Electromagnetic shielding material with ultralow percolation threshold and preparation method and application thereof

Abstract

The application provides an electromagnetic shielding material with an ultralow percolation threshold and a preparation method and application thereof, and belongs to the technical field of polymer processing and electromagnetic shielding, and the electromagnetic shielding material is prepared according to the following mass ratio: polylactic acid: 50-70 parts, thermoplastic polyurethane elastomer: 30-70 parts, chain extender: 0.05-3 parts, modified filler: 0.5-10 parts, and antioxidant: 0.5-3 parts; wherein the modified filler is polyurethane-coated carbon nanotubes with a diameter of 2-20 nm; compared with the prior art, the application provides a preparation method, that is, polylactic acid and carbon nanotubes are first melt-blended to prepare a masterbatch, and then the masterbatch is melt-blended with an elastomer, the processing time of the second stage is controlled so that the carbon nanotubes are in different positions, so that the same content of carbon nanotubes can be used to achieve different electrical conductivity, and thus the electromagnetic shielding material with an ultralow percolation threshold is prepared.

Description

Technical Field

[0001] This invention belongs to the field of polymer processing and electromagnetic shielding technology, specifically relating to an electromagnetic shielding material with an ultra-low percolation threshold, its preparation method, and its application. Background Technology

[0002] With the rapid development of the global economy, the shortage of petroleum resources and environmental pollution have become increasingly prominent issues, making the development of environmentally friendly materials an important research direction in the field of materials science. Polylactic acid (PLA), as a bio-based and biodegradable polymer, has attracted widespread attention due to its renewable and abundant supply advantages, derived from plant resources such as corn. PLA's applications cover multiple fields including packaging, fibers, 3D printing materials, and biomedicine, demonstrating enormous development potential.

[0003] However, in practical applications, research on PLA conductive systems still faces many challenges. Traditional methods often require adding a high content of conductive fillers, such as carbon nanotubes, graphene, or metal nanoparticles, to the PLA matrix to achieve good conductivity. However, high filler content can lead to uneven dispersion within the PLA system, affecting the overall material performance, especially electromagnetic shielding performance. Furthermore, high filler content may also reduce the mechanical and processing properties of PLA, limiting its practical applications. Against this backdrop, researchers have proposed a strategy of constructing selective dispersion structures for conductive fillers in the PLA system or introducing microscopic isolation structures. This approach can significantly reduce the amount of conductive filler used and effectively improve its dispersion, thereby enhancing the material's electromagnetic shielding performance. This method provides a new research direction for developing high-performance, low-cost, and environmentally friendly PLA electromagnetic shielding materials.

[0004] Furthermore, PLA and most elastomers differ significantly in chemical structure, typically exhibiting incompatibility. This incompatibility prevents them from forming a homogeneous phase structure during mixing, instead resulting in mutual repulsion and a two-phase separated system. In this system, the PLA phase and the elastomer phase exist independently, and this separation characteristic facilitates the construction of selectively dispersed or isolated structures. For example, conductive fillers can preferentially distribute in one phase or form a conductive network at the interface between the two phases, thereby further reducing filler usage and optimizing its dispersibility and functional performance. This strategy not only provides theoretical support for improving the electromagnetic shielding performance of PLA-based composites but also opens up new avenues for material structure design. Summary of the Invention

[0005] The technical objective of this invention is to provide an electromagnetic shielding material with an ultra-low percolation threshold, its preparation method, and its application. This material not only has an ultra-low percolation threshold but also excellent electromagnetic shielding performance.

[0006] This invention provides an electromagnetic shielding material with an ultra-low percolation threshold. The electromagnetic shielding material is formulated in the following proportions by weight: polylactic acid: 50-70 parts, thermoplastic polyurethane elastomer: 30-70 parts, chain extender: 0.05-3 parts, modified filler: 0.5-10 parts, antioxidant: 0.5-3 parts; wherein the modified filler is polyurethane-coated carbon nanotubes with a diameter of 2-20 nm.

