A method for preparing a hydroxypropyl modified starch

Abstract

The application relates to the technical field of starch modification, and discloses a preparation method of hydroxypropyl modified starch, which comprises the following steps: obtaining acidified starch milk by acidifying treatment of starch, adjusting the pH of the acidified starch milk to 9-11 to obtain starch milk; uniformly mixing the starch milk, a catalyst and a propylene oxide solution, stirring the mixture at 35-45 DEG C to obtain a reactant; and obtaining the hydroxypropyl modified starch by alcohol precipitation, washing, filtration and drying of the reactant; wherein the catalyst comprises tetraethylammonium hydroxide, sodium carbonate and tetrabutylammonium bromide. The above technical scheme solves the problem of low substitution degree of the hydroxypropyl modified starch in the related art.

Description

TECHNICAL FIELD

[0001] The application relates to the technical field of starch modification, in particular to a preparation method of hydroxypropyl modified starch. BACKGROUND

[0002] As a natural polymer material with rich reserves and low cost in nature, starch has been widely used in food processing, papermaking industry, textile printing and dyeing and other fields due to its excellent biocompatibility, biodegradability and basic thickening and bonding functions. However, the strong hydrogen bond between glucose units in natural starch molecules makes it difficult to meet the performance requirements of complex application scenarios. As a mainstream starch modification method, the introduction of hydroxypropyl groups into the hydroxyl groups of starch glucose units can destroy the intermolecular hydrogen bond, and by adjusting the degree of substitution (DS) of hydroxypropyl, the performance of starch can be comprehensively upgraded.

[0003] Among them, high-substitution hydroxypropyl starch, with strong hydrophilicity and stable structure, plays an irreplaceable role in various fields: it can be used as a sustained-release tablet skeleton or capsule raw material in medicine to achieve long-acting drug release and good biocompatibility; it can be used as a filtrate loss reducer in oil drilling to protect oil and gas reservoirs; it can be used in high-end coatings to adapt to water-based systems and improve coating flatness and scrub resistance; it can also be used as a special paper surface sizing agent to enhance paper performance, or as a thickening stabilizer in cosmetics, etc. These requirements all rely on the unique properties of high-substitution hydroxypropyl starch, and low-substitution hydroxypropyl starch cannot be replaced.

[0004] However, existing industrialized technology is mainly low-substitution hydroxypropyl starch, which is difficult to prepare high-substitution hydroxypropyl starch due to the limitation of preparation process. Long-term reliance on imports and high prices make it difficult to meet the independent application requirements of high-end papermaking, medicine, oil exploration and other fields. Therefore, a preparation method of high-substitution hydroxypropyl modified starch needs to be proposed. SUMMARY

[0005] The application provides a preparation method of hydroxypropyl modified starch, which solves the problem of low substitution degree of hydroxypropyl modified starch in the prior art.

[0006] The technical scheme of the application is as follows:

[0007] The application provides a preparation method of hydroxypropyl modified starch, which includes the following steps:

[0008] S1, acidifying starch to obtain acidified starch milk, and adjusting the pH of the acidified starch milk to 9-11 to obtain starch milk;

[0009] S2, mixing the starch milk, a catalyst and an epoxypropane solution uniformly, and stirring at 35-45 DEG C to obtain a reaction mixture;

[0010] S3, the reactants are precipitated by alcohol, washed, filtered, dried, and crushed to obtain the hydroxypropyl modified starch;

[0011] The catalyst comprises tetraethylammonium hydroxide, sodium carbonate and tetrabutylammonium bromide.

[0012] As a further technical solution, the mass ratio of tetraethylammonium hydroxide, sodium carbonate and tetrabutylammonium bromide in the catalyst is 4-6:9:1, preferably 5:9:1.

[0013] When the mass ratio of tetraethylammonium hydroxide in the catalyst of the preparation method of the hydroxypropyl modified starch of the present application is greater than 6:9:1, the strong alkalinity of tetraethylammonium hydroxide will significantly increase the pH of the system, accelerate the breakage of starch molecular chain glycosidic bond, cause degradation and molecular weight reduction, and intensify the hydrolysis side reaction of propylene oxide, thereby generating a large amount of impurities, reducing etherification selectivity and target product substitution degree; when the mass ratio of tetraethylammonium hydroxide in the catalyst is less than 4:9:1, it cannot provide sufficient activation power for the hydroxyl groups of starch, resulting in insufficient etherification reaction active sites, greatly reduced reaction efficiency, and low substitution degree of hydroxypropyl modified starch. When the mass ratio of tetraethylammonium hydroxide, sodium carbonate and tetrabutylammonium bromide in the catalyst is 4-6:9:1, hydroxypropyl modified starch with higher substitution degree can be obtained.

