Preparation method and application of polyurethane / polyimide composite thermal protection material

Abstract

The invention relates to the field of heat-insulating flame-retardant materials, in particular to a preparation method and application of a polyurethane / polyimide composite thermal protection material, raw materials including methacrylic acid, methacrylonitrile and hydroxyethyl methylacrylate are added into a solvent to be dissolved into a multi-component solution; transferring the multi-component solution to a reaction container, adding a free radical polymerization catalyst, reacting to obtain a polymer solution, and neutralizing an acidic group with organic alkali; adding a catalyst, a chain extender, a foam stabilizer, an anti-aging agent and a foaming agent into the polymer solution to obtain a solution 1; adding isocyanate into a solvent to obtain a solution 2; the solution 1 and the solution 2 are filled into a filling machine or a spraying system for forming, microwave heating curing and further heat treatment curing are performed to obtain the polyurethane / polyimide composite thermal protection material, the polyurethane / polyimide composite thermal protection material has the characteristics of high-temperature heat insulation and flame retardance, flexibility and rapid forming, the stretch rate is 175-235%, the heat conductivity is 0.026 W / (m.K)-0.03 W / (m.K), the UL 94 V-0 level flame retardance level is reached, and the polyurethane / polyimide composite thermal protection material has the good thermal insulation and flame retardance. The method is suitable for the fields of new energy automobiles, energy storage systems, photovoltaic power generation and intelligent power grids.

Description

Technical Field

[0001] The present invention relates to the field of thermal insulation and flame retardant materials, and in particular to a preparation method and application of a polyurethane / polyimide composite thermal protection material. The material has excellent thermal insulation capacity and flame retardant properties and is suitable for new energy vehicles, energy storage systems, photovoltaic power generation and smart grid fields. Background Art

[0002] As a high-performance functional material, polyimide foam combines excellent thermal insulation with inherent flame retardancy. With a thermal decomposition temperature exceeding 400°C, it maintains structural stability in high-temperature environments. The foam's microporous structure effectively blocks both heat conduction and convection, providing durable and reliable thermal insulation. Regarding flame retardancy, polyimide achieves a UL 94 V-0 rating without the addition of flame retardants. Its high oxygen index and carbonization ability effectively isolate it from heat sources and oxygen. Furthermore, it offers low smoke density, safety, and environmental protection, making it particularly suitable for engineering environments requiring high thermal protection and flame retardancy.

[0003] However, polyimide foam still has some shortcomings. Its preparation process is complex and the molding temperature is high, resulting in high energy consumption and high equipment requirements. At the same time, it has poor flexibility and high brittleness. It is easily damaged under vibration or impact conditions, and its structural integrity is difficult to maintain. At the same time, polyurethane foam has the characteristics of rapid molding, mature technology, low cost, and suitability for batch application. It also has excellent elasticity and cushioning properties, and has advantages in structural adaptability and mechanical properties. However, it has poor high temperature resistance and limited aging resistance. Therefore, it is possible to organically combine the two to make up for the shortcomings of polyimide in energy efficiency and processing, give full play to the advantages of polyurethane in flexibility and molding, and achieve complementary optimization of performance and process. The excellent comprehensive performance will make polyurethane / polyimide composites have broad application prospects in multiple fields. Summary of the Invention

[0004] The present invention aims to provide a method for preparing and applying a polyurethane / polyimide composite thermal protection material. By improving the material formulation and manufacturing process, a superior thermal protection material is produced, overcoming significant challenges with existing materials, such as complex preparation processes and limited flexibility. This invented material is suitable for applications requiring high-temperature insulation, such as new energy vehicles, energy storage systems, photovoltaic power generation, and smart grids.

[0005] To solve the above problems, the present invention provides a method for preparing a polyurethane / polyimide composite thermal protection material, comprising the following steps: Step S1: Weigh the raw materials methacrylic acid, methacrylonitrile and hydroxyethyl methacrylate according to the required amount, add them into the solvent in sequence, and stir continuously until they are fully dissolved into a uniform multi-component solution; Step S2: transferring the prepared multi-component solution to a reaction vessel, adding a free radical polymerization catalyst, reacting at 40° C.-80° C. for 1 h-3 h, adjusting the stirring speed for thorough mixing, and reacting to obtain a polymer solution, followed by adding an organic base to neutralize some of the acidic groups; Step S3: Weighing a catalyst, a chain extender, a foaming agent, an anti-aging agent, and a foaming agent as needed and adding them to the polymer solution prepared in step S2, slowly heating and stirring until the mixture is uniform, to obtain a solution 1; Step S4: slowly adding the isocyanate to the solvent and stirring until it is completely dissolved to form a slightly yellow or uniform transparent solution, and then sealing and storing the prepared isocyanate solution in a dry container to obtain Solution 2; Step S5: Solution 1 and solution 2 are loaded into a sealed filling machine or spraying system according to the ratio, formed in a mold using a filling process or a spraying process, and then allowed to stand for microwave heating and further heat treatment curing to obtain the desired polyurethane / polyimide composite thermal protection material.

