Novel graphene modified loofah sponge electric conduction and heat conduction agent

Abstract

The invention discloses a novel graphene modified loofah sponge electric conduction and heat conduction agent. The structure of the agent comprises a pretreated natural loofah sponge fiber network as a three-dimensional porous skeleton; the loofah sponge fiber is used as a raw material, a graphene sheet layer is used as a functional phase, and the graphene sheet layer is uniformly loaded on the surface, internal pores and pore walls of the loofah sponge fiber and is combined with the loofah sponge fiber through physical adsorption and / or chemical bonding to jointly form a continuous and interpenetrating three-dimensional electric conduction and heat conduction network. According to the novel graphene modified loofah sponge electric conduction and heat conduction agent disclosed by the invention, a three-dimensional tubular network which is naturally formed by loofah sponge and is communicated with one another is used as a macroscopic framework, and graphene sheet layers are uniformly and firmly loaded on the surfaces of fibers and in pores through an in-situ modification process; a continuous interpenetrating conduction network penetrating through the whole material from macroscopic to microscopic is constructed, and efficient transmission of electrons and phonons (heat carriers) in a three-dimensional space is achieved.

Description

Technical Field

[0001] This invention relates to the field of new energy electronic materials technology, and in particular to a novel graphene-modified loofah sponge conductive and thermally conductive agent. Background Technology

[0002] With the rapid development of electronic information technology, new energy vehicles and high-end equipment manufacturing, the demand for efficient thermal management and electromagnetic compatibility is becoming increasingly urgent. The continuous increase in the power density of electronic components has made heat dissipation a key bottleneck restricting the performance, reliability and miniaturization of equipment. At the same time, the increasingly complex electromagnetic environment has also put forward higher requirements for the shielding effectiveness of materials. Therefore, the development of functional materials with both excellent thermal conductivity and electrical conductivity has become an important research direction in the field of materials science.

[0003] Currently, mainstream thermal and electrical conductive material systems have the following limitations: Metal-based materials (such as copper and aluminum) have excellent electrical and thermal conductivity, but they are dense, easily corroded, have poor processing flexibility, and exhibit a significant skin effect at high frequencies, which is not conducive to the lightweight and integrated requirements of modern equipment. Carbon-based materials (such as carbon black, carbon nanotubes, and graphene) have attracted widespread attention as emerging fillers due to their lightweight and high electrical and thermal conductivity potential. However, when these nanofillers are directly incorporated into polymer matrices, they often face problems such as difficulty in dispersion, easy agglomeration, high percolation threshold, and high interfacial thermal resistance. To construct effective pathways, extremely high filler content is usually required, which will seriously damage the mechanical properties (such as increased brittleness) and processing fluidity of the matrix material and significantly increase costs. In particular, for graphene, its two-dimensional sheet structure is very easy to align in-plane in composite materials, resulting in strong anisotropy in the thermal and electrical conductivity of the material, that is, excellent in-plane performance but poor performance in the thickness direction, making it difficult to meet the requirements of three-dimensional balanced heat dissipation.

[0004] On the other hand, from the perspective of sustainable development and environmental protection, the production process of traditional thermal and electrical conductive materials is energy-intensive, and their products are difficult to degrade after disposal, which puts pressure on the environment. Therefore, the industry urgently needs to develop a new type of thermal and electrical conductive material that can take into account high performance, lightweight, isotropy, good process adaptability and environmental friendliness.

[0005] In recent years, research on using natural biomass materials as functional substrates or templates has gradually emerged. Loofah sponge, as a natural porous cellulose material, has a unique three-dimensional interconnected network structure, low density, good flexibility, and renewability. Researchers have attempted to carbonize it to use as a conductive framework or to combine it with functional nanomaterials. However, most existing technologies are still at the stage of simple physical filling or direct carbonization of loofah sponge, failing to fully utilize its fine multi-level pore structure. Physical mixing methods are difficult to achieve uniform and firm loading of nanomaterials within the loofah sponge network, easily leading to functional phase aggregation and interface failure. While direct carbonization can achieve conductivity, it destroys its natural flexibility, and the thermal conductivity of carbonization products is limited. How to deeply couple the excellent intrinsic properties of nanomaterials such as graphene with the macroscopic three-dimensional structural advantages of loofah sponge through ingenious modification processes, and construct a stable, efficient, and interpenetrating synergistic network at the microscopic level, thereby achieving a qualitative leap in the comprehensive performance of materials at the macroscopic level, remains a major challenge for current technology.

[0006] Therefore, it is necessary to provide a novel graphene-modified loofah sponge conductive and thermally conductive agent to solve the above-mentioned technical problems. Summary of the Invention

[0007] To address the aforementioned technical problems, this invention provides a novel graphene-modified loofah sponge conductive and thermally conductive agent.

