Method for preparing nano starch particles using alkali treatment process

Abstract

A method for preparing nano starch particles using an alkaline treatment process belongs to the technical field of starch nano particle preparation. The preparation method comprises preparing a sodium aluminate solution of a specific concentration and utilizing it to disrupt hydrogen bonds within and between starch molecules under high temperature and high pressure conditions; centrifuging the resulting mixed solution to wash away impurity ions; and freezing the resulting solid material with liquid nitrogen and freeze-drying it to obtain the nano starch particle product. The present invention treats natural starch with an alkaline sodium aluminate solution under high temperature and high pressure conditions to disrupt hydrogen bonds within and between starch molecules. The impurity ions are then removed through washing and freeze-drying, while simultaneously obtaining homogeneous powdered nano starch particles suitable for further use. The advantages of the present invention are: 1) the prepared nano starch particles have a uniform particle size, all less than 100 nanometers; and 2) the method provided by the present invention offers a simple reaction process, mild conditions, and a yield exceeding 60%, making it suitable for industrial production.

Description

Technical Field

[0001] The invention belongs to the technical field of nano starch particle preparation, and specifically relates to a method for preparing nano starch particles with a particle size of less than 100 nanometers and uniform size by treating natural starch with an alkaline sodium metaaluminate solution. Background Art

[0002] Starch, a biomass material with a wide range of sources, is non-toxic, highly productive, and biodegradable and renewable, has attracted widespread attention. However, the large particle size of natural starch limits its application in areas such as drug delivery and porous material preparation. With the continuous development of nanotechnology, nano-starch, due to its unique physicochemical properties and functional characteristics such as small size, large specific surface area, and abundant hydroxyl groups, has shown broader application prospects in catalysis, medicine, and other industrial fields. Therefore, the development of simple and efficient preparation methods for nano-starch is of great significance for its application development.

[0003] Currently, existing methods for preparing nanostarch mainly include chemical and physical treatments. Among chemical methods, hydrolysis is the most widely used. This involves treating natural starch with high-concentration strong acids such as sulfuric acid and hydrochloric acid at a certain temperature to sequentially hydrolyze its amorphous and crystalline regions. The size of the resulting nanostarch varies significantly depending on the type and concentration of the acid used, the treatment temperature and duration, and the crystallinity of the natural starch. The size of the resulting nanostarch ranges from tens to hundreds of nanometers. While these methods are technically mature and simple to operate, they suffer from long reaction times, disrupted particle structure, low yields, and uneven nanostarch particle size distribution. Chemical treatments such as self-assembly, chemical precipitation, and emulsion crosslinking have high starch concentration requirements and low yields, and their solvent selection is significantly limited. Physical treatments, including mechanical grinding, ultrasonication, high-pressure homogenization, twin-screw extrusion, and irradiation, are relatively simple to operate, time-efficient, less polluting, and offer higher yields than chemical methods. However, they often require more stringent experimental equipment and conditions, and can damage the particle structure and crystallinity to a certain extent.

[0004] In summary, the complex process flow and demanding experimental conditions in current preparation methods have limited the development of nano-starch granules. To date, developing a simplified, rapid, and high-yield method for preparing nano-starch granules with a particle size of less than 100 nanometers and uniform size distribution remains a challenging task. Summary of the Invention

[0005] The purpose of the present invention is to propose a method for preparing nano starch particles with a simple process, a short flow and a high yield, which controls the starch particle size within 100 nanometers and increases the yield of nano starch to more than 60%, so as to overcome the shortcomings of the above-mentioned technology.

[0006] The technical solution of the present invention is as follows: 1) preparing a sodium aluminate solution of a specific concentration, treating it in a hydrothermal reactor at a mass ratio of Al(OH)3, NaOH and starch of 1-30:1-30:1, and utilizing the solution to destroy hydrogen bonds within and between starch molecules under high temperature and high pressure conditions; 2) centrifuging the obtained mixed solution to wash away impurity ions; and 3) freezing the obtained solid matter using liquid nitrogen and freeze-drying it to obtain a nano starch granule product.

