GB263939A - Improvements in or relating to the manufacture of cellulose derivatives - Google Patents

Abstract

263,939. Dreyfus, H. Oct. 6, 1925. Patent abandoned on opposition. Cellulose acetates and other carboxylates.-For the manufacture of cellulose esters, particularly cellulose acetates, from cellulose pretreated with organic carboxylic acids according to the processes described in Specifications 207,562 and 263,938, while employing acetic acid as the solvent in the acetylation &c. mixture in proportion not greater than six times the weight of the cellulose taken, the proportion of the condensing agent, such as sulphuric acid, is reduced to less than 5 per cent of the weight of the cellulose, for example, to 0.5-3 per cent, without deleterious effect on the acetylation process. The pretreatment of the materials may comprise boiling with concentrated acetic acid, or treatment with formic acid in the cold, or passage of acetic or formic acid vapour through the materials. The starting material may be mercerized or unmercerized cotton or wood pulp, preferably such as has been treated according to the process of Specification 249,173. By the addition of non-solvent diluents such as benzene to the reaction mixture, acetylation &c. may be effected in suspension. When, however, the acetylation is carried out in solution, as is usual, small quantities of substances having a high solvent power for the cellulose acetate &c. may be added, in order to prevent precipitation of the acetate and consequent stiffening of the reaction mixture; suitable solvents are ethvlidene diacetate and lactic acid or its acetyl derivatives, the first mentioned being introduced either as such or by adding acetaldehyde to the reaction mixture, and being finally recovered as acetaldehyde and acetic acid. The cellulose acetates or other esters obtained may be subjected to any suitable secondary treatment for the purpose of varying their solubility characteristics, for instance according to the processes described in Specification 20977/11. 20852/12 and 207,562, the products to be treated being either first isolated or the reaction being allowed to proceed in the original esterification solutions or mixtures with or without the addition of water or other agents, such as lactic acid, capable of destroying any remaining anhydride, and after partly or completely neutralizing the condensing agent. Specifications 6463/15, 14101/15, 100,009, and 101,555 also are referred to.