Wood-based piezoelectric material and method for producing the same

Abstract

The application discloses a kind of wood-based piezoelectric material and its preparation method, the wood-based elastic skeleton has several wood fiber layers, wood fiber layer is derived from wood fiber, each wood fiber layer is connected with each other, at least part of the wood fiber layer connected with each other has pore structure, and the pore structure is formed by wood ray organization collapse.The method of the application uses alkaline substance and / or oxide to chemically treat wood raw material, uses alcohol solvent to clean the pretreatment product, to obtain the pretreatment product;The pretreatment product is dried to obtain a dried product;The dried product is heat treated, the wood-based piezoelectric material of the application is light in weight, low in cost, fast in degradation speed, has good elastic performance and better piezoelectricity, the method has the advantages of simple operation, low cost, green environmental protection, raw material is easy to obtain, and is suitable for mass production.

Description

Technical Field

[0001] This invention relates to a wood-based piezoelectric material and its preparation method, belonging to the adjacent fields of wood and piezoelectric materials. Background Technology

[0002] The dwindling supply of fossil fuels and severe environmental pollution have spurred tremendous efforts to find alternative and more sustainable energy sources. Over the past few decades, sustainable and clean energy sources such as wind and solar power have been developed to address the energy crisis; however, these energy sources are highly dependent on weather and other environmental conditions.

[0003] Mechanical energy exists in various forms in daily life, including sound energy and human movement. Extracting mechanical energy from the environment and converting it into electrical energy has led to the widespread research on piezoelectric nanogenerators. Among existing piezoelectric materials, lead zirconate titanate (PZT) piezoelectric ceramics are commonly used in piezoelectric applications. These materials either originate from non-renewable fossil fuels or generate toxic and harmful substances during processing, causing environmental pollution. PZT-based ceramics, for example, are environmentally polluting materials; their toxic PbO exhibits significant volatility during processing and sintering, posing a threat to human health and the environment. The cost of recycling and environmentally friendly treatment of lead-containing piezoelectric ceramic devices far exceeds the original manufacturing cost.

[0004] With increasing societal emphasis on environmental protection, there is an urgent need to explore new green and low-carbon power generation technologies and materials to meet the evolving demands of low-carbon and sustainable social development. In recent years, plant fiber-based power generation materials have become a research hotspot for scientists both domestically and internationally. The abundant polar hydroxyl groups endow cellulose with a large number of dipoles and a strong electron-donating ability, giving it piezoelectric properties. Plant fibers, as the most abundant natural polymer materials in nature, primarily originate from naturally growing plants and possess characteristics such as low density, high mechanical properties, biodegradability, renewability, recyclability, and environmental friendliness.

[0005] Wood is one of the most abundant natural resources on Earth. The cell walls of wood are primarily composed of cellulose (organized in amorphous and crystalline regions), hemicellulose, and lignin. Due to the uniaxial orientation and monoclinic symmetry of the crystalline cellulose protofibrils, wood exhibits piezoelectric properties. However, the relatively poor deformability of wood results in a low piezoelectric effect.

[0006] Therefore, it is an urgent task to find a wood-based piezoelectric material and method that is simple to prepare, low in cost, can generate effective power output without the need for the insertion of additional chemical materials, is more sustainable, and is more suitable for biomedical applications. Summary of the Invention

[0007] To overcome the shortcomings of existing technologies, this invention provides a wood-based piezoelectric material and its preparation method. The wood-based piezoelectric material is lightweight, low-cost, rapidly degrades, and has good elasticity and piezoelectricity. The method is simple, low-cost, environmentally friendly, and uses readily available raw materials, making it suitable for mass production.

[0008] To solve the above-mentioned technical problems, the present invention provides the following technical solution:

[0009] A wood-based piezoelectric material comprising a wood-based elastic skeleton, characterized in that: the wood-based elastic skeleton has a plurality of wood fiber layers, the wood fiber layers being derived from wood fibers, each wood fiber layer being interconnected with the others, and at least some of the interconnected wood fiber layers having a channel structure, the channel structure being formed by the collapse of wood ray tissue.

