Fireproof thermal insulation material and preparation method thereof

Abstract

This invention relates to the field of porous thermal insulation materials, and discloses a fireproof and heat-insulating material and its preparation method. The material is an aerogel comprising a polyimide framework, two-dimensional transition metal carbonitride nanosheets, and phytic acid. The aerogel contains multiple unidirectional, parallel tubular or layered channels, each surrounded by a pore wall. The pore wall is composed of a cross-linked network formed by chemical bonds connecting phytic acid, two-dimensional transition metal carbonitride nanosheets, and the polyimide framework. This invention uses phytic acid as a cross-linking agent and an in-situ catalytic charring agent, overcoming the defect of easy agglomeration of nanosheets and generating a dense carbonized layer upon heating, effectively supporting the pore walls and preventing the porous framework from collapsing. Combined with the heat conduction blocking effect of the unidirectional channels, the material exhibits excellent low thermal conductivity, high mechanical strength, and extremely stable high-temperature shrinkage insulation properties, making it suitable for fireproof and heat-insulating protection in extreme environments.

Description

Technical Field

[0001] This invention relates to the field of porous thermal insulation materials, and in particular to a fireproof and heat-insulating material and its preparation method. Background Technology

[0002] With the increasing demands for safety protection in extreme environments from modern industry, construction, and aerospace, fire-resistant and heat-insulating materials with excellent thermal insulation and flame-retardant properties have become a research hotspot. Aerogels, as three-dimensional porous materials composed of a nanoscale solid framework, are considered ideal thermal insulation materials due to their extremely low porosity and thermal conductivity. Among them, polyimide aerogels overcome the defects of brittleness and powder shedding compared to traditional inorganic silica aerogels, and possess better flexibility and mechanical processing properties.

[0003] However, existing polyimide aerogels still face significant challenges in practical applications. First, when exposed to extreme high-temperature flames such as fires, the traditional polyimide framework is highly susceptible to severe thermal degradation and volume shrinkage, leading to the collapse of the internal porous framework and loss of its physical thermal insulation barrier function. Second, to improve its mechanical strength and flame retardancy, current technologies often attempt to physically blend in two-dimensional nanomaterials (such as MXene and graphene) or traditional halogen / phosphorus-containing flame retardants. However, two-dimensional nanomaterials are prone to layer-by-layer aggregation during aerogel drying, making it difficult to provide ideal physical support; while the simple physical addition of traditional flame retardants not only easily volatilizes or migrates at high temperatures but also disrupts the original microscopic pore uniformity of the aerogel, and may even release toxic fumes during combustion.

[0004] Therefore, how to effectively prevent the stacking of two-dimensional nanomaterials and construct a high-strength thermal insulation skeleton that does not shrink or collapse under high temperature burning, starting from the micro-crosslinking mechanism and meso-pore structure of materials, while avoiding the use of toxic additives, is a technical problem that urgently needs to be solved in this field. Summary of the Invention

[0005] This invention provides a fireproof and heat-insulating material and its preparation method. Through the synergistic effect of the three-dimensional chemical cross-linking network constructed by phytic acid and the directional through-hole structure, the material achieves in-situ charring support under high temperature burning without the skeleton collapsing, which significantly improves the mechanical strength, high temperature shrinkage resistance and heat insulation and flame retardancy of the aerogel under extreme environments.

[0006] This invention provides a fireproof and heat-insulating material, which is an aerogel comprising a polyimide framework, two-dimensional transition metal carbonitride nanosheets, and phytic acid; The aerogel has multiple unidirectional, parallel tubular or layered channels inside, which are surrounded by pore walls. The pore walls are composed of a cross-linked network formed by chemical bonds connecting the phytic acid, two-dimensional transition metal carbonitride nanosheets, and polyimide framework.

