High-dielectric lightweight flame-retardant nylon material and preparation method thereof

Abstract

This invention relates to the field of polymer composite materials technology, specifically to a high-dielectric-weight, lightweight, flame-retardant nylon material and its preparation method. The material comprises a nylon matrix and a three-dimensional hybrid filler dispersed therein. The filler has a three-level structure, consisting of a hexagonal boron nitride three-dimensional network framework, a zinc manganese phytate metal-organic framework layer grown in situ on the surface of the framework, and a polydopamine interface layer covering the outside. The preparation method includes: preparing the three-dimensional hybrid filler through ice template, biomimetic mineralization, and interface polymerization processes, and then melt-blending it with the nylon matrix and molding it to obtain a composite material. This invention achieves precise synergy of component functions through the multi-level structural design of the filler. The material simultaneously possesses high dielectric constant, low dielectric loss, high breakdown strength, high flame retardancy, low density, and good mechanical properties at low filler content, making it suitable for the electronic, electrical, and transportation fields with stringent comprehensive performance requirements.

Description

Technical Field

[0001] This invention relates to the field of polymer composite materials technology, specifically to a high dielectric lightweight flame-retardant nylon material and its preparation method. Background Technology

[0002] Nylon (polyamide), as an engineering plastic with excellent comprehensive performance, is widely used in the fields of electronics, electrical engineering, new energy vehicles, and aerospace. As these fields develop towards high power density, miniaturization, and lightweighting, they place almost stringent requirements on the comprehensive performance of key insulation and structural component materials: they need high dielectric constant to meet energy storage or filtering needs, high breakdown strength to ensure insulation safety, high flame retardancy to ensure safe use, and strict control of material density to achieve lightweighting. At the same time, good mechanical properties are the foundation for structural components.

[0003] Currently, the technology for improving a single property of nylon materials is relatively mature, but it is difficult to achieve synergistic optimization of the above-mentioned multiple properties. For example, in order to obtain a high dielectric constant, fillers such as barium titanate and carbon nanotubes are often added. However, this usually leads to a sharp increase in dielectric loss and a decrease in breakdown strength. Moreover, carbon materials can damage insulation. In order to achieve high-efficiency flame retardancy, a large amount of halogen-based, phosphorus-nitrogen-based or inorganic components (such as magnesium hydroxide and ammonium polyphosphate) are usually added. This inevitably leads to a significant increase in material density, deterioration of mechanical properties (especially toughness), and difficulty in processing. Furthermore, most flame retardants can damage the electrical insulation properties of the material. The traditional technical route is essentially a simple physical blending of additives with different functions. The interfacial compatibility of each component in the matrix is ​​poor, and the functions are difficult to coordinate or even restrict each other, forming a "performance seesaw" effect, which makes it impossible to achieve a comprehensive breakthrough in performance at a low filler content.

[0004] Therefore, developing a new technology that can fundamentally and synergistically improve the dielectric, flame-retardant, and mechanical properties of nylon materials while maintaining low density has become an urgent need in this field. Summary of the Invention

[0005] To address the technical problems existing in the background art, the present invention provides a high dielectric lightweight flame-retardant nylon material and its preparation method.

[0006] To achieve the above objectives, the present invention adopts the following technical solution: In a first aspect, the present invention provides a three-dimensional hybrid filler comprising a three-dimensional porous framework composed of hexagonal boron nitride, a phytic acid-zinc-manganese coordination polymer hybrid layer grown in situ on the surface of the framework, and a polydopamine interface layer covering the hybrid layer, wherein the hybrid layer comprises zinc ions and manganese ions.

[0007] Furthermore, the molar ratio of zinc ions to manganese ions is (1:1) to (3:1).

[0008] Furthermore, the thickness of the polydopamine interface layer is 20-50 nm.

[0009] Furthermore, the density of the three-dimensional hybrid filler is less than 0.1 g / cm³.

[0010] Secondly, the present invention provides a method for preparing the above-mentioned three-dimensional hybrid filler, comprising the following steps: S1. Hexagonal boron nitride nanosheets are dispersed in a solvent and then subjected to directional freezing and freeze-drying to form a three-dimensional porous framework of hexagonal boron nitride; S2. The skeleton obtained in step S1 is immersed in a solution containing phytic acid, zinc salt and manganese salt to carry out the reaction, and a phytic acid-zinc-manganese coordination polymer hybrid layer is grown in situ on the surface of the skeleton to obtain the first composite. S3. The first composite obtained in step S2 is immersed in a dopamine buffer solution to allow dopamine to polymerize, forming a polydopamine interface layer on the surface of the first composite, thus obtaining the three-dimensional hybrid filler.

