Enhanced magnesium-based cementitious material, method for preparing same and use thereof

Abstract

The present application relates to a kind of enhanced magnesium cementitious material and its preparation method.The raw materials of the enhanced magnesium cementitious material include by weight parts: 1-5 parts of carbon dot modified hydrosol, 5-15 parts of magnesium sulfate, 25-35 parts of magnesium chloride, 95-105 parts of magnesium oxide and 0.001-0.01 parts of boric acid, the carbon dot modified hydrosol is prepared by hydrothermal reaction of hydrosol precursor in the presence of crosslinking agent and oxidizing agent, the conditions of the hydrothermal reaction include: temperature 120~150 ℃.The carbon dot modified hydrosol provided by the present application has excellent permeability and bonding strength, magnesium oxychloride inorganic glue enhances the mechanical strength of cementitious material, magnesium sulfate inorganic glue enhances the water resistance of cementitious material, the obtained cementitious material has the advantages of high mechanical and bonding strength, good water resistance under the cooperation of the three, and has good flame retardant effect.The present application also relates to a kind of plywood comprising the above-mentioned enhanced magnesium cementitious material and its preparation method.

Description

Technical Field

[0001] This invention relates to the field of engineered wood products technology, and more particularly to an enhanced magnesium cementitious material and its preparation method, and plywood containing the same and its preparation method. Background Technology

[0002] Plywood is a three- or multi-layered sheet material made by rotary cutting logs into veneers or slicing timber into thin sheets, and then gluing them together with adhesives. As the most produced and used engineered wood product, it has wide applications in furniture manufacturing, construction, and packaging. Currently, over 10 million tons of adhesives are consumed annually in plywood manufacturing, with aldehyde resins accounting for over 90% of the total. These adhesives release free formaldehyde during production and use, posing a health hazard. Furthermore, like wood, plywood is a flammable material, posing a fire risk. Therefore, it is necessary to develop formaldehyde-free, flame-retardant wood adhesives for plywood production, which has significant development potential.

[0003] Among existing inorganic cementitious materials, magnesium sulfate cementitious material is a cementing system formed by mixing active magnesium oxide and magnesium sulfate solution in a certain proportion. It has a series of advantages such as simple preparation process, light weight, fast setting speed, environmental friendliness, fire resistance, and good compatibility with wood. However, the application of magnesium sulfate cementitious material in the field of engineered wood products is limited by its relatively low strength and weak interfacial bonding with wood. Summary of the Invention

[0004] To address the aforementioned problems, one objective of this invention is to provide a reinforced magnesium cementitious material with high mechanical and bonding strength, and a method for its preparation. This reinforced magnesium cementitious material comprises a magnesium sulfate / magnesium oxychloride / carbon dot modified hydrosol composite system, possessing advantages such as high mechanical and bonding strength, good water resistance, and good flame retardant properties.

[0005] Another object of the present invention is to provide a plywood comprising the above-mentioned reinforced magnesium cementitious material with high mechanical strength and high bonding strength, and a method for preparing the same.

[0006] Therefore, in a first aspect, the present invention provides an enhanced magnesium cementitious material, the raw materials of which, by weight, comprise:

[0007]

[0008] The carbon dot modified hydrosol is prepared by hydrothermal reaction of a hydrosol precursor in the presence of a crosslinking agent and an oxidizing agent, wherein the conditions for the hydrothermal reaction include a temperature of 120–150°C.

[0009] The carbon dot modified hydrosol of this invention is produced by hydrothermal reaction (depolymerization and self-assembly) of a hydrosol precursor, an oxidant, and a crosslinking agent, generating carbon nanomaterials (carbon quantum dots, also known as carbon dots). These nanomaterials exhibit good water solubility, self-crosslink to form a film after drying, and are insoluble in water, demonstrating excellent strength and water resistance. During the hydrothermal reaction, a portion of the carbon-containing substances in the hydrothermal system form carbon dots, while a portion of the hydrosol undergoes depolymerization. Because the reaction temperature is not the traditional high temperature above 200°C, the system still maintains good film-forming properties. Therefore, when the carbon dot modified hydrosol is mixed with inorganic cementing components magnesium chloride, magnesium oxide, and magnesium sulfate, the carbon dot modified hydrosol is uniformly distributed in the inorganic cementing system. When applied to the veneer surface, the high-temperature hydrothermal process breaks down the original molecular state of the system, transforming the original linear structure into a modified system dominated by nanoparticles and broken small molecular segments. This allows for better bonding with wood, and the micropores on the veneer surface facilitate the formation of a stronger anchoring effect.

