A bamboo-based aerogel, its preparation method, and a noise-reducing bamboo-based aerogel

Abstract

The present invention provides a bamboo-based aerogel, a preparation method thereof, and a noise-reducing bamboo-based aerogel, belonging to the technical field of aerogels. In the present invention, bamboo with a moisture content greater than or equal to 82% is selected. Through freezing, the weaker transverse tissue of the bamboo can be damaged by ice crystals, and the longitudinal orientation structure can be retained, enabling the softened bamboo to be flattened. In the present invention, impurities such as monosaccharides, fats, and proteins in the softened bamboo are removed through solvent heat treatment to improve the purity of the bamboo-based aerogel. In the present invention, a natural radially gradient porous aerogel can be obtained through drying. The method provided by the present invention is simple to operate and can prepare bamboo-based aerogels on a large scale; the noise-reducing bamboo-based aerogel obtained after its hydrophobic modification has excellent noise reduction effects.

Description

Technical Field

[0001] The present invention relates to the technical field of aerogels, and particularly to a bamboo-based aerogel, a preparation method thereof, and a noise-reducing bamboo-based aerogel. Background Art

[0002] A bamboo-based aerogel is an aerogel with a three-dimensional network structure prepared from bamboo. Its slender nanostructure endows the material with a large specific surface area and low thermal conductivity. The scattering of light and sound is much smaller than that of traditional porous materials, and it has broad application prospects in many fields.

[0003] Currently, the common preparation method of bamboo-based aerogels is the "bottom-up" method. This method prepares nanocellulose with a large aspect ratio from bamboo, then uses the nanocellulose to prepare gel-like blocks, and finally obtains bamboo-based aerogels through freeze-drying. For example, Chinese Patent CN 202110077714.2 discloses a bamboo-based oriented aerogel and its preparation method. Bamboo slices are rolled and split into bamboo filaments. After adding the bamboo filaments to inorganic acid for cooking and stirring, it is cooled to room temperature for filtration and homogenization to obtain bamboo nanocellulose. The obtained bamboo nanocellulose is spread on a plastic tube or plastic sheet, and slow water flow is maintained for a period of time, and then freeze-drying treatment is carried out to finally obtain an oriented aerogel material. Although this method can obtain bamboo-based oriented aerogels, the problems are that it is necessary to first prepare bamboo into nanocellulose, the preparation method is complex, and bamboo-based aerogels cannot be prepared on a large scale; moreover, when the nanocellulose is freeze-dried, the interfacial force is weak, and the bamboo-based aerogel obtained by freeze-thawing is prone to looseness, the shape cannot be customized, and the loose bamboo-based aerogel will have an adverse effect on the noise reduction performance.

[0004] Therefore, there is an urgent need to provide a method for preparing bamboo-based aerogels that can be prepared on a large scale with customizable shapes and high noise reduction performance. Summary of the Invention

[0005] The purpose of the present invention is to provide a bamboo-based aerogel, a preparation method thereof, and a noise-reducing bamboo-based aerogel. The preparation method provided by the present invention can prepare bamboo-based aerogels with customizable shapes and high noise reduction performance on a large scale.

[0006] In order to achieve the above-mentioned invention purpose, the present invention provides the following technical solutions:

[0007] The present invention provides a preparation method of a bamboo-based aerogel, comprising the following steps:

[0008] (1) Freezing and then thawing bamboo in sequence to obtain softened bamboo; the moisture content of the bamboo is greater than or equal to 82%.

[0009] (2) Subject the softened bamboo obtained in step (1) to solvent heat treatment to obtain impurity-removed bamboo.

[0010] (3) Dry the impurity-removed bamboo obtained in step (2) to obtain bamboo-based aerogel.

[0011] Preferably, the temperature for freezing in step (1) is below 0 °C.

[0012] Preferably, the temperature for solvent heat treatment in step (2) is 60 - 100 °C.

[0013] Preferably, the time for solvent heat treatment is 2 - 4 h.

[0014] Preferably, the drying in step (3) includes freeze-drying or supercritical drying.

[0015] Preferably, the temperature for freeze-drying is -20 - -40 °C, and the time for freeze-drying is 24 - 48 h.

[0016] The present invention also provides a bamboo-based aerogel prepared by the preparation method described in the above technical solution. By mass percentage, it includes the following components: cellulose 20 - 50%, hemicellulose 7 - 14%, lignin 2 - 5%, and others 31 - 71%.

