Flexible silica nanofiber membranes with micron-sized fillers and their preparation method

Abstract

This invention relates to a flexible silica nanofiber membrane with micron-sized filler embedded in it and its preparation method. First, a filler / organic polymer mixture and a silica precursor solution are prepared, and then multi-channel combined spinning is performed using electrospinning technology to obtain a composite fiber membrane in which polymer / filler composite fibers and silica precursor hybrid fibers interweave. The organic components in both types of fibers are removed by high-temperature calcination, resulting in a flexible fiber / filler composite membrane with inorganic micron-sized filler embedded in the pores of the silica nanofibers. Because the micron-sized filler in this composite fiber membrane covers the pores between the fibers in situ and can undergo micro-slippage in local spaces, the composite membrane significantly reduces air convection while maintaining the flexibility and lightweight properties of silica fiber membranes. This composite membrane exhibits excellent thermal insulation, flame resistance, and high-temperature stability in scenarios with high-speed air convection, such as high-temperature, combustion, and explosion conditions.

Description

Technical Field

[0001] This invention belongs to the field of synthesis and preparation of inorganic composite ceramic fiber materials, and relates to a flexible silica nanofiber membrane with micron-sized filler embedded and its preparation method. Technical Background

[0002] Silica has extremely low thermal conductivity and coefficient of thermal expansion, while silica fiber membranes are soft / flexible thermal insulation materials with excellent thermal insulation properties and high-temperature stability. They are widely used in battery insulation layers, aerospace fuselage protection, building wall protection, solar collectors, industrial pipeline insulation, and fire-resistant clothing. Heat transfer occurs in three ways: conduction, convection, and radiation. Conduction is the movement of heat from hotter to cooler parts of an object, and silica's extremely low thermal conductivity prevents this conduction, significantly reducing heat transfer. However, under complex and extreme conditions, low thermal conductivity alone is insufficient for industrial applications, placing higher demands on the resistance to convection and radiation in silica fiber membrane materials.

[0003] The presence of numerous pores in fiber membranes allows for heat transfer via gas convection, meaning that heat convection remains a problem even within silica fiber membranes, affecting their thermal insulation performance. Chinese patent CN202211607713.5 discloses a method for preparing a high-strength, low-thermal-conductivity ceramic aerogel material, and Chinese patent CN202210610438.6 discloses a method for preparing a fiber composite aerogel flexible membrane. These patents utilize electrospinning technology to prepare silica fiber membranes, followed by the composite aerogel precursor liquid or the coating of silica sol onto the fiber surface, resulting in excellent heat resistance. However, the impregnation or coating methods can easily lead to increased brittleness in the aged composite fiber membrane, or the membrane may only maintain a certain degree of flexibility under very thin conditions. Surface coating can easily cause delamination during use, and the fiber layer and aerogel layer may not break simultaneously. Composite membrane materials prepared by directly combining fiber membranes with aerogel particles suffer from powder shedding during use, resulting in poor thermal insulation stability and potential environmental hazards. After nanofiber impregnation and loading, the connections between the fibers become tighter and more fixed, resulting in a significant decrease in the material's flexibility and severely affecting its mechanical properties and application range. More importantly, under high-temperature conditions, the heat radiation blocking effect of aerogel particles declines rapidly, necessitating the research of novel composite thermal insulation materials that simultaneously resist heat conduction, heat convection, and heat radiation under high-temperature conditions. Summary of the Invention

[0004] This invention provides a flexible silica nanofiber membrane with micron-sized filler embedded and its preparation method. The silica nanofiber membrane with this composite structure has the characteristics of low porosity, low thermal conductivity and coefficient of thermal expansion, strong high temperature resistance, excellent flexibility, good mechanical properties and excellent material stability.

[0005] This invention provides a method for preparing a flexible silica nanofiber membrane with micron-sized filler embedded in it, the specific steps of which are as follows:

[0006] Step 1: Disperse the inorganic micron filler into the solution of the organic polymer to prepare a polymer / micron filler mixture, which is used as spinning solution 1.

