A preparation method of composite modified hydroxypropyl starch ether

Abstract

This application provides a method for preparing a composite modified hydroxypropyl starch ether, relating to the technical field of starch ether preparation. This application uses corn starch and cassava starch as raw materials, and prepares the modified hydroxypropyl starch ether through premixing, alkalization, and high- and low-temperature layered etherification. Sodium citrate is added as a stabilizer during the etherification process. The resulting product has advantages such as high hydroxypropyl content, high viscosity, high solution transparency, high whiteness, and low ash content. Furthermore, the production cost is reduced, meeting the market demand for high-quality, highly stable, and low-cost starch ethers.

Description

Technical Field

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

[0002] Hydroxypropyl starch ether is a nonionic starch ether prepared from natural tapioca starch, corn starch, and potato starch through processes such as alkalization, etherification, neutralization, and acidification. It has widespread applications in the construction, pharmaceutical, food, and petroleum industries. The various content indicators of the hydroxypropyl starch ether substitution reaction are related to the preparation process, equipment, operating techniques, and raw material quality. Raw material variations have the greatest impact and are also key to controlling production costs. Currently, the main starch raw materials on the market are corn starch, tapioca starch, and potato starch. Corn starch produces products with higher whiteness but lower viscosity, making it a low-end product with a lower price. Tapioca starch produces finished products with lower whiteness but higher viscosity, with high-end products reaching viscosities of 12,000 to 14,000, representing a large market share. Potato starch, due to its inherently high whiteness, is primarily used in high-end products. However, its relatively low gelatinization temperature (64°C) necessitates strict temperature control during the etherification reaction, and the long reaction cycle at low temperatures leads to high processing costs.

[0003] Currently, hydroxypropyl starch ethers on the market are mainly prepared using a single raw material. For example, patent CN116854832A discloses a hydrophobically modified starch ether and its preparation method and application. The method uses corn starch as the raw material, wets the starch with distilled water, adds dimethyl sulfoxide while stirring, and simultaneously adds alkali solution. The starch paste is then heated at 90-100°C to obtain a starch paste. The starch paste is then adjusted to the reaction temperature, and C12-C14 alkyl glycidyl ether is added dropwise. The mixture is stirred and kept warm, and alkali solution is added multiple times during the reaction. After the reaction is completed, the mixture is neutralized with acid, and ethanol is added dropwise to precipitate the starch. After washing, drying, crushing, and sieving, the hydrophobically modified starch ether is obtained. This invention introduces long-chain hydrophobic groups into the hydrophilic starch through ether bonds, resulting in a modified starch ether with high chemical stability. For example, patent CN116769853A provides a method for preparing enzyme-modified corn starch as an alternative to hydroxypropyl starch. The method uses corn starch as the raw material and uses maltogenic amylase and hexose oxidase for enzymatic hydrolysis. The hydrolyzed solution is centrifuged, washed with water, and dried to obtain modified corn starch. The modified corn starch prepared using the dual-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 hydroxypropyl starch ether. For another example, patent CN119143892A discloses a low-cost method for preparing potato hydroxypropyl starch ether. The method first involves thoroughly mixing an alkalizing agent, a solvent, and an inhibitor, then adding potato starch for alkalization. An etherifying agent is then added, and the temperature is raised for modification to obtain potato hydroxypropyl starch ether. The resulting product has advantages such as high hydroxypropyl content, high viscosity, high solution transparency, and low ash content.

[0004] All of the above technologies use a single raw material to produce hydroxypropyl starch ethers. Corn starch-based starch ethers have a viscosity of ≤3,000, a whiteness between 79 and 85, a transmittance of <6%, and a hydroxypropyl content of 15% to 20%. Cassava starch-based starch ethers have a standard viscosity between 3,500 and 5,500, with high-viscosity products ranging from 10,000 to 14,000. They also have a whiteness between 75 and 83, a transmittance of 8% to 15%, and a hydroxypropyl content of 18% to 25%. Potato starch-based starch ethers have a high whiteness of 85 to 95, a viscosity between 8,000 and 14,000, a transmittance of 10% to 20%, and a hydroxypropyl content of 20% to 25%. While potato starch ethers offer superior performance compared to other raw materials, potato starch is relatively expensive, leading to high production costs. In the fiercely competitive market, high-quality starch ethers with stable quality, excellent quality, and low cost are always sought after. Summary of the Invention

