Electromagnetic shielding composite material and preparation method thereof

Abstract

The present invention provides an electromagnetic shielding composite material that combines electrical insulation, thermal conductivity, and electromagnetic shielding. The composite material is prepared using conventional melt processing methods, eliminating the need for organic solvents or complex pre- and post-processing procedures. This method requires minimal equipment and is readily commercializable. The resulting product exhibits a "brick-and-mortar"-like, insulated structure, with distinct components fulfilling their respective functions. This significantly reduces the amount of functional filler required, effectively lowering overall costs. Furthermore, the reduced filler content improves overall processability and helps prevent the agglomeration effect of excessive filler addition, which can significantly reduce the mechanical properties of the product.

Description

Technical Field

[0001] The present invention relates to an electromagnetic shielding composite material with both electrical insulation and heat conduction functions and a preparation method thereof, belonging to the technical field of polymer composite materials. Background Art

[0002] With the rapid development of electronic science and technology, various electronic components are finding wider application in advanced and sophisticated fields. In recent years, electronic components have been moving towards high integration, lightweight design, and multifunctionality, placing higher demands on the functionality of supporting components (such as gaskets and heat dissipation films). The high integration of electronic components dictates that supporting parts must first possess high thermal conductivity. Furthermore, to prevent short circuits, these components must be made of insulating materials. Furthermore, to extend component life and ensure stable operation, these supporting parts must also possess certain electromagnetic shielding capabilities. In other words, the target product must simultaneously possess electrical insulation, thermal conductivity, and electromagnetic shielding. Therefore, the advancement of electronic technology will inevitably drive the rapid development of high-performance materials for supporting components.

[0003] Generally speaking, conductive fillers offer both excellent thermal conductivity and electromagnetic shielding properties. Thermally conductive fillers are categorized into two main types: electrically conductive (e.g., metals and carbon-based fillers) and electrically insulating (e.g., boron nitride, silicon nitride, aluminum nitride, and aluminum oxide). Fillers with high-efficiency electromagnetic shielding properties are also typically electrically conductive. Considering the goal of simultaneously balancing these three functions and the difficulty of achieving them, the target product structure must be rationally designed. In order to electrically insulate conductive fillers, materials and products with both electrical insulation and electromagnetic shielding functions currently generally adopt a multi-layer structure similar to a "sandwich", that is, "insulating layer-conductive layer-insulating layer" and so on, to achieve the purpose of electrical insulation and electromagnetic shielding (CN 110257022A, Chemical Engineering Journal 334 (2018) 247-256, Composites Communications 23(2021) 100593, Composites Science and Technology 136 (2016) 104-110). However, the biggest limitation of this method is that the product structure is relatively simple, the process is complicated and the cost is high, and it is difficult to form parts with more complex structures.

[0004] To this end, the present invention proposes a new idea to solve the above-mentioned problems by constructing an isolation structure similar to "brick-mud", in which the conductive and electromagnetic shielding composite material with a higher melting point is the "brick", and the electrically insulating and thermally conductive composite material with a lower melting point is the "mud", thereby achieving multiple functions of electrical insulation, thermal conductivity, and electromagnetic shielding, and the corresponding products can be continuously produced into profiles or heterogeneous complex parts through traditional processing techniques such as extrusion and injection molding. Summary of the Invention

[0005] In view of the deficiencies in the above-mentioned disclosed technologies, the purpose of the present invention is to provide a composite material with electrical insulation, thermal conductivity, and electromagnetic shielding functions and a preparation method thereof. The target product prepared using the technology of the present invention has an isolation structure similar to "brick-mud", in which the harder conductive and electromagnetic shielding composite material is the "brick" and the softer conductive and thermal conductive composite material is the "mud"; the target product can achieve multiple functions of electrical insulation, thermal conductivity, and electromagnetic shielding at the same time; the matrix resin of the target product is an environmentally friendly biodegradable material with a small burden on the environment, which is conducive to promoting the achievement of the national "dual carbon" goals; the target product is simple to prepare, efficient, easy to shape, and has low equipment requirements. It can be widely used in power transmission, electronic devices, aerospace, automobiles and other fields, and is suitable for industrial promotion.

