Environment-friendly flat adhesive for wooden furniture and preparation method thereof

Abstract

The invention relates to the technical field of bio-based high polymer material modification and adhesive preparation, and discloses an environment-friendly flat adhesive for wooden furniture and a preparation method of the environment-friendly flat adhesive. The flat adhesive is prepared from the following raw materials in parts by weight: 50 to 60 parts of starch, 1.5 to 2.5 parts of succinic anhydride, 1 to 1.5 parts of octenyl succinic anhydride, 15 to 20 parts of maleic anhydride grafted polylactic acid, 3 to 8 parts of modified lignin, 10 to 15 parts of isosorbide, 3 to 6 parts of bio-based wax and 0.2 to 20.7 parts of auxiliaries. The starch is endowed with excellent comprehensive performance through double modification of succinic anhydride and octenyl succinic anhydride. Succinic anhydride introduces polar carboxyl through efficient ring-opening reaction, so that the chemical bonding force between an adhesive layer and wood fibers is remarkably enhanced, and the peel strength is greatly improved; and a long-chain hydrophobic structure of octenyl succinic anhydride improves the compatibility and processing fluidity of starch and a polymer, and further macroscopically strengthens the water resistance of an adhesive layer, so that the finished product meets the performance requirements of the wood furniture flat adhesive on the premise of maintaining the environment-friendly advantages of full bio-based, zero odor and zero residue.

Description

Technical Field

[0001] This invention relates to the field of bio-based polymer material modification and adhesive preparation technology, and particularly to an environmentally friendly flat adhesive for wooden furniture and its preparation method. Background Technology

[0002] With increasingly stringent environmental regulations and rising consumer awareness of environmental protection, the demand for environmentally friendly adhesives in the wood furniture industry is becoming more urgent. Flat-lay adhesives are mainly used for laminating thin paper, thin wood veneer, or PVC film onto the surface of engineered wood panels. Their performance directly determines the surface smoothness, bonding durability, and resistance to environmental changes in the furniture.

[0003] Currently, traditional hot melt adhesives are mostly made of urea-formaldehyde resin or polyvinyl acetate emulsion. The former poses a hazard by continuously releasing formaldehyde, while the latter, although environmentally friendly, has poor creep resistance and heat resistance, and is easily affected by ambient humidity during the drying process. In recent years, starch-based hot melt adhesives have become a research hotspot due to their advantages such as wide availability of raw materials, biodegradability, and low carbon footprint.

[0004] However, existing starch-based hot melt adhesives still face the following key technological bottlenecks in industrial applications: Insufficient heat resistance and stability: Starch and its modified derivatives have poor thermal stability, making adhesives highly susceptible to thermal degradation and carbonization in the hot-melt state. This not only weakens the grafting strength under high-temperature conditions but also causes severe coking and carbon buildup in production equipment, requiring frequent shutdowns for tank cleaning and significantly reducing industrial production efficiency.

[0005] Mechanical properties and bonding defects: The natural semi-crystalline structure of starch makes the adhesive layer brittle and has weak wetting and penetration into the wood substrate, often causing quality problems such as edge curling, delamination and poor resistance to moisture and heat in the flat bonding process.

[0006] Multiphase component aggregation: Nanofillers and bio-based reinforcing phases are difficult to disperse at the molecular level in ultra-high viscosity starch melts, leading to functional component failure and performance fluctuations.

[0007] The contradiction between modification efficiency and environmental protection: Traditional wet modification is energy-intensive and polluting, while existing dry modification often fails to achieve both "high bio-based content" and "high performance" at the same time, resulting in products that sacrifice processing performance and product performance while pursuing environmental protection. Summary of the Invention

[0008] To address the aforementioned shortcomings, the present invention aims to propose an environmentally friendly flat adhesive for wooden furniture and its preparation method. While maintaining an extremely high bio-based content, it solves the problems of poor heat resistance and easy charring of starch-based adhesives, achieving a deep balance between high performance indicators and environmental protection attributes.

[0009] To achieve this objective, the present invention adopts the following technical solution: An environmentally friendly flat adhesive for wooden furniture comprises, by weight, 50-60 parts starch, 1.5-2.5 parts succinic anhydride, 1-1.5 parts octenyl succinic anhydride, 15-20 parts maleic anhydride-grafted polylactic acid, 3-8 parts modified lignin, 10-15 parts isosorbide, 3-6 parts bio-based wax, and 0.2-20.7 parts additives.

[0010] Preferably, the bio-based wax is rice bran wax and hydrogenated modified soybean wax, wherein the ratio of rice bran wax to hydrogenated modified soybean wax is 3:2.

[0011] Preferably, the modified lignin is at least one of enzymatically hydrolyzed lignin or sulfonated lignin that has undergone decolorization treatment.

[0012] Preferably, the adjuvant includes 0.5-1 parts by weight of bio-based nanocellulose.

[0013] Preferably, the additives include 10-15 parts by weight of tackifying resin, wherein the tackifying resin is hydrogenated rosin and terpene resin, and the ratio of hydrogenated rosin to terpene resin is 4:1.

[0014] Preferably, the adjuvants include an antibacterial agent, 1-2 parts by weight of nano zinc oxide, and 0.5-1.2 parts by weight of phytate, wherein the phytate is at least one of calcium phytate or zinc phytate.

[0015] Preferably, the additive includes silane coupling agent KH-560, used in an amount of 0.2-0.5 parts by weight.

