A nano-alumina modified polybenzoxazole fiber aerogel and preparation method thereof

Abstract

The invention discloses a nano-alumina modified polybenzoxazole fiber aerogel and a preparation method thereof. Polybenzoxazole nanofiber is used as an initial raw material, dissolved in an acidic substance, and nano-alumina is added for mixing and stirring to obtain a nano-alumina modified polybenzoxazole fiber sol, which is left to stand in a water bath environment to obtain an initial gel, and then a nano-alumina modified polybenzoxazole fiber aerogel is obtained through aging, solvent replacement and normal pressure drying. The invention introduces nano-alumina and adds an inorganic flame retardant component to improve the flame retardant performance while ensuring thermal conductivity, thereby obtaining a nano-alumina polybenzoxazole fiber aerogel flame retardant and heat insulating material.

Description

Technical Field

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

[0002] Polybenzoxazole aerogel is a new type of high-performance polymer aerogel. Its light weight, high strength, and low thermal conductivity make it have broad application prospects in the field of thermal insulation. According to CN 106221216 A, the density of existing polybenzoxazole aerogel is 0.02g / cm 3 -0.05g / cm 3 ; According to CN 116218023 A and CN 116284980 A, the thermal conductivity of existing polybenzoxazole aerogels is in the range of 0.030W / (m·K)-0.046W / (m·K). However, there is no public report on its flame retardant properties. As a highly efficient flame retardant thermal insulation material, flame retardant properties have always been a key performance that needs to be paid attention to. Therefore, how to ensure the low thermal conductivity of polymer aerogel materials while improving their flame retardant properties has always been a research hotspot in this field.

[0003] Nano-alumina is an inorganic material with unique properties. It has good heat resistance and flame retardancy. Its different particle size ranges determine different performance characteristics. Nano-alumina with a particle size of about 20nm has good reactivity and a high specific surface area; nano-alumina with a particle size of 30nm-60nm has the characteristics of high hardness and good dimensional stability. These particle size ranges and performance characteristics enable it to participate in the reaction very well, and at high temperatures, it helps organic polymers form a carbon layer, isolate the air, reduce the temperature of the material surface, and reduce the generation of combustibles, thereby effectively improving the flame retardancy of the material.

[0004] Therefore, how to combine nano-alumina with polybenzoxazine aerogel so that it forms a three-dimensional network structure with polybenzoxazine fibers in the sol-gel process, while ensuring the low thermal conductivity of polybenzoxazine aerogel and effectively improving its carbon residue rate and flame retardant properties, is a technical problem that researchers in this field urgently need to solve. Summary of the invention

[0005] In view of the problem that the thermal insulation and flame retardant properties of polybenzoxazole fiber aerogel in the prior art need to be further improved, the present invention provides a nano-alumina modified polybenzoxazole fiber aerogel flame retardant thermal insulation material and a preparation method thereof. By introducing nano-alumina and adding inorganic flame retardant components, the flame retardant properties are improved while ensuring thermal conductivity, thereby obtaining a nano-alumina polybenzoxazole fiber aerogel flame retardant thermal insulation material.

[0006] The technical solution of the present invention is as follows:

[0007] The nano-alumina modified polybenzoxazole fiber aerogel of the present invention uses polybenzoxazole nanofiber as the initial raw material, dissolves the polybenzoxazole nanofiber in an acidic substance, adds nano-alumina for mixing and stirring, obtains nano-alumina modified polybenzoxazole fiber sol, and allows the sol to stand in a water bath environment to obtain an initial gel. After aging, solvent replacement and normal pressure drying, a nano-alumina modified polybenzoxazole fiber aerogel is obtained.