[0006] Furthermore, in step S1, the amount of methacrylic acid is 15-20 parts, the amount of methacrylonitrile is 10-25 parts, and the amount of hydroxyethyl methacrylate is 25-55 parts; The solvent is one of N-methylpyrrolidone, N,N-dimethylformamide, N,N-dimethylacetamide, 1,3-dimethyl-2-imidazolidinone, and dimethyl sulfoxide, with an amount of 100 parts; stirring is continued for 1h–3h, and the stirring speed is 100rpm–200rpm.

[0007] Furthermore, in step S1, the raw material is not limited to methacrylic acid, but also includes ethylacrylic acid, propylacrylic acid, methylbutenoic acid, ethylbutenoic acid, propylbutenoic acid, methylpentenoic acid, ethylpentenoic acid or propylpentenoic acid; And not limited to methacrylonitrile, also include ethacrylonitrile, propylacrylonitrile, methylbutenenitrile, ethylbutenenitrile, propylbutenenitrile, methylpentenenitrile, ethylpentenenitrile or propylpentenenitrile; It is not limited to hydroxyethyl methacrylate, but also includes hydroxyethyl ethyl acrylate, hydroxyethyl propyl acrylate, hydroxyethyl methyl crotonate, hydroxyethyl ethyl crotonate, hydroxyethyl propyl crotonate, hydroxyethyl methyl pentenoate, hydroxyethyl ethyl pentenoate or hydroxyethyl propyl pentenoate.

[0008] Furthermore, in step S2, the free radical polymerization catalyst is benzoyl peroxide or azobisisobutyronitrile, and the amount used is 0.5 parts to 2.5 parts; The organic base is triethylamine or N,N-diisopropylethylamine, with an amount of 7-10 parts; The stirring speed is 100 rpm-200 rpm, and the stirring is continued for 1 h–3 h.

[0009] Furthermore, in step S3, the catalyst is triethylenediamine or dibutyltin dilaurate, and the amount used is 0.5 parts to 2 parts; The chain extender is one or a combination of ethylenediamine and ethylene glycol, with an amount of 2 to 8 parts; The foaming agent is polyether modified silicone oil or fatty alcohol polyoxyethylene ether, and the dosage is 1-6 parts; The anti-aging agent is antioxidant BHT, antioxidant 168, ultraviolet absorber UV-326 or UV-327, and the dosage is 0.1 part to 1 part; The foaming agent is 1,1,1,3,3-pentafluoropropane, with an amount of 12-25 parts; The temperature rise rate is 1℃ / min-5℃ / min, the temperature is raised to 50℃-90℃, the stirring speed is 100rpm-200rpm, and the stirring is continued for 1h-3h.

[0010] Furthermore, in step S4, the isocyanate solution is composed of isocyanate and solvent, with a concentration of 25wt%-35wt% and an amount of 180 parts-230 parts of the solution; Wherein, the isocyanate includes toluene diisocyanate, diphenylmethane diisocyanate or polyphenyl polymethyl polyisocyanate; The solvent is the same as step S1; The stirring speed is 100 rpm-200 rpm, and the stirring is continued for 1 h–3 h.

[0011] Furthermore, in step S5, the injection machine is a high-pressure injection machine with a pressure of 10MPa-20MPa, an injection speed of 300mL / s-500mL / s, a mass ratio of solution 1 to solution 2 of 1.2:1-1:1.2, mixing time of 2s-5s, and a mold preheating temperature of 40°C-60°C.

[0012] Furthermore, in step S5, the spraying system is a two-component spraying system, with a pressure of 8MPa-12MPa, a moving speed of 0.5m / s-1m / s, a mass ratio of solution 1 to solution 2 of 1.5:1-1:1.2, mixing for 2s-5s, a spraying distance of 50cm-70cm, a spraying thickness of 8mm-12mm, and a mold preheating temperature of 40℃-60℃.

