Nanometer ettringite particle reinforced aramid nanofiber aerogel, and preparation method and application thereof

Abstract

The application discloses a kind of nano ettringite particles reinforced aramid nanofiber aerogel and its preparation method and application, belong to aerogel technical field.The preparation method provided by the application includes the following steps: calcium source, aluminum source and sulfate are dissolved in water, first surfactant is added, pH is adjusted to 9~12, stirring reaction, after reaction, the solid product is washed to neutral to obtain nano ettringite particles;The nano ettringite particles, para-aramid nanofiber, second surfactant and crosslinking agent are stirred uniformly in water, to obtain ettringite / aramid nanofiber dispersion;The ettringite / aramid nanofiber dispersion is concentrated, directional freezing and freeze-drying in turn, and is obtained.The preparation method of the application is simple, and raw material is easy to obtain, and the obtained nano ettringite particle reinforced aramid nanofiber aerogel has higher mechanical strength and thermal stability.

Description

Technical Field

[0001] This invention relates to the field of aerogel technology, and in particular to a nano-calcite particle-reinforced aramid nanofiber aerogel, its preparation method, and its application. Background Technology

[0002] The information disclosed in the background section of this invention is intended only to enhance the understanding of the overall background of the invention and is not necessarily to be construed as an admission or in any way implying that such information constitutes prior art known to those skilled in the art.

[0003] Aerogels, composed of a three-dimensional network structure of nanoscale particles, possess ultra-low density, extremely high specific surface area, excellent thermal insulation properties, and acoustic characteristics, and have already demonstrated enormous application potential in aerospace, construction, energy, and environmental fields. In recent years, with advancements in preparation technologies and the development of novel aerogel materials, their applications in emerging fields such as flexible electronics, biomedicine, and adsorption separation have been continuously expanding, making them one of the cutting-edge hot topics in materials science research.

[0004] Para-aramid nanofibers are widely used in the preparation of high-performance composite materials due to their excellent heat resistance. However, traditional aramid fiber aerogels suffer from low mechanical strength and significant shrinkage after drying, limiting their application in certain fields. Therefore, providing a modified aramid fiber aerogel with high mechanical strength and low shrinkage is an urgent problem to be solved. Summary of the Invention

[0005] In view of this, the present invention provides a nano-calcite particle-reinforced aramid nanofiber aerogel, its preparation method and application. The present invention introduces nano-calcite particles into aramid nanofiber aerogel to form an organic-inorganic hybrid network structure, thereby significantly improving the mechanical properties and thermal stability of aramid nanofiber aerogel.

[0006] In a first aspect, the present invention provides a method for preparing aramid nanofiber aerogel reinforced with nano-calcite particles, comprising the following steps:

[0007] S1. Dissolve the calcium source, aluminum source and sulfate in water, add the first surfactant, adjust the pH to 9-12, stir the reaction, and wash the solid product until neutral to obtain nano-calcite particles.

[0008] S2. Stir and mix the nano-calcite particles, para-aramid nanofibers, second surfactant and crosslinking agent in water to obtain calcite / aramid nanofiber dispersion.

[0009] S3. The calcite / aramid nanofiber dispersion is successively concentrated, directionally frozen, and freeze-dried to obtain the final product.

[0010] Preferably, the calcium source is selected from one or more of calcium oxide, calcium hydroxide, calcium carbonate, or calcium nitrate; the aluminum source is selected from one or more of aluminum sulfate, aluminum oxide, aluminum chloride, or aluminum nitrate; and the sulfate is selected from one or more of calcium sulfate, aluminum sulfate, potassium sulfate, or sodium sulfate.

[0011] Preferably, among the calcium source, aluminum source, and sulfate, Ca 2+ Al 3+ With SO4 2- The molar ratio is (5.8~6.2):(1.8~2.2):(2.8~3.2).

[0012] Preferably, the first surfactant is selected from one or more of sodium hexametaphosphate, sodium polyacrylate, sodium pyrophosphate, or boric acid; the mass of the first surfactant is 1 to 5 wt% of the total mass of the solute.

[0013] Preferably, in step S1, the stirring reaction time is 4–10 h and the stirring reaction temperature is 10–35 °C; in step S2, the stirring and mixing time in water is 8–20 h and the temperature is 10–35 °C.

