Formaldehyde-free environment-friendly bonding material for high-density fiberboard, preparation method and application

Abstract

The invention relates to a formaldehyde-free environment-friendly bonding material for a high-density fiberboard as well as a preparation method and application of the formaldehyde-free environment-friendly bonding material, and relates to the technical field of bonding materials. The binding material comprises the following components in parts by weight: 70 to 80 parts of diphenylmethane diisocyanate, 15 to 25 parts of microcapsules, 5 to 10 parts of nano zeolite, 1 to 3 parts of an epoxy silane coupling agent, 0.1 to 0.5 part of tetrabutyl titanate, 0.5 to 1 part of a dispersing agent, 1 to 2 parts of a viscosity reducer and 0.1 to 0.3 part of an antioxidant. According to the method, moisture can be eliminated from the source, the CO2 generation amount is reduced to be extremely low, the problem of high-temperature curing bubble release is fundamentally solved, and the interface bonding strength of the high-density fiberboard is remarkably enhanced while good water resistance is achieved.

Description

Technical Field

[0001] The present invention relates to the technical field of adhesive materials, and in particular to an aldehyde-free environmentally friendly adhesive material for high-density fiberboard, a preparation method and application thereof. Background Art

[0002] Fiberboard is widely used in architectural decoration, furniture manufacturing, ship and vehicle interior decoration and other fields due to its advantages such as uniform material, small difference in strength in all directions, and resistance to deformation. In the early stage, technical personnel in this field have researched and developed a high-density, highly water-resistant fiberboard, which has promoted the application of fiberboard in semi-structural fields, humid environments and other fields. Currently, urea-formaldehyde resin or modified urea-formaldehyde resin adhesive is mainly used in fiberboard production. Urea-formaldehyde resin adhesive is widely used in fiberboard due to its abundant raw material sources, low price, convenient operation, relatively good process performance and bonding performance. However, urea-formaldehyde resin adhesive has poor water resistance, and the artificial boards and related products produced using it are generally used indoors. In addition, fiberboard products using urea-formaldehyde resin as adhesive will also release formaldehyde during use, polluting the human living environment and threatening human health.

[0003] The Chinese invention patent application with publication number CN102604573A discloses an E0-grade melamine-modified urea-formaldehyde resin adhesive and its preparation method and application. The adhesive is characterized in that the raw materials included are: E0-grade melamine-modified urea-formaldehyde resin, composite curing agent and composite filler. The E0-grade melamine-modified urea-formaldehyde resin is made of the following raw materials: 100 parts by mass of formaldehyde, 0.1-0.5 parts by mass of polyvinyl alcohol, 100-200 ml of alkaline catalyst, 200-40 ml of acidic catalyst. 0ml, the molar ratio of formaldehyde to urea tridecamethylene melamine F / (U+M)=0.80-0.98; the composite curing agent is made from the following raw materials in the following proportions: 200-250 parts by mass of ammonium chloride, 150-200 parts by mass of oxalic acid, 400-450 parts by mass of citric acid, 100-150 parts by mass of tartaric acid and 500-800 parts by mass of water; the composite filler is made from the following raw materials in the following proportions: 60 parts by mass of industrial flour, 20 parts by mass of 800 mesh light calcium carbonate and 20 parts by mass of 800 mesh wood flour.

[0004] This E0-grade melamine-modified urea-formaldehyde resin adhesive, used for gluing panels, offers advantages such as low free formaldehyde content, low cost, good pre-compression properties, and excellent bonding performance. Despite low formaldehyde emissions, this issue persists. Those skilled in the art have begun researching the use of formaldehyde-free adhesives. A commonly used formaldehyde-free adhesive is isocyanate (MDI) adhesive. During the high-temperature curing process, MDI adhesive's bonding effect primarily stems from the self-crosslinking of isocyanate groups (-NCO) and the reaction of -NCO with -OH groups on the fiber surface to form chemical bonds. This allows for satisfactory product performance, requiring only a small amount of adhesive. This has led to its widespread use in industrial production.

[0005] The Chinese invention patent application with publication number CN104290169A discloses a production process for zero-formaldehyde density fiberboard, which includes the steps of wood peeling → chipping → screening → washing → steaming → fiber separation → gluing → fiber drying → laying and forming → pre-pressing → hot pressing → cooling → sanding → inspection and grading → packaging and warehousing.

[0006] This invention uses diphenylmethane diisocyanate as an adhesive to produce formaldehyde-free density fiberboard. The resulting fiberboard contains no toxic or hazardous substances such as free formaldehyde, with a formaldehyde emission level close to 0 mg / 100g. Simultaneously, the board's joint strength and water resistance are significantly improved, overcoming the formaldehyde emission limitations of existing fiberboards. However, under high-temperature curing conditions, isocyanate adhesive reacts with moisture in the fibers to release CO₂. The greater the amount of adhesive applied, the more CO₂ released, which can easily cause the board to blister. Strictly controlling the moisture content of the fiberboard requires high energy consumption for drying, and the added drying process increases costs. Summary of the Invention

[0007] To address the above technical issues, the present invention provides an environmentally friendly, formaldehyde-free adhesive material for high-density fiberboard, its preparation method, and its application. This material eliminates moisture at the source, minimizing CO2 production and fundamentally resolving the issue of foaming during high-temperature curing. It also exhibits excellent water resistance and significantly enhances the interfacial bonding strength of high-density fiberboard.

