Preparation method of a bio-based fluorine-free high-barrier food packaging paper

Abstract

The application relates to the technical field of food packaging materials, in particular to a preparation method of a bio-based fluorine-free high-barrier food packaging paper. Glycidyl methacrylate is introduced into a sodium lignosulfonate-acrylamide copolymer through enzyme catalysis polymerization to obtain an epoxy-containing polymer A; after beta-cyclodextrin is oxidized through TEMPO, ring-opening esterification is carried out on the polymer A to obtain a polymer-based host material B; adamantylamine is quaternized to obtain an adamantyl quaternary ammonium sulfonate, and nanocellulose is silanized and then combined with the adamantyl quaternary ammonium sulfonate through electrostatic self-assembly to obtain guest functionalized nanocellulose C; finally, the materials B and C are mixed with guar gum to be coated on a paper base, and after drying and hydrothermal treatment, a double dynamic crosslinking network barrier layer based on ionic bonds and host-guest interaction is formed. The packaging paper prepared by the application has a high bio-based content, an oil-proof grade of 9-12, a low water vapor transmission rate, excellent oil-proof and moisture-proof properties and biodegradability.

Description

Technical Field

[0001] This invention relates to the field of food packaging materials technology, specifically to a method for preparing a bio-based, fluorine-free, high-barrier food packaging paper. Background Technology

[0002] With the deepening implementation of global plastic bans and the continuous improvement of consumers' environmental awareness, the food packaging industry's demand for green and sustainable packaging materials is becoming increasingly urgent. Paper packaging is considered an ideal alternative to plastic packaging due to its degradable, recyclable, and renewable characteristics. However, paper itself is a porous hydrophilic material with numerous micron-sized pores between its fibers, making it highly susceptible to permeation by grease and water vapor, and unsuitable for direct use in packaging oily foods or foods stored in high-humidity environments. Traditionally, the food industry has primarily imparted barrier properties to paper by laminating polyethylene (PE) or coating it with fluorinated oil-repellent agents. While PE lamination provides good barrier effects, it is difficult to degrade and recycle, essentially only reducing plastic usage rather than truly solving the "white pollution" problem. Furthermore, fluorinated oil-repellent agents may generate persistent organic pollutants such as perfluorooctanoic acid (PFOA) and perfluorooctane sulfonyl compounds (PFOS) during their production and use lifecycle. These substances are bioaccumulative and pose a serious threat to human health and the environment.

[0003] Currently, various fluorine-free oil-resistant or moisture-proof technologies have emerged in the market to address the aforementioned issues. For example, patent CN120719571A discloses a bio-based oil-resistant agent prepared by synergistic micro-nanoization of pulp fibers, starch, and inorganic particles through high-speed shear grinding. While it has a high bio-based content, it primarily focuses on oil-resistant properties, paying insufficient attention to water vapor barrier capabilities under high temperature and humidity conditions, and its oil-resistant grade is highly dependent on the coating amount. Patent CN118910929B provides a mixed coating liquid composed of silica gel, methylhydrosiloxane / polysiloxane, styrene, and acrylic acid. Although it achieves fluorine-free oil resistance, it extensively uses petroleum-based synthetic polymers and has a low bio-based content, contradicting the initial intention of green environmental protection. Furthermore, existing technologies regarding the application of supramolecular chemistry in paper coating are mostly limited to simple physical inclusion interactions, such as the inclusion interaction between β-cyclodextrin and adamantane. The network strength formed by this simple host-guest interaction is insufficient, exhibiting poor stability under high humidity conditions, and lacking targeted interface design, resulting in insufficient adhesion between the coating and the paper substrate, making it prone to peeling.

[0004] Therefore, there is an urgent need for an innovative technical solution that can construct a stable multi-layer cross-linked network through molecular design without using fluorinated compounds and large amounts of petroleum-based materials, while simultaneously achieving high bio-based content, excellent oil and moisture resistance, and good coating durability. This invention is proposed against this technical background. By precisely chemically modifying the host and guest molecules, a multi-layer dynamic cross-linked network with covalent bonds, ionic bonds, and host-guest interactions is constructed, fundamentally solving the technical problems of the single performance and poor stability of traditional bio-based coatings. Summary of the Invention

[0005] The purpose of this invention is to provide a method for preparing bio-based, fluorine-free, high-barrier food packaging paper, addressing the technical problems of environmental hazards from existing fluorinated oil-repellent agents, the non-biodegradability of petroleum-based coatings, and the insufficient barrier properties of traditional bio-based materials. This method employs a strategy combining enzyme-catalyzed polymerization with host-guest molecular chemical modification to construct a dual dynamic cross-linked network barrier layer possessing both ionic bonds and host-guest interactions. This simultaneously imparts excellent oil and moisture resistance to the paper while ensuring high bio-based content and complete biodegradability, achieving a balance between environmental friendliness and high performance.

[0006] A method for preparing a bio-based, fluorine-free, high-barrier food packaging paper includes the following steps:

[0007] (1) Enzyme-catalyzed polymerization and functional monomer modification: In the aqueous phase, using horseradish peroxidase as a catalyst, sodium lignosulfonate was catalyzed to undergo free radical graft copolymerization with acrylamide and the functional monomer glycidyl methacrylate to obtain polymer A with epoxy groups in the side chain.

