Background Natural colorants from renewable biological resources are increasingly being explored as sustainable alternatives to synthetic textile dyes. In this study, the freshwater green algae Zygnema stellinum was investigated as a natural dye source for cotton, with emphasis on extraction, dyeing optimization, bio-mordanting, and fastness performance. Methods Colorants were extracted from dried algal powder using aqueous and alkaline media. Cotton dyeing conditions were optimized by varying alkali concentration, dyeing time, temperature, salt concentration, and dye liquor ratio. Bio-mordanting was performed using onion peel, turmeric, and neem bark in both pre- and post-mordanting approaches. Dyed samples were evaluated for color strength, fastness properties, and functional groups by Fourier transform infrared spectroscopy. Results Alkaline extraction gave better color yield than aqueous extraction, with 4% sodium hydroxide producing the highest color strength. The optimum dyeing conditions were 30 min dyeing time, 50 °C dyeing temperature, 5% sodium chloride, and 45 mL dye-to-liquor ratio. Bio-mordanting improved color depth and generated a range of shades. In pre-mordanting, 4% onion peel and 3% turmeric or neem bark gave the best results, while in post-mordanting, 3% of each bio-mordant produced the highest color strength. Mordanted samples also showed good to excellent light, washing, and rubbing fastness. Fourier transform infrared spectroscopy indicated the presence of phenolic constituents, which likely contributed to dye-fiber interaction. Conclusion Zygnema stellinum is a promising sustainable natural colorant for cotton dyeing, and bio-mordanting offers an eco-friendly route to improve shade development and fastness properties.
Owais et al. (Wed,) studied this question.