Piezoelectric textiles produced via electrospinning

Abstract

A piezoelectric fabric can include a non-woven continuous fiber mat including a polymer; and a plurality of piezoelectric ceramic particles. The piezoelectric fabric can be produced by electrospinning. An electrospinning method can include forming a continuous fiber of a material including flowing a fluid through a needle, wherein the fluid includes: a polymer; a base fluid; and the piezoelectric ceramic particles; and applying a voltage to create an electric field between a tip of the needle and a collector during the fluid flow; and collecting the continuous fiber on the collector. The piezoelectric fabric can exhibit improved performance and piezoelectric thermal stability.

Description

Technical Field

[0001] Piezoelectric composites can be used to produce electronic textiles. Piezoelectric composites can be formed into continuous fibers, which can then be woven into fabrics via electrospinning. Attached Figure Description

[0002] The features and advantages of certain embodiments will be more readily understood when considered in conjunction with the accompanying drawings. The drawings should not be construed as limiting any preferred embodiment.

[0003] Figure 1 This is a schematic diagram of the electrospinning process.

[0004] Figure 2 This is a schematic diagram of a piezoelectric sensor. Detailed Implementation

[0005] Electronic textiles (often referred to as E-textiles) are fabrics that incorporate electronic components and can be used as fabrics or clothing in addition to their primary intended purpose. This versatile approach has been developed by numerous researchers and has led to scientific advancements worldwide. Various potential applications include wearable computing, clothing design, healthcare, data storage, and interior design technologies that integrate electronic components such as microcontrollers, sensors, and actuators into fabrics or fibers.

[0006] Embedding electronic components within some fibers has achieved some practical success. Well-known materials for smart fabrics include traditional cotton, polyester, and nylon, as well as advanced Kevlar with integrated functionality. However, currently, resistive / conductive fabrics are manufactured by depositing / mixing metallic nanoparticles or semiconductors around or within the woven fibers and fabric. Over time or due to environmental influences, the performance of these fabrics tends to become unstable; therefore, these fabrics are not suitable for long-term performance.

[0007] Recent developments in piezoelectric textile fibers have been reported, aiming to integrate sensing and energy harvesting capabilities into smart textile structures and materials. To obtain useful textile polymer materials, the polymer undergoes one of several spinning processes, such as dry spinning, melt spinning, or electrospinning, i.e., converting (sorting) the material into yarn. Typically, these methods involve converting a polymer solution generated from raw materials (direct spinning) or converting a polymer solution generated by dissolving / melting a polymer resin (melt spinning and electrospinning).

[0008] To realize the function of piezoelectric materials, a strong electric field is required to align the polarization of the electric dipole moment. Polarization is a process performed after the film / disc is made from solid piezoelectric ceramics (such as lead zirconate titanate (PZT) and barium titanate (BT)), polymers with a β phase (such as polyvinylidene fluoride (PVDF) and poly[(vinylidene fluoride-co-trifluoroethylene](PVDF-TrFE)) or composite systems.

[0009] Piezoelectric textiles face several challenges, including difficulty in orienting and maintaining the dipole moment, i.e., polarization, especially when the fiber is freely twisted and rotated. Another challenge is the effectiveness of the fiber for practical applications, such as sensing and energy harvesting. Another current challenge for the wider adoption of electronic textiles is the need to achieve a combination of high output performance, functionalization, and wearing comfort. Furthermore, fibers made from PVDF and PVDF-TrFE are known to degrade at higher temperatures, causing them to lose their polarization and piezoelectric properties.

[0010] Therefore, what is needed and what the industry continues to focus on is smart e-textiles, which will perform additional purposes beyond being fabrics, address current challenges, and strive for a world with “smart” clothing.

[0011] A new class of piezoelectric materials has been discovered that can be produced by combining olefin copolymers and piezoelectric ceramics via electrospinning. Some advantages of this new class of piezoelectric materials include the natural polarization of the fibers during the spinning process, and the excellent performance and thermal stability of the fabric material as a piezoelectric sensor.

[0012] According to some embodiments, a piezoelectric fabric comprises: a nonwoven continuous fiber felt comprising: an olefin copolymer; and a piezoelectric ceramic.

