Multilayer nanofiber thermal insulation material and method for manufacturing the same

Abstract

The application relates to a multilayer nanofiber thermal insulation material and a preparation method thereof. The method comprises the following steps: preparing a nanofiber film; reacting a silicon source precursor, a surfactant and an acid solution to obtain a silica sol; crushing the nanofiber film and adding the same into the silica sol to uniformly disperse, obtaining a mixed slurry, then adding ammonia water into the mixed slurry to uniformly disperse, obtaining a nanofiber slurry, and then performing suction filtration on the nanofiber slurry to obtain nanofiber sheets; alternately arranging a plurality of reflecting screens and a plurality of the nanofiber sheets, and then performing mould pressing and drying to obtain the multilayer nanofiber thermal insulation material; and in the alternately arranging, one nanofiber sheet is arranged between every two reflecting screens. The prepared multilayer nanofiber thermal insulation material has excellent high-temperature radiation resistance and excellent high-temperature mechanical properties.

Description

Technical Field

[0001] This invention belongs to the technical field of multilayer thermal insulation materials, and particularly relates to a multilayer nanofiber thermal insulation material and its preparation method. Background Technology

[0002] Nanofiber insulation materials, characterized by their lightweight, high-temperature resistance, good flexibility, and low thermal conductivity, have become a research hotspot. However, due to their porous structure, nanofibers exhibit poor high-temperature heat radiation shielding performance, resulting in suboptimal high-temperature insulation performance.

[0003] To improve the high-temperature thermal insulation performance of nanofiber insulation materials, researchers have employed various methods to enhance their radiation resistance, including adding radiation-resistant agents to the spinning solution and modifying the surface of the nanofibers for radiation resistance. One method involves adding radiation-resistant agents such as nano-based silicon carbide powder or titanium dioxide to the spinning solution and preparing radiation-resistant nanofibers through electrospinning. However, nanofibers are brittle, and the nanofibers prepared by this method are even more brittle. The internal structure of the fiber is easily affected by the nanoparticles of radiation-resistant agents, leading to frequent breakage. Modification methods for nanofibers often coarsen the nanofiber skeleton, resulting in a higher solid-phase thermal conductivity. Furthermore, due to the porous nature of the material, the radiation resistance effect remains unsatisfactory, especially above 800℃, where the thermal conductivity remains relatively high, limiting the engineering application of nanofiber insulation materials.

[0004] In summary, there is an urgent need to develop new nano-insulation materials to improve the high-temperature radiation resistance and / or high-temperature mechanical properties of nanofiber insulation materials. Summary of the Invention

[0005] To address one or more technical problems existing in the prior art, this invention provides a multilayer nanofiber thermal insulation material and its preparation method. This invention prepares a multilayer nanofiber thermal insulation material with excellent high-temperature radiation resistance and excellent high-temperature mechanical properties.

[0006] In a first aspect, the present invention provides a method for preparing a multilayer nanofiber thermal insulation material, the method comprising the following steps:

[0007] (1) Preparation of nanofiber membranes;

[0008] (2) A reaction was carried out using silicon source precursor, surfactant and acid solution as raw materials to obtain silica sol;

[0009] (3) After the nanofiber membrane is broken, it is added to the silica sol and dispersed evenly to obtain a mixed slurry. Then, ammonia water is added to the mixed slurry and dispersed evenly to obtain a nanofiber slurry. The nanofiber slurry is then filtered to obtain nanofiber sheets.

[0010] (4) Multiple reflective screens and multiple nanofiber sheets are alternately arranged, and then molded and dried to produce a multi-layer nanofiber thermal insulation material; in the alternating arrangement, a nanofiber sheet is arranged between every two reflective screens.

[0011] Preferably, the nanofiber membrane is prepared by electrospinning; and / or the nanofiber membrane is a silica nanofiber membrane.

[0012] Preferably, the silicon source precursor is one or more of methyltrimethoxysilane, methyltriethoxysilane, cage-type polysilsesquioxane, tetraethyl orthosilicate condensate, methyl orthosilicate, and tetraethyl orthosilicate; the surfactant is one or more of sodium dodecylbenzenesulfonate, dodecyltrimethylammonium bromide, and dodecyltrimethylammonium chloride; and / or the acid solution is one or more of acetic acid solution, hydrochloric acid, and oxalic acid solution.

[0013] Preferably, the molar ratio of the silicon source precursor, the surfactant, and the acid contained in the acid solution is (10-90):(0.06-0.6):(0.2-5); and / or the reaction is carried out at room temperature for 20-40 min.

[0014] Preferably, the nanofiber membrane accounts for 30-60% of the mass fraction of the mixed slurry; the silica sol contained in the mixed slurry accounts for 40-70% of the mass fraction; and ammonia water is added to adjust the pH of the mixed slurry to 6.8-7.2, preferably 7.