[0010] To address the issues of low mechanical strength in existing magnesium sulfate inorganic cementitious materials, poor water resistance in magnesium oxychloride inorganic cementitious materials, and weak interfacial bonding between inorganic adhesives and wood, this invention combines magnesium oxychloride and magnesium sulfate inorganic adhesives using carbon dot-modified hydrosols. The carbon dot-modified hydrosols exhibit excellent permeability and bonding strength, while the magnesium oxychloride inorganic adhesive enhances the mechanical strength of the cementitious material, and the magnesium sulfate inorganic adhesive enhances its water resistance. The resulting cementitious material, through the combination of these three components, possesses advantages such as high mechanical and bonding strength, good water resistance, and a good flame-retardant effect.

[0011] As a specific embodiment of the present invention, the conditions for the hydrothermal reaction also include: in a closed environment, for a time of 1 to 3 hours.

[0012] As a specific embodiment of the present invention, the hydrosol precursor is selected from at least one of hyaluronic acid, gelatin, chitosan and sodium alginate.

[0013] In a specific embodiment of the present invention, the number-average molecular weight of the hydrocolloid precursor is 2.0 × 10⁻⁶. 4 ~6.5×10 4 g / mol.

[0014] In a specific embodiment of the present invention, the number-average molecular weight of the gelatin is 2.4 × 10⁻⁶. 4 ~3.6×10 4 g / mol; the number-average molecular weight of the hyaluronic acid is 4.5 × 10⁻⁶ g / mol. 4 ~6.5×10 4 g / mol.

[0015] As a specific embodiment of the present invention, the oxidant is selected from at least one of hydrogen peroxide, sodium hypochlorite, and perchloric acid.

[0016] In a specific embodiment of the present invention, the amount of the oxidant is 1.0 to 2.5% of the mass of the hydrosol precursor.

[0017] As a specific embodiment of the present invention, the crosslinking agent is selected from at least one of cationic polyacrylamide, carboxylated polyacrylamide, and hydroxy polyacrylamide.

[0018] As a specific embodiment of the present invention, the amount of the crosslinking agent is 0.1 to 0.3% of the mass of the hydrosol precursor.

[0019] In a specific embodiment of the present invention, the number-average molecular weight of the crosslinking agent is 2.5 × 10⁻⁶. 6 ~3.5×10 6 g / mol.

[0020] In a specific embodiment of the present invention, the number-average molecular weight of the cationic polyacrylamide is 3 × 10⁻⁶. 6 ~3.4×10 6 g / mol.

[0021] As a specific embodiment of the present invention, the preparation method of the carbon dot modified hydrosol includes the following steps:

[0022] S1. Add crosslinking agent and oxidant to the aqueous solution of the hydrosol precursor and mix them at a first temperature to obtain a mixed solution;

[0023] S2. The mixed solution is placed in a closed reaction vessel for hydrothermal reaction to obtain a carbon dot modified hydrosol solution.

[0024] In a specific embodiment of the present invention, the first temperature is 40-60°C.

[0025] As a specific embodiment of the present invention, the preparation method of the modified hydrosol includes the following steps:

[0026] S10. A mixture of an aqueous solution of a 1-5 wt% hydrosol precursor and cationic polyacrylamide is stirred evenly in a constant temperature water bath at 40-60℃ to obtain a mixed solution.

[0027] S20. Add a 30-45 wt% hydrogen peroxide solution to the mixed solution obtained in step S10 and continue stirring.

