Macromolecule / silicon dioxide composite aerogel and supercritical foaming preparation method thereof

Abstract

The invention provides a polymer / silicon dioxide composite aerogel, the aerogel has a three-stage porous structure, the skeleton of the aerogel is a nano composite material formed by a silicon dioxide network and a polymer material through chemical bonds or strong interaction interpenetration, the density of the aerogel is 0.02-0.2 g / cm < 3 >, the number of cells is 106-108 cells / cm < 3 >, and the heat conductivity coefficient is lower than 0.017 W / (m.K). According to the aerogel structure in the aerogel in which the aerogel skeleton is nested in the foam, extreme light weight and heat insulation are realized. The mechanical properties are as follows: after the strain is 50%, the rebound rate is gt; the content is much higher than that of single-component aerogel. And hydrophobicity: the contact angle is greater than 99 degrees.

Description

Technical Field

[0001] This invention belongs to the field of three-dimensional porous polymer materials, specifically relating to a polymer / silica composite aerogel material with a dual-network interpenetrating structure and its preparation method. In particular, this invention utilizes a unique sol-gel combined with supercritical fluid foaming method to prepare a novel aerogel material possessing ultralight weight, high strength, thermal insulation, and flexibility. Background Technology

[0002] Aerogel materials are the lowest density solid materials known to date, possessing extremely high porosity, a very large specific surface area, and extremely low thermal conductivity. Common aerogel materials can be categorized as follows: Inorganic aerogels (such as silica aerogels) are brittle, have poor toughness, and are prone to powdering, making them difficult to process and shape, which limits their application in flexible wearables.

[0003] Organic polymer aerogels (such as polyimide and cellulose aerogels): have improved mechanical properties, but their thermal stability and insulation at high temperatures are often inferior to those of inorganic aerogels.

[0004] Traditional composite aerogels involve only simple physical blending or surface coating between materials, resulting in weak interfacial bonding between the two phases, making it impossible to achieve synergistic performance enhancement. Furthermore, severe phase separation occurs during the foaming process, making it difficult to effectively control the cell structure.

[0005] Therefore, there is an urgent need for a simple and continuous production method to prepare a high-performance composite aerogel material with a dual continuous structure, which will have a very broad application prospect. Summary of the Invention

[0006] The purpose of this invention is to solve the problems in the background art mentioned above, overcome the defects of existing single-component aerogels, and provide a method for preparing high-performance composite aerogels with nanoscale dual continuous structures through molecular-level interpenetrating network design and in-situ synchronous foaming technology.

[0007] To achieve the above objectives, the present invention employs a technical solution consisting of the following technical measures.

[0008] A method for preparing a polymer / silica composite aerogel and its supercritical foaming material, and its core innovations, mainly include the following steps: (1) Integrated design of "precursor-filler": A homogeneous precursor solution is formed by mixing a polymer precursor, a silicon source, a catalyst, and a solvent. A polymerizable silicon source (such as tetraethyl orthosilicate (TEOS), methyltrimethoxysilane (MTMS), or methyltriethoxysilane) is dissolved together with a polymeric precursor (such as 2-benzylamino-2-methyl-1-propanol, 1,3-bis(dimethylamino)-2-propanol, ethylenediamine disuccinic acid, trisodium methylglycine diacetate, sodium diethyldithiocarbamate, or 4,4'-diaminodiphenyl ether) in a solvent, wherein the solvent includes any one of C1-C3 alcohol solutions, tetrahydrofuran, or dimethyl sulfoxide.

[0009] The catalyst can be mixed with the polymer precursor and silicon source in step (1), or it can be added in a high-pressure reactor after the polymer precursor, silicon source and solvent are mixed.

[0010] The formed silica serves not only as a filler but also as a simultaneously growing inorganic network framework. The silicon source undergoes a sol-gel reaction under acidic or alkaline conditions, while the polymer precursor is polymerized or cross-linked through conditional initiation. The two networks form kinetically matched and mutually inductive interpenetrating networks with chemical bonds (such as Si-OC) or strong hydrogen bonds.

[0011] (2) Supercritical fluid-assisted "gel-foaming" process: The homogeneous precursor solution is placed in an environment containing supercritical fluid. Under the condition that the supercritical fluid is used as both a foaming agent and a drying fluid, the hydrolysis condensation gelation of the silicon source, the polymerization or cross-linking gelation of the polymer monomer, and the supercritical fluid foaming process are carried out simultaneously to form a wet gel foam. The pressure is controlled by an electromagnetic pressure relief valve in the autoclave, with a pressure relief rate of 0.5-1 MPa / min, so that the supercritical fluid escapes, is directly dried and shaped to obtain the composite aerogel.

