A composite piezoelectric fiber and its preparation method

Abstract

The present invention discloses a composite piezoelectric fiber and a preparation method thereof. The composite piezoelectric fiber includes a cortex and a first core layer and a second core layer wrapped inside the cortex. The first core layer contains a magnetized carbon nanotube / metal-organic framework composite material, the second core layer contains polyaniline, and the first core layer and the second core layer are in a helical juxtaposed structure. In the present invention, the magnetized carbon nanotubes are compounded with the metal-organic framework and then added to the spinning solution of the first core layer, and polyaniline is added to the spinning solution of the second core layer. The spinning solutions of the first core layer, the second core layer and the cortex are subjected to three-channel microcontrolled wet spinning. By wrapping the first core layer and the second core layer with the cortex, the core layer fibers are protected. The obtained composite piezoelectric fiber has both excellent piezoelectric and conductive properties, and at the same time has excellent mechanical properties, greatly improving its durability and broadening its applicable range for use in electrical components.

Description

Technical Field

[0001] The present invention relates to the technical field of piezoelectric fibers, and particularly relates to a composite piezoelectric fiber and a preparation method thereof Background Art

[0002] PVDF (polyvinylidene fluoride) and PAN (polyacrylonitrile) materials are widely used in electrochemical research and application fields such as piezoelectricity and triboelectricity due to their good mechanical properties and electrochemical properties. With the progress of technology and the improvement of material properties, the types and quantities of devices such as flexible sensors and nanogenerators based on these two materials have gradually increased. However, the wide application of nanogenerators and sensors has gradually increased the requirements for environmental adaptability. Current technologies have put forward more demanding working requirements under harsh environments. Materials that can still maintain sensitive performance under high temperature, high pressure or high external force conditions have gradually become the mainstream demand. Due to the relatively limited performance of PVDF and PAN materials themselves, it is urgent to combine them with other materials with better performance

[0003] MOF (metal-organic framework) materials are a kind of periodic crystalline porous materials formed by the self-assembly of inorganic metal centers and bridging organic ligands. Due to their rich properties, they are widely used in the fields of electrochemical energy production and energy storage. However, their applications are relatively single and cannot be used in extreme environments. Under high temperature or high external force, the spatial structure of MOF materials is easily damaged, resulting in the loss of their original properties

[0004] Due to its special structure, carbon nanotubes have extremely high tensile strength and elastic modulus, and at the same time have good toughness and hardness. Therefore, they are widely used in automotive, railway, and aerospace materials. On the other hand, due to its special bonding form, there is a large-range delocalized Π bond on the P orbit of carbon atoms, so it exhibits electrical conductivity comparable to that of metals and is widely used in the fields of electricity and superconductivity. However, despite the excellent properties of carbon nanotubes, their difficult-to-disperse characteristics make it difficult to combine with other materials

[0005] In order to cope with the above technological development status, it is an effective means to develop a nanogenerator that has high voltage output, high environmental adaptability and energy storage function, and produces high efficiency. As an important component material of nanogenerators, piezoelectric fiber materials have gradually matured after a long period of development and improvement. The piezoelectric properties of piezoelectric fibers have also shown a trend of gradual improvement, and their types are also becoming increasingly rich, such as fiber membranes, single fibers, and coated yarns. However, in terms of preparation methods, due to production difficulties and costs, most spinning methods still remain at single electrospinning, wet spinning, etc. A small number of studies mention the use of coaxial spinning methods to prepare skin-core fibers, but there is little research on further multi-component multi-channel spinning methods. This makes it difficult for existing piezoelectric fibers to have other properties, such as high temperature resistance and strong deformation resistance. Patent CN111321520A discloses a method for coaxial electrospinning polyvinylidene fluoride / polyacrylonitrile reinforced fiber film piezoelectric properties. PVDF / PAN electrospinning film is prepared by coaxial electrospinning method. While increasing the content of piezoelectric phase β crystal, good mechanical properties are guaranteed. However, for equipment with higher requirements, the piezoelectric capacity still needs to be improved. At the same time, the production efficiency of electrospinning is limited, and the requirements for equipment are relatively high, making it difficult to achieve efficient production. Patent CN117119871A discloses a degradable composite piezoelectric cellulose film based on MOF material and its preparation method and application. MOF and cellulose material are composited by suction filtration film forming. Although this preparation method meets the requirements of environmental protection, the mechanical properties of the product of suction filtration film forming are poor, and it is difficult to adapt to the requirements under harsh environments. Patent CN114874622A discloses a PEI / MOF film and preparation method for energy storage capacitors, which has the characteristics of high dielectric constant, high breakdown strength and good mechanical properties. However, it only has a single energy storage performance and cannot be used more compatible. Patent CN110164717A discloses a method for preparing a π-d conjugated Ni-HITP MOF conductive film and its energy storage application, providing a method for preparing a transparent conductive film electrode using a low-cost and low-energy gas-liquid interface method. The product has good light transmittance and excellent energy storage performance. However, although the film material prepared by this method has a simple process and low requirements for production conditions, due to the large number of uncertain factors at the gas-liquid interface, the uniformity of the prepared film is not high, and the energy storage stability will also decrease accordingly. Summary of the invention

