Environment-friendly inner liner paper and preparation method thereof

Abstract

The present application relates to the technical field of cigarette packaging materials, in particular to an environment-friendly inner liner paper and a preparation method thereof.The present application overcomes the problem of insufficient tensile strength and barrier property of the environment-friendly inner liner paper.The present application uses pulp fiber to compound nanofibrillated cellulose and high-pressure homogenization, compounds cationized lignin sulfonate and nanometer montmorillonite slurry in the homogenized slurry, and uses glyoxal for in-situ crosslinking to build an internal "brick-mud" biomimetic barrier structure; after the paper sheet is formed, the surface is coated with acetylated hemicellulose barrier agent and is heat-cured to cooperatively build a gradient structure, so that the tensile strength, water vapor barrier property and aroma barrier property of the inner liner paper are improved, and the raw materials are derived from biomass and natural minerals, which is green and environment-friendly.

Description

Technical Field

[0001] This invention relates to the field of cigarette packaging materials technology, specifically to an environmentally friendly inner lining paper and its preparation method. Background Technology

[0002] Cigarette lining paper, commonly known as the "silver paper" inside cigarette packs, is one of the key materials in cigarette packaging. Its core function is to protect the quality of tobacco products, mainly in two aspects: first, moisture retention, preventing the moisture in the tobacco from evaporating too quickly and maintaining the smooth taste of the tobacco; second, aroma retention, preventing the unique aroma compounds of tobacco from escaping and preventing the intrusion of external odors. In addition, the lining paper must also possess a certain degree of mechanical strength to withstand the operation of high-speed cigarette packaging machines.

[0003] Currently, the mainstream cigarette liner paper on the market is aluminum foil composite paper, which is made of an extremely thin layer of aluminum foil and a paper base. It utilizes the excellent barrier properties of aluminum foil against gases, water vapor, and light, and can effectively achieve moisture retention and aroma preservation. However, the drawbacks of aluminum foil composite paper are becoming increasingly apparent: the production process of aluminum foil is an energy-intensive industry, and after aluminum foil and paper are combined, their material properties are vastly different, making separation and recycling extremely difficult. As a result, the vast majority of waste aluminum foil paper can only be landfilled or incinerated, which does not meet the current global requirements for sustainable development and "carbon neutrality." In addition, the manufacture of aluminum foil depends on metallic aluminum resources, which are non-renewable resources.

[0004] To overcome the shortcomings of aluminum foil paper, the industry has been exploring alternatives, such as vacuum-metallized paper and high-barrier coated paper. While vacuum-metallized paper reduces the amount of aluminum used, it is still essentially a plastic-aluminum-paper composite material, and degradation and recycling issues remain. Another major direction is the development of fully bio-based coated paper, for example, using bio-based polymers such as modified starch, polyvinyl alcohol, and carboxymethyl cellulose for coating. However, these traditional bio-based coating materials are mostly hydrophilic polymers. Although they have some barrier properties against non-polar gases, their barrier performance drops sharply in high humidity environments, resulting in insufficient water vapor barrier capacity. At the same time, their barrier effect against key polar or weakly polar aroma molecules in tobacco is often not as good as that of aluminum foil. In addition, if environmentally friendly recycled pulp is used as the base paper, its fiber strength decreases, making it difficult to meet the tensile strength requirements of high-speed packaging for inner lining paper.

[0005] In conclusion, it is urgent to develop a new type of inner lining paper that can synergistically achieve high tensile strength and excellent barrier properties while meeting environmental protection requirements. To this end, an environmentally friendly inner lining paper and its preparation method are proposed. Summary of the Invention

[0006] The purpose of this invention is to provide an environmentally friendly inner lining paper and its preparation method.