[0012] The supercritical fluid is supercritical carbon dioxide. Supercritical carbon dioxide (scCO2) is introduced into a solution in which the silicon source and the polymer precursor are co-dissolved. scCO2 can act as a solvent (reducing system viscosity and promoting molecular mixing) as well as a foaming agent and a drying fluid.

[0013] In a high-pressure reactor, the pressure is controlled at 10-14 MPa and the temperature is raised to 40-60℃ to make CO2 reach a supercritical state, and the temperature is maintained for 3-4 hours; then the temperature is raised to 200-300℃ to dehydrate for 30-60 minutes to prepare gel foam.

[0014] In a high-pressure reactor, catalysts such as ammonium fluoride and ammonia are injected into the system, and the temperature is controlled, such as 40-60℃. This triggers the hydrolysis and condensation of the silicon source in the solvent, resulting in a gelation process (formation of inorganic and polymeric networks). Maintaining the temperature at 40-60℃ and the pressure at 10-14 MPa, after the gelation reaction has proceeded for a period, the viscosity of the reaction system increases. Due to supersaturation, scCO2 in the gel automatically undergoes in-situ nucleation and growth. However, when the growth reaches a certain extent, the bubbles are locked by the newly formed dual-network structure, directly forming a micron-sized macroporous framework within the material. This framework itself is a tertiary porous structure composed of nano-sized inorganic / organic dual networks.

[0015] In step (2), the temperature inside the autoclave is raised from 50℃ to 200-300℃ within 30-60 minutes by programmed temperature increase to complete the preparation of gel foam. In step (2), during the preparation of gel foam, raising the temperature from 50℃ to 250-300℃ and holding it for 30-60 minutes can remove organic solvents and water from the system and further condense the silanol groups into a dense Si-O-Si network.

[0016] After depressurization, scCO2 escapes rapidly, eliminating the need for traditional solvent replacement and supercritical drying, thus avoiding skeletal shrinkage and cracking, and achieving efficient and low-cost "gasification drying".

[0017] (3) The unique structure of the resulting composite aerogel: Macroscopically, it is a lightweight block or flexible film that can be bent, compressed, and rebound. During cyclic compression testing (strain 50%, compression rate 10 mm / min), its rebound rate was found to be greater than 93%. After 500 cycles, the material showed no structural damage, and the cell structure showed no obvious deformation or collapse.

[0018] Micrometer-scale open-cell or closed-cell foam structures, with pore diameters ranging from 1 to 50 μm, an average pore diameter of approximately 30 to 40 μm, exhibiting a narrow, single-peak distribution, and a pore count of approximately 10. 6 -10 8 cells / cm 3 This indicates that the pore structure is uniform and dense.

[0019] The foam framework itself is a nanoscale bicontinuous interpenetrating network of silica and polymer, possessing nanopores. Specifically, the silica network is formed by SiO2 nanoparticles connected by Si-O-Si bonds, while the polymer network is a continuous structure formed by polymer chains through cross-linking points, extending throughout the inorganic framework. These two networks are intertwined at the nanoscale, possessing both interfacial regions and porous structures.

[0020] This "aerogel within an aerogel" structure, where an aerogel skeleton is nested within a foam, achieves ultimate lightweighting and thermal insulation.

[0021] Performance characteristics of the composite aerogel of this invention: (1) Density: 0.02 - 0.2 g / cm³ 3 (Adjustable).

[0022] (2) Number of bubbles: >10 6 (The average pore size is approximately 30-40 μm).

[0023] (3) Thermal conductivity: <0.017W / (m·K) (at normal pressure).

[0024] (4) Mechanical properties: After strain of 50%, the rebound rate is >93%, which is far greater than that of single-component aerogels.

[0025] (5) Hydrophobicity: Contact angle > 99°. Detailed Implementation

[0026] The embodiments of this application will be described in detail below with reference to examples. However, those skilled in the art will understand that the following examples are for illustrative purposes only and should not be construed as limiting the scope of this application. Where specific conditions are not specified in the examples, conventional conditions or conditions recommended by the manufacturer shall apply. Where the manufacturers of reagents or instruments are not specified, they are all commercially available conventional products. This application should not be construed as being limited to the specific embodiments described.

[0027] Example 1: Preparation of elastic polyurethane / silica composite aerogel 1. Preparation of precursor solution: Dissolve 2-benzylamino-2-methyl-1-propanol, methyltriethoxysilane (MTMS), and catalyst (ammonia water, ammonium fluoride) in tetrahydrofuran and mix thoroughly. The mass ratio of 2-benzylamino-2-methyl-1-propanol, MTMS, and tetrahydrofuran is 2:4:1, and the catalyst accounts for 1% of the total mass.

