Nano whisker and clay aerogel composite material and preparation method thereof

Abstract

The invention belongs to the technical field of new materials, and discloses a nano whisker and clay aerogel composite material and a preparation method thereof. The composite material comprises nano whiskers and clay aerogel, the clay aerogel is filled with the nano whiskers, and raw materials for preparing the clay aerogel comprise clay, inorganic alkali, acrylic acid and a bonding aid. According to the preparation method, the clay is subjected to surface hydroxylation modification and then reacts with the acrylic acid to prepare the acrylic acid modified clay, so that on one hand, the specific surface area of the clay is increased, and the dispersity and uniformity of the clay are improved; on the other hand, the modified clay has better compatibility with the nanowhisker and the bonding aid, so that various components can be well bonded, and the interface bonding property between the nanowhisker and the clay aerogel is favorably improved, thereby improving the stability and mechanical strength of the nanowhisker and clay aerogel composite material.

Description

Technical Field

[0001] This invention belongs to the field of new materials technology, and specifically relates to a composite material of nanocrystal whiskers and clay aerogel and its preparation method. Background Technology

[0002] Aerogels are amorphous solid materials with a unique three-dimensional network porous structure, formed by the cross-linking of molecules or polymers. Their unique structure endows them with excellent properties such as high porosity, high specific surface area, low density, and low thermal conductivity, attracting widespread attention in aerospace, industry, construction, and other fields. Currently, research on SiO2 aerogels is becoming increasingly mature; however, the preparation of SiO2 aerogels is time-consuming, the properties of the prepared aerogel materials are difficult to control, and the cost is high, significantly limiting the industrial production and application of aerogels. Furthermore, the production of SiO2 aerogels consumes large amounts of fossil fuels and non-renewable energy, placing a burden on environmental protection.

[0003] With the development of aerogel materials and preparation technology, aerogel materials are no longer limited to SiO2 aerogels. Clay aerogels, prepared from clay as raw material through sol and low-temperature vacuum drying processes, have good biocompatibility and degradability. The preparation process is simple and environmentally friendly, and it is considered a promising new type of environmentally friendly aerogel material.

[0004] However, pure clay aerogels inherently suffer from low strength and high brittleness. To overcome these drawbacks, one approach is to enhance the skeletal structure of the aerogel itself by controlling the preparation process parameters. Another approach is to use materials such as fibers as reinforcements to prepare aerogel composites, thereby increasing the toughness and strength of the aerogel and addressing its weak mechanical strength. Among these methods, the fiber-reinforced aerogel integral molding method for preparing composites is currently a relatively effective approach and has become a research hotspot for improving the mechanical properties of aerogels. Numerous domestic and international publications have reported on the use of inorganic fibers to reinforce aerogels. Inorganic fibers effectively improve the strength of aerogel materials. Due to their good temperature resistance and certain shielding effect against high-temperature radiation, inorganic fibers are mostly used for thermal insulation under high-temperature conditions. However, inorganic fibers have relatively large diameters, such as glass fibers (5-25 μm) and ceramic fibers (approximately 2-5 μm). Mullite fibers, on the other hand, are limited in production and application due to the scarcity of this mineral. Hard silicate fibers have smaller diameters but a wide distribution, ranging from a few micrometers to tens of nanometers. This significant difference in scale compared to the particle and pore sizes of aerogels leads to cracking at the fiber-aerogel interface, which is detrimental to the strength, flexibility, and structural stability of aerogels.

[0005] To address the brittleness and poor flexibility of aerogels caused by the brittleness of inorganic fiber components, many researchers have begun to use polymer fibers to replace inorganic fibers, utilizing the flexibility of fibers for reinforcement and toughening. Compared to the brittleness of inorganic fiber components, the inherent flexibility of polymer fibers has significantly improved the mechanical properties of aerogels, especially in terms of flexibility. However, similar to the large diameter of inorganic fibers, the diameter of polymer fibers (approximately tens of micrometers) is much larger than that of clay aerogels (nanometers). This makes them prone to aggregation during the preparation of fiber-aerogel composites, leading to cracking and density inhomogeneity, thus affecting the mechanical structural stability of the fiber-aerogel composites.

