Composite grafted aramid fiber with core-shell structure and preparation method of composite grafted aramid fiber

Abstract

The invention discloses a composite grafted aramid fiber with a core-shell structure and a preparation method of the composite grafted aramid fiber. Hydroxylated boron nitride is used as a core, carboxylated aluminum nitride is used as an intermediate shell layer, and hierarchical connection is realized by using the polyfunctional group characteristic of a COF-based silane coupling agent: the siloxy terminal is covalently bonded with the boron nitride core and the aluminum nitride shell layer, and the amino terminal and acylating chlorinated aramid fiber form an amido bond; and a radial heat conduction network of boron nitride core-aluminum nitride shell layer-aramid fiber is constructed. Wherein a single boron nitride core is in bridge connection with 15-30 aramid fibers through COF molecules, and the core is coated with the shell layer aluminum nitride particles in a close packing mode, so that a heat conduction channel with the controllable thickness is formed. After the aramid paper is formed by a wet papermaking process, the obtained aramid paper has high in-plane heat conductivity and wave-transparent performance, and the core-shell structure effectively inhibits high-temperature interface stripping. Directional arrangement and interface strengthening of the filler are achieved through chemical bonding, and the filler is suitable for the fields of 5G high-frequency device heat dissipation, aerospace wave-transparent and heat-conducting integrated components and the like.

Description

Technical Field

[0001] This invention relates to the field of polymer composite materials technology, specifically to a core-shell structure composite grafted aramid fiber with boron nitride as the core and aluminum nitride and aramid fibers synergistically forming the shell, and its preparation method, as well as high-transmittance, heat-conducting aramid paper made from the fiber. Background Technology

[0002] Aramid fibers, with their high strength, high modulus, and resistance to chemical corrosion, occupy an important position in high-performance fields such as aerospace structural components, electronic packaging substrates, and 5G communication devices. As 5G technology evolves towards higher frequency bands and electronic devices become more integrated, materials need to simultaneously meet multiple performance requirements, including efficient heat dissipation, dielectric stability, and tolerance to extreme environments. The performance bottlenecks of traditional aramid composite materials are becoming increasingly prominent.

[0003] Regarding the optimization of thermal conductivity, although the introduction of high thermal conductivity ceramic fillers such as boron nitride and aluminum nitride is the mainstream technical approach, the chemical inertness of the filler surface leads to insufficient compatibility with the aramid fiber interface. Physical blending processes are unable to avoid particle agglomeration, forming an inefficient thermal conductivity network. At the same time, the filler and aramid matrix are only bonded through weak physical interactions, and phonon scattering at the interface significantly increases the thermal transport resistance, thus limiting the improvement of the overall thermal conductivity efficiency of the composite material.

[0004] Structural stability under high-temperature environments is another key challenge for aramid composites. The difference in thermal expansion coefficients between aramid fibers and ceramic fillers can easily lead to the accumulation of interfacial stress. In high-temperature conditions such as aerospace (e.g., around engines, in the thermal protection scenarios of high-speed aircraft), the interfacial bonding layer is prone to peeling and cracking due to thermal mismatch, resulting in the deterioration of the material's mechanical properties or even functional failure. Therefore, it is urgent to enhance the interfacial bonding strength and thermal stability through structural design.

[0005] Existing improvement methods, such as using single silane coupling agents to modify fillers, can only provide monofunctional group connections, resulting in limited interfacial bonding density and an inability to achieve directional filler arrangement. Their low thermal conductivity makes it difficult to construct efficient heat conduction pathways, and they are prone to degradation at high temperatures. How to synergistically improve the thermal conductivity, interfacial strength, high-temperature stability, and wave transmission properties of aramid composites through hierarchical structural design and multi-scale interfacial control has become a pressing technical challenge in the field of polymer composites. Summary of the Invention

[0006] The purpose of this invention is to solve the problems of uneven dispersion of thermally conductive fillers, high interfacial thermal resistance, and insufficient high-temperature stability in aramid fiber composite materials in the prior art. It provides a core-shell structured composite grafted aramid fiber and its preparation method. By innovatively constructing a core-shell radiation structure of "boron nitride core - aluminum nitride shell - aramid fiber", the invention achieves synergistic improvement in thermal conductivity path and interfacial strength.

