Preparation method and application of pH-responsive liquefied chitin

Abstract

This invention discloses a method for preparing pH-responsive liquefied chitin and its application, belonging to the field of natural polymer material processing technology. Using chitin as a raw material, this invention achieves the dissolution of chitin through liquefaction treatment while retaining a high number of hydrophobic groups. The resulting liquefied chitin exhibits pH-responsive rheological properties. Compared to existing deacetylation processes, this process uses milder conditions, avoiding excessive deacetylation while reducing production costs and being more environmentally friendly. The preparation method of this invention is simple, the degree of deacetylation is more controllable, and the rheological properties of the product are more suitable for the development and application of chitin-based hydrophobic biomaterials.

Description

Technical Field

[0001] This invention relates to a method for preparing pH-responsive liquefied chitin and its application, belonging to the field of natural polymer material processing technology. Background Technology

[0002] Chitin is the second most abundant natural polysaccharide after cellulose, widely found in shrimp and crab shells, insect exoskeletons, and fungal cell walls. Chitin molecules are composed of N-acetyl-D-glucosamine linked by β-(1→4) glycosidic bonds. Its molecular structure contains numerous intermolecular and intramolecular hydrogen bonds, resulting in highly crystalline and dense molecular packing. Therefore, it is difficult to dissolve in water and most common solvents, leading to poor processing properties and limiting its further development and application.

[0003] To improve the processing performance of chitin, industrially, it is typically deacetylated with a strong alkali to remove most of the acetyl groups from the chitin molecule, thus obtaining chitosan. Highly deacetylated chitosan molecules contain a large number of free amino groups, which can be protonated and dissolved in aqueous solutions under acidic conditions, significantly improving their solubility and reactivity. It is widely used in food packaging materials, biomedical materials, drug delivery carriers, water treatment flocculants, and functional coatings.

[0004] However, the high acetyl content in chitosan molecules with high deacetylation degrees damages the original hydrophobic structure of the material, thus limiting its potential applications in waterproof materials, hydrophobic coatings, and interface control.

[0005] Therefore, developing a method that can maintain the partial acetyl structure of chitin while forming a stable liquid processable system with good rheological properties is of great significance for expanding the application of low-deacetylated chitin in hydrophobic materials, hydrophobic bio-based interface materials, and waterproof coatings. Summary of the Invention

[0006] To address the shortcomings of existing technologies, this invention utilizes chitin powder as a raw material and constructs a chitin liquefaction method based on a deacetylation process. This method employs relatively mild reaction conditions, enabling partial deacetylation of chitin while simultaneously forming a stable liquid system. This yields chitin derivatives with adjustable deacetylation degrees that retain their original hydrophobic properties. Compared to traditional deacetylation methods, the liquefied chitin obtained by this invention not only maintains good hydrophobic properties but also exhibits significant pH-responsive rheological characteristics. This significantly enhances the processing performance and application potential of chitin in solution, providing a new technical approach for the further development and utilization of chitin in functional and bio-based materials.

[0007] This invention is achieved through the following technical solution: The first objective of this invention is to provide a method for preparing pH-responsive liquefied chitosan, comprising the following steps: S1. Chitosan powder is dispersed in a sodium hydroxide solution with a mass fraction of 35%-45% to obtain the reaction system; S2, Increase the temperature by 1 unit every 5-10 minutes. o The rate of increase of temperature C, and the rate of increase of temperature per 1°C. o Dilute the reaction solution to 1.5-3 times at step C; terminate the reaction when chitosan with the desired degree of deacetylation is obtained. S3. Separate and obtain the pH-responsive liquefied chitosan.

[0008] In one embodiment of the present invention, in step S1, the ratio of chitin powder to sodium hydroxide solution is 1:6-10 g:g.

[0009] In one embodiment of the present invention, in step S2, the reaction is terminated by diluting the reaction solution with water at a ratio of 10-30 times the mass of the substrate chitin powder.

