High-substitution-degree hydroxypropyl chitosan and preparation method thereof
By precisely controlling the hydroxypropylation reaction conditions, including carrying out the hydroxypropylation reaction at 0–5°C and using glacial acetic acid to neutralize the pH of the reaction solution, the preparation of hydroxypropyl chitosan with a high degree of substitution was achieved, solving the problem of difficulty in achieving the degree of substitution of hydroxypropyl chitosan in the prior art and improving the performance stability of the product.
Patent Information
- Application Number
- CN202511399079.4
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2025-09-28
- Publication Date
- 2026-01-06
AI Technical Summary
Insufficient optimization of process parameters in existing technologies leads to poor solubility of hydroxypropyl chitosan, making it difficult to control the degree of substitution of hydroxypropyl chitosan and resulting in unstable product performance.
By precisely controlling the hydroxypropylation reaction conditions, including carrying out the hydroxypropylation reaction at 0–5°C and using glacial acetic acid as a neutralizing agent by adding glacial acetic acid dropwise to the reaction solution for neutralization, and adding anhydrous ethanol to the reaction solution, the temperature and pH value of the hydroxypropylation reaction were precisely controlled, thus achieving precise regulation of hydroxypropyl chitosan.
This achieved high degree of substitution control of hydroxypropyl chitosan, improving the stability and uniformity of product performance.
Smart Images
Figure CN121270751A_ABST
Abstract
Description
Technical Field
[0001] This invention relates to the field of polymer materials technology, and in particular to a highly substituted hydroxypropyl chitosan and its preparation method. Background Technology
[0002] Chitosan, a natural cationic polysaccharide, has demonstrated significant application value in medicine, food, agriculture, and environmental protection due to its excellent biocompatibility, biodegradability, and antibacterial and film-forming properties. However, the large number of hydrogen bonds within the chitosan molecule results in poor solubility (dissolving only in dilute acid solutions), limiting its processing and application in neutral or alkaline environments. To improve the solubility and functional properties of chitosan, chemical modification has become a key technical approach. Among these, hydroxypropylation modification can significantly enhance the water solubility and bioactivity of chitosan by disrupting intramolecular hydrogen bonds and increasing hydrophilicity, thus expanding its application potential in high-end fields such as drug carriers and tissue engineering scaffolds.
[0003] Currently, the preparation of hydroxypropyl chitosan mainly adopts an alkalization-hydroxypropylation reaction process under isopropanol system. The degree of substitution is controlled by adjusting the reaction conditions (such as alkali concentration, temperature, and time). In the existing process, the degree of substitution in the hydroxypropylation reaction is affected by multiple factors such as alkalization conditions, reaction temperature, and time. However, the process parameters are not optimized enough, resulting in large fluctuations in the degree of substitution. For example, the parameters in the alkalization stage are out of control: the sodium hydroxide concentration, alkalization time, and temperature are not precisely matched, which can easily lead to excessive degradation of the chitosan backbone or insufficient alkalization, resulting in a reduction of substituent insertion sites. The hydroxypropylation reaction conditions fluctuate: the reaction temperature is not strictly controlled within the low temperature range (such as 0-5℃), which can trigger side reactions (epoxidation, crosslinking) and reduce substitution efficiency. The pH control in the neutralization stage is crude: the excessively rapid acceleration of glacial acetic acid drop causes sudden changes in local pH, which destroys the stability of the hydroxypropyl groups and further aggravates the non-uniformity of the degree of substitution.
[0004] In summary, in the existing hydroxypropyl chitosan preparation process, insufficient optimization of process parameters makes it difficult to control the degree of substitution in the hydroxypropylation reaction, resulting in unstable product performance. Summary of the Invention
[0005] The purpose of this invention is to provide a highly substituted hydroxypropyl chitosan and its preparation method, aiming to solve the technical problem in the existing hydroxypropyl chitosan preparation process where insufficient optimization of process parameters leads to difficulty in controlling the degree of substitution in the hydroxypropylation reaction, resulting in unstable product performance.
[0006] To achieve the above objectives, the present invention employs a highly substituted hydroxypropyl chitosan, comprising the following raw materials:
[0007] Chitosan, sodium hydroxide, propylene oxide, and isopropanol.
[0008] This invention also provides a method for preparing highly substituted hydroxypropyl chitosan, comprising the following steps:
[0009] Chitosan raw material was obtained and pretreated. After pretreatment, the chitosan was pulverized into powder.
