Nanoparticle composite polyimide foam material as well as preparation method and application thereof

Abstract

The invention belongs to the technical field of porous wave-absorbing materials, and particularly relates to a nanoparticle composite polyimide foam material as well as a preparation method and application thereof. The preparation method comprises the following steps: mixing a polyamic acid solution and nanoparticles, carrying out first ball milling, and mixing with an emulsifier and a dehydrating agent to obtain a phase A; a solvent of the polyamide acid solution is a polar organic solvent; mixing the phase B and the phase A, and carrying out second ball milling to obtain an emulsion in which the phase A wraps the phase B; the phase B is a non-polar organic solvent; and sequentially standing, washing and carrying out heat treatment on the emulsion in the bag A and the bag B to obtain the nanoparticle composite polyimide foam material. According to the invention, the way of ball-milling the prepolymer and the wave-absorbing agent is innovatively used, so that the wave-absorbing agent is uniformly dispersed in the matrix material. The uniformly dispersed nanoparticles not only can form a three-dimensional network structure in the foam material to provide excellent wave-absorbing performance, but also can provide better mechanical properties for the foam material, and the method is simple and easy to implement and remarkable in effect.

Description

Technical Field

[0001] The invention belongs to the technical field of porous wave-absorbing materials, and in particular relates to a nano-particle composite polyimide foam material and a preparation method and application thereof. Background Art

[0002] In recent years, the trend of information globalization has promoted the rapid development of electronic information technology. Various intelligent information equipment systems have brought great changes and convenience to people's lifestyles, but have also led to more serious electromagnetic radiation and electromagnetic pollution. On the one hand, a large amount of electromagnetic radiation pollution in the environment will affect the normal operation of precision instruments, and on the other hand, it will also bring a certain degree of harm to people's physical and mental health. In the field of detection technology, with the continuous emergence of new radar, infrared and other advanced technologies, the positioning technology of targets has become increasingly accurate, posing a great threat to the survival of fighter jets, armored tanks, underwater submarines and other weapons and equipment. Reducing electromagnetic pollution radiation in life, realizing the wave absorption and stealth of weapons and equipment, and preparing "thin, light, wide and strong" electromagnetic wave absorbing materials have gradually become research hotspots in the field of science and technology in recent years.

[0003] Absorbing materials refer to a type of material that can absorb or significantly reduce the electromagnetic wave energy received on its surface, thereby reducing the interference of electromagnetic waves. They are mainly composed of absorbers and matrix materials. Common matrix materials include polyimide, epoxy resin, polyurethane, etc. There are many materials that can be used as absorbers, including: magnetic nanoparticles (Fe, Co and Ni), ceramic materials (TiO 2 , SiC and TiC) and carbon materials (graphene, carbon black, carbon fiber and carbon nanotubes, etc.). Among them, carbon materials have the characteristics of low density, high dielectric constant and excellent stability, and have great advantages in the field of microwave absorption. However, most carbon materials, such as graphene and carbon black, are difficult to achieve uniform dispersion in commonly used matrix materials due to their relatively fixed morphology and structure, resulting in poor microwave absorption performance. Summary of the invention

[0004] In view of this, the object of the present invention is to provide a nanoparticle composite polyimide foam material and its preparation method and application. The nanoparticle composite polyimide foam material prepared by the present invention has nanoparticles uniformly dispersed in porous polyimide foam and has good wave absorbing performance.

[0005] The present invention provides a method for preparing a nanoparticle composite polyimide foam material, comprising the following steps:

[0006] The polyamic acid solution and the nanoparticles are mixed and subjected to a first ball milling, and the obtained system is mixed with an emulsifier and a dehydrating agent to obtain a phase A; the solvent of the polyamic acid solution is a polar organic solvent;

[0007] Mixing phase B and phase A for a second ball milling to obtain an emulsion containing phase B; phase B is a non-polar organic solvent;

[0008] The emulsion of A package B is sequentially allowed to stand, washed and heat treated to obtain a nanoparticle composite polyimide foam material.

[0009] Preferably, the nanoparticles include one or more of nano-iron tetroxide, graphene, graphene oxide, conductive carbon black and Mxene.

[0010] Preferably, the mass fraction of the nanoparticles in phase A is 1% to 15%.

[0011] Preferably, the rotation speed of the first ball mill is 300-500 rpm, the ball-to-material ratio is (3-5):1, and the time is 3-4 hours.

[0012] Preferably, the second ball mill has a rotation speed of 600-1000 rpm, a ball-to-material ratio of (3-5):1, and a time of 0.5-2 h.

[0013] Preferably, the polar organic solvent includes one or more of dimethyl sulfoxide, N-methylpyrrolidone, dimethylformamide and dimethylacetamide.

[0014] Preferably, the non-polar solvent includes one or more of toluene, xylene, paraffin oil, tetradecane and hexadecane.

[0015] Preferably, the heat treatment temperature is 280-320° C., and the time is 30 min-2 h.

