A core-sheath structure high-performance composite piezoelectric fiber and its preparation method

Abstract

This invention discloses a core-shell composite piezoelectric fiber material and its preparation method. The invention first prepares a core-shell composite nanofiber with PVDF-TrFE as the shell and PC as the core using a coaxial spinning process. Using PC as the core increases the elastic modulus of the composite piezoelectric fiber, resulting in a larger piezoelectric potential than pure PVDF-TrFE fibers under the same strain. Simultaneously, PC forms hydrogen bonds at the interface with PVDF-TrFE, increasing the crystallinity of the PVDF-TrFE shell and thus improving the piezoelectric properties. The core-shell composite piezoelectric fiber has a d... 33 The piezoelectric coefficient can reach 49.1 pC N. ‑1 It is 110% higher than that of pure PVDF-TrFE.

Description

Technical Field

[0001] This invention belongs to the field of energy storage material preparation technology, and relates to a method for preparing piezoelectric materials, particularly a high-performance composite piezoelectric fiber with a core-shell structure and its preparation method. Background Technology

[0002] The piezoelectric effect refers to the phenomenon where bound charges are generated on the corresponding surfaces of a material when it is subjected to external stress. The electromechanical conversion capabilities of piezoelectric materials make them important in fields such as vibration sensors, transducers, and energy harvesting equipment. However, among the currently mainstream piezoelectric materials, inorganic piezoelectric ceramics, while having high piezoelectric coefficients, suffer from high stiffness and poor environmental adaptability, while organic polymer piezoelectric materials, although flexible and easily deformable, have low piezoelectric coefficients and weak piezoelectric output. Overcoming these shortcomings is a key problem that urgently needs to be solved in the development of new piezoelectric materials.

[0003] According to the basic formula of the piezoelectric effect, D=dT, the electric displacement (D) generated by the piezoelectric effect is directly related to the piezoelectric coefficient (d) and the stress (T) in the corresponding direction. The electric displacement corresponds to the surface charge density of the piezoelectric material. To improve the piezoelectric performance of the material, improving the piezoelectric coefficient is the most direct method. At present, the main method to improve the piezoelectric coefficient of organic piezoelectric materials is to add inorganic fillers to form organic-inorganic composite piezoelectric materials. (Su Y,Chen C,Pan H,et al.Muscle fibers inspired high-performance piezoelectric textiles forwearable physiological monitoring[J].Advanced Functional Materials,2021,31(19):2010962.) However, the compatibility between inorganic fillers and polymer matrices is usually poor, making the material brittle and reducing its durability. It is often necessary to perform additional surface modification treatment on inorganic fillers to improve their compatibility with polymer matrices. However, most of these modification methods are costly and complicated, which is not conducive to the large-scale production of materials. (Shi K, Chai B, Zou H, et al. Interface induced performance enhancement in flexible BaTiO3 / PVDF-TrFE based piezoelectric nanogenerators[J]. Nano Energy, 2021, 80: 105515.) Prior to this invention, no all-organic piezoelectric polymer fiber material prepared by coaxial electrospinning process could achieve a piezoelectric coefficient improvement of more than 100% compared to the original pure polymer fibers. Summary of the Invention

[0004] This invention addresses the shortcomings of current organic piezoelectric materials, such as low piezoelectric coefficients and weak piezoelectric outputs, by proposing a core-shell structure high-performance composite piezoelectric fiber and its preparation method. This invention is the first to prepare a novel piezoelectric material with excellent piezoelectric properties. Firstly, PC, as the core layer of the core-shell structure composite piezoelectric fiber, increases the fiber's elastic modulus, enabling it to generate a larger piezoelectric voltage under the same deformation. Simultaneously, hydrogen bonding interactions form at the interface between PC and PVDF-TrFE, increasing the crystallinity of the PVDF-TrFE shell and thus enhancing the piezoelectric coefficient. This invention uses two polymer materials, PVDF-TrFE and PC, to prepare the core-shell structure composite piezoelectric fiber. This invention has high practical value and represents a promising direction for the development of novel piezoelectric materials.

