High-thermal-conductivity fiber reinforced composite material and preparation method thereof

Abstract

The invention belongs to the technical field of resin-based composite materials, and particularly relates to a high-thermal-conductivity fiber-reinforced composite material and a preparation method thereof. The preparation method comprises the following steps: mixing hexagonal boron nitride and bisphenol A cyanate ester resin in proportion, and putting the mixture into a vacuum planetary stirring defoaming machine for shearing, mixing and defoaming; spreading quartz fiber cloth in a suspended manner, uniformly coating the BE mixture, and performing ultrasonic treatment; the fiber cloth is stacked, the BE mixture is coated again when each layer is laid, infiltration of the fiber bundles is ensured through a vacuum auxiliary infiltration device, and after stacking is completed, a low-frequency circulating force field is applied to eliminate interlayer pores; high-frequency ultrasonic force is intermittently loaded in a constant-temperature and pressure-maintaining state of the low-frequency circulating force field; and heating and curing to obtain the composite material product. By utilizing the method and the product, the invention provides the high-thermal-conductivity fiber reinforced composite material which can solve the problems that a steady-state force field is difficult to break and filler agglomeration is difficult, an ultrasonic single field is difficult to assemble in order and is overheated and poor in infiltration, and low-filler high-thermal-conductivity and mechanics are difficult to consider in the prior art.

Description

Technical Field

[0001] This invention belongs to the field of resin-based composite materials technology, and particularly relates to high thermal conductivity fiber-reinforced composite materials and their preparation methods. Background Technology

[0002] In the fields of aerospace and thermal management of electronic devices, resin-based composite materials are widely used in applications such as radomes and aircraft wing components due to their lightweight, corrosion resistance, and ease of processing. These applications require materials with rapid heat dissipation capabilities (vertical thermal conductivity typically needs to be ≥1.0 W / m). K) and structural load-bearing capacity (flexural strength ≥ 400 MPa, interlaminar shear strength ≥ 45 MPa), but the inherent thermal conductivity of the resin matrix is ​​extremely low (only 0.1-0.5 W / m). K), the industry generally constructs thermally conductive pathways by adding high thermal conductivity fillers (such as hexagonal boron nitride (BN, purity > 99%, average particle size 1μm)), while using quartz fiber cloth ( ≥99.95%, 0.1mm plain weave) to reinforce the body and ensure mechanical properties, forming a three-phase system of "resin-filler-fiber".

[0003] Existing technologies for improving the properties of such composite materials involve optimizing fillers (such as selecting flake-shaped BN) and improving molding processes. The mainstream approach is steady-state force field molding (hot pressing / molding, 1-3 MPa pressure) combined with step curing, with some supplemented by ultrasonic assistance. For example, in the quartz fiber reinforced cyanate ester resin (QF / EC) system, when filled with 30 wt% BN under a steady-state force field, the thermal conductivity is approximately 1.02 W / m·K, the flexural strength is 420.36 MPa, and the interlaminar shear strength is 48.62 MPa. Although ultrasound can dissociate micron-sized BN agglomerates, it is limited by the duration of a single field action and cannot achieve the ordered assembly of nanoscale fillers.

[0004] The existing technology faces significant bottlenecks: First, the steady-state force field is insufficient to break filler agglomeration, resulting in insufficient thermal conductivity with low filler content. High filler content (such as 50wt% BN) increases resin viscosity, weakens fiber wettability, and reduces flexural strength to 380.8MPa. Second, single-field ultrasonic treatment cannot achieve orderly arrangement of multi-scale fillers, and continuous action can easily lead to local overheating (e.g., 600J ultrasonic energy can cause a decrease in XRD diffraction peak intensity and a weakening of FTIR characteristic peaks), damaging the resin or fiber structure. Third, there are defects in the impregnation process. Regardless of whether the layering is done before coating or after coating, the resin-filler system is difficult to fully penetrate the fiber bundle with low filler content, and voids are easily formed between layers, increasing interfacial thermal resistance and reducing interfacial shear strength. Ultimately, it is impossible to achieve both high thermal conductivity and excellent mechanical properties with low filler content. Summary of the Invention

[0005] The purpose of this invention is to provide high thermal conductivity fiber-reinforced composite materials and their preparation methods, so as to solve the problems of the prior art, such as the difficulty in breaking filler agglomeration in steady-state force fields, the difficulty in orderly assembly in ultrasonic single-field, overheating, poor wetting, and difficulty in achieving both high thermal conductivity and mechanical properties with low filler content.

[0006] To achieve the above objectives, the present invention provides the following solution:

[0007] Methods for preparing high thermal conductivity fiber-reinforced composite materials include:

[0008] S1. Preparatory steps: Mix hexagonal boron nitride and cyanate ester resin in a certain proportion, and put them into a vacuum planetary mixer for shearing, mixing and degassing to form a BE mixture;

[0009] S2. Fiber pretreatment: Quartz fiber cloth is suspended and laid on a constant temperature forming platform. The BE mixture is uniformly coated using a scraping process, and the BE mixture is fully impregnated with fiber bundles by ultrasonic treatment.

[0010] S3, Laying and Pressurizing: Several pre-treated fiber cloths are laid flat on the mold substrate in sequence to form a stack. The BE mixture is coated again when each layer is laid. The fiber bundles are ensured to be wetted by a vacuum-assisted permeation device. After the stacking is completed, a low-frequency cyclic force field is applied to eliminate interlayer porosity.

[0011] S4. Ultrasonic enhancement: Under the constant temperature and pressure state of the low-frequency cyclic force field, a 20kHz high-frequency ultrasonic force field is intermittently applied, and the cycle is repeated at least twice to break up the agglomeration of the BE mixture and optimize the interface bonding.

