Flexible light-weight heat-insulation streamline oxide nanofiber aerogel as well as preparation method and application of flexible light-weight heat-insulation streamline oxide nanofiber aerogel

Abstract

The invention discloses a flexible light heat-insulation streamline oxide nanofiber aerogel and a preparation method and application thereof.The fiber aerogel is prepared through preparation of a spinning precursor solution, an air flow spinning technology and a heat treatment process, the spinning solution is stretched into fibers through the air flow spinning technology, and under the influence of a flow field, the flexible light heat-insulation streamline oxide nanofiber aerogel is obtained. The fibers present streamlines with different curvatures, high-quality dry fibers are obtained through a heating field, and the high-quality dry fibers are stacked in a receiver to form a three-dimensional structure; and finally, the three-dimensional streamline oxide nanofiber aerogel with ultralow thermal conductivity and low density is obtained by combining thermal treatment with a folding process, has excellent thermal protection performance and can be widely applied as a light high-temperature-resistant thermal insulation material.

Description

TECHNICAL FIELD

[0001] The present application relates to an oxide nanofiber aerogel, in particular to a flexible lightweight thermal insulation streamline oxide nanofiber aerogel, and also relates to a preparation method and application of the aerogel. BACKGROUND

[0002] Aerogel is a material with low thermal conductivity and low density, which is widely used as a thermal insulation material in aerospace, building equipment, textiles and other industries. However, the ceramic aerogel prepared by traditional methods is brittle and the structure is easy to collapse. Nanofiber has the advantages of high porosity, high surface area, multi-scale fiber diameter and pore size, good interconnected pore structure, and light weight and low density. Nanofiber aerogel has the advantages of both, overcoming the disadvantage of brittleness while maintaining excellent temperature-resistant thermal insulation performance. However, traditional fiber spinning technology is low in efficiency, and mainly forms a two-dimensional fiber membrane, which is further processed into a three-dimensional nanofiber aerogel through freeze-drying or 3D printing technology. These methods are not only complicated and energy-consuming, but also do not fully utilize the advantages of nanofiber aerogel.

[0003] High-speed airflow is used as a driving force for spinning fibers from a solution. The airflow-induced shear force at the gas-liquid interface refines the solution extruded from the needle tip, forming a liquid jet along the flow direction. At the same time, the airflow effectively helps the solvent to evaporate, leaving high-quality dry fibers. Solution blowing can quickly produce nanofibers in an efficient and high-yield manner. At the same time, the high-speed airflow blown first forms a jet, and then forms a complex three-dimensional turbulent flow field, which makes the generated nanofibers entangle with each other in a complex trajectory, more effectively forming a random three-dimensional nanofiber aerogel structure. However, based on the existing reports on the principle of airflow spinning, there are still problems such as the influence of air humidity and other environmental factors on the airflow, the easy hardening of the receiver, and the need to use special equipment to form special structures, which makes the operation more complex and requires a higher environment. SUMMARY

[0004] The purpose of the present application is to provide a flexible lightweight thermal insulation streamline oxide nanofiber aerogel with low density, high porosity and high surface area, and to provide a preparation method of the aerogel and its application in flame-retardant thermal insulation materials.

[0005] Technical solution: The flexible lightweight thermal insulation streamline oxide nanofiber aerogel of the present application has a diameter of 100-800 nm and presents a streamline shape, and has a core-shell structure, wherein the inner layer is mainly composed of porous low-thermal-conductivity silicon oxide, and the outer layer is wrapped with dense aluminum oxide, both of which are amorphous materials. The preparation only uses a single inner needle, and the special structure is formed through fluid mechanics mechanism and phase separation in the heating process; the preparation method comprises the following steps:

[0006] (1) Spinning solution configuration: the spinning solution is composed of A bottle and B bottle; the A bottle is: polyvinyl butyral (PVB) and polyvinylpyrrolidone (PVP) are dissolved in ethanol in proportion, and stirring is performed to obtain a uniform and transparent solution with a mass fraction of 8-15 wt.%; the B bottle is: ethanol, water, oxalic acid, and tetraethyl orthosilicate (TEOS) are mixed and stirred to obtain a condensed silicon solution, and then acetic acid, aluminum acetylacetonate, and pore-forming agent cetyltrimethylammonium bromide (CTAB) are added, and stirring is performed for 20 minutes to clarify; the B bottle is mixed into the A bottle, and stirring is performed for 4 hours to obtain a uniform spinning solution;

