Preparation of isotropic flame-retardant bacterial cellulose aerogel and application of isotropic flame-retardant bacterial cellulose aerogel in fire early warning

Abstract

The invention discloses preparation of isotropic flame-retardant bacterial cellulose aerogel and fire early warning application of the isotropic flame-retardant bacterial cellulose aerogel, and belongs to the technical field of aerogel materials. The preparation method of the aerogel comprises the following steps: (1) adding phosphorus / nitrogen-containing bridged organosiloxane and tetraethyl orthosilicate into bacterial cellulose dispersion liquid in proportion, and then stirring to obtain milk white uniform and stable turbid liquid; and (2) heating and curing the milky white turbid liquid, then precooling, and finally freeze-drying to obtain the isotropic flame-retardant bacterial cellulose aerogel. The aerogel disclosed by the invention is a cellulose-based aerogel material with flame-retardant and heat-insulating properties, has a remarkable isotropic flame-retardant characteristic, can effectively resist flame spread in all directions, is high in carbonization efficiency, can realize early detection and early warning of a fire disaster, and has a great application prospect in the field of fire disaster early warning.

Description

Technical Field

[0001] This invention belongs to the field of aerogel material technology, and particularly relates to the preparation of an isotropic flame-retardant bacterial cellulose aerogel and its application in fire early warning. Background Technology

[0002] Aerogels are low-density, three-dimensional nanoporous solid materials composed of a nanoporous network structure formed by the aggregation of colloidal particles or polymer molecules, with gaseous dispersion media filling the pores. They possess extremely low density, making them one of the lightest solids in the world. Aerogels have a porosity as high as 80%-99.8% and a large specific surface area (100-2000 m²). 2 It has extremely low thermal conductivity (0.01-0.04 W / m·K) and excellent thermal insulation properties. It is widely used in aerospace, building insulation, new energy and other fields, and is known as a "miracle material that changes the world".

[0003] Bacterial cellulose is a natural polymer material produced by fermentation of specific bacteria such as *Acetobacter xylitol*. It consists of β-D-glucose linked by β-1,4-glycosidic bonds, possessing an ultra-fine network structure with fiber diameters of only 20-100 nanometers. It exhibits high crystallinity, high degree of polymerization, and excellent mechanical properties, with tensile strength reaching 250-350 MPa. Furthermore, it possesses good biocompatibility and biodegradability. In the biomedical field, it can be used as artificial skin and drug carriers; in the food industry, it serves as a thickener and molding agent, making it a highly promising multifunctional material. Therefore, cellulose-based aerogels prepared from bacterial cellulose are characterized by low cost, good biocompatibility, and also possess thermal insulation and toughness properties, making them a hot topic in materials science. However, the abundant hydroxyl groups and porous structure in bacterial cellulose aerogels result in a rapid oxygen diffusion rate, with a limiting oxygen index (LOI) of only 20-22%, necessitating efficient flame-retardant modification. Summary of the Invention

[0004] Technical issues

[0005] Bacterial cellulose aerogel, as a material with great application potential, has shown promising prospects in many fields. However, its poor flame retardant properties limit its practical application. Therefore, flame retardant modification of bacterial cellulose aerogel is essential. Furthermore, after modification, this material can play an important role in the field of fire early warning, enabling accurate monitoring and warning of early fires.

[0006] Technical content

[0007] The purpose of this invention is to provide a method for preparing isotropic flame-retardant bacterial cellulose aerogel and its application in fire early warning, aiming to solve the problem of insufficient flame retardancy of bacterial cellulose aerogel and to provide a new method for fire early warning applications by utilizing its high carbonization efficiency at high temperatures.

[0008] Traditional flame retardants mainly include halogenated, phosphorus-based, and inorganic flame retardants. Halogenated flame retardants release toxic hydrogen halide gas during combustion and have been gradually replaced by halogen-free flame retardants. Traditional inorganic flame retardants (such as aluminum hydroxide) have limited flame retardant effects, and excessive addition can affect the mechanical properties of materials. In contrast, phosphorus-nitrogen-based flame retardants have advantages such as high efficiency, smokelessness, and low toxicity, and have good development prospects.

[0009] This invention is simple to operate and the conditions are easy to control. The resulting bacterial cellulose aerogel has a significant flame-retardant effect and is promising for application in fire early warning.

[0010] To achieve the above objectives, the technical solution adopted by the present invention is as follows:

[0011] A method for preparing an isotropic flame-retardant bacterial cellulose aerogel for fire early warning includes the following steps:

[0012] (1) Add phosphorus / nitrogen-bridged organosiloxane and tetraethyl orthosilicate to bacterial cellulose dispersion, and then stir to obtain a milky white, uniform and stable suspension;

[0013] (2) The milky white suspension was heated and matured, then pre-cooled, and finally freeze-dried to obtain an isotropic flame-retardant bacterial cellulose aerogel.

[0014] In one embodiment of the present invention, the bacterial cellulose concentration in the bacterial cellulose dispersion in step (1) is 0.5 wt% to 5 wt%.