[0006] The technical problem to be solved by the present invention is to provide a composite piezoelectric fiber and a preparation method thereof. Magnetized carbon nanotubes are composited with a metal organic framework and then added to a first core layer spinning solution, polyaniline is added to a second core layer spinning solution, and the first core layer spinning solution, the second core layer spinning solution and the skin layer spinning solution are wet-spun by a three-channel micro-controlled flow method at a high spinning rate. The obtained composite piezoelectric fiber has excellent piezoelectric and conductive properties as well as excellent mechanical properties, which greatly improves its durability and broadens its application range in electrical components.

[0007] In order to solve the above technical problems, the first aspect of the present invention provides a composite piezoelectric fiber, comprising a skin layer and a first core layer and a second core layer wrapped in the skin layer, the first core layer comprising a first matrix material and a magnetized carbon nanotube / metal organic framework composite material (composite MOF) doped in the first matrix material, and the second core layer comprising a second matrix material and polyaniline (PANI) doped in the second composite material.

[0008] The first core layer and the second core layer are wrapped with a cortex layer to protect the core layer fibers. At the same time, two materials with excellent electrical properties, metal organic framework (MOF) and magnetized carbon nanotubes, are compounded. Compared with the use of two materials alone, the piezoelectric and conductive properties of the composite MOF are improved to a certain extent, and the overall structure of the two materials entangled and connected to each other significantly improves the mechanical properties of the material on the original basis, greatly improves its durability, and broadens its application range for electrical components. PANI, as a conductive polymer, plays a positive role in the charge conduction of the entire fiber, overcoming the disadvantage of decreased charge transfer ability due to too many fiber layers.

[0009] Furthermore, the first core layer and the second core layer are in a spiral parallel structure, with more core layer content per unit fiber length. Due to the interaction between different components and the strong interface effect produced by the spiral structure, the interaction between the fibers is enhanced, so that the mechanical and electrical properties of the three-component fiber are greatly improved, increasing the universality of its application.

[0010] Furthermore, the total mass of the first core layer and the second core layer accounts for more than 40% of the mass of the piezoelectric fiber.

[0011] The second aspect of the present invention provides a method for preparing the composite piezoelectric fiber according to the first aspect, comprising the following steps:

[0012] S1. mixing and dissolving the magnetized carbon nanotube / metal organic framework composite material and the first matrix material to obtain a first core layer spinning solution;

[0013] S2. mixing and dissolving polyaniline and a second matrix material to obtain a second core layer spinning solution;

[0014] S3. Dissolve the third matrix material to obtain the cortical spinning solution;

[0015] S4. Microfluidic wet spinning of the first core layer spinning solution, the second core layer spinning solution, and the cortical spinning solution through a three-channel spinneret to obtain composite piezoelectric fibers.

[0016] Compared with electrospinning and other spinning methods, the wet spinning of the present invention has the characteristics of higher efficiency. Due to the spontaneous aggregation behavior of CNTs, a production process that takes a long time may lead to uneven distribution of functional powders inside the fibers. The wet spinning has a fast speed and regular fiber structure, and can better meet the requirements of material production.

