Polyurethane flame-retardant sound-insulation composite board with multi-layer structure and preparation method thereof

Abstract

The invention discloses a polyurethane flame-retardant sound-insulation composite board with a multi-layer structure and a preparation method thereof, and belongs to the technical field of composite boards, nickel nitrate is used as a nickel source, ferric nitrate is used as an iron source, nickel ferrite powder is obtained through a solvothermal method and a high-temperature calcination method, the nickel ferrite powder is compounded with graphene oxide to obtain composite aerogel powder, the surface of the composite aerogel powder is coated with polydopamine, and the flame-retardant sound-insulation composite board with the multi-layer structure is obtained. The enhanced aerogel powder is obtained; the preparation method comprises the following steps: preparing functional rigid polyurethane foam from polyether polyol, polymethylene polyphenyl polyisocyanate, enhanced aerogel powder, ammonium polyphosphate, magnesium hydroxide and a foaming aid through a one-step foaming method, putting the functional rigid polyurethane foam as a core layer between an aluminum-magnesium-manganese alloy color steel plate and a porous sound insulation plate, and carrying out hot-pressing compounding, so as to obtain the aluminum-magnesium-manganese alloy color steel plate / porous sound insulation plate. The polyurethane flame-retardant sound-insulation composite board with the multi-layer structure is obtained; and comprehensive improvement of flame retardance, sound insulation, heat insulation, electromagnetic shielding and dimensional stability is realized.

Description

Technical Field

[0001] This invention belongs to the field of composite panel technology, specifically relating to multi-layer polyurethane flame-retardant and sound-insulating composite panels and their preparation methods. Background Technology

[0002] Polyurethane composite panels are a new type of panel made with rigid polyurethane foam as the core layer and composite metal plates, fiberglass cloth, and other surface materials on the top and bottom layers through a specific process. They combine multiple functions such as heat insulation, load-bearing, and decoration. As the construction industry upgrades towards high-end and safer construction, the shortcomings of traditional polyurethane composite panels are becoming increasingly apparent. Ordinary polyurethane core layers are easily flammable and release toxic gases when exposed to fire, making it difficult to meet the fire resistance requirements of B1 or higher in the "Technical Specification for Concrete Structures of High-Rise Buildings". In enclosed scenarios such as the exterior walls of high-rise buildings and elevator shafts, the fire hazard is significant. In addition, the closed-cell rate of traditional core foam is mostly around 80%, allowing sound waves to easily penetrate the panels. In scenarios such as sound barriers for rail transit and partition walls of high-end residential buildings, the sound insulation effect is far from meeting the comfort requirements.

[0003] Therefore, there is an urgent need to develop a multi-layer composite panel that combines excellent flame retardancy with high-efficiency sound insulation performance. By optimizing materials and designing the structure in synergy, safety and comfort can be improved, and its application in high-end buildings can be expanded.

[0004] Chinese invention patent application CN112920546A discloses a mineral fiber reinforced environmentally friendly building board and its preparation method. It adopts composite hot pressing molding technology and is a composite material prepared from mineral fiber, magnesium hydroxide, phosphoric acid, expanded perlite, propyltriethylsilane isocyanate, phenolic resin, epoxy resin, plasticizer, hexamethylenetetramine, and polyurethane. Among them, magnesium hydroxide is used as a flame retardant. The flame retardant mechanism is simple and the smoke suppression ability is limited. Once the board is burned, it will rapidly release a large amount of asphyxiating and toxic fumes, causing people to suffocate, be poisoned, and lose their way, making effective evacuation impossible. Summary of the Invention

[0005] The purpose of this invention is to provide a multi-layer polyurethane flame-retardant and sound-insulating composite board and its preparation method. The board uses nickel ferrite / graphene composite aerogel powder as a functional skeleton, enhances its interfacial stability and dispersibility by coating with polydopamine, and synergizes with flame retardants such as ammonium polyphosphate and magnesium hydroxide to form a functional polyurethane rigid foam. This foam is then hot-pressed and cured with a porous sound insulation board and an aluminum-magnesium-manganese alloy color steel plate to achieve a comprehensive improvement in flame retardancy, sound insulation, heat insulation, electromagnetic shielding, and dimensional stability.

