Chitosan-cyanine pigment / carboxylated graphene oxide film and preparation method thereof

Abstract

The application discloses a chitosan-cyanine / carboxylated graphene oxide film and a preparation method thereof. The application uses a glass slide as a substrate, alternately assembles chitosan with opposite charges and carboxylated graphene oxide on the substrate, and dries the film to obtain a layer-by-layer self-assembly film with different double layers. The modified film has greatly improved ultraviolet blocking capacity, maintains good transparency, and has enhanced mechanical performance and water blocking performance, and has good antioxidant performance. The application selects carboxylated graphene oxide as an assembly material for the first time, and has the advantages of mild conditions, simple process, no introduction of other impurities in the modification process, no generation of other by-products and the like.

Description

Technical Field

[0001] This invention belongs to the field of materials technology, specifically relating to a chitosan-anthocyanin / carboxylated graphene oxide layer-by-layer self-assembled thin film and its preparation method. Background Technology

[0002] With the increasing severity of environmental pollution and food safety issues, research and application of biodegradable bio-based food packaging materials have garnered significant attention. Chitosan, the second largest natural renewable resource after cellulose, is the only naturally occurring alkaline polysaccharide that can be obtained through the deacetylation of chitin. Chitosan possesses excellent film-forming properties, biodegradability, and biocompatibility, along with good antibacterial and antioxidant properties, leading to its widespread application in biomedicine, food packaging, water treatment, and electrochemistry. However, when chitosan is used alone to make films, its mechanical properties are too weak to meet the basic requirements of food packaging. Furthermore, its UV blocking ability, water resistance, and thermal stability are relatively poor, limiting its application in high-moisture environments. Existing technologies utilize filler blending, crosslinking, and surface modification to improve certain properties of chitosan-based films, but the overall performance improvement is limited.

[0003] Layer-by-layer self-assembly effectively modulates the physical and chemical properties of composite films by utilizing the interactions between different components, such as electrostatic interactions, hydrogen bonds, and Schiff base bonds. Among these, electrostatic self-assembly achieves layer-by-layer deposition and continuous cross-linking through the electrostatic interactions between polycationic electrolytes and polyanionic electrolytes, thus forming stable films at room temperature. This method offers advantages such as simplicity, controllable conditions, and wide availability of materials, making it a promising candidate for numerous applications.

[0004] The application of graphene oxide in thin film technology has been extensively studied, but its compatibility is poor, and it tends to aggregate and disperse poorly in aqueous solutions. Carboxylated graphene oxide has a similar framework structure to graphene oxide, but it has more hydrophilic groups such as hydroxyl and carboxyl groups on its surface, resulting in better dispersibility in water and a higher anion density in aqueous solutions, which is beneficial for layer-by-layer self-assembly with chitosan. Meanwhile, anthocyanins are non-toxic, water-soluble natural plant pigments rich in hydroxyl groups, possessing natural antioxidant properties, and can form cross-linked network structures with chitosan through hydrogen bonds.

[0005] Based on the above considerations, chitosan doped with anthocyanins was used as a polycationic electrolyte, and carboxylated graphene oxide was used as a polyanionic electrolyte. A layer-by-layer self-assembly method was used to prepare a film with excellent ultraviolet blocking ability, good mechanical properties, water-blocking properties, improved thermal stability, water vapor barrier properties and antioxidant properties, which has broad application prospects in the field of food packaging. Summary of the Invention

[0006] The purpose of this invention is to provide a thin film and a method thereof prepared by layer-by-layer self-assembly of anthocyanin-doped chitosan and carboxylated graphene oxide. This method can modify chitosan-based films, improving their overall performance and producing multifunctional chitosan-anthocyanin / carboxylated graphene oxide films more suitable for the food packaging field.

[0007] The technical solution to achieve the purpose of this invention is as follows:

[0008] In a first aspect, the present invention provides a chitosan-anthocyanin / carboxylated graphene oxide film, wherein anthocyanin-doped chitosan and carboxylated graphene oxide are self-assembled layer by layer to form a multilayer structure.

[0009] In a second aspect, the present invention provides a method for preparing the chitosan-anthocyanin / carboxylated graphene oxide film described in the first aspect, comprising the following steps:

[0010] Step 1: Immerse the glass slide in chitosan film-forming solution for 10 min, then immerse it in deionized water for 5 min, then immerse it in carboxylated graphene oxide dispersion for 5 min, then immerse it in deionized water for 1 min, and dry it to form a bilayer.

[0011] Step 2: Repeat Step 1. For each bilayer assembled, reduce the soaking time in the chitosan film-forming solution by 30s and the soaking time in the carboxylated graphene oxide dispersion by 20s. Alternately deposit to obtain 5 to 10 bilayer self-assembled films.

