Flexible Wood-Based Thin Films Loaded with Silver Nanowires Based on Beveled Wood Blocks and Their Preparation Method

Abstract

This invention discloses a flexible wood-based film based on obliquely cut wood blocks loaded with silver nanowires and its preparation method. The preparation method includes the following steps: 1) cutting wood blocks at an angle of 22.5-67.5° to the direction of wood fiber growth to obtain wood sheets; 2) removing lignin from the wood sheets by delignification treatment; 3) impregnating the delignified wood sheets with deionized water; 4) loading silver nanowires onto the wood sheets using a vacuum-assisted method and drying to obtain delignified wood sheets loaded with silver nanowires; 6) obtaining the flexible wood-based film based on obliquely cut wood blocks loaded with silver nanowires by hot pressing. This invention increases the permeability of the loading material within the wood sheets and improves the loading capacity of the wood sheets by obliquely cutting the wood blocks, while also taking into account the mechanical properties of the wood sheets.

Description

Technical Field

[0001] This invention relates to the field of wood processing technology, and in particular to a method for preparing flexible wood-based films based on silver nanowires loaded on obliquely cut wood blocks, which balances the permeability, load-bearing capacity and mechanical properties of wood by adjusting the wood cutting angle. Background Technology

[0002] Wood, as a natural and renewable material, possesses broad application potential in the field of functionalized material preparation due to its lightweight, high strength, and complex porous cellular structure. In recent years, delignification technology has been used to remove lignin from wood, resulting in delignified wood with high porosity and good permeability. Further compression treatment of delignified wood can produce flexible wood films, which have attracted widespread attention in the fields of flexible electronic devices, packaging materials, and functional composite materials.

[0003] Flexible wood-based films can be prepared by hot-pressing delignified wood blocks. However, due to the anisotropy of wood, the cutting direction significantly affects the properties of the wood-based films. When the wood block is longitudinally cut (i.e., the cutting direction is parallel to the wood fiber growth direction), the hot-pressed wood-based film exhibits excellent mechanical properties; while when it is transversely cut (i.e., the cutting direction is perpendicular to the wood fiber growth direction), the mechanical properties of the prepared wood-based film are significantly poor. Therefore, most current studies use the longitudinal cutting method to prepare delignified wood-based films. However, because the cell cavity structure of wood is elongated, the cell cavity length in the longitudinal direction is relatively long, making it difficult for the load to penetrate deep into the central region of the wood during the infiltration process, especially the core part of the wood cell cavity. This uneven distribution of the load limits the capacity of the load.

[0004] To address the problems of uneven loading permeation, limited loading capacity, and insufficient mechanical properties of wood films in traditional wood modification, it is necessary to develop a flexible wood-based film with excellent loading permeability, loading capacity, and mechanical properties. Summary of the Invention

[0005] The purpose of this invention is to provide a method for preparing flexible wood-based films based on silver nanowires loaded on obliquely cut wood blocks, which can significantly improve the penetration depth and uniformity of the load while maintaining good flexibility and mechanical properties.

[0006] To achieve the above objectives, a method for preparing flexible wood-based thin films loaded with silver nanowires based on obliquely cut wood blocks is provided, the method comprising the following steps:

[0007] 1) Wood pretreatment: Select balsa wood and cut the wood blocks at an angle of 22.5-67.5° to the direction of wood fiber growth to obtain wood veneers with a thickness of 1-3mm;

[0008] 2) Delignification treatment: Immerse the wood chips in sodium chlorite solution at 75-85℃, adjust the pH of the solution to 4.6, and soak for 8-10 hours to remove lignin from the wood chips;

[0009] 3) Cleaning and drying: Soak the wood chips treated with delignification in step 2) with deionized water to remove residual sodium chlorite solution. After the sodium chlorite solution is completely removed, freeze-dry the delignified wood chips to form porous delignified wood chips.

[0010] 4) Modifier loading: The porous delignified wood slabs are immersed in a silver nanowire solution, and the silver nanowires are allowed to penetrate into the cell cavities of the wood slabs with the solution using a vacuum-assisted method.

[0011] 5) Oven drying: Dry the delignified wood sheets loaded with the modified material in step 4) to obtain delignified wood sheets loaded with silver nanowires.

