A method for preparing a polyimide / silica composite aerogel based on a water-based emulsion method
Polyimide/silica composite aerogels were prepared by an aqueous emulsion method. By utilizing polyamic acid molecules and hydroxyethyl cellulose to regulate viscosity and achieve high shear dispersion, the problem of uneven dispersion in the aqueous solution system of the composite aerogel was solved, and high-performance polyimide/silica composite aerogels were prepared.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- HARBIN INST OF TECH
- Filing Date
- 2026-04-21
- Publication Date
- 2026-06-09
AI Technical Summary
In existing composite aerogel aqueous solution systems, hydrophilic aerogels are easily wetted by the aqueous phase, which destroys their pore structure. Low-density particles tend to settle, making it difficult to achieve stable dispersion and affecting thermal insulation performance and processability.
A water-based emulsion method was used to utilize the amphiphilic characteristics of polyamic acid molecules and the viscosity control of hydroxyethyl cellulose, combined with high shear force to disperse hydrophobic silica aerogel powder, to form a stable polyamic acid/hydrophobic silica aerogel slurry, which was then freeze-molded and heat-treated to prepare a composite aerogel.
It achieves stable dispersion of aerogel particles, inhibits drying shrinkage, improves thermal insulation and flame retardant properties, and exhibits excellent material structural stability and mechanical properties.
Smart Images
Figure CN122167816A_ABST
Abstract
Description
Technical Field
[0001] This invention relates to a method for preparing polyimide / silica composite aerogels. Background Technology
[0002] Aerogel materials, due to their low density, high porosity, and excellent thermal insulation properties, have broad application prospects in aerospace, thermal protection, and energy conservation. Among them, silica aerogels have extremely low thermal conductivity, but their inherent brittleness and poor mechanical properties limit their application in complex environments. In contrast, polyimide aerogels combine good flexibility and high-temperature resistance, becoming an important research direction in organic aerogels in recent years. However, polyimide aerogels often suffer from significant imidization shrinkage and easy collapse of the pore structure during preparation, thus affecting their thermal insulation performance and structural stability. To improve these problems, existing technologies typically introduce inorganic fillers (such as silica particles or aerogel powder) to construct organic-inorganic composite aerogel systems, aiming to achieve synergistic performance. However, this approach still has the following shortcomings: on the one hand, fillers are prone to agglomeration or sedimentation in precursor solutions, making uniform dispersion difficult; on the other hand, when the filler content is high, the system viscosity increases significantly, leading to difficulties in molding and processing, making it difficult to balance dispersion stability and processability. In addition, due to insufficient interfacial compatibility, composite materials often suffer from problems such as uneven structure or particle shedding, which affect the final performance.
[0003] Existing research often employs organic solvent systems or high-viscosity systems to improve filler dispersion. However, these methods typically suffer from high environmental impact, complex processes, or limitations in large-scale applications. In contrast, aqueous solutions offer advantages such as being environmentally friendly, cost-effective, and easy to process. However, in these systems, due to the lower viscosity, filler particles, especially low-density aerogel microspheres, are more prone to sedimentation or aggregation, making it difficult to achieve stable dispersion at high concentrations. Furthermore, effective methods for controlling the dispersion state and subsequent structure formation while ensuring system flowability and processability remain lacking. Therefore, there is an urgent need to develop a method for preparing composite aerogels suitable for aqueous systems, ensuring good processability while achieving stable dispersion and structural control of aerogel particles. This would suppress the drying shrinkage of polyimide aerogels and improve the material's thermal insulation and flame-retardant properties. Summary of the Invention
[0004] The present invention aims to address the technical problems in current composite aerogel aqueous solution systems, where hydrophilic aerogels are easily wetted by the aqueous phase during dispersion, causing the solution to easily enter the pores, destroy the internal pore structure, and weaken the thermal insulation performance. At the same time, low-density particles are prone to sedimentation in low-viscosity systems, making it difficult to achieve stable dispersion. The present invention provides a method for preparing polyimide / silica composite aerogels based on an aqueous emulsion method.
[0005] The method for preparing polyimide / silica composite aerogel based on the water-based emulsion method of the present invention is carried out according to the following steps:
[0006] I. Preparation of polyamic acid solution:
[0007] Polyamic acid, triethylamine and deionized water were mixed evenly, and then hydroxyethyl cellulose was added. The viscosity was adjusted by stirring under water bath conditions to obtain a polyamic acid aqueous solution with a viscosity of more than 1000 mPa·s.
