A lightweight, flexural gypsum board reinforced with plant fiber composite

Abstract

This invention relates to the field of inorganic composite materials technology, specifically to a lightweight, flexurally resistant gypsum board reinforced with plant fibers. The plant short fibers used in the gypsum board are impregnated with calcium hydroxide solution and fumigated with sulfur dioxide gas, resulting in an in-situ calcium sulfite / calcium sulfate microcrystalline coating layer on their surface. This enhances the interfacial bonding between the fibers and the gypsum matrix. During preparation, a dry-mixing followed by wet-mixing process ensures component uniformity. A combination of vacuum filtration and hot-pressing is used to achieve rapid dehydration and high-pressure compaction of the slurry. The gypsum board produced by this invention maintains its lightweight nature while exhibiting excellent flexural strength and impact resistance, solving the problem of insufficient mechanical properties in traditional lightweight gypsum boards.

Description

Technical Field

[0001] This invention relates to the field of inorganic composite materials technology, specifically to a lightweight, flexural gypsum board reinforced with plant fiber composites. Background Technology

[0002] Gypsum board, a widely used building material for interior walls, partitions, and ceilings, requires a balance between lightweight and sufficient mechanical strength, especially flexural strength. Traditional gypsum board achieves lightweighting primarily through two methods: one is by incorporating lightweight aggregates into the matrix or introducing chemical foaming to create a porous structure; the other is by using low-density reinforcing fibers. However, these methods often come with a loss of strength, particularly a significant decrease in flexural strength and toughness. This leads to problems such as breakage and edge damage during transportation, installation, and load-bearing, limiting its application in situations requiring high structural safety and dimensional stability.

[0003] Replacing some traditional fibers with plant short fibers, such as straw and rice straw, as a reinforcing phase is considered a potential technical approach due to its lower cost and ability to help adjust material density. However, natural plant fibers have poor physicochemical compatibility with inorganic gypsum matrices, resulting in weak interfacial bonding. On the one hand, the hydrophilicity of the fibers leads to the existence of a water film layer between them and the gypsum slurry, weakening the mechanical anchoring force. On the other hand, the elastic moduli of the two are mismatched, resulting in low stress transfer efficiency. This means that the reinforcing and toughening effect of the fibers does not meet theoretical expectations. Simply adding plant short fibers often results in limited improvement in the bending strength of the board, or even reduces its bending strength due to the introduction of structural defects.

[0004] To further improve interfacial performance, existing technologies employ various pretreatments for fibers, such as alkali treatment and coupling agent coating. While these methods have some effect, they often have limitations: either the chemical bond between the modified layer and the gypsum hydration products is weak, or the processes are complex, significantly increasing costs, and may damage the strength of the fiber itself. Meanwhile, the final performance of the board also depends on the molding process; traditional casting molding and natural dehydration methods struggle to achieve both uniform fiber dispersion and pulp densification.

[0005] In summary, existing gypsum board technology struggles to achieve high flexural strength and high toughness while maintaining lightweight properties. The core issue lies in the lack of a modification method to improve the interfacial bonding between plant fibers and the gypsum matrix, as well as a supporting process to achieve uniform fiber dispersion and molding.

[0006] Chinese patent publication number CN103420662A discloses a monolithically reinforced gypsum board. Specifically, it discloses a monolithically reinforced gypsum board comprising a body and a reinforcing material mesh uniformly disposed within the body. The body's composition by weight is: 100 parts gypsum powder with a fineness of 750-1000 mesh, the gypsum powder being a mixture of hemihydrate gypsum and dihydrate gypsum in a mass ratio of 8:1-1:2; 5-10 parts defibrinated plant fibers with a length of 5-30 mm and a linear density of 10-20 dtex; 100-150 parts fly ash with a fineness of 1000-1200 mesh; 0.5-1 parts coupling agent; 5-7 parts binder; 1-2 parts sodium sulfate; and 40-60 parts water. This invention uses plant fibers and reinforcing material mesh to reinforce gypsum board, effectively improving the strength of the gypsum board, thereby improving its quality, reducing production and process difficulty, and lowering production costs, thus increasing enterprise efficiency. However, the gypsum board produced by this invention only possesses high strength and does not have the advantages of being lightweight and having excellent flexibility. Summary of the Invention

[0007] The purpose of this invention is to provide a lightweight, flexural gypsum board reinforced with plant fibers, in order to solve the problems mentioned in the background art, namely, the lack of a modification method to improve the interfacial bonding between plant fibers and gypsum matrix, and a set of molding processes to achieve uniform fiber dispersion.