[0005] The purpose of the present invention is to overcome the shortcomings of the prior art and provide a method for preparing a composite modified hydroxypropyl starch ether. By adding a stabilizer and adopting a high-low temperature layered etherification process, hydroxypropyl starch ether is prepared using corn starch and cassava starch as composite raw materials to obtain modified hydroxypropyl starch ether with high whiteness, low ash content, light transmittance, and high hydroxypropyl group content, which can better meet the market demand for high-quality, high-stability, and low-cost starch ethers.

[0006] To achieve the above objectives, the technical solutions adopted in this application are as follows:

[0007] A method for preparing a composite modified hydroxypropyl starch ether comprises the following steps:

[0008] (1) Premixing of raw materials: premixing starch, alkalizer, and inhibitor to obtain premixed raw materials;

[0009] (2) Alkalization: adding alcohol to the premixed raw materials and heating them to alkalize them to obtain an alkalized product;

[0010] (3) Low-temperature etherification: Add an etherifying agent, alcohol, and sodium citrate to the alkalized product for low-temperature etherification;

[0011] (4) High temperature etherification: The temperature is raised to carry out high temperature etherification. The high temperature etherification process is divided into stage I high temperature etherification and stage II high temperature etherification;

[0012] (5) Recovery: Condensate and recover the solvent, crush it, and you are done.

[0013] Furthermore, in step (1), the starch is cassava starch and corn starch in a weight ratio of (68-90):(10-32).

[0014] This application selects cassava starch and corn starch as mixed raw materials. The peak viscosity of cassava starch is 800BU, and the peak viscosity of corn starch is 589BU. By optimizing the ratio of the two starches and balancing their peak viscosities, the high-temperature etherification temperature of cassava starch is reduced and the high-temperature etherification time is shortened, which also has a certain impact on the improvement of the viscosity, hydroxypropyl content and light transmittance of the product performance.

[0015] Furthermore, in step (1), the alkalizer is an alkali metal hydroxide, preferably sodium hydroxide and / or potassium hydroxide; and the weight ratio of the alkalizer to the starch is (4-8):100.

[0016] Furthermore, in step (1), the inhibitor is an alkali metal salt, preferably one or more of sodium sulfate, sodium chloride, sodium carbonate, and sodium bicarbonate; and the weight ratio of the inhibitor to starch is (5-7):100.

[0017] Furthermore, in step (1), the premixing temperature is 28-33° C., and the premixing time is 40-60 min.

[0018] In the present application, the raw materials are premixed before the alkalization treatment, which helps to improve the dispersion uniformity between the raw materials, make the subsequent reaction more uniform, and avoid agglomeration caused by direct alkalization reaction; in addition, controlling the premixing temperature can also allow a certain reaction between the starch and the alkali to occur in advance, thereby increasing the degree of alkalization reaction and improving product performance.

[0019] Furthermore, 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.

[0020] Furthermore, in step (2), the alkalization temperature is not higher than 41°C, preferably 35-41°C; and the alkalization time is 60-90 minutes.

[0021] Furthermore, in step (2), after the alkalization is completed, the process further includes: evacuating the chamber for 10 minutes to remove water.

[0022] Furthermore, in step (3), the etherifying agent is selected from one or more of chloroacetic acid, sodium chloroacetate, methyl chloride, ethyl chloride, 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 and sodium chloroacetate is 2:1.

[0023] Furthermore, 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 weight ratio of the alcohol to the starch is (10-20):100.

[0024] 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 starch and etherifying agent, thereby helping to improve the product transmittance, viscosity and hydroxypropyl content, thereby improving product quality.

[0025] Furthermore, in step (3), the weight ratio of sodium citrate to starch is (10-15):100.

[0026] The present application adds sodium citrate during the low-temperature etherification stage to stabilize the reaction process of the blended materials, reduce the formation of particles during the reaction, avoid a sharp increase in pressure or excessive temperature rise, ensure the uniformity of the reaction and the stability of the product, thereby improving the whiteness, transmittance and hydroxypropyl group content of the product to a certain extent.

