A high-strength gypsum-based fiberboard and a method for manufacturing the same

Abstract

This invention relates to the field of building materials and discloses a high-strength gypsum-based fiberboard and its preparation method. The high-strength gypsum-based fiberboard is made from desulfurized hemihydrate gypsum, rapid-hardening sulfoaluminate cement, composite adhesive, chopped alkali-resistant glass fiber, wood fiber, highly substituted anionic starch ether, octyltriethoxysilane powder, tartaric acid and anhydrous sodium sulfate compound powder, highly active amorphous microsilica powder, and highly crystalline natural hard borate micropowder. The method includes: dry mixing the powders, adding water and a water-reducing agent to form a slurry; continuous extrusion with simultaneous laying of alkali-resistant glass fiber mesh on both sides; and step drying of the board blank after initial setting and cutting to obtain the finished product. This invention achieves a dense core through the synergistic construction of internal chopped fibers and surface mesh, enabling in-situ polymer locking and inhibiting adhesive migration to the surface. This helps improve the board's nail-holding power and deformation resistance, giving the product the mechanical properties and processing characteristics to replace wood-based OSB boards.

Description

Technical Field

[0001] This invention relates to the field of building materials technology, specifically to a high-strength gypsum-based fiberboard and its preparation method. Background Technology

[0002] High-strength gypsum-based fiberboard is a type of oriented strand board (OSB) made primarily of desulfurized hemihydrate gypsum as the cementing component, and reinforced with composite organic adhesives and fiber-reinforcing materials. Compared to traditional wood-based OSB, gypsum-based fiberboard combines the fire-retardant properties of inorganic mineral materials with the physical and mechanical properties provided by reinforcing fibers, making it an important functional material for replacing wood with gypsum in the fields of building decoration and structural engineering.

[0003] Existing gypsum-based boards are typically made by mixing desulfurized hemihydrate gypsum with ordinary silicate cement and polyvinyl alcohol binders, followed by extrusion, paving, and high-temperature drying. To improve the flexural strength of the boards, existing manufacturing processes usually incorporate reinforcing materials within the board and use conventional retarders and water-reducing agents to maintain the initial fluidity of the mixture, thus meeting the requirements of continuous extrusion molding production lines in factories.

[0004] The lack of micro-crosslinking and anchoring mechanisms and initial rheological control in existing gypsum-based composite systems leads to deficiencies in production processes and final physical properties. High-dosage, fast-setting cementitious systems undergo intense hydration upon contact with water, causing flash-forming and caking of the mixture in pumping pipelines, disrupting continuous extrusion molding production lines. Because existing ordinary silicate cement does not participate in hydration in the early stages of molding, unreacted mineral phases undergo delayed hydration expansion during the later high-temperature drying stage. The resulting microcracks cut through the continuous gypsum crystal matrix, reducing the macroscopic compressive strength of the finished product. Since organic binder molecules do not form chemical bonds with the inorganic mineral framework, free water carries the binder to the surface of the board during the drying stage, causing a polymer shell to form on the surface while the core debonds and becomes porous. Due to the non-dense core structure, existing boards are far inferior to traditional wood-based OSB boards in terms of nail-holding power, cross-sectional strength, and deformation stability, making it difficult to achieve a deep functional replacement for wood-based boards. Summary of the Invention

[0005] To address the shortcomings of existing technologies, this invention provides a high-strength gypsum-based fiberboard and its preparation method, aiming to solve the problems of flash condensation and caking of mixed materials during continuous production, and the core degumming caused by the migration of organic binder molecules to the surface during the drying stage, which leads to the decline in the mechanical load-bearing capacity and water resistance stability of gypsum-based boards.

[0006] To achieve the above objectives, the present invention provides the following technical solution: In a first aspect, the present invention provides a high-strength gypsum-based fiberboard, which adopts the following technical solution: A high-strength gypsum-based fiberboard comprises the following raw materials in parts by weight: Desulfurized hemihydrate gypsum: 85.0–95.0 parts; rapid-hardening sulfoaluminate cement: 15.0–25.0 parts; composite binder: 2.0–10.0 parts; chopped alkali-resistant glass fiber: 5.0–7.0 parts; wood fiber: 10.0–15.0 parts; highly substituted anionic starch ether: 0.1–2.0 parts; octyltriethoxysilane powder: 0.2–0.8 parts; composed of L-tartaric acid and anhydrous sodium sulfate in a mass ratio of 1… The compounded powder consists of 0.2 to 0.8 parts; highly active amorphous microsilica powder consists of 0.1 to 2.0 parts; highly crystalline natural borosilicate micro powder consists of 0.1 to 0.5 parts; wherein the composite adhesive is composed of cold water-soluble partially hydrolyzed polyvinyl alcohol powder and ethylene-vinyl acetate copolymer dispersible latex powder in a mass ratio of 1:1 to 1:3; the degree of substitution of the highly substituted anionic starch ether is 0.60 to 0.80.

[0007] By adopting the above technical solution, the inorganic minerals and organic polymers in the multi-component composite system, through cross-linking, comprehensively improve the mechanical load-bearing capacity and water resistance of the board. Specifically, during the slurry mixing stage, the L-tartaric acid and anhydrous sodium sulfate compound powder dissolves and releases chelated ions. These ions adsorb onto the surface of rapid-hardening sulfoaluminate cement and hemihydrate gypsum particles, forming a water-blocking adsorption layer that slows down the early absorption of water by the core mineral phase. This not only controls the initial rheological state of the system and reduces the apparent viscosity, but also effectively extends the operating window of the continuous extrusion process, preventing premature caking of materials in the pipeline.

[0008] As the wet slab is extruded and shaped, the spontaneous hydration and exothermic reaction within the system begins to dominate. During this process, hemihydrate gypsum hydrates to form dihydrate gypsum crystals, while rapid-hardening sulfoaluminate cement forms ettringite crystals. The heat released by this series of reactions causes the core temperature of the slab to rise rapidly. This temperature change disrupts the early chelate equilibrium; as the water-blocking effect fails, the active crystal faces of the minerals are exposed and begin to participate in the polymerization reaction of the silicon-oxygen network, leading to a rapid increase in matrix stiffness.

[0009] During the subsequent curing and moisture removal process, the silanol groups on the surface of the highly active amorphous microsilica powder undergo hydrogen bonding association with the hydroxyl groups of polyvinyl alcohol in an alkaline environment. Simultaneously, due to the delayed dissolution properties of natural borosilicate micropowder, it only begins to release borate ions after the system is heated, subsequently undergoing acetal and coordination reactions with the polyvinyl alcohol macromolecular chains to form a three-dimensional cross-linked network within. This series of cross-linking reactions fixes the polymer molecules in situ within the inorganic crystalline framework, effectively preventing internal degumming caused by free water carrying polyvinyl alcohol to the board surface during subsequent drying and evaporation, ensuring the uniformity of the board's cross-sectional density. Meanwhile, the wood fibers, evenly distributed within the matrix, interweave within the inorganic rigid framework to construct a flexible buffer network. The natural plant tissue structure of the wood fibers allows for a dense physical interlocking with the inserted steel nails, while the accompanying short-cut alkali-resistant glass fibers form a three-dimensionally randomized rigid bridging support. This combination of wood fiber and chopped glass fiber, which combines rigidity and flexibility, significantly enhances the density, toughness, and nail-holding power of the core. In addition, the alkyl hydrophobic segments generated by the hydrolysis of octyltriethoxysilane powder are distributed inside the matrix pores, which weakens the capillary water absorption effect of the material and further improves the water resistance stability of the finished product.

