Preparation method of waste plastic sisal fiber structure carbon electromagnetic shielding material

Abstract

The application belongs to the field of electromagnetic shielding materials, and particularly relates to a preparation method of a waste plastic and sisal fiber structure carbon electromagnetic shielding material. The waste plastic and sisal fiber waste are used as main raw materials, so that the high-value utilization of solid waste is realized, the raw material cost is low, the environmental pollution is reduced, and the green and sustainable development requirement is met.

Description

Technical Field

[0001] This invention belongs to the field of electromagnetic shielding materials, specifically relating to a method for preparing a waste plastic sisal fiber structured carbon electromagnetic shielding material. Background Technology

[0002] With the advent of the global communication era and the rapid development of communication technologies, the large-scale utilization of electromagnetic microwaves has become an inevitable trend. Long-term exposure to high-frequency electromagnetic radiation poses a significant threat to human health, the normal operation of equipment, and information security. While traditional EMI materials exhibit excellent conductivity and EMI performance, they suffer from drawbacks such as high density, difficulty in processing, susceptibility to corrosion, and limited performance characteristics. To meet the requirements of lightweight, easy processing, corrosion resistance, and multifunctionality, research on electromagnetic shielding materials such as carbon materials, MXene, and ferrites has attracted considerable attention. However, these novel electromagnetic shielding materials still face challenges such as high cost and difficulty in large-scale production.

[0003] With increasing demand for iron ore resources and decreasing ore grade, the amount of iron tailings generated is increasing year by year, making it difficult to utilize and resulting in large-scale accumulation. The stockpiling of iron tailings not only occupies large amounts of land but also poses significant hazards to the surrounding atmosphere, land, rivers, and groundwater. Furthermore, high-volume tailings dams and open-air storage sites also present serious safety risks. Existing methods for utilizing iron tailings resources suffer from low utilization rates, limited raw material composition, complex processes, and low added value. Meanwhile, the production and use of graphite products are increasing annually, leading to a corresponding increase in graphite tailings. However, graphite tailings suffer from small particle size and low compaction density, resulting in a lack of effective utilization and continued accumulation through stockpiling. The short shelf life, rapid replacement rate, and high production rate of plastic products contribute to the continuous and large-scale generation of waste plastics. Traditional waste plastic treatment methods such as landfill and incineration occupy land and pose risks of water, soil, air, and food chain pollution. Existing methods for the resource utilization of waste plastics also suffer from problems such as decreased mechanical properties of the products, complex processes, and difficulty in utilizing all components. Similarly, the annual production of sisal fiber waste is also substantial, and existing utilization methods have low utilization rates, making it difficult to achieve full component utilization. Therefore, the resource utilization of multi-source solid waste, including iron tailings, graphite tailings, waste plastics, and sisal fiber waste, urgently needs to be addressed.

[0004] Polymer-based composite panels are widely used globally. However, commercially available polymer-based composite materials use a limited range of fillers, primarily calcium powder. The cost of these fillers is rising annually, while their performance gains remain relatively fixed, making it difficult to meet increasingly diverse product demands. Therefore, the development of novel polymer-based composite materials holds significant market potential. Summary of the Invention

[0005] To address the aforementioned problems, this invention provides a method for preparing a carbon electromagnetic shielding material with a waste plastic sisal fiber structure, comprising the following steps: (1) Weigh waste plastic, sisal fiber and melamine in a mass ratio of 5:5:3, mix them and grind them to obtain a mixture; (2) The mixture is sintered in a nitrogen atmosphere at a heating rate of 10℃ / min, a termination temperature of 1200℃, and a holding time of 2h to obtain the sintered product. (3) The sintered product is etched in acetic acid to remove calcium oxide and obtain an etched product; (4) The etching product is washed with water and dried to obtain waste plastic sisal fiber structure carbon electromagnetic shielding material.

[0006] Furthermore, the grinding time in step (1) is 10 min.

[0007] Furthermore, the acetic acid mentioned in step (3) is used to remove calcium oxide generated from the decomposition of calcium carbonate in the sintering product.

