Abstract
Aqueous phase separation (APS) is a recently developed sustainable alternative to the conventional organic solvent based nonsolvent-induced phase separation (NIPS) method to prepare polymeric membranes. In APS, polyelectrolytes are precipitated from aqueous solutions through pH or salinity switches. Although APS differs from NIPS in the polymer and solvents, they share many tuning parameters. In this work, we investigate the APS-based preparation of membranes from poly(styrene-alt-maleic acid) (PSaMA) with a focus on acid concentration in the coagulation bath, and polymer and additive concentration in the casting solution. Nanofiltration membranes are prepared using significantly lower concentrations of acid: 0.3 M HCl compared to the 2 M of either acetic or phosphoric acid used in previous works. It is shown that higher polymer concentrations can be used to prevent defect formation in the top layer. In addition, acetic acid concentration also strongly affects casting solution viscosity and thus can be used to control membrane structure, where lower acetic acid concentrations can prevent the formation of macrovoids in the support structure. The prepared nanofiltration membranes exhibit a very low molecular weight cutoff (210 ± 40 dalton), making these sustainable membranes very relevant for the removal of contaminants of emerging concern. Understanding how the parameters described here affect membrane preparation and performance is essential to optimizing membranes prepared with APS towards this important application.
Highlights
The preparation of polymeric membranes through nonsolvent-induced phase separation (NIPS) has been extensively investigated since its invention in the 1960s [1,2,3,4]
This work investigates how acid concentration in the coagulation bath and polymer casting solution viscosity affect the preparation of membranes using poly(styrene-alt-maleic acid) (PSaMA) in an aqueous phase separation system
Membranes prepared with PSaMA were typically precipitated in coagulation baths consisting of either 2 M acetic or phosphoric acid [26,35]
Summary
The preparation of polymeric membranes through nonsolvent-induced phase separation (NIPS) has been extensively investigated since its invention in the 1960s [1,2,3,4]. The typical tuning parameters for the phase separation include: choice of solvent and polymer [6], polymer concentration [5,7,8], additives in the polymer solution [9,10,11], composition of the nonsolvent [12,13,14], and temperature [15,16]. In recent years there has been quite some research into preparing membranes using different variants of NIPS in an effort to find more sustainable alternatives [17,18]. The alternative solvents include solvents like dimethyl sulfoxide (DMSO) [20], supercritical CO2 [21], ionic liquids [22], and new synthetic solvents [23,24]
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