Fabricated prefabricated composite thermal-insulation environment-friendly wallboard and preparation method thereof

Abstract

The invention relates to an assembly type prefabricated composite heat preservation environment-friendly wallboard and a preparation method thereof, and belongs to the technical field of heat preservation materials. According to the preparation method, a cross-linked polyimide solution, a foaming agent, silicon dioxide nanofibers and a silane coupling agent are used as raw materials, and the fabricated prefabricated composite heat-preservation environment-friendly wallboard is prepared. The modified silicon dioxide nanofiber and a foaming agent are added into a cross-linked polyimide solution, the foaming agent releases gas under the high-temperature condition and expands to prepare polyimide foam, and then the polyimide foam is combined with the silicon dioxide nanofiber to obtain the heat preservation filler. Finally, a hollow wallboard is filled with the obtained composite material, and the fabricated prefabricated composite heat-preservation environment-friendly wallboard is obtained.The heat-preservation filler obtained through the preparation method has a large number of organic / inorganic interfaces, so that heat-transfer phonons are scattered, and the good heat insulation capacity is achieved.

Description

Technical Field

[0001] The present invention belongs to the technical field of thermal insulation materials, and specifically relates to an assembled prefabricated composite thermal insulation and environmental protection wall panel and a preparation method thereof. Background Art

[0002] Thermal insulation wall panels are usually installed on the outer surface of building walls and filled with thermal insulation materials with good heat insulation performance inside, which can effectively block the heat transfer between indoors and outdoors. In winter, the thermal insulation wall panels can effectively prevent the indoor heat from dissipating to the outside and reduce the heating energy consumption. In summer, they can isolate the outside high temperature from entering the room and reduce the air-conditioning cooling load, thus achieving a warm winter and cool summer living environment. With the development of technology, people pay more and more attention to the control of the indoor environment of buildings and the thermal protection and thermal comfort of human life and health. The market also puts forward higher requirements for thermal insulation materials. Currently, commercial polymer thermal insulation materials are difficult to meet the higher requirements of thermal insulation needs. Therefore, there is an urgent need for a thermal insulation wall panel with better thermal insulation performance in the prior art.

[0003] Polyimide is a high-performance polymer material, known as the top material of the polymer material pyramid, with excellent heat resistance and mechanical properties, and good dimensional stability. However, although polyimide has good heat insulation ability, it is not excellent enough. To apply polyimide to the field of thermal insulation wall panels, it is necessary to further reduce the thermal conductivity of polyimide. Based on this, the present invention provides an assembled prefabricated composite thermal insulation and environmental protection wall panel and a preparation method thereof, and prepares a thermal insulation wall panel with polyimide as the thermal insulation filler. Summary of the Invention

[0004] The purpose of the present invention is to provide an assembled prefabricated composite thermal insulation and environmental protection wall panel and a preparation method thereof to solve the problems mentioned in the above background art.

[0005] The purpose of the present invention can be achieved by the following technical solutions: An assembled prefabricated composite thermal insulation and environmental protection wall panel, comprising the following raw materials in parts by mass: 150 - 180 parts of crosslinked polyimide solution, 4 - 6 parts of foaming agent, 12 - 15 parts of silica nanofibers, 2.4 - 3 parts of silane coupling agent; A preparation method of an assembled prefabricated composite thermal insulation and environmental protection wall panel, comprising the following steps: First step, weigh each raw material according to 150 - 180 parts of crosslinked polyimide solution, 4 - 6 parts of foaming agent, 12 - 15 parts of silica nanofibers, 2.4 - 3 parts of silane coupling agent in parts by mass; Second step, dissolve the silane coupling agent and silica nanofibers in an ethanol solution, heat and stir for reaction, then filter, and wash the silica nanofibers with absolute ethanol and deionized water to obtain silane coupling agent - modified silica nanofibers; Step 3: Add the silica nanowires modified by silane coupling agent, blowing agent, and surfactant into the cross-linked polyimide solution. After stirring evenly, thermally cure the polyimide solution to form the thermal insulation filler. Step 4: Fill the thermal insulation filler into the hollow wallboard to obtain an assembled precast composite thermal insulation and environmental protection wallboard.