[0016] The present invention also provides a nano-particle composite polyimide foam material obtained by the preparation method described in the above technical solution. The porosity of the nano-particle composite polyimide foam material is 80% to 95%, and the open hole rate is 100%.

[0017] The present invention also provides the use of the nano-particle composite polyimide foam material described in the above technical solution as a wave absorbing material.

[0018] Compared with the prior art, the present invention has the following beneficial effects:

[0019] The invention provides a preparation method of a nano-particle composite polyimide foam material, comprising the following steps: mixing a polyamic acid solution and nano-particles for a first ball milling, mixing the obtained system with an emulsifier and a dehydrating agent to obtain a phase A; the solvent of the polyamic acid solution is a polar organic solvent; mixing a phase B with the phase A for a second ball milling to obtain an emulsion of A-encapsulating B; the phase B is a non-polar organic solvent; and sequentially standing, washing and heat treating the emulsion of A-encapsulating B to obtain a nano-particle composite polyimide foam material.

[0020] The present invention innovatively uses the method of ball milling prepolymer (polyamic acid) and absorber (nanoparticles) to make the absorber uniformly dispersed in the matrix (porous polyimide foam). During the ball milling process, the nanoparticles are uniformly dispersed in the polyamic acid solution and can be further refined, which is conducive to subsequent good dispersion in the matrix material, overcoming the problem that the absorber itself is easy to agglomerate and difficult to be uniformly dispersed in the matrix. The uniformly dispersed nanoparticles can not only form a three-dimensional network structure in the foaming material with the help of the matrix to provide excellent wave absorbing performance, but also provide better mechanical properties for the foaming material. The present invention forms an emulsion of A encapsulating B, which can provide a high porosity for the composite material, which is conducive to improving the reflection and absorption of electromagnetic waves inside the composite material. The nanoparticle composite polyimide foam material prepared by the present invention has high shielding effectiveness and high compression strength.

[0021] The preparation method of the present invention is simple, has high production efficiency, low equipment requirements, low cost, and is easy to achieve batch production. The present invention adopts an emulsion template method to prepare a nanoparticle composite polyimide foam material, and the emulsion template method can well achieve the controllability of the microstructure of the foaming material. The present invention adjusts the amount of emulsifier, the A / B phase ratio, and the concentration of polyamic acid in the A phase to obtain an emulsion with adjustable droplet size of the dispersed phase, thereby achieving adjustable pore structure and density of the foaming material. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0023] Figure 1 This is a flow chart of the preparation method of the nanoparticle composite polyimide foam material in the embodiment;

[0024] Figure 2 This is a morphology diagram of the nanoparticle composite polyimide foam material prepared in Example 1;

[0025] Figure 3 This is a morphology picture of the nanoparticle composite polyimide foam material prepared in Example 2;

[0026] Figure 4 This is a morphology picture of the nanoparticle composite polyimide foam material prepared in Example 3;

[0027] Figure 5 This is a morphology picture of the nanoparticle composite polyimide foam material prepared in Example 4;

[0028] Figure 6 This is a morphology picture of the nanoparticle composite polyimide foam material prepared in Example 6;

[0029] Figure 7 This is a morphology picture of the nanoparticle composite polyimide foam material prepared in Comparative Example 1;

[0030] Figure 8 This is a morphology picture of the nanoparticle composite polyimide foam material prepared in Comparative Example 2. DETAILED DESCRIPTION

[0031] The present invention provides a method for preparing a nanoparticle composite polyimide foam material, comprising the following steps:

[0032] The polyamic acid solution and the nanoparticles are mixed and subjected to a first ball milling, and the obtained system is mixed with an emulsifier and a dehydrating agent to obtain a phase A; the solvent of the polyamic acid solution is a polar organic solvent;

[0033] Mixing phase B and phase A for a second ball milling to obtain an emulsion containing phase B; phase B is a non-polar organic solvent;

[0034] The emulsion of A package B is sequentially allowed to stand, washed and heat treated to obtain a nanoparticle composite polyimide foam material.

[0035] In the present invention, unless otherwise specified, the materials and equipment used are commercially available products in the art.

[0036] The present invention mixes a polyamic acid solution and nanoparticles for first ball milling, and mixes the obtained system with an emulsifier and a dehydrating agent to obtain a phase A; the solvent of the polyamic acid solution is a polar organic solvent.

[0037] In the present invention, the polyamic acid solution is preferably obtained by mixing a dianhydride monomer, a diamine monomer and a polar organic solvent for polymerization.

[0038] In the present invention, the dianhydride monomer preferably includes one or more of pyromellitic dianhydride, biphenyl dianhydride, diphenyl ether dianhydride, azodiphthalic anhydride, diphenyl sulfide dianhydride, diether dianhydride, diphenyl sulfone dianhydride and 4,4'-oxydiphthalic anhydride.

