Preparation method of composite modified hydroxypropyl starch ether

Abstract

The invention provides a preparation method of composite modified hydroxypropyl starch ether, and relates to the technical field of starch ether preparation. Corn starch and cassava starch are used as raw materials, the modified hydroxypropyl starch ether is prepared through premixing, alkalization and high-low temperature layering etherification, sodium citrate is added in the etherification process to serve as a stabilizer, the produced product has the advantages of being high in hydroxypropyl content, viscosity, solution transparency and whiteness, low in ash content and the like, the production cost is reduced, and the product is suitable for industrial production. The requirements of the market on high-quality, high-stability and low-cost starch ether are met.

Description

Technical Field

[0001] The present application relates to the technical field of starch ether preparation, and particularly relates to a preparation method of a composite modified hydroxypropyl starch ether. Background Art

[0002] Hydroxypropyl starch ether is a non-ionic starch ether prepared from natural cassava starch, corn starch, potato starch, etc. through processes such as alkalization, etherification, neutralization, and acid-base treatment, and is widely used in the fields of construction, medicine, food, petroleum, etc. The content indexes of the substitution reaction of hydroxypropyl starch ether are related to the preparation process, preparation equipment, operation technology, and raw material quality. Among them, the change of raw materials has the greatest impact and is also the key point for controlling production costs. Currently, the main starch raw materials on the market are corn starch, cassava starch, and potato starch. Among them, the products produced from corn starch have a relatively high whiteness, but the finished product viscosity is low, and they can only be used as low-end products in the actual market with a low selling price; the finished products produced from cassava starch have a relatively low whiteness, but a high viscosity, and the viscosity of high-end products can reach (12000 - 14000), accounting for a large proportion in the market; potato starch has a high natural whiteness and is mainly used to produce high-end products, but its gelatinization temperature is relatively low (64°C), with strict requirements for temperature control during the etherification reaction process, and a long low-temperature reaction cycle, resulting in too high processing costs.

[0003] At present, hydroxypropyl starch ethers on the market are mainly prepared using a single raw material. For example, Patent CN116854832A discloses a hydrophobic modified starch ether and its preparation method and application. It uses corn starch as the raw material, wets the starch with distilled water, adds dimethyl sulfoxide under stirring, and simultaneously drops in an alkali solution. Then, it is heated to gelatinize at 90 - 100 °C to obtain a starch paste, and then the starch paste is adjusted to the reaction temperature, and C12 - C14 alkyl glycidyl ether is dropped in, and the reaction is carried out with heat preservation and stirring. The alkali solution is added multiple times during the process. After the reaction ends, it is neutralized with an acid, and ethanol is dropped in to precipitate the starch. After washing, drying, pulverizing, and sieving, a hydrophobic modified starch ether is obtained. The invention introduces long-chain hydrophobic groups through ether bonds on hydrophilic starch to obtain a modified starch ether with high chemical stability. Another example is Patent CN116769853A, which provides a preparation method of enzyme-modified corn starch to replace hydroxypropyl starch. It uses corn starch as the raw material and enzymatically hydrolyzes it with maltogenic amylase and hexose oxidase. The enzymatically hydrolyzed solution is centrifuged, washed with water, and dried to obtain modified corn starch. The modified corn starch prepared by the double-enzyme method has chemical properties such as viscosity, freeze-thaw stability, shear resistance, high temperature resistance, and acid resistance that are close to or better than those of hydroxypropyl starch ether. Another example is Patent CN119143892A, which discloses a preparation method of low-cost potato hydroxypropyl starch ether. First, an alkalizing agent, a solvent, and an inhibitor are fully mixed, then potato starch is added for alkalization, and then an etherifying agent is added, and the temperature is raised for modification to obtain potato hydroxypropyl starch ether. The produced product has the advantages of high hydroxypropyl content, high viscosity, high solution transparency, and low ash content.

