Liquid purification or separation – Filter – Material
Patent
1995-04-07
1999-03-09
Fortuna, Ana
Liquid purification or separation
Filter
Material
21050023, 21050027, 264 41, 264 49, 264178R, B01D 3900
Patent
active
058795545
DESCRIPTION:
BRIEF SUMMARY
FIELD OF THE INVENTION
The invention relates to a synthetic membrane consisting of a mixture of polysulfone and sulfonated polysulfone and no more than 20 wt. % of other polymers. The invention likewise relates to a method for manufacturing this synthetic membrane.
BACKGROUND
Synthetic membranes and separating processes based on them have been known for a long time. In addition to classical applications, for example, seawater desalination using reverse osmosis or ultrafiltration of process water from electrophoretic dip painting to recover the paint, membrane processes are becoming increasingly important in the areas of food technology, medicine, and pharmacy. In the latter cases, membrane separating processes have the great advantage that the materials to be separated are not subjected to thermal stress or even damaged.
Often, an important prerequisite for the usability of membranes in these areas is the sterilizability of the membrane. For safety and ecological reasons at least, steam sterilization is preferred over chemical sterilization, for example, using ethylene oxide, or sterilization by radiation, especially by gamma radiation.
Steam sterilization normally involves a half-hour treatment of the membrane or membrane system with hot steam at temperatures in excess of 110.degree. C. Thus, the criterion of steam sterilizability severely limits the number of potential membrane materials. Thus, for example, membranes made of polyacrylonitrile are basically not steam-sterilizable because exceeding the glass temperature of the polymer results in an irreversible damage to the material and/or the membrane. In addition, hydrolysis-sensitive polymers, for example, certain polycarbonates and polyamides, cannot withstand hot steam sterilization unscathed.
Steam-sterilizable membranes made of polyether imides, polysulfones, or polyvinylidene fluoride are known, for example. A major disadvantage of these membranes consists in the hydrophobic nature of the membrane material, which prevents spontaneous wetting with aqueous media. Consequently, the membrane must be prevented from drying completely or the membrane must be treated with a hydrophobic agent, glycerin, for example, before drying.
Hydrophilic membranes are characterized by the fact that they are wettable with water. A measure of wettability is the wetting angle that a water drop forms with the surface of the membrane. In hydrophilic materials, this edge angle is always greater than 90.degree.. Phenomenologically, the wetting of a dialysis membrane can also be detected by the fact that a drop of water placed on the surface of the membrane penetrates the membrane after a short time.
Another serious disadvantage of hydrophobic materials consists in the fact that they often possess a powerful nonspecific adsorption capacity. Therefore, when hydrophobic membranes are used, frequently a rapid, closely adhering coating of the membrane surface with preferably higher-molecular-weight solution components takes place. This phenomenon, known as fouling, leads to a rapid deterioration of the membrane permeability. Subsequent treatment of the membrane with a hydrophilizing medium cannot prevent fouling in the long term.
Suggestions for hydrophilic membranes have already been proposed that do not suffer from these disadvantages. Thus, DE-OS 3,149,976 proposes using a polymer mixture for making a hydrophilic membrane that contains at least 15 wt. % polyvinylpyrrolidone in addition to polysulfone or polyamide. For hydrophilization of polyimide and polyether sulfone membranes, for example, EP-A-0,228,072 claims the use of polyethylene glycol in amounts from 44 to 70 wt. %, based on the polymer solution.
Hydrophilization of membranes by using large quantities of water-soluble polymers however has the disadvantage that the hydrophilic nature of the membrane constantly decreases when they are used in aqueous media, since the water-soluble polymer is washed out. This can create a situation such that the membrane material recovers its original hydrophobic nature and the nega
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Loffelmann Walter
Passlack Jurgen
Schmitt Harald
Schmitt Michael
Sluma Heinz-Dieter
Akzo Nobel N.V.
Fortuna Ana
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