[0008] (2) Chemical modification and application of the main molecule: β-cyclodextrin is oxidized with 2,2,6,6-tetramethylpiperidine-1-oxy free radical to generate β-cyclodextrin-carboxylic acid; then it is reacted with polymer A obtained in step (1) under alkaline conditions, and β-cyclodextrin is covalently grafted onto the polymer backbone through ring-opening esterification of carboxyl and epoxy groups to obtain polymer-based main material B;

[0009] (3) Chemical modification and application of guest molecules: adamantane and 1,3-propanesulfonic acid lactone were quaternized to generate sulfonic acid adamantane quaternary ammonium salt; at the same time, nanocellulose was silanized with 3-aminopropyltriethoxysilane to obtain aminated nanocellulose; finally, sulfonic acid adamantane quaternary ammonium salt and aminated nanocellulose were combined by electrostatic self-assembly to obtain guest functionalized nanocellulose C.

[0010] (4) Preparation of barrier coating liquid and stimulus-responsive crosslinking: The polymer-based host material B obtained in step (2), the guest functionalized nanocellulose C obtained in step (3), and guar gum are mixed in water in proportion to obtain a pre-coating liquid; the pre-coating liquid is coated on the surface of paper substrate, and after drying, a dynamic three-dimensional network barrier layer based on ionic bonds and host-guest interaction is formed on the paper surface.

[0011] Preferably, in step (1), enzyme-catalyzed polymerization is carried out at pH 6.0-7.0 and temperature 40-60℃; the amount of the functional monomer glycidyl methacrylate added is 10%-30% of the mass of acrylamide; and the epoxy value of polymer A is 0.1-0.4.

[0012] Preferably, in step (2), the degree of substitution of the β-cyclodextrin-carboxylic acid is 4.0-6.0; and its mass ratio with polymer A is 1:(1-5).

[0013] Preferably, in step (3), the degree of quaternization of the sulfonic acid-type adamantane quaternary ammonium salt is greater than 95%; when it is electrostatically self-assembled with aminated nanocellulose, the molar ratio is [-SO3] - ]:[-NH3 + = (1-1.2):1; electrostatic self-assembly is carried out at pH 5.0-7.0 and temperature 25-50℃.

[0014] Preferably, in step (4), the mass percentage of each component, based on the total solids content of the pre-coating liquid, is as follows: polymer-based host material B 25%-55%, guest functionalized nanocellulose C 20%-35%, and guar gum 8%-20%.

[0015] Preferably, in step (4), the solid content of the pre-coating liquid is 5%-15%, and the viscosity is 1000-5000 mPa·s.

[0016] Preferably, in step (4), the coating amount is 5-15 g / m² based on dry matter. 2 .

[0017] Preferably, the nanocellulose mentioned in step (3) is cellulose nanofibers prepared by TEMPO oxidation method, and its surface carboxyl content is 1.0-1.5 mmol / g.

[0018] Preferably, in step (4), after drying, the coated paper can be subjected to wet heat treatment under the following conditions: temperature 70-100℃, relative humidity 80%-95%, time 1-4 hours, in order to promote the maturation and strengthening of the supramolecular network.

[0019] The present invention provides a bio-based, fluorine-free, high-barrier food packaging paper, the barrier layer of which is a dual dynamic reversible cross-linked network structure possessing both ionic bonds and host-guest interactions.

[0020] Related terms and their English abbreviations in this invention:

[0021] Glycidyl methacrylate: GMA;

[0022] 2,2,6,6-Tetramethylpiperidine-1-oxygen radical: TEMPO;

[0023] 3-Aminopropyltriethoxysilane: APTES;

[0024] Core innovations:

[0025] 1. Creative chemical modification of host and guest molecules: from physical inclusion to covalent bonding and ionic interactions.

[0026] This invention completely transcends the traditional approach of simple physical encapsulation, endowing host and guest molecules with entirely new functions and binding mechanisms through precise chemical manipulation. First, we utilize TEMPO oxidation to convert β-cyclodextrin into β-cyclodextrin-carboxylic acid, transforming it from a host molecule into a reactive "linker," and then covalently anchoring it to the enzyme-catalyzed polymer backbone via ring-opening esterification. This "grafting" strategy significantly improves the stability of the host molecule in the coating, preventing leaching during use. Simultaneously, we quaternize adamantane, introducing a positively charged quaternary ammonium salt center and a strongly hydrated sulfonate anion, creating a zwitterionic adamantane derivative. This modification not only retains its cavity recognition ability with β-cyclodextrin but also introduces strong electrostatic interactions and ion hydration.

[0027] 2. Construction of a synergistic crosslinking network with multiple dynamic bonds.

[0028] The core innovation of this invention lies in constructing a multi-layered synergistic crosslinking network composed of covalent bonds, host-guest interactions, and ionic bonds. Covalent bonds (grafted β-cyclodextrin) provide permanent crosslinking points and structural stability; host-guest interactions (β-cyclodextrin cavities and the adamantyl group of sulfonic acid-type adamantane quaternary ammonium salt) endow the network with dynamic reversibility and self-healing potential; while the newly introduced ionic bonds (sulfonate groups and ammonium groups on the surface of nanocellulose) provide strong electrostatic crosslinking that remains stable even under high humidity conditions. These three forces are not simply superimposed but mutually reinforcing: ionic bonds firmly fix guest molecules to the surface of nanocellulose, greatly improving the local concentration and efficiency of supramolecular crosslinking; while the covalently anchored host molecules ensure the spatial uniformity of the crosslinking network. This "three-in-one" design produces a remarkable synergistic effect, enabling the coating to maintain extreme density and structural integrity under both dry and high-temperature / high-humidity environments.

[0029] 3. Interface engineering and intelligent post-processing enhance barrier performance.

