On the organic solvent free preparation of ultrafiltration and nanofiltration membranes using polyelectrolyte complexation in an all aqueous phase inversion process

Sustainable polymeric membrane fabrication aims for processes without the use of hazardous organic solvents or crosslinkers. One promising alternative method represents the fabrication of polyelectrolyte complex (PEC) membranes based on aqueous phase separation. We present the fabrication of PEC membranes from salt dilution induced phase separation. The complexation of the polyanion PSS and polycation PDADMAC is suppressed by an overcritical KBr concentration. The overcritical liquid polymer solution is cast and subsequently immersed in deionized water. The concentration gradient leads to salt diffusion out of, and water into the liquid polymer solution until the composition enters the demixing gap. Further salt dilution induces polyelectrolyte precipitation in the two phase region and forms the final porous PEC membrane. The presented approach shows similarities to the established non-solvent induced phase separation (NIPS), so high potential for the transfer of existing expertise. Most notably, the influence of simultaneous demixing of polyions is observed for different polyanion/ polycation ratios in the liquid polymer solution. Three monomer ratios lead to membranes with different morphologies and separation properties in the range of ultrafiltration and nanofiltration. The presented method can be applied with commercially available polyelectrolytes and is easy to implement. This method is a promising approach to eliminating the use of organic solvents and realizing a sustainable alternative to the state of the art polymeric membrane fabrication processes.

Automated summary

This study introduces a method for fabricating polyelectrolyte complex membranes using salt dilution induced phase separation, resulting in membranes with different morphologies and separation properties. The precipitation of polyelectrolytes is induced by the diffusion of salt and water in the two-phase region, forming porous PEC membranes.