A method for preparing a nanocellulose-reinforced silicone composite aerogel

Abstract

The application discloses a preparation method of nanocellulose-reinforced organic-silicon composite aerogel, which comprises the following steps: (1) preparing a nanocellulose dispersion liquid; (2) adding amino-silane coupling agent and epoxy-silane coupling agent into the nanocellulose dispersion liquid in sequence, and uniformly mixing to obtain a mixed dispersion liquid; (3) standing the mixed dispersion liquid, and forming an organic-inorganic hybrid three-dimensional network hydrogel through sol-gel transformation; (4) performing freezing treatment, and then performing freeze drying to obtain nanocellulose / organic-silicon composite aerogel with a porous structure; and (5) performing heat treatment to obtain nanocellulose-reinforced organic-silicon composite aerogel. Through in-situ interface engineering at a molecular level, the nanocellulose is used as a biological template and a reinforcing framework to guide the accurate growth and crosslinking of an organic-silicon network on the surface of the nanocellulose, and the composite aerogel with a biomimetic coral-like multistage fiber network structure is constructed.

Description

Technical Field

[0001] This invention belongs to the field of functional aerogel materials technology, specifically a method for preparing a nanocellulose-reinforced organosilicon composite aerogel. Background Technology

[0002] The industrial application of inorganic silica aerogels has long been limited by their inherent brittleness. From a microscopic perspective, the root of their fragility lies in their three-dimensional nanonetwork structure built from brittle Si-O-Si bonds: on the one hand, the nanoscale framework (typically 2-5 nm) itself has extremely low bending strength; on the other hand, the sparse "point contact" connections between the framework members and the high porosity (over 90%) make it difficult to effectively disperse external loads, easily leading to cracks that propagate rapidly at stress concentration points, resulting in macroscopic brittle fracture. Clearly, improving mechanical properties is the key bottleneck in enabling aerogels to move from the laboratory to practical applications.

[0003] To overcome this challenge, researchers have developed various reinforcement strategies, among which the organic-inorganic composite strategy has proven particularly effective. This strategy significantly improves the toughness and strength of aerogels by introducing flexible polymers (such as epoxy resins and polyurethanes) into a rigid inorganic network and utilizing the polymer's plastic deformation capabilities to dissipate energy. However, traditional physical blending composite methods often face severe challenges: weak interfacial bonding between the organic and inorganic phases, macroscopic phase separation due to poor compatibility between the two phases, and severe aggregation of inorganic nanoparticles. These problems not only limit the reinforcement efficiency but may also impair other excellent properties of aerogels (such as superhydrophobicity and low thermal conductivity).

[0004] In contrast, organosilicon aerogels (such as polysilsesquioxane) prepared through molecular design using silane coupling agents as precursors offer a more ingenious solution. These materials achieve organic-inorganic hybridization at the molecular scale. The organic groups in their framework effectively enhance network toughness while ensuring component homogeneity, resulting in a qualitative leap in mechanical properties compared to pure silica aerogels. Nevertheless, the framework of such aerogels is essentially still dominated by a brittle Si-O-Si inorganic network, limiting the potential for further improvement in mechanical properties. Brittle fracture may still occur, especially under significant compressive or bending loads. The organosilicon aerogel prepared using methyltrimethoxysilane as a precursor in the literature "Materials Chemistry Frontiers, 2020(4): 2418-2427;Journal of Porous Materials, 2020(2): 1241-1251" achieves a strength as high as 14 MPa; however, this material can only withstand about 50% compressive strain and lacks significant elasticity.

[0005] Combining silane coupling agents with nanocellulose is an effective way to improve the elasticity of aerogels. However, in traditional composite methods, silane coupling agents are often tightly integrated with cellulose, resulting in a dense lamellar structure on the pore walls of the aerogel. This severely reduces its pore connectivity and gas / liquid permeability, thus limiting the application of such materials in filtration, adsorption, and other fields. Application No. 202310488996.4 discloses a method for preparing a highly elastic bacterial cellulose / KH560 composite aerogel. While the aerogel prepared by combining GPTMS and bacterial cellulose possesses good mechanical strength and elasticity, GPTMS forms an amorphous polymer within the cellulose network and is tightly bound to cellulose to form an integral pore wall structure, resulting in blocked internal channels and insufficient permeability. Furthermore, the dense lamellar structure exhibits a very inefficient energy dissipation mechanism under compressive or bending stress, easily leading to stress concentration and brittle fracture. Summary of the Invention

[0006] To address the shortcomings of existing technologies, this invention provides a method for preparing nanocellulose-reinforced organosilicon composite aerogels.

