Chemistry in a spinneret – Formation of hollow fiber membranes with a cross-linked polyelectrolyte separation layer

Hollow fiber membrane modules are backwashable, less prone to fouling and exhibit higher packing densities compared to spiral wound modules. Nevertheless, most commercial nanofiltration membranes are flat sheet membranes because the production process of composite membranes is at the moment only feasible for flat sheet membranes. In this work, we present the complex but robust fabrication of cross-linked polyelectrolyte nanofiltration hollow fiber membranes using our chemistry in a spinneret technique. We combine three processes in one fabrication step: 1. Ionic cross-linking between oppositely charged polyelectrolytes, 2. covalent cross-linking of amine groups and 3. phase inversion of an inert membrane forming polymer. The amine component as reactant is dissolved in the polymer solution, while the bore fluid contains a cross-linker and a negatively charged polyelectrolyte. Morphology, surface elementary composition and surface charge analysis prove the successful formation of the cross-linked polyelectrolyte separation layer on the lumen channel surface of the fabricated fibers. The fibers show nanofiltration properties regarding high salt retentions and a low molecular weight cut-off of 280 Da. The presented spinning technique shows a promising potential to become an attractive alternative to multi step fabrication methods.