Intelligent modified atmosphere packaging film with gas selectivity and dual pH / humidity response, its manufacturing method and application

Abstract

This invention discloses a smart modified atmosphere packaging film with gas selectivity and dual pH / humidity response, its preparation method, and its application. The preparation method includes: mixing thymol emulsion with graphene oxide dispersion and reacting the mixture at room temperature in the dark to obtain graphene oxide-thymol; dissolving chitosan in an aqueous acetic acid solution, then adding graphene oxide-thymol and a plasticizer for ultrasonic dispersion treatment to form a film-forming solution; and using a casting method to form a film, thereby obtaining a smart modified atmosphere packaging film with gas selectivity and dual pH / humidity response. The smart modified atmosphere packaging film prepared by this invention can spontaneously modify the atmosphere, has a uniform and stable structure, and exhibits high encapsulation efficiency, tight coordination, good antibacterial and antioxidant activity, excellent mechanical properties, and gas barrier properties. It can achieve selective gas adsorption and control the release of thymol by responding to changes in pH and humidity in the environment, showing promising application prospects in the field of fruit and vegetable preservation.

Description

Technical Field

[0001] This invention belongs to the field of fruit and vegetable storage and preservation materials, specifically relating to an intelligent modified atmosphere packaging film with gas selectivity and dual pH / humidity response, its manufacturing method and application. Background Technology

[0002] Post-harvest oxidation and microbial spoilage are common problems for fruits and vegetables, leading to quality deterioration and significant economic losses. To address this challenge, various technologies have emerged, including low-temperature storage, chitosan coating, melatonin regulation, and modified atmosphere packaging. However, existing technologies still struggle to achieve an ideal balance between efficacy stability, cost-effectiveness, and consumer safety. Some technologies have faced obstacles in practical application due to significant fluctuations in efficacy, potential safety hazards, or low consumer acceptance. Against this backdrop, the innovative development of preservation technologies that combine high efficiency, safety, and promising market prospects is not only crucial for overcoming industry development bottlenecks but also of paramount importance for reducing post-harvest losses and meeting consumer demand for high-quality, healthy food.

[0003] In recent years, modified atmosphere packaging (MAP) has become a key post-harvest preservation technology, and its strategic importance is increasingly prominent. However, its effectiveness highly depends on the precise control of the gas environment inside the packaging. An ideal MAP material should possess self-modified atmosphere capabilities, meaning that the film should have differentiated selective permeability and adsorption properties for gases such as O2 and CO2 to dynamically balance the respiration of fruits and vegetables and automatically establish and maintain a suitable gaseous microenvironment. However, the gas selectivity control capabilities of existing conventional MAP films (such as polyethylene and polypropylene) are generally insufficient, making it difficult to intelligently respond to the complex respiratory and metabolic changes of fruits and vegetables after harvest. This results in excessively low O2 concentrations or excessively high CO2 concentrations inside the packaging, easily leading to physiological damage such as anaerobic respiration or CO2 poisoning, which accelerates quality deterioration. At the same time, existing MAP products have limited functionality and cannot achieve the synergy of intelligent controlled release and efficient self-modified atmosphere functions, resulting in unsatisfactory preservation effects. Therefore, developing an intelligent MAP film with gas selectivity and dual pH / humidity response is an urgent problem to be solved. Summary of the Invention

[0004] The main objective of this invention is to provide a smart modified atmosphere packaging film with gas selectivity and dual pH / humidity response, as well as its manufacturing method and application, to overcome the shortcomings of the prior art.

[0005] To achieve the aforementioned objectives, the technical solution adopted by this invention includes:

[0006] This invention provides a method for preparing a smart modified atmosphere packaging film with gas selectivity and dual pH / humidity response, comprising:

[0007] Graphene oxide and calcium chloride were dispersed in water to form a graphene oxide dispersion; thymol, emulsifier and ethanol were mixed and emulsified to form a thymol emulsion; then the thymol emulsion and graphene oxide dispersion were mixed and stirred at room temperature in the dark to obtain graphene oxide-thymol.

[0008] Chitosan was dissolved in an aqueous acetic acid solution, and then graphene oxide-thymol and plasticizer were added for ultrasonic dispersion to form a film-forming solution.

[0009] Furthermore, the film-forming solution is subjected to a casting process to form a film, thereby obtaining a smart modified atmosphere packaging film with gas selectivity and dual pH / humidity response.

[0010] The present invention also provides a smart modified atmosphere packaging film with gas selectivity and dual pH / humidity response prepared by the aforementioned preparation method.

[0011] This invention also provides the application of the aforementioned intelligent modified atmosphere packaging film with gas selectivity and dual pH / humidity response in the storage and preservation of fruits and vegetables.

[0012] This invention also provides a method for preserving fruits and vegetables, which includes: sealing and storing fruits or vegetables using the aforementioned intelligent modified atmosphere packaging film with gas selectivity and pH / humidity dual response;

[0013] The storage environment is characterized by an ambient temperature of 20-25°C and a relative humidity of 70-80%.

[0014] This invention also provides a fruit and vegetable storage and preservation material, which includes: the aforementioned intelligent modified atmosphere packaging film with gas selectivity and pH / humidity dual response.

[0015] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0016] (1) The preparation method provided by the present invention has low energy consumption, mild conditions, simple operation and low cost, and the prepared intelligent modified atmosphere packaging film has a uniform and controllable structure and stable performance.

[0017] (2) The intelligent modified atmosphere packaging film prepared by the present invention has gas selectivity and pH / humidity dual response, can spontaneously modify atmosphere, has high encapsulation rate, tight coordination, large specific surface area and pore volume, and strong hydrophobicity.

[0018] (3) The intelligent modified atmosphere packaging film prepared by the present invention has gas selectivity and pH / humidity dual response, has multifunctionality, good antibacterial and antioxidant activity, excellent mechanical properties and gas barrier properties, and can achieve selective adsorption of gases.

[0019] (4) The intelligent modified atmosphere packaging film prepared by the present invention, which has gas selectivity and pH / humidity dual response, can control the release of thymol by responding to changes in pH and humidity in the environment, thereby maximizing the antioxidant and antibacterial effects. Attached Figure Description

[0020] To more clearly illustrate the technical solutions in the embodiments of this application or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments recorded in this application. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0021] Figures 1a-1d The images show the scanning electron microscope (SEM) morphology and X-ray diffraction patterns of the graphite powder, graphene oxide, and graphene oxide-thymol prepared in Example 1.

[0022] Figure 2 Atomic force microscopy (AFM) images, cross-sectional scanning electron microscopy (SEM) images, and water contact angle diagrams of the chitosan films and chitosan / graphene oxide-thymol composite films prepared in Comparative Example 1 and Examples 1-5 are shown.

[0023] Figure 3 Fourier transform infrared spectra of the chitosan films and chitosan / graphene oxide-thymol composite films prepared in Comparative Example 1 and Examples 1-5.

[0024] Figures 4a-4c Graphs showing the specific surface area, pore size, and pore volume of the chitosan films and chitosan / graphene oxide-thymol composite films prepared in Comparative Example 1 and Examples 1-5.

[0025] Figures 5a-5g The graph shows the thickness, mechanical properties, and gas barrier properties of the chitosan film and chitosan / graphene oxide-thymol composite film prepared in Comparative Example 1 and Examples 1-5.

[0026] Figures 6a-6g The graph shows the antibacterial, antioxidant, and hemolytic activities of the chitosan films and chitosan / graphene oxide-thymol composite films prepared in Comparative Example 1 and Examples 1-5.

[0027] Figure 7 The encapsulation efficiency diagrams are for the chitosan / graphene oxide-thymol composite films prepared in Examples 1-5.

[0028] Figures 8a-8d This is a comparison of the adsorption free energies of the chitosan / graphene oxide-thymol composite film prepared in Example 1 for different gases (CO2 and O2).

[0029] Figures 9a-9b The graph shows the humidity and pH response release performance of the chitosan / graphene oxide-thymol composite film prepared in Example 1.