[0008] To achieve the above objectives, the present invention provides the following technical solution:

[0009] A lightweight, flexural gypsum board reinforced with plant fiber composites, comprising the following components in parts by weight:

[0010] 100 parts building gypsum powder, 5-15 parts modified plant short fiber, 1-3 parts cellulose nanofibers, 10-30 parts auxiliary cementitious materials, 0.3-1.2 parts polycarboxylate superplasticizer, 0.3-1.5 parts calcium stearate, and 0.05-0.3 parts protein retarder.

[0011] Preferably, the specific surface area of ​​the building gypsum powder is 300 m². 2 / kg~500m 2 / kg, and its residue on a 120-mesh sieve is <5%.

[0012] Preferably, the raw material for the modified plant short fiber is wheat straw or rice straw, with a length of 1-3 mm and an aspect ratio greater than 20. The preparation steps of the modified plant short fiber are as follows:

[0013] (1) Immerse the plant short fibers in a calcium hydroxide solution with a concentration of 1.5~2.2g / L, with a mass ratio of solution to fiber of 10:1~30:1, and soak at 15~35℃ for 10~60min. After soaking, remove the fibers and drain until there is no dripping to obtain a wet calcified fiber precursor.

[0014] (2) Place the drained calcified fiber in a closed reactor and introduce sulfur dioxide gas with a volume fraction of 5-15%. Fumigate the fiber for 10-30 minutes at a relative humidity of 60-80% and a temperature of 15-35℃. After the reaction is completed, take out the fiber, treat it with tail gas absorption, and dry it in a forced-air drying oven at 60-80℃ to obtain modified plant short fiber.

[0015] Plant short fibers, such as wheat straw or rice straw, are used as reinforcing phases to address the contradiction between lightweighting and improving mechanical properties of gypsum board, leveraging their renewable, low-cost, and low-density characteristics. However, natural plant fibers, due to their smooth surface, strong hydrophilicity, and chemical inertness, exhibit weak interfacial bonding with the gypsum matrix. Direct incorporation not only results in low reinforcement efficiency but also easily becomes a source of defects. Therefore, this invention employs a calcification fumigation method for modification: First, the fibers are immersed in a calcium hydroxide solution, allowing highly reactive calcium ions to adsorb onto their surface. Subsequently, sulfur dioxide gas is introduced under controlled humidity, causing it to react with the calcium on the fiber surface, generating an in-situ micro / nano-scale calcium sulfite / calcium sulfate mineralized crystal coating layer. This mineralized layer is similar to the gypsum matrix in chemical composition and crystal structure, thereby transforming the original weak contact interface into a strong bonding interface. In the final board, these modified short fibers transfer the stress in the gypsum matrix to the fiber body through the strong interface layer on their surface, and play multiple roles in inhibiting crack propagation and absorbing impact energy, ultimately achieving the goal of reducing the density of the board while improving its bending strength and impact resistance.

[0016] Preferably, the auxiliary cementing material is granulated blast furnace slag powder.

[0017] This invention achieves improved structural strength while maintaining the material's lightweight nature through precise control of its components. Specifically, architectural gypsum powder, as the base cementitious material, forms a dense matrix together with auxiliary cementitious materials. The microstructure is optimized using a polycarboxylate superplasticizer. Modified plant short fibers serve as a macroscopic reinforcing phase, achieving a high-strength interfacial bond with the gypsum matrix through their surface inorganic mineralization layer. Cellulose nanofibers further strengthen the matrix at the nanoscale, forming a reinforcing network. Calcium stearate and protein-based retarder ensure material stability and process feasibility by reducing water absorption and controlling setting time, respectively. This formulation system, through the synergistic effect of interfacial modification and microstructure optimization, solves the problem of insufficient flexural strength in lightweight gypsum boards.

