Lignocellulose nanofiber reinforced conductive polyvinyl alcohol gel as well as preparation method and application thereof

Abstract

The invention relates to the technical field of flexible electronic materials, and particularly provides lignocellulose nanofiber reinforced conductive polyvinyl alcohol gel as well as a preparation method and application thereof. According to the conductive gel, lignocellulose nanofibers, polyvinyl alcohol and MXene are blended through a simple'one-pot method 'strategy, rigid phenolic hydroxyl groups of lignin can form dense hydrogen bonds with polyvinyl alcohol and MXene, external stress is eliminated, and then the conductive gel is formed through polymerization in a freeze-thaw cycle mode. The gel prepared by the invention has excellent mechanical property, conductivity, stability and biocompatibility, also has high sensitivity and durability, can be used as a flexible sensor material to detect violent and subtle actions of human beings, and even can identify voice and writing information.

Description

TECHNICAL FIELD

[0001] The present application belongs to the technical field of flexible electronic materials, and particularly relates to a composite conductive hydrogel taking lignocellulose nanofiber as a reinforcing phase, polyvinyl alcohol and MXene as a matrix, a preparation method thereof, and application thereof in the fields of flexible electronics, wearable sensors and the like. BACKGROUND

[0002] Conductive hydrogel has a wide application prospect in the field of flexible electronics due to its combination of the flexibility, biocompatibility of hydrogel and the electrical properties of conductive materials. However, the existing conductive hydrogel is usually composed of natural or synthetic polymers (such as polyvinyl alcohol, polyurethane) and conductive fillers (such as ions, metal nanomaterials, carbon-based materials), which has the problems of poor interfacial compatibility and complex preparation process.

[0003] In recent years, lignocellulose nanofiber has become a research hotspot due to the following advantages: simple preparation, no need to completely remove lignin, saving time and energy; multifunctionality, lignin is rich in phenolic hydroxyl and alcoholic hydroxyl, which can improve the compatibility with polymers and fillers through non-covalent interactions such as hydrogen bonding and π-π stacking; functional expandability, the conjugated structure of lignin endows the properties of photothermal conversion and ultraviolet resistance. However, there is no report on the use of lignocellulose nanofiber to reinforce conductive polyvinyl alcohol gel in the current published patents. Therefore, the present application successfully prepares a reinforced conductive hydrogel by adopting a "one-pot" strategy to blend lignocellulose nanofiber obtained by pretreating biomass with low eutectic solvent, polyvinyl alcohol and MXene. The rigid phenolic hydroxyl of lignin forms a dense hydrogen bond with polyvinyl alcohol and MXene, which significantly improves the mechanical properties of the hydrogel and effectively balances its electrical conductivity. SUMMARY

[0004] The present application aims to solve the problems of poor mechanical properties, insufficient interfacial compatibility and complex preparation process of the existing conductive hydrogel, and provides a lignocellulose nanofiber reinforced conductive polyvinyl alcohol gel with high strength and high conductivity, which is simple to prepare.

[0005] The present application aims to provide a lignocellulose nanofiber reinforced conductive polyvinyl alcohol gel and a preparation method thereof, and simultaneously provides the application thereof in the field of flexible electronic materials.

[0006] To achieve the above-mentioned purpose, the present application adopts the following technical solution, and the specific steps include:

[0007] (1) drying and crushing melon vine to obtain melon vine powder;

[0008] (2) mixing and heating chlorocholine and oxalic acid dihydrate to prepare a chlorocholine / oxalic acid dihydrate DES solution;

[0009] (3) mixing melon vine powder and choline chloride / oxalic acid dihydrate DES solution, heating, then adding ultrapure water to stir, dispersing the solid mixture obtained after water washing to a certain amount of ultrapure water, and obtaining a lignocellulose nanofiber dispersion by ultrasonic crushing;

