A flame-retardant modified polyurethane aerogel and its preparation method

Abstract

This invention discloses a flame-retardant modified polyurethane aerogel and its preparation method, belonging to the technical field of polyurethane aerogel materials. The method involves first reacting DOPO with EDA, then grafting it onto PEG400 to obtain a flame-retardant polyol. The flame-retardant polyol is then uniformly mixed with magnesium hydroxide@silica core-shell powder, followed by the sequential addition of HDI trimer prepolymer and other raw materials. After crosslinking and gelation, a polyurethane wet gel is obtained. Finally, the gel is freeze-dried and aged to obtain the flame-retardant modified polyurethane aerogel. This invention addresses the problems of poor flame retardancy, easy migration of existing flame retardants, and insufficient mechanical properties in traditional polyurethane aerogels through the synergistic effect of reactive phosphorus-nitrogen flame-retardant polyol and magnesium hydroxide@silica core-shell powder. This results in a product with both high flame retardancy and excellent mechanical properties, suitable for applications such as building insulation and aerospace thermal protection.

Description

Technical Field

[0001] This invention belongs to the technical field of polyurethane aerogel materials, specifically a flame-retardant modified polyurethane aerogel and its preparation method. Background Technology

[0002] Polyurethane aerogels are lightweight functional materials with a three-dimensional continuous porous network structure. With their extremely low bulk density, excellent room-temperature thermal insulation properties, and good mechanical toughness, they have shown outstanding application potential in building insulation, aerospace thermal protection, and electronic device packaging, becoming one of the research hotspots in the field of functional materials in recent years. However, polyurethane molecules are rich in carbon, hydrogen, and oxygen elements and lack effective flame-retardant groups, resulting in poor inherent flame retardancy. When exposed to fire, they are prone to continuous combustion, releasing large amounts of heat and smoke, and potentially producing toxic gases such as carbon monoxide and cyanide. This deficiency directly limits their large-scale industrial application in scenarios with specific safety requirements.

[0003] To improve the flame retardant properties of polyurethane aerogels, existing technologies typically employ the addition of flame retardant functional components, including organic flame retardants or inorganic flame retardant fillers. Inorganic flame retardant fillers require high addition amounts and have low flame retardant efficiency. This not only damages the porous structure of polyurethane aerogels and reduces their mechanical toughness, but also increases their thermal conductivity and density. Furthermore, they exhibit poor long-term flame retardant stability and are difficult to suppress the release of toxic fumes.

[0004] Chinese invention patent announcement CN111019185B discloses a low thermal conductivity elastic flame-retardant polyurethane aerogel and its preparation method. The flame retardancy is improved by adding organic flame retardants. However, this method only uses physical mixing and dispersion. During long-term use, the aerogel is prone to migration and precipitation from the aerogel network with temperature changes and humidity fluctuations, resulting in a decrease in flame retardant effect. Summary of the Invention

[0005] The purpose of this invention is to provide a flame-retardant modified polyurethane aerogel and its preparation method. By leveraging the synergistic effect of reactive phosphorus-nitrogen flame-retardant polyols and magnesium hydroxide@silica core-shell powder, this invention solves the problems of poor flame retardancy, easy migration of existing flame retardants, high levels of toxic fumes, and insufficient mechanical properties in traditional polyurethane aerogels. The resulting product combines high flame retardancy, excellent mechanical properties, and low toxic fumes release, making it suitable for applications such as building insulation and aerospace thermal protection.

[0006] The objective of this invention can be achieved through the following technical solutions:

[0007] A method for preparing flame-retardant modified polyurethane aerogel includes the following steps:

[0008] Step 1: Graft DOPO-EDA onto one end of PEG400 to obtain flame-retardant polyol;

[0009] Step 2: Utilize the in-situ hydrolysis and condensation of tetraethyl orthosilicate to form nano-silica and coat it with magnesium hydroxide powder to obtain magnesium hydroxide@silica core-shell powder;

[0010] Step 3: First, mix the flame-retardant polyol with magnesium hydroxide@silica core-shell powder evenly, then add HDI trimer prepolymer, dibutyltin dilaurate and curing agent HT-100 in sequence, and then gel the resulting mixture to obtain polyurethane wet gel.

