A double-crosslinked network structure PBO composite aerogel and its preparation method

Abstract

The present invention relates to the field of nanofiber aerogel technology, and in particular to a double-crosslinked network structure PBO composite aerogel and a preparation method thereof. The double-crosslinked network structure PBO composite aerogel includes a nano-composite aerogel with a double-crosslinked network structure constructed by polybenzoxazine and PBO fibers, and a hydrophobic coating deposited on the surface of the nano-composite aerogel; the hydrophobic coating includes a fluorocarbon resin and fumed silica. The double-crosslinked network structure PBO composite aerogel provided by the present invention has super-hydrophobicity, excellent flame retardant properties, high mechanical properties and low thermal conductivity, and its compressive strength is 1.24-1.53MPa, the contact angle with water is 142.1-152.3°, the combustion grade is UL94V-0, and the thermal conductivity is 0.034-0.038W / (m·K), which overcomes the technical problem that the poor interaction between PBO nanofibers in the prior art makes it difficult to form a stable aerogel.

Description

Technical Field

[0001] The present invention relates to the technical field of nanofiber aerogels, and in particular to a double-crosslinked network structure PBO composite aerogel and a preparation method thereof. Background Art

[0002] Poly(p-phenylene benzobisoxazole) (PBO) fibers have an outstanding thermal decomposition temperature (650°C), extremely high tensile strength (5.8 GPa) and excellent flame retardant properties (limiting oxygen index of 68), and are known as the super fiber of the 21st century. Therefore, PBO nanofibers derived from PBO fibers have broad application prospects in aerospace, electronic information, and 5G communications. However, the interaction between PBO nanofibers is poor, and it is difficult to form stable aerogels, which limits its wider application. At present, there are few reports on the preparation of PBO nanoaerogels. How to improve the interaction between PBO nanofibers and improve the stability of the nanofiber network remains a huge challenge. Summary of the Invention

[0003] The purpose of the present invention is to provide a double-crosslinked network structure PBO composite aerogel and a preparation method thereof, so as to solve the technical problem existing in the above-mentioned prior art that it is difficult to form a stable aerogel due to poor interaction between PBO nanofibers. The double-crosslinked network structure PBO composite aerogel prepared by the present invention has excellent mechanical properties, hydrophobic properties and flame retardant properties, which makes PBO fibers have a broader application prospect.

[0004] To achieve the above object, the present invention provides the following solutions:

[0005] One of the technical solutions of the present invention: a double-crosslinked network structure PBO composite aerogel, the double-crosslinked network structure PBO composite aerogel comprising: a nanocomposite aerogel having a double-crosslinked network structure constructed of polybenzoxazine and PBO nanofibers, and a hydrophobic coating deposited on the surface of the nanocomposite aerogel; the hydrophobic coating comprising a fluorocarbon resin and fumed silica.

[0006] Benzoxazine can be polymerized under acidic conditions to form polybenzoxazine. The present invention uses polybenzoxazine molecular chains and PBO nanofibers to form an interpenetrating network structure to enhance the stability of the aerogel. In addition, the main chain and side chains of the polybenzoxazine molecular chain contain a large number of hydroxyl groups and benzene rings, which form strong hydrogen bonds and other non-covalent interactions with the PBO nanofibers, thereby overcoming the technical problem of weak interactions between PBO nanofibers and making it possible for PBO fibers to form stable aerogels. The present invention not only improves the overall mechanical properties of the nanocomposite aerogel by constructing a double-crosslinked network structure, but also improves the thermal stability and thermal insulation properties of the aerogel; on this basis, a hydrophobic coating is deposited on the surface of the nanocomposite aerogel. By regulating the fluorocarbon resin and fumed silica, the surface free energy of the aerogel surface is reduced and the surface roughness is increased, so that the coating can form a more uniform superhydrophobic structure, thereby having superhydrophobic properties. Therefore, the double-crosslinked network structure PBO composite aerogel provided by the present invention has excellent mechanical properties, superhydrophobic properties, flame retardant properties and low thermal conductivity.

[0007] Preferably, the raw materials of the double-crosslinked network structure PBO composite aerogel include, by weight: 10-50 parts of PBO fibers, 100-300 parts of methanesulfonic acid, 100-300 parts of trifluoroacetic acid, 50-100 parts of benzoxazine, 2-5 parts of anhydrous sodium sulfate, 80-140 parts of fluorocarbon resin and 1-4 parts of fumed silica.

[0008] Preferably, the benzoxazine is a diamine / phenol type benzoxazine.

[0009] Preferably, the preparation method of the nanocomposite aerogel comprises the following steps:

[0010] The PBO fibers are dispersed in a mixed acid solution consisting of methanesulfonic acid and trifluoroacetic acid to obtain a PBO nanofiber dispersion.

[0011] adding benzoxazine and anhydrous sodium sulfate to the PBO nanofiber dispersion to prepare a polybenzoxazine / PBO nanocomposite acid sol;

[0012] The polybenzoxazine / PBO nanocomposite acid gel is subjected to solvent exchange in a solvent and then freeze-dried to obtain the nanocomposite aerogel.

[0013] The invention first uses a mixed acid solution of trifluoroacetic acid and methanesulfonic acid to prepare a PBO nanofiber dispersion, then adds benzoxazine and anhydrous sodium sulfate to the PBO nanofiber dispersion, uses trifluoroacetic acid and methanesulfonic acid as acid catalysts to promote the ring-opening polymerization of benzoxazine to form polybenzoxazine, and simultaneously uses anhydrous sodium sulfate to modify the PBO nanofibers. Sulfate ions can reduce the electrostatic repulsion between the PBO nanofibers and improve the π-π interaction of the PBO nanofibers, so that the polybenzoxazine and the PBO nanofibers form an interpenetrating network structure, thereby obtaining a stable nanocomposite aerogel.

[0014] Because water forms hydrogen bonds with hydrogen ions in the acid, the effect of the acid on the PBO fibers is reduced, so that stable PBO nanofibers cannot be formed. Therefore, the reaction system requires an anhydrous environment. Based on this, the present invention uses anhydrous sodium sulfate as a modifier.

[0015] The present invention uses a mixed acid solution of trifluoroacetic acid and methanesulfonic acid to prepare the PBO nanofiber dispersion because the mixed acid solution of trifluoroacetic acid and methanesulfonic acid has a better dispersion effect on PBO fibers. In addition, benzoxazine can also be polymerized in trifluoroacetic acid and methanesulfonic acid, which is beneficial to the preparation of nanocomposite aerogels.

[0016] Preferably, the mass fraction of the PBO fiber is 20 to 50 parts.

[0017] Preferably, the PBO fiber has a length of 10 to 20 cm and a diameter of 10 to 15 μm.

[0018] Preferably, the mass fraction of the methanesulfonic acid is 100 to 200 parts.

[0019] Preferably, the mass fraction of the trifluoroacetic acid is 100 to 200 parts.

