Preparation method of self-healing polyurethane composite material with heat conduction and electromagnetic shielding functions

Abstract

The invention discloses a preparation method of a heat conduction and electromagnetic shielding self-healing polyurethane composite material, which comprises the following steps: modifying nano cellulose CNF (denoted as CNF-coated PPA) by using polyphenol amine PPA, and depositing silver nanoparticles on the surface of the CNF-coated PPA in situ to obtain a deposited material; the preparation method comprises the following steps: preparing a polyamide epichlorohydrin PAE solution, modifying graphene nanosheets GNP by using the PAE solution, and recording the modified graphene nanosheets GNP as PAE-GNP suspension liquid; cNF (at) PPA (at) Ag is dispersed into the PAE-GNP suspension liquid, and the CNF (at) PPA (at) Ag suspension liquid is marked as CNF-GNP suspension liquid; and preparing waterborne polyurethane WPU, dispersing the CNF-GNP suspension into the WPU, and carrying out vacuum filtration, drying and hot pressing on the mixed solution to obtain the polyurethane composite material. The method is simple in preparation process, mild in reaction condition and stable in product quality, and the polyurethane composite material prepared according to the method has excellent heat conduction, electromagnetic shielding and self-healing performance.

Description

Technical Field

[0001] The present invention relates to the technical field of composite material preparation, and in particular to a method for preparing a self-healing polyurethane composite material that takes into account both thermal conductivity and electromagnetic shielding. Background Art

[0002] With the rapid development of 5G technology, flexible sensors have been widely used in fields such as human-computer interaction and soft actuators. However, with the integration, miniaturization and multifunctionalization of flexible sensors, the heat accumulation generated inside the electronic components will seriously reduce their performance and lifespan. At the same time, electromagnetic radiation is inevitably generated inside the sensor, which not only affects the stable operation of other electronic devices, but also endangers human health. In addition, after suffering external mechanical damage, the performance of flexible sensors is severely reduced, and they may even lose their usability. Therefore, it is of great significance to prepare self-healing polymer composites that take into account both thermal conductivity and electromagnetic shielding. Waterborne polyurethane contains rich reversible dynamic covalent bonds and non-covalent bonds, which give it excellent self-healing properties. Self-healing polyurethane composites that take into account both thermal conductivity and electromagnetic shielding properties can be prepared, which will effectively extend the service life of flexible sensors and maintain their stable movement. Summary of the Invention

[0003] The purpose of the present invention is to provide a method for preparing a polyurethane composite material that combines thermal conductivity with electromagnetic shielding and self-healing properties. The method has a simple preparation process, mild reaction conditions, and stable product quality. The polyurethane composite material prepared according to the method has excellent thermal conductivity, electromagnetic shielding and self-healing properties, solving the problem that existing materials cannot combine high thermal conductivity, excellent electromagnetic shielding and excellent self-healing properties.

[0004] The purpose of the present invention is achieved through the following technical solutions:

[0005] A method for preparing a self-healing polyurethane composite material that combines thermal conductivity and electromagnetic shielding, the method comprising:

[0006] Step 1: using polyphenolamine (PPA) to modify nanocellulose CNF, denoted as CNF@PPA, and then in situ depositing silver nanoparticles on the surface of CNF@PPA to obtain the deposited material, denoted as CNF@PPA@Ag;

[0007] Step 2, preparing a polyamide epichlorohydrin (PAE) solution, and using the PAE solution to modify graphene nanosheets (GNPs), which is recorded as a PAE-GNP suspension;

[0008] Step 3: Disperse the CNF@PPA@Ag obtained in step 1 into the PAE-GNP suspension obtained in step 2, which is referred to as the CNF-GNP suspension;

[0009] Step 4: Prepare waterborne polyurethane (WPU), disperse the CNF-GNP suspension in step 3 into the waterborne polyurethane (WPU), vacuum filter the mixed solution, dry it, and then hot-press it to obtain a self-healing polyurethane composite material that has both thermal conductivity and electromagnetic shielding properties.