[0017] Further, in S1, the preparation method of the composite material is as follows: Dissolve and mix magnetized carbon nanotubes, metal-organic framework materials, dispersants, nucleating agents, and capping agents, adjust the pH to 9 - 10, carry out hydrothermal reaction and then dry to obtain magnetized carbon nanotube / metal-organic framework composite materials.

[0018] Further, the magnetization material of the magnetized carbon nanotubes can be iron, cobalt, nickel, preferably iron magnetized carbon nanotubes (Fe-CNTs). Magnetizing the carbon nanotubes can reduce the occurrence of aggregation.

[0019] Further, the preparation method of the Fe-CNTs is as follows: Ultrasonically mix CNTs with a mass ratio of 1:100 and nitric acid with a concentration of 65% for 0.5 - 4 h, reflux for 6 h at 90 - 120 °C, cool to room temperature, filter the suspension, wash to obtain pretreated CNTs (with negative charges on the surface), dry and then grind for standby; Prepare a mixture powder of FeCl3·6H2O and FeSO4·7H2O with a mass ratio of 2:1, mix the mixture powder with a mass ratio of 1:50 and 0.1 mol / L hydrochloric acid solution. After the solid is completely dissolved, add distilled water to dilute the solution to 1 / 3 - 1 / 2 of the original concentration, then add the pretreated CNTs, stir and mix, add HNO3 to adjust the pH value below 7, then place it in an ultrasonic bath processor for 2 h, and then dry in an N2 atmosphere at 80 °C and grind into a powder to obtain magnetized CNTs, called Fe-CNTs.

[0020] Further, the metal-organic framework is specifically IRMOF (MOF containing cyclodextrin), specifically one or more of IRMOF-1, IRMOF-3, IRMOF-4, IRMOF-5, IRMOF-8, IRMOF-9, IRMOF-10, IRMOF-11, IRMOF-12, IRMOF-13, IRMOF-14, IRMOF-16, IRMOF-18, IRMOF-61, IRMOF-62, preferably IRMOF-5.

[0021] Furthermore, the preparation method of the IRMOF-5 is as follows: Add zinc nitrate heptahydrate (Zn(NO3)2) particles and terephthalic acid (BDC) powder with a mass ratio of 10:1 - 8:1 to a mixed solution of ethanol and DMF (dimethylformamide) with a molar ratio of 6.25:2.8. After dissolving uniformly, add triethanolamine (TEA) and polyvinylpyrrolidone (PVP) with a mass ratio of 1.72:1.32. React at 160 °C for 8 h, then centrifuge and filter after the reaction, and dry in a vacuum environment to obtain MOF-5.

[0022] Furthermore, the MOF-5 and Fe-CNTs are compounded by a solvothermal method, and the composite MOF is obtained after centrifugation and drying.

[0023] Furthermore, the preparation method of the composite MOF is as follows: Add MOF-5 and Fe-CNTs with a mass ratio of 2:1 - 1:1 to a mixed solution of ethanol and DMF with a volume ratio of 31.2:43.8. After ultrasonic mixing and dispersion for 2 h, add a dispersant, a nucleating agent, and a capping agent. After dispersion, adjust the pH value to 9 - 10 with a 1% NaOH solution, place it in a hydrothermal reaction kettle, and react at 160 °C for 6 h. After the reaction, centrifuge and filter, and dry in a vacuum environment (-0.1 kPa - 0 kPa) to obtain the composite MOF.

[0024] Furthermore, the dispersant is one or more of cetyltrimethylammonium bromide (CTAB), sodium dodecylbenzenesulfonate, and polyethylene oxide (PEO).

[0025] Furthermore, the nucleating agent is one or more of triethanolamine (TEA), calcium carbonate, and sodium benzoate.

[0026] Furthermore, the capping agent is a compound containing a protective functional group (such as an acetal group), for example: polyvinylpyrrolidone (PVP), benzoic acid, cyclohexanol, isopentanol, phenol, trimethylchlorosilane.

[0027] Furthermore, the solvents of the three spinning solutions are all DMF solutions, and the concentration of the matrix in the spinning solution is 12 wt% - 20 wt%.