[0027] Furthermore, in step (3), the temperature of the low-temperature etherification is 46-55° C., and the time is 20-50 min.

[0028] Furthermore, in step (4), the temperature of the high-temperature etherification in stage I is 60-65° C., and the time is 2 h to 3 h.

[0029] Furthermore, in step (5), the temperature of the high-temperature etherification in stage II is 80-85° C., and the time is 1.5 h to 2 h.

[0030] Furthermore, in step (6), pulverizing means pulverizing the material until the transmittance through a 100-mesh sieve is greater than 99%.

[0031] The present application adopts a high-low temperature layered etherification method to obtain a composite modified hydroxypropyl starch ether, wherein the low-temperature etherification allows the residual alkali to fully decompose the starch and prolong the alkalization time. At the same time, the low-temperature and mild etherification can also avoid the uncontrollable release pressure due to excessive initial temperature, resulting in an uncontrollable reaction process, thereby affecting the performance of the product; in addition, the early low-temperature etherification first consumes most of the etherifying agent, so that the temperature rise and pressure in the later high-temperature stage are controlled within a certain range. The etherification process of first low temperature and then high temperature is coordinated and controlled to improve the whiteness, transmittance, hydroxypropyl group content, etc. of the product, thereby improving the product quality.

[0032] Compared with the prior art, this application has the following beneficial effects:

[0033] 1. This application uses corn starch and cassava starch as raw materials, and prepares modified hydroxypropyl starch ether through premixing, alkalization, and high and low temperature layered etherification. The cost is low, and the product has different degrees of improvement in indicators such as whiteness, transmittance, and hydroxypropyl group content, meeting the market demand for high-quality, high-stability, and low-cost starch ethers.

[0034] 2. This application prepares composite modified hydroxypropyl starch ether by adopting a high-low temperature layered etherification method and reasonably controlling the etherification conditions to improve the whiteness, transmittance, hydroxypropyl group content, etc. of the product, thereby improving the product quality; adding a certain amount of alcohol during the low-temperature etherification process helps to make the reaction more uniform, thereby being able to improve the transmittance, whiteness and hydroxypropyl content of the product to a certain extent.

[0035] 3. The indicators of the composite modified hydroxypropyl starch ether prepared by the method of the present application are: whiteness can reach more than 90%, 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 is less than 10%, and ash content is ≤13%. DETAILED DESCRIPTION

[0036] The following non-limiting examples are provided to enable those skilled in the art to more fully understand the present application, but are not intended to limit the present application in any way. The following contents are merely illustrative of the scope of protection claimed in the present application. Those skilled in the art may make various changes and modifications to the invention of the present application based on the disclosed contents, and such changes and modifications shall also fall within the scope of protection claimed in the present application.

[0037] Unless otherwise specified, all chemical reagents used in the examples of this application were obtained through conventional commercial channels.

[0038] The present application will be further described below in the form of specific embodiments.

[0039] Example 1

[0040] This embodiment relates to a method for preparing a composite modified hydroxypropyl starch ether, comprising the following steps:

[0041] (1) Premixing of raw materials: 90 parts of cassava starch, 10 parts of corn starch, 4 parts of sodium hydroxide, and 5 parts of sodium sulfate were added to a reactor and premixed at 28°C for 60 minutes to obtain a premixed raw material;

[0042] (2) Alkalization: add 40 parts of ethanol to the premixed raw materials, heat, and alkalize at 35°C for 60 minutes to obtain the alkalized product, and vacuum for 20 minutes to remove the water;

[0043] (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 46°C for 20 minutes;

[0044] (4) Stage I high-temperature etherification: The temperature was raised to 60°C and the stage I high-temperature etherification was carried out for 2 hours;

[0045] (5) Stage II high-temperature etherification: Continue to raise the temperature to 80°C and perform stage II high-temperature etherification for 1.5 hours;

[0046] (6) Recovery: Condensate and recover the solvent, and crush it to a 100 mesh with a transmittance greater than 99%.

[0047] It should be noted that the parts involved in the embodiments are all parts by mass, and the alkalizing agent, inhibitor, alcohol, and etherifying agent can all be replaced with other types specified in this application, and can achieve the technical effects of this application, and do not constitute a limitation on this application.

