Modified multi-walled carbon nanotube / silicon carbide / cellulose nanocrystal heat-conducting composite material and preparation method thereof

Abstract

The application discloses a modified multi-walled carbon nanotube / silicon carbide / cellulose nanocrystal heat-conducting composite material and a preparation method thereof. The preparation method comprises the following steps: adding a liquid silane coupling agent into an ethanol solution and performing ultrasonic hydrolysis, then adding hydroxylated MWCNT, performing water bath heating reaction after uniform dispersion, and obtaining modified MWCNT through centrifugal washing and drying after the reaction is completed; placing SiC in a muffle furnace for oxidation, then performing HF immersion, and obtaining modified SiC through washing and drying; and taking CNC as a matrix, uniformly mixing the CNC with the modified MWCNT and the modified SiC, dispersing the mixture in an organic solvent, and then performing suction filtration to obtain the composite material. Different siloxyl groups are grafted on the MWCNT through the silane coupling agent, and hydroxyl groups are grafted on the silicon carbide through HF treatment, so that the interface bonding between the fillers MWCNT and SiC and the CNC matrix is better, the interface thermal resistance of the composite material is reduced, and the heat-conducting performance of the composite material is improved.

Description

Technical Field

[0001] This invention belongs to the field of composite material preparation technology, specifically, it relates to a modified multi-walled carbon nanotube / silicon carbide / cellulose nanocrystal thermally conductive composite material and its preparation method. Background Technology

[0002] With the development of technology, electronic components are moving towards miniaturization and high integration. These devices generate a significant amount of heat during operation. This heat is conducted to heat sinks through thermal interface materials, and then dissipated through convection of air or other cooling media, ultimately transferring the heat to the external environment. If the waste heat generated by electronic components and equipment cannot be effectively dissipated to control their operating temperature, the operational stability of the devices and equipment will be significantly affected. Therefore, thermal interface materials urgently need to possess better thermal conductivity and heat dissipation properties.

[0003] Polymers are widely used in heat dissipation materials for electronic devices due to their excellent electrical insulation and processing properties. Adding thermally conductive fillers such as boron nitride, silicon carbide, and carbon nanotubes to polymers can significantly improve their thermal conductivity, thereby enhancing the heat dissipation performance of composite materials. However, when using a single filler to fill the polymer matrix, a high filler content is usually required to achieve a higher thermal conductivity, which may lead to a decrease in the mechanical and processing properties of the composite material. Furthermore, excessive filler addition may result in too many harmful interfaces within the composite material, limiting the improvement of its thermal conductivity. Mixing two or more fillers of different types or sizes in appropriate proportions is an effective solution. This approach increases the contact area between fillers, thus facilitating the construction of more effective heat conduction pathways and effectively improving the thermal conductivity of the composite material. One-dimensional carbon nanotubes, due to their high aspect ratio, good thermal stability, excellent mechanical properties, and thermal conductivity, produce a synergistic effect when combined with thermally conductive particulate silicon carbide in the matrix, further enhancing the thermal conductivity of the composite material. However, both multi-walled carbon nanotubes (MWCNTs) and silicon carbide fillers still exhibit significant interfacial thermal resistance with the matrix, limiting a substantial increase in the thermal conductivity of the composite material. Therefore, achieving good interfacial bonding between the filler and the polymer matrix remains a challenging task. Summary of the Invention

[0004] To address the aforementioned problems, this invention provides a modified multi-walled carbon nanotube / silicon carbide / cellulose nanocrystal thermally conductive composite material and its preparation method. This invention improves the interfacial bonding between the two fillers and the cellulose nanocrystal CNC matrix, enhances the dispersibility of carbon nanotubes, and reduces the interfacial thermal resistance between the composite materials, thereby improving the thermal conductivity of the composite material. The specific technical solution of this invention is described below.

[0005] A method for preparing a modified multi-walled carbon nanotube / silicon carbide / cellulose nanocrystal thermally conductive composite material includes the following steps:

[0006] Step 1: Add the liquid silane coupling agent to the ethanol solution and sonicate it for hydrolysis. After hydrolysis, add hydroxylated multi-walled carbon nanotubes and disperse them by sonication.