[0030] We further unlocked the full potential of this chemical system through interface engineering and process innovation. Amino modification of nanocellulose using silanization not only provided sites for electrostatic assembly but also significantly enhanced the compatibility of nanocellulose with the hydrophobic polymer matrix. After coating and molding, we innovatively introduced a hydrothermal post-treatment process. This process utilizes a high-temperature, high-humidity environment to promote the full expansion and reconstruction of guar gum and other biopolysaccharide segments, eliminating internal stress. More importantly, it provides energy and fluidity for the rearrangement of ionic bonds and the deep optimization of host-guest interactions, inducing the "maturation" of the barrier layer network, making its structure more homogeneous and dense. This transforms the system's chemical advantages into stable and superior macroscopic barrier performance. This series of collaborative innovations, from molecular design to macroscopic processes, collectively ensures the overwhelming performance advantage of the final product.

[0031] In summary, the technical solution of this invention solves the problem of insufficient performance of traditional bio-based coatings by constructing a dual dynamic cross-linked network through enzyme-catalyzed polymerization, host-guest chemical modification, and electrostatic self-assembly. The mechanism description provides a detailed explanation of the network formation process (covalent bonds, ionic bonds, and synergistic host-guest interactions), which represents a significant improvement compared to existing technologies (such as simple physical inclusion).

[0032] Beneficial technical effects of the present invention:

[0033] 1. Superior Comprehensive Barrier Performance: The food packaging paper prepared by this invention exhibits both extremely high oil resistance and excellent water vapor barrier performance with relatively low coating weight. Test results show that its kit oil resistance rating can reach 9-12, far exceeding the basic requirement of level 6 for food packaging; under harsh high temperature and high humidity conditions (38℃, 90% RH), the water vapor transmission rate is less than 180g / m³.2 / d, which is more than 90% higher than that of untreated base paper. This "double high" barrier performance comes from a carefully designed dual dynamic cross-linking network: the host-guest interaction between covalently anchored β-cyclodextrin and electrostatically fixed adamantane derivative forms a dense main barrier layer, while ionic cross-linking can maintain network stability in high humidity environments. The synergistic effect of the two effectively blocks the penetration of oil and water molecules.

[0034] 2. Green, Environmentally Friendly, and Safe Characteristics: The entire preparation process does not use any fluorinated compounds or toxic solvents. All major raw materials, including sodium lignosulfonate, nanocellulose, guar gum, and β-cyclodextrin, are derived from renewable natural biomass, resulting in a final product with a bio-based content exceeding 80%. The enzyme-catalyzed polymerization reaction is conducted under mild conditions, conforming to green chemistry principles. The quaternization modification of adamantane introduces sulfonate ions, enhancing the material's hydration and biocompatibility. The resulting product exhibits excellent biodegradability and food safety, and will not cause persistent environmental pollution after disposal, fully meeting the safety and environmental protection requirements of modern food packaging materials.

[0035] 3. Durability and Self-Healing Potential Contributed by the Dynamic Network: The dual dynamic cross-linked network constructed based on ionic bonds and host-guest interactions endows the coating with excellent mechanical properties and durability. Ionic bonds provide strong electrostatic cross-linking, enabling the coating to maintain structural integrity even in high humidity environments; the dynamic reversible nature of host-guest interactions endows the coating with a certain degree of self-healing ability and flexibility. When the coating is slightly damaged, the dissociation and recombination of the host-guest pairs allow the network structure to self-repair to a certain extent. In addition, the unique damp heat post-treatment process further promotes the curing process of the network, making the coating structure more uniform and dense, significantly improving the stability and durability of barrier properties.

[0036] Explanation of the formation mechanism of the dual dynamic crosslinking network of the present invention: (1) Initial state: The initial dispersion state of the polymer backbone, β-cyclodextrin host molecules, adamantane guest molecules and nanocellulose is shown. (2) Covalent grafting: β-cyclodextrin is covalently grafted onto the polymer backbone through ring-opening esterification reaction to form a polymer-based host material. (3) Electrostatic self-assembly: Sulfonic acid-type adamantane quaternary ammonium salt is combined with aminated nanocellulose through electrostatic interaction to form guest-functionalized nanocellulose. (4) Network formation: The polymer-based host material and guest-functionalized nanocellulose form a dual dynamic crosslinking network through host-guest interaction. Attached Figure Description

[0037] Figure 1This is a schematic diagram illustrating the formation mechanism of the dual dynamic crosslinking network of the present invention (showing the mechanism of β-cyclodextrin covalently grafted onto the polymer backbone, sulfonic acid-type adamantane quaternary ammonium salt fixed onto nanocellulose through electrostatic interaction, and the host-guest interaction between the two to form a three-dimensional network; where 101 represents adamantane, 102 represents the polymer backbone, 103 represents nanocellulose, B represents covalent grafting of polymer-based host material, C represents electrostatic assembly: guest functionalized nanocellulose, D represents the formation of the dual dynamic crosslinking network, 105 represents host-guest interaction, and 106 represents ionic bond).

[0038] Figure 2 The process flow diagram for the preparation of this invention (the flow diagram sequentially shows the key steps of enzyme-catalyzed polymerization to introduce epoxy groups, oxidation and grafting of β-cyclodextrin TEMPO, quaternization of adamantane and functionalization of nanocellulose, preparation of coating solution, coating and hydrothermal treatment).

