Porous polyimide aerogel / porous aluminum sound-absorbing material and preparation method thereof

Abstract

This invention discloses a porous polyimide aerogel / porous aluminum sound-absorbing material and its preparation method, belonging to the field of porous materials technology. The invention uses porous aluminum as a matrix and polymethyl methacrylate (PMMA) microspheres as the pore-forming agent for the polyimide aerogel. PMMA microspheres are filled into the pores of the porous aluminum, which is then placed in a polyimide suspension. After vacuum suction, freeze-drying, and heating to remove the PMMA microspheres, a polyimide aerogel with PMMA microsphere pores is finally obtained within the porous aluminum pores. The addition of PMMA microsphere-filled polyimide aerogel to the porous aluminum increases the contact area between sound waves and the aerogel, improving sound wave absorption and reflection, thereby enhancing the sound absorption effect. Furthermore, the skeletal reinforcement effect of porous aluminum better meets the application requirements of high strength and high sound absorption.

Description

Technical Field

[0001] This invention relates to the field of porous sound-absorbing materials technology, specifically a porous polyimide aerogel / porous aluminum composite sound-absorbing material. Background Technology

[0002] With the advancement of industrialization and the improvement of urbanization, noise pollution has become one of the major environmental problems affecting people's quality of life and health. In order to reduce noise pollution in daily life and production, higher requirements have been put forward for related sound-absorbing materials.

[0003] Porous aluminum possesses properties such as high specific strength, non-hygroscopicity, heat resistance, flame retardancy, high thermal conductivity, and recyclability, giving it significant advantages in sound absorption and noise reduction applications subjected to harsh environments such as mechanical stress and high temperatures. However, the sound absorption performance of porous aluminum shows a significant attenuation within a specific frequency range (e.g., 2500~5000Hz), exhibiting a "sound absorption valley" phenomenon on its sound absorption curve. In contrast, the porous structure of polyimide aerogel gives it superior performance in mid-to-wideband absorption, but its mechanical properties are poor, making it prone to breakage under stress or impact.

[0004] To address this, this invention combines porous aluminum and polyimide aerogel, introducing PMMA microspheres as a "stress buffer" during the composite process. The PMMA microspheres effectively alleviate the internal stress and capillary forces experienced by the aerogel during its formation within the micro-spaces of the aluminum foam, ensuring the stable formation and existence of the aerogel structure. This composite structure not only integrates the mechanical strength of porous aluminum with the broadband sound absorption advantages of aerogel, but also further optimizes the sound absorption performance and structural integrity of the material through the pore-forming effect of the PMMA microspheres, ultimately obtaining a PMMA microsphere-porosized polyimide aerogel / porous aluminum composite material that combines high strength and high sound absorption. Summary of the Invention

[0005] To address or partially address the problems existing in related technologies, the primary objective of this invention is to provide a PMMA microsphere porous polyimide aerogel / porous aluminum composite sound-absorbing material. In this composite sound-absorbing material, the porous polyimide aerogel fills the pores of the porous aluminum, the porous aluminum provides basic sound absorption performance and porous framework support, and the polyimide aerogel enhances sound wave absorption. The porosity of the porous polyimide aerogel is 95%~99%.

[0006] Another objective of this invention is to provide a method for preparing a PMMA microsphere porous polyimide aerogel / porous aluminum composite sound-absorbing material. By completing the pore-forming, freezing, and drying process of the polyimide aerogel suspension inside the porous aluminum, the composite of PMMA microsphere porous polyimide aerogel and porous aluminum is achieved. The specific steps are as follows.

[0007] (1) Raw materials: Porous aluminum is used as the matrix material, and a suspension is prepared by electrospun polyimide fibers. PMMA microspheres are used as pore-forming agents for polyimide aerogel.

[0008] (2) Prepare a solution by mixing water and tert-butanol in a volume ratio of 3:1. Then mix the solution with polyimide electrospun fibers in a volume ratio of 1:1. Finally, use a homogenizer to further disperse and cut the mixture to obtain a polyimide suspension.

