Patent GB-713750-A (GB)
Title: Ungelatinized cold water soluble starch ethers
IPC: C08B31/08
Filed: 1951-03-13
Abstract: The invention comprises as a new product a cold water soluble starch ether characterized by the starch ether granules being swollen but ungelatinized.  The starch ether may be obtained by reacting starch with an inorganic base and one or more etherification reagents, at least one of the etherification reagents being one which introduces an hydrophilic group, the base being in concentration and quantity in a degree and amount to swell the starch granules but not to gelatinize the same, and the etherification reagent being in an amount to render the swelled but ungelatinized starch granules cold-water soluble.  The starch used as starting material may be any ungelatinized starch, e.g. that derived from corn, potato, wheat, sago, tapioca, sweet potato, rice, or waxy maize.  The starch may be in its original raw form or it may have undergone previous chemical modification such as partial esterification or partial etherification, oxidation, or partial hydrolysis by acids, provided that the starch, starch derivative, or conversion product, still retains the substantially unbroken, ungelatinized granule structure of the original raw starch.  Specified etherification reagents are the halogenated fatty acids and their salts or esters, e.g. monochloracetic acid, sodium monochlor-acetate, beta-chloropropionic acid; alkyl halides or sulphates, e.g. ethyl chloride, dimethyl sulphate, diethyl sulphate; epoxides or substituted epoxides, e.g. propylene oxide, ethylene oxide or epoxyalkyl sulphonates such as sodium 2,3-epoxypropane sulphonate; halohydrins or substituted halohydrins, e.g. ethylene chlorohydrin, propylene chlorohydrin, sodium 2-hydroxy - 3 - chloropropane sulphonate; haloalkyl sulphonates, e.g. sodium 2-chloro-(or bromo-) ethane-sulphonate.  A small proportion of a hydrophobic or polyfunctional etherification reagent may be present in the etherification reagent used.  Specified inorganic bases are sodium and potassium hydroxides and sodium carbonate. The base may be used in the form of an aqueous solution and it is preferred to add the base to the starch first and then add the etherification reagent, the reaction conditions and the concentration and proportions of reactants are such that the starch is not in liquid suspension so as to avoid gelatinization of the starch.  In general the base is used in the form of a concentrated aqueous solution.  It is preferred to use a strong base such as sodium hydroxide which may be used in aqueous solution of 5 per cent to 80 per cent concentration and if desired the base may be added in molten condition preferably by spraying on to the starch and in some cases a portion of the base may be added in solid form.  The optimum amount of base solution is that which will swell the starch granules but still leaves them in a relatively friable, free flowing and non-caking state.  The quantity of etherification reagent will vary with the type used and with the nature of the starch used and its degree of preconversion as well as with other variables such as time and temperature of reaction.  When the starch ether products are examined with plane polarized light substantially all of the granules should show the polarization crosses typical of ungelatinized starch. The reaction time will depend on the starch and reagents employed and on the proportion of the reagents and the temperature.  In examples (1) corn starch is sprayed with a 40 per cent aqueous sodium hydroxide solution, the temperature being maintained at 23 DEG  C., and a 75 per cent aqueous solution of monochloracetic acid is then added while maintaining the temperature at a maximum of 34 DEG  C. During the next four hours the temperature is allowed to rise to 48 DEG  C. and nitrogen is circulated during this period to reduce the moisture content.  The reaction is then allowed to continue for about an hour at 60-65 DEG  C., a further hour at 70-75 DEG  C. and finally for 2 1/2 hours at 80-85 DEG  C.  The product is granular and ungelatinized and dissolves readily in cold water; (2) as in (1) except that the starch used is a mixture of corn starch and an ungelatinized etherified starch derivative made by suspending corn starch in water, adding sodium hydroxide, and treating with epichlorhydrin at room temperature; (3) as in (1) except that after the four-hour period the reaction mixture is allowed to stand in a closed container at room temperature for about a week; (4) as in (3) except that 30 per cent aqueous sodium hydroxide is used; (5) as in (4) using 49.4 per cent sodium hydroxide solution; (6) waxy maize starch is etherified with sodium monochloracetate using 76 per cent sodium hydroxide solution kept molten by heating; (7) as in (1) except that acid converted waxy maize starch, 49.7 per cent sodium hydroxide solution and 78 per cent monochloracetic acid solution are used; (8) the product of (7) is treated with benzyl chloride in the presence of 49.7 per cent sodium hydroxide solution; (9) predried corn starch is etherified with propylene oxide in an autoclave at 100-115 DEG  C. using a saturated sodium carbonate solution; (10) as in (9) except that corn starch of normal moisture content and 25 per cent sodium hydroxide solution are used; (11) corn starch is etherified with ethyl chloride at 95-100 DEG  C. in the presence of a 40.7 per cent sodium hydroxide solution; (12) corn starch is etherified with ethylene chlorohydrin using a 40.5 per cent sodium hydroxide and then adding sodium hydroxide flakes before completion of the reaction; (13) predried corn starch is etherified with a 37.9 per cent sodium 2-bromoethane sulphonate solution using a 50 per cent sodium hydroxide solution and sodium hydroxide flakes; (14) low-converted white corn dextrine is etherified with a 75 per cent aqueous monochloracetic acid solution using a 25 per cent sodium hydroxide solution.