[0007] Step 2: React the solution obtained in Step 1 at a temperature of 55-65℃ for 5-7 hours. After the reaction is completed, centrifuge and wash with deionized water. Then dry the precipitate to obtain modified hydroxylated multi-walled carbon nanotubes.

[0008] Step 3: Place the silicon carbide particles in a muffle furnace for heat treatment oxidation. After oxidation, add the oxidized sample to a mixed solution of HF and ethanol and stir. After completion, centrifuge and wash with deionized water. Then dry the precipitate to obtain modified silicon carbide particles SiC-OH.

[0009] Step 4: After fully dispersing the modified silicon carbide particles SiC-OH in an organic solvent, add the carboxylated cellulose nanocrystal CNC solution and mix thoroughly by ultrasonication to obtain a SiC-OH / CNC dispersion.

[0010] Step 5: Add the modified hydroxylated multi-walled carbon nanotubes obtained in Step 2 to the SiC-OH / CNC dispersion and mix evenly by ultrasonication;

[0011] Step 6: Vacuum filter the mixed solution obtained in Step 5, and then dry the resulting film to obtain the modified multi-walled carbon nanotube / silicon carbide / cellulose nanocrystal thermally conductive composite material.

[0012] In this invention, in step one, the silane coupling agent is selected from at least one of vinyltriethoxysilane A151, vinyltrimethoxysilane A171, 3-aminopropyltrimethoxysilane KH540, γ-aminopropyltriethoxysilane KH550, γ-glycidoxypropyltrimethoxysilane KH560, γ-(methacryloyloxy)propyltrimethoxysilane KH570, or γ-mercaptopropyltriethoxysilane KH580; in the ethanol solution, the volume ratio of ethanol to water is between 9:1 and 7:1; the volume ratio of ethanol solution to silane coupling agent is between 120:1 and 80:1; the mass ratio of hydroxylated multi-walled carbon nanotubes to silane coupling agent is between 10:1 and 50:1 g / mL; the ultrasonic hydrolysis temperature is between 40-80℃, the ultrasonic frequency is 40 kHz, the ultrasonic power is between 100-500 W, and the ultrasonic time is between 5 min and 30 min.

[0013] In this invention, in step three, the heating temperature of the muffle furnace is 680-720℃, the heating time is 30min-90min, and the heating rate of the muffle furnace is 8-15℃ / min.

[0014] In this invention, in step three, the volume ratio of HF to ethanol in the mixed solution is between 9:1 and 8:3; the stirring time is 10-60 min.

[0015] In this invention, in steps two and three, the centrifugation speed is 9000 r / min and the time is 10 min, and the resulting precipitate needs to be washed with deionized water 3 to 4 times.

[0016] In this invention, in step four, the organic solvent is N,N-dimethylformamide (DMF); the concentration of the CNC solution is 2 wt% to 5 wt%; and in the SiC-OH / CNC dispersion, the mass ratio of modified silicon carbide particles (SiC-OH) to carboxylated cellulose nanocrystals (CNC) is 1:1.

[0017] In this invention, in step five, the content of modified hydroxylated multi-walled carbon nanotubes is 1-6 wt% of the total mass of modified silicon carbide particles SiC-OH and carboxylated cellulose nanocrystals CNC; preferably, it is 4-6%, and most preferably, it is 5%.

[0018] In this invention, in step five, the filter membrane used for vacuum filtration is a nylon membrane. In a specific embodiment, its pore size is 0.22 μm and its diameter is 47 mm.

[0019] In this invention, in steps four and five, the ultrasonic treatment temperature is 20-40℃, the ultrasonic frequency is 40KHz, the ultrasonic power is between 100-500W, and the ultrasonic time is 1-3h.

[0020] In this invention, in steps two, three and six, vacuum drying is used, the drying temperature is between 60-80℃ and the drying time is between 30min-12h.

[0021] The present invention also provides a modified hydroxylated multi-walled carbon nanotube / silicon carbide / cellulose nanocrystal composite material prepared by the above preparation method.

