CN110903511A - Flexible flame-retardant polyimide aerogel and preparation method thereof - Google Patents

Flexible flame-retardant polyimide aerogel and preparation method thereof Download PDF

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CN110903511A
CN110903511A CN201911201830.XA CN201911201830A CN110903511A CN 110903511 A CN110903511 A CN 110903511A CN 201911201830 A CN201911201830 A CN 201911201830A CN 110903511 A CN110903511 A CN 110903511A
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aerogel
polyimide
dianhydride
gel
solution
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周浪
陈玉净
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Wuxi Wound Glory Is Learned Materials Co Ltd
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Wuxi Wound Glory Is Learned Materials Co Ltd
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    • C—CHEMISTRY; METALLURGY
    • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
    • C08J—WORKING-UP; GENERAL PROCESSES OF COMPOUNDING; AFTER-TREATMENT NOT COVERED BY SUBCLASSES C08B, C08C, C08F, C08G or C08H
    • 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
    • C—CHEMISTRY; METALLURGY
    • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
    • C08J—WORKING-UP; GENERAL PROCESSES OF COMPOUNDING; AFTER-TREATMENT NOT COVERED BY SUBCLASSES C08B, C08C, C08F, C08G or C08H
    • C08J2203/00—Foams characterized by the expanding agent
    • C08J2203/06—CO2, N2 or noble gases
    • C—CHEMISTRY; METALLURGY
    • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
    • C08J—WORKING-UP; GENERAL PROCESSES OF COMPOUNDING; AFTER-TREATMENT NOT COVERED BY SUBCLASSES C08B, C08C, C08F, C08G or C08H
    • C08J2203/00—Foams characterized by the expanding agent
    • C08J2203/08—Supercritical fluid
    • C—CHEMISTRY; METALLURGY
    • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
    • C08J—WORKING-UP; GENERAL PROCESSES OF COMPOUNDING; AFTER-TREATMENT NOT COVERED BY SUBCLASSES C08B, C08C, C08F, C08G or C08H
    • C08J2203/00—Foams characterized by the expanding agent
    • C08J2203/12—Organic compounds only containing carbon, hydrogen and oxygen atoms, e.g. ketone or alcohol
    • C—CHEMISTRY; METALLURGY
    • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
    • C08J—WORKING-UP; GENERAL PROCESSES OF COMPOUNDING; AFTER-TREATMENT NOT COVERED BY SUBCLASSES C08B, C08C, C08F, C08G or C08H
    • 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
    • C—CHEMISTRY; METALLURGY
    • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
    • C08J—WORKING-UP; GENERAL PROCESSES OF COMPOUNDING; AFTER-TREATMENT NOT COVERED BY SUBCLASSES C08B, C08C, C08F, C08G or C08H
    • 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
    • C—CHEMISTRY; METALLURGY
    • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
    • C08K—Use of inorganic or non-macromolecular organic substances as compounding ingredients
    • C08K3/00—Use of inorganic substances as compounding ingredients
    • C08K3/18—Oxygen-containing compounds, e.g. metal carbonyls
    • C08K3/20—Oxides; Hydroxides
    • C08K3/22—Oxides; Hydroxides of metals
    • C08K2003/2244—Oxides; Hydroxides of metals of zirconium
    • C—CHEMISTRY; METALLURGY
    • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
    • C08K—Use of inorganic or non-macromolecular organic substances as compounding ingredients
    • C08K2201/00—Specific properties of additives
    • C08K2201/002—Physical properties
    • C08K2201/003—Additives being defined by their diameter
    • C—CHEMISTRY; METALLURGY
    • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
    • C08K—Use of inorganic or non-macromolecular organic substances as compounding ingredients
    • C08K2201/00—Specific properties of additives
    • C08K2201/011—Nanostructured additives

Abstract

The invention relates to a flexible flame-retardant polyimide aerogel and a preparation method thereof, and the flexible flame-retardant polyimide aerogel is characterized in that the porosity of the aerogel is 85-95%, and the density is 0.05-0.15 g/cm3And the limited oxygen index is more than 50%. The polyimide aerogel prepared by the invention has the advantages of simple preparation method, low cost, small density, high porosity and excellent mechanical properties, and is light, and zirconium oxide is dispersed and loaded in a molecular framework, so that the polyimide aerogel has excellent flame retardant property and good flexibility. Therefore, the polyimide aerogel prepared by the method is particularly suitable for being used as heat insulation, flame retardant and insulating materials of aerospace, flame retardant materials in the aspects of building, medical treatment, protection and the like, and the like.

Description

Flexible flame-retardant polyimide aerogel and preparation method thereof
Technical Field
The invention relates to the technical field of aerogel material preparation, in particular to a flexible flame-retardant polyimide aerogel and a preparation method thereof.
Background
Aerogels are solid foams obtained by substituting a gas for the liquid in a wet gel while the network structure of the gel remains substantially unchanged. The aerogel generally has the characteristics of low heat conductivity coefficient, extremely low density, high porosity, nano-scale pore diameter and the like, so the aerogel has wide application prospect in the heat insulation and preservation fields of aerospace light high-temperature-resistant materials, fire-fighting clothing, battery insulation protection layers and the like and the electronic and electric fields of super capacitors, fuel cells and the like.