[0008] The purpose of the present invention is achieved through the following technical solutions:

[0009] A method for preparing a nano-alumina modified polybenzoxazole fiber aerogel comprises the following steps:

[0010] S1, dissolving the polybenzoxazole nanofibers in an acidic substance at a mass ratio of (1-4):50, stirring at room temperature for 10 min-15 min to fully dissolve and evenly disperse the polybenzoxazole nanofibers to obtain a polybenzoxazole nanofiber solution;

[0011] The diameter of the polybenzoxazole nanofibers is 16nm-22nm;

[0012] The acidic substance is one or a mixture of any two of methanesulfonic acid, polyphosphoric acid, trifluoroacetic acid and chlorosulfonic acid;

[0013] S2, adding nano-alumina to the polybenzoxazole nanofiber solution obtained in step S1, wherein the mass ratio of nano-alumina to polybenzoxazole nanofiber is (1-3):6; stirring at room temperature for 10 min-15 min to mix them evenly, to obtain nano-alumina modified polybenzoxazole fiber sol;

[0014] The particle size of the nano-alumina is 18nm-24nm or 30nm-60nm;

[0015] S3, sealing the nano-alumina-modified polybenzoxazole fiber sol obtained in step S2 and placing it in a water bath, the gelation temperature is 55° C.-70° C., the nano-alumina-modified polybenzoxazole fiber sol is gelled, the gelation time is 8h-40h, and the nano-alumina-modified polybenzoxazole fiber initial gel is obtained;

[0016] S4, aging the initial state gel of the nano-alumina-modified polybenzoxazole fiber obtained in step S3 at 40° C.-80° C. for 24-72 hours to obtain an aged gel;

[0017] S5, performing solvent replacement on the aged state gel of nano-alumina-modified polybenzoxazole fiber obtained in step S4 at room temperature to obtain a final state gel of nano-alumina-modified polybenzoxazole fiber;

[0018] 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 10h to 12h;

[0019] S6, drying the nano-alumina-modified polybenzoxazole fiber final gel prepared in step S5 at room temperature and normal pressure until the mass of the gel no longer changes, thereby obtaining a nano-alumina-modified polybenzoxazole fiber aerogel, wherein the nano-alumina-modified polybenzoxazole fiber aerogel exhibits a three-dimensional interconnected nanoporous network structure and has a density of 0.115 g / cm 3 -0.357g / cm 3 , thermal conductivity is 0.0249W / (m·K)-0.0376W / (m·K), residual carbon rate is 58.2%-70.6%, and limiting oxygen index (LOI) is 45.8%-57.9%.

[0020] Furthermore, the acidic substance in step S1 is preferably methanesulfonic acid and polyphosphoric acid; and the mass ratio of the polybenzoxazole nanofibers to the acidic substance is preferably 2:50.

[0021] Furthermore, the particle size of the nano-alumina in step S2 is preferably 18nm-24nm.

[0022] Furthermore, the gel temperature in step S3 is preferably 60°C.

[0023] Furthermore, the aging temperature in step S4 is preferably 50°C.

[0024] 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 11 hours.

[0025] Furthermore, the normal pressure described in step S6 is a standard atmospheric pressure.

[0026] The present invention also relates to a nano-alumina modified polybenzoxazole fiber aerogel, which is obtained according to the preparation method of the nano-alumina modified polybenzoxazole fiber aerogel. The nano-alumina modified polybenzoxazole fiber aerogel presents a three-dimensional interconnected nanoporous network structure with a density of 0.115 g / cm 3 -0.357g / cm 3 The thermal conductivity is 0.0249W / (m·K)-0.0376W / (m·K), the residual carbon rate is 58.2%-70.6%, and the limiting oxygen index (LOI) is 45.8%-57.9%. It has the characteristics of light weight, high residual carbon and high-efficiency flame retardant and heat insulation.

