Biobased Protic Ionic Liquids as Sustainable Solvents for Wool Keratin/Cellulose Simultaneous Dissolution: Solution Properties and Composited Membrane Preparation

In this study, levulinic acid-derived protic ionic liquids (PILs) were identified to be good solvents for wool keratin fiber dissolution and the simultaneous dissolution of wool keratin and cellulose, implying a green dissolution processing platform for regenerated materials preparation derived from both cellulose and keratin. The satisfactory solubility was believed to correlate to the potential keto–enol tautomerism of the ketone group in the levulinate anion, which has particular hydrogen bonding forming ability with cellulose and wool keratin. Cellulose/wool keratin solution properties were first studied systematically, demonstrating that the apparent viscosities of cellulose/wool keratin solution were highly correlated to the mass ratio of cellulose to wool keratin, mass concentration, and test temperature. The values of overlap concentration (C*) were identified to be 0.83, 1.3, and 2.01 wt % in the cases of cellulose, cellulose/wool keratin (5/5), and pure wool keratin, respectively. The aggregation that arose by the potential interaction via hydrogen bonding among cellulose, wool keratin, as well as PILs was demonstrated by dynamic light scattering. Furthermore, the cellulose/wool keratin composite membrane was facilely cast through sol–gel transition when ethanol was used as the coagulation bath, and the membranes were systematically characterized by X-Ray diffraction, Fourier transform infrared spectroscopy (FTIR), thermo gravimetric analysis, as well as scanning electron microscopy. The findings demonstrated that cellulose and wool keratin had high compatibility in the composited membranes. Meanwhile, the composite membranes had satisfactory mechanical properties of tensile strength of up to 60 MPa and an elongation at a break of up to 6%. In addition, the composited membranes also have outstanding oxygen barrier performance and satisfactory thermostability.