[0013] According to some other embodiments, a method of producing a piezoelectric fabric includes: forming continuous fibers of the material, including: flowing a fluid through a needle, wherein the fluid comprises: an olefin copolymer; a base fluid; and piezoelectric ceramic particles; applying a voltage during the fluid flow to generate an electric field between the tip of the needle and a collector; and collecting the continuous fibers on the collector.

[0014] It should be understood that the discussion of any embodiment of the fiber, fabric or any material constituting the fiber or fabric is intended to apply to all method and composition embodiments, without needing to repeat the various embodiments throughout the text.

[0015] Continuous fiber mats can be nonwoven. Fiber mats can be formed via electrospinning. Figure 1An exemplary schematic diagram of an electrospinning process is shown. An electrospinning apparatus 100 typically includes a spinneret 102 (a hypodermic syringe with a needle) connected to a high-voltage (e.g., 0.5 to 30 kV) DC power supply 110, an injection pump (not shown), and a collector 106 grounded to ground 108. A polymer solution is loaded into the syringe and extruded from the needle tip at a constant rate by the injection pump. When a sufficiently high voltage is applied to the droplet, the liquid becomes charged. The droplet is stretched as electrostatic repulsion counteracts surface tension. At a critical point, the liquid stream is ejected from the surface of the needle tip. If the molecular cohesion of the liquid is high enough, the stream does not break, and a charged liquid jet forms and flows out from the needle tip. As the jet dries in air, the current flow pattern changes from an ohmic mode to a convection mode as charge migrates to the surface of the formed fiber 104. The jet is then elongated by electrostatic repulsion until it deposits on the grounded collector 106, as shown. The elongation and thinning of the fiber can result in the formation of uniform fibers with diameters ranging from micrometers to nanometers.

[0016] Several parameters in the electrospinning process can affect the final form of the produced fiber, including whether it forms a continuous fiber or fiber segments. Some parameters can be interrelated. Parameters may include, but are not limited to: the molecular weight and molecular weight distribution of the polymer; the properties of the polymer solution (such as concentration, viscosity, conductivity, and surface tension); the applied voltage; the flow rate; the distance between the needle tip and the collector; processing conditions (such as temperature and humidity); and the needle diameter.

[0017] The method may include: flowing fluid through a needle. The flow rate can be adjusted to form continuous fibers. The selected flow rate may depend on the viscosity of the fluid and other parameters. For example, the flow rate may be related to the viscosity of the fluid. Therefore, as viscosity increases, it may be necessary to increase the flow rate; and as viscosity decreases, it may be necessary to decrease the flow rate. According to any embodiment, the flow rate is selected to produce continuous fibers. According to any embodiment, the flow rate can be in the range of 0.1 to 20 ml / hr. In industrial applications, the flow rate may be different.

[0018] The needle's gauge (i.e., outer diameter) can be varied and selected to produce continuous fibers. The needle gauge can also be related to the fluid's flow rate and viscosity. Therefore, the needle gauge of any embodiment can be selected, particularly based on viscosity and flow rate, to produce continuous fibers. For example, the needle can be in the range of 18 to 15 gauges. The needle can also have a blunt tip.

[0019] The fluid flowing through the needle can contain polymers. Polymers are molecules composed of repeating units typically linked by covalent chemical bonds. Polymers are formed from monomers. During polymer formation, some chemical groups may be lost from each monomer. The portion of the monomer incorporated into the polymer is considered a repeating unit or monomer residue. The polymer backbone is a continuous chain of monomer residues. Polymers may also contain side functional groups attached to the backbone at various locations along its length. Polymer nomenclature is generally based on the type of monomer residues that make up the polymer. Polymers formed from one type of monomer residue are called homopolymers. Polymers formed from two or more different types of monomer residues are called copolymers. The number of repeating units in a polymer is called the polymer chain length. The number of repeating units in a polymer can range from about 11 to greater than 10,000. In copolymers, repeating units from each monomer residue can be arranged along the polymer chain in various ways. For example, repeating units can be random, alternating, periodic, or block. The conditions of the polymerization reaction can be adjusted to help control the average number of repeating units (average chain length) of the polymer. Polymer molecules can be cross-linked. As used in this article, "crosslink" and all its grammatical variations refer to a bond between two or more polymer molecules. Crosslinked polymer molecules can form polymer networks.