[0012] S5. Curing: Heating and curing are carried out to finally obtain high thermal conductivity fiber-reinforced composite material products.

[0013] Preferably, the cyanate resin is a bisphenol A type cyanate resin.

[0014] Preferably, in step S1, the hexagonal boron nitride accounts for 30-50% of the total mass fraction of the BE mixture.

[0015] Preferably, in step S2, the coating amount of the BE mixture is 233-237 g / m². 2 .

[0016] Preferably, in step S2, when the BE mixture is used to fully impregnate the fiber bundle through ultrasonic treatment, a high-frequency ultrasonic treatment of 20kHz is employed.

[0017] Preferably, in step S3, the number of layers of the pretreated fiber cloth is 10-25.

[0018] Preferably, in step S3, the fiber bundle is impregnated by a vacuum-assisted permeation device, which is set to a vacuum of -85 kPa.

[0019] Preferably, after stacking is completed in step S3, a low-frequency cyclic force field of 1 MPa is applied and maintained for 300 s to eliminate interlayer porosity.

[0020] Preferably, in step S4, the ultrasonic energy applied by the 20kHz high-frequency ultrasonic force field is 500J, with 10s constituting one cycle and each cycle lasting 2 minutes.

[0021] Preferably, in step S5, during heat curing, hot pressing curing is performed according to curing curves of 150℃×0.5h, 180℃×0.5h, 220℃×2h, and 230℃×3h to finally obtain a high thermal conductivity fiber reinforced composite material product.

[0022] A high thermal conductivity fiber-reinforced composite material is prepared based on the preparation method of the high thermal conductivity fiber-reinforced composite material.

[0023] Compared with the prior art, the present invention has the following advantages and technical effects:

[0024] In this invention, the preparation method relies on dynamic force field molding process. By combining low-frequency cyclic force field and high-frequency ultrasonic force field, it can not only efficiently disintegrate the agglomeration of thermally conductive filler, but also enhance the wettability of resin and fiber fabric, avoid the problem of increased resin viscosity caused by high filler dosage, and optimize the interfacial bonding state between filler-resin-fiber.

[0025] The corresponding product has significant advantages. It can build a continuous thermal conduction path with low filler content, breaking through the contradiction between "high thermal conductivity requirements and mechanical property degradation". While improving thermal conductivity, it ensures stable bending strength and interlaminar shear strength. Moreover, the improved uniformity of filler dispersion enhances the thermal stability of the product, and the optimized interface further delays the performance degradation under high filler content, making it suitable for aerospace and other scenarios with stringent requirements for the comprehensive performance of materials.

[0026] Using these methods and products, the present invention provides a high thermal conductivity fiber-reinforced composite material that can solve the problems of filler agglomeration in steady-state force fields, difficulty in orderly assembly in ultrasonic single fields, overheating, poor wetting, and difficulty in achieving both high thermal conductivity and mechanical properties with low filler content in existing technologies. Attached Figure Description

[0027] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the embodiments will be briefly described below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0028] Figure 1 The process flow for preparing composite materials by coating and then layup provided by the present invention (Example 1);

[0029] Figure 2 This is a process flow for preparing composite materials by first laying up layers and then coating them, based on the present invention (Example 2);

[0030] Figure 3 a is a surface view of the 25-layer product (product thickness ~5mm), b is a cross-sectional view of the 25-layer product, and c is a cross-sectional view of the 25-layer product.

[0031] Figure 4 The images show cross-sectional views of the 7th, 8th, and 9th layers of a ten-layer quartz fiber cloth, where process A is Example 1 and process B is Example 2.

[0032] Figure 5 Cross-sectional views of 10-QF / BN / EC composite material products treated with a stable force field and 10-QF / BN / EC composite material products treated with dynamic ultrasonic strengthening;

[0033] Figure 6 a) WAXD spectra of QF / BN / EC composite materials prepared under stable voltage and different ultrasonic energies; b) High-resolution WAXD spectra of the samples in the range of 26°-28°; c) High-resolution WAXD spectra of the samples in the range of 41°-43°.

[0034] Figure 7 a represents the thermal conductivity of the QF / BN / EC composite material; b represents the thermal diffusivity of the QF / BN / EC composite material, where the vertical axis represents thermal conductivity (unit: W / (m·K)), the horizontal axis represents the materials with BN content of 30%, 40%, and 50%, respectively, "Regulator" represents the thermal conductivity under steady pressure (unit: W / m·K), and "500J" represents the thermal conductivity under dynamic force (unit: W / m·K).

[0035] Figure 8 Thermogravimetric curves of the QF / BN / EC composite material;

[0036] Figure 9 a) FTIR spectra of QF / BN / EC composite materials prepared under stable voltage and different ultrasonic energies; b) FTIR spectra of samples at 1250-1600 cm⁻¹. -1 High-resolution WAXD spectra within the range; c represents the sample at 1100-1220 cm⁻¹. -1 High-resolution WAXD maps within the range;

[0037] Figure 10a represents the initial state of the sample held by the three-point bending fixture; b represents the bending state; c represents the state about to break; d represents the statistical data of the bending strength test of the QF / BN / EC composite material, where the vertical axis represents the bending strength (unit: MPa), and the horizontal axis represents the materials with BN content of 30%, 40%, and 50%, respectively.

[0038] Figure 11 a represents the initial state of the sample held by the interlaminar shear fixture; b represents the state of imminent failure; c represents the statistical data of interlaminar shear strength test of QF / BN / EC composite material, where the vertical axis represents flexural strength (unit: MPa), and the horizontal axis represents materials with BN content of 30%, 40%, and 50%, respectively. Detailed Implementation

[0039] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and 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.