[0006] Further, the blowing agent is one of azodiisobutyronitrile and azodicarbonamide.

[0007] Further, the silane coupling agent is silane coupling agent kh-550.

[0008] Further, the ethanol solution used in Step 2 is an ethanol aqueous solution with a volume fraction of 90%, and the mass ratio of silica nanowires, silane coupling agent, and ethanol solution is 12 - 15: 2.4 - 3: 35 - 50.

[0009] Further, the temperature condition for the heating and stirring reaction in Step 2 is 40 - 60°C, and the time condition for the heating and stirring reaction is 2 - 4 h.

[0010] Further, the curing condition of the polyimide in Step 3 is to heat to 130°C and keep warm for 90 - 120 min, and then heat to 280°C and keep warm for 120 - 240 min.

[0011] Further, the cross-linked polyimide solution is prepared by the following steps: Step 1: Mix p-nitroacetophenone, 4-(4-nitrophenoxy)benzaldehyde, ammonium acetate, and acetic acid in a three-necked flask. Install a condenser and a thermometer, start magnetic stirring, and react at 110°C for 16 h. Then, perform vacuum filtration. Wash the obtained solid with an ethanol solution with a volume fraction of 75% and dry it to obtain Intermediate 1. Step 2: Mix Intermediate 1, methanol, and N,N-dimethylformamide in a three-necked flask. Start magnetic stirring. After stirring for 30 - 45 min under an ice-water bath condition, add stannous chloride to the three-necked flask, and continue to react under the ice-water bath condition for 4 - 5 h. After the reaction ends, rotary evaporate to remove the solvent, and purify the remaining solid by silica gel column chromatography to obtain Intermediate 2. Step 3: Mix pyromellitic dianhydride and N-methylpyrrolidone in a three-necked flask. Install a condenser and a thermometer, start magnetic stirring, and add 4,4'-diaminodiphenyl ether to the three-necked flask under nitrogen protection. First, react at 110 - 120°C for 2 h, then raise the system temperature to 190°C, and react at 190°C for 6 - 8 h. Finally, add Intermediate 2 to the three-necked flask and react at 200°C for 3 h to obtain the cross-linked polyimide solution.

[0012] Further, the dosage ratio of p-nitroacetophenone, 4-(4-nitrophenoxy)benzaldehyde, ammonium acetate, and acetic acid used in Step 1 is 0.1 mol: 0.05 mol: 0.06 - 0.07 mol: 60 - 80 mL.

[0013] Further, the dosage ratio of Intermediate 1, methanol, N,N-dimethylformamide, and stannous chloride used in Step 2 is 0.02 mol: 32 - 40 mL: 20 - 28 mL: 18 - 20 g.

[0014] Further, the dosage ratio of pyromellitic dianhydride, N,N-dimethylformamide, 4,4'-diaminodiphenyl ether, and Intermediate 2 used in Step 3 is 0.1 mol: 60 - 80 mL: 0.08 mol: 0.01 mol.

[0015] Advantages of the present invention: The present invention uses a cross-linked polyimide solution, a foaming agent, silica nanofibers, and a silane coupling agent as raw materials to prepare an assembled prefabricated composite thermal insulation and environmental protection wall panel. In the present invention, the silica nanofibers are first modified with a silane coupling agent, and then the modified silica nanofibers and the foaming agent are added to the cross-linked polyimide solution. The polyimide foam is prepared by the gas expansion of the foaming agent under high-temperature conditions. The polyimide foam is then combined with the silica nanofibers to obtain a thermal insulation filler. Finally, the obtained composite material is filled into the hollow wall panel to obtain an assembled prefabricated composite thermal insulation and environmental protection wall panel. A large number of organic / inorganic interfaces exist in the thermal insulation filler obtained by the preparation method of the present invention, which can scatter the phonons for heat transfer, thus having good heat insulation ability.