[0027] Compared with the prior art, the present invention has the following beneficial effects:

[0028] 1. The method for preparing a nano-alumina modified polybenzoxazole fiber aerogel described in the present invention comprises introducing nano-alumina into the polybenzoxazole fiber aerogel (S2), uniformly dispersing the nano-alumina in a polybenzoxazole solution through mixing and stirring, performing cross-linking and hybridization under a low temperature and acidic environment to form a nano three-dimensional network gel structure, and preparing a nano-alumina modified polybenzoxazole fiber aerogel through solvent replacement, aging and supercritical drying. The sol-gel process is simple, the reaction conditions are mild, and industrial production can be easily realized.

[0029] 2. The nano-alumina modified polybenzoxazole fiber aerogel prepared by the present invention has the characteristics of low density, low thermal conductivity, high residual carbon rate and high efficiency flame retardant and heat insulation; the density of the nano-alumina modified polybenzoxazole fiber aerogel prepared by the method of the present invention is 0.115g / cm 3 -0.357g / cm 3 , thermal conductivity is 0.0249W / (m·K)-0.0376W / (m·K), residual carbon rate is 58.2%-70.6%, and limiting oxygen index (LOI) is 45.8%-57.9% (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). BRIEF DESCRIPTION OF THE DRAWINGS

[0030] 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.

[0031] Figure 1 The invention discloses a general flow chart of a method for preparing a nano-alumina-modified polybenzoxazole fiber aerogel. DETAILED DESCRIPTION

[0032] 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.

[0033] The technical solution of the present invention is further described below with reference to examples:

[0034] Embodiment 1:

[0035] A method for preparing nano-alumina polybenzoxazole fiber aerogel, such as Figure 1 As shown, the following steps are included:

[0036] S1: dissolving 1 g of polybenzoxazole nanofibers in 50 g of methanesulfonic acid at a mass ratio of 1:50, stirring at room temperature for 12 min until the fibers are fully dissolved and evenly dispersed, thereby obtaining a polybenzoxazole nanofiber solution;

[0037] S2: adding 0.166 g of nano-alumina (18 nm-24 nm) to the polybenzoxazole nanofiber solution obtained in S1, wherein the mass ratio of nano-alumina to polybenzoxazole nanofiber is 1:6; stirring at room temperature for 10 min to mix the mixture evenly, thereby obtaining a nano-alumina-modified polybenzoxazole fiber sol;

[0038] S3: The nano-alumina-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 nano-alumina-modified polybenzoxazole fiber sol for 40 hours to obtain an initial gel of the nano-alumina-modified polybenzoxazole fiber;

[0039] S4: aging the initial state gel of the nano-alumina-modified polybenzoxazole fiber obtained in S3 at 50° C. for 52 h to obtain an aged gel;

[0040] S5: replacing the aged gel of the nano-alumina-modified polybenzoxazole fiber obtained in S4 with an ethanol solvent for three times at room temperature, each time interval being 12 hours, to obtain a final gel of the nano-alumina-modified polybenzoxazole fiber;

[0041] S6: drying the nano-alumina-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 nano-alumina-modified polybenzoxazole fiber aerogel.

[0042] The density of the nano-alumina modified polybenzoxazole fiber aerogel prepared was 0.115 g / cm 3 , thermal conductivity is 0.0249W / (m·K), residual carbon rate is 58.2%, and LOI value is 45.8%.

[0043] Embodiment 2:

[0044] A method for preparing nano-alumina polybenzoxazole fiber aerogel comprises the following steps:

[0045] S1: dissolving 1 g of polybenzoxazole nanofibers in 50 g of methanesulfonic acid at a mass ratio of 1:50, stirring at room temperature for 12 min until the fibers are fully dissolved and evenly dispersed, thereby obtaining a polybenzoxazole nanofiber solution;

[0046] S2: adding 0.166 g of nano-alumina (30 nm-60 nm) to the polybenzoxazole nanofiber solution obtained in S1, wherein the mass ratio of nano-alumina to polybenzoxazole nanofiber is 1:6; stirring at room temperature for 10 min to mix the mixture evenly, thereby obtaining a nano-alumina-modified polybenzoxazole fiber sol;