[0039] Figure 3 The radar charts comparing the performance of the examples and comparative examples are shown below (the radar charts compare the comprehensive performance of the examples and comparative examples from five dimensions: oil resistance, moisture resistance, bio-based content, coating adhesion, and flexibility. 301 represents Example 2, 302 represents Example 1, 303 represents Example 3, 304 represents Comparative Example 3, 305 represents Comparative Example 2, 306 represents Comparative Example 4, 307 represents Comparative Example 1, and 308 represents Comparative Example 5). Detailed Implementation

[0040] Before further describing specific embodiments of the present invention, it should be understood that the scope of protection of the present invention is not limited to the specific embodiments described below; it should also be understood that the terminology used in the embodiments of the present invention is for describing specific embodiments and not for limiting the scope of protection of the present invention. Test methods in the following embodiments that do not specify specific conditions are generally performed under conventional conditions or as recommended by the respective manufacturers.

[0041] When numerical ranges are given in the embodiments, it should be understood that, unless otherwise stated in this invention, both endpoints of each numerical range and any value between the two endpoints may be selected. Unless otherwise defined, all technical and scientific terms used in this invention have the same meaning as commonly understood by those skilled in the art. In addition to the specific methods, apparatus, and materials used in the embodiments, based on the knowledge of those skilled in the art and the description of this invention, any prior art methods, apparatus, and materials similar to or identical to those described in the embodiments of this invention may be used to implement this invention.

[0042] Unless otherwise stated, the test methods, detection methods and preparation methods disclosed in this invention all adopt conventional techniques in this technical field.

[0043] Example 1

[0044] The specific implementation process of Example 1 is as follows: First, an enzyme-catalyzed polymerization reaction was carried out. 10.00 g of sodium lignosulfonate was accurately weighed and dissolved in 200 mL of phosphate buffer solution with a pH of 6.0. Then, 2.00 g of acrylamide and 0.30 g of glycidyl methacrylate (GMA) were added. After complete dissolution, 0.30 g of horseradish peroxidase (HRP) was added as a catalyst. The reaction was initiated by adding 6.0 mL of 5% hydrogen peroxide solution dropwise at a rate of approximately 1.0 mL / 10 minutes in a 40°C constant temperature water bath. Gentle stirring was maintained and the reaction temperature was precisely controlled at 40±1°C. The stirring speed was 200-300 rpm. After the reaction continued for 5 hours, polymer A with an epoxy value of 0.25 was obtained. Next, the main molecule was modified. 5.00 g of β-cyclodextrin was selectively oxidized in a TEMPO / NaClO / NaBr oxidation system, with the reaction pH controlled at 10.0. At 25℃ and a reaction time of 3 hours, β-cyclodextrin-carboxylic acid with a degree of substitution of 5.2 was obtained. Then, 3.00 g of this product was accurately weighed and reacted with 8.00 g of polymer A under alkaline conditions at pH 9.5 in a water bath at 70℃ for 6 hours. β-cyclodextrin was covalently grafted onto the polymer backbone via ring-opening esterification of the carboxyl and epoxy groups, yielding polymer-based host material B. Simultaneously, guest molecule modification was performed. 2.00 g of adamantaneamine and 1,3-propanesulfonic acid lactone were refluxed in anhydrous ethanol at 80℃ for 12 hours to obtain a sulfonic acid-type adamantane quaternary ammonium salt with a degree of quaternization of 98.2%. Separately, 3.00 g of TEMPO oxidized nanocellulose (carboxyl content 1.2 mmol / g) and 0.50 g of APTES were reacted in an acetate-sodium acetate buffer at pH 5.0 at 50℃ for 4 hours for silanization modification to obtain aminated nanocellulose. Finally, the two were combined according to [-SO3]... - ]:[-NH3 + A precise molar ratio of 1.1:1 was used for electrostatic self-assembly at 25℃ and pH 6.0 for 2 hours to obtain guest functionalized nanocellulose C. Finally, coating and post-treatment were performed. 4.00 g of material B, 2.50 g of material C, 1.20 g of guar gum, and deionized water were mixed to prepare a uniform coating solution with a solid content of 8.5%. A wire bar coater was used at a rate of 7.0 g / m². 2 The precise coating amount is uniformly coated on a substrate with a basis weight of 60 g / m³. 2 The surface of the food-grade cardboard is first pre-dried in an 80℃ oven for 3 minutes, and then transferred to a constant temperature and humidity chamber for wet heat treatment at 85℃ and 85% relative humidity for 2 hours, finally obtaining a bio-based fluorine-free high-barrier food packaging paper with a dual dynamic cross-linked network structure.

