Flame-retardant tough heat-insulating cellulose aerogel as well as preparation method and application thereof

Abstract

The invention discloses flame-retardant tough heat-insulating cellulose aerogel as well as a preparation method and application thereof, and belongs to the technical field of aerogel materials. The preparation method of the flame-retardant tough heat-insulation cellulose aerogel comprises the following steps: sequentially adding tetraethyl orthosilicate, 1, 2-bis (triethoxysilyl) ethane and phosphoryl triamide group bridged organosiloxane into a BC dispersion liquid to obtain a pretreated BC base solution; stirring and mixing in a constant-temperature water bath kettle to obtain white uniform turbid liquid; heating and curing, and then pre-cooling and freeze-drying to obtain the flame-retardant tough heat-insulating cellulose aerogel. The cellulose aerogel obtained through the method is a composite aerogel material integrating heat insulation, flame retardance, cyclic compression and recycling, has good flame retardance and heat insulation performance and has good application prospects in the field of building heat preservation and heat insulation.

Description

Technical Field

[0001] This invention relates to a flame-retardant, tough, and heat-insulating cellulose aerogel, its preparation method, and its application, belonging to the field of aerogel material technology. Background Technology

[0002] Cellulose aerogels are ultralight, porous, three-dimensional network structures made from natural cellulose (often derived from wood, crop straw, or bacteria) as a matrix, combined with other functional materials (such as nanoparticles, polymers, and carbon materials), and prepared using processes such as sol-gel, freeze-drying, or supercritical drying. Cellulose composite aerogels, with their ultralight, porous network structure, flexibly tunable functionality, and biodegradability derived from natural cellulose, have shown great potential in several cutting-edge fields. Their main characteristics—including extremely low density, high porosity, excellent thermal insulation, and conductivity and adsorption properties acquired through composite processing—directly drive a wide range of typical applications: such as efficient adsorption of oil and heavy metals in environmental protection; lightweight thermal insulation materials in the construction and aerospace industries; wound dressings or drug carriers in biomedicine; and the construction of sensors or supercapacitor electrodes in flexible electronics and energy storage, etc.

[0003] To further expand the application scenarios of cellulose aerogels, especially to meet the needs of use under complex working conditions such as high temperature and stress, a variety of cellulose-based aerogel materials with flame retardant and heat insulation properties have been developed in the existing technology. For example, Chinese patent CN 120966084 A discloses the preparation of an isotropic flame-retardant bacterial cellulose aerogel and its application in fire early warning. This technology involves adding a phosphorus / nitrogen-bridged organosiloxane (hexachlorocyclotriphosphazene and γ-aminopropyltriethoxysilane triol) and tetraethyl orthosilicate to a bacterial cellulose dispersion, stirring to obtain a milky white, uniform, and stable suspension, and then preparing an isotropic flame-retardant bacterial cellulose aerogel. Chinese patent CN 120248413 A discloses a flame-retardant, recyclable, compressible, and biodegradable cellulose aerogel and its preparation method and application. Its core is to add a phosphorus / nitrogen-bridged organosiloxane (hexachlorocyclotriphosphazene and 3-aminopropyltriethoxysilane) and tetraethyl orthosilicate to a bacterial cellulose dispersion, stirring to obtain a milky white dispersion solution, and then preparing the target aerogel material through subsequent processes.

[0004] However, the research and development of cellulose-based aerogel materials prepared by the aforementioned existing technologies mainly focuses on improving the flame retardant and thermal insulation properties of the materials, with insufficient attention paid to the mechanical strength. This results in aerogels with fragile structures and poor compressive and tensile strength, making them prone to collapse and damage under external forces. This severely limits their practical application in scenarios requiring the bearing of certain loads (such as aerospace structural components, building insulation load-bearing components, and flexible electronic devices). Furthermore, existing technologies struggle to achieve a synergistic improvement in flame retardancy, thermal insulation, and mechanical strength, failing to meet the demands of high-end applications for multifunctional integrated materials. Summary of the Invention

[0005] To address the shortcomings of existing technologies, the present invention aims to provide a flame-retardant, tough, and heat-insulating cellulose aerogel, its preparation method, and its applications, thereby solving the problems of insufficient flame retardancy and poor mechanical properties of existing cellulose aerogels. The cellulose aerogel obtained by the present invention exhibits significant flame retardant, heat insulation, and cyclic compression properties. Furthermore, the preparation process of the present invention is simple to operate, the conditions are easy to control, and it has broad practical application prospects.

