Method for improving thermal conductivity of polymer material and polymer material thereof

Abstract

The invention discloses a method for improving the thermal conductivity of a polymer material and the polymer material thereof.The method comprises the following steps that the polymer material is prepared through the following steps that a polymer fiber bundle is woven, and polymer fibers are obtained; and carrying out hot pressing treatment on the polymer fibers to obtain the polymer material. According to the method, molecular chains are highly and orderly arranged through weaving treatment, so that the thermal conductivity of the polymer is remarkably improved, meanwhile, the excellent electromagnetic wave transmittance is kept, and the thermal conductivity of the material can be adjusted and the requirements of different heat dissipation scenes can be met by adjusting and controlling the weaving density and hot pressing parameters.

Description

Technical Field

[0001] This application relates to the technical field of polymer heat dissipation material preparation processes, and particularly relates to a method for improving the thermal conductivity of polymer materials and the polymer materials thereof. Background Art

[0002] Developing efficient thermal management technology is a key technical guarantee for the miniaturization, integration, and high performance of chips. The power consumption density inside the chips has soared all the way with the achievement of Moore's Law. The thermal power consumption of high-performance GPU and CPU chips has exceeded 800W and 300W respectively, and is about to break through the kW level. And as the temperature rises by 10°C, the computing speed of the chips will decrease by 1.4%, and the failure rate will increase by 10%. Therefore, efficient thermal management technology plays a key role in improving the computing performance and stability of electronic devices.

[0003] Traditional high-power heat dissipation methods mainly transfer the heat generated by the chips to low-temperature areas by using metal heat spreaders or heat pipes, and then use heat exchangers or directly increase the heat transfer area to achieve higher heat dissipation power. However, the high cost, large weight, and low electromagnetic wave transmittance of metal materials make the heat dissipation system based on metal materials not conducive to being applied in small-sized and communication electronic devices. While polymer materials have excellent electrical insulation properties, mechanical properties, electromagnetic wave transmission properties, as well as chemical stability and economy, but the thermal conductivities of existing polymer materials are generally low.

[0004] Therefore, the method for improving the thermal conductivity of polymer materials needs to be further studied. Summary of the Invention

[0005] This application aims to solve at least one of the technical problems existing in the prior art to some extent. For this reason, this application provides a method for improving the thermal conductivity of polymer materials and the polymer materials thereof. This method makes the molecular chains highly ordered through weaving treatment, thereby significantly improving the thermal conductivity of the polymer, while maintaining excellent electromagnetic wave transmittance. By adjusting the weaving density and hot pressing parameters, the thermal conductivity of the material can be adjusted to meet the requirements of different heat dissipation scenarios.

[0006] In the first aspect of the present application, a method for improving the thermal conductivity of a polymer material is proposed, which is characterized by including the following steps to prepare the polymer material: weaving a polymer fiber bundle to obtain polymer fibers; and thermally pressing the polymer fibers to obtain the polymer material. Thus, the thermal conductivity of the polymer material is improved through weaving and thermocompression treatment. The weaving treatment constructs a highly ordered arrangement of molecular chains by weaving the polymer fiber bundle into an intertwined structure, providing an efficient molecular chain network for heat conduction; the thermocompression treatment melts and fuses the fiber surface through high temperature and high pressure, further enhancing the binding force between molecular chains, while retaining the molecular chain order inside the fibers, reducing the interfacial thermal resistance, and improving the thermal conductivity of the material.

[0007] According to an embodiment of the present application, the raw materials of the polymer fiber bundle include ultra-high molecular weight polyethylene, homopolypropylene, copolymerized polypropylene, polyamide 6, polyamide 66, polyethylene terephthalate, polyethylene naphthalate, polylactic acid, polyether ether ketone, and polybutylene terephthalate; preferably ultra-high molecular weight polyethylene.

[0008] According to an embodiment of the present application, the weaving treatment includes plain weaving or parallel arrangement.

[0009] According to an embodiment of the present application, the warp-to-weft ratio of the plain weaving is (2 - 4):1.

[0010] According to an embodiment of the present application, the temperature of the thermocompression treatment is 130 - 160 °C.

[0011] According to an embodiment of the present application, the pressure of the thermocompression treatment is 8 - 12 MPa.

[0012] According to an embodiment of the present application, the time of the thermocompression treatment is 1 - 5 min.