[0039] In the present invention, the diamine monomer preferably includes one or more of phenylenediamine, naphthalenediamine, benzidine, 4,4'-diaminodiphenylmethane, 1,3-di(4-aminophenoxy)benzene, diaminodiphenyl ether and diaminodiphenyl sulfone, and the phenylenediamine is preferably p-phenylenediamine.

[0040] In the present invention, the molar ratio of the dianhydride monomer to the diamine monomer is preferably (1-1.1):1, specifically 1:1, 1.05:1 or 1.1:1.

[0041] In the present invention, the polar organic solvent preferably includes one or more of dimethyl sulfoxide, N-methylpyrrolidone, dimethylformamide and dimethylacetamide.

[0042] In the present invention, the mass ratio of the total mass of the dianhydride monomer and the diamine monomer to the polar organic solvent is preferably (3-7):(15-25).

[0043] In the present invention, the dianhydride monomer, diamine monomer and polar organic solvent are preferably mixed by stirring, the stirring speed is preferably 200-300 rpm, the atmosphere during the mixing is preferably a nitrogen atmosphere, the temperature during the mixing is preferably room temperature, and the present invention preferably dissolves the diamine monomer in the polar organic solvent first and then adds the dianhydride monomer.

[0044] In the present invention, the polymerization reaction time is preferably 10 to 14 hours, more preferably 12 hours. The polymerization reaction is preferably accompanied by stirring. The atmosphere during the polymerization reaction is preferably a nitrogen atmosphere.

[0045] After obtaining the polyamic acid solution, the present invention mixes the polyamic acid solution and nanoparticles for a first ball milling, and mixes the obtained system with an emulsifier and a dehydrating agent to obtain phase A.

[0046] In the present invention, the nanoparticles preferably include one or more of nano-iron tetroxide, graphene, graphene oxide, conductive carbon black and Mxene; the nanoparticles are absorbent materials. In addition, the nanoparticles can also stabilize the emulsion system and replace the role of part of the emulsifier. The particle size of the nanoparticles is preferably 20 to 50 nm.

[0047] In the present invention, the mass fraction of the nanoparticles in phase A is preferably 1% to 15%, specifically 2.9%, 4.3%, 4.5%, 5.6% or 6.9%.

[0048] In the present invention, the emulsifier preferably includes one or more of Tween 20, F127, PL108 and polyglycerol alkenyl succinate.

[0049] In the present invention, the mass fraction of the emulsifier in phase A is preferably 1% to 25%, specifically 12.1%, 12.2%, 12.4%, 12.6%, 17.4% or 18.5%.

[0050] In the present invention, the ratio of the emulsifier to the polyamic acid solution is preferably (0.05-0.2) g / mL.

[0051] In the present invention, the mass fraction of the polyamic acid in the phase A is preferably 10% to 30%, and the polyamic acid is a polymer precursor of polyimide synthesized from a dianhydride monomer and a diamine monomer.

[0052] In the present invention, the dehydrating agent preferably includes acetic anhydride or concentrated sulfuric acid, and the concentrated sulfuric acid is preferably a sulfuric acid aqueous solution with a mass fraction greater than or equal to 70%.

[0053] In the present invention, the mass ratio of the dehydrating agent to the dianhydride monomer is preferably (1-10):1, specifically (2-4):1.

[0054] In the present invention, the rotation speed of the first ball mill is preferably 300-500rpm, more preferably 400rpm, the ball-to-material ratio is preferably (3-5):1, more preferably 4:1, and the time is preferably 3-4h. The first ball milling is preferably carried out under closed conditions. The ball milling speed and time described in the present invention can make the nanoparticles evenly dispersed in the polyamic acid solution, and refinement and dispersion are carried out simultaneously during the ball milling process. If the ball milling time is too long, obvious agglomerated particles will appear, and the mechanical properties of the corresponding foam material will also drop sharply. The present invention uses ball milling to simplify the production process and improve production efficiency.

[0055] After obtaining phase A, the present invention mixes phase B with the phase A and performs a second ball milling to obtain an emulsion containing phase A and phase B; the phase B is a non-polar organic solvent.

[0056] In the present invention, the non-polar solvent preferably includes one or more of toluene, xylene, paraffin oil, tetradecane and hexadecane. The phase B (non-polar solvent) is the inner phase (dispersed phase).

[0057] In the present invention, the volume ratio of the phase A to the phase B is preferably 1:(0.5-10), and the volume ratio of the phase B to the polyamic acid solution is preferably (0.7-5):1.

[0058] The present invention has no special requirements on the mixing method of phase B and phase A.

[0059] In the present invention, the rotation speed of the second ball mill is preferably 600-1000 rpm, more preferably 800 rpm, the ball-to-material ratio is preferably (3-5):1, more preferably 4:1, and the time is preferably 0.5-2 hours. The function of the second ball mill is emulsification to form an emulsion of A in B, with phase A being the continuous phase.

[0060] After obtaining the A-package-B emulsion, the present invention sequentially allows the A-package-B emulsion to stand, wash and heat-treat it to obtain a nanoparticle composite polyimide foam material.

