Silicon modified polybenzoxazole fiber aerogel and preparation method thereof

Abstract

The invention discloses silicon modified polybenzoxazole fiber aerogel and a preparation method thereof.Gas-phase silicon oxide is introduced into the polybenzoxazole fiber aerogel, the particle size of the gas-phase silicon oxide ranges from 7 nm to 20 nm, a formed three-dimensional network framework structure has low solid heat conductivity, and the characteristic of low heat conductivity of an aerogel material is guaranteed; the gas-phase silicon oxide can effectively isolate the contact between the material and external oxygen, effectively prevent external high-temperature heat from being transferred into the material, prevent the material from being further decomposed or combusted, and enable the material to have excellent flame retardant property.

Description

Technical Field

[0001] The invention belongs to the technical field of heat-insulating flame-retardant materials, and specifically relates to a silicon-modified polybenzoxazole fiber aerogel and a preparation method thereof. Background Art

[0002] With the rapid development of advanced aerospace vehicles, their thermal protection systems have an urgent need and higher standards for lightweight, low thermal conductivity, high-performance thermal insulation materials. Polybenzoxazole fiber is a high-performance fiber material with excellent thermal oxidation stability, hydrolysis resistance and solvent resistance. It has attracted attention for its ultra-high strength and modulus, excellent heat resistance and flame retardancy, and has important application value in aerospace and other fields. However, as a fiber material, polybenzoxazole fiber has a relatively high density (1.54g / cm 3 -1.56g / cm 3 ) and large thermal conductivity (60W / (m·K)), making it difficult to achieve lightweight and efficient thermal insulation performance.

[0003] Aerogel materials are porous materials with three-dimensional nanostructures composed of nanoparticles or polymer molecular chains. They have structural characteristics such as low density, high porosity, high pore volume and high specific surface area. They are currently the solid materials with the best thermal insulation performance. Therefore, preparing polybenzoxazole fibers into three-dimensional nanoporous polybenzoxazole aerogel materials through the sol-gel process is one of the research hotspots for obtaining high-performance thermal insulation materials.

[0004] Chinese patent publication number CN 106221216 A provides a polybenzoxazole nanofiber high-strength heat-insulating and fire-resistant aerogel and a preparation method thereof. The diameter of the prepared aerogel nanofiber is 10nm-50nm and the density is 0.02g / cm 3 -0.05g / cm 3 , with a specific surface area of ​​200m 2 / g-400m 2 / g, porosity is 95%-99%, but the patent does not report the thermal conductivity of the material, so the parameters of thermal insulation performance cannot be obtained. Chinese Patent Publication No. CN 116218023 A discloses a thermal insulation polybenzoxazole aerogel and its preparation method and use, with a pore size distribution of 20nm-80nm and a specific surface area of ​​60m 2 / g-190m 2 / g, porosity of 83%-92%, thermal conductivity of 0.030W / (m·K)-0.039W / (m·K), the patent obtained a polybenzoxazole aerogel with relatively low thermal conductivity, but its thermal insulation performance needs to be further improved, and no flame retardant performance characteristics were reported. Zhenchao Qian et al. (J. Mater. Chem. A, 2018, 6, 20769) reported a flame retardant, ultra-light, specific elastic and thermal insulation silicon-containing polybenzoxazole aerogel with excellent density of 0.0036g / cm 3 -0.0157g / cm 3 , thermal conductivity is 0.0262W / (m·K)-0.0377W / (m·K), and the limiting oxygen index (LOI) is as high as 52.8%; however, this material is prepared by adopting a complex sol preparation process and electrospinning method, which makes it difficult to achieve large-scale use and industrial production.

[0005] Therefore, how to use a relatively simple preparation process to synthesize polybenzoxazole fiber aerogel with low thermal conductivity and high-efficiency thermal insulation performance, further improve its flame retardant properties, and successfully obtain polybenzoxazole fiber aerogel with excellent flame retardant and thermal insulation effects has always been a technical problem that researchers in this field need to focus on and overcome. Summary of the invention

[0006] In view of the technical problems in the prior art that polybenzoxazole fiber aerogel has relatively high thermal conductivity, poor flame retardancy, and complex process when improving flame retardancy and thermal insulation performance, the present invention provides a silicon-modified polybenzoxazole fiber aerogel and a preparation method thereof.

