Patent GB-325224-A (GB)
Title: Improvements in the manufacture and treatment of cellulose esters
IPC: C08B3/22
Filed: 1928-08-13
Abstract: 325,224. Dreyfus, H. Aug. 13, 1928. Cellulose carboxylates; preparatory treatment of cellulose-Ripening of cellulose carboxylates is effected in an organic medium in which the cellulose ester is initially insoluble and in which the ripening agents, which are defined as hydroxy bodies, for example water, alcohols such as ethyl alcohol, glycerine, or oxy-acids, such as lactic ncid, are sufficiently soluble to enable the ripening to be effected. Suitable organic media comprise ether, methyl acetate, ethyl acetate, other ethers, or actone. The ripening treatment may be carried out in presence of inorganic or organic acids or acid salts or salts having an acid reaction, for example ferric chloride, or salts of aromatic amines, for instance aniline, and also in presence of the catalysts employed in the esterification process. Although the ripening may be, carried out in suspension throughout, the organic diluent employed may be such that as the result of the ripening treatment the cellulose ester becomes progressively more soluble. Mixtures of ether or like liquids with benzene, toluene, or the like may be used. The ripening process preferably follows an esterification process in suspension in ether or other organic medium, the acetic anhydride or other esterifying agent being preliminarily destroyed by water or other ripening agent, but the primary esters may be prepared by any desired process, for example they may be prepared in solution and the primary product then precipitated and suspended in ether or other organic liquid or the esterification may be carried out in suspension in benzene, toluene or other non-solvent diluent and the diluent then wholly or partly replaced by the ether or other organic diluent having some solvent power for water or other ripening agent. The capacity of the ether or other organic liquid for taking up the water or other ripening agent may be increased by employing it in admixture with a cellulose ester solvent such' as acetic acid. As initial materials for the esterificaton, cotton or other celluloses, or near conversion products thereof, may be employed. Wood pulps, or bamboo, esparto or other cellulosic materials containing encrusting matters and from which the lignin, pentosan and like constituents have been substantially removed, as for example in sulphite pulp. soda pulp or sulphate pulp, may be employed but are preferably subjected prior to esterification to a purifying treatment with alkali as described in Specification 249,173. Fibres, yarns, fabrics, or the like, for example of cotton or other natural cellulosic materials or .of viscose or other regenerated cellulosic artificial fibres may be treated, the ripening being then primarily designed for the purpose of eliminating acids or catalysts employed in the esterification. Preferably the cellulosic materials are subjected to a pretreatment prior to esterification. They may be pretreated with large or small quantities of organic acids in concentrated or dilute form or as described in Specification 263,938 with the vapours of such acids. If desired sulphuric acid or other catalysts may be incorporated in the acetic or other organic acid. Alternatively the cellulosic materials may be treated with dilute sulphuric acid or mav be pretreated with hydrochloric acid or other hydrohalide acid or with a chloride or other halide or mixtures thereof as described in Specification 312,098. Any two or more of these pretreatment processes may be conducted simultaneously or successively. Further materials may be pretreated with the pretreating agent mixed with the medium to be employed in the subsequent esterification, for example with acetic acid and ether. Any desired catalysts, for example sulphuric acid or organically substituted sulphuric acids, such as benzene sulphonic acid, or bistilphates, for example sodium bisulphates, phosphoric acid, or sulphuryl chloride, or the catalysts described in Specifications 308,322, 308,323, 309,201, 311,790, 312,095, and 312,096 may be employed. Esterification or ripening in suspension may be effected, for example at the boiling point of the ether or other non-solvent, under a reflux condenser and the non-solvent may be employed in presence of a solvent or solvents, such as acetic acid. In examples, cotton linters are soaked in a mixture of acetic acid and sulphuric acid, the whole is then added to a mixture of ether and acetic anhydride, and when the desired degree of acetylation has been reached water is added and ripening continued until the desired solubility s attained, whereupon the suspending liquor is run off and the acetate washed first with ether and then with hot water and finally in the usual manner; cotton linters are pretreated with formic acid in liquid or vapour form the formic acid is substantially removed and the cellulose is then esterified after adding to a mixture of ether, acetic anhydride, and sulphuric acid, ripening being effected as in the first example; cellulose is soaked is glacial acetic acid, the whole is then added to a mixture of ether, acetic anhydride, and sulphuric acid, and ripening is effected as above. Specification 325,231 also is referred to. The Provisional Specification refers also to the ripening process being carried out in presence of aromatic amines, such as aniline, and to the fact that the cellulose ester may first become more soluble in the suspending liquid and then progressively less soluble, so that during the ripening the ester dissolves and then precipitates out.