[0006] The objective of this invention can be achieved through the following technical solutions: The preparation method of multi-layer polyurethane flame-retardant and sound-insulating composite board includes the following steps: Step 1: Using nickel nitrate as the nickel source, ferric nitrate as the iron source, and hexamethylenetetramine as the precipitant, nickel ferrite powder is obtained through solvothermal and high-temperature calcination methods. This powder is then combined with graphene oxide through hydrothermal self-assembly to obtain composite aerogel powder. Finally, polydopamine is coated onto the surface through in-situ polymerization to obtain reinforced aerogel powder.

[0007] Step 2: Polyether polyol, polymethylene polyphenyl polyisocyanate, reinforced aerogel powder, ammonium polyphosphate, magnesium hydroxide and foaming agent are foamed in one step to obtain functional polyurethane rigid foam; the functional polyurethane rigid foam is used as the core layer and placed between two layers of aluminum-magnesium-manganese alloy color steel plate and porous sound insulation board, and then hot-pressed to obtain multi-layer polyurethane flame-retardant sound insulation composite board.

[0008] Furthermore, the specific preparation process of nickel ferrite powder is as follows: Nickel nitrate, ferric nitrate, and deionized water were added to a reaction vessel and stirred for 20-30 minutes. Then, hexamethylenetetramine was added and stirred for 2-3 hours. The mixture was kept at 100-110°C for 6-8 hours and cooled to room temperature. The product was washed 3-5 times with deionized water and dried under vacuum to obtain the precursor. The precursor was transferred to a muffle furnace and calcined at 400-500°C at a heating rate of 5°C / min for 2-3 hours. The mixture was then cooled to room temperature with the furnace, ground, and passed through a 300-mesh sieve to obtain nickel ferrite powder.

[0009] Furthermore, the ratio of nickel nitrate, ferric nitrate, deionized water, and hexamethylenetetramine is 1.8-2.5g: 4.8-5.6g: 90-120mL: 10.2-12.4g.

[0010] Furthermore, the specific preparation process of the composite aerogel powder is as follows: Nickel ferrite powder and 0.3 wt% graphene oxide aqueous suspension were mixed at a ratio of 1.5-2 g: 3-4 L and sonicated for 20-30 min. The pH was adjusted to 11 with ammonia water, and the mixture was stirred for 2-3 h. The mixture was then transferred to a reaction vessel and hydrothermally reacted at 120-130℃ for 12-14 h. After cooling to room temperature, the mixture was dialyzed in an 8.1 wt% ethanol aqueous solution for 36-40 h and freeze-dried at -50℃ to -20℃ for 48-50 h. The mixture was then ground and pulverized, and passed through a 300-mesh sieve to obtain composite aerogel powder.

[0011] Furthermore, the ratio of nickel ferrite powder to 0.3 wt% graphene oxide aqueous suspension is 1.5-2 g: 3-4 L.

[0012] Furthermore, the specific preparation process of the enhanced aerogel powder is as follows: The composite aerogel powder was added to a 10wt% ethanol aqueous solution, sonicated for 30-40 min, the pH was adjusted to 8.5 with Tris-HCl buffer, dopamine was added, and the mixture was stirred for 24-30 h. After centrifugation and filtration, the product was washed repeatedly with deionized water 3-5 times and vacuum dried to constant weight to obtain the reinforced aerogel powder.

[0013] Furthermore, the ratio of composite aerogel powder, 10wt% ethanol aqueous solution, and dopamine is 5-8g: 10-12L: 5-8g.

[0014] Furthermore, the specific preparation process of functional polyurethane rigid foam is as follows: Polyether polyol, triethanolamine, dibutyltin dilaurate, silicone oil, ammonium polyphosphate, metal hydroxide flame retardant, and reinforced aerogel powder are added to a beaker and stirred evenly. Then, polymethylene polyphenyl polyisocyanate is added and stirred at high speed for 10-15 seconds until it turns white and expands. The mixture is then quickly poured into a core material mold, allowed to foam naturally, cooled to room temperature, removed from the mold, and cured in an oven at 80-90℃ for 10-12 hours to obtain functional polyurethane rigid foam.