[0010] As a preferred embodiment of the present invention, the content of the wood-based elastic skeleton is 50-90%, preferably 70-80%.

[0011] As a preferred embodiment of the present invention, the wood fiber layer comprises cellulose, hemicellulose and lignin.

[0012] As a preferred embodiment of the present invention, the mass ratio of cellulose, hemicellulose and lignin in the wood-based elastic skeleton is 50-90:1-10:1-10.

[0013] A method for preparing a wood-based piezoelectric material, characterized by comprising the following steps:

[0014] The wood raw material is chemically treated with alkaline substances and / or oxides, and the pretreated product is cleaned with alcohol solvents to obtain the pretreated product.

[0015] The pretreated product is dried to obtain a dried product;

[0016] The dried product is subjected to heat treatment to obtain a wood-based elastic skeleton.

[0017] As a preferred technical solution of the present invention, the drying includes one or more of air drying, freeze drying or supercritical drying. Freeze drying involves placing the pretreated product under a vacuum of 0.1 μPa to 120 Pa and a temperature of -65 ˚C to -45 ˚C for 24 h to 96 h.

[0018] As a preferred embodiment of the present invention, the heat treatment includes heating to 190°C to 1000°C at a heating rate of 1°C / min to 10°C / min, and performing heat treatment for 1 h to 5 h.

[0019] As a preferred embodiment of the present invention, when performing chemical treatment using alkaline substances, a water bath is used for heating, with a heating temperature of 60 ℃ to 150 ℃ and a heating time of 2 h to 48 h.

[0020] As a preferred embodiment of the present invention, when using oxides for chemical treatment, the wood raw material is soaked in an oxide solution with a pH of 3 to 5, the heating temperature is 30 ℃ to 100 ℃, the heating time is 2 h to 36 h, and the mass fraction of oxides in the oxide solution is 0.5% to 30%.

[0021] As a preferred embodiment of the present invention, the oxide includes one or more of H2O2, NaClO2, NaClO, KClO2, and KClO.

[0022] Compared with the prior art, the beneficial effects that the present invention can achieve are as follows:

[0023] 1. This invention provides a wood-based piezoelectric material. It utilizes alkaline substances and oxides to chemically treat wood raw materials, obtaining a pretreated product; the pretreated product is dried to obtain a dried product; the dried product is then heat-treated to obtain a wood-based elastic skeleton, increasing the dynamic deformation capacity of the macroscopic wood and facilitating the displacement of cellulose crystals under small loads. This invention effectively solves the problems of non-degradability of petroleum-based piezoelectric materials and complex molding processes of ceramic-based and other piezoelectric materials. The wood-based piezoelectric material of this invention is lightweight, low-cost, rapidly degradable, and possesses good elasticity and piezoelectric properties.

[0024] 2. The present invention provides a method for preparing wood-based piezoelectric materials. The preparation method is simple and easy to implement, the raw materials are easy to obtain, and it is suitable for mass production. Attached Figure Description

[0025] Figure 1 This is a schematic diagram of the stress-strain curve of Embodiment 1 of the present invention;

[0026] Figure 2 This is a schematic diagram of the stress-strain curve in Embodiment 2 of the present invention;

[0027] Figure 3 This is a schematic diagram of the open-circuit voltage curve of Embodiment 1 of the present invention;

[0028] Figure 4 This is a schematic diagram of the open-circuit voltage curve of Embodiment 2 of the present invention. Detailed Implementation

[0029] To make the technical means, creative features, and achieved objectives and effects of this invention easier to understand, the invention is further described below with reference to specific embodiments. However, the following embodiments are only preferred embodiments of this invention and not all embodiments. Other embodiments obtained by those skilled in the art based on the embodiments described herein without creative effort are all within the protection scope of this invention. Unless otherwise specified, the experimental methods in the following embodiments are conventional methods, and the materials and reagents used in the following embodiments are commercially available unless otherwise specified.