[0045] Example 2

[0046] The specific implementation process of Example 2 is as follows: First, an enzyme-catalyzed polymerization reaction was carried out. 10.00 g of sodium lignosulfonate was accurately weighed and dissolved in 200 mL of phosphate buffer solution with a pH of 6.0. Then, 2.00 g of acrylamide and 0.40 g of glycidyl methacrylate (GMA) were added. The amount of GMA added was 20% of the mass of acrylamide. After complete dissolution, 0.30 g of horseradish peroxidase was added. 6.0 mL of this solution was slowly added dropwise in a 40°C constant temperature water bath (controlling the dropping rate to approximately 1.0 mL). The reaction was initiated with 5% hydrogen peroxide solution (mL / 10 min), with gentle stirring and precise temperature control at 40±1℃ and stirring speed at 250 rpm. After 5 hours of reaction, polymer A with an epoxy value of 0.32 was obtained. Next, the main molecule was modified by selectively oxidizing 5.00 g of β-cyclodextrin in a TEMPO / NaClO / NaBr oxidation system at pH 10.0, temperature 25℃, and reaction time 3.5 hours to obtain β-cyclodextrin-carboxylic acid with a degree of substitution of 5.8. Then, 3.00 g of this product was accurately weighed and mixed with 9.00 g of polymer A at a mass ratio of 1:3 under alkaline conditions at pH 9.5 at 70℃. The reaction was carried out in a water bath for 6 hours, and β-cyclodextrin was covalently grafted onto the polymer backbone through ring-opening esterification of carboxyl and epoxy groups to obtain polymer-based host material B. Simultaneously, guest molecule modification was performed: 2.00 g of adamantane and 1,3-propanesulfonic acid lactone were refluxed in anhydrous ethanol at 80 °C for 12 hours to obtain a sulfonic acid-type adamantane quaternary ammonium salt with a quaternization degree of 98.5%. Separately, 3.00 g of TEMPO oxidized nanocellulose (carboxyl content 1.2 mmol / g) and 0.50 g of APTES were reacted in an acetate-sodium acetate buffer at pH 5.0 at 50 °C for 4 hours for silanization modification to obtain aminated nanocellulose. Finally, the two were combined according to [-SO3]... - ]:[-NH3 + A precise molar ratio of 1:1 was used for electrostatic self-assembly at 25℃ and pH 5.5 for 2 hours to obtain guest functionalized nanocellulose C. Finally, coating and post-treatment were performed. 4.50 g of material B, 2.80 g of material C, 1.50 g of guar gum, and deionized water were mixed to prepare a uniform coating solution with a solid content of 10.5%. A wire bar coater was used at a rate of 9.0 g / m². 2 The precise coating amount is uniformly coated on a substrate with a basis weight of 60 g / m³. 2 The surface of the food-grade cardboard is first pre-dried in an 80℃ oven for 3 minutes, and then transferred to a constant temperature and humidity chamber for wet heat treatment at 90℃ and 90% relative humidity for 2.5 hours, finally obtaining a bio-based fluorine-free high-barrier food packaging paper with a denser network structure.

[0047] Example 3

[0048] The specific implementation process of Example 3 is as follows: First, an enzyme-catalyzed polymerization reaction was carried out. 10.00 g of sodium lignin sulfonate was accurately weighed and dissolved in 200 mL of phosphate buffer solution with a pH of 6.0. Then, 2.00 g of acrylamide and 0.30 g of glycidyl methacrylate (GMA) were added. The amount of GMA added was 15% of the mass of acrylamide. After complete dissolution, 0.30 g of horseradish peroxidase was added. The reaction was initiated by slowly adding 6.0 mL (controlling the dropping rate to approximately 1.0 mL / 10 minutes) of 5% hydrogen peroxide solution in a 40°C constant temperature water bath. Gentle stirring was maintained, and the reaction temperature was precisely controlled at 40±1°C. The stirring speed was 280 rpm. After the reaction continued for 5 hours, polymer A with an epoxy value of 0.18 was obtained. Next, the main molecule was modified. 5.00 g of β-cyclodextrin was selectively oxidized in a TEMPO / NaClO / NaBr oxidation system, controlling the reaction pH at 10.0 and the temperature... At 25°C and 2.5 hours, a β-cyclodextrin-carboxylic acid with a degree of substitution of 4.5 was obtained. Then, 2.50 g of this product was accurately weighed and reacted with 10.00 g of polymer A at a mass ratio of 1:4 in a 70°C water bath under alkaline conditions at pH 9.5 for 6 hours. β-cyclodextrin was covalently grafted onto the polymer backbone via ring-opening esterification of the carboxyl and epoxy groups, yielding polymer-based host material B. Simultaneously, guest molecule modification was performed, with 2.00 g... Amantadine and 1,3-propanesulfonic acid lactone were refluxed in anhydrous ethanol at 80°C for 12 hours to obtain a sulfonic acid-type adamantane quaternary ammonium salt with a quaternization degree of 97.8%. Separately, 3.00 g of TEMPO-oxidized nanocellulose (carboxyl content 1.2 mmol / g) and 0.50 g of APTES were reacted in acetate-sodium acetate buffer at pH 5.0 at 50°C for 4 hours for silanization modification to obtain aminated nanocellulose. Finally, the two were combined according to [-SO3]... - ]:[-NH3 + A precise molar ratio of 1.15:1 was used for electrostatic self-assembly at 25℃ and pH 6.5 for 2 hours to obtain guest functionalized nanocellulose C. Finally, coating and post-treatment were performed. 3.50 g of material B, 2.20 g of material C, 1.00 g of guar gum, and deionized water were mixed to prepare a uniform coating solution with a solid content of 7.0%. A wire bar coater was used at a rate of 5.5 g / m². 2 The precise coating amount is uniformly coated on a substrate with a basis weight of 60 g / m³. 2 The surface of the food-grade cardboard is first pre-dried in an 80℃ oven for 3 minutes, and then transferred to a constant temperature and humidity chamber for wet heat treatment at 75℃ and 80% relative humidity for 3 hours, finally obtaining a bio-based fluorine-free high-barrier food packaging paper with moderate performance and better cost.

[0049] Comparative Example 1

[0050] Comparative Example 1 used a traditional physical inclusion method without any chemical modification: 10.00 g of sodium lignosulfonate was accurately weighed and dissolved in 200 mL of phosphate buffer at pH 6.0. 2.00 g of acrylamide and 0.30 g of glycidyl methacrylate (GMA) were added, along with 0.30 g of horseradish peroxidase. The mixture was reacted at 40°C for 5 hours to obtain polymer A. Then, 3.00 g of ordinary β-cyclodextrin (without TEMPO oxidation) was simply mixed with 8.00 g of polymer A without covalent grafting. Simultaneously, 2.00 g of ordinary adamantane (without quaternization modification) and 3.00 g of ordinary nanocellulose (without silanization modification) were directly mixed. Finally, the above mixture was mixed with 1.20 g of guar gum to prepare a coating solution with a solid content of 8.5%, applied at 7.0 g / m³. 2 Coating amount: 60 g / m 2 The sample was dried at 80°C for 3 minutes on food-grade cardboard without undergoing wet heat treatment, serving only as a comparison sample with traditional supramolecular coatings.

