Food-grade antibacterial packaging paper based on biomass conversion and its preparation method

Abstract

This invention discloses a food-grade antibacterial packaging paper based on biomass conversion and its preparation method, relating to the field of papermaking technology. The packaging paper uses areca leaf mechanical pulp rich in lignin and natural phenols as a substrate. After alkali treatment and oxidase activation of the phenolic hydroxyl groups on the fiber surface, a chitosan-tea polyphenol layer is coated onto its surface, followed by ionic crosslinking and interfacial co-crosslinking with phytic acid to construct a dense fiber-coating network structure. This improves the paper's mechanical strength, water and oil resistance, and inhibition of common pathogenic bacteria while maintaining its renewability, biodegradability, and food contact safety.

Description

Technical Field

[0001] This invention relates to the field of papermaking technology, and in particular to a food-grade antibacterial packaging paper based on biomass conversion and its preparation method. Background Technology

[0002] In existing technologies, common methods for improving the water and oil resistance of paper-based packaging include: extruding and coating the paper with thermoplastic resins such as polyethylene and polypropylene, or coating it with fluorinated oil-repellent agents, paraffin wax, or synthetic resin emulsions. While these methods can significantly improve water and oil resistance, they generally suffer from problems such as incomplete degradation, difficulty in re-pulping and recycling, and the potential migration of fluorinated small molecules into food, which are detrimental to food safety and green recycling. To improve environmental friendliness, some literature has attempted to use biodegradable polymers such as polylactic acid and bio-based polyesters as coatings. However, their interfacial compatibility with cellulose substrates is limited, and the coatings are prone to cracking or peeling during bending or repeated exposure to moisture, leading to a decline in barrier and mechanical properties.

[0003] In research on improving the antibacterial properties of paper-based materials, numerous methods have achieved certain antibacterial effects by introducing inorganic antibacterial agents (metal ions, metal oxides, etc.), quaternary ammonium salts, or chitosan and other antibacterial components onto the paper surface. However, some inorganic or organic antibacterial agents pose potential migration risks, and many formulations are not entirely composed of food-grade or food additive-grade raw materials, making them difficult to directly apply to food-grade packaging paper with higher safety requirements. Furthermore, existing antibacterial papers are mostly simple physical blends or surface coatings, and the antibacterial components are easily washed away or migrated in water or oil media, resulting in insufficient antibacterial durability.

[0004] Existing technology CN115874492A discloses a highly waterproof and environmentally friendly packaging box and its preparation method. This technology uses bamboo chemical pulp and softwood chemical pulp as base pulps, introducing waste paper aerogel obtained by treating waste paper pulp with lithium bromide solution and sodium alginate, and organosilicon gel prepared from amino-terminated siloxanes, thioctic acid-modified fiber nanocrystals, and layered bimetallic hydroxides to toughen and modify the pulp for flame retardancy. Then, a waterproof coating is prepared using the organosilicon gel, carboxymethyl chitosan, and polylactic acid modified with phytic acid, citrulline, genipin, and tannic acid, giving the resulting box good waterproof, oil-proof, flame-retardant, and certain antibacterial properties. This method achieves positive results in improving the overall waterproof, oil-proof, and flame-retardant properties of the box, while also considering a certain degree of environmental friendliness. However, considering the more stringent and specific application requirements of food-grade antibacterial packaging paper, the existing technologies still have the following shortcomings: The raw material system is complex, and some components are not food-grade. They utilize various chemicals such as lithium bromide, tetrahydrofuran, carbodiimide, DMAP, organosilicon networks, and layered bimetallic hydroxides, focusing more on environmentally friendly paper boxes rather than designing them with all components suitable for food contact. For thin packaging paper that comes into long-term or direct contact with food, assessing its migration safety and regulatory compliance is difficult. The fiber-coating interface mainly relies on physical interactions, resulting in insufficient interface durability. Existing solutions mostly achieve cross-linking and densification within the coating, but the interaction with paper fibers is still primarily based on physical wetting and hydrogen bonding, lacking covalent or semi-covalent cross-linking with functional groups on the fiber surface as nodes. This makes them prone to interfacial micro-cracks or delamination in hot water, hot oil, or humid environments, leading to a decline in water and oil resistance and antibacterial properties. Summary of the Invention

[0005] This invention addresses the issues of food-grade safety, antibacterial durability, and fiber and functional coating durability in existing paper-based packaging materials. It proposes a food-grade antibacterial packaging paper based on biomass conversion and its preparation method. This method, without significantly altering the main papermaking process, fully utilizes the natural phenolic structure in high-lignin biomass fibers. Through alkali pretreatment and oxidase activation, the fiber surface participates in the in-situ co-crosslinking of chitosan and phytic acid networks, thereby constructing a dense and robust fiber-coating interface layer. While ensuring that all raw materials are biomass-derived and can be of food-grade or food contact-grade quality, it significantly improves the paper's mechanical properties, water and oil resistance, and antibacterial properties.

[0006] To achieve the above objectives, the present invention provides a method for preparing food-grade antibacterial packaging paper based on biomass conversion, comprising the following steps:

[0007] S1 dilutes areca leaf mechanical pulp to 0.3-1.0 wt%, processes it into paper using papermaking equipment, and controls the dry paper basis weight to be 150-350 g / m³. 2After being made, the wet paper is pressed and dehydrated, and then dried for 8-36 hours at 20-30℃ and 40-60% relative humidity to obtain unbleached areca leaf base paper, which retains the lignin and natural phenols in the fiber.

[0008] S2 involves completely immersing unbleached areca leaf base paper in a 0.5-3.0 wt% sodium hydroxide aqueous solution and treating it at 40-80℃ for 20-60 min to dissolve some hemicellulose and expose the lignin and phenolic hydroxyl groups on the fiber surface; after treatment, it is washed with deionized water until the pH of the washing water is 7.0, and the paper is pre-dried to a moisture content of 5-12 wt% to obtain pre-dried areca leaf base paper.