[0007] The technical solution of this invention to solve the aforementioned technical problem is to provide a method for preparing nanocellulose-reinforced organosilicon composite aerogel, characterized in that the method includes the following steps: (1) The nanocellulose was uniformly dispersed in deionized water to obtain a nanocellulose dispersion; (2) Add one of the amino-based silane coupling agent and the epoxy-based silane coupling agent to the nanocellulose dispersion obtained in step (1) and mix it evenly for the first time so that the silane coupling agent is hydrolyzed and adsorbed onto the nanocellulose; then add the other of the amino-based silane coupling agent and the epoxy-based silane coupling agent and mix it evenly for the second time to obtain a mixed dispersion. (3) The mixed dispersion obtained in step (2) is allowed to stand, and the sol-gel transition occurs, causing it to completely gel and form an organic-inorganic hybrid three-dimensional network hydrogel. (4) The hydrogel obtained in step (3) is frozen and then freeze-dried to remove the ice crystals and obtain a nanocellulose / organosilicon composite aerogel with a porous structure. (5) The nanocellulose / organosilicon composite aerogel obtained in step (4) is subjected to heat treatment to further promote the cross-linking reaction between the residual functional groups of the silane coupling agent, improve the stability and mechanical properties of the network structure, and obtain nanocellulose-reinforced organosilicon composite aerogel.

[0008] Compared with the prior art, the beneficial effects of the present invention are as follows: (1) This invention provides a green, novel, and tunable composite aerogel preparation strategy. Through in-situ interface engineering at the molecular level, using nanocellulose as a biological template and reinforcing framework, this invention guides the precise growth and cross-linking of an organosilicon network on its surface, constructing a composite aerogel with a biomimetic coral-like multi-level fiber network structure. This structure not only fundamentally solves the bottlenecks of single mechanical properties and insufficient permeability in traditional silicon-based or cellulose aerogels, but also achieves a synergistic unity of high strength, high elasticity, excellent flexibility, high porosity, and multifunctionality through biomimetic multi-level structural design, realizing a synergistic improvement in mechanical properties and mass transfer efficiency, thus opening up an effective path for developing a new generation of high-performance, multifunctional porous materials.

[0009] (2) The superior effects of the present invention are specifically reflected in: Superior Mechanical Properties: This invention innovatively utilizes the abundant hydroxyl groups on the surface of nanocellulose as active sites. Through covalent bonding between these hydroxyl groups and silane coupling agents (especially those containing amino and epoxy groups), an organosilicon network is guided to grow and cross-link on the surface of nanocellulose fibers in situ. By using nanocellulose fibers as a "flexible skeleton" and the silane cross-linking network as a "rigid shell," a strong and tough "core-shell" fiber unit is formed. Under compression, through the synergistic effect of the rigid shell and the flexible core, the rigid shell effectively transmits and disperses stress, while the flexible core absorbs energy and inhibits crack propagation. This achieves a perfect balance of high strength, high modulus, high elastic recovery rate, and excellent fatigue resistance, overcoming the shortcomings of traditional aerogels, such as high brittleness and poor plastic deformation.

[0010] Excellent structural permeability: The biomimetic coral-like structure forms a highly interconnected, open-pore macroscopic three-dimensional network. This contrasts sharply with the pore blockage caused by layered structures, ensuring efficient passage of gases and liquids. This provides a crucial structural foundation for the material's practical applications in filtration, separation (especially high-throughput oil-water emulsion separation), and adsorption.

[0011] The greenness of the preparation process: This invention utilizes the alkalinity of aminosilane hydrolysis to simultaneously and autonomously catalyze two key reactions: silanol condensation to form an inorganic framework, and ring-opening of amino and epoxy groups to form organic crosslinks. This process requires no additional catalyst, uses water as a medium, and can be completed at room temperature or low temperature. It synergistically constructs a highly crosslinked organic-inorganic hybrid network, which is tightly bound to the nanocellulose template, achieving synergy between reaction-driven and structure-forming processes. The steps are simple, environmentally friendly, and in line with the principles of green chemistry.