[0018] A method for preparing a plant fiber composite reinforced lightweight flexural gypsum board includes the following steps:

[0019] Step S1: Add building gypsum powder, auxiliary cementitious materials, calcium stearate, and protein retarder to the mixer for the first dry mixing. The mixer speed is 200~400 rpm and the mixing time is 2~5 min. Then add polycarboxylate superplasticizer for the second dry mixing. Increase the mixer speed to 400~600 rpm and the mixing time is 1~3 min to obtain a uniform mixed dry powder.

[0020] Step S2: Pour the mixed dry powder into a mixer. While stirring at 100-200 rpm, first add cellulose nanofibers and water (55-75% of the weight of gypsum powder). Increase the stirring speed to 300-500 rpm and stir for 1-2 minutes to form a uniform matrix slurry. Then add modified plant short fibers and stir at high speed (600-900 rpm) for 2-3 minutes to form a uniformly fluid fiber composite slurry.

[0021] Step S3: Inject the fiber composite slurry into a molding mold lined with a 300-400 mesh filter screen, turn on the vacuum system to make the vacuum degree of the mold -0.08~-0.092MPa, filter and dewater for 1~3 minutes until the moisture content of the slurry is 8~12%, forming a wet slab with a density of 1100~1300kg / m3. Transfer the mold with the wet slab to a hot press, apply a planar pressure of 1~2.5MPa, and simultaneously raise the temperature of the slab to 60~80℃ within 3 minutes, and maintain it at this temperature and pressure for 15~30 minutes.

[0022] Step S4: Release the pressure and demold. Place the slab in a circulating hot air drying oven at 65~80℃ and dry for 4~8 hours. Turn off the heat source and cool the slab to below 40℃ under circulating air. After cutting to length, the plant fiber composite reinforced lightweight flexural gypsum board is obtained.

[0023] Preferably, in step S1, after obtaining a uniform mixed dry powder through the second dry mixing, the mixed dry powder is left to stand and age for 5-15 minutes.

[0024] Aging can eliminate static electricity generated during dry mixing, allowing powder particles to relax stress and reach a more stable state, which is beneficial for subsequent rapid and uniform contact with water.

[0025] Preferably, in step S2, the cellulose nanofibers are mixed with 20 to 50 times their weight of water before being added, and then pre-dispersed by ultrasonic treatment with a power of 300 to 500W for 5 to 15 minutes.

[0026] Preferably, in step S3, while applying vacuum pressure, a vertical mechanical vibration with a frequency of 25~50Hz is applied to the mold, and the vibration duration is the entire filtration and dewatering period.

[0027] Compared with the prior art, the beneficial effects of the present invention are:

[0028] 1. This invention constructs an enhanced composite material structure through inorganic mineralization modification technology on the fiber surface. The short plant fibers treated with calcium hydroxide and sulfur dioxide form an in-situ calcium sulfite / calcium sulfate coating layer on their surface, achieving a highly compatible interface with the gypsum matrix. This solves the problem of poor reinforcement effect of traditional plant fibers. Furthermore, it forms a multi-level reinforcing network with nanoscale cellulose nanofibers, thereby improving the flexural strength and impact strength of the board while maintaining the material's lightweight properties.

[0029] 2. The vacuum filtration, dehydration, and hot-pressing compaction process used in this invention is coordinated with the material system. Vacuum filtration ensures rapid and uniform distribution of fibers and solid particles and initial skeleton compaction, avoiding delamination and defects that are easy to occur in traditional processes. Subsequent hot-pressing curing promotes deep dehydration of the slurry and densification of the matrix. This process plays a role in fiber reinforcement and ensures the stability of product performance. Detailed Implementation

[0030] To enable those skilled in the art to better understand the present application, the technical solutions in the embodiments of the present application will be clearly and completely described below. Obviously, the described embodiments are only some embodiments of the present application, and not all embodiments. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without creative effort should fall within the scope of protection of the present application.

[0031] Example 1

[0032] A lightweight, flexural gypsum board reinforced with plant fiber composites, comprising the following components in parts by weight:

[0033] 100 parts building gypsum powder, 10 parts modified plant short fiber, 2 parts CNF-2000 cellulose nanofibers, 20 parts granulated blast furnace slag powder, ViscoCrete ® -0.8 parts PC 40 polycarboxylate superplasticizer, 1.0 part calcium stearate, Daratard ® 17. Protein retarder 0.2 parts.

