CN113150363B - Porous aerogel and preparation method thereof - Google Patents
Porous aerogel and preparation method thereof Download PDFInfo
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- CN113150363B CN113150363B CN202110516547.7A CN202110516547A CN113150363B CN 113150363 B CN113150363 B CN 113150363B CN 202110516547 A CN202110516547 A CN 202110516547A CN 113150363 B CN113150363 B CN 113150363B
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- C08J9/00—Working-up of macromolecular substances to porous or cellular articles or materials; After-treatment thereof
- C08J9/28—Working-up of macromolecular substances to porous or cellular articles or materials; After-treatment thereof by elimination of a liquid phase from a macromolecular composition or article, e.g. drying of coagulum
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- C08J2201/04—Foams characterised by the foaming process characterised by the elimination of a liquid or solid component, e.g. precipitation, leaching out, evaporation
- C08J2201/048—Elimination of a frozen liquid phase
- C08J2201/0482—Elimination of a frozen liquid phase the liquid phase being organic
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- C08J2201/04—Foams characterised by the foaming process characterised by the elimination of a liquid or solid component, e.g. precipitation, leaching out, evaporation
- C08J2201/048—Elimination of a frozen liquid phase
- C08J2201/0484—Elimination of a frozen liquid phase the liquid phase being aqueous
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- C08J2201/00—Foams characterised by the foaming process
- C08J2201/04—Foams characterised by the foaming process characterised by the elimination of a liquid or solid component, e.g. precipitation, leaching out, evaporation
- C08J2201/054—Precipitating the polymer by adding a non-solvent or a different solvent
- C08J2201/0542—Precipitating the polymer by adding a non-solvent or a different solvent from an organic solvent-based polymer composition
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- C08J2201/00—Foams characterised by the foaming process
- C08J2201/04—Foams characterised by the foaming process characterised by the elimination of a liquid or solid component, e.g. precipitation, leaching out, evaporation
- C08J2201/054—Precipitating the polymer by adding a non-solvent or a different solvent
- C08J2201/0545—Precipitating the polymer by adding a non-solvent or a different solvent from an aqueous solvent-based polymer composition
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- C08J2205/00—Foams characterised by their properties
- C08J2205/02—Foams characterised by their properties the finished foam itself being a gel or a gel being temporarily formed when processing the foamable composition
- C08J2205/026—Aerogel, i.e. a supercritically dried gel
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- C08J2205/00—Foams characterised by their properties
- C08J2205/04—Foams characterised by their properties characterised by the foam pores
- C08J2205/044—Micropores, i.e. average diameter being between 0,1 micrometer and 0,1 millimeter
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- C08J2329/00—Characterised by the use of homopolymers or copolymers of compounds having one or more unsaturated aliphatic radicals, each having only one carbon-to-carbon double bond, and at least one being terminated by an alcohol, ether, aldehydo, ketonic, acetal, or ketal radical; Hydrolysed polymers of esters of unsaturated alcohols with saturated carboxylic acids; Derivatives of such polymer
- C08J2329/02—Homopolymers or copolymers of unsaturated alcohols
- C08J2329/04—Polyvinyl alcohol; Partially hydrolysed homopolymers or copolymers of esters of unsaturated alcohols with saturated carboxylic acids
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- C08J2333/00—Characterised by the use of homopolymers or copolymers of compounds having one or more unsaturated aliphatic radicals, each having only one carbon-to-carbon double bond, and only one being terminated by only one carboxyl radical, or of salts, anhydrides, esters, amides, imides, or nitriles thereof; Derivatives of such polymers
- C08J2333/18—Homopolymers or copolymers of nitriles
- C08J2333/20—Homopolymers or copolymers of acrylonitrile
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- Y02B80/00—Architectural or constructional elements improving the thermal performance of buildings
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Abstract
The invention provides a porous aerogel and a preparation method thereof. The preparation method comprises the following steps: dissolving a polymer in a good solvent to obtain a uniform solution, and freezing the uniform solution; soaking the frozen product in a poor solvent at a temperature between the melting point of the good solvent and the melting point of the poor solvent; and heating and drying the soaked product to obtain the porous aerogel. The porous aerogel prepared by the preparation method disclosed by the invention has excellent mechanical properties and heat insulation properties.
Description
Technical Field
The invention relates to a preparation method of porous aerogel, belonging to the technical field of aerogel material preparation.