[0006] To achieve the above objectives, the technical solution of the present invention is a composite material with electrical insulation, thermal conductivity, and electromagnetic shielding functions and a preparation method thereof. The raw materials include a polymer A with a relatively high melting point (such as biodegradable general-purpose plastics such as L-polylactic acid (PLLA), stereopolymeric polylactic acid (sc-PLA), or polystyrene (PS)), a filler A with high electrical conductivity (such as carbon-based fillers: multi-walled carbon nanotubes (MWCNTs), graphene nanosheets (GNPs), etc., metal fillers: nanosilver particles, silver nanowires, etc., or two-dimensional transition metal titanium, nitride: MXene, etc.), a polymer B with a relatively low melting point (such as biodegradable polycaprolactone (PCL), polybutylene terephthalate-adipate (PBAT), L-polylactic acid, polybutylene succinate (PBS), etc.) and an insulating filler B with high thermal conductivity (such as boron nitride (BN), silicon nitride (Si3N4), aluminum nitride (AlN), etc.). The melting point difference between the selected polymers A and B is greater than 30°C. The raw materials are mixed uniformly in a certain proportion and then prepared according to the steps of the present invention.

[0007] The letters in the above polymers A, B, fillers A, B are only used to distinguish different materials used in different stages for the convenience of description and have no other special meanings.

[0008] In a first aspect, the present invention provides an electromagnetic shielding composite material, wherein the electromagnetic shielding composite material is prepared by the following method:

[0009] (1) After drying polymer A and filler A separately, melt blending and extruding, pelletizing, crushing, screening, and drying to obtain composite material particles A with a particle size of 100-500 μm; the mass of the filler A is 5%-30% (preferably 10%-20%, most preferably 10%) of the total mass of the polymer A and filler A; the polymer A is one of L-polylactic acid, stereopolylactic acid, and polystyrene (preferably L-polylactic acid or stereopolylactic acid), and the filler A is one of a carbon filler, a metal filler, or a two-dimensional transition metal titanium nitride, or a mixture of two thereof;

[0010] It is known to those skilled in the art that the temperature of the melt blending in step (1) is higher than the melting point of the polymer A.

[0011] The electromagnetic shielding performance of composite materials is partially achieved by multiple reflections between conductive particles. The larger the particles, the fewer conductive particles can be accommodated at the same thickness, which reduces the shielding performance achieved by this multiple reflection. In addition, considering the small internal space of general electronic equipment, particles under 500μm are selected as fillers to ensure that the final composite material has high performance while reducing thickness and volume. Since a small amount of filler will fall off during the pulverization process, in order to prevent the fallen filler from affecting the overall insulation performance of the composite material, it is necessary to screen out a portion of the powder. Since the proportion of particles under 100μ is not high during the pulverization process, only particles under 100μ are screened out to increase production.

[0012] (2) After drying polymer B and filler B separately, melt blending and extruding, pelletizing, and drying to obtain composite material B; the mass of polymer B is 20%-60% (preferably 20%-40%, most preferably 40%) of the total mass of polymer B and filler B; polymer B is one of polycaprolactone, polybutylene terephthalate-adipate, left-handed polylactic acid, and polybutylene succinate (preferably polycaprolactone, polybutylene terephthalate-adipate or left-handed polylactic acid, most preferably polycaprolactone), and filler B is one of boron nitride, silicon nitride, and aluminum nitride or a mixture of two (preferably boron nitride); the melting point of polymer B is at least 30°C lower than the melting point of polymer A in step (1);

[0013] It is known to those skilled in the art that the temperature of the melt blending in step (2) is higher than the melting point of the polymer B.

[0014] (3) The composite material particles A of step (1) and the composite material B of step (2) are mixed, melt-blended, extruded, and pelletized to obtain the electromagnetic shielding composite material; the mass of the composite material particles A is 50%-80% (preferably 80%) of the total mass of the composite material particles A and the composite material B; the temperature of the melt blending in step (3) is greater than the melting point of polymer B and less than the melting point of polymer A.

[0015] In an embodiment of the present invention, the drying in step (1) or (2) is performed in a forced air drying oven. Polymer A is dried at 60°C for 12 hours, filler A is dried at 120°C for 12 hours, and composite material particles A are extruded, pelletized, and crushed and then dried at 60°C for 12 hours. Polymer B is dried at 50°C for 12 hours, filler B is dried at 120°C for 12 hours, and composite material B is extruded, pelletized, and then dried at 50°C for 12 hours. The purpose of drying and drying is to remove moisture from the raw materials.

