Uncovering the effects of PEG porogen molecular weight and concentration on ultrafiltration membrane properties and protein purification performance

Developing ultrafiltration (UF) membranes for protein purification requires a critical understanding of the pore engineering and active-layer morphological control. In this study, we systematically explored the use of polyethylene glycol (PEG) with molecular weights (MW, 600–6000 g⋅mol−1) and concentration (3–7.5 wt%) as a pore modifier to prepare polyvinyl difluoride (PVDF) membranes via the non-solvent phase-inversion process. The membranes demonstrated a high degree of control of the structure-property-performance relationship for improving the water flux, bovine serum albumin (BSA) rejection and antifouling properties. We found that the morphology of PEG-modified membranes showed the membrane surface crystal spherulite remarkably decreased, whilst surface pore size increased with increasing porogen MW. Similarly, the increase in membrane pore size correlated very well with porogen MW and concentration exponentially and linearly respectively. Furthermore, the PEG-MW membrane series showed a flux and rejection trade-off, whereas the PEG-concentration membrane series can produce a high BSA rejection and improve the flux owing to the presence of a dense active layer. Overall, the optimized membrane with the best protein separation properties was produced by using 6 wt% PEG with 600 g⋅mol−1, which reached a competitive permeate flux of ~60 LMH⋅bar−1, with excellent flux recovery rate of >90%, and a high BSA rejection rate of 90% at the end of the three test cycle. The results in this study have elucidated and advanced the fundamental knowledge of the interrelationship between porogen and membrane property-performance.