[0011] Step 4: After freeze-drying and aging, the polyurethane wet gel is used to obtain flame-retardant modified polyurethane aerogel.

[0012] Furthermore, the specific preparation steps of the polyurethane wet gel are as follows:

[0013] Flame-retardant polyol and magnesium hydroxide@silica core-shell powder were added to a reactor and stirred at 1500 rpm for 5 min. Polypropylene glycol was added and stirred for 6 min. HDI trimer, dibutyltin dilaurate and curing agent HT-100 were then added and stirred at 1000 rpm for 2 min. Deionized water was then added and stirred at 1800 rpm for 10 s. The mixture was immediately poured into a mold and allowed to stand at 65°C for 9 h to complete gelation, resulting in a polyurethane wet gel.

[0014] Furthermore, the ratio of flame-retardant polyol, magnesium hydroxide@silica core-shell powder, polypropylene glycol, HDI trimer, dibutyltin dilaurate, curing agent HT-100, and deionized water is 80-120g: 35-70g: 50-90g: 15-25g: 0.15-0.5g: 15-25g: 50-90mL.

[0015] Furthermore, the specific preparation steps of magnesium hydroxide@silicon dioxide core-shell powder are as follows:

[0016] Magnesium hydroxide powder, anhydrous ethanol, deionized water, 28 wt% ammonia solution, and hexadecyltrimethylammonium bromide were added to a reaction vessel and stirred until evenly dispersed. Then, alkyl orthosilicate was added dropwise. The reaction was carried out at 25-40℃ and 100-300 r / min for 8-16 h. After the reaction was completed, the mixture was centrifuged and filtered. The precipitate was washed, dried at 50-70℃ for 10-14 h, and calcined at 500-600℃ for 5-8 h to obtain magnesium hydroxide@silica core-shell powder.

[0017] Furthermore, the ratio of magnesium hydroxide powder, hexadecyltrimethylammonium bromide, and tetraethyl orthosilicate is 1-4g:0.6-3g:1-6mL.

[0018] Furthermore, the alkyl orthosilicate is either propyl orthosilicate or tetraethyl orthosilicate.

[0019] Furthermore, the specific preparation steps of flame-retardant polyols are as follows:

[0020] PEG400, DOPO-EDA, triphenylphosphine, and tetrahydrofuran were added to a reaction vessel and stirred at 200-400 r / min until dissolved. Under stirring conditions at 0-5℃, a 0.8 mol / L diethyl azodicarbonate solution was slowly added dropwise to the reaction vessel, with the addition time controlled at 45-75 min. After the addition was completed, the temperature was raised to 25-30℃, and the reaction was continued with stirring for 18-24 h. The product was then evaporated by rotary evaporation, and the product was precipitated with a methanol / dichloromethane mixed solution. After centrifugation, the precipitate was washed 2-3 times with a methanol / dichloromethane mixed solution and dried under vacuum to obtain the flame-retardant polyol.

[0021] The reaction process is as follows:

[0022]

[0023] Furthermore, the ratio of the amounts of PEG400, DOPO-EDA, triphenylphosphine, tetrahydrofuran, and diethyl azodicarbonate solution is 11-13g: 7.7-10.3g: 9.4-11.4g: 200mL: 50mL.

[0024] Furthermore, the volume ratio of methanol to dichloromethane in the methanol / dichloromethane mixed solution is 1:19.

