Thermally conductive and insulating cellulose hybrid material based on electrostatic adsorption-inspired neural network and its preparation method

Abstract

The present invention discloses a thermally conductive and insulating cellulose hybrid material based on an electrostatic adsorption simulated neural network and a preparation method thereof. Based on the electrostatic adsorption mechanism, the present invention adopts a thermally conductive filler with a high thermal conductivity coefficient, such as boron nitride, as a thermally conductive filler, which is loaded on the surface of cellulose nanofibers through electrostatic adsorption, so that the fiber bundles overlap with each other to form a thermal conductive path similar to a neural network, ensuring that the material is insulating while having a high thermal conductivity coefficient and good mechanical strength. The material has broad application prospects in the fields of electronic device heat dissipation, thermal interface materials, etc.

Description

Technical Field

[0001] This invention relates to the field of polymer-based functional composite materials technology, and in particular to a thermally conductive and insulating cellulose composite membrane based on electrostatic adsorption and a neural network-like structure, and its preparation method. Background Technology

[0002] In recent years, with the advancement of technology, electronic components and related equipment have gradually become smaller, lighter, more integrated, and faster. This results in electronic devices generating more heat during use. If this heat cannot be dissipated in time, it will affect the accuracy and lifespan of the equipment. Therefore, improving the heat dissipation performance of electronic equipment is of great significance.

[0003] Polymer materials possess advantages such as lightweight, insulation, and good mechanical properties, making them widely used in the packaging of electronic devices. Among them, cellulose nanofibers (CNFs), as bio-based polymer materials, have attracted widespread attention due to their good biocompatibility and excellent mechanical properties. However, cellulose nanofibers have poor thermal conductivity, which cannot meet the heat dissipation requirements of electronic devices. Therefore, effectively improving their thermal conductivity has become an important goal.

[0004] The human nervous system, composed of over 100 billion nerve fibers, acts as a "track" for signal transmission, rapidly sensing and responding to external stimuli. Constructing thermally conductive pathways similar to neural networks can significantly enhance the heat transfer capabilities of materials. Boron nitride, as an inorganic ceramic filler, possesses excellent theoretical thermal conductivity (TC) and superior electrical insulation properties. Boron nitride nanosheets (BNNS) offer great potential for developing thermally conductive and electrically insulating composite materials. Summary of the Invention

[0005] To overcome the poor thermal conductivity of traditional cellulose nanofiber materials, this invention provides a thermally conductive and insulating cellulose composite film based on electrostatic adsorption-mimicking neural network and its preparation method. The thermally conductive and insulating cellulose composite film of this invention has a high in-plane thermal conductivity, allowing heat generated by electronic components to dissipate rapidly along the plane of the composite film. It maintains high thermal conductivity while exhibiting excellent insulation properties, and the preparation method is simple, environmentally friendly, and practical.

[0006] The technical solution of the present invention is as follows:

[0007] A thermally conductive and insulating cellulose composite membrane based on electrostatic adsorption-mimicking neural network was prepared by the following method:

[0008] (1) Ceramic insulating thermal conductive filler, sodium hydroxide and deionized water are mixed, ultrasonically dispersed and then ball-milled and peeled, followed by centrifugation and drying to obtain hydroxylated modified thermal conductive filler;

[0009] The ceramic insulating and thermally conductive filler is selected from one or more of AlN, BN, SiC, and Al2O3;

[0010] The preferred mass ratio of ceramic insulating and thermally conductive filler to sodium hydroxide is 1:10, and the preferred concentration of sodium hydroxide in the mixed system is 2-8 mol / L;

[0011] The temperature of the ultrasound is controlled at 25-50℃, and the time is controlled at 30-120 minutes.

[0012] During ball milling and peeling, the ball mill speed is controlled at 200-500 rpm, and the ball milling time is controlled at 6-10 hours.

[0013] During centrifugation, the centrifuge speed is 6000-8000 rpm, and the centrifugation time is 20-30 minutes;

[0014] (2) The hydroxylated thermally conductive filler was stirred and mixed with an aqueous solution of cationic thermosetting resin (10-30 min), and then added to an aqueous dispersion of cellulose nanofibers and ultrasonically dispersed to obtain a thermally conductive filler@cellulose nanofiber mixed dispersion.

