A desulfurized gypsum board and its preparation method

Abstract

This application relates to a desulfurized gypsum board and its preparation method. The raw materials for the desulfurized gypsum board include gypsum-based cementitious material, potassium sulfate, aluminum sulfate, calcium silicate seeds, acrylic acid, nano-alumina whiskers, pulp fibers, chitosan-coated casein phosphopeptide microcapsules, and water. The desulfurized gypsum board is prepared by mixing potassium sulfate, aluminum sulfate, acrylic acid, and calcium silicate seeds to obtain an ion-seed dispersion; mixing nano-alumina whiskers and pulp fibers with water to obtain a fiber-whisker suspension; mixing the ion-seed dispersion and the fiber-whisker suspension to obtain a mixed dispersion; and mixing the mixed dispersion, gypsum-based cementitious material, and chitosan-coated casein phosphopeptide microcapsules, followed by low-frequency vibration and gradient drying. This application improves flexural strength and creep resistance under high temperature and high humidity constant load conditions by controlling the gypsum dissolution-crystallization process, strengthening the crystal bridging framework, stabilizing the pore liquid ion environment, and reducing the number of defects.

Description

Technical Field

[0001] This article relates to the field of building materials technology, specifically to an anti-creep desulfurized gypsum board based on solubility control and crystal strengthening, and its preparation method. Background Technology

[0002] When desulfurized gypsum board is used for extended periods in the high-temperature and high-humidity environment of southern regions, it is prone to creep problems such as continuous deflection, bending deformation, local instability, and even cracking, which becomes a major obstacle to its large-scale application. Creep is characterized by the slow deformation of materials under long-term loads, leading to a decrease in structural stability and affecting building safety.

[0003] Through high-temperature and high-humidity accelerated aging tests and constant-load bending tests, the correlation mechanism between gypsum board creep and humidity and temperature was revealed. It was found that for hardened gypsum boards, creep is not simply a continuation of elastic deformation, but is closely related to the crystal overlap structure of dihydrate gypsum, the grain boundary connection state, pore fluid migration, and microcrack propagation. In high-humidity environments, adsorbed water films or pore fluid channels easily form on the surface and grain boundary regions of dihydrate gypsum crystals. Under long-term bending loads, localized high stress is generated at crystal overlap points, grain boundary regions, and crack tips, causing localized dissolution of dihydrate gypsum in high-stress areas. Ion migration and recrystallization then occur through pore fluid or grain boundary water films. This dissolution-migration-recrystallization process leads to the reconstruction of crystal contact relationships, a decrease in grain boundary bonding force, and relative slippage between crystals, ultimately manifesting as long-term deflection growth and creep damage in the board.

[0004] To address the aforementioned problems, existing technologies often employ additives such as surfactants, phosphates, phosphonates, and organic acid salts to improve the deformation resistance of gypsum boards. These chemicals react with the calcium on the surface of gypsum crystals. 2+ Ions form complexes, thereby reducing the dissolution rate of gypsum in water. Anti-creep additives, existing in the form of surfactants, not only affect surface properties but also the shape of gypsum crystals, resulting in a polycrystalline structure with increased strength. Phosphates and phosphonates, such as aminotris(methylenephosphonic acid) and sodium tripolyphosphate, have been industrially applied. Current research focuses on material modification; the addition of organic fibers and composite additives can significantly increase the creep resistance of gypsum boards. For example, incorporating lignin fibers and glass fibers can improve the material's toughness and resistance to deformation, and reduce humidity sensitivity.

[0005] However, while these technologies have improved the creep resistance of gypsum to some extent, they also bring other problems. For example, they may reduce the mechanical strength of gypsum materials to some degree, leading to a longer setting and hardening time. Summary of the Invention

[0006] The following is an overview of the subject matter described in detail herein. This overview is not intended to limit the scope of protection of this application.

[0007] Based on this, this application provides a creep-resistant desulfurized gypsum board preparation technology based on dissolution-crystallization balance control and crystal strengthening. This technology regulates the crystallization process of dihydrate gypsum, strengthens the crystal bonding framework, stabilizes the pore liquid ion environment, inhibits grain boundary slip, and reduces the number of defects. It solves the technical problems of traditional desulfurized gypsum boards, such as weak interlayer bonding of dihydrate gypsum crystals, which easily leads to crystal plane slip under long-term load and creep deformation. This technology achieves simultaneous improvement in the strength and long-term creep resistance of desulfurized gypsum boards.

[0008] The first aspect of this application provides a creep-resistant desulfurized gypsum board based on solubility control and crystal reinforcement. The raw materials of the desulfurized gypsum board include gypsum-based cementitious materials, potassium sulfate, aluminum sulfate, calcium silicate seeds, acrylic acid, nano-alumina whiskers, pulp fibers, chitosan-coated casein phosphopeptide microcapsules, and water.

[0009] In one exemplary embodiment, the desulfurized gypsum board is prepared by mixing potassium sulfate, aluminum sulfate, acrylic acid, and calcium silicate seed crystals to obtain an ion-seed dispersion, mixing nano-alumina whiskers and pulp fibers with water to obtain a fiber-whisker suspension, mixing the ion-seed dispersion and the fiber-whisker suspension to obtain a mixed dispersion, mixing the mixed dispersion, the gypsum-based cementitious material, and chitosan-coated casein phosphopeptide microcapsules, and then subjecting the mixture to low-frequency vibration and gradient drying to obtain the desulfurized gypsum board.

[0010] In one exemplary embodiment, the gypsum-based cementitious material is hemihydrate gypsum powder and type II anhydrous gypsum powder.

[0011] In one exemplary embodiment, the raw materials for the desulfurized gypsum board, by weight, include: 60-85 parts of hemihydrate gypsum powder, 10-20 parts of type II anhydrous gypsum powder, 0.2-1.0 parts of aluminum sulfate, 0.5-1 parts of potassium sulfate, 1-3 parts of calcium silicate seed crystals, 0.1-0.2 parts of acrylic acid, 2-3 parts of nano-alumina whiskers, 1-2 parts of pulp fiber, 0.05-0.1 parts of chitosan-coated casein phosphopeptide microcapsules, and water at 0.45-0.65 times the mass of the gypsum-based cementitious material.

[0012] In one exemplary embodiment, the water content in the raw materials of the desulfurized gypsum board is 0.45-0.60 times the mass of the gypsum-based cementitious material; preferably, it is 0.45-0.5 times.

[0013] In one exemplary embodiment, the raw materials for the desulfurized gypsum board, by weight, include: 80 parts hemihydrate gypsum powder, 10 parts type II anhydrous gypsum powder, 0.5 parts aluminum sulfate, 0.8 parts potassium sulfate, 2.5 parts calcium silicate seed crystals, 0.15 parts acrylic acid, 2.5 parts nano alumina whiskers, 1.5 parts pulp fiber, 0.1 parts chitosan-coated casein phosphopeptide microcapsules, and water at 0.5 times the mass of the gypsum-based cementitious material.

[0014] In one exemplary embodiment, the raw materials for the desulfurized gypsum board, by weight, include: 70 parts hemihydrate gypsum powder, 20 parts type II anhydrous gypsum powder, 0.5 parts aluminum sulfate, 0.8 parts potassium sulfate, 2.5 parts calcium silicate seed crystals, 0.15 parts acrylic acid, 2.5 parts nano alumina whiskers, 1.5 parts pulp fiber, 0.1 parts chitosan-coated casein phosphopeptide microcapsules, and water at 0.5 times the mass of the gypsum-based cementitious material.

[0015] In one exemplary embodiment, the raw materials for the desulfurized gypsum board, by weight, include: 80 parts hemihydrate gypsum powder, 10 parts type II anhydrous gypsum powder, 0.2 parts aluminum sulfate, 0.5 parts potassium sulfate, 2.5 parts calcium silicate seed crystals, 0.15 parts acrylic acid, 2.5 parts nano alumina whiskers, 1.5 parts pulp fiber, 0.1 parts chitosan-coated casein phosphopeptide microcapsules, and water at 0.5 times the mass of the gypsum-based cementitious material.

[0016] In one exemplary embodiment, the raw materials for the desulfurized gypsum board, by weight, include: 80 parts hemihydrate gypsum powder, 10 parts type II anhydrous gypsum powder, 1.0 part aluminum sulfate, 1.0 part potassium sulfate, 2.5 parts calcium silicate seed crystals, 0.15 parts acrylic acid, 2.5 parts nano alumina whiskers, 1.5 parts pulp fiber, 0.1 parts chitosan-coated casein phosphopeptide microcapsules, and water at 0.5 times the mass of the gypsum-based cementitious material.

[0017] In one exemplary embodiment, the raw materials for the desulfurized gypsum board, by weight, include: 80 parts hemihydrate gypsum powder, 10 parts type II anhydrous gypsum powder, 0.5 parts aluminum sulfate, 0.8 parts potassium sulfate, 1.0 part calcium silicate seed crystals, 0.10 parts acrylic acid, 2.5 parts nano alumina whiskers, 1.5 parts pulp fiber, 0.1 parts chitosan-coated casein phosphopeptide microcapsules, and water at 0.5 times the mass of the gypsum-based cementitious material.

[0018] In one exemplary embodiment, the raw materials for the desulfurized gypsum board, by weight, include: 80 parts hemihydrate gypsum powder, 10 parts type II anhydrous gypsum powder, 0.5 parts aluminum sulfate, 0.8 parts potassium sulfate, 3.0 parts calcium silicate seed crystals, 0.20 parts acrylic acid, 2.5 parts nano alumina whiskers, 1.5 parts pulp fiber, 0.1 parts chitosan-coated casein phosphopeptide microcapsules, and water at 0.5 times the mass of the gypsum-based cementitious material.

[0019] In one exemplary embodiment, the raw materials for the desulfurized gypsum board, by weight, include: 80 parts hemihydrate gypsum powder, 10 parts type II anhydrous gypsum powder, 0.5 parts aluminum sulfate, 0.8 parts potassium sulfate, 2.5 parts calcium silicate seed crystals, 0.15 parts acrylic acid, 2.0 parts nano alumina whiskers, 1.0 part pulp fiber, 0.1 parts chitosan-coated casein phosphopeptide microcapsules, and water at 0.5 times the mass of the gypsum-based cementitious material.