[0061] In the present invention, the step of allowing the mixture to stand still further includes a degassing treatment, which is preferably carried out in a planetary agitator, and the time for the degassing treatment is preferably 1 to 2 minutes.

[0062] In the present invention, the standing temperature is preferably 20-50°C, specifically 25°C, 40°C or 50°C, and the time is preferably 6-48h, more preferably 12-24h. The purpose of the standing is to further polymerize the emulsion of A package B, so that short chains form long chains, and the long chains are entangled with each other to form an emulsion gel.

[0063] In the present invention, the washing agent is preferably ethanol, and the purpose of the washing is to remove the polar organic solvent, emulsifier, and unreacted dianhydride monomer and diamine monomer in the dispersed phase and the continuous phase to form a porous foam.

[0064] In the present invention, the washing preferably includes drying, the drying temperature is preferably 60° C., and the drying time is preferably 24 to 48 hours.

[0065] In the present invention, the heat treatment temperature is preferably 280-320°C, specifically 280°C, 300°C or 320°C, and the time is preferably 30min-2h, specifically 30min, 1h or 2h. The heat treatment process further undergoes imidization and cyclization to obtain a nanoparticle composite polyimide foam material.

[0066] The present invention also provides a nano-particle composite polyimide foam material obtained by the preparation method described in the above technical solution. The porosity of the nano-particle composite polyimide foam material is 80% to 95%, and the open hole rate is 100%.

[0067] In the present invention, the porosity of the nanoparticle composite polyimide foam material can be specifically 84%, 85%, 87%, 89% or 91%.

[0068] In the present invention, the pore size of the nanoparticle composite polyimide foam material is preferably 1 to 20 μm.

[0069] In the present invention, the density of the nanoparticle composite polyimide foam material is preferably 0.03 to 0.5 g / cm 3 .

[0070] The present invention also provides the use of the nano-particle composite polyimide foam material described in the above technical solution as a wave absorbing material.

[0071] The nanoparticle composite polyimide foam material of the present invention has high compression strength and good wave absorbing performance. The nanoparticle composite polyimide foam material of the present invention uses porous polyimide foam as a matrix, and the porous polyimide foam has excellent mechanical properties and high temperature resistance, and has good broadband wave permeability, that is, it has a lower dielectric constant and dielectric loss value, and can maximize the absorption and attenuation of electromagnetic waves by the material. At the same time, the porous structure of the polyimide foam increases the specific surface area of ​​the material, and electromagnetic waves are scattered and multi-reflected in the pores, so that the interaction between the material and the wave absorbing agent is enhanced, and the porous material contains a lot of air inside, so that the dielectric constant of the material is improved, and the dielectric constant of the open-cell polyimide foam is 1.2 to 1.5.

[0072] In order to further illustrate the present invention, the nanoparticle composite polyimide foam material provided by the present invention and its preparation method and application are described in detail below in conjunction with the accompanying drawings and examples, but they should not be construed as limiting the scope of protection of the present invention.

[0073] Figure 1 The flowchart of the preparation method of the nanoparticle composite polyimide foam material in the embodiment is as follows: first, dianhydride and diamine monomers are formed into a prepolymer (polyamic acid) in a polar organic solvent; then the nanoparticles and the prepolymer are put into a ball mill for ball milling, and an emulsifier and a dehydrating agent are added to form the prepolymer (A phase); a non-polar organic solvent is used as the B phase, and the B phase is added to the A phase and the ball milling is continued to obtain an emulsion of A encapsulating B; the emulsion is degassed and transferred to a mold, and allowed to stand to form an emulsion gel; the emulsion gel is washed with ethanol to remove the solvent and emulsifier in the B phase and the A phase to obtain a porous material, which is transferred to a high-temperature vacuum oven for further thermal imidization and cyclization to obtain a nanoparticle composite polyimide foam material.

[0074] Example 1

[0075] Take pyromellitic acid dianhydride and 4,4'-diaminodiphenylmethane as monomers. At room temperature, add 4,4'-diaminodiphenylmethane (1.98g, 10mmol) into a 100mL three-necked flask and pass nitrogen, and dissolve it in dimethyl sulfoxide (23.59g) under stirring at 200rpm. Once 4,4'-diaminodiphenylmethane is dissolved, add pyromellitic acid dianhydride (2.18g, 10mmol) to the solution. Stir the reaction in a nitrogen atmosphere for 12h, and polymerize to obtain a light yellow polyamic acid solution.

[0076] 0.5 g of nano-ferroferric oxide and 0.5 g of conductive carbon black were added to the polyamic acid solution, and the mixture was dispersed in a closed ball mill (rotation speed 400 rpm, ball-to-material ratio 4:1) for 4 hours, and then emulsifier F127 (1.5 g) and dehydrating agent acetic anhydride (4.36 g) were added, and the continuous phase (phase A) was used. 24 mL of tetradecane (phase B) was added as the dispersed phase, and the mixture was continued to be ball milled in the ball mill (rotation speed 800 rpm, ball-to-material ratio 4:1) for 1 hour to obtain a non-aqueous emulsion of A encapsulating B.

