Method for regulating and controlling density of polyimide foam by using ethanol

Abstract

The invention discloses a method for regulating and controlling polyimide foam density by using ethanol, and belongs to the technical field of polymer foam materials. The preparation method comprises the following steps: adding dianhydride into a polar solvent, and carrying out esterification reaction dissolution in a mixed esterifying agent of methanol and ethanol; then adding a certain amount of diamine, carrying out full polymerization reaction, and then carrying out drying treatment to obtain precursor powder; and carrying out foaming imidization on the precursor powder in a vacuum heating environment to obtain the polyimide foam. Wherein the density of the polyimide foam is controlled by regulating and controlling the proportion of ethanol in the esterifying agent. According to the method for regulating and controlling the density of the polyimide foam by using the ethanol, the preparation method is simple to operate and easy to produce, the density of the obtained polyimide foam can be regulated and controlled within a certain range, and polyimide foams with different densities can be conveniently produced according to actual requirements; the density of the prepared polyimide foam is controllable, and the mechanical strength is improved; in addition, the use of methanol is reduced to a certain extent, and potential hazards caused by production can be reduced.

Description

Technical Field

[0001] The present invention discloses a method for regulating the density of polyimide foam using ethanol, belonging to the technical field of polymer foam materials. Background Art

[0002] Polyimide foam has properties such as light weight, flame retardancy, low thermal conductivity, resistance to high and low temperatures, and strong chemical stability. As a special engineering plastic foam material, it is widely used in the fields of machinery, energy, environmental protection, etc. Polyimide foams with different densities have different uses. For example, polyimide foam with a density of less than 50 kg / m 3 is mainly used for heat insulation and protection, and polyimide foam with a density of more than 50 kg / m 3 is mainly used as a structural material. However, the vast majority of production processes can only produce polyimide foam of the same density using the same monomer materials, which limits the production range of polyimide foam on the same production line.

[0003] The literature (Hao Zhang, Hengyi Zhou, Gaohui Sun, et al. Easy route to control density of polyimide foams and impact on mechanical and combustion behaviors. Journal of Cellular Plastics, 2021, 57(4), DOI: 10.1177 / 0021955X20943111) discloses a method for regulating the density of polyimide foam using water, and the density of the prepared polyimide foam is between 48 - 157 kg / m 3 However, it adopts the emulsion foaming method, the forming and processing speed is relatively fast, and the precursor in the solution state is not conducive to storage and use, which limits the scope of application.

[0004] Patent CN202111660020 controls the density of polyimide foam by regulating the addition amount of an external foaming agent. However, the external foaming agent has a high cost and will introduce impurities, having certain defects.

[0005] In addition, in the esterification step of synthesizing polyimide foam by the reverse feeding method, the commonly used esterifying agent is pure methanol. This is because the methanol molecule has a small volume and is more likely to undergo an esterification reaction, and the methoxy group is more likely to break away during the thermal imidization process. However, methanol is highly toxic and easily threatens the physical health of operators and ecological environment protection. Summary of the Invention

[0006] In view of the deficiencies of the prior art, the present invention proposes a method for regulating the density of polyimide foam using ethanol. According to the DSC curve, it can be known that the degree of vitrification of the precursor powder obtained by ethanol esterification when heated is lower than that of methanol. Therefore, adding ethanol to the esterification solution can play a role in reducing the foaming degree. This method is simple to operate and easy to produce, and can regulate the density of the obtained polyimide foam within a certain range, facilitating the production of polyimide foams with different densities according to actual needs; the density of the prepared polyimide foam is controllable, and the mechanical strength is improved. In addition, the use of methanol is reduced to a certain extent, which is beneficial to reducing the potential hazards caused by production.

[0007] The technical solution provided by the present invention is as follows: A method for regulating the density of polyimide foam using ethanol. First, add dianhydride to a polar solvent and dissolve it by undergoing an esterification reaction in a mixed esterifying agent of methanol and ethanol; then add a certain amount of diamine, and after sufficient polymerization reaction, perform a drying treatment to obtain a precursor powder; then foam and imidize the above precursor powder in a vacuum heating environment to obtain polyimide foam, wherein the density of the polyimide foam is controlled by regulating the proportion of ethanol in the esterifying agent.