[0012] Performance tunability: By precisely controlling the ratio and concentration of nanocellulose and two silanes, the microstructure, density, porosity, and surface chemical properties of the composite aerogel can be linearly and over a wide range. This allows for precise "on-demand design" of the material's mechanical properties (such as modulus and resilience) and interfacial characteristics (hydrophilic / hydrophobic) according to the target application, achieving performance coverage from flexible elastomers to rigid porous materials.

[0013] Multifunctionality: With its high permeability and adjustable wettability, it exhibits high efficiency and stability in oil-water separation (including difficult-to-handle emulsions). Its high porosity and good thermal insulation properties also make it valuable for applications in thermal insulation, high-efficiency adsorption (oil absorption), and other fields.

[0014] (3) The organosilicon composite aerogel prepared by this invention has a biomimetic coral-like hierarchical porous structure, and possesses high elasticity, moderate modulus, low density, high porosity, and complete structure. Its density is 5~100 mg / cm³. 3 It has a porosity of 90-99%; an elastic recovery rate of ≥90% under 80% compressive strain; a compressive modulus of 1-500 kPa; and exhibits high efficiency in separating oil-water emulsions, with a gravity-driven separation flux of ≥700 L·m⁻¹. -2 ·h -1 It has a separation efficiency of ≥95%; or after hydrophobic modification, its adsorption capacity for various oils is 20 to 60 times its own mass, and oil desorption and aerogel recycling can be achieved through extrusion; it has excellent thermal insulation performance, with a thermal conductivity as low as 29.35mW / m·K at 25℃. Attached Figure Description

[0015] Figure 1 This is a 2000x magnified SEM image of the organosilicon composite aerogel prepared in Example 1 of the present invention. Figure 2 This is a 10,000x magnified SEM image of the organosilicon composite aerogel prepared in Example 1 of the present invention. Figure 3 This is a TEM image of the organosilicon composite aerogel prepared in Example 1 of the present invention, magnified 100,000 times. Figure 4 The elemental distribution of C, N, O and Si in the organosilicon composite aerogel prepared in Example 1 of this invention is shown in the figure. Figure 5 The figure shows the fatigue resistance test results of the organosilicon composite aerogel prepared in Example 1 of the present invention. Figure 6 The graph shows the test results of the adsorption ratio of different oils for the organosilicon composite aerogel prepared in Example 2 of the present invention. Figure 7The figure shows the test results of the organosilicon composite aerogel prepared in Example 2 of the present invention using the mechanical extrusion method to absorb oil in a cyclic manner. Figure 8 This is a 10,000x magnified SEM image of the aerogel prepared in Comparative Example 1 of this invention. Figure 9 This is a 10,000x magnified SEM image of the aerogel prepared in Comparative Example 2 of this invention. Figure 10 This is a 5000x magnified SEM image of the aerogel prepared in Comparative Example 3 of this invention. Figure 11 This is a 2000x magnified SEM image of the aerogel prepared in Comparative Example 4 of this invention. Figure 12 The infrared spectra of the organosilicon composite aerogel prepared in Example 1 of the present invention and the aerogels prepared in Comparative Examples 1 to 3 are shown. Detailed Implementation

[0016] Specific embodiments of the present invention are given below. These specific embodiments are only used to further illustrate the present invention in detail and do not limit the scope of protection of the present invention.

[0017] This invention provides a method for preparing nanocellulose-reinforced organosilicon composite aerogel (hereinafter referred to as the method), characterized in that the method includes the following steps: (1) The nanocellulose was uniformly dispersed in deionized water to obtain a nanocellulose dispersion; Preferably, in step (1), the nanocellulose is at least one of bacterial cellulose (BC) and cellulose nanofibers (CNF).

[0018] Preferably, in step (1), the uniform dispersion process is as follows: stirring is used, the stirring speed is 200~5000 rpm, the stirring time is 10~30 min, and the stirring temperature is room temperature (20~30℃). It is preferably carried out in a magnetic stirrer.

[0019] Preferably, in step (1), the mass of nanocellulose is 0.002~2% of the mass of deionized water.