[0051] Comparative Example 2

[0052] Comparative Example 2 omits the electrostatic self-assembly step, retaining only the host-guest chemical modification: the enzyme-catalyzed polymerization reaction is the same as in Example 1, yielding polymer A with an epoxy value of 0.25; the host molecule modification is the same as in Example 1, yielding polymer-based host material B; however, in the guest molecule modification, sulfonic acid-type adamantane quaternary ammonium salt is not used, but instead 2.00 g of ordinary adamantaneamine and 3.00 g of ordinary nanocellulose (without silanization modification) are simply mixed without electrostatic self-assembly; finally, material B, the ordinary adamantaneamine-nanocellulose mixture, and 1.20 g of guar gum are mixed to form a coating solution with a solid content of 8.5%, applied at 7.0 g / m². 2 The coating was applied, pre-dried at 80°C, and then subjected to wet heat treatment at 85°C and 85%RH for 2 hours as a control sample with a single crosslinking mechanism.

[0053] Comparative Example 3

[0054] Comparative Example 3 omits the wet heat post-treatment process: all raw material preparation and reaction processes were carried out under the same conditions and proportions as in Example 1, including enzyme-catalyzed polymerization to obtain polymer A with an epoxy value of 0.25, modification of the host molecule to obtain polymer-based host material B, modification of the guest molecule to obtain guest-functionalized nanocellulose C, and preparation of the coating solution (solid content 8.5%) and the coating process (coating amount 7.0 g / m³). 2 However, in the post-coating treatment, it was only subjected to conventional drying at 80°C for 3 minutes without any damp heat treatment, serving as a comparative sample for evaluating the importance of the damp heat treatment process.

[0055] Comparative Example 4

[0056] Comparative Example 4 uses a petroleum-based coating material: Following the formulation and process of Example 1 in CN118910929B, accurately weigh 3.0 g of silicone, 2.0 g of methylhydrosiloxane / polysiloxane mixture, 10.0 g of styrene, 6.0 g of acrylic acid, 15.0 g of butyl acrylate, and 64.0 g of deionized water. Emulsify the mixture uniformly in a high-speed disperser to obtain a petroleum-based mixed coating liquid. Adjust the viscosity to 27-30 seconds (25℃, English No. 2 Zahn cup), and apply using an anilox roller coater at 7.0 g / m². 2 The same coating amount is applied to 60 g / m 2 On food-grade cardboard, a petroleum-based high-barrier coating comparison sample was obtained by drying and curing in a hot air drying oven at 110-130℃ for 2 minutes.

[0057] Comparative Example 5

[0058] Comparative Example 5 used a traditional bio-based coating: 5.00 g of sodium alginate was accurately weighed and dissolved in 95 g of deionized water to prepare a 5% sodium alginate solution as the coating liquid. A wire bar coater was used at a rate of 7.0 g / m². 2 The same coating amount is evenly applied to 60g / m 2 The food-grade cardboard surface was dried in an 80°C oven for 3 minutes without any special post-treatment, serving as a benchmark sample for evaluating the performance improvement of the present invention compared to conventional bio-based coatings.

[0059] Performance testing

[0060] Testing standards:

[0061] In this embodiment, the paper oil resistance rating test adopts the internationally recognized standard test method Oil Kit Test-TAPPI T559cm-12. The highest oil resistance rating is 12 and the lowest is 1. The higher the rating, the better the paper's oil resistance effect.

[0062] GB / T 22921-2008 Determination of water vapor transmission rate of paper and paperboard sheet materials by dynamic airflow method and static gas method;

[0063] Bio-based content determination: ASTM D6866;

[0064] GB / T 29649-2013 "Determination of Bio-based Content in Bio-based Materials by Liquid Scintillation Counter Method";

[0065] GB / T 457-2008 Determination of folding endurance of paper and paperboard;

[0066] The significance of Tabor folding endurance: This test evaluates the durability of packaging paper after repeated folding, reflecting its flexibility and mechanical strength. For food packaging, flexibility is important because the packaging needs to resist tearing and breakage during transportation and use.

[0067] The fluoride content was determined according to IEC 62321-3-2:2020.

[0068] Table 1 shows the test results of various embodiments of the present invention.

[0069]

[0070] Table 2 shows the test results of the comparative examples of this invention.

[0071]

[0072] Based on Tables 1 and 2 above, the core conclusion that can be drawn from the test results is that the dual dynamic cross-linking network constructed by the present invention through enzyme-catalyzed polymerization combined with host-guest molecular chemical modification (Examples 1-3) simultaneously achieves excellent oil resistance (Kit grade 9-12) and superior water vapor barrier properties (WVTR 98-165g / m² / d) while maintaining a high bio-based content (80-85%). Its comprehensive performance is significantly better than traditional supramolecular coatings that rely solely on physical binding (Comparative Example 1), single cross-linking systems lacking ionic bond reinforcement (Comparative Example 2), samples without network curing treatment (Comparative Example 3), non-degradable petroleum-based coatings (Comparative Example 4), and conventional bio-based coatings with low barrier properties (Comparative Example 5). This fully demonstrates the effectiveness and innovation of this technical solution in solving the industry problem of balancing high barrier properties and environmental friendliness in bio-based materials.

