Preparation process of fiber-reinforced fireproof flame-retardant plate and plate

Abstract

The invention discloses a preparation process of a fiber-reinforced fireproof flame-retardant plate and the plate, and belongs to the technical field of building materials. The process comprises the following steps: performing three-stage gradient pressure impregnation on a wood base material to form a gradient flame-retardant impregnation layer; the preparation method comprises the following steps: carrying out surface activation on basalt fibers, carrying out in-situ hydrothermal growth of magnesium-aluminum composite nanosheets, and coating with a flame-retardant microlayer to prepare fiber gridding cloth with a grafted nanosheet structure; performing presoaking and hot-pressing compounding to form a fiber reinforced prefabricated layer; and finally compounding the surface compact flame-retardant film. The obtained board has a multi-layer gradient flame-retardant structure from inside to outside, the flame-retardant performance reaches B1-A level, the bending strength is improved by 20% or above, and the board has excellent smoke suppression performance and weather resistance. The process is coherent, efficient, firm in interface bonding and suitable for the fields of building interior decoration, furniture manufacturing and the like.

Description

Technical Field

[0001] This invention belongs to the field of building materials technology, specifically relating to a preparation process and a fiber-reinforced fire-retardant board. Background Technology

[0002] Wood and wood-based panels are commonly used base materials in the construction and furniture industries due to their natural environmental friendliness, excellent processing performance, and high cost-effectiveness. However, the flammable nature of wood poses a serious fire hazard during use, limiting its application in scenarios with high flame retardancy requirements. To improve the flame retardancy of wood-based panels, existing technologies mostly employ wet coating of flame-retardant slurry to treat the wood surface. For example, some patents use a double-layer slurry coating process, which can improve flame retardancy to some extent, but still has many technical shortcomings.

[0003] First, the wet coating process is cumbersome, requiring multiple coatings and drying steps. The drying process is energy-intensive and time-consuming, resulting in low production efficiency. Furthermore, product quality is greatly affected by the uniformity of coating and the degree of drying, leading to poor batch stability. Second, the flame-retardant layer formed by the coating is only physically attached to the wood substrate, resulting in poor interfacial compatibility. Under actual usage environments such as wet-dry cycles and thermal shocks, interfacial stress is easily generated, causing the coating to crack and peel off, thus losing its flame-retardant protective effect. Third, traditional flame-retardant layers are mostly concentrated on the surface of the wood, with a single flame-retardant function. Once the surface coating is damaged due to bumps, wear, or other reasons, the wood inside will be quickly exposed to the fire source, resulting in insufficient flame-retardant durability and reliability.

[0004] Meanwhile, existing flame retardant treatment technologies often come at the cost of sacrificing the mechanical properties of wood-based panels. To compensate for the loss of mechanical properties, some technologies add fibers to the flame retardant slurry. However, the uniformity of dispersion of short-cut fibers in the slurry is difficult to control, and the interfacial bonding strength with the resin matrix is ​​low, resulting in limited reinforcement and failing to achieve a synergistic improvement in flame retardant performance and mechanical properties.

[0005] In addition, the smoke suppression and weather resistance properties of traditional wood-based fire-retardant boards have not received sufficient attention. They are prone to producing large amounts of toxic smoke when a fire occurs, which endangers people's escape and fire rescue. Furthermore, when used outdoors or in humid environments, their flame retardancy and mechanical properties deteriorate rapidly, resulting in a short service life.

[0006] Therefore, developing a wood-based fire-retardant composite board with strong interfacial bonding, good flame retardancy and durability, synergistic improvement in flame retardancy and mechanical properties, simplified process, high batch stability, and excellent smoke suppression and weather resistance has become an urgent technical problem to be solved in the current building materials field. Summary of the Invention

[0007] The purpose of this invention is to overcome the shortcomings of existing flame-retardant treatments for wood-based panels, such as cumbersome processes, poor interfacial bonding, insufficient flame-retardant durability, and difficulty in synergistically improving mechanical and flame-retardant properties. This invention provides a preparation process and a finished fiber-reinforced fire-retardant panel. This process combines gradient flame-retardant impregnation with fiber-reinforced composite materials to achieve synergistic flame retardancy both inside and on the surface of the wood substrate. Simultaneously, it utilizes a fiber network with surface-grafted nanosheet structures to enhance interfacial bonding and mechanical properties, ultimately obtaining a composite panel with excellent flame-retardant properties, mechanical strength, smoke suppression, and weather resistance, meeting the demand for high-flame-retardant wood materials in the construction and furniture industries.

[0008] To achieve the above-mentioned technical objectives, the technical solution adopted by the present invention is as follows: A fiber-reinforced fireproof and flame-retardant board comprises, from the inside out: a wood substrate layer, a gradient flame-retardant impregnation layer, a fiber-reinforced precast layer, and a dense flame-retardant film layer on the surface.

[0009] A process for preparing a fiber-reinforced fire-retardant board includes the following steps: (1) Dry the wood substrate to a moisture content of 8-12% and sand its surface; (2) Gradient flame retardant impregnation: The pretreated wood substrate is immersed in the nano flame retardant impregnation liquid and subjected to three levels of gradient pressure impregnation: the first level is low pressure stage: pressure 0.3~0.5MPa, pressure holding for 40~60 minutes; the second level is medium pressure stage: pressure 0.8~1.0MPa, pressure holding for 30~45 minutes; the third level is high pressure stage: pressure 1.2~1.5MPa, pressure holding for 20~30 minutes; after removal, it is left to air dry at room temperature for 1~4 hours, and then cured and dried at 60~80℃ for 2~6 hours to form a gradient flame retardant impregnation layer; (3) Preparation of flame-retardant reinforced fiber web with surface-grafted nanosheet structure: A. Fiber surface activation: Immerse basalt fibers in a 5-10% silane coupling agent solution, stir in a water bath at 60-80℃ for 1-2 hours, and then remove and dry. B. In-situ growth of nanosheets: Activated fibers are placed in a high-pressure reactor, and a precursor aqueous solution containing magnesium nitrate, aluminum nitrate, and urea is added. The reaction is carried out at 100-120℃ for 6-12 hours, allowing nanosheets to grow in-situ on the fiber surface via hydrothermal growth. After natural cooling, the fibers are removed and dried to obtain fibers grafted with nanosheets. The in-situ grown nanosheets not only significantly increase the specific surface area and surface roughness of the fibers, enhancing the mechanical interlocking and interfacial bonding with the resin, but also, as an inorganic nanosheet layer, effectively delay the diffusion of thermal decomposition gases and oxygen when heated. Furthermore, they exhibit catalytic synergy with flame-retardant components such as polyphosphate esters, promoting the formation of a denser and stronger carbon layer. C. Flame-retardant micro-layer coating: The grafted nanosheet fibers are immersed in a phosphorus-containing flame-retardant emulsion for 5-10 minutes, then removed, the adhesive is controlled, and dried at 80-100℃ to form a mesh fabric. (4) Prefabrication and composite of fiber reinforcement layer: The mesh fabric prepared in step (3) is immersed in flame retardant resin and taken out after full impregnation to obtain prepreg; the prepreg is covered on the surface of the gradient flame retardant impregnation layer of the board obtained in step (2), and hot-pressed at 120~150℃ and 0.8~1.2MPa pressure for 10~30 minutes to form fiber reinforcement prefabrication layer; (5) Surface flame retardant film composite: Cover the surface of the fiber-reinforced prefabricated layer of the board obtained in step (4) with a dense flame retardant film, and hot press it at 140~160℃ and 1.0~1.5MPa for 15~25 minutes to make the flame retardant film tightly composite with the lower layer and completely cured, thus obtaining the composite board.