[0007] (2) Airflow spinning: the uniformly stirred precursor spinning solution is moved into the injector of the airflow spinning process device, the spinning needle, the air jet connector, and the injector are combined under normal pressure environment, the pressure valve connected to the air compressor is adjusted and controlled, the constant output airflow pressure of the spinning solution is about 0.1-0.3 MPa, the solution advancing speed in the pipe is set to 15-30 mL / h, and the solution is connected and wound in the receiver through multi-stage traction in the flow field, and accumulated into a flexible three-dimensional polymer nanofiber material.

[0008] (3) Heat treatment: the obtained flexible three-dimensional polymer nanofiber material is shaped through folding process and then subjected to heat treatment, first increased to 200-300℃ at a heating rate of 1-2℃ / min, so that the organic polymer is decomposed in this process; then increased to 800-1000℃ at a heating rate of 1-3℃ / min, and kept for 90-120 min for calcination, to obtain a flexible lightweight thermal insulation streamline oxide nanofiber aerogel with ultra-low thermal conductivity and three-dimensional structure.

[0009] In step (1), in the A bottle, the molecular weight of the polyvinyl butyral is 90000-1200000, and the molecular weight of the polyvinylpyrrolidone is 80000-1300000; the mass ratio of the high molecular polymers PVB, PVP, and ethanol is 0.15-16:0-0.05:0.79-0.87.

[0010] In the B bottle, the mass ratio of the ethanol, water, oxalic acid, and tetraethyl orthosilicate is 0.48-0.74:0.06-0.12:0.0015-0.003:0.20-0.39; the mass-volume ratio of the silicon solution, aluminum acetylacetonate, acetic acid, and cetyltrimethylammonium bromide is 0.32-0.54:0.13-0.19:0.35-0.55:0.0004-0.0006.

[0011] In step (2), the size of the spinning needle is selected to be 21-25G, and the volume of the injector is 5-100 mL.

[0012] In step (2), the receiver is a combination of a gauze and a mesh basket, and a heating field is arranged between the spinning needle and the receiver at a distance of 40-80 cm to accelerate the volatilization of the solution and obtain high-quality dry fibers.

[0013] In step (2), the pressure of the air compressor is 0.4-0.8 MPa, which is higher than the output pressure to ensure stable airflow; the spinning environment temperature is 10-40 DEG C, and the peripheral humidity is 10-70%.

[0014] In step (3), the folding process is shaped into a square type folding or a Z type folding.

[0015] The flexible lightweight thermal flow line oxide nanofiber aerogel described above can also be applied in flame-retardant thermal insulation materials.

[0016] Invention principle: the flexible lightweight thermal flow line oxide nanofiber aerogel of the application is prepared by high-speed airflow spinning, combined with calcination and folding process, and has a core-shell structure and presents a streamlined fiber aerogel, the preparation method is more efficient and high-speed, safe and convenient, which provides strong support for realizing industrialization and large-scale production, and paves the way for exploring new application fields of nanofiber-based materials requiring large-scale production.

[0017] The application selects nanofibers with large aspect ratio and high specific surface area as basic building blocks for assembling lightweight nanofiber aerogels. Among them, the precursor liquid is prepared by hydrolysis and polycondensation of tetraethyl orthosilicate as raw material to prepare a long-chain silicon matrix, and then acetylacetone aluminum is dissolved in acetic acid, and is mixed with a polymer spinning aid and a pore former, and a homogeneous spinning solution is obtained after stirring. The spinning solution is stretched into fibers by airflow spinning process, and the fibers present different curvature streamline under the influence of the flow field, and high-quality dry fibers are obtained by heating field, and the three-dimensional structure is accumulated in the receiver; the three-dimensional flexible fibers are placed in a muffle furnace for heat treatment, and can be combined with the folding process to shape, and finally the three-dimensional streamlined oxide nanofiber aerogel with ultra-low thermal conductivity and low density is obtained, which is aimed at preparing ceramic nanofiber aerogel with low thermal conductivity, high temperature oxidation resistance, high mechanical strength and lightweight characteristics.

