Carbon nanotube modified high-thermal-conductivity and high-strength carbon fiber network body with gradient pore and hierarchical pore characteristics as well as preparation method and application of carbon nanotube modified high-thermal-conductivity and high-strength carbon fiber network body

Abstract

The invention provides a carbon nanotube modified high-thermal-conductivity and high-strength carbon fiber network body with gradient pore and hierarchical pore characteristics and a preparation method and application thereof, and belongs to the technical field of structure and function integrated composite materials. The preparation method comprises the following steps: blowing carbon fibers and hot-melt polymer fibers into a net through gas to obtain a two-dimensional fiber network body; laying the two-dimensional fiber network body according to the surface density gradient of'low-high-low ', and introducing fibers in the thickness direction for fixing to obtain a three-dimensional carbon fiber network body; sequentially carrying out carbon phase densification and graphitization treatment on the three-dimensional carbon fiber network body to obtain a high-thermal-conductivity three-dimensional carbon fiber network body; and dispersing the high-thermal-conductivity three-dimensional carbon fiber network body into the composite dispersion liquid, and sequentially performing freezing, vacuum drying and magnetic field-assisted induced carbonization to obtain the high-thermal-conductivity three-dimensional carbon fiber composite material. By reasonably designing the pore structure, the mechanical and thermal performance of the carbon fiber network body is improved, and the micro-area heat exchange efficiency of the phase change energy storage composite material is optimized.

Description

Technical Field

[0001] The present invention relates to the technical field of structure-function integrated composite materials, and particularly relates to a high thermal conductivity and high strength carbon fiber network body modified by carbon nanotubes with gradient pore and hierarchical pore characteristics, and a preparation method and application thereof. Background Art

[0002] With the rapid development of social industrialization and life convenience, petrochemical resources are continuously consumed, environmental pollution and global warming are intensifying, and energy problems and environmental problems have gradually become the key factors restricting the future social development. Phase change energy storage technology is an effective means to solve the contradiction between energy supply and demand. However, the intrinsic thermal conductivity of common phase change materials such as paraffin and polyethylene glycol is low (<0.5 W·m -1 ·K -1 ), and the heat storage and release efficiency is low, which seriously restricts their large-scale application. Therefore, how to continuously improve the thermal conductivity of phase change energy storage materials has become a key technical problem to be solved urgently.

[0003] Carbon-based network bodies have the characteristics of light weight and high thermal conductivity, and can effectively make up for the deficiency of low thermal conductivity of traditional phase change materials. As its representative, the ligament structure of high thermal conductivity foam carbon has well-developed graphite microcrystals and high orientation degree, and the thermal conductivity can reach 150 W·m -1 ·K -1 , and it has been widely used in the fields of solar energy utilization, power "peak shaving and valley filling", and aerospace thermal management. However, with the rapid development of new generation electronic devices and energy devices towards miniaturization, integration and intelligence, the highly dense packaging and high-power operation of electronic components have led to a significant increase in internal heat dissipation of the devices, putting forward higher requirements for the heat storage and release efficiency and cyclic service life of thermal management materials, and further putting forward higher requirements for the mechanical and thermal properties of carbon-based network bodies. Due to the large density of microcracks in the ligament structure of high thermal conductivity foam carbon, cracks rapidly proliferate and expand under the action of load, so it is still a huge challenge to achieve the coordinated improvement of the mechanical and thermal properties of carbon-based network bodies.

[0004] Mesophase pitch carbon fiber (CF MP ) is composed of a highly developed graphite microcrystal structure preferentially oriented along the fiber axis, and is a reinforcing material that takes into account both thermal conductivity and mechanical properties. The tensile strength can reach 2.5-3.5 GPa, and the thermal conductivity can reach 600-1100 W·m -1 ·K -1 , and it has great potential in realizing the integrated design of the structure and function of carbon-based network bodies. At present, the preparation of carbon-based network bodies is mainly through resin carbon bonding method and self-bonding method, and an effective heat conduction network has not been formed, so the thermal conductivity and mechanical properties of carbon-based network bodies are not high.

[0005] Based on this, it is very important to provide a high thermal conductivity, high strength carbon fiber network modified with carbon nanotubes, which has a multi-level distribution feature of pore structure and can improve the thermal conductivity, mechanical properties of the carbon-based network and the micro-area heat exchange efficiency of the phase change composite material. Summary of the Invention

[0006] The purpose of the present invention is to provide a high thermal conductivity, high strength carbon fiber network modified with carbon nanotubes having gradient pores and multi-level pore characteristics, and its preparation method and application, so as to solve the technical problem in the prior art that the strength and thermal properties of the carbon fiber network cannot be taken into account at the same time.

[0007] In order to achieve the above-mentioned object of the invention, the present invention provides the following technical solutions:

[0008] The present invention provides a method for preparing a carbon nanotube-modified high-thermal-conductivity, high-strength carbon fiber network having gradient pores and multi-level pores, comprising the following steps:

[0009] 1) carbon fibers and hot-melt polymer fibers are blown into a web by gas to obtain a two-dimensional fiber network;

[0010] 2) The two-dimensional fiber network is laid out in a gradient of "low → high → low" surface density, and fibers are introduced in the thickness direction for fixation to obtain a three-dimensional carbon fiber network;

[0011] 3) performing carbon phase densification and graphitization treatment on the three-dimensional carbon fiber network in sequence to obtain a high thermal conductivity three-dimensional carbon fiber network;

[0012] 4) The high thermal conductivity three-dimensional carbon fiber network is dispersed in a composite dispersion liquid and sequentially subjected to freezing, vacuum drying, and magnetic field-assisted induced carbonization to obtain a high thermal conductivity and high strength carbon fiber network modified with carbon nanotubes having gradient pores and multi-level pores.

