A polyvinyl alcohol-polyethyleneimine composite fluorescent hydrogel and its preparation method

Abstract

The present invention belongs to the technical field of hydrogels, and particularly relates to a polyvinyl alcohol-polyethyleneimine composite fluorescent hydrogel and a preparation method thereof. The polyvinyl alcohol-polyethyleneimine composite fluorescent hydrogel is composed of a first network formed by cross-linking polyethyleneimine and citric acid and a second network formed by freeze-thaw cycling of polyvinyl alcohol. In the polyvinyl alcohol-polyethyleneimine composite fluorescent hydrogel, the first network formed by cross-linking polyethyleneimine and citric acid is stably and uniformly distributed in the second network formed by freeze-thaw cycling of polyvinyl alcohol, significantly improving the mechanical properties of the hydrogel and providing stable fluorescent properties. Moreover, the polyvinyl alcohol crystal domains, as strong bonds, significantly improve the mechanical strength of the hydrogel.

Description

Technical Field

[0001] The present invention belongs to the technical field of hydrogels, and particularly relates to a polyvinyl alcohol-polyethyleneimine composite fluorescent hydrogel and a preparation method thereof. Background Art

[0002] Disclosing the information of this background art section is only intended to enhance the overall understanding of the present invention, and it is not necessarily regarded as an admission or an implication in any form that this information constitutes the prior art already known to those of ordinary skill in the art.

[0003] Polymer hydrogels formed by crosslinking hydrophilic polymer polymers and having a three-dimensional network structure with water as the dispersion medium have become the preferred materials in application fields such as human health monitoring, tissue engineering, environmental protection, agriculture, electronic gel industry, and food industry due to their flexible synthesis methods, adjustable composition and mechanical properties, unique biocompatibility, and high-moisture tissue environment for cell and tissue growth. Artificial gels have been widely used in such traditional fields, but their applications in high-tech fields related to luminescent bodies are limited. Therefore, fluorescent hydrogels with fluorescent emission groups have also been one of the research hotspots of hydrogels in recent years and have attracted extensive attention in the fields of information storage and security, environmental monitoring and protection, drug delivery, and tissue engineering.

[0004] Loading fluorescent materials into the 3D network of hydrogels is a win-win strategy, and hydrogels can provide mechanical and chemical stability for fluorescent components. The introduction of fluorescent components also improves the structure and properties of hydrogels to a certain extent. Traditionally, fluorescent hydrogels are prepared by coupling or doping a hydrogel matrix with fluorescent units such as semiconductor quantum dots, metal ligand complexes, lanthanide ions, and organic dyes. Traditional fluorescent hydrogels have some inherent defects, such as easy photobleaching, poor photostability, and low mechanical strength.

[0005] Some polymers containing only amide groups, carbonyl groups, or aliphatic amines can also exhibit strong fluorescence in the non-traditional intrinsic luminescence phenomenon of fluorescence emission without the presence of traditional fluorescent groups. Although these special luminescent materials exhibit excellent photostability, high luminescence efficiency, good water solubility, biosecurity, and degradability, they lack functional crosslinking molecules and are difficult to be used for preparing hydrogels. Summary of the Invention

[0006] To solve the deficiencies of the prior art, the object of the present invention is to provide a polyvinyl alcohol-polyethyleneimine composite fluorescent hydrogel and a preparation method thereof. In the polyvinyl alcohol-polyethyleneimine composite fluorescent hydrogel, the first network formed by crosslinking of polyethyleneimine and citric acid is stably and uniformly distributed in the second network formed by the freeze-thaw cycle of polyvinyl alcohol, significantly improving the mechanical properties of the hydrogel and providing stable fluorescent properties. And the polyvinyl alcohol crystal domain, as a strong bond, significantly improves the mechanical strength of the hydrogel.

[0007] To achieve the above object, the present invention is realized through the following technical solutions:

[0008] In the first aspect, the present invention provides a polyvinyl alcohol-polyethyleneimine composite fluorescent hydrogel, which is composed of a first network formed by crosslinking of polyethyleneimine and citric acid and a second network formed by the freeze-thaw cycle of polyvinyl alcohol.

[0009] Preferably, the mass ratio of citric acid to polyethyleneimine is 1:(0.5 - 5), and the ratio of the total mass of polyethyleneimine and citric acid to the mass of polyvinyl alcohol is 1:(0.2 - 19.8).

