Polyimide-silicon oxide composite aerogel material and preparation method thereof

Abstract

The invention relates to the technical field of aerogel materials, in particular to a polyimide-silicon oxide composite aerogel material and a preparation method thereof. The preparation method comprises the following steps: adding nano silicon dioxide powder and a cross-linking agent into a polyamide acid solution for cross-linking reaction to obtain polyamide acid-silicon oxide composite sol; the preparation method comprises the following steps: uniformly smearing polyamide acid on the surface of a flexible base material, and carrying out gelation treatment to obtain a polyamide acid-silicon oxide composite gel wet film; mixing the polyamide acid-silicon oxide composite gel wet film, a dehydrating agent and a catalyst, and carrying out chemical imidization treatment to obtain a polyamide acid-silicon oxide composite gel film; and carrying out normal-pressure gradient drying on the polyamide acid-silicon oxide composite gel membrane to obtain the polyamide acid-silicon oxide composite gel diaphragm material. According to the scheme provided by the invention, the polyimide-silicon oxide composite aerogel diaphragm material which is simple in process, low in cost, suitable for continuous production and capable of constructing a stable bicontinuous network structure can be provided.

Description

Technical Field

[0001] This invention relates to the field of aerogel materials technology, and in particular to a polyimide-silica composite aerogel material and its preparation method. Background Technology

[0002] Aerogel materials, due to their extremely high porosity, extremely low density, and low thermal conductivity, have shown great application potential in fields such as thermal insulation, adsorption, energy, and electronics. Silica aerogel is one of the most widely studied aerogels, but its inherent brittleness and poor mechanical strength severely limit its application in flexible devices and load-bearing structures. Polyimide, as a high-performance polymer, possesses excellent thermal stability, mechanical properties, and chemical resistance. Introducing polyimide into aerogel systems is an effective way to improve their mechanical properties. However, the preparation of traditional polyimide aerogels or PI-SiO2 composite aerogels usually relies on supercritical drying technology. This process is expensive, dangerous, energy-intensive, and difficult to achieve continuous and large-scale production, greatly increasing manufacturing costs. In addition, composite materials prepared by existing technologies often suffer from poor two-phase compatibility and discontinuous network structures, resulting in poor performance. Chinese invention patent CN202411976513.6 discloses a "surface-reinforced aerogel composite material and its preparation method," which uses a sol-gel method and supercritical drying to prepare bulk materials. This method cannot directly obtain products in the form of thin films or diaphragms, and the process is complex. Another patent, CN202111200205.0, discloses a "method for preparing polyimide aerogel products by atmospheric pressure drying and its application," which prepares polyimide aerogels through chemical imidization and atmospheric pressure drying. However, it does not introduce inorganic nanophases for composite reinforcement, leaving room for improvement in its mechanical properties and thermal stability. Furthermore, it does not involve a continuous coating production process suitable for diaphragm materials.

[0003] Therefore, developing a method for preparing polyimide-silica composite aerogel membrane materials that is simple in process, low in cost, suitable for continuous production, and capable of constructing a stable dual continuous network structure has become an urgent technical problem to be solved in this field. Summary of the Invention

[0004] This invention provides a polyimide-silica composite aerogel material and its preparation method, which can provide a polyimide-silica composite aerogel membrane material with simple process, low cost, suitable for continuous production, and capable of constructing a stable double continuous network structure.

[0005] In a first aspect, embodiments of the present invention provide a method for preparing a polyimide-silica composite aerogel material, comprising: Nano-silica powder and a crosslinking agent were added to a polyamic acid solution to carry out a crosslinking reaction, resulting in a polyamic acid-silica composite sol. The polyamic acid is uniformly coated on the surface of a flexible substrate and then gelled to obtain a polyamic acid-silica composite gel wet film. The polyamic acid-silica composite gel wet film, dehydrating agent and catalyst are mixed and chemically imidized to obtain polyamic acid-silica composite gel film. The polyamic acid-silica composite gel membrane was subjected to atmospheric pressure gradient drying to obtain a polyamic acid-silica composite gel membrane material.

[0006] In one possible design, the polyamic acid solution is obtained as follows: Aromatic dianhydride and aromatic diamine are dissolved in an organic solvent, and acrylamide monomer is added under nitrogen atmosphere to react and obtain polyamic acid solution.

[0007] In one possible design, the gelation process includes: Gel at 30~50℃ for 1~2 hours.

