A hierarchical flexible wpu / nickel / wood composite material with a convex structure and a preparation method and application thereof

Abstract

This invention belongs to the technical field of biomass-based electromagnetic shielding materials, specifically relating to a layered flexible WPU / Ni / wood composite material with a raised structure, its preparation method, and its applications. Using natural balsa wood as a matrix, a conductive-magnetic network is constructed on the wood surface through chemical nickel plating. This is combined with a flexible composite structure of waterborne polyurethane (WPU), polyethylene glycol (PEG), and a silane coupling agent (KH550), and then cold-pressed to obtain a flexible nickel-plated multilayer wood-based composite material (F-BWN). This composite material exhibits excellent Joule heating properties and adjustable infrared stealth capabilities. This invention provides a new pathway for developing high-performance, sustainable flexible electromagnetic shielding materials, promoting the high-end and diversified application of biomass materials in flexible electronics and intelligent protection, and facilitating the industrial upgrading of green functional materials.

Description

Technical Field

[0001] This invention belongs to the field of biomass-based electromagnetic shielding materials technology, specifically relating to a layered flexible WPU / Ni / wood composite material with a raised structure, its preparation method, and its application. Background Technology

[0002] With the rapid development of 5G communication, wearable electronic devices, intelligent robots, and military stealth technology, electromagnetic interference (EMI) problems are becoming increasingly prominent, making the demand for high-performance electromagnetic shielding materials more urgent. Traditional electromagnetic shielding materials are mainly composed of metals such as copper and aluminum. Although they have excellent conductivity and shielding effectiveness, they are dense, lack flexibility, and are easily corroded, making it difficult to meet the requirements of flexible electronics and lightweight equipment. In recent years, carbon-based materials (such as graphene and carbon nanotubes) and conductive polymer composites have been extensively studied, but bottlenecks such as high preparation costs, complex processes, and insufficient mechanical properties still exist. Biomass materials have advantages such as wide availability, renewability, and unique structure. In particular, natural balsa wood has a three-dimensional porous layered structure, making it an ideal framework for constructing lightweight conductive networks. However, natural wood itself is not conductive and lacks flexibility and versatility. How to endow wood with high conductivity, high shielding effectiveness, good flexibility, and Joule heating properties through simple and environmentally friendly methods, while maintaining its lightweight and sustainability, is a technical problem that urgently needs to be solved in this field. Summary of the Invention

[0003] In view of this, the purpose of this invention is to address the problems existing in the prior art by providing a hierarchical flexible WPU / Ni / wood composite material with a raised structure, its preparation method, and its applications. This method uses natural balsa wood as a matrix, constructs a conductive-magnetic network on the wood surface through chemical nickel plating, and combines it with a flexible composite structure of waterborne polyurethane (WPU), polyethylene glycol (PEG), and a silane coupling agent (KH550). The resulting hierarchical flexible WPU / Ni / wood composite material (F-BWN) with a raised structure is then prepared by cold pressing. The prepared composite material exhibits a uniform structure, good flexibility, high shielding effectiveness, and excellent Joule thermal properties and infrared stealth capabilities. Experiments show that the composite material achieves an average electromagnetic shielding effectiveness of 61.85 dB in the 8.2-12.4 GHz band, and its surface temperature can rise to 163.7 ℃ at 1.75 V, while also exhibiting good environmental durability and cycle stability.

[0004] To achieve the above objectives, the first objective of this invention is to provide a method for preparing a layered flexible WPU / Ni / wood composite material with a raised structure, employing the following technical solution:

[0005] A method for preparing a layered flexible WPU / Ni / wood composite material with a raised structure is disclosed. The method uses natural balsa wood as the matrix, constructs a conductive-magnetic network on the surface of the wood by chemical nickel plating, and combines it with a flexible structure composed of waterborne polyurethane, polyethylene glycol and silane coupling agent. The flexible nickel-plated multilayer wood matrix composite material is then obtained by cold pressing.

[0006] It is worth noting that this invention uses natural balsa wood as the matrix, constructs a conductive-magnetic network on the surface of the wood through chemical nickel plating, and combines a flexible composite structure of water-based polyurethane, polyethylene glycol and silane coupling agent. The flexible nickel-plated multilayer wood-based composite material is obtained through a cold pressing process. During the cold pressing process, the components work synergistically, enabling the material to maintain the porous structure of balsa wood while obtaining excellent flexibility and interfacial bonding strength, effectively solving the problems of high brittleness and easy cracking of traditional wood.

