Preparation method of PI wave-absorbing foam doped with rare earth elements

Abstract

The application provides a preparation method of a rare earth element doped PI wave-absorbing foam and belongs to the technical field of wave-absorbing foam materials.The preparation method comprises pretreatment of spiral carbon fibers, preparation of a PI foam precursor, preparation of a clear transparent viscous solution, foaming and post-treatment.The clear transparent viscous solution is prepared by mixing anhydrous ethanol, tetrahydrofuran and the PI foam precursor, stirring uniformly, adding 3,3',4,4'-benzophenonetetracarboxylic dianhydride, then adding isooctanoic acid stannous, increasing the temperature to 103-105 DEG C, presenting a transparent state, increasing the temperature to 118-124 DEG C, keeping the temperature for 0.8-1.3 h, reducing to room temperature, adding deionized water, a stabilizer, polyethylene glycol, triethanolamine and isooctanoic acid stannous, stirring uniformly and obtaining the clear transparent viscous solution.The PI wave-absorbing foam prepared by the method has good wave-absorbing performance, excellent strength performance and excellent thermal stability.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of wave-absorbing foam materials, and particularly relates to a preparation method of a PI wave-absorbing foam doped with rare earth elements. BACKGROUND

[0002] Wave-absorbing foam material is a material with the characteristics of absorbing and dissipating sound waves or electromagnetic wave energy, and is widely used in sound insulation, stealth, electromagnetic compatibility and other fields; polyimide (PI) foam, as a kind of high-performance material, has a wide application prospect in the fields of aerospace, electronic information, transportation and other fields due to its excellent thermal stability, good mechanical properties, low dielectric constant and excellent flame retardant properties.

[0003] The durability of wave-absorbing foam material is affected by the material properties, and long-term use may cause aging and degradation, reducing the wave-absorbing effect; this means that the stability of the wave-absorbing performance of the foam material is required to be high in long-term use; low-quality wave-absorbing foam material may contain harmful substances, which may cause potential harm to human health and the environment;

[0004] Therefore, when preparing wave-absorbing foam material, special attention should be paid to its environmental friendliness and safety; the preparation method of the special wave-absorbing agent currently studied is complex, and various parameters need to be accurately controlled; the addition of high-performance wave-absorbing agent will further increase the production cost, and the thermal stability and corrosion resistance are not good; therefore, it is necessary to develop a wave-absorbing foam material containing an easily prepared wave-absorbing additive, and having good heat resistance and corrosion resistance.

[0005] Rare earth elements have a wide application in the field of material science due to their unique physical and chemical properties; the addition of rare earth elements in PI foam can further improve the performance of PI foam by changing the molecular structure of the foam, improving the thermal stability of the foam, and improving the electromagnetic properties of the foam; the research on the doping of rare earth gadolinium elements in PI wave-absorbing materials has attracted much attention;

[0006] However, gadolinium oxide itself does not have significant electromagnetic wave absorbing performance, and its direct use in wave-absorbing foam material cannot effectively improve the wave-absorbing performance of PI wave-absorbing foam; however, as a kind of rare earth oxide material, gadolinium oxide can effectively absorb electromagnetic waves under certain conditions, especially when it is compounded with other materials, so as to exhibit wave-absorbing characteristics;

[0007] It can be seen that the doping of rare earth gadolinium elements in the field of PI foam wave-absorbing materials has shown the potential to significantly improve the wave-absorbing performance of the material.

[0008] Carbon fiber is a kind of high-performance fiber material, which is often used to reinforce polymer-based composite materials due to its high strength, high modulus, low density and other characteristics. The addition of carbon fiber to PI foam can significantly improve the mechanical properties, thermal stability and electrical conductivity of the foam. By adding carbon fiber to PI foam, the tensile strength and compressive strength of the foam can be significantly improved, while maintaining good thermal stability and corrosion resistance. The use of carbon fiber and rare earth elements in the preparation of wave-absorbing foam materials has important research significance.

[0009] The applicant has searched and has not found any related literature or patents on the use of rare earth elements and carbon fiber to prepare PI wave-absorbing foam materials. During the research process, the applicant found that the mixing of rare earth gadolinium elements with carbon fiber is not good, which affects the mechanical properties and wave-absorbing properties of the wave-absorbing foam material, and also affects the stability of the product.

