Modified bacterial cellulose-based composite membrane as well as preparation method and application thereof

Abstract

The invention provides a modified bacterial cellulose-based composite film as well as a preparation method and application thereof, and belongs to the technical field of friction materials. The modified bacterial cellulose-based composite membrane comprises a bacterial cellulose-based membrane and a plurality of nanoparticles dispersed in the bacterial cellulose-based membrane, the nanoparticles have a core-shell structure, the core layer is barium titanate, the shell layer is polydopamine, and Ag particles are embedded in the shell layer. According to the preparation method disclosed by the invention, the BTO-PDA-Ag nano-particles can be used for modifying the modified bacterial cellulose base membrane, so that the thermal stability, the mechanical property and the dielectric property of the bacterial cellulose base membrane are improved. The modified bacterial cellulose-based composite film provided by the invention is used as a positive electrode friction material of a friction nano-generator, and the electric output performance of the friction nano-generator is obviously improved.

Description

Technical Field

[0001] The present invention relates to the technical field of friction materials, and particularly relates to a modified bacterial cellulose-based composite film, a preparation method thereof, and an application thereof. Background Art

[0002] In recent years, people not only face the growth of global energy demand, the aggravation of environmental pollution problems, and the trouble of sustainable energy solutions, but also with the continuous progress of sensor technology and the wide application of wearable devices in daily life, new challenges have been posed for the power supply of distributed sensors and wearable devices. Therefore, there is an urgent need to develop environmentally friendly, lightweight, renewable, and sustainable portable energy to power wearable electronic devices. The invention of the triboelectric nanogenerator (abbreviated as TENG) has changed this situation. The triboelectric nanogenerator is based on the coupled effect of triboelectrification and electrostatic induction, and is an effective way to solve the low conversion efficiency of low-frequency mechanical energy in traditional power generation technologies. It can collect mechanical energy in the environment, such as wind energy, tidal energy, etc., and convert it into electrical energy for realizing various self-powered systems. As an energy technology with broad prospects, TENG has attracted extensive attention in various fields, such as biomedical devices, wearable electronic devices, actuation and motion sensing, etc. A key problem faced by TENG in the development process is the low surface charge density and the output performance needs to be improved.

[0003] Currently, there are various methods to improve the output performance of TENG. For example: (1) Molecular surface functionalization, introducing some special functional groups (such as -CF 3 、-NH 2 )or injecting some special ions (such as O 2 - 、O 3 - )on the surface of the friction material by chemical methods. These special ions can effectively change the surface potential, making it easy for electrons to be lost or obtained; (2) Surface topography modification, constructing micro-nano structures by lithography, electrospinning, template method, etc. to increase the surface charge density; (3) Forming a sponge or porous structure in the bulk friction material, increasing the frictional contact area, reducing the effective thickness, and making it have a larger surface area and better compressibility simultaneously; (4) Adding a sub-layer to the bulk friction material, introducing a dielectric transition layer between the bulk friction material and the conductive electrode, which can store the frictional charges during the contact and separation cycles, thereby increasing the surface charge density; (5) Adding nanomaterials (such as BaTiO 3, 1D carbon nanotubes, 2D graphene, MXene) are doped into the friction material to increase the effective dielectric constant or form a micro-capacitor structure with electron trapping sites. These methods contribute to improving the output performance of TENG to some extent, but still have drawbacks such as complex preparation methods and sophisticated instrument requirements. In addition, most reported triboelectric materials are synthetic polymers, which may cause environmental problems in the long run. Therefore, there is still a need to develop a simple and effective method to fabricate environmentally friendly TENGs with high output performance. Summary of the Invention

[0004] In view of the technical problems existing in the background art, the present invention provides a modified bacterial cellulose-based composite film, its preparation method and application, aiming to solve the technical problems of environmental pollution of existing friction materials and the low surface charge density of TENGs prepared from existing friction materials.

[0005] In the first aspect, the present invention provides a modified bacterial cellulose-based composite film, including a bacterial cellulose-based film and a number of nanoparticles dispersed in the bacterial cellulose-based film; The nanoparticles have a core-shell structure, with a barium titanate core layer, a polydopamine shell layer, and Ag particles embedded in the shell layer.