[0006] In conclusion, there is an urgent need to develop a new aerogel material that can improve its mechanical properties and thermal insulation performance while ensuring its lightweight nature. Summary of the Invention

[0007] The present invention aims to solve at least one of the technical problems existing in the prior art. To this end, the present invention proposes a nanocrystalline whisker and clay aerogel composite material and its preparation method. The composite material has good bulking properties, stability and mechanical properties, and is lightweight, environmentally friendly, and has good thermal insulation properties.

[0008] To address the aforementioned technical problems, a first aspect of the present invention provides a composite material comprising nanocrystals and clay aerogel, wherein the nanocrystals are filled within the clay aerogel, and the raw materials for preparing the clay aerogel include clay, inorganic alkali, acrylic acid, and adhesive additives.

[0009] Specifically, this invention uses inorganic alkali and acrylic acid to modify clay, thereby increasing its specific surface area and improving its dispersibility and uniformity. Simultaneously, the modified clay exhibits better compatibility with nanofibers and adhesives, thus enhancing the bonding performance between the clay and nanofibers. This significantly improves the interfacial bonding of the nanofiber-clay aerogel composite material, contributing to improvements in product stability, mechanical strength, and other properties.

[0010] Meanwhile, according to the classical load transfer mechanism, when the polymer-based whisker composite material is subjected to external force, the stress can be transferred from the matrix to the whiskers through the interface layer. The whiskers bear part of the stress, thus dispersing the stress on the matrix. Therefore, when the elastic modulus increases significantly, and the strength of the nanofibers is greater than that of the clay matrix, the interface between the whiskers and clay fills the gaps between the clay layers under the action of the binder, forming a reinforcing skeleton. When the composite material is subjected to external stress, the stress can be transferred from the nanofibers to the nanofibers through the clay matrix, causing stronger stress to act on the nanofibers and thus reducing the stress on the matrix material. When the amount of nanofibers added increases, the stress transmission channels also increase accordingly, which is beneficial to improving the compressive strength of the composite material. Therefore, this invention, by constructing a composite material of nanofibers and clay aerogel, can effectively improve its mechanical properties and stability.

[0011] In some embodiments of the present invention, the nanowhiskers are inorganic whiskers, and the diameter of the nanowhiskers is 1-10 μm and the aspect ratio is 10-500.

[0012] Specifically, inorganic nanofibers are fibers grown in single-crystal form with a highly oriented structure. Due to their highly ordered atomic arrangement, their strength is close to the theoretical value of a perfect crystal, exhibiting high strength, high modulus, and high elongation. Their strength is significantly higher than other chopped fibers, and they are easily composited with polymers, significantly improving the strength of composite materials as reinforcements. Simultaneously, nanofibers have low bulk density and large specific surface area, exhibiting good resistance to high temperatures and acid / alkali corrosion. Therefore, this invention utilizes inorganic nanofibers to improve the mechanical strength and chemical corrosion resistance of composite materials.

[0013] In some embodiments of the present invention, the inorganic whiskers are calcium sulfate whiskers. my country has abundant reserves of calcium sulfate, low cost, and promising market application prospects.

[0014] In some embodiments of the present invention, the clay is selected from at least one of montmorillonite, kaolin, and organobentonite.

[0015] In some embodiments of the present invention, the mass ratio of the nanofibers to the clay aerogel is 1:(30-100); preferably, the mass ratio of the nanofibers to the clay aerogel is 1:(30-60); more preferably, the mass ratio of the nanofibers to the clay aerogel is 1:(30-40).

[0016] In some embodiments of the present invention, the adhesive is selected from at least one of polyimide, polyvinyl alcohol, polyacrylic acid, polystyrene, polyacrylate, polyurethane, polyimide, epoxy resin, pectin, agar, and casein.