[0034] The preparation steps of modified plant short fibers are as follows:

[0035] (1) Wheat short fibers with a length of 2 mm and an aspect ratio of 25 were immersed in a calcium hydroxide solution with a concentration of 1.8 g / L. The mass ratio of solution to fiber was 20:1. The solution was soaked at 25°C for 40 min. After soaking, the fiber was removed and drained until no dripping occurred, thus obtaining a wet calcified fiber precursor.

[0036] (2) Place the drained calcified fiber in a closed reactor, introduce sulfur dioxide gas with a volume fraction of 10%, and fumigate for 30 minutes at a relative humidity of 80% and a temperature of 25℃. After the reaction is completed, take out the fiber, treat it with tail gas absorption, and dry it in a forced-air drying oven at 80℃ to obtain modified plant short fiber.

[0037] A method for preparing a plant fiber composite reinforced lightweight flexural gypsum board includes the following steps:

[0038] Step S1: [The following appears to be a separate, unrelated sentence:] With a specific surface area of ​​400 m²... 2 / kg, and its residue on a 120-mesh sieve is 3% for building gypsum powder, granulated blast furnace slag powder, calcium stearate, Daratard ® 17. Protein-based retarder was added to the mixer for the first dry mixing at 300 rpm for 3 minutes. Then ViscoCrete was added. ® - PC 40 polycarboxylate superplasticizer was subjected to a second dry mixing process. The speed of the mixer was increased to 500 rpm and the mixing time was 2 minutes to obtain a uniformly mixed dry powder.

[0039] Step S2: Let the mixed dry powder stand for 15 minutes to age, then pour it into a mixer. Before adding the CNF-2000 cellulose nanofiber slurry with a solid content of 20%, mix it with 30 times its weight of water and pre-disperse it by ultrasonic treatment at 500W for 15 minutes. Then, under the stirring state of 200rpm, add the pre-dispersed cellulose nanofiber slurry and water accounting for 65% of the weight of gypsum powder, increase the stirring speed to 400rpm, stir for 2 minutes to form a uniform matrix slurry, then add the modified plant short fibers, stir at high speed at 800rpm for 3 minutes to form a fiber composite slurry with uniform flowability.

[0040] Step S3: Inject the fiber composite slurry into a molding die lined with a 400-mesh filter screen. Turn on the vacuum system to achieve a vacuum level of -0.092 MPa in the die. Simultaneously, apply vertical mechanical vibration to the die at a frequency of 40 Hz for the entire filtration and dewatering period. Filter and dewater for 2 minutes until the slurry's moisture content is 10% and its density is 1100 kg / m³. 3The wet slab is transferred to a hot press with a mold containing the wet slab. A planar pressure of 2 MPa is applied, and the temperature of the slab is raised to 75°C within 3 minutes. It is then cured at this temperature and pressure for 20 minutes.

[0041] Step S4: Release the pressure and demold, place the slab in a 70°C circulating hot air drying oven and dry for 5 hours, turn off the heat source, cool the board to 25°C under circulating air, and cut to length to obtain the plant fiber composite reinforced lightweight flexural gypsum board.

[0042] Example 2

[0043] A lightweight, flexural gypsum board reinforced with plant fiber composites, comprising the following components in parts by weight:

[0044] 100 parts building gypsum powder, 5 parts modified plant short fibers, 1 part CNF-2000 cellulose nanofibers, 10 parts granulated blast furnace slag powder, ViscoCrete ® - 0.3 parts PC 40 polycarboxylate superplasticizer, 0.3 parts calcium stearate, Daratard ® 17. Protein retarder 0.05 parts.

[0045] The preparation steps of modified plant short fibers are as follows:

[0046] (1) Wheat short fibers with a length of 2 mm and an aspect ratio of 25 were immersed in a calcium hydroxide solution with a concentration of 1.8 g / L. The mass ratio of solution to fiber was 20:1. The solution was soaked at 25°C for 40 min. After soaking, the fiber was removed and drained until no dripping occurred, thus obtaining a wet calcified fiber precursor.

[0047] (2) Place the drained calcified fiber in a closed reactor, introduce sulfur dioxide gas with a volume fraction of 10%, and fumigate for 30 minutes at a relative humidity of 80% and a temperature of 25℃. After the reaction is completed, take out the fiber, treat it with tail gas absorption, and dry it in a forced-air drying oven at 80℃ to obtain modified plant short fiber.

