Preparation method of degradable polyethylene glycol-dextran anti-ultraviolet fresh-keeping film

Abstract

The present invention relates to a preparation method of a degradable polyethylene glycol-dextran anti-ultraviolet fresh-keeping film, the method comprising the following steps: (1) polyethylene glycol is subjected to terminal hydroxyl amination to obtain a polyethylene glycol derivative, which is recorded as NH2-PEG-NH2; (2) sodium periodate is used to oxidize dextran to prepare aldehyde dextran, which is recorded as ODEX; (3) ODEX solution and NH2-PEG-NH2 solution are prepared; (4) the ODEX solution and the NH2-PEG-NH2 solution are mixed, after adjusting the pH value to weak alkalinity with a dilute alkaline solution, glycerol is added, and stirred at room temperature for 0.5-8h to obtain a film-forming liquid; the film-forming liquid is formed into a film by a casting device to obtain an anti-ultraviolet fresh-keeping film. The preparation method of the present invention is simple and easy, and the obtained fresh-keeping film has the properties of high strength, degradability, and anti-ultraviolet, and has a good application prospect in the food industry and the biological field.

Description

Technical Field

[0001] The invention relates to the technical field of food packaging, in particular to a method for preparing a degradable polyethylene glycol-dextran anti-ultraviolet fresh-keeping film. Background Art

[0002] With the development of the times, people have higher and higher requirements for food packaging materials. Traditional packaging materials are mainly plastics, which have the advantages of light weight, stable chemical composition, strong corrosion resistance and impact resistance, but they also have poor heat resistance, easy aging, difficult to degrade, easy to cause white pollution to the environment, and some residual monomers of plastics can also harm human health. Therefore, finding new biodegradable materials to replace plastics has gradually become one of the frontier research hotspots in the field of food packaging. Among them, natural polysaccharide materials from renewable biomass resources have the characteristics of non-toxicity, good biocompatibility, and degradability, and can be used to develop bio-based functional membrane materials.

[0003] Dextran (DEX) is a microbial polysaccharide, which refers to a polysaccharide polymer composed of glucose as a monosaccharide. The main chain is composed of α-1,6-D-pyranose glucopyranose and contains a small amount of α-1,2, α-1,3, and α-1,4 side chain residues. The dextran molecular chain contains a large number of hydroxyl groups, which provide active groups for its chemical modification. Dextran and its derivatives have good biocompatibility and water solubility, good film-forming properties, low price, non-toxicity, and biodegradability. They are widely used in the food industry and biomedicine. In practical applications, the performance of dextran film can be improved by adding non-toxic and biocompatible polyethylene glycol.

[0004] Existing research mainly improves the plasticity and mechanical properties of membrane materials by mechanically blending polyethylene glycol with other materials. Blending is one of the important ways to achieve polymer modification and produce high-performance new materials. Generally speaking, good compatibility between the two phases is a prerequisite for the good performance (especially mechanical properties) of the two-phase system blending product. However, taking polyethylene glycol and dextran as an example, when the concentration of the aqueous solution of the two reaches the critical concentration, the aqueous solutions are immiscible. Although they are both hydrophilic polymers, they will form two immiscible phases macroscopically under non-steady state. Therefore, above the critical concentration, the compatibility of polyethylene glycol and dextran is not good. At lower concentrations, although polyethylene glycol and dextran are one phase macroscopically, the interaction between the two is insufficient at this time, and they cannot be cast into a film. Therefore, if chemical methods can be used to enhance the interaction between polyethylene glycol and dextran, improve the mechanical properties of dextran-based membranes, and give membrane materials other excellent properties, such as UV resistance, in order to prepare high-strength and multifunctional dextran-based membranes, it is still a problem that scientific researchers need to pay attention to. Summary of the invention

[0005] The technical problem to be solved by the present invention is to provide a method for preparing a degradable polyethylene glycol-dextran anti-ultraviolet fresh-keeping film which can improve multiple properties of the film.