[0006] To achieve the above objectives, the following technical solution is provided: The first objective of this invention is to provide a method for preparing flame-retardant, strong, and heat-insulating cellulose aerogel, the method comprising the following steps: (1) Tetraethyl orthosilicate, 1,2-bis(triethoxysilyl)ethane, and organosiloxane bridged by phosphoryltriamine groups were added sequentially to the BC dispersion to obtain the pretreated BC-based solution. (2) Place the pretreated BC base solution in a constant temperature water bath and stir to obtain a white and uniform suspension; (3) Heat and mature the suspension from step (2), then pre-cool and freeze-dry to obtain flame-retardant, strong and heat-insulating cellulose aerogel.

[0007] In one embodiment, the concentration of the bacterial cellulose (BC) dispersion in step (1) is 0.5-1.0 wt%; preferably 0.8 wt%.

[0008] In one embodiment, the organosiloxane bridged by the phosphoryltriamine group in step (1) is generated by dissolving phosphorus oxychloride in tetrahydrofuran under a protective atmosphere and then reacting it with 3-aminopropyltriethoxysilane.

[0009] In one embodiment, the protective gas includes nitrogen or a rare gas.

[0010] In one embodiment, the reaction is first carried out at a temperature of 40-50°C for 20-30 minutes, and then at 80-85°C for 2-5 hours.

[0011] In one embodiment, the molar ratio of phosphorus oxychloride and 3-aminopropyltriethoxysilane is 1:3.

[0012] In one embodiment, the mass ratio of tetraethyl orthosilicate to BC dispersion in step (1) is 0.1 to 0.5:1.

[0013] In one embodiment, the mass ratio of 1,2-bis(triethoxysilyl)ethane and BC dispersion in step (1) is 0.1 to 0.5:1.

[0014] In one embodiment, the mass ratio of the organosiloxane bridged by the phosphoryltriamine group in step (1) to the BC dispersion is 0.5 to 1:1.

[0015] In one embodiment, the mass ratio of tetraethyl orthosilicate, 1,2-bis(triethoxysilyl)ethane and the organosiloxane bridged by phosphoryltriamine groups in step (1) is 1:1~3:4~10; preferably 1:1:8.

[0016] In one embodiment, the temperature of the constant temperature water bath in step (2) is 30~50℃.

[0017] In one embodiment, the stirring speed in step (2) is 600~1000 r / min, and the stirring time is 60~80 min. In one embodiment, the heating and cooking temperature in step (3) is 60-90°C and the time is 30-50 min.

[0018] In one embodiment, the pre-cooling temperature in step (3) is -20 to -5°C, and the time is 12 to 24 hours.

[0019] In one embodiment, the freeze-drying temperature in step (3) is -80 to -70°C, and the time is 48 to 72 hours.

[0020] A second objective of this invention is to provide a flame-retardant, tough, and heat-insulating cellulose aerogel prepared by the method described above.

[0021] In one embodiment, the density of the flame-retardant, tough, and heat-insulating cellulose aerogel is only 7.5 kg·m³. -3 In terms of mechanical properties: the maximum compressive stress reached 0.168 MPa, which is 223.1% higher than that of pure BC aerogel (0.052 MPa); the fracture strain increased from 65.3% to 82.5%, and the elastic modulus increased from 0.81 MPa to 2.35 MPa, an increase of 190.1%.

[0022] In one embodiment, the thermal conductivity of the flame-retardant, tough, and heat-insulating cellulose aerogel is 28 mW·m. - ¹·K - ¹(25 ℃, 50% relative humidity), this value is much lower than that of most widely used insulation materials on the market, such as Elmwood (48mW·m). 1 ·K 1 ), polystyrene foam (38 mW·m 1 ·K 1 ), and glass wool (41 mW·m 1 ·K 1 The value was significantly lower than that of pure BC aerogel (38.5 mW·m). - ¹·K - ¹).