[0012] 6) Hot pressing treatment: The delignified wood sheet loaded with silver nanowires is placed in a hot press. After the delignified wood sheet loaded with silver nanowires is held between weighing paper and filter paper, it is hot pressed for 6-12 hours to obtain the flexible wood-based film based on obliquely cut wood block loaded with silver nanowires.

[0013] This invention employs the aforementioned technical solution, effectively optimizing the wood's cell cavity structure by adjusting the cutting angle and using a bevel cutting method while controlling the cutting angle. Cutting the wood blocks at an angle of 22.5-67.5° to the direction of wood fiber growth effectively increases the exposed area of ​​the wood cells while shortening the cell cavity length, making it easier for the load to penetrate evenly into the wood. Furthermore, after hot-pressing compaction, the mechanical properties of the bevel-cut wood-based film are significantly improved. Although the mechanical properties of the bevel-cut wood-based film are slightly lower than those of the longitudinally cut wood film, they are still superior to those of the transversely cut wood film, exhibiting good overall mechanical properties.

[0014] This cutting strategy significantly improves the permeability of the load, effectively increases the capacity of the wood load, and takes into account the mechanical properties of the wood-based film after hot pressing, providing performance support for further expanding the application of wood-based films in electromagnetic shielding.

[0015] The flexible wood film prepared by the oblique cutting process of this invention can exhibit excellent performance in a variety of application fields, such as the preparation of functional composite materials such as electromagnetic shielding, flame retardancy, thermal conductivity and magnetic materials.

[0016] Furthermore, in step 1), the obliquely cut wood slab has dimensions of 3cm x 3cm, making it more suitable for subsequent steps of impregnation and loading of finishing materials.

[0017] Furthermore, in step 2), the ratio of the mass of the wood veneer to the volume of the sodium chlorite solution is 0.5:500-600 g / mL, ensuring that the wood veneer can be fully impregnated in the sodium chlorite solution.

[0018] Furthermore, in step 2), the solution is adjusted to pH 4.6 using a sodium acetate buffer solution.

[0019] Furthermore, in step 3), the temperature of the freeze-drying cold trap is -75°C to -70°C.

[0020] Furthermore, in step 4), the modifier loading is subjected to vacuum-assisted modifier permeation at a pressure of -0.1 MPa.

[0021] Furthermore, in step 4), the concentration of the silver nanowire solution is 2-10 mg / mL, and the solvent is deionized water or ethanol.

[0022] Furthermore, in step 5), the drying temperature is 60-100℃.

[0023] Furthermore, in step 6), the hot-pressing treatment is carried out at a temperature of 60-100℃ and a pressure of 5-10MPa. The high-temperature and high-pressure hot-pressing treatment promotes the recombination of cellulose (after delignification, the main components of wood veneer are cellulose and hemicellulose), evaporates moisture, induces chemical cross-linking of cellulose and thermoplastic flow, and at the same time improves the density, smoothness, stability and mechanical properties of the wood-based film by flattening the wood surface.

[0024] The present invention also provides a flexible wood-based thin film based on silver nanowires loaded on obliquely cut wood blocks, which is prepared by the above-described preparation method.

[0025] The beneficial effects of this invention include:

[0026] 1. This invention effectively increases the exposed area of ​​wood cavities and shortens the length of wood cavities by adjusting the cutting angle of the wood, that is, cutting the wood blocks at an angle of 22.5-67.5° to the direction of wood fiber growth. This makes it easier for the load to penetrate evenly into the interior of the wood.

[0027] 2. This invention, by cutting wood blocks at an oblique angle of 22.5-67.5°, can effectively increase the load-bearing capacity of wood while improving the permeability of the load-bearing material.

[0028] 3. The flexible wood-based film based on silver nanowires loaded on obliquely cut wood blocks described in this invention has significantly improved mechanical properties after hot pressing treatment. This achieves the goal of increasing the permeability of the load inside the wood and improving the load capacity of the wood, while also taking into account the mechanical properties of the wood.

[0029] 4. The flexible wood film prepared by this invention can be widely used in the preparation of functional composite materials such as electromagnetic shielding, flame retardancy, thermal conductivity and magnetic materials. Attached Figure Description

[0030] Figure 1a This is a scanning electron microscope image of the flexible wood-based film prepared in Example 1;

[0031] Figure 1b for Figure 1a A magnified view of a portion of the image;

[0032] Figure 2 Stress-strain curves of flexible wood-based films prepared in Examples 1-3 and Comparative Examples 1-2 are shown.

