The role of auxiliaries in the immersion dyeing of textile fibres: Part 10 the influence of inorganic electrolyte on the wash-off of reactive dyes

The depth of shade of dyeings obtained using three commercial reactive dyes on cotton in the absence of added electrolyte at a 1:2 liquor ratio were of similar magnitude to those secured in the presence of 50 gl-1 NaCl at a 1:10 liquor ratio. In the case of both the 2% omf (on mass of fibre) and 5% omf dyeings which had been produced in the complete absence of added inorganic electrolyte at low liquor ratio, substantially modified wash-off processes could be used that required ≥50% fewer wash baths than conventional wash-off processes that must be used in the case of dyeings produced in the presence of added inorganic electrolyte. Use of the modified wash-off processes enables substantial savings in both energy and water compared to their conventional wash-off counterparts; a 50% saving in proprietary wash-off agent was also secured when a 1:5 liquor ratio was employed for the modified wash-off processes. The ensuing electrolyte-free dyeings displayed excellent levels of wash fastness that were characteristic of those exhibited by commercial reactive dyes on cotton and other cellulosic fibres.