[0010] Therefore, it is a technical problem to be solved in the prior art to provide a preparation method of a PI wave-absorbing foam doped with rare earth elements, which has good wave-absorbing properties, good mechanical properties and excellent stability. SUMMARY

[0011] In order to solve the technical problems existing in the prior art, the present application provides a preparation method of a PI wave-absorbing foam doped with rare earth elements, which combines the rare earth doping technology and the excellent performance of spiral carbon fiber. The prepared PI wave-absorbing foam has good wave-absorbing properties, good mechanical properties and excellent thermal stability.

[0012] In order to solve the above technical problems, the present application adopts the following technical solutions:

[0013] A preparation method of a PI wave-absorbing foam doped with rare earth elements, comprising the steps of pretreatment of spiral carbon fiber, preparation of PI foam precursor, preparation of clear and transparent viscous solution, foaming and post-treatment, the specific operation being as follows:

[0014] 1. Pretreatment of spiral carbon fiber

[0015] (1) Preparation of spiral carbon fiber

[0016] After the Sn-MOF is crushed to 140-160 mesh and mixed with anhydrous ethanol, it is uniformly dispersed by ultrasonic to obtain a suspension. The nickel sheet is placed in 3-5 times the mass of the suspension and stirred for 16-25 min. The nickel sheet is dried after being taken out. Anhydrous ethanol is added to deionized water and stirred uniformly to obtain an ethanol solution. The ethanol solution is added as a carbon source to an alcohol lamp, and the soaked nickel sheet is burned for 40-60 min to obtain spiral carbon fiber.

[0017] The mass ratio of Sn-MOF to anhydrous ethanol is 2.3-2.8:8.0-9.0.

[0018] The volume percentage of deionized water in the ethanol solution is 0.25-0.75%;

[0019] The preparation method of the Sn-MOF is as follows: SnCl2·2H2O is dissolved in 6-8 times the mass of ethanol to obtain a stannous chloride solution; 1,2,4-benzenetricarboxylic acid is dissolved in 8-10 times the mass of dimethylacetamide to obtain a 1,2,4-benzenetricarboxylic acid solution; NaOH is dissolved in 18-22 times the mass of deionized water to obtain a NaOH solution; the 1,2,4-benzenetricarboxylic acid solution and the NaOH solution are mixed, and then the stannous chloride solution is added after uniform stirring, and then stirred uniformly, and then transferred into a water bath device for water bath reaction, the water bath time is 2.8-3.2 h, and the water bath temperature is 77-83℃; after the reaction is completed, filtration, washing and drying are performed to obtain the Sn-MOF;

[0020] The molar ratio of SnCl2·2H2O, 1,2,4-benzenetricarboxylic acid and NaOH is 1:1.8-2.3:2.7-3.2;

[0021] (2) Pretreatment

[0022] The helical carbon fiber is soaked in the pretreatment liquid for 23-25 hours, and after the soaking is completed, the solid is filtered out, and the solid is heated to 690-710℃ under an argon atmosphere, and held for 3.8-4.2 h, and after the holding is completed, it is naturally cooled to room temperature under an argon atmosphere to obtain pretreated helical carbon fiber;

[0023] The mass ratio of the helical carbon fiber to the pretreatment liquid is 1:6-10;

[0024] The pretreatment liquid is a mixture of gadolinium nitrate solution and nickel chloride solution, and the mass ratio of the gadolinium nitrate solution to the nickel chloride solution is 1:0.7-1.2; the concentration of the gadolinium nitrate solution is 0.8-1.2 mol / L, and the concentration of the nickel chloride solution is 0.8-1.2 mol / L.

[0025] 2. Preparation of PI foam precursor

[0026] The pretreated helical carbon fiber and carbon black are added to N,N-dimethylformamide, and ultrasonic oscillation treatment is performed, the ultrasonic time is 25-34 min, the ultrasonic frequency is 42-50 kHz, and the ultrasonic power is 130-150 W; after the ultrasonic treatment is completed, a PI foam precursor is obtained;

[0027] The mass ratio of the pretreated helical carbon fiber, carbon black and N,N-dimethylformamide is 5-10:5:85-90.