[0008] In one possible design, the chemical imidization treatment includes: The temperature is controlled within a gradient increase of 50~80℃ and 100~150℃ respectively, and the holding time in each temperature zone is 1~2 hours.

[0009] In one possible design, the atmospheric pressure gradient drying includes the following steps: Treat at 20~30℃ for 0.5~1h, at 50~60℃ for 0.5~1h, and at 90~110℃ for 2~3h, with humidity maintained at 30~40% during the drying process.

[0010] In one possible design, the aromatic dianhydride is selected from at least one of pyromellitic dianhydride, biphenyl dianhydride, and 3,3',4,4'-benzophenone dianhydride. The aromatic diamine is selected from at least one of p-phenylenediamine, 4,4'-diaminodiphenyl ether, and 3,4'-diaminodiphenyl ether; The molar ratio of the dianhydride to the diamine is 1:(0.8~1.2), the mass of the acrylamide is 5% of the total mass of the dianhydride and the diamine, and the mass ratio of the crosslinking agent to the acrylamide is 1:10.

[0011] In one possible design, the flexible substrate is a polyethylene terephthalate film, a polyimide film, or a metal foil with a silane-treated surface, and the coating method is slot extrusion coating or blade coating.

[0012] In one possible design, the particle size of the nano-silica powder is 20~50nm.

[0013] In one possible design, the dehydrating agent is acetic anhydride, and the catalyst is at least one of pyridine and triethylamine; The organic solvent is N-methylpyrrolidone, and the crosslinking agent is N,N'-methylenebisacrylamide.

[0014] Secondly, embodiments of the present invention provide a polyimide-silica composite aerogel material, prepared according to any of the above preparation methods.

[0015] Compared with the prior art, the present invention has at least the following beneficial effects: (1) By introducing acrylamide monomer and its crosslinking agent, this invention simultaneously constructs an interpenetrating organic polymer network during the formation of polyimide, and forms a robust "rigid-flexible" bicontinuous network structure with nano-SiO2 particles. This structure effectively disperses stress, greatly improves the mechanical strength and toughness of the composite aerogel, and overcomes the brittleness of traditional SiO2 aerogels.

[0016] (2) This invention abandons the traditional high-cost and high-risk supercritical drying technology, and innovatively adopts atmospheric pressure gradient drying process. By precisely controlling the humidity (30~40%) during the drying process, the capillary force during solvent evaporation is significantly reduced, and the collapse of the pore structure is successfully avoided, thus realizing the low-cost preparation of high-performance aerogel materials.

[0017] (3) This invention introduces coating technology (such as slot coating) into the preparation of aerogel membranes, which can form a continuous film on a flexible substrate and has good compatibility with existing roll-to-roll production processes, laying a solid foundation for large-scale, high-efficiency and continuous industrial production of aerogel membranes.

[0018] (4) The resulting composite aerogel membrane material possesses both the excellent flexibility and high thermal stability of polyimide and the low thermal conductivity of silicon oxide. It has high porosity, uniform pore size distribution, and low thermal shrinkage (e.g., less than 3% thermal shrinkage after 1 hour at 300°C), making it particularly suitable for lithium-ion battery separators, high-temperature insulation, and flexible electronics fields where safety and stability requirements are extremely high. Attached Figure Description

[0019] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0020] Figure 1Low-magnification SEM image of the cross-sectional morphology of the polyimide-silica composite aerogel membrane material prepared in Example 1; Figure 2 High-magnification SEM image of the cross-sectional morphology of the polyimide-silica composite aerogel membrane material prepared in Example 1; Figure 3 Microscopic morphology of the sampling location of the polyimide-silica composite aerogel membrane material prepared in Example 1; Figure 4 for Figure 3 Carbon element labeling distribution at the sampling location; Figure 5 for Figure 3 Distribution map of oxygen element markers at the sampling locations; Figure 6 for Figure 3 Silicon element labeling distribution at the sampling location; Figure 7 The image shows the EDS spectrum of the sample prepared in Example 1. Detailed Implementation

[0021] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are some embodiments of the present invention, but not all embodiments. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without creative effort are within the scope of protection of the present invention.

[0022] This invention provides a method for preparing a polyimide-silica composite aerogel material, comprising: Nano-silica powder and a crosslinking agent were added to a polyamic acid solution to carry out a crosslinking reaction, resulting in a polyamic acid-silica composite sol. The polyamic acid is uniformly coated on the surface of a flexible substrate and then gelled to obtain a polyamic acid-silica composite gel wet film. The polyamic acid-silica composite gel wet film, dehydrating agent and catalyst are mixed and chemically imidized to obtain polyamic acid-silica composite gel film. The polyamic acid-silica composite gel membrane was subjected to atmospheric pressure gradient drying to obtain a polyamic acid-silica composite gel membrane material.

