A lightweight, high-strength polyurethane particleboard and its preparation method

Abstract

This invention relates to a lightweight, high-strength polyurethane particleboard and its preparation method, belonging to the field of wood-based composite materials and engineered wood products processing. The lightweight, high-strength polyurethane particleboard consists of an upper surface layer, a core layer, and a lower surface layer, with a weight ratio of surface layer to core layer of 2:8 to 5:5. By weight, the surface layer contains 80-97 parts of biomass fines, 3-20 parts of polyisocyanate, and 0.03-1 parts of modified nano-reinforcing particles; the core layer contains 70-95 parts of biomass chips, 3-20 parts of polyisocyanate, and 0.3-6 parts of foaming regulator. It is prepared through biomass unit preparation, nano-reinforcing particle modification treatment, polyurethane system preparation, and polyurethane particleboard molding steps. The lightweight, high-strength polyurethane particleboard of this invention has low density and high strength-to-weight ratio, significantly improved internal bonding strength, and good mechanical properties and water resistance. The method is simple and easy to implement, suitable for industrial production of particleboard, and beneficial for expanding the application range of particleboard.

Description

Technical Field

[0001] This invention relates to a lightweight, high-strength polyurethane particleboard and its preparation method, belonging to the field of wood-based composite materials and engineered wood processing. Background Technology

[0002] Particleboard is one of the three major types of engineered wood products in my country, widely used in furniture manufacturing, custom furniture, and interior decoration. The density of ordinary particleboard is mostly between 650 and 720 kg / m³. 3 With the scarcity of timber resources and the continuous growth in raw material demand, lightweighting has become an important development trend for particleboard products. Lightweight particleboard means using less wood raw material while meeting the same usage requirements. This not only saves timber resources but also reduces energy consumption in production and processing and transportation costs, making the product more competitive in the market. Simultaneously, with the development from traditional furniture to customized furniture, whole-house decoration, and the entire home furnishing industry, the application of particleboard has expanded from furniture panels to diverse fields such as wall panels, large-format tabletops, and integrated high door panels, placing new demands on particleboard for low density, high strength, resistance to deformation, and high environmental friendliness. However, currently, lightweight particleboard suffers from insufficient strength, poor water resistance, and large dimensional variations, making it difficult to meet these new usage requirements.

[0003] A key problem in the manufacture of lightweight particleboard lies in the fact that as the density of the particleboard decreases, the gaps between the wood chips increase, the bonding between structural units weakens, and a uniform continuous phase structure cannot be formed, leading to a significant decrease in the load-bearing capacity and water resistance of the board. Current research mainly uses methods such as introducing lightweight fillers and adhesive foaming to prepare lightweight particleboard. Replacing some wood chips with lightweight fillers (such as polystyrene foam particles) can reduce the density of the particleboard, but the bonding of lightweight fillers consumes adhesives, affecting the internal bonding strength. At the same time, because the lightweight fillers themselves have very low strength, they are difficult to strengthen the particleboard. Adhesive foaming can fill the gaps between wood chips and promote bonding between them, but the mechanical properties and water resistance of the board need further improvement.

[0004] Chinese patent CN111993525A discloses a method for preparing lightweight particleboard. The method involves selecting core and surface particleboard separately, using urea-formaldehyde resin or polyurethane foam adhesive, and employing a segmented hot-pressing process. However, this method suffers from formaldehyde release issues with urea-formaldehyde resin foaming, and the polyurethane foam adhesive is a conventional two-component compound. The two components react immediately upon mixing at room temperature, requiring separate storage and application to the particleboard. This can lead to insufficient contact and reaction between the components, negatively impacting the mechanical strength and water resistance of the lightweight particleboard.

[0005] Chinese patent "CN112388794A" discloses a formaldehyde-free lightweight particleboard and its preparation method. The main raw materials are wood chips, isocyanate, polyether polyol modified with dicarboxylic acid containing benzene rings, tackifier, catalyst, and water. This method only has a certain foaming effect on the core layer of the particleboard. The surface layer composition is the same as that of conventional particleboard. The bending resistance and water resistance of the prepared particleboard need to be further improved.

[0006] Chinese patent "CN106671216A" discloses a method for preparing a novel low-density, low-cost, and high-strength particleboard, including a surface layer, a particle layer, and a core layer. This method requires selecting poplar wood with a diameter greater than 8cm as raw material and processing it into long, narrow, and thin particleboard (90-130mm in length, 5-30mm in width, and 0.5mm-2mm in thickness). It has strict requirements on raw materials and particle shape, falls under the category of oriented strand board (OSB), and the board density needs to be further reduced. Summary of the Invention

[0007] To address the shortcomings of the existing technologies, this invention provides a lightweight, high-strength polyurethane particleboard to solve the problem of insufficient performance of existing lightweight particleboards. Based on structural control and optimization design, a nano-reinforcement structure is constructed on the stressed surface layer, and a uniform and stable microbubble structure is formed in the core layer, thereby achieving lightweight and high strength of the particleboard. The prepared particleboard has low density, high strength-to-weight ratio, significantly improved internal bonding strength, and good water resistance.

[0008] The lightweight, high-strength polyurethane particleboard of this invention comprises a nano-reinforced surface layer and a micro-foamed core layer. The surface layer consists of biomass fines, polyisocyanate, and modified nano-reinforcing particles. The nano-reinforcing particles are modified to ensure uniform dispersion within the polyisocyanate. The application of polyisocyanate further distributes the modified nano-reinforcing particles among the surface fines, strengthening the surface structure and enhancing the overall load-bearing capacity of the particleboard. The core layer consists of biomass shavings, polyisocyanate, and a foaming regulator. The foaming regulator delays foaming and can be thoroughly mixed with polyisocyanate at room temperature before being applied to the core shavings. At high temperatures, it promotes cross-linking and foaming reactions between the polyisocyanate and hydroxyl and water molecules, forming a uniform and stable polyurethane foam structure between the shaving units. This significantly reduces the core layer density while maintaining performance. Through the synergistic effect of surface nanoparticle modification and core polyurethane foaming regulation, the particleboard achieves lightweight and high strength.

[0009] A lightweight, high-strength polyurethane particleboard comprises an upper surface layer, a core layer, and a lower surface layer. The surface layer includes an upper surface layer and a lower surface layer, with a weight ratio of surface layer to core layer of 2:8 to 5:5. By weight, the surface layer contains 80 to 97 parts of biomass fines with a particle size of 0.2 to 1.5 mm, 3 to 20 parts of polyisocyanate, and 0.03 to 1 part of modified nano-reinforcing particles. The core layer contains 70 to 95 parts of biomass chips with a length of 4 to 60 mm, a width of 0.5 to 10 mm, and a thickness of 0.2 to 2 mm, 3 to 20 parts of polyisocyanate, and 0.3 to 6 parts of foaming regulator.

[0010] Preferably, the lightweight high-strength polyurethane particleboard of the present invention has a surface layer to core layer weight ratio of 3:7 to 4:6. By weight, the surface layer contains 90 to 95 parts of biomass fines, 5 to 10 parts of polyisocyanate and 0.05 to 0.5 parts of modified nano-reinforcing particles; the core layer contains 80 to 92 parts of biomass chips, 8 to 15 parts of polyisocyanate and 0.8 to 4.5 parts of foaming regulator.