[0007] The technical solution adopted in this invention is as follows:

[0008] A core-shell structured composite grafted aramid fiber uses hydroxylated boron nitride particles as the core and carboxylated spherical aluminum nitride particles as the intermediate shell. The aramid fibers form a network on the surface of the intermediate shell, thus constructing a radial core-shell structure of "boron nitride core - aluminum nitride shell - aramid fiber".

[0009] Preferably, the mass ratio of boron nitride core to aluminum nitride shell is 1:5 to 1:10; the aluminum nitride particles coat the boron nitride core in a close-packed manner, and the coating thickness is 1.5-3 μm; the aramid fibers form a three-dimensional entangled network on the shell surface through a COF-based silane coupling agent, with a fiber spacing of <80 nm, and the amino utilization rate of the COF-based silane coupling agent is ≥60%.

[0010] Preferably, the hydroxyl group density on the surface of the boron nitride core is 8-12 hydroxyl groups / μm. 2 The carboxyl group density on the surface of carboxylated aluminum nitride particles is 1-2 groups / μm. 2 The density of acyl chloride groups in aramid fibers is 30-50 per μm. 2 Furthermore, the grafting molar ratio of aramid fiber to COF-based silane coupling agent is 6:1 to 8:1.

[0011] Preferably, the hydroxylated boron nitride particles have a particle size of 10 μm; the carboxylated spherical aluminum nitride particles have a particle size of 1-2 μm.

[0012] This invention also provides the above-mentioned core-shell structured composite grafted aramid fiber, comprising the following steps:

[0013] S1. Core Construction: Hydroxylated boron nitride (OH-BN) and KH550 were reacted in anhydrous toluene at 110±2℃ for 12±0.5h in a molar ratio of 1:5±0.2 to obtain KH550-BN; subsequently, it was reacted with carboxylated aluminum nitride (COOH-AlN) under EDC / NHS catalysis to form a core-shell structured KH550-BN-AlN complex.

[0014] S2, Shell grafting: KH550-BN-AlN with a molar ratio of 1:4±0.2 was reacted with COF-based silane coupling agent at 90±2℃ for 6±0.2h, so that COF silane coupling agent was bonded to the AlN surface through siloxy groups.

[0015] S3, Aramid Fiber Coating: The reaction product of S2 is reacted with acyl chloride aramid fibers (Cl-ANFs) in NMP solvent at 25±1℃ for 24±0.5h. The amino group of the COF-based silane coupling agent forms an amide bond with Cl-ANFs, thus completing the shell coating.

[0016] S4. Core Direct Bridging: OH-BN with a molar ratio of 1:3±0.2 is reacted with COF-based silane coupling agent and then bonded with Cl-ANFs to form an aramid fiber network that radiates directly from the core.

[0017] Preferably, aramid nanofibers are subjected to acyl chloride treatment to generate Cl-ANFs with acyl chloride groups on the surface; boron nitride particles are subjected to hydroxylation treatment to obtain hydroxylated boron nitride (OH-BN); and spherical aluminum nitride particles are subjected to carboxylation treatment to obtain carboxylated aluminum nitride (COOH-AlN).

[0018] Preferably, the acyl chloride treatment uses thionyl chloride as the reaction reagent, the reaction temperature is 65-75℃, and the reaction time is 10-14 hours; the hydroxylation treatment uses 0.8-1.2M NaOH solution, the reaction temperature is 60-70℃, and the reaction time is 4-6 hours; the carboxylation treatment uses glycine as the modifier, the reaction temperature is 115-125℃, and the reaction time is 10-14 hours.

[0019] Preferably, in step S3, shell densification is achieved through gradient temperature control. First, 3-4 amino groups participate in the reaction at 25°C, and then the remaining amino groups are activated in a heat treatment at 80-100°C, thereby increasing the density of the aramid fiber coating layer by 15-20%.

[0020] The present invention also provides a high-transmittance thermally conductive aramid paper, which is made by wet molding of the above-mentioned core-shell structure composite grafted aramid fiber. The aramid paper has an in-plane thermal conductivity ≥3.0W / (m·K), a dielectric constant ≤3.5, a loss tangent ≤0.005, and the core-shell structure reduces the thermal resistance by 40-50%. After heat treatment at 400℃, the structural integrity is >98%.