[0006] In order to solve the above problems, the preparation method of a degradable polyethylene glycol-dextran anti-ultraviolet fresh-keeping film according to the present invention comprises the following steps:

[0007] (1) The terminal hydroxyl group of polyethylene glycol is aminated to obtain a polyethylene glycol derivative, which is denoted as NH2-PEG-NH2;

[0008] (2) Use sodium periodate to oxidize dextran to prepare aldehyde dextran, denoted as ODEX;

[0009] (3) Prepare ODEX solution and NH2-PEG-NH2 solution:

[0010] The ODEX and the NH2-PEG-NH2 are mixed with distilled water respectively, and stirred at room temperature to 60°C for 5 to 60 minutes to make them evenly dissolved, to obtain ODEX solution and NH2-PEG-NH2 solution with a concentration of 1 g / 100 mL to 10 g / 100 mL respectively;

[0011] (4) Mix the ODEX solution and the NH2-PEG-NH2 solution, adjust the pH value to weak alkalinity with a dilute alkali solution, add glycerol, and stir at room temperature for 0.5 to 8 hours to obtain a film-forming liquid; the film-forming liquid is formed into a film by a casting device to obtain an anti-ultraviolet cling film.

[0012] The molecular weight of the polyethylene glycol in the step (1) is 2000-10000.

[0013] The molecular weight of the dextran in step (2) is 10,000 to 50,000.

[0014] The degree of oxidation of ODEX in step (2) is 45% to 60%.

[0015] The mixing mass ratio of the ODEX solution and the NH2-PEG-NH2 solution in step (4) is m PEG :m ODEX =1:3~3:1.

[0016] The dilute alkaline solution in step (4) refers to a sodium hydroxide solution with a concentration of 1 mol / L.

[0017] In the step (4), the amount of glycerol added is 0-2% of the sum of the mass of ODEX and NH2-PEG-NH2.

[0018] The working parameters of the casting equipment in step (4) are that the casting speed is 0.4-0.8 m / min and the drying temperature of the casting plate is 45-55°C.

[0019] Compared with the prior art, the present invention has the following advantages:

[0020] 1. The present invention uses dextran and polyethylene glycol as main raw materials, firstly, the terminal hydroxyl group of polyethylene glycol is aminated, then sodium periodate is used to oxidize dextran to prepare aldehyde dextran, and then the polyethylene glycol and dextran can be chemically cross-linked through the imine group formed by the Schiff base reaction between the amino group and the aldehyde group to form a polymer with an interpenetrating network structure.

[0021] 2. The fresh-keeping film obtained by the present invention has the properties of high strength, biodegradability, and UV resistance, and has good application prospects in the food industry and biological fields.

[0022] 3. The preparation method of the present invention is simple and easy. The modified polyethylene glycol and dextran are both water-soluble and react to form a film in an aqueous solution. The obtained composite film has no organic solvent residue and is more suitable for the field of food and biomedicine packaging. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] The specific implementation modes of the present invention are further described in detail below in conjunction with the accompanying drawings.

[0024] Figure 1 This is a digital photo of the composite film of the present invention.

[0025] Figure 2 It is the DSC-TG curve of the composite film of the present invention.

[0026] Figure 3 It is the mechanical property of the composite film of the present invention.

[0027] Figure 4 This is a scanning electron microscope photograph of the surface of the composite film of the present invention.

[0028] Figure 5 is the light transmittance of the composite film of the present invention. DETAILED DESCRIPTION

[0029] A method for preparing a degradable polyethylene glycol-dextran anti-ultraviolet fresh-keeping film comprises the following steps:

[0030] (1) The terminal hydroxyl group of polyethylene glycol with a molecular weight of 2000~10000 is aminated to obtain a polyethylene glycol derivative, which is denoted as NH2-PEG-NH2.

[0031] ⑵ Use sodium periodate to oxidize dextran with a molecular weight of 10,000 to 50,000 to prepare aldehyde dextran, which is recorded as ODEX. The degree of oxidation of ODEX is 45% to 60%.

