A p-MXene Conductive Ink and BC Reinforced Polymer Composite Film, Preparation Method Thereof and Application

Abstract

The present invention relates to the technical field of intelligent materials, and discloses a composite film of p-MXene conductive ink and BC reinforced polymer, its preparation method and application. The composite film includes MXene and bacterial cellulose. The surface of MXene is coated with aqueous polydopamine, and aqueous polyurethane is embedded in the bacterial cellulose. Hydrogen bonds are formed between the hydroxyl groups in the aqueous polydopamine and the amino groups in the aqueous polyurethane to connect MXene and bacterial cellulose. The composite film obtained by the present invention has excellent mechanical properties and electrical properties, and also has comprehensive properties such as electromagnetic shielding and stress-strain sensing.

Description

Technical Field

[0001] The present invention relates to the technical field of intelligent materials, and particularly relates to a p-MXene conductive ink and BC reinforced polymer composite film, a preparation method thereof, and an application thereof. Background Art

[0002] The new generation of bio-based functional composite materials has the advantages of light weight, high strength, high stability, and abundant functional active sites, and can meet the application requirements of high-performance enrichment recognition or wearable functional devices. Bacterial cellulose (BC) is a natural polymer generated by the growth and metabolism of bacteria. It has the characteristics of low density, high tensile strength and elastic modulus, high specific surface area, multi-hydroxyl active interface, and good biocompatibility, and is a relatively widely studied structural substrate material. Compared with plant cellulose and other common materials, BC has the characteristics of high crystallinity, high water retention, high tensile strength and elastic modulus, and also has a typical three-dimensional network porous structure. Based on the special structural characteristics of BC and rich surface modification methods, it is particularly suitable for the composite construction of multi-level ordered structures at the micro-nano scale, further expanding its application in the field of flexible functional composite materials. Although BC still has problems such as low toughness, poor stability, and insufficient mechanical properties at present, its excellent mechanical properties, biocompatibility, degradability, and modifiability make BC hydrogel have inestimable potential in the development of sensors.

[0003] MXene is a class of two-dimensional transition metal carbides and / or nitrides with a large specific surface area and metal-like conductivity, and is considered to be one of the potential candidate materials for preparing wearable composite materials, and was confirmed to be a very promising electromagnetic shielding material in 2016. However, the mechanical strength of the macroscopic material prepared from pure MXene is insufficient, resulting in difficulties in practical applications.

[0004] At present, there are few studies by research scholars on improving the mechanical strength of MXene with bacterial cellulose, which provides a new idea for solving the mechanical strength of MXene. Summary of the Invention

[0005] In order to solve the above technical problems, the present invention provides a p-MXene conductive ink and BC reinforced polymer composite film, a preparation method thereof, and an application thereof. The composite film obtained by the present invention has excellent mechanical properties and electrical properties, and at the same time has comprehensive properties such as electromagnetic shielding and stress-strain sensing.

[0006] The present invention provides a p-MXene conductive ink and BC reinforced polymer composite film, which composite film comprises MXene and bacterial cellulose, the surface of MXene is coated with aqueous polydopamine, aqueous polyurethane is embedded in the bacterial cellulose, and hydrogen bonds are formed between the hydroxyl groups in the aqueous polydopamine and the amino groups in the aqueous polyurethane to connect MXene and bacterial cellulose.

[0007] Further, the length of the bacterial fiber is not less than 20 μm, and the diameter is 50 nm - 100 nm.

[0008] The present invention also provides a preparation method of the p-MXene conductive ink and BC reinforced polymer composite film, which preparation method comprises:

[0009] Step S1: Soak bacterial cellulose in an aqueous polyurethane solution, and dry at room temperature to obtain a bacterial cellulose / aqueous polyurethane nanocomposite;

[0010] Step S2: Dissolve lithium fluoride in a hydrochloric acid solution, add aluminum titanium carbide (Ti 3 AlC 2 ), conduct a first etching reaction, wash the acid, perform solid-liquid separation, conduct a second etching reaction to obtain an intermediate product; add hydrochloric acid dopamine to a tris(hydroxymethyl)aminomethane solution (Tris), conduct a pre-reaction, add a concentrated suspension of the intermediate product, react, perform solid-liquid separation, and retain the precipitate;

[0011] Step S3: Coat the product obtained in Step S2 on the surface of the bacterial cellulose / aqueous polyurethane nanocomposite obtained in Step S1 at least once, and dry at room temperature to obtain a p-MXene conductive ink and BC reinforced polymer composite film.

[0012] Further, in Step S1, the soaking time is 1.5 h - 2.5 h.

[0013] Further, the mass concentration of the aqueous polyurethane solution is 5% - 32%.

[0014] Further, the preparation method of the aqueous polyurethane solution comprises: dissolving and dispersing aqueous polyurethane in deionized water.

[0015] Further, in the present invention, as long as the bacterial cellulose is completely soaked in the aqueous polyurethane solution, by controlling the mass concentration of the aqueous polyurethane solution and the soaking time, it is possible to achieve the penetration of the aqueous polyurethane into the three-dimensional structure of the bacterial cellulose.

[0016] Further, the temperature of the room temperature drying is 10°C - 30°C.

[0017] Further, in Step S1, the time of the room temperature drying is 46 h - 50 h.

[0018] Further, the time for drying at room temperature in step S3 is 23 h - 25 h.

