Environment-friendly paper-based coating based on neosinocalamus affinis, preparation method and application

Abstract

The invention discloses an environment-friendly paper-based coating based on neosinocalamus affinis, a preparation method and application, and belongs to the technical field of paper-based packaging materials. The preparation method of the environment-friendly paper-based coating based on the neosinocalamus affinis comprises three core processes: firstly, preparing a water-containing DES solution based on tetraethylammonium chloride and oxalic acid, and pretreating the neosinocalamus affinis to obtain BNC; performing hydrophobic modification on the BNC through a ternary esterification system consisting of citric acid, polyethylene glycol and sorbitol to obtain H-BNC; and finally coating the H-BNC on the surface of the paper base and drying to obtain the environment-friendly hydrophobic paper base coating. Renewable neosinocalamus affinis is used as a raw material, an environment-friendly reagent is adopted in the whole process, participation of petroleum-based derivatives and harmful chemical substances containing fluorine and silicon is not involved, the prepared coating is easy to biodegrade, and white pollution and ecological health risks can be completely eradicated; and meanwhile, the process is simple, the raw material cost is low, the hydrophobic barrier property is excellent, and the unification of environmental protection, functionality and economical efficiency is realized.

Description

Technical Field

[0001] This invention relates to the field of paper-based packaging materials technology, specifically to an environmentally friendly paper-based coating based on bamboo, its preparation method, and its application. Background Technology

[0002] Paper-based packaging materials have a wide range of applications in food, daily necessities, and industrial product packaging. To meet the demands of use in complex environments and to endow ordinary paper with sufficient high barrier properties, surface modification and coating technologies are typically used to upgrade its functionality. Currently, the mainstream commercial technology paths mainly include the following two categories: The first category is physical coating, which treats the paper surface based on petrochemical derivatives. For example, by coating the paper surface with polymers such as polyethylene (PE) and polypropylene (PP), a dense and continuous physical barrier layer is formed. This method is mature, and the resulting composite material has good barrier effects. The second category is chemical modification, which uses fluorine- or silicon-containing compounds to modify the paper fiber surface. For example, treatment with perfluoroalkyl substances can construct a low surface energy structure on the fiber surface, thereby endowing the paper with excellent hydrophobic and oleophobic properties.

[0003] However, the aforementioned existing methods have the following limitations: First, physical coating methods, represented by polyethylene film coating, while exhibiting good barrier properties, rely on polymers derived from non-renewable resources. These polymers are difficult to degrade in the natural environment after disposal, and long-term accumulation can easily lead to environmental problems such as white pollution. Second, chemical modification methods, represented by fluorinated compounds, while providing excellent hydrophobic and oleophobic properties, may release potentially bioaccumulative, persistent, and toxic substances during production or degradation, posing potential risks to the ecological environment and human health. Furthermore, these raw materials are typically expensive, resulting in high production costs.

[0004] Therefore, how to overcome the dependence of existing methods on petroleum-based materials and harmful chemical reagents, and provide an environmentally friendly preparation method, has become a key technical problem that urgently needs to be solved in this field. Summary of the Invention

[0005] The purpose of this invention is to provide an environmentally friendly paper-based coating, preparation method and application based on bamboo, so as to overcome the problem of insufficient environmental performance caused by the reliance on petroleum-based materials and harmful chemical reagents in the prior art.

[0006] The present invention solves the above-mentioned technical problems through the following technical solution: This invention also provides a method for preparing an environmentally friendly paper-based coating based on bamboo, comprising the following steps: S1. An aqueous DES solution was prepared using tetraethylammonium chloride and oxalic acid as solids and deionized water as the aqueous phase. The aqueous DES solution was used to pretreat bamboo to obtain bamboo nanocellulose (BNC). S2. Bamboo nanocellulose BNC was hydrophobically modified using a ternary esterification system composed of citric acid, polyethylene glycol and sorbitol to obtain hydrophobic bamboo nanocellulose H-BNC. S3. Hydrophobic bamboo nanocellulose H-BNC is coated onto the surface of a paper base and dried to obtain an environmentally friendly hydrophobic paper base coating.

[0007] A further improvement of the present invention is that step S1 specifically includes the following steps: Deionized water was added to tetraethylammonium chloride and oxalic acid, and the mixture was stirred in a first oil bath to obtain an aqueous DES solution. Bamboo was added to the aqueous DES solution, and after stirring in a second oil bath, deionized water was added. The mixture was then centrifuged and washed multiple times to obtain a purified bamboo cellulose suspension. The purified bamboo cellulose suspension was subjected to high-pressure homogenization, centrifugation, and freeze-drying to obtain bamboo nanocellulose (BNC).

[0008] A further improvement of this invention is that the molar ratio of tetraethylammonium chloride, oxalic acid and deionized water is 1:(0.2~3):(1~3); and the solid-liquid ratio of bamboo and aqueous DES solution is 1:(10~30). The temperature of the first oil bath stirring is 70~100℃; the temperature of the second oil bath stirring is 60~90℃, and the time is 3~6 hours; the mass fraction of the purified bamboo cellulose suspension is 0.1~0.5%; the pressure of high-pressure homogenization is 80~100MPa.

