Low-metal-corrosion flame-retardant plywood and preparation method thereof

Abstract

The invention discloses low-metal-corrosion flame-retardant plywood and a preparation method thereof. The plywood comprises a base material which is formed by sequentially and alternately overlapping modified veneers and resin layers; a preparation method of the modified veneer comprises the following steps that the veneer is sequentially placed in a 0.05 mol / L to 0.2 mol / L amino silane coupling agent solution and a 0.06 mol / L to 0.3 mol / L allyl salicylaldehyde solution to be subjected to pressure dipping; then the veneer is placed in a comonomer solution, an initiator is added, the temperature is raised, a free radical copolymerization reaction is carried out, and the composite material is obtained, and comonomers comprise diethyl allyl phosphate and a vinyl nitrogen-containing heterocyclic ring; the concentration of the diethyl allyl phosphate in the comonomer solution is 0.1 mol / L to 0.5 mol / L, and the concentration of the vinyl nitrogen-containing heterocyclic ring in the comonomer solution is 0.05 mol / L to 0.3 mol / L. According to the invention, the problems of low anchoring force between the flame retardant and the plate, easy dissolution loss in a humid and hot environment, poor flame-retardant persistence and serious metal corrosion in the current dipping flame-retardant treatment process of the plate can be solved.

Description

Technical Field

[0001] This application relates to the field of flame retardant materials, and in particular to a low-metal-corrosion flame retardant plywood and its preparation method. Background Technology

[0002] Wood-based plywood is widely used in construction, furniture manufacturing, and transportation due to its excellent processing performance and decorative effect. However, wood itself is a flammable material, and the large amount of heat and toxic fumes released during combustion pose a serious fire hazard. To improve the fire safety performance of wood-based panels, flame-retardant modification has become an inevitable requirement for industry development. Currently, flame-retardant treatment technologies for plywood and other wood-based panels are mainly divided into two categories.

[0003] One method involves physically mixing flame retardants directly with adhesives (such as urea-formaldehyde resin and phenolic resin) to form a flame-retardant adhesive, which is then applied to the surface or interlayer of the veneer using conventional gluing processes. The resulting flame-retardant plywood is then hot-pressed. This method is relatively simple and easily integrated into existing production lines. However, its flame-retardant function relies primarily on the limited thickness of the flame-retardant adhesive layer applied to the veneer surface or interlayer. When exposed to open flames or high temperatures, while this surface or interlayer flame-retardant layer provides some initial barrier effect, its effective flame-retardant components cannot deeply penetrate the wood fibers, and the resulting physical barrier layer is relatively weak. Once the flame penetrates this weak flame-retardant layer or intrudes from incompletely covered areas such as the edges and seams of the board, it can easily and rapidly spread to the insufficiently treated wood matrix inside the board, significantly reducing the flame-retardant effect. The overall flame-retardant performance fails to meet high fire resistance requirements, posing a risk of fire spread.

[0004] Another method involves impregnation, where the finished plywood or veneer is immersed in a flame retardant solution. This allows the flame retardant to penetrate the wood through osmosis, increasing its distribution depth to some extent. However, it's important to note that the flame retardant introduced by impregnation often exists in the wood's pore structure through physical adsorption or simple deposition, failing to form strong and stable chemical bonds with the main components of the wood cell walls (such as cellulose, hemicellulose, and lignin) or the board itself. This unstable bonding means that the flame retardant is prone to leaching, volatilization, or migration during use, especially under prolonged exposure to humid and hot environments and repeated wet-dry cycles. The direct consequence is that the flame retardant efficacy of the plywood significantly decreases over time, resulting in poor flame retardant retention and an inability to guarantee long-term reliable fire safety. In addition, phosphorus-nitrogen and halogen flame retardants are acidic and may hydrolyze in humid environments to produce acidic substances. These flame retardant components released from the boards will undergo electrochemical corrosion reactions with light steel keels, metal connectors, nails, etc., which are widely used in building structures. This not only seriously endangers the service life of metal materials, but also leads to a decrease in their strength and premature failure, posing a potential safety hazard. Summary of the Invention

[0005] To address the problems in current flame-retardant impregnation processes for plywood, such as weak bonding between the flame retardant and the plywood, easy leaching and loss of water-soluble flame retardants in humid environments, and poor flame-retardant retention, this application provides a low-metal-corrosion flame-retardant plywood and its preparation method.