[0020] In one exemplary embodiment, the raw materials for the desulfurized gypsum board, by weight, include: 80 parts hemihydrate gypsum powder, 10 parts type II anhydrous gypsum powder, 0.5 parts aluminum sulfate, 0.8 parts potassium sulfate, 2.5 parts calcium silicate seed crystals, 0.15 parts acrylic acid, 3.0 parts nano alumina whiskers, 2.0 parts pulp fiber, 0.1 parts chitosan-coated casein phosphopeptide microcapsules, and water at 0.5 times the mass of the gypsum-based cementitious material.

[0021] In one exemplary embodiment, the raw materials for the desulfurized gypsum board, by weight, include: 78 parts hemihydrate gypsum powder, 12 parts type II anhydrous gypsum powder, 0.35 parts aluminum sulfate, 0.7 parts potassium sulfate, 2.0 parts calcium silicate seed crystals, 0.13 parts acrylic acid, 2.3 parts nano alumina whiskers, 1.3 parts pulp fiber, 0.1 parts chitosan-coated casein phosphopeptide microcapsules, and water at 0.5 times the mass of the gypsum-based cementitious material.

[0022] In one exemplary embodiment, the hemihydrate gypsum powder is β-type hemihydrate gypsum powder obtained by calcining industrial by-product desulfurized gypsum, wherein the CaSO4·0.5H2O content is ≥95wt%, the attached water content is ≤1.5wt%, the median particle size is 20-100μm, the residue on a 0.15mm square hole sieve is ≤10wt%, the chloride ion content is ≤0.02wt%, and the pH value is 5.5-8.5.

[0023] In one exemplary embodiment, the type II anhydrous gypsum powder is industrial-grade anhydrous calcium sulfate, wherein the CaSO4 content is ≥95wt%, the median particle size is 10-60μm, and the residue on a 0.075mm square hole sieve is ≤10wt%.

[0024] In one exemplary embodiment, the aluminum sulfate is aluminum sulfate octadechydrate, the potassium sulfate is anhydrous potassium sulfate, and both the aluminum sulfate and the potassium sulfate are industrial-grade chemical raw materials with a purity ≥96wt%.

[0025] In one exemplary embodiment, the calcium silicate seed crystal is a hydrated calcium silicate seed crystal, which is prepared by a precipitation reaction of calcium nitrate and sodium silicate; Optionally, the Ca / Si molar ratio of the calcium silicate seed crystals is 1.0-1.3; Optionally, the pH value of the calcium silicate seed crystals is 10-12; Optionally, the calcium silicate seed crystals have an average particle size of 0.1-10 μm and a specific surface area of ​​100-500 m². 2 / g.

[0026] In one exemplary embodiment, the acrylic acid is industrial-grade acrylic acid with a purity ≥98wt%.

[0027] In one exemplary embodiment, the nano-alumina whiskers have a purity ≥95wt%, a diameter of 0.1-1μm, a length of 1-20μm, and an aspect ratio of 15-20.

[0028] In one exemplary embodiment, the pulp fiber is wood pulp fiber with a fiber length of 0.5-3 mm and a moisture content of ≤10 wt%.

[0029] In one exemplary embodiment, the chitosan-coated casein phosphopeptide microcapsules use casein phosphopeptide as the core material and chitosan as the wall material, wherein the particle size of the chitosan-coated casein phosphopeptide microcapsules is 10-100 μm; preferably, it is 20-60 μm.

[0030] The second aspect of this application provides a method for preparing the above-mentioned creep-resistant desulfurized gypsum board, comprising the following steps: S1. Mix the gypsum-based cementitious materials to obtain a mixed powder; S2. Potassium sulfate and aluminum sulfate are added to water and stirred until fully dissolved. Then acrylic acid and calcium silicate seeds are added and stirred to obtain an ion-seed dispersion. Nano alumina whiskers and pulp fibers are added to water and stirred to obtain a fiber-whisker suspension. The ion-seed dispersion and the fiber-whisker suspension are mixed to obtain a mixed dispersion. S3. The mixed dispersion, the mixed powder, and the chitosan-coated casein phosphopeptide microcapsules are mixed to obtain a desulfurized gypsum slurry; S4. Pour the desulfurized gypsum slurry into a mold, apply low-frequency vibration, and after the gypsum has set, obtain a gypsum board blank; S5. The gypsum board blank is subjected to gradient drying to obtain the desulfurized gypsum board.

[0031] In one exemplary embodiment, in step S1, the gypsum-based cementitious material is mixed using a dry mixing method; Optionally, the dry mixing speed is 300-600 r / min, and the dry mixing time is 5 min.

[0032] In one exemplary embodiment, in step S2, the water added to the ion-seed dispersion accounts for 50wt%-70wt% of the total water volume.

[0033] In one exemplary embodiment, in step S2, the water added to the fiber-whisker suspension accounts for 30wt%-50wt% of the total water volume.

[0034] In an exemplary embodiment, in step S2, the stirring speed is 200-500 r / min, and the total stirring time is 9-18 min; Optionally, the stirring speed of the potassium sulfate and aluminum sulfate with water is 200-300 r / min, and the stirring time is 3-5 min; Optionally, the stirring speed after adding the acrylic acid and the calcium silicate seed crystals is 300-500 r / min, and the stirring time is 3-5 min; Optionally, the stirring speed of the nano-alumina whiskers and the pulp fibers with water is 200-500 r / min, and the stirring time is 3-8 min.

[0035] In one exemplary embodiment, step S3 further includes: first mixing the mixed dispersion with the mixed powder under stirring, and then adding the chitosan-coated casein phosphopeptide microcapsules and stirring evenly.

[0036] In one exemplary embodiment, in step S3, a twin-shaft mixer is used for mixing; Optionally, the stirring speed in step S3 is 200-500 r / min, and the total stirring time is 3-4 min.

[0037] In an exemplary embodiment, in step S3, the stirring speed after mixing the mixed dispersion with the mixed powder is 300-500 r / min, and the stirring time is 90-120 s.

[0038] In one exemplary embodiment, in step S3, the stirring speed after adding the chitosan-coated casein phosphopeptide microcapsules is 200-300 r / min, and the stirring time is 90-120 s.

[0039] In one exemplary embodiment, step S4 further includes: applying a gradient temperature field when applying low-frequency vibration; Optionally, the frequency of the low-frequency vibration is 10-20Hz, and the vibration time is 1-5min; Optionally, the gradient temperature field includes: maintaining the temperature at 40°C for 20-40 minutes during the initial molding stage, followed by raising the temperature to 50°C and maintaining it for 1 hour.

[0040] In one exemplary embodiment, step S5, the gradient drying includes: first pre-drying at 40°C for 10-14 hours, and then raising the temperature to 55°C to continue drying for 20-30 hours.

[0041] In one exemplary embodiment, the method further includes the preparation of chitosan-coated casein phosphopeptide microcapsules, comprising: 1) Dissolve casein phosphopeptides in water to obtain a core material solution; dissolve chitosan in a solvent to obtain a wall material solution; 2) Under stirring, the core material solution is slowly added to the wall material solution, and a cross-linking reaction is carried out to form a coating structure; 3) The coating structure is post-processed to obtain chitosan-coated casein phosphopeptide microcapsules.

[0042] In one exemplary embodiment, the core-to-wall mass ratio of the chitosan-coated casein phosphopeptide microcapsules is 1:0.5 to 1:1.

[0043] In one exemplary embodiment, in step 1), the solvent is a 0.5 wt%-1.0 wt% aqueous solution of acetic acid.

[0044] In one exemplary embodiment, in step 2), the stirring speed is 300-800 r / min.

[0045] In one exemplary embodiment, in step 2), the crosslinking reaction takes 10-30 minutes.

[0046] In one exemplary embodiment, step 2) further includes: adding a mild crosslinking agent to the coating structure and then performing a crosslinking reaction; Optionally, the mild crosslinking agent is an aqueous solution of tannic acid; In one exemplary embodiment, the tannic acid aqueous solution has a mass fraction of 5%. Optionally, the amount of the tannic acid aqueous solution added is 3 wt% of the dry weight of chitosan.

[0047] In one exemplary embodiment, step 3) includes the following post-processing steps: after solid-liquid separation, washing with deionized water until the pH of the washing solution is 7-8, and drying at a low temperature of 35-45°C for 12-24 hours.

[0048] The third aspect of this application provides a desulfurized gypsum board prepared by the above method.

[0049] In one exemplary embodiment, the desulfurized gypsum board has a flexural strength of 3.7-4.4 MPa, a water absorption rate of 0.9%-1.5%, and under conditions of temperature of 35-45℃, relative humidity ≥90%, and mechanical load of 5N, a deflection change of 1.5-1.9 mm after 1 day, 2.1-2.8 mm after 3 days, and 2.8-4.1 mm after 7 days.

[0050] The fourth aspect of this application provides a method for preparing chitosan-coated casein phosphopeptide microcapsules, comprising: 1) Dissolve casein phosphopeptides in water to obtain a core material solution; dissolve chitosan in a solvent to obtain a wall material solution; 2) Under stirring, the core material solution is slowly added to the wall material solution, and a cross-linking reaction is carried out to form a coating structure; 3) After cross-linking is completed, the coating structure is post-processed to obtain chitosan-coated casein phosphopeptide microcapsules.

[0051] Compared with existing technologies, the technical solution of this application focuses on the entire process of desulfurized gypsum board from hydration molding to long-term deformation under high temperature and humidity, and constructs a composite anti-creep system with synergistic effects of dissolution-crystallization regulation, crystal skeleton strengthening and defect control: 1) This application addresses the problems of uneven dissolution-crystallization, insufficient nucleation sites, and coarse crystal stacking during the hydration and hardening process of hemihydrate gypsum by constructing a synergistic system of ion regulation, heterogeneous nucleation, and crystal face growth adjustment. The dissolution-crystallization balance of the calcium sulfate system is regulated by type II anhydrous gypsum, aluminum sulfate, and potassium sulfate. Heterogeneous nucleation sites are provided by hydrated calcium silicate seeds, and the carboxyl groups in acrylic acid react with Ca... 2+ It also interacts with the active surface of gypsum dihydrate crystals, regulating the growth rate, morphology, and crystal face development of gypsum dihydrate crystals, enabling gypsum dihydrate to form a fine, interlocking, and continuous crystal skeleton, thereby improving the early strength, initial bending stiffness, and structural uniformity of the slab.