[0028] Furthermore, the flow rates of the three channels are controlled by three solution injection pumps respectively. The flow rates of the first core layer spinning solution and the second core layer spinning solution are 0.3 mL / h, and the concentration of the skin layer spinning solution is 0.3 - 0.4 mL / h.

[0029] Furthermore, the mass of the magnetized carbon nanotube / metal-organic framework composite material is 0.5 wt% - 2 wt% of the first matrix material.

[0030] Further, the mass ratio of the magnetized carbon nanotubes to the metal-organic framework material is 1:(1 - 2).

[0031] Further, the mass of the polyaniline is 0.5 wt% - 5 wt% of the mass of the second matrix material.

[0032] Further, the matrix of the first core layer, the second core layer and the skin layer is selected from any one of polyacrylonitrile and polyvinylidene fluoride. The matrices of the first core layer and the second core layer are different from each other. A mixed material of PAN and PVDF is selected. Compared with a single material, the PAN in the core layer has a higher degree of crystallinity, and there is a strong interaction force at the interface between the two, which is tightly combined, with better mechanical properties and better durability.

[0033] Further, the three channels include a skin layer channel and two helically juxtaposed core layer channels arranged in the skin layer channel. The central angle of the helical structure is between 0° and 180°. By adjusting the bending angle of the helical layer, the ratio of the piezoelectric fiber core layer to the skin layer per unit length can be flexibly controlled to meet the requirements of different application fields.

[0034] Further, after spinning and forming, it is soaked in a deionized water coagulation bath for 24 h, completely solidified into a fibrous shape after passing through the stretching section, and then collected by a winding roller. The rotation speed of the winding roller is 0.4 r / s, and the organic matter residue is removed by heating and drying.

[0035] Further, the stretching distance in the coagulation bath is 25 cm.

[0036] Advantages of the present invention:

[0037] In the present invention, magnetized carbon nanotubes are compounded with a metal-organic framework and then added to the spinning solution of the first core layer, polyaniline is added to the spinning solution of the second core layer, and the spinning solutions of the first core layer, the second core layer and the skin layer are subjected to three-channel micro-controlled wet spinning. The first core layer and the second core layer are wrapped by the skin layer to protect the core layer fibers. The obtained composite piezoelectric fibers have both excellent piezoelectric and conductive properties, and at the same time have excellent mechanical properties, greatly improving their durability and broadening their application scope in electrical components.

[0038] The present invention provides a core layer with a helically juxtaposed structure, which has more core layer content per unit fiber length. Due to the interaction force between different components and the strong interfacial effect generated by the helical structure, the interaction between fibers is enhanced, greatly improving the mechanical and electrical properties of the three-component fibers and increasing the universality of their applications;

[0039] The wet spinning method adopted by the present invention has the characteristic of higher efficiency. Due to the spontaneous agglomeration behavior of CNTs, a production process that takes a long time may lead to uneven distribution of functional powders inside the fibers. The wet spinning method has a high speed and regular fiber structure, and can better meet the requirements of material production;

[0040] The present invention selects a mixed material of PAN and PVDF. Compared with a single material, the PAN in the core layer has a higher degree of crystallinity, and there is a strong interaction force at the interface between the two, with a tight combination, better mechanical properties, and better durability. Brief Description of the Drawings

[0041] Figure 1 is a schematic structural diagram of a three-channel spinneret microfluidic injection device of the present invention;

[0042] Figure 2 is a schematic structural diagram of a composite MOF molecule of the present invention;

[0043] Figure 3 is a SEM image of the composite MOF prepared in Example 1 of the present invention;

[0044] Figure 4 is a piezoelectric voltage output image of the composite piezoelectric fiber prepared in Example 1 of the present invention;

[0045] Figure 5 is a piezoelectric current output image of the composite piezoelectric fiber prepared in Example 1 of the present invention;

[0046] Explanation of the reference numerals in the drawings: 11, cortical channel; 12, core layer channel; 13, injection pump; 21, MOF-5; 22, Fe; 23, CNT. Detailed Embodiments

[0047] The present invention will be further described below in conjunction with the drawings and specific embodiments, so that those skilled in the art can better understand the present invention and implement it, but the embodiments cited are not intended to limit the present invention.

