Food packaging material with high barrier property and preparation method and application thereof

Abstract

The application provides a high-barrier food packaging material and a preparation method and application thereof. The high-barrier food packaging material comprises at least one functional layer, and the functional layer comprises a hydroxyl-containing vinyl polymer and modified nanosheet layer material. The modified nanosheet layer material is modified by a polyphenol hydroxyl compound and a citrate. The nanosheet layer material is modified by the synergistic effect of the polyphenol hydroxyl compound and the citrate, the dispersibility of the nanosheet layer material in the polymer matrix is improved, the gas permeation path is prolonged, the barrier effect retention rate of the material in a wet environment is improved, in addition, the material also has an oxygen removal function, the shelf life of food can be effectively prolonged, and the material is suitable for the field of food packaging with high preservation requirements.

Description

Technical Field

[0001] This application relates to the field of food packaging technology, specifically to a high-barrier food packaging material, its preparation method, and its application. Background Technology

[0002] With the development of the food industry, the demand for food varieties and shelf life is increasing, leading to higher requirements for the oxygen barrier, moisture protection, oil resistance, water resistance, and shelf-life extension properties of food packaging materials. Although traditional polyolefin films such as polyethylene (PE) and polypropylene (PP) are inexpensive and easy to process, their oxygen barrier properties are limited, making it difficult to meet the packaging needs of long-shelf-life foods.

[0003] Currently, widely used high-barrier materials mainly include polyvinyl alcohol (PVA), ethylene-vinyl alcohol copolymer (EVOH), and polyvinylidene chloride (PVDC). EVOH and PVA are widely used in packaging materials; however, PVA / EVOH easily absorbs water and swells under high humidity conditions, leading to a decrease in barrier performance. Therefore, to improve barrier performance, researchers often use nanocomposite materials, such as graphene oxide nanosheets and montmorillonite, to physically block oxygen by extending the gas diffusion path. However, these materials are prone to agglomeration in the polymer matrix, reducing the overall performance of the material. Furthermore, this passive barrier method still allows for the slow penetration of trace oxygen molecules. Based on this, some researchers have added substances such as catechins and iron powder separately in small packets inside the packaging; however, placing oxygen-absorbing substances with food poses a risk of accidental ingestion.

[0004] Therefore, developing a new type of high-barrier food packaging material, and how to maintain the high barrier performance of PVA / EVOH while also maintaining its barrier performance in high humidity environments, and at the same time taking into account active oxygen removal function and intelligent recognition of packaging material status, has become a key technical issue in the design of high-performance food packaging materials. Summary of the Invention

[0005] This application provides a food packaging material with high barrier properties and its preparation method. It provides a barrier film with a functional layer of a composite material of hydroxyl-containing vinyl polymer and graphene oxide nanosheets, wherein alkylated catechol and citrate are used to modify the graphene oxide nanosheets. The aim is to provide a packaging material with oxygen barrier, oxygen removal and intelligent recognition functions, and to solve the problem of oxygen barrier function decline in high humidity environment.

[0006] In a first aspect, this application provides a food packaging material with high barrier properties, comprising an outer layer, an inner layer, and a functional layer disposed between the outer layer and the inner layer, wherein the functional layer comprises a hydroxyl-containing vinyl polymer and a modified nanosheet material, the modified nanosheet material being modified by a polyphenolic hydroxyl compound and a citrate.

[0007] According to this application, the functional layer of the food packaging material is based on a hydroxyl-containing vinyl polymer. By adding nanosheet materials, a certain layered distribution structure can be formed in the system, which can extend the gas permeation path and thus improve the material's barrier properties. At the same time, the modification with polyphenolic hydroxyl compounds can increase the compatibility between the nanosheet materials and the polymer matrix, reduce the aggregation of the nanosheet materials in the polymer matrix, and further improve the material's barrier properties. Furthermore, by modifying the surface of the nanosheets with citrate, metal ions can form coordination with the hydroxyl groups or polyphenolic hydroxyl compounds in the membrane, which can improve the interfacial bonding between the nanosheets and the polymer matrix.

[0008] Specifically, the hydroxyl-containing vinyl polymer is used as the main material. Its chain segments contain a large number of hydroxyl groups, which can form a dense hydrogen bond network, thereby extending the diffusion path of gas molecules in the membrane and having a certain barrier performance. At the same time, the hydroxyl groups serve as reaction sites in the membrane and can form hydrogen bond or esterification cross-linking networks with polyphenolic hydroxy compounds or citrates, reducing the swelling of the membrane in a wet state and the increase in the gas diffusion path.

[0009] Modified nanosheet materials can enhance membrane performance in multiple ways through their two-dimensional layered structure and surface modification. The layered arrangement of nanosheet materials within the polymer matrix can extend the diffusion path of gas molecules, forming a physical barrier and improving the membrane's barrier performance. Furthermore, through surface modification with polyphenolic hydroxyl compounds, hydrogen bonds or covalent bonds are formed between the nanosheet materials and polymer segments, enhancing the uniform dispersion of the nanosheet materials in the polymer matrix, reducing agglomeration, and thus improving the membrane's barrier performance. In addition, the surface of the nanosheet materials is modified with citrate, and the metal ions in the citrate can coordinate with the polyphenolic hydroxyl compounds to form a partially active antioxidant network inside the membrane, thereby further improving oxygen barrier performance.

[0010] By using hydroxyl-containing vinyl polymer hydrogen bond network barrier and modified nanosheet material for physical barrier, combined with polyphenolic hydroxyl compounds and citrate modification, this functional layer not only has high barrier performance, but also good resistance to humid environments and active oxygen removal capability. It solves the problem of oxygen barrier function decline in high humidity environments in existing technologies, and can be widely used in the food packaging field.

[0011] In some embodiments, the modified nanosheet material includes modified graphene oxide nanosheets, which are obtained by modifying graphene oxide nanosheets with polyphenolic hydroxyl compounds and citrate.

