High-dielectric polyamide microsphere and preparation method thereof
The method of preparing core-shell PA6@CNT dielectric microspheres by combining in-situ polymerization and phase separation solves the problem of poor dispersibility of powdered dielectric materials, and achieves improved dielectric performance and simplified process, making it suitable for high energy storage scenarios.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- FUJIAN UNIV OF TECH
- Filing Date
- 2025-12-29
- Publication Date
- 2026-04-28
AI Technical Summary
Existing technologies make it difficult to prepare powdered dielectric materials with uniform particle size and uniform dispersion of conductive fillers. Moreover, the preparation process is complex and costly, which makes it difficult to meet the needs of high energy storage scenarios.
A method combining in-situ polymerization and phase separation was adopted. The amide monomer and the polymer were melt-mixed under stirring, and a catalyst and activator were added to prepare core-shell dielectric microspheres. The microsphere structure formed during the polymerization of PA6 and PS was used to encapsulate CNT conductive filler to form PA6@CNT core-shell structure. Subsequently, the continuous phase PS was removed by solvent extraction to obtain pure PA6@CNT microspheres.
This technology enables efficient dispersion of CNTs, reduces dielectric loss, simplifies the process, lowers production costs, and facilitates composite with other materials, thereby expanding material properties and achieving multifunctionality.
Smart Images
Figure CN121930660A_ABST
Abstract
Description
Technical Field
[0001] This invention belongs to the field of polymer composite materials technology, specifically relating to a high dielectric polyamide microsphere and its preparation method. Background Technology
[0002] Dielectric materials are a class of functional materials that can generate polarization under the influence of an external electric field, store charge, but do not allow current to pass through. Their core characteristic lies in the storage and conversion of electrical energy through polarization response. From the perspective of material systems, dielectric materials are mainly divided into ceramic dielectrics, polymer dielectrics, and composite dielectrics combining both. Since most dielectric composite materials rely entirely on their own components to achieve their performance and cannot be controlled through composite manipulation, the improvement of dielectric performance is limited, making it difficult to meet the needs of high energy storage and other scenarios. Compared with the "uniform and untunable performance" of bulk dielectric materials (such as bulk ceramics) and the "narrow control range" of thin film materials (such as polymer films), powdered dielectric materials can utilize core-shell design for precise control of dielectric performance. By adjusting the composition and thickness ratio of the core and shell layers, or changing the core-shell particle size, a wide range of continuously adjustable dielectric constants from a few to thousands can be achieved. While improving the dielectric constant, leakage losses can be suppressed by leveraging the insulating properties of the polymer matrix, and it is also convenient to manufacture electronic components with complex shapes. It is also easy to combine with other materials. By combining with different polymer matrices, reinforcing materials or functional additives, its properties can be further expanded, and the material can be made multifunctional.
[0003] Therefore, there are still many bottlenecks in preparing powdered dielectric materials with uniform particle size and uniform dispersion of conductive fillers. Whether through suspension polymerization, emulsion polymerization, or spray drying, the powdered dielectric materials first need to form monodisperse droplets, followed by washing, drying, and collection. Both of these processes easily lead to agglomeration of the conductive fillers. This is because conductive fillers have a large specific surface area and extremely high surface energy, resulting in significant intermolecular van der Waals forces and π-π stacking interactions, making them prone to forming chain-like or cluster-like agglomerations within the polymer matrix. Furthermore, the sphericity and particle size distribution of the powder directly affect the dielectric response and processing flowability, but precise control during preparation is difficult to achieve.
[0004] To address the issue of poor dispersibility of conductive fillers in dielectric powders, researchers have proposed several new methods: Solid-state methods are relatively simple, requiring no complex solution preparation, but the resulting powders have large particle sizes and uneven composition, easily leading to fluctuations in dielectric constant. Furthermore, they require high sintering temperatures (>1200℃), resulting in high energy consumption and equipment requirements. Sol-gel methods are costly and complex. Molten salt methods use molten salt as a reaction medium to lower the activation energy of the raw material reaction, promote full ion diffusion, and reduce impurity phase formation. However, molten salt volatilization easily contaminates the furnace, and dielectric properties are generally low. Hydrothermal methods provide favorable conditions for ion diffusion in a hydrothermal environment (high-temperature, high-pressure aqueous solution) and allow for precise control of the crystal phase structure. However, the reaction is difficult to complete, and residual impurities cause a sharp drop in microwave dielectric properties. Microemulsion methods are prone to agglomeration and have complex processes, limiting large-scale applications. Emulsification methods do not require high-temperature sintering and can complete emulsification and solidification at room temperature or lower temperatures. However, imbalances in the oil-water phase ratio and insufficient emulsifier concentration can lead to distorted microsphere morphology, resulting in ellipsoidal or irregular blocky particles.