[0004] The above technologies all use a single raw material to prepare hydroxypropyl starch ether. When using corn starch to prepare starch ether, its viscosity ≤ 3000, whiteness is between 79 - 85, light transmittance < 6%, and hydroxypropyl content is 15% - 20%; when using cassava starch to prepare starch ether, its ordinary viscosity is between 3500 - 5500, and that of the high-viscosity product is between 10000 - 14000, whiteness is between 75 - 83, light transmittance is 8% - 15%, and hydroxypropyl content is 18% - 25%; the starch ether prepared from potato starch raw material has a high whiteness, between 85 - 95, viscosity between 8000 - 14000, light transmittance 10% - 20%, and hydroxypropyl content between 20% - 25%. Although the performance of potato starch ether is superior to that of other raw materials, the price of potato starch is relatively high, resulting in high production costs. In the fierce market competition, high-quality starch ethers with stable quality, excellent quality, and relatively low cost have always been the pursuit goal. Summary of the Invention

[0005] The object of the present invention is to overcome the drawbacks existing in the prior art and provide a preparation method of a composite modified hydroxypropyl starch ether. By adding a stabilizer and adopting a high-low temperature stratified etherification process, hydroxypropyl starch ether is prepared with corn starch and tapioca starch as composite raw materials, and a modified hydroxypropyl starch ether with high whiteness, low ash content, high light transmittance and high hydroxypropyl group content is obtained, which can better meet the market demand for high-quality, high-stability and low-cost starch ether.

[0006] To achieve the above object, the technical solutions adopted in this application are as follows: A preparation method of a composite modified hydroxypropyl starch ether, comprising the following steps: (1) Raw material premixing: Premix starch, alkalizing agent and inhibitor to obtain a premixed raw material; (2) Alkalization: Add alcohol to the premixed raw material and raise the temperature for alkalization to obtain an alkalized product; (3) Low-temperature etherification: Add an etherifying agent, alcohol and sodium citrate to the alkalized product for low-temperature etherification; (4) High-temperature etherification: Raise the temperature for high-temperature etherification, and the high-temperature etherification process is divided into stage I high-temperature etherification and stage II high-temperature etherification; (5) Recovery: Condense and recover the solvent, and pulverize to obtain the product.

[0007] Further, in step (1), the starch is tapioca starch and corn starch with a weight ratio of (68 - 90):(10 - 32).

[0008] This application selects tapioca starch and corn starch as mixed raw materials. The peak viscosity of tapioca starch is 800 BU, and the peak viscosity of corn starch is 589 BU. By optimizing the ratio of the two starches, the peak viscosities of the two are balanced, which not only reduces the temperature of high-temperature etherification of tapioca starch and shortens the high-temperature etherification time, but also has a certain impact on the improvement of the viscosity, hydroxypropyl content and light transmittance of the product performance.

[0009] Further, in step (1), the alkalizing agent is an alkali metal hydroxide, preferably sodium hydroxide and / or potassium hydroxide; the weight ratio of the alkalizing agent to starch is (4 - 8):100.

[0010] Further, in step (1), the inhibitor is an alkali metal salt, preferably one or more of sodium sulfate, sodium chloride, sodium carbonate, and sodium bicarbonate; the weight ratio of the inhibitor to starch is (5 - 7):100.

[0011] Further, in step (1), the premixing temperature is 28 - 33 °C and the time is 40 - 60 min.

[0012] Before the alkalization treatment, the raw materials are premixed in this application, which helps to improve the dispersion uniformity among the raw materials, make the subsequent reaction more uniform, and avoid the agglomeration phenomenon caused by directly carrying out the alkalization reaction. Additionally, by controlling the premixing temperature, a certain reaction can occur in advance between the starch and the alkali, thereby increasing the degree of alkalization reaction and improving the product performance.

[0013] Further, in step (2), the alcohol is selected from one or more of methanol, ethanol, isopropanol, n-butanol, tert-butanol, acetone, and diethylene glycol; the weight ratio of the alcohol to the starch is (40 - 45):100.

[0014] Further, in step (2), the alkalization temperature is not higher than 41°C, preferably 35 - 41°C; the alkalization time is 60 - 90 min.

[0015] Further, in step (2), after the alkalization is completed, it also includes: evacuating for 10 min to discharge water.

[0016] Further, in step (3), the etherifying agent is selected from one or more of chloroacetic acid, sodium chloroacetate, chloromethane, chloroethane, propylene glycol ether, isopropyl glycidyl ether, propylene oxide, and ethylene oxide, and the weight ratio of the etherifying agent to the starch is (45 - 50):100; preferably, the etherifying agent is a mixture of propylene oxide and sodium chloroacetate, and the mixing mass ratio of propylene oxide to sodium chloroacetate is 2:1.

