Investigating the Use of a Lignin-Derived Deep Eutectic Solvent for Nonsolvent-Induced Polymeric Membrane Fabrication

Deep eutectic solvents (DES) are emerging as a promising and sustainable alternative to traditional solvents in various industrial processes. They offer distinct advantages, including low toxicity, biodegradability, cost-effectiveness, and the ability to be tailored to specific applications. This study investigated the fabrication of polysulfone (PSf) membranes using a lignin-derived, hydrophobic deep eutectic solvent (DES) composed of thymol and 2,6- dimethoxyphenol (Thy:Dmp) in a 1:1 molar ratio via non-solvent induced phase separation (NIPS). Hansen solubility parameter calculations confirmed thermodynamic compatibility between PSf and the DES (RED = 0.6), while cloud point measurements established the ternary phase behavior for the PSf/Thy:Dmp/ethanol system. Fourier Transform Infrared spectroscopy (FTIR) spectroscopy confirmed complete solvent removal and polymer structure preservation after membrane formation. The resulting membranes exhibited asymmetric morphology with finger-like macrovoids and 81.2 ± 1.80% porosity. Contact angle measurements indicated moderately hydrophilic membrane surfaces (64.0 ± 1.20°). Membrane performance evaluation displayed water permeability of 58.3 LMH/bar and protein rejection of 94.4%. Preliminary trials with Cellulose Acetate (CA) show similar results in protein rejection at the same polymer contents. These results demonstrate that lignin derived hydrophobic DES can serve as a functional alternative to conventional solvents for polysulfone membrane fabrication.