Adhesive composition for oriented structural plate, oriented structural plate and preparation method of oriented structural plate

Abstract

The invention belongs to the field of oriented structural plates, and relates to an adhesive composition for an oriented structural plate, the oriented structural plate and a preparation method of the oriented structural plate. The adhesive composition for the oriented structural plate is prepared from the following components in parts by weight: 80 to 120 parts of polymerized MDI isocyanate, 5 to 10 parts of epoxidized natural rubber, 1 to 3 parts of carboxylated nanocellulose, 3 to 5 parts of a core-shell structure toughening agent, 1 to 2 parts of a silane coupling agent, 1 to 2 parts of a lignin model compound and 0.5 to 1 part of a latent catalyst. In the core-shell structure toughening agent, the core is polybutadiene, and the shell is polymethyl methacrylate. According to the adhesive composition disclosed by the invention, through multi-component collaborative design, the toughness is remarkably improved on the premise of not weakening the bonding strength, the contradiction between the bending strength and the impact toughness is fundamentally relieved, and a key material basis is provided for preparation of a high-performance formaldehyde-free oriented structural plate.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of oriented structural board, in particular to a kind of adhesive composition for oriented structural board, oriented structural board and preparation method thereof. BACKGROUND

[0002] Oriented structural board (OSB) is a kind of widely used in building, furniture and packaging engineering wood composite material, which is mainly formed by hot pressing after wood flake is laid according to specific direction and glued. Because it has good dimensional stability, high mechanical properties and low production cost, it has become an important substitute for traditional plywood. At present, formaldehyde-free oriented structural board mostly uses isocyanate adhesive, such as polymeric MDI, because it has excellent bonding strength, water resistance and environmental protection performance.

[0003] However, isocyanate adhesive will form highly crosslinked polyurethane structure after curing, and its molecular chain is rigid, which leads to high brittleness of adhesive layer, low elongation at break and poor impact energy absorption capacity. This characteristic makes the oriented structural board prepared by using such adhesive prone to brittle fracture when subjected to dynamic load or external impact, which limits its application in high safety requirement scenarios. At the same time, the oriented structural board prepared by using such adhesive is prone to edge collapse caused by brittleness during subsequent sawing process, which affects the edge sealing quality of the board.

[0004] In addition, because of the inherent contradiction between bending strength and impact toughness in material design, traditional methods often lead to the decrease of toughness while improving the strength, and vice versa, and it is difficult to improve the strength and toughness simultaneously.

[0005] Therefore, how to effectively improve the toughness of adhesive without sacrificing the bending strength, and realize the synergistic optimization of strength and toughness, has become a key problem to be solved in the development of formaldehyde-free oriented structural board technology. SUMMARY

[0006] (I) Technical problem to be solved

[0007] In order to solve the problem that the improvement of bending strength and impact toughness of oriented structural board is contradictory in the prior art, the present application provides an adhesive composition for oriented structural board, oriented structural board and preparation method thereof.

[0008] (II) Technical scheme

[0009] In order to achieve the above purpose, the main technical scheme adopted by the present application includes:

[0010] An adhesive composition for directional structural board, comprising, by weight parts, 80-120 parts of polymeric MDI isocyanate, 5-10 parts of epoxidized natural rubber, 1-3 parts of carboxylated nanocellulose, 3-5 parts of core-shell structure toughening agent, 1-2 parts of silane coupling agent, 1-2 parts of lignin model compound, and 0.5-1 part of latent catalyst.

[0011] In the core-shell structure toughening agent, the core is polybutadiene, and the shell is polymethyl methacrylate.

[0012] Preferably, the particle size of the core-shell structure toughening agent is 50-200 nm, and the mass ratio of polybutadiene to polymethyl methacrylate is (60-80):(40-20).

[0013] Preferably, the coupling agent is KH-550 silane coupling agent or KH-560 silane coupling agent.

[0014] Preferably, the lignin model compound is guaiacol glyceryl ether, eugenol glycidyl ether, or p-hydroxybenzaldehyde glyceryl ether.

[0015] Preferably, the latent catalyst is zinc acetylacetone, aluminum acetylacetone, dibutyltin dilaurate, or stannous octoate.