[0052] 2) This application addresses the problem of instantaneous deflection in gypsum boards under high temperature and humidity conditions during the initial bending load due to pore closure, stress adjustment at crystal overlap points, and deformation of local weak interfaces. It reduces the phenomena of large pores, uneven crystal growth, and component agglomeration by using a low water-to-gypsum ratio, stepwise dispersion, low-frequency vibration molding, and a gradient temperature field. Specifically, the gradient temperature field regulates the dissolution of hemihydrate gypsum, the crystallization of dihydrate gypsum, and the development of crystal faces, promoting uniform crystal growth and continuous overlap, and reducing local weak interfaces caused by uneven hydration. Furthermore, nano-alumina whiskers and pulp fibers form a micro-macro multi-scale reinforcing structure, improving the overall bending stiffness of the board and alleviating the phenomenon of local stress concentration during the initial stage of high temperature and humidity loading.

[0053] 3) This application addresses the problem of continuous deflection growth caused by grain boundary pressure solution migration, crystal contact relationship reconstruction, and relative slip between crystals in dihydrate gypsum under long-term high temperature and high humidity load. It stabilizes the ionic environment of the pore liquid in gypsum board under high temperature and high humidity conditions by utilizing the directional adsorption capacity of aluminum sulfate, potassium sulfate, and type II anhydrous gypsum on gypsum crystal surfaces and the common ion effect of sulfate ions, thereby reducing the tendency of dissolution-migration-recrystallization at the grain boundaries of dihydrate gypsum. At the same time, it reduces the long-term deflection growth of the board and improves the dimensional stability under high temperature and high humidity conditions by using nano-alumina whiskers to pin the grain boundaries and restrict inter-crystal slip.

[0054] 4) This application addresses the problems of easy agglomeration of nano-whiskers, easy entanglement of fibers, and easy generation of initial cracks during drying in ordinary compound systems. It improves the distribution continuity of nano-alumina whiskers, calcium silicate seeds, and pulp fibers in the pulp by stepwise dispersion, and significantly reduces pore size and defect number by low-frequency vibration. It controls the dissolution rate of hemihydrate gypsum, the supersaturation of dihydrate gypsum, and the crystal growth rate by gradient temperature field, and adjusts the crystal growth tendency of dihydrate gypsum. It reduces the difference in moisture migration inside and outside the board and the drying shrinkage stress by gradient drying, thereby reducing grain boundary cracking, paper core interface defects, and internal microcracks, thus delaying the development of the board from steady-state creep to accelerated creep damage stage.

[0055] 5) This application prepared chitosan-coated casein phosphopeptide microcapsules responsive to weakly acidic and high-humidity environments. The chitosan wall material restricts the premature release of casein phosphopeptides during the gypsum hydration stage, preventing them from binding large amounts of Ca. 2+ This affects the rapid hydration of hemihydrate gypsum and the early formation of the dihydrate gypsum crystal framework; when gypsum board is in a high-humidity or weakly acidic moisture-affected service stage, the chitosan wall material gradually dissolves, causing casein phosphopeptides to be gradually released or exposed to the surface and grain boundary regions of the dihydrate gypsum crystals. 2+ The active surface of gypsum dihydrate crystals undergoes multiple interactions, forming a grain boundary stabilizing layer and reducing the Ca content at the grain boundaries. 2+ and SO4 2- The tendency of dissolution, migration and recrystallization is reduced, thereby further suppressing pressure solution creep and deflection growth under long-term high humidity loading.

[0056] Other features and advantages of this application will be set forth in the following description, and will be apparent in part from the description, or may be learned by practicing the application. Other advantages of this application can be realized and obtained by means of the embodiments described in the description and the accompanying drawings. Attached Figure Description

[0057] The accompanying drawings are used to provide an understanding of the technical solutions of this application and constitute a part of the specification. They are used together with the embodiments of this application to explain the technical solutions of this application and do not constitute a limitation on the technical solutions of this application.

[0058] Figure 1 XRD diffraction peaks representing the effect of hydration temperature on the growth process of gypsum crystals; Figure 2 for Figure 1 Crystal orientation distribution diagram; Figure 3 The effects of adding aluminum sulfate and potassium sulfate on the morphology and structure of hydrated crystals; Figure 4 Comparison of SEM images of hydrated crystals before and after the addition of acrylic crystal modifier. Detailed Implementation

[0059] The technical solution of the present invention will be clearly and completely described below with reference to the embodiments of the present invention. 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 of ordinary skill in the art without creative effort are within the scope of protection of the present invention. It should be noted that, unless otherwise specified, the embodiments and features in the embodiments of this application can be arbitrarily combined with each other.

[0060] This application provides a creep-resistant desulfurized gypsum board based on solubility control and crystal reinforcement. The raw materials of the desulfurized gypsum board include gypsum-based cementitious materials, potassium sulfate, aluminum sulfate, calcium silicate seeds, acrylic acid, nano-alumina whiskers, pulp fibers, chitosan-coated casein phosphopeptide microcapsules, and water.

[0061] In this embodiment, the desulfurized gypsum board is prepared by mixing potassium sulfate, aluminum sulfate, acrylic acid and calcium silicate seed crystals to obtain an ion-seed dispersion, mixing nano-alumina whiskers and pulp fibers with water to obtain a fiber-whisker suspension, mixing the ion-seed dispersion and the fiber-whisker suspension to obtain a mixed dispersion, mixing the mixed dispersion, the gypsum-based cementitious material and chitosan-coated casein phosphopeptide microcapsules, and then subjecting the mixture to low-frequency vibration and gradient drying to obtain the desulfurized gypsum board.

[0062] In the embodiments of this application, the gypsum-based cementitious material is hemihydrate gypsum powder and type II anhydrous gypsum powder.

[0063] In this embodiment, the raw materials for the desulfurized gypsum board, by weight, include: 60-85 parts hemihydrate gypsum powder, 10-20 parts type II anhydrous gypsum powder, 0.2-1 parts aluminum sulfate, 0.5-1 parts potassium sulfate, 1-3 parts calcium silicate seed crystals, 0.1-0.2 parts acrylic acid, 2-3 parts nano-alumina whiskers, 1-2 parts pulp fiber, 0.05-0.1 parts chitosan-coated casein phosphopeptide microcapsules, and water as the gypsum-based cementing material. The amount can be 0.45-0.65 times the mass; for example, hemihydrate gypsum powder can be 60 parts, 70 parts, 80 parts, or 85 parts; type II anhydrous gypsum powder can be 10 parts, 11 parts, 12 parts, 13 parts, 14 parts, 15 parts, 16 parts, 17 parts, 18 parts, 19 parts, or 20 parts; aluminum sulfate can be 0.2 parts, 0.4 parts, 0.6 parts, 0.8 parts, or 1 part; potassium sulfate can be 0.5 parts, 0.6 parts, 0.7 parts, 0.8 parts, or 0.9 parts. 1 part; calcium silicate seed crystals can be 1 part, 2 parts, or 3 parts; acrylic acid can be 0.1 part, 0.2 part, 0.3 part, 0.4 part, 0.5 part, 0.6 part, 0.7 part, 0.8 part, 0.9 part, or 1.0 part; nano alumina whiskers can be 2 parts, 2.1 parts, 2.2 parts, 2.3 parts, 2.4 parts, 2.5 parts, 2.6 parts, 2.7 parts, 2.8 parts, 2.9 parts, or 3 parts; pulp fiber can be 1 part, 1.1 parts, 1.2 parts, or 1 part. 3 parts, 1.4 parts, 1.5 parts, 1.6 parts, 1.7 parts, 1.8 parts, 1.9 parts, 2 parts; chitosan-coated casein phosphopeptide microcapsules can be 0.05 parts, 0.06 parts, 0.07 parts, 0.08 parts, 0.09 parts, 0.1 parts; water is 0.45 times, 0.5 times, 0.6 times, 0.65 times the mass of gypsum-based cementitious material, but is not limited to the listed values, and other unlisted values ​​within this range are also applicable.

[0064] In the embodiments of this application, the water content in the raw materials of the desulfurized gypsum board is 0.45-0.60 times the mass of the gypsum-based cementitious material; preferably, it is 0.45-0.5 times.

[0065] In this embodiment of the application, the raw materials of the desulfurized gypsum board, by weight, include: 80 parts of hemihydrate gypsum powder, 10 parts of type II anhydrous gypsum powder, 0.5 parts of aluminum sulfate, 0.8 parts of potassium sulfate, 2.5 parts of calcium silicate seed crystals, 0.15 parts of acrylic acid, 2.5 parts of nano-alumina whiskers, 1.5 parts of pulp fiber, 0.1 parts of chitosan-coated casein phosphopeptide microcapsules, and water at 0.5 times the mass of the gypsum-based cementitious material.

[0066] In this embodiment of the application, the raw materials of the desulfurized gypsum board, by weight, include: 70 parts hemihydrate gypsum powder, 20 parts type II anhydrous gypsum powder, 0.5 parts aluminum sulfate, 0.8 parts potassium sulfate, 2.5 parts calcium silicate seed crystals, 0.15 parts acrylic acid, 2.5 parts nano alumina whiskers, 1.5 parts pulp fiber, 0.1 parts chitosan-coated casein phosphopeptide microcapsules, and water at 0.5 times the mass of the gypsum-based cementitious material.

