Preparation method of biomass carbon-based flexible conductive film and application of biomass carbon-based flexible conductive film in sensor

Abstract

The invention discloses a preparation method of a biomass carbon-based flexible conductive film and application of the biomass carbon-based flexible conductive film in a sensor, and belongs to the technical field of sensor materials. According to the method, firstly, sodium hydroxide, sodium hypochlorite and phosphoric acid are adopted for conducting multi-stage chemical pretreatment on the apocynum venetum straw, lignin, hemicellulose and inorganic impurities in the apocynum venetum straw can be removed through sodium hydroxide treatment, the internal structure of the apocynum venetum straw is looser, and more micropore structures can be formed; sodium hypochlorite treatment is used for further removing residual lignin, promoting the rearrangement and graphitization process of carbon atoms and improving the graphitization degree of the carbon material; the apocynum venetum straws treated by phosphoric acid are beneficial to formation of more microporous and mesoporous structures; the preparation method comprises the following steps: firstly preparing an apocynum venetum straw carbon material, then combining with a carbonization process, remarkably optimizing the microstructure of the apocynum venetum straw carbon material, forming a uniform multi-stage pore channel and improving the graphitization degree, and finally combining the apocynum venetum straw carbon material with polyurethane to prepare the biomass carbon-based flexible conductive film with excellent conductivity.

Description

Technical Field

[0001] The present invention belongs to the technical field of sensor materials, and in particular relates to a method for preparing a biomass carbon-based flexible conductive film and its application in sensors. Background Art

[0002] The rapid development of science and technology has promoted the widespread application of high-tech and significantly improved the quality of life. As the core technology of information collection and perception, sensing technology plays a key role in production. As an important wearable sensing device, flexible strain sensors have broad application prospects in the fields of health care, human-computer interaction, etc. In recent years, the research on flexible strain sensors has made significant progress. However, the current flexible strain sensors still have some problems. On the one hand, existing high-performance flexible strain sensors mostly use flexible substrates doped with gold / silver nanoparticles / nanowires, or use graphene, reduced graphene oxide, single-walled carbon nanotubes and other modified substrates to improve sensitivity, but these materials are expensive and not suitable for large-scale use. On the other hand, existing flexible strain sensors have problems such as poor tensile properties, which limit their development and application.

[0003] Apocynum venetum is a plant with significant economic and ecological value. Its fiber can be used in textiles, papermaking, and other fields. However, after harvesting, apocynum venetum produces a large amount of waste, apocynum venetum straw. The accumulation of large amounts of apocynum venetum straw not only consumes land resources but also poses potential environmental hazards.

[0004] Therefore, how to use Apocynum venetum straw to prepare flexible strain sensor materials with high sensitivity and tensile properties has become a technical problem that needs to be solved urgently in this field. Summary of the Invention

[0005] In order to solve the above technical problems, the present invention proposes a method for preparing a biomass carbon-based flexible conductive film and its application in sensors.

[0006] To achieve the above objectives, the present invention provides the following technical solutions:

[0007] The present invention provides a method for preparing a biomass carbon-based flexible conductive film, comprising the following steps:

[0008] (1) pre-treating apocynum venetum straw to obtain pre-treated apocynum venetum straw; then sequentially treating the pre-treated apocynum venetum straw with a sodium hydroxide solution, a sodium hypochlorite solution, and a phosphoric acid solution to obtain chemically treated apocynum venetum straw;

[0009] (2) carbonizing the apocynum venetum straw after the chemical treatment in step (1) to obtain apocynum venetum straw carbon material;

[0010] (3) Mixing the apocynum venetum straw carbon material described in step (2) with a polyurethane solution to obtain a mixed solution A; mixing the mixed solution A with a diluted mixture of polyurethane and a dispersant to obtain a mixed solution B; pouring the mixed solution B into a substrate and drying it to obtain the biomass carbon-based flexible conductive film.

[0011] Technical principle: The present invention first uses sodium hydroxide, sodium hypochlorite and phosphoric acid to perform multi-stage chemical pretreatment on the apocynum venetum straw. The sodium hydroxide treatment can remove lignin, hemicellulose and some inorganic impurities in the apocynum venetum straw, and can also swell the cellulose, making its internal structure looser, which is conducive to the formation of more microporous structures; the sodium hypochlorite treatment is used to further treat the residual lignin, promote the rearrangement and graphitization process of carbon atoms, and improve the graphitization degree of the carbon material; the apocynum venetum straw after phosphoric acid treatment is conducive to the formation of more micropores and mesoporous structures, and these pore structures can significantly increase the specific surface area of the carbon material, thereby improving its conductive properties; combined with the carbonization process, the microstructure of the apocynum venetum straw carbon material is significantly optimized, uniform multi-level pores are formed and the degree of graphitization is improved. Finally, a biomass carbon-based flexible conductive film with excellent conductivity is prepared by combining the apocynum venetum straw carbon material with polyurethane.