[0033] Figure 3 A photograph showing the flexible wood-based film prepared in Example 1 in a bent state;

[0034] Figure 4 XRD patterns of flexible wood-based film loaded with silver nanowires, unloaded silver nanowires, and silver nanowires prepared in Example 2;

[0035] Figure 5 The graphs show the electromagnetic shielding effectiveness of the flexible wood-based films prepared in Examples 1-3 and Comparative Examples 1-2 as a function of frequency.

[0036] Figure 6 a is a diagram showing how a flexible wood-based film loaded with silver nanowires from a slanted wood block prepared in Example 1 completely encapsulates a mobile phone and blocks its signal.

[0037] Figure 6 Figure b shows the flexible wood-based film with silver nanowires loaded on a slanted wood block prepared in Example 1, which cannot block the mobile phone signal when it is not completely wrapped around the mobile phone. Detailed Implementation

[0038] To better understand the present invention, the specific methods of the present invention will be described in detail below with reference to embodiments, but this does not limit the scope of the present invention.

[0039] Example 1: Preparation of a flexible wood-based thin film supported on silver nanowires from obliquely cut wood blocks

[0040] 1) Wood pretreatment: Select balsa wood and cut the wood blocks at an angle of 22.5° to the direction of wood fiber growth to obtain wood veneers with a size of 3cm×3cm and a thickness of 2mm.

[0041] 2) Delignification treatment: The wood chips are immersed in a sodium chlorite solution at 80°C. The solution is adjusted to pH 4.6 by sodium acetate buffer solution. The immersion time is 9 hours to remove lignin from the wood chips. Since multiple wood chips are immersed at one time in this embodiment, the ratio of the total mass of the wood chips to the volume of the sodium chlorite solution is 0.5:550 g / mL, ensuring that each wood chip undergoes sufficient delignification treatment.

[0042] 3) Cleaning and drying: Soak the delignified wood veneer in deionized water for 6 hours, changing the deionized water 3 times during the soaking period; then dry the wood veneer in a freeze dryer for 48 hours at a cold trap temperature of -75℃ to form a porous delignified wood template.

[0043] 4) Modifier loading: The porous delignified wood slabs were immersed in a silver nanowire solution with a concentration of 5 mg / mL (deionized water as solvent). Under a pressure of -0.1 MPa, the silver nanowires were allowed to penetrate into the cell cavities of the wood slabs with the solution using a vacuum-assisted method.

[0044] 5) Oven drying: The delignified wood sheets loaded with the modification in step (4) are dried at 60°C for 3 hours to obtain delignified wood sheets loaded with silver nanowires.

[0045] 6) Hot pressing treatment: The delignified wood sheet loaded with silver nanowires is placed in a hot press. After the delignified wood sheet is clamped with weighing paper and filter paper to ensure uniform force, it is then hot-pressed at 80°C and 5MPa for 10 hours to obtain the flexible wood-based film based on obliquely cut wood block loaded with silver nanowires.

[0046] Example 2: Preparation of a flexible wood-based thin film based on silver nanowires loaded on obliquely cut wood blocks

[0047] (1) Wood pretreatment: Select balsa wood and cut the wood blocks at a 45° angle to the direction of wood fiber growth to obtain wood veneers with a size of 3cm×3cm and a thickness of 2mm.

[0048] (2) Delignification treatment: Wood chips were immersed in a sodium chlorite solution at 75°C, the solution being adjusted to pH 4.6 using a sodium acetate buffer solution, for 10 hours to remove lignin from the wood. Since multiple wood chips were used for immersion in this embodiment, the ratio of the total mass of the wood chips to the volume of the sodium chlorite solution was 0.5:600 g / mL, ensuring that each wood chip underwent sufficient delignification treatment.

[0049] (3) Cleaning and drying: Soak the delignified wood chips in deionized water for 6 hours, changing the deionized water 3 times during the soaking period; then dry the wood chips in a freeze dryer for 48 hours at a cold trap temperature of -70°C to form porous delignified wood chips.

[0050] (4) Modifier loading: Porous delignified wood slabs were placed in a 10 mg / mL silver nanowire solution (deionized water as solvent), and the silver nanowires were allowed to penetrate into the cell cavities of the wood slabs with the solution under a vacuum-assisted method at a pressure of -0.1 MPa.

[0051] (5) Oven drying: The delignified wood sheets loaded with the modification in step (4) are dried at 80°C for 2.5 h to obtain delignified wood sheets loaded with silver nanowires.

