Degradable multilayer composite heat-sealing ecological paper and preparation method thereof

Abstract

The invention discloses degradable multi-layer composite heat-sealing ecological paper and a preparation method thereof, and belongs to the technical field of papermaking, the ecological paper comprises core layer base paper, a barrier layer and a heat-sealing layer, the core layer base paper comprises agricultural and forestry waste fibers and a papermaking additive, the barrier layer adopts a cross-linked pectin-chitosan compound, and the heat-sealing layer adopts a cross-linked pectin-chitosan compound. The heat sealing layer comprises sodium alginate, konjac glucomannan, cross-linked microcapsules and a dispersing agent; the preparation method of the ecological paper comprises the following steps: S1, processing forestry and agricultural residues into papermaking raw pulp for papermaking to obtain core layer base paper; s2, coating the surface of core layer base paper with the citrus pectin-chitosan compound suspension, and then reacting with a calcium chloride solution to form a barrier layer; s3, mixing sodium alginate, konjac glucomannan, cross-linked microcapsules, a dispersing agent and water ice, and coating the surface of the barrier layer with the mixture to form a heat sealing layer; s4, the ecological paper is obtained after calendaring treatment; the ecological paper disclosed by the invention can be completely biodegraded and has good moisture resistance.

Description

Technical Field

[0001] This invention relates to the field of papermaking technology, specifically to a biodegradable multilayer composite heat-sealed eco-paper and its preparation method. Background Technology

[0002] Currently, most food product packaging is made of non-degradable plastic materials, which easily leads to a series of microplastic hazards—plastic fragments and particles with a diameter of less than 5mm. These can further transform into micron-sized plastics, submicron-sized plastics, and nano-plastics. Due to their tiny size and difficult-to-degrade characteristics, microplastics can easily enter the human body through the food chain, posing a potential threat to human health. Some packaging on the market is made of biodegradable plastics such as polylactic acid, polycaprolactone, and polypropylene succinate. However, the high production cost of these materials makes it difficult for them to widely replace non-degradable plastics in product packaging. Paper, made from natural crop raw materials, is completely biodegradable, making it a more ideal packaging material. However, the barrier and protective properties of current packaging paper differ significantly from those of plastic packaging materials. Packaging paper is easily corroded by moisture in humid environments and cannot effectively protect the product inside from external moisture and other factors for a long time. Therefore, some packaging paper forms a waterproof barrier layer by coating its surface with biodegradable barrier materials. However, the barrier layer inevitably uses non-degradable materials.

[0003] Based on the above, Chinese patent document CN114657816A discloses a packaging paper for sanitary products and its manufacturing process. The packaging paper for sanitary products, starting from the side closest to the contents, sequentially includes a release layer, a heat-sealing layer, a paper substrate, and a heat-sealing layer. The release layer comprises 78-94% water-based acrylic emulsion, 5-20% acrylic-grafted branched polyethylene wax, 0.3-0.8% leveling agent, 0.3-0.6% emulsifier, and 0.4-0.6% defoamer. The preparation method of the acrylic-grafted branched polyethylene wax includes: adding branched polyethylene wax to an organic solvent to obtain a branched polyethylene wax solution; adding acrylic monomer and an initiator to the organic solvent to obtain an acrylic solution; adding the acrylic solution dropwise to the branched polyethylene wax solution to react; adding ethanol to the reaction product, stirring, filtering, drying, and purifying to obtain the final product. The aforementioned patent document discloses a packaging paper with moisture-proof capabilities. The surface of the packaging paper is mainly composed of a release layer formed by water-based acrylic emulsion and acrylic grafted branched polyethylene wax, which improves the moisture-proof performance of the packaging paper surface. However, both water-based acrylic emulsion and acrylic grafted branched polyethylene wax are materials that are difficult to degrade. When the packaging paper is discarded into the natural environment, its release layer is difficult to degrade, resulting in poor environmental performance of the packaging paper. Therefore, the packaging paper disclosed in this patent document still has room for improvement. Summary of the Invention