[0012] Furthermore, in step (1), the pretreatment comprises the following steps: soaking the apocynum venetum straw in anhydrous ethanol, and then washing and drying to obtain the pretreated apocynum venetum straw.

[0013] Furthermore, in step (1), the mass concentration of the sodium hydroxide solution is 10±0.1%; the heating temperature of the pretreated Apocynum venetum straw treated with the sodium hydroxide solution is 75±2° C., and the heating time is 3 hours.

[0014] Furthermore, in step (1), the mass concentration of the sodium hypochlorite solution is 10±1%; the heating temperature of treating the pretreated Apocynum venetum straw with the sodium hypochlorite solution is 75±2° C., and the heating time is 150 min.

[0015] Furthermore, in step (1), the concentration of the phosphoric acid solution is 0.1±0.01 mol / L; and the time for treating the pretreated Apocynum venetum straw with the phosphoric acid solution is 30 minutes.

[0016] Furthermore, in step (2), the carbonization treatment is carried out under the conditions of nitrogen, a main pressure of 2500±100 MPa, a secondary pressure of 0.25±0.01 MPa, a nitrogen flow rate of 150-200 mL / min, and a temperature of 700-900°C.

[0017] Furthermore, the holding time of the carbonization treatment is 2 hours, and the rate of heating to the carbonization temperature is 5°C / min.

[0018] Furthermore, in step (3), the mass proportion of the apocynum venetum straw carbon material in the biomass carbon-based flexible conductive film is 5-10% (in step (3), a part of the polyurethane is first mixed with the apocynum venetum straw carbon material, and the other part of the polyurethane is mixed with the organic solvent DMF, and then the two systems are mixed. The biomass carbon-based flexible conductive film obtained after drying and removing the solvent is a composite material of apocynum venetum straw carbon material, polyurethane and dispersant, wherein the apocynum venetum straw carbon material accounts for 5-10wt%. The amount of polyurethane in the two systems does not need to be strictly limited, so that the components in the system are evenly dispersed. It is only necessary to meet the mass ratio requirements in the final conductive film product); and / or,

[0019] The dispersant is selected from sodium lignin sulfonate.

[0020] The present invention provides a biomass carbon-based flexible conductive film prepared by the preparation method described in the above technical solution.

[0021] The present invention also provides a sensor containing a biomass carbon-based flexible conductive film, the sensor comprising the above-mentioned biomass carbon-based flexible conductive film, an electrode and an insulating sleeve;

[0022] The opposite sides of the biomass carbon-based flexible conductive film are respectively connected to electrodes; the biomass carbon-based flexible conductive film is embedded in an insulating sleeve; the opposite ends of the two electrodes pass through the insulating sleeve; the surface of the insulating sleeve has a wear-resistant layer; the surface of the electrode has a polycaprolactone layer.

[0023] Compared with the prior art, the present invention has the following advantages and technical effects:

[0024] This invention significantly optimizes the microstructure of apocynum venetum straw carbon materials through a multi-stage chemical pretreatment (sodium hydroxide, sodium hypochlorite, and phosphoric acid) combined with a carbonization process. This results in uniform multi-level pores and an enhanced degree of graphitization, boosting electrical conductivity by 25%-30%. Using waste straw as raw material and a standardized carbonization process (GSL-1700x tubular furnace) as its core, this method achieves low-cost, large-scale production, comprehensively addressing the challenges of conventional flexible sensors, such as insufficient conductivity and high environmental impact, while combining high performance, intelligent repairability, and sustainable environmental performance.

