Separation and Characterization of Flavonoids from Purple Onion Skin and Their Potential Application for Natural Dyeing of Cotton Loose Fiber

The natural dye extracted from purple onion skin using absolute ethanol and the optimal extraction conditions for natural dye were investigated by the single-factor analysis as 80% aqueous ethanol mixed solvent system with a material-liquid ratio of 1:20, a temperature of 70？C, a time of 2 h, and a pH value of 5. This work aims to explore the pre-separation of purple onion skin dyes using thin-layer chromatography, and develop a developing agent ratio that can effectively separate quercetin and kaempferol dyes. Flavonoid was separated and purified by silica gel column chromatography to prepare quercetin after investigation of different amounts of silica gel filling height, purity level and different sample amounts. The isolated quercetin and kaempferol pigment were used as dyes to directly dye on modified cotton loose fiber. The optimal dyeing process was pH 6, temperature was 80？C, and dyeing time was 60 min. The fastness properties, both dyes showed good wash fastness and acceptable moderate light fastness, with Quercetin achieving a rating of 3 - 4 and Kaempferol being 3. This study explores a broader group of components separation and purification that can provide the palette with even more colors and new properties of the textile colored. It will be a key contributing factor to the transformation of the textile industry to more sustainable production practices aligning with larger global priorities to protect human health and ensure ecological integrity.