Thermally conductive composite material with three-dimensional network structure and preparation method thereof

Abstract

The application provides a three-dimensional network structure heat-conducting composite material and a preparation method thereof. In the preparation process, the hair grass is modified by using a silane coupling agent and polyethylene imine; the modified hair grass is axially and horizontally immersed in a boron nitride nanosheet solution and a polyethylene imine solution in sequence, and the immersion is repeated for 3-10 times, and the immersion in the boron nitride nanosheet solution is ensured in the last time; finally, the obtained three-dimensional heat-conducting network is axially and horizontally immersed in a boron nitride nanosheet / polyurethane mixed solution, taken out, placed in a mold containing the boron nitride / polyurethane mixed solution, placed in a coagulation bath again, taken out, dried, demolded, cut and trimmed to obtain the three-dimensional network structure heat-conducting composite material. The application constructs a regular and stable heat-conducting path in the interior and surface of the hair grass through the mutual interaction among the hair grass, the polyurethane, the polyethylene imine and the boron nitride; and a porous network structure is reconstructed in the interior of the hair grass, so that the obtained heat-conducting composite material has excellent performance.

Description

Technical Field

[0001] This invention relates to the field of thermally conductive materials technology, and in particular to a three-dimensional network structure thermally conductive composite material and its preparation method. Background Technology

[0002] With the rapid development of electronic technology, computer science, and artificial intelligence, electronic components are becoming increasingly miniaturized and high-powered. Highly integrated electronic devices generate a significant amount of heat during operation. If this heat cannot be dissipated in time, it can cause the operating environment temperature to rise, leading to thermal failures or reduced efficiency. Polyurethane possesses excellent insulation, flexibility, and mechanical properties, making it a promising candidate for use in electronic components. However, its poor thermal conductivity limits its application range. Boron nitride nanosheets, on the other hand, exhibit extremely high thermal conductivity, making them an excellent thermally conductive filler. Therefore, combining polyurethane and boron nitride nanosheets is an effective method for preparing thermally conductive materials. However, directly blending boron nitride nanosheets with polyurethane results in poor affinity between the two materials, making it difficult to form good thermal conductivity pathways. Furthermore, the accumulation of large amounts of boron nitride can easily degrade the mechanical properties of the polyurethane material. Therefore, constructing effective thermal conductivity pathways within polyurethane materials is of great significance.

[0003] The heat transfer process of polymer matrix composites is essentially a phonon propagation process; therefore, constructing a good thermally conductive pathway is a key factor in improving the thermal conductivity of composite materials. Currently, constructing a three-dimensional network pathway in the polymer matrix to arrange inorganic high thermal conductivity fillers in an orderly manner to increase the thermal conductivity of the composite material is an excellent method. Patent application number CN202211278210.8 discloses a two-step method for constructing a dual thermally conductive network polyurethane thermally conductive composite material and its preparation method. Based on an in-situ foaming polymerization process, thermally conductive filler A is used to construct a thermally conductive network 1 within a porous polymer skeleton, and thermally conductive filler B is adsorbed onto the three-dimensional porous skeleton of the polymer to form a thermally conductive network 2. The composite material is then obtained through hot pressing. First, the preparation method is affected by too many process factors, resulting in limited controllability of the prepared thermally conductive composite material. Second, the three-dimensional network prepared by this method exhibits a complex and irregular structure with twisting and turning, leading to unsatisfactory thermal conductivity stability, increased heat transport paths, and limited improvement in thermal conductivity. Third, polyurethane is difficult to fully impregnate and bond with the filler surface, resulting in micropore defects at the interface, which deteriorates the overall thermal conductivity of the structure. Furthermore, the preparation process of this method generates greenhouse gases, which is detrimental to environmental protection.

[0004] Patent application CN202010014231.3 discloses a method for preparing a highly filled hexagonal boron nitride / waterborne polyurethane composite material. This method modifies boron nitride and adds γ-polyglutamic acid as an inorganic filler dispersant to achieve a high content of hexagonal boron nitride in the waterborne polyurethane, thereby forming good thermal conductivity pathways within the composite material and improving thermal conductivity. However, the boron nitride in the polyurethane composite material prepared by this method has a disordered orientation, making it difficult to form thermal conductivity pathways when the filling amount is low, thus affecting the thermal conductivity of the material.

[0005] In view of this, it is necessary to design an improved three-dimensional network structure thermally conductive composite material and its preparation method to solve the above problems. Summary of the Invention

[0006] The purpose of this invention is to provide a three-dimensional network structure thermally conductive composite material and its preparation method. By utilizing the synergistic effects of rush, polyurethane, polyethyleneimine, and boron nitride, regular and stable thermally conductive pathways are constructed inside and on the surface of rush, thereby improving the thermal conductivity. Simultaneously, by utilizing the special network structure of rush and polyurethane, a porous network structure is reconstructed inside rush. While retaining the natural three-dimensional network structure of rush, its mesh structure is further strengthened, resulting in a three-dimensional network structure thermally conductive composite material with excellent mechanical properties and good resilience.

[0007] To achieve the above-mentioned objective, this invention provides a method for preparing a three-dimensional network structure thermally conductive composite material, comprising the following steps:

[0008] S1. Modified Juncus effusus was obtained by using silane coupling agent and polyethyleneimine.

[0009] S2. The modified rush obtained in step S1 is sequentially immersed in boron nitride nanosheet solution and polyethyleneimine solution, 3 to 10 times, and the last immersion is in boron nitride nanosheet solution. After drying, a three-dimensional thermally conductive network is obtained. When the modified rush is immersed in boron nitride nanosheet solution and polyethyleneimine solution, the axis is horizontal in the solution.

[0010] S3. The three-dimensional thermally conductive network obtained in step S2 is horizontally immersed in a boron nitride nanosheet / polyurethane mixed solution for a preset time. After being taken out, it is placed in a mold containing the boron nitride / polyurethane mixed solution, and the mold is placed in a coagulation bath. After being taken out, dried, demolded, and cut, a thermally conductive composite material with a three-dimensional network structure is obtained.