[0030] Example 1: A wood-based piezoelectric material and its preparation method, comprising the following steps: First, wood is cut into 15mm×15mm×15mm blocks. An 8wt% NaOH solution is prepared, and the wood blocks are placed in the solution and heated in a 90℃ water bath for about 8 hours to initially remove hemicellulose. The wood blocks are then rinsed with a large amount of distilled water at a temperature of 10–80℃ to remove any remaining chemicals. A 2wt% NaClO2 (sodium chlorite) solution is prepared, and the pH of the NaClO2 solution is adjusted to 4.4–4.5 using glacial acetic acid. The wood blocks are placed in the NaClO2 solution, the beaker is sealed with plastic wrap, and heated in a water bath at 80℃ for 12 hours. The NaClO2 solution is replaced every 6 hours to obtain a pretreated product. The wood blocks are then rinsed with distilled water to remove any remaining chemicals, and then washed several times with tert-butanol. The replaced wood blocks were placed in a freeze dryer, with the cold trap temperature set to -49℃ and the vacuum degree to approximately 8 Pa, and freeze-dried for 3 days to obtain the dried product. The chemically treated wood blocks were then placed in a tube furnace and heated at 260℃ for 3 hours under a nitrogen atmosphere at a heating rate of 4℃ / min to obtain a wood-based elastic skeleton with a mass of approximately 0.218 g.

[0031] Wood-based materials are obtained by chemically treating wood raw materials with alkaline substances and oxides; specifically, the chemical treatment time is 2h to 48h, preferably 2h to 30h; for example: 5h, 10h, 15h, 20h, 25h, 30h, etc.

[0032] When using alkaline substances for chemical treatment, heating, such as water bath heating, can be employed to accelerate the removal of hemicellulose. Specifically, the heating temperature can be between 60 ℃ and 150 ℃, for example: 70 ℃, 80 ℃, 90 ℃, 100 ℃, 110 ℃, 120 ℃, 130 ℃, 140 ℃, etc.

[0033] The alkali-treated product is oxidized using oxides to remove some of the lignin. Specifically, the oxides are not particularly limited in this invention and can be commonly used oxides in the art. Specifically, the oxides can include one or more combinations of H₂O₂, NaClO₂, NaClO, KClO₂, KClO, etc. The treatment method involves soaking the wood raw material in an oxide solution to obtain the wood-based material. Specifically, the oxides can be dissolved in a solvent. This invention does not particularly limit the specific solvent and can use commonly used polar solvents in the art, such as water. Specifically, the mass fraction of the oxides in the oxide solution is 0.5% to 30%, for example: 2%, 4%, 6%, 8%, 10%, 12%, 14%, 16%, 18%, 20%, 22%, 24%, 26%, 28%, etc. During the preparation process, considering the consumption of oxides, the oxide solution can be replaced periodically, for example, every 3 to 10 hours. In addition, in order to achieve better oxidation treatment, glacial acetic acid needs to be added to adjust the pH of the sodium chlorite solution to be acidic when preparing the oxide solution. The specific pH value can be 3 to 5, preferably 3.5 to 4.5, such as 3.2, 3.8, 4, 4.2, 4.8, etc.

[0034] In some specific implementation schemes, heating can be used during chemical treatment with oxides to accelerate lignin removal. Specifically, the heating temperature can be 30℃ to 100℃, for example: 40℃, 50℃, 60℃, 70℃, 80℃, 90℃, etc.; the heating time can be 2h to 36h, for example: 2h, 4h, 6h, 8h, 12h, 14h, 16h, 18h, 20h, 22h, 24h, 26h, 28h, 30h, 32h, 34h, etc.

[0035] The wood-based material is dried to obtain a dried product. Specifically, the wood-based material can be cleaned to neutrality using a polar solvent, such as water or an alcohol solvent, to facilitate subsequent drying. Furthermore, if the wood-based material is initially cleaned with water before drying, it can be further cleaned with an alcohol solvent to displace the solvent and facilitate drying. Using an alcohol solvent to clean the wood-based material again effectively preserves the morphology of the wood-based elastic material. The drying process is freeze-drying. This drying procedure facilitates subsequent heat treatment. For freeze-drying, in this invention, the freeze-drying includes placing the pretreated product under a vacuum of 0.1 μPa to 120 Pa, such as 10 μPa, 100 μPa, 200 μPa, 500 μPa, 700 μPa, 1 MPa, 5 MPa, 10 MPa, 50 MPa, 100 MPa, 200 MPa, 500 MPa, 800 MPa, 1 Pa, 10 Pa, 50 Pa, 80 Pa, 100 Pa, etc., and drying at a temperature of -65 ˚C to -45 ˚C, such as -62 ˚C, -60 ˚C, -58 ˚C, -55 ˚C, -52 ˚C, -50 ˚C, -48 ˚C, etc., for 24 h to 96 h. h, for example: 25h, 30h, 35h, 40h, 45h, 50h, 55h, 60h, 65h, 70h, 75h, 80h, 85h, 90h, 95h, etc.