[0011] Preferably, the upper and lower surface layers have the same composition and thickness.

[0012] The biomass fines and shavings are prepared from fast-growing plantation timber, bamboo, willow, straw, rice straw, reeds, and / or recycled waste wood materials, and are the basic structural units of lightweight, high-strength polyurethane particleboard. The surface layer uses biomass fines, which are easy to compress and compact, while the core layer uses larger-sized biomass shavings, which have certain strength and compression resistance. This combination helps to form a cross-sectional density gradient with a high surface density and a low core density, thereby ensuring the mechanical strength of the particleboard. At the same time, the high-quality, fine surface is also beneficial for secondary finishing of the particleboard. The preferred amount of biomass fines in the surface layer is 90-95 parts, and the preferred amount of biomass shavings in the core layer is 80-92 parts.

[0013] The polyisocyanate is one of toluene diisocyanate, diphenylmethane diisocyanate, and polymethylene polyphenyl isocyanate, which plays the role of bonding biomass units and is also the main raw material for generating polyurethane foam structure in the core layer; the isocyanate (-NCO) content in the polyisocyanate is 30-35 wt%, the preferred amount added to the surface layer is 5-10 parts, and the preferred amount added to the core layer is 8-15 parts.

[0014] The modified nano-reinforcing particles are silane-modified nano-sized silica with a particle size of 10-100 nm. They can be uniformly dispersed in polyisocyanate and dispersed between the surface fines by the application of polyisocyanate, thereby enhancing the surface structure. The silane is one of 3-aminopropyltriethoxysilane (KH550), γ-glycidoxypropyltrimethoxysilane (KH560), 3-methacryloyloxypropyltrimethoxysilane (KH570), γ-mercaptopropyltrimethoxysilane (KH590), and N-β-(aminoethyl)-γ-aminopropyltrimethoxysilane (KH792).

[0015] The foaming regulator, by weight, comprises 80-100 parts of a compounded polymeric polyol, 5-10 parts of a chain extender or crosslinking agent, 1-5 parts of a surfactant, 1.5-2 parts of a compounded catalyst, and 0.1-0.5 parts of a retarder. At room temperature, it inhibits the reaction of polyisocyanates; at high temperatures, it promotes the crosslinking and foaming reaction of isocyanate ions with hydroxyl groups and water molecules, thereby regulating the structure of the formed cells. The compounded polymeric polyol is composed of a high-hydroxyl-value, high-functionality polyether / polyester polyol and a... The compound system consists of polyether / polyester polyols with low hydroxyl values ​​and low functionality, with an average hydroxyl value of 350–450 mgKOH / g and an average functionality of 3–5. Polyether / polyester polyols with high hydroxyl values ​​and high functionality have a hydroxyl value of 400–450 mgKOH / g and a functionality of 4.5–5. Polyether / polyester polyols with low hydroxyl values ​​and low functionality have a hydroxyl value of 340–390 mgKOH / g and a functionality of 3–3.5. The high hydroxyl value, high functionality polyether / polyester polyols and low hydroxyl value, low functionality polyether / polyester polyols... The mass ratio of polyether / polyester polyol is 3:7-7:3; the chain extender or crosslinker is one or more of diol, triol, diamine and ethanolamine, which can promote the formation of a three-dimensional crosslinked network structure in the polyurethane system and increase the strength of polyurethane cells in particleboard; the surfactant is amino silicone oil or polyether-modified organosilicon, which can improve the mixing uniformity of each component and help form a fine and uniform cell structure; the compound catalyst is composed of amine catalyst and organometallic catalyst, with a weight ratio of 1:1 to 1:6. The amine catalyst is one of dimethylcyclohexylamine, triethanolamine and triethylenediamine, which can promote the reaction of isocyanate with water molecules. The organometallic catalyst is one of bismuth carboxylate, stannous octoate and dibutyltin dilaurate, which can promote the reaction of isocyanate with hydroxyl groups; the retarder is one of oxalic acid, phosphoric acid, tartaric acid and citric acid, which can inhibit the reaction of isocyanate at room temperature and extend the storage time of the polyurethane system.

[0016] This foaming regulator has delayed foaming characteristics and can be uniformly mixed with polyisocyanates to form a polyurethane system for application. At high temperatures, it can promote the cross-linking and foaming reaction of isocyanate groups with hydroxyl groups and water molecules, forming a uniform and stable polyurethane micro-foam structure between the core layer shaving units.

[0017] The density of the lightweight, high-strength polyurethane particleboard is 400–550 kg / m³. 3 The strength-to-weight ratio (static bending strength / density) is not less than 2.5 × 10⁻⁶. 3 .

[0018] Meanwhile, the present invention also provides a method for preparing lightweight high-strength polyurethane particleboard, comprising the following steps:

[0019] (1) Biomass unit preparation: The size of biomass raw materials is reduced by mechanical means such as chipping, shaving, crushing and / or grinding, and the surface fines and core shavings are separated. The moisture content is controlled to be 6-15 wt% by drying or humidification.

[0020] (2) Modification of nano-reinforcing particles: Add nano-silica to an ethanol solution, sonicate it at room temperature to disperse it homogeneously, add silane in proportion, adjust the pH value of the solution, heat and stir to fully react, separate the solid and liquid mixture, wash and dry the solid product to obtain modified nano-reinforcing particles.

[0021] (3) Preparation of polyurethane system: The polyurethane system is composed of foaming regulator and polyisocyanate; weigh the compounded polymer polyol, chain extender / crosslinker, surfactant, compounded catalyst and retarder according to the proportion, and stir at high speed at room temperature to obtain foaming regulator; mix the foaming regulator and polyisocyanate in a certain proportion and stir at high speed to obtain polyurethane system.

[0022] (4) Polyurethane particleboard molding: Weigh the modified nano-reinforcing particles according to the proportion and add them to the polyisocyanate. Stir and mix evenly at room temperature and high speed. Preheat the mixture to reduce the viscosity. Apply it evenly to the surface of the surface fine material using a high-pressure atomization method. After preheating the polyurethane system, apply it evenly to the core layer particleboard using a high-pressure atomization method. Weigh the surface fine material and core layer particleboard after gluing according to the preset board density. After laying, hot pressing (foaming, curing) and cooling (sawing), lightweight high-strength polyurethane particleboard is obtained.

[0023] In step (1), when preparing biomass units, controlling the appropriate moisture content helps the biomass units to be plasticized and compressed during hot pressing. At the same time, water molecules can react with polyisocyanates to form bubbles. However, excessive moisture content will cause a large amount of water vapor to accumulate inside the board during hot pressing, which can easily cause the board to bubble when the pressure is released. The appropriate moisture content is 6-15%.

[0024] In step (2), the nano-reinforcing particle modification treatment involves modifying nano-silica with silane and grafting hydrophobic groups onto the surface of nano-silica to reduce the aggregation of nano-reinforcing particles and improve their dispersibility in polyisocyanates, which is beneficial to better exert the reinforcing effect of nanoparticles. The weight ratio of silane to nano-silica is 1:10 to 2.5:10.