[0010] It can be seen from the technical solution provided by the present invention that the above method has a simple preparation process, mild reaction conditions, and stable product quality. The polyurethane composite material prepared according to this method has excellent thermal conductivity, electromagnetic shielding and self-healing properties, which solves the problem that existing materials cannot take into account high thermal conductivity, excellent electromagnetic shielding and excellent self-healing properties. BRIEF DESCRIPTION OF THE DRAWINGS

[0011] In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the following briefly introduces the drawings required for use in the description of the embodiments. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative work.

[0012] Figure 1 A schematic flow chart of a method for preparing a self-healing polyurethane composite material that combines thermal conductivity and electromagnetic shielding, provided in an embodiment of the present invention. DETAILED DESCRIPTION

[0013] The following is a clear and complete description of the technical solutions in the embodiments of the present invention in conjunction with the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, not all embodiments, and do not constitute a limitation of the present invention. All other embodiments obtained by ordinary technicians in this field based on the embodiments of the present invention without making any creative efforts shall fall within the scope of protection of the present invention.

[0014] like Figure 1 FIG2 is a flow chart of a method for preparing a self-healing polyurethane composite material having both thermal conductivity and electromagnetic shielding provided by an embodiment of the present invention, wherein the method comprises:

[0015] Step 1: using polyphenolamine (PPA) to modify nanocellulose CNF, denoted as CNF@PPA, and then in situ depositing silver nanoparticles on the surface of CNF@PPA to obtain the deposited material, denoted as CNF@PPA@Ag;

[0016] In this step, specifically, 0.05-0.3 g of nanocellulose CNF is added to 50-200 mL of dispersion solution and ultrasonically dispersed at 30-60 kHz for 0.5-2 h to form a CNF suspension;

[0017] 0.01-0.05 g of phenol and 0.01-0.2 g of amine were added to the CNF suspension, and 0.1-0.3 g of Tris was added to adjust the pH value of the solution to 7-9. The stirring speed was set at 500-1000 r / min, and magnetic stirring was carried out at a constant temperature of 20-40°C for 2-4 hours. The suspension was filtered and dried to obtain polyphenolamine (PPA)-modified nanocellulose CNF, which was designated as CNF@PPA.

[0018] Prepare a silver ammonia solution by adding 0.1-1 g of AgNO3 to 50-200 mL of the dispersion and adding an appropriate amount of ammonia water dropwise until the solution changes from turbid to clear.

[0019] 0.1-0.3 g of CNF@PPA was added to 50-200 mL of prepared silver ammonia solution and magnetically stirred at a constant temperature of 20-40°C for 1-3 h. Then, 50-200 mL of glucose solution with a concentration of 10-30 g / L was added dropwise and magnetically stirred at a constant temperature of 20-40°C for 1-3 h. After filtering and drying, the deposited material was obtained, which was recorded as CNF@PPA@Ag.

[0020] In a specific implementation, polyphenolamine PPA is a polymer obtained by reacting phenol and amine;

[0021] wherein the phenol is one or more of resorcinol, catechol, tannic acid, and dopamine hydrochloride;

[0022] The amine is one or more of dopamine hydrochloride, diethylenetriamine, triethylenetetramine, tetraethylenepentamine, pentavinylhexylamine, ethylenediamine, o-phenylenediamine, and polyethyleneimine.

[0023] In addition, the average horizontal size of unmodified nanocellulose CNFs is 1 to 30 μm and the diameter is 1 to 50 nm.

[0024] Step 2: preparing a polyamide epichlorohydrin (PAE) solution, and using the PAE solution to modify graphene nanosheets (GNPs), which is referred to as a PAE-GNP suspension;

[0025] In this step, 30-60 g of diethylenediamine and 20-50 g of adipic acid are added to a flask, reacted at 150-210° C. for 4-8 hours, and then 30-100 mL of deionized water is added to adjust the solid content to 30-50%.