[0010] (4) preparing a hydrofluoric acid solution by heating and stirring lithium fluoride powder and hydrochloric acid solution, mixing aluminum titanium carbide powder and the prepared hydrofluoric acid solution, heating and stirring, then centrifuging, water washing, ultrasonic dispersion, and finally centrifuging to obtain a supernatant to obtain a MXene dispersion;

[0011] (5) mixing the lignocellulose nanofiber dispersion of step (3) and the MXene dispersion of step (4) by one-pot heating and stirring to obtain a mixture, and finally pouring the obtained mixture into a dumbbell-shaped polytetrafluoroethylene mold to polymerize by freeze-thaw cycle to obtain a conductive hydrogel.

[0012] Further, the choline chloride and oxalic acid dihydrate in step (2) are mixed at a molar ratio of 1:1, and the obtained uniform clear liquid, i.e., the choline chloride / oxalic acid dihydrate DES solution, is heated and stirred at 80°C.

[0013] Further, the melon vine powder and the choline chloride / oxalic acid dihydrate DES solution in step (3) are mixed at a mass ratio of 5g:100g, heated at 110°C for 1h, and the obtained mixture is filtered and washed to pH ~6 at room temperature; the ultrasonic crushing is performed in an ultrasonic crusher under ice water bath conditions for 2h, with ultrasonic operation for 3s and stop for 2s, and the power is 600W.

[0014] Further, in step (4), the mass / volume ratio of lithium fluoride to hydrochloric acid solution is 1.25g:20mL, the molar mass of the hydrochloric acid solution is 9M, the heating temperature is 35°C, and the heating time is 20min; the reaction time of aluminum titanium carbide with hydrofluoric acid is 24h, and the reaction temperature is 35°C; the centrifugal speed for water washing is 3500rpm, and the time is 5min; the obtained solid-liquid mixture is ultrasonically dispersed for 1h under ice water temperature, with a frequency of 40KHz and a power of 100%, and then the supernatant is obtained by centrifugation at a speed of 3500rpm for 40min.

[0015] Further, in step (5), the addition amount of the lignocellulose nanofiber dispersion is 15-60mg and 0-100mg, respectively, the addition amount of the MXene dispersion is 35-140mg and 100-0mg, respectively, and the fixed mass of polyvinyl alcohol is 2g; the obtained mixture is frozen at-20°C for 12h in the freezer, then taken out and melted at room temperature for 12h, and the cycle is repeated for 3 times to obtain a conductive hydrogel.

[0016] The beneficial effects achieved by one or more technical solutions of the above-mentioned application are as follows:

[0017] (1) The preparation method of the present application has simple process, mild reaction conditions, is green and low in energy consumption, and is friendly to the environment.

[0018] (2) The lignocellulose nanofiber reinforced conductive polyvinyl alcohol gel prepared by the method has excellent mechanical strength and toughness, a tensile strength of 1.55 MPa, and an elongation at break of 410%, compared with traditional biomass conductive hydrogel. In addition, the conductive hydrogel also has high sensitivity, high conductivity, stability and biocompatibility, and shows potential application value in the fields of flexible electronics and wearable sensors.

[0019] (3) The method effectively solves the problems of poor mechanical properties, insufficient interface compatibility and complex preparation process of existing conductive hydrogel, and provides a lignocellulose nanofiber reinforced conductive polyvinyl alcohol gel which is high-strength and high-conductivity and is simple to prepare, and also provides its application in flexible electronic materials. BRIEF DESCRIPTION OF DRAWINGS

[0020] Figure 1 is a preparation flowchart of the lignocellulose nanofiber reinforced conductive polyvinyl alcohol gel of the present application.

[0021] Figure 2 is a digital photo and a 5000 times surface scanning electron microscope graph of the gel prepared in Example 7.

[0022] Figure 3 is a digital photo and a 4000 times surface scanning electron microscope graph of the gel prepared in Comparative Example 1.

