CN110358138B - Polyimide aerogel with micro-nano hierarchical pore distribution and preparation method thereof - Google Patents
Polyimide aerogel with micro-nano hierarchical pore distribution and preparation method thereof Download PDFInfo
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- C08J9/00—Working-up of macromolecular substances to porous or cellular articles or materials; After-treatment thereof
- C08J9/26—Working-up of macromolecular substances to porous or cellular articles or materials; After-treatment thereof by elimination of a solid phase from a macromolecular composition or article, e.g. leaching out
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- C08J9/00—Working-up of macromolecular substances to porous or cellular articles or materials; After-treatment thereof
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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
- C08J2201/046—Elimination of a polymeric phase
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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
- C08J2201/05—Elimination by evaporation or heat degradation of a liquid phase
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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
- C08J2205/042—Nanopores, i.e. the average diameter being smaller than 0,1 micrometer
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- C08J2379/00—Characterised by the use of macromolecular compounds obtained by reactions forming in the main chain of the macromolecule a linkage containing nitrogen with or without oxygen, or carbon only, not provided for in groups C08J2361/00 - C08J2377/00
- C08J2379/04—Polycondensates having nitrogen-containing heterocyclic rings in the main chain; Polyhydrazides; Polyamide acids or similar polyimide precursors
- C08J2379/08—Polyimides; Polyester-imides; Polyamide-imides; Polyamide acids or similar polyimide precursors
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- C08J2425/00—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 aromatic carbocyclic ring; Derivatives of such polymers
- C08J2425/02—Homopolymers or copolymers of hydrocarbons
- C08J2425/04—Homopolymers or copolymers of styrene
- C08J2425/06—Polystyrene
Abstract
The invention relates to a polyimide aerogel with micro-nano hierarchical pore distribution and a preparation method thereof. The preparation method comprises the following steps: adding the polystyrene emulsion into deionized water, performing ultrasonic treatment, dissolving water-soluble polyamic acid and triethylamine in the obtained polystyrene dispersion liquid, performing sol-gel treatment, freezing the obtained polystyrene/polyamic acid hydrogel, freeze-drying, and performing thermal imidization. The polyimide aerogel prepared by the method is small in mass, high in strength, extremely low in heat conductivity coefficient, cheap and easy to prepare the used pore-forming agent, simple and easy to operate in the aerogel preparation process, low in cost, green and environment-friendly, and applicable to various heat insulation scenes.
Description
Technical Field
The invention belongs to the field of aerogel and a preparation method thereof, and particularly relates to polyimide aerogel with micro-nano hierarchical pore distribution and a preparation method thereof.
Background
The aerogel is a high-dispersion solid material which is formed by mutually coalescing high polymer molecules or colloid particles to form a continuous porous three-dimensional skeleton network structure, and gaseous dispersion media are filled in pores, has the characteristics of low density, high specific surface area, low thermal conductivity and the like, and has wide prospects in the fields of aerospace, petrochemical industry, automobile industry, building heat preservation and the like. The traditional supercritical drying method for preparing the aerogel cannot realize large-scale industrialization due to energy consumption and time consumption and limited product size, so that the freeze-drying method which is relatively green and environment-friendly and low in energy consumption is more and more concerned. Compared with a supercritical drying method, the pores of the aerogel prepared by freeze drying are all in the micron level (5-100 microns), so that the heat insulation capability of the aerogel prepared by freeze drying is limited.
Polyimide (Polyimide) is a special engineering plastic with the advantages of good molding processability, high mechanical strength, good thermal stability and the like, and is widely applied to various fields of national economy. The Polystyrene (Polystyrene) nanospheres are simple and easy to prepare and low in cost, and become good polymer pore forming agents due to the low thermal decomposition temperature and the nanometer size.
Disclosure of Invention
The invention aims to solve the technical problem of providing a polyimide aerogel with micro-nano hierarchical pore distribution and a preparation method thereof, so as to overcome the defect of poor heat insulation performance of the aerogel in the prior art.