[0007] Furthermore, the raw materials for forming the aerogel include: 100 parts of polyamic acid, 1-15 parts of the two-dimensional transition metal carbonitride nanosheets, and 5-20 parts of phytic acid; the polyimide backbone is generated by the thermal imidization reaction of the polyamic acid.

[0008] Furthermore, the two-dimensional transition metal carbonitride nanosheets are monolayer Ti3C2T nanosheets with surface end groups. x Nanosheets, wherein the surface end groups are at least one of hydroxyl, oxygen, or fluorine groups; In the cross-linked network, the phosphate groups of the phytic acid are bonded to the monolayer Ti3C2T x The surface end groups of the nanosheets are connected by hydrogen bonds and coordination bonds.

[0009] Furthermore, the diameter of the tubular or layered channels is 10μm to 50μm.

[0010] Furthermore, the pore walls undergo dehydration and carbonization under heating, resulting in the in-situ formation of a dense carbonized layer containing phosphorus, carbon, and transition metals on the surface of the two-dimensional transition metal carbonitride nanosheets.

[0011] The present invention also provides a method for preparing the fireproof and heat-insulating material as described above, comprising the following steps: (1) The dispersion of the two-dimensional transition metal carbonitride nanosheets is mixed with the aqueous solution of phytic acid, and the mixture is ultrasonically treated to obtain a mixed dispersion. (2) A water-soluble polyamic acid solution is added dropwise to the mixed dispersion at a uniform rate and stirred until homogeneous to obtain a composite precursor liquid; (3) Apply a unidirectional temperature gradient to the composite precursor fluid for directional freezing, so that the solvent inside the solution crystallizes and grows along the direction of the unidirectional temperature gradient. Then freeze-dry to remove the solvent crystals and obtain a precursor aerogel with multiple unidirectionally connected and parallel tubular or layered channels. (4) The precursor aerogel is subjected to programmed heating heat treatment under an inert atmosphere to cause the polyamic acid to undergo a dehydration and ring-closing reaction to generate the polyimide skeleton, and the phytic acid, two-dimensional transition metal carbonitride nanosheets and polyimide skeleton are cross-linked and cured by chemical bonds to obtain the fireproof and heat-insulating material.

[0012] Furthermore, in step (1), the ultrasonic treatment time is 30 min to 60 min, the ultrasonic power is 200 W to 400 W, and both the mixing and ultrasonic treatment are carried out under ice bath conditions.

[0013] Further, in step (2), the water-soluble polyamic acid solution is prepared by polymerizing pyromellitic dianhydride and diaminodiphenyl ether in water and then neutralizing them with an organic base to form a salt, and its mass fraction is 3%~8%.

[0014] Furthermore, in step (3), directional freezing is performed using a mold with the bottom in contact with a cold source and the sides and top insulated. The cold source is liquid nitrogen or a dry ice-ethanol bath, in order to form an axial temperature gradient from bottom to top inside the composite precursor fluid.

[0015] Further, in step (4), the specific conditions for the programmed temperature rise heat treatment are as follows: heating to 100°C at a heating rate of 1°C / min to 3°C / min and holding for 1 hour, then heating to 200°C at the same heating rate and holding for 1 hour, and finally heating to 300°C and holding for 2 hours; the inert atmosphere is a nitrogen atmosphere or an argon atmosphere.

[0016] The beneficial effects of this invention are as follows: This invention utilizes phytic acid as a multifunctional crosslinking agent. Its abundant phosphate groups enable three-dimensional chemical crosslinking of two-dimensional transition metal carbonitride nanosheets with polyimide macromolecular chains, overcoming the defect of easy aggregation of two-dimensional nanosheets and endowing the aerogel pore walls with extremely high mechanical strength and toughness. When exposed to extremely high temperature flames, the phytic acid in the crosslinked network undergoes thermal dehydration and catalyzes the polyimide skeleton, generating a dense carbonized layer containing phosphorus, carbon, and transition metals in situ on the nanosheet surface. This dense carbonized layer has excellent anti-shrinkage ability, maintaining the unidirectional through-tube pore structure formed by directional freezing and preventing skeleton collapse. This dual coupling of chemical in-situ carbonization support and physical directional microchannel insulation hinders heat transfer in the direction perpendicular to the pores through phonon scattering, achieving not only low thermal conductivity but also maintaining volume retention under continuous high-temperature burning, overcoming the defect of traditional aerogels shrinking and failing upon exposure to fire. Attached Figure Description

[0017] Figure 1 This is a schematic flowchart of the preparation method of the fireproof and heat-insulating material of the present invention.

