High-performance degradable intelligent fluorescence response film and preparation method thereof

Abstract

The invention relates to the technical field of degradable high polymer materials, in particular to a high-performance degradable intelligent fluorescence response thin film and a preparation method of the high-performance degradable intelligent fluorescence response thin film. The stability of the carbon dot material and the two-dimensional sheet-shaped self-assembled organic filler is realized through a solvothermal method-organic filler self-assembly technology, and after the carbon dot material and the degradable polymer are compounded to form a film, the mechanical property of the composite film is remarkably improved by utilizing the two-dimensional organic sheet structure characteristics of the composite film; by regulating and controlling the distribution of a multi-hydrogen bond structure of the self-assembled organic filler and the degradable high polymer material and a carbon quantum dot nano structure in a composite film network, accurate and visual monitoring of the film on trace mercaptan markers in the tropical fruit rot process is realized, and the bottleneck of high performance and multi-functionalization of bio-based and degradable films is broken through.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of degradable high molecular materials, and particularly relates to a high-performance degradable intelligent fluorescent response film and a preparation method thereof. BACKGROUND

[0002] The evolution of packaging materials has profoundly reshaped the practice of the food industry, significantly driving the development of preservation and transportation technologies. However, the reliance on non-biodegradable petroleum-based plastics has triggered serious plastic pollution and microplastic risks. Nearly 500 billion plastic bags are used every year, and 180 billion pounds of plastic waste end up in the ocean. Therefore, for decades, sustainable and biodegradable polymers have attracted great attention; however, widely used biodegradable plastic packaging often has defects in mechanical properties and biodegradability (only under industrial composting conditions). Therefore, to balance performance and cost, it is crucial to develop high-performance, multifunctional sustainable packaging materials.

[0003] A Chinese invention patent with application number 201710265928.6 discloses a modification method of bacterial cellulose film. The method first introduces epoxy groups on the bacterial cellulose by substitution reaction through bacterial cellulose and epichlorohydrin, and then grafts with β-cyclodextrin under alkaline conditions to introduce hydrophilic molecules β-cyclodextrin with hydrophobic inner cavity, which can contain both hydrophilic small molecules and hydrophobic molecules without damaging the original properties of bacterial cellulose, and has amphiphilic properties. The bacterial cellulose modified by the method of the patent has significantly improved natural release rate and transdermal release rate of hydrophobic small molecule vitamin E and tea tree oil, and has great application prospect in the field of skin care products.

[0004] A Chinese invention patent with application number 201910294186.9 discloses a preparation method of bacterial cellulose / polymeric cyclodextrin composite material. The method first forms polymeric cyclodextrin by crosslinking cyclodextrin monomers with terephthaloyl chloride, then activates the polymeric cyclodextrin with sodium hydride in N,N-dimethylformamide to obtain polymeric cyclodextrin sodium salt, and finally grafts the cyclodextrin polymer to the bacterial cellulose film through a silane coupling agent to obtain the bacterial cellulose / polymeric cyclodextrin composite material. The patent is simple and convenient, has low synthesis cost, and the prepared bacterial cellulose / polymeric cyclodextrin composite material has good adsorption effect on organic small molecule pollutants in water, and the film material is easy to separate and recycle, and can be reused.

[0005] The increasing trend of intelligence (real-time monitoring) and sustainability (biological sources and biodegradability) in packaging science has led to a huge demand for intelligent packaging materials. However, the film materials of the prior art cannot monitor the damage and rot of packaged food, and the mechanical properties and antibacterial properties need to be improved. SUMMARY

[0006] In order to overcome the shortcomings and deficiencies existing in the prior art, the purpose of the present application is to provide a high-performance degradable intelligent fluorescent response film with high mechanical performance, biodegradability and the ability to monitor food spoilage visually.

[0007] The purpose of the present application is to provide a preparation method of a high-performance degradable intelligent fluorescent response film, which is simple in operation steps, easy to achieve conditions, and can effectively improve the mechanical properties of the material, while balancing the applicability and degradation performance of carbon quantum dots.

[0008] The purpose of the present application is achieved by the following technical scheme: a high-performance degradable intelligent fluorescent response film, the intelligent fluorescent response film comprises the following raw materials by weight:

[0009] 80-120 parts of degradable polymer material

[0010] 20-40 parts of self-assembled organic filler

[0011] 5-15 parts of carbon dot material.