[0023] Figure 4 is a stress-strain curve graph of the gels prepared in Examples and Comparative Examples.

[0024] Figure 5 is a relative current change graph when the lignocellulose nanofiber reinforced conductive polyvinyl alcohol gel prepared in Example 7 is applied to a flexible sensor to detect different bending angles of fingers.

[0025] Figure 6 is a relative current change graph when the lignocellulose nanofiber reinforced conductive polyvinyl alcohol gel prepared in Example 7 is applied to a flexible sensor to detect different bending speeds of necks.

[0026] Figure 7 is a relative current change graph when the lignocellulose nanofiber reinforced conductive polyvinyl alcohol gel prepared in Example 7 is applied to a flexible sensor to detect speech recognition. DETAILED DESCRIPTION

[0027] In order for those skilled in the art to clearly understand the present application, the following will be described in detail in combination with specific examples.

[0028] Example 1

[0029] The embodiment provides a preparation method of lignocellulose nanofiber reinforced conductive polyvinyl alcohol gel, which comprises the following steps:

[0030] (1) 139.62 g of choline chloride and 146.07 g of oxalic acid dihydrate are mixed, heated and stirred at 80 DEG C for 1 h until the solution is transparent, and a eutectic solvent is obtained; then 5 g of pumpkin vine powder is added to 100 g of the eutectic solvent, heated and stirred at 110 DEG C for 1 h, and then a certain amount of ultrapure water is added and stirred, the reaction is stopped after water washing until the pH of the mixture is about 6, the solid mixture is collected and dispersed in a certain amount of ultrapure water, and ultrasonic crushing is carried out in an ultrasonic crushing instrument under the condition of ice water bath for 2 h (power 600 W, ultrasonic operation 3 s and stop 2 s) to obtain a lignocellulose nanofiber dispersion;

[0031] (2) 1.25 g of lithium fluoride powder and 20 mL of hydrochloric acid solution (molar mass 9 M) are mixed and placed in a polytetrafluoroethylene reaction kettle, heated and stirred in a water bath at 35 DEG C for 20 min to obtain an in-situ generated hydrofluoric acid solution; 1 g of carbon titanium aluminum powder is added to the obtained hydrofluoric acid solution, heated and stirred at 35 DEG C for 24 h, and then the obtained solution is centrifuged and washed until the pH is about 6, the centrifugal speed is 3500 rpm, and the centrifugal time is 5 min; the obtained solid-liquid mixture is dispersed in a certain amount of ultrapure water, ultrasonically treated in an argon atmosphere and ice water for 1 h (frequency 40 KHz, power 100%); the obtained solution is centrifuged (speed 3500 rpm, time 40 min), the supernatant is extracted, and the obtained is a MXene dispersion;

[0032] (3) 15 mg of the lignocellulose nanofiber dispersion prepared in step (1), 35 mg of the MXene dispersion prepared in step (2) and 2 g of polyvinyl alcohol solid are mixed in one pot, 14.1 mL of ultrapure water is added, heated and stirred at 80 DEG C for 1 h to obtain a mixed solution; the obtained mixed solution is poured into a dumbbell-shaped polytetrafluoroethylene mold, placed in a freezer at-20 DEG C for freezing for 12 h, and then taken out and placed at room temperature for melting for 12 h, and the freezing and melting cycle is repeated for 3 times to obtain a lignocellulose nanofiber reinforced conductive polyvinyl alcohol gel.