[0015] Preferably, the reflective screen is a metal reflective screen, preferably one or more of molybdenum foil, titanium foil, stainless steel foil, nickel foil, and aluminum foil; and / or the drying is freeze drying or atmospheric pressure drying.

[0016] Preferably, the thickness of the nanofiber sheet is 1-2 mm; and / or the thickness of the reflective screen is 0.025-0.5 mm.

[0017] Preferably, in step (3), after obtaining the mixed slurry, ammonium bicarbonate, ammonium phosphate and ammonia are added to the mixed slurry and dispersed evenly.

[0018] Preferably, the mass ratio of ammonium bicarbonate to ammonium phosphate is (0.8-2):1; and / or the total amount of ammonium bicarbonate and ammonium phosphate is 1-2% of the mass of the mixed slurry.

[0019] In a second aspect, the present invention provides a multilayer nanofiber thermal insulation material prepared by the preparation method described in the first aspect of the present invention.

[0020] Compared with the prior art, the present invention has at least the following beneficial effects:

[0021] (1) Multilayer thermal insulation materials based on micron fibers have been reported, but compared to micron fibers, nanofibers are more brittle and their porous structure is prone to collapse when exposed to water. Current methods for obtaining multilayer micron fiber thermal insulation materials are difficult to apply. For example, the atmospheric pressure drying or freeze-drying methods suitable for micron fibers are not applicable to nanofibers. Furthermore, unlike micron fiber sheets, the thickness of nanofiber sheets is difficult to control. This invention uses nanofibers as the main material. A nanofiber membrane is prepared and then uniformly dispersed in silica sol after being broken down to form a nanofiber slurry containing silica sol micelles. Filtration yields nanofiber sheets shaped and reinforced by silica sol micelles. The thickness of these nanofiber sheets is controllable, reaching 1–2 mm. This invention uses silica sol micelles as a sizing agent, enabling the invention to achieve the desired effect. The thermal insulation material based on nanofibers can be prepared by atmospheric pressure drying or freeze-drying, which is simple and low in cost. Furthermore, the silica sol in this invention not only serves to shape the nanofiber sheets themselves but also to shape the layers of the thermal insulation material, allowing for the preparation of multi-layer nanofiber thermal insulation materials solely through atmospheric pressure drying or freeze-drying. This invention effectively solves the problems of nanofibers' high brittleness, insufficient mechanical strength, easy collapse upon contact with water, and poor high-temperature thermal insulation performance. Through multi-layer structural design and the introduction of a reflective screen, this invention effectively solves the problems of poor high-temperature radiation shielding performance and a sharp decline in thermal insulation effect over long-term use in traditional single-layer nanofiber thermal insulation materials. This invention yields a multi-layer thermal insulation material based on nanofibers. This invention comprehensively improves the high-temperature mechanical strength and high-temperature radiation resistance of nanofiber thermal insulation materials, laying the foundation for the engineering application of nanofibers.

[0022] (2) In some preferred embodiments of the present invention, after the nanofiber membrane is broken and uniformly dispersed in silica sol, ammonium bicarbonate and ammonium phosphate are added. Through the foaming of ammonium bicarbonate and ammonium phosphate and the rigid bonding with silica sol particles, they are used to construct the pore structure and high-strength inorganic network structure of the thermal insulation material, thereby further improving the structural strength and thermal insulation performance of the nanofiber thermal insulation material. Detailed Implementation

[0023] To make the objectives, technical solutions, and advantages of this invention clearer, the technical solutions of this invention will be clearly and completely described below in conjunction with the embodiments of this invention. Obviously, the described embodiments are only some, not all, of the embodiments of this invention. All other embodiments obtained by those skilled in the art based on the embodiments of this invention without creative effort are within the scope of protection of this invention.

[0024] In a first aspect, the present invention provides a method for preparing a multilayer nanofiber thermal insulation material, the method comprising the following steps:

[0025] (1) Preparation of nanofiber membrane; The present invention does not specifically limit the nanofiber membrane, and any nanofiber membrane prepared by conventional methods is acceptable; The thickness of the nanofiber membrane is generally in the micrometer range, for example, generally not greater than 500 μm;

[0026] (2) A reaction is carried out using silicon source precursor, surfactant and acid solution as raw materials to obtain silica sol; specifically, for example, silicon source precursor and surfactant can be added to water in sequence, then dilute acid can be added and mixed evenly, and the silicon source precursor can be hydrolyzed by stirring at room temperature to obtain silica sol.

[0027] (3) After the nanofiber membrane is crushed, it is added to the silica sol and dispersed evenly to obtain a mixed slurry. Then, ammonia water is added to the mixed slurry and dispersed evenly to obtain a nanofiber slurry. The nanofiber slurry is then filtered to obtain nanofiber sheets. The present invention does not make specific limitations on the crushing of the nanofiber membrane, which is a conventional operation. For example, the nanofiber membrane can be crushed into uniformly dispersed fibers by a mechanical crusher.