[0012] In some of the above embodiments, the modified nanosheet material obtained by modifying graphene oxide nanosheets has better compatibility and oxygen barrier properties. This may be because the surface of graphene oxide nanosheets has abundant carboxyl and hydroxyl functional groups, which provide a large number of reaction sites for polyphenolic hydroxyl compounds and citrates, thereby enhancing the interfacial bonding between the nanosheet material and the polymer matrix, promoting the uniform dispersion of the nanosheet material in the film, and improving the barrier performance.

[0013] In some embodiments, the polyphenolic hydroxy compound includes alkylated catechol.

[0014] In some of the above embodiments, alkylated catechol is used to modify graphene oxide nanosheets. On the one hand, the alkylated catechol molecules retain phenolic hydroxyl groups, which can react with oxygen molecules that permeate into the system to undergo redox reactions, consuming oxygen and thus removing trace oxygen molecules while preventing oxygen from entering. On the other hand, the introduced alkyl segments have a certain degree of hydrophobicity, which can reduce the hydrophilicity of the polymer matrix, slow down the swelling of the material in high humidity environments, and enhance the stability of the barrier properties. At the same time, alkylated catechol has polar groups and hydrophobic segments, which can promote the interfacial connection between the graphene oxide surface and the matrix, improve the dispersion of graphene oxide in the matrix, and further extend the gas permeation path.

[0015] In some embodiments, alkylated catechols are prepared by the following steps:

[0016] S10: Dissolve catechins and potassium carbonate in 20-40 mL of N,N-dimethylformamide to obtain a mixed solution of catechins, wherein the molar mass of catechins is 8-10 mmol and the molar mass of potassium carbonate is 16-20 mmol.

[0017] S11: Add bromododecane to the above catechol mixed solution, wherein the molar mass of bromododecane is 8~10 mmol, heat to 55~65℃, and react for 5~7 h;

[0018] S12: After the reaction is complete, the product is extracted three times with ethyl acetate. The organic phase obtained from the extraction is washed until neutral and dried to obtain the crude product.

[0019] S13: The crude product was dissolved in ethyl acetate and purified by column chromatography to obtain alkylated catechol.

[0020] In some embodiments, the citrate comprises cerium citrate and sodium ferrous citrate, wherein the mass ratio of cerium citrate to sodium ferrous citrate is 2 to 5:1.

[0021] In some of the above embodiments, the citrate comprises cerium citrate and sodium ferrous citrate. In this system, cerium ions can form a stable metal-polyphenol complex with the hydroxyl groups of alkylated catechol molecules. Electrons on the ligand shift towards the metal center, and electrons from the metal center also feed back to the antibonding orbitals of the ligand. This interaction lowers the bond energy of the OH bond on the catechol hydroxyl group, making it more susceptible to oxidation. When oxygen acts on this complex structure, cerium ions... 3+ As an electronic mediator, it oxidizes catechols to semiquinones or quinones, while simultaneously generating superoxide anions, Ce. 3+ It may be temporarily oxidized to Ce. 4+ However, it is rapidly reduced to Ce by the complexed polyphenolic hydroxyl compounds. 3+ This achieves localized catalytic cycling, thereby increasing the oxygen removal rate of polyphenolic hydroxyl compounds. Further addition of sodium ferrous citrate can further enhance the oxygen removal function. Ferrous ions can react with permeated oxygen to enhance the system's oxygen removal capacity. On the other hand, the citrate ligand can stabilize ferrous ions; when oxygen molecules enter, Fe... 2+ The reaction does not occur immediately. The polyphenolic hydroxyl compounds in the system are first oxidized. When the catechol antioxidant components in the system are exhausted, sodium ferrous citrate further reacts with the permeated oxygen, resulting in a visible color change accompanied by a change in the redox state, thus indicating that the packaging has expired, providing a smart indicator function. When using cerium citrate and sodium ferrous citrate within the above-mentioned ratio range, cerium citrate acts as the primary oxygen scavenger in the system, while sodium ferrous citrate plays an auxiliary role in oxygen scavenging and smart indicator functions after the polyphenolic hydroxyl compounds are exhausted. As an example, in one embodiment of this application, cerium citrate and sodium ferrous citrate in a mass ratio of 4:1 are used together as a citrate.

[0022] In some embodiments, the method for preparing the modified graphene oxide nanosheets includes the following steps:

[0023] S1: Disperse graphene oxide nanosheets in water to obtain a uniformly dispersed graphene oxide suspension.

[0024] S2: Add an aqueous solution of polyphenolic hydroxyl compound to a graphene oxide suspension to allow the polyphenolic hydroxyl compound to adsorb or covalently modify the surface of graphene oxide, thereby obtaining graphene oxide nanosheets modified with polyphenolic hydroxyl compound.

[0025] S3: The polyphenol hydroxyl compound-modified graphene oxide nanosheets obtained in step S2 are mixed with citrate, so that metal ions further modify the surface of graphene oxide through complexation or electrostatic interaction to obtain modified graphene oxide nanosheets.

[0026] In some of the above embodiments, through steps S1 to S3, polyphenolic hydroxyl compounds are first modified onto the surface of graphene oxide nanosheets to increase their compatibility with the polymer, reduce the aggregation of nanosheets in the film, and provide active sites to provide conditions for subsequent citrate complexation. Further addition of citrate modification forms a metal-polyphenolic hydroxyl complex network on the surface of graphene oxide nanosheets. The above modification not only improves the dispersibility and interfacial bonding of nanosheets in the polymer matrix, but also provides a certain active oxygen removal capability for the functional layer.

[0027] In some embodiments, the concentration of the graphene oxide suspension is 5~15 mg / mL.

[0028] In some of the above embodiments, using the above-mentioned concentration of graphene oxide suspension can fully disperse graphene oxide in the solution, adsorb polyphenolic hydroxyl compounds and complex metal ions, avoid agglomeration, and thus obtain uniform modified graphene oxide nanosheets.

[0029] In some embodiments, the concentration of the aqueous solution of the polyphenolic hydroxy compound is 2-10 mg / mL.