[0012] Preferably, the degradable polymer material includes at least one of cellulose, starch, chitosan and protein. Alternatively, in addition to the above natural degradable polymer materials, the degradable polymer material can also be synthetic degradable polymer materials such as polycaprolactone (PCL), polylactic acid (PLA), polyglycolic acid (PGA), poly(lactic-co-glycolic acid) (PGLA), polyhydroxyalkanoate (PHA) and the like.

[0013] Preferably, the cellulose is nanocellulose with a single fiber diameter of 1-100 nm. The molecular chain of nanocellulose forms a rigid rod-like or fibrous structure through a hydrogen bond network, with characteristics of high crystallinity (54%-88%) and specific surface area (150-250 m 2 / g). The nanocellulose includes at least one of cellulose nanocrystals (CNC), cellulose nanofibers (CNF) and bacterial cellulose (BC). Cellulose nanocrystals (CNC) are extracted from plant cellulose, have high crystallinity and excellent mechanical properties, and are widely used in energy storage, composite materials and other fields. Its high specific surface area and mechanical strength make it outstanding in functional materials; cellulose nanofibers (CNF) are obtained by mechanical or chemical treatment of plant cellulose, have the characteristics of high aspect ratio and good flexibility, and are often used in separator materials, electrode materials and the like. Its surface modification technology can optimize dispersibility and processing performance; bacterial cellulose (BC) is biosynthesized by bacteria, has high purity and biocompatibility, also has high crystallinity, mechanical strength and other advantages, and is suitable for medical, food packaging and other fields.

[0014] Natural cellulose refers to fiber systems extracted directly from living organisms without chemical modification. Based on their source, they can be divided into three categories: plant cellulose, bacterial cellulose, and animal cellulose. Compared to plant cellulose, bacterial cellulose (BC) has characteristics such as high purity (up to 90% or more), high crystallinity (up to 60%), and high mechanical strength (tensile strength up to 50 MPa). Therefore, BC has broad potential in medical and biomedical applications, packaging, electronics, and other fields.

[0015] Alternatively, the nanocellulose may be modified to obtain modified nanocellulose, wherein the modifying groups of the modified nanocellulose include at least one selected from alkyl, hydroxyalkyl, amino, carboxyl, aldehyde, sulfonic acid, boric acid, and phosphate groups. The modified nanocellulose can be nanofibers such as methylcellulose, carboxymethylcellulose, ethylcellulose, hydroxyethylcellulose, hydroxypropylcellulose, hydroxypropylmethylcellulose, cellulose acetate, sulfonated cellulose, or phosphorylated cellulose. Additionally, bacterial cellulose can also be modified.

[0016] Preferably, the intelligent fluorescent responsive film further includes 0.05-0.15 parts of a fluorescent marker. The fluorescent marker includes any one of 2,3-pyrazinediamine, tyrosine, tryptophan, vitamin B2, adenosine triphosphate, reduced coenzyme I, porphyrin, and collagen.

[0017] Preferably, the material of the self-assembling organic filler includes at least one of coconut oil, polyvinylpyrrolidone, and cyclodextrin.

[0018] Preferably, the precursor of the carbon dot material includes at least one of gelatin, citric acid, glucose, and urea.

[0019] Another objective of this invention is achieved through the following technical solution: a method for preparing a high-performance degradable smart fluorescent responsive thin film, comprising the following steps:

[0020] (1) Preparation of carbon dot materials: The precursor required for carbon dot materials is dissolved in an appropriate amount of anhydrous ethanol or deionized water and stirred to form a homogeneous precursor solution; the solution is heated and, after naturally cooling to room temperature, centrifuged, the supernatant is collected, and solid carbon dot materials are obtained by solvent evaporation under reduced pressure; the carbon dot materials are dissolved in distilled water to form an aqueous solution of carbon dot materials, and an aqueous solution of silver ions is added to the aqueous solution of carbon dot materials to quench the carbon dots, thereby forming Ag. + @CDs solution;

[0021] (2) Preparation of self-assembled organic filler: The material of self-assembled organic filler and sodium dodecyl sulfate are dissolved in deionized water at a certain molar ratio, stirred evenly, and the uniform mixture is incubated to obtain two-dimensional sheet-like self-assembled organic filler.

[0022] (3) dispersing the degradable polymer material in deionized water to obtain a degradable polymer material dispersion;

[0023] (4) preparing the smart fluorescent response film: mixing the Ag + @CDs aqueous solution, the cyclodextrin assembly and the degradable polymer material dispersion, stirring, pouring the uniformly dispersed mixture onto a flat polytetrafluoroethylene plate, drying in an oven, and peeling off after drying to form the smart fluorescent response film.