[0010] Furthermore, the nano flame retardant impregnation liquid in step (2) is composed of the following components by mass: 30-50 parts of waterborne polyurethane resin, 10-20 parts of nano aluminum hydroxide, 5-15 parts of nano silica, 0.5-2 parts of silane coupling agent KH-550, and 30-50 parts of water. Each component is mixed evenly by high-speed stirring before use.

[0011] Furthermore, the silane coupling agent in step (3) is KH-560 or KH-550, and the solvent is ethanol with a mass concentration of 50%.

[0012] Furthermore, the precursor aqueous solution mentioned in step (3) is a mixed aqueous solution of magnesium nitrate, aluminum nitrate and urea, with a mass ratio of magnesium nitrate, aluminum nitrate and urea of ​​2~4:1:1 and an aqueous solution concentration of 0.5~1mol / L; the composition of the phosphorus-containing flame retardant emulsion is: 30~40 parts of polyphosphate ester, 20~30 parts of ethylene-vinyl acetate copolymer emulsion, 5~10 parts of nano zinc oxide, 2~5 parts of aqueous dispersant, and deionized water to make up to 100 parts, and a stable emulsion system is obtained after ultrasonic dispersion and homogenization emulsification.

[0013] Furthermore, the aqueous dispersant is sodium polyacrylate or lignin sulfonate, the addition of which effectively improves the dispersion stability and interfacial compatibility of nanoparticles in the emulsion.

[0014] Furthermore, the flame-retardant resin in step (4) is a phosphorus-containing epoxy resin or a nitrogen-containing phenolic resin, with a solid content of 60%~80% and a viscosity of 2000~5000 mPa·s.

[0015] Furthermore, the surface-dense flame-retardant film described in step (5) is made from the following raw materials by weight: 100 parts epoxy resin, 20-40 parts coated ammonium polyphosphate, 5-15 parts zinc borate, 10-20 parts silica sol, and 5-10 parts curing agent dicyandiamide, which are mixed, cast, and semi-cured to form the film material.

[0016] Furthermore, the solid content of the silica sol is 20-30%.

[0017] Furthermore, the preparation method of the coated ammonium polyphosphate is as follows: ammonium polyphosphate particles are added to a high-speed mixer, heated to 80°C, and 8% by mass of a melamine-formaldehyde resin prepolymer solution is sprayed in, and the mixture is stirred continuously for 15 minutes; then, hot air at 60°C is passed through and dried for 30 minutes to obtain the product; the melamine-formaldehyde resin prepolymer solution is prepared by heating melamine and formaldehyde at a molar ratio of 1:2~3 under alkaline conditions of pH 9-10 at 70-80°C for 1 hour.

[0018] Beneficial effects: This invention endows the board with excellent comprehensive performance through multi-dimensional collaborative design. First, the gradient flame-retardant impregnation layer achieves gradient flame-retardant protection of the wood substrate from the inside out. Through three-level pressure impregnation, the nano flame-retardant components are deeply penetrated and evenly distributed. Waterborne polyurethane resin acts as a binder to anchor flame-retardant particles such as nano aluminum hydroxide and nano silica into the wood structure. It not only plays a flame-retardant role in the early stage of combustion by endothermic decomposition and oxygen dilution, but also forms a preliminary char layer inside the substrate, delaying the inward spread of the flame.

[0019] Secondly, the basalt fiber network with surface-grafted nanosheets constructs a highly efficient synergistic system of mechanical reinforcement and flame retardancy: the nanosheets grown in situ on the fiber surface significantly enhance the interfacial bonding force with the flame retardant resin, and fully transfer the high strength and high modulus characteristics of the fiber to the composite system through the mechanical interlocking effect, effectively improving the problem of declining mechanical properties of traditional flame retardant boards; at the same time, the nanosheet layer and the polyphosphate flame retardant microlayer work together to form a dense and tough composite carbon layer when heated, which hinders the transfer of heat and oxygen and inhibits the release of flammable gases, greatly improving the flame retardancy rating and smoke suppression performance of the board. Furthermore, the dense flame-retardant film on the surface serves as the outermost barrier. The epoxy resin matrix contains coated ammonium polyphosphate, zinc borate, and silica sol, which form a multiple flame-retardant mechanism. The coated ammonium polyphosphate releases acidic substances such as phosphoric acid at high temperatures to catalyze carbonization, zinc borate promotes the formation of a glassy flame-retardant coating, and silica sol enhances the structural stability of the carbon layer. The three work together to give the board excellent surface fire resistance and weather resistance, effectively resisting direct external flame attack and environmental factors from corroding the internal structure.

[0020] Furthermore, the entire preparation process organically combines gradient impregnation, fiber reinforcement, and film layer composite, resulting in a streamlined and efficient process that avoids the multiple processing steps required by traditional wet coating methods. Precise control of process parameters at each stage ensures batch-to-batch stability of product quality. Compared to existing technologies, the composite panels prepared by this invention not only possess excellent flame-retardant properties (reaching B1 or even A grade in the GB8624-2012 standard), but also exhibit over 20% improvement in mechanical properties such as flexural strength and modulus of elasticity compared to untreated wood panels. Simultaneously, they possess low smoke toxicity release characteristics and good water resistance and aging resistance, making them widely applicable in fields with high requirements for fire safety and structural performance, such as interior building decoration, furniture manufacturing, and public space partitions, resulting in significant economic and social benefits. Attached Figure Description

[0021] Figure 1 This is an electron microscope image of the fiber in situ grown nanosheets on the fiber surface obtained in step (3)B of Example 1 of the present invention; Figure 2 for Figure 1 A magnified electron microscope image of a localized area on the fiber surface. Detailed Implementation

[0022] The technical solution of the present invention will be further described below with reference to specific embodiments, but it is not limited thereto.