[0009] A further improvement of the present invention is that step S2 specifically includes the following steps: Sorbitol was added to bamboo nanocellulose (BNC), and the mixture was heated to a first preset temperature and stirred. Citric acid was then added dropwise, and the mixture was heated to a second preset temperature and stirred. Polyethylene glycol was then added, and the mixture was stirred again and washed with water until neutral. Finally, it was freeze-dried to obtain hydrophobic bamboo nanocellulose (H-BNC).

[0010] A further improvement of this invention is that the mass percentages of bamboo nanocellulose (BNC) with sorbitol, citric acid, and polyethylene glycol are 1:(0.1~0.2):(0.1~0.3):(0.1~0.3). The first preset temperature is 60~90℃; the second preset temperature is 60~70℃.

[0011] A further improvement of the present invention is that it further includes the following steps: S4. Add deionized water to chitosan quaternary ammonium salt, and then disperse it by ultrasonication, stir it in a water bath, and cool it to obtain a chitosan quaternary ammonium salt dispersion; add deionized water to kaolin, and then disperse it by ultrasonication and centrifuge it to obtain a kaolin supernatant. S5. Using hydrophobic bamboo nanocellulose H-BNC as the solid and deionized water as the aqueous phase, a hydrophobic bamboo nanocellulose H-BNC solution was prepared. Chitosan quaternary ammonium salt dispersion and kaolin supernatant were added sequentially to the hydrophobic bamboo nanocellulose H-BNC solution. After stirring, the precipitate was collected by centrifugation. The precipitate was washed with water until neutral and then dried to obtain the water- and oil-resistant composite additive HO-BNC. The mass percentage of hydrophobic bamboo nanocellulose H-BNC to chitosan quaternary ammonium salt and kaolin was 1: (0.03~0.10)~(0.06~0.2). S6. Apply the water- and oil-resistant composite additive HO-BNC to the surface of the paper base, and after drying, obtain an environmentally friendly water- and oil-resistant paper base coating.

[0012] A further improvement of the present invention is that the concentration of the chitosan quaternary ammonium salt dispersion is 30%~50%; and the concentration of the kaolin supernatant is 30%~50%.

[0013] A further improvement of the present invention is that the polyethylene glycol is PEG-400, PEG-600 or PEG-800.

[0014] The present invention also provides an environmentally friendly paper-based coating based on *Bambusa textilis*, which is prepared by the above-described method for preparing an environmentally friendly paper-based coating based on *Bambusa textilis*.

[0015] The present invention also provides a paper article comprising a paper base and an environmentally friendly paper base coating, as described above, applied to at least one surface of the paper base.

[0016] Compared with the prior art, the positive and progressive effects of the present invention are as follows: This invention provides an environmentally friendly paper-based coating preparation method based on *Bambusa textilis*, comprising three core processes: First, an aqueous DES solution is prepared based on tetraethylammonium chloride and oxalic acid to pretreat *Bambusa textilis* to obtain bamboo nanocellulose (BNC); then, the BNC is hydrophobically modified using a ternary esterification system composed of citric acid, polyethylene glycol, and sorbitol to obtain hydrophobic bamboo nanocellulose H-BNC; finally, the H-BNC is coated onto the paper substrate surface and dried to obtain an environmentally friendly hydrophobic paper-based coating. This invention uses renewable *Bambusa textilis* as raw material, employs environmentally friendly reagents throughout the process, and avoids the use of petroleum-based derivatives and harmful chemicals containing fluorine or silicon. The prepared coating is easily biodegradable, eliminating white pollution and ecological health risks. Simultaneously, the process is simple, the raw material cost is low, and the hydrophobic barrier properties are excellent, achieving a balance between environmental friendliness, functionality, and economy. This provides a new path for the environmental upgrading of paper-based packaging materials and can be widely applied in the fields of food, daily necessities, and industrial product packaging, demonstrating significant technological advancement and promising industrial application prospects. Attached Figure Description

[0017] The accompanying drawings are provided to further understand the invention and constitute a part of this invention. The illustrative embodiments of the invention and their descriptions are used to explain the invention and do not constitute an improper limitation of the invention.

[0018] Figure 1 This is a schematic diagram of the process for preparing an environmentally friendly paper-based coating based on *Bambusa textilis* according to the present invention. Figure 2 This is a schematic diagram of another method for preparing an environmentally friendly paper-based coating based on *Bambusa textilis* according to the present invention. Figure 3 Figure 1 shows the water contact angle test results of the environmentally friendly water-resistant and oil-resistant paper-based coating prepared using the present invention. Figure 2 shows the water contact angle test results of the environmentally friendly water-resistant and oil-resistant paper-based coating prepared in Example 5; Figure 3 shows the water contact angle test results of the environmentally friendly water-resistant and oil-resistant paper-based coating prepared in Example 6. Figure 4 Figure 1 shows the oil resistance performance test results of the environmentally friendly water- and oil-resistant paper-based coating prepared by the present invention. Figure 2 shows the Kit12 level oil droplet penetration test of the environmentally friendly water- and oil-resistant paper-based coating prepared in Example 6. Figure 3 shows the environmentally friendly water- and oil-resistant paper-based coating after wiping Figure 4. Detailed Implementation

[0019] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, 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. The components of the embodiments of the present invention described and shown in the accompanying drawings can generally be arranged and designed in various different configurations.