[0012] Preferably, in step 1, the concentration of the chitosan film-forming solution is 2% to 2.5 wt%, more preferably 2.5 wt%, and its solvent is an acetic acid solution of equal mass concentration, wherein the solvent of the acetic acid solution is water.

[0013] Preferably, in step 1, the selected chitosan has a degree of deacetylation ≥ 95% and a viscosity of 100–200 mPa·s.

[0014] Preferably, in step 1, the anthocyanins used are derived from blueberries and have a content of 5% to 25%.

[0015] Preferably, in step 1, the chitosan film-forming solution contains 20 wt% glycerol and 1 wt% anthocyanins relative to the mass fraction of chitosan.

[0016] Preferably, in step 1, the concentration of the carboxylated graphene oxide dispersion is 0.1–0.2 mg / mL, more preferably 0.1 mg / mL.

[0017] Preferably, in step 1, the drying temperature is 50°C.

[0018] Preferably, in step 2, the number of assembly layers is 10 double layers.

[0019] Thirdly, the present invention provides a food packaging film, which uses the chitosan-anthocyanin / carboxylated graphene oxide film described in the first aspect as the film-making material.

[0020] Compared with the prior art, the advantages of this invention are: (1) The average transmittance of the film prepared by this invention to the ultraviolet light region, especially the UV-B region, is only 1.68%, but the transparency is still relatively high. At the same time, the tensile strength and elongation at break can reach 53.52MPa and 71.81%, respectively. The thermal stability, water resistance, water vapor barrier and antioxidant properties are all improved, and the comprehensive performance of the chitosan-based film is optimized; (2) In this invention, the amount of active additive anthocyanin is only 1% of the mass fraction of chitosan, and the concentration of carboxylated graphene oxide is only 0.1mg / mL. The addition of a small amount of active substances and the application of layer-by-layer self-assembly technology have a significant effect on improving the performance of chitosan-based film; (3) The preparation method of the film described in this invention is mild and easy to operate. The deposition time in the layer-by-layer self-assembly process is clearly defined, which saves the preparation cost to a certain extent. Attached Figure Description

[0021] Figure 1 This is a comparison diagram of the ultraviolet light blocking performance of the chitosan base layer self-assembled film prepared in Example 1 of the present invention and the chitosan cast film prepared in Comparative Example 1.

[0022] Figure 2 This is a comparison diagram of the tensile properties of the chitosan base layer self-assembled film prepared in Example 1 of the present invention and the chitosan cast film prepared in Comparative Example 1.

[0023] Figure 3 This is a comparison diagram of the thermal stability of the chitosan base layer self-assembled film prepared in Example 1 of the present invention and the chitosan cast film prepared in Comparative Example 1.

[0024] Figure 4 This is a comparison diagram of the water contact angle between the chitosan base layer self-assembled film prepared in Example 1 of the present invention and the chitosan cast film prepared in Comparative Example 1.

[0025] Figure 5 This is a comparison diagram of the antioxidant properties of the chitosan base layer self-assembled film prepared in Example 1 of the present invention and the chitosan cast film prepared in Comparative Example 1.

[0026] Figure 6 This is a comparison of the tensile properties of the self-assembled chitosan base layer film with 10 bilayers prepared in Example 1 of the present invention and the three film samples prepared in Examples 2-4.

[0027] Figure 7 This is a comparison of the water contact angles of the self-assembled chitosan base layer self-assembled film with 10 double layers prepared in Example 1 of the present invention and the three film samples prepared in Examples 2-4. Detailed Implementation

[0028] To facilitate a better understanding of the technology of this invention by those skilled in the art, the following embodiments will be used to further illustrate this invention in conjunction with the accompanying drawings.

[0029] The design concept of this invention is as follows: through the hydrogen bonding between chitosan, anthocyanins, and carboxylated graphene oxide, as well as the electrostatic interaction between chitosan and carboxylated graphene oxide, a tight cross-linked network is formed, enhancing the interlayer interaction and improving the mechanical and water-blocking properties of the film. At the same time, as a polyphenolic compound, anthocyanins can absorb ultraviolet light, and the conjugated structure and two-dimensional planar structure of carboxylated graphene oxide can absorb and reflect ultraviolet light, which helps to improve the film's ability to block ultraviolet light. In addition, the natural antioxidant properties of anthocyanins help to enhance the antioxidant capacity of the film.

[0030] The carboxylated graphene oxide described in this invention is based on the literature "Carboxylated Graphene Oxide for Nd22000". 3+ The steps in the paper "Adsorption of [substance name]" (Tao Wuqing, Nuclear Chemistry and Radiochemistry, Vol.44, No.6, 2022, 589-596) are modified as follows:

[0031] 1. Weigh 200 mg of graphene oxide and add it to 100 mL of deionized water. Repeat the sonication for 30 min and stirring for 30 min three times each to obtain a 2 mg / mL graphene oxide dispersion.