[0010] In one embodiment of the present invention, the degree of deacetylation of the pH-responsive liquefied chitosan is 40%-50%.

[0011] In one embodiment of the present invention, in order to obtain liquefied chitin with a degree of deacetylation of 40%-50%, the reaction is terminated in step S2 after 30-50 minutes.

[0012] In one embodiment of the present invention, in step S, the separation is performed by centrifugation.

[0013] In one embodiment of the present invention, the centrifugation is performed under a centrifugal force of 8000-15000 g.

[0014] A second objective of this invention is to provide a pH-responsive liquefied chitosan prepared by the method described above.

[0015] In one embodiment of the present invention, the pH-responsive liquefied chitosan can control the rheological properties of the system by adjusting the pH of the system.

[0016] A third objective of this invention is to provide the application of the aforementioned pH-responsive liquefied chitin in chitin-based hydrophobic biomaterials.

[0017] In one embodiment of the present invention, the application is to prepare a hydrophobic film or hydrophobic coating using pH-responsive liquefied chitin.

[0018] The beneficial effects of this invention are: This invention uses chitin as a raw material and achieves the dissolution of chitin by liquefaction treatment while retaining a high number of hydrophobic groups. At the same time, the obtained liquefied chitin has pH-responsive rheological properties. Compared to existing deacetylation processes, this process has milder processing conditions, which can reduce production costs while avoiding excessive deacetylation and is more environmentally friendly.

[0019] The preparation method of this invention is simple, the degree of deacetylation is more controllable, and the rheological properties of the product are more suitable for the development and application of chitin-based hydrophobic biomaterials (membranes, coatings, etc.). Attached Figure Description

[0020] 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.

[0021] Figure 1 The relationship between the degree of deacetylation of chitin and its hydrophobic properties; Figure 2 Photographs showing the liquefaction process of chitin; Figure 3 This refers to the change in degree of deacetylation during the liquefaction process in Example 2; Figure 4 Membrane properties (A) and hydrophobicity (B) of gradient deacetylated liquefied chitin powder samples. Figure 5 Contact angle stability (A) and water resistance (B) of gradient deacetylated liquefied chitin powder samples; Figure 6 pH-responsive viscosity change of liquefied chitin with a degree of deacetylation of 43.94%; Figure 7 This is a graph showing the change in degree of deacetylation during the liquefaction process in Example 3; Figure 8 This is a graph showing the change in degree of deacetylation during the liquefaction process in Example 4; Figure 9 The change in degree of deacetylation during the liquefaction process at a feed-to-liquid ratio of 1:20; Figure 10 The reaction temperature is 70°C. o Changes in degree of deacetylation during liquefaction at C; Figure 11 This refers to the deacetylation changes during liquefaction under rapid heating. Figure 12 To avoid the impact of stepwise dilution on the degree of deacetylation during liquefaction; Figure 13 The effect of different concentrations of NaOH solution on the degree of deacetylation of chitin under traditional deacetylation treatment. Detailed Implementation

[0022] The present invention will be further illustrated below with specific examples. These embodiments are for illustrative purposes only and are not intended to limit the scope of the invention. Furthermore, after reading the teachings of this invention, those skilled in the art can make various alterations or modifications to the invention, and these equivalent forms also fall within the scope defined by the appended claims.

[0023] Source of raw materials Chitosan powder that has not undergone deacetylation was purchased from Sinopharm Chemical Reagent Co., Ltd.

[0024] 50%, 70%, 80%, 90%, and 95% are commercially available chitosan products with known degrees of deacetylation, purchased from Shanghai Maclean Biochemical Technology Co., Ltd.