[0040] To make the above-mentioned objects, features and advantages of the present invention more apparent and understandable, the present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments.

[0041] Experimental materials: Hexagonal boron nitride (BN, catalog number YY-BN-5, purity > 99%, average particle size 1 μm, density 2.7 g / cm³). 3 Purchased from Suzhou Youyan New Materials Industry Co., Ltd.

[0042] Polymer matrix: Bisphenol A cyanate prepolymer, purity ≥99%, purchased from Hubei Jusheng Technology Co., Ltd.

[0043] Fiber cloth: Quartz fiber cloth (SJ108-10 plain weave), SiO2≥99.95%, 0.1 mm plain weave, purchased from Henan Shenjiu Tianhang New Material Co., Ltd.

[0044] Experimental equipment:

[0045] The vacuum planetary mixer degasser (model: BHZ-150) was purchased from Henan Beihong Industrial Co., Ltd. It has a built-in vacuum device that can eliminate submicron-level bubbles and ensure that different raw materials are fully and evenly mixed.

[0046] Ultrasonic welding machine: JLW2015, Shenzhen Jinliwei Technology Co., Ltd.;

[0047] A space-confined assembly system with a gradient pressure control module (adjustable from 0-50 MPa) was constructed.

[0048] Example 1

[0049] Reference Figure 1 This invention discloses a method for preparing a high thermal conductivity fiber-reinforced composite material, specifically including:

[0050] S1. Preliminary Preparations:

[0051] According to the mass ratio of hexagonal boron nitride (BN, purity > 99%, average particle size 1 μm) to bisphenol A cyanate ester resin (EC, purity ≥ 99%), a total mass of 60 g of mixed raw materials was prepared (BN mass fractions of 30%, 40%, and 50%, corresponding to BN mass of 18.0 g / 24.0 g / 30.0 g and EC mass of 42.0 g / 36.0 g / 30.0 g). The raw materials were placed in a vacuum planetary mixer for degassing and mixed at a high shear speed of 2500 r / min for 5 min. Then, the mixture was continuously degassed in a -90 kPa vacuum environment for 2 hours to eliminate submicron-sized bubbles and form a BN / EC mixture (i.e., BE mixture, named BE-3, BE-4, and BE-5 respectively).

[0052] Table 1. Specific content of filler in BN / EC mixture

[0053]

[0054] S2, Fiber pretreatment:

[0055] Select Quartz fiber cloth with ≥99.95%, 0.1mm plain weave, and surface density of 206g / m² is suspended and laid on a constant temperature forming platform. BE mixture is uniformly coated using a scraping process, with the coating amount controlled at 235±2g / m². Subsequently, an ultrasonic device is activated to ultrasonically treat the fiber cloth at a frequency of 20kHz. High-frequency vibration promotes the full penetration of the BE mixture and impregnation of the fiber bundles.

[0056] S3, Layup Pressurization:

[0057] Pretreated quartz fiber cloth was laid flat on the mold substrate in a 0° / 90° orthogonal direction to prepare 10 layers (thickness 5±0.3mm). BE mixture was coated again on the surface of each layer of fiber cloth using a doctor blade. At the same time, a vacuum-assisted infiltration device was turned on to maintain a negative pressure of -85kPa to ensure that the resin fully wetted the fiber bundles. After all layers were stacked, a low-frequency cyclic force field of 1MPa was applied and maintained for 300s to eliminate interlayer porosity.

[0058] (The core of the low-frequency cyclic force field lies in the lifting mechanism, which adopts a scissor-type structure. The piston rod's movement controls the platform's lifting and pressurization process, ensuring that the material receives uniform and effective pressure during compression. In terms of power, pneumatic pressure is used according to the requirements of the experimental platform, and a corresponding pneumatic cylinder is installed. The forward and backward movement of the pneumatic cylinder's piston rod drives the scissor-type lifting platform to reciprocate up and down, achieving the rated pressure for the spatially confined forced assembly method. This part of the structure is not the focus of this experiment; other devices capable of applying a cyclic force field can also achieve the same result.)

[0059] S4, Ultrasound Enhancement:

[0060] Under constant temperature and pressure conditions in a low-frequency cyclic force field, a 20kHz high-frequency ultrasonic force field was intermittently applied (ultrasonic energy controlled at 500J, each cycle lasting 2 minutes, and each cycle lasting 10 seconds). The cycle was repeated 3 times to break up BN agglomerates through ultrasonic cavitation effect and optimize the interfacial bonding state between resin, filler, and fiber.

[0061] (The high-frequency ultrasonic force field generates high-frequency vibrations through an ultrasonic generator. A transducer (containing a piezoelectric ceramic plate) converts electrical energy into mechanical vibration energy. An amplitude modulator transmits and amplifies the vibration energy. A mold head (available in 200×200mm square and 200mm diameter circular sizes) directly contacts the composite material to transmit ultrasonic energy. A pneumatic transmission system controls the movement of each component to achieve intermittent loading of the ultrasonic force field. Similarly, the specific structure of the high-frequency ultrasonic force field is not the focus of this embodiment; any device capable of applying a high-frequency ultrasonic force field can achieve the content of this embodiment.)

[0062] S5, Curing:

[0063] A stepped heating and curing process is performed on the mold. The specific process is: 150℃ for 0.5h → 180℃ for 0.5h → 220℃ for 2h → 230℃ for 3h. After curing, the mold is naturally cooled to room temperature to obtain a high thermal conductivity quartz fiber reinforced cyanate ester resin-based composite material product (maximum size ≥300mm×300mm×15mm).