[0007] Compared to existing technologies, the carbon nanotube surface coating of this invention is polyurethane. Polyurethane and thermoplastic polyurethane elastomer (TPU) have similar polarity, so as the melt blending time increases, the carbon nanotubes (CNS) located in the polylactic acid matrix gradually migrate to the interface between polylactic acid and thermoplastic polyurethane elastomer, and then migrate into the thermoplastic polyurethane elastomer. When the carbon nanotubes are at the interface between polylactic acid and thermoplastic polyurethane elastomer, they form a microscopic isolation structure, creating a large number of conductive networks, thereby significantly reducing the content of carbon nanotubes forming conductive networks in the polymer matrix. This polyurethane-coated carbon nanotube can both improve the interfacial interaction force between the polylactic acid and thermoplastic polyurethane elastomer copolymer and increase the viscosity of the matrix. Furthermore, the carbon nanotubes can also act as a highly efficient nucleating agent for the polylactic acid matrix, significantly increasing the crystallization rate and mechanical strength of the matrix.

[0008] In some other embodiments, the polylactic acid has a melt index of 3-10 g / 10 min, and the polylactic acid is L-polylactic acid or D-polylactic acid.

[0009] In some other embodiments, the thermoplastic polyurethane elastomer has a structure consisting of alternating hard and soft segments, wherein the soft segments are composed of flexible long chains of polyols and the hard segments are composed of diisocyanates and chain extenders.

[0010] In some other embodiments, the chain extender is selected from one or more compounds containing multiple epoxy groups, compounds containing multiple isocyanate groups, and acid anhydride compounds.

[0011] In some other embodiments, the antioxidant is selected from one or more of pentaerythritol tetrakis[β-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate], tris(2,4-di-tert-butylphenyl) phosphite, triphenyl phosphite, and 4,4'-bis(α,α-dimethylbenzyl)diphenylamine.

[0012] In some other embodiments, the electromagnetic shielding material has an electromagnetic shielding performance of not less than 20 dB in the X-band with a frequency range of 8.2-12.4 GHz.

[0013] In some other embodiments, the modified filler in the electromagnetic shielding material is in the following state: uniformly dispersed in one phase and / or dispersed at the interface between two phases.

[0014] The second objective of this invention is to provide a method for preparing an electromagnetic shielding material, the method specifically comprising the following steps:

[0015] By mixing polylactic acid, thermoplastic polyurethane elastomer, antioxidant, chain extender and modified filler according to the weight ratio, and then melt extruding, an electromagnetic shielding material with an ultra-low percolation threshold can be obtained.

[0016] The third objective of this invention is to provide a method for preparing an electromagnetic shielding material, the method specifically comprising the following steps:

[0017] Polylactic acid, antioxidant, chain extender and modified filler are mixed evenly according to the weight ratio, and then melt-blended. Thermoplastic polyurethane elastomer is added according to the weight ratio, and then melt-blended again to obtain an electromagnetic shielding material with an ultra-low percolation threshold.

[0018] Furthermore, the preparation method specifically includes the following steps:

[0019] Lactic acid, antioxidant, chain extender and modified filler are mixed according to the weight ratio and added to a mixer for melt blending for 5-15 minutes. Then, thermoplastic polyurethane elastomer is added according to the weight ratio and melt blended again for 1-15 minutes to obtain an electromagnetic shielding material with an ultra-low percolation threshold. The melt extrusion temperature is 20-40℃ above the melting point of polylactic acid and the screw speed is 30-80 rpm.

[0020] Compared with existing technologies, the electromagnetic shielding material with ultra-low percolation threshold and its preparation method provided by this invention involve first preparing a masterbatch by melt-blending polylactic acid (PLA) and polyurethane-coated carbon nanotubes. During the melt-blending process, the carbon nanotubes are uniformly dispersed in the PLA matrix, and the masterbatch is then pulverized and dried. The dried masterbatch is then melt-blended with thermoplastic polyurethane elastomer. Due to the significant differences in structure and polarity between PLA and thermoplastic polyurethane elastomer, the physical bonding effect is not ideal, resulting in the formation of a "bicontinuous structure" or "island structure" between the two phases. However, the polyurethane coating on the carbon nanotubes has a similar polarity to the thermoplastic polyurethane elastomer. Therefore, with the extension of the melt-blending time, the carbon nanotubes located in the PLA matrix gradually migrate to the PLA-polyurethane elastomer interface and then migrate into the polyurethane elastomer. When the carbon nanotubes are at the PLA-polyurethane elastomer interface, they form a microscopic isolation structure, creating a large number of conductive networks. This significantly reduces the content of carbon nanotubes forming conductive networks in the polymer matrix. These carbon nanotubes can enhance the interfacial interaction between polylactic acid and polyurethane elastomer copolymers, and also increase the viscosity of the matrix. Furthermore, carbon nanotubes can act as highly efficient nucleating agents for the polylactic acid matrix, significantly increasing the crystallization rate and mechanical strength of the matrix.