[0024] Preferably, in the step (1), the mass-volume ratio of the required precursor of the carbon dot material to anhydrous ethanol or deionized water is 1:20-40; the stirring time is 20-40 min; the heating temperature is 160-180℃; the heating time is 4-12h; the centrifugal speed is 4000-8000rpm / min; the mass concentration of the carbon dot aqueous solution is 0.05-0.15mg / mL; and the molar amount of Ag+ in the silver ion aqueous solution is 1-5mmol.

[0025] Preferably, in the step (2), the molar ratio of the self-assembled organic filler material to sodium dodecyl sulfate is 2-4:1; the stirring temperature is 50-60℃; the stirring time is 2-4h; the incubation temperature is 20-30℃; and the time is 36-60h; in the step (4), the stirring time is 0.2-0.8h; the oven temperature is 50-70℃; and the drying time is 4-8h.

[0026] The present application utilizes degradable polymer materials, self-assembled organic fillers and smart fluorescent response carbon dot materials, realizes the stabilization of carbon dot materials and two-dimensional sheet-shaped organic fillers through solvothermal method-organic filler self-assembly technology, significantly improves the mechanical properties of the composite film by utilizing the two-dimensional organic sheet structure characteristics after compounding with degradable polymers; by adjusting the distribution of self-assembled organic fillers, degradable polymer materials and carbon quantum dot nanostructures in the composite film network, precise and visual monitoring of trace thiol markers in the spoilage process of tropical fruits is realized, and the bottleneck of high performance and multifunctionalization of biological-based and degradable films is broken through.

[0027] The application has the beneficial effects that: based on the carbon dots loaded on the cyclodextrin assembly and bacterial cellulose, the application successfully prepares an intelligent fluorescent response film with high mechanical performance, biodegradability and the ability to monitor food spoilage visually. Benefiting from the interface hydrogen bond interaction and the corresponding closely arranged micro-nano structure, the prepared intelligent fluorescent response film shows excellent mechanical performance and the required water vapor barrier performance. In addition, based on the quenching of carbon dots by the competitive reaction of silver ions to mercapto, the obtained intelligent fluorescent response film provides antibacterial performance and intelligent fluorescent response ability. Through the optical recognition system, quantitative analysis of visual signals, which may open up a new way for real-time monitoring of tropical fruit spoilage during transportation. In addition, the obtained intelligent fluorescent response film can be rapidly biodegraded within 5 days under enzymatic conditions, and the green bean germination test proves that it has no adverse effect on plant growth. The application provides valuable new insights for the high-value utilization of bio-based materials and the enhancement of their multifunctional performance by adjusting the material structure.

[0028] The preparation method of the application has simple operation steps and easy-to-achieve conditions, can effectively improve the mechanical performance of the material, and balances the applicability and degradation performance of the carbon dot material, so that the product has wide application prospects in the field of green degradable packaging. BRIEF DESCRIPTION OF DRAWINGS

[0029] Figure 1 is the physical characterization of the intelligent fluorescent response film of the application;wherein, A is the surface morphology of the dried cyclodextrin nanosheet under SEM, B is the cross-sectional morphology of the original bacterial cellulose, C is the cross-sectional morphology of the film prepared in Example 1, D is the potential determination of the film prepared in Example 1, and E is the FTIR graph.

[0030] Figure 2 is the mechanical performance test of the intelligent fluorescent response film of the application;wherein, A is the stress-strain curve graph, B is the relationship graph of Young's modulus and cyclodextrin assembly content, 2C is the relationship graph of tensile strength and cyclodextrin assembly content, and D is the relationship graph of toughness and cyclodextrin assembly content.

[0031] Figure 3 is the barrier test of the intelligent fluorescent response film of the application;wherein, A is the thermogravimetric curve graph, B is the derivative thermogravimetric curve graph, C is the oxygen and carbon dioxide barrier property, and D is the water vapor barrier property.

[0032] Figure 4 is the antibacterial test of the intelligent fluorescent response film of the application;wherein, A-B are the antibacterial circles of the film against Staphylococcus aureus and Escherichia coli respectively, C is the diameter size statistics of the antibacterial circle, and D is the antibacterial rate of the film.

[0033] Figure 5is the fluorescence response graph obtained when the intelligent fluorescence response film of the application is used for packaging durians.

[0034] Figure 6 is the degradation graph of the intelligent fluorescence response film of the application in a cellulase aqueous solution.