[0009] S3. Add oxidase to a buffer solution with a pH of 4.0-7.0 and a concentration of 10-100mM at an enzyme activity concentration of 3-15U / mL. Immerse the pre-dried areca leaf base paper in the solution until the paper is completely wetted. Treat at 20-50℃ for 30-60 minutes. During the treatment, introduce air and shake to maintain dissolved oxygen. After treatment, remove the paper and gently press to remove excess solution from the surface without washing with water. This allows the generated phenolic radicals and / or quinone intermediates to remain on the fiber surface. Then, let it stand at room temperature for 5-40 minutes to keep the paper surface moist but not dripping, thus obtaining enzyme-activated areca leaf base paper.

[0010] S4 involves fixing enzyme-activated areca leaf-based paper onto a flat substrate, and then uniformly coating the chitosan-tea polyphenol coating solution onto at least one side of the paper surface using a doctor blade coating or rod coating method, controlling the dry coating weight to be 10-40 g / m². 2 The coated paper is pre-dried in hot air at 60-90℃ for 3-10 minutes, so that the coating surface does not flow significantly and is basically not sticky, while retaining a certain amount of moisture inside, thus obtaining pre-dried coated paper.

[0011] S5 involves immersing pre-dried coated paper in a 3-10 wt% phytic acid aqueous solution at 10-40℃ for 5-20 minutes. This allows phytic acid molecules to diffuse into the coating and undergo multi-point ionic cross-linking with the protonated amino groups on the chitosan chains. Simultaneously, under the influence of residual phenolic free radicals and / or quinone structures on the fiber surface, the lignin or phenolic structures in the areca leaf fibers form covalent or semi-covalent connections with chitosan and / or phytic acid, thereby constructing an in-situ co-crosslinking network at the fiber-coating interface. After immersion, the paper is removed, and excess solution is removed by rolling or scraping. It is then dried at 60-90℃ for 10-40 minutes to reduce the paper moisture content to below 8 wt%. Finally, it is equilibrated at 20-30℃ and 40-60% relative humidity for 24-48 hours to obtain food-grade antibacterial packaging paper based on biomass conversion.

[0012] Preferably, the buffer solution is selected from one of citrate-sodium citrate buffer, acetate-sodium acetate buffer, and phosphate buffer.

[0013] Preferably, the oxidase is selected from one or a combination of two or more of laccase, polyphenol oxidase, and horseradish peroxidase. When horseradish peroxidase is used, hydrogen peroxide is added to the buffer solution to make the concentration of hydrogen peroxide in the whole system 0.01-0.5 wt%. More preferably, the oxidase in step S3 is tyrosinase with an enzyme activity of 8-12 U / mL, treated with an acetate-sodium acetate buffer solution at pH 5.0-6.0 and 30-70 mM at 25-35°C for 30-60 min.

[0014] Preferably, the method for preparing the areca leaf mechanical pulp includes: removing moldy and rotten parts from naturally fallen or harvested areca leaf sheaths, washing away mud and impurities with water, drying, and chopping into 2-3 cm pieces; adding areca leaf pieces to a pressure-resistant hydrothermal reactor at a mass ratio of 1:2-5 to water, hydrothermally treating at 120-180℃ for 40-80 minutes, cooling, removing the pulp, washing with water until the pH of the filtrate is neutral, and removing soluble low-molecular-weight impurities; then sending the pulp to a grinding equipment for mechanical grinding to fully fiberize the areca leaves, obtaining a pulp with fiber lengths mainly distributed in the range of 0.5-2.0 mm, screening through a 100-300 mesh sieve to remove undissociated coarse residue, retaining the pulp under the sieve, and adjusting the pulp concentration to 0.2-2.0 wt% for later use.

[0015] Preferably, the preparation method of the chitosan-tea polyphenol coating solution includes: adding chitosan to a 0.5-3.0 wt% acetic acid solution and stirring until completely dissolved, so that the concentration of chitosan in the coating solution is 0.5-3.0 wt%; adding glycerol to the chitosan solution, the amount of glycerol being 10-30 wt% of the mass of chitosan, and stirring to disperse it evenly; then adding tea polyphenol, the amount of tea polyphenol being 0.1-1 wt% of the mass of chitosan, and continuing to stir until the tea polyphenol is evenly dispersed, thus obtaining the chitosan-tea polyphenol coating solution.

[0016] Preferably, in step S2, the concentration of the sodium hydroxide aqueous solution is 0.8-1.5 wt%, the treatment temperature is 55-65℃, and the time is 20-45 min.

[0017] Preferably, in step S5, the concentration of the phytic acid aqueous solution is 3-8 wt%, the soaking time is 5-20 min, and the drying temperature is 60-80℃.

[0018] The beneficial effects of this invention are:

[0019] All the main functional components of this invention can be derived from biomass and can use food-grade or food contact material permitted raw materials. The entire system is aqueously processed under mild conditions, making it suitable for use in food direct contact packaging paper.

[0020] This invention transforms lignin and natural phenols on the fiber surface from inert components into interfacial crosslinking nodes through alkali pretreatment and oxidase activation, thereby achieving in-situ co-crosslinking of the fiber with the chitosan-phytic acid network and significantly improving interfacial bonding and network continuity.

[0021] Based on this interface structure, the tensile index, tear index, bursting index and bending stiffness of the packaging paper are improved by 15-34% compared with the untreated control sample. The water and oil resistance properties are significantly improved, the water absorption is reduced, and the water droplet absorption time and vegetable oil penetration time are significantly extended.

[0022] This invention utilizes the synergistic antibacterial properties of chitosan and tea polyphenols, along with a dense interfacial layer constructed through phytic acid crosslinking, to achieve a stable antibacterial rate of 99% or higher against Escherichia coli and Staphylococcus aureus in packaging paper. This results in higher antibacterial efficiency and better durability with the same amount of antibacterial components. Detailed Implementation

[0023] Raw material parameters and sources for the examples and comparative examples

[0024] Areca leaf sheath: Origin: Hainan, naturally detached leaf sheath; after removing mud and sand, air-dry naturally, with a moisture content of 8-12%.

[0025] Chitosan: Degree of deacetylation 80±5%, number average molecular weight 100-200kDa.