[0020] Preferably, the mass fraction of the benzoxazine is 70 to 100 parts.

[0021] Preferably, the purity of the benzoxazine is ≥95%.

[0022] Preferably, the mass fraction of the anhydrous sodium sulfate is 3 to 5 parts.

[0023] Preferably, the purity of the anhydrous sodium sulfate is ≥95%.

[0024] Preferably, the mass fraction of the fluorocarbon resin is 80 to 120 parts.

[0025] Preferably, the mass fraction of fumed silica is 1 to 3 parts.

[0026] The present invention limits the amounts of each raw material, allowing the components to interact with each other to achieve optimal product performance. The limits on the amounts of each raw material are intended to maintain their specific properties and meet the requirements of process conditions and application areas. Exceeding the dosage range may lead to performance degradation, increased processing difficulty, and safety hazards. The interaction between the raw material amounts determines the overall performance and stability of the aerogel. Therefore, when preparing aerogels, the raw material amounts and their interaction must be strictly controlled to achieve optimal product performance. For example, excessive amounts of fumed silica in the hydrophobic coating will increase the viscosity of the fluorocarbon resin / fumed silica mixture, making it difficult to form a uniform coating on the aerogel surface. Furthermore, PBO fibers can be dispersed in either methanesulfonic acid or trifluoroacetic acid. PBO fibers disperse faster in trifluoroacetic acid, but the resulting PBO nanofibers are uneven. To control the dispersion rate of the PBO fibers in the acid solution, the ratio of 100 to 300 parts methanesulfonic acid to 100 to 300 parts trifluoroacetic acid is used. The present invention utilizes the outstanding thermal decomposition temperature (650°C), extremely high tensile strength (5.8 GPa), and excellent flame retardancy (Limiting Oxygen Index (LOI) of PBO fibers to produce multifunctional nanofiber aerogels. However, using less PBO fibers may reduce the flame retardancy of the resulting nanofiber aerogels.

[0027] A second technical solution of the present invention is a method for preparing the above-mentioned double-crosslinked network structure PBO composite aerogel, comprising the following steps: soaking the nanocomposite aerogel in a mixed solution of fluorocarbon resin and fumed silica to obtain the double-crosslinked network structure PBO composite aerogel.

[0028] Preferably, the preparation method of the nanocomposite aerogel comprises the following steps:

[0029] The PBO fibers are dispersed in a mixed acid solution consisting of methanesulfonic acid and trifluoroacetic acid to obtain a PBO nanofiber dispersion.

[0030] adding benzoxazine and anhydrous sodium sulfate to the PBO nanofiber dispersion to prepare a polybenzoxazine / PBO nanocomposite acid sol;

[0031] The polybenzoxazine / PBO nanocomposite acid gel is subjected to solvent exchange in a solvent and then freeze-dried to obtain the nanocomposite aerogel.

[0032] Preferably, the step of adding benzoxazine and anhydrous sodium sulfate to the PBO nanofiber dispersion to prepare the polybenzoxazine / PBO nanocomposite acid sol specifically comprises: adding benzoxazine and anhydrous sodium sulfate to the PBO nanofiber dispersion, stirring at high speed, and allowing to stand to obtain the polybenzoxazine / PBO nanocomposite acid sol.

[0033] Preferably, the high-speed stirring speed is 10,000 to 18,000 rpm, and the time is 20 to 60 minutes.

[0034] Preferably, the standing is at 20-25° C. for 10-30 hours.

[0035] Preferably, the solvent used in the solvent exchange is deionized water.

[0036] Compared to other solvents, deionized water offers a faster exchange rate and does not damage the nanofiber gel structure. Furthermore, using deionized water as the exchange solvent allows for direct freeze-drying, reducing equipment requirements. Furthermore, other organic solvents may damage the structure of PBO nanofibers and polybenzoxazine to some extent.

[0037] Preferably, the solvent exchange time is 2 to 4 hours.

[0038] Preferably, the number of solvent exchanges is 6 to 10 times.

[0039] Preferably, the freeze-drying temperature is -80 to -60°C.

[0040] Preferably, the freeze-drying time is 30 to 72 hours.

[0041] Preferably, the dispersion is achieved by stirring, the stirring speed is 500 to 1000 rpm, and the stirring time is 48 to 96 hours.

[0042] Preferably, in the mixed acid solution, the mass ratio of methanesulfonic acid to trifluoroacetic acid is 1-2:0.5-1.5.

[0043] Preferably, the mass ratio of the PBO fiber to the mixed acid solution is 10-50:100-300.

[0044] Preferably, the mass ratio of the PBO fiber to benzoxazine is 1-5:5-10.

[0045] Preferably, the mass ratio of the PBO fiber to anhydrous sodium sulfate is 10-50:2-5.

[0046] Preferably, the mass ratio of the fluorocarbon resin to the fumed silica is 80-140:1-4.

[0047] Preferably, the soaking time is 5 to 30 minutes.

[0048] Preferably, the preparation method of the double-crosslinked network structure PBO composite aerogel comprises the following steps:

[0049] (1) An appropriate amount of PBO fibers was placed in a methanesulfonic acid / trifluoroacetic acid mixture and magnetically stirred to obtain a PBO nanofiber dispersion;

[0050] (2) adding benzoxazine and anhydrous sodium sulfate to the PBO nanofiber dispersion, stirring with a high-speed homogenizer to obtain a polybenzoxazine / PBO nanocomposite acid sol, and allowing to stand at room temperature to obtain a polybenzoxazine / PBO nanocomposite acid gel;

[0051] (3) soaking the polybenzoxazine / PBO nanocomposite acid gel in deionized water for solvent exchange to obtain a nanocomposite hydrogel, and freeze-drying to obtain a polybenzoxazine / PBO nanocomposite aerogel;

[0052] (4) The polybenzoxazine / PBO nanocomposite aerogel is immersed in a fluorocarbon resin / fumed silica solution, and then taken out and dried to obtain a double-crosslinked network structure PBO composite aerogel.

[0053] The present invention first puts an appropriate amount of PBO fiber into methanesulfonic acid / trifluoroacetic acid mixed acid, and obtains a PBO nanofiber dispersion after magnetic stirring; then benzoxazine and anhydrous sodium sulfate are added to the PBO nanofiber dispersion, and stirred by a high-speed homogenizer to obtain a polybenzoxazine / PBO nanocomposite acid sol, and the polybenzoxazine / PBO nanocomposite acid gel is obtained by standing at room temperature; the polybenzoxazine / PBO nanocomposite acid gel is then immersed in deionized water for solvent exchange to obtain a nanocomposite hydrogel, and freeze-dried to obtain a polybenzoxazine / PBO nanocomposite aerogel; finally, the polybenzoxazine / PBO nanocomposite aerogel is immersed in a fluorocarbon resin / fumed silica solution, and then taken out and dried to obtain a double-crosslinked network structure PBO composite aerogel, and a super-hydrophobic coating is deposited on the surface of the nanocomposite aerogel by regulating the ratio of fluorocarbon resin and fumed silica. The preparation method provided by the present invention is simple to operate, suitable for industrialized batch production, and the obtained nanocomposite aerogel is expected to be applied to some extreme environments.