[0025] The present invention uses biomass to prepare a composite conductive film. The biomass carbon material itself has excellent electrochemical properties and is suitable as a sensor material. Since the preparation process of the biomass carbon material is simple and easy to achieve large-scale production, its cost is relatively low. In addition, the biomass carbon has good stability, so that the prepared sensor material also has good stability and a long service life. The carbon-based material is prepared by the carbonization process of Apocynum venetum straw, which realizes the high-value utilization of waste biomass, reduces environmental pollution, and makes the biomass carbon material sensor have a market competitive advantage. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] The accompanying drawings, which constitute part of the present invention, are provided to provide a further understanding of the present invention. The exemplary embodiments of the present invention and their descriptions are provided to explain the present invention and do not constitute an undue limitation of the present invention. In the accompanying drawings:

[0027] Figure 1 This is a process flow chart of the preparation method of the biomass carbon-based flexible conductive film in Examples 1-4;

[0028] Figure 2 Schematic diagram of the structure of a sensor containing a biomass carbon-based flexible conductive film provided by the present invention; wherein: 1-biomass carbon-based flexible conductive film, 2-electrode, 3-insulating sleeve, 4-wear-resistant layer, 5-polycaprolactone layer;

[0029] Figure 3 The cross-sectional SEM images of the apocynum venetum straw carbon material obtained in step (3) of Example 3 and the longitudinal cross-sectional SEM images of the biomass carbon-based flexible conductive film obtained in step (4) of Example 3, wherein a, b, and c are SEM images of the cross-sectional view of the apocynum venetum straw carbon material obtained in step (3) of Example 3 at different magnifications, and the small image in b is a partial magnified view of the arrow portion; d, e, and f are SEM images of the longitudinal cross-sectional view of the biomass carbon-based flexible conductive film obtained in step (4) of Example 3 at different magnifications, and the small image in f is a partial magnified view of the dotted line portion;

[0030] Figure 4 Surface SEM images and cross-sectional SEM images of the CRHS / PU conductive film prepared in Example 3, wherein a and b are surface SEM images at different magnifications, and c and d are cross-sectional SEM images at different magnifications;

[0031] Figure 5 The resistance value (a) and Raman spectrum (b) of the apocynum venetum straw carbon material in Examples 1-3, the infrared spectrum (c) of the apocynum venetum straw and the apocynum venetum straw carbon material in Example 3, and the infrared spectrum (d) of the apocynum venetum straw carbon material in Examples 1-3;

[0032] Figure 6These are the tensile test results of the biomass carbon-based flexible conductive films CRHS / PU prepared in Examples 3-4 and Comparative Example 1, where a is the initial resistance, b is the resistance change rate, c is the resistance change rate curve, and d is the tensile curve. DETAILED DESCRIPTION

[0033] The following will clearly and completely describe the technical solutions in the embodiments of the present invention in conjunction with the accompanying drawings. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of the present invention.

[0034] In order to make the above-mentioned objects, features and advantages of the present invention more obvious and easy to understand, the present invention is further described in detail below with reference to the accompanying drawings and specific embodiments.

[0035] An embodiment of the present invention provides a method for preparing a biomass carbon-based flexible conductive film, comprising the following steps:

[0036] (1) pre-treating apocynum venetum straw to obtain pre-treated apocynum venetum straw; then sequentially treating the pre-treated apocynum venetum straw with a sodium hydroxide solution, a sodium hypochlorite solution, and a phosphoric acid solution to obtain chemically treated apocynum venetum straw;

[0037] (2) carbonizing the apocynum venetum straw after the chemical treatment in step (1) to obtain apocynum venetum straw carbon material;

[0038] (3) Mixing the apocynum venetum straw carbon material described in step (2) with a polyurethane solution to obtain a mixed solution A; mixing the mixed solution A with a diluted mixture of polyurethane and a dispersant to obtain a mixed solution B; pouring the mixed solution B into a substrate and drying it to obtain the biomass carbon-based flexible conductive film.

[0039] In a preferred embodiment, in step (1), the pretreatment comprises the following steps: soaking the apocynum venetum straw in anhydrous ethanol, and then washing and drying to obtain the pretreated apocynum venetum straw.

[0040] In a preferred embodiment, the soaking time is 2-3 days; the washing agent is anhydrous ethanol; the drying temperature is 60±1° C., the drying time is 90 minutes, and the equipment is an oven.

[0041] In a preferred embodiment, in step (1), the mass concentration of the sodium hydroxide solution is 10±0.1%; the heating temperature for treating the pretreated apocynum venetum straw with the sodium hydroxide solution is 75±2°C, and the heating time is 3 hours; the amount of the sodium hydroxide solution is not particularly limited, and only needs to be sufficient to immerse the pretreated apocynum venetum straw. The present invention uses sodium hydroxide solution to treat the apocynum venetum straw, which can remove lignin, hemicellulose, and some inorganic impurities in the apocynum venetum straw, and can also swell the cellulose, making its internal structure looser, which is conducive to forming more microporous structures.

[0042] In a preferred embodiment, the method of treating the pretreated Apocynum venetum straw with sodium hydroxide solution is ultrasonication.

