Anti-ultraviolet fluorescent chitin film and preparation method thereof

Abstract

The invention discloses an anti-ultraviolet fluorescent chitin film and a preparation method thereof. The preparation method of the anti-ultraviolet fluorescent chitin film comprises the following steps: S10, adding a chitin film into an organic solution containing a modifier, reacting at 90-150 DEG C for 2-6 hours, and cleaning after the reaction is finished, so as to obtain an acetoacetic acid modified chitin film; and S20, the acetoacetic acid modified chitin film is soaked in a solution containing ammonium salt and aromatic aldehyde compounds for Hantzsch multi-component reaction, the reaction is conducted for 2-24 hours at the temperature of 25-60 DEG C, then cleaning and drying are conducted, the anti-ultraviolet fluorescent chitin film is obtained, the ammonium salt is ammonium acetate or ammonium carbonate or ammonium sulfate, and the aromatic aldehyde compounds are benzaldehyde or vanillin or furfural. A renewable resource chitin film is used as a matrix, and DHP ring and benzene ring are introduced to reconstruct a microstructure of a natural chitin film, so that the anti-ultraviolet performance of the natural chitin film is remarkably enhanced.

Description

Technical Field

[0001] The present invention generally relates to the field of chitosan films, and in particular to an anti-ultraviolet fluorescent chitosan film and a preparation method thereof. Background Art

[0002] Excessive exposure to ultraviolet (UV) light not only threatens human health, but also causes serious damage to materials. Ultraviolet light is mainly divided into three categories: UVA (315-400nm), UVB (280-315nm) and UVC (200-280nm). UVC is almost completely blocked by the atmosphere, while UVA and UVB can penetrate the atmosphere and directly affect the skin, causing sunburn, skin aging, and even increasing the risk of skin cancer. At the same time, many materials (especially organic polymers) will undergo photodegradation under ultraviolet light, resulting in reduced mechanical strength, color fading, surface aging and even cracking. In order to mitigate these hazards, anti-UV products such as sunscreens and parasols have been developed. Films with anti-UV and fluorescent functions can not only provide excellent UV protection, but can also be used in display technology to prevent screens from being damaged by ultraviolet light, thereby extending the service life of the device. In addition, the fluorescent function gives the film a wider application potential in the fields of biological imaging and lighting, combining functionality and safety.

[0003] The traditional method of achieving ultraviolet blocking performance mainly focuses on incorporating ultraviolet absorbers into polymer matrices. For example, patent document CN112281474A discloses a method for preparing a chitosan-based anti-ultraviolet finishing agent, using chitosan (a deacetylated derivative of chitin) as a processing raw material, adding ammonium polyphosphate, sodium lactate, 2,4-dihydroxybenzophenone, 4-nitro-1, titanium dioxide, sodium hydroxide and toluene to make it together, increasing the anti-ultraviolet performance, this physical blending method is often unevenly dispersed during the doping process, resulting in poor material stability, and particles are easily leached from the substrate, not only affecting the performance of the material, but also causing potential harm to the environment. And inorganic nanoparticles such as titanium dioxide are generally photocatalytically active, which can accelerate the degradation of polymers. This greatly limits the promotion and application of anti-ultraviolet films. At present, researchers have developed a variety of anti-ultraviolet materials through chemical modification methods. For example, patent document CN114381073A discloses a chitosan-polyvinyl chloride wood plastic board with UV aging resistance, wherein chitosan modified by benzotriazole-triazine is used as an anti-ultraviolet agent, mixed with polyvinyl chloride and bamboo powder, extruded and pressed to obtain chitosan-polyvinyl chloride wood plastic board with UV aging resistance, and chitosan modified by benzotriazole-triazine has good UV absorption performance, which improves the UV resistance of the wood plastic board. However, the preparation process of chitosan modified by benzotriazole-triazine uses cyanuric chloride, which is unstable in the air, volatile and irritating, and is easily decomposed into cyanuric acid when it meets water and alkali, and releases hydrogen chloride gas at the same time, and the modification process is not green and safe enough.