[0015] The cationic thermosetting resin is selected from one or more of cationic polyacrylamide (CPAM), polyamide epichlorohydrin (PAE), urea-formaldehyde resin (UF), and melamine-formaldehyde resin (MF);

[0016] Based on the total mass of cellulose nanofibers and hydroxylated modified thermally conductive fillers, the proportion of hydroxylated modified thermally conductive fillers is 10–80 wt%.

[0017] The mass ratio of hydroxylated modified thermally conductive filler to cationic thermosetting resin is 2–6:75;

[0018] The aqueous solution concentration of cationic thermosetting resin is 2–8 wt%.

[0019] The concentration of the aqueous dispersion of cellulose nanofibers is 0.1–2 wt%.

[0020] During ultrasonic dispersion, the ultrasonic power is controlled between 100 and 500 W, the frequency is controlled between 20 and 60 kHz, and the ultrasonic time is controlled between 30 and 120 min.

[0021] In this step, the negatively charged thermally conductive filler after exfoliation is mixed with cationic thermosetting resin. The positively charged cationic resin molecules adsorb onto the surface of the thermally conductive filler, causing the overall potential to convert to a positive potential. The magnitude of the positive potential of the mixed system is controlled by adjusting the resin concentration. This is a key step in electrostatic adsorption. Subsequently, it undergoes electrostatic self-assembly with negatively charged cellulose nanofibers (the potential of CNF has been measured in advance as negative) in water. Under the action of electrostatic adsorption, the thermally conductive filler can fully coat the surface of cellulose. The dispersion at this time can be represented as a thermally conductive filler@cellulose nanofiber mixed dispersion (@ indicates that the thermally conductive filler is adsorbed on the cellulose nanofibers).

[0022] (3) Using PP membrane as filter membrane, the thermally conductive filler@cellulose nanofiber mixed dispersion is vacuum filtered to obtain composite membrane material; the obtained composite membrane material is mechanically molded and dried to obtain the thermally conductive and insulating cellulose composite membrane based on electrostatic adsorption simulated neural network.

[0023] During vacuum filtration, the vacuum level is controlled between -0.06 and -0.1 MPa.

[0024] The mechanical molding pressure is 40–50 kPa, and the drying temperature is room temperature;

[0025] In this step, cellulose nanofibers, which are one-dimensional structures, overlap to form a neural network-like structure, and a thermally conductive and insulating composite membrane is prepared by vacuum filtration.

[0026] Compared with the prior art, the present invention has the following beneficial effects:

[0027] 1. The preparation method of this invention is simple, environmentally friendly, and easy to operate;

[0028] 2. This invention uses boron nitride, which has a high thermal conductivity, as a thermally conductive filler. The insulating thermally conductive filler is adsorbed onto the surface of nanocellulose, and then a thermally conductive and insulating cellulose membrane is obtained by filtration. The composite membrane ensures thermal conductivity while also providing insulation.

[0029] 3. The thermally conductive and insulating cellulose membrane prepared by this invention has anisotropy, and its high in-plane thermal conductivity can quickly dissipate the heat generated by electronic components along the plane of the composite membrane. Attached Figure Description

[0030] Figure 1 Infrared spectra of hydroxylated boron nitride and original boron nitride after ball milling.

[0031] Figure 2 Zeta potentials of CNF, BNNS-OH and 7.5 wt% PAE, and the system potentials of BNNS-OH and PAE mixtures at different PAE concentrations.

[0032] Figure 3 Scanning electron microscope image of boron nitride adsorbed on the surface of cellulose nanofibers at a PAE concentration of 7.5 wt%.

[0033] Figure 4 Cross-sectional electron microscope images and elemental analysis spectra of the composite membrane in Example 1. Detailed Implementation

[0034] The present invention is further described below through specific embodiments, but the scope of protection of the present invention is not limited thereto. In the present invention, unless otherwise specified, all equipment and raw materials are commercially available or commonly used in the industry. The methods in the following embodiments are conventional methods in the art unless otherwise specified.

