Flexible veneer, flexible wood-based triboelectric material, and preparation method and application thereof

Abstract

The present invention belongs to the technical field of wood composite materials, and relates to flexible veneer, flexible wood-based triboelectric materials, and preparation methods and applications thereof. In view of the technical problems in the prior art that wood-based triboelectric materials lack flexibility, are difficult to adapt to complex usage environments, and have poor electrical performance, the present application provides a method for preparing flexible veneer, comprising the following steps: S1: slicing wood along the fiber direction of the wood to obtain slicing veneer; S2: delignifying the slicing veneer to obtain delignified veneer; S3: immersing the delignified veneer in cationic polyelectrolyte and anionic polyelectrolyte solutions in turn, removing the unreacted polyelectrolyte solution, and then immersing it in a crosslinker solution to obtain crosslinked veneer; S4: placing the crosslinked veneer in a MXene solution, removing the unreacted MXene, and drying to obtain flexible veneer. The prepared flexible veneer can be used for the preparation of flexible wood-based triboelectric materials, taking into account both mechanical properties and triboelectric properties.

Description

Technical Field

[0001] The present invention belongs to the technical field of wood composite materials, and in particular relates to flexible veneer, flexible wood-based triboelectric materials, and preparation methods and applications thereof. Background Art

[0002] Triboelectric nanogenerators (TENGs) can effectively convert various forms of low-frequency mechanical energy into electrical energy. TENGs primarily consist of positive and negative triboelectric materials, electrode materials, a substrate support material, and external wires. Their operating principle is based on the coupling of triboelectric charging and electrostatic induction. During friction, electron transfer occurs between two materials of different electronegativity, resulting in static charge accumulation, which in turn generates a potential difference and current. Currently, triboelectric materials for the positive electrode of TENGs include metal oxides (ITO, ZnO), metals (Al), cellulose, nylon, and polyamide. Triboelectric materials for the negative electrode of TENGs primarily include polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVDF), fluorinated ethylene propylene (FEP), polyethylene terephthalate (PET), and polydimethylsiloxane (PDMS). During use, metal materials are susceptible to oxidation and corrosion, which can affect the long-term structural stability of TENGs. Synthetic polymers are not directly degradable in the natural environment and can have environmental impacts. Therefore, the development of structurally stable and biodegradable triboelectric materials has attracted widespread attention.

[0003] Wood is a natural polymer material with a multi-layered porous structure. During the process of cellulose microfibrils aggregating to form wood fibers, cellulose, hemicellulose, and lignin intertwine, forming vertically arranged natural pores. This results in high surface roughness, which causes the material to lose electrons during friction and acquire a positive charge, making it a promising material for the positive electrode friction of a TENG (Telescopic Electron Engraving). Chinese invention patent application publication number CN116408860A, filed on March 16, 2023, is titled "A Wood Self-Densifying Film, Its Preparation Method, and Application." The application discloses delignifying wood, impregnating it with an ionic liquid-water mixture (1-ethyl-3-methylimidazolium acetate), and then hot-pressing it to produce the self-densifying film. When assembled with negatively charged PTFE (PTFE) to form a TENG, the film achieves an open-circuit voltage of 68V (2×2cm) in a contact-separation mode. While this solution addresses the low triboelectric effect of natural wood, the resulting TENG only achieves an output voltage of 68V, leaving significant room for improvement in electrical performance. In addition, during the use of TENG, the complexity of the environment also puts higher requirements on its mechanical properties, such as flexibility.

[0004] MXene, a novel two-dimensional layered material, possesses excellent physical and chemical properties. Its surface functional groups (such as -OH, -F, and -O) possess strong electron-capturing properties, favoring the capture of more electrons and increasing the surface charge density. This gives the MXene surface a high electronegativity, enabling enhanced static charge accumulation and thus increasing power generation efficiency. Previous studies have demonstrated the fabrication of a flexible, stretchable, single-electrode triboelectric nanogenerator (MH-TENG) using MXene / polyvinyl alcohol (PVA) hydrogel as electrodes. The MXene nanostructures promote cross-linking of the PVA hydrogel and form microchannels within the hydrogel. This not only enhances the hydrogel's conductivity by improving ion transport but also generates additional triboelectric output through a streaming vibration potential mechanism, reaching 230 V, 270 nA, and 38 nC (2 × 5 cm). However, excessive MXene concentrations can lead to interlayer stacking of the MXene layers, inhibiting ion transport within the hydrogel and consequently reducing the MH-TENG's output performance. Summary of the Invention