[0017] The bamboo-based aerogel has a radial gradient porous structure, and the density of the bamboo-based aerogel in the radial direction increases gradually from the inside to the outside.

[0018] Preferably, the radial density of the bamboo-based aerogel is 48 - 77 mg / cm 3 .

[0019] The present invention also provides a noise-reducing bamboo-based aerogel, which includes the bamboo-based aerogel described in the above technical solution and a hydrophobic modifier modified on the bamboo-based aerogel.

[0020] Preferably, the preparation method of the noise-reducing bamboo-based aerogel includes: mixing the bamboo-based aerogel with a hydrophobic modifier solution and performing a surface modification reaction to obtain the noise-reducing bamboo-based aerogel.

[0021] The present invention provides a method for preparing bamboo-based aerogel, comprising the following steps: freezing and then thawing bamboo successively to obtain softened bamboo; the bamboo having a water content of greater than or equal to 82%; subjecting the softened bamboo to solvent heat treatment to obtain impurity-removed bamboo; and drying the impurity-removed bamboo to obtain bamboo-based aerogel. By selecting bamboo with a water content of greater than or equal to 82%, the fiber cells of the bamboo are in a relatively plump state but not completely saturated. In this state, the bamboo can better maintain its structure and properties during the drying process, forming a low-density and stable aerogel structure. The present invention selects bamboo with a height of 1 - 4 m. The fiber cell walls of this bamboo are thinner and the cellulose content is low, which is beneficial for forming a low-density and high-porosity aerogel. After selecting the above bamboo, freezing can be used to destroy the weaker transverse tissue of the bamboo by ice crystals, retaining the longitudinal orientation structure, so that the softened bamboo can form a radial gradient porous structure. Through solvent heat treatment, the present invention can remove impurities such as monosaccharides, fats, and proteins in the softened bamboo, improving the purity of the bamboo-based aerogel. Through drying, the present invention can use ice crystals to destroy the weaker transverse tissue of the softened bamboo, retaining the longitudinal orientation structure, so that the softened bamboo can form a radial gradient porous structure to obtain bamboo-based aerogel. The method provided by the present invention is simple to operate and can prepare bamboo-based aerogel on a large scale. Moreover, through the selection of bamboo, a low-density, high-porosity, flattenable and shape-customizable aerogel can be obtained after freezing and thawing. The results of the examples show that the bamboo-based aerogel prepared by the present invention has a radial gradient porous structure. The noise reduction coefficient of the noise reduction bamboo-based aerogel obtained after its silane modification is 0.38 when the thickness is 9 mm, which is greater than the noise reduction coefficients of commercial foams, graphene oxide foams, ceramic foams, wood, etc. with the same thickness. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 is a light microscope image of the axial and radial directions of the bamboo used in Example 1 of the present invention;

[0023] Figure 2 is a light microscope image of the axial and radial directions of the softened bamboo prepared in Example 1 of the present invention;

[0024] Figure 3 is a photograph of the bamboo used in Example 1 of the present invention;

[0025] Figure 4 is a photograph of the bamboo-based aerogel prepared in Example 1 of the present invention;

[0026] Figure 5 is a photograph of the bamboo-based aerogel prepared in Example 1 of the present invention with a customized specific morphology;

[0027] Figure 6 is a SEM image of the radial gradient structure of the bamboo used in Example 1 of the present invention;

[0028] Figure 7 SEM image of the radial gradient structure of the bamboo-based aerogel prepared in Example 1 of the present invention;

[0029] Figure 8 SEM images of the axial gradient structure of the bamboo used in Example 1 of the present invention at different scales;

[0030] Figure 9 SEM images of the axial gradient structure of the bamboo-based aerogel prepared in Example 1 of the present invention at different scales;

[0031] Figure 10 SEM image of the radial gradient porous structure of the bamboo and bamboo-based aerogel in Example 1 of the present invention;

[0032] Figure 11 SEM images of the radial gradient structure and axial gradient structure of the bamboo-based aerogel prepared in Example 2 of the present invention;

[0033] Figure 12 Photo of the bamboo-based aerogel prepared in Comparative Example 1 of the present invention;

[0034] Figure 13 SEM images of the radial gradient structure and axial gradient structure of the bamboo-based aerogel prepared in Comparative Example 1 of the present invention;

[0035] Figure 14 Sound absorption coefficient diagrams of the bamboo-based aerogel prepared in Example 1 of the present invention and the noise-reducing bamboo-based aerogel prepared in Example 4 at different frequencies;

[0036] Figure 15 Noise reduction coefficient diagrams of the bamboo-based aerogel prepared in Example 1 of the present invention and the noise-reducing bamboo-based aerogel prepared in Example 4 at different frequencies;

[0037] Figure 16 Noise reduction coefficient comparison diagram of the noise-reducing bamboo-based aerogel prepared in Example 4 of the present invention and the noise-reducing materials provided in Comparative Examples 2-8.