[0016] The present invention uses p-nitroacetophenone, 4-(4-nitrophenoxy)benzaldehyde, and ammonium acetate as raw materials to obtain Intermediate 1 through the Chichibabin pyridine synthesis reaction. Then, using Intermediate 1 as the raw material, three nitro groups in Intermediate 1 are reduced to amino groups by methanol and stannous chloride to obtain Intermediate 2. Finally, using pyromellitic dianhydride and 4,4'-diaminodiphenyl ether as polymerization monomers and Intermediate 2 as a cross-linking agent, a polyimide solution is obtained through a "one-step" reaction. The cross-linked polyimide solution of the present invention selects Intermediate 2 as the cross-linking agent. Intermediate 2 has three amino groups in different planes. Such a spatial structure cannot form effective stacking after cross-linking. Therefore, stable local cavities can be introduced into the polyimide foam, increasing the porosity of the polyimide foam, thereby improving the heat insulation performance of the polyimide foam. In addition, one of the amino groups of Intermediate 2 is also connected to a movable ether bond, which can break the conjugated π-π bond structure in the polyimide chain after polymerization, hindering the transmission of phonons along the polyimide molecular chain and further reducing the thermal conductivity of the polyimide foam.

[0017] An assembled prefabricated composite heat-insulating and environment-friendly wallboard of the present invention has good heat-insulating performance, good heat resistance, excellent mechanical properties, stable dimensions and a low coefficient of thermal expansion, and can be widely applied in the field of heat-insulating materials. Specific embodiments

[0018] The technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts shall fall within the protection scope of the present invention. Embodiment 1

[0019] A crosslinked polyimide solution is prepared by the following steps: Step 1: Mix 0.1 mol of p-nitroacetophenone, 0.05 mol of 4-(4-nitrophenoxy)benzaldehyde, 0.06 mol of ammonium acetate and 60 mL of acetic acid in a three-necked flask, install a condenser and a thermometer, start magnetic stirring, and react at a temperature of 110 °C for 16 h. Then, perform vacuum filtration, and wash and dry the obtained solid with an ethanol solution with a volume fraction of 75% to obtain Intermediate 1; Step 2: Mix 0.02 mol of Intermediate 1, 32 mL of methanol and 20 mL of N,N-dimethylformamide in a three-necked flask, start magnetic stirring, stir for 30 min under an ice-water bath condition, then add 18 g of stannous chloride to the three-necked flask, and continue to react under the ice-water bath condition for 4 h. After the reaction is completed, rotary evaporate to remove the solvent, and purify the remaining solid by silica gel column chromatography to obtain Intermediate 2; Step 3: Mix 0.1 mol of pyromellitic dianhydride and 60 mL of N-methylpyrrolidone in a three-necked flask, install a condenser and a thermometer, start magnetic stirring, add 0.08 mol of 4,4'-diaminodiphenyl ether to the three-necked flask under nitrogen protection, first react at a temperature of 110 °C for 2 h, then raise the system temperature to 190 °C, and react at a temperature of 190 °C for 6 h. Finally, add 0.01 mol of Intermediate 2 to the three-necked flask, and react at a temperature of 200 °C for 3 h to obtain the crosslinked polyimide solution. Embodiment 2

[0020] A crosslinked polyimide solution is prepared by the following steps: Step 1: Mix 0.1 mol of p-nitroacetophenone, 0.05 mol of 4-(4-nitrophenoxy)benzaldehyde, 0.065 mol of ammonium acetate, and 70 mL of acetic acid in a three-necked flask. Install a condenser and a thermometer, start magnetic stirring, and react at 110 °C for 16 h. Then, perform vacuum filtration. The obtained solid is washed with 75% (v / v) ethanol solution and dried to obtain Intermediate 1. Step 2: Mix 0.02 mol of Intermediate 1, 36 mL of methanol, and 24 mL of N,N-dimethylformamide in a three-necked flask. Start magnetic stirring. After stirring for 38 min under an ice-water bath, add 19 g of stannous chloride to the three-necked flask, and continue to react under an ice-water bath for 4.5 h. After the reaction is completed, rotary evaporate to remove the solvent. The remaining solid is purified by silica gel column chromatography to obtain Intermediate 2. Step 3: Mix 0.1 mol of pyromellitic dianhydride and 70 mL of N-methylpyrrolidone in a three-necked flask. Install a condenser and a thermometer, start magnetic stirring, and add 0.08 mol of 4,4'-diaminodiphenyl ether to the three-necked flask under nitrogen protection. First, react at 115 °C for 2 h, then raise the temperature of the system to 190 °C and react at 190 °C for 7 h. Finally, add 0.01 mol of Intermediate 2 to the three-necked flask and react at 200 °C for 3 h to obtain the crosslinked polyimide solution. Example 3