[0006] Preferably, the volume fraction of BTO@PDA-Ag nanoparticles in the modified bacterial cellulose-based composite film is 0.1 vol% - 5 vol%.

[0007] Preferably, the volume fraction of BTO@PDA-Ag nanoparticles in the modified bacterial cellulose-based composite film is 0.5 vol%.

[0008] Preferably, the mass ratio of barium titanate, polydopamine, and Ag particles in the nanoparticles is (60 - 80) : (5 - 15) : (5 - 20).

[0009] Preferably, the mass ratio of barium titanate, polydopamine, and Ag particles in the nanoparticles is 70 : 10 : 15.

[0010] In the second aspect, the embodiment of the present invention provides a preparation method of a modified bacterial cellulose-based composite film, including the following steps: Disperse barium titanate powder into a dopamine solution, heat and stir, and obtain barium titanate particles coated with polydopamine after centrifugation, washing, and drying; disperse the barium titanate particles coated with polydopamine into a silver ammonia solution, stir at room temperature, and obtain nanoparticles after centrifugation, washing, and drying; Disperse the nanoparticles in a bacterial cellulose aqueous suspension, and obtain a modified bacterial cellulose-based composite film after ultrasonic treatment, filtration, and drying.

[0011] Preferably, the temperature for heating and stirring is 50~70°C, and the heating and stirring time is 12~24 h.

[0012] Preferably, the concentration of the silver ammonia solution is 0.02~0.06 mol / L.

[0013] Preferably, the mass concentration of the bacterial cellulose aqueous suspension is 0.5~5 mg / L.

[0014] Preferably, the ultrasonic treatment frequency is 40 KHz; the time is 30~60 min.

[0015] In the present invention, the drying method is not limited, and common drying methods in the art can be selected according to actual situations, such as vacuum drying, etc.; the drying temperature is preferably 60~80°C, and the drying time is preferably 12~24 h.

[0016] In the third aspect, the present invention provides a triboelectric nanogenerator, and the positive friction material of the triboelectric nanogenerator includes the modified bacterial cellulose-based composite film provided in the first aspect of the present invention.

[0017] Preferably, the negative friction material of the triboelectric nanogenerator includes a PVDF-TrFE film.

[0018] Preferably, the film thickness of the modified bacterial cellulose-based composite film is 20~45 μm; the thickness of the PVDF-TrFE film is 20~35 μm.

[0019] The present invention provides a modified bacterial cellulose-based composite film, and its modification material is BTO@PDA-Ag nanoparticles. Among them, barium titanate serves as the core dielectric phase, and an interfacial layer is formed by continuous coating of polydopamine on the surface. Silver nanoparticles are distributed on the surface of the polydopamine layer or embedded inside it through chemical reduction or physical adsorption. Polydopamine serves as an interfacial regulation layer, which not only effectively improves the compatibility between barium titanate and silver particles, but also provides anchoring sites for the stable loading of silver particles with its rich functionalized surface, while suppressing the leakage conduction phenomenon caused by direct contact between barium titanate and silver. The thickness and compactness of the polydopamine layer have a significant impact on the interfacial polarization and charge transport behavior. An overly thick or structurally loose coating layer may lead to an increase in parasitic losses, while appropriate optimization can synergistically enhance the polarization and insulation properties.

[0020] The introduction of silver nanoparticles affects the dielectric response of the composite material through the dual mechanisms of micro-capacitance network construction and local field regulation. As the conductive phase, silver particles form a micro-capacitance structure in the insulating-conductive interface region, and the surface electromagnetic field enhancement effect can activate the ferroelectric domain polarization of barium titanate, thereby increasing the dielectric constant; at the same time, the space charge barrier formed at the silver-polydopamine interface can inhibit the macroscopic migration of carriers and reduce the overall loss of the material. When the silver content approaches the percolation threshold, the composite material exhibits a synergistic optimization of the dielectric constant and loss.