[0028] 3. Preparing a clear transparent viscous solution

[0029] The anhydrous ethanol, tetrahydrofuran and PI foam precursor are mixed, after uniform stirring, 3,3',4,4'-benzophenonetetracarboxylic dianhydride is slowly added, the adding rate is controlled to be 1.8-2.2 g / min, stirring is continuously carried out at the same time, the stirring speed is 90-110 rpm, after the addition is completed, isooctanoic acid stannous is added, the temperature is increased to 103-105 DEG C, when the transparent state is presented, the temperature is increased to 118-124 DEG C, and the temperature is kept for 0.8-1.3 h, after the keeping is completed, the temperature is naturally reduced to room temperature, deionized water, stabilizer, polyethylene glycol, triethanolamine and stannous octoate are added in sequence and stirred, after uniform stirring, the temperature is naturally reduced to room temperature, and a clear transparent viscous solution is obtained;

[0030] The mass ratio of the anhydrous ethanol, tetrahydrofuran, PI foam precursor, 3,3',4,4'-benzophenonetetracarboxylic dianhydride, isooctanoic acid stannous, deionized water, stabilizer, polyethylene glycol, triethanolamine and stannous octoate is 24.7-25.3:48.0-53.0:24.5-25.5:96-103:0.17-0.22:4.7-5.2:4.8-5.3:0.04-0.06:0.01-0.03:0.02-0.04;

[0031] The stabilizer is a mixture of gamma-aminopropyl triethoxysilane and polydimethylsiloxane, and the mass ratio of the gamma-aminopropyl triethoxysilane and polydimethylsiloxane is 1:0.6-1.3.

[0032] 4. Foaming

[0033] The clear transparent viscous solution is uniformly mixed with isocyanate PM-200, stirring is carried out at 1100-1300 rpm for 14.0-17.0 s, and then the primary PI wave-absorbing foam is obtained by transferring into a mold for free foaming.

[0034] The mass ratio of the clear transparent viscous solution and isocyanate PM-200 is 245-253:243-255.

[0035] 5. Post-treatment

[0036] After the primary PI wave-absorbing foam is placed for 28-30 min, the primary PI wave-absorbing foam is transferred into a microwave device for shaping for 0.8-1.2 h, and then is placed into a vacuum oven at 118-123 DEG C for drying for 1.8-2.2 h to remove the solvent, and finally is placed into a high-temperature oven and heated to 246-253 DEG C, and kept for 2.9-3.2 h, and then is naturally reduced to room temperature, and the PI wave-absorbing foam is obtained.

[0037] Compared with the prior art, the application has the beneficial effects:

[0038] 1. The present application is to pretreat the spiral carbon fiber, soak it in a solution containing nickel element and rare earth element, to ensure that the rare earth element and nickel element can fully penetrate into the spiral carbon fiber, enhance the strength performance and thermal stability of the foam, combine the rare earth doping technology with the excellent performance of the spiral carbon fiber, and prepare the PI wave-absorbing foam with excellent wave-absorbing performance in high frequency band and wide frequency band range.

[0039] 2. The PI wave-absorbing foam prepared by the method of the present application has a compressive strength of 11.2-12.8 MPa, a compressive strength of 50% compression deformation of 9.7-11.4 MPa, a compressive strength of 10.5-12.2 MPa after being treated in an environment with a temperature of 360℃ and a pressure of 0.5 MPa for 8.0h.

[0040] 3. The PI wave-absorbing foam prepared by the method of the present application has an effective electromagnetic wave absorption frequency band in the frequency range of 2-18GHz, and a reflection loss value of-73.7dB at a frequency of 5.87GHz and a thickness of 0.8mm. DETAILED DESCRIPTION

[0041] In order to more clearly understand the technical features, objects and effects of the present application, the specific embodiments of the present application will be described.

[0042] Example 1

[0043] 1. Pretreatment of spiral carbon fiber

[0044] (1) Preparation of spiral carbon fiber

[0045] 2.3g Sn-MOF was crushed to 140 mesh and mixed with 8.0g anhydrous ethanol, and then uniformly dispersed by ultrasonic to obtain a suspension; a nickel sheet was placed in 3 times the mass of the suspension and stirred for 16min, then the nickel sheet was taken out and dried to obtain a soaked nickel sheet; deionized water was added to anhydrous ethanol and stirred uniformly to obtain an ethanol solution, which was used as a carbon source and added to an alcohol lamp, and the soaked nickel sheet was burned for 60min to obtain a spiral carbon fiber;

[0046] The volume fraction of deionized water in the ethanol solution is 0.25%;

