Composite aerogel material based on rice hull solid waste resource and preparation method thereof

Abstract

The application belongs to the technical field of biomass functional materials, and particularly relates to a composite aerogel material based on rice husk solid waste resource and a preparation method. The composite aerogel material is prepared from chitosan, polyvinyl alcohol, cellulose and silicon dioxide, wherein the cellulose and the silicon dioxide are both derived from rice husk, the cellulose is long fiber and / or sheet-shaped unhydrolyzed fiber, and the silicon dioxide is amorphous silicon dioxide. The chitosan, polyvinyl alcohol, cellulose and silicon dioxide are prepared into an anisotropic cellulose / polyvinyl alcohol / chitosan-silicon dioxide composite aerogel material through a cross-linking process, and the material has the advantages of ultralight quality, low thermal conductivity, excellent mechanical anisotropy and cyclic compression stability, and can be applied to the fields of building energy saving, power battery thermal management, fireproof and heat insulation and high-end equipment lightweight and heat insulation.

Description

Technical Field

[0001] This invention belongs to the field of biomass functional materials technology, specifically relating to a composite aerogel material based on rice husk solid waste resource utilization and its preparation method. Background Technology

[0002] Currently, the resource utilization of agricultural waste is gradually becoming an important research direction in the field of materials science. Rice husks, as a large-scale agricultural solid waste generated during rice processing, have a huge annual output. Their main components include cellulose, hemicellulose, lignin, and abundant inorganic silicon. The silicon dioxide content typically reaches 15%–20%, and it mostly exists in an amorphous state, making it a high-quality natural silicon source. Currently, a large amount of rice husks are still disposed of through open-air incineration or landfill, which not only wastes resources but also causes serious environmental pollution. Therefore, developing high-value-added utilization technologies that can simultaneously utilize the organic fiber resources and inorganic silicon resources in rice husks is of great significance.

[0003] Aerogels are a class of novel porous materials with ultra-high porosity, ultra-low density, and ultra-low thermal conductivity, showing broad application prospects in thermal insulation, fire retardancy, adsorption separation, and energy fields. Among them, polyvinyl alcohol or cellulose aerogels have attracted widespread attention due to their simple preparation, low cost, and good flexibility. However, traditional aerogels still have the following drawbacks: (1) The skeleton has low strength and is prone to permanent deformation and structural collapse under compressive load; (2) It is prone to thermal degradation under high temperature environment and has insufficient fire resistance; (3) A single polymer system cannot simultaneously achieve high strength, high flexibility and low thermal conductivity; (4) It has poor cyclic compression stability and is prone to performance degradation during long-term service.

[0004] Meanwhile, most existing studies use commercial cellulose and commercial silica as raw materials, and few can simultaneously utilize the cellulose and silica resources in rice husks. Moreover, existing composite aerogels mostly have random porous structures, making it difficult to directionally control their mechanical properties and structural functions.

[0005] Therefore, developing a composite aerogel material based on the full utilization of rice husk resources and possessing anisotropic structure, high thermal insulation performance, and excellent mechanical stability has significant scientific and application value. Summary of the Invention

[0006] To address the shortcomings of the existing technology, the present invention aims to provide a composite aerogel material based on rice husk solid waste resource utilization and its preparation method. This composite aerogel material has excellent thermal insulation performance, load-bearing capacity, cyclic compression stability and resilience, as well as fire resistance and flame retardant potential.

[0007] This invention is achieved through the following technical solution: A composite aerogel material based on the resource utilization of rice husk solid waste is provided. The composite aerogel material is prepared from chitosan, polyvinyl alcohol, cellulose and silica. The cellulose and silica are both derived from rice husk. The cellulose is long fiber and / or sheet-like unhydrolyzed fiber, and the silica is amorphous silica.

[0008] Preferably, the composite aerogel material is a three-dimensional porous network structure, which is a layered pore structure with regular orientation, and the surface of the layered pore structure is uniformly loaded with the amorphous silica.

[0009] Preferably, the length of the long fiber is 100~300µm.

[0010] A method for preparing a composite aerogel material based on rice husk solid waste resource utilization includes the following steps: Step 1: Add polyvinyl alcohol to deionized water, heat and stir until completely transparent to obtain a PVA solution with a mass fraction of 0.5~2wt%; Step 2: Add cellulose and amorphous silica to the PVA solution and disperse them thoroughly to form a uniform suspension system, thus obtaining the PVA / cellulose / silica system; the mass ratio of cellulose, amorphous silica and PVA solution is 3:3:94. Step 3: Add chitosan to an aqueous solution containing 0.5-2 wt% acetic acid and stir until completely dissolved to obtain a chitosan solution with a mass fraction of 1-2 wt%; wherein, acetic acid provides an acidic environment for the dissolution of chitosan; Step 4: After thoroughly mixing the chitosan solution with the PVA / cellulose / silica system, glutaraldehyde is added as a crosslinking agent, and the mixture is stirred at room temperature for 30 minutes to form a composite hydrogel; the mass ratio of the chitosan solution to the PVA / cellulose / silica system is 60:100. It should be noted that increasing the amount of glutaraldehyde and the crosslinking time can improve the stability of the skeleton, but excessive amounts can lead to material embrittlement; increasing the amount of PVA can improve the toughness of the material, but it will cause the material to lose its elasticity; increasing the chitosan content can improve the flame retardant properties and compression recovery. Therefore, choosing an appropriate ratio is the key to preparation. Step 5: Pour the composite hydrogel into a mold and place it under -40℃ to -60℃ for directional freezing; Step six: After freezing, the sample is placed in a freeze dryer and freeze-dried under vacuum conditions to obtain a composite aerogel material with a directional layered pore structure, that is, an anisotropic cellulose / polyvinyl alcohol / chitosan-silica composite aerogel material is prepared.

