Preparation method and application of a low-bath-ratio, high-viscosity hydroxypropyl carboxymethyl composite starch ether

Abstract

This application provides a method for preparing and applying a low-bath-ratio, high-viscosity hydroxypropyl carboxymethyl composite starch ether, relating to the field of starch deep processing technology. The method includes: S1, premixing corn starch with a composite alkali catalyst and magnesium stearate, and spraying the mixture into an ethanol-water solution for alkalization; S2, adding propylene oxide for a first-stage etherification, followed by adding sodium chloroacetate for a second-stage etherification; S3, after the reaction, vacuum drying, pulverizing, and sieving to obtain the high-viscosity hydroxypropyl carboxymethyl composite starch ether; wherein the composite alkali catalyst comprises sodium hydroxide, sodium carbonate, and calcium oxide. The starch ether obtained by this method has a high degree of substitution, high viscosity, low solvent consumption, and reduced energy consumption, overcoming the shortcomings of traditional semi-dry methods.

Description

Technical Field

[0001] This application relates to the field of starch deep processing technology, and in particular to a preparation method and application of a low-bath-ratio, high-viscosity hydroxypropyl carboxymethyl composite starch ether. Background Technology

[0002] Hydroxypropyl carboxymethyl starch ether is a type of modified starch. It consists of starch molecules with both hydroxypropyl and carboxymethyl groups attached simultaneously or stepwise, making it an important category of modified starch. Compared to traditional single-modified starches such as hydroxypropyl starch and carboxymethyl starch, modified starches offer superior performance and can meet a wider range of needs, currently finding widespread application in the food and textile industries.

[0003] Traditional production methods for hydroxypropyl carboxymethyl starch ethers mainly include wet, dry, and semi-dry processes. Wet processes offer uniform reaction but require large amounts of solvent (solvent / starch mass ratio ≥3:1), resulting in high energy consumption in post-treatment and severe wastewater pollution. Dry processes use less solvent but produce uneven reactions, with a degree of substitution (DS) ≤0.15 and viscosity typically below 2000 mPa·s (5% aqueous solution, 25℃). Conventional semi-dry processes reduce solvent usage but suffer from low etherification efficiency and unstable product viscosity (CV value >15%). However, the textile printing and dyeing industry currently demands starch ethers that combine high viscosity (>5000 mPa·s), high dye penetration, and low desizing rate; existing processes struggle to balance performance and environmental friendliness.

[0004] Patent CN104831562A discloses a hydroxypropyl carboxymethyl waxy corn starch acid dye printing paste and its preparation method. The method involves uniformly dissolving waxy corn starch in an ethanol-water solution, adding sodium hydroxide for alkalization, adding propylene oxide for etherification after alkalization, adding chloroacetic acid after etherification, heating to 65-75℃ for 2-3 hours, cooling to 25-35℃, adjusting the pH of the reaction system to neutral with hydrochloric acid, washing, filtering, drying at 80℃, and pulverizing to obtain the product. Hydroxypropyl carboxymethyl waxy corn starch exhibits good acid and alkali resistance, high viscosity, good solubility, and good flowability when the degree of hydroxypropyl substitution (MS) is between 0.30 and 0.40 and the degree of carboxymethyl substitution (DS) is between 0.2 and 0.3. Although the viscosity of this hydroxypropyl carboxymethyl waxy corn starch reaches over 5000 mPa·s, the viscosity still needs improvement, and the solvent / starch mass ratio is 2:1, requiring a large amount of solvent. Therefore, it is necessary to provide a method for preparing and applying a low-bath-ratio, high-viscosity hydroxypropyl carboxymethyl composite starch ether. Summary of the Invention

[0005] The purpose of this application is to address the shortcomings of existing technologies by providing a method for preparing and applying a low-bath-ratio, high-viscosity hydroxypropyl carboxymethyl composite starch ether. By using a stepwise alkalization-composite etherification process combined with a multiphase catalyst system, a starch ether substitution degree DS≥0.25 and viscosity>8000 mPa·s can be achieved, while using less solvent, with a solvent / starch ratio ≤0.25, and reducing energy consumption.

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

[0007] According to one aspect of this application, a method for preparing a low-bath-ratio, high-viscosity hydroxypropyl carboxymethyl composite starch ether is provided, comprising the following steps:

[0008] S1. Premix corn starch with composite alkaline catalyst and magnesium stearate, and then spray it into ethanol for alkalization.