[0008] In a first aspect, the present invention provides an environmentally friendly formaldehyde-free adhesive material for high-density fiberboard. The formaldehyde-free environmentally friendly adhesive material comprises 70-80 parts of diphenylmethane diisocyanate, 15-25 parts of a dehydrating agent, 5-10 parts of nano zeolite, 1-3 parts of an epoxy silane coupling agent, 0.1-0.5 parts of tetrabutyl titanate, 0.5-1 parts of a dispersant, 1-2 parts of a viscosity reducer, and 0.1-0.3 parts of an antioxidant.

[0009] In this technical solution, the reactive -NCO groups of diphenylmethane diisocyanate react with the -OH groups of wood cellulose / hemicellulose to form polyurethane or polyurea bonds, creating a three-dimensional cross-linked network. This gives the adhesive material extremely high internal bonding strength, excellent fluidity at high temperatures, and strong permeability. Its low viscosity allows it to penetrate deep into the fiber pores. Furthermore, the urethane bonds (-NH-COO-) formed by diphenylmethane diisocyanate and wood are more resistant to hydrolysis and have a low water absorption and expansion rate.

[0010] The dehydrating agent first reacts with the water in the fiberboard, consumes the moisture in the fiberboard, and does not produce CO2.

[0011] The pores of nano-zeolites have a high specific surface area, which can adsorb free water and reduce local water activity.

[0012] Tetrabutyl titanate can increase the inhibition rate of the reaction between -NCO and water, ensuring that the dehydrating agent reacts preferentially with water.

[0013] The epoxy groups in the epoxy silane coupling agent react with the hydroxyl groups in the wood to improve water resistance and internal bonding strength.

[0014] Dispersants can stabilize dispersion, prevent nano-zeolite from settling, and ensure uniform sizing.

[0015] Viscosity reducers can reduce the viscosity of high-solid systems, improve fiber surface wettability, are compatible with diphenylmethane diisocyanate, do not interfere with the reactivity of the -NCO group, improve rheological properties, and have high storage stability.

[0016] Antioxidants can block the oxidative degradation of the benzene ring or carbamate bond in diphenylmethane diisocyanate at high temperatures (for example, the formation of quinone chromophores, resulting in yellowing), reduce the corrosion of oxidation byproducts (such as carboxylic acids) on the wood-glue interface, and improve the long-term weather resistance of the board.

[0017] Optionally, the dehydrating agent is a microcapsule with a core-shell structure, comprising 85-90% core material, 10-15% shell material, 0.1-0.3% polyvinyl alcohol, and 0.1-0.5% dibutyltin dilaurate, wherein the core material is vinyltrimethoxysilane and the shell material is isophorone diisocyanate.

[0018] In the above technical solution, the core material vinyltrimethoxysilane will hydrolyze rapidly when it comes into contact with water, preferentially consuming water. The reaction rate is more than 10 times that of -NCO with water, and no CO2 is produced. The shell material is a thermally responsive polyurethane shell with a melting point of 130-150°C. During the storage and gluing stages, the shell layer isolates the vinyltrimethoxysilane from contact with water or isocyanate to prevent pre-reaction. In the initial stage of hot pressing, the shell layer melts and breaks, and the vinyltrimethoxysilane is released on demand to ensure that the dehydration reaction proceeds first. Dibutyltin dilaurate can be used as a catalyst to accelerate the reaction of -NCO with H2O and promote the cross-linking of the shell material. Polyvinyl alcohol can be used as an emulsifier to form a stable O / W emulsion. Polyvinyl alcohol can be adsorbed at the oil-water interface, reduce surface tension, and control the droplet size to 5-10μm. After the reaction, part of the polyvinyl alcohol is embedded in the shell layer, enhancing the hydrophilicity, which is conducive to water penetration and triggering release during hot pressing.

[0019] Vinyltrimethoxysilane reacts rapidly with free water in the fiber to form silanols and methanol, without generating CO₂, thus preventing bubbles from forming at the source. The generated silanol molecules condense to form Si-O-Si bonds and regenerate water. This condensed water is then captured by neighboring vinyltrimethoxysilanes, forming a water recycling chain until the water activity in the system is minimized.

[0020] Some vinyltrimethoxysilane reacts with hydroxyl groups (-OH) on the wood surface, forming high-energy Si-OC bonds, significantly enhancing interfacial adhesion. The resulting methanol (CH3OH) reacts with residual -NCO to form urethane bonds. This methanol is then adsorbed by the hydrophobic nanozeolite and desorbed during the high-temperature pressing stage. The Si-O-Si and Si-OC bonds derived from vinyltrimethoxysilane form an interpenetrating reinforcement phase, enhancing the adhesive's water resistance and stability.

[0021] At the same time, tetrabutyl titanate can accelerate the hydrolysis and condensation of vinyltrimethoxysilane. The epoxy groups in the epoxysilane coupling agent react with the hydroxyl groups of the wood, and the siloxy groups condense with vinyltrimethoxysilane to form a three-dimensional network.

