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United States Patent Application 20180142379
Kind Code A1
Poss; Andrew J. ;   et al. May 24, 2018

ELECTROSPINNING OF FLUOROPOLYMERS

Abstract

Fibers and methods of producing fibers comprising fluorinated polymers having comonomers of tetrafluoropropene are provided. Methods may include providing a solution having a fluorinated polymer dissolved in a solvent, wherein at least one monomer of the polymer comprises a tetrafluoropropene, exposing the solution to an electrostatic field between the solution and a collection electrode, and forming fibers from the solution fluorinated polymer. Fibers may include a fluorinated polymer, wherein at least one of the monomers of the fluorinated polymer comprises tetrafluoropropene.


Inventors: Poss; Andrew J.; (Kenmore, NY) ; Nalewajek; David; (West Seneca, NY) ; Cantlon; Cheryl L.; (Clarence Center, NY) ; Lu; Changqing; (Snyder, NY) ; Wo; Shiming; (Monroe Township, NJ)
Applicant:
Name City State Country Type

Honeywell International Inc.

Morris Plains

NJ

US
Family ID: 1000002995738
Appl. No.: 15/802673
Filed: November 3, 2017


Related U.S. Patent Documents

Application NumberFiling DatePatent Number
62424128Nov 18, 2016

Current U.S. Class: 1/1
Current CPC Class: D01D 5/003 20130101; D01F 6/12 20130101; D01F 6/32 20130101; D04H 1/728 20130101; D06M 10/10 20130101; D10B 2321/042 20130101
International Class: D01D 5/00 20060101 D01D005/00; D01F 6/12 20060101 D01F006/12; D01F 6/32 20060101 D01F006/32; D04H 1/728 20060101 D04H001/728; D06M 10/10 20060101 D06M010/10

Claims



1. A method for producing fibers comprising: providing a solution having a fluorinated polymer dissolved in a solvent, wherein at least one monomer of the polymer comprises a tetrafluoropropene; exposing the solution to an electrostatic field between the solvent and a collection electrode; and forming fibers from the dissolved fluorinated polymer.

2. The method of claim 1, wherein the tetrafluoropropene is 1,3,3,3-tetrafluoropropene, 2,3,3,3-tetrafluoropropene, or mixtures thereof.

3. The method of claim 1, wherein the fluorinated polymer comprises at least one comonomer, wherein the comonomer is a vinylidene fluoride.

4. The method of claim 3, wherein the vinylidene fluoride is polyvinylidene fluoride.

5. The method of claim 1, wherein the solvent is at least one of acetones, ketones, low-molecular weight alcohols, polar aprotic solvents, chloroform, or mixtures thereof.

6. The method of claim 5, wherein the polar aprotic solvents include at least one of dimethylformamide, dimethylacetamide, N-methylpyrrolidone, ethyl acetate, tetrahydrofuran, dimethyl sulfoxide, acetonitrile, or mixtures thereof.

7. The method of claim 5, wherein the low-molecular weight alcohol includes at least one of ethanols, methanols, or mixtures thereof.

8. The method of claim 3, wherein the fluorinated copolymer has a molar ratio of tetrafluoropropene to vinylidene fluoride of about 5:95 to about 95:5.

9. The method of claim 8, wherein the fluorinated copolymer has a molar ratio of tetrafluoropropene to vinylidene fluoride of about 70:30 to about 90:10.

10. The method of claim 1, wherein the fibers are nanofibers.

11. The method of claim 1, wherein the fibers have a diameter between about 50 nanometers and about 10 microns.

12. The method of claim 1, further comprising gathering the fibers to form a nonwoven.

13. A fiber produced by the method of claim 1.

14. The method of claim 1, wherein the exposing the solution to an electrostatic field between the solvent and a collection electrode is electrospinning.

15. The method of claim 1, further comprising polymerizing a plurality of monomers into a polymer, wherein at least one monomer is a tetrafluoropropene.

16. A fiber comprising a fluorinated polymer, wherein at least one of the monomers of the fluorinated polymer comprises tetrafluoropropene.

