Bamboo cellulose micro-nano fiber composite aerogel material as well as preparation method and application thereof

Abstract

The invention discloses a bamboo cellulose micro-nano fiber composite aerogel material and a preparation method and application thereof, and relates to the field of aerogel, the preparation method comprises the following steps: S1, crushing bamboo pulp to obtain bamboo pulp microfibers; s2, adding the bamboo pulp microfiber and bamboo cellulose nanofiber suspension into water, and stirring; s3, sequentially adding silicon dioxide, polysiloxane and boric acid into the dispersion liquid to obtain a premix; s4, adding a polyvinyl alcohol aqueous solution and a glutaraldehyde aqueous solution at room temperature to obtain a reactant; s5, pouring reactants into a mold, and freezing and forming to obtain ice gel; and S6, replacing the ice gel with ethanol, and drying at normal pressure to obtain the composite aerogel material. According to the method, cellulose does not need to be dissolved, cellulose microfibers serve as a firm framework, interpenetrating double networks are constructed through physical entanglement, physical / covalent cross-linking and ice crystal template constraint, multi-scale material interface assembly is achieved, and the composite material can be easily prepared under normal-pressure drying and is expected to serve as a sustainable substitute of plastic foam.

Description

Technical Field

[0001] This invention relates to the field of aerogel technology, and in particular to a bamboo cellulose micro / nano fiber composite aerogel material, its preparation method, and its application. Background Technology

[0002] With the increasing prominence of the global energy crisis and environmental problems, the development of high-performance, sustainable thermal insulation materials has become a key direction for alleviating the scarcity of non-renewable resources and reducing carbon emissions. Cellulose molecules are rich in hydroxyl groups, which can serve as modification sites to produce cellulose fibers. Furthermore, cellulose aerogels can be prepared through hydrogen bonding interactions or participation in cross-linking reactions. Traditional cellulose aerogel preparation involves the dissolution and regeneration of cellulose and the use of large amounts of solvents.

[0003] In recent years, cellulose nanofibers prepared by the TEMPO oxidation method have exhibited excellent water dispersion stability due to their negative charge. Cellulose nanofiber aerogels can be easily prepared by freeze-drying an aqueous suspension of cellulose nanofibers. However, the gel framework constructed from nanoscale pores has weak support capacity and is unable to withstand strong capillary stress, resulting in less than ideal mechanical properties for most cellulose nanofiber aerogels. Under normal pressure drying conditions, they suffer from severe pore collapse and poor structural stability. In contrast, cellulose microfibers can enhance the interaction between adjacent fibers and achieve self-assembly through physical entanglement between fibers, which is more conducive to strengthening structural integrity during the capillary-driven assembly process.

[0004] In recent years, the use of cellulose microfibers to construct cellulose aerogels / foams has been considered an effective solution for improving the robustness and structural stability of porous frameworks. For example, the literature (Small, 2024, 20, 2305857) reports a strategy for preparing all-cellulose aerogels composed of cellulose nanofibers, cellulose microfibers, and regenerated cellulose through partial dissolution combined with unidirectional freeze-drying. Cellulose nanofibers act as a binder, while directional freezing promotes the bridging and assembly of undissolved cellulose microfibers into rigid fulcrums, enhancing the mechanical properties of the aerogel. However, this method requires precise control of the degree of cellulose dissolution. Although directional freeze-drying shapes the gel framework through ice crystal confinement, it consumes liquid nitrogen, and the sublimation and removal of ice crystals rely on time-consuming and energy-intensive specialized drying equipment.

[0005] Chinese invention patent CN119955168A discloses a pulp foam cushioning material, which is prepared by mixing a nanocellulose / wax emulsion with a pulp fiber / flame retardant mixture, removing the liquid phase, and then drying. However, the interfacial bonding of the cellulose skeleton formed solely by physical entanglement is weak, resulting in insufficient mechanical properties of the foam. Furthermore, due to the inherent flammability of cellulose, the mechanical strength, thermal insulation, and flame retardant properties of cellulose aerogel still need further improvement to ensure long-term and stable performance under complex environments.

[0006] Therefore, how to efficiently utilize cellulose micro- and nano-fibers, develop lightweight and high-strength cellulose micro- and nano-fiber aerogels with high porosity and low shrinkage through atmospheric pressure drying, and improve their comprehensive performance is a key technical challenge for accelerating their application and promoting them as a sustainable thermal insulation material based on petroleum foam. Summary of the Invention

[0007] This invention overcomes the shortcomings of the prior art and provides a bamboo cellulose micro / nano fiber composite aerogel material, its preparation method, and its application. It does not require dissolving cellulose, and the preparation process is simple and efficient. With the strong hydrogen bond entanglement, physical / covalent cross-linking, and ice crystal template constraint between cellulose microfibers, the gel skeleton is successfully constructed into a robust and heat-insulating interpenetrating double network, realizing the interfacial assembly of multi-scale materials. The volume shrinkage rate is extremely low under normal pressure drying.

[0008] To achieve the above objectives, the technical solution adopted by the present invention is as follows: Firstly, the present invention provides a method for preparing bamboo cellulose micro / nano fiber composite aerogel material, comprising the following steps:

[0009] S1. Mechanically crush bamboo pulp, wash and dry it to obtain bamboo pulp microfiber;

[0010] S2. Add the suspension of bamboo pulp microfibers and bamboo cellulose nanofibers to water and stir to obtain a dispersion.

[0011] S3. Add hydrophilic silica aerogel powder, polysiloxane microemulsion and boric acid solution to the dispersion in sequence, stir and react to obtain a premix;

[0012] S4. Add polyvinyl alcohol aqueous solution and glutaraldehyde aqueous solution to the premix, stir and react at room temperature to obtain the reactant;

[0013] S5. Pour the reactants into a mold and freeze to obtain an ice gel;

[0014] S6. Displace the ice gel in anhydrous ethanol and dry it at 60-80 °C under normal pressure for 3-5 h to obtain the composite aerogel material.

[0015] In a preferred embodiment of the present invention, in step S1, the drying temperature is 100-110 °C and the drying time is 6-12 h.