[0013] Furthermore, in step 1), the carbon fibers are carbon fibers of different cohesive states and length distributions;

[0014] The carbon fibers of different cohesive states are obtained by controlling the sizing amount of the fibers, wherein the sizing amount is 0.5 to 5 wt.%;

[0015] The carbon fibers and the thermofusible polymer fibers are independently 1 to 15 mm in length;

[0016] The heat-meltable polymer fibers include polyethylene fibers and / or polyester fibers;

[0017] The mass ratio of the carbon fiber to the thermofusible polymer fiber is 90-95:5-10;

[0018] The surface density of the two-dimensional fiber network is 5 to 100 g / m 2 .

[0019] Further, in step 2), the two-dimensional fiber network body is divided into: two-dimensional fiber network body A, two-dimensional fiber network body B, and two-dimensional fiber network body C according to the areal density;

[0020] The areal densities of the two-dimensional fiber network body A, the two-dimensional fiber network body B, and the two-dimensional fiber network body C are 5-20 g / m 2 , 20-50 g / m 2 , 50-100 g / m 2 respectively; the two-dimensional fiber network body is arranged and designed in a gradient stacking manner of AAA-BBB-CCC-BBB-AAA;

[0021] The porosity of the three-dimensional carbon fiber network body is 80-90%, the fiber density in the thickness direction of the three-dimensional carbon fiber network body is 10-60 bundles / cm 2 , the fiber depth of the three-dimensional carbon fiber network body is 4-10 mm, and the density of the three-dimensional carbon fiber network body is 0.13-0.25 g / cm 3 .

[0022] Further, in step 3), the carbon phase densification includes chemical vapor deposition process and / or impregnation pyrolysis;

[0023] In the chemical vapor deposition process, the carbon source gas used in the chemical vapor deposition process includes at least one of C3-C5 alkanes and C3-C5 alkenes, the carrier gas is nitrogen or argon, the pressure is 1-5 kPa, the reaction temperature is 900-1100 °C, the flow rate of the carbon source gas is 15-18 L / min, and the deposition time is 50-90 h;

[0024] The density of the three-dimensional carbon fiber network body after carbon phase densification is 0.50-0.8 g / cm 3 ;

[0025] The three-dimensional fiber network body uses the chemical vapor deposition process to construct pyrolytic carbon on the fiber surface, and the texture type of the pyrolytic carbon is high texture, and the extinction angle is 23°≤Ae≤28°.

[0026] Further, in step 3), in the graphitization treatment, the protective gas used is argon, the temperature is 2800-3100 °C, the heating rate is 5-10 °C / min, and the holding time is 10-60 min.

[0027] Further, in step 4), the preparation method of the composite dispersion liquid includes the following steps:

[0028] Mix the polyvinyl alcohol solution and the polyethylene glycol solution to obtain a mixed solution, then add the metal salt solution and mix, and perform ultrasonic treatment after mixing evenly to obtain the composite dispersion liquid.

[0029] Furthermore, the mass concentration of the polyvinyl alcohol solution is 5-10 wt.%, the mass concentration of the polyethylene glycol solution is 10-20 wt.%, and the molar concentration of the metal salt solution is 0.1-1 mol / L;

[0030] The mass ratio of the polyvinyl alcohol solution to the polyethylene glycol solution is 1:0.5-2;

[0031] The mass ratio of the metal salt in the metal salt solution to the polyvinyl alcohol in the polyvinyl alcohol solution is 1:10-20;

[0032] The metal salt solution includes at least one of a nickel source solution, a cobalt source solution, and an iron source solution;

[0033] The nickel source in the nickel source solution includes one or more of nickel nitrate, nickel chloride, and nickel acetate;

[0034] The dropping rate of the metal salt solution is 1-5 mL / min, and the addition of the metal salt solution is carried out under stirring, and the stirring speed is 600-1000 rpm;

[0035] The molecular weight of the polyvinyl alcohol is 1000-5000, and the molecular weight of the polyethylene glycol is 400-6000;

[0036] The time of the ultrasonic treatment is 10-15 min;

[0037] The pH of the composite dispersion is 7-9, and the reagent used to adjust the pH is ammonia water or sodium hydroxide solution.

[0038] Furthermore, in step 4), the freezing temperature is -170 to -120 °C, and the freezing time is 1-2 h;

[0039] The vacuum drying is carried out in two steps. The temperature of the first vacuum drying is -120 to -40 °C, the time of the first vacuum drying is 4-6 h, the temperature of the second vacuum drying is 150 to 200 °C, and the time of the second vacuum drying is 2-6 h;

[0040] The magnetic field-assisted induced carbonization is carried out under vacuum conditions. The temperature of the magnetic field-assisted induced carbonization is 800-1200 °C, the heating rate of the magnetic field-assisted induced carbonization is 3-8 °C / min, and the time of the magnetic field-assisted induced carbonization is 10-30 min;

[0041] During the magnetic field-assisted induced carbonization process, a magnetic field is applied along the thickness direction, the magnetic field intensity is 0.5-2 T, and the magnetic field direction is parallel to the thickness direction of the three-dimensional fiber network body.

[0042] The present invention provides a highly thermally conductive and high-strength carbon fiber network body modified by carbon nanotubes with gradient pore and hierarchical pore characteristics.

[0043] The present invention also provides an application of the highly thermally conductive and high-strength carbon fiber network body modified by carbon nanotubes with gradient pore and hierarchical pore characteristics in phase change energy storage materials.