[0009] (3) The porous aluminum pre-filled with PMMA microspheres is completely immersed in the polyimide suspension and placed in the defoaming tank. After suction, porous aluminum containing polyimide suspension and PMMA microspheres in the pores is obtained.

[0010] (4) The porous aluminum containing polyimide suspension and PMMA microspheres in the pores is frozen and dried, and then placed in a sealed mold crucible. The PMMA microspheres are removed by heating in an argon atmosphere to obtain PMMA microsphere porous polyimide aerogel / porous aluminum composite sound-absorbing material.

[0011] Preferably, in step (1) of the present invention, a porosity of 83% and a pore size of [missing information] are selected. 0.5mm porous aluminum is used as the matrix material.

[0012] Preferably, in step (1) of the present invention, two types of polyimide electrospun fibers with average diameters of 364 nm and 1.9 µm are selected to prepare the suspension.

[0013] Preferably, in step (1) of the present invention, PMMA microspheres with a particle size of 50~200μm and a filling rate of 75% are selected as polyimide aerogel pore-forming agents.

[0014] Preferably, the conditions for dispersion cutting in step (2) of the present invention are dispersion cutting at 13000 rpm for 25 min.

[0015] Preferably, the suction conditions in step (3) of the present invention are to evacuate to 23000 Pa and hold the pressure for 1 min.

[0016] Preferably, in step (4) of the present invention, the freezing conditions are -65℃ to -20℃ for 6 hours, and the freeze-drying conditions are 1 Pa and -86℃ for 4 days.

[0017] Preferably, the conditions for heating and decomposing to remove PMMA microspheres in step (4) of the present invention are: heating to 330°C and holding for 1 hour.

[0018] The principle of this invention: (1) Mechanism of pore formation and pore structure control principle of PMMA microsphere-forming polyimide aerogel The preparation of PMMA microsphere-based porous polyimide aerogel / porous aluminum composite sound-absorbing material is based on the "sacrificial template method." This process utilizes polymethyl methacrylate (PMMA) microspheres, which have excellent monodispersity, smooth surfaces, and highly uniform particle size, as ideal templates. Due to their good stability in dilute acids, alkalis, and aqueous solutions, they can be uniformly dispersed in a polyimide suspension. After the polyimide suspension freezes and firmly encapsulates the microspheres, heat treatment decomposes the PMMA microspheres, thereby forming regular pores in situ within the aerogel framework that correspond to the size and morphology of the microspheres. Ultimately, this constructs a composite sound-absorbing material with a multi-level structure combining macroporous and mesoporous elements.

[0019] The pore structure of the PMMA microsphere-based porous polyimide aerogel / porous aluminum composite sound-absorbing material, in addition to the pores formed by the aluminum foam and polyimide aerogel themselves during the preparation process, also features new pore structures formed inside the polyimide aerogel by adding PMMA microspheres before freezing the polyimide aerogel and then heating and insulating to decompose the PMMA microspheres. The pore size in the composite material can be controlled by adjusting the particle size of the PMMA microspheres. Furthermore, the freezing process is also particularly important for the formation of the PMMA microsphere-based porous polyimide aerogel. Water / tert-butanol crystals are formed at different freezing temperatures, resulting in secondary pores of different sizes and shapes, thus affecting the final porosity of the PMMA microsphere-based porous polyimide aerogel.

[0020] The average pore size of PMMA microsphere porous polyimide aerogel / porous aluminum composite sound-absorbing material ( ) and the average diameter of PMMA microspheres ( The relationship between them is: in: Average pore size (μm) of PMMA microsphere porous polyimide aerogel / porous aluminum composite sound-absorbing material. The average diameter (μm) of PMMA microspheres.

[0021] The relationship between the porosity of polyimide aerogel and freezing temperature is as follows: in: denoted as porosity (%) of the polyimide aerogel, and T as the freezing temperature (°C).

