Water-resistant enhanced magnesia-chloride cement composite plywood

Abstract

The application discloses a water-resistant reinforced magnesia-chloride cement composite plywood and a preparation method thereof. The composite plywood comprises, from top to bottom, a first waterproof wear-resistant surface layer, an upper glass fiber mesh reinforcement layer, a magnesia-chloride cement wood composite core layer, a lower glass fiber mesh reinforcement layer and a second waterproof wear-resistant surface layer. The core layer is formed by a plurality of wood veneers which are cross-laminated with the fiber directions of adjacent layers being perpendicular to each other, and then impregnated with a modified magnesia-chloride cement slurry containing calcined serpentine superfine powder and aluminum dihydrogen phosphate, and hot-pressed and cured. The alkali-resistant glass fiber mesh is partially embedded in the surface layer and partially embedded in the interface slurry layer of the core layer. The application can improve the water resistance, dimensional stability and interlayer bonding strength of the plywood.

Description

Technical Field

[0001] This invention relates to the field of building materials technology, specifically to a water-resistant reinforced magnesium oxychloride cement composite plywood. Background Technology

[0002] Plywood is one of the most commonly used engineered wood products in the construction, decoration, and furniture manufacturing industries. Traditional plywood is mostly made by applying organic adhesives such as urea-formaldehyde resin, phenolic resin, or melamine-formaldehyde resin, followed by gluing, assembly, and hot pressing. These organic adhesives have problems such as the release of free formaldehyde, insufficient fire resistance, and easy hydrolysis of the adhesive layer in humid environments, leading to delamination of the plywood. Therefore, they fail to meet the environmental and safety performance requirements of standards such as GB / T 39600-2021 and GB 18580-2017.

[0003] Magnesium oxychloride cement (MOC) is an air-hardening inorganic cementitious material formed by the reaction of active magnesium oxide and magnesium chloride aqueous solution. Its main hydration products are 5·1·8 and 3·1·8 phase crystals. Compared with organic adhesives, MOC has advantages such as being formaldehyde-free, having high early strength, being fire-retardant, having good bonding performance with wood fibers, and having a hardened body pH value similar to wood, making it valuable in the field of wood composite materials. However, MOC also has the following drawbacks: the 5·1·8 phase has a certain solubility in water, resulting in a low wet strength retention rate after the board comes into contact with water; excess magnesium chloride easily migrates to the surface of the board with water, forming efflorescence and blooming; and the crystal transformation of the hydration products is accompanied by volume changes, affecting the dimensional stability of the board.

[0004] To address the aforementioned issues, existing technologies have made improvements in both formulation modification and structural design. Regarding formulation modification, previous studies have employed modifiers such as phosphates, nano-silica, and metakaolin to improve the water resistance of magnesium oxychloride cement. For example, CN116574452B discloses a magnesium oxychloride adhesive modified with a phosphate-nano-silica-calcium chloride-isocyanate-EVA emulsion composite, and uses cold pressing to prepare inorganic plywood. However, the resulting plywood has a homogeneous multi-layered wood structure and lacks a dedicated waterproof and wear-resistant functional layer on the surface; the interlayer bonding relies primarily on the physical adhesion of the adhesive. In terms of structural design, CN108117368A discloses a formaldehyde-free flame-retardant flooring made by alternating layers of magnesium oxychloride cement slurry with wood chips, straw chips, and fiberglass mesh, and hot-pressed. The raw materials are mainly pulverized materials, the board has a homogeneous structure, and the fiberglass mesh is completely encapsulated in the slurry, primarily serving a crack-resistant function. CN115745562B discloses a magnesium oxide fireproof board with an asymmetrical structure of alternating layers of ordinary fiberglass cloth and slurry, where the fiberglass cloth and slurry are mainly bonded by surface physical adhesion. These solutions still have room for improvement in terms of water resistance, dimensional stability, and interlayer bonding strength.

[0005] Therefore, how to further improve the water resistance, dimensional stability and interlayer bonding of the board through reasonable design of macrostructure and interface construction, while retaining the advantages of magnesium oxychloride cement such as being formaldehyde-free and fire-retardant, is a technical problem that needs to be solved in this field. Summary of the Invention

[0006] Based on the problems existing in the background technology, the present invention provides a water-resistant reinforced magnesium oxychloride cement composite plywood with reasonable structural design, excellent water resistance, good dimensional stability, and strong interlayer bonding, so as to solve the technical problems of poor water resistance, easy warping and deformation, insufficient interlayer bonding and single surface function that are common in existing magnesium oxychloride cement-based plywood.

[0007] To achieve the above objectives, the present invention provides a water-resistant reinforced magnesium oxychloride cement composite plywood, comprising, from top to bottom, a first waterproof and wear-resistant surface layer, an upper glass fiber mesh reinforcement layer, a magnesium oxychloride cement wood composite core layer, a lower glass fiber mesh reinforcement layer, and a second waterproof and wear-resistant surface layer.

[0008] Both the first and second waterproof and wear-resistant surface layers are formed by curing a first modified magnesium oxychloride cement slurry containing nano-calcium carbonate, organosilicon waterproofing agent and inorganic pigments. The two have the same material composition and equal thickness after curing.

[0009] The magnesium oxychloride cement-wood composite core layer includes multiple layers of wood veneer and a second modified magnesium oxychloride cement slurry cured matrix that fills the pores, conduits and interlayers of the wood veneer surface. The fiber directions of adjacent wood veneers in the multiple layers are perpendicular to each other. The second modified magnesium oxychloride cement slurry contains calcined serpentine ultrafine powder and aluminum dihydrogen phosphate.

[0010] The upper and lower surfaces of the magnesium oxychloride cement-wood composite core layer are provided with an interface slurry layer formed by the second modified magnesium oxychloride cement slurry.

[0011] Both the upper and lower glass fiber mesh reinforcement layers are alkali-resistant glass fiber meshes with square mesh openings, and are respectively disposed between the interface slurry layer on the upper surface of the first waterproof and wear-resistant surface layer and the interface slurry layer on the lower surface of the core layer, and between the second waterproof and wear-resistant surface layer and the lower surface of the core layer. The two are arranged symmetrically above and below the magnesium oxychloride cement-wood composite core layer.

[0012] A portion of the thickness of the alkali-resistant glass fiber mesh is embedded in the corresponding waterproof and wear-resistant surface layer, and another portion of the thickness is embedded in the corresponding interface slurry layer. The waterproof and wear-resistant surface layer and the corresponding interface slurry layer are interconnected through the mesh openings of the mesh and are cured into one piece.

[0013] In the five-layer composite structure of the present invention, a triple synergistic mechanism of "structural symmetry + interface interlocking + skeleton reinforcement" is formed between the layers: First, the structural symmetry mechanism: the first and fifth layers are made of the same material and are arranged symmetrically with equal thickness, while the second and fourth layers are arranged symmetrically with the same mesh fabric. The entire board forms a completely symmetrical laminated structure in the thickness direction with the geometric center plane of the third layer as the neutral plane. This makes the internal stress generated on both sides of the board equal in magnitude, opposite in direction, and cancel each other out when the board absorbs moisture and expands or dries and shrinks. From the structural design level, this significantly reduces the risk of warping deformation caused by the stress difference on both sides in asymmetrical laminated boards.

[0014] Second, the interface interlocking mechanism: The alkali-resistant glass fiber mesh used in the second and fourth layers has a mesh size of 5mm×5mm—this size was determined through experimental optimization. If the mesh is too small (e.g., below 3mm×3mm), the slurry cannot fully penetrate the mesh openings, the slurry on both sides cannot effectively connect, and the mechanical interlocking effect is not significant. If the mesh is too large (e.g., above 10mm×10mm), the number of warp and weft yarn intersections per unit area of ​​the mesh is too small, and the reinforcing effect is weakened. With a mesh size of 5mm×5mm, each square meter of mesh has approximately 40,000 square mesh openings. Under the molding pressure, the surface layer slurry and the core layer slurry enter the mesh openings from the top and bottom of the mesh respectively and converge and fuse within the openings. After curing, a small "cement rivet" is formed in each mesh opening—that is, the surface layer, mesh, and core layer form a microscopic mechanical locking node at each mesh opening position. The collection of tens of thousands of such nodes creates a continuous and dense through-type mechanical interlocking interface between the surface layer and the core layer. This interfacial bonding method is fundamentally different from the weak interfacial bonding method of traditional glass fiber cloth, which relies solely on the physical wetting and adhesion of the slurry to the fiber surface. The latter makes the interface a weak path for crack initiation and propagation when the board is bent or damp. The mechanical interlocking interface of this invention makes interlayer failure only occur by shearing the solidified slurry column (rather than interface peeling), which greatly improves the interfacial bonding strength and interface failure toughness.