[0010] Preferably, the weight ratio range of the raw materials is: Desulfurized hemihydrate gypsum: 88.0–92.0 parts; rapid-hardening sulfoaluminate cement: 18.0–22.0 parts; composite binder: 5.0–7.0 parts; chopped alkali-resistant glass fiber: 5.5–6.5 parts; wood fiber: 11.0–14.0 parts; highly substituted anionic starch ether: 0.8–1.2 parts; octyltriethoxysilane powder: 0.4–0.6 parts; powder composed of L-tartaric acid and anhydrous sodium sulfate in a mass ratio of 1:5: 0.4–0.6 parts; highly active amorphous microsilica powder: 0.8–1.2 parts; highly crystalline natural borosilicate micropowder: 0.2–0.4 parts; The composite adhesive contains a composite adhesive in which the mass ratio of cold water-soluble partially hydrolyzed polyvinyl alcohol powder to ethylene-vinyl acetate copolymer dispersible latex powder is 1:2; and the degree of substitution of the highly substituted anionic starch ether is 0.65 to 0.75.

[0011] By adopting the above technical solution, the limited mass ratio narrows the molar reaction range of each active component. This control allows the crosslinking density between silanol groups, borate groups, and polymer side chain hydroxyl groups to reach a relatively balanced state, preventing the board from becoming brittle due to excessive local inorganic materials, and also avoiding internal expansion stress caused by excessive polymer when heated.

[0012] Preferably, the preparation steps of the highly substituted anionic starch ether are as follows: Natural cassava starch is mixed with a sodium hydroxide aqueous solution with a mass concentration of 20% to 30%, and the molar ratio of starch to sodium hydroxide, calculated as dehydrated glucose units, is controlled to be 1:0.8 to 1.2. The mixture is kneaded and reacted at 35 to 45 degrees Celsius for 30 to 45 minutes. Add an aqueous solution of sodium monochloroacetate to the alkalized system, controlling the molar ratio of sodium monochloroacetate to starch (based on dehydrated glucose units) to be 0.9–1.3:1, and stir the reaction at 65–75 degrees Celsius for 90–120 minutes.

[0013] By adopting the above technical solution, the hydroxyl groups on the natural cassava starch chain are first converted into sodium starch alcohol in an alkaline environment, and then undergo a nucleophilic substitution reaction with sodium monochloroacetate. The resulting anionic starch ether carries a negative charge, which, with the help of steric hindrance and electrostatic repulsion, improves the suspension stability of solid particles inside the slurry. Combined with polycarboxylate superplasticizer, it reduces the segregation of materials after mixing with water.

[0014] Preferably, the oven-dry compressive strength of the high-strength gypsum-based fiberboard ranges from 29.0 to 40.0 MPa, and the oven-dry flexural strength ranges from 15.0 to 22.0 MPa.

[0015] By adopting the above technical solution, the basic physical load-bearing capacity of the board after curing was clearly defined. This ensures that the board can withstand corresponding static loads and a certain degree of dynamic impact in practical applications, meeting the structural safety requirements of building components.

[0016] Preferably, the high-strength gypsum-based fiberboard has a fiber-reinforced composite structure: The chopped alkali-resistant glass fibers and the wood fibers are uniformly distributed in the core slurry of the high-strength gypsum-based fiberboard; The high-strength gypsum-based fiberboard has a layer of alkali-resistant glass fiber mesh fabric laminated on both the front and back sides. The two layers of alkali-resistant glass fiber mesh fabric are respectively located at the bottom of the slurry layer and 1-2 mm below the surface of the high-strength gypsum-based fiberboard.

[0017] By adopting the above technical solution, two layers of mesh fabric form tensile stress zones at the upper and lower edges of the plate cross-section. When the plate is subjected to bending force, the surface or bottom layer of glass fiber can limit the extension of internal microcracks and, in conjunction with the compressive strength of the inorganic cementitious material itself, achieve overall balance of cross-sectional stress.

[0018] Secondly, the present invention provides a method for preparing high-strength gypsum-based fiberboard, employing the following technical solution: A method for preparing a high-strength gypsum-based fiberboard includes the following steps: Weigh out desulfurized hemihydrate gypsum, rapid-hardening sulfoaluminate cement, composite adhesive, alkali-resistant glass fiber, highly substituted anionic starch ether, octyltriethoxysilane powder, powder of L-tartaric acid and anhydrous sodium sulfate in a mass ratio of 1:5, highly active amorphous microsilica powder and highly crystalline natural hard borate micro powder, and put them into a mixing kettle for dry mixing to obtain a dry mixture. The dry mix, water, and polycarboxylate-based high-performance water-reducing agent are mixed and stirred to obtain a thixotropic slurry; The thixotropic slurry is continuously extruded onto a running molding conveyor belt, and two layers of alkali-resistant glass fiber mesh are laid simultaneously. The thixotropic slurry is used to impregnate and wrap the two layers of alkali-resistant glass fiber mesh to obtain a wet slab. The wet slab enters the initial solidification section along the forming conveyor belt to undergo spontaneous hydration reaction and solidify and demold to obtain a continuous slab. The continuous slab is then cut into specified dimensions to obtain a wet slab. The wet board is fed into a continuous roller drying kiln for step drying, and then air-dried to obtain the high-strength gypsum-based fiberboard.

[0019] By employing the above technical solution, this preparation process combines rheological control, extrusion lamination, and the thermophysical phase change process of the material. Operationally, the multi-component materials are first uniformly dispersed in a physical state through dry mixing. Subsequent water addition and stirring stimulate the initial reaction of the additives to generate thixotropy in the slurry. Extrusion and mesh fabric lamination are carried out simultaneously, reducing the risk of interfacial delamination. After molding, curing is driven by the material's spontaneous hydration exothermic reaction, adapting to the time requirements for demolding and cutting in continuous industrial production. The final drying stage removes free water in a stepwise manner, fixing the microstructure of the matrix.

[0020] Preferably, in the step of dry mixing and stirring in a mixing tank to obtain a thixotropic slurry, the dry mixing time ranges from 5 to 10 minutes; the stirring speed ranges from 300 to 450 revolutions per minute; the residence time of the dry mixture in the chamber ranges from 15 to 30 seconds; and the temperature of the discharged thixotropic slurry is controlled within the range of 25 to 30 degrees Celsius.

[0021] By employing the above technical solution, specific dry mixing time and rotation speed ensured the full dispersion of powder particles, while the shear force generated by stirring activated the steric hindrance effect of the polycarboxylate superplasticizer side chains. Strict control of the discharge temperature prevented premature cross-linking of heat-sensitive components and instantaneous solidification of the mineral phase, ensuring smooth subsequent pumping.

[0022] Preferably, in the step of continuously extruding the thixotropic slurry onto the running molding conveyor belt and simultaneously laying two layers of alkali-resistant glass fiber mesh, the running speed of the molding conveyor belt is in the range of 10 to 15 meters per minute; the constant tension range for laying the two layers of alkali-resistant glass fiber mesh is 5 to 10 Newtons per meter.

[0023] By adopting the above technical solution, the conveyor belt's operating speed is matched with the slurry's flow state. Combined with constant tension control, this ensures the mesh fabric remains flat and evenly distributed in the thickness direction. The thixotropic slurry temporarily decreases in viscosity under extrusion shear force, allowing it to easily penetrate the pores of the mesh fabric. When the external force disappears, it quickly returns to its viscous state, thus achieving complete coverage of the mesh fabric's openings.

[0024] Preferably, in the step of the wet slab entering the initial solidification section along the forming conveyor belt to undergo spontaneous hydration reaction and solidify and demold to obtain a continuous slab, the core temperature of the wet slab jumps to the range of 40 to 50 degrees Celsius within 3 to 5 minutes after the wet slab is formed.

[0025] By adopting the above technical solution, the temperature rise within 3 to 5 minutes after molding indicates the end of the initial slow-setting state. At this time, a large number of hydration products rapidly crystallize and intertwine, providing the slab with the necessary early wet strength, enabling it to withstand the mechanical stress applied by the subsequent cutting flying saw.

[0026] Preferably, in the step of feeding the wet plate into a continuous roller drying kiln for stepped drying, the specific parameters of the stepped drying are set as follows: the temperature range of the first zone is 180-220 degrees Celsius, and the residence time in the first zone is 10-15 minutes; the temperature range of the second zone is 120-150 degrees Celsius, and the residence time in the second zone is 20-30 minutes; the temperature range of the third zone is 80-90 degrees Celsius, and the residence time in the third zone is 15-20 minutes.