[0022] Similarly, the porosity of the PMMA microsphere-porosized polyimide aerogel / porous aluminum composite material is similar to that of the polyimide aerogel. The relationship is: P =0.83×[ +0.5×(1- )] in: P Porosity of PMMA microsphere-porous polyimide aerogel / porous aluminum composite material. The porosity (%) of the polyimide aerogel.

[0023] (2) Principle of improving the sound absorption performance of PMMA microsphere porous polyimide aerogel The sound absorption principle of porous materials mainly involves the propagation, reflection, and absorption of sound waves within the material. When sound waves enter the interior of a PMMA microsphere-porosilicate polyimide aerogel / porous aluminum composite sound-absorbing material, the large micropores of the PMMA microsphere-porosilicate polyimide aerogel serve as the main incident channel and viscous dissipation region for the sound waves. Viscoelasticity provides good damping performance, effectively reducing sound wave reflection and dissipating mid-to-low frequency sound energy. Mesopores, as thermoelastic dissipation regions, utilize the two pore structures to construct a hierarchical synergistic mechanism of "macropore viscous dissipation + micropore thermal dissipation," which can more effectively convert sound energy into heat energy compared to rigid porous aluminum, thereby significantly improving the material's sound absorption performance. Furthermore, PMMA microsphere-porosilicate polyimide aerogel is a high-porosity porous material. When filled inside porous aluminum, it can obtain a larger surface area on the basis of porous aluminum, which can more effectively increase the propagation path of sound waves and thus enhance the dissipation of sound energy.

[0024] The average sound absorption coefficient (α) of PMMA microsphere porous polyimide aerogel / porous aluminum composite sound-absorbing material is related to its porosity. P ) and aperture ( D There is a certain functional relationship between the average sound absorption coefficient and porosity obtained in this invention; the relationship between the average sound absorption coefficient and porosity is approximately a quadratic function. By fitting the experimental data with a quadratic polynomial using a fitting method, the relationship model between the porosity of PMMA microsphere porous polyimide aerogel and the average sound absorption coefficient of the composite material in the frequency range of 800~6300Hz can be obtained as follows: α = -27.41 P 2 +45.14 P -0.12 D Where: α is the average sound absorption coefficient of the PMMA microsphere porous polyimide aerogel / porous aluminum composite sound-absorbing material. P Porosity of PMMA microsphere-porous polyimide aerogel / porous aluminum composite material. D The average pore size is given by PMMA microsphere porous polyimide aerogel / porous aluminum composite material.

[0025] The beneficial effects of this invention are: (1) The PMMA microsphere porous polyimide aerogel / porous aluminum composite sound-absorbing material of the present invention has an average sound absorption coefficient of 0.800~0.875 in the frequency range of 800~6300Hz, which is 9.14%~19.37% higher than the average sound absorption coefficient (0.733) of porous aluminum material with the same porosity.

[0026] (2) This invention achieves the composite of PMMA microsphere porous polyimide aerogel and porous aluminum by completing the pore-forming, freezing and drying process of polyimide aerogel suspension inside porous aluminum, and obtains PMMA microsphere porous polyimide aerogel / porous aluminum composite sound-absorbing material to meet the requirements of high strength and high sound absorption of the material. Attached Figure Description

[0027] Figure 1 This is the preparation process of the PMMA microsphere porous polyimide aerogel / porous aluminum composite sound-absorbing material described in this invention.

[0028] Figure 2 This is a macroscopic photograph of the PMMA microsphere porous polyimide aerogel / porous aluminum composite sound-absorbing material in Example 3 of the present invention.

[0029] Figure 3 The microporous structure of the PMMA microsphere porous polyimide aerogel / porous aluminum composite sound-absorbing material in Example 3 of this invention is shown.

[0030] Figure 4 This is a graph showing the sound absorption coefficient-frequency relationship of the PMMA microsphere porous polyimide aerogel / porous aluminum composite sound-absorbing material in Example 3. Detailed Implementation

[0031] The technical solutions of the present invention will be clearly and completely described below with reference to the accompanying drawings of the embodiments of the present invention, but the scope of protection of the present invention is not limited thereto.