[0017] In some embodiments of the present invention, the inorganic base is selected from at least one of sodium hydroxide and potassium hydroxide.

[0018] A second aspect of the present invention provides a method for preparing the above-mentioned composite material, comprising the following steps: (1) Add clay to an inorganic alkaline solution, heat to react, and purify to obtain hydroxylated clay; (2) The hydroxylated clay was added to acrylic acid, ultrasonically heated, and reacted. After purification, modified acrylic acid was obtained. clay; (3) Add the acrylic modified clay to the adhesive additive solution and stir to obtain clay sol; (4) Add nano whiskers to the clay sol, stir and disperse, cool down and react to obtain nano whisker-clay gel; (5) The nano-whisker-clay gel is freeze-dried and heat-dried successively to obtain the composite material.

[0019] Specifically, in the preparation of the composite material of the present invention, the clay is first modified by surface hydroxylation, and then reacted with acrylic acid to obtain acrylic acid modified clay. On the one hand, this is beneficial to increase the specific surface area of ​​the clay and improve its dispersibility and uniformity; on the other hand, the modified clay has better compatibility with nano whiskers and adhesives, enabling good bonding between various components, which is beneficial to improve the interfacial bonding between nano whiskers and clay aerogel, thereby improving the stability and mechanical strength of the product.

[0020] In some embodiments of the present invention, in step (1), the heating temperature is 80-100°C and the heating time is 4-6 h.

[0021] In some embodiments of the present invention, in step (1), the concentration of the inorganic alkaline solution is 20-40 wt%.

[0022] In some embodiments of the present invention, in step (2), the temperature of the ultrasonic heating is 80-100°C and the time of the ultrasonic heating is 4-6 hours.

[0023] In some embodiments of the present invention, in step (2), the ultrasonic power of the ultrasonic heating is 350-450W.

[0024] In some embodiments of the present invention, in step (2), the mass ratio of the hydroxylated clay to acrylic acid is 1:(8-12).

[0025] In some embodiments of the present invention, the purification in steps (1) and (2) includes centrifugation, washing and drying.

[0026] In some embodiments of the present invention, in step (3), the solvent of the adhesive aid solution is selected from at least one of dimethylformamide, acetone, ethanol, isopropanol and water.

[0027] In some embodiments of the present invention, the water is selected from at least one of deionized water, distilled water, and purified water.

[0028] In some embodiments of the present invention, in step (3), the concentration of the adhesive additive solution is 0.1-4 wt%. Preferably, the concentration of the adhesive additive solution is 1-4 wt%.

[0029] In some embodiments of the present invention, in step (3), the mass ratio of the acrylic modified clay to the adhesive additive solution is 1:(30-300); preferably, the mass ratio of the acrylic modified clay to the adhesive additive solution is 1:(30-100); more preferably, the mass ratio of the acrylic modified clay to the adhesive additive solution is 1:(30-50).

[0030] In some embodiments of the present invention, in step (3), the stirring speed is 100-5000 r / min and the stirring time is 1-10 min.

[0031] In some embodiments of the present invention, in step (4), the temperature is reduced to -200°C to -10°C.

[0032] In some embodiments of the present invention, in step (4), the stirring speed is 300-1000 r / min and the stirring time is 10-60 min.

[0033] In some embodiments of the present invention, in step (5), the freeze-drying temperature is -80°C to -10°C, and the freeze-drying time is 12-60 minutes. In some embodiments of the present invention, in step (5), the temperature of the heating and drying is 30-100°C, and the time of the heating and drying is 12-24h.

