Valorization of chicken feathers using aqueous solutions of ionic liquids

The poultry-processing industry generates large quantities of waste rich in keratin, a fibrous protein representing around 90 wt% of chicken feathers, which is currently disposed of by landfilling or incineration. Keratin is commonly recognized as a renewable biopolymer resource used in the preparation of biomaterials (e.g., films and hydrogels) of interest in biomedical applications. Even though research on keratin recovery from chicken feathers started many years ago, very few keratin materials from this source have been developed due to keratin's low solubility in most common solvents and poor protein recovery yield. Although ionic liquids (ILs) have been reported as alternative solvents with high dissolution capability for several biopolymers, keratin recovery from chicken feathers using aqueous solutions of ILs has not been investigated to date. Considering the Green Chemistry Principles (especially the first one: zero waste) and circular economy concepts, in this work, we show that chicken feathers can be effectively dissolved in an aqueous solution of 1-butyl-3-methylimidazolium acetate (80 wt%), greatly enabling keratin recovery and preparation of keratin biofilms. Keratin recovery from the IL aqueous solution was optimized considering the coagulant type, solution : coagulant weight ratio, temperature, and time, with the coagulant type being the variable with higher influence on the recovery process. Under the best conditions (ethanol, 1 : 2 w/w, 5 degrees C, and 1 h), 90 wt% of keratin was recovered. IL recovery and reuse were also evaluated, and 82 wt% of recovery yield was achieved at the end of the third cycle. The recovered keratin was characterized, confirming the required physicochemical properties. A keratin film was finally prepared and characterized through cell viability, oxidative stress and wound healing assays, opening the path for the use of keratin films in biomedical applications.