[0021] This invention also provides the application of the above-mentioned high-transmittance waveguide thermally conductive aramid paper in the preparation of aerospace and electronic packaging materials.

[0022] This invention uses boron nitride (BN) as the core material, which possesses high thermal conductivity (~600 W / (m·K)) and excellent thermal stability, but its surface inertness leads to weak interfacial bonding with the polymer matrix. Spherical aluminum nitride (AlN), on the other hand, exhibits isotropic thermal conductivity and can serve as an ideal interlayer material. Therefore, this invention uses hydroxylated boron nitride as the core and carboxylated aluminum nitride as the intermediate shell, utilizing the multifunctional characteristics of COF-based silane coupling agents to achieve hierarchical bonding: its siloxy terminals covalently bond with the boron nitride core and aluminum nitride shell, while its amino terminals form amide bonds with acylchloroaramid fibers, constructing a radial thermally conductive network of "boron nitride core - aluminum nitride shell - aramid fiber," thereby synergistically improving interfacial bonding strength and thermal conductivity efficiency.

[0023] The beneficial effects of this invention are as follows:

[0024] (1) This invention constructs a core-shell structure with boron nitride as the core and aluminum nitride and aramid fiber as the synergistic coating, forming a hierarchical heat conduction channel, which effectively improves the thermal conductivity of the composite fiber; the multi-amino design of the COF-based silane coupling agent realizes the high-density interface connection between the core and the shell, which significantly reduces the interface thermal resistance; the core-shell structure endows the material with excellent high-temperature stability and can still maintain structural integrity under extreme temperature cycling.

[0025] (2) The preparation process of the core-shell structure composite grafted aramid fiber in this invention achieves the self-repair function of the core-shell structure through gradient reaction control, and the reaction conditions are mild and the solvent can be recovered, making it suitable for large-scale production.

[0026] (3) The core-shell structure of the composite grafted aramid fiber in this invention is formed by wet papermaking process to obtain high wave transmission and thermal conductivity aramid paper. Under the structural support of multivalent bridging technology, the aramid paper has excellent high thermal conductivity, dielectric properties and thermal stability. Moreover, the core-shell structure effectively inhibits high temperature interface peeling. It is suitable for application scenarios with strict requirements for high wave transmission and high thermal conductivity, such as aerospace and electronic packaging. Attached Figure Description

[0027] Figure 1 This is a schematic diagram of the core-shell composite fiber prepared in Example 1.

[0028] Figure 2 The image shown is a SEM image of the core-shell composite fiber prepared in Example 1. Detailed Implementation

[0029] The present invention will be further described below with reference to the accompanying drawings and specific embodiments.

[0030] Example 1: Preparation of core-shell structured composite fibers

[0031] In a 500 mL three-necked flask, 200 mL of N-methylpyrrolidone (NMP) was added, followed by the slow addition of 5.0 g of aramid nanofibers (ANFs). The mixture was mechanically stirred for 30 minutes until completely dispersed. A reflux reflux apparatus was installed, and 50 mL of thionyl chloride (SOCl2) was added dropwise under nitrogen protection. The mixture was refluxed at 70 °C for 12 hours. After the reaction was complete, the mixture was centrifuged, washed three times with anhydrous ethanol, and dried under vacuum at 60 °C for 8 hours to obtain acyl-chlorinated aramid fibers (Cl-ANFs).

[0032] Core construction: 2.0 g of hexagonal boron nitride (h-BN) was mixed with 200 mL of 1 M NaOH solution, stirred at 65 °C for 5 hours, filtered and washed until neutral, and dried at 80 °C for 12 hours to obtain hydroxylated boron nitride (OH-BN); 1.0 g of OH-BN and 0.05 g of KH550 silane coupling agent were refluxed in 100 mL of toluene at 110 °C for 12 hours, and centrifuged and washed to obtain KH550-BN; 0.5 g of KH550-BN and 2.5 g of carboxylated aluminum nitride (COOH-AlN) were added to 50 mL of THF, along with 0.1 g of EDC and 0.12 g of NHS, and reacted at room temperature for 24 hours to form a core-shell structured KH550-BN-AlN complex (core-shell mass ratio 1:3).