[0026] Laccase: Enzyme activity: ≥500U / g solid; Source strain: Trametes versicolor.

[0027] Tea polyphenols: Content: Total polyphenols ≥ 95wt%; Grade: Food grade (can be used as a natural antibacterial / antioxidant).

[0028] Tyrosinase, enzyme activity: ≥1000U / mg, source strain: Agaricus bisporus.

[0029] Horseradish peroxidase, enzyme activity: ≥250U / mg, RZ value ≥3.0.

[0030] In addition to the raw materials mentioned above, the preparation process also uses deionized water or distilled water, which meets the requirements for water used in food contact materials.

[0031] Example 1

[0032] The method for preparing areca leaf mechanical pulp includes the following steps:

[0033] (1) Select the dried areca leaf sheaths and remove any obviously moldy or rotten parts. Rinse them thoroughly with tap water to remove mud and impurities, and then rinse them twice with deionized water. Let the washed leaf sheaths air dry until there are no obvious water marks on the surface. Use a chopper to cut them into small pieces of 2-3 cm for later use.

[0034] (2) Add the above-mentioned chopped areca leaves and water to a pressure-resistant hydrothermal reactor at a mass ratio of 1:4. Heat the reactor to 155°C under stirring and keep it at that temperature for 60 minutes. After the reaction is completed, allow the pressure and temperature to drop naturally to room temperature. Discharge the slurry and wash it with water until the pH of the filtrate is 7 to remove soluble low-molecular-weight impurities.

[0035] (3) The hydrothermal pretreated pulp is fed into a disc mill for mechanical grinding to fully fiberize the areca leaves and form a pulp with fiber length of 0.5-2.0 mm. After grinding, the pulp is screened with a 200-mesh sieve to remove undisintegrated coarse residue and retain the passing part as areca leaf mechanical pulp. The pulp concentration is adjusted to 0.5 wt% and reserved for later use to obtain the areca leaf mechanical pulp.

[0036] Example 2

[0037] The preparation method of food-grade antibacterial packaging paper based on biomass conversion includes the following steps:

[0038] S1. Areca leaf mechanical pulp with a concentration of 0.5 wt% (Example 1) was processed into paper using a laboratory square paper machine according to standard methods, and the wet basis weight was controlled to achieve a dry basis weight of approximately 250 g / m³. 2 After pressing and dehydrating the wet paper on filter paper, it was naturally dried at 23°C and 50% relative humidity for 24 hours to obtain unbleached areca leaf base paper; this base paper retains a high lignin content and natural phenols.

[0039] S2. Unbleached areca leaf base paper was completely immersed in a 1.0 wt% NaOH aqueous solution and treated at 60°C for 30 min to dissolve some hemicellulose and expose the surface lignin and phenolic hydroxyl groups. After treatment, the paper was removed and repeatedly washed with a large amount of deionized water until the pH of the washing water returned to 7. The washed paper was laid flat and pre-dried at room temperature to a moisture content of 10% to obtain pre-dried areca leaf base paper.

[0040] S3. Add laccase to a pH 4.5, 50mM citrate-sodium citrate buffer solution at a concentration of 10 U / mL and stir gently until completely dissolved. Immerse pre-dried areca leaf base paper in the solution until fully saturated. Treat at 30°C for 40 min, during which air can be slowly bubbled in and gently shaken to ensure sufficient dissolved oxygen in the solution and promote the enzymatic oxidation of lignin / phenolic hydroxyl groups. After treatment, remove the paper and gently squeeze it with a rubber roller to remove excess solution, but do not wash it with a lot of water to retain the activated phenolic oxygen free radical intermediates on the fiber surface. Lay the paper flat on an inert substrate and leave it at room temperature for 20 min to keep it moist but not dripping, and immediately proceed to the next coating step.

[0041] S4 is prepared by fixing areca leaf base paper treated with laccase onto a flat substrate; chitosan-tea polyphenol coating solution is evenly coated onto one side of the paper surface using a doctor blade coating method, controlling the coating amount to achieve a dry coating weight of 25 g / m². 2 The coated paper is placed in a 70℃ hot air oven for 5 minutes to pre-dry it so that the coating surface no longer flows obviously and is not sticky, but still retains a certain amount of moisture inside to facilitate subsequent cross-linking and diffusion, thus obtaining the pre-dried coated paper.

[0042] S5. The pre-dried coated paper from step S4 is immersed in a 5wt% phytic acid aqueous solution and left to stand at room temperature for 10 minutes. During the immersion process, phytic acid molecules diffuse into the chitosan coating, causing the protonated amino groups on the chitosan chains to undergo multi-point ionic cross-linking with the phytic acid polyphosphate groups. At the same time, under the conditions of laccase activation and the presence of residual phenolic free radicals, the lignin / phenolic structure on the surface of areca leaf fiber has the opportunity to covalently or semi-covalently connect with chitosan and / or phytic acid, thereby forming an in-situ co-crosslinking network at the fiber-coating interface.

[0043] After impregnation, the paper is removed and gently squeezed through a rubber roller or glass rod to make the phytic acid solution on the surface more evenly distributed and remove excess solution; the paper is dried in a hot air oven at 70°C for 20 minutes until the paper moisture content drops below 8wt%; during the drying process, the ionic cross-linking and interfacial co-cross-linking of phytic acid and chitosan are completed; the dried packaging paper sample is placed at 23°C and 50% relative humidity for more than 24 hours to equilibrate, thus obtaining the food-grade antibacterial packaging paper based on biomass conversion.

[0044] The preparation method of the chitosan-tea polyphenol coating solution is as follows: Weigh 1.0g of glacial acetic acid, add it to 99.0g of deionized water, stir evenly to obtain a 1.0wt% acetic acid aqueous solution; under stirring conditions, slowly add 1.5g of chitosan powder, stir at room temperature for 3h until the chitosan is completely dissolved to obtain a 1.5wt% chitosan aqueous solution; add 0.3g of glycerol to the above solution, and continue stirring for 30min to mix thoroughly; weigh 7.5mg of tea polyphenol, stir for 30min until uniformly dispersed to obtain the chitosan-tea polyphenol coating solution.

