Composite hydrogel as well as preparation method and application thereof
By chemically cross-linking γ-polyglutamic acid and carboxymethyl chitosan to construct a composite hydrogel, the problems of non-degradability and uneven performance of existing food preservative materials are solved, and a coating material with high mechanical strength and biodegradability is achieved, which is suitable for preserving fruits and vegetables.
Patent Information
- Application Number
- CN202510410902.0
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2025-04-02
- Publication Date
- 2025-09-12
AI Technical Summary
Existing food preservation materials such as polyethylene and polypropylene plastic packaging are non-degradable, it is difficult to balance air permeability and moisture barrier properties, chitosan coatings have poor film-forming properties, carboxymethyl cellulose coatings have weak antibacterial properties, chemical preservatives pose health risks, and it is difficult to meet the comprehensive requirements of mechanical strength, barrier properties and biodegradability.
By chemically cross-linking γ-polyglutamic acid and carboxymethyl chitosan and combining polyethylene glycol diglycidyl ether as a cross-linking agent, a composite hydrogel with a dense and uniform three-dimensional network structure is constructed and applied as a coating material on the surface of fruits and vegetables.
It achieves a biodegradable coating with high mechanical strength and controllable pore size, balances gas exchange and moisture barrier functions, avoids the air permeability defects of traditional plastic packaging, and meets the needs of green food packaging.
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Figure CN120623512A_ABST
Abstract
Description
Technical Field
[0001] The present invention belongs to the technical field of coating materials, and specifically relates to a composite hydrogel, a preparation method and an application thereof. Background Art
[0002] At present, food preservation mainly relies on synthetic plastic packaging materials such as polyethylene (PE) and polypropylene (PP), and their non-degradability leads to serious environmental pollution problems. In addition, the air permeability and moisture barrier properties of plastic packaging are difficult to balance, which can easily cause anaerobic respiration of fruits and vegetables or excessive water loss. Although chitosan (CS) coatings have antibacterial properties, they have poor film-forming properties and high brittleness; carboxymethyl cellulose (CMC) coatings have strong water retention but weak antibacterial properties. In the existing technology, it is difficult for a single polymer material to simultaneously meet the comprehensive requirements of mechanical strength, barrier properties and biodegradability. Although chemical preservatives such as sodium benzoate and potassium sorbate can extend the shelf life, they pose potential health risks and do not meet consumers' demand for green food. Summary of the Invention
[0003] In order to overcome some of the problems mentioned in the above background, the present invention provides a composite hydrogel, a preparation method and applications thereof.
[0004] According to the technical solution of the present invention, a method for preparing a composite hydrogel is provided, comprising the following steps:
[0005] S1. dissolving γ-polyglutamic acid in distilled water to obtain a γ-polyglutamic acid aqueous solution;
[0006] S2. dissolving carboxymethyl chitosan in distilled water to obtain a carboxymethyl chitosan aqueous solution;
[0007] S3. The γ-polyglutamic acid aqueous solution and the γ-polyglutamic acid aqueous solution were mixed and homogenized to obtain a mixed solution;
[0008] S4. Add polyethylene glycol diglycidyl ether to the mixed solution for cross-linking reaction to obtain a composite hydrogel.
[0009] Furthermore, the volume ratio of the γ-polyglutamic acid aqueous solution to the carboxymethyl chitosan aqueous solution is 4:(1-16).
[0010] Furthermore, the cross-linking reaction time is 6-10 hours.
[0011] Furthermore, the polyethylene glycol diglycidyl ether is added to the mixed solution, and then a cross-linking reaction is carried out in a constant temperature water bath at 60° C. After the reaction is completed, a composite hydrogel is obtained.
[0012] Furthermore, the concentration of the γ-polyglutamic acid aqueous solution is (9-10) g / 100 mL; the concentration of the carboxymethyl chitosan aqueous solution is (4-5) g / 100 mL.
[0013] Furthermore, the amount of polyethylene glycol diglycidyl ether added to the mixed solution is (0.8-0.9) mL / 100 mL.
