Natural dyeing of wool fabric with Sappan via the atmospheric-pressure non-equilibrium microwave plasma system

This study presents an improved natural dyeing method for wool fabric utilizing Sappan wood, achieved by integrating iron mordant treatment with atmospheric-pressure non-equilibrium microwave plasma irradiation. The dyeing process was conducted at 80 °C with a 2.0 wt% Sappan dye solution, and plasma irradiation was applied both during and after the dyeing procedure. There has been found that colorimetric analysis using the CIE Lab* system demonstrated a significant decrease in L* (brightness) and increases in a* and b* chromaticity values for plasma-treated samples compared with untreated dyeing. These results indicate enhanced color depth and chromatic development. In addition, XPS analysis revealed increased Fe 3p and O 1s peak intensities following plasma irradiation, indicating the formation of oxidized iron species and additional oxygen-containing surface groups. These changes result from reactions among plasma-generated oxygen radicals, iron mordant species, and phenolic hydroxyl groups in Sappan dye molecules, which enhance dye fiber interaction. Therefore, the results indicate that atmospheric-pressure microwave plasma irradiation promotes surface chemical activation and enhances natural dye fixation on wool fibers, offering a promising method for improving natural dyeing processes.