[0018] The simple oxide element silicon aluminum is selected in the application to avoid some existing nanofiber aerogels containing organic components or excessive elements, and excellent force and thermal stability is achieved only through structural design and intrinsic characteristics. The porous streamline fiber structure is prepared through the laminar flow of liquid in the small inner needle and the turbulent flow mechanism in the gas flow, combined with the phase shift mechanism of aluminum in the calcination process. Knudsen effect explains the relationship between pore and gas thermal conductivity coefficient, and the pores in the fiber act as small heat insulation rooms, effectively reducing heat transfer. The different compositions and structures of the inner layer and the outer layer further block heat at the interface, and the structure of the outer layer alumina and the inner layer silicon oxide has excellent heat dissipation effect due to the difference in thermal potential. The streamline structure formed by gas spinning provides a longer propagation path for solid heat conduction, which benefits heat transfer and stress distribution. The high porosity formed in the manufacturing process of three-dimensional fiber aerogel provides sufficient space for air trapping. Since air is a poor thermal conductor, this effectively prevents heat transfer. It is the basis of aerogel and helps excellent thermal insulation performance. The complex network configuration also helps to reduce heat convection. Enough space also leads to lower density. Based on the above cross-scale structural effects, the nanofiber aerogel as a whole exhibits extremely low thermal conductivity. At the same time, a thermal field is introduced to improve the physical field environment of the spinning and accelerate the performance of the solvent, making the process smoother, and a framework design is adopted for the receiver, and a yarn net is used for receiving, which improves the quality of the collected material. Moreover, the calcination temperature gradient is designed in the heat treatment process, which reduces the brittleness of the material caused by rapid heating and improves the flexibility of the oxide nanofiber aerogel.

[0019] The prepared oxide nanofiber and composite material / structure are applied in different functional scenarios including filtration, flame retardation, thermal insulation, explosion prevention, sound insulation, catalysis, etc., meet the functional integration of flexible filling, structure construction, device assembly, etc. heat protection application scenarios, and can be widely used as light weight and high temperature resistant thermal insulation materials.

[0020] Advantages: Compared with the prior art, the application has the following remarkable advantages: (1) The flexible light weight thermal insulation streamline oxide nanofiber aerogel of the application has a core-shell structure, which is beneficial to thermal insulation and rapid heat dissipation; the nanofiber presents a streamline shape, which is more advantageous for prolonging the heat conduction path; the fiber is randomly wound in the airflow field in the receiver and continuously collected, forming a three-dimensional nanofiber aerogel structure with low density, high porosity and high surface area, which improves the thermal insulation performance and mechanical properties; the density of the aerogel is 8-100 mg / cm 3, the thermal conductivity is only 7-22 mW / (m*K), which can expand more functional roles while maintaining temperature-resistant and heat-insulating performance; (2) the preparation method has a simple process flow, high spinning speed, high efficiency, safety and energy saving, is conducive to realizing industrialization and large-scale production, realizing macro rapid and efficient preparation of high-performance multifunctional lightweight temperature-resistant and heat-insulating flexible oxide nanofiber aerogel materials, and meeting the needs of multifunctional applications and complex devices. BRIEF DESCRIPTION OF DRAWINGS

[0021] Figure 1 It is a physical diagram of the flexible lightweight streamlined heat-insulating oxide nanofiber aerogel;

[0022] Figure 2 It is a scanning electron microscope image of the flexible lightweight streamlined heat-insulating oxide nanofiber aerogel, wherein A is the aerogel structure of fiber winding and connection, B is a streamlined nanofiber, and C is a single fiber structure;

[0023] Figure 3 It is a density photo of the flexible lightweight streamlined heat-insulating oxide nanofiber aerogel;

[0024] Figure 4 It is a thermal protection performance diagram of the flexible lightweight streamlined heat-insulating oxide nanofiber aerogel, wherein A is temperature-resistant and flame-retardant performance, and B is a heat-insulating performance infrared thermal imaging diagram. DETAILED DESCRIPTION

[0025] The technical solutions of the present application will be further described below in combination with examples, and the test materials used in the examples can be purchased through a conventional route.