[0032] (3) Prepare ODEX solution and NH2-PEG-NH2 solution:

[0033] ODEX and NH2-PEG-NH2 are mixed with distilled water respectively, and stirred at room temperature to 60°C for 5 to 60 minutes to dissolve them evenly, to obtain ODEX solution and NH2-PEG-NH2 solution with a concentration of 1 g / 100 mL to 10 g / 100 mL, respectively, with a preferred concentration of 3 to 6 g / 100 mL.

[0034] ⑷ Mix ODEX solution and NH2-PEG-NH2 solution at m PEG :m ODEX =1:3~3:1 mass ratio (g / g), preferably 1:2~2:1. After adjusting the pH value to weak alkalinity with a dilute alkali solution (sodium hydroxide solution with a concentration of 1 mol / L), glycerol is added at 0~2% of the sum of the mass of ODEX and NH2-PEG-NH2, and stirred at room temperature for 0.5~8h to obtain a film-forming liquid; the film-forming liquid is formed into a film by a casting device under the conditions of a casting speed of 0.4~0.8m / min and a casting plate drying temperature of 45~55℃, and an anti-ultraviolet cling film is obtained.

[0035] Example 1 A method for preparing a degradable polyethylene glycol-dextran anti-ultraviolet fresh-keeping film comprises the following steps:

[0036] (1) The terminal hydroxyl group of polyethylene glycol is aminated to obtain a polyethylene glycol derivative, which is denoted as NH2-PEG-NH2. The specific preparation process is as follows:

[0037] Accurately weigh 40 g of polyethylene glycol (PEG, molecular weight 2000) using an electronic analytical balance and pour it into a round-bottom flask containing 200 mL of dichloromethane, place it in a constant temperature water bath, stir it at room temperature until it is completely dissolved, then add 100 mL of triethylamine solution containing 11.4 g of p-toluenesulfonyl chloride (TsCl) dropwise into the above solution, react at room temperature for 12 h, and after the reaction is completed, extract it with 3 mol / L HCl (150 mL) three times and combine the organic phases, add solid sodium bicarbonate to the organic phase and stir until there are no bubbles, filter and concentrate to obtain a concentrated solution, add excess ether to the concentrated solution, precipitate a large amount of precipitate and then filter it, and vacuum dry the filter cake at 30°C to obtain a white waxy solid, which is polyethylene glycol p-toluenesulfonate (TsO-PEG-OTs).

[0038] Accurately weigh 23.1 g of TsO-PEG-OTs and 80 mL of ammonia water, add them to a high-pressure reactor at the same time, react at 140 ° C for 6 h, cool to room temperature, extract with excess dichloromethane (50 mL) for several times, combine the organic phases, and then add 100 mL of 1 mol / L sodium hydroxide solution to the organic phase, stir at room temperature for 4 h, separate the organic phase after standing, wash with saturated brine until neutral, add excess anhydrous sodium sulfate to dry, filter and rotary evaporate the filtrate to obtain a white solid product, namely NH2-PEG-NH2.

[0039] (2) Use sodium periodate to oxidize dextran to prepare aldehyde dextran, which is recorded as ODEX. The specific preparation process is as follows:

[0040] Accurately weigh 20 g of dextran (DEX, molecular weight 10000), add it to a round-bottom flask containing 20 mL of deionized water, and stir at room temperature until it is completely dissolved; then weigh 13.2 g of sodium periodate and dissolve it in 120 mL of deionized water to prepare a sodium periodate solution, and store it in the dark; then add the prepared sodium periodate solution dropwise to the DEX solution, and after reacting in the dark for 4 hours, immediately add 10 mL of ethylene glycol solution and react for 15 minutes to terminate the reaction; finally, place the solution in a dialysis bag with a molecular weight cutoff of 300 and dialyze it for 72 hours, then transfer the product to a culture dish, freeze-dry the product, and store it at -20°C for later use, which is recorded as ODEX.