[0028] (4) Multiple reflective screens and multiple nanofiber sheets are alternately arranged, and then molded and dried to produce a multi-layer nanofiber thermal insulation material; in the alternating arrangement, a nanofiber sheet is arranged between every two reflective screens. In this invention, for example, a clamping fixture can be used for the molding. This invention does not have special requirements for the molding parameters, and conventional molding parameters can be used; for example, the molding pressure is 0.5-3 MPa, and the molding time is 10-90 min; this invention does not have special requirements for the number of reflective screens and nanofiber sheets, and can be optimized according to the actual application (e.g., the total thickness requirement of the multi-layer nanofiber thermal insulation material in the actual application); preferably, the thickness of the multi-layer nanofiber thermal insulation material is 5-60 mm.

[0029] Multilayer thermal insulation materials based on microfibers have been reported, but compared to microfibers, nanofibers are more brittle and their porous structure is prone to collapse when exposed to water. Current methods for obtaining multilayer microfiber thermal insulation materials are difficult to apply. For example, the atmospheric pressure drying or freeze-drying methods suitable for microfibers are not applicable to nanofibers. Furthermore, unlike microfiber sheets, the thickness of nanofiber sheets is difficult to control. This invention uses nanofibers as the main material. A nanofiber membrane is prepared, broken down, and uniformly dispersed in silica sol to form a nanofiber slurry containing silica sol micelles. Filtration yields nanofiber sheets shaped and reinforced by silica sol micelles. The thickness of these nanofiber sheets is controllable, reaching 1-2 mm, and the surface is smooth and does not collapse. This invention utilizes silica sol micelles as a sizing agent. This invention enables the nanofiber-based thermal insulation material to be dried under normal pressure or freeze-dried, resulting in a simple preparation process and low cost. Furthermore, the silica sol in this invention not only serves to shape the nanofiber sheets themselves but also to shape the layers of the thermal insulation material, allowing for the preparation of multi-layer nanofiber thermal insulation materials solely through normal pressure drying or freeze-drying. This invention effectively solves the problems of nanofiber's high brittleness, insufficient mechanical strength, easy collapse upon contact with water, and poor high-temperature thermal insulation performance. Through multi-layer structural design and the introduction of a reflective screen, this invention effectively addresses the problems of poor high-temperature radiation shielding performance and a sharp decline in thermal insulation effect over long-term use in traditional single-layer nanofiber thermal insulation materials. The resulting material is a multi-layer thermal insulation material based on nanofibers. This invention comprehensively improves the high-temperature mechanical strength and high-temperature radiation resistance of nanofiber thermal insulation materials, laying the foundation for the engineering application of nanofibers.

[0030] According to some preferred embodiments, nanofiber membranes are prepared by electrospinning. The present invention does not specifically limit the electrospinning process conditions for preparing the nanofiber membranes, and conventional conditions in the art can be used; and / or the nanofiber membrane is a silica nanofiber membrane; in the present invention, it is preferred that the nanofiber membrane is a silica nanofiber membrane, and more preferably, the silica nanofiber membrane is prepared by electrospinning.

[0031] According to some preferred embodiments, the silicon source precursor is one or more of methyltrimethoxysilane, methyltriethoxysilane, cage-type polysilsesquioxane (POSS), tetraethyl orthosilicate condensate (tetraethyl orthosilicate condensate Si-40), methyl orthosilicate, and tetraethyl orthosilicate; the surfactant is one or more of sodium dodecylbenzenesulfonate, dodecyltrimethylammonium bromide, and dodecyltrimethylammonium chloride; and / or the acid solution is one or more of acetic acid solution, hydrochloric acid, and oxalic acid solution, that is, the acid contained in the acid solution is one or more of acetic acid, HCl, and oxalic acid; in this invention, the acetic acid solution refers to an aqueous solution of acetic acid, the hydrochloric acid refers to an aqueous solution of hydrogen chloride, and the oxalic acid solution refers to an aqueous solution of oxalic acid. Preferably, the acid solutions are all dilute acid solutions. In this invention, the concentration of the acid solution can be, for example, 0.03 to 0.1 mol / L, preferably 0.05 mol / L.

[0032] According to some preferred embodiments, the molar ratio of the silicon source precursor, the surfactant, and the acid contained in the acid solution is (10-90):(0.06-0.6):(0.2-5). In this invention, the preferred molar ratio is (10-90):(0.06-0.6):(0.2-5), which is more conducive to obtaining the multilayer nanofiber thermal insulation with excellent high-temperature thermal insulation performance and excellent high-temperature mechanical properties. If the amount of silicon source precursor is too small, while the amount of surfactant and acid is too large, it will be detrimental to the improvement of the high-temperature thermal insulation performance and high-temperature mechanical properties of the nanofiber thermal insulation material to a certain extent; and / or the reaction is a room temperature reaction for 20 to 40 minutes (e.g., 20, 25, 30, 35 or 40 minutes), for example, the reaction can be carried out at room temperature of 15 to 35°C with stirring for 20 to 40 minutes, and the stirring speed is not specifically limited, for example, it can be 100 to 800 r / min.