[0011] As a further improvement of the present invention, step S1 is specifically as follows: first, place the rush pith in a preset amount of water, add a silane coupling agent to it and stir at room temperature for 1 to 3 hours; then add polyethyleneimine to it and continue stirring for 1 to 3 hours; take out the rush pith and dry it to obtain modified rush pith; the silane coupling agent is γ-glycidoxypropyltrimethoxysilane.

[0012] As a further improvement of the present invention, the drying process specifically involves drying the rush pith at 105–120°C for 20–40 minutes.

[0013] As a further improvement of the present invention, in step S2, the concentration of the boron nitride nanosheet solution is 5-10 mg / mL; and the concentration of the polyethyleneimine solution is 1-2 mg / mL.

[0014] As a further improvement of the present invention, in step S3, the preparation method of the boron nitride nanosheet / polyurethane mixed solution is as follows: under continuous stirring, polyurethane particles are slowly added to a mixed solution containing dimethyl sulfoxide, toluene and boron nitride nanosheets until the polyurethane particles are completely dissolved; stirring is continued for 100-140 min, and vacuum degassing is performed to obtain the boron nitride nanosheet / polyurethane mixed solution.

[0015] As a further improvement of the present invention, the stirring rate is 700-900 r / min; the mass ratio of dimethyl sulfoxide, toluene and boron nitride is 1:1:(0.07-0.14); and the mass concentration of polyurethane in the boron nitride nanosheet / polyurethane mixed solution is 9-12%.

[0016] As a further improvement of the present invention, in step S3, the immersion time of the three-dimensional thermally conductive network in the boron nitride nanosheet / polyurethane mixed solution is 5 to 15 minutes; the coagulation bath is water, and the immersion time in the coagulation bath is 0.5 to 1.5 hours; the drying is to dry the mold containing rush pith at 70 to 90°C for 0.5 to 1.5 hours.

[0017] As a further improvement of the present invention, the mass ratio of the rush pith, silane coupling agent, and polyethyleneimine is (0.5-1.5):(0.5-1.5):(0.5-1.5); in the modified solution, the mass concentration of the silane coupling agent is 0.5-1.0%; and the concentration of the polyethyleneimine is 0.5-1.0%.

[0018] As a further improvement of the present invention, in step S2, the drying specifically involves drying the modified rush pith impregnated with boron nitride nanosheet solution and polyethyleneimine solution at 50-70°C for 100-140 min.

[0019] To achieve the above-mentioned objectives, the present invention also provides a three-dimensional network structure thermally conductive composite material, which is prepared by the preparation method of the three-dimensional network structure thermally conductive composite material described in any of the above-mentioned embodiments.

[0020] The beneficial effects of this invention are:

[0021] (1) The method for preparing the thermally conductive composite material with a three-dimensional network structure provided by the present invention firstly modifies Juncus effusus by sequentially adding a silane coupling agent with a specific structure and polyethyleneimine, drying it at a suitable temperature, uniformly bonding the silane coupling agent in the surface and internal pores of Juncus effusus, and bonding polyethyleneimine at the other end of the silane coupling agent to obtain a modified Juncus effusus with a special network structure.

[0022] Next, the modified rush was sequentially impregnated with boron nitride nanosheets and polyethyleneimine solution, ensuring that the last impregnation was with boron nitride nanosheet solution. During the impregnation of the modified rush with boron nitride nanosheet solution and polyethyleneimine solution, the axial direction was horizontal in the solution. The polyethyleneimine-modified rush has good adsorption performance for boron nitride. By utilizing the interaction between boron nitride and polyethyleneimine, a layered bonded sandwich structure of boron nitride nanosheet-polyethyleneimine-boron nitride nanosheet is formed on the surface and inside of the rush, resulting in a three-dimensional thermally conductive network.

[0023] Then, the three-dimensional thermally conductive network was horizontally immersed in a boron nitride nanosheet / polyurethane mixed solution. Under the combined effects of high roughness and high specific surface area, the boron nitride nanosheet layer on the surface of the three-dimensional thermally conductive network adsorbed sufficient boron nitride nanosheet / polyurethane mixed solution, allowing more polyurethane and boron nitride to enter the surface and internal pores of the rush. First, the long molecular chains of polyurethane cross-link and entangle with the network structure of the rush, making the network structure of the rush denser and exhibiting superior elasticity and mechanical properties. Second, the boron nitride nanosheets in the mixed solution are further embedded in the pores of the sandwich structure, forming more interconnected thermal conductive pathways. Third, the cross-linked network structure formed by polyurethane and rush can better bind the thermally conductive filler within its surface and internal pores. Next, the mold containing rush pith and boron nitride / polyurethane mixed solution was placed in a coagulation bath. Dimethyl sulfoxide from the surface and interior of the rush pith continuously entered the coagulation bath. Then, toluene was removed by drying. The evaporation of toluene caused the network structure of the rush pith to shrink. At the same time, the drying process caused the network structure of the rush pith to shrink further. The cross-linking and entanglement structure of polyurethane molecules and rush pith also changed further. The network structure became more orderly and dense, and finally a high-performance three-dimensional network structure thermally conductive composite material was obtained.

[0024] (2) This invention utilizes the unique network structure of rush pith on the one hand, and reconstructs a porous network structure within rush pith through the cross-linking and entanglement of polyurethane and rush pith on the other. While retaining the natural three-dimensional network structure of rush pith, its network structure is further strengthened, resulting in a thermally conductive composite material with excellent mechanical properties and good resilience. Simultaneously, through the interaction between rush pith, polyurethane, polyethyleneimine, and boron nitride, regular and stable thermally conductive pathways are constructed within and on the surface of rush pith, thereby improving the thermal conductivity.