[0041] (3) Prepare ODEX solution and NH2-PEG-NH2 solution:

[0042] 10 g ODEX and 10 g NH2-PEG-NH2 were mixed with 1000 mL distilled water respectively, and stirred at room temperature ~ 60 ° C for 5 min to dissolve them evenly to obtain ODEX solution and NH2-PEG-NH2 solution respectively.

[0043] (4) Mix the ODEX solution and the NH2-PEG-NH2 solution, adjust the pH to weak alkalinity with a 1 mol / L sodium hydroxide solution, add 0.4 g of glycerol, and stir at room temperature for 2 h to obtain a film-forming solution; the film-forming solution is formed into a film by a casting equipment at a casting speed of 0.4 m / min and a casting plate drying temperature of 45-55 °C to obtain an anti-ultraviolet cling film, which is recorded as P-OD-a.

[0044] Example 2 A method for preparing a degradable polyethylene glycol-dextran anti-ultraviolet fresh-keeping film comprises the following steps:

[0045] (1) The terminal hydroxyl group of polyethylene glycol is aminated to obtain a polyethylene glycol derivative, which is denoted as NH2-PEG-NH2. The specific preparation process is the same as that of Example 1.

[0046] (2) Use sodium periodate to oxidize dextran to prepare aldehyde dextran, which is denoted as ODEX. The specific preparation process is the same as that in Example 1.

[0047] (3) Prepare ODEX solution and NH2-PEG-NH2 solution:

[0048] 60 g ODEX and 40 g NH2-PEG-NH2 were mixed with 1000 mL distilled water respectively, and stirred at room temperature ~ 60 ° C for 30 min to dissolve them evenly, to obtain ODEX solution and NH2-PEG-NH2 solution respectively.

[0049] (4) Mix the ODEX solution and the NH2-PEG-NH2 solution, adjust the pH value to weak alkalinity with a sodium hydroxide solution having a concentration of 1 mol / L, and stir at room temperature for 6 hours to obtain a film-forming solution; the film-forming solution is formed into a film by a casting equipment at a casting speed of 0.6 m / min and a casting plate drying temperature of 45-55°C to obtain an anti-ultraviolet cling film, which is recorded as P-OD-b.

[0050] Example 3 A method for preparing a degradable polyethylene glycol-dextran anti-ultraviolet fresh-keeping film comprises the following steps:

[0051] (1) The terminal hydroxyl group of polyethylene glycol is aminated to obtain a polyethylene glycol derivative, which is denoted as NH2-PEG-NH2. The specific preparation process is the same as that of Example 1.

[0052] (2) Use sodium periodate to oxidize dextran to prepare aldehyde dextran, which is denoted as ODEX. The specific preparation process is the same as that in Example 1.

[0053] (3) Prepare ODEX solution and NH2-PEG-NH2 solution:

[0054] 60 g ODEX and 90 g NH2-PEG-NH2 were mixed with 1000 mL distilled water respectively, and stirred at room temperature ~ 60 ° C for 60 min to dissolve them evenly, to obtain ODEX solution and NH2-PEG-NH2 solution respectively.

[0055] (4) Mix the ODEX solution and the NH2-PEG-NH2 solution, adjust the pH to weak alkalinity with a 1 mol / L sodium hydroxide solution, add 0.15 g of glycerol, and stir at room temperature for 8 h to obtain a film-forming solution; the film-forming solution is formed into a film by a casting equipment at a casting speed of 0.8 m / min and a casting plate drying temperature of 45-55 °C to obtain an anti-ultraviolet cling film, which is recorded as P-OD-c.

[0056] The performance tests were performed on P-OD-a, P-OD-b and P-OD-c obtained in Examples 1 to 3, respectively.