[0035] Table 1. Experimental Materials

[0036]

[0037] Example 1

[0038] 2g of hexagonal boron nitride, 20g of sodium hydroxide, and 100ml of deionized water were mixed in a beaker, and the beaker was sealed with sealing film. The mixture was then ultrasonically dispersed at room temperature for 10 minutes, followed by transfer to a ball mill jar. The mixture was ball-milled at 400 rpm for 8 hours. After milling, the slurry was removed and centrifuged at 8000 rpm for 25 minutes. After centrifugation, the slurry was dried in an oven at 80℃ for 4 hours to obtain the thermally conductive filler BNNS-OH.

[0039] 0.02 g of BNNS-OH was mixed with 10 mL of 7.5 wt% PAE aqueous solution under magnetic stirring for 25 min. Then, 8 mL of 1.0 wt% cellulose nanofiber aqueous dispersion (the mass ratio of cellulose nanofiber to thermally conductive filler BNNS-OH was 80 / 20) was added, and the mixture was ultrasonically dispersed at a frequency of 40 kHz for 30 min to obtain a BNNS-OH@CNF mixed dispersion.

[0040] A thermally conductive and insulating composite membrane was prepared by vacuum filtration of a BNNS-OH@CNF mixed dispersion; a PP membrane was used as the filter membrane, and the vacuum degree was controlled at -0.09MPa.

[0041] The composite film is molded at 45 kPa for 24 h and dried at room temperature to obtain an anisotropic thermally conductive and insulating cellulose composite film; the thickness of the thermally conductive and insulating layer on the PP layer is 100 μm.

[0042] Example 2

[0043] 2g of hexagonal boron nitride, 20g of sodium hydroxide, and 100ml of deionized water were mixed in a beaker, and the beaker was sealed with sealing film. The mixture was then ultrasonically dispersed at room temperature for 10 minutes, followed by transfer to a ball mill jar. The mixture was ball-milled at 400 rpm for 8 hours. After milling, the slurry was removed and centrifuged at 8000 rpm for 25 minutes. After centrifugation, the slurry was dried in an oven at 80℃ for 4 hours to obtain the thermally conductive filler BNNS-OH.

[0044] 0.03 g of BNNS-OH was mixed with 10 mL of 7.5 wt% PAE aqueous solution under magnetic stirring for 25 min. Then, 7 mL of 1.0 wt% cellulose nanofiber aqueous dispersion (the mass ratio of cellulose nanofiber to thermally conductive filler BNNS-OH was 70 / 30) was added, and the mixture was ultrasonically dispersed at a frequency of 40 kHz for 30 min to obtain a BNNS-OH@CNF mixed dispersion.

[0045] A thermally conductive and insulating composite membrane was prepared by vacuum filtration of a BNNS-OH@CNF mixed dispersion; a PP membrane was used as the filter membrane, and the vacuum degree was controlled at -0.09 MPa.

[0046] The composite film is molded at 45 kPa for 24 h and dried at room temperature to obtain an anisotropic thermally conductive and insulating cellulose composite film; the thickness of the thermally conductive and insulating layer on the PP layer is 100 μm.

[0047] Example 3

[0048] 2g of hexagonal boron nitride, 20g of sodium hydroxide, and 100ml of deionized water were mixed in a beaker, and the beaker was sealed with sealing film. The mixture was then ultrasonically dispersed at room temperature for 10 minutes, followed by transfer to a ball mill jar. The mixture was ball-milled at 400 rpm for 8 hours. After milling, the slurry was removed and centrifuged at 8000 rpm for 25 minutes. After centrifugation, the slurry was dried in an oven at 80℃ for 4 hours to obtain the thermally conductive filler BNNS-OH.

[0049] 0.04 g of BNNS-OH was mixed with 10 mL of 7.5 wt% PAE aqueous solution under magnetic stirring for 25 min. Then, 6 mL of 1.0 wt% cellulose nanofiber aqueous dispersion (the mass ratio of cellulose nanofiber to thermally conductive filler BNNS-OH was 60 / 40) was added, and the mixture was ultrasonically dispersed at a frequency of 40 kHz for 30 min to obtain a BNNS-OH@CNF mixed dispersion.

