use of auxiliaries has been the only practical success, and this method has been used in industrial production.…”

Adsorption of Urea and Thiourea by Wool

“…Despite many contributions to this field [2][3][4][5], the exact manner in which urea exerts its beneficial influence in this process is not fully understood. Despite many contributions to this field [2][3][4][5], the exact manner in which urea exerts its beneficial influence in this process is not fully understood.…”

“…Attempts have been made to determine the amount of urea adsorbed by wool [5], but the inaccuracy of the methods employed prevented establishment of a definite relation between urea concentration and uptake. Recently it has been suggested [6] that urea does not penetrate uncut wool fibres, although no direct experimental evidence was presented to support this claim.…”