[0025] (3) The thermally conductive composite material with a three-dimensional network structure provided by the present invention has a relatively large adjustable thickness range, which is conducive to better contact between the heat source and the heat sink, filling the gap between the heat source and the heat sink and squeezing out poor conductor air. It can be used as a thermally conductive pad to achieve rapid and uniform heat dissipation of electronic components. At the same time, it can also reduce the process tolerance requirements of the heat sink and heat dissipation structure (more suitable for heat dissipation of heat sources with uneven surfaces) and has a shock absorption effect. Furthermore, the good compression recovery performance of the thermally conductive composite material with a three-dimensional network structure improves its reusability and service life. Attached Figure Description

[0026] Figure 1 The image shown is an electron microscope image of the thermally conductive composite material with a three-dimensional network structure prepared in Example 1 of this invention. The scale bar is 10 μm. Detailed Implementation

[0027] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be described in detail below with reference to the accompanying drawings and specific embodiments.

[0028] It should also be noted that, in order to avoid obscuring the present invention with unnecessary details, only the structures and / or processing steps closely related to the present invention are shown in the accompanying drawings, while other details that are not closely related to the present invention are omitted.

[0029] Additionally, it should be noted that the terms “comprising,” “including,” or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such process, method, article, or apparatus.

[0030] This invention provides a method for preparing a three-dimensional network structure thermally conductive composite material, comprising the following steps:

[0031] S1. Modified Juncus effusus:

[0032] Modified Juncus effusus was obtained by modifying Juncus effusus with silane coupling agent and polyethyleneimine.

[0033] Specifically, the rush pith is first placed in a predetermined amount of water, and a silane coupling agent is added and stirred at room temperature for 1–3 hours; then polyethyleneimine (PEI) is added and stirring continues for 1–3 hours. In the modified solution (i.e., the aqueous solution in which the silane coupling agent and polyethyleneimine are added sequentially), the mass ratio of rush pith, silane coupling agent, and polyethyleneimine is (0.5–1.5):(0.5–1.5):(0.5–1.5), preferably 1:1:1; the mass concentration of both the silane coupling agent and polyethyleneimine is 0.5–1.0%. The silane coupling agent is γ-glycidoxypropyltrimethoxysilane.

[0034] Next, the rush pith was removed from the modification solution and dried in a blower dryer at a temperature of 105-120℃ for 20-40 minutes to obtain modified rush pith.

[0035] In this process, a silane coupling agent is first added to an aqueous solution containing rush pith. The silane coupling agent spreads on the surface of the rush pith, and the alkoxy group at one end of the silane coupling agent molecule hydrolyzes to generate silanol groups. These silanol groups form hydrogen bonds with the abundant hydroxyl, carbonyl, and ester groups on and inside the rush pith surface, leading to a hydrolysis-condensation reaction that uniformly bonds the silane coupling agent to the surface and interior of the rush pith network structure. Next, polyethyleneimine is added to the solution. Polyethyleneimine, due to its high adsorption capacity, first adsorbs and adheres to the surface and interior of the rush pith. Then, the active group (epoxy group) at the other end of the silane coupling agent adsorbed on the surface and interior of the rush pith reacts with the abundant amino and double bond groups of the highly reactive polyethyleneimine, bonding with each other. Finally, at high temperature, the three react further and fully, ultimately resulting in a uniform and dense bonding of polyethyleneimine to the surface and interior of the rush pith, yielding rush pith with a special structure.

[0036] When the concentrations of silane coupling agent and polyethyleneimine are too low, a dense and uniform silane coupling agent and polyethyleneimine adhesion layer cannot be formed on the surface and inside of the rush. When the concentration is too high, on the one hand, the silane coupling agent and polyethyleneimine bonded on the surface and inside of the rush reach saturation, resulting in little improvement in performance; on the other hand, the excessively high concentration increases the viscosity of the solution, which to some extent affects the bonding process.

[0037] S2. Fabrication of a three-dimensional thermally conductive network:

[0038] The modified rush pith obtained in step S1 was sequentially immersed in boron nitride nanosheet (BNNS) solution and polyethyleneimine solution, cyclically 3–10 times, ensuring that the final immersion was in boron nitride nanosheet solution. After drying, a three-dimensional thermally conductive network was obtained. When the modified rush pith was immersed in the boron nitride nanosheet solution and polyethyleneimine solution, its axis was horizontal in the solution. The concentration of the boron nitride nanosheet solution was 5–10 mg / mL; the concentration of the polyethyleneimine solution was 1–2 mg / mL.

[0039] Specifically, the modified rush pith was first horizontally immersed in a boron nitride nanosheet solution for 2 minutes. Polyethylene imine-modified rush pith exhibits excellent adsorption performance for boron nitride. Simultaneously, boron nitride, due to its high specific surface area, adsorbed onto the modified rush pith. Boron nitride was bonded to the polyethyleneimine on the surface and inside of the rush pith through hydrogen bonds. Furthermore, the horizontal orientation of the rush pith in the solution not only allowed the boron nitride nanosheets to bond more firmly to the surface and internal pores of the rush pith, but also enabled the boron nitride nanosheets to be neatly bonded to the surface and internal pores of the rush pith in a specific arrangement, resulting in a more orderly thermally conductive network structure and better thermal conductivity. Next, the rush pith was placed in deionized water to wash away excess boron nitride, at which point a neatly arranged layer of boron nitride nanosheets was formed on the surface and inside of the rush pith. Next, the rush was immersed in a polyethyleneimine solution for 2 minutes. The polyethyleneimine, with its high adsorption capacity, adhered to the surface and interior of the rush and further bonded with the boron nitride on the surface and inside the rush. Then, it was placed in deionized water to wash away excess polyethyleneimine, resulting in a neatly arranged polyethyleneimine layer on the surface and inside the rush. This process was repeated, ensuring a final immersion in a boron nitride nanosheet solution, forming a layered sandwich structure of boron nitride nanosheets-polyethyleneimine-boron nitride nanosheets on the surface and inside the rush. Compared to placing the rush in the solution in any orientation, the layered sandwich structure formed by placing it horizontally along the axis is more orderly and robust, with a superior thermal network structure and better thermal conductivity.