[0004] To address the technical deficiencies in the background art, this invention proposes a biodegradable multilayer composite heat-sealable eco-paper and its preparation method, solving the aforementioned technical problems and meeting practical needs. The specific technical solution is as follows: A biodegradable multilayer composite heat-sealable eco-paper includes a core base paper, a barrier layer, and a heat-sealable layer. A barrier layer is provided on both sides of the core base paper, and the barrier layer completely covers the corresponding surface of the core base paper. The heat-sealable layer is located on the surface of one of the barrier layers away from the core base paper. The core layer base paper comprises the following components by weight: 97%-99% agricultural and forestry waste fiber, and 1%-3% papermaking additives; The barrier layer is a cross-linked pectin-chitosan complex; The heat-sealing layer comprises the following components by weight: 30%-50% sodium alginate, 25%-54% konjac glucomannan, 15%-25% cross-linked microcapsules, and 0.2%-1% dispersant. The cross-linked microcapsules consist of a calcium chloride solution encapsulated within ethyl cellulose.

[0005] As a further technical solution of the present invention, the agricultural and forestry waste fiber is selected from one or more of straw fiber, sugarcane bagasse fiber, bamboo fiber, rice straw fiber, and wheat straw fiber.

[0006] As a further technical solution of the present invention, the papermaking additives include a wet strength agent, a fiber dispersant, a retention and filtration aid, and a dry strength agent. The amount of wet strength agent added is 0.5%-1.5% of the mass of agricultural and forestry waste fiber, the amount of fiber dispersant added is 0.05%-0.2% of the mass of agricultural and forestry waste fiber, the amount of retention and filtration aid added is 0.01%-0.05% of the mass of agricultural and forestry waste fiber, and the amount of dry strength agent added is 0.5%-2% of the mass of agricultural and forestry waste fiber.

[0007] As a further technical solution of the present invention, the wet strength agent is selected from one or more of polyamide epichlorohydrin resin, chitosan, and dialdehyde starch.

[0008] As a further technical solution of the present invention, the fiber dispersant is selected from one or more of sodium carboxymethyl cellulose, guar gum, and oxidized starch.

[0009] As a further technical solution of the present invention, the retention and filtration aid is selected from one or more of cationic starch, chitosan, and bentonite.

[0010] As a further technical solution of the present invention, the dry strength agent is selected from one or more of cationic starch, polyvinyl alcohol, and soybean protein gum.

[0011] As a further technical solution of the present invention, the dispersant is selected from lecithin, sucrose ester, and tea saponin.

[0012] A method for preparing a biodegradable multilayer composite heat-sealable eco-paper includes the following steps: S1. Agricultural and forestry waste is crushed, impurities removed, softened, cooked, pulped and mixed with papermaking additives to obtain papermaking pulp. The papermaking pulp is then processed by papermaking, dewatering and drying to obtain core layer base paper. S2. Powdered citrus pectin-chitosan complex is added to acetic acid solution and stirred evenly to obtain a complex suspension. The complex suspension is evenly coated on both sides of the core layer base paper and then dried at low temperature to remove some of the acetic acid. Then, a mixed solution of calcium chloride and sodium hydroxide is atomized and evenly sprayed on both sides of the core layer base paper. Finally, after low temperature drying, cross-linked pectin-chitosan complex is obtained, and a barrier layer composed of cross-linked pectin-chitosan complex is formed on the surface of the core layer base paper. S3. Sodium alginate and konjac glucomannan are dissolved in deionized water to form a colloidal solution. Cross-linked microcapsules and dispersants are added to the colloidal solution and ultrasonically dispersed to obtain a heat-sealing dispersion. The heat-sealing dispersion is coated on the surface of one of the barrier layers and then dried to form a heat-sealing layer on the surface of the barrier layer. S4. Eco-paper is obtained by calendering the core paper with a barrier layer and a heat-sealing layer on the surface.