[0005] The objective of this invention is achieved through the following technical solution:

[0006] This invention provides a method for preparing a core-sheath composite piezoelectric fiber with a high piezoelectric coefficient, comprising the following steps:

[0007] S1. Dissolve PVDF-TrFE polymer raw material in N,N-dimethylformamide to prepare PVDF-TrFE polymer spinning solution; dissolve PC in tetrahydrofuran to prepare PC polymer spinning solution;

[0008] S2. The PVDF-TrFE polymer spinning solution and the PC polymer spinning solution are coaxially electrospun.

[0009] S3. Collect the electrospun fibers prepared in step S2 using a roller covered with aluminum foil. After peeling off the aluminum foil, a complete electrospun fiber membrane is obtained.

[0010] The core-sheath composite piezoelectric fiber prepared by the method of this invention has a high N-saturation content of 49.1 pC. -1 The high piezoelectric coefficient can be obtained in one step without prior modification of the raw materials, and it has the potential for large-scale production. Furthermore, the prepared fiber membrane has an aluminum foil substrate, which greatly facilitates the subsequent fabrication of piezoelectric generator devices.

[0011] In one embodiment of the present invention, in step S1, the mass fraction of PVDF-TrFE in the PVDF-TrFE polymer spinning solution is 16% to 24%. In some embodiments, the mass fraction of PVDF-TrFE in the PVDF-TrFE polymer spinning solution is 20%.

[0012] In one embodiment of the present invention, in step S1, the mass fraction of PC in the PC polymer spinning solution is 16% to 24%. In some embodiments, the mass fraction of PC in the PC polymer spinning solution is 20%.

[0013] In one embodiment of the present invention, in step S1, the dissolution is achieved by heating in a water bath to 60°C–80°C and stirring for 4–6 hours to completely dissolve the polymer and form a clear solution. In some embodiments, the water bath is heated to 60°C and stirred for 4 hours.

[0014] In one embodiment of the present invention, in step S2, the PC polymer spinning solution is used as the core layer spinning solution.

[0015] As one embodiment of the present invention, in step S2, the coaxial electrospinning uses a syringe equipped with a coaxial needle.

[0016] In one embodiment of the present invention, in step S2, the coaxial needles used in the coaxial electrospinning are of specifications ranging from 18 / 14G to 25 / 18G, corresponding to a core layer needle inner diameter of 0.26 to 0.84 mm and a shell layer needle inner diameter of 0.84 to 1.55 mm. In some embodiments, the coaxial needle specifications are 25G / 18G, corresponding to a core layer needle inner diameter of 0.26 mm and a shell layer needle inner diameter of 0.86 mm.

[0017] In one embodiment of the present invention, in step S2, the parameters of the electrospinning process are set as follows: spinning voltage: 15-22kV; spinning rate: the spinning rate of the PVDF-TrFE shell is 0.5-0.9 mL / h. -1 The spinning rate of the PC core layer is 0.1–0.3 mL / h. -1 In some embodiments, the electrospinning process parameters are as follows: spinning voltage: 18kV; spinning rate: the spinning rate of the PVDF-TrFE shell is 0.7mL / h. -1 The spinning rate of the PC core layer is 0.3 mL / h. -1 .

[0018] In one embodiment of the present invention, in step S3, the distance between the roller collector and the spinning needle is selected to be 15-20 cm, and the rotation speed of the roller collector is maintained at 800-1200 rpm. In some embodiments, the distance between the roller collector and the spinning needle is maintained at 15 cm, and the rotation speed of the roller collector is maintained at 1000 rpm.

[0019] The present invention provides a core-sheath composite piezoelectric fiber prepared according to the aforementioned method.

[0020] Compared with the prior art, the present invention has the following beneficial effects:

[0021] 1. Fiber membranes prepared by electrospinning technology have excellent flexibility. Piezoelectric fiber materials can be used in self-powered devices in various application scenarios, such as wearable devices, power equipment monitoring, and wind energy harvesting.

[0022] 2. Core-shell composite piezoelectric fibers use PC as a rigid core layer to improve the overall elastic modulus of the fiber. Compared with pure PVDF-TrFE fibers, the composite fibers have a higher modulus, so a larger external force is required for the same deformation, resulting in a larger piezoelectric potential in the PVDF-TrFE shell. On the other hand, hydrogen bonds are formed at the interface between PC and PVDF-TrFE, which increases the crystallinity of the PVDF-TrFE shell and thus improves the piezoelectric coefficient.