Background
With the rapid development of thermal insulation materials and cushioning materials, the demand for lightweight porous materials is increasing. Aerogel exhibits excellent thermal insulation properties due to its rich pore structure, polar thermal conductivity and extremely low density. The traditional aerogel is usually inorganic aerogel and has the problems of poor mechanical property, brittle quality, difficult processing and the like. The emerging organic aerogel not only has rich pore channel structures and excellent thermodynamic properties of inorganic aerogel, but also has good mechanical properties, and has the remarkable advantages of good heat insulation performance, strong impact resistance and the like.
The main methods for preparing organic aerogels currently include freeze-drying and supercritical drying. The freeze drying method is a drying method that the material containing the solvent is frozen and then the solid solvent crystal is directly converted into gas to be removed under higher vacuum degree. However, since the sublimation of the support crystal is reduced during drying, the sample is easily deformed, and the time is long. The supercritical drying method is a drying method in which no interface exists between a gas and a liquid in a supercritical state, and a uniform fluid is interposed between the gas and the liquid and is gradually discharged from a gel. The method does not cause the shrinkage deformation and collapse of the structure, but has the advantages of long time consumption, low yield, high price and expensive equipment.
Therefore, research and development on a preparation method of a novel organic aerogel with high efficiency, high quality and low price are important in the field of heat insulation and buffer materials.
Disclosure of Invention
In order to solve the above technical problems, the present invention aims to provide a method for preparing a porous aerogel which is rapid and simple in process.
Another object of the present invention is to provide a porous aerogel having excellent mechanical properties and thermal insulation properties.
In order to achieve any of the above objects, the present invention provides, first, a method for preparing a porous aerogel, the method comprising:
dissolving a polymer in a good solvent to obtain a uniform solution, and freezing the uniform solution;
soaking the frozen product in a poor solvent at a temperature between the melting point of the good solvent and the melting point of the poor solvent;
and heating and drying the soaked product to obtain the porous aerogel.
According to the preparation method of the porous aerogel, the polymer is dissolved in the good solvent through an ice crystal replacement technology, then the uniform solution is poured into a mold, and the mold is placed in a low-temperature environment, so that the solution is completely frozen. And then soaking in a poor solvent, and keeping the soaking temperature between the melting points of the good solvent and the poor solvent to ensure that the good solvent is still in a crystalline state (serving as a pore-forming agent) and the poor solvent is in a liquid state (serving as an etching agent for a polymer precipitation agent and good solvent crystals). And heating and drying to obtain the porous aerogel. The strength of the framework is enhanced due to the precipitation effect of the poor solvent on the polymer network, and the liquid poor solvent replaces the good solvent crystals to be filled in the pores, so that a certain soft supporting effect is provided, and the finally prepared aerogel has a uniform micro-pore structure and better macro-shape retention capability.
In one embodiment of the present invention, the polymer may be one or a mixture of several of non-crosslinked linear polymer, star polymer, comb polymer and crosslinked polymer, which are shown in the following formula, according to the use condition and the mechanical property requirement. Preferably the molecular weight Mw of the polymer is more than or equal to 1 ten thousand; more preferably, the polymer is one or a combination of several of polymethyl methacrylate, polyacrylonitrile, polylactic acid, polyvinylidene fluoride, polyvinyl alcohol and chitosan.
The mixing mass ratio of the polymer to the good solvent is 1:9-5:5, the porosity of the aerogel can be adjusted by adjusting the ratio, and the heat insulation performance and the mechanical performance of the aerogel are influenced finally. Meanwhile, in order to increase the functionality of the aerogel, a composite material can be added when preparing a uniform solution; the composite material preferably added is one or a combination of more of silicon dioxide, graphene, carbon nanotubes and glass fibers.
In one embodiment of the present invention, the freezing temperature is-80 ℃ to-60 ℃ (preferably-70 ℃) to ensure the good solvent is completely frozen, and the freezing time is 3h to 5h (preferably 4 h). The pore size of the aerogel can be adjusted by adjusting the freezing temperature, and the lower the temperature is, the smaller the pore size is; the closer the temperature is to the freezing point of the good solvent, the larger the pores.