[0021] A fourth objective of this invention is to provide an application of electromagnetic shielding material in electronic devices, the automotive industry, or electronic systems.

[0022] Compared with the prior art, the present invention has the following advantages:

[0023] 1. The present invention provides a preparation method in which polylactic acid and carbon nanotubes are melt-blended to prepare a masterbatch, and then melt-blended with an elastomer. By controlling the processing time of the second stage, the carbon nanotubes are placed in different positions, so that the same amount of carbon nanotubes can be used to achieve different electrical conductivity, thereby preparing an electromagnetic shielding material with ultra-low percolation threshold.

[0024] 2. In the material, the conductive filler is concentrated and dispersed at the interface between polylactic acid and thermoplastic polyurethane elastomer. Only a small amount of carbon nanotubes is needed to form a continuous conductive network, solving the problems of easy detachment and poor adhesion of the conductive filler in mechanical coating-hot pressing methods. Furthermore, the dispersion of the conductive filler in this material significantly improves electromagnetic shielding performance. This material has promising application prospects in fields such as electronic communications.

[0025] 3. This invention leverages the triple function of conductive fillers: firstly, they enhance interfacial forces at the interface between polylactic acid and thermoplastic polyurethane elastomer; secondly, they increase the viscosity of the matrix; and thirdly, they act as nucleating agents, significantly improving the crystallinity of the PLA matrix, thereby enhancing the mechanical strength of the matrix.

[0026] 4. The preparation method provided by this invention is simple, efficient, and easy to implement for industrial production. Attached Figure Description

[0027] Figure 1 Figure showing the volumetric conductivity results of PLA / TPU / CNS systems with different CNS contents;

[0028] Figure 2 Figure 1 shows the electromagnetic shielding performance of PLA / TPU / CNS systems with different CNS contents in the X-band.

[0029] Figure 3 The electromagnetic shielding performance results of PLA / TPU / CNS-1wt% (Examples 1-4) systems with different processing times are shown in the figure.

[0030] Figure 4 These are TEM analysis images of samples from Examples 1-4. Detailed Implementation

[0031] To make the above-mentioned objects, features, and advantages of the present invention more apparent and understandable, specific embodiments of the present invention are described in detail below. It should be noted that the following embodiments are only used to illustrate the implementation methods and typical parameters of the present invention, and are not intended to limit the parameter range described in the present invention. Reasonable variations derived therefrom are still within the protection scope of the claims of the present invention.

[0032] It should be noted that the endpoints and any values ​​of the ranges disclosed herein are not limited to the precise 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 the various ranges, the endpoint values ​​of the various ranges and individual point values, and individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered as specifically disclosed herein.

[0033] Unless otherwise defined, all terms, symbols, and other scientific terms used herein are intended to have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains. In some instances, terms having a conventional meaning are defined herein for clarification or ease of reference, and such definitions should not be construed as indicating a significant difference from conventional understanding in the art. The technical methods described or referenced herein are generally well understood by those skilled in the art and employed by conventional methods. Unless otherwise stated, the use of commercially available kits, reagents, and instruments shall be performed according to the manufacturer's instructions and parameters.

[0034] The technical effects of the present invention will be described below with reference to specific embodiments.

[0035] Example 1

[0036] This embodiment provides an electromagnetic shielding material with an ultra-low percolation threshold, which is prepared by the following method: 50 parts of polylactic acid (4032D), 2 parts of polyurethane-coated carbon nanotubes, 1 part of pentaerythritol tetrakis[β-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate], 1 part of tris(2,4-di-tert-butylphenyl) phosphite, and 2 parts of 1,6-hexanediol are added to a mixer and melt-blended for 8 minutes (blending temperature: 190°C, screw speed: 50 rpm); the blended sample is then pulverized, dried, and melt-blended with 50 parts of thermoplastic polyurethane elastomer for 2 minutes (blending temperature: 190°C, screw speed: 50 rpm) to obtain an electromagnetic shielding material with an ultra-low percolation threshold.