[0048] Example 2

[0049] This embodiment relates to a method for preparing a composite modified hydroxypropyl starch ether, comprising the following steps:

[0050] (1) Premixing of raw materials: 88 parts of cassava starch, 12 parts of corn starch, 4 parts of sodium hydroxide, and 5 parts of sodium sulfate were added to a reactor and premixed at 33°C for 60 minutes to obtain a premixed raw material;

[0051] (2) Alkalization: add 40 parts of ethanol to the premixed raw materials, heat, and alkalize at 41°C for 90 minutes to obtain the alkalized product, and evacuate the mixture for 10 minutes to remove the water;

[0052] (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 minutes;

[0053] (4) Stage I high-temperature etherification: The temperature was raised to 65°C and the stage I high-temperature etherification was carried out for 2 hours;

[0054] (5) Stage II high-temperature etherification: Continue to raise the temperature to 85°C and perform stage II high-temperature etherification for 1.5 hours;

[0055] (6) Recovery: Condensate and recover the solvent, and crush it to a 100 mesh with a transmittance greater than 99%.

[0056] Example 3

[0057] The difference from Example 2 is that the starch raw materials are 68 parts of tapioca starch and 32 parts of corn starch, and the rest are the same as in Example 2.

[0058] Example 4

[0059] The difference from Example 3 is that the starch raw materials are 50 parts of tapioca starch and 50 parts of corn starch, and the rest are the same as in Example 3.

[0060] Example 5

[0061] The difference from Example 3 is that the starch raw materials are 40 parts of tapioca starch and 60 parts of corn starch, and the rest are the same as in Example 3.

[0062] Example 6

[0063] The difference from Example 3 is that the low-temperature etherification temperature is 30°C.

[0064] Example 7

[0065] The difference from Example 3 is that the high-temperature etherification temperature of stage I is 55° C., and the rest is the same as Example 3.

[0066] Comparative Example 1

[0067] 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 Example 3.

[0068] Comparative Example 2

[0069] 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 Example 3.

[0070] Comparative Example 3

[0071] The difference from Example 3 is that corn starch is replaced by an equal amount of potato starch, and the rest is the same as Example 3.

[0072] Comparative Example 4

[0073] The difference from Example 3 is that the temperature during the premixing process is 41° C., and the rest is the same as Example 3.

[0074] Comparative Example 5

[0075] This comparative example relates to a method for preparing a composite modified hydroxypropyl starch ether, which differs from Example 3 in that there is no premixing step. The specific steps are as follows:

[0076] (1) Alkalization: 88 parts of cassava starch, 12 parts of corn starch, 4 parts of sodium hydroxide, and 5 parts of sodium sulfate were put into a reactor, 40 parts of ethanol were added, and the reaction was alkalized at 41°C for 90 minutes to obtain an alkalized product. The water was removed by evacuation for 10 minutes.

[0077] (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 perform low-temperature etherification for 20 minutes;

[0078] (3) Stage I high-temperature etherification: The temperature was raised to 65°C and the stage I high-temperature etherification was carried out for 2 hours;

[0079] (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 hours;

[0080] (5) Recovery: Condensate and recover the solvent, and crush it to a 100 mesh with a transmittance greater than 99%.

[0081] Comparative Example 6

[0082] This comparative example relates to a method for preparing a composite modified hydroxypropyl starch ether, which differs from Example 3 in that there is no low-temperature etherification step. The specific steps are as follows:

[0083] (1) Premixing of raw materials: 88 parts of cassava starch, 12 parts of corn starch, 4 parts of sodium hydroxide, and 5 parts of sodium sulfate were added to a reactor and premixed at 33°C for 40 minutes to obtain a premixed raw material;

[0084] (2) Alkalization: add 40 parts of ethanol to the premixed raw materials, heat, and alkalize at 41°C for 90 minutes to obtain the alkalized product, and evacuate the mixture for 10 minutes to remove the water;

[0085] (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 minutes;

[0086] (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 hours;

[0087] (5) Recovery: Condensate and recover the solvent, and crush it to a 100 mesh with a transmittance greater than 99%.

