Effect of Polyethersulfone Molecular Weight on Structure and Performance of Ultrafiltration Membranes

Abstract

Polyethersulfones (PES) with three different molecular weights were chosen to prepare ultrafiltration (UF) membranes by the nonsolvent induced phase separation method using polyvinylpyrrolidone (PVP) and N-methyl-2-pyrrolidone (NMP) as additive and solvent, respectively. The effect of PES molecular weight on the structure and performance of the prepared asymmetric membranes was investigated by means of UF experiments, measurements of membrane thickness and porosity, scanning electron microscopy, and the measurement of bursting strength, given fixed PVP or PES concentrations. It was found that increasing PES molecular weight would lead to a larger pore size in the skin layer but lower membrane porosity, and would result in membranes with higher strength, higher permeability, and lower rejection. Based on the experimental data of PES molecular weight, ternary phase diagram, and cast solution viscosity obtained from gel permeation chromatography, cloud point titration, and coaxial cylinder viscometer measurements, respectively, the underlying causes of membrane structures were accounted for from the combined perspective of thermodynamics and kinetics and polymer aggregate dimensions.

Effects of polymer molecular weight, concentration, and role of polyethylene glycol as additive on polyacrylonitrile homopolymer membranes

“…. Similar observation is reported by several authors , for PEG grafted PAN copolymer system. Comparison of all the FTIR curves clearly reveals that, with the addition of hydrophilic PEG, the amount of hydroxyl and HOH bond is increased and at the same time the absorption at 2250 cm −1 decreases gradually indicating alteration during the stretching of nitrile bond.…”

“…Peak at 3350 cm −1 is for sp CH stretch, due to the presence of hydrogen at the end of the chain; peak at 2250 cm −1 is for symmetrical stretching for nitrile bond and that at 1650 cm −1 is for carbonyl bond. Usually, PEG shows distinct peaks at 1281, 1096, 963, and 841 cm −1 wave numbers . With the addition of PEG, most of the characteristic peaks of PEG (1281, 1096, and 841 cm −1 ) become more distinguishable compared to the pure PAN spectrum shown in Fig.…”

“…Some conflicting and limited results are available in literature on the effect of polymer molecular weight on the membrane structure, membrane properties, and membrane performances . Zhou et al and Zhao et al found that the permeability of the membrane is reduced and the BSA rejection is enhanced with PES and PSF molecular weight. In contrast to the above result, Bildyukevich et al pointed out that the solute rejection increased as well as the permeability increased with decrease in PES molecular weight.…”

Effects of polymer blend composition on membrane properties and separation performance of PEES/PEI blend membrane

“…Membranes formed by delayed demixing mechanism give a porous substructure with a dense, relatively thick skin layer. 18 The porosity of pristine PEES membrane was 19.3% and PEES/PEI blend membranes with composition 10/90, 20/80, and 30/70 have a porosity of 28, 32.9, and 35.2, respectively. The increase in PEI content enhances the pore formation, which also increases the porosity of the membrane.…”

Synthesis of High Molecular Weight Polyetherethersulfone‐Allyl Copolymers of Controlled Glass Transition

“…Higher molecular weights also increase mechanical resistance. On the other hand, molecular weights which are too high have been shown to lead to higher strength membranes with lower membrane porosity and water flux, larger pore sizes at the surface, higher permeability, and lower selectivity . Optimal molecular weights therefore appear to be in the 20 000 to 40 000 g mol −1 range .…”