[0023] Preliminary cross-linked polyamic acid is combined with nano-silica powder under the action of a cross-linking agent to form a polyamic acid-silica composite sol. The polyamic acid-silica composite sol is coated onto a flexible substrate to facilitate the final formation of a film structure. A gelation treatment on the flexible substrate yields a polyamic acid-silica composite gel wet film. The polyamic acid-silica composite gel wet film undergoes chemical imidization treatment to form a polyamic acid-silica composite gel film. During the polyimide formation process, the network formed by the amide functional groups further condenses and ages, simultaneously constructing an interpenetrating organic polymer network, and forming a robust "rigid-flexible" bicontinuous network structure with the nano-silica powder. This structure effectively disperses stress, greatly improving the mechanical strength and toughness of the composite aerogel, overcoming the brittleness defects of traditional SiO2 aerogels.

[0024] This invention abandons the traditional high-cost, high-risk supercritical drying technology and innovatively adopts an atmospheric pressure gradient drying process. By precisely controlling the humidity during the drying process, the capillary force during solvent evaporation is significantly reduced, successfully avoiding the collapse of the pore structure and realizing the low-cost preparation of high-performance aerogel materials.

[0025] This invention introduces coating technology (such as slot coating) into the preparation of aerogel membranes, which can form films continuously on flexible substrates and has good compatibility with existing roll-to-roll production processes, laying a solid foundation for the large-scale, high-efficiency, and continuous industrial production of aerogel membranes.

[0026] The resulting composite aerogel membrane material possesses both the excellent flexibility and high thermal stability of polyimide and the low thermal conductivity of silicon oxide. It exhibits high porosity, uniform pore size distribution, and low thermal shrinkage (e.g., less than 3% thermal shrinkage after 1 hour at 300°C), making it particularly suitable for lithium-ion battery separators, high-temperature insulation, and flexible electronics applications where safety and stability requirements are extremely high.

[0027] In some embodiments of the present invention, the polyamic acid solution is obtained in the following manner: Aromatic dianhydride and aromatic diamine are dissolved in an organic solvent, and acrylamide monomer is added under nitrogen atmosphere to react and obtain polyamic acid solution.

[0028] In this embodiment, a polyamic acid solution can be obtained by preliminary polymerization of aromatic dianhydride, aromatic diamine and acrylamide monomer, which facilitates subsequent chemical imidization treatment to obtain an interpenetrating network structure.

[0029] In some embodiments of the present invention, the gelation treatment includes: Gel at 30~50℃ for 1~2 hours.

[0030] In this embodiment, gelation at 30~50℃ for 1~2 hours is sufficient for complete gelation.

[0031] In some embodiments of the present invention, the chemical imidization treatment includes: The temperature is controlled within a gradient increase of 50~80℃ and 100~150℃ respectively, and the holding time in each temperature zone is 1~2 hours.

[0032] In some embodiments of the present invention, the atmospheric pressure gradient drying includes the following steps: Treat at 20~30℃ for 0.5~1h, at 50~60℃ for 0.5~1h, and at 90~110℃ for 2~3h, with humidity maintained at 30~40% during the drying process.

[0033] In this embodiment, atmospheric pressure gradient drying can better control humidity while drying rapidly, thus obtaining a gel membrane with a superior structure.

[0034] In some embodiments of the present invention, the aromatic dianhydride is selected from at least one of pyromellitic dianhydride, biphenyl dianhydride, and 3,3',4,4'-benzophenone tetracarboxylic dianhydride; The aromatic diamine is selected from at least one of p-phenylenediamine, 4,4'-diaminodiphenyl ether, and 3,4'-diaminodiphenyl ether; The molar ratio of the dianhydride to the diamine is 1:(0.8~1.2), the mass of the acrylamide is 5% of the total mass of the dianhydride and the diamine, and the mass ratio of the crosslinking agent to the acrylamide is 1:10.

[0035] In some embodiments of the present invention, the flexible substrate is a polyethylene terephthalate film, a polyimide film, or a metal foil with a silane-treated surface, and the coating method is slot extrusion coating or blade coating.

[0036] In some embodiments of the present invention, the particle size of the nano-silica powder is 20~50nm.