[0021] In addition, the combined effect of the substrate and the BTO@PDA-Ag filler has an important impact on the comprehensive performance of the composite system. The dielectric constant and the density of polar functional groups of the substrate directly affect the interfacial polarization efficiency with the high-dielectric filler. At the same time, the mechanical properties of the substrate need to match the rigidity of the filler to inhibit mechanical defects caused by interfacial stress concentration. Bacterial cellulose is composed of nanoscale cellulose fibers produced by microbial metabolism and has a highly ordered three-dimensional network structure. This intrinsic nano-topological feature provides it with excellent mechanical support ability and shows significant advantages in terms of micro-pore distribution and specific surface area, which is beneficial to the uniform loading of nano-reinforcing phases (such as BTO@PDA-Ag) and the interfacial interlocking effect, thereby effectively transferring stress and inhibiting structural defects. From the perspective of chemical activity, the surface of bacterial cellulose is rich in hydrophilic functional groups such as hydroxyl groups, which can achieve directional binding with functional nanoparticles. For example, through the adhesion of the polydopamine coating and the in-situ anchoring of silver nanoparticles, it promotes the optimization of the chemical stability and energy dissipation efficiency of the composite interface, creating a molecular-level synergistic mechanism for the multi-dimensional improvement of thermal stability, dielectric and mechanical properties. Compared with traditional petroleum-based or synthetic polymer substrates, bacterial cellulose has both renewable sources and biodegradable characteristics, making it applicable in fields such as flexible electronic devices, intelligent packaging, and biomedicine that have strict requirements for environmental protection attributes. Based on the systematic integration of the above structural and functional characteristics, bacterial cellulose not only provides an ideal platform for the construction of nano-composite systems, but also forms an irreplaceable comprehensive advantage in terms of sustainability, performance tunability, and industrial potential.

[0022] Compared with the prior art, the beneficial effects of the present invention are as follows: (1) The present invention provides a modified bacterial cellulose-based composite membrane, in which core-shell structured BTO@PDA-Ag nanoparticles with Ag particles embedded in the shell are embedded into the bacterial cellulose-based membrane, improving the thermal stability, mechanical properties and dielectric properties of the bacterial cellulose-based membrane. The embedding of the nanoparticles optimizes the dielectric-conductive composite characteristics of the material by enhancing the interfacial polarization effect and constructing a micro-capacitance network, enabling it to prepare efficient charge capture sites through local electric field modulation in the application of triboelectric nanogenerators, and further improving the dynamic accumulation and output stability of triboelectric charges. The modified bacterial cellulose-based composite membrane provided by the present invention as the positive triboelectric material of the triboelectric nanogenerator significantly improves the electrical output performance of the triboelectric nanogenerator.

[0023] (2) The present invention embeds BTO@PDA-Ag nanoparticles into the bacterial cellulose-based membrane, and the inherent antibacterial activity of the silver nanoparticles endows the modified bacterial cellulose-based composite membrane with broad-spectrum antibacterial ability, inhibiting microbial colonization and biofilm formation, which is crucial for its long-term stability in applications such as biomedical dressings or wearable sensors. Description of the Drawings

[0024] Figure 1 shows the SEM images of BTO, BTO@PDA, and the modified bacterial cellulose-based composite film in Example 2 of the present invention. Among them, Fig. 1(a) represents BTO, Fig. 1(b) represents BTO@PDA, and Fig. 1(c) represents the modified bacterial cellulose-based composite film; Figure 2 Fig. shows the TEM images of BTO@PDA-Ag nanoparticles prepared in Example 2 of the present invention at different resolutions; Figure 3 Fig. shows the TG comparison chart of the modified bacterial cellulose-based composite film prepared in Example 2 and the pure bacterial cellulose-based film prepared in Comparative Example 1. Detailed implementation manners

[0025] The embodiments of the technical solutions of the present invention will be described in detail below with reference to the accompanying drawings. The following embodiments are only used to illustrate the technical solutions of the present invention more clearly, so they are only examples and cannot be used to limit the protection scope of the present invention.

[0026] For those technical or conditions not specified in the embodiments, they shall be carried out according to the technologies or conditions described in the literature in this field or according to the product specifications. For the reagents or instruments not specified by the manufacturer, they are all conventional products that can be obtained through commercial purchase.