[0088] Comparative Example 7

[0089] This comparative example relates to a method for preparing a composite modified hydroxypropyl starch ether. The difference from Example 3 is that there is no high-temperature etherification step I. The specific steps are as follows:

[0090] (1) Premixing of raw materials: 88 parts of cassava starch, 12 parts of corn starch, 4 parts of sodium hydroxide, and 5 parts of sodium sulfate were added to a reactor and premixed at 33°C for 40 minutes to obtain a premixed raw material;

[0091] (2) Alkalization: add 40 parts of ethanol to the premixed raw materials, heat, and alkalize at 41°C for 90 minutes to obtain the alkalized product, and evacuate the mixture for 10 minutes to remove the water;

[0092] (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 minutes;

[0093] (4) High-temperature etherification: Heat to 85°C and perform stage II high-temperature etherification for 3.5 hours;

[0094] (5) Recovery: Condensate and recover the solvent, and crush it to a 100 mesh with a transmittance greater than 99%.

[0095] Comparative Example 8

[0096] The difference from Example 3 is that sodium citrate is not added during the low-temperature etherification process in step (3), and the rest is the same as Example 3.

[0097] Comparative Example 9

[0098] The difference from Example 3 is that the sodium citrate in the low-temperature etherification process of step (3) is replaced by an equal amount of citric acid, and the rest is the same as Example 3.

[0099] Comparative Example 10

[0100] The difference from Example 3 is that no ethanol is added during the low-temperature etherification process in step (3), and the rest is the same as Example 3.

[0101] Test example

[0102] 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. The whiteness of the starch ether was tested in accordance with GB / T22727.6-2008, and the whiteness value was calculated by comparing the reflectivity of the sample to blue light (wavelength 457 nm) with the reflectivity of a standard white board; the light transmittance (2% aqueous solution) was tested in accordance with GB / T34263-2017; the viscosity (5% aqueous solution, 20°C detection temperature) was tested in accordance with GB / T22427.7-2023; the hydroxypropyl group content was tested in accordance with GB / T40998-2021; the moisture content (oven method) was tested in accordance with GB / T12087-2008; and the ash content (carbonized by heating in a platinum crucible, dried by calcination in a Maboise furnace and weighed) was tested in accordance with GB / T22427.1-2008.

[0103] The performance test results are shown in Table 1 below.

[0104] Table 1

[0105]

[0106] As can be seen from Table 1, after gradually increasing the proportion of corn starch in Examples 3, 4, and 5, the viscosity decreases gradually, and the hydroxypropyl content and light transmittance also gradually decrease, indicating that the amount of corn starch added has a great influence on the viscosity and hydroxypropyl indexes, and the ratio of cassava starch to corn starch is optimal at 68:32.

[0107] Comparative Example 5 omits the premixing step, and the corresponding two raw materials are mixed unevenly. The whiteness, transmittance, viscosity and hydroxypropyl content of the prepared modified hydroxypropyl starch ether are significantly lower than those of Examples 1, 2 and 3. This shows that the premixing step affects the performance of the product.

[0108] In Comparative Example 6, the material is directly heated to enter the high-temperature etherification stage I after alkalization. It can be seen that its hydroxypropyl content is too low. Firstly, this is because the low-temperature etherification stage is omitted, resulting in a shortened overall etherification time; secondly, the low-temperature etherification stage is also a continuation of the alkalization. The more starch molecules are decomposed, the better the etherification effect.

[0109] In Comparative Examples 6 and 7, the low-temperature etherification stage and the first high-temperature etherification stage were omitted, respectively, and the resulting products had lower transmittance, viscosity, and hydroxypropyl content. Compared with Comparative Examples 7 and 8, the low-temperature etherification temperature and high-temperature etherification conditions were changed in Examples 6 and 7, and the transmittance, viscosity, and hydroxypropyl content of the resulting products were improved, indicating that the high- and low-temperature layered etherification steps help improve product performance. However, the transmittance and hydroxypropyl content of Examples 6 and 7 were also reduced compared to Example 3, indicating that the low-temperature etherification temperature is preferably 46-55°C and the first high-temperature etherification temperature is preferably 60-65°C.