[0030] Figures 10a-10e The images show the application of the chitosan film and chitosan / graphene oxide-thymol composite film prepared in Comparative Example 1 and Example 1 in mango preservation. Detailed Implementation

[0031] In view of the deficiencies of the prior art, the inventors of this invention, through long-term research and extensive practice, have proposed the technical solution of this invention. This invention involves first dispersing graphite powder in concentrated sulfuric acid and then continuously stirring it in an ice bath. After sufficient dispersion, potassium permanganate is added to the solution, and the graphite powder is oxidized under stirring. After thorough stirring, an appropriate amount of distilled water is added to dilute the concentrated sulfuric acid, and then an appropriate amount of hydrogen peroxide is added to consume excess potassium permanganate. Stirring continues to promote the dilution of the concentrated sulfuric acid and the consumption of excess potassium permanganate. The crude product was obtained by centrifugation and discarding the supernatant, washed with distilled water, and then vacuum dried to obtain graphene oxide. Graphene oxide powder was then dispersed in distilled water, with an appropriate amount of calcium chloride powder added, and ultrasonically treated at room temperature to promote uniform dispersion. Thymol was pre-dissolved in anhydrous ethanol, an appropriate amount of Tween 80 was added, and ultrasonic emulsification was performed. Thymol was then slowly added dropwise to the graphene oxide dispersion, and the mixture was stirred at room temperature in the dark to ensure thorough mixing. The crude product was then obtained by centrifugation and discarding the supernatant, washed with anhydrous ethanol, and then vacuum dried to obtain graphene oxide. The graphene-thymol product was then prepared. Chitosan powder was dissolved in an aqueous acetic acid solution, and then graphene oxide-thymol powder in different proportions was added to the chitosan solution. An appropriate amount of glycerol was added as a plasticizer. The mixture was ultrasonically treated in an ice bath to promote uniform dispersion. After full dispersion, the mixture was allowed to stand and degassed to obtain a uniform film-forming solution. Finally, the above solution was cast into a film at room temperature using a casting method. After drying, chitosan / graphene oxide-thymol composite films with different proportions were obtained (the aforementioned intelligent modified atmosphere packaging film with gas selectivity and pH / humidity dual response).

[0032] The technical solution of the present invention will be clearly and completely described below. Obviously, the described embodiments are only some embodiments of the present invention, not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0033] Specifically, as one aspect of the technical solution of this invention, the method for preparing a smart modified atmosphere packaging film with gas selectivity and dual pH / humidity response includes:

[0034] Graphene oxide and calcium chloride were dispersed in water to form a graphene oxide dispersion; thymol, emulsifier and ethanol were mixed and emulsified to form a thymol emulsion; then the thymol emulsion and graphene oxide dispersion were mixed and stirred at room temperature in the dark to obtain graphene oxide-thymol.

[0035] Chitosan was dissolved in an aqueous acetic acid solution, and then graphene oxide-thymol and plasticizer were added for ultrasonic dispersion to form a film-forming solution.

[0036] Furthermore, the film-forming solution is subjected to a casting process to form a film, thereby obtaining a smart modified atmosphere packaging film with gas selectivity and dual pH / humidity response.

[0037] In some preferred embodiments, the preparation method specifically includes: dispersing graphene oxide in water, then adding calcium chloride and ultrasonically dispersing at room temperature to form a graphene oxide dispersion;

[0038] The mass-to-volume ratio of graphene oxide to water is 1g:500mL to 1g:2000mL; the mass-to-volume ratio of calcium chloride to water is 1g:50mL to 1g:200mL; and the ultrasonic dispersion treatment time is 0.5 to 1h.

[0039] In some preferred embodiments, the preparation method specifically includes: dissolving thymol in ethanol, then adding an emulsifier and performing ultrasonic emulsification to form a thymol emulsion;

[0040] The mass-to-volume ratio of thymol to ethanol is 1g:10mL to 1g:20mL; the mass ratio of thymol to emulsifier is 2:1 to 1:1; the emulsifier includes any one or more combinations of Tween 80, Tween 20, Tween 60, sucrose ester, and monoglyceride; and the ultrasonic emulsification treatment time is 10 to 15 minutes.

[0041] In some preferred embodiments, the preparation method specifically includes: slowly adding thymol emulsion dropwise to the graphene oxide dispersion and stirring the mixture at room temperature in the dark for 2-4 hours, followed by centrifugation, washing, and vacuum drying to obtain graphene oxide-thymol;

[0042] The mass ratio of graphene oxide to thymol is 0.5~1:0.2~1.

[0043] The centrifugation process is carried out at a speed of 8000~10000 rpm, a temperature of 20~30℃, and a duration of 10~15 min.

[0044] The washing process includes washing the product obtained by centrifugation with anhydrous ethanol 2 to 3 times;

[0045] The vacuum drying process is carried out at a temperature of 60-80°C for 12-24 hours.

[0046] In some preferred embodiments, the preparation method specifically includes:

[0047] Chitosan was dissolved in an aqueous acetic acid solution, then graphene oxide-thymol and plasticizer were added and ultrasonically dispersed under ice bath conditions, and then allowed to stand to degas, forming a film-forming solution.

[0048] The film-forming solution was cast at room temperature and then dried to obtain a smart modified atmosphere packaging film with gas selectivity and dual pH / humidity response.

[0049] Furthermore, the mass ratio of chitosan to graphene oxide-thymol is 100:1~5.

[0050] Furthermore, the mass-to-volume ratio of chitosan to aqueous acetic acid is 1g:50mL to 1g:200mL.

[0051] Furthermore, the mass-to-volume ratio of the plasticizer to the film-forming solution is 1~2g:100mL.

[0052] Furthermore, the volume concentration of the acetic acid aqueous solution is 1-2%.

[0053] Furthermore, the ultrasonic dispersion treatment time is 1 to 3 hours.

[0054] Furthermore, the temperature for static degassing is 20~30℃, and the time is 12~24h.

[0055] Furthermore, the drying process is carried out at a temperature of 40-50°C for 12-16 hours.

[0056] In some more specific embodiments, the method for preparing the smart modified atmosphere packaging film with gas selectivity and dual pH / humidity response includes:

[0057] (1) Disperse graphite powder in concentrated sulfuric acid and place it in an ice bath and stir continuously. After it is fully dispersed, add potassium permanganate to the solution and oxidize the graphite powder under stirring. After stirring, add an appropriate amount of distilled water to dilute the concentrated sulfuric acid and add an appropriate amount of hydrogen peroxide to consume the excess potassium permanganate. Continue stirring to promote the dilution of concentrated sulfuric acid and the consumption of excess potassium permanganate. Obtain the crude product by centrifugation and discarding the supernatant. Wash with distilled water and then dry under vacuum to obtain graphene oxide product.

[0058] (2) Disperse graphene oxide powder in distilled water, add an appropriate amount of calcium chloride powder, and sonicate at room temperature to promote uniform dispersion. Dissolve thymol in anhydrous ethanol, add an appropriate amount of Tween 80, and sonicate. Then slowly add thymol to the graphene oxide dispersion, stir at room temperature in the dark to mix it thoroughly, and then obtain the crude product by centrifugation and discarding the supernatant. Wash with anhydrous ethanol and then dry under vacuum to obtain the graphene oxide-thymol product.

[0059] (3) Chitosan powder is dissolved in an aqueous acetic acid solution, and then graphene oxide-thymol powder of different proportions is added to the chitosan solution. An appropriate amount of glycerol is added as a plasticizer. The solution is ultrasonically treated in an ice bath to promote uniform dispersion. After full dispersion, the solution is allowed to stand and degas to obtain a uniform film-forming solution. Finally, at room temperature, the above solution is cast into a film by casting. After drying, chitosan / graphene oxide-thymol composite films of different proportions are obtained, namely the aforementioned intelligent modified atmosphere packaging film with gas selectivity and pH / humidity dual response of graphene oxide-thymol.