[0073] Analysis of differences in test results for Examples 1-3:

[0074] The differences in the test results of Examples 1-3 mainly stemmed from the variations in network density caused by minor adjustments to the formulation parameters and process conditions. Example 2 employed the highest GMA addition (20%) and β-cyclodextrin substitution degree (5.8), along with the highest coating amount (9 g / m²). 2The synergistic effect of these parameters—including the most stringent humid heat treatment conditions (90°C, 90%RH)—results in the highest density of crosslinkable epoxy groups on the polymer chain, the most recognition sites on the host molecule, the thickest coating layer, and the most thorough reconstruction and maturation of the network structure during post-treatment. This leads to the formation of the most dense and complete three-dimensional crosslinked network, exhibiting the best barrier properties. Example 1 uses moderate parameters, with a moderate network density and integrity, resulting in balanced performance. Example 3 employs a relatively conservative parameter combination, particularly a lower coating weight (5.5 g / m³). 2 While the relatively mild humid and hot conditions (75℃, 80%RH) ensured a high bio-based content and cost advantage, the resulting barrier layer was slightly insufficient in thickness and network completeness, resulting in slightly lower oil and moisture resistance compared to the former two. This phenomenon, where the final performance can be precisely controlled by key parameters, precisely demonstrates the high controllability and optimizability of the technical solution of this invention.

[0075] Analysis of differences between the test results of the Example and Comparative Example 1:

[0076] The fundamental reason for the performance difference between the Examples and Comparative Example 1 lies in the essential difference between chemical bonding and physical interaction. Comparative Example 1 relies solely on the physical inclusion interaction between β-cyclodextrin and adamantane molecules to construct a network. This van der Waals force interaction is weak and highly reversible, easily dissociating in high humidity or oily environments, leading to network structure collapse and a sharp decline in barrier performance. In contrast, the Examples firmly anchor β-cyclodextrin to the polymer backbone through covalent bonds and stably fix the adamantane derivative to the nanocellulose through ionic bonds, forming a stable network with strong chemical bonds as support points and host-guest interactions as connecting bridges. This "rigid-flexible" structure can effectively resist disturbances from the external environment, maintaining structural integrity and stability, thereby achieving a durable and efficient barrier effect, highlighting the decisive role of host-guest chemical modification.

[0077] Analysis of differences between the test results of the Example and Comparative Example 2:

[0078] The performance difference between the examples and Comparative Example 2 primarily reveals the crucial enhancing role of ionic bonds in the dual dynamic crosslinked network. Comparative Example 2 only retained the host-guest crosslinking mechanism, lacking the ionic bonds introduced by electrostatic self-assembly. Ionic bonds not only provide strong electrostatic attraction, with bond energies far exceeding those of host-guest interactions, significantly enhancing the network's mechanical strength and stability; more importantly, the strong hydration of sulfonate ions can form a robust bound water layer on the coating surface under high humidity conditions. This water film effectively blocks further water vapor penetration. Therefore, the network in Comparative Example 2, lacking the "skeleton" support of ionic bonds and the hydration barrier effect, performs poorly in terms of moisture resistance and coating strength, demonstrating the necessity and superiority of ionic bonds and host-guest interactions synergistically constructing a dual crosslinked network.

[0079] Analysis of differences between the test results of the Example and Comparative Example 3:

[0080] The difference between the examples and Comparative Example 3 directly demonstrates that the hydrothermal post-treatment process is indispensable for achieving optimal performance. Although Comparative Example 3 possessed all the correct chemical components, it omitted the hydrothermal treatment and only performed conventional drying. During conventional drying, the polymer molecular chain segments do not move sufficiently, and the functional groups cannot reach their optimal energy arrangement, resulting in numerous microscopic defects and internal stresses in the formed cross-linked network. In contrast, the hydrothermal treatment used in the examples utilizes high temperature to provide kinetic energy for molecular chain movement, and the high humidity environment acts as a plasticizer to promote chain segment relaxation. This provides crucial conditions for the rearrangement of ionic bonds, optimal pairing of host and guest interactions, and the full "maturation" of the entire three-dimensional network, thereby eliminating structural defects, making the network more uniform and dense, and ultimately fully realizing the intrinsic properties of the material.

[0081] Analysis of differences between the test results of the Example and Comparative Example 4:

[0082] The comparison between the examples and Comparative Example 4 highlights the differences in design concepts and performance characteristics between bio-based smart materials and traditional petroleum-based materials. The petroleum-based coating of Comparative Example 4 relies on a continuous, dense, but rigid polymer film to block small molecules; its moisture resistance is acceptable, but its flexibility is poor, and its bio-based content is extremely low. In contrast, the bio-based coating of the examples employs a dynamic cross-linked network mechanism. Its barrier properties stem not only from physical barriers but also from the significant extension of diffusion paths by the dense network and the auxiliary barrier provided by ion hydration. More importantly, the coating of this invention exhibits dynamic reversibility, excellent flexibility, and a bio-based content exceeding 80%, successfully solving the fundamental problems of non-degradability and environmental unfriendliness of traditional petroleum-based materials, achieving a balance between high performance and green environmental protection.