[0027] By employing the above technical solution, the high temperature in the first zone causes the free moisture on the surface of the board to quickly convert into water vapor, establishing a moisture removal channel from the inside out; the medium temperature in the second zone drives the residual moisture deep inside to continue migrating to the surface; the low temperature stage in the third zone is mainly used for heat preservation, alleviating the thermal stress caused by rapid cooling inside the board. This stepped temperature setting, combined with the hydrogen bond fixation effect inside the material, effectively drains moisture while maintaining the integrity of the structural framework of the matrix.

[0028] This invention provides a high-strength gypsum-based fiberboard and its preparation method. It has the following beneficial effects: 1. The high-strength gypsum-based fiberboard provided by this invention, by introducing a powder composed of L-tartaric acid and anhydrous sodium sulfate to control the initial hydration reaction, is beneficial to the regulation of the rheological properties of the mixed slurry. The chelated ions generated by the dissolution of the compound powder adsorb and aggregate on the surface of the mineral particles of rapid-hardening sulfoaluminate cement and desulfurized hemihydrate gypsum, constructing a dense water-blocking adsorption layer. This physicochemical barrier weakens the early adsorption effect of liquid phase water on the core mineral phase, helps to reduce the initial apparent viscosity of the system, helps to alleviate the hidden danger of premature flash-setting and caking of high-strength cementitious materials in pumping pipelines and equipment, and helps to ensure the continuous and stable operation of industrial production lines.

[0029] 2. This invention utilizes the synergistic crosslinking effect of highly active amorphous microsilica powder and highly crystalline natural borosilicate micropowder, combined with the three-dimensional skeleton support of internal short-cut alkali-resistant glass fibers and wood fibers, to achieve a high-strength, dense core structure. This facilitates the homogenization of the material's microstructure. In the system, the inorganic micropowder locks the organic polymer network between the skeletons, and the uniformly distributed short-cut fibers and wood fibers suppress the degumming phenomenon caused by the migration of adhesive to the surface during the subsequent drying stage. This ensures that the finished board has extremely high density and nail-holding power in the thickness direction, helping to solve the defect of easy core breakage in gypsum-based materials during secondary processing.

[0030] 3. This invention integrates the microscopic bridging effect of internal short-cut fibers and the macroscopic reinforcement effect of the mesh fabric on both sides, as well as the flexible energy absorption effect of wood fibers. Combined with the built-in hydrophobic mechanism, it helps to improve the macroscopic mechanical strength and deformation resistance of the material. While improving the oven-dry strength index of the board, it also endows the product with excellent stress toughness and dimensional flatness. Combined with the fire resistance of the gypsum matrix itself, the product can replace the physical properties of traditional wood OSB boards while meeting stringent fire protection requirements. Attached Figure Description

[0031] Figure 1 This is a numerical distribution diagram of the rheological and coagulation properties of the slurry under different proportion systems of the present invention; Figure 2 This is a numerical distribution diagram of the core mechanical properties of the board material under different proportion systems of the present invention; Figure 3 This is a numerical distribution diagram of the water resistance and interfacial adhesion properties of the board under different formulation systems of the present invention; Figure 4 This is a numerical distribution diagram of the surface and core hardness gradient of the plate under different formulation systems of the present invention. Detailed Implementation

[0032] The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0033] Preparation Examples 1-5: Preparation Example 1: This preparation example provides a method for preparing highly substituted anionic starch ethers, comprising the following steps: Alkalization treatment: Natural cassava starch is placed in a reactor equipped with a high-speed shear kneader, and a 25% sodium hydroxide aqueous solution is sprayed in under vacuum. The molar ratio of starch to sodium hydroxide, based on dehydrated glucose units, is controlled at 1:1.0. The reaction is carried out at 40 degrees Celsius for 40 minutes, causing some of the hydroxyl groups on the starch molecular chains to be converted into sodium starch alcohol.

[0034] Etherification reaction: Aqueous solution of sodium monochloroacetate, the etherifying agent, is atomized and sprayed into the alkalized system. The molar ratio of sodium monochloroacetate to starch (based on dehydrated glucose units) is controlled at 1.1:1. The temperature is slowly increased to 70 degrees Celsius, and the reaction is continuously stirred for 100 minutes.

[0035] Neutralization and purification: After the reaction was completed, the pH of the system was neutralized to 7.0 using glacial acetic acid. The product was then washed and desalted using an 80% aqueous ethanol solution, and finally vacuum dried and pulverized at 60 degrees Celsius, and passed through a 100-mesh sieve to obtain a highly active anionic starch ether powder with a degree of substitution of 0.70.

[0036] Preparation Example 2: This preparation example provides a method for preparing highly substituted anionic starch ethers, comprising the following steps: Alkalization treatment: Natural cassava starch is placed in a reactor equipped with a high-speed shear kneader, and a 20% sodium hydroxide aqueous solution is sprayed in under vacuum. The molar ratio of starch to sodium hydroxide, based on dehydrated glucose units, is controlled at 1:0.8. The reaction is carried out at 35 degrees Celsius for 30 minutes, causing some of the hydroxyl groups on the starch molecular chains to be converted into sodium starch alcohol.

[0037] Etherification reaction: Aqueous solution of sodium monochloroacetate, the etherifying agent, is atomized and sprayed into the alkalized system. The molar ratio of sodium monochloroacetate to starch (based on dehydrated glucose units) is controlled at 0.9:1. The temperature is slowly increased to 65 degrees Celsius, and the reaction is continuously stirred for 90 minutes.

[0038] Neutralization and purification: After the reaction was completed, the pH of the system was neutralized to 6.5 using glacial acetic acid. The product was then washed and desalted using an 80% aqueous ethanol solution, and finally vacuum dried and pulverized at 60 degrees Celsius, and passed through a 100-mesh sieve to obtain a highly active anionic starch ether powder with a degree of substitution of 0.60.

[0039] Preparation Example 3: This preparation example provides a method for preparing highly substituted anionic starch ethers, comprising the following steps: Alkalization treatment: Natural cassava starch is placed in a reactor equipped with a high-speed shear kneader, and a 30% sodium hydroxide aqueous solution is sprayed in under vacuum. The molar ratio of starch to sodium hydroxide, based on dehydrated glucose units, is controlled at 1:1.2. The reaction is carried out at 45 degrees Celsius for 45 minutes, causing some of the hydroxyl groups on the starch molecular chains to be converted into sodium starch alcohol.

[0040] Etherification reaction: Aqueous solution of sodium monochloroacetate, the etherifying agent, is atomized and sprayed into the alkalized system. The molar ratio of sodium monochloroacetate to starch (based on dehydrated glucose units) is controlled at 1.3:1. The temperature is slowly increased to 75 degrees Celsius, and the reaction is continuously stirred for 120 minutes.

[0041] Neutralization and purification: After the reaction was completed, the pH of the system was neutralized to 7.5 using glacial acetic acid. The product was then washed and desalted using an 80% aqueous ethanol solution, and finally vacuum dried and pulverized at 60 degrees Celsius, and passed through a 100-mesh sieve to obtain a highly active anionic starch ether powder with a degree of substitution of 0.80.

[0042] Preparation Example 4: This preparation example provides a method for preparing highly substituted anionic starch ethers, comprising the following steps: Alkalization treatment: Natural cassava starch is placed in a reactor equipped with a high-speed shear kneader, and a 25% sodium hydroxide aqueous solution is sprayed in under vacuum. The molar ratio of starch to sodium hydroxide, based on dehydrated glucose units, is controlled at 1:0.9. The reaction is carried out at 38 degrees Celsius for 35 minutes, causing some of the hydroxyl groups on the starch molecular chains to be converted into sodium starch alcohol.

