High-thermal-conductivity polyolefin composite material and preparation method thereof

Abstract

The invention relates to a high thermal conductivity polyolefin composite material, which comprises: a) polyolefin as a matrix; b) a thermally conductive filler; c) maleic anhydride grafted polyolefin; wherein the heat-conducting filler b) and the maleic anhydride grafted polyolefin c) are embedded between the polyolefin a) to form a framework. The invention also relates to a method for preparing the high-thermal-conductivity polyolefin composite material. The polyolefin composite material disclosed by the invention has remarkably improved heat-conducting property.

Description

Technical Field

[0001] The present invention relates to the technical field of polymer molding and processing. Specifically, it relates to polyolefin composites and a preparation method. More specifically, it relates to a highly thermally conductive polyolefin composite and a preparation method. Background Art

[0002] With the continuous development of technology, due to its outstanding advantages such as lightweight, good processability, and low cost, polymer materials have important applications in people's daily lives and social and economic development. In recent years, thermally conductive polymer composites have received increasing attention in emerging fields such as 5G communication, precision electronics, high-speed transportation, and aerospace. Polyolefins, such as polypropylene (PP) and polyethylene (PE), as a widely used general thermoplastic material, have advantages such as low relative density, corrosion resistance, excellent electrical insulation performance, mechanical properties, and recyclability. Therefore, polypropylene and polyethylene have become the most promising thermoplastic polymer materials today and are widely used in fields such as household appliances, automobiles, high-speed rails, and electronic communications. However, the thermal conductivity of polyolefins is small (for example, the thermal conductivity of PP is about 0.2 - 0.3 W·m -1 ·K -1 ), and the thermal conductivity performance is poor, which severely restricts its application and development in fields such as electronic communications, high-temperature media, and energy storage devices.

[0003] In practical applications, filling with thermally conductive fillers is the most commonly used method to improve the thermal conductivity of polymers. Carbon-based materials, ceramic materials, or metal materials (such as graphite, expanded graphite (EG), graphene (Gra), carbon nanotubes (CNT), and boron nitride (BN)) have excellent mechanical strength, electrical conductivity, and thermal conductivity, and are ideal thermally conductive fillers for polyolefins such as PP and PE. However, the interfacial interaction between these thermally conductive fillers and non-polar polyolefin matrices such as PP and PE is weak, and they are extremely easy to agglomerate inside the matrix, making it difficult to achieve high thermal conductivity performance. Therefore, during the preparation of polyolefin thermally conductive composites, it is necessary to perform surface modification or treatment on polyolefins and thermally conductive fillers to promote the uniform dispersion of thermally conductive fillers in the polyolefin matrix and achieve the improvement of the thermal conductivity of polyolefins.

[0004] However, although the prior art has improved the compatibility between the thermal conductive filler and polyolefin to a certain extent, special processing techniques are often required during the preparation process, and the processing technology is complex. The problems that still need to be solved are that during the preparation of the composite material, the thermal conductive filler is easily covered and wrapped by the polymer, making it difficult to form a continuous thermal conductive network in the matrix, and the thermal conductive filler in the composite material agglomerates and has a high interfacial thermal resistance, ultimately making it difficult to achieve high thermal conductivity of the polyolefin material. Summary of the Invention

[0005] To solve the above technical problems, the present invention is proposed. On the one hand, the present invention aims to provide a polyolefin composite material with simple process, low cost, green environmental protection and high thermal conductivity. The polyolefin composite material of the present invention can form an efficient thermal conductive network and has great application potential in the field of high-end thermal management.

[0006] Therefore, an object of the present invention is to provide a polyolefin composite material, comprising:

[0007] a) Polyolefin, as the matrix;

[0008] b) Thermal conductive filler;

[0009] c) Maleic anhydride grafted polyolefin;

[0010] Wherein, the thermal conductive filler b) and the maleic anhydride grafted polyolefin c) are embedded between the polyolefins a) to form a framework.

[0011] In a preferred embodiment of the polyolefin composite material of the present invention, in the polyolefin composite material, the framework is formed by the thermal conductive filler b) and the maleic anhydride grafted polyolefin c) being embedded between the polyolefins a) and connected.

[0012] In a preferred embodiment of the polyolefin composite material of the present invention, the thermal conductive filler b) is substantially not wrapped by the polyolefin a).

[0013] In a preferred embodiment of the polyolefin composite material of the present invention, the thermal conductive filler b) and the maleic anhydride grafted polyolefin c) are first mixed to form a first mixture, and then mixed with the polyolefin a) to form a second mixture.

[0014] Preferably, the thermal conductive filler b) and the maleic anhydride grafted polyolefin c) are mixed in powder form to form a first mixture, and then mixed with the polyolefin a) to form a second mixture.

[0015] In a preferred embodiment of the polyolefin composite material of the present invention, the second mixture is pressed to obtain the polyolefin composite material. Preferably, the pressing temperature is higher than the melting temperature of the maleic anhydride grafted polyolefin c) and close to the melting temperature of the polyolefin a). More preferably, the pressing temperature is 2-10 °C, preferably 3-7 °C higher than the melting temperature of the maleic anhydride grafted polyolefin c) and differs from the melting temperature of the polyolefin a) by 2-10 °C, preferably 2-8 °C and more preferably 2-5 °C.

[0016] In a preferred embodiment of the polyolefin composite material of the present invention, based on 100 parts by weight of the polyolefin a), the heat conductive filler b) is 3-40 parts, preferably 5-35 parts, and the maleic anhydride grafted polyolefin c) is 5-50 parts, preferably 10-40 parts and more preferably 15-30 parts.

[0017] Another object of the present invention is to provide a method for preparing a polyolefin composite material, comprising:

[0018] 1) Mix the heat conductive filler b) and the maleic anhydride grafted polyolefin c) evenly to form a first mixture;

[0019] 2) Mix the first mixture obtained in step 1) with the polyolefin a) evenly to form a second mixture;

[0020] 3) Press the second mixture obtained in step 2) to obtain the polyolefin composite material;

[0021] Wherein, in step 3), the pressing temperature is higher than the melting temperature of the maleic anhydride grafted polyolefin c) and close to the melting temperature of the polyolefin a).