[0040] Finally, the modified rush impregnated with boron nitride nanosheet solution and polyethyleneimine solution was dried in a blower dryer at a temperature of 50-70℃ for 100-140 minutes.

[0041] S3. Preparation of thermally conductive composite materials with three-dimensional network structures:

[0042] Under continuous stirring, polyurethane particles were slowly added to a mixed solution containing dimethyl sulfoxide, toluene, and boron nitride nanosheets until the polyurethane particles were completely dissolved. The stirring rate was maintained at 700–900 r / min, and stirring continued for 100–140 min. Vacuum degassing was then performed to obtain a boron nitride nanosheet / polyurethane mixed solution. Using a binary mixture of dimethyl sulfoxide and toluene ensures that the boron nitride nanosheets and polyurethane are evenly dispersed in the mixed solution system. Furthermore, it results in a denser three-dimensional network structure with improved properties.

[0043] The mass ratio of dimethyl sulfoxide, toluene, and boron nitride in the obtained boron nitride nanosheet / polyurethane mixed solution is 1:1:(0.07–0.14); the mass concentration of polyurethane in the mixed solution is 9–12%.

[0044] The three-dimensional thermally conductive network obtained in step S2 is immersed horizontally in the boron nitride nanosheet / polyurethane mixed solution prepared above for 5-15 minutes. After that, it is taken out and placed in a mold containing the boron nitride / polyurethane mixed solution prepared above. The mold is then immersed in a water coagulation bath for 0.5-1.5 hours. After that, the mold containing rush pith is dried in a blower dryer at a temperature of 70-90°C for 0.5-1.5 hours. After demolding, it is cut to obtain a thermally conductive composite material with a three-dimensional network structure.

[0045] In this process, since the surface of the three-dimensional thermally conductive network obtained in step S2 is a boron nitride nanosheet layer, it has a higher surface roughness and a higher specific surface area. Under the dual effects of high roughness and high specific surface area, it is easier to adsorb the boron nitride nanosheet / polyurethane mixed solution, allowing more polyurethane and boron nitride to enter the surface and internal pores of the rush. First, the long molecular chains of polyurethane are cross-linked and entangled with the network structure of the rush, making the network structure of the rush more compact and with better elasticity and mechanical properties. Second, compared with the polyurethane single solution, the boron nitride nanosheets in the mixed solution will be further embedded in the pores of the sandwich structure formed in different steps S2, forming a more interconnected thermal conductive pathway. Third, the network structure formed by the cross-linking and entanglement of polyurethane and rush can better bind the thermally conductive filler in its surface and internal pores. Then, the rush is placed again in a mold containing the above-prepared boron nitride / polyurethane mixed solution (the appropriate mold is selected according to the shape of the composite thermally conductive material to be prepared), so that the rushes from different roots form the desired structure. The mold containing rushes is then placed in a coagulation bath (the water in the coagulation bath and the solution in the mold can come into contact with each other). Dimethyl sulfoxide from the surface and interior of the rushes continuously enters the coagulation bath, while the boron nitride / polyurethane mixed solution in the mold solidifies and adheres to the surface of the rushes, bonding the rushes from different roots together. Next, toluene is removed through a drying process. The evaporation of toluene causes the network structure of the rushes to shrink, and the drying process further shrinks the network structure of the rushes. The cross-linking and entanglement structure of the polyurethane molecules and the rushes also changes further. The drying process also solidifies the boron nitride / polyurethane film on the surface of the rushes from different roots and further wraps and binds the rushes, making the network structure more neat and dense. Finally, the mold is demolded and cut to obtain a high-performance three-dimensional network structure thermally conductive composite material.

[0046] The rush is placed in a mold containing a boron nitride / polyurethane mixed solution to obtain the desired final shape. In some embodiments, the three-dimensional thermally conductive network obtained in step S2 can be first immersed axially horizontally in the boron nitride nanosheet / polyurethane mixed solution prepared above for 5-15 minutes, then removed and immersed in a water coagulation bath for 0.5-1.5 hours. Then, the rush is dried in a blower dryer at a temperature of 70-90°C for 0.5-1.5 hours. Next, rushes of different numbers are arranged into the required shapes according to the usage requirements, and then polyurethane / boron nitride solution is sprayed on their surface. They are then placed in a mold and dried.

[0047] The present invention also provides a three-dimensional network structure thermally conductive composite material, which is prepared by the above-described method for preparing a three-dimensional network structure thermally conductive composite material.

[0048] The present invention will now be described in detail through specific embodiments.

[0049] Example 1

[0050] S1. Modified Juncus effusus:

[0051] First, place the rush pith in a predetermined amount of water, add γ-glycidoxypropyltrimethoxysilane, and stir at room temperature for 2 hours; then add polyethyleneimine (PEI) and continue stirring for 2 hours. In the modified solution, the mass ratio of rush pith, silane coupling agent, and polyethyleneimine is 1:1:1; the mass concentrations of both the silane coupling agent and polyethyleneimine are 0.8%.

[0052] Next, the rush pith was removed from the modification solution and dried in a blower dryer at 110°C for 30 minutes to obtain modified rush pith.

[0053] S2. Fabrication of a three-dimensional thermally conductive network:

[0054] The modified rush pith obtained in step S1 was sequentially immersed in boron nitride nanosheet (BNNS) solution and polyethyleneimine solution, cyclically five times, ensuring that the final immersion in boron nitride nanosheet solution (i.e., immersion in boron nitride nanosheet solution once after five cycles) was performed, followed by drying to obtain a three-dimensional thermally conductive network. When the modified rush pith was immersed in the boron nitride nanosheet solution and polyethyleneimine solution, its axis was horizontal in the solution. The concentration of the boron nitride nanosheet solution was 8 mg / mL; the concentration of the polyethyleneimine solution was 1 mg / mL.

[0055] Next, the modified rush impregnated with boron nitride nanosheet solution and polyethyleneimine solution was dried in a blower dryer at 60°C for 120 min.

