A breathable and environmentally friendly fresh-keeping bag for fruits and vegetables and its preparation method

Abstract

The present application discloses a breathable and environmentally friendly fresh-keeping bag for fruits and vegetables and a preparation method thereof, relating to the technical field of packaging bags. The fresh-keeping bag for fruits and vegetables is composed of a composite plastic and graphene; the graphene is nano-graphene with an average particle size of 100 nm; the fresh-keeping bag for fruits and vegetables is composed of the following components by weight percentage: 1-3% of graphene and 97-99% of composite plastic; the composite plastic is composed of polybutylene succinate, polylactic acid and clay; wherein, the clay is nano-clay, and the clay includes small-particle-size clay and large-particle-size clay; the particle size of the small-particle-size clay is 50 nm, and the particle size of the large-particle-size clay is 100-200 nm; the clay includes montmorillonite; it can achieve a higher carbon dioxide permeability rate, and protect the effective performance of graphene in a high-humidity environment, realize long-term effective action, and prevent the deterioration of fruits and vegetables caused by too high carbon dioxide concentration for fruits and vegetables with strong respiration.

Description

Technical Field

[0001] The present invention relates to the technical field of packaging bags, and in particular to a breathable and environmentally friendly fresh-keeping bag for fruits and vegetables and a preparation method thereof. Background Art

[0002] Perishable agricultural products have extremely high requirements for preservation technology. Their perishable and deteriorating characteristics after harvesting lead to a high loss rate in the post-harvest transportation and sales links, seriously restricting the development of the industry. Traditional preservation methods such as low-temperature refrigeration can only delay metabolism, but it is difficult to meet the fresh-keeping requirements for long-distance transportation and shelf life. Now, the modified atmosphere packaging technology is adopted, which effectively inhibits the respiration and microbial reproduction by adjusting the gas environment inside the package, and has become the key means to extend the fresh-keeping period.

[0003] For example, in Chinese Patent, Application No. CN202011167412.6, a fresh-keeping bag for fruits and vegetables with modified atmosphere and its preparation method and application are disclosed. The fresh-keeping bag for fruits and vegetables with modified atmosphere is mainly composed of polyethylene and graphene. By adding graphene to polyethylene, on the one hand, the strength of the fresh-keeping bag can be improved, and on the other hand, the pores of the fresh-keeping bag can be changed to enable it to have the ability to bidirectionally regulate the oxygen and carbon dioxide contents, ensure a suitable humidity inside the bag, effectively regulate the gas index, and achieve the effect of modified atmosphere fresh-keeping. It can keep litchi fresh at low temperature for 20 days with a good fruit rate of over 95%. In addition, the preparation method of the fresh-keeping bag for fruits and vegetables with modified atmosphere is simple and convenient for industrial production.

[0004] However, by only adding graphene as a nucleating agent to increase the crystallinity of the plastic material and reduce the free volume in the amorphous region, the diffusion rate of carbon dioxide is also inhibited, which easily leads to the accumulation of carbon dioxide inside the bag and poisons the fruits and vegetables. And in a high-humidity state, water molecules penetrate into the graphene interlayer, destroying its original structural order and reducing its stability, which easily leads to the failure of bidirectional regulation and ultimately loses the fresh-keeping function. Summary of the Invention

[0005] By providing a breathable and environmentally friendly fresh-keeping bag for fruits and vegetables and a preparation method thereof in the embodiments of the present application, the destruction of the stability of graphene in a high-humidity environment in the prior art is solved, and a long-term fresh-keeping effect is achieved.