[0057]

Film-forming properties

[0058] In order to verify the necessity of chemical modification for film formation, the molecular weight was the same as in Example 1, and the mass concentration was 4 g / 100 mL. However, after the unmodified dextran and polyethylene glycol solution were directly mixed, a thin layer of semi-dry powder was obtained after the cast sheet was dried, and a continuous film could not be obtained. On the contrary, after chemical modification of PEG and DEX, P-OD-a, P-OD-b, and P-OD-c could form a film through Schiff base reaction at the same concentration and ratio as the unmodified raw materials; and as the ratio of NH2-PEG-NH2 increased, the color of the film changed from light yellow to dark yellow, as shown in FIG. Figure 1 shown.

[0059] According to the film-forming theory, whether a film is formed or not or how good the film is is determined by the interaction between particles. When PEG and DEX are physically mixed, hydrogen bonds are formed, and the interaction force is weak and insufficient to form a film. After chemical modification, ODEX reacts with NH2-PEG-NH2 to form chemical bonds, the interaction force is enhanced, and the film-forming property is good.

[0060]

Thermal performance analysis

[0061] A differential scanning calorimetry-thermogravimetric (DSC-TG) simultaneous thermal analyzer was used: 6-8 mg of sample was accurately weighed and placed in an alumina crucible. The test conditions were set to a nitrogen atmosphere with a constant heating rate of 10 °C / min, a temperature range of 30-600 °C, a carrier gas rate of 50 mL / min, and an empty crucible as a blank control to obtain the DSC-TG curve.

[0062] The influence of the mass ratio of NH2-PEG-NH2 to ODEX on the thermal properties of the prepared Schiff base composite film was characterized by TG, DTG and DSC data. Figure 2 And as shown in Table 1.

[0063] Table 1 Thermal properties analysis of composite films

[0064]

[0065] Depend on Figure 2 -a and Figure 2 -b curve, NH2-PEG-NH2 has two mass loss peaks, and ODEX and film both have three mass loss peaks. The mass loss peak before 100℃ is attributed to the evaporation of water molecules in the Schiff base composite film. NH2-PEG-NH2, ODEX, and Schiff base composite films have large mass losses between 300-430℃, 210-350℃, and 210-410℃, respectively, which is attributed to the decomposition of macromolecular chains. From the half-life temperature (T h), the T of the Schiff base composite film increases with the increase of the mass ratio of NH2-PEG-NH2. h The T of P-OD-c membrane increased. h The highest, indicating the best thermal stability; through chemical modification, the increase of NH2-PEG-NH2 content can also enhance the thermal stability of Schiff base composite films. Figure 2 -c curve, it can be seen that the absorption peak appearing near 60℃ corresponds to the glass transition temperature of NH2-PEG-NH2; while among the Schiff base composite films, only P-OD-c has a glass transition temperature near 50℃, which may be caused by the increase in the mass ratio of NH2-PEG-NH2 involved in the reaction. The glass transition temperature of P-OD-c film is close to that of NH2-PEG-NH2. The DSC curves of P-OD-a and P-OD-b are similar, and no obvious glass transition is observed below 100℃, indicating that the reaction of NH2-PEG-NH2 with ODEX changes its thermal properties.

[0066] Comprehensive analysis shows that the mass ratio of NH2-PEG-NH2 has a great influence on the thermal stability of the film. By adjusting the relative ratio of NH2-PEG-NH2 and ODex, the glass transition and thermal decomposition temperature can be regulated.

[0067]

Mechanical performance analysis

[0068] With reference to the "Test Method for Tensile Properties of Plastic Films" (GB / T 1040-2006), the tensile strength (TS) and elongation at break (EAB) of the composite film were tested. Before the test, the sample was cut into rectangular strips of 50 mm × 10 mm. A thickness gauge with an accuracy of 0.001 mm was used to measure the sample at random points 5 times and the average value was taken. Then the two ends of the sample were clamped flatly at the two ports of the microcomputer-controlled electronic universal material testing machine, and the universal testing machine was turned on to start the measurement. The initial distance was set to 50 mm and the tensile speed was set to 5 mm / s. Three groups of parallel tests were performed for each specification. TS and EAB were calculated according to formulas (1) and (2), respectively:

[0069] (1)

[0070] (2)

[0071] Where: F is the maximum tension when the film breaks (N); B is the film width (mm); H is the film thickness (mm); Lmax is the maximum length when the film breaks (mm); L is the initial length of the film (mm).