[0052] (6) Hot pressing treatment: Delignified wood sheets loaded with silver nanowires were placed in a hot press, and weighing paper and filter paper were used to hold the wood sheets to ensure uniform stress. The hot pressing treatment was carried out at 60°C and 8MPa for 12 hours to obtain the flexible wood-based film based on obliquely cut wood blocks loaded with silver nanowires.

[0053] Example 3: Preparation of a flexible wood-based thin film supported on silver nanowires from obliquely cut wood blocks

[0054] (1) Wood pretreatment: Select balsa wood and cut wood blocks at an angle of 67.5° to the direction of wood fiber growth to obtain wood veneers with a size of 3cm×3cm and a thickness of 2mm.

[0055] (2) Delignification treatment: Wood chips were immersed in a sodium chlorite solution at 85°C. The solution was adjusted to pH 4.6 using a sodium acetate buffer solution, and the treatment lasted for 8 hours to remove lignin from the wood. In this embodiment, multiple wood chips were immersed, and the ratio of the total mass of the wood chips to the volume of the sodium chlorite solution was 0.5:500 g / mL, ensuring that each wood chip underwent sufficient delignification treatment.

[0056] (3) Cleaning and drying: Soak the delignified wood chips in deionized water for 6 hours, changing the deionized water 3 times during the soaking period; then dry the wood chips in a freeze dryer for 48 hours at a cold trap temperature of -70°C to form porous delignified wood chips.

[0057] (4) Modifier loading: Porous delignified wood slabs were placed in a 2 mg / mL silver nanowire solution (deionized water as solvent), and the silver nanowires were allowed to penetrate into the cell cavities of the wood slabs with the solution under a vacuum-assisted method at a pressure of -0.1 MPa.

[0058] (5) Oven drying: The delignified wood sheets loaded with the modification in step (4) are dried at 100°C for 2 hours to obtain delignified wood sheets loaded with silver nanowires.

[0059] (6) Hot pressing treatment: Delignified wood sheets loaded with silver nanowires were placed in a hot press, and weighing paper and filter paper were used to hold the wood sheets to ensure uniform stress. The hot pressing treatment was carried out at 100°C and 5MPa for 10 hours to obtain the flexible wood-based film based on obliquely cut wood blocks loaded with silver nanowires.

[0060] Preparation of flexible wood-based films loaded with silver nanowires from longitudinally cut wood blocks (Comparative Example 1)

[0061] (1) Wood pretreatment: Select balsa wood and cut wood blocks at an angle parallel to the direction of wood fiber growth to obtain wood veneers with a size of 3cm×3cm and a thickness of 2mm.

[0062] (2) Delignification treatment: The wood chips were immersed in a sodium chlorite solution at 80°C, the solution of which was adjusted to pH 4.6 by sodium acetate buffer solution, for 8 hours to remove lignin from the wood.

[0063] (3) Cleaning and drying: Soak the delignified wood chips in deionized water for 6 hours, changing the deionized water 3 times during the soaking period; then dry the wood chips in a freeze dryer for 48 hours to form porous delignified wood chips.

[0064] (4) Modifier loading: Porous delignified wood slices were placed in a 5 mg / mL silver nanowire solution. Under a pressure of -0.1 MPa, the silver nanowires were allowed to penetrate into the wood cell cavity with the solution using a vacuum-assisted method.

[0065] (5) Oven drying: Place the delignified wood sheets impregnated with silver nanowires in an oven and dry them at 60°C for 3 hours.

[0066] (6) Hot pressing: Delignified wood chips loaded with silver nanowires were placed in a hot press, and weighing paper and filter paper were used to hold the wood chips to ensure uniform stress. Hot pressing was carried out at a temperature of 80°C and a pressure of 8 MPa for 10 hours to obtain a flexible wood-based film loaded with silver nanowires from longitudinally cut wood blocks.

[0067] Preparation of flexible wood-based films loaded with silver nanowires from cross-sectioned wood blocks (Comparative Example 2)

[0068] (1) Wood pretreatment: Select balsa wood and cut wood blocks at an angle perpendicular to the direction of wood fiber growth to obtain wood veneers with a size of 3cm×3cm and a thickness of 2mm.

[0069] (2) Delignification treatment: The wood chips were immersed in a sodium chlorite solution at 80°C, the solution of which was adjusted to pH 4.6 by sodium acetate buffer solution, for 8 hours to remove lignin from the wood.