[0023] Example 1 A fiber-reinforced fireproof and flame-retardant board comprises, from the inside out: a wood substrate layer, a gradient flame-retardant impregnation layer, a fiber-reinforced precast layer, and a dense flame-retardant film layer on the surface.

[0024] A process for preparing a fiber-reinforced fire-retardant board includes the following steps: (1) Dry the wood substrate to a moisture content of 8-12% and sand its surface; (2) Gradient flame retardant impregnation: The pretreated wood substrate is immersed in nano flame retardant impregnation liquid and subjected to three levels of gradient pressure impregnation: the first level low pressure stage: pressure 0.3MPa, pressure held for 60 minutes; the second level medium pressure stage: pressure 0.8MPa, pressure held for 45 minutes; the third level high pressure stage: pressure 1.2MPa, pressure held for 30 minutes; after removal, it is left to air dry at room temperature for 1 hour, and then cured and dried at 60~80℃ for 2 hours to form a gradient flame retardant impregnation layer; (3) Preparation of flame-retardant reinforced fiber web with surface-grafted nanosheet structure: A. Fiber surface activation: Immerse basalt fibers in a 5% (w / w) silane coupling agent solution, stir in a water bath at 60-80°C for 1 hour, then remove and dry; B. In-situ growth of nanosheets: Activated fibers are placed in a high-pressure reactor, and a precursor aqueous solution containing magnesium nitrate, aluminum nitrate, and urea is added. The reaction is carried out at 100-120℃ for 6 hours, allowing nanosheets to grow in-situ hydrothermally on the fiber surface. After natural cooling, the fibers are removed and dried to obtain fibers grafted with nanosheets. The in-situ grown nanosheets not only significantly increase the specific surface area and surface roughness of the fibers, enhancing the mechanical interlocking and interfacial bonding with the resin, but also, as an inorganic nanosheet layer, effectively delay the diffusion of thermal decomposition gases and oxygen when heated. Furthermore, they exhibit catalytic synergy with flame-retardant components such as polyphosphate esters, promoting the formation of a denser and stronger carbon layer. A small amount of this fiber was observed using a scanning electron microscope, and the results are as follows: Figure 1 , Figure 2 As shown, magnesium-aluminum composite nanosheets grow uniformly and densely on the surface of basalt fibers, with uniform layer thickness and complete morphology, significantly improving the specific surface area and interfacial bonding potential of the fibers.

[0025] C. Flame-retardant micro-coating: The grafted nanosheet fibers are immersed in a phosphorus-containing flame-retardant emulsion for 5 minutes, then removed, the adhesive is controlled, and dried at 80~100℃ to form a mesh fabric. (4) Prefabrication and composite of fiber reinforcement layer: The mesh fabric prepared in step (3) is immersed in flame retardant resin and taken out after full impregnation to obtain prepreg; the prepreg is covered on the surface of the gradient flame retardant impregnation layer of the board obtained in step (2) and hot-pressed at 120~150℃ and 0.8MPa pressure for 30 minutes to form fiber reinforcement prefabrication layer; (5) Surface flame retardant film composite: Cover the surface of the fiber-reinforced prefabricated layer of the board obtained in step (4) with a dense flame retardant film, and hot press it at 140~160℃ and 1.0MPa pressure for 25 minutes to make the flame retardant film tightly composite with the lower layer and completely cured, thus obtaining the composite board.

[0026] The nano flame retardant impregnation liquid in step (2) is composed of the following components by mass: 30 parts of waterborne polyurethane resin, 10 parts of nano aluminum hydroxide, 5 parts of nano silica, 0.5 parts of silane coupling agent KH-550, and 30 parts of water. The components are mixed evenly by high-speed stirring before use.

[0027] The silane coupling agent in step (3) is KH-560, and the solvent is ethanol with a mass concentration of 50%.

[0028] The precursor aqueous solution mentioned in step (3) is a mixed aqueous solution of magnesium nitrate, aluminum nitrate and urea, with a mass ratio of magnesium nitrate, aluminum nitrate and urea of ​​2:1:1 and an aqueous solution concentration of 0.5 mol / L; the composition of the phosphorus-containing flame retardant emulsion is: 30 parts of polyphosphate ester, 20 parts of ethylene-vinyl acetate copolymer emulsion, 5 parts of nano zinc oxide, 2 parts of aqueous dispersant, and deionized water to make up to 100 parts. After ultrasonic dispersion and homogenization emulsification, a stable emulsion system is obtained.

[0029] The flame retardant resin in step (4) is a phosphorus-containing epoxy resin with a solid content of 60%~80% and a viscosity of 2000~5000 mPa·s.

[0030] The surface-dense flame-retardant film described in step (5) is made from the following raw materials by weight: 100 parts epoxy resin, 20 parts coated ammonium polyphosphate, 5 parts zinc borate, 10 parts silica sol, and 5 parts curing agent dicyandiamide. The film material is prepared by mixing, casting, and semi-curing.

[0031] The solid content of the silica sol is 20-30%.

[0032] The preparation method of the coated ammonium polyphosphate is as follows: ammonium polyphosphate particles are added to a high-speed mixer, heated to 80°C, and 8% by mass of melamine-formaldehyde resin prepolymer solution is sprayed in and stirred continuously for 15 minutes; then, hot air at 60°C is passed through and dried for 30 minutes to obtain the product; the melamine-formaldehyde resin prepolymer solution is prepared by heating melamine and formaldehyde at a molar ratio of 1:2 under alkaline conditions of pH 9-10 at 70-80°C for 1 hour.

[0033] Example 2 A fiber-reinforced fireproof and flame-retardant board comprises, from the inside out: a wood substrate layer, a gradient flame-retardant impregnation layer, a fiber-reinforced precast layer, and a dense flame-retardant film layer on the surface.