[0014] Preferably, in step S2, the mass ratio of the para-aramid nanofibers to the nano-ettringite particles is (5-9):(1-5), the mass fraction of the second surfactant is 0.1-1 wt%, and the mass ratio of the crosslinking agent to the para-aramid nanofibers is (2.5-3.5):1; in the ettringite / aramid nanofiber dispersion, the total mass fraction of the nano-ettringite particles and the para-aramid nanofibers is 0.1-0.7 wt%.

[0015] Preferably, the second surfactant is selected from one or more of sodium dodecyl sulfate, sodium dodecylbenzene sulfonate, or hexadecyltrimethylammonium bromide; the crosslinking agent is selected from one or more of methyltrimethoxysilane, γ-aminopropyltriethoxysilane, γ-glycidoxypropyltrimethoxysilane, or toluene diisocyanate.

[0016] Preferably, in step S3, during the concentration step, the total mass fraction of nano-calcite particles and para-aramid nanofibers is controlled to be 1-5 wt%.

[0017] Secondly, the present invention provides nano-calcite particles reinforced with aramid nanofiber aerogel prepared by the above preparation method.

[0018] Thirdly, the present invention provides the application of the above-mentioned nano-calcite particles reinforced aramid nanofiber aerogel in thermal insulation materials.

[0019] Compared with the prior art, the present invention has achieved the following beneficial effects:

[0020] (1) This invention introduces nano-calcite particles into aramid nanofiber aerogels. The shrinkage of traditional aramid nanofiber aerogels is over 40%, while the shrinkage of this invention can be controlled within 18%. This significant reduction in shrinkage makes the aerogel highly suitable for applications requiring high dimensional stability, such as high-temperature insulation and precision instrument protection. In high-temperature insulation applications, it can maintain structural stability for a long time, effectively avoiding insulation gaps caused by shrinkage, thus continuously and stably performing insulation performance and ensuring that the temperature environment inside the equipment or space is not disturbed by external heat flow. In terms of precision instrument protection, it can prevent adverse effects such as compression or displacement of instruments caused by the shrinkage of the aerogel itself, ensuring the accuracy and normal operation of the instruments.

[0021] (2) In the preparation process of nano-calcite particles reinforced aramid nanofiber aerogel, the present invention introduces a crosslinking agent, which promotes the physical entanglement between aramid nanofibers and forms chemical bonding points between nano-calcite particles and aramid nanofibers. This synergistic effect significantly improves the mechanical strength of the composite aerogel and reduces the shrinkage rate.

[0022] (3) The preparation method of the present invention is very simple and the raw materials are readily available, making it suitable for large-scale production. Attached Figure Description

[0023] The accompanying drawings, which form part of this specification, are used to provide a further understanding of the invention. The illustrative embodiments and descriptions of the invention are used to explain the invention and do not constitute an undue limitation thereof. Obviously, those skilled in the art can obtain other drawings based on these drawings without any inventive effort.

[0024] Figure 1 These are transmission electron microscope images of nano-calcite particles in Example 1 of this invention;

[0025] Figure 2 These are shrinkage test images of aerogel materials from Examples 1-8 and Comparative Example 1 of the present invention. Detailed Implementation

[0026] It should be noted that the following detailed descriptions are exemplary and intended to provide further illustration of the invention. Unless otherwise specified, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains.

[0027] This invention provides a method for preparing the above-mentioned nano-calcite particles reinforced aramid nanofiber aerogel, comprising the following steps:

[0028] S1. Dissolve the calcium source, aluminum source and sulfate in water, add the first surfactant, adjust the pH to 9-12, stir the reaction, and wash the solid product until neutral to obtain nano-calcite particles.

[0029] S2. Stir and mix the nano-calcite particles, para-aramid nanofibers, second surfactant and crosslinking agent in water to obtain calcite / aramid nanofiber dispersion.

[0030] S3. The calcite / aramid nanofiber dispersion is successively concentrated, directionally frozen, and freeze-dried to obtain the final product.