[0010] Chitosan was mixed with isopropanol and then alkalized with sodium hydroxide solution to obtain alkalized chitosan.
[0011] The alkalized chitosan was placed in a cooling device for hydroxypropylation.
[0012] Glacial acetic acid was used as a neutralizing agent, and the neutralization reaction was carried out by adding glacial acetic acid dropwise to the reaction solution;
[0013] Anhydrous ethanol was added to the reaction solution, and hydroxypropyl chitosan precipitate was formed. The precipitate was then processed to obtain crude hydroxypropyl chitosan.
[0014] The crude hydroxypropyl chitosan was purified and dried to obtain a highly substituted hydroxypropyl chitosan product.
[0015] In the steps of obtaining chitosan raw material, pre-treating chitosan, and then pulverizing it into powder:
[0016] Use a precision electronic balance to accurately weigh the chitosan raw material;
[0017] Place the weighed chitosan in a drying oven to remove moisture, set the drying temperature to 60-80℃, and the drying time to 1-2 hours;
[0018] The dried chitosan was pulverized using a pulverizer, and the pulverized chitosan was sieved to obtain chitosan powder with a mesh size of 80-120.
[0019] In the step of mixing chitosan with isopropanol and adding sodium hydroxide solution for alkalization to obtain alkalized chitosan:
[0020] Chitosan powder was slowly added to a reaction vessel containing isopropanol and stirred with a stirrer at a speed of 100-200 rpm to form a stable suspension.
[0021] Accurately weigh the sodium hydroxide solid according to the mass of chitosan, and prepare a sodium hydroxide solution with a concentration of 10% to 20% in distilled water.
[0022] Sodium hydroxide solution was slowly added dropwise to a mixture of chitosan and isopropanol, with stirring continued during the addition process. The reaction time was 0.5 to 1 hour until the chitosan was completely alkalized, thus obtaining alkalized chitosan.
[0023] In the step of placing the alkalized chitosan in a cooling device for hydroxypropylation:
[0024] The reaction vessel containing alkalized chitosan was placed in an ice-water bath, and the temperature was controlled at 0-5℃.
[0025] Based on a molar ratio of chitosan to propylene oxide of 1:3 to 5, propylene oxide is slowly added dropwise to the reaction vessel through a dropping funnel, with the addition time controlled at 30 to 60 minutes.
[0026] After the propylene oxide has been added, continue stirring at 0–5°C for 1–2 hours.
[0027] In the step of using glacial acetic acid as a neutralizing agent and carrying out the neutralization reaction by adding glacial acetic acid dropwise to the reaction solution:
[0028] Glacial acetic acid was prepared by mixing it with distilled water to obtain a glacial acetic acid solution with a purity of ≥99.5%.
[0029] The glacial acetic acid solution was slowly added dropwise to the reaction solution to carry out the neutralization reaction, and the mixture was stirred with a stirrer at a speed of 150-250 rpm. During the addition process, the pH value of the reaction solution was monitored in real time using a pH meter.
[0030] To control the endpoint of the neutralization reaction, check whether the pH of the reaction solution is stable at around 7.
[0031] In the step of adding anhydrous ethanol to the reaction solution, causing hydroxypropyl chitosan to precipitate, and then processing the precipitate to obtain crude hydroxypropyl chitosan:
[0032] With the volume ratio of anhydrous ethanol to the reaction solution controlled at 2 to 3:1, anhydrous ethanol is slowly added to the neutralized reaction solution, and the reaction product hydroxypropyl chitosan will precipitate out of the solution.
[0033] Use a vacuum filtration device to filter the precipitate, collect the precipitate, and then wash the precipitate 2-3 times with anhydrous ethanol. Each time you wash, add anhydrous ethanol to the precipitate, stir, and then filter again.
[0034] The washed precipitate was dried in an oven at 60–80°C until constant weight to obtain crude hydroxypropyl chitosan.
[0035] In the step of purifying and drying the crude hydroxypropyl chitosan to obtain a highly substituted hydroxypropyl chitosan product:
[0036] Dissolve the crude hydroxypropyl chitosan in an appropriate amount of distilled water and stir with a stirrer to form a homogeneous solution.
[0037] The solution is purified by passing it through an ion exchange resin column, including cation exchange resin and anion exchange resin, to remove inorganic ions and other impurities from the solution. The flow rate of the solution through the ion exchange resin column is controlled, generally 1 to 2 ml / min.
