The wash-off of dyeings using interstitial water Part 5: Residual dyebath and wash-off liquor generated during the application of disperse dyes and reactive dyes to polyester/cotton fabric

Both 2% and 5% omf dyeings of polycotton fabric which had been produced using commercial grade disperse dyes and reactive dyes can be washed-off using two, novel processes that utilise polyamide beads. The bead wash-off processes provided dyeings that were of similar colour, depth of shade and fastness compared to those which had been subjected to a conventional reduction clearing process in the case of the disperse dyes and a conventional wash-off in the case of the reactive dyes. The wastewater obtained from the bead wash-off of disperse dyes contained considerably lower concentrations of chloride ion as well as lower TDS compared to that secured using a conventional reduction clearing process, which was attributed to the beads having adsorbed vagrant chloride ions. In contrast, bead wash-off of reactive dyes did not reduce either the chloride ion concentration nor TDS content of the wastewater produced, because of the swamping effect of the very high chloride ion concentration. Bead wash-off also enabled significant reductions in both heat energy and water consumption to be achieved.