[0064] Example 2

[0065] Reference Figure 2 As shown, Embodiment 2 provides another method different from Embodiment 1, the only difference being:

[0066] In Example 2, after preparing the mixture, a lay-up and coating process was adopted. Ten layers of quartz fiber fabric were stacked one by one in a 0° / 90° orthogonal lay-up manner to form a preform with a thickness of 5±0.3mm. Then, the BE mixture was coated on both sides of the stacked quartz fiber fabric.

[0067] Example 3

[0068] The only difference between this embodiment and Embodiment 1 is that the pretreated quartz fiber cloth is laid flat on the mold substrate in a 0° / 90° orthogonal direction to prepare a 25-layer (6mm thick) sample.

[0069] Experimental Example 1

[0070] This experimental example is an experimental study on the morphological characterization of composite materials, specifically including:

[0071] S1. Sample pretreatment: The QF / BN / EC composite material sample was subjected to liquid nitrogen brittle fracture to expose the fresh fracture surface. Then, it was subjected to conductivity treatment using an ion sputtering instrument (Au target). The sputtering time was controlled at 90s to avoid the accumulation of surface charge on the sample that would affect the observation.

[0072] S2, Field Emission Scanning Electron Microscopy (FESEM) Characterization

[0073] Instruments and parameters: A Hitachi SU8010 field emission scanning electron microscope was used, with an accelerating voltage of 20kV and a nanometer resolution of ≤3nm, to acquire topological images of the fracture interface of composite materials.

[0074] S3, X-ray diffraction (XRD) characterization

[0075] Instruments and parameters: A RigakuSmartLab X-ray diffractometer was used, with a scanning range of 5°-80° (2θ) and a scanning step size of 0.02° / step; the diffraction data were analyzed using Jade 9.0 software;

[0076] S4. Fourier Transform Infrared Spectroscopy (FTIR) Characterization

[0077] Instruments and parameters: A Nicoleti S50 Fourier transform infrared spectrometer was used, with a scanning wavelength range of 400-4000 cm⁻¹. -1 The resolution is set to 4cm. -1 The transmission spectrum of the sample was acquired; Gaussian peak fitting was performed using OMNIC software.

[0078] Experimental results:

[0079] Figure 4 The cross-sectional morphology of the 7th, 8th and 9th layers of the 10-QF / BN / EC composite material prepared by Example 1 and Example 2 respectively is shown, and the differences in microstructure between the two processes are intuitively compared.

[0080] In the composite material prepared in Example 1, it can be clearly observed that the interfacial bonding between layers is very dense, and the distribution of filler in the matrix exhibits a high degree of uniformity, with no obvious pores, cracks, or other defects found. This uniform filler distribution and tight interlayer bonding provide the composite material with excellent mechanical properties and structural stability, which are important guarantees for its high strength and durability.

[0081] In contrast, the composite material prepared in Example 2 exhibited significant interfacial defects in the cross-sectional morphology of the same layers, particularly between the 8th and 9th layers. The resin and functional fillers failed to adequately impregnate the quartz fiber cloth, resulting in significant interfacial voids in the interlayer bonding area. This insufficient impregnation not only weakens the interlayer bonding force but may also lead to delamination or peeling during use, severely impacting the reliability and service life of the composite material.

[0082] In summary, Example 1 is significantly superior to Example 2 in terms of filler distribution uniformity, interlayer bonding strength, and overall structural integrity, thus better meeting the requirements of high-performance composite materials. Therefore, this invention ultimately selects Example 1 as the preparation method for the composite material to ensure its excellent comprehensive performance.

[0083] Using the preparation method of Example 1, the microstructure of 10-QF / BN / EC composite material products prepared by high-frequency ultrasonic force field treatment was observed (e.g., Figure 5 As shown in the figure, it can be clearly observed that in the 10-QF / BN / EC composite material prepared without high-frequency ultrasonic force field treatment, the BN filler failed to fully penetrate and uniformly wet the interior of the fiber bundles, resulting in obvious voids and interface defects between the fiber bundles. This uneven filler distribution and insufficient interfacial bonding may adversely affect the overall performance of the composite material, particularly in terms of mechanical strength, thermal conductivity, and durability, limiting its potential in high-performance applications.

[0084] In contrast, the microstructure of the 10-QF / BN / EC composite material treated with a high-frequency ultrasonic force field (500J energy) showed significantly improved distribution of BN filler in the fiber bundles, exhibiting higher uniformity and density, while the voids between the fiber bundles were greatly reduced. This optimized filler distribution and interfacial bonding not only enhanced the overall uniformity of the composite material but also significantly improved its mechanical and thermal properties.

[0085] To understand the effect of varying ultrasonic energy parameters of a high-frequency ultrasonic force field on the crystal structure and orientation of composite materials under the same system relaxation time, X-ray diffraction (XRD) was used to further discuss the ultrasonic-induced structural evolution. Figure 6a shows the overall wide-angle X-ray diffraction (WAXD) patterns of 3-25-QF / BN / EC composite materials prepared under continuous voltage stabilization and under dynamic force fields with ultrasonic energies of 300 J, 400 J, 500 J and 600 J respectively.

[0086] All four samples subjected to ultrasound showed peaks similar to those under steady-state conditions, indicating that no crystal transformation occurred during the ultrasound process. Figure 6 Two relatively obvious diffraction peaks can be observed, located at ~27° and ~42°, which can be attributed to the (101) and (100) crystal planes. Figure 6 b. By conducting a more in-depth study of the (101) and (100) crystal planes of each sample under a high-frequency ultrasonic force field, it can be seen that the intensities of (101) and (100) are different under different ultrasonic energies. Among all ultrasonic energies, the 500J sample showed a higher intensity than the other three samples, which suggests that it may have achieved a higher degree of crystallinity.