[0038] Figure 17 Pore size distribution diagrams of the bamboo-based aerogels prepared in Examples 5-8 of the present invention. Detailed implementation manners

[0039] The present invention provides a preparation method of a bamboo-based aerogel, comprising the following steps:

[0040] (1) Freezing and then thawing the bamboo successively to obtain softened bamboo; the moisture content of the bamboo is greater than or equal to 82%;

[0041] (2) Subjecting the softened bamboo obtained in step (1) to solvent heat treatment to obtain impurity-removed bamboo;

[0042] (3) Drying the impurity-removed bamboo material obtained in step (2) to obtain bamboo-based aerogel.

[0043] The present invention freezes and thaws bamboo in sequence to obtain softened bamboo. In the present invention, the moisture content of the bamboo is greater than or equal to 82%, preferably 85-90%, and more preferably 88-90%. When the present invention uses the bamboo with the above moisture content as the raw material for preparing bamboo-based aerogel, the fiber cells of the bamboo are in a relatively full state, but have not yet reached complete saturation. The bamboo in this state can better maintain its structure and performance during the freeze-drying process to form a low-density and stable aerogel structure. When the present invention uses the bamboo with a higher moisture content, the fiber cell wall of the bamboo is thinner, which is conducive to the formation of a low-density, high-porosity aerogel.

[0044] The present invention has no special limitation on the specific part of the bamboo material, and the bamboo material with the above moisture content can be used.

[0045] In the present invention, the bamboo species preferably include one or more of moso bamboo, latifolia bamboo and clump bamboo. The method provided by the present invention can be applied to a variety of bamboo species, and the bamboo species are easy to obtain and the moisture content can meet the above requirements.

[0046] In the present invention, the freezing temperature is preferably below 0°C, more preferably -40 to 0°C, and further preferably -40 to -10°C. The present invention has no special limitation on the freezing time, and it is selected according to the size of the bamboo material, as long as the column material can be completely frozen. The present invention performs freeze-drying at the above temperature, which can effectively prevent the moisture in the bamboo material from evaporating too quickly or expanding too quickly due to ice formation, resulting in uneven pore distribution of the aerogel, and provides a good template for preparing aerogel. The present invention has no special limitation on the freezing device, and a conventional freezing device can be used.

[0047] In an embodiment of the present invention, the freezing temperature is -10°C, and the pore diameter of the obtained bamboo-based aerogel is concentrated at 0.35 mm; the freezing temperature is -20°C, and the pore diameter of the obtained bamboo-based aerogel is concentrated at 0.43 mm; the freezing temperature is -40°C, and the pore diameter of the obtained bamboo-based aerogel is concentrated at 0.4 mm.

[0048] In the present invention, the thawing temperature is preferably room temperature. The present invention can cause transverse fracture of thin-walled cells by thawing at room temperature to form an aerogel with transverse macropores, high porosity and low density.

[0049] In the present invention, the bamboo nodes are preferably removed after thawing to obtain softened bamboo material.

[0050] After obtaining the softened bamboo, the present invention subjects the softened bamboo to solvent heat treatment to obtain impurity-removed bamboo.

[0051] In the present invention, the temperature of the solvent heat treatment is preferably 80 - 100 °C; more preferably 100 °C; the time of the solvent heat treatment is preferably 2 - 4 h, more preferably 4 h. The present invention can remove impurities such as monosaccharides, fats, and proteins in the softened bamboo through solvent heat treatment, improving the purity of the aerogel.

[0052] In the present invention, the solvent for the solvent heat treatment is preferably water, ethanol, ethyl acetate, acid solution or alkali solution, preferably water, ethanol or ethyl acetate; the acid solution is preferably chlorous acid solution. In the present invention, the concentration of the acid solution is preferably 1 - 5 wt%, more preferably 1 wt%. In the present invention, the alkali solution is preferably sodium hydroxide solution or sodium sulfite solution; the concentration of the alkali solution is preferably 5 - 8 wt%, more preferably 5 wt%. Using the above solvents for solvent heat treatment in the present invention can fully remove impurities in the softened bamboo.

