Macromolecular fruit and vegetable fresh-keeping bag and preparation method thereof

Abstract

The invention relates to the technical field of packaging materials, and particularly discloses a macromolecular fruit and vegetable fresh-keeping bag which is prepared from the following raw materials in parts by weight: 30 to 50 parts of polyethylene, 40 to 50 parts of ethylene-vinyl acetate copolymer, 5 to 15 parts of chitosan / cellulose nanocrystalline composite microspheres, 2 to 5 parts of nano silicon dioxide, 0.2 to 0.5 part of antioxidant and 0.5 to 1 part of lubricant. In the chitosan / cellulose nanocrystal composite microspheres, the weight ratio of chitosan to cellulose nanocrystals is 2: (0.8-1.5). On one hand, the polymer fruit and vegetable fresh-keeping bag provided by the invention has a proper O2 / CO2 transmittance ratio, an automatic controlled atmosphere environment can be formed in the fresh-keeping bag, the metabolism speed of fruits and vegetables is slowed down, and the fresh-keeping period is prolonged; on the other hand, ethylene substances generated by fruits and vegetables can be efficiently adsorbed, the situation that fruit and vegetable ripening is accelerated due to the fact that the acidity in the bag is increased is effectively avoided, fruit and vegetable cell damage and quality deterioration are relieved, and the fresh-keeping period is prolonged.

Description

Technical Field

[0001] This application relates to the field of packaging materials technology, specifically to a polymer fruit and vegetable preservation bag and its preparation method. Background Technology

[0002] With the rapid development of the fresh food e-commerce industry, the importance of fruit and vegetable preservation has become increasingly prominent. Cherries, as a typical high-value non-climacteric fruit, have extremely stringent requirements for preservation environments due to their thin skin, high juiciness, and vigorous respiration metabolism. After harvesting, cherries are prone to accelerated ripening and senescence due to ethylene produced by their own respiration. They are also sensitive to low-oxygen and high-carbon dioxide environments. If the preservation environment is not properly controlled, anaerobic respiration can easily lead to anaerobic respiration, resulting in browning of the flesh, off-flavors, and decreased firmness, severely restricting their circulation radius and shelf life.

[0003] Currently, polymer preservation bags are the mainstream packaging form for cherry preservation. Existing technologies mostly use polyethylene, polypropylene, polylactic acid, and other base materials to prepare preservation bags, optimizing air permeability by adjusting the base material ratio. However, existing technologies have significant drawbacks: First, the O2 / CO2 permeability ratio of most preservation bags cannot accurately match the respiration characteristics of cherries, making it difficult to form a stable automatic modified atmosphere environment, leading to gas imbalance inside the bag and accelerating the metabolic deterioration of cherries; second, existing preservation bags with ethylene adsorption functions mostly use traditional adsorbents such as zeolite and activated carbon, which have low adsorption efficiency and are prone to aggregation, failing to effectively remove ethylene produced by cherries, and easily causing an increase in acidity inside the bag, further aggravating cherry spoilage.

[0004] Therefore, developing a cherry-specific preservation bag that combines suitable modified atmosphere performance with efficient ethylene adsorption capacity is of great significance for solving problems such as the short shelf life and easy spoilage of cherries. Summary of the Invention

[0005] To overcome the problems existing in current fruit and vegetable preservation bags, this application provides a polymer fruit and vegetable preservation bag with suitable modified atmosphere performance and high ethylene adsorption capacity, as well as a method for its preparation.

[0006] In the first aspect, this application provides a polymer fruit and vegetable preservation bag, which adopts the following technical solution: A polymer fruit and vegetable preservation bag comprises the following raw materials in parts by weight: 30-50 parts polyethylene, 40-50 parts ethylene-vinyl acetate copolymer, 5-15 parts chitosan / cellulose nanocrystal composite microspheres, 2-5 parts nano silica, 0.2-0.5 parts antioxidant, and 0.5-1 parts lubricant; In the chitosan / cellulose nanocrystal composite microspheres, the weight ratio of chitosan to cellulose nanocrystals is 2:(0.8-1.5).