[0016] A method for preparing an environmentally friendly flat-bonding adhesive for wooden furniture, comprising a multi-section continuous one-time extrusion process, and the following preparation method: S1. Add starch, succinic anhydride, octenyl succinic anhydride, maleic anhydride-grafted polylactic acid, nano zinc oxide, phytate, silane coupling agent KH-560 and nano cellulose to the first zone. The temperature of the first zone is 40-60℃. After the materials are mixed, they enter the second zone. S2. Isosorbide is added to the second zone, the temperature of the second zone is 120-140℃, and the materials are mixed and then enter the third zone. S3, the third zone is the kneading reaction zone, the temperature of the third zone is 160-170℃, and the material enters the fourth zone after the kneading reaction in the third zone. S4. Add bio-based wax and tackifying resin to the fourth section. The temperature of the fourth section is 150-160℃. After the materials are mixed, they enter the fifth section. S5, the fifth zone temperature is 135-150℃, with a negative pressure of -0.08 to -0.1MPa. After the material is cooled and the residual moisture and gas are removed by the negative pressure, it is extruded and granulated to obtain flat adhesive.

[0017] Preferably, before step S1, a preprocessing step is included, comprising the following steps: Modified starch drying: Vacuum dry the modified starch until the moisture content is less than 1%; Silane coupling agent adsorption: After the silane coupling agent and octenyl succinic anhydride are mixed evenly, they are sprayed evenly onto nano zinc oxide. Co-grinding: The dried modified starch, nano zinc oxide adsorbed with silane coupling agent and octenyl succinic anhydride, succinic anhydride, phytate and nano cellulose are co-grinded to 800 mesh~1000 mesh, and the grinding temperature is maintained at 45-55℃. After grinding, it is mixed with maleic anhydride grafted polylactic acid and added to the first interval.

[0018] The technical solution provided by this invention may include the following beneficial effects: 1. The dual modification of succinic anhydride and octenyl succinic anhydride endows starch with excellent comprehensive properties. Succinic anhydride introduces polar carboxyl groups through an efficient ring-opening reaction, significantly enhancing the chemical bonding force between the adhesive layer and wood fibers, and greatly improving peel strength; while the long-chain hydrophobic structure of octenyl succinic anhydride (OSA) improves the compatibility and processing fluidity of starch and polymers, and further enhances the water resistance of the adhesive layer on a macroscopic level. This allows the finished product to meet the performance requirements of wood furniture veneer adhesives while maintaining the environmental advantages of being fully bio-based, odorless, and residue-free.

[0019] Maleic anhydride-grafted polylactic acid (MAH-g-PLA) serves as the core continuous phase, utilizing the polar groups of maleic anhydride to form a strong chemical crosslink with modified starch, balancing the flexibility and cohesive strength of the adhesive layer. Lignin, as a natural polyphenolic reinforcing agent, not only significantly improves the overall heat resistance and antioxidant capacity but also provides a physical tackifying effect through its complex aromatic ring structure. Isosorbide, as a highly efficient bio-based plasticizer, effectively reduces the melting point and viscosity of the system during processing, lowering the plasticizing temperature of starch to 160-170℃, preventing high-temperature charring of starch, and ensuring microscopic uniform plasticization of the material. The addition of bio-based wax precisely regulates melt flow and open time, giving the adhesive layer excellent anti-blocking properties and surface smoothness, enabling the overall formula to exhibit excellent processing stability and long-term bonding reliability under harsh production environments.

[0020] 2. The theoretical bio-based content of the adhesive in this solution can reach over 98%, far exceeding that of traditional petroleum-based hot melt adhesives. Starch derived from recycled crops contributes more than half of the bio-carbon content, providing a highly competitive low-carbon selling point for high-end eco-friendly furniture brands. Regarding indoor environmental safety, since starch and its derivatives do not produce harmful substances such as formaldehyde and benzene during thermoplasticization, it precisely meets the stringent requirements of "odorless and formaldehyde-free" for children's furniture or whole-house customization. Furthermore, starch, lignin, and wood fiber have natural structural similarities, and under hot-pressing conditions, they can bond through hydrogen bonds to generate excellent substrate affinity. Simultaneously, the formula, through macromolecular end-capping and the replacement of volatile small molecules with a natural polyphenol antioxidant system, significantly improves thermal stability, extending the glue tank cleaning cycle in downstream factories by 2-3 times, achieving a dual improvement in environmental ecological value and industrial production efficiency.

[0021] 3. Hydrogenated modified soybean wax possesses excellent dynamic wetting properties, rapidly penetrating the micropores of the wood surface upon pressing, ensuring deep anchoring of the adhesive layer to the substrate and thus guaranteeing peel strength. Rice bran wax, with its rich long-chain fatty acid ester structure, exhibits excellent interfacial compatibility with modified starch, significantly enhancing the high-temperature cohesive strength of the adhesive layer and effectively preventing high-temperature glue overflow. The synergistic effect of these two materials greatly optimizes the thermal stability of the hot melt adhesive, ensuring its stability and resistance to carbonization in high-temperature glue tanks, significantly extending the cleaning and maintenance cycle. Furthermore, this bio-based wax combination forms a dense "biomass protective film" on the adhesive surface, effectively blocking moisture penetration and fundamentally disrupting the humidity environment required for mold growth, giving the flat-lay adhesive superior long-lasting protective performance.