[0010] In the second aspect, the present invention provides a preparation method of the polyvinyl alcohol-polyethyleneimine composite fluorescent hydrogel as described in the first aspect, including the following steps:

[0011] Add citric acid and polyethyleneimine to an aqueous solution of polyvinyl alcohol to obtain a mixed solution, and the polyvinyl alcohol-polyethyleneimine composite fluorescent hydrogel can be obtained after the mixed solution undergoes heating reaction and freeze-thaw cycle.

[0012] Preferably, the mass density of polyvinyl alcohol in the aqueous solution of polyvinyl alcohol is 2 - 20 wt.%.

[0013] Preferably, the total mass concentration of polyethyleneimine and citric acid in the mixed solution is 1 - 20 wt.%.

[0014] Preferably, the temperature of the heating reaction is 80°C - 120°C, and the time is 5 - 100 h.

[0015] Preferably, the freeze-thaw cycle is specifically to place it in an environment of -25°C - 0°C for 1 - 24 h and then in an environment of 0°C - 35°C for 1 - 4 h, and repeat 1 - 5 times.

[0016] Preferably, the aqueous solution of polyvinyl alcohol is obtained by heating and dissolving polyvinyl alcohol in water.

[0017] More preferably, the temperature of heating and dissolving is 90°C - 100°C, and the time is 1 - 2 h.

[0018] In a third aspect, the present invention provides the application of the polyvinyl alcohol-polyethyleneimine composite fluorescent hydrogel as described in the first aspect in the field of anti-counterfeiting.

[0019] The beneficial effects obtained by one or more of the above technical solutions of the present invention are as follows:

[0020] In the polyvinyl alcohol-polyethyleneimine composite fluorescent hydrogel, the first network formed by crosslinking polyethyleneimine and citric acid is stably and uniformly distributed in the second network formed by the freeze-thaw cycle of polyvinyl alcohol, significantly improving the mechanical properties of the hydrogel and providing stable fluorescence characteristics. And the polyvinyl alcohol crystal domain, as a strong bond, significantly improves the mechanical strength of the hydrogel.

[0021] After mixing the raw materials, the first network can be formed by a simple heating reaction, and the second network can be formed by the freeze-thaw cycle. The polyvinyl alcohol-polyethyleneimine composite fluorescent hydrogel can be prepared quickly and simply.

[0022] By controlling the content of the two networks, the strength and toughness of the hydrogel can be adjusted respectively.

[0023] The polyvinyl alcohol-polyethyleneimine composite fluorescent hydrogel has excellent intrinsic photoluminescence characteristics and is expected to have great application potential in fields such as anti-counterfeiting. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] The specification drawings forming a part of the present invention are used to provide a further understanding of the present invention. The schematic embodiments of the present invention and their descriptions are used to explain the present invention and do not constitute an improper limitation of the present invention.

[0025] Figure 1 Absorption spectrum and excitation spectrum of the polyvinyl alcohol-polyethyleneimine composite fluorescent hydrogel obtained in Example 1;

[0026] Figure 2 Fluorescence spectra of the polyvinyl alcohol-polyethyleneimine composite fluorescent hydrogel obtained in Example 1 at different excitation light wavelengths;

[0027] Figure 3 Stress-strain curve spectra of the polyvinyl alcohol-polyethyleneimine composite fluorescent hydrogels obtained in Examples 1 to 6;

[0028] Figure 4 Scanning electron microscope spectra of the polyvinyl alcohol-polyethyleneimine composite high-strength fluorescent hydrogels obtained in Examples 1 to 6. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0029] In order to enable those skilled in the art to more clearly understand the technical solutions of the present invention, the technical solutions of the present invention will be described in detail below in combination with specific examples and comparative examples.

