Polyimide composite aerogel with high mechanical strength and high elasticity and application thereof

Abstract

The invention belongs to the technical field of high polymer material preparation, and particularly relates to polyimide composite aerogel with high mechanical strength and high elasticity and application of the polyimide composite aerogel. The composite aerogel is prepared by the following steps: carrying out random copolymerization reaction on two diamine monomers and one dianhydride monomer in a solvent, then reacting with redox graphene grafted maleic anhydride to obtain a ternary copolymerized polyamide acid precursor solution, and washing, precipitating, filtering and drying to obtain a polyamide acid precursor. Then, the precursor is prepared into a triethylamine aqueous solution, the polyimide composite aerogel is obtained through freeze drying and thermal imidization, and the composite aerogel has excellent mechanical properties and has wide application prospects in the aspects of seawater desalination, sewage treatment, flexible sensors and the like.

Description

Technical Field

[0001] This invention belongs to the field of polymer material preparation technology, specifically relating to a polyimide composite aerogel with high mechanical strength and high elasticity and its applications. Background Technology

[0002] Physical microstructure and chemical structure design are two common strategies for improving the porosity and mechanical properties of aerogels. The former involves constructing a three-dimensional network and replacing the dense matrix with a large amount of air. Advances in sol-gel and UV crosslinking technologies have enabled the fabrication of various 3D network structures with improved mechanical strength. Inorganic nanomaterials such as carbon nanotubes, graphene, and MXene have also been introduced to further optimize porosity and mechanical properties. However, interfacial incompatibility between the polyimide aerogel matrix and the inorganic filler often leads to filler sedimentation or agglomeration, reducing the mechanical strength of the aerogel.

[0003] Chemical structure design can also enhance the mechanical properties of aerogels by breaking and rebuilding bonds. For example, crosslinking with 1,3,5-triaminophenoxybenzene (TAB) has enabled the development of polyimide composite aerogels exhibiting 99% elastic compressive strain in liquid helium. Other crosslinking agents, such as 4-aminophenyl pyridine (TAPP), 1,3,5-tris(aminophenyl)benzene (TAPB), and tris(4-aminophenyl)amine (TPA), have also been used to enhance aerogels. However, these reagents are either not commercially available or extremely expensive. Therefore, designing chemical structures to tune the physical microstructure may be the most promising approach to obtaining aerogels with the desired mechanical properties. Summary of the Invention

[0004] To address the drawbacks of improving the mechanical properties of aerogels through physical or chemical methods as pointed out in the background section, this invention prepares a polyimide composite aerogel with high mechanical strength and high elasticity through structural design.

[0005] The polyimide composite aerogel with high mechanical strength and high elasticity provided by this invention has good mechanical properties and good thermal insulation properties. Its preparation process is as follows:

[0006] (1) Preparation of redox graphene grafted with maleic anhydride

[0007] Redox graphene was dispersed in DMAc, and then maleic anhydride was added. The reaction was carried out at 40 °C under nitrogen protection for 8 h. After the reaction was completed, the product was washed three times with ethanol and dried under vacuum to obtain the product.

[0008] The mass ratio of redox graphene to maleic anhydride is 1:3 to 1:7.

[0009] (2) Preparation of polyamic acid precursor

[0010] Dehydrated DMAc was added to a three-necked flask, followed by two diamine monomers, and stirred until completely dissolved. The dianhydride monomers were added in small, repeated additions (5 times) to ensure the molecular chains were amino-terminated. After reacting at room temperature for 8 hours, a random copolymer was obtained. Then, redox graphene-grafted maleic anhydride was added, the stirring speed was reduced, and the reaction continued for 3 hours. Nitrogen purging was performed three times after each addition to remove air from the reaction apparatus. After the reaction was complete, the product was poured into acetone for solvent replacement for 5 hours, filtered, and dried to obtain the polyamic acid precursor.

[0011] The diamine monomer is two of the following: 4,5-diaminodiphenyl ether, 3,5-diaminobenzoic acid, p-phenylenediamine, 4,4'-diaminodiphenylmethane, 9,9-dimethylfluorene-2,7-diamine, and meta-toluidine; the dianhydride monomer is one of the following: 4,4'-biphenyl ether dianhydride, hexafluorodianhydride, and diethylene glycol (4-tricarboxylic anhydride).

[0012] The molar ratio of diamine monomer to dianhydride monomer is 1.01:1; the molar ratio of the two diamine monomers is 1:1-1:9; and the mass ratio of random copolymer to redox graphene graft product is 20-60:1.