[0045] The feature of this embodiment is that, under the premise of maintaining lignin / natural phenols in the areca leaf base paper, alkaline pretreatment and enzymatic activation are used to induce the lignin / phenolic hydroxyl groups on the fiber surface to participate in the in-situ co-crosslinking of the chitosan-phytic acid network, thereby constructing a dense and strongly adhesive interface layer, and synergistically imparting excellent antibacterial properties to the material with chitosan and tea polyphenols.

[0046] Comparative Example 1

[0047] The preparation method of food-grade antibacterial packaging paper based on biomass conversion includes the following steps:

[0048] 1) Areca leaf mechanical pulp with a concentration of 0.5 wt% (Example 1) was processed into paper using a laboratory square paper machine according to standard methods, and the wet basis weight was controlled to achieve a dry basis weight of approximately 250 g / m³. 2 After pressing and dehydrating the wet paper on filter paper, it was naturally dried at 23°C and 50% relative humidity for 24 hours to obtain unbleached areca leaf base paper; this base paper retains a high lignin content and natural phenols.

[0049] 2) Take unbleached areca leaf base paper and fix it onto a flat substrate; use a doctor blade coating method to evenly coat one side of the paper surface with chitosan-tea polyphenol coating solution, controlling the coating amount to achieve a dry coating weight of 25g / m². 2 The coated paper is placed in a 70℃ hot air oven for 5 minutes to pre-dry it so that the coating surface no longer flows obviously and is not sticky, but still retains a certain amount of moisture inside to facilitate subsequent cross-linking and diffusion, thus obtaining the pre-dried coated paper.

[0050] 3) Immerse the pre-dried coated paper from step 2) in a 5wt% phytic acid aqueous solution and let it stand at room temperature for 10 minutes to allow the phytic acid to diffuse in the coating and form an ionic cross-linking network with the protonated amino groups of chitosan.

[0051] After impregnation, the paper is removed and gently squeezed by a rubber roller or glass rod to make the phytic acid solution on the surface more evenly distributed and remove excess solution; the paper is dried in a hot air oven at 70°C for 20 minutes until the paper moisture content drops below 8wt%; the dried packaging paper sample is placed at 23°C and 50% relative humidity for more than 24 hours to equilibrate, thus obtaining the food-grade antibacterial packaging paper based on biomass conversion.

[0052] In this step, the surface of areca leaf fibers is not enzymatically activated, and the lignin / phenols in the fibers do not participate in cross-linking. The interfacial bonding mainly depends on the physical wetting and hydrogen bonding of the chitosan coating on the paper surface and the electrostatic / ionic cross-linking between phytic acid and chitosan.

[0053] The preparation method of the chitosan-tea polyphenol coating solution is the same as that in Example 2, and will not be repeated here.

[0054] Example 3

[0055] The preparation method of food-grade antibacterial packaging paper based on biomass conversion includes the following steps:

[0056] S1. Areca leaf mechanical pulp with a concentration of 0.5 wt% (Example 1) was processed into paper using a laboratory square paper machine according to standard methods, and the wet basis weight was controlled to achieve a dry basis weight of approximately 250 g / m³. 2 After pressing and dehydrating the wet paper on filter paper, it was naturally dried at 23°C and 50% relative humidity for 24 hours to obtain unbleached areca leaf base paper; this base paper retains a high lignin content and natural phenols.

[0057] S2. Unbleached areca leaf base paper was completely immersed in a 1.0 wt% NaOH aqueous solution and treated at 60°C for 30 min to dissolve some hemicellulose and expose the surface lignin and phenolic hydroxyl groups. After treatment, the paper was removed and repeatedly washed with a large amount of deionized water until the pH of the washing water returned to 7. The washed paper was laid flat and pre-dried at room temperature to a moisture content of 10% to obtain pre-dried areca leaf base paper.

[0058] S3. Add tyrosinase to a pH 5.5, 50mM acetate-sodium acetate buffer solution at a concentration of 10 U / mL and stir gently until completely dissolved. Immerse pre-dried areca leaf-based paper in the solution until fully saturated. Treat at 30°C for 40 minutes, during which air can be slowly bubbled in and gently shaken to ensure sufficient dissolved oxygen in the solution, promoting the enzymatic oxidation of lignin / phenolic hydroxyl groups to generate phenolic radicals and quinone structures. After treatment, remove the paper and gently squeeze it with a rubber roller to remove excess solution, but do not wash it with a lot of water to retain the activated phenolic radical intermediates on the fiber surface. Lay the paper flat on an inert substrate and leave it at room temperature for 20 minutes to keep it moist but not dripping, and immediately proceed to the next coating step.

[0059] S4 uses areca leaf base paper treated with tyrosinase, which is then fixed onto a flat substrate. A chitosan-tea polyphenol coating solution is evenly applied to one side of the paper surface using a doctor blade coating method, controlling the coating amount to achieve a dry coating weight of 25 g / m². 2 The coated paper is placed in a 70℃ hot air oven for 5 minutes to pre-dry it so that the coating surface no longer flows obviously and is not sticky, but still retains a certain amount of moisture inside to facilitate subsequent cross-linking and diffusion, thus obtaining the pre-dried coated paper.

[0060] S5. Immerse the pre-dried coated paper from step S4 into a 5wt% phytic acid aqueous solution and let it stand at room temperature for 10 minutes. After immersion, remove the paper and gently squeeze it with a rubber roller or glass rod to make the phytic acid solution on the surface more evenly distributed and remove excess solution. Dry the paper in a 70℃ hot air oven for 20 minutes until the paper moisture content drops below 8wt%. During drying, the ionic crosslinking and interfacial co-crosslinking of phytic acid and chitosan are completed. Place the dried packaging paper sample at 23℃ and 50% relative humidity for more than 24 hours to equilibrate, thus obtaining the food-grade antibacterial packaging paper based on biomass conversion.