[0070] (3) Cleaning and drying: Soak the delignified wood chips in deionized water for 6 hours, changing the deionized water 3 times during the soaking period; then dry the wood chips in a freeze dryer for 48 hours to form porous delignified wood chips.

[0071] (4) Modifier loading: Porous delignified wood slices were placed in a 5 mg / mL silver nanowire solution. Under a pressure of -0.1 MPa, the silver nanowires were allowed to penetrate into the wood cell cavity with the solution using a vacuum-assisted method.

[0072] (5) Oven drying: Place the delignified wood sheets impregnated with silver nanowires in an oven and dry them at 60°C for 3 hours.

[0073] (6) Hot pressing: Delignified wood chips loaded with silver nanowires were placed in a hot press, and weighing paper and filter paper were used to hold the wood chips to ensure uniform stress. Hot pressing was carried out at a temperature of 80°C and a pressure of 8 MPa for 10 hours to obtain a flexible wood-based film loaded with silver nanowires from a cross-section of the wood block.

[0074] The flexible wood-based films prepared in Examples 1-3 and Comparative Examples 1-2 were subjected to stress-strain curve analysis and electromagnetic shielding performance testing, respectively. The stress-strain curve analysis was performed using an electronic universal testing machine from Instron Corporation (USA). Each sample was cut into dumbbell-shaped specimens (total dimensions, 30 × 15 mm; measurement area, 5 × 22 mm) and tested. Electromagnetic shielding performance was tested using a vector network analyzer via the waveguide method. Each sample was cut into rectangles (22.9 mm × 10.2 mm), and the electromagnetic parameters (S-parameters) of the samples in the frequency range of 8.2-12.4 GHz were tested using an Agilent E5071C vector network analyzer. The electromagnetic shielding effectiveness was calculated. The silver nanowire loading was determined by measuring the weight of the wood before and after impregnation.

[0075] The tensile strength, electromagnetic shielding performance, and silver nanowire loading of the flexible wood-based films prepared in Examples 1-3 and Comparative Examples 1-2 are shown in Table 1 below.

[0076] Table 1 Performance testing of flexible wood-based films prepared in Examples 1-3 and Comparative Examples 1-2

[0077]

[0078] Meanwhile, the flexible wood-based films prepared in Examples 1-3 and Comparative Examples 1-2 were characterized in terms of performance.

[0079] (I) Electron Microscopy Scanning

[0080] The flexible wood-based thin film based on silver nanowires loaded on obliquely cut wood blocks prepared in Example 1 was subjected to electron microscopy scanning, and the results are shown in Figure 1. Figure 1a Image of a flexible wood-based film obtained using normal electron microscopy. Figure 1b for Figure 1a Scanning electron microscopy with 6x magnification of a specific area. Combined with... Figure 1a and Figure 1b It can be seen that the cutting direction of the wood film is arranged at a certain angle to the growth direction of the wood. This cutting method can significantly increase the exposed area of ​​the cell cavity and effectively shorten the impregnation path, thereby improving the penetration efficiency of additives into the wood.

[0081] (II) XRD Spectral Analysis

[0082] XRD patterns were analyzed on the flexible wood-based film (d-AgNWs@CS) based on obliquely cut wood blocks loaded with silver nanowires prepared in Example 2, the obliquely cut delignified flexible wood-based film (d-@CS) without silver nanowires, and the silver nanowires (AgNWs@CS). The results are as follows: Figure 4 As shown. Among them, the preparation method of the obliquely cut delignified flexible wood matrix (d-@CS) without silver nanowires is the same as that in Example 2, except that the modification loading step (4) is omitted.

[0083] from Figure 4 It can be seen that the two diffraction peaks at 2θ = 16.1° and 22.6° correspond to the (101) and (002) planes of crystalline cellulose, respectively. In the XRD pattern of the flexible wood-based film loaded with silver nanowires on d-AgNWs@CS, the typical face-centered cubic (FCC) crystal diffraction peaks of silver can be clearly observed at positions of 38.1° (111), 44.3° (200), 64.4° (220), and 77.5° (311). This result indicates that silver nanowires have been successfully loaded onto the flexible wood-based film, forming a composite material with a uniform structure.