[0015] Third, the skeletal reinforcement mechanism: In the third layer, layers 3-9 of wood veneer are cross-assembled with adjacent layers having their fiber directions perpendicular (orthogonal). Modified magnesium oxychloride cement slurry fully impregnates and fills the surface cracks, vascular cavities, and cell wall gaps of the wood veneer before hot-pressing and curing. The oriented fibers of the wood veneer provide the board with a directional reinforcement skeleton similar to the "reinforcing steel" in reinforced concrete—the wood veneer along the fiber direction bears bending tensile stress, while the modified magnesium oxychloride cement-cured matrix bears compressive stress and interlaminar shear stress, complementing each other in mechanical properties. The perpendicular assembly of adjacent fiber layers gives the board high bending stiffness and strength in both the 0° and 90° principal directions, overcoming the deficiency of insufficient strength in the perpendicular fiber direction of unidirectional fiber-reinforced boards. Simultaneously, the calcined serpentine ultrafine powder in the modified magnesium oxychloride cement slurry forms a dual water-resistant modification of "matrix densification + crystal surface passivation" with aluminum dihydrogen phosphate: the phosphate ions in aluminum dihydrogen phosphate react with Mg... 2+ The reaction generates a coating layer of insoluble magnesium phosphate (MgHPO4·3H2O) on the surface of the 5·1·8 phase crystal, which chemically prevents water molecules from eroding the crystal. The active MgO released by the calcined serpentine ultrafine powder participates in the hydration reaction of the 5·1·8 phase. Amorphous SiO2 undergoes a pozzolanic reaction in an alkaline environment to generate magnesium silicate hydrate (MSH) gel, which fills the capillary pores and interfacial transition zone of the hardened slurry, thereby reducing the total porosity of the matrix and the most probable pore size, and physically hindering the penetration and transport of liquid water into the matrix. At the same time, the fine particles of the calcined serpentine ultrafine powder provide a large number of non-uniform nucleation sites, promoting the refinement and homogenization of the 5·1·8 phase crystal and reducing the micro-cracks associated with coarse needle-like crystals.

[0016] Preferably, the alkali-resistant glass fiber mesh has a mesh size of 5mm × 5mm; 40%-60% of the thickness of the alkali-resistant glass fiber mesh is embedded in the corresponding waterproof and wear-resistant surface layer, and the remaining portion is embedded in the corresponding interface slurry layer. With this mesh size, each square meter of mesh has approximately 40,000 square mesh openings, facilitating the entry of the surface layer slurry and the core layer interface slurry into the mesh openings from both sides of the mesh, where they converge, fuse, and solidify into a single unit. The 40%-60% embedding ratio ensures that the mesh forms a balanced anchorage on both sides of the surface layer and the core layer interface slurry layer.

[0017] Preferably, the calcined serpentine ultrafine powder is obtained by calcining natural serpentine (Mg3Si2O5(OH)4) at 650-750℃ for 1-2 hours and then pulverizing it, with a fineness of 1250-2000 mesh; the amount of the calcined serpentine ultrafine powder is 10%-20% of the mass of light-burned magnesium oxide added to the second modified magnesium oxychloride cement slurry, and the amount of aluminum dihydrogen phosphate (Al(H2PO4)3) is 1.5%-3% of the mass of light-burned magnesium oxide added to the second modified magnesium oxychloride cement slurry.

[0018] Preferably, the nano-calcium carbonate has a particle size of 50-100 nm and is added at a dosage of 5%-12% of the mass of lightly calcined magnesium oxide in the first modified magnesium oxychloride cement slurry; the organosilicon waterproofing agent is an aqueous solution of sodium methylsilicate or potassium methylsilicate, and is added at a dosage of 2%-5% of the mass of lightly calcined magnesium oxide in the first modified magnesium oxychloride cement slurry; the inorganic pigment is an iron oxide pigment, including iron oxide red, iron oxide yellow, iron oxide black or mixtures thereof, and is added at a dosage of 5%-10% of the mass of lightly calcined magnesium oxide in the first modified magnesium oxychloride cement slurry.

[0019] Preferably, the wood veneer is poplar rotary-cut veneer or eucalyptus rotary-cut veneer, with a thickness of 1.5-3.0 mm and a moisture content of 8%-12%. The magnesium oxychloride cement-wood composite core layer is formed by cross-assembling 3, 5, 7, or 9 layers of the aforementioned wood veneer, with the fiber direction of each layer of wood veneer arranged alternately in the longitudinal and transverse directions from bottom to top, and the fiber direction of the bottom and top layers being longitudinal. This moisture content range is beneficial for the wetting and absorption of the second modified magnesium oxychloride cement slurry by the wood veneer.

[0020] Preferably, the alkali-resistant glass fiber mesh has a ZrO2 content of not less than 16.5% and a unit area mass of 120-180 g / m². 2 The thickness is 0.3-0.6mm.

[0021] Preferably, the thickness of the first waterproof and wear-resistant surface layer and the second waterproof and wear-resistant surface layer after curing is 2.0-4.0 mm; the thickness of the magnesium oxychloride cement-wood composite core layer is 6-18 mm; the total thickness of the plywood is 10-25 mm; and the ratio of the thickness of the first waterproof and wear-resistant surface layer to the thickness of the magnesium oxychloride cement-wood composite core layer is 1:3 to 1:9.

[0022] To achieve the above objectives, the present invention also provides a method for preparing the above-mentioned water-resistant reinforced magnesium oxychloride cement composite plywood, comprising the following steps: S1. Prepare a second modified magnesium oxychloride cement slurry containing calcined serpentine ultrafine powder and aluminum dihydrogen phosphate, and a first modified magnesium oxychloride cement slurry containing nano calcium carbonate, organosilicon waterproofing agent and inorganic pigment. S2. Immerse the multi-layer wood veneers in the second modified magnesium oxychloride cement slurry, remove them and scrape off the excess slurry on the surface; assemble the impregnated wood veneers in a manner where the fiber directions of adjacent wood veneers are perpendicular to each other, and hot-press and cure them at a temperature of 130-150℃ and a unit pressure of 2.5-3.0MPa to obtain a magnesium oxychloride cement wood composite core layer. S3. The second modified magnesium oxychloride cement slurry is coated on the upper and lower surfaces of the magnesium oxychloride cement-wood composite core layer to form an interface slurry layer. S4. The first modified magnesium oxychloride cement slurry and the lower glass fiber mesh are sequentially laid at the bottom of the molding mold, so that a portion of the thickness of the lower glass fiber mesh is embedded in the first modified magnesium oxychloride cement slurry on the lower side; the magnesium oxychloride cement wood composite core layer obtained in step S3 is placed on the lower glass fiber mesh, so that the interface slurry layer on the lower surface of the core layer is in contact with the lower glass fiber mesh; the upper glass fiber mesh is laid on the interface slurry layer on the upper surface of the core layer, and then the first modified magnesium oxychloride cement slurry is laid on the upper glass fiber mesh; S5. The overall structure in step S4 is cold-pressed and composited, so that the first modified magnesium oxychloride cement slurry on both sides is interconnected with the corresponding interface slurry layer through the mesh of the mesh cloth and then cured to obtain the water-resistant reinforced magnesium oxychloride cement composite plywood.

[0023] Preferably, the amount of glue applied to one side of the wood veneer after impregnation in step S2 is 350-450 g / m². 2 The hot pressing time is 7-18 minutes, and after the hot pressing is completed, the pressure is released by cooling to below 80°C under the pressure holding state.

[0024] Preferably, the unit pressure of the cold pressing composite in step S5 is 1.0-1.5 MPa, the temperature is 20-30℃, and the holding time is 4-6 hours. Step S5 is followed by natural curing, edge trimming, sanding, and surface sealing. The natural curing conditions are a temperature of 20-30℃, a relative humidity of 60%-75%, and a curing time of 7 days. The surface sealing treatment involves coating both sides of the board with an organosilicon sealant at a coating amount of 50-80 g / m². 2 .

[0025] The beneficial effects of this invention are: (1) The board has good dimensional stability. The first waterproof and wear-resistant surface layer and the second waterproof and wear-resistant surface layer are made of the same material and have the same thickness and are symmetrically arranged with respect to the magnesium oxychloride cement wood composite core layer. The upper glass fiber mesh reinforcement layer and the lower glass fiber mesh reinforcement layer are symmetrically arranged with respect to the magnesium oxychloride cement wood composite core layer. When the board is subjected to changes in environmental humidity, the expansion and contraction stress generated on the upper and lower sides are balanced with each other, and the warping deformation of the board is effectively controlled.

[0026] (2) The water resistance of the board is improved. In the second modified magnesium oxychloride cement slurry used in the core layer, the phosphate ions in the aluminum dihydrogen phosphate can react with the magnesium ions in the hydration products of magnesium oxychloride cement to form a protective layer of insoluble phosphate on the surface of the hydration products; the active magnesium oxide in the calcined serpentine ultrafine powder can supplement the hydration reaction of magnesium oxychloride cement, and its amorphous silica can react with the hydration products in the weakly alkaline environment of magnesium oxychloride cement to fill the pores of the hardened matrix. The two modifiers play a role in protecting the surface of the hydration products and filling the pores of the matrix, respectively, thus improving the water resistance of the core layer matrix.

[0027] (3) The board has good interlayer bonding strength and mechanical strength. The alkali-resistant glass fiber mesh is arranged across the interface with one part of its thickness embedded in the waterproof and wear-resistant surface layer and another part embedded in the core layer interface slurry layer. The slurry in the waterproof and wear-resistant surface layer and the core layer interface slurry are interconnected through the mesh of the mesh and cured into one piece, forming a distributed mechanical anchoring structure between the waterproof and wear-resistant surface layer and the core layer interface slurry layer. The interlayer bonding strength between the waterproof and wear-resistant surface layer and the magnesium oxychloride cement wood composite core layer is higher than that of boards bonded by conventional slurry adhesion. The multi-layer wood veneer in the magnesium oxychloride cement is cross-assembled with adjacent layers of fiber direction perpendicular to each other and cured by hot pressing. The wood veneer and the second modified magnesium oxychloride cement slurry cured matrix form an integral composite structure. The wood veneer bears bending tensile stress along the fiber direction, and the cured matrix bears compressive stress and interlayer shear stress. The board has good mechanical properties in both length and width directions.