[0053] After obtaining the impurity-removed bamboo, the present invention dries the impurity-removed bamboo to obtain bamboo-based aerogel.

[0054] In the present invention, the drying preferably includes freeze-drying or supercritical drying.

[0055] In the present invention, the temperature of the freeze-drying is preferably -20 - -40 °C, more preferably -40 °C; the time of the freeze-drying is preferably 24 - 48 h, more preferably 48 h. Freeze-drying at the above temperature in the present invention is beneficial to the growth of ice crystals to form a porous structure during the freezing process.

[0056] In the examples of the present invention, the temperature of the supercritical drying can be 35 °C; the pressure of the supercritical drying can be 10.3 MPa; the time of the supercritical drying can be 7 h.

[0057] The method provided by the present invention is simple to operate and can prepare bamboo-based aerogel on a large scale; moreover, because the selected bamboo has a high moisture content, a low-density and high-porosity aerogel can be obtained after freeze-drying and thawing, solving the technical problem that it is difficult to prepare bamboo-based aerogel on a large scale by conventional methods.

[0058] The present invention also provides a bamboo-based aerogel prepared by the preparation method described in the above technical solution. By mass percentage, it includes the following components: cellulose 20 - 50%, hemicellulose 7 - 14%, lignin 2 - 5%, and others 31 - 71%.

[0059] In the present invention, the bamboo-based aerogel comprises 20-50% by mass of cellulose, preferably 30-40%. In the present invention, the bamboo-based aerogel comprises 7-14% by mass of hemicellulose, preferably 10-14%. When the cellulose and hemicellulose of the bamboo-based aerogel provided by the present invention are within the above ranges, the aerogel has good mechanical properties, can withstand greater pressure and deformation, exhibits high strength and toughness, making the bamboo-based aerogel customizable; and also has good adsorption capacity, which is more conducive to fully reacting with the hydrophobic modifier.

[0060] In the present invention, the bamboo-based aerogel comprises 2-5% by mass of lignin, preferably 3-5%. When the lignin content of the bamboo-based aerogel provided by the present invention is within the above range, the prepared bamboo-based aerogel has good stability, making the bamboo-based aerogel customizable.

[0061] In the present invention, the bamboo-based aerogel comprises 31-71% by mass of other substances. In the present invention, the other substances are preferably one or more of starch, protein and fat.

[0062] In the present invention, the bamboo-based aerogel has a radial gradient porous structure, and the density of the bamboo-based aerogel in the radial direction increases gradually from the inside to the outside. In the present invention, the radial density of the bamboo-based aerogel is preferably 48-77 mg / cm 3 . Further, in the present invention, the radial gradient porous structure preferably comprises a high-density layer, a medium-density layer and a low-density layer. The density of the high-density layer is 62-77 mg / cm 3 , preferably 62 mg / cm 3 ; the density of the medium-density layer is 54-62 mg / cm 3 , preferably 54 mg / cm 3 ; the density of the low-density layer is 48-54 mg / cm 3 , preferably 48 mg / cm 3 . The bamboo-based aerogel provided by the present invention has the above pore structure and density distribution, which can enable the noise-reducing bamboo-based aerogel prepared from the bamboo-based aerogel to have good noise reduction effect.

[0063] The present invention also provides a noise-reducing bamboo-based aerogel, which comprises the bamboo-based aerogel described in the above technical solution and a hydrophobic modifier modified on the bamboo-based aerogel.

[0064] In the present invention, the preparation method of the noise-reducing bamboo-based aerogel preferably comprises: mixing the bamboo-based aerogel with a hydrophobic modifier and performing a surface modification reaction to obtain the noise-reducing bamboo-based aerogel.

[0065] In the present invention, the hydrophobic modifier solution is preferably a silane modifier. In the present invention, the silane modifier preferably includes methyltrimethoxysilane, cetyltrimethoxysilane or trichloromethylsilane. In the present invention, the volume ratio of the hydrophobic modifier to the mass of the bamboo-based aerogel is preferably (0.6 - 6) mL:1 g, more preferably 1.6 mL:1 g. By using the above hydrophobic modifier solution, the surface of the bamboo-based aerogel can be made rougher, and by introducing hydrophobic groups, the hydrophobicity of the aerogel can be improved, which is more conducive to enhancing the noise reduction effect of the aerogel.

[0066] In the present invention, the method for mixing the bamboo-based aerogel with the hydrophobic modifier solution is preferably chemical vapor deposition. By mixing under the above method, the hydrophobic modifier solution can be fully contacted with the bamboo-based aerogel.