[0025] Detection method: (1) Deacetylation degree detection The degree of deacetylation (DD) was determined by alkaline titration. 0.2000 g of deacetylated chitin sample was accurately weighed and placed in a 250 mL Erlenmeyer flask. 30 mL of 0.1 mol / L HCl standard solution was added. The system was placed on a magnetic stirrer and incubated at 25°C. o Under conditions C, the mixture was stirred continuously at 500 rpm for 1 h to ensure thorough dispersion and complete reaction with hydrochloric acid in the acidic solution. After the reaction was complete, 3 drops of a mixed indicator (methyl orange: aniline blue = 1:2, mass concentration 1 g / L) were added to the system. Titration was then performed using a 0.1 mol / L NaOH standard solution. The titration was stopped when the solution color changed from purple-red to blue-green, and the volume of NaOH solution consumed was recorded. Based on the acid-base consumption, the degree of deacetylation of the sample was calculated using the following formula:

[0026] In the formula, c1 and V1 represent the concentration (mol / L) and volume (mL) of the hydrochloric acid standard solution, respectively; c0 and V0 represent the concentration (mol / L) and volume (mL) of the NaOH standard solution, respectively; 10 -3 is a unit conversion factor used to convert volume units mL to L; 16 is the molar mass of amino (-NH2) (g / mol); m is the sample mass (g); 0.0994 is the theoretical amino content of completely deacetylated chitin, which is calculated from 16 / 161, where 161 is the theoretical relative molecular mass of the repeating structural unit of chitin after deacetylation.

[0027] (2) Determination of hydrophobic properties The static water contact angle of chitin and chitosan samples with different degrees of deacetylation was measured using the seated drop method. The specific procedure was as follows: 20 mg of chitin or chitosan powder with a specific degree of deacetylation was accurately weighed and evenly spread on a 0.25 cm² area... 2 The surface of the square double-sided adhesive was prepared. To ensure the flatness and density of the test surface, a glass slide was used to gently press the powder onto the adhesive surface during the spreading process, forming a uniform, continuous, and as flat as possible solid layer. The double-sided adhesive loaded with the sample was then fixed onto a clean glass slide, ensuring the overall substrate was level and free of significant undulations or warping. The prepared sample slide was placed on the sample stage of the contact angle measuring instrument at 25±1°. o The determination was performed under C conditions. A microsyringe with a flat-tipped needle of 0.45 mm diameter was used to slowly add 2 μL of deionized water to the sample surface using the seated drop method. To reduce the influence of droplet kinetic energy on the test results, the needle was kept about 1 mm away from the sample surface during the dropping process, and the droplet was released at a steady rate to allow it to naturally contact the sample surface.

[0028] (3) Determination of apparent viscosity To characterize the rheological properties and structural stability of the liquefied chitin system, the apparent viscosity of the sample was determined using a rotational viscometer. The specific procedure was as follows: 50 mL of the liquefied chitin sample was placed in a clean, dry 100 mL beaker and allowed to stand for 5 minutes before testing to eliminate the influence of air bubbles. A suitable rotor model (rotors 1-4) was selected based on the sample viscosity range, and the apparent viscosity of the sample was measured stepwise within a rotational speed range of 6-60 rpm. During the test, the percentage of torque measured was controlled within the effective measurement range of 40%-80% to ensure the accuracy and repeatability of the test results. If the torque value exceeded this range, optimization was performed by changing the rotor or adjusting the rotational speed. Preliminary analysis of the apparent viscosity variation at different rotational speeds was used to evaluate the shear response behavior and flow characteristics of the liquefied chitin system.

[0029] (4) Membrane performance measurement Weigh 10 g of liquefied chitosan solution and pour it evenly into a 25 cm² area. 2 In a square polytetrafluoroethylene (PTFE) molded sheet, a self-supporting film is formed by static drying under horizontal conditions. After drying, the film is peeled off from the molded sheet, washed with excess deionized water until neutral, and then placed in a constant temperature and humidity environment (25°C). o After equilibration for 24 hours at C (relative humidity 50%), subsequent tests were conducted. The mechanical properties of the film were determined using a physical property analyzer in tensile mode, using an A / TG tensile fixture. During the test, the probe movement speed was 2 mm / s, and stress-strain curves were obtained through the tensile process.