[0008] Furthermore, the washing described in step (4) involves multiple filtration washings using deionized water.

[0009] Furthermore, the drying temperature in step (4) is 120°C and the drying time is 3 hours.

[0010] This invention also provides the application of the waste plastic sisal fiber structured carbon electromagnetic shielding material prepared by the above preparation method as a functional filler in polymer-based electromagnetic shielding composite materials.

[0011] The present invention has the following beneficial effects: 1. Wide range of raw material sources, low cost and environmentally friendly: This invention uses waste plastics and sisal fiber waste as the main raw materials, realizing the high-value utilization of solid waste, with low raw material cost, while reducing environmental pollution and meeting the requirements of green and sustainable development.

[0012] 2. The preparation process is simple and easy to industrialize: The method only requires steps such as batching, grinding, sintering, acid etching, washing and drying. The process route is simple, the operation is controllable, and no complicated equipment is required, making it suitable for large-scale industrial application.

[0013] 3. The obtained material has a unique mesoporous-multilevel composite structure: through template induction of sisal fiber and loading of porous particles of waste plastic carbon, the prepared material has a fiber through-pore structure, a porous particle structure and a stable composite structure of the two, with a specific surface area of ​​72.58 m²·g⁻¹ and an average pore size of about 4.92 nm. It belongs to mesoporous carbon material, which is beneficial to the multiple reflection and absorption of electromagnetic waves.

[0014] 4. Highly efficient nitrogen doping with controllable structural defects: Using melamine as a nitrogen source and combining it with the nitrogen-containing properties of sisal fiber, chemical bonding doping of nitrogen in the carbon skeleton is achieved. At the same time, the material has a high degree of graphitization, which balances conductivity and structural defects, thus improving electromagnetic shielding performance.

[0015] 5. Excellent electromagnetic shielding performance, mainly due to absorption loss: The obtained material achieves an average electromagnetic shielding effectiveness of 33.29 dB in the Ku band, with an average absorption loss of 27.45 dB and an average reflection loss of only 5.83 dB. The absorption loss accounts for the majority of the total shielding effectiveness, exhibiting typical absorption-type electromagnetic shielding characteristics. Furthermore, the transmittance in the Ku band approaches 0, which can effectively prevent electromagnetic wave leakage.

[0016] 6. Suitable hydrophobicity, which is conducive to composite with polymer matrix: The contact angle of the obtained material is much higher than that of common inorganic fillers, and it has good compatibility with polymer matrix. It can be used as a functional filler to prepare polymer-based electromagnetic shielding composite materials, and has broad application prospects. Attached Figure Description

[0017] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0018] Figure 1 Microscopic morphology characterization results of porous fiber structure of waste plastic / sisal fiber waste carbon: (a) SEM image of porous fiber structure at 3000x; (b) SEM image of porous fiber structure at 10000x; (c) EDS analysis of porous fiber structure and C and N distribution images. Figure 2 Microscopic morphology characterization results of composite structure carbon from waste plastics / sisal fiber waste: (a) SEM images of porous and composite structures at 3000x; (b) SEM images of porous and composite structures at 10000x; (c) EDS analysis and C and N element distribution images of porous and composite structures. Figure 3 BET analysis results of structural carbon from waste plastics / sisal fiber waste: (a) nitrogen adsorption-desorption curve; (b) pore size distribution curve; Figure 4 Characterization results of structural carbon analysis of waste plastic / sisal fiber waste: (a) XRD; (b) Raman; Figure 5XPS and CA characterization results of structural carbon from waste plastics / sisal fiber waste: (a) XPS full spectrum analysis; (b) C 1s orbital peak diagram; (c) N 1s orbital peak diagram; (d) CA; Figure 6 Test results of electromagnetic shielding effectiveness of waste plastic / sisal fiber structure carbon: (a) EMI SE; (b) Ku-band EMI coefficient. Detailed Implementation

[0019] Various exemplary embodiments of the present invention are now described in detail. Unless otherwise specified, the methods used in the embodiments are conventional methods, and the reagents used are commercially available reagents or reagents prepared using conventional methods. This detailed description should not be considered as a limitation of the present invention, but rather as a more detailed description of certain aspects, characteristics, and embodiments of the present invention.