[0017] Further, in step (3), the alcohol is selected from one or more of methanol, ethanol, isopropanol, n-butanol, tert-butanol, acetone, and diethylene glycol. The alcohol added in this step is the same as or different from the alcohol in step (2), and the dosage of the alcohol has a weight ratio of (10 - 20):100 to the starch.

[0018] Experiments have found that adding a certain amount of alcohol during the low-temperature etherification process can, to a certain extent, promote the uniform contact reaction between the starch and the etherifying agent, thereby helping to improve the product light transmittance, viscosity, and hydroxypropyl content, and improving the product quality. Further, in step (3), the weight ratio of sodium citrate to the starch is (10 - 15):100.

[0019] In this application, by adding sodium citrate during the low-temperature etherification stage, it plays a stabilizing role in the reaction process of the blended materials, reduces the formation of particles during the reaction, avoids a sharp increase in pressure or too rapid a temperature rise, ensures the uniformity of the reaction and the stability of the product, and thus can, to a certain extent, improve the whiteness, light transmittance, and hydroxypropyl group content of the product.

[0020] Further, in step (3), the temperature of the low-temperature etherification is 46 - 55°C, and the time is 20 - 50 min.

[0021] Further, in step (4), the temperature of the first-stage high-temperature etherification is 60-65°C, and the time is 2-3 hours.

[0022] Further, in step (5), the temperature of the second-stage high-temperature etherification is 80-85°C, and the time is 1.5-2 hours.

[0023] Further, in step (6), pulverization means that the material is pulverized to a passing rate through a 100-mesh sieve greater than 99%.

[0024] This application uses a high-low temperature stratified etherification method to treat and obtain a composite modified hydroxypropyl starch ether. Among them, low-temperature etherification allows the residual alkali to fully decompose starch, prolongs the alkalization time, and at the same time, low-temperature gentle etherification can also avoid the uncontrollable release of pressure due to too high an initial temperature, resulting in an uncontrollable reaction process, thus affecting the product performance; in addition, most of the etherifying agent is consumed by the low-temperature etherification reaction in the early stage, so that the temperature rise and pressure in the later high-temperature stage are controlled within a certain range. The etherification process from low temperature to high temperature cooperates with and controls the etherification conditions, so that the product is improved in whiteness, light transmittance, hydroxypropyl group content, etc., and the product quality is improved.

[0025] Compared with the prior art, this application has the following beneficial effects: 1. This application uses corn starch and cassava starch as raw materials, and prepares a modified hydroxypropyl starch ether through premixing, alkalization, and high-low temperature stratified etherification. The cost is low, and the product is improved to varying degrees in indicators such as whiteness, light transmittance, and hydroxypropyl group content, meeting the market's demand for high-quality, high-stability, and low-cost starch ethers.

[0026] 2. This application prepares a composite modified hydroxypropyl starch ether by using a high-low temperature stratified etherification method and reasonably controlling the etherification conditions, so that the product is improved in whiteness, light transmittance, hydroxypropyl group content, etc., and the product quality is improved; adding a certain amount of alcohol during the low-temperature etherification process helps the reaction to be more uniform, thereby being able to improve the light transmittance, whiteness, and hydroxypropyl content of the product to a certain extent.

[0027] 3. The indicators of the composite modified hydroxypropyl starch ether prepared by the method of this application are: whiteness can reach more than 90%, light transmittance of 2% aqueous solution is 13-16%, viscosity of 5% aqueous solution is 4900-5100 mPa·s, hydroxypropyl content is 23-25%, moisture content <10%, and ash content ≤13%. Specific embodiments

[0028] The following non-limiting examples can enable those of ordinary skill in the art to more comprehensively understand the present application, but do not limit the present application in any way. The following content is merely an exemplary illustration of the scope claimed in the present application. Those skilled in the art can make various changes and modifications to the invention of the present application based on the disclosed content, and they should also fall within the scope claimed in the present application.

[0029] All kinds of chemical reagents used in the embodiments of the present application are obtained through conventional commercial channels unless otherwise specified.