[0033] Example 2

[0034] The embodiment provides a preparation method of lignocellulose nanofiber reinforced conductive polyvinyl alcohol gel, which comprises the following steps:

[0035] (1) 139.62 g of choline chloride and 146.07 g of oxalic acid dihydrate were mixed, heated and stirred at 80°C for 1 h until the solution became transparent, obtaining a deep eutectic solvent; then 5 g of pumpkin vine powder was added to 100 g of the deep eutectic solvent, heated and stirred at 110°C for 1 h, then a certain amount of ultrapure water was added and stirred, the reaction was stopped after water washing until the pH of the mixture was about 6, the solid mixture was collected and dispersed in a certain amount of ultrapure water, and placed in an ultrasonic crusher under ice water bath conditions, and ultrasonic crushing was carried out for 2 h (power 600 W, ultrasonic operation 3 s and stop 2 s) to obtain a lignocellulose nanofiber dispersion;

[0036] (2) 1.25 g of lithium fluoride powder and 20 mL of hydrochloric acid solution (molar mass 9M) were mixed and placed in a polytetrafluoroethylene reaction kettle, heated and stirred in a water bath at 35°C for 20 min to obtain an in-situ generated hydrofluoric acid solution; 1 g of carbon titanium aluminum powder was added to the obtained hydrofluoric acid solution, heated and stirred at 35°C for 24 h, and the reaction was stopped after the obtained solution was centrifuged and washed to pH ~ 6, the centrifugal speed was 3500 rpm, and the centrifugal time was 5 min; the obtained solid-liquid mixture was dispersed in a certain amount of ultrapure water, ultrasonicated in an argon atmosphere and ice water for 1 h (frequency 40 KHz, power 100%); the obtained solution was centrifuged (speed 3500 rpm, time 40 min), and the supernatant was extracted, and the obtained was MXene dispersion;

[0037] (3) 30 mg of the lignocellulose nanofiber dispersion prepared in step (1), 70 mg of the MXene dispersion prepared in step (2), and 2 g of polyvinyl alcohol solid were mixed in one pot, and 8.2 mL of ultrapure water was added, heated and stirred at 80°C for 1 h to obtain a mixed solution; the obtained mixed solution was poured into a dumbbell-shaped polytetrafluoroethylene mold, placed in a refrigerator at-20°C for freezing for 12 h, and then taken out and placed at room temperature for melting for 12 h, and the freezing and melting cycle was repeated for 3 times to obtain a lignocellulose nanofiber reinforced conductive polyvinyl alcohol gel.

[0038] Example 3

[0039] The embodiment provides a preparation method of a lignocellulose nanofiber reinforced conductive polyvinyl alcohol gel, which comprises the following steps:

[0040] (1) 139.62 g of choline chloride and 146.07 g of oxalic acid dihydrate were mixed, heated and stirred at 80°C for 1 h until the solution became transparent, obtaining a deep eutectic solvent; then 5 g of pumpkin vine powder was added to 100 g of the deep eutectic solvent, heated and stirred at 110°C for 1 h, and then a certain amount of ultrapure water was added and stirred, the mixture was filtered and washed with water until pH ~ 6, the solid mixture was dispersed in a certain amount of ultrapure water, and placed in an ultrasonic crusher under ice water bath conditions, and ultrasonic crushing was carried out for 2 h (power 600 W, ultrasonic operation 3 s and stop 2 s) to obtain a lignocellulose nanofiber dispersion;

[0041] (2) 1.25 g of lithium fluoride powder and 20 mL of hydrochloric acid solution (molar mass 9M) were mixed and placed in a polytetrafluoroethylene reaction kettle, heated and stirred in a water bath at 35°C for 20 min to obtain an in-situ generated hydrofluoric acid solution; 1 g of carbon titanium aluminum powder was added to the obtained hydrofluoric acid solution, heated and stirred at 35°C for 24 h, and after the reaction was completed, the obtained solution was centrifuged and washed until pH ~ 6, the centrifugal speed was 3500 rpm, and the centrifugal time was 5 min; the obtained solid-liquid mixture was dispersed in a certain amount of ultrapure water, ultrasonicated in an argon atmosphere and ice water for 1 h (frequency 40 KHz, power 100%); the obtained solution was centrifuged (speed 3500 rpm, time 40 min), and the supernatant was extracted, and the obtained was MXene dispersion;