[0008] This invention provides a novel graphene-modified loofah sponge conductive and thermally conductive agent, the structure of which includes: The system uses a pretreated natural loofah fiber network as a three-dimensional porous framework; graphene sheets are used as the functional phase, and the graphene sheets are uniformly loaded on the surface, internal pores and pore walls of the loofah fiber, and are combined with the loofah fiber through physical adsorption and / or chemical bonding to form a continuous, interpenetrating three-dimensional conductive and thermally conductive network; the conductive and thermally conductive agent is in powder form or in block or sheet form with a self-supporting structure. The volume resistivity of the conductive and thermally conductive agent is 0.5 × 10⁻⁶. -4 Ω·cm to 1.5×10 -4 It has a thermal conductivity of 50 W / (m·K) to 200 W / (m·K) and a density of 0.3 g / cm³. 3 Up to 1.2 g / cm 3 Furthermore, after undergoing 1000 bending cycles, its electrical and thermal conductivity retention rate is no less than 90%.

[0009] Preferably, the loofah fiber is a natural loofah that has been degreased and dried, and its vascular bundle pore diameter is 50 μm to 300 μm; the size of the graphene sheet is 1 μm to 10 μm, and its weight percentage in the conductive and thermally conductive agent is 0.5% to 30%; the graphene is at least one selected from graphene oxide, reduced graphene oxide, few-layer graphene, and single-layer graphene.

[0010] Preferably, the anisotropy coefficient of the conductive and thermally conductive agent is not greater than 1.2, and the anisotropy coefficient is the ratio of the maximum to the minimum value of the thermal conductivity or electrical conductivity of the material measured in three mutually perpendicular directions.

[0011] Preferably, the tensile strength of the conductive and thermally conductive agent is not less than 20 MPa, and the rate of change of its volume resistivity and thermal conductivity does not exceed ±15% in the temperature range of -60℃ to 220℃.

[0012] A method for preparing a novel conductive and thermally conductive agent based on graphene-modified loofah sponge includes the following steps: S1. Loofah sponge pretreatment: Clean, degrease and dry the natural loofah sponge to obtain a clean loofah sponge skeleton; S2. Functionalization pretreatment: Plasma treatment or chemical activation treatment is performed on the loofah skeleton obtained in step S1 to introduce active functional groups on its fiber surface and pore inner wall. S3. Preparation of graphene dispersion: Graphene raw material is dispersed in a solvent to prepare a uniformly dispersed graphene dispersion. S4. Impregnation and composite: The pretreated loofah skeleton in step S2 is impregnated in the graphene dispersion prepared in step S3, and ultrasonic treatment is applied to allow the graphene dispersion to fully penetrate and adsorb onto the pores and fiber surface of the loofah skeleton. S5. Drying and Reduction: The material impregnated and composited in step S4 is dried to remove the solvent; if the graphene is graphene oxide, it is subjected to thermal reduction or chemical reduction treatment after drying to obtain graphene-modified loofah composite material. S6. Post-processing: The composite material obtained in step S5 is crushed, granulated or compressed according to application requirements to obtain the conductive and thermally conductive agent.

[0013] Preferably, in step S4, the impregnation and composite process is carried out under the assistance of a gradient magnetic field, which is used to guide the graphene sheets to achieve random orientation distribution within the three-dimensional pores of the loofah sponge, so as to reduce the anisotropy of the material.

[0014] Preferably, the plasma treatment in step S2 is a rotary plasma etching treatment, and the active functional groups include hydroxyl and carboxyl groups; the solvent in step S3 is at least one of water, ethanol, and N-methylpyrrolidone; the thermal reduction treatment in step S5 is carried out in an inert atmosphere or vacuum at a temperature of 200°C to 800°C for 1 to 4 hours.

[0015] A composite material prepared by a method for preparing a novel conductive and thermally conductive agent modified with graphene-modified loofah sponge comprises a polymer matrix and a novel conductive and thermally conductive agent modified with graphene-modified loofah sponge dispersed in the polymer matrix, wherein the weight percentage of the novel conductive and thermally conductive agent modified with graphene-modified loofah sponge in the composite material is 1% to 40%.

[0016] A thermally conductive interface material or electromagnetic shielding material made of composite materials.

[0017] Application of a thermally conductive interface material or electromagnetic shielding material in the preparation of heat dissipation components for electronic devices, flexible electronic devices, thermal management components for new energy vehicle batteries, special protective products, or medical thermotherapy devices.

[0018] Compared with related technologies, the graphene-modified loofah sponge novel conductive and thermally conductive agent provided by the present invention has the following beneficial effects: This invention achieves highly efficient three-dimensional isotropic conduction: It utilizes the naturally formed, interconnected three-dimensional tubular network of loofah sponge as a macroscopic framework. Through in-situ modification, graphene sheets are uniformly and firmly loaded onto the fiber surface and inside the pores, constructing a continuous interpenetrating conduction network that runs from macro to micro and throughout the entire material. This enables the efficient transmission of electrons and phonons (heat carriers) in three-dimensional space. This structure effectively overcomes the strong anisotropy problem caused by the directional arrangement of sheets in traditional graphene composite materials, allowing the material to exhibit excellent and balanced electrical and thermal conductivity in any direction, meeting the requirements for uniform heat dissipation and all-round electromagnetic shielding under complex working conditions.