[0020] It should be understood that the terminology used in this invention is merely for describing particular embodiments and is not intended to limit the invention. Furthermore, with respect to numerical ranges in this invention, it should be understood that each intermediate value between the upper and lower limits of the range is also specifically disclosed. Any stated value or intermediate value within a stated range, as well as each smaller range between any other stated value or intermediate value within said range, is also included in this invention. The upper and lower limits of these smaller ranges may be independently included or excluded from the range.

[0021] Unless otherwise stated, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art. While only preferred methods and materials have been described herein, any methods and materials similar or equivalent to those described herein may be used in the implementation or testing of this invention. All references to this specification are incorporated by way of citation to disclose and describe methods and / or materials associated with those references. In the event of any conflict with any incorporated reference, the content of this specification shall prevail.

[0022] Various modifications and variations can be made to the specific embodiments described in this specification without departing from the scope or spirit of the invention, as will be apparent to those skilled in the art. Other embodiments derived from this specification will also be readily apparent to those skilled in the art. This specification and embodiments are merely exemplary.

[0023] The terms “include,” “including,” “have,” “contain,” etc., used in this article are all open-ended terms, meaning that they include but are not limited to.

[0024] Annotation table for symbols, signs, abbreviations, acronyms, terms, nouns, etc.

[0025] 1. Experiment on the preparation of nitrogen-doped waste plastic / sisal fiber structural carbon Based on the research on nitrogen-doped porous carbon from waste plastics, the preparation process of nitrogen-doped structural carbon from waste plastics / sisal fiber waste involves steps such as batching, grinding, sintering, acid etching, filtration and cleaning, and drying. First, according to the formula (5:5:3), WP, SF and melamine were weighed using a precision electronic balance. Second, the three raw materials were placed in a mortar and ground for 10 minutes. Third, the mixed product was placed in a ceramic boat in a tube furnace and sintered under a nitrogen atmosphere at preset temperature parameters (heating rate: 10 ℃ / min; termination temperature: 1200 ℃; holding time: 2 h). Fourth, the sintered product, waste plastic / sisal fiber waste carbon (WPSFC), was thoroughly etched in acetic acid to remove calcium oxide (CaO) produced after the decomposition of the self-sacrificing template agent CaCO3, to obtain waste plastic / sisal fiber waste structured carbon (WPSFSC). Fifth, WPSFSC was placed in a suction funnel covered with filter paper and washed multiple times with deionized water. Sixth, the washed WPSFSC was dried in a 120℃ forced-air drying oven for 3 h. Based on the above process, nitrogen-doped waste plastic / graphite tailings structured carbon was successfully prepared and denoted as WPSFSC.

[0026] 2. Microstructure analysis Carbon materials prepared from SF-modified WPPC possess the porous fibrous structure of SF, the porous particle structure of waste plastic carbon, and a composite structure of the two; therefore, they are named Waste Plastic / Sisal Fiber Structural Carbon (WPSFSC). In WPSFSC, a large number of nanoporous particles are loaded onto the inner walls and cross-sections of the fiber pores within the porous fibrous structure. Figure 1 a and Figure 1 b). Besides carbon (C), nitrogen (N) is widely distributed in the porous fiber structure, especially at the sites supported by nanoporous particles, where the N distribution increases significantly. Figure 1 c), in which C element accounts for approximately 90.89% and N element accounts for approximately 9.11% (Table 1). N element is realized in the WPSFSC porous fiber structure.

