Fabrication of Polysulfone Membranes via Non‐Solvent Induced Phase Separation Using a Lignin‐Derived Hydrophobic Deep Eutectic Solvent

ABSTRACT Deep eutectic solvents (DES) are emerging as promising and sustainable alternatives 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 DES composed of thymol and 2,6‐dimethoxyphenol (Thy:Dmp) in a 1:1 M ratio via non‐solvent induced phase separation (NIPS). The Thy:Dmp DES exhibited a viscosity of 34.9 ± 0.26 mPa·s at 25°C. Hansen solubility parameter (HSP) 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) 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 bovine serum albumin (BSA, 66.5 kDa) rejection of 94.4%. These results demonstrate that lignin‐derived hydrophobic DES can serve as a functional alternative to conventional solvents for polysulfone membrane fabrication.