[0011] Furthermore, in step S1, the freezing rate of the directional freezing is 5-20 K / min.

[0012] Furthermore, in step S2, the reaction temperature is 25-60℃ and the reaction time is 6-24h.

[0013] Furthermore, in step S3, the pH value of the buffer solution is 8.0-8.8.

[0014] Thirdly, the present invention provides a high dielectric lightweight flame-retardant nylon material comprising a nylon matrix and a three-dimensional hybrid filler as described above dispersed in the nylon matrix, wherein the mass of the three-dimensional hybrid filler is 3-20% of the mass of the nylon matrix.

[0015] Furthermore, the mass of the three-dimensional hybrid filler is 5-15% of the mass of the nylon matrix.

[0016] Furthermore, the limiting oxygen index of the nylon material is not less than 30%, the dielectric constant at a frequency of 1 kHz is not less than 6.0, and the breakdown field strength is not less than 25 MV / m.

[0017] Fourthly, the present invention provides a method for preparing the above-mentioned high dielectric lightweight flame-retardant nylon material, comprising: melt-blending the nylon matrix with the three-dimensional hybrid filler, and then molding it.

[0018] Fifthly, the present invention provides applications of the high dielectric lightweight flame-retardant nylon material in fields such as high voltage connectors for new energy vehicles, lightweight cable insulation for aerospace, and high energy density film capacitors.

[0019] The beneficial effects of this invention are: 1. This invention, through a sophisticated integrated design, prepares a hybrid filler with a three-level structure. This filler plays multiple roles in the nylon matrix, and with a low addition amount, it synergistically achieves high dielectric constant, low dielectric loss, high breakdown strength, high flame retardancy, low density and good mechanical properties of the material, solving the problem of mutual performance constraints in traditional solutions.

[0020] 2. Unlike simply adding conductive or high-dielectric fillers, this invention utilizes the strong polarity centers and charge-binding sites introduced by the hybrid layer to effectively bind charge carriers. While generating strong interfacial polarization through a large number of heterogeneous interfaces, it significantly suppresses leakage current and space charge accumulation, thereby achieving a rare combination of "high dielectric constant, low loss, and high breakdown", resulting in an order-of-magnitude increase in energy storage density.

[0021] 3. Zn 2+ and Mn 2+ The PMF structure generates a synergistic catalytic effect, efficiently catalyzing the carbonization of nylon and PDA. Combined with the gas and acid source effects of phytic acid, it promotes the rapid formation of a dense and high-strength expanded carbon layer during combustion. The h-BN sheet plays a reinforcing role in the carbon layer, and PDA serves as a supplementary carbon source. This system is halogen-free flame retardant, with a limiting oxygen index that can easily exceed 35%, achieving the UL-94 V-0 rating, and is free of dripping.

[0022] 4. The filler body is a low-density h-BN three-dimensional aerogel, which enables the composite material to achieve performance improvement while the density increase is minimal. The strong adhesion between the PDA interface layer and the nylon matrix ensures the effective transfer of stress from the matrix to the reinforcing skeleton, so that the composite material can maintain excellent toughness while improving tensile strength, avoiding the embrittlement caused by conventional fillers.

[0023] 5. The filler is prepared using green or mild solution processes such as ice template, biomimetic mineralization, and oxidative polymerization. The composite material is prepared using a universal melt blending technology, which is fully compatible with the existing nylon processing industry chain and is easy to scale up. Detailed Implementation

[0024] The technical solution of the present invention will be clearly and completely described below with reference to the embodiments of the present invention. Obviously, the described embodiments are some embodiments of the present invention, but not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0025] Unless otherwise specified, the raw materials used in this invention are all from commercially available conventional products.

