Bionic small intestinal villus aerogel and preparation method and application thereof

Abstract

The application discloses a kind of bionic small intestine villus aerogel and its preparation method and application, the aerogel includes the aerogel framework with layered structure, and bionic villus structure is grafted on layered structure;Including by mass fraction: carbon source 1-1.5 parts, crosslinking agent 1.5-2.5 parts, catalyst 0.2-0.5 parts, phytic acid-polyethyleneimine ligand 0.5-1 part.It is prepared as follows: polyethyleneimine ligand aqueous solution is adjusted to be acidic, phytic acid aqueous solution is added, and white precipitate is generated by stirring, and ligand is obtained by washing, freeze-drying, and powder is obtained by grinding;Carbon source is dissolved, and crosslinking agent, catalyst are sequentially added, and gel precursor is formed by stirring, and ligand powder is added after stirring, and directional freeze-drying is carried out, and it is prepared.The application grafts biological-based electrolyte ligand into aerogel system with layered structure by in-situ polymerization method, constructs bionic small intestine villus type composite aerogel, enhances flame-retardant and heat-insulating performance, and significantly improves antibacterial performance.

Description

TECHNICAL FIELD

[0001] The present application relates to an aerogel and a preparation method and application thereof, in particular to a biomimetic small intestine villus aerogel and a preparation method and application thereof. BACKGROUND

[0002] Thermal insulation and flame-retardant materials are widely used in the fields of construction, aerospace, transportation, etc., and their performance is directly related to the safety and stability of the materials under high temperature or fire conditions. Existing thermal insulation materials are mostly based on inorganic and organic component composite structures, which achieve thermal insulation performance by filling the internal pores with low thermal conductivity gas, such as aerogels, foam materials, and vacuum insulation panels, etc. In terms of flame-retardant materials, flame-retardant agents are added to the materials or the heat resistance of the material itself is enhanced to inhibit the spread of flames and heat transfer. However, the thermal insulation and flame-retardant performance of these materials may be affected under conditions such as long-term use, mold-prone, and pressure, making it difficult to simultaneously consider structural strength and application life.

[0003] Currently, in order to improve the performance of materials in flame suppression, heat barrier, etc., research has mainly focused on the modification of aerogel matrix structure and the addition of reinforcing phases. For example, some studies use silica aerogel matrix combined with the addition of flame retardants or modified components to achieve preliminary effects of flame retardation and thermal insulation.

[0004] Although existing aerogel materials have made significant progress in thermal insulation and flame-retardant performance, there are still deficiencies under certain specific conditions, especially in terms of long-term stability, structural toughness, and processing cost: ① Insufficient stability and moisture resistance: due to the loose pore structure of most aerogels, the materials are easily affected in mold-prone environments, leading to a decrease in thermal insulation and flame-retardant performance. In addition, traditional aerogels are prone to structural collapse in high-temperature environments, affecting their thermal insulation effect. ② Limited mechanical properties: traditional silica aerogels are prone to pulverization due to their high brittleness after being impacted or under pressure, making them unsuitable for applications in high-load scenarios. Although the introduction of reinforcing phases such as fibers into aerogels can improve toughness, it often affects their low-density characteristics. ③ Environmental impact of flame retardants: many traditional flame retardants may contain harmful substances and produce toxic gases under high-temperature conditions, which have adverse effects on the environment and health. In order to solve this problem, the research on environmentally friendly flame retardants and non-toxic aerogels has become a new research hotspot, but their performance and cost still need to be optimized. ④ Complex processing and high cost: the preparation process of aerogels involves multiple chemical reactions and solvent removal processes, with a long preparation period and relatively high cost, making it difficult to meet the large-scale commercialization demand.

[0005] The above problems are mainly due to the fact that the microstructure of aerogels is easily affected by environmental factors, and the brittleness of inorganic components, the chemical composition of traditional flame retardants, and the complex preparation process all restrict the application potential of aerogels. SUMMARY

[0006] The present application aims to provide a biomimetic small intestinal villus structure aerogel which maintains excellent flame-retardant, antibacterial and heat-insulating properties in a mold-prone, load or high-temperature environment.

[0007] The second object of the present application is to provide a preparation method of the above-mentioned biomimetic small intestinal villus structure aerogel.

[0008] The third object of the present application is to provide an application of the above-mentioned biomimetic small intestinal villus structure aerogel.

[0009] Technical solution: The biomimetic small intestinal villus aerogel comprises an aerogel framework with a layered structure, and the layered structure of the aerogel framework is grafted with a biomimetic villus structure; the biomimetic small intestinal villus aerogel comprises the following components by weight percentage: 1-1.5 parts of a carbon source, 1.5-2.5 parts of a crosslinking agent, 0.2-0.5 parts of a catalyst, and 0.5-1 part of a phytic acid-polyethyleneimine ligand.

[0010] Each layer of the aerogel framework is uniformly grafted with the biomimetic villus structure.

[0011] The phytic acid-polyethyleneimine ligand is prepared by adjusting an aqueous solution of polyethyleneimine to be acidic, adding an aqueous phytic acid solution, stirring to generate a white precipitate, washing, and freeze-drying to obtain the phytic acid-polyethyleneimine ligand; the mass ratio of the polyethyleneimine to the phytic acid is 1:1-2:1; and the molecular weight of the polyethyleneimine is 70,000-250,000 M.W.

[0012] The carbon source is at least one of hydroxypropyl methyl cellulose, cellulose nanocrystals, or cellulose nanofibers; the crosslinking agent is methyltrimethoxysilane and / or hexadecyltrimethoxysilane; and the catalyst is ammonia water and / or sodium hydroxide.