[0036] For heat treatment equipment, it can be equipment commonly used in this field, such as muffle furnace, tube furnace or vacuum furnace, etc.

[0037] In this invention, inert gas refers to gas that does not undergo relevant reactions during the activation process of this invention, such as nitrogen and rare gases, for example: argon, helium, etc.

[0038] Heat treatment can expose the benzene ring structure of the remaining lignin, thereby obtaining a wood-based thermal storage material that achieves photothermal conversion and heat storage. Preferably, the activation temperature for the heat treatment is 190˚C to 1000˚C, for example: 200˚C, 250˚C, 300˚C, 350˚C, 400˚C, 500˚C, 600˚C, 700˚C, 800˚C, etc.; the heat treatment time is 1 to 5 hours, for example: 1.5 hours, 2 hours, 2.5 hours, 3 hours, 3.5 hours, 4 hours, 4.5 hours, etc.; the heating rate is 1˚C / min to 10˚C / min, for example: 2˚C / min, 4˚C / min, 6˚C / min, 8˚C / min, etc.

[0039] Example 2: A wood-based piezoelectric material and its preparation method, differing from Example 1 in that: firstly, wood is cut into blocks of 15mm × 15mm × 10mm. A 2wt% NaClO2 solution is prepared, and the pH value of the NaClO2 solution is adjusted to 4.4–4.5 using glacial acetic acid. The wood blocks are placed in the NaClO2 solution, the mouth of the beaker is sealed with plastic wrap, and heated in a water bath at 80°C for 12 hours, with the NaClO2 solution replaced every 6 hours to obtain a pretreated product. The wood blocks are rinsed with distilled water to remove residual chemicals, and then cleaned and replaced with tert-butanol. The replaced wood blocks are placed in a freeze dryer, with the cold trap temperature set to -49°C and the vacuum degree to approximately 8Pa, and freeze-dried for 3 days to obtain a dried product. The chemically treated wood blocks are placed in a tube furnace and heated at 260°C for 3 hours under a nitrogen atmosphere at a heating rate of 4°C / min to obtain a wood-based elastic skeleton with a mass of approximately 0.218g.

[0040] A wood-based piezoelectric nanogenerator was fabricated using the wood-based piezoelectric material obtained in the examples. Specifically, 20 pre-fabricated 15mm×15mm×15mm wood-based elastic skeletons were connected in parallel, with 70×55mm copper foil adhered to both sides. These were then covered with two 1mm thick wood veneers, and wires were used to assemble a small nanogenerator demonstrator. Various portable low-power electronic devices, such as LEDs and liquid crystal displays (LCDs), were electrically connected. A small LED could be turned on by opening the demonstrator. The number of wood blocks is not specifically limited and can be determined based on the power of the electrical appliances used. For example, 10, 20, 30, or 40 wood blocks could be connected in series to drive commercial LED beads. The electrodes on both sides are not specifically limited and can be conductive sheets such as copper foil, aluminum foil, or silver foil.

[0041] The performance of the wood-based piezoelectric nanogenerator prepared using the wood-based piezoelectric material obtained in the examples is tested as follows:

[0042] 1. Compression Test: The static compression test is suitable for evaluating the compressive properties of elastic materials under static load. The static compression test of elastic materials requires a compression testing machine to apply a load to the specimen at a compression rate of 12±3 mm / min and obtain the corresponding force-displacement curve.