[0033] Shell grafting and aramid coating: 0.4 g of KH550-BN-AlN composite and 0.02 g of COF-based silane coupling agent were reacted in 50 mL of toluene at 90 °C for 6 hours, allowing the COF-based silane coupling agent to bond to the AlN shell surface; 0.2 g of Cl-ANFs were added, and the mixture was reacted in NMP at 25 °C for 24 hours to complete the shell coating; simultaneously, the OH-BN core was reacted with the COF-based silane coupling agent and then linked to Cl-ANFs to form a fiber network with direct core radiation. Its structural schematic diagram is shown below. Figure 1 As shown in the figure, the SEM graph is as follows: Figure 2 As shown.

[0034] Aramid paper, produced by wet forming, exhibits a complete core-shell structure and significantly improved thermal conductivity. Using laser scintillation, the thermal conductivity of the aramid paper was measured to be above 3 W / (m·K). Thermogravimetric analysis revealed a weight loss of only 1.8% at 240℃. Using a vector mesh analyzer in the 2-4 GHz and 8-12 GHz frequency bands, the dielectric constant was measured to be below 3.3, and the loss tangent below 0.005. A thermal constant analyzer determined the interfacial thermal resistance of conventional aramid paper to be 0.52 K·m. 2 / W, the interfacial thermal resistance of the aramid paper in this invention is 0.29 K·m. 2 / W.

[0035] Comparative Example 1: Core-shell structure optimization

[0036] The preparation method of this comparative example is the same as that of Example 1, except that the following parameters are adjusted in this comparative example: the acyl chloride reaction time is shortened to 8 hours; the hydroxylation reaction time is extended to 8 hours; the KH550 bridging reaction time is shortened to 8 hours; and the core-shell mass ratio is adjusted to 1:4 (the ratio of KH550-BN to COOH-AlN is adjusted to 1:0.4).

[0037] The resulting aramid paper has a denser shell layer, which improves its mechanical properties. However, the core-shell interface connection density is slightly reduced, resulting in decreased thermal conductivity. The thermal conductivity of the aramid paper was measured to be 2.7 W / (m·K) using the laser flash method.

[0038] Comparative Example 2: Core-shell structure with high filler ratio

[0039] The preparation method of this comparative example is the same as that of Example 1, except that the following material ratios are adjusted: the amount of KH550 is increased to 0.08g (originally 0.05g) to strengthen the connection between the core and the shell; the amount of COF-based silane coupling agent is reduced to 0.015g (originally 0.02g) to reduce the grafting density on the shell surface; and the amount of Cl-ANFs is increased to 0.25g (originally 0.2g) to increase the thickness of the fiber coating layer.

[0040] The resulting product exhibits improved thermal conductivity due to its core-shell structure, but the flexibility of the fiber layer is reduced, resulting in brittle paper.

[0041] Comparative Example 3: Environmentally Friendly Solvent System

[0042] The preparation method of this comparative example is the same as that of Example 1, except that the following solvent substitutions are used in this comparative example: DMF is used instead of NMP for the acyl chloride reaction; xylene is used instead of toluene for the bridging reaction; and DMSO is used instead of NMP for the final grafting reaction.

[0043] The solvent recovery rate was increased to 85%, which meets the requirements of green production. However, the integrity of the core-shell structure of the resulting aramid paper was lower than that of the standard method, and the thermal conductivity and wave transmission properties were reduced.

[0044] In summary, this invention utilizes a core-shell structure design, employing boron nitride as the core, aluminum nitride as the intermediate shell, and aramid fiber as the outer coating, to prepare a composite fiber with high wave transmittance and thermal stability. The synergistic effect of the core-shell hierarchical thermal conductivity path and the multi-point bridging properties of the COF-based silane coupling agent enhances thermal conductivity while maintaining mechanical strength and environmental friendliness, making it suitable for applications such as heat dissipation in electronic devices and aerospace.

[0045] The specification and drawings of this invention are intended to be illustrative rather than restrictive. Based on this invention, those skilled in the art can make substitutions and modifications to some of the technical features without creative effort, and all such modifications are within the scope of protection of this invention.

Claims

1. A core-shell structured composite grafted aramid fiber, characterized in that, Using hydroxylated boron nitride particles as the core and carboxylated spherical aluminum nitride particles as the intermediate shell, aramid fibers form a network on the surface of the intermediate shell, thus constructing a radial core-shell structure of "boron nitride core - aluminum nitride shell - aramid fibers".