[0043] Etherification reaction: Aqueous solution of sodium monochloroacetate, the etherifying agent, is atomized and sprayed into the alkalized system. The molar ratio of sodium monochloroacetate to starch (based on dehydrated glucose units) is controlled at 1.0:1. The temperature is slowly increased to 68 degrees Celsius, and the reaction is continuously stirred for 100 minutes.

[0044] Neutralization and purification: After the reaction was completed, the pH of the system was neutralized to 7.5 using glacial acetic acid. The product was then washed and desalted using an 80% aqueous ethanol solution, and finally vacuum dried and pulverized at 60 degrees Celsius, and passed through a 100-mesh sieve to obtain a highly active anionic starch ether powder with a degree of substitution of 0.65.

[0045] Preparation Example 5: This preparation example provides a method for preparing highly substituted anionic starch ethers, comprising the following steps: Alkalization treatment: Natural cassava starch is placed in a reactor equipped with a high-speed shear kneader, and a 28% sodium hydroxide aqueous solution is sprayed in under vacuum. The molar ratio of starch to sodium hydroxide, based on dehydrated glucose units, is controlled at 1:1.1. The reaction is carried out at 42 degrees Celsius for 40 minutes, causing some of the hydroxyl groups on the starch molecular chains to be converted into sodium starch alcohol.

[0046] Etherification reaction: Aqueous solution of sodium monochloroacetate, the etherifying agent, is atomized and sprayed into the alkalized system. The molar ratio of sodium monochloroacetate to starch (based on dehydrated glucose units) is controlled at 1.2:1. The temperature is slowly increased to 72 degrees Celsius, and the reaction is continuously stirred for 115 minutes.

[0047] Neutralization and purification: After the reaction was completed, the pH of the system was neutralized to 7.5 using glacial acetic acid. The product was then washed and desalted using an 80% aqueous ethanol solution, and finally vacuum dried and pulverized at 60 degrees Celsius, and passed through a 100-mesh sieve to obtain a highly active anionic starch ether powder with a degree of substitution of 0.75.

[0048] Examples 1-5: Example

[0049] This embodiment provides a method for preparing high-strength gypsum-based fiberboard, including the following steps: S1. Premixing and forced chelation slurry: 90.0 parts by weight of desulfurized hemihydrate gypsum, 20.0 parts by weight of rapid-hardening sulfoaluminate cement, 6.0 parts by weight of composite adhesive, 6.0 parts by weight of chopped alkali-resistant glass fiber, 12.0 parts by weight of wood fiber, 1.0 part by weight of highly substituted anionic starch ether prepared from Preparation Example 1, 0.5 parts by weight of octyltriethoxysilane powder, 0.5 parts by weight of compound powder, 1.0 part by weight of highly active amorphous microsilica powder, and 0.3 parts by weight of highly crystalline natural hard borate micropowder are added to a mixing kettle and dry-mixed for 8 minutes. The dry mixture is then fed into a continuous pin mixer, with 65.0 parts by weight of water and 0.8 parts by weight of polycarboxylate-based high-performance water-reducing agent injected simultaneously. The mixture is stirred at a speed of 380 rpm, with the residence time of the material in the chamber controlled at 20 seconds and the temperature of the discharged slurry controlled at 28 degrees Celsius. The dispersion effect of the highly substituted anionic starch ether is used to form a three-dimensional randomly distributed support network of short fibers inside the slurry.

[0050] S2. In-situ composite of extruded fabric and mesh fabric: A thixotropic slurry containing chopped alkali-resistant glass fibers, which is uniformly stirred, is continuously extruded from the outlet onto a forming conveyor belt with a running speed of 12 meters per minute. At the slurry landing point and in front of the forming pressure roller, two layers of alkali-resistant glass fiber mesh fabric are laid at a constant tension of 8 Newtons per meter at the bottom and 1-2 millimeters below the surface of the slurry layer (i.e., the front and back sides), respectively. The slurry is used to impregnate and wrap the mesh fabric, forming a dense core reinforcement structure containing chopped fibers inside and covered with mesh fabric outside. S3, Hydration exothermic and domino crosslinking solidification: The wet slab with mesh cloth enters the initial solidification section with the conveyor belt to carry out spontaneous hydration reaction. About 4 minutes after the slab is formed, the core temperature naturally jumps to 45 degrees Celsius and solidifies and demolds. Then, the continuous slab is cut into the specified size by the flying saw at the end of the conveyor belt. S4. Multi-temperature zone step drying and chemical anchoring: The cut wet boards are sent into a continuous roller drying kiln for step drying. The first zone is set at a temperature of 200 degrees Celsius and a wind speed of 12 meters per second for 12 minutes; the second zone is set at a temperature of 135 degrees Celsius and a wind speed of 6 meters per second for 25 minutes; the third zone is set at a temperature of 85 degrees Celsius for 18 minutes; finally, the boards are removed from the warehouse and air-dried to obtain the finished product. Example

[0051] This embodiment provides a method for preparing high-strength gypsum-based fiberboard, including the following steps: S1. Premixing and Forced Chelation Pulping: 85.0 parts by weight of desulfurized hemihydrate gypsum, 25.0 parts by weight of rapid-hardening sulfoaluminate cement, 2.0 parts by weight of composite binder, 5.0 parts by weight of chopped alkali-resistant glass fiber, 10.0 parts by weight of wood fiber, 0.1 parts by weight of highly substituted anionic starch ether prepared in Preparation Example 2, 0.2 parts by weight of octyltriethoxysilane powder, 0.2 parts by weight of compound powder, 0.1 parts by weight of highly active amorphous microsilica powder, and 0.1 parts by weight of highly crystalline natural hard borate micropowder powder were added to a mixing tank and dry-mixed for 5 minutes. Then, the mixture was fed into a mixer, and 60.0 parts by weight of water and 0.2 parts by weight of polycarboxylate-based high-performance water-reducing agent were simultaneously injected. The mixture was stirred at 300 rpm, with the material held for 15 seconds, and the discharge temperature was 25 degrees Celsius. S2. In-situ composite of extruded fabric and mesh fabric: The slurry containing chopped alkali-resistant glass fibers is continuously extruded at a speed of 10 meters per minute. Two layers of alkali-resistant glass fiber mesh fabric are composited into the bottom and top slurry layers of the board with a tension of 5 Newtons per meter through the upper and lower unwinding devices, so as to achieve synergistic reinforcement of three-dimensional fibers and two-dimensional mesh. S3, Hydration exothermic and domino crosslinking solidification: The wet slab with mesh cloth moves along the conveyor belt. About 3 minutes after the slab is formed, the core temperature naturally jumps to 40 degrees Celsius and solidifies and demolds. It is then cut into the specified size. S4. Multi-temperature zone step drying and chemical anchoring: The wet board is fed into a continuous roller drying kiln for step drying. The first zone is set at 180 degrees Celsius and held for 10 minutes; the second zone is set at 120 degrees Celsius and held for 20 minutes; the third zone is set at 80 degrees Celsius and held for 15 minutes; finally, it is taken out of the warehouse and air-dried to obtain the finished product. Example

