Method for preparing oxidized starch by mechanochemical method

Abstract

The invention belongs to the field of preparation of oxidized starch, and relates to a method for preparing oxidized starch by a mechanochemical method. Hydroxyl of corn starch is oxidized by hydrogen peroxide to generate modified starch with high carboxyl content, so that the modified starch has wider application. The preparation thought of a full bio-based mechanical method is adopted, the obtained modified starch has good economical efficiency, environmental safety and natural degradability, and the problems that an oxidized starch preparation process in the current market is large in environmental pollution, wastes resources, is tedious in process and the like are solved. According to the invention, biomass is used as a reaction raw material, is renewable and degradable, and accords with the green chemistry concept.

Description

Technical Field

[0001] The invention belongs to the field of oxidized starch preparation and relates to a method for preparing oxidized starch by a mechanochemical method. Background Art

[0002] As a natural polymer with low price, wide source and biodegradability, starch is a renewable resource with great research value. It is a high molecular polymer composed of glucose through α-(1-4) and α-(1-6) linkages. Starch has properties such as viscosity, film-forming, gelation and adhesion, so it can be used in papermaking, textile, food and other industries. However, due to some shortcomings of natural starch, such as the instability of the paste to heat, pH and high shear force, the easy precipitation of the paste, and poor solubility, the application performance of natural starch is greatly affected. Therefore, it is necessary to modify natural starch to improve its application performance.

[0003] Among them, oxidation modification is one of the most important chemical modification methods, which is a method of introducing carbonyl and carboxyl groups into starch by reacting starch with an oxidant. The introduction of carboxyl and carbonyl groups can greatly improve the water solubility of starch and give starch high reactivity, which is convenient for further modification and application.

[0004] The oxidants currently studied for starch oxidation mainly include sodium hypochlorite, hydrogen peroxide, sodium periodate, etc. Different oxidants and reaction conditions will produce different carbonyl and carboxyl content, oxidation position, starch degradation degree and oxidized starch properties. 2 O 2 As a clean oxidant, it does not produce pollution during the oxidation process, and is therefore a green oxidant with broad application prospects.

[0005] At present, oxidized starch is mostly prepared by wet method, which has a complicated process and produces a large amount of wastewater. Therefore, the dry method for preparing oxidized starch has important research significance. The dry method of this patent is mainly a mechanochemical method.

[0006] When materials are crushed by mechanical impact, grinding, extrusion, shearing, bending, etc., the particle size is reduced and the material structure and surface physical and chemical properties are changed. The mechanical force activation method can synthesize structural and functional materials with special properties that cannot be obtained by general chemical methods, and shows unique technical advantages in powder activation and surface modification, toxic waste treatment, etc. Summary of the invention

[0007] In order to solve the problems of large environmental pollution, waste of resources, low production efficiency, etc. in the preparation process of oxidized starch in the current market, the present invention proposes a method for preparing oxidized starch by mechanochemical method. The carboxyl-containing polysaccharide with the characteristics of renewable raw materials, low cost and non-toxicity is prepared by internal mixer. The present invention uses corn starch as raw material, H 2 O 2 As oxidant, CuSO 4 Oxidized starch with high carboxyl content was prepared by mechanochemical method under certain acidic conditions using 2-hydroxy-2-nitropropene as catalyst.

[0008] The technical solution of the present invention:

[0009] A method for preparing oxidized starch by mechanochemical method, comprising the following steps:

[0010] Step 1: In an internal mixer, add corn starch and H 2 O 2 , mix well and add catalyst CuSO 4 , then add concentrated hydrochloric acid and stir to mix;

[0011] Step 2: Heat and knead the reactants in step 1 in an internal mixer for 1-2 hours at a speed of 23-27 Hz;

[0012] Step 3: After the reaction is completed, the product is repeatedly washed with 95% ethanol-water solution for several times until the H 2 O 2 The product was washed with hydrochloric acid, filtered and dried to obtain the final product.