[0034] A process for preparing a fiber-reinforced fire-retardant board includes the following steps: (1) Dry the wood substrate to a moisture content of 8-12% and sand its surface; (2) Gradient flame retardant impregnation: The pretreated wood substrate is immersed in the nano flame retardant impregnation liquid and subjected to three levels of gradient pressure impregnation: the first level low pressure stage: pressure 0.4MPa, pressure held for 50 minutes; the second level medium pressure stage: pressure 0.9MPa, pressure held for 40 minutes; the third level high pressure stage: pressure 1.3MPa, pressure held for 25 minutes; after removal, it is left to air dry at room temperature for 2 hours, and then cured and dried at 60~80℃ for 4 hours to form a gradient flame retardant impregnation layer; (3) Preparation of flame-retardant reinforced fiber web with surface-grafted nanosheet structure: A. Fiber surface activation: Immerse basalt fibers in a 7% (w / w) silane coupling agent solution, stir in a water bath at 60-80°C for 2 hours, then remove and dry; B. In-situ growth of nanosheets: Activated fibers are placed in a high-pressure reactor, and a precursor aqueous solution containing magnesium nitrate, aluminum nitrate, and urea is added. The reaction is carried out at 100-120℃ for 10 hours, allowing nanosheets to grow in situ on the fiber surface via hydrothermal growth. After natural cooling, the fibers are removed and dried to obtain fibers grafted with nanosheets. The in-situ grown nanosheets not only significantly increase the specific surface area and surface roughness of the fibers, enhancing the mechanical interlocking and interfacial bonding with the resin, but also, as an inorganic nanosheet layer, effectively delay the diffusion of thermal decomposition gases and oxygen when heated. Furthermore, they exhibit catalytic synergy with flame-retardant components such as polyphosphate esters, promoting the formation of a denser and stronger carbon layer. C. Flame-retardant micro-coating: The grafted nanosheet fibers are immersed in a phosphorus-containing flame-retardant emulsion for 7 minutes, then removed, the adhesive is controlled, and dried at 80~100℃ to form a mesh fabric. (4) Prefabrication and composite of fiber reinforcement layer: The mesh fabric prepared in step (3) is immersed in flame retardant resin and taken out after full impregnation to obtain prepreg; the prepreg is covered on the surface of the gradient flame retardant impregnation layer of the board obtained in step (2) and hot-pressed at 120~150℃ and 1MPa pressure for 20 minutes to form fiber reinforcement prefabrication layer. (5) Surface flame retardant film composite: Cover the surface of the fiber-reinforced prefabricated layer of the board obtained in step (4) with a dense flame retardant film, and hot press it at 140~160℃ and 1.2MPa pressure for 20 minutes to make the flame retardant film tightly composite with the lower layer and completely cured, thus obtaining the composite board.

[0035] The nano flame retardant impregnation liquid in step (2) is composed of the following components by mass: 40 parts of waterborne polyurethane resin, 15 parts of nano aluminum hydroxide, 10 parts of nano silica, 1 part of silane coupling agent KH-550, and 40 parts of water. The components are mixed evenly by high-speed stirring before use.

[0036] The silane coupling agent in step (3) is KH-550, and the solvent is ethanol with a mass concentration of 50%.

[0037] The precursor aqueous solution mentioned in step (3) is a mixed aqueous solution of magnesium nitrate, aluminum nitrate and urea, with a mass ratio of magnesium nitrate, aluminum nitrate and urea of ​​3:1:1 and an aqueous solution concentration of 0.8 mol / L; the composition of the phosphorus-containing flame retardant emulsion is: 35 parts of polyphosphate ester, 20 parts of ethylene-vinyl acetate copolymer emulsion, 6 parts of nano zinc oxide, 3 parts of aqueous dispersant, and deionized water to make up to 100 parts. After ultrasonic dispersion and homogenization emulsification, a stable emulsion system is obtained.

[0038] The flame-retardant resin in step (4) is a phosphorus-containing epoxy resin or a nitrogen-containing phenolic resin with a solid content of 60%~80% and a viscosity of 2000~5000 mPa·s.

[0039] The surface-dense flame-retardant film described in step (5) is made from the following raw materials by weight: 100 parts epoxy resin, 30 parts coated ammonium polyphosphate, 10 parts zinc borate, 15 parts silica sol, and 8 parts curing agent dicyandiamide. The film material is prepared by mixing, casting, and semi-curing.

[0040] The solid content of the silica sol is 20-30%.

[0041] The preparation method of the coated ammonium polyphosphate is as follows: ammonium polyphosphate particles are added to a high-speed mixer, heated to 80°C, and 8% by mass of melamine-formaldehyde resin prepolymer solution is sprayed in and stirred continuously for 15 minutes; then, hot air at 60°C is passed through and dried for 30 minutes to obtain the product; the melamine-formaldehyde resin prepolymer solution is prepared by heating melamine and formaldehyde at a molar ratio of 1:2 under alkaline conditions of pH 9-10 at 70-80°C for 1 hour.

[0042] Example 3 A fiber-reinforced fireproof and flame-retardant board comprises, from the inside out: a wood substrate layer, a gradient flame-retardant impregnation layer, a fiber-reinforced precast layer, and a dense flame-retardant film layer on the surface.

[0043] A process for preparing a fiber-reinforced fire-retardant board includes the following steps: (1) Dry the wood substrate to a moisture content of 8-12% and sand its surface; (2) Gradient flame retardant impregnation: The pretreated wood substrate is immersed in the nano flame retardant impregnation liquid and subjected to three levels of gradient pressure impregnation in sequence: the first level low pressure stage: pressure 0.5MPa, pressure held for 40 minutes; the second level medium pressure stage: pressure 1.0MPa, pressure held for 30 minutes; the third level high pressure stage: pressure 1.5MPa, pressure held for 20 minutes; after being taken out, it is left to air dry at room temperature for 4 hours, and then cured and dried at 60~80℃ for 6 hours to form a gradient flame retardant impregnation layer; (3) Preparation of flame-retardant reinforced fiber web with surface-grafted nanosheet structure: A. Fiber surface activation: Immerse basalt fibers in a 10% silane coupling agent solution and stir in a water bath at 60~80℃ for 2 hours, then remove and dry. B. In-situ growth of nanosheets: Activated fibers are placed in a high-pressure reactor, and a precursor aqueous solution containing magnesium nitrate, aluminum nitrate, and urea is added. The reaction is carried out at 100-120℃ for 12 hours, allowing nanosheets to grow in situ on the fiber surface via hydrothermal growth. After natural cooling, the fibers are removed and dried to obtain fibers grafted with nanosheets. The in-situ grown nanosheets not only significantly increase the specific surface area and surface roughness of the fibers, enhancing the mechanical interlocking and interfacial bonding with the resin, but also, as an inorganic nanosheet layer, effectively delay the diffusion of thermal decomposition gases and oxygen when heated. Furthermore, they exhibit catalytic synergy with flame-retardant components such as polyphosphate esters, promoting the formation of a denser and stronger carbon layer. C. Flame-retardant micro-coating: The grafted nanosheet fibers are immersed in a phosphorus-containing flame-retardant emulsion for 10 minutes, then removed, the adhesive is controlled, and dried at 80~100℃ to form a mesh fabric. (4) Prefabrication and composite of fiber reinforcement layer: The mesh fabric prepared in step (3) is immersed in flame retardant resin and taken out after full impregnation to obtain prepreg; the prepreg is covered on the surface of the gradient flame retardant impregnation layer of the board obtained in step (2) and hot-pressed at 120~150℃ and 1.2MPa pressure for 10 minutes to form fiber reinforcement prefabrication layer; (5) Surface flame retardant film composite: Cover the surface of the fiber-reinforced prefabricated layer of the board obtained in step (4) with a dense flame retardant film, and hot press it for 15 minutes at 140~160℃ and 1.5MPa pressure to make the flame retardant film tightly composite with the lower layer and completely cured, thus obtaining the composite board.