[0043] like Figure 1 , Figure 2 As shown, by Figure 1 It can be seen that after delignification treatment in Example 1, the material can withstand stresses up to 15 kPa at 40% strain. Figure 2 It can be seen that after delignification heat treatment in Example 2, the material can withstand stresses up to 400 kPa at 90% strain.

[0044] 2. Output Voltage: A Keithley 6514 electrometer was used to measure the piezoelectric output of the sample. A fixed pressure was applied using a linear motor (PL01-28x500 / 420), and the sample was compressed using a 50 N pressure sensing element to monitor the pressure.

[0045] like Figure 1 , Figure 2 As shown, under the same pressure, the output voltage of the material after delignification treatment in Example 1 is 0.6V, and the output voltage of the material after delignification heat treatment in Example 2 is 1.5V.

[0046] 3. Degradability: The wood-based piezoelectric material samples from Examples 1 and 2 were weighed and recorded. The exposed wood sponges were sterilized with ethylene oxide and then placed in Kolle culture flasks containing freshly inoculated *Pseudomonas putida* grown on 75 mL of 4% malt extract Aagar. Three replicates were studied for each culture period (6, 8, and 10 weeks). All cultures were maintained in the dark at 22°C and 70% relative humidity. After the selected culture time, the samples were carefully removed, the fungal biomass was removed from the surface, and the shape of the sponge samples was recorded using a camera. The complete loss of the original shape and significant size reduction confirmed the successful biodegradation of the wood sponges.

[0047] Performance tests show that the wood-based piezoelectric material provided by this invention has good elasticity and piezoelectricity, is lightweight, and degrades quickly.

[0048] The foregoing has shown and described the basic principles, main features, and advantages of the present invention. Those skilled in the art should understand that the present invention is not limited to the above embodiments. The embodiments and descriptions in the specification are merely preferred examples and are not intended to limit the invention. Various changes and modifications can be made to the invention without departing from its spirit and scope, and all such changes and modifications fall within the scope of the present invention as claimed. The scope of protection of the present invention is defined by the appended claims and their equivalents.

Claims

1. A wood-based piezoelectric material, comprising a wood-based elastic skeleton, characterized in that: The wood-based elastic skeleton has several wood fiber layers, which are derived from wood fibers. Each wood fiber layer is connected to the others, and at least some of the connected wood fiber layers have a channel structure formed by the collapse of wood ray tissue. The content of the wood-based elastic skeleton is 50-90%. The wood fiber layers contain cellulose, hemicellulose, and lignin, and the mass ratio of cellulose, hemicellulose, and lignin in the wood-based elastic skeleton is 50-90:1-10:1-10.

2. The wood-based piezoelectric material according to claim 1, characterized in that: The content of the wood-based elastic skeleton is 70-80%.

3. A method for preparing a wood-based piezoelectric material as described in claim 1, characterized in that, Includes the following steps: The wood raw materials are chemically treated with alkaline substances and oxides, and the pretreated products are cleaned with alcohol solvents to obtain the pretreated products. The pretreated product is dried to obtain a dried product. The drying includes one or more of the following: air drying, freeze drying, or supercritical drying. Freeze drying involves placing the pretreated product under a vacuum of 0.1 μPa to 120 Pa and a temperature of -65°C to -45°C for 24 h to 96 h. The dried product is subjected to heat treatment, which includes heating to 190°C to 1000°C at a heating rate of 1°C / min to 10°C / min under the protection of an inert gas, and heat treatment for 1 h to 5 h to obtain a wood-based elastic skeleton.

4. The method according to claim 3, characterized in that: When performing chemical treatment using alkaline substances, a water bath is used for heating at a temperature of 60℃ to 150℃ for a duration of 2 hours to 48 hours.

5. The method according to claim 3, characterized in that: When using oxides for chemical treatment, the wood raw material is soaked in an oxide solution with a pH of 3 to 5, heated at a temperature of 30°C to 100°C for 2 to 36 hours, and the mass fraction of oxides in the oxide solution is 0.5% to 30%.

6. The method according to claim 3, characterized in that: The oxides include one or more of H2O2, NaClO2, NaClO, KClO2, and KClO.

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