[0015] Furthermore, the mass ratio of polyether polyol, triethanolamine, dibutyltin dilaurate, silicone oil, ammonium polyphosphate, metal hydroxide flame retardant, reinforced aerogel powder, and polymethylene polyphenyl polyisocyanate is 200-250:3-3.8:0.5-1:2-2.5:30-40:10-15:10-12:200-260.

[0016] Furthermore, the metal hydroxide flame retardant is either aluminum hydroxide or magnesium hydroxide.

[0017] Furthermore, the specific preparation process of the multi-layer polyurethane flame-retardant and sound-insulating composite board is as follows: The bottom layer of color steel plate, the porous sound insulation board, and the functional polyurethane rigid foam are laid in sequence. After applying adhesive, the top layer of color steel plate is covered to obtain a multi-layer board. The board is then hot-pressed and cured at 60-80℃ and 0.5-0.8MPa for 2-3 hours. After cooling and demolding, a multi-layer polyurethane flame-retardant sound insulation composite board is obtained.

[0018] Furthermore, the porous sound insulation board can be either rock wool board or glass wool board.

[0019] The beneficial effects of this invention are: 1. This invention, through material design and process integration, prepares a multifunctional composite board integrating high-efficiency flame retardancy, excellent sound insulation, and electromagnetic shielding. The "reinforced aerogel powder" filler, prepared through self-assembly and in-situ polymerization, forms a gas-phase-condensed-phase synergistic flame retardant system with ammonium polyphosphate and magnesium hydroxide, enhancing the material's flame retardancy. The aerogel nanostructure also enhances the mechanical strength and broadband sound absorption and insulation properties of the polyurethane foam. The innovative multi-layer structure of "aluminum-magnesium-manganese alloy board - porous sound insulation board - functional polyurethane rigid foam" combined with the excellent interfacial adhesion and hot-press curing process of polydopamine ensures a strong bond between each layer, giving the board excellent overall structural integrity, durability and a higher sound insulation limit.

[0020] 2. In terms of flame retardancy, the nickel ferrite powder in this invention, as a transition metal compound, can catalyze the cross-linking of the polymer matrix at combustion temperature, promoting the formation of a denser and more stable char layer, and significantly improving the char-forming ability and flame-retardant and smoke-suppressing performance of the material; in terms of mechanics, as rigid nanoparticles dispersed in the three-dimensional network of aerogel, it effectively enhances the skeleton structure and overcomes the brittleness of traditional materials; in addition, it also endows the composite material of this invention with electromagnetic shielding function, expanding the application scenarios.

[0021] 3. The enhanced aerogel powder in this invention is produced by hydrothermal self-assembly of nickel ferrite and graphene oxide, supplemented by polydopamine coating. Graphene oxide provides a three-dimensional network framework and specific surface area. When combined with nickel ferrite, it not only endows the material with electromagnetic shielding properties, but also catalyzes the efficient char formation of the matrix during combustion. It also synergistically retards flame with the thermophysical barrier properties of graphene. The polydopamine coating layer not only enhances the mechanical toughness of the aerogel itself and maintains structural integrity during processing and compounding, but also improves the interfacial compatibility with the polyurethane matrix, reduces agglomeration, and optimizes stress transmission. Detailed Implementation

[0022] The technical solutions of the present invention will be clearly and completely described below with reference to the embodiments in the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0023] Example 1: A method for preparing multi-layer polyurethane flame-retardant and sound-insulating composite panels, comprising the following steps: S1: Add 1.8g nickel nitrate, 4.8g ferric nitrate and 90mL deionized water to a reaction vessel and stir for 20min. Then add 10.11g hexamethylenetetramine and stir for 2h. Keep at 100℃ for 6h and cool to room temperature. Wash the product three times with deionized water and vacuum dry to obtain the precursor. Transfer it to a muffle furnace and calcine at 400℃ with a heating rate of 5℃ / min for 2h. Cool to room temperature with the furnace, grind and pass through a 300-mesh sieve to obtain nickel ferrite powder.