[0016] The application also provides a preparation method of the above-mentioned adhesive composition, comprising the following steps:

[0017] S1: At 40-60℃, the epoxidized natural rubber, carboxylated nanocellulose, and core-shell structure toughening agent are added to an organic solvent for ultrasonic dispersion treatment to obtain a premixed emulsion;

[0018] S2: The silane coupling agent and lignin model compound are premixed in the emulsion and stirred for 20-40 min;

[0019] S3: At 60-70℃, the polymeric MDI isocyanate and latent catalyst are added to the mixture obtained in step S2 under water-free conditions, and mixed and stirred for 40-60 min to obtain the adhesive composition.

[0020] The application also provides a preparation method of directional structural board, comprising:

[0021] A1: Providing a wood unit;

[0022] A2: using the adhesive composition prepared by the preparation method described above or the preparation method described in claim 6 to glue the wood units;

[0023] A3: gluing the wood units in a multi-layer and directional manner to form a board blank;

[0024] A4: performing hot-pressing and curing treatment on the board blank to obtain a directional structure board.

[0025] The preparation method described above, preferably, in step A3, the adopted biomimetic asymmetric gradient structure is a five-layer structure, from top to bottom in order:

[0026] The first surface layer is longitudinally 0° directional laying, with a laying density of 750-780 kg / m 3 , and the adhesive gluing amount is 4-6% of the absolute dry weight of the first surface layer;

[0027] The first transition layer is obliquely 45° directional laying, with a laying density of 650-680 kg / m 3 , and the adhesive gluing amount is 4-6% of the absolute dry weight of the first transition layer;

[0028] The core layer is transversely 90° directional laying, with a laying density of 600-620 kg / m 3 , and the adhesive gluing amount is 4-6% of the absolute dry weight of the core layer;

[0029] The second transition layer is obliquely 45° directional laying, with a laying density of 650-680 kg / m 3 , and the adhesive gluing amount is 4-6% of the absolute dry weight of the second transition layer;

[0030] The second surface layer is longitudinally 0° directional laying, with a laying density of 750-780 kg / m 3 , and the adhesive gluing amount is 4-6% of the absolute dry weight of the second surface layer.

[0031] The preparation method described above, preferably, in step A4, the temperature of hot-pressing and curing is 180-220℃, and during the hot-pressing and curing process, the pressure is increased to 3-4 MPa within 0-1 min after the start of hot-pressing, pressure maintaining treatment is performed within 1-8 min, the pressure is decreased to 1.5-2 MPa within 8-9 min, and it is decreased to normal pressure within 9-10 min.

[0032] The present application also provides a directional structure board prepared by the preparation method described above.

[0033] (Three) beneficial effects

[0034] The adhesive composition of the present application introduces a variety of functional components such as epoxidized natural rubber, carboxylated nanocellulose, core-shell structure toughening agent, etc. in the polymeric MDI isocyanate system, and builds a multi-scale synergistic toughening network, effectively improving the problem of high brittleness and insufficient toughness of the traditional isocyanate adhesive after curing.

[0035] Among them, the epoxidized natural rubber as a long-chain elastomer is uniformly dispersed in the polyurethane crosslinking network, and can stretch and retract the macromolecular chain when stressed, absorb and dissipate energy, significantly improve the elongation at break and flexibility of the adhesive layer. At the same time, the epoxy groups on its molecular chain can participate in the curing reaction of isocyanate to realize chemical bonding, avoid phase separation, and ensure that the toughening process does not sacrifice strength.

[0036] The introduction of carboxylated nanocellulose not only plays the reinforcing effect of nanofiller, but also reacts with isocyanate groups through the rich carboxyl and hydroxyl groups on its surface to form a dense and elastic crosslinked structure, further improving the mechanical stability of the adhesive layer.

[0037] The core-shell structure toughening agent has a soft core of polybutadiene and a shell of polymethyl methacrylate. The soft core has excellent elastic deformation ability and can dissipate a large amount of impact energy through cavitation or plastic yield mechanism during crack propagation. The hard shell is beneficial to good compatibility and uniform dispersion with the matrix, preventing agglomeration and playing the role of "energy dissipation microspheres". The core-shell particles synergize with epoxidized natural rubber and carboxylated nanocellulose to form a multi-level toughening mechanism from the molecular scale to the nanoscale and then to the microscale, significantly improving the overall impact resistance of the adhesive.