[0037] Example 2

[0038] This embodiment provides an electromagnetic shielding material with an ultra-low percolation threshold, which is prepared by the following method: 50 parts of polylactic acid (4032D), 2 parts of polyurethane-coated carbon nanotubes, 1 part of tris(2,4-di-tert-butylphenyl) phosphite, 1 part of 4,4'-bis(α,α-dimethylbenzyl)diphenylamine, and 2 parts of diethylaminoethanol (DEAE) are added to a mixer and melt-blended for 8 minutes (blending temperature: 190°C, screw speed: 50 rpm); the blended sample is then pulverized, dried, and melt-blended with 50 parts of thermoplastic polyurethane elastomer for 4 minutes (blending temperature: 190°C, screw speed: 50 rpm) to obtain an electromagnetic shielding material with an ultra-low percolation threshold.

[0039] Example 3

[0040] This embodiment provides an electromagnetic shielding material with an ultra-low percolation threshold, which is prepared by the following method: 50 parts of polylactic acid (4032D), 2 parts of polyurethane-coated carbon nanotubes, 1 part of pentaerythritol tetrakis[β-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate], 1 part of triphenyl phosphite, and 1 part of trimethylolpropane are added to a mixer and melt-blended for 8 minutes (blending temperature: 190°C, screw speed: 50 rpm); the blended sample is then pulverized, dried, and melt-blended with 50 parts of thermoplastic polyurethane elastomer for 6 minutes (blending temperature: 190°C, screw speed: 50 rpm) to obtain an electromagnetic shielding material with an ultra-low percolation threshold.

[0041] Example 4

[0042] This embodiment provides an electromagnetic shielding material with an ultra-low percolation threshold, which is prepared by the following method: 50 parts of polylactic acid (4032D), 2 parts of polyurethane-coated carbon nanotubes, 2 parts of pentaerythritol tetrakis[β-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate], 2 parts of tris(2,4-di-tert-butylphenyl) phosphite, 1 part of N,N-dihydroxy(diisopropyl)aniline (HPA), and 1 part of neopentyl glycol (NPG) are added to a mixer and melt-blended for 8 minutes (blending temperature: 190°C, screw speed: 50 rpm); the blended sample is then pulverized, dried, and melt-blended with 50 parts of thermoplastic polyurethane elastomer for 8 minutes (blending temperature: 190°C, screw speed: 50 rpm) to obtain an electromagnetic shielding material with an ultra-low percolation threshold.

[0043] Example 5

[0044] This embodiment provides an electromagnetic shielding material with an ultra-low percolation threshold, which is prepared by the following method: 50 parts of polylactic acid (4032D), 2 parts of polyurethane-coated carbon nanotubes, 50 parts of thermoplastic polyurethane elastomer, 2 parts of tris(2,4-di-tert-butylphenyl) phosphite, and 2 parts of N,N-dihydroxy(diisopropyl)aniline (HPA) are added to a mixer and melt-blended for 8 minutes (blending temperature is 190°C, screw speed is 50 rpm) to obtain an electromagnetic shielding material with an ultra-low percolation threshold.

[0045] Comparative Example 1

[0046] This comparative example provides an electromagnetic shielding material prepared by the following method: 70 parts of polylactic acid (4032D), 2 parts of polyurethane-coated carbon nanotubes, 30 parts of polymethyl methacrylate, 1 part of pentaerythritol tetrakis[β-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate], 1 part of 4,4'-bis(α,α-dimethylbenzyl)diphenylamine, 1 part of 1,6-hexanediol, and 1 part of sorbitol are added to a twin-screw extruder for continuous extrusion and melt-blended in its runner for 8 minutes (blending zone 1 temperature is 170℃, zone 2 temperature is 200℃, zone 3 temperature is 200℃, and screw speed is 30 rpm).

[0047] Comparative Example 2

[0048] This comparative example provides an electromagnetic shielding material prepared by the following method: 50 parts of polylactic acid (4032D), 2 parts of multi-walled carbon nanotubes, 50 parts of polyether block polyamide elastomer, 1 part of tris(2,4-di-tert-butylphenyl) phosphite, 0.5 parts of triphenyl phosphite, 0.5 parts of 4,4'-bis(α,α-dimethylbenzyl)diphenylamine, 0.5 parts of diethylene glycol (DEG), and 0.5 parts of triethylene glycol are added to a mixer and melt-blended for 8 minutes (blending temperature: 200 ℃, screw speed: 50 rpm) to obtain an electromagnetic shielding material with an ultra-low percolation threshold.