[0019] Achieving a balance between high performance, lightweight, and flexibility: Through the low density and porous nature of loofah sponge and the low filler requirements of graphene, the material obtained by this invention achieves significant lightweighting while maintaining extremely high electrical and thermal conductivity. At the same time, the loofah sponge fiber skeleton endows the material with good intrinsic flexibility and resilience, enabling the conductive and thermal conductive agent or composite materials prepared from it to withstand repeated bending, compression, and other deformations while maintaining structural and performance stability. It is particularly suitable for emerging fields such as flexible electronics and wearable devices, breaking through the dilemma of traditional high-performance fillers being unable to simultaneously achieve toughening and reinforcement.

[0020] It possesses excellent process adaptability and overall stability: This conductive and thermally conductive agent can be flexibly processed into various forms such as powder, granules or self-supporting films. It can be used as a high-efficiency filler to be compounded with various polymers, rubbers and other matrices to improve their functionality, or it can be used directly as an independent functional material. Its unique microstructure also brings lower contact thermal resistance and better interfacial wettability. In addition, the material exhibits performance stability over a wide temperature range and good resistance to environmental aging, ensuring its long-term reliable application in harsh environments.

[0021] In line with the concept of green and sustainable development: This invention uses loofah sponge, a renewable agricultural waste, as the main material. Through a relatively mild and low-energy-consumption modification process, it achieves high-value utilization, reducing the dependence on non-renewable resources and high energy consumption problems of traditional material production. The final product retains the environmental protection characteristics of biomass to a certain extent, providing the electronics and electrical field with a new material path that combines high performance and sustainability. Attached Figure Description

[0022] Figure 1 A schematic diagram illustrating the preparation process of the graphene-based thermally and electrically conductive composite material provided by this invention; Figure 2 A schematic diagram of the chemical reaction process of graphene in the micron-sized channels of loofah sponge provided by the present invention; Figure 3 SEM image of the ordered conductive / thermal conductive network structure formed inside the composite material provided by the present invention; Figure 4 Schematic diagrams of the construction of two-dimensional and three-dimensional conductive networks provided by the present invention; Figure 5 A schematic diagram illustrating the electrical and thermal conductivity properties of the composite material provided by this invention. Detailed Implementation

[0023] The present invention will be further described below with reference to the accompanying drawings and embodiments.

[0024] Example 1 Preparation of a low-density, high-flexibility conductive and thermally conductive agent (powder form): like Figures 1 to 2 As shown, this embodiment prepares a high-performance, low-filling-content conductive and thermally conductive additive suitable for flexible electronic devices and wearable devices, in the form of a powder.

[0025] S1: Loofah sponge pretreatment: Take naturally dried natural loofah sponge and cut it into small pieces of about 3cm×3cm. First, rinse it repeatedly with deionized water to remove surface dust and soluble impurities. Then, immerse the loofah sponge pieces in a 5% sodium hydroxide aqueous solution and heat them in a constant temperature water bath at 80℃ for 2 hours to remove pectin, lignin and other components from the loofah sponge, achieving degreasing and partial bleaching. After that, wash it with deionized water until neutral. Then, place the treated loofah sponge in a forced-air drying oven and dry it at 80℃ for 12 hours to obtain a clean, fluffy white loofah sponge skeleton. The porosity of the skeleton was measured to be about 75%, and the vascular bundle pore diameter was mainly distributed in the range of 80-200μm.

[0026] S2: Functionalization pretreatment. The dried loofah skeleton from step S1 is placed in the reaction chamber of a plasma treatment device and subjected to rotary plasma etching. The working gas is set to oxygen, the gas flow rate to be 50 sccm, the chamber pressure to be 50 Pa, the radio frequency power to be 100 W, and the treatment time to be 10 minutes. During the plasma treatment, the sample stage rotates at a constant speed to ensure that all surfaces and internal pore walls of the three-dimensional loofah skeleton are uniformly exposed to the plasma. After the treatment, the density of oxygen-containing active functional groups such as hydroxyl (-OH) and carboxyl (-COOH) groups on the surface of the loofah fibers and the inner walls of the pores increases significantly, which facilitates their bonding with graphene. S3: Preparation of graphene dispersion: Weigh 0.8 parts (by weight) of graphene oxide powder (sheet size approximately 2-5 μm) and slowly add it to 200 parts of deionized water. First, use a magnetic stirrer to stir at room temperature for 30 minutes for pre-dispersion. Then, transfer it to an ultrasonic cell disruptor and sonicate it for 1 hour under 500W power and ice-water bath cooling conditions to obtain a uniform, stable, and non-precipitated aqueous dispersion of graphene oxide with a concentration of 0.4 wt%.