[0067] In the present invention, the temperature of the surface modification reaction is preferably 80 - 100 °C, more preferably 80 °C; the time of the surface modification reaction is preferably 1 - 10 h, more preferably 2 - 8 h. By carrying out the surface modification reaction at the above temperature and time, the hydrophobic modifier can fully modify the bamboo-based aerogel. In the present invention, the time of the surface modification reaction affects the application of the bamboo-based aerogel. When the time of the surface modification reaction is 1 - 2 h, hydrophobic modification can be achieved; when the time of the surface modification reaction is 5 - 10 h, the noise reduction bamboo-based aerogel obtained after the surface modification reaction has a better noise reduction effect.

[0068] Since the prepared bamboo-based aerogel in the present invention has a radial gradient porous structure and properties of low density and high porosity, after being modified with a hydrophobic modifier, the obtained noise reduction bamboo-based aerogel has excellent noise reduction effect.

[0069] Next, the technical solutions in the present invention will be clearly and completely described in conjunction with the embodiments in the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. Based on the embodiments in the present invention, all other embodiments obtained by those of ordinary skill in the art without making creative efforts shall fall within the protection scope of the present invention.

[0070] Example 1

[0071] A preparation method of a bamboo-based aerogel, the steps are as follows:

[0072] (1) Freeze bamboo (Phyllostachys pubescens) at -23 °C for 24 h, then take it out and thaw it at room temperature, remove the bamboo joints and flatten it to obtain softened bamboo; the bamboo is the bamboo tip, and the moisture content is about 92%.

[0073] (2) Place the softened bamboo obtained in step (1) in water, heat it to a temperature of 100 °C, and perform solvent heat treatment for 4 h to obtain impurity-removed bamboo.

[0074] (3) Freeze-dry the impurity-removed bamboo obtained in step (2) at -40 °C for 48 h to obtain bamboo-based aerogel, denoted as BG.

[0075] Example 2

[0076] A method for preparing bamboo-based aerogel, the steps are as follows:

[0077] (1) Freeze bamboo (clustered bamboo) at -23 °C for 24 h, then take it out and thaw it at room temperature, remove the bamboo joints and flatten it to obtain softened bamboo; the bamboo is bamboo middle, and the moisture content is 88%;

[0078] (2) Place the softened bamboo obtained in step (1) in water, heat it to a temperature of 100 °C, and perform solvent heat treatment for 4 h to obtain impurity-removed bamboo.

[0079] (3) Freeze-dry the impurity-removed bamboo obtained in step (2) at -40 °C for 48 h to obtain bamboo-based aerogel.

[0080] Example 3

[0081] A method for preparing bamboo-based aerogel, the steps are as follows:

[0082] (1) Freeze bamboo (Phyllostachys edulis) at -23 °C for 24 h, then take it out and thaw it at room temperature, remove the bamboo joints and flatten it to obtain softened bamboo; the bamboo is bamboo middle, and the moisture content is 88%;

[0083] (2) Place the softened bamboo obtained in step (1) in water, heat it to a temperature of 100 °C, and perform solvent heat treatment for 4 h to obtain impurity-removed bamboo.

[0084] (3) Perform supercritical drying on the impurity-removed bamboo obtained in step (2) at 35 °C and 10.3 MPa for 7 h to obtain bamboo-based aerogel.

[0085] Comparative Example 1

[0086] A method for preparing bamboo-based aerogel, the steps are as follows:

[0087] (1) Freeze bamboo at -23 °C for 24 h, then take it out and thaw it at room temperature, remove the bamboo joints and flatten it to obtain softened bamboo; the bamboo is the bamboo base part, and the moisture content is 85%;

[0088] (2) Place the softened bamboo obtained in step (1) in water, heat it to 100 °C, and carry out solvent heat treatment for 4 h to obtain impurity-removed bamboo.

[0089] (3) Freeze-dry the impurity-removed bamboo obtained in step (2) at -40 °C for 48 h to obtain bamboo-based aerogel.

[0090] Comparative Example 2

[0091] A method for preparing bamboo-based aerogel, the steps are as follows:

[0092] (1) Freeze bamboo (Phyllostachys pubescens) at -23 °C for 24 h, then take it out and thaw it at room temperature, remove the bamboo knots and flatten it to obtain softened bamboo; the bamboo is bamboo shoots with a moisture content of about 92%.