[0007] To achieve the above objectives, the present invention provides the following technical solution: This invention provides a method for preparing environmentally friendly inner lining paper, the method of which is as follows: S1 Pulp Preparation and Homogenization: Pulp fibers are beaten, and nanofibrillated cellulose suspension is added and mixed evenly. The mixture is then processed by a high-pressure homogenizer to obtain homogenized pulp. S2 Internal Crosslinking Sizing: Add cationic lignin sulfonate, nano-montmorillonite slurry (weigh 5 parts by weight of sodium-based nano-montmorillonite powder (PA42068), add 95 parts by weight of deionized water, and shear and disperse at 10000 rpm for 30 min in a high-speed shearing machine to fully peel it off and form a nano-montmorillonite slurry with 5% solid content) and glyoxal to the homogeneous slurry in sequence, adjust the pH value, and stir to obtain the crosslinking slurry; S3 paper forming and pre-drying: After adding a retention aid to the cross-linked pulp, it is paper-made on a wire, pressed and pre-dried to obtain the paper base layer; S4 Surface Coating: Preparation of acetylated hemicellulose; dissolving 10 parts by weight of acetylated hemicellulose in 90 parts by weight of ethyl acetate to obtain a coating solution; uniformly coating the coating solution onto the still-warm (approximately 40-50℃) paper substrate surface using a curtain coating machine; controlling the coating amount to achieve a dry basis coating weight of 2-5 g / m². 2 The coated paper is obtained; S5 Curing and Molding: The coated paper is immediately sent into a hot air impact drying unit at 110-130℃ and cured for 30-60 seconds, allowing the solvent to evaporate and the acetylated hemicellulose to form a film, resulting in environmentally friendly inner lining paper.

[0008] Preferably, the pulp fiber is bamboo pulp fiber; the cellulose content is 50%-60%; the lignin content is 19%-25%; and the ash content is ≤1%.

[0009] Preferably, the homogeneous pulp preparation method is as follows: 100 parts by weight (octane dry weight) of pulp fiber are selected, loosened, and beaten to a freeness of 30-35°SR; 5-10 parts by weight (dry weight) of nanofibrillated cellulose suspension (aqueous suspension with 3% solid content) are added and stirred evenly to obtain a mixed pulp; the mixed pulp is fed into a high-pressure homogenizer and circulated 3 times under a pressure of 80-100MPa to obtain a homogeneous pulp; the carboxyl content of nanofibrillated cellulose is 0.5-1.2mmol / g.

[0010] Preferably, the crosslinking slurry preparation method is as follows: transfer the homogeneous slurry to the mixing tank, add 3-8 parts by weight of cationic lignin sulfonate and stir for 10 min, add 2-6 parts by weight of nano-montmorillonite slurry and stir for 15 min, add 1-3 parts by weight of glyoxal (40% aqueous solution), continue stirring for 15 min, adjust the pH value to 4.5-5.5 with alum to promote the crosslinking reaction and obtain the crosslinking slurry.

[0011] Preferably, the paper base layer is prepared as follows: 0.5-1.5 parts by weight of cationic polyacrylamide (CPAM, cationicity 20%) is added to the crosslinked slurry as a retention aid. After mixing evenly, the mixture is formed by a wire paper machine. The paper is dewatered in the press section and then enters the pre-drying cylinder drying group to dry the paper to a solid content of 90%-95%, thus obtaining a warm paper base layer.

[0012] The preferred method for preparing acetylated hemicellulose is as follows: 100 parts by weight of hemicellulose are added to 500 parts by weight of formamide solvent, heated to 80°C and stirred for 30 minutes to dissolve, then cooled to 50°C, and 150-200 parts by weight of acetic anhydride are slowly added dropwise while stirring. The reaction is maintained at 50°C for 3-4 hours. After cooling, the reaction solution is poured into 2000 parts by weight of ethanol to precipitate the precipitate. After filtration, the precipitate is washed three times with ethanol and then dried in a vacuum oven at 60°C to obtain acetylated hemicellulose. The hemicellulose is derived from corn cobs and has a xylan content >80%.

