CA1051882A - Method for preparing oxidized hydroxyalkyl starch - Google Patents

Abstract

METHOD FOR PREPARING OXIDIZED HYDROXYALKYL STARCH

Abstract of the Disclosure Oxidized hydroxyalkyl starch is prepared by the sequential steps of:
(a) reacting granular starch with a 1, 2-alkylene epoxide containing 2 to 4 carbon atoms, inclusively, to obtain a hydroxyalkyl D of S of at least 0.02, and (b) oxidizing the hydroxyalkyl starch to introduce an amount of carboxylic groups onto said starch, the amount of carboxylic groups, basis percent by weight dry starch solids, being no greater than about 1.2 minus the product of 7 times the hydroxyalkyl D of S.

Description

lOS188~
BACKGROUND OF THE INVENTION

This invention relates to a method for preparing oxidized hydroxyalkyl starch.
It is known in the starch industry to react starch with alkylene epoxides to form the corresponding hydroxyalkyl ethers of starch. Such hydroxyalkyl ethers of starch are produced by the alkali-catalyzed reaction of aqueous suspensions of granular starch with the epoxides at temperatures below the gelatiniza-tion temperature of the starch granules. This reaction is dis-closed in U.S. 2,516,633 to Kesler et aZ. While hydroxyalkyl starches have better viscosity stability, lower tendency to retrograde and high adhesiveness, the use of dried films prepared from such starches has been limited in paper coatings due to their poor clarity and water solubility. Thus, their use in paper coatings has been limited.
Oxidized starches are commonly made by reaction of anaqueous suspension of granular starch with a sodium or calcium hypochlorite solution. The oxidized starches have higher flui-dity, increased adhesiveness, lower retrogradation rate and some-what better film clarity than untreated or common starch.
Another method of preparing oxidized starches is to reactstarch with a peroxidic compound, e.g., an alkaline peroxide.
While oxidized starches are suitable for surface sizing of paper, they tend to retrograde excessively and their films lack sufficient clarity for use in coating colors.

BRIEF DESCRIPTION OF THE INVENTION
In view of the shortcomings of the starches produced by either oxidation or hydroxyalkylation alone, it has surprisingly been discovered that a combination of both processes yields a

- 2 -starch product having certain improved properties or characteris-tics. Accordingly, the present invention is directed to a method for preparing a gelatinizable oxidized hydroxyalkyl starch by the sequential steps: (a) reacting granular starch in an aqueous me-dium with a 1,2-alkylene epoxide containing 2 to 4 carbon atoms, inclusively, under non-gelatinizing conditions at a pH of above about 10 to obtain a granular starch having a hydroxyalkyl D of S
of from about 0.02 to about 0.18, and tb) oxidizing the hydroxy-alkyl starch under conditions to introduce an amount of carboxy-lic groups onto said starch, the amount of carboxylic groups,percent by weight dry starch basis, being no greater than about 1.2 minus the product of 7 times the hydroxyalkyl D of S.

DETAILED DESCRIPTION OF THE INVENTION
Reactants A wide variety of starches may be utilized in the inven-tion so long as they are granular in character. Thus, the term "starch" includes both root and cereal starches, e.g., corn, potato, tapioca, wheat, waxy sorghum, waxy maize, grain sorghum, rice, whether unmodified or acid modified. However, it will nor-mally be preferred to use unmodified granular corn starches be-cause of economics.
Suitable hydroxyalkylating reagents include 1,2-alkylene epoxides containing 2 to 4 carbon atoms, inclusively, such as ethylene oxide, propylene oxide and butylene oxide. It is pre-ferred to use ethylene oxide because of its higher reaction rate.
Materials suitable as oxidizing agents include alkaline hypochlorites such as alkali metal and alkaline earth metal hypo-chlorites. The preferred oxidizing agents are the monavalent alkali metal salts, e.g., sodium or potassium hypochlorite.