[0048] The embodiment of the present invention provides a composite piezoelectric fiber, which includes a cortex and a first core layer and a second core layer wrapped in the cortex. The first core layer contains a first matrix material and a magnetized carbon nanotube / metal-organic framework composite material doped in the first matrix material, and the second core layer contains a second matrix material and polyaniline doped in the second matrix material.

[0049] The first core layer and the second core layer are wrapped with a cortex layer to protect the core layer fibers. At the same time, two materials with excellent electrical properties, metal organic framework (MOF) and magnetized carbon nanotubes, are compounded. Compared with the use of two materials alone, the piezoelectric and conductive properties of the composite MOF are improved to a certain extent, and the overall structure of the two materials entangled and connected to each other significantly improves the mechanical properties of the material on the original basis, greatly improves its durability, and broadens its application range for electrical components. PANI, as a conductive polymer, plays a positive role in the charge conduction of the entire fiber, overcoming the disadvantage of decreased charge transfer ability due to too many fiber layers.

[0050] Preferably, the first core layer and the second core layer are in a spiral parallel structure, with more core layer content per unit fiber length. Due to the interaction between different components and the strong interface effect generated by the spiral structure, the interaction between the fibers is enhanced, so that the mechanical and electrical properties of the three-component fiber are greatly improved, and its universal application is increased. The total mass of the first core layer and the second core layer accounts for more than 40% of the mass of the piezoelectric fiber.

[0051] The present invention provides a method for preparing a composite piezoelectric fiber, comprising the following steps:

[0052] S1. mixing and dissolving the magnetized carbon nanotube / metal organic framework composite material and the first matrix material to obtain a first core layer spinning solution;

[0053] S2. mixing and dissolving polyaniline and a second matrix material to obtain a second core layer spinning solution;

[0054] S3. dissolving the third matrix material to obtain a cortex spinning solution;

[0055] S4. The first core layer spinning solution, the second core layer spinning solution and the skin layer spinning solution are subjected to microfluidic wet spinning by a three-channel spinneret to obtain a composite piezoelectric fiber.

[0056] Compared with spinning methods such as electrospinning, the wet spinning method of the present invention is more efficient. Due to the spontaneous agglomeration behavior of CNT, the time-consuming production process may lead to uneven distribution of functional powder inside the fiber. The wet spinning method has a fast speed and a regular fiber structure, which can better meet the requirements of material production.

[0057] Preferably, in S1, the preparation method of the composite material is as follows: dissolve and mix magnetized carbon nanotubes, metal-organic framework materials, dispersants, nucleating agents, and capping agents, adjust the pH to 9-10, perform hydrothermal reaction and then dry to obtain magnetized carbon nanotube / metal-organic framework composite materials; the magnetization material of the magnetized carbon nanotubes can be iron, cobalt, nickel, preferably iron magnetized carbon nanotubes (Fe-CNTs), magnetize the carbon nanotubes to reduce agglomeration; the preparation method of the Fe-CNTs is as follows: ultrasonically mix CNTs with a mass ratio of 1:100 and nitric acid with a concentration of 65% for 0.5-4 h, reflux for 6 h at 90-120 °C, cool to room temperature, filter the suspension, wash to obtain pretreated CNTs (with negative charges on the surface), dry and then grind for standby; configure a mixture powder of FeCl3·6H2O and FeSO4·7H2O with a mass ratio of 2:1, mix the mixture powder with a mass ratio of 1:50 and a 0.1 mol / L hydrochloric acid solution, after the solid is completely dissolved, add distilled water to dilute the solution to 1 / 3-1 / 2 of the original concentration, then add the pretreated CNTs, stir and mix, add HNO3 to adjust the pH value below 7, then place it in an ultrasonic bath processor for 2 h, and then dry in a nitrogen atmosphere at 80 °C and grind into a powder to obtain magnetized CNTs, called Fe-CNTs.