[0060] Preferably, in step (1), the graphite powder is dispersed in concentrated sulfuric acid and placed in an ice bath for continuous stirring. The mass of the graphite powder is 1-2g, the volume of the concentrated sulfuric acid is 20-30mL, the mass-to-volume ratio (g / mL) of the graphite powder to the concentrated sulfuric acid is 1:10-1:30, the stirring speed is 200-400rpm, the temperature is 0-5℃, and the duration is 0.5-1h.

[0061] Preferably, after the thorough dispersion described in step (1), potassium permanganate is added to the solution, and the graphite powder is oxidized under stirring. The mass of potassium permanganate is 3~4g, the stirring speed is 400~600rpm, the temperature is 0~5℃, and the duration is 3~5h.

[0062] Preferably, after thorough stirring in step (1), an appropriate amount of distilled water is added to dilute the concentrated sulfuric acid, and an appropriate amount of hydrogen peroxide is added to consume the excess potassium permanganate. Stirring continues to promote the dilution of concentrated sulfuric acid and the consumption of excess potassium permanganate. The volume of distilled water is 100-200 mL, the volume of hydrogen peroxide is 5-10 mL, the stirring speed is 600-800 rpm, the temperature is 0-5℃, and the duration is 1-2 h.

[0063] Preferably, in step (1), the crude product is obtained by centrifugation and discarding the supernatant, washed with distilled water, and then dried under vacuum to obtain the graphene oxide product. The centrifugation conditions are: speed of 10000~12000 rpm, temperature of 20~30℃, duration of 10~15 min, washing with distilled water 2~3 times, and vacuum drying temperature of 80~90℃ for 24~36 h.

[0064] Preferably, in step (2), the graphene oxide powder is dispersed in distilled water, an appropriate amount of calcium chloride powder is added, and ultrasonic treatment is performed at room temperature to promote uniform dispersion. The mass of the graphene oxide powder is 0.5~1g, the volume of the distilled water is 500~1000mL, the mass-volume ratio of graphene oxide to distilled water (g / mL) is 1:500~1:2000, the mass of the calcium chloride powder is 5~10g, the mass-volume ratio of calcium chloride to distilled water (g / mL) is 1:50~1:200, and the ultrasonic treatment time is 0.5~1h.

[0065] Preferably, in step (2), thymol is pre-dissolved in anhydrous ethanol, an appropriate amount of Tween 80 is added, and ultrasonic emulsification is performed. The mass-volume ratio (g / mL) of thymol to anhydrous ethanol is 1:10~1:20, the mass ratio (g / g) of thymol to Tween 80 is 2:1~1:1, and the ultrasonic emulsification time is 10~15 min.

[0066] As a preferred embodiment, in step (2), thymol is slowly added dropwise to the graphene oxide dispersion, and stirred at room temperature in the dark to ensure thorough mixing. The amount of thymol added is 0.2~1g, and the stirring time in the dark is 2~4h.

[0067] Preferably, in step (2), the crude product is obtained by centrifugation and discarding the supernatant, washed with anhydrous ethanol, and then vacuum dried to obtain the graphene oxide-thymol product. The centrifugation conditions are: 8000~10000 rpm, 20~30℃, 10~15 min, 2~3 times of washing with anhydrous ethanol, and 60~80℃ for 12~24 h of vacuum drying.

[0068] Preferably, in step (3), chitosan powder is dissolved in an aqueous acetic acid solution, then graphene oxide-thymol powder in different proportions is added to the chitosan solution, and an appropriate amount of glycerol is added as a plasticizer. The solution is then ultrasonically treated in an ice bath to promote uniform dispersion. The mass of the chitosan is 1-2 g, the concentration of the aqueous acetic acid solution is 1-2% (v / v), the volume is 100-200 mL, and the mass-to-volume ratio (g / mL) of the chitosan to the aqueous acetic acid solution is 1: The ratio of glycerol to the total volume of the solution in the system is 50 to 1:200, and the ultrasonication time is 1 to 3 hours. The amount of graphene oxide-thymol added is 1%, 2%, 3%, 4%, and 5% of the dry weight of chitosan (taking 2g of chitosan as an example, the amount of graphene oxide-thymol added is 0.02g, 0.04g, 0.06g, 0.08g, and 0.10g, respectively). The mass-volume ratio (g / mL) of glycerol added to the total volume of the solution in the system is 1% to 2%, and the ultrasonication time is 1 to 3 hours.

[0069] Preferably, after thorough dispersion as described in step (3), the solution is allowed to stand and degas to obtain a uniform film-forming solution. Finally, at room temperature, the above solution is cast into a film by casting, and after drying, chitosan / graphene oxide-thymol composite films with different proportions are obtained. The temperature for standing and degassing is 20~30℃, and the time is 12~24h. The temperature for drying is 40~50℃, and the time is 12~16h.

[0070] Another aspect of the present invention provides a smart modified atmosphere packaging film with gas selectivity and dual pH / humidity response prepared by the aforementioned preparation method.

[0071] Another aspect of the present invention provides the application of the aforementioned intelligent modified atmosphere packaging film with gas selectivity and dual pH / humidity response in the storage and preservation of fruits and vegetables.

[0072] Another aspect of the present invention provides a method for preserving fruits and vegetables, which includes: sealing and storing fruits or vegetables using the aforementioned intelligent modified atmosphere packaging film with gas selectivity and pH / humidity dual response;

[0073] The storage environment is characterized by an ambient temperature of 20-25°C and a relative humidity of 70-80%.

[0074] Another aspect of the present invention provides a fruit and vegetable storage and preservation material, comprising: the aforementioned intelligent modified atmosphere packaging film with gas selectivity and pH / humidity dual response.

[0075] The technical solution of the present invention will be further described in detail below with reference to several preferred embodiments and accompanying drawings. This embodiment is implemented on the premise of the technical solution of the invention, and provides detailed implementation methods and specific operation processes. However, the protection scope of the present invention is not limited to the following embodiments.

[0076] Unless otherwise specified, the experimental materials used in the examples below can be purchased from conventional biochemical reagent companies.

[0077] Example 1:

[0078] This embodiment provides a method for preparing a smart modified atmosphere packaging film with gas selectivity and dual pH / humidity response, specifically including the following steps:

[0079] (1) 1 g of graphite powder was dispersed in 25 mL of concentrated sulfuric acid and stirred continuously at 200 rpm for 0.5 h in an ice bath. After thorough dispersion, 3 g of potassium permanganate was added to the solution and stirred in an ice bath at 400 rpm for 3 h to oxidize the graphite powder. After thorough stirring, 150 mL of distilled water was added to dilute the concentrated sulfuric acid, and 5 mL of hydrogen peroxide was added to consume the excess potassium permanganate. The mixture was stirred in an ice bath at 600 rpm for 1 h to promote the dilution of the concentrated sulfuric acid and the consumption of excess potassium permanganate. The crude product was obtained by centrifugation (10000 rpm, 25 °C, 10 min) and discarding the supernatant. The crude product was washed twice with distilled water and then vacuum dried at 90 °C for 24 h to obtain graphene oxide.

[0080] (2) Disperse 0.5g of graphene oxide powder in 500mL of distilled water, add 5g of calcium chloride powder, and sonicate at room temperature for 1h to promote uniform dispersion. Predissolve 5g of thymol in 100mL of anhydrous ethanol, add 5g of Tween 80, and sonicate for 10min. Then slowly add 0.8g of thymol (i.e., 16mL of thymol ethanol solution) dissolved in ethanol to the graphene oxide dispersion, and stir at room temperature in the dark for 2h to ensure thorough mixing. Then obtain the crude product by centrifugation (8000rpm, 25℃, 10min) and discarding the supernatant, wash twice with anhydrous ethanol, and then vacuum dry at 60℃ for 12h to obtain the graphene oxide-thymol product.