[0007] This application provides a polymer fruit and vegetable preservation bag. On one hand, the bag has an O2 / CO2 permeability ratio that matches the respiration characteristics of cherries, enabling an automatic modified atmosphere environment inside the bag to slow down the metabolism of fruits and vegetables. On the other hand, it can also efficiently adsorb ethylene-like substances produced by fruits and vegetables, effectively preventing the acidity inside the bag from increasing. Through these dual effects, the bag synergistically alleviates cherry metabolism and quality deterioration, significantly improving the preservation effect. Specifically, this application uses polyethylene and ethylene-vinyl acetate copolymer as a blended base material, combined with a porous network constructed from nano-silica, thereby adjusting the O2 / CO2 permeability ratio to a suitable range for cherry storage. This automatically creates a low-oxygen, high-carbon dioxide modified atmosphere environment inside the bag, effectively slowing down the cherry's metabolism and reducing nutrient consumption. Furthermore, by adding specific chitosan / cellulose nanocrystal composite microspheres, the bag can efficiently capture ethylene produced by cherries, preventing ethylene accumulation and accelerated ripening. Simultaneously, these composite microspheres can also inhibit the accumulation of acidic volatiles inside the bag, preventing increased acidity from damaging cherry cells and effectively alleviating quality deterioration phenomena such as browning and off-flavors. In summary, this application, through the selection of substrate and the introduction of new materials, can significantly extend the shelf life of cherries, solving the problems of short shelf life and easy spoilage of cherries in the prior art.

[0008] In some embodiments, the amount of chitosan / cellulose nanocrystal composite microspheres added can be 5-8 parts, 5-10 parts, 5-13 parts, 5-15 parts, 8-10 parts, 8-13 parts, 8-15 parts, 10-13 parts, 10-15 parts, or 13-15 parts.

[0009] In one specific implementation, the amount of chitosan / cellulose nanocrystal composite microspheres added can also be 5 parts, 8 parts, 10 parts, 13 parts or 15 parts.

[0010] In some embodiments, the weight ratio of chitosan to cellulose nanocrystals in the chitosan / cellulose nanocrystal composite microspheres can be 2:(0.8-1), 2:(0.8-1.3), 2:(1-1.3), 2:(1-1.5), or 2:(1.3-1.5).

[0011] In one specific implementation, the weight ratio of chitosan to cellulose nanocrystals in the chitosan / cellulose nanocrystal composite microspheres can also be 2:0.8, 2:1, 2:1.3 or 2:1.5.

[0012] Optionally, in the chitosan / cellulose nanocrystal composite microspheres, the weight ratio of chitosan to cellulose nanocrystals is 2:(1-1.3).

[0013] In this application, the weight ratio of chitosan to cellulose nanocrystals in the chitosan / cellulose nanocrystal composite microspheres affects the absorption performance of fruit and vegetable preservation bags for ethylene. When the weight ratio is <2:1.5, the relative content of cellulose nanocrystals in the microspheres is slightly higher, which makes the microspheres fragile and reduces the adsorption sites on the surface of the microspheres, resulting in a decrease in the amount of ethylene adsorbed. When the weight ratio is >2:0.8, the relative content of chitosan in the microspheres is higher, which makes chitosan prone to swelling, causing pore collapse, reducing the adsorption sites, and decreasing the adsorption capacity of the preservation bag.

[0014] The relatively high content of cellulose nanocrystals makes the microspheres fragile, reduces the adsorption sites on the surface of the microspheres, and thus reduces the amount of ethylene adsorbed. Optionally, the chitosan / cellulose nanocrystal composite microspheres have a particle size of 30-50 nm.

[0015] Optionally, the melt index of the polyethylene is 0.3-0.5 g / 10 min; and the melt index of the ethylene-vinyl acetate copolymer is 0.5-0.7 g / 10 min.