[0030] Example 1

[0031] Polyvinyl alcohol was added to deionized water and stirred in an oil bath at 95 °C for 1 h until clear to prepare a 10 wt.% polyvinyl alcohol aqueous solution. Then, citric acid and polyethyleneimine were respectively added to the polyvinyl alcohol aqueous solution to obtain a mixed solution, where the mass ratio of citric acid to polyethyleneimine was 1:2, and the total mass of citric acid and polyethyleneimine accounted for 10 wt.% of the total mass of the mixed solution. The mixed solution was transferred to a three-necked flask and heated and stirred at 100 °C for 72 h to complete the amidation reaction between polyethyleneimine and citric acid to form a polyethyleneimine network. Then, a freeze-thaw cycle treatment was carried out: frozen at -20 °C for 18 h, followed by standing at 25 °C for 4 h, and the freeze-thaw cycle was repeated 3 times to form a polyvinyl alcohol network, and finally a polyvinyl alcohol-polyethyleneimine composite fluorescent hydrogel was obtained.

[0032] As Figure 1 and Figure 2 shown, the maximum excitation wavelength of the polyvinyl alcohol-polyethyleneimine composite fluorescent hydrogel is 375 nm, the maximum emission wavelength is 456 nm, and the emission wavelength does not change with the change of the excitation wavelength, indicating that it emits blue light and has no excitation wavelength dependence similar to most intrinsic emitters.

[0033] Example 2

[0034] Polyvinyl alcohol was added to deionized water and stirred in an oil bath at 95 °C for 1 h until clear to prepare a 10 wt.% polyvinyl alcohol aqueous solution. Then, citric acid and polyethyleneimine were respectively added to the polyvinyl alcohol aqueous solution to obtain a mixed solution, where the mass ratio of citric acid to polyethyleneimine was 1:2, and the total mass of citric acid and polyethyleneimine accounted for 5 wt.% of the total mass of the mixed solution. The mixed solution was transferred to a three-necked flask and heated and stirred at 100 °C for 72 h to complete the amidation reaction between polyethyleneimine and citric acid to form a polyethyleneimine network. Then, a freeze-thaw cycle treatment was carried out: frozen at -20 °C for 18 h, followed by standing at 25 °C for 4 h, and the freeze-thaw cycle was repeated 3 times to form a polyvinyl alcohol network, and finally a polyvinyl alcohol-polyethyleneimine composite fluorescent hydrogel was obtained.

[0035] Example 3

[0036] Polyvinyl alcohol was added to deionized water and stirred in an oil bath at 95 °C for 1 h until clear to prepare a polyvinyl alcohol aqueous solution with a mass fraction of 10 wt.%. Then, citric acid and polyethyleneimine were respectively added to the polyvinyl alcohol aqueous solution to obtain a mixed solution, where the mass ratio of citric acid to polyethyleneimine was 1:2, and the total mass of citric acid and polyethyleneimine accounted for 2 wt.% of the total mass of the mixed solution. The mixed solution was transferred to a three-necked flask and heated and stirred at 100 °C for 72 h to complete the amidation reaction between polyethyleneimine and citric acid to form a polyethyleneimine network. Then, a freeze-thaw cycle treatment was carried out: frozen at -20 °C for 18 h, followed by standing at 25 °C for 4 h, and the freeze-thaw cycle was repeated 3 times to form a polyvinyl alcohol network, and finally a polyvinyl alcohol-polyethyleneimine composite fluorescent hydrogel was obtained.

[0037] Example 4

[0038] Polyvinyl alcohol was added to deionized water and stirred in an oil bath at 95 °C for 1 h until clear to prepare a polyvinyl alcohol aqueous solution with a mass fraction of 8 wt.%. Then, citric acid and polyethyleneimine were respectively added to the polyvinyl alcohol aqueous solution to obtain a mixed solution, where the mass ratio of citric acid to polyethyleneimine was 1:2, and the total mass of citric acid and polyethyleneimine accounted for 10 wt.% of the total mass of the mixed solution. The mixed solution was transferred to a three-necked flask and heated and stirred at 100 °C for 72 h to complete the amidation reaction between polyethyleneimine and citric acid to form a polyethyleneimine network. Then, a freeze-thaw cycle treatment was carried out: frozen at -20 °C for 18 h, followed by standing at 25 °C for 4 h, and the freeze-thaw cycle was repeated 3 times to form a polyvinyl alcohol network, and finally a polyvinyl alcohol-polyethyleneimine composite fluorescent hydrogel was obtained.