[0007] Furthermore, the preparation method includes the following steps:

[0008] S1. Cut natural balsa wood into the required size and perform chemical nickel plating to obtain nickel-plated balsa wood;

[0009] S2. Mix waterborne polyurethane, polyethylene glycol and silane coupling agent in a certain proportion to obtain a composite flexible solution.

[0010] S3. The nickel-plated balsa wood obtained in step S1 is immersed in the composite flexible solution of step S2, and then dried and cold-pressed to obtain a flexible nickel-plated multilayer wood-based composite material.

[0011] Furthermore, in step S1, the electroless nickel plating time is 20-30 minutes.

[0012] Preferably, the electroless nickel plating time is 25 min, and the thickness of the resulting nickel-plated balsa wood is 0.3-0.5 mm.

[0013] It is worth noting that this invention employs electroless nickel plating and limits the plating time to 20-30 minutes. If the plating time is too short, the conductive network on the wood surface will be discontinuous, resulting in insufficient conductivity and shielding effectiveness; if the plating time is too long, the metal layer will be too thick, increasing costs and reducing the material's flexibility and lightweight properties. Preferably, 25 minutes is used, at which time the formed nickel layer is uniform and dense, with a conductivity reaching 45.724 S·cm. - ¹.

[0014] Furthermore, in step S2, the composite flexible solution comprises, by weight: 50-70 parts of waterborne polyurethane, 18-25 parts of polyethylene glycol, 1-3 parts of silane coupling agent, and the remainder is deionized water.

[0015] Furthermore, the waterborne polyurethane has a solid content of 30%, the polyethylene glycol has a molecular weight of 400, and the silane coupling agent is KH550.

[0016] Preferably, the composite flexible solution is prepared by mixing waterborne polyurethane (WPU), polyethylene glycol (PEG), and silane coupling agent (KH550) with a solid content of 30% in a mass ratio of 30:11:1.

[0017] Furthermore, in step S3, the drying conditions are vacuum drying at 60-80 ℃ for 8-12 h, and the cold pressing conditions are holding pressure at 15-20 MPa for 10-20 min.

[0018] It is worth noting that the present invention controls the drying process to allow the WPU in the composite flexible solution to undergo preliminary cross-linking and curing under compression. Then, the initial thickness of the nickel-plated balsa wood is compressed to 30%-50% of its original thickness through the pressure holding process of a cold press, thereby working together to form a layered flexible and surface protrusion structure.

[0019] More specifically, this invention employs a cold-pressing process with a pressure limited to 15-20 MPa and a holding time of 10-20 min. During the cold pressing process, waterborne polyurethane serves as a flexible matrix, polyethylene glycol as a plasticizer, and a silane coupling agent as an interfacial bridge. The combined action of these three components compresses and densifies the multi-layered structure of the nickel-plated wood while maintaining a certain degree of resilience, thus endowing the material with good flexibility and mechanical strength. Furthermore, during the cold pressing process, the multi-layered nickel-plated balsa wood undergoes interlayer fusion under pressure, forming a gradient conductive-magnetic structure: the surface nickel layer provides high conductivity and magnetic loss, the internal wood skeleton provides mechanical support and multiple reflection interfaces, and the intermediate composite flexible layer improves impedance matching and imparts flexibility.

[0020] In some embodiments, the preparation method includes the following steps:

[0021] S1. Cut the natural balsa wood into the required size (100 mm × 100 mm × 1 mm), perform chemical nickel plating, control the nickel plating time to 20-30 min, remove it, wash it with deionized water and dry it to obtain nickel-plated balsa wood.

[0022] S2. Waterborne polyurethane (WPU) (30% solid content), polyethylene glycol (PEG) and silane coupling agent (KH550) are mixed evenly in a mass ratio of (30:11:1) to prepare a composite flexible solution;

[0023] S3. The nickel-plated balsa wood obtained in step S1 is immersed in the composite flexible solution of step S2 for 20-30 minutes. After immersion, it is placed in a drying oven and vacuum dried at 60-80 ℃ for 8-12 hours. Then it is placed in a cold press and held under pressure of 15-20 MPa for 10-20 minutes to obtain flexible nickel-plated multilayer wood matrix composite material (F-BWN).