[0019] Further, the mass concentration of lithium fluoride in the hydrochloric acid solution is 2 g / 40 mL.

[0020] Further, the molar concentration of the hydrochloric acid solution is 9 mol / L.

[0021] Further, the preparation method of the hydrochloric acid solution: Dilute hydrochloric acid with deionized water.

[0022] Further, the mass concentration of aluminum titanium carbide in the hydrochloric acid solution is 2 g / 40 mL.

[0023] Further, the specific method of the first etching reaction: Stir at 34°C - 36°C for 23 h - 25 h.

[0024] Further, the specific method of acid washing in step S2: Wash with deionized water until the pH value of the product is close to 6, and then add ethanol.

[0025] In the present invention, adding ethanol is to further wash the acid clean. During the washing process with ethanol, ultrasonic treatment can also be carried out simultaneously. Those skilled in the art should understand that ethanol is used for removing acid, and there is no special limitation on the concentration of ethanol. Anhydrous ethanol can be used, or ethanol with other concentrations can be used. The ultrasonic time is also not limited, as long as the purpose of removing acid can be achieved. As an example, ethanol with the same volume as the hydrochloric acid solution can be added and ultrasonicated for 1 h.

[0026] Further, the specific method of the second etching reaction includes: Add deionized water to the precipitate after solid-liquid separation and centrifuge, and retain the supernatant.

[0027] Further, there is no special requirement for the addition amount of deionized water used in the second etching reaction, which can be adjusted according to the retained supernatant, as long as it can ensure that the added deionized water can achieve the second etching.

[0028] Further, the specific parameters of the centrifugation are: Centrifuge at 3900 rpm - 4100 rpm for 2.5 min - 3.5 min.

[0029] Further, the mass concentration of dopamine hydrochloride in the tris(hydroxymethyl)aminomethane solution is 10 mg / 5 mL.

[0030] Further, the pH value of the tris(hydroxymethyl)aminomethane solution is 8.4 - 8.6.

[0031] Further, the time for the pre-reaction is 1.5 h - 2.5 h.

[0032] Further, the mass ratio of dopamine hydrochloride to the intermediate product is 2.5% - 20%.

[0033] Further, in the step S2, the reaction time is 23h - 25h, stirring is carried out during the reaction, and the stirring speed is 380rpm - 420rpm.

[0034] Further, the preparation method of the concentrated suspension of the intermediate product: after the secondary etching reaction, the supernatant is retained by centrifugation, and the retained supernatant is subjected to freeze-drying treatment to obtain the concentrated suspension of the intermediate product.

[0035] Further, the mass concentration of the concentrated suspension of the intermediate product is 2mg / L.

[0036] The present invention also provides the application of the p-MXene conductive ink and the BC reinforced polymer composite film in a sensor.

[0037] The embodiments of the present invention have the following technical effects:

[0038] 1. In the composite film obtained in the present invention, waterborne polyurethane can fully penetrate into the three-dimensional structure of bacterial cellulose, improving the elongation and toughness of the film without destroying the original mechanical strength of bacterial cellulose; while polydopamine can form a uniform coating layer on the surface of MXene, physically preventing the direct contact of oxygen with MXene, reducing the chance of oxygen molecules diffusing into the interior of the MXene sheet layer, thereby slowing down the occurrence of the oxidation reaction. In addition, polydopamine has a certain thickness and spatial structure, which can form an effective steric hindrance on the surface of MXene, making it difficult for oxygen to approach the active sites of MXene; through the hydroxyl groups (-OH) in polydopamine, not only can hydrogen bonds be formed with the amino groups (-NH 2 ) in waterborne polyurethane; moreover, π-π stacking occurs between the benzene rings in waterborne polydopamine and the aromatic groups (such as benzene rings) in waterborne polyurethane, thereby forming a stable supramolecular structure, thus realizing the stability of the connection between bacterial cellulose and MXene, and on the basis of improving the mechanical strength of the composite film, also ensuring the stability of the structure of the composite film.

[0039] 2. In the present invention, in order to improve the mechanical strength of the composite film, bacterial cellulose with a length of not less than 20 μm, aqueous polydopamine, and aqueous polyurethane are also selected. Bacterial cellulose with a longer length not only has better mechanical strength but also facilitates the full embedding of aqueous polyurethane into the three-dimensional structure of bacterial cellulose while ensuring the structure of bacterial cellulose, thereby further improving the mechanical strength of bacterial cellulose. The use of aqueous polydopamine and aqueous polyurethane enables self-assembly during the coating process, which is conducive to the formation of hydrogen bonds and π-π stacking, thereby enhancing the stability of the structure.

[0040] 3. In the present invention, the addition amounts between aqueous polydopamine and aqueous polyurethane are further restricted. When adjusting the concentrations of aqueous polydopamine and aqueous polyurethane, first, it can control the uniform coating of aqueous polydopamine on the surface of MXene while reducing agglomeration. Second, it can control the number of hydrogen bonds formed by aqueous polydopamine and aqueous polyurethane. Third, it can promote the composite film to have good electrical and mechanical properties.

[0041] 4. The composite film obtained in the present invention has excellent mechanical and electrical properties, and also has comprehensive properties such as electromagnetic shielding and stress-strain sensing. BRIEF DESCRIPTION OF THE DRAWINGS

[0042] In order to more clearly illustrate the specific embodiments of the present invention or the technical solutions in the prior art, the following will briefly introduce the drawings required for the description of the specific embodiments or the prior art. Obviously, the drawings in the following description are some embodiments of the present invention. For those of ordinary skill in the art, without creative efforts, other drawings can also be obtained based on these drawings.