[0039] Example 5

[0040] Polyvinyl alcohol was added to deionized water and stirred in an oil bath at 95 °C for 1 h until clear to prepare a polyvinyl alcohol aqueous solution with a mass fraction of 8 wt.%. Then, citric acid and polyethyleneimine were respectively added to the polyvinyl alcohol aqueous solution to obtain a mixed solution, where the mass ratio of citric acid to polyethyleneimine was 1:2, and the total mass of citric acid and polyethyleneimine accounted for 5 wt.% of the total mass of the mixed solution. The mixed solution was transferred to a three-necked flask and heated and stirred at 100 °C for 72 h to complete the amidation reaction between polyethyleneimine and citric acid to form a polyethyleneimine network. Then, a freeze-thaw cycle treatment was carried out: frozen at -20 °C for 18 h, followed by standing at 25 °C for 4 h, and the freeze-thaw cycle was repeated 3 times to form a polyvinyl alcohol network, and finally a polyvinyl alcohol-polyethyleneimine composite fluorescent hydrogel was obtained.

[0041] Example 6

[0042] Polyvinyl alcohol was added to deionized water and stirred in an oil bath at 95 °C for 1 h until clear to prepare an 8 wt.% polyvinyl alcohol aqueous solution. Then, citric acid and polyethyleneimine were respectively added to the polyvinyl alcohol aqueous solution to obtain a mixed solution, where the mass ratio of citric acid to polyethyleneimine was 1:2, and the total mass of citric acid and polyethyleneimine accounted for 2 wt.% of the total mass of the mixed solution. The mixed solution was transferred to a three-necked flask and heated and stirred at 100 °C for 72 h to complete the amidation reaction between polyethyleneimine and citric acid to form a polyethyleneimine network. Then, freeze-thaw cycling treatment was carried out: frozen at -20 °C for 18 h, and then left standing at 25 °C for 4 h. The freeze-thaw cycle was repeated 3 times to form a polyvinyl alcohol network, and finally a polyvinyl alcohol-polyethyleneimine composite fluorescent hydrogel was obtained.

[0043] As Figure 3 shown, the mechanical properties of the polyvinyl alcohol-polyethyleneimine composite fluorescent hydrogel changed significantly with the change of the feed concentrations of polyvinyl alcohol, polyethyleneimine and citric acid. When any of the feed concentrations decreased, the tensile strength decreased significantly.

[0044] As Figure 4 shown, the polyvinyl alcohol-polyethyleneimine composite fluorescent hydrogel had a uniform network structure and showed obvious regularity. With the increase of the feed concentration, the pore size of the double-network hydrogel became more uniform and dense. The decrease in the pore size of the hydrogel was caused by the increase in the content of the polyethyleneimine network and the chain entanglement and molecular interactions between the double networks. The solid content of the hydrogel increased and the crosslinking sites increased, so the pore structure was denser. Similarly, when the content of the polyethyleneimine network was the same, the increase in the content of the polyethyleneimine network also made the hydrogel denser.

[0045] Example 7

[0046] Polyvinyl alcohol was added to deionized water and stirred in an oil bath at 95 °C for 1 h until clear to prepare a 20 wt.% polyvinyl alcohol aqueous solution. Then, citric acid and polyethyleneimine were respectively added to the polyvinyl alcohol aqueous solution to obtain a mixed solution, where the mass ratio of citric acid to polyethyleneimine was 1:2, and the total mass of citric acid and polyethyleneimine accounted for 20 wt.% of the total mass of the mixed solution. The mixed solution was transferred to a three-necked flask and heated and stirred at 100 °C for 72 h to complete the amidation reaction between polyethyleneimine and citric acid to form a polyethyleneimine network. Then, freeze-thaw cycling treatment was carried out: frozen at -20 °C for 18 h, and then left standing at 25 °C for 4 h. The freeze-thaw cycle was repeated 3 times to form a polyvinyl alcohol network, and finally a polyvinyl alcohol-polyethyleneimine composite fluorescent hydrogel was obtained.

[0047] Example 8

[0048] Polyvinyl alcohol was added to deionized water and stirred in an oil bath at 95 °C for 1 h until clear to prepare a 20 wt.% polyvinyl alcohol aqueous solution. Then, citric acid and polyethyleneimine were respectively added to the polyvinyl alcohol aqueous solution to obtain a mixed solution, where the mass ratio of citric acid to polyethyleneimine was 1:2, and the total mass of citric acid and polyethyleneimine accounted for 1 wt.% of the total mass of the mixed solution. The mixed solution was transferred to a three-necked flask and heated and stirred at 100 °C for 72 h to complete the amidation reaction between polyethyleneimine and citric acid to form a polyethyleneimine network. Then, freeze-thaw cycling treatment was carried out: frozen at -20 °C for 18 h, and then left standing at 25 °C for 4 h. The freeze-thaw cycle was carried out 3 times to form a polyvinyl alcohol network, and finally a polyvinyl alcohol-polyethyleneimine composite fluorescent hydrogel was obtained.