[0014] Furthermore, the present invention also provides a composite hydrogel prepared by the above method, wherein the composite hydrogel has a dense and uniform three-dimensional network structure.
[0015] Furthermore, the pore size distribution range of the three-dimensional network structure in the composite hydrogel is 10-50 μm.
[0016] Furthermore, the present invention provides an application of the composite hydrogel, wherein the composite hydrogel is applied as a coating material to the surface of fruits and vegetables.
[0017] Furthermore, the composite hydrogel is applied as a coating material on the surface of strawberries.
[0018] Compared with the prior art, the present invention has the following beneficial effects:
[0019] The present invention chemically cross-links carboxymethyl chitosan (CMCS) and γ-polyglutamic acid (γ-PGA), combining their advantageous properties (CMCS's antibacterial properties and γ-PGA's water-retention properties), and introduces polyethylene glycol diglycidyl ether (PEGDE) as a cross-linking agent to construct a composite hydrogel with a three-dimensional network structure that combines high mechanical strength, controllable pore size, and biodegradability, meeting the mechanical requirements of food coating materials. At the same time, the controllable pore size distribution effectively balances gas exchange and moisture barrier functions, avoiding the air permeability defects of traditional plastic packaging.
[0020] The present invention is entirely based on natural polymers, avoids white pollution and potential health risks, conforms to the development trend of green food packaging, has a simple preparation process, controllable costs, and has the potential for large-scale application. BRIEF DESCRIPTION OF THE DRAWINGS
[0021] Figure 1 The effect of the ratio of carboxymethyl chitosan and γ-polyglutamic acid solution on the microstructure of the composite hydrogel in the embodiment of the present invention;
[0022] Figure 2 The effect of the ratio of carboxymethyl chitosan and γ-polyglutamic acid solution on the rheological properties of the composite hydrogel in the embodiment of the present invention;
[0023] Figure 3 The effect of cross-linking time on the microstructure of the composite hydrogel in the embodiment of the present invention;
[0024] Figure 4 The effect of cross-linking time on the rheological properties of the composite hydrogel in the embodiment of the present invention;
[0025] Figure 5 The effect of the ratio of carboxymethyl chitosan and γ-polyglutamic acid solution on the water retention rate of the composite hydrogel in the embodiment of the present invention;
[0026] Figure 6 The effect of cross-linking time on the water retention rate of the composite hydrogel in the embodiment of the present invention;
[0027] Figure 7 The effect of different concentrations of composite hydrogels on the L value of strawberries in the embodiments of the present invention;
[0028] Figure 8 The effect of the composite hydrogel coating of the embodiment of the present invention on the soluble solids content of strawberries;
[0029] Figure 9 The effect of the composite hydrogel coating of the embodiment of the present invention on the titratable acid content of strawberries;
[0030] Figure 10 The effect of the composite hydrogel coating of the embodiment of the present invention on the weight loss rate of strawberries;
[0031] Figure 11 These are the changes in strawberries during storage after being treated with composite hydrogels of different concentrations according to the embodiments of the present invention. DETAILED DESCRIPTION
[0032] The following will clearly and completely describe the technical solutions in the embodiments of the present invention in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, rather than all the embodiments; based on the embodiments, all other embodiments obtained by ordinary technicians in this field without making creative work are within the scope of protection.
[0033] Carboxymethyl chitosan is a water-soluble derivative of chitosan. Compared to chitosan gel, carboxymethyl chitosan hydrogel has enhanced antibacterial properties, biocompatibility, and biodegradability. However, its brittleness limits its application in food packaging. γ-Polyglutamate hydrogel is soft but has poor mechanical properties. The composite hydrogel created by combining γ-Polyglutamate and carboxymethyl chitosan based on their performance characteristics has a high water retention rate and exhibits improved fruit preservation during storage.
