U.S. patent application number 15/802673 was filed with the patent office on 2018-05-24 for electrospinning of fluoropolymers.
The applicant listed for this patent is Honeywell International Inc.. Invention is credited to Cheryl L. Cantlon, Changqing Lu, David Nalewajek, Andrew J. Poss, Shiming Wo.
Application Number | 20180142379 15/802673 |
Document ID | / |
Family ID | 62144328 |
Filed Date | 2018-05-24 |
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: |
62144328 |
Appl. No.: |
15/802673 |
Filed: |
November 3, 2017 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
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62424128 |
Nov 18, 2016 |
|
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Current U.S.
Class: |
1/1 |
Current CPC
Class: |
D10B 2321/042 20130101;
D04H 1/728 20130101; D01F 6/12 20130101; D06M 10/10 20130101; D01F
6/32 20130101; D01D 5/003 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.
* * * * *