[0027] In addition to the layered structure, WPSFSC also contains porous particle structures derived from WPPC and composite structures formed by porous particles loaded on the surface of SF fibers. Figure 2 a). In the composite structure, there is significant adhesion between the porous particles and the SF fiber surface ( Figure 2 (b) indicates that the composite structure is relatively stable and not formed by simple contact. The elemental distribution of the composite structure involves C and N elements ( Figure 2c), where C accounts for approximately 90.23% and N accounts for approximately 9.77% (Table 1). At the WPSFSC composite structure, the distribution area of ​​N element coincides with the loading position of porous particles, indicating that not only SF itself but also melamine has achieved N doping of WPGTSC.

[0028] Table 1. Summary of C and N element distribution parameters at different structural locations in structural char from waste plastics / sisal fiber waste.

[0029] Within the range of 0.45 < P / P0, the N2 desorption curve of WPSFSC significantly lags behind the adsorption curve, exhibiting an H4-type hysteresis loop. Figure 3 a) This indicates that WPSFSC exhibits slit-like pores formed by particle aggregation. The non-closing N2 adsorption-desorption curve is due to the porous particles loaded on the fiber pore walls forming an "ink bottle"-like pore structure, hindering N2 desorption, which is consistent with the content presented in the SEM image of WPSFSC. The BET specific surface area of ​​WPSFSC is 72.58 m². 2 ·g -1 The average pore volume of BJH is 0.12 cm³. 3 ·g -1 Its pore size is widely distributed in the range of 0~230 nm, but the proportion of pores in the range of 0 nm~54 nm is higher. Figure 3 (b) The average desorption pore size of BJH is 4.92 nm (Table 2). Therefore, WPSFSC is a mesoporous carbon material.

[0030] Table 2 Summary of specific surface area and porosity parameters of structural carbon from waste plastics / sisal fiber

[0031] On the XRD curves of WPPC-3 and WPSFSC, the diffraction peaks belonging to graphitic carbon (002) appear in the range of 23°~26°, indicating that the self-prepared WPPC-3 and WPSFSC possess a graphitic phase that is easily conductive. Figure 4 a). On the Raman curves of WPPC-3 and WPSFSC, 2371 cm -1 ~3215 cm -1 961 cm -1 ~1489 cm -1 and 1489 cm -1 ~1802 cm -1 The bands showed diffraction peaks belonging to the CH bond of aromatic hydrocarbons, as well as diffraction peaks in the D and G bands. Figure 4b). The appearance of CH bond scattering peaks belonging to aromatic hydrocarbons indicates that the carbon chains of WP and SF form graphite-like structures during pyrolysis, demonstrating the successful preparation of WPPC-3 and WPSFSC. Compared to WPPC-3, the D-band diffraction peak of WPSFSC shifts to the left, indicating the presence of N doping in WPSFSC. The high intensity of the D-band scattering peak indicates the presence of local lattice structure defects in WPPC-3 and WPSFSC due to the lack of hexagonal symmetry. The appearance of the G-band scattering peak indicates the presence of relatively stable two-dimensional six-point lattice carbon atoms (SP) in WPPC-3 and WPSFSC. 2 Orbital hybridization. ID / IG reflects the degree of disorder in a material caused by lattice defects and irregular structures (Table 3). The higher ID / IG values ​​of WPPC-3 and WPSFSC are due to nitrogen doping and various irregular structures. Compared to WPPC-3, the lower ID / IG value of WPSFSC indicates a higher degree of graphitization and a superior conductive structure.

[0032] Table 3. Scattering intensity ratio of D and G peaks for WPPC-3 and WPSFSC

[0033] The presence of N 1s in the XPS full spectrum indicates that WPPC-3 and WPSFSC have achieved N doping. Figure 5 a). In the C 1s orbital, WPSFSC, like WPPC-3, exhibits corresponding peaks belonging to CC / C=C, CN / C=N, and CO / C=O double bonds, as well as a Π-Π* satellite peak ( Figure 5 b). Compared to WPPC-0 without nitrogen doping, the appearance of the CN / C=N peak indicates that the nitrogen element forms a chemical bond with the C framework in WPPC-3 and WPSFSC, rather than physical adsorption. In the N 1s orbital, WPSFSC, like WPPC-3, shows peaks corresponding to pyridine nitrogen, pyrrole nitrogen, and graphitic nitrogen. Figure 5 (c and Table 4) indicate that nitrogen is doped into WPSFSC through chemical bonding. SEM, BET, Raman, XRD and XPS characterization results together show that WPSFSC prepared by modifying WPPC with SF is an nitrogen-doped mesoporous multi-structured carbon material.