[0016] Furthermore, the stereopolymer polylactic acid in step (1) is a mixture of L-polylactic acid and D-polylactic acid, and in one embodiment of the present invention, the mass ratio is 1:1. L-polylactic acid and D-polylactic acid will form stereopolymer crystals during the blending process, and the melting point will be greatly increased.

[0017] Furthermore, the pulverization in step (1) is carried out in a high-speed pulverizer at 15,000-30,000 r / min for 10-60 s.

[0018] Furthermore, in step (1), the carbon-based filler is a mixture of one or two of multi-walled carbon nanotubes (MWCNTs) and graphene nanosheets (GNPs), the metal filler is a mixture of one or two of silver nanoparticles and silver nanowires, and the two-dimensional transition metal titanium nitride is MXene.

[0019] In one embodiment of the present invention, the polymer A in step (1) is poly (L-lactic acid), and the weight average molecular weight Mw of the poly (L-lactic acid) (PLLA) is 223,000 g / mol, wherein the content of L-lactic acid is about 98%.

[0020] Furthermore, the melt blending and extrusion in step (1) are carried out in a twin-screw extruder.

[0021] Furthermore, the temperatures of the solid conveying section, melting section and homogenizing section of the twin-screw extruder are set to 150-180° C., 180-190° C. and 170-190° C. respectively.

[0022] Furthermore, the rotational speeds of the mixing screw and the feeding screw are 60-120 rpm and 5-20 rpm respectively.

[0023] Furthermore, the filler A in step (1) is multi-walled carbon nanotubes, and the multi-walled carbon nanotubes (MWCNTs) (purity of about 98%) have a diameter of 1-2 nm and a length of 10-20 μm.

[0024] In one embodiment of the present invention, the polymer B in step (2) is polycaprolactone, and the weight average relative molecular mass Mw of the polycaprolactone (PCL) is 50,000 g / mol.

[0025] Furthermore, the melt blending and extrusion in step (2) are carried out in a twin-screw extruder.

[0026] Furthermore, the solid conveying section, melting section and homogenizing section of the twin-screw extruder are set to have temperature ranges of 50-90° C., 90-100° C. and 100-70° C. respectively.

[0027] Furthermore, the rotational speeds of the mixing screw and the feeding screw are 60-120 rpm and 5-20 rpm respectively.

[0028] Furthermore, the filler B in step (2) is boron nitride, and the boron nitride (BN) is a flaky particle (purity of about 99%) with a size of about 10-15 μm.

[0029] In one embodiment of the present invention, the polymer A is L-polylactic acid, and the polymer B is polycaprolactone. To ensure that A is a solid "brick" and B is a fluid "mud" during blending, the melt blending and extrusion in step (3) are carried out in a twin-screw extruder.

[0030] Furthermore, the temperatures of the solid conveying section, melting section and homogenizing section of the twin-screw extruder are set to 60-100° C., 100-110° C. and 80-110° C. respectively.

[0031] Furthermore, the rotational speeds of the mixing screw and the feeding screw of the twin-screw extruder are 30-60 rpm and 3-10 rpm, respectively.

[0032] The prepared (A)@(B) composite material has an internal isolation structure similar to "brick-and-mortar", in which the continuous phase B wraps and isolates the A particles. The filler B in the continuous phase B overlaps with each other to form a thermal conductivity path, while the filler A in the isolated A particles forms a local conductive and electromagnetic shielding network. The inherent good electrical insulation properties of the composite material B can simultaneously give the (A)@(B) target composite material excellent electrical insulation, thermal conductivity, and electromagnetic shielding functions.

[0033] Compared with shielding composite materials prepared by traditional methods, the preparation method described in the present invention is simple, pollution-free and efficient; it can be produced through various conventional continuous plastic processing equipment, with low equipment requirements, easy product shaping, and easy industrial promotion; the base resin of the target product can be an environmentally friendly biodegradable material, which is conducive to promoting the achievement of the national "dual carbon" goals; the target product has electrical insulation, thermal conductivity, and electromagnetic shielding functions and can achieve coordination between various functions by adjusting the system formula composition, which has obvious advantages over traditional shielding materials.

