Polyimide / melamine composite foam preparation method and product

Abstract

The invention discloses a method for preparing a polyimide / melamine composite foam and a product. The preparation method of the invention comprises the following steps: dissolving an aromatic dibasic acid anhydride in an organic polar solvent, adding a small molecule monoalcohol and an aromatic diamine to react, and obtaining a polyimide precursor solution; immersing the washed and dried melamine foam in the polyimide precursor solution and vacuum treating it, and obtaining a melamine foam saturated with the polyimide precursor solution; immersing the melamine foam saturated with the polyimide precursor solution in water for solvent exchange, and then freeze-drying and imidizing it, and obtaining a polyimide / melamine composite foam. The preparation method of the invention is simple, and can produce a flexible composite foam with good heat resistance, good flame retardant effect, and excellent sound absorption performance.

Description

Technical Field

[0001] The invention relates to a melamine foam, in particular to a preparation method and product of a polyimide / melamine composite foam. Background Art

[0002] Melamine foam plastic, also known as melamine foam plastic, is an intrinsic flame retardant foam material prepared by melamine formaldehyde resin through a foaming process. It has the advantages of good thermal insulation, stability, moisture and heat resistance, sound absorption and light weight. It has become an indispensable material in the fields of flame retardancy, high temperature, noise absorption, etc. It is a new environmentally friendly material with very good development prospects. The density of melamine foam is 8-10kg / m 3 , elastic modulus is 100-120 kPa, thermogravimetric residual mass in nitrogen atmosphere at 800°C is 4-9%, and limiting oxygen index is 32-33%.

[0003] Polyimide is a polymer material with excellent properties such as high and low temperature resistance, thermal insulation, and flame retardancy. However, due to the high price of polyimide foam products, it is often only used in cutting-edge technology fields such as aerospace, ships, and high-speed trains.

[0004] At present, in order to further improve the heat resistance and flame retardancy of melamine foam and expand its application in high-end and cutting-edge technology fields, relevant personnel have conducted relevant research and made certain achievements. For example, the Chinese invention patent with application number CN103408789A discloses a highly efficient flame retardant modified melamine formaldehyde foam and its preparation method, which uses positive electrolyte aqueous solution and negative electrolyte aqueous solution to form alternating reaction layer by layer self-assembly by immersion or spraying, and deposits on the surface of the pore skeleton to form a multi-layer stable inorganic flame retardant film. The residual mass of the nitrogen atmosphere thermogravimetric test at 700°C is increased from 25.2% to 26.7-32.8%, and the cone calorimeter test state with a power of 50kW is not ignitable. However, the presence of the inorganic flame retardant film will cause the toughness of the melamine formaldehyde foam to decrease, and the improvement of the temperature resistance level is not very obvious. Summary of the invention

[0005] The purpose of the present invention is to provide a method for preparing a polyimide / melamine composite foam and a product thereof. The preparation method of the present invention is simple, and the prepared product has the characteristics of good heat resistance, good flame retardant effect and excellent sound absorption performance.

[0006] The technical solution of the present invention: a method for preparing a polyimide / melamine composite foam comprises the following steps:

[0007] S1, dissolving an aromatic dibasic acid anhydride in an organic polar solvent, then adding a small molecule monoalcohol and an aromatic diamine to react, reacting in a water bath at 40 to 60° C. for 0.5 to 2 hours to obtain a polyimide precursor solution;

[0008] S2, immersing the washed and dried melamine foam in a polyimide precursor solution, and vacuum treating it for 25 to 35 minutes, the vacuum treatment temperature is 25 to 56° C., the vacuum degree of the vacuum treatment is 20 to 80 kPa, and the melamine foam saturated with the polyimide precursor solution is obtained;

[0009] S3, soaking the melamine foam saturated with the polyimide precursor solution in water for solvent exchange, and then freeze-drying to obtain the melamine foam compounded with the polyimide precursor;

[0010] S4, imidizing the melamine foam compounded with the polyimide precursor to obtain a polyimide / melamine composite foam.

[0011] In the aforementioned method for preparing polyimide / melamine composite foam, in S1, the molar ratio of aromatic dibasic acid anhydride to small molecule monoalcohol is 1:0.7-2.1, and the mass fraction of solute in the polyimide precursor solution is 0.7-7%.

