Multistage high-temperature-resistant polyimide nanofiber yarn as well as preparation method and application thereof

Abstract

The invention discloses a multistage high-temperature-resistant polyimide nanofiber yarn and a preparation method and application thereof.The multistage high-temperature-resistant polyimide nanofiber yarn comprises stainless steel yarn, a PI / MXene nanofiber layer and a PI nanofiber layer, the PI / MXene nanofiber layer comprises PI nanofibers and MXene embedded in the PI nanofibers, the PI nanofiber layer is the PI nanofibers, and the PI nanofibers and the PI nanofibers are arranged in the PI nanofiber layer. The PI / MXene nanofiber layer is loaded outside the stainless steel yarn, and the PI nanofiber layer is covered outside the PI / MXene nanofiber layer. MXene is introduced, capture sites are increased, the PI / MXene nanofiber layer is embedded between the friction layer and the internal electrode to serve as a charge capture layer, and by capturing diffused friction charges, attenuation of the friction charges is inhibited, and the output performance of the friction nano-generator is improved. The friction nano-generator prepared by the invention has good flame retardance and high temperature resistance, and overcomes the defects that a friction nano-generator based on a traditional textile cannot maintain stable output in a high-temperature environment and even is burnt and damaged.

Description

Technical Field

[0001] This invention belongs to the field of triboelectric nanogenerator technology, specifically relating to a multi-level high-temperature resistant polyimide nanofiber yarn, its preparation method, and its application. Background Technology

[0002] When a fire occurs, most power supplies and fire sensors requiring external power will fail due to damage to local circuits, lacking stable operation. Therefore, traditional power supply devices and sensors are unsuitable for the unpredictable conditions of a fire, necessitating the development of self-powered fire sensing systems to ensure safety. Fire scenes involve extremely high temperatures and open flames; most fabrics are flammable and easily burned. To address these challenges, a triboelectric nanogenerator (TENG) based on high-temperature resistant yarn has been developed for use in fire environments. This self-powered sensing device enables fire rescue functions, effectively reducing casualties and economic losses caused by fires. [Xiuju Cui, et al. Advanced Materials Technologies 2023, 13, 2202116] reported the preparation of a high-temperature triboelectric entanglement (TENG) based on core-spun yarn by weaving polyethylene terephthalate filaments onto the surface of silver-plated yarn using a high-speed braiding machine. This TENG achieved a limiting oxygen index of 31.3%, with an output voltage of 12V and an output current of 0.36μA. However, at 200℃, the TENG's output performance decreased significantly, retaining only 33.58% of its original performance. The performance of fabric-based TENGs is limited by the textile materials and fabric structure, resulting in a limited effective contact area and significantly higher internal resistance than other types of TENGs. These factors reduce the surface charge density of the triboelectric fabric, limiting its high output performance. Researchers have adopted various strategies to improve the triboelectric properties of fabric TENGs, including surface microstructure design and doping with functional materials, to directly increase the surface charge density of the triboelectric layer. However, electrostatic induction leads to an interfacial electric field between the triboelectric material and the electrode. Triboelectric charges diffuse towards the interface under the influence of this field and combine with induced charges, canceling each other out and causing triboelectric charge attenuation [Xiaoping Chen, et al. Nano Energy 2020, 98, 107236]. Therefore, the output performance of a TENG is a result of the dynamic balance between the generation and attenuation of surface charges. The loss in TENG output performance caused by triboelectric charge attenuation is not negligible. Therefore, researching strategies to reduce triboelectric charge diffusion and suppress triboelectric charge attenuation can also increase surface charge density, thereby enhancing the output performance of the TENG. By embedding a charge trapping layer at the interface between the triboelectric layer and the electrode, the trapping sites can effectively prevent the combination of triboelectric charges and induced charges, reducing triboelectric charge attenuation and improving the output performance of fabric-based TENGs. Although the above methods can improve the output performance of fabric-based TENGs, most of the currently reported fabric-based TENGs struggle to simultaneously achieve high temperature resistance and high output. Summary of the Invention

[0003] To address the shortcomings of existing technologies, the present invention aims to provide a multi-level high-temperature resistant polyimide (PI) nanofiber yarn.

