Exploration of highly sulfonated polyethersulfone (SPES) as a membrane material with the aid of dual-layer hollow fiber fabrication technology for protein separation

The combination of a highly sulfonated polyethersulfone (SPES) material with an ion-exchange capacity (IEC) of 1.11 meq/g polymer and the dual-layer hollow fiber fabrication technology was explored for the first time for protein separation. Three types of dual-layer hollow fibers with different structures and outer-layer compositions were prepared. Both contact angle and zeta potential experiments confirm the highly hydrophilic and charged characteristics of the dual-layer SPES/PES hollow fiber membranes. A binary protein mixture comprising bovine serum albumin (BSA) and hemoglobin (Hb) was separated in this work. The dual-layer hollow fiber consisting of a neat SPES outer layer with the highest IEC value exhibits the best and most durable protein separation performance among all tested fibers. Its BSA/Hb separation factor is maintained above 10 for 1 day. This study demonstrates that the highly sulfonated PES material is a determinant factor for the enhanced protein separation. The positive BSA/Hb separation performance is perhaps due to the fact that the strong electrostatic attraction between Hb molecules and sulfonic groups of SPES withholds the Hb molecules at the retentate side and meanwhile, the shielding effect provided by the adsorbed Hb molecules is speculated to probably promote the BSA molecules to diffuse into the permeate side. The neutral solute rejection results indicate that the pore size and pore size distribution are other factors which may influence the protein separation performance of the charged membranes. Excessively large pore size and broad pore size distribution may weaken the electrostatic attraction between Hb molecules and sulfonic groups of SPES and hence lower the separation factor.