[0034] The present invention provides a method for preparing a composite hydrogel, comprising the following steps:
[0035] S1. dissolving γ-polyglutamic acid in distilled water to obtain a γ-polyglutamic acid aqueous solution;
[0036] S2. dissolving carboxymethyl chitosan in distilled water to obtain a carboxymethyl chitosan aqueous solution;
[0037] S3. The γ-polyglutamic acid aqueous solution and the γ-polyglutamic acid aqueous solution were homogenized to obtain a mixed solution;
[0038] S4. Add polyethylene glycol diglycidyl ether to the mixed solution for cross-linking reaction to obtain a composite hydrogel.
[0039] It should be noted that by chemically cross-linking carboxymethyl chitosan (CMCS) and γ-polyglutamic acid (γ-PGA), combining the advantages of both (the antibacterial properties of CMCS and the water retention of γ-PGA), and introducing polyethylene glycol diglycidyl ether (PEGDE) as a cross-linking agent, a three-dimensional network structure with high mechanical strength, controllable pore size and biodegradability is constructed to replace traditional plastic packaging and chemical preservatives.
[0040] In a further embodiment of this example, the volume ratio of the γ-polyglutamic acid aqueous solution to the carboxymethyl chitosan aqueous solution is 4:(1-16).
[0041] It should be noted that the high cross-linking density of carboxymethyl chitosan can enhance the mechanical properties of hydrogels. The hydrophilic groups of carboxymethyl chitosan (such as -COOH, -NH2) form a stable three-dimensional network through cross-linking to reduce excessive swelling. However, if the proportion of carboxymethyl chitosan is too high, it will lead to over-dense cross-linking and delayed degradation, masking the active sites of γ-PGA, and reducing cell adhesion and signal response capabilities. The natural anionic properties of γ-polyglutamic acid can promote cell adhesion and growth factor adsorption, and it can be ionized in a physiological environment, giving the hydrogel pH-sensitive properties. However, if the proportion of γ-polyglutamic acid is too high, it will lead to insufficient cross-linking, loose gel structure, prone to swelling and rupture, and reduced cross-linking efficiency.
[0042] In a further embodiment of this example, the cross-linking reaction time is 6-10 hours. It should be noted that a short cross-linking time can preserve active groups and avoid excessive consumption of CMCS amino groups due to prolonged reaction, facilitating subsequent functional modification. However, a too short cross-linking time can lead to incomplete cross-linking, resulting in an uneven network structure and reduced mechanical strength and swelling stability. A corresponding cross-linking time can result in a high cross-linking density, forming a dense network, improving the hydrogel's swelling resistance and sustained release properties, and providing strong stability and reducing the risk of structural collapse. However, a too long cross-linking time can increase brittleness, affecting flexibility and conformability, and can also reduce bioactivity and destroy the bioactive groups of CMCS or γ-PGA.
[0043] In a further embodiment of this example, the polyethylene glycol diglycidyl ether is added to the mixed solution, and then a cross-linking reaction is carried out in a constant temperature water bath at 60° C. After the reaction is completed, a composite hydrogel is obtained.
[0044] In a further embodiment of this example, the concentration of the γ-polyglutamic acid aqueous solution is (9-10) g / 100 mL; the concentration of the carboxymethyl chitosan aqueous solution is (4-5) g / 100 mL.
[0045] In a further embodiment of this example, the amount of polyethylene glycol diglycidyl ether added to the mixed solution is (0.8-0.9) mL / 100 mL.
[0046] A further embodiment of the present invention provides a composite hydrogel prepared by the above method, wherein the composite hydrogel has a dense and uniform three-dimensional network structure.
[0047] In a further embodiment of this example, the pore size distribution range of the three-dimensional network structure in the composite hydrogel is 10-50 μm.
[0048] A further embodiment of the present invention provides an application of the composite hydrogel, wherein the composite hydrogel is applied as a coating material to the surface of fruits and vegetables.
[0049] In a further embodiment of this example, the composite hydrogel is applied as a coating material on the surface of strawberries.
[0050] like Figures 1-6 As shown, the water retention rate of the composite hydrogel is greater than 60%, and the storage modulus (G') is characterized by rheological testing as being significantly higher than that of a single-component hydrogel. The water retention rate of the composite hydrogel is greater than 60%, and the storage modulus (G') is characterized by rheological testing as being significantly higher than that of a single-component hydrogel.