[0022] 4. By employing enzymatically hydrolyzed lignin or sulfonated lignin that has undergone decolorization, the limitations of natural lignin, such as its excessively dark color and poor compatibility with starch, are effectively addressed. The decolorization process broadens the application scenarios of the adhesive in light-colored home furnishing finishes. Furthermore, sulfonation or enzymatic modification not only improves the interfacial compatibility between the modified lignin and the starch matrix but also fully leverages the natural antioxidant properties of its polyphenol structure, further enhancing the overall thermal stability and adhesive durability of the adhesive layer. In addition, sulfonated lignin possesses excellent surface activity, acting as a "dispersant" to aid in powder dispersion; while enzymatically hydrolyzed lignin exhibits better hydrophobicity, further improving the water resistance and long-term thermal oxidation resistance of the adhesive layer.

[0023] 5. The ultra-high aspect ratio of bio-based nanocellulose constructs a three-dimensional nano network in the starch matrix, playing an excellent role in skeletal reinforcement, significantly improving the creep resistance and cohesive strength of the adhesive layer, effectively locking the bonding interface, thereby strongly resisting the internal stress of the surface material caused by changes in environmental temperature and humidity, preventing blistering or cracking after moisture exposure, and ensuring the long-term flatness and stability of the furniture surface.

[0024] 6. A 4:1 synergistic system of hydrogenated rosin and terpene resin is employed, leveraging the excellent polarity and wetting properties of natural resins to significantly enhance the initial tack of the adhesive to the board surface. Hydrogenated rosin, as the main tackifying component, provides strong physical anchoring with modified starch and wood-based substrates, ensuring immediate positioning during pressing. Terpene resin further optimizes the viscoelastic properties and open time of the adhesive layer. This synergistic combination maintains the fully bio-based properties while endowing the adhesive with superior initial gripping performance, meeting the high-efficiency and precise pressing requirements of automated production lines.

[0025] 7. By combining nano-zinc oxide and phytate, a unique synergistic antibacterial system is constructed for high-starch content substrates, addressing the problem of easy mold growth in bio-based adhesives. Phytate has extremely strong chelating ability, which can pre-lock trace metal ion impurities in the starch system and play an auxiliary role in preservation by interrupting the catalytic chain of microbial growth. In terms of antibacterial activity, zinc phytate, as a "fast-acting" component, can rapidly release highly bioactive zinc ions when the adhesive layer is damp, achieving immediate killing by destroying bacterial cell membranes, while nano-zinc oxide provides long-term protection by slowly releasing zinc ions. In contrast, the calcium ions in calcium phytate exhibit chemical inertness. Although they do not possess the strong biotoxicity of zinc ions, they can provide basic protection through physical isolation and acid neutralization, maintaining good antibacterial effects while taking cost-effectiveness into account, providing flexible industrial application options for the product.

[0026] 8. The silane coupling agent KH-560 has a reactive epoxy group at one end and a hydrolyzable silica group at the other. This structure endows the flat-lay adhesive with excellent interfacial strengthening effect: the relatively small molecular weight of KH-560 acts as a "microscopic lubricant" and "interfacial connector" in the system. Its epoxy group end can rapidly capture starch molecular chains through ring-opening reaction, while the silica group end, after hydrolysis, forms a stable covalent bond anchor with the hydroxyl groups on the surface of wood fibers or the surface of nano-zinc oxide, thereby constructing a dense, water-resistant covalent bond network between the incompatible bio-based phase and the wood substrate. This not only significantly improves the peel strength stability of the adhesive layer in humid environments, but also ensures the uniform suspension of antibacterial components in the matrix through the pre-coating effect of inorganic fillers, further improving the stability of the flat-lay adhesive.

[0027] 9. Add most of the material in the first zone and preheat and mix at low temperature to ensure that the solid-solid and solid-liquid phases achieve a high degree of macroscopic uniformity before entering the molten state. Low temperature control effectively prevents the powder from getting damp and clumping.

[0028] In the second zone, isosorbide melts and penetrates into the starch granules. By pre-lubricating the surface of the starch granules with isosorbide before entering the high-shear zone, it effectively prevents the torque surge or local scorching of the starch caused by excessive local friction during the subsequent high-shear stage.

[0029] The third zone is the highest temperature zone, where maleic anhydride-grafted polylactic acid (PLA) and modified starch undergo esterification under high shear stress. In the high-temperature reaction zone, the shear stress generated by the high temperature and the kneading blocks in the screw breaks down the crystalline region of the starch, completely transforming the starch from a granular state into a continuous thermoplastic melt. This drives the modified starch to undergo esterification reactions with succinic anhydride, octenyl succinic anhydride, and maleic anhydride-grafted PLA, respectively, achieving modification of bio-based polymers and molecular-level fusion and chain extension.

[0030] Adding bio-based wax and thickening resin in the fourth zone not only utilizes the residual heat from the third zone to achieve uniform coating, but also ensures that the produced granules have a smooth, non-sticky surface, facilitating subsequent storage and use. Simultaneously, it avoids the lubricating effect of adding bio-based wax and thickening resin too early, which could reduce the shear efficiency of the third zone and ensure the plasticizing effect of the starch.

[0031] The fifth zone uses negative pressure for forced exhaust, effectively removing air trapped in the material and trace amounts of volatile byproducts generated during the reaction, such as water vapor, small-molecule acids, or monomer residues. This solves the problem of hollow or air-filled particles caused by trapped air and volatiles within the melt, ensuring that the adhesive will not explode due to gas expansion during later heating. This improves the density of the adhesive layer and significantly reduces the product's odor, meeting the high standards of "environmentally friendly" adhesives. Lowering the temperature increases melt strength, giving the extruded strips sufficient toughness for pelletizing and preventing pellet sticking or residue on the cutter.

