GB568932A - Improvements in or relating to the manufacture of cellulose esters - Google Patents

Abstract

Acetone-soluble cellulose esters of lower fatty acids, e.g acetate or propionate are partially saponified by heating a solution of the ester in hot aqueous ethyl alcohol of concentration 50-85 per cent by volume, in the presence of a small proportion of an inorganic acid until all or nearly all the ester has become soluble in cold aqueous 60-75 per cent ethyl alcohol. The inorganic acid employed may be hydrochloric or sulphuric. The acid may be added to the solution in its concentrated or diluted form and in the case of a volatile acid, in the vapour phase. When the desired degree of hydrolysis is obtained, the ester is precipitated, e.g. by pouring into water, or the acid is neutralized by the addition of, for example, sodium acetate, and the ester recovered by precipitation or by distilling off the alcohol. The process produces esters which are soluble in cold aqueous ethyl alcohol of concentration between 60 and 75 per cent, which may be cast into films or employed in coating compositions and to which may be added other solvents, e.g. diacetone alcohol, plasticizers, fillers and colouring matter. In the examples: (1) cellulose acetate is boiled under reflux with 60 per cent ethyl alcohol containing hydrochloric acid and the acetate is precipitated by pouring the solution into a large amount of cold water; (2) cellulose acetate is boiled under reflux with 62 per cent ethyl alcohol containing sulphuric acid. Sodium acetate is added to neutralize the acid and the alcohol is distilled off. In the Provisional Specification it is stated that the ester may be subjected to treatment in any suitable organic solvent, e.g. acetone or a hot benzene-ethyl alcohol mixture with or without acetone.