GB464843A - Process for the manufacture of highly acetylated cellulose - Google Patents

Abstract

Cellulose acetate in fibrous form is obtained by causing cellulose material to react with a mixture of acetic anhydride, acetic acid, a catalyst and an anti-solvent, a quantity of acetylating liquid greater than 15 times the weight of cellulose being used, and the proportion of anti-solvent being only slightly greater than that just necessary to prevent solution of the cellulose acetate and being always less than 25 per cent of the weight of the acetylating mixture. The use of substances which by themselves boil at temperatures below 0 DEG C. is avoided. If desired, the cellulose may be pretreated with acetic acid at a temperature below 80 DEG C., preferably below 30 DEG C. The proportion of acetylating liquid may be greater than 40 times the weight of cellulose, and the proportion of anti-solvent may be in some cases reduced to less than 10 per cent of the acetylating bath. Ether or benzene may be used as anti-solvent. The acetic anhydride may be greatly in excess of three times and even greater than 10 times the weight of cellulose, and it may be increased so as to take the place of most of the acetic acid. The process may be carried out in rotating apparatus if desired with stirring devices and without cooling devices. Fixed apparatus with stirrers may be used. The acetylating liquor may circulate at high speed through the swollen cellulosic mass. The cellulosic material may be cotton wool, linters, long fibre cotton, woven cotton cloth, or dyed cotton cloth. Cellulose tri-acetates insoluble in most solvents may be obtained. According to the time of reaction, products giving very viscous solutions in methylene chloride-alcohol, or products giving less viscous solutions may be obtained. The acetylating liquid after use may be employed for a subsequent acetylation after eliminating surplus acetic acid and adding the necessary quantity of acetic anhydride, and catalyst. In an example, cotton linters are pretreated with acetic acid and then mixed with a cooled mixture of acetic anhydride, acetic acid, benzene, and sulphuric acid. In other examples, ether is used instead of benzene, and perchloric acid instead of sulphuric acid. The acetylating liquid may be cooled below 0 DEG C. before coming into contact with the cellulose. Specification 231,837, [Class 2 (ii)], is referred to.