[0013] A preferred method for preparing cationic lignin sulfonate is as follows: 50 parts by weight of lignin sulfonate are dissolved in 500 parts by weight of water, sodium hydroxide is added to adjust the pH to 10, the temperature is raised to 70-80℃, and 25 parts by weight of glycidyltrimethylammonium chloride (GTMAC, 70% aqueous solution) is slowly added dropwise under stirring for 4-6 hours. After cooling, the pH is adjusted to neutral to obtain cationic lignin sulfonate; the degree of sulfonation of lignin sulfonate is 1.5-2.0 mmol / g, and the molecular weight is 10000-30000 Da.

[0014] Another aspect of the present invention provides an environmentally friendly inner lining paper, which is prepared by any of the above-mentioned preparation methods; the environmentally friendly inner lining paper includes a paper base layer and a surface barrier layer; the raw materials for preparing the paper base layer include pulp fiber, nanofibrillated cellulose, cationic lignin sulfonate, nano montmorillonite pulp and glyoxal; the surface barrier layer is an acetylated hemicellulose coating.

[0015] Compared with the prior art, the beneficial effects of the present invention are as follows: 1. Nanofibrillated cellulose, as a biomass conversion material, possesses extremely high specific surface area and binding capacity. When mixed with pulp, the mechanical shearing force and cavitation effect of a high-pressure homogenizer allow the nanofibrillated cellulose nanofibers to be fully "woven" and "welded" to the surface and micropores of the pulp fibers. This synergy between the material and the process significantly increases the hydrogen bond area and strength between fibers, forming a dense nanofiber reinforcement network within the paper. This significantly improves the tensile strength and internal density of the paper, laying the foundation for subsequent barrier properties.

[0016] 2. After cationization modification, lignin acquires a positive charge, while pulp fibers and nanofibrillated cellulose both acquire a negative charge. Based on strong electrostatic attraction, cationized lignin sulfonate is efficiently and uniformly adsorbed on the fiber surface. This synergy between substances greatly improves the retention rate of lignin functional groups on the fiber, creating a solid bonding interface for the "brick-and-mortar" structure in subsequent steps.

[0017] 3. In this application, the positively charged cationic lignin sulfonate is first adsorbed onto the fiber. Subsequently, the negatively charged nano-montmorillonite slurry is attracted by electrostatics and bonded to the fiber network by the cationic lignin sulfonate. Finally, the added glyoxal causes the cationic lignin sulfonate and cellulose to cross-link and solidify, firmly fixing the "brick-and-mortar" structure in situ in the fiber gaps. The synergy of these three substances constructs an efficient "maze effect" pathway inside the paper, increasing the difficulty of water vapor penetration and thus giving the paper base layer basic barrier properties.

[0018] 4. After acetylation modification, the hydrophilic hydroxyl groups of hemicellulose are replaced by hydrophobic acetyl groups, transforming it into a hydrophobic thermoplastic biopolymer. Immediately after coating, it undergoes high-temperature thermosetting. The high temperature not only causes rapid solvent evaporation but, more importantly, melts and rearranges the acetylated hemicellulose, forming a dense, continuous, non-porous, non-polar film on the paper surface. This synergy between the material and the process greatly improves the uniformity and density of the coating. This non-polar film exhibits excellent barrier properties against gas molecules.