[0004] Another object of the present invention is to provide a method for preparing the above-mentioned multi-level high-temperature resistant PI nanofiber yarn.

[0005] Another objective of this invention is to provide a TENG. This invention uses a PI nanofiber layer with good thermal stability as a friction layer, and embeds a charge trapping layer (PI / MXene nanofiber layer) at the interface between the friction layer and the internal electrode (stainless steel yarn) to construct the TENG. The charge trapping layer inhibits the diffusion of triboelectric charge, reduces the attenuation of triboelectric charge, and significantly improves the electrical output performance of the TENG.

[0006] The objective of this invention is achieved through the following technical solution.

[0007] A multi-level high-temperature resistant PI nanofiber yarn includes: a stainless steel yarn, a PI / MXene nanofiber layer, and a PI nanofiber layer. The PI / MXene nanofiber layer includes: PI nanofibers and MXene embedded in the PI nanofibers. The PI nanofiber layer is PI nanofibers. The PI / MXene nanofiber layer is loaded on the outside of the stainless steel yarn and the PI nanofiber layer covers the outside of the PI / MXene nanofiber layer.

[0008] In the above technical solution, the diameter of the multi-level high-temperature resistant PI nanofiber yarn is less than 1 mm.

[0009] The above-mentioned method for preparing multi-level high-temperature resistant PI nanofiber yarn includes the following steps:

[0010] Step 1: Pass the stainless steel yarn through the first and second bell mouths, and use PAA / MXene spinning solution to electrospin the stainless steel yarn passing through the first bell mouth, so as to form PAA / MXene nanofibers on the stainless steel yarn passing through the first bell mouth, and obtain the first yarn.

[0011] Electrospinning is performed on the first yarn passing through the second bell mouth using a polyamic acid (PAA) spinning solution to superimpose PAA nanofibers on the PAA / MXene nanofibers. The multi-level structured nanofiber yarn is collected by a winding roller. The PAA / MXene spinning solution is a mixture of MXene, 4,4-diaminodiphenyl ether (ODA), N,N-dimethylformamide (DMF) and 1,2,4,5-pyromellitic dianhydride (PMDA), and the PAA spinning solution is a mixture of ODA, DMF and PMDA.

[0012] In step 1, the method for obtaining the PAA spinning solution is as follows: ODA and DMF are mixed and stirred until ODA is completely dissolved, then PMDA is added and stirred for at least 2 hours to obtain the PAA spinning solution. The ratio of ODA, DMF and PMDA in the PAA spinning solution is (1.5-4):23:(1.7-4.5) by mass.

[0013] In step 1, the method for obtaining the PAA / MXene spinning solution is as follows: the PAA spinning solution and the MXene dispersion are mixed and stirred for at least 1 hour until homogeneous to obtain the PAA / MXene spinning solution, wherein the MXene dispersion is a mixture of MXene and DMF, and the ratio of ODA to MXene in the PAA / MXene spinning solution is 2.61:(0.027~0.112) by mass.

[0014] In the above technical solution, the method for obtaining the MXene dispersion is as follows: MXene and DMF are mixed and ultrasonicated for 10 to 15 minutes until homogeneous to obtain the MXene dispersion, wherein, by mass fraction, the ratio of MXene in the MXene dispersion to DMF in the MXene dispersion is (0.027 to 0.112):(2 to 3).

[0015] In step 1, the power supply voltage for electrospinning is 9–30 kV.

[0016] In step 1, the electrospinning temperature is 15–50°C, and the relative humidity is 25–65% RH.

[0017] In step 1, the rotational speed of the first bell mouth of the electrospinning is 100-300 rpm, the rotational speed of the second bell mouth is 100-300 rpm, and the collection speed of the winding roller is 0.5-2 m / min.

[0018] In step 1, electrospinning using PAA / MXene spinning solution is achieved through a first set of spinning needles, which includes two needles arranged opposite each other.

[0019] In step 1, electrospinning using PAA spinning solution is achieved through a second set of spinning needles, which includes two needles arranged opposite each other.

[0020] In step 1, the straight-line distance between the needles on the same side of the first group of spinning needles and the second group of spinning needles is 14-16 cm.