[0044] Advantages of the present invention:

[0045] 1) In the preparation method of the present invention, a hot-melt polyethylene fiber is used as a pore-forming agent, which forms fiber-like pores by melting and decomposing under vacuum and high-temperature conditions; due to the inconsistent adhesion degree of high-temperature filaments of asphalt carbon fibers with different sizing amounts and the high-temperature melting and decomposition of the hot-melt polyethylene fiber, after fiber cutting, they are blown into a web according to a certain mass ratio by air flow, and the large and small bundles of asphalt carbon fibers are arranged in a staggered manner during web formation to generate hierarchical pores from several microns to dozens of microns to hundreds of microns, obtaining a non-woven fabric with a hierarchical pore structure. The high-temperature melting and decomposition of the polyethylene fiber generates fiber-like pores, further constructing hierarchical pores and improving the micro-region heat exchange efficiency of the phase change composite material;

[0046] 2) The present invention constructs a gradient pore structure by stacking non-woven fabrics with different fiber volume fractions in a gradient manner of "low - high - low" surface density. The material has a gradient pore structure feature with a high surface porosity and large pore size, and the porosity gradually decreases and the pore size gradually becomes smaller towards the inside. It can not only optimize the closed pore problem in the chemical vapor deposition process, reduce surface crusting, reduce peeling, improve the deposition efficiency, but also improve the infiltration efficiency of the phase change material;

[0047] 3) The present invention improves the thermal conductivity in the thickness direction of the network body by introducing fibers in the thickness direction as the carrier for pyrolytic carbon deposition; using highly textured pyrolytic carbon as the carbon phase skeleton, after high-temperature graphitization, the graphite crystallite height is highly developed, constructing a highly efficient thermal channel;

[0048] 4) The present invention uses the ice template method to create pores, while optimizing the hierarchical pores of the network body, loads Fe / Co / Ni source catalysts, and forms secondary (dendrite-like structure) thermal conduction channels by magnetic field-assisted induction catalysis during the carbonization process to further optimize the mechanical and thermal properties of the carbon fiber network body;

[0049] 5) The present invention further improves the thermal conductivity and mechanical properties of the carbon-based network body, optimizes the micro-region heat exchange efficiency of the phase change energy storage composite material, and improves its service performance and cycle life by reasonably designing the pore structure of the CF MP / carbon-based network body and regulating the interface structure of the CF MP / carbon matrix;

[0050] 6) The density of the highly thermally conductive carbon fiber network body with a gradient pore structure prepared by the present invention is 0.30 - 1.0 g / cm3 , the open porosity is 56-80%, and the thermal conductivity in the X / Y direction is 40-240 W·m -1 ·K -1 , and the compressive strength is 5-40 MPa. Description of the Drawings

[0051] Figure 1 This is the scanning electron microscope image of the carbon fiber network body prepared in Example 1 of the present invention. Detailed Embodiments

[0052] The present invention provides a preparation method of a carbon nanotube-modified high-thermal conductivity and high-strength carbon fiber network body with gradient pores and multi-stage pores, including the following steps:

[0053] 1) The carbon fiber and the thermoplastic polymer fiber are blown into a web by gas blowing to obtain a two-dimensional fiber network body;

[0054] 2) The two-dimensional fiber network body is arranged in a gradient of "low → high → low" in terms of areal density, and fibers are introduced in the thickness direction for fixation to obtain a three-dimensional carbon fiber network body;

[0055] 3) The three-dimensional carbon fiber network body is sequentially subjected to carbon phase densification and graphitization treatment to obtain a high-thermal conductivity three-dimensional carbon fiber network body;

[0056] 4) The high-thermal conductivity three-dimensional carbon fiber network body is dispersed in a composite dispersion liquid and sequentially subjected to freezing, vacuum drying, and magnetic field-assisted induced carbonization to obtain a carbon nanotube-modified high-thermal conductivity and high-strength carbon fiber network body with gradient pores and multi-stage pores.

[0057] In the present invention, in the step 1), the carbon fiber is a carbon fiber with different cohesive states and length distributions;

[0058] The carbon fiber with different cohesive states is obtained by controlling the sizing amount of the fiber, and the sizing amount is 0.5-5 wt.%, preferably 1-4.5 wt.%, and more preferably 1.5-4 wt.%.

[0059] In the present invention, the carbon fiber is preferably a pitch-based carbon fiber. The adhesion degrees of carbon fiber filaments with different cohesive states are inconsistent. After the fiber is formed into a web, macropores with a size of 10-200 μm between fiber bundles and micropores with a size of 1-10 μm between single filaments are formed.

[0060] In the present invention, the lengths of the carbon fiber and the thermoplastic polymer fiber are independently 1-15 mm, preferably 3-12 mm, and more preferably 5-10 mm;

[0061] The thermoplastic polymer fiber includes polyethylene fiber and / or polyester fiber, and is preferably polyethylene fiber.

[0062] In the present invention, the thermoplastic polymer fiber mainly serves as a pore-forming agent and generates fibrous pores by melting and decomposing at high temperature.

[0063] In the present invention, the mass ratio of the carbon fiber to the thermoplastic polymer fiber is 90-95:5-10, preferably 91-94:6-9, and more preferably 92-93:7-8;

[0064] The areal density of the two-dimensional fiber network is 5-100 g / m 2 , preferably 10-90 g / m 2 , more preferably 20-80 g / m 2 .

[0065] In the present invention, the two-dimensional fiber network is obtained by air blowing.

[0066] In the present invention, in the step 2), the two-dimensional fiber network is classified according to the areal density into: two-dimensional fiber network A, two-dimensional fiber network B and two-dimensional fiber network C;

[0067] The areal densities of the two-dimensional fiber network A, the two-dimensional fiber network B and the two-dimensional fiber network C are 5-20 g / m 2 , 20-50 g / m 2 , 50-100 g / m 2 , preferably 7-18 g / m 2 , 22-48 g / m 2 , 60-90 g / m 2 , more preferably 10-15 g / m 2 , 25-45 g / m 2 , 70-80 g / m 2 ;

[0068] The two-dimensional fiber network is arranged and designed in a gradient stacking manner of AAA-BBB-CCC-BBB-AAA;

[0069] The porosity of the three-dimensional carbon fiber network is 80-90%, preferably 82-88%, and more preferably 84-86%; the fiber density in the thickness direction of the three-dimensional carbon fiber network is 10-60 bundles / cm 2 , preferably 15-55 bundles / cm 2 , more preferably 20-50 bundles / cm 2 ; the fiber depth of the three-dimensional carbon fiber network is 4-10 mm, preferably 5-9 mm, and more preferably 6-8 mm; the density of the three-dimensional carbon fiber network is 0.13-0.25 g / cm 3 , preferably 0.15-0.23 g / cm 3, further preferably 0.18 to 0.21 g / cm 3 .

[0070] In the present invention, the pore size and porosity of the three-dimensional carbon fiber network body decrease in a gradient from the surface to the interior.