[0027] I. Preparation method Example 1 The preparation method of the BTO@PDA nanoparticle-modified bacterial cellulose-based composite film includes the following steps: S1. Preparation of BTO@PDA-Ag nanoparticles Disperse 0.7 g of barium titanate (BTO) powder (white in color before modification) into 50 mL of 2 g / L dopamine solution, stir at 60 °C for 12 h, then centrifuge the suspension, wash it with deionized water, and dry it at 60 °C for 5 h to obtain BTO powder coated with polydopamine (PDA), which is dark brown in color and denoted as BTO@PDA; Prepare a silver ammonia solution with a concentration of 0.04 mol / L, then pour the above BTO@PDA powder into the prepared silver ammonia solution (35 mL), continuously stir at room temperature for 2 h, and obtain black powder-like Ag-decorated BTO@PDA nanoparticles after centrifugation, washing, and vacuum drying at 60 °C for 12 h, denoted as BTO@PDA-Ag nanoparticles. The mass ratio of barium titanate, polydopamine, and Ag particles in the BTO@PDA-Ag nanoparticles is 70:10:15.

[0028] S2. Preparation of BTO@PDA-Ag modified bacterial cellulose-based composite film Disperse bacterial cellulose (BC) in water to prepare a BC aqueous suspension (1 mg / mL). Subsequently, add BTO@PDA-Ag particles to the BC aqueous suspension and disperse them evenly by ultrasonic treatment for 30 min. The addition amount of BTO@PDA-Ag particles is 0.1 vol% of the total volume of BTO@PDA-Ag particles and BC. Then, filter the mixed solution through an organic (nylon) filter paper (with a diameter of 50 mm and a pore size of 0.22 μm) in a vacuum filtration device for 35 min to obtain a BC / BTO@PDA-Ag composite membrane. Then, dry it at 60 °C for 2 h to separate the BC / BTO@PDA-Ag film layer from the filter paper, and obtain a modified bacterial cellulose-based composite membrane with a BTO@PDA-Ag content of 0.1 vol%.

[0029] Example 2 The difference between this example and Example 1 is that: the addition amount of BTO@PDA-Ag particles is 0.5 vol% of the total volume of BTO@PDA-Ag particles and BC; the remaining steps are the same as those in Example 1; a modified bacterial cellulose-based composite membrane with a BTO@PDA-Ag content of 0.5 vol% is obtained.

[0030] Example 3 The difference between this example and Example 1 is that: the addition amount of BTO@PDA-Ag particles is 1 vol% of the total volume of BTO@PDA-Ag particles and BC; the remaining steps are the same as those in Example 1; a modified bacterial cellulose-based composite membrane with a BTO@PDA-Ag content of 1 vol% is obtained.

[0031] Example 4 The difference between this example and Example 1 is that: the addition amount of BTO@PDA-Ag particles is 3 vol% of the total volume of BTO@PDA-Ag particles and BC; the remaining steps are the same as those in Example 1; a modified bacterial cellulose-based composite membrane with a BTO@PDA-Ag content of 3 vol% is obtained.

[0032] Example 5 The difference between this example and Example 1 is that: the addition amount of BTO@PDA-Ag particles is 5 vol% of the total volume of BTO@PDA-Ag particles and BC; the remaining steps are the same as those in Example 1; a modified bacterial cellulose-based composite membrane with a BTO@PDA-Ag content of 5 vol% is obtained.

[0033] Comparative Example 1 The difference between this comparative example and Example 1 is that: the addition amount of BTO@PDA-Ag nanoparticles is 0, and a bacterial cellulose-based friction material is obtained.

[0034] Comparative Example 2 The difference between this comparative example and Example 2 is that the mass ratio of barium titanate, polydopamine, and Ag particles in the BTO@PDA-Ag nanoparticles is 70:10:2; the remaining steps are the same as those in Example 2.

[0035] Comparative Example 3 The difference between this comparative example and Example 2 is that the mass ratio of barium titanate, polydopamine, and Ag particles in the BTO@PDA-Ag nanoparticles is 70:10:30; the remaining steps are the same as those in Example 2.

[0036] Comparative Example 4 The difference between this comparative example and Example 2 is that the bacterial cellulose-based membrane is replaced with PVDF, and the remaining steps are the same as those in Example 2, obtaining a modified PVDF-based friction material with a BTO@PDA-Ag content of 0.5 vol%.