[0018] Figure 2 This is a comparison chart of the back-fire surface temperature-time curves of Example 1 of the present invention and Comparative Examples 1 and 2 under continuous burning with a flame at 1000°C.

[0019] The realization of the objective, functional features and advantages of the present invention will be further explained in conjunction with the embodiments and with reference to the accompanying drawings. Detailed Implementation

[0020] It should be understood that the specific embodiments described herein are merely illustrative of the invention and are not intended to limit the invention.

[0021] Example 1: A fireproof and heat-insulating material This embodiment provides a fireproof and thermal insulation material, which is macroscopically an aerogel with excellent structural stability. Specifically, the material is an aerogel comprising a polyimide framework, two-dimensional transition metal carbonitride nanosheets, and phytic acid.

[0022] The raw material components and proportions for forming the aerogel described in this embodiment, by mass parts, are: 100 parts polyamic acid, 10 parts the two-dimensional transition metal carbonitride nanosheets, and 15 parts phytic acid. The polyimide backbone is generated by the thermal imidization reaction of the aforementioned polyamic acid.

[0023] In terms of microstructure, the aerogel contains multiple unidirectional, parallel tubular channels, each surrounded by a pore wall. In this embodiment, the average pore diameter of the tubular channels was measured to be 30 μm. The pore walls are composed of a cross-linked network formed by chemical bonds connecting the phytic acid, two-dimensional transition metal carbonitride nanosheets, and a polyimide framework.

[0024] In the cross-linked network, the two-dimensional transition metal carbonitride nanosheets are selected from monolayer Ti3C2T nanosheets with surface end groups. x The nanosheets have surface end groups comprising hydroxyl, oxygen, and fluorine groups. The phosphate groups in the phytic acid molecular structure interact with the monolayer Ti3C2T. x The surface end groups of the nanosheets are tightly connected by hydrogen bonds and coordination bonds, while being anchored to the polyimide backbone.

[0025] In this embodiment, when exposed to fire or heat, the phytic acid inside the pore walls of the fireproof and thermal insulation material undergoes a dehydration and carbonization reaction, forming a dense carbonized layer containing phosphorus, carbon, and transition metals in situ on the surface of the two-dimensional transition metal carbonitride nanosheets. This carbonized layer effectively supports the tubular pore structure, preventing pore wall collapse and thus maintaining the material's integrity and thermal insulation performance under extreme high temperatures.

[0026] Example 2: A method for preparing a fireproof and heat-insulating material This embodiment provides a method for preparing the above-mentioned fireproof and heat-insulating material, the complete process of which includes the following steps: (1) Mixing and Modified Dispersion Take 10 portions of monolayer Ti3C2T xA dispersion of nanosheets was mixed with 15 parts of an aqueous solution of phytic acid. The mixture was then subjected to ultrasonic treatment under ice bath conditions using an ultrasonic homogenizer. The ultrasonic power was set to 300W, and the ultrasonic treatment time was 45 min. Through this step, phytic acid and Ti3C2T were homogenized. x The nanosheets react fully to obtain a uniform and stable mixed dispersion.