[0026] Then add 20-40g of epichlorohydrin dropwise, react at 20-40℃ for 0.3-1h, then heat to 60-70℃ and react for 4-8h. Adjust the pH to 2-3 with sulfuric acid before stopping the reaction;

[0027] Finally, 300 to 800 mL of deionized water is added to adjust the solution to obtain a polyamide epichlorohydrin PAE solution with a content of 5 to 10 wt %. The dispersion liquid used is one of anhydrous ethanol, isopropyl alcohol, acetone or deionized water.

[0028] 0.1-1.0 g of graphene nanosheets GNPs are added to 50-200 mL of PAE solution, ultrasonically crushed at 100-300 W for 0.5-2 h, and magnetically stirred at a constant temperature of 20-40° C. for 2-5 h to form a PAE-GNP suspension.

[0029] In a specific implementation, the average horizontal size of the unmodified graphene nanosheets GNP is 50 to 80 μm, and the average thickness is 1 to 20 nm.

[0030] Step 3: Disperse the CNF@PPA@Ag obtained in step 1 into the PAE-GNP suspension obtained in step 2, which is referred to as the CNF-GNP suspension;

[0031] In this step, 0.1-0.5 g of CNF@PPA@Ag was added to 50-200 mL of PAE-GNP suspension, and ultrasonically crushed at 100-300 W for 0.5-2 h to obtain a CNF-GNP suspension.

[0032] Step 4: Prepare waterborne polyurethane (WPU), disperse the CNF-GNP suspension into the waterborne polyurethane (WPU), filter, dry, and hot-press the mixed solution to obtain a polyurethane composite material with excellent thermal conductivity, electromagnetic shielding, and self-healing properties.

[0033] In this step, 10 to 30 g of polytetrahydrofuran (PTMEG-2000) and 10 to 15 g of hexamethylene diisocyanate (HDI) are added to a three-necked flask, heated to 70 to 90° C., and reacted for 0.5 to 3 hours;

[0034] Then, 1-3 g of 2,2-dihydroxymethylbutyric acid (DMBA) was added and stirred for 0.5-3 h, followed by 4-6 g of dimethylglyoxime (DME) and 5 mL of acetone, and the reaction was continued for 1-3 h.

[0035] Then, the reaction system was cooled to 50-70°C, 1-3 g of triethylamine (TEA) was added to the three-necked flask and stirred for 20-50 min;

[0036] Finally, 80 to 120 mL of deionized water is added to the mixture, and the mixture is emulsified at a speed of 5,000 to 20,000 r / min using a homogenizer for 5 to 20 minutes. After emulsification, the acetone is removed by rotary evaporation at 30 to 50° C. for 0.5 to 2 hours to obtain a waterborne polyurethane with a solid content of 20 to 50 wt%;

[0037] Disperse 50-200 mL of the CNF-GNP suspension obtained in step 3 into 2.7 g of waterborne polyurethane WPU and mechanically stir for 3-6 h to obtain a WPU-CNF-GNP mixed solution;

[0038] The WPU-CNF-GNP mixed solution is filtered, dried in an oven at 40-80°C, and hot pressed at 100-150°C and 5-20 MPa for 20-50 minutes to obtain a polyurethane composite material with excellent thermal conductivity, electromagnetic shielding and self-healing properties.

[0039] The following is a detailed description of the preparation method and performance effects of the polyurethane composite material provided by the present invention using specific examples and comparative examples:

[0040] Implementation Case 1

[0041] 1) Add 0.1 g CNF to 100 mL deionized water and ultrasonically disperse for 1 h to form CNF suspension 1;

[0042] 2) 0.01 g of catechol and 0.04 g of tetraethylenepentamine were added to the above suspension 1, and 0.1 g of Tris was added to adjust the pH to 9. The suspension was placed in a constant temperature magnetic stirrer with a stirring speed of 600 r / min. The mixture was kept at 30°C for 3 h to form CNF@PPA suspension 2. The suspension 2 was filtered and dried to obtain CNF@PPA.