[0028] S30. The mixed solution obtained in step S20 is placed in a closed reaction vessel for hydrothermal reaction to obtain a solution of carbon dot modified hydrosol.

[0029] In a specific embodiment of the present invention, in step S10, the stirring rate is 300-350 r / min and the time is 20-40 min.

[0030] In a specific embodiment of the present invention, in step S20, the stirring rate is 300-350 r / min and the time is 5-20 min.

[0031] Therefore, in a second aspect, the present invention provides a method for preparing the above-mentioned reinforced magnesium cementitious material, comprising the following steps: first mixing carbon dot modified hydrosol, magnesium sulfate, magnesium chloride, and magnesium oxide, and then adding boric acid for a second mixing; preferably, the temperatures of the first mixing and the second mixing are independently 20 to 40°C.

[0032] Therefore, in a third aspect, the present invention provides a plywood, wherein the plywood is bonded using the above-described reinforced magnesium cementitious material or the reinforced magnesium cementitious material prepared by the above-described preparation method; preferably, the plywood is a wood-based plywood.

[0033] Therefore, in a fourth aspect, the present invention provides a method for preparing plywood, comprising the following steps:

[0034] (1) Veneer preparation: Making veneers from wood;

[0035] (2) Apply adhesive to the veneer: The above-mentioned reinforced magnesium cementitious material or the reinforced magnesium cementitious material prepared by the above-mentioned preparation method is evenly applied to both sides of the veneer in step (1).

[0036] (3) Assembly and cold pressing: The veneers after gluing in step (2) are assembled and cold pressed;

[0037] (4) Board curing.

[0038] As a specific embodiment of the present invention, step (1) further includes: drying the veneer to a moisture content of 5-10 wt%.

[0039] In a specific embodiment of the present invention, in step (2), the amount of adhesive applied to one side of the veneer is 200-300 g / m². 2 .

[0040] As a specific embodiment of the present invention, in step (3), the conditions for assembling the blank include: following the principles of odd number of layers, symmetry, and interlayer texture arrangement.

[0041] As a specific embodiment of the present invention, the cold pressing conditions include: a temperature of 10 to 35°C, a pressure of 1.0 to 1.5 MPa, and a time of 24 to 72 hours.

[0042] As a specific embodiment of the present invention, the conditions for curing the board include: curing at 20-70°C for 2-7 days.

[0043] Beneficial effects:

[0044] To address the issues of low mechanical strength in existing magnesium sulfate inorganic cementitious materials, poor water resistance in magnesium oxychloride inorganic cementitious materials, and weak interfacial bonding between inorganic adhesives and wood, this invention combines magnesium oxychloride and magnesium sulfate inorganic adhesives using carbon dot-modified hydrosols. The carbon dot-modified hydrosols exhibit excellent permeability and bonding strength, while the magnesium oxychloride inorganic adhesive enhances the mechanical strength of the cementitious material, and the magnesium sulfate inorganic adhesive enhances its water resistance. The resulting cementitious material, through the combination of these three components, possesses advantages such as high mechanical and bonding strength, good water resistance, and a good flame-retardant effect.

[0045] The enhanced magnesium cementitious material provided by this invention improves the mechanical strength of the cementitious material by blending magnesium oxychloride and magnesium sulfate. When the inorganic cementitious components of carbon dot modified hydrosol—magnesium chloride, magnesium oxide, and magnesium sulfate—are mixed, the carbon dot modified hydrosol is evenly distributed in the inorganic cementitious system. When applied to the veneer surface, the high-temperature hydrothermal process breaks down the molecular state of the original system, transforming the original linear system into a modified system dominated by nanoparticles and broken small molecular chain segments. This allows for better bonding with wood, and the micropores on the veneer surface facilitate the formation of stronger anchoring, enhancing the permeability, bonding strength, and moisture resistance of the cementitious material.

[0046] The reinforced magnesium cementitious material provided by this invention has the advantages of high mechanical and bonding strength, and the preparation process is simple. It releases no formaldehyde during production and use, and also has the advantages of being healthy and environmentally friendly. As a wood cementitious material, it also endows plywood with flame retardant properties and moisture resistance.