[0020] Polymers have an average molecular weight that is directly related to their average chain length. The average molecular weight of a polymer affects some of its physical properties, such as its solubility and dispersibility. For copolymers, each monomer in the monomer group is repeated a certain number of times (the number of repeating units). The average molecular weight of the copolymer (M...) w This can be represented as follows:

[0021] M w =∑w x M x

[0022] Where w x The weight fraction of the molecule is M, and the molecular weight of the molecule is M. x .

[0023] The polymer can be a copolymer. The copolymer can be an olefin copolymer. As used herein, the term "olefin copolymer" refers to a copolymer comprising a first monomer of ethylene or propylene polymerized with any one of 1-butene, 4-methyl-1-pentene, 1-hexene, 1-octene, 1-decene, 1-dodecene, 1-tetradecene, 1-hexadecene, 1-octadecene, and 1-eicosene. In a preferred embodiment, the olefin copolymer may comprise ethylene and octene. The olefin copolymer may comprise an olefin block copolymer, an olefin random copolymer, or some mixture thereof.

[0024] The molecular weight of the polymer can affect the viscosity of the fluid. According to some embodiments, the molecular weight of the polymer is selected such that the fluid has the viscosity required to form continuous fibers. According to any embodiment, the base fluid can have a viscosity in the range of 1 cp to 1,000,000 cp. The concentration of the polymer can also be selected such that continuous fibers are formed. According to any embodiment, the concentration of the polymer can be in the range of 1 to 99.9 wt.% of the base fluid.

[0025] Fluids can include basic fluids. As used herein, a “fluid” is a substance having a continuous phase that, when tested at a temperature of 71°F (22°C) and a pressure of one atmosphere (atm) (0.1 MPa), can flow and conform to the profile of its container. Fluids can be liquids or gases. Homogeneous fluids have only one phase; heterogeneous fluids have more than one distinct phase. Colloids are examples of heterogeneous fluids. Heterogeneous fluids can be: slurries comprising a continuous liquid phase and undissolved solid particles as a dispersed phase; emulsions comprising a continuous liquid phase and at least one dispersed phase of immiscible droplets; foams comprising a continuous liquid phase and a gas as a dispersed phase; or mists comprising a continuous gas phase and droplets as a dispersed phase. Heterogeneous fluids will have only one continuous phase, but may have more than one dispersed phase. It should be understood that any phase of a heterogeneous fluid (e.g., a continuous or dispersed phase) may contain dissolved or undissolved substances or compounds. As used herein, the term “base fluid” refers to the solvent of a solution or the continuous phase of a heterogeneous fluid, and is the liquid with the largest volume percentage of the fluid.

[0026] The base fluid can be a continuous phase of a heterogeneous fluid. The base fluid can dissolve the polymer. According to any embodiment, the base fluid can be selected such that the polymer dissolves. The base fluid can be selected from the group consisting of polar aprotic solvents, such as N,N-dimethylformamide, tetrahydrofuran, and combinations thereof. The surface tension of the base fluid may affect the fiber morphology. The base fluid can be selected such that a desired surface tension is achieved. According to some embodiments, the base fluid has a surface tension in the range of 11 mN / m to 85 mN / m at 20 °C. According to any embodiment, the base fluid can have a conductivity in the range of 5 μS / cm to 5 S / m at 20 °C.

[0027] The fluid may also contain multiple piezoelectric ceramic particles. According to some embodiments, the piezoelectric ceramic particles are not dissolved in the base fluid. Therefore, the fluid can be classified as a slurry, in which the continuous phase comprises the base fluid and a dispersed phase of dissolved copolymers and insoluble piezoelectric ceramic particles.