[0022] The modification principle of this invention is as follows:

[0023] Hydroxylated carbon nanotube modification: First, the silane coupling agent undergoes a hydrolysis reaction to form silanol groups of different chain segments. When hydroxylated MWCNTs are added, the silanol groups undergo a coupling reaction with the MWCNTs, grafting different silanol groups onto the MWCNTs to obtain silanized MWCNTs. After the silanized MWCNTs are added to the CNC matrix, they undergo chemical cross-linking with the CNCs, resulting in uniform dispersion and strong bonding of the MWCNTs within the CNC matrix.

[0024] Silicon carbide modification: SiC does not react with HF at room temperature, while SiO2 can. The purpose of SiC surface oxidation is to remove excess carbon (C) and generate a SiO2 layer. The reaction equation for HF with SiO2 is: SiO2 + 4HF = SiF4 + 2H2O. When HF reacts with and removes SiO2, a large number of coordinated unsaturated atoms are exposed on the SiC surface. When the O atoms at the Si ends of SiC are removed, they form Si-F bonds with F atoms. Simultaneously, the coordinated unsaturated atoms at the C ends interact with H2O molecules to introduce -OH groups, forming SiC-OH. The hydroxyl groups on the SiC-OH surface form hydrogen bonds with the carboxyl groups on the CNC surface, resulting in more uniform dispersion of SiC in the composite material and a tighter bond with the matrix.

[0025] Compared with the prior art, the positive and progressive effects of the present invention are as follows:

[0026] (1) The advantage of the modified hydroxylated multi-walled carbon nanotube / modified silicon carbide / cellulose nanocrystal composite material provided by the present invention is that the thermal conductivity of the composite material is effectively improved by combining two different types of fillers.

[0027] (2) Surface modification of hydroxylated multi-walled carbon nanotubes was carried out using silane coupling agent, and surface modification of silicon carbide was carried out using HF. This reduced the interfacial thermal resistance between the filler and the matrix, resulting in a composite material with better thermal conductivity.

[0028] (3) Modifying hydroxylated multi-walled carbon nanotubes and silicon carbide can improve the dispersibility of fillers in the matrix. Attached Figure Description

[0029] Figure 1 This is a schematic diagram of each reaction step in the preparation method of the present invention.

[0030] Figure 2 The images show the infrared spectra of hydroxylated multi-walled carbon nanotubes before and after modification in this invention.

[0031] Figure 3 The images show the infrared spectra of silicon carbide before and after modification in this invention.

[0032] Figure 4 Thermal conductivity diagrams for silicon carbide / cellulose nanocrystalline thermally conductive composites with different SiC contents.

[0033] Figure 5 Thermal conductivity diagram of the modified multi-walled carbon nanotube / silicon carbide / cellulose nanocrystal thermally conductive composite material. Detailed Implementation

[0034] The preferred embodiments of the present invention are given below with reference to the accompanying drawings to illustrate the technical solution of the present invention in detail.

[0035] Please see Figure 1 As shown, this invention provides a method for preparing a surface-modified composite material of hydroxylated multi-walled carbon nanotubes, comprising the following steps:

[0036] Example 1

[0037] Preparation of modified hydroxylated multi-walled carbon nanotubes: First, use a pipette to draw 1 ml of KH560 and add it to 100 ml of ethanol solution (V 乙醇 V 水 =9:1), KH560 was hydrolyzed by sonication at 60℃ for 10 min, then 3g of hydroxylated multi-walled carbon nanotubes were weighed and added to the solution, and sonicated at 60℃ for 2 h to disperse the multi-walled carbon nanotubes evenly. After completion, the mixed solution was poured into a three-necked flask and heated in a water bath at 60℃ for 6 h. After the reaction was completed, the mixture was centrifuged and the resulting precipitate was washed three times with deionized water. The resulting product was placed in a vacuum drying oven and dried at 80℃ for 12 h to obtain the modified hydroxylated multi-walled carbon nanotubes. Its infrared spectrum is shown in the figure. Figure 2 As shown, the modified hydroxylated multi-walled carbon nanotubes possess the characteristic absorption peak of the siloxane group in KH560 (Si-O, 1080 cm⁻¹). -1 (The presence of the mark indicates successful modification).