[0054] The extreme environments described in this invention refer to environments with relatively high temperatures. For example, as an aerospace material, friction with the atmosphere during a reentry creates a high-temperature environment. The PBO fibers of this invention can thermally decompose to a temperature of 650°C, far exceeding the heat resistance of conventional polymer aerogels (300°C). Therefore, PBO composite aerogels have promising applications in the field of thermal insulation layers for spacecraft.

[0055] The present invention adds anhydrous sodium sulfate to a pre-prepared PBO nanofiber dispersion. The sulfate ions in the anhydrous sodium sulfate combine with the hydrogen ions in the PBO molecular chains, reducing the electrostatic repulsion between the PBO chains and enhancing their interaction, ultimately forming stable PBO nanofibers. The order in which the anhydrous sodium sulfate and benzoxazine are added to the PBO nanofiber dispersion does not affect the modification effect.

[0056] The present invention uses a methanesulfonic acid / trifluoroacetic acid mixed acid to prepare a PBO nanofiber dispersion. By adjusting the ratio of methanesulfonic acid and trifluoroacetic acid, the PBO molecular chains are better dispersed in the acid solution, so as to subsequently form PBO nanofibers.

[0057] A third technical solution of the present invention is the use of the above-mentioned double-crosslinked network structure PBO composite aerogel as a thermal insulation material.

[0058] Optionally, the double-crosslinked network structure PBO composite aerogel can be used in thermal insulation layers in the aerospace field or thermal insulation materials in the construction field.

[0059] The present invention discloses the following technical effects:

[0060] The double-crosslinked network structure PBO composite aerogel provided by the present invention has super hydrophobicity, excellent flame retardant properties, high mechanical properties and low thermal conductivity. Its compressive strength is 1.24-1.53 MPa, the contact angle with water is 142.1-152.3°, the combustion grade is UL94 V-0, and the thermal conductivity is 0.034-0.038 W / (m·K). It has broad application prospects in aerospace, electronic information, transportation, transportation, electronic and electrical fields, and 5G communications. BRIEF DESCRIPTION OF THE DRAWINGS

[0061] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the embodiments. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative work.

[0062] Figure 1 This is an infrared spectrum analysis diagram of benzoxazine, PBO nanofibers and polybenzoxazine / PBO nanocomposite aerogel in Experimental Example 2 of the present invention;

[0063] Figure 2 1 is an SEM image of the PBO composite aerogel and the double-crosslinked network structure PBO composite aerogel in Experimental Example 2 of the present invention;

[0064] Figure 3The contact angles of the polybenzoxazine / PBO nanocomposite aerogel and the double-crosslinked network structure PBO composite aerogel with water in Experimental Example 2 of the present invention;

[0065] Figure 4 Schematic diagram of the preparation of a double-crosslinked network structure PBO composite aerogel according to the present invention;

[0066] Figure 5 This is a reaction diagram of obtaining polybenzoxazine by acid catalysis using benzoxazine used in an embodiment of the present invention. DETAILED DESCRIPTION

[0067] Various exemplary embodiments of the present invention will now be described in detail. This detailed description should not be considered as limiting the present invention, but rather as a more detailed description of certain aspects, features, and embodiments of the present invention.

[0068] It should be understood that the terms described herein are intended only to describe particular embodiments and are not intended to limit the present invention. In addition, for numerical ranges herein, it should be understood that each intermediate value between the upper and lower limits of the range is also specifically disclosed. The intermediate value within any stated value or stated range, and each smaller range between any other stated value or intermediate value within the stated range, is also encompassed within the present invention. The upper and lower limits of these smaller ranges may be independently included or excluded within the scope.

[0069] Unless otherwise indicated, all technical and scientific terms used herein have the same meaning as commonly understood by those skilled in the art. Although only preferred methods and materials are described herein, any methods and materials similar or equivalent to those described herein may also be used in the practice or testing of the present invention. All documents mentioned in this specification are incorporated by reference to disclose and describe the methods and / or materials associated with the documents. In the event of any conflict with any incorporated document, the contents of this specification shall prevail.

[0070] It will be apparent to those skilled in the art that various modifications and variations may be made to the specific embodiments described herein without departing from the scope or spirit of the invention. Other embodiments will be apparent to those skilled in the art from the description of the invention. The description and examples are intended to be illustrative only.

[0071] The words “include,” “including,” “have,” “contain,” etc. used in this document are open-ended terms, meaning including but not limited to.

[0072] The present invention provides a double-crosslinked network structure PBO composite aerogel, the raw material components of which, in parts by mass, include:

[0073]

[0074] The raw materials for the double-crosslinked network structure PBO composite aerogel provided by the present invention preferably include 10 to 50 parts by weight of PBO fibers, preferably 20 to 50 parts, and most preferably 40 parts. In the present invention, the PBO fibers are preferably 10 to 20 cm in length and 10 to 15 μm in diameter. In the present invention, the PBO fibers are preferably commercially available.

[0075] The raw materials of the double-crosslinked network structure PBO composite aerogel provided by the present invention preferably include 100 to 300 parts by mass of methanesulfonic acid, preferably 100 to 200 parts, and most preferably 150 parts. In the present invention, the source of the methanesulfonic acid is preferably commercially available.

[0076] The raw materials of the double-crosslinked network structure PBO composite aerogel provided by the present invention preferably include 100 to 300 parts by mass of trifluoroacetic acid, preferably 100 to 200 parts, and most preferably 150 parts. In the present invention, the source of the trifluoroacetic acid is preferably commercially available.

[0077] The raw materials for the dual-crosslinked network PBO composite aerogel provided by the present invention preferably include 50-100 parts by weight of the PBO fibers, more preferably 70-100 parts, and most preferably 80 parts. In the present invention, the benzoxazine is preferably commercially available, with a purity of ≥95%. In the present invention, the benzoxazine spontaneously polymerizes and crosslinks within the PBO nanofiber network under the catalysis of trifluoroacetic acid and methanesulfonic acid, thereby forming a stable dual-network aerogel structure.

[0078] The raw materials for the double-crosslinked network PBO composite aerogel provided by the present invention preferably include 2 to 5 parts of anhydrous sodium sulfate, more preferably 3 to 5 parts, and most preferably 3 parts, based on the mass fraction of the PBO fibers. In the present invention, the anhydrous sodium sulfate is preferably commercially available and has a purity of ≥95%.

[0079] The raw materials for the double-crosslinked network PBO composite aerogel provided by the present invention preferably include 2 to 5 parts of anhydrous sodium sulfate, more preferably 3 to 5 parts, and most preferably 3 parts, based on the mass fraction of the PBO fibers. In the present invention, the anhydrous sodium sulfate is preferably commercially available and has a purity of ≥95%.