[0008] II. Preparation of polyamic acid / silica aerogel powder emulsion:
[0009] Under mechanical stirring, hydrophobic silica aerogel powder was added to the polyamic acid aqueous solution prepared in step one in 4 to 20 portions, with the same amount added each time. During the entire process of adding hydrophobic silica aerogel powder, the stirring speed was gradually increased from 180 rpm to 200 rpm to 1800 rpm to 2000 rpm. The high shear force dispersed the hydrophobic silica aerogel powder into the polyamic acid solution to form an emulsion. After all the hydrophobic silica aerogel powder was added, stirring was continued for another 5 to 10 minutes to obtain a viscous, homogeneous and stable polyamic acid / hydrophobic silica aerogel slurry.
[0010] III. Preparation of PI / silica composite aerogel:
[0011] The polyamic acid / hydrophobic silica aerogel slurry obtained in step two is sequentially subjected to freeze molding, freeze drying and heat treatment to obtain PI / silica aerogel composite aerogel.
[0012] This invention addresses the problems existing in the preparation of composite aerogels by proposing a method for constructing composite aerogels based on a polyamic acid (PAA) aqueous solution system. Utilizing the amphiphilic nature of PAA molecules, which possess both hydrophilic and hydrophobic groups, and combining viscosity control and shear dispersion strategies, this method achieves stable suspension and uniform dispersion of hydrophobic aerogel particles in an aqueous system, preventing the aerogel's pore structure from being disrupted by the aqueous phase. Inspired by the construction process of emulsion systems, this invention leverages the characteristic of polyamic acid (PAA) molecules containing both hydrophilic and hydrophobic groups. Hydroxyethyl cellulose is introduced into the PAA aqueous solution system to control the viscosity, achieving a solution viscosity of over 1000 mPa·s. Based on this, hydrophobic silica aerogel powder is introduced into the solution in small, multiple batches under high-speed shear conditions. Due to the synergistic effect of the amphiphilic structure of PAA molecules and the appropriate system viscosity, it can effectively promote the wetting and dispersion of aerogel particles in the aqueous phase, thereby forming a uniform and stable composite slurry. After the slurry is freeze-molded, freeze-dried and thermal imidized, a structurally stable polyimide / silica aerogel microsphere composite aerogel material is obtained, which has a low shrinkage rate and excellent heat insulation and flame retardant properties. Attached Figure Description
[0013] Figure 1 This is a comparison diagram of the dispersion of silica aerogel powder in polyamic acid and in water in Experiment 1.
[0014] Figure 2 An optical microscope image of the polyamic acid / hydrophobic silica aerogel slurry prepared in step two of Experiment 1;
[0015] Figure 3 SEM image of the PI / silica aerogel powder composite aerogel prepared in Experiment 1;
[0016] Figure 4 A magnified SEM image of a portion of the PI / silica aerogel powder composite aerogel prepared in Experiment 1;
[0017] Figure 5 The graph shows the shrinkage test data of the aerogels prepared in Experiments 1 to 5;
[0018] Figure 6 The graph shows the mechanical properties of the composite aerogel.
[0019] Figure 7 This is a comparison chart of flame retardant tests. Detailed Implementation
[0020] Specific Implementation Method 1: This implementation method is a method for preparing polyimide / silica composite aerogel based on a water-based emulsion method, specifically carried out according to the following steps:
[0021] I. Preparation of polyamic acid solution:
[0022] Polyamic acid, triethylamine and deionized water were mixed evenly, and then hydroxyethyl cellulose was added. The viscosity was adjusted by stirring under water bath conditions to obtain a polyamic acid aqueous solution with a viscosity of more than 1000 mPa·s.
[0023] II. Preparation of polyamic acid / silica aerogel powder emulsion:
[0024] Under mechanical stirring, hydrophobic silica aerogel powder was added to the polyamic acid aqueous solution prepared in step one in 4 to 20 portions, with the same amount added each time. During the entire process of adding hydrophobic silica aerogel powder, the stirring speed was gradually increased from 180 rpm to 200 rpm to 1800 rpm to 2000 rpm. The high shear force dispersed the hydrophobic silica aerogel powder into the polyamic acid solution to form an emulsion. After all the hydrophobic silica aerogel powder was added, stirring was continued for another 5 to 10 minutes to obtain a viscous, homogeneous and stable polyamic acid / hydrophobic silica aerogel slurry.