[0034] Compared with the prior art material preparation technology, the present invention has the following beneficial effects:

[0035] (1) The composite material with electrical insulation, thermal conductivity and electromagnetic shielding functions and the preparation method thereof described in the present invention adopt conventional melt processing methods throughout the process, without the need to add any organic solvents or adopt cumbersome pretreatment and post-treatment methods, with low equipment requirements and easy industrialization.

[0036] (2) The composite material having electrical insulation, thermal conductivity and electromagnetic shielding functions and the preparation method thereof described in the present invention has an internal isolation structure similar to "brick-mud" in which different components perform their respective functions, which greatly reduces the amount of functional fillers added. On the one hand, it can effectively reduce the overall cost. On the other hand, the lower filler addition improves the overall processability and helps to avoid the agglomeration effect caused by the addition of excessive fillers, which leads to a significant decrease in the mechanical properties of the product.

[0037] (3) The composite material having electrical insulation, thermal conductivity and electromagnetic shielding functions and its preparation method described in the present invention, the interior of the obtained product presents an isolation structure similar to "brick-mud". By adjusting the amount of fillers added to the "brick" and "mud" and the mass ratio of the "brick" and "mud", the coordination of the mechanical properties, electrical insulation properties, thermal conductivity and electromagnetic shielding properties of the target composite material can be achieved.

[0038] (4) The composite material with electrical insulation, thermal conductivity and electromagnetic shielding functions and its preparation method described in the present invention, the composite material with a "brick-mud" isolation structure prepared by the present invention has a high electromagnetic shielding efficiency (when the electromagnetic shielding efficiency is greater than 20dB, it can shield more than 99% of electromagnetic waves and meet commercial standards.), while maintaining high electromagnetic shielding efficiency (when the electromagnetic shielding efficiency is greater than 20dB, it can shield more than 99% of electromagnetic waves and meet commercial standards.), improved thermal conductivity, and greatly increased resistivity to the insulation standard (10 9Ω·cm). For example, in Example 3 of the present invention, when MWCNT accounts for 10% of the mass fraction of PLLA / MWCNT, BN accounts for 40% of the mass fraction of PCL / BN, and the mass ratio of PLLA / MWCNT to PCL / BN is 80:20, the electromagnetic shielding effectiveness, thermal conductivity, and resistivity of the composite material with a "brick-and-mortar" isolation structure are 28.29 dB, 0.60 W·m -1 ·k -1 , 7.24×10 11 Ω·cm. In summary, it is not difficult to find that the composite material with electrical insulation, thermal conductivity and electromagnetic shielding functions described in the present invention has excellent key performance indicators, and the preparation method is green, simple and feasible, which has obvious advantages over the existing technology. BRIEF DESCRIPTION OF THE DRAWINGS

[0039] Figure 1 This is a cross-sectional scanning electron microscope image of the (PLLA / MWCNT)@(PCL / BN) composite material prepared in Example 1;

[0040] Figure 2 This is a cross-sectional scanning electron microscope image of the (PLLA / MWCNT)@(PCL / BN) composite material prepared in Example 2;

[0041] Figure 3 This is a cross-sectional scanning electron microscope image of the (PLLA / MWCNT)@(PCL / BN) composite material prepared in Example 3;

[0042] Figure 4 This is a scanning electron microscope image of the cross section of the PLLA / PCL / MWCNT / BN composite material prepared in Comparative Example 1;

[0043] Figure 5 This is a cross-sectional scanning electron microscope image of the PLLA / PCL / MWCNT / BN composite material prepared in Comparative Example 2;

[0044] Figure 6 This is a cross-sectional scanning electron microscope image of the PLLA / PCL / MWCNT / BN composite material prepared in Comparative Example 3. DETAILED DESCRIPTION

[0045] The present invention will be described in detail below by way of examples. It is necessary to point out that the following examples are only for

[0046] The above is for further explanation of the present invention and should not be construed as limiting the scope of protection of the present invention. Non-essential improvements and adjustments made by persons skilled in the art based on the above invention still fall within the scope of protection of the present invention.