[0013] (3) Preparation of composite aerogel

[0014] The preparation method of PAA composite aerogel is as follows: Polyamic acid precursor is weighed and dissolved in triethylamine aqueous solution, then the solution is poured into a mold and freeze-dried; the obtained PAA composite aerogel is dried in a vacuum oven at 110 °C for 2 h to remove moisture, and then dried at 200 °C. ℃, 280 Imidization was completed at ℃ for 1 hour each time to obtain polyimide aerogel.

[0015] The triethylamine aqueous solution has a mass-to-volume ratio of triethylamine:deionized water = 1:17; the concentration of the polyamic acid precursor in the triethylamine aqueous solution is 0.16-0.3 g / ml; the freeze-drying conditions are -80℃≤temperature≤-50℃, and pressure≤1 Pa.

[0016] Reducing the amount of precursor results in lower mechanical strength of the aerogel, while increasing the amount of precursor, although making the aerogel structure more compact, reduces the pore structure and cannot be called an "aerogel" as defined.

[0017] The polyimide composite aerogel prepared by the above method can be used in seawater desalination, sewage treatment, strain sensing and other fields.

[0018] Beneficial effects

[0019] The polyimide composite aerogel prepared by this invention possesses high mechanical strength and high elasticity, exhibiting excellent compression cycling performance and broad application prospects in water purification. The addition of maleic anhydride-grafted redox graphene during the preparation of the composite aerogel endows it with photothermal conversion capabilities. This approach, unlike traditional simple blending of photothermal materials, avoids the problem of filler sedimentation or agglomeration caused by interfacial incompatibility between the polyimide matrix and inorganic photothermal fillers. Furthermore, thermal imidization crosslinks the polyimide molecular chains, enhancing the mechanical strength of the composite aerogel and reducing the risk of macroscopic pore structure distortion and collapse during freeze-drying solvent removal. Attached Figure Description

[0020] Figure 1 SEM image of the composite aerogel prepared in Example 1.

[0021] Figure 2 The image shows the composite aerogel prepared in Example 1 after ten evaporation tests in 3.5 wt% brine.

[0022] Figure 3 The stress-strain curve of the composite aerogel prepared in Example 1.

[0023] Figure 4 The TGA curves show the redox graphene before and after grafting.

[0024] Figure 5 The images show the Raman curves of the redox graphene before and after grafting. Detailed Implementation

[0025] To more clearly illustrate the present invention, the following description, in conjunction with embodiments, provides further insight. Those skilled in the art should understand that the specific descriptions below are illustrative rather than restrictive, and should not be construed as limiting the scope of protection of the present invention.

[0026] Unless otherwise specified, the experimental methods used in the following examples are conventional methods. The experimental materials and reagents used in the following examples can be obtained commercially or through known experimental methods.

[0027] Example 1

[0028] (1) Preparation of graft products

[0029] 2 g of redox graphene was dispersed in 30 ml of DMAc, and then 10 g of maleic anhydride was added. The reaction was carried out at 40 °C under nitrogen protection for 8 h. After the reaction was completed, the product was washed three times with ethanol and dried in a vacuum oven.

[0030] (2) Preparation of precursors

[0031] Add 40 ml of DMAc to a three-necked flask, along with 7.1 mmol of 4,5-diaminodiphenyl ether and 3,5-diaminobenzoic acid (3 mmol), and stir until completely dissolved. Add the dianhydride monomer 4,4'-biphenyl dianhydride (ODPA, 10 mmol) in small, repeated additions (5 times) to ensure the molecular chain is amino-terminated. After reacting at room temperature for 8 h, add 0.098 g of the grafted product, reduce the stirring speed (from 300 r / min to 200 r / min), and continue reacting for 3 h. After each addition, purge the reaction apparatus three times with nitrogen to remove air. After the reaction is complete, pour the product into acetone for solvent exchange for 5 h, filter, and dry to obtain the precursor.

[0032] (3) Preparation of composite aerogel

[0033] Weigh 3 g of the prepared precursor (containing 0.045 g of redox graphene grafted maleic anhydride) and dissolve it in 18 ml of triethylamine aqueous solution (containing 3 ml of triethylamine). Pour the solution into a mold and freeze-dry it (-80℃≤Temperature≤-50℃, Pressure≤1 Pa) for 48 h to obtain PAA composite aerogel.

[0034] The obtained PAA composite aerogel was placed in a high-temperature oven for thermal imidization reaction to obtain polyimide composite aerogel (vacuum oven 110℃, 2 h to remove moisture, 200℃). ℃, 280 ℃ for 1 hour each).