[0049] Comparative Example 3

[0050] This comparative example provides an electromagnetic shielding material prepared by the following method: 50 parts of polylactic acid (4032D), 2 parts of polyurethane-coated carbon nanotubes, 50 parts of polyether block polyamide elastomer, 2 parts of 4,4'-bis(α,α-dimethylbenzyl)diphenylamine, and 2 parts of N,N-dihydroxy(diisopropyl)aniline (HPA) are added to a mixer and melt-blended for 8 minutes (blending temperature: 200 ℃, screw speed: 50 rpm); thus, an electromagnetic shielding material with an ultra-low percolation threshold is obtained.

[0051] To investigate the electrical properties of the composite materials prepared by the method of this invention, the volume conductivity and electromagnetic shielding of the samples obtained in Examples 1-5 and Comparative Examples 1-3 were tested. The results are as follows: Figures 1-4 As shown, where. Figure 1 The graph shows the volumetric conductivity results of PLA / TPU / CNS systems with different CNS contents; from Figure 1 As can be seen, the percolation threshold exhibits an extremely low level of only 0.03 wt% through linear fitting. Figure 2 The graph shows the electromagnetic shielding performance of PLA / TPU / CNS systems with different CNS contents in the X-band. Figure 2 As can be seen, the percolation threshold, as determined by linear fitting, is an extremely low level of only 0.03 wt%; Figure 3 The electromagnetic shielding performance results of PLA / TPU / CNS-1wt% (Examples 1-4) systems with different processing times are shown in the figure. Figure 4 These are TEM analysis images of samples from Examples 1-4. Figure 4 It can be seen that PLA and TPU have different atomic contrasts. Therefore, PLA presents a "green" region compared to TPU, while TPU presents a "dark" region. Furthermore, it can be seen that as the processing time increases, there is direct evidence that CNS migrates from the PLA phase to the TPU phase.

[0052] While the disclosure is as stated above, its scope of protection is not limited thereto. Those skilled in the art can make various changes and modifications without departing from the spirit and scope of this disclosure, and all such changes and modifications will fall within the protection scope of this invention.

Claims

1. An electromagnetic shielding material with an ultra-low percolation threshold, characterized in that, The electromagnetic shielding material is formulated in the following proportions by weight: polylactic acid: 50-70 parts, thermoplastic polyurethane elastomer: 30-70 parts, chain extender: 0.05-3 parts, modified filler: 0.5-2 parts, antioxidant: 0.5-3 parts; wherein the modified filler is polyurethane-coated carbon nanotubes with a diameter of 2-20 nm. The electromagnetic shielding material has an electromagnetic shielding performance of not less than 20 dB in the X-band with a frequency range of 8.2-12.4 GHz. In the electromagnetic shielding material, the modified filler is in the following state: uniformly dispersed in one phase and / or dispersed at the interface of two phases; The preparation method of the electromagnetic shielding material specifically includes the following steps: Polylactic acid, antioxidant, chain extender and modified filler are mixed according to the weight ratio and added into a mixer for melt blending for 5-15 minutes. Thermoplastic polyurethane elastomer is added according to the weight ratio and melt blended again for 4-8 minutes to obtain an electromagnetic shielding material with an ultra-low percolation threshold. The melt extrusion temperature is 20-40°C above the melting point of polylactic acid and the screw speed is 30-80 rpm.

2. The electromagnetic shielding material as described in claim 1, characterized in that, The polylactic acid has a melt index of 3-10 g / 10 min, and the polylactic acid is L-polylactic acid or D-polylactic acid.

3. The electromagnetic shielding material as described in claim 1, characterized in that, The thermoplastic polyurethane elastomer has a structure consisting of alternating hard and soft segments. The soft segments are composed of flexible long chains of polyols, and the hard segments are composed of diisocyanate and chain extenders.

4. The electromagnetic shielding material as described in claim 1, characterized in that, The chain extender is selected from one or more compounds containing multiple epoxy groups, compounds containing multiple isocyanate groups, and acid anhydride compounds; and / or, the antioxidant is selected from one or more of pentaerythritol tetrakis[β-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate], tris(2,4-di-tert-butylphenyl) phosphite, triphenyl phosphite, and 4,4'-bis(α,α-dimethylbenzyl)diphenylamine.

5. The application of an electromagnetic shielding material as described in any one of claims 1-4 in the fields of electronic equipment, automotive industry, or electronic systems.

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