[0016] Optionally, the particle size of the nano-silica is 10-80 nm.

[0017] Optionally, the thickness of the polymer fruit and vegetable preservation bag is 20-25 μm.

[0018] Optionally, the O2 / CO2 transmittance ratio of the polymer fruit and vegetable preservation bag is (3-4):1.

[0019] Optionally, the antioxidant is antioxidant 1010 and / or antioxidant 168; the lubricant is erucamide and / or oleamide.

[0020] The polymer fruit and vegetable preservation bag provided in this application is suitable for the preservation of cherries and other fruits and vegetables with the same or similar respiration characteristics as cherries.

[0021] Secondly, this application provides a method for preparing a polymer fruit and vegetable preservation bag, comprising the following steps: First, polyethylene and ethylene-vinyl acetate copolymer are premixed at high speed. Then, chitosan / cellulose nanocrystal composite microspheres and nano silica are added and mixed evenly to obtain a blended material. The blended material is melt-extruded, water-cooled, and pelletized to obtain masterbatch for food preservation bags; The masterbatch for preservation bags is blown into film, cooled by a cooling air ring, drawn, and rolled up to obtain a polymer fruit and vegetable preservation bag.

[0022] Optionally, during the melt extrusion process, the extrusion temperature is set as follows: Zone 1 135-145℃, Zone 2 145-155℃, Zone 3 155-165℃, Zone 4 165-175℃, and die head 160-170℃; the screw speed is 250-350 r / min.

[0023] Optionally, during the blown film process, the extrusion temperature is set as follows: Zone 1 145-155℃, Zone 2 155-165℃, Zone 3 165-175℃, and die head 160-170℃; the blow-up ratio is 2.5-3.0, and the traction speed is 30-40m / min.

[0024] In summary, this application has the following beneficial effects: 1. This application uses polyethylene and ethylene-vinyl acetate copolymer as the matrix, and by adding components such as chitosan / cellulose nanocrystal composite microspheres and nano silica, it is possible to obtain a fruit and vegetable preservation bag with a CO2 / O2 permeability ratio of (3.1-3.8):2. This fruit and vegetable preservation bag can match the respiration characteristics of cherries and efficiently adsorb ethylene substances produced by cherries, effectively slowing down the metabolism of cherries and extending their shelf life.

[0025] 2. In this application, the amount of chitosan / cellulose nanocrystal composite microspheres added is controlled at 8-13 parts, and the weight ratio of chitosan to cellulose nanocrystals is controlled in the range of 2:(1-1.3). The resulting fruit and vegetable preservation bag has a better absorption effect on ethylene. When used to preserve cherries for 15 days, the ethylene content in the bag can still be kept below 20μL / L. Detailed Implementation

[0026] A polymer fruit and vegetable preservation bag comprises the following raw materials in parts by weight: 30-50 parts polyethylene, 40-50 parts ethylene-vinyl acetate copolymer, 5-15 parts chitosan / cellulose nanocrystal composite microspheres, 2-5 parts nano silica, 0.2-0.5 parts antioxidant, and 0.5-1 parts lubricant.

[0027] The chitosan / cellulose nanocrystal composite microspheres have a particle size of 30-50 nm, and the weight ratio of chitosan to cellulose nanocrystals is 2:(0.8-1.5). The preparation method of the chitosan / cellulose nanocrystal composite microspheres includes the following steps: (1) Prepare a chitosan acetic acid solution by using chitosan with a 1% glacial acetic acid solution; (2) Add water to the cellulose nanocrystals and ultrasonically disperse them at 200-400W and 40-50Hz for 20-30 minutes to obtain an aqueous dispersion of cellulose nanocrystals; (3) Under the high-speed shear emulsification action of 7000-9000 r / min, the aqueous dispersion of cellulose nanocrystals is slowly added dropwise to the chitosan acetate solution, and the addition is completed in about 15 min; then continue to stir at 200-400 r / min for 20-30 min to obtain chitosan / cellulose nanocrystal composite solution. (4) Add the chitosan / cellulose nanocrystal composite solution dropwise to a 0.5-0.8wt% sodium tripolyphosphate crosslinking agent solution at a rate of 0.3-0.6mL / min, and stir at a speed of 150-250 r / min; after the addition is complete, continue stirring for 2-3 hours. (5) Collect the microspheres by filtering with gauze, wash them repeatedly with deionized water 3-4 times, and wash them once with anhydrous ethanol; after freeze drying, obtain white powdered chitosan / cellulose nanocrystal composite microspheres.