[0013] The beneficial effects of this invention are as follows: This invention discloses an eco-paper with good degradability and moisture resistance, and its manufacturing method. The eco-paper consists of a core base paper, a barrier layer, and a heat-sealing layer. The core base paper, barrier layer, and heat-sealing layer are all made of materials that can be completely biodegraded. The barrier layer has good water resistance and wet strength after cross-linking reaction. The barrier layer is placed on both sides of the eco-paper to prevent liquids in the packaged product from penetrating, and also to prevent external liquids from penetrating. The heat-sealing layer allows the eco-paper to be heat-bonded into a packaging bag for better product packaging. During the heat-sealing process, the cross-linked microcapsules release calcium chloride solution, which reacts with sodium alginate to form water-insoluble calcium alginate, thereby improving the water resistance of the heat-sealing layer after heat sealing. The eco-paper of this invention can be completely biodegraded and has good moisture resistance. Detailed Implementation

[0014] The embodiments of the present invention will be described below with reference to relevant examples. The embodiments of the present invention are not limited to the following examples, and the present invention relates to relevant necessary components in this technical field, which should be regarded as well-known technology in this technical field and can be known and mastered by those skilled in this technical field.

[0015] A biodegradable multilayer composite heat-sealable eco-paper includes a core base paper, a barrier layer, and a heat-sealable layer. A barrier layer is provided on both sides of the core base paper, and the barrier layer completely covers the corresponding surface of the core base paper. The heat-sealable layer is located on the surface of one of the barrier layers away from the core base paper. The core layer base paper comprises the following components by weight: 97%-99% agricultural and forestry waste fiber, and 1%-3% papermaking additives; The barrier layer uses a cross-linked pectin-chitosan complex; The heat-sealing layer comprises the following components by weight: 30%-50% sodium alginate, 25%-54% konjac glucomannan, 15%-25% cross-linked microcapsules, and 0.2%-1% dispersant; The cross-linked microcapsules consist of a calcium chloride solution encapsulated within ethyl cellulose.

[0016] This invention discloses an eco-paper with good degradation properties. This eco-paper is mainly used as packaging paper for food, hygiene products, and other products. The eco-paper is made from agricultural and forestry waste as the base material to obtain the core paper. It uses natural polysaccharides and other raw materials as functional coatings, enabling the eco-paper to achieve moisture-proof performance through the barrier layer. This can prevent the penetration of liquids in the product from affecting the strength of the eco-paper, and can also prevent the penetration of external moisture from affecting the quality of the product packaged by the eco-paper. The eco-paper is also reinforced by the heat-sealing properties of the heat-sealing layer to form a packaging bag or other state, thereby forming a sealed packaging space to wrap the product and isolate the product from the outside air.

[0017] It should be noted that the agricultural and forestry waste fiber is selected from one or more of straw fiber, sugarcane bagasse fiber, bamboo fiber, rice straw fiber, and wheat straw fiber. These agricultural and forestry waste fibers are processed from straw, sugarcane bagasse, bamboo, rice straw, and wheat straw, respectively, realizing the resource utilization of waste. These agricultural and forestry waste raw materials have different characteristics, and different raw materials need to be processed in different ways. After crushing and removing mud and sand, straw can be steamed at 180-200℃ for 3-5 minutes to remove wax or pectin. Then, the straw is boiled at 165-175℃ using the caustic soda-anthraquinone method. Anthraquinone can accelerate the degradation of lignin. Finally, the straw is washed countercurrently to remove residual alkali and centrifuged to separate impurities and cells, thus obtaining straw fiber that can be used to make paper pulp. After crushing, sugarcane bagasse can be screened and air-separated to remove the pith and sand, retaining the main fiber. Then, it can be boiled in hot water or dilute sulfuric acid at 120-140°C to remove soluble sugars and some hemicellulose. Subsequently, lignin is decomposed by heating to 160-175°C using the sulfate or sulfite method. Finally, residual sugars and cooking liquor are washed with hot water, and long fibers and short fibers are separated by pressure sieve. The long fibers are the sugarcane bagasse fibers used in this invention. Bamboo is cut into 3-5cm bamboo strips and the nodes and outer skin are removed. Then, the bamboo strips are boiled at 170-180℃ using the sulfate-anthraquinone method to decompose lignin and retain fiber strength. Subsequently, lignin degradation products are removed by countercurrent washing. Finally, impurities are separated by vibrating screen to obtain bamboo fiber that can be used to make paper pulp. After rice straw and wheat straw are crushed, impurities such as mud, sand and husks are removed. Then, the fibers are softened by soaking in warm water and some soluble ash is removed. Then, the rice straw and wheat straw are boiled at 160-170℃ using the caustic soda method. Afterward, the residual alkali solution is removed by countercurrent washing. Finally, after separating impurities by multi-stage pressure sieve, rice straw fiber and wheat straw fiber that can be used to make paper pulp are obtained. The agricultural and forestry waste fibers obtained after the above-mentioned agricultural and forestry wastes have been processed can be bleached and then pulped into paper pulp. It is preferable to use a variety of different agricultural and forestry waste fibers in combination, such as straw fiber, sugarcane bagasse fiber and bamboo fiber, to make up for the defects of single fiber and improve the mechanical strength of the core layer paper.

