The Effect of a Synthetic Tanning Agent on the Uptake of Acid Dyes by Nylon 6

The effect of pretreating various nylon 6 fibres with a synthetic tanning agent on the rates of dyeing of five acid dyes has been studied. From the adsorption properties of these dyes on nylon 6 samples differing in amine end-group content, it is shown that as the basicity of the dye increases, the saturation value tends to approach more closely to the content of amine end-groups in the fibre. For a monobasic, hydrophobic dye, the saturation value is not governed by the amine end-group content of the fibre. Assuming that an increase in hydrophobicity results in a higher dye anion affinity, it is suggested that as the affinity of the dye for the fibre increases, the rate of dyeing becomes less affected by the presence of the synthetic tanning agent. For dyes of low affinity and greater hydrophilic character, the rate of dyeing of pretreated nylon is initially low but increases as the dyeing proceeds. It is postulated that this is caused by the initial deposition of the syntan in the outer regions of the fibre acting as a partial barrier to dye diffusion. Although the syntan does not desorb significantly during dyeing, it diffuses slowly into the fibre and gradually loses some of its retarding influence