Preparation method and product of polyimide foam with multi-level cell structure

Abstract

The present invention discloses a method for preparing a polyimide foam with a multi-level pore structure and a product. The method of the present invention comprises the following steps: (1) synthesizing a polyamic acid solution by reacting a polyacid anhydride and a polyamine; (2) obtaining a polyamic acid solid after washing and drying; (3) dissolving the polyamic acid solid in a triethylamine aqueous solution to prepare a polyimide precursor solution; (4) placing a polyimide foam with an open-cell structure in the polyimide precursor solution, and finally obtaining a polyimide foam with a multi-level pore structure through a process of saturation impregnation, freeze drying, high-temperature foaming and imidization. The present invention has the characteristics of a simple preparation method and significantly improved sound absorption performance and thermal insulation performance of the product in a low-frequency range.

Description

Technical Field

[0001] The invention relates to a polyimide foam, in particular to a preparation method and a product of a polyimide foam with a multi-level pore structure. Background Art

[0002] Polyimide foam (PIF), also known as polyimide porous material, is a special porous engineering plastic with polyimide (PI) resin as the continuous phase. In order to meet the needs of aerospace, rail transit and other fields for new lightweight, high-performance porous thermal insulation and sound-absorbing materials, polyimide materials that integrate efficient thermal insulation and sound absorption functions have received widespread attention from scientific researchers. Similar to other porous materials, PIF can show relatively good sound absorption performance in the high-frequency range, but the sound absorption performance in the medium and low frequency range has always been poor, especially thin sheets of about 1 cm in size have almost no sound absorption effect in low and medium frequencies, which makes it difficult to meet the technical requirements of existing equipment for efficient sound absorption in low and medium frequencies. At the same time, compared with other insulation foam materials, the thermal conductivity of PIF is between 0.035 and 0.048 W / (m·K). In order to achieve better insulation effect, thicker polyimide foam needs to be laid, which will not only increase the amount of foam material and the construction cost of the application carrier, but also greatly reduce the effective available space in the cabin and reduce the living and working comfort. Therefore, the problem of insufficient insulation performance needs to be solved urgently.

[0003] Chinese patent CN108948409A discloses a sound-absorbing polyimide foam material and a preparation method thereof. By adding fillers, the average sound absorption coefficient of the material is improved to a certain extent. However, its low-frequency and medium-low-frequency sound absorption coefficient is still around 0.2, showing almost no sound absorption effect, and the introduction of fillers causes a decrease in the mechanical properties of the matrix skeleton.

[0004] Chinese patent CN101402743A discloses a polyimide foam and its preparation method, wherein a foam intermediate is obtained by foaming a mixture of black and white materials in one step, and then cured by microwave radiation or / and oven heating to obtain a polyimide foam with a thermal conductivity of 0.042 to 0.048 W / (m·K), and a 2 cm thick foam sheet has an average sound absorption coefficient of 0.12 to 0.16 in the range of 125 to 2000 Hz. Its thermal insulation and sound absorption effect is much lower than that of an ideal polyimide foam.

[0005] Chinese patent CN111040161A discloses a heat-insulating polyimide foam material and its preparation method, which reduces the radiant heat transfer and thermal conductivity by adding an infrared sunscreen to the polyimide foam material and utilizing its scattering and absorption effects. However, there is no research on the relevant sound absorption performance. At the same time, the combined effect of the infrared sunscreen and hot pressing reduces the density of the polyimide foam from 10kg / m 3Increase to 40kg / m 3 The lightweight properties of polyimide foam are lost.

[0006] Moreover, the thermal conductivity of most polyimide foams obtained above and published currently is 0.030-0.050 W / (m·K), and the average sound absorption coefficient of a 1 cm thick sample in the 100-2000 Hz frequency range is only about 0.14.

[0007] In summary, the polyimide foam prepared by the existing polyimide foam preparation method has the problems of poor sound absorption performance in the low frequency band and poor thermal insulation performance. Summary of the invention

[0008] The purpose of the present invention is to provide a method for preparing a polyimide foam with a multi-level cell structure and a product thereof. The present invention has the characteristics of a simple preparation method and significantly improved sound absorption performance and thermal insulation performance of the product in a low-frequency range.