[0008] The dianhydride is selected from at least one of 3,3',4,4'-benzophenone tetracarboxylic dianhydride, 3,3',4,4'-oxydiphthalic anhydride, 3,3',4,4'-biphenyltetracarboxylic dianhydride, bisphenol A dianhydride, and pyromellitic dianhydride.

[0009] The polar solvent is selected from at least one of tetrahydrofuran, dimethylformamide, dimethylacetamide, or N-methylpyrrolidone; preferably, the polar solvent is selected from tetrahydrofuran.

[0010] The diamine is selected from at least one of p-phenylenediamine, 4,4'-diaminodiphenyl ether, 3,4'-diaminodiphenyl ether, and 1,3-bis(4-aminophenoxy)benzene.

[0011] The foam stabilizer is selected from at least one of silicone oil DC-193, silicone oil AK-8805, and silicone oil silok2008N; preferably, the surfactant is selected from silicone oil DC-193.

[0012] In the esterifying agent composed of methanol and ethanol, the molar fraction of ethanol is between 1% and 60%, and the remaining part is methanol;

[0013] Preferably, the molar ratio of ethanol is 5%.

[0014] The molar ratio of the diamine to the dianhydride is 1:(0.95 - 1.05);

[0015] Preferably, the molar ratio of the diamine to the dianhydride is 100:100.

[0016] The mass ratio of the surfactant to the dianhydride is 1:(20 - 500);

[0017] Preferably, the mass ratio of the surfactant to the dianhydride is 1:50.

[0018] The mass ratio of the dianhydride to the polar solvent to the esterifying agent is 1:(2 - 6):(0.5 - 2.5);

[0019] Preferably, the mass ratio of the dianhydride to the polar solvent is 1:4; the mass ratio of the dianhydride to the small molecule esterifying agent is 1:1.

[0020] The temperature for the esterification with heating and stirring is 60 - 100 °C;

[0021] Preferably, the temperature for the esterification with heating and stirring is 75 °C.

[0022] The temperature for the polymerization with heating is 55 - 90 °C, and the time is 4 - 12 h;

[0023] Preferably, the temperature for the polymerization with heating is 70 °C, and the time is 10 h.

[0024] For the foaming and imidization, the absolute pressure under the vacuum condition is 0 - 0.01 MPa, and the heating condition is gradually increasing the temperature from room temperature to 250 - 350 °C within 0.5 - 4 h in a gradient manner, and maintaining for 10 - 60 min when reaching the highest temperature point.

[0025] Preferably, for the foaming and imidization, the heating condition is increasing the temperature from room temperature to 300 °C at a uniform speed within 2 h, and maintaining for 30 min when reaching the highest temperature point.

[0026] The density of the produced polyimide foam is 20 - 80 kg / m 3 , and it can be regulated by the molar ratio of ethanol in the esterifying agent to the total amount of substances.

[0027] Advantageous effects: Compared with the prior art, the present invention regulates the density of the polyimide foam by using ethanol, and obtains the polyimide foam through the vacuum heating foaming and imidization process with a powdery precursor. It can not only effectively regulate the density of the obtained polyimide foam within a certain range without relying on an externally added foaming agent, facilitating the production of polyimide foams with different densities according to actual needs, but also the powder foaming process is conducive to storage and access, and is convenient for production and use.

[0028] Obviously, based on the above content of the present invention, according to the common general knowledge and customary means in the art, without departing from the above basic technical idea of the present invention, various other forms of modifications, substitutions or changes can also be made.

[0029] The following is a further detailed description of the above content of the present invention in the form of specific embodiments. However, it should not be understood that the scope of the above subject matter of the present invention is limited to the following examples. Any technology implemented based on the above content of the present invention belongs to the scope of the present invention. Brief Description of the Drawings

[0030] Figure 1 It is the DSC curve of the precursor powder obtained by esterification with ethanol and the precursor powder obtained by esterification with methanol.

[0031] Figure 2 It is the curve of the change in the density of the polyimide foam prepared in Examples 1 to 6 and Comparative Example 1 with the molar fraction of ethanol.

[0032] Figure 3 It is the flexural strength of the polyimide foam prepared in Examples 1 to 8 and Comparative Examples 1 to 3.

[0033] Figure 4 It is the compressive strength of the polyimide foam prepared in Examples 1 to 8 and Comparative Examples 1 to 3. Specific Embodiments

[0034] The present invention will be described in detail below, and the features and advantages of the present invention will become clearer and more distinct with these descriptions.