[0005] Driven by the concept of green chemistry, and in order to reduce the use of organic solvents and the complexity of processes, research on improving the dispersion of conductive fillers in dielectric powders has received widespread attention from scholars in recent years. Summary of the Invention
[0006] The purpose of this invention is to overcome the shortcomings and deficiencies of the prior art and to provide a high-dielectric polyamide microsphere and its preparation method.
[0007] To achieve the above objectives, the technical solution adopted by the present invention is as follows: A method for preparing high-dielectric polyamide microspheres includes the following steps: 1) Place the amide monomer in a three-necked flask and melt it by stirring at 75~85℃; 2) After complete melting, add the polymer and conductive filler, heat to 95~105℃, and stir continuously to accelerate melting while heating, so that the three raw materials are fully mixed; 3) After stirring for 1.5 to 1.8 hours, add the catalyst and fill the three-necked flask with an inert protective gas. Heat the mixture again to 180 to 200°C to remove the moisture in the system. Then add the activator, pour the mixture into a preheated iron container, and heat it in an oven to obtain the composite material. 4) The composite material was transferred to a Soxhlet extraction device containing tetrahydrofuran (THF) and heated in an oil bath at 80-90°C for 45-50 h to remove the polymer. After natural drying, high dielectric polyamide microspheres were obtained.
[0008] The amide monomer is at least one of caprolactam (CPL), butyrolactam, octyllactam, and dodecyllactam.
[0009] The polymers mentioned are polystyrene (PS), polyethylene glycol, polyvinylpyrrolidone, etc.
[0010] The conductive filler is carbon nanotube (CNT), BaTiO3, or ZnO.
[0011] The catalyst is an alkali metal hydride such as NaOH, NaH, or LiH, or an alkali metal hydroxide.
[0012] The activator is toluene diisocyanate.
[0013] The mass ratio of the amide monomer to the polymer is 3:1 to 9:1.
[0014] The amount of conductive filler used is 0.5-2% of the total mass of the amide monomer and the polymer.
[0015] The catalyst dosage is 0.8-1.2% of the total mass of the amide monomer and the polymer. The amount of activator used is 3.8 to 4.2% of the total mass of the amide monomer and the polymer.
[0016] The heating described in step 3) is performed in an oven at 150~170℃ for 15~18 minutes.
[0017] Taking CPL as the amide monomer, PS as the polymer, and CNT as the conductive filler as an example, this invention utilizes anionic ring-opening polymerization of polyamide to prepare a core-shell dielectric microsphere. The core is a CNT matrix, and the outer shell is PA6. Since the shell thickness is smaller than the charge diffusion layer thickness, the interfacial polarization intensity is linearly related to the CNT content, avoiding the polarization saturation and nonlinear loss growth caused by CNT agglomeration in conventional systems. Efficient dispersion of CNTs is achieved during in-situ polymerization, solving the problem of poor dispersion of conductive fillers in dielectric powders and reducing dielectric loss. Furthermore, the core-shell particle size and thickness can be controlled to prepare microsphere powders with different dielectric properties.
[0018] This invention employs a combination of in-situ polymerization and phase separation. During the polymerization of PA6 and PS, as the system temperature increases and the viscosity of the mixture changes, PA6 gradually undergoes cross-linking and solidification. Simultaneously, due to intermolecular forces and interfacial adsorption effects, CNTs dispersed in the system are uniformly encapsulated internally, forming a "PA6-encapsulated CNT" core-shell structure. After the polymerization reaction is complete, the continuous PS phase in the system is removed through specific solvent extraction or heat treatment processes to obtain pure PA6@CNT dielectric microspheres. This unique microsphere structure not only effectively isolates CNTs and prevents aggregation, but the core-shell structure also endows the microspheres with good geometric regularity and surface compatibility, enabling them to overcome interfacial repulsion and achieve a more uniform spatial distribution when subsequently compounded with matrix materials.