17. The fiber of claim 16, wherein the tetrafluoropropene is 1,3,3,3-tetrafluoropropene, 2,3,3,3-tetrafluoropropene, or mixtures thereof.

18. The fiber of claim 16, wherein the fluorinated polymer is a copolymer of tetrafluoropropene and vinylidene fluoride having a molar ratio of tetrafluoropropene to vinylidene fluoride of about 5:95 to about 95:5.

19. The fiber of claim 18, wherein the vinylidene fluoride is polyvinylidene fluoride.

20. The fiber of claim 16, wherein the polymer has a viscosity molecular weight between about 30,000 to about 1,500,000 as measured by gel phase chromatography.
Description



CROSS REFERENCE TO RELATED APPLICATIONS

[0001] This application claims the benefit under Title 35, U.S.C. .sctn. 119(e) of U.S. Provisional Patent Application Ser. No. 62/424,128, entitled ELECTROSPINNING OF FLUOROPOLYMERS, filed on Nov. 18, 2016, the entire disclosure of which is expressly incorporated herein.

FIELD

[0002] The present disclosure relates generally to fibers and methods of producing fibers of fluorinated polymers formed from monomers or comonomers of tetrafluoropropene. The present disclosure also provides fiber materials, such as membranes, fabrics, and mats made from the aforementioned fibers.

BACKGROUND

[0003] Electrospinning is used to produce small diameter continuous fibers, for example, fibers below about 25 microns in size. In the electrospinning process, a charge of about 5 kV to about 30 kV (e.g., about 10 kV to about 20 kV) is applied by an electrode to a polymer solution. The charged polymer solution is separated at a defined distance from a collector, which is also charged with an opposite polarity to the electrode. In this manner, a static electric field is established between the charged polymer solution and the collector to form a Taylor Cone from the charged polymer which is ejected from a nozzle.

[0004] The Taylor Cone forms due to the competing forces of the static electric field and the polymer solution's surface tension. If the concentration of the polymer in solution is sufficiently high to cause molecular chain entanglement, a fiber is drawn from the tip of the Taylor cone onto the collector. The charged polymer solution is usually ejected from a nozzle of a spinneret to form a jet which is deposited onto the oppositely charged collector. While the jet travels from the nozzle to the collector, the solvent of the polymer solution evaporates, and a polymer fiber accumulates on the collector. The charge on the fibers then dissipates (e.g., evaporates) into the surrounding environment. Often, fibers produced by this technique have a diameter between about 50 nanometers to about 10 microns.

[0005] Electrospinning was first introduced in U.S. Pat. No. 1,975,504, which issued to Anton Formhals of Germany on Oct. 2, 1934. Formhals concentrated his efforts on using an electrical field in combination with a movable spool collection device to create a supply of relatively parallel, silk-like threads. Subsequent efforts by Formhals, such as those described in U.S. Pat. No. 2,160,962, were directed toward increasing the distance between the solution feeding device and the collecting electrode such that the threads are completely dry when collected and, thus, do not stick to each other.

[0006] Electrospinning did not become a viable manufacturing method for decades following Formhals's efforts because it failed to yield sufficient quantities of material, the output was inconsistent and of low quality, and the technological needs were insufficient to drive serious development of the process.

[0007] Fluoropolymers possess excellent properties such as outstanding chemical resistance, weather stability, low surface energy, low coefficient of friction, and low dielectric constant. These properties are derived from the special electronic structure of the fluorine atom, the stable carbon-fluorine covalent bonding, and the unique intramolecular and intermolecular interactions between the fluorinated polymer segments and the main chains. Due to their special chemical and physical properties, fluoropolymers have found many applications in building, automotive and petrochemical industries, microelectronics, aeronautics, aerospace, optics and for the treatment of textile, paper and stone.

[0008] However, fluorinated polymers are extremely difficult to process via electrospinning to form electrospun fibers, partially due to their solubility properties in most organic solvents, especially those solvents with the dipole moment needed to respond to an applied field. Thus, viable methods for electrospinning fluorinated polymers are desired.