In the development process of the aerogel, the most mature application is the silica aerogel, but the poor mechanical property of easy brittle fracture limits the development of the aerogel in industrialization, and the complicated drying method cannot be ideally solved all the time. Further, research shows that the mechanical properties of the organic polymer aerogel are more stable than those of inorganic aerogels, and chitosan aerogel (CN102417606A), multi-element composite aerogel (CN102584010A), polyvinyl alcohol aerogel (CN108579626A), polyurethane aerogel (CN103951966B) and the like have been successfully prepared so far. However, these organic polymer aerogels are insufficient in high and low temperature resistance, insulation properties, and dielectric properties. In addition, the molecular structure of these organic polymer aerogels is dominated by C, H element, which results in easy combustion of the aerogel and extremely poor flame retardant property. These deficiencies limit their use in thermal insulation for aerospace devices, battery materials requiring insulation, integrated circuit materials, and the like.
On the other hand, Polyimide (PI) is an organic polymer having an imide ring in the main chain, and has particularly excellent high and low temperature resistance due to the heterocyclic structure in the main chain, and also has excellent mechanical properties, abrasion resistance, insulating properties, low dielectric properties, and the like, and polyimide aerogel has attracted attention due to its excellent properties. In addition, because the polyimide molecular chain has a large number of aromatic heterocyclic rings, the flame retardance of the polyimide aerogel is superior to that of other organic polymer aerogels. On the other hand, although the flame retardancy of polyimide aerogel is superior to that of other organic polymer aerogels, the flame retardancy level is still not ideal. In contrast, CN109679133A discloses a flame retardant high performance polyimide aerogel, which is prepared by reacting aromatic dianhydride with diamine to obtain polyamic acid, adding a polyamino monomer containing phosphazene ring (such as hexa (p-aminophenoxy) cyclotriphosphazene) to form an organic network structure, and dehydrating and drying to obtain a high performance crosslinked polyimide aerogel. CN109679097A discloses a preparation method of high-flame-retardancy polyimide aerogel based on cyclophosphazene, which adopts a sol-gel method, namely, aromatic dibasic acid anhydride and aromatic diamine are adopted as monomers to prepare a precursorPolyamide acid oligomer, cross-linking polyamide acid structure with hexa (4-amino phenoxy) cyclotriphosphazene monomer as cross-linking agent, standing for ageing to obtain polyamide acid wet gel, imidizing to obtain polyimide wet gel, and supercritical CO2And (3) drying or freeze-drying to prepare the polyimide aerogel. Therefore, in the methods, a hexa (4-aminophenoxy) cyclotriphosphazene monomer is used as a cross-linking agent, and although the hexa (4-aminophenoxy) cyclotriphosphazene monomer has high phosphorus and nitrogen content and is beneficial to flame retardance, research finds that when a small amount of the hexa (4-aminophenoxy) cyclotriphosphazene monomer is added, the flame retardance effect is limited, and with the increase of the addition amount of the hexa (4-aminophenoxy) cyclotriphosphazene monomer, the mechanical property of the aerogel is remarkably reduced, so that the application of the polyimide aerogel is limited.
Disclosure of Invention
Based on the defects in the prior art, the invention aims to overcome the defects and provide the polyimide aerogel which is simple and convenient in preparation method, low in cost, and excellent in flexibility, mechanical property and flame retardant property. Further, the invention also provides a preparation method of the polyimide aerogel.
According to the technical scheme provided by the invention, the flexible flame-retardant polyimide aerogel is provided, and the porosity of the aerogel is 85-95%, and the density of the aerogel is 0.05-0.15 g/cm3And the limited oxygen index is more than 50%.
The invention also provides a preparation method of the flexible flame-retardant polyimide aerogel, which comprises the following steps:
(1) adding diamine into a polar organic solvent, dissolving, and slowly adding dianhydride and a cross-linking agent to prepare a polyamic acid solution;
(2) adding nano zirconia aerogel micro powder into the polyamic acid solution, and uniformly dispersing;
(3) adding a catalyst and a dehydrating agent into the mixed solution to perform chemical imidization to obtain polyimide wet gel;
(4) adding acetone into the polyimide wet gel for solvent exchange;
(5) and (4) performing supercritical drying to obtain the polyimide aerogel.
The nano zirconia aerogel micro powder is prepared by dissolving inorganic zirconium salt in absolute ethyl alcohol to prepare a solution with the zirconium salt concentration of 0.2-0.4 mol/L, and dropwise adding organic acid into the zirconium salt solution under stirring until the molar ratio of zirconium salt to organic acid is 1.5-2: 1, sealing the obtained product in an oven at the temperature of 40-60 ℃ to obtain zirconia gel, scattering the gel, further performing secondary gel in the oven at the temperature of 40-60 ℃, performing solvent replacement by using absolute ethyl alcohol, and drying the obtained product in the oven at the temperature of 40-60 ℃ to obtain the nano zirconia aerogel micro powder.
In addition, the zirconium salt is ZrOCl2·8H2O、Zr(NO3)4·xH2O、ZrO(NO3)2·xH2O、ZrCl4、Zr(SO4)2·4H2One of O; the organic acid is one of citric acid, L-malic acid and gluconic acid.
In addition, the supercritical drying is carried out under the conditions that the temperature is raised to 80-100 ℃ at the rate of 2 ℃/min and the pressure is kept at 20-40 MPa for 2-4 hours, and CO is used2Ethanol or methanol as a supercritical fluid.
In addition, the molar ratio of the dianhydride to the diamine is 1-1.2: 1, the cross-linking agent is 1-5% of the total amount of the dianhydride and the diamine, and the nano zirconia aerogel micro powder is 5-20% of the total amount of the dianhydride and the diamine.
