An Environmentally Sustainable Dyeing Approach for the Production of Ecofriendly Colored Wool Yarns via the Application of Millettia laurentii Natural Dye in Conjunction with Metal Salts and Biomordants

Abstract

Reduced environmental impact is key to sustainable textile dyeing and finishing. The use of synthetic dyes generates substantial amounts of wastewater discharges with a high load of heavy metal ions. As part of a long-term, environmentally friendly strategy, natural dyes with low concentrations of eco-friendly metal salts (alum, ferrous sulfate, copper sulfate, etc.) and biomordants produce natural shades with good colorimetric and fastness characteristics. The current study presents an eco-friendly strategy for dyeing and finishing wool with Millettia laurentii natural dye in conjunction with biomordants and metal salts. The research findings were summed up in terms of colorimetric analysis, color fastness (wash, rub, and light), and UV protection. Further, research analysis was conducted to assess the levels of chemical and biological oxygen demand in the resulting dyeing wastewater. The binary combinations of metal salts (ferrous sulfate and copper sulfate) and biomordants (sumac, pomegranate peel, gallnut, and yellow myrobalan) provided wool samples with a better color depth (K/S) values with a maximum value of 18.58 for copper sulfate and gallnut combination. Overall, mordanted samples showed better fastness and ultraviolet shielding properties compared to control dyed samples. The chemical and biological oxygen demand of the generated wastewater was found to be low in mixed metal-biomordant combinations compared to singly used biomordants with the lowest value of 832 and 537 mg O₂/L, respectively for yellow myrobalan and ferrous sulfate combination (Fe + YM). The use of Millettia laurentii natural dye and a copper-gallnut mordant combination provided a practical solution for developing an environmentally sustainable technique of dyeing wool, with the added benefit of strong UV blocking effectiveness and minimization in corresponding COD and BOD values.