[0038] The addition of lignin model compounds plays a molecular-level bridging role between the adhesive and the wood unit. The phenolic hydroxyl groups in its molecule can have affinity or hydrogen bonding with lignin in the wood component, while the active groups at the other end participate in the curing reaction of the adhesive, enhancing the interfacial bonding strength and reducing the risk of crack initiation due to interfacial debonding. At the same time, the introduction of latent catalyst makes the adhesive stable at room temperature, facilitating the gluing and paving operation, and rapidly activates during the hot pressing stage to promote the adhesive to fully penetrate and quickly complete crosslinking and curing, ensuring process adaptability and optimizing the structural uniformity and density of the final adhesive layer. DETAILED DESCRIPTION

[0039] In order to better explain the present application, the following will describe the present application in detail in combination with specific embodiments.

[0040] This invention provides an adhesive composition for oriented strand board (OSB) panels, comprising, by weight, 80-120 parts polymeric MDI isocyanate, 5-10 parts epoxidized natural rubber, 1-3 parts carboxylated nanocellulose, 3-5 parts core-shell toughening agent, 1-2 parts silane coupling agent, 1-2 parts lignin model compound, and 0.5-1 part latent catalyst. In the core-shell toughening agent, the core is polybutadiene, and the shell is polymethyl methacrylate.

[0041] The adhesive composition of the present invention significantly improves toughness without weakening the bonding strength through multi-component synergistic design, fundamentally alleviating the contradiction between bending strength and impact toughness, and providing a key material basis for the preparation of high-performance formaldehyde-free oriented strand board.

[0042] Specifically, epoxidized natural rubber, as a long-chain elastomer, is uniformly dispersed in the polyurethane crosslinking network. Under stress, it can extend and retract its macromolecular chains, absorbing and dissipating energy, significantly improving the elongation at break and flexibility of the adhesive layer. At the same time, the epoxy groups on its molecular chains can participate in the curing reaction of isocyanate, achieving chemical bonding, avoiding phase separation, and ensuring that the toughening process does not sacrifice strength.

[0043] The introduction of carboxylated nanocellulose not only exerts the reinforcing effect of nanofillers, but its abundant carboxyl and hydroxyl groups on the surface can also react with isocyanate groups to form a dense and elastic cross-linked structure, further improving the mechanical stability of the adhesive layer.

[0044] The core-shell toughening agent uses polybutadiene as the core and polymethyl methacrylate as the shell. Its soft core possesses excellent elastic deformation capabilities, dissipating a large amount of impact energy during crack propagation through cavitation or plastic yielding mechanisms. The hard shell, on the other hand, facilitates good compatibility and uniform dispersion with the matrix, preventing agglomeration and acting as an "energy-dissipating microsphere." These core-shell particles, in synergy with epoxidized natural rubber and carboxylated nanocellulose, form a multi-level toughening mechanism from the molecular scale to the nanoscale and then to the microscale, significantly improving the overall impact resistance of the adhesive.

[0045] The addition of lignin model compounds acts as a molecular-level bridge between the adhesive and the wood units. The phenolic hydroxyl groups in these compounds can interact with lignin in the wood components through affinity or hydrogen bonding, while the active groups at the other end participate in the adhesive's curing reaction, enhancing interfacial bonding strength and reducing the risk of crack initiation due to interfacial debonding. Simultaneously, the introduction of a latent catalyst ensures the adhesive remains stable at room temperature, facilitating application and installation. During hot pressing, it is rapidly activated, promoting full penetration of the adhesive and rapid cross-linking and curing, thus ensuring process adaptability and optimizing the structural uniformity and density of the final adhesive layer.

[0046] Preferably, the particle size of the core-shell structure toughening agent is 50-200 nm, and the mass ratio of polybutadiene to polymethyl methacrylate is (60-80):(40-20). The coupling agent can be KH-550 silane coupling agent or KH-560 silane coupling agent. The lignin model compound can be guaiacol glyceryl ether, eugenol glyceryl ether or p-hydroxybenzaldehyde glyceryl ether. The latent catalyst can be zinc acetylacetonate, aluminum acetylacetonate, dibutyltin dilaurate or stannous octoate.

[0047] The core-shell structure toughening agent can be prepared by a two-step emulsion polymerization method, specifically including the following steps:

[0048] 1. Preparation of polybutadiene seed emulsion:

[0049] Deionized water, emulsifiers such as sodium dodecyl sulfate, and initiators such as potassium persulfate are added to a reaction kettle, stirred and heated to 70-75°C, and then butadiene monomer is slowly added dropwise. Free radical emulsion polymerization is carried out under inert gas protection such as nitrogen, and the reaction is carried out for 2-4 h to obtain a stable polybutadiene latex seed, which is the "core".