[0032] Example 1 A method for preparing a PMMA microsphere porous polyimide aerogel / porous aluminum composite sound-absorbing material, such as... Figure 1 As shown, the specific steps include: (1) Porous aluminum with a porosity of 83% and a pore size of 0.5 mm was selected as the matrix material; two types of polyimide electrospun fibers with average diameters of 364 nm and 1.9 µm were selected to prepare the suspension; PMMA microspheres with a particle size of 50 µm were selected as the polyimide aerogel pore-forming agent.

[0033] (2) Prepare a 50 mL solution with water and tert-butanol in a volume ratio of 3:1, and select two different diameter polyimide electrospun fibers after cutting in a 1:1 ratio. Use a homogenizer to further disperse and cut the fibers at 13000 rpm for 25 min. Then, put the porous aluminum filled with microspheres into the polyimide suspension until it is submerged and put it into a defoaming tank.

[0034] (3) Vacuum the defoaming tank to 23000Pa and hold the pressure for 1 minute. Then, draw the polyimide suspension into the porous aluminum filled with microspheres to obtain porous aluminum with polyimide suspension and PMMA microspheres in the pores.

[0035] (4) The porous aluminum containing polyimide suspension and PMMA microspheres was placed in a refrigerator and frozen at -20°C for 6 hours, and then vacuum freeze-dried in a cold trap at 1 Pa and -86°C for 4 days.

[0036] (5) The dried polyimide / porous aluminum composite material containing PMMA microspheres was placed in a sealed mold crucible and heated to 330°C in an argon atmosphere for 1 hour to decompose and remove the PMMA microspheres, thereby obtaining PMMA microsphere-porosized polyimide aerogel / porous aluminum composite sound-absorbing material; the aerogel has an average pore size of 50µm and a porosity of 95%.

[0037] The PMMA microsphere porous polyimide aerogel / porous aluminum composite sound-absorbing material obtained in this embodiment has an average sound absorption coefficient of 0.800 in the frequency range of 800~6300Hz, which is 9.14% higher than the average sound absorption coefficient of porous aluminum of 0.733.

[0038] Example 2 A method for preparing a PMMA microsphere porous polyimide aerogel / porous aluminum composite sound-absorbing material, such as... Figure 1 As shown, the specific steps include: (1) Porous aluminum with a porosity of 83% and a pore size of 0.5 mm was selected as the matrix material; two types of polyimide electrospun fibers with average diameters of 364 nm and 1.9 µm were selected to prepare the suspension; PMMA microspheres with a particle size of 100 µm were selected as the polyimide aerogel pore-forming agent.

[0039] (2) Prepare a 50 mL solution with water and tert-butanol in a volume ratio of 3:1, and select two different diameter polyimide electrospun fibers after cutting in a 1:1 ratio. Use a homogenizer to further disperse and cut the fibers at 13000 rpm for 25 min. Then, put the porous aluminum filled with microspheres into the polyimide suspension until it is submerged and put it into a defoaming tank.

[0040] (3) Vacuum the defoaming tank to 23000Pa and hold the pressure for 1 minute. Then, draw the polyimide suspension into the porous aluminum filled with microspheres to obtain porous aluminum with polyimide suspension and PMMA microspheres in the pores.

[0041] (4) The porous aluminum containing polyimide suspension and PMMA microspheres was placed in a refrigerator and frozen at -30°C for 6 hours, and then vacuum freeze-dried in a cold trap at 1 Pa and -86°C for 4 days.

[0042] (5) The dried polyimide / porous aluminum composite material containing PMMA microspheres was placed in a sealed mold crucible and heated to 330°C in an argon atmosphere for 1 hour to decompose and remove the PMMA microspheres, thus obtaining PMMA microsphere-porosized polyimide aerogel / porous aluminum composite sound-absorbing material. The aerogel has an average pore size of 100µm and a porosity of 96%.

[0043] The PMMA porous polyimide aerogel / porous aluminum composite sound-absorbing material obtained in this embodiment has an average sound absorption coefficient of 0.841 in the frequency range of 800~6300Hz, which is 14.73% higher than the average sound absorption coefficient of porous aluminum of 0.733.