[0051] It should be noted that: Figure 1 A corresponds to the composite hydrogel microstructure prepared in Example 1, B corresponds to the composite hydrogel microstructure prepared in Example 2, C corresponds to the composite hydrogel microstructure prepared in Example 3, D corresponds to the composite hydrogel microstructure prepared in Example 4, and E corresponds to the composite hydrogel microstructure prepared in Example 5;
[0052] Figure 3 A corresponds to the composite hydrogel microstructure prepared in Example 6, B corresponds to the composite hydrogel microstructure prepared in Example 7, C corresponds to the composite hydrogel microstructure prepared in Example 4, D corresponds to the composite hydrogel microstructure prepared in Example 8, and E corresponds to the composite hydrogel microstructure prepared in Example 9.
[0053] Under the optimized ratio (CMCS:γ-PGA = 1:2, cross-linking time 6 hours), the composite hydrogel formed a dense and uniform three-dimensional network structure (pore size 10-50μm), with a significantly higher storage modulus than single-component hydrogels, indicating excellent mechanical strength and deformation resistance, meeting the mechanical requirements of food coating materials. Furthermore, the controlled pore size distribution effectively balanced gas exchange and moisture barrier functions, avoiding the air permeability defects of traditional plastic packaging.
[0054] Example 1
[0055] 9.9 g of γ-polyglutamic acid was dissolved in 100 ml of distilled water and stirred until completely dissolved to obtain a γ-polyglutamic acid aqueous solution; 5 g of carboxymethyl chitosan was dissolved in 100 ml of distilled water and stirred until completely dissolved to obtain a carboxymethyl chitosan aqueous solution.
[0056] The carboxymethyl chitosan aqueous solution and the γ-polyglutamic acid aqueous solution were mixed in a volume ratio of 4:1 to obtain a mixed solution.
[0057] Ethylene glycol diglycidyl ether was added to the mixed solution at a rate of 0.85 mL / 100 mL of the mixed solution, and the cross-linking reaction was carried out in a constant temperature water bath at 60°C for 8 h to form a composite hydrogel.
[0058] Example 2
[0059] 9.9 g of γ-polyglutamic acid was dissolved in 100 ml of distilled water and stirred until completely dissolved to obtain a γ-polyglutamic acid aqueous solution; 5 g of carboxymethyl chitosan was dissolved in 100 ml of distilled water and stirred until completely dissolved to obtain a carboxymethyl chitosan aqueous solution.
[0060] The carboxymethyl chitosan aqueous solution and the γ-polyglutamic acid aqueous solution were mixed in a volume ratio of 2:1 to obtain a mixed solution.
[0061] Ethylene glycol diglycidyl ether was added to the mixed solution at a rate of 0.85 mL / 100 mL of the mixed solution, and the cross-linking reaction was carried out in a constant temperature water bath at 60°C for 8 h to form a composite hydrogel.
[0062] Example 3
[0063] 9.9 g of γ-polyglutamic acid was dissolved in 100 ml of distilled water and stirred until completely dissolved to obtain a γ-polyglutamic acid aqueous solution; 5 g of carboxymethyl chitosan was dissolved in 100 ml of distilled water and stirred until completely dissolved to obtain a carboxymethyl chitosan aqueous solution.
[0064] The carboxymethyl chitosan aqueous solution and the γ-polyglutamic acid aqueous solution were mixed in a volume ratio of 1:1 to obtain a mixed solution.
[0065] Ethylene glycol diglycidyl ether was added to the mixed solution at a rate of 0.85 mL / 100 mL of the mixed solution, and the cross-linking reaction was carried out in a constant temperature water bath at 60°C for 8 h to form a composite hydrogel.