[0011] It is important to note that the faster the freezing rate, the smaller the pore size; the more stable the directional temperature gradient, the more regular the layered structure arrangement; and the alignment of the channels along the freezing direction can significantly improve axial compressive strength and radial resilience. Therefore, selecting appropriate freezing rates and appropriate directional temperatures is crucial.

[0012] Furthermore, in step one, the molecular weight (Mw) of the polyvinyl alcohol is 10000-205000 g / mol.

[0013] Furthermore, in step one, the dissolution conditions are: heating to 60-90°C, stirring speed of 50-300 r / min, stirring time of 30-90 min, and allowing the mixture to stand for at least 8 hours to remove bubbles after dissolution. Preferably, the stirring speed is 50-60 r / min, using a low speed to reduce gas introduction.

[0014] Furthermore, in step four, the amount of glutaraldehyde added accounts for 50% to 100 wt% of the total mass of polyvinyl alcohol and chitosan, and the crosslinking time is 10 to 90 min.

[0015] Preferably, in step five, the directional freezing temperature is -50°C and the directional freezing time is 30 minutes.

[0016] Preferably, in step six, the freeze-drying vacuum degree is 1 Pa, and the freeze-drying time is 24~72 h.

[0017] The present invention also provides a method for extracting the cellulose and amorphous silica, the steps of which include: S1. Wash and dry the rice husks, then grind them into 100-mesh powder; S2. Add a certain amount of rice husk powder to a 0.5~3mol / L hydrochloric acid solution and mix at a solid-liquid mass ratio of 1:10~1:30. Stir magnetically at room temperature for 0.5~4h, then filter and wash with deionized water until neutral. The acid washing is mainly to remove metal ions and inorganic impurities to improve the purity of subsequent silica extraction. S3. Add the acid-washed rice husks to a 0.5-5 mol / L sodium hydroxide solution, stir at a solid-liquid mass ratio of 1:10-1:30 in a 60℃ water bath for 1-6 hours, and filter to obtain a silica-containing filtrate and crude cellulose, respectively. S4. After evaporating and drying the silicon-containing filtrate, place it in a tube furnace and carbonize it at 600~700℃ for 0.5~1h to obtain rice husk ash; S5. Add the obtained rice husk ash to a 0.5~5 mol / L sodium hydroxide solution, and stir for 1~6 h in a water bath at 60~95℃ at a solid-liquid mass ratio of 1:20 to obtain a sodium silicate solution. S6. Adjust the pH of the sodium silicate solution to 7-9 by hydrochloric acid titration, let it stand for 10-30 minutes to form silica gel precipitate, filter it, and then dry it in a 40℃ drying oven for 24 hours to obtain amorphous silica. In this step, both oven drying and freeze drying can be used. Freeze drying can reduce the particle size of amorphous silica, but it has no significant effect on the subsequent aerogel properties. To reduce energy consumption, oven drying is preferred here. S7. Add crude cellulose to a 1-5 wt% sodium chlorite solution, and adjust the pH of the system to 4-6 using hydrochloric acid. Stir at 40-80℃ for 2-8 hours with a solid-liquid mass ratio of 1:20. Then wash repeatedly until the cellulose turns white to obtain purified cellulose. It should be noted that appropriately extending the rinsing time can reduce the number of rinsing times. The purity of cellulose can be determined by observing the gradual change of cellulose color from yellow to white and the significant weakening of the characteristic peak of the lignin aromatic ring in FTIR.

[0018] Preferably, in step S5, the concentration of the sodium hydroxide solution is 1 mol / L.

[0019] Compared with the prior art, the present invention has the following beneficial effects: (1) To achieve high-value utilization of all components of rice husk resources, this invention uses rice husk as the sole biomass raw material source and achieves simultaneous separation and extraction of cellulose and silicon components through acid-base synergistic treatment. Among them, cellulose is purified and used as a framework reinforcing phase, while silicon components are further prepared into amorphous silica and introduced into the aerogel system as an inorganic functional phase, thus realizing the synergistic utilization of organic and inorganic resources of rice husk. Compared with the traditional technical route that only utilizes a single component of rice husk, this invention significantly improves the utilization rate of agricultural waste resources and realizes the high-value-added transformation of rice husk resources.

[0020] (2) An ultra-lightweight porous structure was obtained by constructing a three-dimensional porous network structure through directional freezing and freeze-drying processes. The resulting composite aerogel had a density of only 0.093 g / cm³. 3 This indicates that a large number of continuous and uniformly distributed pore structures have formed inside the material. This density is much lower than that of traditional inorganic insulation materials and most polymer foam materials, significantly reducing the material's weight while ensuring structural stability. This is beneficial for applications in fields with high lightweighting requirements, such as building energy conservation, transportation, and aerospace.

[0021] (3) It possesses excellent thermal insulation properties. The directional layered porous structure constructed in this invention can effectively suppress gas heat convection, while rice husk-derived amorphous silica has low solid thermal conductivity. The synergistic effect of the two significantly reduces the material's heat transfer efficiency. Tests show that the thermal conductivity of the resulting composite aerogel is only 0.0238 W·m. -1 ·K -1This value is significantly lower than that of traditional insulation materials such as rock wool, foam glass, and foamed concrete. This indicates that the material of the present invention has excellent thermal barrier properties and insulation performance, and can significantly reduce heat loss.

[0022] (4) Formation of a significant mechanical anisotropic structure: This invention employs directional freezing technology to induce ice crystals to preferentially grow along a fixed temperature gradient. During the freezing process, cellulose, PVA, chitosan, and amorphous silica are gradually displaced and enriched in the interstitial regions of the ice crystals, ultimately forming a layered porous structure with regular orientation. When compression tests are conducted along the freezing direction (axial direction), the material exhibits excellent load-bearing capacity, with a compressive strength of 220 kPa at 5% compressive strain. This indicates that the directionally arranged layered pore walls can effectively bear external loads and significantly improve the structural stability of the material. Therefore, the material of this invention maintains the low-density characteristics of ultralight aerogels while overcoming the problem of insufficient mechanical strength in traditional aerogels.