[0022] In a preferred embodiment of the method of the present invention, in step 1), the heat conductive filler b) is mixed with the powder of the maleic anhydride grafted polyolefin c) to form a first mixture.

[0023] In a preferred embodiment of the method of the present invention, in step 3), the pressing temperature is 2-10 °C, preferably 3-7 °C higher than the melting temperature of the maleic anhydride grafted polyolefin c) and differs from the melting temperature of the polyolefin a) by 2-10 °C, preferably 2-8 °C and more preferably 2-5 °C.

[0024] In a preferred embodiment of the method of the present invention, based on 100 parts by weight of the polyolefin a), the heat conductive filler b) is 3-40 parts, preferably 5-35 parts, and the maleic anhydride grafted polyolefin c) is 5-50 parts, preferably 10-40 parts and more preferably 15-30 parts.

[0025] Another object of the present invention is to provide a polyolefin composite material prepared according to the method of the present invention.

[0026] In the polyolefin composite material of the present invention or in the polyolefin composite material obtained by the method of the present invention, maleic anhydride grafted polyolefin and thermal conductive filler are embedded between polyolefins to form a three-dimensional framework structure. By utilizing the interaction of the polar groups of maleic anhydride grafted polyolefin with polyolefin and thermal conductive filler, on the one hand, the interfacial bonding between polyolefin and thermal conductive material is enhanced, and on the other hand, the mutual overlap between thermal conductive fillers is improved, so as to form a multiple thermal conductive network between polyolefins, reduce the scattering of phonons at the interface, and well solve the problem that the thermal conductive filler in the melt blending composite material is easily wrapped by the polymer melt and difficult to form a continuous thermal conductive network, and avoid the agglomeration of thermal conductive filler and high interfacial thermal resistance in the composite material, thereby realizing the high thermal conductivity of polyolefin materials. In addition, the preparation process of the method of the present invention is simple, the cost is low, and it has a good application prospect. Brief Description of the Drawings

[0027] Figure 1 is the DSC melting curve of polypropylene particles and maleic anhydride grafted polypropylene particles.

[0028] Figure 2 is a schematic diagram of the three-dimensional framework structure of the high thermal conductivity polyolefin composite material of the present invention. Detailed Embodiments

[0029] The technical solution of the present invention will be further described in detail below in conjunction with specific embodiments and the accompanying drawings, but the protection scope and implementation manner of the present invention are not limited thereto.

[0030] In this article, unless otherwise specified, all terms and parameters have the meanings commonly understood in the art, all steps are carried out at normal temperature and pressure, and in addition, for steps or processing methods without special instructions, they are carried out in the conventional manner in the art.

[0031] On the one hand, the present invention provides a polyolefin composite material, including:

[0032] a) polyolefin, as the matrix;

[0033] b) thermal conductive filler;

[0034] c) maleic anhydride grafted polyolefin;

[0035] Wherein, the thermal conductive filler b) and the maleic anhydride grafted polyolefin c) are embedded between the polyolefins a) to form a framework.

[0036] In a preferred embodiment of the polyolefin composite material of the present invention, the polyolefin composite material is a high thermal conductivity polyolefin composite material. Preferably, the polyolefin composite material is prepared by a hot pressing method from raw materials including polyolefin, maleic anhydride grafted polyolefin, and a thermal conductive filler. In the polyolefin composite material of the present invention, a three-dimensional structure thermal conductive network is formed with polyolefin as the matrix, and maleic anhydride grafted polyolefin and the thermal conductive filler as the framework.

[0037] In this text, polyolefins may include, for example, polyethylene (PE), polypropylene (PP), polybutylene (PB). Preferably, the polyolefin is a homopolymer or copolymer of α-olefins. The α-olefins are, for example, ethylene, propylene, 1-butene.

[0038] In this text, preferably, the polyolefin is polyethylene or polypropylene. In this text, more preferably, the polyolefin is polypropylene.

[0039] In this text, the thermal conductive filler can be any material used to increase the thermal conductivity of polyolefins. For example, the thermal conductive fillers used in this text can be carbon-based materials, ceramic materials, or metal materials (such as graphite, expanded graphite (EG), graphene (Gra), carbon nanotubes (CNT), and boron nitride (BN), etc.). In a preferred embodiment of the polyolefin composite material of the present invention, the thermal conductive filler is a metal material, such as graphite, expanded graphite (EG), graphene (Gra), carbon nanotubes (CNT), and boron nitride (BN), etc. In a more preferred embodiment of the polyolefin composite material of the present invention, the thermal conductive filler is graphene (Gra).

[0040] In this text, maleic anhydride grafted polyolefin (polyolefin-g-MAH) can be prepared by grafting maleic anhydride onto polyolefin according to the grafting methods commonly used in the art, or commercially available products can be used. In this text, the maleic anhydride grafted polyolefin may have a grafting rate of about 1% - 3%. For example, the maleic anhydride grafted polyolefin used in this text, such as maleic anhydride grafted polypropylene particles 9903 purchased from Maoming Shihua Dongcheng Chemical Co., Ltd., with a melting point of 158 - 162 °C, and maleic anhydride grafted polyethylene particles H542 purchased from Shanghai Yizeng Plasticizing Co., Ltd., with a melting point of 123 - 127 °C.

[0041] In the polyolefin composite material of the present invention, the heat-conducting filler b) and the maleic anhydride-grafted polyolefin c) are embedded between the polyolefins a), forming a framework and forming a continuous three-dimensional heat-conducting network in the polyolefin a). The "framework" refers to being formed by the maleic anhydride-grafted polyolefin and the heat-conducting filler in the polyolefin composite material of the present invention. The polyolefin a) serves as a matrix in the polyolefin composite material of the present invention. Therefore, the polyolefin composite material of the present invention has a three-dimensional structure with polyolefin as the matrix, and the maleic anhydride-grafted polyolefin and the heat-conducting filler as the framework. The "framework" is as Figure 2 shown, where the maleic anhydride-grafted polyolefin 2 and the heat-conducting filler 3 are connected as the framework. Figure 2 In it, the maleic anhydride-grafted polyolefin 2 and the heat-conducting filler 3 are connected as the framework, and the polyolefin 1 serves as the matrix to form a three-dimensional material.