In addition, the dianhydride is one or more of 3,3 ', 4, 4' -biphenyl tetracarboxylic dianhydride, 3 ', 4, 4' -benzophenone tetracarboxylic dianhydride, 4,4 '- (hexafluoroisopropyl) diphthalic dianhydride, pyromellitic dianhydride and 4, 4' -oxydiphthalic anhydride; the diamine is one or more of 4,4 '-diaminodiphenyl ether, 1, 4-p-phenylenediamine, 3' -dimethylbenzidine and 4, 4-diaminodiphenylmethane.
In addition, the cross-linking agent is one of tri (2-aminoethyl) amine, tri (4-aminophenyl) amine and 1,3, 5-tri (4-aminophenoxy) benzene.
In addition, the polar organic solvent is one or more of N-methyl pyrrolidone, N-dimethylformamide and N, N-dimethylacetamide.
In addition, in the step (3), the catalyst is one or more of triethylamine, pyridine and isoquinoline, and the dehydrating agent is acetic anhydride.
The invention has the beneficial effects that: the preparation method of the polyimide aerogel is simple and convenient, the cost is low, and the prepared aerogel has excellent flexibility, mechanical properties and flame retardant properties.
Detailed Description
The present invention is described more specifically by way of examples, but the present invention is not limited to these examples, and various modifications can be made by those skilled in the art within the technical spirit of the present invention.
In the invention, the prepared polyimide aerogel has certain flame retardant property because the polyimide molecular skeleton is provided with a large amount of aromatic rings. In addition, the cross-linking agent is added into the polyimide acid solution to form a three-dimensional network structure, the molecular framework of the three-dimensional network structure is dispersed and loaded with the nano zirconia aerogel micro powder, the nano zirconia is light in weight, low in thermal conductivity and good in flame retardant material, and the aerogel micro powder has good porosity, so that the flame retardant property of the polyimide aerogel loaded with the nano zirconia in the molecular framework is further improved, the bending resistance is also improved, and the polyimide aerogel is flexible and has flame retardant property.
The polyimide aerogel prepared by the invention has the porosity of 85-95% and the density of 0.05-0.15 g/cm3The aerogel with high porosity and low density is suitable for being used as light adsorption, heat insulation, heat preservation and other materials. In addition, the limiting oxygen index refers to the volume fraction concentration of oxygen in the polymer in the oxygen and nitrogen mixture when just supporting its combustion. Is an index for characterizing the burning behavior of the material, wherein the oxygen index is between 22 and 27 percent, and the oxygen index is a combustible material>27 percent of the polyimide aerogel belongs to a flame-retardant material, and the limit oxygen index of the polyimide aerogel prepared by the invention is more than 50 percent, so the polyimide aerogel belongs to a flame-retardant material with very good flame retardance.
The preparation of the nano zirconia aerogel can be prepared by taking inorganic salt as a raw material and then processing the inorganic saltThe preparation method of the zirconia aerogel micro powder can be roughly divided into the following steps: 1) a precipitation method: obtaining Zr (OH) by adjusting the pH of the inorganic zirconium salt4Precipitating, and then carrying out sol gelation treatment to obtain ZrO2. The method has the advantages of simple process, low cost of raw materials, easy realization and overcoming the defects of expensive raw materials, difficult process control and the like of the zirconium alkoxide hydrolysis method. 2) Alcohol-aqueous solution heating method: when an alcohol aqueous solution of an inorganic salt is heated, the dielectric constant and solvating power of the solution are significantly reduced, so that the solution becomes supersaturated and forms a colloid. The gel prepared by the method has the advantages of large specific surface area, fine particle size and good thermal stability. 3) A method of dropping propylene oxide: the method mainly uses inorganic salt as a raw material and organic epoxypropane as a 'gel accelerator', and has the advantages of simple and universal process and low cost. However, from the viewpoint of suitably preparing the nano zirconia aerogel fine powder for addition to the polyimide aerogel of the present invention, a method is suitably used which is: dissolving inorganic zirconium salt in absolute ethyl alcohol to prepare a solution with the zirconium salt concentration of 0.2-0.4 mol/L, and dropwise adding organic acid into the zirconium salt solution while stirring until the molar ratio of the zirconium salt to the organic acid is 1.5-2: 1, sealing the obtained product in an oven at the temperature of 40-60 ℃ to obtain zirconia gel, scattering the gel, further performing secondary gel in the oven at the temperature of 40-60 ℃, performing solvent replacement by using absolute ethyl alcohol, and drying the obtained product in the oven at the temperature of 40-60 ℃ to obtain the nano zirconia aerogel micro powder. The prepared nano zirconia aerogel micro powder has good dispersibility in the polyamic acid solution, is not easy to agglomerate, and the finally prepared polyimide aerogel has excellent flexibility and pore-forming property. The zirconium salt is not particularly limited, and may be one of the following inorganic zirconium salts: ZrOCl2·8H2O、Zr(NO3)4·xH2O、ZrO(NO3)2·xH2O、ZrCl4、Zr(SO4)2·4H2O; the organic acid is not particularly limited, and may be one of citric acid, L-malic acid, and gluconic acid. In addition, the average particle size of the prepared nano zirconia aerogel micro powder is not particularly limited, and can be 5-500 nm, preferably 5-200 nm, further preferably 10-100 nm, and even more preferably 10-50 nm, and within the preferable particle size rangeThe nanometer zirconia aerogel micro powder is easier to disperse and not easy to agglomerate, and the finally prepared polyimide aerogel has stable chemical properties. The nano zirconia aerogel micro powder is 5-20% of the total amount of dianhydride and diamine, preferably 5-10%, and more preferably 8-10%.