[0072] The experimental results are as follows Figure 3As shown. When the mass ratio of NH2-PEG-NH2 to ODEX increased from 1:1.5 to 1.5:1, the tensile strength of the film increased from 31.11 MPa to 48.89 MPa, and the elongation at break increased from 43.17% to 87.67%. The results show that when the amount of ODEX added increases, the density of ODEX particles increases, and even agglomeration occurs (such as Figure 4 As shown in the scanning electron microscope photo, the mechanical properties of the composite film are reduced; when the amount of NH2-PEG-NH2 added increases, the ODEX particles are well dispersed and the mechanical properties of the composite film are improved, indicating that the flexible polyethylene glycol macromolecular chain can improve the toughness and impact strength of the film. At present, the tensile strength of commercially available petroleum-based polymer films is about 20 MPa. Therefore, the Schiff base composite film provided by the present invention has high tensile strength and elongation at break, can well resist external applied forces, and provides the possibility for preparing special packaging materials.

[0073]

Light transmission performance

[0074] The transmittance (T) of the film was measured at 300, 350, 400, 460, 480, 540, and 600 nm using a UV2600A UV-visible spectrophotometer. Using air as a control, the composite film was cut into 40 mm × 10 mm rectangular strips, attached to the inner wall of the cuvette with tweezers, and placed in a UV-visible spectrophotometer for measurement. Three positions were randomly selected for each sample for measurement, and the average value was taken. Ultraviolet blocking performance is an important indicator for the development of active food packaging, because many organic foods are very sensitive to ultraviolet rays, which will cause oxidation due to ultraviolet rays, resulting in discoloration of packaged food, loss of nutrients and lipid oxidation. Therefore, the required packaging should be a film that blocks ultraviolet light to meet the storage requirements of special foods.

[0075] The light transmittance of polyethylene glycol / dextran Schiff base composite film is as follows Figure 5 As shown in the figure, the transmittance of the three Schiff base composite films, P-OD-a, P-OD-b and P-OD-c, in the ultraviolet region is less than 20%, showing excellent ultraviolet shielding performance; below 350 nm, the transmittance is zero, completely blocking the transmission of ultraviolet rays. This is mainly attributed to the production of C=N bonds in the Schiff base reaction, the unsaturated bonds containing heteroatoms as ultraviolet chromophores, and the unoxidized hydroxyl groups in ODEX as auxochromophores, which enhance the shielding function of the Schiff base composite film against ultraviolet light, resulting in a decrease in transmittance.

[0076] In the visible light region (400-600 nm), as the wavelength increases, the transmittance of the three films P-OD-a, P-OD-b and P-OD-c gradually increases. When the mass ratio of NH2-PEG-NH2 to ODEX is 1:1 and the wavelength is 600 nm, the transmittance is close to 90%; as the content of NH2-PEG-NH2 or the content of ODEX increases, the transmittance of the film decreases; depending on the degree of reaction, the color of the polymer Schiff base film changes from light yellow to orange (such as Figure 1 As shown in the figure), when the mass ratio of NH2-PEG-NH2 / ODEX changes, the color of the film changes accordingly, and the change in color also changes the light transmittance of the film.

[0077] Comprehensive analysis shows that the three Schiff base composite films can shield ultraviolet light and show good light transmittance in the visible light region. Therefore, under different light transmittance requirements for packaging materials, Schiff base composite films with different ratios can be selected.