[0033] According to some preferred embodiments, the nanofiber membrane constitutes 30-60% (e.g., 30%, 35%, 40%, 45%, 50%, 55%, or 60%) of the mixed slurry by mass fraction, and the silica sol contained in the mixed slurry contains 40-70% (e.g., 40%, 45%, 50%, 55%, 60%, 65%, or 70%). The mass fraction of the nanofiber membrane in the mixed slurry and the mass fraction of the mixed slurry containing the nanofiber membrane are related. The sum is 100%, which is conducive to ensuring that a multilayer nanofiber thermal insulation material with excellent high-temperature thermal insulation performance and excellent high-temperature mechanical properties is obtained; ammonia water is added to adjust the pH of the mixed slurry to 6.8-7.2, preferably 7; the present invention does not make specific limitations on the source and amount of the ammonia water, as long as the pH of the mixed slurry is adjusted to neutral, for example, 6.8-7.2. Specifically, the ammonia water can be commercially available ammonia water, for example, a commercially available aqueous solution containing 25-28% NH3.

[0034] According to some preferred embodiments, the reflective screen is a metal reflective screen, preferably one or more of molybdenum foil, titanium foil, stainless steel foil, nickel foil, and aluminum foil; the present invention does not impose any particular restrictions on the source of the molybdenum foil, titanium foil, stainless steel foil, nickel foil, and aluminum foil, for example, directly purchased products or those obtained by existing methods are acceptable; and / or the drying is freeze-drying or atmospheric pressure drying; the present invention does not impose specific limitations on the conditions of freeze-drying and atmospheric pressure drying, which are conventional techniques.

[0035] According to some preferred embodiments, the thickness of the nanofiber sheet is 1 to 2 mm; and / or the thickness of the reflective screen is 0.025 to 0.5 mm.

[0036] According to some specific embodiments, the preparation of the multilayer nanofiber thermal insulation material includes the following steps:

[0037] 1) Prepare a spinning solution for silica nanofibers, prepare a silica nanofiber membrane using electrospinning technology, and crush the nanofiber membrane using a mechanical crusher;

[0038] 2) Preparation of dispersion solution: Add silicon source precursor and surfactant to water in sequence, add dilute acid, and stir at room temperature to complete the hydrolysis of silicon source precursor to obtain silica sol;

[0039] 3) Weigh the broken nanofiber membrane, stir and disperse it in the above silica sol to obtain a mixed slurry, add ammonia water dropwise to the mixed slurry to adjust the pH to neutral, stir evenly to obtain nanofiber slurry; then, quickly filter to obtain nanofiber sheets (thin wet sheets);

[0040] 4) The metal reflective screen is stacked with the above-mentioned nanofiber sheet in a layer-by-layer manner of "reflective screen-thin wet sheet-reflective screen", and finally molded and dried to obtain a multilayer nanofiber thermal insulation material.

[0041] According to some preferred embodiments, in step (3), after obtaining the mixed slurry, ammonium bicarbonate, ammonium phosphate and ammonia are added to the mixed slurry and dispersed evenly.

[0042] In this invention, it is preferable that after the nanofiber membrane is broken up and uniformly dispersed in silica sol, ammonium bicarbonate and ammonium phosphate are added. Through the foaming of ammonium bicarbonate and ammonium phosphate and their rigid bonding with silica sol particles, they are used to construct the pore structure and high-strength inorganic network structure of the thermal insulation material, thereby further improving the structural strength and thermal insulation performance of the nanofiber thermal insulation material.

[0043] According to some preferred embodiments, the mass ratio of ammonium bicarbonate to ammonium phosphate is (0.8-2):1; and / or the total amount of ammonium bicarbonate and ammonium phosphate is 1-2% of the mass of the mixed slurry.

[0044] In a second aspect, the present invention provides a multilayer nanofiber thermal insulation material prepared by the preparation method described in the first aspect of the present invention.

[0045] The present invention will be further described below by way of examples, but the scope of protection of the present invention is not limited to these embodiments.

[0046] Example 1

[0047] ①Silica nanofiber membranes were prepared by electrospinning.

[0048] ② Add methyl orthosilicate (silicon precursor) and dodecyltrimethylammonium bromide (surfactant) sequentially to water, then add hydrochloric acid with a concentration of 0.05 mol / L and stir at room temperature for 30 min to obtain silica sol; wherein the molar ratio of silica precursor, surfactant and HCl contained in hydrochloric acid is 10:0.6:0.2.

[0049] ③ The silica nanofiber membrane prepared in step ① is crushed by a mechanical crusher and then stirred and dispersed into the silica sol to obtain a mixed slurry. The silica nanofiber membrane accounts for 60% of the mass fraction of the mixed slurry. Then, ammonia water is added dropwise to the mixed slurry to adjust the pH of the mixed slurry to 7, and the mixture is stirred evenly to obtain a nanofiber slurry. Then, the mixture is filtered to obtain nanofiber sheets with a thickness of 2 mm.