[0077] The non-aqueous emulsion was placed in a planetary agitator and stirred for degassing for 1 minute, then transferred into a PTFE mold and sealed. The mold was placed at 25°C for gelation for 12 hours, and the obtained block-shaped porous material was replaced with ethanol for 24 hours to remove impurities such as the dispersed phase tetradecane, the solvent dimethyl sulfoxide in the continuous phase, and the emulsifier. After the replacement was completed, the sample was placed in a 60°C vacuum oven for drying for 24 hours, and then the vacuum oven temperature was further increased to 300°C and maintained for 1 hour to obtain a nanoparticle composite polyimide foam material.

[0078] The morphology of the foam materials was observed using a field emission scanning electron microscope (FESEM, Hitachi S-4800, Japan). Figure 2 As shown, the pore size of the obtained foam material is about 10 μm.

[0079] The mass and volume of the porous foam material were measured by a balance and a vernier caliper, and the porosity was calculated. The density of the foam material was about 0.19 g / cm 3 , the porosity is 91% and the open porosity is 100%.

[0080] The electromagnetic properties of the foam material were tested using a vector network analyzer (Agilent N5234A), and the shielding effectiveness of the foam material was 6 dB.

[0081] The compression properties of the foam material were tested using an electronic universal testing machine (LABSANS LD23.104), and the compression strength of the foam material was 5.15 MPa.

[0082] Example 2

[0083] The only difference between this embodiment and embodiment 1 is that the amount of conductive carbon black used is 1.0 g, and the other steps are the same.

[0084] The morphology of the foam materials was observed using a field emission scanning electron microscope (FESEM, Hitachi S-4800, Japan). Figure 3 As shown, the pore size of the obtained foam material is about 7 μm.

[0085] The mass and volume of the porous foam material were measured by a balance and a vernier caliper, and the porosity was calculated. The density of the foam material was about 0.20 g / cm 3 , the porosity is 89% and the open porosity is 100%.

[0086] The electromagnetic properties of the foam material were tested using a vector network analyzer (Agilent N5234A), and the shielding effectiveness of the foam material was 20 dB.

[0087] The compression properties of the foam material were tested using an electronic universal testing machine (LABSANS LD23.104), and the compression strength of the foam material was 5.21 MPa.

[0088] Example 3

[0089] The only difference between this embodiment and embodiment 1 is that the amount of conductive carbon black used is 1.5 g, and the other steps are the same.

[0090] The morphology of the foam materials was observed using a field emission scanning electron microscope (FESEM, Hitachi S-4800, Japan). Figure 4 As shown, the pore size of the obtained foam material is about 4 μm.

[0091] The mass and volume of the porous foam material were measured by a balance and a vernier caliper, and the porosity was calculated. The density of the foam material was about 0.21 g / cm 3 , the porosity is 87% and the open porosity is 100%.

[0092] The electromagnetic properties of the foam material were tested using a vector network analyzer (Agilent N5234A), and the shielding effectiveness of the foam material was 28 dB.

[0093] The compression properties of the foam material were tested using an electronic universal testing machine (LABSANS LD23.104), and the compression strength of the foam material was 5.49 MPa.

[0094] Example 4

[0095] The only difference between this embodiment and embodiment 1 is that the amount of conductive carbon black used is 2.0 g, and the other steps are the same.

[0096] The morphology of the foam material was observed using a scanning electron microscope (SEM, S-3400N, JEOL). Figure 5 As shown, the pore size of the obtained foam material is about 3 μm.

[0097] The mass and volume of the porous foam material were measured by a balance and a vernier caliper, and the porosity was calculated. The density of the foam material was about 0.23 g / cm 3, the porosity is 84% ​​and the open porosity is 100%.

[0098] The electromagnetic properties of the foam material were tested using a vector network analyzer (Agilent N5234A), and the shielding effectiveness of the foam material was 33 dB.

[0099] The compression properties of the foam material were tested using an electronic universal testing machine (LABSANS LD23.104), and the compression strength of the foam material was 4.48 MPa.

[0100] It can be seen from Examples 1 to 4 that different degrees of wave absorbing effects can be obtained by adjusting the amount of nanoparticles. Within a certain range, increasing the amount of nanoparticles, the more perfect the three-dimensional network formed by the nanoparticles in the matrix material, the better the wave absorbing performance; the filling of nanoparticles has an enhancing effect on the mechanical properties of the matrix material, but too much nanoparticle content will affect the uniformity of the material, resulting in reduced mechanical properties. When the amount of nanoparticles exceeds the total mass of the monomer, it will affect the polymerization of the emulsion, and a stable emulsion cannot be formed, and the sample cannot be successfully made.