[0031] Etnacite is a common cement hydration product with the chemical formula 3CaO·Al₂O₃·3CaSO₄·32H₂O. It possesses a unique needle-like crystal structure and high mechanical strength. This invention introduces nano-ettlite particles into the structure of aramid nanofiber aerogels, forming an organic-inorganic hybrid network structure, thereby improving the mechanical properties and thermal stability of the aerogel. The nano-ettlite particles contain a large amount of water of crystallization. Under high-temperature conditions, this water of crystallization is gradually released, producing a significant endothermic effect and effectively reducing the heating rate of the aerogel. After dehydration, the ettlite transforms into a dense metal oxide layer, which has excellent barrier properties, effectively preventing oxygen penetration and heat conduction, thus protecting the aerogel material from further thermal damage. This invention introduces nano-sized ettringite particles into aramid nanofiber aerogels. Traditional aramid nanofiber aerogels exhibit shrinkage exceeding 40%, while the shrinkage in this study can be controlled to within 18%, and even below 10%. This significant reduction in shrinkage makes the aerogel highly suitable for applications requiring high dimensional stability, such as high-temperature insulation and precision instrument protection. The nano-sized ettringite particles of this invention are prepared using a solution method, which is simple.

[0032] In this invention, the calcium source is selected from one or more of calcium oxide, calcium hydroxide, calcium carbonate, or calcium nitrate; the aluminum source is selected from one or more of aluminum sulfate, aluminum oxide, aluminum chloride, or aluminum nitrate; and the sulfate is selected from one or more of calcium sulfate, aluminum sulfate, potassium sulfate, or sodium sulfate. The metal salts mentioned above may also be selected from hydrated salts of the corresponding metal salts, and this invention does not impose any special limitations on this.

[0033] In the calcium source, aluminum source, and sulfate described in this invention, Ca 2+ Al 3+ With SO4 2- The molar ratio is (5.8–6.2):(1.8–2.2):(2.8–3.2), more preferably 6:2:3. This invention does not impose any special limitations on the method of pH adjustment; any method commonly used in the art for pH adjustment may be employed.

[0034] In this invention, the first surfactant is selected from one or more of sodium hexametaphosphate, sodium polyacrylate, sodium pyrophosphate, or boric acid; the mass of the first surfactant is 1-5 wt% of the total solute mass. The addition of the first surfactant selectively adsorbs calcium ions on the surface of ettringite crystals, reducing the surface energy of the crystals and inhibiting further growth on the crystal surface, thereby controlling the particle size of nano-ettringite. This invention does not impose special limitations on the amount of water added as long as the reaction proceeds normally.

[0035] In step S1 of this invention, the stirring reaction time is 4–10 hours, and the stirring reaction temperature is 10–35°C; in step S2, the stirring and mixing time in water is 8–20 hours, and the temperature is 10–35°C. Both steps S1 and S2 of this invention can be carried out at room temperature, resulting in low energy consumption and simple operation.

[0036] In step S2 of this invention, the mass ratio of the para-aramid nanofibers to the nano-ettringite particles is (5-9):(1-5), more preferably (6-8):(2-4), and most preferably 6:4. If the amount of nano-ettringite particles added is too low, the improvement effect on the properties of the aramid nanofiber aerogel is not significant. If the amount of nano-ettringite particles added is too high, the distance between the particles is too close, and dispersants such as surfactants may not be able to completely prevent particle aggregation, resulting in the formation of agglomerates. This leads to uneven distribution of the reinforcing phase in the aramid nanofiber aerogel. When the aerogel is subjected to external forces, stress concentration will occur around these agglomerates; furthermore, it increases cost and preparation difficulty.

[0037] In this invention, the amount of the second surfactant added is 0.1–1 wt%, more preferably 0.2–0.5 wt%, which is relative to the total mass of all substances. The mass ratio of the crosslinking agent to the para-aramid nanofibers is (2.5–3.5):1; in the ettringite / aramid nanofiber dispersion, the total mass fraction of the nano-ettringite particles and the para-aramid nanofibers is 0.1–0.7 wt%, more preferably 0.2–0.6 wt%. This mass fraction ensures that the para-aramid fibers are fully dispersed, thereby better and more uniformly mixed with the nano-ettringite.

[0038] In this invention, the second surfactant is selected from one or more of sodium dodecyl sulfate, sodium dodecylbenzene sulfonate, or hexadecyltrimethylammonium bromide. The hydrophobic group of the second surfactant can interact with the surface of the nano-ettringite particles, while the hydrophilic group extends into the aqueous phase, thereby forming an adsorption layer on the particle surface. This prevents direct contact between particles, effectively preventing aggregation and allowing the nano-ettringite particles to be uniformly dispersed in the system. Secondly, it can promote the dispersion of para-aramid nanofibers, allowing them to be better dispersed in the system. This helps to form a more uniform fiber network structure, providing a good foundation for the preparation of aerogels and thus improving the uniformity of aerogel performance.