In the invention, diamine and dianhydride are uniformly mixed in a polar solvent, a cross-linking agent is added, then nano zirconia aerogel micro powder is uniformly dispersed in polyamic acid, and the polyimide wet gel is formed by chemical imidization dehydration cyclization firstly, so that the chemical imidization temperature is low, cyclization can be more stable, and the shrinkage rate of polyimide in the chemical imidization process is low, thus the method is a preferred imidization mode. The specific chemical imidization process can be carried out at 60-100 ℃ for 2-10 hours. Further, as the degree of dehydration cyclization of the polyamic acid increases, the rigidity of the molecular chain gradually increases, so that the solubility thereof in the solvent gradually decreases to gel (form a wet polyimide gel). In the chemical imidization, one or more of triethylamine, pyridine and isoquinoline are used as a catalyst, acetic anhydride is used as a dehydrating agent, and the amount of the catalyst and the dehydrating agent is not particularly limited, so that the chemical imidization can be smoothly performed, for example, the molar ratio of the dehydrating agent to the catalyst is preferably 2-5: 1, and more preferably 3: 1. In addition, the molar ratio of the dehydrating agent to the dianhydride is preferably 7 to 10:1, and more preferably 8: 1.
After the polyimide wet gel is formed, the solvent is further dried to remove the solvent to form the aerogel, and the drying can be CO2And ethanol or methanol as supercritical fluid, and maintaining the supercritical fluid at 2 deg.C/min to 80-100 deg.C and 20-40 MPa for 2-4 hr.
In the present invention, the dianhydride is preferably an aromatic dianhydride, and specifically, for example, one or more of 3,3 ', 4, 4' -biphenyltetracarboxylic dianhydride, 3 ', 4, 4' -benzophenonetetracarboxylic dianhydride, 4,4 '- (hexafluoroisopropyl) bisphthalic dianhydride, pyromellitic dianhydride, and 4, 4' -oxydiphthalic anhydride; the diamine can be one or more of 4,4 '-diaminodiphenyl ether, 1, 4-p-phenylenediamine, 3' -dimethylbenzidine and 4, 4-diaminodiphenylmethane. In the present invention, the solid content of the polyamic acid solution in which the dianhydride, the diamine, and the crosslinking agent are dissolved may be controlled to 5 to 40 wt%, and the solid content is preferably 15 to 30 wt% in order to obtain a more stable polyamic acid solution, and further the viscosity distribution of the polyamic acid solution is 50000-2000000cps (20 ℃), more preferably 50000-1500000cps (20 ℃) from the viewpoint of obtaining polyimide aerogel having more excellent properties.
The polyimide aerogel prepared by the invention is light in weight, and has excellent flame retardant performance and good flexibility because zirconia is dispersed and loaded in a three-dimensional network molecular framework. Therefore, the polyimide aerogel prepared by the method is particularly suitable for being used as heat insulation, flame retardant and insulating materials of aerospace, flame retardant materials in the aspects of building, medical treatment, protection and the like, and the like.
In addition, the raw materials used in the examples of the present invention are all conventional commercial products.
Example 1
Preparing nano zirconia aerogel micro powder:
0.6mol of inorganic zirconium salt ZrOCl2·8H2Dissolving O (America Amresco) in 2L of absolute ethyl alcohol to prepare a solution with a zirconium salt concentration of 0.3mol/L, dropwise adding 0.4mol of citric acid into the zirconium salt solution under stirring, then sealing the zirconium salt solution in an oven at 50 ℃ to obtain zirconium oxide gel, scattering the gel, further carrying out secondary gel in the oven at 50 ℃, carrying out solvent replacement by absolute ethyl alcohol, and then drying the zirconium oxide gel in the oven at 60 ℃ to obtain fluffy nano zirconium oxide aerogel micro powder with the average particle size of 50nm (measured by ZetasizerPro).
Preparing polyimide aerogel:
(1) adding 0.5mol (100.12g) of 4,4 ' -diaminodiphenyl ether into 809.4g of polar organic solvent N, N-dimethylformamide, slowly adding 0.55mol (161.82g) of 3,3 ', 4,4 ' -biphenyltetracarboxylic dianhydride and 7.86g of cross-linking agent tris (2-aminoethyl) amine after dissolving to prepare a polyamic acid solution with a solid content of 25%;
(2) adding 13.10g of nano zirconia aerogel micro powder into the polyamic acid solution, and uniformly dispersing;
(3) adding 1.5mol of triethylamine and 4.4mol of acetic anhydride into the mixed solution to carry out chemical imidization to obtain polyimide wet gel;
(4) adding acetone into the polyimide wet gel for solvent exchange, and exchanging the acetone solution once every 3 hours for 4 times;
(5) with CO2Is supercritical fluid, the temperature is raised to 80 ℃ at the rate of 2 ℃/min, and the pressure is kept for 4 hours under the condition of 30MPa, thus obtaining the massive polyimide aerogel.
Example 2
Preparing nano zirconia aerogel micro powder:
0.6mol of inorganic zirconium salt ZrOCl2·8H2Dissolving O (America Amresco) in 2L of absolute ethyl alcohol to prepare a solution with a zirconium salt concentration of 0.3mol/L, dropwise adding 0.3mol of citric acid into the zirconium salt solution under stirring, then sealing the zirconium salt solution in an oven at 50 ℃ to obtain zirconium oxide gel, scattering the gel, further carrying out secondary gel in the oven at 50 ℃, carrying out solvent replacement by absolute ethyl alcohol, and then drying the zirconium oxide gel in the oven at 50 ℃ to obtain fluffy nano zirconium oxide aerogel micro powder with the average particle size of 50nm (measured by ZetasizerPro).