[0044] Example 3 A method for preparing a PMMA microsphere porous polyimide aerogel / porous aluminum composite sound-absorbing material, such as... Figure 1 As shown, the specific steps include: (1) Porous aluminum with a porosity of 83% and a pore size of 0.5 mm was selected as the matrix material; two types of polyimide electrospun fibers with average diameters of 364 nm and 1.9 µm were selected to prepare the suspension; PMMA microspheres with a particle size of 150 µm were selected as the polyimide aerogel pore-forming agent.

[0045] (2) Prepare a 50 mL solution with water and tert-butanol in a volume ratio of 3:1, and select two different diameter polyimide electrospun fibers after cutting in a 1:1 ratio. Use a homogenizer to further disperse and cut the fibers at 13000 rpm for 25 min. Then, put the porous aluminum filled with microspheres into the polyimide suspension until it is submerged and put it into a defoaming tank.

[0046] (3) Vacuum the defoaming tank to 23000Pa and hold the pressure for 1 minute. Then, draw the polyimide suspension into the porous aluminum filled with microspheres to obtain porous aluminum containing polyimide suspension and PMMA microspheres in the pores.

[0047] (4) The porous aluminum containing polyimide suspension and PMMA microspheres was placed in a refrigerator and frozen at -45°C for 6 hours, and then vacuum freeze-dried in a cold trap at 1 Pa and -86°C for 4 days.

[0048] (5) The dried polyimide / porous aluminum composite material containing PMMA microspheres was placed in a sealed mold crucible and heated to 330°C in an argon atmosphere for 1 hour to decompose and remove the PMMA microspheres, thus obtaining a PMMA microsphere-porosized polyimide aerogel / porous aluminum composite sound-absorbing material; the aerogel has an average pore size of 150µm and a porosity of 97%; its macroscopic photograph is shown below. Figure 2 As shown, the microporous structure is as follows Figure 3 As shown.

[0049] The PMMA porous polyimide aerogel / porous aluminum composite sound-absorbing material obtained in this embodiment has the following relationship between its sound absorption coefficient and frequency in the frequency range of 800~6300Hz: Figure 4 As shown, its average sound absorption coefficient in the frequency range of 800~6300Hz is 0.875, which is 19.37% higher than the average sound absorption coefficient of porous aluminum of 0.733.

[0050] Example 4 A method for preparing a PMMA microsphere porous polyimide aerogel / porous aluminum composite sound-absorbing material, such as... Figure 1 As shown, the specific steps include: (1) Porous aluminum with a porosity of 83% and a pore size of 0.5 mm was selected as the matrix material; two types of polyimide electrospun fibers with average diameters of 364 nm and 1.9 µm were selected to prepare the suspension; PMMA microspheres with a particle size of 200 µm were selected as the polyimide aerogel pore-forming agent.

[0051] (2) Prepare a 50 mL solution with water and tert-butanol in a volume ratio of 3:1, and select two different diameter polyimide electrospun fibers after cutting in a 1:1 ratio. Use a homogenizer to further disperse and cut the fibers at 13000 rpm for 25 min. Then, put the porous aluminum filled with microspheres into the polyimide suspension until it is submerged and put it into a defoaming tank.

[0052] (3) Vacuum the defoaming tank to 23000Pa and hold the pressure for 1 minute. Then, draw the polyimide suspension into the porous aluminum filled with microspheres to obtain porous aluminum with polyimide suspension and PMMA microspheres in the pores.

[0053] (4) The porous aluminum containing polyimide suspension and PMMA microspheres was placed in a refrigerator and frozen at -65°C for 6 hours, and then vacuum freeze-dried in a cold trap at 1 Pa and -86°C for 4 days.

[0054] (5) The dried polyimide / porous aluminum composite material containing PMMA microspheres was placed in a sealed mold crucible and heated to 330°C in an argon atmosphere for 1 hour to decompose and remove the PMMA microspheres, thus obtaining PMMA microsphere-porosized polyimide aerogel / porous aluminum composite sound-absorbing material. The aerogel has an average pore size of 200µm and a porosity of 99%.