[0020] Therefore, the following detailed description of the embodiments of the invention provided in the accompanying drawings is not intended to limit the scope of the claimed invention, but merely to illustrate selected embodiments of the invention. All other embodiments obtained by those skilled in the art based on the embodiments of the invention without inventive effort are within the scope of protection of the invention.

[0021] It should be noted that similar labels and letters in the following figures indicate similar items. Therefore, once an item is defined in one figure, it does not need to be further defined and explained in subsequent figures.

[0022] In the description of the embodiments of the present invention, it should be noted that if terms such as "upper," "lower," "horizontal," or "inner" indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings, or the orientation or positional relationship commonly used when the product of the invention is in use, they are only for the convenience of describing the present invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation, and therefore should not be construed as a limitation of the present invention. Furthermore, terms such as "first" and "second" are only used to distinguish descriptions and should not be construed as indicating or implying relative importance.

[0023] Furthermore, it should be noted that, unless otherwise explicitly specified and limited, the terms "set," "install," "connect," and "link" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral connection; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; and they can refer to the internal connection of two components. Those skilled in the art can understand the specific meaning of the above terms in this invention according to the specific circumstances.

[0024] The present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments. This is an explanation of the present invention and not a limitation thereof.

[0025] Cellulose, as the most abundant natural polymer material, possesses inherent advantages such as renewability, complete biodegradability, and good biocompatibility. Its nanoscale derivatives—nanocellulose, particularly bamboo nanocellulose (BNC)—have become ideal substrates for developing bio-based high-performance functional materials due to their larger specific surface area, more surface active sites, and superior mechanical strength. However, existing technologies have failed to fully and efficiently utilize this green and sustainable cellulose resource to develop paper-based barrier coatings that combine high performance with environmental friendliness.

[0026] See Figure 1Based on this, the present invention provides an environmentally friendly paper-based coating preparation method based on bamboo, comprising the following steps: S1. An aqueous DES solution was prepared using tetraethylammonium chloride and oxalic acid as solids and deionized water as the aqueous phase. The aqueous DES solution was used to pretreat bamboo to obtain bamboo nanocellulose (BNC). S2. Bamboo nanocellulose BNC was hydrophobically modified using a ternary esterification system composed of citric acid, polyethylene glycol and sorbitol to obtain hydrophobic bamboo nanocellulose H-BNC. S3. Hydrophobic bamboo nanocellulose H-BNC is coated onto the surface of a paper base and dried to obtain an environmentally friendly hydrophobic paper base coating.

[0027] This invention provides an environmentally friendly paper-based coating preparation method based on *Bambusa textilis*, comprising three core processes: First, an aqueous DES solution is prepared based on tetraethylammonium chloride and oxalic acid to pretreat *Bambusa textilis* to obtain bamboo nanocellulose (BNC); then, the BNC is hydrophobically modified using a ternary esterification system composed of citric acid, polyethylene glycol, and sorbitol to obtain hydrophobic bamboo nanocellulose H-BNC; finally, the H-BNC is coated onto the paper substrate surface and dried to obtain an environmentally friendly hydrophobic paper-based coating. This invention uses renewable *Bambusa textilis* as raw material, employs environmentally friendly reagents throughout the process, and avoids the use of petroleum-based derivatives and harmful chemicals containing fluorine or silicon. The prepared coating is easily biodegradable, eliminating white pollution and ecological health risks. Simultaneously, the process is simple, the raw material cost is low, and the hydrophobic barrier properties are excellent, achieving a balance between environmental friendliness, functionality, and economy. This provides a new path for the environmental upgrading of paper-based packaging materials and can be widely applied in the fields of food, daily necessities, and industrial product packaging, demonstrating significant technological advancement and promising industrial application prospects.

[0028] Specifically, step S1 includes the following steps: adding deionized water to tetraethylammonium chloride and oxalic acid, and stirring in a first oil bath to obtain an aqueous DES solution; adding bamboo to the aqueous DES solution, stirring in a second oil bath, adding deionized water, and then centrifuging and washing multiple times to obtain a purified bamboo cellulose suspension; and subjecting the purified bamboo cellulose suspension to high-pressure homogenization, centrifugation, and freeze-drying to obtain bamboo nanocellulose (BNC).

[0029] Specifically, the molar ratio of tetraethylammonium chloride, oxalic acid and deionized water is 1:(0.2~3):(1~3); the solid-liquid ratio of bamboo and aqueous DES solution is 1:(10~30). The temperature of the first oil bath stirring is 70~100℃; the temperature of the second oil bath stirring is 60~90℃, and the time is 3~6 hours; the mass fraction of the purified bamboo cellulose suspension is 0.1~0.5%; the pressure of high-pressure homogenization is 80~100MPa.