[0020] (2) Add one of the amino-based silane coupling agent and the epoxy-based silane coupling agent to the nanocellulose dispersion obtained in step (1) and mix it evenly for the first time so that the silane coupling agent is hydrolyzed and adsorbed onto the nanocellulose; then add the other of the amino-based silane coupling agent and the epoxy-based silane coupling agent and mix it evenly for the second time to obtain a uniform mixed dispersion. Preferably, in step (2), the amino silane coupling agent is at least one of γ-aminopropyltriethoxysilane (APTES) and γ-aminopropyltrimethoxysilane; the epoxy silane coupling agent is at least one of γ-glycidoxypropyltrimethoxysilane (GPTMS) and γ-glycidoxypropyltriethoxysilane.

[0021] Preferably, in step (2), the process of first mixing is as follows: stirring is used, the stirring speed is 200~5000 rpm, the stirring time is 10~60 min, and the stirring temperature is room temperature.

[0022] Preferably, in step (2), the second mixing process is as follows: stirring is used, the stirring speed is 200~5000 rpm, the stirring time is no more than 15 min (preferably no more than 5 min, and even more preferably no more than 3 min), and the stirring temperature is 4~80℃ (preferably 4~50℃) to avoid the gel network formed by the reaction of the two silane coupling agents being destroyed by stirring.

[0023] Preferably, in step (2), when an amino silane coupling agent is added first and then an epoxy silane coupling agent is added, both mixing processes must be carried out in an airless environment (i.e., a carbon dioxide-free environment) to prevent the amino silane coupling agent from reacting with carbon dioxide in the air; when an epoxy silane coupling agent is added first and then an amino silane coupling agent is added, the second mixing process must be carried out in an airless environment (i.e., a carbon dioxide-free environment), and there is no requirement for the first mixing process to prevent the amino silane coupling agent from reacting with carbon dioxide in the air.

[0024] Preferably, in step (2), the molar ratio of amino-based silane coupling agent to epoxy-based silane coupling agent is 1:1 to 5; the total mass concentration of amino-based silane coupling agent and epoxy-based silane coupling agent is 0.5 to 15% (preferably 2 to 6%) (that is, the sum of the masses of amino-based silane coupling agent and epoxy-based silane coupling agent accounts for 0.5 to 15% of the sum of the masses of amino-based silane coupling agent, epoxy-based silane coupling agent and nanocellulose dispersion, more preferably 2 to 6%).

[0025] (3) The mixed dispersion obtained in step (2) is allowed to stand, and the sol-gel transition occurs, causing it to completely gel and form a stable organic-inorganic hybrid three-dimensional network hydrogel. Preferably, in step (3), the alkaline environment provided by the hydrolysis of the amino silane coupling agent promotes the condensation between silanol groups, while its amino groups undergo ring-opening reactions with the epoxy groups of the epoxy silane coupling agent to form a cross-linked network; the nanocellulose serves as a three-dimensional flexible template, and the hydroxyl groups on its surface bond with the hydrolysis products or intermediates of the silane coupling agent, guiding the organosilicon network to grow and coat in situ on the surface of the nanocellulose fiber to form a hydrogel; Preferably, in step (3), the standing time is 3~48h (preferably 6~12h) and the gel temperature is 4~80℃ (preferably 5~50℃).

[0026] (4) The hydrogel obtained in step (3) is frozen and then freeze-dried to remove the ice crystals (deionized water) to obtain a nanocellulose / organosilicon composite aerogel with a porous structure. Preferably, in step (4), the freezing temperature is -10~-80℃ and the time is 12~72h.

[0027] Preferably, in step (4), the freeze-drying time is 24~96h and the temperature is -50~-70℃.

[0028] (5) Heat treatment: The nanocellulose / organosilicon composite aerogel obtained in step (4) is subjected to heat treatment to further promote the cross-linking reaction between the residual functional groups of the silane coupling agent, improve the stability and mechanical properties of the network structure, and obtain nanocellulose-reinforced organosilicon composite aerogel (hereinafter referred to as organosilicon composite aerogel).

[0029] Preferably, in step (5), the heat treatment temperature is 80~200℃ and the time is 10~120min.

[0030] Preferably, the method further includes step (6) hydrophobic modification: the nanocellulose-reinforced organosilicon composite aerogel obtained in step (5) is subjected to chemical vapor deposition reaction with a volatile hydrophobic reagent to graft hydrophobic groups onto the surface and internal pore walls of the aerogel.