[0071] In the present invention, in step 3), the carbon phase densification includes chemical vapor deposition process and / or impregnation pyrolysis, preferably the chemical vapor deposition process;

[0072] In the chemical vapor deposition process, the carbon source gas used in the chemical vapor deposition process includes at least one of C3 - C5 alkanes and C3 - C5 alkenes, preferably at least one of C3 - C5 alkenes; the carrier gas is nitrogen or argon, preferably argon; the pressure is 1 - 5 kPa, preferably 1.5 - 4.5 kPa, further preferably 2 - 4 kPa; the reaction temperature is 90℃ - 1100℃, preferably 950 - 1050℃, further preferably 1000℃; the flow rate of the carbon source gas is 15 - 18 L / min, preferably 15.5 - 17.5 L / min, further preferably 16 - 17 L / min; the deposition time is 50 - 90 h, preferably 55 - 85 h, further preferably 60 - 80 h;

[0073] The density of the three-dimensional carbon fiber network body after carbon phase densification is 0.50 - 0.8 g / cm 3 , preferably 0.55 - 0.75 g / cm 3 , further preferably 0.6 - 0.7 g / cm 3 ;

[0074] The three-dimensional fiber network body constructs pyrolytic carbon on the fiber surface by chemical vapor deposition process. The texture type of the pyrolytic carbon is high texture, and the extinction angle is 23° ≤ Ae ≤ 28°, preferably 23.5° ≤ Ae ≤ 27.5°, further preferably 24° ≤ Ae ≤ 27°.

[0075] In the present invention, in step 3), in the graphitization treatment, the protective gas used is argon, the temperature is 2800 - 3100℃, preferably 2900 - 3000℃, further preferably 3000℃; the heating rate is 5 - 10℃ / min, preferably 6 - 9℃ / min, further preferably 7 - 8℃ / min; the heat preservation time is 10 - 60 min, preferably 15 - 55 min, further preferably 20 - 50 min.

[0076] In the present invention, the purpose of the graphitization treatment is to stimulate the thermal conductivity of the pitch carbon fiber and pyrolytic carbon.

[0077] In the present invention, in step 4), the preparation method of the composite dispersion liquid includes the following steps:

[0078] Mix the polyvinyl alcohol solution and the polyethylene glycol solution to obtain a mixed solution, then add a metal salt solution and mix. After mixing evenly, perform ultrasonic treatment to obtain a composite dispersion liquid.

[0079] In the present invention, the mass concentration of the polyvinyl alcohol solution is 5-10 wt.%, preferably 6-9 wt.%, and more preferably 7-8 wt.%; the mass concentration of the polyethylene glycol solution is 10-20 wt.%, preferably 12-18 wt.%, and more preferably 14-16 wt.%; the molar concentration of the metal salt solution is 0.1-1 mol / L, preferably 0.2-0.8 mol / L, and more preferably 0.4-0.6 mol / L;

[0080] The mass ratio of the polyvinyl alcohol solution to the polyethylene glycol solution is 1:0.5-2, preferably 1:0.8-1.5, and more preferably 1:1.

[0081] In the present invention, the mass ratio of the metal salt in the metal salt solution to the polyvinyl alcohol in the polyvinyl alcohol solution is 1:10-20, preferably 1:12-18, and more preferably 1:14-16;

[0082] The metal salt solution includes at least one of a nickel source solution, a cobalt source solution, and an iron source solution, preferably a nickel source solution or a cobalt source solution, and more preferably a nickel source solution;

[0083] The nickel source in the nickel source solution includes one or more of nickel nitrate, nickel chloride, and nickel acetate, preferably nickel nitrate and / or nickel chloride, and more preferably nickel nitrate;

[0084] The dropping rate of the metal salt solution is 1-5 mL / min, preferably 2-4 mL / min, and more preferably 3 mL / min; adding the metal salt solution and mixing are carried out under stirring, and the stirring speed is 600-1000 rpm, preferably 650-950 rpm, and more preferably 700-900 rpm.

[0085] In the present invention, the molecular weight of the polyvinyl alcohol is 1000-5000, preferably 1500-4500, and more preferably 2000-4000; the molecular weight of the polyethylene glycol is 400-6000, preferably 500-5500, and more preferably 600-5000.

[0086] In the present invention, the polyvinyl alcohol solution is obtained by dissolving polyvinyl alcohol in hot water at 80-90 °C, and the dissolution is carried out under stirring, and the stirring time is 30-60 min;

[0087] The polyethylene glycol solution is obtained by dissolving polyethylene glycol in water under the condition of 20-50°C, and the dissolution is carried out with stirring for 20-40 min.

[0088] In the present invention, the time of the ultrasound is 10-15 min, preferably 12-14 min, and further preferably 13 min.

[0089] In the present invention, the power of the ultrasound is 50-150 W, preferably 70-130 W, and further preferably 100 W; the frequency of the ultrasound is 30-50 kHz, preferably 35-45 kHz, and further preferably 40 kHz.

[0090] In the present invention, the pH of the composite dispersion is 7-9, preferably 7.5-8.5, and further preferably 8; the reagent used to adjust the pH is ammonia water or sodium hydroxide solution, preferably ammonia water.

[0091] In the present invention, in step 4), the freezing temperature is -170 to -120°C, preferably -160 to -130°C, and further preferably -150 to -140°C; the freezing time is 1-2 h, preferably 1.2-1.8 h, and further preferably 1.4-1.6 h.

[0092] In the present invention, in step 4), the vacuum drying is carried out in two times. The temperature of the first vacuum drying is -120 to -40°C, preferably -110 to -50°C, and further preferably -100 to -60°C; the time of the first vacuum drying is 4-6 h, preferably 4.5-5.5 h, and further preferably 5 h; the temperature of the second vacuum drying is 150-200°C, preferably 160-190°C, and further preferably 170-180°C; the time of the second vacuum drying is 2-6 h, preferably 3-5 h, and further preferably 4 h.