[0007] The technical solution of the present invention is as follows: The silicon-modified polybenzoxazole fiber aerogel of the present invention is prepared by dissolving polybenzoxazole nanofibers as initial raw materials in an acidic substance, adding fumed silicon oxide powder for stirring and dispersion to obtain silicon-modified polybenzoxazole fiber sol, and placing the sol in a water bath to obtain an initial gel. The silicon-modified polybenzoxazole fiber aerogel is obtained by aging, solvent replacement and normal pressure drying.

[0008] The purpose of the present invention is achieved through the following technical solutions: A method for preparing a silicon-modified polybenzoxazole fiber aerogel comprises the following steps: S1, dissolving polybenzoxazole nanofibers in an acidic substance at a mass ratio of (1-10):100, stirring at room temperature for 10 min-15 min to fully dissolve and evenly disperse the polybenzoxazole nanofibers to obtain a polybenzoxazole nanofiber solution; The diameter of the polybenzoxazole nanofibers is 16nm-22nm; The acidic substance is one of methanesulfonic acid, polyphosphoric acid, trifluoroacetic acid and chlorosulfonic acid, or a mixture of any two thereof; S2, adding fumed silicon oxide to the polybenzoxazole nanofiber solution obtained in step S1, wherein the mass ratio of fumed silicon oxide to polybenzoxazole nanofiber is 1:(2-5); stirring at room temperature for 10 min-15 min to mix evenly, to obtain a silicon-modified polybenzoxazole fiber sol; The particle size of the fumed silicon oxide is 7nm-20nm; S3, sealing the silicon-modified polybenzoxazole fiber sol obtained in step S2 and placing it in a water bath, with a gel temperature of 50° C.-70° C., to gel the silicon-modified polybenzoxazole fiber sol, with a gel time of 10 h-48 h, to obtain an initial gel of silicon-modified polybenzoxazole fiber; S4, aging the initial state gel of the silicon-modified polybenzoxazole fiber obtained in step S3 at 40° C.-60° C. for 24 h-48 h to obtain an aged state gel of the silicon-modified polybenzoxazole fiber; S5, performing solvent replacement on the aged silicon-modified polybenzoxazole fiber gel obtained in step S4 at room temperature to obtain a final silicon-modified polybenzoxazole fiber gel; The solvent replacement adopts ethanol, isopropanol or tert-butanol as the replacement solvent, the number of solvent replacement is 3 to 5 times, and the time of each replacement is 8h to 12h; S6, drying the final state gel of the silicon-modified polybenzoxazole fiber prepared in step S5 at room temperature and normal pressure until the mass of the gel no longer changes, thereby obtaining a silicon-modified polybenzoxazole fiber aerogel, wherein the silicon-modified polybenzoxazole fiber aerogel exhibits a three-dimensional interconnected nanoporous network structure and has a density of 0.086 g / cm 3 -0.339g / cm 3 , thermal conductivity is 0.0196W / (m·K)-0.0379W / (m·K), and limiting oxygen index (LOI) is 48.2%-59.6%.

[0009] Furthermore, the acidic substance in step S1 is preferably methanesulfonic acid or polyphosphoric acid; the mass ratio of the polybenzoxazole nanofibers to the acidic substance is preferably 4:100; Furthermore, the mass ratio of the fumed silicon oxide to the polybenzoxazole nanofibers in step S2 is preferably 1:3; Furthermore, the gel temperature in step S3 is preferably 55°C; Furthermore, the aging temperature in step S4 is preferably 50°C; Furthermore, in the solvent replacement in step S5, the replacement solvent used is preferably ethanol, the number of solvent replacements is preferably 4 times, and the time for each replacement is preferably 10 hours; Furthermore, the normal pressure in step S6 is a standard atmospheric pressure.