[0013] According to an embodiment of the present application, the polymer fibers are mixed with a thermal conductive material, and then the obtained mixture is subjected to the thermocompression treatment to obtain the polymer material doped with the thermal conductive material; the thermal conductive material includes at least one of boron nitride, graphene, carbon nanotubes, and metal particles; preferably boron nitride; and / or, the doping amount of the thermal conductive material in the polymer material is 5% - 35 wt%.

[0014] According to an embodiment of the present application, before the weaving treatment, the polymer fiber bundle is wound.

[0015] According to an embodiment of the present application, the winding treatment is carried out by a constant tension winding device.

[0016] According to an embodiment of the present application, the draw ratio of the winding treatment is 1:(1.3 - 1.7); preferably 1:1.5.

[0017] According to an embodiment of the present application, before performing the hot pressing treatment, 2 to 5 pieces of the polymer fibers are stacked.

[0018] According to an embodiment of the present application, the diameter of the polymer fiber bundle is 20 to 30 μm.

[0019] According to an embodiment of the present application, the thickness of the polymer material is 50 to 800 μm.

[0020] In a second aspect of the present application, the present application provides a polymer material. According to an embodiment of the present application, the polymer material is prepared by the method described in the first aspect.

[0021] Additional aspects and advantages of the present application will be given in part in the following description, become apparent in part from the following description, or be learned through the practice of the present application. Description of the Drawings

[0022] The above and / or additional aspects and advantages of the present application will become apparent and be readily understood from the description of the embodiments in conjunction with the following drawings, where:

[0023] Figure 1 is a schematic diagram of the process flow in an embodiment of the present application;

[0024] Figure 2 is a diagram of the thermal conductivity measurement method in a test example of the present application, where Figure 2 (a) is a schematic diagram of a T-shaped method thermal conductivity test sample; Figure 2 (b) is a physical diagram;

[0025] Figure 3 is a diagram of the electromagnetic wave transmittance measurement results in a test example of the present application. Detailed Description of the Embodiments

[0026] Embodiments of the present application will be described in detail below. The embodiments described below are exemplary and are only used to explain the present application and should not be construed as a limitation to the present application.

[0027] It should be noted that the terms "first" and "second" are only used for descriptive purposes and cannot be construed as indicating or implying relative importance or implicitly indicating the number of the indicated technical features. Thus, the features defined with "first" and "second" may explicitly or implicitly include one or more of such features. Further, in the description of the present application, unless otherwise specified, the meaning of "a plurality" is two or more.

[0028] The endpoints and any values in the ranges disclosed herein are not limited to the exact ranges or values, and these ranges or values should be understood to include values close to these ranges or values. For numerical ranges, the endpoint values of each range, between the endpoint values of each range and individual point values, and between individual point values can be combined with each other to obtain one or more new numerical ranges, and these numerical ranges should be regarded as specifically disclosed herein.

[0029] As used herein, the term "comprising" or "including" is an open-ended expression, that is, it includes the content specified in this application, but does not exclude other aspects of the content.

[0030] As used herein, the terms "optionally", "optional" or "option" generally mean that the subsequent events or conditions may but do not necessarily occur, and this description includes the cases where the events or conditions occur and the cases where the events or conditions do not occur.

[0031] Terms and Definitions

[0032] As used herein, the term "warp-to-weft ratio" is the ratio of the warp density to the weft density; the warp is the yarn arranged longitudinally in the fabric, and the warp is fixed during the weaving process and extends along the length direction of the fabric; the weft is the yarn arranged transversely in the fabric, and is usually introduced into the fabric by a shuttle or a weft feeding device of a loom.

[0033] Methods for Improving the Thermal Conductivity of Polymer Materials

[0034] In the first aspect of the present application, the present application provides a method for improving the thermal conductivity of a polymer material. According to the embodiments of the present application, it includes preparing the polymer material by the following steps: weaving a polymer fiber bundle to obtain polymer fibers; thermally pressing the polymer fibers to obtain the polymer material. Thus, the thermal conductivity of the polymer material is improved by weaving and thermally pressing. By weaving the polymer fiber bundle into an intertwined structure, a basis for highly ordered arrangement of molecular chains is constructed, providing an efficient molecular chain network for heat conduction; the thermal pressing treatment melts and fuses the fiber surface through high temperature and high pressure, further enhancing the binding force between molecular chains, while retaining the molecular chain order inside the fibers, reducing the interfacial thermal resistance, and improving the thermal conductivity of the material.