[0052] This embodiment provides a method for preparing high-strength gypsum-based fiberboard, including the following steps: S1. Premixing and Forced Chelation Pulping: 95.0 parts by weight of desulfurized hemihydrate gypsum, 15.0 parts by weight of rapid-hardening sulfoaluminate cement, 10.0 parts by weight of composite binder, 7.0 parts by weight of chopped alkali-resistant glass fiber, 15.0 parts by weight of wood fiber, 2.0 parts by weight of highly substituted anionic starch ether prepared in Preparation Example 3, 0.8 parts by weight of octyltriethoxysilane powder, 0.8 parts by weight of compound powder, 2.0 parts by weight of highly active amorphous microsilica powder, and 0.5 parts by weight of highly crystalline natural hard borate micropowder powder were added to a mixing tank and dry-mixed for 10 minutes. Then, the mixture was fed into a mixer, and 70.0 parts by weight of water and 1.5 parts by weight of polycarboxylate-based high-performance water-reducing agent were simultaneously injected. The mixture was stirred at 450 rpm, with the material held for 30 seconds, and the discharge temperature was 30 degrees Celsius. S2. In-situ composite of extruded fabric and mesh fabric: The slurry containing short-cut fibers is continuously extruded at a speed of 15 meters per minute. Simultaneously, two layers of alkali-resistant glass fiber mesh fabric are composited under the front and back surfaces of the board with a tension of 10 Newtons per meter. The high content of adhesive and fiber together construct an extremely tough wood-like board structure. S3, Hydration exothermic and domino crosslinking solidification: The wet slab with mesh cloth moves along the conveyor belt. About 5 minutes after the slab is formed, the core temperature jumps to 50 degrees Celsius and solidifies and is demolded. It is then cut into the specified size. S4. Multi-temperature zone step drying and chemical anchoring: The wet board is sent into the drying kiln for step drying. The first zone is set at 220 degrees Celsius and held for 15 minutes; the second zone is set at 150 degrees Celsius and held for 30 minutes; the third zone is set at 90 degrees Celsius and held for 20 minutes; finally, it is taken out of the warehouse and air-dried to obtain the finished product. Example

[0053] This embodiment provides a method for preparing high-strength gypsum-based fiberboard, including the following steps: S1. Premixing and Forced Chelation Pulping: 88.0 parts by weight of desulfurized hemihydrate gypsum, 18.0 parts by weight of rapid-hardening sulfoaluminate cement, 5.0 parts by weight of composite binder, 5.5 parts by weight of chopped alkali-resistant glass fiber, 11.0 parts by weight of wood fiber, 0.8 parts by weight of highly substituted anionic starch ether prepared in Preparation Example 4, 0.4 parts by weight of octyltriethoxysilane powder, 0.4 parts by weight of compound powder, 0.8 parts by weight of highly active amorphous microsilica powder, and 0.2 parts by weight of highly crystalline natural hard borate micropowder powder were added to a mixing tank and dry-mixed for 8 minutes. Then, the mixture was fed into a mixer, and 62.0 parts by weight of water and 0.5 parts by weight of polycarboxylate-based high-performance water-reducing agent were simultaneously injected. The mixture was held for 20 seconds, and the discharge temperature was 28 degrees Celsius. S2. In-situ composite of extruded fabric and mesh fabric: The slurry containing short-cut fibers is continuously extruded to a forming line with an operating speed of 12 meters per minute. Simultaneously, two layers of alkali-resistant glass fiber mesh fabric are applied to the bottom of the board and 1.5 mm away from the surface, respectively. The wetting effect of the thixotropic slurry is used to fuse the fiber mesh with the core containing short-cut fibers. S3, Hydration exothermic and domino crosslinking solidification: The wet slab with mesh cloth enters the initial solidification section with the conveyor belt to carry out spontaneous hydration reaction. About 4 minutes after the slab is formed, the core temperature naturally jumps to 45 degrees Celsius and solidifies and demolds. Then, the continuous slab is cut into the specified size by the flying saw at the end of the conveyor belt. S4. Multi-temperature zone step drying and chemical anchoring: The cut wet boards are sent into a continuous roller drying kiln for step drying. The first zone is set at a temperature of 200 degrees Celsius and a wind speed of 12 meters per second for 12 minutes; the second zone is set at a temperature of 135 degrees Celsius and a wind speed of 6 meters per second for 25 minutes; the third zone is set at a temperature of 85 degrees Celsius for 18 minutes; finally, the boards are removed from the warehouse and air-dried to obtain the finished product. Example

[0054] This embodiment provides a method for preparing high-strength gypsum-based fiberboard, including the following steps: S1. Premixing and Forced Chelation Pulping: 92.0 parts by weight of desulfurized hemihydrate gypsum, 22.0 parts by weight of rapid-hardening sulfoaluminate cement, 7.0 parts by weight of composite binder, 6.5 parts by weight of chopped alkali-resistant glass fiber, 14.0 parts by weight of wood fiber, 1.2 parts by weight of highly substituted anionic starch ether prepared in Preparation Example 5, 0.6 parts by weight of octyltriethoxysilane powder, 0.6 parts by weight of compound powder, 1.2 parts by weight of highly active amorphous microsilica powder, and 0.4 parts by weight of highly crystalline natural hard borate micropowder powder were added to a mixing tank and dry-mixed for 8 minutes. Then, the mixture was fed into a mixer, and 68.0 parts by weight of water and 1.0 part by weight of polycarboxylate-based high-performance water-reducing agent were simultaneously injected. The mixture was held for 20 seconds, and the discharge temperature was 28 degrees Celsius. S2. In-situ composite of extruded fabric and mesh fabric: The slurry containing short-cut fibers is continuously extruded at a speed of 12 meters per minute. Simultaneously, two layers of alkali-resistant glass fiber mesh fabric are composited on the front and back of the board respectively. The strong tensile properties of the mesh fabric and the dense core formed by the internal short-cut filaments are used to resist stress deformation during the drying process. S3, Hydration exothermic and domino crosslinking solidification: The wet slab with mesh cloth enters the initial solidification section with the conveyor belt to carry out spontaneous hydration reaction. About 4 minutes after the slab is formed, the core temperature naturally jumps to 45 degrees Celsius and solidifies and demolds. Then, the continuous slab is cut into the specified size by the flying saw at the end of the conveyor belt. S4. Multi-temperature zone step drying and chemical anchoring: The cut wet boards are sent into a continuous roller drying kiln for step drying. The parameters of the high-temperature zones are adjusted. Specifically, the temperature of the first zone is set at 180 degrees Celsius, the wind speed is 12 meters per second, and the residence time is 15 minutes; the temperature of the second zone is set at 135 degrees Celsius, the wind speed is 6 meters per second, and the residence time is 25 minutes; the temperature of the third zone is set at 85 degrees Celsius, and the residence time is 18 minutes; finally, the boards are removed from the warehouse and air-dried to obtain the finished product.

[0055] Comparative Examples 1-5: Comparative Example 1: Compared with Example 1, the difference is that in the premixing and forced chelation slurrying steps, the rapid-hardening sulfoaluminate cement was replaced with an equal part by weight of ordinary silicate cement, and the rest were the same.

[0056] Comparative Example 2: Compared with Example 1, the difference is that the powder composed of L-tartaric acid and anhydrous sodium sulfate in a mass ratio of 1:5 was not added in the premixing and forced chelation pulping steps, while the rest were the same.

[0057] Comparative Example 3: Compared with Example 1, the difference is that in the premixing and forced chelation pulping steps, the highly crystalline natural hard borate powder was replaced with an equal part by weight of conventional easily soluble borax powder, and all other steps were the same.

[0058] Comparative Example 4: Compared with Example 1, the difference is that in the premixing and forced chelation pulping steps, the highly active amorphous microsilica powder was replaced with an equal part by weight of conventional heavy calcium carbonate powder, and all other steps were the same.

[0059] Comparative Example 5: Compared with Example 1, the difference is that in the premixing and forced chelation pulping steps, no fast-hardening sulfoaluminate cement, highly substituted anionic starch ether obtained from Preparation Example 1, powder compounded by L-tartaric acid and anhydrous sodium sulfate in a mass ratio of 1:5, highly active amorphous microsilica powder, and highly crystalline natural borosilicate micro powder were added; all other steps were the same.

[0060] Test Examples 1-4: Test Example 1: Thixotropic pulps from Examples 1 to 5 and Comparative Examples 1 to 5, taken at the moment of completion of the premixing and forced chelation pulping steps, were used as parallel experimental subjects. Two liters of each sample were taken and quickly divided into two equal portions.

[0061] Fill the first portion of slurry into the truncated conical mold at the center of a horizontal glass plate. After smoothing the surface with a scraper, lift the mold vertically and at a constant speed. After the slurry stops spreading freely under gravity, use a vernier caliper to measure the diffusion diameter in two mutually perpendicular directions and take the average value as the initial flowability.