[0031] Preferably, in step (6), the volatile hydrophobicating agent is at least one of alkyl silane coupling agents and fluoroalkyl silane coupling agents; the alkyl silane coupling agent is preferably methyltrimethoxysilane, methyltrichlorosilane, dimethyldimethoxysilane, dimethyldichlorosilane, octyltrichlorosilane, octyltrimethoxysilane, octadecyltrichlorosilane or dodecyltrimethoxysilane; the fluoroalkyl silane coupling agent is preferably tridecafluorooctyltrichlorosilane or heptadecafluorodecyltrimethoxysilane.

[0032] Preferably, in step (6), the reaction environment is a closed environment, the reaction temperature is 50~150℃, and the reaction time is 2~48h.

[0033] Preferably, in step (6), the mass ratio of the volatile hydrophobic reagent to the nanocellulose-reinforced organosilicon composite aerogel is 1~10:1~10.

[0034] The present invention also provides a method for preparing the nanocellulose-reinforced organosilicon composite aerogel, and the nanocellulose-reinforced organosilicon composite aerogel obtained therefrom.

[0035] This invention also provides an application of the aforementioned nanocellulose-reinforced organosilicon composite aerogel, which is used for oil-in-water emulsion separation, oil absorption, and thermal insulation.

[0036] Example 1: (1) Prepare 10g of uniformly dispersed BC dispersion, wherein the mass of BC is 0.08% of the mass of deionized water. Stir and disperse thoroughly at a speed of 1000rpm for 20min at a temperature of room temperature. (2) Add 0.095 g of APTES to the BC dispersion and stir magnetically at 1000 rpm for 30 min at room temperature and without carbon dioxide; then add 0.305 g of GPTMS and continue stirring magnetically at 1000 rpm for 5 min at room temperature and without carbon dioxide to obtain a uniform mixed dispersion. (3) Transfer the mixed dispersion into a mold and let it stand at room temperature for 12 hours to form a stable organic-inorganic hybrid three-dimensional network hydrogel; (4) The hydrogel and the mold were placed in a -18℃ freezer for 24h, and then the completely frozen sample was transferred to a freeze dryer and vacuum freeze-dried at -50℃ for 48h to obtain BC / organosilicon composite aerogel. (5) The BC / organosilicon composite aerogel was placed in an oven and heat-treated at 120°C for 20 min to obtain BC-reinforced APTES / GPTMS composite aerogel.

[0037] Depend on Figure 1-3 It can be seen that the BC-reinforced APTES / GPTMS composite aerogel has a unique biomimetic coral-like hierarchical fiber structure.

[0038] Depend on Figure 4 As can be seen, the EDS energy dispersive spectroscopy scan shows that the C, N, O and Si elements are evenly distributed on the fiber structure, indicating that the two silane coupling agents are evenly mixed with BC.

[0039] Tests showed that the BC-reinforced APTES / GPTMS composite aerogel exhibited excellent mechanical properties, emulsion separation performance, and thermal insulation properties; specific results are shown in Table 1. Figure 5 As can be seen, the organosilicon composite aerogel of Example 1 still has an elastic recovery rate of up to 93% after 100 cycles of compression at 80% strain, indicating that it has excellent fatigue resistance.

[0040] Example 2: This embodiment is exactly the same as embodiment 1, except that: step (6) is performed to perform hydrophobic modification on the BC-reinforced APTES / GPTMS composite aerogel; the specific steps of hydrophobic modification are as follows: in a sealed container, take 0.1g of BC-reinforced APTES / GPTMS composite aerogel, and then place 0.2g of methyltrimethoxysilane at the bottom of it. The methyltrimethoxysilane, which is easy to evaporate, is adsorbed by the aerogel on the top. The silane and the aerogel do not come into direct contact. Then heat to 80°C and maintain for 12h to obtain hydrophobic BC-reinforced APTES / GPTMS composite aerogel.

[0041] Tests showed that the hydrophobic BC-reinforced APTES / GPTMS composite aerogel exhibited excellent mechanical properties, oil absorption capacity, and thermal insulation properties, as detailed in Table 1. The water contact angle of this hydrophobic BC-reinforced APTES / GPTMS composite aerogel, measured using a water contact angle meter, reached as high as 156°±5°, demonstrating excellent selective adsorption capacity for oils (see Table 1). Figure 6 and Figure 7 ).Depend on Figure 6 It can be seen that the composite aerogel has an adsorption capacity of 25~57g / g for different types of oil. Figure 7 In this study, dichloroethane was used as the model oil. Its cyclic oil absorption performance was verified through mechanical extrusion (specifically, by first adsorbing, then extruding the oil, and then performing another adsorption). Figure 7 It can be seen that after the composite aerogel adsorbs dichloroethane, it can be recycled after mechanical extrusion. After 50 adsorption-desorption cycles, its adsorption ratio is still above 50, showing good cycle stability.