[0101] Example 5

[0102] Take biphenyl dianhydride and p-phenylenediamine as monomers. At room temperature, p-phenylenediamine (1.08 g, 10 mmol) was added to a 100 mL three-necked flask and nitrogen was introduced, and dissolved in 20 g of N-methylpyrrolidone under stirring at 300 rpm. Once p-phenylenediamine was dissolved, biphenyl dianhydride (3.09 g, 10.5 mmol) was added to the solution. The reaction was stirred in a nitrogen atmosphere for 12 hours to obtain a polyamic acid solution.

[0103] 1.5 g of graphene was added to the polyamic acid solution, and the mixture was dispersed in a ball mill (rotation speed 400 rpm, ball to material ratio 4:1) for 3 h, and then emulsifier PL108 (1.5 g) and dehydrating agent acetic anhydride (6.18 g) were added, and the mixture was used as the continuous phase (phase A). 18 mL of hexadecane (phase B) was added as the dispersed phase, and the mixture was continued to be milled in the ball mill for 0.5 h (rotation speed 800 rpm, ball to material ratio 4:1), and a non-aqueous emulsion of A encapsulating B was obtained.

[0104] The non-aqueous emulsion was placed in a planetary agitator and stirred for degassing for 1 minute, then transferred into a PTFE mold and sealed. The mold was placed at 25°C for gelation for 12 hours, and the obtained blocky porous material was replaced with ethanol for 24 hours to remove impurities such as the dispersed phase hexadecane, the solvent N-methylpyrrolidone in the continuous phase, and the emulsifier. After the replacement was completed, the sample was placed in a 60°C vacuum oven for drying for 24 hours, and then the vacuum oven temperature was further increased to 320°C and maintained for 1 hour to obtain a nanoparticle composite polyimide foam material.

[0105] The morphology of the foam material was observed using a field emission scanning electron microscope (FESEM, Hitachi S-4800, Japan), and the pore size of the obtained foam material was about 12 μm.

[0106] The mass and volume of the porous foam material were measured by a balance and a vernier caliper, and the porosity was calculated. The density of the foam material was about 0.18 g / cm 3 , the porosity is 91% and the open porosity is 100%.

[0107] The electromagnetic properties of the foam material were tested using a vector network analyzer (Agilent N5234A), and the shielding effectiveness of the foam material was 24 dB.

[0108] The compression properties of the foam material were tested using an electronic universal testing machine (LABSANS LD23.104), and the compression strength of the foam material was 4.86 MPa.

[0109] Example 6

[0110] 4,4'-oxydiphthalic anhydride and 1,3-bis(4-aminophenoxy)benzene were used as monomers. At room temperature, 1,3-bis(4-aminophenoxy)benzene (2.92 g, 10 mmol) was added to a 100 mL three-necked flask and nitrogen was introduced, and dissolved in 20 g of dimethylformamide under stirring at 300 rpm. Once 1,3-bis(4-aminophenoxy)benzene was dissolved, 4,4'-oxydiphthalic anhydride (3.10 g, 10 mmol) was added to the solution. The reaction was stirred in a nitrogen atmosphere for 12 hours, and a polyamic acid solution was obtained by polymerization.

[0111] 0.5 g of nano-ferroferric oxide and 1.5 g of graphene were added to the polyamic acid solution, and the mixture was dispersed in a ball mill (rotation speed 400 rpm, ball-to-material ratio 4:1) for 4 hours, and then emulsifier F127 (1.5 g) and dehydrating agent acetic anhydride (6.2 g) were added, and the mixture was used as the continuous phase (phase A). 20 mL of tetradecane (phase B) was added as the dispersed phase, and the mixture was continued to be milled in a ball mill (rotation speed 800 rpm, ball-to-material ratio 4:1) for 1 hour to obtain a non-aqueous emulsion of A encapsulating B.

[0112] The non-aqueous emulsion was placed in a planetary agitator and stirred for degassing for 1 minute, then transferred into a PTFE mold and sealed. The mold was placed at 50°C for gelation for 12 hours, and the obtained blocky porous material was replaced with ethanol for 24 hours to remove impurities such as the dispersed phase tetradecane, the solvent dimethylformamide in the continuous phase, and the emulsifier. After the replacement was completed, the sample was placed in a 60°C vacuum oven for drying for 24 hours, and then the vacuum oven temperature was further increased to 280°C and maintained for 1 hour to obtain a nanoparticle composite polyimide foam material.

[0113] The morphology of the foam material was observed using a scanning electron microscope (SEM, S-3400N, JEOL). Figure 6 As shown, the pore size of the obtained foam material is about 12 μm.

[0114] The mass and volume of the porous foam material were measured by a balance and a vernier caliper, and the porosity was calculated. The density of the foam material was about 0.23 g / cm 3 , porosity is 85% and open pore size is 100%.

[0115] The electromagnetic properties of the foam material were tested using a vector network analyzer (Agilent N5234A), and the shielding effectiveness of the foam material was 26 dB.