[0009] The technical solution of the present invention is a method for preparing a polyimide foam with a multi-level pore structure, comprising the following steps:

[0010] S1. According to the molar ratio of amino group to anhydride group of 1.04:1 to 1.08:1, the polyanhydride and the polyamine are reacted to synthesize a polyamic acid solution having a weight fraction of 15 to 30%:

[0011] S2. The polyamic acid solution is washed with water and dried to obtain a polyamic acid solid:

[0012] S3. The polyamic acid solid is dissolved in a concentration of 0.05 to 0.4 mol / L triethylamine aqueous solution to prepare a polyimide precursor solution;

[0013] S4. Immerse the polyimide foam substrate with an open-pore structure into a polyimide precursor solution, and perform freeze-drying to remove water, high-temperature foaming and imidization to obtain a polyimide foam with a multi-level pore structure.

[0014] In the aforementioned method for preparing polyimide foam with a multi-level pore structure, the synthesis environment temperature of the polyamic acid solution described in S1 is -5 to 30°C; the reaction treatment of the polyacid anhydride and the polyamine is: the polyamine is divided into 4 to 6 parts, added in batches to the polar solvent solution containing the polyacid anhydride, and stirred for reaction for 1 to 3 hours.

[0015] In the aforementioned method for preparing a polyimide foam having a multi-level pore structure, the polyacid anhydride described in S1 includes: one or a mixture of at least two of pyromellitic anhydride, 4,4'-biphenyl ether dianhydride, 3,3',4,4'-diphenyl ether tetracarboxylic anhydride, 3,3',4,4'-biphenyl tetracarboxylic anhydride, 3,3',4,4'-benzophenone tetracarboxylic anhydride, 2,3,3',4'-diphenyl ether tetracarboxylic anhydride, 4,4'-(4,4'-isopropyldiphenoxy)tetracarboxylic anhydride, maleic anhydride, succinic anhydride, and mellitic anhydride; The polyamine includes: 3,4'-diaminodiphenyl ether, 4,4'-diaminodiphenyl ether, 4,4'-diaminobenzophenone, 1,3-bis(3-aminophenoxy)benzene, m-phenylenediamine, p-phenylenediamine, 3,3'-diaminodiphenyl sulfone, 4,4'-diaminodiphenyl sulfone, 4-bis(4-bisaminophenoxy)diphenyl sulfone, 4-bis(3-bisaminophenoxy)phenyl sulfone, 4,4'-bis(3-aminophenoxy)biphenyl, 1,5-pentanediamine, 1,3-propylenediamine, 2,4,6-triaminopyrimidine or a mixture of at least two thereof.

[0016] In the aforementioned method for preparing polyimide foam with a multi-level pore structure, S2 is specifically: pouring the polyamic acid solution into deionized water, stirring and washing to remove the solvent and unreacted small molecules, changing the water every 1 to 3 hours, soaking and washing for 18 to 24 hours, filtering and placing in a culture dish, and drying in an oven at 100 to 120°C to obtain a polyamic acid solid.

[0017] In the aforementioned method for preparing a polyimide foam with a multi-level pore structure, in S3, the stirring temperature of the triethylamine aqueous solution containing polyamic acid is 10 to 30° C., and the stirring time is 6 to 10 hours.

[0018] In the aforementioned method for preparing a polyimide foam with a multi-level pore structure, in S3, the weight fraction of the polyamic acid in the polyimide precursor solution is 1-15%.

[0019] In the aforementioned method for preparing the polyimide foam with a multi-level pore structure, in S4, freeze-drying to remove water is: first freezing at -25 to -35°C for 4 to 6 hours, and then freeze-drying at -50 to -70°C for 36 to 60 hours.

[0020] In the aforementioned method for preparing the polyimide foam with a multi-level pore structure, in S4, the high-temperature foaming and imidization are as follows: baking at 200-300° C. for 1-3 hours.

[0021] A polyimide foam with a multi-level cell structure is prepared by the above method.

[0022] In the aforementioned polyimide foam with a multi-level pore structure, the polyimide foam comprises two levels of pores, the average pore diameter of one level of blast holes is 0.2-0.4 mm, and the average pore diameter of the other level of blast holes is 0.9-1.4 mm, and the 0.2-0.4 mm pores are formed by in-situ foaming of a polyimide precursor in 0.9-1.4 mm pores; the thermal conductivity of the polyimide foam is 0.02-0.035 W / (m·K); the average sound absorption coefficient of the polyimide foam in the low-frequency band of 100-2000 Hz is increased by 70-125% compared with the polyimide foam substrate with an open-pore structure.