[0028] (4) The surface of the board has waterproof, wear-resistant and decorative functions. The nano-calcium carbonate incorporated in the first modified magnesium oxychloride cement slurry participates in filling and compacting the surface layer matrix. The organosilicon waterproofing agent forms hydrophobic siloxane components during the surface layer curing process. The inorganic pigment imparts decorative color to the surface layer. Both the first waterproof and wear-resistant surface layer and the magnesium oxychloride cement wood composite core layer use magnesium oxychloride cement as the matrix, and the interlayer compatibility between the two is good.

[0029] (5) The board uses magnesium oxychloride cement as the cementing material and no additional formaldehyde-containing organic adhesive is added, so the formaldehyde release of the board is low; magnesium oxychloride cement itself has flame-retardant properties, so the board has good fire resistance.

[0030] (6) The preparation method provided by the present invention adopts a two-step molding process: first, hot-press curing is used to prepare the magnesium oxychloride cement-wood composite core layer, and then cold-pressing is used to composite the waterproof and wear-resistant surface layer and the glass fiber mesh reinforcement layer. In the hot-pressing step, the second modified magnesium oxychloride cement slurry is tightly bonded to the wood veneer under the action of temperature and pressure; in the cold-pressing step, the first modified magnesium oxychloride cement slurry on both sides is interconnected with the corresponding interface slurry layer through the mesh of the mesh and cured, so that the overall board structure is stable. Attached Figure Description

[0031] The accompanying drawings are provided to further explain the invention and form part of the specification. They are used together with the embodiments of the invention to explain the invention and do not constitute a limitation thereof. In the drawings: Figure 1 This is a three-dimensional structural diagram of the plate material of the present invention; Figure 2 This is a schematic diagram of the cross-sectional structure of the plate material of the present invention; Figure 3 This is a schematic diagram of the cross-assembly structure of the core layer wood veneer in the board of the present invention; Figure 4 This is a comparison diagram of the microstructure of the surface layer-core layer interface between an embodiment of the present invention and a comparative example of a fiberglass mesh-free fabric; wherein... Figure 4 (a) The morphology of the interface between the surface layer and the core layer in direct contact without glass fiber mesh. Figure 4 (b) To set the interface morphology of the back layer slurry and the core layer slurry after the glass fiber mesh is laid out and cured through the interpenetration of the mesh to form a mechanically interlocked interface morphology; Figure 5 These are comparison images of the microstructure of the magnesium oxychloride cement matrix before and after core layer modification according to the present invention; wherein Figure 5 (a) shows the microstructure of magnesium oxychloride cement matrix after composite modification with calcined serpentine ultrafine powder and aluminum dihydrogen phosphate. Figure 5 (b) shows the microstructure of the unmodified magnesium oxychloride cement matrix. Detailed Implementation

[0032] The technical solution of the present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments, but the scope of protection of the present invention is not limited to the following embodiments.

[0033] See Figure 1 , Figure 2 and Figure 3The water-resistant reinforced magnesium oxychloride cement composite plywood provided by this invention includes, from top to bottom, a first waterproof and wear-resistant surface layer 1, an upper glass fiber mesh reinforcement layer 2, a magnesium oxychloride cement wood composite core layer 3, a lower glass fiber mesh reinforcement layer 4, and a second waterproof and wear-resistant surface layer 5. The first waterproof and wear-resistant surface layer 1 and the second waterproof and wear-resistant surface layer 5 are arranged symmetrically with respect to the magnesium oxychloride cement wood composite core layer 3, and the upper glass fiber mesh reinforcement layer 2 and the lower glass fiber mesh reinforcement layer 4 are also arranged symmetrically with respect to the magnesium oxychloride cement wood composite core layer 3, thereby forming a five-layer symmetrical composite structure.

[0034] The first waterproof and wear-resistant surface layer 1 and the second waterproof and wear-resistant surface layer 5 have the same material composition and equal thickness after curing. Both are formed by curing a first modified magnesium oxychloride cement slurry containing nano-calcium carbonate, organosilicon waterproofing agent, and inorganic pigments. The thickness of both the first waterproof and wear-resistant surface layer 1 and the second waterproof and wear-resistant surface layer 5 after curing is 2.0-4.0 mm.

[0035] The magnesium oxychloride cement-wood composite core layer 3 is formed by cross-assembling multiple layers of wood veneer and impregnating them with a second modified magnesium oxychloride cement slurry, followed by hot-pressing and curing. The fiber directions of adjacent wood veneers in the multiple layers are perpendicular to each other. For example... Figure 3 As shown, the magnesium oxychloride cement-wood composite core layer 3 includes longitudinal wood veneers 31 and transverse wood veneers 32. The fiber direction of the longitudinal wood veneers 31 is parallel to the length direction of the board, and the fiber direction of the transverse wood veneers 32 is perpendicular to the length direction of the board. The longitudinal wood veneers 31 and transverse wood veneers 32 are arranged alternately along the thickness direction of the board. A second modified magnesium oxychloride cement slurry cured matrix 33 is filled between each wood veneer and in the pores, vessels, and cracks on the surface of the wood veneers, forming an integral composite structure between the wood veneers and the cured matrix 33. The thickness of the magnesium oxychloride cement-wood composite core layer 3 is 6-18 mm, and the total thickness of the plywood is 10-25 mm.

[0036] Both the upper and lower surfaces of the magnesium oxychloride cement-wood composite core layer 3 are provided with an interface slurry layer formed by the second modified magnesium oxychloride cement slurry. The upper glass fiber mesh reinforcement layer 2 is disposed between the first waterproof and wear-resistant surface layer 1 and the interface slurry layer on the upper surface of the magnesium oxychloride cement-wood composite core layer 3, and the lower glass fiber mesh reinforcement layer 4 is disposed between the second waterproof and wear-resistant surface layer 5 and the interface slurry layer on the lower surface of the magnesium oxychloride cement-wood composite core layer 3.

[0037] Both the upper glass fiber mesh reinforcement layer 2 and the lower glass fiber mesh reinforcement layer 4 are made of alkali-resistant glass fiber mesh, with a mesh size of 5mm × 5mm and a unit area mass of 120-180g / m². 2The thickness is 0.3-0.6 mm, and the ZrO2 content is not less than 16.5%. For example... Figure 2 As shown, 40%-60% of the thickness of the upper glass fiber mesh reinforcement layer 2 is embedded in the first waterproof and wear-resistant surface layer 1, and the remaining portion is embedded in the interface slurry layer on the upper surface of the magnesium oxychloride cement-wood composite core layer 3; 40%-60% of the thickness of the lower glass fiber mesh reinforcement layer 4 is embedded in the second waterproof and wear-resistant surface layer 5, and the remaining portion is embedded in the interface slurry layer on the lower surface of the magnesium oxychloride cement-wood composite core layer 3. The first waterproof and wear-resistant surface layer 1 and the interface slurry layer on the upper surface of the magnesium oxychloride cement-wood composite core layer 3 are interconnected and cured into one unit through the mesh of the upper glass fiber mesh reinforcement layer 2, and the second waterproof and wear-resistant surface layer 5 and the interface slurry layer on the lower surface of the magnesium oxychloride cement-wood composite core layer 3 are interconnected and cured into one unit through the mesh of the lower glass fiber mesh reinforcement layer 4.

[0038] The second modified magnesium oxychloride cement slurry contains calcined serpentine ultrafine powder and aluminum dihydrogen phosphate. The calcined serpentine ultrafine powder is obtained by calcining natural serpentine (Mg3Si2O5(OH)4) at 650-750℃ for 1-2 hours followed by ultrafine grinding, with a fineness of 1250-2000 mesh. The amount of calcined serpentine ultrafine powder is 10%-20% of the mass of light-burned magnesium oxide added to the second modified magnesium oxychloride cement slurry, and the amount of aluminum dihydrogen phosphate is 1.5%-3% of the mass of light-burned magnesium oxide added to the second modified magnesium oxychloride cement slurry.

[0039] The first modified magnesium oxychloride cement slurry contains nano-calcium carbonate, organosilicon waterproofing agent, and inorganic pigments. The nano-calcium carbonate has a particle size of 50-100 nm and is added at 5%-12% of the mass of light-burned magnesium oxide in the first modified magnesium oxychloride cement slurry; the organosilicon waterproofing agent is an aqueous solution of sodium methylsilicate or potassium methylsilicate, and is added at 2%-5% of the mass of light-burned magnesium oxide in the first modified magnesium oxychloride cement slurry; the inorganic pigment is an iron oxide pigment, including iron oxide red, iron oxide yellow, iron oxide black, or mixtures thereof, and is added at 5%-10% of the mass of light-burned magnesium oxide in the first modified magnesium oxychloride cement slurry.

[0040] The wood veneer is poplar rotary-cut veneer or eucalyptus rotary-cut veneer, with a thickness of 1.5-3.0 mm and a moisture content of 8%-12%. The magnesium oxychloride cement wood composite core layer 3 is formed by cross-assembling 3, 5, 7, or 9 layers of the aforementioned wood veneer, with the fiber direction of each layer of wood veneer arranged alternately in the longitudinal and transverse directions from bottom to top, and the fiber direction of the bottom and top layers is both longitudinal.