[0021] A crosslinked polyimide solution is prepared by the following steps: Step 1: Mix 0.1 mol of p-nitroacetophenone, 0.05 mol of 4-(4-nitrophenoxy)benzaldehyde, 0.07 mol of ammonium acetate, and 80 mL of acetic acid in a three-necked flask. Install a condenser and a thermometer, start magnetic stirring, and react at 110 °C for 16 h. Then, perform vacuum filtration. The obtained solid is washed with 75% (v / v) ethanol solution and dried to obtain Intermediate 1. Step 2: Mix 0.02 mol of Intermediate 1, 40 mL of methanol, and 28 mL of N,N-dimethylformamide in a three-necked flask. Start magnetic stirring. After stirring for 45 min under an ice-water bath, add 20 g of stannous chloride to the three-necked flask, and continue to react under an ice-water bath for 5 h. After the reaction is completed, rotary evaporate to remove the solvent. The remaining solid is purified by silica gel column chromatography to obtain Intermediate 2. Step 3: Mix 0.1 mol of pyromellitic dianhydride and 80 mL of N-methylpyrrolidone in a three-necked flask. Install a condenser and a thermometer, start magnetic stirring, and add 0.08 mol of 4,4'-diaminodiphenyl ether to the three-necked flask under nitrogen protection. React at 120 °C for 2 h first, then raise the system temperature to 190 °C and react at 190 °C for 8 h. Finally, add 0.01 mol of intermediate 2 to the three-necked flask and react at 200 °C for 3 h to obtain the crosslinked polyimide solution. Example 4

[0022] An assembled precast composite thermal insulation and environmentally friendly wallboard contains the following raw materials in parts by mass: 150 parts of the crosslinked polyimide solution obtained in Example 1, 4 parts of azobisisobutyronitrile, 12 parts of silica nanofibers, and 2.4 parts of silane coupling agent kh-550; A preparation method of an assembled precast composite thermal insulation and environmentally friendly wallboard includes the following steps: First step: Weigh each raw material according to 150 parts by mass of the crosslinked polyimide solution obtained in Example 1, 4 parts of azobisisobutyronitrile, 12 parts of silica nanofibers, and 2.4 parts of silane coupling agent kh-550; Second step: Dissolve silane coupling agent kh-550 and silica nanofibers in an ethanol aqueous solution with a volume fraction of 90%, stir and react at 40 °C for 2 h, then filter, and wash the silica nanofibers with absolute ethanol and deionized water to obtain silane coupling agent-modified silica nanofibers. The mass ratio of the silica nanofibers, silane coupling agent kh-550, and ethanol aqueous solution with a volume fraction of 90% used in this step is 12:2.4:35; Third step: Add the silane coupling agent-modified silica nanofibers, foaming agent, and surfactant to the crosslinked polyimide solution obtained in Example 1, stir evenly, then heat the polyimide solution to 130 °C and keep it warm for 90 min, and then heat it to 280 °C and keep it warm for 120 min to obtain the thermal insulation filler; Fourth step: Fill the thermal insulation filler into the hollow wallboard to obtain an assembled precast composite thermal insulation and environmentally friendly wallboard. Example 5