[0015] Preferably, the bacterial cellulose concentration in the bacterial cellulose dispersion in step (1) is 0.8 wt% to 2 wt%.

[0016] Specifically, optionally, the bacterial cellulose concentration in the bacterial cellulose dispersion in step (1) is 0.8 wt%.

[0017] In one embodiment of the present invention, the phosphorus / nitrogen-bridged organosiloxane in step (1) is prepared by reacting hexachlorocyclotriphosphazene and γ-aminopropylsilanetriol.

[0018] Furthermore, the reaction needs to be carried out under a protective atmosphere, which includes nitrogen or a rare gas.

[0019] In one embodiment of the present invention, the specific preparation process of the phosphorus / nitrogen-bridged organosiloxane is as follows:

[0020] In a nitrogen or rare gas environment, hexachlorocyclotriphosphazene and γ-aminopropylsilanetriol are mixed at a mass ratio of 1:3 to 4, and then stirred at 45 to 55 °C for 20 to 40 min. After that, the temperature is raised to 75 to 85 °C and the reaction is continued for 2 to 4 h to obtain phosphorus / nitrogen-bridged organosiloxane.

[0021] In one embodiment of the present invention, the mass ratio of the phosphorus / nitrogen-bridged organosiloxane and bacterial cellulose in step (1) is 0.3 to 3:1.

[0022] Preferably, the mass ratio of the phosphorus / nitrogen-bridged organosiloxane and bacterial cellulose in step (1) is 0.5 to 2:1. More preferably, it is 0.5 to 1:1.

[0023] Specifically, the mass ratio of phosphorus / nitrogen-bridged organosiloxane and bacterial cellulose in step (1) can be 0.5:1, 1:1, or 2:1.

[0024] In one embodiment of the present invention, the mass ratio of tetraethyl orthosilicate to bacterial cellulose in step (1) is 0.2 to 3:1.

[0025] Preferably, the mass ratio of tetraethyl orthosilicate to bacterial cellulose in step (1) is 0.3 to 1:1.

[0026] Specifically, the mass ratio of tetraethyl orthosilicate to bacterial cellulose in step (1) can be 0.3:1 or 0.5:1.

[0027] In one embodiment of the present invention, in step (1), the phosphorus / nitrogen-bridged organosiloxane and tetraethyl orthosilicate need to be added dropwise to the bacterial cellulose dispersion.

[0028] In one embodiment of the present invention, in step (1), tetraethyl orthosilicate is added after an interval of 20 to 30 minutes following the addition of the phosphorus / nitrogen-bridged organosiloxane.

[0029] In one embodiment of the present invention, the stirring time in step (1) is 60 to 90 minutes.

[0030] In one embodiment of the present invention, the heating and cooking temperature in step (2) is 60-80°C and the time is 30-50 min.

[0031] In one embodiment of the present invention, the pre-cooling temperature in step (2) is -80 to -10°C, and the time is 12 to 24 hours.

[0032] In one embodiment of the present invention, the freeze-drying temperature in step (2) is -80 to -70°C; and the freeze-drying time is 48 to 72 hours.

[0033] This invention provides an isotropic flame-retardant bacterial cellulose aerogel prepared according to the above method.

[0034] The present invention provides the application of an isotropic flame-retardant bacterial cellulose aerogel in the field of fire early warning.

[0035] The present invention also provides a method for improving the response sensitivity and response intensity of fire early warning equipment, which utilizes the above-mentioned isotropic flame-retardant bacterial cellulose aerogel as a functional component.

[0036] The present invention also provides a fire early warning device with high response sensitivity and response intensity, comprising the above-mentioned isotropic flame-retardant bacterial cellulose aerogel.

[0037] In one embodiment of the present invention, the response sensitivity is 1.1s and the flame response intensity is 92.1%.

[0038] The present invention has the following beneficial effects:

[0039] (1) This invention introduces phosphorus / nitrogen-bridged organosiloxane and tetraethyl orthosilicate into bacterial cellulose aerogel. First, cyclotriphosphazene decomposes at high temperature to generate phosphoric acid, which promotes the formation of a char layer and releases non-flammable gas to dilute oxygen. The organosilicon network pyrolyzes to generate a SiO2 ceramic layer, which isolates heat and oxygen diffusion, forming a phosphorus-nitrogen-silicon triple flame retardant mechanism. This significantly improves the flame retardant performance of bacterial cellulose aerogel. Furthermore, due to the isotropic nature of the aerogel, it has high flame retardancy and heat insulation properties in all directions.

[0040] (2) When a fire occurs, the flame-retardant bacterial cellulose aerogel is sensitive to temperature changes due to the presence of its flame-retardant network. Furthermore, the aerogel exhibits high carbonization efficiency at high temperatures, forming a dense graphite carbon layer on its surface. This alters the surface resistance, causing the alarm light to emit a warning signal, thus achieving a fire early warning effect. Moreover, its flame response sensitivity is as low as 1.1 seconds, and its flame response intensity is as high as 92.1%.