[0010] The present invention also relates to a silicon-modified polybenzoxazole fiber aerogel, which is obtained by the above-mentioned preparation method of silicon-modified polybenzoxazole fiber aerogel. The silicon-modified polybenzoxazole fiber aerogel presents a three-dimensional interconnected nanoporous network structure with a density of 0.086 g / cm 3 -0.339g / cm 3 The thermal conductivity is 0.0196W / (m·K)-0.0379W / (m·K), and the limiting oxygen index (LOI) is 48.2%-59.6%. It has the characteristics of low density, low thermal conductivity and high efficiency flame retardancy.

[0011] Compared with the prior art, the present invention has the following beneficial effects: 1. The method for preparing a silicon-modified polybenzoxazole fiber aerogel described in the present invention introduces fumed silicon oxide into the polybenzoxazole fiber aerogel (S2), wherein the particle size of the fumed silicon oxide is 7nm-20nm, and the formed three-dimensional network skeleton structure has a low solid thermal conductivity, thereby ensuring the low thermal conductivity characteristic of the aerogel material. Secondly, the fumed silicon oxide can effectively isolate the material from contact with external oxygen, effectively prevent external high-temperature heat from transferring to the inside of the material, prevent the material from further decomposing or burning, and make the material have excellent flame retardant properties.

[0012] 2. The silicon-modified polybenzoxazole fiber aerogel prepared by the present invention has the characteristics of low density, low thermal conductivity and high-efficiency flame retardant and heat insulation; the density of the silicon-modified polybenzoxazole fiber aerogel prepared by the method of the present invention is 0.086 g / cm 3 -0.339g / cm 3 , thermal conductivity is 0.0196W / (m·K)-0.0379W / (m·K), and limiting oxygen index (LOI) is 48.2%-59.6% (when the LOI value is greater than 27, the material can be regarded as a flame retardant material, and the higher the LOI value, the better the flame retardant performance of the material).

[0013] 3. The silicon-modified polybenzoxazole fiber aerogel of the present invention has a simple preparation process, adopts a sol-gel and normal pressure drying method to prepare the material, and has the characteristics of low cost and large-scale production. BRIEF DESCRIPTION OF THE DRAWINGS

[0014] The accompanying drawings are used to provide further understanding of the present invention and constitute a part of the specification. They are used to explain the present invention together with the embodiments of the present invention and do not constitute a limitation of the present invention.

[0015] Figure 1The present invention discloses a general flow chart of a method for preparing a silicon-modified polybenzoxazole fiber aerogel. DETAILED DESCRIPTION

[0016] The present invention is further described in detail below by way of examples, but these examples should not be considered as limiting the present invention.

[0017] Embodiment 1: A method for preparing silicon-modified Kevlar aerogel, such as Figure 1 As shown, the following steps are included: The technical solution of the present invention is further described below with reference to examples: like Figure 1 As shown, embodiment 1 of the present invention includes the following steps: S1: 0.5 g of polybenzoxazole nanofibers were dissolved in 50 g of methanesulfonic acid, with a mass ratio of 1:100, and stirred at room temperature for 10 min until the fibers were fully dissolved and evenly dispersed, thereby obtaining a polybenzoxazole nanofiber solution; S2: adding 0.1 g of fumed silica to the polybenzoxazole nanofiber solution obtained in S1, wherein the mass ratio of fumed silica to polybenzoxazole nanofiber is 1:5; stirring at room temperature for 10 min to mix the mixture evenly; and obtaining a silicon-modified polybenzoxazole fiber sol; S3: The silicon-modified polybenzoxazole fiber sol prepared in S2 is sealed and placed in a water bath at a gelling temperature of 70°C to gel the silicon-modified polybenzoxazole fiber sol for 48 h to obtain the initial state gel of silicon-modified polybenzoxazole fiber; S4: The initial state gel of the silicon-modified polybenzoxazole fiber obtained in S3 was aged at 60 °C for 48 h to obtain an aged state gel; S5: The aged gel of the silicon-modified polybenzoxazole fiber obtained in S4 is replaced with an ethanol solvent at room temperature for 4 times, with an interval of 8 hours each time, to obtain a final gel of the silicon-modified polybenzoxazole fiber; S6: drying the silicon-modified polybenzoxazole fiber final gel prepared in S5 at room temperature and normal pressure until the mass of the gel no longer changes, thereby obtaining a silicon-modified polybenzoxazole fiber aerogel.