[0062] Seal the first remaining slurry and place it in a standard constant temperature environment of 25 degrees Celsius. After standing for 20 minutes, stir it again for 15 seconds to restore its state. Repeat the circular mold spreading steps and measure and calculate the flowability after 20 minutes.

[0063] The second portion of slurry was injected into the frustum mold of a standard Vicat apparatus, and the setting time was continuously measured under room temperature and spontaneous hydration exothermic conditions.

[0064] Record the time span from when the slurry is mixed with water until the standard test needle sinks into the neat slurry and is 4 mm away from the bottom plate as the initial setting time. Turn the specimen over, and when the test needle sinks into the specimen by 0.5 mm, that is, when the ring attachment can no longer leave a mark on the specimen, record this time point as the final setting time.

[0065] Table 1. Test data on rheological dynamics and setting time of slurry under different formulation systems Group Initial flowability (mm) Flowability (mm) after 20 minutes Initial setting time (minutes) Final setting time (minutes) Example 1 243.6 228.4 4.1 5.7 Example 2 208.5 192.4 3.0 4.2 Example 3 292.4 279.6 5.8 7.6 Example 4 225.1 210.7 3.8 5.2 Example 5 258.3 242.1 4.5 6.1 Comparative Example 1 254.9 247.3 185.3 242.8 Comparative Example 2 134.2 0.0 0.8 1.4 Comparative Example 3 168.4 112.5 3.9 5.1 Comparative Example 4 251.2 235.8 4.4 6.0 Comparative Example 5 267.5 252.1 8.5 12.3 The test results are as follows: Figure 1 The horizontal axis corresponds to the mixing systems used in Examples 1 to 5 and Comparative Examples 1 to 5, respectively. The left vertical axis represents the millimeter value of slurry diffusion, and the right vertical axis represents the logarithmic value of setting time. The solid line trajectory with circular markers shows the difference in the initial fluidity of the slurry under different systems, the dashed line trajectory with square markers represents the evolution of fluidity over twenty minutes, and the dotted line with triangle markers and the dotted line with diamond markers respectively pinpoint the kinetic time nodes of the initial and final setting of the system.

[0066] From the data in Table 1 and Figure 1It can be determined that even under the boundary condition of cutting off the excessive intake of conventional retarder, relatively precise rheological time difference control still occurred within the mixed system. The test sample in Comparative Example 2 without the introduction of tartaric acid compound powder showed extreme rheological hindrance. The slurry underwent uncontrollable and violent hydration upon contact with water, and its initial fluidity was limited to 134.2 mm and completely lost its workability within twenty minutes. This is completely consistent with the flash-setting and hardening phenomenon observed in high-dosage rapid-hardening cement systems in previous factory pilot lines. The dissolution of mineral phases directly deprived the material of the physical conditions for flow in the pumping pipeline.

[0067] When the compound powder was introduced in the specific proportions of Examples 1 to 5, the initial flowability of the system increased sharply to 243.6 mm or higher. This improvement in workability overcame the problem of high-strength cement phases being unable to be continuously extruded over long distances. The chelated ions released by the dissolution of the compound rearranged on the surface of the mineral particles to form a dense water-blocking barrier, weakening the early strong adsorption effect of liquid phase water on the core aluminate crystals, and causing the apparent viscosity to decrease sharply under hydration conditions.

[0068] Continuous Vicat penetration monitoring confirmed that the thermodynamic equilibrium within the mixed system underwent thermal phase change reforming after slab extrusion molding, and the continuously rising core hydration heat completely shattered the dormant valve mechanism. These released active crystal faces directly intervened in the network polymerization cycle of silicon-oxygen tetrahedra, forcing the slurry to undergo a macroscopic stiffness leap. The initial setting times of the example groups in Table 1, which converged within an extremely narrow range of 3.0 to 5.8 minutes, confirm this temperature-triggered point release and phase change solidification mechanism. This dynamic rheological path, constructed by ion chelation, maintains high early ductility while eliminating the huge dependence of conventional ordinary Portland cement (such as the initial setting time of up to 185.3 minutes in Comparative Example 1) on molding line length and molds, thus eliminating the risk of material blockage and jamming in continuous extrusion processes and the high cost of equipment downtime and cleaning.

[0069] Test Example 2: Wet slabs from Examples 1 to 5 and Comparative Examples 1 to 5, after curing and demolding in the initial setting stage, were extracted, and the finished slabs after final drying in the continuous roller kiln were also extracted as parallel mechanical test objects.

[0070] Two hours after demolding, the wet slab was cut into standard mechanical test blocks using a CNC cutting machine. Samples with visible microcracks on the edges were removed to control stress concentration errors caused by boundary effects.

[0071] The standard wet specimen was horizontally positioned on the testing platform of the computer-controlled universal testing machine. The center of the loading head was adjusted to coincide with the geometric center of the specimen. A constant displacement loading rate was set to continuously press down on the specimen until macroscopic brittle fracture occurred. The peak load was recorded and the early demolding wet flexural strength was calculated.

[0072] The completely dried finished boards are cut into specified sizes and placed in a constant temperature and humidity test chamber for 24 hours to release the residual thermal stress accumulated inside the core of the board during the high-temperature drying process.

[0073] The dry test blocks were mechanically tested using a universal tensile testing machine equipped with a four-point bending test fixture. A vertical uniform load was applied to the core solid area of ​​another batch of parallel test blocks to determine the compressive strength. The modulus of fracture and ultimate failure load were summarized, and the dry flexural strength and dry compressive strength of the boards in each group were calculated.

[0074] Table 2. Test data of mechanical properties of sheet metal under different mix proportions Group Early demolding wet flexural strength (MPa) Oven-dry flexural strength (MPa) Oven-dry compressive strength (MPa) Example 1 3.42 19.20 35.60 Example 2 3.98 21.85 39.65 Example 3 3.15 16.85 29.35 Example 4 3.65 16.85 31.50 Example 5 3.65 20.40 38.25 Comparative Example 1 1.15 6.43 12.88 Comparative Example 2 0.84 4.12 8.56 Comparative Example 3 1.42 7.85 15.32 Comparative Example 4 2.65 10.24 19.65 Comparative Example 5 2.05 9.56 18.23 The test results are as follows: Figure 2 This is a numerical distribution diagram of various mechanical strength indicators of the embodiments and comparative examples of the present invention. The horizontal axis in the diagram corresponds sequentially to the mix proportions used in Examples 1 to 5 and Comparative Examples 1 to 5. The left vertical axis represents the stress resistance value of the slab in the early stage of demolding, and the right vertical axis represents the ultimate resistance to damage value after complete drying. The solid line trajectory with circular markings shows the fluctuation distribution of wet flexural strength under different matrices, while the dashed line trajectory with square markings and the dotted line with triangular markings represent the span evolution of flexural and compressive strength of the slab in the oven-dry state, respectively.

[0075] According to the data in Table 2, the synergistic effect of multi-temperature zone stepped drying and chemical anchoring helps to construct a stress network interwoven with mineral crystalline phases and polymer macromolecules within the hybrid system. Comparative Example 5, the basic blank formulation, exhibits the typical mechanical limitations of pure hemihydrate gypsum materials, with its oven-dry flexural strength remaining at 9.56 MPa. During the pilot-scale production in the workshop, it was observed that this single inorganic system is prone to brittle fracture under point impact, and the lack of a flexible framework prevents the matrix from effectively dispersing concentrated stress.

[0076] When the active amorphous silica fume was replaced by conventional heavy calcium carbonate, the wet strength of Comparative Example 4 remained within the range of 2.65 MPa in the early stage of demolding. However, its oven-dry compressive strength was inhibited and decreased after leaving the high-temperature drying kiln. The evaporation of moisture to the outside caused the flexible polyvinyl alcohol lacking active silanol binding to migrate and accumulate on the surface of the board. The core of the board, due to debonding, reduced its wrapping force on the mesh and interlayer cohesion. This change in macroscopic mechanical data essentially stemmed from the peeling of the cross-linked network in the microstructure, confirming that the hydrogen bond anti-migration anchoring mechanism is beneficial for maintaining the uniformity of the slab's cross-sectional strength. Observation of Comparative Example 1, which introduced conventional ordinary Portland cement, revealed that its oven-dry compressive strength reached 12.88 MPa. The tricalcium silicate mineral phase, which did not participate in the early reaction, underwent irreversible delayed hydration expansion in the later drying and molding stage, and the derivation of microcracks cut through the continuous gypsum crystal matrix.