[0041] In the above structure of the present invention, the upper glass fiber mesh reinforcement layer 2 and the lower glass fiber mesh reinforcement layer 4 respectively form a cross-interface mesh structure between the surface layer and the core layer interface slurry layer. The calcined serpentine ultrafine powder and aluminum dihydrogen phosphate in the second modified magnesium oxychloride cement slurry used in the core layer modify the magnesium oxychloride cement in terms of both matrix filling and surface protection of hydration products. The nano-calcium carbonate, the organosilicon waterproofing agent, and the inorganic pigments in the first modified magnesium oxychloride cement slurry used in the surface layer respectively impart properties such as dense filling, surface hydrophobicity, and decorative coloring to the surface layer.

[0042] The technical solution of the present invention will be further explained below through specific preparation examples.

[0043] Example 1: This example provides a water-resistant reinforced magnesium oxychloride cement composite plywood with a total thickness of 15mm. The preparation process is as follows: (a) Raw material preparation: (1) Lightly calcined magnesium oxide (MgO): MgO content ≥85%, active MgO content ≥60%, residue on 200 mesh sieve ≤5%.

[0044] (2) Magnesium chloride hexahydrate (MgCl2·6H2O): Industrial grade, purity ≥96%, white flaky crystals.

[0045] (3) Water: tap water or industrial water, pH value 6.5-7.5.

[0046] (4) Wood veneer: Poplar rotary-cut veneer, veneer thickness 2.0mm, moisture content 8%-12%, veneer surface is flat, without obvious decay, insect holes and cracks.

[0047] (5) Aluminum dihydrogen phosphate (Al(H2PO4)3): Industrial grade, purity ≥98%, white powder.

[0048] (6) Calcined serpentine ultrafine powder: It is obtained by calcining natural serpentine at 700℃ for 1.5h and then ultrafine grinding it to 1500 mesh. It is a light gray-green powder with MgO content ≥38%, SiO2 content ≥35%, and specific surface area ≥800m². 2 / kg.

[0049] (7) Alkali-resistant glass fiber mesh: ZrO2 content ≥16.5%, unit area mass 150g / m 2 The grid size is 5mm×5mm, the thickness is 0.4mm, and the width is 1270mm.

[0050] (8) Organosilicon waterproofing agent: sodium methylsilicate aqueous solution, solid content 30%, pH value 12-13.

[0051] (9) Inorganic pigment: Iron oxide yellow pigment powder, passed through a 325-mesh sieve.

[0052] (10) Nano-calcium carbonate: particle size 50-100nm, specific surface area ≥20m² 2 / g, CaCO3 content ≥95%, surface treated with stearic acid wet activation.

[0053] (II) Preparation of the second modified magnesium oxychloride cement slurry: a) Preparation of magnesium chloride aqueous solution: Weigh 18.0 kg of magnesium chloride hexahydrate, add 13.0 kg of water, and stir in a stirred tank at 120 r / min for 15 min until completely dissolved to obtain a magnesium chloride aqueous solution with a Baume degree of 26-28°Bé. Let it stand and cool to room temperature.

[0054] b) Preparation of modifier premix: Weigh 0.4 kg of aluminum dihydrogen phosphate (accounting for 2.0% of the mass of light-burned magnesium oxide) and 3.0 kg of calcined serpentine ultrafine powder (accounting for 15% of the mass of light-burned magnesium oxide), premix with 6.0 kg of water, and stir at 250 r / min for 15 min until uniformly dispersed.

[0055] c) Slowly add the modifier suspension from step b) to the magnesium chloride aqueous solution from step a), and stir for 5 minutes until homogeneous; add 20.0 kg of lightly calcined magnesium oxide in batches, and stir at 300 r / min for 8-10 minutes until the slurry is homogeneous, to obtain the second modified magnesium oxychloride cement slurry. The initial setting time of this slurry at 25℃ is 50-70 minutes.

[0056] (III) Preparation of the first modified magnesium oxychloride cement slurry: a) Preparation of magnesium chloride aqueous solution: Weigh 6.0 kg of magnesium chloride hexahydrate and dissolve it in 4.3 kg of water, stirring until completely dissolved.

[0057] b) Preparation of functional filler dispersion: Weigh 0.6 kg of nano calcium carbonate (9% of the mass of light-burned magnesium oxide), 0.3 kg of organosilicon waterproofing agent (4.5% of the mass of light-burned magnesium oxide), and 0.5 kg of iron oxide yellow pigment (7.5% of the mass of light-burned magnesium oxide), mix with 3.0 kg of water, and stir at 300 r / min for 10 min to ensure uniform dispersion of each component.

[0058] c) Add the mixture from step b) to the magnesium chloride solution from step a) and stir until homogeneous. Then, add 6.7 kg of lightly calcined magnesium oxide in batches and stir at 300 r / min for 5-8 min until the slurry is homogeneous to obtain the first modified magnesium oxychloride cement slurry.

[0059] (iv) Molding of magnesium oxychloride cement-wood composite core layer 3: a) Impregnation of wood veneer: Take 5 sheets of poplar rotary-cut veneer (1220mm × 2440mm in size) and immerse them one by one in the second modified magnesium oxychloride cement slurry obtained in step (II), impregnating for 5-8 minutes per sheet to ensure the slurry fully wets the surface and internal conduits of the wood veneer. After removal, use a scraper to evenly scrape off excess slurry from the surface, controlling the amount of adhesive applied to one side to be 350-450g / m². 2 .

[0060] b) Cross-assembly: The five impregnated wood veneers are assembled from bottom to top in the order of "longitudinal, transverse, longitudinal, transverse, longitudinal". The fiber direction of the longitudinal wood veneer 31 is parallel to the length direction of the board, and the fiber direction of the transverse wood veneer 32 is perpendicular to the length direction of the board. After assembly, a core layer blank is formed with a thickness of about 12mm. A 20mm trimming allowance is reserved in each of the length and width directions.

[0061] c) Hot-press curing: The core layer blank is fed into a hot press at a temperature of 140±5℃, a unit pressure of 2.8±0.2MPa, and a pressing time of 12±1min. After hot pressing, the core layer blank is cooled to below 80℃ under pressure and then released to obtain the magnesium oxychloride cement-wood composite core layer 3. Under these hot-pressing conditions, the lightly calcined magnesium oxide in the second modified magnesium oxychloride cement slurry undergoes a neutralization reaction with magnesium chloride hexahydrate, generating hydration products mainly composed of 5Mg(OH)2·MgCl2·8H2O (5·1·8 phase) and 3Mg(OH)2·MgCl2·8H2O (3·1·8 phase). The hot-pressing temperature (140±5℃) and pressure (2.8±0.2MPa) accelerate the hydration reaction rate and increase the amount of hydration products generated, resulting in more complete development of the 5·1·8 phase crystals. Simultaneously, the hot-pressing temperature moderately softens the wood veneer, making the vessel cavities and intercellular spaces on the surface of the wood veneer easier to wet and fill with the second modified magnesium oxychloride cement slurry. After cooling and depressurization, the cured matrix 33 tightly bonds with the fiber structure of each layer of wood veneer, forming an integral composite structure.

[0062] (v) Composite molding of surface layer and fiberglass mesh reinforcement layer: a) Core layer interface slurry coating: Take the second modified magnesium oxychloride cement slurry obtained in step (ii), add an appropriate amount of water to adjust it to a paste with a fluidity of about 150 mm, and uniformly scrape a layer of the second modified magnesium oxychloride cement slurry with a thickness of about 1.0 mm on the upper and lower surfaces of the magnesium oxychloride cement wood composite core layer 3 to form an interface slurry layer.

[0063] b) Laying of the lower side layer and the lower glass fiber mesh reinforcement layer 4: The first modified magnesium oxychloride cement slurry obtained in step (iii) is evenly laid on the bottom surface of the molding mold to a thickness of about 2.0 mm and scraped flat; a sheet of alkali-resistant glass fiber mesh is laid flat on the slurry and rolled with a pressure roller so that about 50% of the thickness of the mesh is embedded in the first modified magnesium oxychloride cement slurry.

[0064] c) Placement of the core layer: The magnesium oxychloride cement-wood composite core layer 3 obtained in step a) is placed on the lower glass fiber mesh obtained in step b), so that the interface slurry layer on the lower surface of the core layer is attached to the other side of the mesh, and another part of the thickness of the mesh (about 50%) is embedded in the interface slurry layer on the lower surface of the core layer to form the lower glass fiber mesh reinforcement layer 4.

[0065] d) Laying of the upper glass fiber mesh reinforcement layer 2 and the upper side layer: Lay a second alkali-resistant glass fiber mesh on the interface slurry layer on the upper surface of the magnesium oxychloride cement-wood composite core layer 3, and roll it with a pressure roller so that about 50% of the thickness of the mesh is embedded in the interface slurry layer on the upper surface of the core layer; evenly lay about 2.0 mm thick of the first modified magnesium oxychloride cement slurry obtained in step (iii) on the exposed side of the mesh and scrape it flat, and another part of the thickness of the mesh (about 50%) is embedded in the first modified magnesium oxychloride cement slurry to form the first waterproof and wear-resistant surface layer 1 and the upper glass fiber mesh reinforcement layer 2.

[0066] e) Cold-pressed composite: The entire sheet material, along with the mold, is fed into a cold press at a unit pressure of 1.3±0.2MPa and a temperature of 20-30℃ for 6±1 hours. Under pressure, the first modified magnesium oxychloride cement slurry on both sides becomes interconnected with the corresponding core layer interface slurry layer through the 5mm×5mm square mesh of the alkali-resistant glass fiber mesh, forming a through-type cured structure at each mesh location after curing.