[0042] In this text, the polyolefin in the "maleic anhydride-grafted polyolefin" may have the same meaning as the polyolefin in the above-mentioned "polyolefin". That is to say, the polyolefin described above for "polyolefin" also applies to the polyolefin in the "maleic anhydride-grafted polyolefin". In this text, the polyolefin in the "maleic anhydride-grafted polyolefin" and the polyolefin in the "polyolefin" can be the same polyolefin. Preferably, the polyolefin in the "maleic anhydride-grafted polyolefin" and the polyolefin in the "polyolefin" are the same polyolefin. More preferably, the polyolefin in the "maleic anhydride-grafted polyolefin" and the polyolefin in the "polyolefin" are polyethylene or polypropylene; that is to say, the "maleic anhydride-grafted polyolefin" is polypropylene-graft-maleic anhydride (PP-g-MAH) or polyethylene-graft-maleic anhydride (PE-g-MAH). Even more preferably, the polyolefin in the "maleic anhydride-grafted polyolefin" and the polyolefin in the "polyolefin" are polypropylene; that is to say, the "maleic anhydride-grafted polyolefin" is polypropylene-graft-maleic anhydride (PP-g-MAH).

[0043] In the polyolefin composite material of the present invention, the maleic anhydride-grafted polyolefin and the heat-conducting filler are embedded between the polyolefins to form a three-dimensional framework structure. By utilizing the interaction between the polar groups of the maleic anhydride-grafted polyolefin and the polyolefin and the heat-conducting filler, on the one hand, the interfacial bonding between the polyolefin and the heat-conducting material is enhanced, and on the other hand, the mutual overlap between the stone electric materials is improved to form a multiple heat-conducting network between the polyolefins, reducing the scattering of phonons at the interface, and well solving the problem that the heat-conducting filler in the melt-blended composite material is easily wrapped by the polymer melt and difficult to form a continuous heat-conducting network, and avoiding the agglomeration of the heat-conducting filler and the high interfacial thermal resistance in the composite material, thereby achieving the high heat-conducting performance of the polyolefin material.

[0044] The following description of the structure of the polyolefin composite material of the present invention, although taking PP and PP-g-MAH as examples, is not limited to PP and PP-g-MAH. In fact, the described structure is applicable to all polyolefins described herein.

[0045] For example, in the polyolefin composite material of the present invention, preferably, the polyolefin is polypropylene (PP), and the maleic anhydride grafted polyolefin is maleic anhydride grafted polypropylene (PP-g-MAH). In this way, the formed polyolefin composite material is a polypropylene composite material, with PP as the matrix, and PP-g-MAH and the thermal conductive filler as the framework, forming a three-dimensional material. Due to the three-dimensional framework structure in which PP-g-MAH and the thermal conductive filler are embedded between PP particles, by utilizing the interaction of the polar groups of MAH-g-PP with PP and the thermal conductive filler, on the one hand, the interfacial bonding between PP particles and the thermal conductive filler is enhanced, and on the other hand, the mutual overlap between the thermal conductive fillers is improved, so as to form a multiple thermal conductive network between PP particles, reducing the scattering of phonons at the interface, and well solving the problem that the thermal conductive filler in the melt blending composite material is easily wrapped by the polymer melt and difficult to form a continuous thermal conductive network, and avoiding the agglomeration of the thermal conductive filler and the high interfacial thermal resistance in the composite material, thereby realizing the high thermal conductivity of the polyolefin material.

[0046] For example, in the polyolefin composite material of the present invention, preferably, the polyolefin is polypropylene particles (PP), the maleic anhydride grafted polyolefin is maleic anhydride grafted polypropylene (PP-g-MAH), and the thermal conductive filler is graphene. In this way, the formed polyolefin composite material is a polypropylene composite material, with PP particles as the matrix, and PP-g-MAH and graphene as the framework, forming a three-dimensional material. Due to the three-dimensional framework structure in which PP-g-MAH and graphene are embedded between PP particles, by utilizing the interaction of the polar groups of MAH-g-PP with PP and graphene, on the one hand, the interfacial bonding between PP particles and graphene is enhanced, and on the other hand, the mutual overlap between the graphene sheets is improved, so as to form a multiple thermal conductive network between PP particles, reducing the scattering of phonons at the interface, and well solving the problem that the thermal conductive filler in the melt blending composite material is easily wrapped by the polymer melt and difficult to form a continuous thermal conductive network, and avoiding the agglomeration of the thermal conductive filler and the high interfacial thermal resistance in the composite material, thereby realizing the high thermal conductivity of the polyolefin material.

[0047] In the polyolefin composite material of the present invention, preferably, the framework is formed by the thermal conductive filler b) and the maleic anhydride grafted polyolefin c) being embedded between and connected to the polyolefin a). The maleic anhydride grafted polyolefin and the thermal conductive filler are dispersed in the polyolefin to form a thermal conductive network. The polar groups of the maleic anhydride grafted polyolefin interact with the polyolefin and the thermal conductive filler, on the one hand, enhancing the interfacial bonding between the polyolefin and the thermal conductive filler, and on the other hand, improving the mutual overlap between the thermal conductive fillers, so as to form a multiple thermal conductive network between the polyolefins.

[0048] In this text, the statement that the thermal conductive filler b) and the maleic anhydride grafted polyolefin c) are "embedded in" the polyolefin means that the maleic anhydride grafted polyolefin and the thermal conductive filler are dispersed in the polyolefin serving as the matrix. This dispersion is a tight embedding. This means that in the polyolefin composite material of the present invention, only the outer surface of the polyolefin a) melts during the hot pressing process to ensure the molding of the composite material, while there are boundaries between the internal particles to ensure the smoothness of the graphene heat conduction channels.