[0006] In a first aspect, this application provides a low-metal-corrosion flame-retardant plywood, comprising a substrate formed by alternating layers of modified veneer and resin; the method for preparing the modified veneer is as follows: The veneer was impregnated under pressure in a 0.05–0.2 mol / L aminosilane coupling agent solution and a 0.06–0.3 mol / L allyl salicylic aldehyde solution to obtain a vinyl-modified veneer. The vinyl-modified veneer is impregnated in a comonomer solution, an initiator is added, and a free radical copolymerization reaction is carried out by heating. The comonomer includes diethyl allyl phosphate and a vinyl nitrogen-containing heterocyclic compound. The concentrations of allyl phosphate diethyl ester and vinyl nitrogen-containing heterocycle in the copolymer monomer solution were 0.1–0.5 mol / L and 0.05–0.3 mol / L, respectively.

[0007] In any of the above technical solutions, the temperature for pressurized impregnation of the veneer in allyl salicylaldehyde solution is 55-65℃, the impregnation time is 2-3.5h, and the pH is 6-7 (adjusted with acetic acid).

[0008] In any of the above technical solutions, the solvent for the allyl salicylaldehyde solution is an ethanol-water mixture with a volume ratio of ethanol to water of 2 to 3:1.

[0009] In any of the above technical solutions, the solvent of the comonomer solution is an ethanol-water mixture with a volume ratio of ethanol to water of 1:1.

[0010] In any of the above technical solutions, the temperature of the free radical copolymerization reaction is 75-82°C, and the initiator concentration is 1%-3% of the total mass of the monomers.

[0011] In any of the above technical solutions, after the free radical copolymerization reaction, the single plate is impregnated under pressure in a metal ion solution with a concentration of 0.05-0.3 mol / L and an alkaline solution with a concentration of 0.1-0.5 mol / L.

[0012] In any of the above technical solutions, the metal ion is selected from Ca. 2+ Mg 2+ Al 3+ At least one of them.

[0013] In any of the above technical solutions, the pressure of the pressure impregnation is 1.1 to 1.5 MPa.

[0014] In any of the above technical solutions, the aminosilane coupling agent is selected from any one or more of γ-aminopropyltriethoxysilane (KH-550), γ-aminopropyltrimethoxysilane (A-1110), N-β-aminoethyl-γ-aminopropyltrimethoxysilane (KH-792), N-β-aminoethyl-γ-aminopropyltriethoxysilane (A-1120), γ-ureapropyltriethoxysilane (A-1160), γ-aminopropylmethyldimethoxysilane (KH-563), and N-phenyl-γ-aminopropyltrimethoxysilane (KH-580).

[0015] In any of the above technical solutions, the aminosilane coupling agent solution uses ethanol as a solvent.

[0016] In any of the above technical solutions, the vinyl nitrogen-containing heterocycle is selected from any one or more of vinylpyrrolidone, vinylimidazolium, and vinylpyridine.

[0017] This application introduces active amino groups onto veneer wood fibers using an aminosilane coupling agent, followed by an aldehyde-amine condensation reaction with an allyl salicylaldehyde solution, stabilizing the grafting of vinyl functional groups onto the veneer wood fibers. This modified veneer is then subjected to a free radical copolymerization reaction with a solution of comonomers containing allyl diethyl phosphate (a phosphorus-based flame retardant) and a vinyl nitrogen-containing heterocycle (a nitrogen-based flame retardant). In the reaction, the vinyl-modified veneer serves as the polymerization backbone, while the phosphorus / nitrogen flame retardant monomers form a three-dimensional network with the wood fibers through covalent bonds, solving the problem of easy loss caused by the physical adsorption of traditional flame retardants. In the resulting copolymer, the phosphate groups promote the formation of a char layer at high temperatures, and the nitrogen-containing heterocycles decompose to release inert gases that dilute oxygen, synergistically exerting a gas-phase-condensed-phase flame retardant mechanism.

[0018] Furthermore, after copolymerization, the veneer is impregnated with a metal ion solution. The metal ions form multidentate coordination complexes with the phosphate esters and nitrogen-containing heterocycles in the copolymer, creating a dense metal-organic coordination network. This network not only enhances the stability of the flame retardant but also strengthens the char layer through the catalytic char formation of metal oxides / hydroxides. Subsequent alkaline impregnation further optimizes the coordination structure and generates metal hydroxides (such as aluminum hydroxide) with residual metal ions. During combustion, these hydroxides decompose endothermically and release water vapor, further isolating heat and oxygen. In summary, the phosphorus-nitrogen-metal ternary synergistic system achieves deep anchoring and long-lasting effectiveness of the flame retardant within the wood through chemical bonding and coordination cross-linking.