[0047] The reinforced magnesium cementitious material provided by this invention can be applied in panels at room temperature without hot pressing, which is energy-saving and environmentally friendly.

[0048] The plywood provided by this invention has excellent physical and mechanical properties, flame retardant properties, and moisture resistance. Furthermore, it is free of volatile formaldehydes, which can avoid harming the environment. This further improves the added value and applicability of the plywood, and its promotion prospects are promising. Attached Figure Description

[0049] Figure 1 This is a schematic diagram of the internal structure of the plywood prepared according to Embodiment 1 of the present invention. Detailed Implementation

[0050] The technical solution of the present invention will be further illustrated below through specific embodiments. Those skilled in the art should understand that the embodiments are merely illustrative of the invention and should not be considered as specific limitations thereof. Where specific conditions are not specified in the embodiments, conventional conditions or conditions recommended by the manufacturer shall apply. Reagents or instruments whose manufacturers are not specified are all commercially available conventional products.

[0051] In the examples, the number-average molecular weight of the gelatin was 3.0 × 10⁻⁶. 4 The number-average molecular weight of cationic polyacrylamide is 3.2 × 10⁻⁶. 6 The number-average molecular weight of hyaluronic acid is 5.4 × 10 g / mol. 4 .

[0052] Example 1

[0053] The preparation of reinforced magnesium cementitious materials is carried out according to the following steps:

[0054] (1) Weigh 100g of gelatin aqueous solution (concentration of 2wt%) and 0.002g of cationic polyacrylamide, and stir at 320r / min for 30min in a constant temperature water bath at 50℃ to fully dissolve and mix the above components to obtain a mixed solution.

[0055] (2) Take 0.15g of 37wt% hydrogen peroxide aqueous solution and add it to the mixed solution obtained in step (1), and stir at 320r / min for 10min;

[0056] (3) Place the mixed solution obtained in step (2) into a closed reaction vessel (250 mL) and carry out a hydrothermal reaction at 120°C for 2 hours, so that the hydrosol precursor, oxidant and crosslinking agent can undergo depolymerization and self-assembly reaction under high temperature hydrothermal conditions. After the reaction is completed, cool to room temperature to obtain a light yellow solution.

[0057] (4) 100g of carbon dot modified hydrosol solution (2wt%) obtained in step (3) is stirred with 10g magnesium sulfate, 30g magnesium chloride and 100g magnesium oxide at a speed of 320r / min for 30min. Then, 1.0mg of boric acid is added under stirring to obtain the reinforced magnesium cementitious material.

[0058] Example 2

[0059] The preparation of reinforced magnesium cementitious materials is carried out according to the following steps:

[0060] (1) Weigh 100g of hyaluronic acid aqueous solution (concentration of 2wt%) and 0.002g of cationic polyacrylamide, and stir at 320r / min for 30min in a constant temperature water bath at 50℃ to fully dissolve and mix the above components to obtain a mixed solution.

[0061] (2) Take 0.15g of 37wt% hydrogen peroxide aqueous solution and add it to the mixed solution obtained in step (1), and stir at 320r / min for 10min;

[0062] (3) Place the mixed solution obtained in step (2) into a closed reaction vessel (250 mL) and carry out a hydrothermal reaction at 120°C for 2 hours, so that the hydrosol precursor, oxidant and crosslinking agent can undergo depolymerization and self-assembly reaction under high temperature hydrothermal conditions. After the reaction is completed, cool to room temperature to obtain a light yellow solution.

[0063] (4) 100g of carbon dot modified hydrosol solution (2wt%) obtained in step (3) is stirred with 10g magnesium sulfate, 30g magnesium chloride and 100g magnesium oxide at a speed of 320r / min for 30min. Then, 1.0mg of boric acid is added under stirring to obtain the reinforced magnesium cementitious material.