[0030] Specifically, step S2 includes the following steps: Sorbitol was added to bamboo nanocellulose (BNC), and the mixture was heated to a first preset temperature and stirred. Citric acid was then added dropwise, and the mixture was heated to a second preset temperature and stirred. Polyethylene glycol was then added, and the mixture was stirred again and washed with water until neutral. Finally, it was freeze-dried to obtain hydrophobic bamboo nanocellulose (H-BNC).

[0031] Specifically, the mass percentages of bamboo nanocellulose (BNC) with sorbitol, citric acid, and polyethylene glycol are 1:(0.1~0.2):(0.1~0.3):(0.1~0.3). The first preset temperature is 60~90℃; the second preset temperature is 60~70℃.

[0032] Cellulose, as the most abundant natural polymer in nature, possesses inherent advantages such as renewability, biodegradability, and good biocompatibility. Bamboo nanocellulose (BNC), as a nanoscale derivative of cellulose, has become an ideal substrate for preparing high-performance functional materials due to its larger specific surface area, more active reaction sites, and superior mechanical properties. Preparing hydrophobic and oleophobic materials based on BNC aligns with the trend of green development and reduces dependence on petroleum resources, representing an important pathway to replace traditional synthetic materials. However, the preparation of BNC and most nanocellulose (CNF) relies heavily on traditional methods such as strong acid hydrolysis and enzymatic hydrolysis. Strong acid hydrolysis easily damages the fiber structure and generates large amounts of acidic wastewater, while enzymatic hydrolysis suffers from high costs and long reaction cycles. Furthermore, in terms of hydrophobic and oleophobic modification, using single modification methods or toxic and harmful modifying reagents not only makes it difficult to achieve synergistic improvement in hydrophobic and oleophobic functions but also presents technical bottlenecks such as low modification efficiency, poor functional durability, and heavy environmental burden, severely limiting the large-scale application and industrialization of BNC-based hydrophobic and oleophobic materials. As a widely cultivated fast-growing bamboo species, *Bambusa textilis* has a short growth cycle, high cellulose content, and abundant resources, making it a high-quality raw material for the preparation of bio-nucleated natriuretic peptides (BNCs). However, research on the green and efficient preparation and synergistic functional modification of *Bambusa textilis*-derived BNCs is still relatively scarce.

[0033] See Figure 2 Against this backdrop, the present invention also provides an environmentally friendly paper-based coating preparation method based on bamboo, comprising the following steps: Aqueous DES solution was prepared using tetraethylammonium chloride and oxalic acid as solids and deionized water as the aqueous phase. Bamboo nanocellulose (BNC) was obtained by pretreating bamboo with aqueous DES solution. Bamboo nanocellulose (BNC) was hydrophobically modified using a ternary esterification system composed of citric acid, polyethylene glycol, and sorbitol to obtain hydrophobic bamboo nanocellulose (H-BNC). Deionized water was added to chitosan quaternary ammonium salt, and the mixture was then subjected to ultrasonic dispersion, water bath stirring, and cooling to obtain a chitosan quaternary ammonium salt dispersion. Deionized water was added to kaolin, and the mixture was then subjected to ultrasonic dispersion and centrifugation to obtain a kaolin supernatant. Hydrophobic bamboo nanocellulose H-BNC solution was prepared using hydrophobic bamboo nanocellulose H-BNC as solid and deionized water as aqueous phase. Chitosan quaternary ammonium salt dispersion and kaolin supernatant were added to the hydrophobic bamboo nanocellulose H-BNC solution in sequence. After stirring, the precipitate was collected by centrifugation. The precipitate was washed with water until neutral and then dried to obtain water-resistant and oil-resistant composite additive HO-BNC. The water- and oil-resistant composite additive HO-BNC is applied to the surface of a paper base and dried to obtain an environmentally friendly water- and oil-resistant paper base coating.

[0034] Preferably, the mass percentage of hydrophobic bamboo nanocellulose H-BNC to chitosan quaternary ammonium salt and kaolin is 1: (0.03~0.10)~(0.06~0.2).

[0035] The tetraethylammonium chloride-oxalic acid binary system DES (eutectic solvent) used in the preparation method of this invention has the advantages of being green, environmentally friendly, recyclable, and having minimal damage to the fiber structure. It can efficiently destroy the hydrogen bond network of cellulose-hemicellulose-lignin in bamboo fiber, achieving green dissociation of BNC. The citric acid-polyethylene glycol-sorbitol ternary modification system is non-toxic, has a mild reaction, and high modification efficiency, and can precisely introduce hydrophobic groups and optimize the functional structure. Chitosan quaternary ammonium salt and kaolin have the advantages of good biocompatibility, low cost, and strong synergistic oil-repellent properties, which can further improve the oil-repellent performance and stability of the material. Developing green preparation and hydrophobic-oil-repellent synergistic modification technology of bamboo-derived BNC based on the above-mentioned high-quality reagents can not only break through the existing technical bottlenecks and promote the high-value utilization of BNC, but also provide important theoretical and technical support for alleviating plastic pollution and promoting the upgrading of the natural polymer functional materials industry, which has significant academic value and application prospects.

