Patent GB-311790-A (GB)
Title: Improvements in or relating to the manufacture of cellulose esters
IPC: C08B3/02
Filed: 1927-12-17
Abstract: 311,790. Dreyfus, H. Dec. 17, 1927 . Cellulose carboxylates.-Cellulose acetates and cellulose esters of higher homologues of acetic acid or mixed cellulose esters thereof are prepared by subjecting cellulosic materials to a pretreatment 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 one or more chlorides or other halides of antimony, arsenic, or phosphorus, or mixtures thereof, with or without hydrochloric or other hydrohalide acid or mixtures thereof. The halide is preferably present in proportions of 10-25 per cent but when using halide and acid both are preferably present in from 5-15 per cent on the weight of the cellulose. As initial materials, there may be employed fibres, fabrics, or the like, for example cotton or other celluloses or near conversion products thereof, or alternatively viscose silk or other regenerated cellulosic artificial fibres Wood pulps, bamboo, espacto, or other materials containing encrusting matter from which the lignin, pentosan, resin and like constituents 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 pretreat. ment with organic acids may be carried out in any suitable manner such as with concentrated or dilute acids, for example, with 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 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. 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 cellulosic material, but esters of especially high viscosity can be prepared when the solvent is present in a quantity, for example, equal to 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 as indicated in Specification 263,939 or may be produced in solution, for example by addition of acetaldehyde to produce ethylidene diacztate by reaction with the acetic anhydride. Alternatively the esterification may be conducted in suspension in liquid non-solvents as described in Specification 20977/11, for example in benzene or toluene. or in mixtures thereof with solvents such as acetic acid but in the latter case, the 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 75-85 per cent strength and if desired washed, centrifuged, or dried, after which the pretreated material is introduced into a mixture of acetic anhydride, glacial acetic acid, and antimony pentachloride at atmospheric temperature and stirred constantly until a clear solution of cellulose acetate is obtained; cotton linters pretreated as above are esterified in the presence of antimony pentachloride and hydrochloric acid; cotton linters are pretreated with a mixture of formic acid of 35 per cent strength and glacial acetic acid and after being hydrcestracted and dried are esterified in presence of phosphorous pentachloride, glacial acetic acid, and acetic anhydride. The cellulose esters obtained may be subjected to secondary treatments either in the primary esterification solutions or suspensions preferably without removing any acid present and after destroying any remaining anhydride with water or other agents such as hydroxyl derivatives, oxyacids, for instance lactic acids, alcohols &c. If desired hydrochloric or other hydrohalide acid 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. 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. 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 masses, moulding powders, &c. either in their primary esterification solutions or as primary or secondary esters in solution in suitable solvents, for 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. 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 kerosene, 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, diaeetone 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 Specifications 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 249,173 also is referred to.