[0048] A method for preparing a plant fiber composite reinforced lightweight flexural gypsum board includes the following steps:

[0049] Step S1: [The following appears to be a separate, unrelated sentence:] With a specific surface area of ​​400 m²... 2 / kg, and its residue on a 120-mesh sieve is 3% for building gypsum powder, granulated blast furnace slag powder, calcium stearate, Daratard ® 17. Protein-based retarder was added to the mixer for the first dry mixing at 300 rpm for 3 minutes. Then ViscoCrete was added. ®- PC 40 polycarboxylate superplasticizer was subjected to a second dry mixing process. The speed of the mixer was increased to 500 rpm and the mixing time was 2 minutes to obtain a uniformly mixed dry powder.

[0050] Step S2: Let the mixed dry powder stand for 15 minutes to age, then pour it into a mixer. Before adding the CNF-2000 cellulose nanofiber slurry with a solid content of 20%, mix it with 30 times its weight of water and pre-disperse it by ultrasonic treatment at 500W for 15 minutes. Then, under the stirring state of 200rpm, add the pre-dispersed cellulose nanofiber slurry and water accounting for 65% of the weight of gypsum powder, increase the stirring speed to 400rpm, stir for 2 minutes to form a uniform matrix slurry, then add the modified plant short fibers, stir at high speed at 800rpm for 3 minutes to form a fiber composite slurry with uniform flowability.

[0051] Step S3: Inject the fiber composite slurry into a molding die lined with a 400-mesh filter screen. Turn on the vacuum system to achieve a vacuum level of -0.092 MPa in the die. Simultaneously, apply vertical mechanical vibration to the die at a frequency of 40 Hz for the entire filtration and dewatering period. Filter and dewater for 2 minutes until the slurry's moisture content is 10% and its density is 1100 kg / m³. 3 The wet slab is transferred to a hot press with a mold containing the wet slab. A planar pressure of 2 MPa is applied, and the temperature of the slab is raised to 75°C within 3 minutes. It is then cured at this temperature and pressure for 20 minutes.

[0052] Step S4: Release the pressure and demold, place the slab in a 70°C circulating hot air drying oven and dry for 5 hours, turn off the heat source, cool the board to 25°C under circulating air, and cut to length to obtain the plant fiber composite reinforced lightweight flexural gypsum board.

[0053] Example 3

[0054] A lightweight, flexural gypsum board reinforced with plant fiber composites, comprising the following components in parts by weight:

[0055] 100 parts building gypsum powder, 15 parts modified plant short fibers, 3 parts CNF-2000 cellulose nanofibers, 30 parts granulated blast furnace slag powder, ViscoCrete ® - 1.2 parts PC 40 polycarboxylate superplasticizer, 1.5 parts calcium stearate, Daratard ® 17. Protein retarder 0.3 parts.

[0056] The preparation steps of modified plant short fibers are as follows:

[0057] (1) Wheat short fibers with a length of 2 mm and an aspect ratio of 25 were immersed in a calcium hydroxide solution with a concentration of 1.8 g / L. The mass ratio of solution to fiber was 20:1. The solution was soaked at 25°C for 40 min. After soaking, the fiber was removed and drained until no dripping occurred, thus obtaining a wet calcified fiber precursor.

[0058] (2) Place the drained calcified fiber in a closed reactor, introduce sulfur dioxide gas with a volume fraction of 10%, and fumigate for 30 minutes at a relative humidity of 80% and a temperature of 25℃. After the reaction is completed, take out the fiber, treat it with tail gas absorption, and dry it in a forced-air drying oven at 80℃ to obtain modified plant short fiber.

[0059] A method for preparing a plant fiber composite reinforced lightweight flexural gypsum board includes the following steps:

[0060] Step S1: [The following appears to be a separate, unrelated sentence:] With a specific surface area of ​​400 m²... 2 / kg, and its residue on a 120-mesh sieve is 3% for building gypsum powder, granulated blast furnace slag powder, calcium stearate, Daratard ® 17. Protein-based retarder was added to the mixer for the first dry mixing at 300 rpm for 3 minutes. Then ViscoCrete was added. ® - PC 40 polycarboxylate superplasticizer was subjected to a second dry mixing process. The speed of the mixer was increased to 500 rpm and the mixing time was 2 minutes to obtain a uniformly mixed dry powder.