[0067] In this embodiment of the application, the raw materials of the desulfurized gypsum board, by weight, include: 80 parts of hemihydrate gypsum powder, 10 parts of type II anhydrous gypsum powder, 0.2 parts of aluminum sulfate, 0.5 parts of potassium sulfate, 2.5 parts of calcium silicate seed crystals, 0.15 parts of acrylic acid, 2.5 parts of nano-alumina whiskers, 1.5 parts of pulp fiber, 0.1 parts of chitosan-coated casein phosphopeptide microcapsules, and water at 0.5 times the mass of the gypsum-based cementitious material.

[0068] In this embodiment of the application, the raw materials of the desulfurized gypsum board, by weight, include: 80 parts of hemihydrate gypsum powder, 10 parts of type II anhydrous gypsum powder, 1.0 part of aluminum sulfate, 1.0 part of potassium sulfate, 2.5 parts of calcium silicate seed crystals, 0.15 parts of acrylic acid, 2.5 parts of nano-alumina whiskers, 1.5 parts of pulp fiber, 0.1 parts of chitosan-coated casein phosphopeptide microcapsules, and water at 0.5 times the mass of the gypsum-based cementitious material.

[0069] In this embodiment of the application, the raw materials of the desulfurized gypsum board, by weight, include: 80 parts of hemihydrate gypsum powder, 10 parts of type II anhydrous gypsum powder, 0.5 parts of aluminum sulfate, 0.8 parts of potassium sulfate, 1.0 part of calcium silicate seed crystals, 0.10 parts of acrylic acid, 2.5 parts of nano-alumina whiskers, 1.5 parts of pulp fiber, 0.1 parts of chitosan-coated casein phosphopeptide microcapsules, and water at 0.5 times the mass of the gypsum-based cementitious material.

[0070] In the embodiments of this application, the raw materials of the desulfurized gypsum board, by weight, include: 80 parts of hemihydrate gypsum powder, 10 parts of type II anhydrous gypsum powder, 0.5 parts of aluminum sulfate, 0.8 parts of potassium sulfate, 3.0 parts of calcium silicate seed crystals, 0.20 parts of acrylic acid, 2.5 parts of nano-alumina whiskers, 1.5 parts of pulp fiber, 0.1 parts of chitosan-coated casein phosphopeptide microcapsules, and water at 0.5 times the mass of the gypsum-based cementitious material.

[0071] In the embodiments of this application, the raw materials of the desulfurized gypsum board, by weight, include: 80 parts of hemihydrate gypsum powder, 10 parts of type II anhydrous gypsum powder, 0.5 parts of aluminum sulfate, 0.8 parts of potassium sulfate, 2.5 parts of calcium silicate seed crystals, 0.15 parts of acrylic acid, 2.0 parts of nano-alumina whiskers, 1.0 part of pulp fiber, 0.1 parts of chitosan-coated casein phosphopeptide microcapsules, and water at 0.5 times the mass of the gypsum-based cementitious material.

[0072] In this embodiment of the application, the raw materials of the desulfurized gypsum board, by weight, include: 80 parts of hemihydrate gypsum powder, 10 parts of type II anhydrous gypsum powder, 0.5 parts of aluminum sulfate, 0.8 parts of potassium sulfate, 2.5 parts of calcium silicate seed crystals, 0.15 parts of acrylic acid, 3.0 parts of nano-alumina whiskers, 2.0 parts of pulp fiber, 0.1 parts of chitosan-coated casein phosphopeptide microcapsules, and water at 0.5 times the mass of the gypsum-based cementitious material.

[0073] In the embodiments of this application, the raw materials of the desulfurized gypsum board, by weight, include: 78 parts of hemihydrate gypsum powder, 12 parts of type II anhydrous gypsum powder, 0.35 parts of aluminum sulfate, 0.7 parts of potassium sulfate, 2.0 parts of calcium silicate seed crystals, 0.13 parts of acrylic acid, 2.3 parts of nano-alumina whiskers, 1.3 parts of pulp fiber, 0.1 parts of chitosan-coated casein phosphopeptide microcapsules, and water at 0.5 times the mass of the gypsum-based cementitious material.

[0074] In the embodiments of this application, the hemihydrate gypsum powder is β-type hemihydrate gypsum powder obtained by calcining industrial by-product desulfurization gypsum, wherein the CaSO4·0.5H2O content is ≥95wt%, the attached water content is ≤1.5wt%, the median particle size is 20-100μm, the residue on a 0.15mm square hole sieve is ≤10wt%, the chloride ion content is ≤0.02wt%, and the pH value is 5.5-8.5.

[0075] In the embodiments of this application, the type II anhydrous gypsum powder is industrial-grade anhydrous calcium sulfate, wherein the CaSO4 content is ≥95wt%, the median particle size is 10-60μm, and the residue on a 0.075mm square hole sieve is ≤10wt%.

[0076] In this embodiment, the aluminum sulfate is aluminum sulfate octadechydrate, the potassium sulfate is anhydrous potassium sulfate, and both the aluminum sulfate and the potassium sulfate are industrial-grade chemical raw materials with a purity ≥96wt%.

[0077] In this embodiment, the calcium silicate seed crystal is a hydrated calcium silicate seed crystal, which is obtained by precipitation reaction of calcium nitrate and sodium silicate; Optionally, the Ca / Si molar ratio of the calcium silicate seed crystals is 1.0-1.3; Optionally, the pH value of the calcium silicate seed crystals is 10-12; Optionally, the calcium silicate seed crystals have an average particle size of 0.1-10 μm and a specific surface area of ​​100-500 m². 2 / g.

[0078] In the embodiments of this application, the acrylic acid is industrial grade acrylic acid with a purity ≥98wt%.

[0079] In the embodiments of this application, the purity of the nano-alumina whiskers is ≥95wt%, the diameter is 0.1-1μm, the length is 1-20μm, and the aspect ratio is 15-20.

[0080] In the embodiments of this application, the pulp fiber is wood pulp fiber with a fiber length of 0.5-3 mm and a moisture content of ≤10 wt%.

[0081] In this embodiment, the chitosan-coated casein phosphopeptide microcapsules use casein phosphopeptide as the core material and chitosan as the wall material, wherein the microcapsule particle size is 10-100 μm; preferably, the capsule particle size is 20-60 μm.

[0082] This application also provides a method for preparing the above-mentioned creep-resistant desulfurized gypsum board, comprising the following steps: S1. Mix the gypsum-based cementitious materials to obtain a mixed powder; S2. Potassium sulfate and aluminum sulfate are added to water and stirred until fully dissolved. Then acrylic acid and calcium silicate seeds are added and stirred to obtain an ion-seed dispersion. Nano alumina whiskers and pulp fibers are added to water and stirred to obtain a fiber-whisker suspension. The ion-seed dispersion and the fiber-whisker suspension are mixed to obtain a mixed dispersion. S3. Mix the mixed dispersion, the mixed powder, and chitosan-coated casein phosphopeptide microcapsules to obtain a desulfurized gypsum slurry; S4. Pour the desulfurized gypsum slurry into a mold, apply low-frequency vibration, and after the gypsum has set, obtain a gypsum board blank; S5. The gypsum board blank is subjected to gradient drying to obtain the desulfurized gypsum board.

[0083] In this embodiment of the application, in step S1, the gypsum-based cementitious material is mixed by a dry mixing method; Optionally, the dry mixing speed is 300-600 r / min, and the dry mixing time is 5 min.

[0084] In this embodiment of the application, in step S2, the water added to the ion-seed dispersion accounts for 50wt%-70wt% of the total water volume.

[0085] In this embodiment of the application, in step S2, the water added to the fiber-whisker suspension accounts for 30wt%-50wt% of the total water volume.

[0086] In this embodiment of the application, in step S2, the stirring speed is 200-500 r / min, and the total stirring time is 9-18 min; Optionally, the stirring speed of the potassium sulfate and aluminum sulfate with water is 200-300 r / min, and the stirring time is 3-5 min; Optionally, the stirring speed after adding the acrylic acid and the calcium silicate seed crystals is 300-500 r / min, and the stirring time is 3-5 min; Optionally, the stirring speed of the nano-alumina whiskers and the pulp fibers with water is 200-500 r / min, and the stirring time is 3-8 min.

[0087] In this embodiment of the application, step S3 further includes: first mixing the mixed dispersion with the mixed powder under stirring, and after the slurry is initially uniform, adding the chitosan-coated casein phosphopeptide microcapsules and stirring evenly to make the microcapsules uniformly dispersed in the slurry.

[0088] In this embodiment of the application, a twin-shaft mixer is used for stirring in step S3; Optionally, the stirring speed in step S3 is 200-500 r / min, and the total stirring time is 3-4 min.

[0089] In this embodiment of the application, in step S3, the stirring speed after the mixed dispersion and the mixed powder are mixed is 300-500 r / min, and the stirring time is 90-120 s.

[0090] In this embodiment of the application, in step S3, after adding the chitosan-coated casein phosphopeptide microcapsules, the stirring speed is 200-300 r / min and the stirring time is 90-120 s.

[0091] In this embodiment of the application, step S4 further includes: applying a gradient temperature field when applying low-frequency vibration; Optionally, the frequency of the low-frequency vibration is 10-20Hz, and the vibration time is 1-5min; Optionally, the gradient temperature field includes: maintaining the temperature at 40°C for 20-40 minutes during the initial molding stage, followed by raising the temperature to 50°C and maintaining it for 1 hour.

[0092] In this embodiment of the application, step S5, the gradient drying includes: first pre-drying at 40°C for 10-14 hours, and then raising the temperature to 55°C to continue drying for 20-30 hours.

[0093] In this embodiment of the application, the method further includes the preparation of chitosan-coated casein phosphopeptide microcapsules, comprising: 1) Dissolve casein phosphopeptides in water to obtain a core material solution; dissolve chitosan in a solvent to obtain a wall material solution; 2) Under stirring, the core material solution is slowly added to the wall material solution, so that casein phosphopeptides and chitosan undergo electrostatic recombination and cross-linking reaction to form a coating structure; 3) After the cross-linking reaction, the coating structure is post-processed to obtain chitosan-coated casein phosphopeptide microcapsules.

[0094] In the embodiments of this application, the core-to-wall mass ratio of the chitosan-coated casein phosphopeptide microcapsules is 1:0.5 to 1:1.

