The Synthesis of Binary DES and Its Application in the Pretreatment of Wool Keratin Extraction by the L-cysteine Redox Method

Deep Eutectic Solvent (DES) has extraordinary dissolving power for metal oxides, cellulose fibers and protein fibers, and it is an ideal green solvent for wool dissolution or pretreatment. Previous literature used L-cys/urea redox system to extract keratin from waste wool, but this method consumed an array of raw materials and heat energy. In this study, choline chloride (ChCl) and oxalic acid (OA·2H2O) were mixed to successfully synthesize binary DES that could make wool dissolution rate up to 60.2% and keratin extraction rate up to 30.74%. After pretreating wool with ChCl/OA·2H2O DES, the extraction process of L-cysteine redox method was optimized simultaneously. The results showed that after optimization, the reaction time was shortened, the dosage of urea was remarkably saved. Additionally, the extracted keratin retained the amide structure for practical application.