[0047] S3: The nano-alumina-modified polybenzoxazole fiber sol prepared in S2 is sealed and placed in a water bath at a gelling temperature of 68°C to gel the nano-alumina-modified polybenzoxazole fiber sol for 35 hours to obtain an initial gel of nano-alumina-modified polybenzoxazole fiber;

[0048] S4: aging the initial state gel of the nano-alumina-modified polybenzoxazole fiber obtained in S3 at 50° C. for 60 h to obtain an aged state gel;

[0049] S5: The aged gel of the nano-alumina-modified polybenzoxazole fiber obtained in S4 is replaced with an ethanol solvent at room temperature for 4 times, each time interval being 11 hours, to obtain a final gel of the nano-alumina-modified polybenzoxazole fiber;

[0050] S6: drying the nano-alumina-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 nano-alumina-modified polybenzoxazole fiber aerogel.

[0051] The density of the nano-alumina modified polybenzoxazole fiber aerogel prepared was 0.128 g / cm 3 , thermal conductivity is 0.0276W / (m·K), residual carbon rate is 59.6%, and LOI value is 48.9%.

[0052] Embodiment 3:

[0053] A method for preparing nano-alumina polybenzoxazole fiber aerogel comprises the following steps:

[0054] S1: dissolving 4 g of polybenzoxazole nanofibers in 50 g of polyphosphoric acid at a mass ratio of 4:50, stirring at room temperature for 12 min until the nanofibers are fully dissolved and evenly dispersed, thereby obtaining a polybenzoxazole nanofiber solution;

[0055] S2: adding 2 g of nano-alumina (18-24 nm) to the polybenzoxazole nanofiber solution obtained in S1, wherein the mass ratio of nano-alumina to polybenzoxazole nanofiber is 3:6; stirring at room temperature for 15 min to mix the mixture evenly; obtaining a nano-alumina modified polybenzoxazole fiber sol;

[0056] S3: The nano-alumina-modified polybenzoxazole fiber sol prepared in S2 is sealed and placed in a water bath at a gelling temperature of 60° C. to gel the nano-alumina-modified polybenzoxazole fiber sol for 12 hours to obtain an initial gel of the nano-alumina-modified polybenzoxazole fiber;

[0057] S4: aging the initial state gel of the nano-alumina-modified polybenzoxazole fiber obtained in S3 at 40° C. for 72 h to obtain an aged state gel;

[0058] S5: replacing the aged gel of the nano-alumina-modified polybenzoxazole fiber obtained in S4 with an ethanol solvent at room temperature for 5 times, each time interval being 10 hours, to obtain a final gel of the nano-alumina-modified polybenzoxazole fiber;

[0059] S6: drying the nano-alumina-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 nano-alumina-modified polybenzoxazole fiber aerogel.

[0060] The density of the nano-alumina modified polybenzoxazole fiber aerogel prepared was 0.339 g / cm 3 , thermal conductivity is 0.0358W / (m·K), residual carbon rate is 68.3%, and LOI value is 56.3%.

[0061] Embodiment 4:

[0062] A method for preparing nano-alumina polybenzoxazole fiber aerogel comprises the following steps:

[0063] S1: dissolving 4 g of polybenzoxazole nanofibers in 50 g of trifluoroacetic acid at a mass ratio of 4:50, stirring at room temperature for 15 min until the nanofibers are fully dissolved and evenly dispersed, thereby obtaining a polybenzoxazole nanofiber solution;

[0064] S2: adding 2 g of nano-alumina (30 nm-60 nm) to the polybenzoxazole nanofiber solution obtained in S1, wherein the mass ratio of nano-alumina to polybenzoxazole nanofiber is 3:6; stirring at room temperature for 15 min to mix the mixture evenly, thereby obtaining a nano-alumina-modified polybenzoxazole fiber sol;