[0024] Preferably, the natural balsa wood in step S1 is balsa wood with a density of 0.10-0.15 g / cm³ and a cutting thickness of 1 mm. The electroless nickel plating solution comprises: 20-30 g / L nickel sulfate, 20-30 g / L sodium hypophosphite, 25-30 g / L sodium citrate, 0.01-0.05 g / L thiourea, pH adjusted to 9.0, and temperature 60-70 °C.

[0025] It is worth noting that the specific electroless nickel plating time should be determined based on the actual needs of the product. For high conductivity, 20-30 minutes should be selected, while for high flexibility, 10-15 minutes should be selected.

[0026] Preferably, in step S3, the pressure and time of the cold pressing process need to be controlled in a coordinated manner. Considering that excessive pressure or excessive holding time will lead to excessive material density and reduced flexibility, while insufficient pressure or insufficient holding time will result in weak interlayer bonding and reduced shielding effectiveness, the present invention preferably uses 20 MPa and 15 min, at which time the tensile strength of the composite material reaches 87.3 MPa.

[0027] A second objective of this invention is to provide a layered flexible WPU / Ni / wood composite material with a raised structure, prepared using the method described above. The technical solution is as follows:

[0028] A layered flexible WPU / Ni / wood composite material with a raised structure, the composite material having a conductive-magnetic structure gradient distributed from the surface inward.

[0029] It is worth noting that the layered structure of the composite material is characterized by a gradient decrease in nickel content from the surface to the interior, while the material compressibility increases in a gradient.

[0030] Furthermore, the surface of the composite material is a composite layer in which nickel nanoparticles and WPU networks interweave; the middle layer is a periodic array of protrusions wrapped in nickel; and the inner layer is a porous structure of natural wood that has not been fully compressed.

[0031] It is worth noting that in the gradient conductive-magnetic structure within the layered flexible WPU / Ni / wood composite material with a raised structure described in this invention, the surface nickel layer provides high conductivity and magnetic loss, the internal wood skeleton provides mechanical support and a multi-reflection interface, and the intermediate flexible composite layer improves impedance matching and imparts flexibility. Therefore, the gradient conductive-magnetic structure within the material effectively optimizes interface impedance matching, enhances the multiple absorption losses of electromagnetic waves, and enables the composite material to simultaneously possess good flexibility, environmental durability, and cycle stability.

[0032] Furthermore, the composite material exhibits an average electromagnetic shielding effectiveness of 60-70 dB in the 8.2 to 12.4 GHz frequency band and an electrical conductivity of 30-50 S·cm. - ¹, Tensile strength is 70-90 MPa.

[0033] It is worth noting that the electrical conductivity was measured at room temperature using the four-probe method, and the tensile strength was measured according to the GB / T1040.3 standard.

[0034] A third objective of this invention is to provide an application of the layered flexible WPU / Ni / wood composite material with a raised structure as described above. The technical solution adopted is as follows:

[0035] Application of a layered flexible WPU / Ni / wood composite material electromagnetic shielding device, thermal management device, and flexible equipment with a raised structure.

[0036] It is worth noting that the layered flexible WPU / Ni / wood composite material with a raised structure disclosed in this invention has an electrical conductivity of up to 45.724 S·cm. - ¹, significantly higher than conventional conductive wood, providing a foundation for highly efficient electromagnetic shielding. The average electromagnetic shielding effectiveness reaches 61.85 dB in the 8.2–12.4 GHz band, meeting commercial and military protection requirements. Furthermore, the gradient conductive-magnetic structure optimizes interface impedance matching, enhancing the multi-absorption loss of electromagnetic waves.

[0037] Furthermore, the layered flexible WPU / Ni / wood composite material with raised structure has excellent Joule thermal properties, with a surface temperature that can rise to 163.7 ℃ at a low voltage of 1.75 V, and has adjustable infrared stealth capability, making it suitable for intelligent thermal management and military stealth applications.

[0038] Finally, the layered flexible WPU / Ni / wood composite material with raised structure has good flexibility, tensile strength of up to 87.3 MPa, can be bent without cracking, and has excellent environmental durability and cycle stability. After multiple bending or thermal cycles, the shielding effectiveness retains more than 90%, which can meet the technical requirements of flexible equipment.

[0039] Therefore, this invention uses natural balsa wood as the matrix, combined with chemical nickel plating and a composite flexible structure. The raw materials are renewable, the process is simple and the conditions are controllable, making it suitable for large-scale production. The prepared composite material can be widely used in flexible electronic device housings, wearable shielding suits, military tents, smart packaging and other fields, effectively expanding the high-end application avenues of biomass materials.