[0050] 2. Coating of poly(methyl methacrylate) shell (PMMA):

[0051] Methyl methacrylate monomer, emulsifier and initiator are continuously added to the above polybutadiene emulsion, and the poly(methyl methacrylate) is polymerized in situ on the surface of the polybutadiene particles to form a "core-shell" structure. The reaction continues for 3-5 h until the monomer is completely converted.

[0052] 3. Post-treatment: After the polymerization is completed, the pH of the system is adjusted to 7-8, and the gel is removed by filtration to obtain a stable PBD / PMMA core-shell structure emulsion. Powdered products can be obtained by spray drying or freeze drying, which are convenient for storage and subsequent addition to the adhesive system.

[0053] The application also provides a preparation method of the above-mentioned adhesive composition, which includes the following steps:

[0054] S1: At 40-60°C, the epoxidized natural rubber, carboxylated nanocellulose and core-shell structure toughening agent are added to an organic solvent such as acetone, ethanol or ethyl acetate, and ultrasonic dispersion treatment is carried out to obtain a premixed emulsion.

[0055] S2: The silane coupling agent and the lignin model compound are premixed into the emulsion, and stirred and reacted for 20-40 min.

[0056] S3: Under water-free conditions at 60-70°C, the polymeric MDI isocyanate and the latent catalyst are added to the mixture obtained in step S2, and mixed and stirred for 40-60 min to obtain the adhesive composition.

[0057] The present application also provides a preparation method of the oriented structural board, which comprises:

[0058] A1: providing wood units.

[0059] A2: applying adhesive composition to the wood units.

[0060] A3: assembling the glued wood units in a multi-layer oriented manner to form a board blank.

[0061] A4: performing hot pressing and curing treatment on the board blank to obtain the oriented structural board.

[0062] In step A1, the wood units can be eucalyptus / pine veneers with an aspect ratio of ≥4,

[0063] The thickness of the wood unit veneer can be 1.7 mm, 2.0 mm, 2.2 mm, 2.4 mm, or 2.6 mm, etc.; the wood units need to be dried to a moisture content of ≤3% to ensure full curing of the adhesive and interfacial bonding strength.

[0064] In step A3, the adopted bionic asymmetric gradient structure is a five-layer structure, from top to bottom:

[0065] The first surface layer is oriented in the longitudinal direction 0°, with a laying density of 750-780 kg / m 3 , and the adhesive application amount is 4-6% of the absolute dry weight of the first surface layer.

[0066] The first transition layer is oriented at an angle of 45°, with a laying density of 650-680 kg / m 3 , and the adhesive application amount is 4-6% of the absolute dry weight of the first transition layer.

[0067] The core layer is oriented in the transverse direction 90°, with a laying density of 600-620 kg / m 3 , and the adhesive application amount is 4-6% of the absolute dry weight of the core layer.

[0068] The second transition layer is oriented at an angle of 45°, with a laying density of 650-680 kg / m 3 , and the adhesive application amount is 4-6% of the absolute dry weight of the second transition layer.

[0069] The second surface layer is oriented in the longitudinal direction 0°, with a laying density of 750-780 kg / m 3 , and the adhesive application amount is 4-6% of the absolute dry weight of the second surface layer.

[0070] The five-layer biomimetic asymmetric gradient structure paving method used in step A3 realizes the optimization of stress transmission path and the spatial matching of mechanical properties through the synergistic design of the directional angle, density and sizing amount of different layers. The structure simulates the hierarchical and anisotropic structural characteristics formed in the growth process of natural wood, so that the board can more effectively disperse and conduct load when subjected to macro stress, avoid stress concentration, and significantly improve the bending stiffness and impact resistance of the overall structure. The surface layer paved longitudinally has a higher paving density and sizing amount, can bear the main in-plane tensile and compressive stress, provide excellent surface hardness and compression resistance, and at the same time enhance the initial resistance to external impact.

[0071] The first transition layer and the second transition layer are paved at 45°, forming a mechanical transition zone between the upper and lower surface layers and the core layer, which functions to relieve the modulus jump between different directional fiber layers and promote the smooth transmission of interlayer stress. The oblique structure can produce micro-scale shear deformation when subjected to bending or shear force, absorb part of the energy and inhibit the propagation of cracks from the surface layer to the core layer. At the same time, the moderate paving density and sizing amount of this layer ensure good bonding strength and permeability, avoiding the difficulty of hot pressing caused by too high density, and preventing the influence on structural integrity caused by too low density. This transition design effectively reduces the risk of interlayer peeling and improves the integrity and durability of the board.