[0026] Example 1 S1: 100 mg of hexagonal boron nitride nanosheets were added to 20 mL of deionized water and sonicated in an ice-water bath for 4 hours to obtain a uniform and stable suspension (5 mg / mL). The suspension was injected into a polytetrafluoroethylene mold and placed on a cold stage pre-cooled to -20 °C for unidirectional freezing. After complete freezing, the sample was transferred to a freeze dryer and dried at -50 °C and a vacuum degree of less than 10 Pa for 48 hours to obtain a white, lightweight h-BN three-dimensional network framework (aerogel). S2: Preparation of precursor solution: Add 2.100g of phytic acid (C6H4O3) to a solution containing phytic acid (C6H4O3). 18 O 24 P6 (70% aqueous solution), 0.595g Zn(NO3)2·6H2O and 0.490g Mn(CH3COO)2·4H2O were dissolved in 40mL of a 1:1 mixture of deionized water and ethanol. The mixture was magnetically stirred for 30 minutes (the molar ratio of phytic acid to the total metal ions was calculated to be approximately 1:8). The h-BN aerogel obtained in S1 was completely immersed in the above precursor solution and allowed to stand at 40°C for 12 hours. After the reaction was completed, the aerogel was washed three times alternately with anhydrous ethanol and deionized water to remove unreacted ions. Then, it was freeze-dried again to obtain a BN-coordination hybrid layer composite aerogel loaded with a phytic acid-zinc-manganese coordination polymer hybrid layer. S3: Preparation of polymerization solution: Dissolve 200 mg of dopamine hydrochloride in 200 mL of Tris-HCl buffer solution with pH=8.5. Immerse the BN-coordination hybrid layer composite aerogel obtained in S2 into the solution and slowly stir magnetically at room temperature for 24 hours. After the reaction is completed, wash with deionized water until the washing solution is colorless. Finally, freeze dry to obtain the final black BN-coordination hybrid layer@PDA three-dimensional hybrid filler. S4: The BN-coordination hybrid layer @PDA filler prepared above was vacuum dried at 80℃ for 12 hours, and nylon 6 (PA6, grade B3S) chips were blown dry at 80℃ for 12 hours. They were weighed at a mass ratio of 9:1 (PA6: filler) and premixed in a high-speed mixer for 5 minutes. The mixture was then melt-blended using a twin-screw extruder. The extruder temperature from the feed inlet to the die head was set to 220℃, 230℃, 235℃, 240℃, and 240℃, and the screw speed was 150 rpm. The extruded strips were water-cooled, pelletized, and dried to obtain composite nylon masterbatch. The masterbatch was then molded into standard test strips on an injection molding machine, with the injection temperature set to 240-250℃.

[0027] Example 2 The difference between this embodiment and Example 1 is that, in the second step of preparing the precursor solution, the amounts of Zn(NO3)2·6H2O and Mn(CH3COO)2·4H2O are adjusted so that the molar ratio of Zn to Mn is 1:1. The remaining steps and parameters are exactly the same as in Example 1.

[0028] Example 3 The difference between this embodiment and Example 1 is that, in the second step of preparing the precursor solution, the amounts of Zn(NO3)2·6H2O and Mn(CH3COO)2·4H2O are adjusted so that the molar ratio of Zn to Mn is 3:1. The remaining steps and parameters are exactly the same as in Example 1.

[0029] Example 4 The difference between this embodiment and Example 1 is that, in the fourth step of preparing the composite material, the mass ratio of PA6 to BN-coordination hybrid layer @PDA filler (Zn:Mn=2:1) ​​is adjusted to 19:1 (i.e., the filler addition amount is 5wt.%). The remaining steps and parameters are exactly the same as in Example 1.

[0030] Example 5 The difference between this embodiment and Example 1 is that, in the fourth step of preparing the composite material, the mass ratio of PA6 to BN-coordination hybrid layer @PDA filler (Zn:Mn=2:1) ​​is adjusted to 17:3 (i.e., the filler addition amount is 15wt.%). The remaining steps and parameters are exactly the same as in Example 1.

[0031] Comparative Example 1 This comparative example uses pure nylon 6 (PA6) material. PA6 slices were directly injection molded according to the process described in step 4 of Example 1 to obtain pure PA6 test strips.

[0032] Comparative Example 2 The difference between this comparative example and Example 1 is that BN-coordination hybrid layer @PDA filler is not used. Instead, unmodified h-BN nanosheets are directly melt-blended with PA6 at a ratio of 10 wt.%. Before blending with PA6, the h-BN nanosheets are also dried at 80°C for 12 hours.

[0033] Comparative Example 3 The difference between this comparative example and Example 1 is that the PDA interface coating in the third step is omitted. Instead, the BN-coordination hybrid layer composite aerogel (without PDA treatment) prepared in the second step is directly melt-blended with PA6 at a ratio of 10 wt.% to prepare the composite material.