[0014] As a further technical solution, the total mass of the catalyst is 0.5%-1.5% of the mass of the starch, preferably 0.9%.

[0015] As a further technical solution, in step S2, the mixing is first mixing and stirring the starch milk, tetraethylammonium hydroxide and sodium carbonate for 20-40 min, then uniformly mixing with tetrabutylammonium bromide for 8-12 min, and then adding propylene oxide solution for mixing.

[0016] In the preparation method of the hydroxypropyl modified starch of the present application, the method of first mixing and stirring the starch milk, tetraethylammonium hydroxide and sodium carbonate for 20-40 min, then adding tetrabutylammonium bromide for mixing for 8-12 min, and then adding propylene oxide can make the two alkaline catalysts of tetraethylammonium hydroxide and sodium carbonate fully act, and gradually establish a stable alkaline environment, which can not only avoid excessive local alkalinity causing starch gelatinization or degradation, but also allow the starch particles to swell moderately and activate the hydroxyl groups; subsequently, the phase transfer catalyst tetrabutylammonium bromide is uniformly dispersed within 8-12 min, thereby better improving the contact probability and reaction efficiency of propylene oxide and activated hydroxyl groups in the subsequent process, and significantly improving the hydroxypropyl substitution degree of the product.

[0017] As a further technical solution, the volume to mass ratio of the propylene oxide solution to the starch is 1-3 mL:1 g.

[0018] As a further technical solution, the preparation method of the propylene oxide solution comprises the following steps: dissolving propylene oxide in a solvent to obtain a propylene oxide solution.

[0019] As a further technical solution, the solvent comprises one of methanol, ethanol, alkyl ketone, and isopropyl alcohol, and preferably isopropyl alcohol.

[0020] As a further technical solution, the volume ratio of propylene oxide to the solvent is 1:15-20.

[0021] As a further technical solution, the starch comprises at least one of cassava starch, potato starch, corn starch, sweet potato starch, and wheat starch.

[0022] As a further technical solution, in step S1, the acidification treatment is adding an aqueous acetic acid solution with a mass fraction of 10% into the starch, the mass of the aqueous acetic acid solution is 15-40% of the mass of the starch, and the acidification time is 1.5-4 hours.

[0023] The working principle and beneficial effects of the present application are as follows:

[0024] The present application selects tetraethylammonium hydroxide, sodium carbonate, and tetrabutylammonium bromide as catalysts to jointly improve the substitution degree of hydroxypropyl modified starch through the synergistic effect of the three. Tetraethylammonium hydroxide can quickly capture the hydrogen protons of the hydroxyl groups of starch to generate highly active oxygen anions, thereby providing sufficient active sites for etherification reaction, but its strong alkalinity can easily cause degradation of the starch chain and hydrolysis of propylene oxide. At this time, sodium carbonate plays a buffering role through the ionization equilibrium of CO3 2- / HCO3 - to stabilize the pH of the system in the weak alkaline range, thereby avoiding damage to the starch molecules by strong alkali and maintaining the active state of the hydroxyl anions. On this basis, tetrabutylammonium bromide as a phase transfer catalyst can transfer the active hydroxyl anions in the aqueous phase to the organic phase where propylene oxide is located through ion pair action, thereby solving the poor solubility of the starch milk and the propylene oxide solution and greatly improving the collision reaction efficiency of propylene oxide and active hydroxyl groups. The synergistic effect of the three ultimately realizes the efficient preparation of high-substitution-degree hydroxypropyl modified starch. DETAILED DESCRIPTION

[0025] The technical solutions in the embodiments of the present application will be clearly and completely described below in combination with the embodiments of the present application. Obviously, the described embodiments are only part of the embodiments of the present application, rather than all the embodiments. Based on the embodiments in the present application, all other embodiments obtained by those of ordinary skill in the art without creative labor are within the scope of protection of the present application.

