Homogeneous thermal insulation material and preparation method thereof

Abstract

The invention discloses a homogeneous thermal insulation material and a preparation method thereof, and belongs to the technical field of thermal insulation materials. The preparation method of the material comprises the following steps: (1) mixing a graphene oxide aqueous solution with metal salt, and adding a sodium hydroxide or potassium hydroxide solution to obtain a graphene oxide composite inorganic flame retardant solution; (2) adding a surface modifier into the graphene oxide composite inorganic flame retardant solution to obtain a powdery modified graphene oxide composite inorganic flame retardant; (3) mixing 50-60 parts of polyether polyol, 40-50 parts of polyester polyol, 3-5 parts of a foam stabilizer, 2-3 parts of a catalyst, 15-18 parts of a foaming agent, 80-100 parts of modified expandable graphite, 160-220 parts of a modified graphene oxide composite inorganic flame retardant, 15-20 parts of an organic phosphorus flame retardant and 0.9-1.5 parts of water to obtain a mixed liquid; and (4) adding 100-110 parts of diisocyanate into the mixed liquid, stirring, pouring into a mold, foaming and curing, thereby obtaining the polyurethane foaming material. The method is simple in process, low in production cost and relatively high in flame retardant property, thermal insulation property, mechanical property and thermal stability.

Description

[0001] This application claims the priority of a Chinese patent application titled "A Homogeneous Thermal Insulation Material and Its Preparation Method" with the application number "202410570458.4" filed with the Chinese Patent Office on May 9, 2024. The entire content thereof is incorporated herein by reference. Technical Field

[0002] This application relates to a homogeneous thermal insulation material and its preparation method, belonging to the technical field of thermal insulation materials. Background Art

[0003] Generally, the method of adding flame retardants to a polyurethane matrix is chosen to improve the flame retardancy of polyurethane thermal insulation materials. Currently, common flame retardants include halogen compounds, metal hydroxides, expandable graphite, and phosphorus-based compounds, etc. Due to its unique chemical stability and certain flame retardancy, graphene oxide has also gradually been used by researchers in polyurethane materials to synergistically improve the flame retardancy of the materials. Currently, mainly through physical mixing or chemical bonding methods, graphene is compounded with other flame retardants to improve the flame retardancy and compatibility of the flame retardants.

[0004] For example, Patent CN112679938B provides a homogeneous polyurethane foam, which mainly obtains a material with better flame retardancy through the modification of inorganic materials and the improvement of product processes, but there are still obvious problems: one is that the filling ratio of inorganic materials is too high. During the production process, it is difficult to achieve uniform mixing of high-proportion inorganic fillers with polyurethane foam, and it is difficult to ensure the homogeneous characteristics of the material, and at the same time, the mechanical properties are usually greatly affected; the second is that this technical solution does not mention the influence on the thermal insulation performance of the rigid polyurethane matrix. While filling inorganic powders to improve the flame retardant characteristics, it is difficult to take into account the characteristics of thermal insulation products. Therefore, this technical product does not meet the market demand for energy conservation and environmental protection.

[0005] Another example is Patent CN106496518A, which provides a graphene-modified polyurethane thermal insulation board. By premixing graphene and a flame retardant to form a white material premix to improve the compatibility of graphene and the flame retardant, a thermal insulation board that takes into account both thermal insulation performance and flame retardancy is obtained. However, it only premixes graphite powder, graphene, and the white material through a high-speed dispersion method, and the mixed solution cannot form a uniform and stable state. The flame retardant will settle, and the graphite powder is also prone to forming aggregates, greatly affecting the mechanical properties of the product.

[0006] Therefore, although the existing technologies have improved the flame retardancy and compatibility of flame retardants to a certain extent, there are still some problems and disadvantages. One is that the existing compounding methods often require complex process conditions and high costs; the second is that the flame retardancy and thermal insulation performance of the existing compound flame retardants still need to be improved; the third is that the existing compound flame retardants may have an adverse impact on other properties of polymer materials (such as mechanical properties, thermal stability, etc.). Summary of the Invention

[0007] To solve the above problems, a homogeneous thermal insulation material and a preparation method thereof are provided. The homogeneous thermal insulation material prepared by this method can solve the above technical problems. The production process of the thermal insulation material is simple, the production cost is reduced, and the flame retardancy, thermal insulation performance, mechanical properties and thermal stability are all relatively high.

[0008] According to one aspect of the present application, a preparation method of a homogeneous thermal insulation material is provided, including the following steps:

[0009] (1) Heat the aqueous solution of graphene oxide to 60 - 70 °C, then add a metal salt and stir to obtain a mixed solution. Add a sodium hydroxide or potassium hydroxide solution to the mixed solution and continuously stir for 1 - 2 h, where the molar ratio of the metal salt to sodium hydroxide or potassium hydroxide is 1:3 - 3.5, to obtain a graphene oxide composite inorganic flame retardant solution. The metal salt is selected from aluminum salts and / or magnesium salts;

[0010] (2) Add a surface modifier to the graphene oxide composite inorganic flame retardant solution, modify it at 70 - 80 °C for 2 - 3 h, and then spray dry to obtain a powdery modified graphene oxide composite inorganic flame retardant;

[0011] (3) Mix 50 - 60 parts of polyether polyol, 40 - 50 parts of polyester polyol, 3 - 5 parts of foam stabilizer, 2 - 3 parts of catalyst, 15 - 18 parts of blowing agent, 80 - 100 parts of modified expandable graphite, 160 - 220 parts of modified graphene oxide composite inorganic flame retardant, 15 - 20 parts of organophosphorus flame retardant and 0.9 - 1.5 parts of water to obtain a mixed liquid;

[0012] (4) Add 100 - 110 parts of diisocyanate to the mixed liquid, stir and then pour it into a mold for foaming and curing to obtain a homogeneous thermal insulation material.