[0019] This invention utilizes the dispersed phase with a microsphere structure formed during the polymerization of amides to achieve the encapsulation and dispersion of conductive fillers, thus preparing dielectric microspheres. This process requires no modification treatment or dispersants, greatly simplifying the process flow, reducing production costs, and making it easier to achieve large-scale mass production. Furthermore, the microspheres are easy to combine with other materials. By combining them with different polymer matrices, reinforcing materials, or functional additives, their properties can be further expanded, realizing the multifunctionality of the materials. Attached Figure Description
[0020] Figure 1 This is a schematic diagram of the preparation process of PA6@CNT microspheres described in Examples 1, 2, and 3.
[0021] Figure 2 Here are SEM images: (A) Composite material of Example 2; (B) Microspheres of Example 2; (C) Composite material of Comparative Example 1; (D) Microspheres of Comparative Example 1.
[0022] Figure 3 These are XRD images of the microspheres prepared in Examples 1, 2, and 3.
[0023] Figure 4 The images show (A) of the CPPC composite material and tetrahydrofuran dispersion, and (B) of the TEM image of the CPPC composite material.
[0024] Figure 5 The dielectric properties of the CPPC composite materials prepared in Examples 1, 2, and 3 are as follows: (A) dielectric constant; (B) dielectric loss.
[0025] Figure 6 This is a graph showing the dielectric properties of PA6@CNT coated PS.
[0026] Figure 7 This is a schematic diagram of PA6@CNT filled PVDF.
[0027] Figure 8This is a comparison of the dielectric properties of PA6@CNT filled PVDF before and after foaming. Detailed Implementation Example 1
[0028] Preparation of PA6@CNT dielectric microspheres Weigh the two matrix materials, caprolactam (CPL) and polystyrene (PS), at a mass ratio of 75:25.
[0029] Weigh out 0.5% of the total mass of the two matrices of conductive filler CNT.
[0030] Weigh out 1% of the total mass of the two matrices of the catalyst sodium hydroxide (NaOH).
[0031] Weigh out 4% of the total mass of the two matrices as the activator toluene diisocyanate (TDI).
[0032] First, CPL was placed in a three-necked flask and melted by stirring and heating at 80°C. After complete melting, PS and CNT were added separately, and the temperature was raised to 100°C while continuously stirring to accelerate melting and ensure thorough mixing of the three components. After stirring for about 1.5 h, sodium hydroxide (NaOH) was added as a catalyst, and nitrogen (N2) was introduced into the three-necked flask as an inert protective gas. The temperature was raised again to 190°C and maintained for about 0.5 h to remove moisture from the system. Then, toluene diisocyanate (TDI) was added as an activator, poured into a preheated iron container, and placed in a 160°C oven. After 15 min, the container was removed, and the resulting PA6@CNT / PS (CPPC) composite material was loaded into a Soxhlet extraction apparatus containing tetrahydrofuran (THF). After heating in an oil bath at 85°C for 48 h, PS was removed, and the product was naturally dried to obtain PA6@CNT microspheres. Example 2
[0033] Preparation of PA6@CNT dielectric microspheres Weigh the two matrix materials, caprolactam (CPL) and polystyrene (PS), at a mass ratio of 75:25.
[0034] The CNT content of the conductive filler is 1% of the total mass of the two matrices.
[0035] The remaining steps are as described in Example 1. Example 3
[0036] Preparation of PA6@CNT dielectric microspheres Weigh the two matrix materials, caprolactam (CPL) and polystyrene (PS), at a mass ratio of 75:25.
[0037] The CNT content of the conductive filler is 2% of the total mass of the two matrices.
[0038] The remaining steps are as described in Example 1. Example 4
[0039] Preparation of PA6@CNT dielectric microspheres Weigh the two matrix materials, caprolactam (CPL) and polystyrene (PS), at a mass ratio of 80:20.
[0040] The CNT content of the conductive filler is 0.5% of the total mass of the two matrices.
[0041] The remaining steps are as described in Example 1. Example 5
[0042] Preparation of PA12@CNT dielectric microspheres Weigh out the two matrix materials, dodecyl lactam and polystyrene (PS), in a mass ratio of 75:25.
[0043] The CNT content of the conductive filler is 0.5% of the total mass of the two matrices.