[0009] S2. Add propylene oxide for a first-stage etherification, then add sodium chloroacetate for a second-stage etherification;

[0010] S3. After the reaction is complete, vacuum dry, pulverize and sieve to obtain high-viscosity hydroxypropyl carboxymethyl composite starch ether.

[0011] Further, in step S1, the composite alkali catalyst comprises sodium hydroxide, sodium carbonate and calcium oxide, and the mass ratio of sodium hydroxide, sodium carbonate and calcium oxide is 1:(0.1~1):(0.1~1), preferably 1:0.2:0.3; the amount of the composite alkali catalyst added is 3~5% of the dry weight of starch.

[0012] In the composite alkali catalyst, sodium hydroxide plays an initial catalytic role. During the reaction, sodium carbonate and calcium oxide can absorb the water generated from the reaction and continue to generate sodium hydroxide, maintaining water stability under this low bath ratio condition, preventing side reactions, and improving the utilization rate of raw materials. The purity and degree of substitution of the obtained hydroxypropyl carboxymethyl composite starch ether are improved. On the other hand, during the reaction, sodium carbonate and calcium oxide absorb the water generated from the reaction and also generate a certain amount of calcium carbonate. Calcium carbonate is highly inert and will not affect the subsequent reactions of starch. It can also fill the gaps between starch particles to reduce agglomeration and maintain the stability of subsequent production.

[0013] Furthermore, the moisture content of the corn starch is ≤14%.

[0014] Furthermore, the mass ratio of ethanol to corn starch is (0.1-0.25):1, preferably 0.2:1; the mass fraction of the ethanol is ≥90%.

[0015] This application utilizes the inherent moisture in starch to achieve the melting and alkalization of alkali. The addition of ethanol with a mass fraction ≥90%, combined with the moisture content of the starch raw material, ensures that the moisture content of the reaction system is controlled within a certain range. This facilitates heat transfer during the reaction, ensuring reaction efficiency, while simultaneously preventing swelling and dissolution of starch ethers due to moisture generated during the reaction, thereby improving product performance. Furthermore, the ethanol-to-starch ratio used in this application is (0.1–0.25):1, meaning that high reaction efficiency and product performance can be guaranteed even under low bath ratio (solvent / starch ratio ≤0.25) and low solvent usage conditions.

[0016] Unless otherwise specified in this application, the mass / weight of corn starch refers to its dry weight.

[0017] Furthermore, in step S1, the alkalization temperature is 40–55°C and the time is 20–40 min.

[0018] In a further embodiment, in step S1, the amount of magnesium stearate added is 0.05 to 0.2% of the dry weight of corn starch.

[0019] This study found that adding a small amount of magnesium stearate during alkalization can cause it to adhere to the starch surface, forming an isolation layer to prevent starch granules from directly contacting and sticking together, maintaining the granule dispersion state, ensuring the normal operation of subsequent production, and improving the uniformity and stability of the product. On the other hand, the presence of magnesium stearate is beneficial to the dispersion of the etherifying agent and its penetration into the starch raw material, improving reaction efficiency, shortening reaction time, and increasing the degree of substitution and viscosity of the obtained product.

[0020] Further, in step S2, the amount of propylene oxide added is 15-25% of the dry weight of corn starch, preferably 20% of the dry weight of corn starch; the temperature of the first-stage etherification is 60-75°C and the time is 20-30 min.

[0021] Further, in step S2, the amount of sodium chloroacetate added is 20-25% of the dry weight of corn starch, preferably 22% of the dry weight of corn starch; the temperature of the two-stage etherification is 70-85°C and the time is 40-70 min.

[0022] Furthermore, in step S3, the vacuum drying temperature and vacuum degree are not specifically limited. Vacuum drying can be carried out at room temperature or at high temperature, as long as the product is dried to a moisture content ≤10%. Preferably, the vacuum drying temperature is 80-100℃ and the vacuum degree is -0.08 to -0.095 MPa, more preferably the vacuum drying temperature is 90℃ and the vacuum degree is -0.09 MPa.

[0023] Furthermore, to reduce oxidation during starch ether production, an antioxidant can be added during the alkalization process. The antioxidant can be added directly or dissolved in ethanol first, with an ethanol mass fraction ≥95%. The antioxidant is selected from one or more of butylated hydroxyanisole (BHA), butylated hydroxytoluene (BHT), propyl gallate (PG), and tert-butylhydroquinone (TBHQ), and the mass ratio of the antioxidant to corn starch is (0.01–0.1):1. Additionally, after alkalization, the reaction vessel can be evacuated and purged with nitrogen to remove oxygen.