[0028] The method for preparing the polymer fruit and vegetable preservation bag provided in this application includes the following steps: (1) First, polyethylene and ethylene-vinyl acetate copolymer are added to a high-speed mixer and mixed for 5-10 minutes at 80-90℃ and 800-1000r / min. Then, chitosan / cellulose nanocrystal composite microspheres and nano silica are added and mixed for 5-10 minutes at 80-90℃ and 1200-1500r / min to obtain the blend material. (2) Add the blended material into a twin-screw extruder and set the extrusion temperature as follows: Zone 1 135-145℃, Zone 2 145-155℃, Zone 3 155-165℃, Zone 4 165-175℃, and die head 160-170℃; the screw speed is 250-350r / min. After extrusion, water cooling, and pelletizing, the material is used to obtain masterbatch for food preservation bags. (3) Add the masterbatch into the blown film machine and set the extrusion temperature as follows: Zone 1 145-155℃, Zone 2 155-165℃, Zone 3 165-175℃, and head 160-170℃; the blow-up ratio is 2.5-3.0, the traction speed is 30-40m / min, and the film thickness is 20-25μm. After cooling by the cooling air ring, traction, and winding, a polymer fruit and vegetable preservation bag is obtained.

[0029] In this application, the polyethylene is LDPE (low-density polyethylene) with a melt index of 0.3-0.5 g / 10 min, purchased from Dongguan Shangpin New Material Technology Co., Ltd.; the ethylene-vinyl acetate copolymer is DuPont 53007, with a vinyl acetate (VA) content of 12% and a melt index of 0.5-0.7 g / 10 min, purchased from Dongguan Shangpin New Material Technology Co., Ltd.; the nano-silica has a particle size of 10-20 nm, 30-50 nm, or 70-80 nm; the cellulose nanocrystals are RH-01519, purchased from Guangdong Daxiao Chemical Co., Ltd.; all raw materials, reagents, solvents, etc. used in this application are commercially available.

[0030] The following describes this application in further detail with reference to preparation examples, embodiments, and performance testing. Preparation Example 1

[0031] Preparation Example 1 provides a chitosan / cellulose nanocrystal composite microsphere.

[0032] The preparation method of the above-mentioned chitosan / cellulose nanocrystal composite microspheres includes the following steps: (1) Prepare a 1wt% chitosan acetic acid solution by mixing chitosan with a 1% glacial acetic acid solution; (2) Add water to cellulose nanocrystals and ultrasonically disperse at 300W and 40Hz for 30min to obtain a 1wt% aqueous dispersion of cellulose nanocrystals. (3) Under the high-speed shear emulsification action of 8000 r / min, 50 mL of cellulose nanocrystal aqueous dispersion was slowly added dropwise to 100 mL of chitosan acetate solution, and the addition was completed in about 15 min; then the mixture was stirred at 400 r / min for 30 min to obtain chitosan / cellulose nanocrystal composite solution. (4) The chitosan / cellulose nanocrystal composite solution was added dropwise at a rate of 0.4 mL / min to 100 mL of 0.6 wt% sodium tripolyphosphate crosslinking agent solution (0.6 g sodium tripolyphosphate dissolved in 100 mL deionized water) under stirring at a speed of 200 r / min; after the addition was completed, stirring was continued for 3 h. (5) Collect the microspheres by filtering with gauze, wash them repeatedly with deionized water 3 times and with anhydrous ethanol once; after freeze drying, obtain white powdered chitosan / cellulose nanocrystal composite microspheres. Preparation Examples 2-4

[0033] Preparation Examples 2-4 provide chitosan / cellulose nanocrystal composite microspheres, respectively.