[0047] Example 1

[0048] This embodiment is a method for preparing a (PLLA / MWCNT)@(PCL / BN) composite material, and the steps are as follows:

[0049] (1) Preparation of PLLA / MWCNT composites: PLLA (NatureWorks 4032D, USA) and MWCNT (NC7000) were dried at 60°C and 120°C for 12 hours, respectively, and then melt-blended in a twin-screw extruder at a mass ratio of 95:5 to obtain PLLA / MWCNT composites. The temperatures of the solid conveying section, melting section, and homogenizing section were set at 150-180°C, 180-190°C, and 170-190°C, respectively. The speeds of the mixing screw and feeding screw of the extruder were 80 rpm and 15 rpm, respectively. The extrudate was pelletized and dried at 60°C for later use.

[0050] (2) Crushing and screening the PLLA / MWCNT composite material: The prepared PLLA / MWCNT composite material was crushed using a high-speed crusher at a speed of 28,000 rpm for 30 seconds, and composite material particles with a particle size of 100-500 μm were screened out and dried at 60°C for later use;

[0051] (3) Preparation of PCL / BN composite materials: PCL (Perstorp 6500, Sweden) and BN (10-15 μm, Shandong Pengcheng Special Ceramics Co., Ltd.) were dried at 50 °C and 120 °C for 12 h, respectively, and then melt-blended in a twin-screw extruder at a mass ratio of 80:20 to obtain PCL / BN composite materials. The temperatures of the solid conveying section, melting section, and homogenization section were set at 50-90 °C, 90-100 °C, and 70-100 °C, respectively. The speeds of the mixing screw and feeding screw of the extruder were 80 rpm and 15 rpm, respectively. The extrudate was pelletized and dried at 50 °C for later use.

[0052] (4) Preparation of (PLLA / MWCNT)@(PCL / BN) composite material: The prepared PLLA / MWCNT composite material particles were mixed with PCL / BN composite material in a mass ratio of 80:20, and melt-blended using a twin-screw extruder to obtain a (PLLA / MWCNT)@(PCL / BN) composite material with a "brick-mud" isolation structure and electrical insulation, thermal conductivity, and electromagnetic shielding functions. The temperatures of the solid conveying section, melting section, and homogenization section were set to 60-100°C, 100-110°C, and 80-110°C, respectively. The speeds of the extruder mixing screw and feeding screw were 45 rpm and 8 rpm, respectively.

[0053] Example 2

[0054] This embodiment is a method for preparing a (PLLA / MWCNT)@(PCL / BN) composite material, and the steps are as follows:

[0055] (1) Preparation of PLLA / MWCNT composite materials: PLLA and MWCNT were dried at 60°C and 120°C for 12 hours, respectively, and then melt-blended in a twin-screw extruder at a mass ratio of 90:10 to obtain PLLA / MWCNT composite materials. The temperatures of the solid conveying section, melting section, and homogenizing section were set at 150-180°C, 180-190°C, and 170-190°C, respectively. The speeds of the mixing screw and feeding screw of the extruder were 80 rpm and 15 rpm, respectively. The extrudate was pelletized and dried at 60°C for later use.

[0056] (2) Crushing and screening the PLLA / MWCNT composite material: The prepared PLLA / MWCNT composite material was crushed using a high-speed crusher at a speed of 28,000 rpm for 30 seconds, and composite material particles with a particle size of 100-500 μm were screened out and dried at 60°C for later use;

[0057] (3) Preparation of PCL / BN composite material: PCL and BN were dried at 50°C and 120°C for 12 hours, respectively, and then melt-blended in a twin-screw extruder at a mass ratio of 80:20 to obtain PCL / BN composite material. The temperatures of the solid conveying section, melting section, and homogenization section were set to 50-90°C, 90-100°C, and 70-100°C, respectively. The speeds of the mixing screw and feeding screw of the extruder were 80 rpm and 15 rpm, respectively. The extrudate was pelletized and dried at 50°C for later use.

[0058] (4) Preparation of (PLLA / MWCNT)@(PCL / BN) composite material: The prepared PLLA / MWCNT composite material particles were mixed with PCL / BN composite material in a mass ratio of 80:20, and melt-blended using a twin-screw extruder to obtain a (PLLA / MWCNT)@(PCL / BN) composite material with a "brick-mud" isolation structure and electrical insulation, thermal conductivity, and electromagnetic shielding functions. The temperatures of the solid conveying section, melting section, and homogenization section were set to 60-100°C, 100-110°C, and 80-110°C, respectively. The speeds of the extruder mixing screw and feeding screw were 45 rpm and 8 rpm, respectively.