[0013] In step (1), the graphene oxide composite inorganic flame retardant is synthesized by a chemical method to improve the dispersibility of the inorganic flame retardant and avoid problems such as incomplete compounding and low bonding degree leading to shedding caused by the physical coating method. At the same time, it solves the problem of excessive usage of traditional inorganic flame retardants in the direct addition method, greatly reduces the usage amount of aluminum hydroxide flame retardant, and improves the flame retardancy efficiency. In step (2), the surface modifier is used to modify the surface of the graphene oxide composite inorganic flame retardant to obtain a modified graphene oxide composite inorganic flame retardant, which can improve the compatibility of the modified graphene oxide composite inorganic flame retardant with the substrate and the modified expandable graphite, thereby improving the uniformity of the material.

[0014] Graphene oxide has an extremely large specific surface area, which is beneficial to improving the compatibility between inorganic flame retardants and polymer materials. At the same time, it forms a barrier layer with a huge local area to block the transfer of heat. Based on the modified graphene oxide composite inorganic flame retardant, this material adds modified expandable graphite and organic phosphorus-based flame retardants, which can achieve a synergistic flame retardant effect, and the above substances can reach a stable mixing state in the material, and are not prone to sedimentation and agglomeration, thereby improving the heat preservation performance, mechanical properties and thermal stability of the material.

[0015] Optionally, the metal salt is an aluminum salt and a magnesium salt with a molar ratio of 1:1.

[0016] Optionally, the aluminum salt is selected from at least one of aluminum chloride, aluminum sulfate, and aluminum nitrate;

[0017] The magnesium salt is selected from at least one of magnesium chloride, magnesium sulfate, and magnesium nitrate.

[0018] Optionally, the surface modifier is selected from at least one of titanate, silane, and aluminate.

[0019] The weight ratio of the surface modifier to the metal salt is (3-5):1.

[0020] Optionally, the concentration of the graphene oxide aqueous solution is 0.5-0.7%, and the weight ratio of the metal salt to the graphene oxide aqueous solution is 1:(10-150), preferably 1:(50-120).

[0021] Optionally, the foam stabilizer is hydroxy silicone oil.

[0022] Hydroxy silicone oil has good compatibility with polyurethane materials, can reduce the surface tension of the solid-gas two phases during the foaming process of polyurethane materials, make the bubbles of the material uniform and fine, thereby improving the heat preservation performance, mechanical properties and thermal stability of the material, and further playing a foam stabilizing function to improve the uniformity of the internal bubbles of the material.

[0023] Optionally, the polyether polyol is selected from polyether triol or polyether tetrol, and the hydroxyl value of the polyether polyol is 350-650 mg KOH / g;

[0024] The polyester polyol is selected from polycaprolactone polyol, polycarbonate polyol or polyacrylate polyol, and the hydroxyl value of the polyester polyol is 350-650 mg KOH / g;

[0025] The catalyst is selected from at least one of dibutyltin dilaurate, bis(dimethylaminoethyl) ether, N,N-dimethylcyclohexylamine, and 1,4-dimethylpiperazine;

[0026] The blowing agent is selected from at least one of n-pentane, n-hexane, and cyclohexane;

[0027] The organic phosphorus-based flame retardant is selected from at least one of dimethyl methylphosphonate, triphenyl phosphite, tributyl phosphate, and tris(β-chloroethyl) phosphate;

[0028] The diisocyanate is selected from at least one of toluene diisocyanate, isophorone diisocyanate, diphenylmethane diisocyanate, dicyclohexylmethane diisocyanate, and hexamethylene diisocyanate.

[0029] On the one hand, the organic phosphorus-based flame retardant decomposes when heated to produce phosphoric acid, metaphosphoric acid, and polyphosphoric acid. These phosphoric acids have strong dehydrating properties and can dehydrate and carbonize the polymer surface. Since elemental carbon cannot undergo evaporation combustion or decomposition combustion that produces flames, it has a flame retardant effect. On the other hand, when heated, it generates PO· free radicals, which can absorb a large amount of H· and HO· free radicals, thus interrupting the combustion reaction.

[0030] The functions of the modified expandable graphite are as follows: First, it can form a tough carbon layer on the surface of the polymer, separating the combustible from the heat source; second, it can absorb a large amount of heat during the expansion process, reducing the temperature of the system; third, it can release the acid radical ions in the interlayer during the expansion process, promoting dehydration and carbonization, and can combine with the free radicals generated by combustion to interrupt the chain reaction.

[0031] Optionally, the particle size of the modified expandable graphite is 0.5 - 10 μm, and the expansion coefficient is 250 - 290 ml / g.

[0032] Optionally, the modification method of the modified expandable graphite is as follows:

[0033] S10: Mix phosphoric acid and urea in a molar ratio of (0.5 - 1):1, react at 80 - 100 °C to obtain urea phosphate, add expandable graphite, a dispersant, and an emulsifier to the urea phosphate, continue stirring at 80 - 100 °C to obtain a colloid, emulsify the colloid in an emulsifier, and then transfer it to a polymerization furnace to polymerize at 150 - 240 °C and 10 - 45 Kpa to obtain a composite material. Cool, dry, and crush the composite material to obtain intermediate microspheres A;

[0034] S20: Mix the intermediate microspheres A and N-aminoethyl-3-aminopropyltriethoxysilane in a solvent and heat to 80 °C for reaction, filter, wash, and dry to obtain intermediate microspheres B with amino groups;

[0035] S30: React monomer A, a formaldehyde-based compound, and the intermediate microspheres B under an acidic catalyst, filter, wash, and dry to obtain intermediate microspheres C. Monomer A is selected from at least one of p-acetoxystyrene, diacetone acrylamide, and benzalacetone;

[0036] S40: Place the intermediate microsphere C in a 3-mercaptopropyltriethoxysilane solution, react it under a radical initiator, then perform suction filtration, washing, and drying to obtain modified expandable graphite.