[0004] How to ensure the safety and long-term stability of materials while providing effective UV protection is the focus of the research. Summary of the invention

[0005] In view of the above defects or deficiencies in the prior art, it is desirable to provide a safe and stable UV-resistant fluorescent chitosan film and a preparation method thereof.

[0006] In a first aspect, the method for preparing the UV-resistant fluorescent chitosan film of the present invention comprises the following steps:

[0007] S10, adding the chitosan film to an organic solution containing a modifier, reacting at 90 to 150° C. for 2 to 6 hours, and cleaning after the reaction to obtain an acetoacetic acid modified chitosan film, wherein the molar ratio of the chitosan film to the modifier is 1:1 to 15, the modifier in the organic solution containing the modifier is tert-butyl acetoacetate, diketene or 2,2,6-trimethyl-4-hydrogen-1,3-dioxacyclo-4-one, and the concentration of the modifier in the organic solution containing the modifier is 0.008 to 0.3 g / mL;

[0008] S20, immersing the acetoacetic acid modified chitosan film in a solution containing ammonium salt and aromatic aldehyde compounds to carry out a Hantzsch multi-component reaction, reacting at 25-60° C. for 2-24 hours, and then washing and drying to obtain an anti-ultraviolet fluorescent chitosan film, wherein the ammonium salt is ammonium acetate, ammonium carbonate or ammonium sulfate, and the aromatic aldehyde compound is benzaldehyde, vanillin or furfural.

[0009] In a second aspect, the anti-ultraviolet fluorescent chitosan film of the present invention is prepared by a method for preparing an anti-ultraviolet fluorescent chitosan film.

[0010] According to the technical solution provided in the embodiment of the present application, the microstructure of the natural chitosan film is reconstructed by introducing DHP rings and benzene rings using the renewable resource chitosan film as the matrix, thereby significantly enhancing its anti-ultraviolet performance.

[0011] During the multi-component reaction process, the DHP ring and the benzene ring structure work synergistically to form a conjugated dense structure, which significantly enhances the UV shielding ability of the UV-resistant fluorescent chitosan film, making the UV-resistant fluorescent chitosan film have excellent UV resistance.

[0012] Aromatic aldehyde compounds are not simply doped into the film, but are covalently bonded to the film structure through chemical modification. Therefore, compared with weak interactions such as hydrogen bonds, they have a stronger binding effect, greatly reducing the possibility of leakage. In addition, the conjugated structure of the DHP ring absorbs ultraviolet radiation energy and converts it into visible fluorescence with AIE characteristics, which can be used in anti-counterfeiting, biological imaging and other applications. This makes the anti-ultraviolet fluorescent chitin film have excellent stability and fluorescence properties. BRIEF DESCRIPTION OF THE DRAWINGS

[0013] Other features, objects and advantages of the present application will become more apparent by reading the detailed description of non-limiting embodiments made with reference to the following drawings:

[0014] Figure 1 is a reaction equation involved in step S10 of a method for preparing an anti-ultraviolet fluorescent chitosan film according to an embodiment of the present invention;

[0015] Figure 2 is a reaction equation involved in step S30 of a method for preparing an anti-ultraviolet fluorescent chitosan film according to an embodiment of the present invention;

[0016] Figure 3 A photograph of an anti-ultraviolet fluorescent chitosan film according to another embodiment of the present invention;

[0017] Figure 4 This is a photograph of an anti-ultraviolet fluorescent chitosan film according to another embodiment of the present invention emitting bright fluorescence under ultraviolet light;

[0018] Figure 5 It is a data diagram of the anti-ultraviolet effect of Comparative Examples 1-2 and Examples 1-9 of the present invention. DETAILED DESCRIPTION

[0019] The present application is further described in detail below in conjunction with the accompanying drawings and embodiments. It is to be understood that the specific embodiments described herein are only used to explain the relevant invention, rather than to limit the invention. It is also necessary to explain that, for ease of description, only the parts related to the invention are shown in the accompanying drawings.

