In British Pat. No. 2,026,934 A of the same Applicant, a process has been described for the preparation of regenerated cellulose formed bodies from solutions of cellulose derivatives in organic solvents, which process comprises precipitating the cellulose derivative from its solution in a coagulating bath, the main component of which is an organic liquid which does not dissolve and does not regenerate the cellulose, and subsequently drawing and regenerating the coagulated body in successive baths. The cellulose derivatives in question are generally designated as "methylol derivatives" and their chemical nature is discussed in the aforesaid specification, in which numerous cellulose non-solvents, non-regenerating agents are also listed, among them the alcohols and preferably methanol. The solvents of the cellulose derivative solution are dimethylsulphoxide (DMSO), dimethylformamide (DMF), dimethylacetamide (DMAC) and N-methylpyrrolidone.
If a good coagulation from the solvents described above is to be obtained, the formaldehyde content of the solution, and therefore the CH.sub.2 O/cellulose ratio, should not exceed certain limits, e.g., if the solvent is DMSO, the limits should be, as expressed by an MS ratio (which is the molar ratio of the CH.sub.2 O units that can be titrated by the sodium sulphite method to the anhydroglucosidic units of the cellulose), close to 1, and consequently low CH.sub.2 O% contents and cellulose contents which do not reach 6%, in the solutions. (All percentages in this description are by weight).
USPTO Backgrounds
USPTO Backgrounds