[0027] (2) Preparation of the composite precursor fluid Prepare a 5% (w / w) water-soluble polyamic acid solution. This solution is prepared by polymerizing pyromellitic dianhydride and diaminodiphenyl ether as monomers in water, followed by neutralization with an organic base (such as triethylamine) to form a salt. Add the water-soluble polyamic acid solution, equivalent to 100 parts of polyamic acid solids, dropwise at a uniform rate to the mixed dispersion obtained in step (1). Maintain continuous mechanical stirring during the dropwise addition until the mixture is homogeneous, resulting in a uniform composite precursor liquid.

[0028] (3) Directional freezing and freeze drying The composite precursor fluid obtained in step (2) is injected into a dedicated directional freezing mold, which is designed with a bottom contact with the cold source and side and top insulation. In this embodiment, liquid nitrogen (-196°C) is used as the bottom cold source. During the directional freezing process, an axial temperature gradient is formed inside the composite precursor fluid from bottom to top, driving the solvent (water) inside the solution to crystallize and grow along the direction of the unidirectional temperature gradient (vertically upward). After complete freezing, the sample is transferred to a freeze dryer, and the solvent crystals are sublimated under vacuum conditions to obtain a precursor aerogel with multiple unidirectional and parallel tubular channels.

[0029] (4) Thermal imidization and cross-linking curing The precursor aerogel obtained in step (3) was placed in a tube furnace and subjected to programmed temperature rise heat treatment under a nitrogen atmosphere with a purity of 99.99%.

[0030] The specific temperature ramp conditions in this embodiment are as follows: heat to 100°C at a ramp rate of 2°C / min and hold for 1 hour; then continue heating to 200°C at a ramp rate of 2°C / min and hold for 1 hour; finally, heat to 300°C at a ramp rate of 2°C / min and hold for 2 hours. Allow to cool naturally to room temperature.

[0031] During this heat treatment process, polyamic acid undergoes a dehydration and ring-closure reaction to form a rigid polyimide backbone, while simultaneously promoting the formation of phytic acid and monolayer Ti3C2T. x Deep cross-linking and curing are achieved between the nanosheets and the polyimide framework through chemical bonds. The final result is an anisotropic fireproof and thermal insulation material that combines high mechanical strength with excellent flame retardant properties. Example

[0032] This embodiment provides a fireproof and heat-insulating material and its preparation method. The main difference between this embodiment and Embodiments 1 and 2 lies in the ratio of raw material components and the freezing conditions in the preparation method.

[0033] Specifically, by mass, the raw material components in this embodiment are: 100 parts polyamic acid, and the monolayer Ti3C2T x Five parts of nanosheets and five parts of phytic acid were used. In step (3) of the preparation method, the cold source for directional freezing was a dry ice-ethanol bath (-78°C). The remaining structural features and specific preparation steps were consistent with those of Examples 1 and 2. Measurements showed that the average pore size of the tubular channels in the fireproof and heat-insulating material prepared in this example was approximately 50 μm. Example

[0034] This embodiment provides a fireproof and heat-insulating material and its preparation method. The only difference between this embodiment and Embodiments 1 and 2 is the ratio of the raw material components.

[0035] Specifically, by mass, the raw material components in this embodiment are: 100 parts polyamic acid, and the monolayer Ti3C2T x The nanosheets consist of 15 parts, and the phytic acid consists of 20 parts. All other structural features and preparation methods are the same as in Examples 1 and 2.

[0036] Comparative Example 1 This comparative example provides a conventional aerogel and its preparation method. The only difference between this comparative example and Examples 1 and 2 is that the phytic acid was not added to the raw material components. All other component ratios and preparation steps are exactly the same as in Examples 1 and 2.

[0037] Comparative Example 2 This comparative example provides an isotropic aerogel and its preparation method. The raw material composition ratio of this comparative example is the same as that of Example 1. The only difference between this comparative example and Example 2 is that in step (3), a directional freezing mold is not used, but the composite precursor fluid is directly placed in a conventional freezer at -20°C for isotropic freezing, and no unidirectional temperature gradient is formed inside. The remaining preparation steps are the same as those in Example 2.

