SOLUTE REJECTION OF DEXTRAN BY EVAL MEMBRANES WITH ASYMMETRIC AND PARTICULATE MORPHOLOGIES

EVAL copolymer was precipitated from water and octanol to form, respec tively, asymmetric and particulate membranes in an isothermal immersio n precipitation process. Permeability of these membranes was examined with respect to dextran samples of various sizes. The results indicate that asymmetric membranes reject large dextran molecules and let thro ugh small molecules for the pressure range of 0.25-0.75 kg/cm(2). The particulate membranes, however, exhibit an unusual filtration behaviou r; i.e. there exists a maximum rejection at intermediate dextran molec ular weight. This implies that small molecules tend to be trapped insi de the nano-pores within the EVAL particles whereas large molecules tr avel through the tortuous channels outside the particles during a filt ration operation. (C) 1998 Elsevier Science Ltd. All rights reserved.