[0018] The density of the final prepared silicon-modified polybenzoxazole fiber aerogel is 0.086 g / cm 3 , thermal conductivity is 0.0196 W / (m·K), and LOI value is 48.2%.

[0019] Embodiment 2: S1: 0.5 g of polybenzoxazole nanofibers were dissolved in 50 g of methanesulfonic acid, with a mass ratio of 1:100, and stirred at room temperature for 10 min until the fibers were fully dissolved and evenly dispersed, thereby obtaining a polybenzoxazole nanofiber solution; S2: adding 0.25 g of fumed silica to the polybenzoxazole nanofiber solution obtained in S1, wherein the mass ratio of fumed silica to polybenzoxazole nanofiber is 1:2; stirring at room temperature for 10 min to mix the mixture evenly; and obtaining a silicon-modified polybenzoxazole fiber sol; S3: The silicon-modified polybenzoxazole fiber sol prepared in S2 is sealed and placed in a water bath at a gel temperature of 60°C to gel the silicon-modified polybenzoxazole fiber sol for 45 h to obtain the initial state gel of silicon-modified polybenzoxazole fiber; S4: The initial state gel of the silicon-modified polybenzoxazole fiber obtained in S3 was aged at 50°C for 36 h to obtain an aged state gel; S5: The aged gel of silicon-modified polybenzoxazole fiber obtained in S4 is replaced with ethanol solvent at room temperature for 4 times, with an interval of 10 h each time, to obtain the final gel of silicon-modified polybenzoxazole fiber; S6: drying the silicon-modified polybenzoxazole fiber final gel prepared in S5 at room temperature and normal pressure until the mass of the gel no longer changes, thereby obtaining a silicon-modified polybenzoxazole fiber aerogel.

[0020] The density of the final prepared silicon-modified polybenzoxazole fiber aerogel is 0.112 g / cm 3 , thermal conductivity is 0.0215 W / (m·K), and LOI value is 50.2%.

[0021] Embodiment 3: S1: 5 g of polybenzoxazole nanofibers were dissolved in 50 g of a mixture of methanesulfonic acid and polyphosphoric acid, the mass ratio of which was 10:100, and stirred at room temperature for 15 min until the mixture was fully dissolved and evenly dispersed, thereby obtaining a polybenzoxazole nanofiber solution; S2: adding 1 g of fumed silica to the polybenzoxazole nanofiber solution obtained in S1, with the mass ratio of fumed silica to polybenzoxazole nanofiber being 1:5; stirring at room temperature for 15 min to mix the mixture evenly; obtaining a silicon-modified polybenzoxazole fiber sol; S3: The silicon-modified polybenzoxazole fiber sol prepared in S2 is sealed and placed in a water bath at a gel temperature of 55°C to gel the silicon-modified polybenzoxazole fiber sol for 15 h to obtain the initial state gel of silicon-modified polybenzoxazole fiber; S4: The initial state gel of the silicon-modified polybenzoxazole fiber obtained in S3 was aged at 40°C for 36 h to obtain an aged state gel; S5: The aged gel of silicon-modified polybenzoxazole fiber obtained in S4 is replaced with ethanol solvent at room temperature for 5 times, with an interval of 8 hours each time, to obtain the final gel of silicon-modified polybenzoxazole fiber; S6: drying the silicon-modified polybenzoxazole fiber final gel prepared in S5 at room temperature and normal pressure until the mass of the gel no longer changes, thereby obtaining a silicon-modified polybenzoxazole fiber aerogel.

[0022] The density of the final prepared silicon-modified polybenzoxazole fiber aerogel is 0.301 g / cm 3 , thermal conductivity is 0.0362 W / (m·K), and LOI value is 55.6%.