[0020] It should be noted that, in the absence of conflict, the embodiments and features in the embodiments of the present application can be combined with each other. The present application will be described in detail below with reference to the accompanying drawings and in combination with the embodiments.

[0021] A method for preparing an ultraviolet-resistant fluorescent chitosan film comprises the following steps:

[0022] S10, adding the chitosan film to an organic solution containing a modifier, reacting at 90 to 150° C. for 2 to 6 hours, and cleaning after the reaction to obtain an acetoacetic acid modified chitosan film, wherein the molar ratio of the chitosan film to the modifier is 1:1 to 15, the modifier in the organic solution containing the modifier is tert-butyl acetoacetate, diketene or 2,2,6-trimethyl-4-hydrogen-1,3-dioxacyclo-4-one, and the concentration of the modifier in the organic solution containing the modifier is 0.008 to 0.3 g / mL;

[0023] S20, immersing the acetoacetic acid modified chitosan film in a solution containing ammonium salt and aromatic aldehyde compounds to carry out a Hantzsch multi-component reaction, reacting at 25-60° C. for 2-24 hours, and then washing and drying to obtain an anti-ultraviolet fluorescent chitosan film, wherein the ammonium salt is ammonium acetate, ammonium carbonate or ammonium sulfate, and the aromatic aldehyde compound is benzaldehyde, vanillin or furfural.

[0024] Furthermore, in step S10, the organic solvent in the organic solution containing the modifier is DMF, DMSO or ethanol.

[0025] Furthermore, in step S10, after the reaction is completed, the mixture is cleaned with ethanol, deionized water or ethanol-water solution.

[0026] Furthermore, in step S10, after the reaction is completed, washing is performed 6 times with ethanol, deionized water or ethanol aqueous solution.

[0027] Furthermore, in the solution containing ammonium salt and aromatic aldehyde compound in step S20, the concentration of ammonium salt is 0.005-0.8 g / mL, and the concentration of aromatic aldehyde compound is 0.01-0.6 g / mL.

[0028] Furthermore, in the solution containing the ammonium salt and the aromatic aldehyde compound in step S20, the solvent is ethanol, deionized water or ethanol aqueous solution.

[0029] Furthermore, in step S20, after the reaction is completed, the mixture is cleaned with ethanol, deionized water or ethanol-water solution.

[0030] Further, in step S20, after the reaction is completed, washing is performed 6 times with ethanol, deionized water or ethanol aqueous solution.

[0031] The present invention uses chitosan film as a matrix, such as Figure 1 As shown in FIG. 1 , acetoacetate groups are introduced into the chitosan molecular chain through an ester exchange reaction to obtain an acetoacetate modified chitosan film. Figure 2As shown, the modified film is immersed in an ethanol aqueous solution containing ammonium salt and aromatic aldehyde compounds, and the acetoacetic modified chitin film reacts with ammonium salt and aromatic aldehyde to generate DHP ring through multi-component Hantzsch reaction, and is covalently bonded to the chitin film matrix, thereby obtaining a chitin film with high efficiency anti-ultraviolet and fluorescence stabilization function. The film uses DHP ring and benzene ring as ultraviolet absorption groups, can completely block UVA, UVB and UVC full-band ultraviolet rays, and has stable fluorescence performance.

[0032] The following is a description with reference to specific embodiments.