[0035] Figure 7 is the green bean germination growth experiment result graph of the intelligent fluorescence response film of the application; wherein A is the growth condition at 0 days, 3 days, 7 days and 10 days, and B is the root stem growth condition after 10 days. DETAILED DESCRIPTION

[0036] For the convenience of those skilled in the art, the following will be combined with the examples and the accompanying drawings to understand the application. Figures 1-7 The application is further described, and the content mentioned in the embodiments is not a limitation of the application.

[0037] Example 1

[0038] (1) Preparation of carbon dot material: 1 g of citric acid and 0.01 g of 2,3-pyrazine diamine were dissolved in 30 ml of anhydrous ethanol, and stirred for 30 min to form a uniform precursor solution; the solution was transferred to a polytetrafluoroethylene reaction kettle, and heated at 170℃ for 4h, after natural cooling to room temperature, the crude product was centrifuged at 4000 rpm / min to remove large insoluble particles, the supernatant was collected, and the solid carbon dot material (CDs) was obtained by solvent evaporation under reduced pressure; 1 g of carbon dot material was dissolved in distilled water to form a carbon dot material aqueous solution with a concentration of 0.1 mg / ml, 2 mmol of silver nitrate aqueous solution was added to the carbon quantum dot aqueous solution to quench the carbon dots, thereby forming Ag + @CDs solution.

[0039] (2) Preparation of self-assembled organic filler: β-cyclodextrin (β-CD) and sodium dodecyl sulfate (SDS) were dissolved in deionized water at a molar ratio of 2:1, continuously stirred at 60℃ for 2h, and the uniform mixture was incubated at 25℃ for 48h, thereby obtaining two-dimensional sheet-like cyclodextrin assembly β-CD@SDS.

[0040] (3) Dispersion of degradable polymer material: 10 g of bacterial cellulose (BC) was added to deionized water for dispersion to obtain a bacterial cellulose dispersion.

[0041] (4) Preparation of intelligent fluorescence response film: the Ag +The CDs aqueous solution, 2.75 g of the cyclodextrin assembly, and the bacterial cellulose dispersion liquid were mixed and stirred for 0.5 h, and the uniformly dispersed mixture was poured onto a flat polytetrafluoroethylene plate, dried in a 50°C oven, and after drying for 6 h, it was peeled off to form the smart fluorescent response film BCCF.

[0042] Example 2

[0043] (1) Preparation of carbon dot material: 1 g of glucose was dissolved in deionized water and stirred for 30 min to form a uniform precursor solution; the solution was transferred to a polytetrafluoroethylene reaction kettle and heated at 180°C for 12 h, and after natural cooling to room temperature, the crude product was centrifuged at 6000 rpm / min to remove large insoluble particles, the supernatant was collected, and the solid carbon dot material (CDs) was obtained by solvent evaporation under reduced pressure; 1 g of carbon dot material was dissolved in distilled water to form a carbon dot material aqueous solution with a concentration of 0.1 mg / ml, 2 mmol of silver nitrate aqueous solution was added to the carbon quantum dot aqueous solution to quench the carbon dots, thereby forming Ag + @CDs solution.

[0044] (2) Preparation of organic filler: β-cyclodextrin (β-CD) and sodium dodecyl sulfate (SDS) were dissolved in deionized water at a molar ratio of 3:1, and continuously stirred at 55°C for 3 h, and the uniform mixture was incubated at 25°C for 36 h to obtain two-dimensional sheet-like cyclodextrin assembly β-CD@SDS.

[0045] (3) Dispersion of degradable high molecular material: 10 g of bacterial cellulose (BC) was added to deionized water for dispersion to obtain a bacterial cellulose dispersion liquid.

[0046] (4) Preparation of smart fluorescent response film: the above prepared Ag + @CDs aqueous solution, 3.67 g of the cyclodextrin assembly, and the bacterial cellulose dispersion liquid were mixed and stirred for 0.5 h, and the uniformly dispersed mixture was poured onto a flat polytetrafluoroethylene plate, dried in a 60°C oven, and after drying for 4 h, it was peeled off to form the smart fluorescent response film BCCF.