[0030] The present application will be further described below by way of specific examples.

[0031] Example 1 This example relates to a preparation method of a composite modified hydroxypropyl starch ether, which includes the following steps: (1) Raw material premixing: 90 parts of tapioca starch, 10 parts of corn starch, 4 parts of sodium hydroxide, and 5 parts of sodium sulfate are put into a reaction kettle, and premixed at 28°C for 60 minutes to obtain premixed raw materials; (2) Alkalization: 40 parts of ethanol are added to the premixed raw materials, heated, and alkalized at 35°C for 60 minutes to obtain an alkalized product, and the water is discharged by vacuum for 20 minutes; (3) Low-temperature etherification: 30 parts of propylene oxide, 15 parts of sodium chloroacetate, 10 parts of ethanol, and 10 parts of sodium citrate are added to the alkalized product, and low-temperature etherification is carried out at 46°C for 20 minutes; (4) Stage I high-temperature etherification: The temperature is raised to 60°C, and stage I high-temperature etherification is carried out for 2 hours; (5) Stage II high-temperature etherification: The temperature is continuously raised to 80°C, and stage II high-temperature etherification is carried out for 1.5 hours; (6) Recovery: The solvent is recovered by condensation, crushed to a mesh size of 100, and the transmittance is greater than 99%, thus obtaining the product.

[0032] It should be noted that the parts involved in the examples are all parts by mass. The alkalizing agent, inhibitor, alcohol, and etherifying agent can all be replaced with other types defined in the present application, and the technical effects of the present application can be achieved, which does not constitute a limitation to the present application.

[0033] Example 2 This example relates to a preparation method of a composite modified hydroxypropyl starch ether, which includes the following steps: (1) Raw material premixing: 88 parts of tapioca starch, 12 parts of corn starch, 4 parts of sodium hydroxide, and 5 parts of sodium sulfate are put into a reaction kettle, and premixed at 33°C for 60 minutes to obtain premixed raw materials; (2) Alkalization: 40 parts of ethanol are added to the premixed raw materials, heated, and alkalized at 41°C for 90 minutes to obtain an alkalized product, and the water is evacuated for 10 minutes to discharge the water; (3) Low-temperature etherification: Add 30 parts of propylene oxide, 15 parts of sodium chloroacetate, 10 parts of ethanol, and 10 parts of sodium citrate to the alkalized product, and carry out low-temperature etherification at 55 °C for 50 min; (4) High-temperature etherification in stage I: Raise the temperature to 65 °C and carry out high-temperature etherification in stage I for 2 h; (5) High-temperature etherification in stage II: Continue to raise the temperature to 85 °C and carry out high-temperature etherification in stage II for 1.5 h; (6) Recovery: Condense and recover the solvent, and pulverize it to a mesh size of 100 with a transmittance greater than 99% to obtain the product.

[0034] Example 3 The difference from Example 2 is that the starch raw material is 68 parts of cassava starch and 32 parts of corn starch, and the rest is the same as in Example 2.

[0035] Example 4 The difference from Example 3 is that the starch raw material is 50 parts of cassava starch and 50 parts of corn starch, and the rest is the same as in Example 3.

[0036] Example 5 The difference from Example 3 is that the starch raw material is 40 parts of cassava starch and 60 parts of corn starch, and the rest is the same as in Example 3.

[0037] Example 6 The difference from Example 3 is that the low-temperature etherification temperature is 30 °C.

[0038] Example 7 The difference from Example 3 is that the high-temperature etherification temperature in stage I is 55 °C, and the rest is the same as in Example 3.

[0039] Comparative Example 1 The difference from Example 3 is that the starch raw material is only 100 parts of corn starch, and the rest is the same as in Example 3.

[0040] Comparative Example 2 The difference from Example 3 is that the starch raw material is only 100 parts of cassava starch, and the rest is the same as in Example 3.

[0041] Comparative Example 3 The difference from Example 3 is that the corn starch is replaced with an equal amount of potato starch, and the rest is the same as in Example 3.

[0042] Comparative Example 4 The difference from Example 3 is that the temperature during the premixing process is 41 °C, and the rest is the same as in Example 3.