[0080] Based on the mass fraction of the PBO fibers, the raw materials for the double-crosslinked network structure PBO composite aerogel provided by the present invention preferably include 80 to 140 parts of fluorocarbon resin, more preferably 80 to 120 parts, and most preferably 80 parts. In the present invention, the source of the fluorocarbon resin is preferably commercially available.

[0081] Based on the mass fraction of the PBO fibers, the raw materials for the double-crosslinked network structure PBO composite aerogel provided by the present invention preferably include 1 to 4 parts of fumed silica, more preferably 1 to 3 parts, and most preferably 2 parts. In the present invention, the source of the fumed silica is preferably commercially available.

[0082] In the present invention, the fluorocarbon resin and silica have excellent hydrophobicity, and can impart super-hydrophobic properties to the nanocomposite aerogel by simple soaking and drying.

[0083] The present invention provides a method for preparing the above-mentioned double-crosslinked network structure PBO composite aerogel, comprising the following steps:

[0084] (1) An appropriate amount of PBO fibers was placed in a methanesulfonic acid / trifluoroacetic acid mixture and magnetically stirred to obtain a PBO nanofiber dispersion;

[0085] (2) adding benzoxazine and anhydrous sodium sulfate to the PBO nanofiber dispersion, stirring with a high-speed homogenizer to obtain a polybenzoxazine / PBO nanocomposite acid sol, and allowing to stand at room temperature to obtain a polybenzoxazine / PBO nanocomposite acid gel;

[0086] (3) soaking the polybenzoxazine / PBO nanocomposite acid gel in deionized water for solvent exchange to obtain a nanocomposite hydrogel, and freeze-drying to obtain a polybenzoxazine / PBO nanocomposite aerogel;

[0087] (4) The polybenzoxazine / PBO nanocomposite aerogel is immersed in a fluorocarbon resin / fumed silica solution, and then taken out and dried to obtain a double-crosslinked network structure PBO composite aerogel.

[0088] In the present invention, the solvent for the acid dispersion of PBO fibers is a mixed acid of methanesulfonic acid and trifluoroacetic acid. The mass concentration of the methanesulfonic acid is preferably ≥ 99%, and the mass concentration of the trifluoroacetic acid is preferably ≥ 99%. The mass ratio of methanesulfonic acid to trifluoroacetic acid in the mixed acid is preferably 1-2:0.5-1.5, more preferably 1:1. The magnetic stirring time is preferably 48-96 hours, more preferably 72 hours.

[0089] Methanesulfonic acid and trifluoroacetic acid are both strongly acidic solvents that provide a protonating environment, generating hydrogen bonding and charge interactions between electron-rich atoms such as nitrogen and oxygen in PBO molecules. Due to the high rigidity and strong π-π stacking interactions between PBO molecules, ordinary solvents are difficult to disperse. The strong acidic environment of methanesulfonic acid and trifluoroacetic acid helps to disrupt these interactions between PBO molecules.

[0090] In the present invention, the magnetic stirring rate is preferably 500-1000 rpm, more preferably 800 rpm. In the present invention, during the stirring and mixing process, the PBO fibers are dissolved in the mixed acid to form a stable PBO nanofiber dispersion.

[0091] In the present invention, in the PBO fiber dispersion, the mass ratio of the PBO fiber to the methanesulfonic acid / trifluoroacetic acid mixed acid is 10-50:100-300, more preferably 40:300.

[0092] In the present invention, the mass ratio of the added benzoxazine and anhydrous sodium sulfate is preferably 1-5:5-10, more preferably 4:8; the mass ratio of PBO fiber to anhydrous sodium sulfate is 10-50:2-5, preferably 40:3.

[0093] In the present invention, the high-speed homogenizing stirring time is preferably 20 to 60 minutes, more preferably 40 minutes; the rotation speed is 10,000 to 18,000 rpm, more preferably 15,000 rpm, so that the PBO nanofibers, benzoxazine and anhydrous sodium sulfate are uniformly mixed.

[0094] In the present invention, the room temperature standing time is preferably 10 to 30 hours, more preferably 24 hours.

[0095] In the present invention, the solvent exchange process between the mixed acid and distilled water removes excess acid from the PBO nanofiber acid gel, facilitating freeze-drying in the next step. Therefore, the number of solvent exchanges is determined by the solution reaching neutrality. The solvent exchange process preferably lasts 2 to 4 hours, more preferably 3 hours, and the number of solvent exchanges is preferably 6 to 10, more preferably 8.

[0096] In the present invention, the freeze-drying process is completed in a vacuum freeze dryer, and the temperature setting is preferably -80 to -60°C, more preferably -80°C; the equipment operation time is preferably 30 to 72 hours, more preferably 48 hours.

[0097] In the present invention, the mass ratio of fluorocarbon resin to fumed silica in the fluorocarbon resin / fumed silica solution is preferably 80-140:1-4, more preferably 80:2; the immersion time is preferably 5-30 minutes, more preferably 10 minutes.

[0098] The present invention introduces benzoxazine into a poly(p-phenylene benzobisoxazole) (PBO) nanofiber dispersion, and further prepares a dual-network polybenzoxazine / PBO nanocomposite aerogel via a sol-gel method. The benzoxazine / PBO nanocomposite aerogel is then immersed in a fluorocarbon resin / fumed silica solution, removed and air-dried to obtain a dual-crosslinked network PBO composite aerogel. The present invention utilizes trifluoroacetic acid and methanesulfonic acid as acid catalysts to promote the ring-opening polymerization of benzoxazine into polybenzoxazine, thereby forming an interpenetrating network structure with the PBO nanofibers to obtain a stable nanocomposite aerogel. By adjusting the ratio of fluorocarbon resin to fumed silica, a superhydrophobic coating is deposited on the surface of the nanocomposite aerogel, resulting in superhydrophobic properties.

[0099] The following is a detailed description of a double-crosslinked network structure PBO composite aerogel and its preparation method provided by the present invention in conjunction with the examples. However, they should not be construed as limiting the scope of protection of the present invention.

[0100] The embodiment of the present invention does not limit the amount and quality of the materials, as long as the required raw materials are added according to the mass fraction.

[0101] The structural formula of the benzoxazine used in the embodiment of the present invention is as follows. The reaction process of obtaining polybenzoxazine by acid catalysis of the benzoxazine is as follows: Figure 5 As shown:

[0102]

[0103] Other diamine / phenol-type benzoxazines (such as the following structural formula) can also be used to prepare the double-crosslinked network structure PBO composite aerogel of the present invention without affecting the final technical effect.

[0104]

[0105] The room temperature condition in the embodiments of the present invention is: 20-25°C.

[0106] The fluorocarbon resin used in the embodiment of the present invention is specifically a fluorinated liquid produced by Shenzhen Zhongfu Technology Co., Ltd., model number Fluere 1706.