[0021] In step 1, the straight-line distance between the two needles in the first group of spinning needles is 10-30cm, and the straight-line distance between the two needles in the second group of spinning needles is 10-30cm.

[0022] In the above technical solution, each of the first group of spinning needles and the second group of spinning needles is connected to a pusher, and the extrusion rate of each pusher is 0.2 to 2.5 mL / h.

[0023] Step 2: The multi-level structured nanofiber yarn is heated to 250-400℃ for thermal imidization, so that the PAA / MXene nanofibers are transformed into PI / MXene nanofiber layers and the PAA nanofibers are transformed into PI nanofiber layers. After cooling, multi-level high-temperature resistant PI nanofiber yarn is obtained.

[0024] In step 2, the heating rate is 1 to 10 °C / min.

[0025] In step 2, the temperature is first raised to 100℃ and held for 0.5 to 3 hours, then raised to 200℃ and held for 0.5 to 3 hours, and finally raised to 250 to 400℃ and held for 0.5 to 3 hours.

[0026] The above-mentioned multi-level high-temperature resistant PI nanofiber yarns are used in TENG.

[0027] In the above technical solution, the multi-level high-temperature resistant PI nanofiber yarn is woven through a textile process to obtain a friction layer of TENG fabric.

[0028] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0029] 1. In this invention, MXene is introduced into the PI / MXene nanofiber layer, which increases the number of capture sites. The PI / MXene nanofiber layer is embedded between the tribological layer and the internal electrode as a charge capture layer. By capturing the diffused triboelectric charge, the decay of triboelectric charge is suppressed, thereby improving the output performance of the TENG.

[0030] 2. The present invention has a core-shell structure. Compared with TENG based on traditional textiles, the TENG of the present invention has a higher degree of integration of internal electrodes and friction layer, more sufficient contact, and higher charge transfer efficiency.

[0031] 3. The TENG prepared by this invention has good flame retardancy and high temperature resistance, overcoming the defects of TENG based on traditional textiles that cannot maintain stable output in high temperature environments, or even suffer from combustion damage. Attached Figure Description

[0032] Figure 1 A roadmap for the preparation of multi-level high-temperature resistant PI nanofiber yarn;

[0033] Figure 2The images are scanning electron microscope images. a is the pure PI nanofiber yarn in Comparative Example 1 and the PI / MXene nanofiber yarn in Comparative Example 2. b is an enlarged view of the box in a. c is a cross-section of the multi-level high-temperature resistant PI nanofiber yarn prepared in Example 3.

[0034] Figure 3 Let a be the dielectric constant, b be the dielectric loss, and c be the conductivity of the PI / MXene nanofiber layer.

[0035] Figure 4 The output voltage (a) and output current (b) of the TENGs prepared in Examples 6-10 are shown.

[0036] Figure 5 a) Output voltage and output current, b) Output power density, and c) Output voltage after 5000 cycles of continuous operation of the TENG prepared in Example 8;

[0037] Figure 6 Thermogravimetric analysis of PI nanofiber layer and PI / MXene nanofiber layer is shown in section a.

[0038] Figure 6 b represents the output voltage of the TENG prepared in Example 8 at different temperatures;

[0039] Figure 6 c represents the output current of the TENG prepared in Example 8 at different temperatures;

[0040] Figure 6 d represents the limiting oxygen index (LOI) of the PI nanofiber layer and the PI / MXene nanofiber layer;

[0041] Figure 6 e represents the PHRR (heat release rate) data for the PI nanofiber layer and the PI / MXene nanofiber layer;

[0042] Figure 6 f represents the THR data (total heat of THR release) for the PI nanofiber layer and the PI / MXene nanofiber layer;

[0043] Figure 6 g represents the combustion test appearance of the TENG prepared in Example 8;

[0044] Figure 6 h represents the output voltage of the TENG prepared in Example 8 before and after damage;

[0045] Figure 6 i represents the output current of the TENG prepared in Example 8 before and after damage.

[0046] Among them, 1 is the first flared mouth, 2 is the second flared mouth, 3 is the first group of spinning needles, and 4 is the second group of spinning needles. Detailed Implementation

[0047] The technical solution of the present invention will be further described below with reference to specific embodiments.