[0007] The specific preparation steps are:

[0008] 1) In a water bath at 30-100°C, prepare a 1-10 mol / L Al(OH)3 solution and a 5-15 mol / L NaOH solution, respectively, and continue stirring until the solutions are clear and transparent to obtain the corresponding sodium aluminate solutions. Add the starch to the sodium aluminate solution in a mass ratio of Al(OH)3, NaOH, and starch of 1-30:1-30:1 to form a mixed solution, which is then placed in a hydrothermal reactor at a predetermined volume ratio and insulated.

[0009] 2) The homogeneous mixture solution obtained after opening the autoclave is centrifuged at 5000-10000 rpm for 5-30 minutes, and washed multiple times until neutral.

[0010] 3) Freezing the obtained solid in liquid nitrogen for about 5 to 30 minutes, and after being completely frozen, placing it in a freeze dryer and drying it for 10 to 48 hours to obtain a white homogeneous nano starch powder.

[0011] The volume ratio of step 1) is that the mixed liquid accounts for 25%-35% of the volume of the hydrothermal reactor.

[0012] The heat preservation treatment in step 1) is to keep the temperature in a blast drying oven at 70 to 200° C. for 2 to 20 hours.

[0013] The starch includes: cassava starch, potato starch, corn starch, mung bean starch, wheat starch, sweet potato starch, water chestnut starch, lotus root starch, water chestnut starch, sweet potato starch, pea starch, arrowroot starch, sago starch, etc.

[0014] The advantages of the present invention are: 1) Starch is a covalent polymer formed by dehydrating glucose, linked together by glycosidic bonds. It is typically composed of amylose and amylopectin. Amylose molecules are crystalline, formed by intermolecular hydrogen bonds, and are not easily hydrolyzed or decomposed, while amorphous amylopectin molecules are easily hydrolyzed or decomposed. Starch itself does not react with alkali, but decomposition is facilitated by heating in an alkaline environment. The present invention, in an alkaline sodium metaaluminate solution, combines high temperature conditions with the self-pressure generated by the hydrothermal reactor during heating to more easily break the hydrogen bonds within and between starch molecules, promoting the decomposition of the amorphous and crystalline regions of starch granules. By controlling the experimental conditions, the size of nano starch particles can be controlled to below 100 nanometers. Because the alkali does not over-hydrolyze the starch, but instead breaks the starch molecular chains into "fragments," the resulting nano starch yield is relatively high. 2) When synthesizing nano starch particles using acid hydrolysis, the acid continues to react with the starch after hydrolysis or decomposition, resulting in a low final starch yield. Preparation of nano-starch particles through methods such as emulsification and cross-linking requires large amounts of organic reagents, is repetitive and laborious, and ultimately results in extremely low nano-starch yields, limiting industrial applications. In contrast, the method provided by the present invention is simple, employs relatively mild conditions, and achieves starch yields exceeding 60%, making it suitable for industrial production. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] Figure 1 This is a scanning electron microscope photograph of nano starch particles dispersed in an ethanol phase obtained in Example 1 of the present invention.

[0016] Figure 2 This is a scanning electron microscope photograph of solid nano starch particles obtained in Example 1 of the present invention.

[0017] Figure 3 This is a scanning electron microscope photograph of solid nano starch particles obtained in Example 2 of the present invention. DETAILED DESCRIPTION

[0018] The technical solution of the present invention is further described below in conjunction with specific implementation methods.

[0019] Implementation Case 1

[0020] 1) Prepare 4.20 mol / L Al(OH)3 solution and 8.96 mol / L NaOH solution in a 40°C water bath, mix and stir until the solution is clear and transparent, obtaining 12.7 mL of 3.98 mol / L sodium aluminate solution. Add 0.76 g corn starch to a 30 mL hydrothermal reactor, approximately one-third by volume, and incubate in an oven at 120°C for 5 hours. The mass ratio of Al(OH)3, NaOH, and starch is 3:4.7:1. 2) Centrifuge the resulting homogeneous mixture at 8000 rpm for 20 minutes, and repeat washing five times until neutral.

[0021] 3) The obtained solid was frozen in liquid nitrogen for about 6 minutes, and after being completely frozen, it was placed in a freeze dryer and dried for 20 hours to obtain a white homogeneous nano starch powder.

[0022] from Figure 1 、 Figure 2 The nanostarch is stable, with distinct boundaries, clearly visible in both ethanol and solid-state scanning. The nanostarch particles are uniform in size, all less than 100 nanometers. Weighing the product on an electronic balance yielded 0.4667 g, for a yield of 61.4%.

