Internal and surface structure characterization of cellulose triacetate hollow-fiber dialysis membranes

A cellulose triacetate (CTA) dialysis membrane is generally regarded as a homogeneous membrane. The objective of the present study was to characterize the internal structure of CTA dialysis membranes. We used FB-150E, FB-150F, and FB-150UH CTA hollow-fiber membrane dialyzers. The pore-size distribution and porosity of the CTA membrane surfaces were calculated from surface image data obtained by using atomic force microscopy (AFM). The internal porosity of the CTA membranes was measured by weight analysis. Further, the pore diameter of the CTA membranes was calculated from data on pure-water permeability and diffusive permeability using a pore diffusion model. The pore diameters on the inner surface of the CTA membranes were much greater than those on the outer surface. The surface porosity determined using AFM was much lesser than the internal porosity determined using weight analysis. The pore diameters on the inner and outer surfaces of the CTA membranes determined using AFM were much lesser than pore diameter calculated on the basis of the permeability data. We conclude that the CTA dialysis membrane, which is generally regarded as a homogeneous membrane, is actually a multilayer membrane. The CTA dialysis membrane has tight layers at the inner and outer surfaces, and has a loose layer inside the membrane.