[0018] Furthermore, the papermaking additives include wet strength agents, fiber dispersants, retention and filtration aids, and dry strength agents. The amount of wet strength agent added is 0.5%-1.5% of the mass of agricultural and forestry waste fiber, the amount of fiber dispersant added is 0.05%-0.2% of the mass of agricultural and forestry waste fiber, the amount of retention and filtration aid added is 0.01%-0.05% of the mass of agricultural and forestry waste fiber, and the amount of dry strength agent added is 0.5%-2% of the mass of agricultural and forestry waste fiber. Papermaking additives are mainly used to improve the overall performance of the core layer base paper. Among them, the wet strength agent is selected from one or more of polyamide epichlorohydrin resin, chitosan, and dialdehyde starch. The wet strength agent can form a covalent cross-linked network between the fibers inside the core layer base paper, thereby significantly improving the strength of the core layer base paper in a wet state, so that the core layer base paper maintains structural stability during the subsequent coating process of barrier layer and heat seal layer. The fiber dispersant is selected from one or more of sodium carboxymethyl cellulose, guar gum, and oxidized starch. The fiber dispersant can improve the suspension uniformity of agricultural and forestry waste fibers in water, that is, the fibers in the paper pulp can be more evenly dispersed and fiber sedimentation is avoided, so that the fibers of the paper pulp are more evenly distributed on the wire surface during the papermaking process, which is beneficial to improving the thickness uniformity of the core layer base paper. Retention and filtration aids are selected from one or more of cationic starch, chitosan, and bentonite. These aids help fine fibers and fillers remain in the paper sheet through charge neutralization or bridging, improving raw material utilization and the uniformity of core layer paper thickness. They also increase the dewatering speed after papermaking, which is beneficial to improving the efficiency of core layer paper manufacturing. The dry strength agent is selected from one or more of cationic starch, polyvinyl alcohol, and soybean protein gum. By increasing the hydrogen bond points and area between fibers in the core layer paper, the dry strength agent effectively improves the tensile strength, bursting strength, and folding endurance of the core layer paper in the dry state, thereby making the final eco-paper better protect the products inside the packaging.

[0019] After the core layer paper is manufactured, a barrier layer needs to be formed on its surface. This barrier layer is key to the moisture-proof performance of eco-paper. The cross-linked pectin-chitosan complex is a product of citrus pectin-chitosan complex after a specific cross-linking reaction. The citrus pectin-chitosan complex is a polyelectrolyte complex formed in solution by electrostatic attraction between pectin rich in negatively charged carboxyl groups and chitosan rich in positively charged amino groups. The citrus pectin-chitosan complex can form a dense film through deposition. Its tight network structure can effectively block the penetration of oils, water or other small molecules, giving the core layer paper strong moisture-proof performance. After the citrus pectin-chitosan complex is coated on the surface of the core base paper, it is cross-linked by spraying calcium chloride solution. The calcium ions in calcium chloride can specifically bind to multiple carboxyl groups on the pectin molecular chain to form a stable egg-box structure cross-linked pectin-chitosan complex, which is the barrier layer on the surface of the core base paper. This ionic cross-linking reaction can further strengthen the citrus pectin-chitosan composite network, significantly reduce its swelling in water, and significantly improve the water resistance and wet strength of the barrier layer.