[0047] Example 3

[0048] (1) Preparation of carbon dot material: 1 g of urea was dissolved in deionized water and stirred for 30 min to form a uniform precursor solution; the solution was transferred to a polytetrafluoroethylene reaction kettle and heated at 160°C for 8 h, after natural cooling to room temperature, the crude product was centrifuged at 8000 rpm / min to remove large insoluble particles, the supernatant was collected, and the solid carbon dot material (CDs) was obtained by solvent evaporation under reduced pressure; 1 g of carbon dot material was dissolved in distilled water to form a carbon dot material aqueous solution with a concentration of 0.1 mg / ml, 2 mmol of silver nitrate aqueous solution was added to the carbon quantum dot aqueous solution to quench the carbon dots, thereby forming Ag + @CDs solution.

[0049] (2) Preparation of organic filler: β-cyclodextrin (β-CD) and sodium dodecyl sulfate (SDS) were dissolved in deionized water at a molar ratio of 4:1, continuously stirred at 50°C for 4 h, and the uniform mixture was incubated at 25°C for 60 h to obtain two-dimensional sheet-like cyclodextrin assemblies β-CD@SDS.

[0050] (3) Dispersion of degradable polymer material: 10 g of bacterial cellulose (BC) was added to deionized water for dispersion to obtain a bacterial cellulose dispersion.

[0051] (4) Preparation of smart fluorescent response film: the above prepared Ag + @CDs aqueous solution, 3 g of cyclodextrin assembly, and bacterial cellulose dispersion were mixed and stirred for 0.5 h, the uniformly dispersed mixture was poured onto a flat polytetrafluoroethylene plate, dried in a 60°C oven, and after drying for 4 h, it was peeled off to form the smart fluorescent response film BCCF.

[0052] Comparative Example 1

[0053] 10 g of bacterial cellulose (BC) was added to deionized water for dispersion to obtain a bacterial cellulose dispersion, which was poured onto a flat polytetrafluoroethylene plate and dried in a 50°C oven, and after drying for 6 h, it was peeled off to form a film.

[0054] Comparative Example 2

[0055] β-cyclodextrin (β-CD) and sodium dodecyl sulfate (SDS) were dissolved in deionized water at a molar ratio of 2:1, continuously stirred at 60°C for 2 h, and the uniform mixture was incubated at 25°C for 48 h to obtain two-dimensional sheet-like cyclodextrin assemblies β-CD@SDS.

[0056] 10 g of bacterial cellulose (BC) was added to deionized water for dispersion to obtain a bacterial cellulose dispersion.

[0057] The 2.75 g cyclodextrin assembly and the bacterial cellulose dispersion liquid were mixed and stirred for 0.5 h, and the uniformly dispersed mixture was poured onto a flat polytetrafluoroethylene plate and dried in an oven at 50°C. After drying for 6 h, it was peeled off to form a film.

[0058] Comparative Examples 3-5

[0059] Comparative Examples 3-5 differ from Example 1 described above in that the amount of cyclodextrin assembly used is 1.22 g, 1.94 g and 4.71 g, respectively.

[0060] Performance test: The film prepared in Comparative Example 1 (labeled BC), the film prepared in Comparative Example 2 (labeled 2β-BC), the film prepared in Comparative Example 3 (cyclodextrin assembly content 10%, labeled BCCF-0.10), the film prepared in Comparative Example 4 (cyclodextrin assembly content 15%, labeled BCCF-0.15), the film prepared in Example 1 (cyclodextrin assembly content 20%, labeled BCCF-0.20), the film prepared in Example 2 (cyclodextrin assembly content 25%, labeled BCCF-0.25), and the film prepared in Comparative Example 5 (cyclodextrin assembly content 30%, labeled BCCF-0.30) were tested, respectively.

[0061] I. Physical characterization

[0062] 1. SEM measurement

[0063] The cyclodextrin nanosheet, bacterial cellulose and the film prepared in Example 1 were subjected to SEM measurement, and the microstructure of the samples was observed using a JSM-6710F scanning electron microscope (SEM) and energy dispersive x-ray spectrometer (EDS) from Hitachi, Japan. The experimental results are shown in Figure 1 A-1C. Figure 1 A is the surface morphology of the cyclodextrin nanosheet after drying under SEM, Figure 1 B is the cross-sectional morphology of the original bacterial cellulose, Figure 1 C is the cross-sectional morphology of the film prepared in Example 1. It can be seen that the film prepared in Example 1 exhibits a significantly enhanced cross-linking degree, thereby constructing a more compact three-dimensional network structure. The increase in cross-linking degree directly improves the mechanical properties of the film, including higher tensile strength, elastic modulus and compressive strength.