[0049] Example 9

[0050] Polyvinyl alcohol was added to deionized water and stirred in an oil bath at 95 °C for 1 h until clear to prepare a 2 wt.% polyvinyl alcohol aqueous solution. Then, citric acid and polyethyleneimine were respectively added to the polyvinyl alcohol aqueous solution to obtain a mixed solution, where the mass ratio of citric acid to polyethyleneimine was 1:2, and the total mass of citric acid and polyethyleneimine accounted for 20 wt.% of the total mass of the mixed solution. The mixed solution was transferred to a three-necked flask and heated and stirred at 100 °C for 72 h to complete the amidation reaction between polyethyleneimine and citric acid to form a polyethyleneimine network. Then, freeze-thaw cycling treatment was carried out: frozen at -20 °C for 18 h, and then left standing at 25 °C for 4 h. The freeze-thaw cycle was carried out 3 times to form a polyvinyl alcohol network, and finally a polyvinyl alcohol-polyethyleneimine composite fluorescent hydrogel was obtained.

[0051] Example 10

[0052] Polyvinyl alcohol was added to deionized water and stirred in an oil bath at 95 °C for 1 h until clear to prepare a 2 wt.% polyvinyl alcohol aqueous solution. Then, citric acid and polyethyleneimine were respectively added to the polyvinyl alcohol aqueous solution to obtain a mixed solution, where the mass ratio of citric acid to polyethyleneimine was 1:2, and the total mass of citric acid and polyethyleneimine accounted for 1 wt.% of the total mass of the mixed solution. The mixed solution was transferred to a three-necked flask and heated and stirred at 100 °C for 72 h to complete the amidation reaction between polyethyleneimine and citric acid to form a polyethyleneimine network. Then, freeze-thaw cycling treatment was carried out: frozen at -20 °C for 18 h, and then left standing at 25 °C for 4 h. The freeze-thaw cycle was carried out 3 times to form a polyvinyl alcohol network, and finally a polyvinyl alcohol-polyethyleneimine composite fluorescent hydrogel was obtained.

[0053] Example 11

[0054] Polyvinyl alcohol was added to deionized water and stirred in an oil bath at 90 °C for 2 h until clear to prepare a 10 wt.% polyvinyl alcohol aqueous solution. Then, citric acid and polyethyleneimine were respectively added to the polyvinyl alcohol aqueous solution to obtain a mixed solution, where the mass ratio of citric acid to polyethyleneimine was 1:2, and the total mass of citric acid and polyethyleneimine accounted for 10 wt.% of the total mass of the mixed solution. The mixed solution was transferred to a three-necked flask and heated and stirred at 100 °C for 72 h to complete the amidation reaction between polyethyleneimine and citric acid to form a polyethyleneimine network. Then, freeze-thaw cycling treatment was carried out: frozen at -20 °C for 18 h, and then left standing at 25 °C for 4 h. The freeze-thaw cycle was repeated 3 times to form a polyvinyl alcohol network, and finally a polyvinyl alcohol-polyethyleneimine composite fluorescent hydrogel was obtained.

[0055] Example 12

[0056] Polyvinyl alcohol was added to deionized water and stirred in an oil bath at 100 °C for 1 h until clear to prepare a 10 wt.% polyvinyl alcohol aqueous solution. Then, citric acid and polyethyleneimine were respectively added to the polyvinyl alcohol aqueous solution to obtain a mixed solution, where the mass ratio of citric acid to polyethyleneimine was 1:2, and the total mass of citric acid and polyethyleneimine accounted for 10 wt.% of the total mass of the mixed solution. The mixed solution was transferred to a three-necked flask and heated and stirred at 100 °C for 72 h to complete the amidation reaction between polyethyleneimine and citric acid to form a polyethyleneimine network. Then, freeze-thaw cycling treatment was carried out: frozen at -20 °C for 18 h, and then left standing at 25 °C for 4 h. The freeze-thaw cycle was repeated 3 times to form a polyvinyl alcohol network, and finally a polyvinyl alcohol-polyethyleneimine composite fluorescent hydrogel was obtained.