[0041] Furthermore, this aerogel can be combined with other functional materials to further expand its fire early warning function. Attached Figure Description

[0042] To more clearly illustrate the technical solutions of the embodiments of the present invention, it is necessary to briefly describe the accompanying drawings involved in the embodiments. It should be understood that the drawings shown below correspond only to some embodiments of the present invention. However, based on these embodiments, those skilled in the art can deduce all other embodiments without creative effort, and these embodiments are also within the protection scope of the present invention.

[0043] Figure 1 Scanning electron microscope (SEM) images of an isotropic flame-retardant bacterial cellulose aerogel prepared in Example 1 of this invention, in radial and axial directions.

[0044] Figure 2 This refers to an isotropic flame-retardant bacterial cellulose aerogel prepared according to Example 1 of the present invention. 29 SiMAS NMR spectrum.

[0045] Figure 3 This is a comparison chart of the limiting oxygen index (LOI) values ​​of the isotropic flame-retardant bacterial cellulose aerogel prepared in Example 1 of the present invention in the XY, XZ, and YZ directions, and the pure bacterial cellulose aerogel prepared in Comparative Example 1.

[0046] Figure 4 This is a comparison of the heat release rate (HRR) and total heat release (THR) of the isotropic flame-retardant bacterial cellulose aerogel prepared in Example 1 of the present invention in the XY, XZ, and YZ directions, and that of the pure bacterial cellulose aerogel prepared in Comparative Example 1.

[0047] Figure 5 The images show physical and conceptual diagrams of an isotropic flame-retardant bacterial cellulose aerogel prepared in Example 1 of this invention, which serves as a fire warning system under butane flame combustion conditions.

[0048] Figure 6 Images of the front and back sides of an isotropic flame-retardant bacterial cellulose aerogel prepared in Example 1 of this invention after being subjected to continuous burning with a butane flame for 180 seconds.

[0049] Figure 7 The temperature change curves in the XZ and YZ directions of an isotropic flame-retardant bacterial cellulose aerogel prepared in Example 1 of the present invention after being subjected to continuous burning with a butane flame for 180 s. Detailed Implementation

[0050] In the embodiments of the present invention, the technical solutions will be clearly and comprehensively described with reference to the accompanying drawings. It should be understood that the embodiments described herein cover only a part of the present invention, not all of it. For those skilled in the art, all other embodiments derived from the disclosed embodiments of the present invention without inventive effort are included within the protection scope of the present invention.

[0051] Source of raw materials

[0052] Bacterial cellulose (0.8 wt%) was purchased from Shanghai Titan Technology Co., Ltd.; hexachlorocyclotriphosphazene and γ-aminopropylsilanetriol were both purchased from Shanghai Maclean Chemical Reagent Co., Ltd.

[0053] Phosphorus / nitrogen-bridged organosiloxanes were prepared by reacting hexachlorocyclotriphosphazene with γ-aminopropylsilanetriol in an oil bath. The specific synthetic procedure is as follows: 4.2 g of hexachlorocyclotriphosphazene and 16.0 g of γ-aminopropylsilanetriol were weighed. A 50 mL three-necked flask was placed in an oil bath, and then a rotor and hexachlorocyclotriphosphazene were added to the flask. The flask was then connected to a nitrogen cylinder. The initial temperature of the oil bath was set to 22 °C, and magnetic stirring was started. γ-aminopropylsilanetriol was added dropwise. After the addition was complete, the temperature of the oil bath was raised to 50 °C, and after 30 min, it was raised to 80 °C and the reaction was continued for 3 h. A nitrogen atmosphere was maintained throughout the reaction. Finally, a pale yellow phosphorus / nitrogen-bridged organosiloxane was obtained.

[0054] Example 1

[0055] Add 100g of bacterial cellulose dispersion (0.8wt%) to a three-necked flask and stir mechanically at 1000r / min. Weigh 0.8g of phosphorus / nitrogen-bridged organosiloxane and add it dropwise to the bacterial cellulose dispersion. Stir mechanically for 30min. Then weigh 0.24g of tetraethyl orthosilicate and add it dropwise to the bacterial cellulose dispersion. Stir mechanically for 30min until a uniform and stable milky white suspension is formed.

[0056] The obtained milky white suspension was placed in a mold and heated in a 60℃ electric thermostatic drying oven for 30 minutes for maturation. Then, the matured bacterial cellulose dispersion was pre-frozen with liquid nitrogen or a refrigerator at a temperature of -80℃ to -10℃ for 12 to 24 hours. Finally, the pre-frozen sample was freeze-dried in a freeze dryer at a temperature of -80℃ for 48 to 72 hours to obtain an isotropic flame-retardant bacterial cellulose aerogel, denoted as BC / PMO.

[0057] Example 2

[0058] Add 100g of bacterial cellulose dispersion (1wt%) to a three-necked flask and stir mechanically at 1000r / min. Weigh 1g of phosphorus / nitrogen-bridged organosiloxane and add it dropwise to the bacterial cellulose dispersion. Stir mechanically for 30min. Then weigh 0.3g of tetraethyl orthosilicate and add it dropwise to the bacterial cellulose dispersion. Stir mechanically for 30min until a uniform and stable milky white suspension is formed.