[0023] (5) It exhibits excellent cyclic compression stability and resilience. Due to the flexible organic network structure formed by PVA and chitosan, the reinforcing skeleton of cellulose, and the further enhancement of pore wall stability by amorphous silica, the resulting composite aerogel, obtained through directional freezing pore formation, possesses good recoverable deformation capability. During cyclic compression testing perpendicular to the freezing direction (radial), the material exhibits a compressive strength of 125 kPa under 40% compressive strain. After 100 consecutive cyclic compressions, it maintains its intact structure without significant cracking, collapse, or pulverization. After the cyclic test, the material still retains a compressive strength of approximately 100 kPa. This demonstrates that the material of this invention possesses excellent fatigue resistance and long-term service stability, and can adapt to complex working conditions such as vibration, impact, and repeated pressure.

[0024] (6) It possesses excellent fire resistance and flame retardant potential. The amorphous silica introduced in this invention has excellent thermal stability and non-flammability, and can form a stable inorganic thermal insulation barrier under high-temperature conditions. Chitosan, after being heated, can promote the formation of a continuous carbon layer structure, further hindering the transfer of heat and oxygen into the material. At the same time, the large number of closed and semi-closed pores inside the material can effectively reduce the heat diffusion rate. Therefore, the material of this invention has both excellent thermal insulation performance and fire resistance and flame retardant potential, which can meet the application needs in fields such as building fire protection and thermal insulation, thermal protection of new energy batteries, and industrial high-temperature thermal insulation. The material remains intact after being burned at 800°C for 10 minutes in an open flame, with only surface carbonization and no combustion occurring throughout the process. Attached Figure Description

[0025] Figure 1 This is a scanning electron microscope image of the cellulose extracted in Example 1 of the present invention.

[0026] Figure 2These are scanning electron microscope (SEM) images and energy dispersive spectroscopy (EDS) analysis results of silica extracted in Example 1 of this invention.

[0027] Figure 3 This is the stress-strain curve of the composite aerogel material in Embodiment 1 of the present invention when compressed along the directional freezing direction.

[0028] Figure 4 This is the stress-strain curve of the composite aerogel material in Embodiment 1 of the present invention under cyclic compression perpendicular to the directional freezing direction.

[0029] Figure 5 This is a diagram illustrating the good elasticity of the composite aerogel material prepared in Example 1 of the present invention.

[0030] Figure 6 This is a scanning electron microscope image of the pore size of the composite aerogel material in Example 1 of the present invention after directional freezing.

[0031] Figure 7 This is a scanning electron microscope (SEM) image of the amorphous silica distribution on the surface of the composite aerogel material matrix of the present invention, as shown in Example 1 of the present invention.

[0032] Figure 8 This is a physical image of the composite aerogel material prepared in Example 1 of the present invention. Detailed Implementation

[0033] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention.

[0034] This invention belongs to the fields of agricultural solid waste resource utilization, biomass functional materials, and aerogel preparation technology. Specifically, it relates to a method for preparing a cellulose / polyvinyl alcohol (PVA) / chitosan-silica composite aerogel material by synergistic extraction of cellulose and silicon resources from rice husks. This material possesses ultra-lightweight properties, low thermal conductivity, excellent mechanical anisotropy, and cyclic compression stability, and can be applied in building energy conservation, power battery thermal management, fireproofing and insulation, and lightweight thermal insulation for high-end equipment.

[0035] This invention relates to anisotropic cellulose / polyvinyl alcohol / chitosan-silica composite aerogel material and its preparation method based on the resource utilization of rice husk solid waste. The extraction process in this invention is not aimed at obtaining a high-purity single component, but rather at the needs of subsequent composite aerogel construction. It specifically regulates the morphology of cellulose and the activity of silica, so that the obtained cellulose maintains a long fiber structure and the obtained silica maintains an amorphous structure with nano-particle size. This allows it to directly participate in the construction of the anisotropic composite aerogel framework, realizing an integrated design of extraction and utilization.

[0036] This invention introduces fiber reinforcement, inorganic nanoparticles, and natural polymer components to construct an organic-inorganic composite aerogel system. Cellulose provides excellent mechanical reinforcement; amorphous silica exhibits superior thermal insulation and flame retardancy; and chitosan enhances the skeletal toughness and promotes the formation of a stable hydrogen bond network.

[0037] This invention aims to construct high-performance anisotropic composite aerogel materials by synergistically extracting and targeting the utilization of cellulose and silicon resources from rice husks. The extraction process is optimized for subsequent aerogel construction and has the following characteristics: 1. Retaining the long fiber structure of cellulose (100~300 micrometers, retaining some sheet-like cellulose structure) instead of further preparing nanocellulose using strong acids, so that cellulose can form a continuous reinforcing skeleton in the aerogel system, improving the material's mechanical strength and compression recovery performance; 2. A highly active amorphous silica is obtained using an acid-washing-alkali extraction-low-temperature ashing process, avoiding silica crystallization under high-temperature conditions, which is beneficial for improving its dispersibility and interfacial bonding ability in the aerogel system. Since lignin and hemicellulose are not required subsequently, hemicellulose and lignin are not separated compared to existing extraction processes. 3. The extracted cellulose and amorphous silica are directly used for subsequent aerogel construction, achieving an integrated "extraction-utilization" design and avoiding the increased energy consumption caused by reprocessing of raw materials after extraction in traditional processes. The extraction process uses low acid and alkali concentrations and mild processing temperatures, resulting in a simple and low-cost process with good potential for industrial application.