[0043] Comparative Example 5 This comparative example relates to a preparation method of a composite modified hydroxypropyl starch ether. The difference from Example 3 is that there is no premixing step. The specific steps are as follows: (1) Alkalization: Put 88 parts of cassava starch, 12 parts of corn starch, 4 parts of sodium hydroxide, and 5 parts of sodium sulfate into a reaction kettle, add 40 parts of ethanol, alkalize at 41°C for 90 min to obtain an alkalized product, and evacuate for 10 min to remove water; (2) Low-temperature etherification: Add 30 parts of propylene oxide, 15 parts of sodium chloroacetate, 10 parts of ethanol, and 10 parts of sodium citrate to the alkalized product, and carry out low-temperature etherification for 20 min; (3) Stage I high-temperature etherification: Raise the temperature to 65°C and carry out Stage I high-temperature etherification for 2 h; (4) Stage II high-temperature etherification: Continue to raise the temperature to 85°C and carry out Stage II high-temperature etherification for 1.5 h; (5) Recovery: Condense and recover the solvent, pulverize to a 100-mesh transmittance greater than 99%, and that's it.

[0044] Comparative Example 6 This comparative example relates to a preparation method of a composite modified hydroxypropyl starch ether. The difference from Example 3 is that there is no low-temperature etherification step. The specific steps are as follows: (1) Raw material premixing: Put 88 parts of cassava starch, 12 parts of corn starch, 4 parts of sodium hydroxide, and 5 parts of sodium sulfate into a reaction kettle, premix at 33°C for 40 min to obtain premixed raw materials; (2) Alkalization: Add 40 parts of ethanol to the premixed raw materials, raise the temperature, and alkalize at 41°C for 90 min to obtain an alkalized product, and evacuate for 10 min to remove water; (3) Stage I high-temperature etherification: Add 30 parts of propylene oxide, 15 parts of sodium chloroacetate, 10 parts of ethanol, and 10 parts of sodium citrate to the alkalized product, raise the temperature to 65°C, and carry out Stage I high-temperature etherification for 140 min; (4) Stage II high-temperature etherification: Continue to raise the temperature to 85°C and carry out Stage II high-temperature etherification for 1.5 h; (5) Recovery: Condense and recover the solvent, pulverize to a 100-mesh transmittance greater than 99%, and that's it.

[0045] Comparative Example 7 This comparative example relates to a preparation method of a composite modified hydroxypropyl starch ether. The difference from Example 3 is that there is no Stage I high-temperature etherification step. The specific steps are as follows: (1) Raw material premixing: Put 88 parts of cassava starch, 12 parts of corn starch, 4 parts of sodium hydroxide, and 5 parts of sodium sulfate into a reaction kettle, premix at 33°C for 40 min to obtain premixed raw materials; (2) Alkalization: Add 40 parts of ethanol to the premixed raw materials, heat up, alkalize at 41°C for 90 min to obtain an alkalized product, and evacuate for 10 min to remove water; (3) Low-temperature etherification: Add 30 parts of propylene oxide, 15 parts of sodium chloroacetate, 10 parts of ethanol, and 10 parts of sodium citrate to the alkalized product, and carry out low-temperature etherification for 20 min; (4) High-temperature etherification: Heat up to 85°C and carry out the second-stage high-temperature etherification for 3.5 h; (5) Recovery: Condense and recover the solvent, crush to a mesh size of 100 with a transmittance greater than 99% to obtain the product.

[0046] Comparative Example 8 The difference from Example 3 is that sodium citrate is not added during the low-temperature etherification in step (3), and the rest is the same as in Example 3.

[0047] Comparative Example 9 The difference from Example 3 is that sodium citrate in the low-temperature etherification process of step (3) is replaced with an equal amount of citric acid, and the rest is the same as in Example 3.

[0048] Comparative Example 10 The difference from Example 3 is that ethanol is not added during the low-temperature etherification in step (3), and the rest is the same as in Example 3.

