GB539804A - Improvements in or relating to cellulose derivatives - Google Patents

Abstract

539,804. Cellulose esters. BRITISH CELANESE, Ltd. March 21, 1940, No. 5302. Convention date, March 25, 1939. [Class 2 (ii)] Cellulose esters of organic acids are ripened in solution in the presence of magnesium sulphate, sulphuric acid and a quantity of water not exceeding 20 per cent of the weight of the original cellulose, and arresting the ripening while the acyl value of the ester is still high. The operation preferably takes place while the esters are still in the primary solution in which they are formed. The magnesium sulphate is formed in the solution by adding a magnesium compound such as magnesium oxide or salts of magnesium and a weak acid ; this is added to the primary solution so that free sulphuric acid remains in the solution to the extent of from 4 per cent to 8 per cent of the cellulose used as the starting material. The amount of water present is from 6 per cent to 20 per cent of the weight of the cellulose. In the preparation of acetone soluble cellulose acetate, magnesium oxide, or carbonate, or acetate is added to the primary solution which consists of cellulose acetate dissolved in acetic acid with residual acetic anhydride and sulphuric acid ; the requisite quantity of water is also added. The magnesium oxide or salt is added as a dry powder, or a salt may be suspended in glacial acetic acid and added with stirring; the stirring may be continued for about an hour. To shorten the time for ripening the temperature may be raised to 35‹ C.