[0023] The third objective of this invention is to provide an application of the flame-retardant, tough, and heat-insulating cellulose aerogel described above in the field of building thermal insulation.

[0024] A fourth objective of this invention is to provide a method for improving the flame retardant, thermal insulation, and compressive stress properties of cellulose aerogel, the method comprising the following steps: (1) Tetraethyl orthosilicate, 1,2-bis(triethoxysilyl)ethane, and organosiloxane bridged by phosphoryltriamine groups were added sequentially to the BC dispersion to obtain the pretreated BC-based solution. (2) Place the pretreated BC base solution in a constant temperature water bath and stir to obtain a white and uniform suspension; (3) Heat and mature the suspension from step (2), then pre-cool and freeze-dry to obtain flame-retardant, strong and heat-insulating cellulose aerogel.

[0025] Beneficial effects: (1) This invention introduces tetraethyl orthosilicate, 1,2-bis(triethoxysilyl)ethane, and phosphoryltriamine-linked organosiloxane into cellulose aerogel. First, tetraethyl orthosilicate constructs an inorganic framework: after hydrolysis and condensation, it forms a nano-silica (SiO2) network, which serves as a reinforcing phase, greatly improving the mechanical strength, thermal stability, and barrier and heat insulation properties of the aerogel. Second, 1,2-bis(triethoxysilyl)ethane acts as a flexible coupling agent and toughening agent. Its ethylene (-CH2CH2-) structure imparts flexibility and reduces rigidity. The SiO2 network introduces brittleness, while simultaneously acting as a "molecular bridge" connecting BC and SiO2; the organosiloxanes bridged by phosphoryltriamine groups provide phosphorus as a highly efficient flame retardant, promoting dehydration and char formation to create a heat-insulating char layer; this method is simple, rapid, and suitable for large-scale mass production; the prepared cellulose aerogel also possesses excellent heat insulation and resilience properties, making it an aerogel that integrates flame retardancy, heat insulation, and cyclic compression degradation properties, and can effectively provide heat insulation and flame retardancy, showing great application potential in building thermal insulation; (2) The flame-retardant, tough, and heat-insulating cellulose aerogel of the present invention can be dissolved in aqueous solutions such as dilute acetic acid or dilute hydrochloric acid and then freeze-dried to become a complete aerogel. The reshaped aerogel still has good flame-retardant, heat-insulating, and cyclic compression properties. Furthermore, since the cellulose aerogel of the present invention also has good biodegradability, it can be completely degraded in moist soil within three weeks. Attached Figure Description

[0026] Figure 1 The images are scanning electron microscope (SEM) images of the flame-retardant, tough, and heat-insulating cellulose aerogel prepared in Example 1 of the present invention in the radial and axial directions; (a) is a radial SEM image of the flame-retardant, tough, and heat-insulating cellulose aerogel; (b) is an axial SEM image of the flame-retardant, tough, and heat-insulating cellulose aerogel. Figure 2 The images show the flame-retardant, tough, and heat-insulating cellulose aerogel prepared in Example 1 of the present invention and the pure cellulose aerogel prepared in Comparative Example 1 under a 1 kg weight load; (I, II) are of Example 1; (III, IV) are of Comparative Example 1.

[0027] Figure 3 The stress-strain curves of the flame-retardant, tough, and heat-insulating cellulose aerogel prepared in Example 1 of the present invention and the pure BC aerogel prepared in Comparative Example 1 under different compressive loads are shown. Figure 4 This is a schematic diagram of the thermogravimetric test curves of the flame-retardant, tough, and heat-insulating cellulose aerogel prepared in Example 1 of the present invention and the pure BC aerogel prepared in Comparative Example 1. Figure 5 Infrared thermal imaging of the flame-retardant, tough, and heat-insulating cellulose aerogel prepared in Example 1 of this invention on the surface of a heated stage. Detailed Implementation

[0028] The technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are only a part of the embodiments of the present invention, and not all of the 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. The specific embodiments described below further illustrate the present invention.

