| http://www.w3.org/ns/prov#value | - The partial hydrolysis of the polyphosphoric acid in step H) leads to strengthening of the membrane and to a decrease in the layer thickness and formation of a membrane having a thickness between 15 and 3000 ??m, preferably between 20 and 2000 ??m, in particular between 20 and 1500 ??m, which is self-supporting.
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