[0030] The technical solution of the present invention will be described in detail below with reference to specific embodiments. In the following embodiments, unless otherwise specified, the reagents, materials and equipment used can be purchased commercially, prepared by conventional methods, or commonly used in the industry.

[0031] Example 1: This invention first clarifies the relationship between the degree of deacetylation and hydrophobicity, and the results are as follows: Figure 1 As shown, when the degree of deacetylation is 4%, 16%, 50%, 70%, 80%, 90%, and 95% (where 4% and 16% are self-made chitin with a measured degree of deacetylation, and 50%, 70%, 80%, 90%, and 95% are commercially available chitin products with known degrees of deacetylation), the corresponding water contact angles are 116°, 114°, 110.45°, 88.4°, 60°, 52.35°, and 51.6°, respectively. Overall, the contact angle shows a continuous decreasing trend with increasing degree of deacetylation, indicating that the wettability of the material surface gradually increases while the hydrophobicity gradually decreases. To further quantitatively analyze the relationship between the two, Boltzmann nonlinear fitting was performed on the experimental data. The results show that the degree of deacetylation (x) and the contact angle (y) conform to a typical S-shaped decay function relationship. Therefore, in order to retain the hydrophobic properties of chitin itself, it is necessary to obtain chitin samples with low degree of deacetylation and film-forming properties during deacetylation treatment.

[0032] Example 2: Preparation method of liquefied chitin: (1) Weigh out the chitin powder and disperse it fully in a 38% sodium hydroxide solution at a material-to-liquid ratio of 1:8 (g / g).

[0033] (2) Connect the reaction system to a circulating water bath and run it at a rate of 1 rpm for 90 minutes. o The temperature was increased from 40°C to 9°C using a gradient heating method over 9 minutes. o C increased to 50 o C. Meanwhile, for every 1 degree Celsius increase in temperature... o C. Deionized water, at a mass equal to that of the substrate, was added to dilute the reaction solution. During the heating process, samples were continuously taken at set time intervals to obtain chitin with different degrees of deacetylation. After determining the degree of deacetylation at different times, the reaction was terminated by adding 20 times the mass of deionized water to the system to dilute the reaction solution.

[0034] (3) Centrifuge at 10000g to obtain the lower wet base precipitate, and fully disperse the precipitate in 5 times the mass of deionized water to obtain a transparent chitin solution (at this time the pH of the system is 14).

[0035] (4) The pH of the system was adjusted by using a 17% hydrochloric acid solution to obtain pH-responsive liquefied chitin with controllable viscosity and degree of deacetylation.

[0036] In Example 2, during the liquefaction process, the chitin particles gradually undergo structural relaxation and swelling, and further disperse and dissolve, ultimately forming a uniform and transparent liquefied chitin system (e.g., Figure 2 As shown in the figure, a liquefied chitin material that is easy to process is obtained.

[0037] The change in degree of deacetylation during the reaction process is measured as follows: Figure 3 As shown, by controlling the reaction conditions, the deacetylation process can be made more mild and controllable, thereby obtaining chitin samples with a gradual gradient change in the degree of deacetylation within the range of 15%-60%.

[0038] Chitosan samples with varying degrees of deacetylation at different time points (31.82%, 36.33%, 43.94%, 45.88%, and 48.11%) were tested for hydrophobic stability and water resistance. The results are as follows: Figure 4 As shown, samples with deacetylation degrees of 48.11% and 45.88% exhibited a rapid decrease in contact angle to below 20° within 10-250 ms after contact with water droplets, indicating that the water droplets spread and penetrated within a very short time. Simultaneously, their water absorption rate rapidly increased to nearly 100%, suggesting that the internal pores or intermolecular networks of the material are easily penetrated by water molecules, resulting in weak structural stability. In contrast, samples with deacetylation degrees in the range of 31.82%–43.94% maintained a relatively stable contact angle (135°–82°) within 500 ms after contact with water droplets, and their water absorption rate remained at a low level (0.92%–10%), demonstrating significantly delayed wetting and penetration behavior. This indicates that liquefied chitin with low deacetylation degrees possesses good water resistance.