[0056] S3. Preparation of thermally conductive composite materials with three-dimensional network structures:

[0057] Under continuous stirring, polyurethane particles were slowly added to a mixed solution containing dimethyl sulfoxide, toluene, and boron nitride nanosheets until the polyurethane particles were completely dissolved. The stirring rate was maintained at 800 r / min, and stirring continued for 120 min. Vacuum degassing was then performed to obtain a boron nitride nanosheet / polyurethane mixed solution. The mass ratio of dimethyl sulfoxide, toluene, and boron nitride in the obtained boron nitride nanosheet / polyurethane mixed solution was 1:1:0.1; the mass concentration of polyurethane in this mixed solution was 10%.

[0058] The three-dimensional thermally conductive network obtained in step S2 was immersed horizontally in the boron nitride nanosheet / polyurethane mixed solution prepared above for 10 min. Afterward, it was removed and placed in a mold containing the prepared boron nitride nanosheet / polyurethane mixed solution. The mold was then immersed in a water coagulation bath for 1.0 h. After removal, the mold containing rush pith was dried in a forced-air dryer at 80℃ for 1.0 h. It was then demolded, cut, and obtained as shown. Figure 1 The thermally conductive composite material with a three-dimensional network structure is shown. (The structure is made of...) Figure 1 It can be seen that a dense thermally conductive layer is formed on the surface of the three-dimensional network structure of rush pith.

[0059] The resulting three-dimensional network structure of the thermally conductive composite material is a cuboid with dimensions of 8cm × 5cm × 0.5cm.

[0060] Examples 2-3 and Comparative Examples 1-2

[0061] The preparation method of a three-dimensional network structure thermally conductive composite material differs from that of Example 1 in that the drying temperature is different in step S1, while the rest is roughly the same as that of Example 1, and will not be repeated here.

[0062] The thermally conductive composite materials with three-dimensional network structures prepared in Examples 1-3 and Comparative Examples 1-2 were subjected to performance tests, and the results are shown in Table 1.

[0063] Compression recovery rate refers to the recovery effect within elastic deformation.

[0064] The thermal conductivity of rush pith is 0.06 W / (m·K).

[0065] Table 1. Thermally conductive composite materials with three-dimensional network structures prepared in Examples 1-3 and Comparative Examples 1-2.

[0066]

[0067]

[0068] As shown in Table 1, within a certain range, with the increase of drying temperature (Examples 1, 2, and 3), the compression recovery rate and electrical conductivity initially increase and then decrease. Simultaneously, the resistivity of the obtained three-dimensional network structure thermally conductive composite material is very high, essentially approaching that of an insulating material. Therefore, the obtained three-dimensional network structure thermally conductive composite material exhibits good overall elastic and thermal conductivity properties, while being essentially non-conductive. When placed between a heat source and a heat sink in electronic components, its good elasticity allows for better contact between the heat source and the heat sink, its high thermal conductivity facilitates better heat dissipation, and its high resistance prevents short circuits in the electronic components, improving safety.

[0069] In addition, the thermal conductivity of the original rush is only 0.06 W / (m·K), while the thermal conductivity of the composite thermally conductive material obtained after treatment using the method of this application is significantly improved.

[0070] When the reaction temperature is low (Comparative Example 1), the thermal conductivity of the resulting three-dimensional network structure thermally conductive composite material is low. This is mainly because the reaction between the silane coupling agent and polyethyleneimine and rush pith is insufficient at low temperatures, resulting in insufficient modification of rush pith, which affects the subsequent bonding of boron nitride nanosheets and thus affects the thermal conductivity.

[0071] When the reaction temperature is high (Comparative Example 2), the thermal conductivity of the obtained three-dimensional network structure thermally conductive composite material is significantly reduced, and the elastic recovery rate tends to decrease. This may be because the high temperature destroys the three-dimensional network structure of Juncus effusus, thereby affecting the performance of the obtained composite material.

[0072] Examples 4-5 and Comparative Examples 3-4

[0073] The preparation method of a three-dimensional network structure thermally conductive composite material differs from that of Example 1 in that the number of cycles for impregnating boron nitride nanosheet solution and polyethyleneimine solution in step S2 is different. The rest is roughly the same as that of Example 1 and will not be repeated here.

[0074] The thermally conductive composite materials with three-dimensional network structures prepared in Examples 4-5 and Comparative Examples 3-4 were subjected to performance tests, and the results are shown in Table 2.

[0075] Table 2. Thermally conductive composite materials with three-dimensional network structures prepared in Examples 4-5 and Comparative Examples 3-4.

[0076] Example 1 5 96 3.060 <![CDATA[2.7×10 14 ]]> Example 4 3 95 2.632 <![CDATA[2.6×10 14 ]]> Example 5 10 97 3.181 <![CDATA[2.9×10 14 ]]> Comparative Example 3 2 94 2.176 <![CDATA[2.1×10 14 ]]> Comparative Example 4 12 95 3.227 <![CDATA[3.0×10 14 ]]>

[0077] As shown in Table 2, with the increase of the number of cycles of impregnating boron nitride nanosheet solution and polyethyleneimine solution, the compression recovery of the prepared composite thermally conductive material first increases and then decreases. The thermal conductivity and resistivity show a trend of first rapidly increasing and then gradually increasing. This is mainly because with the increase of the number of cycles of impregnating boron nitride nanosheet solution and polyethyleneimine solution, the content of boron nitride loaded on the three-dimensional network structure of Juncus effusus also increases, making the thermally conductive network structure richer. However, when the boron nitride loading increases to a certain amount, further increases in the number of cycles lead to near saturation of the boron nitride loading, with little impact on the thermally conductive network structure, and the thermal conductivity basically stabilizes. At the same time, excessive boron nitride loading may affect the elastic properties of the obtained composite thermally conductive material.

[0078] Examples 6-7 and Comparative Examples 5-6

[0079] A method for preparing a three-dimensional network structure thermally conductive composite material differs from Example 1 in that the concentration of the impregnated boron nitride nanosheet solution is different in step S2. Otherwise, it is largely the same as Example 1 and will not be described again here.