[0036] By controlling the degree of esterification in hydrophobic modification, while ensuring hydrophobic properties, the retained hydroxyl groups form strong hydrogen bonds with the oil-repellent components, solving the key problem of weak interfacial adhesion between the hydrophobic and oil-repellent layers. The resulting coating adheres firmly to the paper substrate and exhibits excellent water, oil, oxygen, and water vapor resistance. Furthermore, all components are environmentally friendly and biodegradable, making it suitable for green packaging applications such as food packaging.

[0037] Specifically, the concentration of the chitosan quaternary ammonium salt dispersion is 30%~50%; the concentration of the kaolin supernatant is 30%~50%.

[0038] Specifically, the polyethylene glycol is PEG-400, PEG-600, or PEG-800; among them, PEG-600 exhibits the best viscosity performance during the synthesis process.

[0039] Based on the unified inventive concept, the present invention also provides an environmentally friendly paper-based coating based on *Bambusa textilis*, which is prepared by the above-described method for preparing an environmentally friendly paper-based coating based on *Bambusa textilis*.

[0040] Based on the unified inventive concept, the present invention also provides a paper article comprising a paper base and an environmentally friendly paper base coating, as described above, applied to at least one surface of the paper base.

[0041] Example 1 An environmentally friendly paper-based coating preparation method based on *Bambusa textilis* includes the following steps: Weigh tetraethylammonium chloride, oxalic acid, and deionized water in a molar ratio of 1:0.2:1, place them in a round-bottom flask, and melt them in a first oil bath at 100℃ to prepare an aqueous DES solution. Add bamboo shoots at a solid-liquid ratio of 1:10, and stir in a second oil bath at 90℃ for 6 hours (with manual stirring every 30 minutes). After the reaction, add water until all the bamboo shoot cellulose is back-precipitated, and homogenize under high pressure at 80 MPa for 5 times. Centrifuge at 10000 r / min for 20 minutes, collect the supernatant, and freeze-dry for 12 hours to obtain bamboo nanocellulose (BNC). Preparation of H-BNC: By mass percentage, BNC was placed in a three-necked flask, 10% sorbitol was added and stirred at 90℃ for 30 min; 10% citric acid was slowly added dropwise, the temperature was raised to 70℃ and stirred at 150 r / min for 6 h; 10% PEG-600 was added and stirring was continued for 2 h, the mixture was washed with water until neutral and then freeze-dried for 8 h to obtain H-BNC.

[0042] Preparation of environmentally friendly hydrophobic paper-based coating: Add deionized water to H-BNC and ultrasonically disperse for 15-30 minutes to obtain a uniform suspension with a mass concentration of 20%. Coat the suspension evenly onto a paper base (10cm×10cm) with a coating amount of 10g / m² using a doctor blade. Vacuum dry at 60℃ for 1-2 hours to obtain an environmentally friendly hydrophobic paper base coating, which can be used as hydrophobic food packaging paper.

[0043] Example 2 A method for preparing an environmentally friendly paper-based coating based on bamboo includes the following steps: Weigh tetraethylammonium chloride, oxalic acid, and deionized water in a 1:1:2 molar ratio, place them in a round-bottom flask, and melt them in an oil bath at 80°C to prepare an aqueous DES solution. Add bamboo cellulose at a solid-liquid ratio of 1:20 to purify the bamboo, and stir in a second oil bath at 70°C for 5 hours (with manual stirring every 30 minutes). After the reaction, add water until all the bamboo cellulose is back-precipitated, and homogenize under high pressure at 90 MPa four times. Centrifuge at 10000 r / min for 20 minutes, collect the supernatant, and freeze-dry for 12 hours to obtain bamboo nanocellulose (BNC).

[0044] Preparation of H-BNC: BNC was placed in a three-necked flask, and 16% sorbitol was added and stirred at 60°C for 30 min. 20% citric acid was slowly added dropwise, and the temperature was raised to 70°C and stirred at 150 r / min for 5 h. 20% PEG-600 was added and stirring was continued for 3 h. After washing with water until neutral, H-BNC was freeze-dried for 10 h to obtain H-BNC.

[0045] Preparation of environmentally friendly hydrophobic paper-based coating: Add deionized water to H-BNC and ultrasonically disperse for 15-30 minutes to obtain a uniform suspension with a mass concentration of 25%. Coat the suspension evenly onto a paper base (10cm×10cm) with a coating amount of 10g / m². Vacuum dry at 60℃ for 1-2 hours to obtain an environmentally friendly hydrophobic paper base coating, which can be used as hydrophobic food packaging paper.

[0046] Example 3 An environmentally friendly paper-based coating preparation method based on *Bambusa textilis* includes the following steps: Weigh tetraethylammonium chloride, oxalic acid, and deionized water in a 1:3:3 molar ratio, place them in a round-bottom flask, and melt them in a first oil bath at 70°C to prepare an aqueous DES solution. Add bamboo cellulose at a solid-liquid ratio of 1:30 to purify the bamboo, and stir in a second oil bath at 70°C for 6 hours (with manual stirring every 30 minutes). After the reaction, add water until all the bamboo cellulose is back-precipitated, and homogenize three times under high pressure at 100 MPa. Centrifuge at 10000 r / min for 20 minutes, collect the supernatant, and freeze-dry for 12 hours to obtain bamboo nanocellulose (BNC).

