A new method to determine the skin thickness of asymmetric UF-membranes using colloidal gold particles

In this paper a new method is presented for the determination of the skin thickness of asymmetric ultrafiltration membranes. The method is based on the use of well-defined, uniformly sized colloidal gold particles, permeated from the sublayer side of the membrane, combined with electron microscopic analysis of the membrane afterward. Using this method poly(2,6-dimethyl-1,4-phenylene oxide) (PPO) and polysulfone (PSf) membranes were investigated. PPO membranes appeared to have a well-defined skin layer with a thickness of about 0.2 μm and a pore size distinctly different from that in the macroporous layer underneath. In the case of PSf such a distinct skin layer cannot be defined. The size of the pores in these membranes gradually increases from skin to sublayer

Characterization of hemodialysis membranes by inverse size exclusion chromatography

Inverse size exclusion chromatography (i-SEC) was used to characterize three different cellulosic hollow fiber hemodialysis membranes, i.e. low-flux cuprophan and hemophan and high-flux RC-HP400A. With the i-SEC technique the pore size distribution and porosity of a membrane can be determined and adsorption phenomena can be studied. The membranes showed clear differences in pore size and porosity, the high-flux RC-HP400A membrane has a larger pore size as well as a higher porosity. For all the membranes it was found that the elution curves were best described by a homoporous pore volume distribution. It appeared that the bound or non-freezing water in the membranes was at least partly accessible to solutes. The test molecules creatinine and vitamin B 12 both adsorbed to the cellulosic membranes. The adsorption behavior of creatinine was strongly dependent on the NaCl concentration present. The observations could be explained by assuming that cuprophan and RC-HP400A are negatively charged whereas hemophan is positively charged due to the modification with N,N-diethylaminoethyl ether. The net charge of the hemophan is smaller

Characterization of hollow fiber hemodialysis membranes: pore size distribution and performance

The effect of two commonly used sterilization methods for artificial kidneys on the morphology and performance of hollow fiber Hemophan® hemodialysis membranes was studied. A relatively new membrane characterization method, thermoporometry, was used to determine the pore size distributions and porosities of the differently treated membrane samples. The samples used for this study were not treated with a concentrated glycerol solution before sterilization. Hemophan was found to have a pore size distribution with pore radii between 1.5 and 12 nm, the volume porosity was 20%. The sample sterilized with ethylene oxide (EtO) had a volume porosity of 18% which was due to a decrease of the pore volume of the smallest pores. The applied dry steam sterilization treatment resulted in a drastic collapse of the large pores while smaller pores were formed. The calculated porosity was only 10%. The `tortuous capillary pore model¿ was used to predict the performance of the artificial kidneys from the pore size distribution in the membrane material. In vitro dialysis experiments with creatinine and vitamin B12 were carried out to compare the calculated and measured clearance rates. Also the ultrafiltration capacity of the devices was determined. It was found that a reasonable estimation of the ultrafiltration capacity could be made. The calculated clearance rates were systematically underestimated, although the relative dependence of the clearance rates on the applied sterilization methods was approximated reasonably