[0028] Piezoelectric ceramic particles can be selected from the group consisting of: lead zirconate titanate (PZT), hydroxyapatite, apatite, lithium sulfate monohydrate, sodium bismuth titanate, quartz, tartaric acid fiber, poly(vinylidene fluoride) fiber, barium titanate, having the formula (K,Na) 1-t Li t Li-doped potassium sodium niobate (KNLN) of NbO3 (where the variable 't' ranges from greater than 0.01 to less than 1 (0.01 < t < 1.00)), potassium sodium niobate (KNaNb)O3 (KNN), and combinations thereof. According to any embodiment, the concentration of the piezoelectric ceramic particles can be in the range of 0.01 wt.% to 99 wt.% of the base fluid. The piezoelectric ceramic particles can also have an average particle size in the range of 20 nanometers to 100 micrometers. Different from other piezoelectric fabrics (such as PVDF) that typically thermally degrade and lose functionality at or below 60°C, it has been unexpectedly found that the disclosed embodiments containing polymers and piezoelectric ceramic particles have excellent thermal stability. The disclosed piezoelectric fabric can be piezo-thermally stable up to 140°C.

[0029] The method includes: applying a voltage during fluid flow to generate an electric field between the tip of the needle and the collector. During the application of the voltage, charges accumulate at the fluid surface. When the electrostatic repulsion is higher than the surface tension of the fluid, the meniscus of the fluid deforms into a conical structure called a Taylor cone. Once the Taylor cone is formed, a charged liquid jet is ejected towards the collector. Depending on the solution viscosity, as the solvent evaporates due to the whipping motion that occurs during the flight time from the Taylor cone to the collector, solid fibers will be formed. The result is a non-woven fiber mat deposited on the collector. The applied voltage can also be varied and selected to produce continuous fibers. The applied voltage can be in the range of 0.50 V to 90 V. In addition, the distance between the tip of the needle and the collector can also affect the formation of continuous fibers. This distance can be selected such that continuous fibers are formed. According to any embodiment, the distance between the tip of the needle and the surface of the collector can be in the range of 1 cm to 30 cm.

[0030] The method can also include collecting continuous fibers on the collector. The collector can be of various shapes and sizes. Larger sizes can be used to form larger non-woven fiber mats. The collector can be selected from a stationary flat plate, a drum, a mandrel, and a disk. The produced fiber mat can have a thickness ranging from millimeters to nanometers. Without being limited by theory, it is believed that micro or nano fibers can improve the performance of e-textiles by providing an increased surface area and affecting the space between the fibers of the mat. For example, for micro fibers or nano fibers, the amount of spacing and the space size in the mat can be reduced.

[0031] Figure 2This is a schematic diagram of a representative piezoelectric sensor structure 200. In a piezoelectric material, voltage or charge is generated through mechanical stress. A circuit is created by connecting the positive terminal 208, grounded to ground 210, and the negative terminal 212 to the sensor. Piezoelectric material 204 is contained between a top electrode 202 and a bottom electrode 206. Mechanical stress applied to the sensor generates voltage or charge. This effect is reversible (i.e., the piezoelectric material will produce a mechanical action when excited by an electric potential). Conveniently, extremely flexible fabrics with the intelligence to sense touch, force, vibration, flow, tension, and strain are used. Essentially, piezoelectricity works due to the asymmetric arrangement of atoms in a solid crystal. As pressure is applied to the crystal, charge flows through it due to this asymmetry. The charge travels to the surface of the material and is then collected by a conductive layer on either side of the piezoelectric layer.

[0032] Therefore, this disclosure is well adapted to achieve the stated purposes and advantages, as well as those inherent therein. The specific embodiments disclosed above are merely illustrative, as this disclosure can be modified and practiced in different but equivalent ways that will be apparent to those skilled in the art who benefit from the teachings herein. Furthermore, the details of the constructions or designs shown herein are not intended to limit the scope of the disclosure, except as described in the appended claims. Therefore, it will be apparent that the specific illustrative embodiments disclosed above can be altered or modified, and all such changes are considered to be within the scope and spirit of this disclosure.

[0033] As used herein, the terms “comprising,” “having,” “including,” and all their grammatical variations are each intended to have an open, non-restrictive meaning that does not exclude additional elements or steps. While compositions, systems, and methods are described in relation to various components or steps “comprising,” “containing,” or “including,” compositions, systems, and methods may also be described as “consisting substantially of various components and steps” or “consisting of various components and steps.” It should also be understood that, as used herein, “first,” “second,” and “third” are arbitrarily designated and are intended only to distinguish two or more materials, steps, etc., as the case may be, and do not indicate any order. Furthermore, it should be understood that the use of the term “first” alone does not require the existence of any “second,” and the use of the term “second” alone does not require the existence of any “third,” etc.

