Preparation method of high-stability cross-linked hydroxypropyl starch ether

Abstract

The invention provides a preparation method of high-stability cross-linked hydroxypropyl starch ether, and relates to the technical field of starch ether processing. The method comprises the following steps: adding water into a starch raw material to prepare starch milk, adding part of an alkalizer, and stirring for activation; raising the temperature to a first temperature, adding the residual alkalizer, and uniformly stirring and mixing; adding an etherifying agent, heating to a second temperature, carrying out first-stage etherification, adding a cross-linking agent after the hydroxypropyl substitution degree DS of the starch reaches 0.10, and carrying out second-stage etherification at the second temperature; and finally, carrying out post-treatment on the etherified product to prepare the cross-linked hydroxypropyl starch ether. According to the cross-linked hydroxypropyl starch ether produced by the method, the problems of local gelatinization and by-product residue of the existing cross-linked hydroxypropyl starch ether are solved, the industrial production of the high-stability food-grade safe hydroxypropyl cross-linked starch ether is realized, and the product better meets the market demand.

Description

Technical Field

[0001] This application relates to the field of starch ether processing technology, and in particular to a method for preparing highly stable cross-linked hydroxypropyl starch ether. Background Technology

[0002] Hydroxypropyl starch ether (HPSE) is a modified starch produced by the etherification reaction of starch and propylene oxide under alkaline conditions. The hydroxypropyl group (-O-CH2-CHOHCH3) in its molecular structure replaces the hydroxyl groups on the starch glucose units, endowing the product with certain thickening stability, low-temperature stability, transparency, solubility, and acid and alkali resistance. However, hydroxypropyl starch ether struggles to meet the demands of complex processing and usage environments, and its stability and functionality remain insufficient for the production requirements of some high-end products. Therefore, there is an urgent need to improve the overall performance of starch ethers.

[0003] Crosslinking during the production of hydroxypropyl starch ethers can impart superior comprehensive properties to starch based on hydroxypropyl etherification modification, meeting its stability and functionality requirements under harsh conditions. Crosslinked hydroxypropyl starch ethers combine the advantages of both modification methods, endowing the product with the required stability and tolerance under harsh conditions such as high temperature, high shear, acid / alkaline environments, and repeated freeze-thaw cycles. This makes it an ideal choice for applications with extremely high stability requirements in the food industry (especially for products requiring high-temperature processing, mechanical processing, or frozen storage), the pharmaceutical industry (sustained-release carriers), and the paper industry (wet-end additives).

[0004] Currently, most cross-linked hydroxypropyl starch ether production methods on the market use glyoxal as a cross-linking agent. By adding a large amount of glyoxal, a solvent method is used to react with starch at high temperature to obtain cross-linked hydroxypropyl starch ether. For example, patent CN113444185A discloses the following raw material ratio: 10 parts potato starch, 2-5 parts propylene oxide, 50-200 parts ethanol, and 0.2-1 parts glyoxal. After adding potato starch, pre-alkalization is carried out at 70℃, followed by low-temperature alkalization for a period of time, then simultaneous addition of propylene oxide and glyoxal, followed by etherification reaction at 70-80℃. Finally, the product is obtained after neutralization and washing. In this preparation method, the reaction temperature >70℃ easily causes starch gelatinization, leading to molecular degradation. The viscosity retention rate at 95℃ is <70%, indicating poor stability. Using glyoxal as a cross-linking agent under alkaline conditions results in hydrolysis, generating formaldehyde residue that cannot be completely removed by washing. The amount of ethanol used is 5-20 times the mass of starch, resulting in high recycling costs.

[0005] The academic journal article [1] Zhang Jiayan, Liang Shuying, Xiong Jianwen, et al. Response surface optimization microwave method for preparing potato crosslinked starch [J]. China Food Additives, 2016(10):7.DOI:10.3969 / j.issn.1006-2513.2016.10.014. mentions that sodium hexametaphosphate is used as a crosslinking agent, and the production process is: sodium hexametaphosphate mass fraction 0.6%, starch milk mass fraction 24%, pH10, temperature 44℃, sedimentation volume 4.86mL. However, the microwave method is prone to surface gelatinization due to local microwave overheating, making it difficult to form industrial production; the addition of sodium hexametaphosphate of 0.6% results in bound phosphorus residue >500 ppm (EU food additive limit ≤50 ppm), which cannot be used in infant food; the phosphate ester bond is easily hydrolyzed under acidic conditions, resulting in serious viscosity loss and poor stability, which cannot meet the needs of acidic food and high-temperature industry, and the scope of application is greatly limited.