[0035] The special word "exemplary" here means "serving as an example, embodiment or illustration". Any embodiment described as "exemplary" here does not have to be construed as superior to or better than other embodiments.

[0036] The raw materials and equipment used in the specific embodiments of the present invention are all known products and are obtained by purchasing commercially available products.

[0037] Example 1

[0038] Step (1): Add 31 g (0.1 mol) of 3,3',4,4'-oxydiphthalic anhydride to 124 g of tetrahydrofuran, and add an esterifying agent with a total mass of 31 g, in which ethanol accounts for 1% of the molar amount and the rest is methanol. Heat to complete esterification at 75 °C to obtain an esterified dianhydride solution.

[0039] Step (2): Add 20 g (0.1 mol) of 4,4'-diaminodiphenyl ether to the esterification reaction solution obtained in step (1). Heat for a polymerization reaction at 70 °C for 10 h, then add 0.62 g of DC-193. After stirring and dissolving, perform drying and pulverization treatments in sequence to obtain a precursor powder.

[0040] Step (3): Keep the absolute pressure of the precursor powder obtained in step (2) at 0 to 0.01 MPa, and uniformly heat it from room temperature to 300 °C within 2 h. Keep it for 30 min when reaching the highest temperature point to obtain polyimide foam.

[0041] Example 2

[0042] Except that the molar percentage of ethanol in the esterifying agent in step (1) of Example 1 was changed to 2.5%, the remaining operations were the same as those in Example 1.

[0043] Example 3

[0044] Except that the molar percentage of ethanol in the esterifying agent in step (1) of Example 1 was changed to 5%, the remaining operations were the same as those in Example 1.

[0045] Example 4

[0046] Except that the molar percentage of ethanol in the esterifying agent in step (1) of Example 1 was changed to 10%, the remaining operations were the same as those in Example 1.

[0047] Example 5

[0048] Except that the molar percentage of ethanol in the esterifying agent in step (1) of Example 1 was changed to 20%, the remaining operations were the same as those in Example 1.

[0049] Example 6

[0050] Except that the molar percentage of ethanol in the esterifying agent in step (1) of Example 1 was changed to 60%, the remaining operations were the same as those in Example 1.

[0051] Comparative Example 1

[0052] Except that the esterifying agent in step (1) of Example 1 was changed to pure methanol, the remaining operations were the same as those in Example 1.

[0053] Measure the density of the polyimide foams prepared in Examples 1 to 6 and Comparative Example 1, and the measurement results are as Figure 2 ; Test the flexural strength according to GB / T 8812.1-2007, and the test results are as Figure 3 ; Test the 10% compressive strength according to GB / T 8813-2020, and the test results are as Figure 4 . From Figure 2 , Figure 3 , Figure 4 The above experimental results are tabulated in Table 1.

[0054] Table 1 Performance comparison between examples and comparative examples

[0055]

[0056] Example 3: In the esterifying agent, ethanol accounts for 5% of the molar amount. The density increases slightly, but the flexural strength doubles and the compressive strength also increases, with relatively good cost performance.

[0057] Example 7

[0058] Except that in step (1) of Example 3, the variety and quality of the dianhydride are changed to a mixture of 27.9 g (0.07 mol) of 3,3',4,4'-oxydiphthalic anhydride and 6.54 g (0.03 mol) of pyromellitic dianhydride, the remaining operations are the same as those in Example 3.

[0059] The density of the polyimide foam obtained in this example is 28.5 kg / m 3 ; The flexural strength test is carried out in accordance with GB / T8812.1-2007. It can be seen from Figure 3 that the maximum flexural strength is 155.3 kPa; The compressive strength test is carried out in accordance with GB / T 8813-2020. It can be seen from Figure 4 that the 10% compressive strength is 26.3 kPa.

[0060] Comparative Example 2

[0061] Except that the esterifying agent in step (1) of Example 7 is changed to pure methanol, the remaining operations are the same as those in Example 7.

[0062] The density of the polyimide foam obtained in this comparative example is 17.2 kg / m 3 ; The flexural strength test is carried out in accordance with GB / T8812.1-2007. It can be seen from Figure 3 that the maximum flexural strength is 86.1 kPa; The compressive strength test is carried out in accordance with GB / T 8813-2020. It can be seen from Figure 4 that the 10% compressive strength is 11.7 kPa.