[0044] The remaining steps are as described in Example 1. Example 6
[0045] Preparation of PA6@CNT dielectric microspheres Weigh the two matrix materials, caprolactam (CPL) and polyethylene glycol (PEG), at a mass ratio of 75:25.
[0046] The CNT content of the conductive filler is 0.5% of the total mass of the two matrices.
[0047] The remaining steps are as described in Example 1. Example 7
[0048] Preparation of PA6@BaTiO3 dielectric microspheres Weigh the two matrix materials, caprolactam (CPL) and polystyrene (PS), at a mass ratio of 75:25.
[0049] The content of the conductive filler BaTiO3 is 0.5% of the total mass of the two matrices.
[0050] The remaining steps are as described in Example 1. Comparative Example 1
[0051] Preparation of PA6 microspheres Weigh the two matrix materials, caprolactam (CPL) and polystyrene (PS), at a mass ratio of 75:25.
[0052] Weigh out 1% of the total mass of the two matrices of the catalyst sodium hydroxide (NaOH).
[0053] Weigh out 4% of the total mass of the two matrices as the activator toluene diisocyanate (TDI).
[0054] First, CPL was placed in a three-necked flask and melted by stirring and heating at 80°C. After complete melting, PS was added, and the temperature was raised to 100°C while continuously stirring to accelerate melting and ensure thorough mixing of the two components. After stirring for about 1.5 h, sodium hydroxide (NaOH) was added as a catalyst, and nitrogen (N2) was introduced into the three-necked flask as an inert protective gas. The temperature was raised again to 190°C and maintained for about 0.5 h to remove moisture from the system. Then, toluene diisocyanate (TDI) was added as an activator, and the mixture was poured into a preheated iron container and placed in a 160°C oven. After 15 min, it was removed to obtain PA6 / PS composite material. The composite material was placed in a Soxhlet extraction apparatus containing tetrahydrofuran (THF) and heated in an oil bath at 85°C for 48 h to remove PS. After natural drying, PA6 microsphere powder was obtained.
[0055] like Figure 1 The diagram shows the preparation of PA6@CNT dielectric microspheres. PS and CNTs were added to molten CPL, and the mixture was continuously stirred at a high speed to accelerate melting and ensure thorough mixing of the three components. Then, sodium hydroxide (NaOH) was added, and nitrogen gas was introduced into a three-necked flask to remove moisture from the system. Toluene diisocyanate (TDI) was then added, and the mixture was poured into a preheated iron container and placed in an oven. The prepared composite material was then subjected to THF treatment to remove PS, yielding PA6@CNT microspheres.
[0056] like Figure 2 SEM images of the composite materials and corresponding microspheres prepared in Example 2 and Comparative Example 1 are shown. Figure A shows that the CPPC composite material prepared in Example 2 has a honeycomb structure. Due to the introduction of CNTs, its morphology is worse than that of the dispersed phase in Comparative Example 1 (Figure C), with the average particle size increasing from 8 μm to 40 μm. Figure B shows the PA6@CNT microspheres after PS removal. Compared with PA6 microspheres without CNTs (Figure D), the microsphere particle size is larger and the morphology is worse.
[0057] Figure 3 The XRD patterns of PA6@CNT microspheres and CNTs are shown in Figure A. In Figure A, CNTs exhibit a distinct diffraction peak around 2θ = 25°. However, in Figure B, the XRD pattern of PA6@CNT microspheres does not show a significant CNT diffraction peak, indicating the disappearance of the regular and periodic structure of CNTs. This suggests that CNTs exist in a disordered and loose form within the PA6 matrix. This also indirectly demonstrates the good compatibility between CNTs and PA6 and their good dispersion within the PA6 matrix. The crystal form of PA6 did not change significantly after the introduction of CNTs, indicating that the molecular chain arrangement of PA6 was not affected by CNTs. The PA6@CNT microspheres remain predominantly α-crystalline, and this α-crystalline form provides better mechanical properties and thermal stability to the PA6 material compared to the γ-crystalline form.
