Bi-oriented intrinsic heat-conducting polymer material and preparation method thereof

Abstract

The invention provides a double-orientation intrinsic type heat-conducting polymer material and a preparation method thereof, and relates to the technical field of high polymer materials, and the double-orientation intrinsic type heat-conducting polymer material is prepared by introducing anisotropic amorphous nanophases between in-plane oriented extended chain crystals (ECCs) in a vertical arrangement form. The polyvinylidene fluoride (PVDF) material with a multi-scale structure is prepared by introducing anisotropic amorphous nanophases among in-plane oriented extended chain crystals (ECCs) in a vertical arrangement form, and results show that in-plane and out-plane heat conductivities are respectively improved by 4.35 W m <-1 > K <-1 > and 1.99 W m <-1 > K <-1 >, and in addition, the in-plane and out-plane heat conductivities are improved by 1.99 W m <-1 > K <-1 > and 1.99 W m <-1 > K <-1 >. The unique multi-scale architecture also significantly improves the dimensional stability and thermal stability, the heat dissipation performance of the polymer material is intuitively researched through finite element numerical analysis and heat exchanger application, and a feasible solution is provided for preparing a low-cost intrinsic heat-conducting polymer material from the perspective of practical application.

Description

Technical Field

[0001] The present invention belongs to the technical field of polymer materials, and more specifically, particularly relates to a dual-oriented intrinsic thermal conductive polymer material and a preparation method thereof. Background Art

[0002] Polymer materials have outstanding advantages such as light weight, low cost, easy molding, and corrosion resistance, and are widely used in modern technology. However, there is a key bottleneck of low inherent thermal conductivity (~0.2 W m-1 K-1), which has largely hindered its development in heat-related fields, especially in thermal management. In order to solve the problem of low thermal conductivity, it is a feasible and effective strategy to dope polymers with high thermal conductive fillers such as metals, ceramics, and carbon-based materials to prepare polymer composites. The addition of high thermal conductive fillers can form a permeable thermal conductive network to improve the thermal conductivity of the polymer. At the same time, the use of field orientation, template method and other directional techniques can make the thermal conductive fillers form a heat transfer channel with a specific orientation. However, expensive additives and complex preparation processes will inevitably lead to problems such as increased costs and environmental pollution.

[0003] The researchers proposed that single-chain polymers composed of carbon-carbon covalent bonds have intrinsically high thermal conductivity in the linear orientation direction. The use of advanced technologies such as ultra-stretching, nano-templates and electrospinning can achieve a high degree of orientation of molecular chains, so that pure polymers form nanostructures, thereby obtaining ultra-high thermal conductivity without adding any thermally conductive fillers. The basis of the pure polymer preparation strategy is to minimize chain entanglements from the perspective of structural manipulation to obtain high thermal conductivity. Studies have shown that the crystal structure of extended chain crystals (ECCs) has a smaller number of entanglements and can enhance thermal conductivity by increasing crystallinity. In addition, linear UHMWPE films can obtain ultra-high thermal conductivity through single-oriented crystalline chains and amorphous chains. Therefore, achieving anisotropic or even uniform orientation in the amorphous region is crucial for the preparation of intrinsic thermally conductive polymer materials.

[0004] However, most current research focuses on the design of in-plane structures in pure polymers. During the structure formation process, the thermal conductivity perpendicular to the plane tends to decrease or remain unchanged. Therefore, multi-scale structural regulation and simultaneous improvement of in-plane and out-of-plane thermal conductivity are crucial for expanding the application range of practical thermal management. At present, the design and preparation of multi-scale structures in pure polymers have not been reported.

[0005] In view of this, the present invention is proposed. Summary of the invention

[0006] In order to solve the above technical problems, the present invention provides a dual-oriented intrinsic thermal conductive polymer material and a preparation method thereof to solve the above problems.

[0007] Dual-oriented intrinsic thermally conductive polymer materials are prepared by introducing anisotropic amorphous nanophases in a vertically aligned form between in-plane oriented extended chain crystals (ECCs).

[0008] Another technical problem to be solved by the present invention is to provide a method for preparing a dual-oriented intrinsic thermally conductive polymer material, comprising the following steps: S1: PVDF particles (20 wt%) were dissolved in DMF solvent at 60 °C and stirred for 2 h, then cast into a custom square mold and cooled in liquid nitrogen for 72 h to obtain a casting precursor with a fully interwoven network; S2: The casting precursor was sealed in a horizontal slit with a homemade piston device, melted at 0.1 MPa and 220°C for 20-30 min, then the melt was cooled to 150°C, and horizontal pressure was continuously applied along the slit inlet for 60-90 min to assemble the polymer segments into crystal chains with vertical alignment; S3: The melt was extruded into air (25±3°C) under three pressure conditions (10MPa, 50MPa, 100MPa), horizontally stretched to a uniform state and cooled to form a bi-oriented structure.