[0042] Example 3: This embodiment is exactly the same as embodiment 1, except that: in step (1), the mass of BC is 0.2% of the mass of deionized water and the stirring rate is 2000 rpm; in step (2), the amount of APTES is 0.128 g and the amount of GPTMS is 0.272 g. The organosilicon composite aerogel of Example 3 was tested and found to have excellent mechanical properties, emulsion separation properties and thermal insulation properties. The specific results are shown in Table 1.

[0043] Example 4: This embodiment is exactly the same as embodiment 1, except that in step (2), the amount of APTES is 0.19g, the amount of GPTMS is 0.61g, the stirring rate is 2000rpm, and the stirring time for the second mixing is 3min.

[0044] The organosilicon composite aerogel of Example 4 was tested and found to have excellent mechanical properties, emulsion separation properties and thermal insulation properties. The specific results are shown in Table 1.

[0045] Example 5: This embodiment is exactly the same as embodiment 1, except that: in step (2), the stirring temperature is 50°C; in step (3), it is left to stand at room temperature for 48 hours; in step (4), the freezing time is 36 hours; and in step (5), it is heat-treated at 150°C for 10 minutes.

[0046] The organosilicon composite aerogel of Example 5 was tested and found to have excellent mechanical properties, emulsion separation properties and thermal insulation properties. The specific results are shown in Table 1.

[0047] Comparative Example 1: This comparative example is exactly the same as Example 1, except that in step (2), only APTES, a silane coupling agent, is used, and GPTMS is not added. Step (2) is as follows: 0.4g of APTES is added to the BC dispersion, and the mixture is magnetically stirred at 1000rpm for 30min at room temperature and without carbon dioxide to obtain a uniform dispersion; Depend on Figure 8 As can be seen, the composite aerogel prepared in Comparative Example 1 has a dense and smooth lamellar structure, similar to the microstructure of aerogels obtained by combining traditional nanocellulose and silane coupling agents, without a clear multi-level fiber network. Meanwhile, its mechanical properties are poor, and its separation efficiency is extremely low (see Table 1).

[0048] Comparative Example 2: This comparative example is exactly the same as Example 1, except that: step (2) is as follows: 0.295g of APTES is added to the BC dispersion, and magnetic stirring is performed at 1000rpm for 30min at room temperature and without carbon dioxide; then 0.105g of GPTMS is added to the mixture, and magnetic stirring is performed at 1000rpm for 5min at room temperature and without carbon dioxide to obtain a uniform mixed dispersion. Depend on Figure 9 It can be seen that the composite aerogel prepared in Comparative Example 2 has an internal lamellar structure, but it is coarser than that in Comparative Example 1 and lacks a multi-level fibrous structure. At the same time, its mechanical properties are poor, and its separation efficiency and separation flux are extremely low (see Table 1).

[0049] Comparative Example 3: This comparative example is exactly the same as Example 1, except that: step (2) is as follows: 0.034g of APTES is added to the BC dispersion, and magnetic stirring is performed at 1000rpm for 30min at room temperature and without carbon dioxide; then 0.366g of GPTMS is added to the mixture, and magnetic stirring is performed at 1000rpm for 5min at room temperature and without carbon dioxide to obtain a uniform mixed dispersion. Depend on Figure 10As can be seen, the composite aerogel prepared in Comparative Example 3 contains grape-like microspheres with a diameter exceeding 1 μm, and the overall structure tends to be fused, with almost no pores. At the same time, its mechanical properties are poor and its separation efficiency is extremely low (see Table 1).