The invention provides a preparation method of polyimide aerogel with micro-nano hierarchical pore distribution, which comprises the following steps:
(1) adding the polystyrene emulsion into deionized water, and performing ultrasonic treatment to obtain a uniformly dispersed polystyrene dispersion liquid, wherein the volume ratio of the polystyrene emulsion to the deionized water is 0.9-1: 25-35;
(2) dissolving water-soluble polyamic acid and triethylamine in the polystyrene dispersion liquid in the step (1), uniformly mixing, and carrying out sol-gel to obtain polystyrene/polyamic acid hydrogel, wherein the mass ratio of the polystyrene to the water-soluble polyamic acid to the triethylamine is 7.5-60:100: 100;
(3) and (3) freezing the polystyrene/polyamic acid hydrogel obtained in the step (2), and then freezing, drying and thermal imidizing to obtain the polyimide aerogel with micro-nano hierarchical pore distribution.
The preparation method of the polystyrene emulsion in the step (1) comprises the following steps: adding water, sodium dodecyl sulfate and sodium carbonate into styrene, stirring, and carrying out emulsion polymerization at the temperature of 60-80 ℃ for 18-25 h, wherein the proportion of the styrene to the water to the sodium dodecyl sulfate to the sodium carbonate is 1-10mL to 90-100mL to 0.01-0.1g to 0.1-0.5 g.
The rotating speed of the stirring is 300-500 r/min.
The preparation method of the water-soluble polyamic acid in the step (2) refers to Chinese patent CN107337927A (named as graphene oxide/polyamic acid hydrogel with self-repairing function and preparation method thereof), and comprises the following steps: firstly, dissolving monomer diamine for synthesizing polyimide in a polar solvent, adding another monomer dicarboxylic anhydride, carrying out polymerization reaction in an ice-water bath for a period of time, adding triethylamine, and continuously reacting for a period of time to prepare a polyamic acid solution; slowly pouring the polyamic acid solution into deionized water for precipitation to obtain polyamic acid wires, and freeze-drying the polyamic acid wires to obtain the water-soluble polyamic acid.
The monomer diamine is 4, 4' -diaminodiphenyl ether (ODA); the monomer binary anhydride is pyromellitic dianhydride (PMDA).
The polar solvent is dimethylacetamide (DMAc).
The sol-gel time in the step (2) is 12-24 h.
And (4) freezing in the step (3) by adopting liquid nitrogen.
The freeze-drying time in the step (3) is 24-72h, the freeze-drying temperature is-40 to-60 ℃, and the freeze-drying vacuum degree is 15-25 Pa.
The thermal imidization in the step (3) comprises the following technological parameters: heating the mixture in a tube furnace at 1-3 ℃/min to 350-380 ℃ from room temperature, and keeping the temperature for 0.5-1.5 h. Thermal imidization can thermally decompose polystyrene.
The invention also provides the polyimide aerogel with the micro-nano hierarchical pore distribution, which is prepared by the method.
The invention also provides an application of the polyimide aerogel with the micro-nano hierarchical pore distribution prepared by the method.
The polyimide aerogel synthesized by the invention has nano holes and micro holes, extremely low thermal conductivity coefficient which is lower than 0.040W/(mK) and as low as 0.028W/(mK), strong heat insulation capability, good mechanical property, low cost, environmental protection and good heat insulation material with wide application prospect.
Advantageous effects
(1) The invention successfully realizes the distribution of nano pores in the aerogel prepared by freeze drying, has simple preparation process and easy operation, and is a green and environment-friendly preparation method.
(2) The method has the advantages of ingenious design: the invention adopts the emulsion of polystyrene, and directly adds the emulsion into the water of sol, thus solving the problem of dispersion of nano microsphere polystyrene in polyamic acid; the polystyrene microspheres can be removed in the thermal imidization process, and the energy consumption is not increased in the pore-forming process.
(3) The polyamic acid and the polystyrene are uniformly dispersed in water, and the method is simple in process and environment-friendly.
(4) The polyimide aerogel prepared by the method disclosed by the invention is small in mass, high in strength, extremely low in heat conductivity coefficient, cheap and easy to prepare the used pore-forming agent, simple and easy to operate in the aerogel preparation process, low in cost, green and environment-friendly, and suitable for various heat insulation scenes.