SUMMARY

[0009] The present disclosure provides electrospun fibers including tetrafluoropropene and methods of electrospinning fibers from polymers (e.g., homopolymers or copolymers) having tetrafluoropropene. Advantageously, these fluoropolymers possess excellent properties such as outstanding chemical resistance, weather stability, low surface energy, low coefficient of friction, and low dielectric constant, which in turn allow their electrospun fibers to have many of these same properties and, thus, may find uses in applications such as membranes in distillation and air filtration.

[0010] According to various aspects of this disclosure, methods for producing fibers may include providing a solution having a fluorinated polymer dissolved in a solvent. The polymer dissolved in the solvent may have at least one monomer that is a tetrafluoropropene. Then the solution may be exposed to an electrostatic field between the solvent and a collection electrode and, thus, forming fibers from the dissolved fluorinated polymer.

[0011] The tetrafluoropropene contained in the polymer is not particularly limited and in various aspects may be 1,3,3,3-tetrafluoropropene, 2,3,3,3-tetrafluoropropene, or mixtures thereof. Furthermore, in some aspects or embodiments, the fluorinated polymer may include at least one comonomer, such as vinylidene fluoride (e.g., polyvinylidene fluoride). In some aspects, the fluoropolymer itself may be provided, in other embodiments, the method may include first polymerizing a plurality of monomers into a polymer, wherein at least one monomer is a tetrafluoropropene. The fluorinated copolymer may have a molar ratio of tetrafluoropropene to vinylidene fluoride of about 5:95 to about 95:5, or a molar ratio of tetrafluoropropene to vinylidene fluoride of about 70:30 to about 90:10.

[0012] Various solvents may be used in the various embodiments disclosed herein. Such solvents may include acetones, ketones, low-molecular weight alcohols, polar aprotic solvents, chloroform, or mixtures thereof. Exemplary polar aprotic solvents include at least one of dimethylformamide, dimethylacetamide, N-methylpyrrolidone, ethyl acetate, tetrahydrofuran, dimethyl sulfoxide, acetonitrile, or mixtures thereof. Exemplary low-molecular weight alcohol includes at least one of ethanols, methanols, or mixtures thereof.

[0013] The fibers produced by the methods disclosed herein may include fibers having a diameter between about 50 nanometers and about 10 microns. Thus, the fibers produced by the various methods disclosed herein may include nanofibers, which may be understood to be fibers with a diameter of less than 1,000 nm. Such fibers may be gathered to form a nonwoven.

[0014] Thus, the fibers disclosed herein are fibers that include a fluorinated polymer, wherein at least one of the monomers of the fluorinated polymer comprises tetrafluoropropene. The tetrafluoropropene may be 1,3,3,3-tetrafluoropropene, 2,3,3,3-tetrafluoropropene, or mixtures thereof in various embodiments. While the fluorinated polymer may be a homopolymer, it some aspects, the fluorinated polymer may be a copolymer, such as vinylidene fluoride (e.g., polyvinylidene fluoride).

[0015] In various aspects in which the fluoropolymer is a copolymer, the fluorinated copolymer may have a molar ratio of tetrafluoropropene to vinylidene fluoride of about 5:95 to about 95:5. The polymer may have a viscosity molecular weight between about 30,000 to about 1,500,000 as measured by gel phase chromatography.

[0016] The fibers produced herein may also include dopants and may be used to form nonwoven articles, such as mats and/or membranes. Suitable uses for such membranes include molecular distillation and air filtration.

BRIEF DESCRIPTION OF THE DRAWINGS

[0017] The above mentioned and other features of the invention, and the manner of attaining them, will become more apparent and the invention itself will be better understood by reference to the following description of embodiments of the invention taken in conjunction with the accompanying drawings.

[0018] FIG. 1 illustrates an exemplary schematic for an electrospinning apparatus;

[0019] FIG. 2 illustrates an exemplary schematic for an electrospinning apparatus having a roller according to an aspect of this disclosure; and

[0020] FIG. 3 is a flow diagram of an exemplary method for producing nanofibers having fluorinated polymers that have comonomers of tetrafluoropropene.