[0013] Furthermore, in step S5, the mixture is allowed to stand at room temperature for 2h-4h, then placed in a microwave oven, heated at a rate of 1°C / min-5°C / min, and cured at 80°C-100°C for 2h, and then further cured at 200°C-250°C for 2h-3h.

[0014] A polyurethane / polyimide composite thermal protection material has excellent thermal insulation and flame retardancy, with an elongation of 175%-235%, a thermal conductivity of 0.026W / (m·K)-0.03W / (m·K), and a UL 94 V-0 flame retardancy rating. It is suitable for new energy vehicles, energy storage systems, photovoltaic power generation, and smart grids.

[0015] The present invention adopts the above technical solution, and its beneficial effects are as follows: 1. Pioneering integration of high-performance material properties to achieve excellent thermal protection capabilities This composite material organically combines the high-temperature thermal insulation and flame retardant properties of polyimide with the flexibility and rapid prototyping of polyurethane, improving the toughness and rapid foaming ability of polyimide foam. It has both high energy efficiency and process adaptability, and can continue to play a protective role in multiple heat load environments, demonstrating wide applicability and engineering value in high-end thermal management applications.

[0016] 2. Lead innovation and upgrading in the field of functional materials and promote the development of advanced manufacturing The preparation method combines high efficiency and controllability, achieving precise regulation of material properties. It not only meets the stringent requirements of cutting-edge industrial fields, but also provides new ideas for intelligent and green manufacturing, helping to optimize industrial structure and upgrade technology.

[0017] 3. Wide range of environmental adaptability and application potential Polyurethane / polyimide composite thermal protection material has excellent thermal insulation and flame retardant properties, with an elongation of 175%-235% and a thermal conductivity of 0.026W / (m·K)-0.03W / (m·K). It achieves UL 94 V-0 flame retardancy and is suitable for use in new energy vehicles, energy storage systems, photovoltaic power generation, and smart grids, meeting the needs of modern industry for multifunctional thermal protection materials.

[0018] The basic technical principles of the present invention provide relevant technical personnel with the possibility of various improvements, replacements or adjustments to the present invention by utilizing existing professional knowledge and conventional technical means without deviating from the core principles. DETAILED DESCRIPTION

[0019] The following further describes the specific embodiments of the present invention with reference to examples. It should be noted that the description of these embodiments is intended to facilitate understanding of the present invention and does not constitute a limitation of the present invention. In addition, the technical features involved in the various embodiments of the present invention described below may be combined with each other as long as they do not conflict with each other.

[0020] The raw materials and equipment used in the specific embodiments of the present invention are all known products and are obtained by purchasing commercially available products.

[0021] Example 1, a method for preparing a polyurethane / polyimide composite thermal protection material, comprising the following steps: Step S1: 15 g of methacrylic acid, 10 g of methacrylonitrile, and 25 g of hydroxyethyl methacrylate are sequentially added to 100 g of N-methylpyrrolidone solvent at room temperature, and stirred at 200 rpm for 2 h to obtain a fully dissolved multicomponent solution; Step S2: The multi-component solution was transferred to a 500 mL reactor, and 1 g of benzoyl peroxide was added. The mixture was heated to 65° C. and stirred at 150 rpm for 2 h to obtain a uniform polymer solution. 8 g of triethylamine was then added and stirred at 150 rpm for 1 h to neutralize some of the acidic groups. Step S3: 0.8 g of triethylenediamine, 2.5 g of ethylenediamine, 2.5 g of polyether-modified silicone oil, 0.2 g of antioxidant BHT, and 18 g of 1,1,1,3,3-pentafluoropropane were weighed respectively, and added to the polymer solution in sequence. The temperature was adjusted to 70° C. at a temperature rise rate of 2° C. / min, and the mixture was rotated at 200 rpm for 1.5 h to obtain Solution 1. Step S4: prepare 200 g of a 30 wt% isocyanate solution with 60 g of diphenylmethane diisocyanate and 140 g of N-methylpyrrolidone, and continue the mixture at 150 rpm for 1 hour to obtain a solution 2, which is then sealed and stored dry at room temperature; Step S5, preheat the metal mold to 50°C, mix 180g of solution 1 and 180g of solution 2 for 3s, and then add them together into a high-pressure injection machine at a pressure of 12MPa and an injection speed of 300mL / s. Let them stand at room temperature for 2h. The preliminarily cured foam material is placed in a microwave oven, heated to 90°C at a rate of 2°C / min and continued to cure for 2h. Thereafter, the foam material is transferred to a drying oven, heated to 250°C at the same rate, and continued to cure for 2h to obtain the desired polyurethane / polyimide composite thermal protection material.