[0019] More importantly, this invention anchors the flame-retardant components within the wood fiber network through robust chemical bonding and coordination cross-linking technology, preventing the flame retardant from coming into contact with the light steel keel and metal connectors in the building structure due to precipitation or migration. This not only completely eliminates the risk of electrochemical corrosion of metal materials by acidic flame retardant components, ensuring the service life and structural safety of metal components, but also ensures the long-term stability of the flame-retardant plywood's own performance, extending the service life of the entire building decoration system. Even in high-temperature or humid environments, the flame retardant will not leak from the board, thereby reducing safety hazards such as strength reduction and structural failure caused by corrosion of metal connectors.

[0020] In any of the above technical solutions, the comonomer solution contains 2-5 wt% alkenylsiloxane-modified silica.

[0021] In any of the above technical solutions, the alkenylsiloxane-modified silica is obtained by blending and modifying silica and alkenylsiloxane in a mass ratio of 100:5 to 10.

[0022] In any of the above technical solutions, the alkenylsiloxane is selected from any one or more of 3-acryloyloxypropyltrimethoxysilane, 3-acryloyloxypropyltriethoxysilane, 3-acryloyloxypropylmethyldimethoxysilane, vinyltrimethoxysilane, vinyltriethoxysilane, vinylmethyldimethoxysilane, and vinylmethyldiethoxysilane.

[0023] In any of the above technical solutions, the average particle size of the silicon dioxide is 1 to 30 micrometers, preferably 5 to 20 micrometers.

[0024] Adding alkenylsiloxane-modified silica to the comonomer solution allows the surface alkenyl groups to participate in free radical copolymerization, enabling the silica to be embedded in the copolymer network via chemical bonds. During high-temperature combustion, the modified silica undergoes a ceramic transformation on the char surface, generating a hard siloxane inorganic barrier layer. This ceramic layer, together with the expanded char layer formed by phosphorus-based flame retardants and the decomposition products of metal hydroxides (such as Al2O3), forms a synergistic barrier system involving physical isolation, catalytic char formation, and endothermic cooling. Specifically, the ceramic layer isolates oxygen and heat transfer, the phosphorus / nitrogen system promotes the formation of a dense char layer, and the endothermic decomposition of metal compounds lowers the combustion temperature. Simultaneously, the introduction of silica enhances the thermal stability of the copolymer, slows down the thermal degradation process, and further inhibits flame spread.

[0025] In any of the above technical solutions, the raw material of the resin layer is urea-formaldehyde resin, preferably melamine-modified urea-formaldehyde resin.

[0026] Melamine-modified urea-formaldehyde resin contains triazine rings, which have strong coordination ability. They can coordinate with the metal active centers of the complexes formed by the aforementioned impregnation, thereby enhancing the adhesion between the resin layer and the veneer, improving the stability of the complexed flame retardant, and improving the sustained flame retardant performance of the board.

[0027] Secondly, this application provides a method for preparing a low-metal-corrosion flame-retardant plywood. The method involves uniformly applying a resin adhesive to modified veneers to form a resin layer, according to the raw material composition of any of the plywoods described, and then stacking the adhesive-coated veneers to form a board blank. The board is then subjected to cold pressing and hot pressing sequentially. The cold pressing temperature is 20–30°C, the pressure is 0.6–1.0 MPa, and the time is 1–2 h; the hot pressing temperature is 100–120°C, the pressure is 0.8–1.2 MPa, and the time is 5–15 min.

[0028] The number of veneers in the plywood of this application can be stacked and compounded according to actual needs. Generally, 3-7 veneers are used to form a board blank. The surface of the plywood can be laminated with decorative materials such as high-temperature decorative film, engineered wood, and calcium silicate board.

[0029] In summary, this application has the following beneficial effects: This application utilizes the aldehyde-amine condensation of an aminosilane coupling agent and allyl salicylic aldehyde to construct vinyl active sites on the veneer, which are then copolymerized with phosphorus / nitrogen-containing flame-retardant monomers to form a chemically bonded three-dimensional flame-retardant network, fundamentally solving the problem of weak bonding and easy loss of flame retardants in the veneer. Subsequent metal ion coordination complexation and alkaline treatment form a phosphorus-nitrogen-metal ternary synergistic system, significantly improving the quality and thermal stability of the char layer. The introduced alkenylsiloxane-modified silica is copolymerized and transformed into a ceramic barrier layer at high temperatures, synergistically enhancing the heat insulation and smoke suppression performance with the organic flame-retardant system. The resulting low-metal-corrosion flame-retardant plywood possesses both long-lasting flame retention and a high flame-retardant rating, solving the problems of insufficient flame retardancy, poor flame retention, and corrosion of metal components in existing technologies. Detailed Implementation Preparation Example

[0030] Preparation Example 1: Alkenylsiloxane-modified silica was prepared by the following operation: Take 100g of silica with an average particle size of 10μm, 7.5g of 3-acryloyloxypropyltrimethoxysilane, and 300mL of anhydrous ethanol.