[0038] 4. To achieve simultaneous extraction and synergistic utilization of cellulose and silicon resources in rice husks; to construct an organic-inorganic composite aerogel system using rice husk-derived cellulose and rice husk-derived amorphous silica; to improve the stability and fire resistance of the skeleton by adopting a quaternary synergistic reinforcement structure of cellulose / PVA / chitosan-silica; to construct an anisotropic layered porous structure using directional freezing technology; to form a dual-functional mechanical system with "axial high strength and radial high elasticity"; and to achieve a synergistic combination of agricultural solid waste resource utilization and high-performance thermal insulation material preparation.

[0039] The present invention will be further described below through specific embodiments: Example 1:

[0040] This embodiment first requires the extraction of cellulose and amorphous silica from rice husks. The specific extraction process is as follows: (1) Wash and dry the rice husks and then grind them into 100-mesh powder; (2) Weigh a certain amount of rice husk powder and add it to a 1 mol / L hydrochloric acid solution. Mix the solid-liquid mass ratio of 1:20 and stir magnetically for 1 h at room temperature. Then filter and wash with deionized water until neutral. (3) Add the acid-washed rice husks to a 1 mol / L sodium hydroxide solution, stir for 2 hours in a 60℃ water bath at a solid-liquid mass ratio of 1:20, and filter to obtain a silica-containing filtrate and crude cellulose respectively. (4) After evaporating and drying the silicon-containing filtrate, place it in a tube furnace and carbonize it at 600°C for 1 hour to obtain rice husk ash; (5) Add the obtained rice husk ash to a 1 mol / L sodium hydroxide solution and stir for 1 h in a water bath at 80℃ at a solid-liquid mass ratio of 1:20 to obtain a sodium silicate solution; (6) The pH of the sodium silicate solution was adjusted to 8-9 by hydrochloric acid titration, and the silica gel precipitate was formed after standing for 10 min. After filtration, the silica gel was dried in a 40℃ drying oven for 24 h to obtain amorphous silica. (7) Add crude cellulose to a 2wt% sodium chlorite solution and adjust the pH of the system to 5-6 with hydrochloric acid. Stir at 60℃ for 2 hours at a solid-liquid mass ratio of 1:20. Then wash repeatedly until the cellulose turns white to obtain purified cellulose.

[0041] Next, the amorphous silica and cellulose extracted above were used to prepare a composite aerogel material. The detailed preparation process is as follows: (1) Weigh 0.5g of polyvinyl alcohol and add it to 93.5g of deionized water. Heat and stir at 90°C until completely transparent to obtain a PVA solution. The molecular weight (Mw) of the polyvinyl alcohol used in this example is 205,000g / mol. The stirring rate is 50r / min and the stirring time is 90min. After dissolution, let it stand for more than 8 hours to remove bubbles. (2) Weigh 3g of cellulose and 3g of amorphous silica and add them to 94g of the above PVA solution to fully disperse and form a uniform suspension PVA / cellulose / silica system; (3) Weigh 1.2g of chitosan and add it to 58.8g of an aqueous solution containing 1wt% acetic acid, and stir until completely dissolved; (4) After thoroughly mixing the chitosan solution with the PVA / cellulose / silica system, add 2g of glutaraldehyde as a crosslinking agent and stir at room temperature for 30min to form a composite hydrogel; (5) Pour the obtained hydrogel into a mold and freeze it at -50℃ for 30 min; (6) After freezing, the sample was placed in a freeze dryer and freeze-dried for 72 hours under a vacuum of 1 Pa to obtain a composite aerogel material with an oriented layered pore structure.

[0042] Figure 1 This is a scanning electron microscope (SEM) image of the cellulose extracted in Example 1 of this invention. The scanning equipment parameters were: imaging detector: ETD secondary electron detector, accelerating voltage: 20.00 kV, beam spot: 13.0, working distance WD: 7.8252 mm, field of view HFW: 1.38 mm, scale bar: 300 µm. From the image, we can see that the obtained cellulose exhibits a long fibrous morphology, with fiber lengths mainly ranging from 100 to 300 µm. The overall structure is relatively intact, without obvious breakage or excessive refinement. This indicates that the extraction process of this invention effectively preserves the long fibrous structure of cellulose while removing non-cellulose components, providing a reinforcing phase for the subsequent construction of the composite aerogel material skeleton, which is beneficial for improving the mechanical properties and structural stability of the material. Simultaneously, the relatively rough fiber surface, possessing a certain natural texture, is conducive to enhancing the interfacial bonding between the fiber and the polymer matrix.

[0043] Figure 2 This is a scanning electron microscope (SEM) image and energy dispersive spectroscopy (EDS) analysis result of the silica extracted in Example 1 of this invention. The scanning equipment parameters were: imaging detector: ETD secondary electron detector, accelerating voltage: 20.00 kV, beam spot: 13.0, working distance WD: 7.8843 mm, field of view HFW: 41.4 mm, scale bar: 5 µm. As shown in the image, the obtained silica exhibits a micron-sized aggregated particle morphology, with particle sizes mainly distributed between 1 and 3 µm. The EDS analysis results indicate that the sample is mainly composed of O and Si elements, with mass fractions of 65.8% and 33.6%, respectively. Only small amounts of Na (0.5%) and Mg (0.1%) were detected, while Al was not detected, indicating that the obtained silica has a low impurity content and high purity. Based on its SEM morphology characteristics, it is shown that the extraction process adopted in this invention can obtain silica with high purity and fine particles, providing a good inorganic reinforcing phase for subsequent particle dispersion and construction of composite aerogel.