[0029] The source of raw materials involved in this invention: Bacterial cellulose BC dispersion (0.8 wt%) was purchased from Shanghai Maclean Chemical Reagent Co., Ltd. Tetraethyl orthosilicate was purchased from Sinopharm Chemical Reagent Co., Ltd. 1,2-Di(triethoxysilyl)ethane was purchased from Shanghai Maclean Biochemical Technology Co., Ltd.

[0030] The phosphoric acid triamine-bridged organosiloxane (TESPA) is generated by dissolving phosphorus oxychloride in tetrahydrofuran and then reacting it with 3-aminopropyltriethoxysilane through a series of reactions. The specific synthesis steps are as follows: Under a nitrogen atmosphere, 0.002 mol of phosphorus oxychloride was dissolved in 100 ml of tetrahydrofuran. Then, 0.006 mol of 3-aminopropyltriethoxysilane was added dropwise to the above solution at 45 °C. After reacting for 30 min, the temperature was raised to 80 °C and the reaction was continued for 5 h to obtain a light yellow solution. The THF solvent was removed by vacuum rotary evaporation at 60 °C to obtain a light yellow viscous liquid product.

[0031] Example 1 A method for preparing a flame-retardant, tough, and heat-insulating cellulose aerogel includes the following steps: (1) Take 150 g of BC dispersion with a concentration of 0.8 wt% and place it in a beaker. Add 0.12 g tetraethyl orthosilicate (TEOS), 0.12 g 1,2-bis(triethoxysilyl)ethane (BTSE), and 0.96 g phosphoric acid triamine-bridged organosiloxane (TESPA) dropwise to obtain the pretreated BC-based solution. (2) Transfer the pretreated BC base solution to a 250 mL three-necked flask and stir mechanically. Place it in a 30 ℃ constant temperature water bath and stir mechanically for 60 min at a speed of 900 r / min to allow the components to mix initially and undergo in-situ hydrolysis, condensation and chemical bonding reactions until a uniform and stable white viscous suspension is formed. (3) The obtained white suspension was transferred to a polytetrafluoroethylene mold and reacted at a constant temperature of 90 °C for 30 min in a vacuum oven with a vacuum degree of 10 Pa to complete the biomimetic mineralization crosslinking. The mineralized crosslinked sol was pre-frozen with liquid nitrogen at a temperature of -40 °C. The pre-frozen sample was then placed in a freeze dryer for freeze drying at -78 °C for 72 h to obtain flame-retardant, tough, and heat-insulating cellulose aerogel.

[0032] Example 2 A method for preparing a flame-retardant, tough, and heat-insulating cellulose aerogel includes the following steps: (1) Take 150 g of BC dispersion with a concentration of 0.8 wt% and place it in a beaker. Add 0.20 g of tetraethyl orthosilicate (TEOS), 0.20 g of 1,2-bis(triethoxysilyl)ethane (BTSE), and 0.4 g of phosphoric acid triamine-bridged organosiloxane (TESPA) dropwise to obtain the pretreated BC-based solution. (2) Transfer the pretreated BC base solution to a 250 mL three-necked flask and stir mechanically. Place it in a 30 ℃ constant temperature water bath and stir mechanically for 60 min at a speed of 900 r / min to allow the components to mix initially and undergo in-situ hydrolysis, condensation and chemical bonding reactions until a uniform and stable white viscous suspension is formed. (3) The obtained white suspension was transferred to a polytetrafluoroethylene mold and reacted at a constant temperature of 90 °C for 30 min in a vacuum oven with a vacuum degree of 10 Pa to complete the biomimetic mineralization crosslinking. The mineralized crosslinked sol was pre-frozen with liquid nitrogen at a temperature of -40 °C. The pre-frozen sample was then placed in a freeze dryer for freeze drying at -78 °C for 72 h to obtain flame-retardant, tough, and heat-insulating cellulose aerogel.