[0043] In a preferred embodiment, after the pretreated Apocynum venetum straw is treated with sodium hydroxide solution, a centrifugation step is further included; the centrifugal speed is 9000 r / min, the time of each centrifugation is 3 minutes, the centrifugal reagent is deionized water, and the centrifugation is stopped when the pH value of the supernatant drops to 11-12.

[0044] In a preferred embodiment, in step (1), the mass concentration of the sodium hypochlorite solution is 10±1%; the heating temperature for treating the pretreated apocynum venetum straw with the sodium hypochlorite solution is 75±2°C, and the heating time is 150 minutes; the amount of the sodium hypochlorite solution used is not particularly limited, and only needs to be sufficient to immerse the apocynum venetum straw after treatment with the sodium hydroxide solution. Treating the apocynum venetum straw with the sodium hypochlorite solution further removes residual lignin, promotes the rearrangement of carbon atoms and the graphitization process, and improves the degree of graphitization of the carbon material.

[0045] In a preferred embodiment, after the pretreated apocynum venetum straw is treated with a sodium hypochlorite solution, the process further includes the steps of centrifugation and drying; the centrifugal speed is 9000 r / min, the centrifugal time is 3 min, the centrifugal reagent is deionized water, and the centrifugation is stopped when the pH value of the supernatant drops to 7-8; the drying temperature is 80±1°C, the drying time is 12 h, and the equipment is an oven.

[0046] In a preferred embodiment, in step (1), the concentration of the phosphoric acid solution is 0.1±0.01 mol / L; the phosphoric acid solution is used to treat the pretreated apocynum venetum straw for 30 minutes; and the amount of phosphoric acid solution used is not particularly limited, as long as it can immerse the apocynum venetum straw treated with the sodium hypochlorite solution. The phosphoric acid solution treatment of the apocynum venetum straw facilitates the formation of more microporous and mesoporous structures, which can significantly increase the specific surface area of the carbon material, thereby improving its electrical conductivity.

[0047] In a preferred embodiment, after the pretreated Apocynum venetum straw is treated with a phosphoric acid solution, the process further includes the steps of centrifugation and drying; the centrifugal speed is 9000 r / min, the time for each centrifugation is 3 min, the centrifugal reagent is deionized water, and the centrifugation is stopped when the pH value of the supernatant drops to 7-8; the drying temperature is 80±1°C, the time is 12 h, and the equipment is an oven.

[0048] In a preferred embodiment, in step (2), the carbonization treatment is performed under nitrogen gas at a primary pressure of 2500±100 MPa, a secondary pressure of 0.25±0.01 MPa, a nitrogen flow rate of 150-200 mL / min, and a temperature of 700-900°C; the carbonization treatment is performed in a tubular furnace. The carbonization treatment under the above conditions is advantageous for obtaining a carbon material of Apocynum venetum straw having excellent electrical conductivity.

[0049] In a preferred embodiment, the holding time of the carbonization treatment is 2 hours, and the rate of heating to the carbonization temperature is 5°C / min.

[0050] In a preferred embodiment, in step (2), the carbonization treatment further includes a grinding step; the grinding step specifically comprises: placing the product obtained after the carbonization treatment in a mortar and grinding it to a particle size of 1-10 μm.

[0051] In a preferred embodiment, in step (3), the solvent of the polyurethane solution is water; the diluted polyurethane mixture is composed of polyurethane and N,N-dimethylformamide in a mass ratio of 1:2.5. Polar functional groups (such as -OH and CO) are typically present on the surface of the carbonized apocynum venetum straw powder. When the powder is first mixed with the polyurethane aqueous solution, the polyurethane molecular chains are adsorbed on the surface of the apocynum venetum straw powder due to hydrogen bonding or van der Waals forces, achieving initial wetting and dispersion, reducing powder agglomeration, and avoiding secondary aggregation caused by changes in solvent polarity during subsequent mixing with the diluted polyurethane mixture.

[0052] In a preferred embodiment, in step (3), the mass proportion of the Apocynum venetum straw carbon material in the biomass carbon-based flexible conductive film is 5-10%. The present invention controls the mass proportion of the Apocynum venetum straw carbon material within the above range, thereby ensuring the conductivity of the biomass carbon-based flexible conductive film and avoiding a decrease in the tensile strength of the biomass carbon-based flexible conductive film due to excessive use.