[0047] The preparation method of the Sn-MOF is as follows: SnCl2·2H2O is dissolved in 6 times mass of ethanol to obtain a stannous chloride solution; 1,2,4-benzene tricarboxylic acid is dissolved in 10 times mass of dimethylacetamide to obtain a 1,2,4-benzene tricarboxylic acid solution; NaOH is dissolved in 18 times mass of deionized water to obtain a NaOH solution; the 1,2,4-benzene tricarboxylic acid solution and the NaOH solution are mixed, and then the stannous chloride solution is added after uniform stirring, and then the mixture is stirred uniformly and transferred into a water bath device for water bath reaction, the water bath time is 2.8 h, the water bath temperature is 77℃, after the reaction is completed, the product is filtered, washed and dried to obtain the Sn-MOF;

[0048] The molar ratio of SnCl2·2H2O, 1,2,4-benzene tricarboxylic acid and NaOH is 1:1.8:2.7;

[0049] (2) Pretreatment

[0050] The helical carbon fiber is soaked in 6 times mass of the pretreatment solution for 23 hours, after the soaking is completed, the solid is filtered out, and the solid is heated to 690℃ under an argon atmosphere and kept for 4.2 h, after the keeping is completed, the solid is naturally cooled to room temperature under an argon atmosphere to obtain the pretreated helical carbon fiber;

[0051] The pretreatment solution is a mixture of gadolinium nitrate solution and nickel chloride solution, the mass ratio of the gadolinium nitrate solution and the nickel chloride solution is 1:0.7; the concentration of the gadolinium nitrate solution is 0.8 mol / L, and the concentration of the nickel chloride solution is 1.2 mol / L.

[0052] 2. Preparation of PI foam precursor

[0053] The pretreated helical carbon fiber and carbon black are added into N,N-dimethylformamide, and ultrasonic oscillation treatment is performed, the ultrasonic time is 25 min, the ultrasonic frequency is 42 kHz, and the ultrasonic power is 130 W, after the ultrasonic treatment is completed, the PI foam precursor is obtained;

[0054] The mass ratio of the pretreated helical carbon fiber, carbon black and N,N-dimethylformamide is 7:5:88.

[0055] 3. Preparation of clear transparent viscous solution

[0056] Mix 24.7 g of anhydrous ethanol, 48.0 g of tetrahydrofuran and 24.5 g of PI foam precursor, after stirring uniformly, slowly add 96 g of 3,3',4,4'-benzophenonetetracarboxylic dianhydride, control the adding rate to be 1.8 g / min, continuously stir while adding, the stirring speed is 90 rpm, after adding, add 0.17 g of isooctanoic acid stannous, increase the temperature to 103℃, when it presents a transparent state, increase the temperature to 118℃, keep for 1.3 h, after keeping, naturally reduce to room temperature, sequentially add 4.7 g of deionized water, 4.8 g of stabilizer, 0.04 g of polyethylene glycol, 0.01 g of triethanolamine and 0.02 g of stannous octoate for stirring, after stirring uniformly, wait for the temperature to naturally reduce to room temperature, to obtain a clear and transparent viscous solution;

[0057] The stabilizer is a mixture of γ-aminopropyltriethoxysilane and polydimethylsiloxane, and the mass ratio of the γ-aminopropyltriethoxysilane and polydimethylsiloxane is 1:0.6.

[0058] 4. Foaming

[0059] Mix 245 g of the clear and transparent viscous solution with 243 g of isocyanate PM-200 uniformly, stir at 1100 rpm for 14.0 s, and then transfer into a mold for free foaming to obtain a primary PI wave-absorbing foam.

[0060] 5. Post-processing

[0061] After the primary PI wave-absorbing foam is placed for 28 min, it is transferred into a microwave device for shaping for 0.8 h, then placed into a vacuum oven at 118℃ for drying for 1.8 h to remove the solvent, and finally placed into a high-temperature oven to increase the temperature to 246℃, and kept for 3.2 h, and then naturally reduced to room temperature to obtain a PI wave-absorbing foam.

[0062] The PI wave-absorbing foam prepared by the method of Example 1 has a compressive strength of 11.2 MPa, a compressive strength of 9.7 MPa at 50% compression deformation, a compressive strength of 10.5 MPa after being treated in an environment at a temperature of 360℃ and a pressure of 0.5 MPa for 8.0 h, and an effective electromagnetic wave absorption frequency band in a frequency range of 2-18 GHz, and a reflection loss value of -66.5 dB at a frequency of 5.87 GHz and a thickness of 0.8 mm.