[0107] Example 1

[0108] 30 parts by weight of PBO fibers were placed in 300 parts by weight of a 1:1 methanesulfonic acid / trifluoroacetic acid mixture and magnetically stirred for 72 hours to dissolve the PBO fibers in the acid mixture, resulting in a stable PBO nanofiber dispersion. Both methanesulfonic acid and trifluoroacetic acid are strongly acidic solvents that provide a protonating environment, generating hydrogen bonding and charge interactions with electron-rich atoms such as nitrogen and oxygen in the PBO molecules. Due to the high rigidity and strong π-π stacking interactions between PBO molecules, ordinary solvents are difficult to disperse. The strong acidic environment of methanesulfonic acid and trifluoroacetic acid helps disrupt these interactions.

[0109] 3 parts by weight of anhydrous sodium sulfate and 90 parts by weight of benzoxazine were added to the PBO nanofiber dispersion and stirred in a high-speed homogenizer (15,000 rpm) for 40 minutes to produce a polybenzoxazine / PBO nanocomposite acid sol. The polybenzoxazine / PBO nanocomposite acid sol was then poured into a beaker and allowed to stand at room temperature for 24 hours to produce a polybenzoxazine / PBO nanocomposite acid gel.

[0110] The acid gel was then immersed in deionized water for solvent exchange to obtain a polybenzoxazine / PBO nanocomposite hydrogel. The solvent exchange time was 3 hours and the number of solvent exchanges was 8.

[0111] Then, the polybenzoxazine / PBO nanocomposite hydrogel was freeze-dried to obtain the polybenzoxazine / PBO nanocomposite aerogel, and the freeze-drying temperature was set to -80°C, and the freeze-drying time was set to 48 hours.

[0112] Subsequently, 80 parts by weight of fluorocarbon resin and 2 parts by weight of fumed silica were prepared into a mixed solution, and the polybenzoxazine / PBO nanocomposite aerogel was immersed in the above solution for 10 minutes, and then taken out and dried to obtain a double-crosslinked network structure PBO composite aerogel.

[0113] Example 2

[0114] 40 parts by weight of PBO fibers were placed in 300 parts by weight of a 0.5:1.3 methanesulfonic acid / trifluoroacetic acid mixture and magnetically stirred for 96 hours to obtain a PBO nanofiber dispersion. Both methanesulfonic acid and trifluoroacetic acid are strongly acidic solvents, providing a protonating environment that promotes hydrogen bonding and charge interactions between electron-rich atoms such as nitrogen and oxygen in the PBO molecules. Due to the high rigidity and strong intermolecular π-π stacking interactions of PBO, ordinary solvents are difficult to disperse. The strong acidic environment of methanesulfonic acid and trifluoroacetic acid helps disrupt these interactions.

[0115] 4 parts by weight of anhydrous sodium sulfate and 80 parts by weight of benzoxazine were added to a poly(benzoxazine) boron phosphate (PBO) nanofiber dispersion and stirred for 30 minutes in a high-speed homogenizer (12,000 rpm) to obtain a poly(benzoxazine) / PBO nanocomposite acid sol. The poly(benzoxazine) / PBO nanocomposite acid sol was then poured into a beaker and allowed to stand at room temperature for 15 hours to obtain a poly(benzoxazine) / PBO nanocomposite acid gel. The acid gel was then immersed in deionized water and solvent exchanged six times for two hours to obtain a poly(benzoxazine) / PBO nanocomposite hydrogel.

[0116] The polybenzoxazine / PBO nanocomposite hydrogel was then freeze-dried at -60°C for 30 hours to obtain a polybenzoxazine / PBO nanocomposite aerogel. Subsequently, the polybenzoxazine / PBO nanocomposite aerogel was immersed in a mixed solution of 140 parts by weight of fluorocarbon resin and 1 part by weight of fumed silica for 5 minutes before being removed and air-dried to obtain a PBO composite aerogel with a double-crosslinked network structure.

[0117] Example 3

[0118] 20 parts by weight of PBO fibers were placed in 200 parts by weight of a 1.8:1.2 methanesulfonic acid / trifluoroacetic acid mixture and magnetically stirred for 96 hours to obtain a PBO nanofiber dispersion. Both methanesulfonic acid and trifluoroacetic acid are strongly acidic solvents, providing a protonating environment that generates hydrogen bonding and charge interactions with electron-rich atoms such as nitrogen and oxygen in the PBO molecules. Due to the high rigidity and strong intermolecular π-π stacking interactions of PBO, ordinary solvents are difficult to disperse. The strong acidic environment of methanesulfonic acid and trifluoroacetic acid helps disrupt these interactions.

[0119] 5 parts by weight of anhydrous sodium sulfate and 80 parts by weight of benzoxazine were added to a poly(benzoxazine boron phosphate) nanofiber dispersion and stirred for 50 minutes in a high-speed homogenizer (18,000 rpm) to obtain a poly(benzoxazine boron phosphate) nanocomposite acid sol. The poly(benzoxazine boron phosphate) nanocomposite acid sol was then poured into a beaker and allowed to stand at room temperature for 30 hours to obtain a poly(benzoxazine boron phosphate) nanocomposite acid gel. The acid gel was then immersed in deionized water and solvent exchanged 10 times for 4 hours to obtain a poly(benzoxazine boron phosphate) nanocomposite hydrogel.

[0120] The polybenzoxazine / PBO nanocomposite hydrogel was then freeze-dried at -80°C for 72 hours to produce a polybenzoxazine / PBO nanocomposite aerogel. Subsequently, the polybenzoxazine / PBO nanocomposite aerogel was immersed in a mixed solution of 80 parts by weight of fluorocarbon resin and 4 parts by weight of fumed silica for 30 minutes before being removed and air-dried to produce a PBO composite aerogel with a dual-crosslinked network structure.

[0121] Examples 4-6

[0122] Same as Example 1, except that the raw material ratios are different, as shown in Table 1.

[0123] Table 1

[0124] Example 4 Example 5 Example 6 PBO fiber 50 servings 30 servings 40 servings Methanesulfonic acid 300 copies 100 copies 200 copies Trifluoroacetic acid 100 copies 300 copies 200 copies Benzoxazine 50 servings 80 servings 70 servings Anhydrous sodium sulfate 3 servings 4 servings 5 servings Fluorocarbon resin 130 copies 120 servings 80 servings Fumed silica 1 serving 4 servings 2 servings

[0125] Comparative Example 1

[0126] A PBO composite aerogel was prepared according to the method of Example 1, except that anhydrous sodium sulfate and benzoxazine were not added, as follows:

[0127] 30 parts by weight of PBO fibers were added to 300 parts by weight of a 1:1 methanesulfonic acid / trifluoroacetic acid mixture. The mixture was magnetically stirred for 72 hours to obtain a PBO nanofiber dispersion. This dispersion was then stirred in a high-speed homogenizer (15,000 rpm) for 40 minutes to obtain a PBO nanocomposite acid sol. The PBO nanocomposite acid sol was then poured into a beaker and allowed to stand at room temperature for 24 hours to obtain a PBO nanocomposite acid gel. The acid gel was then immersed in deionized water and solvent exchanged eight times over three hours to obtain a PBO nanocomposite hydrogel.