[0022] The polyurethane / polyimide composite thermal protection material prepared in Example 1 has an elongation of 235%, a thermal conductivity of 0.028 W / (m·K), and a UL 94 V-0 flame retardancy level, and has excellent heat insulation and flame retardancy effects.

[0023] Example 2, a method for preparing a polyurethane / polyimide composite thermal protection material, comprising the following steps: Step S1: at room temperature, 16 g of ethyl acrylic acid, 12 g of ethyl acrylonitrile, and 25 g of hydroxyethyl ethyl acrylate were sequentially added with 100 g of N,N-dimethylformamide solvent, and stirred at 180 rpm for 2.5 h to obtain a fully dissolved multicomponent solution; Step S2: The multi-component solution was transferred to a 500 mL reactor, and 1.2 g of azobisisobutyronitrile was added. The mixture was heated to 65° C. and stirred at 180 rpm for 2 h to obtain a uniform polymer solution. 8 g of triethylamine was then added, and the mixture was stirred at 180 rpm for 1 h. Step S3: 1.0 g of dibutyltin dilaurate, 2.5 g of ethylene glycol, 2 g of fatty alcohol polyoxyethylene ether, 0.3 g of ultraviolet absorber UV-326, and 18 g of 1,1,1,3,3-pentafluoropropane were weighed respectively, and added to the polymer solution in sequence. The temperature was adjusted to 70° C. at a temperature rise rate of 2° C. / min, and the mixture was rotated at 200 rpm for 2 h to obtain Solution 1. Step S4: prepare 200 g of a 32 wt% isocyanate solution with 64 g of toluene diisocyanate and 136 g of N,N-dimethylformamide, and continue the mixture at 180 rpm for 1 hour to obtain a solution 2, which is then sealed and stored dry at room temperature; In step S5, the PTFE mold is preheated to 55°C, the spraying distance is adjusted to 50 cm, 180 g of solution 1 and 180 g of solution 2 are mixed for 3 seconds, and then added to a two-component spray system. The mixture is sprayed into the PTFE plastic mold multiple times at a pressure of 10 MPa and a moving speed of 0.5 m / s, with each spray thickness controlled to 10 mm, until the entire mold is formed. The foam material is then allowed to stand at room temperature for 2 hours. The initially cured foam material is placed in a microwave oven and heated to 90°C at a rate of 2°C / min, where it is cured for another 2 hours. The foam material is then transferred to a drying oven, heated to 250°C at the same rate, and cured for another 2 hours to obtain the desired polyurethane / polyimide composite thermal protection material.

[0024] The polyurethane / polyimide composite thermal protection material prepared in Example 2 has an elongation of 205%, a thermal conductivity of 0.026 W / (m·K), and a UL 94 V-0 flame retardancy level, and has excellent thermal insulation and flame retardancy effects.

[0025] Example 3, a method for preparing a polyurethane / polyimide composite thermal protection material, comprising the following steps: Step S1: at room temperature, 16 g of propyl acrylic acid, 12 g of propyl acrylonitrile, and 26 g of propyl hydroxyethyl acrylate were sequentially added to 100 g of N-methylpyrrolidone solvent, and stirred at 180 rpm for 2 h to obtain a fully dissolved multi-component solution; Step S2: The multi-component solution was transferred to a 500 mL reactor, and 0.9 g of azobisisobutyronitrile was added. The mixture was heated to 70° C. and stirred at 180 rpm for 2 h to obtain a uniform polymer solution. 8 g of N,N-diisopropylethylamine was then added and stirred at 180 rpm for 1 h to neutralize some of the acidic groups. Step S3, 0.9 g of dibutyltin dilaurate, 1.5 g of ethylene glycol, 1.5 g of ethylenediamine, 2.8 g of fatty alcohol polyoxyethylene ether, 0.3 g of antioxidant 168, and 19 g of 1,1,1,3,3-pentafluoropropane were weighed respectively, and added to the polymer solution in sequence. The temperature was adjusted to 75° C. at a temperature rise rate of 2° C. / min, and the mixture was rotated at 180 rpm for 1.5 hours to obtain Solution 1; Step S4: prepare 200 g of a 30 wt% isocyanate solution with 60 g of diphenylmethane diisocyanate and 140 g of N-methylpyrrolidone, and continue the mixture at 180 rpm for 1.5 h to obtain Solution 2, which is then sealed and stored dry at room temperature; Step S5, preheat the metal mold to 55°C, mix 185g of solution 1 and 185g of solution 2 for 3s, and then add them together into a high-pressure injection machine at a pressure of 15MPa and an injection speed of 350mL / s. Let it stand at room temperature for 2h. The preliminarily cured foam material is placed in a microwave oven, heated to 95°C at a rate of 2°C / min and continued to cure for 2h. Thereafter, the foam material is transferred to a drying oven, heated to 230°C at the same rate, and continued to cure for 2.5h to obtain the required polyurethane / polyimide composite thermal protection material.