[0043] Figure 1 It is the micrograph of bacterial cellulose provided in Example 2 of the present invention.

[0044] Figure 2 It is the micrograph of aqueous polyurethane embedded in bacterial cellulose in Example 2 of the present invention.

[0045] Figure 3 It is the micrograph of the composite film in Example 1.

[0046] Figure 4 It is the Fourier transform infrared spectrum of the comparative example.

[0047] Figure 5 It is the XRD pattern of the examples and the comparative example.

[0048] Figure 6 It is the elemental distribution map of Example 1, where Figure 6In (a) is the distribution of each element in Example 1, Figure 6 In (b) is the distribution of O element, Figure 6 In (c) is the distribution of C element, Figure 6 In (d) is the distribution of Ti element.

[0049] Figure 7 is a schematic diagram of the p-MXene@WPU / BC composite film prepared in Example 5 applied in a stress sensor.

[0050] Figure 8 is the data acquisition after being applied to the sensor, where Figure 8 in (a) is the relationship between the applied pressure and the ohms of the composite film, Figure 8 in (b) is the R-T curve during the compression-recovery cycle.

[0051] Figure 9 is the data acquisition of the composite film prepared in Example 5 applied to the sensor, where Figure 9 in (a) is for the finger, Figure 9 in (b) is for the wrist, Figure 9 in (c) is for the elbow joint, Figure 9 in (d) is for the face, Figure 9 in (e) is for detecting human movement.

[0052] Figure 10 is the Fourier transform infrared spectrum of the examples and comparative examples. Detailed implementation manners

[0053] To make the objectives, technical solutions and advantages of the present invention clearer, the technical solutions of the present invention will be clearly and completely described below. Apparently, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts fall within the scope of protection of the present invention.

[0054] In a first aspect, in some embodiments of the present invention, a p-MXene conductive ink and BC reinforced polymer composite film are provided. The composite film includes MXene and bacterial cellulose. The surface of MXene is coated with aqueous polydopamine, and aqueous polyurethane is embedded in the bacterial cellulose. Hydrogen bonds are formed between the hydroxyl groups in the aqueous polydopamine and the amino groups in the aqueous polyurethane to connect MXene and bacterial cellulose.

[0055] In some embodiments, the length of the bacterial fiber is not less than 20 μm, and the diameter is 50 nm - 100 nm.

[0056] Second aspect, in some embodiments of the present invention, a method for preparing the p-MXene conductive ink and the BC reinforced polymer composite film is further provided, and the preparation method includes:

[0057] Step S1: Immerse bacterial cellulose in an aqueous polyurethane solution and dry at room temperature to obtain a bacterial cellulose / aqueous polyurethane nanocomposite;

[0058] Step S2: Dissolve lithium fluoride in a hydrochloric acid solution, add aluminum titanium carbide, perform a first etching reaction, wash the acid, separate the solid and liquid, perform a second etching reaction to obtain an intermediate product; add hydrochloric acid dopamine to a tris(hydroxymethyl)aminomethane solution, perform a pre-reaction, add a concentrated suspension of the intermediate product, react, separate the solid and liquid, and retain the precipitate;

[0059] Step S3: Coat the product obtained in Step S2 on the surface of the bacterial cellulose / aqueous polyurethane nanocomposite obtained in Step S1 at least once and dry at room temperature to obtain a p-MXene conductive ink and BC reinforced polymer composite film.

[0060] In some embodiments, in Step S1, the immersion time is 1.5 h - 2.5 h.

[0061] In some embodiments, the mass concentration of the aqueous polyurethane solution is 5% - 32%.

[0062] In some embodiments, the preparation method of the aqueous polyurethane solution includes: dissolving and dispersing aqueous polyurethane in deionized water.

[0063] In some embodiments, the temperature for drying at room temperature is 10°C - 30°C.

[0064] In some embodiments, the drying time at room temperature in Step S1 is 46 h - 50 h.

[0065] In some embodiments, the drying time at room temperature in Step S3 is 23 h - 25 h.

[0066] In some embodiments, the mass concentration of lithium fluoride in the hydrochloric acid solution is 2 g / 40 mL.

[0067] In some embodiments, the molar concentration of the hydrochloric acid solution is 9 mol / L.

[0068] In some embodiments, the preparation method of the hydrochloric acid solution: Dilute hydrochloric acid with deionized water to obtain it.

[0069] In some embodiments, the mass concentration of aluminum titanium carbide in the hydrochloric acid solution is 2 g / 40 mL.

[0070] In some embodiments, the specific method of the primary etching reaction is as follows: stirring is carried out at 34°C - 36°C for 23h - 25h.

[0071] In some embodiments, the specific method of acid washing in step S2 is as follows: washing is carried out with deionized water until the pH value of the product is close to 6, and then ethanol is added.

[0072] In some embodiments, the specific method of the secondary etching reaction includes: adding deionized water to the precipitate after solid-liquid separation, and centrifuging to retain the supernatant.

[0073] In some embodiments, the specific parameters of the centrifugation are: centrifuging at 3900rpm - 4100rpm for 2.5min - 3.5min

[0074] In some embodiments, the mass concentration of dopamine hydrochloride in the tris(hydroxymethyl)aminomethane solution is 10mg / 5mL.

