Ultrafiltration membranes and RO reverse osmosis are all driven by working pressure, with the same membrane raw materials and similar membrane preparation methods, similar systems and functions, and similar applications. Therefore, it is difficult to establish a definitive boundary that separates the two. Sorirakin believes that ultrafiltration membranes can be treated as ro reverse osmosis membranes with a large average diameter.

The physical structure of ultrafiltration membranes is irreversible and can be divided into two layers. One layer is a thin active layer with a diameter of 5.0-20.0nm, which plays a key role in separating aqueous solutions. The other layer is a porous structure layer with a thickness of about 75-125um and a diameter of about 0.4um, which has high water absorption and only serves as a support point.

The separation characteristics of ultrafiltration membranes refer to their permeability, diffusion coefficient, and retention rate, which are related to the pore structure of the membrane. The testing standards for the pore structure of the membrane are different from commonly used instruments and equipment, and the results obtained by individuals vary greatly. Therefore, it is necessary to clearly state the testing standards when presenting data information. Naturally, if it is better, standardized testing standards will be available for comparison. The measurement of throughput and aqueous solution should include two values: pure water throughput and aqueous solution throughput. The kinetic energy of pure water should be calculated and experimentally determined. The interception ability of the membrane is indicated by the cutting molecular weight Mw (Mwcut off), but the definition and measurement standards for cutting molecular weight are not yet strict enough in terms of overall goals. Generally, the retention rate is measured using the concentration of substances with similar molecular weight differences, under the standard of not easily causing concentration polarization. The molecular weight of substances with a conductivity retention rate Robs of 90% to 95% is included in the molecular weight of the cut.

Splitting molecular weight to indicate the characteristics of ultrafiltration membranes is a satisfactory approach for homologues of molecules such as hemoglobin. However, in reality, the retention rate is not only related to molecular weight, but also to factors such as the appearance of molecules, their plasticity, and the interaction between molecules and membranes. When the molecular weight is constant, the retention rate of spherical molecules by the membrane is much higher than that of linear molecules. Therefore, the qualitative analysis of the concentration characteristics of intercepted substances in membranes using molecular weight Mw is not very accurate. The critical retention rate refers to the retention rate of a membrane towards a national standard substance with a relatively small molecular weight, which is the cutting molecular weight of the membrane.

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