[0026] The polyurethane / polyimide composite thermal protection material prepared in Example 3 has an elongation of 225%, a thermal conductivity of 0.03 W / (m·K), and a UL 94 V-0 flame retardancy level, and has excellent thermal insulation and flame retardancy effects.

[0027] Example 4, a method for preparing a polyurethane / polyimide composite thermal protection material, comprising the following steps: Step S1: at room temperature, 18 g of ethyl acrylic acid, 15 g of methylpentenenitrile, and 30 g of hydroxyethyl methylpentenoate were sequentially added with 100 g of N,N-dimethylacetamide solvent, and stirred at 200 rpm for 2.5 h to obtain a fully dissolved multicomponent solution; Step S2: The multi-component solution was transferred to a 500 mL reactor, and 1.5 g of benzoyl peroxide was added. The mixture was heated to 70° C. for 2 h while stirring at 200 rpm to obtain a uniform polymer solution. 9 g of N,N-diisopropylethylamine was then added, and the mixture was stirred at 200 rpm for 1.5 h. Step S3: 1.2 g of triethylenediamine, 2.6 g of ethylenediamine, 2.2 g of polyether-modified silicone oil, 0.3 g of ultraviolet absorber UV-326, and 18.5 g of 1,1,1,3,3-pentafluoropropane were weighed respectively, and added to the polymer solution in sequence. The temperature was adjusted to 75° C. at a temperature rise rate of 2° C. / min, and the mixture was rotated at 200 rpm for 2 h to obtain Solution 1. Step S4: 200 g of a 30 wt% isocyanate solution was prepared with 60 g of diphenylmethane diisocyanate and 140 g of N,N-dimethylacetamide, and the mixture was stirred at 200 rpm for 1 hour to obtain a solution 2, which was then sealed and dried and stored at room temperature; In step S5, the PTFE mold is preheated to 58°C, the spraying distance is adjusted to 55 cm, 180 g of solution 1 and 185 g of solution 2 are mixed for 3 seconds, and then added to a two-component spray system. The mixture is sprayed into the PTFE plastic mold multiple times at a pressure of 12 MPa and a moving speed of 0.5 m / s, with each spray thickness controlled to 10 mm, until the entire mold is formed. The foam material is then allowed to stand at room temperature for 2 hours. The initially cured foam material is placed in a microwave oven and heated to 95°C at a rate of 2°C / min, where it is cured for another 2 hours. The foam material is then transferred to a drying oven, heated to 250°C at the same rate, and cured for another 2 hours to obtain the desired polyurethane / polyimide composite thermal protection material.

[0028] The polyurethane / polyimide composite thermal protection material prepared in Example 4 has an elongation of 175%, a thermal conductivity of 0.027 W / (m·K), and a UL 94 V-0 flame retardancy level, and has excellent thermal insulation and flame retardancy effects.