[0031] Silica was dried at 105℃ for 2 hours to remove adsorbed water. The dried silica was dispersed in anhydrous ethanol, and the mixture was stirred and heated to 75℃ under nitrogen protection. 3-Acryloyloxypropyltrimethoxysilane was slowly added dropwise over 30 minutes, and the reaction was maintained at 75℃ for 3 hours. The reaction solution was cooled to room temperature, and the solid was collected by filtration. The solid was washed twice with anhydrous ethanol and twice with water to remove unreacted silane. The silica was then dried under vacuum at 60℃ for 12 hours to obtain alkenylsiloxane-modified silica.

[0032] Preparation Example 2: Alkenylsiloxane-modified silica was prepared by the following operation: Take 100g of silica with an average particle size of 5μm, 5g of 3-acryloyloxypropyltrimethoxysilane, and 250mL of anhydrous ethanol.

[0033] Silica was dried at 105℃ for 3 hours to remove adsorbed water. The dried silica was dispersed in anhydrous ethanol, and the mixture was stirred and heated to 70℃ under nitrogen protection. Vinyltrimethoxysilane was slowly added dropwise over 30 minutes, and the reaction was maintained at 70℃ for 2 hours. The reaction solution was cooled to room temperature, and the solid was collected by filtration. The solid was washed twice with anhydrous ethanol and twice with water to remove unreacted silane. The silica was then dried under vacuum at 65℃ for 10 hours to obtain alkenylsiloxane-modified silica.

[0034] Preparation Example 3: Alkenylsiloxane-modified silica was prepared by the following operation: Take 100g of silica with an average particle size of 20μm, 10g of 3-acryloyloxypropyltriethoxysilane, and 350mL of anhydrous ethanol.

[0035] Silica was dried at 115℃ for 2 hours to remove adsorbed water. The dried silica was dispersed in anhydrous ethanol, and the mixture was stirred and heated to 75℃ under nitrogen protection. 3-Acryloyloxypropyltriethoxysilane was slowly added dropwise over 30 minutes, and the reaction was maintained at 80℃ for 3 hours. The reaction solution was cooled to room temperature, and the solid was collected by filtration. The solid was washed twice with anhydrous ethanol and twice with water to remove unreacted silane. The silica was then dried under vacuum at 70℃ for 12 hours to obtain alkenylsiloxane-modified silica.

[0036] Preparation Example 4, modified silica, differs from Preparation Example 1 in that an equal amount of aminopropyltrimethoxysilane is used to replace 3-acryloyloxypropyltrimethoxysilane. Example

[0037] Example 1: A low-metal-corrosion flame-retardant plywood was prepared by the following steps: Preparation of modified single-layer boards: Immerse eucalyptus veneer (2.6 mm thick) in 0.1 mol / L KH-550 ethanol solution and impregnate at 1.2 MPa for 1 hour. Drain the solution and remove the veneer to drain.

[0038] Remove the veneer and immerse it in a 0.18 mol / L 3-allyl salicylaldehyde solution (the solvent is a mixture of ethanol and water, ethanol:water = 2.5:1). Adjust the pH to 6.5 with acetic acid, and then immerse it at 60℃ / 1.3MPa for 3 hours. Drain the solution, remove the veneer and drain it to obtain the vinyl-modified veneer.

[0039] Prepare an ethanol-water mixture (ethanol:water = 1:1) containing 0.3 mol / L allyl phosphate diethyl ester, 0.18 mol / L vinylpyrrolidone, and 3.5 wt% of the alkenylsiloxane-modified silica obtained in Preparation Example 1. Then immerse the vinyl-modified veneer in the comonomer solution. Add 2% by weight of ammonium persulfate of the total monomers (allyl phosphate diethyl ester, vinylpyrrolidone, and alkenylsiloxane-modified silica), and react at 80°C for 4 hours under nitrogen protection. After the reaction, drain the solution, remove the veneer, and drain. After copolymerization, the veneer is immersed in a 0.18 mol / L aluminum chloride solution under pressure of 1.3 MPa for 1.5 hours, then the solution is drained, and the wood is removed and drained. The veneer is then immersed in a 0.3 mol / L NaOH solution under pressure of 1.3 MPa for 1.5 hours, the solution is drained, and the wood is removed and drained. Finally, the wood is rinsed with tap water 3-5 times and dried at 60℃ until the moisture content is 8%, yielding the modified veneer.