[0034] The difference between the above preparation example and preparation example 1 is that: In Preparation Example 2, the amount of cellulose nanocrystal aqueous dispersion added was 40 mL, and the weight ratio of chitosan to cellulose nanocrystals was 2:0.8. In Preparation Example 3, the amount of cellulose nanocrystal aqueous dispersion added was 65 mL, and the weight ratio of chitosan to cellulose nanocrystals was 2:1.3. In Preparation Example 4, the amount of cellulose nanocrystal aqueous dispersion added was 75 mL, and the weight ratio of chitosan to cellulose nanocrystals was 2:1.5. Examples 1-4

[0035] Examples 1-4 each provide a polymer fruit and vegetable preservation bag.

[0036] The difference between the above embodiments is that the chitosan / cellulose nanocrystal composite microspheres used in the polymer fruit and vegetable preservation bags are derived from preparation examples 1-4.

[0037] The preparation method of the polymer fruit and vegetable preservation bag provided in Examples 1-4 includes the following steps: (1) First, add 400g of polyethylene and 450g of ethylene-vinyl acetate copolymer to a high-speed mixer and mix for 5 minutes at 85℃ and 1000r / min. Then add 80g of chitosan / cellulose nanocrystal composite microspheres, 30g of nano silica (particle size 10-20nm), 1.5g of antioxidant 1010, 1.5g of antioxidant 168 and 5g of oleamide. Continue mixing for 10 minutes at 85℃ and 1400r / min to obtain the blend material. (2) Add the blended material into a twin-screw extruder and set the extrusion temperature as follows: Zone 1 140℃, Zone 2 150℃, Zone 3 160℃, Zone 4 170℃, and die head 165℃; the screw speed is 300r / min. The material is extruded, water-cooled, and pelletized to obtain masterbatch for food preservation bags. (3) Add the masterbatch into the blown film machine and set the extrusion temperature as follows: Zone 1 150℃, Zone 2 160℃, Zone 3 170℃, and head 165℃; the blow-up ratio is 2.8, the traction speed is 35m / min, and the film thickness is 20μm. After cooling, traction, and winding by the cooling air ring, a polymer fruit and vegetable preservation bag is obtained. Example 5

[0038] Example 5 provides a polymer fruit and vegetable preservation bag.

[0039] The difference between the above embodiment and embodiment 3 is that the particle size of the nano-silica is 30-50nm. Example 6

[0040] Example 6 provides a polymer fruit and vegetable preservation bag.

[0041] The difference between the above embodiment and embodiment 3 is that the particle size of the nano-silica is 70-80nm. Example 7

[0042] Example 7 provides a polymer fruit and vegetable preservation bag.

[0043] The difference between the above embodiment and embodiment 3 is that the amount of chitosan / cellulose nanocrystal composite microspheres added is 50g. Example 8

[0044] Example 8 provides a polymer fruit and vegetable preservation bag.

[0045] The difference between the above embodiment and embodiment 3 is that the amount of chitosan / cellulose nanocrystal composite microspheres added is 100g. Example 9

[0046] Example 9 provides a polymer fruit and vegetable preservation bag.

[0047] The difference between the above embodiment and embodiment 3 is that the amount of chitosan / cellulose nanocrystal composite microspheres added is 130g. Example 10

[0048] Example 10 provides a polymer fruit and vegetable preservation bag.

[0049] The difference between the above embodiment and embodiment 3 is that the amount of chitosan / cellulose nanocrystal composite microspheres added is 150g. Example 11

[0050] Example 11 provides a polymer fruit and vegetable preservation bag.

[0051] The difference between the above embodiment and embodiment 3 is that the amount of polyethylene added is 300g and the amount of ethylene-vinyl acetate copolymer added is 500g. Example 12

[0052] Example 12 provides a polymer fruit and vegetable preservation bag.