[0024] Hexamethylenetetramine is hydrolyzed under hydrothermal conditions using a solvothermal and high-temperature calcination method to generate hydroxide ions, which then undergo homogeneous precipitation with nickel and iron ions in the solution to form nickel-iron hydroxide precursors. These precursors are then calcined at medium temperature to obtain nickel-ferrite powder.

[0025] S2: Add 1.5g of nickel ferrite powder to 3L of 0.3wt% graphene oxide aqueous suspension, sonicate for 20min, adjust the pH to 11 with ammonia, stir for 2h, transfer to a reaction vessel, hydrothermally react at 120℃ for 12h, cool to room temperature, dialyze in 8.1wt% ethanol aqueous solution for 36h, freeze dry at -50℃ for 48h, grind and pulverize, and pass through a 300-mesh sieve to obtain composite aerogel powder.

[0026] By utilizing intermolecular forces such as electrostatic interactions, π-π stacking, and hydrogen bonding, graphene oxide sheets are driven to undergo hydrothermal self-assembly with magnetic nickel ferrite nanoparticles.

[0027] S3: Add 5g of composite aerogel powder to 10L of 10wt% ethanol aqueous solution, sonicate for 30min, adjust the pH to 8.5 with Tris-HCl buffer, add 5g of dopamine, stir for 24h, centrifuge and filter, wash the product repeatedly with deionized water 3 times, and vacuum dry to constant weight to obtain reinforced aerogel powder.

[0028] Dopamine monomers undergo in-situ polymerization under the action of dissolved oxygen. The resulting polydopamine is coated on the surface of the aerogel through interactions such as covalent bonds, hydrogen bonds, and π-π stacking between the catechol and amino functional groups in the molecule.

[0029] S4: Add 200g of polyether polyol, 3g of triethanolamine, 0.5g of dibutyltin dilaurate, 2g of silicone oil, 30g of ammonium polyphosphate, 10g of magnesium hydroxide and 10g of reinforced aerogel powder to a beaker and stir evenly. Then add 200g of polymethylene polyphenyl polyisocyanate and stir at high speed for 10s until it turns white and expands. Quickly pour it into the core material mold, allow it to foam naturally, cool to room temperature, remove the mold, and cure in an 80℃ oven for 10 hours to obtain functional polyurethane rigid foam.

[0030] S5: Lay a layer of aluminum-magnesium-manganese alloy color steel plate (face down) at the bottom of the mold, lay a layer of rock wool board (i.e., porous sound insulation board) flat on the color steel plate, then place functional polyurethane rigid foam on the porous sound insulation board, coat the surface with a layer of polyurethane adhesive, and cover the coated surface with a second layer of aluminum-magnesium-manganese alloy color steel plate (face up) to obtain a multi-layer board; transfer the multi-layer board to a hot press, hot press and cure at 60℃ and 0.5MPa for 2 hours, cool naturally to room temperature, remove the mold, and obtain a multi-layer polyurethane flame-retardant sound insulation composite board.

[0031] Example 2: This example provides a method for preparing a multi-layer polyurethane flame-retardant and sound-insulating composite board. The difference from Example 1 is that in step S2, the ratio of nickel ferrite powder to 0.3wt% graphene oxide aqueous suspension is 2g:4L, and a multi-layer polyurethane flame-retardant and sound-insulating composite board is prepared.

[0032] Example 3: This example provides a method for preparing a multi-layer polyurethane flame-retardant and sound-insulating composite board. The difference from Example 1 is that in step S3, the ratio of composite aerogel powder, 10wt% ethanol aqueous solution and dopamine is 8g:12L:8g, and a multi-layer polyurethane flame-retardant and sound-insulating composite board is prepared.

[0033] Example 4: This example provides a method for preparing a multi-layer polyurethane flame-retardant and sound-insulating composite board. The difference from Example 1 is that aluminum hydroxide is used instead of magnesium hydroxide in step S4 to prepare a multi-layer polyurethane flame-retardant and sound-insulating composite board.