[0061] Step S2: Let the mixed dry powder stand for 15 minutes to age, then pour it into a mixer. Before adding the CNF-2000 cellulose nanofiber slurry with a solid content of 20%, mix it with 30 times its weight of water and pre-disperse it by ultrasonic treatment at 500W for 15 minutes. Then, under the stirring state of 200rpm, add the pre-dispersed cellulose nanofiber slurry and water accounting for 65% of the weight of gypsum powder, increase the stirring speed to 400rpm, stir for 2 minutes to form a uniform matrix slurry, then add the modified plant short fibers, stir at high speed at 800rpm for 3 minutes to form a fiber composite slurry with uniform flowability.

[0062] Step S3: Inject the fiber composite slurry into a molding die lined with a 400-mesh filter screen. Turn on the vacuum system to achieve a vacuum level of -0.092 MPa in the die. Simultaneously, apply vertical mechanical vibration to the die at a frequency of 40 Hz for the entire filtration and dewatering period. Filter and dewater for 2 minutes until the slurry's moisture content is 10% and its density is 1100 kg / m³. 3The wet slab is transferred to a hot press with a mold containing the wet slab. A planar pressure of 2 MPa is applied, and the temperature of the slab is raised to 75°C within 3 minutes. It is then cured at this temperature and pressure for 20 minutes.

[0063] Step S4: Release the pressure and demold, place the slab in a 70°C circulating hot air drying oven and dry for 5 hours, turn off the heat source, cool the board to 25°C under circulating air, and cut to length to obtain the plant fiber composite reinforced lightweight flexural gypsum board.

[0064] Comparative Example 1

[0065] The only difference from Example 1 is that 100 parts of building gypsum powder, 4 parts of modified plant short fiber, 0.5 parts of cellulose nanofiber, 8 parts of auxiliary cementitious material, 0.2 parts of polycarboxylate superplasticizer, 0.2 parts of calcium stearate, and 0.2 parts of protein retarder are weighed out for later use.

[0066] Comparative Example 2

[0067] The only difference from Example 1 is that: 100 parts of building gypsum powder, 20 parts of modified plant short fiber, 5 parts of cellulose nanofiber, 40 parts of auxiliary cementitious material, 1.5 parts of polycarboxylate superplasticizer, 2.0 parts of calcium stearate, and 0.2 parts of protein retarder are prepared for use.

[0068] Comparative Example 3

[0069] The only difference from Example 1 is that unmodified plant short fibers are used.

[0070] Comparative Example 4

[0071] The only difference from Example 1 is that the plant short fibers are soaked in calcium hydroxide solution for 70 minutes in the modified preparation step (1).

[0072] Comparative Example 5

[0073] The only difference from Example 1 is that in the preparation step (2) of the modified plant short fiber, sulfur dioxide gas with a volume fraction of 20% is introduced.

[0074] Comparative Example 6

[0075] The only difference from Example 1 is that granulated blast furnace slag powder is not added, and the amount of building gypsum powder is adjusted to 120 parts to keep the total powder amount roughly the same.

[0076] Comparative Example 7

[0077] The only difference from Example 1 is that modified plant fibers with a length of 0.5 mm and an aspect ratio of 10 are used.

[0078] Comparative Example 8

[0079] The only difference from Example 1 is that modified plant fibers with a length of 4 mm and an aspect ratio of 10 are used.

[0080] Comparative Example 9

[0081] The only difference from Example 1 is that in step S1, after obtaining a uniform mixed dry powder through the second dry mixing, the mixed dry powder is not left to stand for aging.

[0082] Comparative Example 10

[0083] The only difference from Example 1 is that in step S3, after the slurry is injected into a regular mold without a filter screen, it is allowed to stand and solidify at normal pressure and room temperature, and then dried and shaped in an oven at 40°C for 24 hours.

[0084] Comparative Example 11

[0085] The only difference from Example 1 is that in step S3, the slurry is dehydrated by suction for 2 minutes until the moisture content is 15% and the density is 1000 kg / m³. 3 The wet slab is then hot-pressed.

