Abstract
Polyimide (PI) membranes are attractive for demanding separation processes, but their fabrication typically relies on dipolar aprotic solvents that conflict with current environmental and safety targets. Here, we show that a commercial poly (amic acid) can be converted into a water-soluble poly (amic acid) salt (PAAS) and processed entirely from aqueous media to yield highly porous asymmetric PI membranes. The membranes are formed from a water-based PAAS casting solution through salt-conditioned, temperature-triggered phase separation, followed by glycerol-assisted thermal imidization that preserves the asymmetric macrovoid structure. The resulting PI films combine a thin dense skin with a highly porous sublayer of high overall porosity, delivering high pure-water permeance while maintaining a tensile strength close to 50 MPa with excellent thermal stability characteristic of aromatic PI. Liquid–liquid displacement porometry and SEM confirm a well-developed, interconnected pore network that underpins the permeation performance, while filtration tests demonstrate stable water fluxes under elevated transmembrane pressures over multiple cycles. This work establishes an aqueous, PAAS-based route as a viable and scalable strategy for producing high-flux PI ultrafiltration (UF) supports. A comparative life cycle assessment further demonstrates that replacing NMP with water in the membrane formation step significantly reduces the environmental impacts and overall environmental cost, contributing to more sustainable polymeric separation materials.