[0080] The thermally conductive composite materials with three-dimensional network structures prepared in Examples 6-7 and Comparative Examples 5-6 were subjected to performance tests, and the results are shown in Table 3.

[0081] Table 3. Thermally conductive composite materials with three-dimensional network structures prepared in Examples 6-7 and Comparative Examples 5-6.

[0082]

[0083]

[0084] As shown in Table 3, with the increase of the concentration of the impregnated boron nitride nanosheet solution, the compression recovery rate of the prepared composite thermally conductive material first increases and then decreases, while the thermal conductivity shows an increasing-to-plate trend, and the electrical resistance first increases and then decreases. This is mainly because with the increase of the concentration of the impregnated boron nitride nanosheet solution, the number of bonded boron nitride nanosheets in the three-dimensional network on the surface and inside of the rush pith increases and the distribution becomes more uniform, resulting in a higher density of the thermally conductive network and thus better thermal conductivity. However, with further increases in the concentration of the impregnated boron nitride nanosheet solution (Comparative Example 5), the thermal conductivity basically stabilizes.

[0085] Example 8 and Comparative Examples 7-8

[0086] A method for preparing a three-dimensional network structure thermally conductive composite material differs from Example 1 in that the concentration of the impregnating polyethyleneimine solution is different in step S2. Otherwise, it is largely the same as Example 1 and will not be described again here.

[0087] The performance of the thermally conductive composite materials with three-dimensional network structures prepared in Example 8 and Comparative Examples 7-8 was tested, and the results are shown in Table 4:

[0088] Table 4. Thermally conductive composite materials with three-dimensional network structures prepared in Example 8 and Comparative Examples 7-8

[0089]

[0090] As shown in Table 4, with the increase of the concentration of the impregnating polyethyleneimine solution, the compression recovery rate and thermal conductivity of the prepared composite thermally conductive material first increase and then tend to stabilize. This is mainly because the increase of the concentration of the impregnating polyethyleneimine solution results in a greater and more uniform number of polyethyleneimine molecules bonded to the surface of the boron nitride nanosheets, which in turn makes the boron nitride nanosheet-polyethyleneimine-boron nitride nanosheet sandwich structure more compact. The boron nitride content loaded in the three-dimensional network structure of rush pith also increases slightly, resulting in a richer thermally conductive network structure and better thermal conductivity.

[0091] Examples 9-10 and Comparative Examples 9-10

[0092] A method for preparing a three-dimensional network structure thermally conductive composite material differs from Example 1 in that, in step S3, the mass ratio of dimethyl sulfoxide, toluene, and boron nitride in the boron nitride nanosheet / polyurethane mixed solution is different. The other steps are largely the same as in Example 1 and will not be repeated here.

[0093] The thermally conductive composite materials with three-dimensional network structures prepared in Examples 9-10 and Comparative Examples 9-10 were subjected to performance tests, and the results are shown in Table 5.

[0094] Table 5. Thermally conductive composite materials with three-dimensional network structures prepared in Examples 9-10 and Comparative Examples 9-10

[0095] Example 1 1:1:0.1 96 3.060 <![CDATA[2.7×10 14 ]]> Example 9 1:1:0.07 97 2.148 <![CDATA[1.7×10 14 ]]> Example 10 1:1:0.14 96 4.585 <![CDATA[4.5×10 14 ]]> Comparative Example 9 1:1:0.05 98 1.907 <![CDATA[1.2×10 14 ]]> Comparative Example 10 1:1:0.2 95 4.495 <![CDATA[4.6×10 14 ]]>

[0096] As shown in Table 5, with the increase of boron nitride content, the compression recovery rate of the resulting composite thermally conductive material does not change significantly, while the thermal conductivity and resistivity gradually increase. This is mainly because with the increase of the boron nitride mass ratio, boron nitride nanosheets are more easily embedded in the pores of the sandwich structure formed in step S2, thereby making the internal thermal conductive pathways of the composite thermally conductive material more interconnected and significantly improving the thermal conductivity. However, with further increases in boron nitride content, the thermal conductivity of the composite thermally conductive material basically tends to stabilize.

[0097] Examples 11-12 and Comparative Examples 11-12

[0098] A method for preparing a three-dimensional network structure thermally conductive composite material differs from Example 1 in that the mass concentration of polyurethane in the boron nitride nanosheet / polyurethane mixed solution is different in step S3. Otherwise, it is roughly the same as Example 1 and will not be described again here.

[0099] The thermally conductive composite materials with three-dimensional network structures prepared in Examples 11-12 and Comparative Examples 11-12 were subjected to performance tests, and the results are shown in Table 6.

[0100] Table 6. Thermally conductive composite materials with three-dimensional network structures prepared in Examples 11-12 and Comparative Examples 11-12.

[0101] Example 1 10 96 3.060 <![CDATA[2.7×10 14 ]]> Example 11 9 88 3.088 <![CDATA[2.9×10 14 ]]> Example 12 12 98 2.939 <![CDATA[3.3×10 14 ]]> Comparative Example 11 8 80 3.116 <![CDATA[2.4×10 14 ]]> Comparative Example 12 14 99 2.940 <![CDATA[2.2×10 14 ]]>

[0102] As shown in Table 6, with the increase of polyurethane mass concentration, the compression recovery rate of the resulting composite thermally conductive material gradually increases, while the overall thermal conductivity and resistivity are relatively high. This is mainly because with the increase of polyurethane mass concentration, the polyurethane molecular chains intertwine more firmly with the network structure of rush, thus resulting in better elastic properties of the resulting composite thermally conductive material; at the same time, the mutual entanglement of polyurethane molecular chains with the network structure of rush makes the thermally conductive network structure on and inside the rush surface more dense and uniform, thus resulting in better overall thermal conductivity.