[0032] 2. Slowly add 10g of chloroacetic acid to the graphene oxide dispersion, stir magnetically, and after it is completely dissolved, add 10g of sodium hydroxide, stir in a water bath at room temperature for 12 hours, and wait for the reaction to be complete.

[0033] 3. Transfer the solution to a centrifuge tube, centrifuge at 10000 r / min for 10 min, and centrifuge until the supernatant is neutral. Collect the lower precipitate, freeze-dry it, and you can obtain carboxylated graphene oxide.

[0034] Example 1

[0035] This embodiment provides a method for preparing a chitosan base layer self-assembled film, including the following steps:

[0036] 1. Add 2.5g of chitosan powder to 97.5g of 2.5% acetic acid solution and stir at 1000rpm for 6 hours at room temperature. Then add 0.5g of glycerol (20% w / w chitosan) and stir for 1 hour. Finally, add 0.025g of anthocyanin (1% w / w chitosan) and stir for 1 hour to obtain a 2.5wt% chitosan film-forming solution. After ultrasonic elimination of bubbles, refrigerate for later use.

[0037] 2. Add 10 mg of carboxylated graphene oxide to 100 mL of deionized water, and alternate between sonication for 30 min and stirring for 30 min three times to obtain a carboxylated graphene oxide dispersion with a concentration of 0.1 mg / mL.

[0038] 3. Immerse a 7.5cm×2cm glass slide in chitosan film-forming solution for 10min, then immerse it in deionized water for 5min, then immerse it in carboxylated graphene oxide dispersion for 5min, then immerse it in deionized water for 1min, and dry it at 50℃ to form a bilayer.

[0039] 4. Repeat the above steps. For each bilayer assembled, reduce the soaking time in the chitosan film-forming solution by 30s and the soaking time in the carboxylated graphene oxide dispersion by 20s. Alternately deposit to obtain 6 samples of layer-by-layer self-assembled films with 5, 6, 7, 8, 9 and 10 bilayers respectively. After drying, store in a desiccator containing saturated Ca(NO3)2 solution and a relative humidity of 50%.

[0040] Comparative Example 1

[0041] 1. Add 2.5g of chitosan powder to 97.5g of 2% acetic acid solution, stir at 1000rpm for 6h at room temperature, then add 0.5g of glycerol (20% w / w chitosan), stir for 1h, and sonicate to eliminate bubbles;

[0042] 2. Pour 2.5 wt% chitosan film-forming solution into a petri dish and dry it at a constant temperature of 50℃ in an oven for 12 hours. After peeling, chitosan casting film is obtained.

[0043] The performance of the six samples in Example 1 and Comparative Example 1 was tested, including UV blocking properties, tensile properties, thermal stability, wettability and antioxidant properties. Figure 1 This indicates that the film with 10 double layers assembled in Example 1 has the lowest average ultraviolet transmittance in the UV-B region, at only 1.68%, demonstrating excellent ultraviolet blocking ability. At the same time, the film still maintains good visible light transmittance, with minimal impact on the film's appearance. Figure 2The results show that the film with 10 double layers assembled in Example 1 has the best tensile properties, with a tensile strength that is 15.41 MPa higher than that of Comparative Example 1 and an elongation at break that is 40.52% higher than that of Comparative Example 1. It is evident that the tensile properties of the film prepared by the present invention are significantly improved. Figure 3 This indicates that the thermal stability of the thin film samples prepared in Example 1 is significantly improved compared to that of Comparative Example 1. Figure 4 The results show that the film with 10 bilayers assembled in Example 1 has the largest water contact angle, reaching 104.1°, exhibiting the best hydrophobicity and the strongest water-blocking ability. This invention measures the antioxidant performance of the film by its ABTS free radical scavenging activity. Figure 5 This indicates that the ABTS radical scavenging activity of the film with 10 assembled bilayers in Example 1 is the strongest, reaching 91.22%. In summary, the film with 10 assembled bilayers in Example 1 exhibits the best overall performance.

[0044] Example 2

[0045] Step 1 in Example 1 was modified by adding 2g of chitosan powder to 98g of 2% acetic acid solution, stirring at 1000rpm for 6 hours at room temperature, adding 0.4g of glycerol, stirring for 1 hour, and finally adding 0.02g of anthocyanin and stirring for 1 hour to obtain a chitosan film-forming solution with a 2% mass fraction. The remaining steps were the same as in Example 1, except that the number of assembled layers was 10 bilayers, and the resulting sample was denoted as A.