[0039] The above samples (degree of deacetylation 31.82%, 36.33%, 43.94%, 45.88%, and 48.11%) were used to prepare films, and their contact angles and film properties are as follows. Figure 5 As shown, the results indicate that the chitin sample with a degree of deacetylation of 43.94% can maintain high hydrophobicity while exhibiting good film-forming properties (e.g., Figure 5 As shown in Figure B), the hydrophobic properties decrease when the degree of deacetylation is higher than 43.94%, and a good film cannot be formed when the degree of deacetylation is lower than 43.94%. Figure 5 As shown in Figure A, the membranes prepared at degrees of deacetylation of 31.82% and 36.33% could not be subjected to stress tests.

[0040] Further, a chitin sample with a degree of deacetylation of 43.94% was selected for pH response testing. It was prepared into liquefied chitin samples of different concentrations (0.15, 0.12, 0.09, 0.06, 0.03 g / mL). The relationship between the change in apparent viscosity and pH is as follows: Figure 6 As shown, during the process of gradually adjusting the pH of the system from 14 to 1, the apparent viscosity of the liquefied chitin system at different concentrations exhibited obvious concentration dependence and phased changes. For the 0.15 g / mL system, the apparent viscosity under initial strongly alkaline conditions was 1353.60 mPa. As pH decreases, viscosity increases rapidly, reaching a peak of 10986.50 mPa at pH=12. The pressure then gradually decreased, stabilizing at approximately 1926.00 mPa in the strongly acidic region. The viscosity increased rapidly over a period of approximately 1000 μs. The process exhibited a significant trend of "first a sharp increase followed by a sustained decrease," with the peak viscosity being more than eight times the initial value, indicating a strong structural remodeling within a specific pH range. The 0.12 g / mL system showed a similar pattern, with the viscosity increasing from 1301.73 mPa. s rose to a peak of 7110.10 mPa. The value of s then gradually decreased and stabilized at approximately 1299.67 mPa under acidic conditions. Compared to the 0.15 g / mL system, the peak value was significantly lower, and the fluctuation range was reduced. When the concentration was reduced to 0.09 g / mL, the peak viscosity was 3029.63 mPa. s, then slowly decreased to approximately 1006.56 mPa. The peak value of the 0.06 g / mL system was 1270.13 mPa. The variation in viscosity further decreased; while the 0.03 g / mL system showed the smallest overall fluctuation, with viscosity remaining basically between 873.77 and 1078.50 mPa. Between s, the viscosity fluctuates only slightly. In summary, the apparent viscosity of the liquefied chitin system is pH-regulated, and the high-concentration system exhibits a significant peak viscosity phenomenon in a specific pH range (pH=9-13).

[0041] The liquefied chitosan with a degree of deacetylation of over 40% obtained in Example 2 exhibits a dynamic equilibrium between the acetyl and amino groups on the liquefied chitosan molecular chain as the pH changes from alkaline to acidic. This results in a responsive change in viscosity to pH, influenced by a combination of charge regulation and ionic strength shielding effects. This phenomenon is most pronounced in liquefied chitosan samples with a degree of deacetylation around 43.94%; samples with excessively high or low degrees of deacetylation show little pH responsiveness.

[0042] Example 3: Preparation method of liquefied chitin: (1) Weigh out the chitin powder and disperse it fully in a 35% sodium hydroxide solution at a material-to-liquid ratio of 1:6 (g / g).

[0043] (2) Connect the reaction system to a circulating water bath and run it at a rate of 1 rpm for 50 minutes. o The temperature was increased from 45°C to 5°C over a gradient of 5 minutes. o C increased to 55 o C. Meanwhile, for every 1 degree Celsius increase in temperature... o C then adds one times the mass of deionized water relative to the substrate to dilute the reaction solution. During the heating process, samples are continuously taken at set time intervals to obtain chitin with different degrees of deacetylation.