[0061] The preparation method of the chitosan-tea polyphenol coating solution is as follows: Weigh 1.0g of glacial acetic acid, add it to 99.0g of deionized water, stir evenly to obtain a 1.0wt% acetic acid aqueous solution; under stirring conditions, slowly add 1.5g of chitosan powder, stir at room temperature for 3h until the chitosan is completely dissolved to obtain a 1.5wt% chitosan aqueous solution; add 0.3g of glycerol to the above solution, and continue stirring for 30min to mix thoroughly; weigh 7.5mg of tea polyphenol, stir for 30min until uniformly dispersed to obtain the chitosan-tea polyphenol coating solution.

[0062] The feature of this embodiment is that tyrosinase belongs to the polyphenol oxidase class and has high catalytic activity for phenolic substrates. It can efficiently oxidize the phenolic hydroxyl groups on the surface of areca leaf fibers into quinone intermediates. These intermediates can undergo condensation or quasi-covalent bonding with the amino groups of chitosan and the polyphosphate groups of phytate, which is beneficial to increasing the co-crosslinking density of the fiber-coating interface and further enhancing the mechanical properties, barrier properties and antibacterial properties of the paper.

[0063] Example 4

[0064] The preparation method of food-grade antibacterial packaging paper based on biomass conversion includes the following steps:

[0065] S1. Areca leaf mechanical pulp with a concentration of 0.5 wt% (Example 1) was processed into paper using a laboratory square paper machine according to standard methods, and the wet basis weight was controlled to achieve a dry basis weight of approximately 250 g / m³. 2After pressing and dehydrating the wet paper on filter paper, it was naturally dried at 23°C and 50% relative humidity for 24 hours to obtain unbleached areca leaf base paper; this base paper retains a high lignin content and natural phenols.

[0066] S2. Unbleached areca leaf base paper was completely immersed in a 1.0 wt% NaOH aqueous solution and treated at 60°C for 30 min to dissolve some hemicellulose and expose the surface lignin and phenolic hydroxyl groups. After treatment, the paper was removed and repeatedly washed with a large amount of deionized water until the pH of the washing water returned to 7. The washed paper was laid flat and pre-dried at room temperature to a moisture content of 10% to obtain pre-dried areca leaf base paper.

[0067] S3. Horseradish peroxidase was added to a pH 6.0, 50mM phosphate buffer solution at a concentration of 5 U / mL. The solution was gently stirred until completely dissolved. 30wt% H2O2 aqueous solution was added to make the H2O2 content in the system 0.05wt%. Pre-dried areca leaf base paper was immersed in the solution until it was completely saturated. The paper was treated at 30°C for 40 min, during which air could be slowly bubbled in and the paper gently shaken. After treatment, the paper was removed and gently squeezed with a rubber roller to remove excess solution, but no large amount of water washing was performed to retain the activated phenolic oxygen free radical intermediates on the fiber surface. The paper was laid flat on an inert substrate and left at room temperature for 20 min to keep it moist but not dripping. The next coating step was then carried out immediately.

[0068] S4 uses areca leaf base paper treated with horseradish peroxidase, which is then fixed onto a flat substrate. A chitosan-tea polyphenol coating solution is evenly applied to one side of the paper surface using a doctor blade coating method, controlling the coating amount to achieve a dry coating weight of 25 g / m². 2 The coated paper is placed in a 70℃ hot air oven for 5 minutes to pre-dry it so that the coating surface no longer flows obviously and is not sticky, but still retains a certain amount of moisture inside to facilitate subsequent cross-linking and diffusion, thus obtaining the pre-dried coated paper.

[0069] S5. Immerse the pre-dried coated paper from step S4 into a 5wt% phytic acid aqueous solution and let it stand at room temperature for 10 minutes. After immersion, remove the paper and gently squeeze it with a rubber roller or glass rod to make the phytic acid solution on the surface more evenly distributed and remove excess solution. Dry the paper in a 70℃ hot air oven for 20 minutes until the paper moisture content drops below 8wt%. During drying, the ionic crosslinking and interfacial co-crosslinking of phytic acid and chitosan are completed. Place the dried packaging paper sample at 23℃ and 50% relative humidity for more than 24 hours to equilibrate, thus obtaining the food-grade antibacterial packaging paper based on biomass conversion.

[0070] The preparation method of the chitosan-tea polyphenol coating solution is as follows: Weigh 1.0g of glacial acetic acid, add it to 99.0g of deionized water, stir evenly to obtain a 1.0wt% acetic acid aqueous solution; under stirring conditions, slowly add 1.5g of chitosan powder, stir at room temperature for 3h until the chitosan is completely dissolved to obtain a 1.5wt% chitosan aqueous solution; add 0.3g of glycerol to the above solution, and continue stirring for 30min to mix thoroughly; weigh 7.5mg of tea polyphenol, stir for 30min until uniformly dispersed to obtain the chitosan-tea polyphenol coating solution.

[0071] When the horseradish peroxidase (HRP) activity concentration exceeds 5 U / mL or the H2O2 concentration exceeds 0.05 wt%, although the oxidation degree of lignin / phenols on the surface of areca leaf fibers is enhanced, the tensile strength and tear strength of the paper begin to decrease significantly, and the color darkens slightly. Therefore, this embodiment uses an HRP system with an enzyme activity of 5 U / mL and an H2O2 concentration of 0.05 wt%, which ensures the interfacial activation effect while taking into account the stability of the cellulose main structure and the final mechanical properties of the packaging paper.

[0072] The features of this embodiment are: the HRP / H2O2 system has a high oxidation potential, which can oxidize a wider spectrum of lignin structures, thereby generating more active sites on the surface of areca leaf fibers and improving the degree of interfacial co-crosslinking; at the same time, by controlling the H2O2 concentration and treatment time, the degradation of the cellulose backbone is kept at a low level, so as to obtain a good interfacial reinforcement effect while avoiding a significant decrease in paper strength.

[0073] Test Example 1

[0074] Mechanical performance testing

[0075] In accordance with the provisions of GB / T 10739-2023 "Standard Atmospheric Conditions for the Treatment and Testing of Paper, Paperboard and Pulp Samples", the paper samples obtained from the examples and comparative examples were cut into the specified dimensions and equilibrated in a standard atmosphere at a temperature of 23±1℃ and a relative humidity of 50±2% for more than 24 hours.