[0087] Furthermore, compared with other ultrasonic energy samples, the (101) and (100) diffraction peaks of the 500J sample showed a significant rightward shift, indicating a decrease in interplanar spacing (dhkl) [84,85]. The ultrasonic cavitation effect (i.e., the physical process of ultrasound) manifests as ultrasound causing the medium to alternately generate high and low pressure cycles, forming microbubbles. When the bubbles reach a certain volume, they rupture, generating shear force and releasing a large amount of energy.

[0088] High-energy ultrasonic treatment at 500J induces local compressive stress within the composite material, particularly at the interface between quartz fiber and cyanate ester resin or around the BN filler, through ultrasonic cavitation and mechanical vibration. This leads to lattice shrinkage of the quartz fiber and BN filler, indicating that ultrasonic energy can promote the dispersion and interfacial bonding of BN filler in the resin matrix, enhance the matrix's constraint on the filler, and further compress the lattice. However, ultra-high energy at 600J causes local overheating (the instantaneous high temperature during ultrasonic cavitation can reach thousands of K), resulting in the breakage of the cyanate ester resin main chain or the destruction of the cross-linked network. This reduces the matrix's constraint on the filler, releasing the compressive stress and causing the lattice to rebound. This is reflected in the figure as an increase in dhkl and a leftward shift of the peak position. Furthermore, excessively high ultrasonic energy may cause amorphization on the surface of the quartz fiber or disordered layering of BN, leading to a decrease in crystallinity, which is reflected in the figure as a reduction in peak area.

[0089] Therefore, it can be clearly seen that in the low-energy region (<500J), the energy is mainly used to overcome filler agglomeration and weak interfacial bonding; in the critical energy region (500J), the optimal stress-structure control threshold is reached, and compressive stress and interfacial bonding are synergistically strengthened; in the energy overload region (>500J), the energy exceeds the material's thermo-mechanical bearing capacity limit, causing thermal damage and performance degradation. Therefore, the ultrasonic energy should be stably controlled between 450-550J to avoid the risk of thermal damage, and intermittent loading should be adopted to reduce the cumulative temperature rise.

[0090] Example 2

[0091] This embodiment studies the characterization of the thermal conductivity properties of composite materials, specifically including:

[0092] S1, Sample Pretreatment

[0093] Before testing, the surface of the QF / BN / EC composite material sample needs to be polished to ensure that the surface roughness Ra < 2μm. This is to avoid uneven surface that could lead to poor contact between the probe and the sample, affecting the accuracy of thermal conduction signal acquisition.

[0094] S2. Preparation of Experimental Equipment

[0095] The HotDisk TPS2500 transient planar thermal source analyzer, manufactured by HotDisk AB of Sweden, was used. Based on transient planar thermal source technology (TPS), the thermal conductivity of the material was calculated by analyzing the thermal response signal when the probe came into contact with the sample.

[0096] S3, Test Parameter Settings

[0097] Environmental conditions: The ambient temperature was controlled at 25±0.2℃ to eliminate the interference of temperature fluctuations on the thermal conductivity measurement;

[0098] Loading parameters: The test power applied to the sample is 50mW, and the single test time is set to 3.2s, balancing test efficiency and data accuracy;

[0099] Repeatability requirement: To ensure data reliability, each sample is tested three times, and the average of the three test results is taken as the thermal conductivity data of the sample.

[0100] Experimental results:

[0101] Figure 7 In step a, multiple thermal conductivity tests were conducted on different regions of different samples to obtain an average thermal conductivity value. The specific data are shown in Table 2.

[0102] As can be seen, the thermal conductivity of the samples treated with a dynamic force field is significantly higher than that of the samples under a steady pressure field. Furthermore, when the BN filling amount is 30%, the thermal conductivity of the samples treated with a dynamic force field reaches 1.48 W / (m·K). On the one hand, the BN particles in the samples treated with a steady pressure field may agglomerate, forming localized high thermal conductivity zones, but the overall thermal conductivity is limited. High-frequency ultrasound can effectively break up BN agglomerates, allowing them to be uniformly dispersed in the resin matrix, forming a continuous thermal conduction network. On the other hand, the interface between BN and resin in the samples treated with a steady pressure field may have pores or weak bonding, increasing interfacial thermal resistance. High-frequency ultrasound treatment can enhance the interfacial bonding between BN and resin, reduce phonon scattering, and improve thermal conduction efficiency.

[0103] Similarly, through the thermal diffusivity ( Figure 7 (b) The rate of heat transfer within the sample was measured. It can be seen that the high-frequency ultrasonic force field not only increases thermal conductivity but also significantly affects the thermal diffusivity. The thermal diffusivity (α) is determined by three parameters: thermal conductivity (k), density (ρ), and specific heat capacity (Cp). The thermal diffusivity of high-frequency ultrasonic processes is generally higher because the increase in thermal conductivity (k) is dominant, and small changes in ρ and Cp synergistically enhance the rate of heat diffusion.

[0104] In summary, high-frequency ultrasound improves the dispersion and interfacial bonding of BN, reduces thermal resistance, and accelerates heat diffusion.