[0040] Compared with existing technologies, the advantages of this invention are as follows: Through a specific process of "chemical nickel plating - flexible solution impregnation - drying - high-pressure cold pressing," this invention successfully constructs a hierarchical flexible composite material with a gradient distribution of conductive and magnetic structures from the surface to the interior. This gradient structure, characterized by high surface conductivity / magnetism and high internal flexibility, cannot be obtained through simple blending or single-layer coating in existing technologies. Based on the aforementioned gradient conductive and magnetic structure, the material of this invention achieves a tensile strength as high as 30-50 S·cm while maintaining excellent flexibility (tensile strength 70-90 MPa). - ¹ The surface conductivity is significantly better than that of existing composite materials with the same level of flexibility. Furthermore, this invention uses waterborne polyurethane (WPU) as a flexible binder, combined with polyethylene glycol plasticizer and silane coupling agent interface modification, successfully solving the interfacial compatibility problems between the metallic nickel layer and the wood substrate, as well as between the hard nickel layer and the flexible WPU layer. Attached Figure Description

[0041] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on the provided drawings without creative effort.

[0042] Figure 1 The image shows the actual thickness of the WPU / Ni / wood composite material (F-BWN) prepared in Example 1 of this invention.

[0043] Figure 2 This is a diagram illustrating the F-BWN sample obtained in Example 1 of the present invention;

[0044] Figure 3 The stress-strain curves and their average values ​​of different samples obtained in Experimental Example 1 of this invention are shown below (BalsaWood: balsa wood, BWN: nickel plated, BWN-W: impregnated with WPU, BWN-WP: impregnated with PEG, F-BWN: impregnated with KH550). Among them, a is the stress-strain curve of the tensile test and b is the bar chart of tensile strength comparison.

[0045] Figure 4These are Joule thermal infrared images of the F-BWN sample obtained in Example 1 of the present invention under different voltages.

[0046] Figure 5 The results of the acid and alkali resistance test of the F-BWN sample obtained in Example 1 of this invention;

[0047] Figure 6 The surface roughness of different samples obtained in Experimental Example 1 of this invention is shown below, where a is the surface roughness of BWN, b is the surface roughness of BWN-W, c is the surface roughness of BWN-WP, d is the surface roughness of F-BWN, e is the surface roughness of F-BWN after immersion in room temperature and normal pressure for 20 minutes, f is the surface roughness of F-BWN after immersion in a vacuum environment for 20 minutes, and g is a bar chart of average surface roughness.

[0048] Figure 7 The following are demonstration diagrams of the electromagnetic shielding effect of the Tesla coil obtained in the embodiments of the present invention (a: without shielding, b: after shielding with balsa wood, c: after shielding with F-BWN, d: schematic diagram of Tesla coil shielding, e: comparison of electromagnetic shielding performance of balsa wood and F-BWN).

[0049] Figure 8 The magnetic test results of the F-BWN sample obtained in Experimental Example 1 of this invention;

[0050] Figure 9 This is a schematic diagram of the microstructure of the F-BWN sample obtained in Example 1 of the present invention (a: cellulose fiber and nickel-plated cellulose fiber after electroless nickel plating; b: activation and electroless nickel plating process; c: composite effect of waterborne polyurethane, polyethylene glycol and silane coupling agent during cold pressing; d: schematic diagram of the high conductivity, flexible curling, infrared stealth and magnetic multifunctional integration of the final material).

[0051] Figure 10 This study investigates the electromagnetic attenuation mechanism of the composite material of the F-BWN sample obtained in Example 1 of this invention. Detailed Implementation

[0052] The technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0053] The term "embodiment" used herein, as an example, is not necessarily to be construed as superior to or better than other embodiments. Performance testing in the embodiments of this application, unless otherwise specified, employs conventional testing methods in the art. It should be understood that the terminology used in this application is merely for describing particular implementations and is not intended to limit the scope of this disclosure.

[0054] Unless otherwise stated, the technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application pertains; other experimental methods and technical means not specifically mentioned herein refer to experimental methods and technical means commonly used by one of ordinary skill in the art.

[0055] To better illustrate the content of this application, numerous specific details are provided in the following detailed embodiments. Those skilled in the art should understand that this application can be implemented even without certain specific details. In the embodiments, some methods, means, instruments, and devices well-known to those skilled in the art are not described in detail in order to highlight the main points of this application.