[0046] Example 3

[0047] Step 1 in Example 1 was modified by adding 2g of chitosan powder to 98g of 2% acetic acid solution, stirring at 1000rpm for 6h at room temperature, then adding 0.4g of glycerol and stirring for 1h, and finally adding 0.02g of anthocyanin and stirring for 1h to obtain a chitosan film-forming solution with a 2% mass fraction. Step 2 was modified by adding 20mg of carboxylated graphene oxide to 100mL of deionized water, and the remaining steps were the same as in Example 1, except that the number of assembled layers was 10 bilayers, and the resulting sample was designated as B.

[0048] Example 4

[0049] Step 2 in Example 1 was changed to adding 20 mg of carboxylated graphene oxide to 100 mL of deionized water. The remaining steps were the same as in Example 1, except that the number of assembled layers was 10 bilayers, and the resulting sample was denoted as C.

[0050] Tensile properties and wettability tests were performed on the 10-layer bilayer film assembled in Example 1 and the three samples from Examples 2-4. The results are as follows: Figure 6 and Figure 7 As shown. Figure 6 and Figure 7The results show that the sample with 10 bilayers assembled in Example 1 has the best tensile properties, with the highest tensile strength and elongation at break. It also has the largest water contact angle, the best hydrophobicity, and the strongest water-blocking ability. This indicates that the 10 bilayer films prepared by layer-by-layer self-assembly using 2.5 wt% chitosan film-forming solution and 0.1 mg / mL carboxylated graphene oxide dispersion as components have the best overall performance.

[0051] The present invention relates to a chitosan-anthocyanin / carboxylated graphene oxide layer-by-layer self-assembled film and its preparation method. Glycerin is added to chitosan as a plasticizer and anthocyanin as an active substance, serving as a polycationic electrolyte. Carboxylated graphene oxide serves as a polyanionic electrolyte. Utilizing the hydrogen bonding between anthocyanin, chitosan, and carboxylated graphene oxide, as well as the electrostatic interaction between chitosan and carboxylated graphene oxide, the film is prepared through layer-by-layer self-assembly. This method significantly improves the film's UV blocking ability while maintaining good transparency, effectively enhancing its tensile properties, thermal stability, water resistance, and antioxidant properties. It holds promise as a multifunctional food packaging film for application in the food packaging industry.

Claims

1. A chitosan-anthocyanin / carboxylated graphene oxide film, characterized in that, A multilayer structure is formed by the self-assembly of anthocyanin-doped chitosan and carboxylated graphene oxide. Prepared by the following steps: Step 1: Immerse the glass slide in chitosan film-forming solution for 10 min, then immerse it in deionized water for 5 min, then immerse it in carboxylated graphene oxide dispersion for 5 min, then immerse it in deionized water for 1 min, and dry it to form a bilayer. Step 2: Repeat Step 1. For each bilayer assembled, reduce the soaking time in the chitosan film-forming solution by 30 s and the soaking time in the carboxylated graphene oxide dispersion by 20 s. Alternately deposit to obtain 10 bilayer self-assembled films.

2. A method for preparing a chitosan-anthocyanin / carboxylated graphene oxide film as described in claim 1, characterized in that, Includes the following steps: Step 1: Immerse the glass slide in chitosan film-forming solution for 10 min, then immerse it in deionized water for 5 min, then immerse it in carboxylated graphene oxide dispersion for 5 min, then immerse it in deionized water for 1 min, and dry it to form a bilayer. Step 2: Repeat Step 1. For each bilayer assembled, reduce the soaking time in the chitosan film-forming solution by 30 s and the soaking time in the carboxylated graphene oxide dispersion by 20 s. Alternately deposit to obtain 10 bilayer self-assembled films.

3. The method as described in claim 2, characterized in that, In step 1, the concentration of the chitosan film-forming solution is 2% to 2.5 wt%, and its solvent is an acetic acid solution of equal mass concentration, with water as the solvent for the acetic acid solution.

4. The method as described in claim 3, characterized in that, In step 1, the concentration of the chitosan film-forming solution is 2.5 wt%.

5. The method as described in claim 2, characterized in that, In step 1, the selected chitosan has a degree of deacetylation ≥95% and a viscosity of 100–200 mPa·s.

6. The method as described in claim 2, characterized in that, In step 1, the anthocyanins used are derived from blueberries, with a content of 5% to 25%.

7. The method as described in claim 2, characterized in that, In step 1, the chitosan film-forming solution contains 20 wt% glycerol and 1 wt% anthocyanins relative to the mass fraction of chitosan.

8. The method as described in claim 2, characterized in that, In step 1, the concentration of the carboxylated graphene oxide dispersion is 0.1–0.2 mg / mL.

9. The method as described in claim 8, characterized in that, In step 1, the concentration of the carboxylated graphene oxide dispersion is 0.1 mg / mL.

10. The method as described in claim 2, characterized in that, In step 1, the drying temperature is 50℃.

11. A food packaging film, characterized in that, The chitosan-anthocyanin / carboxylated graphene oxide film as described in claim 1 is used as the film-forming material.

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