[0105] Table 2. Comparison of thermal conductivity data of composite materials under different processes

[0106]

[0107] Experimental Example 3

[0108] This experimental example studies the thermal stability of composite materials, specifically including:

[0109] S1. Sample Preparation

[0110] QF / BN / EC composite material samples with different BN filling amounts (30wt%, 40wt%, 50wt%) were selected. All samples were prepared using a dynamic force field forming process (low-frequency cyclic force field + 500J high-frequency ultrasonic force field). Before testing, the samples were ensured to be dry and free of impurities. An appropriate amount of sample was placed in a special crucible, and the sample chamber of the instrument was placed in the crucible before the heating program was started.

[0111] S2, Instrument Parameters

[0112] A TAQ500 thermogravimetric analyzer was used; the test atmosphere was air, and the gas flow rate was controlled at 50 mL / min; the temperature program was to increase from room temperature to 800℃ at a rate of 10℃ / min; thermogravimetric (TGA) curves and derivative thermogravimetric (DTG) curves were acquired using the instrument's software.

[0113] Experimental results:

[0114] Figure 8 The thermogravimetric analysis (TGA) curves of composite material samples prepared using dynamic ultrasonic force fields show that, overall, the higher the BN content, the greater the residual mass, the later the decomposition temperature, and the stronger the thermal stability.

[0115] In the initial stage (200-400℃), the weak bonds (such as ester groups and ether bonds) in the cyanate ester resin are mainly broken, releasing small molecule gases (such as CO2, H2O, etc.). The dynamic ultrasonic force field optimizes the interfacial bonding, reduces the exposed surface area of ​​the resin, and inhibits the release of volatile products.

[0116] In the main decomposition stage (400-600℃), the main chain breaks, generating carbonized residues and volatile products, while the dynamic ultrasonic force field makes the composite material more compact, inhibits oxygen penetration, and slows down oxidative decomposition.

[0117] During the high-temperature residual carbon stage (600-800℃), the residues are mainly BN, quartz fiber, and a small amount of resin carbonization residue.

[0118] Traditional hot pressing processes have certain drawbacks. BN (bond nanoparticles) tends to agglomerate, leading to localized resin enrichment, an increase in thermal decomposition initiation points, and decreased thermal stability. Samples prepared under a dynamic ultrasonic force field, however, reduce the risk of localized resin overheating and suppress the escape pathways of decomposition gases, thus delaying mass loss. Figure 8 It can be seen that the TGA curve of the QF / BN-5 / EC sample has a gentler slope, which means that the BN thermally conductive network slows down the resin decomposition kinetics process. Furthermore, after 450℃, the curve of the QF / BN-5 / EC sample shifts to the right overall, indicating that the thermal stability has been improved.

[0119] Table 3. Comparison of thermogravimetric data of composite materials with different BN contents

[0120]

[0121] To gain a deeper understanding of the impact mechanism of ultrasonic treatment on the structure and interface of composite materials, Fourier transform infrared spectroscopy (FTIR) was used to analyze the chemical bond vibration characteristics by measuring the absorption or transmission characteristics of infrared light by the sample. The total spectrum is shown below. Figure 9 As shown in a.

[0122] As can be seen from the figure, the samples under stable voltage and under dynamic force fields with applied ultrasonic energies of 300 J, 400 J, and 500 J, respectively, exhibit similar peaks, while the sample with applied ultrasonic energy of 600 J shows significant differences. (1500 cm⁻¹) -1 and 1100cm -1 The peak intensity gradually increases with increasing ultrasonic energy, reaches a peak, and then suddenly decreases. It can be seen that at 1500 cm⁻¹...-1 The nearby broad peaks are significantly weakened (e.g.) Figure 9 (b) This is due to the C=C stretching vibration or NH bending vibration of the aromatic ring in the cyanate ester resin. On the one hand, high-energy ultrasound may disrupt the resin structure; higher ultrasound energy (600J) may induce resin molecular chain breakage or reduce the degree of cross-linking, leading to a decrease in characteristic peak intensity. On the other hand, high-energy ultrasound enhances interfacial interactions, promoting better dispersion of BN in the cyanate ester resin, strengthening interfacial bonding, and restricting resin molecular vibration, resulting in a decrease in peak width and peak area. Furthermore, the sample subjected to 600J ultrasound energy showed a decrease in peak intensity at 1100 cm⁻¹. -1 The nearby twin peaks are extremely faint or even disappear (e.g.) Figure 9 (c) This may be due to the Si-O-Si antisymmetric stretching vibration of the quartz fiber. On the one hand, the cavitation effect of high-energy ultrasound physically damages the surface of the quartz fiber, leading to local destruction of the Si-O-Si structure and weakening of characteristic peaks; on the other hand, it may cause the reconstruction of interfacial chemical bonds. High-energy ultrasound promotes the chemical bonding between the resin and BN, forming Si-OC or BOC bonds, while the original Si-O-Si vibration mode is suppressed; furthermore, high-energy ultrasound improves the dispersion of the filler and reduces the scattering interference caused by agglomeration, making the peaks "cleaner" or merged.

[0123] Therefore, it can be concluded that high-frequency ultrasound at 600J makes the BN filler more uniformly dispersed, but may cause resin degradation or fiber surface damage, resulting in changes in FTIR characteristic peaks. This proves that there is an energy threshold (500J), beyond which the interface / structure undergoes abrupt changes.

[0124] Therefore, using 500J of high-frequency ultrasonic energy is the optimal choice.

[0125] Test Example 4

[0126] This experimental example aims to characterize the mechanical properties of composite materials, specifically including:

[0127] S1. Sample Preparation

[0128] A 25-layer (6mm thick) QF / BN / EC composite material product (Example 3) was selected, and three BN filling gradients of 30wt%, 40wt%, and 50wt% were set. For each filling amount, two process samples were prepared (curing under stable pressure field and dynamic force field forming assisted by high-frequency ultrasonic force field (500J)). The sample size met the requirements of the three-point bending test, and the surface was free of defects such as cracks and bubbles.