[0013] The preparation method of the above-mentioned biomimetic small intestinal villus aerogel comprises the following steps:

[0014] (1) Adjusting an aqueous solution of a polyethyleneimine ligand to be acidic, adding an aqueous phytic acid solution, stirring to generate a white precipitate, washing, and freeze-drying to obtain the phytic acid-polyethyleneimine ligand, and grinding to obtain a phytic acid-polyethyleneimine ligand powder;

[0015] (2) Dissolving the carbon source, adding the crosslinking agent to hydrolyze and form a Si-O-Si network, and then adding the catalyst to crosslink the carbon source and the crosslinking agent to form a gel precursor;

[0016] (3) adding phytic acid-polyethylene imine ligand powder into the gel precursor, stirring until the phytic acid-polyethylene imine ligand is dissolved and dispersed in the gel precursor;

[0017] (4) performing directional freeze-drying to obtain the biomimetic small intestinal villus aerogel.

[0018] In step (1), the mass ratio of the polyethylene imine to the phytic acid is 1:1-2:1.

[0019] In step (1), the molecular weight of the polyethylene imine is 70,000-250,000 M.W.

[0020] In step (1), the aqueous solution of the polyethylene imine ligand is adjusted to a pH value of 3-4.

[0021] In step (1), the freeze-drying is performed for 48-54 h at a temperature of -55 to -60℃.

[0022] In step (1), the polyethylene imine is dispersed in water, and high-speed stirring is performed until the polyethylene imine is completely dissolved and uniform, forming an aqueous polyethylene imine solution; the stirring speed is 800-850 r / min; after the pH value of the aqueous polyethylene imine solution is adjusted to 3-4 by adding acetic acid, low-speed stirring is performed to completely protonate the polyethylene imine; the stirring speed is 250-300 r / min.

[0023] In step (1), the phytic acid is dispersed in water to form an aqueous phytic acid solution; the aqueous phytic acid solution is added to the aqueous polyethylene imine solution, and high-speed stirring is performed to generate white precipitates; the stirring speed is 800-850 r / min; the white precipitates are washed by a vacuum filter, and after being washed clean, the precipitates are preferably frozen at -20℃ for 8 h and then freeze-dried for 36 h.

[0024] The mass of the carbon source, the crosslinking agent, the catalyst, and the phytic acid-polyethylene imine ligand powder accounts for 1-1.5%, 1.5-2.5%, 0.2-0.5%, and 0.5-1% of the mass of the entire system obtained in step (3), respectively.

[0025] In step (2), after the crosslinking agent is added, stirring is performed for hydrolysis; the hydrolysis time is 1-2 h; if the time is shorter, the silane coupling agent is not completely hydrolyzed; if the time is longer, the crosslinking is too dense; after the catalyst is added, stirring is performed for crosslinking; the stirring time is 2.5-3.5 h; if the stirring time is shorter, the crosslinking is not complete; if the stirring time is longer, the crosslinking is too dense to form the small intestinal villus structure.

[0026] In step (2), the carbon source is dissolved in water, and the mass of water accounts for 94.5-96.8% of the mass of the whole system obtained in step (3).

[0027] In step (4), the time for directional freeze-drying is 48-54, and the temperature is -55 to -60 DEG C; the directional freezing method is a common directional freezing method in the prior art.

[0028] The application of the biomimetic small intestine villus aerogel in thermal insulation materials, flame-retardant materials and antibacterial materials.

[0029] Invention principle: Based on biomass PA molecules, the six strong negative charge active phosphate groups on the surface of the biomass PA molecules and the high strength cationic charge density of PEI(H + ) surface are used to combine PEI(H + ) and the phosphate groups of PA through electrostatic chelation, and an environmentally friendly electrolyte ligand is successfully constructed. Then, HPMC is used as a carbon source, MTMS is used as a crosslinking agent, and ammonia is used as a catalyst, and the bio-based electrolyte ligand with different PEI and PA mass ratios is grafted into the HPMC-MTMS system through in-situ polymerization to successfully construct HPMC-MTMS-PP biomimetic small intestine villus composite aerogel. The results show that when the mass ratio of PEI to PA is 2:1 and 1:1, the electrostatic and hydrogen bond interactions between the ligands and the hydrogen bond interactions of the whole system reach a balanced state, and the composite aerogel forms a biomimetic small intestine villus structure.

[0030] Advantages: Compared with the prior art, the present application has the following remarkable effects:

[0031] (1) The bio-based electrolyte phytic acid-polyethyleneimine ligand is grafted into the aerogel system with a layered structure formed by a carbon source, a crosslinking agent and a catalyst through in-situ polymerization, and a biomimetic small intestine villus composite aerogel is successfully constructed, which enhances the flame retardance (LOI can reach 30.2%, reaches UL-94-V0 flame retardant level, and PHRR and THR can be reduced by 61.14% and 58.21% at most) and thermal insulation performance (thermal conductivity is as low as 0.0319 W / (m·K)) of the aerogel, and also significantly improves the antibacterial performance of the material (resistance to E. coli is 94.36%, and resistance to Staphylococcus aureus is 82.10%).

[0032] (2) The product formula of the present application is more green and environmentally friendly, and the preparation process is more simple, which can be carried out at room temperature, reduces energy consumption and increases the high-value utilization of waste wood fibers.

