A green bulk modification for imparting a green VIPS membrane with antifouling properties

Background

Membrane preparation and membrane modification processes have long involved the use of toxic solvents. The present work proposes to only use envrionmentally-friendly solvents for both the fabrication and the surface modification of hydrophobic microfiltration membranes. In addition, coating processes for membrane modification are essentially surface modification processes. However, spray-coating may be a suitable method for both surface and bulk modification.

Methods

After dissolving poly(vinylidene fluoride) in dimethylsulfoxide, membranes were formed by the vapor-induced phase separation process, and then modified using an aqeous solution of an amphiphilic copolymer containing poly(ethylene glycol) methyl ether methacrylate units. Then, a variety of physicochemical techniques were employed to characterize the membrane structure and prove the effectiveness of the surface/bulk modification. Antifouling tests in static and dynamic conditions were conducted.

Significant findings

It is possible to reduce the water contact angle of the top surface of the membrane from 135° to 0° and that of the bottom surface from 126° to 0° within <10 s, indicating successful hydrophilization of the membrane on the one hand, and top-to-bottom modification, despite solely exposing the top surface to the spray, on the other hand. This conclusion was confirmed by deidcated surface chemistry analyses. Besides, the membranes maintained their original highly porous and symmetric structure with light effects on surface porosity and pore size following the spray-coating process. The drasting improvement of hydrophilicity resulted in effective mitigation of fibrinogen adsorption (reduced by 85 %) and Escherichia coli adhesion (reduced by 86 %). Fouling during cyclic filtration involving a bacterial suspension was also effectively reduced with a flux recovery ratio of 53 % (against 37 % for a commercial hydrophilic membrane) and an irreversible flux decline ratio of 47 % (against 63 % for a commercial hydrophilic membrane) in the conditions of the test.