[0026] Example 1

[0027] The preparation method of the flexible lightweight heat-insulating streamlined oxide nanofiber aerogel of the present application comprises the following steps:

[0028] (1) A bottle: 3g of polyvinyl butyral is weighed and dissolved in 30mL of ethanol, stirred overnight to obtain a uniform transparent solution; B bottle: 20mL of ethanol, 2mL of water, 0.05g of oxalic acid, 6.25g of tetraethyl orthosilicate are weighed and stirred overnight to obtain a long-chain silicon solution after condensation, then 40mL of acetic acid and 9.72g of aluminum acetylacetone and 0.3g of cetyltrimethylammonium bromide are added, and the mixture is stirred for twenty minutes to clarify; the B bottle is mixed into the A bottle, and after stirring for four hours, a uniform spinning solution is obtained;

[0029] (2) The uniformly stirred precursor spinning solution is moved into a 50 mL syringe of the air flow spinning process device, and the bubble in the extrusion tube is extruded. At room temperature, a relative humidity of 30%, and a normal pressure environment, a 21G spinning needle, a gas spray joint, and the syringe are combined. The air compressor is adjusted to 0.6 MPa, the connected pressure valve is constant at about 0.15 MPa, the set advancing speed is 20 mL / h, the spinning needle and the receiver are 50 cm apart, a heating field is arranged therebetween, a gauze is covered in the frame as a receiver to collect the yarn, and the accumulated flexible three-dimensional polymer nanofiber material is stacked;

[0030] (3) Heat treatment: The flexible fiber material obtained in the above step is folded into a block in a zigzag shape, placed in a box furnace for heat treatment, first raised to 200℃ at a heating rate of 2℃ / min, so that the organic polymer is decomposed in this process; then raised to 900℃ at a heating rate of 3℃ / min, and kept at 900℃ for 2h, finally obtained a flexible lightweight thermal insulation streamline oxide nanofiber aerogel with ultra-low thermal conductivity and three-dimensional structure. Due to its good flexibility, shapeability and thermal protection performance, it can be assembled with devices and expand more functional scene effects.

[0031] Example 2

[0032] The preparation method of the flexible lightweight thermal insulation streamline oxide nanofiber aerogel of the present application comprises the following steps:

[0033] (1) A bottle: 3g of polyvinylpyrrolidone and 1g of polyvinyl butyral are weighed and dissolved in 30mL of ethanol, stirred overnight to obtain a uniform transparent solution; B bottle: 20mL of ethanol, 2mL of water, 0.05g of oxalic acid, 6.25g of tetraethyl orthosilicate are weighed and stirred overnight to obtain a long-chain silicon solution after condensation, then 40mL of acetic acid and 9.72g of aluminum acetylacetonate and 0.3g of cetyltrimethylammonium bromide are added, stirred for twenty minutes, and then clarified; the B bottle is mixed into the A bottle, stirred for four hours, and then a uniform spinning solution is obtained;

[0034] (2) The uniformly stirred precursor spinning solution is moved into a 50 mL syringe of the air flow spinning process device, and the bubble in the extrusion tube is extruded. At room temperature, a relative humidity of 30%, and a normal pressure environment, a 21G spinning needle, a gas spray joint, and the syringe are combined. The air compressor is adjusted to 0.6 MPa, the connected pressure valve is constant at about 0.15 MPa, the set advancing speed is 20 mL / h, the spinning needle and the receiver are 50 cm apart, a heating field is arranged therebetween, a gauze is covered in the frame as a receiver to collect the yarn, and the accumulated flexible three-dimensional polymer nanofiber material is stacked;

[0035] (3) heat treatment: the flexible fiber material obtained in the above step is folded into a block in a zigzag manner, placed in a box furnace for heat treatment, first raised to 200℃ at a temperature rising rate of 2℃ / min, so that the organic polymer is decomposed in this process; then raised to 900℃ at a temperature rising rate of 3℃ / min, and kept at 900℃ for 2h, finally obtaining the flexible lightweight heat-insulating flow line oxide nanofiber aerogel with ultra-low thermal conductivity and three-dimensional structure.