[0063] Example 2

[0064] 1. Pretreatment of helical carbon fibers

[0065] (1) Preparation of helical carbon fibers

[0066] After 2.8 g of Sn-MOF is crushed to 160 mesh and mixed with 9.0 g of anhydrous ethanol, a suspension is obtained after ultrasonic dispersion; the nickel sheet is placed in 5 times the mass of the suspension and stirred for 25 min, and then the nickel sheet is taken out and dried to obtain the soaked nickel sheet; deionized water is added to the anhydrous ethanol and stirred uniformly to obtain an ethanol solution, and the ethanol solution is used as a carbon source and added to an alcohol lamp to burn the soaked nickel sheet, with a burning time of 50 min to obtain a spiral carbon fiber;

[0067] In the ethanol solution, the volume percentage of deionized water is 0.50%;

[0068] The preparation method of the Sn-MOF is as follows: SnCl2·2H2O is dissolved in 6 times the mass of ethanol to obtain a stannous chloride solution; 1,2,4-benzenetricarboxylic acid is dissolved in 10 times the mass of dimethylacetamide to obtain a 1,2,4-benzenetricarboxylic acid solution; NaOH is dissolved in 22 times the mass of deionized water to obtain a NaOH solution; the 1,2,4-benzenetricarboxylic acid solution and the NaOH solution are mixed, and then the stannous chloride solution is added, and after stirring uniformly, it is transferred to a water bath device for water bath reaction, with a water bath time of 3.2 h and a water bath temperature of 83℃; after the reaction is completed, the product is filtered, washed and dried to obtain the Sn-MOF;

[0069] The molar ratio of SnCl2·2H2O, 1,2,4-benzenetricarboxylic acid and NaOH is 1:2.3:3.2;

[0070] (2) Pretreatment

[0071] The spiral carbon fiber is soaked in 10 times the mass of the pretreatment solution for 25 hours, and after the soaking is completed, the solid is filtered out, and the solid is heated to 710℃ under an argon atmosphere and kept for 3.8 h, and after the keeping is completed, it is naturally cooled to room temperature under an argon atmosphere to obtain pretreated spiral carbon fiber;

[0072] The pretreatment solution is a mixture of gadolinium nitrate solution and nickel chloride solution, and the mass ratio of the gadolinium nitrate solution and the nickel chloride solution is 1:1.2; the concentration of the gadolinium nitrate solution is 1.2 mol / L, and the concentration of the nickel chloride solution is 0.8 mol / L.

[0073] 2. Preparation of PI foam precursor

[0074] The pretreated spiral carbon fiber and carbon black are added to N,N-dimethylformamide and subjected to ultrasonic oscillation treatment, with an ultrasonic time of 34 min, an ultrasonic frequency of 50 kHz and an ultrasonic power of 150 W, and after the ultrasonic treatment is completed, a PI foam precursor is obtained;

[0075] The mass ratio of the pretreated helical carbon fiber, carbon black and N,N-dimethylformamide is 10:5:90.

[0076] 3. Preparation of a clear transparent viscous solution

[0077] After 25.3 g of anhydrous ethanol, 53.0 g of tetrahydrofuran and 25.5 g of PI foam precursor are mixed and stirred uniformly, 103 g of 3,3',4,4'-benzophenonetetracarboxylic dianhydride is slowly added at a rate of 2.2 g / min, stirring is continued during the addition at a stirring speed of 110 rpm, after the addition is completed, 0.22 g of isooctanoic acid stannous is added, the temperature is increased to 105°C, when a transparent state is presented, the temperature is increased to 124°C, and the temperature is maintained for 0.8 h, after the temperature maintaining is completed, the temperature is naturally reduced to room temperature, 5.2 g of deionized water, 5.3 g of a stabilizer, 0.06 g of polyethylene glycol, 0.03 g of triethanolamine and 0.04 g of stannous octoate are sequentially added and stirred, after the stirring is uniform, the temperature is naturally reduced to room temperature, and a clear transparent viscous solution is obtained;

[0078] The stabilizer is a mixture of γ-aminopropyltriethoxysilane and polydimethylsiloxane, and the mass ratio of the γ-aminopropyltriethoxysilane and polydimethylsiloxane is 1:1.3.

[0079] 4. Foaming

[0080] After 253 g of the clear transparent viscous solution and 255 g of isocyanate PM-200 are uniformly mixed, stirring is performed at 1300 rpm for 17.0 s, and the mixture is transferred into a mold to perform free foaming, and a primary PI wave-absorbing foam is obtained.