[0006] Therefore, there is currently a lack of a method for preparing highly stable cross-linked hydroxypropyl starch ethers. Summary of the Invention

[0007] The purpose of this application is to address the shortcomings of existing technologies by providing a method for preparing highly stable cross-linked hydroxypropyl starch ethers. This method overcomes the problems of localized gelatinization and by-product residues in current cross-linked hydroxypropyl starch ethers, enabling the industrial production of highly stable, food-grade safe hydroxypropyl cross-linked starch ethers, thus better meeting market demands.

[0008] To achieve the above objectives, the technical solution adopted in this application is as follows: A method for preparing highly stable cross-linked hydroxypropyl starch ether includes the following steps: S1. Alkalization: Mix starch raw materials with water to prepare starch milk, add part of the alkalizing agent and stir to activate; then raise to the first temperature, add the remaining alkalizing agent and stir to mix well; S2, Etherification: Add an etherifying agent, raise the temperature to the second temperature for a first-stage etherification until the degree of hydroxypropyl substitution of starch (DS) reaches 0.10, then add a crosslinking agent and carry out a second-stage etherification at the second temperature; S3. Post-treatment: The etherified product is post-treated to obtain the final product.

[0009] Further, in step S1, the starch raw material is selected from any one or more of corn starch, cassava starch, and potato starch, preferably potato starch; the mass ratio of the starch raw material to water is 100:(120-180).

[0010] Further, in step S1, the alkalizing agent is an aqueous solution of an alkali metal hydroxide, and the mass concentration of the alkalizing agent is 20-40%; the alkali metal hydroxide is selected from potassium hydroxide, sodium hydroxide, or a mixture of the two, and the mass ratio of the two in the mixture of potassium hydroxide and sodium hydroxide is preferably 3:2; based on the weight of the alkali metal oxide, the mass ratio of the alkali metal oxide to starch is (2.2-3):100.

[0011] Furthermore, in step S1, the portion of the alkalizing agent is 50-60% of the total amount of alkalizing agent.

[0012] Furthermore, in step S1, the stirring activation time is 25–35 min.

[0013] Furthermore, in step S1, the first temperature is 40–45°C.

[0014] This application first uses an appropriate amount of alkalizing agent to alkalize the starch to form a moderately swollen layer, then adds the remaining alkalizing agent and an etherifying agent to raise the temperature for etherification. At this time, etherification and alkalization are carried out simultaneously. This process can activate the hydroxyl groups deep in the starch raw material, avoid local pH over-excessive pH caused by partial alkalization, and prevent the formation of a gelatinized layer, thereby helping to improve product quality. It can also reduce process changeover time, shorten the production cycle, and avoid the impact of multiple heating and cooling on product stability.

[0015] Further, in step S2, the etherifying agent is selected from one or more of chloroacetic acid, chloromethane, chloroethane, propylene glycol ether, propylene oxide, and ethylene oxide, preferably propylene oxide; the mass ratio of the etherifying agent to the starch raw material is (28-35):100.

[0016] Furthermore, in step S2, the second temperature is 50–55°C.

[0017] Further, in step S2, the crosslinking agent is selected from any one or more of phosphorus oxychloride, epichlorohydrin, and borax, preferably epichlorohydrin; the weight ratio of the crosslinking agent to the starch raw material is (0.05~0.15):100.

[0018] This study found that when a crosslinking agent is added after the first-stage etherification reaction reaches a hydroxypropyl substitution degree (DS) of 0.10 in starch, the swelling degree of starch granules observed under a microscope is in the range of 35-40%. Adding the crosslinking agent at this time can ensure that the molecular chains are fully extended. The crosslinking reaction occurs simultaneously during the second-stage etherification process, and the crosslinking efficiency is effectively improved. This results in the establishment of a denser, more uniform, or more stable network structure between the molecular chains, which can significantly improve the acid and alkali resistance and thermal stability of starch ethers.