[0036] Example 3

[0037] The preparation method of the flexible lightweight heat-insulating flow line oxide nanofiber aerogel of the present application comprises the following steps:

[0038] (1) A bottle: 3g of polyvinylpyrrolidone and 1g of polyvinyl butyral are weighed and dissolved in 30mL of ethanol, stirred overnight to obtain a uniform transparent solution; B bottle: 10mL of ethanol, 2mL of water, 0.05g of oxalic acid, 6.25g of tetraethyl orthosilicate are weighed and stirred overnight to obtain a long-chain silicon solution after condensation, then 30mL of acetic acid and 6.48g of aluminum acetylacetone and 0.3g of cetyltrimethylammonium bromide are added, stirred for twenty minutes and then clarified; the B bottle is mixed into the A bottle, and after stirring for four hours, a uniform spinning solution is obtained;

[0039] (2) The uniformly stirred precursor spinning solution is moved into a 50mL syringe of the air flow spinning process device, the bubbles in the extrusion tube, at room temperature, relative humidity 30%, normal pressure environment, the 21G spinning needle, air jet connector and syringe are combined, the air compressor is adjusted to 0.6MPa, the connected pressure valve is constant at about 0.15MPa, the setting advancing speed is 20mL / h, the distance between the spinning needle and the receiver is 50cm, a heating field is set between them, the yarn net is covered in the frame as the receiver to collect the yarn, and accumulated into a flexible three-dimensional polymer nanofiber material;

[0040] (3) heat treatment: the flexible fiber material obtained in the above step is folded into a block in a zigzag manner, placed in a box furnace for heat treatment, first raised to 200℃ at a temperature rising rate of 2℃ / min, so that the organic polymer is decomposed in this process; then raised to 900℃ at a temperature rising rate of 3℃ / min, and kept at 900℃ for 2h, finally obtaining the flexible lightweight heat-insulating flow line oxide nanofiber aerogel with ultra-low thermal conductivity and three-dimensional structure.

[0041] Example 4

[0042] The preparation method of the flexible lightweight heat-insulating flow line oxide nanofiber aerogel of the present application comprises the following steps:

[0043] (1) A bottle: 3g of polyvinylpyrrolidone and 1g of polyvinyl butyral are weighed and dissolved in 30mL of ethanol, stirred overnight to obtain a uniform transparent solution; B bottle: 10mL of ethanol, 2mL of water, 0.05g of oxalic acid, 6.25g of tetraethyl orthosilicate are weighed and stirred overnight to obtain a long-chain silicon solution after condensation, then 25mL of acetic acid and 4.86g of aluminum acetylacetone and 0.3g of cetyltrimethylammonium bromide are added, and the mixture is stirred for 20 minutes to clarify; the B bottle is mixed into the A bottle, and after stirring for four hours, a uniform spinning solution is obtained;

[0044] (2) The uniformly stirred precursor spinning solution is moved into a 50mL syringe of the air flow spinning process device, and the bubbles in the extrusion pipe are removed; at room temperature, a relative humidity of 30%, and a normal pressure environment, a 21G spinning needle, a gas jet connector, and a syringe are combined, the air compressor is adjusted to 0.6MPa, the connected pressure valve is constant at about 0.15MPa, the push speed is set to 20mL / h, the spinning needle is 50cm away from the receiver, a heating field is set between them, a yarn net is covered in the frame as a receiver to collect the yarn, and a flexible three-dimensional polymer nanofiber material is accumulated.

[0045] (3) Heat treatment: the flexible fiber material obtained in the above step is folded into a block in a zigzag shape and placed in a box furnace for heat treatment; first, the temperature is raised to 200℃ at a rate of 2℃ / min, so that the organic polymer is decomposed in this process; then, the temperature is raised to 900℃ at a rate of 3℃ / min, and the temperature is kept at 900℃ for 2h, finally, a flexible lightweight thermal insulation streamline oxide nanofiber aerogel with ultra-low thermal conductivity and three-dimensional structure is obtained.