[0048] The raw materials involved in the following examples are as follows:

[0049]

[0050] The synthesis method of MXene is described in ACS Nano, 2021, 15:8676-8685.

[0051] Examples 1-5

[0052] like Figure 1 As shown, a method for preparing multi-level high-temperature resistant PI nanofiber yarn includes the following steps:

[0053] The preparation of multi-level high-temperature resistant PI nanofiber yarns utilizes a nanofiber collection device, such as... Figure 1 As shown, the nano-yarn collecting device includes a first flared mouth 1, a second flared mouth 2, four propellers, a first set of spinning needles 3 and a second set of spinning needles 4. Each of the first set of spinning needles 3 and the second set of spinning needles 4 includes two needles. One needle is connected to one end of each of the four propellers. The first set of spinning needles 3 is used to spray PAA / MXene spinning solution, and the second set of spinning needles 4 is used to spray PAA spinning solution. The power supply voltage for electrospinning is 9.5kV.

[0054] Step 1: Pass the stainless steel yarn through the first flared end and the second flared end, and use PAA / MXene spinning solution to electrospin the stainless steel yarn passing through the first flared end, so as to form PAA / MXene nanofibers on the stainless steel yarn passing through the first flared end 1, and obtain the first yarn.

[0055] The first yarn passing through the second flared end is electrospun using PAA spinning solution to superimpose PAA nanofibers onto the PAA / MXene nanofibers. The multi-level structured nanofiber yarn is collected by a winding roller. The electrospinning temperature is 25℃, the relative humidity is 30%RH, the rotation speed of the first flared end 1 is 200 rpm, the rotation speed of the second flared end 2 is 200 rpm, and the collection speed of the winding roller is 0.9 m / min.

[0056] Electrospinning using PAA / MXene spinning solution is achieved through the first set of spinning needles 3. The first set of spinning needles 3 includes two needles arranged opposite each other. The straight-line distance between the two needles arranged opposite each other in the first set of spinning needles 3 is 20cm. Each needle in the first set of spinning needles 3 is located on the horizontal plane where the axis of the first flared mouth 1 is located. The closest distance between each needle and the bottom edge of the first flared mouth 1 is 10cm.

[0057] Electrospinning using PAA spinning solution is achieved through a second set of spinning needles 4. The second set of spinning needles includes two needles arranged opposite each other. The straight-line distance between the two needles arranged opposite each other in the second set of spinning needles 4 is 20 cm. Each needle in the second set of spinning needles 4 is located on the horizontal plane of the axis of the second bell mouth 2. The closest distance between each needle and the bottom edge of the second bell mouth 2 is 10 cm. The straight-line distance between the needles on the same side of the first set of spinning needles 3 and the second set of spinning needles 4 is 15 cm. Each needle in the first set of spinning needles 3 and the second set of spinning needles 4 is connected to a pusher. The extrusion rate of each pusher is 1.2 mL / h.

[0058] The method for obtaining PAA / MXene spinning solution is as follows: PAA spinning solution and MXene dispersion are mixed and stirred for 1 hour until homogeneous to obtain PAA / MXene spinning solution. PAA spinning solution is a mixture of ODA, DMF and PMDA, and MXene dispersion is a mixture of MXene and DMF.

[0059] The ratio of ODA to MXene in the PAA / MXene spinning solution is X by mass. The method for obtaining the PAA spinning solution is as follows: ODA (powder) is slowly added to DMF and stirred until ODA is completely dissolved. Then PMDA is added and stirred for 2 hours to obtain the PAA spinning solution. The ratio of ODA, DMF and PMDA by mass is 2.61:23:2.83.

[0060] The method for obtaining the MXene dispersion is as follows: MXene (powder) is added to DMF and sonicated for 10 minutes until homogeneous to obtain the MXene dispersion. The ratio of MXene to DMF in the MXene dispersion by mass is Y. The values ​​of X and Y are shown in Table 1.