[0033] (3) ①Optimization of flame retardant performance: In order to inhibit flame propagation and high-temperature oxidation, the environmentally friendly flame retardant formed by the PA-PEI ligand with high-efficiency flame-retardant function is introduced into the formula of the present application, and at the same time, the hierarchical porous structure of the small intestine villi is simulated, a heat barrier is formed in the aerogel by the multi-level pore layer, not only the flame penetration time is prolonged, but also the carbon layer is formed to protect the matrix structure, which further improves the flame retardant performance of the material. ②Improve the antibacterial performance: The porous structure of the aerogel provides a potential living space for microorganisms, and the formula of the present application specially adds phytic acid, a natural antibacterial ingredient, combined with the high surface area of the small intestine villi biomimetic structure, to achieve a lasting antibacterial effect, which can effectively prevent bacteria and fungi from adhering and breeding on the surface of the material, and prolong the service life of the aerogel. ⑤Enhance the heat insulation performance: In order to achieve high-efficiency heat insulation, the present application adopts a biomimetic multi-level pore structure with low thermal conductivity, which significantly prolongs the heat conduction path inside the aerogel. At the same time, the three heat transfer modes of conduction, convection and radiation are effectively isolated by the hierarchical structure to achieve excellent heat insulation effect. This material can still maintain thermal stability in extreme environments, and is suitable for high-efficiency heat insulation applications in the fields of building, industry, aerospace, etc.

[0034] (4) In order to realize the biomimetic structure of the small intestine villi, the present application uses biomass electrolyte phytic acid-polyethyleneimine ligand and special self-assembly process method, so that the material naturally grows into a biomimetic porous structure during the forming process. This process precisely controls the proportion of biomass ligand to ensure the uniformity and stability of the villi structure.

[0035] (5) The aerogel of the present application can be applied to building partitions, fire-fighting equipment shells and high-temperature pipeline insulation, which can provide excellent flame retardant protection under high-temperature conditions such as fire; can be applied to medical devices, protective equipment, air purification equipment lining, etc., to prevent bacterial breeding and reduce pollution risk, meet the long-term clean and safe demand; can be applied to the insulation layer of building, aerospace and industrial equipment, to provide a lightweight and efficient heat insulation solution, and to provide thermal protection support for high-end equipment. BRIEF DESCRIPTION OF DRAWINGS

[0036] Figure 1 Scanning electron microscope images of the aerogels of various examples and comparative examples;

[0037] Figure 2 Flame retardant performance test results of the aerogels of various examples and comparative examples;

[0038] Figure 3 Limiting oxygen index and effective heat of combustion test results of the aerogels of various examples and comparative examples;

[0039] Figure 4 Peak change graph of heat release rate of the aerogels of various examples and comparative examples;

[0040] Figure 5 Comparison chart of heat release rate and total heat release of aerogels of each embodiment and comparative example;

[0041] Figure 6 Comparison chart of total smoke release and CO release peak of aerogels of each embodiment and comparative example;

[0042] Figure 7 Comparison chart of carbon residue photos of aerogels of each embodiment and comparative example;

[0043] Figure 8 Comparison chart of thermal conductivity of aerogels of each embodiment and comparative example;

[0044] Figure 9 Schematic diagram of heat insulation mechanism;

[0045] Figure 10 Comparison chart of antibacterial effect of composite aerogels of embodiments 1, 2 and comparative examples 2, 3, and pure H-M aerogel of comparative example 1;

[0046] Figure 11 Pressure-strain curve of composite aerogels of embodiments 1, 2 and comparative examples 2, 3, and pure H-M aerogel of comparative example 1;

[0047] Figure 12 Comparison chart of mechanical properties of several materials in the prior art and aerogels obtained from embodiment 1. DETAILED DESCRIPTION

[0048] The present application will be described in further detail below.

[0049] Embodiment 1

[0050] A biomimetic small intestine villus aerogel with high flame retardant, antibacterial and heat insulation properties guided by a bio-based electrolyte ligand has a hierarchical porous structure, which includes an aerogel skeleton with a layered structure, and a biomimetic villus structure is uniformly grafted on each layer of the aerogel skeleton. The biomimetic small intestine villus aerogel comprises the following components by mass fraction: 1 part of carbon source, 2 parts of crosslinking agent, 0.5 parts of catalyst, and 0.5 parts of phytic acid-polyethyleneimine ligand; wherein the carbon source is hydroxypropyl methyl cellulose, abbreviated as HPMC, type II, viscosity: 4000 mpa.s; the crosslinking agent is methyltrimethoxysilane, abbreviated as MTMS; and the catalyst is ammonia.

[0051] The preparation method of the above-mentioned biomimetic small intestine villus aerogel comprises the following steps:

[0052] (1) At room temperature, 10 g of polyethyleneimine (hereinafter referred to as PEI) with a weight average molecular weight of 70000 is dissolved in 40 g of deionized water, and high-speed stirring is carried out for 5 min, and then stirring is continued until the PEI is completely and uniformly dissolved;

[0053] (2) After adding 15ml acetic acid to the completely dissolved PEI aqueous solution to adjust the pH to 3-4, low-speed stirring is performed for 0.5h to completely protonate the PEI, and then 20g of a 50% mass concentration phytic acid (PA) aqueous solution is added, and a white precipitate is immediately formed by high-speed stirring; wherein the mass ratio of PEI to PA is 1:1;

[0054] (3) The precipitate is washed by using a vacuum filter, and after being washed clean, the precipitate is frozen at-20℃ for 8h and then freeze-dried for 36h to obtain the bio-based electrolyte PEI-PA complex;

[0055] (4) The bio-based electrolyte obtained by freeze-drying is dried in an oven at 60℃ for 8h, and then ground into powder for storage;

[0056] (5) At room temperature, HPMC is dissolved in an appropriate amount of deionized water and stirred at high speed until completely dissolved to form a transparent viscous liquid;

[0057] (6) MTMS is added to the HPMC aqueous solution after dissolution, and high-speed stirring is performed for 1.5h;

[0058] (7) Ammonia is added as a catalyst, and high-speed stirring is performed for 3h to form a light blue wet gel precursor; wherein;

[0059] (8) The complex powder is added, and high-speed stirring is performed for 3h until the complex is completely dissolved and dispersed in the entire wet gel precursor; wherein the mass percentages of HPMC, MTMS, ammonia, and complex powder in the entire system obtained in step (8) are 1wt%, 2%, 0.5%, and 0.5%, respectively.