[0072] The core layer is paved transversely (90°), mainly bearing the dimensional stability and shear resistance of the board in the transverse direction, preventing transverse cracking or deformation due to humidity changes or external forces during use. Its lower paving density reduces the overall board's compression resistance while ensuring adequate structural support, facilitating the vertical penetration of adhesives and the discharge of internal moisture during hot pressing, reducing internal stress accumulation. The moderate sizing amount of the core layer meets the basic bonding requirements while avoiding the problem of increased brittleness caused by excessive accumulation of adhesives. Overall, the five-layer asymmetric gradient structure realizes the synergistic effect of "high-strength surface layer - toughness transition - stable core layer" through spatial functional zoning, not only improving the bending strength and elastic modulus of the board, but also significantly improving its impact toughness and fatigue resistance, solving the technical problem of balancing strength and toughness in traditional symmetric uniform structures.

[0073] In the above step A4, the temperature for hot pressing and curing is 180-220°C.

[0074] The process conditions for hot pressing and curing are as follows:

[0075] The segmented pressure control mode is adopted, specifically:

[0076] 0-1min: apply pressure to 3.0-4.0MPa to achieve rapid closure of the board blank, discharge internal air and water vapor, and prevent bubbling.

[0077] 1-8min: maintain pressure, promote the full flow and penetration of the adhesive between the wood units, and enhance the interface wettability.

[0078] 8-9min: reduce the pressure to 1.5-2MPa.

[0079] 9-10min: gradually reduce to normal pressure.

[0080] The present application fully utilizes the rheological properties and reaction kinetics advantages of the modified adhesive through the synergistic cooperation of the multi-layer directional paving structure design and the segmented pressure hot-pressing process. The high-pressure initial segment quickly seals the surface to prevent "glue spraying" and void formation; the medium-pressure segment ensures the penetration depth of the glue solution; and the low-pressure holding segment realizes stress release, finally obtaining a directional structural board with high density, low internal stress, high strength and high toughness.

[0081] In order to further clarify the present application and its technical progress, the following specific examples and technical effects are described.

[0082] Example 1

[0083] The present embodiment provides a preparation method of an adhesive composition, comprising the following steps:

[0084] S1: At 50℃, 8 parts of epoxidized natural rubber, 2 parts of carboxylated nanocellulose and 4 parts of core-shell structure toughener are added to acetone for ultrasonic dispersion treatment to obtain a premix emulsion. The particle size of the core-shell structure toughener is 120nm, and the mass ratio of polybutadiene to polymethyl methacrylate is 70:30.

[0085] S2: 1.5 parts of KH-550 silane coupling agent and 1.5 parts of guaiacol glyceryl ether are added to the premix emulsion and stirred for 30min.

[0086] S3: At 65℃, 100 parts of polymeric MDI isocyanate and 0.8 parts of zinc acetylacetone are added to the mixture obtained in step S2 under water-free conditions, and mixed and stirred for 50min to obtain an adhesive composition.

[0087] The above-mentioned adhesive composition is used to prepare a directional structural board:

[0088] A1: Selecting pine wood flakes with water content ≤3%, length-width ratio of 4 and thickness of 2mm.

[0089] A2: Using the adhesive composition to glue the wood units.

[0090] A3: The glued wood units are assembled into a board blank in a multi-layer directional paving manner.

[0091] A4: The billet is subjected to hot pressing and curing treatment to obtain a directional structure board. The temperature of hot pressing and curing is 200℃. Specifically, the pressure is increased to 3.5MPa within 0-1min, pressure maintaining treatment is performed within 1-8min, the pressure is decreased to 1.7MPa within 8-9min, and then to normal pressure within 9-10min.

[0092] In step A3, the adopted bionic asymmetric gradient structure is a five-layer structure, from top to bottom: a first surface layer, which is longitudinally 0° oriented and laid with a laying density of 760kg / m 3 , and the adhesive application amount is 5% of the absolute dry weight. A first transition layer, which is obliquely 45° oriented and laid with a laying density of 670kg / m 3 , and the adhesive application amount is 5% of the absolute dry weight. A core layer, which is transversely 90° oriented and laid with a laying density of 610kg / m 3 , and the adhesive application amount is 5% of the absolute dry weight. A second transition layer, which is obliquely 45° oriented and laid with a laying density of 670kg / m 3 , and the adhesive application amount is 5% of the absolute dry weight. A second surface layer, which is longitudinally 0° oriented and laid with a laying density of 760kg / m 3 , and the adhesive application amount is 5% of the absolute dry weight.