[0084] (III) Stress-Strain Curve Analysis

[0085] Stress-strain curve analysis was performed on the flexible wood-based films based on silver nanowires loaded with obliquely cut wood blocks prepared in Examples 1-3 and Control Examples 1-2. The test results are shown in Table 1. Figure 2 As shown.

[0086] Combined with Table 1 and Figure 2It can be seen that when the cutting angles are 0°, 22.5°, 45°, 67.5°, and 90°, the corresponding fracture strengths of the flexible wood-based films loaded with silver nanowires are 328.8 MPa, 200.5 MPa, 173.5 MPa, 109.8 MPa, and 20.35 MPa, respectively. This indicates that the fracture strength of the flexible wood-based films loaded with silver nanowires gradually decreases with increasing cutting angle. During the transition from the oblique cutting direction to the transverse cutting direction, i.e., at a cutting angle of 90°, the mechanical properties of the flexible wood-based films loaded with silver nanowires significantly decrease. Compared to the transversely cut flexible wood-based films loaded with silver nanowires, the obliquely cut flexible wood-based films maintain superior mechanical properties. Although the mechanical properties of the obliquely cut flexible wood-based films in Examples 1-3 are slightly lower than those of the longitudinally cut wood films, they are still superior to the transversely cut wood films and possess better overall mechanical properties.

[0087] The flexible wood-based film based on silver nanowires loaded onto obliquely cut wood blocks prepared in Example 1 was folded. Figure 3 As can be seen from the example, the flexible wood-based film based on silver nanowires loaded on obliquely cut wood blocks prepared in Example 1 has good flexibility, which provides a basis for the application of flexible electromagnetic shielding composite materials.

[0088] (iv) Electromagnetic shielding performance analysis

[0089] The electromagnetic shielding effectiveness of the flexible wood-based films based on silver nanowires loaded with obliquely cut wood blocks prepared in Examples 1-3 and Comparative Examples 1-2 was tested in the frequency range of 8.2-12.4 GHz. The test results are as follows: Figure 5 As shown.

[0090] Combination Figure 5 A comprehensive analysis of Table 1 shows that, compared to longitudinally cut delignified wood veneers, obliquely cut and transversely cut delignified wood can load more silver nanowires, thus significantly improving the electromagnetic shielding performance of flexible wood-based films. Within the test range, when the cutting angles were 0° (longitudinal), 22.5°, 45°, 67.5°, and 90° (transverse), the electromagnetic shielding effectiveness of the silver nanowire-loaded flexible wood-based films was 18.8-17.1 dB, 29.6-27.6 dB, 27.4-26.4 dB, 31.4-30.2 dB, and 34.9-30.9 dB, respectively. It is evident that the electromagnetic shielding performance of transversely and obliquely cut silver nanowire-loaded flexible wood-based films is significantly better than that of longitudinally cut samples. This is mainly because obliquely and transversely cut wood is more conducive to the uniform loading and distribution of silver nanowires, thus improving the shielding performance of the flexible wood-based film.

[0091] The flexible wood-based thin film (d-AgNWs@CS) prepared in Example 1, which is based on silver nanowires loaded on obliquely cut wood blocks, can completely encapsulate a mobile phone, thus completely blocking the mobile phone signal and preventing the phone from communicating. (See Example 1.) Figure 6 b. When the phone is not encased (part of its structure is exposed) on a flexible wood-based film loaded with silver nanowires from a diagonally cut wooden block, it can communicate normally. See details... Figure 6 As shown in Figure a, it can be seen that the flexible wood-based film based on silver nanowires loaded on obliquely cut wood blocks prepared in Example 1 can successfully shield mobile phone signals and has electromagnetic shielding function.

[0092] In summary, although transversely cut wood exhibits excellent silver nanowire loading, its mechanical properties significantly decrease after compression preparation of flexible wood-based films, resulting in poor mechanical strength. Conversely, longitudinally cut wood shows the opposite trend, exhibiting the worst silver nanowire loading, thus affecting its electromagnetic shielding function. However, longitudinally cut wood films show the best mechanical properties after compression preparation of flexible wood-based films. The obliquely cut flexible wood-based film of this invention achieves a good balance between mechanical and shielding performance. Taking breaking strength as an example, compared to longitudinally cut delignified flexible wood-based films, transversely cut flexible wood-based films show a 93.81% decrease in mechanical properties, almost completely losing their load-bearing capacity; while obliquely cut flexible wood-based films with a cutting angle of 22.5° show only a 39.02% decrease in mechanical properties, still maintaining a breaking strength of 200.5 MPa, while possessing significantly improved electromagnetic shielding performance (29.6-27.6 dB).

