GB616304A - Cellulose ethers and the process for producing the same - Google Patents

Abstract

Cellulosic material is subjected in the presence of alkali to the action of an etherifying agent so as to form a hydrophilic cellulose ether and the reaction mixture is treated with an acid which neutralizes the alkali and removes free water by forming a salt hydrate which is stable at temperatures up to 35 DEG C. The major portion of the remaining water in the product may be removed by drying at a temperature below the decomposition temperature of the hydrate or by adding to the mixture an anhydrous salt similar to the hydrate produced by the neutralization. The amount of free water is thus at all times kept below the amount which causes gelling, which is usually about 25 per cent by weight of the cellulose, and the product is obtained in the form of dry free-flowing granules. The hydrophilic cellulose ether may be water-soluble or alkali-soluble. The cellulosic starting material may be wood-pulp, cotton linters, or a cellulosic conversion product such as regenerated cellulose or cellulose hydrate. The alkali used may be caustic soda or potash. The cellulose may be first converted into alkali cellulose which is then pressed to remove excess alkali solution and then treated with etherifying agent while still wet with the alkali. After draining off the alkali, the alkali cellulose may be pressed to 2.5 to 3.0 times the weight of the air-dry cellulose. The alkali-cellulose is then shredded and it may be aged. The etherifying agent may be dimethyl sulphate, methyl sodium sulphate, ethyl chloride, benzyl chloride, ethylene oxide, propylene oxide, a glycide, or a halohydrin. The temperature during etherification should not be allowed to rise above 70 DEG C. A gaseous etherifying agent may be used. After the etherification, the neutralizing acid may be added in solid or liquid form or as a concentrated aqueous solution. The acid used may be ortho-, pyro- or meta-phosphoric acid, glycero-phosphoric acid, arsenic acid, sulphurous acid, aluminium hydrogen sulphate, metantimonic acid or molybdic acid. The mixture of cellulose ether and hydrated salt is removed from the reaction vessel, spread in a thin layer and dried. The major portion of the remaining free water may be driven out while heating to a temperature lower than the decomposition of the hydrate, and the drying may be completed by allowing the temperature to rise gradually to 100 DEG C. If desired, the salt may be removed from the dried product by dissolving the product and dialyzing.