[0044] The nano flame retardant impregnation liquid in step (2) is composed of the following components by mass: 50 parts of waterborne polyurethane resin, 20 parts of nano aluminum hydroxide, 15 parts of nano silica, 2 parts of silane coupling agent KH-550, and 50 parts of water. The components are mixed evenly by high-speed stirring before use.

[0045] The silane coupling agent in step (3) is KH-550, and the solvent is ethanol with a mass concentration of 50%.

[0046] The precursor aqueous solution mentioned in step (3) is a mixed aqueous solution of magnesium nitrate, aluminum nitrate and urea, with a mass ratio of magnesium nitrate, aluminum nitrate and urea of ​​4:1:1 and an aqueous solution concentration of 1 mol / L; the composition of the phosphorus-containing flame retardant emulsion is: 40 parts of polyphosphate ester, 30 parts of ethylene-vinyl acetate copolymer emulsion, 10 parts of nano zinc oxide, 5 parts of aqueous dispersant, and deionized water to make up to 100 parts, and a stable emulsion system is obtained after ultrasonic dispersion and homogenization emulsification.

[0047] The flame-retardant resin in step (4) is a phosphorus-containing epoxy resin or a nitrogen-containing phenolic resin with a solid content of 60%~80% and a viscosity of 2000~5000 mPa·s.

[0048] The dense flame-retardant film described in step (5) is made from the following raw materials by weight: 100 parts epoxy resin, 40 parts coated ammonium polyphosphate, 15 parts zinc borate, 20 parts silica sol, and 10 parts dicyandiamide curing agent. The film is prepared by mixing, casting, and semi-curing.

[0049] The solid content of the silica sol is 20-30%.

[0050] The preparation method of the coated ammonium polyphosphate is as follows: ammonium polyphosphate particles are added to a high-speed mixer, heated to 80°C, and 8% by mass of melamine-formaldehyde resin prepolymer solution is sprayed in and stirred continuously for 15 minutes; then, hot air at 60°C is passed through and dried for 30 minutes to obtain the product; the melamine-formaldehyde resin prepolymer solution is prepared by heating melamine and formaldehyde at a molar ratio of 1:3 under alkaline conditions of pH 9-10 at 70-80°C for 1 hour.

[0051] Comparative Example 1 In this comparative example, except for the absence of a gradient flame-retardant impregnation process and the use of a single pressure (0.3 MPa pressure impregnation), the remaining steps and raw materials are completely identical to those in Example 1, namely: A fiber-reinforced fireproof and flame-retardant board comprises, from the inside out: a wood substrate layer, a gradient flame-retardant impregnation layer, a fiber-reinforced precast layer, and a dense flame-retardant film layer on the surface.

[0052] A process for preparing a fiber-reinforced fire-retardant board includes the following steps: (1) Dry the wood substrate to a moisture content of 8-12% and sand its surface; (2) Flame retardant impregnation: The pretreated wood substrate is immersed in nano flame retardant impregnation liquid and pressure impregnation is performed in sequence: pressure 0.3MPa, pressure holding for 135 minutes; after taking it out, it is left to air at room temperature for 1 hour, and then cured and dried at 60~80℃ for 2 hours to form a flame retardant impregnation layer. (3) Preparation of flame-retardant reinforced fiber web with surface-grafted nanosheet structure: A. Fiber surface activation: Immerse basalt fibers in a 5% (w / w) silane coupling agent solution, stir in a water bath at 60-80°C for 1 hour, then remove and dry; B. In-situ growth of nanosheets: The activated fibers are placed in a high-pressure reactor, and an aqueous precursor solution containing magnesium nitrate, aluminum nitrate and urea is added. The reaction is carried out at 100-120℃ for 6 hours to allow the nanosheets to grow in-situ hydrothermally on the fiber surface. After natural cooling, the fibers are taken out and dried to obtain the grafted nanosheet fibers. C. Flame-retardant micro-coating: The grafted nanosheet fibers are immersed in a phosphorus-containing flame-retardant emulsion for 5 minutes, then removed, the adhesive is controlled, and dried at 80~100℃ to form a mesh fabric. (4) Prefabrication and composite of fiber reinforcement layer: The mesh fabric prepared in step (3) is immersed in flame retardant resin and taken out after full impregnation to obtain prepreg; the prepreg is covered on the surface of the flame retardant impregnation layer of the board obtained in step (2) and hot-pressed at 120~150℃ and 0.8MPa pressure for 30 minutes to form fiber reinforcement prefabrication layer; (5) Surface flame retardant film composite: Cover the surface of the fiber-reinforced prefabricated layer of the board obtained in step (4) with a dense flame retardant film, and hot press it at 140~160℃ and 1.0MPa pressure for 25 minutes to make the flame retardant film tightly composite with the lower layer and completely cured, thus obtaining the composite board.

[0053] Comparative Example 2 In this comparative example, except for the absence of a gradient flame-retardant impregnation process and the use of a single pressure (0.8 MPa pressure impregnation), the remaining steps and raw materials are completely identical to those in Example 1, namely: A fiber-reinforced fireproof and flame-retardant board comprises, from the inside out: a wood substrate layer, a gradient flame-retardant impregnation layer, a fiber-reinforced precast layer, and a dense flame-retardant film layer on the surface.