[0078]

Water vapor permeability

[0079] The water vapor permeability coefficient (WVP) is determined according to GB1037-1970, using the pseudo-cup method and a water vapor permeability tester. The composite film is cut into a circle of appropriate size, placed in a test cup, and a certain amount of deionized water is added to it. Then, it is placed under the conditions of 90% experimental humidity and 25°C temperature, and the test interval is set to 15 min. The data is recorded. Three sets of parallel experiments are performed for each sample. The water vapor permeability is calculated according to formula (3):

[0080] (3)

[0081] Where: WVP is the water vapor transmission rate of the sample, g·mm / (h·m 2 kPa); ∆m is the mass increment in time t, g; d is the thickness of the membrane, mm; S is the area of ​​the membrane, m 2 ; t is the measurement time interval, h; ∆p is the water vapor pressure difference on both sides of the membrane, kPa.

[0082] Table 2 shows the water vapor permeability coefficients of the three composite films of P-OD-a, P-OD-b and P-OD-c. From the data in the table, it can be seen that with the increase of ODEX content, the water vapor permeability coefficient decreases, especially when the mass ratio of NH2-PEG-NH2 to ODEX is 1:1.5, the water vapor permeability coefficient decreases to 0.855. It is speculated that PEG is a linear polymer, and only the amino group at the chain end reacts with the aldehyde group to form a bond. When the content of polyethylene glycol increases, the excess NH2-PEG-NH2 causes the free volume in the molecule to increase, and the water vapor permeability increases accordingly.

[0083] Table 2 Water vapor permeability coefficient of composite films

[0084]

Claims

1. A method for preparing a degradable polyethylene glycol-dextran anti-ultraviolet fresh-keeping film, comprising the following steps: (1) The terminal hydroxyl group of polyethylene glycol is aminated to obtain a polyethylene glycol derivative, which is denoted as NH2-PEG-NH2; (2) Use sodium periodate to oxidize dextran to prepare aldehyde dextran, denoted as ODEX; (3) Prepare ODEX solution and NH2-PEG-NH2 solution: The ODEX and the NH2-PEG-NH2 are mixed with distilled water respectively, and stirred at room temperature to 60°C for 5 to 60 minutes to make them evenly dissolved, to obtain ODEX solution and NH2-PEG-NH2 solution with a concentration of 1 g / 100 mL to 10 g / 100 mL respectively; (4) The ODEX solution and the NH2-PEG-NH2 solution are mixed, the pH value is adjusted to weak alkalinity with a dilute alkali solution, glycerol is added, and the mixture is stirred at room temperature for 0.5 to 8 hours to obtain a film-forming solution; the film-forming solution is formed into a film by a casting device to obtain an anti-ultraviolet cling film; the mixing mass ratio of the ODEX solution and the NH2-PEG-NH2 solution is m PEG :m ODEX =1:3~3:

1.

2. The method for preparing a degradable polyethylene glycol-dextran anti-ultraviolet fresh-keeping film according to claim 1, characterized in that: The molecular weight of the polyethylene glycol in the step (1) is 2000-10000.

3. The method for preparing a degradable polyethylene glycol-dextran anti-ultraviolet fresh-keeping film according to claim 1, characterized in that: The molecular weight of the dextran in step (2) is 10,000 to 50,000.

4. The method for preparing a degradable polyethylene glycol-dextran anti-ultraviolet fresh-keeping film according to claim 1, characterized in that: The degree of oxidation of ODEX in step (2) is 45% to 60%.

5. The method for preparing a degradable polyethylene glycol-dextran anti-ultraviolet fresh-keeping film according to claim 1, characterized in that: The dilute alkaline solution in step (4) refers to a sodium hydroxide solution with a concentration of 1 mol / L.

6. The method for preparing a degradable polyethylene glycol-dextran anti-ultraviolet fresh-keeping film according to claim 1, characterized in that: In the step (4), the amount of glycerol added is 0-2% of the sum of the mass of ODEX and NH2-PEG-NH2.

7. The method for preparing a degradable polyethylene glycol-dextran anti-ultraviolet fresh-keeping film according to claim 1, characterized in that: The working parameters of the casting equipment in step (4) are that the casting speed is 0.4-0.8 m / min and the drying temperature of the casting plate is 45-55°C.

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