[0065] S3: The nano-alumina-modified polybenzoxazole fiber sol prepared in S2 is sealed and placed in a water bath at a gelling temperature of 55°C to gel the nano-alumina-modified polybenzoxazole fiber sol for 8 hours to obtain an initial gel of the nano-alumina-modified polybenzoxazole fiber;

[0066] S4: aging the initial state gel of the nano-alumina-modified polybenzoxazole fiber obtained in S3 at 40° C. for 24 hours to obtain an aged state gel;

[0067] S5: replacing the aged gel of the nano-alumina-modified polybenzoxazole fiber obtained in S4 with an ethanol solvent for three times at room temperature, each time interval being 12 hours, to obtain a final gel of the nano-alumina-modified polybenzoxazole fiber;

[0068] S6: drying the nano-alumina-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 nano-alumina-modified polybenzoxazole fiber aerogel.

[0069] The density of the nano-alumina modified polybenzoxazole fiber aerogel prepared was 0.357 g / cm 3 , thermal conductivity is 0.0376W / (m·K), residual carbon rate is 70.6%, and LOI value is 57.9%.

[0070] Embodiment 5:

[0071] A method for preparing nano-alumina polybenzoxazole fiber aerogel comprises the following steps:

[0072] S1: dissolving 1 g of polybenzoxazole nanofibers in 50 g of methanesulfonic acid and polyphosphoric acid in a mass ratio of 1:50, stirring at room temperature for 12 min until the fibers are fully dissolved and evenly dispersed, thereby obtaining a polybenzoxazole nanofiber solution;

[0073] S2: adding 0.5 g of nano-alumina (18 nm-24 nm) to the polybenzoxazole nanofiber solution obtained in S1, wherein the mass ratio of nano-alumina to polybenzoxazole nanofiber is 3:6; stirring at room temperature for 15 min to mix the mixture evenly; obtaining a nano-alumina modified polybenzoxazole fiber sol;

[0074] S3: The nano-alumina-modified polybenzoxazole fiber sol prepared in S2 is sealed and placed in a water bath at a gelling temperature of 65°C to gel the nano-alumina-modified polybenzoxazole fiber sol for 35 hours to obtain a nano-alumina-modified polybenzoxazole fiber initial gel;

[0075] S4: aging the initial state gel of the nano-alumina-modified polybenzoxazole fiber obtained in S3 at 80° C. for 36 h to obtain an aged gel;

[0076] S5: replacing the aged gel of the nano-alumina-modified polybenzoxazole fiber obtained in S4 with an ethanol solvent at room temperature for 4 times, each time interval being 10 hours, to obtain a final gel of the nano-alumina-modified polybenzoxazole fiber;

[0077] S6: drying the nano-alumina-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 nano-alumina-modified polybenzoxazole fiber aerogel.

[0078] The density of the nano-alumina modified polybenzoxazole fiber aerogel prepared was 0.187 g / cm 3, thermal conductivity is 0.0277W / (m·K), residual carbon rate is 65.3%, and LOI value is 49.2%.

[0079] Embodiment 6:

[0080] A method for preparing nano-alumina polybenzoxazole fiber aerogel comprises the following steps:

[0081] S1: dissolving 1 g of polybenzoxazole nanofibers in 50 g of methanesulfonic acid at a mass ratio of 1:50, stirring at room temperature for 12 min until the fibers are fully dissolved and evenly dispersed, thereby obtaining a polybenzoxazole nanofiber solution;

[0082] S2: adding 0.5 g of nano-alumina (30 nm-60 nm) to the polybenzoxazole nanofiber solution obtained in S1, wherein the mass ratio of nano-alumina to polybenzoxazole nanofiber is 3:6; stirring at room temperature for 15 min to mix the mixture evenly, thereby obtaining a nano-alumina-modified polybenzoxazole fiber sol;

[0083] S3: The nano-alumina-modified polybenzoxazole fiber sol prepared in S2 is sealed and placed in a water bath at a gelling temperature of 65°C to gel the nano-alumina-modified polybenzoxazole fiber sol for 20 hours to obtain a nano-alumina-modified polybenzoxazole fiber initial gel;