[0040] Plywood preparation: Melamine-modified urea-formaldehyde resin (MUF-230, solid content 50%) was uniformly applied to the surface of the modified veneer, with a double-sided application rate of 220 g / m². 2After gluing, the grain direction of the veneer wood is crisscrossed. Three veneers are combined to form a board blank. After cold pressing (temperature 25℃, pressure 0.8MPa, time 1.5h) and hot pressing (temperature 110℃, pressure 1.0MPa, time 10min), low metal corrosion flame retardant plywood is obtained.

[0041] Example 2: A low-metal-corrosion flame-retardant plywood was prepared according to the following steps: Preparation of modified single-layer boards: Immerse eucalyptus veneer (2.6 mm thick) in 0.06 mol / L A-1110 ethanol solution and impregnate at 1.1 MPa for 1 hour. Drain the solution and remove the veneer to drain.

[0042] Remove the veneer and immerse it in a 0.08 mol / L 3-allyl salicylaldehyde solution (the solvent is a mixture of ethanol and water, ethanol:water = 2:1). Adjust the pH to 6 with acetic acid, and then immerse it at 55℃ / 1.1MPa for 2.5 h. Drain the solution, remove the veneer and drain it to obtain the vinyl-modified veneer.

[0043] Prepare an ethanol-water mixture (ethanol:water = 1:1) containing 0.12 mol / L allyl phosphate diethyl ester, 0.06 mol / L vinylimidazole, and 2.2 wt% of the alkenylsiloxane-modified silica obtained in Preparation Example 2. Then immerse the vinyl-modified veneer in the comonomer solution. Add 1.5% by weight of potassium persulfate (total mass of monomers (allyl phosphate diethyl ester, vinylpyrrolidone, and alkenylsiloxane-modified silica) and react at 75°C for 3 hours under nitrogen protection. After the reaction, drain the solution, remove the veneer, and drain. After copolymerization, the veneer is immersed in a 0.06 mol / L magnesium chloride solution under pressure of 1.1 MPa for 1 hour, the solution is drained, and the wood is removed and drained. The veneer is then immersed in a 0.12 mol / L NaOH solution under pressure of 1.1 MPa for 0.5 hours, the solution is drained, and the wood is removed and drained. Finally, the wood is rinsed with tap water 3-5 times and dried at 60℃ until the moisture content is 7%, yielding the modified veneer.

[0044] Plywood preparation: Melamine-modified urea-formaldehyde resin (MUF-230, solid content 50%) was uniformly applied to the surface of the modified veneer, with a double-sided application rate of 220 g / m². 2 After gluing, the grain direction of the veneer wood is crisscrossed. Three veneers are combined to form a board blank. After cold pressing (temperature 25℃, pressure 0.8MPa, time 1.5h) and hot pressing (temperature 110℃, pressure 1.0MPa, time 10min), low metal corrosion flame retardant plywood is obtained.

[0045] Example 3: A low-metal-corrosion flame-retardant plywood was prepared according to the following steps: Preparation of modified single-layer boards: Immerse eucalyptus veneer (2.6 mm thick) in 0.2 mol / L KH-792 ethanol solution, pressurize at 1.5 MPa for 1.5 h, drain the solution, and remove the veneer to drain.

[0046] Remove the veneer and immerse it in a 0.28 mol / L 3-allyl salicylaldehyde solution (the solvent is a mixture of ethanol and water, ethanol:water = 3:1). Adjust the pH to 6 with acetic acid, and then immerse it at 65℃ / 1.5MPa for 3.5 h. Drain the solution, remove the veneer and drain it to obtain the vinyl-modified veneer.

[0047] Prepare an ethanol-water mixture (ethanol:water = 1:1) containing 0.5 mol / L allyl phosphate diethyl ester, 0.28 mol / L vinylpyrrolidone, and 5 wt% of the alkenylsiloxane-modified silica obtained in Preparation Example 3. Then immerse the vinyl-modified veneer in the comonomer solution. Add 3% by weight of ammonium persulfate of the total monomers (allyl phosphate diethyl ester, vinylpyrrolidone, and alkenylsiloxane-modified silica), and react at 80°C for 5 hours under nitrogen protection. After the reaction, drain the solution, remove the veneer, and drain. After copolymerization, the veneer is immersed in a 0.3 mol / L aluminum chloride solution under pressure of 1.5 MPa for 1.5 hours, the solution is drained, and the wood is removed and drained. The veneer is then immersed in a 0.5 mol / L NaOH solution under pressure of 1.5 MPa for 1 hour, the solution is drained, and the wood is removed and drained. Finally, the wood is rinsed with tap water 3-5 times and dried at 60℃ until the moisture content is 8%, yielding the modified veneer.