[0056] Without conflict, the technical features disclosed in the embodiments of this application can be combined arbitrarily, and the resulting technical solution belongs to the content disclosed in the embodiments of this application.

[0057] This invention discloses a layered flexible WPU / Ni / wood composite material with a raised structure, its preparation method, and its applications, belonging to the field of bio-based electromagnetic shielding materials technology. Using natural balsa wood as a matrix, a conductive-magnetic network is constructed on the wood surface through chemical nickel plating. This is combined with a flexible composite structure of waterborne polyurethane (WPU), polyethylene glycol (PEG), and a silane coupling agent (KH550), and then cold-pressed to obtain a flexible nickel-plated multilayer wood-based composite material (F-BWN). This composite material is uniform, flexible, and has high shielding effectiveness, exhibiting excellent Joule thermal properties and infrared stealth capabilities. The gradient conductive-magnetic structure within the material effectively optimizes interfacial impedance matching, enhances the multiple absorption losses of electromagnetic waves, and also possesses good flexibility, environmental durability, and cycle stability. This invention provides a new path for developing high-performance, sustainable flexible electromagnetic shielding materials, promotes the high-end and diversified application of biomass materials in flexible electronics and intelligent protection, and facilitates the industrial upgrading of green functional materials.

[0058] To better understand the present invention, the following embodiments are provided for further detailed description of the present invention, but they should not be construed as limiting the present invention. Any non-essential improvements and adjustments made by those skilled in the art based on the above-described invention are also considered to fall within the protection scope of the present invention.

[0059] Example 1

[0060] A hierarchical flexible WPU / Ni / wood composite material with a raised structure and its preparation method:

[0061] S1. Substrate pretreatment: Natural balsa wood (density 0.10-0.15 g / cm³) is cut into 100 mm × 100 mm × 1 mm thin slices, ultrasonically cleaned with deionized water for 15 min and ultrasonically cleaned with anhydrous ethanol for 10 min in sequence, and then dried in a 60 °C oven for 2 h.

[0062] S2. Activation treatment: Immerse the dried balsa wood in the sensitization solution (NiSO4 15 g / L, HCl 12 g / L) for 15 min at room temperature, then rinse with deionized water; then immerse it in the activation solution (NaBH4 15 g / L, NaOH 12 g / L) for 1.5 min at room temperature, then rinse thoroughly with deionized water.

[0063] Nickel sulfate 20-30 g / L, sodium hypophosphite 20-30 g / L, sodium citrate 25-30 g / L, thiourea 0.01-0.05 g / L, pH adjusted to 9.0, temperature 60-70 °C.

[0064] S3. Electroless Nickel Plating: Weigh 25 g of nickel sulfate, 25 g of sodium hypophosphite, 30 g of sodium citrate, and 0.03 g of thiourea per liter of plating solution. Add approximately 700 mL of deionized water and stir to dissolve. Adjust the volume to 1 L and adjust the pH to 9.0 with ammonia. Heat the plating solution to 65 °C. Completely immerse the activated balsa wood in the plating solution and plating for 25 minutes, gently stirring the solution every 5 minutes during the plating process. After nickel plating, remove the balsa wood, rinse it repeatedly with deionized water three times, and dry it in a 60 °C vacuum drying oven for 4 hours to obtain nickel-plated balsa wood (BWN).

[0065] S4. Preparation of composite flexible solution: Take 40 mL of waterborne polyurethane emulsion (30% solid content), add 26.668 mL of deionized water for dilution, add 4 mL of polyethylene glycol (PEG), and separately add 0.4 mL of silane coupling agent (KH550) and 1 mL of anhydrous ethanol for pre-hydrolysis to the above mixture. Stir evenly to obtain composite flexible solution.

[0066] S5. Impregnation and Cold Pressing: The nickel-plated balsa wood obtained in step S3 is impregnated in the composite flexible solution of step S4 for 20 min. It is then dried in an oven at 65 °C for 12 h. After removal, it is placed in a cold press and held under pressure of 20 MPa for 15 min to obtain a flexible nickel-plated multilayer wood matrix composite material (F-BWN).

[0067] Example 2

[0068] A hierarchical flexible WPU / Ni / wood composite material with a raised structure and its preparation method:

[0069] S1, Same as Example 1.

[0070] S2, same as Example 1.

[0071] S3, Electroless Nickel Plating: The composition of the plating solution is the same as in Example 1, but the nickel plating time is changed to 10 min, and other conditions remain unchanged.