Drawings
FIG. 1 is a scanning electron micrograph of polystyrene nanospheres (a) and polyimide aerogel (b, c) in example 3 of the present invention; wherein (c) is a scanning electron micrograph of the aerogel wall at a greater magnification.
FIG. 2 is a photograph of a final sample of the polyimide aerogel of example 1 of the present invention.
FIG. 3 is a graph showing the thermal conductivity at room temperature of the polyimide aerogels obtained in examples 1 to 4 of the present invention.
FIG. 4 is a digital photograph of an aerogel having petals of 10mm thick placed in example 3 of the present invention after being roasted for 5min on an alcohol lamp.
FIG. 5 is a stress-strain curve of 80% compression of aerogel in example 3 of the present invention, wherein 30% means that the mass ratio of polyamic acid PAA to polystyrene PS is 1: 0.3.
Detailed Description
The invention will be further illustrated with reference to the following specific examples. It should be understood that these examples are for illustrative purposes only and are not intended to limit the scope of the present invention. Further, it should be understood that various changes or modifications of the present invention may be made by those skilled in the art after reading the teaching of the present invention, and such equivalents may fall within the scope of the present invention as defined in the appended claims.
N, N-dimethylacetamide (DMAc), Triethylamine (TEA),4, 4' -diaminodiphenyl ether (ODA), and terephthalic anhydride (PMDA) were all purchased from Chinese herbs.
Example 1
A preparation method of polyimide aerogel with micro-nano hierarchical pore distribution comprises the following specific steps:
(1) n, N-dimethylacetamide is used as a solvent, and 4, 4' -diaminodiphenyl ether and terephthalic anhydride in equal molar ratio are subjected to condensation polymerization in an ice-water bath to prepare polyamic acid with the solid content of 15%. The specific process is as follows: 8.0096g of 4, 4' -diaminodiphenyl ether is dissolved in 95.57g N, N-dimethylacetamide, 8.8556g of pyromellitic dianhydride is added, and the mixture is reacted in an ice-water bath for 5 hours. Then, 4.0476g of triethylamine was added, and the reaction was continued for 5 hours to prepare a water-soluble polyamic acid solution having a solid content of 15%. Precipitating the prepared water-soluble polyamic acid by using deionized water, and then washing and freeze-drying to obtain the water-soluble polyamic acid for later use.
(2) Preparing polystyrene nano microsphere emulsion: 100ml of water, 0.067g of sodium lauryl sulfate and 0.167g of sodium carbonate were added to 10ml of Styrene (Styrene) and emulsion polymerization was carried out at a rotational speed of 300r/min and a temperature of 60 ℃ for 20 hours.
(3) Preparation of polystyrene/Polyamic acid hydrogel: putting 0.94mL of the PS emulsion obtained in the step (2) into 30mL of deionized water, and carrying out ultrasonic treatment for 10min to obtain a uniformly dispersed polystyrene dispersion liquid; dissolving 1g of water-soluble polyamic acid and 1g of triethylamine in the polystyrene dispersion liquid, uniformly mixing, and carrying out a sol-gel process for 24 hours to obtain the polystyrene/polyamic acid hydrogel.
(4) The polystyrene/polyamic acid hydrogel was placed in a mold, which was then frozen in liquid nitrogen until completely frozen. Drying in a freeze drier at-50 deg.C under vacuum degree of 20Pa for 48 hr. And (3) performing thermal imidization, wherein the thermal imidization is performed in a tubular furnace, the temperature is increased from room temperature to 380 ℃ at the speed of 2 ℃/min, and the temperature is kept for 1h to obtain the polyimide aerogel with micro-nano hierarchical pore distribution, and the mark is PI-7.5%.
FIG. 2 shows that: the aerogel has good formability.
Example 2
Similar to example 1, except that the amount of the polystyrene emulsion used in the step (3) is 1.88ml, the obtained polyimide aerogel with the micro-nano hierarchical pore distribution is marked as PI-15%, and the rest is the same as example 1.