[0050] ④ Six metal reflective screens (molybdenum foils) and five nanofiber sheets are alternately arranged (in the alternating arrangement, one nanofiber sheet is arranged between every two metal reflective screens), and after being molded under a pressure of 1 MPa for 60 min, they are freeze-dried for 12 h to obtain a multilayer nanofiber thermal insulation material; the thickness of each molybdenum foil is 0.025 mm.

[0051] Example 2

[0052] ①Silica nanofiber membranes were prepared by electrospinning.

[0053] ② Methyltriethoxysilane (silicon precursor) and dodecyltrimethylammonium bromide (surfactant) were added to water in sequence, followed by the addition of an acetic acid solution with a concentration of 0.05 mol / L and stirring at room temperature for 30 min to obtain silica sol; wherein the molar ratio of silica precursor, surfactant and acetic acid in acetic acid solution was 10:0.06:0.2.

[0054] ③ The silica nanofiber membrane prepared in step ① is crushed by a mechanical crusher and then dispersed into the silica sol to obtain a mixed slurry. The silica nanofiber membrane accounts for 30% of the mass fraction of the mixed slurry. Then, ammonia water is added dropwise to the mixed slurry to adjust the pH of the mixed slurry to 7, and the mixture is stirred evenly to obtain a nanofiber slurry. Then, the mixture is filtered to obtain nanofiber sheets with a thickness of 1 mm.

[0055] ④ Eleven metal reflective screens (molybdenum foils) and ten nanofiber sheets are alternately arranged (in the alternating arrangement, one nanofiber sheet is arranged between every two metal reflective screens), and after being molded under a pressure of 1 MPa for 60 min, they are dried at 120°C and normal pressure for 12 h to obtain a multilayer nanofiber thermal insulation material; the thickness of each molybdenum foil is 0.025 mm.

[0056] Example 3

[0057] ①Silica nanofiber membranes were prepared by electrospinning.

[0058] ② Add cage-type polysilsesquioxane (POSS) and sodium dodecylbenzenesulfonate (surfactant) sequentially to water, then add acetic acid solution with a concentration of 0.05 mol / L and stir at room temperature for 30 min to obtain silica sol; wherein, the molar ratio of silica precursor, surfactant and acetic acid contained in acetic acid solution is 30:0.18:5.

[0059] ③ The silica nanofiber membrane prepared in step ① is crushed by a mechanical crusher and then dispersed into the silica sol to obtain a mixed slurry. The silica nanofiber membrane accounts for 30% of the mass fraction of the mixed slurry. Then, ammonia water is added dropwise to the mixed slurry to adjust the pH of the mixed slurry to 7, and the mixture is stirred evenly to obtain a nanofiber slurry. Then, the mixture is filtered to obtain nanofiber sheets with a thickness of 2 mm.

[0060] ④ Six metal reflective screens (molybdenum foils) and five nanofiber sheets are alternately arranged (in the alternating arrangement, one nanofiber sheet is arranged between every two metal reflective screens), and after being molded under a pressure of 1 MPa for 60 min, they are freeze-dried for 12 h to obtain a multilayer nanofiber thermal insulation material; the thickness of each molybdenum foil is 0.025 mm.

[0061] Example 4

[0062] ①Silica nanofiber membranes were prepared by electrospinning.

[0063] ② Add tetraethyl orthosilicate condensate (Si-40) and dodecyltrimethylammonium chloride (surfactant) sequentially to water, then add acetic acid solution with a concentration of 0.05 mol / L and stir at room temperature for 30 min to obtain silica sol; wherein, the molar ratio of silica precursor, surfactant and acetic acid contained in acetic acid solution is 90:0.6:5.

[0064] ③ The silica nanofiber membrane prepared in step ① is crushed by a mechanical crusher and then stirred and dispersed into the silica sol to obtain a mixed slurry. The silica nanofiber membrane accounts for 40% of the mass fraction of the mixed slurry. Then, ammonia water is added dropwise to the mixed slurry to adjust the pH of the mixed slurry to 7, and the mixture is stirred evenly to obtain a nanofiber slurry. Then, the mixture is filtered to obtain nanofiber sheets with a thickness of 2 mm.

[0065] ④ Six metal reflective screens (molybdenum foils) and five nanofiber sheets are alternately arranged (in the alternating arrangement, one nanofiber sheet is arranged between every two metal reflective screens), and after being molded under a pressure of 1 MPa for 60 min, they are dried at 120°C and normal pressure for 12 h to obtain a multilayer nanofiber thermal insulation material; the thickness of each molybdenum foil is 0.025 mm.

[0066] Example 5

[0067] ①Silica nanofiber membranes were prepared by electrospinning.