[0060] (9) The gel precursor obtained in step (8) is freeze-dried for 48h by using a directional freezing drying method under a liquid nitrogen environment at-196℃ to obtain an aerogel sample, which is denoted as H-M-PP(1:1).

[0061] Example 2

[0062] On the basis of Example 1, the difference from Example 1 is that the mass ratio of PEI to PA is 2:1, and the obtained aerogel is denoted as H-M-PP(2:1).

[0063] Example 3

[0064] On the basis of Example 1, the difference from Example 1 is that in the entire system obtained in step (8), the mass percentage of HPMC is 1.5%, the mass percentage of MTMS is 2.5%, the mass percentage of ammonia is 0.2%, and the mass percentage of the complex powder is 1%.

[0065] Comparative Example 1

[0066] On the basis of Example 1, different from Example 1, steps (1)-(4) and step (8) are omitted, that is, no ligand powder is added to the gel precursor, and pure H-M aerogel is prepared.

[0067] Comparative Example 2

[0068] On the basis of Example 1, different from Example 1, the mass ratio of PEI to PA is 1:2.

[0069] Comparative Example 3

[0070] On the basis of Example 1, different from Example 1, the mass ratio of PEI to PA is 1:3.

[0071] Comparative Example 4

[0072] Several materials in the prior art and the aerogel obtained in Example 1 are compared in terms of mechanical properties, as shown in Table 1. Figure 12 Table 1 Figure 12 “CNC / MTMS” in Table 1 comes from the literature: Bioinspired “aerogel grating” with metasurfaces for durable daytime radiative cooling for year-round energy savings, Chenyang Cai, etc. Nano Energy.

[0073] “CNF” comes from the literature: Defect reduction to enhance the mechanical strength of nanocellulose carbon aerogel, Haihong Lai, etc. Chinese Chemical Letters.

[0074] “MXene / NCF” comes from the literature: MXene / N-Doped Carbon Foam with Three-Dimensional Hollow Neuron-like Architecture for Freestanding, Highly Compressible All Solid-State Supercapacitors, Li Sun, etc. ACS Applied Materials & Interfaces.

[0075] “CNF / HTDMS” from the document: Enhancing the Oil Adsorption Properties of Cellulose Nanofiber Aerogels Through Chemical Modification, Sara Sadat Fazel, et al. Journal of Polymers and the Environment.

[0076] “Cellulose” from the document: Aerogel nanoarchitectonics based on cellulose nanocrystals and nanofibers from eucalyptus pulp: preparation and comparative study, Wenkai Zhu, et al. Cellulose.

[0077] “Silylated CNF” from the document: Ultralight, hydrophobic, anisotropic bamboo-derived cellulose nanofibrils aerogels with excellent shape recovery via freeze-casting, Xuexia Zhang, et al. Carbohydrate Polymers.

[0078] “CNFs / CNC” from the document: Rice straw agri-waste for water pollutant adsorption: Relevant mesoporous super hydrophobic cellulose aerogel, Mandana Dilamian, et al. Carbohydrate Polymers.

[0079] Comparative Example 5

[0080] On the basis of Example 1, different from Example 1 is that in step (6), the stirring time is 0.5 h. The cross-linked structure is uneven, and the aerogel is fragile and soft.

[0081] Comparative Example 6

[0082] On the basis of Example 1, different from Example 1 is that in step (7), the stirring time is 2 h. The structure is soft, easy to collapse and break.

[0083] Figure 1 The electron microscope microstructure of several composite aerogels, wherein (a) is the pure H-M aerogel prepared in Comparative Example 1, (b) is the aerogel obtained in Example 2, wherein the mass ratio of PEI to PA is 2:1; (c) is the aerogel obtained in Example 1, wherein the mass ratio of PEI to PA is 1:1; (d) is the aerogel obtained in Comparative Example 2, wherein the mass ratio of PEI to PA is 1:2; and (e) is the aerogel obtained in Comparative Example 3, wherein the mass ratio of PEI to PA is 1:3. It can be seen that the pure H-M aerogel exhibits a regular pore distribution and a uniform skeleton structure, while in the H-M-PP(2:1) and H-M-PP(1:1) composite aerogels Figure 1 ), biomimetic bifurcated villus structures appear on the Si-O-C skeleton formed by HPMC and MTMS. These villus structures are closely grafted on the layered framework of the composite aerogel and exhibit a multi-layered villus arrangement.