[0063] Example 8

[0064] Except that in step (1) of Example 3, the variety and quality of the diamine are changed to a mixture of 14 g (0.07 mol) of 4,4'-diaminodiphenyl ether and 8.77 g (0.03 mol) of 1,3-bis(4-aminophenoxy)benzene, the remaining operations are the same as those in Example 3.

[0065] The density of the polyimide foam obtained in this example is 29.8 kg / m 3 ; The flexural strength test is carried out in accordance with GB / T8812.1-2007. It can be seen from Figure 3 that the maximum flexural strength is 291.6 kPa; The compressive strength test is carried out in accordance with GB / T 8813-2020. It can be seen from Figure 4 that the 10% compressive strength is 73.0 kPa.

[0066] Comparative Example 3

[0067] Except that the esterification agent in step (1) of Example 8 is changed to pure methanol, the remaining operations are the same as those of Example 8.

[0068] The density of the polyimide foam obtained in this comparative example is 23.2 kg / m 3 ; According to GB / T8812.1-2007, the bending strength test is carried out. Figure 3 It can be seen that the maximum bending strength is 219.1kPa; the compression strength test is carried out according to GB / T 8813-2020. Figure 4 It can be seen that the 10% compressive strength is 55.2 kPa.

[0069] Finally, it should be pointed out that the above embodiments are only representative examples of the present invention. Obviously, the technical solution of the present invention is not limited to the above embodiments, and there are many variations. All variations that can be directly derived or associated with the content disclosed by ordinary technicians in this field should be considered as the protection scope of the present invention.

Claims

1. A method for regulating the density of polyimide foam using ethanol, characterized in that The following steps are involved: Step (1), heating and stirring the dianhydride in a polar solvent and an esterifying agent consisting of methanol and ethanol to cause an esterification reaction to completely dissolve the dianhydride, thereby obtaining an esterified dianhydride solution; Step (2), adding diamine to the esterified dianhydride solution, continuing heating and stirring to react, obtaining a precursor solution, adding a uniform foaming agent to the precursor solution, stirring and dissolving, and sequentially performing drying and pulverizing treatments to obtain a precursor powder; Step (3), heating the precursor powder in a vacuum environment to perform foaming and imidization to obtain polyimide foam.

2. The method for regulating the density of polyimide foam using ethanol according to claim 1, characterized in that: In the esterification agent composed of methanol and ethanol, the total molar ratio of ethanol is between 1% and 60%; The dianhydride is selected from at least one of 3,3',4,4'-benzophenonetetracarboxylic dianhydride, 3,3',4,4'-oxydiphthalic anhydride, 3,3',4,4'-biphenyltetracarboxylic dianhydride, bisphenol A dianhydride and pyromellitic dianhydride; The polar solvent is selected from at least one of tetrahydrofuran, dimethylformamide, dimethylacetamide or N-methylpyrrolidone; The diamine is selected from at least one of p-phenylenediamine, 4,4'-diaminodiphenyl ether, 3,4'-diaminodiphenyl ether, and 1,3-di(4-aminophenoxy)benzene; The foam leveling agent is selected from at least one of silicone oil DC-193, silicone oil AK-8805 and silicone oil silok2008N.

3. A method for regulating the density of polyimide foam using ethanol according to claim 2, characterized in that: The molar ratio of the diamine to the dianhydride is 1:(0.95-1.05); The mass ratio of the foam leveling agent to the dianhydride is 1:(20-500); The mass ratio of the dianhydride to the polar solvent to the esterifying agent is 1:(2-6):(0.5-2.5).

4. The method for regulating the density of polyimide foam using ethanol according to claim 1, characterized in that: The temperature of the heating and stirring esterification is 60-100°C; The heating polymerization temperature is 55 to 90° C. and the time is 4 to 12 hours; The absolute pressure of the vacuum conditions for foaming and imidization is 0-0.01 MPa, and the heating conditions are to gradually increase the temperature from room temperature to 250-350° C. within 0.5-4 hours, and maintain the temperature for 10-60 minutes when the temperature reaches the highest point.

5. The method for regulating the density of polyimide foam using ethanol according to claim 2, characterized in that: The molar percentage of ethanol in the esterification agent is 5%; the dianhydride is a mixture of 3,3',4,4'-oxydiphthalic anhydride and pyromellitic anhydride; the diamine is a mixture of 4,4'-diaminodiphenyl ether and 1,3-di(4-aminophenoxy)benzene.

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