[0024] Furthermore, the high-viscosity hydroxypropyl carboxymethyl composite starch ether has a degree of substitution ≥ 0.25, where the degree of substitution is the total degree of substitution, i.e., the sum of the degree of substitution of hydroxypropyl and the degree of substitution of hydroxypropyl, and the viscosity is > 8000 mPa·s; preferably, when the degree of substitution of hydroxypropyl is ≥ 0.18 and the degree of substitution of carboxymethyl is 0.1, the viscosity of the starch ether can be maximized, and the viscosity of the starch ether can reach more than 10000 mPa·s.

[0025] According to another aspect of this application, an application is provided for the high-viscosity hydroxypropyl carboxymethyl composite starch ether prepared by the above method in textile printing and dyeing auxiliaries, the application including its use as a thickener.

[0026] Compared with the prior art, this application has the following beneficial effects:

[0027] 1. This application provides a method for preparing a low-bath-ratio, high-viscosity hydroxypropyl carboxymethyl composite starch ether. By combining a stepwise alkalization-composite etherification process with a multiphase catalyst system, a degree of substitution DS≥0.25, viscosity>8000mPa·s, cold water solubility>90% is achieved, and the amount of solvent used is small, with a solvent / starch ratio≤0.25 (i.e., low bath ratio), thus reducing energy consumption.

[0028] 2. The preparation method of low-bath-ratio high-viscosity hydroxypropyl carboxymethyl composite starch ether of this application achieves high viscosity and high degree of substitution while significantly reducing the amount of solvent used. Compared with the traditional semi-dry method, the amount of solvent used is reduced by more than 50%, COD emissions are reduced (by more than 65%), and the energy consumption of subsequent processing is reduced (drying energy consumption is reduced by 40%), resulting in a 25% reduction in overall production costs. Attached Figure Description

[0029] Figure 1 It is the infrared characteristic peak of the hydroxypropyl carboxymethyl complex starch ether in Example 1 of this application. Detailed Implementation

[0030] The following non-limiting embodiments are intended to enable those skilled in the art to gain a more comprehensive understanding of this application, but do not limit this application in any way. The following content is merely an exemplary description of the scope of protection claimed in this application, and those skilled in the art can make various changes and modifications to the invention based on the disclosed content, which should also fall within the scope of protection claimed in this application.

[0031] The present application will be further described below by way of specific embodiments. Unless otherwise specified, all chemical reagents used in the embodiments of this application are obtained through conventional commercial means.

[0032] Example 1

[0033] A method for preparing a low-bath-ratio, high-viscosity hydroxypropyl carboxymethyl composite starch ether includes the following steps:

[0034] S1. Premix 1000g of corn starch (moisture content 14%), composite alkali catalyst, and magnesium stearate, then spray it into an ethanol aqueous solution (mass fraction 90%) and alkalize it at 40℃ for 40min.

[0035] The composite alkali catalyst comprises sodium hydroxide, sodium carbonate, and calcium oxide in a mass ratio of 1:0.1:0.1; the amount of composite alkali catalyst added is 3% of the dry weight of starch; the mass ratio of ethanol to corn starch is 0.1:1; and the amount of magnesium stearate added is 0.05% of the dry weight of corn starch.

[0036] S2. Add 15% of the dry weight of corn starch in propylene oxide and carry out the etherification reaction at 60°C for 20 min; then add 25% of the dry weight of corn starch in sodium chloroacetate and carry out the etherification reaction at 70°C for 40 min.

[0037] S3. After the reaction is complete, the mixture is dried under vacuum at 100℃ and -0.095 MPa, pulverized, and sieved to obtain high-viscosity hydroxypropyl carboxymethyl composite starch ether. Its infrared spectrum is shown below. Figure 1 As shown, it can be seen that 1420cm -1 -COO - The stretching vibration peak, 1381 cm⁻¹ -1 The peak at 1152 cm⁻¹ represents the stretching vibration of the methyl group. -1 The peak at this point represents the stretching vibration of COC, indicating the introduction of carboxymethyl and hydroxypropyl groups into the starch.

[0038] Example 2

[0039] A method for preparing a low-bath-ratio, high-viscosity hydroxypropyl carboxymethyl composite starch ether includes the following steps:

[0040] S1. Premix 1000g of corn starch (moisture content 14%), composite alkali catalyst, and magnesium stearate, then spray in ethanol (mass fraction 90%) and alkalize at 40℃ for 40min.