[0023] Compared with the prior art, the present invention has the following beneficial effects:

[0024] Compared with the prior art, the present invention provides a method for preparing a high-performance polyimide foam with a multi-level pore structure, which utilizes a polyimide precursor solution to undergo freeze-drying to remove water, high-temperature foaming and imidization processes to achieve in-situ foaming and filling of polyamic acid in the pores to form a polyimide foam with a multi-level pore structure.

[0025] This preparation method innovatively introduces a secondary cell structure in situ in the open-cell polyimide foam to effectively improve the low-frequency and medium-low frequency sound absorption effects, getting rid of the previous dilemma of simply increasing the thickness of the material or constructing a macro structure to improve the medium-low frequency sound absorption performance. It can not only greatly save the effective available space in the cabin and improve the comfort of living and working, but also reduce the problem of complex construction process of medium-low frequency special effect sound absorbers. At the same time, this method can achieve the simultaneous improvement of the sound absorption performance and thermal insulation performance in the medium-low frequency range without affecting the basic physical and chemical properties of the material through simple methods and process paths, and realize the construction of a multi-level cell structure polyimide material that integrates high-efficiency thermal insulation and sound absorption, breaking through the bottleneck that the improvement of the sound absorption performance in the medium-low frequency range of polyimide foam in the past often leads to a decrease in thermal insulation effect (increase in thermal conductivity).

[0026] The obtained polyimide foam with a multi-level pore structure comprises two levels of pores, wherein the average pore diameter of one level of blast holes is 0.2-0.4 mm, and the average pore diameter of the other level of blast holes is 0.9-1.4 mm, and the pores of 0.2-0.4 mm are formed by in-situ foaming of a polyimide precursor in pores of 0.9-1.4 mm; the thermal conductivity of the polyimide foam is 0.02-0.035 W / (m·K); and the average sound absorption coefficient of the polyimide foam in a medium-to-low frequency band of 100-2000 Hz is increased by 70-125% compared with a polyimide foam substrate with an open-pore structure. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Figure 1 This is a diagram of a polyimide foam with a multi-level cell structure prepared in Example 1 of the present invention;

[0028] Figure 2 It is a sound absorption coefficient curve diagram of comparative example 1 and embodiments 1 and 2 of the present invention. DETAILED DESCRIPTION

[0029] The present invention will be further described below in conjunction with the embodiments, but they are not intended to limit the present invention.

[0030] Embodiment 1:

[0031] S1. At 20°C, add 50 g of 4,4'-biphenyl ether dianhydride (0.16 mol) to a three-necked flask containing 255 g of N-methylpyrrolidone. After stirring and dissolving completely, add 33.9 g of 4,4'-diaminodiphenyl ether (0.17 mol) into the three-necked flask in five batches, stir and react for 2 hours to obtain a polyamic acid solution with a weight fraction of 25%.

[0032] S2. Pour 400 ml of deionized water into a beaker, add a magnetic bar and start stirring at a speed of 500 r / min, slowly pour the polyamic acid solution into the deionized water to precipitate the polyamic acid solid, change the water every 2 hours, soak and wash for 20 hours, filter and place in a culture dish, and dry in a 100°C oven for 1 hour to obtain a polyamic acid solid.

[0033] S3. Grind the dried polyamic acid solid into powder; mix 0.63g triethylamine (0.0062mol) with 98g water to obtain a triethylamine aqueous solution with a concentration of 0.06mol / L; weigh 1.37g polyamic acid powder, add it to 100ml triethylamine aqueous solution with a concentration of 0.06mol / L, add a magnetic bar and start stirring, set the temperature to 25°C, set the speed to 400r / min, stir for 8h, and obtain a polyimide precursor solution, the weight fraction of polyamic acid in the polyimide precursor solution is 1.37%.

[0034] S4. Pour the polyimide precursor solution into a culture dish, immerse a cylindrical polyimide foam substrate with a radius of 5 cm, a thickness of 1 cm, an open porosity of 85%, and an average pore size of 1 mm, and control the liquid level to completely cover the upper surface of the polyimide foam substrate; put it into a freezer and freeze it at -30°C for 5 hours, and then put it into a freeze dryer and freeze-dry it at -60°C for 48 hours to freeze-dry and remove water; finally, put it into an oven at 220°C for 2 hours for high-temperature foaming and imidization treatment, and obtain a polyimide foam with a multi-level pore structure, such as Figure 1 shown.