[0035] Example 2

[0036] The difference between this embodiment and Example 1 is that the molar ratio of the diamine monomers 4,5-diaminodiphenyl ether and 3,5-diaminobenzoic acid is 1:1 when synthesizing the precursor. All other treatment methods are the same as in Example 1.

[0037] Example 3

[0038] The difference between this embodiment and Example 1 is that the molar ratio of the diamine monomers 4,5-diaminodiphenyl ether and 3,5-diaminobenzoic acid is 3:1 when synthesizing the precursor. All other treatment methods are the same as in Example 1.

[0039] Example 4

[0040] The difference between this embodiment and Example 1 is that the molar ratio of the diamine monomers 4,5-diaminodiphenyl ether and 3,5-diaminobenzoic acid is 9:1 when synthesizing the precursor. All other treatment methods are the same as in Example 1.

[0041] Example 5

[0042] The difference between this embodiment and Example 1 is that the mass ratio of redox graphene to maleic anhydride is 1:3 when synthesizing the grafted product, while other conditions are the same as in Example 1.

[0043] Example 6

[0044] The difference between this embodiment and Example 1 is that the mass ratio of redox graphene to maleic anhydride is 1:7 when synthesizing the grafted product, while other conditions are the same as in Example 1.

[0045] Example 7

[0046] The difference between this embodiment and Example 1 is that the amount of redox graphene grafted with maleic anhydride added during the synthesis of the precursor is 0.046 g, while the other treatment methods are the same as in Example 1.

[0047] Example 8

[0048] The difference between this embodiment and Example 1 is that the amount of redox graphene grafted with maleic anhydride added during the synthesis of the precursor is 0.144 g, while the other treatment methods are the same as in Example 1.

[0049] Example 9

[0050] The difference between this embodiment and Example 1 is that the amount of redox graphene grafted with maleic anhydride added during the synthesis of the precursor is 0.196 g, while the other treatment methods are the same as in Example 1.

[0051] Example 10

[0052] The difference between this embodiment and Example 1 is that the amount of redox graphene grafted with maleic anhydride added during the synthesis of the precursor is 0.23 g, while the other treatment methods are the same as in Example 1.

[0053] Example 11

[0054] The difference between this embodiment and Example 1 is that the diamine monomer used in the synthesis of the precursor is p-phenylenediamine (7.1 mmol) and 4,4'-diaminodiphenylmethane (3 mmol), and the dianhydride monomer is hexafluorodianhydride (10 mmol). All other conditions are the same as in Example 1.

[0055] Example 12

[0056] The difference between this embodiment and Example 11 is that the dianhydride monomer used in the synthesis of the precursor is diethylene glycol (4-tricarboxylic anhydride) (10 mmol), while all other conditions are the same as in Example 1.

[0057] Example 13

[0058] The difference between this embodiment and Example 1 is that the diamine monomer used in the synthesis of the precursor is 9,9-dimethylfluorene-2,7-diamine (7.1 mmol) and meta-toluidine (3 mmol), and the dianhydride monomer is diethylene glycol (4-tricarboxylic anhydride) (10 mmol). All other conditions are the same as in Example 1.

[0059] Example 14

[0060] The difference between this embodiment and Example 1 is that the dianhydride monomer used in the synthesis of the precursor is hexafluorodianhydride (10 mmol), while all other conditions are the same as in Example 1.

[0061] Comparative Example 1

[0062] (1) Preparation of precursor: 4,5-diaminodiphenyl ether (7.1 mmol), 3,5-diaminobenzoic acid (3 mmol), and dianhydride monomer 4,4'-biphenyl ether dianhydride (ODPA, 10 mmol) were reacted at room temperature for 8 h, and then 2 mmol of maleic anhydride was added to obtain the precursor;

[0063] (2) Weigh 3 g of the prepared precursor and dissolve it in 18 ml of triethylamine aqueous solution (containing 3 ml of triethylamine), then add reduced graphene oxide (2 mmol, 0.1 g), pour it into a mold and freeze dry (under the same conditions as in Example 1) to obtain PAA composite aerogel.

[0064] (3) The obtained PAA composite aerogel was placed in a high-temperature oven for thermal imidization reaction to obtain polyimide composite aerogel (vacuum oven 110℃, 2 h to remove moisture, 200℃, 280℃ for 1 h each).