[0129] S2, Bending Strength Test

[0130] According to the GB / T1449-2005 standard, the three-point bending test method is used to determine the bending strength of composite materials. By applying a bending load perpendicular to the ply direction to the sample, the maximum load at which the sample breaks is recorded, and the bending strength is calculated in combination with the sample size, which reflects the material's ability to resist bending deformation and fracture.

[0131] Clamp the sample using a three-point bending fixture. Figure 10 As shown in the figure, ensure that the fixture is in close contact with the sample and that the force is uniform; apply bending load at the same loading rate, record the load change of the sample from initial deformation to imminent fracture, and obtain the maximum load data; perform multiple repeated tests on samples of each process and each BN content, and take the average value as the final bending strength data.

[0132] S3, Interlaminar Shear Strength Test

[0133] Based on the ASTM D2344 short beam shear method, the span-to-thickness ratio L / h was set to 4. By applying a concentrated load to the short beam sample, shear stress was generated between the layers of the sample. The load at which the sample failed between the layers was recorded, and the interlaminar shear strength was calculated to reflect the interfacial bonding ability of the composite material.

[0134] Samples were fixed using interlayer shear fixtures. Figure 11 (State a) Ensure the load line is perpendicular to the sample layup direction; apply load at a constant loading rate and observe interlaminar deformation until near failure. Figure 11 (b state) Record the maximum shear load; repeat the test multiple times for each sample and calculate the interlaminar shear strength by taking the average value.

[0135] Experimental results:

[0136] The flexural strength of the 25-QF / BN / EC composite material was evaluated, and the specific data are shown in Table 4.

[0137] The samples were prepared using two different processes: one was pressure-stabilized curing at 1 MPa, and the other was applying 500 J of ultrasonic energy to the samples under a high-frequency ultrasonic force field. Figure 10 'a' represents the initial state of the sample held by the three-point bending fixture. The applied force starts from the lower central support point, causing the sample to bend. The bending deformation intensifies with increasing force. Figure 10 b), until it approaches the fracture state ( Figure 10 c).

[0138] Figure 10 As can be seen, under both the stabilizing condition and the high-frequency ultrasonic force field, the flexural strength of 30wt% BN is the highest, at 420.39MPa and 469.6MPa respectively. However, as the BN content increases, the flexural strength of the samples decreases to varying degrees under both process conditions.

[0139] Specifically, under stable pressure, as the BN content increases, on the one hand, the BN content exceeds the resin's encapsulation capacity, causing the BN network to directly bear the load and the fiber strain to lag. On the other hand, the high BN content increases the resin viscosity, inhibiting resin penetration into the fiber bundle and creating unwetted pores. However, in the sample under a high-frequency ultrasonic force field, when the BN content is 30%, the ultrasonic cavitation effect generates microjets, effectively breaking up the BN aggregates. Through thermal mismatch, compressive stress is generated at the interface, improving the bonding strength. But when the BN content exceeds 30%, there is a significant downward trend, indicating that the ultrasonic energy is insufficient to disperse the high-concentration BN, resulting in stress concentration, breakdown of the interfacial bonding, and brittle fracture. In particular, a key data point shows that at 50 wt% BN, the flexural strength of the stabilized treatment (280.21 MPa) surpasses that of the ultrasonic treatment (270.68 MPa). This is likely because when the BN filling amount is too high, the energy of the microjets generated by ultrasonic cavitation is insufficient to overcome the van der Waals forces, leading to secondary agglomeration. These agglomerates become stress concentration elements, resulting in an increased crack propagation rate. In contrast, continuous stabilization does not present thermal damage issues. This indicates that at low BN filling amounts, dispersion optimization is dominant, while at high BN filling amounts, densification becomes more critical.

[0140] Table 4. Comparison of flexural strength data of composite materials with different BN contents

[0141]

[0142] Similarly, the interlaminar shear strength of the 25-QF / BN / EC composite was evaluated, and the specific data are shown in Table 5. It can be seen that, for all BN contents, the shear strength under high-frequency ultrasonic force field was significantly higher than that under pure pressure stabilization treatment, with an average increase of approximately 45%. Furthermore, the interlaminar shear strength of the samples treated with high-frequency ultrasonication decreased more slowly with increasing BN filling amount. This may be because the 500J high-frequency ultrasound generates microjets and shock waves, effectively breaking up the initial BN agglomerates. Ultrasound also induces the resin molecular chains to form more hydrogen bond networks with the hydroxyl groups (-OH) on the BN surface. Even with a BN content of 50wt%, the hydrogen bond network treated by ultrasound can still maintain the percolation threshold, microscopically improving the interfacial bonding energy and energy dissipation capacity. In contrast, pressure stabilization treatment, due to uneven dispersion, forms isolated hydrogen bond "islands," which macroscopically manifests as a significant delay in the decay of interlaminar shear strength in high-BN-filled composites.

[0143] Table 5. Comparison of shear strength data of composite materials with different BN contents

[0144]

[0145] Multiple experimental examples have demonstrated that the product of this invention achieves synergistic improvements in filler dispersion, thermal conductivity, thermal stability, and mechanical properties through a dynamic force field molding process (low-frequency cyclic force field + high-frequency ultrasonic force field synergy). All technical effects are verified based on experimental data.