[0037] In this preparation method, the expandable graphite layer in the intermediate microsphere A obtained in step S10 contains ammonium polyphosphate, which can improve the adhesion between expandable graphite, thereby enhancing the flame retardancy effect of expandable graphite. In step S20, N-aminoethyl-3-aminopropyltriethoxysilane reacts with the intermediate microsphere A to obtain the intermediate microsphere B. Firstly, it can improve the compatibility between the intermediate microsphere B and the polyurethane substrate, enabling the expandable graphite and the matrix to form a uniform and stable state, avoiding the sedimentation and aggregation of expandable graphite, and thus improving the performance uniformity of the polymer matrix and the flame retardancy uniformity of expandable graphite on the matrix. Secondly, the intermediate microsphere B contains NH and NH2 groups, which can not only absorb toxic gases, reducing the combustion hazard, but also participate in the reaction of isocyanate to form polyurethane, forming a chemical bond connection with the polyurethane matrix, enhancing the binding force between expandable graphite and the matrix, so that the flame retardant carbon layer is tightly combined with the matrix, improving the protection of the matrix, and can also react with the monomer A formaldehyde compound in step S30 to obtain the intermediate microsphere C. Due to the presence of the monomer A substance in the intermediate microsphere C prepared in step S30, functional groups such as benzene rings, carbonyl groups, ester groups, and amino groups can be introduced into the expandable graphite. The benzene ring can strengthen the matrix and improve the mechanical properties of the matrix. The carbonyl group and ester group can further increase the compatibility with the polyurethane matrix, and the amino group can further increase the number of binding sites with the polyurethane matrix and enhance the adsorption of toxic gases. Since the monomer A in step S30 all contains double bonds, 3-mercaptopropyltriethoxysilane is used to react with the double bond in step S40 to obtain a silane-capped modified expandable graphite, which can further improve the dispersibility and stability of expandable graphite in the matrix, and enhance the adhesion between expandable graphite, making the strength and compactness of the flame retardant carbon layer increase, thereby adsorbing and effectively blocking toxic gases, reducing the harm of toxic gases to the human body.

[0038] The intermediate microspheres A obtained in the above step S10 make ammonium polyphosphate contained between the graphite layers, which not only improves the binding force between expandable graphite, increases the strength of the flame-retardant carbon layer, but also can synchronously improve the flame-retardant characteristics of expandable graphite because ammonium polyphosphate itself also has flame retardancy; in steps S20 - S40, the surface of expandable graphite contains modified molecular chains, which can, first, adsorb toxic gases; second, improve the compatibility between expandable graphite and the matrix, improve the dispersion uniformity of expandable graphite, avoid sedimentation or agglomeration of expandable graphite, and also improve the performance uniformity of the polyurethane composite material; third, can chemically combine with the polyurethane matrix, make the flame-retardant carbon layer tightly combine with the matrix, effectively block toxic gases, and also improve the density, uniformity and mechanical strength of the flame-retardant carbon layer, and can resist open fire impact or heat convection impact.

[0039] Due to the more uniform dispersion of the modified expandable graphite prepared by the above method, when it is used as a flame retardant, the usage amount can be effectively reduced, thereby reducing the density of the material, and also avoiding the problem of falling off due to excessive mass when used as an exterior wall of a building.

[0040] Optionally, in step S10, the expandable graphite accounts for 5 - 30% of the weight of urea phosphate, the dispersant accounts for 0.5% of the weight of urea phosphate, and the emulsifier accounts for 0.5% of the weight of urea phosphate.

[0041] The intermediate microspheres A are obtained by using a homogenization emulsification process in the above step S10, which can solve the problem of difficult dispersion of expandable graphite and ammonium polyphosphate emulsion. Under the high shear force of the homogenization emulsifier, numerous small droplets are formed inside the emulsion, realizing the microstructure of ammonium polyphosphate emulsion wrapping expandable graphite particles. During the polymerization process, expandable graphite particles can be evenly dispersed, thereby improving the modification effect of ammonium polyphosphate on expandable graphite.

[0042] Since ammonium polyphosphate is contained between the expandable graphite layers, when ammonium polyphosphate decomposes upon heating, it decomposes into ammonia gas and polymeric phosphoric acid. Ammonia gas can dilute the oxygen concentration, and polymeric phosphoric acid has good thermal stability. When expandable graphite is heated, its volume expands rapidly, which can effectively isolate the oxygen required for combustion. At the same time, it has a porous structure inside, absorbs the flue gas of combustion, reduces the possibility of re - combustion, and can also effectively isolate the oxygen of combustion, improving the flame - retardant characteristics of the material.

[0043] Optionally, in the above step S20, the weight ratio of the intermediate microspheres A to N - aminoethyl - 3 - aminopropyltriethoxysilane is 1:(1 - 2);

[0044] The heating reaction time in step S20 is 8 - 10h.

[0045] The surface of expandable graphite contains a large number of hydroxyl groups. Through the reaction of N-aminoethyl-3-aminopropyltriethoxysilane and intermediate microsphere A, N-aminoethyl-3-aminopropyltriethoxysilane can react with the hydroxyl groups to achieve the grafting of N-aminoethyl-3-aminopropyltriethoxysilane on the surface of expandable graphite. The above reaction conditions can improve the reaction rate of N-aminoethyl-3-aminopropyltriethoxysilane and intermediate microsphere A, and control the amount of N-aminoethyl-3-aminopropyltriethoxysilane on the surface of expandable graphite, thereby synergistically improving the flame retardancy, strengthening, adsorption of toxic gases, and densification effects of the modified expandable graphite on the matrix.

[0046] If the weight of N-aminoethyl-3-aminopropyltriethoxysilane is too much, the amount of N-aminoethyl-3-aminopropyltriethoxysilane on the surface of expandable graphite increases. Combining with the reactions in subsequent steps S30 and S40, too many molecular chains are introduced on the surface of expandable graphite, which instead weakens the binding force between expandable graphite, and there will still be problems with cracks in the flame retardant carbon layer, and the flame retardancy and the barrier effect on toxic gases are reduced; if the weight of N-aminoethyl-3-aminopropyltriethoxysilane is too little, the modification effect of expandable graphite will be reduced, and the effects of flame retardancy, strengthening, adsorption of toxic gases, and densification on the matrix will all decline.