[0007] Step 2: The mixture of silicon source, solvent and catalyst is subjected to hydrolysis and condensation reaction under stirring to obtain silicon source hydrolysate. Then, polymer solution is added and mixed evenly to prepare silica precursor solution, which is used as spinning solution 2.

[0008] Step 3: Spinning solution 1 and spinning solution 2 are injected into different syringes, and electrospinned according to their proportions and combinations to prepare a composite fiber membrane with interwoven polymer / filler composite fibers and polymer / silica precursor hybrid fibers. Organic components in both types of fibers are removed by high-temperature calcination to obtain a flexible silica nanofiber membrane with micron-sized filler embedded in it.

[0009] As a preferred technical solution:

[0010] In the first step, dispersion can be carried out by means of ultrasound, stirring, etc., so that the filler is evenly dispersed in the organic polymer solution.

[0011] The inorganic micron filler is one or more of the following: hollow silica spheres, hollow glass microspheres, montmorillonite sheets, boron nitride nanosheets, graphene oxide nanosheets, and graphene nanosheets, with a filler size of 5µm-100nm.

[0012] In the first step, the polymer / micron filler mixture has excellent compatibility, which means that the filler does not undergo visible sedimentation when the polymer solution is left to stand for a long time.

[0013] The polymers used in the first step and the second step can be the same or different. The polymer can be one or more of polyvinyl alcohol, polyvinyl butyral, and polyvinylpyrrolidone.

[0014] In the second step, the silicon source is one or more of tetramethyl silicate, tetraethyl silicate, tetrapropyl silicate, tetrabutyl silicate, tetraphenyl silicate, silicon tetrachloride, and silicates; the solvent is one or more of deionized water, anhydrous ethanol, and N,N-dimethylformamide; and the catalyst is one or more of oxalic acid, phosphoric acid, hydrochloric acid, acetic acid, sulfuric acid, and nitric acid.

[0015] In the third step, spinning solution 1 and spinning solution 2 are simultaneously extruded for spinning and received by the same receiving device, with the number of syringes and injection rate of each being independent of each other.

[0016] In the third step, the ratio and combination of spinning solution 1 and spinning solution 2 make the mass ratio of silica nanofibers to micron fillers in the final fiber membrane 1:0.25-5. Electrospinning refers to the process of feeding the spinneret of the electrospinning equipment at a flow rate of 0.1-50 mL / h under conditions of 15-35℃ and relative humidity of 20-70%, while the spinneret is connected to a 10-100kV high-voltage power supply for electrospinning. The distance between the receiving device and the spinneret is 3-70 cm.

[0017] In the third step, the polymer / filler composite fiber refers to the filler being entirely or partially bound inside the fiber, with other parts of the filler exposed outside the fiber; the polymer / silica precursor hybrid fiber refers to the uniform distribution of silica and polymer components within the fiber; the interweaving refers to the random stacking and crossing of the polymer / filler composite fiber and the polymer / silica precursor hybrid fiber in three-dimensional space.

[0018] In the third step, the high-temperature calcination involves raising the temperature to 200-800℃ at a rate of 0.1-10℃ / min and maintaining it at the highest temperature for 10-360min.

[0019] In the third step, embedding refers to the calcined inorganic filler being trapped in the pores between the silica fibers and unable to fall off. There is no hard sintering between the inorganic filler and the silica, and the inorganic filler can rotate and slide slightly in the pores between the fibers.

[0020] This invention utilizes electrospinning technology to prepare a flexible silica nanofiber membrane with micron-sized fillers embedded in a single process. The uniformly distributed inorganic fillers in the resulting nanofiber membrane not only possess high-temperature resistance, but also exhibit random stacking and cross-linking of the fillers and fibers in three-dimensional space. This results in low heat convection and low heat transfer properties while maintaining excellent flexibility and strength. Compared to existing methods where aerogels adhere to the surface of the fiber membrane or penetrate into its pores, the composite nanofiber membrane of this invention has a larger pore coverage, and the cross-stacked fiber structure provides stronger binding force to the fillers, preventing them from detaching. Furthermore, the inorganic fillers can undergo slight rotation and sliding within the pores between the fibers, ensuring the nanofiber membrane's flexibility and other excellent mechanical properties, making it an ideal material for thermal insulation films.