[0022] Optionally, the nano zeolite is a modified nano zeolite, and the preparation steps of the modified nano zeolite are: dispersing the nano zeolite in ethanol, adding hexadecyltrimethoxysilane, the mass ratio of the nano zeolite to hexadecyltrimethoxysilane is 18-22:1, refluxing at 75-85°C for 3-5h, and centrifuging and drying to obtain the modified nano zeolite.

[0023] In this technical solution, the hydrophobically modified nano-zeolite possesses an ultra-high specific surface area. In addition to preferentially adsorbing free water molecules from the fiber, it also reacts with methanol (CH3OH) generated by the hydrolysis of vinyltrimethoxysilane, thereby reducing the local water activity in the system. The hydrophobic modification makes the zeolite more inclined to adsorb non-polar molecules (such as methanol) while reducing adsorption of polar diphenylmethane diisocyanate monomers, thereby preventing interference with the curing reaction. The added epoxysilane coupling agent reacts simultaneously with the zeolite surface, the hydroxyl groups of the wood, and diphenylmethane diisocyanate, forming a three-dimensional covalent bond network and enhancing interfacial bonding strength. The zeolite's high-temperature resistance also mitigates local overheating during hot pressing, reducing the risk of thermal degradation of diphenylmethane diisocyanate.

[0024] In a second aspect, the present invention provides a method for preparing an environmentally friendly formaldehyde-free adhesive material for high-density fiberboard, the method comprising the following steps: The preparation method comprises the following steps: uniformly mixing diphenylmethane diisocyanate with a viscosity reducer, a dispersant, and an antioxidant at 35-45° C., sequentially adding nano zeolite, tetrabutyl titanate, and an epoxy silane coupling agent, dispersing the mixture at high speed at 1800-2200 rpm for 15-25 minutes, and finally adding a dehydrating agent and stirring the mixture at low speed at 400-600 rpm for 8-12 minutes to obtain the formaldehyde-free environmentally friendly adhesive material.

[0025] Adding nano-zeolite before the dehydrating agent allows for pre-adsorption of some water, preventing premature decomposition of the dehydrating agent during the mixing phase. Adding tetrabutyl titanate before the epoxy silane coupling agent ensures even dispersion of the catalyst and prevents localized over-catalysis of the silane.

[0026] Optionally, the preparation method further includes a microcapsule preparation step, which includes mixing vinyltrimethoxysilane, isophorone diisocyanate, and dibutyltin dilaurate to form an oil phase, dripping the oil phase into polyvinyl alcohol under high-speed stirring at 1400-1600 rpm to form an emulsion (droplet size 5-10 μm), heating to 55-65°C, reacting for 1-3 hours, cooling to room temperature, filtering, and washing to obtain white powdery core-shell microcapsules.

[0027] In this technical solution, isophorone diisocyanate diffuses from the interior of the oil phase droplets toward the interface, reacting with trace amounts of -OH groups in the water to form a cross-linked polyurethane shell with a thickness of 0.2-0.5 μm on the surface of the vinyltrimethoxysilane droplets. Dibutyltin dilaurate acts as a catalyst to selectively accelerate the reaction of -NCO with HO, ensuring rapid cross-linking of the shell around the vinyltrimethoxysilane rather than the reaction of the core itself. Polyvinyl alcohol (PVA) acts as an emulsifier in the aqueous phase, reducing the oil / water interfacial tension and forming a stable O / W emulsion. High shear (1400-1600 rpm) mechanically disperses the oil phase into tiny droplets, with the particle size distribution controlled by the shear rate and PVA concentration. A temperature of 55-65°C balances the reaction rate and emulsion stability. Too high a temperature results in demulsification, while too low a temperature results in incomplete reaction. Cooling, filtration, and washing remove unreacted isophorone diisocyanate, PVA, and byproducts, yielding pure white powdery microcapsules.

[0028] In a third aspect, the present invention provides a high-density fiberboard using the above-mentioned formaldehyde-free environmentally friendly adhesive material or a formaldehyde-free environmentally friendly adhesive material prepared using the above-mentioned method for preparing a formaldehyde-free environmentally friendly adhesive material for high-density fiberboard.

[0029] In a fourth aspect, the present invention provides a high-density fiberboard for use in the furniture manufacturing industry, interior decoration industry, office equipment manufacturing industry, automobile manufacturing industry, and cultural and sports equipment manufacturing industry.

[0030] In summary, the present invention includes at least one of the following beneficial technical effects: 1. By adding diphenylmethane diisocyanate, the active -NCO group of diphenylmethane diisocyanate reacts with the -OH of wood cellulose / hemicellulose to form polyurethane or polyurea bonds, constructing a three-dimensional cross-linked network, providing mechanical strength, good fluidity at high temperatures, and strong permeability.

[0031] 2. By adding dehydrating agent, it will first react with the water in the fiberboard, consume the moisture in the fiberboard, and will not produce CO2.

[0032] 3. By adding nano zeolite, nano zeolite with a higher specific surface area can adsorb free water and reduce local water activity.

[0033] 4. By adding epoxy silane coupling agent, the epoxy group in the epoxy silane coupling agent reacts with the hydroxyl group in the wood to improve water resistance and internal bonding strength.

[0034] 5. By adding tetrabutyl titanate, the reaction inhibition rate of -NCO and water can be increased, ensuring that the dehydrating agent reacts with water first. DETAILED DESCRIPTION

[0035] The present invention is further described in detail below with reference to the examples.