[0064] Example 3

[0065] The preparation of reinforced magnesium cementitious materials is carried out according to the following steps:

[0066] (1) Weigh 100g of sodium alginate aqueous solution (concentration of 2wt%) and 0.002g of cationic polyacrylamide, and stir at 320r / min for 30min in a constant temperature water bath at 50℃ to fully dissolve and mix the above components to obtain a mixed solution.

[0067] (2) Take 0.15g of 37wt% hydrogen peroxide aqueous solution and add it to the mixed solution obtained in step (1), and stir at 320r / min for 10min;

[0068] (3) Place the mixed solution obtained in step (2) into a closed reaction vessel (250 mL) and carry out a hydrothermal reaction at 120°C for 2 hours, so that the hydrosol precursor, oxidant and crosslinking agent can undergo depolymerization and self-assembly reaction under high temperature hydrothermal conditions. After the reaction is completed, cool to room temperature to obtain a light yellow solution.

[0069] (4) 100g of carbon dot modified hydrosol solution (concentration of 2wt%) obtained in step (3) is stirred with 10g magnesium sulfate, 30g magnesium chloride and 100g magnesium oxide at a speed of 320r / min for 30min. Then, 1.0mg of boric acid is added under stirring to obtain the reinforced magnesium cementitious material.

[0070] Example 4

[0071] The preparation of reinforced magnesium cementitious materials is carried out according to the following steps:

[0072] (1) Weigh 100g of gelatin aqueous solution (concentration of 2wt%) and 0.004g of cationic polyacrylamide, and stir at 320r / min for 30min in a constant temperature water bath at 50℃ to fully dissolve and mix the above components to obtain a mixed solution.

[0073] (2) Take 0.15g of 37wt% perchloric acid aqueous solution and add it to the mixed solution obtained in step (1), and stir at 320r / min for 10min;

[0074] (3) Place the mixed solution obtained in step (2) into a closed reaction vessel (250 mL) and carry out a hydrothermal reaction at 120°C for 2 hours, so that the hydrosol precursor, oxidant and crosslinking agent can undergo depolymerization and self-assembly reaction under high temperature hydrothermal conditions. After the reaction is completed, cool to room temperature to obtain a light yellow solution.

[0075] (4) 100g of carbon dot modified hydrosol solution (concentration of 2wt%) obtained in step (3) is stirred with 10g magnesium sulfate, 35g magnesium chloride and 105g magnesium oxide at a speed of 320r / min for 30min. Then, 2.0mg of boric acid is added under stirring to obtain the reinforced magnesium cementitious material.

[0076] Comparative Example 1

[0077] The difference from Example 1 is that the temperature of the hydrothermal reaction in step (3) is 160°C.

[0078] Comparative Example 2

[0079] The difference from Example 1 is that the temperature of the hydrothermal reaction in step (3) is 180°C.

[0080] Comparative Example 3

[0081] The difference from Example 1 is that the hydrosol modification only involves the addition of cationic polyacrylamide and not hydrogen peroxide. The following steps were followed:

[0082] (1) Weigh 100g of gelatin aqueous solution (concentration of 2wt%) and 0.002g of cationic polyacrylamide, and stir at 320r / min for 30min in a constant temperature water bath at 50℃ to fully dissolve and mix the above components to obtain a mixed solution.

[0083] (2) Place the mixed solution obtained in step (1) into a closed reaction vessel (250 mL) and carry out a hydrothermal reaction at 120°C for 2 hours, so that the hydrosol precursor and crosslinking agent can undergo depolymerization and self-assembly under high temperature hydrothermal conditions. After the reaction is completed, cool to room temperature to obtain a light yellow solution.

[0084] (3) 100g of the mixed solution (2wt%) obtained in step (2) is stirred with 10g of magnesium sulfate, 30g of magnesium chloride and 100g of magnesium oxide at a speed of 320r / min for 30min. Then, 1.0mg of boric acid is added under stirring to obtain the gelling material.

[0085] Comparative Example 4

[0086] The difference from Example 1 is that the hydrosol modification only involves the addition of hydrogen peroxide and not cationic polyacrylamide. The following steps were followed:

[0087] (1) Weigh 100g of gelatin aqueous solution (concentration of 2wt%) and stir it at 320r / min for 30min in a constant temperature water bath at 50℃ to fully dissolve the above components;

[0088] (2) Take 0.15g of 37wt% hydrogen peroxide solution and add it to the solution in step (1), and stir at 320r / min for 10min.