[0005] 1. Technical problem to be solved by the invention

[0006] In response to the technical problems in the existing technology that wood-based triboelectric materials lack flexibility, are difficult to adapt to complex usage environments, and have poor electrical performance, this application provides a method for preparing flexible veneer. The prepared flexible veneer can be used to prepare flexible wood-based triboelectric materials, taking into account both mechanical properties and triboelectric properties.

[0007] 2. Technical solution

[0008] In order to achieve the above objectives, the technical solutions provided are:

[0009] The method for preparing the flexible veneer of the present invention comprises the following steps:

[0010] S1: Veneer preparation, slicing the wood along the fiber direction to obtain sliced ​​veneer;

[0011] S2: delignification, delignifying the sliced ​​veneer to obtain delignified veneer;

[0012] S3: polyelectrolyte impregnation, immersing the delignified veneer in a cationic polyelectrolyte solution and an anionic polyelectrolyte solution in sequence, removing unreacted polyelectrolyte solution, and then immersing the veneer in a crosslinking agent solution to obtain a crosslinked veneer;

[0013] S4: MXene impregnation, placing the cross-linked veneer in a MXene solution, removing unreacted MXene, and drying to obtain the flexible veneer.

[0014] Preferably, the wood is sliced ​​longitudinally (along the grain), that is, the wood is sliced ​​along the fiber direction of the wood, and the sliced ​​thickness is 100 to 200 μm.

[0015] Preferably, the delignification process is as follows: the sliced ​​veneer is placed in a 1-2 wt% NaClO2 / CH3COOH buffer solution (pH 4-5) for delignification treatment at a temperature of 60-85°C for 1-2 hours to obtain delignified veneer.

[0016] Furthermore, the cationic polyelectrolyte solution is one or more of chitosan, polyethyleneimine, and polydopamine; and the anionic polyelectrolyte solution is one or more of phytic acid, ammonium polyphosphate, and sodium alginate.

[0017] Furthermore, the cross-linking agent solution is a polyacrylamide solution.

[0018] Preferably, the delignified veneer is placed in a 1-2wt% cationic polyelectrolyte solution and an anionic polyelectrolyte solution in sequence and vacuum immersed for 1-2 hours, and the unreacted polyelectrolyte solution is removed with deionized water. Then, the veneer is vacuum immersed in a 1-2wt% polyacrylamide solution for 1-2 hours, and the unreacted polyacrylamide solution is removed with deionized water. The veneer is kept at 50-60°C for 1-2 hours to promote the cross-linking reaction of the polyacrylamide to obtain the cross-linked veneer.

[0019] Furthermore, the concentrations of the cationic polyelectrolyte solution, the anionic polyelectrolyte solution and the cross-linking agent solution are 1 to 2 wt%.

[0020] Furthermore, the MXene is Ti3C2T x 、Ti2CT x 、V2CT x , the concentration of the MXene solution is 8 to 10 mg / mL.

[0021] Preferably, the cross-linked veneer is placed in a MXene solution with a concentration of 8 to 10 mg / mL, vacuum impregnated for 30 to 45 minutes, then washed with deionized water to remove unreacted MXene, and dried at room temperature for 10 to 30 minutes to obtain a flexible veneer.

[0022] The flexible veneer is prepared by the preparation method.

[0023] The invention relates to a method for preparing a flexible wood-based triboelectric material, comprising assembling a plurality of the flexible veneers along the fiber direction and the grain, and performing hot pressing.

[0024] Furthermore, the number of assembled layers is 2 to 10 layers; the hot pressing process is: maintaining at 60 to 85° C. and 1.2 to 5.5 MPa for 1 to 2 hours, then lowering the temperature to room temperature while maintaining the pressure, and continuing to maintain for 22 to 24 hours.