[0036] The materials used in the following examples can all be purchased from the market.

[0037] Example 1: This example discloses an aldehyde-free environmentally friendly adhesive material #1 for high-density fiberboard and a preparation method thereof.

[0038] The formaldehyde-free environmentally friendly adhesive material includes 70 parts of diphenylmethane diisocyanate, 15 parts of dehydrating agent, 5 parts of nano zeolite, 1 part of epoxy silane, 0.1 part of tetrabutyl titanate, 0.5 parts of dispersant, 1 part of viscosity reducer, and 0.1 parts of antioxidant. In this embodiment, the dehydrating agent is p-toluenesulfonyl isocyanate, and the epoxy silane is selected from KH-560 silane coupling agent. In other embodiments, A187 silane coupling agent can also be selected. The dispersant is modified polyether siloxane. In other embodiments, dispersants such as polyester amine can also be selected. The viscosity reducer is PEG-60 hydrogenated castor oil. In other embodiments, viscosity reducers such as benzyl benzoate and white oil can also be selected. The antioxidant is antioxidant 1010. In other embodiments, antioxidants such as antioxidant 168 and dilauryl thiodipropionate can also be selected.

[0039] The preparation method comprises the following steps: Diphenylmethane diisocyanate was mixed evenly with PEG-60 hydrogenated castor oil, modified polyether siloxane, and antioxidant 1010 at 35°C. Nanozeolite, tetrabutyl titanate, and KH-560 silane coupling agent were added in sequence and dispersed at high speed at 1800 rpm for 25 min. Finally, p-toluenesulfonyl isocyanate was added and stirred at low speed at 400 rpm for 12 min to obtain formaldehyde-free environmentally friendly adhesive material #1.

[0040] Example 2: This example discloses a formaldehyde-free environmentally friendly adhesive material #2 for high-density fiberboard and a preparation method thereof.

[0041] The formaldehyde-free environmentally friendly adhesive material includes 80 parts of diphenylmethane diisocyanate, 25 parts of p-toluenesulfonyl isocyanate, 10 parts of nano zeolite, 3 parts of A187 silane coupling agent, 0.5 parts of tetrabutyl titanate, 1 part of polyesteramine, 2 parts of benzyl benzoate, and 0.3 parts of antioxidant 168.

[0042] The preparation method comprises the following steps: Diphenylmethane diisocyanate was mixed with benzyl benzoate, polyesteramine, and antioxidant 168 at 35-45°C, and modified nano-zeolite, tetrabutyl titanate, and A187 silane coupling agent were added in sequence. The mixture was dispersed at high speed at 2200 rpm for 15 minutes. Finally, p-toluenesulfonyl isocyanate was added and stirred at low speed at 600 rpm for 8 minutes to obtain formaldehyde-free environmentally friendly adhesive material #2.

[0043] Example 3: This example discloses a formaldehyde-free environmentally friendly adhesive material #3 for high-density fiberboard and its preparation method.

[0044] The formaldehyde-free environmentally friendly adhesive material includes 70-80 parts of diphenylmethane diisocyanate, 15-25 parts of p-toluenesulfonyl isocyanate, 5-10 parts of nano zeolite, 1-3 parts of KH-560 silane coupling agent, 0.1-0.5 parts of tetrabutyl titanate, 0.5-1 parts of modified polyether silicone, 1-2 parts of PEG-60 hydrogenated castor oil, and 0.1-0.3 parts of antioxidant 1010.

[0045] The preparation method comprises the following steps: Diphenylmethane diisocyanate was mixed evenly with PEG-60 hydrogenated castor oil, modified polyether silicone, and antioxidant 1010 at 40°C. Nanozeolite, tetrabutyl titanate, and KH-560 silane coupling agent were added in sequence and dispersed at high speed at 2000 rpm for 20 min. Finally, p-toluenesulfonyl isocyanate was added and stirred at low speed at 500 rpm for 10 min to obtain formaldehyde-free environmentally friendly adhesive material #3.

[0046] Example 4: This example discloses a formaldehyde-free environmentally friendly adhesive material #4 for high-density fiberboard and a preparation method thereof.

[0047] The formaldehyde-free environmentally friendly adhesive material includes 70-80 parts of diphenylmethane diisocyanate, 15-25 parts of microcapsules, 5-10 parts of nano-zeolite, 1-3 parts of KH-560 silane coupling agent, 0.1-0.5 parts of tetrabutyl titanate, 0.5-1 parts of modified polyether silicone, 1-2 parts of PEG-60 hydrogenated castor oil, and 0.1-0.3 parts of antioxidant 1010. The microcapsules have a core-shell structure and include 87.5% core material, 12% shell material, 0.2% polyvinyl alcohol, and 0.3% dibutyltin dilaurate. The core material is vinyltrimethoxysilane, and the shell material is isophorone diisocyanate.

[0048] The preparation method comprises the following steps: S1. Preparation of microcapsules: Vinyltrimethoxysilane, isophorone diisocyanate, and dibutyltin dilaurate were mixed to form an oil phase. Under high-speed stirring at 1400-1600 rpm, the oil phase was dropped into polyvinyl alcohol to form an emulsion (droplet size 5-10 μm). The temperature was raised to 55-65°C, the reaction was carried out for 1-3 hours, and the mixture was cooled to room temperature, filtered, and washed to obtain white powdery core-shell microcapsules.