[0077] Data from the example groups validated the effectiveness of the matrix synergistic mechanism. The oven-dry compressive strength of Example 1 was 35.60 MPa, and the wet flexural strength in the early demolding stage reached 3.42 MPa. The rapid phase transformation of sulfoaluminate cement endowed the slab with good early stiffness to meet the cutting requirements of the conveyor belt. The hydrated calcium sulfoaluminate crystals generated, together with the anchoring network constructed by octylsilane and microsilica, improved the multi-dimensional physical and mechanical properties of the slab.

[0078] Test Example 3: The oven-dried finished boards from Examples 1 to 5 and Comparative Examples 1 to 5 were used as test subjects.

[0079] Some of the board samples were immersed in a standard constant temperature water bath at 20 degrees Celsius. After soaking for 72 hours, they were taken out, the surface water was wiped dry, and the thickness change was measured at multiple points using vernier calipers. The water absorption thickness expansion rate was calculated.

[0080] A universal testing machine was used to test the flexural strength of the specimen after it had been immersed in water for 72 hours. The measured wet strength was compared with the oven-dry flexural strength to calculate the softening coefficient of the material.

[0081] To assess the interfacial bonding performance of the mesh fabric, another batch of oven-dry board substrate was pre-cut to expose the ends of the internal alkali-resistant glass fiber mesh fabric. The test block was fixed in the lower clamp of a tensile testing machine, and the peeled mesh fabric ends were folded upwards by 180 degrees and fixed in the upper clamp. A constant tensile speed was set for the peeling operation, and the average tensile force during the peeling process was recorded and converted into the interfacial peeling force per unit width.

[0082] Table 3. Test data on water resistance and interfacial adhesion properties of the boards under different formulation systems. Group 72-hour water absorption thickness expansion rate (percentage) Softening coefficient Interfacial peel force (Newtons per millimeter) Example 1 1.30 0.86 4.52 Example 2 1.52 0.82 4.15 Example 3 1.14 0.88 4.86 Example 4 1.42 0.84 4.30 Example 5 1.35 0.87 4.68 Comparative Example 1 3.56 0.65 2.54 Comparative Example 2 4.25 0.61 1.85 Comparative Example 3 2.84 0.70 1.24 Comparative Example 4 2.55 0.72 1.56 Comparative Example 5 4.82 0.55 2.15 The test results are as follows: Figure 3 This is a numerical distribution diagram of the water resistance and interfacial adhesion properties of the board under different formulation systems of this invention. The horizontal axis corresponds sequentially to the formulation systems used in each embodiment and comparative example. The left vertical axis comprehensively represents the percentage expansion and softening coefficient of the board after immersion in water, and the right vertical axis represents the tensile force required to peel the mesh fabric from the matrix. The solid line trajectory with circular markers shows the fluctuation distribution of the thickness expansion rate, while the dashed line trajectory with square markers and the dotted line with triangular markers represent the evolution of the softening coefficient and interfacial peel force, respectively.

[0083] According to the data in Table 3, the crosslinking of inorganic minerals and organic polymers under specific conditions helps to establish a durable physicochemical barrier at the material interface. Comparative Example 5, with its basic formulation, exhibits the limitations of conventional gypsum materials in terms of water resistance, with a 72-hour water absorption thickness expansion rate of 4.82 and a softening coefficient of only 0.55. In simulated evaluations of actual water-related environments, it was observed that water molecules easily penetrate and disrupt the original crystalline bonding network, leading to a softening and crumbling of the matrix. When readily soluble conventional borax was introduced to replace the hard borate, the interfacial peeling force of Comparative Example 3 showed a numerical decline, with a measured value of only 1.24 Newtons per millimeter. This decrease in adhesive force stems from the premature crosslinking of polyvinyl alcohol molecular chains during the cold water pulping stage, resulting in a viscous, viscous paste-like state in the slurry, which prevents it from effectively penetrating and wrapping the mesh of the alkali-resistant glass fiber mesh during continuous extrusion. Comparative Example 4, due to the use of conventional calcium carbonate causing polymer migration outward, had insufficient adhesive components remaining in the core area, and its peel force also remained at a low level of 1.56 Newtons per millimeter. When subjected to external tearing, the mesh fabric easily detached from the inside of the board in pieces.

[0084] The engineering value of the aforementioned mechanism can be confirmed by combining the data from the example groups. The interfacial peel force of Example 1 reached 4.52 N / mm, and the softening coefficient after immersion in water remained in the range of 0.85. The delayed crosslinking characteristics provided by the highly crystalline borosilicate during the exothermic hydration stage preserve the necessary flow state for the full wetting of the mesh fabric in the early stage. The subsequently generated three-dimensional crosslinked network works synergistically with the hydrophobic molecules of octylsilane to limit the volume expansion of the matrix under long-term immersion conditions, thereby improving the interlayer peel resistance and water resistance stability of the overall material.

[0085] Test Example 4: The oven-dried finished boards from Examples 1 to 5 and Comparative Examples 1 to 5 were used as test subjects.

[0086] Place the board to be tested horizontally on the test table, and use a Shore D hardness tester to randomly select multiple test points on the upper surface of the board for vertical pressing test. Record and calculate the average surface hardness.

[0087] The sheet metal was horizontally sliced ​​along its thickness using a band saw to expose the internal core section. After cleaning the dust from the section, the core section was subjected to multi-point hardness testing using the same hardness tester and pressing standard, and the average value was calculated.

[0088] Subtracting the surface hardness value from the core hardness value yields the hardness difference value, which characterizes the uniformity of cross-sectional properties.

[0089] Table 4. Test data on surface and core hardness gradient of the sheet material under different formulation systems Group Surface hardness (Shore D) Core hardness (Shore D) surface and core hardness difference Example 1 65.2 64.8 0.4 Example 2 68.5 67.8 0.7 Example 3 62.1 61.5 0.6 Example 4 63.5 62.8 0.7 Example 5 66.8 65.2 0.6 Comparative Example 1 52.3 50.1 2.2 Comparative Example 2 48.5 47.0 1.5 Comparative Example 3 55.4 53.2 2.2 Comparative Example 4 72.1 42.3 29.8 Comparative Example 5 58.6 57.2 1.4 The test results are as follows: Figure 4 This is a numerical distribution diagram of the hardness gradient between the surface and core of the sheet material under different formulation systems of this invention. The horizontal axis corresponds sequentially to the formulation systems used in each embodiment and comparative example. The left vertical axis represents the Shore D hardness values ​​of the sheet material surface and core, and the right vertical axis represents the hardness difference between the two. The solid line trajectory with circular markers shows the fluctuation distribution of surface hardness, while the dashed line trajectory with square markers and the dotted line with triangular markers represent the evolution of core hardness and hardness gradient, respectively.

[0090] According to the data in Table 4, the distribution of the polymer during the drying process affected the uniformity of the physical properties of the board cross-section. Comparative Example 4, which used conventional heavy calcium carbonate to replace amorphous silica powder, exhibited an abnormal hardness distribution, with a surface hardness of 72.1 and a core hardness of 42.3, a difference of 29.8. Previous inspections of the drying process have shown that when the board enters the high-temperature drying kiln, internal moisture evaporates to the surface, and polyvinyl alcohol molecules lacking chemical bond anchoring migrate and accumulate along with the water molecules. This degumming phenomenon leads to the formation of a hard polymer shell on the surface, while the core becomes a loose structure due to the loss of the binder, reducing the overall nail-holding power and impact resistance of the board. Comparative Examples 1 to 3 and Comparative Example 5, due to limitations in overall matrix strength, exhibited relatively low surface and core hardness.