[0093] Example 2

[0094] The present embodiment provides a preparation method of an adhesive composition, comprising the following steps:

[0095] S1: At 40℃, 5 parts of epoxidized natural rubber, 1 part of carboxylated nanocellulose and 3 parts of core-shell structure toughening agent are subjected to ultrasonic dispersion treatment in ethanol to obtain a premixed emulsion. The particle size of the core-shell structure toughening agent is 50nm, and the mass ratio of polybutadiene to polymethyl methacrylate is 60:40.

[0096] S2: 1 part of KH-560 silane coupling agent and 1 part of eugenol glycidyl ether are added to the premixed emulsion and stirred for 20min.

[0097] S3: At 60℃, 80 parts of polymeric MDI isocyanate and 0.5 parts of aluminum acetylacetone are added to the mixture obtained in step S2 under water-free conditions, and mixed and stirred for 40min to obtain an adhesive composition.

[0098] The above adhesive composition is used to prepare a directional structure board:

[0099] A1: Selecting pine wood flakes with a moisture content of ≤3%, a length-width ratio of 4 and a thickness of 2.0mm.

[0100] A2: The wood units are coated with the adhesive composition.

[0101] A3: The glued wood units are assembled into a mat in a multi-layer directional laying manner to form a mat.

[0102] A4: The mat is subjected to hot pressing and curing treatment to obtain a directional structure board. The temperature of the hot pressing and curing is 180℃. Specifically, the pressure is increased to 3MPa within 0-1min, pressure maintaining treatment is performed within 1-8min, the pressure is decreased to 1.5MPa within 8-9min, and the pressure is decreased to normal pressure within 9-10min.

[0103] In step A3, the adopted bionic asymmetric gradient structure is a five-layer structure, from top to bottom: a first surface layer, which is laid in a longitudinal 0° direction with a laying density of 750kg / m 3 , and the adhesive application amount is 4% of the absolute dry weight. A first transition layer, which is laid in a diagonal 45° direction with a laying density of 650kg / m 3 , and the adhesive application amount is 4% of the absolute dry weight. A core layer, which is laid in a transverse 90° direction with a laying density of 600kg / m 3 , and the adhesive application amount is 4% of the absolute dry weight. A second transition layer, which is laid in a diagonal 45° direction with a laying density of 650kg / m 3 , and the adhesive application amount is 4% of the absolute dry weight. A second surface layer, which is laid in a longitudinal 0° direction with a laying density of 750kg / m 3 , and the adhesive application amount is 4% of the absolute dry weight.

[0104] Example 3

[0105] The present embodiment provides a preparation method of an adhesive composition, comprising the following steps:

[0106] S1: At 60℃, 10 parts of epoxidized natural rubber, 3 parts of carboxylated nanocellulose and 5 parts of core-shell structure toughener are added into ethyl acetate for ultrasonic dispersion treatment to obtain a premix emulsion. The particle size of the core-shell structure toughener is 200nm, and the mass ratio of polybutadiene to polymethyl methacrylate is 80:20.

[0107] S2: 2 parts of KH-550 silane coupling agent and 2 parts of p-hydroxybenzaldehyde glyceryl ether are added into the premix emulsion, and stirred for 40min.

[0108] S3: At 70℃, under water-free conditions, 120 parts of polymeric MDI isocyanate and 1 part of dibutyltin dilaurate are added into the mixture obtained in step S2, mixed and stirred for 60min to obtain an adhesive composition.

[0109] The above adhesive composition is used to prepare a directional structure board:

[0110] A1: Selecting pine wood flakes with moisture content ≤3%, aspect ratio ≥4, and thickness of 2mm.

[0111] A2: Applying adhesive composition to the wood units.

[0112] A3: Assembling the wood units after gluing in a multi-layer directional laying manner to form a board blank.

[0113] A4: Performing hot-pressing and curing treatment on the board blank to obtain a directional structure board. The temperature of hot-pressing and curing is 220℃. Specifically, the pressure is increased to 4MPa within 0-1min, pressure maintaining treatment is performed within 1-8min, the pressure is decreased to 2MPa within 8-9min, and the pressure is decreased to normal pressure within 9-10min.