[0016] In a preferred embodiment of the present invention, in step S2, the cellulose nanofibers are bamboo cellulose nanofibers prepared by the TEMPO / NaBr / NaClO oxidation system, with a carboxyl content of 1.2-1.8 mmol / g; the concentration of the bamboo cellulose nanofiber suspension is 2-3 wt%, the total amount of bamboo cellulose fibers in the dispersion is 2-4 wt%, and the amount of bamboo cellulose nanofibers used accounts for 20-30 wt% of the total cellulose fibers; the stirring speed is 8000-12000 rpm, and the stirring time is 20-40 min.

[0017] In a preferred embodiment of the present invention, in step S3, the amount of the hydrophilic silica aerogel powder is 2.5-6.5 wt% of the dispersion; the polysiloxane microemulsion is a polymethylhydrosiloxane microemulsion with a Si-H bond content of 1-1.5%, a solid content of 25-35%, a particle size D50 of 200-500 nm, and an amount of 2-3.5% of the dispersion; the concentration of the boric acid solution is 8-15 wt%, and the amount of boric acid solid is 0.8-1.8% of the mixed dispersion.

[0018] In a preferred embodiment of the present invention, in step S3, the temperature of the stirring reaction is 20-30 ℃, the rotation speed is 6000-10000 rpm, and the time is 30-60 min.

[0019] In a preferred embodiment of the present invention, in step S4, the concentration of the polyvinyl alcohol aqueous solution is 8-12 wt%, and the amount used accounts for 30-50% of the dry weight of cellulose; the concentration of the glutaraldehyde aqueous solution is 40-60 wt%, and the amount used accounts for 1-3% of the total mass of the dispersion; the stirring reaction temperature is 20-30 ℃, the stirring speed is 2000-4000 rpm, and the time is 0.5-2 h.

[0020] In a preferred embodiment of the present invention, in step S5, the temperature for freezing is -15 ℃ to -25 ℃, and the freezing time is 24-48 h.

[0021] In a preferred embodiment of the present invention, in step S6, the number of replacements is 2-4 times, each time for 8-14 hours.

[0022] Secondly, the present invention provides a bamboo cellulose micro / nano fiber composite aerogel material, which is prepared by any of the preparation methods described above.

[0023] Thirdly, the present invention provides an application of the aforementioned bamboo cellulose micro-nano fiber composite aerogel material in the field of high-temperature thermal protection.

[0024] This invention addresses the shortcomings of the prior art and has the following beneficial effects:

[0025] (1) This invention provides a bamboo cellulose micro / nano fiber composite aerogel material, its preparation method and application. It adopts a non-dissolved cellulose strategy to construct a stable gel network with microfibers as the skeleton, nanofibers as the reinforcing phase and inorganic fillers uniformly dispersed. The microfibers are physically entangled by strong hydrogen bonds to form macroscopic support. The nanofibers, with their high specific surface area and surface charge, can insert into the microfiber aggregates to weaken the hydrogen bond effect and improve the dispersion uniformity. The silica powder interacts with the hydroxyl groups of cellulose fibers through hydrogen bonds formed by the silanol groups on its surface, and is tightly embedded in the cellulose network. This can form a strong and tough three-dimensional network structure in which micro / nano multi-scale fibers and inorganic particles are interpenetrated, so that the gel skeleton has extremely high structural integrity and can effectively resist the damage caused by capillary forces during normal pressure drying. The resulting aerogel has extremely low volume shrinkage rate under normal pressure drying and can maintain high porosity and low density, while obtaining excellent mechanical strength, thereby solving the problem of the fragile skeleton of conventional cellulose aerogel and easy shrinkage and collapse during drying.

[0026] (2) In this invention, by introducing polysiloxane microemulsion and boric acid solution as functional ceramic precursors, cellulose is pyrolyzed at high temperature to generate carbon skeleton, while polysiloxane decomposes to generate active silicon species, and boric acid is dehydrated to generate borosilicate glass phase. Under high temperature drive, it migrates to carbon layer and undergoes a series of reactions such as carbothermic reduction with carbon and silicon dioxide to generate high-hardness ceramic phases such as silicon carbide and borosilicate glass phase in situ, so that it can effectively fill and embed in the porous carbon skeleton, transforming the originally loose and fragile carbon layer into a continuous, dense and high-strength ceramic carbon composite barrier layer. Compared with the prior art, where cellulose aerogel only forms a loose carbon layer similar to charcoal after heating, the aerogel material of this invention can effectively resist thermal stress and airflow erosion, avoid carbon layer peeling, thereby extending the effective protection time of the material for the backing structure and meeting the needs of the high-temperature thermal protection field.

[0027] (3) In this invention, a high proportion of bamboo cellulose nanofibers are used to construct an initial micro-nano fiber network, which is then synergistically crosslinked with polysiloxane microemulsion and boric acid solution. The bamboo cellulose nanofibers are negatively charged, which can weaken the hydrogen bond aggregation tendency between microfibers, improve dispersibility, and form a denser initial network, providing more carbon sources and reaction interfaces for high-temperature reactions. The active groups of polysiloxane interact with the hydroxyl groups of cellulose and polyvinyl alcohol, which can enhance the interfacial bonding, so that the initial aerogel skeleton has better structural stability and mechanical properties. As a result, the skeleton can withstand higher compressive stress, resulting in a low volume shrinkage rate under normal pressure drying and a more complete ceramicization reaction at high temperature, thereby significantly improving the thermal shock cycle resistance.

[0028] (4) In this invention, a non-dissolved cellulose strategy and atmospheric pressure drying process are adopted. Aqueous microemulsion and aqueous solution system are introduced. Bamboo pulp microfibers and nanofibers are dispersed in the aqueous phase by high-speed shearing, which can avoid the use of organic solvents. The ice crystal template promotes the formation of the skeleton. After ethanol replacement, atmospheric pressure drying can obtain aerogel. The preparation process is simple and efficient, without special equipment, with low energy consumption and easier operation. In this way, the material can be produced on a large scale. The material is degradable and meets the requirements of sustainable development, thus providing a green alternative for petroleum-based foam materials. Attached Figure Description

[0029] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments recorded in the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0030] Figure 1 This is a schematic diagram, a physical sample image, and a large-scale production sample image of the bamboo cellulose micro-nano fiber composite aerogel material in the complex "mouse" shape standing on a flower, as shown in Embodiment 1 of the present invention.

