Process Optimization and Dye–Fiber Interaction in Microwave-Assisted Acidic Dyeing of Proteinous Textiles

Background Acidic dyeing of protein-based textiles commonly requires elevated temperature, prolonged treatment, and significant amounts of auxiliaries, which increase both energy demand and wastewater treatment. Microwave-assisted processing has been explored as a promising route to improve coloration efficiency, yet a detailed optimization of this approach for silk and wool remains insufficiently documented. Method Silk and wool were colored with an azo acid dye after controlled microwave exposure of the dye liquor and/or fabric substrates for selected time intervals. Dyeing variables including bath temperature, processing time, pH, salt level, and liquor volume were adjusted systematically. Experimental optimization was performed through a central composite design within an RSM framework. Color yield and tonal properties were determined from K/S and CIE color coordinates, while fastness, FTIR, and SEM were used to assess performance and material changes. Results Microwave exposure enhanced coloration performance in both substrates, giving higher color yield than the untreated condition. The best silk result was obtained at 55 °C for 45 min with a 45 mL dye bath at pH 5 containing aluminum sulfate, whereas wool performed best under comparable conditions when potassium sulfate was used. Citric acid gave the most favorable pH adjustment for silk, while acetic acid was more suitable for wool. Spectroscopic examination indicated no major chemical alteration of the fibers, and SEM suggested mild surface modification associated with improved dye deposition. Fastness ratings were in the good-to-excellent range. Conclusion These findings show that microwave-assisted acidic dyeing can improve the coloration of silk and wool under milder operating conditions, offering a practical alternative to conventional processing with lower thermal demand and reduced chemical input.