[0059] The obtained milky white suspension was placed in a mold and heated in a 60℃ electric thermostatic drying oven for 30 minutes for maturation. Then, the matured bacterial cellulose dispersion was pre-frozen with liquid nitrogen or a refrigerator at a temperature of -80℃ to -10℃ for 12 to 24 hours. Finally, the pre-frozen sample was placed in a freeze dryer for freeze drying at a temperature of -80℃ for 48 to 72 hours to obtain an isotropic flame-retardant bacterial cellulose aerogel.

[0060] Example 3

[0061] Add 100g of bacterial cellulose dispersion (1.5wt%) to a three-necked flask and stir mechanically at 1000r / min. Weigh 1.5g of phosphorus / nitrogen-bridged organosiloxane and add it dropwise to the bacterial cellulose dispersion. Stir mechanically for 30min. Then weigh 0.45g of tetraethyl orthosilicate and add it dropwise to the bacterial cellulose dispersion. Stir mechanically for 30min until a uniform and stable milky white suspension is formed.

[0062] The obtained milky white suspension was placed in a mold and heated in a 60℃ electric thermostatic drying oven for 30 minutes for maturation. Then, the matured bacterial cellulose dispersion was pre-frozen with liquid nitrogen or a refrigerator at a temperature of -80℃ to -10℃ for 12 to 24 hours. Finally, the pre-frozen sample was placed in a freeze dryer for freeze drying at a temperature of -80℃ for 48 to 72 hours to obtain an isotropic flame-retardant bacterial cellulose aerogel.

[0063] Example 4

[0064] Add 100g of bacterial cellulose dispersion (2wt%) to a three-necked flask and stir mechanically at 1000r / min. Weigh 2g of phosphorus / nitrogen-bridged organosiloxane and add it dropwise to the bacterial cellulose dispersion. Stir mechanically for 30min. Then weigh 0.6g of tetraethyl orthosilicate and add it dropwise to the bacterial cellulose dispersion. Stir mechanically for 30min until a uniform and stable milky white suspension is formed.

[0065] The obtained milky white suspension was placed in a mold and heated in a 60℃ electric thermostatic drying oven for 30 minutes for maturation. Then, the matured bacterial cellulose dispersion was pre-frozen with liquid nitrogen or a refrigerator at a temperature of -80℃ to -10℃ for 12 to 24 hours. Finally, the pre-frozen sample was placed in a freeze dryer for freeze drying at a temperature of -80℃ for 48 to 72 hours to obtain an isotropic flame-retardant bacterial cellulose aerogel.

[0066] Example 5

[0067] Add 100g of bacterial cellulose dispersion (0.8wt%) to a three-necked flask and stir mechanically at 1000r / min. Weigh 0.4g of phosphorus / nitrogen-bridged organosiloxane and add it dropwise to the bacterial cellulose dispersion. Stir mechanically for 30min. Then weigh 0.24g of tetraethyl orthosilicate and add it dropwise to the bacterial cellulose dispersion. Stir mechanically for 30min until a uniform and stable milky white suspension is formed.

[0068] The obtained milky white suspension was placed in a mold and heated in a 60℃ electric thermostatic drying oven for 30 minutes for maturation. Then, the matured bacterial cellulose dispersion was pre-frozen with liquid nitrogen or a refrigerator at a temperature of -80℃ to -10℃ for 12 to 24 hours. Finally, the pre-frozen sample was placed in a freeze dryer for freeze drying at a temperature of -80℃ for 48 to 72 hours to obtain an isotropic flame-retardant bacterial cellulose aerogel.

[0069] Example 6

[0070] Add 100g of bacterial cellulose dispersion (0.8wt%) to a three-necked flask and stir mechanically at 1000r / min. Weigh 1.6g of phosphorus / nitrogen-bridged organosiloxane and add it dropwise to the bacterial cellulose dispersion. Stir mechanically for 30min. Then weigh 0.24g of tetraethyl orthosilicate and add it dropwise to the bacterial cellulose dispersion. Stir mechanically for 30min until a uniform and stable milky white suspension is formed.

[0071] The obtained milky white suspension was placed in a mold and heated in a 60℃ electric thermostatic drying oven for 30 minutes for maturation. Then, the matured bacterial cellulose dispersion was pre-frozen with liquid nitrogen or a refrigerator at a temperature of -80℃ to -10℃ for 12 to 24 hours. Finally, the pre-frozen sample was placed in a freeze dryer for freeze drying at a temperature of -80℃ for 48 to 72 hours to obtain an isotropic flame-retardant bacterial cellulose aerogel.

[0072] Example 7

[0073] Add 100g of bacterial cellulose dispersion (0.8wt%) to a three-necked flask and stir mechanically at 1000r / min. Weigh 0.8g of phosphorus / nitrogen-bridged organosiloxane and add it dropwise to the bacterial cellulose dispersion. Stir mechanically for 30min. Then weigh 0.4g of tetraethyl orthosilicate and add it dropwise to the bacterial cellulose dispersion. Stir mechanically for 30min until a uniform and stable milky white suspension is formed.