[0012] In the above-mentioned polyimide / melamine composite foam preparation method, in S1, the aromatic dibasic acid anhydride is one or a mixture of at least two of pyromellitic acid anhydride, 3,3',4,4'-benzophenone tetracarboxylic acid anhydride, 4,4'-oxydiphthalic anhydride, 3,4'-oxydiphthalic anhydride, 3,3',4,4'-diphenyl sulfone tetracarboxylic acid anhydride, triphenyl diether tetracarboxylic acid anhydride, and 3,3',4,4'-biphenyl tetracarboxylic acid anhydride; the organic polar solvent is an aprotic polar solvent, including N-methylpyrrolidone, N , N,N-dimethylformamide, N,N-dimethylacetamide, tetrahydrofuran, one or a mixture of at least two of them; the small molecule monoalcohol is one or at least two of methanol, ethanol, and propanol; the aromatic diamine is one or a mixture of at least two of p-phenylenediamine, m-phenylenediamine, 3,3'-diaminodiphenyl sulfone, 4,4'-diaminodiphenyl sulfone, 3,3'-dimethyl-4,4'-diaminodiphenylmethane, 2,2'-bis[4-(4-aminophenoxy)phenyl]propane, diaminodiphenyl ether and diaminodiphenylmethane.

[0013] In the aforementioned method for preparing polyimide / melamine composite foam, in S2, the polyimide precursor solution includes a solution of polyester ammonium salt or polyester ammonium salt-polyamic acid copolymer.

[0014] In the aforementioned method for preparing polyimide / melamine composite foam, in S2, the washing and drying treatment method of the melamine foam is: washing with one or a mixture of at least two of anhydrous ethanol, acetone, methanol, and deionized water, and drying at 66°C to 100°C for 45min to 90min.

[0015] In the aforementioned method for preparing polyimide / melamine composite foam, in S3, the freeze-drying temperature is -37 to -58°C, and the freeze-drying time is 24 to 48 hours.

[0016] In the above-mentioned method for preparing polyimide / melamine composite foam, in S4, the imidization temperature is 220° C. to 260° C., and the imidization time is 0.5 to 2 hours.

[0017] A polyimide / melamine composite foam is prepared by the above preparation method.

[0018] In the aforementioned polyimide / melamine composite foam, the density of the composite foam is 10 to 32 kg / m3, the average sound absorption coefficient under the same thickness conditions is increased by 30% to 113% compared with pure melamine foam, the elastic modulus is 25 to 55 kPa, the thermogravimetric residual mass in nitrogen atmosphere at 800°C is 35 to 40%, and the limiting oxygen index is 35 to 40%.

[0019] Compared with the prior art, the present invention has the following beneficial effects:

[0020] In order to effectively ensure the flexibility of melamine foam, further improve the flame retardancy and heat resistance grade of melamine foam and effectively increase the use temperature range of the material, the present invention provides a method for reinforcing the melamine foam skeleton to obtain a flexible polyimide / melamine composite foam with excellent heat resistance, good flame retardant effect and excellent sound absorption performance. The present invention uses melamine foam as a matrix, introduces a flexible polyimide precursor on the melamine foam skeleton, attaches it to the melamine foam skeleton as a reinforcing phase through amidation, and the elastic modulus is reduced from 100 to 120 kPa of pure melamine foam to 25 to 55 kPa, and only a smaller stress is required to achieve the same strain, and the flexibility is significantly improved; under the same thickness conditions, the average sound absorption coefficient of the composite foam is 30% to 113% higher than that of pure melamine foam, and the ability to absorb noise is greatly improved; after being treated with liquid nitrogen at -196°C for 12 hours, it can maintain a complete form and improve stability; at 800°C, the residual mass in nitrogen atmosphere thermogravimetrically increases from 4 to 9% of pure melamine foam to 35 to 40% of the composite foam of the present invention, and the limiting oxygen index is increased from 32 to 33% to 35 to 40%, and the flame retardant performance is improved. At the same time, the introduction of polyimide effectively improves the hydrophobicity, reduces the moisture absorption rate of melamine foam, and further broadens its application field. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 This is a digital photo of a polyimide / melamine composite foam prepared in Example 1 of the present invention after being bent;

[0022] Figure 2 The stress-strain diagrams of a polyimide / melamine composite foam and a pure melamine foam prepared in Example 1 of the present invention;

[0023] Figure 3 The thermogravimetric diagrams of a polyimide / melamine composite foam and a pure melamine foam prepared in Example 1 of the present invention. DETAILED DESCRIPTION

[0024] The present invention will be further described below in conjunction with the embodiments, but they are not intended to limit the present invention.