[0054] A process for preparing a fiber-reinforced fire-retardant board includes the following steps: (1) Dry the wood substrate to a moisture content of 8-12% and sand its surface; (2) Flame retardant impregnation: The pretreated wood substrate is immersed in nano flame retardant impregnation liquid and pressure impregnation is carried out in sequence: pressure 0.8MPa, pressure holding for 135 minutes; after taking it out, it is left to air at room temperature for 1 hour, and then cured and dried at 60~80℃ for 2 hours to form a flame retardant impregnation layer. (3) Preparation of flame-retardant reinforced fiber web with surface-grafted nanosheet structure: A. Fiber surface activation: Immerse basalt fibers in a 5% (w / w) silane coupling agent solution, stir in a water bath at 60-80°C for 1 hour, then remove and dry; B. In-situ growth of nanosheets: The activated fibers are placed in a high-pressure reactor, and an aqueous precursor solution containing magnesium nitrate, aluminum nitrate and urea is added. The reaction is carried out at 100-120℃ for 6 hours to allow the nanosheets to grow in-situ hydrothermally on the fiber surface. After natural cooling, the fibers are taken out and dried to obtain the grafted nanosheet fibers. C. Flame-retardant micro-coating: The grafted nanosheet fibers are immersed in a phosphorus-containing flame-retardant emulsion for 5 minutes, then removed, the adhesive is controlled, and dried at 80~100℃ to form a mesh fabric. (4) Prefabrication and composite of fiber reinforcement layer: The mesh fabric prepared in step (3) is immersed in flame retardant resin and taken out after full impregnation to obtain prepreg; the prepreg is covered on the surface of the flame retardant impregnation layer of the board obtained in step (2) and hot-pressed at 120~150℃ and 0.8MPa pressure for 30 minutes to form fiber reinforcement prefabrication layer; (5) Surface flame retardant film composite: Cover the surface of the fiber-reinforced prefabricated layer of the board obtained in step (4) with a dense flame retardant film, and hot press it at 140~160℃ and 1.0MPa pressure for 25 minutes to make the flame retardant film tightly composite with the lower layer and completely cured, thus obtaining the composite board.

[0055] Comparative Example 3 In this comparative example, except for the absence of a gradient flame-retardant impregnation process and the use of a single pressure (1.2 MPa pressure impregnation), the remaining steps and raw materials are completely identical to those in Example 1, namely: A fiber-reinforced fireproof and flame-retardant board comprises, from the inside out: a wood substrate layer, a gradient flame-retardant impregnation layer, a fiber-reinforced precast layer, and a dense flame-retardant film layer on the surface.

[0056] A process for preparing a fiber-reinforced fire-retardant board includes the following steps: (1) Dry the wood substrate to a moisture content of 8-12% and sand its surface; (2) Flame retardant impregnation: The pretreated wood substrate is immersed in nano flame retardant impregnation liquid and pressure impregnation is performed in sequence: pressure 1.2MPa, pressure holding for 135 minutes; after taking it out, it is left to air dry at room temperature for 1 hour, and then cured and dried at 60~80℃ for 2 hours to form a flame retardant impregnation layer. (3) Preparation of flame-retardant reinforced fiber web with surface-grafted nanosheet structure: A. Fiber surface activation: Immerse basalt fibers in a 5% (w / w) silane coupling agent solution, stir in a water bath at 60-80°C for 1 hour, then remove and dry; B. In-situ growth of nanosheets: The activated fibers are placed in a high-pressure reactor, and an aqueous precursor solution containing magnesium nitrate, aluminum nitrate and urea is added. The reaction is carried out at 100-120℃ for 6 hours to allow the nanosheets to grow in-situ hydrothermally on the fiber surface. After natural cooling, the fibers are taken out and dried to obtain the grafted nanosheet fibers. C. Flame-retardant micro-coating: The grafted nanosheet fibers are immersed in a phosphorus-containing flame-retardant emulsion for 5 minutes, then removed, the adhesive is controlled, and dried at 80~100℃ to form a mesh fabric. (4) Prefabrication and composite of fiber reinforcement layer: The mesh fabric prepared in step (3) is immersed in flame retardant resin and taken out after full impregnation to obtain prepreg; the prepreg is covered on the surface of the flame retardant impregnation layer of the board obtained in step (2) and hot-pressed at 120~150℃ and 0.8MPa pressure for 30 minutes to form fiber reinforcement prefabrication layer; (5) Surface flame retardant film composite: Cover the surface of the fiber-reinforced prefabricated layer of the board obtained in step (4) with a dense flame retardant film, and hot press it at 140~160℃ and 1.0MPa pressure for 25 minutes to make the flame retardant film tightly composite with the lower layer and completely cured, thus obtaining the composite board.

[0057] Comparative Example 4 This comparative example is identical to Example 1 in all steps and raw materials except for the use of conventional basalt fiber. A fiber-reinforced fireproof and flame-retardant board comprises, from the inside out: a wood substrate layer, a gradient flame-retardant impregnation layer, a fiber-reinforced precast layer, and a dense flame-retardant film layer on the surface.

[0058] A process for preparing a fiber-reinforced fire-retardant board includes the following steps: (1) Dry the wood substrate to a moisture content of 8-12% and sand its surface; (2) Gradient flame retardant impregnation: The pretreated wood substrate is immersed in nano flame retardant impregnation liquid and subjected to three levels of gradient pressure impregnation: the first level low pressure stage: pressure 0.3MPa, pressure held for 60 minutes; the second level medium pressure stage: pressure 0.8MPa, pressure held for 45 minutes; the third level high pressure stage: pressure 1.2MPa, pressure held for 30 minutes; after removal, it is left to air dry at room temperature for 1 hour, and then cured and dried at 60~80℃ for 2 hours to form a gradient flame retardant impregnation layer; (3) Preparation of flame-retardant reinforced fiber web: A. Fiber surface activation: Immerse basalt fibers in a 5% (w / w) silane coupling agent solution, stir in a water bath at 60-80°C for 1 hour, then remove and dry; B. Flame-retardant micro-coating: The fibers obtained in step A are immersed in a phosphorus-containing flame-retardant emulsion for 5 minutes, then removed, the adhesive is controlled, and the fibers are dried at 80~100℃ to form a mesh fabric. (4) Prefabrication and composite of fiber reinforcement layer: The mesh fabric prepared in step (3) is immersed in flame retardant resin and taken out after full impregnation to obtain prepreg; the prepreg is covered on the surface of the gradient flame retardant impregnation layer of the board obtained in step (2) and hot-pressed at 120~150℃ and 0.8MPa pressure for 30 minutes to form fiber reinforcement prefabrication layer; (5) Surface flame retardant film composite: Cover the surface of the fiber-reinforced prefabricated layer of the board obtained in step (4) with a dense flame retardant film, and hot press it at 140~160℃ and 1.0MPa pressure for 25 minutes to make the flame retardant film tightly composite with the lower layer and completely cured, thus obtaining the composite board.