[0033] Example 1

[0034] A fluorescent chitosan film with UV resistance, the preparation method of which comprises the following steps:

[0035] 1. Weigh 1g of hot-pressed chitosan film;

[0036] 2. Weigh 5g of tert-butyl acetoacetate and completely dissolve it in 50mL of DMF solution. Place the chitosan film in this solution and place it in a constant temperature environment at 90°C. The reaction time is controlled to be 2 hours. After the reaction is completed, immediately use anhydrous ethanol to wash the obtained film sample 6 times to ensure that the surface residue is completely removed to obtain an acetoacetic modified chitosan film;

[0037] 3. The acetoacetic acid modified chitin film prepared in step 2 was immersed in 50 mL of ethanol solution containing 10 mg of ammonium acetate and 25 μL of vanillin (the molar ratio of ammonium acetate to vanillin was 1:1), and reacted at 30° C. for 8 hours;

[0038] 4. After the reaction is completed, the chitosan film is taken out, washed with ethanol for 6 times, and dried to obtain an anti-ultraviolet fluorescent chitosan film.

[0039] Example 2

[0040] A fluorescent chitosan film with UV resistance, the preparation method of which comprises the following steps:

[0041] 1. Weigh 1g of hot-pressed chitosan film;

[0042] 2. Weigh 5g of tert-butyl acetoacetate and completely dissolve it in 50mL of DMF solution. Place the chitosan film in this solution and place it in a constant temperature environment at 100°C. The reaction time is controlled to be 2 hours. After the reaction is completed, immediately use anhydrous ethanol to wash the obtained film sample 6 times to ensure that the surface residue is completely removed to obtain an acetoacetic modified chitosan film;

[0043] 3. The acetoacetic acid modified chitin film prepared in step 2 was immersed in 50 mL of ethanol solution containing 30 mg of ammonium acetate and 75 μL of vanillin (the molar ratio of ammonium acetate to vanillin was 1:1), and reacted at 30° C. for 8 hours;

[0044] 4. After the reaction is completed, the chitosan film is taken out, washed with ethanol for 6 times, and dried to obtain an anti-ultraviolet fluorescent chitosan film.

[0045] Example 3

[0046] A fluorescent chitosan film with UV resistance, the preparation method of which comprises the following steps:

[0047] 1. Weigh 1g of hot-pressed chitosan film;

[0048] 2. Weigh 5g of tert-butyl acetoacetate and completely dissolve it in 50mL of DMF solution. Place the chitosan film in this solution and place it in a constant temperature environment of 120℃. The reaction time is controlled to be 2 hours. After the reaction is completed, immediately use anhydrous ethanol to wash the obtained film sample 6 times to ensure that the surface residue is completely removed to obtain the acetoacetic modified chitosan film;

[0049] 3. The acetoacetic acid modified chitin film prepared in step 2 was immersed in 50 mL of ethanol solution containing 60 mg of ammonium acetate and 150 μL of vanillin (the molar ratio of ammonium acetate to vanillin was 1:1), and reacted at 30° C. for 8 hours;

[0050] 4. After the reaction is completed, the chitosan film is taken out, washed with ethanol for 6 times, and dried to obtain an anti-ultraviolet fluorescent chitosan film.

[0051] Example 4

[0052] A fluorescent chitosan film with UV resistance, the preparation method of which comprises the following steps:

[0053] 1. Weigh 1g of hot-pressed chitosan film;

[0054] 2. Weigh 10g of tert-butyl acetoacetate and completely dissolve it in 50mL of DMF solution. Place the chitosan film in this solution and place it in a constant temperature environment of 130°C. The reaction time is controlled to be 2 hours. After the reaction is completed, immediately use anhydrous ethanol to wash the obtained film sample 6 times to ensure that the surface residue is completely removed to obtain an acetoacetic modified chitosan film;

[0055] 3. The acetoacetic acid modified chitin film prepared in step 2 was immersed in 50 mL of ethanol solution containing 60 mg of ammonium acetate and 150 μL of vanillin (the molar ratio of ammonium acetate to vanillin was 1:1), and reacted at 30° C. for 8 hours;

[0056] 4. After the reaction is completed, the chitosan film is taken out, washed with ethanol for 6 times, and dried to obtain an anti-ultraviolet fluorescent chitosan film.