[0019] 5. This invention constructs a functionally graded structure through a combination of internal sizing and surface coating. Internally, a high-strength labyrinthine barrier core is synergistically constructed using cationic lignin sulfonate, nano-montmorillonite slurry, and glyoxal; on the surface, a dense barrier layer is constructed using acetylated hemicellulose. This synergy between the two processes and their product structures creates a functional gradient from the inside out. The internal structure is responsible for bearing mechanical stress and most of the moisture barrier, while the surface coating provides the final barrier. The combination of these two approaches results in a final product with overall performance far exceeding that of a single barrier method. Attached Figure Description

[0020] Figure 1 The figures show the barrier performance test results of Embodiments 2, 4-5, and Comparative Examples 4-8 of the present invention. Detailed Implementation

[0021] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0022] Please see Figure 1 This invention provides an environmentally friendly inner lining paper and its preparation method, the technical solution of which is as follows: Example 1

[0023] S1 Pulp Preparation and Homogenization: 100 parts by weight (octane dry weight) of pulp fiber were selected for delamination and beaten to a freeness of 30°SR; 5 parts by weight (dry weight) of nanofibrillated cellulose suspension (aqueous suspension with 3% solid content) were added and stirred evenly to obtain a mixed pulp; the mixed pulp was fed into a high-pressure homogenizer and circulated 3 times under a pressure of 80MPa to obtain a homogenized pulp; the pulp fiber was bamboo pulp fiber; S2 Internal Crosslinking Sizing: Transfer the homogeneous slurry to the mixing tank, add 3 parts by weight of cationic lignin sulfonate and stir for 10 min, add 2 parts by weight of nano-montmorillonite slurry and stir for 15 min, add 1 part by weight of glyoxal (40% aqueous solution), continue stirring for 15 min, adjust the pH value to 4.5 with alum to promote the crosslinking reaction and obtain the crosslinked slurry; Dissolve 50 parts by weight of lignin sulfonate in 500 parts by weight of water, add sodium hydroxide to adjust the pH to 10, heat to 70°C, and slowly add 25 parts by weight of glycidyl trimethylammonium chloride (GTMAC, 70% aqueous solution) dropwise while stirring. React for 4 hours, cool, and adjust the pH to neutral to obtain cationic lignin sulfonate. Weigh 5 parts by weight of sodium-based nano-montmorillonite powder, add 95 parts by weight of deionized water, and shear and disperse it for 30 minutes at 10,000 rpm in a high-speed shearing machine to fully peel it off and form a nano-montmorillonite slurry with a solid content of 5%. S3 paper forming and pre-drying: 0.5 parts by weight of cationic polyacrylamide (CPAM) is added to the crosslinked pulp as a retention aid. After mixing evenly, the paper is formed by a wire paper machine. The paper is dewatered in the press section and then enters the pre-drying cylinder drying group to dry the paper to a solid content of 90% to obtain a warm paper base layer. S4 Surface Coating: Preparation of acetylated hemicellulose; dissolving 10 parts by weight of acetylated hemicellulose in 90 parts by weight of ethyl acetate to obtain a coating solution; uniformly coating the coating solution onto the still-warm (approximately 40-50℃) paper substrate surface using a curtain coating machine; controlling the coating amount to achieve a dry basis coating weight of 2 g / m². 2 The coated paper is obtained; Weigh 100 parts by weight of corn cob hemicellulose and add it to 500 parts by weight of formamide solvent. Heat the mixture to 80°C and stir to dissolve for 30 minutes. Cool the mixture to 50°C and slowly add 150 parts by weight of acetic anhydride while stirring. Keep the mixture at 50°C for 3 hours. After cooling the reaction solution, pour it into 2000 parts by weight of ethanol to precipitate the precipitate. After filtration, wash the precipitate three times with ethanol and then dry it in a vacuum oven at 60°C to obtain acetylated hemicellulose. S5 Curing and Molding: The coated paper is immediately sent into a 110°C hot air impact drying unit and cured for 30 seconds, allowing the solvent to evaporate and the acetylated hemicellulose to form a film, resulting in environmentally friendly inner lining paper.

[0024] Example 2-3 The preparation method and parameters of Example 1 are similar, with specific differences shown in Table 1.

[0025] Comparative Example 1 The preparation method and parameters were the same as in Example 1, except that no nanofibrillated cellulose suspension was added.