[0081] (3) Dissolve 2g of chitosan powder in 100mL of 1% acetic acid aqueous solution and sonicate for 2h to promote complete dissolution. Then add the above graphene oxide-thymol powder (0.06g, accounting for 3% of the dry weight of chitosan) to the chitosan solution and add 1.5g of glycerol as a plasticizer. Sonicate in an ice bath for 1h to promote uniform dispersion. After sufficient dispersion, allow to stand at room temperature for 12h to degas and obtain a uniform film-forming solution. Finally, cast the above solution into a film at room temperature by casting. After drying at 45℃ for 12h, a chitosan / graphene oxide-thymol composite film is obtained.

[0082] (4) In an orchard in Anhui Province, China, fresh mangoes were carefully selected to ensure that the selected fruits were similar in shape, size, color, and ripeness, and had no obvious visual defects or diseases. After harvesting, the fruits were quickly transported to the laboratory for further processing. In the laboratory, the fruits were first thoroughly washed with distilled water and air-dried. Then, square “micro-windows” measuring 5×5 cm were cut from the lids of plastic boxes of uniform size and specifications. The composite film from Comparative Example 1 and Example 1 was adhered to the “micro-windows” to form a sealed environment, with plastic boxes without “micro-windows” serving as the control group. The fruits were then divided into three groups and sealed in three different types of plastic boxes. Each group had 20 boxes, with 3 mangoes in each box. After treatment, the boxes were stored in an incubator at 25°C and 75% relative humidity. Samples were collected periodically on days 0, 2, 4, 6, and 8, and various parameters such as browning index, flesh firmness, weight loss, decay rate, total soluble solids content, and microbial indicators were measured and optical photographs were taken. Each group had three replicates, and all operations were performed at room temperature.

[0083] Figures 1a-1d The images show the scanning electron microscope (SEM) morphology and X-ray diffraction patterns of the graphite powder, graphene oxide, and graphene oxide-thymol prepared in Example 1. Figure 1a The images show the scanning electron microscope (SEM) morphology of graphite powder. Figure 1b These are scanning electron microscope (SEM) images of graphene oxide. Figure 1c This is a scanning electron microscope (SEM) image of graphene oxide-thymol. Figure 1d The X-ray diffraction patterns of the three are shown. Figures 1a-1d As shown, in terms of morphology, the graphite powder sample exhibits irregular clusters composed of densely stacked layered structures. After oxidation, the resulting graphene oxide exhibits a disordered stacked sheet structure with a significantly increased degree of surface wrinkling. However, after loading thymol, the graphene oxide-thymol composite transforms into a structure with continuous, dense, and more uniformly ordered sheet distribution. Regarding crystal structure, the X-ray diffraction patterns corroborate the morphological evolution. Graphite powder exhibits a sharp and high-intensity diffraction peak near 26.5 degrees, indicating a highly ordered crystal structure. After oxidation, this characteristic peak completely disappears, and a broadened diffraction peak appears in the 10-12 degree range, confirming that the oxidation process successfully disrupted the original crystal form of graphite, generating disordered, amorphous layered graphene oxide. Furthermore, after loading thymol, the diffraction peak of the graphene oxide-thymol composite in the 10-12 degree range disappears, and a new, broader characteristic peak appears near 20 degrees. This phenomenon indicates that thymol molecules have successfully intervened between the graphene oxide sheets, disrupting their original stacking order, thus confirming the successful loading of thymol at the structural level.

[0084] Figure 2 Atomic force microscopy (AFM) images, cross-sectional scanning electron microscopy (SEM) images, and water contact angles of the chitosan films and chitosan / graphene oxide-thymol composite films prepared in Comparative Example 1 and Examples 1-5 are shown. Figure 2 As shown, in terms of three-dimensional surface morphology, the pure chitosan film of Comparative Example 1 has a relatively smooth and uniform surface. In stark contrast, the composite films of Examples 1-5 all exhibit irregular three-dimensional protrusion structures, with sheet-like or wrinkled graphene oxide features emerging from the originally uniform chitosan substrate. At lower composite addition levels, the number of sheet-like structures on the film surface gradually increases with the increase of graphene oxide-thymol content. Among them, the film of Example 1 has the most uniform sheet distribution and the most regular protrusion structure. However, when the addition level increases to a higher level, the graphene oxide sheets show obvious stacking and aggregation, forming larger and more irregular protrusions, resulting in a decrease in film surface continuity and the generation of more grooves and pores. At the same time, cross-sectional morphology analysis further confirms the above trend. The cross-section of the film of Comparative Example 1 also shows a smooth and uniform characteristic. With the increase of composite addition, the cross-sectional morphology of the films of Examples 1-5 shows a synergistic change pattern, with Example 1 consistently exhibiting the best dispersion uniformity and morphological structure. Furthermore, water contact angle tests showed that the pure chitosan film in Comparative Example 1 exhibited the highest hydrophilicity. With the introduction and increasing amount of the graphene oxide-thymol composite, the hydrophobic properties of the films in Examples 1-5 showed an increasing trend. This phenomenon demonstrates that the introduction of this composite effectively improves the hydrophobicity of the film, laying a solid foundation for its excellent water vapor barrier performance.

[0085] Figure 3 Fourier transform infrared spectra of the chitosan films and chitosan / graphene oxide-thymol composite films prepared in Comparative Example 1 and Examples 1-5. Figure 3 As shown, in the infrared spectrum, compared to the pure chitosan film of Comparative Example 1, all composite films of Examples 1-5 showed an infrared spectrum of 1516 cm⁻¹. -1 With 1755 cm -1 Two new characteristic absorption peaks appeared at 3413 cm⁻¹, which are attributed to the benzene ring skeletal vibration of thymol and the stretching vibration of the carboxyl group of graphene oxide, respectively. Meanwhile, a peak was observed at 3413 cm⁻¹. -1 The hydroxyl stretching vibration peaks in the vicinity exhibit a significant narrowing trend in the composite film. These spectral changes, including the appearance of new characteristic peaks and the alteration of existing absorption peak shapes, collectively constitute clear evidence that the graphene oxide-thymol composite has been successfully introduced into the film substrate. These phenomena further reveal significant intermolecular interactions among chitosan, graphene oxide, and thymol, primarily characterized by hydrogen bonding and π-π stacking.

[0086] Figures 4a-4cThe graph shows the specific surface area, pore size, and pore volume of the chitosan films and chitosan / graphene oxide-thymol composite films prepared in Comparative Example 1 and Examples 1-5. Figure 4a The graph shows the specific surface area of ​​the chitosan film and the chitosan / graphene oxide-thymol composite film prepared in Comparative Example 1 and Examples 1-5. Figure 4b The graph shows the pore size of the chitosan film and the chitosan / graphene oxide-thymol composite film prepared in Comparative Example 1 and Examples 1-5. Figure 4c The diagram shows the pore volume of the chitosan films and chitosan / graphene oxide-thymol composite films prepared in Comparative Example 1 and Examples 1-5. Figures 4a-4c As shown, regarding specific surface area and pore volume, with the increase of the graphene oxide-thymol composite addition, the specific surface area and pore volume of all composite films exhibit a trend of first increasing and then decreasing, reaching their maximum values ​​in Example 1. In contrast, the average pore size of the composite films shows a continuous upward trend with increasing addition. At lower addition levels, the pore size growth is relatively gradual; however, when the addition level is further increased to a higher level, the pore size increases sharply, which may be attributed to the stacking and aggregation of graphene oxide sheets. The above results collectively indicate that the composite addition amount corresponding to Example 1 is the key balance point for achieving the optimal pore structure. Under this condition, the film maintains a moderate pore size while constructing the richest pore network, thus obtaining excellent specific surface area and pore volume characteristics.