[0084] When the mass ratio of PA to PEI(H + ) is 2:1 and 1:1, the system reaches a certain balance state, which helps to form a uniform and directional self-assembly behavior. This balance state indicates that the electrostatic interaction between the two ratios of ligands is relatively weak. In the H-M system, the hydrogen bonds and electrostatic interactions between the hydroxyl groups on the surface of HPMC and the Si-O-Si and Si-O-C networks formed after the hydrolysis of MTMS, as well as the ligands (amino and phosphate groups), compete with the electrostatic interaction of PP itself, thus enabling the ligand structure to be uniformly dispersed throughout the system, promoting the formation of an ordered and directional microstructure, and exhibiting villus-like structures. In addition, the presence of HPMC provides more polar groups and hydrogen bond donors / acceptors for the system, which can interact more effectively with the functional groups of PEI(H + ) and PA, reducing the tendency of ligand aggregation in the system. At the same time, HPMC significantly increases the viscosity of the solution, helping to stabilize the ligand particles dispersed in the system, preventing their rapid sedimentation or aggregation, and making the dissociation and dissolution process of the electrolyte ligand more controllable.

[0085] When the ratio of PP ligand is 1:2 or 1:3, this balance state is broken, forming an irregular self-assembly mode. Due to the high proportion of PA, the network structure may become more dense and uniform, and the ligands tend to aggregate into nanoscale spherical particle structures. This structure is more compact but lacks directionality, thus forming a spherical microstructure. In addition, during the freeze-drying process, the spherical aggregates of ligands are difficult to arrange directionally during ice crystal growth, ultimately remaining as spherical structures. Therefore, a higher PA content leads to a different self-assembly mode, thereby affecting the formation of the final structure.

[0086] As Figure 2 , 3 , 4, 5 shown, the aerogel samples were subjected to vertical combustion (UL-94), limiting oxygen index (LOI), cone calorimeter test, and the carbon residue microstructure thereof was shown as Figure 7 . As Figure 3 shown, the LOI of pure H-M and H-M-PP composite aerogels were 19.5%, 27.8%, 30.2%, 30.5% and 31.6% respectively, and the bio-based electrolyte PP ligand in the composite aerogel played a very obvious inhibitory effect on the combustion of Si-O-Si and Si-O-C in the H-M skeleton, and the introduction of the ligand improved the composite aerogel to the incombustible level. In addition, the aerogel samples were subjected to cone calorimeter test under the radiation intensity of 35Kw / m 2 The results of peak heat release rate (PHRR), heat release rate (HRR), total heat release (THR), effective combustion heat (EHC), total smoke release (TSP) and CO release peak were shown as Figure 3 , 4 , 5, 6. Figure 5 Among them, the peak value of the first stage represents the rapid generation of a carbon protective layer on the surface of the aerogel after the flame ignites the sample, and as the temperature rises, the carbon layer breaks down and a large amount of combustible molecules are released, thus forming the second stage PHRR. Compared with pure H-M aerogel, the PHRR of H-M-PP (2:1) and H-M-PP (1:1) composite aerogels in the second stage can be reduced by about 21.92%. In addition, as Figure 5 shown, the PHRR and THR of the composite aerogel can be reduced by about 61.14% and 58.21% respectively, and as the proportion of phytic acid in the PP ligand increases, the HRR and THR show a slight increase. As Figure 3As shown, EHC represents the ratio of HRR to mass loss rate, reflecting the combustion rate of volatile gases in a meteorological flame. With the increase of PA in PP, more CO2 and water molecules are generated. Therefore, HM-PP (1:2) and HM-PP (1:3) composite aerogels exhibit higher EHC. In contrast, HM-PP (2:1) and HM-PP (1:1) at system equilibrium have fewer free PA molecules, resulting in lower EHC, reaching as low as 4.48 MJ / kg. The EHC of pure HM is more than 10 times higher than that of the composite aerogel, at 51.02 MJ / kg. Furthermore, during combustion, the TSP of pure HM and HM-PP composite aerogels shows a trend of first decreasing and then increasing, while CO release shows a continuous decreasing phenomenon. Therefore, when the PP ligand ratio is 2:1 and 1:1, the char layer after ignition forms the densest structure. This structure effectively inhibits the combustion of combustible molecules and minimizes the release of TSP and CO, ultimately exhibiting the lowest HRR and THR. On the one hand, Figure 7 It can also be observed that, compared to the thin char structure of pure HM aerogel, the char residues of HM-PP (1:2) and HM-PP (1:3) exhibit deformation and void formation, while the char layer structures of HM-PP (2:1) and HM-PP (1:1) show a relatively complete and dense structure. This is because excessive PA leads to the generation of more CO2 and water molecules. If the rapid release of a large amount of gas is trapped inside the char layer, it may expand at high temperatures, causing local char layer rupture or separation, ultimately forming voids.

[0087] like Figure 8 As shown, the thermal conductivity of HM aerogel is as low as 0.0344 W / (m). 2 The thermal conductivity of HM-PP composite aerogels with different proportions of ligands decreased slightly. The average thermal conductivity of HM-PP (2:1), HM-PP (1:1), HM-PP (1:2), and HM-PP (1:3) composite aerogels were 0.0280, 0.0275, 0.0305, and 0.0315 W / (m²), respectively. 2 ·K). On the one hand, the biomimetic villous structure formed by HM-PP (2:1) and HM-PP (1:1) increases the specific surface area of ​​the composite aerogel, further increasing the heat transfer path and enhancing the air trapping capacity inside the aerogel. Air, as a good insulator, can effectively prevent heat conduction, such as… Figure 9As shown. On the other hand, since thermal convection is an important mechanism for heat transfer inside a gas, limiting convection helps to further improve the thermal insulation performance of the material. The biomimetic fluff structure can effectively limit the flow of air inside the material and effectively suppress the occurrence of thermal convection.

