Evaluation of the structure of asymmetric hollow-fiber dialysis membranes by dye adsorption

Abstract

To develop high performance dialysis membranes, the asymmetric structure should be positively accepted and the relationship between asymmetric structure and diffusive permeability should be further clarified. A little information on the asymmetric structure can be obtained from SEM observation. The objective of the present study is to propose a new method for evaluating asymmetric hollow-fiber dialysis membranes by dye adsorption. Adsorption experiments were carried out using mini-modules composed of test membranes (AM-SD-M, PS-UW, PEPA, PAN-DX, PAN-CX2) of which the inside was packed with paraffin to make solutes diffuse only from the outside inward, or of which the outside was packed with paraffin to make solutes diffuse only from the inside outward. The amount of solutes (cytochrome C, Evans blue, Congo red, ethidium bromide) transferred into the membranes was plotted as a function of time. In membranes of asymmetric structure the shape of the transfer rate curves differed with the direction of transfer, and a difference in the rate of solute transfer was produced which is due to the asymmetric structure of the membrane. Further, depending on the solute size and on the membrane, the directional difference in the transfer rate curves appeared either in the middle portion or the initial portion of the curves. It is concluded that the adsorption technique can be used to evaluate the asymmetric structure and diffusive permeability.