[0066] Example 4
[0067] 9.9 g of γ-polyglutamic acid was dissolved in 100 ml of distilled water and stirred until completely dissolved to obtain a γ-polyglutamic acid aqueous solution; 5 g of carboxymethyl chitosan was dissolved in 100 ml of distilled water and stirred until completely dissolved to obtain a carboxymethyl chitosan aqueous solution.
[0068] The carboxymethyl chitosan aqueous solution and the γ-polyglutamic acid aqueous solution were mixed in a volume ratio of 1:2 to obtain a mixed solution.
[0069] Ethylene glycol diglycidyl ether was added to the mixed solution at a rate of 0.85 mL / 100 mL of the mixed solution, and the cross-linking reaction was carried out in a constant temperature water bath at 60°C for 8 h to form a composite hydrogel.
[0070] Example 5
[0071] 9.9 g of γ-polyglutamic acid was dissolved in 100 ml of distilled water and stirred until completely dissolved to obtain a γ-polyglutamic acid aqueous solution; 5 g of carboxymethyl chitosan was dissolved in 100 ml of distilled water and stirred until completely dissolved to obtain a carboxymethyl chitosan aqueous solution.
[0072] The carboxymethyl chitosan aqueous solution and the γ-polyglutamic acid aqueous solution were mixed in a volume ratio of 1:4 to obtain a mixed solution.
[0073] Ethylene glycol diglycidyl ether was added to the mixed solution at a rate of 0.85 mL / 100 mL of the mixed solution, and the cross-linking reaction was carried out in a constant temperature water bath at 60°C for 8 h to form a composite hydrogel.
[0074] Example 6
[0075] 9.9 g of γ-polyglutamic acid was dissolved in 100 ml of distilled water and stirred until completely dissolved to obtain a γ-polyglutamic acid aqueous solution; 5 g of carboxymethyl chitosan was dissolved in 100 ml of distilled water and stirred until completely dissolved to obtain a carboxymethyl chitosan aqueous solution.
[0076] The carboxymethyl chitosan aqueous solution and the γ-polyglutamic acid aqueous solution were mixed in a volume ratio of 1:2 to obtain a mixed solution.
[0077] Ethylene glycol diglycidyl ether was added to the mixed solution at a rate of 0.85 mL / 100 mL of the mixed solution, and the cross-linking reaction was carried out in a constant temperature water bath at 60°C for 6 h to form a composite hydrogel.
[0078] Example 7
[0079] 9.9 g of γ-polyglutamic acid was dissolved in 100 ml of distilled water and stirred until completely dissolved to obtain a γ-polyglutamic acid aqueous solution; 5 g of carboxymethyl chitosan was dissolved in 100 ml of distilled water and stirred until completely dissolved to obtain a carboxymethyl chitosan aqueous solution.
[0080] The carboxymethyl chitosan aqueous solution and the γ-polyglutamic acid aqueous solution were mixed in a volume ratio of 1:2 to obtain a mixed solution.
[0081] Ethylene glycol diglycidyl ether was added to the mixed solution at a rate of 0.85 mL / 100 mL of the mixed solution, and the cross-linking reaction was carried out in a constant temperature water bath at 60°C for 7 h to form a composite hydrogel.
[0082] Example 8
[0083] 9.9 g of γ-polyglutamic acid was dissolved in 100 ml of distilled water and stirred until completely dissolved to obtain a γ-polyglutamic acid aqueous solution; 5 g of carboxymethyl chitosan was dissolved in 100 ml of distilled water and stirred until completely dissolved to obtain a carboxymethyl chitosan aqueous solution.
[0084] The carboxymethyl chitosan aqueous solution and the γ-polyglutamic acid aqueous solution were mixed in a volume ratio of 1:2 to obtain a mixed solution.
[0085] Ethylene glycol diglycidyl ether was added to the mixed solution at a rate of 0.85 mL / 100 mL of the mixed solution, and the cross-linking reaction was carried out in a constant temperature water bath at 60°C for 9 hours to form a composite hydrogel.