[0039] In this invention, the crosslinking agent is selected from one or more of methyltrimethoxysilane, γ-aminopropyltriethoxysilane, γ-glycidyl etheroxypropyltrimethoxysilane, or toluene diisocyanate. These crosslinking agents promote physical entanglement between aramid nanofibers in the system and form chemical bonding points between the nano-ettringite particles and the aramid nanofibers. This synergistic effect significantly improves the mechanical strength of the composite aerogel. Furthermore, the introduction of the crosslinking agent enhances the hydrophobicity of the aerogel, improving the environmental stability of the aerogel material.

[0040] In step S3 of this invention, during the concentration step, the total mass fraction of nano-calcite particles and para-aramid nanofibers is controlled to be 1–5 wt%, more preferably 2–4 wt%. By adjusting this mass fraction, the density and mechanical properties of the final hydrogel can be controlled. This invention does not impose special restrictions on the concentration method; filtration, vacuum filtration, distillation, rotary evaporation, etc., can be used. This invention preferably uses vacuum filtration for concentration. If the concentration is too high after concentration, a specific mass of deionized water is added to achieve the set mass fraction.

[0041] This invention does not impose any particular limitations on the methods of directional freezing and freeze-drying; methods commonly used in the field can be employed. Directional freezing can control the direction of ice crystal growth, forming an ordered pore structure. The generated pores are relatively uniform in size and orderly arranged, which can increase the specific surface area of ​​the aerogel. The ordered microstructure helps to enhance the mechanical properties of the aerogel. When the pore structure of the aerogel exhibits a regular arrangement, it can better disperse stress when subjected to external forces. In addition, due to the ordered nature of the pore structure, air convection in the pores is effectively restricted, while the heat conduction path of the solid skeleton becomes more complex. Directional freezing is preferably performed using liquid nitrogen.

[0042] This invention also provides a nano-calcite particle-reinforced aramid nanofiber aerogel prepared by the above-described method, wherein the nano-calcite particles fill and embeded in the pores of the aramid nanofiber aerogel matrix. The nano-calcite particle-reinforced aramid nanofiber aerogel of this invention exhibits excellent mechanical properties and thermal stability.

[0043] This invention also provides the application of the above-mentioned nano-calcite particles reinforced aramid nanofiber aerogel in thermal insulation materials. The thermal conductivity of the nano-calcite particles reinforced aramid nanofiber aerogel of this invention is 30 mW·m. -1 ·K -1 The aerogel exhibits excellent thermal insulation properties. In high-temperature insulation applications, it can maintain structural stability for extended periods, effectively preventing insulation gaps caused by shrinkage, thus ensuring continuous and stable insulation performance and protecting the temperature environment within the equipment or space from external heat flow interference. In the protection of precision instruments, it can prevent adverse effects such as compression or displacement of instruments caused by the shrinkage of the aerogel itself, ensuring the accuracy and normal operation of the instruments.

[0044] The technical solution of the present invention will be further described below with reference to specific embodiments. The present invention does not impose any special restrictions on the source of reagents used in the following embodiments; commercially available products well known to those skilled in the art can be used.

[0045] Example 1

[0046] This embodiment provides a method for preparing ettringite / aramid nanofiber aerogel.

[0047] (1) Preparation of nano-calcite particles: Dissolve 13.33 g, 0.02 mol of aluminum sulfate octahydrate and 6.73 g, 0.12 mol of calcium oxide in a molar ratio of 1:6 in 200 mL of water, add 2 wt% sodium hexametaphosphate, add 0.2 mol / L sodium hydroxide solution, adjust the pH of the solution to 10, stir at room temperature for 5 h, add sodium hydroxide solution every 2 h to maintain the pH of the solution at 10, let stand for 12 h after preparation, vacuum filter the obtained suspension using a vacuum filtration device, and wash until neutral, and dilute the obtained nano-calcite particles with deionized water for later use. Figure 1 The images show transmission electron microscopy (TEM) images of nano-ettringite particles. As can be seen, the particle size of the nano-ettringite particles is less than 200 nm, and there is no large aggregation. When added to the para-aramid nanofiber dispersion to prepare aerogel, both of which are nanomaterials, it is beneficial to form a more uniform pore structure in the aerogel. Nanomaterials have a large specific surface area and a relatively large number of surface atoms, thus exhibiting high chemical reactivity and providing more reaction sites.