[0023] 3. Core-sheath composite piezoelectric fibers have a high N-value of 49.1 pC. -1The voltage coefficient is 110% higher than that of the original PVDF-TrFE fiber. Attached Figure Description

[0024] Other features, objects, and advantages of the present invention will become more apparent from the following detailed description of non-limiting embodiments with reference to the accompanying drawings:

[0025] Figure 1 Scanning electron microscope (SEM) image of the core-sheath composite piezoelectric fiber prepared according to an embodiment of the present invention;

[0026] Figure 2 Transmission electron microscopy (TEM) image of the core-sheath composite piezoelectric fiber prepared according to an embodiment of the present invention;

[0027] Figure 3 A transmission electron microscope cross-sectional image of the core-sheath composite piezoelectric fiber prepared according to an embodiment of the present invention;

[0028] Figure 4 The piezoelectric coefficient of the core-sheath composite piezoelectric fiber prepared for the embodiments of the present invention is compared with that of pure PVDF-TrFE fiber and PVDF-TrFE and PC blend. Detailed Implementation

[0029] The present invention will now be described in detail with reference to specific embodiments. These embodiments will help those skilled in the art to further understand the present invention, but do not limit the invention in any way. It should be noted that those skilled in the art can make several changes and improvements without departing from the concept of the present invention. These all fall within the scope of protection of the present invention.

[0030] Example 1

[0031] The process for preparing PVDF-TrFE / PC core-sheath composite piezoelectric fibers according to the method provided by the present invention is as follows:

[0032] 1. Weigh 4.0g of N,N-dimethylformamide, add 1.0g of PVDF-TrFE raw material, and stir magnetically for 4 hours in a 60℃ water bath until the polymer is completely dissolved.

[0033] 2. Weigh 5.0g of tetrahydrofuran, add 1.0g of PC raw material, and stir magnetically for 4 hours in a 60℃ water bath until the polymer is completely dissolved.

[0034] 3. Inject the prepared polymer solution into syringes equipped with coaxial needles, and spin the polymer using an electrospinning machine. The coaxial needle specifications are 25G / 18G, corresponding to a core needle inner diameter of 0.26mm and a shell needle inner diameter of 0.86mm. The electrospinning process parameters are: spinning voltage: 18kV; spinning rate: 0.7mL / h for the PVDF-TrFE shell. -1 The spinning rate of the PC core layer is 0.3 mL / h. -1 .

[0035] 4. Collect the electrospun fibers using a roller covered with aluminum foil. Maintain a distance of 15 cm between the roller collector and the spinning needle, and keep the roller collector rotating at 1000 rpm. After removing the aluminum foil, a complete electrospun fiber membrane is obtained. A scanning electron microscope image of the composite piezoelectric fiber is shown below. Figure 1 As shown. The core-sheath structure of the composite piezoelectric fiber can be observed through transmission electron microscopy (TEM) images, such as... Figure 2 and Figure 3 As shown. Figure 4 The comparison of piezoelectric coefficients among different types of fibers is shown. It can be seen that the core-sheath composite piezoelectric fiber prepared by coaxial electrospinning has the highest piezoelectric coefficient. The piezoelectric coefficient d0 is measured by piezoelectric power microscopy (PFM). 33 Up to 49.1 pC N -1 .

[0036] Example 2

[0037] The process for preparing PVDF-TrFE / PC core-sheath composite piezoelectric fibers according to the method provided by the present invention is as follows:

[0038] 1. Weigh 2.4g of N,N-dimethylformamide and 1.6g of acetone. Mix the two to form a mixed solvent. Add 1.0g of PVDF-TrFE raw material to the mixture and stir magnetically for 4 hours in a 60°C water bath until the polymer is completely dissolved.

[0039] 2. Weigh 4.0g of tetrahydrofuran, add 1.0g of PC raw material, and stir magnetically for 4 hours in a 60℃ water bath until the polymer is completely dissolved.