[0044] Figure 3This is the stress-strain curve of the composite aerogel material in Embodiment 1 of the present invention under compression along the directional freezing direction. As shown in the figure, the material compression process mainly involves a linear elastic stage (0–10% strain), a yield plateau stage (10%–60% strain), and a strain hardening stage (60%–80% strain). Specifically, the compressive stress is approximately 260 kPa at 10% compressive strain and reaches 1200 kPa at 80% compressive strain. With increasing compressive strain, the material does not exhibit a significant stress drop or skeletal instability; instead, it shows significant strain hardening characteristics in the high-strain region. This indicates that the anisotropic layered porous structure constructed by directional freezing can effectively improve the mechanical properties of the composite aerogel material along the freezing direction, enabling the material to possess both high load-bearing capacity, good compressive deformation capacity, and excellent energy absorption performance.

[0045] Figure 4 The figure shows the stress-strain curves of the composite aerogel material of Example 1 of this invention under cyclic compression perpendicular to the directional freezing direction. As can be seen from the figure, after 1, 10, and 100 compression cycles, the stress-strain curves maintain good consistency overall, with no obvious yield collapse or stress drop observed in any of the cycle curves. After 100 compression cycles, the material exhibits only a small amount of residual deformation, with an overall height retention rate of approximately 80%, and no significant skeletal collapse or structural instability occurs. This indicates that the composite aerogel prepared by this invention has good compression recovery performance, cyclic stability, and resistance to cyclic compression, and can maintain good structural integrity and mechanical properties under multiple cyclic loading conditions.

[0046] Figure 5 This is a diagram illustrating the good elasticity of the composite aerogel material prepared in Example 1 of the present invention.

[0047] Figure 6This is a scanning electron microscope (SEM) image of the pore size of the composite aerogel material in Example 1 of this invention after directional freezing. The scanning equipment parameters were: imaging detector: ETD secondary electron detector, accelerating voltage: 20.00 kV, beam spot: 13.0, working distance WD: 8.4074 mm, field of view HFW: 2.07 mm, scale bar: 500 µm. As shown in the image, a regular and ordered layered porous structure is formed inside the material. The pores are parallel, continuous, and unidirectional along the directional freezing direction, exhibiting obvious oriented interconnection characteristics. The overall pore arrangement direction is consistent, the interlayer connections are continuous, and the pore size distribution is relatively uniform. No obvious large pores, disordered closed pores, or skeletal collapse were observed. This demonstrates that the directional freezing process used in this invention can effectively construct a long-range, ordered, interlayer-interconnected anisotropic interconnected pore structure. During unidirectional freezing, ice crystals grow directionally along the temperature gradient, displacing the cellulose / amorphous silica composite slurry into the gaps between the ice crystals. After freeze-drying to remove the ice crystals, a regular and continuous parallel channel structure is formed, thus endowing the material with significant structural anisotropy. This structure not only ensures the integrity and continuity of the composite aerogel framework but also improves the material's mechanical stability, compression cycle stability, and thermal insulation performance. Furthermore, the complete and continuous channel structure, without obvious filler agglomeration leading to pore wall defects, indicates that amorphous silica can be uniformly dispersed in the composite framework and form a stable composite structure with cellulose / PVA / chitosan, providing a good microstructural basis for improving the material's overall performance.

[0048] Figure 7 This is a scanning electron microscope (SEM) image of the amorphous silica distribution on the matrix surface of the composite aerogel material in Example 1 of this invention. As shown in the image, the three-dimensional porous framework structure of the composite aerogel is completely preserved. The amorphous silica is uniformly attached to the surface of the cellulose-PVA-chitosan composite framework, with no obvious particle aggregation observed. The silica is tightly bonded to the matrix interface, forming continuous bridging structures in local areas. This indicates that the preparation method of this invention can achieve uniform loading of amorphous silica extracted from rice husks onto the surface of the composite aerogel framework, forming a continuous and stable inorganic reinforcing phase. This effectively avoids filler aggregation and pore blockage while ensuring the integrity of the porous framework. The uniformly distributed amorphous silica can form a continuous high-temperature resistant protective layer on the surface of the composite framework, effectively inhibiting thermal decomposition of the framework and hindering heat transfer under high-temperature conditions. Simultaneously, the completely preserved three-dimensional porous structure further reduces the internal thermal conductivity of the material, giving it both excellent fire resistance and thermal insulation properties. The above results show that the present invention achieves a synergistic improvement in lightweight, high-efficiency thermal insulation and fire resistance by uniformly coating and modifying amorphous silica and constructing a porous framework, providing a reliable microstructure basis for the application of composite aerogels in building insulation, fireproofing and heat insulation and high-temperature thermal management.

[0049] Figure 8This is a physical image of the composite aerogel material prepared in Example 1 of the present invention.

[0050] Example 2:

[0051] This embodiment first requires the extraction of cellulose and amorphous silica from rice husks. The specific extraction process is as follows: (1) Wash and dry the rice husks and then grind them into 100-mesh powder; (2) Weigh a certain amount of rice husk powder and add it to a 3 mol / L hydrochloric acid solution. Mix the solid-liquid mixture at a mass ratio of 1:10 and stir magnetically for 4 hours at room temperature. Then filter the mixture and wash it with deionized water until it is neutral. (3) Add the acid-washed rice husks to a 5 mol / L sodium hydroxide solution, stir for 2 hours in a 60℃ water bath at a solid-liquid mass ratio of 1:10, and filter to obtain a silica-containing filtrate and crude cellulose respectively. (4) After evaporating and drying the silicon-containing filtrate, place it in a tube furnace and carbonize it at 700°C for 0.5 h to obtain rice husk ash; (5) Add the obtained rice husk ash to a 1 mol / L sodium hydroxide solution and stir for 1 h in a water bath at 80℃ at a solid-liquid mass ratio of 1:20 to obtain a sodium silicate solution; (6) The pH of the sodium silicate solution was adjusted to 8-9 by hydrochloric acid titration, and the silica gel precipitate was formed after standing for 15 minutes. After filtration, the silica gel was dried in a 40℃ drying oven for 24 hours to obtain amorphous silica. (7) Add crude cellulose to a 5wt% sodium chlorite solution and adjust the pH of the system to 5-6 with hydrochloric acid. Stir at 60℃ for 8 hours at a solid-liquid mass ratio of 1:20. Then wash repeatedly until the cellulose turns white to obtain purified cellulose.