[0026] Embodiment 1

[0027] A preparation method of a hydroxypropyl modified starch, comprising the following steps:

[0028] S1, 100g of corn starch is placed in a reactor, 15mL of 10% acetic acid aqueous solution is added, and after acidification for 4h, an acidified starch milk is obtained, then sodium hydroxide is added to adjust the pH to 10, and the starch milk is obtained;

[0029] S2, the starch milk is uniformly mixed with tetrabutylammonium bromide for 10min, then tetraethylammonium hydroxide and sodium carbonate are added, and after mixing and stirring for 30min, 200mL of propylene oxide solution is added, and the mixture is stirred at 40℃ for 2h to obtain a reaction product;

[0030] S3, after the reaction product is cooled to room temperature, 1500mL of ethanol is added, and after standing and layering, washing is performed, and the operation is repeated for 3 times, then filtration and drying are performed to obtain a hydroxypropyl modified starch;

[0031] The mass ratio of tetraethylammonium hydroxide, sodium carbonate and tetrabutylammonium bromide is 4:9:1, and the sum of the mass of tetrabutylammonium bromide and tetraethylammonium hydroxide and sodium carbonate is 0.5% of the mass of cassava starch;

[0032] The preparation method of the propylene oxide solution comprises the following steps: 11mL of propylene oxide is dissolved in 187mL of methanol to obtain a propylene oxide solution.

[0033] Example 2

[0034] A preparation method of a hydroxypropyl modified starch, comprising the following steps:

[0035] S1, 100g of cassava starch is placed in a reactor, 30mL of 10% acetic acid aqueous solution is added, and after acidification for 3h, an acidified starch milk is obtained, then sodium hydroxide is added to adjust the pH to 10, and the starch milk is obtained;

[0036] S2, the starch milk is uniformly mixed with tetrabutylammonium bromide for 10min, then tetraethylammonium hydroxide and sodium carbonate are added, and after mixing and stirring for 30min, 200mL of propylene oxide solution is added, and the mixture is stirred at 40℃ for 2h to obtain a reaction product;

[0037] S3, after the reaction product is cooled to room temperature, 1500mL of ethanol is added, and after standing and layering, washing is performed, and the operation is repeated for 3 times, then filtration and drying are performed to obtain a hydroxypropyl modified starch;

[0038] The mass ratio of tetraethylammonium hydroxide, sodium carbonate and tetrabutylammonium bromide is 4:9:1, and the sum of the mass of tetrabutylammonium bromide and tetraethylammonium hydroxide and sodium carbonate is 0.9% of the mass of cassava starch;

[0039] The preparation method of the propylene oxide solution comprises the following steps: dissolving 11 mL of propylene oxide in 187 mL of isopropyl alcohol to obtain a propylene oxide solution.

[0040] Example 3

[0041] A preparation method of a hydroxypropyl modified starch comprises the following steps:

[0042] S1, 100g of wheat starch is placed in a reactor, 40mL of 10% acetic acid aqueous solution is added, and the starch is acidified for 1.5h to obtain an acidified starch milk, and then sodium hydroxide is added to adjust the pH to 10 to obtain a starch milk;

[0043] S2, the starch milk is uniformly mixed with tetrabutylammonium bromide for 10min, then tetraethylammonium hydroxide and sodium carbonate are added, and stirred for 30min, then 200mL of propylene oxide solution is added, and stirred at 40℃ for 2h to obtain a reaction product;

[0044] S3, after the reaction product is cooled to room temperature, 1500mL of ethanol is added, and after standing and layering, it is washed and the operation is repeated for 3 times, and then filtered, dried to obtain a hydroxypropyl modified starch;

[0045] The mass ratio of tetraethylammonium hydroxide, sodium carbonate and tetrabutylammonium bromide is 4:9:1, and the sum of the mass of tetrabutylammonium bromide, tetraethylammonium hydroxide and sodium carbonate is 1.5% of the mass of cassava starch.

[0046] The preparation method of the propylene oxide solution comprises the following steps: dissolving 11 mL of propylene oxide in 187 mL of isopropyl alcohol to obtain a propylene oxide solution.

[0047] Example 4

[0048] Compared with example 2, the difference of example 4 is only that the mass ratio of tetraethylammonium hydroxide, sodium carbonate and tetrabutylammonium bromide in this example is 5:9:1.

[0049] Example 5

[0050] Compared with example 2, the difference of example 5 is only that the mass ratio of tetraethylammonium hydroxide, sodium carbonate and tetrabutylammonium bromide in this example is 6:9:1.

[0051] Example 6

[0052] Compared with example 2, the difference of example 6 is only that in step S2, the starch milk is uniformly mixed with tetrabutylammonium bromide, tetraethylammonium hydroxide and sodium carbonate, stirred for 30min, then 198mL of propylene oxide solution is added, and stirred at 40℃ for 2h to obtain a reaction product.

[0053] Comparative example 1

[0054] The difference between Comparative Example 1 and Example 6 is that, in the catalyst of the present comparative example, the tetraethylammonium hydroxide is replaced by an equivalent amount of sodium hydroxide.