[0023] An assembled precast composite thermal insulation and environmentally friendly wallboard contains the following raw materials in parts by mass: 150 parts of the crosslinked polyimide solution obtained in Example 2, 6 parts of azobisisobutyronitrile, 12 parts of silica nanofibers, and 2.4 parts of silane coupling agent kh-550; A preparation method of an assembled precast composite thermal insulation and environmentally friendly wallboard includes the following steps: Step 1: Weigh each raw material according to 150 parts by mass of the crosslinked polyimide solution obtained in Example 2, 6 parts of azobisisobutyronitrile, 12 parts of silica nanofibers, and 2.4 parts of silane coupling agent KH-550; Step 2: Dissolve the silane coupling agent KH-550 and silica nanofibers in an ethanol aqueous solution with a volume fraction of 90%, stir and react at a temperature of 50 °C for 3 h, then filter, and wash the silica nanofibers with absolute ethanol and deionized water to obtain silane coupling agent-modified silica nanofibers. The mass ratio of the silica nanofibers, silane coupling agent KH-550, and ethanol aqueous solution with a volume fraction of 90% used in this step is 12:2.4:42; Step 3: Add the silane coupling agent-modified silica nanofibers, foaming agent, and surfactant into the crosslinked polyimide solution obtained in Example 2, stir evenly, first heat the polyimide solution to 130 °C and keep it warm for 105 min, and then heat it to 280 °C and keep it warm for 180 min to obtain heat-insulating filler; Step 4: Fill the heat-insulating filler into the hollow wallboard to obtain an assembled precast composite heat-insulating and environmentally friendly wallboard. Example 6

[0024] An assembled precast composite heat-insulating and environmentally friendly wallboard contains the following raw materials in parts by mass: 180 parts of the crosslinked polyimide solution obtained in Example 3, 4 parts of azodicarbonamide, 15 parts of silica nanofibers, and 3 parts of silane coupling agent KH-550; A preparation method of an assembled precast composite heat-insulating and environmentally friendly wallboard includes the following steps: Step 1: Weigh each raw material according to 180 parts by mass of the crosslinked polyimide solution obtained in Example 3, 4 parts of azodicarbonamide, 15 parts of silica nanofibers, and 3 parts of silane coupling agent KH-550; Step 2: Dissolve the silane coupling agent KH-550 and silica nanofibers in an ethanol aqueous solution with a volume fraction of 90%, stir and react at a temperature of 60 °C for 4 h, then filter, and wash the silica nanofibers with absolute ethanol and deionized water to obtain silane coupling agent-modified silica nanofibers. The mass ratio of the silica nanofibers, silane coupling agent KH-550, and ethanol aqueous solution with a volume fraction of 90% used in this step is 15:3:50; Step 3: Add the silane coupling agent-modified silica nanofibers, foaming agent, and surfactant into the crosslinked polyimide solution obtained in Example 3, stir evenly, first heat the polyimide solution to 130 °C and keep it warm for 120 min, and then heat it to 280 °C and keep it warm for 240 min to obtain heat-insulating filler; Step 4: Fill the heat-insulating filler into the hollow wallboard to obtain an assembled precast composite heat-insulating and environmentally friendly wallboard.

[0025] Comparative Example 1 An assembled precast composite heat-insulating and environmentally friendly wallboard contains the following raw materials in parts by mass: 180 parts of the crosslinked polyimide solution obtained in Example 3, 4 parts of azodicarbonamide, and 15 parts of silica nanofibers. A preparation method of an assembled precast composite heat-insulating and environmentally friendly wallboard includes the following steps: Step 1: Weigh each raw material according to 180 parts by mass of the crosslinked polyimide solution obtained in Example 3, 4 parts of azodicarbonamide, and 15 parts of silica nanofibers. Step 2: Add the silica nanofibers, foaming agent, and surfactant together to the crosslinked polyimide solution obtained in Example 3, stir evenly, first heat the polyimide solution to 130°C and keep it warm for 120 min, and then heat it to 280°C and keep it warm for 240 min to obtain the heat-insulating filler. Step 3: Fill the heat-insulating filler into the hollow wallboard to obtain an assembled precast composite heat-insulating and environmentally friendly wallboard.

[0026] Comparative Example 2 This comparative example is the polyimide thermoplastic liquid sold by Shandong Linyuan Chemical Co., Ltd.