[0038] Collect the purified solution and concentrate it under reduced pressure using a rotary evaporator to a certain volume;
[0039] The concentrated solution was poured into a drying tray and placed in a vacuum drying oven for drying. The drying temperature was set to 40–60°C and the vacuum degree to 0.08–0.1 MPa. The solution was dried to constant weight to obtain a highly substituted hydroxypropyl chitosan product.
[0040] This invention discloses a highly substituted hydroxypropyl chitosan and its preparation method, comprising the following steps using chitosan, sodium hydroxide, propylene oxide, and isopropanol: obtaining chitosan raw material and pretreating the chitosan, followed by pulverizing it into powder; mixing chitosan with isopropanol and adding sodium hydroxide solution for alkalization treatment to obtain alkalized chitosan; placing the alkalized chitosan in a cooling device for hydroxypropylation reaction; using glacial acetic acid as a neutralizing agent, neutralizing the reaction solution by adding glacial acetic acid dropwise; adding anhydrous ethanol to the reaction solution, causing hydroxypropyl chitosan precipitate to form, and treating the precipitate to obtain crude hydroxypropyl chitosan; purifying the crude hydroxypropyl chitosan and drying it to obtain a highly substituted hydroxypropyl chitosan product. Through the above method, precise control of the substitution degree of the hydroxypropylation reaction is achieved, improving the product's performance stability. Attached Figure Description
[0041] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.
[0042] Figure 1 This is a flowchart illustrating the steps of preparing the highly substituted hydroxypropyl chitosan and its preparation method according to the present invention.
[0043] Figure 2 This is a flowchart of steps S100 of the present invention.
[0044] Figure 3 This is a flowchart of steps S200 of the present invention.
[0045] Figure 4 This is a flowchart of steps S300 of the present invention.
[0046] Figure 5 This is a flowchart of steps S400 of the present invention.
[0047] Figure 6 This is a flowchart of steps S500 of the present invention.
[0048] Figure 7 This is a flowchart of steps S600 of the present invention. Detailed Implementation
[0049] Exemplary embodiments will now be described in detail, examples of which are illustrated in the accompanying drawings. When the following description relates to the drawings, unless otherwise indicated, the same numbers in different drawings represent the same or similar elements. The embodiments described in the following exemplary embodiments do not represent all embodiments consistent with this application.
[0050] The terminology used in this application is for the purpose of describing particular embodiments only and is not intended to be limiting of the application. The singular forms “a,” “the,” and “the” used in this application and the appended claims are also intended to include the plural forms unless the context clearly indicates otherwise. It should also be understood that the term “and / or” as used herein refers to and includes any or all possible combinations of one or more of the associated listed items.
[0051] It should be understood that although the terms first, second, third, etc., may be used in this application to describe various information, such information should not be limited to these terms. These terms are only used to distinguish information of the same type from one another. For example, without departing from the scope of this application, first information may also be referred to as second information, and similarly, second information may also be referred to as first information. Depending on the context, the word "if" as used herein may be interpreted as "when," "when," or "in response to determination."
[0052] This invention provides a highly substituted hydroxypropyl chitosan, comprising the following raw materials:
[0053] Chitosan, sodium hydroxide, propylene oxide, and isopropanol.
[0054] Please see Figures 1 to 7 The present invention also provides a method for preparing highly substituted hydroxypropyl chitosan, comprising the following steps:
[0055] S100: Obtain chitosan raw material and pre-treat the chitosan, then pulverize it into powder.
[0056] In this embodiment, chitosan raw material is obtained and pretreated. After pretreatment, the chitosan is pulverized into powder. The specific process is as follows:
[0057] S101: Use a precision electronic balance to accurately weigh the chitosan raw material;
[0058] S102: Place the weighed chitosan in a drying oven to remove moisture, set the drying temperature to 60-80℃, and the drying time to 1-2 hours;
[0059] S103: The dried chitosan is pulverized using a pulverizer, and the pulverized chitosan is sieved to obtain chitosan powder of 80-120 mesh.
[0060] In the above process, firstly, the chitosan raw material is accurately weighed using a precision electronic balance; then, the weighed chitosan is placed in a drying oven to remove moisture, and the drying temperature is set to 60-80℃ for 1-2 hours; then, the dried chitosan is pulverized using a pulverizer, and the pulverized chitosan is sieved to obtain 80-120 mesh chitosan powder.
[0061] S200: Chitosan is mixed with isopropanol and then alkalized with sodium hydroxide solution to obtain alkalized chitosan.