[0065] Comparative Example 2

[0066] (1) Preparation of precursor: 4,5-diaminodiphenyl ether (7.1 mmol), 3,5-diaminobenzoic acid (3 mmol), and dianhydride monomer 4,4'-biphenyl ether dianhydride (ODPA, 10 mmol) were reacted at room temperature for 8 h, and then reduced graphene oxide (2 mmol, 0.1 g) was added to continue the reaction to obtain the precursor;

[0067] (2) Weigh 3 g of the prepared precursor and dissolve it in 18 ml of triethylamine aqueous solution (containing 3 ml of triethylamine), pour it into a mold and freeze dry to obtain PAA composite aerogel. The preparation of PI composite aerogel is the same as in Example 1.

[0068] (3) Other conditions are the same as in Example 1.

[0069] Comparative Example 3

[0070] (1) 2 g of redox graphene was dispersed in 30 ml of DMAc, and then 10 g of 4-phenylethynyl phthalic anhydride (PEPA) was added. The reaction was carried out at 40 °C under nitrogen protection for 8 h. After the reaction was completed, the product was washed three times with ethanol and dried in a vacuum oven.

[0071] (2) The preparation of the precursor is the same as in Example 1.

[0072] (3) The preparation of the composite aerogel is the same as in Example 1.

[0073] Comparative Example 4

[0074] (1) The preparation of the grafted product is the same as in Example 1.

[0075] (2) Preparation of precursor: 3,5-diaminobenzoic acid (10.1 mmol) was reacted with dianhydride monomer 4,4'-biphenyl dianhydride (ODPA, 10 mmol), and other treatment methods were the same as in Example 1.

[0076] (3) The preparation of the composite aerogel is the same as in Example 1.

[0077] The evaporation rates of the polyimide composite aerogels prepared in Examples 1-10 and Comparative Examples 1-4 were tested, and the results are shown in Table 1.

[0078] Table 1

[0079] sample <![CDATA[Evaporation rate (kg m -2 h -1 )]]> Compressive strength (30%, MPa) Example 1 4.77 21.5 Example 2 1.17 4.1 Example 3 1.35 5.6 Example 4 3.73 14.8 Example 5 3.27 10.7 Example 6 3.46 10.2 Example 7 4.17 13.6 Example 8 3.87 12.9 Example 9 2.51 10.1 Example 10 2.43 10.5 Example 11 4.63 20.4 Example 12 4.57 21.2 Example 13 4.39 19.8 Example 14 4.33 20.5 Comparative Example 1 4.19 11.4 Comparative Example 2 3.42 6.7 Comparative Example 3 4.03 15.3 Comparative Example 4

[0080] As shown in Table 1, the polyimide composite aerogel prepared in Example 1 exhibits improved evaporation rate and compressive strength. This is because cross-linking results in a more uniform distribution of the reduced graphene oxide in the photothermal filler, and the cross-linked nodes formed after molecular chain cross-linking provide nucleation sites for ice crystals during freeze-drying. Furthermore, under external force, the cross-linked nodes can alleviate stress concentration, thus preventing structural damage to the composite aerogel. In Examples 2-4, the two amino groups (-NH2) of 3,5-diaminobenzoic acid are located at the 3 and 5 positions of the benzene ring, and are in a meta-position with the carboxyl group (-COOH). The carboxyl group itself is a large group located between two amino groups. In polymerization reactions (especially with dianhydride monomers), it creates a steric hindrance to the approach and attack of the amino groups, acting like an "obstacle" next to the reaction site. On the other hand, the carboxyl group is a strong electron-withdrawing group. Through the conjugated system of the benzene ring, it reduces the electron cloud density on the two amino nitrogen atoms, weakening the nucleophilicity (attack ability) of the amino group. A less nucleophilic amino group reacts more slowly with the dianhydride, resulting in a lower precursor molecular weight and a looser material structure, leading to lower evaporation rate and compressive strength. A low molecular weight can also reduce mechanical properties or even prevent the aerogel from forming properly when preparing composite aerogels. In Example 5, the grafting rate was low due to the small amount of maleic anhydride, resulting in a lower degree of crosslinking. Furthermore, photothermal material aggregation occurred during freeze-drying, affecting performance. In Example 6, the grafting degree was higher, and the relative graphene content increased, which easily blocked the channels of the aerogel, hindering water vapor transport. In Examples 7, 8, and 9, the amount of photothermal material added during the synthesis of the precursor was small, resulting in a relatively low content of photothermal material in the prepared composite material and a weak light absorption capacity. In the case of adding excessive photothermal material during the preparation of the precursor, the prepared composite material would exhibit uneven dispersion of the photothermal material, which would harm the material properties.