[0037] Comparative Example 5 The difference between this comparative example and Example 2 is that the bacterial cellulose-based membrane is replaced with CNF; the remaining steps are the same as those in Example 2, obtaining a modified CNF-based friction material with a BTO@PDA-Ag content of 0.5 vol%.

[0038] II. Test Methods 1. Microscopic Morphology Characterization of BTO@PDA-Ag Nanoparticles The microscopic morphology of BTO, BTO@PDA, and BTO@PDA-Ag particles in Example 2 was tested using a scanning electron microscope and a transmission electron microscope.

[0039] 2. Dielectric Properties of Modified Bacterial Cellulose-Based Composite Membranes A dielectric / impedance analyzer (4294A, Agilent Technologies, Inc., USA) was used, with a frequency range from 10 -1 Hz to 10 6 Hz, a test voltage of 1V, and the dielectric constants of the membrane materials prepared in different examples and comparative examples were tested at room temperature. The dielectric constants ( ɛ r ) of different membrane samples at 100 Hz were statistically analyzed.

[0040] 3. Thermal Stability Test of Modified Bacterial Cellulose-Based Composite Membranes A thermogravimetric analyzer (TG-209 F3, Netzsch-Gerätebau GmbH, Germany) was used to perform thermal stability analysis on the bacterial cellulose-based membrane and the modified bacterial cellulose-based composite membrane, with a purge temperature ranging from room temperature to 800 °C.

[0041] 4. Mechanical Property Test of Modified Bacterial Cellulose-Based Composite Membranes The mechanical properties of the membrane materials prepared in different examples and comparative examples were tested using a universal testing machine (UTM2103, Shenzhen Sansi Zongheng Technology Co., Ltd., China) at a speed of 3 mm / min, and the tensile strength and elongation at break of the composite membranes were tested.

[0042] 5. Electrical Output Performance Test of Triboelectric Nanogenerator (TENG) Preparation of Triboelectric Nanogenerator (TENG): (1) Preparation of negative triboelectric material (PVDF-TrFE): DMF and P(VDF-TrFE) were mixed at a molar ratio of 4:1, and the resulting solution was stirred in a magnetic stirrer until it was uniform and stable. Then, the fully dissolved solution was poured onto a glass plate, and a relatively uniform solution thickness was produced using a scraper. Wait for the formation of the cast film, and then place it in an oven until the solvent is completely evaporated to produce a flat and uniform film as the negative triboelectric layer material.

[0043] (2) One side of the BTO@PDA-Ag modified bacterial cellulose-based composite membranes prepared by the preparation methods of Examples 1-5 was connected to a copper foil with an area smaller than that of the composite membrane, and then fixed. Then, a wire was led out between the copper foil and the composite membrane as the positive triboelectric layer, while the negative triboelectric layer was a combination of a P(VDF-TrFE) film and a copper foil. The thickness of the positive triboelectric material modified bacterial cellulose-based composite membrane was 30 μm, and the thickness of the negative triboelectric material (PVDF-TrFE) film was 30 μm. TENG was assembled using the positive and negative materials; two soft plastic sheets (10 cm long and 5 cm wide) were cut with scissors as the substrates of the simple TENG. Then, two long strip-shaped foam strips were cut and glued to both ends of the plastic sheet. The prepared positive and negative triboelectric layers were respectively fixed in the middle of the plastic sheet, and then combined and fixed to make a simple TENG that could be pressed by hand.

[0044] The two electrodes of the triboelectric nanogenerators prepared using the triboelectric materials obtained in Examples 1-5 were respectively connected to an electrometer to test the output performance of the TENG. During the repeated contact and separation movement cycle at a test frequency of 2 Hz, a triboelectric layer spacing of 10 mm, and a contact force of 15 N in the contact-separation cycle, the open-circuit voltage ( V oc )、short-circuit current ( I sc ) and transferred charge ( Q ) of different TENGs were measured.