[0038] Preparation of modified silicon carbide: 3g of silicon carbide particles were placed in a muffle furnace and heated at 700℃ for 1 hour for oxidation. After oxidation, the particles were added to a mixed solution of HF and ethanol (V 乙醇 V HF =8:2) Stir for 15 min, centrifuge, and wash the precipitate three times with deionized water. Place the product in an oven and dry at 70℃ to obtain modified silicon carbide particles. Its infrared spectrum is shown below. Figure 3 As shown, oxidized silicon carbide (SiC-700) at 1100-1200 cm⁻¹ -1 A distinct absorption band is observed at this point, corresponding to the asymmetric stretching vibration of the Si-O bond, which can be attributed to surface SiO2. After HF treatment, the characteristic absorption band of SiO2 almost disappears, indicating that the etching process successfully removed the oxide layer on the surface of the SiC nanosheets. A 3400 cm⁻¹ absorption band can also be observed in the spectrum of the SiC-HF sample. -1 The presence of characteristic peaks belonging to hydroxyl groups in the vicinity, while the disappearance of characteristic peaks of Si-O bonds, indicates that the etching process not only removed SiO2 but also introduced some hydroxyl groups, demonstrating successful modification.

[0039] Preparation of composite material: 0.15g of modified silicon carbide was added to N,N-dimethylformamide (DMF) solution and stirred at room temperature for 2h on a magnetic stirrer. After stirring, 3g of CNC solution with a content of 5wt% was added and sonicated at 30℃ for 2h. Then, 0.003g of modified MWCNT was added to SiC / CNC solution and sonicated at 30℃ for 2h. After sonication, the resulting mixed solution was transferred to a vacuum filtration flask in three parts for vacuum filtration. After filtration, the film adhering to the filter membrane was dried in an oven at 60℃ for 2min. Then, the filter membrane was removed and the film was dried for another 30min to obtain a MWCNT / SiC / CNC composite film with a modified MWCNT content of 1wt%.

[0040] Example 2

[0041] Preparation of composite material: 0.15g of modified silicon carbide was added to N,N-dimethylformamide (DMF) solution and stirred at room temperature for 2h on a magnetic stirrer. After stirring, 3g of 5% CNC solution was added to SiC solution and sonicated at 30℃ for 2h. Then, 0.006g of modified MWCNT was added to SiC / CNC solution and sonicated at 30℃ for 2h. After sonication, the resulting mixed solution was transferred to a vacuum filtration flask in three parts for vacuum filtration. After filtration, the film adhering to the filter membrane was dried in an oven at 60℃ for 2min. Then, the filter membrane was removed and the film was dried for another 30min to obtain a MWCNT / SiC / CNC composite film with a modified MWCNT content of 2wt%.

[0042] Example 3

[0043] Preparation of composite material: 0.15g of modified silicon carbide was added to N,N-dimethylformamide (DMF) solution and stirred at room temperature for 2h on a magnetic stirrer. After stirring, 3g of 5% CNC solution was added to SiC solution and sonicated at 30℃ for 2h. Then, 0.009g of modified MWCNT was added to SiC / CNC solution and sonicated at 30℃ for 2h. After sonication, the resulting mixed solution was transferred to a vacuum filtration flask in three parts for vacuum filtration. After filtration, the film adhering to the filter membrane was dried in an oven at 60℃ for 2min. Then, the filter membrane was removed and the film was dried for another 30min to obtain a MWCNT / SiC / CNC composite film with a modified MWCNT content of 3wt%.

[0044] Example 4

[0045] Preparation of composite material: 0.15g of modified silicon carbide was added to N,N-dimethylformamide (DMF) solution and stirred at room temperature for 2h on a magnetic stirrer. After stirring, 3g of 5% CNC solution was added to SiC solution and sonicated at 30℃ for 2h. Then, 0.012g of modified MWCNT was added to SiC / CNC solution and sonicated at 30℃ for 2h. After sonication, the resulting mixed solution was transferred to a vacuum filtration flask in three parts for vacuum filtration. After filtration, the film adhering to the filter membrane was dried in an oven at 60℃ for 2min. Then, the filter membrane was removed and the film was dried for another 30min to obtain a MWCNT / SiC / CNC composite film with a modified MWCNT content of 4wt%.