[0021] Corresponding reference characters indicate corresponding parts throughout the several views. The exemplifications set out herein illustrate exemplary embodiments of the invention and such exemplifications are not to be construed as limiting the scope of the invention in any manner.

DETAILED DESCRIPTION

[0022] As briefly described above, this disclosure provides a method for production of fibers, such as nanofibers, from fluorinated polymers and copolymers including monomers or comonomers of tetrafluoropropene through electrostatic spinning. The disclosure also provides methods of use of such fibers, such as with mats or membranes made from the fibers in various applications such as molecular distillation, or air filters, for example.

[0023] As used herein, the modifier "about" used in connection with a quantity is inclusive of the stated value and has the meaning dictated by the context (for example, it includes at least the degree of error associated with the measurement of the particular quantity). When used in the context of a range, the modifier "about" should also be considered as disclosing the range defined by the absolute values of the two endpoints. For example, the range "from about 2 to about 4" also discloses the range "from 2 to 4."

[0024] Environmental concerns, such as global climate change and ozone depletion has led to the development of various new monomers, comonomers, and polymers to address such issues.

[0025] Recently, however, one-dimensional (1D) nanostructured organic materials have gained a growing scientific, technological, and industrial interest, with possible applications spreading in different fields such as air and water filtration, drug delivery, tissue engineering and regenerative medicine, besides many others involving active materials for photonics or electronics. Electrospinning offers a unique technology, not only for its unequalled operational simplicity, but also because it can be effectively scaled up, opening practical applications in industrial production.

[0026] In 2011 Honeywell Fluorine Products, a division of Honeywell International Inc., a Delaware corporation, announced the launch of the SOLSTICE.TM. brand for its family of low-global-warming-potential materials. The SOLSTICE.TM. brand reflected the products' break-through environmental properties, including their insulating capabilities for foam and their superior cooling capabilities for automotive air conditioning and refrigerant applications. The SOLSTICE.TM. hydrofluoro-olefins (HFOs) can also be used as monomers for the preparation of fluoropolymers. For example, fluoropolymers have been made from HFO-1234yf and HFO-1234ze, such as those described in U.S. patent application Ser. No. 13/645,437 entitled POLYMERIZATION OF 2,3,3,3-TETRAFLUOROPROPENE AND POLYMERS FORMED FROM 2,3,3,3-TETRAFLUOROPROPENE. These HFO materials may also form copolymers with vinylidene difluoride (VDF), and these copolymers have shown unusual solubility in standard organic solvents. A homopolymer can also be made from HFO-1234yf which also has good solubility properties in standard organic solvents.

[0027] Tetrafluoropropenes have been found to be suitable solutions to many of the aforementioned issues in various applications, such as those disclosed in U.S. Pat. No. 8,008,244 entitled COMPOSITIONS OF TETRAFLUOROPROPENE AND HYDROCARBONS, the entire disclosure of which is incorporated by reference in its entirety herein.

[0028] For example, the polymerization of trans-1,3,3,3-tetrafluoroprop-1-ene (or "trans-HFO-1234ze"), which is described in U.S. patent application Publication Ser. No. 13/801,474, POLYMERIZATION OF MONOMERS USING FLUORINATED PROPYLENE SOLVENTS, the entire disclosure of which is incorporated by reference in its entirety herein, may help to resolve some of the aforementioned issues because trans-1,3,3,3-tetrafluoroprop-1-ene has zero ozone depletion potential (ODP), and a global warming potential (GWP) of 6, which is very low. The toxicity and flammability of hydrofluorocarbons and hydrofluoro-olefins is also of potential concern. Hydrofluoro-olefins, in particular, are often toxic and flammable; however, tetrafluoropropenes also address this toxicity issue. For example, trans-HFO-1234ze is both non-toxic and is not highly flammable. Additionally, trans-HFO-1234ze, can reduce the flammability of some monomers (e.g., isobutylene) when used in combination with those monomers.