[0025] Nano-silica is added to an ethanol solution and ultrasonically dispersed for 10–20 min. After adding silane, the pH of the solution is adjusted to 4–5, and the mixture is stirred at 60–80 °C for 2–3 h to fully react. The mixture is then separated into solid and liquid phases by vacuum filtration or high-speed centrifugation.

[0026] In step (3), the polyurethane system is prepared using a foaming regulator that has delayed foaming properties. At room temperature, it can be mixed with polyisocyanate to form a polyurethane system. During hot pressing, the foaming regulator promotes the reaction of isocyanate ions with hydroxyl groups and water molecules, regulating the formation of a polyurethane micro-foam structure in the core layer. Too little foaming regulator will not achieve the desired foaming effect, while too much will result in a high viscosity of the polyurethane system, making it difficult to apply. The weight ratio of the foaming regulator to polyisocyanate is 1:10 to 3:10. The high-speed stirring speed is 500 to 2000 r / min.

[0027] In step (4), the polyurethane particleboard is formed by dispersing modified nano-reinforcing particles in polyisocyanate. To ensure uniform application, the mixture is preheated at 40-60°C for 5-20 minutes to reduce viscosity. It is then applied by high-pressure atomization to ensure that the modified nano-reinforcing particles are evenly distributed on the surface fines to enhance the surface structure. The polyurethane system is preheated at 40-60°C for 2-10 minutes to reduce viscosity and then evenly applied to the core particleboard.

[0028] According to the preset board density, the surface fine material and core wood shavings after sizing are laid in sequence to form a board blank, and then placed in a hot press. It is hot-pressed at 140-180℃ for 4-10 minutes and at a pressure of 2-3MPa. During the hot pressing process, the isocyanate groups react fully. After cooling, it is taken out to obtain a lightweight high-strength polyurethane particleboard. During the hot pressing process, the board blank is compressed and compacted, the polyisocyanate on the surface undergoes a curing reaction, and the polyurethane system in the core undergoes a cross-linking and foaming reaction.

[0029] Before applying the surface polyisocyanate mixture and the core polyurethane system, preheating is performed at a temperature of 40–60°C. The preheating time for the polyisocyanate mixture is 5–20 min, and the preheating time for the polyurethane system is 2–10 min. This effectively reduces the viscosity of the polyisocyanate and polyurethane systems and improves the uniformity of application. The hot pressing temperature of the slab is 140–180°C, the time is 4–10 min, and the pressure is 2–3 MPa. During the hot pressing process, the core polyurethane system reacts fully to form a uniform and continuous micro-foamed structure.

[0030] The present invention has the following beneficial effects:

[0031] I. The lightweight, high-strength polyurethane particleboard of this invention, based on microstructure regulation and optimization, constructs a composite structure of a modified nanoparticle-reinforced surface layer and a uniformly stable micro-foamed core layer. The modified nanoparticles in the surface layer are distributed within the cross-linked network structure of isocyanate, enhancing the surface structure, thereby improving the overall load-bearing capacity and the mechanical properties of the particleboard. During hot pressing, the polyurethane system in the core layer reacts with water molecules in the particleboard to generate gas, simultaneously undergoing a cross-linking reaction. The resulting pore structure fills the gaps between the particleboard particles, creating a stable, continuous phase structure in the core layer. This significantly improves the internal bonding strength while reducing density. Through the synergistic effect of surface nanoparticle modification and core polyurethane foaming regulation, the particleboard achieves lightweight yet high strength.

[0032] II. The method for preparing lightweight high-strength polyurethane particleboard of the present invention uses a polyurethane system for the core layer, which is composed of a foaming regulator and a polyisocyanate. The foaming regulator has the characteristic of delayed reaction and can be mixed uniformly with the polyisocyanate at room temperature to form a polyurethane system, which is then applied to the surface of the core layer particleboard. This allows the components of the polyurethane system to come into full contact and react completely during the subsequent hot pressing process, avoiding the negative impact of residual unreacted components on the performance of the particleboard.

[0033] Third, the lightweight high-strength polyurethane particleboard of the present invention has a significantly reduced density while maintaining the performance of ordinary particleboard. Compared with existing lightweight particleboard, it has a higher strength-to-weight ratio, significantly improved mechanical properties and water resistance, which is conducive to expanding the application range of particleboard. Moreover, the preparation method is simple and easy to implement, without the need for additional special equipment, making it suitable for industrial production of particleboard and with good prospects for industrial application. Attached Figure Description

[0034] Figure 1 The image shows a scanning electron microscope (SEM) image of the modified nanoparticles in Example 1.

[0035] Figure 2 This is a super-depth-of-field three-dimensional microscope image of the core layer of the particleboard in Comparative Example 1.

[0036] Figure 3 The image shows a super-depth-of-field three-dimensional microscope image of the core layer of the particleboard in Comparative Example 2.

[0037] Figure 4 This is a super-depth-of-field three-dimensional microscope image of the core layer of the lightweight high-strength polyurethane particleboard in Example 1.

[0038] Figure 5 Example 2: Ultra-depth-of-field three-dimensional microscope image of the core layer of a lightweight, high-strength polyurethane particleboard. Detailed Implementation

[0039] The technical solution of the present invention will be described in more detail below with reference to the embodiments. The following embodiments are only some embodiments of the present invention, and not all embodiments. Unless otherwise specified, all raw materials can be obtained through commercial means, all parts are parts by weight, and all equipment is conventional equipment in the art.

[0040] The lightweight, high-strength polyurethane particleboard of this invention has a composite structure of a nanoparticle-reinforced surface layer and a micro-foamed core layer. The modified nanoparticles, after being modified with silane, exhibit enhanced dispersibility and are uniformly dispersed among the surface fines by the application of polyisocyanate, thereby enhancing the load-bearing capacity of the surface layer and the overall strength of the board. The foaming regulator has delayed foaming characteristics and can be uniformly mixed with polyisocyanate to form a polyurethane system for application. At high temperatures, it promotes the cross-linking and foaming reaction of isocyanate groups with hydroxyl groups and water molecules, forming a uniform and stable polyurethane micro-foamed structure between the core layer particle units.

[0041] This invention relates to a lightweight, high-strength polyurethane particleboard, comprising a nano-reinforced surface layer and a micro-foamed core layer. The weight ratio of the surface layer to the core layer is 2:8 to 5:5. By weight, the surface layer consists of 80-97 parts of biomass fines (particle size 0.2-1.5 mm), 3-20 parts of polyisocyanate, and 0.03-1 part of modified nano-reinforcing particles. The core layer consists of 70-95 parts of biomass shavings (length 4-60 mm, width 0.5-10 mm, thickness 0.2-1.5 mm), 3-20 parts of polyisocyanate, and 0.03-1 part of modified nano-reinforcing particles. Composed of 3-6 parts foaming regulator; polyisocyanate acts as a binder for biomass units, and the foaming regulator has the characteristic of delayed foaming at room temperature. At high temperatures, it can promote the cross-linking and foaming reaction of polyisocyanate with hydroxyl and water molecules, forming a uniform and stable microbubble structure between the particle units; the nano-reinforcing particles are modified to enhance dispersibility, and with the application of polyisocyanate, they are evenly distributed in the surface cross-linked network structure, enhancing the strength of the surface and the board; the density of the lightweight high-strength polyurethane particleboard is 400-550 kg / m³. 3 .

