Patent GB-690700-A (GB)
Title: Improvements relating to the manufacture of cellulose esters
Inventor: GROOMBRIDGE WALTER HENRY
IPC: C08B3/24
Filed: 1949-08-31
Abstract: Organic acid esters of cellulose having less than the theoretical maximum acyl value are produced by forming a solution of a cellulose triester (which may initially be in the fibrous form) in a substantially anhydrous solvent mixture of which one component is an alcohol and which is substantially free from organic carboxylic acids, and ripening the cellulose triester in the solution so obtained until it has the desired acyl value.  In particular cellulose triacetate (i.e. cellulose acetate of acetyl value above about 60 per cent) is ripened in solution in a substantially anhydrous mixture of a chlorinated aliphatic hydrocarbon such as methylene chloride, chloroform, or tetrachlorethane, and a lower aliphatic alcohol, such as methanol, ethanol or isopropanol, e.g. a mixture containing about 8-15 per cent by volume of methanol.  The weight of the solvent mixture may be 5-8 times that of the cellulose triacetate.  The solution should contain an alcoholysis catalyst, preferably a mineral acid, e.g. hydrogen chloride, sulphuric acid or perchloric acid.  The ripening may be carried out at 20-150 DEG  C., particularly 55-75 DEG  C., and the catalyst should be present in amount below 15 per cent and preferably below 5 per cent of the dry weight of the cellulose triester.  The ripening process may be halted by neutralizing the catalyst with a compound of an alkali or alkaline earth metal or of magnesium, e.g. the carbonate or acetate.  The ripened cellulose ester may be isolated from the solution by distilling off the solvent and the ester formed from the alcohol in the ripening, or may be precipitated from the solution by the addition of a non-solvent such as water or alcohol.  A solution of ripened cellulose acetate in acetone may be obtained by adding to the ripening solution more acetone than is required in the final cellulose acetate solution, and distilling off the methylene chloride, methanol, methyl acetate, and excess acetone.  Cellulose triesters of other lower carboxylic acids, e.g. cellulose tripropionate and tributyrate, may be ripened under substantially the same conditions as cellulose triacetate, or may be dissolved for ripening in a mixture of acetone and a small proportion, e.g. up to 10-15 per cent, of methanol, ethanol or other lower aliphatic alcohol, without using a halogenated hydrocarbon.  In an example, a fibrous cellulose triacetate (obtained by an acetylation process of the suspension type) dissolved in 6.5 times its weight of a 9 : 1 (by volume) mixture of methylene chloride and methanol containing 0.5 per cent (on the weight of the cellulose triacetate) of anhydrous hydrogen chloride is maintained at 65 DEG  C., the solution is neutralized with an aqueous solution of sodium acetate in slight excess, and boiling water is rapidly added to precipitate the cellulose acetate and distil off the organic liquids.  In another example an equal volume of acetone is added to a solution prepared and neutralized as above and the mixture is distilled until a clear solution of cellulose acetate in acetone is obtained as a residue. Specification 690,688 is referred to.