[0050] Comparative Example 4: This comparative example is exactly the same as Example 1, except that: step (1) is only 10g of deionized water; step (2) is specifically: add 0.095g of APTES to 10g of deionized water, and magnetically stir at 1000rpm for 30min at room temperature and without carbon dioxide; then add 0.305g of GPTMS to the mixture, and continue to magnetically stir at 1000rpm for 5min at room temperature and without carbon dioxide to obtain a uniform mixed dispersion. Depend on Figure 11 It can be seen that the product of Comparative Example 4 consists of particles with a diameter of more than 1 micrometer and smooth sheets, without a fibrous multi-level structure. The resulting material has a loose structure and is easily crushed, indicating that this structure is not conducive to molding and processing. Furthermore, it cannot be tested for mechanical properties and oil-water separation.

[0051] The aerogels prepared in Examples 1-5 and Comparative Examples 1-4 were tested for elasticity, compressive modulus, emulsion separation performance (separation flux and separation efficiency), and thermal conductivity. The results are shown in Table 1. Elasticity and modulus were calculated from the results of compressive stress-strain tests (compressive strain 80%, compression cycles 2 times). Specifically, the elastic recovery rate was the ratio of the height recovered by the aerogel after complete release of compressive stress to the initial height before compression; the compressive modulus was the ratio of the stress value corresponding to 5% strain to the strain. The emulsion separation performance test used corn oil as a model. First, a water-in-oil emulsion (oil-to-water ratio 1:99) was obtained by high-speed homogenization stirring. Then, the aerogel was fixed in an oil-water separator, and separation was performed using gravity. The separation efficiency was calculated by detecting the organic matter content in the filtrate, and the separation flux was calculated by measuring the liquid volume passing through the aerogel per unit time. The thermal conductivity was measured using the planar heat source method; a lower value indicates better thermal insulation performance.

[0052] Table 1

[0053] The infrared spectra of the products of Example 1 and Comparative Examples 1-3 were measured using a Fourier transform infrared spectrometer, as shown below. Figure 12 As shown. By Figure 12As can be seen, Comparative Example 1 shows a clear amino stretching vibration peak, Comparative Example 3 shows a clear epoxy group stretching vibration peak, and Comparative Example 2 shows a clear imine peak. This indicates that the amino and epoxy groups react after the two silanes are mixed. The characteristic peak of the epoxy group is still visible in Example 1, which is due to the excess GPTMS. All samples show obvious Si-O-Si characteristic peaks, indicating that the silane coupling agents also form polymers through the condensation of silanols. In summary, the two silane coupling agents form a strong polymer cross-linking network on the surface of nanocellulose, which is the chemical basis for its excellent mechanical properties.

[0054] Further analysis of the charts yielded the following conclusions: (1) Nanocellulose is an essential component. Comparative Example 4 shows that without BC as a template and reinforcing framework, a complete aerogel with practical mechanical strength cannot be obtained. (2) The silane ratio is a key regulatory factor. Comparative Examples 1-3 show that the ratio of APTES to GPTMS directly affects the microstructure and mechanical properties of the product. Only when the ratio of the two is appropriate (as in Examples 1-5) can the synergy of amino-epoxy crosslinking and silanol polycondensation be achieved, constructing a biomimetic coral-like structure that combines rigidity and flexibility, thereby simultaneously obtaining a high elastic recovery rate (99.3%) and a high modulus (43.2 kPa), as well as excellent fatigue resistance (the elastic recovery rate after 100 compressions is as high as 93%). Figure 5 The particle-packed structure makes aerogels brittle, unable to take shape, and with weak mechanical properties.

[0055] Any aspects not covered in this invention are applicable to existing technologies.

Claims

1. A method for preparing a nanocellulose-reinforced organosilicon composite aerogel, characterized in that, The method includes the following steps: (1) The nanocellulose was uniformly dispersed in deionized water to obtain a nanocellulose dispersion; (2) Add one of the amino-based silane coupling agent and the epoxy-based silane coupling agent to the nanocellulose dispersion obtained in step (1) and mix it evenly for the first time so that the silane coupling agent is hydrolyzed and adsorbed onto the nanocellulose; then add the other of the amino-based silane coupling agent and the epoxy-based silane coupling agent and mix it evenly for the second time to obtain a mixed dispersion. (3) The mixed dispersion obtained in step (2) is allowed to stand, and the sol-gel transition occurs, causing it to completely gel and form an organic-inorganic hybrid three-dimensional network hydrogel. (4) The hydrogel obtained in step (3) is frozen and then freeze-dried to remove the ice crystals and obtain a nanocellulose / organosilicon composite aerogel with a porous structure. (5) The nanocellulose / organosilicon composite aerogel obtained in step (4) is subjected to heat treatment to further promote the cross-linking reaction between the residual functional groups of the silane coupling agent, improve the stability and mechanical properties of the network structure, and obtain nanocellulose-reinforced organosilicon composite aerogel.