[0026] Comparative Example 2 The preparation method and parameters are the same as in Example 1, except that the high-pressure homogenizer is used at a pressure of 50 MPa.

[0027] Comparative Example 3 The preparation method and parameters are the same as in Example 1, except that the high-pressure homogenizer is used at a pressure of 120 MPa.

[0028] Experimental Example 1: Tensile Strength Test The tensile strength was tested according to the standard GB / T 12914-2018; the results are shown in Table 1.

[0029] Table 1 Tensile strength tests of Examples 1-3 and Comparative Examples 1-3

[0030] As shown in Table 1, in Examples 1-3, nanofibrillated cellulose, as a biomass nano-reinforcing material, has an extremely high specific surface area and strong hydrogen bonding ability; the high-pressure homogenizer provides mechanical shear force and cavitation effect. The synergistic effect of the two is that the high-pressure homogenizer not only makes the nanofibrillated cellulose uniformly dispersed, but more importantly, it fully "weaves" and "welds" the nanofibrillated cellulose nanofibrils to the surface and micropores of bamboo pulp fibers. At the same time, it also "roughens" (microfibrils) the surface of bamboo pulp fibers to a certain extent, thereby forming a dense and highly integrated three-dimensional nano-reinforcing network between fibers and between fibers and nanofibrillated cellulose, thus significantly improving the tensile strength of paper to 2.4-2.7 kN / m. In Comparative Example 1, no nanofibrillated cellulose suspension was added, thus lacking the crucial nano-reinforcing phase of nanofibrillated cellulose. Although the cationic lignin sulfonate and glyoxal crosslinking system in S2 could provide some fiber bonding and reinforcement, its scale of action (molecular level) differed from that of nanofibrillated cellulose (nanoscale). Without nanofibrillated cellulose as a "nano-reinforcing bar" to bridge defects and transfer stress between fibers, the overall mechanical strength of the paper was severely insufficient, relying solely on the bamboo pulp fiber and crosslinking agent network. In Comparative Example 2, the high-pressure homogenizer was used at a pressure of 50 MPa. The energy provided by the homogenizer was insufficient to achieve optimal synergy between nanofibrillated cellulose and the homogenization process. On the one hand, the energy was insufficient to fully dissociate and "weld" the nanofibrillated cellulose nanobundles to the surface of the bamboo pulp fibers; on the other hand, the energy was also insufficient to generate sufficient microfibrilation on the surface of the bamboo pulp fibers to form effective entanglement with the nanofibrillated cellulose. This resulted in the nanofibrillated cellulose existing more as a "filler" than a "structural reinforcement" in the fiber network, thus its strength was far lower than that of Example 1. In Comparative Example 3, the high-pressure homogenizer was processed at a pressure of 120 MPa. The excessive mechanical shearing not only "welded" the fibers but also began to "cut" them. The high-pressure homogenizer's shearing effect on the fibers (including bamboo pulp fibers and nanofibrillated cellulose) at 120 MPa was too strong, resulting in a significant reduction in the average fiber length. In paper structure, fiber length is a key factor in bearing tensile stress. After the fibers are cut short, although the bonds between the fibers may still be dense, the stress transmission capacity of the overall network decreases, leading to a reduction in macroscopic tensile strength. Example 4

[0031] The preparation method and parameters were the same as in Example 2, except that when preparing cationic lignin sulfonate, sodium hydroxide was added to adjust the pH value, the temperature was raised to 75°C, GTMAC was added dropwise, and the reaction was carried out for 5 hours; the amount of cationic lignin sulfonate was 6 parts, the amount of nano-montmorillonite slurry was 4 parts, the amount of glyoxal was 2 parts, and alum was used to adjust the pH value to 5.0; the dry coating amount was 3 g / m². 2 . Example 5

[0032] The preparation method and parameters were the same as in Example 2, except that when preparing cationic lignin sulfonate, sodium hydroxide was added to adjust the pH value, the temperature was raised to 80°C, GTMAC was added dropwise, and the reaction was carried out for 6 hours; the amount of cationic lignin sulfonate was 8 parts, the amount of nano-montmorillonite slurry was 6 parts, the amount of glyoxal was 3 parts, and alum was used to adjust the pH value to 5.5; the dry coating amount was 5 g / m². 2 .