[0055] The PMMA microsphere porous polyimide aerogel / porous aluminum composite sound-absorbing material obtained in this embodiment has an average sound absorption coefficient of 0.824, which is 12.41% higher than the average sound absorption coefficient of porous aluminum (0.733).

[0056] In summary, by compositing PMMA porous polyimide aerogel into porous aluminum, a PMMA porous polyimide aerogel / porous aluminum composite sound-absorbing material is obtained, in which PMMA porous polyimide aerogel fills the pores of porous aluminum, and the sound absorption performance of the material can be significantly improved.

[0057] Finally, it should be noted that the above preferred embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit it. Although the present invention has been described in detail through the above preferred embodiments, those skilled in the art should understand that various changes in form and detail can be made without departing from the scope defined by the claims of the present invention.

Claims

1. A porous polyimide aerogel / porous aluminum composite sound-absorbing material, characterized in that, The polyimide aerogel, after pore formation, fills the pores of the porous aluminum.

2. The porous polyimide aerogel / porous aluminum composite sound-absorbing material according to claim 1, characterized in that, Porous aluminum provides basic sound absorption properties and a porous framework for support, while polyimide aerogel enhances sound wave absorption. The porosity of the polyimide aerogel after pore formation is 95%~99%.

3. The preparation method of the porous polyimide aerogel / porous aluminum composite sound-absorbing material according to claim 1, characterized in that, Specifically, the following steps are included: (1) Raw materials: Porous aluminum is used as the matrix material, and a suspension is prepared by electrospun polyimide fibers. PMMA microspheres are used as pore-forming agents for polyimide aerogel. (2) Prepare a solution by mixing water and tert-butanol in a volume ratio of 3:1, then mix the solution with polyimide electrospun fibers in a volume ratio of 1:1, and then further disperse and cut the mixture using a homogenizer to obtain a polyimide suspension. (3) The porous aluminum pre-filled with PMMA microspheres was completely immersed in the polyimide suspension and placed in the defoaming tank. After suction, porous aluminum containing polyimide suspension and PMMA microspheres in the pores was obtained. (4) The porous aluminum containing polyimide suspension and PMMA microspheres in the pores is frozen and freeze-dried, and then placed in a sealed mold crucible. The PMMA microspheres are removed by heating in an argon atmosphere to obtain a porous polyimide aerogel / porous aluminum composite sound-absorbing material.

4. The preparation method of a porous polyimide aerogel / porous aluminum composite sound-absorbing material according to claim 3, characterized in that, In step (1), a porosity of 83% and a pore size of [missing information] are selected. 0.5 mm porous aluminum was used as the matrix material; two types of polyimide electrospun fibers with average diameters of 364 nm and 1.9 µm were selected to prepare the suspension, with a mass ratio of 1:1; PMMA microspheres with a particle size of 50~200 μm and a filling rate of 75% were selected as the pore-forming agent for the polyimide aerogel.

5. The method for preparing a porous polyimide aerogel / porous aluminum composite sound-absorbing material according to claim 3, characterized in that, In step (2), the conditions for dispersion cutting are 13000 rpm for 25 min.

6. The method for preparing a porous polyimide aerogel / porous aluminum composite sound-absorbing material according to claim 3, characterized in that, In step (3), the suction conditions are to evacuate to 23000 Pa and hold the pressure for 1 min.

7. The method for preparing a porous polyimide aerogel / porous aluminum composite sound-absorbing material according to claim 3, characterized in that, In step (4), the freezing conditions are -65℃ to -20℃ for 6 hours, and the freeze-drying conditions are 1 Pa and -86℃ for 4 days.

8. The method for preparing a porous polyimide aerogel / porous aluminum composite sound-absorbing material according to claim 3, characterized in that, The conditions for removing PMMA microspheres by heating in step (4) are: heating to 330℃ and holding for 1 hour.

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