[0013] The corn starch and H 2 O 2 The molar ratio is 1:0.7 to 1:1.1;

[0014] The concentration of the concentrated hydrochloric acid is 12 mol / L; the mass ratio of the concentrated hydrochloric acid to corn starch is (0.3% to 0.5%):1;

[0015] The catalyst CuSO 4 The mass ratio of corn starch is (0.02% to 0.06%): 1;

[0016] In step 3, the reaction temperature is 30°C to 70°C, and the reaction time is 1h to 2h.

[0017] Compared with the prior art, the present invention has the following beneficial effects:

[0018] (1) The present invention introduces an internal mixer as a reaction apparatus and uses a solvent-free dry mechanical internal mixer. No solvent is used in the preparation process to avoid chemical pollution to the environment and no dangerous operation is involved. The preparation process is simple, safe and green.

[0019] (2) The starch used in the present invention is a natural biomass resource with abundant sources and is easy to produce. 2 O 2 Clean and pollution-free, the decomposition products are only oxygen and water, which is environmentally friendly and non-toxic.

[0020] (3) The prepared oxidized starch has a high carboxyl content and good water solubility, and can be widely used in industries such as petroleum, food, medicine, textile and papermaking. The preparation process is green and pollution-free, and has the advantages of a wide source of raw materials and environmental friendliness. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 is the infrared spectra of the raw starch and the product oxidized starch in Example 1;

[0022] Figure 2 It is the XRD spectra of the raw starch and the product oxidized starch in Example 1. DETAILED DESCRIPTION

[0023] The specific implementation of the present invention is further described below in conjunction with the accompanying drawings and technical solutions.

[0024] Embodiment 1:

[0025] Weigh corn starch (35 g, 0.216 mol), 30% H 2 O 2 Aqueous solution (17.13 g) and CuSO 4 The solid (0.0105 g) was crushed and mixed evenly in a soybean milk machine, and then added to an internal mixer, heated at 30°C under closed conditions, and the mechanical mixing rotor speed was set to 23 Hz. After the mixture began to flow, 280 μL of concentrated hydrochloric acid (HCl) was added dropwise, and mixed for 1 hour. After the reaction was completed, the obtained crude product was repeatedly washed several times with a 95% ethanol-water solution until the impurities were washed clean, and filtered and dried to obtain the final product, oxidized starch.

[0026] Figure 1 This is a comparison of the infrared spectra of raw starch and oxidized starch. According to the Fourier transform infrared spectrum, compared with the original starch, the 3400cm -1 The OH stretching vibration of the nearby hydrogen bond is weakened, indicating that the reaction consumes some hydroxyl groups. -1 The absorption vibration peaks of COC near oxidized starch show that the absorption peak of ether bond of oxidized starch is significantly weakened compared with that of native starch, indicating that oxidized starch is degraded. -1 The absorption vibration peak of C=O appeared nearby, indicating that the starch was oxidized.

[0027] Embodiment 2:

[0028] Weigh corn starch (35 g, 0.216 mol), 30% H 2 O 2 Aqueous solution (26.91 g) and CuSO 4 The solid (0.021 g) was crushed and mixed evenly by a soybean milk machine, and then added to an internal mixer, heated at 70°C under closed conditions, and the mechanical mixing rotor speed was set to 27 Hz. After the mixture began to flow, 400 μL of concentrated hydrochloric acid (HCl) was added dropwise, and mixed for 2 hours. After the reaction was completed, the obtained crude product was repeatedly washed several times with a 95% ethanol-water solution until the impurities were washed clean, and filtered and dried to obtain the final product, oxidized starch.

[0029] The prepared oxidized starch was dissolved in water, hydrochloric acid, sodium hydroxide, DMSO and acetone to examine the solubility of the oxidized starch in different solvents. After soaking at 30°C for 24 hours, it was found that it was only insoluble in acetone. The raw starch was insoluble in water, hydrochloric acid, sodium hydroxide, DMSO and acetone. The prepared oxidized starch had a high carboxyl content, and the hydrogen bond network in the starch was severely damaged, which effectively improved the solubility of the starch in water, acid-base solution and DMSO.