[0047] Optionally, the weight ratio of monomer A, formaldehyde compound, and intermediate microsphere B in step S30 is (1 - 2):(1 - 3):1;

[0048] The reaction temperature of step S30 is 50 - 60 °C, and the reaction time is 8 - 12 h;

[0049] Preferably, the acidic catalyst is selected from at least one of nicotinic acid, sulfuric acid, acetic acid, and nitric acid.

[0050] The above weight ratio and reaction conditions can improve the reaction efficiency of monomer A, formaldehyde compound, and intermediate microsphere B, promote monomer A and formaldehyde compound to react with the amino group in N-aminoethyl-3-aminopropyltriethoxysilane, thereby introducing new functional groups, increasing the number of functional groups in intermediate microsphere B, and further synergistically improving the flame retardancy and strengthening effects of expandable graphite on the matrix.

[0051] Optionally, monomer A is selected from diacetone acrylamide and benzalacetone;

[0052] The formaldehyde compound is selected from trioxymethylene and / or paraformaldehyde.

[0053] Optionally, the molar ratio of diacetone acrylamide and benzalacetone is 3:1.

[0054] It has been verified that when a single type of monomer A reacts with a formaldehyde-based compound and intermediate microsphere B, after monomer A is attached to intermediate microsphere B, it will hinder the subsequent reaction of monomer A, thus reducing the reaction participation rate of monomer A. As a result, in the molecular chain on the surface of intermediate microsphere C, a part is capped with monomer A, and the other part is still capped with N-aminoethyl-3-aminopropyltriethoxysilane. Selecting the above-mentioned diacetone acrylamide and benzylidene acetone with a molar ratio of 3:1 as monomer A can increase the reaction participation rate of monomer A, making the reaction rate of N-aminoethyl-3-aminopropyltriethoxysilane on the surface of intermediate microsphere B with monomer A greater than 98%. And it can also endow intermediate microsphere C with two functional groups, amino and benzene ring at the same time, enhancing the mechanical strength of the matrix and the chemical binding property with the matrix, so as to achieve a tight and uniform connection between the modified expandable graphite and the matrix.

[0055] Optionally, in step S40, the weight ratio of intermediate microsphere C to 3-mercaptopropyltriethoxysilane is 1:(5-10);

[0056] Preferably, the radical initiator is AIBN, the reaction temperature is 60-70 °C, and the reaction lasts for at least 5 h.

[0057] Capping the surface of intermediate microsphere C with monomer A can make the surface of the intermediate microsphere contain a large number of double bonds. In step S40, the double bonds react with thiol groups, which can introduce siloxane molecular chains into the modified expandable graphite again. At this time, both ends of the molecular chain on the surface of the modified expandable graphite are siloxane molecular chains, which can improve the dispersibility and stability of the modified expandable graphite in the matrix. On the premise of dispersion stability, it can improve the reaction uniformity of the amino group and isocyanate in the molecular chain on the surface of the modified expandable graphite, and further improve the uniformity of chemical binding with the matrix, embedding the modified expandable graphite evenly in the matrix. In a high-temperature environment, the binding force between the modified expandable graphite and the matrix is strong, and it can adsorb and block the toxic matrix of the matrix in the first time, improving the use safety of the material.

[0058] According to another aspect of the present application, there is provided a homogeneous thermal insulation material prepared by the preparation method of the homogeneous thermal insulation material described in any one of the above.

[0059] The beneficial effects of the present application include but are not limited to:

[0060] 1. The preparation method of the homogeneous thermal insulation material of the present application has a simple preparation method and low production cost. The inorganic flame retardant loaded on graphene oxide synthesized by chemical method can improve the dispersibility of the inorganic flame retardant and its compatibility with other substances, and the performance of the prepared thermal insulation material in all aspects has been improved.

[0061] 2. The homogeneous thermal insulation material of the present application can solve the problem of excessive usage caused by the direct addition method of traditional flame retardants, thereby significantly reducing the usage amount of inorganic flame retardants, and can also improve the flame retardancy efficiency on the basis of reducing the usage amount of flame retardants.

[0062] 3. In the homogeneous thermal insulation material of the present application, the modified inorganic flame retardant, modified expandable graphite, and organophosphorus-based flame retardant can cooperate with each other to improve the flame retardant effect of the material, and can improve the density and uniformity of the internal foam of the material under the action of a foam stabilizer, so as to obtain a thermal insulation material with excellent performance in all aspects. Detailed Embodiments

[0063] The present application will be described in detail below with reference to the embodiments, but the present application is not limited to these embodiments.

[0064] Unless otherwise specified, the raw materials in the embodiments of the present application are all purchased through commercial channels, and the phosphoric acid is an 85% phosphoric acid solution.

[0065] Unless otherwise specified, the methods used in the embodiments of the present application are conventional methods in the prior art.

[0066] The graphene oxide used in Example 2 was prepared by the Hummers method.

[0067] Example 1

[0068] This example relates to the preparation of modified expandable graphite, which includes the following steps:

[0069] S10: Mix phosphoric acid and urea with a molar ratio of (0.5 - 1):1, react at 80 - 100 °C to obtain urea phosphate, add expandable graphite, a dispersant, and an emulsifier to the urea phosphate, continue to stir at 80 - 100 °C to obtain a colloid, emulsify the colloid in an emulsifier and then transfer it to a polymerization furnace to polymerize at 150 - 240 °C and 10 - 45 KPa to obtain a composite material, cool, dry, and crush the composite material to obtain intermediate microspheres A;

[0070] S20: Mix intermediate microspheres A and N-aminoethyl-3-aminopropyltriethoxysilane in a solvent and heat to 80 °C for reaction, filter, wash, and dry to obtain amino-group-containing intermediate microspheres B;

[0071] S30: React monomer A, a formaldehyde compound, and intermediate microspheres B under an acidic catalyst, filter, wash, and dry to obtain intermediate microspheres C, and monomer A is selected from at least one of p-acetoxystyrene, diacetone acrylamide, and benzalacetone;

[0072] S40: Place intermediate microspheres C in a 3-mercaptopropyltriethoxysilane solution, react under a radical initiator, filter, wash, and dry to obtain the modified expandable graphite.

