Abstract
A more sustainable dialysis and water filtration membrane has been developed, by using the new, safer, bio-based solvent Cyrene® in place of N-methyl pyrrolidinone (NMP). The effects of solvent choice, solvent evaporation time, the temperature of casting gel, and coagulation bath together with the additive concentration on porosity and pore size distribution were studied. The results, combined with infrared spectra, SEM images, porosity results, water contact angle (WCA), and water permeation, confirm that Cyrene® is better media to produce polyethersulfone (PES) membranes. New methods, Mercury Intrusion Porosimetry (MIP) and NMR-based pore structure model, were applied to estimate the porosity and pore size distribution of the new membranes produced for the first time with Cyrene® and PVP as additive. Hansen Solubility Parameters in Practice (HSPiP) was used to predict polymer-solvent interactions. The use of Cyrene® resulted in reduced polyvinylpyrrolidone (PVP) loading than required when using NMP and gave materials with larger pores and overall porosity. Two different conditions of casting gel were applied in this study: a hot (70°C) and cold gel (17°C) were cast to obtain membranes with different morphologies and water filtration behaviours.
Highlights
The growing use of filtration membranes is the result of increasing attention paid to environmental problems linked to the availability of and growing demand for clean water [1,2,3]
The membranes are coded based on the solvent used (PES/C is the membrane produced with Cyrene5 while PES/N represents the one with N-methyl pyrrolidinone (NMP)) and the concentration of PVP used, e.g., “0” means a membrane produced with no PVP, while “0.1” through to ‘’10” means a membrane produced with 0.1% through to 10% PVP, respectively (Table 2)
It was found that no additive is necessary to form pores when Cyrene5 is applied as solvent, PES/C0 having the same pore diameter as NMP-based membranes produced with 5% PVP (PES/N5), meaning that no additive many not be necessary for the role of pore forming when using Cyrene5
Summary
The growing use of filtration membranes is the result of increasing attention paid to environmental problems linked to the availability of and growing demand for clean water [1,2,3]. Fouling of the membrane is as a result of the hydrophobicity of PES, making separation unpredictable and shortening its lifetime due to a higher energy demand to push the water through the pores [15, 16]. To reduce the fouling effect, the PES membranes are modified via bulk modification, surface modification, and blending (a type of surface modification), with the latter being the most widely used method [17]
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