[0046] Example 5

[0047] The preparation method of the flexible lightweight thermal insulation streamline oxide nanofiber aerogel of the present application comprises the following steps:

[0048] (1) A bottle: 3g of polyvinylpyrrolidone and 1g of polyvinyl butyral are weighed and dissolved in 30mL of ethanol, stirred overnight to obtain a uniform transparent solution; B bottle: 10mL of ethanol, 2mL of water, 0.05g of oxalic acid, 6.25g of tetraethyl orthosilicate are weighed and stirred overnight to obtain a long-chain silicon solution after condensation, then 25mL of acetic acid and 4.86g of aluminum acetylacetone and 0.3g of cetyltrimethylammonium bromide are added, and the mixture is stirred for 20 minutes to clarify; the B bottle is mixed into the A bottle, and after stirring for four hours, a uniform spinning solution is obtained;

[0049] (2) The stirring uniform precursor spinning solution is moved into a 50 mL syringe of the air flow spinning process device, the bubble in the extrusion tube, at room temperature, relative humidity 30%, normal pressure environment, the 21G spinning needle, air spray joint and the syringe are combined, the air compressor is adjusted to 0.6 MPa, the connected pressure valve is constant about 0.15 MPa, the setting advancing speed is 30 mL / h, the spinning needle and the receiver distance is 50 cm, the heating field is set between them, the gauze is covered in the frame, as the receiver receives the yarn, and the flexible three-dimensional polymer nanofiber material is accumulated;

[0050] (3) Heat treatment: the flexible fiber material obtained in the above step is folded into a block in a zigzag shape, placed in a box furnace for heat treatment, first increased to 200 DEG C at a heating rate of 2 DEG C / min, so that the organic polymer is decomposed in this process; then increase to 900 DEG C at a heating rate of 3 DEG C / min, and keep at 900 DEG C for 2h, finally obtain flexible lightweight thermal insulation streamline oxide nanofiber aerogel with ultra-low thermal conductivity and three-dimensional structure.

[0051] Example 6

[0052] The preparation method of the flexible lightweight thermal insulation streamline oxide nanofiber aerogel of the application comprises the following steps:

[0053] (1) A bottle: 3g of polyvinylpyrrolidone and 1g of polyvinyl butyral are weighed and dissolved in 30mL of ethanol, stirred overnight to obtain a uniform transparent solution; B bottle: 10mL of ethanol, 2mL of water, 0.05g of oxalic acid, 6.25g of tetraethyl orthosilicate are weighed and stirred overnight to obtain a long-chain silicon solution after condensation, then 40mL of acetic acid and 9.72g of aluminum acetylacetonate and 0.3g of cetyltrimethylammonium bromide are added, stirred for twenty minutes, and then clarified; the B bottle is mixed into the A bottle, stirred for four hours to obtain a uniform spinning solution;

[0054] (2) The stirring uniform precursor spinning solution is moved into a 50 mL syringe of the air flow spinning process device, the bubble in the extrusion tube, at room temperature, relative humidity 30%, normal pressure environment, the 21G spinning needle, air spray joint and the syringe are combined, the air compressor is adjusted to 0.6 MPa, the connected pressure valve is constant about 0.15 MPa, the setting advancing speed is 30 mL / h, the spinning needle and the receiver distance is 50 cm, the heating field is set between them, the gauze is covered in the frame, as the receiver receives the yarn, and the flexible three-dimensional polymer nanofiber material is accumulated;

[0055] (3) heat treatment: the flexible fiber material obtained in the above step is folded into a block in a zigzag manner, placed in a box furnace for heat treatment, first raised to 200℃ at a temperature rising rate of 2℃ / min, so that the organic polymer is decomposed in this process; then raised to 900℃ at a temperature rising rate of 3℃ / min, and kept at 900℃ for 2h, finally obtained the flexible lightweight heat-insulating flow line oxide nanofiber aerogel with ultra-low thermal conductivity and three-dimensional structure.