[0052] Next, the amorphous silica and cellulose extracted above were used to prepare a composite aerogel material. The detailed preparation process is as follows: (1) Weigh 1g of polyvinyl alcohol and add it to 93g of deionized water. Heat and stir at 90°C until completely transparent to obtain a PVA solution. The molecular weight (Mw) of polyvinyl alcohol used in this example is 205000g / mol. The stirring rate is 60r / min and the stirring time is 90min. After dissolution, let it stand for more than 8 hours to remove bubbles. (2) Weigh 3g of cellulose and 3g of amorphous silica and add them to 94g of the above PVA solution to fully disperse and form a uniform suspension PVA / cellulose / silica system; (3) Weigh 1g of chitosan and add it to 59g of an aqueous solution containing 2wt% acetic acid, and stir until completely dissolved; (4) After thoroughly mixing the chitosan solution with the PVA / cellulose / silica system, add 3g of glutaraldehyde as a crosslinking agent and stir at room temperature for 60min to form a composite hydrogel; (5) Pour the obtained hydrogel into a mold and freeze it at -60℃ for 30 min; (6) After freezing, the sample was placed in a freeze dryer and freeze-dried for 72 hours under a vacuum of 1 Pa to obtain a composite aerogel material with an oriented layered pore structure.

[0053] Example 3:

[0054] This embodiment first requires the extraction of cellulose and amorphous silica from rice husks. The specific extraction process is as follows: (1) Wash and dry the rice husks and then grind them into 100-mesh powder; (2) Weigh a certain amount of rice husk powder and add it to 0.5 mol / L hydrochloric acid solution. Mix the solid and liquid at a mass ratio of 1:30 and stir magnetically for 3 hours at room temperature. Then filter and wash with deionized water until neutral. (3) Add the acid-washed rice husks to a 1 mol / L sodium hydroxide solution, stir for 2 hours in a 60℃ water bath at a solid-liquid mass ratio of 1:20, and filter to obtain a silica-containing filtrate and crude cellulose respectively. (4) After evaporating and drying the silicon-containing filtrate, place it in a tube furnace and carbonize it at 650°C for 0.8 h to obtain rice husk ash; (5) Add the obtained rice husk ash to a 0.5 mol / L sodium hydroxide solution and stir for 1 h in a water bath at 60℃ at a solid-liquid mass ratio of 1:20 to obtain a sodium silicate solution; (6) The pH of the sodium silicate solution was adjusted to 7-8 by hydrochloric acid titration, and the silica gel precipitate was formed after standing for 20 min. After filtration, the silica gel was dried in a 40℃ drying oven for 24 h to obtain amorphous silica. (7) Add crude cellulose to a 1 wt% sodium chlorite solution and adjust the pH of the system to 4-5 with hydrochloric acid. Stir at 60°C for 4 hours at a solid-liquid mass ratio of 1:20. Then wash repeatedly until the cellulose turns white to obtain purified cellulose.

[0055] Next, the amorphous silica and cellulose extracted above were used to prepare a composite aerogel material. The detailed preparation process is as follows: (1) Weigh 1.5g of polyvinyl alcohol and add it to 92.5g of deionized water. Heat and stir at 90°C until completely transparent to obtain a PVA solution. The molecular weight (Mw) of the polyvinyl alcohol used in this example is 150000g / mol. The stirring rate is 70r / min and the stirring time is 90min. After dissolution, let it stand for 8 hours to remove bubbles. (2) Weigh 3g of cellulose and 3g of amorphous silica and add them to 94g of the above PVA solution to fully disperse and form a uniform suspension PVA / cellulose / silica system; (3) Weigh 0.8g of chitosan and add it to 58.8g of an aqueous solution containing 1wt% acetic acid, and stir until completely dissolved; (4) After thoroughly mixing the chitosan solution with the PVA / cellulose / silica system, add 1.8g of glutaraldehyde as a crosslinking agent and stir at room temperature for 60min to form a composite hydrogel; (5) Pour the obtained hydrogel into a mold and freeze it at -50℃ for 30 min; (6) After freezing, the sample was placed in a freeze dryer and freeze-dried for 72 hours under a vacuum of 1 Pa to obtain a composite aerogel material with an oriented layered pore structure.

[0056] Example 4:

[0057] This embodiment first requires the extraction of cellulose and amorphous silica from rice husks. The specific extraction process is as follows: (1) Wash and dry the rice husks and then grind them into 100-mesh powder; (2) Weigh a certain amount of rice husk powder and add it to a 2 mol / L hydrochloric acid solution. Mix the solid-liquid mass ratio of 1:20 and stir magnetically for 1 h at room temperature. Then filter and wash with deionized water until neutral. (3) Add the acid-washed rice husks to a 2 mol / L sodium hydroxide solution, stir for 2 h in a 60℃ water bath at a solid-liquid mass ratio of 1:20, and filter to obtain a silica-containing filtrate and crude cellulose respectively. (4) After evaporating and drying the silicon-containing filtrate, place it in a tube furnace and carbonize it at 700°C for 0.5 h to obtain rice husk ash; (5) Add the obtained rice husk ash to a 2 mol / L sodium hydroxide solution and stir for 2 h at 80℃ water bath with a solid-liquid mass ratio of 1:20 to obtain a sodium silicate solution; (6) The pH of the sodium silicate solution was adjusted to 8-9 by hydrochloric acid titration, and the silica gel precipitate was formed after standing for 20 min. After filtration, the silica gel was dried in a 40℃ drying oven for 24 h to obtain amorphous silica. (7) Add crude cellulose to a 3wt% sodium chlorite solution and adjust the pH of the system to 5-6 with hydrochloric acid. Stir at 60℃ for 5 hours at a solid-liquid mass ratio of 1:20. Then wash repeatedly until the cellulose turns white to obtain purified cellulose.