[0073] Prepare modified expandable graphite 1# - 8# and comparative modified expandable graphite D1# - D4# according to the above preparation steps as follows:

[0074] Modified expandable graphite 1#

[0075] The preparation method of this modified expandable graphite 1# includes the following steps:

[0076] S10: Mix phosphoric acid and urea with a molar ratio of 0.5:1, react at 100°C to obtain urea phosphate, add expandable graphite, dispersant, and emulsifier to the urea phosphate. The expandable graphite accounts for 5% of the weight of the urea phosphate, the dispersant accounts for 0.5% of the weight of the urea phosphate, and the emulsifier accounts for 0.5% of the weight of the urea phosphate. Continue to stir at 100°C to obtain a colloid. Emulsify the colloid in the emulsifier and then transfer it to a polymerization furnace to polymerize at 240°C and 10 Kpa to obtain a composite material. Cool, dry, and pulverize the composite material to obtain intermediate microspheres A with a particle size of 0.5 μm;

[0077] S20: Mix intermediate microspheres A and N-(2-aminoethyl)-3-aminopropyltriethoxysilane with a weight ratio of 1:1 in N,N-dimethylformamide and heat to 80°C. React for 10 h under nitrogen protection, filter, wash, and dry to obtain amino-containing intermediate microspheres B;

[0078] S30: Mix p-acetoxystyrene, trioxane, and intermediate microspheres B with a weight ratio of 1:1:1 in methanol, slowly add 37% concentrated hydrochloric acid, and the addition amount of the concentrated hydrochloric acid is 30% of the weight of the intermediate microspheres B. Then react at 50°C under nitrogen protection for 12 h. Neutralize the reaction solution with sodium bicarbonate to neutrality, filter, wash, and dry to obtain intermediate microspheres C;

[0079] S40: Place intermediate microspheres C with a weight ratio of 1:5 in a solution of 3-mercaptopropyltriethoxysilane. The solvent uses a mixed solvent of ethanol and water with a volume ratio of 5:1. Then add AIBN accounting for 1% of the weight of the intermediate microspheres. React at 70°C under nitrogen protection for 5 h, then filter, wash, and dry to obtain modified expandable graphite 1#.

[0080] Modified expandable graphite 2#

[0081] The preparation method of this modified expandable graphite 2# includes the following steps:

[0082] S10: Mix phosphoric acid and urea with a molar ratio of 1:1, react at 80 °C to obtain urea phosphate, add expandable graphite, dispersant, and emulsifier to the urea phosphate. The expandable graphite accounts for 30% of the weight of the urea phosphate, the dispersant accounts for 0.5% of the weight of the urea phosphate, and the emulsifier accounts for 0.5% of the weight of the urea phosphate. Continue stirring at 80 °C to obtain a colloid. Emulsify the colloid in an emulsifier and then transfer it to a polymerization furnace to polymerize at 150 °C and 45 Kpa to obtain a composite material. Cool, dry, and crush the composite material to obtain intermediate microspheres A with a particle size of 10 μm.

[0083] S20: Mix intermediate microspheres A and N-(2-aminoethyl)-3-aminopropyltriethoxysilane with a weight ratio of 1:2 in N,N-dimethylformamide and heat to 80 °C. React for 8 h under nitrogen protection, filter, wash, and dry to obtain intermediate microspheres B with amino groups. The reaction equation is as follows:

[0084]

[0085] S30: Mix monomer A, trioxane, and intermediate microspheres B with a weight ratio of 2:3:1 in methanol, slowly add 37% concentrated hydrochloric acid, and the addition amount of the concentrated hydrochloric acid is 30% of the weight of intermediate microspheres B. Then react at 60 °C under nitrogen protection for 8 h. Neutralize the reaction solution to neutral with sodium bicarbonate, filter, wash, and dry to obtain intermediate microspheres C. Monomer A is selected from diacetone acrylamide and benzalacetone with a molar ratio of 3:1. The reaction equation is as follows:

[0086]

[0087] Wherein R represents monomer A. In this step, both amino groups in intermediate microspheres B can participate in the reaction, thus obtaining two compounds with the structure of formula 1 and formula 2. The proportion of the compound with the structure of formula 1 in the above reaction is greater than 70%.

[0088] S40: Place intermediate microspheres C with a weight ratio of 1:10 in a solution of 3-mercaptopropyltriethoxysilane. The solvent uses a mixed solvent of ethanol and water with a volume ratio of 5:1. Then add AIBN accounting for 1% of the weight of the intermediate microspheres. React at 60 °C under nitrogen protection for 8 h, then filter, wash, and dry to obtain modified expandable graphite 2#. In this step, the carbon-carbon double bond in monomer A and 3-mercaptopropyltriethoxysilane undergo an addition reaction.

[0089] Modified expandable graphite 3#

[0090] The difference between this modified expandable graphite 3# and modified expandable graphite 2# is that in step S10, the expandable graphite accounts for 40% of the weight of the urea phosphate, and the other steps are the same as those of modified expandable graphite 2#.

[0091] Modified expandable graphite 4#

[0092] The difference between this modified expandable graphite 4# and the modified expandable graphite 2# is that in step S20, the weight ratio of the intermediate microspheres A and N-aminoethyl-3-aminopropyltriethoxysilane is 1:0.5, and the remaining steps are the same as those of the modified expandable graphite 2#.