[0048] (2) Preparation of ettringite / aramid nanofiber aerogel:

[0049] 0.9 g of para-aramid nanofibers and nano-calcite particles (mass ratio 6:4) were dispersed in 400 mL of deionized water. Sodium dodecyl sulfate and methyltrimethoxysilane (mass ratio of methyltrimethoxysilane to para-aramid nanofibers 3:1) were added at a mass fraction of 0.3 wt%, and the mixture was stirred at room temperature for 12 h to obtain a suspension.

[0050] The prepared suspension was filtered to a certain extent using a vacuum filtration device, and then deionized water was added to control the total mass fraction of para-aramid nanofibers and nano-ettringite particles to be 1.5 wt%. After being stirred evenly using a high-speed dispersion homogenizer, it was loaded into a copper orientation mold and orientedly frozen with liquid nitrogen for 30 min. Then it was placed in a vacuum freeze dryer and frozen at -80℃ for 64 h to obtain ettringite / aramid nanofiber aerogel.

[0051] Example 2

[0052] This embodiment provides a method for preparing ettringite / aramid nanofiber aerogel. In this embodiment, the preparation method of the nano-ettringite particles is the same as in Example 1.

[0053] 1.2 g of para-aramid nanofibers and nano-calcite particles (mass ratio 6:4) were dispersed in 400 mL of deionized water. Sodium dodecyl sulfate and methyltrimethoxysilane (mass ratio of methyltrimethoxysilane to para-aramid nanofibers 3:1) were added at a mass fraction of 0.3 wt%, and the mixture was stirred at room temperature for 12 h to obtain a suspension.

[0054] The prepared suspension was filtered to a certain extent using a vacuum filtration device, and then deionized water was added to control the total mass fraction of para-aramid nanofibers and nano-ettringite particles to be 2wt%. After being stirred evenly using a high-speed dispersion homogenizer, it was loaded into a copper orientation mold and oriented frozen with liquid nitrogen for 30 min. Then it was placed in a vacuum freeze dryer and frozen at -80℃ for 64 h to obtain ettringite / aramid nanofiber aerogel.

[0055] Example 3

[0056] This embodiment provides a method for preparing ettringite / aramid nanofiber aerogel. In this embodiment, the preparation method of the nano-ettringite particles is the same as in Example 1.

[0057] 1.8 g of para-aramid nanofibers and nano-calcite particles (mass ratio 6:4) were dispersed in 400 mL of deionized water. Sodium dodecyl sulfate and methyltrimethoxysilane (mass ratio of methyltrimethoxysilane to para-aramid nanofibers 3:1) were added at a mass fraction of 0.3 wt%, and the mixture was stirred at room temperature for 12 h to obtain a suspension.

[0058] The prepared suspension was filtered to a certain extent using a vacuum filtration device, and then deionized water was added to control the total mass fraction of para-aramid nanofibers and nano-ettringite particles to be 3wt%. After being stirred evenly using a high-speed dispersion homogenizer, it was loaded into a copper orientation mold and oriented frozen with liquid nitrogen for 30 min. Then it was placed in a vacuum freeze dryer and frozen at -80℃ for 64 h to obtain ettringite / aramid nanofiber aerogel.

[0059] Example 4

[0060] This embodiment provides a method for preparing ettringite / aramid nanofiber aerogel. In this embodiment, the preparation method of the nano-ettringite particles is the same as in Example 1.

[0061] 2.4 g of para-aramid nanofibers and nano-calcite particles (mass ratio 6:4) were dispersed in 400 mL of deionized water. Sodium dodecyl sulfate and methyltrimethoxysilane (mass ratio of methyltrimethoxysilane to para-aramid nanofibers 3:1) were added at a mass fraction of 0.3 wt%, and the mixture was stirred at room temperature for 12 h to obtain a suspension.