[0055] Comparative Example 2

[0056] The difference between Comparative Example 2 and Example 6 is that, in the catalyst of the present comparative example, the tetraethylammonium hydroxide and sodium carbonate are present in a mass ratio of 4:9.

[0057] Comparative Example 3

[0058] The difference between Comparative Example 3 and Example 6 is that, in the catalyst of the present comparative example, the tetraethylammonium hydroxide and tetrabutylammonium bromide are present in a mass ratio of 4:1.

[0059] Comparative Example 4

[0060] The difference between Comparative Example 4 and Example 6 is that, in the catalyst of the present comparative example, the tetraethylammonium hydroxide is the only catalyst.

[0061] The hydroxypropyl-modified starches prepared in Examples 1-6 and Comparative Examples 1-4 were tested according to the following method:

[0062] 1. Test method for the degree of substitution of hydroxypropyl-modified starch: The content of the hydroxypropyl group in the hydroxypropyl-modified starch was determined according to the experimental method specified in the standard GB / T 20376-2006 “Determination of the content of hydroxypropyl in modified starch by proton nuclear magnetic resonance spectroscopy”, and was denoted as W; the degree of substitution (i.e. the ratio of hydroxypropyl to anhydroglucose group) was calculated according to the following formula: DS = 162W / [(100-W) x 58];

[0063] In the formula: W is the content of the hydroxypropyl group (%); 162 is the relative molecular mass of anhydroglucose; and 58 is the relative molecular mass of propylene oxide.

[0064] The test results are shown in Table 1:

[0065] Table 1. Test results for the degree of substitution of hydroxypropyl-modified starch

[0066]

[0067] As can be seen from the data in Table 1, compared with Comparative Examples 1-4, the hydroxypropyl-modified starches prepared in Examples 1-6 have a greater content of hydroxypropyl and a greater degree of substitution, indicating that the addition of a catalyst composed of tetraethylammonium hydroxide, sodium carbonate and tetrabutylammonium bromide can significantly improve the degree of substitution of the hydroxypropyl-modified starch.

[0068] The above merely preferred embodiments of the present application are not used to limit the present application, any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present application should be included in the protection scope of the present application.

Claims

1. A method for preparing hydroxypropyl-modified starch, characterized in that, Includes the following steps: S1. After acidifying the starch, acidified starch milk is obtained. Then, the pH of the acidified starch milk is adjusted to 9-11 to obtain starch milk. S2. Mix starch milk, catalyst and propylene oxide solution evenly and stir at 35~45℃ to obtain reactants; S3. The reactants were subjected to alcohol precipitation, washing, filtration and drying to obtain hydroxypropyl modified starch; The catalyst comprises tetraethylammonium hydroxide, sodium carbonate, and tetrabutylammonium bromide in a mass ratio of 4~6:9:1; The total mass of the catalyst is 0.5% to 1.5% of the starch mass.

2. The method for preparing hydroxypropyl modified starch according to claim 1, characterized in that, In step S2, the mixing process involves first mixing starch milk, tetraethylammonium hydroxide, and sodium carbonate for 20-40 minutes, then uniformly mixing with tetrabutylammonium bromide for 8-12 minutes, and finally adding propylene oxide solution for further mixing.

3. The method for preparing hydroxypropyl modified starch according to claim 1, characterized in that, The volume-to-mass ratio of the propylene oxide solution to starch is 1-3 mL: 1 g.

4. The method for preparing hydroxypropyl modified starch according to claim 1, characterized in that, The preparation method of propylene oxide solution includes the following steps: dissolving propylene oxide in a solvent to obtain propylene oxide solution.

5. The method for preparing hydroxypropyl modified starch according to claim 4, characterized in that, The solvent includes one of methanol, ethanol, alkyl ketone, and isopropanol.

6. The method for preparing hydroxypropyl modified starch according to claim 4, characterized in that, The volume ratio of propylene oxide to solvent is 1:15~20.

7. The method for preparing hydroxypropyl modified starch according to claim 1, characterized in that, The starch includes at least one of cassava starch, potato starch, corn starch, sweet potato starch, and wheat starch.

8. The method for preparing hydroxypropyl modified starch according to claim 1, characterized in that, In step S1, the acidification treatment involves adding a 10% (w / w) aqueous acetic acid solution to the starch, wherein the mass of the aqueous acetic acid solution is 15-40% of the starch mass, and the acidification time is 1.5-4 hours.

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