[0042] The surface fines and core wood shavings are prepared from biomass such as fast-growing plantation timber, bamboo, willow, straw, rice straw, reeds, and recycled waste wood materials; the polyisocyanate is one of toluene diisocyanate, diphenylmethane diisocyanate, and polymethylene polyphenyl isocyanate, with an isocyanate content of 30-35%; the modified nano-reinforcing particles are silane-modified nano-silica with a particle size of 10-100 nm, uniformly dispersed in the polyisocyanate, utilizing the polyisocyanate... High-pressure atomization disperses the silane between the fine particles in the surface layer, enhancing the surface structure; the silane is one of 3-aminopropyltriethoxysilane (KH550), γ-glycidyl etheroxypropyltrimethoxysilane (KH560), 3-methacryloyloxypropyltrimethoxysilane (KH570), γ-mercaptopropyltrimethoxysilane (KH590), and N-β-(aminoethyl)-γ-aminopropyltrimethoxysilane (KH792); the foaming regulator is composed of 80... The compound consists of approximately 90 parts of a compounded polymerized polyol, 5-10 parts of a chain extender / crosslinker, 1-5 parts of a surfactant, 1.5-2 parts of a compounded catalyst, and 0.1-0.5 parts of a retarder. The compounded polymerized polyol comprises a high-hydroxyl-value, high-functionality polyether / polyester polyol and a low-hydroxyl-value, low-functionality polyether / polyester polyol. The average hydroxyl value of the compounded system is 350-450 mg KOH / g, and the average functionality is 3-5. The chain extender / crosslinker is a diol and a triol. The catalyst is composed of one or more of the following: a non-metallic alcohol, a diamine, and an ethanolamine; the surfactant is an amino silicone oil or a polyether-modified organosilicon; the compound catalyst is composed of an amine catalyst and an organometallic catalyst in a weight ratio of 1:1 to 1:6; the amine catalyst is one of dimethylcyclohexylamine, triethanolamine, or triethylenediamine; the organometallic catalyst is one of bismuth carboxylic acid, stannous octoate, or dibutyltin dilaurate; and the retarder is one of oxalic acid, phosphoric acid, tartaric acid, or citric acid.

[0043] The lightweight, high-strength polyurethane particleboard is prepared through biomass unit preparation, nano-reinforcing particle modification, polyurethane system preparation, and polyurethane particleboard molding. Its preparation is carried out according to the following steps:

[0044] 1) Reduce the size of biomass raw materials by mechanical means such as chipping, planing, crushing, and grinding, separate the surface fines and core shavings, and control the moisture content to 6-15% by drying or humidifying methods;

[0045] 2) Add nano-silica to an ethanol solution and sonicate for 10-20 min at room temperature to homogeneously disperse it. Add silane in proportion, with a weight ratio of silane to nano-silica of 1:10-2.5:10. Adjust the pH of the solution to 4-5 and stir at 60-80℃ for 2-3 h to allow the reaction to proceed. Separate the mixture into solid and liquid phases by vacuum filtration or high-speed centrifugation. Repeatedly wash and dry the solid product to obtain modified nano-reinforced particles.

[0046] 3) Weigh out the compounded polyol, chain extender / crosslinker, surfactant, compounded catalyst, and retarder according to the proportion, and stir at 500-2000 r / min for 2-15 min at room temperature to obtain the foaming regulator; mix the foaming regulator with polyisocyanate at a weight ratio of 1:10-3:10, and stir at 500-2000 r / min for 0.5-5 min at room temperature to obtain the polyurethane system;

[0047] 4) Weigh out the nano-reinforcing particles according to the ratio and add them to the polyisocyanate. Stir at 500-2000 r / min for 2-10 min at room temperature to obtain a polyisocyanate mixture containing nano-reinforcing particles. Preheat the mixture at 40-60℃ for 5-20 min and apply it evenly to the surface of the surface wood chips using a high-pressure atomization method. Weigh out the polyurethane system according to the ratio and preheat it at 40-60℃ for 2-10 min. Apply it evenly to the surface of the core wood chips using a high-pressure atomization method. According to the preset board density, lay the surface fine material and core wood chips in sequence to form a board blank. Then put it into a hot press and hot press at 140-180℃ for 4-10 min at a pressure of 2-3 MPa to allow the polyisocyanate and polyurethane system to react fully. After cooling, remove and trim the edges to obtain a lightweight high-strength polyurethane particleboard.

[0048] Example 1

[0049] A lightweight, high-strength polyurethane particleboard comprises upper and lower surface layers and a core layer, with a weight ratio of upper surface layer:core layer:lower surface layer = 2:6:2. By weight, the surface layer consists of 93 parts poplar wood chips, 6 parts polymethylene polyphenyl isocyanate CW-20, and 0.06 parts silane-modified nano-silica. The core layer consists of 90 parts poplar wood chips and 10 parts a polyurethane system composed of polyisocyanate and a foaming regulator.

[0050] The preparation method of the above-mentioned lightweight high-strength polyurethane particleboard includes the following steps:

[0051] 1) Poplar branches and shavings are chipped and planed to prepare wood units. Surface fines and core shavings are separated. The particle size of the surface fines is 0.5-1mm, and the core shavings are 5-30mm long, 1-4mm wide, and 0.8-1.5mm thick. The moisture content of the surface fines is controlled at about 12%, and the moisture content of the core shavings is controlled at about 8%.

[0052] 2) Weigh nano-silica (S861577 type, average particle size 20nm) into a 95% ethanol solution at a weight ratio of 1.5:10. Sonicate at room temperature for 15min to homogeneously disperse the nano-silica. Adjust the pH of the solution to about 4. Then add 3-aminopropyltriethoxysilane (KH550) at a weight ratio of 1:10 to nano-silica. Stir at 80℃ for 2h to allow the nano-silica to react fully. Vacuum filter the mixture, collect the solid product and wash it repeatedly with deionized water. Vacuum dry at 60℃ to constant weight to obtain modified nano-reinforced particles.

[0053] 3) Take 100 parts by weight of the compounded polyol (polyether R8241: polyether MN500 = 4:6 weight ratio), 6 parts by weight of the crosslinking / chain extender (ethylene glycol: glycerol = 1:1 weight ratio), 2 parts by weight of amino silicone oil OFX-8803, 1.5 parts by weight of the compounded catalyst (dimethylcyclohexylamine: organic bismuth catalyst AC83 = 1:3 weight ratio), and 0.2 parts by weight of phosphoric acid. Stir the mixture with an electric stirrer at 1500 r / min for 5 min to obtain a foaming regulator. Mix the foaming regulator with polyisocyanate at a weight ratio of 2:10 and stir at 2000 r / min for 0.5 min at room temperature to obtain a polyurethane system. The polyether R8241 has a hydroxyl value of about 410 mg KOH / g, a functionality of 4.5, and an average molecular weight of about 600. The polyether MN500 has a hydroxyl value of about 340 mg KOH / g, a functionality of 3, and an average molecular weight of about 500.