[0030] In some embodiments, the mass ratio of the graphene oxide suspension to the aqueous solution of the polyphenol hydroxyl compound is 1:0.2~0.8;

[0031] In some of the above embodiments, using the above-mentioned concentration of polyphenol hydroxyl compound aqueous solution and the above-mentioned mass ratio of graphene oxide suspension and polyphenol hydroxyl compound aqueous solution can provide better oxygen removal and oxygen barrier functions for graphene oxide nanosheets. Too low a concentration of polyphenol hydroxyl compound will reduce the oxygen removal efficiency of the system, while too high a concentration of polyphenol hydroxyl compound may affect the film formation efficiency of the system.

[0032] In some embodiments, the mass ratio of the polyphenol hydroxyl compound-modified graphene oxide nanosheets to citrate is 1:0.1 to 0.5. Based on the above embodiments, with the above-mentioned mass ratio of polyphenol hydroxyl compound-modified graphene oxide nanosheets and citrate, metal ions can form stable complexes with the surface of the polyphenol hydroxyl compound-modified graphene oxide nanosheets. As an example, in one embodiment of this application, a mass ratio of polyphenol hydroxyl compound-modified graphene oxide nanosheets and citrate is used.

[0033] In some embodiments, the functional layer further includes polypyrrole nanosheets and boron nitride nanosheets, wherein the mass ratio of the modified graphene oxide nanosheets, polypyrrole nanosheets and boron nitride nanosheets is 1:0.05~0.2:0.05~0.2.

[0034] In some of the above embodiments, the π-conjugated structure of the polypyrrole nanosheets can form an electron conduction network within the nanosheet layer. When the polyphenolic hydroxyl compound is oxidized to quinone by the permeating oxygen, electrons are released, Ce... 3+ / Ce 4+ When electrons are transferred back to the polyphenolic hydroxyl compounds, they can be reduced. Polypyrrole nanosheets can promote this electron cycle, thereby accelerating the regeneration rate of the polyphenolic hydroxyl compounds and enhancing their oxygen removal capacity. Simultaneously, the polypyrrole nanosheets dispersed in the nanosheet network enhance the interfacial bonding between the nanosheets and the polymer matrix, maintain the uniformity and integrity of the film structure, and form a semi-dense layer to further hinder oxygen diffusion. Boron nitride nanosheets, with their high diameter and low thickness, facilitate the formation of physical barrier pathways in the composite network, prolonging the oxygen permeation time in the functional layer and providing more reaction time for oxygen removal. Furthermore, the hydrophobicity of boron nitride nanosheets increases the hydrophobicity of the functional layer, making it less prone to water absorption, swelling, or hydrolysis, thus extending the lifespan of the oxygen barrier / removal function. Therefore, by adding polypyrrole nanosheets and boron nitride nanosheets to the system, the oxygen barrier and removal functions of the functional layer can be enhanced. Modified graphene oxide nanosheets serve as the main nanosheets, providing a barrier effect. Furthermore, their surface is modified with polyphenolic hydroxyl compounds and citrate, enhancing the oxygen removal function of the functional layer. Polypyrrole nanosheets provide an electronic conduction network within the nanosheet layer, promoting the redox cycle of polyphenolic hydroxyl compounds and improving oxygen removal efficiency. Boron nitride nanosheets provide additional physical barrier pathways in this system, extending oxygen permeation time. At the aforementioned mass ratio, a functional layer with balanced oxygen barrier and removal performance can be obtained.

[0035] In some embodiments, the graphene oxide nanosheets have a diameter of 1-10 μm and a thickness of 1-5 nm, while the boron nitride nanosheets have a diameter of 0.1-0.5 μm and a thickness of 1-5 nm. As an example, in one embodiment of this application, the graphene oxide nanosheets have a diameter of 4 μm and a thickness of 2 nm, while the boron nitride nanosheets have a diameter of 0.3 μm and a thickness of 1 nm.

[0036] In some embodiments, the polypyrrole nanosheets are prepared by the following method:

[0037] Add pyrrole, polyvinylpyrrolidone, and NaCl to 60 mL of ethanol solvent, where the molar concentration of pyrrole is 0.03~0.1 mol / L, the molar concentration of polyvinylpyrrolidone is 0.0005~0.005 mol / L, and the molar concentration of NaCl is 0.5~2 mol / L. Stir until completely dissolved, then add 10 mL of ferric chloride aqueous solution, where the molar concentration of ferric chloride is 0.1~0.3 mol / L. Heat and stir at 70~90℃ for 40~80 min.

[0038] In some embodiments, the outer layer comprises at least one of high-density polyethylene and metallocene polyethylene; the thickness of the outer layer is 10-500 μm. As an example, in one embodiment of this application, high-density polyethylene is used as the outer polymer substrate, and the outer layer thickness is 200 μm.

[0039] In some embodiments, the inner layer comprises at least one of high-density polyethylene and metallocene polyethylene; the thickness of the inner layer is 10-500 μm. In another embodiment, metallocene polyethylene is used as the inner layer polymer substrate, and the inner layer thickness is 200 μm.

[0040] In some embodiments, the high-density polyethylene has a weight-average molecular weight of 50,000 to 250,000 Da, and the metallocene polyethylene has a weight-average molecular weight of 100,000 to 200,000 Da. As an example, in one embodiment of this application, the high-density polyethylene used has a weight-average molecular weight of 215,000 Da, and the metallocene polyethylene used has a weight-average molecular weight of 140,000 Da.

[0041] In some embodiments, the thickness of the functional layer is 10-50 μm. Based on the above embodiments, selecting an appropriate functional layer thickness can reduce the amount of packaging material used and lower production costs while ensuring oxygen barrier function. As an example, in one embodiment of this application, a functional layer with a thickness of 20 μm is selected as the functional layer.