[0067] (vi) Maintenance and post-treatment: a) After cold pressing, demold the boards and stack them horizontally in a well-ventilated curing workshop. Separate the boards with pads of equal thickness and allow them to cure naturally for 7 days in an environment with a temperature of 20-30℃ and a relative humidity of 60%-75%.

[0068] b) After curing, use a precision panel saw to cut 10mm off each of the four sides of the board to obtain a finished board with a size of 1220mm×2440mm; use a wide belt sander to lightly sand both sides of the board (sand belt grit 180 mesh).

[0069] c) After sanding, apply a layer of silicone sealant (5% diluted sodium methylsilicate aqueous solution) to both sides of the board using spraying or roller coating, with a coating amount of 50-80 g / m². 2 Dry at room temperature for 30 minutes.

[0070] According to GB / T 17657-2022 "Test Methods for Physical and Chemical Properties of Wood-based Panels and Decorative Wood-based Panels", the performance of the boards obtained in the embodiments of this invention was tested. The main test items and methods include: static bending strength and modulus of elasticity were determined according to Section 4.7 (three-point bending method); interlayer bond strength was determined according to Section 4.17 (Class II plywood conditions, tested after soaking in hot water at 63℃ for 3 hours); 24-hour water absorption thickness expansion rate was determined according to Section 4.4 (method 1); wet strength retention rate was determined by combining Sections 4.7 and 4.9 (i.e., testing the static bending strength in the dry state and after soaking in water at 70℃ for 2 hours, and calculating the percentage of strength after soaking to dry strength); warpage was determined according to Section 4.35 (placed in an environment of 40℃ and 90% relative humidity for 72 hours); formaldehyde release was determined according to Section 4.28 (1m 3 The rating was determined according to GB / T 39600-2021 using the climate chamber method; the flammability was determined according to GB 8624-2012.

[0071] The main performance indicators of the water-resistant reinforced magnesium oxychloride cement composite plywood obtained in this embodiment are as follows: static bending strength 42.3 MPa, elastic modulus 6310 MPa, interlaminar bond strength (immersed in hot water at 63℃ for 3 hours) 1.37 MPa, 24-hour water absorption thickness expansion rate 1.2%, wet strength retention rate 0.82%, warpage 0.14 mm / 100 mm, and formaldehyde emission less than 0.025 mg / m². 3 Combustion performance rating: B1.

[0072] Example 2: This example provides a water-resistant reinforced magnesium oxychloride cement composite plywood, the preparation process of which is basically the same as that of Example 1, except that: The magnesium oxychloride cement wood composite core layer 3 is formed by cross-assembling 3 poplar rotary-cut veneers. The fiber directions of each veneer layer from bottom to top are longitudinal, transverse, and longitudinal, respectively. The veneer thickness is 2.0 mm and the moisture content is 8%-12%.

[0073] In the second modified magnesium oxychloride cement slurry, the amount of lightly calcined magnesium oxide is 20.0 kg, the amount of aluminum dihydrogen phosphate is 1.5% of the mass of lightly calcined magnesium oxide, and the amount of calcined serpentine ultrafine powder is 10% of the mass of lightly calcined magnesium oxide; the calcined serpentine ultrafine powder is obtained by calcining natural serpentine at 650℃ for 2 hours and then ultrafine grinding it to 1250 mesh.

[0074] The core layer is hot-pressed at a temperature of 135±5℃, a unit pressure of 2.5±0.2MPa, and a hot-pressing time of 8±1min. The cured thickness of both the first waterproof and wear-resistant surface layer 1 and the second waterproof and wear-resistant surface layer 5 is approximately 2.0mm. Approximately 50% of the thickness of the alkali-resistant glass fiber mesh is embedded in the corresponding waterproof and wear-resistant surface layer, with the remaining portion embedded in the corresponding core layer interface slurry layer.

[0075] The board obtained in this embodiment forms a five-layer symmetrical composite structure from top to bottom: a first waterproof and wear-resistant surface layer 1, an upper glass fiber mesh reinforcement layer 2, a magnesium oxychloride cement-wood composite core layer 3, a lower glass fiber mesh reinforcement layer 4, and a second waterproof and wear-resistant surface layer 5.

[0076] Example 3: This example provides a water-resistant reinforced magnesium oxychloride cement composite plywood, the preparation process of which is basically the same as that of Example 1, except that: The magnesium oxychloride cement wood composite core layer 3 is formed by cross-assembling 7 poplar rotary-cut veneers. The fiber directions of each veneer layer from bottom to top are longitudinal, transverse, longitudinal, transverse, longitudinal, transverse, longitudinal; the veneer thickness is 2.0 mm and the moisture content is 8%-12%.

[0077] In the second modified magnesium oxychloride cement slurry, the amount of lightly calcined magnesium oxide is 20.0 kg, the amount of aluminum dihydrogen phosphate is 3.0% of the mass of lightly calcined magnesium oxide, and the amount of calcined serpentine ultrafine powder is 20% of the mass of lightly calcined magnesium oxide; the calcined serpentine ultrafine powder is obtained by calcining natural serpentine at 750℃ for 1 hour and then ultrafine grinding it to 2000 mesh.

[0078] The core layer is hot-pressed at a temperature of 145±5℃, a unit pressure of 3.0±0.2MPa, and a hot-pressing time of 14±2min. The thickness of both the first waterproof and wear-resistant surface layer 1 and the second waterproof and wear-resistant surface layer 5 after curing is approximately 2.5mm.

[0079] The board obtained in this embodiment has a relatively thick seven-layer cross-reinforced wood veneer core, which is suitable for applications requiring higher thickness and higher rigidity.

[0080] Example 4: This example provides a water-resistant reinforced magnesium oxychloride cement composite plywood, the preparation process of which is basically the same as that of Example 1, except that: The wood veneer in the magnesium oxychloride cement wood composite core layer 3 is made of eucalyptus rotary-cut veneer with a thickness of 1.8mm and a moisture content of 8%-12%. The core layer is composed of 5 eucalyptus veneers cross-assembled, and the fiber direction of each layer of wood veneer from bottom to top is longitudinal, transverse, longitudinal, transverse, longitudinal.

[0081] In the first modified magnesium oxychloride cement slurry, the organosilicon waterproofing agent is potassium methylsilicate aqueous solution, and the inorganic pigment is iron oxide red pigment; the dosages of nano calcium carbonate, potassium methylsilicate aqueous solution and iron oxide red pigment are 8%, 3% and 5% of the mass of lightly calcined magnesium oxide, respectively.

[0082] The remaining raw material ratios, mesh fabric specifications, embedding ratios, hot pressing and cold pressing processes are the same as in Example 1.

[0083] The board material obtained in this embodiment verifies the applicability of the present invention to different wood veneer species and different types of silicone waterproofing agents.

[0084] Example 5: This example provides a water-resistant reinforced magnesium oxychloride cement composite plywood, the preparation process of which is basically the same as that of Example 1, except that: The magnesium oxychloride cement wood composite core layer 3 is formed by cross-assembling 9 poplar rotary-cut veneers. The fiber directions of each veneer layer from bottom to top are longitudinal, transverse, longitudinal, transverse, longitudinal, transverse, longitudinal, transverse, longitudinal, transverse, longitudinal; the veneer thickness is 2.0 mm and the moisture content is 8%-12%.

[0085] In the second modified magnesium oxychloride cement slurry, the amount of aluminum dihydrogen phosphate is 2.5% of the mass of light-burned magnesium oxide, and the amount of calcined serpentine ultrafine powder is 17.5% of the mass of light-burned magnesium oxide; the calcined serpentine ultrafine powder is obtained by calcining natural serpentine at 700℃ for 1.5 hours and then ultrafine grinding it to 1500 mesh.

[0086] The core layer is hot-pressed at a temperature of 145±5℃, a unit pressure of 3.0±0.2MPa, and a hot-pressing time of 16±2min. The thickness of both the first waterproof and wear-resistant surface layer 1 and the second waterproof and wear-resistant surface layer 5 after curing is approximately 2.5mm.

[0087] The board obtained in this embodiment has a thick nine-layer cross-reinforced wood veneer core, making it suitable for applications requiring higher thickness, higher rigidity, and higher load-bearing capacity.

[0088] To illustrate the impact of the various technical features of this invention on the performance of the plywood, four sets of comparative examples were set up for parallel testing based on Example 1. Except for the changes specifically mentioned, all comparative examples used the same raw materials, proportions, and processes as Example 1; the number of test samples n=6, and the results were averaged.

[0089] Comparative Example A: To illustrate the effect of the symmetrical arrangement of the first waterproof and wear-resistant surface layer 1 and the second waterproof and wear-resistant surface layer 5, and the upper glass fiber mesh reinforcement layer 2 and the lower glass fiber mesh reinforcement layer 4 on the performance of the board, the following comparative example is set up: Comparative Example A1: Only the first waterproof and wear-resistant surface layer 1, the upper glass fiber mesh reinforcement layer 2, and the magnesium oxychloride cement wood composite core layer 3 from Example 1 are retained, while the lower glass fiber mesh reinforcement layer 4 and the second waterproof and wear-resistant surface layer 5 are omitted. The lower surface of the core layer is exposed, forming an asymmetric three-layer structure.

[0090] Comparative Example A2: The thickness of the second waterproof and wear-resistant surface layer 5 in Example 1 was reduced from 2.0 mm to 0.3 mm, while the thickness of the first waterproof and wear-resistant surface layer 1 remained at 2.0 mm. The rest of the structure was the same as in Example 1, forming an asymmetrical structure of upper and lower surface layer thicknesses.