[0049] In the polyolefin composite material of the present invention, preferably, the polyolefin is polypropylene particles (PP), and the maleic anhydride grafted polyolefin is maleic anhydride grafted polypropylene (PP-g-MAH). PP-g-MAH and the thermal conductive filler are dispersed in the polyolefin to form a thermal conduction network. The polar groups of PP-g-MAH interact with PP and the thermal conductive filler. On the one hand, it enhances the interfacial bonding between the PP particles and the thermal conductive filler, and on the other hand, it improves the mutual overlap between the thermal conductive fillers to form a multiple thermal conduction network between the PP particles.

[0050] In the polyolefin composite material of the present invention, preferably, the polyolefin is polypropylene (PP), the maleic anhydride grafted polyolefin is maleic anhydride grafted polypropylene (PP-g-MAH), and the thermal conductive filler is graphene. PP-g-MAH and graphene are dispersed in polypropylene to form a thermal conduction network. The polar groups of PP-g-MAH interact with PP and graphene. On the one hand, it enhances the interfacial bonding between the PP particles and graphene, and on the other hand, it improves the mutual overlap between the graphene sheets to form a multiple thermal conduction network between the PP particles.

[0051] Figure 2 A schematic diagram showing the internal structure of the polyolefin composite material of the present invention. Figure 2 In it, the polyolefin 1 serves as the matrix, the maleic anhydride grafted polyolefin 2 and the thermal conductive filler 3 serve as the framework to form a three-dimensional material. The interaction of the polar groups of the maleic anhydride grafted polyolefin with the polyolefin and the thermal conductive filler, on the one hand, enhances the interfacial bonding between the polyolefin and the thermal conductive material, and on the other hand, improves the mutual overlap between the thermal conductive fillers to form a multiple thermal conduction network between the polyolefins, reducing the scattering of phonons at the interface, so that the heat 4 can be well conducted inside the polyolefin composite material of the present invention.

[0052] In the polyolefin composite material of the present invention, more preferably, the thermal conductive filler b) is embedded between the incompletely melted polyolefin a). This embedding is a tight embedding. This means that in the polyolefin composite material of the present invention, only the outer surface of the polyolefin a) melts during the hot pressing process to ensure the molding of the composite material, while there are boundaries between the internal particles to ensure the smoothness of the graphene heat conduction channels.

[0053] In a more preferred embodiment of the polyolefin composite material of the present invention, the heat-conducting filler b) and the maleic anhydride-grafted polyolefin c) are first mixed to form a first mixture, and then mixed with the polyolefin a) to form a second mixture;

[0054] Preferably, the heat-conducting filler b) is mixed with the powder of the maleic anhydride-grafted polyolefin c) to form a first mixture, and then mixed with the polyolefin a) to form a second mixture.

[0055] In this article, the powder of the maleic anhydride-grafted polyolefin c) can be obtained by grinding the maleic anhydride-grafted polyolefin c) particles. The grinding can be carried out using common grinding equipment in the art, such as the YXA-1000 type grinder purchased from Suzhou Shengya Precision Machinery Co., Ltd. The maleic anhydride-grafted polyolefin c) particles are ground to obtain the maleic anhydride-grafted polyolefin c) powder, and the particle size of the obtained powder can be 30-250 mesh, preferably 50-200 mesh.

[0056] In the polyolefin composite material of the present invention, preferably, based on 100 parts by weight of the polyolefin a), the heat-conducting filler b) is 3-40 parts, preferably 5-35 parts, and the maleic anhydride-grafted polyolefin c) is 5-50 parts, preferably 10-40 parts and more preferably 15-30 parts.

[0057] In the polyolefin composite material of the present invention, more preferably, the weight ratio of the heat-conducting filler b) to the maleic anhydride-grafted polyolefin c) is 1-5:1-4, preferably 1-4:1-3, such as 1:2, 2:3, 1:1 or 3:2.

[0058] In the polyolefin composite material of the present invention, preferably, the polyolefin composite material is obtained after pressing the second mixture.

[0059] In the polyolefin composite material of the present invention, more preferably, the pressing temperature is higher than the melting temperature of the maleic anhydride-grafted polyolefin c) and close to the melting temperature of the polyolefin a).

[0060] In this article, "close to" the melting temperature of the polyolefin a) means that since the polyolefin is a polymer and the melting temperature is usually a range, "close to" means pressing at a temperature within ±5°C, preferably ±3°C and more preferably ±2°C of the polyolefin melting temperature range. That is to say, the pressing temperature can be 0-5°C, preferably 2-3°C higher than the lower limit of the polyolefin melting temperature range or 0-5°C, preferably 2-3°C lower than the upper limit. For example, in the case of polypropylene as the polyolefin, the melting temperature of polypropylene is usually 163-168°C, and the pressing temperature can be, for example, 165°C; in the case of polyethylene as the polyolefin, the melting temperature of polyethylene is usually 123-127°C, and the pressing temperature can be, for example, 130°C.

[0061] In an even more preferred embodiment of the polyolefin composite of the present invention, the pressing temperature is 2-10°C, preferably 3-7°C, higher than the melting temperature of the maleic anhydride grafted polyolefin c), and differs from the melting temperature of the polyolefin a) by 2-10°C, preferably 2-8°C, and more preferably 2-5°C.

[0062] The inventors surprisingly found that there is a difference between the melting temperature of the maleic anhydride grafted polyolefin and the melting temperature of the polyolefin, and the melting temperature of the maleic anhydride grafted polyolefin is generally lower than that of the polyolefin. By utilizing the above temperature difference and setting the pressing temperature higher than the melting temperature of the maleic anhydride grafted polyolefin c) and close to the melting temperature of the polyolefin a) in the above manner, during the hot pressing process, the maleic anhydride grafted polyolefin c) is completely melted, while only the outer surface of the polyolefin particles a) is melted and the inside of the particles is not melted. In this way, the melted outer surface ensures the molding of the composite material, and there are boundaries between the un-melted internal particles, ensuring the smoothness of the graphene heat conduction channels.