Preparing polyimide aerogel:
(1) adding 0.5mol (54.07g) of 1, 4-p-phenylenediamine into 680.04g of polar organic solvent N, N-dimethylformamide, slowly adding 0.55mol (161.82g) of 3,3 ', 4, 4' -biphenyltetracarboxylic dianhydride and 10.79g of cross-linking agent tris (2-aminoethyl) amine after dissolving to prepare a polyamic acid solution with a solid content of 25%;
(2) adding 21.59g of nano zirconia aerogel micro powder into the polyamic acid solution, and uniformly dispersing;
(3) adding 0.77mol of triethylamine and 3.85mol of acetic anhydride into the mixed solution for chemical imidization to obtain polyimide wet gel;
(4) adding acetone into the polyimide wet gel for solvent exchange, and exchanging the acetone solution once every 3 hours for 4 times;
(5) with CO2Is supercritical fluid, and is maintained for 4 hours under the conditions that the temperature is raised to 80 ℃ at the speed of 2 ℃/min and the pressure is 30MPa to prepare blocky polymerAn imide aerogel.
Example 3
Preparing nano zirconia aerogel micro powder:
1mol of inorganic zirconium salt Zr (NO)3)4·5H2Dissolving O (analytically pure, Macklin) in 2.5L of absolute ethyl alcohol to prepare a solution with a zirconium salt concentration of 0.4mol/L, dropwise adding 0.63mol of L-malic acid into the zirconium salt solution under stirring, sealing the solution in an oven at 50 ℃ to obtain zirconium oxide gel, scattering the zirconium oxide gel, further performing secondary gelation in the oven at 50 ℃, performing solvent replacement by absolute ethyl alcohol, and drying the gel in the oven at 50 ℃ to obtain fluffy nano zirconium oxide aerogel micro powder with the average particle size of 100nm (measured by Zetasizer Pro).
Preparing polyimide aerogel:
(1) adding 0.5mol (100.12g) of 4,4 ' -diaminodiphenyl ether into 906.84g of polar organic solvent N, N-dimethylformamide, slowly adding 0.6mol (193.34g) of 3,3 ', 4,4 ' -benzophenonetetracarboxylic dianhydride and 8.80g of cross-linking agent tris (4-aminophenyl) amine after dissolving to prepare a polyamic acid solution with the solid content of 25%;
(2) adding 23.48g of nano zirconia aerogel micro powder into the polyamic acid solution, and uniformly dispersing;
(3) adding 2.4mol of triethylamine and 4.8mol of acetic anhydride into the mixed solution to carry out chemical imidization to obtain polyimide wet gel;
(4) adding acetone into the polyimide wet gel for solvent exchange, and exchanging the acetone solution once every 3 hours for 4 times;
(5) with CO2Is supercritical fluid, the temperature is raised to 80 ℃ at the rate of 2 ℃/min, and the pressure is kept for 4 hours under the condition of 30MPa, thus obtaining the massive polyimide aerogel.
Example 4
Preparing nano zirconia aerogel micro powder:
1mol of inorganic zirconium salt Zr (NO)3)4·5H2Dissolving O (analytically pure, Macklin) in 5L of anhydrous ethanol to obtain a solution with a zirconium salt concentration of 0.2mol/L, dropwise adding 0.56mol L-malic acid into the zirconium salt solution while stirring, and sealing in an oven at 50 ℃ to obtain zirconium oxideAnd (3) gelling, namely breaking the gel, further gelling in an oven at 50 ℃ for the second time, performing solvent replacement by using absolute ethyl alcohol, and then drying in the oven at 60 ℃ to obtain fluffy nano zirconia aerogel micro powder with the average particle size of 50nm (measured by Zetasizer Pro).
Preparing polyimide aerogel:
(1) adding 0.5mol (98.64g) of 3, 3' -dimethylbenzidine into 648.03g of polar organic solvent N-methylpyrrolidone, slowly adding 0.5mol (109.06g) of pyromellitic dianhydride and 8.31g of cross-linking agent tris (4-aminophenyl) amine after dissolving to prepare a polyamic acid solution with the solid content of 25%;
(2) adding 20.77g of nano zirconia aerogel micro powder into the polyamic acid solution, and uniformly dispersing;
(3) adding 2.5mol of triethylamine and 5mol of acetic anhydride into the mixed solution to carry out chemical imidization to obtain polyimide wet gel;
(4) adding acetone into the polyimide wet gel for solvent exchange, and exchanging the acetone solution once every 3 hours for 4 times;
(5) with CO2Is supercritical fluid, the temperature is raised to 80 ℃ at the rate of 2 ℃/min, and the pressure is kept for 4 hours under the condition of 30MPa, thus obtaining the massive polyimide aerogel.
Example 5
Preparing nano zirconia aerogel micro powder:
1mol of inorganic zirconium salt ZrO (NO)3)2·2H2Dissolving O (analytically pure, Beijing Heng Mitsui chemical Co., Ltd.) in 3.3L of absolute ethanol to obtain a solution with a zirconium salt concentration of 0.3mol/L, dropwise adding 0.67mol of citric acid into the zirconium salt solution under stirring, sealing the solution in an oven at 40 ℃ to obtain zirconium oxide gel, scattering the gel, further performing secondary gel in the oven at 40 ℃, performing solvent replacement by using absolute ethanol, and drying the gel in the oven at 40 ℃ to obtain fluffy nano zirconium oxide aerogel micro powder with an average particle size of 200nm (measured by Zetasizer Pro).