[0048] Plywood preparation: Melamine-modified urea-formaldehyde resin (MUF-230, solid content 50%) was uniformly applied to the surface of the modified veneer, with a double-sided application rate of 320 g / m². 2 After gluing, the grain direction of the veneer wood is crisscrossed. Three veneers are combined to form a board blank. After cold pressing (temperature 30℃, pressure 1.0MPa, time 2h) and hot pressing (temperature 120℃, pressure 1.2MPa, time 15min), low metal corrosion flame retardant plywood is obtained.

[0049] Example 4, a low-metal-corrosion flame-retardant plywood, differs from Example 1 in that alkenylsiloxane-modified silica is not added to the comonomer solution.

[0050] Example 5, a low-metal-corrosion flame-retardant plywood, differs from Example 1 in that, after the copolymerization reaction, the veneers are not immersed in aluminum chloride solution and sodium hydroxide solution; the low-metal-corrosion flame-retardant plywood is obtained immediately after the copolymerization reaction. Comparative Example

[0051] Comparative Example 1, a low-metal-corrosion flame-retardant plywood, differs from Example 5 in that an equal amount of diethyl allyl phosphate is used instead of vinylpyrrolidone in the comonomer solution.

[0052] Comparative Example 2, a low-metal-corrosion flame-retardant plywood, differs from Example 5 in that, in the comonomer solution, an equal amount of vinylpyrrolidone is used instead of diethyl allyl phosphate.

[0053] Comparative Example 3, a low-metal-corrosion flame-retardant plywood, differs from Example 1 in that a 0.18 mol / L allyl phosphate diethyl ester solution (ethanol and water mixture, ethanol:water = 2.5:1) is used instead of a 0.18 mol / L 3-allyl salicylaldehyde solution (ethanol and water mixture, ethanol:water = 2.5:1).

[0054] Comparative Example 4, a low-metal-corrosion flame-retardant plywood, was prepared by the following method: Preparation of modified single-layer boards: Eucalyptus veneer (2.6 mm thick) was immersed in a 1 mol / L ammonium polyphosphate (XS-APPII-040) aqueous solution and impregnated at 1.2 MPa for 2 hours. The solution was drained, and the veneer was removed and drained. The wood was rinsed with tap water 3-5 times and dried at 60℃ until the moisture content was 8% to obtain modified veneer.

[0055] Plywood preparation: Melamine-modified urea-formaldehyde resin (MUF-230, solid content 50%) was uniformly applied to the surface of the modified veneer, with a double-sided application rate of 220 g / m². 2 After gluing, the grain direction of the veneer wood is crisscrossed. Three veneers are combined to form a board blank. After cold pressing (temperature 25℃, pressure 0.8MPa, time 1.5h) and hot pressing (temperature 110℃, pressure 1.0MPa, time 10min), low metal corrosion flame retardant plywood is obtained.

[0056] Comparative Example 5: A type of plywood was prepared according to the following method: Melamine-modified urea-formaldehyde resin (MUF-230, 50% solids content) was applied evenly to the surface of eucalyptus veneer (2.6mm thick), with a double-sided application rate of 220g / m². 2 After gluing, the grain direction of the veneer wood is crisscrossed. Three veneers are combined to form a board blank. After cold pressing (temperature 25℃, pressure 0.8MPa, time 1.5h) and hot pressing (temperature 110℃, pressure 1.0MPa, time 10min), ordinary plywood is obtained. Performance testing

[0057] Test 1: Flame Retardant Performance (LOI) Test The test was conducted according to GB / T 2406.2-2009, "Determination of Combustion Behavior by Oxygen Index Method for Plastics - Part 2: Room Temperature Test". Samples measuring 100mm × 10mm × 2.6mm were cut from the low-metal corrosion flame-retardant plywood samples of the examples and comparative examples. The samples were vertically fixed in the combustion chamber of the oxygen indexer, and a nitrogen-oxygen mixture (flow rate 10 L / min) was introduced. The top of the sample was ignited, and the minimum oxygen concentration (accurate to 0.1%) required for a combustion damage length of 50mm was recorded. The test was repeated until a stable LOI value was obtained, which was recorded as the initial LOI. Five parallel samples were tested in each group, and the average value was taken.