[0040] 3. Inject the prepared polymer solution into syringes equipped with coaxial needles, and spin the polymer using an electrospinning machine. The coaxial needle specifications are 25G / 18G, corresponding to a core needle inner diameter of 0.26mm and a shell needle inner diameter of 0.86mm. The electrospinning process parameters are: spinning voltage: 18kV; spinning rate: 0.7mL / h for the PVDF-TrFE shell. -1 The spinning rate of the PC core layer is 0.3 mL / h. -1 .

[0041] 4. Collect the electrospun fibers using a roller covered with aluminum foil. Maintain a distance of 15 cm between the roller collector and the spinning needle, and keep the roller collector rotating at 1000 rpm. After removing the aluminum foil, a complete electrospun fiber membrane is obtained. The d-structure of PVDF-TrFE / PC core-sheath composite piezoelectric fiber... 33 The piezoelectric coefficient reaches 50.4 pC N. -1 .

[0042] Example 3

[0043] The process for preparing PVDF-TrFE / PC core-sheath composite piezoelectric fibers according to the method provided by the present invention is as follows:

[0044] 1. Weigh 3.2g of N,N-dimethylformamide and 1.8g of acetone. Mix the two to form a mixed solvent. Add 1.0g of PVDF-TrFE raw material to the mixture and stir magnetically for 4 hours in an 80°C water bath until the polymer is completely dissolved.

[0045] 2. Weigh 5.0g of tetrahydrofuran, add 1.0g of PC raw material, and stir magnetically for 4 hours in an 80℃ water bath until the polymer is completely dissolved.

[0046] 3. Inject the prepared polymer solution into syringes equipped with coaxial needles, and spin the polymer using an electrospinning machine. The coaxial needle specifications are 22G / 17G, corresponding to a core needle inner diameter of 0.41mm and a shell needle inner diameter of 1.01mm. The electrospinning process parameters are: spinning voltage: 22kV; spinning rate: 0.8mL / h for the PVDF-TrFE shell. -1 The spinning rate of the PC core layer is 0.2 mL / h. -1 .

[0047] 4. Collect the electrospun fibers using a roller covered with aluminum foil. Maintain a distance of 15 cm between the roller collector and the spinning needle, and keep the roller collector rotating at 800 rpm. After removing the aluminum foil, a complete electrospun fiber membrane is obtained. The d-structure of PVDF-TrFE / PC core-sheath composite piezoelectric fiber... 33 The piezoelectric coefficient reaches 45.2 pC N. -1 .

[0048] Comparative Example 1

[0049] This comparative example relates to a PVDF / PMMA core-sheath composite piezoelectric fiber; the specific preparation is basically the same as in Example 1. The piezoelectric coefficient of the obtained core-sheath composite piezoelectric fiber is 35.7 pC N. -1 .

[0050] Comparative Example 2

[0051] This comparative example relates to a PVDF-TrFE / TPU core-sheath composite piezoelectric fiber; the specific preparation is basically the same as in Example 1. The piezoelectric coefficient of the obtained core-sheath composite piezoelectric fiber is 19.8 pC N. -1 .

[0052] Comparative Example 3

[0053] This comparative example involves a pure PVDF-TrFE piezoelectric fiber; the specific preparation process is as follows:

[0054] 1. Weigh 2.4g of N,N-dimethylformamide and 1.6g of acetone. Mix the two to form a mixed solvent. Add 1.0g of PVDF-TrFE raw material to the mixture and stir magnetically for 4 hours in a 60°C water bath until the polymer is completely dissolved.

[0055] 2. Inject the prepared polymer solution into a syringe equipped with a spinning needle, and spin using an electrospinning machine. The coaxial needle specifications are: 25G, corresponding to a needle inner diameter of 0.26mm; the electrospinning process parameters are: spinning voltage: 18kV; spinning rate: the spinning rate of PVDF-TrFE is 1.0mL / h. -1 .

[0056] The piezoelectric coefficient of the pure PVDF-TrFE electrospun piezoelectric fiber obtained was 23.4 pC N. -1 .

[0057] Comparative Example 4

[0058] This comparative example relates to a pure PVDF-TrFE / PC blend piezoelectric fiber; the specific preparation method is basically the same as Comparative Example 3. The piezoelectric coefficient of the obtained pure PVDF-TrFE / PC blend piezoelectric fiber is 19.4 pC N. -1 .