Preparing polyimide aerogel:
(1) adding 0.5mol (99.15g) of 4, 4-diaminodiphenylmethane into 833.13g of polar organic solvent N-methylpyrrolidone, slowly adding 0.55mol (170.62g) of 4, 4' -oxydiphthalic anhydride and 8.08g of cross-linking agent tris (2-aminoethyl) amine after dissolving to prepare a polyamic acid solution with a solid content of 25%;
(2) 40.46g of nano zirconia aerogel micro powder is added into the polyamic acid solution and uniformly dispersed;
(3) adding 1.65mol of pyridine and 4.95mol of acetic anhydride into the mixed solution to carry out chemical imidization to obtain polyimide wet gel;
(4) adding acetone into the polyimide wet gel for solvent exchange, and exchanging the acetone solution once every 3 hours for 4 times;
(5) with CO2Is supercritical fluid, the temperature is raised to 80 ℃ at the rate of 2 ℃/min, and the pressure is kept for 4 hours under the condition of 30MPa, thus obtaining the massive polyimide aerogel.
Example 6
Preparing nano zirconia aerogel micro powder:
1mol of inorganic zirconium salt ZrO (NO)3)2·2H2Dissolving O (analytically pure, Beijing Heng Mitsui chemical Co., Ltd.) in 2.5L of anhydrous ethanol to obtain a solution with a zirconium salt concentration of 0.4mol/L, dropwise adding 0.67mol of L-malic acid into the zirconium salt solution under stirring, sealing the solution in an oven at 40 ℃ to obtain zirconium oxide gel, scattering the gel, further performing secondary gel in the oven at 40 ℃, performing solvent replacement by using the anhydrous ethanol, and drying the gel in the oven at 40 ℃ to obtain fluffy nano zirconium oxide aerogel micro powder with an average particle size of 50nm (measured by Zetasizer Pro).
Preparing polyimide aerogel:
(1) adding 0.5mol (99.15g) of 4, 4-diaminodiphenylmethane into 833.58g of polar organic solvent N, N-dimethylformamide, slowly adding 0.55mol (170.62g) of 4, 4' -oxydiphthalic anhydride and 8.09g of cross-linking agent tris (2-aminoethyl) amine after dissolving to prepare a polyamic acid solution with a solid content of 25%;
(2) adding 40.47g of nano zirconia aerogel micro powder into the polyamic acid solution, and uniformly dispersing;
(3) adding 1.5mol of pyridine and 4.4mol of acetic anhydride into the mixed solution to carry out chemical imidization to obtain polyimide wet gel;
(4) adding acetone into the polyimide wet gel for solvent exchange, and exchanging the acetone solution once every 3 hours for 4 times;
(5) methanol is used as supercritical fluid, the temperature is raised to 80 ℃ at the rate of 2 ℃/min, and the pressure is kept for 4 hours under the condition of 20MPa, so that the blocky polyimide aerogel is prepared.
Example 7
Preparing nano zirconia aerogel micro powder:
1mol of inorganic zirconium salt Zr (SO)4)2·4H2Dissolving O (Meclin Z828406) in 3.3L of absolute ethanol to prepare a solution with the zirconium salt concentration of 0.3mol/L, dropwise adding 0.56mol of L-malic acid into the zirconium salt solution under stirring, sealing the solution in an oven at 50 ℃ to obtain zirconium oxide gel, scattering the gel, further performing secondary gel in the oven at 50 ℃, performing solvent replacement by the absolute ethanol, and drying the gel in the oven at 60 ℃ to obtain fluffy nano zirconium oxide aerogel micro powder with the average particle size of 50nm (measured by Zetasizer Pro).
Preparing polyimide aerogel:
(1) 0.5mol (100.12g) of 4,4 '-diaminodiphenyl ether is added into 1054.02g of polar organic solvent N, N-dimethylformamide, and after dissolution, 0.55mol (244.33g) of 4, 4' - (hexafluoroisopropyl) bisphthalic dianhydride and 6.89g of crosslinking agent tris (2-aminoethyl) amine are slowly added to prepare a polyamic acid solution with a solid content of 25%;
(2) adding 27.56g of nano zirconia aerogel micro powder into the polyamic acid solution, and uniformly dispersing;
(3) adding 1.5mol of isoquinoline and 4.4mol of acetic anhydride into the mixed solution to carry out chemical imidization to obtain polyimide wet gel;
(4) adding acetone into the polyimide wet gel for solvent exchange, and exchanging the acetone solution once every 3 hours for 4 times;
(5) methanol is taken as supercritical fluid, the temperature is raised to 100 ℃ at the rate of 2 ℃/min, and the pressure is kept for 2 hours under the condition of 40MPa, so that the blocky polyimide aerogel is prepared.
Example 8
Preparing nano zirconia aerogel micro powder:
1mol of inorganic zirconium salt Zr (SO)4)2·4H2Dissolving O (Meclin Z828406) in 2.5L of absolute ethanol to prepare a solution with the zirconium salt concentration of 0.4mol/L, dropwise adding 0.63mol of gluconic acid into the zirconium salt solution under stirring, then sealing the solution in an oven at 60 ℃ to obtain zirconium oxide gel, scattering the gel, further carrying out secondary gel in the oven at 60 ℃, carrying out solvent replacement by the absolute ethanol, and then drying the gel in the oven at 60 ℃ to obtain fluffy nano zirconium oxide aerogel micro powder with the average particle size of 50nm (measured by Zetasizer Pro).