[0089] (3) Place the mixed solution obtained in step (2) into a closed reaction vessel (250 mL) and carry out a hydrothermal reaction at 120°C for 2 hours, so that the hydrosol precursor, oxidant and crosslinking agent can undergo depolymerization and self-assembly reaction under high temperature hydrothermal conditions. After the reaction is completed, cool to room temperature to obtain a light yellow solution.

[0090] (4) 100g of carbon dot modified hydrosol solution (2wt%) obtained in step (3) is stirred with 10g magnesium sulfate, 30g magnesium chloride and 100g magnesium oxide at a speed of 320r / min for 30min. Then, 1.0mg of boric acid is added under stirring to obtain the reinforced magnesium cementitious material.

[0091] Comparative Example 5

[0092] The difference from Example 1 is that the mass of magnesium oxide is changed from 100g to 90g.

[0093] Comparative Example 6

[0094] The difference from Example 1 is that the mass of boric acid was changed from 1 mg to 0.5 mg.

[0095] Application Example 1

[0096] The preparation of plywood is carried out according to the following steps:

[0097] (1) Use a rotary cutter to cut eucalyptus wood into veneers with a thickness of 2.0mm±0.2mm, dry them to a moisture content of 8wt%, and cut them into a size of 1200mm×600mm.

[0098] (2) Veneer application: The cementitious materials prepared in Examples 1-4 and Comparative Examples 1-6 were mixed and evenly coated on both sides of the core veneer. The outermost two veneers were coated only on the inner layer. The amount of adhesive applied to one side of the veneer was 250 g / m². 2 ;

[0099] (3) The single boards obtained in step (2) are assembled according to the principle of odd number of layers, symmetry and interlayer texture. Then, they are cold-pressed at room temperature (25℃) and 1.2MPa pressure for 48 hours. The cold pressing pressure is 1.2MPa.

[0100] (4) Curing of plywood: After depressurization, the plywood is cured at 70°C for 2 days, and then cured at room temperature for 5 days. Each plywood is designated as P1-4 (corresponding to Examples 1-4) and DP1-6 (corresponding to Examples 1-6).

[0101] Mechanical strength, moisture resistance, and flame retardant properties of boards P1-4 and DP1-6 were tested respectively. The test methods and results are as follows:

[0102] (1) Static bending strength test: The static bending strength of the board is tested in accordance with GB / T 17657-2022 "Test methods for physical and chemical properties of wood-based panels and decorative wood-based panels", where the span is 20 times the thickness of the board.

[0103] (2) Moisture Resistance Test: Referring to GB / T 17657-2022 "Test Methods for Physical and Chemical Properties of Wood-based Panels and Decorative Wood-based Panels", the 24-hour water absorption thickness swelling rate and Class II immersion peel performance of the plywood were tested. The 24-hour water absorption thickness swelling rate (TS-24h) was measured by immersing a 50mm × 50mm sample in room temperature water for 24 hours, and the smaller the TS-24h, the less water absorption swelling the plywood had, indicating better moisture resistance. The Class II immersion peel test involved immersing a 75mm × 75mm sample in 65℃ water for 3 hours, followed by heat treatment in a 65℃ oven for 3 hours. The adhesive layers of the plywood were then observed for delamination and cracking, and the crack length on one side of the adhesive layer was recorded. In this test, samples with cracks exceeding 25mm on one side were considered unqualified.

[0104] (3) Flame retardant performance test: Refer to GB / T 2406.2-2009 "Determination of burning behavior of plastics by oxygen index method" to test the oxygen index of the board. The higher the oxygen index, the better the flame retardant performance. According to production practice, the oxygen index (LOI) of plywood is more than 35% (≥35%), which indicates that the flame retardant effect is good. The oxygen index is less than 35% but more than 30% (30%≤LOI<35%), which indicates that there is a certain flame retardant effect, but the flame retardant effect is weak. The oxygen index is less than 30% (<30%) and is recorded as a combustible material.