[0042] In some embodiments, the hydroxyl-containing vinyl polymer includes at least one of polyvinyl alcohol (PVA) and ethylene-vinyl alcohol copolymer. Each unit of PVA has -OH groups, which facilitates the interfacial bonding of polyphenolic hydroxyl compounds and metal ions; ethylene-vinyl alcohol copolymer has a lower hydroxyl density than PVA, but better moisture resistance and processability. The combination of the two can improve the material's resistance to moisture environments while providing a large number of hydroxyl groups. As an example, in one embodiment of this application, PVA and ethylene-vinyl alcohol copolymer in a mass ratio of 1:4 are used together as the hydroxyl-containing vinyl polymer.

[0043] In some embodiments, the polyvinyl alcohol has a weight-average molecular weight of 80,000 to 150,000 Da, the ethylene-vinyl alcohol copolymer has a weight-average molecular weight of 70,000 to 120,000 Da, and the ethylene content is 32 to 38 wt%. As an example, in one embodiment of this application, the polyvinyl alcohol used has a weight-average molecular weight of 100,000 Da, the ethylene-vinyl alcohol copolymer used has a weight-average molecular weight of 80,000 Da, and the ethylene content is 32 wt%.

[0044] In some embodiments, the mass ratio of the hydroxyl-containing vinyl polymer to the modified nanosheet material is 2 to 10:1.

[0045] In some of the above embodiments, the hydroxyl-containing vinyl polymer and the modified nanosheet material in the above mass ratio can maintain the continuity of the polymer matrix while having enough nanosheet material to form a better barrier network in the polymer matrix and prolong the oxygen diffusion path.

[0046] Secondly, this application provides a method for preparing a food packaging material with high barrier properties, comprising:

[0047] Provide raw materials comprising the outer layer, inner layer, and functional layer of the food packaging material according to any embodiment of the first aspect;

[0048] The raw materials contained in the outer layer, inner layer and functional layer are mixed and co-extruded to obtain a food packaging material with a three-layer co-extruded structure consisting of an outer layer, a functional layer and an inner layer.

[0049] According to this application, the method can prepare a food packaging material with high barrier properties in the first aspect, thus having the beneficial effects in the first aspect. The obtained food packaging material with high barrier properties has good oxygen barrier and oxygen removal properties.

[0050] Thirdly, this application provides a food packaging bag, including food packaging material prepared according to any embodiment of the first aspect or food packaging material prepared according to any embodiment of the second aspect.

[0051] According to this application, the high-barrier food packaging bag is used in the food packaging field. It has high barrier and oxygen removal properties, which can extend the shelf life of food. At the same time, the packaging material can indicate whether the barrier performance of the packaging material has failed, and has a certain intelligent indication function.

[0052] Compared with the prior art, the beneficial effects of this application are at least as follows:

[0053] 1. This application combines hydroxyl-containing vinyl polymers with modified nanosheet materials to further form a layered barrier structure inside the barrier material, which can prolong the diffusion path of oxygen inside the material and thus improve the oxygen barrier performance of the packaging material.

[0054] 2. Alkylated catechols and cerium citrate / sodium ferrous citrate are introduced, which can react with the permeated oxygen and consume trace amounts of oxygen molecules, thereby improving the material's oxygen removal capacity and further reducing oxygen permeation.

[0055] 3. By utilizing the hydrophobic segments of alkylated catechol, the layered structure of graphene oxide and boron nitride nanosheets, the hydrophobic properties of the functional layer are improved, the expansion of the functional layer in high humidity environments is reduced, thereby enhancing the stability of the barrier properties.

[0056] 4. After the polyphenolic hydroxyl compounds are consumed, the sodium ferrous citrate begins to oxidize and changes color, which can intuitively show the state of the packaging material and achieve a certain degree of intelligent identification. Detailed Implementation

[0057] The various embodiments or implementation schemes in this specification are described in a progressive manner, with each embodiment focusing on the differences from other embodiments.

[0058] In the description of this specification, the references to terms such as "one embodiment," "some embodiments," "illustrative embodiment," "example," "specific example," or "some examples," etc., refer to specific features, structures, materials, or characteristics described in connection with an implementation or example that are included in at least one implementation or example of this application. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same implementation or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more implementations or examples.

[0059] Furthermore, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of technical features indicated. Thus, a feature defined as "first" or "second" may explicitly or implicitly include at least one of that feature. In the description of this application, "multiple" means at least two, such as two, three, etc., unless otherwise explicitly specified.

[0060] In this specification, unless otherwise specified, "parts" refers to "parts by weight".

[0061] The following describes embodiments of this application. The embodiments described below are exemplary and are only used to explain this application, and should not be construed as limiting this application. Where specific techniques or conditions are not specified in the embodiments, they are performed according to the techniques or conditions described in the literature in this field or according to the product instructions. Reagents or instruments used, unless otherwise specified, are all conventional products that can be obtained commercially.

[0062] Polyvinyl alcohol, model 17-88, weight average molecular weight 100,000 Da;

[0063] Ethylene-vinyl alcohol copolymer, model F104B, ethylene content 32%, weight average molecular weight 80000 Da;

[0064] Graphene oxide nanosheets, with a diameter of 4 μm and a thickness of 2 nm;

[0065] Polypyrrole nanosheets were prepared as follows: Pyrrole, polyvinylpyrrolidone, and NaCl were added to 60 mL of ethanol solvent, wherein the molar concentration of pyrrole was 0.05 mol / L, the molar concentration of polyvinylpyrrolidone was 0.001 mol / L, and the molar concentration of NaCl was 1 mol / L. The mixture was stirred until completely dissolved, and then 10 mL of an aqueous solution of ferric chloride with a molar concentration of 0.3 mol / L was added. The mixture was heated and stirred at 80 °C for 60 min.