[0029] Similarly, the polymerization of 2,3,3,3-Tetrafluoropropene (also known as "1234yf" or "HFO-1234yf") is described in U.S. patent application Ser. No. 13/645,437, entitled POLYMERIZATION OF 2,3,3,3-TETRAFLUOROPROPENE AND POLYMERS FORMED FROM 2,3,3,3-TETRAFLUOROPROPENE, and is hereby incorporated by reference in its entirety, may also help to resolve some of the aforementioned issues.

[0030] Two general types of parameters affect the morphology of electrospun fibers: system parameters and process parameters. System parameters may be understood to include the types of polymer, the types of solvent, viscosity, conductivity, and surface tension of the polymer, while process parameters may be understood to include electric potential, flow rate, polymer concentration, distance between the capillary and collection screen, temperature, humidity, and air velocity in the electrospinning chamber. Adjusting these parameters may result in electrospun fibers with various hydrophobic and super hydrophobic surface properties.

[0031] While many polymers and their blends may be electrospun in different solvents, solvents and solvent blends may vary depending on the monomers, comonomers, polymers, and/or copolymers used. For example, in some aspects it may be desirable for the polymer used in electrospinning to have a moderate molecular weight to make the process easier. If the molecular weight is too high, then electrospinning may be either impossible or may result in large-diameter fibers when small-diameter or nanofibers are desired. On the other hand, if the molecular weight is low, then various pores and beads will form on the surface of the fibers. The solvent should be such that it dissolves the polymer easily and completely and is less harmful.

[0032] Viscosity may also play a major role in electrospinning and may have a significant influence on the diameters of electrospun fibers. A high viscosity may result in large-diameter fibers. Pores and beaded structures are less likely to be formed when the viscosity is high. In various aspects of this disclosure, the viscosity (which may be determined by a conventional rotation viscometer) of the solution containing the solvent and the polymer(s) may be as low as 200 Cp, 250 Cp, and 500 Cp, as high as 500 Cp, 1,000 Cp, 2,000 Cp, or may be within any range defined by any two of the foregoing values, such as between about 200 Cp to about 2,000 Cp, for example.

[0033] Higher electrical conductivity may also have significant influence on the fiber diameter. In general, smaller diameter fibers can be produced from fluoropolymer solutions having a relatively higher electrical charge. By reducing the surface tension of the polymeric solution, the resulting fibers may be mostly free of beads.

[0034] Different solvents may result in different surface tensions of solutions. However, a low surface tension solvent is not always suitable for electrospinning even though in various processes, low surface tension solution may help the electrospinning process to perform better at a low electrostatic field. Thus, the selection of the polymer, copolymers, and solvent must carefully be considered when electrospinning. In various aspects, the surface tension (which may be determined with a conventional digital automatic tension meter) may be as little as about 20 J/m.sup.2, 25 J/m.sup.2, 30 J/m.sup.2, as high as about 45 J/m.sup.2, 50 J/m.sup.2, 55 J/m.sup.2, or within any range defined by any two of the foregoing values, such as between about 20 J/m.sup.2 and about 55 J/m.sup.2, for example.

[0035] FIGS. 1 and 2 illustrate various electrospinning apparatuses capable of performing the various methods of electrospinning disclosed herein. FIG. 1 illustrates electrospinning system 1 with controller 20. Controller 20 may direct a solution having a fluorinated polymer dissolved in a solvent, wherein at least one monomer of the polymer comprises a tetrafluoropropene, from tank 2 through pump 4 and into syringe 6. Pump 4 is not particularly limited and may include a suitable pump for transporting the solution containing the convent and polymers. In some aspects, it may be desirable to have pumps that provide a flow rate into syringe 6 as little as about 0.1 ml/h, 0.3 ml/h, 0.5 ml/h, or as high as 1 ml/h, 3 ml/h, 5 ml/h, or within any range defined by any two of the foregoing values, such as about 0.1 ml/h to about 5 ml/h, for example.