[0068] ② Tetraethyl orthosilicate (silicon precursor) and dodecyltrimethylammonium bromide (surfactant) were added to water in sequence, followed by the addition of hydrochloric acid with a concentration of 0.05 mol / L and stirring at room temperature for 30 min to obtain silica sol; wherein the molar ratio of silica precursor, surfactant and HCl contained in hydrochloric acid is 10:0.06:0.5.

[0069] ③ The silica nanofiber membrane prepared in step ① is crushed by a mechanical crusher and then dispersed into the silica sol to obtain a mixed slurry. The silica nanofiber membrane accounts for 30% of the mass fraction of the mixed slurry. Then, ammonia water is added dropwise to the mixed slurry to adjust the pH of the mixed slurry to 7, and the mixture is stirred evenly to obtain a nanofiber slurry. Then, the mixture is filtered to obtain nanofiber sheets with a thickness of 2 mm.

[0070] ④ Six metal reflective screens (molybdenum foils) and five nanofiber sheets are alternately arranged (in the alternating arrangement, one nanofiber sheet is arranged between every two metal reflective screens), and after being molded under a pressure of 1 MPa for 60 min, they are freeze-dried for 12 h to obtain a multilayer nanofiber thermal insulation material; the thickness of each molybdenum foil is 0.025 mm.

[0071] Example 6

[0072] ①Silica nanofiber membranes were prepared by electrospinning.

[0073] ② Methyltrimethoxysilane (silicon precursor) and dodecyltrimethylammonium bromide (surfactant) were added to water in sequence, followed by the addition of 0.05 mol / L hydrochloric acid and stirring at room temperature for 30 min to obtain silica sol; wherein the molar ratio of silica precursor, surfactant and HCl contained in hydrochloric acid is 10:0.06:0.5.

[0074] ③ The silica nanofiber membrane prepared in step ① is crushed by a mechanical crusher and then dispersed into the silica sol to obtain a mixed slurry. The silica nanofiber membrane accounts for 50% of the mass fraction of the mixed slurry. Then, ammonia water is added dropwise to the mixed slurry to adjust the pH of the mixed slurry to 7, and the mixture is stirred evenly to obtain a nanofiber slurry. Then, the mixture is filtered to obtain nanofiber sheets with a thickness of 1.5 mm.

[0075] ④ Eight metal reflective screens (molybdenum foils) and seven nanofiber sheets are alternately arranged (in the alternating arrangement, one nanofiber sheet is arranged between every two metal reflective screens), and after being molded under a pressure of 1 MPa for 60 min, they are dried at 120°C and normal pressure for 12 h to obtain a multilayer nanofiber thermal insulation material; the thickness of each molybdenum foil is 0.025 mm.

[0076] Example 7

[0077] Example 7 is basically the same as Example 6, except that:

[0078] Step ③ is as follows: The silica nanofiber membrane prepared in step ① is crushed by a mechanical crusher, and then stirred and dispersed into the silica sol to obtain a mixed slurry. The silica nanofiber membrane accounts for 20% of the mass fraction of the mixed slurry. Then, ammonia water is added dropwise to the mixed slurry to adjust the pH of the mixed slurry to 7, and the mixture is stirred evenly to obtain a nanofiber slurry. Then, the mixture is filtered to obtain nanofiber sheets with a thickness of 1.5 mm.

[0079] Example 8

[0080] Example 8 is basically the same as Example 6, except that:

[0081] Step ③ is as follows: The silica nanofiber membrane prepared in step ① is crushed by a mechanical crusher, and then stirred and dispersed into the silica sol to obtain a mixed slurry. The silica nanofiber membrane accounts for 70% of the mass fraction of the mixed slurry. Then, ammonia water is added dropwise to the mixed slurry to adjust the pH of the mixed slurry to 7, and the mixture is stirred evenly to obtain a nanofiber slurry. Then, the mixture is filtered to obtain nanofiber sheets with a thickness of 1.5 mm.

[0082] Example 9

[0083] Example 9 is basically the same as Example 6, except that:

[0084] Step ③ is as follows: The silica nanofiber membrane prepared in step ① is crushed using a mechanical crusher, and then stirred and dispersed into the silica sol to obtain a mixed slurry. The silica nanofiber membrane accounts for 50% of the mass fraction of the mixed slurry. Then, ammonium bicarbonate and ammonium phosphate are added to the mixed slurry, and ammonia water is added dropwise to adjust the pH of the mixed slurry to 7. The mixture is stirred evenly to obtain a nanofiber slurry. Then, the slurry is filtered to obtain nanofiber sheets with a thickness of 1.5 mm. The mass ratio of ammonium bicarbonate to ammonium phosphate is 1.5:1. The sum of the amounts of ammonium bicarbonate and ammonium phosphate is 1% of the mass of the mixed slurry.