[0031] Figure 2 These are the compressive stress-strain curves of Embodiment 1, Comparative Example 1, and Comparative Example 2 of the present invention;

[0032] Figure 3 The bamboo cellulose micro-nano fiber composite aerogel of Example 1 of the present invention, together with commercially available EPS foam, EPE foam and silica aerogel felt, are top infrared thermal images taken when they are placed on a 100 ℃ hot table for 5 min.

[0033] Figure 4 This is a diagram showing the refractory state of the bamboo cellulose micro-nano fiber composite aerogel of Example 1 of the present invention under the action of butane flame at different times. Detailed Implementation

[0034] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0035] Many specific details are set forth in the following description in order to provide a full understanding of the invention. However, the invention may also be practiced in other ways different from those described herein. Therefore, the scope of protection of the invention is not limited to the specific embodiments disclosed below.

[0036] Application Overview:

[0037] To improve the flame retardant and thermal insulation properties of cellulose aerogels, existing technologies typically introduce inorganic functional fillers, such as silica (SiO2) aerogel powder, into the system. Silica aerogel itself has extremely low thermal conductivity and good thermal stability; its addition can improve the thermal insulation effect of the composite material and delay the combustion process to a certain extent.

[0038] The applicant's in-depth research revealed that when composite materials obtained by the aforementioned traditional methods are subjected to sudden high-intensity thermal shocks, such as direct burning by flames exceeding 800 °C, the surface cellulose of the material rapidly pyrolyzes and carbonizes upon heating. The resulting carbon layer has a loose structure, high porosity, and low inherent strength, making it prone to microcracks under thermal stress. Simultaneously, the carbonized layer is mainly bonded to the incompletely pyrolyzed gel matrix inside through physical means, resulting in weak interfacial bonding. Under the influence of flame erosion, airflow disturbance, or the material's own thermal expansion stress, it is extremely easy to peel off. Once the carbon layer is damaged or detached, the thermal attack front will rapidly advance into the material's interior, causing its thermal barrier effect to be extremely short-lived and unable to provide sufficient reliable protection for the backing structure for a sufficiently long time.

[0039] To address the aforementioned problems, this invention proposes a bamboo cellulose micro / nanofiber composite aerogel material, its preparation method, and its applications. By introducing polysiloxane microemulsion and boric acid solution as functional ceramic precursors, and synergistically combining a polyvinyl alcohol / glutaraldehyde crosslinking system with low-temperature freeze-forming and atmospheric-pressure drying processes, a composite aerogel material with an interpenetrating network structure is constructed. This material can generate a continuous and dense ceramic-carbon composite barrier layer through in-situ reaction at high temperatures, effectively solving the problems of loose carbonized layers, easy peeling, and short-lived thermal barrier properties. This significantly improves the material's high-temperature protection performance, peeling resistance, and thermal shock stability, thus providing a feasible solution for the large-scale application of cellulose aerogels in the field of high-temperature thermal protection.

[0040] It should be noted that the raw materials, equipment and reagents used in this invention can all be purchased from the market or obtained through existing preparation methods.

[0041] like Figure 1 As shown, a method for preparing a bamboo cellulose micro / nano fiber composite aerogel material includes the following steps:

[0042] S1. Mechanically crush bamboo pulp, wash and dry it to obtain bamboo pulp microfiber;

[0043] S2. Add the suspension of bamboo pulp microfibers and bamboo cellulose nanofibers to water and stir to obtain a dispersion.

[0044] S3. Add hydrophilic silica (SiO2) aerogel powder, polysiloxane microemulsion and boric acid solution to the dispersion in sequence, stir and react to obtain a premix;

[0045] S4. Add polyvinyl alcohol (PVA) aqueous solution and glutaraldehyde aqueous solution to the premix, stir and react at room temperature to obtain the reactants;

[0046] S5. Pour the reactants into a mold and freeze to obtain an ice gel;

[0047] S6. Displace the ice gel in anhydrous ethanol and dry it at 60-80 °C under normal pressure for 3-5 h to obtain the composite aerogel material.

[0048] In some specific embodiments, in step S1, the drying temperature is 100-110 °C and the drying time is 6-12 h.

[0049] In some specific embodiments, in step S2, the cellulose nanofibers are bamboo cellulose nanofibers prepared by the TEMPO / NaBr / NaClO oxidation system, with a carboxyl content of 1.2-1.8 mmol / g; the concentration of the bamboo cellulose nanofiber suspension is 2-3 wt%, the total amount of bamboo cellulose fibers in the dispersion is 2-4 wt%, and the amount of bamboo cellulose nanofibers used accounts for 20-30 wt% of the total cellulose fibers; the stirring speed is 8000-12000 rpm, and the stirring time is 20-40 min.

[0050] In some specific embodiments, in step S3, the amount of the hydrophilic silica aerogel powder is 2.5-6.5 wt% of the dispersion; the polysiloxane microemulsion is a polymethylhydrosiloxane (PMHS) microemulsion with a Si-H bond content of 1-1.5%, a solid content of 25-35%, a particle size D50 of 200-500 nm, and an amount of 2-3.5% of the dispersion; the concentration of the boric acid solution is 8-15 wt%, and the amount of boric acid solids is 0.8-1.8% of the mixed dispersion.

[0051] In some specific embodiments, in step S3, the temperature of the stirring reaction is 20-30 ℃, the rotation speed is 6000-10000 rpm, and the time is 30-60 min.