[0029] Example 5, a method for preparing a polyurethane / polyimide composite thermal protection material, comprising the following steps: Step S1: 15 g of methacrylic acid, 12 g of ethylcrotonitrile, and 28 g of hydroxyethyl propyl acrylate are sequentially added to 100 g of N,N-dimethylformamide solvent at room temperature, and stirred at 200 rpm for 2 h to obtain a fully dissolved multi-component solution; Step S2: The polyvalent solution was transferred to a 500 mL reactor, and 1 g of benzoyl peroxide was added. The mixture was heated to 60° C. for 2.5 hours with a stirring rate of 200 rpm to obtain a uniform polymer solution. 8.5 g of triethylamine was then added and stirred at 200 rpm for 1 hour to neutralize some of the acidic groups. In step S3, 1 g of triethylenediamine, 2.8 g of ethylenediamine, 3 g of polyether-modified silicone oil, 0.3 g of antioxidant BHT, and 20 g of 1,1,1,3,3-pentafluoropropane were weighed respectively, and the polymer solution was added in sequence. The temperature was adjusted to 70°C at a temperature rise rate of 2°C / min, and the rotation speed was maintained at 200 rpm for 2 h to obtain solution 1.

[0030] In step S4, 200 g of a 25 wt % isocyanate solution was prepared with 50 g of toluene diisocyanate and 150 g of N,N-dimethylformamide, and the mixture was rotated at 180 rpm for 1 hour to obtain a solution 2, which was then sealed and dried and stored at room temperature.

[0031] In step S5, the PTFE mold is preheated to 55°C, the spraying distance is adjusted to 60 cm, 185 g of solution 1 and 180 g of solution 2 are mixed for 3 seconds, and then added to a two-component spray system. The mixture is sprayed into the PTFE plastic mold multiple times at a pressure of 10 MPa and a moving speed of 0.6 m / s, with each spray thickness controlled to 10 mm, until the entire mold is formed. The foam material is then allowed to stand at room temperature for 2 hours. The initially cured foam material is placed in a microwave oven and heated to 95°C at a rate of 2°C / min, where it is cured for another 2 hours. The foam material is then transferred to a drying oven, heated to 230°C at the same rate, and cured for another 2.5 hours to obtain the desired polyurethane / polyimide composite thermal protection material.

[0032] The polyurethane / polyimide composite thermal protection material prepared in Example 5 has an elongation of 185%, a thermal conductivity of 0.028 W / (m·K), and a UL 94 V-0 flame retardancy level, and has excellent thermal insulation and flame retardancy effects.

[0033] The above examples demonstrate the effectiveness of the present invention through experimental verification. The results demonstrate that the polyurethane / polyimide composite thermal protection material exhibits excellent thermal protection, exceptional low heat transfer, and high flame retardancy. It is suitable for use in new energy vehicles, energy storage systems, photovoltaic power generation, and smart grids, demonstrating broad application prospects.

[0034] Although the embodiments of the present invention have been shown and described, those skilled in the art will appreciate that various changes, modifications, substitutions, and variations may be made to these embodiments without departing from the principles and intent of the present invention. The scope of the present invention is defined by the claims and their equivalents. Any technical solution developed in accordance with the core principles of the present invention is intended to be within the scope of protection of the present invention.

Claims

1. A method for preparing a polyurethane / polyimide composite thermal protection material, characterized in that: The following steps are involved: Step S1: Weigh the raw materials methacrylic acid, methacrylonitrile and hydroxyethyl methacrylate according to the required amount, add them into the solvent in sequence, and stir continuously until they are fully dissolved into a uniform multi-component solution; Step S2: transferring the multi-component solution to a reaction vessel, adding a free radical polymerization catalyst, reacting at 40° C.-80° C. for 1 h-3 h, adjusting the stirring speed for thorough mixing, and reacting to obtain a polymer solution, followed by adding an organic base to neutralize some of the acidic groups; Step S3: weighing a catalyst, a chain extender, a foaming agent, an anti-aging agent, and a foaming agent, and adding them to the polymer solution prepared in step S2, slowly heating and stirring until the mixture is uniform, to obtain a solution 1; Step S4: slowly adding the isocyanate to the solvent and stirring until it is completely dissolved to form a slightly yellow or uniform transparent solution, and then sealing and storing the prepared isocyanate solution in a dry container to obtain Solution 2; Step S5: Solution 1 and solution 2 are loaded into a sealed filling machine or spraying system according to the ratio, formed in a mold using a filling process or a spraying process, and then allowed to stand for microwave heating and further heat treatment curing to obtain the desired polyurethane / polyimide composite thermal protection material.

2. The preparation method according to claim 1, wherein: In step S1, the amount of methacrylic acid is 15-20 parts, the amount of methacrylonitrile is 10-25 parts, and the amount of hydroxyethyl methacrylate is 25-55 parts; The solvent is one of N-methylpyrrolidone, N,N-dimethylformamide, N,N-dimethylacetamide, 1,3-dimethyl-2-imidazolidinone, and dimethyl sulfoxide, with an amount of 100 parts; stirring is continued for 1h–3h, and the stirring speed is 100rpm–200rpm.