[0072] S4, Same as Example 1.

[0073] S5. Change the cold pressing pressure to 15 MPa and hold the pressure for 20 min. Other steps are the same as in Example 1.

[0074] Example 3

[0075] A hierarchical flexible WPU / Ni / wood composite material with a raised structure and its preparation method:

[0076] S1. The thickness of the balsa wood is changed to 0.50 mm, and the rest is the same as in Example 1.

[0077] S2, same as Example 1.

[0078] S3, Electroless Nickel Plating: The composition of the plating solution is the same as in Example 1, but the nickel plating time is changed to 30 min, and other conditions remain unchanged.

[0079] S4, Same as Example 1.

[0080] S5. Change the cold pressing pressure to 25 MPa and hold the pressure for 10 minutes. Other steps are the same as in Example 1.

[0081] Example 4

[0082] A hierarchical flexible WPU / Ni / wood composite material with a raised structure and its preparation method:

[0083] S1, Same as Example 1.

[0084] S2, same as Example 1.

[0085] S3. Electroless nickel plating: Weigh 20 g of nickel sulfate, 20 g of sodium hypophosphite, 25 g of sodium citrate, and 0.03 g of thiourea per liter of plating solution. Adjust the pH to 9.0, set the plating solution temperature to 65 °C, and the plating time to 20 min. Other steps are the same as in Example 1.

[0086] S4, Same as Example 1.

[0087] S5, same as Example 1.

[0088] Testing showed that the F-BWN composite material prepared in Example 1 had a thickness of 0.39 mm, which allowed it to be easily placed on paper. Figure 1 ), demonstrating its lightweight properties; such as Figure 2 As shown, this material can be rolled up arbitrarily without cracking, demonstrating excellent flexibility; Figure 3 As shown, the F-BWN prepared in Example 1 achieved a tensile strength of 87.3 MPa and an electrical conductivity of 45.724 S·cm. - ¹.

[0089] To further demonstrate the beneficial effects of the present invention and to better understand the present invention, the following comparative examples and experimental examples further illustrate the characteristics and application performance of the layered flexible WPU / Ni / wood composite material with a raised structure disclosed in the present invention and its preparation method. However, these should not be construed as limiting the present invention. Other methods and applications obtained by those skilled in the art based on the above-described invention and their applications are also considered to fall within the protection scope of the present invention.

[0090] Comparative Example 1

[0091] Raw materials: Only natural balsa wood substrate is used, without chemical nickel plating or composite flexible structure treatment.

[0092] Preparation steps:

[0093] Natural balsa wood was cut into the same dimensions as in Example 1 (100 mm × 100 mm × 1 mm), then washed and dried sequentially with deionized water and anhydrous ethanol. No nickel plating or impregnation treatment was performed; it was used directly as a control sample (Balsa Wood).

[0094] Comparative Example 2

[0095] Test subject: Nickel-plated balsa wood (BWN) that has only undergone chemical nickel plating but has not been treated with a composite flexible structure.

[0096] Preparation method:

[0097] Nickel-plated balsa wood was prepared according to steps S1-S3 of Example 1 (nickel plating for 25 min); then, without impregnation with the composite flexible solution and cold pressing, it was directly used as a control sample (BWN).

[0098] Comparative Example 3

[0099] A composite material (BWN-WP) was prepared using the same electroless nickel plating process but with a different flexible matrix (waterborne polyurethane only, without the addition of PEG and KH550).

[0100] Preparation method:

[0101] Nickel-plated balsa wood was prepared according to steps S1-S3 of Example 1;

[0102] Preparation of composite flexible solution: Take only 40 mL of aqueous polyurethane emulsion (30% solid content), add 26.668 mL of deionized water for dilution, without adding PEG and KH550;

[0103] After impregnation, the sample was cold-pressed (20 MPa, 15 min) as in Example 1.

[0104] Experimental Example 1

[0105] The F-BWN composite material prepared in Example 1 was subjected to the following performance tests compared with Comparative Example 1 (Balsa Wood), Comparative Example 2 (BWN), and Comparative Example 3 (BWN-WP):

[0106] Conductivity test: Conductivity was measured using the four-probe method.

[0107] Mechanical property testing: Tensile strength was determined using a universal testing machine with a gauge length of 15 mm and a tensile rate of 2 mm / min.