[0033] Example 3 A method for preparing a flame-retardant, tough, and heat-insulating cellulose aerogel includes the following steps: (1) Take 150 g of 0.8 wt% BC dispersion and place it in a beaker. Add 0.10 g tetraethyl orthosilicate (TEOS), 0.20 g 1,2-bis(triethoxysilyl)ethane (BTSE), and 0.50 g phosphoric acid triamine-bridged organosiloxane (TESPA) dropwise to obtain the pretreated BC-based solution. (2) Transfer the pretreated BC base solution to a 250 mL three-necked flask and stir mechanically. Place it in a 30 ℃ constant temperature water bath and stir mechanically for 60 min at a speed of 900 r / min to allow the components to mix initially and undergo in-situ hydrolysis, condensation and chemical bonding reactions until a uniform and stable white viscous suspension is formed. (3) The obtained white suspension was transferred to a polytetrafluoroethylene mold and reacted at a constant temperature of 90 °C for 30 min in a vacuum oven with a vacuum degree of 10 Pa to complete the biomimetic mineralization crosslinking. The mineralized crosslinked sol was pre-frozen with liquid nitrogen at a temperature of -40 °C. The pre-frozen sample was then placed in a freeze dryer for freeze drying at -78 °C for 72 h to obtain flame-retardant, tough, and heat-insulating cellulose aerogel.

[0034] Example 4 A method for preparing a flame-retardant, tough, and heat-insulating cellulose aerogel includes the following steps: (1) Take 150 g of BC dispersion with a concentration of 0.8 wt% and place it in a beaker. Add 0.09 g of tetraethyl orthosilicate (TEOS), 0.18 g of 1,2-bis(triethoxysilyl)ethane (BTSE), and 0.27 g of phosphoric acid triamine-bridged organosiloxane (TESPA) dropwise to obtain the pretreated BC-based solution. (2) Transfer the pretreated BC base solution to a 250 mL three-necked flask and stir mechanically. Place it in a 30 ℃ constant temperature water bath and stir mechanically for 60 min at a speed of 900 r / min to allow the components to mix initially and undergo in-situ hydrolysis, condensation and chemical bonding reactions until a uniform and stable white viscous suspension is formed. (3) The obtained white suspension was transferred to a polytetrafluoroethylene mold and reacted at a constant temperature of 90 °C for 30 min in a vacuum oven with a vacuum degree of 10 Pa to complete the biomimetic mineralization crosslinking. The mineralized crosslinked sol was pre-frozen with liquid nitrogen at a temperature of -40 °C. The pre-frozen sample was then placed in a freeze dryer for freeze drying at -78 °C for 72 h to obtain flame-retardant, tough, and heat-insulating cellulose aerogel.

[0035] Example 5 A method for preparing a flame-retardant, tough, and heat-insulating cellulose aerogel includes the following steps: (1) Take 150 g of 0.8 wt% BC dispersion and place it in a beaker. Add 0.08 g tetraethyl orthosilicate (TEOS), 0.08 g 1,2-bis(triethoxysilyl)ethane (BTSE), and 0.8 g phosphoric acid triamine-bridged organosiloxane (TESPA) dropwise to obtain the pretreated BC-based solution. (2) Transfer the pretreated BC base solution to a 250 mL three-necked flask and stir mechanically. Place it in a 30 ℃ constant temperature water bath and stir mechanically for 60 min at a speed of 900 r / min to allow the components to mix initially and undergo in-situ hydrolysis, condensation and chemical bonding reactions until a uniform and stable white viscous suspension is formed. (3) The obtained white suspension was transferred to a polytetrafluoroethylene mold and reacted at a constant temperature of 90 °C for 30 min in a vacuum oven with a vacuum degree of 10 Pa to complete the biomimetic mineralization crosslinking. The mineralized crosslinked sol was pre-frozen with liquid nitrogen at a temperature of -40 °C. The pre-frozen sample was then placed in a freeze dryer for freeze drying at -78 °C for 72 h to obtain flame-retardant, tough, and heat-insulating cellulose aerogel.