[0058] Preferably, the metal-organic framework is specifically IRMOF (MOF containing cyclodextrin), specifically one or several of IRMOF-1, IRMOF-3, IRMOF-4, IRMOF-5, IRMOF-8, IRMOF-9, IRMOF-10, IRMOF-11, IRMOF-12, IRMOF-13, IRMOF-14, IRMOF-16, IRMOF-18, IRMOF-61, IRMOF-62, preferably IRMOF-5; the preparation method of the IRMOF-5 is as follows: add zinc nitrate hexahydrate (Zn(NO3)2) particles and terephthalic acid (BDC) powder with a mass ratio of 10:1-8:1 to a mixed solution of ethanol and DMF (dimethylformamide) with a molar ratio of 6.25:2.8, dissolve evenly, then add TEA and PVP with a mass ratio of 1.72:1.32, react at 160 °C for 8 h, after the reaction, centrifuge, filter, and dry in a vacuum environment to obtain MOF-5.

[0059] Preferably, the MOF-5 and Fe-CNTs are compounded by a solvothermal method, and the composite MOF is obtained after centrifugation and drying. The preparation method of the composite MOF is as follows: Add MOF-5 and Fe-CNTs with a mass ratio of 2:1 - 1:1 to a mixed solution of ethanol and DMF with a volume ratio of 31.2:43.8. After ultrasonic mixing and dispersion for 2 h, add a dispersant, a nucleating agent, and a capping agent. After dispersion, adjust the pH value to 9 - 10 with a 1% NaOH solution, place it in a hydrothermal reaction kettle, and react at 160 °C for 6 h. After the reaction, centrifuge and filter, and dry in a vacuum environment (-0.1 kPa - 0 kPa) to obtain the composite MOF. The molecular structure is shown in Figure 2 , MOF-5 21 is bound to the Fe 22 magnetized CNT 23; The dispersant is one or more of cetyltrimethylammonium bromide (CTAB), sodium dodecylbenzenesulfonate, and polyethylene oxide (PEO); The nucleating agent is one or more of triethanolamine (TEA), calcium carbonate, and sodium benzoate; The capping agent is a compound containing a protective functional group (such as an acetal group), for example: polyvinylpyrrolidone (PVP), benzoic acid, cyclohexanol, isopentanol, phenol, and trimethylchlorosilane.

[0060] Preferably, the solvent of the three spinning solutions is a DMF solution, and the concentration of the matrix in the spinning solution is 12 wt% - 20 wt%.

[0061] Preferably, as Figure 1 shown, the three channels include a cortical channel 11 and two helically juxtaposed core channels 12 arranged in the cortical channel. The central angle of the helical structure is between 0° and 180°, Figure 1 and the central angle is 180° in . By adjusting the bending angle of the helical layer, the ratio of the piezoelectric fiber core layer and the cortical layer per unit length can be flexibly controlled to meet the requirements of different application fields. The flow rates of the three channels are respectively controlled by three solution injection pumps 13. The flow rates of the first core layer spinning solution and the second core layer spinning solution are 0.3 mL / h, and the concentration of the cortical spinning solution is 0.3 - 0.4 mL / h.

[0062] Preferably, the mass of the magnetized carbon nanotube / metal organic framework composite material is 0.5 wt% - 2 wt% of the first matrix material; The mass ratio of the magnetized carbon nanotubes to the metal organic framework material is 1:(1 - 2); The mass of the polyaniline is 1 wt% - 5 wt% of the mass of the second matrix material.

[0063] Preferably, the matrix of the first core layer, the second core layer and the skin layer is selected from any one of polyacrylonitrile and polyvinylidene fluoride. The matrices of the first core layer and the second core layer are different from each other. When using a mixture of PAN and PVDF, compared with a single material, the PAN in the core layer has a higher degree of crystallinity, and there is a strong interaction force at the interface between the two, which is tightly combined, has better mechanical properties and better durability.

[0064] Preferably, after spinning and forming, it is soaked in a deionized water coagulation bath for 24 h, completely solidified into a fibrous shape after passing through the stretching section, and then collected by a winding roller. The rotation speed of the winding roller is 0.4 r / s, and it is heated and dried to remove organic matter residues; the stretching distance in the coagulation bath is 25 cm.