[0063] Figure 1 The DSC melting curves of, for example, polypropylene particles and maleic anhydride grafted polypropylene particles are shown. Figure 1 The DSC curve of shows that the melting temperature of the maleic anhydride grafted polypropylene particles is lower than that of the polypropylene particles.

[0064] In this article, pressing can be carried out using commonly used pressing equipment in the art, such as the LSV1-25 type flat vulcanizer purchased from Guangzhou Putong Experimental Analysis Instrument Co., Ltd.

[0065] In this article, the pressing temperature is 2-10°C, preferably 3-7°C, higher than the melting temperature of the maleic anhydride grafted polyolefin c), and differs from the melting temperature of the polyolefin a) by 2-10°C, preferably 2-8°C, and more preferably 2-5°C. Specifically, the above temperature difference can be achieved, for example, by setting the temperature of the instrument. For example, when pressing the second mixture, the pressing temperature of the pressing equipment is set to be close to the melting temperature of the polyolefin a), that is, it differs from the melting temperature of the polyolefin a) by 2-10°C, preferably 2-8°C, and more preferably 2-5°C, and is 2-10°C, preferably 3-7°C, higher than the melting temperature of the maleic anhydride grafted polyolefin c).

[0066] In a more preferred embodiment of the polyolefin composite of the present invention, the thermal conductivity of the polyolefin composite is 0.50-9.00 W / (m·K), preferably 3.00-8.50 W / (m·K), more preferably 5.00-8.00 W / (m·K), even more preferably 6.00-8.00 W / (m·K), and still more preferably 6.50-8.00 W / (m·K).

[0067] In a more preferred embodiment of the polyolefin composite material of the present invention, the thermal diffusivity of the polyolefin composite material is 0.30 - 6.00 m 2 / s, preferably 2.00 - 5.50 m 2 / s, more preferably 3.00 - 5.00 m 2 / s, and even more preferably 3.50 - 5.00 m 2 / s.

[0068] In this article, the thermal diffusivity and thermal conductivity of the polyolefin composite material are tested according to the laser flash method specified in GB / T42919.4 - 2023 "Determination of Thermal Conductivity and Thermal Diffusivity of Plastics - Part 4: Laser Flash Method". In this article, the specific test steps for the thermal diffusivity and thermal conductivity of the polyolefin composite material are as follows: First, take a sample block of the polyolefin composite material with a length and width of 10 mm and a thickness of 2 mm; then use a multi-functional electronic density meter to test the density of the sample block; then spray a uniform ink coating with a thickness of 10 - 20 μm on the upper and lower surfaces of the sample block using graphite spray; at a test temperature of 25°C, test the thermal diffusivity and specific heat capacity of the sample block at three different positions of each sample block, calculate the thermal conductivity at the three different positions of the sample block through the formula, and take the average value as the thermal conductivity of the polyolefin composite material.

[0069] The calculation formula for the thermal conductivity of the polyolefin composite material is as follows:

[0070] λ = α·ρ·c p

[0071] Wherein,

[0072] λ is the thermal conductivity, with the unit of W / (m·K);

[0073] α is the thermal diffusivity, with the unit of m 2 / s;

[0074] ρ is the density, with the unit of kg / m 3

[0075] c p is the specific heat capacity, with the unit of J / (kg·K).

[0076] On the other hand, the present invention provides a method for preparing a polyolefin composite material, including:

[0077] 1) Mix the thermal conductive filler b) and the maleic anhydride grafted polyolefin c) evenly to form a first mixture;

[0078] 2) Mix the first mixture obtained in step 1) with the polyolefin a) evenly to form a second mixture;

[0079] 3) Press the second mixture obtained in step 2) to obtain the polyolefin composite material;

[0080] Among them, in step 3), the pressing temperature is higher than the melting temperature of maleic anhydride grafted polyolefin c) and close to the melting temperature of polyolefin a).

[0081] In a preferred embodiment of the method of the present invention, the pressing temperature is close to the melting temperature of polyolefin a) and higher than the melting temperature of maleic anhydride grafted polyolefin c). Preferably, the pressing temperature is 2-10 °C, preferably 3-7 °C higher than the melting temperature of maleic anhydride grafted polyolefin c) and differs from the melting temperature of polyolefin a) by 2-10 °C, preferably 2-8 °C, and more preferably 2-5 °C.

[0082] Step 1)

[0083] In step 1), the heat-conducting filler b) is mixed uniformly with the maleic anhydride grafted polyolefin c) to form a first mixture. The mixing can be carried out using common mixing equipment in the art, such as the XU-DK-008 type ultrasonic mixer purchased from Shanghai Xiniu Laibo Instrument Co., Ltd.

[0084] Step 2)

[0085] In step 2), the first mixture obtained in step 1) is mixed uniformly with polyolefin a) to form a second mixture. The mixing can be carried out using common mixing equipment in the art, such as the DF-101S type magnetic stirrer purchased from Henan Yuhua Instrument Co., Ltd.

[0086] Step 3)

[0087] In step 3), the second mixture obtained in step 2) is pressed to obtain the polyolefin composite material. Herein, the pressing can be carried out using common pressing equipment in the art, such as the LSV1-25 type flat vulcanizer purchased from Guangzhou Putong Experimental Analysis Instrument Co., Ltd.

[0088] In step 3), the pressing temperature is higher than the melting temperature of maleic anhydride grafted polyolefin c) and close to the melting temperature of polyolefin a). Preferably, the pressing temperature is 2-10 °C, preferably 3-7 °C higher than the melting temperature of maleic anhydride grafted polyolefin c) and differs from the melting temperature of polyolefin a) by 2-10 °C, preferably 2-8 °C and more preferably 2-5 °C. Specifically, the above temperature difference can be achieved, for example, by setting the temperature of the instrument. For example, when pressing the second mixture, the pressing temperature of the pressing equipment is set to be close to the melting temperature of polyolefin a), that is, it differs from the melting temperature of polyolefin a) by 2-10 °C, preferably 2-8 °C and more preferably 2-5 °C, and is 2-10 °C, preferably 3-7 °C higher than the melting temperature of maleic anhydride grafted polyolefin c).