[0036] Example 6 A method for preparing a flame-retardant, tough, and heat-insulating cellulose aerogel includes the following steps: (1) Take 150 g of BC dispersion with a concentration of 0.8 wt% and place it in a beaker. Add 0.10 g of tetraethyl orthosilicate (TEOS), 0.10 g of 1,2-bis(triethoxysilyl)ethane (BTSE), and 0.60 g of phosphoric acid triamine-bridged organosiloxane (TESPA) dropwise to obtain the pretreated BC-based solution. (2) Transfer the pretreated BC base solution to a 250 mL three-necked flask and stir mechanically. Place it in a 30 ℃ constant temperature water bath and stir mechanically for 60 min at a speed of 900 r / min to allow the components to mix initially and undergo in-situ hydrolysis, condensation and chemical bonding reactions until a uniform and stable white viscous suspension is formed. (3) The obtained white suspension was transferred to a polytetrafluoroethylene mold and reacted at a constant temperature of 90 °C for 30 min in a vacuum oven with a vacuum degree of 10 Pa to complete the biomimetic mineralization crosslinking. The mineralized crosslinked sol was pre-frozen with liquid nitrogen at a temperature of -40 °C. The pre-frozen sample was then placed in a freeze dryer for freeze drying at -78 °C for 72 h to obtain flame-retardant, tough, and heat-insulating cellulose aerogel.

[0037] Comparative Example 1 The only difference from Example 1 is that the addition of tetraethyl orthosilicate, 1,2-di(triethoxysilyl)ethane and phosphoryltriamine-bridged organosiloxane is omitted; all other parameters and conditions are the same as in Example 1.

[0038] Comparative Example 2 The only difference from Example 1 is that 1,2-bis(triethoxysilyl)ethane is replaced with methyltrimethoxysilane; all other parameters and conditions are the same as in Example 1.

[0039] As a result, a rigid, dense, and inflexible SiO2 thin layer forms on the fiber surface, which easily leads to embrittlement and decreased toughness of cellulose aerogel.

[0040] Comparative Example 3 The only difference from Example 1 is that 1,2-bis(triethoxysilyl)ethane is replaced with methyltriethoxysilane (MTES), while all other parameters and conditions are the same as in Example 1.

[0041] As a result, a rigid, dense, and inflexible SiO2 thin layer forms on the fiber surface, which easily leads to embrittlement and decreased toughness of cellulose aerogel.

[0042] Comparative Example 4 The only difference from Example 1 is that 1,2-bis(triethoxysilyl)ethane is replaced with trimethylmethoxysilane (TMMS), while all other parameters and conditions are the same as in Example 1.

[0043] As a result, TMMS hydrolysis and condensation easily form oligomers and small molecules, which cannot form a continuous polymer network, resulting in inherently insufficient strength and toughness of cellulose aerogel.

[0044] Results Analysis 1. Scanning electron microscopy was performed on the flame-retardant, tough, and heat-insulating cellulose aerogel prepared in Example 1 in both radial and axial directions. The results are as follows Figure 1 As shown, the flame-retardant, tough, and heat-insulating cellulose aerogel exhibits a layered structure in the radial direction and a honeycomb structure in the axial direction, conforming to the basic structure of biomimetic mineralization. The phosphorus-nitrogen-containing organosilicon network generated using biomimetic mineralization has the following advantages: 1. It can form a strong interfacial thermal resistance with the cellulose matrix, reducing the thermal conductivity to 28 mW·m. - ¹·K - ¹ (25℃, 50% relative humidity), improving flame retardant performance; 2. The synergistic flame retardant effect between phosphorus, nitrogen, and silicon elements improves flame retardant performance; 3. The dual-network structure of cellulose matrix and organosilicon can improve mechanical strength and toughness through stress transfer, with a maximum compressive stress of 0.168 MPa and an elastic modulus increased from 0.81 MPa to 2.35 MPa; 4. The cellulose composite aerogel no longer collapses due to capillary force during natural drying and can be prepared by room temperature drying at normal pressure, eliminating the need for energy-intensive freeze-drying technology or traditional normal pressure preparation processes. In contrast, patent CN120966084 A uses a three-dimensional cellulose fiber network as a framework, exhibiting a multi-level porous structure with no inorganic mineral phase deposition on the surface, thus failing to form a biomimetic mineralized structure, and its mechanical properties are inferior to this invention.