[0062] The prepared suspension was filtered to a certain extent using a vacuum filtration device, and then deionized water was added to control the total mass fraction of para-aramid nanofibers and nano-calcite particles to be 4 wt%. After being stirred evenly using a high-speed dispersion homogenizer, it was loaded into a copper orientation mold and oriented frozen with liquid nitrogen for 30 min. Then it was placed in a vacuum freeze dryer and frozen at -80℃ for 64 h to obtain calcite / aramid nanofiber aerogel.

[0063] Example 5

[0064] This embodiment provides a method for preparing ettringite / aramid nanofiber aerogel. In this embodiment, the preparation method of the nano-ettringite particles is the same as in Example 1.

[0065] 0.9 g of para-aramid nanofibers and nano-calcite particles (mass ratio 8:2) were dispersed in 400 mL of deionized water. Sodium dodecyl sulfate and methyltrimethoxysilane (mass ratio of methyltrimethoxysilane to para-aramid nanofibers 3:1) were added at a mass fraction of 0.3 wt%, and the mixture was stirred at room temperature for 12 h to obtain a suspension.

[0066] The prepared suspension was filtered to a certain extent using a vacuum filtration device, and then deionized water was added to control the total mass fraction of para-aramid nanofibers and nano-ettringite particles to be 1.5 wt%. After being stirred evenly using a high-speed dispersion homogenizer, it was loaded into a copper orientation mold and orientedly frozen with liquid nitrogen for 30 min. Then it was placed in a vacuum freeze dryer and frozen at -80℃ for 64 h to obtain ettringite / aramid nanofiber aerogel.

[0067] Example 6

[0068] This embodiment provides a method for preparing ettringite / aramid nanofiber aerogel. In this embodiment, the preparation method of the nano-ettringite particles is the same as in Example 1.

[0069] 1.2 g of para-aramid nanofibers and nano-calcite particles (mass ratio 8:2) were dispersed in 400 mL of deionized water. Sodium dodecyl sulfate and methyltrimethoxysilane (mass ratio of methyltrimethoxysilane to para-aramid nanofibers 3:1) were added at a mass fraction of 0.3 wt%, and the mixture was stirred at room temperature for 12 h to obtain a suspension.

[0070] The prepared suspension was filtered to a certain extent using a vacuum filtration device, and then deionized water was added to control the total mass fraction of para-aramid nanofibers and nano-ettringite particles to be 2wt%. After being stirred evenly using a high-speed dispersion homogenizer, it was loaded into a copper orientation mold and oriented frozen with liquid nitrogen for 30 min. Then it was placed in a vacuum freeze dryer and frozen at -80℃ for 64 h to obtain ettringite / aramid nanofiber aerogel.

[0071] Example 7

[0072] This embodiment provides a method for preparing ettringite / aramid nanofiber aerogel. In this embodiment, the preparation method of the nano-ettringite particles is the same as in Example 1.

[0073] 1.8 g of para-aramid nanofibers and nano-calcite particles (mass ratio 8:2) were dispersed in 400 mL of deionized water. Sodium dodecyl sulfate and methyltrimethoxysilane (mass ratio of methyltrimethoxysilane to para-aramid nanofibers 3:1) were added at a mass fraction of 0.3 wt%, and the mixture was stirred at room temperature for 12 h to obtain a suspension.

[0074] The prepared suspension was filtered to a certain extent using a vacuum filtration device, and then deionized water was added to control the total mass fraction of para-aramid nanofibers and nano-ettringite particles to be 3wt%. After being stirred evenly using a high-speed dispersion homogenizer, it was loaded into a copper orientation mold and oriented frozen with liquid nitrogen for 30 min. Then it was placed in a vacuum freeze dryer and frozen at -80℃ for 64 h to obtain ettringite / aramid nanofiber aerogel.

[0075] Example 8

[0076] 2.4 g of para-aramid nanofibers and nano-calcite particles (mass ratio 8:2) were dispersed in 400 mL of deionized water. Sodium dodecyl sulfate and methyltrimethoxysilane (mass ratio of methyltrimethoxysilane to para-aramid nanofibers 3:1) were added at a mass fraction of 0.3 wt%, and the mixture was stirred at room temperature for 12 h to obtain a suspension.

