Tailoring Polyetherimide Ultrafiltration Membranes via Non-Solvent- and Vapor-Induced Phase Separation: Effects of Fabrication Pathway and Membrane Formulation on Morphology and Bovine Serum Albumin Separation Performance.

Polyetherimide (PEI) ultrafiltration membranes were fabricated for bovine serum albumin (BSA) separation using nonsolvent-induced phase separation (NIPS) and vapor-induced phase separation (VIPS). In the NIPS approach, membranes containing varying amounts of Pluronic P-123, with or without graphene nanoplatelets (GNPs), were prepared. Pluronic P-123 acted as a pore-forming agent, while GNPs enhanced permeability without compromising rejection. The membrane with 1 wt.% Pluronic P-123 achieved a pure water flux (PWF) of 355 LMH and 90% BSA rejection. Incorporating 1 wt.% GNPs further improved performance to 747 LMH and 98% rejection. VIPS membranes were fabricated using the same composition as N10, containing 17 wt.% PEI and 1 wt.% Pluronic P-123 without GNPs, to isolate the effect of the fabrication pathway. Increasing vapor exposure time reduced PWF but generally improved BSA rejection, whereas higher RH increased PWF while decreasing rejection. The composition-matched NIPS membrane, N10, exhibited a PWF of 355 LMH and approximately 91% BSA rejection. In comparison, the highest PWF and BSA rejection among the VIPS membranes were 91 LMH and 76.5%, respectively, and the selected balanced VIPS condition at 30 min and 65% RH yielded approximately 49 LMH and 55% rejection. The higher performance of N11, which achieved 747 LMH and 98% rejection, is attributed to GNP incorporation within the NIPS series and was not used to isolate the fabrication-pathway effect. Overall, the composition-matched comparison demonstrates that NIPS produced a more favorable morphology and BSA separation performance than VIPS under the investigated conditions.