[0066] Boron nitride nanosheets, with a diameter of 0.3 μm and a thickness of 1 nm;

[0067] Catechol, CAS No.: 52936-64-8;

[0068] Bromododecane, CAS No.: 143-15-7;

[0069] Sodium ferrous citrate, CAS No.: 43160-25-4;

[0070] High-density polyethylene, model HTA108, weight-average molecular weight 215,000 Da;

[0071] Metallocene polyethylene, model EXCEED 2012RA, weight average molecular weight 140,000 Da;

[0072] Preparation Example 1

[0073] Preparation of modified nanosheet materials:

[0074] S1: Disperse 1 part by mass of graphene oxide in 100 parts by mass of water to obtain a graphene oxide suspension;

[0075] S2: Dissolve 2 parts by mass of catechol and 5 parts by mass of potassium carbonate in 28 parts by mass of N,N-dimethylformamide, then add 5 parts by mass of bromododecane. React at 60°C for 6 hours. After the reaction, extract three times with 50 mL of ethyl acetate. Combine the organic phases, wash with deionized water until neutral, and remove the solvent by rotary evaporation to obtain the crude product. Dissolve the crude product in 10 mL of ethyl acetate and purify by silica gel column chromatography to obtain a pale yellow solid, namely alkylated catechol. Disperse 1 part by mass of alkylated catechol in 100 parts by mass of water to prepare an aqueous solution of alkylated catechol.

[0076] S3: Add the alkylated catechol aqueous solution to the graphene oxide suspension, the mass ratio of the graphene oxide suspension to the alkylated catechol aqueous solution is 2:1, stir for 4 hours to obtain a polyphenol hydroxyl compound modified graphene oxide nanosheet suspension.

[0077] S4: Cerium citrate and sodium ferrous citrate are added to the suspension of graphene oxide nanosheets modified with polyphenolic hydroxyl compounds. The mass ratio of graphene oxide nanosheets modified with polyphenolic hydroxyl compounds, cerium citrate and sodium ferrous citrate is 1:0.08:0.02. After reacting for 2 hours, the mixture is filtered, washed and dried under vacuum to obtain the modified nanosheet material.

[0078] Preparation Example 2

[0079] Preparation of modified nanosheet materials:

[0080] S1: Disperse 1 part by mass of graphene oxide in 100 parts by mass of water to obtain a graphene oxide suspension;

[0081] S2: Disperse 1 part by mass of catechol in 100 parts by mass of water to obtain a catechol aqueous solution. Add the catechol aqueous solution to the graphene oxide suspension. The mass ratio of the graphene oxide suspension to the catechol aqueous solution is 2:1. Stir for 4 hours to obtain a polyphenol hydroxyl compound modified graphene oxide nanosheet suspension.

[0082] S3: Cerium citrate and sodium ferrous citrate are added to the suspension of graphene oxide nanosheets modified with polyphenolic hydroxyl compounds. The mass ratio of graphene oxide nanosheets modified with polyphenolic hydroxyl compounds, cerium citrate and sodium ferrous citrate is 1:0.08:0.02. After reacting for 2 hours, the mixture is filtered, washed and dried under vacuum to obtain the modified nanosheet material.

[0083] Preparation Example 3

[0084] Preparation of modified nanosheet materials:

[0085] S1: Disperse 1 part by mass of polypyrrole nanosheets in 100 parts by mass of water to obtain a polypyrrole nanosheet suspension;

[0086] S2: Dissolve 2 parts by mass of catechol and 5 parts by mass of potassium carbonate in 28 parts by mass of N,N-dimethylformamide, then add 5 parts by mass of bromododecane. React at 60°C for 6 hours. After the reaction, extract three times with 50 mL of ethyl acetate. Combine the organic phases, wash with deionized water until neutral, and remove the solvent by rotary evaporation to obtain the crude product. Dissolve the crude product in 10 mL of ethyl acetate and purify by silica gel column chromatography to obtain a pale yellow solid, namely alkylated catechol. Disperse 1 part by mass of alkylated catechol in 100 parts by mass of water to prepare an aqueous solution of alkylated catechol.

[0087] S3: Add the alkylated catechol aqueous solution to the polypyrrole nanosheet suspension, wherein the mass ratio of the polypyrrole nanosheet suspension to the alkylated catechol aqueous solution is 2:1, stir for 4 hours to obtain a polyphenol hydroxy compound modified polypyrrole nanosheet suspension.

[0088] S4: Cerium citrate and sodium ferrous citrate are added to the polypyrrole nanosheet suspension modified with the polyphenol hydroxyl compound. The mass ratio of polypyrrole nanosheets modified with the polyphenol hydroxyl compound, cerium citrate and sodium ferrous citrate is 1:0.08:0.02. After reacting for 2 hours, the mixture is filtered, washed and dried under vacuum to obtain the modified nanosheet material.

[0089] Preparation Example 4

[0090] Preparation of modified nanosheet materials:

[0091] S1: Disperse 1 part by mass of graphene oxide in 100 parts by mass of water to obtain a graphene oxide suspension;

[0092] S2: Dissolve 2 parts by mass of catechol and 5 parts by mass of potassium carbonate in 28 parts by mass of N,N-dimethylformamide, then add 5 parts by mass of bromododecane. React at 60°C for 6 hours. After the reaction, extract three times with 50 mL of ethyl acetate. Combine the organic phases, wash with deionized water until neutral, and remove the solvent by rotary evaporation to obtain the crude product. Dissolve the crude product in 10 mL of ethyl acetate and purify by silica gel column chromatography to obtain a pale yellow solid, namely alkylated catechol. Disperse 1 part by mass of alkylated catechol in 100 parts by mass of water to prepare an aqueous solution of alkylated catechol.

[0093] S3: Add the alkylated catechol aqueous solution to the graphene oxide suspension, the mass ratio of the graphene oxide suspension to the alkylated catechol aqueous solution is 2:1, stir for 4 hours to obtain a polyphenol hydroxyl compound modified graphene oxide nanosheet suspension.

[0094] S4: Add cerium citrate to the suspension of graphene oxide nanosheets modified with polyphenol hydroxyl compounds, wherein the mass ratio of graphene oxide nanosheets modified with polyphenol hydroxyl compounds to cerium citrate is 1:0.1. After reacting for 2 hours, filter and wash, and then vacuum dry to obtain the modified nanosheet material.