[0074] The obtained milky white suspension was placed in a mold and heated in a 60℃ electric thermostatic drying oven for 30 minutes for maturation. Then, the matured bacterial cellulose dispersion was pre-frozen with liquid nitrogen or a refrigerator at a temperature of -80℃ to -10℃ for 12 to 24 hours. Finally, the pre-frozen sample was placed in a freeze dryer for freeze drying at a temperature of -80℃ for 48 to 72 hours to obtain an isotropic flame-retardant bacterial cellulose aerogel.

[0075] Example 8

[0076] Add 100g of bacterial cellulose dispersion (0.8wt%) to a three-necked flask and stir mechanically at 1000r / min. Weigh 0.8g of phosphorus / nitrogen-bridged organosiloxane and add it dropwise to the bacterial cellulose dispersion. Stir mechanically for 30min. Then weigh 0.8g of tetraethyl orthosilicate and add it dropwise to the bacterial cellulose dispersion. Stir mechanically for 30min until a uniform and stable milky white suspension is formed.

[0077] The obtained milky white suspension was placed in a mold and heated in a 60℃ electric thermostatic drying oven for 30 minutes for maturation. Then, the matured bacterial cellulose dispersion was pre-frozen with liquid nitrogen or a refrigerator at a temperature of -80℃ to -10℃ for 12 to 24 hours. Finally, the pre-frozen sample was placed in a freeze dryer for freeze drying at a temperature of -80℃ for 48 to 72 hours to obtain an isotropic flame-retardant bacterial cellulose aerogel.

[0078] Example 9

[0079] Add 100g of bacterial cellulose dispersion (0.8wt%) to a three-necked flask and stir mechanically at 1000r / min. Weigh 1.6g of phosphorus / nitrogen-bridged organosiloxane and add it dropwise to the bacterial cellulose dispersion. Stir mechanically for 30min. Then weigh 1.6g of tetraethyl orthosilicate and add it dropwise to the bacterial cellulose dispersion. Stir mechanically for 30min until a uniform and stable milky white suspension is formed.

[0080] The obtained milky white suspension was placed in a mold and heated in a 60℃ electric thermostatic drying oven for 30 minutes for maturation. Then, the matured bacterial cellulose dispersion was pre-frozen with liquid nitrogen or a refrigerator at a temperature of -80℃ to -10℃ for 12 to 24 hours. Finally, the pre-frozen sample was placed in a freeze dryer for freeze drying at a temperature of -80℃ for 48 to 72 hours to obtain an isotropic flame-retardant bacterial cellulose aerogel.

[0081] Example 10

[0082] Add 100g of bacterial cellulose dispersion (0.8wt%) to a three-necked flask and stir mechanically at 1000r / min. Weigh 2.4g of phosphorus / nitrogen-bridged organosiloxane and add it dropwise to the bacterial cellulose dispersion. Stir mechanically for 30min. Then weigh 2.4g of tetraethyl orthosilicate and add it dropwise to the bacterial cellulose dispersion. Stir mechanically for 30min until a uniform and stable milky white suspension is formed.

[0083] The obtained milky white suspension was placed in a mold and heated in a 60℃ electric thermostatic drying oven for 30 minutes for maturation. Then, the matured bacterial cellulose dispersion was pre-frozen with liquid nitrogen or a refrigerator at a temperature of -80℃ to -10℃ for 12 to 24 hours. Finally, the pre-frozen sample was placed in a freeze dryer for freeze drying at a temperature of -80℃ for 48 to 72 hours to obtain an isotropic flame-retardant bacterial cellulose aerogel.

[0084] Comparative Example 1

[0085] 100g of bacterial cellulose dispersion (0.8wt%) was placed in a mold and heated in a 60℃ electric thermostatic drying oven for 30 minutes for maturation. Then, the matured bacterial cellulose dispersion was pre-frozen with liquid nitrogen or a refrigerator at a temperature of -80 to -10℃ for 12 to 24 hours. Finally, the pre-frozen sample was freeze-dried in a freeze dryer at a temperature of -80℃ for 48 to 72 hours to obtain pure bacterial cellulose aerogel, denoted as BC.

[0086] To verify the flame retardant and thermal insulation properties of the cellulose aerogel samples in Examples 1-10 and Comparative Example 1, the axial and radial peak heat release rates, limiting oxygen index, and thermal conductivity of the aerogels in each example and comparative example were measured. The test results are shown in Table 1 below.

