Synergistic ultrasonic dyeing of wool: optimisation of a single-bath process with Rubia and Reseda extracts for eco-friendly textiles.

L. The main goal is to enhance dyeing efficiency while reducing the environmental impact of conventional processes. A Box-Behnken design was applied to optimise key parameters (pH, time, and temperature) based on the colour strength (K/S). Optimal conditions were identified at pH 4, 60 min, and 50-60 °C depending on the dye. The combined use of a metallic mordant (aluminium sulphate) and a bio-mordant (tannins) significantly improved colour fastness. Scanning electron microscopy confirmed uniform dye distribution without fibre damage. The results demonstrated good compatibility of the dye extracts, producing a broad spectrum of shades and excellent UV protection (UPF > 66). Overall, this work highlights a sustainable and efficient pathway for industrial wool dyeing with natural dyes.