Anti-fouling Ultrafiltration Membranes

Ultrafiltration membranes are membranes that exhibit pores in their selective layer in the range of 1-100 nm. Such membranes find application in industrial processes, water treatment and renal dialysis, but are highly susceptible to fouling by proteins, polysaccharides and other biomolecules, and suffer from low selective layer porosity. Current methods to reduce UF membrane fouling often involve enhancing the hydrophilicity of the membrane surface by surface graft polymerization of hydrophilic monomers. However, these methods can significantly increase manufacturing costs and often leave internal pores unmodified, while the resulting surface coatings tend to reduce the intrinsic flux and incorporate ungrafted polymers that are subject to removal.

Our group has devised an alternate strategy for surface modification that 1) adds no extra manufacturing costs; 2) provides a mechanism for self-healing a damaged surface; 3) increases the intrinsic porosity of the membrane and hence the flux; and 4) modifies both external membrane surfaces and interior pore surfaces. In this approach, amphiphilic comb copolymers comprising hydrophobic backbones and hydrophilic side chains are added into the membrane casting solution. Upon immersion into the coagulant bath, the comb copolymers surface segregate to all polymer-water interfaces of the forming membrane and self-organize, creating a hydrophilic brush-like layer with high fouling resistance. Because the additive is water insoluble, it does not dissolve from the membrane surface during use. Moreover, additive that is chemically removed by harsh cleaning operations can be replenished through a simple hot water anneal. The additive further acts as a porogen during membrane casting, increasing the fractional porosity on the membrane selective layer. We have demonstrated this strategy to be effective for for UF membranes fabricated from polyvinylidene fluoride (PVDF), polysulfone (PSf) and most recently polyacrylonitrile (PAN), employing amphiphilic combs that have backbones miscible with the membrane matrix polymer and side chains of PEO.