[0086] Comparative Example 12

[0087] The only difference from Example 1 is that in step S3, the slurry is dehydrated by suction for 2 minutes until the moisture content is 6% and the density is 1400 kg / m³. 3 The wet slab is then hot-pressed.

[0088] Performance testing:

[0089] Dry density: Calculated by measuring the mass and volume of the sample after drying.

[0090] Flexural strength: Refer to GB / T 17669.3-1999 "Determination of Mechanical Properties of Building Gypsum", and use the three-point bending method for testing. The higher the value, the stronger the load-bearing capacity.

[0091] Impact strength: The pendulum impact method was used, and an unnotched specimen was tested using a pendulum impact testing machine. The specimens were cut from finished plates and machined to standard dimensions (80mm long, 10mm wide, thickness equal to the plate thickness), with a span of 62mm. The impact strength α (kJ / m²) is calculated using the formula α = A / (b×d)×10 3 Calculate, where A is the impact absorption energy (J), b is the sample width (m), and d is the sample thickness (m).

[0092] Modulus of elasticity: Referring to GB / T 17669.3-1999 "Determination of mechanical properties of building gypsum", it can usually be calculated from the initial linear segment of the load-deflection curve of the flexural strength test, that is, the flexural modulus of elasticity.

[0093] Table 1. Test results of the examples and comparative examples.

[0094]

[0095] The formulations in Examples 1-3 are all within the preferred scope of the claims of this invention and employ a complete preparation process. Data shows that while maintaining a low dry density, they achieved excellent flexural strength and impact strength, and the elastic modulus was also at an appropriate level. This demonstrates that the multi-level reinforcement system of modified plant fibers and cellulose nanofibers, combined with a vacuum filtration and hot-pressing compaction process, can achieve the goal of lightweight, high strength, and high toughness.

[0096] In Comparative Example 1, the insufficient amounts of modified plant short fibers, cellulose nanofibers, auxiliary cementitious materials, polycarboxylate superplasticizers, and calcium stearate resulted in an imperfect matrix and reinforcing network, high density, and extremely poor strength, demonstrating that insufficient reinforcement cannot form an effective structure. In Comparative Example 2, the excessive amounts of modified plant short fibers, cellulose nanofibers, auxiliary cementitious materials, polycarboxylate superplasticizers, and calcium stearate led to fiber agglomeration, poor slurry workability, uneven structure after molding, high density, but negligible strength improvement, resulting in an extremely low performance-cost ratio, proving that excessive amounts are not beneficial. Comparative Example 3 used unmodified fibers, achieving a density comparable to or even higher than the examples, but with decreased strength. This demonstrates the decisive role of inorganic mineralization modification on the fiber surface in establishing an effective stress transfer mechanism in a low-density matrix; unmodified fibers become a complete defect in the matrix. In Comparative Example 4, the excessively long calcification time caused fiber embrittlement. Although still superior to Comparative Example 3, its strength was slightly lower than Example 1, proving that the calcification time needs to be moderate. Comparative Example 5: Excessive sulfur dioxide concentration may lead to an overly thick or cracked mineralized layer, affecting interfacial bonding efficiency and slightly reducing performance. Comparative Example 6: Ungranulated blast furnace slag powder, while having a decent density, exhibits average strength, demonstrating the contribution of active materials to optimizing matrix properties. Comparative Example 7: Short fibers result in poor bridging, making it lightweight but with limited reinforcing effect. Comparative Example 8: Excessively long fibers lead to poor dispersion, introducing defects, resulting in heaviness, brittleness, and low strength. Comparative Example 9: Unaged fibers exhibit significantly lower strength than the examples, proving that aging promotes component homogenization. Comparative Example 10: Traditional static aging process produces a decent density and acceptable flexural strength, but extremely poor impact strength, demonstrating that vacuum filtration and hot pressing are irreplaceable for achieving high impact strength in low-density systems. Comparative Example 11: High moisture content and low density of the wet green after filtration necessitate the removal of more water during hot pressing, leading to easy deformation of the green body, poor interfacial formation, and ultimately low density but insufficient strength. Comparative Example 12 had too low moisture content and too high density of wet green after filtration, resulting in poor plasticity of the green body. Hot pressing made it difficult to further optimize the structure, leading to a final product that was not lightweight and had poor impact strength.