[0021] This invention discloses a flexible silica nanofiber membrane with micron-sized filler embedded in it and its preparation method. The method utilizes electrospinning technology to prepare a composite structure in which the filler and fibers are randomly stacked and intersected in three-dimensional space. This overcomes the adverse effects of heat convection in the pores of the fiber membrane on its thermal insulation performance, as well as the drawbacks of traditional thermal insulation hybrid membranes, such as their rigidity and the ease with which the covering material detaches. Furthermore, the preparation method of this invention is simple, and the resulting nanofiber membrane possesses advantages such as low porosity, low thermal conductivity, high temperature resistance, flame retardancy, thermal dimensional stability, excellent mechanical properties, good flexibility, and minimal material component detachment. Attached Figure Description

[0022] Figure 1 This is a SEM image of the flexible silica nanofiber membrane with micron-sized filler embedded in Example 1. Detailed Implementation

[0023] The present invention will be further described below with reference to specific embodiments. It should be understood that these embodiments are for illustrative purposes only and are not intended to limit the scope of the invention. Furthermore, it should be understood that after reading the teachings of this invention, those skilled in the art can make various alterations or modifications to the invention, and these equivalent forms also fall within the scope defined by the appended claims.

[0024] Example 1

[0025] Step 1: Disperse 1g of boron nitride nanosheets uniformly by ultrasonication, then add them to a mixed solution of 5g of 20wt% polyvinylpyrrolidone in N,N-dimethylformamide and 4g of anhydrous ethanol, and stir magnetically for 10h to prepare a polyvinylpyrrolidone / boron nitride nanosheet mixture with excellent compatibility, which is used as spinning solution 1.

[0026] Step 2: A mixture of 30g tetraethyl silicate, 27g N,N-dimethylformamide, 4.5g deionized water and 0.3g phosphoric acid was magnetically stirred for 10h to carry out a hydrolysis and condensation reaction to obtain a silicon source hydrolysate. Then, 22g of 20wt% polyvinylpyrrolidone solution was added and stirred for another 10h to mix evenly, thus preparing a silica precursor solution, which was used as spinning solution 2.

[0027] Step 3: Spinning solution 1 and spinning solution 2 were injected into different syringes, and their ratio and combination were adjusted for electrospinning to achieve a 1:1 mass ratio of silica nanofibers to boron nitride nanosheet fillers in the final fiber membrane. Both spinning solutions were simultaneously extruded and received by the same receiving device. The spinning temperature was 23℃, relative humidity was 49%, injection speed was 0.8 mL / h, spinning voltage was 22 kV, and receiving distance was 15 cm. A composite fiber membrane consisting of interwoven polyvinylpyrrolidone / boron nitride nanosheet composite fibers and polyvinyl alcohol / silica precursor hybrid fibers was prepared. Organic components in both fibers were removed by calcining at a rate of 5℃ / min from room temperature to 600℃ and holding at the highest temperature for 300 min, resulting in a flexible fiber / filler composite membrane with inorganic micron-fillers embedded in the pores of silica nanofibers. Its morphology is as follows. Figure 1 As shown, from Figure 1 As can be seen, the boron nitride nanosheets are bound inside the silica fibers, randomly stacking and intersecting with the silica fibers in three-dimensional space, while simultaneously covering and blocking the pores where the fibers intersect. Furthermore, the boron nitride nanosheets can undergo small-amplitude rotation and sliding within the pores between the fibers. This flexible silica nanofiber membrane, inlaid with micron-sized boron nitride nanosheets, does not burn under the outer flame of an alcohol lamp; after calcination at 1000℃ for 2 hours, it only experiences a heat loss of 0.5% and retains its flexibility, folding up to 180°; the air permeability of this flexible silica nanofiber / boron nitride nanosheet composite membrane is 210 (KPa·s / m) / mm; its thermal insulation performance on a 600℃ hot table is as follows: after standing for 5 minutes, the cold surface of the flexible silica nanofiber / boron nitride nanosheet composite membrane only heats up to 100℃, and the heating rate does not exceed 1℃ / s, meeting the thermal insulation requirements of the national standard GB38031-2020 "Safety Requirements for Electric Vehicle Batteries". Example 2