[0091] Comparative Example A3: Only the magnesium oxychloride cement-wood composite core layer 3 of Example 1 is retained, and the other layers are omitted as a single core layer control.

[0092] The test results for Group A are shown in Table 1.

[0093] Table 1 Test Results for Group A Static bending strength (MPa) 42.3 34.2 38.7 25.5 Elastic modulus (MPa) 6310 5140 5820 4060 Interlayer bond strength (MPa, immersion in water at 63℃ for 3 hours) 1.37 0.83 1.05 — 24-hour water absorption thickness expansion rate (%) 1.2 2.7 2.0 4.9 Wet strength retention rate (immersion in 70℃ water for 2 hours) 0.82 0.59 0.67 0.43 Warpage (mm / 100mm) 0.14 0.52 0.40 0.43 Note: Comparative Example A3 has no surface layer / mesh fabric in its pure core layer, so conventional interlayer bond strength tests cannot be performed. It is indicated by "—".

[0094] The results from Group A show that Comparative Example A1 (three-layer asymmetric structure) exhibited a warpage of 0.52 mm / 100 mm, 3.7 times that of Example 1 (0.14 mm / 100 mm), directly demonstrating the crucial role of the perfectly symmetrical surface layer-mesh fabric-core layer structure in suppressing board warpage. Notably, Comparative Example A2 (asymmetric surface layer thickness only) also showed significant warpage (0.40 mm / 100 mm), a value between Example 1 and Comparative Example A1, indicating that even asymmetric surface layer thickness alone can generate a non-negligible bending moment due to the difference in the rates of wet expansion and shrinkage between the upper and lower surfaces. The warpage of Comparative Example A3 (pure core layer) (0.43 mm / 100 mm) was slightly lower than that of Comparative Example A1 (0.52 mm / 100 mm). This is because the three-layer asymmetric structure of A1 introduced additional interfacial stress mismatch, exacerbating warpage—demonstrating that asymmetric multilayer structures may exhibit more complex deformation behavior than single-layer structures.

[0095] Comparative Example B: To illustrate the impact of the mesh size (5mm × 5mm) and embedding method (approximately 50% embedded in the surface layer and the remaining portion embedded in the core layer interface slurry layer) of the alkali-resistant glass fiber mesh on the performance of the board, the following comparative example was set up: Comparative Example B1: The upper and lower glass fiber mesh reinforcement layers 2 and 4 of Example 1 are omitted. The first modified magnesium oxychloride cement slurry is directly laid on the upper and lower surfaces of the core layer, and the rest is the same as in Example 1.

[0096] Comparative Example B2: The mesh fabric of Example 1 was replaced with the same mass per unit area (150 g / m²). 2 The alkali-resistant glass fiber plain weave fabric (10 warp and weft threads / cm, no mesh openings, 0.25mm thickness) is laid in the same way as in Example 1.

[0097] Comparative Example B3: The grid size was changed from 5mm×5mm to 3mm×3mm, and the rest was the same as in Example 1.

[0098] Comparative Example B4: The grid size was changed from 5mm×5mm to 10mm×10mm, and the rest was the same as in Example 1.

[0099] Comparative Example B5: The upper and lower glass fiber mesh reinforcement layers 2 and 4 are completely embedded in the corresponding waterproof and wear-resistant surface layers. The mesh does not contact the core layer interface slurry layer. The rest is the same as in Example 1.

[0100] The test results for Group B are shown in Table 2.

[0101] Table 2 Test Results for Group B Static bending strength (MPa) 42.3 28.7 34.8 39.2 37.2 35.7 Elastic modulus (MPa) 6310 4630 5310 5880 5620 5440 Interlayer bond strength (MPa, immersion in water at 63℃ for 3 hours) 1.37 0.53 0.74 0.95 0.99 0.70 24-hour water absorption thickness expansion rate (%) 1.2 2.2 1.9 1.6 1.4 1.9 Warpage (mm / 100mm) 0.14 0.26 0.20 0.17 0.16 0.19 The results of Group B indicate that interlayer bond strength is the core indicator of this experiment. The interlayer bond strength (1.37 MPa) of Example 1 (5 mm mesh) is significantly better than all comparative examples. Specific comparisons: Comparative Example B1 (without mesh) showed an interlayer bond strength of only 0.53 MPa, a 61% decrease compared to Example 1, demonstrating that the mechanical interlocking of the mesh is the core source of interlayer bond strength. In Comparative Example B1, without the mesh, the bond between the first modified magnesium oxychloride cement slurry and the core layer interface slurry layer mainly relies on the mutual wetting and adhesion of the slurry interfaces during curing, resulting in limited bond strength. In Example 1, a portion of the thickness of the alkali-resistant glass fiber mesh is embedded in the first waterproof and wear-resistant surface layer, and the remaining portion is embedded in the core layer interface slurry layer. The first modified magnesium oxychloride cement slurry and the core layer interface slurry contact and permeate each other through the 5mm × 5mm square mesh openings of the mesh, forming a columnar cured structure penetrating the mesh at each mesh opening location after curing. When the first waterproof and wear-resistant surface layer and the magnesium oxychloride cement-wood composite core layer 3 are subjected to peeling or shear loads, the load needs to break the columnar cured structures at each mesh opening location to separate the interface, thereby improving the interlayer bond strength of the plywood.

[0102] The interlayer bonding strength of Comparative Example B2 (ordinary fiberglass cloth) was 0.74 MPa, which was better than B1 but still much lower than Example 1. This is because although fiberglass cloth can provide fiber reinforcement, it has a low effective opening rate and weak slurry penetration ability, and the interlayer bonding is still mainly physical adhesion.

[0103] The interlayer bonding strength of Comparative Example B3 (3mm mesh) was 0.95MPa, which was 31% lower than that of Example 1. The reason is that the 3mm mesh is too small, and it is difficult for the surface slurry with high viscosity to penetrate fully. The slurry on both sides cannot effectively merge and fuse within the mesh, which reduces the formation rate of "cement rivets".

[0104] The interlayer bond strength of Comparative Example B4 (10mm mesh) was 0.99MPa, which was 28% lower than that of Example 1. The reason is that although the 10mm mesh is conducive to the penetration of grout, the number of mesh holes per unit area is only 1 / 4 of that of the 5mm mesh, the density of "cement rivets" is insufficient, and the interlayer bond strength is reduced.

[0105] The interlayer bonding strength of comparative example B5 (fully embedded surface layer) is only 0.70 MPa, which is close to that of ordinary fiberglass cloth (B2). This is because the mesh is completely wrapped by the surface layer slurry and does not come into contact with the core layer slurry. The mesh openings contain only the surface layer slurry and cannot form the interpenetration of "surface layer slurry - core layer slurry" within the mesh openings, thus losing the bridging mechanical interlocking function.

[0106] See Figure 4 , Figure 4 (a) When no glass fiber mesh is provided, the surface layer and the core layer mainly rely on the direct adhesion of the slurry to bond together. Local cracks, pores or discontinuous contact areas can be seen at the interface, indicating that the interface between the two phases is prone to become a weak point for crack initiation and propagation. Figure 4 In (b), the fiberglass mesh spans the interface between the surface layer and the core layer. The surface layer slurry and the core layer interface slurry partially interpenetrate, coat, and solidify around the mesh, forming a continuous bridging and interlocking structure between the surface layer, the fiberglass mesh, and the core layer, thereby improving the interfacial bonding stability. Experiments in Group B revealed the technical optimality of a 5mm×5mm mesh size with a 40%-60% semi-embedded structure: mesh sizes that are too large or too small lead to a decrease in interlayer bonding strength, while full embedding results in a loss of bridging effect. The 5mm×5mm mesh achieves the optimal balance between slurry penetration and anchor point density.

[0107] Comparative Example C: To illustrate the influence of the cross-assembly method of wood veneers and the hot-pressing curing process on the performance of the wood composite core layer 3 of magnesium oxychloride cement, the following comparative example is set up: Comparative Example C1: The fiber direction of the 5 layers of wood veneer in the magnesium oxychloride cement wood composite core layer 3 is parallel to the length direction of the board (all longitudinally assembled), and the rest is the same as in Example 1.

[0108] Comparative Example C2: The magnesium oxychloride cement wood composite core layer 3 is composed of 3 layers of wood veneer cross-assembled, with the fiber direction from bottom to top being longitudinal, transverse, and longitudinal in sequence, and the rest is the same as in Example 1.

[0109] Comparative Example C3: The magnesium oxychloride cement-wood composite core layer 3 is cold-pressed at a unit pressure of 1.5 MPa, a temperature of 20-25°C, and a holding time of 8 hours. No hot pressing is performed. The rest is the same as in Example 1.

[0110] The test results for Group C are shown in Table 3.