[0035] According to an embodiment of the present application, the raw materials of the polymer fiber bundle include ultra-high molecular weight polyethylene, homopolypropylene, copolymer polypropylene, polyamide 6, polyamide 66, polyethylene terephthalate, polyethylene naphthalate, polylactic acid, polyetheretherketone, polybutylene terephthalate; preferably ultra-high molecular weight polyethylene. Therefore, ultra-high molecular weight polyethylene becomes the preferred raw material due to its highly ordered arrangement of molecular chains, which helps to further improve the thermal conductivity and overall performance of the polymer material. In some embodiments, the molecular weight of the ultra-high molecular weight polyethylene is greater than 1.5 million.

[0036] According to an embodiment of the present application, the weaving process includes plain weaving or parallel arrangement. Thus, the polymer fibers are arranged in order through the weaving process. Plain weaving forms a stable three-dimensional network by weaving the polymer fiber bundles into an interlaced structure in a warp and weft manner, so that the molecular chains are arranged in order, so that phonons can be efficiently transported in the highly ordered molecular chains, thereby improving the thermal conductivity of the material.

[0037] According to an embodiment of the present application, the warp and weft ratio of the plain weave is (2-4):1; for example, it can be 2:1, 3:1, 4:1, etc.; thereby, the thermal conductivity of the material is further improved, and the application of the material in different scenarios can be adapted by adjusting the warp and weft ratio.

[0038] According to an embodiment of the present application, the temperature of the hot pressing treatment is 130-160° C. Thus, a melting temperature close to that of ultra-high molecular weight polyethylene is adopted to ensure that the fiber surface is melt-bonded and the internal molecular chain orientation is retained, thereby improving the overall thermal conductivity of the material.

[0039] According to an embodiment of the present application, the pressure of the heat pressing treatment is 8-12 MPa, thereby making the polymer fibers fully contact and tightly bonded, reducing the gaps between the fibers, thereby reducing the interface thermal resistance and improving the overall thermal conductivity of the material.

[0040] According to an embodiment of the present application, the heat pressing treatment lasts for 1 to 5 minutes. Thus, the short-time treatment avoids the disordering of the molecular chains and further improves the thermal conductivity of the material.

[0041] According to an embodiment of the present application, the polymer fiber is mixed with a thermally conductive material, and the resulting mixture is then subjected to the hot pressing treatment to obtain the polymer material doped with the thermally conductive material; the thermally conductive material includes at least one of graphene, carbon boron nitride, nanotubes and metal particles; preferably boron nitride.

[0042] According to an embodiment of the present application, the doping amount of the heat-conducting material in the polymer material is 5%-35 wt%. Thereby, during the hot pressing process, the gaps between the fibers are filled, the high heat-conducting phase is increased, the interfacial thermal resistance between the original fibers is reduced, and an efficient heat conduction path can also be formed in the structure of the final polymer material, further improving the thermal conductivity of the polymer material while still maintaining a better electromagnetic wave transmittance.

[0043] According to an embodiment of the present application, before performing the hot pressing process, 2 to 5 pieces of the polymer fibers are stacked, for example, it can be 2 pieces, 3 pieces, 4 pieces, or 5 pieces. Thereby, it can be a single-layer polymer fiber fabric, or the thickness of the polymer fiber fabric can be increased by multi-layer stacking, and different high heat-conducting polymer materials in the range from film-like to plate-like can be obtained, so as to obtain a flexible high heat-conducting film, or a high heat-conducting polymer plate with a certain stiffness can also be obtained to meet the requirements of different scenarios.

[0044] According to an embodiment of the present application, the diameter of the polymer fiber bundle is 20 to 30 μm. Thereby, a finer intertwined structure can be formed during the weaving process, increasing the contact area between the fibers, helping to improve the orientation degree and arrangement orderliness of the molecular chains, thereby enhancing the phonon transport efficiency and improving the thermal conductivity.

[0045] According to an embodiment of the present application, the thickness of the polymer material is 50 to 800 μm. Thereby, the thermal conductivity of the polymer material is further improved.

[0046] According to some specific embodiments of the present application, the process flow of the method is as Figure 1 shown.