[0095] In the embodiments of this application, in step 1), the solvent is a 0.5-1.0 wt% aqueous solution of acetic acid.

[0096] In this embodiment of the application, in step 2), the stirring speed is 300-800 r / min.

[0097] In this embodiment of the application, in step 2), the crosslinking reaction takes 10-30 minutes.

[0098] In this embodiment of the application, step 2) further includes: adding a mild crosslinking agent to the coating structure and then carrying out a crosslinking reaction; Optionally, the mild crosslinking agent is an aqueous solution of tannic acid.

[0099] In this embodiment of the application, the mass fraction of the tannic acid aqueous solution is 5%. Optionally, the amount of the tannic acid aqueous solution added is 3 wt% of the dry weight of chitosan.

[0100] In this embodiment of the application, step 3) includes the following post-processing: after solid-liquid separation, washing with deionized water until the pH of the washing solution is 7-8, and drying at a low temperature of 35-45℃ for 12-24 hours.

[0101] This application also provides a desulfurized gypsum board prepared by the above method.

[0102] In the embodiments of this application, the desulfurized gypsum board has a flexural strength of 3.7-4.4 MPa, a water absorption rate of 0.9%-1.5%, and under conditions of temperature of 35-45℃, relative humidity ≥90%, and mechanical load of 5N, the deflection change is 1.5-1.9 mm after 1 day, 2.1-2.8 mm after 3 days, and 2.8-4.1 mm after 7 days.

[0103] This application also provides a method for preparing chitosan-coated casein phosphopeptide microcapsules, comprising: 1) Dissolve casein phosphopeptides in water to obtain a core material solution; dissolve chitosan in a solvent to obtain a wall material solution; 2) Under stirring, the core material solution is slowly added to the wall material solution, and a cross-linking reaction is carried out to form a coating structure; 3) After cross-linking is completed, the coating structure is post-processed to obtain chitosan-coated casein phosphopeptide microcapsules.

[0104] The present application will be further described in detail below with reference to specific embodiments, but these embodiments should not be construed as limiting the present application. All other embodiments obtained by those skilled in the art based on the embodiments in this application without inventive effort are within the scope of protection of this invention.

[0105] The raw materials used in this application are all conventional products on the market.

[0106] Unless otherwise specified, all materials and reagents used in the embodiments of this application are commercially available.

[0107] Experimental methods not specified in the examples are generally performed under standard conditions or as recommended by the manufacturer.

[0108] In the examples and comparative examples: The hemihydrate gypsum powder is a β-type hemihydrate gypsum powder obtained by calcining industrial by-product desulfurized gypsum. The content of CaSO4·0.5H2O is ≥95wt%, the content of attached water is ≤1.5wt%, the median particle size is 20-100μm, the residue on a 0.15mm square hole sieve is ≤10wt%, the chloride ion content is ≤0.02wt%, and the pH value is 5.5-8.5. Type II anhydrous gypsum powder is industrial-grade anhydrous calcium sulfate, with a CaSO4 content ≥95wt%, a median particle size of 10-60μm, and a residue of ≤10wt% on a 0.075mm square-hole sieve. Aluminum sulfate and potassium sulfate are aluminum sulfate octahydrate and anhydrous potassium sulfate, respectively. Both inorganic salts are industrial-grade chemical raw materials with a purity ≥96wt%. The nano-alumina whiskers have a purity of ≥95wt%, a diameter of 0.1-1μm, a length of 1-20μm, and an aspect ratio of 15-20. The acrylic acid is industrial grade, with a purity of ≥98wt%. Chitosan-coated casein phosphopeptide microcapsules use casein phosphopeptide as the core material and chitosan as the wall material, with a microcapsule particle size of 20-60 μm. The calcium silicate seed crystals have a Ca / Si molar ratio of 1.0-1.3, a pH value of 10-12, an average particle size of 0.1-10 μm, and a specific surface area of ​​100-500 m². 2 / g; The pulp fiber is wood pulp fiber with a fiber length of 0.5-3mm and a moisture content of ≤10wt%.

[0109] Example 1 This embodiment is based on a creep-resistant desulfurized gypsum board with solubility control and crystal reinforcement. The board is composed of the following raw materials in parts by weight: The mixture consists of 80 parts hemihydrate gypsum powder, 10 parts type II anhydrous gypsum powder, 0.5 parts aluminum sulfate, 0.8 parts potassium sulfate, 2.5 parts nano alumina whiskers, 0.15 parts acrylic acid, 2.5 parts calcium silicate seed crystals, 1.5 parts pulp fiber, and 0.1 parts chitosan-coated casein phosphopeptide microcapsules, with a water-to-gypsum ratio of 0.50.

[0110] The preparation method includes the following steps: S1. Add hemihydrate gypsum powder and type II anhydrous gypsum powder to the mixer and mix at a speed of 500 r / min for 5 min to obtain mixed powder. S2, aluminum sulfate and potassium sulfate are added to water accounting for 70 wt% of the total water volume, and stirred at 250 r / min for 5 min until fully dissolved. Then, acrylic acid and calcium silicate seeds are added, and stirred at 400 r / min for 5 min to obtain an ion-seed dispersion. Alumina whiskers and pulp fibers are added to the remaining 30 wt% of water, and stirred at 300 r / min for 5 min to obtain a fiber-whisker suspension. Finally, the dispersion and suspension are mixed to obtain a mixed solution. S3, the mixed dispersion obtained in step S2 and the mixed powder obtained in step S1 are added to a biaxial mixer and stirred at 300 r / min for 90 s. Then, chitosan-coated casein phosphopeptide microcapsules are added, and stirring continues at 200 r / min for 90 s to obtain a uniform desulfurized gypsum slurry. The chitosan-coated casein phosphopeptide microcapsules are prepared as follows: casein phosphopeptides are added to water and stirred to dissolve, obtaining a core material solution; chitosan is added to a 1.0 wt% acetic acid aqueous solution and stirred to dissolve, obtaining... The core material solution was slowly added to the chitosan solution under stirring at 300 r / min, so that casein phosphopeptides and chitosan could electrostatically recombine and form a coating structure. Then, tannic acid aqueous solution was added for mild cross-linking for 10 min. After cross-linking, the mixture was separated into solid and liquid components, washed with deionized water until the pH of the washing solution was 7, and dried at 35℃ for 12 h to obtain chitosan-coated casein phosphopeptide microcapsules. The core-to-wall mass ratio of the microcapsules was 1:0.5 and the particle size was 60 μm.

[0111] S4. Pour the desulfurized gypsum slurry obtained in step S3 into the mold, smooth it, apply 15Hz low-frequency vibration for 120s, and keep it in a 40℃ environment for 30min. Then raise the temperature to 50℃ and keep it for 1h. After hardening, take out the gypsum board blank. S5, the gypsum board blank is first pre-dried at 40℃ for 12h, then heated to 55℃ and dried for another 24h, and then cooled to obtain creep-resistant desulfurized gypsum board.

[0112] Example 2 This example is based on a creep-resistant desulfurized gypsum board with solubility control and crystal reinforcement, which is composed of the following raw materials by weight: The mixture consists of 70 parts hemihydrate gypsum powder, 20 parts type II anhydrous gypsum powder, 0.5 parts aluminum sulfate, 0.8 parts potassium sulfate, 2.5 parts nano alumina whiskers, 0.15 parts acrylic acid, 2.5 parts calcium silicate seed crystals, 1.5 parts pulp fiber, and 0.1 parts chitosan-coated casein phosphopeptide microcapsules, with a water-to-gypsum ratio of 0.50.

[0113] The preparation method is the same as in Example 1.

[0114] Example 3 This example describes a creep-resistant desulfurized gypsum board based on solubility control and crystal reinforcement. The board is composed of the following raw materials in parts by weight: The mixture consists of 80 parts hemihydrate gypsum powder, 10 parts type II anhydrous gypsum powder, 0.2 parts aluminum sulfate, 0.5 parts potassium sulfate, 2.5 parts nano alumina whiskers, 0.15 parts acrylic acid, 2.5 parts calcium silicate seed crystals, 1.5 parts pulp fiber, and 0.1 parts chitosan-coated casein phosphopeptide microcapsules, with a water-to-gypsum ratio of 0.50.

[0115] The preparation method is the same as in Example 1.

[0116] Example 4 This example describes a creep-resistant desulfurized gypsum board based on solubility control and crystal reinforcement. The board is composed of the following raw materials in parts by weight: The mixture contains 80 parts hemihydrate gypsum powder, 10 parts type II anhydrous gypsum powder, 1.0 part aluminum sulfate, 1.0 part potassium sulfate, 2.5 parts nano alumina whiskers, 0.15 parts acrylic acid, 2.5 parts calcium silicate seed crystals, 1.5 parts pulp fiber, and 0.1 parts chitosan-coated casein phosphopeptide microcapsules, with a water-to-gypsum ratio of 0.50.

[0117] The preparation method is the same as in Example 1.

[0118] Example 5 This example describes a creep-resistant desulfurized gypsum board based on solubility control and crystal reinforcement. The board is composed of the following raw materials in parts by weight: The mixture consists of 80 parts hemihydrate gypsum powder, 10 parts type II anhydrous gypsum powder, 0.5 parts aluminum sulfate, 0.8 parts potassium sulfate, 2.5 parts nano alumina whiskers, 0.10 parts acrylic acid, 1.0 part calcium silicate seed crystals, 1.5 parts pulp fiber, and 0.1 parts chitosan-coated casein phosphopeptide microcapsules, with a water-to-gypsum ratio of 0.50.

[0119] The preparation method is the same as in Example 1.

[0120] Example 6 This example demonstrates the preparation of a creep-resistant desulfurized gypsum board based on solubility control and crystal reinforcement. The board is composed of the following raw materials in parts by weight: The mixture consists of 80 parts hemihydrate gypsum powder, 10 parts type II anhydrous gypsum powder, 0.5 parts aluminum sulfate, 0.8 parts potassium sulfate, 2.5 parts nano alumina whiskers, 0.20 parts acrylic acid, 3.0 parts calcium silicate seed crystals, 1.5 parts pulp fiber, and 0.1 parts chitosan-coated casein phosphopeptide microcapsules, with a water-to-gypsum ratio of 0.50.