[0023] Embodiment 4: S1: 5 g of polybenzoxazole nanofibers were dissolved in 50 g of a mixture of methanesulfonic acid and polyphosphoric acid, the mass ratio of which was 10:100, and stirred at room temperature for 15 min until the mixture was fully dissolved and evenly dispersed, thereby obtaining a polybenzoxazole nanofiber solution; S2: adding 2.5 g of fumed silica to the polybenzoxazole nanofiber solution obtained in S1, wherein the mass ratio of fumed silica to polybenzoxazole nanofiber is 1:2; stirring at room temperature for 15 min to mix the mixture evenly; and obtaining a silicon-modified polybenzoxazole fiber sol; S3: The silicon-modified polybenzoxazole fiber sol prepared in S2 is sealed and placed in a water bath at a gel temperature of 50°C to gel the silicon-modified polybenzoxazole fiber sol for 10 h to obtain the initial state gel of silicon-modified polybenzoxazole fiber; S4: The initial state gel of the silicon-modified polybenzoxazole fiber obtained in S3 was aged at 45°C for 30 h to obtain an aged state gel; S5: The aged gel of the silicon-modified polybenzoxazole fiber obtained in S4 is replaced with an ethanol solvent at room temperature for 5 times, each time interval being 12 hours, to obtain a final gel of the silicon-modified polybenzoxazole fiber; S6: drying the silicon-modified polybenzoxazole fiber final gel prepared in S5 at room temperature and normal pressure until the mass of the gel no longer changes, thereby obtaining a silicon-modified polybenzoxazole fiber aerogel.

[0024] The density of the final prepared silicon-modified polybenzoxazole fiber aerogel is 0.339 g / cm 3 , thermal conductivity is 0.0379 W / (m·K), and LOI value is 59.6%.

[0025] Embodiment 5: S1: 2.5 g of polybenzoxazole nanofibers were dissolved in 50 g of a mixture of trifluoroacetic acid and polyphosphoric acid, the mass ratio of which was 5:100, and stirred at room temperature for 15 min until the mixture was fully dissolved and evenly dispersed, thereby obtaining a polybenzoxazole nanofiber solution; S2: adding 0.5 g of fumed silica to the polybenzoxazole nanofiber solution obtained in S1, wherein the mass ratio of fumed silica to polybenzoxazole nanofiber is 1:5; stirring at room temperature for 12 min to mix the mixture evenly; and obtaining a silicon-modified polybenzoxazole fiber sol; S3: The silicon-modified polybenzoxazole fiber sol prepared in S2 was sealed and placed in a water bath with a gel temperature of 65°C to gel the silicon-modified polybenzoxazole fiber sol for 28 h to obtain the initial gel of silicon-modified polybenzoxazole fiber; S4: The initial state gel of the silicon-modified polybenzoxazole fiber obtained in S3 was aged at 50°C for 36 h to obtain an aged state gel; S5: The aged gel of the silicon-modified polybenzoxazole fiber obtained in S4 is replaced with an ethanol solvent at room temperature for 3 times, each time interval being 12 hours, to obtain a final gel of the silicon-modified polybenzoxazole fiber; S6: drying the silicon-modified polybenzoxazole fiber final gel prepared in S5 at room temperature and normal pressure until the mass of the gel no longer changes, thereby obtaining a silicon-modified polybenzoxazole fiber aerogel.

[0026] The density of the final prepared silicon-modified polybenzoxazole fiber aerogel is 0.257 g / cm 3 , thermal conductivity is 0.0274 W / (m·K), and LOI value is 53.5%.

[0027] Embodiment 6: S1: 2.5 g of polybenzoxazole nanofibers were dissolved in 50 g of a mixture of trifluoroacetic acid and polyphosphoric acid, the mass ratio of which was 5:100, and stirred at room temperature for 15 min until the mixture was fully dissolved and evenly dispersed, thereby obtaining a polybenzoxazole nanofiber solution; S2: adding 1.25 g of fumed silica to the polybenzoxazole nanofiber solution obtained in S1, wherein the mass ratio of fumed silica to polybenzoxazole nanofiber is 1:2; stirring at room temperature for 15 min to mix the mixture evenly; obtaining a silicon-modified polybenzoxazole fiber sol; S3: The silicon-modified polybenzoxazole fiber sol prepared in S2 is sealed and placed in a water bath with a gel temperature of 60°C to gel the silicon-modified polybenzoxazole fiber sol for 24 h to obtain the initial state gel of silicon-modified polybenzoxazole fiber; S4: The initial state gel of the silicon-modified polybenzoxazole fiber obtained in S3 was aged at 40°C for 32 h to obtain an aged state gel; S5: The aged gel of silicon-modified polybenzoxazole fiber obtained in S4 is replaced with ethanol solvent at room temperature for 4 times, with an interval of 9 hours each time, to obtain the final gel of silicon-modified polybenzoxazole fiber; S6: drying the silicon-modified polybenzoxazole fiber final gel prepared in S5 at room temperature and normal pressure until the mass of the gel no longer changes, thereby obtaining a silicon-modified polybenzoxazole fiber aerogel.