[0093] In the present invention, in step 4), the magnetic field-assisted induced carbonization is carried out under vacuum conditions. The temperature of the magnetic field-assisted induced carbonization is 800-1200°C, preferably 850-1150°C, and further preferably 900-1100°C; the heating rate of the magnetic field-assisted induced carbonization is 3-8°C / min, preferably 4-7°C / min, and further preferably 5-6°C / min; the time of the magnetic field-assisted induced carbonization is 10-30 min, preferably 15-25 min, and further preferably 20 min;

[0094] During the magnetic field-assisted induced carbonization process, a magnetic field is applied along the thickness direction, the magnetic field intensity is 0.5-2 T, preferably 0.8-1.5 T, and further preferably 1 T; the magnetic field direction is parallel to the thickness direction of the three-dimensional fiber network body.

[0095] In the present invention, the role of the magnetic field-assisted induced carbonization is to induce the directional growth of carbon nanotubes along the magnetic field direction and optimize the hierarchical pore structure of the carbon fiber / carbon-based network body.

[0096] This application provides a highly thermally conductive and high-strength carbon fiber network body modified with carbon nanotubes having gradient pore and hierarchical pore characteristics.

[0097] This application also provides an application of the highly thermally conductive and high-strength carbon fiber network body modified with carbon nanotubes having gradient pore and hierarchical pore characteristics in phase change energy storage materials.

[0098] The technical solutions provided by the present invention will be described in detail below with reference to the embodiments, but they should not be construed as limiting the protection scope of the present invention.

[0099] Example 1

[0100] The sized pitch carbon fiber high-temperature filaments with a sizing amount of 8 wt.% are cut into 10 mm, and the thermoplastic polyethylene fibers are cut into 10 mm. The chopped filaments of pitch carbon fiber and polyethylene fiber with a mass ratio of 90:10 are mixed, and then blown into a web by air flow to obtain a two-dimensional fiber network body with a basis weight of 5-100 g / m 2 The basis weights of the two-dimensional fiber network bodies A, B, and C are 10 g / m 2 , 20 g / m 2 , 50 g / m 2 respectively. The two-dimensional fiber network bodies are arranged and designed in a gradient stacking manner of AAA-BBB-CCC-BBB-AAA, and a certain amount of needle-punched fibers are introduced in the thickness direction for fixation. The needle-punching density is 10 tufts / cm 2 , the depth is 7 mm, and a three-dimensional fiber network body with a density of 0.13 g / cm 3 is obtained;

[0101] The three-dimensional carbon fiber network body is used to construct pyrolytic carbon on the fiber surface by chemical vapor deposition. The texture type of the pyrolytic carbon is high texture, and the extinction angle Ae is 25°; in the chemical vapor deposition process, the carbon source gas is propylene, the flow rate of the carbon source gas is 16 L / min, the carrier gas is nitrogen, the reaction temperature is 1020 °C, the reaction pressure is 1 kPa, and the reaction time is 50 h. A three-dimensional carbon fiber network body with a density of 0.52 g / cm 3 and an open porosity of 82% after carbon phase densification is obtained. Subsequently, graphitization treatment is carried out under the conditions of an argon atmosphere and a temperature of 2900 °C for 2 h to activate the thermal conductivity of the pitch carbon fiber and pyrolytic carbon, and a highly thermally conductive three-dimensional carbon fiber network body is obtained;

[0102] It is obtained by dissolving polyvinyl alcohol (PVA) in hot water at 90 °C. The dissolution is carried out with stirring for 60 min to obtain a polyvinyl alcohol solution with a concentration of 10 wt.%. Polyethylene glycol (PEG) is dissolved in water at 30 °C. The dissolution is carried out with stirring for 40 min to obtain a polyethylene glycol solution with a concentration of 10 wt.%. Nickel nitrate is dissolved in deionized water to obtain a Ni(NO3)2·6H2O solution with a concentration of 0.1 mol / L. The PVA solution and the PEG solution with a mass ratio of 1:1 are mixed and stirred evenly to form a homogeneous mixture. Under the condition of a stirring speed of 1000 rpm, the Ni(NO3)2·6H2O solution is added dropwise to the mixture at a dropping speed of 2 mL / min, and the mass ratio of Ni(NO3)2·6H2O to PVA is controlled to be 1:20. After mixing evenly, ultrasonic treatment is carried out. The time of ultrasonic treatment is 15 minutes, the power of ultrasonic treatment is 150 W, and the frequency of ultrasonic treatment is 40 kHz. Then, ammonia water is used to adjust the pH to 8 to obtain a composite dispersion.

[0103] The composite dispersion is poured into a high-thermal-conductivity three-dimensional carbon fiber network body and then placed on the surface of a copper block. The bottom of the copper block is immersed in liquid nitrogen and frozen at -150 °C, and then the first vacuum drying is carried out at -40 °C for 4 h. Then, the second vacuum drying is carried out at 150 °C for 2 h to obtain a precursor. Finally, the precursor is put into a vacuum sintering furnace and heated to 3000 °C at a rate of 5 °C / min for carbonization treatment for 30 min. During the carbonization treatment, a magnetic field is applied along the thickness direction, the magnetic field intensity is 1 T, and the magnetic field direction is parallel to the thickness direction of the network body to induce the directional growth of carbon nanotubes along the magnetic field direction, optimize the hierarchical pore structure of the carbon fiber / carbon-based network body, and obtain a high-thermal-conductivity and high-strength carbon nanotube-modified carbon fiber network body with gradient pores and multi-level pore characteristics.

[0104] The high-thermal-conductivity and high-strength carbon nanotube-modified carbon fiber network body with gradient pores and multi-level pore characteristics prepared in Example 1 is tested. The test results are as follows: the density of the carbon fiber network body is 0.65 g / cm 3 , the open porosity is 72%, the thermal conductivity in the XY direction is 82.62 W·m -1 ·K -1 , the thermal conductivity along the thickness Z direction is 22.34 W / (m·K), and the compressive strength is 12.86 MPa.