[0089] In a preferred embodiment of the method of the present invention, in step 1), the heat-conducting filler b) is mixed with the powder of maleic anhydride grafted polyolefin c) to form a first mixture. Herein, the powder of maleic anhydride grafted polyolefin c) can be obtained by grinding maleic anhydride grafted polyolefin c) particles. The grinding can be carried out using commonly used grinding equipment in the art, such as the YXA-1000 type grinder purchased from Suzhou Shengya Precision Machinery Co., Ltd. The maleic anhydride grafted polyolefin c) particles are ground to obtain the powder of maleic anhydride grafted polyolefin c), and the particle size of the obtained powder can be 30-250 mesh, preferably 50-200 mesh.

[0090] In a preferred embodiment of the method of the present invention, in step 3), the pressing temperature is set according to the specific polyolefin in the manner of "the pressing temperature is higher than the melting temperature of maleic anhydride grafted polyolefin c) and close to the melting temperature of polyolefin a)" described herein. For example, in the case where the polyolefin is polypropylene, the melting point of polypropylene particles is 163-168 °C, and the pressing temperature can be set to 162-170 °C, preferably 162-168 °C and more preferably 163-165 °C; in the case where the polyolefin is polyethylene, the melting point of polyethylene particles is 128-132 °C, and the pressing temperature can be set to 128-138 °C, preferably 128-135 °C and more preferably 130-132 °C.

[0091] In a preferred embodiment of the method of the present invention, based on 100 parts by weight of polyolefin a), the heat-conducting filler b) is 3-40 parts, preferably 5-35 parts, and the maleic anhydride grafted polyolefin c) is 5-50 parts, preferably 10-40 parts and more preferably 15-30 parts. More preferably, the weight ratio of the heat-conducting filler b) to the maleic anhydride grafted polyolefin c) is 1-5:1-4, preferably 1-4:1-3, such as 1:2, 2:3, 1:1 or 3:2.

[0092] In a more preferred embodiment of the method of the present invention, the thermal conductivity of the prepared polyolefin composite is 0.50 - 9.00 W / (m·K), preferably 3.00 - 8.50 W / (m·K), more preferably 5.00 - 8.00 W / (m·K), even more preferably 6.00 - 8.00 W / (m·K), and still more preferably 6.50 - 8.00 W / (m·K).

[0093] In a more preferred embodiment of the method of the present invention, the thermal diffusivity of the prepared polyolefin composite is 0.30 - 6.00 m 2 / s, preferably 2.00 - 5.50 m 2 / s, more preferably 3.00 - 5.00 m 2 / s, and even more preferably 3.50 - 5.00 m 2 / s.

[0094] In the polyolefin composite prepared by the method of the present invention, maleic anhydride grafted polyolefin and the thermal conductive filler are embedded between polyolefins to form a three-dimensional framework structure. By utilizing the interaction between the polar groups of maleic anhydride grafted polyolefin and polyolefin and the thermal conductive filler, on the one hand, the interfacial bonding between polyolefin and the thermal conductive material is enhanced, and on the other hand, the mutual lap between the stone electric materials is improved, so as to form a multiple thermal conductive network between polyolefins, reduce the scattering of phonons at the interface, and well solve the problem that the thermal conductive filler in the melt blending composite is easily wrapped by the polymer melt and difficult to form a continuous thermal conductive network, and avoid the agglomeration of the thermal conductive filler and the high interfacial thermal resistance in the composite material, thereby realizing the high thermal conductivity performance of the polyolefin material.

[0095] On the other hand, the present invention provides a polyolefin composite prepared by the above method, preferred method or more preferred method of the present invention.

[0096] The above-described preferred and more preferred embodiments for the polyolefin composite of the present invention are equally applicable to the method of the present invention and the polyolefin composite prepared by the method of the present invention, and will not be repeated here.

[0097] Examples

[0098] The present invention will be further described below in conjunction with specific embodiments. However, the embodiments provided by the present invention are intended to enable those skilled in the art to know the present invention by way of examples, rather than to limit the present invention in any form.

[0099] Unless otherwise specified, the raw material reagents used in the embodiments of the present invention are conventional raw material reagents purchased.

[0100] Raw material

[0101] Polypropylene granules, T03, melting point 163 - 168 °C, Maoming Shihua Dongcheng Chemical Co., Ltd.;

[0102] Polyethylene granules, M80064, melting point 128 - 132 °C, Maoming Shihua Dongcheng Chemical Co., Ltd.;

[0103] Maleic anhydride grafted polypropylene granules, 9903, melting point 158 - 162 °C, Maoming Shihua Dongcheng Chemical Co., Ltd.;

[0104] Maleic anhydride grafted polyethylene granules, H542, melting point 123 - 127 °C, Shanghai Yizeng Plasticizing Co., Ltd.;

[0105] Graphene, HE - 1, Sichuan Kenye Technology Development Co., Ltd.

[0106] Instrument

[0107] Grinder, YXA - 1000, Suzhou Shengya Precision Machinery Co., Ltd.;

[0108] Ultrasonic mixer, XU - DK - 008, Shanghai Xiniu Laibo Instruments Co., Ltd.;

[0109] Magnetic stirrer, DF - 101S, Henan Yuhua Instruments Co., Ltd.;

[0110] Plate vulcanizer, LSV1 - 25, Guangzhou Putong Experimental Analysis Instruments Co., Ltd.;

[0111] Laser thermal conductivity meter, LAF467, Netzsch Instruments Germany GmbH;

[0112] Multifunctional electronic density meter, MH - 300, Shanghai Lichen Bangxi Instrument Technology Co., Ltd.

[0113] Example 1 of the invention

[0114] The preparation steps of the high - thermal - conductivity polypropylene composite material in this example are as follows:

[0115] Step 1), prepare the first mixture of graphene and maleic anhydride grafted polypropylene (PP - g - MAH).