[0036] Syringe 6 may include a nozzle 8 which may have needle 10 in electrical communication with controller 20. The needle is not particularly limited and may include needles having an internal diameter as small as about 0.5 mm, 0.8 mm, and as large as about 1 mm, 1.5 mm, 2 mm, or within any range defined by any two of the foregoing values, such as between about 0.5 mm and 2 mm, for example. In various aspects, controller 20 may be configured to provide a high voltage to needle 10 (via needle circuit 18) and to the grounded plate 14 (via collection circuit 17), which may be grounded via ground 16. As the solution passes through the needle 10, it is spun into a fiber 12 and is collected on the grounded plate 14.

[0037] Similar to exemplary electrospinning system 1 illustrated in FIG. 1, FIG. 2 illustrates an exemplary electrospinning roller system. Electrospinning roller system 3 may comprise a very similar setup to system 1 of FIG. 1, but instead of grounded plate 14, electrospinning roller system 3 may comprise a grounded roller 15, which may spin (exemplified by axial rotational direction 13) as fiber 12 is being spun.

[0038] Thus, various methods for producing fibers with varying systems are disclosed herein. FIG. 3 illustrates a flow chart of an exemplary method 30 of producing electrospun fibers. Method 30 may include a first step (step 31) of providing a solution having a fluorinated polymer dissolved in a solvent (e.g., in storage tank 2), wherein at least one monomer of the polymer comprises a tetrafluoropropene. The solution may then be exposed to an electrostatic field (step 33) between the solvent and a collection electrode (e.g., grounded plate 14 or grounded roller 15. Finally, fibers may be formed from the solution containing the dissolved fluorinated polymer on the collection electrode, illustrated as step 35.

[0039] As many of skill in the art with the benefit and aid of this disclosure will recognize, when a sufficiently high voltage is applied to a liquid droplet of the solution (e.g., a droplet leaving needle 10), the body of the liquid becomes charged, and electrostatic repulsion counteracts the surface tension and the droplet is stretched. At a critical point, a stream of liquid will then erupts from the surface. This point of eruption is known as the Taylor cone. If the molecular cohesion of the liquid is sufficiently high, stream breakup does not occur and a charged liquid jet is formed. If the molecular cohesion of the liquid is relatively low, droplets of the fluoropolymer are electrosprayed.

[0040] The fiber diameter decreases as it progresses to the target because of the evaporation of the solvent from the fiber and continuous stretching of the fiber by electrostatic forces acting on the polymeric molecules. The fiber diameter decreases as the applied electrical potential increases. The morphology of fibers may be affected by the flow rate of the solution. Typically, in various aspects a higher flow rate will likely produce fibers with various levels of beads and pores.

[0041] The tetrafluoropropene polymers disclosed herein are not particularly limited and may include 1,3,3,3-tetrafluoropropene, 2,3,3,3-tetrafluoropropene, or mixtures thereof. In various aspects of this disclosure, homopolymers or copolymers, where at least one polymer of tetrafluoropropene are used, may be electrospun into fibers. For example, in some aspects, 2,3,3,3-Tetrafluoropropene may be a homopolymer dissolved in a solution. In other aspects, copolymers, such as copolymers having comonomer such as vinylidene fluoride (e.g., polyvinylidene fluoride), may be used. For example, in some aspects, the fluorinated copolymer may have a molar ratio of tetrafluoropropene to vinylidene fluoride as little as about 5:95, 25:95, 70:30, and as great as about 80:20, 90:10, 95:5, or within any range defined by any two of the foregoing values, such as about 25:95 to about 95:5, for example.

[0042] Solvents must be carefully selected depending on the application, manufacturing conditions, and polymers used. Suitable solvents for tetrafluoropropene polymers include acetones, ketones, low-molecular weight alcohols, polar aprotic solvents, chloroform, or mixtures thereof.

[0043] As used herein, the term "low-molecular weight alcohols" may include alcohols with boiling points below about 90.degree. C. (at atmospheric pressure at sea level). Thus, exemplary "low-molecular weight alcohols" is understood to include methanol, ethanol, and mixtures thereof.