[0006] The embodiments of the present application provide a breathable and environmentally friendly fresh-keeping bag for fruits and vegetables, which is composed of composite plastic and graphene; the graphene is nano-graphene with an average particle size of 100 nm;

[0007] The fresh-keeping bag for fruits and vegetables is composed of the following components in weight percentage: 1-3% of graphene and 97-99% of composite plastic;

[0008] The composite plastic is composed of polybutylene succinate, polylactic acid, and clay;

[0009] Among them, the clay is nano-clay, including montmorillonite, and the clay includes small-particle-size clay and large-particle-size clay; the particle size of the small-particle-size clay is 50 nm, and the particle size of the large-particle-size clay is 100 - 200 nm.

[0010] Furthermore, the total of polybutylene succinate and polylactic acid in the composite plastic accounts for 94% - 98% of the total weight of the composite plastic; the mass of the clay accounts for 1% - 3% of the total weight of the composite plastic.

[0011] Furthermore, the mass ratio of polybutylene succinate to polylactic acid is 7:3.

[0012] Furthermore, the mass ratio of the small-particle-size clay to the large-particle-size clay is 2:1.

[0013] Furthermore, the clay is divided into tubular clay and flaky clay.

[0014] Furthermore, the tubular clay is prepared from clay particles and AlCl₃·6H₂O; the specific preparation process is as follows: taking the clay particles as the silicon source and AlCl₃·6H₂O as the aluminum source, mixing them according to a silicon:aluminum molar ratio of 1:1, dispersing the mixture in water, and adjusting the slurry concentration to 10 wt%; reacting at 180 °C for 48 h, centrifuging, washing, and drying, then stirring in 1 mol / L HCl at 60 °C for 2 h to remove the unreacted montmorillonite, and then obtaining the crude tubular clay through high-temperature calcination;

[0015] Disperse the crude tubular clay in toluene, add 3-aminopropyltriethoxysilane, use triethylamine as the catalyst, and stir under a nitrogen atmosphere at 80 °C for 24 hours; wash successively with ethanol and deionized water, and dry in vacuum at 50 °C to obtain the tubular clay.

[0016] Furthermore, the fresh-keeping bag has a double-layer film, and the laminated composite double-layer film is used. The inner and outer layer structures of the double-layer film are different, and carbon dioxide gas is filled in the middle.

[0017] Furthermore, the outer layer adopts the combination of resin + graphene + flaky clay, and the inner layer adopts the combination of resin + graphene + tubular clay. Carbon dioxide gas is filled between the two layers, and the concentration of carbon dioxide in the filled gas is 10% - 20%.

[0018] The preparation method of the above-mentioned breathable and environmentally friendly fresh-keeping bag for fruits and vegetables includes the following steps:

[0019] S1. Mix the composite plastic and graphene in a high-speed disperser, and then put them into a twin-screw granulator, and make them into particles after passing through temperature zones of 130 °C, 140 °C, 150 °C, and 160 °C in sequence;

[0020] S2. After extruding the particles at 160 - 170 °C through an extruder, they are then successively processed through blow molding, cooling, pinching, traction, and rolling out to form a film, and finally a fresh - keeping bag for fruits and vegetables with specifications of 43 cm × 38.1 cm × 10 μm is made.

[0021] One or more technical solutions provided in the embodiments of the present application have at least the following technical effects or advantages:

[0022] First, the key to fruit and vegetable freshness preservation is low oxygen and high carbon dioxide, but too high carbon dioxide is also harmful. Therefore, it is necessary to reduce oxygen as much as possible and maintain an appropriate carbon dioxide concentration. By using the combination of graphene and clay, the oxygen permeability is reduced, the carbon dioxide permeability is increased, and the wet stability of graphene is improved.

[0023] Second, the combination of small - particle - size clay and large - particle - size clay can form a combined effect of small - particle - size adsorption and large - particle - size transportation, increasing the CO2 transportation ability while complicating the barrier network.

[0024] Third, by preparing clay particles into tubular clay particles and performing amination treatment, the adsorption ability is greatly improved, the water - retaining ability is enhanced, the diffusion path is optimized, and the cycle stability is increased.