[0025] III. Preparation of PI / silica composite aerogel:
[0026] The polyamic acid / hydrophobic silica aerogel slurry obtained in step two is sequentially subjected to freeze molding, freeze drying and heat treatment to obtain PI / silica aerogel composite aerogel.
[0027] Specific Implementation Method Two: This implementation method differs from Specific Implementation Method One in that the mass of the polyamic acid mentioned in step one is twice the mass of triethylamine. Everything else is the same as in Specific Implementation Method One.
[0028] Specific Implementation Method 3: This implementation method differs from Specific Implementation Method 1 or 2 in that the mass of the polyamic acid mentioned in step 1 is 6% to 10% of the mass of deionized water. Everything else is the same as in Specific Implementation Method 1 or 2.
[0029] Specific Implementation Method Four: This implementation method differs from Specific Implementation Methods One to Three in that the mass of hydroxyethyl cellulose mentioned in step one is 0.1% to 1% of the sum of the masses of polyamic acid, triethylamine, and deionized water. Everything else is the same as in Specific Implementation Methods One to Three.
[0030] Specific Implementation Method Five: This implementation method differs from Specific Implementation Method Four in that the water bath temperature in step one is 50°C. Everything else is the same as in Specific Implementation Method Four.
[0031] Specific Implementation Method Six: This implementation method differs from Specific Implementation Method Five in that the stirring time in step one is 0.5 hours. Everything else is the same as in Specific Implementation Method Five.
[0032] Specific Implementation Method Seven: This implementation method differs from Specific Implementation Method Six in that the average particle size of the hydrophobic silica aerogel powder described in step two is 15 μm. Everything else is the same as in Specific Implementation Method Six.
[0033] Specific Implementation Method Eight: This implementation method differs from Specific Implementation Method Seven in that the mass of the hydrophobic silica aerogel powder mentioned in step two is 25% to 100% of the mass of the polyamic acid mentioned in step one. Everything else is the same as in Specific Implementation Method Seven.
[0034] Specific Implementation Method Nine: This implementation method differs from Specific Implementation Method Eight in that: the freeze-forming in step three is directional freeze-forming; and the freeze-drying time in step three is 24h~72h. Everything else is the same as in Specific Implementation Method Eight.
[0035] Specific Implementation Method Ten: This implementation method differs from Specific Implementation Method Nine in that the heat treatment process described in step three is as follows: The material is placed in a muffle furnace for heat treatment. First, the temperature is increased to 100°C at a rate of 5°C / min and held for 1 hour. Then, the temperature is increased to 200°C at a rate of 5°C / min and held for 1 hour. Next, the temperature is increased to 300°C at a rate of 2°C / min and held for 1 hour. Finally, the temperature is decreased to 30°C at a rate of 5°C / min to obtain a PI / silica aerogel powder composite aerogel. Everything else is the same as in Specific Implementation Method Nine.
[0036] The invention was verified using the following experiments:
[0037] Experiment 1: This experiment demonstrates a method for preparing polyimide / silica composite aerogels based on a water-based emulsion method, specifically carried out according to the following steps:
[0038] I. Preparation of polyamic acid solution:
[0039] Polyamic acid, triethylamine and deionized water were mixed evenly, and then hydroxyethyl cellulose was added. The mixture was stirred in a water bath at 50°C for 0.5 h to adjust the viscosity, resulting in a polyamic acid aqueous solution with a viscosity of over 1000 mPa·s.
[0040] The polyamic acid mentioned is a commercially available product, and the precursors are pyromellitic anhydride and 4,4-diaminodiphenyl ether, with a molecular weight of 150,000 da.
[0041] The mass of the polyamic acid is twice the mass of triethylamine, and the mass of the polyamic acid is 8% of the mass of deionized water.
[0042] The mass of the hydroxyethyl cellulose is 0.5% of the sum of the masses of polyamic acid, triethylamine, and deionized water.