[0025] The flexible wood-based triboelectric material is prepared by the preparation method, and the thickness of the flexible wood-based triboelectric material is 200-800 μm.

[0026] Preferably, the content of MXene in the flexible wood-based triboelectric material is 10 to 20 wt%.

[0027] The application of flexible veneer or flexible wood-based triboelectric material is characterized in that the flexible veneer or flexible wood-based triboelectric material is applied to the preparation of a triboelectric nanogenerator.

[0028] 3. Beneficial effects

[0029] Compared with the existing known technologies, the technical solution provided by the present invention has the following beneficial effects:

[0030] (1) The preparation method and flexible veneer of the present invention, by delignifying the wood, "creates pores" in the wood cell wall, providing abundant nanoscale spaces and binding sites for the penetration of anionic and cationic polyelectrolytes, and the self-assembly between the micro-nano layers of the wood cell wall. The pores are then interwoven with a cross-linking agent (such as polyacrylamide), further constructing a three-dimensional network system within the micro-nano gaps of the wood. Hydrogen bonds, amide bonds, and electrostatic interactions simultaneously impart strength and flexibility to the wood-based material. The micro-nanoscale layered structure of the wood itself can effectively inhibit the occurrence of MXene interlayer stacking and prevent its oxidation. At the same time, the excellent electron capture ability of MXene can further improve the electrical performance of the wood-based TENG.

[0031] (2) The preparation method of the flexible wood-based triboelectric material and the flexible wood-based triboelectric material of the present invention are as follows: flexible veneers are assembled along the fiber direction and pressed into a laminated material, and highly oriented cellulose fibrils are assembled with polyelectrolytes and MXene (such as Figure 3 、 4 ), which can quickly generate carriers (ions, electrons) and quickly transmit them in the constructed three-dimensional network system (such as Figure 7 Mechanical properties tests show that the tensile strength of the flexible wood-based triboelectric material is 35.98-55.82 MPa, the toughness is 7.86-20.06 MJ / m, and it can be folded and bent (such as Figure 5 ).

[0032] (3) The application of the flexible veneer or flexible wood-based triboelectric material of the present invention is to assemble the flexible wood-based triboelectric material into a single-electrode triboelectric nanogenerator, and the output electrical performance can reach 165.44~207.36V, 11.41~14.31μA, 66.16~83.94nC, and it can also maintain excellent output electrical performance after 25,000 cycles, with the output voltage drop within 5% and the mechanical performance drop within 4% (such as Figure 8 ). BRIEF DESCRIPTION OF THE DRAWINGS

[0033] Figure 1 Schematic diagram of the wood planing proposed for this application.

[0034] Figure 2 SEM images of a single layer of flexible wood-based triboelectric material proposed in this application, including: (a) planed veneer; (b) delignified veneer; (c) flexible veneer; (d) MXene / flexible veneer (single layer); (e) MXene / wood-based triboelectric material.

[0035] Figure 3 XPS graph of the flexible wood-based triboelectric material proposed in this application.

[0036] Figure 4 SAXS graph of the flexible wood-based triboelectric material proposed in this application.

[0037] Figure 5 A diagram demonstrating the flexibility of the flexible wood-based triboelectric material proposed in this application.

[0038] Figure 6 This is the assembly structure diagram of the single-electrode TENG of wood-based triboelectric material proposed in this application.

[0039] Figure 7 The open circuit voltage of the wood-based triboelectric material proposed for this application is affected by the relative content of MXene.

[0040] Figure 8 Output electrical properties of the wood-based triboelectric material proposed in this application after 25,000 cycles, including: (a) open circuit voltage; (b) short circuit current; (c) output charge; (d) comparison of mechanical properties before the cycle. DETAILED DESCRIPTION

[0041] The technical solutions in the embodiments of the present invention are clearly and completely described below in conjunction with the accompanying drawings. Obviously, the described embodiments are only part of the embodiments of the present invention, rather than all the embodiments; based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative work are within the scope of protection of the present invention.

[0042] Abbreviations and Glossary

[0043] TENG, Triboelectric nanogenerator, nano friction generator;

[0044] CS, Chitosan.