[0110] Compared to Comparative Examples 1 and 2, the modified hydroxypropyl starch ether prepared in Example 3 exhibited relatively balanced transmittance, viscosity, and hydroxypropyl content. Furthermore, compared to Comparative Example 2, the raw materials in Example 3 were cassava starch and corn starch in a ratio of 68:32. Since corn starch is cheaper than cassava starch, the production cost of Example 3 was lower than that of Comparative Example 2.

[0111] In addition, compared with Example 3, the low-temperature etherification process of Comparative Example 8 did not add sodium citrate, and the whiteness, transmittance, viscosity, and hydroxypropyl content of the obtained product all decreased significantly; Comparative Example 9 used citric acid 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 shows that the addition of sodium citrate during the low-temperature etherification process stabilizes the reaction process of the mixed material, reduces the formation of particles during the reaction, avoids a sharp increase in pressure or excessive temperature rise, ensures the uniformity of the reaction and the stability of the product, thereby improving the whiteness, transmittance, and hydroxypropyl group content of the product to a certain extent, while citric acid cannot achieve the effect of the present application. The low-temperature etherification process of Comparative Example 10 did not add ethanol, and the 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 be concluded that the addition of alcohol and sodium citrate during the low-temperature etherification process also has a certain synergistic effect. When alcohol and sodium citrate are added at the same time, the comprehensive performance of the obtained product reaches the best.

[0112] In summary, the present application uses a certain proportion of corn starch and cassava starch as raw materials, and prepares modified hydroxypropyl starch ether through premixing, alkalization, and high and low temperature layered etherification. The production cost is reduced, and the product has high whiteness, transmittance, and hydroxypropyl group content, meeting the market demand for high-quality, high-stability, and low-cost starch ethers.

[0113] The above description of the embodiments is intended to facilitate understanding and use of the invention by those skilled in the art. It will be apparent that those skilled in the art can readily make various modifications to these embodiments and apply the general principles described herein to other embodiments without requiring inventive effort. Therefore, this application is not limited to the above-described embodiments. Any improvements and modifications made by those skilled in the art based on the disclosure of this application, without departing from the scope of this application, should be within the scope of protection of this application.

Claims

1. A method for preparing a composite modified hydroxypropyl starch ether, characterized in that: The following steps are involved: (1) Premixing of raw materials: premixing starch, alkalizer, and inhibitor to obtain premixed raw materials; (2) Alkalization: adding alcohol to the premixed raw materials and heating them to alkalize them 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: The temperature is raised to carry out high temperature etherification, which is divided into stage I high temperature etherification and stage II high temperature etherification; (5) Recovery: Condensate and recover the solvent, crush it, and obtain the product; The starch is cassava starch and corn starch in a weight ratio of (68-90): (10-32); The premixing temperature is 28-33°C and the premixing time is 40-60 minutes; The temperature of the low-temperature etherification is 46-55°C, and the time is 20-50 minutes; the temperature of the high-temperature etherification in stage I is 60-65°C, and the time is 2 hours to 3 hours; the temperature of the high-temperature etherification in stage II is 80-85°C, and the time is 1.5 hours to 2 hours.

2. The method for preparing the composite modified hydroxypropyl starch ether according to claim 1, wherein In step (1), the alkalizer is an alkali metal hydroxide, and the weight ratio of the alkalizer to the starch is (4-8):100; the inhibitor is an alkali metal salt, and the weight ratio of the inhibitor to the starch is (5-7):

100.

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

100.

4. The method for preparing the composite modified hydroxypropyl starch ether according to claim 1, wherein In step (2), the alkalization temperature is not higher than 41° C., and the alkalization time is 60 to 90 minutes.

5. The method for preparing the composite modified hydroxypropyl starch ether according to claim 1, wherein In step (3), the etherifying agent is selected from one or more of chloroacetic acid, sodium chloroacetate, methyl chloride, ethyl chloride, 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.

6. The method for preparing the composite modified hydroxypropyl starch ether according to claim 1, wherein In step (3), the weight ratio of sodium citrate to starch is (10-20):

100.

7. The method for preparing 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 and diethylene glycol, and the weight ratio of the alcohol to starch is (10-15):100.

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