[0027] S4. Impregnation and composite: The loofah skeleton treated with plasma in step S2 is completely immersed in the graphene oxide dispersion prepared in step S3. The entire system is placed in an ultrasonic cleaner and ultrasonic-assisted impregnation is performed at 40kHz and 300W power for 2 hours to ensure full impregnation. The cavitation effect generated by ultrasound can effectively promote the graphene oxide dispersion to overcome surface tension and quickly and deeply penetrate into the complex vascular bundles and micron-sized pores of the loofah, and uniformly adsorb and adhere to the fiber surface and pore walls.

[0028] S5: Drying and Reduction. After impregnation, carefully remove the loofah composite material loaded with graphene oxide with tweezers, drain off excess droplets, and then transfer it to a vacuum drying oven to dry at 60°C for 24 hours to completely remove moisture.

[0029] The dried composite material was placed in a tube furnace for thermal reduction. The specific conditions were as follows: under the protection of argon (inert atmosphere), the temperature was raised to 400℃ at a rate of 5℃ / min and held at this temperature for 2 hours, followed by natural cooling to room temperature. During this process, graphene oxide was reduced to reduced graphene oxide (rGO), and its conductivity was greatly restored. At the same time, hydrogen bonds or chemical bonds may be formed between the loofah fibers and graphene sheets through residual oxygen-containing functional groups, making the bond stronger.

[0030] S6: Post-processing: The black, lightweight, self-supporting graphene-modified loofah composite material block obtained after thermal reduction is placed in a high-speed pulverizer and intermittently pulverized. The pulverization conditions are: 10 seconds of operation each time, 30 seconds of cooling interval, repeated 5 times. After that, it is passed through a 100-mesh sieve to obtain black graphene-modified loofah novel conductive and thermally conductive agent powder (denoted as sample SLF-1).

[0031] Performance testing and characterization: Microstructure: The cross-section of powder particles in sample SLF-1 was observed using scanning electron microscopy (SEM). like Figure 3 As shown, it can be clearly observed that the skeletal structure of the loofah fiber is completely preserved, the graphene sheets are uniformly coated on the surface of the single fiber, and a continuous conductive and thermally conductive film and network are formed at the fiber intersections and inside the pores, constructing a three-level interpenetrating structure of "main channel (loofah vascular bundle) - branch channel (graphene film) - micro channel (graphene sheet stacking and bridging)".

[0032] Conductivity: The volume resistivity of the powder after compression was measured using a four-probe resistance meter (RTS-9 type). An appropriate amount of SLF-1 powder was compressed into a disc with a diameter of 10 mm and a thickness of approximately 2 mm under a pressure of 10 MPa. The measured volume resistivity was 0.9 × 10⁻⁶. -4 Ω·cm.

[0033] Thermal conductivity: The thermal diffusivity of the powder tablet was tested using a laser flash thermal conductivity analyzer (LFA467HyperFlash), and the thermal conductivity was calculated by combining the specific heat capacity and density. The measured thermal conductivity was 68 W / (m·K).

[0034] Density: The tap density of the powder sample was measured using a true density analyzer (AccuPycII1340), and the result was 0.45 g / cm³. 3 .

[0035] Flexibility and durability: SLF-1 powder was mixed with silicone rubber (Dow Corning 184) at a ratio of 5 wt% to form a flexible sheet with a thickness of 1 mm. According to relevant flexible electronics testing standards, the sheet was subjected to repeated bending tests (bending radius of 5 mm). After 1000 cycles of testing, the volume resistivity of the sheet was measured and the surface heat distribution uniformity was evaluated by a thermal imager. It was calculated that the retention rate of its electrical and thermal conductivity was 93%.

[0036] Anisotropy: SLF-1 powder was pressed into a mold under the same pressure from different directions. The thermal conductivity of the molded samples in different directions (X, Y, Z) was tested. The anisotropy coefficient (maximum / minimum) was calculated to be 1.15, indicating that the material has near isotropic characteristics.

[0037] Example 2 Preparation of a high thermal conductivity, low anisotropic electrical conductivity thermal conductive agent (sheet-like self-supporting film); This embodiment aims to prepare a self-supporting sheet material that can be directly used as a chip heat dissipation interface material or an electromagnetic shielding pad.

[0038] S1: Loofah sponge pretreatment, same as step S1 in Example 1, but the loofah sponge is cut and flattened into a sheet with a thickness of about 5mm, which is beneficial for the subsequent formation of sheet products.

[0039] S2: Functional pretreatment, using chemical activation treatment as an alternative, involves immersing the pretreated sheet loofah sponge in a 1 mol / L nitric acid solution at 60°C for 6 hours, then washing it thoroughly with deionized water until neutral, and finally drying it at 80°C. This process can introduce more oxygen-containing functional groups onto the surface of the loofah sponge fibers and further purify and expand the pores.

[0040] S3: Preparation of graphene dispersion: Weigh 2.0 parts of few-layer graphene (sheet size about 5-10μm, number of layers 3-5) and 0.1 parts of sodium dodecylbenzenesulfonate (SDBS) dispersant, add them to 200 parts of N-methylpyrrolidone (NMP), and disperse using a high-speed shear emulsifier (10000rpm, 30 minutes) to obtain a stable graphene / NMP dispersion.