[0023] Implementation Case 2

[0024] 1) Prepare a 9.50 mol / L Al(OH)3 solution and a 13.26 mol / L NaOH solution in a 90°C water bath. Mix and stir until the solution is clear, yielding 15.7 mL of a 9.01 mol / L sodium metaaluminate solution. Add 3.20 g of potato starch to a 50 mL hydrothermal reactor and heat in an oven at 180°C for 15 h. The mass ratio of Al(OH)3:NaOH:starch is 6:8:1.

[0025] 2) The homogeneous mixture solution obtained after opening the autoclave was centrifuged at 10,000 rpm for 7 minutes, and washed four times until neutral.

[0026] 3) The obtained solid was frozen in liquid nitrogen for about 10 minutes, and after being completely frozen, it was placed in a freeze dryer and dried for 36 hours to obtain a white homogeneous nano starch powder.

[0027] from Figure 3 The nano starch had clear boundaries, and the solid phase scanning clearly showed that the nano starch particles were all less than 100 nanometers in size and had a relatively uniform morphology. The product was weighed on an electronic balance and weighed 1.9296 g, with a yield of 60.3%.

[0028] Implementation Case 3

[0029] 1) Prepare 7.30 mol / L Al(OH)3 solution and 10.30 mol / L NaOH solution in a 70°C water bath. Mix and stir until the solution is clear and transparent, yielding 14.5 mL of 6.83 mol / L sodium metaaluminate solution. Add 2.11 g of corn starch to a 50 mL hydrothermal reactor and incubate in an oven at 90°C for 10 h. The mass ratio of Al(OH)3:NaOH:starch is 6.3:7:1.

[0030] 2) The homogeneous mixture solution obtained after opening the autoclave was centrifuged at 9000 rpm for 15 min, and washed five times until neutral.

[0031] 3) The obtained solid was frozen in liquid nitrogen for about 15 minutes. After being completely frozen, it was placed in a freeze dryer and dried for 36 hours to obtain a white homogeneous nano starch powder.

[0032] According to the experimental results, nano starch particles with a size less than 100 nanometers and relatively uniform were successfully prepared. After weighing on an electronic balance, the product mass was 1.2829 g, with a yield of 60.8%.

Claims

1. A method for preparing nano starch particles by an alkali treatment process, characterized in that: The preparation steps are: 1) preparing a sodium aluminate solution of a specific concentration, adding starch to the sodium aluminate solution in a hydrothermal reactor at a mass ratio of Al(OH)3, NaOH, and starch of 1-30:1-30:1 to form a mixed solution, wherein the mixed solution accounts for 25%-35% of the volume of the hydrothermal reactor, and the reactor is insulated; 2) centrifuging the obtained mixed solution to wash away impurity ions; 3) freezing the obtained solid material using liquid nitrogen and freeze-drying it to obtain a nano starch particle product; The sodium aluminate solution of a specific concentration is prepared in step 1) by preparing a 1-10 mol / L Al(OH)3 solution and a 5-15 mol / L NaOH solution in a water bath at 30-100°C, respectively, and stirring them until the solution becomes clear and transparent to obtain a sodium aluminate solution.

2. The method for preparing nano starch granules by alkali treatment process according to claim 1, wherein The centrifugation of the mixed solution in step 2) to wash away impurity ions is performed by centrifuging the uniform mixture solution obtained after opening the autoclave, separating at 5000-10000 rpm for 5-30 minutes, and washing multiple times until neutral.

3. The method for preparing nano starch granules by alkali treatment process according to claim 1, wherein The liquid nitrogen freezing and drying in step 3) is to freeze the obtained solid in liquid nitrogen for 5 to 30 minutes, and after being completely frozen, put it into a freeze dryer and dry it for 10 to 48 hours to obtain a white homogeneous nano starch powder.

4. The method for preparing nano starch granules by alkali treatment process according to claim 1, wherein The heat preservation treatment described in step 1) is to keep the temperature in a forced air drying oven at 70-200°C for 2-20 hours.

5. The method for preparing nano starch particles by alkali treatment process according to claim 1, characterized in that, The starch includes: cassava starch, potato starch, corn starch, mung bean starch, wheat starch, sweet potato starch, water chestnut starch, lotus root starch, water chestnut starch, sweet potato flour, pea starch, arrowroot starch, and sago starch.

Images