[0116] Grind the PP - g - MAH granules into a powder with a mesh size of 50 - 200. Add 10 parts by weight of the ground PP - g - MAH powder and 5 parts by weight of graphene to ethanol for ultrasonic mixing. The ultrasonic mixing temperature is 60 °C and the mixing time is 2 hours to obtain a uniform mixture of PP - g - MAH and graphene, which is the first mixture.

[0117] Step 2), prepare the second mixture of polypropylene granules and the first mixture.

[0118] The first mixture of PP-g-MAH and graphene obtained in step 1) is mixed with 100 parts by weight of polypropylene particles under magnetic stirring. The magnetic stirring mixing temperature is 60 °C and the mixing time is 1 hour, so that the mixture of PP-g-MAH and graphene is uniformly dispersed among the PP particles, obtaining a uniform mixture of PP-g-MAH, graphene and PP particles, which is the second mixture.

[0119] Step 3), preparing a highly thermally conductive polypropylene composite material by solid-state hot pressing.

[0120] The second mixture of PP-g-MAH, graphene and PP particles obtained in step 2) is placed in a mold with a length of 10 mm, a width of 10 mm and a thickness of 2 mm, and hot pressing is carried out on a flat vulcanizing machine. The heating temperature of the flat vulcanizing machine is set at 165 °C and the hot pressing time is set at 15 minutes. After hot pressing, a polypropylene composite material with a three-dimensional framework structure in which PP-g-MAH and graphene are embedded among PP particles is prepared.

[0121] Examples 2 - 5 of the invention

[0122] Prepare the polypropylene composite material according to the method of Invention Example 1, except that the amounts of PP-g-MAH, graphene and PP particles are adjusted. The detailed parameters are shown in Table 1 below.

[0123] Example 6 of the invention

[0124] Prepare the polypropylene composite material according to the method of Invention Example 1, except that PE-g-MAH is used instead of PP-g-MAH and a PE matrix is used instead of a PP matrix. The detailed parameters are shown in Table 1 below.

[0125] Comparative Example 1

[0126] This comparative example provides a traditional hot-pressed polypropylene sheet. The preparation steps refer to step 3) of Example 1: Place PP particles in a mold and carry out hot pressing on a flat vulcanizing machine. The heating temperature of the flat vulcanizing machine is set at 165 °C and the hot pressing time is set at 15 minutes. After hot pressing, a pure PP sheet is prepared.

[0127] Comparative Example 2

[0128] The preparation steps of the polypropylene composite material in this comparative example are as follows:

[0129] Step S1), pretreating graphene.

[0130] Add 5 parts by weight of graphene to ethanol and carry out ultrasonic treatment at a temperature of 60 °C for 1 hour to obtain treated graphene.

[0131] Step S2), prepare a mixture of graphene and PP particles.

[0132] Mix the treated graphene obtained in step 1) with 100 parts by weight of polypropylene particles under magnetic stirring. The magnetic stirring mixing temperature is 60°C and the mixing time is 1 hour, so that the graphene mixture is uniformly dispersed among the PP particles to obtain a uniform mixture of graphene and PP particles.

[0133] Step 3), prepare a polypropylene composite by solid-state hot pressing.

[0134] Place the second mixture of graphene and PP particles obtained in step 2) in a mold with a length of 10 mm, a width of 10 mm, and a thickness of 2 mm, and perform hot pressing on a flat vulcanizer. The heating temperature of the flat vulcanizer is set to 165°C and the hot pressing time is set to 15 minutes. After hot pressing, a polypropylene composite of graphene and PP is prepared.

[0135] Comparative Example 3

[0136] Prepare a polypropylene composite according to the method of Invention Example 1, except that the hot pressing temperature is adjusted. The detailed parameters are shown in Table 1 below.

[0137] Comparative Example 4

[0138] Prepare a polypropylene composite according to the method of Invention Example 1, except that PP-g-MAH particles are used instead of PP-g-MAH powder. The detailed parameters are shown in Table 1 below.

[0139] Table 1 Raw material dosages and parameters of each step in the examples and comparative examples of the present invention

[0140]

[0141] Performance test

[0142] Thermal conductivity

[0143] The thermal diffusivity and thermal conductivity of the polyolefin composites prepared in each embodiment of the present invention and the materials prepared in the comparative examples were tested according to the laser flash method specified in GB / T 42919.4-2023 "Plastics - Determination of thermal conductivity and thermal diffusivity - Part 4: Laser flash method". The specific test steps are as follows: First, take a sample block with length, width and thickness of 10 mm, 10 mm and 2 mm respectively; then use a multifunctional electronic density meter to test the density of the sample block; then spray a uniform graphite coating with a thickness of 15 μm on the upper and lower surfaces of the sample block using graphite spray; at a test temperature of 25 °C, test the thermal diffusivity and specific heat capacity of the sample block at three different positions of each sample block, and calculate the thermal conductivity at three different positions of the sample block through the formula, and take the average value as the thermal conductivity of the polyolefin composite material.

[0144] The formula for calculating the thermal conductivity is as follows:

[0145] λ = α·ρ·c p

[0146] Where,

[0147] λ is the thermal conductivity, with the unit of W / (m·K);

[0148] α is the thermal diffusivity, with the unit of m 2 / s;

[0149] ρ is the density, with the unit of kg / m 3

[0150] c p is the specific heat capacity, with the unit of (J / kg·K).

[0151] The specific test results of the thermal conductivity are shown in Table 2.