[0019] Furthermore, in step S2, the time for the second-stage etherification is 7–9 hours.

[0020] Further, the post-processing includes: cooling the etherified product to room temperature, adjusting the pH to neutral with acid, and then washing, drying, and pulverizing to obtain cross-linked hydroxypropyl starch ether.

[0021] Optionally, in the post-processing, the acid is dilute hydrochloric acid or dilute sulfuric acid, and the washing is performed using anhydrous ethanol.

[0022] Compared with the prior art, this application has the following beneficial effects: The cross-linked hydroxypropyl starch ether preparation method provided in this application has high utilization rate of alkalizing agent and etherifying agent, is highly efficient, low cost, and improves production stability; it has a low cross-linking temperature, requires less cross-linking agent, has high cross-linking efficiency, and low additive residue; the obtained cross-linked starch ether can maintain high viscosity, is not prone to over-gelatinization or degradation, has excellent acid resistance, is more stable in acidic foods or environments, and is not prone to thinning; it also has good shear resistance, and the viscosity loss is very small under mechanical action such as pumping, stirring, and homogenization. Attached Figure Description

[0023] Figure 1 This is the infrared spectrum of the crosslinked hydroxypropyl starch ether in Example 2 of this application. Detailed Implementation

[0024] 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.

[0025] 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.

[0026] Example 1 A method for preparing highly stable cross-linked hydroxypropyl starch ether includes the following steps: S1. Alkalization: Mix 100 parts of potato starch with 120 parts of deionized water to prepare starch milk, then add 5.5 parts of KOH solution (20% by mass) and stir to activate for 25 min; then heat to 40℃, add 5.5 parts of KOH solution (20% by mass) and stir to mix well; S2, Etherification: Add 28 parts of chloroacetic acid, heat to 50℃ and react at a constant temperature until the degree of hydroxypropyl substitution of starch reaches 0.10; then add 0.05 parts of phosphorus oxychloride and continue to react at 50℃ for 7 hours; S3. Post-treatment: Cool the etherified product to room temperature, adjust the pH to neutral with dilute hydrochloric acid, wash with anhydrous ethanol, dry, and pulverize to obtain the final product.

[0027] Example 2 A method for preparing highly stable cross-linked hydroxypropyl starch ether includes the following steps: S1. Alkalization: Mix 100 parts corn starch with 150 parts deionized water to prepare starch milk, then add 4 parts KOH solution (40% by mass) and stir to activate for 30 min; then heat to 45℃, add 3 parts KOH solution (40% by mass) and stir to mix well; S2, Etherification: Add 28 parts of propylene oxide, heat to 55℃ and react at a constant temperature until the degree of hydroxypropyl substitution of starch reaches 0.10; then add 0.1 parts of epichlorohydrin and continue to react at 55℃ for 7 hours. S3. Post-treatment: Cool the etherified product to room temperature, adjust the pH to neutral with dilute hydrochloric acid, wash with anhydrous ethanol, dry, and pulverize to obtain the final product.

[0028] The cross-linked hydroxypropyl starch ether prepared in this embodiment was compressed with KBr into tablets, and tested using a Nicolet Nexus 460 infrared spectrometer. The infrared spectra obtained are shown below. Figure 1 As shown. It can be seen that 3415cm -1 The absorption peak near the -OH stretching vibration is at 1378 cm⁻¹. -1 The nearby peak is a characteristic peak of -CH3, at 1262 cm⁻¹. -1 The nearest distance is 1150cm. -1 The peak near the ether bond stretching vibration is 920 cm⁻¹. -1 The presence of vibrational peaks near the epoxy groups indicates that cross-linked hydroxypropyl starch was successfully prepared.

[0029] Example 3 A method for preparing highly stable cross-linked hydroxypropyl starch ether includes the following steps: S1. Alkalization: Mix 100 parts corn starch with 180 parts deionized water to prepare starch milk, then add 5 parts KOH solution (30% by mass) and stir to activate for 35 min; then heat to 45℃, add 5 parts KOH solution (30% by mass) and stir to mix well; S2, Etherification: Add 35 parts of propylene oxide, heat to 55℃ and react at a constant temperature until the degree of hydroxypropyl substitution of starch reaches 0.10; then add 0.15 parts of epichlorohydrin and continue to react at 55℃ for 7 hours. S3. Post-treatment: Cool the etherified product to room temperature, adjust the pH to neutral with dilute hydrochloric acid, wash with anhydrous ethanol, dry, and pulverize to obtain the final product.