[0028] The density of the final prepared silicon-modified polybenzoxazole fiber aerogel is 0.289 g / cm 3 , thermal conductivity is 0.0305 W / (m·K), and LOI value is 57.8%.

[0029] Embodiment 7: S1: 3 g of polybenzoxazole nanofibers were dissolved in 50 g of a mixture of trifluoroacetic acid and polyphosphoric acid, the mass ratio of which was 6:100, and stirred at room temperature for 15 min until the mixture was fully dissolved and evenly dispersed, thereby obtaining a polybenzoxazole nanofiber solution; S2: adding 1 g of fumed silica to the polybenzoxazole nanofiber solution obtained in S1, with the mass ratio of fumed silica to polybenzoxazole nanofiber being 1:3; stirring at room temperature for 15 min to mix the mixture evenly; obtaining a silicon-modified polybenzoxazole fiber sol; S3: The silicon-modified polybenzoxazole fiber sol prepared in S2 was sealed and placed in a water bath with a gel temperature of 55°C to gel the silicon-modified polybenzoxazole fiber sol for 22 h to obtain the initial gel of silicon-modified polybenzoxazole fiber; S4: The initial state gel of the silicon-modified polybenzoxazole fiber obtained in S3 was aged at 50°C for 36 h to obtain an aged state gel; S5: The aged gel of silicon-modified polybenzoxazole fiber obtained in S4 is replaced with ethanol solvent at room temperature for 4 times, with an interval of 10 h each time, to obtain the final gel of silicon-modified polybenzoxazole fiber; S6: drying the silicon-modified polybenzoxazole fiber final gel prepared in S5 at room temperature and normal pressure until the mass of the gel no longer changes, thereby obtaining a silicon-modified polybenzoxazole fiber aerogel.

[0030] The density of the final prepared silicon-modified polybenzoxazole fiber aerogel is 0.295 g / cm 3 , thermal conductivity is 0.0326 W / (m·K), and LOI value is 57.9%.

[0031] Embodiment 8: S1: 4 g of polybenzoxazole nanofibers were dissolved in 50 g of polyphosphoric acid mixed solution, the mass ratio of the two being 8:100, and stirred at room temperature for 15 min until the nanofibers were fully dissolved and evenly dispersed, thereby obtaining a polybenzoxazole nanofiber solution; S2: adding 1 g of fumed silica to the polybenzoxazole nanofiber solution obtained in S1, with the mass ratio of fumed silica to polybenzoxazole nanofiber being 1:4; stirring at room temperature for 15 min to mix the mixture evenly; obtaining a silicon-modified polybenzoxazole fiber sol; S3: The silicon-modified polybenzoxazole fiber sol prepared in S2 is sealed and placed in a water bath at a gel temperature of 50°C to gel the silicon-modified polybenzoxazole fiber sol for 20 h to obtain the initial state gel of silicon-modified polybenzoxazole fiber; S4: The initial state gel of the silicon-modified polybenzoxazole fiber obtained in S3 was aged at 55°C for 40 h to obtain an aged state gel; S5: The aged gel of silicon-modified polybenzoxazole fiber obtained in S4 is replaced with ethanol solvent at room temperature for 5 times, with an interval of 8 hours each time, to obtain the final gel of silicon-modified polybenzoxazole fiber; S6: drying the silicon-modified polybenzoxazole fiber final gel prepared in S5 at room temperature and normal pressure until the mass of the gel no longer changes, thereby obtaining a silicon-modified polybenzoxazole fiber aerogel.