[0059] It should be noted that without using the coaxial electrospinning process in the preparation method of this embodiment, it is impossible to prepare the required core-sheath composite piezoelectric fiber. Core-sheath fiber has strict requirements on the solution concentration, spinning rate and voltage during spinning. If the parameters are not adjusted properly, core-sheath composite fiber may not be obtained, and instead, separate PVDF-TrFE fiber and PC fiber may be obtained.

[0060] In summary, this invention first prepares core-shell composite nanofibers with PVDF-TrFE as the shell and PC as the core using a coaxial spinning process. Using PC as the core increases the elastic modulus of the composite piezoelectric fiber, resulting in a larger piezoelectric potential than pure PVDF-TrFE fibers under the same strain. Simultaneously, PC forms hydrogen bonds at the interface with PVDF-TrFE, increasing the crystallinity of the PVDF-TrFE shell and thus improving the piezoelectric properties. The core-shell composite piezoelectric fiber's d... 33 The piezoelectric coefficient can reach 49.1 pCN. -1 It is 110% higher than pure PVDF-TrFE.

[0061] It is particularly important to note that highly polar polymers, such as polyacrylonitrile (PAN), are typically used in this field, as the composite of polar polymers enhances the piezoelectricity of PVDF. A key feature of this invention is the use of PC as the core layer of the piezoelectric fiber. PC is traditionally considered a weakly polar, non-piezoelectric polymer. This invention successfully achieves excellent piezoelectric properties in PVDF-TrFE / PC core-sheath structure fibers, yielding unexpected results. This is likely a combined result of interfacial hydrogen bonding inducing a polar β phase and the high-modulus core layer modulation. Using other high-modulus polymer materials, such as PMMA used in Comparative Example 1, can also achieve similar effects, but the improvement in piezoelectricity is significantly less than that of PC.

[0062] Various changes or modifications have been made to the specific embodiments of the present invention within the scope of the claims, which do not affect the essence of the present invention. Unless otherwise specified, the embodiments and features described herein can be arbitrarily combined with each other.

Claims

1. A method for preparing a core-sheath composite piezoelectric fiber with a high piezoelectric coefficient, characterized in that, Includes the following steps: S1. Dissolve PVDF-TrFE polymer raw material in N,N-dimethylformamide to prepare PVDF-TrFE polymer spinning solution, wherein the mass fraction of PVDF-TrFE in the PVDF-TrFE polymer spinning solution is 16%~24%; dissolve PC in tetrahydrofuran to prepare PC polymer spinning solution, wherein the mass fraction of PC in the PC polymer spinning solution is 16%~24%; the PC polymer spinning solution is used as the core layer spinning solution; S2. The PVDF-TrFE polymer spinning solution and the PC polymer spinning solution are coaxially electrospun; the parameters of the electrospinning process are set as follows: spinning voltage: 15~22 kV; spinning rate: the spinning rate of the PVDF-TrFE shell is 0.5~0.9 mL h. -1 The spinning rate of the PC core layer is 0.1~0.3 mL / h. -1 ; S3. Collect the electrospun fibers prepared in step S2 using a roller covered with aluminum foil. After removing the aluminum foil, a complete electrospun fiber membrane is obtained.

2. The method for preparing the core-sheath composite piezoelectric fiber according to claim 1, characterized in that, In step S1, the dissolution is achieved by heating in a water bath to 60°C~80°C and stirring for 4~6 hours to completely dissolve the polymer and form a clear solution.

3. The method for preparing the core-sheath composite piezoelectric fiber according to claim 1, characterized in that, The coaxial needles used in the coaxial electrospinning are 18 / 14G to 25 / 18G, with corresponding core layer needle inner diameters of 0.26 to 0.84 mm and shell layer needle inner diameters of 0.84 to 1.55 mm.

4. The method for preparing the core-sheath composite piezoelectric fiber according to claim 1, characterized in that, In step S3, the distance between the roller collector and the spinning needle is selected to be 15~20 cm, and the rotation speed of the roller collector is maintained at 800~1200~1000 rpm.

5. A core-sheath composite piezoelectric fiber prepared by the method according to any one of claims 1-4.

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