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Process Variables The hydroxyalkylation reaction must be carried out in highly alkaline slurry, i.e., at a pH of above about 10, for rea-sonable reaction efficiencies. However, the pH must not be high enough to substantially damage the starch granules. To facili-tate the use of higher pH's and temperatures, it is preferred to include in the reaction mixture a gelatinization inhibitor in order to maintain the starch reaction product in granular form.
Saturated solutions of neutral alkali metal and alkali earth metal salts such as NaCl, Na2SO4 and MgSO4 are useful for this purpose in which case alkali concentrations as high as 0.2 mole per anhydroglucose unit may be used without causing substantial damage to the starch granule.
It is necessary that the starch be hydroxyalkylated to a D of S of at least about 0.02 and preferably at least about 0.03.
At exceedingly higher D of S, for example above about 0.18, the starch loses its native granule form. At a D of S of less than 0.02 there is no apparent improvement in the properties of such starches.
The oxidation reaction may be-carried out at the same pH
as the hydroxyalkylation step. However, it is preferred that the pH of the hydroxyalkylated starch be lowered to the range of from about 6 to about 8 by addition of acid prior to the oxidation re-action being carried out. Performing the oxidation reaction in the lower pH range reduces the loss of soluble starch during sub-sequent handling.
Starch concentration is not a critical variable during either the hydroxyalkylation or oxidation step. Practical starch concentrations range from about 25 to about 45 percent by weight.
Reaction temperature in either step of the process of the ~05188Z
invention is not critical, although the temperature must be below that which causes substantial damage to the starch granule. In this regard, it is preferred to perform both reactions below about 38C and most preferably below about 29C.
The sequence of hydroxyalkylation followed by oxidation results in less starch solubles being lost during subsequent handling and the efficiency of utilization of the alkylene oxide is increased as compared to the reactions being performed in the reverse manner.
The oxidized hydroxyalkyl starch may be treated with an acid to reduce further the viscosity imparted by oxidation. High concentrations of carboxyl groups are detrimental when the pro-duct is to be used in coating application since it will tend to cause pigments to redisperse resulting in hlgh pigment losses when repulped broke is recycled to the furnish section of a con-ventional paper-making machine.
Of particular importance in practising the invention is the relationship between the degree of hydroxyalkylation and the extent of oxidation. In general, at high degrees of hydroxyal-kylation, lower amounts of carboxyl groups are necessary. Moreparticularly, it has been found that the amount of carboxyl groups, as measured by the total carboxyl content of starch (per-cent by weight), must not exceed a value corresponding to about 1.2-(7 xD of S) where D of S is the degree of substitution of hydroxyalkyl groups on the starch. When the above-defined value of carboxyl content is surpassed, the resultant product is ex-tremely difficult to filter and becomes virtually incapable of recovery and purification by other than exceptional finishing techniques, such as centrifugation and alcohol precipitation.

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DEFINITIONS, ANALYTICAL AND TEST METHODS