[0064] 2. Potential measurement

[0065] The zeta potential of the films prepared in Example 1 and Comparative Example 1 was measured using a Zetasizer nano ZS90(UK) potential analyzer, and the experimental results are shown in Figure 1As shown in D, it can be seen that the film prepared in Example 1 has a higher potential value and better stability compared with the film prepared in Comparative Example 1.

[0066] 3. FTIR detection

[0067] The carbon dot material CDs, the cyclodextrin assembly β-CD@SDS, the bacterial cellulose BC and the film BCCF prepared in Example 1 were subjected to FTIR detection, and FTIR analysis was recorded by an FTIR spectrometer (Frontier Dual Ranger model, PerkinElmer, Waltham, MA, USA) in an attenuated total reflection (ATR) mode at room temperature at 400 to 4000 cm -1 , with a resolution of 4 cm -1 , and scanning 32 times. The experimental results are shown in Figure 1 E. Figure 1 E is an FTIR graph, and it can be seen that the film prepared in Example 1 retains a large amount of the basic chemical structure of β-CD@SDS and increases new groups to obtain a brand-new composite material.

[0068] II. Mechanical property test

[0069] The films prepared in Examples 1-2 and Comparative Examples 1, 3-5 were subjected to a mechanical property test, and the stress-strain curve of the film was obtained by a mechanical-electric universal testing machine (INSTRON 3367 USA). The film thickness was 40 μm, and the dumbbell-shaped sample with a width of 3 mm was cut before measurement. The tensile speed was set to 5 mm / min, and the experimental results are shown in Figure 2 A-2E. Figure 2 A is a stress-strain curve graph, and it can be seen that with the increase of the content of the cyclodextrin assembly, the strength, stiffness and toughness of the film are comprehensively improved, and the best is achieved when the content of the cyclodextrin assembly is 20%, and with the further increase of the content of the cyclodextrin assembly, the strength, stiffness and toughness of the film gradually decrease. Figure 2 B is a graph of the relationship between the Young's modulus and the content of the cyclodextrin assembly, and it can be seen that with the increase of the content of the cyclodextrin assembly, the Young's modulus of the film gradually increases, and reaches a maximum value of 4.93 GPa when the content of the cyclodextrin assembly is 20%, and with the further increase of the content of the cyclodextrin assembly, the Young's modulus of the film gradually decreases. Figure 2 C is a graph of the relationship between the tensile strength and the content of the cyclodextrin assembly, and it can be seen that with the increase of the content of the cyclodextrin assembly, the tensile strength of the film gradually increases, and reaches a maximum value of 126.84 MPa when the content of the cyclodextrin assembly is 20%, and with the further increase of the content of the cyclodextrin assembly, the tensile strength of the film gradually decreases. Figure 2D is the relationship between toughness and cyclodextrin assembly content. It can be seen that as the cyclodextrin assembly content increases, the film toughness first increases and then decreases, reaching a maximum of 4.37 MJ / m when the cyclodextrin assembly content is 20%. 3 . Figure 2 E is a graph showing the relationship between tensile strain capacity and cyclodextrin assembly content. It can be seen that as the cyclodextrin assembly content increases, the tensile strain capacity of the film first increases and then decreases, reaching its maximum value when the cyclodextrin assembly content is 20%.

[0070] III. Barrier Test

[0071] The films prepared in Example 1 and Comparative Example 1 were subjected to thermogravimetric analysis (TGA) using a STA449F5 thermogravimetric analyzer. Simultaneous thermal analyzer (

[0072] Thermogravimetric analysis (Tg) and derivative thermogravimetric analysis (DTG) were performed at GmbH, Selb, Germany, and recorded simultaneously. The membrane (approximately 4 mg) was placed in an aluminum pot and heated to 50 cm⁻¹. 3 At a nitrogen flow rate of / min, the temperature was increased from 30℃ to 600℃ at a rate of 10℃ / min. The experimental results are as follows: Figure 3 As shown in A-3B. Figure 3 A is the thermogravimetric curve. Figure 3 B is the thermogravimetric curve of the microstructure. It can be seen that the film prepared in Example 1 has better thermal stability than the film prepared in Comparative Example 1.