[0097] Those skilled in the art should understand that the discussion of any of the above embodiments is merely exemplary; within the framework of this invention, the technical features of the above embodiments or different embodiments can also be combined, the steps can be implemented in any order, and there are many other variations of the different aspects of the invention as described above, which are not provided in detail for the sake of brevity.

[0098] This invention is intended to cover all such substitutions, modifications, and variations that fall within the broad scope of the appended claims. Therefore, any omissions, modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of this invention should be included within the scope of protection of this invention.

Claims

1. A lightweight, flexural gypsum board reinforced with plant fiber composite, characterized in that, The components include the following parts by weight: 100 parts building gypsum powder, 5-15 parts modified plant short fiber, 1-3 parts cellulose nanofibers, 10-30 parts auxiliary cementitious materials, 0.3-1.2 parts polycarboxylate superplasticizer, 0.3-1.5 parts calcium stearate, and 0.05-0.3 parts protein retarder; The modified plant short fiber is made from wheat straw or rice straw, with a length of 1-3 mm and an aspect ratio greater than 20. The preparation steps of the modified plant short fiber are as follows: (1) Immerse the plant short fibers in a calcium hydroxide solution with a concentration of 1.5~2.2g / L, with a mass ratio of solution to fiber of 10:1~30:1, and soak at 15~35℃ for 10~60min. After soaking, remove the fibers and drain until there is no dripping to obtain a wet calcified fiber precursor. (2) Place the drained calcified fiber in a closed reactor, introduce sulfur dioxide gas with a volume fraction of 5-15%, and fumigate for 10-30 minutes under the conditions of relative humidity of 60-80% and temperature of 15-35℃. Take out the fiber and dry it at 60-80℃ to obtain modified plant short fiber.

2. The plant fiber composite reinforced lightweight flexural gypsum board according to claim 1, characterized in that, The specific surface area of ​​the building gypsum powder is 300m². 2 / kg~500m 2 / kg, and its residue on a 120-mesh sieve is <5%.

3. The plant fiber composite reinforced lightweight flexural gypsum board according to claim 1, characterized in that, The auxiliary cementing material is granulated blast furnace slag powder.

4. A method for preparing a lightweight, flexural gypsum board reinforced with plant fibers as described in any one of claims 1 to 3, characterized in that, Includes the following steps: Step S1: Mix the building gypsum powder, auxiliary cementitious materials, calcium stearate, and protein retarder in a first dry mix, then add polycarboxylate superplasticizer in a second dry mix to obtain a uniform mixed dry powder. Let the mixed dry powder stand and age for 5-15 minutes. Step S2: Pour the mixed dry powder into a mixer. While mixing, first add cellulose nanofibers and water accounting for 55-75% of the weight of gypsum powder. Mix for 1-2 minutes to form a uniform matrix slurry. Then add modified plant short fibers and mix at high speed to form a uniform fiber composite slurry. Step S3: Inject the fiber composite slurry into a molding die lined with a 300-400 mesh filter screen. Turn on the vacuum system to achieve a vacuum level of -0.08 to -0.092 MPa in the die. Filter and dewater until the slurry has a moisture content of 8-12% and a density of 1100-1300 kg / m³. 3 The wet slab is then transferred to a hot press and cured for 15-30 minutes at a plane pressure of 1-2.5 MPa and a temperature of 60-80°C. Step S4: Release the pressure and demold, place the slab in a circulating hot air drying oven to dry, and cut to length to obtain the plant fiber composite reinforced lightweight flexural gypsum board.

5. The method for preparing the plant fiber composite reinforced lightweight flexural gypsum board according to claim 4, characterized in that, In step S2, before adding the cellulose nanofibers, they are first mixed with water at a mass of 20 to 50 times, and then pre-dispersed by ultrasonic treatment at a power of 300 to 500W for 5 to 15 minutes.

6. The method for preparing the plant fiber composite reinforced lightweight flexural gypsum board according to claim 4, characterized in that, In step S3, while applying vacuum pressure, a vertical mechanical vibration with a frequency of 25~50Hz is applied to the mold, and the vibration lasts for the entire filtration and dewatering period.

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