[0057] Example 13

[0058] Polyvinyl alcohol was added to deionized water and stirred in an oil bath at 95 °C for 1 h until clear to prepare a 10 wt.% polyvinyl alcohol aqueous solution. Then, citric acid and polyethyleneimine were respectively added to the polyvinyl alcohol aqueous solution to obtain a mixed solution, where the mass ratio of citric acid to polyethyleneimine was 1:2, and the total mass of citric acid and polyethyleneimine accounted for 10 wt.% of the total mass of the mixed solution. The mixed solution was transferred to a three-necked flask and heated and stirred at 120 °C for 5 h to complete the amidation reaction between polyethyleneimine and citric acid to form a polyethyleneimine network. Then, freeze-thaw cycling treatment was carried out: frozen at -20 °C for 18 h, and then left standing at 25 °C for 4 h. The freeze-thaw cycle was repeated 3 times to form a polyvinyl alcohol network, and finally a polyvinyl alcohol-polyethyleneimine composite fluorescent hydrogel was obtained.

[0059] Example 14

[0060] Polyvinyl alcohol was added to deionized water and stirred in an oil bath at 95 °C for 1 h until clear to prepare a 10 wt.% polyvinyl alcohol aqueous solution. Then, citric acid and polyethyleneimine were respectively added to the polyvinyl alcohol aqueous solution to obtain a mixed solution, where the mass ratio of citric acid to polyethyleneimine was 1:2, and the total mass of citric acid and polyethyleneimine accounted for 10 wt.% of the total mass of the mixed solution. The mixed solution was transferred to a three-necked flask and heated and stirred at 80 °C for 100 h to complete the amidation reaction between polyethyleneimine and citric acid to form a polyethyleneimine network. Then, freeze-thaw cycling treatment was carried out: frozen at -20 °C for 18 h, and then left standing at 25 °C for 4 h. The freeze-thaw cycle was carried out 3 times to form a polyvinyl alcohol network, and finally a polyvinyl alcohol-polyethyleneimine composite fluorescent hydrogel was obtained.

[0061] Example 15

[0062] Polyvinyl alcohol was added to deionized water and stirred in an oil bath at 95 °C for 1 h until clear to prepare a 10 wt.% polyvinyl alcohol aqueous solution. Then, citric acid and polyethyleneimine were respectively added to the polyvinyl alcohol aqueous solution to obtain a mixed solution, where the mass ratio of citric acid to polyethyleneimine was 1:2, and the total mass of citric acid and polyethyleneimine accounted for 10 wt.% of the total mass of the mixed solution. The mixed solution was transferred to a three-necked flask and heated and stirred at 100 °C for 72 h to complete the amidation reaction between polyethyleneimine and citric acid to form a polyethyleneimine network. Then, freeze-thaw cycling treatment was carried out: frozen at -25 °C for 1 h, and then left standing at 0 °C for 4 h. The freeze-thaw cycle was carried out 3 times to form a polyvinyl alcohol network, and finally a polyvinyl alcohol-polyethyleneimine composite fluorescent hydrogel was obtained.

[0063] Example 16

[0064] Polyvinyl alcohol was added to deionized water and stirred in an oil bath at 95 °C for 1 h until clear to prepare a 10 wt.% polyvinyl alcohol aqueous solution. Then, citric acid and polyethyleneimine were respectively added to the polyvinyl alcohol aqueous solution to obtain a mixed solution, where the mass ratio of citric acid to polyethyleneimine was 1:2, and the total mass of citric acid and polyethyleneimine accounted for 10 wt.% of the total mass of the mixed solution. The mixed solution was transferred to a three-necked flask and heated and stirred at 100 °C for 72 h to complete the amidation reaction between polyethyleneimine and citric acid to form a polyethyleneimine network. Then, freeze-thaw cycling treatment was carried out: frozen at 0 °C for 24 h, and then left standing at 35 °C for 1 h. The freeze-thaw cycle was carried out 3 times to form a polyvinyl alcohol network, and finally a polyvinyl alcohol-polyethyleneimine composite fluorescent hydrogel was obtained.

