GB815792A - Improvements in the manufacture of cellulose esters - Google Patents

Abstract

Organic acid esters of cellulose having a degree of substitution below 2.25 are prepared by hydrolysing a cellulose ester of the same organic acid or acids having a degree of substitution above 2.25 using as hydrolysing catalyst an acid having a degree of ionisation of at least 0.1 measured in normal aqueous solution at 18 DEG C., the catalyst being present in amount of at least 0.5 gram mol. per litre of solution. The method is particularly suitable for the preparation of lowly substituted cellulose esters of fatty acids containing up to 4 carbon atoms. The starting material, i.e. the ester having a degree of substitution above 2.25, prepared, for example, by treating cellulose with an acid anhydride using an acid catalyst, may be precipitated and washed before being redissolved for hydrolysis, but it is preferable to carry out the hydrolysis without any such intermediate precipitation. Sulphuric acid, perchloric acid, nitric acid and hydrochloric acid are suitable hydrolysing catalysts, and the hydrolysis is preferably carried out at 15-50 DEG C. When the hydrolysis has proceeded as far as is desired the catalyst may be neutralized with a suitable compound of an alkali metal, an alkaline earth metal, magnesium, zinc or aluminium, e.g. an alkaline-earth metal acetate or magnesium acetate. The ester may be precipitated in the usual way, i.e. by running into water or dilute acetic acid and stirring, but the solution is preferably extruded in the form of filaments into the liquid precipitant, e.g. water or aqueous acetic acid of concentration below 20 per cent. The spaghetti-like product may then be cut into short lengths and broken down or ground. The precipitated ester may be stabilized by incorporating in it an acid-neutralizing salt, e.g. an alkali or alkaline earth metal bicarbonate, or a buffer mixture of salts such as a mixture of sodium phosphates giving a pH of 6-7.5. The esters obtained are suitable for the production by wet or dry spinning of textile articles having a considerable affinity for substantive dyes. Cellulose acetate of acetyl value below 47.5 per cent obtained as described above, may be spun from solution in aqueous acetone, for example, into water or a dilute solution of acetone preferably maintained at 10-25 DEG C. The filaments obtained may be softened by hot water and stretched by passing through a bath of hot water. They may be saponified with dilute caustic alkali, preferably containing an alkali metal acetate, to give products of still lower acyl value or substantially unsubstituted cellulose. Specifications 782,903 and 790,039 are referred to.