[0083] Analysis of differences between the test results of the Example and Comparative Example 5:

[0084] The significant performance difference between the Examples and Comparative Example 5 profoundly reveals the overwhelming advantage of sophisticated molecular design over traditional methods of simple blending. The sodium alginate coating in Comparative Example 5 relies solely on hydrogen bonds and chain entanglements between polysaccharide molecular chains to form a barrier. This interaction is weak and easily swells upon contact with water, resulting in a porous and unstable film with poor oil and moisture resistance. In contrast, the Examples utilize multiple sophisticated chemical techniques, including enzyme-catalyzed polymerization, host-guest chemical modification, and electrostatic self-assembly, to construct a dense three-dimensional network structure at the molecular scale, characterized by synergistic stability through covalent bonds, ionic bonds, and host-guest interactions. This structure fundamentally alters the physicochemical properties of the coating, giving it superior barrier properties and durability that are difficult for traditional bio-based materials to achieve, highlighting the immense value of the core innovation of this invention.

[0085] The reason why the flexibility / Tabor folding resistance of Comparative Example 4 and Comparative Example 5 is so low is likely due to the following reasons: Comparative Example 4 (petroleum-based coating) has high material rigidity, is brittle, and has poor folding resistance; Comparative Example 5 (sodium alginate coating) has poor flexibility and is brittle.

[0086] Finally, it should be noted that the above embodiments are used to illustrate the technical solutions of the present invention and not to limit the scope of protection of the present invention. Although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can be made to the technical solutions of the present invention without departing from the essence and scope of the technical solutions of the present invention.

Claims

1. A method for preparing a bio-based, fluorine-free, high-barrier food packaging paper, characterized in that, Includes the following steps: (1) Enzyme-catalyzed polymerization and functional monomer modification: In the aqueous phase, horseradish peroxidase was used as a catalyst and hydrogen peroxide was added as an initiator to catalyze the free radical graft copolymerization reaction of sodium lignosulfonate with acrylamide and functional monomer glycidyl methacrylate to obtain polymer A with epoxy groups in the side chain. (2) Chemical modification and application of the main molecule: β-cyclodextrin is oxidized with 2,2,6,6-tetramethylpiperidine-1-oxy free radical to generate β-cyclodextrin-carboxylic acid; then it is reacted with polymer A obtained in step (1) under alkaline conditions, and β-cyclodextrin is covalently grafted onto the polymer backbone through ring-opening esterification of carboxyl and epoxy groups to obtain polymer-based main material B; (3) Chemical modification and application of guest molecules: adamantane and 1,3-propanesulfonic acid lactone were quaternized to generate sulfonic acid adamantane quaternary ammonium salt; at the same time, nanocellulose was silanized with 3-aminopropyltriethoxysilane to obtain aminated nanocellulose; finally, sulfonic acid adamantane quaternary ammonium salt and aminated nanocellulose were combined by electrostatic self-assembly to obtain guest functionalized nanocellulose C. (4) Preparation of barrier coating liquid and stimulus-responsive crosslinking: The polymer-based host material B obtained in step (2), the guest functionalized nanocellulose C obtained in step (3), and guar gum are mixed in water in proportion to obtain a pre-coating liquid; the pre-coating liquid is coated on the surface of paper substrate, and after drying, a dynamic three-dimensional network barrier layer based on ionic bond and host-guest interaction is formed on the paper surface; In step (1), the epoxy value of polymer A is 0.1-0.4; In step (2), the degree of substitution of the β-cyclodextrin-carboxylic acid is 4.0-6.0; its mass ratio with polymer A is 1:(1-5); the reaction in step (2) is carried out at pH 9.0-10.0 and temperature 60-80℃ for 4-8 hours. In step (3), when the sulfonic acid type adamantane quaternary ammonium salt and aminated nanocellulose undergo electrostatic self-assembly, the molar ratio of the feed is [-SO3]. - ]:[-NH3 + ] = (1-1.2):1; electrostatic self-assembly is carried out at pH 5.0-7.0 and temperature 25-50℃; In step (4), based on the total solids content of the pre-coating liquid, the mass percentage of each component is as follows: polymer-based host material B 25%-55%, guest functionalized nanocellulose C 20%-35%, and guar gum 8%-20%; after drying, the coated paper can be subjected to wet heat treatment.

2. The method according to claim 1, characterized in that: In step (1), enzyme-catalyzed polymerization is carried out at pH 5.0-7.0 and temperature 30-60℃ for 3-6 hours; the amount of the functional monomer glycidyl methacrylate added is 10%-30% of the mass of acrylamide; the hydrogen peroxide is added in the form of an aqueous solution with a mass concentration of 3%-6%, and its addition amount is 1.0%-3.0% of the total mass of the reaction system; the hydrogen peroxide solution is added slowly dropwise over a period of 0.5-1 hour. The enzyme-catalyzed polymerization reaction was carried out under stirring conditions, with a stirring speed of 150-400 rpm.

3. The method according to claim 1, characterized in that: In step (3), the degree of quaternization of the sulfonic acid type adamantane quaternary ammonium salt is greater than 95%.

4. The method according to claim 1, characterized in that: In step (4), the solid content of the pre-coating liquid is 5%-15%, and the viscosity is 1000-5000 mPa·s.

5. The method according to claim 1, characterized in that: In step (4), the coating amount is 5-15 g / m² on a dry matter basis. 2 .

6. The method according to claim 1, characterized in that: The nanocellulose mentioned in step (3) is cellulose nanofibers prepared by TEMPO oxidation method, and its surface carboxyl content is 1.0-1.5 mmol / g.

7. The method according to claim 1, characterized in that, The damp heat treatment conditions are: temperature 70-100℃, relative humidity 80%-95%, time 1-4 hours, to promote the maturation and strengthening of the supramolecular network.

8. A bio-based fluorine-free high-barrier food packaging paper prepared by the method according to any one of claims 1-7, characterized in that: Its barrier layer is a dual dynamic reversible cross-linked network structure that combines ionic bonds and host-guest interactions.

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