[0088] like Figure 10 As shown, pure HM aerogel exhibited different antibacterial effects against *Escherichia coli* and *Staphylococcus aureus*. For Gram-negative *Escherichia coli*, pure HM aerogel showed almost no antibacterial activity, while composite aerogels incorporating different proportions of PP ligands all produced inhibition zones of varying sizes, which decreased with increasing PA content in the ligands. Specifically, when the weight ratio of PEI to PA in the ligands was 2:1, the PA content in the ligands increased significantly within the PEI(H) ligand ratio. + There are still vacant sites on the active site of PEI(H) during this process. + The amino groups in the compound aerogel enhanced its overall antibacterial effect and formed the largest inhibition zone. For Gram-positive Staphylococcus aureus, pure HM aerogel produced the greatest antibacterial effect, and the antibacterial effect weakened with increasing PA ratio in the ligands. The inhibition zones of HM-PP (2:1), HM-PP (1:1), HM-PP (1:2), and HM-PP (1:3) composite aerogels were 26, 19, 17, and 13 mm, respectively. The diameters of the largest inhibition zones formed by the composite aerogel against Escherichia coli and Staphylococcus aureus were 26 mm and 20 mm, respectively. Overall, the composite aerogel showed a slightly stronger antibacterial effect against Escherichia coli than against Staphylococcus aureus.

[0089] OD value can quantitatively evaluate the antibacterial rate of composite materials. Activated Escherichia coli and Staphylococcus aureus were treated with 1 lb broth for rejuvenation, and the concentration of the bacterial suspension was further controlled by measuring the OD value (recorded as the total bacterial count) to maximize the uniformity of each test sample (5 tests recorded as the average). 1 ml of composite aerogel precursor liquid was added to the bacterial suspension, and after shaking at 37℃ for 12 h, the antibacterial rate was calculated by OD value test and formula (1) as shown in Table 1. It can be found that as the proportion of PA in the ligand increases, the antibacterial rate of the composite gel against Escherichia coli decreased from a maximum of 94.36% to a minimum of 47.98%. A similar decreasing pattern of antibacterial effect was observed against Staphylococcus aureus, with a maximum and minimum of 82.10% and 35.63%, respectively.

[0090] Formula for calculating antibacterial rate:

[0091]

[0092] Note: OD b and OD aThe values ​​represent the optical density of the bacterial suspension before and after the addition of the aerogel sample.

[0093] Table 1

[0094]

[0095]

[0096] To further understand the antibacterial mechanism of this ligand-composite aerogel, SEM analysis was performed on the microstructure of bacteria (Escherichia coli and Staphylococcus aureus) after 12 hours of incubation for antibacterial performance testing. Figure 10 As shown, the cell membrane structure of *E. coli* in the pure HM aerogel bacterial suspension remained intact, and the cells were highly active. However, in the bacterial suspension incubated with HM-PP composite aerogel, some bacterial cell membranes exhibited rupture, tearing, and leakage of contents. This is partly due to the difference between PEI (H...) and... + PA itself is a positively charged cation, which interacts with the negatively charged bacterial cell membrane surface. This electrostatic interaction causes the bacterial cell wall to rupture, leading to leakage of cell contents and thus producing antibacterial properties. On the other hand, PA reacts with PEI(H) + The chelating effect of PEI (Hypericarpium Polytetrafluoroethylene) inhibits bacterial metabolism, and the synergistic effects of the high molecular weight cationic strength of PEI result in good stability of the hybrid. This also allows for the sustained release of antibacterial components, prolonging the duration of the antibacterial effect. Therefore, the biomimetic composite aerogel exhibits excellent anti-Escherichia coli properties. In contrast, the cell membranes of Staphylococcus aureus in the pure HM aerogel bacterial suspension showed rupture, tearing, and even leakage of contents. However, the cell disruption effect in the bacterial suspension of the composite aerogel with added PP ligand decreased progressively. With the increase of PA in the ligand, PEI(Hypericarpium Polytetrafluoroethylene)... + The electrostatic interaction between MTMS and the Staphylococcus aureus cell membrane is competitively generated by phosphate groups, resulting in a weakening effect, consistent with the OD value test results. Furthermore, the siloxane network formed by MTMS on the material surface is hydrophobic and chemically inert, which can disrupt the integrity of the bacterial cell wall or membrane, inhibiting bacterial attachment and reproduction. In summary, HM-PP (2:1) exhibits superior antibacterial properties against both Escherichia coli and Staphylococcus aureus.

[0097] like Figure 11As shown, further study of the pressure-strain curve of pure H-M aerogel and H-M-PP composite aerogel shows that the compressive stress of pure H-M aerogel is the lowest at 80% strain, about 20.63 KPa. With the increase of PA ratio, the compressive strength of PP ligand hybrid aerogel first increases and then decreases, and the maximum compressive strength is about 126.21 KPa (H-M-PP (1:1)). This shows that the strain resistance of the matrix structure is more uniform in the vertical direction, thus showing considerable compressive effect, which has certain advantages compared with previous studies, such as Figure 12 As shown. However, irregular spherical aggregates make the internal stress of the material not concentrated, resulting in a decrease in compressive stress.

[0098] The test standards and processes related to the present application are as follows:

[0099] 1. Flame retardant test of aerogel:

[0100] According to the UL-94 vertical burning grade test standard steps of GBT2408-2021:

[0101] ① Equipment preparation: the sample size generally requires the sample thickness to be between 0.1 mm and 12.7 mm, and the length is usually 125 mm x width 13 mm. Flame source: use a suitable burner to produce a 40±2 mm blue flame. Burning environment: the test is carried out in a closed combustion chamber without wind to ensure stable environment.