[0043] 3) Add 0.5 g of silver nitrate to 100 mL of deionized water and add an appropriate amount of aqueous ammonia dropwise until the solution becomes clear to prepare a silver ammonia solution, designated as Solution 3.

[0044] 4) Add 0.1 g of CNF@PPA to solution 3 and stir magnetically at 25°C for 1 h to form suspension 4;

[0045] 5) 100 mL of 20 g / L glucose solution was added dropwise to suspension 4 through a separatory funnel at a rate of 2 drops / s. The suspension was magnetically stirred at 25°C for 2 h to obtain suspension 5, which was filtered and dried to obtain CNF@PPA@Ag.

[0046] 6) 27 g of diethylenediamine and 36.5 g of adipic acid were added to a flask and reacted at 180° C. for 5 h. Subsequently, 56 mL of deionized water was added to adjust the solid content to 45%. 23 g of epichlorohydrin was then added dropwise and reacted at 30° C. for 0.5 h. The temperature was then raised to 65° C. and reacted for 6 h. The pH was adjusted to 2-3 with sulfuric acid before stopping the reaction. Finally, 624 mL of deionized water was added to obtain a 5 wt% polyamide epichlorohydrin (PAE) solution 6.

[0047] 7) Add 0.1 g of GNPs to 100 mL of the above solution 6, ultrasonically disrupt the solution at 200 W for 1 h, and then place the solution in a thermostatic magnetic stirrer at 600 rpm for 3 h at 25°C to form a PAE-GNP suspension 7;

[0048] 8) 0.1 g of CNF@PPA@Ag was added to suspension 7 and ultrasonicated at 200 W for 1 h to form suspension 8;

[0049] 9) Add 20g of polytetrahydrofuran (PTMEG-2000) and 13.8g of hexamethylene diisocyanate (HDI) to a three-necked flask, heat to 85°C, and react for 1 hour. Subsequently, add 1.7g of 2,2-dimethylolbutanoic acid (DMBA) and stir for 1 hour. Then, add 5.11g of dimethylglyoxime (DME) and 5mL of acetone and continue to react for 2 hours. The reaction system is then cooled to 60°C, and 1.16g of triethylamine (TEA) is added to the three-necked flask and stirred for 30 minutes. Finally, add 97.5mL of deionized water to the mixture, emulsify it at 10,000 rpm for 10 minutes using a homogenizer. After emulsification, remove the acetone by rotary evaporation at 45°C for 1 hour to obtain an aqueous polyurethane emulsion 9 with a solids content of 30 wt%.

[0050] 10) Suspension 8 was added to 2.7 g of emulsion 9 and mechanically stirred for 5 h to form suspension 10;

[0051] 11) The suspension 10 was vacuum filtered, dried in an oven at 60° C., and then hot-pressed at 120° C. and 10 MPa for 30 min to obtain a polyurethane composite material having excellent thermal conductivity, electromagnetic shielding, and self-healing properties.

[0052] The thermal conductivity and electromagnetic shielding efficiency of the polyurethane composite material prepared in Example 1 were measured before and after self-healing. The test results are shown in Tables 1 and 2.

[0053] Implementation Case 2: The preparation method is the same as Implementation Case 1, except that 0.02 g of dopamine hydrochloride and 0.04 g of pentavinylhexylamine are added in step 2). The thermal conductivity and electromagnetic shielding efficiency of the prepared polyurethane composite material are measured before and after self-healing. The test results are shown in Tables 1 and 2.