[0116] The compression properties of the foam material were tested using an electronic universal testing machine (LABSANS LD23.104), and the compression strength of the foam material was 4.78 MPa.

[0117] Comparative Example 1

[0118] The preparation method of the polyamic acid solution is the same as that in Example 2.

[0119] 0.5g of nano-ferroferric oxide and 1.0g of conductive carbon black were added to the polyamic acid solution and stirred at room temperature for 2h at 500rpm. Emulsifier F127 (1.5g) and dehydrating agent acetic anhydride (4.36g) were added, and nitrogen was continuously introduced, and the mixture was mixed until the emulsifier was completely dissolved under mechanical stirring, as a continuous phase (phase A). 24mL of tetradecane was used as a dispersed phase (phase B), and the dispersed phase was dripped into the continuous phase dropwise under 500rpm mechanical stirring, until the dispersed phase was completely dripped off, stirred for 2min, and a non-aqueous emulsion of A package B was obtained.

[0120] After the non-aqueous emulsion was placed in a planetary agitator and stirred for degassing for 1 minute, it was transferred into a PTFE mold and sealed. The mold was placed at 25°C for gelation for 12 hours. The obtained blocky porous material was replaced with ethanol for 24 hours to remove impurities such as the dispersed phase tetradecane, the solvent dimethyl sulfoxide in the continuous phase, and the emulsifier, and then the sample was washed with water for 12 hours. The sample was then placed in a vacuum oven and dried at 60°C for 24 hours, and the vacuum oven temperature was further increased to 300°C and maintained for 1 hour to obtain a nanoparticle composite polyimide foam material.

[0121] The morphology of the foam materials was observed using a field emission scanning electron microscope (FESEM, Hitachi S-4800, Japan). Figure 7 As shown, the pore size of the obtained foam material is about 7 μm.

[0122] The mass and volume of the porous foam material were measured by a balance and a vernier caliper, and the porosity was calculated. The density of the foam material was about 0.22 g / cm3 The porosity of the obtained foam material is 70% and the open cell rate is 90%.

[0123] The electromagnetic properties of the foam material were tested using a vector network analyzer (Agilent N5234A), and the shielding effectiveness of the foam material was 2 dB.

[0124] The compression properties of the foam material were tested using an electronic universal testing machine (LABSANS LD23.104), and the compression strength of the foam material was 0.85 MPa.

[0125] It can be seen from Example 2 and Comparative Example 1 that mechanical stirring cannot make the absorbent material evenly dispersed in the matrix material, resulting in the inability to form a three-dimensional network structure and poor absorbing performance.

[0126] Comparative Example 2

[0127] The preparation method of the polyamic acid solution is the same as that of Example 2, except that the mass of dimethyl sulfoxide is 13.59 g.

[0128] At room temperature, 0.5 g of nano-iron tetroxide and 1.0 g of conductive carbon black were added to 10 g of dimethyl sulfoxide and ultrasonically dispersed for 2 h. After dispersion, they were added to the polyamic acid solution. Emulsifier F127 (1.5 g) and dehydrating agent acetic anhydride (4.36 g) were added at 25 ° C, transferred to a 100 mL round-bottom flask, and nitrogen was continuously introduced. The mixture was mixed under mechanical stirring until the emulsifier was completely dissolved as a continuous phase. 24 mL of tetradecane was used as a dispersed phase, and the dispersed phase was dripped into the continuous phase drop by drop under mechanical stirring at 500 rpm. After the dispersed phase was completely dripped, it was stirred for 2 min to obtain a polyamic acid non-aqueous emulsion.

[0129] After the non-aqueous emulsion was placed in a planetary agitator and stirred for degassing for 1 minute, it was transferred into a PTFE mold and sealed. The mold was placed at 25°C for gelation for 12 hours. The obtained blocky porous material was replaced with ethanol for 24 hours to remove impurities such as the dispersed phase tetradecane, the solvent dimethyl sulfoxide in the continuous phase, and the emulsifier, and then the sample was washed with water for 12 hours. The sample was then placed in a vacuum oven and dried at 60°C for 24 hours, and the vacuum oven temperature was further increased to 300°C and maintained for 1 hour to obtain a nanoparticle composite polyimide foam material.

[0130] The morphology of the foam material was observed using a scanning electron microscope (SEM, S-3400N, JEOL). Figure 8 As shown, the pore size of the obtained foam material is about 7 μm.

[0131] The mass and volume of the porous foam material were measured by a balance and a vernier caliper, and the porosity was calculated. The density of the foam material was about 0.21 g / cm 3The porosity of the obtained foam material is 78% and the open pore size is 90%.

[0132] The electromagnetic properties of the foam material were tested using a vector network analyzer (Agilent N5234A), and the shielding effectiveness of the foam material was 5 dB.

[0133] The compression properties of the foam material were tested using an electronic universal testing machine (LABSANS LD23.104), and the compression strength of the foam material was 1.22 MPa.

