Constructing novel nanofibrous polyacrylonitrile (PAN)-based anion exchange membrane adsorber for protein separation

Purification of biopharmaceutical streams is essential for producing high quality therapeutic bioproducts. This work developed a novel polyacrylonitrile (PAN)-based nanofibrous membrane with strong anion exchange functionality via electrospinning. The key material functionality was obtained via RAFT copolymerization of acrylonitrile and dimethylaminoethyl acrylate (pAD), followed by quaternization to form quaternary amine (QA) ligands, namely pAQ, a series of nanofibrous PAN-pAQ membranes were electrospun by blending the pAQ copolymer with PAN homopolymer at varying ratios. The chemistry of the respective pAQ copolymer and resulting membranes was confirmed by NMR and FTIR, evidencing successful functionalization. As compared to the reference pure membrane PAN4 that was negatively charged, the resulting composite membranes showed a positive surface charge. The investigation on surface morphology revealed that the nanofiber diameter increased from 300 nm to 1 μm with an increasing blend ratio from 1:4 to 1:7 for the PAN-pAQ membranes. Such trend in surface micro/nano morphology changes strongly influenced other surface properties such as increased pore size, reduced specific surface area and increased hydrophobicity. The static binding of model protein BSA of PAN-pAQ membranes firstly increased with blend ratio from 1:4 to 1:5, and then decreased at 1:7, which was attributed to the complex trade-off relationship between surface micro/nano-structure and hence distribution/density of quaternary functional groups. The PAN-pAQ membranes showed about a 10-fold increase in static binding capacity compared to PAN4, up to 310–320 mg·g−1 at a blend ratio of 1:5. Thus through this study, we were able to demonstrate a facile route to incorporate pre-functionalized copolymers into conventional polymers to form chromatographic membranes, with many possibilities to tailor membrane functionality for a wide range of applications.