[0025] Comparative Example 1:

[0026] Pure melamine foam, density 9.5kg / m 3 , the elastic modulus is 101.5kPa, the average sound absorption coefficient is maintained at 0.31, the thermal conductivity is 0.031W / (m·K), the thermogravimetric residual mass in nitrogen atmosphere at 800℃ is 4.5%, the limiting oxygen index is 32.3%, and the decomposition temperature of 10% is 189.5℃.

[0027] Embodiment 1:

[0028] S1. Weigh 1.95 g of 3,3',4,4'-benzophenonetetracarboxylic dianhydride and dissolve it in 350.05 g of tetrahydrofuran solvent, then add 0.4 g of methanol to carry out esterification reaction. After the reaction is complete, add 1.2 g of diaminodiphenylmethane and react in a 45° C. water bath environment for 1 hour to obtain a polyimide precursor solution.

[0029] S2, cut 12cm 3 The melamine foam is washed alternately with ethanol and deionized water for three times, then put into an oven, set the temperature to 70°C, and dry for 60 minutes to obtain dry melamine foam; the washed and dried melamine foam is immersed in the prepared polyimide precursor solution, placed in an oven with a temperature of 25°C and a vacuum degree of 80 kPa for 25 minutes, taken out, and the excess solution is poured off to obtain melamine foam saturated with the polyimide precursor solution.

[0030] S3, soaking the melamine foam saturated with the polyimide precursor solution in water for solvent exchange treatment three times, placing the treated foam in a freeze dryer for freeze drying at -55°C for 48 hours, to obtain a polyimide precursor-compounded melamine foam;

[0031] S4, placing the polyimide precursor-compounded melamine foam in an oven at 260° C. for 30 min to complete imidization, thereby obtaining a polyimide / melamine composite foam product, such as Figure 1 shown.

[0032] The density of polyimide / melamine composite foam is 10.3kg / m 3 The elastic modulus is 50.1 kPa, the average sound absorption coefficient under the same thickness conditions is increased by 45% compared with that of comparative example 1, the thermal conductivity is 0.036 W / (m·K), the limiting oxygen index can reach 35.1%, the thermogravimetric residual mass in nitrogen atmosphere at 800°C is 39.87%, and the decomposition temperature of 10% is 396.8°C.

[0033] The performance comparison of polyimide / melamine composite foam and pure melamine foam of comparative example 1 is shown in Figure 2 and Figure 3 As shown. Figure 2 It can be seen that the polyimide / melamine composite foam only needs a smaller stress to achieve the same strain, and the flexibility is significantly improved; Figure 3 It can be seen that compared with pure melamine foam, the residual mass of polyimide / melamine composite foam in nitrogen atmosphere thermogravimetric analysis at 800°C is improved, and the temperature also increases by 207.3°C when the mass is decomposed by 10%, indicating that the heat resistance level of the composite foam product is significantly improved.

[0034] Embodiment 2:

[0035] This embodiment is basically the same as Embodiment 1, except that:

[0036] The mass of the weighed 3,3',4,4'-benzophenonetetracarboxylic dianhydride was 2.55 g, the mass of the tetrahydrofuran was 70.01 g, the mass of the methanol was 0.51 g, and the mass of the diaminodiphenylmethane was 1.57 g.

[0037] The density of the obtained polyimide / melamine composite foam product is 31.0 kg / m 3 The elastic modulus is 49.8 kPa, the average sound absorption coefficient under the same thickness conditions is increased by 65% ​​compared with that of comparative example 1, the thermal conductivity is 0.035 W / (m·K), the limiting oxygen index can reach 35.7%, the thermogravimetric residual mass in nitrogen atmosphere at 800°C is 39.84%, and the decomposition temperature of 10% is 396.6°C.

[0038] Embodiment 3:

[0039] This embodiment is basically the same as Embodiment 1, except that:

[0040] The aromatic dibasic acid anhydride used is pyromellitic dianhydride, the mass of pyromellitic dianhydride is 0.98 g, the mass of tetrahydrofuran is 70.01 g, the mass of methanol is 0.29 g, and the mass of diaminodiphenylmethane is 0.89 g.

[0041] The density of the obtained polyimide / melamine composite foam product is 20.1 kg / m 3 The elastic modulus is 41.6 kPa, the average sound absorption coefficient under the same thickness conditions is increased by 35% compared with that of comparative example 1, the thermal conductivity is 0.033 W / (m·K), the limiting oxygen index can reach 35.5%, the thermogravimetric residual mass in nitrogen atmosphere at 800°C is 41.45%, and the decomposition temperature of 10% is 397.1°C.