[0058] Next, the amorphous silica and cellulose extracted above were used to prepare a composite aerogel material. The detailed preparation process is as follows: (1) Weigh 2g of polyvinyl alcohol and add it to 92g of deionized water. Heat and stir at 90°C until completely transparent to obtain a PVA solution. The molecular weight (Mw) of polyvinyl alcohol used in this example is 200000g / mol. The stirring rate is 50r / min and the stirring time is 90min. After dissolution, let it stand for more than 8 hours to remove bubbles. (2) Weigh 3g of cellulose and 3g of amorphous silica and add them to 94g of the above PVA solution to fully disperse and form a uniform suspension PVA / cellulose / silica system; (3) Weigh 1.0g of chitosan and add it to 59g of an aqueous solution containing 2 wt% acetic acid, and stir until completely dissolved; (4) After thoroughly mixing the chitosan solution with the PVA / cellulose / silica system, add 2.5g of glutaraldehyde as a crosslinking agent and stir at room temperature for 30min to form a composite hydrogel; (5) Pour the obtained hydrogel into a mold and freeze it at -60℃ for 30 min; (6) After freezing, the sample was placed in a freeze dryer and freeze-dried for 72 hours under a vacuum of 1 Pa to obtain a composite aerogel material with an oriented layered pore structure.

[0059] The following describes some application scenarios and performance characteristics of the composite aerogel material of this invention: Application Scenario 1: Integrated building exterior wall insulation and fireproofing materials The cellulose / PVA / chitosan-silica composite aerogel material prepared in Example 1 of this invention was processed into the core material of an insulation board and then composited with an inorganic decorative panel to form an integrated thermal insulation and fireproof building exterior wall panel. Testing showed that the density of the composite aerogel material prepared in Example 1 was only 0.078 g / cm³. 3 Its thermal conductivity is significantly lower than that of traditional inorganic insulation boards and foamed concrete materials, thus significantly reducing the self-weight of the building envelope. Simultaneously, the material forms a highly ordered, oriented layered porous structure, resulting in a thermal conductivity as low as 0.0236 W·m. -1 ·K -1 0.06~0.10 W·m -1 ·K -1 Significantly lower than traditional rock wool boards (approximately 0.035~0.045 or 0.06~0.10 W·m). -1 ·K -1） And foamed concrete (approximately 0.08~0.15 W·m⁻²) -1 ·K -1This aerogel exhibits excellent building insulation and energy-saving effects. Furthermore, the aerogel incorporates a cellulose-reinforced skeleton, a chitosan flame-retardant network, and amorphous silica refractory components, effectively improving the material's high-temperature stability and fire safety. When the exterior wall is subjected to flame impact, the silica forms a stable inorganic barrier layer, and the chitosan, when heated, forms a carbon layer structure, jointly inhibiting flame spread and heat transfer.

[0060] Application Scenario 2: New energy vehicle power battery heat insulation buffer layer The composite aerogel material prepared in Example 2 of this invention was fabricated into flexible thermal insulation pads and installed between individual power battery cells and inside battery modules to suppress the propagation of thermal runaway. The thermal conductivity of the aerogel prepared in Example 2 is only 0.0238 W·m. -1 ·K -1 This can effectively reduce the heat transfer rate between individual battery cells. When thermal runaway occurs in a local cell, it can significantly delay the spread of heat to surrounding cells, providing the battery management system with a longer warning and response time.

[0061] Meanwhile, because the material density is only 0.087 g / cm³ 3 While ensuring excellent thermal insulation performance, it adds almost no weight to the power battery system, which is beneficial to improving the driving range of new energy vehicles. The material has significant mechanical anisotropy characteristics. Along the directional freezing direction, its compressive strength at 5% compressive strain reaches 220 kPa, which can withstand the mechanical loads during battery module assembly; while perpendicular to the freezing direction, the material has excellent flexibility and compression recovery ability, maintaining structural integrity after 100 cycles of compression at 40% compressive strain, with a compressive strength remaining above 50 kPa, and can adapt to vehicle vibration and impact conditions for a long time.

[0062] Application Scenario 3: Flexible thermal insulation and protection materials Utilizing the excellent flexibility and cyclic compression properties of the composite aerogel material of Example 3 of this invention, it can be further processed into flexible thermal insulation pads, thermal insulation linings, and protective packaging materials. The material can withstand 40% compressive strain in the radial direction and complete 100 cycles of compression without structural failure, demonstrating its excellent fatigue resistance and deformation recovery ability. Simultaneously, its thermal conductivity is only 0.0239 W·m. -1 ·K -1 It can effectively block the transfer of external heat.

[0063] Therefore, the composite aerogel material prepared in Example 3 can be applied to fields such as heat-insulating packaging for electronic devices, heat-insulating pads for high-temperature equipment, cushioning materials for transporting precision instruments, and flexible thermal management systems.

[0064] Application Scenario 4: Lightweight thermal insulation materials for aerospace and drones The composite aerogel material prepared in Example 4 of this invention possesses both ultra-low density and excellent thermal insulation properties, making it suitable as a lightweight thermal insulation material for aerospace vehicles, drones, and high-end equipment. The material density is only 0.093 g / cm³. 3 Thermal conductivity as low as 0.0241 W·m -1 ·K -1 It can achieve highly efficient thermal protection with extremely low weight gain. At the same time, the cellulose-reinforced framework and chitosan / PVA crosslinked network endow the material with good structural integrity and durability, enabling it to adapt to complex vibration environments.