[0045] III. Analysis of Test Results of Each Example and Comparative Example 1. Results of Microscopic Morphology and Structure Characterization of Modified Bacterial Cellulose-Based Composite Membranes The SEM test results of the BTO, BTO@PDA nanoparticles, and modified bacterial cellulose-based composite film obtained in Example 2 are shown in Figure 1. Among them, Figure 1(a) is BTO, Figure 1(b) is BTO@PDA, and Figure 1(c) is the modified bacterial cellulose-based composite film; Figure 2 are the transmission electron microscope test images of BTO@PDA-Ag at different resolutions. As can be seen from Figures 1(a) and (b), the surface of BTO without the action of polydopamine is relatively rough with many small protrusions, while the surface of BTO treated with polydopamine is relatively smooth; the reason for making BTO smooth is that a thin white translucent polydopamine layer (PDA) uniformly covers the surface of BTO, as can be seen from the results of TEM Figure 2 (c). As Figure 2 (b) and Figure 2 (c) show, many continuous spherical particles are decorated on the BTO@PDA-Ag nanoparticles, and its surface morphology is similar to that of a strawberry. The high-resolution TEM images of the modified nanoparticles Figure 2 (a)~(e) show that the crystal plane spacings are 0.241 nm and 0.209 nm, belonging to the (111) and (200) crystal planes of metallic Ag, indicating that Ag + is reduced to metallic Ag, and the Ag particles can be attached to the surface of BTO through polydopamine (PDA) to form a strawberry shell-like structure.

[0046] 2. Dielectric property test results of the modified bacterial cellulose-based composite film The dielectric constants ( ɛ r ) and dielectric loss test results of different-component modified bacterial cellulose-based composite films at a test frequency of 100 Hz are shown in Table 1 below.

[0047] Table 1

[0048] The results in Table 1 show that as the content of BTO@PDA-Ag nanoparticles (0.1 vol% - 5 vol%) gradually increases, the relative dielectric constant of the BC / BTO@PDA-Ag composite film gradually increases.

[0049] The results of Example 2 and Comparative Examples 2-3 show that the content of nano-Ag particles also has a certain influence on the dielectric properties of the composite film material. If the Ag content is relatively high, Ag nanoparticles form a conductive network through tunneling effect or direct contact, inducing a sharp increase in leakage current. As a result, the composite material transforms from a dielectric to a quasi-conductor. Macroscopically, this is manifested as a non-linear increase in the dielectric constant of the composite film, a sudden increase in dielectric loss, and local field distortion in the composite film, which may lead to local heat accumulation and a decrease in breakdown field strength. If the Ag content is relatively low, a micro-scale capacitive structure is formed between isolated Ag particles and the semiconductor BTO@PDA, and the dielectric constant of the composite film slowly increases under the action of space charge polarization.

[0050] The results of Comparative Examples 4-5 and Example 2 show that there are certain differences in the dielectric properties of the BC-based film after being compounded with BTO@PDA-Ag particles compared with PVDF and CNF matrices. Compared with semi-crystalline synthetic polymers such as PVDF and PVDF-TrFE, and CNF as carriers of BTO@PDA-Ag nanocomposites, the BC matrix exhibits unique advantages in terms of environmental protection attributes, material functionalization potential, and comprehensive performance adaptability. From the perspective of green chemistry, BC is synthesized by static microbial fermentation, and its raw materials are mostly waste sugars or agricultural and forestry by-products, without relying on petroleum resources and having biodegradable characteristics. In contrast, the monomer synthesis and polymerization processes of PVDF-based materials require high-energy-consuming processes, and their non-degradability makes it difficult to harmlessly treat end-of-life waste. In terms of material functionalization, the three-dimensional nanofiber network structure of BC and its high-density hydroxyl groups on the surface provide physical anchoring points and chemical cross-linking active sites for the uniform loading of nanoparticles and interface optimization. Through the adhesion of the polydopamine coating, the synergistic dispersion efficiency of BTO and Ag can be improved simultaneously, thereby realizing the directional regulation of mechanical and dielectric properties under high interface bonding strength. From the perspective of application scenario adaptability, the intrinsic breathability, hygroscopicity, and biocompatibility of BC highly match the functional requirements in fields such as intelligent sensing and biomedicine. Even though there is a significant difference in mechanical toughness compared with PVDF, the BC matrix can meet the performance requirements of relevant scenarios through topological optimization of nanostructures and efficient loading of fillers, while forming an irreplaceable core competitiveness at the ecological benefit level.