[0056] Example 7

[0057] The preparation method of the flexible lightweight heat-insulating flow line oxide nanofiber aerogel of the present application comprises the following steps:

[0058] (1) A bottle: 3g of polyvinylpyrrolidone and 1g of polyvinyl butyral are weighed and dissolved in 30mL of ethanol, stirred overnight to obtain a uniform transparent solution; B bottle: 10mL of ethanol, 2mL of water, 0.05g of oxalic acid, 6.25g of tetraethyl orthosilicate are weighed and stirred overnight to obtain a long-chain silicon solution after condensation, then 40mL of acetic acid and 9.72g of aluminum acetylacetonate and 0.3g of cetyltrimethylammonium bromide are added, stirred for twenty minutes and then clarified; the B bottle is mixed into the A bottle, and after stirring for four hours, a uniform spinning solution is obtained;

[0059] (2) The uniformly stirred precursor spinning solution is moved into a 50mL syringe of the air flow spinning process device, and the air bubbles in the extrusion tube are removed. In a room temperature, relative humidity 30%, normal pressure environment, the 21G spinning needle, air jet connector and syringe are combined, the air compressor is adjusted to 0.6MPa, the connected pressure valve is constant at about 0.15MPa, the setting advancing speed is 20mL / h, the distance between the spinning needle and the receiver is 50cm, a heating field is set between them, the yarn net is covered in the frame as the receiver to collect the yarn, and the flexible three-dimensional polymer nanofiber material is accumulated.

[0060] (3) heat treatment: the flexible fiber material obtained in the above step is folded into a block in a zigzag manner, placed in a box furnace for heat treatment, first raised to 200℃ at a temperature rising rate of 2℃ / min, so that the organic polymer is decomposed in this process; then raised to 900℃ at a temperature rising rate of 3℃ / min, and kept at 900℃ for 2h, finally obtained the flexible lightweight heat-insulating flow line oxide nanofiber aerogel with ultra-low thermal conductivity and three-dimensional structure.

[0061] Examples 1-4 change the proportion of polymer addition and the proportion of silicon and aluminum elements, which will affect the density of the flexible lightweight heat-insulating flow line oxide nanofiber aerogel finally formed. The structure of PVB after calcination is more compact than that of PVP, and the porous amorphous structure of silicon oxide also reduces the density, while the flame-retardant and temperature-resistant heat-insulating capacity remains stable, and the functionality is good, all of which can be flame-retardant and heat-insulating at a temperature of 1300℃.

[0062] Examples 5-7 obtained three-dimensional nanofiber material under different pressure conditions and the speed of the propelling, the fiber will be thin with the increase of pressure, too high will be fiber short cut, low propelling speed will make the fiber more continuous, but the morphology and structure of the fiber in the suitable range of examples have no obvious difference, indicating that the solution propelling speed can be appropriately increased under low pressure conditions, the fiber efficiency is improved, and the spinning process performance is greatly improved; changing the calcination temperature, there is no obvious change at 800-1000℃, keeping the basic performance stable.

[0063] As shown in Figure 1 , it is a real picture of flexible lightweight thermal flow oxide nanofiber aerogel, it can be seen that the nanofiber aerogel has the characteristics of flexibility and light weight, the preparation of large-volume fiber aerogel is realized through airflow spinning technology, and it can float on the grass, and from the fine nanofiber aerogel bundle to the block, it can be arbitrarily bent and folded, showing good flexibility.

[0064] As shown in Figure 2 , the scanning electron microscope image of the flexible lightweight thermal flow oxide nanofiber aerogel can be seen that the streamlined nanofiber has different structures inside and outside, and is randomly wound and connected to form a three-dimensional nanofiber aerogel, which is a structural advantage of good thermal insulation performance.

[0065] As shown in Figure 3 , it is a density photo of the flexible lightweight thermal flow oxide nanofiber aerogel, the nanofiber aerogel block can be placed on the dog tail grass without deformation, reflecting the low density and light weight characteristics.

[0066] The performance of the flexible lightweight thermal flow oxide nanofiber aerogel is verified:

[0067] As shown in Figure 4 A, the flexible lightweight thermal flow oxide nanofiber aerogel of the present application is burned at 1300℃, and no burning marks appear on the surface of the aerogel. As shown in Figure 4 B, under high-temperature heat source, the back surface can be as low as below 100℃, which can achieve the effect of flame-retardant thermal insulation. In summary Figure 4 , based on the characteristics of lightweight, low thermal conductivity and high flexibility of nanofiber aerogel, high-efficiency flame-retardant temperature-resistant thermal insulation effect can be achieved.