[0028] Step 1: Disperse 1g of hollow silica microspheres uniformly by ultrasonication for 30min, then add them to an aqueous solution of 7.3g of 12.5 wt% polyvinyl alcohol and stir magnetically for 10h to prepare a polyvinyl alcohol / hollow silica microsphere mixture with excellent compatibility, which is used as spinning solution 1.

[0029] Step 2: A mixture of 33g tetraethyl silicate, 27.3g water and 0.3g phosphoric acid was magnetically stirred for 10h to carry out a hydrolysis and condensation reaction to obtain a silicon source hydrolysate. Then, 24.1g of 12.5wt% polyvinyl alcohol solution was added and stirred for another 10h to mix evenly, thus preparing a silica precursor solution, which was used as spinning solution 2.

[0030] Step 3: Spinning solution 1 and spinning solution 2 were injected into different syringes, and their ratio and combination were adjusted for electrospinning to achieve a 1:1 mass ratio of silica nanofibers to hollow silica microsphere fillers in the final fiber membrane. Both spinning solutions were simultaneously extruded and received by the same receiving device. The spinning temperature was 24℃, relative humidity was 45%, injection speed was 0.7 mL / h, spinning voltage was 20 kV, and receiving distance was 20 cm. A composite fiber membrane consisting of interwoven polyvinyl alcohol / hollow silica microsphere composite fibers and polyvinyl alcohol / silica precursor hybrid fibers was prepared. Organic components in both fibers were removed by calcining at a rate of 3℃ / min from room temperature to 700℃ and holding at the highest temperature for 240 min, resulting in a flexible fiber / filler composite membrane with inorganic micron-fillers embedded in the pores of silica nanofibers. The product obtained in this example has a similar composite structure to that of Example 1, with random stacking and crossing of fillers and fibers in three-dimensional space. The flexible silica nanofiber membrane embedded with hollow silica microspheres does not burn under the outer flame of an alcohol lamp; after calcination at 1000℃ for 2 hours, it only loses 0.4% of its heat and remains flexible enough to be folded 180°; the air permeability of the flexible silica nanofiber / hollow silica microsphere composite membrane is 188 (KPa·s / m) / mm; the thermal insulation performance on a 600℃ hot plate is as follows: after standing for 5 minutes, the cold surface of the flexible silica nanofiber / hollow silica microsphere composite membrane only rises to 113℃, and the heating rate does not exceed 1℃ / s, which meets the thermal insulation requirements in the national standard GB38031-2020 "Safety Requirements for Electric Vehicle Batteries".

[0031] Example 3

[0032] Step 1: 1g of graphene oxide nanosheets were ultrasonically dispersed for 6 hours and then added to an ethanol solution of 7.3g of 12.5wt% polyvinyl butyral solution. The mixture was magnetically stirred for 10 hours to prepare a polyvinyl butyral / graphene oxide nanosheet mixture with excellent compatibility, which was used as spinning solution 1.

[0033] Step 2: A mixture of 20g tetraethyl silicate, 14g water and 0.16g oxalic acid was magnetically stirred for 10h to carry out a hydrolysis and condensation reaction to obtain a silicon source hydrolysate. Then, 15g of 12.5wt% polyvinyl alcohol solution was added and stirred for another 10h to mix evenly, thus preparing a silica precursor solution, which was used as spinning solution 2.