[0134] It can be seen from Example 2 and Comparative Example 2 that ultrasonic dispersion of the absorber material in the continuous phase cannot make the absorber uniformly dispersed in the matrix material. Due to its own characteristics, the absorber is easy to agglomerate, and agglomerates again during the stirring process after ultrasonic dispersion, resulting in the inability to form a three-dimensional network structure and poor absorbing performance.

[0135] Comparative Example 3

[0136] 4,4′-diaminodiphenylmethane (10 mmol) was dissolved in dimethylacetamide (20 mL) solvent by stirring, and then pyromellitic dianhydride (10 mmol) was dissolved in the above solution, and stirred in an ice-water bath for about 3 h to obtain a polyamic acid solution.

[0137] 0.5g of nano-ferroferric oxide and 1.0g of conductive carbon black were mixed into the polyamic acid solution and put into a ball mill for ball milling dispersion (rotation speed 400rpm, ball-to-material ratio 4:1) for 4h. After the ball milling, the polyamic acid solution was poured into deionized water for precipitation, the resulting precipitate was washed with deionized water several times, and the residual water was removed by freeze drying. Subsequently, at room temperature, 2.8mL of triethylamine was added to dissolve the solid polyamic acid in deionized water to obtain a water-soluble polyimide precursor solution. The water-soluble polyimide precursor solution was freeze-dried to obtain polyamic acid foam. Subsequently, the polyamic acid foam was heated at a temperature of 150°C for 0.5h, 250°C for 0.5h, and 300°C for 2h in sequence to induce thermal imidization to obtain polyimide foam.

[0138] The polyimide foam prepared in this comparative example has a porous structure with random pores, but the open cell degree is very low, only 38%.

[0139] The electromagnetic properties of the foam material were tested using a vector network analyzer (Agilent N5234A), and the shielding effectiveness of the foam material was 14 dB.

[0140] It can be seen from Example 2 and Comparative Example 3 that the foam material prepared in Comparative Example 3 has a low open pore degree, and electromagnetic waves will be lost when hitting the surface of the material, but there is no multiple reflection loss and absorption attenuation in the internal space, and the wave absorbing performance is reduced. The wave absorbing performance of the porous structure composite foam in Example 2 is significantly improved compared with the closed-cell structure composite foam, indicating that the porous structure is also crucial to the improvement of the wave absorbing performance.

[0141] It can be seen from the above examples and comparative data that the preparation method of the nanoparticle composite polyimide foam material of the present invention uses a ball milling dispersion method to evenly distribute the nanoparticles in the matrix material and form a three-dimensional network structure, which not only improves the wave absorbing performance of the nanoparticle composite polyimide foam material, but also further enhances the strength of the foam material.

[0142] Although the above-mentioned embodiments have made a detailed description of the present invention, they are only some embodiments of the present invention, rather than all embodiments. People can also obtain other embodiments based on the embodiments of the present invention without creative work, and these embodiments all fall within the scope of protection of the present invention.

Claims

1. A method for preparing a nanoparticle composite polyimide foam material, characterized in that: The following steps are involved: The polyamic acid solution and the nanoparticles are mixed and subjected to a first ball milling, and the obtained system is mixed with an emulsifier and a dehydrating agent to obtain a phase A; the solvent of the polyamic acid solution is a polar organic solvent; Mixing phase B and phase A for a second ball milling to obtain an emulsion containing phase B; phase B is a non-polar organic solvent; The emulsion of A package B is sequentially allowed to stand, washed and heat treated to obtain a nanoparticle composite polyimide foam material.

2. The preparation method according to claim 1, characterized in that: The nanoparticles include one or more of nano-iron tetroxide, graphene, graphene oxide, conductive carbon black and Mxene.

3. The preparation method according to claim 1 or 2, characterized in that: The mass fraction of the nanoparticles in phase A is 1% to 15%.

4. The preparation method according to claim 1, characterized in that: The rotation speed of the first ball mill is 300-500 rpm, the ball-to-material ratio is (3-5):1, and the time is 3-4 hours.

5. The preparation method according to claim 1 or 4, characterized in that: The rotation speed of the second ball mill is 600-1000 rpm, the ball-to-material ratio is (3-5):1, and the time is 0.5-2h.

6. The preparation method according to claim 1, characterized in that: The polar organic solvent includes one or more of dimethyl sulfoxide, N-methylpyrrolidone, dimethylformamide and dimethylacetamide.

7. The preparation method according to claim 1 or 6, characterized in that: The non-polar solvent includes one or more of toluene, xylene, paraffin oil, tetradecane and hexadecane.

8. The preparation method according to claim 1, characterized in that: The temperature of the heat treatment is 280-320° C., and the time is 30 min-2 h.

9. The nanoparticle composite polyimide foam material obtained by the preparation method according to any one of claims 1 to 8, characterized in that: The porosity of the nano-particle composite polyimide foam material is 80% to 95%, and the open-pore rate is 100%.

10. Use of the nanoparticle composite polyimide foam material according to claim 9 as a wave absorbing material.

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