[0049] S2. Mixing of materials: Diphenylmethane diisocyanate, PEG-60 hydrogenated castor oil, modified polyether silicone, and antioxidant 1010 were mixed evenly at 40°C, and nano-zeolite, tetrabutyl titanate, and KH-560 silane coupling agent were added in sequence. The mixture was dispersed at high speed at 2000 rpm for 20 minutes. Finally, microcapsules were added and stirred at low speed at 500 rpm for 10 minutes to obtain formaldehyde-free environmentally friendly adhesive material #4.

[0050] Example 5: This example discloses a formaldehyde-free environmentally friendly adhesive material #5 for high-density fiberboard and its preparation method.

[0051] The formaldehyde-free environmentally friendly adhesive material includes 70-80 parts of diphenylmethane diisocyanate, 15-25 parts of p-toluenesulfonyl isocyanate, 5-10 parts of modified nano zeolite, 1-3 parts of KH-560 silane coupling agent, 0.1-0.5 parts of tetrabutyl titanate, 0.5-1 parts of modified polyether silicone, 1-2 parts of PEG-60 hydrogenated castor oil, and 0.1-0.3 parts of antioxidant 1010.

[0052] The preparation method comprises the following steps: S1. Preparation of modified nano zeolite: disperse nano zeolite in ethanol, add hexadecyltrimethoxysilane, the mass ratio of nano zeolite to hexadecyltrimethoxysilane is 20:1, reflux at 80° C. for 4 h, and centrifuge to obtain modified nano zeolite.

[0053] S2. Diphenylmethane diisocyanate was mixed with PEG-60 hydrogenated castor oil, modified polyether silicone, and antioxidant 1010 at 40°C, and modified nano zeolite, tetrabutyl titanate, and KH-560 silane coupling agent were added in sequence. The mixture was dispersed at high speed at 2000 rpm for 20 min. Finally, p-methylbenzenesulfonyl isocyanate was added and stirred at low speed at 500 rpm for 10 min to obtain formaldehyde-free environmentally friendly adhesive material #5.

[0054] Example 6: This example discloses a formaldehyde-free environmentally friendly adhesive material #6 for high-density fiberboard and a preparation method thereof.

[0055] The formaldehyde-free environmentally friendly adhesive material includes 70-80 parts of diphenylmethane diisocyanate, 15-25 parts of microcapsules, 5-10 parts of modified nano-zeolite, 1-3 parts of KH-560 silane coupling agent, 0.1-0.5 parts of tetrabutyl titanate, 0.5-1 parts of modified polyether silicone, 1-2 parts of PEG-60 hydrogenated castor oil, and 0.1-0.3 parts of antioxidant 1010. The microcapsules have a core-shell structure and include 87.5% core material, 12% shell material, 0.2% polyvinyl alcohol, and 0.3% dibutyltin dilaurate. The core material is vinyltrimethoxysilane, and the shell material is isophorone diisocyanate.

[0056] The preparation method comprises the following steps: S1. Preparation of microcapsules: Vinyltrimethoxysilane, isophorone diisocyanate, and dibutyltin dilaurate were mixed to form an oil phase. Under high-speed stirring at 1400-1600 rpm, the oil phase was dropped into polyvinyl alcohol to form an emulsion (droplet size 5-10 μm). The temperature was raised to 55-65°C, the reaction was carried out for 1-3 hours, and the mixture was cooled to room temperature, filtered, and washed to obtain white powdery core-shell microcapsules.

[0057] S2. Preparation of modified nano zeolite: disperse nano zeolite in ethanol, add hexadecyltrimethoxysilane, the mass ratio of nano zeolite to hexadecyltrimethoxysilane is 20:1, reflux at 80° C. for 4 h, and centrifuge to obtain modified nano zeolite.

[0058] S3. Mixing of materials: Diphenylmethane diisocyanate, PEG-60 hydrogenated castor oil, modified polyether silicone, and antioxidant 1010 were mixed evenly at 40°C, and modified nano-zeolite, tetrabutyl titanate, and KH-560 silane coupling agent were added in sequence. The mixture was dispersed at high speed at 2000 rpm for 20 minutes. Finally, microcapsules were added and stirred at low speed at 500 rpm for 10 minutes to obtain formaldehyde-free environmentally friendly adhesive material #6.

[0059] Comparative Example 1: This comparative example provides a comparative formaldehyde-free environmentally friendly adhesive material D1 which is the same as Example 6, except that the formaldehyde-free environmentally friendly adhesive material does not include microcapsules.

[0060] Comparative Example 2: This comparative example provides a comparative formaldehyde-free environmentally friendly adhesive material D2 which is the same as Example 6, except that the formaldehyde-free environmentally friendly adhesive material does not include modified nano-zeolite.

[0061] Comparative Example 3: This comparative example provides a comparative formaldehyde-free environmentally friendly adhesive material D1 which is the same as Example 6, except that hexamethylene diisocyanate is used instead of diphenylmethane diisocyanate.