[0075] Further, the pH value of the tris(hydroxymethyl)aminomethane solution is 8.4 - 8.6.

[0076] In some embodiments, the time of the pre-reaction is 1.5h - 2.5h.

[0077] In some embodiments, the mass ratio of dopamine hydrochloride to the intermediate product is 2.5% - 20%.

[0078] In some embodiments, in step S2, the reaction time is 23h - 25h, stirring is carried out during the reaction, and the stirring speed is 380rpm - 420rpm.

[0079] In a third aspect, in some embodiments of the present invention, the application of the p-MXene conductive ink and the BC reinforced polymer composite film in a sensor is also provided.

[0080] The following is elaborated in combination with specific examples and comparative examples:

[0081] Example 1:

[0082] (1) After taking out the purchased bacterial cellulose, it is soaked in a 0.1mol / L sodium hydroxide solution and treated in a constant temperature water bath at 80°C for 12h to remove nutrients and live bacteria; after rinsing with deionized water until the pH is 7.0, a treated bacterial cellulose membrane is obtained;

[0083] (2) Immerse the bacterial cellulose obtained in (1) in an aqueous polyurethane solution to obtain a WPU / BC film. Immerse the bacterial cellulose film in 50 mL of an aqueous polyurethane solution with a mass concentration of 32% for 2 hours to prepare a bacterial cellulose / polyurethane nanocomposite. Subsequently, take out the film from the dispersion and dry it at room temperature (26 °C) for 2 days to obtain a transparent nanocomposite film;

[0084] (3) Using Ti 3 AlC 2 powder (400 mesh) as the substrate, prepare MXene by the LiF (lithium fluoride) / HCl (hydrochloric acid) solution etching method. Usually, dissolve 2 g of lithium fluoride in 9 M hydrochloric acid solution (40 mL), stir in a polytetrafluoroethylene container for 30 minutes, and slowly add 2 g of Ti 3 AlC 2 powder in an ice bath reaction container, stir at 35 °C for 24 h, wash repeatedly with deionized water (3500 rpm, 10 minutes) until the pH value is close to 6. Add 40 mL of ethanol, ultrasonicate for 1 h, centrifuge (10000 rpm, 10 minutes) to collect the precipitate, then add 20 mL of deionized water to the precipitate and centrifuge at 4000 rpm for 3 min, retain the supernatant, which is the MXene material. Obtain a concentrated suspension of MXene by freeze-drying the MXene, and the mass concentration of the concentrated suspension of MXene is 2 mg / mL, for later use.

[0085] (4) Add 10 mg of dopamine hydrochloride (DA) to 5 mL of tris(hydroxymethyl)aminomethane solution (pH ≈ 8.5), pre-react for 2 h to reduce the amino content in the solution and avoid electrostatic flocculation after adding MXene, and then slowly add 200 mL of the concentrated suspension of MXene. Under the condition of strong stirring at 400 rpm, the reaction lasts for 24 h. After the reaction, centrifuge the MXene suspension (3500 rpm, 5 min) to collect the precipitate. According to the feed mass ratio of DA to MXene (2.5 wt%), name the modified MXene as p-MXene-2.5. Finally, evenly coat the prepared p-MXene-2.5 on the WPU / BC film, dry at room temperature for 24 h, and repeat several times to finally obtain a composite film, denoted as: p-MXene-2.5@WPU / BC.

[0086] Example 2:

[0087] (1) The same as Example 1;

[0088] (2) The same as Example 1;

[0089] (3) The same as Example 1;

[0090] (4) Add 10 mg of dopamine hydrochloride to 5 mL of tris(hydroxymethyl)aminomethane solution (pH ≈ 8.5), and pre-react for 2 h to reduce the amino content in the solution and avoid electrostatic flocculation after adding MXene. Then slowly add 100 mL of the concentrated suspension of MXene. Under strong stirring conditions, the reaction lasts for 24 h. After the reaction is completed, centrifuge the MXene suspension (3500 rpm, 5 min) and collect the precipitate by centrifugation. According to the feed mass ratio of DA to MXene (5 wt%), the modified MXene is named p-MXene-5. Finally, uniformly coat the prepared p-MXene-5 onto the WPU / BC membrane, dry at room temperature for 24 h, and repeat several times to finally obtain a composite film, denoted as: p-MXene-5@WPU / BC.

[0091] Example 3:

[0092] (1) The same as Example 1;

[0093] (2) The same as Example 1;

[0094] (3) The same as Example 1;

[0095] (4) Add 10 mg of dopamine hydrochloride to 5 mL of tris(hydroxymethyl)aminomethane solution (pH ≈ 8.5), and pre-react for 2 h to reduce the amino content in the solution and avoid electrostatic flocculation after adding MXene. Then slowly add 50 mL of the concentrated suspension of MXene. Under strong stirring conditions, the reaction lasts for 24 h. After the reaction is completed, centrifuge the MXene suspension (3500 rpm, 5 min) and collect the precipitate by centrifugation. According to the feed mass ratio of DA to MXene (10 wt%), the modified MXene is named p-MXene-10. Finally, uniformly coat the prepared p-MXene-10 onto the WPU / BC membrane, dry at room temperature for 24 h, and repeat several times to finally obtain a composite film, denoted as: p-MXene 10 @WPU / BC.

