Solvent nanofiltration through high permeability glassy polymers: Effect of polymer and solute nature

Abstract

The effect of solute nature on the retention performance of membrane materials based on PTMSP, PMP and PIM-1 has been investigated in ethanol media. Using the examples of PMP and PIM-1, it was shown that membrane swelling could enhance the solvent transport across the membrane, regardless of the initial gas permeability. All polymers show the same level and order of retention for low molecular weight dyes (350Da) regardless of the difference in polymer nature; in particular, negative retention of the neutral dye Solvent Blue 35 was observed for PTMSP, PMP and PIM-1: −17%, −11% and −4%, respectively. This retention behavior was explained by a “blocking effect” due to high dye-membrane interaction and comparable size of the solute (Vcalc=685Å3) and available free volume elements within the polymer (5–12Å). An increase of dye retention is attributed to a decrease of solute-membrane interaction; for example, PIM-1: Solvent Blue 35 (K=1107; |δPIM−1−δsolute|=4.2)<Safranine O (K=47.0; |δPIM−1−δsolute|=6.1)<Orange II (K=3.3; |δPIM−1−δsolute|=9.7). The retention of higher molecular weight solutes is expected to be limited mainly by free volume size. Thus, it is possible to control nanofiltration parameters by proper selection of the polymer and the variety in the chemical nature of high permeability glassy polymers provides additional flexibility in solvent resistance and further modifications (e.g. cross-linking). A new possible application of PIM-1 as a polymeric sorbent with selectivity towards dissolved neutral compounds is proposed.