[0081] In Comparative Example 1, directly adding a crosslinking agent improves the mechanical properties of the aerogel to some extent. However, simple blending with photothermal materials leads to uneven distribution of the photothermal materials, causing stress concentration during stress application and damaging the aerogel structure. In Comparative Example 2, without a crosslinking agent, the aerogel exhibits poorer mechanical properties. This is because crosslinking creates crosslinking nodes, which buffer stress concentration; without the crosslinking agent, the aerogel's skeletal structure is directly destroyed under stress. In Comparative Example 3, the added crosslinking agent, due to its large functional groups, exhibits steric hindrance during synthesis, making it less effective than the structurally simple maleic anhydride. In Comparative Example 4, because carboxyl groups are strong hydrogen bond donors and acceptors, the presence of numerous carboxyl groups leads to strong self-association of monomers or oligomers in solution via hydrogen bonds, forming dimers or larger aggregates. This severely hinders the diffusion and proximity of active end groups, making chain growth reactions extremely slow and difficult, resulting in lower molecular weight and poorer material properties.

[0082] The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention in any way. Although the present invention has been disclosed above with reference to preferred embodiments, it is not intended to limit the present invention. Any person skilled in the art can make some modifications or alterations to the above-described technical content to create equivalent embodiments without departing from the scope of the present invention. Any simple modifications, equivalent changes, and alterations made to the above embodiments based on the technical essence of the present invention without departing from the scope of the present invention shall still fall within the scope of the present invention.

Claims

1. A polyimide composite aerogel with high mechanical strength and high elasticity, characterized in that, The polyimide composite aerogel is obtained by random copolymerization of two diamine monomers and one dianhydride monomer in a solvent to obtain a random copolymer, which is then reacted with maleic anhydride grafted onto redox graphene to obtain a polyamic acid precursor. The polyamic acid precursor is then dissolved in a triethylamine aqueous solution and subjected to freeze-drying and thermal imidization to obtain the polyimide composite aerogel.

2. The polyimide composite aerogel with high mechanical strength and high elasticity according to claim 1, characterized in that, The random copolymer was prepared by adding dehydrated DMAc to a three-necked flask and stirring two diamine monomers until they were completely dissolved. Then, dianhydride monomers were added and the reaction was carried out at room temperature under nitrogen protection for 8 hours.

3. The polyimide composite aerogel with high mechanical strength and high elasticity according to claim 2, characterized in that, The diamine monomer is two of the following: 4,5-diaminodiphenyl ether, 3,5-diaminobenzoic acid, p-phenylenediamine, 4,4'-diaminodiphenylmethane, 9,9-dimethylfluorene-2,7-diamine, and meta-toluidine; the dianhydride monomer is one of the following: 4,4'-biphenyl ether dianhydride, hexafluorodianhydride, and diethylene glycol (4-tricarboxylic anhydride).

4. The polyimide composite aerogel with high mechanical strength and high elasticity according to claim 2, characterized in that, The molar ratio of diamine monomer to dianhydride monomer is 1.01:1; the molar ratio of the two diamine monomers is 1:1-9.

5. The polyimide composite aerogel with high mechanical strength and high elasticity according to claim 1, characterized in that, The preparation method of graphene grafted with maleic anhydride is as follows: graphene is dispersed in DMAc, and then maleic anhydride is added to carry out the reaction.

6. The polyimide composite aerogel with high mechanical strength and high elasticity according to claim 5, characterized in that, The mass ratio of redox graphene to maleic anhydride was 1:3 to 1:7; the reaction conditions were 40℃ and nitrogen protection for 8 hours.

7. The polyimide composite aerogel with high mechanical strength and high elasticity according to claim 1, characterized in that, The mass ratio of the random copolymer to the redox graphene graft product is 20-60:

1.

8. The polyimide composite aerogel with high mechanical strength and high elasticity according to claim 1, characterized in that, The concentration of the polyamic acid precursor in the triethylamine aqueous solution is 0.16-0.3 g / ml.

9. The polyimide composite aerogel with high mechanical strength and high elasticity according to claim 1, characterized in that, The freeze-drying conditions are -80℃≤Temperature≤-50℃, Pressure≤1 Pa; the thermal imidization process is as follows: remove moisture at 110℃ for 2 h, and complete imidization at 200℃ and 280℃ for 1 h each.

10. An application of the polyimide composite aerogel with high mechanical strength and high elasticity according to claim 1, characterized in that, The polyimide composite aerogel is used in seawater desalination, wastewater treatment, and strain sensing.

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