Solute transport and structural properties of polysulfone/β-cyclodextrin polyurethane mixed-matrix membranes

Abstract

This paper discusses the solute and structural properties of polysulfone (PSf)/β-cyclodextrin (β-CD) polyurethane (PU) mixed-matrix membranes. Relative to a commercial PSf membrane, β-CD polyurethane (β-CDPU) was blended with PSf at concentration levels of 0–10% to prepare mixed-matrix membranes using a convectional phase-inversion technique. The surface morphology and the porous structure were evaluated by scanning electron microscopy (SEM). Dynamic mechanical analysis was used to determine the mechanical stability (stiffness) of the membranes: mixed-matrix membranes (MMMs) were found to be mechanically stable even at elevated temperatures (30–350°C). Pure water sorption results show a Fickian diffusion mode mechanism for the PSf membrane (n=0.50), PSf/5% β-CDPU shows an anomalous transport mechanism (n=0.80) while the PSf/8 %β-CDPU and PSf/10% β-CDPU membranes followed a non-Fickian diffusion mode (n=1.1). Pure water permeability and glucose rejection characteristics were carried out using a cross-flow system. These results reveal that pure water and solute permeability increase with an increase in pressure. The hydrophilicity and surface energy of the MMMs were determined using a sessile-drop (contact-angle) method. Mixed-matrix PSf/β-CDPU membranes were found to be more hydrophilic (<49°) compared to the PSf membrane in the case of PSf/5% β-CDPU, while for 8 and 10% PSf/β-CDPU the contact angle values did not differ significantly (60–66°). Higher pure water permeability and glucose rejection of up to 99.88% was also obtained. This study demonstrates that the crystal structure of MMMs lacks sorption sites to allow high mass transfer of water and glucose molecules through the membranes which resulted in higher glucose rejection.