[0065] Example 1

[0066] 0.2 g of CNTs and nitric acid with a concentration of 65% were ultrasonically mixed for 4 h, refluxed for 6 h at 120 °C. After the mixture was completely cooled to room temperature, the suspension was filtered, washed to obtain pretreated CNTs with a negatively charged surface, dried and then ground; a mixture powder prepared from FeCl3·6H2O and FeSO4·7H2O in a mass ratio of 0.6 g:0.3 g was dissolved in a 0.1 mol / L hydrochloric acid solution. After the solid was completely dissolved, distilled water was added to dilute the solution to 1 / 3 - 1 / 2 of the original concentration, and then the pretreated CNTs were added and stirred until evenly mixed; HNO3 was added to the mixed solution to adjust the pH value to 3, and then the mixed solution was placed in an ultrasonic bath processor for 2 h, and then dried under a N2 atmosphere at 80 °C. The dried particles were crushed into a powder to obtain Fe-CNTs.

[0067] 3.125 mol of ethanol and 1.4 mol of DMF solution were mixed. 18.6 g of Zn(NO3) and 2.3 g of BDC powder were added thereto and stirred evenly, then 1.72 g of TEA and 1.32 g of PVP were added. After dissolving evenly, the reaction was carried out at 160 °C for 8 h. After the reaction, it was centrifuged, filtered, and dried in a vacuum environment to obtain MOF-5 powder.

[0068] 31.2 mL of ethanol and 43.8 mL of DMF solution were mixed. 1 g of MOF-5, 0.5 g of Fe-CNTs and 5 mg of CTAB powder were added thereto, and they were dispersed under ultrasonic conditions for 2 h. After dispersing evenly, 0.9 g of TEA and 1.2 g of PVP were added. After stirring evenly and dissolving completely, the pH value of the solution system was titrated to 9 with a 1% NaOH solution. Then, in a hydrothermal reaction kettle, the reaction was carried out at 160 °C for 6 h. After the reaction, it was centrifuged, filtered, and dried in a vacuum environment to obtain the composite MOF. The SEM image is shown in Figure 3 , with a uniform and stable structure;

[0069] Weigh 27.9 mg of composite MOF powder and 1.9 g of PAN powder, add them to 16 mL of DMF solution, stir and mix evenly, and ultrasonically disperse for 2 h to obtain the first core layer spinning solution;

[0070] Weigh 0.12 g of PANI powder and 1.52 g of PVDF particles, add them to 16 mL of DMF solution, stir and mix evenly, and then ultrasonically disperse for 3 h to obtain the second core layer spinning solution;

[0071] Weigh 2.1 g of PVDF particles and add them to 16 mL of DMF solution to obtain the skin layer spinning solution.

[0072] After the spinning solution is filtered, it is formed by three-channel microfluidic wet spinning. Among them, the spiral structure of the core layer is a semi-circle with a central angle of 180°. The flow rates of the first core layer spinning solution and the second core layer spinning solution are 0.3 mL / h, and the concentration of the skin layer spinning solution is 0.3 mL / h; the stretching distance in the coagulation bath is 25 cm. After forming, it is soaked in deionized water for 24 h and heated and dried to remove organic residue to obtain composite piezoelectric fibers.

[0073] Example 2

[0074] Based on Example 1, in this example, the mass of MOF-5 is adjusted to 0.5 g, and other steps remain unchanged.

[0075] Example 3

[0076] Based on Example 1, in this example, the mass of PAN powder in the first core layer spinning solution is adjusted to 1.52 g, and other steps remain unchanged.

[0077] Comparative Example 1

[0078] Based on Example 1, in this comparative example, the matrix material of the first core layer spinning solution is adjusted to PVDF, and other steps remain unchanged.

[0079] Comparative Example 2

[0080] Based on Example 1, in this comparative example, the magnetized carbon nanotubes are adjusted to non-magnetized carbon nanotubes, and other steps remain unchanged.

[0081] Comparative Example 3

[0082] Based on Example 1, in this comparative example, PANI is not added to the second core layer spinning solution, and other steps remain unchanged.

[0083] Comparative Example 4

[0084] Based on Example 1, in this comparative example, the two core layer spinning solutions are mixed as the core layer spinning solution and coaxial wet spinning is carried out with the skin layer spinning solution, and other steps remain unchanged.