[0035] Embodiment 2:

[0036] This embodiment is basically the same as Embodiment 1, except that:

[0037] 4 g of polyamic acid powder was weighed and dissolved in 96 ml of a 0.19 mol / L triethylamine aqueous solution, and the weight fraction of the polyamic acid in the obtained polyimide precursor solution was 4%.

[0038] Embodiment 3:

[0039] S1. At 20°C, add 34.9 g of pyromellitic anhydride (0.16 mol) to a three-necked flask containing 240 g of N-methylpyrrolidone. After stirring and dissolving completely, add 33.9 g of 4,4'-diaminodiphenyl ether (0.17 mol) into the three-necked flask in five batches, stir and react for 2 hours to obtain a polyamic acid solution with a weight fraction of 22%.

[0040] S2. Pour 400 ml of deionized water into a beaker, add a magnetic bar and start stirring at a speed of 500 r / min, slowly pour the polyamic acid solution into the deionized water to precipitate the polyamic acid solid, change the water every 2 hours, soak and wash for 20 hours, filter and place in a culture dish, and dry in a 100°C oven for 1 hour to obtain a polyamic acid solid.

[0041] S3. Grind the dried polyamic acid solid into powder; weigh 1.5g of polyamic acid powder, dissolve it in 100ml of 0.06mol / L triethylamine aqueous solution, add a magnetic bar and start stirring, set the temperature to 25°C, set the speed to 400r / min, stir for 8h, and obtain a polyimide precursor solution, the weight fraction of polyamic acid in the polyimide precursor solution is 1.5%.

[0042] S4. Pour the polyimide precursor solution into a culture dish, immerse a cylindrical polyimide foam substrate with a radius of 5 cm, a thickness of 1 cm, an open porosity of 85%, and an average pore size of 1 mm therein, and control the liquid level to completely cover the upper surface of the polyimide foam substrate; put it in a freezer and freeze it at -30°C for 5 hours, and then put it in a freeze dryer and freeze-dry it at -60°C for 48 hours to freeze-dry and remove water; finally, put it in an oven at 270°C for 2 hours for high-temperature foaming and imidization treatment to obtain a polyimide foam with a multi-level pore structure.

[0043] Embodiment 4:

[0044] This embodiment is basically the same as the embodiment 3, except that a cylindrical polyimide foam substrate with a radius of 5 cm, a thickness of 1 cm, an open cell degree of 95%, and an average cell diameter of 1 mm is used.

[0045] Embodiment 5:

[0046] This embodiment is basically the same as the embodiment 3, except that a cylindrical polyimide foam substrate with a radius of 5 cm, a thickness of 1 cm, an open cell degree of 95%, and an average cell diameter of 1.4 mm is used.

[0047] Comparative Example 1:

[0048] A cylindrical polyimide foam substrate with a radius of 5 cm, a thickness of 1 cm, an open cell degree of 85%, and an average cell diameter of 1 mm.

[0049] The comparative sample and the example sample were tested for thermal conductivity and average sound absorption coefficient in the frequency range of 100 to 2000 Hz. The test results are shown in Tables 1 and Figure 2 shown.

[0050] Table 1 Thermal conductivity and average sound absorption coefficient of samples in the embodiment of the present invention at 100-2000 Hz

[0051]

[0052]

[0053] The thermal conductivity of comparative example 1 is 0.043W / (m·K), and the average sound absorption coefficient in the frequency band of 100-2000Hz is 0.14; while the thermal conductivity of the polyimide foam with a multi-level pore structure prepared by the present invention can reach 0.026W / (m·K), and the average sound absorption coefficient in the low-frequency band of 100-2000Hz is 0.31, and the improvement percentage reaches 121%. Without affecting the basic physical and chemical properties of the material, a simple method and process path are used to achieve the simultaneous improvement of the sound absorption performance and the thermal insulation performance in the low-frequency range, and to realize the construction of a multi-level pore structure polyimide material integrating high-efficiency thermal insulation and sound absorption.

