GB568047A - Improvements in the production of cellulose esters - Google Patents

Abstract

Organic esters of cellulose are obtained by esterifying cellulose with an organic acid anhydride in the presence of an acid catalyst, e.g. sulphuric and/or phosphoric acid, and a solvent for the ester, and ripening the primary ester with water in solution in at least two stages, the commencement of each of which is marked by an increase in the amount of water and a decrease in the amount of catalyst present in the solution. Further ripening stages may be effected with increased amounts of water. The ripening treatment may be carried out at elevated temperatures. The catalyst content is decreased by neutralizing with a salt or mixture of salts of magnesium, calcium or zinc, e.g. the acetates, or with magnesium, calcium, aluminium, barium, copper, lithium or strontium carbonate, or with zinc oxide or an oxide or hydroxide of aluminium, barium, copper, lithium or strontium. The neutralizing agent may be added to the solution with the water for ripening or in solution in glacial acetic acid or separately, in powder form. Cellulose, which may be subjected to a pretreatment with, for example, acetic and/or formic acid in the presence of sulphuric acid, is employed in the form of cotton, cotton linters, wood-pulp, regenerated cellulose, or cellulose material obtained from grass, straw, or husks. The process is particularly applicable to the manufacture of cellulose acetate, but other esters such as the propionate, butyrate, acetate-propionate and acetate-butyrate may be obtained thereby. The cellulose esters so prepared have a high stability and heat-resistance and have improved moulding properties. They may be employed for the manufacture of filaments, fibres, moulding compositions, &c. Numerous examples indicating various ripening treatments are given.