In one embodiment of the present invention, the good solvent and the poor solvent are selected to be mutually soluble, and in the same system, the good solvent and the poor solvent are different, and the melting point of the good solvent is higher than that of the poor solvent; the soaking temperature needs to be between the melting points of the good solvent and the poor solvent, so as to ensure that the good solvent is still in a crystalline state (as a pore-forming agent) and the poor solvent is in a liquid state (as an etching agent for a polymer precipitation agent and good solvent crystals). Preferably, the good solvent is one or a mixture of more of dimethyl sulfoxide, 1, 4-epoxyhexaalkane and water; the poor solvent is preferably one or more of ethanol, acetone, methanol and water.
In one embodiment of the invention, the soaking time is 3h to 5h (preferably 4 h). The temperature for heating and drying is 70-90 ℃ (preferably 80 ℃).
In order to achieve the above technical objects, the present invention also provides a porous aerogel prepared by the method for preparing the porous aerogel of the present invention. The pore size of the porous aerogel is about 5-20 microns. The porous aerogel has good pore retentivity, simple preparation and low price. The heat conductivity coefficient of the porous aerogel is 0.012-0.024W/K (25 ℃) through testing, and the porous aerogel has better durability. In addition, the porous aerogel also has excellent mechanical properties, the compression strength is up to 27MPa, and the porous aerogel has impact resistance.
The preparation process of the porous aerogel is simple, the preparation is rapid, and the equipment is simple. The prepared aerogel has excellent mechanical property and heat insulation property.
Drawings
Fig. 1 is a schematic view of a process for preparing a porous aerogel by using ice crystal instead of hair according to example 1 of the present invention.
FIG. 2 is a macro-topographic map of the porous aerogel obtained in example 1 of the present invention.
FIG. 3 is a microscopic topography of various aerogels prepared with different polymers as substrates using ice crystal replacement;
fig. 4 is a mechanical property diagram of the porous aerogel.
Detailed Description
The invention relates to a method for preparing porous aerogel by replacing ice crystals, which comprises the steps of freezing and crystallizing a good solvent solution of a polymer at low temperature, soaking the good solvent solution of the polymer in a poor solvent of the polymer (the poor solvent and the good solvent are mutually soluble), and carrying out solvent replacement and heating drying through the precipitation effect of the poor solvent on a polymer network and the erosion and dissolution effect on the good solvent ice crystals to obtain the porous aerogel.
Further, the good solvent is one or a mixture of more of organic/inorganic solvents such as dimethyl sulfoxide, 1, 4-epoxyhexaalkane, water and the like; the poor solvent is one or a mixture of more of organic/inorganic solvents such as ethanol, acetone, methanol, water and the like, the melting point of the poor solvent in the same system is ensured to be lower than that of the good solvent, and the soaking temperature is required to be between the melting points of the good solvent and the poor solvent.
The method for preparing the porous aerogel by replacing the ice crystals comprises the following steps:
(a) adding the polymer into a good solvent, heating and dissolving;
(2) pouring the obtained uniform solution into a mold with the thickness of 1cm, and freezing the uniform solution at-70 ℃ for 4h to ensure that the good solvent is completely crystallized;
(3) soaking the frozen product into a precooled poor solvent, and keeping the temperature between the melting points of the good solvent and the poor solvent;
(4) after soaking for 4h (the soaking time can be properly adjusted according to the thickness of the sample), taking out the sample, and heating and drying the sample at 80 ℃ to obtain the porous aerogel. The porous aerogel realizes heat insulation and impact resistance due to the abundant pore channel structure, the heat conductivity of the polar region, the extremely low density and the excellent mechanical property.
Example 1
The embodiment provides a method for preparing porous aerogel by using ice crystal replacement, the process flow is shown in fig. 1, and the method comprises the following steps:
adding 1g of polyacrylonitrile (Mw: 15W) into 9g of dimethyl sulfoxide solution, heating and stirring at 80 ℃ for 8 hours to completely dissolve the polyacrylonitrile; and then pouring the polymer solution into a polytetrafluoroethylene mould with the thickness of 1cm, freezing for 4h at-70 ℃, then soaking in a pre-cooled aqueous solution for 4h, keeping the temperature between 0 and 14 ℃, finally taking out, heating for 2h at 80 ℃, and completely drying to obtain the porous aerogel.
Fig. 2 is a macro-topographic view of the porous aerogel of example 1, and it can be seen from fig. 2 that the obtained porous aerogel has better shape retention.
