The first step in producing membranes is the preparation of a lacquer (2), which consists of nitrocellulose polymer dissolved in a mixture of solvents and nonsolvents. Nitrocellulose would be insoluble in the nonsolvents if they were included at a sufficiently high concentration. Nevertheless, they are necessary for the formation of a microporous structure and are included at a concentration low enough to ensure the solubility of the nitrocellulose. The mixture must also be chemically stable for the duration of a casting run, which can last several days.
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