[0059] Comparative Example 5 Except for changing the composition of the dense flame-retardant film on the surface (not using coated ammonium polyphosphate), the steps and raw materials in this comparative example are completely the same as in Example 1, that is: A fiber-reinforced fireproof and flame-retardant board comprises, from the inside out: a wood substrate layer, a gradient flame-retardant impregnation layer, a fiber-reinforced precast layer, and a dense flame-retardant film layer on the surface.

[0060] The surface-dense flame-retardant film described in step (5) is made from the following raw materials by weight: 100 parts epoxy resin, 20 parts ammonium polyphosphate, 5 parts zinc borate, 10 parts silica sol, and 5 parts dicyandiamide curing agent. The film material is prepared by mixing, casting, and semi-curing.

[0061] The solid content of the silica sol is 20-30%.

[0062] Comparative Example 6 Except for changing the composition of the dense flame-retardant film on the surface (not using zinc borate), the steps and raw materials in this comparative example are completely the same as in Example 1, that is: The surface-dense flame-retardant film described in step (5) is made from the following raw materials by weight: 100 parts epoxy resin, 20 parts coated ammonium polyphosphate, 10 parts silica sol, and 5 parts curing agent dicyandiamide. The film is prepared by mixing, casting, and semi-curing.

[0063] Comparative Example 7 Except for changing the composition of the dense flame-retardant film on the surface (not using silica sol), the steps and raw materials in this comparative example are completely the same as in Example 1, that is: The dense flame-retardant film described in step (5) is made from the following raw materials by weight: 100 parts epoxy resin, 20 parts coated ammonium polyphosphate, 5 parts zinc borate, and 5 parts curing agent dicyandiamide. The film is prepared by mixing, casting, and semi-curing.

[0064] Performance testing The flame retardant properties, mechanical properties, smoke suppression properties, and weather resistance of the boards were comprehensively tested in accordance with relevant national and industry standards. The core criteria are as follows: Flame retardant performance: GB8624-2012, using the Classification Test Method for Burning Performance of Building Materials and Products to determine the flammability rating of the sample (A / B1 / B2 / B3).

[0065] Oxygen Index (LOI): GB / T 2406.2-2009, is the minimum oxygen concentration required for a sample to sustain combustion, determined using an oxygen index meter. The higher the value, the better the flame retardancy.

[0066] Horizontal burning rate: GB / T 8332-2018, determines the flame propagation rate of a sample in a horizontal state and assesses the flame spread trend.

[0067] Mechanical properties: GB / T 17657-2013. Bending strength is determined by a three-point bending test using a universal testing machine to measure the maximum bending stress at which the sample breaks.

[0068] Surface bond strength: GB / T 17657-2013, determines the bonding force between the surface layer of the board and the substrate, and evaluates the stability of the interfacial bond.

[0069] Smoke suppression performance: The "Test Method for Smoke Density of Building Materials During Combustion or Decomposition" (GB / T 8627-2007) uses a smoke density chamber to determine the smoke density of the sample during combustion. The lower the grade, the better the smoke suppression performance.

[0070] Aging resistance: Thermal aging performance: GB / T 17657-2013, the sample was aged in an oven at 100℃ for 72h, and the retention rate of flexural strength and the change of flame retardant properties before and after aging were measured.

[0071] Thermal cycling stability: GB / T 3512-2014, -20℃ (2h) → room temperature (1h) → 80℃ (2h) is one cycle, for a total of 20 cycles. The surface condition of the sample is observed and the mechanical properties are tested.

[0072] Sample preparation Fiber-reinforced fire-retardant boards prepared in Examples 1, 2, 3 and Comparative Examples 1-7 were selected. Blank wood boards without any flame-retardant treatment were selected as blank control groups. All samples were processed into standard test specimens with specifications that met the above-mentioned standard requirements. The number of specimens in each group was ≥5, and the test results were taken as the average value.

[0073] Table 1 Performance test results of the embodiments Table 2 Comparative Performance Test Results As can be seen from the data in Tables 1-2, the fiber-reinforced fire-retardant boards prepared in Examples 1-3 are significantly superior to the blank control group and the comparative examples in all performance indicators. Regarding flame retardant performance, Examples 2 and 3 achieved a Class A flammability rating, with oxygen indices (LOI) as high as 48.3% and 49.1% respectively, and horizontal burning rates of <1.0 mm / min, demonstrating excellent flame retardant effect and self-extinguishing properties. Example 1 also achieved a Class B1 rating, with an oxygen index of 42.5% and a horizontal burning rate of only 2.1 mm / min. In contrast, the blank control group achieved a Class B3 flammability rating, with an oxygen index of only 15.2% and a horizontal burning rate as high as 25.6 mm / min, showing a significant difference. Although the flame retardant performance of each comparative example was improved compared with the blank group, the combustion performance level was mostly B2, the oxygen index was generally between 30% and 38%, and the horizontal burning rate was much higher than that of the example. This indicates that the present invention can effectively improve the flame retardant performance of the board through the synergistic effect of gradient flame retardant impregnation, flame retardant reinforced fiber network grafted with nanosheet structure on the surface, and surface dense flame retardant film with specific composition.

[0074] In terms of mechanical properties, the flexural strengths of Examples 1-3 were 35.2 MPa, 38.5 MPa, and 40.2 MPa, respectively, and the surface bonding strengths were 2.5 MPa, 2.8 MPa, and 3.1 MPa, respectively, all significantly higher than the blank control group (flexural strength 25.6 MPa, surface bonding strength 0.8 MPa). In particular, Comparative Example 4, which used only conventional basalt fibers without surface grafting of nanosheets, showed significantly lower flexural strength (29.2 MPa) and surface bonding strength (1.0 MPa) than the Examples. This fully demonstrates that in-situ growth of nanosheet structures on the fiber surface can effectively enhance the interfacial bonding force between the fiber and the resin, thereby improving the overall mechanical properties of the board.

[0075] In terms of smoke suppression performance, the smoke density ratings (SDR) of the embodiments were 21, 15 and 12, respectively, which were much lower than the blank control group of 89 and the comparative examples (38-60), indicating that the board of the present invention can effectively suppress the generation of smoke when burning, which is crucial for personnel evacuation and rescue in fire.

[0076] In terms of weather resistance, after thermal aging and thermal cycling, the flexural strength retention rate of Examples 1-3 remained at a high level (88.6%-93.1% after thermal aging and 88.6%-91.5% after thermal cycling), while the retention rate of the blank control group and each comparative example was relatively low. This indicates that the plate prepared by the present invention has good thermal stability and environmental adaptability and can maintain good mechanical properties under different working conditions.