[0054] 4) Add the modified nano-reinforcing particles obtained in step 2) to the polyisocyanate in proportion, stir at 1000 r / min for 5 min at room temperature, preheat the mixture at 50℃ for 10 min, and then apply it evenly to the surface fines in a mixer after high-pressure atomization; preheat the polyurethane system obtained in step 3) at 40℃ for 5 min, and then apply it evenly to the core layer shavings in a mixer after high-pressure atomization; according to the designed board density of 550 kg / m³. 3 Weigh out the surface fines and core shavings after applying the adhesive according to the proportion, lay them in sequence to form a board blank, and then put it into a hot press. Press it at 180℃ for 4 minutes with a pressure of 2.5MPa and control the board blank thickness to 18mm. After cooling, take it out and trim the edges to obtain a lightweight high-strength polyurethane particleboard.

[0055] Example 2

[0056] A lightweight, high-strength polyurethane particleboard, comprising upper and lower surface layers and a core layer, wherein the surface layer is oriented as follows: : Core layer : Lower surface layer

[0057] = 1.5:7:1.5 (weight ratio); by weight, the surface layer consists of 90 parts eucalyptus wood fines, 10 parts polymethylene polyphenyl isocyanate PM-200, and 0.08 parts silane-modified nano silica; the core layer consists of 90 parts eucalyptus wood shavings and 10 parts polyurethane system composed of polyisocyanate and foaming regulator.

[0058] The preparation method of the above-mentioned lightweight high-strength polyurethane particleboard includes the following steps:

[0059] 1) Eucalyptus branches are chipped and shaving to prepare wood units. Surface fines and core shavings are separated. The particle size of the surface fines is 0.2-1 mm, and the length of the core shavings is 10-35 mm, the width is 3-8 mm, and the thickness is 0.5-2 mm. The moisture content of the surface fines is controlled at about 14%, and the moisture content of the core shavings is controlled at about 10%.

[0060] 2) Weigh nano-silica (Brofos-SiO2-50, average particle size 50nm) at a weight ratio of 1.8:10 and add it to a 95% ethanol solution. Sonicate at room temperature for 20 minutes to homogenize it. Adjust the pH of the solution to about 4. Then add 3-methacryloyloxypropyltrimethoxysilane (KH570). The weight ratio of silane to nano-silica is 1:10. Stir at 70℃ for 2.5 hours to allow it to react fully. Vacuum filter the mixture, collect the solid product and wash it repeatedly with deionized water. Vacuum dry at 60℃ to constant weight to obtain modified nano-reinforced particles.

[0061] 3) Take 100 parts of a compounded polyol (polyether R8345: polyether MN500 = 3:7 weight ratio), 10 parts of a crosslinking / chain extender (ethylene glycol: glycerol = 1:1 weight ratio), 3 parts of amino silicone oil OFX-8803, 1.5 parts of a compounded catalyst (triethanolamine: organic bismuth catalyst = 1:5 weight ratio), and 0.3 parts of phosphoric acid. Mix them evenly at room temperature by stirring at 1000 r / min for 8 min to obtain a foaming regulator. Mix the above foaming regulator with polyisocyanate at a mass ratio of 3:10 and stir at room temperature by stirring at 1000 r / min for 2 min to obtain a polyurethane system. The polyether R8345 has a hydroxyl value of 450 mg KOH / g and a functionality of 4.5, and the polyether MN500 has a hydroxyl value of 350 mg KOH / g and a functionality of 3. The organic bismuth catalyst is BiCAT8118.

[0062] 4) Add the modified nano-reinforcing particles obtained in step 2) to the polyisocyanate in proportion, stir at 1000 r / min for 6 min at room temperature, preheat the mixture at 45℃ for 15 min, and then apply it evenly to the surface fines in a mixer after high-pressure atomization; preheat the polyurethane system obtained in step 3) at 50℃ for 6 min, and then apply it evenly to the core layer shavings in a mixer after high-pressure atomization; according to the designed board density of 550 kg / m³. 3 Weigh out the surface fines and core shavings after applying the adhesive, lay them in sequence to form a board blank, and then put it into a hot press. Press it at 170℃ for 6 minutes with a pressure of 3MPa and control the board blank thickness to 15mm. After cooling, take it out and trim the edges to obtain a lightweight high-strength polyurethane particleboard.

[0063] Example 3

[0064] A lightweight, high-strength polyurethane particleboard, comprising upper and lower surface layers and a core layer, wherein the surface layer is oriented as follows: : Core layer : Lower surface layer

[0065] = 2:6:2 (weight ratio); by weight, the surface layer consists of 90 parts of biomass fines, 10 parts of polymethylene polyphenyl isocyanate PM-200, and 0.03 parts of silane-modified nano-silica; the core layer consists of 95 parts of biomass shavings and 5 parts of a polyurethane system composed of polyisocyanate and foaming regulator.

[0066] The preparation method of the above-mentioned lightweight high-strength polyurethane particleboard includes the following steps:

[0067] 1) The waste building templates are chipped and crushed to separate the surface fine material and the core shavings. The surface fine material has a particle size of 0.5-1.5mm, and the core shavings have a length of 5-20mm, a width of 1.5-4mm, and a thickness of 0.3-1mm. The moisture content of the surface fine material is controlled at about 12%, and the moisture content of the core shavings is controlled at about 10%.

[0068] 2) Weigh nano-silica (S861577 type, average particle size 20nm) at a weight ratio of 1.8:10 and add it to a 95% ethanol solution. Disperse the solution ultrasonically at room temperature for 20 minutes and adjust the pH of the solution to about 4. Then add 3-methacryloyloxypropyltrimethoxysilane (KH570). The weight ratio of silane to nano-silica is 1:8. Transfer the solution to a three-necked flask and stir at 70°C for 2.5 hours to allow it to react fully. After cooling, vacuum filter the mixture, collect the solid product and wash it repeatedly with deionized water. Dry it under vacuum at 60°C to constant weight to obtain modified nano-reinforced particles.

[0069] 3) Take 100 parts of the compounded polyol (polyether R8240: polyether MN500 = 3:7 weight ratio), 10 parts of the crosslinking agent glycerol, 3 parts of dimethyl silicone oil, 1.5 parts of the compounded catalyst (triethanolamine: dibutyltin dilauric acid = 1:2 weight ratio) and 0.3 parts of oxalic acid, and stir at 800 r / min for 10 min to obtain a foaming regulator; mix the above foaming regulator with polyisocyanate at a mass ratio of 2:10, and stir at 1500 r / min for 1 min at room temperature to obtain a polyurethane system; the hydroxyl value of polyether R8240 is 400 mg KOH / g and the functionality is 5, and the hydroxyl value of polyether MN500 is 350 mg KOH / g and the functionality is 3;

[0070] 4) Add the modified nano-reinforcing particles obtained in step 2) to the polyisocyanate in proportion, stir at 1200 r / min for 5 min at room temperature, preheat the mixture at 50℃ for 10 min, and then apply it evenly to the surface fines in a mixer after high-pressure atomization; preheat the polyurethane system obtained in step 3) at 55℃ for 4 min, and then apply it evenly to the core layer shavings in a mixer after high-pressure atomization; according to the designed board density of 520 kg / m³. 3 Weigh out the surface fines and core shavings after applying the adhesive, lay them in sequence to form a board blank, and then put it into a hot press. Press it at 170℃ for 6 minutes with a pressure of 3MPa and control the board blank thickness to 18mm. After cooling, take it out and trim the edges to obtain a lightweight high-strength polyurethane particleboard.