[0025] The beneficial effects of this invention are:

[0026] 1. The raw material of the flame-retardant modified polyurethane aerogel of the present invention includes a flame-retardant polyol, which is obtained by reacting DOPO with EDA. It not only retains the excellent flame-retardant properties of DOPO itself, but also introduces nitrogen element. Phosphorus and nitrogen will produce a synergistic effect during combustion, which can significantly promote char formation and inhibit the generation of combustible gases, thereby greatly improving the flame-retardant efficiency. Subsequently, the synthesized DOPO-EDA is grafted onto the PEG400 chain segment through a nucleophilic substitution reaction to form an inherently flame-retardant polyol, which becomes part of the polyurethane molecular chain. It is not easy to migrate and precipitate, and can maintain the flame-retardant effect for a long time, while having less impact on the mechanical properties of the material itself.

[0027] 2. This invention adds magnesium hydroxide@silica core-shell powder to a polyurethane system undergoing polymerization, ultimately fixing it uniformly and fixed within the three-dimensional network structure of the aerogel. As a reinforcing phase, it significantly improves the mechanical properties and structural stability of the composite aerogel. During combustion, it effectively delays the escape of combustible gases generated by polymer decomposition and blocks the inward penetration of oxygen and heat, acting as a physical barrier. Furthermore, as a char-forming agent, it catalyzes the formation of a dense and robust char layer within the polymer matrix, protecting the internal materials from further combustion. While magnesium hydroxide powder itself possesses good flame retardancy and biocompatibility, it is hygroscopic and prone to agglomeration in the system. Coating its surface with a layer of silica reduces hard agglomeration between magnesium hydroxide particles, improving its dispersibility within the polymer matrix and contributing to enhanced thermal stability of the flame-retardant modified polyurethane aerogel. Detailed Implementation

[0028] The technical solutions of the present invention will be clearly and completely described below with reference to the embodiments of 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.

[0029] Example 1: A method for preparing flame-retardant modified polyurethane aerogel

[0030] S1: 45.4 g of 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide (DOPO) and 200 mL of dichloromethane were added to a reaction vessel and stirred for 15 min at 3 °C and 250 r / min. Then, 21.1 g of triethylamine was added to the reaction vessel and stirring was continued for 5-10 min. Next, 6 g of anhydrous ethylenediamine (EDA) was added and stirring was continued for 3-5 min. At 15 °C and 350 r / min, 32.3 g of carbon tetrachloride was added dropwise to the vessel. After the addition was complete, the reaction was carried out at 25 °C and 300 r / min for 12 h. After the reaction was completed, the reaction product was filtered and the precipitate was washed repeatedly with deionized water and ethanol 3-5 times to remove triethylamine hydrochloride and unreacted DOPO. Finally, the washed product was vacuum dried for 12 h to obtain the white solid product DOPO-EDA.

[0031] Using carbon tetrachloride as a bridge, a two-step nucleophilic substitution reaction is carried out: first, the amino group of ethylenediamine attacks carbon tetrachloride to form a CN bond, and the generated HCl is neutralized by triethylamine; then, the P atom of DOPO attacks the intermediate to form a PC bond, connecting the two; the reaction is accelerated to completion by controlling the temperature and rate, and after washing and drying, DOPO-EDA containing PN bonds is obtained.

[0032] S2: Add 12g PEG400, 10.3g DOPO-EDA, 10.4g triphenylphosphine and 200mL tetrahydrofuran to the reactor and stir at 300r / min until dissolved. Adjust the temperature to 3℃ and continue stirring. Slowly add 50mL of 0.8mol / L diethyl azodicarbonate (DEAD) solution (tetrahydrofuran solvent) to the reactor, controlling the addition time to 1h. After the addition is completed, raise the temperature of the reactor to 25℃ and continue stirring for 20h. After the reaction is completed, the product is rotary evaporated to remove most of the tetrahydrofuran. Then, a methanol / dichloromethane mixed solution with a volume ratio of 1:19 is added to precipitate the product. Centrifuge and wash the precipitate 2-3 times with the methanol / dichloromethane mixed solution. After vacuum drying, the flame-retardant polyol is obtained.

[0033] Triphenylphosphine and diethyl azodicarbonate form an active phosphonium salt intermediate in solution at low temperature, which activates the primary hydroxyl group at the end of polyethylene glycol 400 as an easily leaving group. Subsequently, the primary amino group in the DOPO-EDA molecule acts as a nucleophile to attack the activated site, resulting in a nucleophilic substitution reaction and forming a CN covalent bond, thus achieving the grafting of DOPO-EDA at the end of PEG.