[0032] 10. Achieving efficient integration and activity retention of multiphase micro / nano components through pretreatment: First, modified starch is vacuum dried to a moisture content of less than 1%, reducing the adverse effects of moisture on the production process and product performance from the source. Second, using nano-zinc oxide as a high specific surface area carrier, a relatively small amount of liquid component KH-560 is premixed with OSA and sprayed onto the surface of nano-zinc oxide, greatly improving the dispersion efficiency of small amounts of difficult-to-disperse liquid in the matrix. Finally, through mechanical collision generated by grinding, nano-zinc oxide, succinic anhydride, and phytate are uniformly "kneaded" into 800-1000 mesh ultrafine starch particles, and the hydroxyl groups on the surface of nanocellulose are further activated. The fibers of nanocellulose are tightly anchored to the surface of starch particles through strong hydrogen bonds, which not only solves the problem of nanoparticle aggregation, but also precisely maintains the starch from thermal denaturation at 45-55℃ and stimulates the fluidity of coupling agents, ensuring uniform material dispersion and completely eliminating the problem of product quality fluctuations caused by uneven material dispersion. Detailed Implementation

[0033] To facilitate understanding of the present invention, a more complete description is provided below. The present invention can be implemented in many different forms and is not limited to the embodiments described herein. Rather, these embodiments are provided to provide a thorough and complete understanding of the disclosure of the present invention.

[0034] Where specific techniques or conditions are not specified in the examples, they shall be performed in accordance with the techniques or conditions described in the literature in this field or in accordance with the product instructions. Reagents or instruments whose manufacturers are not specified are all commercially available conventional products.

[0035] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains. The terminology used herein in the specification of this invention is for the purpose of describing particular embodiments only and is not intended to be limiting of the invention. The term "and / or" as used herein includes any and all combinations of one or more of the associated listed items.

[0036] An environmentally friendly flat adhesive for wooden furniture comprises, by weight, 50-60 parts starch, 1.5-2.5 parts succinic anhydride, 1-1.5 parts octenyl succinic anhydride, 15-20 parts maleic anhydride-grafted polylactic acid, 3-8 parts modified lignin, 10-15 parts isosorbide, 3-6 parts bio-based wax, and 0.2-20.7 parts additives.

[0037] The dual modification of succinic anhydride and octenyl succinic anhydride endows starch with excellent comprehensive properties. Succinic anhydride introduces polar carboxyl groups through an efficient ring-opening reaction, significantly enhancing the chemical bonding force between the adhesive layer and wood fibers, and greatly improving peel strength; while the long-chain hydrophobic structure of octenyl succinic anhydride (OSA) improves the compatibility and processing fluidity of starch and polymers, and further enhances the water resistance of the adhesive layer on a macroscopic level. This allows the finished product to meet the performance requirements of wood furniture veneer adhesives while maintaining the environmental advantages of being fully bio-based, odorless, and residue-free.

[0038] Maleic anhydride-grafted polylactic acid (MAH-g-PLA) serves as the core continuous phase, utilizing the polar groups of maleic anhydride to form a strong chemical crosslink with modified starch, balancing the flexibility and cohesive strength of the adhesive layer. Lignin, as a natural polyphenolic reinforcing agent, not only significantly improves the overall heat resistance and antioxidant capacity but also provides a physical tackifying effect through its complex aromatic ring structure. Isosorbide, as a highly efficient bio-based plasticizer, effectively reduces the melting point and viscosity of the system during processing, lowering the plasticizing temperature of starch to 160-170℃, preventing high-temperature charring of starch, and ensuring microscopic uniform plasticization of the material. The addition of bio-based wax precisely regulates melt flow and open time, giving the adhesive layer excellent anti-blocking properties and surface smoothness, enabling the overall formula to exhibit excellent processing stability and long-term bonding reliability under harsh production environments.

[0039] The theoretical bio-based content of this adhesive can reach over 98%, far exceeding that of traditional petroleum-based hot melt adhesives. Starch derived from recycled crops contributes more than half of the bio-carbon content, providing a highly competitive low-carbon selling point for high-end eco-friendly furniture brands. Regarding indoor environmental safety, since starch and its derivatives do not produce harmful substances such as formaldehyde and benzene during thermoplasticization, it precisely meets the stringent requirements of "odorless and formaldehyde-free" for children's furniture or whole-house customization. Furthermore, starch, lignin, and wood fiber have natural structural similarities, and under hot-pressing conditions, they can bond through hydrogen bonds to generate excellent substrate affinity. Simultaneously, the formula, through macromolecular end-capping and the replacement of volatile small molecules with a natural polyphenol antioxidant system, significantly improves thermal stability, extending the glue tank cleaning cycle in downstream factories by 2-3 times, achieving a dual improvement in environmental ecological value and industrial production efficiency.

[0040] Preferably, the bio-based wax is rice bran wax and hydrogenated modified soybean wax, wherein the ratio of rice bran wax to hydrogenated modified soybean wax is 3:2.

[0041] Hydrogenated modified soybean wax possesses excellent dynamic wetting properties, rapidly penetrating the micropores of the wood surface upon pressing to ensure deep anchoring of the adhesive layer to the substrate, thereby guaranteeing peel strength. Rice bran wax, with its rich long-chain fatty acid ester structure, exhibits excellent interfacial compatibility with modified starch, significantly enhancing the high-temperature cohesive strength of the adhesive layer and effectively preventing high-temperature glue overflow. The synergistic effect of these two materials greatly optimizes the thermal stability of the hot melt adhesive, ensuring its stability and resistance to carbonization in high-temperature glue tanks, and significantly extending the can cleaning and maintenance cycle. Furthermore, this bio-based wax combination forms a dense "biomass protective film" on the adhesive surface, effectively blocking moisture penetration and fundamentally disrupting the humidity environment required for mold growth, thus endowing the flat-lay adhesive with superior long-lasting protective performance.