[0077] Comprehensive analysis of the comparative examples reveals that Comparative Examples 1-3, which did not employ the gradient flame-retardant impregnation process, exhibited poor performance across all aspects. Comparative Example 4, lacking the grafted nanosheets, suffered from compromised mechanical and flame-retardant properties. Comparative Examples 5-7, respectively, lacked the coating of ammonium polyphosphate, zinc borate, or silica sol in their dense flame-retardant surface films, resulting in reduced flame retardancy, smoke suppression, and weather resistance. These results further validate that the gradient flame-retardant impregnation process, the flame-retardant reinforcing fiber web grafted with nanosheets, and the dense flame-retardant surface film with a specific composition are crucial for achieving the superior overall performance of the board material; the absence of any one of these elements weakens the overall effect.

[0078] It should be noted that the above embodiments are merely some preferred embodiments of the present invention, and not all embodiments. Obviously, based on the above embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort should fall within the scope of protection of the present invention.

Claims

1. A preparation process for a fiber-reinforced fire-retardant board, characterized in that, The preparation steps include the following: (1) Dry the wood substrate to a moisture content of 8-12% and sand its surface; (2) Gradient flame retardant impregnation: The pretreated wood substrate is immersed in the nano flame retardant impregnation liquid and subjected to three levels of gradient pressure impregnation: the first level is low pressure stage: pressure 0.3~0.5MPa, pressure holding for 40~60 minutes; the second level is medium pressure stage: pressure 0.8~1.0MPa, pressure holding for 30~45 minutes; the third level is high pressure stage: pressure 1.2~1.5MPa, pressure holding for 20~30 minutes; after removal, it is left to air dry at room temperature for 1~4 hours, and then cured and dried at 60~80℃ for 2~6 hours to form a gradient flame retardant impregnation layer; (3) Preparation of flame-retardant reinforced fiber web with surface-grafted nanosheet structure: A. Fiber surface activation: Immerse basalt fibers in a 5-10% silane coupling agent solution, stir in a water bath at 60-80℃ for 1-2 hours, and then remove and dry. B. In-situ growth of nanosheets: The activated fibers are placed in a high-pressure reactor, and an aqueous precursor solution containing magnesium nitrate, aluminum nitrate and urea is added. The reaction is carried out at 100-120℃ for 6-12 hours, so that the nanosheets grow in situ on the fiber surface by hydrothermal growth. After natural cooling, the fibers are taken out and dried to obtain the grafted nanosheet fibers. C. Flame-retardant micro-layer coating: The grafted nanosheet fibers are immersed in a phosphorus-containing flame-retardant emulsion for 5-10 minutes, then removed, the adhesive is controlled, and dried at 80-100℃ to form a mesh fabric. (4) Prefabrication and composite of fiber reinforcement layer: The mesh fabric prepared in step (3) is immersed in flame retardant resin and taken out after full impregnation to obtain prepreg; the prepreg is covered on the surface of the gradient flame retardant impregnation layer of the board obtained in step (2), and hot-pressed at 120~150℃ and 0.8~1.2MPa pressure for 10~30 minutes to form fiber reinforcement prefabrication layer; (5) Surface flame retardant film composite: Cover the surface of the fiber-reinforced prefabricated layer of the board obtained in step (4) with a dense flame retardant film, and hot press it at 140~160℃ and 1.0~1.5MPa for 15~25 minutes to make the flame retardant film tightly composite with the lower layer and completely cured, thus obtaining the composite board.

2. The preparation process of the fiber-reinforced fire-retardant board according to claim 1, characterized in that, The nano flame retardant impregnation liquid in step (2) is composed of the following components by mass: 30-50 parts of waterborne polyurethane resin, 10-20 parts of nano aluminum hydroxide, 5-15 parts of nano silica, 0.5-2 parts of silane coupling agent KH-550, and 30-50 parts of water. The components are mixed evenly by high-speed stirring before use.

3. The preparation process of the fiber-reinforced fire-retardant board according to claim 1, characterized in that, The silane coupling agent in step (3) is KH-560 or KH-550, and the solvent is ethanol with a mass concentration of 50%.

4. The preparation process of the fiber-reinforced fire-retardant board according to claim 1, characterized in that, The precursor aqueous solution mentioned in step (3) is a mixed aqueous solution of magnesium nitrate, aluminum nitrate and urea, with a mass ratio of magnesium nitrate, aluminum nitrate and urea of ​​2~4:1:1 and an aqueous solution concentration of 0.5~1mol / L; the composition of the phosphorus-containing flame retardant emulsion is: 30~40 parts of polyphosphate ester, 20~30 parts of ethylene-vinyl acetate copolymer emulsion, 5~10 parts of nano zinc oxide, 2~5 parts of aqueous dispersant, and deionized water to make up to 100 parts. After ultrasonic dispersion and homogenization emulsification, a stable emulsion system is obtained.

5. The preparation process of the fiber-reinforced fire-retardant board according to claim 1, characterized in that, The flame-retardant resin in step (4) is a phosphorus-containing epoxy resin or a nitrogen-containing phenolic resin with a solid content of 60%~80% and a viscosity of 2000~5000 mPa·s.

6. The preparation process of the fiber-reinforced fire-retardant board according to claim 1, characterized in that, The surface-dense flame-retardant film described in step (5) is made from the following raw materials by weight: 100 parts epoxy resin, 20-40 parts coated ammonium polyphosphate, 5-15 parts zinc borate, 10-20 parts silica sol, and 5-10 parts curing agent dicyandiamide. The film material is prepared by mixing, casting, and semi-curing.

7. The preparation process of the fiber-reinforced fire-retardant board according to claim 6, characterized in that, The solid content of the silica sol is 20-30%.

8. The preparation process of the fiber-reinforced fire-retardant board according to claim 6, characterized in that, The preparation method of the coated ammonium polyphosphate is as follows: ammonium polyphosphate particles are added to a high-speed mixer, heated to 80°C, and 8% by mass of melamine-formaldehyde resin prepolymer solution is sprayed in and stirred continuously for 15 minutes; then, hot air at 60°C is passed through and dried for 30 minutes to obtain the product; the melamine-formaldehyde resin prepolymer solution is prepared by heating melamine and formaldehyde at a molar ratio of 1:2~3 under alkaline conditions of pH 9-10 at 70-80°C for 1 hour.

9. A sheet material obtained by any one of the preparation processes of claims 1-8, characterized in that, The board comprises, from the inside out: a wood substrate layer, a gradient flame-retardant impregnation layer, a fiber-reinforced precast layer, and a dense flame-retardant film layer.

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