The preparation of cationic starch is a well known commercial process. The basic water-slurry process for the quaternization of starch employing the reaction product of epichlorohydrin and an amine is taught in U.S. patent 2,876,217. The art also teaches that in such a process an alkali metal salt, e.g. NaCl or Na ₂ S0 ₄ should be used to inhibit gelatinization. The starch is usually slurried in water at a dry weight (d.b.) of from about 10 to about 42 percent. Reaction times are generally from 12 to 20 hours, the slurry is maintained at a pH between 11 and 12 and the- temperature must be low to prevent gelatinization during the process, generally from room temperature up to 50°C. The reaction product must then be neutralized and washed to remove salts. According to teachings of U.S. 3,422,087 cationic starch products can be made in the absence of alkali and-at temperatures much higher than normal, up to just under 200°C, which is the browning temperature of the polysaccharide.

This invention is directed to a process for preparing cationic starch by reacting in an aqueous medium said starch with a halohydrin quaternary amine in the presence of an alkaline catalyst characterized by (1) initiating said reaction with an alkali metal oxide or hydroxide and (2) thereafter adding an alkaline earth metal oxide or hydroxide to complete the reaction.

The use of a combination of an alkali metal oxide or hydroxide and an alkaline earth metal oxide or hydroxide as catalysts in a particular order in the reaction for making cationic starch reduces viscosity and permits use of starch solids up to 46 percent (d.b.) which results in superior yield of desired product compared to the use of either an alkali metal oxide, a hydroxide or an alkaline earth metal oxide or hydroxide alone. When the halohydrin quaternary amine is reacted with the alkali metal oxide or hydroxide, an epoxide group is formed from the halohydrin group.

^* The catalyst of the present invention is a combination of an alkali metal oxide or hydroxde and an alkaline earth metal oxide or hydroxide employed in sequence, the latter being added after the reaction has been initiated by the former. The alkali metal oxide or hydroxide catalyst is employed at a concentration of from 0.35 to 1.2 percent by weight and preferably from 0.6 to 1.0 percent; while the alkaline earth metal oxide or hydroxide is employed at a concentration of from 0.15 to 0.8 percent by weight, preferably from 0.3 to 0.6 percent. The use of less than the indicated amount of either catalyst will give low yields and, in the case of adding insufficient lime, gelation can occur. Too much of either is uneconomical and mixing

the slurry of reactants becomes difficult with too much alkaline earth metal oxide or hydroxide and filtering is difficult with too much alkali metal oxide or hydroxide. Preferably, the alkali metal is sodium or potassium and the alkaline earth metal is calcium or barium.

Preferably, the halohydrin quaternary amine has the formula

X-CH ₂

X is chlorine or bromine, R ¹ , R ² and R ³ are independently selected from the group of ^-0 ₄ straight or branched alkyl radicals with the proviso that the total number of carbon atoms in R ¹ , R ² , and R ³ does not exceed 8, and n is 1-3. Thus, for example, starch is reacted with 3-chloro-2-hydroxypropyltrimethylammonium chloride according to the method of the present invention by employing an aqueous starch slurry of 40 to 46 percent by weight of dry starch with from 2 to 4 percent by weight of 3-chloro-2-hydroxypropyltrimethylammonium chloride in the presence of 0.5 to 2.0 percent by weight of a gelatinization inhibitor, all based on total reaction mixture. At lower temperatures, which reduce the rate of gelatinization, the use of a gelatin- ization inhibitor can be omitted, but in order to shorten the time of reaction the temperature should be increased and a gelatinization inhibitor used. Even at lower temperatures it is preferred to use a gelatin¬ ization inhibitor since this, of itself, increases the rate of reaction.

Below 40 percent starch in the slurry the yields become unacceptably low, whereas above 46 percent stirring of the reactants becomes difficult and gelatin¬ ization is likely to occur. When the cationic reagent is employed at less than the lower operable limit the product becomes less effective as a paper additive. More than the indicated operable amount is uneconomical and of no additional benefit. More than the operable level of gelatinization inhibitor is likewise uneconom¬ ical and of no further benefit.

The time of reaction is from 4 to 14 hours, depending upon the temperature, and preferably from 7 to 10 hours. Temperatures in the range of from 35° to 60°C are employed and preferably from 45° to 55°C.

The yields of the process of the present invention are from 70 to 85 percent. This compares to yields in the range of 55 percent to 60 percent known and practiced in the prior art. In addition to the yield advantage, shorter reaction times and reduction in waste effluents are achieved.

Although corn starch is exemplified in the following experiments, wheat, rice, potato and (waxy) maize starches can also be employed in the present process.

Suitable gelatinization inhibitors include, for example, Na ₂ S0 ₄ , NaCl, KC1, K ₂ S0 ₄ , Na ₂ C0 ₃ and

K ₂ C0 ₃ . The sulfates are preferred.

After the reaction is complete, the resultant cationic starch is ordinarily neutralized with an acid,

such as, for example, hydrochloric, citric, nitric, phosphoric, or adipic, to a pH of neutral or below, usually about 6. After neutralization, the product is usually filtered and washed. The product obtained normally is dried before use.

The following experiments are representative of the invention and of the known art for comparison.