3. The preparation method according to claim 1, wherein: In step S1, the raw material is not limited to methacrylic acid, but also includes ethylacrylic acid, propylacrylic acid, methylbutenoic acid, ethylbutenoic acid, propylbutenoic acid, methylpentenoic acid, ethylpentenoic acid or propylpentenoic acid; And not limited to methacrylonitrile, also include ethacrylonitrile, propylacrylonitrile, methylbutenenitrile, ethylbutenenitrile, propylbutenenitrile, methylpentenenitrile, ethylpentenenitrile or propylpentenenitrile; It is not limited to hydroxyethyl methacrylate, but also includes hydroxyethyl ethyl acrylate, hydroxyethyl propyl acrylate, hydroxyethyl methyl crotonate, hydroxyethyl ethyl crotonate, hydroxyethyl propyl crotonate, hydroxyethyl methyl pentenoate, hydroxyethyl ethyl pentenoate or hydroxyethyl propyl pentenoate.

4. The preparation method according to claim 1, wherein: In step S2, the free radical polymerization catalyst is benzoyl peroxide or azobisisobutyronitrile, and the amount used is 0.5 parts to 2.5 parts; The organic base is triethylamine or N,N-diisopropylethylamine, with an amount of 7-10 parts; The stirring speed is 100 rpm-200 rpm, and the stirring is continued for 1 h–3 h.

5. The preparation method according to claim 1, wherein: In step S3, the catalyst is triethylenediamine or dibutyltin dilaurate, and the amount used is 0.5 parts to 2 parts; The chain extender is one or a combination of ethylenediamine and ethylene glycol, with an amount of 2 to 8 parts; The foaming agent is polyether modified silicone oil or fatty alcohol polyoxyethylene ether, and the dosage is 1-6 parts; The anti-aging agent is antioxidant BHT, antioxidant 168, ultraviolet absorber UV-326 or UV-327, and the dosage is 0.1 part to 1 part; The foaming agent is 1,1,1,3,3-pentafluoropropane, with an amount of 12-25 parts; The temperature rise rate is 1℃ / min-5℃ / min, the temperature is raised to 50℃-90℃, the stirring speed is 100rpm-200rpm, and the stirring is continued for 1h-3h.

6. The preparation method according to claim 1, wherein: In step S4, the isocyanate solution is composed of isocyanate and solvent, with a concentration of 25wt%-35wt% and an amount of 180 parts-230 parts of the solution; Wherein, the isocyanate includes toluene diisocyanate, diphenylmethane diisocyanate or polyphenyl polymethyl polyisocyanate; The solvent is the same as step S1; The stirring speed is 100 rpm-200 rpm, and the stirring is continued for 1 h–3 h.

7. The preparation method according to claim 1, wherein: In step S5, the injection machine is a high-pressure injection machine with a pressure of 10MPa-20MPa, an injection speed of 300mL / s-500mL / s, a mass ratio of solution 1 to solution 2 of 1.2:1-1:1.2, mixing for 2s-5s, and a mold preheating temperature of 40°C-60°C.

8. The preparation method according to claim 1, wherein: In step S5, the spraying system is a two-component spraying system with a pressure of 8 MPa-12 MPa, a moving speed of 0.5 m / s-1 m / s, a mass ratio of solution 1 to solution 2 of 1.5:1-1:1.2, mixing time of 2s-5s, a spraying distance of 50 cm-70 cm, a spraying thickness of 8 mm-12 mm, and a mold preheating temperature of 40°C-60°C.

9. The preparation method according to claim 1, wherein: In step S5, the mixture is allowed to stand at room temperature for 2 h-4 h, then placed in a microwave oven, heated at a rate of 1°C / min-5°C / min, and cured at 80°C-100°C for 2 h, and then further cured at 200°C-250°C for 2 h-3 h.

10. An application of a polyurethane / polyimide composite thermal protection material, characterized by: The elongation is 175%-235%, the thermal conductivity is 0.026W / (m·K)-0.03W / (m·K), and it reaches the UL 94 V-0 flame retardant level. It is used in new energy vehicles, energy storage systems, photovoltaic power generation and smart grid fields.