[0033] Comparative Example 4 The preparation method and parameters are the same as in Example 2, except that the lignin sulfonate was not cationized.

[0034] Comparative Example 5 The preparation method and parameters were the same as in Example 2, except that cationic lignin sulfonate was not added.

[0035] Comparative Example 6 The preparation method and parameters were the same as in Example 2, except that no nano-montmorillonite slurry was added.

[0036] Comparative Example 7 The preparation method and parameters of Example 2 are the same, except that a curtain coating machine is used to uniformly coat the coating liquid onto the surface of the paper substrate after it has been cooled to room temperature.

[0037] Comparative Example 8 The preparation method and parameters are the same as in Example 2, except that the dry coating amount is 8 g / m². 2 .

[0038] Experiment Example 2 Barrier Performance Test Referring to GB / T 1037-2021, the inner lining paper sample was sealed in a permeation cup containing desiccant and placed in a constant temperature and humidity environment of 38℃ and 90% relative humidity. The mass of water vapor passing through a unit area of ​​the inner lining paper sample within 24 hours was calculated. Air permeability was tested according to GB / T12655-1998. The results are shown in Table 2 and... Figure 1 As shown.

[0039] Table 2 Barrier performance tests of Examples 2, 4-5 and Comparative Examples 4-8

[0040] From Table 2 and Figure 1As can be seen from Examples 2 and 4-5, the lignin, after cationization modification, acquires a positive charge, while the pulp fibers and nanofibrillated cellulose are both negatively charged. The positively charged cationic lignin sulfonate is first adsorbed onto the fibers. Subsequently, the negatively charged nano-montmorillonite slurry is electrostatically attracted and bonded to the fiber network by the cationic lignin sulfonate. Finally, the addition of glyoxal causes the cationic lignin sulfonate and cellulose to cross-link and solidify, firmly fixing the "brick-and-mortar" structure in situ within the fiber gaps. Internally, a high-strength labyrinthine barrier core is constructed through the synergistic effect of cationic lignin sulfonate, nano-montmorillonite slurry, and glyoxal. On the surface, a dense barrier layer is constructed through acetylated hemicellulose, forming a functional gradient from the inside out. This results in the final product's comprehensive performance far exceeding that of a single barrier method, with a water vapor transmission rate of 4.8-5.2 g / m³. 2 • After 24 hours, the air permeability was 4.4-5.0 CU. In Comparative Example 4, the lignin sulfonate was not cationic modified. The compatibility of the uncationic lignin sulfonate with pulp fibers and nano-montmorillonite decreased, the cross-linking reaction was insufficient, the internal structure of the paper sheet was not dense enough, and the gas and water vapor channels increased. In Comparative Example 5, no cationic lignin sulfonate was added. Without lignin sulfonate to participate in the cross-linking reaction between glyoxal and montmorillonite, the internal density of the paper base was poor, the porosity increased significantly, and the barrier performance decreased. In Comparative Example 6, no nano-montmorillonite pulp was added. After the cationic lignin sulfonate was cross-linked with glyoxal, it could indeed fill the pores between fibers and provide a certain basic barrier. However, the layered structure of nano-montmorillonite provided a "maze effect." Without nano-montmorillonite, the gas permeation path degenerated from a "maze" mode to a "filling" mode, and the barrier efficiency decreased. In Comparative Example 7, a curtain coating machine was used to evenly coat the coating solution onto the surface of the paper substrate after it had cooled to room temperature. The warm substrate facilitated the spreading of the coating solution and the initial evaporation of the solvent, which was beneficial for forming a more uniform and defect-free barrier film. Coating on a cold substrate would result in uneven film formation, poor leveling, or pinholes, damaging the integrity of the surface coating and creating tiny gaps that became penetration channels. In Comparative Example 8, the dry coating amount was 8 g / m². 2 Excessive coating amount leads to excessive coating thickness, which can easily cause cracks and internal stress during drying and curing, damaging the integrity of the coating and reducing its barrier effect. Example 6