[0073] The films prepared in Example 1 and Comparative Example 1 were subjected to barrier tests. The water vapor transmission rate of the gel film and G-OCSI was measured using a water vapor transmission rate tester (W3 / 060, Jinan Labthink Electromechanical Technology Co., Ltd.), with the test repeated three times. The parameters of the testing instrument were adjusted to ensure a temperature of 38°C and a relative humidity of 90%. The oxygen and carbon dioxide permeability of the composite film was measured using a gas transmission meter. Rectangular specimens (10×10mm) were used. 2 The device was installed in a test chamber. The test was conducted at 23°C and 50% relative humidity, using high-purity oxygen (99.999%) and carbon dioxide (99.999%) as permeating gases. The experimental results are as follows: Figure 3 As shown in C-3D. Figure 3 C represents the oxygen and carbon dioxide barrier properties. It can be seen that, compared to the film prepared in Comparative Example 1, the film prepared in Example 1 achieves a barrier value of 432 cm⁻¹ for both oxygen and carbon dioxide. 3 / m 2 / Tianhe 1186cm 3 / m 2 / sky. Figure 3D is the water vapor barrier property. Compared with the film prepared in Comparative Example 1, the film prepared in Example 1 has ideal water vapor barrier property (168.9 g / m 2 / day).

[0074] IV. Antibacterial test

[0075] The films prepared in Example 1 and Comparative Examples 1-2 were subjected to antibacterial test, and the antibacterial activity of the composite film based on bacterial cellulose (BC) against E. coli and S. aureus was tested by measuring the diameter of the inhibition zone after exposure to the sample. A bacterial suspension with a concentration of about 10 -5 -10 -6 CFU / mL was prepared using sterile normal saline. Subsequently, the composite film based on BC was cut into 15 mm discs and sterilized by ultraviolet irradiation for 30 min. 10 mL of beef extract peptone agar medium was added to a sterile petri dish, followed by inoculation of 50 μL of the bacterial suspension.

[0076] S. aureus and E. coli were used as model microorganisms to evaluate the antibacterial effect of BCCF. All samples were sterilized using a pressure steam sterilizer (115°C, 30 min) (YXQ-LB-30SII, Shanghai Boyun, China). In a 24-well plate, 500 microliters of bacterial suspension (bacterial strain density 1 x 10 -7 CFU / mL) was added to the completely sterilized samples and incubated at 37°C for 2 h. The experimental results are shown in Figure 4 A-4D.

[0077] Figure 4 A-4B is the inhibition zone of the film against S. aureus and E. coli, respectively, Figure 4 C is the size statistics of the inhibition zone diameter, and it can be seen that the film prepared in Example 1 exhibits excellent antibacterial performance (inhibition zone diameter of 2.46 mm) compared with the films of Comparative Examples 1-2 which do not add carbon dot materials. Figure 4 D is the antibacterial rate of the film, and it can be seen that the antibacterial rate of the film prepared in Example 1 against S. aureus can reach 99.20%, and the antibacterial rate against E. coli can reach 99.52%, which has excellent antibacterial performance.

[0078] V. Fluorescence response test

[0079] The film prepared in Example 1 was subjected to fluorescence response test, and the experimental results are shown in Figure 5 , Figure 5 is the fluorescence response graph obtained when the film is used for packaging durians, and it can be seen that the film prepared in the present application can be used for quantitative analysis of visual signals, which may open up a new way for real-time monitoring of tropical fruit spoilage during transportation.

[0080] Six, biodegradation test

[0081] The film prepared in Example 1 was subjected to biodegradation test, and the experimental results are shown in Figure 6 Figure 6 The degradation of the film in the cellulase aqueous solution is shown in the figure, and it can be seen that the film prepared in the application can be degraded by the cellulase solution, and the degradation time is about 5 days.

[0082] Seven, mung bean germination and growth test

[0083] The film prepared in Example 1 was subjected to mung bean germination and growth test, and the experimental results are shown in Figure 7 Figure 7 The tap water (blank control) and the film in water were used to evaluate the growth of mung bean sprouts in water culture at room temperature for 10 days, and it can be seen that the growth, color and root length of the bean sprouts were not significantly affected.

[0084] The application develops an intelligent fluorescent response film using degradable polymer materials and carbon dot materials (CDs). The film not only can monitor the damage of fruits, but also has high strength. The tensile test results show that the synergistic effect between the hydrogen bond network of bacterial cellulose and the cyclodextrin assembly (β-CD@SDS) endows the composite film with excellent mechanical properties (the tensile strength can exceed 120 MPa, and the Young's modulus is 4.93 GPa) and ideal water vapor barrier performance (168.9 g / m 2 / day). In addition, the research based on density functional theory (DFT) confirms that there are a large number of non-covalent interactions (hydrogen bonds) in the network of the intelligent fluorescent response film (BCCF). By adding a quenched carbon dot solution, the intelligent fluorescent response film shows the luminescent response characteristics of thiol groups, and can visualize and monitor the damage of tropical fruits. Notably, this intelligent fluorescent response film can be rapidly degraded (5 days) under the action of cellulase, and has no negative effect on plant growth. Due to the presence of silver ions, the film shows excellent antibacterial performance (the diameter of the inhibition zone is 2.46 mm). The application provides a valuable example for fruit packaging film, and provides a feasible strategy for realizing high-strength, monitorable intelligent film, and also provides an important example and idea for designing a new fruit packaging film network structure.