[0093] (2) Place the softened bamboo obtained in step (1) in water, heat it to 100 °C, and carry out solvent heat treatment for 4 h to obtain impurity-removed bamboo.

[0094] (3) Dry the impurity-removed bamboo obtained in step (2) at 60 °C to obtain bamboo-based aerogel.

[0095] Example 4

[0096] A noise-reducing bamboo-based aerogel, its preparation method is: place the bamboo-based aerogel prepared in Example 1 in a dryer with a silane modifier (methyltrimethoxysilane), the volume ratio of the silane modifier to the mass of the bamboo-based aerogel is 1.6 mL:1 g, carry out surface modification reaction at 80 °C for 7 h, and obtain the noise-reducing bamboo-based aerogel after drying, denoted as SiBG.

[0097] Comparative Example 3

[0098] A noise-reducing material, graphene oxide sponge (GO sponge), from Yang, Likai, et al. “Superior broadband sound absorption in hierarchical ultralight graphene oxide aerogels achieved through emulsion freeze-casting.” Chemical Engineering Journal 469 (2023): 143896.

[0099] Comparative Example 4

[0100] A noise reduction material, graphene ultrathin drums (Graphene ultrathin Drums), from Pang, Kai, et al. “Highly efficient cellular acoustic absorber of graphene ultrathin drums.” Advanced Materials 34.14 (2022): 2103740.

[0101] Comparative Example 5

[0102] A noise reduction material, gradient CNC / SiO2 aerogel (Gradient CNC / SiO2 aerogel), from Zong, Dingding, et al. “Gradient pore structured elastic ceramic nanofiber aerogels with cellulose nanonets for noise absorption.” Advanced Functional Materials 33.31 (2023): 2301870.

[0103] Comparative Example 6

[0104] A noise reduction material, ceramic sponges (Ceramic sponges), from Jia, C., et al. “Highly compressible and anisotropic lamellar ceramic sponges with superior thermal insulation and acoustic absorption performances. Nat. Commun. 11, 3732 (2020).” Ceram. Int 46 (2020): 768 - 774..

[0105] Comparative Example 7

[0106] A noise reduction material, ceramic nanofibrous sponges, from Zong, Dingding, et al. “Flexible ceramic nanofibrous sponges with hierarchically entangled graphene networks enable noise absorption.” Nature communications 12.1 (2021): 6599.

[0107] Comparative Example 8

[0108] A noise reduction material, PET / silica aerogel, from Thai, Quoc Ba, et al. “Recycling of waste tire fibers into advanced aerogels for thermal insulation and sound absorption applications.” Journal of Environmental Chemical Engineering 8.5 (2020): 104279.

[0109] Comparative Example 9

[0110] A noise reduction material, Wood, from Thai, Quoc Ba, et al. “Recycling of waste tire fibers into advanced aerogels for thermal insulation and sound absorption applications.” Journal of Environmental Chemical Engineering 8.5 (2020): 104279.

[0111] Example 5

[0112] A method for preparing a bamboo-based aerogel, which is different from Example 1 in that the freezing temperature in step (1) is -5°C, and the remaining steps are the same as those in Example 1.

[0113] Example 6

[0114] A method for preparing a bamboo-based aerogel, which is different from Example 1 in that the freezing temperature in step (1) is -10°C, and the remaining steps are the same as those in Example 1.

[0115] Example 7

[0116] A preparation method of bamboo-based aerogel, which is different from Example 1 in that the freezing temperature in step (1) is -20 °C, and the remaining steps are the same as those in Example 1.

[0117] Example 8

[0118] A preparation method of bamboo-based aerogel, which is different from Example 1 in that the freezing temperature in step (1) is -40 °C, and the remaining steps are the same as those in Example 1.

[0119] Test Example 1

[0120] The light microscope images of the bamboo used in Example 1 in the axial and radial directions are as shown in Figure 1 In Figure 1 , the left figure is the light microscope image of the bamboo in the axial direction, and the right figure is the light microscope image of the bamboo in the radial direction. The light microscope images of the softened bamboo prepared in step (1) of Example 1 in the axial and radial directions are as shown in Figure 2 In Figure 2 , the left figure is the light microscope image of the softened bamboo in the axial direction, and the right figure is the light microscope image of the softened bamboo in the radial direction. It can be seen from Figure 1 and Figure 2 that the softened bamboo prepared by the present invention has transverse cracks, and the transverse cracks help to increase the transverse interaction and flatten after thawing.