[0028] 2. Supercritical Co-gelling and Foaming: The solution was transferred to an autoclave, CO2 was introduced to a pressure of 10 MPa, and the temperature was raised to 60°C to bring the CO2 to a supercritical state, followed by holding at this temperature for 4 hours. Subsequently, diisocyanate (MDI) accounting for 25% of the total weight of the solution was rapidly injected through a high-pressure metering pump. In the scCO2 atmosphere, MDI and 2-benzylamino-2-methyl-1-propanol rapidly polymerized to form a polyurethane network, while MTMS hydrolyzed and condensed under the catalysis of a catalyst to form a hydrophobic SiO2 network. During the formation of the double network, the scCO2 was supersaturated, and then uniform nucleation and foaming occurred. However, when the growth reached a certain extent, the bubbles were locked by the newly formed double network structure, directly forming a micron-sized macroporous framework inside the material, and the framework itself was a tertiary porous structure composed of nano-sized inorganic / organic double networks. The temperature was then raised to 230°C (the pressure was slowly released during the heating process to ensure constant pressure), and dehydration was carried out for 40 minutes to prepare the gel foam.

[0029] 3. Depressurization: Slowly depressurize (at a rate of 1 MPa / min) to atmospheric pressure, allowing scCO2 to escape and extracting excess water from the system. After removal, age at 80℃ for 2 hours to obtain an elastic hydrophobic composite aerogel. Specifically, the average pore size is 40-50 μm, and the number of pores is 10. 6 -10 8 cells / cm 3 .

[0030] Example 2: Preparation of high-temperature resistant polyimide / silica composite aerogel 1. Preparation of precursor solution: Ethylenediamine disuccinic acid and 4,4'-diaminodiphenyl ether (ODA) were mixed with dimethyl sulfoxide (DMSO), tetraethyl orthosilicate (TEOS), a small amount of water, a catalyst (ammonia, ammonium fluoride), and SiC nanowires surface-treated with a silane coupling agent (γ-aminopropyltriethoxysilane KH550, provided by Dongguan Kangjin New Materials Technology Co., Ltd.), and continuously ultrasonically dispersed to form a homogeneous sol. The mass ratio of ethylenediamine disuccinic acid, 4,4'-diaminodiphenyl ether (ODA), dimethyl sulfoxide (DMSO), and tetraethyl orthosilicate was 2:2:1:5, the catalyst accounted for 1% of the total weight, and the SiC nanowires surface-treated with the silane coupling agent also accounted for 1%.

[0031] 2. Supercritical Simultaneous Gel-Foaming-Imidification: The sol was placed in an autoclave and charged with scCO2 (12 MPa, 60℃) and held at this temperature for 4 hours. Under these conditions, TEOS hydrolyzes and condenses to form a SiO2 gel network, while scCO2 nucleates and foams simultaneously. Subsequently, under constant pressure, the system was heated to 250℃, causing the gel network to transform into a polyimide (PI) network and achieving complete removal of solvent and byproducts.

[0032] 3. Depressurization to obtain the finished product: After slow depressurization, a high-temperature resistant, lightweight, and high-strength PI / SiO2 composite aerogel is obtained. The average pore diameter is 27 μm, and the number of pores is 10. 7 -10 8 cells / cm 3 .

[0033] Comparative Example 1: Pure silica aerogel (traditional sol-gel method, supercritical drying).

[0034] 1. Sol Preparation: A silica sol is formed by mixing a silicon source (such as tetraethyl orthosilicate, TEOS) with a solvent (ethanol, water) and a catalyst (ammonia, ammonium fluoride) and reacting the mixture through hydrolysis and condensation reactions (at 60°C for 50 min). The ratio of raw materials used is 3:6:1 (silicon source:ethanol:water) and 1% (catalyst by weight).

[0035] 2. Gelation and Aging: The sol was allowed to stand at room temperature for 8 hours to further condense and form a three-dimensional network, resulting in a wet gel. It was then aged at 50°C for one day to enhance network strength.

[0036] 3. Supercritical Drying: The wet gel is placed in an autoclave, and residual solvents such as ethanol and water are replaced with supercritical CO2. After maintaining the pressure at 10 MPa and 40°C for 12 hours, the pressure is slowly released. This process completely eliminates the gas-liquid interface and capillary forces, thus obtaining a product with a complete aerogel structure. The number of pores is 10. 3 -10 4 cells / cm 3 .

[0037] Comparative Example 2: Pure polyurethane foam (traditional chemical foaming method).

[0038] 1. Raw material mixing: Polyether polyol (PPG), catalyst (ammonia and ammonium fluoride), surfactant (silicone oil, used to stabilize cells), and chemical foaming agent (water) are mixed at room temperature and pressure to form component A (white material). The mass ratio of PPG:surfactant:water is 100:5:5, and the catalyst accounts for 1% of the total weight.

