WORLD JOURNAL OF ADVANCE
HEALTHCARE RESEARCH

Mahmoud M. Barakat*, Saleh Al. Rahel

ABSTRACT

Indigo is one of the most significant vat dyes used in cotton fiber dyeing; however, its traditional reduction to the water-soluble leuco form relies heavily on reducing agents—primarily sodium dithionite—which pose severe environmental challenges due to the generation of toxic sulfurous by-products. This study evaluates the feasibility of indirect electrochemical reduction as an eco-friendly alternative for indigo dyeing using an iron–triethanolamine (Fe–TEA) complex as a redox mediator and a stainless steel (SS) electrode as the cathode. The electrochemical reduction was conducted in an alkaline medium, and the resulting leuco-indigo solution was applied to 100% woven bleached cotton fabrics via the dip-oxidation method. Key process variables were systematically investigated, including dye concentration (0.5%, 1%, and 2% owf), sodium hydroxide concentration in the dye bath (11, 13, 15, and 17 g/L), and dye bath recyclability over five consecutive dyeing cycles. For comparison, traditional indigo reduction was performed using sodium dithionite (Na2S2O4) in an alkaline sodium hydroxide medium, followed by dip-oxidation dyeing under identical dye concentrations. Dyeing performance was rigorously evaluated through spectrophotometric reflectance measurements, color yield (K/S) determination, CIELAB color coordinates, and colorfastness tests to washing, light, and dry/wet rubbing. The results demonstrated that increasing the indigo concentration in both methods led to a significant increase in K/S values and a corresponding decrease in lightness (L*), indicating deeper color shades. The electrochemical method achieved superior color yield and shade depth compared to the traditional method at high dye concentrations, whereas both methods showed comparable performance at low concentrations. Regarding colorfastness, the electrochemical approach exhibited better fastness to light, washing, and rubbing at lower dye concentrations than the traditional method, while the traditional method displayed slightly higher fastness ratings at high dye concentrations. Increasing the NaOH concentration in the electrochemical dye bath enhanced color yield while maintaining excellent wash and light fastness, with only a minor decrease in rubbing fastness. Recyclability trials confirmed that the electrochemical dye bath could be reused for five consecutive cycles without compromising dyeing efficiency. Overall, indirect electrochemical reduction using the Fe–TEA complex and SS cathode presents a highly promising, sustainable alternative to conventional indigo dyeing, offering significant environmental benefits, bath recyclability, and robust colorimetric and fastness properties.

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