2. The method for preparing the nanocellulose-reinforced organosilicon composite aerogel according to claim 1, characterized in that, In step (1), the nanocellulose is at least one of bacterial cellulose and cellulose nanofibers; In step (1), the process of uniform dispersion is as follows: stirring is used, the stirring speed is 200~5000 rpm, the stirring time is 10~30 min, and the stirring temperature is room temperature; In step (1), the mass of nanocellulose is 0.002~2% of the mass of deionized water.

3. The method for preparing the nanocellulose-reinforced organosilicon composite aerogel according to claim 1, characterized in that, In step (2), the amino silane coupling agent is at least one of γ-aminopropyltriethoxysilane and γ-aminopropyltrimethoxysilane; the epoxy silane coupling agent is at least one of γ-glycidoxypropyltrimethoxysilane and γ-glycidoxypropyltriethoxysilane.

4. The method for preparing the nanocellulose-reinforced organosilicon composite aerogel according to claim 1, characterized in that, In step (2), the first process of uniform mixing is as follows: stirring is used, the stirring speed is 200~5000 rpm, the stirring time is 10~60 min, and the stirring temperature is room temperature; In step (2), the second mixing process is as follows: stirring is used, the stirring speed is 200~5000 rpm, the stirring time does not exceed 15 min, and the stirring temperature is 4~80℃; In step (2), when amino-based silane coupling agent is added first and then epoxy-based silane coupling agent is added, both mixing processes must be carried out in a carbon dioxide-free environment to prevent the amino-based silane coupling agent from reacting with carbon dioxide in the air; when epoxy-based silane coupling agent is added first and then amino-based silane coupling agent is added, the second mixing process must be carried out in a carbon dioxide-free environment to prevent the amino-based silane coupling agent from reacting with carbon dioxide in the air.

5. The method for preparing the nanocellulose-reinforced organosilicon composite aerogel according to claim 1, characterized in that, In step (2), the molar ratio of amino silane coupling agent to epoxy silane coupling agent is 1:1~5; the total mass concentration of amino silane coupling agent and epoxy silane coupling agent is 0.5~15%.

6. The method for preparing the nanocellulose-reinforced organosilicon composite aerogel according to claim 1, characterized in that, In step (3), the standing time is 3~48h and the gel temperature is 4~80℃.

7. The method for preparing the nanocellulose-reinforced organosilicon composite aerogel according to claim 1, characterized in that, In step (4), the freezing temperature is -10~-80℃ and the time is 12~72h; In step (4), the freeze-drying time is 24~96h and the temperature is -50~-70℃.

8. The method for preparing the nanocellulose-reinforced organosilicon composite aerogel according to claim 1, characterized in that, In step (5), the heat treatment temperature is 80~200℃ and the time is 10~120min.

9. The method for preparing the nanocellulose-reinforced organosilicon composite aerogel according to claim 1, characterized in that, The method also includes step (6) hydrophobic modification: the nanocellulose-reinforced organosilicon composite aerogel obtained in step (5) is subjected to chemical vapor deposition reaction with a volatile hydrophobic reagent to graft hydrophobic groups onto the surface and internal pore walls of the aerogel.

10. The method for preparing the nanocellulose-reinforced organosilicon composite aerogel according to claim 9, characterized in that, In step (6), the volatile hydrophobicating agent is at least one of alkyl silane coupling agents and fluoroalkyl silane coupling agents; the alkyl silane coupling agent is preferably methyltrimethoxysilane, methyltrichlorosilane, dimethyldimethoxysilane, dimethyldichlorosilane, octyltrichlorosilane, octyltrimethoxysilane, octadecyltrichlorosilane, or dodecyltrimethoxysilane; the fluoroalkyl silane coupling agent is preferably tridecafluorooctyltrichlorosilane or heptadecafluorodecyltrimethoxysilane. In step (6), the reaction environment is a closed environment, the reaction temperature is 50~150℃, and the reaction time is 2~48h; In step (6), the mass ratio of the volatile hydrophobic reagent to the nanocellulose-reinforced organosilicon composite aerogel is 1~10:1~10.

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