[0076] Quantitative (g / m 2 According to GB / T 451.2-2023 "Paper and Paperboard - Part 2: Determination of Basis Weight", cut 100cm... 2 The sample was weighed precisely and converted to g / m³. 2 Ten tablets of each sample were tested, and the average value was taken.

[0077] Thickness (mm): According to GB / T 451.3-2002 "Determination of thickness, density and volume of paper and paperboard", a micrometer-type thickness gauge is used to measure the thickness at 5 different positions of each sheet of paper under a contact pressure of 50 kPa. The average value is taken as the thickness of the sample. The average value is then taken for multiple samples.

[0078] Tensile strength and tensile index were determined according to GB / T 12914-2018 "Determination of tensile strength of paper and paperboard by constant speed tensile test"; sample size: 15mm×180mm, longitudinal and transverse tests were conducted separately, and longitudinal data were used for comparison in this test; test speed: 20mm / min.

[0079] Calculation of tensile index (N·m / g):

[0080] Tensile index = Tensile strength (N / m) / Basis weight (g / m) 2 )

[0081] Tear strength and tear index, refer to: GB / T 455-2002 "Determination of tear strength of paper and paperboard"; sample size: 63mm×50mm, longitudinal sample prepared according to standard requirements, and tested using Elmendorf tear tester.

[0082] Tear resistance index (mN·m) 2 Calculation of / g):

[0083] Tear resistance index = tear strength (mN) × basis weight (g / m) 2 )

[0084] Bursting strength and bursting index were determined according to GB / T 454-2020 "Determination of Paper Bursting Strength", using a Mollen bursting strength tester to test the bursting strength (kPa).

[0085] Bursting index (kPa·m) 2 Calculation of burst index (g): Bursting index = Bursting strength (kPa) / basis weight (g / m³) 2 )

[0086] For bending stiffness, referencing GB / T 22364-2018 "Determination of bending stiffness of paper and paperboard", a single cantilever bending stiffness tester was used. Bending was applied at a distance of 50 mm from the clamping end, and the bending stiffness value (mN·m) was recorded. The longitudinal data was used for comparison.

[0087] Each sample underwent mechanical property testing no less than five times, and the arithmetic mean was taken as the final result.

[0088] Table 1 Comparison of physical and mechanical properties of the embodiments and comparative examples

[0089] sample <![CDATA[Quantitative g / m 2 > Thickness (mm) Tensile index (N·m / g) <![CDATA[Tear resistance index mN·m 2 / g]]> <![CDATA[Bursting index kPa·m 2 / g]]> Bending stiffness mN·m Comparative Example 1 251 0.400 14.3 5.7 0.53 13.0 Example 2 252 0.412 16.8 6.6 0.66 15.4 Example 3 252 0.415 17.9 7.0 0.71 16.5 Example 4 252 0.410 16.5 6.3 0.62 14.8

[0090] Compared with Comparative Example 1, all three enzymatically activated examples significantly improved the mechanical properties of the packaging paper: the tensile index increased from 14.3 N·m / g to 16.5-17.9 N·m / g, an increase of 15%-25%; among them, Example 3 had the highest value of 17.9 N·m / g, an increase of 25% compared with Comparative Example 1, and also significantly higher than Examples 2 and 4. The tear resistance index increased from 5.7 mN·m 2 / g increased to 6.3-7.0 mN·m 2 / g, an increase of 11%-23%; Example 3 achieved 7.0 mN·m 2 / g, which is the highest among the three enzyme systems. The durability index is 0.53 kPa·m. 2 / g increased to 0.62-0.71 kPa·m 2 / g, increasing by 17%-34%; among which Example 3 reached 0.71kPa·m 2 / g, with the largest increase. Bending stiffness increased from 13.0mN·m to 14.8-16.5mN·m, an increase of 14%-27%; Example 3 also had the highest value, at 16.5mN·m, indicating that the overall stiffness and forming stiffness of the paper were the best.

[0091] Among the three oxidase systems, Example 3 showed the highest tensile index, tear index, bursting index, and bending stiffness, indicating that polyphenol oxidase more fully activates the phenolic hydroxyl groups on the surface of areca leaf fibers. This is more conducive to constructing a fiber-coating co-crosslinked network with more efficient load transfer and stronger interfacial bonding, and is the preferred embodiment of the present invention in terms of mechanical properties.

[0092] Example 4 is also significantly better than Comparative Example 1 in terms of tensile strength and burst resistance. However, due to the high oxidation potential of the HRP / H2O2 system, it may cause a certain degree of non-selective oxidation of cellulose. Therefore, the overall mechanical properties are slightly lower than those of Example 3, but still significantly better than Comparative Example 1 without enzyme treatment and the baseline level before optimization by laccase system alone.

[0093] Test Example 2

[0094] Water and oil blocking performance test

[0095] Cobb water absorption 60 Tested according to GB / T 1540-2002 "Determination of water absorption of paper and paperboard (Cobb method)", sample size: 100cm. 2 Operating procedures: Fix the sample onto the Cobb test tube, add 100 mL of deionized water into the tube; allow the water to contact the sample surface for 60 seconds; pour off the water, quickly and gently press the surface moisture with absorbent paper, and weigh immediately; calculate the Cobb mass based on the mass difference before and after water absorption. 60 Value (g / m 2 ).

[0096] Water droplet absorption time test: Place the paper sample horizontally and use a 10μL micropipette to add 10μL of deionized water to the paper surface; start the stopwatch and record the time (min) from when the water droplet is added until it is completely absorbed and no longer presents a raised droplet shape; repeat 5 times for each sample and take the average value.

[0097] For the grease resistance (Kit grade) test, refer to GB / T 22805.2-2008 "Determination of grease resistance of paper and paperboard - Part 2: Surface repulsion method".

[0098] The oil penetration time test was conducted in accordance with GB / T 22805.3-2025 "Determination of grease resistance of paper and paperboard - Part 3: Turpentine method".

[0099] Each sample was tested 3-5 times, and the average value was taken.