[0037] In some embodiments of the present invention, the dehydrating agent is acetic anhydride, and the catalyst is at least one of pyridine and triethylamine; The organic solvent is N-methylpyrrolidone, and the crosslinking agent is N,N'-methylenebisacrylamide.

[0038] This invention provides a polyimide-silica composite aerogel material, prepared according to any of the above preparation methods.

[0039] To more clearly illustrate the technical solution and advantages of the present invention, several embodiments are described in detail below.

[0040] Example 1 S1. In a dry, N2-protected reactor, 4,4'-diaminodiphenyl ether was added to N-methylpyrrolidone and completely dissolved. Then, equimolar amounts of pyromellitic dianhydride were added in batches, and the mixture was stirred at room temperature for 6 hours to obtain a viscous polyamic acid solution. Subsequently, 5% (by mass) of acrylamide monomer (based on the total mass of dianhydride and diamine) was added, and the mixture was stirred for 0.5 hours. Next, nano-SiO2 powder with an average particle size of 30 nm (50% of the solid mass of polyamic acid PAA) and N,N'-methylenebisacrylamide crosslinking agent (at a mass ratio of 1:10 to acrylamide AM) were added, and the mixture was dispersed by high-speed stirring for 4 hours to obtain a uniform and stable polyamic acid-silica composite sol.

[0041] S2. The composite sol is transferred to the feed trough of a slot extrusion coating machine and continuously and uniformly coated onto a polyethylene terephthalate carrier film using a coating die with a width of 200 μm. Subsequently, the coated film is transferred to a drying tunnel at 40°C and allowed to gel for 1.5 hours to form a polyamic acid-silica composite gel wet film.

[0042] S3. The PET substrate with the wet gel film is passed through a chemical imidization channel, which is divided into two temperature zones. First, in the 60°C zone, a mixed solution of acetic anhydride and pyridine (volume ratio 2:1) is sprayed for dehydration catalysis and held for 2 hours; then, in the 130°C zone, it is held for 1 hour to complete chemical imidization and network aging.

[0043] S4. The imidized gel film is peeled off from the PET substrate and placed in a humidity-controlled drying oven. It is then dried at 25°C (35% humidity), 55°C (35% humidity), and 100°C (35% humidity) for 1 hour, 1 hour, and 2.5 hours, respectively, to obtain a polyimide-silica composite aerogel membrane material with a thickness of approximately 50 μm.

[0044] Figure 1 The image shows a low-magnification SEM image of the cross-sectional morphology of the polyimide-silica composite aerogel membrane material prepared in Example 1. The overall grayscale contrast is uniform and there is no obvious phase interface, indicating that polyimide and silica have achieved good uniform dispersion at the microscale.

[0045] Figure 2 The image shows a high-magnification SEM image of the cross-sectional morphology of the polyimide-silica composite aerogel membrane material prepared in Example 1. As can be seen from the image, AM and MBAM crosslinking agents simultaneously construct an interpenetrating organic polymer network during the formation of polyimide, and form a strong "rigid-flexible" bicontinuous network structure with nano-SiO2 particles, which effectively inhibits pore collapse during the normal pressure drying process and improves the mechanical properties of the aerogel membrane.

[0046] Figures 3 to 7 The image shows the EDS spectrum of the polyimide-silica composite aerogel membrane material prepared in Example 1. It can be seen that C, O, Si and other elements are uniformly distributed without local element aggregation, which verifies that the polyimide and nano-silica are uniformly distributed inside the composite aerogel material.

[0047] Example 2 It is basically the same as Example 1, except that: In step S1, the aromatic dianhydride is biphenyltetracarboxylic dianhydride, and the aromatic diamine is p-phenylenediamine. The average particle size of the nano-SiO2 powder is 20 nm.

[0048] In step S3, the temperatures of the two temperature zones for chemical imidization are set to 80°C and 160°C, and the residence time in each temperature zone is 1.5 hours.

[0049] Example 3 It is basically the same as Example 1, except that: In step S2, the flexible substrate is a copper foil with an aminosilane-treated surface.

[0050] In step S4, the atmospheric pressure gradient drying process is as follows: drying at 30℃ (40% humidity) for 0.5 hours, drying at 60℃ (40% humidity) for 0.5 hours, and drying at 110℃ for 2 hours (40% humidity).

[0051] Comparative Example 1 Comparative Example 1 is basically the same as Example 1, except that in step S3, the temperature is kept at 100°C for 2 hours.