[0111] Table 3 Test Results for Group C Static bending strength (MPa, parallel to fiber direction) 43.9 51.0 37.1 32.0 Static bending strength (MPa, perpendicular to fiber direction) 40.6 20.5 28.7 30.2 Static bending strength parallel / perpendicular ratio 1.08 2.49 1.29 1.06 Elastic modulus parallel (MPa) 6520 7520 5530 4790 Elastic modulus vertical (MPa) 6100 2960 4520 4450 Bond strength between veneers (MPa, immersion in water at 63℃ for 3 hours) 1.37 1.14 1.07 0.73 24-hour water absorption thickness expansion rate (%) 1.2 1.8 1.6 2.6 Wet strength retention rate (immersion in 70℃ water for 2 hours) 0.82 0.73 0.76 0.53 Warpage (mm / 100mm) 0.14 0.33 0.19 0.23 The results of Group C show that, in Comparative Example C1 (all parallel plywood), the static bending strength along the fiber direction (parallel) is as high as 51.0 MPa, but only 20.5 MPa perpendicular to the fiber direction (perpendicular), with a parallel / perpendicular ratio of 2.48, exhibiting severe mechanical anisotropy. Simultaneously, the warpage is as high as 0.33 mm / 100 mm (0.14 mm in Example 1). This is because the difference in the rate of moisture expansion in the fiber direction and perpendicular to the fiber direction is significant (typically about 0.1% in the fiber direction, and up to 6-8% in the tangential direction). In the case of all parallel plywood, the cumulative moisture expansion stress in the width direction of each layer cannot be offset by adjacent layers, resulting in significant bending deformation of the board in the width direction. This result directly proves the necessity of cross-ply wood plywood.

[0112] Comparative Example C2 (3-layer cross-assembly): Its parallel / perpendicular ratio is 1.29, showing a significant improvement in mechanical anisotropy compared to C1, but still lower than Example 1 (5 layers) at 1.08. This is because the 5-layer assembly has more fiber orientation alternations (4 fiber orientation changes vs. 2), resulting in smaller local stress abrupt changes caused by differences in fiber orientation between layers, and the overall structure is closer to quasi-isotropy. Simultaneously, the inter-vessel bonding strength of the 5-layer assembly (1.37 MPa) is also higher than that of the 3-layer assembly (1.07 MPa), because the increased number of layers increases the number of bonding interfaces, allowing the load to be distributed and transferred across more interfaces.

[0113] Comparative Example C3 (cold-pressed): Its inter-veneer bonding strength (0.73 MPa) was only about 53% of that of Example 1 (1.37 MPa), and its wet strength retention rate (0.53) was 35% lower than that of Example 1 (0.82). This is because under hot pressing conditions (135-145℃), the hydration reaction rate of magnesium oxychloride cement is significantly accelerated, the degree of hydration is higher, and the 5·1·8 phase crystals are more fully developed. At the same time, the high temperature moderately softens the wood veneer and forms a tighter interfacial contact with the mortar under pressure. Under cold pressing conditions, the hydration reaction is slow, the amount of hydration products is insufficient, and the matrix density and interfacial bonding are greatly reduced. This comparison confirms the key role of the hot pressing process in the core layer performance of magnesium oxychloride cement plywood.

[0114] The above results indicate that the cross-assembly of five layers of wood veneer with the fiber directions of adjacent layers perpendicular to each other, combined with a hot-press curing process at 130-150℃, has a good effect on the mechanical properties and interlayer bonding performance of the magnesium oxychloride cement-wood composite core layer 3.

[0115] Comparative Example D: To illustrate the role of calcined serpentine ultrafine powder and aluminum dihydrogen phosphate in the second modified magnesium oxychloride cement slurry and the effect of their combination, the following comparative example was set up: Comparative Example D1: The second modified magnesium oxychloride cement slurry did not contain calcined serpentine ultrafine powder and aluminum dihydrogen phosphate, and the rest was the same as in Example 1.

[0116] Comparative Example D2: The second modified magnesium oxychloride cement slurry only added aluminum dihydrogen phosphate (accounting for 2.0% of the mass of lightly calcined magnesium oxide), without adding calcined serpentine ultrafine powder, and the rest was the same as in Example 1.

[0117] Comparative Example D3: The second modified magnesium oxychloride cement slurry only added calcined serpentine ultrafine powder (accounting for 15% of the mass of light-burned magnesium oxide), without adding aluminum dihydrogen phosphate, and the rest was the same as in Example 1.

[0118] Comparative Example D4: A three-layer structure was adopted (only the first waterproof and wear-resistant surface layer 1, the magnesium oxychloride cement-wood composite core layer 3, and the second waterproof and wear-resistant surface layer 5 were included), omitting the upper and lower glass fiber mesh reinforcement layers 2 and 4; all five core layer wood veneers were assembled longitudinally in parallel and cold-pressed; the second modified magnesium oxychloride cement slurry did not contain calcined serpentine ultrafine powder or aluminum dihydrogen phosphate; the first modified magnesium oxychloride cement slurry did not contain organosilicon waterproofing agent. This comparative example served as a comprehensive blank control.

[0119] The test results for Group D are shown in Table 4.

[0120] Table 4 Test Results for Group D Static bending strength (MPa) 42.3 37.6 39.1 40.6 24.2 Elastic modulus (MPa) 6310 5860 6010 6120 4030 Interlayer bond strength (MPa, immersion in water at 63℃ for 3 hours) 1.37 1.01 1.14 1.10 0.49 24-hour water absorption thickness expansion rate (%) 1.2 3.8 2.2 2.7 5.3 Wet strength retention rate (immersion in 70℃ water for 2 hours) 0.82 0.44 0.71 0.64 0.40 Warpage (mm / 100mm) 0.14 0.23 0.19 0.20 0.56 The results of Group D indicate that: (1) Comparison of the effects of a single modifier: The wet strength retention rate of Comparative Example D2 (aluminum dihydrogen phosphate only) was 0.71, which was significantly better than that of D1 (without modifier, 0.44). Aluminum dihydrogen phosphate improved the wet strength retention rate by 62%, proving that its chemical protection mechanism (formation of insoluble magnesium phosphate coating) is the main contributor to water resistance modification.

[0121] The static flexural strength of Comparative Example D3 (calcined serpentine ultrafine powder only) was 40.6 MPa, which was better than D2 (39.1 MPa) and D1 (37.6 MPa). Its wet strength retention rate was 0.64, which was better than D1 (0.44) but lower than D2 (0.71). This indicates that calcined serpentine ultrafine powder mainly improves matrix density and mechanical strength by releasing active MgO to supplement the hydration reaction and the pozzolanic reaction of amorphous SiO2, possibly generating MSH gel to fill pores. It also has an auxiliary effect on improving water resistance (reducing capillary porosity and minimizing water penetration channels).

[0122] (2) Complementary enhancement effect of modifiers: Example 1 (calcined serpentine ultrafine powder + aluminum dihydrogen phosphate composite) showed significantly better wet strength retention (0.82) and 24-hour water absorption thickness expansion rate (1.2%) than Comparative Examples D2 and D3 when used alone. The combined use was superior to either one alone. Aluminum dihydrogen phosphate plays a role at the "crystal surface passivation" level (forming a protective layer of insoluble magnesium phosphate), while calcined serpentine ultrafine powder plays a role at the "matrix densification" level (releasing active MgO to replenish hydration + reacting amorphous SiO2 volcanic ash to generate MSH gel to fill pores + providing nucleation sites to refine grains). The mechanisms of action of the two are complementary and they act on different physicochemical processes, resulting in simultaneous improvement at both levels when used in combination.

[0123] (3) “Structural scaling and modification” – the core synergistic effect of this invention: A noteworthy phenomenon in this group of experiments is the change in interlayer bonding strength. Comparing Example 1 and Comparative Example D1, both are identical in their five-layer symmetrical structure and mesh fabric semi-embedded interface; the only difference lies in whether the core layer contains a composite modifier of calcined serpentine ultrafine powder and aluminum dihydrogen phosphate. The interlayer bonding strength of Example 1 is approximately 36% higher than that of Comparative Example D1 (1.37 vs 1.01), while the interlayer bonding strength of Comparative Example D4 (blank control, no structural innovation and no modification) is only 0.49 MPa. The modified core layer matrix has higher strength, and the shear strength of the columnar mechanically locked nodes formed by the mesh fabric holes is also increased accordingly—the interfacial bonding force between the surface layer and the core layer gains an additional gain beyond the direct contribution of the modifier due to the reinforcement of the core layer matrix itself. The introduction of the modifier not only improves the water resistance of the core layer matrix itself (wet strength retention rate from 0.44 → 0.82), but also further enhances the interlayer bonding strength through a "structural amplification" effect. This positive feedback mechanism of "structural amplification and modification" cannot be reasonably expected from the prior art and constitutes an important part of the outstanding substantive features of this invention.

[0124] See Figure 5 , Figure 5 (a) The core layer magnesium oxychloride cement matrix structure after composite modification is more compact, with reduced pores and microcracks, and more uniform distribution of hydration products; Figure 5 (b) shows that the unmodified magnesium oxychloride cement matrix exhibits numerous pores, loose regions, and coarse crystal structures. A comparison of the two indicates that the composite modification of calcined serpentine ultrafine powder and aluminum dihydrogen phosphate is beneficial for improving the density and water resistance of the core matrix.

[0125] By comparing the above four groups of 15 comparative examples with Example 1, it can be seen that: (i) The five-layer symmetrical structure (Group A empirical) is the structural basis for the dimensional stability of the sheet material, and its warpage control capability (0.14 mm / 100 mm) is 3.7 times that of the asymmetrical structure (0.52 mm / 100 mm).

[0126] (ii) The mechanical interlocking interface formed by the 5mm×5mm glass fiber mesh with a semi-embedded structure of 40%-60% embedding ratio (Group B empirical) is the core contributing factor to the interlayer bonding force. The 5mm mesh size achieves an optimal balance between grout penetration and anchor point density. The determination of this optimal parameter can only be obtained through systematic experiments and cannot be directly derived from existing technologies.

[0127] (iii) The cross-assembly of 5-layer wood veneer with hot-press curing (C group empirical) achieved quasi-isotropic mechanical properties (parallel / perpendicular ratio 1.08). At the same time, the hot-pressing process made the interlayer bonding strength of the core layer 1.88 times that of the cold-pressing process, and the wet strength retention rate 1.53 times.