[0105] Table 1 Test results of plywood in each group

[0106]

[0107]

[0108] Table 1 shows that experimental groups P1 to P4 all exhibit good static bending strength, low water absorption thickness swelling rate, good impregnation peeling performance, and excellent flame retardant oxygen index performance. The carbon dot modified hydrosol has good water solubility, can self-crosslink to form a film after drying, and is insoluble in water, exhibiting excellent strength and water resistance. To avoid being limited by theory, it is believed that during the hydrothermal process, some carbon-containing substances in the hydrothermal system form carbon dots, while some hydrosols undergo depolymerization. When the carbon dot modified hydrosol is mixed with inorganic cementing components magnesium chloride, magnesium oxide, and magnesium sulfate, the carbon dot modified hydrosol is uniformly distributed in the inorganic cementing system. When applied to the veneer surface, the high-temperature hydrothermal process breaks down the molecular state of the original system, transforming the original linear system into a modified system dominated by nanoparticles and broken small molecular segments. This allows for better bonding with the wood, and the micropores on the veneer surface facilitate the formation of stronger anchoring.

[0109] The plywood prepared by control groups DP1 and DP2 exhibited low strength, poor moisture resistance, and unsatisfactory flame retardant effects. It is believed that, to avoid being limited by theory, the high hydrothermal reaction temperature led to excessive degradation of the hydrosol precursor under the high-temperature hydrothermal action of oxidants, crosslinking agents, and aqueous solutions. The resulting carbon-dot modified hydrosol failed to maintain good film-forming properties, and after subsequent mixing with other components, it did not form an effective anchoring effect, leading to imbalance and increased porosity in the cementitious material system. The plywood prepared by control group DP3 also exhibited low strength, poor moisture resistance, and unsatisfactory flame retardant effects. It is believed that, to avoid being limited by theory, the absence of an oxidant weakened the fracture and recombination behavior of cationic polyacrylamide under high-temperature hydrothermal conditions. The plywood prepared by control group DP4 also exhibited low strength, poor moisture resistance, and unsatisfactory flame retardant effects. It is believed that, to avoid being limited by theory, the absence of a crosslinking agent resulted in poor water resistance of the organic components in the cementitious material. During high-temperature heat treatment, the lack of crosslinking components prevented the formation of a good three-dimensional crosslinked structure, resulting in poor overall performance. The plywood prepared in the control group DP5 exhibited low strength, poor moisture resistance, and unsatisfactory flame retardant properties. It is believed that, to avoid being limited by theory, reducing the magnesium oxide content in the cementitious material significantly alters the raw material ratio during the formation of the inorganic reinforcing phase, resulting in poor reinforcing phase performance. The plywood prepared in the control group DP6 also exhibited low strength, poor moisture resistance, and unsatisfactory flame retardant properties. It is believed that, to avoid being limited by theory, the low boric acid content in the cementitious material prevents the formation of an effective three-dimensional network cross-linked structure, leading to a decline in the overall performance of the cementitious material.

[0110] The above description of the embodiments is provided to enable those skilled in the art to understand and apply the present invention. It will be apparent to those skilled in the art that various modifications can be easily made to these embodiments, and the general principles described herein can be applied to other embodiments without inventive effort. Therefore, the present invention is not limited to the embodiments described herein, and any improvements and modifications made by those skilled in the art based on the disclosure of the present invention without departing from the scope of the invention should be within the protection scope of the present invention.

Claims

1. A reinforced magnesium cementitious material, characterized in that, By weight, its raw materials include: 1-5 parts of carbon dot modified hydrosol 5-15 parts magnesium sulfate 25-35 parts magnesium chloride 95-105 parts magnesium oxide Boric acid 0.001~0.01 parts, The carbon dot modified hydrosol is prepared by hydrothermal reaction of a hydrosol precursor in the presence of a crosslinking agent and an oxidizing agent. The conditions for the hydrothermal reaction include a temperature of 120~150℃. The hydrosol precursor is selected from at least one of hyaluronic acid, gelatin, chitosan and sodium alginate; The crosslinking agent is selected from at least one of cationic polyacrylamide, carboxylated polyacrylamide, and hydroxy polyacrylamide.