[0085] The piezoelectric fibers obtained from the examples and comparative examples were subjected to performance analysis. The test method for the piezoelectric coefficient d33 was referenced from the article "Principles and Test Methods for Measuring Piezoelectric Coefficients of Thin Film Piezoelectric Materials". The basic operation was to paste and arrange 50 fibers horizontally and vertically in a cross pattern with a PI film to form a film with thickness. The basic principle of the test was to utilize the piezoelectric effect of the piezoelectric material. When the material was deformed under an external force, opposite charges were generated on the two surfaces, and the charges disappeared after the external force was removed. The film was vertically loaded with a vertical pressure, the specimen underwent compressive deformation and charges were generated, and the magnitude of the piezoelectric output could be visually observed through an oscilloscope.

[0086] The elongation at break (ΔL) of the specimen was measured by the constant rate of extension method to characterize the breaking strength of the specimen. That is, the specimen was fixed on a constant rate of extension (CRE) tester. When it was stretched to break on both sides, the ratio of the elongation of the specimen to the original length of the specimen was referenced from the standard "GB / T 3923.1-2013 Determination of breaking force and elongation at break (strip method)".

[0087] The performance parameters of the examples and comparative examples are shown in Table 1:

[0088] Table 1

[0089]

[0090] As can be seen from Table 1, compared with Comparative Examples 1-4, the composite piezoelectric fibers prepared by the methods of Examples 1-3 of the present invention have excellent output voltage, output current, and piezoelectric coefficient. Among them, the output voltage of Example 1 can reach 10.4 V, and the output current can reach 0.4 μA. Refer to Figure 4 and Figure 5 , and at the same time, they have excellent mechanical properties, and their elongation at break can reach 59.2%.

[0091] The above-mentioned examples are only preferred examples given to fully illustrate the present invention, and the protection scope of the present invention is not limited thereto. Equivalent substitutions or transformations made by those skilled in the art on the basis of the present invention are all within the protection scope of the present invention. The protection scope of the present invention is subject to the claims.

Claims

1. A preparation method of a composite piezoelectric fiber, characterized in that The composite piezoelectric fiber includes a cortical layer and a first core layer and a second core layer wrapped in the cortical layer, and the preparation method includes the following steps: S1. Mix and dissolve the magnetized carbon nanotube / metal-organic framework composite material with the first matrix material to obtain a spinning solution for the first core layer; S2. Mix and dissolve polyaniline with the second matrix material to obtain a spinning solution for the second core layer; S3. Dissolve the third matrix material to obtain a spinning solution for the cortical layer; S4. Perform microfluidic wet spinning on the spinning solution for the first core layer, the spinning solution for the second core layer, and the spinning solution for the cortical layer through a three-channel spinneret to obtain the composite piezoelectric fiber; Wherein, the matrixes of the first core layer, the second core layer, and the cortical layer are selected from polyacrylonitrile or polyvinylidene fluoride, and the matrixes of the first core layer and the second core layer are different from each other; the three channels include a cortical channel and two helically juxtaposed core layer channels arranged in the cortical channel.

2. The preparation method of the composite piezoelectric fiber according to claim 1, wherein In S1, the preparation method of the composite material is: dissolve and mix magnetized carbon nanotubes, metal-organic frameworks, dispersants, nucleating agents, and capping agents, adjust the pH to 9-10, and dry after hydrothermal reaction to obtain the magnetized carbon nanotube / metal-organic framework composite material.

3. The preparation method of the composite piezoelectric fiber according to claim 1, characterized in that, The mass of the magnetized carbon nanotube / metal-organic framework composite material is 0.5 wt%-2 wt% of the mass of the first matrix material.

4. The preparation method of the composite piezoelectric fiber according to claim 2, characterized in that, The mass ratio of the magnetized carbon nanotubes to the metal-organic framework is 1:(1-2).

5. The preparation method of the composite piezoelectric fiber according to claim 1, characterized in that, The mass of the polyaniline is 1 wt%-5 wt% of the mass of the second matrix material.

6. A composite piezoelectric fiber prepared by the preparation method according to any one of claims 1-5.

7. The composite piezoelectric fiber according to claim 6, characterized in that, The total mass of the first core layer and the second core layer accounts for more than 40% of the mass of the piezoelectric fiber.

Images