[0042] Preferably, the modified lignin is at least one of enzymatically hydrolyzed lignin or sulfonated lignin that has undergone decolorization treatment.

[0043] Unmodified lignin is typically dark in color and has poor compatibility with starch. Enzymatic hydrolysis or sulfonated lignin, after decolorization, effectively overcomes the limitations of natural lignin's dark color and poor starch compatibility. The decolorization process broadens the application scenarios of adhesives in light-colored home furnishing finishes; while sulfonation or enzymatic modification not only improves the interfacial compatibility between modified lignin and the starch matrix but also fully leverages the natural antioxidant properties of its polyphenol structure, further enhancing the overall thermal stability and adhesive durability of the adhesive layer. Furthermore, sulfonated lignin possesses excellent surface activity, acting as a "dispersant" to aid in powder dispersion; while enzymatically hydrolyzed lignin exhibits better hydrophobicity, further improving the adhesive layer's water resistance and long-term thermal oxidation resistance.

[0044] Preferably, the adjuvant includes 0.5-1 parts by weight of bio-based nanocellulose.

[0045] The ultra-high aspect ratio of bio-based nanocellulose constructs a three-dimensional nano network in the starch matrix, playing an excellent role in skeletal reinforcement, significantly improving the creep resistance and cohesive strength of the adhesive layer, effectively locking the bonding interface, thereby strongly resisting the internal stress of the surface material caused by changes in environmental temperature and humidity, preventing blistering or cracking after moisture exposure, and ensuring the long-term flatness and stability of the furniture surface.

[0046] Preferably, the additives include 10-15 parts by weight of tackifying resin, wherein the tackifying resin is hydrogenated rosin and terpene resin, and the ratio of hydrogenated rosin to terpene resin is 4:1.

[0047] A 4:1 synergistic system of hydrogenated rosin and terpene resin is employed, leveraging the excellent polarity and wetting properties of natural resins to significantly enhance the initial tack of the adhesive to the board surface. Hydrogenated rosin, as the main tackifying component, provides strong physical anchoring with modified starch and wood-based substrates, ensuring immediate positioning during pressing. The terpene resin further optimizes the viscoelastic properties and open time of the adhesive layer. This synergistic combination maintains the fully bio-based properties while endowing the adhesive with superior initial gripping performance, meeting the high-efficiency and precise pressing requirements of automated production lines.

[0048] Preferably, the adjuvants include an antibacterial agent, 1-2 parts by weight of nano zinc oxide, and 0.5-1.2 parts by weight of phytate, wherein the phytate is at least one of calcium phytate or zinc phytate.

[0049] By combining nano-zinc oxide and phytate, a unique synergistic antibacterial system is constructed for high-starch-content substrates, addressing the problem of mold growth in bio-based adhesives. Phytate possesses strong chelating ability, pre-locking trace metal ion impurities within the starch system and acting as an auxiliary preservative by disrupting the catalytic chain of microbial growth. In terms of antibacterial activity, zinc phytate, as a "fast-acting" component, rapidly releases highly bioactive zinc ions when the adhesive layer becomes damp, achieving immediate sterilization by disrupting bacterial cell membranes. Nano-zinc oxide, on the other hand, provides long-lasting protection through the slow release of zinc ions. In contrast, the calcium ions in calcium phytate exhibit chemical inertness. While lacking the potent biotoxicity of zinc ions, they provide basic protection through physical isolation and acid neutralization, maintaining good antibacterial effects while also being cost-effective, offering flexible industrial application options for the product.

[0050] It should be noted that the metal ion impurities in the phytate complex system can prevent metal ion-catalyzed oxidation reactions, and the nano-zinc oxide can shield ultraviolet rays, preventing photo-oxidative degradation of the adhesive layer under sunlight. Combined with the modified lignin's endogenous phenolic hydroxyl structure, the system possesses excellent self-antioxidant properties, eliminating the need for additional synthetic antioxidants. If further improvement in the product's antioxidant properties is required, 0.1 parts by weight of antioxidant 1010 and 0.1 parts by weight of antioxidant 168 can be added.

[0051] Preferably, the additive includes silane coupling agent KH-560, used in an amount of 0.2-0.5 parts by weight.

[0052] The silane coupling agent KH-560 has a reactive epoxy group at one end and a hydrolyzable silica group at the other. This structure endows the flat-lay adhesive with excellent interfacial strengthening effects: the relatively small molecular weight of KH-560 acts as a "microscopic lubricant" and "interfacial connector" in the system. Its epoxy group can rapidly capture starch molecular chains through ring-opening reactions, while the silica group, after hydrolysis, forms a stable covalent bond anchor with the hydroxyl groups on the surface of wood fibers or the surface of nano-zinc oxide. This constructs a dense, water-resistant covalent bond network between the incompatible bio-based phase and the wood substrate. This not only significantly improves the peel strength stability of the adhesive layer in humid environments, but also ensures the uniform suspension of antibacterial components in the matrix through the pre-coating effect on inorganic fillers, further enhancing the stability of the flat-lay adhesive.