[0045] 2. The thermal insulation and flame retardant properties of the cellulose aerogels prepared in the examples and comparative examples were tested; the thermal conductivity was determined according to ASTM C518 / ISO 8301; the limiting oxygen index (LOI) was determined according to ISO 4589-2 / ASTM D2863. The results are shown in Table 1. Table 1. Thermal insulation and flame retardant properties of aerogel samples from Examples 1-7 and Comparative Example 1.

[0046] As shown in Table 1 above, Example 1 exhibits low axial and radial thermal conductivity, indicating that the cellulose aerogel prepared in Example 1 has the best thermal insulation effect. However, due to the porous structure of pure BC in Comparative Example 1, which still hinders heat conduction, its thermal conductivity is lower than that of Examples 4-5, which have extremely low component content. This aligns with the basic principle that "porous materials have better thermal insulation than dense materials." Furthermore, Example 1 begins to burn within an oxygen index range of 34-39%, far exceeding the national flame retardant standard limiting oxygen index of 27%, and significantly higher than the limiting oxygen index of pure bacterial cellulose foam in Comparative Example 1, demonstrating excellent flame retardant properties.

[0047] 3. The mechanical properties of the cellulose aerogels prepared in the examples and comparative examples were tested, and the results are shown in Table 2. Table 2 Comparison of mechanical properties of aerogel materials prepared in Example 1 and existing patents

[0048] [Literature 1] Wu X, Liu M, Xie L, Duan Y, Shen K, Hu M, et al. Mechanicallyrobust cellulose nanofiber / sepiolite aerogel composites with superior flameretardant properties. Cellulose. 2025;32(3):1685-98. [Literature 2] Huang Y, Yang H, Yu Y, Li H, Li H, Bai J, et al. Bacterialcellulose biomass aerogels for oil-water separation and thermal insulation. Journal of Environmental Chemical Engineering. 2023;11(5):110403. As shown in Table 2 above, the maximum compressive stress of the cellulose-based foam prepared in Example 1 reached 158 kPa, which is higher than that of the cellulose-based aerogel prepared in the prior art without the addition of 1,2-bis(triethoxysilyl)ethane. The specific compressive modulus is significantly different from that of the cellulose aerogel prepared in Reference 2, indicating that the mechanical strength of the cellulose-based foam prepared in Example 1 has been greatly improved.

[0049] The flame-retardant, tough, and heat-insulating cellulose aerogel prepared in Example 1 has a density of only 7.5 kg·m³. 3 In terms of mechanical properties: the maximum compressive stress reached 0.168 MPa, which is 223.1% higher than that of pure BC aerogel (0.052 MPa); the fracture strain increased from 65.3% to 82.5%, and the elastic modulus increased from 0.81 MPa to 2.35 MPa, an increase of 190.1%.

[0050] The flame-retardant, tough, and heat-insulating cellulose aerogel prepared by this invention achieves synergistic optimization of high strength, high toughness, and high stiffness at extremely low density, exhibiting excellent comprehensive mechanical properties and possessing broad application prospects.

[0051] Figure 2 The images show photographs of the flame-retardant, tough, and heat-insulating cellulose aerogel prepared in Example 1 of this invention and the pure cellulose aerogel prepared in Comparative Example 1 under a 1 kg weight load. As can be seen from the images, the flame-retardant, tough, and heat-insulating cellulose aerogel can be compressed when a 1 kg weight is placed on it, demonstrating its compressibility. However, under the same experimental conditions, compared to the pure cellulose aerogel, Example 1 exhibits a better elastic modulus and is less prone to deformation. This is because siloxanes construct a high-strength covalent cross-linked network within the cellulose fiber network. Tetraethyl orthosilicate forms a rigid silica reinforcing phase, bifunctional silanes establish strong connections between fibers, and phosphoryltriamine siloxanes further participate in cross-linking and introduce flexible segments. The synergistic effect of these three components significantly strengthens the aerogel's skeletal structure at the nanoscale, giving it a higher elastic modulus and resistance to deformation than pure cellulose aerogel.