[0108] Electromagnetic shielding effectiveness test: The shielding effectiveness was tested in the range of 8.2-12.4 GHz (X-band) using a vector network analyzer.

[0109] Joule thermal performance test: DC voltages of 0.25V, 0.5V, 0.75V, 1.0V, 1.25V, 1.5V, and 1.75V were applied to both ends of the sample, and the surface temperature changes were recorded using an infrared thermal imager.

[0110] Infrared stealth performance test: Cover the surface of the heat source with F-BWN and record the temperature change of the heat source surface before and after the shielding.

[0111] like Figure 3 As shown, the tensile strength of F-BWN prepared in Example 1 reached 87.3 MPa, which is much higher than that of Comparative Example 1 (BalsaWood, about 15 MPa), Comparative Example 2 (BWN, about 30 MPa) and Comparative Example 3 (BWN-WP, about 60 MPa), proving that the composite flexible structure disclosed in this invention has a significant reinforcing effect.

[0112] like Figure 4As shown in the Joule thermal infrared thermograms of the F-BWN prepared in Example 1 at different voltages, the surface temperature is as follows: 0.25 V, 25.5 °C; 0.5 V, 38.9 °C; 0.75 V, 59.8 °C; 1 V, 86.8 °C; 1.25 V, 142.9 °C; 1.5 V, 153.7 °C; 1.75 V, 163.7 °C. This demonstrates that the WPU / Ni / wood composite material (F-BWN) disclosed in this invention exhibits rapid heating, uniform temperature distribution, and excellent electrothermal conversion performance.

[0113] like Figure 5 As shown, the layered flexible WPU / Ni / wood composite material F-BWN with a raised structure prepared in Example 1 was completely immersed in an acidic solution with pH=2 (dilute hydrochloric acid was added to deionized water to make pH=2) and an alkaline solution with pH=12 (ammonium hydroxide was added to deionized water to make pH=12), respectively.

[0114] The surface roughness of the F-BWN prepared in Example 1 is as follows: Figure 6 As shown: The surface roughness of the nickel-plated sample BWN is 16.88 μm ( Figure 6 a); In the BWN-W sample with added WPU, the polymer filled the voids between nickel particles, reducing the roughness to 12.26 μm ( Figure 6 b); The addition of PEG to the BWN-WP sample further improved the surface smoothness through plasticization and rheological optimization, reducing the roughness to 11.73 μm. Figure 6 c); After further addition of silane coupling agent KH-550, the roughness of sample F-BWN slightly increased to 13.04 μm. Figure 6 d), which may be related to its molecular aggregation behavior. Figure 6 ef shows that cold pressing has little effect on surface roughness. Figure 6 The results showed that the average surface roughness Sa of different samples was 10-20 μm. This result is attributed to the synergistic effect of WPU, PEG, and KH550: PEG induces phase separation to form protrusions, KH550 enhances the interfacial bonding force to fix the protrusions, and cold pressing further densifies the protrusion structure. The absence of any one component prevents the complete synergy of "protrusion formation" and "protrusion fixation," resulting in lower roughness. Therefore, after optimizing the ratio (30% WPU, 4 mL PEG, 0.4 mL KH550) and cold pressing, the preferred flexible wood-based composite material F-BWN was finally obtained.

[0115] like Figure 7As shown, electromagnetic interference tests were conducted using a Tesla coil to generate high-voltage discharge. It can be seen that the electric field strength was 287 V / m without shielding, 244 V / m after shielding with balsa wood, and dropped to 0 V / m after covering with F-BWN, proving that the material can completely shield electromagnetic interference generated by high-voltage discharge.

[0116] like Figure 8 As shown, when a permanent magnet is brought close to the F-BWN composite material prepared in Example 1 of this invention, the sample exhibits a significant magnetic response behavior, being rapidly attracted and firmly adsorbed by the magnet. Therefore, the F-BWN composite material disclosed in Example 1 of this invention possesses a certain degree of magnetism.

[0117] like Figure 9 As shown, this invention constructs a conductive-magnetic network through chemical nickel plating, combined with a WPU / PEG / KH550 composite flexible structure, and then densifies it through cold pressing, achieving integrated conductivity, magnetism, flexibility, Joule heating properties, and infrared stealth performance. The components synergistically enhance each other: the nickel plating layer provides high conductivity and magnetic loss; WPU imparts flexibility and film-forming properties; PEG plasticizes and improves bending performance; KH550 strengthens interfacial bonding; and the cold pressing process densifies the multilayer structure and forms a gradient interface. The resulting F-BWN significantly outperforms the comparative example in terms of electromagnetic shielding effectiveness, mechanical flexibility, environmental durability, and multifunctional integration.