[0047] Polymer material

[0048] In the second aspect of the present application, the present application proposes a polymer material. According to an embodiment of the present application, the polymer material is prepared by the method described in the first aspect.

[0049] Those skilled in the art can understand that the features and advantages described above for the method in the first aspect also apply to this polymer material and will not be elaborated here.

[0050] Next, the solution of the present application will be explained in conjunction with embodiments. Those skilled in the art will understand that the following embodiments are only used to illustrate the present application and should not be regarded as limiting the scope of the present application. For those not specified in the embodiments regarding specific technologies or conditions, they shall be carried out according to the technologies or conditions described in the literature in the art or according to the product specifications. For reagents or instruments not specified by the manufacturer, they are all conventional products that can be obtained through commercial purchase.

[0051] Example 1

[0052] Select a ultra-high molecular weight polyethylene fiber bundle with a single fiber diameter of 25 microns (molecular weight greater than 1.5 million). Eliminate the residual stress inside the fiber through constant tension winding. The draw ratio is 1:1.5 to improve the degree of molecular chain orientation. Arrange the polyethylene fiber bundles parallel in the same direction to form a unidirectionally arranged fiber layer. Construct a thin fabric layer by the parallel arrangement method. Sandwich it between two stainless steel plates, put it into a flat hot press, heat up to 150 °C and then apply a pressure of 10 MPa, hold for 2 minutes, and then naturally cool to 80 °C to demold, obtaining a dense polyethylene film with a thickness of 50 microns.

[0053] Example 2

[0054] Select a ultra-high molecular weight polyethylene fiber bundle with a single fiber diameter of 25 microns (molecular weight greater than 1.5 million). Eliminate the residual stress inside the fiber through constant tension winding. The draw ratio is 1:1.5 to improve the degree of molecular chain orientation. Construct a polyethylene fiber fabric by plain weave, with a warp-to-weft ratio of 4:1. Sandwich the fabric between two stainless steel plates, put it into a flat hot press, heat up to 150 °C and then apply a pressure of 10 MPa, hold for 2 minutes, and then naturally cool to 80 °C to demold, obtaining a dense polyethylene film with a thickness of 200 microns.

[0055] Example 3

[0056] Compared with Example 2, the warp-to-weft ratio of the polyethylene fiber fabric in this example is 2:1.

[0057] Example 4

[0058] Compared with Example 2, the warp-to-weft ratio of the polyethylene fiber fabric in this example is 1:2.

[0059] Example 5

[0060] Compared with Example 2, the warp-to-weft ratio of the polyethylene fiber fabric in this example is 1:4.

[0061] Example 6

[0062] Select a ultra-high molecular weight polyethylene fiber bundle with a single fiber diameter of 25 microns (molecular weight greater than 1.5 million). Eliminate the residual stress inside the fiber through constant tension winding. The draw ratio is 1:1.5 to improve the degree of molecular chain orientation. Construct a polyethylene fiber fabric by plain weave, with a warp-to-weft ratio of 1:4. Stack two fabric layers, sandwich them between two stainless steel plates, put it into a flat hot press, heat up to 160 °C and then apply a pressure of 10 MPa, hold for 5 minutes, and then naturally cool to 80 °C to demold, obtaining a dense polyethylene film with a thickness of 400 microns.

[0063] Example 7

[0064] Compared with Example 6, in this example, five pieces of fabric were stacked to obtain a dense polyethylene film with a thickness of 800 microns.

[0065] Example 8

[0066] Select a ultra-high molecular weight polyethylene fiber bundle with a single fiber diameter of 25 microns (molecular weight greater than 1.5 million). Eliminate the internal residual stress of the fiber by constant tension winding, with a draw ratio of 1:1.5 to improve the degree of molecular chain orientation. Construct a polyethylene fiber fabric by plain weave, with a warp-to-weft ratio of 4:1. Immerse the fabric in a 10 mg / mL boron nitride suspension so that boron nitride fully covers the surface of all fibers, especially the interfaces between fibers. Sandwich it between two stainless steel plates, place it in a flat hot press, heat it to 160 °C and then apply a pressure of 10 MPa for 5 minutes. Then, naturally cool it to 80 °C and demold to obtain a dense polyethylene-boron nitride composite film with a thickness of 300 microns, where the doping amount of boron nitride is 35% by mass fraction.

[0067] Example 9

[0068] Compared with Example 8, in this example, the doping amount of boron nitride is 5% by mass fraction.