[0084] S4: aging the initial state gel of the nano-alumina-modified polybenzoxazole fiber obtained in S3 at 60° C. for 54 h to obtain an aged state gel;

[0085] S5: replacing the aged gel of the nano-alumina-modified polybenzoxazole fiber obtained in S4 with an ethanol solvent for three times at room temperature, each time interval being 12 hours, to obtain a final gel of the nano-alumina-modified polybenzoxazole fiber;

[0086] S6: drying the nano-alumina-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 nano-alumina-modified polybenzoxazole fiber aerogel.

[0087] The density of the nano-alumina modified polybenzoxazole fiber aerogel prepared was 0.198 g / cm 3 , thermal conductivity is 0.0286W / (m·K), residual carbon rate is 68.5%, and LOI value is 52.4%.

[0088] Embodiment 7:

[0089] A method for preparing nano-alumina polybenzoxazole fiber aerogel comprises the following steps:

[0090] S1: dissolving 4 g of polybenzoxazole nanofibers in 50 g of polyphosphoric acid at a mass ratio of 4:50, stirring at room temperature for 12 min until the nanofibers are fully dissolved and evenly dispersed, thereby obtaining a polybenzoxazole nanofiber solution;

[0091] S2: adding 0.67 g of nano-alumina (18 nm-24 nm) to the polybenzoxazole nanofiber solution obtained in S1, wherein the mass ratio of nano-alumina to polybenzoxazole nanofiber is 2:6; stirring at room temperature for 15 min to mix the mixture evenly, thereby obtaining a nano-alumina-modified polybenzoxazole fiber sol;

[0092] S3: The nano-alumina-modified polybenzoxazole fiber sol prepared in S2 is sealed and placed in a water bath at a gelling temperature of 63°C to gel the nano-alumina-modified polybenzoxazole fiber sol for 26 hours to obtain an initial gel of the nano-alumina-modified polybenzoxazole fiber;

[0093] S4: aging the initial state gel of the nano-alumina-modified polybenzoxazole fiber obtained in S3 at 45° C. for 60 h to obtain an aged state gel;

[0094] S5: replacing the aged gel of the nano-alumina-modified polybenzoxazole fiber obtained in S4 with an ethanol solvent for three times at room temperature, each time interval being 12 hours, to obtain a final gel of the nano-alumina-modified polybenzoxazole fiber;

[0095] S6: drying the nano-alumina-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 nano-alumina-modified polybenzoxazole fiber aerogel.

[0096] The density of the nano-alumina modified polybenzoxazole fiber aerogel prepared was 0.286 g / cm 3 , thermal conductivity is 0.0301W / (m·K), residual carbon rate is 60.6%, and LOI value is 51.4%.

[0097] Embodiment 8:

[0098] A method for preparing nano-alumina polybenzoxazole fiber aerogel comprises the following steps:

[0099] S1: dissolving 4 g of polybenzoxazole nanofibers in 50 g of polyphosphoric acid at a mass ratio of 4:50, stirring at room temperature for 12 min until the nanofibers are fully dissolved and evenly dispersed, thereby obtaining a polybenzoxazole nanofiber solution;

[0100] S2: adding 0.67 g of nano-alumina (30-60 nm) to the polybenzoxazole nanofiber solution obtained in S1, wherein the mass ratio of nano-alumina to polybenzoxazole nanofiber is 1:6; stirring at room temperature for 15 min to mix the mixture evenly, thereby obtaining a nano-alumina-modified polybenzoxazole fiber sol;

[0101] S3: The nano-alumina-modified polybenzoxazole fiber sol prepared in S2 is sealed and placed in a water bath at a gelling temperature of 58°C to gel the nano-alumina-modified polybenzoxazole fiber sol for 22 hours to obtain an initial gel of the nano-alumina-modified polybenzoxazole fiber;