A~kaZine Paste FZuidity: The alkaline paste fluidity was determined by the method described by Fetzer et aZ. in CereaZ
Chemistry, Vol. 36, No. 2 (March 1959), entitled "The Estimation of Starch Paste Fluidities". The funnel used is described on page 114 of this article.
Brabender Cooks: Performed using a VISCO/Amylo/GRAPH in-strument manufactured by C. W. Brabender Instruments Inc., South Hackensack, New Jersey. The instrument was standardized against a reference curve provided by C. W. Brabender Instruments Inc.
from their standard instrument, and employed a sample of the starch used for making the reference curve. For this test, an appropriate amount of dry basis starch sample was weighed out and mixed thoroughly into about 450 ml of distilled water. The pH of the mixture was adjusted to 6.5 using dilute acid or base as re-required. The volume of the mixture was made up to 500 ml. The instrument was activated and run through the following time-temperature cycles: 30 minutes from 50 to 95C; 30 minutes held at 95C; 30 minutes from 95 to 50C; and 30 minutes held at 50C.
The 700 cm-gm load cartridge was used. The chart readings, as Chart Units or C.U., were read and reported directly for the peak, 60-minute and 120-minute viscosities.
Aged Ge~ Strength: At the end of the final hold period, the paste from the Brabender cook was poured into Gaertner gel test jars. Discs fastened to hangers were positioned in the paste.
The surface of the paste was then flooded with light mineral oil.
The paste was stored for 24 hours at 25C to permit formation of a gel. The strength of the aged gel was measured by determining the force required to break the embedded disc from from the gel.
This force was determined with a Gelometer manufactured by Gaertner Scientific Corp., Chicago, Illinois. The procedure for the gel strength measurement was described by E. T. Hjermstad in Cerea~ Chemistry, Vol. 32, No. 3 (May 1955), "~ Recording Gel Tester".
Paste C~arity: An appropriate amount of dry basis starch sample was mixed with distilled water. The pH of the mixture was adjusted to 6.5. The mixture was heated to boiling and held at a gentle rolling boil for a suitable period. Water was added to restore the weight of the paste to the original mixture weight.
The paste was cooled to 25C. A Nessler tube was positioned over a white paper with its flat, closed end centered on a black spot placed on the paper. Paste was added to the tube until the spot could barely be discerned through the paste. The depth of the paste in centimeters in the tube was measured and reported as the paste clarity.
Degree of Substitution (D of S): Determined using the pro-cedure of Harlan J. Lortz, Ana~ytica~ Chemistry, Vol. 28, No. 5, 892 (May 1956), "Determination of Hydroxyalkyl Groups in Low-Substituted Starch Ethers". The values are reported as the num-ber of hydroxyalkyl groups per anhydroglucose unit.
Carbo~y~ic Acid Groups: 5.00 g of dry basis starch samplewere mixed into 50 ml of 0.1 normal hydrochloric acid solution.
The mixture was stirred periodically for 30 minutes at room tem-perature. The sample was recovered on a medium porosity sintered glass filter. The sample was washed with distilled water until the filtrate was found to be free of chloride ions. The sample was then washed from the filter and the mixture made up to 300 ml with distilled water. The mixture was heated to and held at a gentle rolling boil for 5 to 7 minutes. After the addition of 8 to 10 drops of phenolphthalein indicator solution, the paste was ~5188Z
titrated hot with 0.1 normal sodium hydroxide solution to the first permanent (15 seconds) light pink color. The amount of carboxyl groups was calculated from the titer.
FiZm Preparation: Starch samples were cooked in distilled water at concentrations which gave pastes suitable for casting.
The samples were cooked at or near a rolling boil for a minimum of 5 minutes. The resulting pastes were cooled with gentle stir-ring and placed under partial vacuum to eliminate most of the air bubbles. Suitable pastes were cast on freshly cleaned plate glass using a Boston-~radley applicator doctor blade. The gap of the doctor blade was adjusted so that the dried film thickness would be near 1 mil. The films were dried under ambient condi-tions. Sections of the films were then stripped from the plates and sections which appeared free from flaws were selected for testing.
FiZm AnaZysis:
(a) TensiZe strength and fiZm stretch. Sections of films were cut into strips measuring 4 inches by exactly 2 inch after being conditioned for at least 24 hours at 22C and 50 per-cent relative humidity. Film thickness was measured at 3 placeson each strip and the results averaged. Tensile strength and amount of stretch at the instant of rupture were measured with the Instron Universal Testing Instrument, manufactured by Instron Corporation, Canton, Mass. The instrument conditions were as follows: cross-head speed, ~ inch/minute; load cell, CM; and initial jaw separation, 2.000 inches. Eight to ten strips were tested for each product. The average and standard deviation were calculated for thickness, tensile and stretch.
(b) FiZm soZubiZity. Sections of the film not suit-able for tensile strength and film stretch evaluation were ground ~05188Z
in a Wiley mill to pass 40 mesh sieve (U.S. Standard) and testedfor solubility in water. 2.00 g of dry basis film were weighed into a 100-ml centrifuge bottle and made up to 100 g of suspen-sion with distilled water. The bottle was held in a 76.7C water bath for 30 minutes while stirring the mixture sufficiently to keep the film particles suspended. The bottle was taken from the bath, the outside dried, and the original weight restored by the additîon of water. The bottle was centrifuged for 15 minutes at 1800 rpm in an International Centrifuge, Size 2, Model V. 50.00 g of supernatant were weighed into a platinum crucible and evapo-rated to dryness under a heat lamp. The percent soluble starch was calculated from the amount of residue.
Ash: 5 g of dry basis starch sample were weighed into a tared platinum crucible and charred over a low flame. The charred starch-containing crucible was then placed in a muffle furnace and maintained at 533C to constant weight. The weight of the residue in the crucible was determined and is reported as percent Ash, basis dry weight of the sample.
In order to more clearly describe the nature of the pre-sent invention, specific examples will hereinafter be described.
It should be understood, however, that this is done solely by way of example and is intended neither to delineate the scope of the invention nor limit the ambit of the appended claims. In the preceding description and in the following examples, all percent-ages are based upon the dry substance weight of starch present, unless otherwise indicated.

EXAMPLE I

This example illustrates the preparation of oxidized hydroxyethyl starch on a commercial scale.