[0045] Example 1

[0046] The method for preparing the flexible veneer of this embodiment includes the following steps:

[0047] (1) Veneer preparation: longitudinal (along the grain) slicing, that is, slicing the wood along the fiber direction, with a slicing thickness of 100-150 μm.

[0048] (2) Delignification: The planed veneer was placed in a 1.5 wt% NaClO2 / CH3COOH buffer solution (pH 4.5) for delignification at a temperature of 75°C for 1.5 h to obtain delignified veneer.

[0049] (3) Polyelectrolyte impregnation: The delignified veneer was placed in a 1.5 wt% cationic polyelectrolyte solution and an anionic polyelectrolyte solution in turn and vacuum impregnated for 1.5 h. The unreacted polyelectrolyte solution was removed with deionized water. Then, the veneer was vacuum impregnated in a 1.5 wt% polyacrylamide solution for 1.5 h. The unreacted polyacrylamide solution was removed with deionized water. The veneer was kept at 55°C for 1.5 h to promote the cross-linking reaction of the polyacrylamide and obtain cross-linked veneer.

[0050] (4) MXene impregnation: The flexible veneer prepared in step (3) was placed in a 9 mg / mL MXene solution and vacuum impregnated for 40 min. The solution was then washed with deionized water to remove unreacted MXene and dried at room temperature for 20 min to obtain a flexible veneer loaded with MXene.

[0051] The cationic polyelectrolyte solution used in this embodiment is chitosan; the anionic polyelectrolyte solution is phytic acid.

[0052] The MXene used in this example is Ti3C2T x MXene.

[0053] The properties of the flexible veneer prepared in this example are shown in Table 1.

[0054] Example 2

[0055] The method for preparing the flexible veneer of this embodiment is basically the same as that of Example 1, except for some process parameters, and includes the following steps:

[0056] (1) Veneer preparation: longitudinal (along the grain) slicing, that is, slicing the wood along the fiber direction, with a slicing thickness of 100 to 200 μm.

[0057] (2) Delignification: The planed veneer was placed in a 1 wt% NaClO2 / CH3COOH buffer solution (pH 4) for delignification at a temperature of 60°C for 2 h to obtain delignified veneer.

[0058] (3) Polyelectrolyte impregnation: The delignified veneer is placed in a 1 wt% cationic polyelectrolyte solution and an anionic polyelectrolyte solution in turn and vacuum impregnated for 2 h. The unreacted polyelectrolyte solution is removed with deionized water. Then, the veneer is vacuum impregnated in a 1 wt% polyacrylamide solution for 2 h. The unreacted polyacrylamide solution is removed with deionized water. The veneer is kept at 50°C for 2 h to promote the cross-linking reaction of the polyacrylamide to obtain cross-linked veneer.

[0059] (4) MXene impregnation: The flexible veneer prepared in step (3) was placed in a MXene solution with a concentration of 8 mg / mL and vacuum impregnated for 45 min. The solution was then washed with deionized water to remove unreacted MXene and dried at room temperature for 10 min to obtain a flexible veneer loaded with MXene.

[0060] The cationic polyelectrolyte solution used in this embodiment is polyethyleneimine; the anionic polyelectrolyte solution is ammonium polyphosphate.

[0061] The MXene used in this example is Ti2CT x MXene.

[0062] The properties of the flexible veneer prepared in this embodiment are basically the same as those in Example 1, indicating that the technical effect can be achieved under these process parameters.

[0063] Example 3

[0064] The method for preparing the flexible veneer of this embodiment is basically the same as that of Example 1, except for some process parameters, and includes the following steps:

[0065] (1) Veneer preparation: longitudinal (along the grain) slicing, that is, slicing the wood along the fiber direction, with a slicing thickness of 100 to 200 μm.

[0066] (2) Delignification: The planed veneer was placed in a 2 wt% NaClO2 / CH3COOH buffer solution (pH 5) for delignification at a temperature of 85°C for 1 h to obtain delignified veneer.

