Process for the manufacture of starch derivatives

Hydrophobic grains of starch esters are made by treating granular starch with a mixture consisting of (1) an organic acid; (2) an organic acid or chloride and (3) an esterification catalyst in the presence of an organic liquid which is inert to the starch ester to be formed, the treatment being carried out at temperatures varying from room temperature to the boiling-point of the inert liquid, e.g. 40-75 DEG C., whereupon the granular starch ester is separated and dried. The starch granules may be derived from e.g. maize, rice, wheat, tapioca, sago, sweet potato or batatas, and is preferably dried to a moisture content of 5-15% by weight. The esterification catalyst may be e.g. sulphuric acid, zinc chloride or perchloric acid. Specified organic acids, with their respective chlorides or anhydrides are acetic, propionic, butyric, and stearic acids. The inert organic liquid may be an aromatic hydrocarbon, e.g. benzene, xylene, or toluene, or an ether, e.g. di-isopropyl ether. The proportion by weight of total liquids to total solids in the reaction mixture is preferably 15: 1. The esterification may be facilitated by allowing the dried starch grains to swell in the organic liquid at room temperature before addition of the reagents. Examples describe the preparation of rice starch acetate, maize starch butyrate, and maize starch stearate. The hydrophobic starch grains are used in the manufacture of photographic materials (see Division G2).