[0086] Example 9
[0087] 9.9 g of γ-polyglutamic acid was dissolved in 100 ml of distilled water and stirred until completely dissolved to obtain a γ-polyglutamic acid aqueous solution; 5 g of carboxymethyl chitosan was dissolved in 100 ml of distilled water and stirred until completely dissolved to obtain a carboxymethyl chitosan aqueous solution.
[0088] The carboxymethyl chitosan aqueous solution and the γ-polyglutamic acid aqueous solution were mixed in a volume ratio of 1:2 to obtain a mixed solution.
[0089] Ethylene glycol diglycidyl ether was added to the mixed solution at a rate of 0.85 mL / 100 mL of the mixed solution, and the cross-linking reaction was carried out in a constant temperature water bath at 60°C for 10 h to form a composite hydrogel.
[0090] The test method used in this embodiment is as follows:
[0091] Determination of the microstructure of the composite hydrogel: The freeze-dried composite hydrogel was cut into slices, and after gold spraying, the structure of the hydrogel was determined using a scanning electron microscope.
[0092] Rheological properties of the composite hydrogel were measured using a rotational rheometer at 25°C with a parallel plate diameter of 40 mm, a strain of 0.5%, and a frequency range of 0.1 Hz to 40 Hz.
[0093] Determination of water retention of composite hydrogels: After the prepared composite hydrogel is placed in sufficient distilled water to reach saturation, a certain amount of the hydrogel is placed in a container and weighed every 24 hours at a constant temperature. The formula is as follows: R (%) = (Wt / W0) × 100%, where R is the water retention rate of the hydrogel, Wt is the mass of the hydrogel at time t, and W0 is the initial weight of the hydrogel.
[0094] Strawberry Pretreatment: Selected strawberries of similar size and maturity were washed and air-dried. They were then immersed in the composite coating solution at varying concentrations for 3 minutes, allowed to air-dry at room temperature, and sealed in PE fresh-keeping bags for storage at room temperature. Quality indicators were measured daily. For the control group, washed strawberries were immersed in distilled water for 3 minutes and stored under the same conditions as the hydrogel-coated strawberries.
[0095] Determination of strawberry weight loss rate: The weight loss rate of strawberries was measured by weighing, and the weight of the strawberries before storage was compared with the weight of the strawberries after storage. The formula is as follows: Weight loss rate (%) = ((initial mass - mass after storage) / initial mass) × 100%
[0096] Determination of color difference changes of strawberries: A 3nh colorimeter was used to measure the color of strawberries, and the L value (brightness) was selected as the evaluation index in the experiment.
[0097] Determination of changes in soluble solids content in strawberries: Use a handheld refractometer to measure the soluble solids content in strawberries. After slicing the strawberries, squeeze out the strawberry juice and put it into the refractometer. The results are expressed as a percentage.
[0098] To determine changes in the titratable acid content of strawberries: Weigh a certain amount of strawberries, grind them, and transfer them to a 100mL volumetric flask. Add distilled water to the mark, shake well, let stand for 30 minutes, and filter. Transfer 10mL of the filtrate to a 100mL Erlenmeyer flask, add two drops of phenolphthalein indicator, and titrate with a standardized sodium hydroxide solution until a slightly reddish color appears and does not fade after 30 seconds. Record the amount of sodium hydroxide solution used. Simultaneously, titrate using 10mL of distilled water as a blank using the same method. Repeat three times. The calculation formula for titratable acid is as follows: titratable acid content (%) = ((V*(V1-V0)*f*C) / Vs*W)*100%, wherein: V is the total volume of the extract (mL); V1 is the milliliters of NaOH solution consumed when titrating the filtrate (mL); V0 is the milliliters of NaOH solution consumed when titrating distilled water (mL); Vs is the total volume of the extract during titration (mL); C is the molar concentration of the NaOH titrant (mol / L); W is the sample weight (g); and f is the conversion factor (g / mmoL) calculated as malic acid, which is 0.067.
