Performance Evaluation of Poly(amide-imide) Incorporated Cellulose Acetate Ultrafiltration Membranes in the Separation of Proteins and Its Fouling Propensity by AFM Imaging

Polymeric membranes intended to be used in protein separation must be fouling resistant in order to reduce the interactions with proteins during operation. Therefore, cellulose acetate (CA) membranes with superior properties were prepared by phase inversion technique using high-performance thermoplastic poly(amide-imide) (PAI) as the modification agent. The prepared membranes were characterized using attenuated total reflectance Fourier transform infrared spectroscopy (ATR-FTIR), scanning electron microscopy (SEM), atomic force microscopy (AFM), molecular weight cutoff, and pore size to investigate the influence of PAI on the properties of the resultant membranes. Intermolecular interactions between the components in blend membranes were established by ATR-FTIR and SEM analysis showed that the blend CA membranes have thinner top layer and higher porosity in the sublayer. These prepared membranes were subjected to the separation of proteins such as bovine serum albumin, egg albumin, pepsin, and trypsin. The fouling-resistant capability of the membranes was studied by bovine serum albumin as the model protein and increase in resistance during protein filtration was calculated by means of resistance in series model analysis. The fouled membranes were characterized by AFM imaging and these membranes were cleaned by washing with deionized water and subsequent sonication. From the AFM images of the fouled membranes it was clear that preferential adsorption takes place at specific locations on the membrane surface and is a function of surface roughness and membrane hydrophilicity. It is worth mentioning that the incorporation of poly(amide-imide) into the cellulose acetate matrix is an effective method for the development of low fouling ultrafiltration membranes for the separation of proteins.