[0059] Example 3

[0060] This embodiment is a method for preparing a (PLLA / MWCNT)@(PCL / BN) composite material, and the steps are as follows:

[0061] (1) Preparation of PLLA / MWCNT composite materials: PLLA and MWCNT were dried at 60°C and 120°C for 12 hours, respectively, and then melt-blended in a twin-screw extruder at a mass ratio of 90:10 to obtain PLLA / MWCNT composite materials. The temperatures of the solid conveying section, melting section, and homogenizing section were set at 150-180°C, 180-190°C, and 170-190°C, respectively. The speeds of the mixing screw and feeding screw of the extruder were 80 rpm and 15 rpm, respectively. The extrudate was pelletized and dried at 60°C for later use.

[0062] (2) Crushing and screening the PLLA / MWCNT composite material: The prepared PLLA / MWCNT composite material was crushed using a high-speed crusher at a speed of 28,000 rpm for 30 seconds, and composite material particles with a particle size of 100-500 μm were screened out and dried at 60°C for later use;

[0063] (3) Preparation of PCL / BN composite material: PCL and BN were dried at 50°C and 120°C for 12 hours, respectively, and then melt-blended in a twin-screw extruder at a mass ratio of 60:40 to obtain PCL / BN composite material. The temperatures of the solid conveying section, melting section, and homogenization section were set to 50-90°C, 90-100°C, and 70-100°C, respectively. The speeds of the mixing screw and feeding screw of the extruder were 80 rpm and 15 rpm, respectively. The extrudate was pelletized and dried at 50°C for later use.

[0064] (4) Preparation of (PLLA / MWCNT)@(PCL / BN) composite material: The prepared PLLA / MWCNT composite material particles were mixed with PCL / BN composite material in a mass ratio of 80:20, and melt-blended using a twin-screw extruder to obtain a (PLLA / MWCNT)@(PCL / BN) composite material with a "brick-mud" isolation structure and electrical insulation, thermal conductivity, and electromagnetic shielding functions. The temperatures of the solid conveying section, melting section, and homogenization section were set to 60-100°C, 100-110°C, and 80-110°C, respectively. The speeds of the extruder mixing screw and feeding screw were 45 rpm and 8 rpm, respectively.

[0065] Example 4

[0066] This embodiment is a method for preparing a (sc-PLA / MWCNT)@(PLLA / BN) composite material, and the steps are as follows:

[0067] (1) Preparation of sc-PLA / MWCNT composites: PLLA, PDLA, and MWCNT were dried at 60°C and 120°C for 12 hours, respectively, and then melt-blended in a twin-screw extruder at a mass ratio of 45:45:10 to obtain a PLLA / MWCNT composite. The temperatures of the solid conveying section, melting section, and homogenization section were set at 160-190°C, 190-240°C, and 240-230°C, respectively. The speeds of the mixing screw and feeding screw of the extruder were 80 rpm and 15 rpm, respectively. The extrudate was pelletized and dried at 60°C for later use.

[0068] (2) Crushing and screening the sc-PLA / MWCNT composite material: The prepared sc-PLA / MWCNT composite material was crushed using a high-speed crusher at a speed of 28,000 rpm for 20 seconds, and composite material particles with a particle size of 100-500 μm were screened out and dried at 60°C for later use;

[0069] (3) Preparation of PLLA / BN composite material: PLLA and BN were dried at 60°C and 120°C for 12 hours, respectively, and then melt-blended in a twin-screw extruder at a mass ratio of 60:40 to obtain PLLA / BN composite material. The temperatures of the solid conveying section, melting section, and homogenizing section were set to 150-180°C, 180-190°C, and 170-190°C, respectively. The speeds of the mixing screw and feeding screw of the extruder were 80 rpm and 15 rpm, respectively. The extrudate was pelletized and dried at 60°C for later use.

[0070] (4) Preparation of (sc-PLA / MWCNT)@(PLLA / BN) composite material: The prepared sc-PLA / MWCNT composite material particles were mixed with the PLLA / BN composite material in a mass ratio of 80:20, and melt-blended using a twin-screw extruder to obtain a (sc-PLA / MWCNT)@(PLLA / BN) composite material with a "brick-mud" isolation structure and electrical insulation, thermal conductivity, and electromagnetic shielding functions. The temperatures of the solid conveying section, melting section, and homogenization section were set to 150-180°C, 180-190°C, and 170-190°C, respectively. The speeds of the extruder mixing screw and feeding screw were 45 rpm and 8 rpm, respectively.