[0041] Referring to the preparation method and parameters of Example 4, the difference is that when preparing the paper base layer, the amount of CPAM is 1.0 part, and the paper is dried to a solid content of 93%; when preparing acetylated hemicellulose, 185 parts by weight of acetic anhydride are added, and the reaction is carried out at 50°C for 3.5 hours; when curing, the coated paper is immediately sent into a hot air impact drying unit at 120°C and cured for 45 seconds. Example 7

[0042] Referring to the preparation method and parameters of Example 4, the difference is that when preparing the paper base layer, the amount of CPAM is 1.5 parts, and the paper is dried to a solid content of 95%; when preparing acetylated hemicellulose, 200 parts by weight of acetic anhydride are added, and the reaction is carried out at 50°C for 4 hours; when curing, the coated paper is immediately sent into a hot air impact drying unit at 130°C and cured for 60 seconds.

[0043] Comparative Example 9 The preparation method and parameters of Example 4 were used, except that the corn cob hemicellulose was not modified.

[0044] Comparative Example 10 The preparation method and parameters of Example 4 are the same, except that the paper substrate layer is not coated.

[0045] Comparative Example 11 The preparation method and parameters are the same as in Example 4, except that the curing time of the coated paper is 100s.

[0046] Experiment Example 3 Barrier Performance Test The barrier performance was tested according to the method in Experiment Example 2; the results are shown in Table 3.

[0047] Table 3 Barrier performance tests of Examples 4, 6-7 and Comparative Examples 9-11

[0048] As shown in Table 3, in Examples 4 and 6-7, after acetylation modification of hemicellulose, the hydrophilic hydroxyl groups were replaced by hydrophobic acetyl groups, transforming it into a hydrophobic thermoplastic biopolymer. Immediately after coating, it underwent high-temperature thermosetting. The high temperature not only caused rapid solvent evaporation but, more importantly, melted and rearranged the acetylated hemicellulose, forming a dense, continuous, non-porous, non-polar film on the paper surface. This synergy between the material and the process maximized the uniformity and density of the coating. This non-polar film exhibits excellent barrier properties against gas molecules, resulting in a water vapor permeability of 4.5-4.8 g / m³. 2• After 24 hours, the air permeability was 4.0-4.4 CU. In Comparative Example 9, the corn cob hemicellulose was not modified. Unmodified corn cob hemicellulose has strong hydrophilicity and weak intermolecular forces, making it impossible to form a dense hydrophobic barrier film after coating, allowing water vapor to easily permeate. In Comparative Example 10, the paper substrate layer was not surface coated. Surface coating is a key step in forming the outer barrier layer. Without it, the micropores and fiber gaps of the paper substrate layer are directly exposed, significantly reducing the resistance to gas and water vapor permeation. In Comparative Example 11, the curing time of the coated paper was 100 s. The excessively long curing time caused the already formed barrier film to undergo thermal degradation, embrittlement, or the formation of microcracks, thereby destroying the density and integrity of the film and creating gaps in the barrier pathway.

[0049] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims and their equivalents.