Preparing polyimide aerogel:
(1) adding 0.5mol (100.12g) of 4,4 '-diaminodiphenyl ether into 995.73g of polar organic solvent N, N-dimethylacetamide, slowly adding 0.5mol (222.12g) of 4, 4' - (hexafluoroisopropyl) diphthalic dianhydride and 9.67g of crosslinking agent 1,3, 5-tris (4-aminophenoxy) benzene after dissolving to prepare a polyamic acid solution with a solid content of 25%;
(2) adding 32.22g of nano zirconia aerogel micro powder into the polyamic acid solution, and uniformly dispersing;
(3) adding 2.0mol of isoquinoline and 4.0mol of acetic anhydride into the mixed solution to carry out chemical imidization to obtain polyimide wet gel;
(4) adding acetone into the polyimide wet gel for solvent exchange, and exchanging the acetone solution once every 3 hours for 4 times;
(5) ethanol is used as supercritical fluid, the temperature is raised to 80 ℃ at the rate of 2 ℃/min, and the pressure is kept for 4 hours under the condition of 30MPa, so that the blocky polyimide aerogel is prepared.
Example 9
Preparing nano zirconia aerogel micro powder:
1mol of inorganic zirconium salt ZrCl4(Meclin Z820722) is dissolved in 3.3L of absolute ethyl alcohol to prepare a solution with the zirconium salt concentration of 0.3mol/L, 0.5mol of gluconic acid is dropwise added into the zirconium salt solution under stirring, then the solution is sealed in an oven at 60 ℃ to obtain zirconium oxide gel, the gel is scattered, the gel is further subjected to secondary gel in the oven at 60 ℃, the absolute ethyl alcohol is used for carrying out solvent replacement, and the gel is dried in the oven at 60 ℃ to obtain fluffy nano zirconium oxide aerogel micro powder with the average particle size of 50nm (measured by Zetasizer Pro)Fixed).
Preparing polyimide aerogel:
(1) adding 0.5mol (100.12g) of 4,4 ' -diaminodiphenyl ether into 778.77g of polar organic solvent N, N-dimethylacetamide, slowly adding 0.5mol (147.11g) of 3,3 ', 4,4 ' -biphenyltetracarboxylic dianhydride and 12.36g of crosslinking agent 1,3, 5-tris (4-aminophenoxy) benzene after dissolving to prepare a polyamic acid solution with a solid content of 25%;
(2) adding 24.72g of nano zirconia aerogel micro powder into the polyamic acid solution, and uniformly dispersing;
(3) adding 1.5mol of triethylamine and 4.0mol of acetic anhydride into the mixed solution to carry out chemical imidization to obtain polyimide wet gel;
(4) adding acetone into the polyimide wet gel for solvent exchange, and exchanging the acetone solution once every 3 hours for 4 times;
(5) ethanol is used as supercritical fluid, the temperature is raised to 80 ℃ at the rate of 2 ℃/min, and the pressure is kept for 4 hours under the condition of 30MPa, so that the blocky polyimide aerogel is prepared.
Example 10
Preparing nano zirconia aerogel micro powder:
1mol of inorganic zirconium salt ZrCl4(Meclin Z820722) is dissolved in 2.5L of absolute ethyl alcohol to prepare a solution with the zirconium salt concentration of 0.4mol/L, 0.5mol of citric acid is dropwise added into the zirconium salt solution under stirring, then the solution is sealed in an oven at 50 ℃ to obtain zirconium oxide gel, the gel is scattered, the gel is further secondarily gelled in the oven at 50 ℃, the absolute ethyl alcohol is used for carrying out solvent replacement, and the gel is dried in the oven at 60 ℃ to obtain fluffy nano zirconium oxide aerogel micro powder with the average particle size of 50nm (measured by Zetasizer Pro).
Preparing polyimide aerogel:
(1) adding 0.5mol (100.12g) of 4,4 ' -diaminodiphenyl ether into 809.4g of polar organic solvent N, N-dimethylformamide, slowly adding 0.55mol (161.82g) of 3,3 ', 4,4 ' -biphenyl tetracarboxylic dianhydride and 7.86g of cross-linking agent 1,3, 5-tri (4-aminophenoxy) benzene after dissolving to prepare a polyamic acid solution with the solid content of 25%;
(2) 52.39g of nano zirconia aerogel micro powder is added into the polyamic acid solution and uniformly dispersed;
(3) adding 1.0mol of triethylamine and 4.0mol of acetic anhydride into the mixed solution to carry out chemical imidization to obtain polyimide wet gel;
(4) adding acetone into the polyimide wet gel for solvent exchange, and exchanging the acetone solution once every 3 hours for 4 times;
(5) with CO2Is supercritical fluid, the temperature is raised to 80 ℃ at the rate of 2 ℃/min, and the pressure is kept for 4 hours under the condition of 30MPa, thus obtaining the massive polyimide aerogel.
Comparative example 1
The same as example 1 was repeated except that the nano zirconia aerogel fine powder was not added in the step (2) of preparing the polyimide aerogel.
Comparative example 2
The same as example 2 was repeated except that the nano zirconia aerogel fine powder was not added in the step (2) of preparing the polyimide aerogel.
Performance testing
(1) The dielectric constant and the dielectric loss are tested by an Agilent vector analyzer, the size of a test sample is cylindrical, the length, the width and the height of the test sample are 50mm multiplied by 30mm multiplied by 10mm, electrode layers (silver paste) are coated on the upper surface and the lower surface of the cylinder, the cylinder is dried at the temperature of 100 ℃, and the test frequency is 0-0.35 MHz.