[0077] The prepared suspension was filtered to a certain extent using a vacuum filtration device, and then deionized water was added to control the total mass fraction of para-aramid nanofibers and nano-calcite particles to be 4 wt%. After being stirred evenly using a high-speed dispersion homogenizer, it was loaded into a copper orientation mold and oriented frozen with liquid nitrogen for 30 min. Then it was placed in a vacuum freeze dryer and frozen at -80℃ for 64 h to obtain calcite / aramid nanofiber aerogel.

[0078] Example 9

[0079] The difference between this embodiment and Example 3 is that methyltrimethoxysilane is replaced with γ-aminopropyltriethoxysilane.

[0080] Example 10

[0081] The difference between this embodiment and Example 3 is that sodium dodecyl sulfate is replaced with sodium dodecylbenzenesulfonate.

[0082] Comparative Example 1

[0083] The difference between this comparative example and Example 3 is that this comparative example does not contain nano-calcite particles, but only prepares aramid nanofiber aerogels. The preparation method is as follows:

[0084] 1.8 g of para-aramid nanofibers were dispersed in 400 mL of deionized water, and 0.3 wt% sodium dodecyl sulfate and methyltrimethoxysilane (the mass ratio of methyltrimethoxysilane to para-aramid nanofibers was 3:1) were added. The mixture was stirred at room temperature for 12 h to obtain a suspension.

[0085] The prepared suspension was filtered to a certain extent using a vacuum filtration device, and then deionized water was added to control the mass fraction of para-aramid nanofibers to 3wt%. After being stirred evenly using a high-speed dispersion homogenizer, it was loaded into a copper orientation mold and orientedly frozen with liquid nitrogen for 30 min. Then it was placed in a vacuum freeze dryer and frozen at -80℃ for 64 h to obtain aramid nanofiber aerogel.

[0086] Comparative Example 2

[0087] The difference between this comparative example and Example 3 is that methyltrimethoxysilane is not added to this comparative example.

[0088] Test case

[0089] 1. Mechanical property testing:

[0090] The mechanical properties of the aerogel materials in the examples and comparative examples were determined using a tensile testing machine, and the test results are summarized in Table 1.

[0091] Table 1. Mechanical property test results of the aerogel materials in the examples and comparative examples.

[0092]

[0093]

[0094] The data from Examples 1-4 and Examples 5-8 show that the mechanical properties initially increase and then decrease with increasing total mass fraction of nano-ettringite particles and para-aramid nanofibers, reaching a maximum at 3 wt%. Furthermore, the mass ratio of nano-ettringite particles to para-aramid nanofibers also affects the mechanical properties; comparatively, a mass ratio of 6:4 for para-aramid nanofibers to ettringite particles results in better tensile properties than 8:2. The mechanical property data from the Examples show a significant difference compared to Comparative Example 1, demonstrating the reinforcing effect of nano-ettringite particles in the para-aramid nanofiber aerogel. The comparison between Comparative Example 2 and Example 3 illustrates that the crosslinking agent plays a reinforcing role in enhancing tensile properties, promoting crosslinking and improving the mechanical properties of the aerogel.

[0095] 2. Shrinkage performance test

[0096] Shrinkage tests were conducted on the aerogel materials of Examples 4-5 and Comparative Examples 1-2. The test results are shown in Table 2 and... Figure 2 The specific testing method is as follows: The height change of the aerogel is measured using a steel ruler. The initial sample shape is a cube with a side length of 30 mm. After drying, the dimensions of the aerogel sample are measured using a micrometer. When calculating the shrinkage, the initial dimension is subtracted from the treated dimension, and the average value of the dimensional change in each direction is obtained. The shrinkage is expressed as an absolute shrinkage value (e.g., millimeters) and a relative shrinkage rate (e.g., (initial dimension - treated dimension) / initial dimension × 100%). "+" indicates an increase in dimension after drying, and "-" indicates a decrease in dimension after drying.

[0097] Table 2. Shrinkage change test results of aerogel materials in the examples and comparative examples.

[0098] serial number Absolute shrinkage value (mm) Relative shrinkage rate (%) Example 1 +2 +6.67％ Example 2 +1 +3.33％ Example 3 +2 +6.67％ Example 4 +2 +6.67％ Example 5 0 0％ Example 6 -5 -16.67％ Example 7 -1 -3.33％ Example 8 0 0％ Comparative Example 1 -13 -43.33％ Comparative Example 2 -10 -33.3％

[0099] As shown in Table 2, the aerogels of Examples 1-4 showed no shrinkage but slight expansion. This is because the addition of sodium dodecyl sulfate to the dispersion caused slight foaming of the aerogel. A comparison between Examples and Comparative Example 1 shows that ettringite significantly improved the shrinkage of the aerogel. A comparison between Comparative Example 2 and Example 3 shows that the crosslinking agent also played a promoting role in improving aerogel shrinkage.