[0061] Table 1

[0062] Example X Y serial number Example 1 (for comparison) 2.61:0 0:3 0wt% Example 2 2.61:0.027 0.027:3 0.5wt% Example 3 2.61:0.054 0.054:3 1wt% Example 4 2.61:0.082 0.082:3 1.5wt% Example 5 2.61:0.112 0.112:3 2wt%

[0063] Step 2: The multi-level structured nanofiber yarn is placed in a muffle furnace and subjected to thermal imidization by gradient heating (first heating to 100℃ and holding for 40 min, then heating to 200℃ and holding for 40 min, and finally heating to 300℃ and holding for 40 min) to transform PAA / MXene nanofibers into PI / MXene nanofiber layers and PAA nanofibers into PI nanofiber layers. After cooling to room temperature, a multi-level high-temperature resistant PI nanofiber yarn with a diameter of less than 1 mm is obtained. The multi-level high-temperature resistant PI nanofiber yarn includes stainless steel yarn, PI / MXene nanofiber layers and PI nanofiber layers. The PI / MXene nanofiber layers are loaded on the outside of the stainless steel yarn, and the PI nanofiber layers cover the outside of the PI / MXene nanofiber layers. The heating rate is 4℃ / min.

[0064] In Examples 1-5, the numbering is based on the following: 0 wt% represents a concentration of 0 wt% of MXene in MXene, ODA, and PMDA; 0.5 wt% represents a concentration of 0.5 wt% of MXene in MXene, ODA, and PMDA; 1 wt% represents a concentration of 1 wt% of MXene in MXene, ODA, and PMDA; 1.5 wt% represents a concentration of 1.5 wt% of MXene in MXene, ODA, and PMDA; and 2 wt% represents a concentration of 2 wt% of MXene in MXene, ODA, and PMDA.

[0065] Examples 6-10

[0066] A TENG (single-electrode working mode) was constructed using a fabric woven from multi-level high-temperature resistant PI nanofiber yarn (reed number 50, warp density 50 threads / 10cm, weft density 135 threads / 10cm). The outer PI nanofiber layer of the fabric served as the negative friction layer, and the PA fabric served as the positive friction layer. Because it was a single-electrode working mode, only the stainless steel yarn in the fabric needed to be connected to the testing equipment (6517 electrometer). The multi-level high-temperature resistant PI nanofiber yarn was one of the multi-level high-temperature resistant PI nanofiber yarns prepared in Examples 1-5. Examples representing different multi-level high-temperature resistant PI nanofiber yarns are shown in the table below.

[0067] Example Multi-level high-temperature resistant PI nanofiber yarn Example 6 Example 1 Example 7 Example 2 Example 8 Example 3 Example 9 Example 4 Example 10 Example 5

[0068] Comparative Example 1 (Pure PI Fiber Nanofiber Yarn)

[0069] The pure PI nanofiber yarn comprises stainless steel yarn and a PI nanofiber layer, with the PI nanofiber layer covering the stainless steel yarn. The preparation method of the pure PI nanofiber yarn is basically the same as that of "a method for preparing a multi-level high-temperature resistant PI nanofiber yarn" in Example 3, the only difference being that only PAA spinning solution is used for electrospinning on the stainless steel yarn (i.e., non-electrospinning PAA / MXene spinning solution).

[0070] Comparative Example 2 (PI / MXene nanofiber yarn)

[0071] The PI / MXene nanofiber yarn comprises a stainless steel yarn and a PI / MXene nanofiber layer, with the PI / MXene nanofiber layer loaded on the outside of the stainless steel yarn. The preparation method of the PI / MXene nanofiber yarn is basically the same as that of "a method for preparing a multi-level high-temperature resistant PI nanofiber yarn" in Example 3, the only difference being that only PAA / MXene spinning solution is used for electrospinning on the stainless steel yarn (i.e., non-electrospinning PAA spinning solution).

[0072] from Figure 2 As can be seen in a, the PI / MXene nanofiber layer completely covers the surface of the stainless steel yarn, and the yarn is of uniform thickness overall. Figure 2 As can be seen from b, the PI / MXene nanofiber layer has a smooth and uniform surface, exhibiting a certain degree of orientation. The average diameter of the fibers in the PI / MXene nanofiber layer is 310–330 nm. From Figure 2 As can be seen from c, the cross-section of the multi-level high-temperature resistant PI nanofiber yarn consists of stainless steel yarn and nanofibers (PI / MXene nanofiber layer and PI nanofiber layer) from the inside out. The stainless steel yarn is tightly wrapped around the PI / MXene nanofiber layer and the PI nanofiber layer are tightly bonded together to form a cross-section with a uniform diameter and approximately circular shape.