[0034] S3: Add 2g of magnesium hydroxide powder, 1120mL of anhydrous ethanol, 280mL of deionized water and 20mL of 28wt% ammonia solution to the reaction vessel, stir and disperse evenly, then add 4mL of tetraethyl orthosilicate dropwise, and react at 30℃ and 200r / min for 12h. After the reaction is completed, centrifuge and filter, wash the precipitate, and dry it at 60℃ for 12h to obtain magnesium hydroxide@silica core-shell powder.

[0035] Using magnesium hydroxide powder as the core, under alkaline conditions provided by ammonia, tetraethyl orthosilicate is hydrolyzed and condensed to form an amorphous silica layer on the surface of the magnesium hydroxide powder, stabilizing the silica network structure, and finally forming a core-shell material magnesium hydroxide@silica core-shell powder with a mesoporous structure.

[0036] S4: Add 100g of flame-retardant polyol and 55g of magnesium hydroxide@silica core-shell powder to the reactor and stir at 1500r / min for 5min. Add 70g of polyoxypropylene glycol in three portions and stir at 1500r / min for 6min. Then add 20g of HDI trimer, 0.25g of dibutyltin dilaurate as catalyst and 20g of curing agent HT-100 and stir at 1000r / min for 2min. Then add 70mL of deionized water and stir at 1800r / min for 10s. Immediately pour the mixture into a mold and let it stand at 65℃ for 9h to complete gelation and obtain polyurethane wet gel.

[0037] The hydroxyl groups of flame-retardant polyol and polypropylene glycol react with the polyisocyanate groups of HDI trimer under the catalysis of dibutyltin dilaurate to initially form a polyurethane crosslinking network through the addition reaction of hydroxyl groups and isocyanate groups. Then, the crosslinking reaction is initiated by curing agent HT-100. After adding deionized water, the mixture is stirred at high speed for a short time to quickly disperse and trigger the reaction.

[0038] S5: Transfer 100g of polyurethane wet gel to a freezing autoclave and pre-freeze at -10℃ to -15℃ for 12h, then cool to -35℃ to -40℃ and freeze for 24h. Subsequently, vacuum dry at -20℃ to -15℃ for 48-60h, remove moisture by ice sublimation, and age at 40-50℃ for 24h to promote further crosslinking of unreacted -NCO and -OH, optimize the skeleton structure, and finally obtain flame-retardant modified polyurethane aerogel.

[0039] Examples 2-4: A method for preparing flame-retardant modified polyurethane aerogel. The difference from Example 1 is that the amount of substance added in step S2 is different, while the other steps and parameters remain the same. The specific amounts added are shown in Table 1 below.

[0040] Table 1. Comparison of Material Usage in Step S2

[0041] project PEG400 (g) DOPO-EDA(g) Triphenylphosphine (g) Tetrahydrofuran (mL) Diethyl azodicarbonate solution (mL) Example 2 11 7.7 9.4 200 50 Example 3 12 9.0 10 200 50 Example 4 13 10.3 11.4 200 50

[0042] Example 5: A method for preparing flame-retardant modified polyurethane aerogel, the difference from Example 1 is that tetraethyl orthosilicate in step S3 is replaced with propyl orthosilicate, while the remaining steps and parameters remain the same.

[0043] Examples 6-8: A method for preparing flame-retardant modified polyurethane aerogel. The difference from Example 1 is that the amount of substance added in step S4 is different, while the other steps and parameters remain the same. The specific amounts added are shown in Table 2 below.

