GB565812A - Improvements in the production of cellulose derivatives - Google Patents

Abstract

Cellulose is pretreated with a mixture of lower fatty acids, one of which is formic acid, containing a small proportion of a mineral acid catalyst, and the pretreated material is esterified by means of a fatty acid esterifying agent which is added in at least two stages. Cellulose acetate may be obtained by pretreating cellulosic material with a mixture containing formic acid, acetic acid, and sulphuric acid, and then after pretreatment, acetylating the cellulosic material in two stages with acetic anhydride. The pretreatment increases the reactivity of the cellulosic material, and the resulting cellulose acetate yields solutions and products of increased clarity. Propionic, or butyric acid may be used instead of acetic acid in the pretreatment. The formic acid may be used in an amount of 1-20 parts per 100 parts by weight of cellulose; the amount of sulphuric acid may be 0.5-2 parts; and the amount of glacial acetic acid may be 20-200 parts. The pretreatment mixture may be anhydrous or may contain a small proportion of water. The cellulose used may be derived from wood, cotton, bamboo, reeds, jute, esparto, straws, grasses, barks, or hulls of nuts. The esterification may be carried out in a plurality of stages by the progressive addition of anhydride to the pretreated cellulose material. A partial esterification may be effected by adding a portion of the anhydride to the activated cellulose material in presence of the sulphuric acid used in the pretreatment. The remainder of the anhydride and of the catalyst is added subsequently so as to continue the esterification. Perchloric acid or sulphoacetic acid may be used as catalyst in the esterification treatments. Esterification may be carried out so that the cellulose ester is obtained in solution or so that it is obtained in suspension. Toluene, benzene, or other non-solvent diluents may be present. The first stage of esterification may be carried to the point where the cellulose material has an acetyl value of 17-35 per cent, calculated as acetic acid. The esterification may subsequently be carried to the triester stage and the product may be ripened to the desired degree of solubility. Artificial yarns of high tenacity may be obtained from solutions of the cellulose acetate product.