[0054] Implementation Case 3: The preparation method is the same as Implementation Case 1, except that the amount of silver nitrate added in step 3) is 1 g. The thermal conductivity and electromagnetic shielding efficiency of the prepared polyurethane composite material are measured before and after self-healing. The test results are shown in Tables 1 and 2.

[0055] Implementation Case 4: The preparation method is the same as Implementation Case 1, except that in step 6), 315 mL of deionized water is finally added to adjust the PAE content in the solution to 10 wt%. The thermal conductivity and electromagnetic shielding efficiency of the prepared polyurethane composite material are measured before and after self-healing. The test results are shown in Tables 1 and 2.

[0056] Example 5: The preparation method is the same as that of Example 1, except that 0.2 g of GNPs is added in step 7) and 2.3 g of WPU is added in step 10). The thermal conductivity and electromagnetic shielding efficiency of the prepared polyurethane composite material are measured before and after self-healing. The test results are shown in Tables 1 and 2.

[0057] Example 6: The preparation method is the same as that of Example 1, except that 0.3 g of GNPs is added in step 7) and 2 g of WPU is added in step 10). The thermal conductivity and electromagnetic shielding efficiency of the prepared polyurethane composite material are measured before and after self-healing. The test results are shown in Tables 1 and 2.

[0058] Example 7: The preparation method is the same as Example 1, except that 0.4 g of GNPs is added in step 7) and 1.7 g of WPU is added in step 10). The thermal conductivity and electromagnetic shielding efficiency of the prepared polyurethane composite material are measured before and after self-healing. The test results are shown in Tables 1 and 2.

[0059] Comparative Case 1

[0060] (1) Add 3 g of WPU to 100 mL of deionized water and mechanically stir for 5 h to form a WPU suspension;

[0061] (2) The WPU suspension was vacuum filtered and hot pressed at 120°C and 10 MPa for 30 min to obtain a polyurethane film.

[0062] The thermal conductivity and electromagnetic shielding efficiency of the prepared polyurethane film were measured before and after self-healing. The test results are shown in Tables 1 and 2.

[0063] Comparative Case 2

[0064] (1) 0.4 g of GNPs were added to 100 mL of deionized water and ultrasonicated at 200 W for 1 h to prepare GNP suspension 1;

[0065] (2) 0.1 g CNF was added to 100 mL deionized water and ultrasonically dispersed for 1 h to prepare CNF suspension 2;

[0066] (3) Disperse suspension 2 into suspension 1 and ultrasonically crush at 200W for 1 h to obtain suspension 3;

[0067] (4) Suspension 3 was dispersed into 1.7 g of WPU and mechanically stirred for 5 h to prepare suspension 4;

[0068] (5) The suspension 4 was vacuum filtered, dried in an oven at 60°C, and hot pressed at 120°C and 10 MPa for 30 min to obtain a polyurethane composite material.

[0069] The thermal conductivity and electromagnetic shielding efficiency of the prepared polyurethane composite material were measured before and after self-healing. The test results are shown in Tables 1 and 2.

[0070] Performance testing:

[0071] The materials obtained from Examples 1 to 7 of the present invention and Comparative Examples 1 to 2 were tested for in-plane and out-of-plane thermal conductivity. A single scratch, 10 mm long and 0.1 mm wide, was created on the surface of the material. After heat treatment at 120°C for 5 hours, the scratch disappeared. The self-healed material was then tested for in-plane and out-of-plane thermal conductivity using an LFA 467 Hyper Flash laser thermal conductivity meter. The test results are shown in Table 1 below:

[0072] Table 1

[0073]

[0074]

[0075] The electromagnetic shielding efficiency of the materials obtained in Examples 1 to 7 of the present invention and Comparative Examples 1 to 2 was tested. A single scratch with a length of 10 mm and a width of 0.1 mm was made on the surface of the material. After heat treatment at 120°C for 5 hours, the scratch disappeared. The electromagnetic shielding efficiency of the self-healed material was tested using an N5244B microwave network analyzer. The test results are shown in Table 2 below:

[0076] Table 2

[0077]

[0078] The above test results show that the polyurethane composite material prepared by the method described in the embodiment of the present invention has a maximum in-plane thermal conductivity of 104.36 W·m -1 ·K -1 , the out-of-plane thermal conductivity reaches 16.29W·m -1 ·K -1 The electromagnetic shielding efficiency reaches 82.35dB and the self-healing efficiency reaches 98%, which solves the problem that existing materials cannot take into account high thermal conductivity, excellent electromagnetic shielding and excellent self-healing performance.

