Patent GB-316160-A (GB)
Title: The manufacture and treatment of cellulose derivatives
IPC: C08B3/16
Filed: 1928-04-18
Abstract: 316,160. Dreyfus, H. April 18, 1928. Cellulose carboxylates.-Cellulose derivatives of hydroxy-aliphatic acids are prepared by treating cellulose or materials containing cellulose with anhydrides of the hydroxy-aliphatic acids, for example glycollic lactic and hydracrylic anhydrides which may be prepared, for instance, by treating the sodium, potassium or other metallic salts of the acids or mixtures thereof with thionyl chloride. Mixed esters may be prepared by employing another anhydride, for example acetic anhydride, in addition to the hydroxy-aliphatic anhydrides and the hydroxy groups of the hydroxy-aliphatic acid derivatives of cellulose mav be esterified, for instance with acetic anhydride. As initial materials, there may be employed cotton or any other cellulose or near conversion products thereof or bamboo, esparto or wood pulps from which the lignin, pentosan, resin and like constituents have been substantially removed, as for example in sulphite, soda, and sulphate pulps. The cellulosic materials may be pretreated with organic acids, particularly formic or acetic acid, or with hydroxy-aliphatic acids in large or small quantities. Chemical pulps are preferably subjected to an alkaline purifying treatment, as described in Specification 249,173, followed by the treatment with organic acids prior to acylation. The pretreatment with organic acids may be carried out, for example, with concentrated or dilute acids or with the vapours of the acids as described in Specification 263,938. Formic acid, except when employed in small quantities, should be substantially removed before acidylation, but if an acid, such as acetic acid, is used which will serve as a solvent diluent in the subsequent acylation its removal is of course unnecessary. Alternatively, the cellulosic materials may be pretreated with hydrochloric or other hydrohalide acids or mixtures thereof as described in Specification 312,098 or if the metallic halide catalysts referred to below are used in conjunction with hydrochloric or other hydrohalide acid in the acylation, they may be used either alone or with the acid as pretreating agents. The pretreatment with hydrohalide acids may be combined with a pretreatment with organic acids, the two treatments being conducted simultaneously or successively or the pretreatment with organic acids may be combined with a pretreatment with other mineral acids, for example sulphuric acid. The acylation process may be carried out in any convenient manner, for example it may be conducted in presence of a solvent or mixture of solvents for the cellulose derivative produced, such as acetic acid or other lower fatty acids with the exception of formic acid. The solvent or solvent mixture may be present in any desired quantitv such as 4 to 6 times the weight of the cellulosic material, but derivatives of especially high viscosity can be obtained if the solvent is present in an amount greater than 6 times, for example 8 to 20 times or more the weight of the cellulosic material. The acylation may further be conducted in suspension in non-solvsnts or mixtures of solvents with non-solvents, provided that the latter are present in sufficient quantity to prevent solution of the cellulose derivative produced. In this manner fibres, fabrics or the like may be acylated in suspension. As condensing agents in the acylation process, there may be employed, for example, sulphuric acid or organically substituted sulphuric acids such as benzene, sulphonic acid, bisulphates, e.g. sodium bisulphate, phosphoric acid, sulphuryl chloride, zinc chloride, or the like. Metallic halides, for example the chlorides of manganese, copper, nickel, or cobalt, may be used in conjunction with hydrochloric or other hydrohalide acids, and ferric or stannic chlorides may be used with or without hvdrochloric or other hydrohalide acids. In order to avoid degradation of the cellulose molecule, . acylation should be conducted at temperatures preferably below 50‹ C. In one example, cotton linters are pretreated with formic acid, washed, centrifuged, and dried. The pretreated cellulose is then acylated in a mixture of acetic acid, glycollic anhydride, and sulphuric acid. Slight heating may be applied to initiate the reaction, but the temperature should not be allowed to rise much above 50‹ C. throughout the reaction. When solution is complete the cellulose glycollate may be separated by the addition of a non-solvent, for example water. The cellulose glycollate is soluble in chloroform diluted with alcohol and in aqueous acetone. In another example, the process is the same as in the previous example except that sulphuryl chloride is used as catalyst and the temperature is maintained at 60-70‹ C. during acylation. In a further example, cotton linters are impregnated with a mixture of ferric chloride and hydrochloric acid. The pretreated material is then introduced into a mixture of acetic acid and glycollic anhydride and the temperature is maintained at 40-50‹ C. until solution is complete, whereupon water is added to destroy the excess of the anhydride. Mixed esters may be produced by employing another anhydride, for example acetic anhydride, in addition to the hydroxyaliphatic acid anhydrides or by treating the cellulosic material first with a hydroxy-aliphatic acid anhydride and then with a fatty acid anhydride. The cellulose derivative of acetyl glycollic acid may. for example, be obtained by treating the cellulose glycollate with acetic anhydride, whilst if the anhydride is in sufficient excess a mixed cellulose acetate-acetylglycollate is obtained. In an example, cotton linters pretreated with formic acid as above are acidylated in a mixture of acetic acid, glycollic anhydride, and sulphuric acid for about 5 hours at 20-30‹ C. and then a mixture of acetic anhydride and sulphuric acid is added. The reaction is continued as in the manufacture of cellulose acetate and the resulting cellulose acetate-acetylglycollate is very similar in solubility and other properties to cellulose acetate. The cellulose derivatives prepared according to the above processes may be subjected to secondary treatments for the purpose of changing their solubilities, for example in the presence of inorganic or organic acids or acid salts, the treatment being arrested when the required solubility has been reached. In an example, the primary acylation solution prepared as in the first example is treated with water at about 35‹ C. The cellulose glycollate becomes progressively soluble in organic solvents, for example acetone containing more and more water, and the treatment is stopped when the required solubility is obtained. While the secondary treatments may be conducted at ordinary temperatures, the reaction may be quickened by heating even up to 80-100‹ C., but in such cases the presence of free mineral acid should preferably be avoided. The Provisional Specification refers also the use of zinc chloride in conjunction with a hydrohalide acid, for example hydrochloric acid, as a catalyst in the acylation process and to the fact that esterification of the hydroxyaliphatic acid derivatives of cellulose may be effected by using either the primary or secondary hydroxy derivatives and that the products may be subjected to secondary treatments even if the hydroxy derivatives have been previously subjected to secondary treatments.