[0032] The density of the final prepared silicon-modified polybenzoxazole fiber aerogel is 0.309 g / cm 3 , thermal conductivity is 0.0337 W m -1 K -1 , the LOI value is 54.6%.

[0033] Comparative Example 1: The difference between Comparative Example 1 and Example 1 is that the addition of fumed silicon oxide in step S2 is missing, and the rest is the same as Example 1; The density of the obtained polybenzoxazole fiber aerogel is 0.091 g / cm 3 , thermal conductivity is 0.0212 W / (m·K), and LOI value is 29.2%.

[0034] Comparative Example 2: The difference between Comparative Example 2 and Example 1 is that the mass of the polybenzoxazole nanofiber added in step S1 is 0.4 g, and the rest is the same as Example 1; It is not possible to obtain silicon-modified polybenzoxazole fiber aerogel.

[0035] Comparative Example 3: The difference between Comparative Example 3 and Example 3 is that the mass of the polybenzoxazole nanofiber added in step S1 is 6 g, and the rest is the same as Example 3; It is not possible to obtain silicon-modified polybenzoxazole fiber aerogel.

[0036] Comparative Example 4: The difference between Comparative Example 4 and Example 2 is that the mass of fumed silicon oxide added in step S2 is 0.5 g, and the rest is the same as Example 2; It is not possible to obtain silicon-modified polybenzoxazole fiber aerogel.

[0037] Results and Discussion: 1. The results of the examples show that the mass ratio of fumed silica to polybenzoxazole nanofibers is too high (higher than 1:2). The introduction of excessive fumed silica will make the gel formation process difficult to control, thereby destroying the reaction conditions of the silicon-modified polybenzoxazole fiber aerogel and failing to obtain the silicon-modified polybenzoxazole fiber aerogel.

[0038] During the preparation process, the acidic substance is mainly used to dissolve the polybenzoxazole nanofibers, and the type or combination ratio of the acidic substance has little effect on the performance of the material; as long as the gel temperature, aging time and temperature, the type of solvent in the solvent replacement, the number of replacements and the replacement time are within the stated range, the effects on the density, thermal conductivity and flame retardant properties (LOI value) of the silicon-modified polybenzoxazole fiber aerogel can be basically ignored.

[0039] The density, thermal conductivity and flame retardant properties of silicon-modified polybenzoxazole fiber aerogel are mainly affected by the mass ratio of polybenzoxazole nanofibers to acidic substances and the mass ratio of fumed silica to polybenzoxazole nanofibers. The greater the mass ratio of polybenzoxazole nanofibers to acidic substances, the greater the material density and the greater the thermal conductivity. The greater the mass ratio of fumed silica to polybenzoxazole nanofibers, the better the flame retardant properties of the material.

[0040] 2. The results of comparative example 1 show that the introduction of fumed silica can improve the thermal insulation performance of polybenzoxazole fiber aerogel and effectively improve its flame retardant properties.

[0041] 3. The results of Comparative Example 2 show that the mass ratio of polybenzoxazole fiber to acidic substance is too low (less than 1:100). Too low a solid content makes it difficult to form a gel skeleton with a three-dimensional network structure, and silicon-modified polybenzoxazole fiber aerogel cannot be obtained.

[0042] 4. The results of comparative example 3 show that the mass ratio of polybenzoxazole fiber to acidic substance is too high (higher than 10:100). Too high solid content increases the reaction activity of the raw materials, easily leading to precipitation of larger particles, making it difficult to form a gel, and thus it is impossible to obtain silicon-modified polybenzoxazole fiber aerogel.

[0043] 5. The results of Comparative Example 4 show that the ratio of fumed silica to polybenzoxazole fiber is too high (higher than 1:2) and the amount of fumed silica is too large, the viscosity of the sol increases, the particle growth rate is fast, precipitation is easy to occur, and it is difficult to obtain a stable gel.

[0044] The above are only preferred implementations of the present invention. The protection scope of the present invention is not limited to the above embodiments. Various process schemes that are not substantially different from the concept of the present invention are within the protection scope of the present invention.