[0034] Compared with the prior art, the above-described technical solution of the present invention has at least the following technical effects or advantages: (1) The present invention first modifies the surface of clay by hydroxylation and then reacts it with acrylic acid to obtain acrylic acid modified clay. On the one hand, it is beneficial to increase the specific surface area of ​​clay and improve the dispersibility and uniformity of clay. On the other hand, the modified clay has better compatibility with nano whiskers and adhesives, enabling good bonding between various components and improving the interfacial bonding between nano whiskers and clay aerogel, thereby improving the stability and mechanical strength of nano whisker and clay aerogel composite materials.

[0035] (2) This invention utilizes the classical load transfer mechanism to prepare a composite material of nanofibers and clay aerogel. This composite material possesses both good mechanical strength and thermal insulation properties, achieving a density of 0.11-0.12 g / cm³. 3 At that time, the thermal conductivity was as low as 0.036-0.050 W·m. -1 ·K -1 The compressive strength is 2.58-4.21 MPa. Attached Figure Description

[0036] Figure 1 This is a process flow diagram for preparing the nano-whisker-clay aerogel composite material of the present invention. Detailed Implementation

[0037] The present invention will now be described in detail with reference to embodiments to facilitate understanding of the invention by those skilled in the art. It is particularly important to note that the embodiments are merely illustrative of the invention and should not be construed as limiting the scope of protection of the invention. Non-essential improvements and adjustments made to the invention by those skilled in the art based on the above description should still fall within the scope of protection of the invention. Furthermore, all raw materials mentioned below, unless otherwise specified, are commercially available products; all process steps or preparation methods not mentioned in detail are process steps or preparation methods known to those skilled in the art.

[0038] The raw materials used in the following examples and comparative examples are as follows: Polyvinyl alcohol is [C2H4O]. n The relative molecular mass is 25,000-35,000, and it was purchased from Tianjin Zhiyuan Chemical Reagent Co., Ltd.

[0039] Pectin is [C5H] 10 O5] n The relative molecular mass is 20,000-100,000, and it was purchased from Shanghai Aladdin Biochemical Technology Co., Ltd.

[0040] The nanocrystals are calcium sulfate whiskers with a diameter of 1-10 μm and an aspect ratio of 10-500, purchased from Tsinghua University.

[0041] Example 1 A method for preparing a composite material of nanocrystals and clay aerogel, the preparation process flow is as follows: Figure 1 As shown, the specific steps include the following: (1) Montmorillonite was immersed in a sufficient amount of 30wt% sodium hydroxide solution, heated and stirred at 90℃ for 6h, cooled, centrifuged, washed and dried to obtain hydroxylated montmorillonite; (2) Hydroxylated montmorillonite and acrylic acid in a mass ratio of 1:10 were added to the reactor and stirred evenly. The mixture was then ultrasonically stirred at 100°C for 4 hours under a nitrogen atmosphere (ultrasonic power 400W). After cooling, the mixture was centrifuged, washed, and dried to obtain modified clay. (3) Polyvinyl alcohol and deionized water with a mass ratio of 3:97 were mixed and stirred at 85°C until dissolved to obtain a polyvinyl alcohol solution for adhesive additives; then modified clay and polyvinyl alcohol solution with a mass ratio of 3:103 were mixed and stirred at 5000 r / min for 2 min to obtain clay-adhesive additive sol. (4) Add calcium sulfate nanocrystals with a mass ratio of 3:106 to clay-adhesive sol and stir at 5000 r / min for 2 min to obtain nanocrystal-clay sol; then react the nanocrystal-clay sol at -80℃ for 5 min to obtain nanocrystal / clay gel. (5) The nano-whisker-clay gel was placed in a freeze dryer and freeze-dried at -45°C for 12 hours, and then heat-dried at 60°C for 12 hours to obtain the nano-whisker-clay aerogel composite material of this embodiment.