An aqueous slurry of about 60,000 pounds of common corn starch in granular form (33.8 percent by weight starch) was pumped into a reaction tank in which it was constantly agitated.
Sufficient caustic-salt solution was added to provide a concen-tration of 1.65 percent NaOH and 6.1 percent NaCl. The caustic-salt solution contained 0.55 pounds per gallon of NaOH and 2.13 pounds per gallon of NaCl.
The resultant alkaline slurry was warmed to 42C and ethylene oxide was added to a concentration of 2.67 percent.
After 9 hours, the hydroxyethyl starch slurry was neutralized with HCl to a pH of 7 to 7.5. The slurry was heated to 49C and sufficient sodium hypochlorite was added to provide in the slurry 2 percent available chlorine. After about 5 hours, the slurry was acidified to 12 filtrate acidity (titer of 10 ml of filtrate using 0.10 N NaOH). The slurry was maintained under these condi-tions until the product had an alkaline paste fluidity of 363, and then was neutralized to a pH of 5.5 to 6. The slurry was vacuum filtered, washed and dried to a moisture level of 10 to 13 percent.
EXAMPLE II
This example illustrates alternate methods of preparing oxidized hydroxyethyl starches and compares the properties of such starches with the properties of oxidized and hydroxyethyl starches.
Into a slurry containing 35.5 percent by weight common corn starch at a pH of 6.0 and a temperature of 43C, was incor-porated a sufficient amount of a solution of sodium hypochlorite to provide 3.50 percent available chlorine. After 18 hours of constant stirring at 43C a portion of the slurry was filtered, washed and dried at an air temperature of 71C in a Proctor and Schwartz drier (Product No. 1). The remaining portion of the slurry was made alkaline by adding a solution containing 6.6 g of sodium hydroxide and 25.6 g of sodium chloride per 100 ml of slurry. To this slurry was added 2.67 percent ethylene oxide.
At the end of 22 hours at 43C, the pH of the slurry was adjusted to 6 to 6.5 with HCl, filtered, washed and dried at an air tem-perature of 71C in a Proctor and Schwartz drier (Product No. 2).
Another portion of an identical corn starch slurry was made alkaline in the manner described above. 2.67 percent ethy-lene oxide was added to the slurry and after 18 hours the pH wasadjusted to 6 with HCl. A portion of the slurry was held for 24 hours and filtered, washed and dried at an air temperature of 71C in a Proctor and Schwartz drier (Product No. 3). Into the remaining slurry was incorporated a sodium hypochlorite solution to provide 3.50 percent available chlorine. After 20 hours at 43C the slurry was filtered, washed and dried at an air temper-ature of 71C in a Proctor and Schwartz drier (Product No. 4).
Various properties of the aforeprepared starch products were determined and are set forth in Table 1, below.

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The data in Table 1 show that Products 2 and 3 had mark-edly lower aged gel strength than the Product 1, although all three had nearly the same fluidity.
Product 4 had to be cooked at a much lower starch concen-tration than the others because of its excessive viscosity.
Therefore, the low gel strength for Product 4 was due to low solids as well as to low retrogradation.
The sequence of the steps of oxidation and hydroxyethyl-ation is important. Hydroxyethylation of oxidized starch re-sulted in a lower hydroxyethyl D of S than when such reactions were performed in the reverse order.
Product No. 3 had better paste clarity than the other three products.
EXAMPLE III
This example compares the properties of an oxidized hydroxyethyl starch with certain prior art starch products.
Preparation of Hydroxyethy~ Starch ~Product No. 5). Into a slurry containing 35.5 percent common corn starch at a tempera-ture of 43C was incorporated an amount of a caustic-salt solu-tion sufficient to provide 0.63 g of NaOH and 2.33 g NaCl per 100 ml of slurry. To the slurry was added 2.67 percent ethylene ox-ide. After 16 hours with stirring at a temperature of 43C, HCl was added to adjust the pH to 6. The slurry was heated to 49C
with stirring and a sufficient amount of a solution of sodium hypochlorite was added to provide 3.5 percent available chlorine.
After 5~ hours a small amount of sodium bisulfite was added to reduce the residual hypochlorite, and the pH of the slurry was adjusted to 6 by the addition of HCl. The slurry was filtered, washed and dried at an air temperature of 71C in a Proctor and Schwartz drier.