[0053] A method for preparing an environmentally friendly flat-bonding adhesive for wooden furniture, comprising a multi-section continuous one-time extrusion process, and the following preparation method: S1. Add starch, succinic anhydride, octenyl succinic anhydride, maleic anhydride-grafted polylactic acid, nano zinc oxide, phytate, silane coupling agent KH-560 and nano cellulose to the first zone. The temperature of the first zone is 40-60℃. After the materials are mixed, they enter the second zone. Most of the material is added in the first zone and preheated and mixed at a low temperature to ensure that the solid-solid and solid-liquid phases achieve a high degree of macroscopic uniformity before entering the molten state. Low temperature control effectively prevents the powder from getting damp and clumping.

[0054] S2. Isosorbide is added to the second zone, the temperature of the second zone is 120-140℃, and the materials are mixed and then enter the third zone. In the second zone, isosorbide melts and penetrates into the starch granules. By pre-lubricating the surface of the starch granules with isosorbide before entering the high-shear zone, it effectively prevents the torque surge or local scorching of the starch caused by excessive local friction during the subsequent high-shear stage.

[0055] S3, the third zone is the kneading reaction zone, the temperature of the third zone is 160-170℃, and the material enters the fourth zone after the kneading reaction in the third zone. The third zone is the highest temperature zone, where maleic anhydride-grafted polylactic acid (PLA) and modified starch undergo esterification under high shear stress. In the high-temperature reaction zone, the shear stress generated by the high temperature and the kneading blocks in the screw breaks down the crystalline region of the starch, completely transforming the starch from a granular state into a continuous thermoplastic melt. This drives the modified starch to undergo esterification reactions with succinic anhydride, octenyl succinic anhydride, and maleic anhydride-grafted PLA, respectively, achieving modification of bio-based polymers and molecular-level fusion and chain extension.

[0056] S4. Add bio-based wax and tackifying resin to the fourth section. The temperature of the fourth section is 150-160℃. After the materials are mixed, they enter the fifth section. Adding bio-based wax and thickening resin in the fourth zone not only utilizes the residual heat from the third zone to achieve uniform coating, but also ensures that the produced granules have a smooth, non-sticky surface, facilitating subsequent storage and use. Simultaneously, it avoids the lubricating effect of adding bio-based wax and thickening resin too early, which could reduce the shear efficiency of the third zone and ensure the plasticizing effect of the starch.

[0057] S5, the fifth zone temperature is 135-150℃, with a negative pressure of -0.08 to -0.1MPa. After the material is cooled and the residual moisture and gas are removed by the negative pressure, it is extruded and granulated to obtain flat adhesive.

[0058] The fifth zone uses negative pressure for forced exhaust, effectively removing air trapped in the material and trace amounts of volatile byproducts generated during the reaction, such as water vapor, small-molecule acids, or monomer residues. This solves the problem of hollow or air-filled particles caused by trapped air and volatiles within the melt, ensuring that the adhesive will not explode due to gas expansion during later heating. This improves the density of the adhesive layer and significantly reduces the product's odor, meeting the high standards of "environmentally friendly" adhesives. Lowering the temperature increases melt strength, giving the extruded strips sufficient toughness for pelletizing and preventing pellet sticking or residue on the cutter.

[0059] Preferably, before step S1, a preprocessing step is included, comprising the following steps: Modified starch drying: Vacuum dry the modified starch until the moisture content is less than 1%; Silane coupling agent adsorption: After the silane coupling agent and octenyl succinic anhydride are mixed evenly, they are sprayed evenly onto nano zinc oxide. Co-grinding: The dried modified starch, nano zinc oxide adsorbed with silane coupling agent and octenyl succinic anhydride, succinic anhydride, phytate and nano cellulose are co-grinded to 800 mesh~1000 mesh, and the grinding temperature is maintained at 45-55℃. After grinding, it is mixed with maleic anhydride grafted polylactic acid and added to the first interval.

[0060] Highly efficient integration and activity retention of multiphase micro / nano components are achieved through pretreatment: First, modified starch is vacuum dried to a moisture content of less than 1%, reducing the adverse effects of moisture on the production process and product performance from the source. Second, using nano-zinc oxide as a high specific surface area carrier, a relatively small amount of liquid component KH-560 is premixed with OSA and sprayed onto the surface of nano-zinc oxide, greatly improving the dispersion efficiency of small amounts of difficult-to-disperse liquid in the matrix. Finally, the mechanical collision generated by grinding uniformly "kneads" nano-zinc oxide, succinic anhydride, and phytate into 800-1000 mesh ultrafine starch particles, and induces further activation of hydroxyl groups on the surface of nanocellulose. The fibers of nanocellulose are tightly anchored to the surface of starch particles through strong hydrogen bonds, which not only solves the problem of nanoparticle aggregation, but also precisely maintains the starch from thermal denaturation at 45-55℃ and stimulates the fluidity of coupling agents, ensuring uniform material dispersion and completely eliminating the problem of product quality fluctuations caused by uneven material dispersion.

[0061] It should be noted that when phytate is co-milled with zinc phytate and nano-zinc oxide after pretreatment, based on the Lewis acid-base synergistic catalysis principle, the alkaline sites on the surface of nano-zinc oxide and the phosphate groups in zinc phytate provide a weakly alkaline environment, inducing deprotonation of starch hydroxyl groups to activate nucleophilic attack. Simultaneously, the Lewis acid effect of zinc ions in zinc phytate polarizes the anhydride and epoxy groups, thus significantly reducing the reaction activation energy. This heterogeneous synergistic mechanism not only achieves efficient interfacial chemical grafting at lower temperatures but also avoids the problem of starch thermal degradation caused by traditional strong bases, ensuring high strength and high whiteness of the finished product. When using calcium phytate or a co-milling process without pretreatment, the temperatures of the second and third zones can be appropriately increased to the upper limit of the process range, and the reaction time extended, or 0.05 parts by weight of sodium carbonate can be added as an alkaline catalyst.