[0052] In some specific embodiments, in step S4, the concentration of the polyvinyl alcohol aqueous solution is 8-12 wt%, and the amount used accounts for 30-50% of the dry weight of cellulose; the concentration of the glutaraldehyde aqueous solution is 40-60 wt%, and the amount used accounts for 1-3% of the total mass of the dispersion; the stirring reaction temperature is 20-30 ℃, the stirring speed is 2000-4000 rpm, and the time is 0.5-2 h.

[0053] In some specific embodiments, in step S5, the temperature for freeze forming is -15 ℃ to -25 ℃, and the freezing time is 24-48 h.

[0054] In some specific implementations, in step S6, the number of replacements is 2-4 times, each time for 8-14 hours.

[0055] Secondly, the present invention provides a bamboo cellulose micro / nano fiber composite aerogel material, which is prepared by any of the preparation methods described above.

[0056] Thirdly, the present invention provides an application of the aforementioned bamboo cellulose micro-nano fiber composite aerogel material in the field of high-temperature thermal protection.

[0057] To further simplify and make the present invention achieve its objectives and effects, the present invention will be further illustrated in conjunction with the following specific embodiments and comparative examples, but the present invention is not limited to the scope of the embodiments described herein.

[0058] It should be noted that in the examples and comparative examples, the bamboo cellulose nanofiber suspension was prepared using the TEMPO oxidation system, which included the following steps: 10g of bamboo pulp was taken and added to an aqueous solution (1000mL) containing 0.16g of TEMPO and 1.0g of NaBr (sodium bromide). After stirring evenly, 12 wt% NaClO solution was slowly added dropwise until the pH of the system stabilized at 10.5. The reaction was carried out at room temperature for 2 h. After the reaction was completed, the pH was adjusted to 7 with hydrochloric acid. The suspension was centrifuged at 12000 rpm for 15 min, washed with water 3 times, and ultrasonically dispersed at 800 W for 30 min to obtain a bamboo cellulose nanofiber suspension with a carboxyl content of 1.5 mmol / g.

[0059] PMHS microemulsion: PMHS was mixed with Tween 80 (5% by mass of PMHS) and water, and sheared at 12,000 rpm for 20 min to prepare a PMHS microemulsion with a solid content of 30% and a particle size D50 of 350 nm.

[0060] Boric acid solution: Dissolve analytical grade boric acid in water to prepare a clear solution with a concentration of 8-15 wt%.

[0061] The raw materials used in the preparation are as follows: Hydrophilic SiO2 aerogel powder: thermal conductivity 0.014-0.016 W(m·K), particle size 200 mesh, purchased from Langmiao Environmental Protection Technology; PMHS: CAS No. 63148-57-2, purity ≥99%, purchased from Jinan Yuanyang Chemical; Boric acid: CAS No. 10043-35-3, purity ≥99%, purchased from Jinan Jingyu Chemical; Glutaraldehyde: purchased from Jinan Jingyu Chemical; TEMPO: molecular weight 156.25, purity ≥99%, purchased from Zhongshan Dixing Chemical; NaBr: molecular weight 102.894, density: 3.203 g / cm³. 3 Purchased from Jinan Kaichuang Chemical; PVA: Model 2099L, purchased from Jinan Qihang Chemical.

[0062] Example 1:

[0063] A method for preparing a bamboo cellulose micro / nano fiber composite aerogel material includes the following steps:

[0064] S1. The bamboo pulp is mechanically crushed, passed through a 100-mesh sieve, washed with water three times, and dried at 105 ℃ for 8 h to obtain bamboo pulp microfibers with an average length of 100-200 μm and an average diameter of 10-20 μm.

[0065] S2. Add a suspension of bamboo pulp microfibers and bamboo cellulose nanofibers with a concentration of 2.5 wt% to water, and stir continuously at 10,000 rpm for 30 min to obtain a dispersion; wherein the total amount of bamboo cellulose fibers in the dispersion is 3 wt%, and the amount of bamboo cellulose nanofibers accounts for 24 wt% of the total amount of cellulose fibers.

[0066] S3. Hydrophilic SiO2 aerogel powder, PMHS microemulsion, and boric acid solution were added sequentially to the dispersion. The system temperature was maintained at 25 ℃, and the mixture was stirred at 8000 rpm for 60 min to obtain a premix. The amount of hydrophilic SiO2 aerogel powder was 4 wt% of the dispersion mass; the Si-H bond content of the PMHS microemulsion was 1.2%, and the amount used was 2.8% of the dispersion mass; the concentration of the boric acid solution was 10 wt%, and the amount used, based on boric acid solids, was 1.3% of the mixed dispersion mass.

[0067] S4. Add a 10 wt% PVA aqueous solution and a 50 wt% glutaraldehyde aqueous solution to the premix, and stir at 3000 rpm for 1.5 h at 25 ℃ to obtain the reactant; wherein the amount of PVA aqueous solution accounts for 40% of the dry weight of cellulose, and the amount of glutaraldehyde aqueous solution accounts for 2% of the total mass of the dispersion.

[0068] S5. Pour the reactants into a mold of a predetermined shape and freeze at -20 °C for 36 h to obtain an ice gel;

[0069] S6. Remove the ice gel from the mold and immerse it in sufficient anhydrous ethanol. Replace the solvent three times, each time for 12 hours. Dry the replaced gel at 70 °C under normal pressure for 4 hours to obtain the composite aerogel material.

[0070] Comparative Example 1:

[0071] This comparative example differs from Example 1 in that it uses a traditional cellulose aerogel employing a cellulose dissolution strategy; a method for preparing a bamboo cellulose aerogel material includes the following steps:

[0072] S1. The bamboo pulp is mechanically crushed, passed through a 100-mesh sieve, washed with water three times, and dried at 105 ℃ for 8 h to obtain bamboo pulp microfibers with an average length of 100-200 μm and an average diameter of 10-20 μm.

[0073] S2. Add 5 g of bamboo pulp microfiber to 100 g of NaOH / urea / water solution with a mass ratio of 7:12:81, ensuring that the concentration of cellulose in the solution is 3 wt%, to obtain a dispersion.