[0042] Embodiment 4:

[0043] This embodiment is basically the same as Embodiment 1, except that:

[0044] The mass of the weighed 3,3',4,4'-benzophenonetetracarboxylic dianhydride was 1.56 g, the mass of tetrahydrofuran was 66.4 g, the mass of ethanol was 0.22 g, and the mass of diaminodiphenylmethane was 0.96 g.

[0045] The obtained polyimide / melamine composite foam product has a density of 23.9 kg / m 3 The elastic modulus is 29.0 kPa, the average sound absorption coefficient under the same thickness conditions is increased by 32% compared with that of comparative example 1, the thermal conductivity is 0.032 W / (m·K), the limiting oxygen index can reach 35.4%, the thermogravimetric residual mass in nitrogen atmosphere at 800°C is 35.82%, and the decomposition temperature of 10% is 397.0°C.

Claims

1. A method for preparing a polyimide / melamine composite foam, characterized in that: The following steps are involved: S1. dissolving an aromatic dibasic acid anhydride in an organic polar solvent, then adding a small molecule monoalcohol and an aromatic diamine, wherein the molar ratio of the aromatic dibasic acid anhydride to the small molecule monoalcohol is 1:0.7-2.1, and reacting for 0.5-2h in a water bath at 40-60°C to obtain a polyimide precursor solution having a mass fraction of the solute of 0.7-7%; S2, immersing the washed and dried melamine foam in a polyimide precursor solution, and vacuum treating it for 25 to 35 minutes, the vacuum treatment temperature is 25 to 56° C., the vacuum degree of the vacuum treatment is 20 to 80 kPa, and the melamine foam saturated with the polyimide precursor solution is obtained; S3, soaking the melamine foam saturated with the polyimide precursor solution in water for solvent exchange, and then freeze-drying to obtain the melamine foam compounded with the polyimide precursor; S4, imidizing the melamine foam compounded with the polyimide precursor to obtain a polyimide / melamine composite foam.

2. The method for preparing a polyimide / melamine composite foam according to claim 1, characterized in that: In S1, the aromatic dibasic acid anhydride is one or a mixture of at least two of pyromellitic acid anhydride, 3,3',4,4'-benzophenone tetracarboxylic acid anhydride, 4,4'-oxydiphthalic anhydride, 3,4'-oxydiphthalic anhydride, 3,3',4,4'-diphenylsulfone tetracarboxylic acid anhydride, triphenylene diether tetracarboxylic acid anhydride, and 3,3',4,4'-biphenyltetracarboxylic acid anhydride; the organic polar solvent is an aprotic polar solvent, including N-methylpyrrolidone, N,N-dimethylformamide, N , N-dimethylacetamide, tetrahydrofuran, one or a mixture of at least two of them; the small molecule monoalcohol is one or at least two of methanol, ethanol, and propanol; the aromatic diamine is one or a mixture of at least two of p-phenylenediamine, m-phenylenediamine, 3,3'-diaminodiphenyl sulfone, 4,4'-diaminodiphenyl sulfone, 3,3'-dimethyl-4,4'-diaminodiphenylmethane, 2,2'-bis[4-(4-aminophenoxy)phenyl]propane, diaminodiphenyl ether and diaminodiphenylmethane.

3. The method for preparing a polyimide / melamine composite foam according to claim 1, characterized in that: In S2, the polyimide precursor solution includes a solution of polyester ammonium salt or polyester ammonium salt-polyamic acid copolymer.

4. The method for preparing a polyimide / melamine composite foam according to claim 1, characterized in that: In S2, the washing and drying treatment method of the melamine foam is: washing with one or a mixture of at least two of anhydrous ethanol, acetone, methanol, and deionized water, and drying at 66° C. to 100° C. for 45 min to 90 min.

5. The method for preparing a polyimide / melamine composite foam according to claim 1, characterized in that: In S3, the freeze-drying temperature is -37 to -58°C, and the freeze-drying time is 24 to 48 hours.

6. The method for preparing a polyimide / melamine composite foam according to claim 1, characterized in that: In S4, the imidization temperature is 220° C. to 260° C., and the imidization time is 0.5 to 2 hours.

7. A polyimide / melamine composite foam prepared by the preparation method according to any one of claims 1 to 6.

8. The polyimide / melamine composite foam according to claim 7, characterized in that: The composite foam density is 10-32 kg / m 3 Under the same thickness conditions, the average sound absorption coefficient is increased by 30% to 113% compared with pure melamine foam, the elastic modulus is 25 to 55 kPa, the thermogravimetric residual mass in nitrogen atmosphere at 800°C is 35 to 40%, and the limiting oxygen index is 35 to 40%.

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