[0128] The PBO nanocomposite hydrogel was then freeze-dried at -80°C for 48 hours to obtain a PBO nanocomposite aerogel. Subsequently, a mixed solution of 80 parts by weight of fluorocarbon resin and 2 parts by weight of fumed silica was prepared. The PBO nanocomposite aerogel was immersed in the solution for 10 minutes and then air-dried to obtain the PBO composite aerogel.

[0129] Comparative Example 2

[0130] Polybenzoxazine / PBO nanocomposite aerogel was prepared according to the method of Example 1, except that fluorocarbon resin and fumed silica were not added, as follows:

[0131] 30 parts by weight of PBO fibers were added to 300 parts by weight of a 1:1 methanesulfonic acid / trifluoroacetic acid mixed acid, and magnetically stirred for 72 hours to obtain a PBO nanofiber dispersion.

[0132] 3 parts by weight of anhydrous sodium sulfate and 90 parts by weight of benzoxazine were added to a poly(benzoxazine) boron phosphate (PBO) nanofiber dispersion and stirred for 40 minutes in a high-speed homogenizer (15,000 rpm) to produce a poly(benzoxazine) / PBO nanocomposite acid sol. The poly(benzoxazine) / PBO nanocomposite acid sol was then poured into a beaker and allowed to stand at room temperature for 24 hours to produce a poly(benzoxazine) / PBO nanocomposite acid gel. The acid gel was then immersed in deionized water and solvent exchanged eight times for three hours to produce a poly(benzoxazine) / PBO nanocomposite hydrogel.

[0133] Then, the polybenzoxazine / PBO nanocomposite hydrogel was freeze-dried to obtain the polybenzoxazine / PBO nanocomposite aerogel, and the freeze-drying temperature was set to -80°C, and the freeze-drying time was set to 48 hours.

[0134] Comparative Example 3

[0135] A double-crosslinked network structure PBO composite aerogel was prepared according to the method of Example 1, except that anhydrous sodium sulfate was not added, as follows:

[0136] 30 parts by weight of PBO fibers were added to 300 parts by weight of a 1:1 methanesulfonic acid / trifluoroacetic acid mixed acid, and magnetically stirred for 72 hours to obtain a PBO nanofiber dispersion.

[0137] 90 parts by weight of benzoxazine was added to the PBO nanofiber dispersion and stirred for 40 minutes using a high-speed homogenizer (15,000 rpm) to produce a polybenzoxazine / PBO nanocomposite acid sol. The polybenzoxazine / PBO nanocomposite acid sol was then poured into a beaker and allowed to stand at room temperature for 24 hours to produce a polybenzoxazine / PBO nanocomposite acid gel.

[0138] The acid gel was then immersed in deionized water for solvent exchange to obtain a polybenzoxazine / PBO nanocomposite hydrogel. The solvent exchange time was 3 hours and the number of solvent exchanges was 8.

[0139] Then, the polybenzoxazine / PBO nanocomposite hydrogel was freeze-dried to obtain the polybenzoxazine / PBO nanocomposite aerogel, and the freeze-drying temperature was set to -80°C, and the freeze-drying time was set to 48 hours.

[0140] Subsequently, 80 parts by weight of fluorocarbon resin and 2 parts by weight of fumed silica were prepared into a mixed solution, and the polybenzoxazine / PBO nanocomposite aerogel was immersed in the above solution for 10 minutes, and then taken out and dried to obtain a double-crosslinked network structure PBO composite aerogel.

[0141] Comparative Example 4

[0142] A double-crosslinked network structure PBO composite aerogel was prepared according to the method of Example 1, except that fumed silica was not added and 82 parts of fluorocarbon resin were used; the details are as follows:

[0143] 30 parts by weight of PBO fibers were added to 300 parts by weight of a 1:1 methanesulfonic acid / trifluoroacetic acid mixed acid, and magnetically stirred for 72 hours to obtain a PBO nanofiber dispersion.

[0144] 3 parts by weight of anhydrous sodium sulfate and 90 parts by weight of benzoxazine were added to the PBO nanofiber dispersion and stirred in a high-speed homogenizer (15,000 rpm) for 40 minutes to produce a polybenzoxazine / PBO nanocomposite acid sol. The polybenzoxazine / PBO nanocomposite acid sol was then poured into a beaker and allowed to stand at room temperature for 24 hours to produce a polybenzoxazine / PBO nanocomposite acid gel.

[0145] The acid gel was then immersed in deionized water for solvent exchange to obtain a polybenzoxazine / PBO nanocomposite hydrogel. The solvent exchange time was 3 hours and the number of solvent exchanges was 8.

[0146] Then, the polybenzoxazine / PBO nanocomposite hydrogel was freeze-dried to obtain the polybenzoxazine / PBO nanocomposite aerogel, and the freeze-drying temperature was set to -80°C, and the freeze-drying time was set to 48 hours.

[0147] Subsequently, 82 parts by weight of fluorocarbon resin was prepared into a mixed solution, and the polybenzoxazine / PBO nanocomposite aerogel was immersed in the solution for 10 minutes, and then taken out and dried to obtain a double-crosslinked network structure PBO composite aerogel.

[0148] Comparative Example 5

[0149] A double-crosslinked network structure PBO composite aerogel was prepared according to the method of Example 1, except that trifluoroacetic acid was used instead of the methanesulfonic acid / trifluoroacetic acid mixed acid, that is, only trifluoroacetic acid was used as the acid catalyst; the details are as follows:

[0150] 30 parts by weight of PBO fibers were added to 300 parts by weight of trifluoroacetic acid and magnetically stirred for 72 hours to obtain a PBO nanofiber dispersion.

[0151] 3 parts by weight of anhydrous sodium sulfate and 90 parts by weight of benzoxazine were added to the PBO nanofiber dispersion and stirred in a high-speed homogenizer (15,000 rpm) for 40 minutes to produce a polybenzoxazine / PBO nanocomposite acid sol. The polybenzoxazine / PBO nanocomposite acid sol was then poured into a beaker and allowed to stand at room temperature for 24 hours to produce a polybenzoxazine / PBO nanocomposite acid gel.

[0152] The acid gel was then immersed in deionized water for solvent exchange to obtain a polybenzoxazine / PBO nanocomposite hydrogel. The solvent exchange time was 3 hours and the number of solvent exchanges was 8.

[0153] Then, the polybenzoxazine / PBO nanocomposite hydrogel was freeze-dried to obtain the polybenzoxazine / PBO nanocomposite aerogel, and the freeze-drying temperature was set to -80°C, and the freeze-drying time was set to 48 hours.