[0100] Table 2 Comparison of water and oil resistance properties of packaging paper in the examples and comparative examples

[0101] sample <![CDATA[Cobb 60 g / m 2 ]]> Water droplet absorption time (min) Kit Level Infiltration time h Comparative Example 1 15.6 38 11 24.3 Example 2 12.5 61 12 31.2 Example 3 11.3 69 12 34.1 Example 4 13.1 56 12 29.6

[0102] Compared with Comparative Example 1, the Cobb60 values ​​of Examples 2-4 were significantly reduced, and the water absorption per unit area decreased by 16%-28%, indicating that all three enzymatic activation schemes could significantly improve the waterproof ability of the packaging paper; at the same time, the water droplet absorption time increased from 38 min to 56-69 min, indicating that the coating has a more durable barrier effect against liquid water.

[0103] In terms of water-blocking performance, Example 3 performed best: Cobb 60 The lowest value was 11.3 g / m³. 2 Compared to Comparative Example 1, the absorption time was reduced by 28%, which was also lower than that of Examples 2 and 4. The water droplet absorption time was the longest, at 69 minutes, indicating that the fiber-coating interface layer constructed by the tyrosinase system was more dense and continuous, with fewer interface micropores, and thus had the most significant barrier effect against water penetration.

[0104] Regarding oil resistance, the Kit grades of all three enzymatic examples reached level 12, higher than the level 11 of Comparative Example 1; the oil penetration time was extended from 24.3 h to 29.6-34.1 h, an increase of 22%-40%. Among them, Example 3 had the longest oil penetration time, 34.1 h, which was significantly better than Examples 2 and 4, indicating that the co-crosslinked network formed under tyrosinase activation conditions not only improved water barrier but also further enhanced the barrier ability against oils.

[0105] The combined mechanical properties and water / oil resistance properties show that: Comparative Example 1 relies solely on the density of the chitosan-phytic acid coating itself and its physical wetting of the paper surface, resulting in numerous interfacial micro-defects; Examples 2-4 activate the lignin / phenolic hydroxyl groups on the surface of areca leaf fibers through different oxidase systems, enabling them to participate in the chitosan-phytic acid network to form an in-situ co-crosslinked interfacial layer, significantly reducing interfacial micro-cracks and pores.

[0106] Test Example 3

[0107] Antibacterial performance test

[0108] The tested strains were all commercially available conventional strains: Escherichia coli (ATCC 25922); Staphylococcus aureus (ATCC 6538).

[0109] The antibacterial properties were tested in accordance with GB / T 21866-2025 "Determination of Antibacterial Properties and Antibacterial Effects of Antibacterial Coatings (Films)", with appropriate adjustments made based on the characteristics of paper-based materials.

[0110] (1) Preparation of bacterial suspension

[0111] The strain was inoculated into nutrient broth medium and cultured at 37°C with shaking for 18-24 hours to obtain a bacterial suspension in the logarithmic growth phase.

[0112] Dilute the bacterial suspension with sterile physiological saline to approximately 1×10⁻⁶. 5 -1×10 6 CFU / mL.

[0113] (2) Sample preparation

[0114] Cut the paper patterns of the examples and comparative examples into 50mm×50mm sheets;

[0115] Place it in a clean ultra-clean workbench and sterilize the surface by irradiating each side with ultraviolet lamps for 30 minutes.

[0116] (3) Inoculation and contact culture

[0117] 0.4 mL of bacterial suspension was evenly dropped onto the surface of each sample and covered with sterile polyethylene film to prevent drying.

[0118] The sample was placed in a 37℃ constant temperature incubator and incubated for 24 hours.

[0119] (4) Bacterial recovery and counting

[0120] After the culture is completed, each sample is placed in a sterile Erlenmeyer flask containing 20 mL of neutralization solution and shaken vigorously for 1 min to ensure that the bacteria on the sample surface are completely introduced into the liquid phase.

[0121] The neutralizing solution was serially diluted with appropriate multiples and inoculated onto nutrient agar plates using the plate spread method.

[0122] The number of colonies produced after culturing at 37℃ for 24 hours was counted, converted to CFU / mL, and recorded as blank control colony number N0 and sample colony number N.

[0123] (5) Calculation of antibacterial rate and logarithmic reduction value

[0124] Antibacterial rate (%): (Number of bacteria in blank control - Number of bacteria in sample) / Number of bacteria in blank control × 100%

[0125] Table 3 Comparison of antibacterial properties against common pathogens

[0126] sample Test strain Antibacterial rate % Comparative Example 1 Escherichia coli 97.1 Example 2 Escherichia coli 99.4 Example 3 Escherichia coli 99.8 Example 4 Escherichia coli 99.1 Comparative Example 1 Staphylococcus aureus 94.9 Example 2 Staphylococcus aureus 99.0 Example 3 Staphylococcus aureus 99.6 Example 4 Staphylococcus aureus 98.7

[0127] In Comparative Example 1, the paper relied solely on the antibacterial effects of chitosan and a small amount of tea polyphenols, achieving antibacterial rates of 97.1% and 94.9% against E. coli and S. aureus, respectively, demonstrating a certain antibacterial effect.

[0128] Based on this, Examples 2-4 activated the lignin / phenolic hydroxyl groups on the surface of areca leaf fibers using different oxidase systems, enabling chitosan, tea polyphenols, and phytic acid to construct a denser and more uniform functional interface layer on the fiber surface, further significantly improving the antibacterial properties: Example 2 showed antibacterial rates of 99.4% and 99.0% against E. coli and S. aureus, respectively, which were significantly higher than Comparative Example 1; the antibacterial packaging paper of Example 4 showed antibacterial rates of 99.1% and 98.7% against E. coli and S. aureus, respectively, which were also significantly better than Comparative Example 1; the antibacterial packaging paper of Example 3 had the highest antibacterial rate: 99.8% against E. coli and 99.6% against S. aureus, which were the highest values ​​among the three enzyme systems. This indicates that polyphenol oxidase (tyrosinase) oxidizes the phenolic hydroxyl groups on the surface of areca leaf fibers more fully, generating more quinone intermediates, promoting the fixation and sustained release of tea polyphenols in the coating, and enhancing the anchoring and long-term exposure effect of the chitosan-phytic acid network on antibacterial components, thereby achieving higher antibacterial efficiency with the same amount of chitosan and tea polyphenols added.