[0096] Example 4:

[0097] (1) The same as Example 1;

[0098] (2) The same as Example 1;

[0099] (3) The same as Example 1;

[0100] (4) 10 mg of dopamine hydrochloride was added to 5 mL of tris(hydroxymethyl)aminomethane solution (pH ≈ 8.5), and pre-reacted for 2 h to reduce the amino content in the solution and avoid electrostatic flocculation after adding MXene. Then, a concentrated suspension of MXene with a volume of 33 mL was slowly added. Under strong stirring conditions, the reaction continued for 24 h. After the reaction, the MXene suspension was centrifuged (3500 rpm, 5 min), and the precipitate was collected by centrifugation. According to the feed mass ratio of DA to MXene (15 wt%), the modified MXene was named p-MXene-15. Finally, the prepared p-MXene-15 was evenly coated on the WPU / BC film and dried at room temperature for 24 h. This was repeated several times to finally obtain a composite film, denoted as: p-MXene-15@WPU / BC.

[0101] Example 5:

[0102] (1) The same as Example 1;

[0103] (2) The same as Example 1;

[0104] (3) The same as Example 1;

[0105] (4) 10 mg of dopamine hydrochloride was added to 5 mL of tris(hydroxymethyl)aminomethane solution (pH ≈ 8.5), and pre-reacted for 2 h to reduce the amino content in the solution and avoid electrostatic flocculation after adding MXene. Then, a concentrated suspension of MXene with a volume of 25 mL was slowly added. Under strong stirring conditions, the reaction continued for 24 h. After the reaction, the MXene suspension was centrifuged (3500 rpm, 5 min), and the precipitate was collected by centrifugation. According to the feed mass ratio of DA to MXene (20 wt%), the modified MXene was named p-MXene-20. Finally, the prepared p-MXene-20 was evenly coated on the WPU / BC film and dried at room temperature for 24 h. This was repeated several times to finally obtain a composite film, denoted as: p-MXene-20@WPU / BC.

[0106] Comparative Example 1: The purchased bacterial cellulose was taken out and soaked in 0.1 mol / L NaOH solution, and treated in a constant temperature water bath at 80 °C for 12 h to remove nutrients and live bacteria; after rinsing with deionized water until the pH was 7.0, the treated bacterial cellulose membrane was obtained. Denoted as: BC.

[0107] Comparative Example 2:

[0108] (1) The same as Comparative Example 1;

[0109] (2) Immerse the bacterial cellulose obtained in (1) in an aqueous polyurethane solution to obtain a WPU / BC film. Immerse the bacterial cellulose film in 50 mL of an aqueous polyurethane solution with a mass concentration of 5% for 2 hours to prepare a bacterial cellulose / polyurethane nanocomposite. Subsequently, take the film out of the dispersion and dry it at room temperature (26 °C) for 2 days to obtain a transparent nanocomposite film. Name the prepared nanocomposite BC / WPU5.

[0110] Comparative Example 3:

[0111] (1) The same as Comparative Example 1;

[0112] (2) Immerse the bacterial cellulose obtained in (1) in an aqueous polyurethane solution to obtain a WPU / BC film. Immerse the bacterial cellulose film in 50 mL of an aqueous polyurethane solution with a mass concentration of 7% for 2 hours to prepare a bacterial cellulose / polyurethane nanocomposite. Subsequently, take the film out of the dispersion and dry it at room temperature (26 °C) for 2 days to obtain a transparent nanocomposite film. Name the prepared nanocomposite BC / WPU7.

[0113] Comparative Example 4:

[0114] (1) The same as Comparative Example 1;

[0115] (2) Immerse the bacterial cellulose obtained in (1) in an aqueous polyurethane solution to obtain a WPU / BC film. Immerse the bacterial cellulose film in 50 mL of an aqueous polyurethane solution with a mass concentration of 9% for 2 hours to prepare a bacterial cellulose / polyurethane nanocomposite. Subsequently, take the film out of the dispersion and dry it at room temperature (26 °C) for 2 days to obtain a transparent nanocomposite film. Name the prepared nanocomposite BC / WPU9.

[0116] Comparative Example 5:

[0117] (1) The same as Comparative Example 1;

[0118] (2) Immerse the bacterial cellulose obtained in (1) in an aqueous polyurethane solution to obtain a WPU / BC film. Immerse the bacterial cellulose film in 50 mL of an aqueous polyurethane solution with a mass concentration of 12% for 2 hours to prepare a bacterial cellulose / polyurethane nanocomposite. Subsequently, take the film out of the dispersion and dry it at room temperature (26 °C) for 2 days to obtain a transparent nanocomposite film. Name the prepared nanocomposite BC / WPU12.

[0119] Comparative Example 6:

[0120] (1) The same as Comparative Example 1;

[0121] (2) Immerse the bacterial cellulose obtained in (1) in an aqueous polyurethane solution to obtain a WPU / BC film. Immerse the bacterial cellulose film in 50 mL of an aqueous polyurethane solution with a mass concentration of 32% for 2 hours to prepare a bacterial cellulose / polyurethane nanocomposite. Subsequently, take the film out of the dispersion and dry it at room temperature (26 °C) for 2 days to obtain a transparent nanocomposite film. Name the prepared nanocomposite 32% BC / WPU.