lOS188Z
Preparation of Acid Modified HydroxyethyZ Star~h ~Product No. 6). Into a slurry containing 35.5 percent common corn starch at a temperature of 43C was incorporated an amount of caustic-salt solution sufficient to provide 0.63 g of NaOH and 2.33 g NaCl per 100 ml of slurry. To the slurry was added 2.67 percent ethylene oxide. After 16 hours with stirring at a temperature of 43C, HCl was added to provide a filtrate acidity of 20.5. After 12 hours, the slurry was filtered, washed and dried at an air temperature of 71C in a Proctor and Schwartz dri~r.
o Preparation of Acid Modified Starch (Produet No. ~).
Into a slurry containing 35.5 percent common corn starch at a temperature of 43C was incorpoxated sufficient HCl to provide a filtrate acidity of 24.5. The slurry was maintained at a temper-ature of 43C for 12 hours with constant stirring and then fil-tered, washed and dried at an air temperature of 71C in a Proc-tor and Schwartz drier.
The above three starch products and Product No. 1 (Exam-ple I) were tested for various characteristics and properties.
The results of this testing are set forth in Table 2.

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From Table 2 it is seen that the alkaline paste fluidi-ties of all four products are substantially equal which indicates that the average molecular weights are also substantially equal.
From this one skilled in the art would presume that the charae-teristics or properties of the starch products would be about the same, all other factors being equal. However, it is apparent from Table 2 that the aged gel strength of the oxidized hydroxy-ethylated produet was significantly lower than the other products and the paste clarity oE this product was also significantly bet-ter than the paste clarity of the other products.
The difference between the 90-minute viscosity and the 120-minute viscosity is an indication of paste stability; the smaller the difference the better the paste stability. The oxi-dized hydroxyethyl starch product had a better paste stability than the other three starch products.

EXAMPLE IV

This example illustrates the limits of the present inven-tion in respect to the maximum allowable amount of carboxylic acid groups.
A series of products was prepared by the following general method:
Into a starch slurry containing 35.5 percent common corn starch was incorporated an amount of caustic-salt solution suffi-cient to provide 0.57 g NaOH per 100 ml of slurry and the amount of salt shown in Table 3. The slurry was heated to 43~C and ethylene oxide added with constant stirring. After 16 hours suf-ficient HCl was added to adjust the pH of the slurry to 6. Into this slurry was incorporated a solution of sodium hypochlorite to provide the required amount of available chlorine. After 24 1051~38Z
hours, the pH of the slurry was adjusted to 6, filtered, washed and dried at an air temperature of 71C in a Proctor and Schwartz drier. The exact conditions of preparing each of the products . are set forth in Table 3. The filtering and washing characteris-tics of each of the products were observed and the observations also entered in Table 3.

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From the above Table it is seen that when the filtration and washing characteristics of the products were poor, the amounts of carboxylic groups were greater than 1.2 minus the product of 7 times the hydroxyethyl groups. Poor filtration characteristics indicate the degree of starch granule damage.
In commercial scale starch granular damage must be minimized if such products are to be recovered and washed by conventional means.
In Table 4, the rhelogical properties of the products are set forth. It is apparent from the Table that the oxidized hydroxyethyl products had a lower aged gel strength than the pro-ducts which were simply hydroxyethylated.

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In l~ble ~ there are set forth the ~oiuDili ~y, clarity and ~ilm propertics of the previou~ly p-s~eFared products.

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In Table 5 there are set forth the solubility, clarity and film properties of the previously prepared products.
From the above Table it is seen that as the amount of carboxylic groups and/or the hydroxyethyl D of S is increased, the water solubility also increases.

EXAMPLE V

This example illustrates a method of preparing an oxi-dized hydroxyethyl starch whereby oxidation with hypochlorite is performed at a highly alkaline pH.
Into a starch slurry containing 35.5 percent common corn starch was added an amount of caustic-salt solution sufficient to obtain 0.60 g NaOH per 100 ml of slurry and 2.21 g NaCl per 100 ml of slurry. The slurry was heated to 43C and 2.67 percent ethylene oxide was added with constant stirring. After 16 hours at a pH of 11.5, the slurry was divided into two portions. One portion of the slurry was adjusted to a pH of 6 by the addition of HCl. Both portions were cooled to 35.5DC and sufficient hypo-chlorite solution added to each slurry to provide 3.5 percent available chlorine. After 32 hours, the pH of the slurry (slurry which was adjusted to pH 6) was 7.5 and the pH of the other slurry was 11.2. The pH of both slurries was then adjusted to 6.0 with HCl, filtered, washed and dried at an air temperature of 71C in a Proctor and Schwartz drier.
Certain of the characteristics or properties of the two starch products were determined and are set forth in Table 6 below.