[0034] Example 5: This example provides a method for preparing a multi-layer polyurethane flame-retardant and sound-insulating composite board. The difference from Example 1 is that in step S4, the mass ratio of polyether polyol, triethanolamine, dibutyltin dilaurate, silicone oil, ammonium polyphosphate, magnesium hydroxide, reinforced aerogel powder, and polymethylene polyphenyl polyisocyanate is 250:3.8:1:2.5:40:15:12:260, thus preparing a multi-layer polyurethane flame-retardant and sound-insulating composite board.

[0035] In the multi-layer polyurethane flame-retardant and sound-insulating composite panels prepared in Examples 1-5 of this application, the thickness of the functional polyurethane rigid foam is 30mm, the thickness of the aluminum-magnesium-manganese alloy color steel plate is 0.5mm, and the thickness of the porous sound insulation board is 10mm. The polyurethane adhesive used is from Yiligao, and the product model is UR5608 polyurethane resin. In addition to rock wool board, the porous sound insulation board can also be selected from high-efficiency sound-absorbing materials such as glass wool board. All other raw materials are commercially available products.

[0036] Comparative Example 1: The difference from Example 1 is that nickel ferrite powder is not added in step S2, while the other steps remain unchanged, and a multi-layer polyurethane flame-retardant and sound-insulating composite board is prepared.

[0037] Comparative Example 2: The difference from Example 1 is that step S3 is omitted, and the composite aerogel powder in step S2 is used to replace the reinforcing aerogel powder in step S4. The remaining steps remain unchanged, and a multilayer polyurethane flame-retardant and sound-insulating composite board is prepared.

[0038] Comparative Example 3: The difference from Example 1 is that no reinforcing aerogel powder is added in step S4, while the other steps remain unchanged, and a multilayer polyurethane flame-retardant and sound-insulating composite board is prepared.

[0039] The multilayer polyurethane flame-retardant and sound-insulating composite panels prepared in Examples 1-5 and Comparative Examples 1-3 were cut into 10cm × 10cm samples and subjected to the following performance tests: Dimensional stability: Refer to GB / T8811-2008 "Test method for dimensional stability of rigid foamed plastics" and place the sample in an oven at 70℃ for 48 hours, then measure the rate of dimensional change.

[0040] Thermal conductivity: Refer to GB / T10294-2008 "Determination of steady-state thermal resistance and related properties of thermal insulation materials - protective hot plate method" and record the data.

[0041] Average sound insulation: Referring to GB / Z 27764-2011 "Measurement of sound transmission loss in acoustic impedance tubes by transfer matrix method", the samples were tested in a large-diameter impedance tube with a diameter of 100mm and a test frequency of 100-1600Hz and a small-diameter impedance tube with a diameter of 30mm and a test frequency of 1600-6300Hz. The test data were analyzed and fitted using VA-Lab4 software, and the average sound insulation was recorded.

[0042] Electromagnetic shielding effectiveness: Refer to GB / T30142-2013 "Measurement Method for Shielding Effectiveness of Planar Electromagnetic Shielding Materials" and record the data.

[0043] Flame retardancy: Refer to GB / T2406.2-2009 "Determination of burning behavior of plastics by oxygen index method - Part 2: Room temperature test", conduct the test in an oxygen index tester, ignite by top surface ignition, measure the minimum oxygen concentration required for the sample to maintain stable combustion for at least 3 minutes in a nitrogen-oxygen mixed gas flow, and record the limiting oxygen index value.