[0062] Comparative Example 4: This comparative example provides a comparative formaldehyde-free environmentally friendly adhesive material D2 that is the same as Example 6, except that KH-550 silane coupling agent is used instead of KH-560 silane coupling agent.

[0063] Comparative Example 5: This comparative example provides a comparative formaldehyde-free environmentally friendly adhesive material D3 which is the same as Example 6, except that tetraethyl titanate is used instead of tetrabutyl titanate.

[0064] Comparative Example 6: This comparative example provides a comparative formaldehyde-free environmentally friendly adhesive material D4, which is the same as Example 6, except that methyltrimethoxysilane is used instead of vinyltrimethoxysilane.

[0065] Comparative Example 7: This comparative example provides a comparative formaldehyde-free environmentally friendly adhesive material D5 which is the same as Example 6, except that hexamethylene diisocyanate is used instead of isophorone diisocyanate.

[0066] The formaldehyde-free, environmentally friendly adhesive materials #1-#6 prepared in Examples 1-6 and the comparative formaldehyde-free, environmentally friendly adhesive materials D1-D7 prepared in Comparative Examples 1-7 were applied to the surface of poplar wood fibers using high-pressure atomization. The applied fibers were manually laid in a mold, pre-pressed to form a slab, and then placed in a hot press for hot pressing. The fiberboard had a width of 250 mm × 250 mm, a thickness of (7.0 ± 0.5) mm, and a set density of (900 ± 50) kg / m 3 , hot pressing temperature is 190℃, hot pressing time is 1mm / min. Prepare multiple test plates for each test condition, and then select the density of (900±20)kg / m 3 Three boards were sawn. According to GB / T17657-2013, "Test Methods for Physical and Chemical Properties of Wood-Based Panels and Veneer Wood-Based Panels," the panels were tested for internal bonding strength, static bending strength, elastic modulus, 24-hour water absorption thickness expansion, and moisture content. Each parameter was averaged across six valid test pieces. The results were evaluated according to GB / T31765-2015, "High-Density Fiberboard."

[0067] Table 1 Example Performance Static bending strength (MPa) Thickness expansion rate after water absorption (%) Moisture content (%) Internal bonding strength (MPa) Elastic modulus (MPa) Example 1 40.5 4.9 5.8 1.35 3550 Example 2 40.8 4.7 5.7 1.38 3620 Example 3 41.2 4.5 5.5 1.44 3695 Example 4 41.9 3.7 4.6 1.49 3874 Example 5 43.2 3.9 5.1 1.48 4027 Example 6 44.5 3.5 4.3 1.55 4288 Comparative Example 1 38.8 7.4 7.7 1.45 3902 Comparative Example 2 36.6 6.9 7.1 1.28 3399 Comparative Example 3 34.3 4.2 5.4 1.04 3182 Comparative Example 4 43.8 3.7 4.6 1.17 3964 Comparative Example 5 42.9 3.9 5.2 1.47 3975 Comparative Example 6 42.4 5.2 6.3 1.51 4147 Comparative Example 7 42.2 5.4 6.6 1.49 4098 The data from Examples 1-3, especially Example 3, show that the high-density fiberboard obtained using the adhesive material of the present application exhibits excellent properties such as static bending strength, water absorption thickness expansion rate, moisture content, internal bonding strength, and elastic modulus due to the reasonable proportion of the adhesive material of the present application. This is because the active -NCO groups of diphenylmethane diisocyanate react with the -OH groups of wood cellulose / hemicellulose to form polyurethane or polyurea bonds, constructing a three-dimensional cross-linked network that provides mechanical strength, good fluidity at high temperatures, and strong permeability. The dehydrating agent reacts first with the water in the fiberboard, consuming the water in the fiberboard without producing CO2. The pores of the nano zeolite have a high specific surface area, which can adsorb free water and reduce local water activity. Tetrabutyl titanate can increase the inhibition rate of the reaction between -NCO and water, ensuring that the dehydrating agent reacts preferentially with water. The epoxy groups in the epoxysilane coupling agent react with the hydroxyl groups in the wood, improving water resistance and internal bonding strength. The dispersant can stabilize the dispersion, prevent the nano zeolite from settling, and ensure uniform sizing. Viscosity reducers can reduce the viscosity of high-solid systems, improve fiber surface wettability, are compatible with diphenylmethane diisocyanate, do not interfere with the reactivity of the -NCO group, improve rheological properties, and provide high storage stability. Antioxidants can block the oxidative degradation of the benzene ring or carbamate bond in diphenylmethane diisocyanate at high temperatures (e.g., the formation of quinone chromophores, which causes yellowing). They can also reduce the corrosion of oxidation byproducts (such as carboxylic acids) on the wood-glue interface, thereby improving the long-term weathering resistance of the board.