[0041] The composite alkali catalyst comprises sodium hydroxide, sodium carbonate, and calcium oxide in a mass ratio of 1:0.2:0.3; the amount of composite alkali catalyst added is 5% of the dry weight of starch; the mass ratio of ethanol to corn starch is 0.2:1; and the amount of magnesium stearate added is 0.2% of the dry weight of corn starch.

[0042] S2. Add 20% of the dry weight of corn starch in propylene oxide and carry out the etherification reaction at 60°C for 20 min; then add 22% of the dry weight of corn starch in sodium chloroacetate and carry out the etherification reaction at 70°C for 40 min.

[0043] S3. After the reaction is complete, the mixture is dried under vacuum at 90℃ and -0.09Mpa, pulverized, and sieved to obtain high-viscosity hydroxypropyl carboxymethyl composite starch ether.

[0044] Example 3

[0045] S1. Premix 1000g of corn starch (moisture content 12%), composite alkali catalyst, and magnesium stearate, then spray in ethanol (mass fraction 95%) and alkalize at 55℃ for 40min.

[0046] The composite alkali catalyst comprises sodium hydroxide, sodium carbonate, and calcium oxide in a mass ratio of 1:1:1; the amount of composite alkali catalyst added is 5% of the dry weight of starch; the mass ratio of ethanol to corn starch is 0.25:1; and the amount of magnesium stearate added is 0.2% of the dry weight of corn starch.

[0047] S2. Add 25% of the dry weight of corn starch in propylene oxide and carry out the etherification reaction at 75°C for 30 min; then add 20% of the dry weight of corn starch in sodium chloroacetate and carry out the etherification reaction at 85°C for 70 min.

[0048] S3. After the reaction is complete, the mixture is dried under vacuum at 80℃ and -0.08Mpa, pulverized, and sieved to obtain high-viscosity hydroxypropyl carboxymethyl composite starch ether.

[0049] Example 4

[0050] The difference from Example 2 is that the composite base catalyst contains sodium hydroxide, sodium carbonate and calcium oxide in a mass ratio of 1:1:1.5, while the total amount of the composite base catalyst remains unchanged.

[0051] Example 5

[0052] The difference from Example 2 is that the composite base catalyst contains sodium hydroxide, sodium carbonate and calcium oxide in a mass ratio of 1:1.5:1, while the total amount of composite base catalyst remains unchanged.

[0053] Example 6

[0054] The difference from Example 2 is that the amount of magnesium stearate added is 0.5% of the dry weight of corn starch.

[0055] Comparative Example 1

[0056] The difference from Example 2 is that the mass fraction of ethanol is 80%, while the amount remains the same.

[0057] Comparative Example 2

[0058] The difference from Example 2 is that the mass fraction of ethanol remains unchanged, and its amount is used in a mass ratio of 0.5:1 to corn starch.

[0059] Comparative Example 3

[0060] The difference from Example 2 is that the amount of propylene oxide used is 28% of the dry weight of corn starch; and the amount of sodium chloroacetate used is 14% of the dry weight of corn starch.

[0061] Comparative Example 4

[0062] The difference from Example 2 is that the amount of propylene oxide used is 12% of the dry weight of corn starch; and the amount of sodium chloroacetate used is 30% of the dry weight of corn starch.

[0063] Comparative Example 5

[0064] The difference from Example 2 is that no calcium oxide was added to the composite alkali catalyst, and the total amount of composite alkali catalyst remained unchanged.

[0065] Comparative Example 6

[0066] The difference from Example 2 is that sodium carbonate was not added to the composite alkali catalyst, and the total amount of composite alkali catalyst remained unchanged.

[0067] Comparative Example 7

[0068] The difference from Example 2 is that magnesium stearate was not added in step S1.

[0069] Comparative Example 8

[0070] This comparative example uses a traditional semi-dry method to prepare hydroxypropyl carboxymethyl complex starch ether, as follows:

[0071] 1000g of corn starch (moisture content 14%) and sodium hydroxide were premixed at a mass ratio of 1:0.1. Then, 30% of the corn starch mass was sprayed into ethanol (mass fraction 50%), and the mixture was alkalized at 40℃ for 40 min. 5% of the dry weight of corn starch propylene oxide and 8% of sodium chloroacetate were added, and the mixture was etherified at 70℃ for 16 h. After the reaction was completed, the mixture was dried under vacuum at 90℃ and -0.09 MPa, pulverized, and sieved to obtain high-viscosity hydroxypropyl carboxymethyl composite starch ether.