[0052] Figure 3 The figures show the stress-strain curves of the flame-retardant, tough, and heat-insulating cellulose aerogel prepared in Example 1 and the pure BC aerogel prepared in Comparative Example 1 under different compressive loads. As can be seen from the figures, the aerogel prepared in Comparative Example 1 exhibits large strain under very small stress, while the aerogel in Example 1 exhibits large strain under larger stress, has a larger Young's modulus, and better mechanical properties.

[0053] Figure 4 This is a schematic diagram of the thermogravimetric analysis (TGA) curves of the flame-retardant, tough, and heat-insulating cellulose aerogel prepared in Example 1 and the pure BC aerogel prepared in Comparative Example 1. As can be seen from the figure, the thermal stability of Example 1 is significantly better than that of Comparative Example 1, maintaining structural integrity better at high temperatures and reducing mass loss due to thermal degradation. Example 1, through its excellent thermal stability and efficient charring ability, significantly outperforms Comparative Example 1 in flame-retardant and heat-insulating performance. The dense char layer formed in the medium-to-high temperature region effectively blocks the transfer of heat and oxygen, providing stronger fire protection for the material.

[0054] Figure 5 The images show infrared thermographic images of the flame-retardant and tough cellulose foam material prepared in Example 1 of this invention on the surface of a hot plate at different temperatures. As can be seen from the images, the flame-retardant and tough heat-insulating cellulose aerogel prepared in this invention can effectively absorb infrared radiation emitted from the surface of the hot plate at various temperatures, thus playing a role in heat insulation.

[0055] The embodiments provided above are not intended to limit the scope of the invention, nor are the described steps intended to limit the order of execution. Any obvious modifications made to the invention by those skilled in the art based on existing common knowledge also fall within the scope of protection defined by the claims.

Claims

1. A method for preparing a flame-retardant, tough, and heat-insulating cellulose aerogel, characterized in that, The method includes the following steps: (1) Tetraethyl orthosilicate, 1,2-bis(triethoxysilyl)ethane, and an organosiloxane bridged by phosphoryltriamine groups were added sequentially to the bacterial cellulose BC dispersion to obtain the pretreated BC-based solution. (2) Place the pretreated BC base solution in a constant temperature water bath and stir to obtain a white and uniform suspension; (3) Heat and mature the suspension from step (2), then pre-cool and freeze-dry to obtain flame-retardant, strong and heat-insulating cellulose aerogel.

2. The method according to claim 1, characterized in that, The concentration of the bacterial cellulose BC dispersion in step (1) is 0.5-1.0 wt%.

3. The method according to claim 1, characterized in that, The mass ratio of tetraethyl orthosilicate and BC dispersion in step (1) is 0.1 to 0.5:

1.

4. The method according to claim 1, characterized in that, The mass ratio of 1,2-bis(triethoxysilyl)ethane and BC dispersion in step (1) is 0.1 to 0.5:

1.

5. The method according to claim 1, characterized in that, The mass ratio of the organosiloxane bridged by the phosphoryltriamine group in step (1) to the BC dispersion is 0.5 to 1:

1.

6. The method according to claim 1, characterized in that, The mass ratio of tetraethyl orthosilicate, 1,2-bis(triethoxysilyl)ethane and the organosiloxane bridged by phosphoryltriamine groups in step (1) is 1:1~3:4~10.

7. The method according to claim 1, characterized in that, The heating and cooking temperature in step (3) is 60-90℃ and the time is 30-50 min.

8. The flame-retardant, tough, and heat-insulating cellulose aerogel prepared by the method according to any one of claims 1 to 7.

9. The application of the flame-retardant, tough, and heat-insulating cellulose aerogel according to claim 8 in the field of building thermal insulation.

10. A method for improving the flame retardant, thermal insulation, and compressive stress properties of cellulose aerogel, characterized in that, The method includes the following steps: (1) Tetraethyl orthosilicate, 1,2-bis(triethoxysilyl)ethane, and organosiloxane bridged by phosphoryltriamine groups were added sequentially to the BC dispersion to obtain the pretreated BC-based solution. (2) Place the pretreated BC base solution in a constant temperature water bath and stir to obtain a white and uniform suspension; (3) Heat and mature the suspension from step (2), then pre-cool and freeze-dry to obtain flame-retardant, strong and heat-insulating cellulose aerogel.

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