[0069] Example 10

[0070] Compared with Example 2, in this example, the pressure of the hot pressing treatment is 2 MPa.

[0071] Example 11

[0072] Compared with Example 2, in this example, the temperature of the hot pressing treatment is 200 °C.

[0073] Example 12

[0074] Compared with Example 2, in this example, the time of the hot pressing treatment is 30 min.

[0075] Comparative Example

[0076] Select a commercially available ordinary polyethylene material (purchased from Yili Plastics Industry, model 1.4S polyethylene plastic film).

[0077] Test Example

[0078] 1. Conduct thermal conductivity tests on the polyethylene films obtained in Examples 1-12 and the Comparative Example. The specific test method is as follows: Set up a T-method thermal conductivity test system, as Figure 2As shown in the figure. A silicon wafer with a size of ~60 mm × 20 mm is used as the sample base to ensure that the base can reach the required temperature in a short time. At the same time, in order to connect the hot wire, the sample to be measured, and the wires used to measure the electrical signal, three heat sinks made of silicon wafers (~10 mm × 7 mm) and copper blocks are adhesively bonded to the base using conductive silver paste. The thickness of the copper block used is ~5 mm, which can effectively prevent the hot wire and the sample to be measured from touching the base. In addition, compared with the platinum wire hot wire and the sample, the silicon wafer and the copper block have a larger specific heat capacity and a higher thermal conductivity. Therefore, it can be considered that their temperatures are always the same as the base temperature throughout the measurement process. Subsequently, the two ends of the platinum wire hot wire are connected to the two heat sinks and fixed using silver paste. After that, two copper wires with a diameter of 150 μm are respectively placed on the two heat sinks where the hot wire is connected and fixed using silver paste as well. At this time, the sample for hot wire calibration is completed and placed in Figure 2 the system shown in the figure. After calibrating the hot wire thermal conductivity using the hot wire method, one end of the sample to be measured is fixed to the third heat sink using conductive silver paste, and the other end is adhesively bonded to the middle position of the hot wire using silver paste. Thus, the preparation of the fixed-length T-shaped method sample is completed. To reduce measurement errors and improve measurement accuracy, the above test sample is fixed in a vacuum system to weaken the convective heat dissipation loss of the hot wire and the sample to be measured as much as possible. To reduce the influence of radiative heat dissipation, a radiation heat shield made of aluminum foil paper with a high reflectivity is added in the vacuum chamber. The main process is as follows:

[0079] (1) Fabricate the sample for hot wire calibration, take a photo of it using a microscope to measure the hot wire length, and then place the sample in the measurement system;

[0080] (2) Turn on the mechanical pump to evacuate the vacuum chamber. When the pressure in the chamber is lower than 20 Pa, turn on the molecular pump to continue pumping. After about 2 - 3 h, the pressure inside the chamber stabilizes and reaches 10-3 - 10-4 Pa. At this time, turn on the temperature control part of the measurement system and set the heat sink temperature and the heat shield temperature;

[0081] (3) After the temperature stabilizes, apply a series of voltages to both ends of the hot wire, and each voltage is measured multiple times to obtain the experimental data points of the change in its resistance ΔR with the heating power P. Thus, the hot wire calibration is completed;

[0082] (4) After calibrating the hot wire, take out the hot wire method sample, and adhesively bond the two ends of the sample to be measured to the middle of the hot wire and the heat sink respectively using conductive silver paste. Thus, the preparation of the fixed-length T-shaped method sample is completed. Then, after measuring the geometric dimensions of the sample to be measured using a microscope, place the sample in the vacuum chamber;

[0083] (5) Repeat step 2, and when the temperature is stable, apply a series of voltages to the hot wire again (each voltage requires multiple measurements), and obtain the experimental data points of the change in its resistance ΔR with the heating power P, thus completing the measurement of the thermal conductivity of the sample under test at this heat sink temperature;

[0084] (6) Use the temperature control part of the experimental system to re-adjust the heat sink temperature and the radiation shield temperature, and repeat the above steps, so as to obtain a series of experimental data points of the change in the hot wire resistance ΔR with the heating power P at different temperatures, thus completing the variable-temperature measurement of the fixed-length steady-state T-shaped method.