[0072] Test case

[0073] The hydroxypropyl carboxymethyl composite starch ethers obtained in the above examples and comparative examples were subjected to the following tests:

[0074] Degree of substitution: The degree of substitution of hydroxypropyl D1 was tested by spectrophotometry (propylene glycol method), and the degree of substitution of carboxymethyl D2 was tested by ashing-acid-base titration method. The total degree of substitution (total D) was calculated.

[0075] Viscosity (5% solution, 25°C): Calculated using BROOKFIELD DV-II + Tested using a Pro viscometer;

[0076] Solubility in 4℃ cold water: The dried hydroxypropyl carboxymethyl starch ether (m0) was placed in 4℃ cold water and shaken or stirred under constant temperature conditions to fully dissolve the soluble portion. Undissolved starch granules and the supernatant were then separated by high-speed centrifugation. The supernatant was transferred to a pre-dried weighing bottle (m1) to constant weight. The weighing bottle was dried to constant weight, removed, and placed in a desiccator to cool to room temperature. The total mass (m2) was then weighed. The solubility was calculated as (m2 - m1) / m0 × 100%.

[0077] The test results are shown in Table 1 below.

[0078] Table 1. Test results of hydroxypropyl carboxymethyl starch ether

[0079]

[0080] As shown in the table, in Comparative Example 8, the conventional one-step method for producing hydroxypropyl carboxymethyl starch ether only achieved a degree of substitution of 0.14 after 16 hours of reaction, indicating a low degree of substitution. In contrast, the hydroxypropyl carboxymethyl starch ethers prepared using the method provided in this application achieved a degree of substitution of over 0.25, demonstrating a high degree of substitution. Furthermore, the reaction time was short, with a high degree of substitution achieved in just 60 minutes of etherification. The ethers also exhibited higher viscosity and solubility, with a viscosity exceeding 9000 mPa·s and a solubility >90%. This demonstrates that compared to conventional methods for producing hydroxypropyl carboxymethyl starch ethers, the method provided in this application offers higher production efficiency and produces products with higher degrees of substitution, viscosity, and solubility.

[0081] Compared to Example 2, in Comparative Examples 5 and 6, no sodium carbonate or calcium oxide was added to the composite alkali catalyst, and the degree of substitution, viscosity, and solubility of the resulting products all decreased. This indicates that adding a certain amount of sodium carbonate or calcium oxide during the production of hydroxypropyl carboxymethyl starch ether helps to improve the degree of substitution, viscosity, and solubility of the product. In Comparative Example 7, no magnesium stearate was added, and the degree of substitution, viscosity, and solubility of the resulting product decreased to a certain extent. This indicates that the addition of magnesium stearate helps to improve the performance of the product.

[0082] It can also be seen that although hydroxypropyl carboxymethyl composite starch ethers with a degree of substitution of 0.2 or higher can be obtained in Comparative Examples 3 and 4, their viscosity is lower and their solubility is reduced. This indicates that the amounts of propylene oxide and sodium chloroacetate, the two etherifying agents, need to be controlled within a certain range to achieve high degree of substitution, high viscosity, and high solubility of hydroxypropyl carboxymethyl composite starch ethers. The concentration of ethanol used in Comparative Example 1 was low, meaning that the water content in the reaction system was high. In Comparative Example 2, excess solvent was used, resulting in a decrease in the degree of substitution, viscosity, and solubility of the product. Therefore, controlling the ratio of ethanol to starch raw materials and the water content of starch, thereby controlling the water content of the reaction system, can significantly reduce the amount of solvent used while achieving high viscosity and high degree of substitution.

[0083] Experimental Example 2

[0084] High dye penetration refers to the ability of pigments or dyes to effectively penetrate into the fabric (such as between fibers and yarn gaps), rather than merely remaining on the fabric surface. This determines the color yield, color vibrancy, hand feel, and rubbing fastness of the print. Low desizing rate means that after printing or sizing, the required starch ether paste can be washed away more easily, quickly, and thoroughly during the finishing washing process, while consuming less water, energy, and chemicals. Residual paste can affect the hand feel and cause subsequent problems. This application evaluates the performance of hydroxypropyl carboxymethyl starch ether as a textile printing and dyeing auxiliary by testing its dye penetration and dyeing properties.