[0121] The preparation method is the same as in Example 1.

[0122] Example 7 This example demonstrates the preparation of a creep-resistant desulfurized gypsum board based on solubility control and crystal reinforcement. The board is composed of the following raw materials in parts by weight: The mixture contains 80 parts hemihydrate gypsum powder, 10 parts type II anhydrous gypsum powder, 0.5 parts aluminum sulfate, 0.8 parts potassium sulfate, 2.0 parts nano alumina whiskers, 0.15 parts acrylic acid, 2.5 parts calcium silicate seed crystals, 1.0 part pulp fiber, and 0.1 parts chitosan-coated casein phosphopeptide microcapsules, with a water-to-gypsum ratio of 0.50.

[0123] The preparation method is the same as in Example 1.

[0124] Example 8 This example demonstrates the preparation of a creep-resistant desulfurized gypsum board based on solubility control and crystal reinforcement. The board is composed of the following raw materials in parts by weight: The mixture contains 80 parts hemihydrate gypsum powder, 10 parts type II anhydrous gypsum powder, 0.5 parts aluminum sulfate, 0.8 parts potassium sulfate, 3.0 parts nano alumina whiskers, 0.15 parts acrylic acid, 2.5 parts calcium silicate seed crystals, 2.0 parts pulp fiber, and 0.1 parts chitosan-coated casein phosphopeptide microcapsules, with a water-to-gypsum ratio of 0.50.

[0125] The preparation method is the same as in Example 1.

[0126] Example 9 This example demonstrates the preparation of a creep-resistant desulfurized gypsum board based on solubility control and crystal reinforcement. The board is composed of the following raw materials in parts by weight: The mixture contains 78 parts hemihydrate gypsum powder, 12 parts type II anhydrous gypsum powder, 0.35 parts aluminum sulfate, 0.7 parts potassium sulfate, 2.3 parts nano alumina whiskers, 0.13 parts acrylic acid, 2.0 parts calcium silicate seed crystals, 1.3 parts pulp fiber, and 0.1 parts chitosan-coated casein phosphopeptide microcapsules, with a water-to-gypsum ratio of 0.50.

[0127] The preparation method is the same as in Example 1.

[0128] Comparative Example 1 This comparative example provides a desulfurized gypsum board and its preparation method.

[0129] The raw materials for desulfurized gypsum board are the same as in Example 1, except that type II anhydrous gypsum is not added and the amount of hemihydrate gypsum powder is adjusted to 90 parts by weight.

[0130] The preparation method is the same as in Example 1.

[0131] Comparative Example 2 This comparative example provides a desulfurized gypsum board and its preparation method.

[0132] The raw materials for desulfurized gypsum board are the same as in Example 1, except that aluminum sulfate and potassium sulfate are not added.

[0133] The preparation method is the same as in Example 1.

[0134] Comparative Example 3 This comparative example provides a desulfurized gypsum board and its preparation method.

[0135] The raw materials for desulfurized gypsum board are the same as in Example 1, except that calcium silicate seed crystals and acrylic acid are not added.

[0136] The preparation method is the same as in Example 1.

[0137] Comparative Example 4 This comparative example provides a desulfurized gypsum board and its preparation method.

[0138] The raw materials for desulfurized gypsum board are the same as in Example 1, except that nano-alumina whiskers are not added.

[0139] The preparation method is the same as in Example 1.

[0140] Comparative Example 5 This comparative example provides a desulfurized gypsum board and its preparation method.

[0141] The raw materials for desulfurized gypsum board are the same as in Example 1, except that no pulp fiber is added.

[0142] The preparation method is the same as in Example 1.

[0143] Comparative Example 6 This comparative example provides a desulfurized gypsum board and its preparation method.

[0144] The raw material for desulfurized gypsum board is the same as in Example 1, except that chitosan-coated casein phosphopeptide microcapsules are not added.

[0145] The preparation method is the same as in Example 1.

[0146] Comparative Example 7 This comparative example provides a desulfurized gypsum board and its preparation method.

[0147] The raw material for desulfurized gypsum board is prepared in accordance with Example 1, except that 0.1 parts of chitosan-coated casein phosphopeptide microcapsules are replaced with 0.1 parts of uncoated casein phosphopeptide.

[0148] The preparation method is the same as in Example 1.

[0149] Comparative Example 8 This comparative example provides a desulfurized gypsum board and its preparation method.

[0150] The preparation method is the same as in Example 1, except that in step S2, all raw materials and water are added to the mixer at once and mixed.

[0151] The raw materials for desulfurized gypsum board are prepared in accordance with the method described in Example 1.

[0152] Comparative Example 9 This comparative example provides a desulfurized gypsum board and its preparation method. The preparation method is the same as in Example 1, except that low-frequency vibration is not performed in step S4.

[0153] The raw materials for desulfurized gypsum board are prepared in accordance with the method described in Example 1.

[0154] Comparative Example 10 This comparative example provides a desulfurized gypsum board and its preparation method. The preparation method is the same as in Example 1, except that gradient drying is not used in step S5, but rather the board is dried in one go at 55°C for 36 hours.

[0155] The raw materials for desulfurized gypsum board are prepared in accordance with the method described in Example 1.

[0156] Performance testing: 1. The flexural strength of the gypsum boards prepared in each embodiment and comparative example was tested in accordance with GB / T17669.3-1999 "Determination of Mechanical Properties of Building Gypsum".

[0157] 2. The method for measuring the water absorption rate of gypsum board is as follows: After drying each group of gypsum samples to constant weight, measure the absolute dry mass of the samples. Then, completely immerse them in water until the sample is saturated and its mass is constant. Remove them, wipe them dry, and weigh them to measure the mass of the samples after water absorption. Define m0 as the mass before water absorption and m1 as the mass after water absorption. Calculate the water absorption rate.

[0158] 3. The static three-point bending method was used to test the creep process of the gypsum boards in each embodiment and comparative example under constant load in a high temperature and high humidity environment. The test was carried out in a constant temperature and humidity chamber with the following environmental conditions: temperature 35℃, relative humidity 95%, sample size 300mm×50mm×5mm, span 250mm, mechanical load of 5N applied at the center of the gypsum board for 7 days, and continuous change of deflection of the sample measured by a laser rangefinder, and the deflection magnitude at 1d, 3d and 7d was recorded.

[0159] The test results obtained from Examples 1-9 and Comparative Examples 1-10 are shown in Table 1.

[0160] Table 1 According to Table 1: Compared with Example 1, Example 2 showed a decrease in flexural strength, an increase in water absorption, and a decline in flexural creep resistance. This is because, while type II anhydrous gypsum powder can regulate the dissolution-crystallization balance of the calcium sulfate system to some extent, excessive dosage reduces the relative proportion of rapidly hydrated hemihydrate gypsum in the system, affecting the early formation of the continuous dihydrate gypsum crystal framework, thus leading to a decrease in the initial strength and creep resistance of the slab.

[0161] Compared to Example 1, Example 3 showed a smaller decrease in the basic strength of the slab, but a more significant increase in 7-day deflection, indicating insufficient inhibition of long-term constant-load bending deformation. This is because while lower amounts of aluminum sulfate and potassium sulfate can still regulate the pore liquid ion environment, their effects on promoting the uniform growth of dihydrate gypsum crystals during the hydration stage of hemihydrate gypsum and inhibiting the pressure-dissolution migration of dihydrate gypsum under high temperature and humidity conditions are weaker than in Example 1.

[0162] Compared to Example 1, Example 4 showed a significant decrease in flexural strength, an increase in water absorption, and a marked decline in creep resistance. This is because excessive aluminum sulfate and potassium sulfate increase the ionic strength of the slurry, easily causing localized flocculation. This affects the uniform dispersion of hemihydrate gypsum particles, calcium silicate seeds, and nano-alumina whiskers, and also leads to uneven crystal overlap and increased local weak interfaces, resulting in decreased flexural strength, increased water absorption, and reduced creep resistance.

[0163] Compared to Example 1, Example 5 showed a decrease in flexural strength, an increase in water absorption, and a significant increase in long-term deflection. This is because insufficient calcium silicate seed crystals reduce the heterogeneous nucleation sites of gypsum dihydrate, and insufficient acrylic acid reduces the carboxyl groups' influence on Ca... 2+The regulatory effect of the active surface of gypsum dihydrate crystals is weakened, making it difficult to effectively regulate ion release, supersaturation and crystal growth rate during the hydration process of hemihydrate gypsum. This makes gypsum dihydrate crystals prone to forming large, unevenly stacked structures, leading to increased porosity defects and local stress concentration, ultimately affecting various properties.

[0164] Compared to Example 1, Example 6 showed little change in the water absorption rate of the board, but a decrease in strength and creep resistance. This is because a higher dosage of the crystal-refining component enhances crystal refinement, but when the amount of acrylic acid is too high, its carboxyl groups excessively complex with Ca. 2+ Excessive adsorption of calcium silicate seeds onto the active surface of gypsum dihydrate crystals can excessively delay the hydration of hemihydrate gypsum and the formation of the gypsum dihydrate crystal framework, thus affecting early strength development. Simultaneously, an excessive number of calcium silicate seeds may also cause localized agglomeration, reducing the uniformity of the crystal structure.

[0165] Compared with Example 1, the strength, water absorption rate and 1d deflection of the plate in Example 7 remained almost unchanged, but the 3d deflection and 7d deflection increased significantly. This is because when the amount of nano-alumina whiskers and pulp fibers is insufficient, the grain boundary pinning structure and the fiber bridging network in the tension zone are not sufficient. The plate's ability to restrict grain boundary slip and microcrack propagation under long-term constant load decreases. In the later stage of steady-state creep and accelerated creep stage, the plate's ability to impede grain boundary slip and crack propagation is lower than that in Example 1, so the deflection growth is more obvious in the later stage.