[0049] Test Example The composite modified hydroxypropyl starch ethers prepared in the above examples and comparative examples were tested for whiteness, light transmittance, ash content, hydroxypropyl group, and moisture content. The whiteness of the starch ether was tested according to the standard of GB / T22727.6 - 2008. The whiteness value was calculated by comparing the reflectance of the sample to blue light (wavelength 457 nm) with the reflectance of the standard white board. The light transmittance (2% aqueous solution) was tested according to GB / T34263 - 2017; the viscosity (5% aqueous solution, detection temperature 20°C) was tested according to GB / T22427.7 - 2023; the hydroxypropyl group content was tested according to GB / T40998 - 2021; the moisture content (oven method) was tested according to GB / T12087 - 2008; the ash content (by heating and carbonizing in a platinum crucible, and weighing after burning and drying in a muffle furnace) was tested with reference to GB / T22427.1 - 2008.

[0050] The performance test results are shown in Table 1 below.

[0051] Table 1

[0052] As can be seen from Table 1, after gradually increasing the proportion of corn starch in Examples 3, 4, and 5, the viscosity decreased in a gradient manner, and the hydroxypropyl content and light transmittance also gradually decreased, indicating that the addition amount of corn starch had a great impact on the viscosity and hydroxypropyl index. The optimal ratio of tapioca starch to corn starch was 68:32.

[0053] In Comparative Example 5, the premixing step was omitted, and the corresponding mixing of the two raw materials was uneven. There were obvious differences in the whiteness, light transmittance, viscosity, and hydroxypropyl content of the prepared modified hydroxypropyl starch ether compared with Examples 1, 2, and 3. It can be seen that the premixing step would affect the performance of the product.

[0054] In Comparative Example 6, the temperature of the material was directly increased to enter the high-temperature etherification in the first stage after alkalization. It can be seen that its hydroxypropyl content was too low. One reason was that the low-temperature etherification stage was omitted, resulting in a shortened overall etherification time; the other reason was that the low-temperature etherification stage was also a continuation of alkalization, and the more the number of decomposed starch molecules, the better the etherification effect.

[0055] In Comparative Examples 6 and 7, the low-temperature etherification stage and the high-temperature etherification stage in the first stage were omitted respectively, and the light transmittance, viscosity, and hydroxypropyl content of the obtained products were relatively low. Compared with Comparative Examples 7 and 8, in Examples 6 and 7, the low-temperature etherification temperature and high-temperature etherification conditions were changed, and the light transmittance, viscosity, and hydroxypropyl content of the obtained products were improved, indicating that the high-low temperature stratified etherification step was helpful to improve the performance of the product. However, the light transmittance and hydroxypropyl content of Examples 6 and 7 were also decreased compared with Example 3, indicating that the preferred low-temperature etherification temperature was 46-55 °C, and the preferred high-temperature etherification temperature in the first stage was 60-65 °C.

[0056] Compared with Comparative Example 1 and Comparative Example 2, the light transmittance, viscosity, and hydroxypropyl content of the modified hydroxypropyl starch ether prepared in Example 3 were relatively balanced. In addition, compared with Comparative Example 2, in Example 3, the raw materials were tapioca starch and corn starch with a ratio of 68:32, and the price of corn starch was cheaper than that of tapioca starch. Therefore, the production cost of Example 3 was reduced compared with Comparative Example 2.

[0057] In addition, compared with Example 3, sodium citrate was not added in the low-temperature etherification process of Comparative Example 8, and the whiteness, light transmittance, viscosity, and hydroxypropyl content of the obtained product decreased significantly; in Comparative Example 9, citric acid was used instead of sodium citrate in the low-temperature etherification process, and the whiteness, viscosity, and hydroxypropyl content of the obtained product were significantly lower than those of Example 3; this indicates that adding sodium citrate in the low-temperature etherification process plays a stabilizing role in the reaction process of the blended materials, reduces the formation of particles during the reaction, avoids a sharp increase in pressure or too rapid a temperature rise, and ensures the uniformity of the reaction and the stability of the product, thereby improving the whiteness, light transmittance, and hydroxypropyl group content of the product to a certain extent, while citric acid cannot achieve the effects of this application. Ethanol was not added in the low-temperature etherification process of Comparative Example 10, and the light transmittance, whiteness, and hydroxypropyl content of the obtained product decreased; this shows that a certain amount of ethanol in the low-temperature etherification process helps to improve the performance of the product. In addition, compared with Example 3, Comparative Example 8, and Comparative Example 10, it can also be concluded that there is a certain synergistic effect between adding alcohol and sodium citrate in the low-temperature etherification process. When alcohol and sodium citrate are added simultaneously, the comprehensive performance of the obtained product reaches the optimum.