[0044] The results are shown in Table 1: Table 1 Performance Test Results of Multilayer Polyurethane Flame-Retardant and Sound-Insulating Composite Panels project Example 1 Example 2 Example 3 Example 4 Example 5 Comparative Example 1 Comparative Example 2 Comparative Example 3 Dimensional stability (%) 0.36 0.39 0.38 0.37 0.39 0.38 0.92 0.63 Thermal conductivity (W / m·K) 0.018 0.020 0.019 0.022 0.023 0.022 0.025 0.035 Average sound insulation (dB) 49.8 48.8 49.3 48.6 49.1 47.6 48.3 45.1 Electromagnetic shielding effectiveness (dB) 55.4 54.6 54.9 54.6 55.0 18.5 45.1 2.1 Limiting oxygen index (%) 32.1 31.8 31.5 31.7 32.0 30.4 29.8 26.0 As shown in Table 1, the multilayer polyurethane flame-retardant and sound-insulating composite panels prepared in Examples 1-5 are significantly superior to those in Comparative Examples 1-3. This is achieved by combining nickel ferrite with graphene oxide to construct an effective electromagnetic wave absorption and reflection network, greatly improving electromagnetic shielding performance. Furthermore, the surface coating of the composite aerogel powder with polydopamine enhances the mechanical strength of the aerogel and its bonding force with the polyurethane matrix, collectively achieving a comprehensive improvement in flame retardancy, sound insulation, heat insulation, electromagnetic shielding, and dimensional stability.

[0045] In Comparative Example 3, the thermal conductivity, average sound insulation, electromagnetic shielding effectiveness, and oxygen index all decreased. This may be because the addition of reinforcing aerogel powder prevented the construction of an effective conductive-magnetic dual network within the polyurethane matrix, allowing electromagnetic waves to penetrate almost unimpeded and resulting in a complete deterioration of electromagnetic shielding effectiveness. At the same time, the nanoporous structure of the aerogel also lost its ability to block heat flow and multiple scattering of sound waves, leading to an increase in thermal conductivity, a decrease in average sound insulation, and a reduction in flame retardant performance.

[0046] The significant decrease in dimensional stability observed in Comparative Example 2 may be due to the lack of polydopamine coating on the composite aerogel powder. The aerogel and polyurethane matrix rely solely on weak physical adsorption, lacking robust chemical bonds and interfacial forces. During foaming and subsequent thermal environments, this weak interface cannot effectively transfer and disperse stress, making the foam more prone to shrinkage and deformation under thermal conditions, resulting in a significant decrease in dimensional stability.

[0047] The decrease in electromagnetic shielding effectiveness and oxygen index in Comparative Example 1 may be due to the absence of nickel ferrite powder. Nickel ferrite itself has excellent electromagnetic wave absorption capabilities, and can be used in conjunction with graphene oxide to construct a highly efficient electromagnetic shielding system. Its absence directly leads to a significant reduction in shielding performance. In terms of flame retardancy, nickel ferrite can catalyze the cross-linking of polymer matrix into carbon during combustion and enhance the density and thermal stability of the carbon layer, thus playing a synergistic flame retardant role.

[0048] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and variations can be made to these embodiments without departing from the principles and spirit of the invention.

Claims

1. A method for preparing a multilayer structure polyurethane fire-retardant soundproof composite board material, characterized in that, Comprise the following steps: Step one: with nickel nitrate as nickel source, iron nitrate as iron source, hexamethylenetetramine as precipitant, through solvothermal method and high temperature calcination method, get nickel ferrite powder, composite with graphene oxide through hydrothermal self-assembly, get composite aerogel powder, then through in-situ polymerization, coated with polydopamine on the surface, get enhanced aerogel powder; Step two: polyether polyol, polymethylene polyphenyl polyisocyanate, enhanced aerogel powder, ammonium polyphosphate, magnesium hydroxide and foaming aid through one-step foaming method, get functional polyurethane rigid foam; With functional polyurethane rigid foam as core layer, placed between two layers of aluminum magnesium manganese alloy color steel plate and porous sound insulation plate, through hot pressing composite, get multilayer structure polyurethane flame-retardant sound insulation composite board.

2. The method for preparing the multi-layer polyurethane flame-retardant and sound-insulating composite board according to claim 1, characterized in that, The specific preparation process of the nickel ferrite powder is as follows: Nickel nitrate, iron nitrate and deionized water are added to the reaction kettle, stirred for 20-30 min, then hexamethylenetetramine is added, stirred for 2-3 h, incubated at 100-110℃ for 6-8 h, cooled to room temperature, the product is washed with deionized water for 3-5 times, vacuum dried, get the precursor, transfer to the muffle furnace, with the heating rate of 5℃ / min to 400-500℃, calcine for 2-3 h, cool to room temperature with the furnace, grind, pass through 300 mesh sieve, get nickel ferrite powder; The amount ratio of the nickel nitrate, iron nitrate, deionized water and hexamethylenetetramine is 1.8-2.5g:4.8-5.6g:90-120mL:10.2-12.4g.