FIG. 3 shows that the polymer of example 1 is substituted for a different polymer to obtain aerogels having a rich pore structure (pore size of about 5-20 μm as shown in FIG. 3. the porous aerogels have been tested to have a thermal conductivity of 0.012-0.024W/K (25 deg.C) and a better durability.
In addition, the porous aerogel also has excellent mechanical properties (figure 4), the compressive strength is up to 27MPa, and the porous aerogel has impact resistance.
Example 2
This example provides a method for preparing porous aerogel by using ice crystal replacement, and its specific process is substantially the same as that in example 1, except that: 1g of polyvinyl alcohol (Mw ═ 30W) and 0.5g of silica nanoparticles were added to 9g of the aqueous solution, and stirred at 90 ℃ for 8 hours to completely dissolve/disperse them; and then pouring the polymer solution into a polytetrafluoroethylene mould with the thickness of 1cm, freezing for 4h at-70 ℃, then soaking in a precooled acetone solution for 4h, keeping the temperature between-20 ℃ and 0 ℃, finally taking out, heating for 2h at 40 ℃ and completely drying to obtain the porous aerogel. The prepared porous aerogel has the average pore diameter of about 1.2-5.7 microns, the thermal conductivity of 0.018-0.025W/K (25 ℃), the compressive strength of 27MPa and the compressibility of 92%.
Comparative example 1
This comparative example provides a method of producing an aerogel, which is substantially the same as example 1 except that ethanol is used as the poor solvent.
The pore size of this comparative example is 23-81 microns. The heat conductivity coefficient of the porous aerogel is 0.137-0.152W/K (25 ℃) through tests, the compressive strength is 19MPa, and the compression ratio is 47%.
Comparative example 2
This comparative example provides a method of making an aerogel which is essentially the same as example 1, except that 15g of dimethylsulfoxide solution is added.
The pore size of this comparative example is 11-2 microns. The heat conductivity coefficient of the porous aerogel is 0.024-0.047W/K (25 ℃), the compressive strength is 14MPa, and the compression ratio is 93%.
Comparative example 3
This comparative example provides a method of making an aerogel which is essentially the same as example 1, except that the temperature at which it was frozen is-150 ℃.
The pore size of this comparative example is 1.4-3.7 microns. The heat conductivity coefficient of the porous aerogel is tested to be 0.0192-0.0217W/K (25 ℃), the compression strength is 17MPa, and the compression ratio is 90%.
The above embodiments are merely illustrative of the technical ideas and features of the present invention, and the purpose thereof is to enable those skilled in the art to understand the contents of the present invention and implement the present invention, and not to limit the protection scope of the present invention. All equivalent changes and modifications made according to the spirit of the present invention should be covered in the protection scope of the present invention.
Claims (5)
1. A method for preparing a porous aerogel, the method comprising:
dissolving a polymer in a good solvent to obtain a uniform solution, and freezing the uniform solution; the polymer is one or a mixture of several of non-crosslinked linear polymer, star polymer, comb polymer and crosslinked polymer; molecular weight M of the polymerwNot less than 1 ten thousand; the good solvent is one or a mixture of more of dimethyl sulfoxide, 1, 4-epoxyhexaalkane and water; the mixing mass ratio of the polymer to the good solvent is 1:9-5: 5; the freezing temperature is-80 ℃ to-60 ℃, and the freezing time is 3h to 5 h;
soaking the frozen product in a poor solvent at a temperature between the melting point of the good solvent and the melting point of the poor solvent; the poor solvent is one or a mixture of more of acetone, methanol and water;
heating and drying the soaked product to obtain porous aerogel;
in the same system, the good solvent is different from the poor solvent, and the melting point of the poor solvent is lower than that of the good solvent.
2. The preparation method according to claim 1, wherein the polymer is one or more of polymethyl methacrylate, polyacrylonitrile, polylactic acid, polyvinylidene fluoride, polyvinyl alcohol and chitosan.
3. The method of claim 1, wherein the soaking time is 3-5 hours.
4. The method of claim 1, wherein the temperature of the heat drying is 70 ℃ to 90 ℃.
5. The method of claim 1, further comprising the step of adding a composite material;
adding the composite material while preparing a homogeneous solution;
the composite material is one or a combination of more of silicon dioxide, graphene, carbon nanotubes and glass fibers.
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