[0058] In summary, this application uses corn starch and tapioca starch in a certain proportion as raw materials, and prepares modified hydroxypropyl starch ether through premixing, alkalization, and high- and low-temperature stratified etherification, reducing the production cost, and the product has high whiteness, light transmittance, and hydroxypropyl group content, meeting the market demand for high-quality, high-stability, and low-cost starch ether.

[0059] The above description of the embodiments is for the convenience of those of ordinary skill in the art to understand and use the invention. It is obvious that those skilled in the art can easily make various modifications to these embodiments and apply the general principles described herein to other embodiments without creative labor. Therefore, this application is not limited to the above embodiments, and the improvements and modifications made by those skilled in the art without departing from the scope of this application should be within the protection scope of this application.

Claims

1. A preparation method of a composite modified hydroxypropyl starch ether, characterized in that, It includes the following steps: (1) Raw material premixing: Premix starch, alkalizing agent, and inhibitor to obtain premixed raw materials; (2) Alkalization: Add alcohol to the premixed raw materials, raise the temperature for alkalization to obtain an alkalized product; (3) Low-temperature etherification: Add an etherifying agent, alcohol, and sodium citrate to the alkalized product for low-temperature etherification; (4) High-temperature etherification: Raise the temperature for high-temperature etherification, and the high-temperature etherification is divided into stage I high-temperature etherification and stage II high-temperature etherification; (5) Recovery: Condense and recover the solvent, and pulverize to obtain the product.

2. The preparation method of the composite modified hydroxypropyl starch ether according to claim 1, characterized in that, The starch is cassava starch and corn starch with a weight ratio of (68 - 90):(10 - 32).

3. The preparation method of the composite modified hydroxypropyl starch ether according to claim 1, characterized in that, In step (1), the alkalizing agent is an alkali metal hydroxide, and the weight ratio of the alkalizing agent to starch is (4 - 8):100; the inhibitor is an alkali metal salt, and the weight ratio of the inhibitor to starch is (5 - 7):

100.

4. The preparation method of the composite modified hydroxypropyl starch ether according to claim 1, characterized in that, In step (1), the premixing temperature is 28 - 33°C, and the time is 40 - 60 min.

5. The preparation method of the composite modified hydroxypropyl starch ether according to claim 1, characterized in that, In step (2), the alcohol is selected from one or more of methanol, ethanol, isopropanol, n-butanol, tert-butanol, acetone, and diethylene glycol, and the weight ratio of the alcohol to starch is (40 - 45):

100.

6. The preparation method of the composite modified hydroxypropyl starch ether according to claim 1, characterized in that, In step (2), the alkalization temperature is not higher than 41°C, and the alkalization time is 60 - 90 min.

7. The preparation method of the composite modified hydroxypropyl starch ether according to claim 1, characterized in that, In step (3), the etherifying agent is selected from one or more of chloroacetic acid, sodium chloroacetate, chloromethane, chloroethane, propylene glycol ether, isopropyl glycidyl ether, propylene oxide, and ethylene oxide, and the weight ratio of the etherifying agent to starch is (45 - 50):

100.

8. The preparation method of the composite modified hydroxypropyl starch ether according to claim 1, characterized in that, In step (3), the weight ratio of sodium citrate to starch is (10 - 20):

100.

9. The preparation method of the composite modified hydroxypropyl starch ether according to claim 1, wherein, In step (3), the alcohol is selected from one or more of methanol, ethanol, isopropanol, n-butanol, tert-butanol, acetone, and diethylene glycol, and the weight ratio of the alcohol to starch is (10 - 15):

100.

10. The preparation method of the composite modified hydroxypropyl starch ether according to claim 1, characterized in that, The temperature of the low-temperature etherification is 46 - 55°C, and the time is 20 - 50 min; the temperature of the stage I high-temperature etherification is 60 - 65°C, and the time is 2 h - 3 h; the temperature of the stage II high-temperature etherification is 80 - 85°C, and the time is 1.5 h - 2 h.

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