GB675793A - Stabilized starch derivatives - Google Patents

Abstract

Starch ethers and esters of poly-beta-hydroxy aliphatic acids are obtained by reacting starches with lactones of the acids. Alkaline reaction conditions give esters and neutral or acid conditions yield ethers (c.f. Group IV(b)). The term starch includes its conversion products or derivatives which contain free hydroxyl groups. Many lactones are specified, representative being beta propio-, isobutyro- and valero-lactone.ALSO:Starch reacted with an inner ester of a beta hydroxy aliphatic acid yields esters under alkaline conditions and ethers under neutral or acid conditions. Starch or its conversion products or derivatives which contain free hydroxyl groups may be used. Inner esters specified are beta-propio-, -butyro-, -isobutyro-, -valero- and -iso-valero-lactone. Room or higher temperatures may be used. The products form aqueous dispersions of substantially the same viscosity as those obtained from the untreated starch but retain their clarity and viscosity for longer. Desirably moisture is present during reaction, e.g. a minimum of approximately 10 per cent, based on dry weight of starch. Quantities of inner ester mentioned are 0.1 and 300 per cent of the weight of dry starch, higher proportions leading to a product which absorbs and swells in alcohols, e.g. glycerine and glycols. The lactone may react with the substituent of the starch to yield an ether or ester of a polyacid. The lactone may be added to an aqueous dispersion of the starch. Preferably the ratio of starch/water is not in excess of 5/1. Inorganic and organic alkalies are specified, preferably in amounts of 0.1-3 per cent of the starch. Large amounts of lactone, e.g. 10 per cent, are added at intervals as is the alkali so as to maintain a pH of about 10. The lactone may also be blended, e.g. by spraying, with an ordinary air-dry starch which may contain the alkali. In examples: (1) an ungelatinized thin-boiling corn starch, (2) tapioca British gum, (3) and (5) corn starch, and (4) thin-boiling potato starch are treated in aqueous caustic soda suspension with beta-propiolactone; (6) corn starch is made alkaline by treatment with sodium hydroxide, dried to a moisture content of 10-15 per cent, and treated by spraying with beta-propiolactone; (7) wheat starch suspended in aqueous caustic potash is treated with beta-butyro-lactone; (8) corn starch in aqueous suspension is treated with beta-propiolactone; and (9) corn starch is treated in hydrochloric acid suspension, pH 3.0, with beta-propiolactone. The products may be marketed as mixtures of the reactants, the reaction then taking place on addition to water.