[0081] 5. Post-treatment

[0082] After the primary PI wave-absorbing foam is placed for 30 min, the foam is transferred into a microwave device to be shaped for 1.2 h, then is placed into a vacuum oven at 123°C to remove the solvent for 2.2 h, and finally is placed into a high-temperature oven to be heated to 253°C, and the temperature is maintained for 2.9 h, and after the temperature is naturally reduced to room temperature, a PI wave-absorbing foam is obtained.

[0083] The PI wave-absorbing foam is prepared by the method of Example 2, the compressive strength is 11.7 MPa, the compressive strength at 50% compression deformation is 10.2 MPa, the compressive strength is 11.6.2 MPa after being treated in an environment at a temperature of 360°C and a pressure of 0.5 MPa for 8.0 h, and the PI wave-absorbing foam has an effective electromagnetic wave absorption frequency band in a frequency range of 2-18 GHz, and the reflection loss value is -68.2 dB at a frequency of 5.87 GHz and a thickness of 0.8 mm.

[0084] Example 3

[0085] 1. Pretreatment of helical carbon fiber

[0086] (1) Preparation of helical carbon fiber

[0087] After 2.5 g of Sn-MOF is crushed to 150 mesh and mixed with 8.3 g of anhydrous ethanol, a suspension is obtained after ultrasonic dispersion; the nickel sheet is placed in 4 times the mass of the suspension and stirred for 20 min, and then the nickel sheet is taken out and dried to obtain the soaked nickel sheet; deionized water is added to the anhydrous ethanol and stirred uniformly to obtain an ethanol solution, and the ethanol solution is added as a carbon source to an alcohol lamp to burn the soaked nickel sheet, with a burning time of 40 min, to obtain a helical carbon fiber;

[0088] In the ethanol solution, the volume percentage of deionized water is 0.75%;

[0089] The preparation method of the Sn-MOF is as follows: SnCl2·2H2O is dissolved in 8 times the mass of ethanol to obtain a stannous chloride solution; 1,2,4-benzenetricarboxylic acid is dissolved in 8 times the mass of dimethylacetamide to obtain a 1,2,4-benzenetricarboxylic acid solution; NaOH is dissolved in 20 times the mass of deionized water to obtain a NaOH solution; the 1,2,4-benzenetricarboxylic acid solution and the NaOH solution are mixed, stirred uniformly, and then the stannous chloride solution is added, stirred uniformly, and then transferred to a water bath device for water bath reaction, with a water bath time of 3.0 h and a water bath temperature of 80℃; after the reaction is completed, the product is filtered, washed, and dried to obtain the Sn-MOF;

[0090] The molar ratio of SnCl2·2H2O, 1,2,4-benzenetricarboxylic acid, and NaOH is 1:2:3;

[0091] (2) Pretreatment

[0092] The helical carbon fiber is soaked in 8 times the mass of the pretreatment liquid for 24 hours, and after the soaking is completed, the solid is filtered out, and the solid is heated to 700℃ under an argon atmosphere and kept for 4.0 h, and after the keeping is completed, it is naturally cooled to room temperature under an argon atmosphere to obtain a pretreated helical carbon fiber;

[0093] The pretreatment liquid is a mixture of gadolinium nitrate solution and nickel chloride solution, and the mass ratio of the gadolinium nitrate solution and the nickel chloride solution is 1:1; the concentration of the gadolinium nitrate solution is 1.0 mol / L, and the concentration of the nickel chloride solution is 1.0 mol / L.

[0094] 2. Preparation of PI foam precursor

[0095] The pretreated helical carbon fiber and carbon black are added to N,N-dimethylformamide and subjected to ultrasonic oscillation treatment, with an ultrasonic time of 30 min, an ultrasonic frequency of 46 kHz, and an ultrasonic power of 140 W, to obtain a PI foam precursor after the ultrasonic treatment is completed.

[0096] The mass ratio of the pretreated helical carbon fiber, carbon black and N,N-dimethylformamide is 5:5:85.