[0034] Comparative Example 4 This comparative example uses physically mixed fillers. h-BN nanosheets, zinc phytate, manganese phytate powder (converted according to the molar ratio of Zn:Mn=2:1) ​​and dopamine hydrochloride powder of the same mass as in Example 1 were weighed. All powder components were simply physically ground and mixed in a mortar for 5 minutes. Then, this mixed powder was melt-blended with PA6 chips at a total addition amount of 10 wt.%, and the process parameters were the same as in step 4 of Example 1.

[0035] Comparative Example 5 This comparative example uses a traditional commercial filler blending system, in which ammonium polyphosphate and barium titanate nanoparticles are physically mixed at a mass ratio of 2:1 to obtain a mixed filler. This mixed filler is then melt-blended with PA6 chips at a total addition amount of 15 wt.%, with the process parameters being the same as in step four of Example 1.

[0036] Effect verification example Testing and characterization methods: Density: Measured on an electronic density balance using the displacement method according to standard GB / T 1033.1-2008; Limiting oxygen index: Tested according to standard GB / T 2406.2-2009 using a limiting oxygen index tester under sample size of 100mm×10mm×4mm. Vertical flammability rating: Tested according to standard GB / T 2408-2021 (corresponding to UL-94) using a vertical flammability test chamber with a sample thickness of 1.6 mm; Dielectric properties: According to standard GB / T 1409-2006, the dielectric constant and dielectric loss tangent were tested on a sample film (thickness ~100μm) with gold electrodes at room temperature and frequency of 1kHz using a broadband dielectric impedance spectrometer. Breakdown field strength: According to standard GB / T 1408.1-2016, a high-voltage breakdown tester is used to test at least 10 samples in silicone oil at a rate of 500V / s, and the characteristic breakdown field strength is calculated using the Weber distribution. Energy storage density: based on the linear dielectric formula Calculation, where It is the vacuum permittivity; Mechanical properties: Tensile strength and elongation at break were tested using a universal testing machine at a tensile rate of 50 mm / min, in accordance with standard GB / T 1040.2-2022.

[0037] The results are shown in Tables 1 and 2: Table 1. Test results of basic composition, density and flame retardant properties of composite materials

[0038] Table 2. Test results of dielectric, energy storage and mechanical properties of composite materials

[0039] The data in Tables 1 and 2 clearly show the significant advantages of the BN-coordination hybrid layer@PDA / PA6 composite material prepared in this invention compared to the comparative sample. Firstly, in terms of lightweighting and flame retardancy, the density of Examples 1-3 increased by only about 4% compared to pure PA6, which is due to the low density characteristics of the h-BN three-dimensional network skeleton. In contrast, Comparative Example 5, due to the use of traditional fillers with high filler content, had a density increase of about 14.0%, and the lightweight advantage was significantly lost.

[0040] Flame retardant performance test results show that the present invention achieves high-efficiency flame retardancy. Pure PA6 is extremely flammable, with an LOI of only 21.5% and severe dripping. Adding h-BN alone (Comparative Example 2) or simply physically mixing the components (Comparative Example 4) only brings limited improvement. However, by constructing a ZnMn-PMF layer in situ, even without PDA (Comparative Example 3), the LOI can be significantly improved to 32.0%, indicating that this catalytic layer is the key to efficient char formation. When a PDA interface layer is further introduced (Examples 1-3), the LOI is further improved to over 35%, and all reach the UL-94 V-0 rating, with no dripping. This confirms that PDA not only enhances the interfacial bonding, but also participates in the formation of a high-quality expanded char layer as a carbon source, and interacts with Zn in the PMF. 2+ / Mn 2+ The catalytic center produced an excellent synergistic flame retardant effect. Among them, the synergistic catalytic efficiency was optimal and the LOI value was the highest when the molar ratio of Zn to Mn was 2:1 (Example 1).

[0041] In terms of dielectric and energy storage performance, the present invention has achieved significant improvements. In Example 1, while obtaining a dielectric constant as high as 10.5, the dielectric loss was successfully suppressed to a low level of 0.022, and the breakdown strength was significantly improved to 30.5 MV / m. This is mainly due to the introduction of a large number of strongly polar centers and charge-binding sites in the phytic acid-zinc-manganese hybrid layer, which effectively suppresses carrier migration and space charge accumulation. Thus, while using the strong polarization generated by the heterojunction to improve the dielectric constant, high insulation reliability (high breakdown and low loss) is ensured. Although Comparative Example 5 has a higher dielectric constant, the loss increases dramatically and the breakdown strength decreases significantly.