[0087] Figures 5a-5g The graphs show the thickness, mechanical properties, and gas barrier properties of the chitosan films and chitosan / graphene oxide-thymol composite films prepared in Comparative Example 1 and Examples 1-5. Figure 5a The thickness diagrams show the chitosan films and chitosan / graphene oxide-thymol composite films prepared in Comparative Example 1 and Examples 1-5. Figure 5b The tensile strength diagrams are for the chitosan films and chitosan / graphene oxide-thymol composite films prepared in Comparative Example 1 and Examples 1-5. Figure 5c The graph shows the elongation at break of the chitosan film and the chitosan / graphene oxide-thymol composite film prepared in Comparative Example 1 and Examples 1-5. Figure 5d The graph shows the water vapor transmission rate of the chitosan film and the chitosan / graphene oxide-thymol composite film prepared in Comparative Example 1 and Examples 1-5. Figure 5e The graph shows the carbon dioxide transmittance of the chitosan film and the chitosan / graphene oxide-thymol composite film prepared in Comparative Example 1 and Examples 1-5. Figure 5f The graph shows the oxygen permeability of the chitosan film and the chitosan / graphene oxide-thymol composite film prepared in Comparative Example 1 and Examples 1-5. Figure 5gGas selectivity (CO2 / O2) plots of the chitosan films and chitosan / graphene oxide-thymol composite films prepared in Comparative Example 1 and Examples 1-5. Figures 5a-5c As shown, regarding thickness and mechanical properties, with the increase of the amount of graphene oxide-thymol composite added, the thickness and tensile strength of all composite films showed a continuous upward trend, with Example 1 exhibiting a relatively moderate thickness and a high tensile strength value. Meanwhile, the elongation at break of the composite film gradually decreased with increasing addition, but Example 1 still maintained a high elongation at break under these conditions. Furthermore, as... Figure 5d-Figure 5g As shown, regarding gas barrier performance, the water vapor, oxygen, and carbon dioxide permeability of the composite film all exhibited a pattern of first decreasing and then increasing with the amount added, reaching their lowest values ​​in Example 1. Notably, the decrease in water vapor and oxygen permeability was significantly greater than that of carbon dioxide, indicating that the film of Example 1, while possessing excellent overall barrier performance, also exhibits a high selective permeability to carbon dioxide. Further gas selectivity (CO2 / O2) calculations and analyses showed that the film of Example 1 performed significantly better than other groups in this aspect, fully demonstrating its outstanding application potential in the field of selective modified atmosphere packaging materials.

[0088] Figures 6a-6g The graph shows the antibacterial, antioxidant, and hemolytic activities of the chitosan films and chitosan / graphene oxide-thymol composite films prepared in Comparative Example 1 and Examples 1-5. Figure 6a The images show colony counts of the chitosan films and chitosan / graphene oxide-thymol composite films prepared in Comparative Example 1 and Examples 1-5. Figure 6b The graph shows the Staphylococcus aureus inhibition rate of the chitosan film and the chitosan / graphene oxide-thymol composite film prepared in Comparative Example 1 and Examples 1-5. Figure 6c The graph shows the Escherichia coli inhibition rate of the chitosan film and the chitosan / graphene oxide-thymol composite film prepared in Comparative Example 1 and Examples 1-5. Figure 6d The graph shows the botrytis cinerea inhibition rate of the chitosan film and the chitosan / graphene oxide-thymol composite film prepared in Comparative Example 1 and Examples 1-5. Figure 6e The graph shows the DPPH radical scavenging rates of the chitosan films and chitosan / graphene oxide-thymol composite films prepared in Comparative Example 1 and Examples 1-5. Figure 6f The graph shows the ABTS radical scavenging rates of the chitosan films and chitosan / graphene oxide-thymol composite films prepared in Comparative Example 1 and Examples 1-5. Figure 6g The hemolysis rate graphs are shown for the chitosan films and chitosan / graphene oxide-thymol composite films prepared in Comparative Example 1 and Examples 1-5. Antibacterial properties are a key indicator for food packaging materials. For example... Figures 6a-6dAs shown, antibacterial performance tests indicate that the chitosan / graphene oxide-thymol composite film exhibits significant broad-spectrum inhibitory effects against Staphylococcus aureus, Escherichia coli, and Botrytis cinerea. Examples 1 and 4 show inhibition rates exceeding 99%, almost achieving complete inhibition, and their antibacterial performance is far superior to the pure chitosan film of Comparative Example 1. Simultaneously, regarding antioxidant activity, such as... Figures 6e-6f As shown, the films of Examples 1 and 4 exhibited superior free radical scavenging capabilities, with DPPH (1,1-diphenyl-2-trinitrophenylhydrazine) radical scavenging rates of 88.38% and 86.72%, respectively, and ABTS (2,2'-azino-bis(3-ethylbenzothiazoline-6-sulfonic acid)) radical scavenging rates of 87.26% and 85.23%, respectively. Both indicators were significantly higher than those of Comparative Example 1. Furthermore, biocompatibility assessment results showed that, as Figure 6g As shown, the hemolysis rate of all tested films ranged from 0.16% to 0.75%, which is far below the 5% biosafety threshold, fully demonstrating that the material has excellent blood compatibility and providing a reliable safety basis for its practical application in the food packaging field.

[0089] Figure 7 The encapsulation efficiency of the chitosan / graphene oxide-thymol composite films prepared in Examples 1-5 is shown. Figure 7 As shown, the encapsulation efficiencies of the films in Examples 1-5 were 85.40%, 92.02%, 89.59%, 73.36%, and 58.57%, respectively, generally showing a gradual decrease with increasing addition of the graphene oxide-thymol composite. At lower addition levels, the encapsulation efficiency decreased relatively slowly; however, when the addition level increased, the encapsulation efficiency decreased significantly. Notably, despite the higher addition level, Example 1 still achieved a high retention of the active composite components, maintaining an excellent encapsulation efficiency of approximately 85.40%.

[0090] Figures 8a-8d This is a comparison of the adsorption free energies of the key graphene oxide-thymol composite in the chitosan / graphene oxide-thymol composite film prepared in Example 1 for different gases (CO2 and O2). Figure 8a This is a comparison of the adsorption free energies of the key graphene oxide-thymol composite in the chitosan / graphene oxide-thymol composite film prepared in Example 1 for different gases (CO2 and O2). Figure 8b This is a comparison of the adsorption distances of the key graphene oxide-thymol composite in the chitosan / graphene oxide-thymol composite film prepared in Example 1 for different gases (CO2 and O2). Figure 8cThis is a model diagram of CO2 adsorption by the key graphene oxide-thymol complex in the chitosan / graphene oxide-thymol composite film prepared in Example 1. Figure 8d This is a model diagram of the adsorption of O2 by the key graphene oxide-thymol composite in the chitosan / graphene oxide-thymol composite film prepared in Example 1. Figures 8a-8d As shown, in the gas adsorption free energy test, the composite film in Example 1 exhibited a higher adsorption free energy and a closer adsorption distance for O2, indicating a stronger interaction force between it and O2, resulting in relatively weaker O2 permeability in the film. This finding confirms, from the perspective of gas adsorption mechanism, that the film possesses higher selective permeability for CO2, providing a key theoretical basis for its application in the field of selective modified atmosphere packaging.

[0091] Figures 9a-9b The graph shows the humidity and pH response release performance of the chitosan / graphene oxide-thymol composite film prepared in Example 1. Figure 9a This is a pH-responsive release performance graph of the chitosan / graphene oxide-thymol composite film prepared in Example 1. Figure 9b This is a humidity-responsive release performance diagram of the chitosan / graphene oxide-thymol composite film prepared in Example 1. Figures 9a-9b As shown, the film in Example 1 exhibits excellent dual-response release characteristics based on pH and humidity, highly matching the slightly acidic environment (pH 5-6) and high humidity conditions (>85% RH) of post-harvest fruit storage. Experimental results show that when the ambient humidity increases from 30% to 90%, the cumulative release of thymol from the film in Example 1 significantly increases from 19.51% to 87.80% within 48 hours. This phenomenon can be attributed to the hydrophilic swelling effect of the graphene oxide-thymol complex under high humidity conditions. Simultaneously, the film also exhibits significant acid-promoted release behavior, with a thymol release of 2.72 mg at pH 5.0, more than nine times the release at neutral conditions (0.29 mg). This process mainly stems from the polymer network expansion caused by the protonation of amino groups in chitosan molecules, and the breaking of non-covalent interactions between graphene oxide and thymol molecules. This intelligent release mechanism achieves dual regulation: high humidity ensures basic release, while a slightly acidic environment triggers accelerated release, which not only prolongs the effect of active ingredients but also avoids premature depletion, providing a precise and controllable active substance delivery system for fruit preservation.