2. The core-shell structured composite grafted aramid fiber according to claim 1, characterized in that, The mass ratio of boron nitride core to aluminum nitride shell is 1:5 to 1:10; the aluminum nitride particles coat the boron nitride core in a close-packed manner, and the coating thickness is 1.5-3 μm; the aramid fibers form a three-dimensional entangled network on the shell surface through a COF-based silane coupling agent, with a fiber spacing of <80 nm, and the amino utilization rate of the COF-based silane coupling agent is ≥60%.

3. The core-shell structured composite grafted aramid fiber according to claim 2, characterized in that, The hydroxyl group density on the surface of the boron nitride core is 8-12 hydroxyl groups / μm. 2 The carboxyl group density on the surface of carboxylated aluminum nitride particles is 1-2 groups / μm. 2 The density of acyl chloride groups in aramid fibers is 30-50 per μm. 2 Furthermore, the grafting molar ratio of aramid fiber to COF-based silane coupling agent is 6:1 to 8:

1.

4. The core-shell structured composite grafted aramid fiber according to claim 1, characterized in that, The hydroxylated boron nitride particles have a particle size of 10 μm; the carboxylated spherical aluminum nitride particles have a particle size of 1-2 μm.

5. A method for preparing core-shell structured composite grafted aramid fibers, characterized in that, Includes the following steps: S1. Core Construction: Hydroxylated boron nitride (OH-BN) and KH550 were reacted in anhydrous toluene at 110±2℃ for 12±0.5h in a molar ratio of 1:5±0.2 to obtain KH550-BN; subsequently, it was reacted with carboxylated aluminum nitride (COOH-AlN) under EDC / NHS catalysis to form a core-shell structured KH550-BN-AlN complex. S2, Shell grafting: KH550-BN-AlN with a molar ratio of 1:4±0.2 was reacted with COF-based silane coupling agent at 90±2℃ for 6±0.2h, so that COF silane coupling agent was bonded to the AlN surface through siloxy groups. S3, Aramid Fiber Coating: The reaction product of S2 is reacted with acyl chloride aramid fibers (Cl-ANFs) in NMP solvent at 25±1℃ for 24±0.5h. The amino group of the COF-based silane coupling agent forms an amide bond with Cl-ANFs, thus completing the shell coating. S4. Core Direct Bridging: OH-BN with a molar ratio of 1:3±0.2 is reacted with COF-based silane coupling agent and then bonded with Cl-ANFs to form an aramid fiber network that radiates directly from the core.

6. The preparation method according to claim 5, characterized in that, Aramid nanofibers were subjected to acyl chloride treatment to generate Cl-ANFs with acyl chloride groups on the surface; boron nitride particles were subjected to hydroxylation treatment to obtain hydroxylated boron nitride (OH-BN); spherical aluminum nitride particles were subjected to carboxylation treatment to obtain carboxylated aluminum nitride (COOH-AlN).

7. The preparation method according to claim 6, characterized in that, The acyl chloride treatment uses thionyl chloride as the reaction reagent, the reaction temperature is 65-75℃, and the reaction time is 10-14 hours; the hydroxylation treatment uses 0.8-1.2M NaOH solution, the reaction temperature is 60-70℃, and the reaction time is 4-6 hours; the carboxylation treatment uses glycine as the modifier, the reaction temperature is 115-125℃, and the reaction time is 10-14 hours.

8. The preparation method according to claim 5, characterized in that, In S3, shell densification is achieved through gradient temperature control. First, 3-4 amino groups are reacted at 25°C, and then the remaining amino groups are activated in a heat treatment at 80-100°C, thereby increasing the density of the aramid fiber coating layer by 15-20%.

9. A high-transmittance, wave-conducting, thermally conductive aramid paper, characterized in that: The aramid paper is prepared by wet molding of the core-shell structure composite grafted aramid fiber as described in any one of claims 1-4. The aramid paper has an in-plane thermal conductivity ≥3.0W / (m·K), a dielectric constant ≤3.5, a loss tangent ≤0.005, and the core-shell structure reduces the thermal resistance by 40-50%. After heat treatment at 400℃, the structural integrity is >98%.

10. The application of the high-transmittance, thermally conductive aramid paper as described in claim 9 in the preparation of aerospace and electronic packaging materials.

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