[0057] Example 5

[0058] A fluorescent chitosan film with UV resistance, the preparation method of which comprises the following steps:

[0059] 1. Weigh 1g of hot-pressed chitosan film;

[0060] 2. Weigh 10g of tert-butyl acetoacetate and completely dissolve it in 50mL of DMF solution. Place the chitosan film in this solution and place it in a constant temperature environment of 140°C. The reaction time is controlled to be 2 hours. After the reaction is completed, immediately use anhydrous ethanol to wash the obtained film sample 6 times to ensure that the surface residue is completely removed to obtain an acetoacetic modified chitosan film;

[0061] 3. The acetoacetic acid modified chitin film prepared in step 2 was immersed in 50 mL of ethanol solution containing 60 mg of ammonium acetate and 150 μL of vanillin (the molar ratio of ammonium acetate to vanillin was 1:1), and reacted at 30° C. for 8 hours;

[0062] 4. After the reaction is completed, the chitosan film is taken out, washed with ethanol for 6 times, and dried to obtain an anti-ultraviolet fluorescent chitosan film.

[0063] Example 6

[0064] A fluorescent chitosan film with UV resistance, the preparation method of which comprises the following steps:

[0065] 1. Weigh 1g of hot-pressed chitosan film;

[0066] 2. Weigh 10g of tert-butyl acetoacetate and completely dissolve it in 50mL of DMF solution. Place the chitosan film in this solution and place it in a constant temperature environment at 150℃. The reaction time is controlled to be 2 hours. After the reaction is completed, immediately use anhydrous ethanol to wash the obtained film sample 6 times to ensure that the surface residue is completely removed to obtain the acetoacetic modified chitosan film;

[0067] 3. The acetoacetic acid modified chitin film prepared in step 2 was immersed in 50 mL of ethanol solution containing 60 mg of ammonium acetate and 150 μL of vanillin (the molar ratio of ammonium acetate to vanillin was 1:1), and reacted at 30° C. for 8 hours;

[0068] 4. After the reaction is completed, the chitosan film is taken out, washed with ethanol for 6 times, and dried to obtain an anti-ultraviolet fluorescent chitosan film.

[0069] Example 7

[0070] A fluorescent chitosan film with UV resistance, the preparation method of which comprises the following steps:

[0071] 1. Weigh 1g of hot-pressed chitosan film;

[0072] 2. Weigh 5g of tert-butyl acetoacetate and completely dissolve it in 50mL of DMF solution. Place the chitosan film in this solution and place it in a constant temperature environment of 120℃. The reaction time is controlled to be 2 hours. After the reaction is completed, immediately use anhydrous ethanol to wash the obtained film sample 6 times to ensure that the surface residue is completely removed to obtain the acetoacetic modified chitosan film;

[0073] 3. The acetoacetic acid modified chitin film prepared in step 2 was immersed in 50 mL of ethanol solution containing 60 mg of ammonium acetate and 150 μL of vanillin (the molar ratio of ammonium acetate to vanillin was 1:1), and reacted at 40° C. for 10 hours;

[0074] 4. After the reaction is completed, the chitosan film is taken out, washed with ethanol for 6 times, and dried to obtain an anti-ultraviolet fluorescent chitosan film.

[0075] Example 8

[0076] A fluorescent chitosan film with UV resistance, the preparation method of which comprises the following steps:

[0077] 1. Weigh 1g of hot-pressed chitosan film;

[0078] 2. Weigh 5g of tert-butyl acetoacetate and completely dissolve it in 50mL of DMF solution. Place the chitosan film in this solution and place it in a constant temperature environment of 120℃. The reaction time is controlled to be 2 hours. After the reaction is completed, immediately use anhydrous ethanol to wash the obtained film sample 6 times to ensure that the surface residue is completely removed to obtain the acetoacetic modified chitosan film;

[0079] 3. The acetoacetic acid modified chitin film prepared in step 2 was immersed in 50 mL of ethanol solution containing 60 mg of ammonium acetate and 150 μL of vanillin (the molar ratio of ammonium acetate to vanillin was 1:1), and reacted at 50 °C for 10 hours;

[0080] 4. After the reaction is completed, the chitosan film is taken out, washed with ethanol for 6 times, and dried to obtain an anti-ultraviolet fluorescent chitosan film.