[0103] Comparative Example 13

[0104] A method for preparing a three-dimensional network structure thermally conductive composite material, compared with Example 1, differs in that, in step S1, the silane coupling agent is γ-methacryloyloxypropyltrimethoxysilane; otherwise, it is largely the same as Example 1 and will not be repeated here. The three-dimensional network structure thermally conductive composite material obtained in Comparative Example 13 has a compression recovery rate of 94%, a thermal conductivity of 1.987 W / (m·K), and a resistivity of 1.2 × 10⁻⁶. 14 The Ω·cm performance is inferior to that of Example 1, indicating that only silane coupling agents with specific structures can produce high-performance thermally conductive composite materials with a three-dimensional network structure.

[0105] Comparative Example 14

[0106] A method for preparing a three-dimensional network structure thermally conductive composite material differs from Example 1 in that, in step S1, only a silane coupling agent is added, and polyethyleneimine is not added. The other steps are largely the same as in Example 1 and will not be repeated here. The three-dimensional network structure thermally conductive composite material obtained in Comparative Example 14 has a compression recovery rate of 95%, a thermal conductivity of 2.223 W / (m·K), and a resistivity of 1.6 × 10⁻⁶. 14The performance of the Ω·cm was inferior to that of Example 1. This is mainly because when polyethyleneimine was not added in step S1, boron nitride was directly bonded to rush pith through a silane coupling agent during the impregnation of the boron nitride nanosheet solution. This bonding structure was poor, which affected the bonding of the boron nitride nanosheet-polyethyleneimine-boron nitride nanosheet sandwich structure and ultimately affected the performance of the thermally conductive composite material with the obtained three-dimensional network structure.

[0107] Comparative Example 15

[0108] A method for preparing a three-dimensional network structure thermally conductive composite material differs from Example 1 in that, in step S1, a silane coupling agent and polyethyleneimine are added simultaneously. The other steps are largely the same as in Example 1 and will not be repeated here. The three-dimensional network structure thermally conductive composite material obtained in Comparative Example 15 exhibits a compression recovery rate of 96%, a thermal conductivity of 2.316 W / (m·K), and a resistivity of 1.5 × 10⁻⁶. 14 The performance of the thermally conductive composite material with a Ω·cm ratio is inferior to that of Example 1. This is mainly because the simultaneous addition of silane coupling agent and polyethyleneimine results in a more disordered bonding structure on and inside the surface of Juncus effusus, which affects the subsequent bonding of the boron nitride nanosheet-polyethyleneimine-boron nitride nanosheet sandwich structure and ultimately affects the performance of the resulting three-dimensional network structure thermally conductive composite material.

[0109] Comparative Example 16

[0110] A method for preparing a three-dimensional network structure thermally conductive composite material differs from Example 1 in that, in step S2, the final impregnation with the polyethyleneimine solution (i.e., 5 cycles) is performed. The other steps are largely the same as in Example 1 and will not be repeated here. The three-dimensional network structure thermally conductive composite material obtained in Comparative Example 16 exhibits a compression recovery rate of 90%, a thermal conductivity of 2.400 W / (m·K), and a resistivity of 2.3 × 10⁻⁶. 14 The performance of the boron nitride nanosheets was lower than that of Example 1, indicating that the high surface roughness and high specific surface area of ​​the boron nitride nanosheets made it easier to adsorb the boron nitride nanosheet / polyurethane mixed solution, allowing more polyurethane and boron nitride to enter the surface and internal pores of the rush. The resulting three-dimensional network structure thermally conductive composite material had better performance.

[0111] Comparative Example 17

[0112] A method for preparing a three-dimensional network structure thermally conductive composite material differs from Example 1 in that, in step S2, excess boron nitride or polyethyleneimine is not washed away before cyclic impregnation. The rest of the method is largely the same as in Example 1 and will not be repeated here. The three-dimensional network structure thermally conductive composite material obtained in Comparative Example 17 has a compression recovery rate of 95%, a thermal conductivity of 2.592 W / (m·K), and a resistivity of 2.6 × 10⁻⁶. 14The performance was worse than that of Example 1, indicating that the excess boron nitride nanosheets or polyethyleneimine would affect the sandwich structure and thus the performance of the thermally conductive composite material with a three-dimensional network structure.

[0113] Comparative Example 18

[0114] A method for preparing a three-dimensional network structure thermally conductive composite material differs from Example 1 in that, in step S3, the mass ratio of dimethyl sulfoxide, toluene, and boron nitride is 1:1:0 (i.e., boron nitride nanosheets are not added, and a simple polyurethane solution is prepared). Other steps are largely the same as in Example 1 and will not be repeated here. The three-dimensional network structure thermally conductive composite material obtained in Comparative Example 18 has a compression recovery rate of 98%, a thermal conductivity of 1.703 W / (m·K), and a resistivity of 1.8 × 10⁻⁶. 14 The performance was worse than that of Example 1, which further illustrates that the presence of boron nitride nanosheets makes the conductive pathway more connected, thus resulting in better performance.

[0115] Comparative Example 19

[0116] A method for preparing a three-dimensional network structure thermally conductive composite material differs from Example 1 in that, in step S3, the solvent in the boron nitride nanosheet / polyurethane mixed solution is only dimethyl sulfoxide. The other steps are largely the same as in Example 1 and will not be repeated here. The three-dimensional network structure thermally conductive composite material obtained in Comparative Example 19 has a compression recovery rate of 88%, a thermal conductivity of 2.102 W / (m·K), and a resistivity of 1.7 × 10⁻⁶. 14 Ω·cm, performance is inferior to Example 1.

[0117] Comparative Example 20

[0118] A method for preparing a three-dimensional network structure thermally conductive composite material differs from Example 1 in that, in step S3, the material is not soaked in a coagulation bath; instead, it is directly dried to remove dimethyl sulfoxide and toluene. The rest of the method is largely the same as in Example 1 and will not be repeated here. The three-dimensional network structure thermally conductive composite material obtained in Comparative Example 20 has a compression recovery rate of 82%, a thermal conductivity of 2.237 W / (m·K), and a resistivity of 1.3 × 10⁻⁶. 14 Ω·cm, performance is inferior to Example 1.