[0100] 3. Density test

[0101] Density tests were conducted on the aerogel materials of Examples 4-5 and Comparative Examples 1-2, and the test results are shown in Table 3.

[0102] Table 3 Density test results

[0103] serial number <![CDATA[Density (kg / m 3 )]]> Example 1 16 Example 2 25 Example 3 45 Example 4 47 Example 5 30 Example 6 26 Example 7 50 Example 8 71 Comparative Example 1 44 Comparative Example 2 45

[0104] As can be seen from Table 3, the higher the proportion of nano-calcite particles, the lower the corresponding density; the density generally shows an increasing trend with the increase of mass fraction.

[0105] 4. Thermal conductivity test

[0106] Table 4 Thermal conductivity test results

[0107]

[0108]

[0109] As can be seen from Table 4, the thermal conductivity of para-aramid nanofiber aerogel was reduced by using nano-calcite particles and crosslinking agents.

[0110] The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A method for preparing aramid nanofiber aerogel reinforced with nano-calcite particles, characterized in that, Includes the following steps: S1. Dissolve the calcium source, aluminum source and sulfate in water, add the first surfactant, adjust the pH to 9-12, stir the reaction, and wash the solid product until neutral to obtain nano-calcite particles. S2. The nano-calcite particles, para-aramid nanofibers, second surfactant and crosslinking agent are stirred and mixed in water to obtain calcite / aramid nanofiber dispersion; the mass ratio of para-aramid nanofibers to nano-calcite particles is (5~9): (1~5); S3. The ettringite / aramid nanofiber dispersion is sequentially concentrated, directionally frozen, and freeze-dried to obtain the final product. In the concentration step, the total mass fraction of the ettringite nanoparticles and para-aramid nanofibers is controlled to be 2-4 wt%.

2. The preparation method according to claim 1, characterized in that, The calcium source is selected from one or more of calcium oxide, calcium hydroxide, calcium carbonate, or calcium nitrate; the aluminum source is selected from one or more of aluminum sulfate, aluminum oxide, aluminum chloride, or aluminum nitrate; and the sulfate is selected from one or more of calcium sulfate, aluminum sulfate, potassium sulfate, or sodium sulfate.

3. The preparation method according to claim 1, characterized in that, Among calcium sources, aluminum sources, and sulfates, Ca 2+ Al 3+ With SO4 2- The molar ratio is (5.8~6.2): ​​(1.8~2.2): (2.8~3.2).

4. The preparation method according to claim 1, characterized in that, The first surfactant is selected from one or more of sodium hexametaphosphate, sodium polyacrylate, sodium pyrophosphate, or boric acid; the mass of the first surfactant is 1 to 5 wt% of the total mass of the solute.

5. The preparation method according to claim 1, characterized in that, In step S1, the stirring reaction time is 4~10h and the stirring reaction temperature is 10~35℃; in step S2, the stirring and mixing time in water is 8~20h and the temperature is 10~35℃.

6. The preparation method according to claim 1, characterized in that, In step S2, the mass fraction of the second surfactant is 0.1~1wt%, and the mass ratio of the crosslinking agent to the para-aramid nanofiber is (2.5~3.5):1; in the ettringite / aramid nanofiber dispersion, the total mass fraction of the nano-ettringite particles and the para-aramid nanofiber is 0.1~0.7wt%.

7. The preparation method according to claim 1, characterized in that, The second surfactant is selected from one or more of sodium dodecyl sulfate, sodium dodecylbenzene sulfonate, or hexadecyltrimethylammonium bromide; the crosslinking agent is selected from one or more of methyltrimethoxysilane, γ-aminopropyltriethoxysilane, γ-glycidoxypropyltrimethoxysilane, or toluene diisocyanate.

8. The nano-calcite particles reinforced aramid nanofiber aerogel prepared by the preparation method according to any one of claims 1 to 7.

9. The application of the nano-calcite particle-reinforced aramid nanofiber aerogel as described in claim 8 in thermal insulation materials.

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