[0065] The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included within the protection scope of the present invention. The above content is a further detailed description of the present invention in conjunction with specific preferred embodiments, and it should not be considered that the specific implementation of the present invention is limited to these descriptions. For those skilled in the art, several simple deductions or substitutions can be made without departing from the concept of the present invention, and all such deductions or substitutions should be considered to fall within the protection scope of the present invention.

Claims

1. A composite aerogel material based on the resource utilization of rice husk solid waste, characterized in that, The composite aerogel material is prepared from chitosan, polyvinyl alcohol, cellulose and silica. The cellulose and silica are both derived from rice husks. The cellulose is long fiber and / or sheet-like unhydrolyzed fiber. The silica is amorphous silica. The composite aerogel material is an ultralight and low-density material.

2. The composite aerogel material based on rice husk solid waste resource utilization according to claim 1, characterized in that, The composite aerogel material has a three-dimensional porous network structure, which is a layered pore structure with regular orientation, and the surface of the layered pore structure is uniformly loaded with the amorphous silica.

3. The composite aerogel material based on rice husk solid waste resource utilization according to claim 1, characterized in that, The length of the long fiber is 100~300µm.

4. A method for preparing a composite aerogel material based on rice husk solid waste resource utilization as described in any one of claims 1 to 3, characterized in that, The method includes the following steps: Step 1: Add polyvinyl alcohol to deionized water, heat and stir until completely transparent to obtain a PVA solution with a mass fraction of 0.5~2wt%; Step 2: Add cellulose and amorphous silica to the PVA solution and disperse them thoroughly to form a uniform suspension system, thus obtaining the PVA / cellulose / silica system; the mass ratio of cellulose, amorphous silica and PVA solution is 3:3:

94. Step 3: Add chitosan to an aqueous solution containing 0.5-2 wt% acetic acid and stir until completely dissolved to obtain a chitosan solution with a mass fraction of 1-2 wt%. Step 4: After thoroughly mixing the chitosan solution with the PVA / cellulose / silica system, glutaraldehyde is added as a crosslinking agent, and the mixture is stirred at room temperature to form a composite hydrogel; the mass ratio of the chitosan solution to the PVA / cellulose / silica system is 60:

100. Step 5: Pour the composite hydrogel into a mold and place it under -40℃ to -60℃ for directional freezing; Step six: After freezing, the sample is placed in a freeze dryer and freeze-dried under vacuum conditions to obtain a composite aerogel material with a directional layered pore structure, that is, an anisotropic cellulose / polyvinyl alcohol / chitosan-silica composite aerogel material is prepared.

5. The method for preparing composite aerogel material based on rice husk solid waste resource utilization according to claim 4, characterized in that, In step one, the molecular weight (Mw) of the polyvinyl alcohol is 10,000-205,000 g / mol.

6. The method for preparing composite aerogel material based on rice husk solid waste resource utilization according to claim 4, characterized in that, In step one, the dissolution conditions are: heating temperature of 60~90℃, stirring rate of 50~300r / min, stirring time of 30~90min, and after dissolution, the mixture must be allowed to stand for degassing for more than 8 hours.

7. The method for preparing composite aerogel material based on rice husk solid waste resource utilization according to claim 4, characterized in that, In step four, the amount of glutaraldehyde added accounts for 50% to 100 wt% of the total mass of polyvinyl alcohol and chitosan, and the crosslinking time is 10 to 90 min.

8. The method for preparing composite aerogel material based on rice husk solid waste resource utilization according to claim 4, characterized in that, In step five, the directional freezing temperature is -50℃ and the directional freezing time is 30 minutes.

9. The method for preparing composite aerogel material based on rice husk solid waste resource utilization according to claim 4, characterized in that, In step six, the freeze-drying vacuum degree is 1 Pa, and the freeze-drying time is 24~72 h.

10. The method for preparing composite aerogel material based on rice husk solid waste resource utilization according to claim 4, characterized in that, The extraction method of cellulose and amorphous silica includes: S1. Wash and dry the rice husks, then grind them into 100-mesh powder; S2. Add rice husk powder to 0.5~3mol / L hydrochloric acid solution and mix at a solid-liquid mass ratio of 1:10~1:

30. Stir magnetically at room temperature for 0.5~4h, then filter and wash with deionized water until neutral. S3. Add the acid-washed rice husks to a 0.5-5 mol / L sodium hydroxide solution, stir at a solid-liquid mass ratio of 1:10-1:30 in a 60℃ water bath for 1-6 hours, and filter to obtain a silica-containing filtrate and crude cellulose, respectively. S4. After evaporating and drying the silicon-containing filtrate, place it in a tube furnace and carbonize it at 600~700℃ for 0.5~1h to obtain rice husk ash; S5. Add the obtained rice husk ash to a 0.5~5 mol / L sodium hydroxide solution, and stir for 1~6 h in a water bath at 60~95℃ at a solid-liquid mass ratio of 1:20 to obtain a sodium silicate solution. S6. Adjust the pH of the sodium silicate solution to 7-9 by hydrochloric acid titration, let it stand for 10 min to form silica gel precipitate, filter it and dry it in a 40℃ drying oven for 24 h to obtain amorphous silica. S7. Add crude cellulose to a 1-5 wt% sodium chlorite solution, and adjust the pH of the system to 4-6 with hydrochloric acid. Stir at 40-80℃ for 2-8 hours at a solid-liquid mass ratio of 1:

20. Then wash repeatedly until the cellulose turns white to obtain purified cellulose.

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