[0102] ② Sample fixation: the top of the sample is fixed on the clamp and hung vertically in the combustion chamber, and cotton or absorbent paper is placed below the sample to observe whether there is molten drop falling.

[0103] ③ Vertical burning test steps: first ignition: the flame is close to the bottom end of the sample, 10 mm away from the sample, and ignited, and the burning time is set to 10 seconds. After the flame is removed, the sample self-ignition time is recorded, and whether the flame can automatically extinguish is observed. Record the extinguishing time and observe whether there is burning drop. If there is drop, record whether it ignites the cotton below. Second ignition: if the sample is extinguished after the first burning, immediately re-close the flame to the bottom end of the sample and continue to burn for 10 seconds. Similarly, record the extinguishing time and drop condition.

[0104] ④ Observation and recording: record the sample self-extinguishing time, drop condition, etc. after two ignitions, and observe whether the sample meets the requirements of the corresponding grade in the UL-94 standard. According to the characteristics of the sample in the test, the sample is rated as follows:

[0105] V-0 level: the sample can be self-extinguished within 10 seconds in two burnings, and there is no drop igniting cotton.

[0106] V-1 rating: Sample self-extinguishes within 30 seconds in both burns and has no drips that ignite the cotton.

[0107] V-2 rating: Sample self-extinguishes within 30 seconds in both burns but has drips that ignite the cotton.

[0108] ⑤ Analysis and Judgment: Based on the recorded burning time, drip behavior, and self-extinguishing conditions, determine whether the sample meets the UL-94 V-0, V-1, or V-2 rating requirements. The results are as follows: Figure 2 .

[0109] According to the Limiting Oxygen Index test standard of GB2406-80 and ASTM D2863:

[0110] ① LOI tester: Usually a vertical burning column with different concentrations of oxygen-nitrogen mixed gas flowing inside to control the oxygen content. Sample size: According to the test standard, usually need to cut into 80mm long x 10mm wide x 4mm thick sample strips.

[0111] ② Set the initial oxygen concentration: Set the oxygen concentration in the gas flow to an initial value, for example, between 21-25%, and then gradually adjust to find the lowest oxygen concentration at which the material can continue to burn.

[0112] ③ Ignite the sample: Fix the sample vertically in the burning column and ignite the upper end of the sample. Usually use a small flame to ignite for 3-5 seconds, then remove the flame.

[0113] ④ Adjust the oxygen concentration: Observe the sample burning and adjust the oxygen concentration

[0114] ⑤ Record LOI: LOI <21%: Material flammable, poor flame retardant performance. 21% < LOI < 26%: Material flame retardant is general. LOI > 26%: Material has good flame retardant performance. LOI > 32%: Material has strong flame retardant performance, often used in special fireproof requirements, such as Figure 3 indicated.

[0115] Test equipment preparation according to GB / T16172-2007 Cone Calorimeter Test Standard:

[0116] ① Cone Calorimeter Test: Usually use Cone Calorimeter, its main components include: sample tray: for placing the sample to be tested. Oxygen / nitrogen gas mixture flow: provides oxygen for the sample and maintains the atmosphere required by the fire source. Fire source: a predetermined flame (usually a 35kW / m 2 of radiant heat source) used to ignite the sample. Temperature sensor: used to monitor the surface temperature of the sample and the heat release in the test chamber.

[0117] ② Sample Preparation: The sample size is typically 10 cm x 10 cm square, with a thickness of 2-5 mm, as required by the test standard. The sample should be as flat as possible, with no dirt or impurities on the surface.

[0118] ③ Mounting the Sample: Secure the sample on the sample tray of the cone calorimeter. Ensure that the sample surface is aligned with the radiation surface of the heat source, allowing the material surface to be uniformly heated during testing.

[0119] ④ Test Procedure: Start the instrument and set the appropriate radiant heat source, typically 50 kW / m 2 , to simulate the actual fire environment of the material. Ignite the sample and record the heat release rate (HRR), total heat release (THR), smoke production rate (SPR), CO and CO2 release, etc. during combustion. Measure and record parameters such as sample surface temperature, heat release rate, burning time, oxygen consumption, etc.

[0120] ⑤ Data Analysis: Heat Release Rate (HRR): HRR is the rate of heat released by the material during combustion, with units of kW / m 2 . It reflects the intensity of the material's combustion, with higher values indicating more heat released by the material during combustion. Total Heat Release (THR): is the total amount of heat released by the sample per unit time. This value can reflect the scale of the material's fire. Smoke Production Rate (SPR): refers to the amount of smoke produced per unit time, usually in m 2 / s. A high SPR value indicates that the material will produce a large amount of smoke during combustion. Flame Spread Rate (TSP): the speed at which the flame spreads along the surface of the material, often used to evaluate the speed of fire spread.

[0121] 2. Test steps for bacteriostatic samples:

[0122] ① Preparation of Aerogel Samples: Use scissors to cut the sample into a 10 mm ± 0.5 mm diameter disc, and use ultraviolet irradiation method to sterilize the sample.

[0123] ② Activation of Bacteria: Mix LB agar with pure water in a certain proportion and place it in a 121° high-pressure sterilization pot for 15 minutes, then pour the agar nutrient solution into a petri dish and solidify. Use a loop to inoculate E. coli and S. aureus into the petri dish, and incubate in a constant temperature and humidity incubator at 37°C and 60% humidity for 24 hours,

[0124] ③ Bacterial rejuvenation: Subsequently, the activated bacterial strains were mixed with LB broth and distilled water in a certain proportion and placed in a 121 ° autoclave for 15 min. Then the broth nutrient solution was poured into a culture dish and solidified. The activated E. coli and S. aureus were inoculated into the culture dish using a sterile inoculation loop, and cultured in a shaking incubator at 37 °C for 24 h. This process is the bacterial rejuvenation process.