[0042] Example 2 A method for preparing a composite material of nanocrystals and clay aerogel, the preparation process flow is as follows: Figure 1 As shown, the specific steps include the following: (1) Montmorillonite was immersed in a sufficient amount of 30wt% sodium hydroxide solution, heated and stirred at 90℃ for 6h, cooled, centrifuged, washed and dried to obtain hydroxylated montmorillonite; (2) Hydroxylated montmorillonite and acrylic acid in a mass ratio of 1:10 were added to the reactor and stirred evenly. The mixture was then ultrasonically stirred at 100°C for 4 hours under a nitrogen atmosphere (ultrasonic power 400W). After cooling, the mixture was centrifuged, washed, and dried to obtain modified clay. (3) Pectin and deionized water with a mass ratio of 3:97 were mixed and stirred at 60°C until dissolved to obtain an adhesive pectin solution; then modified clay with a mass ratio of 3:103 and pectin solution were mixed and stirred at 5000 r / min for 2 min to obtain a clay-adhesive sol. (4) Add calcium sulfate nanocrystals with a mass ratio of 3:106 to clay-adhesive sol and stir at 5000 r / min for 2 min to obtain nanocrystal-clay sol; then react the nanocrystal-clay sol at -80℃ for 5 min to obtain nanocrystal / clay gel. (5) The nano-whisker-clay gel was placed in a freeze dryer and freeze-dried at -45°C for 60 h, and then heat-dried at 60°C for 24 h to obtain the nano-whisker-clay aerogel composite material of this embodiment.

[0043] Example 3 A method for preparing a composite material of nanocrystals and clay aerogel, the preparation process flow is as follows: Figure 1 As shown, the specific steps include the following: (1) Kaolin was immersed in a sufficient amount of 30wt% sodium hydroxide solution, heated and stirred at 90℃ for 6h, cooled, centrifuged, washed and dried to obtain hydroxylated montmorillonite; (2) Hydroxylated kaolin and acrylic acid with a mass ratio of 1:10 were added to the reaction vessel and stirred evenly. The mixture was then ultrasonically stirred at 100°C for 4 hours under a nitrogen atmosphere (ultrasonic power 400W). After cooling, the mixture was centrifuged, washed, and dried to obtain modified clay. (3) Pectin and deionized water with a mass ratio of 3:97 were mixed and stirred at 60°C until dissolved to obtain an adhesive pectin solution; then modified clay with a mass ratio of 3:103 and pectin solution were mixed and stirred at 5000 r / min for 2 min to obtain a clay-adhesive sol. (4) Add calcium sulfate nanocrystals with a mass ratio of 3:106 to clay-adhesive sol and stir at 5000 r / min for 2 min to obtain nanocrystal-clay sol; then react the nanocrystal-clay sol at -80℃ for 5 min to obtain nanocrystal / clay gel. (5) The nano-whisker-clay gel was placed in a freeze dryer and freeze-dried at -45°C for 24 hours, and then heat-dried at 60°C for 18 hours to obtain the nano-whisker-clay aerogel composite material of this embodiment.

[0044] Comparative Example 1 The difference between Comparative Example 1 and Example 1 is that the nano-whisker-clay aerogel composite material of Comparative Example 1 does not contain steps (1) and (2) in the preparation process, that is, the montmorillonite is not modified.

[0045] Comparative Example 2 The difference between Comparative Example 1 and Example 1 is that, in the preparation process of the composite material of Comparative Example 1, carboxymethyl cellulose of equal mass is used to replace the calcium sulfate nanocrystals of Example 1 in step (4).

[0046] Performance testing The density, thermal conductivity, and compressive strength of the composite material samples prepared in Examples 1-3 and Comparative Examples 1-2 were tested, and the test methods are as follows: Density: Cut the sample into regular shapes, measure the length, width, and height of the regular sample using calipers or a ruler, and calculate its volume V (cm³). 3Then, the mass m (g) of the sample is measured using a precision balance, and the sample density is calculated using the formula density ρ=m / V.

[0047] Thermal conductivity: The thermal conductivity of the composite material was determined using a thermal constant analysis instrument, model TPS1500, manufactured by HotDisk GmbH, Sweden.

