Patent GB-713330-A (GB)
Title: Improvements in the manufacture and use of cellulose esters
Inventor: BATES HAROLD
IPC: D01F2/28
Filed: 1951-03-28
Abstract: Cellulose triesters of aliphatic acids containing 2-4 carbon atoms in the molecule, which have been made by a process of the suspension type, are ripened by forming a solution of the ester in a mixture of a lower aliphatic acid and a minor proportion of water or of an alcohol (especially a lower aliphatic alcohol, which is miscible with the acid in the proportion in which it is present, the mixture being substantially free from inorganic acids, and ripening the ester in the solution at a temperature above 100 DEG C.  The triesters may be cellulose tripropionate, cellulose tributyrate and particularly cellulose triacetate, and mixed esters such as cellulose acetate-propionates and acetate-butyrates.  Cellulose triacetate, for example, may be dissolved in hot aqueous acetic acid containing about 2-15 per cent. by weight of water, and ripened by maintaining the solution at a temperature above 110 DEG C., e.g. up to about 190 DEG -200 DEG C., particularly if the process is continuous.  The concentration of the triacetate may be about 15-30 and especially 17-26 per cent. Preferably the aqueous acetic acid contains above 3 per cent. and especially 4-12 per cent. by weight of water, and the solution is heated to a temperature between 115 DEG  or 120 DEG C. and 140 DEG  or 145 DEG C., preferably about 130-135 DEG C.  After ripening, the cellulose acetate may be precipitated by the addition of water or of an alcohol miscible with the aqueous acetic acid, but the ripened solution is preferably directly converted into shaped articles such as filaments and films by extruding or casting the solution (preferably containing about 20-30 and particularly 23-26 per cent. of the cellulose acetate) into a liquid coagulating agent. This may be a liquid acyclic monohydric alcohol having 2 or more carbon atoms in the molecule, an acyclic di- or poly-hydric alcohol, a carboxylic ester particularly a high-boiling ester, a mixture of an ester with water, a chlorinated hydrocarbon, or a mixture of chlorinated hydrocarbons, which are non-solvents for cellulose acetates, but are miscible with the acetic acid of the spinning solution.  Examples of coagulating liquids are ethanol, isopropanol, amyl alcohol, ethylene glycol, 1:3-butanediol and glycerol, preferably initially anhydrous or having a water content below 3 and especially below 1 per cent.  Mixtures of a glycol or glycerol with a monohydric alcohol containing 2-6 carbon atoms in the molecule may be used.  Other examples are aqueous ethylene glycol diacetate and diethylene glycol diacetate, especially 30-35 per cent. aqueous diethylene glycol diacetate, and mixtures of methylene chloride and carbon tetrachloride, preferably containing 50-65 per cent. by weight of the latter.  The filaments are preferably stretched to 5-12 times their unstretched length when drawn from the spinning jet, and when fully set may be washed free from coagulating liquid by water-washing or evaporation. Filaments may be obtained direct from the ripened solution by dry spinning methods.  In an example fibrous cellulose triacetate prepared by a suspension method and washed free from catalyst is mixed with 4 times its weight of 90 per cent. aqueous acetic acid, the mixture is heated to 134 DEG C., and the resulting solution is maintained at this temperature for 2 hours.  The solution of ripened cellulose acetate is filtered and extruded at 20 DEG C. through a spinning jet into a bath of a mixture of equal volumes of isopropanol and 1:3-butane-diol.  During their passage through the bath the filaments are stretched tenfold and then washed with water and dried in warm air.