[0095] Preparation Example 5

[0096] Preparation of modified nanosheet materials:

[0097] S1: Disperse 1 part by mass of graphene oxide in 100 parts by mass of water to obtain a graphene oxide suspension;

[0098] S2: Dissolve 2 parts by mass of catechol and 5 parts by mass of potassium carbonate in 28 parts by mass of N,N-dimethylformamide, then add 5 parts by mass of bromododecane. React at 60°C for 6 hours. After the reaction, extract three times with 50 mL of ethyl acetate. Combine the organic phases, wash with deionized water until neutral, and remove the solvent by rotary evaporation to obtain the crude product. Dissolve the crude product in 10 mL of ethyl acetate and purify by silica gel column chromatography to obtain a pale yellow solid, namely alkylated catechol. Disperse 1 part by mass of alkylated catechol in 100 parts by mass of water to prepare an aqueous solution of alkylated catechol.

[0099] S3: Add the alkylated catechol aqueous solution to the graphene oxide suspension, the mass ratio of the graphene oxide suspension to the alkylated catechol aqueous solution is 2:1, stir for 4 hours to obtain a polyphenol hydroxyl compound modified graphene oxide nanosheet suspension.

[0100] S4: Add sodium ferrous citrate to the suspension of graphene oxide nanosheets modified with polyphenol hydroxyl compounds. The mass ratio of graphene oxide nanosheets modified with polyphenol hydroxyl compounds to sodium ferrous citrate is 1:0.1. After reacting for 2 hours, filter, wash, and vacuum dry to obtain the modified nanosheet material.

[0101] Comparative Preparation Example 1

[0102] Preparation of modified nanosheet materials:

[0103] S1: Disperse 1 part by mass of graphene oxide in 100 parts by mass of water to obtain a graphene oxide suspension;

[0104] S2: Dissolve 2 parts by mass of catechol and 5 parts by mass of potassium carbonate in 28 parts by mass of N,N-dimethylformamide, then add 5 parts by mass of bromododecane. React at 60°C for 6 hours. After the reaction, extract three times with 50 mL of ethyl acetate. Combine the organic phases, wash with deionized water until neutral, and remove the solvent by rotary evaporation to obtain the crude product. Dissolve the crude product in 10 mL of ethyl acetate and purify by silica gel column chromatography to obtain a pale yellow solid, namely alkylated catechol. Disperse 1 part by mass of alkylated catechol in 100 parts by mass of water to prepare an aqueous solution of alkylated catechol.

[0105] S3: Add the alkylated catechol aqueous solution to the graphene oxide suspension, with a mass ratio of graphene oxide suspension to alkylated catechol aqueous solution of 2:1. Stir for 4 hours, filter and wash, and vacuum dry to obtain modified nanosheet material.

[0106] Comparative Preparation Example 2

[0107] Preparation of modified nanosheet materials:

[0108] S1: Disperse 1 part by mass of graphene oxide in 100 parts by mass of water to obtain a graphene oxide suspension;

[0109] S2: Cerium citrate and sodium ferrous citrate are added to the graphene oxide nanosheet suspension. The mass ratio of graphene oxide nanosheets, cerium citrate and sodium ferrous citrate is 1:0.08:0.02. After reacting for 2 hours, the mixture is filtered, washed, and dried under vacuum to obtain the modified nanosheet material.

[0110] Example 1

[0111] Preparation of food packaging materials with high barrier properties:

[0112] 20 parts by mass of polyvinyl alcohol, 80 parts by mass of ethylene-vinyl alcohol copolymer, 10 parts by mass of the modified nanosheet material obtained in Preparation Example 1, 1 part by mass of polypyrrole nanosheets, and 1 part by mass of boron nitride nanosheets were mixed evenly as the raw material for the functional layer. High-density polyethylene HTA108 was used as the outer layer raw material, and metallocene polyethylene EXCEED 2012RA was used as the inner layer raw material. The mixture was then co-extruded in three layers at 160°C to obtain a food packaging material with high barrier properties. The inner layer thickness was 200 μm, the outer layer thickness was 200 μm, and the functional layer thickness was 20 μm.

[0113] Example 2

[0114] Preparation of food packaging materials with high barrier properties:

[0115] It is largely the same as Example 1, except that the modified nanosheet material obtained in Preparation Example 2 is used.

[0116] Example 3

[0117] Preparation of food packaging materials with high barrier properties:

[0118] It is largely the same as Example 1, except that the modified nanosheet material obtained in Preparation Example 3 is used.

[0119] Example 4

[0120] Preparation of food packaging materials with high barrier properties:

[0121] It is largely the same as Example 1, except that the modified nanosheet material obtained in Preparation Example 4 is used.

[0122] Example 5

[0123] Preparation of food packaging materials with high barrier properties:

[0124] It is largely the same as Example 1, except that the modified nanosheet material obtained in Preparation Example 5 is used.

[0125] Example 6

[0126] Preparation of food packaging materials with high barrier properties:

[0127] 20 parts by mass of polyvinyl alcohol, 80 parts by mass of ethylene-vinyl alcohol copolymer, 10 parts by mass of the modified nanosheet material obtained in Preparation Example 1, and 1 part by mass of boron nitride nanosheets were mixed evenly as the raw material for the functional layer. High-density polyethylene HTA108 was used as the outer layer raw material and metallocene polyethylene EXCEED 2012RA was used as the inner layer raw material. The mixture was then co-extruded in three layers at 160°C to obtain a food packaging material with high barrier properties. The inner layer thickness was 200 μm, the outer layer thickness was 200 μm, and the functional layer thickness was 20 μm.

[0128] Example 7

[0129] Preparation of food packaging materials with high barrier properties:

[0130] 20 parts by mass of polyvinyl alcohol, 80 parts by mass of ethylene-vinyl alcohol copolymer, 10 parts by mass of the modified nanosheet material obtained in Preparation Example 1, and 1 part by mass of polypyrrole nanosheets were mixed evenly as the functional layer raw material. High-density polyethylene HTA108 was used as the outer layer raw material, and metallocene polyethylene EXCEED 2012RA was used as the inner layer raw material. The mixture was then co-extruded in three layers at 160°C to obtain a food packaging material with high barrier properties. The inner layer thickness was 200 μm, the outer layer thickness was 200 μm, and the functional layer thickness was 20 μm.