Examples 1 Through 12 and Comparative Runs A, Through D For Example 1, a 500 ml round bottom flask, equipped with stirrer and placed in a 50°C constant temperature bath. To the flask was added 15.4 g of a 50 percent solution of 3-chloro-2-hydroxypropyltrimethyl- ammonium chloride plus a caustic solution made of 2 g NaOH diluted with 97 g of water. The contents was stirred and after formation of the epoxide which was determined by a drop of the pH from 13.2 to 12.3 (approximately 2 minutes), 121.74 g of corn starch mixed with 2.7 g of Na ₂ S0 ₄ was fed into the pot at a rate insuring uniform dispersion (10-15 minutes). This mixture was heated with stirring at 50°C for 10 minutes, during which time the pH dropped to about 10. Then a slurry of 1 g Caό in 3 g of water was added, increasing the pH from 10.0 up to 11.4. The mixture of reactants was maintained at that temperature with stirring for 8 hours. At the end of this reaction period, 10 ml of water was poured in to further reduce the viscosity. Then the pH was lowered to 6.5 by neutralizing with IN HC1. The starch slurry was filtered and washed four times with 100 ml quantities of water. A nitrogen content of 0.463 percent was obtained for this run which was a 79 percent yield based on the 3-chloro- -2-hydroxypropyltrimethylammonium chloride reactant.

Examples 2 through 12 and Comparative Runs A through D were conducted in a similar manner. The addition order (except where noted) was always (1) sodium hydroxide, (2) water, (3) chlorohydrin quaternary amine salt, (4) starch + salt inhibitor and (5) calcium oxide.

The temperature at which the reactions were conducted were: Examples 2-6 and Comparative Run D (45°C); Examples 7-12 and Comparative Runs A through C (50°C). The times of reaction were all 8 hours.

The amounts of catalysts (a) NaOH and (b) CaO are given for each example and comparative run as are the amounts of quaternary salt (quat), water, starch and inhibitor salt (Na ₂ S0 ₄ ).

All samples were neutralized to pH 6 at the end of the reaction, filtered and washed four times with 100 ml or 10 ml of water depending upon size of reaction. Yield was measured by the increase of nitrogen as analyzed by the Kjeldahl method.

EXAMPLES

Catalysts ^{4 5} Quat ¹ H ₂ 0 Starch ² Na ₂ S0 ₄ Dry Starch Reaction Filtration, Viscosity ³ Yie

Ex. (g) (g) ( g) (g) % by wt. PH min. cps (Pa ^» s) %

2 (a) 0.16 1.19 10 12.17 0.27 44.9 11.9 <30 65 (0.065) 7

(b) 0.1

3 (a) 1.6 11.9 100 121.7 2.7 44.9 11.9 <30 65 (0.065) 8 (b) 1.0

4 (a) 0.16 1.19 12 12.17 0.27 41.4 11.9 <30 30 (0.030) 8 (b) 0.1

5 (a) 2.0 15.4 100 121.7 2.7 44.2 11.5 <30 65 (0.065) 7 (b) 1.0

6 (a) 2.46 19.25 97 121.7 2.7 43.4 11.5 <30 65 (0.065) 6 (b) 1.0 3

7 (a) 2.46 19.25 97 121.7 2.7 43.4 11.5 <30 65 (0.065) gel (b) 1.0 3

8 (a) 2.0 15.4 97 121.7 2.7 44.2 11.5 <30 65 (0.065) 7 (b) 1.0 3

9 (a) 2.0 15.4 87 121.7 2.7 46.1 11.5 <30 >65 (>0.065) 8 (b) 1.0 3

10 (a) 2.0 15.4 197 121.7 2.7 31.3 11.5 <30 20 (0.020)

*

COMPARATIVE RUNS

Comp. Catalysts ^{4 5} Quat ¹ H ₂ 0 Starch ² Na ₂ S0 ₄ Dry Starch Reaction Filtration , Viscosity ³ Yiel

Run (q) ( g ) ( g ) ( g ) % by wt. PH min. cps (Pa*s)

A (a) 2.0 15.4 100 121.7 2.7 44.4 10 <30 300 (0.300) 35

B (a) 2.7 15.4 100 121.7 5.5 43.7 11 >4 hr. 300 (0.300) —

C (a) 2.0 15.4 100 121.7 2.7 40.1 11.4 <30 25 (0.025) 63 (a) 0.7 25

D (b) 3.5 15.4 95 121.7 2.7 44.1 11.6 <30 130 (0.130) 72 5

¹ 50% aqueous solution of 3-chloro-2-hydroxypropyltrimethylammonium chloride.

² Grams of corn starch with 11.9% water content.

³ As measured with a Brookfield Viscometer (spindle #2).

⁴ Note that the (b) CaO was mixed with 3 g of water before addition in Examples 6-12 and in

Comparative Run D with 5 g of water. ⁵ Example 2 - CaO added immediately after starch; Examples 3 and 4 - CaO added 5 minutes afte starch; Examples 5-10, 12 and Comparative Run D - CaO added 10 minutes after starch;

Example 11 - CaO added 30 minutes after starch; Comparative Runs A and B had no CaO added;

Comparative Run C had NaOH added in two increments, but no CaO.