[0079] It should be noted that the contents not described in detail in the embodiments of the present invention belong to the prior art known to those skilled in the art.

[0080] The above description is only a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any changes or substitutions that can be easily thought of by any person skilled in the art within the technical scope disclosed in the present invention should be included in the scope of protection of the present invention. Therefore, the scope of protection of the present invention should be based on the scope of protection of the claims. The information disclosed in the background technology section of this article is only intended to deepen the understanding of the overall background technology of the present invention, and should not be regarded as an admission or any form of implication that the information constitutes prior art already known to those skilled in the art.

Claims

1. A method for preparing a self-healing polyurethane composite material that combines thermal conductivity and electromagnetic shielding, characterized in that: The method comprises: Step 1: using polyphenolamine (PPA) to modify nanocellulose CNF, denoted as CNF@PPA, and then in situ depositing silver nanoparticles on the surface of CNF@PPA to obtain the deposited material, denoted as CNF@PPA@Ag; Step 2: preparing a polyamide epichlorohydrin (PAE) solution, and using the PAE solution to modify graphene nanosheets (GNPs), which is referred to as a PAE-GNP suspension; Step 3: Disperse the CNF@PPA@Ag obtained in step 1 into the PAE-GNP suspension obtained in step 2, which is referred to as the CNF-GNP suspension; Step 4: Prepare waterborne polyurethane (WPU), disperse the CNF-GNP suspension into the waterborne polyurethane (WPU), filter, dry, and hot-press the mixed solution to obtain a polyurethane composite material with excellent thermal conductivity, electromagnetic shielding, and self-healing properties.

2. The method for preparing a self-healing polyurethane composite material with both thermal conductivity and electromagnetic shielding according to claim 1, characterized in that: The process of step 1 is specifically as follows: 0.05-0.3 g of nanocellulose CNF was added to 50-200 mL of dispersion solution and ultrasonically dispersed at 30-60 kHz for 0.5-2 h to form a CNF suspension; 0.01-0.05 g of phenol and 0.01-0.2 g of amine were added to the CNF suspension, and 0.1-0.3 g of Tris was added to adjust the pH value of the solution to 7-9. The stirring speed was set at 500-1000 r / min, and magnetic stirring was carried out at a constant temperature of 20-40°C for 2-4 hours. The suspension was filtered and dried to obtain polyphenolamine (PPA)-modified nanocellulose CNF, which was designated as CNF@PPA. Prepare a silver ammonia solution by adding 0.1-1 g of AgNO3 to 50-200 mL of the dispersion and adding an appropriate amount of ammonia water dropwise until the solution changes from turbid to clear. 0.1-0.3 g of CNF@PPA was added to 50-200 mL of prepared silver ammonia solution and magnetically stirred at a constant temperature of 20-40°C for 1-3 h. Then, 50-200 mL of glucose solution with a concentration of 10-30 g / L was added dropwise and magnetically stirred at a constant temperature of 20-40°C for 1-3 h. After filtering and drying, the deposited material was obtained, which was recorded as CNF@PPA@Ag.

