Investigation of parameters affecting morphology of microfiltration and ultrafiltration membranes fabricated via phase separation microfabrication

Bolat, Cankut Kaan
This study examines the factors affecting the morphology of polyethersulfone membranes produced via phase separation microfabrication technique. Flat and corrugated membranes were prepared using a combination of vapor induced and liquid induced phase separation, and characterized using scanning electron microscopy, pure water permeance tests and Baker’s yeast (Saccharomyces Cerevisiae) fouling tests. An inverse asymmetric morphology was tried to be achieved for corrugated membranes, in order to increase the effectiveness of filtration for a polymer solution containing 10% polyethersulfone, 60% polyethylene glycol (PEG-400), 25% N-methyl-2-pyrollidone (NMP) and 5% pure water by weight. Membrane morphologies were tried to be tuned by altering humid air flow rate, humid air exposure time and relative humidity during vapor induced phase separation. Results showed that the closest structure to desired inverse asymmetric membrane was the membrane exposed to humid air for 4 minutes at 80% relative humidity with the flow rate of 0.9 L/min, which was chosen with its flat counterpart for further investigation. Chosen membranes were also exposed to polydopamine coating for pore size reduction and increasing the surface hydrophilicity. Coated and uncoated membranes were compared for their pure water permeance and fouling during yeast filtration. Polydopamine coating decreased the pure water permeance on both type of membranes as expected, however all the membranes performed no rejection to BSA solutions. Moreover, it was observed that polydopamine coated membranes have shown worse fouling performances when compared to their uncoated counterparts. Corrugated membranes had higher pure water permeances and better fouling behavior compared to their flat counterparts.