[0073] PI / MXene nanofiber layers were obtained by electrospinning (i.e., electrospinning without stainless steel yarn) using each PAA / MXene spinning solution in Examples 1-5, such as... Figure 3 As shown in Figure a, at a frequency of 1 Hz, the dielectric constant of the PI / MXene nanofiber layer increases rapidly with the increase of MXene content in the PAA / MXene spinning solution, increasing from 2.1 to 42.8. This is because MXene forms multiple microcapacitors in the PI / MXene nanofiber layer, and the number of these microcapacitors increases with the increase of MXene content.

[0074] like Figure 3As shown in b, the dielectric loss also shows a trend of increasing with the increase of MXene content, but still remains within 0.02 to 0.04, which means low current leakage.

[0075] like Figure 3 As shown in c, the conductivity of the PI / MXene nanofiber layer is less affected by the MXene concentration, and is relatively stable at 10⁻⁶. -1 ~10 7 It exhibits insulating behavior across the entire frequency range.

[0076] Figure 4 'a' represents the output voltage of the TENG prepared in Examples 6-10. Figure 4 b represents the output current of the TENG prepared in Examples 6-10. Figure 4 a and Figure 4 In b, 0 wt% represents TENG prepared in Example 6, 0.5 wt% represents TENG prepared in Example 7, 1 wt% represents TENG prepared in Example 8, 1.5 wt% represents TENG prepared in Example 9, and 2 wt% represents TENG prepared in Example 10.

[0077] Figure 4 The results showed that with the increase of MXene concentration in the PAA / MXene spinning solution, both the output voltage and current of the TENG exhibited a significant increasing trend. The output voltage of the TENG increased by 42–117%, and the output current increased by 7–210%. This performance enhancement is mainly attributed to the charge-trapping ability of MXene; as the MXene content increases, the number of charge-trapping sites also increases accordingly. However, when the MXene content is excessive (i.e., the MXene concentration in the PAA / MXene spinning solution > 1 wt%), the output performance of the TENG begins to decrease with the increase of MXene content. This is mainly because excessive MXene agglomerates, leading to a reduction in the number of effective trapping sites, thereby reducing the charge-trapping efficiency and thus affecting the output performance of the TENG.

[0078] The TENG (Transformer Engagement Unit) was used as a power supply device, forming a circuit with a resistor. A 6517 electrometer was connected in parallel across the TENG to measure its voltage. The test results are as follows: Figure 5 The output voltage of a is shown; the current of TENG is measured by connecting a 6517 electrometer in series with TENG and a resistor, and the test results are as follows. Figure 5 The output current is shown in section a. The resistance of the resistor mentioned above is 10. 4 ~10 10 Ω, TENG is the TENG prepared in Example 8. According to Figure 5 The output power density calculated by a is as follows: Figure 5 As shown in b.

[0079] The output voltage of a TENG generator was simulated under operating conditions of 25N mechanical force and 5Hz contact frequency for 5000 consecutive cycles. The test results are as follows: Figure 5 As shown in c;

[0080] like Figure 5 As shown in Figure a, with the increase of the resistance value, the output voltage shows an increasing trend from low to high, while the output current shows a decreasing trend. Figure 5 As shown in Figure b, the output power density of the TENG is 0.03-0.84 W / m² when the resistance is between 10kΩ and 10GΩ. 2 .

[0081] A long-cycle test was conducted using a vibrator to simulate the operating conditions of a mechanical force of 25N and a contact frequency of 5Hz, with 5000 continuous cycles (each cycle lasting 0.2s) performed, and the output voltage of the TENG was continuously monitored. Figure 5 As shown in c ( Figure 5 (A magnified view of 795-800s is shown in c). The TENG was continuously run for 5000 cycles, and the output voltage value of the TENG remained stable without significant changes. This indicates that the TENG can maintain stable output performance under long-term, high-frequency working conditions, which proves that the TENG prepared in Example 8 has good durability and stability.

