GB813541A - A method of preparing glyoxalated compounds of starch - Google Patents

Abstract

A water paint comprises chalk whitening moistened with water to which is added the product of heating, while stirring, a dispersion of starch in an aqueous solution of glyoxal first at a temperature less than 75 DEG C. until a gel is formed and secondly at a higher temperature, less than 100 DEG C., until the said gel is liquefied. (For details see Group V.) A detailed example is given.ALSO:A glyoxalated-starch compound is formed by heating a mixture of a starchy material (e.g. native starch, starch-flour, partly hydrolysed starch, dextrin, etherified or esterified starch) with a compound having the formula R.CO.CHO, where R is hydrogen or an alkyl radical, and water, to a temperature preferably less than 75 DEG C., until a gel is formed. An acid catalyst, such as oxalic or sulphuric acid, may be added to the mixture before the heating. On heating to a higher temperature less than 100 DEG C., preferably between 95 DEG and 100 DEG C., and if necessary with the addition of water, liquefaction of the starch-glyoxal gel takes place, the original molecular aggregate breaking down into shorter molecules by fission at the glycosidic linkages between the glucose unit. The liquefied gel may be used as an adhesive which on cooling sets to a consistent jelly. To stop the reaction at this stage, any acid present should be neutralized by addition of alkali. When then heating is carried beyond the stage of simple liquefaction of the gel in order to concentrate the adhesive, further reticulation of the molecules takes place via the hydroxyl radicals introduced by the glyoxal with the formation of a different molecular aggregate which is practically insoluble in water. In examples: (1) maize starch, glyoxal, water and sodium pentachlorophenate are treated, with stirring, at 65 DEG to 70 DEG C. until a starch-glyoxal gel is formed; the heating is then continued in the presence of oxalic acid, the temperature being maintained at 95 DEG to 100 DEG C. until the gel is liquefied; (2) potato starch, glyoxal, water and sulphuric acid as catalyst are heated, with stirring, to 65 DEG C. until a starch-glyoxal gel forms, after which the heating is continued while stirring, the temperature being raised and maintained at 95 DEG to 100 DEG C. for about 2 hours until the gel is liquefied. The adhesives obtained may be used for cold gluing of paper, for varnishing of paper and cardboard, as a constituent of coatings for laid paper, for textile fillers, as a colour constituent for washable wall-papers (see Group VIII), and as a constituent of water paints (see Group III).ALSO:An adhesive jelly giving by mere drying after use a film substantially insoluble in water, is prepared by heating a mixture of a starchy material (e.g. native starch, starch-flour, partly hydrolysed starch, dextrin, etherified or esterified starch) with a compound having the formula R.CO.CHO, where R is a hydrogen atom or an alkyl radical, and water, to a temperature preferably less than 75 DEG C., until the gel is formed and resuming heating at a higher temperature less than 100 DEG C., and preferably between 95 and 100 DEG C., until the said gel is liquified. An acid catalyst such as oxalic acid or sulphuric acid may be added to the mixture before heating, and to stop the reaction at the stage of liquefaction of the gel an alkali should be added to neutralise any acid present. The liquefied gel may be used as an adhesive in either hot or cold state; when it is allowed to cool the adhesive sets in the form of a consistant jelly. When the heating is carried beyond the stage of simple liquefaction of the gel, a fairly liquid adhesive can be obtained which cannot be jellified by cooling to room temperature. In examples, (1) maize starch, glyoxal, water and sodium pentachlorophenate are heated, with stirring, at 65 to 70 DEG C. until a starch-glyoxal gel is formed; the heating is then continued in the presence of oxalic acid, the temperature being maintained at 95 to 100 DEG C. until the gel is liquefied; (2) potato starch, glyoxal water and sulphuric acid as catalyst are heated, with stirring, to 65 DEG C. until a starch-glyoxal gel forms, after which the heating is continued while stirring, the temperature being raised and maintained at 95 to 100 DEG C for about 2 hours until the gel is liquefied. The adhesives so obtained may be used for cold glueing of paper, for varnishing of paper and cardboard, as a constituent of coatings for laid paper, for textile fillers, as a colour constituent for washable wallpapers, (see Group VIII), and as a constituent of water paints. (See Group III).