[0081] Example 9

[0082] A fluorescent chitosan film with UV resistance, the preparation method of which comprises the following steps:

[0083] 1. Weigh 1g of hot-pressed chitosan film;

[0084] 2. Weigh 5g of tert-butyl acetoacetate and completely dissolve it in 50mL of DMF solution. Place the chitosan film in this solution and place it in a constant temperature environment of 120℃. The reaction time is controlled to be 2 hours. After the reaction is completed, immediately use anhydrous ethanol to wash the obtained film sample 6 times to ensure that the surface residue is completely removed to obtain the acetoacetic modified chitosan film;

[0085] 3. The acetoacetic acid modified chitin film prepared in step 2 was immersed in 50 mL of ethanol solution containing 60 mg of ammonium acetate and 150 μL of vanillin (the molar ratio of ammonium acetate to vanillin was 1:1), and reacted at 60° C. for 10 hours;

[0086] 4. After the reaction is completed, the chitosan film is taken out, washed with ethanol for 6 times, and dried to obtain an anti-ultraviolet fluorescent chitosan film.

[0087] Comparative Example 1

[0088] A fluorescent chitosan film with UV resistance, the preparation method of which comprises the following steps:

[0089] 1. Weigh 1g of hot-pressed chitosan film;

[0090] 2. Weigh 1g of tert-butyl acetoacetate and completely dissolve it in 50mL of DMF solution. Place the solution in a constant temperature environment at 30°C and control the reaction time to 6 hours. After the reaction is completed, immediately use anhydrous ethanol to wash the obtained film sample 6 times to ensure that the surface residue is completely removed to obtain an acetoacetic modified chitin film;

[0091] 3. The acetoacetic acid modified chitin film prepared in step 2 was immersed in 50 mL of ethanol solution containing 10 mg of ammonium acetate and 25 μL of vanillin (the molar ratio of ammonium acetate to vanillin was 1:1), and reacted at 100° C. for 8 hours;

[0092] 4. After the reaction is completed, take out the chitosan film, wash it with ethanol 6 times, and dry it to obtain the sample.

[0093] Comparative Example 2

[0094] A fluorescent chitosan film with UV resistance, the preparation method of which comprises the following steps:

[0095] 1. Weigh 1g of hot-pressed chitosan film;

[0096] 2. Weigh 2 g of tert-butyl acetoacetate and completely dissolve it in 50 mL of DMF solution. Place the solution in a constant temperature environment at 60 ° C and control the reaction time to 4 hours. After the reaction is completed, immediately use anhydrous ethanol to wash the obtained film sample 6 times to ensure that the surface residue is completely removed to obtain an acetoacetic modified chitin film;

[0097] 3. The acetoacetic acid modified chitin film prepared in step 2 was immersed in 50 mL of ethanol solution containing 60 mg of ammonium acetate and 150 μL of vanillin (the molar ratio of ammonium acetate to vanillin was 1:1), and reacted at 10° C. for 10 hours;

[0098] 4. After the reaction is completed, take out the chitosan film, wash it with ethanol 6 times, and dry it to obtain the sample.

[0099] The visible light transmittance of the fluorescent chitosan film with stable anti-ultraviolet function prepared by the present invention was tested using an ultraviolet spectrophotometer. The test sample size was 3 cm × 3 cm. During the experiment, air was used as the control group, the transmittance of air was set as the baseline, and the test wavelength range was 200 to 800 nm. The test results are shown in Table 1, which shows the transmittance of the film at different wavelengths, thereby evaluating its ultraviolet blocking performance.