[0093] Modified expandable graphite 5#

[0094] The difference between this modified expandable graphite 5# and the modified expandable graphite 2# is that in step S30, the weight ratio of monomer A, formaldehyde-based compound and intermediate microspheres B is 0.8:3:1, and the remaining steps are the same as those of the modified expandable graphite 2#.

[0095] Modified expandable graphite 6#

[0096] The difference between this modified expandable graphite 6# and the modified expandable graphite 2# is that in step S30, monomer A is selected from diacetone acrylamide and benzalacetone with a molar ratio of 1:3, and the remaining steps are the same as those of the modified expandable graphite 2#.

[0097] Modified expandable graphite 7#

[0098] The difference between this modified expandable graphite 7# and the modified expandable graphite 2# is that in step S40, the weight ratio of the intermediate microspheres C and 3-mercaptopropyltriethoxysilane is 1:3, and the remaining steps are the same as those of the modified expandable graphite 2#.

[0099] Modified expandable graphite 8#

[0100] The difference between this modified expandable graphite 8# and the modified expandable graphite 2# is that the particle size of the intermediate microspheres A is 15 μm, and the remaining steps are the same as those of the modified expandable graphite 2#.

[0101] Comparative modified expandable graphite D1#

[0102] The difference between this comparative modified expandable graphite D1# and the modified expandable graphite 2# is that step S10 is not carried out, and in step S20, expandable graphite and N-aminoethyl-3-aminopropyltriethoxysilane with a weight ratio of 1:2 are directly reacted. The particle size of the expandable graphite is 10 μm, and the remaining steps are the same as those of the modified expandable graphite 2#.

[0103] Comparative modified expandable graphite D2#

[0104] The difference between this comparative modified expandable graphite D2# and the modified expandable graphite 2# is that steps S20 - S40 are not carried out, and the intermediate microspheres A are the final modified expandable graphite, and the remaining steps are the same as those of the modified expandable graphite 2#.

[0105] Comparative modified expandable graphite D3#

[0106] The difference between this comparative modified expandable graphite D3# and the modified expandable graphite 2# is that step S40 is not carried out, and the intermediate microsphere C is the final modified expandable graphite, and the remaining steps are the same as those of the modified expandable graphite 2#.

[0107] Comparative modified expandable graphite D4#

[0108] The difference between this comparative modified expandable graphite D4# and the modified expandable graphite 2# is that in step S20, 3-aminopropyltriethoxysilane is used to replace N-aminoethyl-3-aminopropyltriethoxysilane, and the remaining steps are the same as those of the modified expandable graphite 2#.

[0109] Test Example 1

[0110] The prepared modified expandable graphite was subjected to gas adsorption tests. The test results are shown in Table 1, and the test method is as follows:

[0111] Experimental group: Place 1 g of modified expandable graphite in the non-combustible plate of the reactor, fix and hang the polyurethane sheet (5 cm long * 5 cm wide * 1 cm thick) without adding a flame retardant in the reactor, introduce oxygen (100 ml / min) into the reactor, and use a lighter device to ignite the polyurethane sheet for combustion until it burns completely, and test the concentrations of HCN, CO2, CO, NO, and NO2 in the reactor.

[0112] Blank group: Fix and hang the polyurethane sheet of the same material and size in the reactor, and do not place anything in the non-combustible plate. After the combustion is over, record the concentrations of HCN, CO2, CO, NO, and NO2 in the reactor.

[0113] The polyurethane sheets in both the experimental group and the blank group were prepared by placing polyether polyol, foam stabilizer, catalyst, foaming agent, and water with a weight ratio of 75:2.7:1.5:1.5:1 in a container, mixing and stirring with a high-speed stirrer for 2 min to obtain a uniformly mixed liquid, and then adding PAPI and stirring at high speed for 20 s. The weight ratio of PAPI to water is 100:1. The mixture was quickly added to a mold for foaming, the temperature of the closed mold was controlled at 65 °C, and the time was maintained for 30 min for curing. After the foaming was completed, the mold was opened and cut into 5 cm long * 5 cm wide * 1 cm thick.

[0114] The modified expandable graphite prepared in Example 1 was successively subjected to the experimental group tests. According to the comparison of the measured gas concentrations with those of the blank group, the adsorption rates of various gases were calculated. The calculation method is as follows:

[0115] HCN adsorption rate = (blank group HCN concentration - experimental group HCN concentration) / blank group HCN concentration * 100;

[0116] CO₂ adsorption rate = (CO₂ concentration in the blank group - CO₂ concentration in the experimental group) / CO₂ concentration in the blank group × 100;

[0117] CO adsorption rate = (CO concentration in the blank group - CO concentration in the experimental group) / CO concentration in the blank group × 100;

[0118] NO adsorption rate = (NO concentration in the blank group - NO concentration in the experimental group) / NO concentration in the blank group × 100;

[0119] NO₂ adsorption rate = (NO₂ concentration in the blank group - NO₂ concentration in the experimental group) / NO₂ concentration in the blank group × 100.

[0120] Table 1

[0121]

[0122] According to the data in Table 1, it can be seen that the modified expandable graphite can adsorb HCN, CO₂, CO, NO, and NO₂. Therefore, when it is used in polyurethane boards, it can adsorb and block the toxic gases generated in the initial stage of combustion, reducing the combustion hazard.

