Ionic Liquids and Deep Eutectic Solvents and Their Use for Dissolving Animal Hair

Abstract

In recent years, one of the priority areas of research in chemistry has become the processes carried out in an environment of liquid organic salts, the so-called ionic liquids (ILs), which are assessed as environmentally friendly or "green" alternatives to conventional organic solvents. ILs are non-volatile, highly polar solvents that dissolve many organic, inorganic, and organometallic compounds. Since they have no detectable vapor pressure, ILs are considered as potential substitutes for volatile organic compounds traditionally used as solvents. So-called deep eutectic solvents (DES) is a group of ILs that are liquid mixtures of a number of organic and (or) inorganic components taken in a certain ratio (eutectic or close to eutectic). DES deserve a special attention due to their negligible saturated vapor pressure, availability, low cost, as well as ability to dissolve at relatively high concentration of metal salts, metal oxides and various polymers. Particularly DES based on a mixture of choline chloride with urea (DES-1) or a mixture of choline chloride and adduct of urea with hydrogen peroxide (DES-2) give eutectics that are liquid at ambient temperature and have unusual solvent properties, including an ability to dissolve an animal hair in the presence of low concentration of sodium sulfide or ammonium thioglycolate. It was found that depending on the ratio between DES-1 and DES-2 in the mixture of two Deep Eutectic Solvents and the nature of sulfur-containing additive, the solubility of rabbit hair under used conditions, varies from 51% to 79%.

Closing the Loop with Keratin-Rich Fibrous Materials

“…The molecular weight obtained for keratin was ranging from 3.8 to 5.8 kDa, comparable to the conventional methods [ 67 ]. In another study, Sakhno et al [ 102 ] measured the solubility of rabbit hair in a mixture of two DES in a different composition. DES 1 consisted of a combination of choline chloride and urea and DES 2 in a combination of choline chloride and urea-hydrogen peroxide adduct both with the molar ratio of 1:2.…”

“…The extraction was carried out for 10 h at a temperature of 30 °C. Results showed that the mixture of DES 1 and DES 2 (1:2) had the highest solubility (79%) for the rabbit hair [ 102 ].…”

Valorization of waste wool to keratin with a green solvent based on a deep eutectic mixture of choline chloride and lactic acid

“…[28] The ability of DESs to disturb the hydrogen bonding and electrostatic bonds present in wool enhances the dissolution of keratin [16,29,30]. This also results in the formation of random coil and β-sheet structures [4].…”

Keratinases as Versatile Enzymatic Tools for Sustainable Development

“…The main physicochemical methods of keratin treatment are solubilization in organic solvents or ionic liquids, hydrothermal treatment, acid or alkaline hydrolysis, oxidation or reduction in disulfide bridges by the addition of chemicals, and degradation of hydrogen bonds, e.g., by urea [ 23 , 24 , 31 , 32 , 33 ]. The choice of the treatment method has a significant impact on the composition of the extracted keratin and keratin hydrolysate and largely depends on the intended future use of the final product [ 30 , 31 , 34 , 35 , 36 ]. A comparison of various physicochemical treatment methods with their advantages and disadvantages are presented in Table 2 .…”