Effect of N -Methyl-2-pyrrolidone/Dichloromethane Solvent Ratio towards the Retention of Magnesium Sulfate and Ibuprofen by Polylactic Acid Membranes

Abstract Polylactic acid (PLA) membranes are sustainable alternatives to petroleum-based polymers, yet inherent fragility often necessitates leachable additives for mechanical robustness that may contaminate the permeate. Cost-effective PLA 4032D pellets were used in this work to fabricate additive-free membranes via an evaporation-assisted non-solvent-induced phase separation (E-NIPS), employing N-methyl-2-pyrrolidone/dichloromethane (NMP/DCM) blends as a tuning parameter. E-NIPS implementation decoupled solvent evaporation from liquid–liquid demixing, facilitating a robust, high-crystallinity asymmetric structure. Optimized solvent ratio improved performance stability, yielding higher pure-water flux and enhanced rejection of ibuprofen and magnesium sulfate, chosen as representative pharmaceutical and salt contaminants. At an optimal 10:1 NMP/DCM ratio, membranes achieved a tensile strength of 9.65 ± 1.09 MPa and thermal stability onset near 345 °C. Differential scanning calorimetry confirmed that delayed demixing in NMP-rich formulations provided a kinetic window for ordered lamellae formation, significantly increasing crystallinity relative to DCM-rich amorphous structures. Additionally, 30 week soil burial tests revealed a controlled biodegradation profile regulated by the high-crystallinity matrix. These findings establish a sustainable framework for engineering high-performance, biodegradable membranes for pharmaceutical and salt removal.