Claims

1. A method for preparing food-grade antibacterial packaging paper based on biomass conversion, characterized in that, Includes the following steps: S1 dilutes areca leaf mechanical pulp to 0.3-1.0 wt%, processes it into paper using papermaking equipment, and controls the dry paper basis weight to be 150-350 g / m³. 2 After being made, the wet paper is pressed and dehydrated, and then dried for 8-36 hours at 20-30℃ and 40-60% relative humidity to obtain unbleached areca leaf base paper, which retains the lignin and natural phenols in the fiber. S2 involves completely immersing unbleached areca leaf base paper in a 0.5-3.0 wt% sodium hydroxide aqueous solution and treating it at 40-80℃ for 20-60 min to dissolve some hemicellulose and expose the lignin and phenolic hydroxyl groups on the fiber surface; after treatment, it is washed with deionized water until the pH of the washing water is 7.0, and the paper is pre-dried to a moisture content of 5-12 wt% to obtain pre-dried areca leaf base paper. S3. Add oxidase to a buffer solution with a pH of 4.0-7.0 and a concentration of 10-100mM at an enzyme activity concentration of 3-15U / mL. Immerse the pre-dried areca leaf base paper in the solution until the paper is completely wetted. Treat at 20-50℃ for 30-60 minutes. During the treatment, introduce air and shake to maintain dissolved oxygen. After treatment, remove the paper, gently press to remove excess solution from the surface without washing with water, and then let it stand at room temperature for 5-40 minutes to keep the paper surface moist but not dripping, thus obtaining enzyme-activated areca leaf base paper. S4 involves fixing enzyme-activated areca leaf-based paper onto a flat substrate, and then uniformly coating the chitosan-tea polyphenol coating solution onto at least one side of the paper surface using a doctor blade coating or rod coating method, controlling the dry coating weight to be 10-40 g / m². 2 The coated paper is pre-dried in hot air at 60-90℃ for 3-10 minutes, so that the coating surface does not flow significantly and is basically not sticky, while retaining a certain amount of moisture inside, thus obtaining pre-dried coated paper. S5 involves immersing the pre-dried coated paper in a 3-10 wt% phytic acid aqueous solution at 10-40℃ for 5-20 minutes. After immersion, the paper is removed, excess solution is removed by rolling or scraping, and the paper is dried at 60-90℃ for 10-40 minutes to reduce the moisture content to below 8 wt%. The paper is then equilibrated at 20-30℃ and 40-60% relative humidity for 24-48 hours to obtain food-grade antibacterial packaging paper based on biomass conversion.

2. The method for preparing food-grade antibacterial packaging paper based on biomass conversion as described in claim 1, characterized in that: The buffer solution is selected from one of citrate-sodium citrate buffer, acetate-sodium acetate buffer, and phosphate buffer.

3. The method for preparing food-grade antibacterial packaging paper based on biomass conversion as described in claim 1, characterized in that: The oxidase is selected from one or more combinations of laccase, polyphenol oxidase and horseradish peroxidase.

4. The method for preparing food-grade antibacterial packaging paper based on biomass conversion as described in claim 3, characterized in that: When using horseradish peroxidase, add hydrogen peroxide to the buffer solution to make the concentration of hydrogen peroxide in the system 0.01-0.5 wt%.

5. The method for preparing food-grade antibacterial packaging paper based on biomass conversion as described in claim 3, characterized in that: The oxidase mentioned in step S3 is tyrosinase with an enzyme activity of 8-12 U / mL. It is treated with an acetate-sodium acetate buffer solution at pH 5.0-6.0 and 30-70 mM for 30-60 min at 25-35°C.

6. The method for preparing food-grade antibacterial packaging paper based on biomass conversion as described in claim 1, characterized in that: The method for preparing areca leaf mechanical pulp includes: removing moldy and rotten parts from naturally fallen or harvested areca leaf sheaths, washing away mud and impurities with water, drying, and chopping into 2-3 cm pieces; adding areca leaf pieces to a pressure-resistant hydrothermal reactor at a mass ratio of 1:2-5 to water, hydrothermally treating at 120-180℃ for 40-80 minutes, cooling, removing the pulp, washing with water until the pH of the filtrate is neutral, and removing soluble low-molecular-weight impurities; then sending the pulp to a grinding equipment for mechanical grinding to fully fiberize the areca leaves, obtaining a pulp with fiber lengths mainly distributed in the range of 0.5-2.0 mm, screening through a 100-300 mesh sieve to remove undissociated coarse residue, retaining the pulp under the sieve, and adjusting the pulp concentration to 0.2-2.0 wt% for later use.

7. The method for preparing food-grade antibacterial packaging paper based on biomass conversion as described in claim 1, characterized in that: The preparation method of the chitosan-tea polyphenol coating solution includes: adding chitosan to a 0.5-3.0 wt% acetic acid solution and stirring until completely dissolved, so that the concentration of chitosan in the coating solution is 0.5-3.0 wt%; adding glycerol to the chitosan solution, the amount of glycerol being 10-30 wt% of the mass of chitosan, and stirring to disperse it evenly; then adding tea polyphenol, the amount of tea polyphenol being 0.1-1 wt% of the mass of chitosan, and continuing to stir until the tea polyphenol is evenly dispersed, thus obtaining the chitosan-tea polyphenol coating solution.

8. The method for preparing food-grade antibacterial packaging paper based on biomass conversion as described in claim 1, characterized in that: In step S2, the concentration of the sodium hydroxide aqueous solution is 0.8-1.5 wt%, the treatment temperature is 55-65℃, and the time is 20-45 min.

9. The method for preparing food-grade antibacterial packaging paper based on biomass conversion as described in claim 1, characterized in that: In step S5, the concentration of the phytic acid aqueous solution is 3-8 wt%, the soaking time is 5-20 min, and the drying temperature is 60-80℃.

10. A food-grade antibacterial packaging paper based on biomass conversion, characterized in that: It is prepared by the method described in any one of claims 1-9.