[0042] (3) 45 mg of the lignocellulose nanofiber dispersion prepared in step (1), 105 mg of the MXene dispersion prepared in step (2), and 2 g of polyvinyl alcohol solid were mixed in one pot, and 2.5 mL of ultrapure water was added, heated and stirred at 80°C for 1 h to obtain a mixed solution; the obtained mixed solution was poured into a dumbbell-shaped polytetrafluoroethylene mold, placed in a refrigerator at-20°C for freezing for 12 h, and then taken out and placed at room temperature for melting for 12 h, and the freezing and melting cycle was repeated for 3 times to obtain a lignocellulose nanofiber reinforced conductive polyvinyl alcohol gel.

[0043] Example 4

[0044] The embodiment provides a preparation method of a lignocellulose nanofiber reinforced conductive polyvinyl alcohol gel, which comprises the following steps:

[0045] (1) 139.62 g of choline chloride and 146.07 g of oxalic acid dihydrate were mixed, heated and stirred at 80°C for 1 h until the solution became transparent to obtain a deep eutectic solvent; then 5 g of pumpkin vine powder was added to 100 g of the deep eutectic solvent, heated and stirred at 110°C for 1 h, and then a certain amount of ultrapure water was added and stirred, the mixture was filtered and washed with water until the pH was about 6, the solid mixture was collected and dispersed in a certain amount of ultrapure water, and placed in an ultrasonic crusher under ice water bath conditions, and ultrasonic crushing was performed for 2 h (power 600 W, ultrasonic operation 3 s and stop 2 s) to obtain a lignocellulose nanofiber dispersion;

[0046] (2) 1.25 g of lithium fluoride powder and 20 mL of hydrochloric acid solution (molar mass 9 M) were mixed and placed in a polytetrafluoroethylene reaction kettle, heated and stirred in a water bath at 35°C for 20 min to obtain an in-situ generated hydrofluoric acid solution; 1 g of carbon titanium aluminum powder was added to the obtained hydrofluoric acid solution, heated and stirred at 35°C for 24 h, and then the obtained solution was centrifuged and washed until the pH was about 6, the centrifugal speed was 3500 rpm, and the centrifugal time was 5 min; the obtained solid-liquid mixture was dispersed in a certain amount of ultrapure water, ultrasonicated in an argon atmosphere under ice water temperature for 1 h (frequency 40 KHz, power 100%); the obtained solution was centrifuged (speed 3500 rpm, time 40 min), the supernatant was extracted, and the obtained was MXene dispersion;

[0047] (3) 60 mg of the lignocellulose nanofiber dispersion prepared in step (1), 140 mg of the MXene dispersion prepared in step (2), and 2 g of polyvinyl alcohol solid were mixed in one pot, heated and stirred at 80°C for 1 h to obtain a mixed solution; the obtained mixed solution was poured into a dumbbell-shaped polytetrafluoroethylene mold, placed in a freezer at-20°C for freezing for 12 h, and then taken out and placed at room temperature for melting for 12 h, and the freezing and melting cycle was repeated for 3 times to obtain a lignocellulose nanofiber reinforced conductive polyvinyl alcohol gel.

[0048] Examples 5-11, the specific experimental steps are the same as those of Example 1, except that the amounts of lignocellulose nanofiber dispersion, MXene dispersion and ultrapure water are different, the lignocellulose nanofiber is added in an amount of 0, 10, 30, 50, 70, 90, 100 mg, the MXene is added in an amount of 100, 90, 70, 50, 30, 10, 0 mg, and the ultrapure water is added in an amount of 12.4, 11.4, 10.8, 10.1, 9.2, 12, 9.5 mL.