[0030] Example 4 A method for preparing highly stable cross-linked hydroxypropyl starch ether includes the following steps: S1. Alkalization: Mix 100 parts corn starch with 180 parts deionized water to prepare starch milk, then add 6 parts KOH solution (30% by mass) and stir to activate for 35 min; then heat to 45℃, add 4 parts NaOH solution (30% by mass) and stir to mix well; S2, Etherification: Add 35 parts of propylene oxide, heat to 55℃ and react at a constant temperature until the degree of hydroxypropyl substitution of starch reaches 0.10; then add 0.15 parts of epichlorohydrin and continue to react at 55℃ for 7 hours. S3. Post-treatment: Cool the etherified product to room temperature, adjust the pH to neutral with dilute hydrochloric acid, wash with anhydrous ethanol, dry, and pulverize to obtain the final product.

[0031] Comparative Example 1 A method for preparing highly stable cross-linked hydroxypropyl starch ether includes the following steps: S1. Alkalization: Mix 100 parts corn starch with 150 parts deionized water to prepare starch milk, then add 4 parts KOH solution (40% by mass) and stir to activate for 30 min; then heat to 45℃, add 3 parts KOH solution (40% by mass) and stir to mix well; S2, Etherification: Add 28 parts of propylene oxide and 0.1 parts of epichlorohydrin, heat to 55℃ and react at a constant temperature for 7 hours; S3. Post-treatment: Cool the etherified product to room temperature, adjust the pH to neutral with dilute hydrochloric acid, wash with anhydrous ethanol, dry, and pulverize to obtain the final product.

[0032] Comparative Example 2 A method for preparing highly stable cross-linked hydroxypropyl starch ether includes the following steps: S1. Alkalization: Mix 100 parts corn starch with 150 parts deionized water to prepare starch milk, then add 4 parts KOH solution (40% by mass) and 0.1 parts epichlorohydrin, stir and activate for 30 min; then heat to 45℃, add 3 parts KOH solution (40% by mass), and stir to mix well; S2, Etherification: Add 28 parts of propylene oxide and heat to 55℃ for 7 hours; S3. Post-treatment: Cool the etherified product to room temperature, adjust the pH to neutral with dilute hydrochloric acid, wash with anhydrous ethanol, dry, and pulverize to obtain the final product.

[0033] Comparative Example 3 A method for preparing highly stable cross-linked hydroxypropyl starch ether includes the following steps: S1. Alkalization: Mix 100 parts corn starch with 150 parts deionized water to prepare starch milk, then add 4 parts KOH solution (40% by mass) and stir to activate for 30 min; then heat to 45℃, add 3 parts KOH solution (40% by mass) and stir to mix well; S2, Etherification: Add 28 parts of propylene oxide and heat to 55℃ for 7 hours; Then add 0.1 parts of epichlorohydrin and continue the reaction at a constant temperature for 2 hours to complete the crosslinking reaction; S3. Post-treatment: Cool the etherified product to room temperature, adjust the pH to neutral with dilute hydrochloric acid, wash with anhydrous ethanol, dry, and pulverize to obtain the final product.

[0034] Comparative Example 4 A method for preparing highly stable cross-linked hydroxypropyl starch ether includes the following steps: S1. Alkalization: Mix 100 parts corn starch with 150 parts deionized water to prepare starch milk, then add 4 parts KOH solution (40% by mass) and stir to activate for 30 min; then heat to 45℃, add 3 parts KOH solution (40% by mass) and stir to mix well; S2, Etherification: Add 28 parts of propylene oxide, heat to 55℃ and react at a constant temperature until the degree of hydroxypropyl substitution of starch reaches 0.08; then add 0.1 parts of epichlorohydrin and continue to react at 55℃ for 7 hours. S3. Post-treatment: Cool the etherified product to room temperature, adjust the pH to neutral with dilute hydrochloric acid, wash with anhydrous ethanol, dry, and pulverize to obtain the final product.