[0025] Fourth, through multi - layer combination, the outer layer blocks oxygen and the inner layer permeates CO2. Combined with initial inflation, a low - oxygen environment is quickly established, humidity is synergistically controlled, and the risks of water loss and mildew of fruits and vegetables are reduced. Detailed implementation manners

[0026] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by those skilled in the technical field to which this invention belongs; the terms used in the specification of this invention are only for the purpose of describing specific implementation manners and are not intended to limit the present invention; the term "and / or" used herein includes any and all combinations of one or more of the related listed items.

[0027] Example 1: The present application provides a breathable and environmentally friendly fresh - keeping bag for fruits and vegetables, and the fresh - keeping bag is composed of composite plastic and graphene;

[0028] The graphene is nano - graphene; the average particle size is 100 nm;

[0029] The composite plastic is composed of polybutylene succinate (PBS), polylactic acid (PLA), and clay;

[0030] The clay is nano - clay, with a particle size of 50 - 200 nm; the clay includes montmorillonite;

[0031] The fruit and vegetable fresh-keeping bag is composed of the following components in percentage by weight: 1-3% of graphene and 97-99% of composite plastic;

[0032] In the composite plastic, the total of PBS and PLA accounts for 94%-98% of the total weight of the composite plastic; the mass ratio of PBS to PLA is 7:3, and the mass of clay accounts for 1-3% of the total weight of the composite plastic;

[0033] The preparation method of the fruit and vegetable fresh-keeping bag includes the following steps:

[0034] S1. Mix the composite plastic and graphene in a high-speed disperser, and then put them into a twin-screw granulator, and make them into particles after passing through temperature zones of 130°C, 140°C, 150°C, and 160°C in sequence;

[0035] S2. After extruding the particles at 160-170°C through an extruder, then form a film through processes of blow molding, cooling, pinching, traction, and rolling out in sequence, and finally make a fruit and vegetable fresh-keeping bag with specifications of 43 cm × 38.1 cm × 10 μm (length, width, and thickness).

[0036] The technical solutions in the embodiments of the present application above have at least the following technical effects or advantages:

[0037] The key in fruit and vegetable preservation is low oxygen and high carbon dioxide, but too high carbon dioxide is also harmful. Therefore, it is necessary to reduce the oxygen concentration as much as possible and maintain an appropriate carbon dioxide concentration;

[0038] By combining graphene and clay; reducing the oxygen permeability, increasing the carbon dioxide permeability, and improving the wet stability of graphene;

[0039] The structure of graphene has a nano-sheet barrier effect, and the O2 molecule is small and non-polar, and it depends more on the free volume diffusion path. The graphene sheet layer hinders it more significantly, reducing the O2 permeability. There are a small amount of oxygen-containing groups on the surface of graphene, forming a micro-region polar interface with the non-polar chain segments of PBS, preferentially adsorbing CO2 and water molecules, thus selectively capturing and releasing CO2, and finally forming a dynamic balance. Graphene reduces the free volume in the amorphous region, further inhibiting gas diffusion; while the polarity of CO2 enables it to diffuse through the interface region, and the decrease in permeability is less than that of O2 and is less affected;

[0040] Clay is a layered silicate, and the surface of the lamellae is rich in polar hydroxyl groups (-OH). It forms a multi-level barrier network with graphene, which has the same effect as graphene in terms of oxygen barrier and carbon dioxide permeation. It can also form a gradient interface with the polarity difference of graphene, enhancing the affinity for CO2 while maintaining a high barrier to O2. Through the gradient design of the polar interface (clay) and the non-polar lamellae (graphene), the reverse regulation of the O2 / CO2 permeability is achieved, which is suitable for the fresh-keeping needs of fruits and vegetables with high respiration intensity;

[0041] Using graphene and clay in combination forms a three-dimensional porous structure, which can prevent the shrinkage of pores and the leakage of liquid substances, and also endows the material with excellent adsorption properties. As the clay content increases, the surface of the hybrid material becomes rougher, but the overall stability of the porous structure is maintained, and it still has good structural stability in multiple high-humidity cold-hot cycle experiments;

