Highly Asymmetric Polysulfone Membranes Made From PSF-DMAc-IBA System

The concept of highly asymmetric membrane was brought forward by Wrasidlo in 1986. He found that by lowering the temperature or by the addition of a non-solvent, phase separation generally occurred spontaneously as evidenced by the appearance of a marked turbidity. The system became a liquid-liquid dispersion whose stability depended markedly on how far the system was within the binodal. By this specific property, various volume ratios of each phase can be got from different molecular weight and its distribution of the polymer, compositions of polymer solutions, and preparing conditions. Specific compositions and volume ratios of each phase can provide specific properties to the membrane, i.e., the morphology, the average pore size and its distribution in the membrane, the strength of break, and the ratio of pore sizes at the inner and outer surface of the hollow fiber membrane (which should be more than 125).The highly asymmetric membrane is an integral membrane that comprises a skin and a highly porous asymmetric support. The pore size in the membrane increases along the direction from the skin to the deep of the sublayer. There is a three-dimensional open network of interconnecting fibrous strand and open interstitial flow channels in the highly asymmetric membrane. So its permeability is much higher than usually ultrafiltration membranes, and the retention property is excellent, while the fluid resistance is smaller. The highly asymmetric membrane thathas large pore sizes is very useful in separation of big particles, especially in the filed of blood cell separation. For example, it can be used to separate big cells from the blood, such as leucocytes, lymphocytes, neutrophilic granulocytes, and so on. This kind of membrane can endure downstream processing, i.e., modification on the membrane and the pore surfaces, or grafting smart groups to improve its hydrophilicity to resist protein fouling from the blood, or getting rid of harmful substances from blood or body fluid.As a membrane material used in blood purification, polysulfone (PSF) has advantages in aspects of biocompatibility, chemostability, and mechanical strength, which make it popular in the field of biomedical materials. Hence, research and development on the PSF highly asymmetric membrane is meaningful and necessary.In this thesis, thermodynamic properties of PSF - N,N-dimethylacetamide (DMAc)-iso-butyl alcohol (IBA) system is studied firstly.Several alcohols are used as nonsolvent in the system. The binodal of PSF -DMAc - alcohols systems is calculated by the improved Reuvers' calculation method. Cloud point curves from experiment verify the calculation results. Both the calculation and the experiment show that different nonsolvents have different precipitation abilities on PSF-DMAc solution. The sequence of the precipitation ability of nonsolvents is water > glycerol > 1,2-propylene glycol (PG) > ethanol > iso-propanol (IPA) > iso-butyl alcohol (IBA) > iso-amyl alcohol (IAA). In their thermodynamic phase diagrams, miscible area increases by the same turn.The effect of interaction parameter g;>on the binodal in the thermodynamic phase diagram is discussed. The effect of solvent-nonsolvent interaction parameter g12 on phase diagram is obvious. The value of g,2 increases at following sequence-- water < glycerol < 1,2-propylene glycol (PG) < ethanol < iso-propanol (IPA)