[0114] In step A3, the adopted biomimetic asymmetric gradient structure is a five-layer structure, from top to bottom: a first surface layer, which is laid in a longitudinal 0° direction with a laying density of 780kg / m 3 , and the adhesive gluing amount is 6% of the absolute dry weight. A first transition layer, which is laid in a diagonal 45° direction with a laying density of 680kg / m 3 , and the adhesive gluing amount is 6% of the absolute dry weight. A core layer, which is laid in a transverse 90° direction with a laying density of 620kg / m 3 , and the adhesive gluing amount is 6% of the absolute dry weight. A second transition layer, which is laid in a diagonal 45° direction with a laying density of 680kg / m 3 , and the adhesive gluing amount is 6% of the absolute dry weight. A second surface layer, which is laid in a longitudinal 0° direction with a laying density of 780kg / m 3 , and the adhesive gluing amount is 6% of the absolute dry weight.

[0115] Example 4

[0116] The embodiment provides a preparation method of an adhesive composition, which is different from that of example 1 in that the latent catalyst is stannous octoate.

[0117] Example 5

[0118] The embodiment provides a preparation method of an adhesive composition, which comprises the following steps:

[0119] S1: At 55℃, 7 parts of epoxidized natural rubber, 2.2 parts of carboxylated nanocellulose and 4.3 parts of core-shell structure toughener are added into ethanol for ultrasonic dispersion treatment to obtain a premixed emulsion. The particle size of the core-shell structure toughener is 120nm, and the mass ratio of polybutadiene to polymethyl methacrylate is 65:35.

[0120] S2: Add 1.8 parts of KH-550 silane coupling agent and 1.4 parts of guaiacol glycerol ether to the premixed emulsion and stir for 35 min.

[0121] S3: At 68°C and under water-protected conditions, 110 parts of polymeric MDI isocyanate and 0.7 parts of zinc acetylacetonate were added to the mixture obtained in step S2 and stirred for 53 minutes to obtain an adhesive composition.

[0122] Oriented composite panels were prepared using the above adhesive composition:

[0123] A1: Select pine wood shavings with a moisture content of ≤3%, an aspect ratio of 4, and a thickness of 2mm.

[0124] A2: Apply adhesive composition to the wood unit.

[0125] A3: Assemble the glued wood units in a multi-layer oriented layup manner to form a board blank.

[0126] A4: The slab is subjected to hot-press curing to obtain oriented strand board. The hot-press curing temperature is 186℃. Specifically, the pressure is increased to 3.8MPa in the first 0-1 minute, held for 1-8 minutes, reduced to 1.9MPa in the first 8-9 minutes, and then reduced to atmospheric pressure in the first 9-10 minutes.

[0127] In step A3, the biomimetic asymmetric gradient structure used is a five-layer structure, from top to bottom as follows: the first surface layer, which is laid longitudinally at 0° orientation with a laying density of 770 kg / m³. 3 The adhesive application rate is 3.5% of its oven-dry weight. The first transition layer is laid at a 45° angle with a density of 660 kg / m². 3 The adhesive application rate is 3.5% of its oven-dry weight. The core layer is laid in a 90° transverse orientation with a density of 600 kg / m². 3 The adhesive application rate is 3.5% of its oven-dry weight. The second transition layer is laid at a 45° angle with a density of 670 kg / m². 3 The adhesive application rate is 3.5% of its oven-dry weight. The second surface layer is laid longitudinally at 0° directional, with a laying density of 770 kg / m². 3 The amount of adhesive applied is 3.5% of its oven-dry weight.

[0128] Comparative Example 1

[0129] This comparative example provides a method for preparing an adhesive composition, which differs from Example 1 in that a core-shell toughening agent is not used.

[0130] Comparative Example 2

[0131] The comparative example provides a preparation method of an adhesive composition, which is different from example 1 in that carboxylated nanocellulose is not used.

[0132] Comparative example 3

[0133] The comparative example provides a preparation method of an adhesive composition, which is different from example 1 in that epoxidized natural rubber is not used.

[0134] Comparative example 4

[0135] The comparative example provides a preparation method of an adhesive composition, which is different from example 1 in that a lignin model compound is not used.

[0136] The performance of the oriented structural boards prepared from examples 1-5 and comparative examples 1-4 is detected, and table 1 is obtained.