[0042] PBS is a degradable plastic material with good toughness and degradability. It can be decomposed into harmless substances in the natural environment, providing flexibility and tensile strength. PLA is a biodegradable plastic made from renewable plant raw materials, increasing stiffness and hardness; PBS and PLA have good complementarity. The addition of PBS can improve the flexibility and impact strength of PLA, making it more suitable for application fields such as packaging materials and single-use products. The addition of PLA can improve the rigidity and processing performance of PBS, enhancing the overall performance of the material; Clay can provide attachment points for microorganisms in the soil degradation environment, promoting biodegradation. The non-polar segments of PBS form microdomain dispersion with the polar interface of clay, inhibiting aggregation.

[0043] For the fresh-keeping bag material prepared in Example 1, use a gas permeation instrument (ASTM D1434 standard) to measure the permeabilities of O2 and CO2 at 25°C. The results are shown in Table 1 and Table 2;

[0044] According to GB / T 2423.34, conduct a temperature / humidity combined cycle test. The high-temperature stage (2h) of the temperature cycle is 60°C and 95% humidity, the low-temperature stage (1h) is -10°C, and the cooling rate is 1.5°C / min. Cycle 10 times; The results are shown in Table 3;

[0045] Table 1

[0046] ;

[0047] Table 2

[0048] ;

[0049] Table 3

[0050] ;

[0051] The use of the combination of graphene and clay increases the permeability to carbon dioxide and reduces the oxygen permeability, which can reduce the accumulation of carbon dioxide in the packaging bag environment and further prevent oxygen from entering and aerobic respiration, facilitating the packaging of fruits and vegetables with a relatively high respiration intensity. The temperature and humidity cycle causes partial relaxation of the amorphous region and a slight increase in free volume, but the graphene-clay network still effectively inhibits gas diffusion.

[0052] Example 2: In the above example, by using a degradable plastic and combining it with clay and graphene, a degradable and moisture-resistant packaging bag for fruits and vegetables is obtained. Based on Example 1, it is further improved for the process of differential adsorption and transport by dividing the work of clay particles.

[0053] The clay includes small-particle-size clay and large-particle-size clay; the particle size of the small-particle-size clay is 50 nm, the particle size of the large-particle-size clay is 200 nm, and the mass ratio of the small-particle-size clay to the large-particle-size clay is 2:1.

[0054] The technical solutions in the embodiments of the present application at least have the following technical effects or advantages:

[0055] The combination of small-particle-size clay and large-particle-size clay can form a combined effect of small-particle-size adsorption and large-particle-size transport, increasing the CO2 transport capacity while complicating the barrier network;

[0056] The small-particle-size clay is rich in hydroxyl groups (-OH) and cations on its surface. It preferentially captures CO2 molecules through polar adsorption and hydrogen bond interactions to form a locally high-concentration region. The surface charge distribution of the small-particle-size clay is uneven, enhancing the electrostatic adsorption of CO2. Also, the small-particle-size clay is easily adsorbed around the large-particle-size clay, forming CO2 agglomerated around the small-particle-size particles and the small-particle-size particles agglomerated around the large-particle-size particles. The large-particle-size particles form a structure with an expanded interlayer spacing through intercalation or exfoliation, providing a fast diffusion path for CO2, reducing the diffusion resistance, filling the amorphous region of the matrix, reducing the free volume, and inhibiting the non-polar diffusion of O2. The combination of the two, the small-particle-size clay adsorbs CO2 and then transports and diffuses it through the large-particle-size clay. And the hydrophobic surface of graphene and the polar interface of the small-particle clay form a dynamic CO2 transport chain, further optimizing the CO2 transport path.