[0092] Figures 10a-10e The figures show the application of the chitosan film and chitosan / graphene oxide-thymol composite film prepared in Comparative Example 1 and Example 1 in mango preservation. Figure 10aThe images show the changes in the appearance of mangoes when the chitosan films and chitosan / graphene oxide-thymol composite films prepared in Comparative Example 1 and Example 1 were used for mango preservation. Figure 10b The image shows the red-green value of mangoes when comparing the chitosan films and chitosan / graphene oxide-thymol composite films prepared in Comparative Example 1 and Example 1 for mango preservation. Figure 10c The image shows the mango firmness of the chitosan film and chitosan / graphene oxide-thymol composite film prepared in Comparative Example 1 and Example 1 when used for mango preservation. Figure 10d The image shows the weight loss of mangoes when the chitosan films and chitosan / graphene oxide-thymol composite films prepared in Comparative Example 1 and Example 1 are used for mango preservation. Figure 10e The image shows the mango rot rate when the chitosan film and chitosan / graphene oxide-thymol composite film prepared in Comparative Example 1 and Example 1 are used for mango preservation. Figures 10a-10e As shown, the composite film exhibits significant effects in mango preservation. The results indicate that, compared to the films in the control group and Comparative Example 1, the film in Example 1 effectively maintains the quality indicators of mangoes during storage: maintaining lower [specific parameters / specific parameters]. The film exhibits enhanced color vibrancy, slows down firmness decline (inhibits cell wall component degradation), reduces weight loss (reduces transpiration and respiration), and significantly inhibits mango spoilage (inhibits microbial growth). This comprehensive preservation effect stems from the film's unique multifunctional synergistic mechanism. Its excellent gas selective adsorption capacity creates a suitable spontaneous modified atmosphere environment; its high barrier properties effectively delay quality deterioration; its sustained antibacterial and antioxidant activity inhibits microbial invasion and oxidation reactions; and its intelligent humidity and pH-responsive release characteristics enable precise controlled release of active ingredients. The synergistic effect of these properties collectively demonstrates the practical application value of this composite film as a new generation of multifunctional modified atmosphere packaging material.

[0093] Comparative Example 1:

[0094] (1) Dissolve 2g of chitosan powder in 100mL of 1% acetic acid aqueous solution and sonicate for 2h to promote complete dissolution. Then add 1.5g of glycerol as a plasticizer and sonicate in an ice bath for 1h to promote uniform dispersion. After sufficient dispersion, allow to stand at room temperature for 12h to degas and obtain a uniform film-forming solution. Finally, cast the above solution into a film at room temperature by casting and dry at 45℃ for 12h to obtain the chitosan film in Comparative Example 1.

[0095] Comparative Example 2:

[0096] (1) 1 g of graphite powder was dispersed in 25 mL of concentrated sulfuric acid and stirred continuously at 200 rpm for 0.5 h in an ice bath. After thorough dispersion, 3 g of potassium permanganate was added to the solution and stirred in an ice bath at 400 rpm for 3 h to oxidize the graphite powder. After thorough stirring, 150 mL of distilled water was added to dilute the concentrated sulfuric acid, and 5 mL of hydrogen peroxide was added to consume the excess potassium permanganate. The mixture was stirred in an ice bath at 600 rpm for 1 h to promote the dilution of the concentrated sulfuric acid and the consumption of excess potassium permanganate. The crude product was obtained by centrifugation (10000 rpm, 25 °C, 10 min) and discarding the supernatant. The crude product was washed twice with distilled water and then vacuum dried at 90 °C for 24 h to obtain graphene oxide.

[0097] (2) Dissolve 2g of chitosan powder in 100mL of 1% acetic acid aqueous solution and sonicate for 2h to promote complete dissolution. Then add the above graphene oxide powder (0.06g, accounting for 3% of the dry weight of chitosan) to the chitosan solution and add 1.5g of glycerol as a plasticizer. Sonicate under ice bath for 1h to promote uniform dispersion. After sufficient dispersion, allow to stand at room temperature for 12h to degas and obtain a uniform film-forming solution. Finally, cast the above solution into a film at room temperature by casting method and dry at 45℃ for 12h to obtain a chitosan / graphene oxide composite film.

[0098] Comparative Example 3:

[0099] (1) Dissolve 2g of chitosan powder in 100mL of 1% acetic acid aqueous solution and sonicate for 2h to promote complete dissolution. Predissolve 5g of thymol in 100mL of anhydrous ethanol, add 5g of Tween 80, and sonicate for 10min. Then slowly add 0.8g of thymol (i.e., 16mL of thymol ethanol solution) dissolved in ethanol to the chitosan solution, and add 1.5g of glycerol as a plasticizer. Stir at room temperature in the dark for 2h to ensure thorough mixing. After thorough mixing, allow to stand at room temperature for 12h to degas and obtain a uniform film-forming solution. Finally, cast the above solution into a film at room temperature using a casting method, and dry at 45℃ for 12h to obtain the chitosan / thymol composite film in Comparative Example 3.

[0100] Comparative Example 4:

[0101] (1) 1 g of graphite powder was dispersed in 25 mL of concentrated sulfuric acid and stirred continuously at 200 rpm for 0.5 h in an ice bath. After thorough dispersion, 3 g of potassium permanganate was added to the solution and stirred in an ice bath at 400 rpm for 3 h to oxidize the graphite powder. After thorough stirring, 150 mL of distilled water was added to dilute the concentrated sulfuric acid, and 5 mL of hydrogen peroxide was added to consume the excess potassium permanganate. The mixture was stirred in an ice bath at 600 rpm for 1 h to promote the dilution of the concentrated sulfuric acid and the consumption of excess potassium permanganate. The crude product was obtained by centrifugation (10000 rpm, 25 °C, 10 min) and discarding the supernatant. The crude product was washed twice with distilled water and then vacuum dried at 90 °C for 24 h to obtain graphene oxide.

[0102] (2) Disperse 5g of graphene oxide powder in 500mL of distilled water, add 5g of calcium chloride powder, and sonicate at room temperature for 1h to promote uniform dispersion. Predissolve 5g of thymol in 100mL of anhydrous ethanol, add 5g of Tween 80, and sonicate for 10min. Then slowly add 0.8g of thymol (i.e., 16mL of thymol ethanol solution) dissolved in ethanol to the graphene oxide dispersion, and stir at room temperature in the dark for 2h to ensure thorough mixing. Then obtain the crude product by centrifugation (8000rpm, 25℃, 10min) and discarding the supernatant, wash twice with anhydrous ethanol, and then vacuum dry at 60℃ for 12h to obtain the graphene oxide-thymol product.

[0103] (3) Dissolve 2g of chitosan powder in 100mL of 1% acetic acid aqueous solution and sonicate for 2h to promote complete dissolution. Then add the above graphene oxide-thymol powder (0.06g, accounting for 3% of the dry weight of chitosan) to the chitosan solution and add 1.5g of glycerol as a plasticizer. Sonicate for 1h in an ice bath to promote uniform dispersion. After sufficient dispersion, allow to stand at room temperature for 12h to degas and obtain a uniform film-forming solution. Finally, cast the above solution into a film at room temperature by casting. After drying at 45℃ for 12h, the chitosan / graphene oxide-thymol composite film of Comparative Example 4 is obtained.

[0104] Comparative Example 5:

[0105] (1) 1 g of graphite powder was dispersed in 25 mL of concentrated sulfuric acid and stirred continuously at 200 rpm for 0.5 h in an ice bath. After thorough dispersion, 3 g of potassium permanganate was added to the solution and stirred in an ice bath at 400 rpm for 3 h to oxidize the graphite powder. After thorough stirring, 150 mL of distilled water was added to dilute the concentrated sulfuric acid, and 5 mL of hydrogen peroxide was added to consume the excess potassium permanganate. The mixture was stirred in an ice bath at 600 rpm for 1 h to promote the dilution of the concentrated sulfuric acid and the consumption of excess potassium permanganate. The crude product was obtained by centrifugation (10000 rpm, 25 °C, 10 min) and discarding the supernatant. The crude product was washed twice with distilled water and then vacuum dried at 90 °C for 24 h to obtain graphene oxide.