[0053] The difference between the above embodiment and embodiment 3 is that the amount of polyethylene added is 500g and the amount of ethylene-vinyl acetate copolymer added is 400g. Comparative Example 1

[0054] Comparative Example 1 provides a polymer fruit and vegetable preservation bag.

[0055] The difference between the above comparative example and Example 3 is that the chitosan / cellulose nanocrystal composite microspheres were replaced with an equal amount of chitosan. Comparative Example 2

[0056] Comparative Example 2 provides a polymer fruit and vegetable preservation bag.

[0057] The difference between the above comparative example and Example 3 is that the chitosan / cellulose nanocrystal composite microspheres are replaced with an equal amount of cellulose nanocrystals. Comparative Example 3

[0058] Comparative Example 3 provides a polymer fruit and vegetable preservation bag.

[0059] The difference between the above comparative example and Example 3 is that the amount of chitosan / cellulose nanocrystal composite microspheres added is 0. Comparative Example 4

[0060] Comparative Example 4 provides a polymer fruit and vegetable preservation bag.

[0061] The difference between the above comparative example and Example 3 is that, in the preparation of chitosan / cellulose nanocrystal composite microspheres, the amount of cellulose nanocrystal aqueous dispersion added is 15 mL, and the weight ratio of chitosan to cellulose nanocrystals is 2:0.3. Comparative Example 5

[0062] Comparative Example 5 provides a polymer fruit and vegetable preservation bag.

[0063] The difference between the above comparative example and Example 3 is that, in the preparation of chitosan / cellulose nanocrystal composite microspheres, the amount of cellulose nanocrystal aqueous dispersion added is 100 mL, and the weight ratio of chitosan to cellulose nanocrystals is 1:1. Comparative Example 6

[0064] Comparative Example 6 provides a polymer fruit and vegetable preservation bag.

[0065] The difference between the above comparative example and Example 3 is that the ethylene-vinyl acetate copolymer is replaced with an equal amount of polyethylene. Comparative Example 7

[0066] Comparative Example 7 provides a polymer fruit and vegetable preservation bag.

[0067] The difference between the above comparative example and Example 3 is that polyethylene is replaced with an equal amount of ethylene-vinyl acetate copolymer. Comparative Example 8

[0068] Comparative Example 8 provides a polymer fruit and vegetable preservation bag.

[0069] The difference between the above comparative example and Example 3 is that the ethylene-vinyl acetate copolymer was replaced with an equal amount of polylactic acid. Performance testing

[0070] The performance of the polymer fruit and vegetable preservation bags obtained in Examples 1-12 and Comparative Examples 1-8 was tested, and the results are shown in Table 1 below.

[0071] (1) CO2 / O2 transmittance ratio: The CO2 transmittance and O2 transmittance of the packaging material were measured separately, and then the CO2 / O2 transmittance ratio was calculated according to the following formula: CO2 / O2 transmission rate ratio = CO2 transmission rate / O2 transmission rate × 100% The CO2 and O2 permeability were both measured using a GTR-721 thin-film differential pressure gas permeator, with the measurement method conforming to GB 1038.

[0072] (2) Prepare three-sided sealed polymer fruit and vegetable preservation bags with an external size of 22×25 cm according to each example. Put 500g of cherries into each preservation bag, tie the bag tightly, and store them in an environment of 25±5℃. Collect the gas inside the bag at 1d, 7d and 15d respectively, and use a gas chromatograph to detect the ethylene concentration in the gas inside the preservation bag; and record the rotten fruit rate of cherries in each preservation bag at 15g.

