Sustainable fabrication of cellulose ultrafiltration membranes: Optimizing performance with novel N-methylmorpholine-N-oxide/deep eutectic solvent systems

The increasing demand for sustainable filtration has driven the development of cellulose-based ultrafiltration membranes using green solvents. In the present study, microcrystalline cellulose (MCC) was dissolved in a co-solvent system combining N-methylmorpholine-N-oxide (NMMO) and a choline chloride (ChCl)/lactic acid (LA) deep eutectic solvent (DES) and cast into regenerated cellulose (RC) membranes via the nonsolvent-induced phase separation (NIPS). The effects of dope solution composition, preparation conditions, and post-treatment on membrane performance were systematically evaluated. Results indicated that dissolving 6 wt% MCC in an NMMO/DES mixture, with a mass ratio 80:20 (DES comprised ChCl and LA in a 1:2 molar ratio), followed by casting at 60 °C using a 300 μm knife gap, produced membranes with a permeability of around 30 L/m 2 ·h·bar (LMH/bar) and a bovine serum albumin (BSA) rejection rate of approximately 96 %. Replacing the water coagulation bath with a 40 % (v/v) ethanol aqueous solution increased permeability to about 46 LMH/bar while maintaining a high BSA rejection of about 93 %. Moreover, Hansen solubility parameters were utilized to assess the thermodynamic interactions among the polymer, solvent, and nonsolvent, elucidating their effect on membrane structure and performance. These findings highlight the potential of sustainable solvent system for fabricating RC membranes, thereby advancing sustainable filtration technologies.