[0093] Therefore, obliquely cut flexible wood-based films offer a novel approach to the preparation of wood composites. By optimizing the cutting angle, not only can the loading rate of functional additives (such as silver nanowires) on the flexible wood-based film be significantly improved, but the film's permeability can also be significantly enhanced. Furthermore, it achieves excellent mechanical properties during subsequent hot-pressing, resolving the contradiction between mechanical and functional properties in traditional longitudinally or transversely cut flexible wood-based films. This provides technical support and theoretical basis for the development of high-performance wood-based composites.

[0094] This description illustrates the technical solutions of the present invention, but is not intended to limit it. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features. Modifications or substitutions made without departing from the spirit of the present invention are all within the scope of protection claimed by the present invention.

Claims

1. A method for preparing flexible wood-based thin films loaded with silver nanowires based on obliquely cut wood blocks, characterized in that, The method includes the following steps: 1) Wood pretreatment: Select balsa wood and cut the wood blocks at an angle of 22.5-67.5° to the direction of wood fiber growth to obtain wood veneers with a thickness of 1-3mm; 2) Delignification treatment: Immerse the wood chips in sodium chlorite solution at 75-85℃, adjust the pH of the solution to 4.6, and soak for 8-10 hours to remove lignin from the wood chips; 3) Cleaning and drying: Soak the wood chips treated with delignification in step 2) with deionized water to remove residual sodium chlorite solution. After the sodium chlorite solution is completely removed, freeze-dry the delignified wood chips to form porous delignified wood chips. 4) Modifier loading: The porous delignified wood slabs are immersed in a silver nanowire solution, and the silver nanowires are allowed to penetrate into the cell cavities of the wood slabs with the solution using a vacuum-assisted method. 5) Oven drying: Dry the delignified wood sheets loaded with the modified material in step 4) to obtain delignified wood sheets loaded with silver nanowires. 6) Hot pressing treatment: The delignified wood sheet loaded with silver nanowires is placed in a hot press. After the delignified wood sheet loaded with silver nanowires is held between weighing paper and filter paper, it is hot pressed for 6-12 hours to obtain the flexible wood-based film based on obliquely cut wood block loaded with silver nanowires.

2. The method for preparing a flexible wood-based thin film based on silver nanowires loaded on obliquely cut wood blocks according to claim 1, characterized in that, In step 1), the dimensions of the obliquely cut wood slab are 3cm x 3cm.

3. The method for preparing a flexible wood-based thin film based on silver nanowires loaded on obliquely cut wood blocks according to claim 1 or 2, characterized in that, In step 2), the ratio of the mass of the wood veneer to the volume of the sodium chlorite solution is 0.5:500-600 g / mL.

4. The method for preparing a flexible wood-based thin film based on silver nanowires loaded on obliquely cut wood blocks according to claim 1 or 2, characterized in that, In step 2), the solution is adjusted to pH 4.6 using sodium acetate buffer solution.

5. The method for preparing a flexible wood-based thin film based on silver nanowires loaded on obliquely cut wood blocks according to claim 1 or 2, characterized in that, In step 3), the temperature of the freeze-drying cold trap is -75°C to -70°C.

6. The method for preparing a flexible wood-based thin film based on silver nanowires loaded on obliquely cut wood blocks according to claim 1, characterized in that, In step 4), the modifier loading is subjected to vacuum-assisted modifier permeation at a pressure of -0.1 MPa.

7. The method for preparing a flexible wood-based thin film based on silver nanowires loaded on obliquely cut wood blocks according to claim 1, characterized in that, In step 4), the concentration of the silver nanowire solution is 2-10 mg / mL, and the solvent is deionized water or ethanol.

8. The method for preparing a flexible wood-based thin film based on silver nanowires loaded on obliquely cut wood blocks according to claim 1, characterized in that, In step 5), the drying temperature is 60-100℃.

9. The method for preparing a flexible wood-based thin film based on silver nanowires loaded on obliquely cut wood blocks according to claim 1, characterized in that, The hot pressing process in step 6) is carried out at a temperature of 60-100℃ and a pressure of 5-10MPa.

10. A flexible wood-based thin film based on silver nanowires loaded on obliquely cut wood blocks, characterized in that: It is prepared by the preparation method described in any one of claims 1-9.

Images