[0074] S3. After stirring the dispersion for 0.5 h, freeze at -10 ℃. After thawing at room temperature, add 5 mL of epichlorohydrin to undergo a cross-linking reaction for 0.5 h. Pour into a mold and bake in a 50 ℃ oven for 3 h for sol-gel transformation and aging. After cooling to room temperature, immerse the resulting gel in water until the pH reaches 7.

[0075] S4. The obtained hydrogel was pre-frozen at -10 ℃ and then frozen at -20 ℃ for 36 h to obtain bamboo cellulose aerogel.

[0076] Comparative Example 2:

[0077] This comparative example is basically the same as Example 1, except that it does not contain a ceramic precursor, i.e., it does not contain PMHS microemulsion and boric acid solution; the specific steps of S3 are as follows: hydrophilic SiO2 aerogel powder is added to the dispersion in sequence, the system temperature is maintained at 25 ℃, and the mixture is stirred at 8000 rpm for 60 min to obtain a premix; wherein, the amount of hydrophilic SiO2 aerogel powder is 4 wt% of the mass of the dispersion.

[0078] To verify the successful acquisition of the bamboo cellulose micro / nano fiber composite aerogel material in Example 1 Figure 1 The diagram shows the lightweight properties of the bamboo cellulose micro-nano fiber composite aerogel material in the complex "mouse" shape standing on a flower, as shown in Embodiment 1 of the present invention, along with a physical sample image and a sample image of large-scale production. Figure 2The diagram shows the compressive stress-strain curves of Embodiment 1, Comparative Example 1, and Comparative Example 2 of the present invention. Figure 3 The image shows the top infrared thermal images of the bamboo cellulose micro-nano fiber composite aerogel (Example 1 of the present invention) and commercially available EPS foam, EPE foam and silica aerogel felt when placed on a 100 ℃ hot table for 5 min. Figure 4 The image shows the refractory state of the bamboo cellulose micro / nano fiber composite aerogel of Example 1 of the present invention at different times under the action of butane flame.

[0079] like Figure 1 As shown, the bamboo cellulose micro / nano fiber composite aerogel material prepared in Example 1 can easily stand on flowers, fully demonstrating its lightweight properties. At the same time, through a controllable process route of synergistic assembly between composite materials, ice crystal template-induced molding, and atmospheric pressure drying, it can be designed into a complex shape resembling a "mouse," indicating that the composite aerogel has excellent structure retention ability under atmospheric pressure drying. This process can also achieve the scale-up preparation of large-size aerogels while maintaining the uniformity of material structure and performance, indicating that this process and the prepared aerogel material with bamboo microfiber as the gel skeleton have the potential for large-scale application and production.

[0080] like Figure 2 As shown, the compressive stress-strain curves of the bamboo cellulose micro / nanofiber composite aerogel of Example 1, the bamboo cellulose aerogel of Comparative Example 1, and the bamboo cellulose micro / nanofiber aerogel of Comparative Example 2 were compared. It was found that the aerogel in Comparative Example 1, constructed solely of cellulose, had a compressive strength of 300 kPa at 80% strain. The aerogel in Comparative Example 2, constructed from micro / nanocellulose fibers, had a compressive strength increased to 510 kPa at 80% strain. The aerogel in Example 1, constructed from both micro / nanocellulose fibers and the composite material, had a compressive strength increased to 2.18 MPa at 80% strain. This indicates that bamboo cellulose nanofibers, as an additive, form abundant hydrogen bonds with the microfibers, bridging adjacent fibers and enhancing the inter-fiber bonding strength, thereby improving the mechanical properties of the aerogel. Simultaneously, during the preparation process, the excessively strong hydrogen bond interactions between bamboo pulp microfibers resulted in poor dispersion of the bamboo pulp microfibers under high-speed shear in water. When negatively charged bamboo cellulose nanofibers were introduced, their passage through the flocculents effectively weakened the tendency of hydrogen bond aggregation between cellulose microfibers, thus ensuring the dispersion stability of the mixed dispersion. Silica aerogel powder further enhances the rigidity and network density of the gel skeleton through hydrogen bonding interactions with micro and nanofibers, thereby significantly improving the compressive strength of bamboo cellulose micro and nanofiber composite aerogel materials.

[0081] like Figure 3The thermal insulation performance of the bamboo cellulose micro / nanofiber composite aerogel of Example 1, compared with commercially available EPS foam, EPE foam, and silica composite aerogel felt, was tested on a 100°C hot table. The results showed that the surface temperature of the bamboo cellulose micro / nanofiber composite aerogel of Example 1 was only 31.2°C, lower than that of EPS foam and EPE foam. This is because the large-pore structure of commercial plastic foam facilitates gas convection and solid-phase conduction, thereby accelerating heat transfer. Furthermore, the bamboo cellulose micro / nanofiber composite aerogel of the same size is lighter than silica composite aerogel felt, yet still possesses considerable thermal insulation performance. Moreover, commercially available foams soften at 200-300°C, making it difficult to maintain their thermal insulation effect above their melting point temperature.

[0082] In summary, the aerogel material of Embodiment 1 of the present invention not only has excellent thermal insulation capabilities, but also is not derived from petroleum-based raw materials, and compared with commercial foam, it also helps to alleviate environmental pressure.

[0083] To further illustrate the flame retardancy of the bamboo cellulose micro / nano fiber composite aerogel in Example 1 under extreme conditions, such as... Figure 4 As shown, a fire resistance assessment device was assembled, with an infrared thermal imager used to monitor the temperature of the aerogel's back side when not in contact with the flame. After continuous contact with a butane torch flame, a black carbonized layer and a white silica aerogel insulation layer appeared on the aerogel surface to block heat, resulting in an edge temperature of only 37.5°C on the back side under intense flame impact (~1300°C). Therefore, the bamboo cellulose micro / nano fiber composite aerogel in Example 1 exhibits excellent fire resistance and high-temperature insulation properties.

[0084] To further illustrate the present invention, preferred embodiment 1 is used as the basis for further embodiments and comparative examples.

[0085] Example 2:

[0086] This embodiment is basically the same as Embodiment 1, except that the Si-H bond content in the PMHS microemulsion is different. Specifically, the Si-H bond content of the PMHS microemulsion is 1%.