[0058] Test 2: Test of sustained flame retardant performance Accelerated aging was conducted according to Chapter 4.26 "Resistance to Damp Heat Cycling" of GB / T 17657-2022 "Test Methods for Physical and Chemical Properties of Wood-based Panels and Decorative Wood-based Panels". Aging test conditions: Damp heat cycling: 70℃ / 95%RH treatment for 12h → drying at 40℃ for 12h constitutes one cycle, with a total of 15 cycles (simulating a 5-year service environment). After damp heat cycling, the LOI of the samples was tested according to Test 1 method and recorded as the LOI after damp heat aging. The flame retardant retention rate was calculated as follows: LOI retention rate (%) = (LOI after aging / Initial LOI) × 100.

[0059] Experiment 3: Metal Corrosion Rate Test Experimental steps: (1) Specimen preparation Prepare dimensions 80×40×9mm 3 The plywood was tested, and a metal sheet measuring 50×25×1.5mm was used. The metal sheet was made of carbon steel (Q235). The metal sheet was cleaned of grease with a 1:1 mixture of ethanol and acetone, and then wiped clean with paper towels. The metal sheet was then dried at 40℃ for 1 hour, weighed, and recorded as m1. It was then placed in a desiccator for later use.

[0060] (2) Corrosion test Plywood was kept in a constant temperature and humidity chamber (50℃, 90% humidity) for 3 days. A metal sheet was placed between two pieces of plywood and fixed with screws to prepare a rust sample. The samples were then treated in a constant temperature and humidity chamber (50℃, 90% humidity), with one group exposed for 360 hours and the other for 720 hours. The metal samples were then removed, rinsed with clean water, and gently brushed with a nylon brush to remove loose corrosion products from the sample surface. The metal sheet was chemically cleaned with a metal cleaning solution, and then gently scrubbed with a nylon brush until no corrosion products were left on the metal surface. The metal sheet was rinsed with pure water 3-6 times, and then dried in a 40℃ oven for 12 hours. The mass of the metal sheet was measured and recorded as m2'.

[0061] (3) Control group experiment Clean the metal sheet with a 1:1 mixture of ethanol and acetone to remove grease, then wipe it clean with paper towels. Dry the metal sheet at 40°C for 1 hour, weigh it, and record its mass as m3. Place it in a desiccator for later use. Chemically clean the metal sheet with a metal cleaning solution, then gently scrub with a nylon brush until no corrosion products remain on the metal surface. Rinse the metal sheet 3-6 times with pure water, then dry it in a 40°C oven for 12 hours. Weigh the metal sheet and record its mass as m4.

[0062] Calculate the mass loss of the control group: Δm = m3 - m4.

[0063] (4) Corrosion rate calculation Mass of the metal sheet after corrosion: m2 = m2' + Δm Corrosion rate of metal sample: R = C × (m1 - m2) / (A × T × D) R—corrosion rate, in micrometers per year (μm / a), accurate to 0.01 μm / a; C—Conversion constant, C=8.76×10 7 (h·μm) / (a·cm); The mass of the metal sample before corrosion, expressed in grams (g). m2—The mass of the metal sample after corrosion, in grams (g); A—Metal contact surface area, in square centimeters (cm²) 2 ); T—Exposure time, in hours (h); D—Metal density, measured in grams per cubic centimeter (g / cm³) 3 ).

[0064] Table 1. Performance Test Results

[0065] Analysis of experimental results: Example 4 (without the addition of alkenylsiloxane-modified silica in the copolymerization reaction) showed a decrease in both the initial LOI and LOI retention rate compared to Example 1, while the metal corrosion rate increased slightly. This may be because the copolymer product lacks silica, preventing the formation of a ceramicized physical barrier layer during combustion and reducing the efficiency of phase condensation barrier. Simultaneously, the absence of the hydrophobic effect of modified SiO2 makes the flame retardant prone to loss in humid and hot environments.

[0066] In Example 5 (without metal ion / alkali treatment), both the initial LOI and LOI retention rate decreased to some extent, while the metal corrosion rate increased. This may be because the veneer was not immersed in a metal ion solution, preventing the formation of a phosphorus-nitrogen-metal coordination network and resulting in the lack of endothermic decomposition and catalytic char formation by metal hydroxides. Simultaneously, the flame retardant lacked coordination cross-linking anchoring, leading to a decrease in the anchoring effect of the flame retardant components and exacerbating metal corrosion.

