GB777058A - Improvements in or relating to starch ethers - Google Patents

Abstract

Starch ethers are prepared by reacting starch with an etherifying agent in the presence of an etherifying catalyst and under conditions such that the starch is not gelatinized nor rendered water-soluble, washing the etherification catalyst from the etherified starch with water and filtering the substantially catalyst-free material, forming an aqueous slurry of the filtered starch product, said slurry containing between 45 and 95 per cent, preferably 60-75 per cent, of water, and gelatinizing and drying the starch product, for example by passing over heated rolls, by spray drying or by forming the slurry into a paste which is spray dried. Any type of raw starch such as corn, wheat, grain sorghum, tapioca or rice starches, may be used as the starting material. Modified starches which have not been gelatinized, e.g. thin-boiling starches, may also be used. Suitable etherifying agents are epoxyalkanes and substituted epoxyalkanes, e.g. ethylene oxide, propylene oxide, epichlorhydrin, styrene oxide, butadiene monoxide, glycidol and alkyl, aryl, aralkyl, or halogen derivatives; or a salt of chloracetic acid, e.g. sodium chloracetate, may be used. When employing polyfunctional etherifying agents, the amount of etherifying agent should not exceed 0.1 to 0.5 per cent of the weight of starch. Suitable catalysts are alkali, e.g. NaOH, salts, alkaline earth oxides or hydroxides, e.g. Ca(OH)2, and organic bases, e.g. tetraethanolammonium hydroxide, triethanolamine, tri-(hydroxy-ethyl) hydroxyisopropyl ammonium hydroxide, triethylamine, trimethylamine, or trimethylbenzylammonium hydroxide, or mixtures thereof. When using an alkaline catalyst preferably 0.025 to 0.075 mol. of catalyst per anhydroglucose unit of starch is employed when aqueous starch is etherified, or 0.04 to 0.10 mol. per anhydroglucose unit of starch when etherifying dry starch. Gelatinization is avoided during the etherification by maintaining the temperature sufficiently low or by adding salts to increase the gelatinization temperature. In a preferred embodiment of the process, an aqueous starch slurry is reacted with an epoxyalkane, styrene oxide or glycidyl isopropyl ether and an amount of calcium hydroxide sufficient to give an alkalinity to the starch of 0.05 to 0.15 at a temperature not exceeding 50 DEG C., neutralizing the calcium hydroxide, washing and filtering the starch ether, and reslurrying, gelatinizing and drying as described above. The etherification is suitably terminated after 80-90 per cent of the etherifying agent has been consumed. The term "alkalinity" means the number of mols. of hydrochloric acid required to adjust the pH of an alkaline slurry containing 162 g. of starch to 5.5. The roll dried starch ether products may be used as additives in oil well drilling fluids. In such cases, borax may be added to the starch ether before passing over heated rolls. The products may also be used to give body to edible products, e.g. puddings, without cooking, and as a laundry size. In examples: (1) a slurry of starch is treated with ethylene oxide in the presence of lime at 80 DEG to 130 DEG F. for 8 hours, the pH was adjusted to 6 with hydrochloric acid, the slurry washed with water and filtered and the starch ether reslurried to form a mixture containing 65 per cent water and passed over a heated rotary drum and pressed out in a thin layer to gelatinize and dry the product; (2) starch is etherified with propylene oxide by the same method, borax being added to the slurry before roll drying; (3) dry corn starch is mixed with isopropyl alcohol and tetraethanolammonium hydroxide and then treated with propylene oxide at 50 DEG C. for 5 hours; the product is washed in water, filtered, reslurried and then roll-dried; (4) an aqueous slurry of 80-fluidity grain sorghum starch containing sodium hydroxide is treated with ethylene oxide at 35 DEG F. for 24 hours, HCl is added to pH 6.5 and the product is washed, filtered, reslurried and roll-dried; corn starch is also reacted with sodium hydroxide and sodium chloracetate in aqueous solution and worked up as before. Specifications 714,701 and 741,742 are referred to.ALSO:A starch hydroxyethyl ether, prepared by reacting starch with ethylene oxide in the presence of aqueous sodium hydroxide, washing, filtering and reslurrying the product in water and p gelatinizing and drying over heated rollers, is mixed in cold water to form a relatively thin sol for use as a laundry size. Specifications 714,701 and 741,742 [Group IV(b)] are referred to.ALSO:A starch hydroxypropyl ether, prepared by reacting corn starch with propylene oxide in isopropanol and in the presence of tetraethanol ammonium hydroxide, washing, filtering, reslurrying in water and then gelatinzing and drying over heater rollers, disperses in water to give a smooth and viscous paste suited for giving body to edible products without cooking. In an example, the starch ether is blended with cane sugar, dextrose, cocoa and flavouring constituents, and the powder mixture is stirred with cold milk to form, without heating, a smooth-textured pudding. Specifications 714,701 and 741,742 [Group IV(b)] are referred to.