The role of auxiliaries in the immersion dyeing of textile fibres: Part 8 practical aspects of the role of inorganic electrolytes in dyeing cellulosic fibres with commercial reactive dyes

The colour strength of 2% omf dyeings, as well as the extents of both exhaustion and fixation, achieved for three commercial grade reactive dyes on cotton, were promoted by the addition of 50 gl-1 NaCl at each of seven liquor ratios (1:50, 1:20, 1:10, 1:6, 1:3, 1:2 and 1:1.5). The depth of shade of dyeings obtained in the absence of added electrolyte using a 1:1.5 liquor ratio were of similar magnitude to those secured using a 1:10 liquor ratio in the presence of 50 gl-1 NaCl. The promotion of dye uptake imparted by both added electrolyte and reduced liquor ratio was interpreted in terms of their effects on the substantivity of the reactive dyes towards the cotton substrate. It was concluded that the two, ostensibly different actions of adding electrolyte such as NaCl or Na2SO4 to a reactive dye dyebath and reducing the liquor ratio used for dyeing have the same result, namely that of promoting dye aggregation in the dyebath which reduces the aqueous solubility of the anionic dye, which, in turn, results in the inherent preference of the dye to favour the aqueous phase shifting towards the fibre phase. The results show that it is possible to dye cotton using commercial grade reactive dyes in the complete (ie 100%) absence of added inorganic electrolyte. The dyeings obtained were of realistic depths of shade and displayed excellent levels of wash fastness.