Effect of a Sulfonated Poly(ether sulfone) Additive on the Bubble Point-Permeability Trade-Off of Polyethersulfone...

Polyethersulfone (PES) microfiltration (MF) membranes are widely used in bioprocessing and water treatment, but their bubble point (BP), which reflects the largest limiting pore, and their pure water permeability (PWP) are usually coupled in opposite directions, so that gains in throughput are paid for by a loss of pore-size control. Most hydrophilic-additive studies on PES have addressed ultrafiltration membranes cast at laboratory scale, and the effect of a sulfonated poly(ether sulfone) (SPES) additive on the BP-PWP trade-off of MF membranes produced on a continuous line has not been reported. Here, an in-house SPES (potassium form; 25 mol% sulfonated hydroquinone in the monomer feed) was substituted for 0.5 and 1.0 wt% of the PES in casting dopes of constant polymer content, and the dopes were processed into flat-sheet MF membranes on a roll-to-roll vapor-induced/non-solvent-induced phase separation (VIPS/NIPS) line, in which the pore structure is generated by delayed demixing followed by leaching of the water-soluble pore formers poly(vinylpyrrolidone) and poly(ethylene glycol). All membrane series retained the expected negative BP-PWP relation, but the SPES-containing membranes occupied a higher-PWP region than the PES-only control at the same BP; at a matched BP of about 2500 mbar, PWP increased by 10% and 17% at 0.5 and 1.0 wt% SPES. The matched-BP membranes had similar sponge-like morphologies and similar hydraulic mean pore radii, whereas porosity and water uptake increased with SPES content. The results indicate that a small SPES loading expands the control-relative BP-PWP performance window of continuously cast PES MF membranes mainly by increasing the water-accessible void volume rather than by enlarging the pores, and identify SPES as a compositional lever that is compatible with existing industrial casting lines.