[0131] Comparative Example 1

[0132] Preparation of food packaging materials with high barrier properties:

[0133] 20 parts by mass of polyvinyl alcohol, 80 parts by mass of ethylene-vinyl alcohol copolymer, 10 parts by mass of the modified nanosheet material obtained in Comparative Preparation Example 1, 1 part by mass of polypyrrole nanosheets, and 1 part by mass of boron nitride nanosheets were mixed evenly as the functional layer raw material. High-density polyethylene HTA108 was used as the outer layer raw material, and metallocene polyethylene EXCEED 2012RA was used as the inner layer raw material. The mixture was then co-extruded in three layers at 160°C to obtain a food packaging material with high barrier properties. The inner layer thickness was 200 μm, the outer layer thickness was 200 μm, and the functional layer thickness was 20 μm.

[0134] Comparative Example 2

[0135] Preparation of food packaging materials with high barrier properties:

[0136] 20 parts by mass of polyvinyl alcohol, 80 parts by mass of ethylene-vinyl alcohol copolymer, 10 parts by mass of the modified nanosheet material obtained in Comparative Preparation Example 2, 1 part by mass of polypyrrole nanosheets, and 1 part by mass of boron nitride nanosheets were mixed evenly as the raw material for the functional layer. High-density polyethylene HTA108 was used as the outer layer raw material, and metallocene polyethylene EXCEED 2012RA was used as the inner layer raw material. The mixture was then co-extruded in three layers at 160°C to obtain a food packaging material with high barrier properties. The inner layer thickness was 200 μm, the outer layer thickness was 200 μm, and the functional layer thickness was 20 μm.

[0137] Comparative Example 3

[0138] Preparation of food packaging materials with high barrier properties:

[0139] 20 parts by mass of polyvinyl alcohol, 80 parts by mass of ethylene-vinyl alcohol copolymer, 10 parts by mass of graphene oxide nanosheets, 1 part by mass of polypyrrole nanosheets, and 1 part by mass of boron nitride nanosheets were mixed evenly as the raw material for the functional layer. High-density polyethylene HTA108 was used as the outer layer raw material, and metallocene polyethylene EXCEED 2012RA was used as the inner layer raw material. The mixture was then co-extruded in three layers at 160℃ to obtain a food packaging material with high barrier properties. The inner layer thickness was 200 μm, the outer layer thickness was 200 μm, and the functional layer thickness was 20 μm.

[0140] Test section

[0141] The packaging materials prepared in the above embodiments and comparative examples have a thickness of 0.42 mm and a functional layer thickness of 20 μm. The oxygen barrier coefficient of the film was tested according to GB / T 1038.1-2022, "Test Methods for Gas Permeability of Plastic Films and Sheets Part 1: Differential Pressure Method". The unit is cm. 3 / m 2 •d•Pa;

[0142] The packaging materials prepared in the above embodiments and comparative examples, with a thickness of 0.42 mm and a functional layer thickness of 20 μm, were immersed in water at 25°C for 24 hours. The barrier coefficients of the films to oxygen and water vapor were tested according to GB / T 1038.1-2022, "Test Methods for Gas Permeability of Plastic Films and Sheets Part 1: Differential Pressure Method". The units are cm. 3 / m 2 •d•Pa, calculate the oxygen barrier performance retention rate (%) = (oxygen barrier rate after immersion ÷ initial oxygen barrier rate) × 100%;

[0143] Oxygen removal performance test: The packaging materials prepared in the above examples and comparative examples, with a thickness of 0.42 mm and a length and width of 5 cm, were placed in a 250 mL sealed bottle. The initial oxygen concentration was recorded. After 48 h, the oxygen concentration in the bottle was detected by gas chromatography. The oxygen removal rate was calculated as (oxygen concentration after 48 h / initial oxygen concentration) × 100%.

[0144] Testing equipment: differential pressure gas permeameter, gas chromatograph

[0145] The results are shown in Table 1.

[0146] Table 1

[0147]

[0148] According to Table 1, each embodiment showed better oxygen barrier properties, moisture resistance, and oxygen removal performance compared to Comparative Examples 1, 2, and 3, indicating that the high-barrier food packaging material provided in this application has certain advantages in oxygen barrier performance, oxygen barrier performance retention rate under humid conditions, and oxygen removal performance. The reasons may be as follows: In Comparative Example 1, only alkylated catechol was used for modification, lacking the metal-phenolic hydroxyl coordination structure formed by metal ions in citrate, resulting in poor overall structural stability of the material and a decrease in its barrier properties and water resistance; In Comparative Example 2, only citrate was used for modification. Although metal ions can improve the dispersibility of nanosheets to some extent through coordination, the lack of phenolic hydroxyl groups and hydrophobic long-chain structures of alkylated catechol resulted in poor dispersibility. At the same time, citrate has an oxygen removal effect, but its efficiency is lower than that of alkylated catechol; In Comparative Example 3, no modified graphene oxide nanosheets were used. The surface contains a large number of hydroxyl groups, which are prone to agglomeration due to hydrogen bonding when blended with hydrophilic polymers such as PVA / EVOH, resulting in an uneven layered barrier structure. In addition, without modification, there is no active oxygen removal system composed of alkylated catechol and citrate.

[0149] As can be seen from Examples 1 and 2, in Example 2, the use of unalkylated catechols resulted in more severe water absorption by the modified graphene oxide nanosheets in an aqueous environment, leading to a decrease in the material's barrier properties. However, in Example 1, after introducing long alkyl groups onto the catechols and then modifying them onto the surface of the graphene oxide nanosheets, both the oxygen barrier properties and the retention rate of oxygen barrier properties in a humid environment were improved to a certain extent. This indicates that introducing alkylated catechols can improve the oxygen barrier properties and moisture resistance of the material.