[0044] Table 2. Comparison of material usage in step S4

[0045] project Flame-retardant polyols (g) Magnesium hydroxide@silicon dioxide core-shell powder (g) Polypropylene glycol (g) HDI trimer (g) Dibutyltin dilaurate (g) Curing agent HT-100 (g) Example 6 80 35 50 15 0.15 15 Example 7 110 60 75 22 0.35 22 Example 8 120 70 90 25 0.5 25

[0046] In this invention, 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide (DOPO), triethylamine, carbon tetrachloride, and dibutyltin dilaurate were purchased from Shanghai Aladdin Biochemical Technology Co., Ltd.; polypropylene glycol was PPG1000; curing agent HT100 was purchased from Jinan Hongwang Chemical Co., Ltd.; HDI trimer was purchased from Jiangsu Raine Environmental Protection Technology Co., Ltd.; and PEG400, ethylenediamine, triphenylphosphine, tetrahydrofuran, and magnesium hydroxide powder were purchased from Shanghai Maclean Biochemical Technology Co., Ltd.

[0047] Comparative Example 1: Based on Example 1, steps S1-S2 (DOPO-EDA grafted with PEG400 to prepare flame-retardant polyol) were omitted, and unmodified PEG400 was replaced in step S4. An equivalent amount of additive DOPO was added in step S4. Other steps and parameters remained unchanged, resulting in a flame-retardant modified polyurethane aerogel.

[0048] Comparative Example 2: Based on Example 1, step S3 was omitted to avoid preparing magnesium hydroxide@silica core-shell powder, and magnesium hydroxide@silica core-shell powder was not added in step S4. Only the organic flame retardant system of reactive flame retardant polyol was retained, and other steps and parameters remained unchanged to obtain a flame retardant modified polyurethane aerogel.

[0049] Comparative Example 3: Based on Example 1, magnesium hydroxide@silica core-shell powder was replaced with pure magnesium hydroxide powder without silica coating and used in subsequent steps, while other steps and parameters remained unchanged, to obtain a flame-retardant modified polyurethane aerogel.

[0050] The flame-retardant modified polyurethane aerogels prepared in Examples 1-8 and Comparative Examples 1-3 were subjected to performance tests. All samples underwent accelerated migration treatment, which involved immersing them in a 50 wt% ethanol solution at 40°C for 24 hours.

[0051] The oxygen index was determined according to the test method specified in GB / T2406.2-2009 standard; the higher the value, the better the flame retardant effect. The vertical burning rating was determined according to the test method specified in GB / T2408-2021 standard, and the flammability rating was determined by self-extinguishing time and the ignition of dripping materials; the lower the rating, the better the flame retardant performance. The compressive strength was determined according to the test method specified in GB / T8813-2022 standard, quantifying the material's ability to resist compressive deformation; the higher the value, the better the mechanical properties. Tensile strength and elongation at break were determined according to the test method specified in GB / T1040.1-2006 standard. CO emission was determined according to the test method specified in GB / T20284-2006 standard, quantifying the amount of toxic CO gas released during combustion; the lower the value, the more environmentally friendly it is. The test results are shown in Table 3.

[0052] Table 3. Performance Test Results of Flame-Retardant Modified Polyurethane Aerogel

[0053]

[0054] As can be seen from Table 3, Examples 1-8 adopted a composite flame retardant system using reactive phosphorus-nitrogen flame retardant polyols and magnesium hydroxide@silica core-shell powder core-shell materials. Through stepwise modification of DOPO-EDA synthesis, PEG grafting, core-shell preparation, and gel crosslinking, the flame retardant properties, mechanical properties, and low toxic smoke release of polyurethane aerogel were synergistically improved. In Examples 2-4, the grafting efficiency of reactive flame-retardant groups on the PEG chain segment was gradually optimized by adjusting the amounts of PEG400, DOPO-EDA, and triphenylphosphine in step S2. In Example 5, tetraethyl orthosilicate in step S3 was replaced with propyl orthosilicate. Since the hydrolysis and condensation characteristics of the two are similar, the performance test results are very similar to those of Example 1, proving that the replacement of the functionally equivalent silicon source can improve the adaptability of process raw materials. In Examples 6-8, the synergistic effect of organic flame retardancy and inorganic enhancement was gradually strengthened by optimizing the amounts of flame-retardant polyol, HDI trimer, and magnesium hydroxide@silica core-shell powder in step S4. This ensured both uniform dispersion of the flame retardant and integrity of the cross-linking network, and avoided the imbalance between mechanical properties and flame-retardant effect.