[0042] In terms of mechanical properties, Examples 1-3 maintained excellent elongation at break while improving tensile strength. This is attributed to the strong interfacial adhesion established by the PDA interface layer, which ensures the effective transfer of stress from the matrix to the filler. In stark contrast, Comparative Example 3, which lacks a PDA layer, and Comparative Example 4, which is a simple physical mixture, became stress concentration points due to extremely poor interfacial bonding. The materials exhibited brittle fracture, and the elongation at break dropped sharply.

[0043] In summary, the experimental data fully demonstrate that the BN-coordination hybrid layer@PDA three-dimensional hybrid filler constructed by the ice template-biomimetic mineralization-interfacial polymerization process of this invention successfully integrates a lightweight reinforcing framework (BN), a catalytic / trap functional center (ZnMn-PMF), and a strong interfacial layer (PDA) into one. When this filler is applied to PA6 in a moderate proportion (e.g., 10 wt.%), it can produce a multi-scale synergistic effect, thus overcoming the long-standing technical challenge of simultaneously achieving multiple objectives such as high dielectric constant, low dielectric loss, high breakdown strength, high flame retardancy, good mechanical properties, and low density in polymer materials. In particular, the optimal formulation shown in Example 1 has the most balanced and excellent comprehensive performance, demonstrating great application potential.

[0044] In the description of this specification, the terms "preparation example," "example," "various examples," etc., refer to specific features, structures, materials, or characteristics described in connection with that example or preparation example, which are included in at least one example or preparation example of the present invention. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same example or preparation example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more examples or preparation examples.

[0045] The above description is only a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any equivalent substitutions or modifications made by those skilled in the art within the scope of the technology disclosed in the present invention, based on the technical solution and inventive concept of the present invention, should be covered within the scope of protection of the present invention.

Claims

1. A three-dimensional hybrid filler, characterized in that, It includes a three-dimensional porous framework composed of hexagonal boron nitride, a phytic acid-zinc-manganese coordination polymer hybrid layer grown in situ on the surface of the framework, and a polydopamine interface layer covering the hybrid layer, wherein the hybrid layer contains zinc ions and manganese ions.

2. The three-dimensional hybrid filler of claim 1, wherein, The molar ratio of zinc ions to manganese ions is (1:1)-(3:1).

3. The three-dimensional hybrid packing according to claim 1 or 2, characterized in that, The thickness of the polydopamine interface layer is 20-50 nm.

4. The three-dimensional hybrid packing according to any one of claims 1-3, characterized in that, The density of the three-dimensional hybrid filler is less than 0.1 g / cm 3 .

5. A method for preparing the three-dimensional hybrid filler according to any one of claims 1-4, characterized in that, Includes the following steps: S1. Hexagonal boron nitride nanosheets are dispersed in a solvent and then subjected to directional freezing and freeze-drying to form a three-dimensional porous framework of hexagonal boron nitride; S2. The skeleton obtained in step S1 is immersed in a solution containing phytic acid, zinc salt and manganese salt to carry out the reaction, and a phytic acid-zinc-manganese coordination polymer hybrid layer is grown in situ on the surface of the skeleton to obtain the first composite. S3. The first composite obtained in step S2 is immersed in a dopamine buffer solution to allow dopamine to polymerize, forming a polydopamine interface layer on the surface of the first composite, thus obtaining the three-dimensional hybrid filler.

6. The preparation method according to claim 5, characterized in that, In step S1, the freezing rate of the directional freezing is 5-20 K / min. In step S2, the reaction temperature is 25-60℃ and the reaction time is 6-24 h. The molar ratio of phytic acid to the total of zinc ions and manganese ions is 1:(6-12).

7. A high-dielectric, lightweight, flame-retardant nylon material, characterized in that, The nylon matrix comprises a nylon matrix and a three-dimensional hybrid filler as described in any one of claims 1-4 dispersed in the nylon matrix, wherein the mass of the three-dimensional hybrid filler is 3-20% of the mass of the nylon matrix.

8. The high-dielectric lightweight flame-retardant nylon material according to claim 7, characterized in that, The mass of the three-dimensional hybrid filler is 5-15% of the mass of the nylon matrix.

9. The high-dielectric lightweight flame-retardant nylon material according to claim 7 or 8, characterized in that, The limiting oxygen index of the nylon material is not less than 30%, the dielectric constant at 1kHz is not less than 6.0, and the breakdown field strength is not less than 25MV / m.

10. A method for preparing a high-dielectric, lightweight, flame-retardant nylon material as described in any one of claims 7-9, characterized in that, include: The nylon matrix is ​​melt-blended with the three-dimensional hybrid filler and then molded.

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