[0071] Example 4

[0072] A lightweight, high-strength polyurethane particleboard comprises upper and lower surface layers and a core layer, with a weight ratio of upper surface layer:core layer:lower surface layer = 2:6:2. By weight, the surface layer consists of 94 parts biomass fines, 6 parts polymethylene polyphenyl isocyanate CW-20, and 0.06 parts silane-modified sodium silicate. The core layer consists of 90 parts biomass particleboard and 10 parts a polyurethane system composed of polyisocyanate and a foaming regulator.

[0073] The preparation method of the above-mentioned lightweight high-strength polyurethane particleboard includes the following steps:

[0074] 1) The remaining bamboo processing material is shaved and planed to separate the surface fines and core shavings. The surface fines have a particle size of 1-1.6 mm, and the core shavings have a length of 25-30 mm, a width of 2-5 mm, and a thickness of 0.4-0.6 mm. The moisture content of the surface fines is controlled at about 14%, and the moisture content of the core shavings is controlled at about 10%.

[0075] 2) Weigh nano-silica (Brofos-SiO2-50, average particle size 50nm) into anhydrous ethanol at a weight ratio of 2:10, and sonicate for 20 minutes to disperse it evenly; mix 3-methacryloyloxypropyltrimethoxysilane (KH550) with water at a weight ratio of 1:2, and stir to fully hydrolyze the silane; add the silane aqueous solution to the silica-ethanol mixture at a volume ratio of 1:6, with the weight ratio of silane to nano-silica being 1:10, adjust the pH of the solution to 4, and magnetically stir at 70℃ for 2.5h. Vacuum filter the reaction solution, wash repeatedly, and vacuum dry at 70℃ to constant weight to obtain modified nano-reinforced particles;

[0076] 3) Take 100 parts of the compounded polyol (polyether R8243: polyether MN500 = 3:7 weight ratio), 8 parts of the crosslinking / chain extender (ethylene glycol: glycerol = 2:3 weight ratio), 3 parts of dimethyl silicone oil, 1.5 parts of the compounded catalyst (triethanolamine: dibutyltin dilauric acid = 1:2 weight ratio), and 0.3 parts of tartaric acid, and mix them evenly at room temperature with electric stirring at 1000 r / min for 8 min to obtain a foaming regulator; mix the above foaming regulator with polyisocyanate at a mass ratio of 2:10, and stir at room temperature with stirring at 1000 r / min for 2 min to obtain a polyurethane system; the hydroxyl value of polyether R8243 is 400 mg KOH / g and the functionality is 5, and the hydroxyl value of polyether MN500 is 350 mg KOH / g and the functionality is 3;

[0077] 4) Weigh the modified nano-reinforcing particles obtained in step 2) according to the proportion and add them to the polyisocyanate. Stir at 1000 r / min for 10 min at room temperature to disperse evenly. Preheat the mixture at 50℃ for 10 min, and after high-pressure atomization, apply it evenly to the surface fine material in a mixer. Preheat the polyurethane system obtained in step 3) at 50℃ for 5 min, and after high-pressure atomization, apply it evenly to the core layer shavings surface in a mixer. The board density should be 450 kg / m³ as designed. 3 Weigh out the surface fines and core shavings after applying the adhesive, lay them in sequence to form a board blank, and then put it into a hot press. Press it at 180℃ for 4 minutes with a pressure of 2.5MPa and control the board blank thickness to 18mm. After cooling, take it out and trim the edges to obtain a lightweight high-strength polyurethane particleboard.

[0078] Example 5

[0079] A lightweight, high-strength polyurethane particleboard comprises upper and lower surface layers and a core layer, with a weight ratio of upper surface layer:core layer:lower surface layer = 2:6:2. The surface layer consists of 90 parts poplar wood chips, 10 parts polymethylene polyphenyl isocyanate CW-20, and 0.1 parts modified nano-silica particles. The core layer consists of 92 parts poplar wood chips and 8 parts a polyurethane system composed of polyisocyanate and a foaming regulator.

[0080] The preparation method of the above-mentioned lightweight high-strength polyurethane particleboard includes the following steps:

[0081] 1) The poplar branches and shavings are chipped and planed to separate the fine surface material and the coarse core shavings. The fine surface material has a particle size of 0.5-1.2 mm, and the core shavings have a length of 8-40 mm, a width of 2-4 mm, and a thickness of 0.8-1.5 mm. The moisture content of the fine surface material is controlled at about 14%, and the moisture content of the core shavings is controlled at about 10%.

[0082] 2) Weigh nano-silica (S861577 type, average particle size 20nm) at a weight ratio of 1:10 and add it to a 75% ethanol solution. Disperse it ultrasonically at room temperature for 10 min, adjust the pH of the solution to about 4.5, and then add γ-mercaptopropyltrimethoxysilane (KH590). The weight ratio of silane to nano-silica is 1:5. Transfer it to a three-necked flask and stir the reaction at 70℃ for 2.5 h. After cooling, filter under vacuum, wash the solid product repeatedly, and dry it under vacuum at 80℃ to constant weight to obtain modified nano-reinforced particles.

[0083] 3) Take 100 parts of polymeric polyol (polyester PS400A: polyether CP450 = 3:7 weight ratio), 8 parts of chain extender glycerol, 2 parts of silicone oil B8433, 1.8 parts of compound catalyst (triethylenediamine: dibutyltin dilaurate = 1:3 weight ratio), and 0.3 parts of oxalic acid, and stir at 1000 r / min for 5 min at room temperature to obtain a foaming regulator; mix the above foaming regulator with polyisocyanate at a mass ratio of 3:10, and stir at 1000 r / min for 1 min at room temperature to obtain a polyurethane system; the hydroxyl value of polyester PS400A is about 400 mg KOH / g and the functionality is 4.5, and the hydroxyl value of polyether CP450 is 370-390 mg KOH / g and the functionality is 3;

[0084] 4) Weigh the modified nano-reinforcing particles obtained in step 2) according to the proportion and add them to the polyisocyanate. Stir at 1000 r / min for 10 min at room temperature to disperse evenly. Preheat the mixture at 50℃ for 10 min, and then apply it evenly to the surface of the surface fine material after high-pressure atomization. Preheat the polyurethane system obtained in step 3) at 40℃ for 6 min, and then apply it evenly to the surface of the core layer shavings after high-pressure atomization. The board density should be 450 kg / m³ as designed. 3 Weigh out the surface fines and core shavings after applying the adhesive, lay them in sequence to form a board blank, and then put it into a hot press. Press it at 180℃ for 4 minutes with a pressure of 2.5MPa and control the board blank thickness to 18mm. After cooling, take it out and trim the edges to obtain a lightweight high-strength polyurethane particleboard.