[0123] Example 2

[0124] This example relates to a preparation method of a homogeneous thermal insulation material, including the following steps:

[0125] (1) Heat the graphene oxide aqueous solution to 60 - 70 °C, then add a metal salt and stir to obtain a mixed solution. Add a sodium hydroxide or potassium hydroxide solution to the mixed solution and continuously stir for 1 - 2 h, where the molar ratio of the metal salt to sodium hydroxide or potassium hydroxide is 1:3 - 3.5, to obtain a graphene oxide composite inorganic flame retardant solution. The metal salt is selected from aluminum salts and / or magnesium salts;

[0126] (2) Add a surface modifier to the graphene oxide composite inorganic flame retardant solution, modify it at 70 - 80 °C for 2 - 3 h, and then spray dry to obtain a powdered modified graphene oxide composite inorganic flame retardant;

[0127] (3) Mix 50 - 60 parts of polyether polyol, 40 - 50 parts of polyester polyol, 3 - 5 parts of foam stabilizer, 2 - 3 parts of catalyst, 15 - 18 parts of foaming agent, 80 - 100 parts of modified expandable graphite, 160 - 220 parts of modified graphene oxide composite inorganic flame retardant, 15 - 20 parts of organophosphorus flame retardant, and 0.9 - 1.5 parts of water to obtain a mixed liquid;

[0128] (4) Add 100 - 110 parts of diisocyanate to the mixed liquid, stir and then pour it into a mold for foaming and curing to obtain the homogeneous thermal insulation material.

[0129] Prepare materials 1# - 6# and comparative materials D1# - D2# according to the above preparation method. The specific preparation method is as follows:

[0130] Material 1#

[0131] Preparation of modified expandable graphite:

[0132] Put expandable graphite with a particle size of 0.5 μm into a 3 - aminopropyltriethoxysilane solution. The weight ratio of expandable graphite to 3 - aminopropyltriethoxysilane is 10:1. Stir at 60°C for 3 h, then centrifuge and dry to obtain modified expandable graphite.

[0133] The preparation of Material 1# includes the following steps:

[0134] (1) Heat the 0.07% graphene oxide aqueous solution to 60°C, then add aluminum nitrate and stir to obtain a mixed solution. The weight ratio of aluminum nitrate to the graphene oxide aqueous solution is 1:10. Add sodium hydroxide solution to the mixed solution and continuously stir for 1 h, where the molar ratio of aluminum nitrate to sodium hydroxide is 1:3, to obtain a graphene oxide composite inorganic flame retardant solution;

[0135] (2) Add 3 - aminopropyltriethoxysilane to the graphene oxide composite inorganic flame retardant solution. The weight ratio of 3 - aminopropyltriethoxysilane to aluminum nitrate is 3:1. Modify at 80°C for 2 h, then spray - dry to obtain a powdery modified graphene oxide composite inorganic flame retardant;

[0136] (3) Mix 50 parts of polyether triol (hydroxyl value 350 mg KOH / g), 40 parts of polycaprolactone polyol (hydroxyl value 650 mg KOH / g), 3 parts of hydroxyl silicone oil, 2 parts of dibutyltin dilaurate, 15 parts of n - pentane, 80 parts of modified expandable graphite, 160 parts of modified graphene oxide composite inorganic flame retardant, 15 parts of triphenyl phosphite, and 0.9 parts of water to obtain a mixed liquid;

[0137] (4) Add 100 parts of hexamethylene diisocyanate to the mixed liquid, stir and pour it into a mold, and foam and cure at 65°C to obtain a homogeneous thermal insulation material.

[0138] Material 2#

[0139] The particle size of the expandable graphite is 10 μm. The steps and dosage of the modified expandable graphite are the same as those of Material 1#.

[0140] The preparation of Material 2# includes the following steps:

[0141] (1) Heat the 0.05% graphene oxide aqueous solution to 70 °C, then add magnesium sulfate and stir to obtain a mixed solution. The weight ratio of magnesium sulfate to the graphene oxide aqueous solution is 1:150. Add potassium hydroxide solution to the mixed solution and continuously stir for 2 h, where the molar ratio of magnesium nitrate to potassium hydroxide is 1:3.5, to obtain a graphene oxide composite inorganic flame retardant solution;

[0142] (2) Add 3-aminopropyltriethoxysilane to the graphene oxide composite inorganic flame retardant solution. The weight ratio of 3-aminopropyltriethoxysilane to aluminum nitrate is 5:1. Modify at 70 °C for 3 h, then spray dry to obtain a powdered modified graphene oxide composite inorganic flame retardant;

[0143] (3) Mix 60 parts of polyether tetraol (hydroxyl value 400 mg KOH / g), 50 parts of polycarbonate polyol (hydroxyl value 400 mg KOH / g), 5 parts of hydroxyl silicone oil, 3 parts of dibutyltin dilaurate, 18 parts of n-pentane, 100 parts of modified expandable graphite, 220 parts of modified graphene oxide composite inorganic flame retardant, 20 parts of dimethyl methylphosphonate, and 1.5 parts of water to obtain a mixed liquid;

[0144] (4) Add 110 parts of hexamethylene diisocyanate to the mixed liquid, stir and pour it into a mold, and foam and cure at 65 °C to obtain a homogeneous thermal insulation material.

[0145] Material 3#

[0146] The difference between this Material 3# and Material 2# is that aluminum chloride and magnesium chloride with a molar ratio of 1:1 are used to replace magnesium sulfate, and the rest is the same as Material 2#.

[0147] Material 4#

[0148] The difference between this Material 4# and Material 3# is that the modified expandable graphite 2# of Example 1 is used as the modified expandable graphite, and the rest is the same as Material 3#.

[0149] Material 5#

[0150] The difference between this Material 5# and Material 3# is that the comparative modified expandable graphite D1# of Example 1 is used as the modified expandable graphite, and the rest is the same as Material 3#.

[0151] Material 6#

[0152] The difference between this Material 6# and Material 3# is that the comparative modified expandable graphite D2# of Example 1 is used as the modified expandable graphite, and the rest is the same as Material 3#.

[0153] Comparative Material D1#

[0154] The difference between this comparative material D1# and material 3# is that steps (1) and (2) are not adopted to coat and surface-modify the inorganic flame retardant with graphene oxide. In step (3), aluminum hydroxide and magnesium hydroxide with a weight ratio of 1:1 are directly used as the inorganic flame retardant, and the rest is the same as material 3#.