[0020] After the barrier layer is formed on the surface of the core paper, a heat-sealing layer needs to be coated on one side of the barrier layer to obtain the eco-paper of the present invention. The heat-sealing layer is usually coated along the edge of the barrier layer to avoid material waste. However, when the eco-paper needs to be processed into packaging bags, sodium alginate and konjac glucomannan can form a colloid with good film-forming and adhesive properties. After the colloid forms a film on the barrier layer surface, it can be wetted and then heated to activate hydrogen bond recombination, which softens the colloid. Then, pressure is applied to make the positions of the eco-paper coated with the heat-sealing layer contact and squeeze each other, which promotes the molecular chains of the two contact surfaces to diffuse and entangle with each other. After cooling, a strong sealing interface composed of a large number of hydrogen bonds is formed, thereby bonding and fixing the positions of the eco-paper coated with the heat-sealing layer through the heat-sealing layer. When the heat-sealing layer is heat-bonded, the heating temperature is 250-300℃. The cross-linked microcapsules inside are heated until they soften and rupture. That is, the ethyl cellulose shell of the cross-linked microcapsules is heated above the melting point, which releases the calcium chloride solution encapsulated inside the ethyl cellulose. The calcium chloride can undergo an ion exchange reaction with the surrounding sodium alginate to form calcium alginate, which is insoluble in water. After the eco-paper is heat-sealed to form a packaging bag, some of the sodium alginate in the heat-sealing layer of the packaging bag is converted into calcium alginate, thereby improving the water resistance of the heat-sealing layer after heat sealing. This can prevent the packaging bag from losing its adhesion performance due to water absorption by the heat-sealing layer in a humid environment. When preparing colloids by blending sodium alginate, konjac glucomannan, and cross-linked microcapsules, a dispersant needs to be added to improve the dispersibility of the cross-linked microcapsules in the colloid. The dispersant is selected from lecithin, sucrose ester, and tea saponin. Since ethyl cellulose is hydrophobic, the dispersant reduces the interfacial tension of the colloid and forms a hydrophilic film on the surface of the cross-linked microcapsules, which helps the cross-linked microcapsules to be stably suspended in the colloid and uniformly dispersed. It should be noted that the concentration of calcium chloride solution in the cross-linked microcapsules is 35%-40%, and the mass ratio of calcium chloride solution to ethyl cellulose is 2:(1-2). During heat sealing, the cross-linked microcapsules release the calcium chloride solution and react with sodium alginate. Sodium alginate is in excess in this reaction, meaning that there will be sodium alginate that has not been converted into calcium alginate in the heat-sealed layer after heat sealing. However, because the cross-linked microcapsules are uniformly dispersed in the heat-sealed layer, the calcium alginate formed by the reaction of calcium chloride and sodium alginate will be uniformly distributed in the heat-sealed layer in a network. Even if there is water penetration at the edge of the heat-sealed layer, this water will be blocked by calcium alginate and will be difficult to penetrate further, thus ensuring the water resistance of the heat-sealed layer after heat sealing.

[0021] This invention also discloses a method for preparing biodegradable multilayer composite heat-sealable eco-paper, comprising the following steps: S1. Agricultural and forestry waste is crushed, impurities removed, softened, cooked, pulped and mixed with papermaking additives to obtain papermaking pulp. The papermaking pulp is then processed by papermaking, dewatering and drying to obtain core layer base paper. S2. Powdered citrus pectin-chitosan complex is added to acetic acid solution and stirred evenly to obtain a complex suspension. The complex suspension is evenly coated on both sides of the core layer base paper and then dried at low temperature to remove some of the acetic acid. Then, a mixed solution of calcium chloride and sodium hydroxide is atomized and evenly sprayed on both sides of the core layer base paper. Finally, after low temperature drying, cross-linked pectin-chitosan complex is obtained, and a barrier layer composed of cross-linked pectin-chitosan complex is formed on the surface of the core layer base paper. S3. Sodium alginate and konjac glucomannan are dissolved in deionized water to form a colloidal solution. Cross-linked microcapsules and dispersants are added to the colloidal solution and ultrasonically dispersed to obtain a heat-sealing dispersion. The heat-sealing dispersion is coated on the surface of one of the barrier layers and then dried to form a heat-sealing layer on the surface of the barrier layer. S4. Eco-paper is obtained by calendering the core paper with a barrier layer and a heat-sealing layer on the surface.