[0085] Comparative Example 1

[0086] A particleboard comprises upper and lower surface layers and a core layer, with a weight ratio of upper surface layer:core layer:lower surface layer = 2:6:2. By weight, the surface layer consists of 94 parts poplar wood chips and 6 parts polymethylene polyphenyl isocyanate CW-20, and the core layer consists of 90 parts poplar wood shavings and 10 parts polymethylene polyphenyl isocyanate CW-20. The surface layer wood chips have a particle size of 0.5–1 mm, and the core layer shavings have a length of 4–25 mm, a width of 1–4 mm, and a thickness of 0.2–1.2 mm.

[0087] Prepare according to the following steps:

[0088] 1) Slice and shave the poplar and eucalyptus branches, sieve out the surface fines and core shavings, and dry the shavings to a moisture content of about 3%.

[0089] 2) Weigh out the polymethylene polyphenyl isocyanate according to the proportion and spray it onto the surface of the surface wood shavings and the core wood shavings respectively;

[0090] 3) The designed board density is 550 kg / m³. 3 Weigh out the surface and core layer shavings after applying adhesive, lay them in sequence to form a board blank, and then put it into a hot press. Press it at 190℃ for 4 minutes with a pressure of 2.5MPa and control the board blank thickness to 18mm. After cooling, take it out to obtain particleboard.

[0091] Comparative Example 2

[0092] A particleboard comprises upper and lower surface layers and a core layer, with a top surface layer:core layer:bottom surface layer ratio of 1.5:7:1.5 (by weight). The surface layer consists of 94 parts poplar fine shavings and 6 parts polymethylene polyphenyl isocyanate PM-200 by weight, while the core layer consists of 90 parts poplar coarse shavings, 9 parts polymethylene polyphenyl isocyanate PM-200, 1 part compounded polymerized polyol, and 0.06 parts amino silicone oil.

[0093] The fine and coarse poplar shavings are the same as in Example 1.

[0094] Prepare according to the following steps:

[0095] 1) Slice and shave the poplar and eucalyptus branches, sieve out the surface fines and core shavings, and dry the shavings to a moisture content of about 6%.

[0096] 2) Weigh out the polymethylene polyphenyl isocyanate according to the proportion and spray it onto the surface of the wood shavings;

[0097] 3) Weigh out the compounded polyol (R8345:MN500 = 3:7) and amino silicone oil according to the ratio, stir at high speed of 1000 r / min for 3 min at room temperature, and apply the mixture to the core layer shavings after atomization; then weigh out the polymethylene polyphenyl isocyanate according to the ratio, and apply it to the core layer shavings after atomization.

[0098] 4) The designed board density is 450 kg / m³. 3 Weigh out the surface fines and core shavings after applying the adhesive, lay them in sequence to form a board blank, and then put it into a hot press. Press it at 190℃ for 4 minutes with a pressure of 2.5MPa and control the board blank thickness to 18mm. After cooling, take it out to obtain particleboard.

[0099] like Figure 1 As shown, this is a scanning electron microscope image of the modified nano-reinforced particles used in Example 1. It can be seen that there is no obvious aggregation and the dispersion is relatively uniform.

[0100] like Figure 2 The image shown is a super-depth-of-field three-dimensional microscope image of the core layer of the particleboard prepared in Comparative Example 1. It can be seen that there are some obvious gaps between the particleboard particles in the core layer.

[0101] like Figure 3 As shown, this is a super-depth-of-field three-dimensional microscope image of the core layer of the particleboard prepared in Comparative Example 2. It can be seen that there are a small number of pore structures, but there are still some gaps between the core layer shavings, and no continuous phase structure has been formed.

[0102] like Figure 4 As shown, this is a super depth-of-field three-dimensional microscope image of the core layer of the lightweight high-strength particleboard prepared in Example 1. It can be seen that there is a continuous cell structure around the wood chips, and the gaps between the wood chips are basically filled or covered by the cells.

[0103] like Figure 5 As shown, this is a super depth-of-field three-dimensional microscope image of the core layer of the lightweight high-strength particleboard prepared in Example 2. It can be seen that there is a continuous pore structure around the shavings, and the gaps between the shavings are basically filled or covered by the pores.

[0104] The particleboard prepared in the above embodiments and comparative examples was subjected to performance testing. The performance testing methods are as follows:

[0105] 1. Internal bond strength: Test method 4.11 for internal bond strength determination as specified in GB / T 17657—2013 "Test Methods for Physical and Chemical Properties of Wood-based Panels and Decorative Wood-based Panels";

[0106] 2. Static bending strength and modulus of elasticity: Test method - 4.7 Determination of static bending strength and modulus of elasticity (three-point bending) as specified in GB / T 17657—2013 "Test Methods for Physical and Chemical Properties of Wood-based Panels and Decorative Wood-based Panels".

[0107] 3.24h water absorption thickness swelling rate: Test method specified in GB / T 17657—2013 "Test Methods for Physical and Chemical Properties of Wood-based Panels and Decorative Wood-based Panels" - 4.4 Determination of water absorption thickness swelling rate - Method 1.

[0108] 4. Strength-to-weight ratio: The ratio of static bending strength to density.

[0109] Please refer to Table 1 for the test results.

[0110] Table 1. Performance of the Examples and Comparative Examples

[0111]

[0112] As shown in Table 1, the lightweight high-strength particleboard of Examples 1-5 exhibits significantly improved internal bonding strength compared to the particleboard of Comparative Examples 1 and 2, exceeding twice that of the comparative examples; Examples 1 and 2, compared to particleboard of the same density (550 kg / m³), show significantly improved internal bonding strength. 3 Compared with Comparative Example 1, the static bending strength increased by more than 40%, the elastic modulus increased by more than 30%, and the strength-to-weight ratio increased to 2.5×10⁻⁶. 3 Above, the 24-hour water absorption thickness swelling rate decreased to below 8%; Examples 4 and 5 were compared with the same density (450 kg / m³). 3 Compared to Comparative Example 2, all performance aspects have been significantly improved.

[0113] The lightweight, high-strength polyurethane particleboard of this invention, through microstructure regulation and optimized design, leverages the synergistic effect of surface-modified nanoparticle reinforcement and core-layer polyurethane system foaming. A nanoparticle-reinforced structure is formed on the stressed surface layer, and a uniform and stable micro-foamed structure is constructed in the core layer. This allows the particleboard to achieve both lightweight properties and high strength-to-weight ratio, good internal bonding strength, mechanical strength, and water resistance, thus realizing lightweight and high-strength particleboard.

[0114] The lightweight, high-strength polyurethane particleboard prepared by this invention has low density and high strength-to-weight ratio, significantly improved internal bonding strength, and good mechanical properties and water resistance. The method is simple and easy to implement, suitable for industrial production of particleboard, and conducive to expanding the application range of particleboard.

[0115] The above description is merely a preferred embodiment of the present invention and does not limit the patent scope of the present invention. Any equivalent structural transformations made using the content of the present invention specification, or direct or indirect applications in the technical fields of other related products, are similarly included within the patent protection scope of the present invention.