[0034] Step 3: Spinning solution 1 and spinning solution 2 were injected into different syringes, and their ratio and combination were adjusted for electrospinning. The mass ratio of silica nanofibers to graphene oxide nanosheet fillers in the final fiber membrane was 2:1, and both spinning solutions were extruded simultaneously and received by the same receiving device. The spinning temperature was 24℃, the relative humidity was 40%, the injection speed was 0.7mL / h, the spinning voltage was 18kV, and the receiving distance was 10cm. A composite fiber membrane with interwoven polyvinyl butyral / graphene oxide nanosheet composite fibers and polyvinyl alcohol / silica precursor hybrid fibers was prepared. The organic components in the two fibers were removed by calcining at a heating rate of 3℃ / min from room temperature to 800℃ and holding at the highest temperature for 150min, resulting in a flexible fiber / filler composite membrane with inorganic micron-fillers embedded in the pores of silica nanofibers. The product obtained in this example has a similar composite structure of random stacking and crossing of fillers and fibers in three-dimensional space as in Example 1. The flexible silica nanofiber membrane embedded with micron-sized graphene oxide nanosheets does not burn under the outer flame of an alcohol lamp; after calcination at 1000℃ for 2 hours, it only loses 0.5% of its heat and remains flexible enough to be folded 180°; the air permeability of the flexible silica nanofiber / graphene oxide nanosheet composite membrane is 200 (KPa·s / m) / mm; the thermal insulation performance on a 600℃ hot plate is as follows: after standing for 5 minutes, the cold surface of the flexible silica nanofiber / graphene oxide nanosheet composite membrane only rises to 105℃, and the heating rate does not exceed 1℃ / s, which meets the thermal insulation requirements in the national standard GB38031-2020 "Safety Requirements for Electric Vehicle Batteries".

[0035] Comparative Example 1

[0036] Step 1: A mixture of 33g tetraethyl silicate, 27.3g water and 0.195ml phosphoric acid was magnetically stirred for 10h to carry out a hydrolysis and condensation reaction to obtain a silicon source hydrolysate. Then, 24.1g of 12.5wt% polyvinyl alcohol solution was added and stirred for another 10h to mix evenly, thus preparing a silica precursor solution, which was used as a spinning solution.

[0037] Step 2: The spinning solution was injected into a syringe for electrospinning at a temperature of 24℃, a relative humidity of 45%, an injection rate of 0.7 mL / h, a spinning voltage of 20 kV, and a receiving distance of 20 cm. A fiber membrane composed of polyvinyl alcohol / silica precursor hybrid fibers was prepared. Organic components in the fibers were removed by calcining at a rate of 3℃ / min from room temperature to 700℃ and holding at the highest temperature for 240 min, resulting in a flexible silica nanofiber membrane without micron-filler embeddings. The flexible silica nanofiber membrane does not burn under the outer flame of an alcohol lamp; after calcination at 1000℃ for 2 hours, it only loses 0.3% of its heat and remains flexible enough to be folded 180°; its heat insulation performance on a 600℃ hot plate is as follows: after standing for 5 minutes, the cold surface of the flexible silica nanofiber membrane heats up to 300℃, and the heating rate exceeds 1℃ / s, which does not meet the heat insulation requirements in the national standard GB38031-2020 "Safety Requirements for Electric Vehicle Batteries".

[0038] The embodiments described above are merely illustrative of several implementations of the present invention, and while the descriptions are detailed, they should not be construed as limiting the scope of the present invention. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of the present invention, and these modifications and improvements all fall within the scope of protection of the present invention. Therefore, the scope of protection of the present invention should be determined by the appended claims.