[0154] Subsequently, 80 parts by weight of fluorocarbon resin and 2 parts by weight of fumed silica were prepared into a mixed solution, and the polybenzoxazine / PBO nanocomposite aerogel was immersed in the above solution for 10 minutes, and then taken out and dried to obtain a double-crosslinked network structure PBO composite aerogel.

[0155] Comparative Example 6

[0156] A double-crosslinked network structure PBO composite aerogel was prepared according to the method of Example 1, except that methanesulfonic acid was used instead of the methanesulfonic acid / trifluoroacetic acid mixed acid, that is, only methanesulfonic acid was used as the acid catalyst; the details are as follows:

[0157] 30 parts by weight of PBO fibers were added to 300 parts by weight of methanesulfonic acid and magnetically stirred for 72 hours to obtain a PBO nanofiber dispersion.

[0158] 3 parts by weight of anhydrous sodium sulfate and 90 parts by weight of benzoxazine were added to the PBO nanofiber dispersion and stirred in a high-speed homogenizer (15,000 rpm) for 40 minutes to produce a polybenzoxazine / PBO nanocomposite acid sol. The polybenzoxazine / PBO nanocomposite acid sol was then poured into a beaker and allowed to stand at room temperature for 24 hours to produce a polybenzoxazine / PBO nanocomposite acid gel.

[0159] The acid gel was then immersed in deionized water for solvent exchange to obtain a polybenzoxazine / PBO nanocomposite hydrogel. The solvent exchange time was 3 hours and the number of solvent exchanges was 8.

[0160] Then, the polybenzoxazine / PBO nanocomposite hydrogel was freeze-dried to obtain the polybenzoxazine / PBO nanocomposite aerogel, and the freeze-drying temperature was set to -80°C, and the freeze-drying time was set to 48 hours.

[0161] Subsequently, 80 parts by weight of fluorocarbon resin and 2 parts by weight of fumed silica were prepared into a mixed solution, and the polybenzoxazine / PBO nanocomposite aerogel was immersed in the above solution for 10 minutes, and then taken out and dried to obtain a double-crosslinked network structure PBO composite aerogel.

[0162] Comparative Example 7

[0163] A PBO composite aerogel was prepared according to the method of Example 1, except that silicon dioxide was used instead of benzoxazine; the details are as follows:

[0164] 30 parts by weight of PBO fibers were added to 300 parts by weight of a methanesulfonic acid / trifluoroacetic acid mixed acid (mass ratio of 1:1), and the mixture was magnetically stirred for 72 hours to obtain a PBO nanofiber dispersion.

[0165] 3 parts by weight of anhydrous sodium sulfate and 90 parts by weight of silica were added to a PBO nanofiber dispersion and stirred for 40 minutes using a high-speed homogenizer (15,000 rpm) to produce a silica / PBO nanocomposite acid sol. The silica / PBO nanocomposite acid sol was then poured into a beaker and allowed to stand at room temperature for 24 hours to produce a silica / PBO nanocomposite acid gel.

[0166] The acid gel was then immersed in deionized water for solvent exchange to obtain silica / PBO nanocomposite hydrogel. The solvent exchange time was 3 hours and the number of solvent exchanges was 8.

[0167] Then, the silica / PBO nanocomposite hydrogel was freeze-dried to obtain silica / PBO nanocomposite aerogel, and the freeze-drying temperature was set to -80°C, and the freeze-drying time was set to 48 hours.

[0168] Subsequently, 80 parts by weight of fluorocarbon resin and 2 parts by weight of fumed silica were prepared into a mixed solution, and the silica / PBO nanocomposite aerogel was immersed in the solution for 10 minutes, and then taken out and dried to obtain the PBO composite aerogel.

[0169] Test Example 1

[0170] The products prepared in the above examples and comparative examples were subjected to performance tests, and the test results are listed in Table 2. The test method is as follows:

[0171] (1) Compression strength: The compressive strength of the specimens was tested using a mechanical testing machine in accordance with ISO 844:2014. If the total strain was greater than 10%, the stress at 10% deformation was taken as the yield stress (compressive strength); if the total strain was less than 10%, the maximum yield stress was taken.

[0172] (2) Flame retardant test: Vertical burning test (UL94) was carried out on FTT0082 instrument in accordance with GB / T 8333-2008.

[0173] (3) Contact angle test: According to ASTM D5725, the contact angle between aerogel and water was recorded using a contact angle meter (JY-82B Kruss DSA, Germany).

[0174] (4) Density: The density of the aerogel is calculated by processing the sample into a standard cylinder and calculating the volume and mass.

[0175] (5) Thermal conductivity: The thermal conductivity of aerogel is tested by a Hot disk thermal conductivity tester.

[0176] (6) Porosity: The porosity (P) of aerogel is calculated by the mass volume method. The calculation formula is:

[0177]

[0178] Where P is the porosity of the sample; ρ is the density of anhydrous ethanol; V is the volume of the aerogel; W1 is the mass of the aerogel; and W2 is the mass of the aerogel and anhydrous ethanol.

[0179] Table 2

[0180]

[0181] As can be seen from the performance data in Table 2, the present invention effectively improves the mechanical properties of the PBO composite aerogel by introducing benzoxazine and PBO nanofibers to form a double-crosslinked network structure; and effectively improves the hydrophobicity of the PBO composite aerogel by introducing fluorocarbon resin and fumed silica. As can be seen from the comparative examples, the PBO composite aerogel without the addition of benzoxazine or fluorocarbon resin / fumed silica has low mechanical strength or hydrophobicity, which is difficult to meet the requirements of practical engineering applications. In addition, the aerogel with a double-crosslinked network structure has a lower density and thermal conductivity and a higher porosity. Compared with the examples, if trifluoroacetic acid or methanesulfonic acid is used alone as an acid solvent, its dispersion effect on PBO nanowires is not good, and its mechanical properties, density, thermal conductivity and porosity are still somewhat lower than those of the examples. In general, the double-crosslinked network structure PBO composite aerogel prepared by the present invention has broad application prospects in the fields of aerospace, transportation, and electronics.

[0182] Test Example 2

[0183] (1) The benzoxazine, PBO nanofibers and polybenzoxazine / PBO nanocomposite aerogel (benzoxazine / PBO nanofibers) in Example 1 were subjected to infrared spectroscopy analysis. Figure 1 . Figure 1 It is shown that for benzoxazine, due to the asymmetric stretching vibration of the tertiary amine, the -1 The characteristic absorption peak of benzene and o-oxazine ring is at 939cm -1 For PBO nanofibers, 1620, 1500, and 3058 cm -1The bands near the spectral peaks correspond to the stretching vibration peaks of C=C, CC and CH of the benzene ring. In addition, the vibration peak of the oxazole ring appears at 1628 cm -1 (C=N) and 1050cm -1 After the introduction of benzoxazine into PBO nanofibers, in addition to the basic characteristic peaks of PNF and BOZ, the peak at 3400 cm -1 A new characteristic peak appeared near the oxazine ring, while the characteristic peak of the oxazine ring disappeared. This is mainly due to the opening of the oxazine ring to form -OH, proving that the ring-opening polymerization of benzoxazine and PBO nanofibers formed a double network structure.