[0051] 3. Thermal stability test results of the modified bacterial cellulose-based composite film The thermal stability test results of the modified bacterial cellulose-based composite film obtained in Example 2 are as Figure 3 shown. From Figure 3It can be seen that the TGA curve of the pure BC film shows a drastic weight loss (65.2%), along with a strong exothermic region at approximately 300 °C, which is the combined result of the dehydration of cellulose chains, the thermal cleavage of glycosidic linkages, and the formation of free radicals, leading to the complete disintegration of the cellulose structure. At temperatures above 400 °C, aromatization and intramolecular condensation result in a thermally stable fused-ring structure, with a weight loss of 9.7% over a wide temperature range (400 - 800 °C). The thermal degradation of cellulose occurs through successive stages such as dehydration, depolymerization, bond cleavage, rearrangement, and volatilization. In the temperature range of 330 °C to 400 °C, the loss rate of the BC composite film is the fastest. In contrast, the initial weight loss of the BC cellulose-based composite film modified with 0.5% vol of BTO@PDA-Ag nanoparticles is 47.1% below 300 °C. The experimental results indicate that BTO@PDA-Ag nanoparticles can effectively improve the thermal stability of the BC composite film.

[0052] 4. Test Results of the Mechanical Properties of the Modified Bacterial Cellulose-Based Composite Film The test results of the mechanical properties of different friction material samples are shown in Table 2 below.

[0053] Table 2

[0054] The results in Table 2 show that the mechanical properties are optimal when the content of BTO@PDA-Ag nanoparticles is 0.5 vol%. The increase in elongation may be due to the slight wrinkles of the film after the introduction of the nanoparticles. As the content of BTO@PDA-Ag nanoparticles further increases, the tensile strength and elongation at break gradually decrease. This is because within the low filling amount range, the abundant polar groups on the surface of the polydopamine-modified BTO@PDA-Ag nanoparticles can form multi-level hydrogen bonding interactions and physical entanglements with the three-dimensional nanofiber network of bacterial cellulose, thereby optimizing the stress distribution and inhibiting the crack propagation path. At the same time, the rigid characteristics of the nanoparticles further reinforce the resistance of the matrix chain segments to slip. However, when the nanoparticle content exceeds the critical threshold, the phenomenon of particle agglomeration dominated by intermolecular forces increases significantly. The agglomerates accelerate the generation and transmission of microcracks through the physical barrier and stress concentration effects on the hydrogen bond cross-linking sites in the cellulose network. At the same time, the high filling ratio leads to a decrease in the matrix continuity, weakening the intrinsic high ductility characteristics of bacterial cellulose. Since the BTO@PDA-Ag modified bacterial cellulose-based material exhibits good mechanical flexibility and the ability to resist repeated mechanical bending and deformation, the BTO@PDA-Ag modified bacterial cellulose-based material can be easily integrated with mobile electronic devices when applied to the preparation of TENG and harvest energy from human movements.

[0055] The results of Comparative Example 4, Comparative Example 5 and Example 2 show that there are certain differences in the mechanical properties after different base films are compounded with BTO@PDA-Ag particles. The differences in the mechanical properties of the BTO@PDA-Ag / BC composite material compared with the BTO@PDA-Ag / PVDF and BTO@PDA-Ag / CNF systems mainly stem from the intrinsic properties of the matrix material and the microscopic mechanism of its interaction with nanoparticles. As a semi-crystalline synthetic polymer, PVDF endows the matrix with higher potential for plastic deformation due to the flexibility of its molecular chain segments and the ability of chain slip. This enables nanoparticles in the matrix to not only enhance the modulus through interfacial interactions, but also delay crack initiation through the rearrangement of molecular chains and stress dissipation, thus achieving synergistic enhancement between strength and ductility. Bacterial cellulose (BC), as a natural biopolymer material, although its three-dimensional nanofiber network has a high hydrogen bond cross-linking density and crystallization characteristics, the rigid conformation of its molecular chains and limited ductility lead to local stress concentration in the matrix under external stress. Even though the introduction of BTO@PDA-Ag nanoparticles can optimize the load transfer efficiency through interfacial bonding, the inherent high modulus characteristics and low fracture strain ability of the matrix still limit the effective extension of the crack propagation path. Compared with traditional synthetic polymer substrates, the nanoscale fiber network of BC not only provides a high specific surface area and a three-dimensional interpenetrating structure, but also realizes strong interfacial coupling with functional fillers through the chemical reactivity of surface hydroxyl groups, thereby regulating the mechanical, thermal and functional properties of the composite material at the nanoscale.