[0097] 3. Preparing a clear transparent viscous solution

[0098] After mixing 25.0 g of anhydrous ethanol, 50.0 g of tetrahydrofuran and 25.0 g of PI foam precursor uniformly, 100 g of 3,3',4,4'-benzophenonetetracarboxylic dianhydride is slowly added at a rate of 2.0 g / min, and stirring is continuously performed at a stirring speed of 100 rpm. After the addition is completed, 0.20 g of isooctanoic acid stannous is added, the temperature is increased to 100℃, and when a transparent state is presented, the temperature is increased to 120℃, and the temperature is maintained for 1.0 h. After the temperature is naturally reduced to room temperature, 5.0 g of deionized water, 5.0 g of a stabilizer, 0.05 g of polyethylene glycol, 0.02 g of triethanolamine and 0.03 g of stannous octoate are sequentially added and stirred. After the temperature is naturally reduced to room temperature, a clear transparent viscous solution is obtained.

[0099] The stabilizer is a mixture of γ-aminopropyltriethoxysilane and polydimethylsiloxane, and the mass ratio of the γ-aminopropyltriethoxysilane and polydimethylsiloxane is 1:1.

[0100] 4. Foaming

[0101] After 250 g of the clear transparent viscous solution and 250 g of isocyanate PM-200 are uniformly mixed, stirring is performed at 1200 rpm for 15.0 s, and the mixture is transferred into a mold to perform free foaming, and a primary PI wave-absorbing foam is obtained.

[0102] 5. Post-treatment

[0103] After the primary PI wave-absorbing foam is placed for 25 min, the foam is transferred into a microwave device to be shaped for 1.0 h, and then the foam is placed into a vacuum oven at 120℃ to be dried for 2.0 h to remove the solvent. Finally, the foam is placed into a high-temperature oven to be heated to 250℃, and the temperature is maintained for 3.0 h. After the temperature is naturally reduced to room temperature, a PI wave-absorbing foam is obtained.

[0104] The PI wave-absorbing foam prepared by the method of Example 3 has a compressive strength of 12.8 MPa, and a compressive strength of 11.4 MPa at a 50% compression deformation. After being treated in an environment at a temperature of 360℃ and a pressure of 0.5 MPa for 8.0 h, the compressive strength is 12.2 MPa. The PI wave-absorbing foam has an effective electromagnetic wave absorption frequency band in a frequency range of 2-18 GHz, and a reflection loss value of -73.7 dB at a frequency of 5.87 GHz and a thickness of 0.8 mm.

[0105] Unless otherwise specified, the proportions described in the present application are mass proportions, and the percentages described are mass percentages.

[0106] Finally, it should be noted that the above description is only the preferred embodiments of the present application, and is not intended to limit the present application. Although the present application has been described in detail with reference to the foregoing embodiments, those skilled in the art will appreciate that modifications can be made to the technical solutions described in the foregoing embodiments, or some of the technical features thereof can be replaced by equivalent features. Any modifications, equivalent replacements, improvements, and the like made within the spirit and principles of the present application shall be included in the protection scope of the present application.

Claims

1. A method for preparing PI microwave absorbing foam doped with rare earth elements, characterized in that, The process includes pretreatment of helical carbon fibers, preparation of PI foam precursor, preparation of clear and transparent viscous solution, foaming, and post-treatment steps. The pretreatment step of the spiral carbon fiber includes the preparation of spiral carbon fiber and the pretreatment step. The pretreatment step is as follows: the spiral carbon fiber is immersed in the pretreatment solution for 23-25 ​​hours. After immersion, the solid is filtered out and heated to 690-710℃ in an argon atmosphere for 3.8-4.2 hours. After the heating is completed, the solid is naturally cooled to room temperature in an argon atmosphere to obtain the pretreated spiral carbon fiber. The mass ratio of the spiral carbon fiber to the pretreatment liquid is 1:6-10; The pretreatment solution is a mixture of gadolinium nitrate solution and nickel chloride solution, wherein the mass ratio of gadolinium nitrate solution to nickel chloride solution is 1:0.7-1.2; The concentration of the gadolinium nitrate solution is 0.8-1.2 mol / L, and the concentration of the nickel chloride solution is 0.8-1.2 mol / L. The step of preparing the PI foam precursor is as follows: pretreated spiral carbon fibers and carbon black are added to N,N-dimethylformamide and subjected to ultrasonic oscillation treatment. The ultrasonic time is 25-34 min, the ultrasonic frequency is 42-50 kHz, and the ultrasonic power is 130-150 W. After the ultrasonic treatment, the PI foam precursor is obtained. The mass ratio of the pretreated spiral carbon fiber, carbon black and N,N-dimethylformamide is 5-10:5:85-90; The steps for preparing a clear, transparent, viscous solution are as follows: Anhydrous ethanol, tetrahydrofuran, and PI foam precursor are mixed and stirred evenly. Then, 3,3',4,4'-benzophenone tetracarboxylic dianhydride is added at a rate of 1.8-2.2 g / min, while stirring at 90-110 rpm. Stannous isooctanoate is then added, and the temperature is raised to 103-105℃. When the solution becomes transparent, the temperature is raised to 118-124℃ and kept at that temperature for 0.8-1.3 h. The solution is then lowered to room temperature, and deionized water, stabilizer, polyethylene glycol, triethanolamine, and stannous octoate are added sequentially. The mixture is stirred evenly to obtain a clear, transparent, viscous solution. The mass ratio of anhydrous ethanol, tetrahydrofuran, PI foam precursor, 3,3',4,4'-benzophenone tetracarboxylic dianhydride, stannous isooctanoate, deionized water, stabilizer, polyethylene glycol, triethanolamine, and stannous octoate is 24.7-25.3:48.0-53.0:24.5-25.5:96-103:0.17-0.22:4.7-5.2:4.8-5.3:0.04-0.06:0.01-0.03:0.02-0.04; The stabilizer is a mixture of γ-aminopropyltriethoxysilane and polydimethylsiloxane, wherein the mass ratio of γ-aminopropyltriethoxysilane to polydimethylsiloxane is 1:0.6-1.