[0121] Figure 3 is a photo of the bamboo used in Example 1, Figure 4 is a photo of the bamboo-based aerogel prepared in step (3), Figure 5 is a photo of the bamboo-based aerogel prepared in step (3) with a customized specific morphology. It can be seen from Figures 3-5 that the method of the present invention can prepare a flattenable and shape-customizable bamboo-based aerogel.

[0122] The SEM image of the radial gradient structure of the bamboo in step (1) of Example 1 is as shown in Figure 6 ; the SEM image of the radial gradient structure of the bamboo-based aerogel prepared in step (3) of Example 1 is as shown in Figure 7 ; the SEM images of the axial gradient structure of the bamboo in step (1) of Example 1 at different scales are as shown in Figure 8 ; the SEM images of the axial gradient structure of the bamboo-based aerogel prepared in step (3) of Example 1 at different scales are as shown in Figure 9 It can be seen from Figure 6 and 8 that the vascular bundles and the basic tissue structure composed of parenchyma cells in the bamboo are intact. And it can be seen from Figure 7 and 9It can be seen that during the drying process, the weakly connected tissue structures in the bamboo shoots are stretched open during the formation of ice crystals. During the drying process, air gradually replaces the position of ice crystals to form a high-porosity, low-density aerogel. In the radial direction, it can be seen that the vascular bundles in the bamboo shoots are stretched open by ice crystals to form a gradient porous structure, and the surrounding area is a honeycomb structure composed of thin-walled cells connected to each other, and there are obvious intercellular spaces between the cells. In addition, Figure 9 As shown in the illustration in the figure, it can be seen that in the axial direction, the ice crystals stretch and squeeze the basic tissue structure, forming a layered structure formed after the air replaces the ice crystals, and a layered structure formed by the basic tissue being squeezed by the ice crystals. This shows that ice crystals play an important role in weakening the interaction between the various tissues of young bamboo during the freezing and thawing process.

[0123] Figure 10 This is the SEM image of the radial gradient porous structure of bamboo and bamboo-based aerogel in Example 1; Figure 10 In the figure, the left figure is a SEM image of the radial gradient porous structure of the bamboo material in step (1), and the right figure is a SEM image of the radial gradient porous structure of the bamboo-based aerogel prepared in step (3) of Example 1. Figure 10 It can be seen that the bamboo-based aerogel prepared in Example 1 is a radial gradient porous structure, which includes a high-density layer, a medium-density layer and a low-density layer. The method of Example 1 can improve the pore structure and significantly reduce the density of the bamboo material.

[0124] Test Example 2

[0125] The SEM images of the radial gradient structure and axial gradient structure of the bamboo-based aerogel prepared in step (3) of Example 2 are as follows: Figure 11 As shown. Figure 11 In the figure, the left picture is the SEM picture of the radial gradient structure of bamboo-based aerogel; the right picture is the SEM picture of the axial gradient structure of bamboo-based aerogel. Figure 11 It can be seen that the thin-walled cells in the bamboo after freezing and thawing are mainly damaged by ice crystals, while the structure of the vascular bundle is basically intact. This is mainly due to the thickening of the secondary wall of the fiber cells in the bamboo, which strengthens the interaction between the cells in the vascular bundle. Compared with the surrounding thin-walled cells, ice crystals begin to form in the weakest part of the entire structure. Therefore, the basic tissue mainly damaged by ice crystals is the thin-walled cells.

[0126] Test Example 3

[0127] The photo of the bamboo-based aerogel prepared in step (3) of comparative example 1 is as follows Figure 12 As shown. Figure 12 It can be seen that when the bamboo material of Comparative Example 1 (i.e., aged bamboo material with a low water content) is used, the obtained bamboo-based aerogel cannot be flattened and customized in shape.

[0128] The SEM images of the radial gradient structure and axial gradient structure of the bamboo-based aerogel prepared in step (3) of Comparative Example 1 are as follows Figure 13 shown. In Figure 13 , the left figure is the SEM image of the radial gradient structure of the bamboo-based aerogel; the right figure is the SEM image of the axial gradient structure of the bamboo-based aerogel. It can be seen from Figure 13 that near the vascular bundles and the basic tissue structure is intact, only some parenchyma cells in the bamboo flesh and near the bamboo yellow part are damaged. This is mainly attributed to the fact that during the growth process of bamboo, the lignification process mainly occurs gradually from the bamboo green to the bamboo yellow, and the interaction force of each tissue on the outside is stronger than that on the inside. Therefore, compared with the bamboo shoots in the middle of the bamboo, the degree of damage by ice crystals is smaller. Due to the strong interaction force between the bamboo green parts, it is difficult for the ice crystals to weaken the interaction force, making it difficult to flatten them after freeze-thawing.