[0082] PI / MXene nanofiber layers were obtained by electrospinning with the PAA / MXene spinning solution from Example 3 (i.e., electrospinning without stainless steel yarn); PI nanofiber layers were obtained by electrospinning with the PAA spinning solution from Example 3 (i.e., electrospinning without stainless steel yarn). Thermogravimetric analysis (TGA), limiting oxygen test (LOI), and cone calorimetry (CONE) tests were performed to evaluate the PI / MXene nanofiber layers and the PI nanofiber layers. The high-temperature resistance, flame retardancy, and output performance of the TENG at different temperatures were also evaluated. The test results are as follows: Figure 6 As shown.

[0083] like Figure 6 As shown in a, the PI nanofiber layer was tested by TGA. Figure 6 The "Pure PI nanofiber" in a) and the PI / MXene nanofiber layer ( Figure 6The thermal stability of PI / MXene 1wt% nanofiber (a) was examined. The TGA curves of the PI nanofiber layer and the PI / MXene nanofiber layer showed similar decomposition modes. Within the range of 25 to 453 °C, the mass of the PI nanofiber layer and the PI / MXene nanofiber layer only decreased slightly, which corresponds to the dehydration process. The higher decomposition temperature indicates that the PI nanofiber layer and the PI / MXene nanofiber layer both exhibit good thermal stability in air.

[0084] like Figure 6 b and Figure 6 As shown in Figure c, to investigate the effect of temperature on the output performance of the TENG, a constant-temperature heating plate was used to simulate the output performance of the TENG prepared in Example 8 in an environment of 25–500°C. Figure 6 b and Figure 6 As can be seen from Figure c, the output performance of TENG decreases slightly with increasing temperature, but it can maintain stable operation in high-temperature environments of 25–400℃. However, when the temperature exceeds 500℃, both the output voltage and output current drop significantly. This is because the excessively high temperature causes the PI nanofiber layer and the PI / MXene nanofiber layer to decompose, and the friction layer (PI nanofiber layer) and the charge trapping layer (PI / MXene nanofiber layer) are damaged, resulting in a decrease in the output performance of TENG.

[0085] Flame retardancy is one of the important indicators for evaluating the safety performance of materials. For example... Figure 6 As shown in d, PI nanofiber layer ( Figure 6 The d in "PI nanofiber" and PI / MXene nanofiber layer ( Figure 6 The limiting oxygen index (LOI) values ​​of the PI / MXene nanofiber in the d sample are all 50%, indicating good flame retardant properties.

[0086] Two key parameters, Peak Heat Release Rate (PHRR) and Total Heat Release (THR), were obtained using cone calorimetry. PHRR represents the maximum heat released by the material during combustion, while THR represents the total heat released by the material during combustion under a preset incident flow intensity. Figure 6 e and Figure 6 As shown in f, compared with the PI nanofiber layer, the PI / MXene nanofiber layer introduces MXene, and the PHRR of the PI / MXene nanofiber layer decreases by 27-27.25%, and the THR decreases by 4.5-5.5%. The flame retardancy of the PI / MXene nanofiber layer is improved compared with that of PI nanofiber, and the improvement in flame retardancy is attributed to the addition of MXene.

[0087] like Figure 6As shown in g, when the back side of the TENG prepared in Example 8 was exposed to the flame of an alcohol lamp, no combustion occurred, and no molten material dripped from the part in contact with the flame; instead, a dense carbon layer was formed on the surface.

[0088] TENG (prepared in Example 8 before damage) Figure 6 The TENG (in h and i, "original") and the TENG prepared in Example 8 after backside damage. Figure 6 The output performance of h and i ("burned") was tested positively, such as Figure 6 As shown in h and i, the output voltage and output current of TENG did not change significantly before and after the damage, and TENG was still able to maintain stable output performance after the back side was damaged.

[0089] In summary, a series of tests have demonstrated that the TENG of this invention possesses excellent thermal stability and flame retardancy, and has the potential to become a smart wearable electronic device in high-temperature environments.

[0090] The present invention has been described above by way of example. It should be noted that any simple modifications, alterations or other equivalent substitutions that can be made by those skilled in the art without creative effort without departing from the core of the present invention fall within the protection scope of the present invention.