[0062] In this embodiment, chitosan is mixed with isopropanol, and then alkalized with sodium hydroxide solution to obtain alkalized chitosan. The specific process is as follows:
[0063] S201: Slowly add chitosan powder to a reaction vessel containing isopropanol, and stir with a stirrer at a speed of 100-200 rpm to form a stable suspension.
[0064] S202: Accurately weigh the sodium hydroxide solid according to the mass of chitosan, and prepare a sodium hydroxide solution with a concentration of 10% to 20% in distilled water.
[0065] S203: Slowly add sodium hydroxide solution dropwise to the mixture of chitosan and isopropanol, stirring continuously during the addition process. The reaction time is 0.5 to 1 hour until the chitosan is completely alkalized, thus obtaining alkalized chitosan.
[0066] In the above process, chitosan powder is first slowly added to a reaction vessel containing isopropanol, and stirred with a stirrer at a speed of 100-200 rpm to form a stable suspension. Then, sodium hydroxide solid is accurately weighed according to the mass of chitosan, and a sodium hydroxide solution with a concentration of 10%-20% is prepared in distilled water. The sodium hydroxide solution is then slowly added dropwise to the mixture of chitosan and isopropanol, and stirring is continued during the addition process. The reaction time is 0.5-1 hour until the chitosan is completely alkalized, and alkalized chitosan is obtained.
[0067] S300: The alkalized chitosan is placed in a cooling device for hydroxypropylation.
[0068] In this embodiment, the alkalized chitosan is placed in a cooling device for hydroxypropylation reaction. The specific process is as follows:
[0069] S301: Place the reaction vessel containing alkalized chitosan in an ice-water bath, and control the temperature at 0-5℃.
[0070] S302: Based on the molar ratio of chitosan to propylene oxide of 1:3 to 5, slowly add propylene oxide dropwise into the reaction vessel through a dropping funnel, and control the dropping time to 30 to 60 minutes.
[0071] S303: After the propylene oxide has been added, continue stirring at 0-5℃ for 1-2 hours.
[0072] In the above process, the reaction vessel containing alkalized chitosan is first placed in an ice-water bath, and the temperature is controlled at 0-5℃. Then, according to the molar ratio of chitosan to propylene oxide of 1:3-5, propylene oxide is slowly added dropwise to the reaction vessel through a dropping funnel, and the dropping time is controlled at 30-60 minutes. After the propylene oxide is completely added, the reaction is stirred at 0-5℃ for 1-2 hours.
[0073] S400: Glacial acetic acid is used as a neutralizing agent, and the neutralization reaction is carried out by adding glacial acetic acid dropwise to the reaction solution.
[0074] In this embodiment, glacial acetic acid is used as a neutralizing agent. The neutralization reaction is carried out by adding glacial acetic acid dropwise to the reaction solution. The specific process is as follows:
[0075] S401: Prepare a glacial acetic acid solution by mixing glacial acetic acid with distilled water, wherein the purity of the glacial acetic acid is ≥99.5%.
[0076] S402: Slowly add glacial acetic acid solution dropwise to the reaction solution to carry out the neutralization reaction, and use a stirrer to stir at a speed of 150-250 rpm. During the dropwise addition, use a pH meter to monitor the pH value of the reaction solution in real time.
[0077] S403: Controls the endpoint of the neutralization reaction by checking whether the pH of the reaction solution is stable at around 7.
[0078] In the above process, glacial acetic acid is first prepared by mixing it with distilled water to obtain a glacial acetic acid solution with a purity of ≥99.5%. Then, the glacial acetic acid solution is slowly added dropwise to the reaction solution to carry out the neutralization reaction, and a stirrer is used to stir the solution at a speed of 150-250 rpm. During the addition, a pH meter is used to monitor the pH value of the reaction solution in real time. The endpoint of the neutralization reaction is then controlled by checking whether the pH value of the reaction solution is stable at around 7. When the pH value of the reaction solution approaches 7, the dropping rate of glacial acetic acid is slowed down to dropwise addition, and stirring is continued while monitoring the pH value. When the pH meter shows that the pH value of the reaction solution is stable at around 7, the addition of glacial acetic acid is stopped, and the neutralization reaction is completed. Precise control of the neutralization endpoint can avoid excessive acidification or alkalization of the product and ensure product quality.
[0079] S500: Anhydrous ethanol is added to the reaction solution, and hydroxypropyl chitosan precipitates out. The precipitate is then processed to obtain crude hydroxypropyl chitosan.