[0041] S4: Impregnation and composite: The sheet-like loofah skeleton processed in step S2 is fixed on a specially made non-magnetic impregnation frame, and then immersed in the graphene dispersion in step S3. The entire impregnation device is placed in the center of an electromagnetic coil that can generate a gradient magnetic field. While starting ultrasonic assistance (under the same conditions as in Example 1), a gradient magnetic field with an intensity of 0.5T and a direction that changes periodically in three-dimensional space is applied for 2 hours. The gradient magnetic field can generate an orientation force on the antimagnetic graphene sheets, guiding them to achieve a more random spatial orientation in the three-dimensional pores of the loofah, avoiding directional arrangement caused by gravity or hydrodynamics, thereby effectively reducing the anisotropy of the final material.

[0042] S5: Drying and solvent replacement. After impregnation, take out the sample and first use filter paper to absorb the excess dispersion on the surface. Since NMP has a high boiling point, direct high-temperature drying may cause graphene agglomeration. Therefore, first immerse the sample in anhydrous ethanol twice (1 hour each time) to replace the NMP, and then dry it in a vacuum drying oven at 60°C for 12 hours.

[0043] S6: Post-processing. The dried composite material is placed in the mold of a flat vulcanizing machine. At 120°C, a pressure of 10 MPa is applied and held for 10 minutes. This process not only shapes the material into a dense sheet with uniform thickness (about 2 mm), but also further increases the contact between graphene sheets through compression, improving the connectivity of the conductive and thermally conductive network. After cooling and demolding, a self-supporting black sheet-like conductive and thermally conductive agent (referred to as sample SLF-2) is obtained.

[0044] Performance testing and characterization: Structure and properties: SEM showed that graphene was evenly distributed in the compressed sheet, forming a denser three-dimensional network.

[0045] Thermal conductivity: The thermal conductivity of SLF-2 sheet in the thickness direction (Z direction) and in the plane direction (X direction) was tested using a steady-state heat flow thermal conductivity meter. The measured thermal conductivity of Z direction was 105 W / (m·K), the thermal conductivity of X direction was 98 W / (m·K), and the anisotropy coefficient was 1.07, which showed excellent isotropic thermal conductivity and solved the problem of poor thermal conductivity in the vertical direction of traditional graphene films.

[0046] Electrical conductivity: Volume resistivity is 0.7 × 10⁻⁶ -4 Ω·cm.

[0047] Contact thermal resistance: The SLF-2 sheet was sandwiched between two copper blocks with known surface roughness, a certain pressure was applied, and the contact thermal resistance was measured using a contact thermal resistance tester. The results showed that its contact thermal resistance was significantly lower than that of commercial thermal grease pads of the same thickness. This is due to the elasticity of the loofah porous structure, which allows it to better conform to rough surfaces.

[0048] Electromagnetic shielding effectiveness (ESE): In the 1-3 GHz frequency range, the electromagnetic shielding effectiveness of SLF-2 sheet was tested using a vector network analyzer. Its average shielding effectiveness exceeded 65 dB, indicating that it has good electromagnetic interference shielding capability.

[0049] Example 3 Preparation of a weather-resistant conductive and thermally conductive agent (particulate form) for high-temperature operating conditions; like Figure 4 As shown in the figure, this embodiment prepares a conductive and thermally conductive additive suitable for new energy vehicle battery modules, outdoor electronic devices, etc., which require resistance to high and low temperature cycles and corrosion resistance. The additive is in the form of regular particles.

[0050] S1: Loofah sponge pretreatment is basically the same as step S1 in Example 1, but an additional step of "controlled enzymatic hydrolysis" is added to adjust the porosity. After alkali treatment, the loofah sponge is immersed in phosphate buffer (pH 4.8) containing cellulase (activity unit 500 U / g) and enzymatically hydrolyzed at 50°C for 3 hours. By controlling the enzymatic hydrolysis time, the amorphous cellulose can be partially hydrolyzed, so that the porosity of the loofah sponge skeleton increases from 75% to about 85% while maintaining its strength, and more nanoscale microfibers are generated, increasing the specific surface area.

[0051] S2: Functionalization pretreatment, using rotary plasma etching, under the same conditions as step S2 in Example 1. S3: Preparation of graphene dispersion: Weigh 2.5 parts of reduced graphene oxide (rGO, pre-reduced, with good conductivity) and 0.5 parts of polydopamine (as a green binder and dispersion promoter), disperse them in a mixed solvent of 200 parts of ethanol and water (volume ratio 1:1), and sonicate for 2 hours to form a uniform dispersion.

[0052] S4: Impregnation and composite: The enzymatically hydrolyzed and plasma-treated loofah sponge skeleton is impregnated in the above dispersion using a combined ultrasonic and microwave impregnation method. First, it is impregnated under ultrasonic conditions (40kHz) for 1 hour, and then transferred to a microwave reactor. The reaction is continued for 30 minutes at 300W power and 80℃. The rapid bulk heating characteristics of microwaves can promote the polymerization and adhesion of polydopamine on the surface of loofah sponge and graphene, achieving a stronger composite. S5: Drying and post-treatment. After impregnation, the material is taken out and vacuum dried at 80°C. The dried block material is then coarsely crushed and melt-extruded and pelletized at 150°C using a twin-screw extruder to obtain cylindrical regular particles with a particle size of about 2-3 mm (referred to as sample SLF-3).

