Membranes from poly(vinyl alcohol) for dialyzing soda lyes from viscose rayon processes
A method for the preparation of membranes to dialyze (squeezed-out) soda lyes from viscose rayon processes has been presented. Membranes were prepared from aqueous poly(vinyl alcohol) (PVAL) solutions containing a crosslinking agent (mainly a urea-formaldehyde precondensate), plasticizer (ethylene glycol), and a catalyst. The membranes were either cast from the solution or formed by coating a textile substrate by the so-called „suspended-knife" method. The best conditions for making membrane to dialyze a 18% soda lye containing hemicelluloses were determined experimentally. Effects of the amount of the crosslinking agent (5—20%) on the degree of membrane crystallinity, average pore diameter and pore size distribution were measured. Transport properties of the membranes were also characterized, viz., water permeability (mechanical coefficient of filtration), NaOH permeability and capability of hemicelluloses retention. Results obtained with these PVAL membranes in the commercial process of viscose rayon manufacture are briefly presented.
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