Claims

1. A method for preparing silicon-modified polybenzoxazole fiber aerogel, characterized in that: The following steps are involved: S1, dissolving the polybenzoxazole nanofibers in an acidic substance at a mass ratio of (1-10):100, stirring at room temperature for 10 min-15 min to fully dissolve and evenly disperse the polybenzoxazole nanofibers to obtain a polybenzoxazole nanofiber solution; The diameter of the polybenzoxazole nanofibers is 16nm-22nm; The acidic substance is one of methanesulfonic acid, polyphosphoric acid, trifluoroacetic acid and chlorosulfonic acid, or a mixture of any two thereof; S2, adding fumed silicon oxide to the polybenzoxazole nanofiber solution obtained in step S1, wherein the mass ratio of fumed silicon oxide to polybenzoxazole nanofiber is 1:(2-5); stirring at room temperature for 10 min-15 min to mix them evenly, to obtain a silicon-modified polybenzoxazole fiber sol; The particle size of the fumed silicon oxide is 7nm-20nm; S3, sealing the silicon-modified polybenzoxazole fiber sol obtained in step S2 and placing it in a water bath, with a gel temperature of 50° C.-70° C., to gel the silicon-modified polybenzoxazole fiber sol, with a gel time of 10 h-48 h, to obtain an initial gel of silicon-modified polybenzoxazole fiber; S4, aging the initial state gel of the silicon-modified polybenzoxazole fiber obtained in step S3 at 40° C.-60° C. for 24 h-48 h to obtain an aged state gel of the silicon-modified polybenzoxazole fiber; S5, performing solvent replacement on the aged silicon-modified polybenzoxazole fiber gel obtained in step S4 at room temperature to obtain a final silicon-modified polybenzoxazole fiber gel; The solvent replacement adopts ethanol, isopropanol or tert-butanol as the replacement solvent, the number of solvent replacement is 3 to 5 times, and the time of each replacement is 8h to 12h; S6, drying the final state gel of the silicon-modified polybenzoxazole fiber prepared in step S5 at room temperature and normal pressure until the mass of the gel no longer changes, thereby obtaining a silicon-modified polybenzoxazole fiber aerogel, wherein the silicon-modified polybenzoxazole fiber aerogel exhibits a three-dimensional interconnected nanoporous network structure and has a density of 0.086 g / cm 3 -0.339g / cm 3 , thermal conductivity is 0.0196W / (m·K)-0.0379W / (m·K), and limiting oxygen index is 48.2%-59.6%.

2. The method for preparing a silicon-modified polybenzoxazole fiber aerogel according to claim 1, characterized in that: The acidic substance in step S1 is methanesulfonic acid or polyphosphoric acid; the mass ratio of the polybenzoxazole nanofibers to the acidic substance is 4:

100.

3. The method for preparing a silicon-modified polybenzoxazole fiber aerogel according to claim 1, characterized in that: The mass ratio of the fumed silicon oxide to the polybenzoxazole nanofibers in step S2 is 1:

3.

4. The method for preparing a silicon-modified polybenzoxazole fiber aerogel according to claim 1, characterized in that: The gel temperature described in step S3 is 55°C.

5. The method for preparing a silicon-modified polybenzoxazole fiber aerogel according to claim 1, characterized in that: The aging temperature in step S4 is 50°C.

6. The method for preparing a silicon-modified polybenzoxazole fiber aerogel according to claim 1, characterized in that: In the solvent replacement described in step S5, the replacement solvent used is ethanol, the number of solvent replacements is 4 times, and the time for each replacement is 10 hours.

7. A silicon-modified polybenzoxazole fiber aerogel, characterized in that: The silicon-modified polybenzoxazole fiber aerogel prepared by the method of any one of claims 1 to 6 has a three-dimensional interconnected nanoporous network structure and a density of 0.086 g / cm 3 -0.339g / cm 3 , thermal conductivity is 0.0196W / (m·K)-0.0379W / (m·K), limiting oxygen index is 48.2%-59.6%, and it has low density, low thermal conductivity and high efficiency flame retardant properties.

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