A method for preparing a high-substitution hydroxypropyl distarch phosphate

Abstract

The application discloses a preparation method of high-substitution-degree hydroxypropyl distarch phosphate, which comprises the following steps: preparing a starch milk solution; performing multi-gradient pretreatment on the starch suspension emulsion; collecting the pretreated starch sample; placing anhydrous Na2SO4 in water, stirring until completely dissolved, then adding the pretreated starch sample, and uniformly stirring; adjusting the pH value of a reaction system, adding propylene oxide, and reacting; adding sodium tripolyphosphate and sodium trimetaphosphate, and reacting; and stopping the reaction to obtain high-substitution-degree hydroxypropyl starch. The preparation technology of the high-substitution-degree hydroxypropyl distarch phosphate in the application does not use organic solvents and does not pollute the environment; the modification reaction process in the technology can be carried out in a closed manner at normal temperature, and the requirement on equipment is low; and the hydroxypropyl substitution degree of the hydroxypropyl distarch phosphate prepared by using the patent technology is between 0.5 and 1.0.

Description

Technical Field

[0001] This invention relates to the field of starch-based biodegradable materials, specifically to a method for preparing a highly substituted hydroxypropyl distarch phosphate. Background Technology

[0002] Petroleum-based plastics, with their flexibility, plasticity, lightweight, and low cost, have brought numerous conveniences to human life. However, their non-degradability leads to white pollution, threatening the natural environment, and non-renewable petroleum resources are increasingly scarce. Currently, my country is strongly advocating green and low-carbon development, and starch-based biodegradable films, which can be utilized by microorganisms in a short time and ultimately decomposed into carbon dioxide and water, are considered the most promising natural biodegradable materials to replace petroleum-based plastics. However, because natural starch is a polyhydroxy polymer, it has a strong binding effect with water, resulting in starch-based film materials being highly sensitive to water molecules and having poor barrier properties, exhibiting poor stability in humid environments. Furthermore, the strong hydrogen bonds between starch molecules cause its glass transition temperature and melting temperature to be higher than its decomposition temperature, thus preventing direct thermoplastic processing. Modifying natural starch and then blending it with hydrophobic biodegradable polyester through extrusion has become the main method for producing starch-based biodegradable materials.

[0003] Scientific research shows that hydroxypropyl distarch phosphate combines the excellent properties of both cross-linked starch and hydroxypropyl starch, such as low gelatinization temperature, high viscosity, strong acid resistance, strong shear resistance, and good freeze-thaw stability, indicating broad application prospects. Furthermore, starch films prepared using this as the main raw material exhibit significantly better mechanical and barrier properties than starch films prepared from native starch, oxidized starch, cationic starch, and other modified starches. Moreover, the performance of the starch film improves with increasing hydroxypropyl content. However, the synthesis of highly substituted hydroxypropyl distarch phosphate generally employs solvent methods and microemulsion methods, which involve the extensive use of organic reagents, leading to environmental pollution. Additionally, the relatively complex technology results in high production costs and consequently, high market prices for the end products, hindering their widespread adoption. Summary of the Invention

[0004] This invention discloses a method for preparing highly substituted hydroxypropyl distarch phosphate. Starch is dispersed in water, and the starch emulsion is pretreated in a multi-gradient manner by changing the ultrasonic time and frequency. This causes partial swelling of starch granules, which promotes the enlargement of micropores on the surface of starch granules. This exposes a large number of easily reactive hydroxyl groups buried in the internal crystalline structure of starch molecules, thereby improving the reaction efficiency of propylene oxide with hydroxyl groups on the pyran ring of starch. At the same time, it also improves the efficiency of phosphorylation reaction, thus obtaining highly substituted hydroxypropyl distarch phosphate.

[0005] The technical solution of the present invention is as follows:

[0006] A method for preparing highly substituted hydroxypropyl distarch phosphate includes the following steps:

[0007] 1. Preparation of starch suspension emulsion

[0008] Accurately weigh 5-10 parts of starch and disperse them in 90-95 parts of water to prepare a 5-10% starch emulsion solution.

[0009] 2. Multi-gradient pretreatment of starch suspension emulsions

[0010] Place the starch emulsion solution into an ultrasonic cleaner with an ultrasonic frequency of 20Hz~80Hz, and each treatment session lasts 5-15 minutes; specific treatment parameters are set as follows:

[0011]

[0012] Studies have shown that when the pretreatment frequency is between 20 Hz and 80 Hz, the viscosity of the starch solution hardly changes, indicating that the starch granules swell to a limited extent, the starch crystal structure is destroyed, and the crystallinity is significantly reduced.

[0013] 3. Collection of pretreated starch samples

[0014] The pretreated starch solution was allowed to stand for 3 hours. After the layers separated, the lower precipitate was collected and freeze-dried for 24 hours to obtain the pretreated starch sample.

[0015] 4. Preparation of highly substituted hydroxypropyl starch

[0016] Place 4-7 parts of anhydrous Na2SO4 in 40-80 parts of water and stir until completely dissolved. Then add 35-65 parts of the pretreated starch sample and stir evenly. Adjust the pH of the reaction system to 10.5-11.0, add 5-15 parts of propylene oxide, and maintain the reaction time for 25-30 hours at a temperature of 45°C. Add 1-2 parts of sodium tripolyphosphate and 15-20 parts of sodium trimetaphosphate, and maintain the reaction time for 3-5 hours.

