Patent GB-312095-A (GB)
Title: Improvements in or relating to the manufacture of cellulose esters
IPC: C08B3/02
Filed: 1927-12-17
Abstract: 312,095. Dreyfus, H. Dec. 17, 1927. Cellulose carboxylates.-Cellulose acetates and cellulose esters of higher homologues of acetic acid or mixed cellulose esters therof are prepared by subjecting cellulosic materials to a pretreat,- ment with organic acids, particularly lower fatty acids such as formic or acetic acids, and then to esterification by means of fatty acid anhydrides, particularly acetic anhydride, in presence of ferric chloride or ferric bromide or a mixture thereof, the ferric halide being present preferably in proportions of 10-30 per cent on the weight of cellulose. As initial materials, there may be employed fibres, fabrics or the like, for example, cotton or other celulloses or near conversion products thereof or alternatively viscose silk or other regenerated cellulosic artificial fibres. Wood pulps, bamboo, or esparto or other materials containing encrusting matter from which the lignin, pentosan, resin, and like constitiuents have been substantially removed, as in sulphite, soda, sulphate or other chemical pulps may be employed but are preferably subjected to an alkaline purifying treatment followed by pretreatment with organic acids as described in Specification 249,173. The pretreatment with organic acids may be carried out in any suitable manner, such as with concentrated or dilute acids, for example, formic acid, preferably of 80-100 per cent strength, or acetic acid or mixtures thereof, or with the vapours of these acids as described in Specification 263,938. After the treatment with organic acids, the cellulosic materials may be subjected to a stream of air or inert gas or to suction or vacuum to remove the organic acids wholly or partially. In order to avoid degradation of the cellulose molecule, the esterification should be conducted at temperatures not exceeding 50‹ C., and may be conducted at 0‹ C. or even lower. The ferric salt may be added as such or formed in situ and may be incorporated in the cellulosic material prior to esterification. Esterification may be performed 'in presence of a solvent for the cellulose ester, particularly acetic acid, the quantity of the solvent being for example from 4 to 6 times the weight, of the cellulose material, but esters of especially high viscosity can be prepared when the solvent is present in a quantity, for example, equal to from 8 to 20 times or :more the weight of the cellulosic material as described in Specification 207,562. Small quantities e.g. 0.5-10 per cent of more powerful organic solvents such for example as ethylidene diacetate, lactic acid, or its acetyl derivatives may be added to the acetic acid or other solvent as indicated in Specification 263,939 or may be produced in solution, for example by addition of acetaldehyde to produce ethylidene diacetate by reaction with the acetic anhydride. Alternatively, the esterification may be conducted in suspension in liquid non- solvents for example benzene or toluene as described in Specification 20977/11 or in mixtures thereof with solvents such as acetic acid but in the latter case, the non-solvent should be present in sufficient quantity to prevent solution of the cellulose ester. The esterification may further be performed substantially in absence of liquid solvents or non-solvents by employing the vapours of acetic anhydride or other esterifying agent as described in Specification 264,937. In examples, cotton linters are pretreated with formic acid of 75-100 per cent strength or with a mixture of formic acid of 85 per cent strength and glacial acetic acid in the cold and then if desired, washed and centrifuged or dried after which the pretreated material is introduced into a mixture of glacial acetic acid, acetic anhydride, and ferric chloride at atmospheric temperature and stirred constantly until a clean solution of cellulose acetate is obtained. The cellulose esters obtained may be subjected to secondary treatments either in the primary esterification solutions or suspensions, preferably without eliminating the ferric chloride present and after destroying any remaining anhydride with water or other agents, such as hydroxyl derivatives, oxy acids such as lactic acid, alcohols, &c., hydrochloric or other hydrohalide acids may be added to accelerate the reaction. Alternatively, the esters, either precipitated from the primary solutions or those obtained other than in solution, may be dissolved or suspended and then subjected to the secondary treatments. Inorganic or organic acids, acid salts, or other suitable agents may be added, the treatment being stopped when the required solubility has been reached. It is particularly advantageous to conduct the further treatments in the joint presence of hydrochloric acid and ferric chloride or other combined catalysts used according to Specification 309,201. The secondary treatments may be conducted at ordinary temperatures or at temperatures up to 80‹-100‹ C. but in the latter case, the presence of free mineral acid is preferably to be avoided. To obtain acetone solubility, it is in general unnecessary to carry the secondary treatments so far as hitherto and consequently the acidyl content of the acetone-solouble esters may be higher. Cellulose esters soluble in acetone or very low boiling solvents, such as methyl formate, acetaldehyde, formaldehyde, &c. may be prepared by these processes and high boiling solvents, plasticizing agents, or softening agents can readily be incorporated with them or with their solutions in volatile solvents. The esters may be employed for the production of artificial silks, films, celluloid substitutes or other thermo-plastic massess, moulding powders, &c. either in their primary esterfication solutions or as primary or secondary esters in solution in suitable solvents, or example acetone, ethyl alcohol-acetone, methyl alcohol-acetone, or the low boiling point solvents already referred to or in mixtures of such solvents. For wet or dry spinning processes, the esters may be employed in solutions containing 5-30 per cent or more of the ester. Artificial silks &c. prepared from the secondary esters are much more resistant to delustring by boiling or hot aqueous solutions or moist steam and may even resist delustring altogether. Suitable precipitating liquids for use in wet spinning comprise alcohols for example methyl or ethyl alcohols or their homologues, coal tar, petroleum or other hydrocarbons, for instance benzene, toluene, and their homologues, gasoline, or kerosine, and aqueous liquids containing mineral acids, for example sulphuric acid, and acid salts, for example bisulphates, neutral salts for example sodium, potassium, calcium, or magnesium chloride, or substances, which have a latent solvent power for the cellulose esters for example thiocyanates, zinc chloride, acetone, diacetone alcohol, alcohol, acetic acid, or formic acid or other salts as described in Specifications 177,868 and 179,234. Such precipitant liquids may also be incorporated in the spinning solutions prior to extrusion. Apparatus for dry spinning may be of the type described in Specification 165,519, 198,023, 203,092, 300,998 and 304,674. For wet spinning, any suitable apparatus may be used, for example apparatus of the type employed in the spinning of viscose, cuprammonium, or nitrocellulose artificial silks. Specification 309,201 and 312,098 also are referred to.