Ongoing phase separation inside hollow fiber membranes via non-solvent induced phase separation

This study investigates the critical influence of residual solvent on pore evolution during the non-solvent induced phase separation (NIPS) process. Employing a comprehensive multi-technique approach, including FT-IR spectroscopy, UV absorbance, contact angle, mechanical testing, shrinkage analysis, and confocal fluorescence microscopy, membrane's morphological evolution is elucidated. The findings demonstrate that residual solvent, particularly under elevated cleaning temperatures, significantly promotes pore collapse, leading to a substantial reduction in water flux. To mitigate this issue, we develop a tailored cleaning solution (methanol, water, and calcium chloride) that effectively enhances solvent exchange while maintaining the rejection performance for bovine serum albumin (BSA). Crucially, this research reveals that residual solvent significantly affects membrane performance, influencing pore structure in ways that go beyond the traditional understanding of the initial phase separation process.