[0017] 5. Reaction terminated

[0018] The reaction system was adjusted to pH 5.0-5.5 with 6.0% dilute hydrochloric acid to terminate the reaction. The product was then centrifuged, washed, dried in an oven, pulverized, and passed through a 100-mesh sieve to obtain highly substituted hydroxypropyl starch.

[0019] Beneficial effects

[0020] The preparation technology of high hydroxypropyl distarch phosphate in this patent does not use organic solvents and does not pollute the environment; the modification reaction process in this technology can be carried out in a closed system at room temperature with low equipment requirements; the degree of hydroxypropyl substitution of hydroxypropyl distarch phosphate prepared by this patent technology is between 0.5 and 0.8. Detailed Implementation

[0021] The embodiments of the present invention are described in detail below. These embodiments are implemented based on the technical solution of the present invention, and provide detailed implementation methods and specific operation processes. However, the scope of protection of the present invention is not limited to the following embodiments.

[0022] Example 1

[0023] A method for preparing highly substituted hydroxypropyl distarch phosphate includes the following steps:

[0024] ① Preparation of starch suspension emulsion

[0025] Accurately weigh 50g of starch and disperse it in 950g of water to prepare a 5% starch emulsion solution.

[0026] ② Pretreatment of starch suspension emulsion

[0027] Place the starch into the ultrasonic cleaner, and set the specific processing parameters as follows:

[0028]

[0029] ③ Collection of pretreated starch samples

[0030] The pretreated starch solution was allowed to stand for 3 hours. After the layers separated, the lower precipitate was collected and freeze-dried for 24 hours to obtain the hydrothermally pretreated starch sample.

[0031] ④ Preparation of hydroxypropyl distarch phosphate with high degree of hydroxypropyl substitution

[0032] 60g of anhydrous Na₂SO₄ was placed in 700g of distilled water and stirred until completely dissolved. Then, 300g of the pretreated starch sample collected above was added and stirred evenly. The pH of the system was adjusted to 10-11 with NaOH solution, 50g of propylene oxide was added, and the reaction was maintained for 24 hours at 45℃. Then, 150g of sodium trimetaphosphate and 10g of sodium tripolyphosphate were added, and the reaction was maintained for 3 hours at 40℃.

[0033] ⑤ Reaction terminated

[0034] The reaction system was adjusted to pH 5.0-5.5 with dilute sulfuric acid to terminate the reaction. Then, the product was centrifuged, washed, dried in an oven, pulverized, and passed through a 100-mesh sieve to obtain high-hydroxypropyl-substituted hydroxypropyl distarch phosphate.

[0035] Example 2

[0036] A method for preparing highly substituted hydroxypropyl distarch phosphate includes the following steps:

[0037] ① Preparation of starch suspension emulsion

[0038] Accurately weigh 100g of starch and disperse it in 900g of water to prepare a 10% starch emulsion solution.

[0039] ② Pretreatment of starch suspension emulsion

[0040] Place the starch into the ultrasonic cleaner, and set the specific processing parameters as follows:

[0041]

[0042] ③ Collection of pretreated starch samples

[0043] The pretreated starch solution was allowed to stand for 3 hours. After the layers separated, the lower precipitate was collected and freeze-dried for 24 hours to obtain the hydrothermally pretreated starch sample.

[0044] ④ Preparation of hydroxypropyl distarch phosphate with high degree of hydroxypropyl substitution

[0045] 60g of anhydrous Na₂SO₄ was placed in 700g of distilled water and stirred until completely dissolved. Then, 300g of the pretreated starch sample collected above was added and stirred evenly. The pH of the system was adjusted to 10-11 with NaOH solution, and 100g of propylene oxide was added. The reaction time was maintained for 24 hours at 45℃. Then, 180g of sodium trimetaphosphate and 15g of sodium tripolyphosphate were added, and the reaction time was maintained for 3 hours at 40℃.

[0046] ⑤ Reaction terminated

[0047] The reaction system was adjusted to pH 5.0-5.5 with dilute sulfuric acid to terminate the reaction. Then, the product was centrifuged, washed, dried in an oven, pulverized, and passed through a 100-mesh sieve to obtain high-hydroxypropyl-substituted hydroxypropyl distarch phosphate.

[0048] Example 3

[0049] A method for preparing highly substituted hydroxypropyl distarch phosphate includes the following steps:

[0050] ① Preparation of starch suspension emulsion

[0051] Accurately weigh 80g of starch and disperse it in 920g of water to prepare an 8% starch emulsion solution.

[0052] ② Pretreatment of starch suspension emulsion

[0053] Place the starch into the ultrasonic cleaner, and set the specific processing parameters as follows:

[0054]

[0055] ③ Collection of pretreated starch samples

[0056] The pretreated starch solution was allowed to stand for 3 hours. After the layers separated, the lower precipitate was collected and freeze-dried for 24 hours to obtain the hydrothermally pretreated starch sample.