[0047] Preparation of H-BNC: BNC was placed in a three-necked flask, and 20% sorbitol was added and stirred at 85°C for 30 min. 30% citric acid was slowly added dropwise, and the temperature was raised to 65°C and stirred at 150 r / min for 4 h. 30% PEG-600 was added and stirring was continued for 5 h. After washing with water until neutral, H-BNC was freeze-dried for 10 h to obtain H-BNC.

[0048] Preparation of environmentally friendly hydrophobic paper-based coating: Add deionized water to H-BNC and ultrasonically disperse for 15-30 minutes to obtain a uniform suspension with a mass concentration of 30%. Coat the suspension evenly onto a paper base (10cm×10cm) with a coating amount of 10g / m². Vacuum dry at 60℃ for 1-2 hours to obtain an environmentally friendly hydrophobic paper base coating, which can be used as hydrophobic food packaging paper.

[0049] Performance test results: The environmentally friendly hydrophobic paper-based coatings obtained in Examples 1 to 3 were measured using a water contact angle (WCA) meter. The water contact angles were all greater than 70° and could be maintained for more than 1 minute without rapid wetting.

[0050] The test results for Example 1 were 72±2°; for Example 2, they were 82±2°; and for Example 3, they were 80±2°.

[0051] Example 4 The difference between this embodiment and Embodiment 1 is that: It also includes the following steps: Add deionized water to chitosan quaternary ammonium salt, sonicate at 300W for 20 min, stir and dissolve in a 60℃ water bath and cool to obtain a 30% chitosan quaternary ammonium salt dispersion for later use; add deionized water to kaolin to prepare a 30% solution; sonicate at 300W for 40 min, centrifuge at 8000 r / min for 10 min and take the supernatant of kaolin for later use.

[0052] Add deionized water to H-BNC to prepare a 4% solution, and sonicate at 300W for 30 min; add 3% of the above chitosan quaternary ammonium salt dispersion, and stir at 50℃ and 150 r / min for 1 h; then add 6% kaolin supernatant and continue stirring for 2 h (sonicating for 5 min every 20 min to prevent aggregation), centrifuge at 9000 r / min for 20 min to collect the precipitate, wash with water until neutral and dry for 8 h to obtain HO-BNC; Add deionized water to HO-BNC to prepare a 10% solution; ultrasonically disperse for 30 min to obtain a uniform suspension; adjust the Brookfield viscosity of the uniform suspension to 800 seconds, and use a 0.64mm nozzle airless sprayer to spray onto a 10cm×10cm paper base under the conditions of 150 bar pressure, nozzle-paper distance of 25cm, and spraying speed of 2m / min, with a coating amount of 10g / m²; dry at 80℃ for 10-30 min to obtain an environmentally friendly water- and oil-resistant paper base coating.

[0053] Example 5 The difference between this embodiment and Embodiment 2 is that: It also includes the following steps: Add deionized water to chitosan quaternary ammonium salt to prepare a 45% solution; disperse by ultrasonication at 300W for 20 min, stir and dissolve in a water bath at 60℃ and cool to obtain a chitosan quaternary ammonium salt dispersion for later use; add deionized water to kaolin to prepare a 45% solution; disperse by ultrasonication at 300W for 40 min, centrifuge at 8000 r / min for 10 min and take the supernatant of kaolin for later use.

[0054] Add deionized water to H-BNC to prepare a 3.5% solution, and sonicate at 300W for 30 min; add 8% of the above chitosan quaternary ammonium salt dispersion, and stir at 60℃ and 150 r / min for 2 h; then add 15% kaolin supernatant, and continue stirring for 3 h (sonicating for 5 min every 20 min to prevent aggregation), centrifuge at 9000 r / min for 20 min to collect the precipitate, wash with water until neutral, and dry for 8 h to obtain HO-BNC; Add deionized water to HO-BNC to prepare a 10% solution; ultrasonically disperse for 25 min to obtain a uniform suspension; adjust the Brookfield viscosity of the uniform suspension to 600 seconds, and use a 0.64mm nozzle airless sprayer to spray onto the base paper (10cm×10cm) under the conditions of 150 bar pressure, nozzle-paper distance of 25cm, and spraying speed of 2m / min, with a coating amount of 10g / m²; dry at 80℃ for 10-30 min to obtain an environmentally friendly water- and oil-resistant paper base coating.

[0055] Example 6 The difference between this embodiment and Embodiment 3 is that: It also includes the following steps: Add deionized water to chitosan quaternary ammonium salt to prepare a 50% solution; ultrasonically disperse at 300W for 20 min, stir and dissolve in a water bath at 60℃ and cool to obtain a chitosan quaternary ammonium salt dispersion for later use; add deionized water to kaolin to prepare a 50% solution; ultrasonically disperse at 300W for 40 min, centrifuge at 8000 r / min for 10 min and take the supernatant of kaolin for later use.