[0068] Compared to Example 3, Example 4 uses microcapsules as a dehydrating agent. The high-density fiberboard obtained by applying formaldehyde-free, environmentally friendly adhesive material #4 from Example 4 exhibits further improved properties compared to the high-density fiberboard applied with formaldehyde-free, environmentally friendly adhesive material #3. This is because vinyltrimethoxysilane rapidly reacts with free water in the fibers to produce silanols and methanol, without generating CO₂, thus preventing bubbles from forming at the source. The generated silanol molecules condense to form Si-O-Si bonds and regenerate water. The regenerated water is further captured by neighboring vinyltrimethoxysilanes, forming a water recycling chain until the water activity of the system is minimized. Some vinyltrimethoxysilane reacts with hydroxyl groups (-OH) on the wood surface to form high-energy Si-OC bonds, significantly enhancing interfacial bonding. The generated methanol (CH₃OH) reacts with residual -NCO to form urethane bonds. It is also adsorbed by the hydrophobic nanozeolite and desorbed during the high-temperature pressing stage. The Si-O-Si and Si-OC bonds derived from vinyltrimethoxysilane form an interpenetrating reinforcement phase, which improves the water resistance and stability of the adhesive material.

[0069] Compared to Example 3, Example 5 utilizes modified nano-zeolites. The high-density fiberboard obtained by applying the formaldehyde-free, environmentally friendly adhesive #5 from Example 5 exhibits improved properties compared to the high-density fiberboard applied with formaldehyde-free, environmentally friendly adhesive #3. This is because the hydrophobic modification makes the zeolite more prone to adsorbing non-polar molecules (such as methanol) while reducing its adsorption of polar diphenylmethane diisocyanate monomers, thus preventing interference with the curing reaction. The added epoxy silane coupling agent reacts simultaneously with the zeolite surface, the hydroxyl groups of the wood, and diphenylmethane diisocyanate, forming a three-dimensional covalent bond network and further enhancing interfacial bonding strength.

[0070] Compared to Example 3, Example 6 uses microcapsules as the dehydrating agent and modified nanozeolites. The high-density fiberboard produced by applying the formaldehyde-free, environmentally friendly adhesive material #6 from Example 6 exhibits superior performance compared to the high-density fiberboard produced by applying the formaldehyde-free, environmentally friendly adhesive material #3. This is because the hydrophobically modified nanozeolites have an extremely high specific surface area. In addition to preferentially adsorbing free water molecules in the fibers, they also react with methanol (CH3OH) generated by the hydrolysis of vinyltrimethoxysilane, reducing the local water activity in the system.

[0071] Comparative Example 1 Compared with Example 6, the formaldehyde-free environmentally friendly adhesive material does not include microcapsules. The various properties of the obtained high-density fiberboard have declined to varying degrees, especially the 24h water absorption thickness expansion rate and moisture content have declined the fastest. This is because the microcapsules as dehydrating agents will first react with the water in the fiberboard, consume the moisture in the fiberboard, and do not produce CO2. The core material vinyltrimethoxysilane will hydrolyze rapidly when it comes into contact with water, preferentially consume moisture, and the reaction rate is more than 10 times that of -NCO and water, and does not produce CO2. The shell material is a thermally responsive polyurethane shell with a melting point of 130-150°C. During the storage and gluing stages, the shell layer isolates the vinyltrimethoxysilane from contact with moisture or isocyanate to prevent pre-reaction. In the early stage of hot pressing, the shell layer melts and breaks, and the vinyltrimethoxysilane is released as needed to ensure that the dehydration reaction proceeds first. Dibutyltin dilaurate can be used as a catalyst to accelerate the reaction of -NCO and H2O and promote the cross-linking of the shell material. Polyvinyl alcohol (PVA) acts as an emulsifier to form a stable O / W emulsion. It adsorbs at the oil-water interface, reducing surface tension and controlling the droplet size to 5-10 μm. After the reaction, some of the PVA embeds into the shell, enhancing its hydrophilicity and facilitating water penetration during hot pressing to trigger release.

[0072] Comparative Example 2, compared with Example 6, does not include modified nano-zeolites in the formaldehyde-free, environmentally friendly adhesive material. The resulting high-density fiberboard exhibited varying degrees of decline in static bending strength, water absorption thickness expansion, internal bonding strength, and elastic modulus. This is because the hydrophobically modified nano-zeolites possess an extremely high specific surface area. In addition to preferentially adsorbing free water molecules from the fibers, they also react with methanol (CH3OH) generated by hydrolysis of vinyltrimethoxysilane, reducing the local water activity of the system. The hydrophobic modification makes the zeolite more inclined to adsorb non-polar molecules (such as methanol) while reducing adsorption of polar diphenylmethane diisocyanate monomers, thereby avoiding interference with the curing reaction. The zeolite's high-temperature resistance can also buffer local overheating during hot pressing, reducing the risk of thermal degradation of diphenylmethane diisocyanate.

[0073] Comparative Example 3, compared with Example 6, uses hexamethylene diisocyanate instead of diphenylmethane diisocyanate. The resulting high-density fiberboard exhibited varying degrees of decline in various properties, particularly in static bending strength, internal bond strength, and elastic modulus. This is because, although hexamethylene diisocyanate has similar properties to diphenylmethane diisocyanate, it has low reactivity, requires a strong catalyst, and cures slowly. Its excessive flexibility and insufficient elastic modulus make it unsuitable for boards requiring high density and high hardness.

[0074] Comparative Example 4, compared to Example 6, uses KH-550 silane coupling agent instead of KH-560. The resulting high-density fiberboard exhibits varying degrees of decline in various properties, particularly internal bond strength. This is because the epoxy groups in the epoxy silane coupling agent react with the hydroxyl groups in the wood, improving water resistance and internal bond strength. KH-550 silane coupling agent, on the other hand, does not contain epoxy groups.