[0184] (2) The PBO composite aerogel of Comparative Example 1 and the double cross-linked network structure PBO composite aerogel of Example 1 were subjected to SEM analysis. The results are shown in FIG. Figure 2 . Figure 2 The results show that the PBO composite aerogel and the dual-crosslinked network PBO composite aerogel exhibit mesoporous structures. The dual-crosslinked network PBO composite aerogel has a uniform porous structure, with well-dispersed polybenzoxazine / PBO nanofibers interlocking like a web, forming a dual-crosslinked network structure. In contrast, the PBO composite aerogel without benzoxazine exhibits localized nanofiber aggregation due to a certain degree of shrinkage.

[0185] (3) Contact angle analysis was performed on the benzoxazine / PBO nanocomposite aerogel of Comparative Example 2 (left) and the double-crosslinked network structure PBO composite aerogel of Example 1 (right). Figure 3 . Figure 3 It is shown that compared with the PBO composite aerogel without adding fluorocarbon resin and fumed silica, the PBO composite aerogel with a double cross-linked network structure introducing fluorocarbon resin and fumed silica has excellent hydrophobicity, with a contact angle with water as high as 152.3°.

[0186] Figure 4 Schematic diagram of the preparation of double cross-linked network structure PBO composite aerogel in the present invention ( Figure 4 In the embodiment of the present invention, the polybenzoxazine / PBO nanoacid gel and the polybenzoxazine / PBO nanocomposite acid gel described in Example 1 have the same meaning, and the polybenzoxazine / PBO aerogel and the polybenzoxazine / PBO nanocomposite aerogel described in Example 1 have the same meaning).

[0187] Figure 5 The present invention provides a route for the polymerization of benzoxazines into polybenzoxazines.

[0188] The embodiments described above are merely descriptions of preferred embodiments of the present invention and are not intended to limit the scope of the present invention. Without departing from the spirit of the present invention, various modifications and improvements made to the technical solutions of the present invention by persons skilled in the art should fall within the scope of protection defined by the claims of the present invention.

Claims

1. A double-crosslinked network structure PBO composite aerogel, characterized in that: The double-crosslinked network structure PBO composite aerogel comprises: a nanocomposite aerogel with a double-crosslinked network structure constructed of polybenzoxazine and PBO nanofibers, and a hydrophobic coating deposited on the surface of the nanocomposite aerogel; the hydrophobic coating comprises a fluorocarbon resin and fumed silica; The raw materials of the double-crosslinked network structure PBO composite aerogel include, by weight, 10 to 50 parts of PBO fibers, 100 to 300 parts of methanesulfonic acid, 100 to 300 parts of trifluoroacetic acid, 50 to 100 parts of benzoxazine, 2 to 5 parts of anhydrous sodium sulfate, 80 to 140 parts of fluorocarbon resin, and 1 to 4 parts of fumed silica.

2. The double-crosslinked network structure PBO composite aerogel according to claim 1, characterized in that: The mass fraction of the PBO fiber is 20 to 50 parts; and / or, The PBO fiber has a length of 10 to 20 cm and a diameter of 10 to 15 μm; and / or The mass fraction of the methanesulfonic acid is 100 to 200 parts; and / or, The mass fraction of the trifluoroacetic acid is 100 to 200 parts; and / or, The mass fraction of the benzoxazine is 70 to 100 parts; and / or, The purity of the benzoxazine is ≥95%; and / or, The mass fraction of the anhydrous sodium sulfate is 3 to 5 parts; and / or, The purity of the anhydrous sodium sulfate is ≥95%; and / or, The mass fraction of the fluorocarbon resin is 80 to 120 parts; and / or, The mass fraction of the fumed silica is 1 to 3 parts.

3. A method for preparing a double-crosslinked network structure PBO composite aerogel according to any one of claims 1-2, characterized in that: The following steps are involved: The nano composite aerogel is immersed in a mixed solution of fluorocarbon resin and fumed silica to obtain the double-crosslinked network structure PBO composite aerogel.

4. The method for preparing a double-crosslinked network structure PBO composite aerogel according to claim 3, characterized in that: The preparation method of the nanocomposite aerogel comprises the following steps: The PBO fibers are dispersed in a mixed acid solution consisting of methanesulfonic acid and trifluoroacetic acid to obtain a PBO nanofiber dispersion. adding benzoxazine and anhydrous sodium sulfate to the PBO nanofiber dispersion to prepare a polybenzoxazine / PBO nanocomposite acid sol; The polybenzoxazine / PBO nanocomposite acid gel is subjected to solvent exchange in a solvent and then freeze-dried to obtain the nanocomposite aerogel.

5. The method for preparing a double-crosslinked network structure PBO composite aerogel according to claim 4, characterized in that: The step of adding benzoxazine and anhydrous sodium sulfate to the PBO nanofiber dispersion to prepare the polybenzoxazine / PBO nanocomposite acid sol specifically comprises: adding benzoxazine and anhydrous sodium sulfate to the PBO nanofiber dispersion, stirring at a high speed, and allowing the mixture to stand to obtain the polybenzoxazine / PBO nanocomposite acid sol; The high-speed stirring speed is 10,000 to 18,000 rpm and the stirring time is 20 to 60 minutes; and / or, The standing still step is standing still at 20-25° C. for 10-30 hours.

6. The method for preparing a double-crosslinked network structure PBO composite aerogel according to claim 4, characterized in that: The solvent used in the solvent exchange is deionized water; and / or, The solvent exchange time is 2 to 4 hours; and / or, The number of solvent exchanges is 6 to 10 times; and / or, The freeze-drying temperature is -80 to -60°C; and / or, The freeze-drying time is 30 to 72 hours.

7. The method for preparing a double-crosslinked network structure PBO composite aerogel according to claim 4, characterized in that: The dispersion is achieved by stirring, the stirring speed is 500 to 1000 rpm, and the stirring time is 48 to 96 hours; and / or, In the mixed acid solution, the mass ratio of methanesulfonic acid to trifluoroacetic acid is 1-2:0.5-1.5; and / or, The mass ratio of the PBO fiber to the mixed acid solution is 10-50:100-300; and / or, The mass ratio of the PBO fiber to benzoxazine is 1-5:5-10; and / or, The mass ratio of the PBO fiber to anhydrous sodium sulfate is 10-50:2-5.

8. The method for preparing a double-crosslinked network structure PBO composite aerogel according to claim 3, characterized in that: The mass ratio of the fluorocarbon resin to the fumed silica is 80-140:1-4; and / or, The soaking time is 5 to 30 minutes.

9. Use of the double-crosslinked network structure PBO composite aerogel according to any one of claims 1 to 2 as a thermal insulation material.

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