[0034] The contact angle reflects the hydrophobicity of a material and is inversely proportional to its specific surface energy. Compared to WPGTSC, WPSFSC exhibits a significant decrease in hydrophobicity. Figure 5 (d), but still much higher than common inorganic fillers, indicating that WPSFSC can be used as a functional filler for polymer-based composite materials.

[0035] Table 4 Summary of peak parameters of WPPC-0, WPPC-3 and WPSFSC in C 1s and N 1s orbitals

[0036] 3. Electromagnetic shielding effectiveness analysis Coaxial EMI test samples for WPSFSC in the frequency range of 2.0 GHz to 18.0 GHz were prepared by mixing WPGTSC and paraffin in a 6:4 ratio. As the electromagnetic wave frequency increases, the EMI SE of WPSFSC in the frequency range of 2.0 GHz to 18.0 GHz... T Increase first, then decrease, EMI SE A Gradually increasing, while EMI SE R Gradually decrease ( Figure 6 a). Compared to the average EMI SE in the C-band T and average EMI SE A The average EMI SE of WPSFSC in the Ku band T (33.29 dB) and average EMI SE A (27.45 dB) increases of 3.16% and 11.13% respectively, indicating that the EMI performance values ​​of WPGTSC are similar in the 2.0 GHz to 18.0 GHz frequency range. WPSFSC EMI SE A The maximum value is obtained in the Ku band, at which point the average EMI SE R and average EMI SE A The ratio (0.21) approaches 0 (Table 5), indicating that the WPSFSC mainly achieves EMI function in the Ku band through absorption loss. The T of the WPGTSC in the Ku band approaches 0, indicating that electromagnetic waves in the Ku band basically do not transmit when they come into contact with the WPSFSC. Figure 6 (b) can be used as a functional filler for low-cost multi-source solid waste-based LDPE composite EMI materials.

[0037] Table 5. Summary of average shielding effectiveness of waste plastic / sisal fiber structural carbon in C, X, and Ku bands.

[0038] The embodiments described above are merely preferred embodiments of the present invention and are not intended to limit the scope of the present invention. Various modifications and improvements made by those skilled in the art to the technical solutions of the present invention without departing from the spirit of the present invention should fall within the protection scope defined by the claims of the present invention.

Claims

1. A method for preparing a waste plastic sisal fiber structured carbon electromagnetic shielding material, characterized in that, Includes the following steps: (1) Weigh waste plastic, sisal fiber and melamine in a mass ratio of 5:5:3, mix them and grind them to obtain a mixture; (2) The mixture is sintered in a nitrogen atmosphere at a heating rate of 10℃ / min, a termination temperature of 1200℃, and a holding time of 2h to obtain the sintered product. (3) The sintered product is etched in acetic acid to remove calcium oxide and obtain an etched product; (4) The etching product is washed with water and dried to obtain waste plastic sisal fiber structure carbon electromagnetic shielding material.

2. The preparation method according to claim 1, characterized in that, The grinding time in step (1) is 10 min.

3. The preparation method according to claim 1, characterized in that, The acetic acid mentioned in step (3) is used to remove calcium oxide generated from the decomposition of calcium carbonate in the sintering product.

4. The preparation method according to claim 1, characterized in that, The washing process described in step (4) involves multiple filtration washings using deionized water.

5. The preparation method according to claim 1, characterized in that, The drying temperature in step (4) is 120°C and the drying time is 3 hours.

6. The application of the waste plastic sisal fiber structured carbon electromagnetic shielding material prepared by any one of claims 1-5 as a functional filler in polymer-based electromagnetic shielding composite materials.

Images