[0102] S4: aging the initial state gel of the nano-alumina-modified polybenzoxazole fiber obtained in S3 at 50° C. for 70 h to obtain an aged state gel;

[0103] S5: The aged gel of the nano-alumina-modified polybenzoxazole fiber obtained in S4 is replaced with an ethanol solvent at room temperature for 4 times, each time interval being 11 hours, to obtain a final gel of the nano-alumina-modified polybenzoxazole fiber;

[0104] S6: drying the nano-alumina-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 nano-alumina-modified polybenzoxazole fiber aerogel.

[0105] The density of the nano-alumina modified polybenzoxazole fiber aerogel prepared was 0.299 g / cm 3 , thermal conductivity is 0.0324W / (m·K), residual carbon rate is 61.2%, and LOI value is 52.8%.

[0106] Comparative Example 1:

[0107] The difference between Comparative Example 1 and Example 1 is that the addition of nano-alumina in step S2 is missing, and the rest is the same as Example 1;

[0108] The density of the obtained polybenzoxazole fiber aerogel is 0.131 g / cm 3 , thermal conductivity is 0.0249W / (m·K), residual carbon rate is 44.5%, and LOI value is 28.7%.

[0109] Comparative Example 2:

[0110] The difference between Comparative Example 2 and Example 1 is that the mass of the polybenzoxazole nanofiber added in step S1 is 0.9 g, and the rest is the same as Example 1;

[0111] Nano-alumina-modified polybenzoxazole fiber aerogel cannot be obtained.

[0112] Comparative Example 3:

[0113] The difference between Comparative Example 3 and Example 3 is that the mass of the polybenzoxazole nanofiber added in step S1 is 4.2 g, and the rest is the same as Example 3;

[0114] Nano-alumina-modified polybenzoxazole fiber aerogel cannot be obtained.

[0115] Comparative Example 4:

[0116] The difference between Comparative Example 4 and Example 3 is that the mass of nano-alumina added in step S2 is 2.2 g, and the rest is the same as Example 2;

[0117] Nano-alumina-modified polybenzoxazole fiber aerogel cannot be obtained.

[0118] Results and Discussion:

[0119] 1. The results of the examples show that, in 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 range, the influence on the density, thermal conductivity and flame retardancy of the prepared nano-alumina modified polybenzoxazole fiber aerogel can be basically ignored.

[0120] The density, thermal conductivity, residual carbon rate and flame retardant properties of the prepared nano-alumina modified polybenzoxazole fiber aerogel are mainly affected by the mass ratio of polybenzoxazole nanofibers to acidic substances, the mass ratio of nano-alumina to polybenzoxazole nanofibers, the size of nano-alumina particles, etc.; among them, the greater the mass ratio of polybenzoxazole nanofibers to acidic substances, the greater the density of the material and the greater the thermal conductivity; the greater the mass ratio of boron compounds to polybenzoxazole nanofibers, the better the flame retardant properties of the material, the larger the nano-alumina particle size, the greater the density, the higher the thermal conductivity and residual carbon rate, and the better the flame retardant properties.

[0121] 2. The results of comparative example 1 show that the introduction of nano-alumina can improve the thermal insulation performance of polybenzoxazole fiber aerogel and effectively improve its flame retardant properties.

[0122] 3. The results of Comparative Example 2 show that the mass ratio of polybenzoxazole fiber aerogel to acidic substance is too low (less than 1:50). Too low solid content makes it difficult to form a gel skeleton with a three-dimensional network structure, and a nano-alumina-modified polybenzoxazole fiber aerogel cannot be obtained.

[0123] 4. The results of Comparative Example 3 show that the mass ratio of polybenzoxazole nanofiber aerogel to acidic substance is too high (higher than 4:50. Too high solid content increases the reaction activity of the raw materials, and it is easy to obtain large particles of precipitation, which makes it difficult to form a gel, and a nano-alumina modified polybenzoxazole fiber aerogel cannot be obtained.