[0067] Comparative Example 1 (without nitrogen-based flame-retardant monomers in the copolymerization reaction) showed a significant decrease in initial LOI. This may be due to the absence of a nitrogen-containing heterocyclic gas-phase flame-retardant mechanism (oxygen dilution / free radical blocking), leading to the breakdown of the phosphorus-nitrogen synergistic effect, and low char formation efficiency relying solely on phosphorus-based monomers. Comparative Example 2 (without phosphorus-based flame-retardant monomers in the copolymerization reaction) also showed a significant decrease in initial LOI. This may be due to the absence of the catalytic dehydration and char formation function of phosphate esters, resulting in the failure of condensed-phase flame retardancy and accelerated flame spread during combustion. Comparative Example 3 (without allyl salicylic acid) showed a certain decrease in initial LOI due to the absence of aldehyde-amine condensation, but the decrease in LOI retention was more significant, and the metal corrosion rate increased significantly. This may be because the vinyl active sites were not constructed through aldehyde-amine condensation; the flame-retardant copolymer was only adsorbed onto the fiber surface through physical action, resulting in a decrease in the effective flame-retardant components and their anchoring ability, and more severe metal corrosion.

[0068] Comparative Example 4 (direct impregnation with flame retardant solution) showed a significant decrease in both initial LOI and LOI retention rate, and a significant increase in metal corrosion rate. This may be because ammonium polyphosphate (APP) only physically fills the pores and cannot form chemical bonds with wood fibers, making it prone to migration and dissolution. This results in a high loss rate under humid and hot conditions, a rapid decline in flame retardant performance, and a sharp increase in metal corrosion.

[0069] This specific embodiment is merely an explanation of this application and is not intended to limit it. After reading this specification, those skilled in the art can make modifications to this embodiment without contributing any inventive step, but such modifications are protected by patent law as long as they fall within the scope of the claims of this application.

Claims

1. A low-metal-corrosion flame-retardant plywood, characterized in that, The substrate comprises a modified veneer and a resin layer alternately stacked; the modified veneer is prepared by the following method: The veneer was impregnated under pressure in a 0.05–0.2 mol / L aminosilane coupling agent solution and a 0.06–0.3 mol / L allyl salicylic aldehyde solution to obtain a vinyl-modified veneer. The vinyl-modified veneer is impregnated in a comonomer solution, an initiator is added, and a free radical copolymerization reaction is carried out by heating. The comonomer includes diethyl allyl phosphate and a vinyl nitrogen-containing heterocyclic compound. The concentrations of allyl phosphate diethyl ester and vinyl nitrogen-containing heterocycle in the copolymer monomer solution were 0.1–0.5 mol / L and 0.05–0.3 mol / L, respectively.

2. The low-metal-corrosion flame-retardant plywood according to claim 1, characterized in that, After the free radical copolymerization reaction, the veneer is impregnated under pressure in a metal ion solution with a concentration of 0.05–0.3 mol / L and an alkaline solution with a concentration of 0.1–0.5 mol / L.

3. The low-metal-corrosion flame-retardant plywood according to claim 2, characterized in that, The metal ion is selected from Ca. 2+ Mg 2+ Al 3+ At least one of them.

4. The low-metal-corrosion flame-retardant plywood according to claim 1, characterized in that, The pressure for the pressure impregnation is 1.1 to 1.5 MPa.

5. The low-metal-corrosion flame-retardant plywood according to claim 1, characterized in that, The comonomer solution contains 2-5 wt% alkenylsiloxane-modified silica.

6. The low-metal-corrosion flame-retardant plywood according to claim 5, characterized in that, The alkenylsiloxane-modified silica is obtained by blending silica and alkenylsiloxane in a mass ratio of 100:5 to 10.

7. The low-metal-corrosion flame-retardant plywood according to claim 5, characterized in that, The alkenylsiloxane is selected from any one or more of 3-acryloyloxypropyltrimethoxysilane, 3-acryloyloxypropyltriethoxysilane, 3-acryloyloxypropylmethyldimethoxysilane, vinyltrimethoxysilane, vinyltriethoxysilane, vinylmethyldimethoxysilane, and vinylmethyldiethoxysilane.

8. The low-metal-corrosion flame-retardant plywood according to claim 1, characterized in that, The vinyl nitrogen-containing heterocycle is selected from any one or more of vinylpyrrolidone, vinylimidazolium, and vinylpyridine.

9. The low-metal-corrosion flame-retardant plywood according to claim 1, characterized in that, The raw material for the resin layer is melamine-modified urea-formaldehyde resin.

10. A method for preparing a low-metal-corrosion flame-retardant plywood, characterized in that, According to the raw material composition of the plywood according to any one of claims 1 to 9, a resin adhesive is used to uniformly apply resin to the modified veneer to form a resin layer, and the glued veneers are stacked together to form a board blank, which is then subjected to cold pressing and hot pressing in sequence. The cold pressing temperature is 20-30℃, the pressure is 0.6-1.0MPa, and the time is 1-2h, and the hot pressing temperature is 100-120℃, the pressure is 0.8-1.2MPa, and the time is 5-15min.

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