[0050] A thermally conductive and insulating composite membrane was prepared by vacuum filtration of a BNNS-OH@CNF mixed dispersion; a PP membrane was used as the filter membrane, and the vacuum degree was controlled at -0.09 MPa.

[0051] The composite film is molded at 45 kPa for 24 h and dried at room temperature to obtain an anisotropic thermally conductive and insulating cellulose composite film; the thickness of the thermally conductive and insulating layer on the PP layer is 100 μm.

[0052] Example 4

[0053] 2g of hexagonal boron nitride, 20g of sodium hydroxide, and 100ml of deionized water were mixed in a beaker, and the beaker was sealed with sealing film. The mixture was then ultrasonically dispersed at room temperature for 10 minutes, followed by transfer to a ball mill jar. The mixture was ball-milled at 400 rpm for 8 hours. After milling, the slurry was removed and centrifuged at 8000 rpm for 25 minutes. After centrifugation, the slurry was dried in an oven at 80℃ for 4 hours to obtain the thermally conductive filler BNNS-OH.

[0054] 0.05 g of BNNS-OH was mixed with 10 mL of 7.5 wt% PAE aqueous solution under magnetic stirring for 25 min. Then, 5 mL of 1.0 wt% cellulose nanofiber aqueous dispersion (the mass ratio of cellulose nanofiber to thermally conductive filler BNNS-OH was 50 / 50) was added and ultrasonically dispersed at a frequency of 40 kHz for 30 min to obtain a BNNS-OH@CNF mixed dispersion.

[0055] A thermally conductive and insulating composite membrane was prepared by vacuum filtration of a BNNS-OH@CNF mixed dispersion; a PP membrane was used as the filter membrane, and the vacuum degree was controlled at -0.09 MPa.

[0056] The composite film is molded at 45 kPa for 24 h and dried at room temperature to obtain an anisotropic thermally conductive and insulating cellulose composite film; the thickness of the thermally conductive and insulating layer on the PP layer is 100 μm.

[0057] Example 5

[0058] 2g of hexagonal boron nitride, 20g of sodium hydroxide, and 100ml of deionized water were mixed in a beaker, and the beaker was sealed with sealing film. The mixture was then ultrasonically dispersed at room temperature for 10 minutes, followed by transfer to a ball mill jar. The mixture was ball-milled at 400 rpm for 8 hours. After milling, the slurry was removed and centrifuged at 8000 rpm for 25 minutes. After centrifugation, the slurry was dried in an oven at 80℃ for 4 hours to obtain the thermally conductive filler BNNS-OH.

[0059] 0.06 g of BNNS-OH was mixed with 10 mL of 7.5 wt% PAE aqueous solution under magnetic stirring for 25 min. Then, 4 mL of 1.0 wt% cellulose nanofiber aqueous dispersion (the mass ratio of cellulose nanofiber to thermally conductive filler BNNS-OH was 40 / 60) was added, and the mixture was ultrasonically dispersed at a frequency of 40 kHz for 30 min to obtain a BNNS-OH@CNF mixed dispersion.

[0060] A thermally conductive and insulating composite membrane was prepared by vacuum filtration of a BNNS-OH@CNF mixed dispersion; a PP membrane was used as the filter membrane, and the vacuum degree was controlled at -0.09 MPa.

[0061] The composite film is molded at 45 kPa for 24 h and dried at room temperature to obtain an anisotropic thermally conductive and insulating cellulose composite film; the thickness of the thermally conductive and insulating layer on the PP layer is 100 μm.

[0062] Comparative Example 1 (Pure Cellulose Membrane)

[0063] 10 mL of a 1.0 wt% cellulose nanofiber aqueous dispersion was ultrasonically dispersed at a frequency of 40 kHz for 30 min to obtain a pure CNF aqueous dispersion.

[0064] A thermally conductive and insulating composite membrane was prepared by vacuum filtration of a cellulose nanofiber dispersion; a PP membrane was used as the filter membrane, and the vacuum degree was controlled at -0.09 MPa.

[0065] The membrane is molded at 45 kPa for 24 h and dried at room temperature to obtain an anisotropic thermally conductive and insulating cellulose membrane; the thickness of the thermally conductive and insulating layer on the PP layer is 100 μm.