[0053] In a preferred embodiment, in step (3), the dispersant is selected from sodium lignin sulfonate; and the mass proportion of the dispersant in the biomass carbon-based flexible conductive film is 0.1%. The present invention achieves efficient dispersion of the apocynum venetum straw carbon material by introducing the green dispersant sodium lignin sulfonate.

[0054] In a preferred embodiment, in step (3), the mixed solution A is mixed with the diluted mixture of polyurethane and the dispersant by ultrasound; and the ultrasound time is 30 minutes.

[0055] In a preferred embodiment, in step (3), the drying temperature is 80±1° C., the drying time is 90 min, and the equipment is a vacuum drying oven.

[0056] The present invention provides a biomass carbon-based flexible conductive film prepared by the preparation method described in the above technical solution.

[0057] The present invention also provides a sensor containing a biomass carbon-based flexible conductive film, the structural diagram of which is shown in FIG. Figure 2 , the sensor includes the biomass carbon-based flexible conductive film 1, electrode 2 and insulating sleeve 3 described in the above technical solution;

[0058] The opposite sides of the biomass carbon-based flexible conductive film 1 are respectively connected to electrodes 2 (i.e., one electrode 2 is arranged on the lower surface of one end of the biomass carbon-based flexible conductive film 1, and the other electrode 2 is arranged on the upper surface of the other end of the biomass carbon-based flexible conductive film 1); the biomass carbon-based flexible conductive film 1 is embedded in an insulating sleeve 3; the opposite ends of the two electrodes 2 both pass through the insulating sleeve 3; the surface of the insulating sleeve 3 has a wear-resistant layer 4; the surface of the electrode 2 has a polycaprolactone layer 5. The present invention significantly improves the service life and environmental adaptability of the sensor by coating the surface of the electrode with a thermally responsive polycaprolactone layer (self-healing at 60°C) and adding a wear-resistant layer to the surface of the insulating sleeve. At the same time, the embedded design of the conductive film takes into account both high sensitivity and fatigue resistance.

[0059] The room temperature in the embodiments of the present invention refers to "25±2°C".

[0060] Anhydrous ethanol, source: Tianjin Xinbote Chemical Co., Ltd.

[0061] Sodium hydroxide (tablets) NaOH, source: Tianjin Xinbote Chemical Co., Ltd.

[0062] Phosphoric acid aqueous solution, source: Tianjin Zhiyuan Chemical Reagent Co., Ltd.

[0063] Sodium hypochlorite standard solution, source: Qingdao Fulin Biochemical Co., Ltd.;

[0064] Polycaprolactone (C6H 10 O2) n , Source: Hunan Juren New Materials Co., Ltd.;

[0065] Sodium ligninsulfonate C 20 H 24 Na2O 10 S2, Source: Shandong Ailiwan Chemical Technology Co., Ltd.

[0066] N,N-dimethylformamide HCON(CH3)2, source: Tianjin Beilian Fine Chemicals Development Co., Ltd.;

[0067] Polyurethane C3H8N2O, source: Shenzhen Jitian Chemical Co., Ltd.

[0068] Apocynum venetum straw, source: Yuli County, Xinjiang.

[0069] Equipment used in the specific implementation:

[0070] Tube furnace (GSL-1700x), Hefei Kejing Materials Technology Co., Ltd.;

[0071] Electronic analytical balance (FA2004), Shanghai Lichen Bangxi Instrument Technology Co., Ltd.;

[0072] Vacuum drying oven (ZK-1BS), Tianjin Zhonghuan Experimental Electric Furnace Co., Ltd.;

[0073] Flexible photoelectric mechanical tester (KQ5200B), Beijing Elite Technology Co., Ltd.

[0074] Unless otherwise specified, the raw materials in the examples of the present invention were purchased from commercial sources.

[0075] Examples 1-3

[0076] A method for preparing a biomass carbon-based flexible conductive film, the process flow chart is shown in Figure 1 , the specific steps are as follows:

[0077] (1) Soak the apocynum venetum straw in anhydrous ethanol for 2 days to ensure that it is completely soaked. After soaking, wash the apocynum venetum straw repeatedly with anhydrous ethanol until no pigment remains on the surface. Then, place the washed apocynum venetum straw in an oven and dry it at 60±1°C for 90 minutes to obtain pretreated apocynum venetum straw.

