Procedure for Casting Flat-Sheet Membranes

In general, the procedure for casting anisotropic UF membranes can be thought of as a six-step process  

SCHEMATIC DIAGRAM OF A LOEB-SOURIRAJAN MEMBRANE CASTING MACHINE 

It is advisable to use Dl water in the gel tank. The author has successfully cast many large batches of UF membranes using tap water in the quench bath. However, this often results in membrane product which is discolored (iron oxide) and variable with the seasons as the tap water quality changes. Dl water with an 18Mfi resistivity is the best standard. However, it must be borne in mind that high resistivity water will result in faster leach rates of solvent from the gelling casting solution which may affect the pore size of the final membrane. 

When producing membranes for use in the pharmaceutical industry, the use of depyrogenated water is required. Otherwise, pyrogens will be incorporated in the cast membrane and some will leach out in the filtrate with use. Depyrogeniza-tion may be accomplished by filtering water from the ion exchange columns with a 10,000 MWCO UF membrane. 

Water in the gel bath must be replaced periodically or better yet, continuously to minimize the buildup of solvents or other contaminants in the quench bath. If bacteria slime or turbid water is noted, the tank should be drained and cleaned. 

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