[0056] Add deionized water to H-BNC to prepare a 3% solution, and sonicate at 300W for 30 min; add 10% of the above chitosan quaternary ammonium salt dispersion, and stir at 70℃ and 150 r / min for 3 h; then add 20% kaolin supernatant, and continue stirring for 4 h (sonicating for 5 min every 20 min to prevent aggregation), centrifuge at 9000 r / min for 20 min to collect the precipitate, wash with water until neutral, and dry for 8 h to obtain HO-BNC; Add deionized water to HO-BNC to prepare a 15% solution; ultrasonically disperse for 20 min to obtain a uniform suspension; adjust the Brookfield viscosity of the uniform suspension to 400 seconds, and use a 0.64mm nozzle airless sprayer to spray onto the base paper (10cm×10cm) under the conditions of 150 bar pressure, nozzle-paper distance of 25cm, and spraying speed of 2m / min, with a coating amount of 10g / m²; dry at 80℃ for 10-30 min to obtain an environmentally friendly water- and oil-resistant paper base coating.

[0057] Performance testing: The environmentally friendly water- and oil-resistant paper-based coatings obtained in Examples 4 to 6 were measured using a water contact angle (WCA) meter. All coatings showed a water contact angle greater than 92° and maintained this angle for more than one minute without rapid wetting. See also... Figure 3 Figure (a) shows the water contact angle test results of the environmentally friendly water-resistant and oil-resistant paper-based coating prepared in Example 5; Figure (b) shows the water contact angle test results of the environmentally friendly water-resistant and oil-resistant paper-based coating prepared in Example 6. The contact angles are all above 95°, which meets certain superhydrophobic effects.

[0058] Meanwhile, the environmentally friendly water- and oil-resistant paper-based coatings obtained in Examples 4 to 6 were subjected to Kit tests in accordance with the TAPPIT 559cm-02 standard. The test results are shown in Table 1.

[0059] Table 1 Test Results

[0060] See Figure 4 Figure (A) is a schematic diagram of the Kit12 level oil droplet penetration test of the environmentally friendly water-resistant and oil-resistant paper-based coating prepared in Example 6; Figure (B) is a schematic diagram of the environmentally friendly water-resistant and oil-resistant paper-based coating after wiping Figure (A). Under the Kit12 level oil droplet penetration test, the environmentally friendly water-resistant and oil-resistant paper-based coating prepared in Example 6 has reached level 12 with no penetration.

[0061] This invention, through specific component design and process control, can successfully prepare a fully bio-based water- and oil-resistant paper with excellent comprehensive performance. The finished product has a water contact angle ≥92°, an oil resistance rating of up to level 12, and long-lasting hydrophobic and oil-resistant effects; tensile strength ≥26MPa, good flexibility, and is not easily damaged; it contains no harmful residues and meets food contact safety standards; its performance is stable within the temperature range of 0℃ to 120℃, and its comprehensive performance far exceeds that of traditional cellulose-based materials, meeting the needs of multiple application scenarios. The barrier properties of this paper-based material have broad application prospects in the field of green packaging. With its green degradability, functional stability, safety, and non-toxicity, it can be widely used in food packaging, textiles, filtration, and other fields, with great market potential.

[0062] The purified bamboo cellulose used in this invention can be pre-processed in the following ways: Using a plant sample pulverizer, dry bamboo (moisture content ≤5%) to constant weight is fed into the pulverizer hopper in batches, with each batch not exceeding 1 / 3 of the hopper volume. The pulverization time is set to 1-2 minutes. After standard pulverization, the bamboo is passed through a 100-120 mesh standard inspection sieve (sieve aperture diameter 125-150μm). Pulverizing the bamboo to 100-120 mesh can significantly increase its contact area with the aqueous DES solution. The sieved bamboo powder is collected for later use, and the unsieved portion is discarded. The sieved bamboo powder must be sealed and stored in a desiccator to prevent moisture absorption from affecting the subsequent wetting effect of the DES system.

[0063] Finally, it should be noted that the embodiments listed above are merely one or more specific manifestations of the technical solution of this invention. Their purpose is to clearly illustrate the concept, principle, and application of this invention through specific examples, and is by no means intended to limit the scope of protection of this invention to these specific embodiments. In fact, the true value of this invention lies in its proposed technical ideas and innovations, rather than its manifestations or implementation methods.

[0064] For those skilled in the art, after thoroughly reading and understanding the technical solution of this invention, they are fully capable of making various changes, modifications, or equivalent substitutions to the specific implementation of the invention based on their own professional knowledge and skills. These changes may include, but are not limited to: adjusting the range of technical parameters, optimizing the algorithm flow to improve efficiency, and replacing some technical components to achieve better compatibility or reduce costs. As long as these modified technical solutions substantially retain the technical features claimed by the original invention, that is, they can still achieve the core functions and effects of this invention, then these changes should be considered to fall within the scope of protection of the pending claims of this invention.

[0065] Furthermore, with the continuous progress and development of technology, new technical means and methods are constantly emerging, which provides ample space for further improvement and perfection of this invention. Therefore, the scope of protection of this invention should also include reasonable and foresightful improvements and extensions based on existing technology. As long as these improvements and extensions do not depart from the basic principles and core concepts of this invention, they should be considered equivalents of this invention and are equally protected by patent rights.