Claims

1. A method for preparing a flexible, lightweight, thermally insulating streamlined oxide nanofiber aerogel, characterized in that: The following steps are involved: (1) Preparation of spinning solution: The spinning solution consists of bottle A and bottle B; bottle A is prepared by dissolving polyvinyl butyral and polyvinyl pyrrolidone in ethanol in proportion and stirring to obtain a uniform and transparent solution with a mass fraction of 8-15 wt.%; bottle B is prepared by mixing ethanol, water, oxalic acid, and tetraethyl orthosilicate to obtain a polycondensed silicon solution, then adding acetic acid, aluminum acetylacetonate, and a pore-forming agent, hexadecyltrimethylammonium bromide, stirring, and clarifying; bottle B is mixed into bottle A and stirred for four hours to obtain a uniform spinning solution; (2) Air-spinning: The stirred precursor spinning solution is transferred into the syringe of the air-spinning process device. Under normal pressure, the spinning needle, air jet connector and syringe are combined, and the pressure valve connected to the air compressor is adjusted to output a constant air flow of about 0.1-0.3 MPa to the spinning solution. The solution propulsion speed in the tube is set to 15-30 mL / h. After multi-stage traction in the flow field, the solution is connected and wound in the receiver to form a flexible three-dimensional polymer nanofiber material. (3) Heat treatment: The obtained flexible three-dimensional polymer nanofiber material is shaped by a folding process and then heat treated. The temperature is first raised to 200-300°C at a heating rate of 1-2°C / min, and then raised to 800-1000°C at a heating rate of 1-3°C / min. The material is kept warm for 90-120 minutes and calcined to obtain a flexible, lightweight, thermally insulating streamlined oxide nanofiber aerogel with a three-dimensional structure and ultra-low thermal conductivity.

2. The preparation method according to claim 1, characterized in that In step (1), in bottle A, the molecular weight of the polyvinyl butyral is 90,000-1,200,000, and the molecular weight of polyvinyl pyrrolidone is 80,000-1,300,000; the mass ratio of the high molecular weight polymers PVB, PVP and ethanol is 0.15-16:0-0.05:0.79-0.

87.

3. The preparation method according to claim 1, characterized in that In step (1), in bottle B, the mass ratio of ethanol, water, oxalic acid, and tetraethyl orthosilicate is 0.48-0.74: 0.06-0.12: 0.0015-0.003: 0.20-0.39; the mass volume ratio of silicon solution, aluminum acetylacetonate, acetic acid, and hexadecyltrimethylammonium bromide is 0.32-0.54: 0.13-0.19: 0.35-0.55: 0.0004-0.0006.

4. The preparation method according to claim 1, characterized in that In step (2), the size of the spinning needle is selected to be 21-25G, and the volume of the syringe is 5-100 mL.

5. The preparation method according to claim 1, characterized in that In step (2), the receiver is a combination of a gauze and a mesh basket, and a heating field is set between the spinning needle and the receiver, with a distance of 40 to 80 cm.

6. The preparation method according to claim 1, characterized in that In step (2), the pressure of the air compressor is 0.4-0.8 MPa; the spinning environment temperature is 10-40° C., and the ambient humidity is 10-70%.

7. The preparation method according to claim 1, characterized in that In step (3), the folding process is shaped into a square folding or a Z-shaped folding.

8. A flexible, lightweight, thermally insulating streamlined oxide nanofiber aerogel prepared by the preparation method according to claim 1.

9. The nanofiber aerogel according to claim 8, characterized in that The nanofiber aerogel has a diameter of 100 to 800 nm, is streamlined, and has a core-shell structure. The outer layer is a dense and tough aluminum oxide layer, and the inner layer is a porous low-thermal-conductivity silicon oxide layer.

10. Use of the flexible, lightweight, thermally insulating streamlined oxide nanofiber aerogel according to claim 8 in flame retardant thermal insulation materials.

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