[0085] Example 10

[0086] Example 10 is basically the same as Example 6, except that:

[0087] Step ③ is as follows: The silica nanofiber membrane prepared in step ① is crushed using a mechanical crusher, and then stirred and dispersed into the silica sol to obtain a mixed slurry. The silica nanofiber membrane accounts for 50% of the mass fraction of the mixed slurry. Then, ammonium bicarbonate and ammonium phosphate are added to the mixed slurry, and ammonia water is added dropwise to adjust the pH of the mixed slurry to 7. The mixture is stirred evenly to obtain a nanofiber slurry. Then, the mixture is filtered to obtain nanofiber sheets with a thickness of 1.5 mm. The mass ratio of ammonium bicarbonate to ammonium phosphate is 1:1. The sum of the amounts of ammonium bicarbonate and ammonium phosphate is 2% of the mass of the mixed slurry.

[0088] Comparative Example 1

[0089] ①Silica nanofiber membranes were prepared by electrospinning.

[0090] ② Methyltrimethoxysilane (silicon precursor) and dodecyltrimethylammonium bromide (surfactant) were added to water in sequence, followed by the addition of hydrochloric acid with a concentration of 0.05 mol / L and stirring at room temperature for 30 min to obtain silica sol; wherein the molar ratio of silica precursor, surfactant and HCl contained in hydrochloric acid is 10:0.06:0.5.

[0091] ③ The silica nanofiber membrane prepared in step ① is crushed by a mechanical crusher and then dispersed into the silica sol to obtain a mixed slurry. The silica nanofiber membrane accounts for 50% of the mass fraction of the mixed slurry. Then, ammonia water is added dropwise to the mixed slurry to adjust the pH of the mixed slurry to 7, and the mixture is stirred evenly to obtain a nanofiber slurry. Then, the mixture is filtered to obtain nanofiber sheets with a thickness of 1.5 mm.

[0092] ④ The seven nanofiber sheets are stacked and molded under a pressure of 1 MPa for 60 min, and then dried at 120°C and normal pressure for 12 h to obtain a multilayer nanofiber thermal insulation material.

[0093] Comparative Example 2

[0094] ①Silica nanofiber membranes were prepared by electrospinning.

[0095] ② Methyltrimethoxysilane (silicon precursor) and dodecyltrimethylammonium bromide (surfactant) were added to water in sequence, followed by the addition of hydrochloric acid with a concentration of 0.05 mol / L and stirring at room temperature for 30 min to obtain silica sol; wherein the molar ratio of silica precursor, surfactant and HCl contained in hydrochloric acid is 9:1:5.

[0096] ③ The silica nanofiber membrane prepared in step ① is crushed by a mechanical crusher and then dispersed into the silica sol to obtain a mixed slurry. The silica nanofiber membrane accounts for 50% of the mass fraction of the mixed slurry. Then, ammonia water is added dropwise to the mixed slurry to adjust the pH of the mixed slurry to 7, and the mixture is stirred evenly to obtain a nanofiber slurry. Then, the mixture is filtered to obtain nanofiber sheets with a thickness of 1.5 mm.

[0097] ④ Eight metal reflective screens (molybdenum foils) and seven nanofiber sheets are alternately arranged (in the alternating arrangement, one nanofiber sheet is arranged between every two metal reflective screens), and after being molded under a pressure of 1 MPa for 60 min, they are dried at 120°C and normal pressure for 12 h to obtain a multilayer nanofiber thermal insulation material; the thickness of each molybdenum foil is 0.025 mm.

[0098] Comparative Example 3

[0099] ①Silica nanofiber membranes were prepared by electrospinning.

[0100] ②The silica nanofiber membrane is crushed by a mechanical crusher, then layered and stacked, and after being molded under a pressure of 1MPa for 60 minutes, a nanofiber thermal insulation material with a total thickness of 10.5mm is obtained.

[0101] Comparative Example 4

[0102] ①Silica nanofiber membranes were prepared by electrospinning.

[0103] ② The silica nanofiber membrane prepared in step ① was crushed by a mechanical crusher and then dispersed in water to obtain a slurry. The silica nanofiber membrane accounted for 50% of the mass fraction of the slurry. After filtration, nanofiber sheets with controllable thickness and smooth surface could not be obtained, and subsequent preparation of multilayer nanofiber thermal insulation materials was not carried out.

[0104] Comparative Example 5

[0105] ①Silica nanofiber membranes were prepared by electrospinning.

[0106] ② Methyltrimethoxysilane (silicon precursor) and dodecyltrimethylammonium bromide (surfactant) were added to water in sequence, followed by the addition of 0.05 mol / L hydrochloric acid and stirring at room temperature for 30 min. The pH was then adjusted to 7 with ammonia to obtain silica sol. The molar ratio of silica precursor, surfactant and HCl in hydrochloric acid was 10:0.06:0.5.