[0129] Test Example 4

[0130] The sound absorption coefficients of the bamboo-based aerogel prepared in Example 1 and the noise-reducing bamboo-based aerogel prepared in Example 4 at different frequencies are as follows Figure 14 shown, and the noise reduction coefficient (NRC) is as follows Figure 15 shown. In Figure 14 and 15 , BG represents the bamboo-based aerogel before modification, and SiBG represents the modified bamboo-based aerogel. It can be seen from Figure 14 and Figure 15 that the noise-reducing bamboo-based aerogel prepared by the present invention can improve the noise reduction effect of the bamboo-based aerogel through silane modification.

[0131] Figure 16 is a comparison chart of the noise reduction coefficients of the noise-reducing bamboo-based aerogel prepared in Example 4 and the noise-reducing materials provided in Comparative Examples 3-9 at a thickness of 9 mm. It can be seen from Figure 16 that the noise-reducing bamboo-based aerogel prepared by the present invention has a higher noise reduction coefficient at low thickness compared with conventional noise-reducing aerogels, and has application prospects in the field of sound absorption.

[0132] Test Example 5

[0133] The pore size distribution diagrams of the bamboo-based aerogels prepared in Examples 5-8 are as follows Figure 17 described. It can be seen from Figure 17 that when the freezing temperature is -10 °C, the pore size of the obtained bamboo-based aerogel is concentrated at 0.35 mm; when the freezing temperature is -20 °C, the pore size of the obtained bamboo-based aerogel is concentrated at 0.43 mm; when the freezing temperature is -40 °C, the pore size of the obtained bamboo-based aerogel is concentrated at 0.4 mm. This shows that the freezing temperature can affect the pore size.

[0134] It can be seen from the above experimental results that the method provided by the present invention can prepare bamboo-based aerogels with a radially gradient porous structure on a large scale. This porous structure includes a high-density layer, a medium-density layer, and a low-density layer, making the bamboo-based aerogel have the characteristics of low density, high porosity, flattenability, and customizable shape. The noise reduction coefficient of the silane-modified bamboo-based aerogel is 0.38 when the thickness is 9 mm, which is greater than the noise reduction coefficients of commercial foams, graphene oxide foams, ceramic foams, wood, etc. with the same thickness.

[0135] The above description is only the preferred embodiment of the present invention. It should be noted that for those of ordinary skill in the art, without departing from the principle of the present invention, several improvements and refinements can be made, and these improvements and refinements should also be regarded as the protection scope of the present invention.

Claims

1. A preparation method of bamboo-based aerogel, comprising the following steps: (1) Freezing and then thawing bamboo successively to obtain softened bamboo; the moisture content of the bamboo is greater than or equal to 88%; (2) Subjecting the softened bamboo obtained in step (1) to solvent heat treatment to obtain impurity-removed bamboo; (3) Drying the impurity-removed bamboo obtained in step (2) to obtain bamboo-based aerogel; The temperature of freezing in step (1) is below 0 °C; The temperature of solvent heat treatment in step (2) is 60-100 °C; The time of solvent heat treatment is 2-4 h; The drying in step (3) includes freeze-drying or supercritical drying; The temperature of freeze-drying is -20 to -40 °C.

2. The preparation method according to claim 1, characterized in that, The time of freeze-drying is 24-48 h.

3. The bamboo-based aerogel prepared by the preparation method according to any one of claims 1 to 2, by mass percentage, comprises the following components: cellulose 20-50%, hemicellulose 7-14%, lignin 2-5% and others 31-71%; The bamboo-based aerogel is a radially gradient porous structure, and the density of the bamboo-based aerogel in the radial direction increases gradually from the inside to the outside.

4. The bamboo-based aerogel according to claim 3, wherein The radial density of the bamboo-based aerogel is 48-77 mg / cm 3 .

5. A noise-reducing bamboo-based aerogel, which comprises the bamboo-based aerogel according to claim 4 and a hydrophobic modifier modified on the bamboo-based aerogel.

6. The noise-reducing bamboo-based aerogel according to claim 5, wherein, The preparation method of the noise-reducing bamboo-based aerogel comprises: mixing the bamboo-based aerogel with a hydrophobic modifier solution and carrying out a surface modification reaction to obtain the noise-reducing bamboo-based aerogel.

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