The Migration of Non–substantive Dyes on Fabrics and its Relation to Saturation Regain and Fibre Surface Structure

The migration of non–substantive dyes on fabrics woven from a range of fibres has been studied at room temperature and the regains below which migration does not occur, i. e. the critical regains, determined. It has been found that for most fibres the critical regain is just below the imbibition value and is independent of the dye used to determine it. However, this is not so for viscose rayon, where the critical regain depends on the molecular size of the dye. This effect is caused by the presence of small continuous channels in the surface of viscose rayon fibres, which are flooded and can therefore transport dye at humidities less than saturation. The use of a non–penetrative dye–restrainer complex in determining the amount of surface water left on fibres after centrifuging is described, and the results combined with the critical regain determinations to clarify the behaviour of fibre–water systems at high humidities and to estimate “true” saturation regains.