[0150] As can be seen from Examples 1 and 3, in Example 3, polypyrrole nanosheets were used instead of graphene oxide nanosheets. The physical barrier effect of polypyrrole nanosheets was poor. At the same time, the functional groups on the surface of polypyrrole were few, and only a certain amount of hydrogen bonding could be generated. This may lead to a weakening of the binding with alkylated catechols and citrates, resulting in a decrease in the oxygen removal effect. Therefore, the type of nanosheets has a certain impact on the barrier performance, moisture resistance and oxygen removal effect of the material. When graphene oxide nanosheets were selected for modification, the resulting material had the best barrier performance, moisture resistance and oxygen removal effect.

[0151] As can be seen from Examples 1, 4, and 5, cerium citrate and sodium ferrous citrate were used as citrates in Examples 4 and 5, respectively, and Ce was missing. 3+ / Ce 4+ The system's catalytic cycle for alkylated catechols, or the lack of Fe... 2+ Additional oxygen scavengers are used, and in Example 1, cerium citrate and sodium ferrous citrate are used as a citrate. It can be seen that the type of citrate has a certain impact on the barrier properties, moisture resistance and oxygen removal effect of the material. When a suitable ratio of cerium citrate and sodium ferrous citrate is selected, the barrier properties, moisture resistance and oxygen removal effect of the material are the best.

[0152] As shown in Examples 1, 6, and 7, the type of nanosheets added has a certain impact on the material's performance. In Example 6, the absence of polypyrrole nanosheets resulted in a decrease in the material's electron conductivity, leading to a decrease in the regeneration efficiency of alkylated catechols and thus affecting the oxygen removal efficiency. In Example 7, the absence of boron nitride nanosheets decreased the material's hydrophobic properties, resulting in a decrease in its moisture resistance. Therefore, the food packaging material obtained by adding a certain proportion of polypyrrole nanosheets and boron nitride nanosheets exhibits the best barrier properties, moisture resistance, and oxygen removal effect.

[0153] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of this application, and are not intended to limit them. Although this application has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features therein. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of this application.

Claims

1. A food packaging material having high barrier properties, characterized in that, The food packaging material comprises: an outer layer, an inner layer and a functional layer arranged between the outer layer and the inner layer, the functional layer comprising a hydroxyl-containing vinyl polymer and a modified nanosheet layer material, the modified nanosheet layer material being modified by a polyphenol hydroxyl compound and a citrate.

2. The food packaging material according to claim 1, characterized in that The modified nanosheet layer material comprises modified graphene oxide nanosheets, the modified graphene oxide nanosheets being obtained by modifying graphene oxide nanosheets by a polyphenol hydroxyl compound and a citrate.

3. The food packaging material according to claim 1, characterized in that The polyphenol hydroxyl compound comprises an alkylated catechol.

4. The food packaging material according to claim 1, characterized in that The citrate comprises cerium citrate and sodium ferrous citrate, and the mass ratio of the cerium citrate and the sodium ferrous citrate is 2-5:

1.

5. The food packaging material according to claim 2, characterized in that The preparation method of the modified graphene oxide nanosheets comprises the following steps: S1: dispersing graphene oxide nanosheets in water to obtain a uniformly dispersed graphene oxide suspension; S2: adding an aqueous solution of a polyphenol hydroxyl compound to the graphene oxide suspension to allow the polyphenol hydroxyl compound to adsorb or covalently modify the surface of the graphene oxide, thereby obtaining polyphenol hydroxyl compound-modified graphene oxide nanosheets; S3: mixing the polyphenol hydroxyl compound-modified graphene oxide nanosheets obtained in step S2 with a citrate to allow metal ions to further modify the surface of the graphene oxide by complexation or electrostatic interaction, thereby obtaining modified graphene oxide nanosheets.

6. The food packaging material according to claim 5, characterized in that The modified graphene oxide nanosheets satisfy at least one of the following conditions: 1) the concentration of the graphene oxide suspension is 5-15 mg / mL; 2) the concentration of the aqueous solution of the polyphenol hydroxyl compound is 2-10 mg / mL; 3) the mass ratio of the graphene oxide suspension to the aqueous solution of the polyphenol hydroxyl compound is 1:0.2-0.8; 4) the mass ratio of the polyphenol hydroxyl compound-modified graphene oxide nanosheets to the citrate is 1:0.1-0.

5.

7. The food packaging material according to claim 2, characterized in that The functional layer further comprises polypyrrole nanosheets and boron nitride nanosheets, and the mass ratio of the modified graphene oxide nanosheets, the polypyrrole nanosheets and the boron nitride nanosheets is 1:0.05-0.2:0.05-0.

2.

8. The food packaging material according to any one of claims 1 to 7, characterized in that The food packaging material satisfies at least one of the following conditions: 1) the outer layer comprises at least one of high-density polyethylene and metallocene polyethylene; the thickness of the outer layer is 10-500 μm; 2) the inner layer comprises at least one of high-density polyethylene and metallocene polyethylene; the thickness of the inner layer is 10-500 μm; 3) the thickness of the functional layer is 10-50 μm; 4) the hydroxyl-containing vinyl polymer comprises at least one of polyvinyl alcohol and ethylene-vinyl alcohol copolymer; 5) the mass ratio of the hydroxyl-containing vinyl polymer to the modified nanosheet layer material is 2-10:

1.

9. A method of producing a food packaging material with high barrier properties, characterized in that, The food packaging material comprises: providing raw materials for the outer layer, the inner layer and the functional layer of the food packaging material according to any one of claims 1-8; mixing the raw materials for the outer layer, the inner layer and the functional layer respectively and then co-extruding to obtain a food packaging material having a three-layer co-extrusion structure of the outer layer, the functional layer and the inner layer in sequence.

10. A food packaging bag characterized by The food packaging material with high barrier performance according to any one of claims 1-8 or prepared by the method according to claim 9.

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