[0027] An assembled precast composite heat-insulating and environmentally friendly wallboard contains the following raw materials in parts by mass: 180 parts of the polyimide thermoplastic liquid sold by Shandong Linyuan Chemical Co., Ltd., 4 parts of azodicarbonamide, 15 parts of silica nanofibers, and 3 parts of silane coupling agent KH-550. A preparation method of an assembled precast composite heat-insulating and environmentally friendly wallboard includes the following steps: Step 1: Weigh each raw material according to 180 parts by mass of the polyimide thermoplastic liquid sold by Shandong Linyuan Chemical Co., Ltd., 4 parts of azodicarbonamide, 15 parts of silica nanofibers, and 3 parts of silane coupling agent KH-550. Step 2: Dissolve the silane coupling agent KH-550 and silica nanofibers in an ethanol aqueous solution with a volume fraction of 90%, stir and react at 60°C for 4 h, then filter, and wash the silica nanofibers with absolute ethanol and deionized water to obtain silane coupling agent-modified silica nanofibers. The mass ratio of the silica nanofibers, silane coupling agent KH-550, and ethanol aqueous solution with a volume fraction of 90% used in this step is 15:3:50. Step 3: Add the silica nanometer fiber modified by silane coupling agent, blowing agent and surfactant into the polyimide thermoplastic liquid sold by Shandong Linyuan Chemical Co., Ltd. After stirring evenly, heat the polyimide solution to 130 °C first and keep it warm for 120 min, and then heat it to 280 °C and keep it warm for 240 min to obtain the heat-insulating filler; Step 4: Fill the heat-insulating filler into the hollow wallboard to obtain an assembled prefabricated composite heat-insulating and environment-friendly wallboard.

[0028] Comparative Example 3 This comparative example is a heat-insulating wallboard sold by Langfang Chuangbo Heat-insulating Materials Co., Ltd.

[0029] Respectively refer to JGJ144-2004 "Technical Specification for External Thermal Insulation Engineering of Buildings" to test the thermal conductivity of the assembled prefabricated composite heat-insulating and environment-friendly wallboards obtained in Examples 4-6 and Comparative Examples 1-2 and the heat-insulating wallboard in Comparative Example 3. The test results are shown in Table 1: Table 1 Project <![CDATA[Thermal conductivity (0.04 W·m -1 ·K -1 ).]]> Example 4 0.022 Example 5 0.026 Example 6 0.025 Comparative Example 1 0.038 Comparative Example 2 0.054 Comparative Example 3 0.043 As can be seen from Table 1, the thermal conductivities of the assembled prefabricated composite heat-insulating and environment-friendly wallboards prepared by the present invention in Examples 4-6 are all less than those of the commercially available heat-insulating wallboards, indicating that the assembled prefabricated composite heat-insulating and environment-friendly wallboard of the present invention has better heat-insulating ability. Comparative Examples 1-2 respectively conduct control experiments on the crosslinked polyimide solution and silane coupling agent used in the present invention. Combining Table 1, it can be seen that the thermal conductivity of the wallboard prepared in Comparative Example 2 without using the crosslinked polyimide solution of the present invention to prepare polyimide foam increases significantly. In Comparative Example 1, not using the silane coupling agent to modify the silica nanometer fiber will also cause the thermal conductivity to increase. In summary, the assembled prefabricated composite heat-insulating and environment-friendly wallboard prepared by the present invention has better heat-insulating ability and can be widely used in the field of heat-insulating materials.

[0030] The above has introduced in detail an assembled prefabricated composite heat-insulating and environment-friendly wallboard and its preparation method provided by the present invention. Specific examples are used in this article to elaborate on the principle and implementation manner of the present invention. The description of the above embodiments is only used to help understand the method and its core idea of the present invention, including the best mode, and also enables any person skilled in the art to practice the present invention, including manufacturing and using any device or system, and implementing any combined method. It should be noted that for those of ordinary skill in the art in this technical field, without departing from the principle of the present invention, several improvements and modifications can be made to the present invention. In particular, as long as there is no structural conflict, the various features in the embodiments disclosed by the present invention can be combined with each other in any way, and the exhaustive description of these combinations is not given in this specification only for the consideration of saving space and resources. Therefore, the present invention is not limited to the specific embodiments disclosed in the text, but includes all technical solutions falling within the scope of the claims.