[0022] In the production of eco-paper, this invention first involves pulping treated agricultural and forestry waste fibers and mixing them with papermaking additives to create a papermaking pulp. The pulp has a freeness of 30-50°SR and a concentration of 8%-10%. The pulp is then spread evenly on the surface of a wire screen in a headbox and shaped by a finishing roller. After finishing, the pulp is dried to form the core layer base paper, and the basis weight needs to be maintained at 20 g / m². 2 In summary, if the basis weight of the core layer paper is too low and the thickness is too thin, it is not suitable as packaging paper. The actual basis weight of the core layer paper should be adjusted according to the needs. In step S2, a complex suspension is obtained by mixing an acetic acid solution with a pH of 2-3 with the citrus pectin-chitosan complex and coating it onto the surface of the core layer base paper. Then, it is dried at a low temperature of 30-50°C. The acetic acid in the complex suspension will evaporate more quickly, causing its pH value to rise. Subsequently, the sprayed calcium chloride and sodium hydroxide mixed solution will mix with the complex suspension to form a mixed solution, raising the pH value of the mixed solution to 5-6. Then, the core layer base paper is dried at a low temperature of 30-50°C. During the drying process, the calcium ions in the calcium chloride can specifically bind to multiple carboxyl groups on the pectin molecular chain to form a stable egg-box structure cross-linked pectin-chitosan complex. After the solution on the surface of the core layer base paper is completely dried, the cross-linked pectin-chitosan complex is deposited on the surface of the core layer base paper and forms a barrier layer. In step S3, the cross-linked microcapsules can be prepared by common microcapsule preparation methods. Ethyl cellulose is dissolved in a mixed solvent of toluene and ethanol to obtain an ethyl cellulose solution. The ratio of toluene to ethanol in the mixed solvent is 7:3. The ethyl cellulose solution is mixed with an aqueous calcium chloride solution and emulsified into a water-in-oil emulsion under the action of a suitable emulsifier. The ethyl cellulose solution is used as the oil phase and the aqueous calcium chloride solution is used as the aqueous phase. The emulsion is heated to 50°C and stirred to allow the mixed solution of ethyl cellulose solution to evaporate and condense into a film on the surface of the aqueous phase. After the mixed solvent has completely evaporated, cross-linked microcapsules of ethyl cellulose encapsulating calcium chloride solution are obtained. Finally, the cross-linked microcapsules are washed to remove residual solvent on the surface and dried. In step S4 of this invention, a smooth-surfaced eco-paper is obtained through calendering. This eco-paper consists of a core base paper, a barrier layer, and a heat-sealing layer. The core base paper, barrier layer, and heat-sealing layer are all made of materials that can achieve complete biodegradability. The barrier layer has good water resistance and wet strength after cross-linking reaction. The barrier layer is placed on both sides of the eco-paper to prevent liquids in the product from penetrating when packaging the product, and also to prevent external liquids from penetrating. The heat-sealing layer allows the eco-paper to be heat-bonded into a packaging bag, which can better package the product. During the heat-sealing process, the cross-linked microcapsules release calcium chloride solution, which reacts with sodium alginate to form water-insoluble calcium alginate, thereby improving the water resistance of the heat-sealing layer after heat sealing. The eco-paper of this invention can achieve complete biodegradability and has good moisture-proof performance.