[0046] Example 5

[0047] Preparation of composite material: 0.15g of modified silicon carbide was added to N,N-dimethylformamide (DMF) solution and stirred at room temperature for 2h on a magnetic stirrer. After stirring, 3g of 5% CNC solution was added to SiC solution and sonicated at 30℃ for 2h. Then, 0.015g of modified MWCNT was added to SiC / CNC solution and sonicated at 30℃ for 2h. After sonication, the resulting mixed solution was transferred to a vacuum filtration flask in three parts for vacuum filtration. After filtration, the film adhering to the filter membrane was dried in an oven at 60℃ for 2min. Then, the filter membrane was removed and the film was dried for another 30min to obtain a MWCNT / SiC / CNC composite film with a modified MWCNT content of 5wt%.

[0048] Example 6

[0049] Preparation of composite material: 0.15g of modified silicon carbide was added to N,N-dimethylformamide (DMF) solution and stirred at room temperature for 2h on a magnetic stirrer. After stirring, 3g of 5% CNC solution was added to SiC solution and sonicated at 30℃ for 2h. Then, 0.018g of modified MWCNT was added to SiC / CNC solution and sonicated at 30℃ for 2h. After sonication, the resulting mixed solution was transferred to a vacuum filtration flask in three parts for vacuum filtration. After filtration, the film adhering to the filter membrane was dried in an oven at 60℃ for 2min. Then, the filter membrane was removed and the film was dried for another 30min to obtain a MWCNT / SiC / CNC composite film with a modified MWCNT content of 6wt%.

[0050] Comparative Example

[0051] The preparation method of modified SiC / CNC composite film is as follows: 0.15g of modified silicon carbide is added to N,N-dimethylformamide (DMF) solution and stirred at room temperature for 2 hours on a magnetic stirrer. After stirring, 3g of 5% CNC solution is added to the SiC solution, and the mixture is sonicated at 30℃ for 2 hours. After sonication, the resulting mixed solution is transferred to a vacuum filtration flask in three portions for filtration. After filtration, the film adhering to the filter membrane is dried in an oven at 60℃ for 2 minutes, then the filter membrane is removed and dried for another 30 minutes to obtain a modified SiC / CNC composite film with a SiC content of 50wt%. Silicon carbide / cellulose nanocrystal thermally conductive composite materials with other modified silicon carbide contents can be obtained by adjusting the amount of modified silicon carbide added.

[0052] Thermal conductivity of composite materials:

[0053] The thermal conductivity (λ) of the composite material is calculated according to the formula λ=α×Cp×ρ, where the thermal diffusivity (α) is measured by the LFA467 thermal conductivity meter of NETZSCH GmbH, Germany, and the specific heat capacity Cp and density ρ are obtained by theoretical calculation.

[0054] Figure 4 Thermal conductivity diagrams for silicon carbide / cellulose nanocrystal thermally conductive composites with different modified silicon carbide contents. Figure 5 Thermal conductivity diagrams of modified multi-walled carbon nanotube / silicon carbide / cellulose nanocrystal thermally conductive composite materials are disclosed; Table 1 shows the thermal conductivity values ​​of the composite materials in Examples 1-6. According to... Figure 4 , Figure 5 As shown in Table 1, the thermal conductivity of the composite material after SiC modification is much lower than that of the composite material after both MWCNT and SiC modification are added without the addition of MWCNT.

[0055] In addition, according to Figure 5 The thermal conductivity of the composite material reaches its highest value of 1.725 W / m when the MWCNT content reaches 5 wt%. -1 K -1 It improved by 7% compared to the unmodified MWCNT / SiC / CNC composite material.

[0056] Table 1 Thermal conductivity of composite materials in Examples 1-6

[0057] Example 1 Example 2 Example 3 Example 4 Example 5 Example 6 <![CDATA[Thermal conductivity (Wm -1 K -1 )]]> 1.06 1.187 1.349 1.595 1.725 1.670

[0058] The above embodiments are preferred embodiments of the present invention, but the embodiments of the present invention are not limited to the above embodiments. Any changes, modifications, substitutions, combinations, or simplifications made without departing from the spirit and principle of the present invention shall be considered equivalent substitutions and shall be included within the protection scope of the present invention.

