Asymmetric polyethersulfone (PES) membranes were fabricated from the PES/γ-butyrolactone (GBL)/polyvinylpyrrolidone (PVP) system using non-solvent induced phase separation (NIPS) process. Two types of PVP with different molecular weights (PVP–K30 and PVP-K15) were added as dual pore-forming agents in the dope solution to modify the morphological, physical, permeation, and separation properties of the membranes. Our results demonstrate that high concentration of PVP-K30 in the dope favors the formation of a top skin layer and macrovoids, whereas the PVP-K15 can open the pores on the top surface, shrink the macrovoids, and transform the bi-continuous porous structure toward cellular pores. In the optimal composition of PVP additives (i.e. 8 wt% PVP-K30 and 5 wt% PVP-K15 in this work), the resulted PES membrane exhibits a water flux of 563 L m−2h−1 and a remarkable rejection coefficient over 99% for blue dextran solution, showing a promising potential in ultrafiltration applications.
