Reuse of waste dye bathes for sustainable wool dyeing by depletion of metal salts and plant-based dyes

Natural dyes and natural dyeing have been on the agenda of the scientific community for a long time due to their many advantages. Nonetheless, low affinity, low fixation rates of natural dyes, and occurrence of closely related metal-containing waste baths can be listed as disadvantages. This paper offers a different approach to eliminate these disadvantages. To that end, wool fabrics were dyed in the presence of four different natural dye sources (green walnut shells/husks, barberry shrub roots, madder roots, and alkanet roots) and three metal-based (aluminum, copper, and iron) mordanting agents. Baths remaining from the first dyeings were used an extra four times for repetitive dyeings. It was revealed that satisfying/acceptable colors and sufficient color yields could be obtained for all-natural dyes even after the 5th dyeing using the same dye bath. However, it was regarded as reasonable to obtain lighter colors and lower color yields with an increasing number of repetitions. The color shifts started to be observed especially after the second dyeings, which could be attributed to the significantly reduced amount of natural dye and the mordanting agent left in the waste dye baths. This divergence was seen at least in barberry shrub root-based dyeings. In addition, it was interesting to note that wet fastnesses of all dyeings with all mordants were generally good and even improved with repeated dyeings, while light fastnesses were initially medium-low and decreased slightly with repeated dyeings. © 2024 Elsevier Ltd