[0100] Table 1 Anti-ultraviolet test results of comparative examples 1-2 and embodiments 1-9

[0101]

[0102]

[0103] The UV transmittance of some bands was selected to evaluate the UV blocking ability of the prepared chitosan film, and the transmittance at 550nm was used to evaluate the transparency of the film. Figure 5 , Examples 1 to 9 completely shield the ultraviolet light band (200-400 nm), and all examples have the characteristic of high transparency (the transmittance at 550 nm is about 86%).

[0104] refer to Figure 3 , a piece of paper printed with the English word "Chitin" is covered with an anti-UV fluorescent chitin film. The English word "Chitin" can be seen through the anti-UV fluorescent chitin film, which reflects the high transparency of the anti-UV fluorescent chitin film.

[0105] refer to Figure 4 The anti-ultraviolet fluorescent chitin film emits bright fluorescence under ultraviolet light.

[0106] The above description is only a preferred embodiment of the present application and an explanation of the technical principles used. Those skilled in the art should understand that the scope of the invention involved in the present application is not limited to the technical solution formed by a specific combination of the above technical features, but should also cover other technical solutions formed by any combination of the above technical features or their equivalent features without departing from the inventive concept. For example, the above features are replaced with (but not limited to) technical features with similar functions disclosed in the present application.

Claims

1. A method for preparing an anti-ultraviolet fluorescent chitosan film, characterized in that: The following steps are involved: S10, adding the chitosan film to an organic solution containing a modifier, reacting at 90 to 150° C. for 2 to 6 hours, and cleaning after the reaction to obtain an acetoacetic acid modified chitosan film, wherein the molar ratio of the chitosan film to the modifier is 1:1 to 15, the modifier in the organic solution containing the modifier is tert-butyl acetoacetate, diethyl ketone or 2,2,6-trimethyl-4-hydrogen-1,3-dioxacyclo-4-one, and the concentration of the modifier in the organic solution containing the modifier is 0.008 to 0.3 g / mL; S20, immersing the acetoacetic acid modified chitosan film in a solution containing ammonium salt and aromatic aldehyde compounds to carry out a Hantzsch multi-component reaction, reacting at 25-60° C. for 2-24 hours, and then washing and drying to obtain an anti-ultraviolet fluorescent chitosan film, wherein the ammonium salt is ammonium acetate, ammonium carbonate or ammonium sulfate, and the aromatic aldehyde compound is benzaldehyde, vanillin or furfural.

2. The preparation method according to claim 1, characterized in that: In step S10, the organic solvent in the organic solution containing the modifier is DMF, DMSO or ethanol.

3. The preparation method according to claim 1, characterized in that: In step S10, after the reaction is completed, the substrate is cleaned with ethanol, deionized water or ethanol aqueous solution.

4. The preparation method according to claim 3, characterized in that: In step S10, after the reaction is completed, washing is performed 6 times with ethanol, deionized water or ethanol aqueous solution.

5. The preparation method according to claim 1, characterized in that: In the solution containing the ammonium salt and the aromatic aldehyde compound in step S20, the concentration of the ammonium salt is 0.005 to 0.8 g / mL, and the concentration of the aromatic aldehyde compound is 0.01 to 0.6 g / mL.

6. The preparation method according to claim 1, characterized in that: In the solution containing the ammonium salt and the aromatic aldehyde compound in step S20, the solvent is ethanol, deionized water or ethanol aqueous solution.

7. The preparation method according to claim 1, characterized in that: In step S20, after the reaction is completed, the substrate is cleaned with ethanol, deionized water or ethanol-water solution.

8. The preparation method according to claim 7, characterized in that: In step S20, after the reaction is completed, washing is performed 6 times with ethanol, deionized water or ethanol aqueous solution.

9. An anti-ultraviolet fluorescent chitosan film, characterized in that: The anti-ultraviolet fluorescent chitosan film is prepared by the preparation method of any one of claims 1 to 8.

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