[0053] Performance testing and characterization: Basic properties: The thermal conductivity of granular SLF-3 is 82 W / (m·K), and the volume resistivity is 1.2 × 10⁻⁶. -4Ω·cm, density is 0.55 g / cm³ 3 .

[0054] High and low temperature cycling test: SLF-3 particles were filled into a test container and placed in a high and low temperature test chamber for temperature cycling from -60℃ (hold for 1 hour) to 220℃ (hold for 1 hour) for a total of 100 cycles. Before and after the test, the change rate of thermal conductivity of the particles was -4.5% and the change rate of volume resistivity was +6.1%, both within ±15%, showing excellent wide temperature range stability.

[0055] Corrosion resistance: After immersing the particles in sulfuric acid solution (pH=3) and sodium hydroxide solution (pH=10) for 7 days, they were removed, washed, and dried. The performance degradation rate was less than 10%.

[0056] Long life test: SLF-3 particles were combined with epoxy resin to make test strips, and accelerated aging tests were carried out in an environment of 85℃ / 85%RH (high temperature and high humidity). After 1000 hours, the electrical conductivity of the composite material decreased by 7% and the thermal conductivity decreased by 9%, which is far better than the unmodified loofah filler material.

[0057] Example 4 Application of graphene-modified loofah fiber conductive and thermally conductive agent in polymer composites; In this embodiment, the powdered conductive and thermally conductive agent (SLF-1) prepared in Example 1 is applied to a thermoplastic polymer to prepare a high thermal conductivity composite material.

[0058] For the preparation of the composite material, polypropylene (PP) granules were dried at 80°C for 4 hours. The following were weighed by weight: 70 parts of polypropylene, 30 parts of SLF-1 powder prepared in Example 1, and 0.5 parts of a small amount of coupling agent (silane coupling agent KH-550).

[0059] First, dilute the coupling agent with an appropriate amount of ethanol, spray it onto the surface of SLF-1 powder and stir evenly. Let it air dry at room temperature to allow the coupling agent to treat the surface of the filler.

[0060] Then, the treated SLF-1 powder and PP granules are premixed in a high-speed mixer for 5 minutes.

[0061] Finally, a twin-screw extruder was used for melt blending, extrusion granulation, and the temperature of each section of the extruder was set as follows: Zone 1 170℃, Zone 2 180℃, Zone 3 185℃, Zone 4 190℃, Die head 195℃, and the screw speed was 100 rpm.

[0062] The obtained composite material granules are injection molded into standard tensile test specimens, square plates, etc. on an injection molding machine.

[0063] Composite material performance testing like Figure 5 As shown, the thermal conductivity of the injection-molded square plate is 2.8 W / (m·K), which is more than 12 times higher than that of pure PP (approximately 0.22 W / (m·K)).

[0064] Electrical conductivity: Volume resistivity is 10 3 It has an Ω·cm range and possesses antistatic properties.

[0065] Mechanical properties: Tensile strength is 28MPa, which is improved compared to pure PP; impact toughness remains good.

[0066] Microscopic analysis: SEM observation of the cross-section of the composite material showed that SLF-1 powder was uniformly dispersed in the PP matrix without serious agglomeration. Its own three-dimensional network structure was preserved to a certain extent, forming an effective heat conduction pathway.

[0067] Example 5 Preparation and application of thermally conductive interface materials (TIM) based on conductive and thermally conductive agents; In this embodiment, the self-supporting sheet (SLF-2) prepared in Example 2 is used directly as the thermal interface material.

[0068] TIM sheet processing involves cutting the SLF-2 sheet into correspondingly sized gaskets using a laser cutting machine, based on common chip sizes (20mm x 20mm). The gasket thickness can be selected between 0.5-2mm as needed (by adjusting the compression molding pressure and time in Example 2).

[0069] To enhance insulation, an extremely thin polyimide (PI) film (thickness ≤10μm) can be hot-pressed onto one or both sides of the SLF-2 sheet.

[0070] Heat dissipation performance simulation test: A test platform for simulating chip heat dissipation was built: a surface mount device (SMD) heating element with adjustable heat flux density simulated a chip, and a copper heat sink was used. The following tests were conducted between the heating element and the heat sink: without adding any TIM; with adding commercial thermal grease; with adding the SLF-2 pad of this invention (1mm thick). Under the same heating power (5W), the steady-state temperature of the "chip" surface was monitored using thermocouples.

[0071] Test results: When using the SLF-2 pad, the steady-state temperature of the "chip" surface is about 8°C lower than when using commercial silicone grease and about 25°C lower than when there is no TIM, which proves the high efficiency of the material of this invention as a TIM. Its porous elastic structure reduces the contact thermal resistance, while the three-dimensional isotropic graphene network enables rapid lateral diffusion and longitudinal transfer of heat.