[0071] Example 5

[0072] This embodiment is a method for preparing a (PLLA / MWCNT)@(PBAT / BN) composite material, and the steps are as follows:

[0073] (1) Preparation of PLLA / MWCNT composite materials: PLLA and MWCNT were dried at 60°C and 120°C for 12 hours, respectively, and then melt-blended in a twin-screw extruder at a mass ratio of 90:10 to obtain PLLA / MWCNT composite materials. The temperatures of the solid conveying section, melting section, and homogenizing section were set at 150-180°C, 180-190°C, and 170-190°C, respectively. The speeds of the mixing screw and feeding screw of the extruder were 80 rpm and 15 rpm, respectively. The extrudate was pelletized and dried at 60°C for later use.

[0074] (2) Crushing and screening the PLLA / MWCNT composite material: The prepared PLLA / MWCNT composite material was crushed using a high-speed crusher at a speed of 28,000 rpm for 30 seconds, and composite material particles with a particle size of 100-500 μm were screened out and dried at 60°C for later use;

[0075] (3) Preparation of PBAT / BN composite material: PBAT and BN were dried at 60°C and 120°C for 12 hours, respectively, and then melt-blended in a twin-screw extruder at a mass ratio of 60:40 to prepare the PBAT / BN composite material. The temperatures of the solid conveying section, melting section, and homogenizing section were set at 90-110°C, 110-140°C, and 130-140°C, respectively. The speeds of the mixing screw and feeding screw of the extruder were 80 rpm and 15 rpm, respectively. The extrudate was pelletized and dried at 60°C for later use.

[0076] (4) Preparation of (PLLA / MWCNT)@(PBAT / BN) composite material: The prepared PLLA / MWCNT composite material particles were mixed with the PBAT / BN composite material in a mass ratio of 80:20, and melt-blended using a twin-screw extruder to obtain a (PLLA / MWCNT)@(PBAT / BN) composite material having a "brick-mud" isolation structure and having electrical insulation, thermal conductivity, and electromagnetic shielding functions. The temperatures of the solid conveying section, melting section, and homogenization section were set to 90-110°C, 110-130°C, and 120-130°C, respectively. The speeds of the extruder mixing screw and feeding screw were 45 rpm and 8 rpm, respectively.

[0077] Comparative Example 1

[0078] This comparative example is a method for preparing a PLLA / PCL / MWCNT / BN composite material, and the steps are as follows:

[0079] PLLA, PCL, MWCNT, and BN were dried at 60°C, 50°C, 120°C, and 120°C for 12 hours, respectively, and then melt-blended in a twin-screw extruder at a mass ratio of 76:16:4:4 to prepare a PLLA / PCL / MWCNT / BN composite material. The temperatures of the solid conveying section, melting section, and homogenization section were set at 150-180°C, 180-190°C, and 170-190°C, respectively. The speeds of the extruder mixing screw and feeding screw were 80 rpm and 15 rpm, respectively.

[0080] Comparative Example 2

[0081] This comparative example is a method for preparing a PLLA / PCL / MWCNT / BN composite material, and the steps are as follows:

[0082] PLLA, PCL, MWCNT, and BN were dried at 60°C, 50°C, 120°C, and 120°C for 12 hours, respectively, and then melt-blended in a twin-screw extruder at a mass ratio of 72:16:8:4 to prepare a PLLA / PCL / MWCNT / BN composite material. The temperatures of the solid conveying section, melting section, and homogenization section were set at 150-180°C, 180-190°C, and 170-190°C, respectively. The speeds of the extruder mixing screw and feeding screw were 80 rpm and 15 rpm, respectively.

[0083] Comparative Example 3

[0084] This comparative example is a method for preparing a PLLA / PCL / MWCNT / BN composite material, and the steps are as follows:

[0085] PLLA, PCL, MWCNT, and BN were dried at 60°C, 50°C, 120°C, and 120°C for 12 hours, respectively, and then melt-blended in a twin-screw extruder at a mass ratio of 72:12:8:8 to prepare a PLLA / PCL / MWCNT / BN composite material. The temperatures of the solid conveying section, melting section, and homogenization section were set at 150-180°C, 180-190°C, and 170-190°C, respectively. The speeds of the extruder mixing screw and feeding screw were 80 rpm and 15 rpm, respectively.