[0034] Whenever a numerical range with a lower and upper limit is disclosed, any number falling within that range and any included range are specifically disclosed. In particular, the range of each value disclosed herein (in the form of “from about a to about b,” or equivalently “from about a to b,” or equivalently “from about ab”) should be understood to describe each number and range contained within a wider range of values. Furthermore, unless otherwise expressly and clearly defined by the patentee, the terms in the claims have their ordinary, common meaning. Additionally, the indefinite articles “a” or “an” used in the claims are defined herein as referring to one or more elements introduced therein. If the use of words or terms in this specification conflicts in any way with one or more patents or other documents that may be incorporated herein by reference, the definitions consistent with this specification shall prevail.

Claims

1. A method for producing piezoelectric fabrics, comprising: The continuous fibers forming the material include: A fluid is passed through the needle, wherein the fluid comprises: olefin copolymers; Basic fluids; and Multiple piezoelectric ceramic particles, The base fluid dissolves the olefin copolymer; and A voltage is applied during fluid flow to generate an electric field between the tip of the needle and the collector; and The continuous fiber is collected on this collector.

2. The method of claim 1, wherein the piezoelectric fabric is nonwoven.

3. The method according to claim 1 or claim 2, wherein the olefin copolymer comprises ethylene and octene.

4. The method according to any one of the preceding claims, wherein the olefin copolymer has a molecular weight in the range of 10,000 g / mol to 100,000 g / mol.

5. The method according to any one of the preceding claims, wherein the concentration of the olefin copolymer is in the range of 1 to 99.9% by weight of the base fluid.

6. The method according to any one of the preceding claims, wherein the base fluid has a surface tension in the range of 11 mN / m to 85 mN / m at 20°C.

7. The method according to any one of the preceding claims, wherein the base fluid has a conductivity in the range of 5 μS / cm to 5 S / m at 20°C.

8. The method according to any one of the preceding claims, wherein the base fluid is a heterogeneous fluid comprising: a continuous phase comprising the base fluid and a polymer solution; and an internal phase comprising dispersed piezoelectric ceramic particles.

9. The method according to any one of the preceding claims, wherein the concentration of the piezoelectric ceramic particles is in the range of 0.01 to 99% by weight of the base fluid.

10. The method according to any one of the preceding claims, wherein the piezoelectric ceramic particles are selected from the group consisting of: lead zirconate titanate (PZT), hydroxyapatite, apatite, lithium sulfate monohydrate, sodium bismuth titanate, quartz, tartaric acid fiber, poly(vinylidene fluoride) fiber, barium titanate, lithium-doped potassium sodium niobate (KNLN), potassium sodium niobate (KNN), and combinations thereof.

11. A piezoelectric fabric comprising: A nonwoven continuous fiber mat comprising: olefin copolymer polymers; and Multiple piezoelectric ceramic particles, For an 8 N force event, the piezoelectric fabric has an average charge output of at least 6 nC.

12. The piezoelectric fabric of claim 11, wherein the olefin copolymer comprises ethylene and octene.

13. The piezoelectric fabric of claim 11, wherein the olefin copolymer has a molecular weight in the range of 10,000 g / mol to 100,000 g / mol.

14. The piezoelectric fabric according to claim 11, wherein the plurality of piezoelectric ceramic particles are selected from the group consisting of: lead zirconate titanate (PZT), hydroxyapatite, apatite, lithium sulfate monohydrate, sodium bismuth titanate, quartz, tartaric acid fiber, poly(vinylidene fluoride) fiber, barium titanate, lithium-doped potassium sodium niobate (KNLN), potassium sodium niobate (KNN), and combinations thereof.

15. The piezoelectric fabric of claim 11, wherein the plurality of piezoelectric ceramic particles have an average particle size in the range of 20 nanometers to 100 micrometers.

16. The piezoelectric fabric of claim 11, wherein the piezoelectric fabric is thermally stable at a maximum of 140°C.

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