[0106] (2) Disperse 0.05g of graphene oxide powder in 500mL of distilled water, add 5g of calcium chloride powder, and sonicate at room temperature for 1h to promote uniform dispersion. Predissolve 5g of thymol in 100mL of anhydrous ethanol, add 5g of Tween 80, and sonicate for 10min. Then slowly add 0.8g of thymol (i.e., 16mL of thymol ethanol solution) dissolved in ethanol to the graphene oxide dispersion, and stir at room temperature in the dark for 2h to ensure thorough mixing. Then obtain the crude product by centrifugation (8000rpm, 25℃, 10min) and discarding the supernatant, wash twice with anhydrous ethanol, and then vacuum dry at 60℃ for 12h to obtain the graphene oxide-thymol product.

[0107] (3) Dissolve 2g of chitosan powder in 100mL of 1% acetic acid aqueous solution and sonicate for 2h to promote complete dissolution. Then add the above graphene oxide-thymol powder (0.06g, accounting for 3% of the dry weight of chitosan) to the chitosan solution and add 1.5g of glycerol as a plasticizer. Sonicate for 1h in an ice bath to promote uniform dispersion. After sufficient dispersion, allow to stand at room temperature for 12h to degas and obtain a uniform film-forming solution. Finally, cast the above solution into a film at room temperature by casting. After drying at 45℃ for 12h, the chitosan / graphene oxide-thymol composite film of Comparative Example 5 is obtained.

[0108] Comparative Example 6:

[0109] The method is the same as in Example 1, except that: graphene oxide-thymol powder (0.006 g, accounting for 0.3% of the dry weight of chitosan).

[0110] Comparative Example 7:

[0111] The method is the same as in Example 1, except that: graphene oxide-thymol powder (0.3g, accounting for 15% of the dry weight of chitosan).

[0112] The films prepared in Example 1 and Comparative Examples 1-7 were tested, and their properties are shown in Table 1.

[0113] Table 1

[0114]

[0115] Example 2:

[0116] (1) 1 g of graphite powder was dispersed in 25 mL of concentrated sulfuric acid and stirred continuously at 200 rpm for 0.5 h in an ice bath. After thorough dispersion, 3 g of potassium permanganate was added to the solution and stirred in an ice bath at 400 rpm for 3 h to oxidize the graphite powder. After thorough stirring, 150 mL of distilled water was added to dilute the concentrated sulfuric acid, and 5 mL of hydrogen peroxide was added to consume the excess potassium permanganate. The mixture was stirred in an ice bath at 600 rpm for 1 h to promote the dilution of the concentrated sulfuric acid and the consumption of excess potassium permanganate. The crude product was obtained by centrifugation (10000 rpm, 25 °C, 10 min) and discarding the supernatant. The crude product was washed twice with distilled water and then vacuum dried at 90 °C for 24 h to obtain graphene oxide.

[0117] (2) Disperse 0.5g of graphene oxide powder in 500mL of distilled water, add 5g of calcium chloride powder, and sonicate at room temperature for 1h to promote uniform dispersion. Predissolve 5g of thymol in 100mL of anhydrous ethanol, add 5g of Tween 80, and sonicate for 10min. Then slowly add 0.8g of thymol (i.e., 16mL of thymol ethanol solution) dissolved in ethanol to the graphene oxide dispersion, and stir at room temperature in the dark for 2h to ensure thorough mixing. Then obtain the crude product by centrifugation (8000rpm, 25℃, 10min) and discarding the supernatant, wash twice with anhydrous ethanol, and then vacuum dry at 60℃ for 12h to obtain the graphene oxide-thymol product.

[0118] (3) Dissolve 2g of chitosan powder in 100mL of 1% acetic acid aqueous solution and sonicate for 2h to promote complete dissolution. Then add the above graphene oxide-thymol powder (0.02g, accounting for 1% of the dry weight of chitosan) to the chitosan solution and add 1.5g of glycerol as a plasticizer. Sonicate under ice bath for 1h to promote uniform dispersion. After sufficient dispersion, allow to stand at room temperature for 12h to degas and obtain a uniform film-forming solution. Finally, cast the above solution into a film at room temperature by casting and dry at 45℃ for 12h to obtain a chitosan / graphene oxide-thymol composite film.

[0119] Example 3:

[0120] (1) 1 g of graphite powder was dispersed in 25 mL of concentrated sulfuric acid and stirred continuously at 200 rpm for 0.5 h in an ice bath. After thorough dispersion, 3 g of potassium permanganate was added to the solution and stirred in an ice bath at 400 rpm for 3 h to oxidize the graphite powder. After thorough stirring, 150 mL of distilled water was added to dilute the concentrated sulfuric acid, and 5 mL of hydrogen peroxide was added to consume the excess potassium permanganate. The mixture was stirred in an ice bath at 600 rpm for 1 h to promote the dilution of the concentrated sulfuric acid and the consumption of excess potassium permanganate. The crude product was obtained by centrifugation (10000 rpm, 25 °C, 10 min) and discarding the supernatant. The crude product was washed twice with distilled water and then vacuum dried at 90 °C for 24 h to obtain graphene oxide.

[0121] (2) Disperse 0.5g of graphene oxide powder in 500mL of distilled water, add 5g of calcium chloride powder, and sonicate at room temperature for 1h to promote uniform dispersion. Predissolve 5g of thymol in 100mL of anhydrous ethanol, add 5g of Tween 80, and sonicate for 10min. Then slowly add 0.8g of thymol (i.e., 16mL of thymol ethanol solution) dissolved in ethanol to the graphene oxide dispersion, and stir at room temperature in the dark for 2h to ensure thorough mixing. Then obtain the crude product by centrifugation (8000rpm, 25℃, 10min) and discarding the supernatant, wash twice with anhydrous ethanol, and then vacuum dry at 60℃ for 12h to obtain the graphene oxide-thymol product.

[0122] (3) Dissolve 2g of chitosan powder in 100mL of 1% acetic acid aqueous solution and sonicate for 2h to promote complete dissolution. Then add the above graphene oxide-thymol powder (0.04g, accounting for 2% of the dry weight of chitosan) to the chitosan solution and add 1.5g of glycerol as a plasticizer. Sonicate under ice bath for 1h to promote uniform dispersion. After sufficient dispersion, allow to stand at room temperature for 12h to degas and obtain a uniform film-forming solution. Finally, cast the above solution into a film at room temperature by casting method and dry at 45℃ for 12h to obtain a chitosan / graphene oxide-thymol composite film.

[0123] Example 4:

[0124] (1) 1 g of graphite powder was dispersed in 25 mL of concentrated sulfuric acid and stirred continuously at 200 rpm for 0.5 h in an ice bath. After thorough dispersion, 3 g of potassium permanganate was added to the solution and stirred in an ice bath at 400 rpm for 3 h to oxidize the graphite powder. After thorough stirring, 150 mL of distilled water was added to dilute the concentrated sulfuric acid, and 5 mL of hydrogen peroxide was added to consume the excess potassium permanganate. The mixture was stirred in an ice bath at 600 rpm for 1 h to promote the dilution of the concentrated sulfuric acid and the consumption of excess potassium permanganate. The crude product was obtained by centrifugation (10000 rpm, 25 °C, 10 min) and discarding the supernatant. The crude product was washed twice with distilled water and then vacuum dried at 90 °C for 24 h to obtain graphene oxide.