[0105] Example 2

[0106] The pitch carbon fiber high-temperature filaments with a sizing amount of 5 wt.% are cut into 10 mm, and the meltable polyethylene fibers are cut into 10 mm. The short-cut filaments of pitch carbon fiber and polyethylene fiber with a mass ratio of 95:5 are mixed, and then blown into a web by air flow to obtain a two-dimensional fiber network body with a basis weight of 5-100 g / m 2 The basis weights of the two-dimensional fiber network bodies A, B, and C are 10 g / m 2 , 30 g / m 2 , 70 g / m 2 , respectively. The two-dimensional fiber network bodies are arranged and designed in a gradient stacking manner of AAA-BBB-CCC-BBB-AAA, and a certain amount of needle-punched fibers are introduced in the thickness direction for fixation. The needle-punching density is 20 tufts / cm 2 , and the depth is 10 mm to obtain a three-dimensional fiber network body with a density of 0.25 g / cm 3 ;

[0107] The three-dimensional carbon fiber network body is used to construct pyrolytic carbon on the fiber surface by chemical vapor deposition. The texture type of the pyrolytic carbon is high texture, and the extinction angle Ae is 25°. In the chemical vapor deposition process, the carbon source gas is propylene, the flow rate of the carbon source gas is 16 L / min, the carrier gas is nitrogen, the reaction temperature is 1020 °C, the reaction pressure is 1 kPa, and the reaction time is 70 h to obtain a three-dimensional carbon fiber network body with a density of 0.62 g / cm 3 and an open porosity of 75% after carbon phase densification. Subsequently, graphitization treatment is carried out in an argon atmosphere at a temperature of 3000 °C for 2 h to stimulate the thermal conductivity of the pitch carbon fiber and pyrolytic carbon, and a high-thermal-conductivity three-dimensional carbon fiber network body is obtained;

[0108] Polyvinyl alcohol (PVA) is dissolved in hot water at 90 °C. The dissolution is carried out with stirring for 60 min to obtain a 10 wt.% polyvinyl alcohol solution; polyethylene glycol (PEG) is dissolved in water at 30 °C. The dissolution is carried out with stirring for 40 min to obtain a 10 wt.% polyethylene glycol solution; nickel nitrate is dissolved in deionized water to obtain a 0.1 mol / L Ni(NO3)2·6H2O solution; the PVA solution and the PEG solution with a mass ratio of 1:1 are mixed and stirred evenly to form a homogeneous mixture; under the condition of a stirring speed of 1000 rpm, the Ni(NO3)2·6H2O solution is added dropwise to the mixture at a dropping speed of 2 mL / min, and the mass ratio of Ni(NO3)2·6H2O to PVA is controlled to be 1:20. After mixing evenly, ultrasonic treatment is carried out. The time of ultrasonic treatment is 15 minutes, the power of ultrasonic treatment is 150 W, and the frequency of ultrasonic treatment is 40 kHz, and the pH is adjusted to 8 with ammonia water to obtain a composite dispersion;

[0109] The composite dispersion was poured into a high-thermal-conductivity three-dimensional carbon fiber network body and then placed on the surface of a copper block. The bottom of the copper block was immersed in liquid nitrogen and frozen at -150°C. Then, the first vacuum drying was carried out at -40°C for 4 hours. After that, the second vacuum drying was carried out at 150°C for 2 hours to obtain a precursor. Finally, the precursor was placed in a vacuum sintering furnace and heated to 3000°C at a rate of 5°C / min for carbonization treatment for 30 minutes. During the carbonization treatment, a magnetic field was applied along the thickness direction with a magnetic field strength of 1 T, and the magnetic field direction was parallel to the thickness direction of the network body to induce the directional growth of carbon nanotubes along the magnetic field direction, optimize the hierarchical pore structure of the carbon fiber / carbon-based network body, and obtain a high-thermal-conductivity and high-strength carbon fiber network body modified by carbon nanotubes with gradient pore and multi-stage pore characteristics.

[0110] The high-thermal-conductivity and high-strength carbon fiber network body modified by carbon nanotubes with gradient pore and multi-stage pore characteristics prepared in Example 2 was tested. The test results were as follows: the density of the carbon fiber network body was 0.80 g / cm 3 , the open porosity was 64%, the thermal conductivity in the XY direction was 118.01 W·m -1 ·K -1 , the thermal conductivity along the thickness Z direction was 31.67 W / (m·K), and the compressive strength was 18.63 MPa.

[0111] Example 3

[0112] The high-temperature filaments of pitch carbon fiber with a sizing amount of 5 wt.% were cut into 10 mm short pieces, and the hot-melt polyethylene fibers were cut into 10 mm short pieces. The short cut filaments of pitch carbon fiber and polyethylene fiber with a mass ratio of 95:5 were mixed, and then blown into a web by air flow to obtain a two-dimensional fiber network body with a basis weight of 5 - 100 g / m 2 . The basis weights of two-dimensional fiber network body A, two-dimensional fiber network body B, and two-dimensional fiber network body C were 20 g / m 2 , 50 g / m 2 , and 80 g / m 2 , respectively. The two-dimensional fiber network bodies were arranged and designed in a gradient stacking manner of AAA - BBB - CCC - BBB - AAA, and a certain amount of needle-punched fibers were introduced in the thickness direction for fixation. The needle-punching density was 20 bundles / cm 2 , and the depth was 10 mm to obtain a three-dimensional fiber network body with a density of 0.25 g / cm 3 .