[0137] Table 1: Performance statistics table of oriented structural boards prepared from examples 1-5 and comparative examples 1-4

[0138]

[0139] Finally, it should be noted that: the above examples are only used to illustrate the technical solutions of the present application, and not to limit them; although the present application has been described in detail with reference to the foregoing examples, those skilled in the art should understand that: it can still modify the technical solutions recorded in the foregoing examples, or make equivalent replacement for part or all of the technical features; and these modifications or replacements do not make the essence of the corresponding technical solutions deviate from the scope of the technical solutions of the embodiments of the present application.

Claims

1. An adhesive composition for use in the orientation of structural boards, characterized in that, The adhesive composition comprises 80-120 parts by weight of polymeric MDI isocyanate, 5-10 parts by weight of epoxidized natural rubber, 1-3 parts by weight of carboxylated nanocellulose, 3-5 parts by weight of core-shell structure toughening agent, 1-2 parts by weight of silane coupling agent, 1-2 parts by weight of lignin model compound and 0.5-1 part by weight of latent catalyst. In the core-shell structure toughening agent, the core is polybutadiene and the shell is polymethyl methacrylate.

2. The adhesive composition for a directional structural panel according to claim 1, wherein The particle size of the core-shell structure toughening agent is 50-200 nm, and the mass ratio of polybutadiene to polymethyl methacrylate is (60-80):(40-20).

3. The adhesive composition for a directional structural panel according to claim 1, wherein The coupling agent is KH-550 silane coupling agent or KH-560 silane coupling agent.

4. The adhesive composition for a directional structural panel according to claim 1, wherein The lignin model compound is guaiacol glyceryl ether, syringyl alcohol glycidyl ether or p-hydroxybenzaldehyde glyceryl ether.

5. The adhesive composition for a directional structural panel according to claim 1, wherein The latent catalyst is zinc acetylacetonate, aluminum acetylacetonate, dibutyltin dilaurate or stannous octoate.

6. A method of producing the adhesive composition according to any one of claims 1 to 5, characterized by, The method comprises the following steps: S1: at 40-60℃, the epoxidized natural rubber, carboxylated nanocellulose and core-shell structure toughening agent are added to an organic solvent for ultrasonic dispersion treatment to obtain a premixed emulsion; S2: the silane coupling agent and the lignin model compound are premixed in the emulsion and stirred for 20-40 min; S3: at 60-70℃, the polymeric MDI isocyanate and the latent catalyst are added to the mixture obtained in step S2 under water-free conditions, and mixed and stirred for 40-60 min to obtain the adhesive composition.

7. A method of making a directional structural panel, characterized by, The method comprises: A1: providing a wood unit; A2: sizing the wood unit with the adhesive composition of any one of claims 1-5 or the adhesive composition prepared by the method of claim 6; A3: forming a board blank by layering the sized wood unit in a multi-layer directional manner; A4: performing hot pressing and curing treatment on the board blank to obtain a directional structure board.

8. The preparation method according to claim 7, characterized in that, In step A3, the adopted biomimetic asymmetric gradient structure is a five-layer structure, from top to bottom in turn: The first surface layer is laid in longitudinal 0° orientation with a laying density of 750-780 kg / m 3 The adhesive application amount is 4-6% of the dry weight of the first surface layer. The first transition layer is oriented and laid at 45°, and the laying density is 650-680 kg / m 3 The adhesive application amount is 4-6% of the dry weight of the first transition layer. Core layer, using transverse 90° orientation laying, laying density is 600-620kg / m 3 , adhesive glue amount is 4-6% of core layer absolute dry weight; The second transition layer is oriented and laid at an angle of 45°, and the laying density is 650-680 kg / m 3 The adhesive application amount is 4-6% of the second transition layer dry weight. The second surface layer is oriented at 0° in the longitudinal direction and has a density of 750-780 kg / m 3 The adhesive is applied at a rate of 4-6% of the dry weight of the second surface layer.

9. The preparation method according to claim 7, characterized in that, In step A4, the temperature of hot pressing and curing is 180-220℃, and during the hot pressing and curing process, the pressure is increased to 3-4 MPa within 0-1 min after the start of hot pressing, pressure maintaining treatment is performed within 1-8 min, the pressure is reduced to 1.5-2 MPa within 8-9 min, and the pressure is reduced to normal pressure within 9-10 min.

10. A directional structural panel, characterized by, Prepared by the method of any one of claims 7-9.

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