[0056] 5. Test results of the electrical output performance of BC / BTO@PDA-Ag / / P(VDF-TrFE) TENG The triboelectric nanogenerators prepared from the modified bacterial cellulose-based materials obtained in Examples 1 to 5 were tested at a frequency of 2 Hz in the contact-separation cycle, with a friction layer spacing of 10 mm and a contact force of 15 N. The open-circuit voltage ( V oc ), short-circuit current ( I sc ), and transferred charge ( Q ) results of different TENGs are shown in Table 3 below.

[0057] Table 3

[0058] The results in Table 3 show that when BTO@PDA-Ag nanoparticles are added to the BC matrix, as the content of BTO@PDA-Ag increases, the output performance first increases and then decreases, and the short-circuit current and open-circuit voltage of the BC / 0.5 vol% BTO@PDA-Ag type TENG reach the maximum values.

[0059] It should be noted that the present invention is not limited to the above-described embodiments. The above embodiments are merely examples, and embodiments having the same constitution as the technical idea and exhibiting the same effects within the scope of the technical solution of the present invention are all included in the technical scope of the present invention. In addition, within the scope not departing from the gist of the present invention, various modifications that can be conceived by those skilled in the art to the embodiments, and other modes constructed by combining some constituent elements in the embodiments are also included in the scope of the present invention.

Claims

1. A modified bacterial cellulose-based composite membrane, characterized in that: It includes a bacterial cellulose-based film and a plurality of nanoparticles dispersed in the bacterial cellulose-based film; The nanoparticles have a core-shell structure, wherein the core layer is barium titanate, the shell layer is polydopamine, and Ag particles are embedded in the shell layer.

2. A modified bacterial cellulose-based composite membrane according to claim 1, characterized in that: The volume fraction of the nanoparticles in the modified bacterial cellulose-based composite membrane is 0.1 vol% to 5 vol%.

3. A modified bacterial cellulose-based composite membrane according to claim 2, characterized in that: The volume fraction of the nanoparticles in the modified bacterial cellulose-based composite membrane is 0.5 vol%.

4. The modified bacterial cellulose-based composite membrane according to claim 1, characterized in that: The mass ratio of barium titanate, polydopamine and Ag particles in the nanoparticles is (60-80): (5-15): (5-20).

5. A method for preparing a modified bacterial cellulose-based composite membrane as claimed in any one of claims 1 to 4, characterized in that: The steps include: The barium titanate powder is dispersed in a dopamine solution, heated and stirred, and then centrifuged, washed and dried to obtain polydopamine-coated barium titanate particles; the polydopamine-coated barium titanate particles are dispersed in a silver ammonia solution, stirred at room temperature, and then centrifuged, washed and dried to obtain the nanoparticles; The nanoparticles are dispersed in a bacterial cellulose water suspension, and the modified bacterial cellulose-based composite membrane is obtained after ultrasonic treatment, filtration and drying.

6. The method for preparing a modified bacterial cellulose-based composite membrane according to claim 5, characterized in that: The heating and stirring temperature is 50-70° C., and the heating and stirring time is 12-24 hours.

7. The method for preparing a modified bacterial cellulose-based composite membrane according to claim 5, characterized in that: The concentration of the silver ammonia solution is 0.02-0.06 mol / L.

8. The method for preparing a modified bacterial cellulose-based composite membrane according to claim 5, characterized in that: The mass concentration of the bacterial cellulose aqueous suspension is 0.5-5 mg / L.

9. The method for preparing a modified bacterial cellulose-based composite membrane according to claim 5, characterized in that: The frequency of the ultrasonic treatment is 40 KHz, and the time of the ultrasonic treatment is 30 to 60 minutes.

10. A friction nanogenerator, characterized in that: The positive electrode friction material of the friction nanogenerator comprises the modified bacterial cellulose-based composite film described in any one of claims 1 to 4.

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