Claims

1. A method for preparing a polyimide foam with a multi-level cell structure, characterized in that: The following steps are involved: S1. According to the molar ratio of amino group to anhydride group of 1.04:1 to 1.08:1, the polyanhydride and the polyamine are reacted to synthesize a polyamic acid solution having a weight fraction of 15 to 30%: S2. The polyamic acid solution is washed with water and dried to obtain a polyamic acid solid: S3. The polyamic acid solid is dissolved in a triethylamine aqueous solution at a concentration of 0.05 to 0.4 mol / L to prepare a polyimide precursor solution; the weight fraction of the polyamic acid in the polyimide precursor solution is 1 to 15%; S4. Immerse the polyimide foam substrate with an open-pore structure in a polyimide precursor solution, first freeze it at -25 to -35°C for 4 to 6 hours, then freeze-dry it at -50 to -70°C for 36 to 60 hours to remove water, and finally bake it at 200 to 300°C for 1 to 3 hours for high-temperature foaming and imidization to obtain a polyimide foam with a multi-level pore structure; the polyimide foam includes two levels of pores, one level of pores has an average pore diameter of 0.2 to 0.4 mm, and the other level of pores has an average pore diameter of 0.9 to 1.4 mm, and the pores of 0.2 to 0.4 mm are formed by in-situ foaming of the polyimide precursor in the pores of 0.9 to 1.4 mm.

2. The method for preparing a polyimide foam having a multi-level cell structure according to claim 1, wherein: The synthesis environment temperature of the polyamic acid solution described in S1 is -5 to 30°C; the reaction treatment of the polyacid anhydride and the polyamine is as follows: the polyamine is divided into 4 to 6 parts, added in batches to the polar solvent solution containing the polyacid anhydride, and stirred for reaction for 1 to 3 hours.

3. The method for preparing a polyimide foam having a multi-level cell structure according to claim 1, characterized in that: In S1, the polyacid anhydride includes one or a mixture of at least two of the following: pyromellitic anhydride, 4,4'-biphenyl ether anhydride, 3,3',4,4'-diphenyl ether tetracarboxylic anhydride, 3,3',4,4'-biphenyl tetracarboxylic anhydride, 3,3',4,4'-benzophenone tetracarboxylic anhydride, 2,3,3',4'-diphenyl ether tetracarboxylic anhydride, 4,4'-(4,4'-isopropyldiphenoxy)tetracarboxylic anhydride, maleic anhydride, succinic anhydride, and mellitic anhydride; the polyamine includes: 3,4' -diaminodiphenyl ether, 4,4'-diaminodiphenyl ether, 4,4'-diaminobenzophenone, 1,3-bis(3-aminophenoxy)benzene, m-phenylenediamine, p-phenylenediamine, 3,3'-diaminodiphenyl sulfone, 4,4'-diaminodiphenyl sulfone, 4-bis(4-bisaminophenoxy)diphenyl sulfone, 4-bis(3-bisaminophenoxy)phenyl sulfone, 4,4'-bis(3-aminophenoxy)biphenyl, 1,5-pentanediamine, 1,3-propylenediamine, 2,4,6-triaminopyrimidine or a mixture of at least two thereof.

4. The method for preparing a polyimide foam having a multi-level cell structure according to claim 1, characterized in that: S2 is specifically as follows: pouring the polyamic acid solution into deionized water, stirring and washing to remove the solvent and unreacted small molecules, changing the water every 1 to 3 hours, soaking and washing for 18 to 24 hours, filtering and placing in a culture dish, and drying in an oven at 100 to 120° C. to obtain a polyamic acid solid.

5. The method for preparing a polyimide foam having a multi-level cell structure according to claim 1, characterized in that: In S3, the stirring temperature of the triethylamine aqueous solution in which the polyamic acid is dissolved is 10 to 30°C, and the stirring time is 6 to 10 hours.

6. A polyimide foam with a multi-level cell structure, characterized in that: Prepared by the method described in any one of claims 1 to 5.

7. The polyimide foam with a multi-level cell structure according to claim 6, characterized in that: The thermal conductivity of the polyimide foam is 0.02-0.035 W / (m·K); the average sound absorption coefficient of the polyimide foam in the low-frequency range of 100-2000 Hz is increased by 70-125% compared with the polyimide foam substrate with an open-cell structure.

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