[0119] Comparative Example 21

[0120] A method for preparing a three-dimensional network structure thermally conductive composite material is disclosed. Compared to Example 1, the difference lies in replacing *Juncus effusus* with *Tetrapanax papyriferus*. Otherwise, the method is largely the same as in Example 1 and will not be repeated here. The three-dimensional network structure thermally conductive composite material obtained in Comparative Example 21 exhibits a compression recovery rate of 90%, a thermal conductivity of 1.629 W / (m·K), and a resistivity of 1.9 × 10⁻⁶. 14The thermal conductivity of this porous material is 0.053 W / (m·K), which is worse than that of Example 1. This indicates a unique interaction between the rush pith, boron nitride nanosheets, and polyethyleneimine, with the synergistic effect among the three enhancing the thermal conductivity.

[0121] Comparative Example 22

[0122] A method for preparing a three-dimensional network structure thermally conductive composite material is disclosed. Compared to Example 1, the difference lies in replacing *Rush wick* with polyurethane foam; otherwise, the method is largely the same as in Example 1 and will not be repeated here. The three-dimensional network structure thermally conductive composite material obtained in Comparative Example 22 exhibits a compression recovery rate of 97%, a thermal conductivity of 2.533 W / (m·K), and a resistivity of 2.2 × 10⁻⁶. 14 The thermal conductivity was lower than that of Example 1 (Ω·cm). This further illustrates the unique interaction between Juncus effusus, boron nitride nanosheets, and polyethyleneimine, with the synergistic effect among the three enhancing thermal conductivity.

[0123] In summary, the three-dimensional network structure thermally conductive composite material and its preparation method provided by this invention, through the synergistic effects of rush, polyurethane, polyethyleneimine, and boron nitride, construct regular and stable thermally conductive pathways within and on the surface of rush, thereby improving the thermal conductivity. Simultaneously, by utilizing the special network structure of rush and polyurethane, a porous network structure is reconstructed within rush, further reinforcing its mesh structure while preserving its natural three-dimensional network structure. This results in a three-dimensional network structure thermally conductive composite material with excellent mechanical properties and good resilience.

[0124] The above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit it. Although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can be made to the technical solutions of the present invention without departing from the spirit and scope of the technical solutions of the present invention.

Claims

1. A method for preparing a thermally conductive composite material with a three-dimensional network structure, characterized in that, Includes the following steps: S1. Modified Juncus effusus was obtained by using silane coupling agent and polyethyleneimine. S2. The modified rush obtained in step S1 is sequentially immersed in boron nitride nanosheet solution and polyethyleneimine solution, 3 to 10 times, and the last immersion is in boron nitride nanosheet solution. After drying, a three-dimensional thermally conductive network is obtained. When the modified rush is impregnated with boron nitride nanosheet solution and polyethyleneimine solution, the axis is horizontal in the solution; S3. The three-dimensional thermally conductive network obtained in step S2 is horizontally immersed in a boron nitride nanosheet / polyurethane mixed solution for a preset time. After being taken out, it is placed in a mold containing the boron nitride / polyurethane mixed solution. The mold is placed in a coagulation bath, taken out, dried, demolded, and cut to obtain a thermally conductive composite material with a three-dimensional network structure. Step S1 is as follows: First, place the rush pith in a predetermined amount of water, add a silane coupling agent and stir at room temperature for 1-3 hours; then add polyethyleneimine and continue stirring for 1-3 hours; remove the rush pith and dry it to obtain modified rush pith; the silane coupling agent is γ-glycidoxypropyltrimethoxysilane. The drying process specifically involves drying the rush pith at 105–120°C for 20–40 minutes. The concentration of the boron nitride nanosheet solution is 5–10 mg / mL; In step S3, the preparation method of the boron nitride nanosheet / polyurethane mixed solution is as follows: under continuous stirring, polyurethane particles are slowly added to a mixed solution containing dimethyl sulfoxide, toluene and boron nitride nanosheets until the polyurethane particles are completely dissolved. Continue stirring for 100–140 min, then degas under vacuum to obtain the boron nitride nanosheet / polyurethane mixed solution. The mass ratio of dimethyl sulfoxide, toluene, and boron nitride is 1:1:(0.07–0.14).

2. The method for preparing the three-dimensional network structure thermally conductive composite material according to claim 1, characterized in that, In step S2, the concentration of the polyethyleneimine solution is 1-2 mg / mL.

3. The method for preparing the thermally conductive composite material with a three-dimensional network structure according to claim 1, characterized in that, The stirring rate is 700–900 r / min; the mass concentration of polyurethane in the boron nitride nanosheet / polyurethane mixed solution is 9–12%.

4. The method for preparing the thermally conductive composite material with a three-dimensional network structure according to claim 1, characterized in that, In step S3, the immersion time of the three-dimensional thermally conductive network in the boron nitride nanosheet / polyurethane mixed solution is 5 to 15 minutes; the coagulation bath is water, and the immersion time in the coagulation bath is 0.5 to 1.5 hours; the drying is to dry the mold containing rush pith at 70 to 90°C for 0.5 to 1.5 hours.

5. The method for preparing the thermally conductive composite material with a three-dimensional network structure according to claim 1, characterized in that, The mass ratio of rush pith, silane coupling agent, and polyethyleneimine is (0.5–1.5):(0.5–1.5):(0.5–1.5); in the modified solution, the mass concentration of the silane coupling agent is 0.5–1.0%; and the concentration of the polyethyleneimine is 0.5–1.0%.

6. The method for preparing the thermally conductive composite material with a three-dimensional network structure according to claim 1, characterized in that, In step S2, the drying process specifically involves drying the modified rush pith impregnated with boron nitride nanosheet solution and polyethyleneimine solution at 50–70°C for 100–140 min.

7. A thermally conductive composite material with a three-dimensional network structure, characterized in that, The thermally conductive composite material with a three-dimensional network structure as described in any one of claims 1 to 6 was prepared.

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