3.

2. The method for preparing a rare-earth-doped PI microwave absorbing foam according to claim 1, characterized in that, The steps for preparing spiral carbon fibers are as follows: Sn-MOF is pulverized to 140-160 mesh, mixed with anhydrous ethanol, and ultrasonically dispersed to obtain a suspension; nickel sheets are placed in 3-5 times their mass of the suspension and stirred for 16-25 minutes; the nickel sheets are then removed and dried to obtain soaked nickel sheets; deionized water is added to anhydrous ethanol and stirred to obtain an ethanol solution; the ethanol solution is used as a carbon source and added to an alcohol lamp to burn the soaked nickel sheets for 40-60 minutes to obtain spiral carbon fibers. The mass ratio of Sn-MOF to anhydrous ethanol is 2.3-2.8:8.0-9.0; The volume percentage of deionized water in the ethanol solution is 0.25-0.75%.

3. The method for preparing a rare-earth-doped PI microwave absorbing foam according to claim 2, characterized in that, The preparation method of Sn-MOF is as follows: SnCl2·2H2O is dissolved in 6-8 times its mass of ethanol and stirred evenly to obtain a stannous chloride solution; 1,2,4-benzenetricarboxylic acid is dissolved in 8-10 times its mass of dimethylacetamide and stirred evenly to obtain a 1,2,4-benzenetricarboxylic acid solution; NaOH is dissolved in 18-22 times its mass of deionized water and stirred evenly to obtain a NaOH solution; the 1,2,4-benzenetricarboxylic acid solution and NaOH solution are mixed and stirred evenly, then the stannous chloride solution is added and stirred evenly, and then the mixture is transferred to a water bath for water bath reaction. The water bath time is 2.8-3.2 hours and the water bath temperature is 77-83℃. After the reaction is completed, the mixture is filtered, washed and dried to obtain Sn-MOF. The molar ratio of SnCl2·2H2O, 1,2,4-benzenetricarboxylic acid and NaOH is 1:1.8-2.3:2.7-3.

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4. The method for preparing a rare-earth-doped PI microwave absorbing foam according to claim 1, characterized in that, The foaming step is as follows: a clear, transparent, viscous solution is mixed evenly with isocyanate PM-200, stirred at 1100-1300 rpm for 14.0-17.0 s, and then transferred into a mold for free foaming to obtain primary PI absorbent foam. The mass ratio of the clear, transparent, viscous solution to isocyanate PM-200 is 245-253:243-255.

5. The method for preparing a rare-earth-doped PI microwave absorbing foam according to claim 1, characterized in that, The post-processing steps are as follows: after the primary PI microwave absorbing foam is left to stand for 28-30 minutes, it is transferred to a microwave device for shaping for 0.8-1.2 hours, then placed in a vacuum oven at 118-123°C for drying for 1.8-2.2 hours to remove the solvent, and finally placed in a high-temperature oven to be heated to 246-253°C and kept at that temperature for 2.9-3.2 hours. After naturally cooling to room temperature, the PI microwave absorbing foam is obtained.