[0146] Regarding filler dispersion and interfacial bonding, the product of Example 1 showed no interlayer voids, with BN filler uniformly dispersed between the resin matrix and quartz fiber bundles. In contrast, Example 2 and the unultrasonicated product under a stable pressure field exhibited BN agglomeration and insufficient fiber-resin impregnation. At 500J ultrasonic energy, the (101) and (100) crystal plane diffraction peaks of BN showed the highest intensity and a rightward shift in position, at 1500cm⁻¹. -1 (Resin aromatic ring C=C vibration), 1100cm -1 The characteristic peak intensity of (fiber Si-O-Si vibration) is the best, and the interfacial hydrogen bonding effect is the strongest. The crystallinity will decrease and the characteristic peak will weaken due to energy overload of 600J ultrasound.

[0147] With low BN filler content, the dynamic force field process significantly improves thermal conductivity. At 30wt% BN filler, the thermal conductivity of the dynamically force field-molded product reaches 1.45 W / m. K, compared to products with stable pressure fields, increased by 42.16%; when filled with 40wt% and 50wt% BN, the dynamic force field thermal conductivity was 1.50 W / m. K, 1.59W / m K is 19.05% and 13.57% higher than that of the steady pressure field, respectively, and the thermal diffusion coefficient of the high-frequency ultrasonic force field process products is generally higher than that of the steady pressure field, and the heat transfer speed is accelerated.

[0148] Thermal stability increases with increasing BN content. With 50wt% BN, the residual mass of the product at 500℃ is 90.97% and at 800℃ is 85.91%, which are 2.89% and 5.85% higher than those with 30wt% BN, respectively. The thermogravimetric curve of the product under dynamic force field is more gentle. The thermal conductivity network of BN can slow down the resin decomposition kinetics and reduce mass loss at high temperatures.

[0149] In terms of mechanical properties, in Example 3, with 30wt% BN filling, the flexural strength of the product under high-frequency ultrasonic force field reached 469.6MPa, which is 11.71% higher than that under stable pressure field. Even when the BN content increased to 50wt%, the flexural strength of the product under dynamic force field remained at 367.68MPa, and the performance degradation was lower than that under stable pressure field. The interlaminar shear strength further highlights the advantages of dynamic force field. With 30wt% BN, the product under high-frequency ultrasonic force field reached 65.05MPa, which is 33.79% higher than that under stable pressure field. With 50wt% BN, the improvement rate reached 57.40%. The optimization of interface bonding effectively delayed the degradation of interlaminar performance under high filler content.

[0150] The embodiments described above are merely preferred embodiments of the present invention and are not intended to limit the scope of the present invention. Various modifications and improvements made by those skilled in the art to the technical solutions of the present invention without departing from the spirit of the present invention should fall within the protection scope defined by the claims of the present invention.

Claims

1. A method for producing a high thermally conductive fiber-reinforced composite material, characterized by, Comprising: S1, preliminary preparation: mix hexagonal boron nitride and cyanate ester resin in proportion, put into a vacuum planetary stirring defoaming machine for shearing mixing and defoaming to form a BE mixture, the cyanate ester groups contained in the cyanate ester resin in this process can form a highly cross-linked network with triazine ring as the basic unit through cyclization trimerization reaction, which provides the necessary structural basis for the full play of the reinforcing effect of hexagonal boron nitride filler; S2, fiber pretreatment: place the quartz fiber cloth on the constant temperature molding platform, uniformly coat the BE mixture by scraping coating process, and let the BE mixture fully infiltrate the fiber tows by ultrasonic treatment; S3, layer pressing: place several pretreated fiber cloths in order on the mold base plate to form a stack, re-coat the BE mixture during each layer laying, ensure the infiltration of the fiber tows by vacuum assisted infiltration device, and eliminate interlayer pores by applying a low frequency cyclic force field after completing the stacking; S4, ultrasonic strengthening: under the condition of constant temperature and pressure of low frequency cyclic force field, intermittently load 20kHz high frequency ultrasonic force field, and operate at least 2 times to break the agglomeration of the BE mixture and optimize the interfacial bonding; S5, curing: heat curing to finally obtain a high thermal conductivity fiber reinforced composite product.

2. The method of claim 1, wherein: In step S1, the hexagonal boron nitride accounts for 5-50% of the total mass fraction of the BE mixture.

3. The method for preparing the high thermal conductivity fiber-reinforced composite material according to claim 1, characterized in that: The coating amount of the BE mixture in the step S2 is 230-240 g / m 2 .

4. The method for preparing the high thermal conductivity fiber-reinforced composite material according to claim 1, characterized in that: In step S2, the BE mixture is fully infiltrated into the fiber tows by ultrasonic treatment, and 20kHz high frequency ultrasonic treatment is used.

5. The method for preparing the high thermal conductivity fiber-reinforced composite material according to claim 1, characterized in that: In step S3, the number of layers of the pretreated fiber cloth is 1-100 layers.

6. The method of making a high thermally conductive fiber reinforced composite of claim 1, wherein: In step S3, the vacuum assisted infiltration device is set to-85kPa vacuum to ensure the infiltration of the fiber tows.

7. The method of making a high thermally conductive fiber reinforced composite of claim 1, wherein: In step S3, after completing the stacking, a 1MPa low frequency cyclic force field is applied and maintained for 300s to eliminate interlayer pores.

8. The method of claim 1, wherein: In step S4, the ultrasonic energy of the 20kHz high frequency ultrasonic force field is 500J, 10s is one cycle, and each round lasts for 2min.

9. The method of claim 1, wherein: In step S5, during heat curing, heat pressing curing is carried out according to the curing curve of 150℃×0.5h, 180℃×0.5h, 220℃×2h, 230℃×3h, and finally a high thermal conductivity fiber reinforced composite product is obtained.

10. A high thermal conductivity fiber reinforced composite material prepared according to the method of any one of claims 1-9.

Images