3. The method for preparing a self-healing polyurethane composite material with both thermal conductivity and electromagnetic shielding according to claim 1, characterized in that: The process of step 2 is specifically as follows: Add 30-60 g of diethylenediamine and 20-50 g of adipic acid into a flask, react at 150-210° C. for 4-8 hours, then add 30-100 mL of deionized water to adjust the solid content to 30-50%; Then add 20-40g of epichlorohydrin dropwise, react at 20-40℃ for 0.3-1h, then heat to 60-70℃ and react for 4-8h. Adjust the pH to 2-3 with sulfuric acid before stopping the reaction; Finally, 300-800 mL of deionized water was added to adjust the mixture to obtain a polyamide epichlorohydrin (PAE) solution having a content of 5-10 wt %; 0.1-1.0 g of graphene nanosheets GNPs are added to 50-200 mL of PAE solution, ultrasonically crushed at 100-300 W for 0.5-2 h, and magnetically stirred at a constant temperature of 20-40° C. for 2-5 h to form a PAE-GNP suspension.

4. The method for preparing a self-healing polyurethane composite material with both thermal conductivity and electromagnetic shielding according to claim 1, characterized in that: The process of step 3 is specifically as follows: 0.1-0.5 g of CNF@PPA@Ag was added to 50-200 mL of PAE-GNP suspension and ultrasonically crushed at 100-300 W for 0.5-2 h to obtain a CNF-GNP suspension.

5. The method for preparing a self-healing polyurethane composite material with both thermal conductivity and electromagnetic shielding according to claim 1, characterized in that: The process of step 4 is specifically as follows: Add 10-30g of polytetrahydrofuran and 10-15g of hexamethylene diisocyanate into a three-necked flask, heat to 70-90°C, and react for 0.5-3h; Then add 1-3 g of 2,2-dihydroxymethylbutyric acid and stir for 0.5-3 h, then add 4-6 g of dimethylglyoxime and 5 mL of acetone and continue the reaction for 1-3 h; Then cool the reaction system to 50-70°C, add 1-3 g of triethylamine to the three-necked flask and stir for 20-50 minutes; Finally, 80 to 120 mL of deionized water is added to the mixture, and the mixture is emulsified at a speed of 5,000 to 20,000 r / min using a homogenizer for 5 to 20 minutes. After emulsification, the acetone is removed by rotary evaporation at 30 to 50° C. for 0.5 to 2 hours to obtain a waterborne polyurethane with a solid content of 20 to 50 wt%; Disperse 50-200 mL of the CNF-GNP suspension obtained in step 3 into 2.7 g of waterborne polyurethane WPU and mechanically stir for 3-6 h to obtain a WPU-CNF-GNP mixed solution; The WPU-CNF-GNP mixed solution is filtered, dried in an oven at 40-80°C, and hot pressed at 100-150°C and 5-20 MPa for 20-50 minutes to obtain a polyurethane composite material with excellent thermal conductivity, electromagnetic shielding and self-healing properties.

6. The method for preparing a self-healing polyurethane composite material with both thermal conductivity and electromagnetic shielding according to claim 1, characterized in that: In step 1, polyphenolamine (PPA) is a polymer obtained by reacting phenol and amine; wherein the phenol is one or more of resorcinol, catechol, tannic acid, and dopamine hydrochloride; The amine is one or more of dopamine hydrochloride, diethylenetriamine, triethylenetetramine, tetraethylenepentamine, pentavinylhexylamine, ethylenediamine, o-phenylenediamine, and polyethyleneimine.

7. The method for preparing a self-healing polyurethane composite material with both thermal conductivity and electromagnetic shielding according to claim 1, characterized in that: In step 1, the average horizontal size of the unmodified nanocellulose CNFs was 1–30 μm and the diameter was 1–50 nm; In step 2, the average horizontal size of the unmodified graphene nanosheets GNP is 50-80 μm, and the average thickness is 1-20 nm.

8. The method for preparing a self-healing polyurethane composite material with both thermal conductivity and electromagnetic shielding according to claim 2, characterized in that: The dispersion liquid used is one of anhydrous ethanol, isopropyl alcohol, acetone or deionized water.

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