Efficient and regulable extraction of keratin from yak hair using imidazolium-based ionic liquids

Yak hair is very difficult to dissolve in most conventional solvents due to the stable three-dimensional structure of keratin, which limits its application. In this study, a series of imidazole-based ionic liquids (ILs) were screened out and used to extract keratin from yak hair. The results indicated that the time of 8 wt% yak hair completely dissolved in five ILs at 130.C was in the sequence of 1-allyl-3-methylimidazolium chloride ([Amim]Cl) > 1-butyl-3-methylimidazolium chloride ([Bmim]Cl) > 1-ethyl-3-methylimidazolium chloride ([Emim]Cl) > 1-ethyl3-methylimidazolium diethylphosphate ([Emim]DEP) > 1-ethyl-3-methylimidazolium acetate ([Emim]OAc), and the anion played an essential role in the dissolution process. However, the XRD and the solid-state 13C NMR results showed that the secondary structure of regenerated yak hair keratin changed from beta-sheet and random coil conformation to a-helix for [Emim]DEP, [Bmim]Cl, [Emim]Cl, while the regenerated yak hair keratin from [Emim]OAc was damaged greatly. The regenerated yak hair keratin using [Emim]DEP had the highest disulfide bond content and relatively complete structure. Furthermore, [Emim]DEP has an excellent performance in dissolving human hair and goat wool, and the secondary structure of the regenerated keratins was also maintained. Meanwhile, the dissolution performance of the fifth recycled [Emim]DEP remained steady, suggesting that [Emim]DEP is a potentially efficient solvent for the extraction keratin from hairs.