[0118] like Figure 10 As shown, the electromagnetic shielding mechanism of the F-BWN composite material disclosed in this invention is mainly based on a gradient conductive-magnetic network: the surface nickel layer provides high conductivity and eddy current loss, the internal wood skeleton provides multiple reflection interfaces, and the middle composite flexible layer improves impedance matching. The three work together to achieve a highly efficient shielding effect of "absorption-reflection-multiple losses".

[0119] Therefore, experiments have demonstrated that the hierarchical flexible WPU / Ni / wood composite material with a raised structure disclosed in this invention achieves an average electromagnetic shielding effectiveness of 61.85 dB in the 8.2-12.4 GHz band, and its surface temperature can rise to 163.7 ℃ at 1.75 V, while also exhibiting good environmental durability and cycle stability. This invention provides a new pathway for developing high-performance, sustainable flexible electromagnetic shielding materials.

[0120] The above description of the disclosed embodiments enables those skilled in the art to make or use the invention. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the invention. Therefore, the invention is not to be limited to the embodiments shown herein, but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A method for preparing a layered flexible WPU / Ni / wood composite material with a raised structure, characterized in that, Using natural balsa wood as the matrix, a conductive-magnetic network is constructed on the surface of the wood through chemical nickel plating. Combined with a flexible composite structure of waterborne polyurethane, polyethylene glycol and silane coupling agent, a flexible nickel-plated multilayer wood-based composite material is obtained through cold pressing.

2. The method for preparing the layered flexible WPU / Ni / wood composite material with a raised structure according to claim 1, characterized in that, Includes the following steps: S1. Cut natural balsa wood into the required size and perform chemical nickel plating to obtain nickel-plated balsa wood; S2. Mix waterborne polyurethane, polyethylene glycol and silane coupling agent in a certain proportion to obtain a composite flexible solution. S3. The nickel-plated balsa wood obtained in step S1 is immersed in the composite flexible solution of step S2, and then dried and cold-pressed to obtain a flexible nickel-plated multilayer wood-based composite material.

3. The method for preparing the layered flexible WPU / Ni / wood composite material with a raised structure according to claim 2, characterized in that, In step S1, the electroless nickel plating time is 20-30 min.

4. The method for preparing the layered flexible WPU / Ni / wood composite material with a raised structure according to claim 2, characterized in that, In step S2, the composite flexible solution comprises, by weight: 50-70 parts of waterborne polyurethane, 18-25 parts of polyethylene glycol, 1-3 parts of silane coupling agent, and the remainder is deionized water.

5. The method for preparing the layered flexible WPU / Ni / wood composite material with a raised structure according to claim 4, characterized in that, The waterborne polyurethane has a solid content of 30%, the polyethylene glycol has a molecular weight of 400, and the silane coupling agent is KH550.

6. The method for preparing the layered flexible WPU / Ni / wood composite material with a raised structure according to claim 2, characterized in that, In step S3, the drying conditions are vacuum drying at 60-80 ℃ for 8-12 h, and the cold pressing conditions are holding pressure at 15-20 MPa for 10-20 min.

7. A layered flexible WPU / Ni / wood composite material with a raised structure obtained by the preparation method according to any one of claims 1 to 6, characterized in that, The composite material has a conductive-magnetic structure that is gradient-distributed from the surface inward.

8. The layered flexible WPU / Ni / wood composite material with a raised structure according to claim 7, characterized in that, The surface of the composite material is a composite layer in which nickel nanoparticles and WPU networks interweave; the middle layer is a periodic array of protrusions wrapped in nickel; and the core is a porous structure of natural wood that has not been fully compressed.

9. The layered flexible WPU / Ni / wood composite material with a raised structure according to claim 7, characterized in that, The composite material exhibits an average electromagnetic shielding effectiveness of 60-70 dB in the 8.2 to 12.4 GHz frequency band and an electrical conductivity of 30-50 S·cm. - ¹, Tensile strength is 70-90 MPa.

10. The application of a layered flexible WPU / Ni / wood composite material with a raised structure as described in any one of claims 7 to 9, characterized in that, Application of the layered flexible WPU / Ni / wood composite material with raised structure in electromagnetic shielding equipment, thermal management devices, and flexible equipment.

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