Claims

1. A method for preparing an environmentally friendly paper-based coating based on *Bambusa textilis*, characterized in that, Includes the following steps: S1. An aqueous DES solution was prepared using tetraethylammonium chloride and oxalic acid as solids and deionized water as the aqueous phase. Bamboo nanocellulose (BNC) was obtained by pretreating bamboo with an aqueous DES solution. S2. Bamboo nanocellulose BNC was hydrophobically modified using a ternary esterification system composed of citric acid, polyethylene glycol and sorbitol to obtain hydrophobic bamboo nanocellulose H-BNC. S3. Hydrophobic bamboo nanocellulose H-BNC is coated onto the surface of a paper base and dried to obtain an environmentally friendly hydrophobic paper base coating.

2. The method for preparing an environmentally friendly paper-based coating based on *Bambusa textilis* according to claim 1, characterized in that, Step S1 specifically includes the following steps: Deionized water was added to tetraethylammonium chloride and oxalic acid, and the mixture was stirred in a first oil bath to obtain an aqueous DES solution. Bamboo was added to the aqueous DES solution, and after stirring in a second oil bath, deionized water was added. The mixture was then centrifuged and washed multiple times to obtain a purified bamboo cellulose suspension. The purified bamboo cellulose suspension was subjected to high-pressure homogenization, centrifugation, and freeze-drying to obtain bamboo nanocellulose (BNC).

3. The method for preparing an environmentally friendly paper-based coating based on *Bambusa textilis* according to claim 2, characterized in that, The molar ratio of tetraethylammonium chloride, oxalic acid and deionized water is 1:(0.2~3):(1~3); the solid-liquid ratio of bamboo and aqueous DES solution is 1:(10~30). The temperature for stirring in the first oil bath is 70~100℃; the temperature for stirring in the second oil bath is 60~90℃, and the time is 3~6 hours. The mass fraction of purified bamboo cellulose suspension was 0.1-0.5%; the pressure for high-pressure homogenization was 80-100 MPa.

4. The method for preparing an environmentally friendly paper-based coating based on *Bambusa textilis* according to claim 1, characterized in that, Step S2 specifically includes the following steps: Sorbitol was added to bamboo nanocellulose (BNC), and the mixture was heated to a first preset temperature and stirred. Citric acid was then added dropwise, and the mixture was heated to a second preset temperature and stirred. Polyethylene glycol was then added, and the mixture was stirred again and washed with water until neutral. Finally, it was freeze-dried to obtain hydrophobic bamboo nanocellulose (H-BNC).

5. The method for preparing an environmentally friendly paper-based coating based on *Bambusa textilis* according to claim 4, characterized in that, The mass percentages of bamboo nanocellulose (BNC) with sorbitol, citric acid, and polyethylene glycol were 1:(0.1~0.2):(0.1~0.3):(0.1~0.3). The first preset temperature is 60~90℃; the second preset temperature is 60~70℃.

6. The method for preparing an environmentally friendly paper-based coating based on *Bambusa textilis* according to claim 1, characterized in that, It also includes the following steps: S4. Add deionized water to chitosan quaternary ammonium salt, and then disperse it by ultrasonication, stir it in a water bath, and cool it to obtain a chitosan quaternary ammonium salt dispersion; add deionized water to kaolin, and then disperse it by ultrasonication and centrifuge it to obtain a kaolin supernatant. S5. Using hydrophobic bamboo nanocellulose H-BNC as the solid and deionized water as the aqueous phase, a hydrophobic bamboo nanocellulose H-BNC solution was prepared. Chitosan quaternary ammonium salt dispersion and kaolin supernatant were added sequentially to the hydrophobic bamboo nanocellulose H-BNC solution. After stirring, the precipitate was collected by centrifugation. The precipitate was washed with water until neutral and then dried to obtain the water- and oil-resistant composite additive HO-BNC. The mass percentage of hydrophobic bamboo nanocellulose H-BNC to chitosan quaternary ammonium salt and kaolin was 1: (0.03~0.10)~(0.06~0.2). S6. Apply the water- and oil-resistant composite additive HO-BNC to the surface of the paper base, and after drying, obtain an environmentally friendly water- and oil-resistant paper base coating.

7. The method for preparing an environmentally friendly paper-based coating based on *Bambusa textilis* according to claim 6, characterized in that, The concentration of the chitosan quaternary ammonium salt dispersion is 30%~50%; the concentration of the kaolin supernatant is 30%~50%.

8. The method for preparing an environmentally friendly paper-based coating based on *Bambusa textilis* according to claim 1, characterized in that, The polyethylene glycol is PEG-400, PEG-600 or PEG-800.

9. An environmentally friendly paper-based coating based on bamboo, characterized in that, It is prepared by an environmentally friendly paper-based coating preparation method based on bamboo as described in any one of claims 1 to 8.

10. A paper product, characterized in that, It includes a paper base and an environmentally friendly paper base coating based on bamboo as described in claim 9, which is coated on at least one surface of the paper base.

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