[0044] (3) Centrifuge at 10000g to obtain the lower wet base precipitate, and fully disperse the precipitate in 8 times the mass of deionized water to obtain a transparent chitin solution (the pH of the system is 14 at this time).

[0045] (4) The pH of the system was adjusted using a 17% (v / v) hydrochloric acid solution to obtain pH-responsive liquefied chitosan with controllable viscosity and degree of deacetylation. The change in degree of deacetylation during the reaction process was measured as follows: Figure 7 As shown Example 4: Preparation method of liquefied chitin: (1) Weigh out the chitin powder and disperse it fully in a 40% sodium hydroxide solution at a material-to-liquid ratio of 1:10 (g / g).

[0046] (2) Connect the reaction system to a circulating water bath and run it at a rate of 1 rpm for 80 min. o The temperature was increased from 35°C to 8°C over an 8-minute gradient. o C increased to 45 o C. Meanwhile, for every 1 degree Celsius increase in temperature... o C then adds one times the mass of deionized water relative to the substrate to dilute the reaction solution. During the heating process, samples are continuously taken at set time intervals to obtain chitin with different degrees of deacetylation.

[0047] (3) Centrifuge at 10000g to obtain the lower wet base precipitate, and fully disperse the precipitate in 8 times the mass of deionized water to obtain a transparent chitin solution (the pH of the system is 14 at this time).

[0048] (4) The pH of the system was adjusted using a 17% (v / v) hydrochloric acid solution to obtain pH-responsive liquefied chitosan with controllable viscosity and degree of deacetylation. The change in degree of deacetylation during the reaction process was measured as follows: Figure 8 As shown Comparative Example 1: Effect of feed-to-liquid ratio on the rate of increase in degree of deacetylation The material-to-liquid ratio in step (1) of Example 2 was modified to 1:20 (g / g), while other steps and parameters remained consistent with Example 2. The change in degree of deacetylation during the reaction was measured, and the results are as follows: Figure 9 As shown, the degree of deacetylation in Comparative Example 1 rapidly increased to over 50% within 20 minutes after the start of the reaction, and the final degree of deacetylation was significantly higher than that in Example 2.

[0049] Comparative Example 2: Effect of reaction temperature on the rate of increase in degree of deacetylation The initial temperature in step (2) of Example 2 was modified to 60°C. o C, the final temperature is changed to 70. o C. Other steps and parameters remained consistent with Example 2. The change in the degree of deacetylation during the reaction was measured, and the results are as follows: Figure 10 As shown, the degree of deacetylation in Comparative Example 2 rapidly increased to over 50% within 20 minutes after the start of the reaction, and the final degree of deacetylation was significantly higher than that in Example 2.

[0050] Comparative Example 3: Effect of heating rate on the rate of increase in degree of deacetylation The heating rate in step (2) of Example 2 is modified to be 10 within 9 minutes. o The temperature was increased to 50°C using a gradient heating method of C / 9 min. o C. Other steps and parameters remained consistent with Example 2. The change in the degree of deacetylation during the reaction was measured, and the results are as follows: Figure 11 As shown, the degree of deacetylation in Comparative Example 3 rapidly increased to over 50% within 20 minutes after the start of the reaction, and the final degree of deacetylation was significantly higher than that in Example 2.

[0051] Comparative Example 4: Effect of stepwise dilution on the rate of increase in degree of deacetylation The gradual dilution in step (3) of Example 2 was removed, while other steps and parameters remained consistent with Example 2. The change in degree of deacetylation during the reaction was measured, and the results are as follows: Figure 12 As shown, the degree of deacetylation in Comparative Example 4 rapidly increased to over 50% within 20 minutes after the start of the reaction, and the final degree of deacetylation was significantly higher than that in Example 2.