[0073] Table 1. Performance test results of polymer fruit and vegetable preservation bags in Examples 1-12 and Comparative Examples 1-8

[0074] According to the test results in Table 1, the CO2 / O2 permeability ratio of the polymer fruit and vegetable preservation bags provided in Examples 1-12 of this application is (3.1-3.8):2. When used for cherry packaging and preservation, the 15-day rot rate is only 15.4-23.2%. In contrast, the polymer fruit and vegetable preservation bags provided in Comparative Examples 1-8 have a 15-day rot rate as high as 35.6-50.5% when used for cherry packaging and preservation. Therefore, this application uses polyethylene and ethylene-vinyl acetate copolymer as the matrix, and by adding components such as chitosan / cellulose nanocrystal composite microspheres and nano-silica, it is possible to obtain a fruit and vegetable preservation bag that matches the respiration characteristics of cherries and can efficiently adsorb ethylene substances produced by fruits and vegetables. When used for cherry preservation, it can effectively slow down the metabolism of cherries and extend their shelf life.

[0075] Although the present invention has been described in detail above with general descriptions and specific embodiments, modifications or improvements can be made to it, which will be obvious to those skilled in the art. Therefore, all such modifications or improvements made without departing from the spirit of the present invention fall within the scope of protection claimed by the present invention.

Claims

1. A polymer fruit and vegetable fresh-keeping bag, characterized in that, The raw materials include the following components by weight: polyethylene 30-50 parts, ethylene-vinyl acetate copolymer 40-50 parts, chitosan / cellulose nanocrystal composite microspheres 5-15 parts, nano-silica 2-5 parts, antioxidant 0.2-0.5 parts, and lubricant 0.5-1 part; In the chitosan / cellulose nanocrystal composite microspheres, the weight ratio of chitosan to cellulose nanocrystal is 2: (0.8-1.5).

2. The polymer fruit and vegetable fresh-keeping bag according to claim 1, characterized in that, The particle size of the chitosan / cellulose nanocrystal composite microspheres is 30-50 nm.

3. The polymer fruit and vegetable fresh-keeping bag according to claim 1, characterized in that, The polyethylene has a melt index of 0.3-0.5 g / 10 min; and the ethylene-vinyl acetate copolymer has a melt index of 0.5-0.7 g / 10 min.

4. The polymer fruit and vegetable fresh-keeping bag according to claim 1, characterized in that, The nano-silica has a particle size of 10-80 nm.

5. The polymeric fruit and vegetable preservative bag according to claim 1, wherein The high-molecular fruit and vegetable preservative bag has a thickness of 20-25 µm.

6. The polymeric fruit and vegetable preservative bag according to claim 1, wherein The high-molecular fruit and vegetable preservative bag has an O2 / CO2 permeability ratio of (3-4):

1.

7. The polymeric fruit and vegetable preservative bag according to claim 1, wherein The antioxidant is antioxidant 1010 and / or antioxidant 168; and the lubricant is erucic acid amide and / or oleic acid amide.

8. The method for preparing the polymer fruit and vegetable preservation bag according to any one of claims 1-7, characterized in that, The method includes the following steps: First, the polyethylene and ethylene-vinyl acetate copolymer are premixed at high speed, then the chitosan / cellulose nanocrystal composite microspheres and nano-silica are added and uniformly mixed to obtain a blended material; The blended material is melt-extruded, water-cooled, and pelletized to obtain a preservative bag master batch; The preservative bag master batch is blown into a film, cooled by a cooling air ring, pulled, and wound to obtain a high-molecular fruit and vegetable preservative bag.

9. The method for preparing the polymer fruit and vegetable preservation bag according to claim 8, characterized in that, During the melt-extrusion process, the extrusion temperature is set as follows: zone 1, 135-145°C; zone 2, 145-155°C; zone 3, 155-165°C; zone 4, 165-175°C; and die head, 160-170°C; and the screw rotation speed is 250-350 r / min.

10. The method for preparing the polymer fruit and vegetable preservation bag according to claim 8, characterized in that, During the film blowing process, the extrusion temperature is set as follows: zone 1, 145-155°C; zone 2, 155-165°C; zone 3, 165-175°C; and die head, 160-170°C; the blow-up ratio is 2.5-3.0; and the pulling speed is 30-40 m / min.

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