Relating thin film composite membrane performance to support membrane morphology fabricated using lignin additive

• Thin film composite membranes were formed on different nonwoven fabrics.
• Reverse osmosis permeability is strongly positively correlated with fabric porosity, permeability and pore size.
• Forward osmosis water flux is strongly positively correlated with fabric porosity and the substructure porosity.
• Membrane structural parameters of different layers of composite membranes were determined by physical measurements.
• Physical measurements do not match experimental determination of membrane structural parameter.

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.