[0122] Comparative Example 7:

[0123] Using Ti 3 AlC 2 powder (400 mesh) as the substrate, prepare MXene by the LiF / HCl solution etching method. Generally, dissolve 2 g of lithium fluoride in 9 M hydrochloric acid solution (40 mL), stir in a polytetrafluoroethylene container for 30 minutes, and slowly add 2 g of Ti 3 AlC 2 powder, stir at 35 °C for 24 h, wash repeatedly with deionized water (3500 rpm, 10 minutes) until the pH value is close to 6. Add 40 mL of ethanol, ultrasonicate for 1 h, centrifuge (10000 rpm, 10 minutes) and collect the precipitate by centrifugation, then add 20 mL of deionized water to the precipitate and centrifuge at 4000 rpm for 3 min to obtain the MXene material.

[0124] Comparative Example 8:

[0125] (1) The same as Comparative Example 7

[0126] (2) Add 10 mg of dopamine hydrochloride to 5 mL of tris(hydroxymethyl)aminomethane solution (pH ≈ 8.5), pre-react for 2 h to reduce the amino content in the solution and avoid electrostatic flocculation after adding MXene, and then slowly add a concentrated suspension of MXene with a volume of 50 mL. Under strong stirring conditions, the reaction lasts for 24 h. After the reaction is completed, centrifuge the MXene suspension (3500 rpm, 5 min) and collect the precipitate by centrifugation. Name the modified MXene p-MXene-10 according to the feeding mass ratio of DA to MXene (10 wt%).

[0127] Comparative Example 9:

[0128] (1) Take out the purchased bacterial cellulose and immerse it in 0.1 mol / L NaOH solution, and treat it in a constant temperature water bath at 80 °C for 12 h to remove nutrients and live bacteria; after rinsing with deionized water until the pH is 7.0, obtain the treated bacterial cellulose film;

[0129] (2) Immerse the bacterial cellulose obtained in (1) in an aqueous polyurethane solution to obtain a WPU / BC film. Immerse the bacterial cellulose film in 50 mL of an aqueous polyurethane solution with a mass concentration of 32% for 2 hours to prepare a bacterial cellulose / polyurethane nanocomposite. Subsequently, take out the film from the dispersion and dry it at room temperature (26 °C) for 2 days to obtain a transparent nanocomposite film;

[0130] (3) Using Ti 3 AlC 2 powder (400 mesh) as the matrix, prepare MXene by the LiF / HCl solution etching method. Generally, dissolve 2 g of lithium fluoride in 9 M hydrochloric acid solution (40 mL), stir in a polytetrafluoroethylene container for 30 minutes, slowly add 2 g of Ti 3 AlC 2 powder in an ice bath reaction container, stir at 35 °C for 24 h, wash repeatedly with deionized water (3500 rpm, 10 minutes) until the pH value is close to 6. Add 40 mL of ethanol, ultrasonicate for 1 h, centrifuge (10000 rpm, 10 minutes) to collect the precipitate, then add 20 mL of deionized water to the precipitate and centrifuge at 4000 rpm for 3 min to obtain the MXene material. The MXene is obtained by freeze-drying to obtain a concentrated suspension of MXene with a mass concentration of 2 mg / mL for standby.

[0131] (4) Uniformly coat the prepared MXene ink on the WPU / BC film and dry it at room temperature for 24 h. Repeat several times to finally obtain a composite film, denoted as MXene@WPU / BC.

[0132] Comparative Example 10: Break the BC and dissolve it in deionized water to prepare a solution of about 2 mg / mL; mix it with an aqueous polyurethane with a mass concentration of 32% at a volume ratio of 1:1, ultrasonicate (10 min), and prepare a WPU / BC thin film by vacuum filtration.

[0133] Test the examples and comparative examples in the present invention:

[0134] Mechanical property determination: Prepare test samples (specification: 100 mm × 7 mm) of the composite films prepared in the examples and comparative examples according to the requirements of the thin film strength test, and use a tensile strength measuring instrument (model: PT-990T) to conduct a strength test.

[0135] Results and analysis:

[0136] Table 1 Mechanical property test results of examples and comparative examples

[0137]

[0138] Table 2 Test Results of Electromagnetic Shielding Performance of Examples and Comparative Examples

[0139]

[0140] In the composite film obtained in the present invention, bacterial cellulose is used to improve the mechanical properties of the MXene material. In the bacterial cellulose obtained in the present invention, waterborne polyurethane is also embedded. The waterborne polyurethane can fully penetrate into the three-dimensional structure of the bacterial cellulose. On the basis of not destroying the original mechanical strength of the bacterial cellulose, the elongation and toughness of the film are improved. It can be found from Comparative Example 1 and Comparative Examples 2-6 that the waterborne polyurethane can further improve the mechanical strength of the bacterial cellulose. In the present invention, the waterborne polyurethane can not only fully penetrate into the three-dimensional structure of the bacterial cellulose and improve the mechanical structure of the bacterial cellulose, but also form hydrogen bonds with the waterborne polydopamine on the surface of the MXene material, which is beneficial to the improvement of the MXene material by the bacterial cellulose.