[0030] Embodiment 3:

[0031] Weigh corn starch (35 g, 0.216 mol), 30% H 2 O 2 Aqueous solution (22.02 g) and CuSO 4 The solid (0.014 g) was crushed and mixed evenly by a soybean milk machine, and then added to an internal mixer, heated at 50°C under closed conditions, and the mechanical mixing rotor speed was set to 25 Hz. After the mixture began to flow, 320 μL of concentrated hydrochloric acid (HCl) was added dropwise, and mixed for 1 h 30 min. After the reaction was completed, the obtained crude product was repeatedly washed several times with a 95% ethanol-water solution until the impurities were washed clean, and filtered and dried to obtain the final product, oxidized starch.

[0032] Figure 2It is the XRD spectrum of raw starch and product oxidized starch. As can be seen from the figure, the characteristic peak of oxidized starch is quite different from the diffraction pattern of raw starch, the characteristic absorption peak of starch partially disappears, and the polycrystalline particles present an amorphous structure, indicating that the hydrogen bonds between starch molecules are opened, most of the crystalline and microcrystalline areas are destroyed, and the corresponding amorphous areas increase. This is because under the action of mechanical forces such as shear, collision, and impact, the hydrogen bonds between starch molecules are broken, the starch particles are continuously refined, the particle size is continuously reduced, the crystalline structure and microcrystalline area inside the starch particles are crushed by mechanical forces, and the long straight-chain starch mixed in the microcrystalline and crystalline areas is released, the disorder of molecular arrangement is enhanced, the activated hydroxyl groups on the molecular chain increase, and the oxidizing agent can fully contact the inside of the starch particles, increasing the reactive sites and making them fully react.

[0033] Embodiment 4:

[0034] Weigh corn starch (35 g, 0.216 mol), 30% H 2 O 2 Aqueous solution (19.93 g) and CuSO 4 The solid (0.0105 g) was crushed and mixed evenly by a soybean milk machine, and then added to an internal mixer, heated at 60°C under closed conditions, and the mechanical mixing rotor speed was set to 26 Hz. After the mixture began to flow, 320 μL of concentrated hydrochloric acid (HCl) was added dropwise, and mixed for 1 h 30 min. After the reaction was completed, the obtained crude product was repeatedly washed several times with a 95% ethanol-water solution until the impurities were washed clean, and filtered and dried to obtain the final product, oxidized starch.

[0035] The molecular weight of the oxidized starch prepared in Examples 1-4 was tested, and the molecular weight of the oxidized starch was about 30,000, indicating that the glycosidic bonds of the starch were hydrolyzed, the molecular chain length was reduced, and the starch was degraded.

[0036] In summary, the present invention discloses a method for preparing oxidized starch with high carboxyl content by mechanochemical method. 2 O 2 The reaction is performed to obtain oxidized starch with a high carboxyl content, which has the advantages of high reaction efficiency and simple preparation method, and is in line with the concept of green chemistry.

Claims

1. A method for preparing oxidized starch by mechanochemical method, characterized in that: Here are the steps: Step 1: Add corn starch and H2O2 into an internal mixer, mix well, then add catalyst CuSO4, then drop concentrated hydrochloric acid, and stir to mix well; Step 2: Heat and knead the reactants in step 1 in an internal mixer for 1-2 hours at a speed of 23-27 Hz; Step 3: After the reaction is completed, the product is repeatedly washed several times with a 95% ethanol-water solution until the H2O2 and hydrochloric acid are washed clean, and then filtered and dried to obtain the final product.

2. The method for preparing oxidized starch by mechanochemical method according to claim 1, characterized in that: The molar ratio of corn starch to H2O2 is 1:0.7 to 1:1.

1.

3. The method for preparing oxidized starch by mechanochemical method according to claim 1, characterized in that: The concentration of the concentrated hydrochloric acid is 12 mol / L; the mass ratio of the concentrated hydrochloric acid to corn starch is (0.3%-0.5%):

1.

4. The method for preparing oxidized starch by mechanochemical method according to claim 1, characterized in that: The mass ratio of the catalyst CuSO4 to corn starch is (0.02%-0.06%):

1.

5. The method for preparing oxidized starch by mechanochemical method according to claim 1, characterized in that: In step 3, the reaction temperature is 30°C to 70°C, and the reaction time is 1h to 2h.

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