[0052] As can be seen from the above examples and Comparative Examples 1-4, under unsuitable reaction conditions, the deacetylation reaction rate is relatively fast, and the degree of deacetylation rises rapidly to over 50% after the reaction starts, making it impossible to obtain liquefied chitin products with a degree of deacetylation of 40%-50% in a gentle and controllable manner. The methods proposed in Examples 2-4, by controlling the reaction conditions, make the deacetylation process more gentle and controllable, thereby obtaining chitin samples with a degree of deacetylation within a suitable range. The products prepared by liquefaction have higher controllability and reproducibility in terms of degree of deacetylation control.

[0053] Comparative Example 5: Chitosan treated with conventional deacetylation The specific steps of traditional chitin liquefaction processing are as follows: (1) Weigh out the chitin powder and disperse it fully in sodium hydroxide solutions with mass fractions of 20%, 30%, 40% and 50% at a material-to-liquid ratio of 1:30 (g / g).

[0054] (2) Connect the reaction system at a temperature of 90°C. o The device was used in a circulating water bath and stirred continuously for 6 hours, during which time samples were taken to determine the degree of deacetylation.

[0055] (3) After the reaction is complete, centrifuge at 10,000 g to obtain the lower wet precipitate and wash the precipitate with deionized water until neutral. Dry to obtain chitin with a high degree of deacetylation.

[0056] The change in degree of deacetylation during the reaction was measured, and the results are as follows: Figure 13 As shown in the figure. The results revealed that under high-concentration NaOH solution and a high feed-to-liquid ratio, chitin underwent significant deacetylation within a short time, leading to a rapid increase in the degree of deacetylation. Traditional methods, however, failed to effectively liquefy chitin under lower-concentration NaOH solution conditions. This indicates that under traditional strong alkali and high feed-to-liquid ratio conditions, it is often difficult to stably obtain chitin with a low degree of deacetylation (DD = 30%–50%), while also easily causing excessive damage to the chitin structure and loss of hydrophobic properties.

[0057] The embodiments provided above are not intended to limit the scope of the invention, nor are the described steps intended to limit the order of execution. Any obvious modifications made to the invention by those skilled in the art based on existing common knowledge also fall within the scope of protection defined by the claims.

Claims

1. A method for preparing pH-responsive liquefied chitosan, characterized in that, Includes the following steps: S1. Chitosan powder is dispersed in a sodium hydroxide solution with a mass fraction of 35%-45% to obtain the reaction system; S2, Increase the temperature by 1 unit every 5-10 minutes. o The rate of increase of temperature C, and the rate of increase of temperature per 1°C. o Dilute the reaction solution to 1.5-3 times at step C; terminate the reaction when chitosan with the desired degree of deacetylation is obtained. S3. Separate and obtain the pH-responsive liquefied chitosan.

2. The preparation method according to claim 1, characterized in that, In step S1, the ratio of chitin powder to sodium hydroxide solution is 1:6-10 g:g.

3. The preparation method according to claim 1, characterized in that, In step S2, the reaction is terminated by diluting the reaction solution with 10-30 times the mass of the substrate chitin powder with water.

4. The preparation method according to claim 1, characterized in that, The degree of deacetylation of the pH-responsive liquefied chitosan is 40%-50%.

5. The preparation method according to claim 4, characterized in that, To obtain liquefied chitin with a degree of deacetylation of 40%-50%, the reaction is terminated in step S2 after 30-50 minutes.

6. The preparation method according to claim 1, characterized in that, In step S, separation is carried out by centrifugation, which is performed under a centrifugal force of 8000-15000 g.

7. A pH-responsive liquefied chitosan prepared by the method according to any one of claims 1-6.

8. The application according to claim 7, characterized in that, The pH-responsive liquefied chitosan can control the rheological properties of the system by adjusting the system pH.

9. The application of the pH-responsive liquefied chitin according to claim 7 or 8 in chitin-based hydrophobic biomaterials.

10. The application according to claim 9, characterized in that, The application involves using pH-responsive liquefied chitin to prepare hydrophobic films or coatings.

Images