[0113] A three-dimensional carbon fiber network body is used to construct pyrolytic carbon on the fiber surface by chemical vapor deposition. The texture type of the pyrolytic carbon is high texture, and the extinction angle Ae is 25°. In the chemical vapor deposition process, the carbon source gas is propylene, the flow rate of the carbon source gas is 16 L / min, the carrier gas is nitrogen, the reaction temperature is 1020 °C, the reaction pressure is 1 kPa, and the reaction time is 90 h, obtaining a three-dimensional carbon fiber network body with a density of 0.72 g / cm 3 , after the carbon phase with an open porosity of 65% is densified, it is then graphitized under the conditions of an argon atmosphere and a temperature of 3000 °C for 2 h to stimulate the thermal conductivity of the pitch carbon fiber and pyrolytic carbon, obtaining a high-thermal-conductivity three-dimensional carbon fiber network body;

[0114] Polyvinyl alcohol (PVA) is dissolved in hot water at 90 °C. The dissolution is carried out with stirring for 60 min to obtain a polyvinyl alcohol solution with a concentration of 10 wt.%. Polyethylene glycol (PEG) is dissolved in water at 30 °C. The dissolution is carried out with stirring for 40 min to obtain a polyethylene glycol solution with a concentration of 10 wt.%. Nickel nitrate is dissolved in deionized water to obtain a Ni(NO3)2·6H2O solution with a concentration of 0.1 mol / L. The PVA solution and the PEG solution with a mass ratio of 1:1 are mixed and stirred evenly to form a homogeneous mixture. Under the condition of a stirring speed of 1000 rpm, the Ni(NO3)2·6H2O solution is added dropwise to the mixture at a dropping speed of 2 mL / min, controlling the mass ratio of Ni(NO3)2·6H2O to PVA to be 1:20. After mixing evenly, ultrasonic treatment is carried out for 15 minutes, the power of ultrasonic treatment is 150 W, the frequency of ultrasonic treatment is 40 kHz, and ammonia water is used to adjust the pH to 8 to obtain a composite dispersion;

[0115] The composite dispersion is poured into the high-thermal-conductivity three-dimensional carbon fiber network body and then placed on the surface of a copper block. The bottom of the copper block is immersed in liquid nitrogen and frozen at -150 °C, and then vacuum dried for the first time at -40 °C for 4 h, and then vacuum dried for the second time at 150 °C for 2 h to obtain a precursor. Finally, the precursor is put into a vacuum sintering furnace and heated to 3000 °C at a rate of 5 °C / min for carbonization treatment for 30 min, and a magnetic field is applied along the thickness direction during the carbonization treatment, the magnetic field intensity is 1 T, and the magnetic field direction is parallel to the thickness direction of the network body to induce the directional growth of carbon nanotubes along the magnetic field direction, optimizing the hierarchical pore structure of the carbon fiber / carbon-based network body, obtaining a carbon nanotube-modified high-thermal-conductivity and high-strength carbon fiber network body with gradient pore and multi-level pore characteristics.

[0116] The highly thermally conductive and high-strength carbon fiber network modified with carbon nanotubes having gradient pore and hierarchical pore characteristics prepared in Example 3 was tested, and the test results were as follows: the density of the carbon fiber network was 1.0 g / cm 3 , the open porosity was 56%, the thermal conductivity in the XY direction was 180.34 W·m -1 ·K -1 , the thermal conductivity in the thickness Z direction was 42.86 W / (m·K), and the compressive strength was 24.13 MPa.

[0117] Comparative Example 1

[0118] Compared with Example 3, the difference was that in Comparative Example 1, no magnetic field was applied during the carbonization process, no oriented carbon nanotubes were generated during the carbonization process, and no secondary (dendritic-like structure) heat conduction channels were formed, resulting in a lower thermal conductivity in the thickness direction of the carbon fiber network.

[0119] The carbon fiber network prepared in Comparative Example 1 was tested, and the test results were as follows: the density of the carbon fiber network was 1.0 g / cm 3 , the open porosity was 58%, the thermal conductivity in the XY direction was 185.62 W·m -1 ·K -1 , the thermal conductivity in the thickness Z direction was 12.46 W / (m·K), and the compressive strength was 18.13 MPa.

[0120] As can be seen from the above examples, the present invention provides a highly thermally conductive and high-strength carbon fiber network modified with carbon nanotubes having gradient pore and hierarchical pore characteristics, and its preparation method and application. The carbon fiber and the thermoplastic polymer fiber are blown into a web by gas to obtain a two-dimensional fiber network; the two-dimensional fiber network is arranged in a gradient of areal density "low → high → low" and fibers are introduced in the thickness direction for fixation to obtain a three-dimensional carbon fiber network; the three-dimensional carbon fiber network is sequentially subjected to carbon phase densification and graphitization treatment to obtain a highly thermally conductive three-dimensional carbon fiber network; the highly thermally conductive three-dimensional carbon fiber network is dispersed in a composite dispersion liquid and sequentially subjected to freezing, vacuum drying, and magnetic field-assisted induced carbonization to obtain a carbon nanotube-modified highly thermally conductive and high-strength carbon fiber network. The present invention improves the mechanical and thermal properties of the carbon fiber network by reasonably designing the pore structure and optimizes the micro-region heat exchange efficiency of the phase change energy storage composite material.

[0121] The above are only the preferred embodiments of the present invention. It should be noted that for those of ordinary skill in the art, without departing from the principle of the present invention, several improvements and refinements can be made, and these improvements and refinements should also be regarded as the protection scope of the present invention.

Claims

1. A preparation method of a high thermal conductivity and high strength carbon fiber network body modified by carbon nanotubes with gradient pore and hierarchical pore characteristics, which is characterized in that, It includes the following steps: 1) Blow carbon fibers and thermoplastic polymer fibers into a web by gas to obtain a two-dimensional fiber network body; 2) Arrange the two-dimensional fiber network body in a gradient of "low → high → low" in areal density, and introduce fibers in the thickness direction for fixation to obtain a three-dimensional carbon fiber network body; 3) Subject the three-dimensional carbon fiber network body to carbon phase densification and graphitization treatment in sequence to obtain a highly thermally conductive three-dimensional carbon fiber network body; 4) Disperse the highly thermally conductive three-dimensional carbon fiber network body in a composite dispersion liquid, and successively perform freezing, vacuum drying, and magnetic field-assisted induced carbonization to obtain a carbon nanotube-modified highly thermally conductive and high-strength carbon fiber network body with gradient pores and hierarchical pore characteristics.