[0124] 5. The results of Comparative Example 4 show that the mass ratio of nano-alumina to polybenzoxazole nanofibers is too high (higher than 3:1). The introduction of excessive nano-alumina will make the gel formation process difficult to control, thereby destroying the reaction conditions of a nano-alumina-modified polybenzoxazole fiber aerogel, and a nano-alumina-modified polybenzoxazole fiber aerogel cannot be obtained.

[0125] 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 nano-alumina 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 (1-4):50, 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 or a mixture of any two of methanesulfonic acid, polyphosphoric acid, trifluoroacetic acid and chlorosulfonic acid; S2, adding nano-alumina to the polybenzoxazole nanofiber solution obtained in step S1, wherein the mass ratio of nano-alumina to polybenzoxazole nanofiber is (1-3):6; stirring at room temperature for 10 min-15 min to mix them evenly, to obtain nano-alumina modified polybenzoxazole fiber sol; The particle size of the nano-alumina is 18nm-24nm or 30nm-60nm; S3, sealing the nano-alumina-modified polybenzoxazole fiber sol obtained in step S2 and placing it in a water bath, the gelation temperature is 55° C.-70° C., the nano-alumina-modified polybenzoxazole fiber sol is gelled, the gelation time is 8h-40h, and the nano-alumina-modified polybenzoxazole fiber initial gel is obtained; S4, aging the initial state gel of the nano-alumina-modified polybenzoxazole fiber obtained in step S3 at 40° C.-80° C. for 24-72 hours to obtain an aged gel; S5, performing solvent replacement on the aged state gel of nano-alumina-modified polybenzoxazole fiber obtained in step S4 at room temperature to obtain a final state gel of nano-alumina-modified polybenzoxazole fiber; 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 replacement time of each time is 10h to 12h; S6, drying the nano-alumina-modified polybenzoxazole fiber final gel prepared in step S5 at room temperature and normal pressure until the mass of the gel no longer changes, thereby obtaining a nano-alumina-modified polybenzoxazole fiber aerogel, wherein the nano-alumina-modified polybenzoxazole fiber aerogel exhibits a three-dimensional interconnected nanoporous network structure and has a density of 0.115 g / cm 3 -0.357g / cm 3 , thermal conductivity is 0.0249W / (m·K)-0.0376W / (m·K), residual carbon rate is 58.2%-70.6%, and limiting oxygen index is 45.8%-57.9%.

2. The method for preparing a nano-alumina modified polybenzoxazole fiber aerogel according to claim 1, characterized in that: The acidic substances in step S1 are methanesulfonic acid and polyphosphoric acid; the mass ratio of the polybenzoxazole nanofibers to the acidic substances is 2:

50.

3. The method for preparing a nano-alumina modified polybenzoxazole fiber aerogel according to claim 1, characterized in that: The particle size of the nano-alumina in step S2 is 18nm-24nm.

4. The method for preparing a nano-alumina modified polybenzoxazole fiber aerogel according to claim 1, characterized in that: The gel temperature described in step S3 is 60°C.

5. The method for preparing a nano-alumina 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 nano-alumina 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 11 hours.

7. A nano-alumina modified polybenzoxazole fiber aerogel, characterized in that: The method for preparing a nano-alumina-modified polybenzoxazole fiber aerogel according to any one of claims 1 to 6, wherein the nano-alumina-modified polybenzoxazole fiber aerogel exhibits a three-dimensional interconnected nanoporous network structure and has a density of 0.115 g / cm 3 -0.357g / cm 3 The thermal conductivity is 0.0249W / (m·K)-0.0376W / (m·K), the residual carbon rate is 58.2%-70.6%, and the limiting oxygen index is 45.8%-57.9%. It has the characteristics of light weight, high residual carbon and high-efficiency flame retardant and heat insulation.

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