[0065] Example 17

[0066] Polyvinyl alcohol was added to deionized water and stirred in an oil bath at 95 °C for 1 h until clear to prepare a 10 wt.% polyvinyl alcohol aqueous solution. Then, citric acid and polyethyleneimine were respectively added to the polyvinyl alcohol aqueous solution to obtain a mixed solution, where the mass ratio of citric acid to polyethyleneimine was 1:2, and the total mass of citric acid and polyethyleneimine accounted for 10 wt.% of the total mass of the mixed solution. The mixed solution was transferred to a three-necked flask and heated and stirred at 100 °C for 72 h to complete the amidation reaction between polyethyleneimine and citric acid to form a polyethyleneimine network. Then, freeze-thaw cycle treatment was carried out: frozen at -20 °C for 18 h, and then left standing at 25 °C for 4 h, and freeze-thawed once to form a polyvinyl alcohol network, and finally a polyvinyl alcohol-polyethyleneimine composite fluorescent hydrogel was obtained.

[0067] Example 18

[0068] Polyvinyl alcohol was added to deionized water and stirred in an oil bath at 95 °C for 1 h until clear to prepare a 10 wt.% polyvinyl alcohol aqueous solution. Then, citric acid and polyethyleneimine were respectively added to the polyvinyl alcohol aqueous solution to obtain a mixed solution, where the mass ratio of citric acid to polyethyleneimine was 1:2, and the total mass of citric acid and polyethyleneimine accounted for 10 wt.% of the total mass of the mixed solution. The mixed solution was transferred to a three-necked flask and heated and stirred at 100 °C for 72 h to complete the amidation reaction between polyethyleneimine and citric acid to form a polyethyleneimine network. Then, freeze-thaw cycle treatment was carried out: frozen at -20 °C for 18 h, and then left standing at 25 °C for 4 h, and freeze-thawed 5 times to form a polyvinyl alcohol network, and finally a polyvinyl alcohol-polyethyleneimine composite fluorescent hydrogel was obtained.

[0069] The above are only the preferred embodiments of the present invention and are not intended to limit the present invention. For those skilled in the art, the present invention can have various changes and modifications. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principle of the present invention shall be included within the protection scope of the present invention.

Claims

1. A polyvinyl alcohol-polyethyleneimine composite fluorescent hydrogel, characterized in that: It consists of a first network formed by cross-linking polyethyleneimine and citric acid and a second network formed by freeze-thaw cycles of polyvinyl alcohol; The mass ratio of citric acid to polyethyleneimine is 1:(0.5-5), and the ratio of the total mass of polyethyleneimine and citric acid to the mass of polyvinyl alcohol is 1:(0.2-19.8).

2. A method for preparing the polyvinyl alcohol-polyethyleneimine composite fluorescent hydrogel as claimed in claim 1, characterized in that: The following steps are involved: Citric acid and polyethyleneimine are added to a polyvinyl alcohol aqueous solution to obtain a mixed solution, and the mixed solution is subjected to a heating reaction and a freeze-thaw cycle to obtain a polyvinyl alcohol-polyethyleneimine composite fluorescent hydrogel.

3. The preparation method according to claim 2, characterized in that: The mass density of polyvinyl alcohol in the polyvinyl alcohol aqueous solution is 2 to 20 wt.%.

4. The preparation method according to claim 2, characterized in that: The total mass concentration of polyethyleneimine and citric acid in the mixed solution is 1-20wt.%.

5. The preparation method according to claim 2, characterized in that: The heating reaction temperature is 80°C to 120°C, and the time is 5 to 100 hours.

6. The preparation method according to claim 2, characterized in that: The freeze-thaw cycle is specifically placed in an environment of -25°C to 0°C for 1 to 24 hours and then placed in an environment of 0°C to 35°C for 1 to 4 hours, and repeated 1 to 5 times.

7. The preparation method according to claim 2, characterized in that: The polyvinyl alcohol aqueous solution is obtained by placing polyvinyl alcohol in water and heating it to dissolve it.

8. The preparation method according to claim 7, characterized in that: The temperature for heating and dissolving is 90℃~100℃, and the time is 1~2h.

9. Use of the polyvinyl alcohol-polyethyleneimine composite fluorescent hydrogel as claimed in claim 1 in the field of anti-counterfeiting.

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