[0058] like Figure 4 As shown, to further investigate the dispersion of CNTs, we dissolved the CPPC composite material in THF solution to observe its dissolution phenomenon, such as... Figure 4 As shown in (A), after 48 hours, the upper layer is a colorless and transparent solution, while the lower layer is a black solid, indicating that CNT and PA6 have good compatibility and can be well dispersed in the PA6 phase. Figure 4 (B) is a TEM image of the CPPC composite material. CNTs are encapsulated in PA6 as the dispersed phase, while PS serves as the continuous phase. All of the above indicates that CNTs are selectively dispersed in PA6 within the CPPC composite material. Therefore, after etching away the PS phase with tetrahydrofuran, PA6@CNT microspheres are obtained.
[0059] like Figure 5 The dielectric properties of CPPC composite materials are as follows: the dielectric constant and dielectric loss increase with the increase of CNT content. Compared with pure PA6, the dielectric constant of Example 2 is increased by 35%, while the dielectric loss remains low at 0.27.
[0060] Figure 6 (A) is a pure PS circular image of the actual object. Figure 6 (B) is a physical image of PA6@CNT microspheres coated with PS, as shown. Figure 6 As shown in (C), PA6@CNT can be used as a dielectric coating material for any polymer material. With polyvinyl acetate as the coating matrix, only 4% of PA6@CNT microspheres were added to the total coating matrix. Even with such a small amount of coating, the dielectric properties of the polymer were relatively improved.
[0061] like Figure 7 The diagram illustrates the addition of PA6@CNT microspheres, comprising 25% of the total mass of the composite material (PVDF + microspheres), as a polymer filler to PVDF. The two materials are first melt-blended, then hot-pressed. To further reduce dielectric loss, CO2 critical foaming is utilized. Figure 8 The figure shows a comparison of dielectric properties before and after CO2 critical foaming. Before foaming, the dielectric constant at 1 kHz is about 50% higher than that of pure PVDF, and the dielectric loss is also relatively low at about 0.07. Furthermore, the dielectric constant decreases with increasing frequency, while the dielectric loss increases with increasing frequency. Comparing the dielectric properties before and after foaming, after CO2 critical foaming, the dielectric loss is reduced to 0.02.
Claims
1. A method for preparing high-dielectric polyamide microspheres, characterized in that, Includes the following steps: 1) Place the amide monomer in a three-necked flask and melt it by stirring at 75~85℃; 2) After complete melting, add the polymer and conductive filler, heat to 95~105℃, and stir continuously to accelerate melting while heating, so that the three raw materials are fully mixed; 3) After stirring for 1.5 to 1.8 hours, add the catalyst and fill the three-necked flask with an inert protective gas. Heat the mixture again to 180 to 200°C to remove the moisture in the system. Then add the activator, pour the mixture into a preheated iron container, and heat it in an oven to obtain the composite material. 4) The composite material was transferred to a Soxhlet extraction device containing tetrahydrofuran and heated in an oil bath at 80-90°C for 45-50 h to remove the polymer. After drying, high dielectric polyamide microspheres were obtained.
2. The method for preparing high-dielectric polyamide microspheres according to claim 1, characterized in that, The amide monomer is at least one of caprolactam (CPL), butyrolactam, octyllactam, and dodecyllactam.
3. The method for preparing high-dielectric polyamide microspheres according to claim 1, characterized in that, The polymer is at least one of polystyrene, polyethylene glycol, and polyvinylpyrrolidone.
4. The method for preparing high-dielectric polyamide microspheres according to claim 1, characterized in that, The conductive filler is CNT, BaTiO3, or ZnO.
5. The method for preparing high-dielectric polyamide microspheres according to claim 1, characterized in that, The catalyst is an alkali metal hydride or an alkali metal hydroxide.
6. The method for preparing high-dielectric polyamide microspheres according to claim 1, characterized in that, The activator is toluene diisocyanate.
7. The method for preparing high-dielectric polyamide microspheres according to claim 1, characterized in that, The mass ratio of the amide monomer to the polymer is 3:1 to 9:1, and the amount of conductive filler is 0.5-2% of the total mass of the amide monomer and the polymer.
8. The method for preparing high-dielectric polyamide microspheres according to claim 1, characterized in that, The catalyst dosage is 0.8-1.2% of the total mass of the amide monomer and the polymer, and the activator dosage is 3.8-4.2% of the total mass of the amide monomer and the polymer.
9. The method for preparing high-dielectric polyamide microspheres according to claim 1, characterized in that, Step 3) involves heating in an oven at 150-170°C for 15-18 minutes.
10. High-dielectric polyamide microspheres obtained by the preparation method according to any one of claims 1 to 9.