[0044] Exemplary polar aprotic solvents include at least one of dimethylformamide, dimethylacetamide, N-methylpyrrolidone, ethyl acetate, tetrahydrofuran, dimethyl sulfoxide, acetonitrile, or mixtures thereof.

[0045] In some aspects therefore, the polymer/solvent concentration may be comprised between minimum and maximum levels. If the polymer concentration is too high, then a beaded structure may result. The diameter of electrospun fibers increases as the polymer concentration increases. The shape of the beaded structure changes from spherical to spindle, when the polymer concentration increases. For example, in some aspects, the polymer concentration may be as little as about 5%, 7%, 10% and as great as about 15%, 20%, 25%, or within any range defined by any two of the foregoing values, such as about 5% to about 25%, for example.

[0046] Molecular weight may also greatly influence rheological properties of a polymeric solution. It was observed that low-molecular weight solutions produced beads and pores rather than fine fibers, while high-molecular weight solutions produce fibers with larger diameters. For example, in various aspects, viscosity molecular weight may be between about 30,000 to about 1,500,000 as measured by gel phase chromatography.

[0047] The fiber diameter may be reduced as the distance between the capillary and the collection screen increases. When this distance is too small, the jet may not have enough time to experience plastic stretching, thereby possibly producing larger and beaded fibers. At larger distances between the capillary and the collection screen, the jet may have enough time to undergo plastic stretching, thus leading to finer fibers with a reduced bead density. Thus, various methods disclosed herein may be configured to produce fibers that have a diameter that are about 50 nanometers to about 10 microns. In some aspects, various methods may produce fibers that are nanofibers.

[0048] Such fibers may include other functional groups or dopants (e.g., catalysts) depending on application. The fibers may also be formed into a nonwoven. For example, the nonwoven may be formed from layering or piling nanofibers. As one of ordinary skill in the art would recognize with the benefit of this disclosure, the aligning of the fibers to form the nonwoven may be altered depending on the application. Moreover, the thickness of the nonwoven (e.g., a mat) may be adjusted depending on application, for example, a thicker mat may be produced by electrospinning for a longer duration.

[0049] Also, the fibers may form a membrane, such as membranes use in molecular distillation, which is a process of separation, purification, and concentration of natural products, such as desalination of water from sea water. Without being limited to any theory, this is believed to be possible because layers of nanofibers produced through electrostatic spinning of fluorinated polymer or copolymer have advantageous properties, as such, nanofibrous layers that are permeable to water vapor, but at the same time it is hydrophobic, thus non-permeable for liquid water.

[0050] While electrospinning processes are generally carried out at room temperature under normal conditions, at high-temperature electrospinning, the evaporation rate of the solvent increases, thus leading to fibers with larger diameters. In some aspects, a higher temperature may change the solution viscosity may have an adverse effect on the fiber diameter as well. While tetrafluoropropene may be electrospun at temperatures as high as about 250.degree. C., in various aspects, the temperature may be as low as about 10.degree. C., 15.degree. C., 18.degree. C., as high as about 25.degree. C., 30.degree. C., 50.degree. C., 100.degree. C. or within any range defined by any two of the foregoing values, such as between about 10.degree. C. to about 100.degree. C., for example.

[0051] Without being limited to any theory, it is believed that relative humidity may also affect various electrospinning processes. High relative humidity during electrospinning may lead to the formation of microscale and nanoscale pores on the fiber surface. Evaporation of the solvent may cool down the jet surface, resulting in the condensation of moisture present in the air, thus leading to imprints in the form of pores on the surface of fibers. High humidity can increase or decrease fiber diameter depending upon the types of polymers used in the electrospinning process. The presence of high moisture contents in the surroundings prohibits evaporation and affects the morphology of the fiber surface. High airflow tends to increase the evaporation rate as the result of natural convection, thus leading to a larger fiber diameter. Thus, in various aspects, the humidity may be greater than about 0%, 10%, 20%, or less than about 60%, 50%, 40%, or within any range defined by any two of the foregoing values, such as about 0% to about 60% relative humidity. While the aforementioned relative humidity values are preferred, in some aspects of this disclosure, some methods and aspects may include electrospinning at higher temperatures and greater relative humidity, such as around 250.degree. C. and 100% relative humidity.

