Patent GB-312098-A (GB)
Title: Improvements in or relating to the production of cellulose esters and cellulose ester products therefrom
IPC: C08B3/00
Filed: 1928-01-14
Abstract: 312,098. Dreyfus, H. Jan. 14, 1928. Cellulose carboxylates; preparatory treatment of cellulose.-Cellulosic materials are rendered more reactive for subsequent acidylation by a treatment with hydrochloric, hydrobromic, or hydriodic acids, or with mixtures thereof or with mixtures of such hydrohalide acids with organic acids, such as acetic acid. Alternatively, the treatment may be effected with the ferric, stannic, manganese, cobalt, nickel, and copper salts of these acids, particularly ferric chloride and stannic chloride, either alone or in conjunction with the hydrohalide pretreating agents and/or in conjunction with organic acids, particularly acetic acid. Such combined pretreatments are preferably carried out simultaneously but the simultaneous presence of formic acid and the hydrohalide acids and/or the halide salts should be avoided. Alternatively, the pretreating agents may be used successively. The hydrohalide acid and/or halide salt may be dissolved or diluted with a liquid, for example water, or the hydrohalide acid may be used as a gas with or without vapours of organic acids. The quantity of hydrohalide acid must not substantially exceed 50 per cent of the weight of the cellulose and should not be substantially less than 2 per cent thereof. The preferred quantity is 5-10 per cent of the weight of cellulose, which corresponds to about 15-30 per cent of commercial acid in the case of hydrochloric acid. An initial materials, there may be employed mercerized or non-mercerized cotton or other cellulosic materials, which may be used dry or may contain the usual amount of moisture, for example 4-8 per cent. Wood pulps, or bamboo, esparto, or other materials containing encrusting matter and from which the lignin, pentosan, resin and like constituents have been substantially removed, as for example in sulphite, soda, or sulphate pulps, may be employed but such chemical pulps are preferably subjected to an alkaline purifying treatment as described in Specification 249,173 followed by the present pretreatment process in place of the treatment with aliphatic acid described in Specification 249,173. The pretreating agents may be distributed evenly over the cellulosic material, for instance by spraying, and are then left to stand for 1-24 hours or more. The pretreatment time varies with the nature of the cellulosic materials, the concentration of the pretreatment agents and the temperature of pretreatment, which is preferably carried out at ordinary temperatures but may be accelerated by the use of slightly higher temperatures. The use of temperatures which would result in disintegration of the cellulose must be avoided. The subsequent acetylation or esterification mav be carried out, for example, as described in Specifications 14101/15, 6463/15, 100,009, 101,555, and 207,562. Hydrohalide acid if used in the pretreatment and if not required in smaller quantity in the esterification process, may be wholly or partially neutralized, for example by the addition of sodium or other acetate. Formic acid when employed prior to a pretreatment with hydrohalide acid and/or halide should be removed but acetic acid may be left in the cellulosic material. The best results are obtained when the subsequent esterification is carried out as described in Specifications 309,201, 312,095 and 312,096. The hydrohalide acid and/ or halide need not then be removed. If both hydrohalide acid and halide are required during esterification, both may be used in the pretreatment or one may be used and the other added to the pretreated cellulose separately or together with the esterifying agent. The halide may, if desired, be formed in situ in the esterifying mixture, for example ferric oxide or acetate may be added to form the required halide by reaction with the whole or part of the hydrohalide acid already present in the cellulose. The acetylation or other esterification may be conducted in presence of a solvent or non-solvent for the cellulose ester formed or by employing a vaporous esterifying agent. In examples, cotton linters are sprayed with concentrated hydrochloric acid or a mixure of concentrated hydrochloric acid and glacial acetic acid and after standing at ordinary temperature are acetylated with a mixture of glacial acetic acid, acetic anhydride, and ferric chloride; cotton linters are introduced into a mixture of glacial acetic acid and concentrated hydrochloric acid and after standing are acetylated with a mixture of stannic chloride and acetic anhydride; cotton linters are introduced into a mixture of glacial acetic acid and ferric chloride and after standing are acetylated by the addition of acetic anhydride; cotton linters are sprayed with a mixture of concentrated hydrochloric acid. ferric chloride or stannic chloride, and glacial acetic acid and after standing acetylation is effected by introducing the pretreated mass into acetic anhydride and glacial acetic acid. The cellulose esters obtained may be subjected to secondary treatments for the purpose of changing their solubilities either in the primary esterification solutions or suspensions, preferably without neutralizing the hydrochloric or other hydrohalide acid, if present, and preferably without eliminating any halide catalyst and after destroying any remaining anhydride by the addition of water or other anhydride destroying agents, such as hydroxyl derivatives, oxy acids, for example lactic acid, and alcohols. If no acid catalyst be used in the esterification, hydrochloric or other hydrohalide acid may, if desired, be added to accelerate the reaction. Alternatively, the esters either precipitated from the primary esterification solutions or those obtained other than in solution may be dissolved or suspended and then subjected to the secondary treatments. The secondary treatments may be carried out with or without the addition of inorganic or organic acids, acid salts, or other suitable agents, the treatment being stopped when the desired solubility is reached. The, secondary treatments may be conducted at ordinary temperatures or at higher temperatures up to 80-100‹ C. or even higher but in such cases the presence of free mineral acids is preferably avoided. A continuous series of processes is therefore possible, for example a cellulose material may be pretreated with hydrochloric acid in aqueous solution, a quantity of ferric chloride added together with acetic anhydride and acetic acid and finally after acetylation, a secondary process may be carried out directly in presence of hydrochloric acid and ferric chloride. 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 thermoplastic 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 alcoholacetone, 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 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, 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 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 nitro-cellulose artificial silks. Specifications 207,562 and 263,938 also are referred to.