Green Conversion of Litsea cubeba Fruit Residues: Extraction of Polyphenolic Plant Dyes Using Deep Eutectic Solvents for Sustainable Silk Dyeing

As global attention to sustainable development continues to grow, plant dyes, as natural, renewable, and biodegradable biobased materials, are gradually becoming an ideal choice to replace traditional synthetic dyes due to their environmental friendliness, low toxicity, and sustainability. However, the application of plant dyes still faces challenges, including low extraction efficiency, poor dyeing performance, and the complexity and unclear nature of the dye components. This study presents a novel polyphenolic plant dye derived from the residues of Litsea cubeba fruits after essential oil extraction, and utilizes green deep eutectic solvent (DES) technology for efficient extraction and application. By screening and optimizing extraction conditions using response surface methodology, choline chloride/oxalic acid (ChCl/OA) DES was identified as the optimal solvent. Under conditions of 18% moisture content, a molar ratio of 0.75, and a solid-to-liquid ratio of 0.1, it significantly increased the polyphenol content in L. cubeba fruit residues. Compared to traditional extraction methods, the dye extracted using this method demonstrated significant advantages in both dyeing performance and antibacterial effects on silk. Furthermore, enzyme modification of the dye extracted with ChCl/OA successfully enhanced the color fastness of the fabric. More importantly, it was found that monomers such as p-hydroxycinnamic acid, trans-ferulic acid, and quercetin 3-β-d-glucoside play a key role in fabric dyeing performance, especially in enhancing dyeing strength and color fastness. This study provides theoretical support for the efficient extraction and application of polyphenolic plant dyes and promotes the sustainable development of green dyeing technologies.