Relating thin film composite membrane performance to support membrane morphology fabricated using lignin additive
Journal of Membrane Science
University of Johannesburg, Department of Applied Chemistry, Johannesburg, South Africa; University of California, Department of Civil and Environmental Engineering, Los Angeles, CA, United States; University of California, Department of Bioengineering, Los Angeles, CA, United States
In this study, three nonwoven fabrics were used as supports to form thin film composite membranes for forward osmosis (FO) applications. Lignin additive was added to the polysulfone layer in two different concentrations to increase the porosity of the substructure. The fabrics were characterized in terms of their Frazier permeability, tortuosity, porosity, thickness, structural parameter and capillary pressure. It was found that the fabric tortuosity and thickness had strong negative correlations with FO water flux, while fabric porosity had a strong positive correlation. The fabric capillary pressure was found to be indicative of how well the polysulfone layer adhered to the fabric layer. The membrane structural parameter of the fabric, unsupported and supported polysulfone layers were measured and compared using a "resistance-in-series" model. Although seepage of the casting solution into the fabric layer was physically observed, the addition of the individual structural parameters of the layers offered a good approximation of the composite membrane structural parameter. Membrane structural parameters calculated for fabric supported composite membranes using reverse osmosis (RO) permeability parameters and FO/RO established transport equations were much larger than structural parameters obtained from physical measurements. The difference may be due to compaction of composite membranes in reverse osmosis experiments, casting solution seepage partially plugging the upper layers of the support fabric and other non-idealities not captured in the established FO/RO transport equations. © 2014 Elsevier B.V.
Capillarity; Capillary tubes; Lignin; Nonwoven fabrics; Porosity; Reverse osmosis; Seepage; Forward osmosis; Membrane morphology; Negative correlation; Physical measurement; Positive correlations; Structural parameter; Thin film composite membranes; Transport equation; Composite membranes; lignin; polysulfone; water; article; capillary pressure; controlled study; electric conductivity; film; hydrophilicity; membrane permeability; membrane structure; membrane technology; osmotic pressure; porosity; priority journal; reverse osmosis; scanning electron microscopy; thickness; water permeability