[0009] Preferably, during the preparation of the casting precursor, the temperature is 60°C.

[0010] Preferably, the melting time in the slit is 20-30 minutes.

[0011] Preferably, the horizontal pressure is applied in the slit for 60-90 minutes.

[0012] Preferably, the pressure during extrusion is 10 MPa, 50 MPa or 100 MPa.

[0013] Preferably, the cooling temperature after extrusion is 25±3°C.

[0014] Preferably, the constant temperature and constant pressure conditions are controlled by two proportional integral derivative controllers (PID), with errors of ±0.1°C and ±0.035MPa, respectively.

[0015] Compared with the prior art, the present invention has the following beneficial effects: 1. A polyvinylidene fluoride (PVDF) material with a multi-scale structure is prepared by introducing anisotropic amorphous nanophases in a vertically arranged form between in-plane oriented extended chain crystals (ECCs). The results show that the in-plane and out-of-plane thermal conductivities are increased by 4.35 and 1.99 W m-1 K-1, respectively. In addition, this unique multi-scale architecture also significantly improves dimensional stability and thermal stability. Its heat dissipation performance is intuitively studied through finite element numerical analysis and heat exchanger application. The present invention provides a feasible solution for the preparation of low-cost intrinsic thermal conductive polymer materials from the perspective of practical application.

[0016] 2. Based on the dual-orientation structure design in pure PVDF, an intrinsic thermally conductive polymer material was developed to achieve ultra-high thermal conductivity without adding any thermally conductive fillers.

[0017] 3. Use liquid nitrogen cooling technology to cool the PVDF solution to obtain a casting precursor with a fully cross-linked network. The formation of a cross-linked network is conducive to reducing the entanglement of polymer molecular chains and laying the foundation for the realization of high thermal conductivity.

[0018] 4. The pressure-induced technology is used to self-assemble and rearrange the PVDF high-temperature melt, first assembling the polymer chain segments into vertically arranged crystal chains, then horizontally stretching them to an in-plane oriented state and cooling them. Not only are the vertical layered lattices rearranged into horizontally assembled ECCs sheets, but the amorphous chain molecules between different lattice layers are also tightened to form an amorphous arrangement assembly structure oriented in the vertical direction, and finally a dual-oriented intrinsic thermal conductive polymer material is obtained.

[0019] 5. In order to solve the problems of high cost, complex process, environmental pollution, etc. caused by doping high thermal conductive fillers into polymers to prepare high thermal conductive polymer composites, a strategy for preparing dual-oriented intrinsic thermal conductive polymer materials is proposed, so that the polymer can obtain ultra-high thermal conductivity without adding any thermal conductive fillers.

[0020] 6. In view of the problem that existing research focuses on the design of in-plane structures of pure polymers, which leads to the thermal conductivity perpendicular to the plane tending to decrease or remain unchanged, a multi-scale structural design and regulation is proposed to simultaneously improve the in-plane and out-of-plane thermal conductivity of the polymer to meet the application expansion of actual thermal management.

[0021] 7. In view of the fact that most existing technologies only focus on the uniformity of crystal chain orientation, a strategy is proposed to achieve anisotropic or even uniform orientation in the amorphous region, which is crucial for the preparation of intrinsic thermally conductive polymer materials. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 is a cross-sectional SEM image of the intrinsic PVDF material of the present invention; Figure 2is the thermal conductivity of the intrinsic PVDF material in the present invention; Figure 3 is the experimental heat transfer coefficient of PVDF heat exchange application in the present invention; Figure 4 is the thermal stability of the intrinsic thermally conductive PVDF material in the present invention; Figure 5 It is the dimensional stability of the intrinsic thermal conductive PVDF material in the present invention. DETAILED DESCRIPTION

[0023] The following embodiments of the present invention are described in further detail in conjunction with the accompanying drawings and examples. The following examples are used to illustrate the present invention, but are not intended to limit the scope of the present invention.

[0024] See also Figure 1-Figure 5 The present invention provides a dual-oriented intrinsic thermally conductive polymer material, which is prepared by introducing anisotropic amorphous nanophases in a vertically arranged form between in-plane oriented extended chain crystals (ECCs).

[0025] Preparation of intrinsic thermally conductive polymers: The original PVDF has a semi-crystalline structure, with crystalline regions and amorphous regions (non-crystalline regions), and the non-crystalline regions are embedded between the layered crystalline regions, such as Figure 1-Ⅰ First, the polymer chains were made to form a uniform network structure: PVDF particles (20 wt%) were dissolved in DMF solvent at 60 °C and stirred for 2 h, then cast into a custom square mold and cooled in liquid nitrogen for 72 h to obtain a casting precursor with a fully interwoven network ( Figure 1-Ⅱ ).

