Dye diffusion and the phenomenon of barriness on polyamide fabrics

Dyed polyamide fabrics tend to exhibit barriness, particularly when acid dyes of good wet fastness are used. The causes of this phenomenon have been investigated by studying the diffusion kinetics of the dyeing process. The conditions used in the pretreatment of the yarn have been considered, in particular the effect of mechanical and thermal conditions during thermal pretreatment. It has been demonstrated that barriness is dependent only on the kinetics of diffusion. If drawing is increased, the rate of dye diffusion is reduced, whereas an increase in the texturising temperature tends to increase it. The influence of dye diffusion decreases as the dyeing temperature rises. The traditional practice of dyers to attempt to reduce barriness by raising the dyebath temperature very slowly therefore makes matters worse. To reduce barring it would be preferable to introduce the dyestuff to the dyebath only once the dyeing temperature has been reached.