Aqueous Phase Separation: a novel and sustainable approach for membrane preparation

This thesis investigates and demonstrates how polymeric membranes can be prepared using the new and more sustainable aqueous phase separation (APS) approach. Polymeric membranes are used on huge scales for kidney dialysis, wastewater treatment, drinking water production, and as a less energy intensive alternative to conventional industrial separation processes. However, the vast majority of polymeric membranes are produced via an unsustainable and environmentally unfriendly process which uses large amounts of reprotoxic chemicals like N methyl 2 pyrrolidinone (NMP) and dimethylformamide (DMF). Unlike the conventional methods the APS approach uses a water based system using a pH or salinity switch instead of toxic organic solvents to prepare membranes. This allows for a more sustainable membrane production process without the use of reprotoxic solvents. This thesis investigates the single-polyelectrolyte approach, where a responsive polyelectrolyte solution is precipitated by a pH switch. Two different polyelectrolytes are used, poly(4 vinyl pyridine) (P4VP) which is soluble in acids and insoluble in base, and polystyrene-alt-maleic acid (PSaMA) which is soluble at neutral and basic conditions and insoluble in acid. Using a variety of parameters such as polymer concentration, acid type and concentration, salt type and concentration both open microfiltration (MF) and ultrafiltration (UF) membranes as well as dense nanofiltration (NF) membranes are prepared. These membranes can match commercially available membranes with retention in aqueous environments, have high mechanical stability and are resistant to various organic solvents. This demonstrates that the single-polyelectrolyte APS approach can match the versatility of conventional preparation methods. While there still plenty of room for improvement, this thesis marks the beginning of a new method that has the potential to significantly improve the sustainability of the membrane industry.