[0087] Example 3:

[0088] This embodiment is basically the same as Embodiment 1, except that the Si-H bond content in the PMHS microemulsion is different. Specifically, the Si-H bond content of the PMHS microemulsion is 1.5%.

[0089] Example 4:

[0090] This embodiment is basically the same as Embodiment 1, except that the amount of boric acid solution used is different. Specifically, the amount of boric acid solution used is 0.8% of the mass of the mixed dispersion, based on boric acid solids.

[0091] Example 5:

[0092] This embodiment is basically the same as Embodiment 1, except that the amount of boric acid solution used is different. Specifically, the amount of boric acid solution used is 1.8% of the mass of the mixed dispersion, based on boric acid solids.

[0093] Comparative Example 3:

[0094] This comparative example is basically the same as Example 1, except that hydrophilic SiO2 aerogel powder was not added. The specific steps in S3 are as follows: PMHS microemulsion and boric acid solution are added to the dispersion in sequence, the system temperature is maintained at 25 °C, and the mixture is stirred at 8000 rpm for 60 min to obtain a premix. The Si-H bond content of the PMHS microemulsion is 1.2%, and the amount used is 2.8% of the mass of the dispersion. The concentration of the boric acid solution is 10 wt%, and the amount used is 1.3% of the mass of the mixed dispersion based on boric acid solids.

[0095] Comparative Example 4:

[0096] This comparative example is basically the same as Example 1, except that: the ceramic precursor contains only PMHS microemulsion, and step S3 is as follows: hydrophilic SiO2 aerogel powder and PMHS microemulsion are added sequentially to the dispersion, the system temperature is maintained at 25 ℃, and the mixture is stirred at 8000 rpm for 60 min to obtain a premix; wherein, the amount of hydrophilic SiO2 aerogel powder is 4 wt% of the mass of the dispersion; the Si-H bond content of the PMHS microemulsion is 1.2%, and the amount is 2.8% of the mass of the dispersion.

[0097] Comparative Example 5:

[0098] This comparative example is basically the same as Example 1, except that the Si-H bond content in the PMHS microemulsion is different. Specifically, the Si-H bond content of the PMHS microemulsion is 0.8%.

[0099] Comparative Example 6:

[0100] This comparative example is basically the same as Example 1, except that the Si-H bond content in the PMHS microemulsion is different. Specifically, the Si-H bond content of the PMHS microemulsion is 1.7%.

[0101] Comparative Example 7:

[0102] This comparative example is basically the same as Example 1, except that: the ceramic precursor contains only boric acid solution, and step S3 is as follows: hydrophilic SiO2 aerogel powder and boric acid solution are added to the dispersion in sequence, the system temperature is maintained at 25°C, and the mixture is stirred at 8000 rpm for 60 min to obtain a premix; wherein, the amount of hydrophilic SiO2 aerogel powder is 4 wt% of the mass of the dispersion; the concentration of boric acid solution is 10 wt%, and the amount of boric acid solid is 1.3% of the mass of the mixed dispersion.

[0103] Comparative Example 8:

[0104] This comparative example is basically the same as Example 1, except that the amount of boric acid solution used is different. Specifically, the amount of boric acid solution used is 0.5% of the mass of the mixed dispersion, based on boric acid solids.

[0105] Comparative Example 9:

[0106] This comparative example is basically the same as Example 1, except that the amount of boric acid solution used is different. Specifically, the amount of boric acid solution used is 2% of the mass of the mixed dispersion, based on boric acid solids.

[0107] Comparative Example 10:

[0108] This comparative example is basically the same as Example 1, except that the premix was not chemically cross-linked, specifically, step S4 was omitted.

[0109] Performance testing: The volume shrinkage, compressive strength, Young's modulus and thermal conductivity of the aerogel materials prepared in Examples 1-5 and Comparative Examples 1-10 were statistically calculated, and the results are shown in Table 1; the back-temperature radiative heat, residual carbon content and thermal shock resistance were statistically calculated, and the results are shown in Table 2.

[0110] Volume shrinkage rate: Take the mold used to prepare the ice gel, and use vernier calipers to measure the length, width and height inside the mold to calculate the initial volume V0; take out the aerogel sample, and use vernier calipers to measure its actual length, width and height to calculate the volume V1 after drying. The volume shrinkage rate is (V0-V1) / V0×100%. Each sample is measured 3 times and the average value is taken.

[0111] Compressive strength and Young's modulus: The sample was cut into a rectangular specimen of 10mm×10mm×20mm and placed between the upper and lower plates of the universal testing machine. The compression rate was set to 1 mm / min and the compression was stopped when the strain reached 80%. The stress-strain curve was recorded. The compressive strength is the stress value corresponding to 80% strain in the curve, and the Young's modulus is the slope of the initial linear segment of the curve (strain 0-5%).

[0112] Thermal conductivity: The thermal conductivity meter of the heat flow method was used. The sample was processed into a thin film of 20mm×20mm×10mm and placed between a cold plate and a hot plate. The temperature of the cold plate was set to 25 ℃ and the temperature of the hot plate was set to 50 ℃. After the readings stabilized, the thermal conductivity value was recorded. Each sample was tested 3 times and the average value was taken.

[0113] Back-temperature radiant heating: A 20 mm thick sample was prepared, fixed to a high-temperature resistant support, with a K-type thermocouple attached to the center of the back side. A butane torch was used, with a flame temperature of approximately 1300 ℃ and a heat flux density of approximately 100 kW / m³. 2 The flame tip was placed 5 cm away from the sample and the front center was vertically impacted. The temperature on the back side was monitored in real time, and the time it took to rise from room temperature to 200 °C was recorded.

[0114] Carbon residue rate: Take about 10 mg of dry sample and put it into a muffle furnace. Heat it to 800 ℃ at 10 ℃ / min in air atmosphere, keep it at the temperature for 2 h and then cool it. Weigh the mass of the residual solid. The carbon residue rate is the ratio of the residual mass to the initial mass × 100%. Each sample is tested 3 times and the average value is taken.