[0048] Compressive strength: The compressive strength of the composite material was determined using a microcomputer-controlled electronic universal testing machine, model CMT6503, manufactured by Shenzhen Sansi Technology Co., Ltd.

[0049] The test results are shown in Table 1.

[0050] Table 1:

[0051] As shown in Table 1, the composite materials of nanocrystals and clay aerogels prepared in Examples 1-3 all exhibit good mechanical strength and thermal insulation properties, achieving densities of 0.11-0.12 g / cm³. 3 At that time, the thermal conductivity was as low as 0.036-0.050 W·m. -1 ·K -1 The compressive strength is 2.58-4.21 MPa, and its mechanical strength and thermal insulation performance are significantly higher than those of Comparative Example 1, which was not modified with clay, and Comparative Example 2, which was made from cellulose.

[0052] For those skilled in the art, several simple deductions or substitutions can be made without departing from the inventive concept, without requiring creative effort. Therefore, any simple improvements made to this invention by those skilled in the art based on the disclosure of this invention should be within the scope of protection of this invention. The above embodiments are preferred embodiments of this invention, and all processes similar to this invention and equivalent changes should fall within the scope of protection of this invention.

Claims

1. A composite material, characterized by, The composite material comprises nanowhiskers and clay aerogel, the nanowhiskers are filled in the clay aerogel, and the raw materials for preparing the clay aerogel comprise clay, inorganic alkali, acrylic acid and adhesion aid.

2. The composite material of claim 1, wherein, The nanowhiskers are inorganic whiskers, the diameter of the nanowhiskers is 1-10 μm, and the length-diameter ratio is 10-500. And / or, the clay is selected from at least one of montmorillonite, kaolin and organic bentonite. And / or, the adhesion aid is selected from at least one of polyimide, polyvinyl alcohol, polypropylene alcohol, polyacrylic acid, polystyrene, polyacrylate, polyurethane, polyimide, epoxy resin, pectin, agar, casein.

3. The composite material of claim 1, wherein, The mass ratio of the nanowhiskers and the clay aerogel is 1: (30-100).

4. A method of producing a composite material as claimed in any one of claims 1 to 3, characterised in that, The method comprises the following steps: (1) adding clay into inorganic alkali solution, heating, reacting, purifying, and obtaining hydroxylated clay; (2) adding the hydroxylated clay into acrylic acid, ultrasonic heating, reacting, purifying, and obtaining acrylic acid modified clay; (3) adding the acrylic acid modified clay into adhesion aid solution, stirring, and obtaining clay sol; (4) adding nanowhiskers into the clay sol, stirring and dispersing, cooling, and reacting, and obtaining nanowhisker-clay gel; (5) sequentially performing freeze drying and heat drying on the nanowhisker-clay gel, and obtaining the composite material. In step (1), the heating temperature is 80-100 ℃, and the heating time is 4-6 h.

5. The method of claim 4, wherein the composite material is prepared by a method comprising: In step (2), the ultrasonic heating temperature is 80-100 ℃, and the ultrasonic heating time is 4-6 h.

6. The method of claim 4, wherein the composite material is prepared by a method comprising: In step (2), the mass ratio of the hydroxylated clay and the acrylic acid is 1: (8-12).

7. The method of claim 4, wherein the step of applying the coating is performed by a method selected from the group consisting of: spray coating, dip coating, and spin coating. In step (3), the concentration of the adhesion aid solution is 0.1-4 wt%, and the mass ratio of the acrylic acid modified clay and the adhesion aid solution is 1: (30-300).

8. The method of claim 4, wherein the composite material is prepared by a method comprising: In step (4), the cooling is to-200 ℃ to-10 ℃.

9. The method of claim 4, wherein the composite material is prepared by a method comprising: In step (5), the freeze drying temperature is-80 ℃ to-10 ℃, and the freeze drying time is 12-60 h; the heat drying temperature is 30-100 ℃, and the heat drying time is 12-24 h.

10. The method of claim 4, wherein the composite material is prepared by a method comprising: ​

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