[0052] The resulting polyimide-silica composite aerogel membrane material exhibited uneven pore size distribution and localized collapse. This was mainly attributed to insufficient replacement of the N-methylpyrrolidone solvent in the composite gel system during the chemical imidization process. Subsequently, during the deep imidization process, the residual N-methylpyrrolidone solvent caused the membrane to remain in a swollen state, resulting in excessive shrinkage and stress concentration.

[0053] Comparative Example 2 Comparative Example 2 is basically the same as Example 1, except that in step S4, the humidity in each stage of the atmospheric pressure gradient drying process is 25%.

[0054] When the humidity is at 25% during the gradient atmospheric pressure drying stage, the surface of the polyimide-silica composite aerogel membrane material will form a skin too quickly. The dense "hard shell" will rapidly form on the surface of the film, which will hinder the escape of the internal solvent and reaction byproducts. This will cause bubbles, voids or delamination to form inside the aerogel, resulting in uneven pore size distribution inside the aerogel membrane material and a significant reduction in heat resistance and mechanical properties.

[0055] Comparative Example 3 Comparative Example 3 is basically the same as Example 1, except that in step S4, the humidity at each stage of the atmospheric pressure gradient drying process is 50%.

[0056] When the humidity is 50% during the gradient atmospheric pressure drying stage, the capillary force inside the polyimide-silica composite aerogel membrane material is prone to increase sharply, leading to pore collapse. In addition, high humidity can easily cause hydrolysis of the polyimide-silica composite aerogel membrane, weakening the skeleton structure and ultimately affecting the mechanical strength and stiffness of the aerogel material.

[0057] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A method for preparing a polyimide-silica composite aerogel material, characterized in that, include: Nano-silica powder and a crosslinking agent were added to a polyamic acid solution to carry out a crosslinking reaction, resulting in a polyamic acid-silica composite sol. The polyamic acid is uniformly coated on the surface of a flexible substrate and then gelled to obtain a polyamic acid-silica composite gel wet film. The polyamic acid-silica composite gel wet film, dehydrating agent and catalyst are mixed and chemically imidized to obtain polyamic acid-silica composite gel film. The polyamic acid-silica composite gel membrane was subjected to atmospheric pressure gradient drying to obtain a polyamic acid-silica composite gel membrane material.

2. The preparation method according to claim 1, characterized in that, The polyamic acid solution is obtained in the following manner: Aromatic dianhydride and aromatic diamine are dissolved in an organic solvent, and acrylamide monomer is added under nitrogen atmosphere to react and obtain polyamic acid solution.

3. The preparation method according to claim 1, characterized in that, The gelation treatment includes: Gel at 30~50℃ for 1~2 hours.

4. The preparation method according to claim 1, characterized in that, The chemical imidization treatment includes: The temperature is controlled within a gradient increase of 50~80℃ and 100~150℃ respectively, and the holding time in each temperature zone is 1~2 hours.

5. The preparation method according to claim 1, characterized in that, The atmospheric pressure gradient drying includes the following steps: Treat at 20~30℃ for 0.5~1h, at 50~60℃ for 0.5~1h, and at 90~110℃ for 2~3h, with humidity maintained at 30~40% during the drying process.

6. The preparation method according to claim 2, characterized in that, The aromatic dianhydride is selected from at least one of pyromellitic dianhydride, biphenyl dianhydride, and 3,3',4,4'-benzophenone tetracarboxylic dianhydride. The aromatic diamine is selected from at least one of p-phenylenediamine, 4,4'-diaminodiphenyl ether, and 3,4'-diaminodiphenyl ether; The molar ratio of the dianhydride to the diamine is 1:(0.8~1.2), the mass of the acrylamide is 5% of the total mass of the dianhydride and the diamine, and the mass ratio of the crosslinking agent to the acrylamide is 1:

10.

7. The preparation method according to claim 2, characterized in that, The flexible substrate is a polyethylene terephthalate film, a polyimide film, or a metal foil with a silane-treated surface, and the coating method is slot extrusion coating or blade coating.

8. The preparation method according to claim 1, characterized in that, The particle size of the nano-silica powder is 20~50nm.

9. The preparation method according to claim 1, characterized in that, The dehydrating agent is acetic anhydride, and the catalyst is at least one of pyridine and triethylamine; The organic solvent is N-methylpyrrolidone, and the crosslinking agent is N,N'-methylenebisacrylamide.

10. A polyimide-silica composite aerogel material, characterized in that, It is prepared by any of the preparation methods according to claims 1-9.

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