[0043] II. Preparation of polyamic acid / silica aerogel powder emulsion:
[0044] Under mechanical stirring, hydrophobic silica aerogel powder was added to the polyamic acid aqueous solution prepared in step one in 10 portions, with the same amount added each time. During the entire process of adding hydrophobic silica aerogel powder, the stirring speed was gradually increased from 180 rpm to 200 rpm to 1800 rpm to 2000 rpm. The high shear force dispersed the hydrophobic silica aerogel powder into the polyamic acid solution to form an emulsion. After all the hydrophobic silica aerogel powder was added, stirring was continued for another 5 min to 10 min to obtain a viscous, uniform and stable polyamic acid / hydrophobic silica aerogel slurry.
[0045] The average particle size of the hydrophobic silica aerogel powder is 15 μm; the mass of the hydrophobic silica aerogel powder is 75% of the mass of the polyamic acid mentioned in step one.
[0046] III. Preparation of PI / silica composite aerogel:
[0047] The polyamic acid / hydrophobic silica aerogel powder slurry obtained in step two was cast into a green embryo by directional freezing. The green embryo was placed in a freeze dryer and dried for 50 hours. After that, the green embryo was taken out and placed in a muffle furnace for heat treatment. First, the temperature was increased to 100℃ at 5℃ / min and held for 1 hour, then increased to 200℃ at 5℃ / min and held for 1 hour, then increased to 300℃ at 2℃ / min and held for 1 hour, and then decreased to 30℃ at 5℃ / min to obtain the PI / silica aerogel powder composite aerogel, denoted as P8S6.
[0048] Figure 1 This is a comparison diagram of the dispersion of silica aerogel powder in polyamic acid emulsion and in water. The bottle on the left is the polyamic acid / hydrophobic silica aerogel powder slurry prepared in step two of Experiment 1. The bottle on the right is the result of dispersing the same hydrophobic silica aerogel powder in water. The comparison shows that the method of the present invention can stably disperse silica hydrophobic aerogel in the aqueous phase, while silica hydrophobic aerogel cannot be dispersed in water.
[0049] Figure 2 The image shows an optical microscope photograph of the polyamic acid / hydrophobic silica aerogel powder slurry prepared in step two of Experiment 1. As can be seen from the image, the slurry prepared by the method of the present invention is uniform and stable, and can meet various needs to achieve 3D printing.
[0050] Figure 3 The image shows a SEM image of the PI / silica aerogel composite aerogel prepared for Experiment 1. It can be seen that a microstructure of continuous PI structure encapsulating hydrophobic aerogel particles is formed in the aerogel.
[0051] Figure 4The image shows a magnified SEM image of the PI / silica aerogel composite aerogel prepared in Experiment 1. It can be seen that PI encapsulates silica aerogel particles. The prepared composite aerogel exhibits significantly less shrinkage than the PI aerogel.
[0052] Experiment 2: This experiment differs from Experiment 1 in that the mass of the hydrophobic silica aerogel powder mentioned in step 2 is 25% of the mass of the polyamic acid mentioned in step 1; the final PI / silica aerogel composite aerogel is denoted as P8S2. Everything else is the same as Experiment 1.
[0053] Experiment 3: This experiment differs from Experiment 1 in that the mass of the hydrophobic silica aerogel powder mentioned in step 2 is 50% of the mass of the polyamic acid mentioned in step 1; the final PI / silica aerogel composite aerogel is denoted as P8S4. Everything else is the same as Experiment 1.
[0054] Experiment 4: This experiment differs from Experiment 1 in that the mass of the hydrophobic silica aerogel powder mentioned in step 2 is 100% of the mass of the polyamic acid mentioned in step 1; the final PI / silica aerogel composite aerogel is denoted as P8S8. Everything else is the same as Experiment 1.
[0055] Experiment 5: This experiment differs from Experiment 1 in that hydrophobic silica aerogel powder is not added in step two, and the final PI aerogel is recorded as 8% PI. Everything else is the same as Experiment 1.
[0056] Figure 5 The graph shows the shrinkage test data of the aerogels prepared in experiments one through five. It can be seen that the shrinkage of the composite aerogel obtained by the method of the present invention is significantly less than that of the PI aerogel without hydrophobic silica aerogel.
[0057] The thermal conductivity of the P8S6 composite aerogel prepared in Experiment 1 was 0.05 W / m·K, while the thermal conductivity of the 8% PI aerogel prepared in Experiment 5 was 0.063 W / m·K. Therefore, the thermal conductivity of the PI / silica aerogel powder composite aerogel obtained by the method of this invention is significantly lower than that of PI aerogel with the same solid content.