[0062] Example 1 The preparation method employs a pretreatment combined with a multi-zone continuous one-pass extrusion process using a twin-screw extruder. The temperatures in the first zone are 50℃, the second zone 130℃, the third zone 165℃, the fourth zone 155℃, and the fifth zone 145℃. The raw material formulation by weight is as follows: Starch, 60 parts Succinic anhydride, 2.5 parts Octenyl succinic anhydride, 1.5 parts Maleic anhydride grafted with polylactic acid, 15 parts Modified lignin, enzymatically hydrolyzed lignin: decolorized sulfonated lignin = 1:1, 5 parts. Isosorbide, 12 parts Bio-based wax, rice bran wax: hydrogenated modified soybean wax = 3:2, 4 parts. Bio-based nanocellulose, 0.5 parts Tackifying resin, hydrogenated rosin: terpene resin = 4:1, 12 parts. Nano zinc oxide, 1 part Phytate, zinc phytate: calcium phytate = 1:1, 0.5 parts. Silane coupling agent KH-560, 0.2 parts; It balances bio-based content, peel strength, and heat resistance, exhibiting excellent overall performance and meeting the flat-lay requirements of most indoor wooden furniture.

[0063] Example 2 Using the same preparation method as in Example 1, the raw material formulation is as follows by weight: Starch, 60 parts Succinic anhydride, 2 parts Octenyl succinic anhydride, 3 parts Maleic anhydride grafted with polylactic acid, 18 parts Modified lignin, enzymatically hydrolyzed lignin, 5 parts. Isosorbide, 10 parts Bio-based wax, rice bran wax: hydrogenated modified soybean wax = 3:2, 3 parts. Bio-based nanocellulose, 0.5 parts Tackifying resin, hydrogenated rosin: terpene resin = 4:1, 12 parts. Nano zinc oxide, 1.5 parts Phytate, zinc phytate, 0.5 parts Silane coupling agent KH-560, 0.5 parts; By synergistically regulating the hydrophobic modification of octenyl succinic anhydride and its covalent cross-linking with the silane coupling agent KH-560 at the interface, the problem of starch-based adhesives easily absorbing moisture and softening in environments with relatively high temperature and humidity, such as indoor bathrooms or kitchens, is solved. The long carbon chains introduced by octenyl succinic anhydride form a hydrophobic shielding layer in the starch microstructure, combined with a highly coordinated nano-zinc oxide ion network, greatly improving the dimensional stability and adhesion durability of the adhesive layer in high humidity environments, making it more suitable for areas with high temperature and humidity.

[0064] Example 3 Starch, 60 parts Succinic anhydride, 1.5 parts Octenyl succinic anhydride, 2.5 parts Maleic anhydride grafted with polylactic acid, 12 parts Modified lignin, sulfonated lignin treated with decolorization, 4 parts. Isosorbide, 15 parts Bio-based wax, rice bran wax: hydrogenated modified soybean wax = 3:2, 5 parts. Bio-based nanocellulose, 0.3 parts Tackifying resin, hydrogenated rosin: terpene resin = 4:1, 15 parts Nano zinc oxide, 0.8 parts Phytate, zinc phytate, 0.4 parts Silane coupling agent KH-560, 0.2 parts; Increasing the amount of isosorbide and OSA improves the flexibility of the adhesive layer and its wettability to low-polarity substrates; increasing the tackifying resin aims to achieve higher initial tack, making it suitable for highly automated flat lamination production lines.

[0065] Example 4 The difference from Example 1 is that the preparation method does not include a pretreatment step, but only dries the starch and grinds it separately to 800-1000 mesh, which relatively increases the length of the first interval and the material mixing time.

[0066] Although extending the pre-mixing time can improve the distribution of each component and obtain a starch-based hot melt adhesive with a certain adhesive strength, its overall performance is still significantly lower than that of Example 1, which has undergone co-grinding pretreatment.

[0067] Comparative Example 1 The difference from Example 1 is that succinic anhydride and octenyl succinic anhydride are not used.

[0068] Due to the absence of esterification modification of starch hydroxyl groups by succinic anhydride and octenyl succinic anhydride, the starch matrix retains its original high hydrophilicity, and the water absorption rate of the resulting granules increases significantly; at the same time, due to the lack of covalent crosslinking, the bonding strength is extremely low.

[0069] Comparative Example 2 The difference from Example 1 is that nano zinc oxide and phytate are not used.

[0070] The lack of a Lewis acid-base synergistic catalytic center resulted in a significant decrease in the ring-opening esterification efficiency of succinic anhydride and octenyl succinic anhydride. Infrared spectroscopy revealed a low degree of esterification, indicating that the material exhibited a physically mixed state rather than a chemically grafted state during extrusion. The finished adhesive layer was highly brittle, and due to the ineffective plasticization and modification of starch, its flowability was poor, leading to extremely poor wettability to wood-based substrates, with a peel strength less than 40% of that in Example 1.

[0071] Comparative Example 3 The difference from Example 1 is that isosorbide is not used.