[0141] In terms of the improvement of the mechanical strength of the bacterial cellulose by the waterborne polyurethane, only when the waterborne polyurethane can stably penetrate into the three-dimensional structure of the bacterial cellulose can the mechanical strength of the bacterial cellulose be better optimized. Therefore, in the present invention, first, the length of the bacterial cellulose is not less than 20 μm, which is beneficial to realizing the penetration of the waterborne polyurethane into the three-dimensional structure of the bacterial cellulose on the basis of ensuring the mechanical strength of the bacterial cellulose itself. The mechanical properties of Comparative Example 10 are worse than those of Comparative Example 6 because the bacterial cellulose is broken. Secondly, in the present invention, the waterborne polyurethane needs to penetrate into the three-dimensional structure of the bacterial cellulose to achieve the modification of the bacterial cellulose. When the concentration of the waterborne polyurethane is low, the modification of the bacterial cellulose is not significant, and when the concentration of the waterborne polyurethane is high, the fluidity is poor and it is difficult for the waterborne polyurethane to penetrate. Therefore, in this case, the mass concentration of the waterborne polyurethane solution is further selected to be 5%-32%. By comparing Comparative Examples 2-6, the mass concentration of the waterborne polyurethane solution is further preferably 32%.

[0142] The waterborne polyurethane can also form hydrogen bonds with the waterborne polydopamine on the surface of the MXene material, which is beneficial to the improvement of the MXene material by the bacterial cellulose. This can be verified by comparing Comparative Example 9 with Examples 1-5.

[0143] On this basis, the mass concentration of aqueous polydopamine was further studied. When the mass concentration of aqueous polydopamine was low, fewer hydrogen bonds were formed between aqueous polydopamine and aqueous polyurethane. When the mass concentration of aqueous polydopamine was high, aqueous polydopamine would agglomerate and could not be coated, which affected the self-assembly of aqueous polydopamine and aqueous polyurethane, and ultimately led to a decrease in the electrical and mechanical properties of the obtained composite film. Comparative verification was carried out through Examples 1-5 in Table 1.

[0144] Figure 10 It can be found that by comparing Comparative Example 9 and Example 3, it was found that the formation of hydrogen bonds usually caused the stretching vibration absorption peak to shift towards the lower wavenumber (red shift) direction. This was because the formation of hydrogen bonds reduced the force constant between the hydrogen atom and the atom it was connected to, resulting in a decrease in the vibration frequency. Absorption peak intensity and width: The presence of hydrogen bonds could also increase the absorption intensity of certain vibration modes and broaden the absorption peak. These changes reflected the influence of hydrogen bonds on the molecular vibration state, as well as the strength and quantity of the hydrogen bonds themselves. It further verified that hydrogen bonds were formed by the self-assembly of aqueous polydopamine and aqueous polyurethane in the present invention.

[0145] In Table 2, by comparing Comparative Example 1 and Comparative Example 2, it was found that embedding aqueous polyurethane in bacterial cellulose could improve the electromagnetic shielding ability of bacterial cellulose. By comparing Examples 1-5, it was found that the addition of polydopamine could further enhance the electromagnetic shielding effect of the composite film. However, with the addition of polydopamine, its electromagnetic shielding effect first increased and then decreased. The reason was that excessive addition of polydopamine led to the agglomeration of MXene, a decrease in conductivity, and a reduction in electromagnetic shielding performance. Therefore, further preferably, the mass ratio of dopamine hydrochloride to MXene was 2.5%-15%.

[0146] Figure 1 The bacterial cellulose obtained in Example 2 had a high-strength 3D interconnected network structure. Figure 2 It can be seen that the bacterial cellulose presented a typical compact layered structure with a nanofiber conformation. This was because a large amount of aqueous polyurethane was embedded in the bacterial cellulose in Example 2 and interacted with BC containing a large number of OH groups, realizing the self-assembly process of aqueous polydopamine and aqueous polyurethane. Figure 3 It was shown that p-MXene in Example 1 was uniformly coated on the WPU / BC composite film, and the two were closely combined.

[0147] Figure 4 The Fourier transform infrared spectrum showed that PDA successfully modified MXene in Comparative Example 8, and p-MXene-10 showed an N-H bending mode (1460 cm -1 ) of aromatic secondary amines different from MXene and a C-N stretch (1250 cm -1)。In Figure 5 In the X-ray diffraction (XRD) pattern of 3 Ti 2 AlC 3 Ti 2 AlC

[0148] From Figure 6 the elemental analysis diagram, it can be seen that the elements in Example 1 are evenly distributed.

[0149] The p-MXene@WPU / BC composite film prepared in Example 5 was applied to a stress sensor. Conductive copper glue was pasted at both ends of the composite film, and copper wires were led out to act as electrodes, which were respectively connected to the electrodes of a digital multimeter for collecting electrical signals, as Figure 7 shown. The resistance changes under different presses were recorded, and the results are as Figure 8 shown.

[0150] Figure 8 In (a), the slope of the curve increases and the resistance decreases, which corresponds well to the increase in the applied pressure, showing good Ohmic contact and a stable linear relationship. Figure 8 In (b), during 550 compression-recovery cycles, the change in current is rapid and stable, and the fluctuation of the R-T curve is small and almost the same during the test. From the above experiments, it can be known that the p-MXene@WPU / BC composite film has excellent stress sensing performance.

[0151] For the preparation of a strain sensor, conductive glue was pasted on both sides of the composite film prepared in Example 5, wires were connected, and at the same time, a digital multimeter was connected to monitor the joint movements of fingers, wrists, and elbow joints, as Figure 9 shown.

