Interesting behavior for filtration of macromolecules through EVAL membranes

The objective of this article is to investigate the permeation characterist ics of several polydispersed macromolecules through the asymmetric and the particulate poly (ethylene-co-vinyl alcohol) (EVAL) membranes. The solutes in examination include two nonionic solutes, dextran and polyethylene glyco l (PEG), and one anionic solute, sodium polyacrylate (SPA). The ultrafiltra tion results indicate that the rejection coefficients increase monotonicall y with the molecular weights of test solutes permeating through the asymmet ric EVAL membranes. This is consistent with the behavior of normal commerci al ultrafiltration membranes. For the particulate membranes, the rejection curves show different trends. In most cases, there exist two local minima i n the rejection curves, having the shape of "W". This unusual behavior is f ound to be associated with the dual-pore character of the particulate membr ane. To this context, a parallel composite membrane model is proposed to ex plain this specific rejection in terms of rejection coefficients for the sm all and the large pores. (C) 1999 Elsevier Science Ltd. All rights reserved .