[0058] The P8S6 composite aerogel prepared in Experiment 1 was weighed and showed to be 1.01 g (e.g., ...). Figure 6 (as shown in the left image), 1 kg of water can be placed on top of it (e.g. Figure 6 (As shown in the right figure), it can withstand a load of more than a thousand times its own weight, overcoming the brittleness of inorganic aerogels, and the aerogel has excellent mechanical properties.
[0059] The P8S6 composite aerogel prepared in Experiment 1 and PU were compared in flame retardancy tests, such as... Figure 7 As shown, the P8S6 composite aerogel prepared in Experiment 1 still does not ignite after 15 seconds of ignition, demonstrating its extremely strong flame retardant ability.
Claims
1. A method for preparing polyimide / silica composite aerogels based on a water-based emulsion method, characterized in that... The method is performed according to the following steps: I. Preparation of polyamic acid solution: Polyamic acid, triethylamine and deionized water were mixed evenly, and then hydroxyethyl cellulose was added. The viscosity was adjusted by stirring under water bath conditions to obtain a polyamic acid aqueous solution with a viscosity of more than 1000 mPa·s. II. Preparation of polyamic acid / silica aerogel powder emulsion: Under mechanical stirring, hydrophobic silica aerogel powder was added to the polyamic acid aqueous solution prepared in step one in 4 to 20 portions, with the same amount added each time. During the entire process of adding hydrophobic silica aerogel powder, the stirring speed was gradually increased from 180 rpm to 200 rpm to 1800 rpm to 2000 rpm. The high shear force dispersed the hydrophobic silica aerogel powder into the polyamic acid solution to form an emulsion. After all the hydrophobic silica aerogel powder was added, stirring was continued for another 5 to 10 minutes to obtain a viscous, homogeneous and stable polyamic acid / hydrophobic silica aerogel slurry. III. Preparation of PI / silica composite aerogel: The polyamic acid / hydrophobic silica aerogel slurry obtained in step two is sequentially subjected to freeze molding, freeze drying and heat treatment to obtain PI / silica aerogel composite aerogel.
2. The method for preparing polyimide / silica composite aerogel based on water-based emulsion method according to claim 1, characterized in that... The mass of the polyamic acid mentioned in step one is twice the mass of the triethylamine.
3. The method for preparing polyimide / silica composite aerogel based on water-based emulsion method according to claim 2, characterized in that... The mass of the polyamic acid mentioned in step one is 6% to 10% of the mass of deionized water.
4. The method for preparing polyimide / silica composite aerogel based on water-based emulsion method according to claim 3, characterized in that... The mass of the hydroxyethyl cellulose mentioned in step one is 0.1% to 1% of the sum of the masses of polyamic acid, triethylamine, and deionized water.
5. The method for preparing polyimide / silica composite aerogel based on water-based emulsion method according to claim 1, characterized in that... The water bath temperature in step one is 50℃.
6. The method for preparing polyimide / silica composite aerogel based on water-based emulsion method according to claim 5, characterized in that... The stirring time in step one is 0.5 hours.
7. The method for preparing polyimide / silica composite aerogel based on water-based emulsion method according to claim 1, characterized in that... The average particle size of the hydrophobic silica aerogel powder mentioned in step two is 15 μm.
8. The method for preparing polyimide / silica composite aerogel based on water-based emulsion method according to claim 1, characterized in that... The mass of the hydrophobic silica aerogel powder mentioned in step two is 25% to 100% of the mass of the polyamic acid mentioned in step one.
9. The method for preparing polyimide / silica composite aerogel based on water-based emulsion method according to claim 1, characterized in that... The freeze-forming process described in step three is directional freezing; the freeze-drying time described in step three is 24h~72h.
10. The method for preparing polyimide / silica composite aerogel based on water-based emulsion method according to claim 9, characterized in that... The heat treatment process described in step three is as follows: heat treatment is carried out in a muffle furnace. First, the temperature is increased to 100℃ at 5℃ / min and held for 1 hour. Then, the temperature is increased to 200℃ at 5℃ / min and held for 1 hour. Then, the temperature is increased to 300℃ at 2℃ / min and held for 1 hour. Finally, the temperature is decreased to 30℃ at 5℃ / min to obtain PI / silica aerogel powder composite aerogel.