2. The preparation method of the high thermal conductivity and high strength carbon fiber network body modified by carbon nanotubes with gradient pore and hierarchical pore characteristics according to claim 1, characterized in that, In the step 1), the carbon fibers are carbon fibers with different cohesive states and length distributions; The carbon fibers with different cohesive states are obtained by controlling the sizing amount of the fibers, and the sizing amount is 0.5-5 wt.%; The lengths of the carbon fibers and the thermoplastic polymer fibers are independently 1-15 mm; The thermoplastic polymer fibers include polyethylene fibers and / or polyester fibers; The mass ratio of the carbon fibers to the thermoplastic polymer fibers is 90-95:5-10; The areal density of the two-dimensional fiber network body is 5 to 100 g / m 2 .

3. The preparation method of the high thermal conductivity and high strength carbon fiber network body modified by carbon nanotubes with gradient pores and hierarchical pores according to claim 2, characterized in that, In the step 2), the two-dimensional fiber network body is divided into: two-dimensional fiber network body A, two-dimensional fiber network body B, and two-dimensional fiber network body C according to the areal density; The areal densities of the two-dimensional fiber network body A, the two-dimensional fiber network body B, and the two-dimensional fiber network body C are 5 to 20 g / m 2 , 20 to 50 g / m 2 , 50 to 100 g / m 2 ; The two-dimensional fiber network body is arranged and designed in a gradient stacking manner of AAA - BBB - CCC - BBB - AAA; The porosity of the three-dimensional carbon fiber network body is 80-90%, and the fiber density in the thickness direction of the three-dimensional carbon fiber network body is 10-60 bundles / cm 2 , the fiber depth of the three-dimensional carbon fiber network body is 4-10 mm, and the density of the three-dimensional carbon fiber network body is 0.13-0.25 g / cm 3 .

4. The preparation method of the high thermal conductivity and high strength carbon fiber network body modified by carbon nanotubes with gradient pores and hierarchical pore characteristics according to claim 3, characterized in that, In the step 3), the carbon phase densification includes chemical vapor deposition process and / or impregnation pyrolysis; In the chemical vapor deposition process, the carbon source gas used in the chemical vapor deposition process includes at least one of C3-C5 alkanes and C3-C5 alkenes, the carrier gas is nitrogen or argon, the pressure is 1-5 kPa, the reaction temperature is 900-1100 °C, the flow rate of the carbon source gas is 15-18 L / min, and the deposition time is 50-90 h; The density of the three-dimensional carbon fiber network body after carbon phase densification is 0.50 to 0.8 g / cm 3 ; The three-dimensional fiber network body constructs pyrolytic carbon on the fiber surface by chemical vapor deposition process, and the texture type of the pyrolytic carbon is high texture, and the extinction angle is 23° ≤ Ae ≤ 28°; 5. The preparation method of the highly thermally conductive and high-strength carbon fiber network body modified by carbon nanotubes with gradient pore and hierarchical pore characteristics according to claim 4, characterized in that, In the step 3), in the graphitization treatment, the protective gas used is argon, the temperature is 2800-3100 °C, the heating rate is 5-10 °C / min, and the holding time is 10-60 min; 6. The preparation method of the high thermal conductivity and high strength carbon fiber network body modified by carbon nanotubes with gradient pores and hierarchical pore characteristics according to claim 5, characterized in that, In the step 4), the preparation method of the composite dispersion liquid includes the following steps: Mix the polyvinyl alcohol solution and the polyethylene glycol solution to obtain a mixed solution, then add the metal salt solution and mix, and perform ultrasonic treatment after mixing evenly to obtain the composite dispersion liquid; 7. The preparation method of the highly thermally conductive and high-strength carbon fiber network body modified with carbon nanotubes having gradient pore and hierarchical pore characteristics according to claim 6, characterized in that, The mass concentration of the polyvinyl alcohol solution is 5-10 wt.%, the mass concentration of the polyethylene glycol solution is 10-20 wt.%, and the molar concentration of the metal salt solution is 0.1-1 mol / L; The mass ratio of the polyvinyl alcohol solution to the polyethylene glycol solution is 1:0.5-2; The mass ratio of the metal salt in the metal salt solution to the polyvinyl alcohol in the polyvinyl alcohol solution is 1:10-20; The metal salt solution includes at least one of a nickel source solution, a cobalt source solution, and an iron source solution; The nickel source in the nickel source solution includes one or more of nickel nitrate, nickel chloride, and nickel acetate; The dropping rate of the metal salt solution is 1-5 mL / min, and the addition of the metal salt solution is carried out under stirring, with the stirring speed being 600-1000 rpm; The molecular weight of the polyvinyl alcohol is 1000-5000, and the molecular weight of the polyethylene glycol is 400-6000; The time of the ultrasonic treatment is 10-15 min; The pH of the composite dispersion is 7-9, and the reagent used to adjust the pH is ammonia water or sodium hydroxide solution.

8. The preparation method of the high thermal conductivity and high strength carbon fiber network body modified by carbon nanotubes with gradient pores and hierarchical pore characteristics according to claim 7, characterized in that, In step 4), the freezing temperature is -170 to -120 °C, and the freezing time is 1-2 h; The vacuum drying is carried out in two steps. The temperature of the first vacuum drying is -120 to -40 °C, and the time of the first vacuum drying is 4-6 h. The temperature of the second vacuum drying is 150-200 °C, and the time of the second vacuum drying is 2-6 h; The magnetic field-assisted induced carbonization is carried out under vacuum conditions. The temperature of the magnetic field-assisted induced carbonization is 800-1200 °C, the heating rate of the magnetic field-assisted induced carbonization is 3-8 °C / min, and the time of the magnetic field-assisted induced carbonization is 10-30 min; During the magnetic field-assisted induced carbonization process, a magnetic field is applied along the thickness direction, the magnetic field intensity is 0.5-2 T, and the magnetic field direction is parallel to the thickness direction of the three-dimensional fiber network body.

9. A high thermal conductivity and high strength carbon fiber network body modified with carbon nanotubes having gradient pores and hierarchical pores, prepared by the preparation method according to any one of claims 1-8.

10. An application of the high thermal conductivity and high strength carbon fiber network body modified with carbon nanotubes having gradient pores and hierarchical pores according to claim 9 in phase change energy storage materials.

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