(2) The density, the density of the aerogel, is obtained by dividing the mass of the sample by the volume. And measuring the diameter and the height of the cylindrical sample by using a vernier caliper, measuring the mass of the cylindrical sample by using an electronic balance, and calculating to obtain the density of the aerogel.
(3) Limiting oxygen index, tested according to ASTM D2863-2009.
(4) Porosity, the polyimide aerogel is respectively made into films with the length and width of 3cm multiplied by 1cm, and the density is measured. Then, the apparent density measurement was performed using an apparent density measuring instrument (equipment name micromeritics saccucc 1330), and the polyimide aerogel was filled with helium gas or argon gas to measure the apparent density (apparent density). And then, converting the ratio of the density to the apparent density to obtain the polyimide aerogel porosity.
(5) The polyimide aerogel can be bent to the maximum angle, and the polyimide aerogel is respectively made into film materials with the length and width of 5cm multiplied by 5 cm. Then, 1 kg of external force is applied to the membrane materials respectively to bend the membrane materials, and the maximum bending angle of the membrane materials when the membrane materials are not broken is measured.
(6) Tensile strength and elongation at break, determined according to ASTM D6382003.
(7) The thermal conductivity is measured according to the national standard GB/T10801.1-2002.
TABLE 1 Performance test results of polyimide aerogels prepared in examples and comparative examples
Figure BDA0002296076930000101
The embodiment and the comparative example show that the polyimide aerogel prepared by the invention has the advantages of small density, high porosity and excellent mechanical properties, and the polyimide aerogel prepared by the invention is light in weight, has zirconium oxide dispersed and loaded in a molecular framework, and has excellent flame retardant property and good flexibility. Therefore, the polyimide aerogel prepared by the method is particularly suitable for being used as heat insulation, flame retardant and insulating materials of aerospace, flame retardant materials in the aspects of building, medical treatment, protection and the like, and the like.

Claims (10)

1. The flexible flame-retardant polyimide aerogel is characterized in that the porosity of the aerogel is 85-95%, and the density of the aerogel is 0.05-0.15 g/cm3And the limited oxygen index is more than 50%.
2. A method for preparing a flexible flame retardant polyimide aerogel according to claim 1, comprising the steps of:
(1) adding diamine into a polar organic solvent, dissolving, and slowly adding dianhydride and a cross-linking agent to prepare a polyamic acid solution;
(2) adding nano zirconia aerogel micro powder into the polyamic acid solution, and uniformly dispersing;
(3) adding a catalyst and a dehydrating agent into the mixed solution to perform chemical imidization to obtain polyimide wet gel;
(4) adding acetone into the polyimide wet gel for solvent exchange;
(5) and (4) performing supercritical drying to obtain the polyimide aerogel.
3. The preparation method according to claim 2, wherein the nano zirconia aerogel micro powder is prepared by dissolving inorganic zirconium salt in absolute ethanol to obtain a solution with a zirconium salt concentration of 0.2-0.4 mol/L, and dropwise adding organic acid into the zirconium salt solution under stirring until the molar ratio of the zirconium salt to the organic acid is 1.5-2: 1, sealing the obtained product in an oven at the temperature of 40-60 ℃ to obtain zirconia gel, scattering the gel, further performing secondary gel in the oven at the temperature of 40-60 ℃, performing solvent replacement by using absolute ethyl alcohol, and drying the obtained product in the oven at the temperature of 40-60 ℃ to obtain the nano zirconia aerogel micro powder.
4. The method according to claim 3, wherein the zirconium salt is ZrOCl2·8H2O、Zr(NO3)4·xH2O、ZrO(NO3)2·xH2O、ZrCl4、Zr(SO4)2·4H2One of O; the organic acid is one of citric acid, L-malic acid and gluconic acid.
5. The method according to claim 3, wherein the supercritical drying is carried out at a temperature of from 2 ℃/min to 80 to 100 ℃ and a pressure of from 20 to 40MPa for from 2 to 4 hours by using CO2Ethanol or methanol as a supercritical fluid.
6. The preparation method according to claim 2, wherein the molar ratio of the dianhydride to the diamine is 1-1.2: 1, the cross-linking agent is 1-5% of the total amount of the dianhydride and the diamine, and the nano zirconia aerogel micro powder is 5-20% of the total amount of the dianhydride and the diamine.
7. The preparation method according to claim 2, wherein the dianhydride is one or more of 3,3 ', 4, 4' -biphenyltetracarboxylic dianhydride, 3 ', 4, 4' -benzophenonetetracarboxylic dianhydride, 4,4 '- (hexafluoroisopropyl) bisphthalic dianhydride, pyromellitic dianhydride, and 4, 4' -oxydiphthalic anhydride; the diamine is one or more of 4,4 '-diaminodiphenyl ether, 1, 4-p-phenylenediamine, 3' -dimethylbenzidine and 4, 4-diaminodiphenylmethane.
8. The method of claim 2, wherein the crosslinking agent is one of tris (2-aminoethyl) amine, tris (4-aminophenyl) amine, and 1,3, 5-tris (4-aminophenoxy) benzene.
9. The preparation method according to claim 2, wherein the polar organic solvent is one or more of N-methylpyrrolidone, N-dimethylformamide and N, N-dimethylacetamide.
10. The preparation method according to claim 2, wherein in the step (3), the catalyst is one or more of triethylamine, pyridine and isoquinoline, and the dehydrating agent is acetic anhydride.
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