[0125] (2) Disperse 0.5g of graphene oxide powder in 500mL of distilled water, add 5g of calcium chloride powder, and sonicate at room temperature for 1h to promote uniform dispersion. Predissolve 5g of thymol in 100mL of anhydrous ethanol, add 5g of Tween 80, and sonicate for 10min. Then slowly add 0.8g of thymol (i.e., 16mL of thymol ethanol solution) dissolved in ethanol to the graphene oxide dispersion, and stir at room temperature in the dark for 2h to ensure thorough mixing. Then obtain the crude product by centrifugation (8000rpm, 25℃, 10min) and discarding the supernatant, wash twice with anhydrous ethanol, and then vacuum dry at 60℃ for 12h to obtain the graphene oxide-thymol product.

[0126] (3) Dissolve 2g of chitosan powder in 100mL of 1% acetic acid aqueous solution and sonicate for 2h to promote complete dissolution. Then add the above graphene oxide-thymol powder (0.08g, accounting for 4% of the dry weight of chitosan) to the chitosan solution and add 1.5g of glycerol as a plasticizer. Sonicate in an ice bath for 1h to promote uniform dispersion. After sufficient dispersion, allow to stand at room temperature for 12h to degas and obtain a uniform film-forming solution. Finally, cast the above solution into a film at room temperature by casting and dry at 45℃ for 12h to obtain a chitosan / graphene oxide-thymol composite film.

[0127] Example 5:

[0128] (1) 1 g of graphite powder was dispersed in 25 mL of concentrated sulfuric acid and stirred continuously at 200 rpm for 0.5 h in an ice bath. After thorough dispersion, 3 g of potassium permanganate was added to the solution and stirred in an ice bath at 400 rpm for 3 h to oxidize the graphite powder. After thorough stirring, 150 mL of distilled water was added to dilute the concentrated sulfuric acid, and 5 mL of hydrogen peroxide was added to consume the excess potassium permanganate. The mixture was stirred in an ice bath at 600 rpm for 1 h to promote the dilution of the concentrated sulfuric acid and the consumption of excess potassium permanganate. The crude product was obtained by centrifugation (10000 rpm, 25 °C, 10 min) and discarding the supernatant. The crude product was washed twice with distilled water and then vacuum dried at 90 °C for 24 h to obtain graphene oxide.

[0129] (2) Disperse 0.5g of graphene oxide powder in 500mL of distilled water, add 5g of calcium chloride powder, and sonicate at room temperature for 1h to promote uniform dispersion. Predissolve 5g of thymol in 100mL of anhydrous ethanol, add 5g of Tween 80, and sonicate for 10min. Then slowly add 0.8g of thymol (i.e., 16mL of thymol ethanol solution) dissolved in ethanol to the graphene oxide dispersion, and stir at room temperature in the dark for 2h to ensure thorough mixing. Then obtain the crude product by centrifugation (8000rpm, 25℃, 10min) and discarding the supernatant, wash twice with anhydrous ethanol, and then vacuum dry at 60℃ for 12h to obtain the graphene oxide-thymol product.

[0130] (3) Dissolve 2g of chitosan powder in 100mL of 1% acetic acid aqueous solution and sonicate for 2h to promote complete dissolution. Then add the above graphene oxide-thymol powder (0.1g, accounting for 5% of the dry weight of chitosan) to the chitosan solution and add 1.5g of glycerol as a plasticizer. Sonicate in an ice bath for 1h to promote uniform dispersion. After sufficient dispersion, allow to stand at room temperature for 12h to degas and obtain a uniform film-forming solution. Finally, cast the above solution into a film at room temperature by casting and dry at 45℃ for 12h to obtain a chitosan / graphene oxide-thymol composite film.

[0131] In addition, the inventors of this case also conducted experiments with other raw materials, process operations, and process conditions described in this specification, referring to the aforementioned embodiments, and obtained relatively ideal results in all cases.

[0132] It should be understood that the technical solutions of the present invention are not limited to the specific embodiments described above. Any technical modifications made to the technical solutions of the present invention without departing from the spirit and scope of the claims are within the scope of protection of the present invention.

Claims

1. A method for preparing a smart modified atmosphere packaging film with gas selectivity and dual pH / humidity response, characterized in that, include: Graphene oxide and calcium chloride are dispersed in water to form a graphene oxide dispersion; wherein the mass-to-volume ratio of graphene oxide to water is 1g:500mL to 1g:2000mL. Thymol, emulsifier, and ethanol are mixed and emulsified to form a thymol emulsion. Then, the thymol emulsion and the graphene oxide dispersion were mixed and stirred at room temperature in the dark to prepare graphene oxide-thymol; wherein the mass ratio of graphene oxide to thymol was 0.5~1:0.2~1. Chitosan is dissolved in an aqueous acetic acid solution, and then graphene oxide-thymol and a plasticizer are added for ultrasonic dispersion to form a film-forming solution; wherein the mass ratio of chitosan to graphene oxide-thymol is 100:1~5. Furthermore, the film-forming solution is subjected to a casting process to form a film, thereby obtaining a smart modified atmosphere packaging film with gas selectivity and dual pH / humidity response.

2. The preparation method according to claim 1, characterized in that, Specifically, it includes: Graphene oxide was dispersed in water, then calcium chloride was added and ultrasonically dispersed at room temperature to form a graphene oxide dispersion. The mass-to-volume ratio of calcium chloride to water is 1g:50mL to 1g:200mL; the ultrasonic dispersion treatment time is 0.5 to 1h.

3. The preparation method according to claim 1, characterized in that, Specifically, it includes: Thymol is dissolved in ethanol, and then an emulsifier is added for ultrasonic emulsification to form a thymol emulsion. The mass-to-volume ratio of thymol to ethanol is 1g:10mL to 1g:20mL; the mass ratio of thymol to emulsifier is 2:1 to 1:1; the emulsifier includes any one or more combinations of Tween 80, Tween 20, Tween 60, sucrose ester, and monoglyceride; and the ultrasonic emulsification treatment time is 10 to 15 minutes.

4. The preparation method according to claim 1, characterized in that, Specifically, it includes: The thymol emulsion was slowly added dropwise to the graphene oxide dispersion and stirred at room temperature in the dark for 2-4 hours. After centrifugation, washing, and vacuum drying, graphene oxide-thymol was obtained. The centrifugation process is carried out at a speed of 8000~10000 rpm, a temperature of 20~30℃, and a duration of 10~15 min. The washing process includes washing the product obtained by centrifugation with anhydrous ethanol 2 to 3 times; The vacuum drying process is carried out at a temperature of 60-80°C for 12-24 hours.

5. The preparation method according to claim 1, characterized in that, Specifically, it includes: Chitosan was dissolved in an aqueous acetic acid solution, then graphene oxide-thymol and plasticizer were added and ultrasonically dispersed under ice bath conditions, and then allowed to stand to degas, forming a film-forming solution. The film-forming solution was cast at room temperature and then dried to obtain a smart modified atmosphere packaging film with gas selectivity and dual pH / humidity response.

6. The preparation method according to claim 5, characterized in that: The mass-to-volume ratio of chitosan to aqueous acetic acid solution is 1g:50mL to 1g:200mL. And / or, the mass-to-volume ratio of the plasticizer to the film-forming solution is 1~2g:100mL; And / or, the volume concentration of the acetic acid aqueous solution is 1-2%; And / or, the ultrasonic dispersion treatment time is 1~3 hours; And / or, the temperature for the static degassing is 20~30℃, and the time is 12~24h; And / or, the drying process is carried out at a temperature of 40~50℃ for a time of 12~16h.

7. A smart modified atmosphere packaging film with gas selectivity and dual pH / humidity response, prepared by the method according to any one of claims 1-6.

8. The application of the intelligent modified atmosphere packaging film with gas selectivity and pH / humidity dual response as described in claim 7 in the storage and preservation of fruits and vegetables.

9. A method for preserving fruits and vegetables, characterized in that, include: Fruits or vegetables are sealed and stored using the intelligent modified atmosphere packaging film with gas selectivity and pH / humidity dual response as described in claim 7; The storage environment is characterized by an ambient temperature of 20-25°C and a relative humidity of 70-80%.

10. A fruit and vegetable storage and preservation material, characterized in that, include: The intelligent modified atmosphere packaging film with gas selectivity and dual pH / humidity response as described in claim 7.

Images