[0080] In this embodiment, anhydrous ethanol is added to the reaction solution, causing hydroxypropyl chitosan to precipitate. The precipitate is then treated to obtain crude hydroxypropyl chitosan. The specific process is as follows:
[0081] S501: According to the volume ratio of anhydrous ethanol to reaction solution controlled at 2 to 3:1, anhydrous ethanol is slowly added to the neutralized reaction solution, and the reaction product hydroxypropyl chitosan will precipitate out of the solution.
[0082] S502: Use a vacuum filter to filter the precipitate, collect the precipitate, and wash the precipitate 2 to 3 times with anhydrous ethanol. Add anhydrous ethanol to the precipitate each time you wash it, stir it, and then filter it again.
[0083] S503: The washed precipitate is dried in an oven at 60-80°C until constant weight to obtain crude hydroxypropyl chitosan.
[0084] In the above process, firstly, anhydrous ethanol is slowly added to the neutralized reaction solution according to the volume ratio of anhydrous ethanol to the reaction solution of 2 to 3:1. The reaction product hydroxypropyl chitosan will precipitate from the solution. Then, the precipitate is filtered using a vacuum filtration device and collected. The precipitate is then washed 2 to 3 times with anhydrous ethanol, with anhydrous ethanol added to the precipitate each time, stirred, and filtered again. The washed precipitate is then placed in an oven at 60 to 80°C and dried to constant weight to obtain crude hydroxypropyl chitosan.
[0085] S600: The crude hydroxypropyl chitosan is purified and dried to obtain a highly substituted hydroxypropyl chitosan product.
[0086] In this embodiment, the crude hydroxypropyl chitosan is purified and dried to obtain a highly substituted hydroxypropyl chitosan product. The specific process is as follows:
[0087] S601: Dissolve crude hydroxypropyl chitosan in an appropriate amount of distilled water and stir with a stirrer to form a homogeneous solution;
[0088] S602: The solution is purified by passing it through an ion exchange resin column, including cation exchange resin and anion exchange resin, to remove inorganic ions and other impurities from the solution, and the flow rate of the solution through the ion exchange resin column is controlled, generally 1 to 2 ml / min.
[0089] S603: Collect the purified solution and concentrate it under reduced pressure using a rotary evaporator to a certain volume;
[0090] S604: Pour the concentrated solution into a drying tray and place it in a vacuum drying oven for drying. Set the drying temperature to 40-60℃ and the vacuum degree to 0.08-0.1MPa. Dry until constant weight to obtain a highly substituted hydroxypropyl chitosan product.
[0091] In the above process, crude hydroxypropyl chitosan is first dissolved in an appropriate amount of distilled water and stirred with a stirrer to form a homogeneous solution. Then, the solution is purified by passing it through an ion exchange resin column, including cation exchange resin and anion exchange resin, to remove inorganic ions and other impurities from the solution. The flow rate of the solution through the ion exchange resin column is controlled, generally 1-2 ml / min. The purified solution is then collected and concentrated under reduced pressure using a rotary evaporator to concentrate the solution to a certain volume. Finally, the concentrated solution is poured into a drying tray and placed in a vacuum drying oven for drying. The drying temperature is set at 40-60℃ and the vacuum degree is 0.08-0.1 MPa. The solution is dried to constant weight to obtain a highly substituted hydroxypropyl chitosan product.
[0092] Other embodiments of this application will readily occur to those skilled in the art upon consideration of the specification and practice of the disclosure herein. This application is intended to cover any variations, uses, or adaptations of this application that follow the general principles of this application and include common knowledge or customary techniques in the art not disclosed herein.
[0093] It should be understood that this application is not limited to the precise structure described above and shown in the accompanying drawings, and various modifications and changes can be made without departing from its scope.
Claims
1. A high degree of substitution hydroxypropyl chitosan, characterized in that, The raw materials include the following: Chitosan, sodium hydroxide, propylene oxide and isopropyl alcohol.
2. A method for preparing high-substituted hydroxypropyl chitosan, such as the high-substituted hydroxypropyl chitosan according to claim 1, characterized by, The steps include the following: Obtain chitosan raw materials, and pretreat the chitosan, then crush it into powder after pretreatment; Mix the chitosan with isopropyl alcohol, add sodium hydroxide solution for alkalization treatment, and obtain alkalized chitosan; Place the alkalized chitosan in a cooling device for hydroxypropylation reaction; Use glacial acetic acid as a neutralizing agent, and perform neutralization reaction by adding glacial acetic acid dropwise in the reaction solution; Add anhydrous ethanol to the reaction solution, and the reaction solution precipitates hydroxypropyl chitosan, and the precipitate is treated to obtain crude hydroxypropyl chitosan; Purify and dry the crude hydroxypropyl chitosan to obtain high-substitution hydroxypropyl chitosan product.