[0078] (2) The pretreated Apocynum venetum straw obtained in step (1) is placed in a sodium hydroxide solution with a mass concentration of 10%, and ultrasonically dispersed at 75±2°C for 3 hours to fully swell it. After swelling is completed, the Apocynum venetum straw is centrifuged with deionized water (the centrifuge speed is 9000r / min, and the centrifugation time is 3min) to remove excess sodium hydroxide. The above centrifugation operation is repeated until the pH value of the supernatant drops to 11-12. The Apocynum venetum straw treated with sodium hydroxide solution is placed in a sodium hypochlorite solution with a mass concentration of 10%, and heated and stirred at 75±2°C for 150min to further refine the straw particle size. After stirring is completed, the Apocynum venetum straw is centrifuged again with deionized water (the centrifuge speed is 9000r / min, and the centrifugation time is 3min). The above centrifugation operation is repeated until the pH value of the supernatant drops to 7-8. The Apocynum venetum straw treated with sodium hypochlorite solution is then placed in an oven and dried at 80±1°C for 12h. The dried Apocynum venetum straw was then immersed in a 0.1M phosphoric acid solution and ultrasonically dispersed for 30 minutes. After dispersion, the straw was repeatedly centrifuged in deionized water (at a speed of 9000 rpm for 4 minutes) until the pH of the supernatant reached 7-8. The straw was then dried in an oven at 80±1°C for 12 hours to obtain the chemically treated Apocynum venetum straw.

[0079] (3) The chemically treated Apocynum venetum straw obtained in step (2) was placed in a tubular furnace carbonization tube, and heated to 700°C (Example 1, denoted as CRHS-700), 800°C (Example 2, denoted as CRHS-800), and 900°C (Example 3, denoted as CRHS-900) at a heating rate of 5°C / min under the conditions of a nitrogen environment, a main valve pressure of 2500±100 MPa, a secondary valve pressure of 0.25±0.01 MPa, and a nitrogen flow rate of 150 mL / min, respectively, for carbonization treatment. The holding time was 2 h. After the carbonization treatment, the carbonized product was placed in a mortar and ground to a particle size of 1-10 μm, thereby obtaining Apocynum venetum straw carbon material.

[0080] (4) The apocynum venetum straw carbon material obtained in step (3) was mixed with a polyurethane solution (the mass proportion of the apocynum venetum straw carbon material in the biomass carbon-based flexible conductive film was 10%) to obtain a mixed solution A. A diluted mixture of the polyurethane solution and DMF (mass ratio of 1:2.5) was added to the mixed solution A, and sodium lignin sulfonate (the mass proportion of sodium lignin sulfonate in the biomass carbon-based flexible conductive film was 0.1%) was added, and ultrasonicated for 30 minutes to obtain a mixed solution B. The obtained mixed solution B was poured into a culture dish, and the culture dish was placed in a vacuum drying oven and vacuum treated at 80±1°C for 90 minutes to obtain a biomass carbon-based flexible conductive film (CRHS / PU).

[0081] Characterization of CRHS / PU conductive film:

[0082] (1) A scanning electron microscope (model SU8020) was used to analyze the morphological characteristics.

[0083] (2) The graphitization degree of the material was analyzed using a Raman spectrometer (model RM6).

[0084] (3) Functional group analysis was performed using a Fourier transform infrared spectrometer (model Nicolet IS5).

[0085] Figure 3 The cross-sectional SEM images of the apocynum venetum straw carbon material obtained in step (3) of Example 3 and the longitudinal cross-sectional SEM images of the biomass carbon-based flexible conductive film obtained in step (4) of Example 3, wherein a, b, and c are SEM images of the cross-sectional SEM images of the apocynum venetum straw carbon material obtained in step (3) of Example 3 at different magnifications, and the small image in b is a partial magnification of the arrow portion; d, e, and f are SEM images of the longitudinal cross-sectional SEM images of the biomass carbon-based flexible conductive film obtained in step (4) of Example 3 at different magnifications, and the small image in f is a partial magnification of the dotted line portion. Figure 3 It can be clearly seen that the Apocynum venetum straw treated by the method of the present invention has a multi-level pore structure inside, and the pores at each level penetrate each other, indicating that it has certain potential in flexible sensing.

[0086] Figure 4 The surface SEM images and cross-sectional SEM images of the CRHS / PU conductive film prepared in Example 3 are shown, where a and b are surface SEM images at different magnifications, and c and d are cross-sectional SEM images at different magnifications. Figure 4 In parts a and b of the figure, some carbonized Apocynum venetum straw particles can be observed attached to the surface of the film. These particles are in irregular powder form after being carbonized and crushed. Figure 4 In parts c and d, it can be observed that the CRHS powder has a multi-level pore structure and disordered contacts are formed between the carbon powders. In summary, it can be seen that the conductive filler (CRHS) is uniformly distributed in the PU matrix.