[0152] Among them Figure 9 (a)- Figure 9 (c) are the joint movements of fingers, wrists, and elbow joints respectively. The composite film strain sensing material deforms, causing the resistance of the sensor to change, and the relative resistance change value increases with the increase in the knee joint bending angle, indicating that the sensor can accurately measure joint movements at different angles and has good stability and repeatability; Figure 9 (d) shows the change in the resistance of the sensor caused by the change in facial muscles when speaking;Figure 9 (e) The sensor can detect human movement. 550 stretching and recovery cycles were carried out, proving that the sensor of the present invention has good stability.

[0153] In summary, the composite film obtained by the present invention has excellent mechanical and electrical properties, and also has comprehensive properties such as electromagnetic shielding and stress-strain sensing.

[0154] It should be noted that the terms used in the present invention are only for describing specific embodiments and do not limit the scope of the present application. As shown in the specification of the present invention, unless the context clearly indicates an exception, words such as "a", "an", "one" and / or "the" are not specifically singular and may also include plural. The term "comprising", "including" or any other variant thereof is intended to cover non-exclusive inclusion, so that a process, method or device including a series of elements not only includes those elements, but also includes other elements not expressly listed, or also includes elements inherent to such process, method or device. Without further limitation, an element defined by the statement "including one..." does not exclude the existence of additional identical elements in the process, method or device including the said element.

[0155] It should also be noted that the orientation or positional relationship indicated by terms such as "center", "upper", "lower", "left", "right", "vertical", "horizontal", "inner", "outer", etc. is based on the orientation or positional relationship shown in the drawings, and is only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore cannot be understood as a limitation of the present invention. Unless otherwise clearly specified and defined, terms such as "installed", "connected", "connected" should be understood in a broad sense. For example, it can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection or an electrical connection; it can be directly connected or indirectly connected through an intermediate medium, and it can be the communication inside two elements. For those of ordinary skill in the art, the specific meanings of the above terms in the present invention can be understood according to specific circumstances.

[0156] Finally, it should be noted that: the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it; although the present invention has been described in detail with reference to the foregoing embodiments, those of ordinary skill in the art should understand that: they can still modify the technical solutions recorded in the foregoing embodiments, or perform equivalent replacements on some or all of the technical features; and these modifications or replacements do not make the essence of the corresponding technical solutions deviate from the technical solutions of the embodiments of the present invention.

Claims

1. Application of p-MXene conductive ink and BC reinforced polymer composite film in stress sensor, characterized in that: The composite film comprises MXene and bacterial cellulose, wherein the surface of MXene is coated with water-based polydopamine, water-based polyurethane is embedded in the bacterial cellulose, and hydroxyl groups in the water-based polydopamine and amino groups in the water-based polyurethane form hydrogen bonds to connect MXene and bacterial cellulose; The preparation method of the composite film comprises: Step S1: soaking bacterial cellulose in an aqueous polyurethane solution and drying at room temperature to obtain a bacterial cellulose / aqueous polyurethane nanocomposite material; Step S2: dissolving lithium fluoride in a hydrochloric acid solution, adding titanium aluminum carbide, performing a primary etching reaction, washing with acid, performing solid-liquid separation, performing a secondary etching reaction, and obtaining an intermediate product; adding dopamine hydrochloride to a trihydroxyaminomethane solution, performing a pre-reaction, adding a concentrated suspension of the intermediate product, reacting, performing solid-liquid separation, and retaining a precipitate; Step S3: coating the product obtained in step S2 at least once on the surface of the bacterial cellulose / aqueous polyurethane nanocomposite material obtained in step S1, and drying at room temperature to obtain a p-MXene conductive ink and BC-reinforced polymer composite film; The mass ratio of the dopamine hydrochloride to the intermediate product is 2.5%-20%.

2. The use according to claim 1, characterized in that: The length of the bacterial fiber is not less than 20 μm, and the diameter is 50 nm-100 nm.

3. The use according to claim 1, characterized in that: In step S1, the soaking time is 1.5h-2.5h; The mass concentration of the aqueous polyurethane solution is 5%-32%.

4. The use according to claim 1, characterized in that: The mass concentration of lithium fluoride in the hydrochloric acid solution is 2g / 40mL; The molar concentration of the hydrochloric acid solution is 9 mol / L; The mass concentration of the titanium aluminum carbide in the hydrochloric acid solution is 2 g / 40 mL.

5. The use according to claim 1, characterized in that: The specific method of the first etching reaction is: stirring at 34° C.-36° C. for 23 h-25 h; The specific method of washing the acid in step S2 is: washing with deionized water until the pH value of the product is close to 6, and then adding ethanol; The specific method of the secondary etching reaction includes: adding deionized water to the precipitate after solid-liquid separation, centrifuging, and retaining the supernatant.

6. The use according to claim 1, characterized in that: The specific parameters of the centrifugation are: centrifugation at 3900rpm-4100rpm for 2.5min-3.5min.

7. The use according to claim 1, characterized in that: The mass concentration of dopamine hydrochloride in the trishydroxyaminomethane solution is 10 mg / 5 mL; The mass concentration of the concentrated suspension of the intermediate product is 2 mg / L.

8. The use according to claim 1, characterized in that: The pre-reaction time is 1.5h-2.5h; In step S2, the reaction time is 23h-25h, and stirring is performed during the reaction at a speed of 380rpm-420rpm.

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