[0086] Table 1 Comparison of properties of the composite materials prepared in Examples 1-5 and Comparative Examples 1-3 (including electrical insulation properties, thermal conductivity and electromagnetic shielding effectiveness)

[0087]

Claims

1. An electromagnetic shielding composite material, characterized in that The electromagnetic shielding composite material is prepared by the following method: (1) After drying polymer A and filler A separately, melt blending and extruding, pelletizing, crushing, screening, and drying to obtain composite material particles A with a particle size of 100-500 μm; the mass of the filler A is 5%-30% of the total mass of the polymer A and filler A; the polymer A is one of L-polylactic acid, stereopolylactic acid, and polystyrene, and the filler A is one of a carbon filler, a metal filler, or a two-dimensional transition metal titanium nitride, or a mixture of two thereof; (2) After drying polymer B and filler B separately, melt-blending and extruding, pelletizing, and drying to obtain composite material B; the mass of polymer B is 20%-60% of the total mass of polymer B and filler B; polymer B is one of polycaprolactone, polybutylene terephthalate-adipate, polylactic acid, and polybutylene succinate, and filler B is one of boron nitride, silicon nitride, and aluminum nitride or a mixture of two; the melting point of polymer B is at least 30°C lower than the melting point of polymer A in step (1); (3) The composite material particles A described in step (1) are mixed with the composite material B described in step (2), melt-blended, extruded, and pelletized to obtain the electromagnetic shielding composite material; the mass of the composite material particles A is 50%-80% of the total mass of the composite material particles A and the composite material B; the temperature of the melt blending in step (3) is greater than the melting point temperature of the polymer B described in step (2) and less than the melting point temperature of the polymer A described in step (1).

2. The electromagnetic shielding composite material according to claim 1, wherein: The mass of the filler A in step (1) is 10%-20% of the total mass of the polymer A and the filler A.

3. The electromagnetic shielding composite material according to claim 1, wherein: In step (1), the carbon-based filler is a mixture of one or two of multi-walled carbon nanotubes and graphene nanosheets, the metal filler is a mixture of one or two of nanosilver particles and silver nanowires, and the two-dimensional transition metal titanium nitride is MXene.

4. The electromagnetic shielding composite material according to claim 1, wherein: The polymer A in step (1) is L-polylactic acid with a weight-average relative molecular mass Mw of 223,000 g / mol.

5. The electromagnetic shielding composite material according to claim 4, wherein: The melt blending and extrusion in step (1) are carried out in a twin-screw extruder; the temperatures of the solid conveying section, melting section, and homogenizing section of the twin-screw extruder are set to 150-180°C, 180-190°C, and 170-190°C, respectively, and the speeds of the mixing screw and feeding screw are 60-120 rpm and 5-20 rpm, respectively.

6. The electromagnetic shielding composite material according to claim 1, wherein: The filler A in step (1) is a multi-walled carbon nanotube, and the multi-walled carbon nanotube has a diameter of 1-2 nm and a length of 10-20 μm.

7. The electromagnetic shielding composite material according to claim 1, wherein: The polymer B in step (2) is polycaprolactone with a weight-average molecular weight Mw of 50,000 g / mol.

8. The electromagnetic shielding composite material according to claim 7, wherein: The melt blending and extrusion in step (2) are carried out in a twin-screw extruder; the solid conveying section, melting section, and homogenizing section of the twin-screw extruder are set to a temperature range of 50-90°C, 90-100°C, and 100-70°C, respectively, and the speeds of the mixing screw and the feeding screw are 60-120 rpm and 5-20 rpm, respectively.

9. The electromagnetic shielding composite material according to claim 1, wherein: The filler B in step (2) is boron nitride.

10. The electromagnetic shielding composite material according to claim 1, wherein: The polymer A is L-polylactic acid, and the polymer B is polycaprolactone. The melt blending and extrusion in step (3) are carried out in a twin-screw extruder. The temperatures of the solid conveying section, the melting section, and the homogenizing section of the twin-screw extruder are set to 60-100° C., 100-110° C., and 80-110° C., respectively; the speeds of the mixing screw and the feeding screw of the twin-screw extruder are 30-60 rpm and 3-10 rpm, respectively.

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