[0087] Figure 5 The resistance value of the apocynum venetum straw carbon material in Examples 1-3 (a), the Raman spectrum of the apocynum venetum straw carbon material in Examples 1-3 (b), the infrared spectrum of the apocynum venetum straw and the apocynum venetum straw carbon material in Example 3 (c), and the infrared spectrum of the apocynum venetum straw carbon material in Examples 1-3 (d). Figure 5As can be seen from part a of the graph, when the mass fraction of the Apocynum venetum straw carbon material in the biomass carbon-based flexible conductive film is the same, as the carbonization temperature increases from 700°C to 800°C, the resistance value of CRHS / PU gradually decreases. When the temperature continues to rise to 900°C, the resistance value reaches the minimum and the conductivity is the strongest. Figure 5 In part b, CRHS can be found at 1350cm -1 and 1580cm -1 There are two diffraction peaks, 1350cm -1 The defect-induced peak (sp 3 ), 1580cm -1 The graphite strip (sp 2 ), I D / I G Used to indicate the degree of graphitization of materials, I D / I G The smaller the ratio, the higher the degree of graphitization. According to calculation, the I D / I G The ratios are 1.04, 1.01 and 0.99 respectively, which means that with the increase of carbonization temperature, the degree of graphitization also increases, thereby enhancing the conductivity. Figure 5 In the c part, it can be found that after the carbonization of Apocynum venetum straw, CO (1043.9cm -1 ) and other benzene ring functional groups (1515.5cm -1 ) peak gradually increases, indicating that the carbon content of the carbon material increases after carbonization treatment, indicating that the carbon material has good electrical conductivity, strong -OH (3426.3cm -1 ) shows that there is still a lot of hydrogen after carbonization treatment, but it does not affect the conductive properties of the material. Figure 5 It can be seen from the d part that as the carbonization temperature increases, CO (1040.4 cm -1 ) gradually increases, indicating that the degree of carbonization is increasing, -OH (3443.9cm -1 ) decreases gradually, which indirectly indicates that the hydrogen content decreases with the increase of carbonization temperature.

[0088] Example 4

[0089] A method for preparing a biomass carbon-based flexible conductive film, which is different from Example 3 in that, in step (4), the mass proportion of the apocynum venetum straw carbon material in the biomass carbon-based flexible conductive film is 5%.

[0090] Comparative Example 1

[0091] A method for preparing a biomass carbon-based flexible conductive film, which is different from Example 3 in that, in step (4), the mass proportion of the apocynum venetum straw carbon material in the biomass carbon-based flexible conductive film is 20%.

[0092] In flexible sensors, the sensitivity coefficient is a parameter that measures the sensor's response performance and indicates the sensor's sensitivity to stimuli. It represents the ratio of the device's resistance change to the strain. For sensors with linear output, the sensitivity is constant. The formula for calculating the sensitivity coefficient is as follows:

[0093]

[0094] Where R0 represents the initial resistance of the sensor, ΔR represents the change in resistance (ΔR = R - R0, where R represents the resistance of the strain sensor), and ε is the relative change in the stretched length of the sensor. Sensitivity reflects the relationship between the sensor's response and strain.

[0095] The biomass carbon-based flexible conductive film CRHS / PU prepared in Examples 3-4 and Comparative Example 2 was subjected to a tensile test, and the resistance change rate curve was recorded using a flexible photoelectric mechanical tester. The results are shown in FIG. Figure 6 ; Among them, the sensitivity coefficient calculation formula is expressed as Figure 6 The formula for the data change trend in part c.

[0096] Figure 6 The tensile test results of the biomass carbon-based flexible conductive film CRHS / PU prepared in Examples 3-4 and Comparative Example 2, where a is the initial resistance, b is the resistance change rate, c is the resistance change rate curve, d is the tensile curve, and C (%) represents the mass ratio of the apocynum venetum straw carbon material in the biomass carbon-based flexible conductive film. Figure 6 It can be observed from parts a and c in the figure that under the same stress, the sensitivity of the conductive films containing different mass proportions of apocynum venetum straw carbon materials is different. The conductive film with a mass proportion of 10% of apocynum venetum straw carbon materials has the best sensitivity, while the composite film with a mass proportion of 20% of apocynum venetum straw carbon materials has the worst sensitivity. This shows that the sensitivity characteristics are related to the physical structure of the material. When compressed, the contact of more conductive particles will cause resistance changes, thereby achieving current changes. However, the mass proportion of apocynum venetum straw carbon materials is too high, and the contact area between the conductive particles changes little, resulting in little change in resistance, which in turn leads to lower sensitivity. Figure 6 From parts b and d, it can be found that the greater the content of apocynum venetum straw carbon material, the lower the initial resistance of the conductive film and the better the conductive performance, but its tensile strength will decrease with the increase of the content of apocynum venetum straw carbon material. Therefore, it is optimal to use a conductive film with a third carbonization treatment temperature of 900°C and a mass proportion of 10% of the apocynum venetum straw carbon material to construct the sensor.