[0128] (iv) Calcined serpentine ultrafine powder and aluminum dihydrogen phosphate form a water-resistant modification synergy at two levels: “crystal surface protection” and “matrix pore filling” (Group D empirical). Moreover, the effect of the modifier can be amplified by the five-layer symmetrical + mesh fabric semi-embedded structure (interlayer bonding strength is increased by an additional 35%), that is, there is a positive feedback effect of “structural amplification modification”.

[0129] (v) The overall performance improvement of Example 1 compared to the blank control D4 can be decomposed into the following: the five-layer symmetrical structure, the cross-interface mechanical interlocking structure of the mesh cloth, the cross-assembled hot-pressed core layer of wood veneer, and the calcined serpentine ultrafine powder / aluminum dihydrogen phosphate composite modification system are not simply superimposed, but show obvious synergistic improvement effects in terms of interlayer bonding strength, wet strength retention rate and dimensional stability.

[0130] Finally, it should be noted that the above embodiments are merely illustrative of several implementations of the present invention and are not intended to limit the scope of the invention. For those skilled in the art, any modifications, equivalent substitutions, or improvements made without departing from the concept of the present invention should be included within the scope of protection of the present invention. Therefore, the scope of protection of this patent should be determined by the appended claims.

Claims

1. A water-resistant reinforced magnesium oxychloride cement composite plywood, characterized in that, It includes a first waterproof and wear-resistant surface layer (1), an upper glass fiber mesh reinforcement layer (2), a magnesium oxychloride cement wood composite core layer (3), a lower glass fiber mesh reinforcement layer (4), and a second waterproof and wear-resistant surface layer (5) arranged sequentially from top to bottom. The first waterproof and wear-resistant surface layer (1) and the second waterproof and wear-resistant surface layer (5) are both formed by curing a first modified magnesium oxychloride cement slurry containing nano calcium carbonate, organosilicon waterproofing agent and inorganic pigment. The two have the same material composition and the same thickness after curing. The magnesium oxychloride cement wood composite core layer (3) includes multiple layers of wood veneer and a second modified magnesium oxychloride cement slurry cured matrix (33) filling the pores, conduits and interlayers of the wood veneer surface. The multiple layers of wood veneer include longitudinal wood veneer (31) and transverse wood veneer (32), and the fiber directions of adjacent wood veneers are perpendicular to each other. The second modified magnesium oxychloride cement slurry contains calcined serpentine ultrafine powder and aluminum dihydrogen phosphate. The upper and lower surfaces of the magnesium oxychloride cement-wood composite core layer (3) are provided with an interface slurry layer formed by the second modified magnesium oxychloride cement slurry; The upper glass fiber mesh reinforcement layer (2) and the lower glass fiber mesh reinforcement layer (4) are both alkali-resistant glass fiber mesh with square mesh holes, respectively disposed between the interface slurry layer on the upper surface of the first waterproof and wear-resistant surface layer (1) and the upper surface of the magnesium oxychloride cement wood composite core layer (3), and between the interface slurry layer on the lower surface of the second waterproof and wear-resistant surface layer (5) and the lower surface of the magnesium oxychloride cement wood composite core layer (3). The upper glass fiber mesh reinforcement layer (2) and the lower glass fiber mesh reinforcement layer (4) are arranged symmetrically above and below the magnesium oxychloride cement wood composite core layer (3). A portion of the thickness of the alkali-resistant glass fiber mesh is embedded in the corresponding waterproof and wear-resistant surface layer, and another portion of the thickness is embedded in the corresponding interface slurry layer. The waterproof and wear-resistant surface layer and the corresponding interface slurry layer are interconnected through the mesh openings of the mesh and are cured into one piece.

2. The water-resistant reinforced magnesium oxychloride cement composite plywood according to claim 1, characterized in that, The alkali-resistant glass fiber mesh has a mesh size of 5mm×5mm; 40%-60% of the thickness of the alkali-resistant glass fiber mesh is embedded in the corresponding waterproof and wear-resistant surface layer, and the remaining part is embedded in the corresponding interface slurry layer.

3. The water-resistant reinforced magnesium oxychloride cement composite plywood according to claim 1, characterized in that, The calcined serpentine ultrafine powder is obtained by calcining natural serpentine at 650-750℃ for 1-2 hours and then pulverizing it, with a fineness of 1250-2000 mesh; the dosage of the calcined serpentine ultrafine powder is 10%-20% of the mass of light-burned magnesium oxide added to the second modified magnesium oxychloride cement slurry; the dosage of aluminum dihydrogen phosphate is 1.5%-3% of the mass of light-burned magnesium oxide in the second modified magnesium oxychloride cement slurry.

4. The water-resistant reinforced magnesium oxychloride cement composite plywood according to claim 1, characterized in that, The nano-calcium carbonate has a particle size of 50-100 nm and is added at a rate of 5%-12% of the mass of lightly calcined magnesium oxide in the first modified magnesium oxychloride cement slurry; the organosilicon waterproofing agent is an aqueous solution of sodium methylsilicate or potassium methylsilicate and is added at a rate of 2%-5% of the mass of lightly calcined magnesium oxide in the first modified magnesium oxychloride cement slurry; the inorganic pigment is an iron oxide pigment and is added at a rate of 5%-10% of the mass of lightly calcined magnesium oxide in the first modified magnesium oxychloride cement slurry.

5. The water-resistant reinforced magnesium oxychloride cement composite plywood according to claim 1, characterized in that, The wood veneer is poplar rotary-cut veneer or eucalyptus rotary-cut veneer, with a thickness of 1.5-3.0 mm and a moisture content of 8%-12%. The magnesium oxychloride cement wood composite core layer is formed by cross-assembling 3, 5, 7 or 9 layers of the aforementioned wood veneer. From bottom to top, the fiber direction of each layer of wood veneer is arranged alternately in the longitudinal and transverse directions, and the fiber direction of the bottom layer and the top layer is longitudinal.

6. The water-resistant reinforced magnesium oxychloride cement composite plywood according to claim 1, characterized in that, The alkali-resistant glass fiber mesh has a ZrO2 content of not less than 16.5% and a unit area mass of 120-180 g / m². 2 The thickness is 0.3-0.6mm.

7. The water-resistant reinforced magnesium oxychloride cement composite plywood according to claim 1, characterized in that, The thickness of the first waterproof and wear-resistant surface layer and the second waterproof and wear-resistant surface layer after curing is 2.0-4.0 mm; the thickness of the magnesium oxychloride cement-wood composite core layer is 6-18 mm; the total thickness of the plywood is 10-25 mm; the ratio of the thickness of the first waterproof and wear-resistant surface layer to the thickness of the magnesium oxychloride cement-wood composite core layer is 1:3 to 1:

9.

8. A method for preparing a water-resistant reinforced magnesium oxychloride cement composite plywood as described in any one of claims 1-7, characterized in that, Includes the following steps: S1. Prepare a second modified magnesium oxychloride cement slurry containing calcined serpentine ultrafine powder and aluminum dihydrogen phosphate, and a first modified magnesium oxychloride cement slurry containing nano calcium carbonate, organosilicon waterproofing agent and inorganic pigment. S2. Immerse the multi-layer wood veneers in the second modified magnesium oxychloride cement slurry, remove them and scrape off the excess slurry on the surface; assemble the impregnated wood veneers in a manner where the fiber directions of adjacent wood veneers are perpendicular to each other, and hot-press and cure them at a temperature of 130-150℃ and a unit pressure of 2.5-3.0MPa to obtain a magnesium oxychloride cement wood composite core layer. S3. The second modified magnesium oxychloride cement slurry is coated on the upper and lower surfaces of the magnesium oxychloride cement-wood composite core layer to form an interface slurry layer. S4. Lay the first modified magnesium oxychloride cement slurry and the lower glass fiber mesh in sequence at the bottom of the molding mold, so that a portion of the thickness of the lower glass fiber mesh is embedded in the first modified magnesium oxychloride cement slurry on the lower side; place the magnesium oxychloride cement wood composite core layer obtained in step S3 on the lower glass fiber mesh, so that the interface slurry layer on the lower surface of the core layer is in contact with the lower glass fiber mesh; A glass fiber mesh is laid on the interface slurry layer on the upper surface of the core layer, and then the first modified magnesium oxychloride cement slurry is laid on the upper glass fiber mesh. S5. The overall structure in step S4 is cold-pressed and composited, so that the first modified magnesium oxychloride cement slurry on both sides is interconnected with the corresponding interface slurry layer through the mesh of the mesh cloth and then cured to obtain the water-resistant reinforced magnesium oxychloride cement composite plywood.

9. The preparation method according to claim 8, characterized in that, In step S2, the amount of glue applied to one side of the wood veneer after impregnation is 350-450 g / m². 2 The hot pressing time is 7-18 minutes, and after the hot pressing is completed, the pressure is released by cooling to below 80°C under the pressure holding state.

10. The preparation method according to claim 8, characterized in that, In step S5, the unit pressure for cold pressing is 1.0-1.5 MPa, the temperature is 20-30℃, and the holding time is 4-6 hours. Following step S5 are natural curing, edge trimming, sanding, and surface sealing treatment. The natural curing conditions are a temperature of 20-30℃, a relative humidity of 60%-75%, and a curing time of 7 days. The surface sealing treatment involves coating both sides of the board with an organosilicon sealant at a coating amount of 50-80 g / m². 2 .

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