[0152] Table 2 Thermal conductivity test data of Examples 1-6 and Comparative Examples 1-4 of the present invention

[0153] <![CDATA[Thermal diffusivity, m 2 / s]]> Thermal conductivity, W / (m·K) Example 1 of the invention 0.46 0.88 Example 2 of the invention 1.72 3.27 Example 3 of the invention 2.65 5.04 Example 4 of the invention 4.53 7.80 Example 5 of the invention 3.85 7.23 Example 6 of the invention 3.31 6.28 Comparative Example 1 0.13 0.22 Comparative Example 2 0.31 0.59 Comparative Example 3 2.72 5.17 Comparative Example 4 2.81 6.34

[0154] The test results in Table 2 show that the thermal diffusivity and thermal conductivity of the polypropylene composites in the embodiments of the present invention are significantly improved compared to those of the composites prepared in the comparative examples. In particular, the thermal conductivity of the polypropylene composites prepared in Embodiments 2-5 of the present invention reaches 3.27–7.8 W / (m·K). This is because a three-dimensional framework structure is formed in the polypropylene composite composed of PP-g-MAH / graphene / PP particles, resulting in a high-thermal-conductivity polypropylene composite. Among them, for the composite without PP-g-MAH in Comparative Example 2, the thermal conductivity is 0.59 W / (m·K), while in Example 1 of the invention where PP-g-MAH is added, the thermal conductivity of the prepared polypropylene composite reaches 0.88 W / (m·K), an increase of 50%; this shows that the three-dimensional framework structure constructed in the present invention with PP particles as the matrix and PP-g-MAH and graphene as the framework can well improve the thermal conductivity of polypropylene. As shown in Table 2, the thermal conductivity of the three-dimensional framework structure thermal-conductivity polypropylene composites prepared with different contents of graphene in Examples 1-3 of the invention increases with the increase in the content of graphene, thus proving that the thermal conductivity can be regulated by changing the structure of the thermal conduction network through the content of graphene. In addition, for Examples 4-5 of the invention where the content of PP-g-MAH is changed, the change in the prepared three-dimensional framework structure thermal-conductivity polypropylene composites is not obvious, indicating that PP-g-MAH plays a role in improving the interfacial bonding between PP and graphene, and its content has a better effect within a certain range. The data in the table show that the thermal conductivity of the three-dimensional framework structure thermal-conductivity polypropylene composite prepared in Example 4 can be as high as 7.8 W / (m·K).

[0155] The above embodiments are preferred embodiments of the present invention, but the embodiments of the present invention are not limited to the above embodiments. Any other changes, modifications, substitutions, combinations, and simplifications made without departing from the spirit and principle of the present invention shall be equivalent replacement methods and shall be included in the protection scope of the present invention.

[0156] In addition, each numerical range of the present invention includes any combination of any lower limit and any upper limit mentioned in the specification, and also includes any range formed by the specific content of this component in each specific embodiment as the upper limit or lower limit combination; all these ranges are covered within the scope of the present invention. Only for the sake of saving space, these combined ranges are not listed one by one in the specification. Each feature of the present invention listed in the specification can be combined with any other feature of the present invention, and such combinations are also within the disclosure scope of the present invention; only for the sake of saving space, these combined ranges are not listed one by one in the specification.

Claims

1. A polyolefin composite material comprising: a) polyolefin, as matrix; b) thermally conductive fillers; c) maleic anhydride grafted polyolefin; The thermal conductive filler b) and the maleic anhydride grafted polyolefin c) are embedded between the polyolefin a) to form a frame.

2. The polyolefin composite material according to claim 1, wherein The framework is formed by the thermal conductive filler b) and the maleic anhydride grafted polyolefin c) being embedded between the polyolefin particles a) and connected.

3. The polyolefin composite material according to any one of claims 1 to 2, wherein: The thermally conductive filler b) is substantially not encapsulated by the polyolefin a).

4. The polyolefin composite material according to any one of claims 1 to 3, wherein: The thermally conductive filler b) is first mixed with the maleic anhydride grafted polyolefin c) to form a first mixture, and then mixed with the polyolefin a) to form a second mixture; Preferably, the powder of the thermally conductive filler b) and the maleic anhydride grafted polyolefin c) are first mixed to form a first mixture, and then mixed with the polyolefin a) to form a second mixture.

5. The polyolefin composite material according to any one of claims 1 to 4, wherein: The second mixture is pressed to obtain the polyolefin composite material; Preferably, the pressing temperature is higher than the melting temperature of the maleic anhydride grafted polyolefin c) and close to the melting temperature of the polyolefin a); More preferably, the pressing temperature is 2-10°C, preferably 3-7°C above the melting temperature of the maleic anhydride grafted polyolefin c) and 2-10°C, preferably 2-8°C and more preferably 2-5°C different from the melting temperature of the polyolefin a).

6. The polyolefin composite material according to any one of claims 1 to 5, wherein: Based on 100 parts by weight of the polyolefin a), the thermally conductive filler b) is 3-40 parts, preferably 5-35 parts, and the maleic anhydride grafted polyolefin c) is 5-50 parts, preferably 10-40 parts and more preferably 15-30 parts.

7. A method for preparing a polyolefin composite material, comprising: 1) uniformly mixing the thermal conductive filler b) and the maleic anhydride grafted polyolefin c) to form a first mixture; 2) uniformly mixing the first mixture obtained in step 1) with the polyolefin a), forming a second mixture; 3) pressing the second mixture obtained in step 2) to obtain the polyolefin composite material; Wherein, in step 3), the pressing temperature is higher than the melting temperature of the maleic anhydride grafted polyolefin c) and close to the melting temperature of the polyolefin a); More preferably, the pressing temperature is 2-10°C, preferably 3-7°C above the melting temperature of the maleic anhydride grafted polyolefin c) and 2-10°C, preferably 2-8°C and more preferably 2-5°C different from the melting temperature of the polyolefin a).

8. The method according to claim 7, wherein: In step 1), a thermally conductive filler b) is mixed with a powder of a maleic anhydride grafted polyolefin c) to form a first mixture.

9. The method according to any one of claims 6 to 8, wherein: Based on 100 parts by weight of polyolefin a), the thermally conductive filler b) is 3-40 parts, preferably 5-35 parts, and the maleic anhydride grafted polyolefin c) is 5-50 parts, preferably 10-40 parts and more preferably 15-30 parts.

10. A polyolefin composite material prepared according to the method according to any one of claims 7 to 9.

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