Recyclable urea-polyols solvents as molecular scissors for extracting keratin from waste feather

Keratin, as a natural biopolymer, holds great promise for industrial applications. In this work, a series of renewable urea-polyol solvents were designed for keratin extraction from waste chicken feathers. Urea-ethylene glycol (U-EG) exhibited the highest solubility of 18.1 % (181 mg feather/g solvent) for feather keratin at 120 °C, with a significant enhancement to 29.4 % achieved by adding 5 wt% arginine (Arg). Structural analysis indicates that the extracted keratin mostly maintained its original primary structure. These solvents substantially disrupted the disulfide bonds, affecting the secondary structure by converting some α-helix to β-sheet and amorphous structures like random coils. Molecular dynamics simulations revealed that U-EG could act as molecular scissors, synergistically reinforced by Arg, by disrupting the intermolecular interactions of solvents. This disruption liberated more free solvent molecules to interact with keratin via van der Waals forces, Coulomb forces, and hydrogen bonding interactions. U-EG exhibited excellent recyclability, maintaining high solubility of 86 % after five cycles of reuse.