[0072] Example 6 Applications in special protective equipment; This embodiment illustrates the application of conductive and thermally conductive agents in functional rubber.

[0073] For the preparation of composite latex, take 100 parts of natural latex (dry weight), grind the weather-resistant particles (SLF-3) prepared in Example 3 through a 400-mesh sieve to obtain a finer powder, and weigh 15 parts of the powder.

[0074] SLF-3 powder is ground with dispersants, stabilizers and other additives in an aqueous phase to form a slurry, which is then slowly added to natural latex while stirring to ensure uniform dispersion.

[0075] Subsequently, vulcanizing agents, accelerators, antioxidants, etc., are added according to the conventional latex product process.

[0076] The gloves are dipped and molded using a hand mold dipping process, in which the hand mold is immersed in the above-mentioned composite latex liquid, then lifted, dried, and vulcanized to produce functional latex gloves containing graphene-modified loofah fiber conductive and thermally conductive agent.

[0077] Performance evaluation: Thermal conductivity: When wearing gloves to come into contact with hot objects, the hands can perceive the temperature more evenly, avoiding localized overheating and improving comfort and safety.

[0078] Cutting and tearing performance: According to the ANSI / ISEA105 standard test, the cut resistance and tear strength of this glove are significantly improved compared with ordinary latex gloves, thanks to the high-strength loofah fiber skeleton and graphene reinforcement in SLF-3 particles.

[0079] Antistatic properties: The surface resistance of the gloves drops to 10. 6 -10 7 Ω has excellent anti-static properties and is suitable for applications such as precision electronic assembly.

[0080] Comparative Example 1 Take the same pretreated loofah skeleton as in Example 1 but without plasma treatment, dry it at 80°C, and then directly use a ball mill to dry-mix it with an equal amount of graphene oxide powder (same as in Example 1) for 2 hours. After mixing, perform thermal reduction under the same conditions (400°C in argon for 2 hours), and then pulverize and sieve.

[0081] Test results: The thermal conductivity of the obtained powder is only 15 W / (m·K), and the volume resistivity is as high as 5 × 10⁻⁶. -2 Ω·cm, density is 0.5 g / cm³ 3 SEM images showed that the graphene and loofah fibers were loosely bonded, with a large amount of graphene agglomerating and failing to form a continuous network. This indicates that simple physical mixing cannot achieve a leap in performance.

[0082] Comparative Example 2 Take the same mass of graphene oxide dispersion as in Example 3, and prepare a pure graphene film with a similar thickness (2 mm) to the sheet in Example 2 by vacuum filtration. Then, perform thermal reduction under the same conditions.

[0083] Test results: The thermal conductivity of the film in the in-plane direction (X direction) is as high as 120 W / (m·K), but its thermal conductivity in the thickness direction (Z direction) is very low (<5 W / (m·K)), the anisotropy coefficient is extremely large (>24), and the film is brittle. Cracks appear after bending several times, and the performance drops sharply. This highlights the key role of introducing the three-dimensional skeleton of loofah in the present invention in obtaining isotropy, flexibility and structural stability.

[0084] Comparative Example 3 Use other biomass carbonizations; The loofah sponge was replaced with an equal weight of bamboo powder (which was also treated with alkali and dried), and then plasma treatment, impregnation with graphene oxide, reduction and pulverization were performed in the same manner as in Example 1.

[0085] Test results: The thermal conductivity of the obtained bamboo powder-based composite material is 25 W / (m·K), and the volume resistivity is 8×10⁻⁶. -3 The performance of bamboo powder is far inferior to that of loofah-based products, which is because bamboo powder lacks the natural, interconnected macroscopic three-dimensional tubular network structure of loofah. It cannot build efficient long-range continuous pathways for graphene and can only form locally dispersed conductive and thermally conductive islands.

[0086] As can be seen from Examples 1-6 and Comparative Examples 1-3 above, the graphene-modified loofah sponge novel conductive and thermally conductive agent and its preparation method provided by the present invention, through cross-scale composite of "loofah sponge three-dimensional framework" and "graphene nanosheets", and with the help of key processes such as plasma / chemical activation, ultrasonic / microwave / magnetic field-assisted impregnation, successfully constructed a continuous, interpenetrating, and stable three-dimensional conductive and thermally conductive network. This material has high conductivity, high thermal conductivity, low density, low anisotropy, excellent flexibility and wide temperature range stability. As an additive or self-supporting material, it can significantly improve the thermal and electrical conductivity of polymer-based composite materials, and can be directly used to prepare efficient thermally conductive interface materials, electromagnetic shielding materials and special functional products, showing great application potential in multiple fields such as consumer electronics, new energy vehicles, flexible wearables, and special protection.

[0087] The above description is merely an embodiment of the present invention and does not limit the patent scope of the present invention. Any equivalent structural or procedural transformations made based on the content of the present invention's specification and drawings, or direct or indirect applications in other related technical fields, are similarly included within the patent protection scope of the present invention.