Claims

1. A multi-level high-temperature resistant PI nanofiber yarn, characterized in that, include: The stainless steel yarn, the PI / MXene nanofiber layer, and the PI nanofiber layer, wherein the PI / MXene nanofiber layer comprises PI nanofibers and MXene embedded in the PI nanofibers, the PI nanofiber layer is PI nanofibers, the PI / MXene nanofiber layer is loaded on the outside of the stainless steel yarn, and the PI nanofiber layer covers the outside of the PI / MXene nanofiber layer.

2. The multi-stage high-temperature resistant PI nanofiber yarn according to claim 1, characterized in that, The diameter of the multi-level high-temperature resistant PI nanofiber yarn is less than 1mm.

3. The method for preparing multi-level high-temperature resistant PI nanofiber yarn as described in claim 1, characterized in that, Includes the following steps: Step 1: Pass the stainless steel yarn through the first and second bell mouths, and use PAA / MXene spinning solution to electrospin the stainless steel yarn passing through the first bell mouth, so as to form PAA / MXene nanofibers on the stainless steel yarn passing through the first bell mouth, and obtain the first yarn. Electrospinning is performed on the first yarn passing through the second bell mouth using PAA spinning solution to superimpose PAA nanofibers on PAA / MXene nanofibers. The multi-level structured nanofiber yarn is collected by the winding roller. The PAA / MXene spinning solution is a mixture of MXene, ODA, DMF and PMDA, and the PAA spinning solution is a mixture of ODA, DMF and PMDA. Step 2: The multi-level structured nanofiber yarn is heated to 300°C for thermal imidization, so that the PAA / MXene nanofibers are transformed into PI / MXene nanofiber layers and the PAA nanofibers are transformed into PI nanofiber layers. After cooling, multi-level high-temperature resistant PI nanofiber yarn is obtained.

4. The preparation method according to claim 3, characterized in that, In step 1, the method for obtaining the PAA spinning solution is as follows: ODA and DMF are mixed and stirred until ODA is completely dissolved, then PMDA is added and stirred for at least 2 hours to obtain the PAA spinning solution. The ratio of ODA, DMF and PMDA in the PAA spinning solution is (1.5-4):23:(1.7-4.5) by mass.

5. The preparation method according to claim 4, characterized in that, In step 1, the method for obtaining the PAA / MXene spinning solution is as follows: the PAA spinning solution and the MXene dispersion are mixed and stirred for at least 1 hour until homogeneous to obtain the PAA / MXene spinning solution. The MXene dispersion is a mixture of MXene and DMF, and the ratio of ODA to MXene in the PAA / MXene spinning solution is 2.61:(0.027~0.112) by mass.

6. The preparation method according to claim 5, characterized in that, The method for obtaining the MXene dispersion is as follows: MXene and DMF are mixed and sonicated for 10 to 15 minutes until homogeneous to obtain the MXene dispersion. The ratio of MXene in the MXene dispersion to DMF in the MXene dispersion is (0.027 to 0.112):(2 to 3) by mass.

7. The preparation method according to claim 3, characterized in that, In step 1, the power supply voltage for electrospinning is 9–30 kV; In step 1, the electrospinning temperature is 15–50°C, and the relative humidity of the electrospinning is 25–65%RH. In step 1, the first flared end of the electrospinning spindle rotates at 100-300 rpm, the second flared end rotates at 100-300 rpm, and the winding roller collection speed is 0.5-2 m / min. In step 2, the heating rate is 1 to 10 °C / min.

8. The preparation method according to claim 3, characterized in that, In step 2, the temperature is first raised to 100℃ and held for 0.5 to 3 hours, then raised to 200℃ and held for 0.5 to 3 hours, and finally raised to 250 to 400℃ and held for 0.5 to 3 hours.

9. The use of the multi-level high-temperature resistant PI nanofiber yarn as described in claim 1 in a triboelectric nanogenerator.

10. The application according to claim 9, characterized in that, The multi-level high-temperature resistant PI nanofiber yarn is woven into a fabric using a textile process, which serves as the friction layer of the triboelectric nanogenerator.

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