[0107] ③ Place the silica sol obtained in step ② in the lower layer of the mold, and place the 7 layers of silica nanofiber membrane prepared in step ① in the upper layer of the mold. Mix the 7 layers of silica nanofiber membrane with the silica sol under negative pressure to obtain nanofiber sol; wherein, the mass ratio of the 7 layers of silica nanofiber membrane to silica sol is 1:1.

[0108] ④ The nanofiber sol was kept at a constant temperature of 25°C for 2 hours in a closed environment until it gelled. The gelled material was then placed in a container filled with ethanol and aged in a constant temperature water bath at 70°C for 3 days. The aged nanofiber gel was then dried using supercritical carbon dioxide for 48 hours to obtain fiber composite aerogel. The temperature of the supercritical carbon dioxide drying was 40°C and the pressure was 10 MPa.

[0109] Comparative Example 6

[0110] Comparative Example 6 is basically the same as Comparative Example 5, except that:

[0111] Step ④ is as follows: The nanofiber sol is kept at a constant temperature of 25°C for 2 hours in a closed environment until it gels. After that, the gelled material is placed in a container filled with ethanol and aged in a constant temperature water bath at 70°C for 3 days. Then, the aged nanofiber gel is replaced with water as a solvent and then freeze-dried for 72 hours to obtain a fiber composite aerogel with cracked surface.

[0112] Comparative Example 7

[0113] Comparative Example 7 is basically the same as Comparative Example 5, except that:

[0114] Step ④ is as follows: The nanofiber sol is kept at a constant temperature of 25°C for 2 hours in a closed environment until it gels. After that, the gelled material is placed in a container filled with ethanol and aged in a constant temperature water bath at 70°C for 3 days. Then, the aged nanofiber gel is dried at 100°C and normal pressure for 48 hours to obtain a fiber composite aerogel with cracks on the surface.

[0115] The thermal conductivity at 1000℃ and the compressive strength at 1000℃ of the materials finally prepared in each embodiment and comparative example were measured in this invention, and the results are shown in Table 1.

[0116] Table 1: Performance of the thermal insulation materials finally obtained in each embodiment and comparative example.

[0117]

[0118] The parts of this invention not described in detail are techniques known to those skilled in the art.

[0119] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A method for producing a multilayer nanofiber thermal insulation material, characterized by, The method comprises the following steps: (1) preparing a nanofiber membrane; (2) reacting a silicon source precursor, a surfactant and an acid solution to obtain a silica sol; the molar ratio of the silicon source precursor, the surfactant and the acid contained in the acid solution is (10-90):(0.06-0.6):(0.2-5), and the reaction is a room temperature reaction for 20-40 min; (3) crushing the nanofiber membrane and adding it into the silica sol and uniformly dispersing to obtain a mixed slurry, then adding ammonium bicarbonate, ammonium phosphate and ammonia water into the mixed slurry and uniformly dispersing to obtain a nanofiber slurry, and then performing suction filtration on the nanofiber slurry to obtain a nanofiber sheet; the mass ratio of the ammonium bicarbonate to the ammonium phosphate is (0.8-2):1; the total amount of the ammonium bicarbonate and the ammonium phosphate is 1-2% of the mass of the mixed slurry; the mass fraction of the nanofiber membrane in the mixed slurry is 30-60%, and the mass fraction of the silica sol contained in the mixed slurry is 40-70%; the pH of the mixed slurry is adjusted to 6.8-7.2 by adding ammonia water; (4) alternately arranging a plurality of reflecting screens and a plurality of the nanofiber sheets, and then performing molding and drying to obtain a multilayer nanofiber thermal insulation material; in the alternately arranging, one nanofiber sheet is arranged between every two reflecting screens.

2. The preparation method according to claim 1, wherein: the nanofiber membrane is prepared by electrospinning; and / or the nanofiber membrane is a silica nanofiber membrane.

3. The preparation method according to claim 1, wherein: the silicon source precursor is one or more of methyltrimethoxysilane, methyltriethoxysilane, cage polysilsesquioxane, tetraethyl orthosilicate condensate, methyl orthosilicate and ethyl orthosilicate; the surfactant is one or more of sodium dodecyl benzene sulfonate, dodecyl trimethyl ammonium bromide and dodecyl trimethyl ammonium chloride; and / or the acid solution is one or more of acetic acid solution, hydrochloric acid and oxalic acid solution.

4. The preparation method according to claim 1, wherein: the pH of the mixed slurry is adjusted to 7 by adding ammonia water.

5. The preparation method according to claim 1, wherein: the reflecting screen is a metal reflecting screen; and / or the drying is freeze drying or normal pressure drying.

6. The preparation method according to claim 5, wherein: the reflecting screen is one or more of molybdenum foil, titanium foil, stainless steel foil, nickel foil and aluminum foil.

7. The preparation method according to claim 1, wherein: the thickness of the nanofiber sheet is 1-2 mm; and / or the thickness of the reflecting screen is 0.025-0.5 mm.

8. A multilayer nanofiber thermal insulation material prepared by the preparation method according to any one of claims 1 to 7. ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​

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