[0052] Below are various examples of methods of producing electrospun fibers from tetrafluoropropene. As used herein, the term "1234yf" or "HFO-1234yf" may be understood to be 2,3,3,3-Tetrafluoropropene, which is a hydrofluoro-olefin (HFO) with the formula CH.sub.2.dbd.CFCF.sub.3. Also, the term "1234ze" or "HFO-1234ze" may be understood to be 1,3,3,3-Tetrafluoropropene. Both HFO-1234yf and HFO1234ze are commercially available from the Honeywell International Inc., a Delaware corporation.

EXAMPLES

[0053] The electrospinning setup consisted of a plastic syringe and a steel needle in an INOVENSO.TM. Ne100, a commercially available electrospinning device available from Inovenso Ltd. Co., a Turkish corporation. The needle was connected to a high-voltage power supply. The electrospun fibers were deposited on an aluminum sheet, such as that exemplified in FIG. 1.

Example 1

[0054] A copolymer having about a 70:30 molar ratio of 1234yf to vinylidene difluoride (VDF) was prepared. The polymer was then dissolved in ethyl acetate having a concentration of 15 wt %. The fibers were spun with a needle that had a gauge of 20 (about 0.9081 mm) and a voltage of 20 kV was applied to the needle. The pump produced a flow rate of 2 m L/hr to the aluminum sheet (collector plate) that was 20 cm from the distal end of the needle. The environmental temperature was between 22.degree. C. and 25.degree. C. and had a relative humidity of 25%.

Example 2

[0055] A copolymer having about a 90:10 molar ratio of 1234ze to VDF was prepared. The polymer was then dissolved in ethyl acetate having a concentration of 15 wt %. The fibers were spun with a needle that had a gauge of 18 (about 1.270 mm) and a voltage of 20 kV was applied to the needle. The pump produced a flow rate of 2 m L/hr to the aluminum sheet (collector plate) that was 22 cm from the distal end of the needle. The environmental temperature was between 22.degree. C. and 25.degree. C. and had a relative humidity of 22%-25%.

Example 3

[0056] A homopolymer of 1234yf was prepared. The polymer was then dissolved in tetrahydrofuran having a concentration of 45 wt %. The fibers were spun with a needle that had a gauge of 20 (about 0.9081 mm) and a voltage of 50 kV was applied to the needle. The pump produced a flow rate of 5 mL/hr to the aluminum sheet (collector plate) that was 22 cm from the distal end of the needle. The environmental temperature was between 22.degree. C. and 25.degree. C. and had a relative humidity of 25%.

[0057] The morphology and microstructures of the electrospun nanofibers were determined using a scanning electron microscope. The dimensions of the fibers produced were as follows:

TABLE-US-00001 TABLE 1 1234yf:VDF 1234ze:VDF 1234yf Homopolymer Dimensions 3.3 .+-. 1.1 .mu.m 1.2 .+-. 0.2 .mu.m 1.6 .+-. 0.5 .mu.m

[0058] It was found that such fibers with the aforementioned dimensions were suitable for various applications, such as molecular distillation.

[0059] As used herein, the singular forms "a", "an" and "the" include plural unless the context clearly dictates otherwise. Moreover, when an amount, concentration, or other value or parameter is given as either a range, preferred range, or a list of upper preferable values and lower preferable values, this is to be understood as specifically disclosing all ranges formed from any pair of any upper range limit or preferred value and any lower range limit or preferred value, regardless of whether ranges are separately disclosed. Where a range of numerical values is recited herein, unless otherwise stated, the range is intended to include the endpoints thereof, and all integers and fractions within the range.

[0060] From the foregoing, it will be appreciated that although specific examples have been described herein for purposes of illustration, various modifications may be made without deviating from the spirit or scope of this disclosure. It is therefore intended that the foregoing detailed description be regarded as illustrative rather than limiting, and that it be understood that it is the following claims, including all equivalents, that are intended to particularly point out and distinctly claim the claimed subject matter.

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