Fabrication of a two-layer integrated skin asymmetric polyetherimide nanofiltration membrane

A two-layer integrated skin asymmetric polyetherimide (PEI) nanofiltrationmembrane was fabricated by a double-blade casting technique. This techniqueallows us to use different polymeric solutions in each layer and provide bettercontrol over membrane morphology. PEI solutions with different polymerconcentrations were used for each layer. The solution with higher polymerconcentration was employed to form the selective top-layer while the thinnersolution with lower polymer concentration was used to form a porous sub-layerwith low hydraulic resistance. Among the various effective parameters on theformation and performance of the final membrane, polymer concentration ineach layer, evaporation time, and top-layer thickness were of the greatestimportance that were considered in this study. The results showed that there isan optimum polymer concentration for the top-layer at which a dense anddefect-free top-layer could be formed. This optimum concentration was foundto be 19 wt% of PEI. Higher concentrations of the polymer solution for the toplayerincreased the solution viscosity and would lead to rupture of the top-layer.Moreover, it has been found that certain evaporation time is necessary in orderto achieve a membrane pore size in the range of nanofiltration. Finally, it hasbeen discovered that this method is not suitable for fabricating the top-layersthinner than 15 μm.

Keywords:

Nanofiltration , co-casting technique , two-layer membrane , polyetherimide