[0085] The above embodiments are the preferred implementation of the application, in addition to this, the application can be implemented in other ways, any obvious replacement without departing from the concept of the application is within the protection scope of the application.​​

Claims

1. A high-performance degradable smart fluorescent response film, characterized in that: The intelligent fluorescent response film comprises raw materials in the following proportions by weight: 80-120 parts of degradable polymer material; 20-40 parts of self-assembled organic filler; 5-15 parts of carbon dot material.

2. The high-performance degradable smart fluorescent response film according to claim 1, characterized in that: The degradable polymer material comprises at least one of cellulose, starch, chitosan and protein. 3.The high-performance degradable smart fluorescent response film according to claim 2, characterized in that: The cellulose is nanocellulose with a single fiber diameter of 1-100 nm.

4. The high-performance degradable smart fluorescent response film according to claim 3, characterized in that: The nanocellulose comprises at least one of cellulose nanofiber, cellulose nanowhisker and bacterial cellulose.

5. The high-performance degradable smart fluorescent response film according to claim 1, characterized in that: The intelligent fluorescent response film further comprises 0.05-0.15 parts of fluorescent marker.

6. The high-performance degradable smart fluorescent response film according to claim 1, characterized in that: The material of the self-assembled organic filler comprises at least one of coconut oil, polyvinylpyrrolidone and cyclodextrin.

7. The high-performance degradable smart fluorescent response film according to claim 1, characterized in that: The precursor of the carbon dot material comprises at least one of gelatin, citric acid, glucose and urea.

8. A method for preparing a high-performance degradable smart fluorescent response film, characterized in that: The method comprises the following steps: (1) Preparation of carbon dot material: Dissolve the precursor required for the carbon dot material in an appropriate amount of anhydrous ethanol or deionized water, and stir to form a uniform precursor solution; heat the solution, and after natural cooling to room temperature, centrifuge, collect the supernatant, and obtain a solid carbon dot material by solvent evaporation under reduced pressure; dissolve the carbon dot material in distilled water to form a carbon dot material aqueous solution, add an aqueous silver ion solution to the carbon dot material aqueous solution, quench the carbon dots, and thus form Ag + @CDs solution; (2) Preparation of self-assembled organic filler: the material of the self-assembled organic filler and sodium dodecyl sulfate are dissolved in deionized water at a certain molar ratio, stirred uniformly, and the uniform mixture is incubated to obtain two-dimensional sheet-shaped self-assembled organic filler; (3) Dispersion of degradable polymer material: the degradable polymer material is added to deionized water for dispersion to obtain a degradable polymer material dispersion; (4) Intelligent fluorescent response film: the Ag + @CDs aqueous solution, cyclodextrin assembly and degradable polymer material dispersion liquid are mixed and stirred, and the uniformly dispersed mixture is poured onto a flat polytetrafluoroethylene plate, dried in an oven, and after drying is completed, it is peeled off to form the intelligent fluorescent response film.

9. The method according to claim 8, wherein the method is characterized by: In the step (1), the mass-volume ratio of the required precursor of the carbon dot material to anhydrous ethanol or deionized water is 1:20-40; the stirring time is 20-40 min, the heating temperature is 160-180℃, the heating time is 4-12h, the centrifugal speed is 4000-8000rpm / min, the mass concentration of the carbon dot aqueous solution is 0.05-0.15mg / mL, and the molar amount of Ag + in the silver ion aqueous solution is 1-5mmol.

10. The method according to claim 8, wherein the method is characterized by: In the step (2), the molar ratio of the material of the self-assembled organic filler to sodium dodecyl sulfate is 2-4:1, the stirring temperature is 50-60℃, the stirring time is 2-4h, the incubation temperature is 20-30℃, and the time is 36-60h; in the step (3), the stirring time is 0.2-0.8h, the oven temperature is 50-70℃, and the drying time is 4-8h.

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