[0072] Due to the lack of plasticizer, the system melt temperature is too high. The material is still difficult to plasticize at 170°C. The back pressure of the extruder is too high, and local overheating in the extruder causes the starch to caramelize and turn black at high temperature.

[0073] Comparative Example 4 The difference from Example 1 is that maleic anhydride grafted polylactic acid is not used.

[0074] Without the support of a robust macromolecular framework, the starch, although plasticized, exhibits insufficient cohesive strength after film formation, resulting in a sticky and weak adhesive layer. In creep resistance tests, the adhesive layer slipped under a constant temperature of 60°C and a load.

[0075] Comparative Example 5 The difference from Example 1 is that modified lignin and bio-based nanocellulose are not used.

[0076] The system's anti-aging properties decreased, and its color significantly darkened to a deep brown after 48 hours of thermo-oxidative aging at 180℃. Simultaneously, due to the loss of the microscopic reinforcing effect of nanocellulose, the adhesive exhibited sagging during high-grammage, high-temperature coating.

[0077] Based on GB / T 39715.3-2021 "Plastics - Bio-based Content Part 3: Determination of Bio-based Synthetic Polymer Content", GB / T 2790-2014 "Adhesives - 180° Peel Strength Test Method - Flexible Materials vs. Rigid Materials", GB / T16998-1997 "Hot Melt Adhesives - Determination of Thermal Stability", and after soaking in deionized water for 24 hours to test the water absorption rate of the adhesive particles, the results are summarized in the table below: Table 1 Test Performance Table

[0078] The technical features of the above embodiments can be combined in any way. For the sake of brevity, not all possible combinations of the technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0079] The embodiments described above are merely illustrative of several implementations of the present invention, and while the descriptions are relatively specific and detailed, they should not be construed as limiting the scope of the invention patent. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of the present invention, and these all fall within the protection scope of the present invention. Therefore, the protection scope of this invention patent should be determined by the appended claims.

Claims

1. An environmentally friendly flat adhesive for wooden furniture, characterized in that: According to the weight ratio, the raw materials include 50-60 parts starch, 1.5-2.5 parts succinic anhydride, 1-1.5 parts octenyl succinic anhydride, 15-20 parts maleic anhydride-grafted polylactic acid, 3-8 parts modified lignin, 10-15 parts isosorbide, 3-6 parts bio-based wax, and 0.2-20.7 parts additives.

2. The environmentally friendly wood furniture adhesive according to claim 1, characterized in that: The bio-based waxes are rice bran wax and hydrogenated modified soybean wax, with the ratio of rice bran wax to hydrogenated modified soybean wax being 3:

2.

3. The environmentally friendly wood furniture adhesive according to claim 1, characterized in that: The modified lignin is at least one of enzymatically hydrolyzed lignin or sulfonated lignin that has undergone decolorization treatment.

4. The environmentally friendly wood furniture adhesive according to claim 1, characterized in that: The adjuvants include 0.5-1 parts by weight of bio-based nanocellulose.

5. The environmentally friendly wood furniture adhesive according to claim 1, characterized in that: The additives include 10-15 parts by weight of tackifying resin, which is hydrogenated rosin and terpene resin, wherein the ratio of hydrogenated rosin to terpene resin is 4:

1.

6. The environmentally friendly wood furniture adhesive according to claim 1, characterized in that: The adjuvants include antibacterial agents, 1-2 parts by weight of nano zinc oxide, and 0.5-1.2 parts by weight of phytate, wherein the phytate is at least one of calcium phytate or zinc phytate.

7. The environmentally friendly wood furniture adhesive according to claim 1, characterized in that: The additives include silane coupling agent KH-560, used in amounts of 0.2-0.5 parts by weight.

8. A method for preparing an environmentally friendly flat adhesive for wooden furniture, characterized in that, The adhesive used to prepare the flat adhesive according to any one of claims 1-7 is prepared using a multi-section continuous one-time extrusion process, and is prepared by the following method: S1. Add starch, succinic anhydride, octenyl succinic anhydride, maleic anhydride-grafted polylactic acid, nano zinc oxide, phytate, silane coupling agent KH-560 and nano cellulose to the first zone. The temperature of the first zone is 40-60℃. After the materials are mixed, they enter the second zone. S2. Isosorbide is added to the second zone, the temperature of the second zone is 120-140℃, and the materials are mixed and then enter the third zone. S3, the third zone is the kneading reaction zone, the temperature of the third zone is 160-170℃, and the material enters the fourth zone after the kneading reaction in the third zone. S4. Add bio-based wax and tackifying resin to the fourth section. The temperature of the fourth section is 150-160℃. After the materials are mixed, they enter the fifth section. S5, the fifth zone temperature is 135-150℃, with a negative pressure of -0.08 to -0.1MPa. After the material is cooled and the residual moisture and gas are removed by the negative pressure, it is extruded and granulated to obtain flat adhesive.

9. The preparation method according to claim 8, characterized in that: Before step S1, preprocessing is also included, including the following steps: Modified starch drying: Vacuum dry the modified starch until the moisture content is less than 1%; Silane coupling agent adsorption: After the silane coupling agent and octenyl succinic anhydride are mixed evenly, they are sprayed evenly onto nano zinc oxide. Co-grinding: The dried modified starch, nano zinc oxide adsorbed with silane coupling agent and octenyl succinic anhydride, succinic anhydride, phytate and nano cellulose are co-grinded to 800 mesh~1000 mesh, and the grinding temperature is maintained at 45-55℃. After grinding, it is mixed with maleic anhydride grafted polylactic acid and added to the first interval.

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