[0038] The samples prepared in the above embodiments and comparative examples were cut into standard test blocks of 50mm×50mm×10mm and relevant performance tests were conducted. The test results are shown in Table 1.

[0039] Group Limiting Oxygen Index (LOI) Radial thermal conductivity (W / m·K) Compressive strength (MPa) at 50% strain Volume retention rate after high-temperature calcination Example 1 38.5% 0.018 0.45 92% Example 3 33.2% 0.022 0.31 85% Example 4 41.0% 0.016 0.52 95% Comparative Example 1 28.5% 0.025 0.12 45% (severe contraction) Comparative Example 2 38.0% 0.035 0.35 88% As shown in Table 1, the fireproof and thermal insulation material of this invention achieves significant synergistic improvements in several core performance aspects. A comparison of Example 1 and Comparative Example 1 reveals that the introduction of the phytic acid crosslinking network not only dramatically increases the limiting oxygen index (LOI) from 28.5% to 38.5%, but also improves the volume retention rate from 45% to 92% under high-temperature burning, completely overcoming the fatal defect of traditional aerogels being prone to skeletal collapse under heat. Simultaneously, its compressive strength is increased by nearly three times (0.45 MPa vs. 0.12 MPa), confirming the strong structural support effect of the chemical crosslinking network on the physical pore walls. On the other hand, a comparison between Example 1 and Comparative Example 2 shows that the unidirectional through-hole structure significantly reduces the radial thermal conductivity of the material (0.018 W / m·K vs. 0.035 W / m·K), greatly enhancing its heat-blocking ability. Data from Examples 3 and 4 further verify that, within the controlled parameter range, the solutions of this invention maintain excellent overall performance.

[0040] like Figure 2 The back-fired surface temperature-time curve is shown in the figure. A butane flame torch at 1000℃ was used to continuously burn the front of each 10mm thick sample, and the temperature change of the back-fired surface was measured. Comparative Example 2 (isotropic pore structure) showed that the temperature on the unexposed surface rapidly rose to over 150°C within 3 minutes of burning, indicating that the phonon scattering efficiency of the disordered pores was low and the thermal insulation failed quickly. Comparative Example 1 (without phytic acid crosslinking network) experienced severe carbonization and shrinkage of the polyimide skeleton due to the lack of crosslinking support after about 5 minutes of burning, which caused the flame to penetrate the material skeleton directly, and the temperature of the unexposed surface instantly exceeded 300°C. In contrast, during the test cycle of continuous burning at 1000°C for 15 minutes in Example 1, the temperature of the back-fired surface remained consistently below 85°C. This result indicates that, under heated conditions, the phytic acid within the pore walls undergoes dehydration and carbonization, and this process occurs in Ti3C2T... x A dense carbonized layer containing phosphorus, carbon, and transition metals was generated in situ on the surface of the nanosheets. This dense carbonized layer effectively supports the unidirectional tubular channels, greatly hindering heat transfer in the direction perpendicular to the channels, thus achieving a synergistic improvement in flame retardant and thermal insulation properties.

[0041] It should be noted that, in this document, the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, apparatus, article, or method that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such process, apparatus, article, or method. Unless otherwise specified, an element defined by the phrase "comprising one..." does not exclude the presence of other identical elements in the process, apparatus, article, or method that includes that element.

[0042] The above description is merely a preferred embodiment of the present invention and does not limit the patent scope of the present invention. Any equivalent structural or procedural transformations made based on the content of the present invention's specification and drawings, or direct or indirect applications in other related technical fields, are similarly included within the patent protection scope of the present invention.

Claims

1. A fireproof and heat-insulating material, characterized in that, The material is an aerogel comprising a polyimide framework, two-dimensional transition metal carbonitride nanosheets, and phytic acid. The aerogel has multiple unidirectional, parallel tubular or layered channels inside, which are surrounded by pore walls. The pore walls are composed of a cross-linked network formed by chemical bonds connecting the phytic acid, two-dimensional transition metal carbonitride nanosheets, and polyimide framework.