Claims

1. A method for preparing environmentally friendly inner lining paper, characterized in that, The process includes the following steps: S1, 100 parts by weight of oven-dried bamboo pulp fiber is loosened and beaten to a beatness of 30-35°SR, 5-10 parts by weight of a 3% dry weight nanofibrillated cellulose suspension is added, and after stirring evenly, it is subjected to high-pressure homogenization and circulation treatment at 80-100 MPa for 3 times to obtain a homogeneous pulp; S2, 3-8 parts by weight of cationic lignin sulfonate is added to the homogeneous pulp and stirred for 10 min, 2-6 parts by weight of 5% solid content nano-montmorillonite pulp is added and stirred for 15 min, 1-3 parts by weight of 40% glyoxal aqueous solution is added and stirred for another 15 min, and then the pH value is adjusted to 4.5-5.5 with alum to obtain a crosslinked pulp; wherein, the nano-montmorillonite pulp is composed of 5 parts by weight of sodium-based nano-montmorillonite. S3. Soil powder is added to 95 parts by weight of deionized water and sheared and dispersed at 10,000 rpm for 30 min to obtain the following: S4. Cationic polyacrylamide is added to the crosslinked slurry as a retention aid, and after being mixed evenly, it is paper-made on a wire mesh, pressed, and dried in a pre-drying cylinder to a solid content of 90% to 95%, resulting in a paper base layer with a residual temperature of 40 to 50°C; S5. 10 parts by weight of acetylated hemicellulose is dissolved in 90 parts by weight of ethyl acetate to obtain a coating liquid, and the coating liquid is applied to the surface of the paper base layer in a curtain coating manner, with a dry basis coating amount of 2 to 5 g / m², to obtain coated paper; S6. The coated paper is immediately sent to a hot air impact drying unit at 110 to 130°C for curing for 30 to 60 seconds, so that the ethyl acetate evaporates and the acetylated hemicellulose forms a film, to obtain the environmentally friendly inner lining paper.

2. The method for preparing an environmentally friendly inner lining paper according to claim 1, characterized in that: The cationic polyacrylamide is used in an amount of 0.5 to 1.5 parts by weight, and the cationicity is 20%. The cross-linked pulp is formed by a wire paper machine, and the paper sheet is dewatered in the press section and then dried in the pre-drying cylinder.

3. The method for preparing an environmentally friendly inner lining paper according to claim 1, characterized in that: The preparation method of the acetylated hemicellulose is as follows: 100 parts by weight of hemicellulose are weighed and added to 500 parts by weight of formamide solvent. The mixture is heated to 80°C and stirred to dissolve for 30 minutes. The temperature is then lowered to 50°C, and 150-200 parts by weight of acetic anhydride are slowly added dropwise while stirring. The mixture is kept at 50°C for 3-4 hours. After the reaction solution is cooled, it is poured into 2000 parts by weight of ethanol to precipitate the precipitate. The precipitate is filtered and washed three times with ethanol. Then it is dried in a vacuum oven at 60°C to obtain the acetylated hemicellulose. The hemicellulose is derived from corn cob and has a xylan content of more than 80%.

4. The method for preparing an environmentally friendly inner lining paper according to claim 1, characterized in that: The preparation method of the cationic lignin sulfonate is as follows: 50 parts by weight of lignin sulfonate are dissolved in 500 parts by weight of water, sodium hydroxide is added to adjust the pH value to 10, the temperature is raised to 70-80℃, and 25 parts by weight of a 70% glycidyltrimethylammonium chloride aqueous solution is slowly added dropwise under stirring for 4-6 hours. After cooling, the pH value is adjusted to neutral to obtain the cationic lignin sulfonate; the degree of sulfonation of the lignin sulfonate is 1.5-2.0 mmol / g, and the molecular weight is 10000-30000 Da.

5. An environmentally friendly inner lining paper, characterized in that: The environmentally friendly inner lining paper is prepared by the preparation method described in any one of claims 1 to 4; the environmentally friendly inner lining paper includes a paper base layer and a surface barrier layer; the raw materials for preparing the paper base layer include bamboo pulp fiber, nanofibrillated cellulose, cationic lignin sulfonate, nano montmorillonite pulp and glyoxal; the surface barrier layer is an acetylated hemicellulose coating.

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