The novel lab-scale hollow fiber membrane module was fabricated to determine the apparent sieving coefficient ( \({SC}_{obs}\) ) of commercial hemodiafiltration membranes, MFX-SW eco (polyethersulfone, Sample A) and NVF-P (polysulfone, Sample B), using the aqueous solution of dextran with a broader molecular weight distribution. All the molecular weight cut-off curves plotted as \({SC}_{obs}\) versus filtration flow rate (QF) exhibited smooth profiles without intersecting each other, showing distinct variations depending on QF across a wide range of molecular weights. Field emission scanning electron microscopy (FE-SEM) observations revealed that the equivalent pore diameters of samples A and B were nearly identical at 23.0 ± 15.5 nm and 23.3 ± 15.5 nm, respectively. Although the surface porosity of sample A (14.5 ± 3.9%) was higher than that of sample B (10.2 ± 3.2%), the difference was not statistically significant. These numerical data were in excellent agreement with the qualitative morphological findings obtained from the FE-SEM images. Furthermore, it is suggested that the subtle structural differences between the two membranes are also reflected in the relationship between the real sieving coefficients ( \({SC}_{real}\) ) calculated by using \({SC}_{obs}\) and the equivalent pore diameters. Since the lab-scale modules are fabricated relatively easily by hand, this methodology is extremely valuable to rigorously define membrane performance.