[0049] Comparative Example 1

[0050] (1) 2 g of polyvinyl alcohol solid was directly mixed with 20 mL of ultrapure water in one pot, heated and stirred at 80°C for 1 h to obtain a mixed solution;

[0051] (2) Pour the solution obtained in step (1) into a dumbbell-shaped polytetrafluoroethylene mold, place it in a refrigerator at -20℃ for freezing for 12h, and then take it out and place it at room temperature for melting for 12h, and freeze-thaw cycle for 3 times to obtain a polyvinyl alcohol hydrogel.

[0052] The wood cellulose nanofiber reinforced conductive polyvinyl alcohol hydrogel prepared in the application exhibits excellent sensitivity in the sensing performance test. Figure 5 As shown in the accompanying drawings, the material can accurately identify the angle change when the finger bends, and realize real-time monitoring through the relative current change; the accompanying drawings Figure 6 further demonstrate that it can effectively capture the difference in neck bending speed; the accompanying drawings Figure 7 show that the hydrogel has excellent performance in the application of flexible sensors, and can accurately identify various dynamic signals such as slight actions, voice signals and writing tracks. The experimental results show that the conductive hydrogel as a flexible sensor material can not only monitor large-scale limb movements (such as bending of finger joints at different angles and neck bending movements), but also can sensitively detect slight body movements (such as speaking), and even can identify written information, and has broad application prospects in the field of flexible electronic devices.

[0053] The mechanical properties and conductivity of the gel materials prepared in Examples 1-11 and Comparative Example 1 were tested. The tensile strength and elongation at break of the materials were tested by a universal mechanical testing machine, and the relative current was measured by an electrochemical workstation under the condition of 3V constant voltage to calculate the conductivity. The test results (Table 1) show that the gel materials of Examples 1-11 are significantly better than Comparative Example 1 in mechanical properties. Among them, Example 9 shows the most excellent mechanical properties, with a tensile strength of 1.55MPa and an elongation at break of up to 410%, showing excellent flexibility and strength. In addition, the conductivity test results (Table 2) show that the gels of Examples 1-11 all have high conductivity, especially Example 3, whose conductivity can reach 0.13S / m, indicating that the material has good conductivity.

[0054] In summary, the method strategy provided by the application successfully prepares a wood cellulose nanofiber reinforced conductive polyvinyl alcohol hydrogel, and the prepared gel has excellent mechanical strength and conductivity, and has broad application prospects in the fields of flexible electronics, wearable sensors and the like.

[0055] Table 1 Mechanical property test results

[0056] Indicator Comparative Example 1 Example 1 Example 2 Example 3 Example 4 Example 5 Example 6 Example 7 Example 8 Example 9 Example 10 Example 11 Tensile strength / MPa 0.51 0.99 1.27 1.15 0.57 0.87 1.00 1.27 1.12 1.55 1.08 1.09 Elongation at break / % 370 360 370 400 250 250 270 370 450 410 330 330 toughness / (MJ / m -3 ) 0.82 1.59 2.44 2.12 0.66 0.96 1.26 2.04 2.12 2.82 1.68 1.63 .

[0057] Table 2 Conductivity test results

[0058] Serial number Example 1 Example 2 Example 3 Example 4 Example 5 Example 6 Example 7 Example 8 Example 9 Example 10 Example 11 Electrical conductivity (S / m, 25°C) 0.11 0.11 0.13 0.12. 0.08 0.10 0.11 0.09 0.08 0.07 0.07

[0059] The scope of protection of the application is not limited to the specific description of the above embodiments, any reasonable modification or equivalent replacement based on the technical concept of the application shall belong to the scope of protection of the claims of the application. The technical improvement and optimization made by the person skilled in the art without departing from the design principle of the application shall be regarded as the protection content of the application.