[0066] Comparative Example 2 (Direct blending of boron nitride and cellulose nanofibers)

[0067] 4 mL of 1.0 wt% cellulose nanofiber aqueous dispersion was mixed with 0.06 g of hexagonal boron nitride (the mass ratio of cellulose nanofiber to thermally conductive filler hexagonal boron nitride was 40 / 60), and ultrasonically dispersed at a frequency of 40 kHz for 30 min to obtain a BN / CNF mixed dispersion ( / indicates direct blending with no adsorption effect).

[0068] A thermally conductive and insulating composite membrane was prepared by vacuum filtration of a BN / CNF mixed dispersion; a PP membrane was used as the filter membrane, and the vacuum degree was controlled at -0.09 MPa.

[0069] The composite film is molded at 45 kPa for 24 h and dried at room temperature to obtain an anisotropic thermally conductive and insulating cellulose composite film; the thickness of the thermally conductive and insulating layer on the PP layer is 100 μm.

[0070] Comparative Example 3 (Borne nitride was ball-milled and then blended with cellulose nanofibers)

[0071] 2g of hexagonal boron nitride and 100ml of deionized water were mixed in a beaker, and the beaker was sealed with sealing film. The mixture was then ultrasonically dispersed at room temperature for 10 minutes, and then transferred to a ball mill jar. The mixture was ball-milled at 400 rpm for 8 hours. After ball milling, the slurry was removed and centrifuged at 8000 rpm for 25 minutes. After centrifugation, the mixture was dried in an oven at 80℃ for 4 hours to obtain the thermally conductive filler BNNS.

[0072] 4 mL of 1.0 wt% cellulose nanofiber aqueous dispersion was mixed with 0.06 g BNNS (the mass ratio of cellulose nanofiber to thermally conductive filler BNNS was 40 / 60), and ultrasonically dispersed at a frequency of 40 kHz for 30 min to obtain a BNNS / CNF mixed dispersion.

[0073] A thermally conductive and insulating composite membrane was prepared by vacuum filtration of a BNNS / CNF mixed dispersion; a PP membrane was used as the filter membrane, and the vacuum degree was controlled at -0.09 MPa.

[0074] The composite film is molded at 45 kPa for 24 h and dried at room temperature to obtain an anisotropic thermally conductive and insulating cellulose composite film; the thickness of the thermally conductive and insulating layer on the PP layer is 100 μm.

[0075] Comparative Example 4 (Boron nitride was ball-milled and hydroxylated, then blended with cellulose nanofibers)

[0076] 2g of hexagonal boron nitride, 20g of sodium hydroxide, and 100ml of deionized water were mixed in a beaker, and the beaker was sealed with sealing film. The mixture was then ultrasonically dispersed at room temperature for 10 minutes, followed by transfer to a ball mill jar. The mixture was ball-milled at 400 rpm for 8 hours. After milling, the slurry was removed and centrifuged at 8000 rpm for 25 minutes. After centrifugation, the slurry was dried in an oven at 80℃ for 4 hours to obtain the thermally conductive filler BNNS-OH.

[0077] 4 mL of 1.0 wt% cellulose nanofiber aqueous dispersion was mixed with 0.06 g of BNNS-OH (the mass ratio of cellulose nanofiber to thermally conductive filler BNNS-OH was 40 / 60), and ultrasonically dispersed at a frequency of 40 kHz for 30 min to obtain a BNNS-OH / CNF dispersion.

[0078] A thermally conductive and insulating composite membrane was prepared by vacuum filtration of a BNNS-OH / CNF dispersion; a PP membrane was used as the filter membrane, and the vacuum degree was controlled at -0.09 MPa.

[0079] The composite film is molded at 45 kPa for 24 h and dried at room temperature to obtain an anisotropic thermally conductive and insulating cellulose composite film; the thickness of the thermally conductive and insulating layer on the PP layer is 100 μm.

