The deformation of dextran molecules. Causes and consequences in ultrafiltration

The transfer of dextran T70 solutions through a skinned polysulfone hollow fiber membrane was studied with and without applied pressure. The molecular weight distributions of dextran in the feed and in the permeate were obtained by high pressure liquid chromatography. Two different phenomena appear to play important roles with regard to solute transfer. One is related to the shear stress imposed by the flow at the pore entrances, i.e. to permeate flux, and the other is related to the influence of solute concentration on the expansion of the macromolecular chains. These phenomena explain the observed variations with operating conditions of the overall rejection coefficient.