2. The cementitious material according to claim 1, characterized in that, The conditions for the hydrothermal reaction also include: in a closed environment, for 1 to 3 hours.

3. The cementitious material according to claim 1, characterized in that, The number-average molecular weight of the hydrosol precursor is 2.0 × 10⁻⁶. 4 ~6.5×10 4 g / mol.

4. The cementitious material according to claim 3, characterized in that, The number-average molecular weight of the gelatin is 2.4 × 10⁻⁶. 4 ~3.6×10 4 g / mol; the number-average molecular weight of the hyaluronic acid is 4.5 × 10⁻⁶ g / mol. 4 ~6.5×10 4 g / mol.

5. The cementitious material according to any one of claims 1-4, characterized in that, The oxidant is selected from at least one of hydrogen peroxide, sodium hypochlorite, and perchloric acid; and / or, The amount of oxidant used is 1.0 to 2.5% of the mass of the hydrosol precursor.

6. The cementitious material according to any one of claims 1-4, characterized in that, The amount of the crosslinking agent is 0.1 to 0.3% of the mass of the hydrosol precursor.

7. The cementitious material according to claim 6, characterized in that, The number-average molecular weight of the crosslinking agent is 2.5 × 10⁻⁶. 6 ~3.5×10 6 g / mol.

8. The cementitious material according to claim 7, characterized in that, The number-average molecular weight of the cationic polyacrylamide is 3 × 10⁻⁶. 6 ~3.4×10 6 g / mol.

9. The cementitious material according to any one of claims 1-4, characterized in that, The preparation method of the carbon dot modified hydrosol includes the following steps: S1. Add crosslinking agent and oxidant to the aqueous solution of the hydrosol precursor and mix them at a first temperature to obtain a mixed solution; S2. The mixed solution is placed in a closed reaction vessel for hydrothermal reaction to obtain a carbon dot modified hydrosol solution.

10. The cementitious material according to claim 9, characterized in that, The first temperature is 40~60℃.

11. A method for preparing the reinforced magnesium cementitious material according to any one of claims 1-4, characterized in that, The process includes the following steps: first mixing carbon dot modified hydrosol, magnesium sulfate, magnesium chloride, and magnesium oxide, and then adding boric acid for a second mixing.

12. The preparation method according to claim 11, characterized in that, The temperatures of the first mixture and the second mixture are independently 20~40℃.

13. A type of plywood, characterized in that, The plates are bonded using the reinforced magnesium cementitious material according to any one of claims 1-10 or the reinforced magnesium cementitious material prepared by the preparation method according to claim 11 or 12.

14. The plywood according to claim 13, characterized in that, The board material is a wood-based board.

15. A method for preparing plywood, characterized in that, Includes the following steps: (1) Veneer preparation: Making veneers from wood; (2) Applying adhesive to the veneer: uniformly apply the reinforced magnesium cementitious material as described in any one of claims 1-10 or the reinforced magnesium cementitious material prepared by the preparation method described in claim 11 or 12 to both sides of the veneer in step (1); (3) Assembly and cold pressing: The veneers after gluing in step (2) are assembled and cold pressed; (4) Board curing.

16. The preparation method according to claim 15, characterized in that, Step (1) further includes: drying the veneer to a moisture content of 5-10 wt%; and / or In step (2), the amount of adhesive applied to one side of the veneer is 200~300 g / m². 2 ; and / or In step (3), the conditions for assembling the blank include: arranging the blanks according to the principles of odd number of layers, symmetry, and interlayer texture; and / or, the conditions for cold pressing include: a temperature of 10~35℃, a pressure of 1.0~1.5MPa, and a time of 24~72h; In step (4), the conditions for curing the board include curing at 20~70℃ for 2~7 days.

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