[0057] Small-sized particles agglomerate around large-sized particles and compete with graphene for water molecule adsorption. The interlayer cations of clay have a stronger adsorption capacity than graphene (especially small-sized clay). While increasing the adsorption of water molecules, it also increases the polarity, resulting in an increase in the adsorption capacity of carbon dioxide. During the extrusion blow molding process, the clay platelets are oriented along the flow direction, forming a layered barrier structure. The clay platelets are evenly dispersed in the matrix (especially large-sized clay), wrapping graphene in a "pocket", blocking the water penetration path, reducing the contact between graphene and water molecules. During the cooling process, the clay and the plastic matrix contract synchronously, closing the residual pores and enhancing the moisture resistance of graphene.

[0058] For the plastic material prepared in Example 2, a gas permeation tester (ASTM D1434 standard) was used to measure the permeabilities of O2 and CO2 at 25 °C. The results are shown in Table 4;

[0059] According to GB / T 2423.34, a temperature / humidity combined cycle test was carried out. The high-temperature stage (2 h) of the temperature cycle was 60 °C and 95% humidity, the low-temperature stage (1 h) was -10 °C, and the cooling rate was 1.5 °C / min. The cycle was carried out 10 times; the results are shown in Table 5;

[0060] Table 4

[0061] ;

[0062] Table 5

[0063] ;

[0064] Example 3: The combination of clays with different particle sizes in Example 2 not only increases the adsorption and transport capacity of carbon dioxide, taking into account both the adsorption capacity and the channel continuity, but also further improves the stability of graphene under high humidity conditions. To improve the interlayer spacing of the clay and optimize the transmission path, further improvements were made.

[0065] The clay was modified and then aminated to obtain tubular clay. Specifically:

[0066] Montmorillonite was used as the silicon source and AlCl3·6H2O was used as the aluminum source. They were mixed according to a silicon:aluminum molar ratio of 1:1. The mixture was dispersed in water, and the slurry concentration was adjusted to 10 wt%. The reaction was carried out at 180 °C for 48 h, followed by centrifugation, washing, and drying. Then, it was stirred in 1 mol / L HCl at 60 °C for 2 h to remove the unreacted montmorillonite, and then calcined at high temperature (500 °C / 2 h) to obtain the crude tubular clay;

[0067] The crude tubular clay was dispersed in toluene, 3-aminopropyltriethoxysilane was added, and triethylamine was used as the catalyst. It was stirred under a nitrogen atmosphere at 80 °C for 24 hours; washed successively with ethanol and deionized water, and dried under vacuum at 50 °C to obtain the tubular clay.

[0068] The technical solutions in the embodiments of the present application at least have the following technical effects or advantages:

[0069] By preparing clay particles into tubular clay particles and performing amination treatment, the adsorption capacity is greatly improved, the water retention capacity is enhanced, the diffusion path is optimized, and the cycle stability is increased.

[0070] Montmorillonite is a flaky clay that forms a dense barrier network and has strong barrier properties against O2, but has limitations in the adsorption and transport effect of CO2. By preparing tubular clay particles with a hollow tube shape (diameter 20 - 50 nm, length 200 - 1000 nm) to form a directional channel, CO2 can rapidly diffuse along the lumen, which can greatly improve the permeability and increase the diffusion rate of CO2 molecules in the nanotubes. Then, through amination modification, its adsorption capacity for carbon dioxide is further increased. Small-sized tubular clay has a high surface energy and strong water absorption capacity. After aggregating on the surface of large-sized tubular clay particles, the aggregates form a core-shell structure, with the outer layer becoming densified, and the internal pores inhibit the penetration of liquid water due to capillary action, preventing water molecules from leaking out and reducing the contact area between water molecules and graphene;