Example 3
Similar to example 1, except that the amount of the polystyrene emulsion used in step (3) is 3.75ml, the obtained polyimide aerogel with the micro-nano hierarchical pore distribution is marked as PI-30%, and the rest is the same as example 1.
FIG. 1 shows that: (a) the size of the nanospheres can be seen to be about 50 nm; (b) showing a micron-sized hole structure in three-dimensional connection with aerogel; (c) the nano-pores of about 50nm in the aerogel pore walls can be seen.
FIG. 4 shows that: the petals of the aerogel with the thickness of 10mm in the embodiment are roasted on an alcohol lamp for 5min, and the petals still keep moisture, which shows that the aerogel has excellent heat insulation capability.
FIG. 5 shows that: after compression, no destructive mutation occurs, so that the toughness and excellent mechanical properties of the aerogel are achieved.
Example 4
Similar to example 1, except that the amount of the polystyrene emulsion used in step (3) is 7.5ml, the obtained polyimide aerogel with the micro-nano hierarchical pore distribution is marked as PI-60%, and the rest is the same as example 1.
The thermal conductivity of the polyimide aerogels obtained in examples 1 to 4 of the present invention at room temperature was measured by HOT DISK thermal analyzer, as shown in fig. 3, illustrating the excellent thermal insulation ability of the aerogels obtained in the present invention.
Compared with the Chinese patent CN108864473A, the raw materials used in the invention are polyamic acid and polystyrene, the price is low, the mass preparation can be realized, the electrostatic spinning technology used in the Chinese patent CN108864473A has low yield and high cost, the large-scale preparation is not suitable, and the lowest thermal conductivity of the sample at room temperature is as low as 0.028W/(mK).
Claims (8)
1. A preparation method of polyimide aerogel with micro-nano hierarchical pore distribution comprises the following steps:
(1) adding a polystyrene emulsion into deionized water, and performing ultrasonic treatment to obtain a polystyrene dispersion liquid, wherein the volume ratio of the polystyrene emulsion to the deionized water is 0.9-8: 25-35, and the polystyrene emulsion is a polystyrene nano microsphere emulsion;
(2) dissolving water-soluble polyamic acid and triethylamine in the polystyrene dispersion liquid in the step (1), uniformly mixing, and carrying out sol-gel to obtain polystyrene/polyamic acid hydrogel, wherein the mass ratio of the polystyrene to the water-soluble polyamic acid to the triethylamine is 7.5-60:100: 100;
(3) and (3) freezing the polystyrene/polyamic acid hydrogel obtained in the step (2), and then freezing, drying and thermal imidizing to obtain the polyimide aerogel with micro-nano hierarchical pore distribution.
2. The method according to claim 1, wherein the preparation method of the polystyrene emulsion in the step (1) comprises: adding water, sodium dodecyl sulfate and sodium carbonate into styrene, stirring, and carrying out emulsion polymerization at the temperature of 60-80 ℃ for 18-25 h, wherein the proportion of the styrene to the water to the sodium dodecyl sulfate to the sodium carbonate is 1-10mL to 90-100mL to 0.01-0.1g to 0.1-0.5 g.
3. The method according to claim 1, wherein the sol-gel time in step (2) is 12-24 h.
4. The method according to claim 1, wherein the freezing in the step (3) is performed by liquid nitrogen freezing.
5. The method as claimed in claim 1, wherein the freeze-drying time in step (3) is 24-72h, the freeze-drying temperature is-40 to-60 ℃, and the freeze-drying vacuum degree is 15-25 Pa.
6. The method according to claim 1, wherein the thermal imidization in step (3) is performed according to the following process parameters: heating the mixture in a tube furnace at 1-3 ℃/min to 350-380 ℃ from room temperature, and keeping the temperature for 0.5-1.5 h.
7. Polyimide aerogel with micro-nano hierarchical pore distribution prepared by the method of claim 1.
8. Application of the polyimide aerogel with micro-nano hierarchical pore distribution prepared by the method of claim 1.
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