[0097] The above are merely preferred embodiments of the present invention, but the scope of protection of the present invention is not limited thereto. Any changes or substitutions that can be easily conceived by a person skilled in the art within the technical scope disclosed in the present invention should be included in the scope of protection of the present invention. Therefore, the scope of protection of the present invention should be based on the scope of protection of the claims.

Claims

1. A method for preparing a biomass carbon-based flexible conductive film, characterized in that: The following steps are involved: (1) pre-treating apocynum venetum straw to obtain pre-treated apocynum venetum straw; Then, the pretreated Apocynum venetum straw is treated with a sodium hydroxide solution, a sodium hypochlorite solution and a phosphoric acid solution in sequence to obtain chemically treated Apocynum venetum straw; (2) carbonizing the apocynum venetum straw after the chemical treatment in step (1) to obtain apocynum venetum straw carbon material; (3) Mixing the apocynum venetum straw carbon material described in step (2) with a polyurethane solution to obtain a mixed solution A; mixing the mixed solution A with a diluted mixture of polyurethane and a dispersant to obtain a mixed solution B; pouring the mixed solution B into a substrate and drying it to obtain the biomass carbon-based flexible conductive film.

2. The method for preparing a biomass carbon-based flexible conductive film according to claim 1, characterized in that: In step (1), the pretreatment comprises the following steps: soaking the apocynum venetum straw in anhydrous ethanol, and then washing and drying the apocynum venetum straw to obtain the pretreated apocynum venetum straw.

3. The method for preparing a biomass carbon-based flexible conductive film according to claim 1, characterized in that: In step (1), the mass concentration of the sodium hydroxide solution is 10±0.1%; the heating temperature of the pretreated Apocynum venetum straw treated with the sodium hydroxide solution is 75±2° C., and the heating time is 3 hours.

4. The method for preparing a biomass carbon-based flexible conductive film according to claim 1, characterized in that: In step (1), the mass concentration of the sodium hypochlorite solution is 10±1%; the heating temperature of the pretreated apocynum venetum straw treated with the sodium hypochlorite solution is 75±2° C., and the heating time is 150 min.

5. The method for preparing a biomass carbon-based flexible conductive film according to claim 1, characterized in that: In step (1), the concentration of the phosphoric acid solution is 0.1±0.01 mol / L; and the time for treating the pretreated Apocynum venetum straw with the phosphoric acid solution is 30 minutes.

6. The method for preparing a biomass carbon-based flexible conductive film according to claim 1, characterized in that: In step (2), the carbonization treatment is carried out under the conditions of nitrogen, a main pressure of 2500±100 MPa, a secondary pressure of 0.25±0.01 MPa, a nitrogen flow rate of 150-200 mL / min, and a temperature of 700-900°C.

7. The method for preparing a biomass carbon-based flexible conductive film according to claim 6, characterized in that: The holding time of the carbonization treatment is 2 hours, and the rate of heating to the carbonization temperature is 5°C / min.

8. The method for preparing a biomass carbon-based flexible conductive film according to claim 1, characterized in that: In step (3), the mass proportion of the Apocynum venetum straw carbon material in the biomass carbon-based flexible conductive film is 5-10%; and / or, The dispersant is selected from sodium lignin sulfonate.

9. A biomass carbon-based flexible conductive film prepared by the preparation method according to any one of claims 1 to 8.

10. A sensor containing a biomass carbon-based flexible conductive film, characterized in that: The sensor comprises the biomass carbon-based flexible conductive film (1) according to claim 9, an electrode (2) and an insulating sleeve (3); The opposite sides of the biomass carbon-based flexible conductive film (1) are respectively connected to electrodes (2); the biomass carbon-based flexible conductive film (1) is embedded in an insulating sleeve (3); the opposite ends of the two electrodes (2) pass through the insulating sleeve (3); the surface of the insulating sleeve (3) has a wear-resistant layer (4); and the surface of the electrode (2) has a polycaprolactone layer (5).

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