[0115] Thermal shock resistance cycling: First, measure the initial compressive strength and thermal conductivity of the sample; place the sample in a muffle furnace, rapidly heat to 1000 ℃ and hold for 5 min, remove and air cool to 25 ℃ to complete one cycle, repeat 10 times; test the compressive strength and thermal conductivity again, the strength retention rate is the ratio of the initial compressive strength after cycling to the initial compressive strength × 100%, the thermal conductivity increment is the ratio of (after cycling - initial) to the initial thermal conductivity × 100%, and each sample is tested 3 times and the average value is taken.

[0116] Table 1:

[0117]

[0118]

[0119] Table 2:

[0120]

[0121]

[0122] As shown in Tables 1 and 2:

[0123] A comparison between Example 1 and Comparative Example 1 reveals that: Comparative Example 1 employs a traditional cellulose dissolution-regeneration strategy. During this process, cellulose molecular chains undergo depolymerization and rearrangement in a strong alkali / urea system. Although a gel network can be formed, the natural skeletal structure of the microfibers is destroyed, losing the physical entanglement and support provided by the micron-scale fibers. The regenerated cellulose network has a fragile pore structure and is prone to severe shrinkage during drying due to capillary forces, with a volume shrinkage rate as high as 25.88% and a compressive strength of only 0.3 MPa. This is because the regenerated cellulose network lacks the physical entanglement and ceramic phase reinforcement of micro / nano fibers; its thermal conductivity increases to 0.055 W·m. -1 ·K -1 This is due to enhanced gas convection caused by uneven pore structure. At high temperatures, the regenerated carbon layer lacks ceramic phase filling, making it easy to peel off. It only takes 55 seconds for the back temperature to rise to 200 ℃, and the residual carbon rate is only 15.26%.

[0124] A comparison between Example 1 and Comparative Example 2 reveals that Comparative Example 2 does not contain a ceramic precursor and relies solely on SiO2 aerogel powder as a filler. While SiO2 can improve thermal insulation and some mechanical properties at room temperature, the hydrogen bonding between its surface silanol groups and cellulose is limited, preventing it from participating in the in-situ ceramicization reaction at high temperatures. At high temperatures, cellulose pyrolysis forms a loose carbon layer, lacking active silicon species provided by PMHS decomposition and borosilicate glass phase formed by boric acid dehydration. Therefore, a continuous and dense carbon-ceramic composite barrier layer cannot be formed. This results in the carbon layer easily peeling off under flame impact, a shortened back-temperature heating time to 86 s, a residual carbon rate of only 25.42%, and a significant decrease in strength retention to 50.25% after thermal shock cycling.

[0125] A comparison between Example 1 and Comparative Example 3 reveals that Comparative Example 3, lacking the addition of SiO2 aerogel powder, resulted in the absence of an inorganic reinforcing phase with mesoporous structure and high specific surface area in the gel network. Silica powder not only enhances network rigidity by forming strong hydrogen bonds with cellulose fibers through surface silanol groups, but also acts as a physical barrier to inhibit heat conduction and convection. Its absence reduces the density of the gel skeleton, exacerbates shrinkage during drying, and significantly reduces compressive strength and Young's modulus. Furthermore, silica can participate in the ceramization reaction as a silicon source at high temperatures; its absence leads to insufficient formation of ceramic phases such as SiC in the final ceramic layer, affecting the continuity and stability of the high-temperature barrier.

[0126] A comparison between Example 1 and Comparative Example 4 reveals that Comparative Example 4 contains only PMHS microemulsion and no boric acid. While PMHS decomposes at high temperatures to provide active silicon species that react with carbon to form SiC, it lacks the boron source provided by boric acid, namely the B2O3 glass phase. The boron oxide glass phase can flow at high temperatures and fill the gaps between ceramic particles, acting as a bond and sealant, thus improving the density and anti-scraping properties of the ceramic layer. When PMHS is used alone, the bonding between ceramic particles in the resulting ceramic layer is weak, making it prone to microcracks and spalling under thermal stress. Although the back-temperature protection time of 134 s and the residual carbon rate of 35.62% are better than the system without a ceramic precursor, they are still significantly lower than those of the embodiments of this invention.

[0127] A comparison of Examples 1-3 and Comparative Examples 5-6 reveals that the Si-H bond content of the PMHS microemulsion in Examples 1-3 is controlled within the range of 1-1.5%. This content ensures the provision of an appropriate amount of active silicon species during high-temperature decomposition, enabling carbothermic reduction reactions with the cellulose carbon skeleton and silica to generate a uniformly distributed SiC ceramic phase. A suitable Si-H bond content facilitates moderate interaction with the hydroxyl groups of cellulose and PVA during the premixing stage, enhancing interfacial bonding without affecting dispersibility.

[0128] In Comparative Example 5, the Si-H bond content was relatively low, the active silicon species were insufficient, the ceramization reaction was incomplete, and the ceramic layer was thin and discontinuous. In Comparative Example 6, the Si-H bond content was relatively high, and PMHS was excessively cross-linked or agglomerated during the premixing stage, which affected its uniform dispersion in the network. The intense local reaction at high temperature may lead to cracking of the ceramic layer and a decrease in overall performance.

[0129] A comparison of Example 1 and Comparative Example 7 reveals that Comparative Example 7 contains only boric acid and no PMHS. The dehydration of boric acid forms a borosilicate glass phase, which can flow at high temperatures and encapsulate carbon particles, improving the continuity and oxidation resistance of the residual carbon layer. However, the lack of active silicon species provided by PMHS prevents the formation of high-hardness SiC and other ceramic phases, resulting in insufficient overall hardness and strength of the ceramic layer and weak resistance to thermal stress and airflow erosion. Therefore, although its back-temperature protection time of 117 s and residual carbon rate of 34.41% are better than the system without ceramics, they are still far lower than Example 1, which exhibits the synergistic effect of PMHS and boric acid.