[0035] Comparative Example 5 A method for preparing highly stable cross-linked hydroxypropyl starch ether includes the following steps: S1. Alkalization: Mix 100 parts corn starch with 150 parts deionized water to prepare starch milk, then add 4 parts KOH solution (40% by mass) and stir to activate for 30 min; then heat to 45℃, add 3 parts KOH solution (40% by mass) and stir to mix well; S2, Etherification: Add 28 parts of propylene oxide, heat to 52℃ and react at a constant temperature until the degree of hydroxypropyl substitution of starch reaches 0.15; then add 0.1 parts of epichlorohydrin and continue to react at 55℃ for 7 hours. S3. Post-treatment: Cool the etherified product to room temperature, adjust the pH to neutral with dilute hydrochloric acid, wash with anhydrous ethanol, dry, and pulverize to obtain the final product.

[0036] Comparative Example 6 A method for preparing highly stable cross-linked hydroxypropyl starch ether includes the following steps: S1. Alkalization: Mix 100 parts corn starch with 150 parts deionized water to prepare starch milk, then add 7 parts KOH solution (40% by mass) and stir to activate for 30 min; S2, Etherification: Add 28 parts of propylene oxide, heat to 52℃ and react at a constant temperature until the degree of hydroxypropyl substitution of starch reaches 0.10; then add 0.1 parts of epichlorohydrin and continue to react at 55℃ for 7 hours. S3. Post-treatment: Cool the etherified product to room temperature, adjust the pH to neutral with dilute hydrochloric acid, wash with anhydrous ethanol, dry, and pulverize to obtain the final product.

[0037] Experimental Example Using the cross-linked hydroxypropyl starch ethers obtained in the above examples and comparative examples, as well as three commercially available products (products A, B, and C), the following tests were conducted: (1) Degree of cross-linking: Cross-linked starch is insoluble in water, but it can absorb solvent and swell in water to form a gel. The higher the degree of cross-linking, the tighter the three-dimensional network structure, the less water it absorbs, and the smaller the degree of swelling or swelling volume. Therefore, the degree of cross-linking of products can be indirectly characterized and compared by measuring the degree of swelling (SC) or swelling volume (SV). In this experiment, the degree of cross-linking of cross-linked starch was evaluated by measuring the degree of swelling (SC) after water absorption and swelling. Specifically, 5.00 g of each sample was taken and dried in an oven at 105 ℃ until constant weight. The weight was accurately weighed (m1). Then, the dried samples were placed in 250 mL of deionized water and allowed to swell at 25 ℃ for 24 h to ensure swelling equilibrium. Excess water was drained off until no more water dripped. The mass (m2) was immediately weighed and then calculated according to the formula. Calculate the degree of swelling (SC).

[0038] (2) Viscosity retention rate at 95℃: The sample was mixed with water to prepare starch milk. The viscosity of the starch milk at room temperature and 95℃ was tested using a Brabender viscometer and recorded as viscosity I and viscosity II, respectively. The viscosity retention rate was calculated using the ratio of viscosity I to viscosity II.

[0039] (3) Freeze-thaw water separation rate (-18℃ / 5 times): Accurately weigh 6.00g of sample, add water to prepare 6% starch milk, place in a 90℃ water bath and stir to gelatinize for 30min to obtain a uniform and transparent starch paste; pour the starch paste into two weighed 50mL stoppered centrifuge tubes (W0) while hot, cool to room temperature, place in a 4℃ refrigerator for aging for 24h to form starch gel; take it out and weigh it again (W1), and accurately record the total mass of each sample; Freeze-thaw cycle: Place the centrifuge tubes in a -18℃ freezer for 18 hours, then remove them and thaw them in a 25℃ constant temperature water bath for 6 hours to complete one freeze-thaw cycle. Repeat this process for a total of 5 cycles. Then place the sample in a high-speed centrifuge and centrifuge at 4000 r / min for 30 minutes. Pour off the supernatant that has precipitated in the centrifuge tubes and blot dry any remaining moisture at the tube opening with absorbent paper. Weighing calculation: Weigh the total weight (W2) of the centrifuge tube and the remaining gel. Calculate the freeze-thaw separation rate using the following formula: Freeze-thaw separation rate (%) = [(W1-W2) / (W1-W0)] × 100%.