[0087] Table 1. Flame retardant and thermal insulation properties of aerogel samples from Examples 1-10 and Comparative Example 1

[0088]

[0089] As shown in Table 1 above, the axial peak heat release rate (PHRR) and radial peak heat release rate (PHRR) of Examples 1-10 are significantly lower than those of Comparative Example 1, and their thermal conductivity is also lower. This indicates that all examples have good flame retardant and heat insulation effects. However, in Examples 8-10, the addition of excessive phosphorus / nitrogen-bridged organosiloxanes and tetraethyl orthosilicate reduces the porosity of the bacterial cellulose aerogel and significantly increases the thermal conductivity. Therefore, the heat insulation effect of Examples 8-10 is not as good as that of Examples 1-7. In addition, Examples 1-10 begin to burn between an oxygen index of 34-38%, exceeding the national flame retardant standard limiting oxygen index of 27%, and is much higher than the limiting oxygen index of the pure bacterial cellulose aerogel in Comparative Example 1, demonstrating excellent flame retardant effects.

[0090] Figure 1 The images show scanning electron microscope (SEM) images of the isotropic flame-retardant bacterial cellulose aerogel prepared in Example 1 of this invention, in the radial and axial directions. As can be seen from the SEM images, the pore distribution of the flame-retardant bacterial cellulose aerogel prepared in Example 1 does not differ significantly in the radial and axial directions.

[0091] Figure 2 This refers to an isotropic flame-retardant bacterial cellulose aerogel prepared according to Example 1 of the present invention. 29 SiMA SMR spectrum. (From...) Figure 2 It can be seen that silicon mainly forms Q. 3 The peak corresponds to the (SiO)3^Si-OH form of silicon. In addition, T also exists. 2 T 3 The peaks correspond to the forms (SiO)2(OH)SiC and (SiO)3SiC, respectively, indicating that silicon was successfully grafted onto the cellulose molecule.

[0092] Figure 3 This is a comparison of the limiting oxygen index (LOI) values ​​of the isotropic flame-retardant bacterial cellulose aerogel prepared in Example 1 of the present invention in the XY, XZ, and YZ directions, and that of the pure bacterial cellulose aerogel prepared in Comparative Example 1. Figure 3 It can be seen that the limiting oxygen index (LOI) values ​​of the aerogel prepared in Example 1 are much higher than those of pure bacterial cellulose aerogel in the XY, XZ, and YZ directions, exhibiting excellent flame retardant properties. Meanwhile, the LOI values ​​in the three directions are essentially the same, demonstrating the isotropic flame retardant properties of this aerogel.

[0093] Figure 4 This is a comparison of the heat release rate (HRR) and total heat release (THR) in the XY, XZ, and YZ directions of the isotropic flame-retardant bacterial cellulose aerogel prepared in Example 1 of the present invention, and that of the pure bacterial cellulose aerogel prepared in Comparative Example 1. Figure 4It can be seen that the heat release rate (HRR) and total heat release (THR) of the aerogel prepared in Example 1 in the XY, XZ, and YZ directions are much lower than those of pure bacterial cellulose aerogel, indicating that the aerogel prepared in Example 1 releases less heat during combustion and has higher fire safety performance. At the same time, the heat release rate (HRR) and total heat release (THR) in the three directions are basically the same, demonstrating the isotropic flame retardant properties of this aerogel.

[0094] Figure 5 These are physical images and conceptual diagrams of an isotropic flame-retardant bacterial cellulose aerogel prepared in Example 1 of this invention, demonstrating its fire warning function under butane flame combustion. Figure 5 It can be seen that during the combustion of butane flame, the surface of the aerogel rapidly carbonizes to form a dense graphite carbon layer. Since graphite has a certain conductivity, it changes the resistance of the aerogel surface, causing the alarm light to emit an alarm signal, thus achieving the effect of fire early warning.

[0095] Figure 6 Images of the front and back sides of an isotropic flame-retardant bacterial cellulose aerogel prepared in Example 1 of this invention after being subjected to continuous butane flame combustion for 180 seconds. Figure 6 As can be seen, after the aerogel prepared in Example 1 was subjected to continuous combustion in a butane flame at 1200°C for 180 seconds, a dense carbon layer was formed on the front side to prevent heat from being transferred to the interior, while only the back side was partially carbonized and was not burned through, demonstrating the excellent flame retardant effect of the aerogel.

[0096] Figure 7 The figure shows the temperature changes in the XZ and YZ directions of an isotropic flame-retardant bacterial cellulose aerogel prepared in Example 1 of this invention after being subjected to continuous butane flame combustion for 180 s. As can be seen from the figure, even under continuous butane flame combustion at 1200℃, the temperature of the aerogel in the XZ and YZ directions only remained at around 70℃, indicating its excellent heat insulation and flame-retardant effects. Furthermore, the temperature difference between the aerogel in these two directions is small, demonstrating excellent isotropy.

[0097] The flame response sensitivity and flame response intensity of Example 1 were compared with those of chitosan aerogel prepared in literature CN120192580A, sodium alginate / cellulose aerogel prepared in literature CN120173289A, and bacterial cellulose aerogel fiber prepared in CN119736793A to demonstrate the application advantages of an isotropic flame-retardant bacterial cellulose aerogel in fire early warning.

