Formation of an externally unskinned polysulfone capillary membrane

The production protocol of internally skinned ultrafiltration membranes with no exterior skin layer was rationalized. The membranes were intended for use in bioreactor and filtration operations. The unique substructure morphology was designed to have low resistance to liquid transport and a large external surface area. The polysulfone and polyethersulfone membranes that were produced had well-defined internal skin layers, integrally part of a substructure that consisted entirely of closely packed and narrow-bore microvoids that extended from just below the internal skin layer of the membrane to the periphery. The regularly shaped microvoids open into the membrane periphery as there is no outer skin layer to bridge the cavities. The structures formed may be the result of rapid demixing of the internal skin layer, followed by nucleation and growth of the polymer-lean phase, coupled with coalescence at the membrane periphery.