[0040] (4) Acid resistance (viscosity loss at pH 4.0): The samples were prepared into neutral starch milk and starch milk with pH 4.0 by adding water. The viscosity was tested using a Brabender viscometer and recorded as viscosity I and viscosity II, respectively. The viscosity loss was calculated using the formula (viscosity I - viscosity II) / viscosity I.

[0041] (5) Chloropropanol residue: Tested according to GB / T 5009.191-2016; (6) Formaldehyde residue: Tested according to GB / T 31604.48-2016; (7) Phosphorus residue: Tested according to GB / T 5009.268-2016; (8) Ash content: Tested according to GB / T 5009.4-2016.

[0042] The test results are shown in Tables 1 and 2 below.

[0043] Table 1. Properties of Crosslinked Hydroxypropyl Starch Ethers

[0044] Table 2. Properties of cross-linked hydroxypropyl starch ethers

[0045] As shown in the table, compared with commercially available hydroxypropyl crosslinked starch ethers A, B, and C, the crosslinked hydroxypropyl starch ether obtained in this application significantly improves the degree of crosslinking, and also significantly enhances heat resistance, acid resistance, and freeze-thaw stability, while reducing ash content. Furthermore, the product obtained in this application, after washing with 70% ethanol, has a trace amount of chloropropanol residue ≤0.12 ppm (meeting the EU limit), while product A has phosphorus residue exceeding the limit by 10 times (EU limit 50 ppm), product B is a crosslinked hydroxypropyl starch ether produced using glyoxal as a crosslinking agent, and its formaldehyde residue (5.8 ppm) poses a carcinogenic risk, and product C has a high amount of chloropropanol residue. Therefore, the crosslinked hydroxypropyl starch ether produced by the method provided in this application has advantages such as high degree of crosslinking, high viscosity retention, good freeze-thaw stability, low chloropropanol residue, and low ash content, which can meet industry needs; it overcomes the industry pain points of localized gelatinization and by-product residue, realizing the industrial production of highly stable, food-grade safe hydroxypropyl crosslinked starch ether, and expanding the product's application range.

[0046] 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 highly stable cross-linked hydroxypropyl starch ether, characterized in that, Includes the following steps: S1. Alkalization: Mix starch raw materials with water to prepare starch milk, add part of the alkalizing agent and stir to activate; then raise to the first temperature, add the remaining alkalizing agent and stir to mix well; S2, Etherification: Add an etherifying agent, raise the temperature to the second temperature for a first-stage etherification until the degree of hydroxypropyl substitution of starch (DS) reaches 0.10, then add a crosslinking agent and carry out a second-stage etherification at the second temperature; S3. Post-treatment: The etherified product is post-treated to obtain the final product.

2. The preparation method according to claim 1, characterized in that, The starch raw material is selected from any one or more of corn starch, cassava starch, and potato starch.

3. The preparation method according to claim 1, characterized in that, In step S1, the alkalizing agent is an aqueous solution of alkali metal hydroxide, and the mass concentration of the alkalizing agent is 20-40%; the mass ratio of alkali metal oxide to starch is (2.2-3):100 based on the weight of alkali metal oxide.

4. The preparation method according to claim 1, characterized in that, In step S1, the alkalizing agent accounts for 50-60% of the total alkalizing agent.

5. The preparation method according to claim 1, characterized in that, In step S1, the first temperature is 40-45℃.

6. The preparation method according to claim 1, characterized in that, In step S2, the etherifying agent is selected from any one or more of chloroacetic acid, chloromethane, chloroethane, propylene glycol ether, propylene oxide, and ethylene oxide; the mass ratio of the etherifying agent to the starch raw material is (28-35):

100.

7. The preparation method according to claim 1, characterized in that, In step S2, the crosslinking agent is selected from any one or more of phosphorus oxychloride, epichlorohydrin, and borax; the weight ratio of the crosslinking agent to the starch raw material is (0.05-0.15):

100.

8. The preparation method according to claim 1, characterized in that, In step S2, the second temperature is 50–55°C.

9. The preparation method according to claim 1, characterized in that, In step S2, the second-stage etherification takes 7–9 hours.

10. The preparation method according to claim 1, characterized in that, Post-processing includes: The etherified product was cooled to room temperature, the pH was adjusted to neutral by adding acid, and then washed, dried and pulverized to obtain cross-linked hydroxypropyl starch ether.

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