[0098] Comparative Example 2

[0099] Add 0.5g chitosan, 0.5g acetic acid, and 99mL deionized water to the reaction apparatus and stir magnetically until the chitosan is completely dissolved to obtain a chitosan solution with a chitosan aqueous solution mass fraction of 0.5wt% and an acetic acid concentration of 0.5wt%. Transfer the chitosan solution to a three-necked flask and stir mechanically at 900r / min. Weigh 0.5g of phosphorus / nitrogen-bridged organosiloxane and add it dropwise to the chitosan solution, stirring mechanically for 20min. Then weigh 0.15g of tetraethyl orthosilicate and add it dropwise to the chitosan solution, stirring mechanically for 40min until a uniform and stable white suspension is formed.

[0100] The obtained white suspension was placed in a mold and dried in a 60℃ electric thermostatic drying oven for 30 minutes for maturation. Then, the matured dispersion was pre-frozen with liquid nitrogen or a refrigerator at a temperature of -78 to -5℃ for 12 to 48 hours. Finally, the pre-frozen sample was placed in a freeze dryer for freeze drying at a temperature of -76℃ for 48 to 72 hours to obtain a flame-retardant, recyclable, compressible, reusable, and biodegradable chitosan aerogel.

[0101] Comparative Example 3

[0102] 0.5 g of sodium alginate and 99.5 mL of deionized water were added to the reaction apparatus and magnetically stirred until the sodium alginate was completely dissolved to obtain an aqueous solution of sodium alginate with a mass fraction of 0.5 wt%. 53.6 g of bacterial cellulose dispersion (bacterial cellulose content of 0.8 wt%, solvent of water) was added to the sodium alginate aqueous solution, and then stirred at 900 r / min for 40 min to obtain a sodium alginate / cellulose solution. 0.7 g of phosphorus / nitrogen-bridged organosiloxane was weighed and added dropwise to the sodium alginate / cellulose solution, and mechanically stirred for 20 min to obtain a mixture. Then, 0.26 g of tetraethyl orthosilicate was weighed and added dropwise to the mixture, and mechanically stirred for 40 min until a uniform and stable white suspension was formed.

[0103] The obtained white suspension was placed in a mold and dried in a 60℃ electric thermostatic drying oven for 30 minutes for maturation. The matured white suspension was pre-frozen using liquid nitrogen or a refrigerator at a temperature of -78 to -5℃ for 12 to 48 hours. The pre-frozen sample was then freeze-dried in a freeze dryer at a temperature of -76℃ for 48 to 72 hours to obtain flame-retardant, high-modulus, biodegradable sodium alginate / cellulose aerogel.

[0104] Comparative Example 4

[0105] Preparation of flame-retardant fire early warning bacterial cellulose aerogel fibers:

[0106] (1) Preparation of bacterial cellulose hydrogel fibers: 1g of bacterial cellulose powder was weighed and dissolved in 19g of 7% LiCl solution (solvent is N,N-dimethylacetamide), and ultrasonically stirred for 5h to prepare bacterial cellulose spinning solution; the above spinning solution was placed in a wet spinning device for spinning, the inner diameter of the spinning needle was 0.7mm, the extrusion rate was 80μL / min, and after 1.2 times stretching in a deionized water coagulation bath, bacterial cellulose hydrogel fibers were obtained;

[0107] (2) Preparation of PA@PPy flame-retardant conductive layer: Weigh 2.468g (0.036mol) of pyrrole, 4.052g (0.006mol) of phytic acid and 20g of isopropanol and mix them to obtain a mixture. Place the bacterial cellulose hydrogel fiber obtained in step (1) into the mixture and let it stand for 5min. Weigh 3.68g of ammonium persulfate and dissolve it in 20mL of water to obtain an ammonium persulfate solution. Then quickly add the ammonium persulfate solution to the mixture and let it stand for 5min. Finally, take out the soaked bacterial cellulose hydrogel fiber and wash it with deionized water 2-3 times to remove excess polypyrrole on the surface to obtain conductive cellulose hydrogel fiber.

[0108] (3) Preparation of ZnO@MXene nanohybrid material: 2g of lithium fluoride was added to 40mL of 9M hydrochloric acid aqueous solution and reacted at 25℃ for 30min. Then the temperature was raised to 35℃ and 2g of Ti3AlC2 was added. The reaction was continued for 24h. After that, the reaction solution was centrifuged, the lower precipitate was retained and washed with water until its pH was 7±0.5. Then the washed precipitate was mixed with water and sonicated for 60min. The upper suspension was collected and freeze-dried to obtain 2D Ti3C2Tx monolayer nanosheets (MXene powder). 1.04g of zinc nitrate hexahydrate, 1.6g of sodium hydroxide and 0.665g of MXene powder were weighed and added to 50mL of deionized water. After sonication for 30min, the mixture was transferred to a hydrothermal reactor and hydrothermally reacted at 120℃ for 12h. Finally, the reaction product was washed with water and dried to obtain ZnO@MXene nanohybrid material.