3. The method for preparing highly substituted hydroxypropyl chitosan as described in claim 2, characterized in that, In the step of obtaining chitosan raw materials, and pretreating the chitosan, and crushing it into powder after pretreatment: Use a precision electronic balance to accurately weigh the chitosan raw materials; Place the weighed chitosan in a drying oven to remove moisture, set the drying temperature to 60-80℃, and the drying time to 1-2h; Use a crusher to crush the dried chitosan, and sieve the crushed chitosan to obtain 80-120 mesh chitosan powder.
4. The method for preparing highly substituted hydroxypropyl chitosan as described in claim 2, characterized in that, In the step of mixing the chitosan with isopropyl alcohol, adding sodium hydroxide solution for alkalization treatment, and obtaining alkalized chitosan: Slowly add the chitosan powder to a reaction container containing isopropyl alcohol, and use a stirrer to stir at a speed of 100-200 rpm to form a stable suspension; Accurately weigh sodium hydroxide solid according to the mass of chitosan, and prepare a 10%-20% sodium hydroxide solution in distilled water; Slowly add the sodium hydroxide solution to the mixture of chitosan and isopropyl alcohol, continue stirring during the addition process, and the reaction time is 0.5-1h until the chitosan is completely alkalized to obtain alkalized chitosan.
5. The method for preparing highly substituted hydroxypropyl chitosan as described in claim 2, characterized in that, In the step of placing the alkalized chitosan in a cooling device for hydroxypropylation reaction: Place the reaction container containing alkalized chitosan in an ice water bath, and control the temperature at 0-5℃; According to the molar ratio of chitosan to propylene oxide being 1:3-5, slowly add propylene oxide to the reaction container through a dropping funnel, and control the addition time to be 30-60min; After the addition of propylene oxide is completed, continue stirring at 0-5℃ for 1-2h.
6. The method for preparing highly substituted hydroxypropyl chitosan as described in claim 2, characterized in that, In the step of using glacial acetic acid as a neutralizing agent, and performing neutralization reaction by adding glacial acetic acid dropwise in the reaction solution: Prepare a glacial acetic acid solution by mixing glacial acetic acid with distilled water, and the purity of glacial acetic acid is ≥99.5%; Slowly add the glacial acetic acid solution to the reaction solution for neutralization reaction, and use a stirrer to stir at a speed of 150-250 rpm, and use a pH meter to monitor the pH value of the reaction solution in real time during the addition process; Control the end point of the neutralization reaction by checking whether the pH value of the reaction solution is stable at about 7.
7. The method for preparing highly substituted hydroxypropyl chitosan as described in claim 2, characterized in that, In the step of adding anhydrous ethanol to the reaction solution, and the reaction solution precipitates hydroxypropyl chitosan, and the precipitate is treated to obtain crude hydroxypropyl chitosan: According to the volume ratio of anhydrous ethanol to the reaction liquid is controlled at 2-3:1, the anhydrous ethanol is slowly added to the neutralized reaction liquid, and the reaction product hydroxypropyl chitosan is precipitated from the solution; The precipitate is filtered using a suction filtration device, and the precipitate is collected. The precipitate is washed with anhydrous ethanol for 2-3 times. Anhydrous ethanol is added to the precipitate each time, stirred, and then filtered again. The washed precipitate is placed in an oven at 60-80℃ and dried to constant weight to obtain crude hydroxypropyl chitosan.
8. The method for preparing highly substituted hydroxypropyl chitosan as described in claim 2, characterized in that, In the step of purifying and drying the crude hydroxypropyl chitosan to obtain a high-substitution hydroxypropyl chitosan product: Dissolve the crude hydroxypropyl chitosan in an appropriate amount of distilled water and use a stirrer to stir to form a uniform solution; The solution is purified by passing through an ion exchange resin column, including cation exchange resin and anion exchange resin, to remove inorganic ions and other impurities in the solution, and the flow rate of the solution through the ion exchange resin column is controlled, generally 1-2 ml / min; Collect the purified solution and use a rotary evaporator to concentrate under reduced pressure to a certain volume. Pour the concentrated solution into a drying pan and place it in a vacuum drying oven. Set the drying temperature to 40-60℃ and the vacuum degree to 0.08-0.1 MPa. Dry to constant weight to obtain a high-substitution hydroxypropyl chitosan product.