Claims

1. A method for preparing a modified multi-walled carbon nanotube / silicon carbide / cellulose nanocrystal thermally conductive composite material, characterized in that, Includes the following steps: Step 1: Add the liquid silane coupling agent to the ethanol solution and sonicate it for hydrolysis. After hydrolysis, add hydroxylated multi-walled carbon nanotubes and disperse them by sonication. Step 2: React the solution obtained in Step 1 at a temperature of 55-65 ℃ for 5-7 h. After the reaction is completed, centrifuge and wash with deionized water. Then dry the precipitate to obtain modified hydroxylated multi-walled carbon nanotubes. Step 3: Place the silicon carbide particles in a muffle furnace for heat treatment oxidation. After oxidation, add the oxidized sample to a mixed solution of HF and ethanol and stir. After completion, centrifuge and wash with deionized water. Then dry the precipitate to obtain modified silicon carbide particles SiC-OH. Step 4: After fully dispersing the modified silicon carbide particles SiC-OH in an organic solvent, add the carboxylated cellulose nanocrystal CNC solution and mix thoroughly by ultrasonication to obtain a SiC-OH / CNC dispersion. Step 5: Add the modified hydroxylated multi-walled carbon nanotubes obtained in Step 2 to the SiC-OH / CNC dispersion and mix evenly by ultrasonication; Step Six: Vacuum filter the mixed solution obtained in Step Five, and then dry the resulting film to obtain the modified multi-walled carbon nanotube / silicon carbide / cellulose nanocrystal thermally conductive composite material; wherein: In step four, the organic solvent is N,N-dimethylformamide (DMF); the concentration of the CNC solution is 2wt%~5wt%; in the SiC-OH / CNC dispersion, the mass ratio of modified silicon carbide particles (SiC-OH) to carboxylated cellulose nanocrystals (CNC) is 1:

1. In step five, the content of modified hydroxylated multi-walled carbon nanotubes is 1-6 wt% of the total mass of modified silicon carbide particles (SiC-OH) and carboxylated cellulose nanocrystals (CNC).

2. The method for preparing the modified hydroxylated multi-walled carbon nanotube / modified silicon carbide / cellulose nanocrystal composite material according to claim 1, characterized in that, In step one, the silane coupling agent is selected from at least one of vinyltriethoxysilane A151, vinyltrimethoxysilane A171, 3-aminopropyltrimethoxysilane KH540, γ-aminopropyltriethoxysilane KH550, γ-glycidoxypropyltrimethoxysilane KH560, γ-(methacryloyloxy)propyltrimethoxysilane KH570, or γ-mercaptopropyltriethoxysilane KH580; in the ethanol solution, the volume ratio of ethanol to water is between 9:1 and 7:1; the volume ratio of ethanol solution to silane coupling agent is between 120:1 and 80:1; the mass ratio of hydroxylated multi-walled carbon nanotubes to silane coupling agent is between 10:1 and 50:1 g / mL; the ultrasonic hydrolysis temperature is between 40 and 80℃, and the ultrasonic time is between 5 min and 30 min.

3. The method for preparing the modified hydroxylated multi-walled carbon nanotube / modified silicon carbide / cellulose nanocrystal composite material according to claim 1, characterized in that, In step three, the heating temperature of the muffle furnace is 680-720℃, and the heating time is 30-90 minutes.

4. The method for preparing the modified hydroxylated multi-walled carbon nanotube / modified silicon carbide / cellulose nanocrystal composite material according to claim 1, characterized in that, In step three, the volume ratio of HF to ethanol in the mixed solution is between 9:1 and 8:3; the stirring time is 10-60 min.

5. The method for preparing the modified hydroxylated multi-walled carbon nanotube / silicon carbide / cellulose nanocrystal composite material according to claim 1, characterized in that, In steps four and five, the ultrasonic treatment temperature is 20-40 ℃ and the time is 1-3 h.

6. The method for preparing the modified hydroxylated multi-walled carbon nanotube / silicon carbide / cellulose nanocrystal composite material according to claim 1, characterized in that, In steps two, three, and six, vacuum drying is used, with a drying temperature between 60-80℃ and a drying time between 30 minutes and 12 hours.

7. A modified hydroxylated multi-walled carbon nanotube / silicon carbide / cellulose nanocrystal composite material prepared by the preparation method according to any one of claims 1-6.

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