[0109] (4) Preparation of fire warning layer: The ZnO@MXene nano-hybrid material obtained in step (3) is added to water and ultrasonically stirred for 1 h to prepare a dispersion with a concentration of 5 mg / mL. The conductive cellulose hydrogel fiber obtained in step (2) is immersed in the above dispersion for 20 min. The immersed conductive cellulose hydrogel fiber is then taken out and freeze-dried (freeze-drying temperature is -40℃, time is 48 h) to obtain flame-retardant fire warning bacterial cellulose aerogel fiber.

[0110] This invention uses a DMM5100 resistance meter to determine the flame warning performance of an isotropic flame-retardant bacterial cellulose aerogel. In Example 1 and Comparative Examples 1-3, 2cm×2cm×1cm block aerogels were prepared. In Comparative Example 4, a 2cm×2cm fabric woven from aerogel fibers was prepared for testing. The test flame was a butane flame.

[0111] Table 2 Flame response performance of aerogel samples from Example 1 and Comparative Examples 1-4

[0112] sample Flame response sensitivity (s) Flame response intensity (%) Example 1 1.1 92.1 Comparative Example 1 none none Comparative Example 2 9.8 31.2 Comparative Example 3 11.7 23.9 Comparative Example 4 1.3 89.3

[0113] As shown in the table above, Example 1 exhibits a significantly reduced flame response time and a significantly improved flame response intensity compared to Comparative Examples 1-3. Furthermore, Example 1 demonstrates superior flame response performance compared to the flame-retardant fire warning bacterial cellulose aerogel fiber represented by Comparative Example 4, indicating that Example 1 possesses excellent flame response performance and can be used in the field of fire warning.

[0114] The above embodiments are merely illustrative and do not constitute a limitation on the scope of protection of this invention. The order of steps described is also not restrictive. Any obvious optimizations and improvements made to this invention by those skilled in the art based on existing common knowledge are included within the scope of protection defined by the claims of this invention.

Claims

1. A process for the preparation of an isotropic fire-retardant bacterial cellulose aerogel for fire warning, characterized by, The method comprises the following steps: (1) adding phosphorus / nitrogen bridged organosiloxane and tetraethyl orthosilicate into bacterial cellulose dispersion liquid in proportion, then stirring to obtain a milky white uniform stable suspension; the phosphorus / nitrogen bridged organosiloxane is prepared by the reaction of hexachlorocyclotriphosphazene and γ-aminopropylsilanetriol; (2) heating and aging the milky white suspension, then pre-cooling, and finally freeze-drying to obtain isotropic flame-retardant bacterial cellulose aerogel.

2. The production method according to claim 1, characterized by, The cellulose concentration in the bacterial cellulose dispersion liquid in step (1) is 0.5wt%-5wt%.

3. The production method according to claim 2, characterized by, The cellulose concentration in the bacterial cellulose dispersion liquid in step (1) is 0.8wt%-2wt%.

4. The production method according to claim 1, characterized by, The preparation process of the phosphorus / nitrogen bridged organosiloxane in step (1) is as follows: under nitrogen environment, hexachlorocyclotriphosphazene and γ-aminopropylsilanetriol are mixed in a mass ratio of 1:3-4, then stirring at 45-55℃ for 20-40min, then increasing the temperature to 75-85℃ and continuing to react for 2-4h to obtain a light yellow phosphorus / nitrogen bridged organosiloxane.

5. The preparation method according to claim 1, characterized in that, The mass ratio of the phosphorus / nitrogen bridged organosiloxane and bacterial cellulose in step (1) is 0.3-3:

1.

6. The production method according to claim 5, wherein The mass ratio of the phosphorus / nitrogen bridged organosiloxane and bacterial cellulose in step (1) is 0.5-2:

1.

7. The preparation method according to claim 1, characterized in that, The mass ratio of the tetraethyl orthosilicate and bacterial cellulose in step (1) is 0.2-3:

1.

8. The production method according to claim 7, characterized by, The mass ratio of the tetraethyl orthosilicate and bacterial cellulose in step (1) is 0.3-1:

1.

9. The method of claim 1, wherein, The stirring time in step (1) is 60-90min.

10. The method of claim 1, wherein, The heating and aging temperature in step (2) is 60-80℃, and the time is 30-50min.

11. The method of any one of claims 1-10, wherein, The pre-cooling temperature in step (2) is -80--10℃, and the time is 12-24h; the freeze-drying temperature is -80--70℃; and the freeze-drying time is 48-72h.

12. An isotropic fire-retardant bacterial cellulose aerogel, characterized in that, The bacterial cellulose aerogel is prepared according to the preparation method in any one of claims 1-11.

13. The use of the isotropic flame-retardant bacterial cellulose aerogel in claim 12 in the field of fire warning.

14. A method of improving the response sensitivity and response strength of a fire warning device, characterized by, The use of the isotropic flame-retardant bacterial cellulose aerogel in claim 13 as a functional component.

15. A fire early warning device with high response sensitivity and response strength, characterized in that, The use of the isotropic flame-retardant bacterial cellulose aerogel in claim 13.

16. The fire warning device according to claim 15, characterized in that The response sensitivity is 1.1s, and the flame response intensity is 92.1%.

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