[0080] Comparative Example 5 (Boron nitride was mixed with PAE and then mixed with cellulose nanofibers)

[0081] 0.06 g of thermally conductive filler BN was mixed with 10 mL of 7.5 wt% PAE aqueous solution under magnetic stirring for 25 min. Then, 4 mL of 1.0 wt% cellulose nanofiber aqueous dispersion (the mass ratio of cellulose nanofiber to thermally conductive filler BN was 40 / 60) was added, and the mixture was ultrasonically dispersed at a frequency of 40 kHz for 30 min to obtain BN@CNF dispersion.

[0082] A thermally conductive and insulating composite membrane was prepared by vacuum filtration of BN@CNF dispersion; PP membrane was used as the filter membrane, and the vacuum degree was controlled at -0.09MPa.

[0083] The composite film is molded at 45 kPa for 24 h and dried at room temperature to obtain an anisotropic thermally conductive and insulating cellulose composite film; the thickness of the thermally conductive and insulating layer on the PP layer is 100 μm.

[0084] The performance of the composite membrane samples from Examples 1-5 and Comparative Examples 1-4 was tested, and the test results are shown in Table 2:

[0085] Table 2. Measurement results of composite membranes in Examples 1-5 and Comparative Examples 1-4

[0086]

[0087]

[0088] As shown in Table 2, the pure cellulose membrane has poor thermal conductivity. Adding thermally conductive fillers improves the thermal conductivity, but the resistivity remains high, maintaining the original electrical insulation properties. While the composite membrane obtained by simple blending and filtration with boron nitride shows improved thermal conductivity, its mechanical properties decrease significantly. Ball milling improves the mechanical properties compared to direct blending. Simultaneous hydroxylation during ball milling does not significantly alter the performance compared to ball milling alone. Furthermore, the thermal conductivity of the thermally conductive and insulating composite membranes prepared in Examples 1-5 increases with the proportion of thermally conductive fillers. Due to anisotropy, the heat accumulated by electronic components dissipates along the planar direction, extending the lifespan of the electronic components. The thermally conductive fillers are electrostatically attracted to the surface of cellulose nanofibers, and then vacuum filtration forms a dense composite membrane. This facilitates the formation of thermally conductive pathways. However, the addition of thermally conductive fillers must be moderate; excessive filler load will affect film formation and severely impact mechanical properties, rendering the membrane unusable.

Claims

1. A thermally conductive and insulating cellulose composite membrane based on electrostatic adsorption-mimicking neural network, characterized in that, It is prepared according to the following method: (1) Hexagonal boron nitride, sodium hydroxide and deionized water are mixed, ultrasonically dispersed and then ball-milled and peeled, followed by centrifugation and drying to obtain hydroxylated modified thermally conductive filler; (2) The hydroxylated thermally conductive filler was stirred and mixed with an aqueous solution of polyamide epichlorohydrin, and then added to an aqueous dispersion of cellulose nanofibers. The mixture was ultrasonically dispersed to obtain a thermally conductive filler@cellulose nanofiber mixed dispersion. The aqueous solution concentration of polyamide epichlorohydrin is 7.5 wt%. The concentration of the aqueous dispersion of cellulose nanofibers was 1.0 wt%. The feed ratio of hydroxylated modified thermally conductive filler to aqueous solution of polyamide epichlorohydrin and aqueous dispersion of cellulose nanofibers was 0.06 g: 10 mL: 4 mL. (3) Using PP membrane as filter membrane, the thermally conductive filler@cellulose nanofiber mixed dispersion is vacuum filtered to obtain composite membrane material; the obtained composite membrane material is mechanically molded and dried to obtain the thermally conductive and insulating cellulose composite membrane based on electrostatic adsorption simulated neural network.

2. The thermally conductive and insulating cellulose composite membrane based on electrostatic adsorption simulated neural network as described in claim 1, characterized in that, In step (1), the mass ratio of hexagonal boron nitride to sodium hydroxide is 1:10, and the concentration of sodium hydroxide in the mixed system is 2~8 mol / L.

3. The thermally conductive and insulating cellulose composite membrane based on electrostatic adsorption simulated neural network as described in claim 1, characterized in that, In step (1), during ball milling and peeling, the ball mill speed is controlled at 200~500 rpm and the ball milling time is controlled at 6~10h.

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