2. The fireproof and heat-insulating material according to claim 1, characterized in that, The raw materials for forming the aerogel include: 100 parts of polyamic acid, 1-15 parts of the two-dimensional transition metal carbonitride nanosheets, and 5-20 parts of phytic acid; the polyimide backbone is generated by the thermal imidization reaction of the polyamic acid.

3. The fireproof and heat-insulating material according to claim 1, characterized in that, The two-dimensional transition metal carbonitride nanosheets are monolayer Ti3C2T with surface end groups. x Nanosheets, wherein the surface end groups are at least one of hydroxyl, oxygen, or fluorine groups; In the cross-linked network, the phosphate groups of the phytic acid are bonded to the monolayer Ti3C2T x The surface end groups of the nanosheets are connected by hydrogen bonds and coordination bonds.

4. The fireproof and heat-insulating material according to claim 1, characterized in that, The diameter of the tubular or layered channels is 10μm to 50μm.

5. The fireproof and heat-insulating material according to claim 1, characterized in that, The pore walls undergo dehydration and carbonization under heat, resulting in the in-situ formation of a dense carbonized layer containing phosphorus, carbon, and transition metals on the surface of the two-dimensional transition metal carbonitride nanosheets.

6. A method for preparing a fireproof and heat-insulating material as described in any one of claims 1 to 5, characterized in that, Includes the following steps: (1) The dispersion of the two-dimensional transition metal carbonitride nanosheets is mixed with the aqueous solution of phytic acid, and then ultrasonically treated to obtain a mixed dispersion. (2) A water-soluble polyamic acid solution is added dropwise to the mixed dispersion at a uniform rate and stirred until homogeneous to obtain a composite precursor liquid; (3) Apply a unidirectional temperature gradient to the composite precursor fluid for directional freezing, so that the solvent inside the solution crystallizes and grows along the direction of the unidirectional temperature gradient. Then freeze-dry to remove the solvent crystals and obtain a precursor aerogel with multiple unidirectionally connected and parallel tubular or layered channels. (4) The precursor aerogel is subjected to programmed heating heat treatment under an inert atmosphere to cause the polyamic acid to undergo a dehydration and ring-closing reaction to generate the polyimide skeleton, and the phytic acid, two-dimensional transition metal carbonitride nanosheets and polyimide skeleton are cross-linked and cured by chemical bonds to obtain the fireproof and heat-insulating material.

7. The method for preparing the fireproof and heat-insulating material according to claim 6, characterized in that, In step (1), the ultrasonic treatment time is 30 min to 60 min, the ultrasonic power is 200 W to 400 W, and both mixing and ultrasonic treatment are carried out under ice bath conditions.

8. The method for preparing the fireproof and heat-insulating material according to claim 6, characterized in that, In step (2), the water-soluble polyamic acid solution is prepared by polymerizing pyromellitic dianhydride and diaminodiphenyl ether in water and then neutralizing them with an organic base to form a salt, with a mass fraction of 3% to 8%.

9. The method for preparing the fireproof and heat-insulating material according to claim 6, characterized in that, In step (3), directional freezing is performed using a mold with the bottom in contact with a cold source and the sides and top insulated. The cold source is liquid nitrogen or a dry ice-ethanol bath, in order to form an axial temperature gradient from bottom to top inside the composite precursor fluid.

10. The method for preparing the fireproof and heat-insulating material according to claim 6, characterized in that, In step (4), the specific conditions for the programmed temperature rise heat treatment are as follows: heat to 100°C at a heating rate of 1°C / min to 3°C / min and hold for 1 hour, then heat to 200°C at the same heating rate and hold for 1 hour, and finally heat to 300°C and hold for 2 hours; the inert atmosphere is a nitrogen atmosphere or an argon atmosphere.

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