_ Product numher ............................ 23 24 Oxidation pH, initial ..................... 6.0 11.5 D of S, moles of hydroxyethyl per AGV0.0590.051 Carboxyl content, % wt, dry basis ......... 0.56 0.41 Alkaline paste fluidity ................... 467 474 Brabender cooks (pH 6.5):
starch concentration, % wt ............. 20 20 peak viscosity ......................... 970 285 60-minute viscosity, end 95C hold 30 20 120-minute viscosity, end 50C hold 115 65 Aged gel strength, g-cm ................... 7 7 The above Table shows that when oxidation is performed at high alkaline pH's, the D of S and carboxyl content are lower than when the oxidation is performed at lower pH's.

EXAMPLE VI
This example illustrates the preparation of oxidized hydroxypropyl starch.
Into a starch slurry containing 33.8 percent common corn starch was added an amount of caustic-salt solution sufficient to obtain 0.60 g NaOH and 2.21 g NaCl per 100 ml of slurry. The slurry was heated to 29.5C and 1 percent additional NaCl was added. 8 percent propylene oxide was incorporated into the slurry and after 65 hours with constant stirring, the pH was adjusted to 6.5 by the addition of HCl. The temperature of the slurry was raised to 43C and a sufficient amount of hypochlorite was added slowly to provide 4.92 percent available chlorine. At this point the product had an alkaline paste fluidity of 363.
After 16 hours, the pH of the slurry was adjusted to 5.5 using HCl and the product filtered, washed and dried at an air tempera-ture of 71C in a Proctor and Schwartz drier. It was observed 2~

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that during drying the starch in the center of the filter cake lumps was starting to gelatinize. When this was observed, the drying air temperature was reduced to 60C and drying completed.
The oxidized hydroxypropyl starch product had a D of S of 0.102 and an alkaline paste fluidity of 365. The product, when gelatinized in water, formed a paste having good clarity and lit-tle tendency to retrograde. Dried film of the product was clear, had good strength and was completely soluble in water.
The terms and expressions which have been employed are used as terms of description and not of limitation, and it is not intended in the use of such terms and expressions to exclude any equivalents of the features shown and described or portions thereof, since it is recognized that various modifications are possible within the scope of the invention claimed.

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Claims (8)

THE EMBODIMENTS OF THE INVENTION IN WHICH AN EXCLUSIVE
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:

1. A method for preparing a gelatinizable oxidized hydroxyalkyl starch by the sequential steps of:
(a) reacting granular starch in an aqueous medium with a 1,2-alkylene epoxide containing 2 to 4 carbon atoms, inclusively, under non-gelatinizing conditions at a pH of above about 10 to obtain a granular starch having a hydroxyalkyl D of S of from about 0.02 to about 0.18, and (b) oxidizing the hydroxyalkyl starch under conditions to intro-duce an amount of carboxylic groups onto said starch, the amount of carboxylic groups, percent by weight dry starch basis, being no greater than about 1.2 minus the product of 7 times the hydroxyalkyl D of S.

2. A method for preparing a gelatinizable oxidized hydroxyalkyl starch as defined in Claim 1, including the step of adjusting the pH of the hydroxyalkyl starch to a range of from about 6 to about 8, and wherein the hydroxyalkyl starch is oxidized at a pH in said range.

3. A method for preparing a gelatinizable oxidized hydroxyalkyl starch as defined in Claim 2, wherein the granular starch is reacted with a 1,2-alkylene epoxide in the presence of a starch gelatinization inhibitor.

4. A method for preparing a gelatinizable oxidized hydroxy-alkyl starch as defined in Claim 3, wherein the granular starch is reacted with a 1,2-alkylene epoxide under non-gelatinizing conditions to obtain a granular starch having a hydroxyalkyl D
of S of from about 0.03 to about 0.18.

5. A method for preparing a gelatinizable oxidized hydroxy-alkyl starch as defined in Claim 4, wherein the 1,2-alkylene epoxide is ethylene oxide.

6. A method for preparing a gelatinizable oxidized hydroxy alkyl starch as defined in Claim 5, wherein the hydroxyalkyl starch is oxidized by the use of a alkaline hypochlorite.

7. A method for preparing a gelatinizable oxidized hydroxy-alkyl starch as defined in Claim 6, wherein the alkaline hypochlorite is sodium or potassium hypochlorite.

8. A method for preparing a gelatinizable oxidized hydroxy-alkyl starch as defined in Claim 7, wherein the granular starch is corn starch.