[0091] The engineering effect of the hydrogen bond anti-migration anchoring mechanism can be understood by combining the data from the example groups. In Example 1, the surface hardness was 65.2, and the core hardness was 64.8, with the hardness difference maintained within a small range of 0.4. The microsilica powder with a large specific surface area has active silanol groups on its surface. These groups form a hydrogen bond network with the hydroxyl groups of polyvinyl alcohol during the slurry mixing stage. This anchoring effect provides in-situ locking during moisture evaporation, limiting the thermal migration of polymer chain segments. The core retains the required cross-linking network, maintaining material homogeneity in the thickness direction, which helps to provide stable physical load-bearing performance in subsequent applications.

Claims

1. A high-strength gypsum-based fiberboard, characterized in that, The ingredients include the following parts by weight: Desulfurized hemihydrate gypsum: 85.0–95.0 parts; Rapid-hardening sulfoaluminate cement: 15.0–25.0 parts; Composite adhesive: 2.0–10.0 parts; Short-cut alkali-resistant glass fiber: 5.0–7.0 parts; Wood fiber: 10.0–15.0 parts; Highly substituted anionic starch ether: 0.1–2.0 parts; Octyltriethoxysilane powder: 0.2–0.8 parts; Powder composed of L-tartaric acid and anhydrous sodium sulfate in a mass ratio of 1:5: 0.2–0.8 parts; Highly active amorphous microsilica powder: 0.1–2.0 parts; Highly crystalline natural borosilicate powder: 0.1–0.5 parts; Water: 60.0–70.0 parts; Polycarboxylate-based high-performance water-reducing agent: 0.2–1.5 parts; The composite adhesive is composed of cold water-soluble partially hydrolyzed polyvinyl alcohol powder and ethylene-vinyl acetate copolymer dispersible latex powder in a mass ratio of 1:1 to 1:3; the degree of substitution of the highly substituted anionic starch ether is 0.60 to 0.

80.

2. The high-strength gypsum-based fiberboard according to claim 1, characterized in that, The weight ratio range of the raw materials is: Desulfurized hemihydrate gypsum: 88.0–92.0 parts; Rapid-hardening sulfoaluminate cement: 18.0–22.0 parts; Composite adhesive: 5.0–7.0 parts; Short-cut alkali-resistant glass fiber: 5.5–6.5 parts; Wood fiber: 10.0–15.0 parts; Highly substituted anionic starch ether: 0.6–0.8 parts; Octyltriethoxysilane powder: 0.4–0.6 parts; Powder composed of L-tartaric acid and anhydrous sodium sulfate in a mass ratio of 1:5: 0.4–0.6 parts; Highly active amorphous microsilica powder: 0.8–1.2 parts; Highly crystalline natural borosilicate powder: 0.2–0.4 parts; Water: 62.0–68.0 parts; Polycarboxylate-based high-performance water-reducing agent: 0.5–1.0 parts The composite adhesive contains a composite adhesive in which the mass ratio of cold water-soluble partially hydrolyzed polyvinyl alcohol powder to ethylene-vinyl acetate copolymer dispersible latex powder is 1:2; and the degree of substitution of the highly substituted anionic starch ether is 0.65 to 0.

75.

3. The high-strength gypsum-based fiberboard according to claim 1, characterized in that, The preparation steps of the highly substituted anionic starch ether are as follows: Natural cassava starch is mixed with a sodium hydroxide aqueous solution with a mass concentration of 20% to 30%, and the molar ratio of starch to sodium hydroxide, calculated as dehydrated glucose units, is controlled to be 1:0.8 to 1.

2. The mixture is kneaded and reacted at 35 to 45 degrees Celsius for 30 to 45 minutes. Add an aqueous solution of sodium monochloroacetate to the alkalized system, controlling the molar ratio of sodium monochloroacetate to starch (based on dehydrated glucose units) to be 0.9–1.3:1, and stir the reaction at 65–75 degrees Celsius for 90–120 minutes.

4. The high-strength gypsum-based fiberboard according to claim 1, characterized in that, The oven-dry compressive strength of the high-strength gypsum-based fiberboard ranges from 29.0 to 40.0 MPa, and the oven-dry flexural strength ranges from 15.0 to 22.0 MPa.

5. The high-strength gypsum-based fiberboard according to claim 1, characterized in that, The high-strength gypsum-based fiberboard has a fiber-reinforced composite structure. The chopped alkali-resistant glass fibers and the wood fibers are uniformly distributed in the core slurry of the high-strength gypsum-based fiberboard; The high-strength gypsum-based fiberboard has a layer of alkali-resistant glass fiber mesh fabric laminated on both the front and back sides. The two layers of alkali-resistant glass fiber mesh fabric are respectively located at the bottom of the slurry layer and 1-2 mm below the surface of the high-strength gypsum-based fiberboard.

6. A method for preparing a high-strength gypsum-based fiberboard as described in any one of claims 1-5, characterized in that, Includes the following steps: Weigh out desulfurized hemihydrate gypsum, rapid-hardening sulfoaluminate cement, composite adhesive, alkali-resistant glass fiber, wood fiber, highly substituted anionic starch ether, octyltriethoxysilane powder, powder of L-tartaric acid and anhydrous sodium sulfate in a mass ratio of 1:5, highly active amorphous microsilica powder and highly crystalline natural hard borate micropowder, and put them into a mixing kettle for dry mixing to obtain a dry mixture. The dry mix, water, and polycarboxylate-based high-performance water-reducing agent are mixed and stirred to obtain a thixotropic slurry; The thixotropic slurry is continuously extruded onto a running molding conveyor belt, and two layers of alkali-resistant glass fiber mesh are laid simultaneously. The thixotropic slurry is used to impregnate and wrap the two layers of alkali-resistant glass fiber mesh to obtain a wet slab. The wet slab enters the initial solidification section along the forming conveyor belt to undergo spontaneous hydration reaction and solidify and demold to obtain a continuous slab. The continuous slab is then cut into specified dimensions to obtain a wet slab. The wet board is fed into a continuous roller drying kiln for step drying, and then air-dried to obtain the high-strength gypsum-based fiberboard.

7. The preparation method according to claim 6, characterized in that, In the step of dry mixing and stirring in a mixing tank to obtain a thixotropic slurry, the dry mixing time ranges from 5 to 10 minutes; the stirring speed ranges from 300 to 450 revolutions per minute; the residence time of the dry mixture in the chamber ranges from 15 to 30 seconds; and the temperature of the discharged thixotropic slurry is controlled within the range of 25 to 30 degrees Celsius.

8. The preparation method according to claim 6, characterized in that, In the step of continuously extruding the thixotropic slurry onto a running molding conveyor belt and simultaneously laying two layers of alkali-resistant glass fiber mesh, the running speed of the molding conveyor belt is in the range of 10 to 15 meters per minute; the constant tension of the two layers of alkali-resistant glass fiber mesh is in the range of 5 to 10 Newtons per meter.

9. The preparation method according to claim 6, characterized in that, In the step of the wet slab entering the initial solidification section along the forming conveyor belt to undergo spontaneous hydration reaction and solidify and demold to obtain a continuous slab, the core temperature of the wet slab jumps to the range of 40 to 50 degrees Celsius within 3 to 5 minutes after the wet slab is formed.

10. The preparation method according to claim 6, characterized in that, In the step of feeding the wet plate into a continuous roller dryer for stepped drying, the specific parameters for the stepped drying are set as follows: The temperature range for the first zone is 180 to 220 degrees Celsius, and the time spent in the first zone is 10 to 15 minutes. The temperature range for the second zone is 120–150 degrees Celsius, and the time spent in the second zone is 20–30 minutes. The temperature range for the third zone is 80 to 90 degrees Celsius, and the time spent in the third zone is 15 to 20 minutes.

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