[0130] A comparison of Examples 1, 4-5 and Comparative Examples 8-9 reveals that the appropriate amount of boric acid used in Examples 1 and 4-5 is optimal. Boric acid acts as a B source, dehydrating to generate a B2O3 glass phase, which effectively fills and binds the ceramic particles and carbon skeleton, forming a dense barrier. In Comparative Example 8, when the amount of boric acid is relatively too low, insufficient glass phase formation occurs, resulting in weak bonding between ceramic particles and easy detachment. In Comparative Example 9, when the amount of boric acid is relatively too high, excessive boric acid may react prematurely with the cellulose hydroxyl groups, affecting the network structure, or generate too much low-viscosity glass phase at high temperatures, leading to excessive flow, deformation, or even loss of the ceramic layer, thus reducing the stability and mechanical support of the barrier.

[0131] A comparison between Example 1 and Comparative Example 10 reveals that Comparative Example 10 did not undergo chemical cross-linking, meaning the cross-linking system of PVA and glutaraldehyde was not introduced. The hydroxyl groups on the PVA molecular chain react with cellulose fibers and glutaraldehyde to form a covalent network, significantly enhancing the interfacial bonding between the micro / nano fibers and the inorganic filler, thus improving the overall integrity and mechanical strength of the gel network. Without chemical cross-linking, the network mainly relies on physical entanglement and hydrogen bonds, resulting in weak bonding. During drying, it cannot effectively resist capillary stress, leading to a volume shrinkage rate of 15.53% and a strength of 0.86 MPa due to the lack of strong covalent bonds. At high temperatures, the network easily decomposes, with a residual carbon rate of only 32.33% and a strength retention rate decreasing to 45.66%.

[0132] The above description is based on the preferred embodiments of the present invention. It will be apparent to those skilled in the art that the present invention is not limited to the details of the exemplary embodiments described above, and that the invention can be implemented in other specific forms without departing from its spirit or essential characteristics. Therefore, the embodiments should be considered exemplary and non-limiting in all respects. The scope of the invention is defined by the appended claims rather than the foregoing description, and all variations falling within the meaning and scope of equivalents of the claims are intended to be included within the present invention. No reference numerals in the claims should be construed as limiting the scope of the claims.

[0133] Furthermore, it should be understood that although this specification describes embodiments, not every embodiment contains only one independent technical solution. This narrative style is merely for clarity. Those skilled in the art should consider the specification as a whole, and the technical solutions in each embodiment can also be appropriately combined to form other embodiments that can be understood by those skilled in the art.

Claims

1. A method for preparing a bamboo cellulose micro-nano fiber composite aerogel material, characterized in that, It comprises the following steps: S1, mechanically pulverize the bamboo pulp, wash and dry to obtain bamboo pulp microfiber; S2, add bamboo pulp microfiber and bamboo cellulose nanofiber suspension into water, stir to obtain a dispersion; S3, add hydrophilic silica aerogel powder, polysiloxane microemulsion and boric acid solution into the dispersion in sequence, stir and react to obtain a premix; S4, add polyvinyl alcohol aqueous solution and glutaraldehyde aqueous solution into the premix, stir and react at room temperature to obtain a reaction product; S5, pour the reaction product into a mold, freeze form to obtain an ice gel; S6, replace the ice gel in anhydrous ethanol, dry at 60-80 ℃ under normal pressure for 3-5 h to obtain a composite aerogel material.

2. The preparation method of the bamboo cellulose micro-nanofiber composite aerogel material according to claim 1, characterized in that: In the step S1, the drying temperature is 100-110 ℃, and the drying time is 6-12 h.

3. The preparation method of the bamboo cellulose micro-nanofiber composite aerogel material according to claim 1, characterized in that: In the step S2, the cellulose nanofiber is bamboo cellulose nanofiber prepared by TEMPO / NaBr / NaClO oxidation system, and the carboxyl content is 1.2-1.8 mmol / g; the concentration of the bamboo cellulose nanofiber suspension is 2-3 wt%, the total amount of bamboo cellulose fiber in the dispersion is 2-4 wt%, and the amount of bamboo cellulose nanofiber accounts for 20-30 wt% of the total amount of cellulose fiber; the stirring speed is 8000-12000 rpm, and the time is 20-40 min.

4. The preparation method of the bamboo cellulose micro-nanofiber composite aerogel material according to claim 1, characterized in that: In the step S3, the amount of hydrophilic silica aerogel powder is 2.5-6.5 wt% of the mass of the dispersion; the polysiloxane microemulsion is polymethylhydrogen siloxane microemulsion, the Si-H bond content is 1-1.5 %, the solid content is 25-35 %, the particle size D50 is 200-500 nm, and the amount is 2-3.5 % of the mass of the dispersion; the concentration of the boric acid solution is 8-15 wt%, and the amount is 0.8-1.8 % of the mass of the mixed dispersion.

5. The method according to claim 1, wherein the method is characterized by: In the step S3, the stirring and reaction temperature is 20-30 ℃, the stirring speed is 6000-10000 rpm, and the time is 30-60 min.

6. The method according to claim 1, wherein the method is characterized by: In the step S4, the concentration of the polyvinyl alcohol aqueous solution is 8-12 wt%, and the amount accounts for 30-50 % of the dry weight of cellulose; the concentration of the glutaraldehyde aqueous solution is 40-60 wt%, and the amount accounts for 1-3 % of the total mass of the dispersion; the stirring and reaction temperature is 20-30 ℃, the stirring speed is 2000-4000 rpm, and the time is 0.5-2 h.

7. The method according to claim 1, wherein the method is characterized by: In the step S5, the freeze forming temperature is -15 ℃ to -25 ℃, and the freeze time is 24-48 h.

8. The method according to claim 1, wherein the method is characterized by: In the step S6, the replacement is performed 2-4 times, and each time is 8-14 h.

9. A bamboo cellulose micro-nanofiber composite aerogel material, characterized in that: The composite aerogel material is prepared by the preparation method of any one of claims 1-8.

10. The application of the bamboo cellulose micro-nanofiber composite aerogel material in claim 9 in the field of high-temperature thermal protection.

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