[0071] Small-sized tubular clay particles are prone to entanglement and aggregation by themselves, reducing the CO2 transmission efficiency. However, the binding degree between graphene and aminated tubular clay increases. Flaky graphene is more likely to insert into the gaps between aggregated tubular clay, preventing aggregation through steric hindrance. Moreover, graphene has a hydrophobic surface, which can reduce the interfacial energy of the mixed system and reduce the driving force for aggregation. The sp 2 hybrid carbon network can form weak interactions with the oxygen atoms in the silicon-oxygen tetrahedral layer on the outer surface of the tubular clay, increasing the adsorption capacity. The addition of graphene reduces the viscosity of the dispersion system, improves fluidity, and inhibits the formation of aggregates;

[0072] For the plastic material prepared in Example 3, a gas permeation tester (ASTM D1434 standard) was used to measure the permeabilities of O2 and CO2 at 25°C. The results are shown in Table 6; among them, the tubular clay is the aminated tubular clay obtained by tubular modification and amination of the multi-particle size combination group in Example 2; the flaky clay is the clay of the multi-particle size combination used in Example 2;

[0073] According to GB / T 2423.34, a temperature / humidity combined cycle test was carried out. The high-temperature stage (2 h) of the temperature cycle was 60°C and 95% humidity, the low-temperature stage (1 h) was -10°C, and the cooling rate was 1.5°C / min. The cycle was carried out 10 times; the results are shown in Table 7;

[0074] Table 6

[0075] ;

[0076] Table 7

[0077] ;

[0078] Example 4: Based on Example 3, by using tubular clay, the ability to transport carbon dioxide is greatly enhanced, and the structure of the plastic fresh-keeping bag is further improved for overall optimization.

[0079] The fresh-keeping bag has a double-layer film;

[0080] The double-layer film is a double-layer film made by lamination. The inner and outer layers of the double-layer film have different structures. Specifically:

[0081] The outer layer adopts a combination of resin + graphene + flaky clay, and the inner layer adopts a combination of resin + graphene + tubular clay. Carbon dioxide gas is filled between the two layers, and the concentration of carbon dioxide in the filled gas is 10-20% (this concentration is the concentration of carbon dioxide in the filled gas).

[0082] The technical solutions in the embodiments of the present application at least have the following technical effects or advantages:

[0083] Through multi-layer combination, the outer layer blocks oxygen and the inner layer permeates CO2. Combining with initial inflation, a low-oxygen environment is quickly established, and humidity is synergistically controlled to reduce the risk of water loss and mildew of fruits and vegetables.

[0084] The flaky clay and graphene form a dense network, significantly reducing the oxygen permeability rate, blocking the entry of external oxygen, and also reducing the penetration of external water vapor to keep the humidity inside the bag stable; the hollow channels and amino-functionalized modification of the tubular clay enhance the carbon dioxide adsorption and diffusion ability. Carbon dioxide gas is added to the interlayer, and the concentration difference is used to control the carbon dioxide concentration inside the bag. After a large amount of carbon dioxide is generated, it promotes the external discharge of CO2 inside the bag to avoid excessive concentration; moreover, the polar surface of the tubular clay adsorbs water molecules to reduce the water loss of fruits and vegetables, which not only ensures the humidity of fruits and vegetables to prevent water loss, but also protects graphene from reducing its function due to high humidity; when fruits and vegetables are just put into the bag, inflation can directly reduce the O2 concentration inside the bag, inhibit the aerobic respiration of fruits and vegetables, and reduce metabolic consumption.

[0085] Taking apples as an example, in an environment with a low oxygen content, the anaerobic respiration of apples is still relatively strong, producing carbon dioxide and alcohol; in a moisturized state, the appearance of the respiration peak is postponed, which is beneficial to reducing respiration.

[0086] The fresh-keeping bags for fruits and vegetables prepared in Example 4 were tested for fresh-keeping effect. Specifically: The apples of the same batch without damage and with good appearance collected from Yantai, Shandong were put into the fresh-keeping bags for fruits and vegetables (two in each bag). After tying the bag mouths tightly, they were stored at 1-3°C. After 100 days, the browning rate and the good fruit rate were measured; the results are shown in Table 8;

[0087] Table 8

[0088] ;

[0089] The above are only the preferred embodiments of the present invention and are not intended to limit the present invention. For those skilled in the art, various modifications and variations can be made to the present invention. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included within the protection scope of the present invention.