[0055] Comparative Example 1, by omitting the grafting of DOPO-EDA in steps S1 and S2 and replacing the reactive flame-retardant polyol with unmodified PEG400 and added DOPO, lacks the core function of covalent grafting to prevent flame retardant migration. This results in a decrease in the oxygen index and vertical burning rating of the aerogel, as well as a reduction in the synergistic inhibition effect on CO release, failing to meet basic flame-retardant requirements. Its mechanical properties are reduced, possibly because the migration of added DOPO affects the integrity of the soft and hard microphase separation of the polyurethane aerogel. The increased CO release significantly raises the risk of toxic fumes, making it unsuitable for safety-sensitive scenarios and posing a potential structural failure hazard.

[0056] Comparative Example 2, by omitting the magnesium hydroxide@silica core-shell powder preparation process in step S3 and retaining only the organic flame-retardant system of reactive flame-retardant polyols, suffers from several drawbacks. On the one hand, the lack of physical barrier from the inorganic core-shell material results in a decrease in the oxygen index of the aerogel due to reliance solely on the char formation and flame-retardant mechanism of organic phosphorus and nitrogen. On the other hand, the absence of magnesium hydroxide powder's adsorption effect on toxic fumes leads to a significant increase in CO release and a deterioration in the toxic fumes suppression effect. Simultaneously, the lack of inorganic filler's reinforcing effect on the aerogel network results in a decrease in mechanical properties. This verifies the necessity of magnesium hydroxide@silica core-shell powder for balancing the flame retardancy, toxicity suppression, and mechanical properties of aerogels.

[0057] In Comparative Example 3, the magnesium hydroxide@silica core-shell powder was replaced with pure magnesium hydroxide powder without silica coating. The silica shell layer lacked its role in sealing and dispersing the hydroxyl groups on the magnesium hydroxide powder surface, leading to easy agglomeration of the pure magnesium hydroxide powder within the polyurethane matrix. On one hand, uneven flame retardant dispersion resulted in weak local flame retardancy; although the aerogel's vertical burning rating remained V-0, the oxygen index decreased. On the other hand, the agglomerates disrupted the continuity of the aerogel's three-dimensional network, reducing compressive strength. Simultaneously, agglomeration reduced the toxic smoke adsorption efficiency of the magnesium hydroxide powder, increasing CO release. This fully demonstrates the crucial role of the magnesium hydroxide@silica core-shell powder's core-shell structure in improving flame retardant dispersibility and enhancing the overall performance of the aerogel.

[0058] It should be noted that, in this document, terms such as “comprising,” “including,” or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such process, method, article, or apparatus.

[0059] 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 alterations can be made to these embodiments without departing from the principles and spirit of the invention.