[0166] Compared with Example 1, the strength, water absorption rate and creep resistance of the board in Example 8 decreased slightly. This is because when there is an excess of nano-alumina whiskers and pulp fibers, whisker agglomeration and fiber entanglement are likely to occur, which increases the water absorption demand, reduces the uniformity of pulp dispersion, forms local weak interfaces and fiber enrichment areas, and leads to a decrease in overall performance.

[0167] In Example 9, all components are within the preferred range of the present invention and can achieve the effects of hydration regulation of hemihydrate gypsum, crystal skeleton refinement, grain boundary pinning and fiber bridging. However, its ion regulation component, seed crystal component, and fiber nano alumina whiskers and pulp fiber are slightly lower than those in Example 1. The crystal skeleton refinement, grain boundary pinning and crack bridging effects are slightly weaker. Therefore, the overall performance is slightly lower than that of Example 1.

[0168] As observed in Example 1 and Comparative Example 1, the absence of Type II anhydrous gypsum powder leads to a slight decrease in the strength and hygrothermal stability of the slab. The fundamental reason is that Type II anhydrous gypsum powder can stabilize the dissolution-crystallization balance during the hydration process of hemihydrate gypsum during service. Without Type II anhydrous gypsum powder, the nucleation and growth process of dihydrate gypsum crystals becomes uneven, and the continuity of the crystal skeleton decreases, resulting in a reduction in the flexural stiffness and creep resistance of the slab.

[0169] Examples 1 and 2 show that the absence of aluminum sulfate and potassium sulfate significantly reduces the strength of the gypsum board and increases high-temperature and high-humidity creep deformation. The root cause is that aluminum sulfate and potassium sulfate can synergistically regulate the pore liquid ionic environment in stages. During the hydration stage of hemihydrate gypsum, aluminum sulfate promotes the growth of dihydrate crystals, forming more regular columnar gypsum crystals. In the creep stage of the gypsum board, the common ion effect of sulfate ions and Al... 3+ K + The adsorption effect on the (020) crystal plane of gypsum reduces SO4 at the grain boundaries of dihydrate gypsum. 2- and Ca 2+ The dissolution-migration-recrystallization tendency is evident; without this ion regulation system, the growth of gypsum dihydrate crystals is less complete, and under long-term load, pressure solution migration and grain boundary reconstruction are more likely to occur, ultimately resulting in lower flexural strength and greater deflection.

[0170] As observed in Examples 1 and 3, the absence of acrylic acid and calcium silicate seed crystals also leads to a decrease in the flexural strength of the slab and an increase in deflection. The fundamental reason is that calcium silicate seed crystals provide heterogeneous nucleation sites for dihydrate gypsum crystals, forming a denser, continuous framework structure and reducing pore size; acrylic acid, as a small-molecule carboxylic acid crystal modifier, can react with Ca through its carboxyl groups. 2+ And the active surface of dihydrate gypsum crystals acts to regulate the Ca content during the hydration process of hemihydrate gypsum. 2+ The release rate affects the growth rate of gypsum dihydrate crystals, preventing them from growing too rapidly and coarsely. Without either, gypsum dihydrate crystals tend to form large, unevenly stacked structures, increasing localized high-stress contact points and porosity defects, leading to accelerated bending deformation and creep in the slab.

[0171] Examples 1 and 4 show that the absence of nano-alumina whiskers leads to a significant increase in 3-day and 7-day deflection. The fundamental reason is that nano-alumina whiskers can form bridging, interlocking, and pinning effects between gypsum dihydrate crystals, restricting relative slip between crystals and hindering microcrack propagation. The absence of nano-alumina whiskers reduces the anti-slip ability of grain boundaries, making microcracks more likely to propagate and connect, resulting in an increased creep rate in the later stages of steady-state creep and the accelerated creep stage.

[0172] As observed in Example 1 and Comparative Example 5, the absence of pulp fibers leads to a decrease in flexural strength and an increase in deflection. The fundamental reason is that pulp fibers, as short-cut fibers dispersed within the gypsum core material, can form a flexible bridging network in the gypsum matrix, bridging microcracks in the tension zone and undertaking a binding effect; without pulp fibers, microcracks are easily and rapidly connected, ultimately leading to a decrease in creep resistance.

[0173] Examples 1 and 6 show that the absence of chitosan-coated casein phosphopeptide microcapsules has little impact on the initial flexural strength and water absorption of the slab. However, the strength retention after water absorption and the long-term creep resistance under high temperature and humidity significantly decrease. This is because the chitosan-coated casein phosphopeptide microcapsules, through the coating effect of the chitosan wall material, limit the premature release of casein phosphopeptides during the gypsum hydration and molding stage, and do not significantly interfere with the rapid hydration of hemihydrate gypsum and the early formation of the dihydrate gypsum crystal framework. Under weakly acidic or high-humidity conditions, the chitosan wall material absorbs water and swells, causing casein phosphopeptides to be gradually released to the surface and grain boundary regions of the dihydrate gypsum crystals. Since the phosphate groups in the casein phosphopeptide molecules can rapidly react with Ca... 2+ The active surface of gypsum dihydrate crystals undergoes multi-point coordination or adsorption, forming an interfacial stabilizing layer containing phosphate groups on the crystal surface and grain boundary regions, significantly reducing the Ca2+ content at the grain boundaries. 2+ and SO4 2- It inhibits the dissolution, migration, and recrystallization tendencies of gypsum dihydrate, thereby suppressing grain boundary pressure solution, crystal contact relationship reconstruction, and relative slip between crystals.

[0174] As observed in Example 1 and Comparative Example 7, the flexural strength of the slab significantly decreased after replacing the casein phosphopeptide with uncoated casein phosphopeptide, and the deflection at 24 h and 72 h was still significantly higher than that in Example 1. This indicates that uncoated casein phosphopeptide participates in the hydration reaction prematurely and damages the early crystal framework, while also failing to maintain its grain boundary stabilizing effect during long-term high-humidity loading. The fundamental reason is that uncoated casein phosphopeptide is directly exposed to the hydration system during the gypsum slurry mixing stage, and the phosphate groups in its molecules react prematurely with Ca. 2+ Complexation occurs, and the gypsum adsorbs onto the active surfaces of hemihydrate and newly formed dihydrate crystals. This disrupts the processes of hemihydrate dissolution, dihydrate nucleation, and crystal scaffold formation, thereby reducing the early strength and crystal structure continuity of the slab. On the other hand, uncoated casein phosphopeptides are consumed or fixed on the early crystal surface during the initial hydration stage, making it difficult for them to continuously migrate to high-stress areas such as grain boundaries, crystal scaffolds, and crack tips during long-term high-temperature and high-humidity loading. Therefore, they are insufficient in inhibiting later grain boundary pressure dissolution, ion migration, and intercrystalline slip.

[0175] As observed in Example 1 and Comparative Example 8, directly mixing all raw materials leads to a significant decrease in the strength and creep resistance of the board. The fundamental reason is that nano-alumina whiskers and pulp fibers are prone to agglomeration when not dispersed in stages, and calcium silicate seeds are difficult to distribute uniformly, resulting in discontinuous grain boundary pinning structures and fiber bridging networks. Staged mixing can effectively improve the uniformity of pulp dispersion and the continuity of the creep-resistant structure of the board.

[0176] As observed in Example 1 and Comparative Example 9, the absence of low-frequency vibration leads to a decrease in the strength of the sheet material, a significant increase in water absorption, and a greater change in deflection. The fundamental reason is that low-frequency vibration can promote the degassing of the slurry and the uniform distribution of components, reducing large pores and local defects. Without low-frequency vibration, the porosity and stress concentration points caused by microbubbles inside the sheet material increase, making pressure solution creep and crack propagation more likely to occur.

[0177] As observed in Example 1 and Comparative Example 10, the absence of gradient drying resulted in lower flexural strength and significantly increased 3-day and 7-day deflections in the sheet. The fundamental reason is that direct high-temperature drying easily leads to uneven moisture migration inside and outside the slab, causing grain boundary cracking, drying shrinkage stress concentration, and internal microcracks. Gradient drying, on the other hand, can slowly remove internal moisture, reduce drying defects, thereby reducing crack initiation during subsequent bending creep and improving creep resistance.

[0178] Where there is no conflict, the features in the above embodiments and comparative examples can be combined with each other.

[0179] In summary, the technical solution of this application focuses on the entire process of desulfurized gypsum board from hydration molding to long-term deformation under high temperature and humidity, and constructs a composite anti-creep system with synergistic effects of dissolution-crystallization regulation, crystal skeleton strengthening, and defect control: 1) This application addresses the problems of uneven dissolution-crystallization, insufficient nucleation sites, and coarse crystal stacking during the hydration and hardening process of hemihydrate gypsum by constructing a synergistic system of ion regulation, heterogeneous nucleation, and crystal face growth adjustment. The dissolution-crystallization balance of the calcium sulfate system is regulated by type II anhydrous gypsum, aluminum sulfate, and potassium sulfate. Heterogeneous nucleation sites are provided by hydrated calcium silicate seeds, and the carboxyl groups in acrylic acid react with Ca... 2+ It also interacts with the active surface of gypsum dihydrate crystals, regulating the growth rate, morphology, and crystal face development of gypsum dihydrate crystals, enabling gypsum dihydrate to form a fine, interlocking, and continuous crystal skeleton, thereby improving the early strength, initial bending stiffness, and structural uniformity of the slab.

[0180] 2) This application addresses the problem of instantaneous deflection in gypsum boards under high temperature and humidity conditions during the initial bending load due to pore closure, stress adjustment at crystal overlap points, and deformation of local weak interfaces. It reduces the phenomena of large pores, uneven crystal growth, and component agglomeration by using a low water-to-gypsum ratio, stepwise dispersion, low-frequency vibration molding, and a gradient temperature field. Specifically, the gradient temperature field regulates the dissolution of hemihydrate gypsum, the crystallization of dihydrate gypsum, and the development of crystal faces, promoting uniform crystal growth and continuous overlap, and reducing local weak interfaces caused by uneven hydration. Furthermore, nano-alumina whiskers and pulp fibers form a micro-macro multi-scale reinforcing structure, improving the overall bending stiffness of the board and alleviating the phenomenon of local stress concentration during the initial stage of high temperature and humidity loading.