Claims

1. A method for preparing a flexible silica nanofiber membrane with micron-sized filler embedded in it, characterized in that, Includes the following steps: Step 1: Disperse the inorganic micron filler in the solution of the organic polymer to prepare a polymer / micron filler mixture, which is used as spinning solution 1; Step 2: The mixture of silicon source, solvent and catalyst is subjected to hydrolysis and condensation reaction under stirring to obtain silicon source hydrolysate. Then, polymer solution is added and mixed evenly to prepare silica precursor solution as spinning solution 2. Step 3: Spinning solution 1 and spinning solution 2 are injected into different syringes respectively, and electrospinned according to the ratio and combination to prepare a composite fiber membrane with polymer / filler composite fibers and polymer / silica precursor hybrid fibers interwoven. The organic components in the two fibers are removed by high-temperature calcination to obtain a flexible silica nanofiber membrane with micron-filler embedded. In step 3, spinning solution 1 and spinning solution 2 are extruded simultaneously for spinning and received by the same receiving device. The number of syringes and injection rate of each are independent. The ratio and combination of spinning solution 1 and spinning solution 2 make the mass ratio of silica nanofibers to micron-filler in the final fiber membrane 1:0.25-5. Electrospinning refers to the process of feeding the spinneret of the electrospinning equipment at a flow rate of 0.1-50 mL / h under the conditions of 15-35 ℃ and relative humidity of 20-70%, while the spinneret is connected to a 10-100 kV high-voltage power supply for electrospinning. The distance between the receiving device and the spinneret is 3-70 cm.

2. The method for preparing a flexible silica nanofiber membrane with micron-sized filler embedded according to claim 1, characterized in that, In the first step, the inorganic micron filler is one or more of the following: hollow silica spheres, hollow glass microspheres, montmorillonite sheets, boron nitride nanosheets, graphene oxide nanosheets, and graphene nanosheets, and the inorganic micron filler has a mass percentage of 1-50 wt% in the spinning solution 1.

3. The method for preparing a flexible silica nanofiber membrane with micron-sized filler embedded according to claim 1, characterized in that, The polymers in the first step and the second step may be the same or different. The polymers are one or more of polyvinyl alcohol, polyvinyl butyral, and polyvinylpyrrolidone. The polymers have a mass percentage of 30-70 wt% in spinning solution 1 and a mass percentage of 20-40 wt% in spinning solution 2.

4. The method for preparing a flexible silica nanofiber membrane with micron-sized filler embedded according to claim 1, characterized in that, The silicon source mentioned in the second step is one or more of tetramethyl silicate, tetraethyl silicate, tetrapropyl silicate, tetrabutyl silicate, tetraphenyl silicate, silicon tetrachloride, and silicates, and the silicon source accounts for 30-50 wt% of the spinning solution 2 by mass; the solvent is one or more of deionized water, anhydrous ethanol, and N,N-dimethylformamide, and the solvent accounts for 25-45 wt% of the spinning solution 2 by mass; the catalyst is one or more of oxalic acid, phosphoric acid, hydrochloric acid, acetic acid, sulfuric acid, and nitric acid, and the catalyst accounts for 0.1-1 wt% of the spinning solution 2 by mass.

5. The method for preparing a flexible silica nanofiber membrane with micron-sized filler embedded according to claim 1, characterized in that, In the third step, the polymer / filler composite fiber refers to the filler being entirely or partially bound inside the fiber, with other parts of the filler exposed outside the fiber; the polymer / silica precursor hybrid fiber refers to the uniform distribution of silica and polymer components within the fiber; the interweaving refers to the random stacking and crossing of the polymer / filler composite fiber and the polymer / silica precursor hybrid fiber in three-dimensional space.

6. The method for preparing a flexible silica nanofiber membrane with micron-sized filler embedded according to claim 1, characterized in that, In the third step, the high-temperature calcination is carried out by raising the temperature to 200-800℃ at a rate of 0.1-10℃ / min and maintaining it at the highest temperature for 10-360 min.

7. The method for preparing a flexible silica nanofiber membrane with micron-sized filler embedded according to claim 1, characterized in that, In the third step, the embedding refers to the calcined inorganic filler being trapped in the pores between the silica fibers and unable to fall off. There is no hard sintering between the inorganic filler and the silica, and the inorganic filler undergoes a small-amplitude rotation and sliding in the pores between the fibers.

8. A flexible silica nanofiber membrane with micron-filler embedded in it, prepared by the method of any one of claims 1-7.

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