Claims

1. A novel conductive and thermally conductive agent based on graphene-modified loofah sponge, characterized in that, Its structure includes: The system uses a pretreated natural loofah fiber network as a three-dimensional porous framework; graphene sheets are used as the functional phase, and the graphene sheets are uniformly loaded on the surface, internal pores and pore walls of the loofah fiber, and are combined with the loofah fiber through physical adsorption and / or chemical bonding to form a continuous, interpenetrating three-dimensional conductive and thermally conductive network; the conductive and thermally conductive agent is in powder form or in block or sheet form with a self-supporting structure. The volume resistivity of the conductive and thermally conductive agent is 0.5 × 10⁻⁶. -4 Ω·cm to 1.5×10 -4 It has a thermal conductivity of 50 W / (m·K) to 200 W / (m·K) and a density of 0.3 g / cm³. 3 Up to 1.2 g / cm 3 Furthermore, after undergoing 1000 bending cycles, its electrical and thermal conductivity retention rate is no less than 90%.

2. The novel conductive and thermally conductive agent modified with graphene from loofah sponge according to claim 1, characterized in that: The loofah fiber is a natural loofah that has been degreased and dried, and its vascular bundle pore diameter is 50μm to 300μm; the size of the graphene sheet is 1μm to 10μm, and its weight percentage in the conductive and thermally conductive agent is 0.5% to 30%; the graphene is at least one selected from graphene oxide, reduced graphene oxide, few-layer graphene, and monolayer graphene.

3. The novel conductive and thermally conductive agent of graphene-modified loofah sponge according to claim 2, characterized in that: The anisotropy coefficient of the conductive and thermally conductive agent is no greater than 1.

2. The anisotropy coefficient is the ratio of the maximum to the minimum value of the thermal conductivity or electrical conductivity of the material measured in three mutually perpendicular directions.

4. The novel conductive and thermally conductive agent modified with graphene from loofah sponge according to claim 3, characterized in that: The tensile strength of the conductive and thermally conductive agent is not less than 20 MPa, and the rate of change of its volume resistivity and thermal conductivity does not exceed ±15% in the temperature range of -60℃ to 220℃.

5. A method for preparing a novel conductive and thermally conductive agent based on graphene-modified loofah sponge according to any one of claims 1 to 4, characterized in that, Includes the following steps: S1. Loofah sponge pretreatment: Clean, degrease and dry the natural loofah sponge to obtain a clean loofah sponge skeleton; S2. Functionalization pretreatment: Plasma treatment or chemical activation treatment is performed on the loofah skeleton obtained in step S1 to introduce active functional groups on its fiber surface and pore inner wall. S3. Preparation of graphene dispersion: Graphene raw material is dispersed in a solvent to prepare a uniformly dispersed graphene dispersion. S4. Impregnation and composite: The pretreated loofah skeleton in step S2 is impregnated in the graphene dispersion prepared in step S3, and ultrasonic treatment is applied to allow the graphene dispersion to fully penetrate and adsorb onto the pores and fiber surface of the loofah skeleton. S5. Drying and Reduction: The material impregnated and composited in step S4 is dried to remove the solvent; if the graphene is graphene oxide, it is subjected to thermal reduction or chemical reduction treatment after drying to obtain graphene-modified loofah composite material. S6. Post-processing: The composite material obtained in step S5 is crushed, granulated or compressed according to application requirements to obtain the conductive and thermally conductive agent.

6. The preparation method of a novel graphene-modified loofah sponge conductive and thermally conductive agent according to claim 5, characterized in that: In step S4, the impregnation and composite process is carried out with the assistance of a gradient magnetic field. The gradient magnetic field is used to guide the graphene sheets to achieve random orientation distribution within the three-dimensional pores of the loofah sponge, so as to reduce the anisotropy of the material.

7. The preparation method of a novel graphene-modified loofah sponge conductive and thermally conductive agent according to claim 6, characterized in that: The plasma treatment in step S2 is a rotary plasma etching process, and the active functional groups include hydroxyl and carboxyl groups; the solvent in step S3 is at least one of water, ethanol, and N-methylpyrrolidone; the thermal reduction treatment in step S5 is carried out in an inert atmosphere or vacuum at a temperature of 200°C to 800°C for 1 to 4 hours.

8. A composite material prepared based on the method for preparing a novel conductive and thermally conductive agent modified with graphene-modified loofah sponge according to claim 7, characterized in that, It comprises a polymer matrix and a novel graphene-modified loofah fiber conductive and thermally conductive agent dispersed in the polymer matrix, wherein the graphene-modified loofah fiber conductive and thermally conductive agent comprises 1% to 40% by weight in the composite material.

9. A thermally conductive interface material or electromagnetic shielding material made from the composite material of claim 8.

10. The application of the thermally conductive interface material or electromagnetic shielding material of claim 9 in the preparation of heat dissipation components for electronic devices, flexible electronic devices, thermal management components for new energy vehicle batteries, special protective products, or medical thermotherapy devices.

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