[0067] (3) Polyelectrolyte impregnation: The delignified veneer is placed in a 2 wt% cationic polyelectrolyte solution and an anionic polyelectrolyte solution in turn and vacuum impregnated for 1 hour. The unreacted polyelectrolyte solution is removed with deionized water. Then, the veneer is vacuum impregnated in a 2 wt% polyacrylamide solution for 1 hour. The unreacted polyacrylamide solution is removed with deionized water. The veneer is kept at 60°C for 1 hour to promote the cross-linking reaction of polyacrylamide to obtain cross-linked veneer.

[0068] (4) MXene impregnation: The flexible veneer prepared in step (3) was placed in a 10 mg / mL MXene solution and vacuum impregnated for 45 min. The solution was then washed with deionized water to remove unreacted MXene and dried at room temperature for 30 min to obtain a flexible veneer loaded with MXene.

[0069] The cationic polyelectrolyte solution used in this embodiment is polydopamine; the anionic polyelectrolyte solution is sodium alginate.

[0070] The MXene used in this example is V2CT x MXene.

[0071] The properties of the flexible veneer prepared in this embodiment are basically the same as those in Example 1, indicating that the technical effect can be achieved under these process parameters.

[0072] Example 4

[0073] The method for preparing the flexible wood-based triboelectric material of this embodiment, using the flexible veneer of Example 1, includes the following steps:

[0074] Hot pressing: The flexible veneer loaded with MXene in step (4) of Example 1 was assembled along the grain direction of the veneer fibers in three layers. The temperature was maintained at 75°C and 3 MPa for 1.5 h. The temperature was then lowered to room temperature while maintaining the pressure for another 23 h to obtain a flexible wood-based triboelectric material with a thickness of 200 to 300 μm.

[0075] The relative content of MXene in the flexible wood-based triboelectric material prepared in this embodiment is 15%.

[0076] The properties of the flexible wood-based triboelectric material prepared in this example are shown in Table 1.

[0077] Example 5

[0078] The preparation method of the flexible wood-based triboelectric material of this embodiment is basically the same as that of Example 4, except that the number of assembled layers is 5, and the thickness is 300-400 μm.

[0079] The properties of the flexible wood-based triboelectric material prepared in this example are shown in Table 1.

[0080] Example 6

[0081] The preparation method of the flexible wood-based triboelectric material of this embodiment is basically the same as that of Example 4, except that the number of assembled layers is 10, and the thickness is 700-800 μm.

[0082] The properties of the flexible wood-based triboelectric material prepared in this example are shown in Table 1.

[0083] Comparative Example 1

[0084] The wood-based triboelectric material of this comparative example is basically the same as that of Example 4, except that pure wood is used.

[0085] The properties of the wood-based triboelectric material prepared in this comparative example are shown in Table 1.

[0086] Comparative Example 2

[0087] The wood-based triboelectric material of this comparative example is basically the same as that of Example 4, except that MXene is not added.

[0088] The properties of the wood-based triboelectric material prepared in this comparative example are shown in Table 1.

[0089] Comparative Example 3

[0090] The wood-based triboelectric material of this comparative example is basically the same as that of Example 4, except that it is soaked in a cationic polyelectrolyte solution and an anionic polyelectrolyte solution.

[0091] The properties of the wood-based triboelectric material prepared in this comparative example are shown in Table 1.

[0092] Comparative Example 4

[0093] The wood-based triboelectric material of this comparative example is basically the same as that of Example 3, except that the veneer is sliced ​​transversely in the preparation of step (1).

[0094] The properties of the wood-based triboelectric material prepared in this comparative example are shown in Table 1.

[0095] Example 7

[0096] The preparation method of the flexible wood-based triboelectric material of this embodiment is basically the same as that of Example 4 except that the process parameters of the hot pressing are:

[0097] Hot pressing: The flexible veneer loaded with MXene in step (4) of Example 1 was assembled along the grain direction of each layer of veneer fiber, maintained at 60°C and 1.2 MPa for 2 h, and then the temperature was lowered to room temperature while maintaining the pressure for another 24 h to obtain a flexible wood-based triboelectric material.

[0098] The performance of the flexible wood-based triboelectric material prepared in this embodiment is basically the same as that in Example 4, indicating that the technical effect can be achieved under these process parameters.