[0181] 3) This application addresses the problem of continuous deflection growth caused by grain boundary pressure solution migration, crystal contact relationship reconstruction, and relative slip between crystals in dihydrate gypsum under long-term high temperature and high humidity load. It stabilizes the ionic environment of the pore liquid in gypsum board under high temperature and high humidity conditions by utilizing the directional adsorption capacity of aluminum sulfate, potassium sulfate, and type II anhydrous gypsum on gypsum crystal surfaces and the common ion effect of sulfate ions, thereby reducing the tendency of dissolution-migration-recrystallization at the grain boundaries of dihydrate gypsum. At the same time, it reduces the long-term deflection growth of the board and improves the dimensional stability under high temperature and high humidity conditions by using nano-alumina whiskers to pin the grain boundaries and restrict inter-crystal slip.

[0182] 4) This application addresses the problems of easy agglomeration of nano-whiskers, easy entanglement of fibers, and easy generation of initial cracks during drying in ordinary compound systems. It improves the distribution continuity of nano-alumina whiskers, calcium silicate seeds, and pulp fibers in the pulp by stepwise dispersion, and significantly reduces pore size and defect number by low-frequency vibration. It controls the dissolution rate of hemihydrate gypsum, the supersaturation of dihydrate gypsum, and the crystal growth rate by gradient temperature field, and adjusts the crystal growth tendency of dihydrate gypsum. It reduces the difference in moisture migration inside and outside the board and the drying shrinkage stress by gradient drying, thereby reducing grain boundary cracking, paper core interface defects, and internal microcracks, thus delaying the development of the board from steady-state creep to accelerated creep damage stage.

[0183] 5) This application prepared chitosan-coated casein phosphopeptide microcapsules responsive to weakly acidic and high-humidity environments. The chitosan wall material restricts the premature release of casein phosphopeptides during the gypsum hydration stage, preventing them from binding large amounts of Ca. 2+ This affects the rapid hydration of hemihydrate gypsum and the early formation of the dihydrate gypsum crystal framework; when gypsum board is in a high-humidity or weakly acidic moisture-affected service stage, the chitosan wall material gradually dissolves, causing casein phosphopeptides to be gradually released or exposed to the surface and grain boundary regions of the dihydrate gypsum crystals. 2+ The active surface of gypsum dihydrate crystals undergoes multiple interactions, forming a grain boundary stabilizing layer and reducing the Ca content at the grain boundaries. 2+ and SO4 2- The tendency of dissolution, migration and recrystallization is reduced, thereby further suppressing pressure solution creep and deflection growth under long-term high humidity loading.

[0184] Although embodiments of this application have been shown and described above, it is understood that the above embodiments are exemplary and should not be construed as limiting this application. Those skilled in the art can make changes, modifications, substitutions and variations to the above embodiments within the scope of this application.

Claims

1. A desulfurized gypsum board, wherein the raw materials of the desulfurized gypsum board include gypsum-based cementitious materials, potassium sulfate, aluminum sulfate, calcium silicate seeds, acrylic acid, nano-alumina whiskers, pulp fibers, chitosan-coated casein phosphopeptide microcapsules, and water; in, The gypsum-based cementitious material is hemihydrate gypsum powder and type II anhydrous gypsum powder; The desulfurized gypsum board is prepared by mixing potassium sulfate, aluminum sulfate, acrylic acid, and calcium silicate seed crystals to obtain an ion-seed dispersion, mixing nano-alumina whiskers and pulp fibers with water to obtain a fiber-whisker suspension, mixing the ion-seed dispersion and the fiber-whisker suspension to obtain a mixed dispersion, mixing the mixed dispersion, the gypsum-based cementitious material, and chitosan-coated casein phosphopeptide microcapsules, and then subjecting the mixture to low-frequency vibration and gradient drying to obtain the desulfurized gypsum board.

2. The desulfurized gypsum board according to claim 1, wherein, The raw materials for the desulfurized gypsum board, by weight, include: 60-85 parts hemihydrate gypsum powder, 10-20 parts type II anhydrous gypsum powder, 0.2-1.0 parts aluminum sulfate, 0.5-1 parts potassium sulfate, 1-3 parts calcium silicate seed crystals, 0.1-0.2 parts acrylic acid, 2-3 parts nano alumina whiskers, 1-2 parts pulp fiber, 0.05-0.1 parts chitosan-coated casein phosphopeptide microcapsules, and water at 0.45-0.65 times the mass of the gypsum-based cementitious material.

3. The desulfurized gypsum board according to claim 1 or 2, wherein, The hemihydrate gypsum powder is a β-type hemihydrate gypsum powder obtained by calcining industrial by-product desulfurized gypsum, wherein the CaSO4·0.5H2O content is ≥95wt%, the attached water content is ≤1.5wt%, the median particle size is 20-100μm, the residue on a 0.15mm square-hole sieve is ≤10wt%, the chloride ion content is ≤0.02wt%, and the pH value is 5.5-8.5; and / or The type II anhydrous gypsum powder is industrial-grade anhydrous calcium sulfate, wherein the CaSO4 content is ≥95wt%, the median particle size is 10-60μm, and the residue on a 0.075mm square-hole sieve is ≤10wt%; and / or The aluminum sulfate is aluminum sulfate octadechydrate, and the potassium sulfate is anhydrous potassium sulfate. Both the aluminum sulfate and the potassium sulfate are industrial-grade chemical raw materials with a purity ≥96wt%; and / or The calcium silicate seed crystals are hydrated calcium silicate seed crystals with a Ca / Si molar ratio of 1.0-1.3, a pH value of 10-12, an average particle size of 0.1-10 μm, and a specific surface area of ​​100-500 m². 2 / g; and / or The acrylic acid is industrial grade acrylic acid with a purity ≥98wt%; and / or The nano-alumina whiskers have a purity ≥95wt%, a diameter of 0.1-1μm, a length of 1-20μm, and an aspect ratio of 15-20; and / or The pulp fibers are wood pulp fibers with a fiber length of 0.5-3 mm and a moisture content of ≤10 wt%; and / or The chitosan-coated casein phosphopeptide microcapsules have a particle size of 10-100 μm.

4. The desulfurized gypsum board according to claim 1 or 2, wherein, The desulfurized gypsum board has a flexural strength of 3.7-4.4 MPa and a water absorption rate of 0.9%-1.5%. Under conditions of temperature 35-45℃, relative humidity ≥90%, and mechanical load of 5N, the deflection change is 1.5-1.9 mm after 1 day, 2.1-2.8 mm after 3 days, and 2.8-4.1 mm after 7 days.

5. A method for preparing desulfurized gypsum board according to any one of claims 1 to 4, comprising the following steps: S1. Mix the gypsum-based cementitious materials to obtain a mixed powder; S2. Potassium sulfate and aluminum sulfate are added to water and stirred until fully dissolved. Then acrylic acid and calcium silicate seeds are added and stirred to obtain an ion-seed dispersion. Nano alumina whiskers and pulp fibers are added to water and stirred to obtain a fiber-whisker suspension. The ion-seed dispersion and the fiber-whisker suspension are mixed to obtain a mixed dispersion. S3. The mixed dispersion, the mixed powder, and the chitosan-coated casein phosphopeptide microcapsules are mixed to obtain a desulfurized gypsum slurry; S4. Pour the desulfurized gypsum slurry into a mold, apply low-frequency vibration, and after the gypsum has set, obtain a gypsum board blank; S5. The gypsum board blank is subjected to gradient drying to obtain the desulfurized gypsum board.

6. The method according to claim 5, wherein, In step S1, the gypsum-based cementitious material is mixed using a dry mixing method; Optionally, the dry mixing speed is 300-600 r / min, and the dry mixing time is 5 min.

7. The method according to claim 5 or 6, wherein, In step S2, the water added to the ion-seed dispersion accounts for 50wt%-70wt% of the total water volume; and / or The water added to the fiber-whisker suspension accounts for 30wt%-50wt% of the total water volume; and / or The stirring speed is 200-500 r / min, and the total stirring time is 9-18 min.

8. The method according to claim 5 or 6, wherein, Step S3 further includes: first mixing the mixed dispersion with the mixed powder under stirring, and then adding the chitosan-coated casein phosphopeptide microcapsules and stirring evenly. Optionally, a twin-shaft mixer is used for mixing in step S3; Optionally, the stirring speed in step S3 is 200-500 r / min, and the total stirring time is 3-4 min.

9. The method according to claim 5 or 6, wherein, Step S4 also includes: applying a gradient temperature field when applying low-frequency vibration; Optionally, the frequency of the low-frequency vibration is 10-20Hz, and the vibration time is 1-5min; Optionally, the gradient temperature field includes: maintaining the temperature at 40°C for 20-40 minutes during the initial molding stage, followed by raising the temperature to 50°C and maintaining it for 1 hour.

10. The method according to claim 5 or 6, wherein, In step S5, the gradient drying includes: first pre-drying at 40°C for 10-14 hours, and then raising the temperature to 55°C to continue drying for 20-30 hours.

11. The method according to claim 5 or 6, wherein, The method also includes the preparation of chitosan-coated casein phosphopeptide microcapsules, including: 1) Dissolve casein phosphopeptides in water to obtain a core material solution; dissolve chitosan in a solvent to obtain a wall material solution; 2) Under stirring, the core material solution is slowly added to the wall material solution, and a cross-linking reaction is carried out to form a coating structure; 3) Post-process the coating structure to obtain chitosan-coated casein phosphopeptide microcapsules; Optionally, the solvent is a 0.5 wt%-1.0 wt% aqueous solution of acetic acid; Optionally, the core-to-wall mass ratio of the chitosan-coated casein phosphopeptide microcapsules is 1:0.5 to 1:1; Optionally, the crosslinking reaction takes 10-30 minutes; Optionally, in step 3), the post-processing includes: after solid-liquid separation, washing with deionized water until the pH of the washing solution is 7-8, and drying at a low temperature of 35-45℃ for 12-24 hours.

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