[0075] Comparative Example 5, compared to Example 6, uses tetraethyl titanate instead of tetrabutyl titanate. The resulting high-density fiberboard exhibits varying degrees of decline in various properties. This is because, while tetraethyl titanate has similar properties to tetrabutyl titanate, tetrabutyl titanate accelerates the hydrolysis and condensation of vinyltrimethoxysilane. Tetraethyl titanate, on the other hand, has lower catalytic activity, hydrolyzes very slowly with vinyltrimethoxysilane, and readily generates acetaldehyde, which interferes with curing.

[0076] Comparative Example 6, compared to Example 6, uses methyltrimethoxysilane instead of vinyltrimethoxysilane. The resulting high-density fiberboard exhibits varying degrees of decline in various properties. This is because methyltrimethoxysilane contains trimethoxysilane (-Si(OCH3)3), which hydrolyzes and condenses to form a Si-O-Si network. However, its dehydration rate is slow, failing to meet the requirements for rapid dehydration.

[0077] Comparative Example 7, compared to Example 6, uses hexamethylene diisocyanate instead of isophorone diisocyanate. The resulting high-density fiberboard exhibits varying degrees of decline in various properties. This is because, although hexamethylene diisocyanate and isophorone diisocyanate have similar properties, hexamethylene diisocyanate has low reactivity, a slow cure rate, and high volatility. In contrast, isophorone diisocyanate has low viscosity, moderate reactivity, and releases no small molecules during cure.

[0078] From this we can see that missing or replaced materials cannot play a role in formaldehyde-free environmentally friendly adhesive materials, but will instead reduce the performance of formaldehyde-free environmentally friendly adhesive materials. Therefore, each component cannot be arbitrarily replaced by other materials.

[0079] The above are all preferred embodiments of the present invention, and are not intended to limit the scope of protection of the present invention. Therefore, any equivalent changes made based on the structure, shape, and principle of the present invention should be included in the scope of protection of the present invention.

Claims

1. A formaldehyde-free environmentally friendly adhesive material for high-density fiberboard, characterized in that: The adhesive material includes the formaldehyde-free environmentally friendly adhesive material including 70-80 parts of diphenylmethane diisocyanate, 15-25 parts of dehydrating agent, 5-10 parts of nano zeolite, 1-3 parts of epoxy silane coupling agent, 0.1-0.5 parts of tetrabutyl titanate, 0.5-1 parts of dispersant, 1-2 parts of viscosity reducer, and 0.1-0.3 parts of antioxidant.

2. The formaldehyde-free environmentally friendly adhesive material for high-density fiberboard according to claim 1, characterized in that: The dehydrating agent is a microcapsule with a core-shell structure, comprising 85-90% core material, 10-15% shell material, 0.1-0.3% polyvinyl alcohol, and 0.1-0.5% dibutyltin dilaurate. The core material is vinyltrimethoxysilane, and the shell material is isophorone diisocyanate.

3. The formaldehyde-free environmentally friendly adhesive material for high-density fiberboard according to claim 1 or 2, characterized in that: The nano zeolite is a modified nano zeolite. The preparation steps of the modified nano zeolite are: dispersing the nano zeolite in ethanol, adding hexadecyltrimethoxysilane, the mass ratio of the nano zeolite to hexadecyltrimethoxysilane is 18-22:1, refluxing at 75-85°C for 3-5h, and centrifuging and drying to obtain the modified nano zeolite.

4. A method for preparing an environmentally friendly formaldehyde-free adhesive material for high-density fiberboard according to any one of claims 1 to 3, characterized in that: The preparation method comprises the following steps: uniformly mixing diphenylmethane diisocyanate with a viscosity reducer, a dispersant, and an antioxidant at 35-45° C., sequentially adding nano zeolite, tetrabutyl titanate, and an epoxy silane coupling agent, dispersing the mixture at high speed at 1800-2200 rpm for 15-25 minutes, and finally adding a dehydrating agent and stirring the mixture at low speed at 400-600 rpm for 8-12 minutes to obtain the formaldehyde-free environmentally friendly adhesive material.

5. The method for preparing an environmentally friendly formaldehyde-free adhesive material for high-density fiberboard according to claim 4, characterized in that: The preparation method also includes a microcapsule preparation step, which includes mixing vinyltrimethoxysilane, isophorone diisocyanate, and dibutyltin dilaurate to form an oil phase, dripping the oil phase into polyvinyl alcohol under high-speed stirring at 1400-1600 rpm, heating to 55-65°C, reacting for 1-3 hours, cooling to room temperature, filtering, and washing to obtain white powdery core-shell microcapsules.

6. A high-density fiberboard, characterized in that: The high-density fiberboard uses the formaldehyde-free environmentally friendly adhesive material for high-density fiberboard as described in any one of claims 1-3 or the formaldehyde-free environmentally friendly adhesive material prepared by the preparation method of the formaldehyde-free environmentally friendly adhesive material for high-density fiberboard as described in any one of claims 5-6.

7. Use of the high-density fiberboard according to claim 6 in furniture manufacturing, interior decoration, office equipment manufacturing, automobile manufacturing, and cultural and sports equipment manufacturing.