[0125] ④ Preparation of bacterial suspension: The cultured bacterial strains were diluted with sterile water to an appropriate concentration, generally about 10^8 CFU / mL.

[0126] Coating bacterial solution: The prepared agar medium was poured into a sterile culture dish and allowed to solidify. Then the diluted bacterial suspension was uniformly coated on the surface of the agar medium using a sterile coating rod or glass rod.

[0127] ⑤ Place aerogel: The sterilized aerogel sample was carefully placed on the surface of the agar medium coated with the bacterial solution, ensuring good contact between the sample and the medium surface.

[0128] ⑥ Sample incubation: The inoculated culture dish was incubated in a 37 °C incubator for 24-48 hours. Observe the inhibition zone: Observe whether an inhibition zone, i.e. a sterile growth area, forms around the aerogel sample. Measure the diameter of the inhibition zone with a ruler, unit: millimeters, and record the measurement results. The results are shown in Table 1. Figure 10 .

[0129] ⑦ According to the diameter of the inhibition zone, evaluate the antibacterial performance of the aerogel sample. Compare the diameter of the inhibition zone with the control group (sample without antibacterial treatment) to determine the significance of the antibacterial effect.

[0130] Calculation of antibacterial rate: Control group OD value - experimental group OD value / control group OD value * 100%, the results are shown in Table 1.

Claims

1. A biomimetic small intestinal villus aerogel, characterized in that, The biomimetic small intestinal villus aerogel comprises an aerogel framework with a layered structure, and a biomimetic villus structure is grafted on the layered structure of the aerogel framework; the biomimetic small intestinal villus aerogel comprises the following components in mass fraction: 1-1.5 parts of a carbon source, 1.5-2.5 parts of a crosslinking agent, 0.2-0.5 parts of a catalyst, and 0.5-1 part of a phytic acid-polyethyleneimine complexing agent; The carbon source is at least one of hydroxypropyl methyl cellulose, cellulose nanocrystals, or cellulose nanofibers; the crosslinking agent is methyltrimethoxysilane and / or hexadecyltrimethoxysilane; and the catalyst is ammonia water and / or sodium hydroxide. The preparation method of the biomimetic small intestinal villus aerogel comprises the following steps: (1) adjusting an aqueous polyethyleneimine solution to be acidic, adding an aqueous phytic acid solution, stirring to generate a white precipitate, washing and freeze-drying to obtain a phytic acid-polyethyleneimine complexing agent, and grinding to obtain phytic acid-polyethyleneimine complexing agent powder; the mass ratio of the polyethyleneimine to the phytic acid is 1:1-2:1; (2) dissolving the carbon source, adding the crosslinking agent to perform hydrolysis and form a Si-O-Si network, then adding the catalyst to perform crosslinking between the carbon source and the crosslinking agent and form a gel precursor; the stirring time after adding the crosslinking agent is 1-2 h, and the stirring time after adding the catalyst is 2.5-3.5 h; (3) adding the phytic acid-polyethyleneimine complexing agent powder to the gel precursor and stirring until the phytic acid-polyethyleneimine complexing agent is dissolved and dispersed in the gel precursor; (4) performing directional freeze-drying to obtain the biomimetic small intestinal villus aerogel.

2. A method of preparing the biomimetic small intestinal villus aerogel of claim 1, characterized by, The preparation method of the biomimetic small intestinal villus aerogel comprises the following steps: (1) adjusting an aqueous polyethyleneimine solution to be acidic, adding an aqueous phytic acid solution, stirring to generate a white precipitate, washing and freeze-drying to obtain a phytic acid-polyethyleneimine complexing agent, and grinding to obtain phytic acid-polyethyleneimine complexing agent powder; the mass ratio of the polyethyleneimine to the phytic acid is 1:1-2:1; (2) dissolving the carbon source, adding the crosslinking agent to perform hydrolysis and form a Si-O-Si network, then adding the catalyst to perform crosslinking between the carbon source and the crosslinking agent and form a gel precursor; the stirring time after adding the crosslinking agent is 1-2 h, and the stirring time after adding the catalyst is 2.5-3.5 h; (3) adding the phytic acid-polyethyleneimine complexing agent powder to the gel precursor and stirring until the phytic acid-polyethyleneimine complexing agent is dissolved and dispersed in the gel precursor; (4) performing directional freeze-drying to obtain the biomimetic small intestinal villus aerogel.

3. The method of claim 2, wherein the biomimetic small intestinal villus aerogel is prepared by the steps of: In step (1), the molecular weight of the polyethyleneimine is 70,000-250,000 M.W.

4. The method of claim 2, wherein the biomimetic small intestinal villus aerogel is prepared by the steps of: The mass of the carbon source, the crosslinking agent, the catalyst, and the phytic acid-polyethyleneimine complexing agent powder accounts for 1-1.5%, 1.5-2.5%, 0.2-0.5%, and 0.5-1% of the mass of the entire system obtained in step (3), respectively.

5. The method for preparing biomimetic intestinal villus aerogel according to claim 2, characterized in that, In step (1), the aqueous polyethyleneimine solution is adjusted to have a pH value of 3-4.

6. Use of the biomimetic small intestinal villus aerogel of claim 1 in the preparation of thermal insulation materials, flame-retardant materials, and antibacterial materials.

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