Claims

1. A breathable and environmentally friendly fruit and vegetable fresh-keeping bag, characterized in that: The fruit and vegetable fresh-keeping bag is composed of composite plastic and graphene; the graphene is nanographene; the average particle size is 100nm; The fruit and vegetable fresh-keeping bag is composed of the following components in percentage by weight: 1-3% graphene and 97-99% composite plastic; The composite plastic is composed of polybutylene succinate, polylactic acid and clay; Among them, the clay is nano clay, including montmorillonite, and the clay includes small-particle clay and large-particle clay; the particle size of small-particle clay is 50nm, the particle size of large-particle clay is 100-200nm, the mass ratio of small-particle clay to large-particle clay is 2:1, and the clay is divided into tubular clay and flaky clay.

2. A breathable and environmentally friendly fruit and vegetable fresh-keeping bag as claimed in claim 1, characterized in that: In the composite plastic, the polybutylene succinate and polylactic acid together account for 94%-98% of the total weight of the composite plastic; and the mass of clay accounts for 1-3% of the total weight of the composite plastic.

3. A breathable and environmentally friendly fruit and vegetable fresh-keeping bag as claimed in claim 2, characterized in that: The mass ratio of polybutylene succinate:polylactic acid is 7:

3.

4. A breathable and environmentally friendly fruit and vegetable fresh-keeping bag as claimed in claim 1, characterized in that: The tubular clay is prepared by modifying clay particles and AlCl3·6H2O and then aminated. The specific preparation process is as follows: clay particles are used as silicon source and AlCl3·6H2O is used as aluminum source, mixed in a silicon:aluminum molar ratio of 1:1, the mixture is dispersed in water, and the slurry concentration is adjusted to 10wt%; reacted at 180°C for 48h, centrifuged, washed, dried, and then stirred in 1mol / L HCl at 60°C for 2h to remove unreacted montmorillonite, and then calcined at high temperature to obtain a crude tubular clay; The crude tubular clay was dispersed in toluene, 3-aminopropyltriethoxysilane was added, triethylamine was used as a catalyst, and the mixture was stirred at 80° C. for 24 hours under a nitrogen atmosphere; the mixture was washed with ethanol and deionized water in sequence, and vacuum dried at 50° C. to obtain tubular clay.

5. A breathable and environmentally friendly fruit and vegetable fresh-keeping bag as claimed in claim 4, characterized in that: The fresh-keeping bag has a double-layer film, which uses a laminated composite double-layer film. The inner and outer layers of the double-layer film have different structures and are filled with carbon dioxide gas in the middle.

6. A breathable and environmentally friendly fruit and vegetable fresh-keeping bag as claimed in claim 5, characterized in that: The outer layer uses a combination of resin + graphene + flaky clay, and the inner layer uses a combination of resin + graphene + tubular clay. Carbon dioxide gas is filled between the two layers, and the concentration of carbon dioxide in the filled gas is 10-20%.

7. A method for preparing a breathable and environmentally friendly fruit and vegetable fresh-keeping bag according to any one of claims 1 to 6, characterized in that: The preparation method comprises the following steps: S1, mixing the composite plastic and graphene in a high-speed disperser, and then putting them into a twin-screw granulator, and then passing through the temperature zones of 130°C, 140°C, 150°C, and 160°C to form granules; S2. The particles are extruded through an extruder at 160-170°C, and then film-formed through blow molding, cooling, clamping, pulling, and rolling processes in sequence, and finally made into fruit and vegetable fresh-keeping bags with specifications of 43cm×38.1cm×10μm.