[0023] The above description is only a preferred embodiment of the present invention. It should be noted that those skilled in the art can make several improvements and modifications without departing from the principle of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A biodegradable multilayer composite heat-sealable eco-paper, comprising a core base paper, a barrier layer, and a heat-sealable layer, characterized in that, Both sides of the core base paper are provided with a barrier layer, which completely covers the corresponding surface of the core base paper. The heat-sealing layer is located on the surface of one of the barrier layers away from the core base paper. The core layer base paper comprises the following components by weight: 97%-99% agricultural and forestry waste fiber, and 1%-3% papermaking additives; The barrier layer is a cross-linked pectin-chitosan complex; The heat-sealing layer comprises the following components by weight: 30%-50% sodium alginate, 25%-54% konjac glucomannan, 15%-25% cross-linked microcapsules, and 0.2%-1% dispersant. The cross-linked microcapsules consist of a calcium chloride solution encapsulated within ethyl cellulose.

2. The biodegradable multilayer composite heat-sealable eco-paper according to claim 1, characterized in that, The agricultural and forestry waste fiber is selected from one or more of straw fiber, sugarcane bagasse fiber, bamboo fiber, rice straw fiber, and wheat straw fiber.

3. The biodegradable multilayer composite heat-sealable eco-paper according to claim 1, characterized in that, The papermaking additives include a wet strength agent, a fiber dispersant, a retention and filtration aid, and a dry strength agent. The wet strength agent is added at a rate of 0.5%-1.5% of the mass of agricultural and forestry waste fiber, the fiber dispersant is added at a rate of 0.05%-0.2% of the mass of agricultural and forestry waste fiber, the retention and filtration aid is added at a rate of 0.01%-0.05% of the mass of agricultural and forestry waste fiber, and the dry strength agent is added at a rate of 0.5%-2% of the mass of agricultural and forestry waste fiber.

4. The biodegradable multilayer composite heat-sealable eco-paper according to claim 3, characterized in that, The wet strength agent is selected from one or more of polyamide epichlorohydrin resin, chitosan, and dialdehyde starch.

5. The biodegradable multilayer composite heat-sealable eco-paper according to claim 3, characterized in that, The fiber dispersant is selected from one or more of sodium carboxymethyl cellulose, guar gum, and oxidized starch.

6. The biodegradable multilayer composite heat-sealable eco-paper according to claim 3, characterized in that, The retention and filtration aid is selected from one or more of cationic starch, chitosan, and bentonite.

7. The biodegradable multilayer composite heat-sealable eco-paper according to claim 3, characterized in that, The dry strength agent is selected from one or more of cationic starch, polyvinyl alcohol, and soybean protein gum.

8. The biodegradable multilayer composite heat-sealable eco-paper according to claim 1, characterized in that, The dispersant is selected from lecithin, sucrose ester, and tea saponin.

9. A method for preparing biodegradable multilayer composite heat-sealable eco-paper as described in any one of claims 1-8, characterized in that, Includes the following steps: S1. Agricultural and forestry waste is crushed, impurities removed, softened, cooked, pulped and mixed with papermaking additives to obtain papermaking pulp. The papermaking pulp is then processed by papermaking, dewatering and drying to obtain core layer base paper. S2. Powdered citrus pectin-chitosan complex is added to acetic acid solution and stirred evenly to obtain a complex suspension. The complex suspension is evenly coated on both sides of the core layer base paper and then dried at low temperature to remove some of the acetic acid. Then, a mixed solution of calcium chloride and sodium hydroxide is atomized and evenly sprayed on both sides of the core layer base paper. Finally, after low temperature drying, cross-linked pectin-chitosan complex is obtained, and a barrier layer composed of cross-linked pectin-chitosan complex is formed on the surface of the core layer base paper. S3. Sodium alginate and konjac glucomannan are dissolved in deionized water to form a colloidal solution. Cross-linked microcapsules and dispersants are added to the colloidal solution and ultrasonically dispersed to obtain a heat-sealing dispersion. The heat-sealing dispersion is coated on the surface of one of the barrier layers and then dried to form a heat-sealing layer on the surface of the barrier layer. S4. Eco-paper is obtained by calendering the core paper with a barrier layer and a heat-sealing layer on the surface.