[0085] (1) Dye penetration test method: The fabric section microscopy observation method was used for testing. Specifically, the printed fabric sample was sliced ​​vertically to make an ultrathin slice sample. The slice was placed under a microscope for observation, and cross-sectional photographs were taken to directly observe the penetration of dye between the warp and weft yarns of the fabric and inside individual fibers. It should be noted that the fabric in the fundamental test was printed using conventional processes. The difference was that the hydroxypropyl carboxymethyl starch ether provided in this application was added as a dyeing auxiliary agent. Therefore, the specific process steps will not be repeated. Generally, the more uniform the dye distribution and the deeper the penetration depth, the better the dye penetration of the paste. Through testing, the degree of resistance to dye penetration of different hydroxypropyl carboxymethyl starch ethers can be clearly compared (labeled as poor, average, normal, good, and excellent from low to high).

[0086] (2) Desizing test method: The desizing loss method is used for testing. Specifically, the printed / sized fabric is dried to constant weight and accurately weighed and recorded as W1; the fabric is then subjected to standardized desizing treatment, and the desized and thoroughly washed fabric is dried again to constant weight and accurately weighed and recorded as W2. Calculate the desizing rate: Desizing rate = (W1 - W2) / W1 × 100%. Generally, the lower the desizing rate, the easier it is to wash off the paste. However, it should be noted that this value also includes possible losses such as lint shedding in the fabric itself, and a blank fabric control group needs to be set up for correction (the desizing effect is generally marked from low to high as poor (desizing rate ≥ 4%), average (desizing rate between 3.9% and 3%), normal (desizing rate between 2.9% and 2%), good (desizing rate between 1.9% and 1.0%), and excellent (desizing rate < 1.0%).

[0087] The results of the above tests on permeability and desizing performance are shown in Table 2 below. It can be seen that, compared with the hydroxypropyl carboxymethyl composite starch ether produced by the traditional one-step method, the hydroxypropyl carboxymethyl composite starch ether prepared by the method provided in this application has significantly better permeability and desizing performance.

[0088] Table 2. Results of tests on dye penetration and desizing properties

[0089]

[0090] The above description of the embodiments is provided to enable those skilled in the art to understand and use the invention. It will be apparent to those skilled in the art that various modifications can be made to these embodiments, and the general principles described herein can be applied to other embodiments without inventive effort. Therefore, this application is not limited to the above embodiments, and 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 protection scope of this application.

Claims

1. A method for preparing a low-bath-ratio, high-viscosity hydroxypropyl carboxymethyl composite starch ether, characterized in that, Includes the following steps: S1. Premix corn starch with a composite alkali catalyst and magnesium stearate, then spray with ethanol for alkalization; the amount of magnesium stearate added is 0.05-0.2% of the dry weight of corn starch; S2. Add propylene oxide for a first-stage etherification, then add sodium chloroacetate for a second-stage etherification; the temperature of the first-stage etherification is 60-75℃ and the time is 20-30 min; the temperature of the second-stage etherification is 70-85℃ and the time is 40-70 min. S3. After the reaction is complete, vacuum dry, pulverize, and sieve to obtain high-viscosity hydroxypropyl carboxymethyl composite starch ether; wherein, The composite alkali catalyst comprises sodium hydroxide, sodium carbonate, and calcium oxide in a mass ratio of 1:(0.1-1):(0.1-1); the amount of composite alkali catalyst added is 3-5% of the dry weight of corn starch. The mass ratio of the ethanol aqueous solution to corn starch is (0.1-0.25):1; the mass fraction of the ethanol aqueous solution is ≥90%.

2. The preparation method according to claim 1, characterized in that, The mass ratio of sodium hydroxide, sodium carbonate, and calcium oxide is 1:0.2:0.

3.

3. The preparation method according to claim 1, characterized in that, The moisture content of the corn starch is ≤14%.

4. The preparation method according to claim 1, characterized in that: The amount of propylene oxide added is 15-25% of the dry weight of corn starch.

5. The preparation method according to claim 1, characterized in that: The amount of sodium chloroacetate added is 20-25% of the dry weight of corn starch.

6. The preparation method according to any one of claims 1-5, characterized in that, The degree of substitution of high-viscosity hydroxypropyl carboxymethyl starch is ≥0.25, and the viscosity is >8000 mPa·s.

7. The application of the high-viscosity hydroxypropyl carboxymethyl composite starch prepared by the preparation method according to any one of claims 1-6 in textile printing and dyeing auxiliaries.

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