Claims

1. A lightweight, high-strength polyurethane particleboard, characterized in that: It consists of an upper surface layer, a core layer, and a lower surface layer. The surface layer includes an upper surface layer and a lower surface layer, with a weight ratio of surface layer to core layer of 2:8 to 5:

5. By weight, the surface layer contains 80 to 97 parts of biomass fines with a particle size of 0.2 to 1.5 mm, 3 to 20 parts of polyisocyanate, and 0.03 to 1 part of modified nano-reinforcing particles. The core layer contains 70 to 95 parts of biomass shavings with a length of 4 to 60 mm, a width of 0.5 to 10 mm, and a thickness of 0.2 to 2 mm, 3 to 20 parts of polyisocyanate, and 0.3 to 6 parts of foaming regulator. The method for preparing the lightweight, high-strength polyurethane particleboard includes the following steps: (1) Biomass unit preparation: The surface fines and core shavings are separated by mechanical means of chipping, shaving, crushing and / or grinding, and the moisture content is controlled to be 6-15% by drying or humidification. (2) Modification of nano-reinforcing particles: Add nano-silica to an ethanol solution, sonicate it at room temperature to disperse it homogeneously, add silane in proportion, adjust the pH value of the solution, heat and stir to fully react, separate the solid and liquid mixture, wash and dry the solid product to obtain modified nano-reinforcing particles. (3) Preparation of polyurethane system: Weigh out the compounded polymer polyol, chain extender / crosslinker, surfactant, compounded catalyst and delay agent according to the proportion, and stir at high speed at room temperature to obtain foaming regulator; mix the foaming regulator with polyisocyanate according to the proportion, and stir at high speed to obtain polyurethane system. (4) Polyurethane particleboard molding: Weigh the modified nano-reinforcing particles according to the proportion and add them to the polyisocyanate. Stir and mix evenly at room temperature and high speed. Preheat the mixture and apply it evenly to the surface of the surface fine material using a high-pressure atomization method. Preheat the polyurethane system and apply it evenly to the core layer particleboard using a high-pressure atomization method. Weigh the surface fine material and core layer particleboard after gluing according to the preset board density. After laying, hot pressing and cooling, lightweight and high-strength polyurethane particleboard is obtained.

2. The lightweight, high-strength polyurethane particleboard according to claim 1, characterized in that: The biomass fines and shavings are prepared from fast-growing plantation timber, bamboo, sand willow, straw, rice straw, reeds and / or waste recycled wood materials; the polyisocyanate is one of toluene diisocyanate, diphenylmethane diisocyanate and polymethylene polyphenyl isocyanate, and the isocyanate content in the polyisocyanate is 30-35%; the modified nano-reinforcing particles are silane-modified nano-sized silica with a particle size of 10-100 nm.

3. The lightweight, high-strength polyurethane particleboard according to claim 2, characterized in that: The silane is one of 3-aminopropyltriethoxysilane, γ-glycidoxypropyltrimethoxysilane, 3-methacryloyloxypropyltrimethoxysilane, γ-mercaptopropyltrimethoxysilane, and N-β-(aminoethyl)-γ-aminopropyltrimethoxysilane.

4. The lightweight, high-strength polyurethane particleboard according to claim 1, characterized in that: The foaming regulator comprises, by weight, 80-100 parts of a compounded polymeric polyol, 5-10 parts of a chain extender or crosslinking agent, 1-5 parts of a surfactant, 1.5-2 parts of a compounded catalyst, and 0.1-0.5 parts of a retarder; the compounded polymeric polyol is composed of a high hydroxyl value and high functionality polyether / polyester polyol and a low hydroxyl value and low functionality polyether / polyester polyol, with an average hydroxyl value of 350-450 mgKOH / g and an average functionality of 3-5; the compounded catalyst is composed of an amine catalyst and an organometallic catalyst.

5. The lightweight, high-strength polyurethane particleboard according to claim 4, characterized in that: The chain extender or crosslinker is one or more of diols, triols, diamines, and ethanolamines; the surfactant is amino silicone oil or polyether-modified organosilicon; in the compound catalyst, the weight ratio of amine catalyst to organometallic catalyst is 1:1 to 1:6, the amine catalyst is one of dimethylcyclohexylamine, triethanolamine, and triethylenediamine, and the organometallic catalyst is one of bismuth carboxylate, stannous octoate, and dibutyltin dilaurate; the retarder is one of oxalic acid, phosphoric acid, tartaric acid, and citric acid.

6. A method for preparing lightweight high-strength polyurethane particleboard according to any one of claims 1-5, comprising the following steps: (1) Biomass unit preparation: The surface fines and core shavings are separated by mechanical means of chipping, shaving, crushing and / or grinding, and the moisture content is controlled to be 6-15% by drying or humidification. (2) Modification of nano-reinforcing particles: Add nano-silica to an ethanol solution, sonicate it at room temperature to disperse it homogeneously, add silane in proportion, adjust the pH value of the solution, heat and stir to fully react, separate the solid and liquid mixture, wash and dry the solid product to obtain modified nano-reinforcing particles. (3) Preparation of polyurethane system: Weigh out the compounded polymer polyol, chain extender / crosslinker, surfactant, compounded catalyst and delay agent according to the proportion, and stir at high speed at room temperature to obtain foaming regulator; mix the foaming regulator with polyisocyanate according to the proportion, and stir at high speed to obtain polyurethane system. (4) Polyurethane particleboard molding: Weigh the modified nano-reinforcing particles according to the proportion and add them to the polyisocyanate. Stir and mix evenly at room temperature and high speed. Preheat the mixture and apply it evenly to the surface of the surface fine material using a high-pressure atomization method. Preheat the polyurethane system and apply it evenly to the core layer particleboard using a high-pressure atomization method. Weigh the surface fine material and core layer particleboard after gluing according to the preset board density. After laying, hot pressing and cooling, lightweight and high-strength polyurethane particleboard is obtained.

7. The method for preparing lightweight high-strength polyurethane particleboard according to claim 6, characterized in that: In the modification treatment of nano-reinforcing particles, the weight ratio of silane to nano-silica is 1:10 to 2.5:

10.

8. The method for preparing lightweight high-strength polyurethane particleboard according to claim 6, characterized in that: The weight ratio of the foaming regulator to the polyisocyanate is 1:10 to 3:

10.

9. The method for preparing lightweight high-strength polyurethane particleboard according to claim 6, characterized in that: The modified nano-reinforcing particles are dispersed in polyisocyanate, the mixture is preheated at 40-60℃ for 5-20 min, and applied by high-pressure atomization to make the modified nano-reinforcing particles evenly distributed on the surface fine material. Preheat the polyurethane system at 40–60°C for 2–10 minutes and apply it evenly to the core layer of wood shavings.

10. The method for preparing lightweight high-strength polyurethane particleboard according to claim 6, characterized in that: According to the preset board density, the surface fine material and core wood chips after gluing are laid in sequence to form a board blank, and then placed in a hot press. The board is hot-pressed at 140-180℃ for 4-10 minutes at a pressure of 2-3MPa. During the hot pressing process, the isocyanate groups react fully. After cooling, the board is taken out to obtain a lightweight high-strength polyurethane particleboard.

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