[0085] Table 1. Thermal conductivity of polymer materials under different conditions (W·m -1 ·K -1 )

[0086]

[0087] The results are shown in Table 1. Compared with the commercially available ordinary polyethylene material (purchased from Yili Plastics Industry, model 1.4S polyethylene plastic film), the thermal conductivity of the ordinary polyethylene material is 0.21 W·m -1 ·K -1 , and the thermal conductivity of the polyethylene film prepared by the method of this application can reach 11 W·m -1 ·K -1 , and its thermal conductivity performance has been improved by about 53 times. Among them, the thermal conductivity of the polyethylene film in Example 2 is better.

[0088] 2. Conduct electromagnetic wave performance tests on the polyethylene film prepared in Example 2 and the comparative example. The specific test method is as follows:

[0089] Cut the sample to be tested into a 2 mm × 2 mm thin film, and use the VNA waveguide method to measure the electromagnetic shielding performance. The test instrument is Ceyear 3672B (China Electronic Science Instrument Co., Ltd.). Grind the sample until the surface is smooth and free of bending to avoid magnetic leakage or reflection errors, and then tightly embed it in the waveguide fixture to ensure no gap with the inner wall of the waveguide. The VNA emits a swept-frequency signal through the waveguide port and measures the amplitude and phase of the reflected signal (S11) and the transmitted signal (S21) of the sample. Use a directional coupler to separate the incident wave and the reflected wave, continuously scan within the set frequency band, and calculate the S parameters through the vector comparison of the reference signal and the received signal. S11 is the input reflection coefficient, that is, the input return loss, S21 is the forward transmission coefficient, that is, the gain, S22 is the output reflection coefficient, that is, the output return loss, and S12 is the reverse transmission coefficient, that is, the isolation. Therefore, the electromagnetic wave transmittance is S21, and the results are as Figure 3As shown in the figure, FPE in the figure is a woven and hot-pressed PE film, and PPE is an ordinary granule hot-pressed film, that is, a conventional PE film. It can be seen that the polymer material prepared in this application can have both high electromagnetic wave transmittance while maintaining a high thermal conductivity.

[0090] Although the embodiments of the present application have been shown and described above, it can be understood that the above embodiments are exemplary and should not be construed as limiting the present application. Those of ordinary skill in the art can make changes, modifications, substitutions, and variations to the above embodiments within the scope of the present application.

Claims

1. A method for improving the thermal conductivity of a polymer material, characterized in that, Including preparing the polymer material by the following steps: Weaving a polymer fiber bundle to obtain polymer fibers; Performing hot pressing on the polymer fibers to obtain the polymer material.

2. The method according to claim 1, wherein The raw materials of the polymer fiber bundle include ultra-high molecular weight polyethylene, homopolypropylene, copolymerized polypropylene, polyamide 6, polyamide 66, polyethylene terephthalate, polyethylene naphthalate, polylactic acid, polyether ether ketone, polybutylene terephthalate; preferably ultra-high molecular weight polyethylene.

3. The method according to claim 1, wherein The weaving treatment includes plain weave or parallel arrangement.

4. The method according to claim 3, wherein The warp-to-weft ratio of the plain weave is (2-4):

1.

5. The method according to claim 1, characterized in that, The temperature of the hot pressing treatment is 130-160°C; Optionally, the pressure of the hot pressing treatment is 8-12 MPa; Optionally, the time of the hot pressing treatment is 1-5 min.

6. The method according to claim 1, characterized in that Mixing the polymer fibers with a thermal conductive material, and then performing the hot pressing treatment on the obtained mixture to obtain the polymer material doped with the thermal conductive material; The thermal conductive material includes at least one of boron nitride, graphene, carbon nanotubes and metal particles; preferably boron nitride; And / or, the doping amount of the thermal conductive material in the polymer material is 5%-35 wt%.

7. The method according to claim 1, characterized in that, Before performing the weaving treatment, winding the polymer fiber bundle; Optionally, the winding treatment is carried out by a constant tension winding device; Optionally, the draw ratio of the winding treatment is 1:(1.3-1.7); preferably 1:1.

5.

8. The method according to claim 1, wherein Before performing the hot pressing treatment, stacking 2-5 pieces of the polymer fibers.

9. The method according to claim 1, wherein The diameter of the polymer fiber bundle is 20-30 μm; Optionally, the thickness of the polymer material is 50-800 μm.

10. A polymer material, characterized in that, The polymer material is prepared by the method according to any one of claims 1-9.

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