[0155] Comparative material D2#

[0156] The difference between this comparative material D2# and material 3# is that modified expandable graphite is not added, and the rest is the same as material 3#.

[0157] Test example 2

[0158] The materials prepared in Example 2 were tested for density, thermal conductivity, flame retardancy, and mechanical properties. The results are shown in Table 2 below, where the flame retardancy performance was evaluated according to the GB8624-2012 standard.

[0159] Table 2

[0160]

[0161]

[0162] Test example 3

[0163] The materials prepared in Example 2 were placed at 60°C and 50% humidity for 30 days, and then the compressive strength of the materials was tested. The test results are shown in Table 3 below. In addition, the dimensional stability of the materials prepared in Example 2 was tested according to GBT8811-2008, and the test results are shown in Table 3 below.

[0164] Table 3

[0165]

[0166] As described above, the above are only the embodiments of the present application. The protection scope of the present application is not limited by these specific embodiments, but is determined by the claims of the present application. For those skilled in the art, various changes and modifications can be made to the present application. Any modification, equivalent replacement, improvement, etc. made within the technical idea and principle of the present application shall be included in the protection scope of the present application.

Claims

1. A preparation method of a homogeneous thermal insulation material, characterized in that, It includes the following steps: (1) Heat the graphene oxide aqueous solution to 60 - 70 °C, then add a metal salt and stir to obtain a mixed solution. Add a sodium hydroxide or potassium hydroxide solution to the mixed solution and continuously stir for 1 - 2 h, where the molar ratio of the metal salt to sodium hydroxide or potassium hydroxide is 1:3 - 3.5, to obtain a graphene oxide composite inorganic flame retardant solution. The metal salt is selected from aluminum salts and / or magnesium salts; (2) Add a surface modifier to the graphene oxide composite inorganic flame retardant solution, modify it at 70 - 80 °C for 2 - 3 h, and then spray dry to obtain a powdered modified graphene oxide composite inorganic flame retardant; (3) Mix 50 - 60 parts of polyether polyol, 40 - 50 parts of polyester polyol, 3 - 5 parts of foam stabilizer, 2 - 3 parts of catalyst, 15 - 18 parts of blowing agent, 80 - 100 parts of modified expandable graphite, 160 - 220 parts of modified graphene oxide composite inorganic flame retardant, 15 - 20 parts of organophosphorus flame retardant, and 0.9 - 1.5 parts of water to obtain a mixed liquid; (4) Add 100 - 110 parts of diisocyanate to the mixed liquid, stir and then pour it into a mold for foaming and curing to obtain a homogeneous thermal insulation material.

2. The preparation method according to claim 1, wherein The metal salt is an aluminum salt and a magnesium salt with a molar ratio of 1:

1.

3. The preparation method according to claim 2, characterized in that, The aluminum salt is selected from at least one of aluminum chloride, aluminum sulfate, and aluminum nitrate; The magnesium salt is selected from at least one of magnesium chloride, magnesium sulfate, and magnesium nitrate.

4. The preparation method according to claim 1, characterized in that, The surface modifier is selected from at least one of titanate, silane, and aluminate.

5. The preparation method according to claim 1, characterized in that, The concentration of the graphene oxide aqueous solution is 0.5 - 0.7%, and the weight ratio of the metal salt to the graphene oxide aqueous solution is 1:(10 - 150).

6. The preparation method according to claim 1, characterized in that, The foam stabilizer is hydroxy silicone oil.

7. The preparation method according to claim 1, characterized in that, The polyether polyol is selected from polyether triol or polyether tetrol, and the hydroxyl value of the polyether polyol is 350 - 650 mg KOH / g; The polyester polyol is selected from polycaprolactone polyol, polycarbonate polyol, or polyacrylate polyol, and the hydroxyl value of the polyester polyol is 350 - 650 mg KOH / g; The catalyst is selected from at least one of dibutyltin dilaurate, bis(dimethylaminoethyl) ether, N,N - dimethylcyclohexylamine, and 1,4 - dimethylpiperazine; The blowing agent is selected from at least one of n - pentane, n - hexane, and cyclohexane; The organophosphorus flame retardant is selected from at least one of dimethyl methylphosphonate, triphenyl phosphite, tributyl phosphate, and tris(β - chloroethyl) phosphate; The diisocyanate is selected from at least one of toluene diisocyanate, isophorone diisocyanate, diphenylmethane diisocyanate, dicyclohexylmethane diisocyanate, and hexamethylene diisocyanate.

8. The preparation method according to claim 1, characterized in that, The modification method of the modified expandable graphite is: S10: Mix phosphoric acid and urea with a molar ratio of (0.5 - 1):1, react at 80 - 100 °C to obtain urea phosphate, add expandable graphite, a dispersant, and an emulsifier to the urea phosphate, continue stirring at 80 - 100 °C to obtain a colloid, emulsify the colloid in an emulsifier and then transfer it to a polymerization furnace to polymerize at 150 - 240 °C and 10 - 45 Kpa to obtain a composite material, cool, dry, and pulverize the composite material to obtain intermediate microspheres A; S20: Mix the intermediate microspheres A and N - aminoethyl - 3 - aminopropyltriethoxysilane in a solvent and heat to react at 6 to 80 °C, filter, wash, and dry to obtain amino - containing intermediate microspheres B; S30: React monomer A, a formaldehyde - based compound, and the intermediate microspheres B under an acidic catalyst, filter, wash, and dry to obtain intermediate microspheres C, where monomer A is selected from at least one of p - acetoxystyrene, diacetone acrylamide, and benzalacetone; S40: Place the intermediate microspheres C in a 3 - mercaptopropyltriethoxysilane solution, react under a radical initiator, filter, wash, and dry to obtain modified expandable graphite.

9. The homogeneous thermal insulation material prepared by the preparation method of the homogeneous thermal insulation material according to any one of claims 1 - 8.

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