GB871634A - Improvements in or relating to water-resistant films comprising esters of amylose - Google Patents

Abstract

Amylose derivatives which form stable dispersions, from which water-resistant films may be produced, are obtained by reacting amylose with an esterification or etherification reagent to introduce substituent branches to a degree of substitution in the range of 0,02 to 0,15. Esterification may be effected with an organic acid anhydride, mixed anhydride or acid halide, preferably in the presence of an esterification catalyst such as pyridine, triethylamine, or an alkali metal hydroxide. Specified anhydrides are acetic, propionic, butyric and isobutyric. Etherification may be effected by acrylonitrile, dimethyl sulphate, monochloroacetic acid, benzyl chloride, propylene oxide or allyl bromide. The amylose may first be dispersed in water, preferably at superatmospheric pressure, or in dimethyl sulphoxide, concentrated sodium hydroxide solution, ethylamine, methylamine, aminoethanol, mixtures of hot aqueous formamide and dimethyl formamide, hot aqueous formaldehyde solutions, 50% calcium chloride or 50% calcium nitrate in aqueous solution, aqueous phosphoric acid or aqueous formic acid. The amylose derivative may be precipitated, e.g. by pouring into an excess of ethyl alcohol and then drying in the air or over heated drums. The initial amylose may be extracted from starch or may be used as an unseparated component of a starch which contains at least 50% of amylose.