Dissolution of wool in the choline chloride/oxalic acid deep eutectic solvent

Abstract

A great amount of wool wastes are produced every year in the world, leading to the discard of keratin resources and causing environmental pollution. The recycling of wool is of great significance for the application of keratin. In this work, the dissolution of wool in a benign choline chloride/oxalic acid (ChCl-OA) deep eutectic solvent (DES) solvent was presented, and the dissolution conditions were discussed. After dissolution, keratin was separated by dialysis, filtration and freeze-drying. The resulting keratin powder was characterized by X-ray diffraction, thermogravimetry/differential scanning calorimetry, protein electrophoresis, scanning electron microscope, and amino acid analysis. The optimized dissolution conditions were the following: ChCl-OA molar ratio 1:2; wool-DES weight ratio 5%; 110–125 °C; 2 h. In the dissolution process, the disulfide bonds of wool molecules were broken, and the α-helix structure of wool was destroyed. The molecular weight of the as-prepared keratin was between 3.3 kDa and 7.8 kDa, and the freeze-dried keratin displayed flake structures.