3. The method for preparing the multi-layer polyurethane flame-retardant and sound-insulating composite board according to claim 1, characterized in that, The specific preparation process of the composite aerogel powder is as follows: Mix the nickel ferrite powder and 0.3wt% graphene oxide water suspension according to the amount ratio of 1.5-2g:3-4L and ultrasonic for 20-30 min, adjust the pH value to 11 with ammonia water, stir for 2-3 h, transfer to the reaction kettle, hydrothermal reaction at 120-130℃ for 12-14 h, cool to room temperature, dialysis in 8.1wt% ethanol aqueous solution for 36-40 h, freeze-drying at minus 50℃ to minus 20℃ for 48-50 h, grind, pass through 300 mesh sieve, get composite aerogel powder.

4. The method for preparing the multi-layer polyurethane flame-retardant and sound-insulating composite board according to claim 1, characterized in that, The specific preparation process of the enhanced aerogel powder is as follows: Add the composite aerogel powder into 10wt% ethanol aqueous solution, ultrasonic for 30-40 min, adjust the pH value to 8.5 with Tris-HCl buffer, then add dopamine, stir for 24-30 h, centrifugal filtration, the product is repeatedly washed with deionized water for 3-5 times, vacuum dried to constant weight, get enhanced aerogel powder.

5. The method for preparing the multi-layer polyurethane flame-retardant and sound-insulating composite board according to claim 4, characterized in that, The amount ratio of the composite aerogel powder, 10wt% ethanol aqueous solution and dopamine is 5-8g:10-12L:5-8g.

6. The method for preparing the multi-layer polyurethane flame-retardant and sound-insulating composite board according to claim 1, characterized in that, The specific preparation process of the functional polyurethane rigid foam is as follows: Polyether polyol, triethanolamine, dibutyl tin dilaurate, silicone oil, ammonium polyphosphate, metal hydroxide flame retardant and enhanced aerogel powder are added into a beaker and stirred uniformly, then polymeric methylene polyphenyl polyisocyanate is added, and high-speed stirring is carried out for 10-15 s until whitening and swelling, then the mixture is quickly poured into a core material mold, natural foaming is carried out, cooling to room temperature is carried out, the mold is removed, and curing is carried out in an oven at 80-90 DEG C for 10-12 h to obtain functional polyurethane rigid foam.

7. The method for preparing the multi-layer polyurethane flame-retardant and sound-insulating composite board according to claim 6, characterized in that, The mass ratio of the polyether polyol, triethanolamine, dibutyl tin dilaurate, silicone oil, ammonium polyphosphate, metal hydroxide flame retardant, enhanced aerogel powder and polymeric methylene polyphenyl polyisocyanate is 200-250:3-3.8:0.5-1:2-2.5:30-40:10-15:10-12:200-260. The metal hydroxide flame retardant is any one of aluminum hydroxide or magnesium hydroxide.

8. The method for preparing the multi-layer polyurethane flame-retardant and sound-insulating composite board according to claim 1, characterized in that, The specific preparation process of the multilayer structure polyurethane flame-retardant sound-insulating composite board is as follows: The bottom color steel plate, the porous sound-insulating plate and the functional polyurethane rigid foam are sequentially laid, the top color steel plate is covered after coating adhesive, and the multilayer plate is obtained, hot-pressing curing is carried out at 60-80 DEG C and 0.5-0.8 MPa for 2-3 h, cooling and demolding are carried out, and the multilayer structure polyurethane flame-retardant sound-insulating composite board is obtained.

9. The method for preparing the multi-layer polyurethane flame-retardant and sound-insulating composite board according to claim 8, characterized in that, The porous sound-insulating plate is any one of rock wool board and glass wool board. 10.A multilayer structure polyurethane flame-retardant sound-insulating composite board prepared according to the preparation method of the multilayer structure polyurethane flame-retardant sound-insulating composite board according to any one of claims 1-9.