Claims

1. An assembled prefabricated composite thermal insulation environmentally friendly wall panel, characterized in that: The invention comprises the following raw materials in parts by weight: 150-180 parts of a cross-linked polyimide solution, 4-6 parts of a foaming agent, 12-15 parts of silicon dioxide nanofibers, and 2.4-3 parts of a silane coupling agent; Wherein, the cross-linked polyimide solution is prepared by the following steps: Step 1, p-nitroacetophenone, 4-(4-nitrophenoxy)benzaldehyde, ammonium acetate and acetic acid are mixed in a container, stirred evenly, and reacted at 110° C. for 16 h to obtain intermediate 1; Step 2, intermediate 1, methanol and N,N-dimethylformamide are mixed in a container, stirred in an ice-water bath for 30-45 minutes, then stannous chloride is added to the container, and the reaction is continued in an ice-water bath for 4-5 hours to obtain intermediate 2; Step 3: Mix pyromellitic anhydride and N-methylpyrrolidone in a container, stir evenly, add 4,4'-diaminodiphenyl ether to the container under nitrogen protection, first react at 110-120°C for 2h, then raise the system temperature to 190°C, and react at 190°C for 6-8h, finally add intermediate 2 to the container, and react at 200°C for 3h to obtain the cross-linked polyimide solution.

2. The prefabricated composite thermal insulation environmentally friendly wallboard according to claim 1, characterized in that: The amount ratio of p-nitroacetophenone, 4-(4-nitrophenoxy)benzaldehyde, ammonium acetate and acetic acid used in step 1 is 0.1 mol: 0.05 mol: 0.06-0.07 mol: 60-80 mL.

3. The prefabricated composite thermal insulation and environmentally friendly wallboard according to claim 1, characterized in that: The amount ratio of intermediate 1, methanol, N,N-dimethylformamide and stannous chloride used in step 2 is 0.02 mol: 32-40 mL: 20-28 mL: 18-20 g.

4. The prefabricated composite thermal insulation and environmentally friendly wallboard according to claim 1, characterized in that: The amount ratio of pyromellitic anhydride, N,N-dimethylformamide, 4,4'-diaminodiphenyl ether and intermediate 2 used in step 3 is 0.1 mol: 60-80 mL: 0.08 mol: 0.01 mol.

5. A method for preparing an assembled prefabricated composite thermal insulation and environmentally friendly wallboard according to any one of claims 1 to 4, characterized in that: The method comprises the following preparation steps: The first step is to weigh the raw materials according to the mass proportions: 150-180 parts of cross-linked polyimide solution, 4-6 parts of foaming agent, 12-15 parts of silica nanofibers, and 2.4-3 parts of silane coupling agent; The second step is to dissolve the silane coupling agent and the silica nanofibers in an ethanol solution, heat and stir to react, then filter, and wash the silica nanofibers with anhydrous ethanol and deionized water to obtain silane coupling agent modified silica nanofibers; The third step is to add the silane coupling agent modified silica nanofiber, foaming agent and surfactant into the cross-linked polyimide solution, stir evenly and then thermally cure the polyimide solution to obtain a thermal insulation filler; The fourth step is to fill the hollow wall panel with thermal insulation filler to obtain an assembled prefabricated composite thermal insulation environmentally friendly wall panel.

6. The method for preparing an assembled prefabricated composite thermal insulation environmentally friendly wallboard according to claim 5, characterized in that: The foaming agent is one of azobisisobutyronitrile and azodicarbonamide.

7. The method for preparing an assembled prefabricated composite thermal insulation and environmentally friendly wallboard according to claim 5, characterized in that: The silane coupling agent is silane coupling agent kh-550.

8. The method for preparing an assembled prefabricated composite thermal insulation and environmentally friendly wallboard according to claim 5, characterized in that: The ethanol solution used in the second step is an ethanol aqueous solution with a volume fraction of 90%, and the mass ratio of the silica nanofibers, the silane coupling agent, and the ethanol solution is 12-15:2.4-3:35-50.

9. The method for preparing an assembled prefabricated composite thermal insulation environmentally friendly wallboard according to claim 5, characterized in that: The temperature condition of the heating and stirring reaction in the second step is 40-60°C, and the time condition of the heating and stirring reaction is 2-4h.

10. The method for preparing an assembled prefabricated composite thermal insulation environmentally friendly wallboard according to claim 5, characterized in that: In the third step, the polyimide is cured under the conditions of heating to 130° C. and keeping the temperature for 90-120 min, and then heating to 280° C. and keeping the temperature for 120-240 min.