Claims

1. A method of making a flame-retardant modified polyurethane aerogel, the method comprising: The polyurethane wet gel is freeze-dried and aged, characterized in that the polyurethane wet gel is prepared by the following steps: Step 1: Graft DOPO-EDA onto one end of PEG400 to obtain flame-retardant polyol; 45.4 g of 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide and 200 mL of dichloromethane were added to a reaction vessel and stirred for 15 min at 3 °C and 250 r / min. Then, 21.1 g of triethylamine was added to the reaction vessel and stirring was continued for 5-10 min. Next, 6 g of anhydrous ethylenediamine was added and stirring was continued for 3-5 min. 32.3 g of carbon tetrachloride was added dropwise to the vessel at 15 °C and 350 r / min. After the addition was complete, the reaction was carried out at 25 °C and 300 r / min for 12 h. After the reaction was completed, the reaction product was filtered and the precipitate was washed repeatedly with deionized water and ethanol 3-5 times to remove triethylamine hydrochloride and unreacted DOPO. Finally, the washed product was vacuum dried for 12 h to obtain a white solid product DOPO-EDA. PEG400, DOPO-EDA, triphenylphosphine, and tetrahydrofuran were added to a reaction vessel and stirred at 200-400 r / min until dissolved. Under stirring conditions at 0-5℃, a 0.8 mol / L diethyl azodicarbonate solution was added dropwise to the reaction vessel at a time of 45-75 min. After the addition was completed, the mixture was stirred at 25-30℃ for 18-24 h. The product was then evaporated by rotary evaporation. The product was precipitated with a methanol / dichloromethane mixture, centrifuged, and the precipitate was washed 2-3 times with the methanol / dichloromethane mixture. The product was then dried under vacuum to obtain the flame-retardant polyol. Step 2: Utilize the in-situ hydrolysis and condensation of tetraethyl orthosilicate to form nano-silica and coat it with magnesium hydroxide powder. Calcine at 500-600℃ for 5-8 hours to obtain magnesium hydroxide@silica core-shell powder. Step 3: First, mix the flame-retardant polyol with magnesium hydroxide@silica core-shell powder evenly, then add HDI trimer prepolymer, dibutyltin dilaurate and curing agent HT-100 in sequence, and then gel the resulting mixture to obtain polyurethane wet gel. The ratio of the following components is used: flame-retardant polyol, magnesium hydroxide@silica core-shell powder, polypropylene glycol, HDI trimer, dibutyltin dilaurate, curing agent HT-100, and deionized water. The ratio is 80-120g: 35-70g: 50-90g: 15-25g: 0.15-0.5g: 15-25g: 50-90mL.

2. The method for preparing a flame-retardant modified polyurethane aerogel according to claim 1, characterized in that, The specific preparation steps of the polyurethane wet gel are as follows: Flame-retardant polyol and magnesium hydroxide@silica core-shell powder were added to a reactor and stirred at 1500 rpm for 5 min. Polypropylene glycol was added and stirred for 6 min. HDI trimer, dibutyltin dilaurate and curing agent HT-100 were then added and stirred at 1000 rpm for 2 min. Deionized water was then added and stirred at 1800 rpm for 10 s. The mixture was immediately poured into a mold and allowed to stand at 65°C for 9 h to complete gelation, resulting in a polyurethane wet gel.

3. The method for preparing a flame-retardant modified polyurethane aerogel according to claim 2, characterized in that, The specific preparation steps of the magnesium hydroxide@silicon dioxide core-shell powder are as follows: Magnesium hydroxide powder, anhydrous ethanol, deionized water, 28 wt% ammonia solution, and hexadecyltrimethylammonium bromide were added to a reaction vessel and stirred until evenly dispersed. Then, tetraethyl orthosilicate was added dropwise. The reaction was carried out at 25-40℃ and 100-300 r / min for 8-16 h. After the reaction was completed, the mixture was centrifuged and filtered. The precipitate was washed, dried, and calcined at 500-600℃ for 5-8 h to obtain magnesium hydroxide@silica core-shell powder.

4. The method for preparing a flame-retardant modified polyurethane aerogel according to claim 3, characterized in that, The ratio of magnesium hydroxide powder, hexadecyltrimethylammonium bromide, and tetraethyl orthosilicate is 1-4g:0.6-3g:1-6mL.

5. The method for preparing a flame-retardant modified polyurethane aerogel according to claim 1, characterized in that, The ratio of the amounts of PEG400, DOPO-EDA, triphenylphosphine, tetrahydrofuran, and diethyl azodicarbonate solution is 11-13g: 7.7-10.3g: 9.4-11.4g: 200mL: 50mL.

6. The method for preparing a flame-retardant modified polyurethane aerogel according to claim 1, characterized in that, The volume ratio of methanol to dichloromethane in the methanol / dichloromethane mixed solution is 1:

19.

7. A flame-retardant modified polyurethane aerogel, characterized in that, It is prepared by the preparation method described in any one of claims 1-6.

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