[0099] Determination of changes in strawberry vitamin C content: The vitamin C content in strawberries was determined using the 2,6-dichlorophenol indophenol method. A certain amount of strawberries was weighed and ground in oxalic acid extract. The mixture was transferred to a 100mL volumetric flask and brought to volume with oxalic acid extract. The mixture was shaken and allowed to stand for 10 minutes before filtering. 10mL of the filtrate was placed in a 100mL Erlenmeyer flask and titrated with a standardized 2,6-dichlorophenol indophenol solution until a slight reddish color appeared and did not fade after 15 seconds. The amount of dye used was recorded. Simultaneously, the same titration was performed using 10mL of 2% oxalic acid solution as a blank. Repeat this procedure three times.
[0100] The calculation formula of vitamin C is as follows: Vc (mg / 100g) = ((V*(V1-V0)*C) / Vs*W)*100%, where V1 is the volume of the dye solution consumed when titrating the sample solution, V0 is the volume of the dye solution consumed when titrating the blank, C is the amount of ascorbic acid equivalent to 1 mL of dye solution, VS is the volume of the sample solution taken during titration, V is the total volume of the sample extract, and W is the weight of the sample.
[0101] The effects of different concentrations of composite hydrogel on the vitamin C content of strawberries are shown in Table 1 below:
[0102] Table 1
[0103]
[0104] like Figure 7-11 As shown, the weight loss rate of strawberries was reduced to 0.45%, significantly inhibiting water evaporation. The L value (brightness) changed little, indicating that the color was well maintained and browning was delayed. The soluble solids and titratable acid content decreased slowly, demonstrating that the hydrogel effectively slowed respiration and nutrient loss in fruits and vegetables.
[0105] The foregoing description is merely a preferred embodiment of the present invention and is not intended to limit the present invention. Those skilled in the art will readily appreciate that various modifications and variations of the present invention are possible. Any modifications, equivalent substitutions, or improvements made within the spirit and principles of the present invention are intended to be within the scope of protection of the present invention.
Claims
1. A method for preparing a composite hydrogel, characterized in that: The following steps are involved: S1. dissolving γ-polyglutamic acid in distilled water to obtain a γ-polyglutamic acid aqueous solution; S2. dissolving carboxymethyl chitosan in distilled water to obtain a carboxymethyl chitosan aqueous solution; S3. The γ-polyglutamic acid aqueous solution and the γ-polyglutamic acid aqueous solution were mixed and homogenized to obtain a mixed solution; S4. Add polyethylene glycol diglycidyl ether to the mixed solution for cross-linking reaction to obtain a composite hydrogel.
2. The method for preparing the composite hydrogel according to claim 1, wherein The volume ratio of the gamma-polyglutamic acid aqueous solution to the carboxymethyl chitosan aqueous solution is 4:(1-16).
3. The method for preparing the composite hydrogel according to claim 1, wherein: The cross-linking reaction time is 6-10 hours.
4. The method for preparing the composite hydrogel according to claim 1, wherein After the polyethylene glycol diglycidyl ether is added into the mixed solution, a cross-linking reaction is carried out in a constant temperature water bath at 60° C., and a composite hydrogel is obtained after the reaction is completed.
5. The method for preparing the composite hydrogel according to claim 1, wherein: The concentration of the gamma-polyglutamic acid aqueous solution is (9-10) g / 100 mL; the concentration of the carboxymethyl chitosan aqueous solution is (4-5) g / 100 mL.
6. The method for preparing the composite hydrogel according to claim 1, wherein: The amount of polyethylene glycol diglycidyl ether added to the mixed solution is (0.8-0.9) mL / 100 mL.
7. A composite hydrogel, characterized in that The composite hydrogel prepared according to any one of claims 1 to 6, wherein the composite hydrogel has a dense and uniform three-dimensional network structure.
8. The composite hydrogel according to claim 7, characterized in that The pore size distribution range of the three-dimensional network structure in the composite hydrogel is 10-50 μm.
9. An application of a composite hydrogel, characterized in that: The composite hydrogel is applied as a coating material on the surface of fruits and vegetables.
10. The use of the composite hydrogel according to claim 9, characterized in that: The composite hydrogel is applied as a coating material on the surface of strawberries.