[0039] 2. Foaming and curing: Mix component A and component B diisocyanate (black material, in a ratio of 2:1 with A) at high speed for 2 minutes, then quickly pour into the mold, let stand for 5 minutes, and then demold.

[0040] 3. Curing: After demolding, the foam is placed at 50℃ for 24 hours to allow the reaction to complete and reach its final strength. The resulting product has a cell count of 10. 3 -10 5 cells / cm 3.

[0041] Comparative Example 3 1. Preparation of precursor solution: Dissolve polyether polyol (PPG), tetraethyl orthosilicate silane (TEOS), catalyst (dibutyltin dilaurate), and hexadecyltrimethylammonium bromide in tetrahydrofuran and mix thoroughly.

[0042] 2. Supercritical Cogelling and Foaming: The solution was transferred to a high-pressure reactor, and CO2 was introduced to a pressure of 10 MPa. The temperature was raised to 60°C to bring the CO2 to a supercritical state, and maintained at this temperature for 4 hours. Subsequently, a measured amount of diisocyanate (MDI) was rapidly injected using a high-pressure metering pump. In the scCO2 atmosphere, MDI and PPG rapidly polymerized to form a polyurethane network, while TEOS hydrolyzed and condensed under the catalysis of a catalyst to form a hydrophobic SiO2 network. During the formation of the dual network, the scCO2 became supersaturated, leading to uniform nucleation and foaming. The temperature was then raised to 230°C for dehydration for 40 minutes to obtain the gel foam.

[0043] 3. Depressurization: Slowly depressurize (at a rate of 1 MPa / min) to atmospheric pressure, allowing scCO2 to escape and extracting excess water from the system. After removal, age at 80℃ for 2 hours to obtain an elastic hydrophobic composite aerogel. The number of cells is 10. 5 -10 6 cells / cm 3 .

[0044] Effect comparison:

Claims

1. A polymer / silica composite aerogel, characterized in that, The aerogel has a tertiary porous structure, and its framework is a nanocomposite material composed of a silica network and polymer materials interpenetrating through chemical bonds or strong interactions. The density of the aerogel is 0.02-0.2 g / cm³. 3 The number of bubbles is 10 6 -10 8 cells / cm 3 The thermal conductivity is less than 0.017 W / (m·K).

2. The composite aerogel according to claim 1, characterized in that, The precursor of the polymer material is selected from at least one of 2-benzylamino-2-methyl-1-propanol, ethylenediamine disuccinic acid, 4,4'-diaminodiphenyl ether, and diisocyanate.

3. The composite aerogel according to claim 1, characterized in that, The silica network is prepared by alkoxysilane via a sol-gel method, wherein the alkoxysilane includes tetraethyl orthosilicate, methyltrimethoxysilane, methyltriethoxysilane, or mixtures thereof.

4. A method for preparing the polymer / silica composite aerogel as described in any one of claims 1-3, characterized in that, Includes the following steps: (1) Mix the precursor of the polymer material, the silicon source, the catalyst and the solvent to form a homogeneous precursor solution; (2) The homogeneous precursor solution is placed in an environment containing supercritical fluid in an autoclave. Under the condition that the supercritical fluid is used as both a foaming agent and a drying fluid, the hydrolysis condensation gelation of the silicon source, the polymerization or cross-linking gelation of the polymer monomer, and the supercritical fluid foaming process are carried out to form a gel foam. (3) The pressure is controlled by an electromagnetic pressure relief valve in the autoclave, wherein the pressure relief rate is 0.5-1 MPa / min, so that the supercritical fluid escapes, is directly dried and shaped to obtain the composite aerogel.

5. The method according to claim 4, characterized in that, The supercritical fluid is supercritical carbon dioxide.

6. The method according to claim 4, characterized in that, In step (1), the catalyst is selected from one or more combinations of ammonium fluoride and ammonia water.

7. The method according to claim 6, characterized in that, In step (2), the pressure is controlled at 10-14 MPa and the temperature is raised to 40-60℃ in the autoclave to make CO2 reach the supercritical state and keep it at that temperature for 3-4 hours. The mixture is then heated to 200-300℃ and dehydrated for 30-60 minutes to prepare gel foam.

8. The method according to claim 4, characterized in that, The precursor solution also contains functional nanomaterials selected from carbon nanotubes, graphene, or ceramic nanowires.

9. An application of the polymer / silica composite aerogel as described in any one of claims 1-3, characterized in that, Thermal insulation components for aerospace, battery pack insulation for new energy vehicles, thermal insulation materials for construction, and thermal insulation layers for flexible wearable devices.

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