[0026] Secondly, the casting precursor was sealed in a horizontal slit with a homemade piston device and melted at 0.1 MPa and 220 °C for 20-30 min. The melt was then cooled to 150 °C and horizontal pressure was applied along the slit entrance for 60-90 min to assemble the polymer segments into vertically aligned crystal chains ( Figure 1-III ).

[0027] Finally, the melt was extruded into air (25±3 °C) under three pressure conditions (10, 50, 100 MPa), stretched horizontally to a uniform state and cooled. At this time, not only the layered lattice was rearranged into horizontally assembled ECCs sheets, but also the amorphous chain molecules between different lattice layers were tightened and untied, forming an amorphous arrangement assembly structure oriented in the vertical direction ( Figure 1-IVThe bi-oriented structure was named BONs, and the corresponding samples obtained under different pressures were named BONs-1, BONs-2, and BONs-3. The constant temperature and constant pressure conditions were controlled by two proportional integral differential controllers (PIDs), with errors of ±0.1 °C and ±0.035 MPa, respectively.

[0028] Based on the dual-orientation structure design in pure PVDF, an intrinsic thermally conductive polymer material was developed to achieve ultra-high thermal conductivity without adding any thermally conductive fillers.

[0029] Liquid nitrogen cooling technology is used to cool the PVDF solution to obtain a casting precursor with a fully cross-linked network. The formation of a cross-linked network is conducive to reducing the entanglement of polymer molecular chains, laying the foundation for the realization of high thermal conductivity.

[0030] The pressure-induced technology is used to self-assemble and rearrange the PVDF high-temperature melt, first assembling the polymer chain segments into vertically arranged crystal chains, then horizontally stretching them to an in-plane oriented state and cooling them. Not only does the vertical layered lattice rearrange itself into horizontally assembled ECCs sheets, but the amorphous chain molecules between different lattice layers are also tightened to form an amorphous arrangement assembly structure oriented in the vertical direction, and finally a dual-oriented intrinsic thermal conductive polymer material is obtained.

[0031] The embodiments of the present invention are given for the purpose of illustration and description, and are not intended to be exhaustive or to limit the invention to the disclosed forms. Many modifications and variations will be apparent to those of ordinary skill in the art. The embodiments are selected and described in order to better illustrate the principles and practical applications of the present invention and to enable those of ordinary skill in the art to understand the present invention and thereby design various embodiments with various modifications suitable for specific uses.

Claims

1. Double-oriented intrinsic thermal conductive polymer material, characterized in that: They are prepared by introducing anisotropic amorphous nanophases in a vertically aligned form between in-plane oriented extended-chain crystals (ECCs).

2. A method for preparing a dual-oriented intrinsic thermally conductive polymer material, characterized in that: The following steps are involved: S1: PVDF particles (20 wt%) were dissolved in DMF solvent at 60 °C and stirred for 2 h, then cast into a custom square mold and cooled in liquid nitrogen for 72 h to obtain a casting precursor with a fully interwoven network; S2: The casting precursor was sealed in a horizontal slit with a homemade piston device, melted at 0.1 MPa and 220°C for 20-30 min, then the melt was cooled to 150°C, and horizontal pressure was continuously applied along the slit inlet for 60-90 min to assemble the polymer segments into crystal chains with vertical alignment; S3: The melt was extruded into air (25±3°C) under three pressure conditions (10MPa, 50MPa, 100MPa), horizontally stretched to a uniform state and cooled to form a bi-oriented structure.

3. The method for preparing a dual-oriented intrinsic thermally conductive polymer material according to claim 1, characterized in that: During the preparation of the casting precursor, the temperature was 60°C.

4. The method for preparing a dual-oriented intrinsic thermally conductive polymer material according to claim 1, characterized in that: The melting time in the slit is 20-30 minutes.

5. The method for preparing a dual-oriented intrinsic thermally conductive polymer material according to claim 1, characterized in that: The horizontal pressure is applied in the slit for 60-90 minutes.

6. The method for preparing a dual-oriented intrinsic thermally conductive polymer material according to claim 1, characterized in that: The pressure during extrusion is 10 MPa, 50 MPa or 100 MPa.

7. The method for preparing a dual-oriented intrinsic thermally conductive polymer material according to claim 1, characterized in that: The cooling temperature after extrusion was 25 ± 3 °C.

8. The method for preparing a dual-oriented intrinsic thermally conductive polymer material according to claim 1, characterized in that: Constant temperature and constant pressure conditions were controlled by two proportional integral derivative (PID) controllers with errors of ±0.1°C and ±0.035MPa, respectively. 9 . A dual-oriented intrinsic thermally conductive polymer material prepared according to the method for preparing a dual-oriented intrinsic thermally conductive polymer material according to any one of claims 2 to 8 .

10. Use of the dual-oriented intrinsic thermally conductive polymer material according to claim 1 or 9 in the field of thermal conduction.

Images