[0057] ④ Preparation of hydroxypropyl distarch phosphate with high degree of hydroxypropyl substitution

[0058] 60g of anhydrous Na₂SO₄ was placed in 700g of distilled water and stirred until completely dissolved. Then, 300g of the pretreated starch sample collected above was added and stirred evenly. The pH of the system was adjusted to 10-11 with NaOH solution, 50g of propylene oxide was added, and the reaction was maintained for 24 hours at 45℃. Then, 150g of sodium trimetaphosphate and 10g of sodium tripolyphosphate were added, and the reaction was maintained for 3 hours at 40℃.

[0059] ⑤ Reaction terminated

[0060] The reaction system was adjusted to pH 5.0-5.5 with dilute sulfuric acid to terminate the reaction. Then, the product was centrifuged, washed, dried in an oven, pulverized, and passed through a 100-mesh sieve to obtain high-hydroxypropyl-substituted hydroxypropyl distarch phosphate.

[0061] Comparative Example 1

[0062] The difference from Example 1 is that the ultrasonic treatment time was 60 minutes, the power was 20 Hz, and all other conditions were the same.

[0063] Comparative Example 2

[0064] The difference from Example 1 is that the ultrasonic treatment time was 60 minutes, the power was 80 Hz, and all other conditions were the same.

[0065] Comparative Example 3

[0066] The difference from Example 1 is that the ultrasonic treatment conditions are: power of 80 Hz for 30 min, power of 20 Hz for 30 min, and so on, with all other conditions being the same.

[0067] The hydroxypropyl distarch phosphate prepared in the above examples and comparative examples was tested to obtain its performance parameters.

[0068] 1. Test method for degree of hydroxypropyl substitution: determined according to national standard GB / T40998-2021.

[0069] 2. Phosphorus content test method: Carbonize 0.5g of sample and incinerate at 550°C for 3 hours. Dissolve the ash in 1mL of 29% (w / v) nitric acid and heat at 100°C for 30 minutes. Quantitatively transfer the solution to a 10mL volumetric flask. Mix the solution with 1mL of 0.25% (w / v) ammonium vanadate and 1mL of 5% (w / v) ammonium molybdate, and dilute to 10mL with water. After 10 minutes, measure the absorbance at 420nm for the sample blank.

[0070] Table 1 shows the test results of hydroxypropyl distarch phosphate in Examples 1-3 and Comparative Examples 1-3.

[0071]

[0072] As can be seen from Table 1, the hydroxypropyl distarch phosphate prepared by the method of the examples has a significantly higher degree of hydroxypropyl substitution and phosphorus content than the hydroxypropyl distarch phosphate prepared by the method of the comparative example.

Claims

1. A method for preparing highly substituted hydroxypropyl distarch phosphate, characterized in that, Includes the following steps: (1) Preparation of starch suspension emulsion: Prepare starch emulsion solution; (2) Multi-gradient pretreatment of starch suspension emulsion: The starch emulsion solution was placed in an ultrasonic cleaner with an ultrasonic frequency of 20Hz~80Hz and a treatment time of 5-15min for each segment; The specific parameters for the multi-gradient pretreatment of starch suspension emulsions are as follows: ； (3) Collection of pretreated starch samples: After the starch solution has been left to stand, the precipitate is collected and dried; (4) Preparation of highly substituted hydroxypropyl starch: Anhydrous Na2SO4 was placed in water and stirred until completely dissolved. Then, the pretreated starch sample was added and stirred evenly. The pH value of the reaction system was adjusted, propylene oxide was added, and the reaction was carried out. Sodium tripolyphosphate and sodium trimetaphosphate were added, and the reaction was carried out. (5) Reaction termination: Adjust the pH value, centrifuge, wash, dry in an oven, pulverize, and sieve to obtain highly substituted hydroxypropyl starch.

2. The method for preparing a highly substituted hydroxypropyl distarch phosphate according to claim 1, characterized in that, The concentration of the starch emulsion solution in step (1) is 5-10%.

3. The method for preparing a highly substituted hydroxypropyl distarch phosphate according to claim 1, characterized in that, The settling time in step (3) is 3 hours.

4. The method for preparing a highly substituted hydroxypropyl distarch phosphate according to claim 1, characterized in that, The specific preparation method of high-substituted hydroxypropyl starch in step (4) is as follows: 4-7 parts of anhydrous Na2SO4 are placed in 40-80 parts of water and stirred until completely dissolved. Then, 35-65 parts of the pretreated starch sample are added and stirred evenly. The pH value of the reaction system is adjusted to 10.5-11.0, 5-15 parts of propylene oxide are added, the reaction time is maintained at 25-30 h, and the reaction temperature is 45℃. 1-2 parts of sodium tripolyphosphate and 15-20 parts of sodium trimetaphosphate are added, and the reaction time is maintained at 3-5 h.

5. The method for preparing a highly substituted hydroxypropyl distarch phosphate according to claim 1, characterized in that, In step (5), the pH value is adjusted to 5.0-5.5 using 6.0% dilute hydrochloric acid to terminate the reaction.

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