Claims

1. A method for preparing a lignocellulose nanofiber-reinforced conductive polyvinyl alcohol gel, characterized in that: (1) Dry and pulverize the melon vines to obtain melon vine powder; (2) Prepare a choline chloride / oxalate dihydrate DES solution by mixing choline chloride and oxalate dihydrate with heating and stirring; (3) Mix and heat the melon vine powder and choline chloride / oxalic acid dihydrate DES solution, then add ultrapure water and stir. After filtering and washing, disperse the solid mixture into a certain amount of ultrapure water and ultrasonically crush it to obtain a lignocellulose nanofiber dispersion. (4) Prepare hydrofluoric acid solution by heating and stirring lithium fluoride powder with hydrochloric acid solution; mix aluminum carbide powder with the prepared hydrofluoric acid solution, heat and stir, then centrifuge and wash the mixture with water, collect the residual solid and disperse it in a certain amount of ultrapure water, ultrasonically disperse it in an argon atmosphere and ice water environment, and finally centrifuge to obtain MXene dispersion. (5) The lignocellulose nanofiber dispersion from step (3), the MXene dispersion from step (4), and polyvinyl alcohol are heated and mixed in one pot to obtain a mixture. Finally, the mixture is poured into a dumbbell-shaped polytetrafluoroethylene mold and polymerized by freeze-thaw cycle to obtain a conductive hydrogel.

2. The preparation method according to claim 1, characterized in that, In step (2), the molar ratio of choline chloride to oxalic acid dihydrate solid is 1:

1. After mixing, the mixture is heated and stirred for 1 hour at a temperature of 80°C.

3. The preparation method according to claim 1, characterized in that, In step (3), the mass ratio of melon vine powder to eutectic solvent is 5g:100g. After mixing, the mixture is heated and stirred for 1 hour at a temperature of 110℃.

4. The preparation method according to claim 1, characterized in that, Step (3) Add the melon vine powder to the eutectic solvent and heat and stir to obtain a solid mixture. Wash with water to pH ~6, collect the solid mixture, disperse it in a certain amount of ultrapure water, and crush it with an ultrasonic crusher for 2 hours and 600W (ultrasonic on for 3 seconds, off for 2 seconds).

5. The preparation method according to claim 1, characterized in that, In step (4), the mass-to-volume ratio of lithium fluoride powder to hydrochloric acid solution is 1.25 g: 20 mL. The two are mixed together in a polytetrafluoroethylene reactor and heated and stirred for 20 min at a temperature of 35 °C. The hydrofluoric acid solution generated in situ is mixed with 1 g of aluminum carbide powder for 24 h at a temperature of 35 °C.

6. The preparation method according to claim 1, characterized in that, After the hydrofluoric acid solution generated in situ in step (4) is mixed and reacted with aluminum carbide powder, the collected mixture is centrifuged and washed with water to pH ~6, the centrifugation time is 5 min, and the centrifugation speed is 3500 rpm.

7. The preparation method according to claim 1, characterized in that, Step (4) After washing and dispersing the carbon-titanium compound mixture with water, the mixture was sonicated and then centrifuged to obtain the supernatant, which yielded the MXene dispersion. The centrifugation time was 40 min and the centrifugation speed was 3500 rpm. The sonication time was 1 h, the sonication frequency was 40 kHz, and the sonication power was 100%.

8. The preparation method according to claim 1, characterized in that, In step (5), the lignocellulose nanofiber dispersion, polyvinyl alcohol and MXene dispersion are mixed in one pot. The amount of lignocellulose nanofiber dispersion added is 15-60mg and 0-100mg, respectively. The amount of MXene dispersion added is 35-140mg and 100-0mg, respectively. The fixed mass of polyvinyl alcohol is 2g. The resulting mixture is placed in the freezer compartment of the refrigerator at -20℃ for 12h, and then taken out and thawed at room temperature for 12h. This cycle is repeated 3 times to obtain conductive hydrogel.

9. The lignocellulose nanofiber reinforced conductive polyvinyl alcohol gel obtained by the preparation method according to any one of claims 1-8.

10. The application of the conductive hydrogel according to claim 9 in a flexible sensor.

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