[0099] Example 8

[0100] The preparation method of the flexible wood-based triboelectric material of this embodiment is basically the same as that of Example 4 except that the process parameters of the hot pressing are:

[0101] Hot pressing: The flexible veneer loaded with MXene in step (4) of Example 1 was assembled along the grain direction of each layer of veneer fiber, maintained at 85°C and 5.5 MPa for 1 hour, and then the temperature was lowered to room temperature while maintaining the pressure and maintained for another 22 hours to obtain a flexible wood-based triboelectric material.

[0102] The performance of the flexible wood-based triboelectric material prepared in this embodiment is basically the same as that in Example 4, indicating that the technical effect can be achieved under these process parameters.

[0103] Table 1 Summary of flexible wood-based triboelectric materials prepared in Examples and Comparative Examples and their mechanical and electrical properties

[0104]

[0105]

[0106] Note: WF-15-1 means single layer.

[0107] In summary, hot pressing after delignification of wood greatly improves the density of hydrogen bonds, and enhances the strength and output voltage of wood-based TENG. However, existing wood-based triboelectric materials lack flexibility and are difficult to adapt to complex usage environments. In this application, after delignification of wood, cationic polyelectrolytes and anionic polyelectrolytes are sequentially introduced, and polyacrylamide is interwoven to construct a three-dimensional network system within the micro-nano gaps of wood, simultaneously giving the wood-based material strength and flexibility, and providing a conductive channel for charge transfer; on this basis, MXene two-dimensional nanosheets with excellent conductive properties are infiltrated into the micro-nano space of wood, and the electrons generated by MXene and the ions generated by polyelectrolytes further enhance the triboelectric output performance of wood-based materials.

Claims

1. A method for preparing flexible veneer for flexible wood-based triboelectric materials, characterized by: The following steps are involved: S1: Veneer preparation, slicing the wood along the fiber direction to obtain sliced ​​veneer; S2: delignification, delignifying the sliced ​​veneer to obtain delignified veneer; S3: polyelectrolyte impregnation, immersing the delignified veneer in a cationic polyelectrolyte solution and an anionic polyelectrolyte solution in sequence, removing unreacted polyelectrolyte solution, and then immersing the veneer in a crosslinking agent solution to obtain a crosslinked veneer; S4: MXene impregnation, placing the cross-linked veneer in a MXene solution, removing unreacted MXene, and drying to obtain the flexible veneer for the flexible wood-based triboelectric material; The cationic polyelectrolyte solution is one or more of chitosan, polyethyleneimine, and polydopamine; the anionic polyelectrolyte solution is one or more of phytic acid, ammonium polyphosphate, and sodium alginate; The cross-linking agent solution is a polyacrylamide solution; The concentrations of the cationic polyelectrolyte solution, the anionic polyelectrolyte solution and the crosslinking agent solution are 1 to 2 wt %; The MXene is Ti3C2T x or Ti2CT x or V2CT x Any one of the above, wherein the concentration of the MXene solution is 8-10 mg / mL.

2. Flexible veneer for flexible wood-based triboelectric materials, characterized by: The flexible wood-based triboelectric material is prepared by the method for preparing flexible veneer according to claim 1.

3. A method for preparing a flexible wood-based triboelectric material, characterized in that: A plurality of flexible wood-based triboelectric materials according to claim 2 are assembled with flexible veneer along the fiber direction and hot pressed.

4. The method for preparing a flexible wood-based triboelectric material according to claim 3, wherein: The number of assembled layers is 2 to 10; the hot pressing process is: maintaining at 60 to 85°C and 1.2 to 5.5 MPa for 1 to 2 hours, then lowering the temperature to room temperature while maintaining the pressure, and continuing to maintain the pressure for 22 to 24 hours.

5. Flexible wood-based triboelectric material, characterized by: The flexible wood-based triboelectric material is prepared by the preparation method of any one of claims 3 or 4, wherein the thickness of the flexible wood-based triboelectric material is 200-800 μm.

6. Application of flexible veneer or flexible wood-based triboelectric material, characterized by: The flexible wood-based triboelectric material flexible veneer described in claim 2 or the flexible wood-based triboelectric material described in claim 5 is used in the preparation of a triboelectric nanogenerator.

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