U.S. patent application number 13/061232 was filed with the patent office on 2011-07-07 for article formed from electrospinning a dispersion.
This patent application is currently assigned to DOW CORNING CORPORATION. Invention is credited to Randal M. Hill, Eric J. Joffre, Donald T. Liles, Bonnie J. Ludwig.
Application Number | 20110165811 13/061232 |
Document ID | / |
Family ID | 41631762 |
Filed Date | 2011-07-07 |
United States Patent
Application |
20110165811 |
Kind Code |
A1 |
Hill; Randal M. ; et
al. |
July 7, 2011 |
Article Formed From Electrospinning A Dispersion
Abstract
An article of fibers includes a cured compound. The fibers are
formed from electrospinning a dispersion. The dispersion includes a
liquid and a condensation curable compound. A content of the liquid
in the dispersion is reduced such that the condensation curable
compound cures. The article is formed from a method of
manufacturing which includes the step of forming the dispersion.
The method also includes the step of electro spinning the
dispersion to reduce the content of the liquid such that the
condensation curable compound cures.
Inventors: |
Hill; Randal M.; (Cambridge,
MA) ; Joffre; Eric J.; (Midland, MI) ; Liles;
Donald T.; (Midland, MI) ; Ludwig; Bonnie J.;
(Midland, MI) |
Assignee: |
DOW CORNING CORPORATION
Midland
MI
|
Family ID: |
41631762 |
Appl. No.: |
13/061232 |
Filed: |
August 28, 2009 |
PCT Filed: |
August 28, 2009 |
PCT NO: |
PCT/US2009/055386 |
371 Date: |
February 28, 2011 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
61092979 |
Aug 29, 2008 |
|
|
|
Current U.S.
Class: |
442/401 ;
264/465 |
Current CPC
Class: |
Y10T 442/681 20150401;
D01D 5/38 20130101; D01D 5/0038 20130101 |
Class at
Publication: |
442/401 ;
264/465 |
International
Class: |
D01D 5/38 20060101
D01D005/38; D01D 5/00 20060101 D01D005/00; D04H 3/16 20060101
D04H003/16 |
Claims
1. A method of manufacturing an article comprising fibers formed
from a dispersion, said method comprising the steps of: A. forming
the dispersion comprising; (i) a liquid, and (ii) a condensation
curable silicone rubber, and B. electrospinning the dispersion to
reduce a content of the liquid such that the condensation curable
silicone rubber cures via condensation.
2. A method as set forth in claim 1 wherein the dispersion further
comprises a surfactant.
3. A method as set forth in claim 2 wherein the surfactant is
combined with the liquid before the dispersion is formed.
4. A method as set forth in claim 2 wherein the surfactant is
present in the dispersion in an amount of from 0.5 to 5 percent by
weight based on a weight of the condensation curable compound.
5. A method as set forth in claim 1 wherein the dispersion further
comprises a thickener.
6. A method as set forth in claim 5 wherein the thickener is
further defined as polyethylene oxide.
7. A method as set forth in claim 5 wherein the thickener is
combined with the liquid before the dispersion is formed.
8. A method as set forth in claim 5 wherein the thickener is
present in the dispersion in an amount of from 0.05 to 5 percent by
weight based on a weight of the dispersion.
9. (canceled)
10. (canceled)
11. (canceled)
12. (canceled)
13. A method as set forth in any one of claims 1-8 wherein the
dispersion further comprises a condensation curable organic
compound.
14. A method as set forth in any one of claims 1-8 wherein the
dispersion comprises from 20 to 80 parts by weight of the
condensation curable silicone rubber per 100 parts by weight of the
dispersion so long as a total amount of the dispersion does not
exceed 100 parts by weight.
15. A method as set forth in claim 14 wherein the dispersion
comprises from 20 to 80 parts by weight of the liquid per 100 parts
by weight of the dispersion so long as a total amount of the
dispersion does not exceed 100 parts by weight.
16. A method as set forth in any one of claims 1-8 wherein, the
liquid is further defined as water.
17. A method as set forth in claim 16 wherein the condensation
curable silicone rubber is dispersed in the water.
18. A method as set forth in any one of claims 1-8 further
comprising the step of drying the fibers to further reduce a
content of the liquid such that the condensation curable silicone
rubber.
19. A method as set forth in claim 1 wherein the dispersion
comprises a dispersed phase comprising the condensation curable
silicone rubber and a continuous phase comprising the liquid, a
surfactant, and a thickener.
20. A method as set forth in any one of claims 1-8 wherein the
fibers have a stress of at least 15 psi at break and a strain of at
least 100 percent at break.
21. An article of fibers comprising a cured compound and formed
from electrospinning a dispersion comprising: A. a liquid; and B. a
condensation curable silicone rubber; wherein a content of said
liquid is reduced such that said condensation curable silicone
rubber.
22. An article as set forth in claim 21 wherein said dispersion
further comprises a surfactant.
23. An article as set forth in claim 22 wherein said surfactant is
combined with said liquid before said dispersion is formed.
24. An article as set forth in claim 22 wherein said surfactant is
present in said dispersion in an amount of from 0.5 to 5 percent by
weight based on a weight of said condensation curable silicone
rubber.
25. An article as set forth in claim 21 wherein said dispersion
further comprises a thickener.
26. An article as set forth in claim 25 wherein said thickener is
further defined as polyethylene oxide.
27. An article as set forth in claim 25 wherein said thickener is
combined with said liquid before said dispersion is formed.
28. An article as set forth in claim 25 wherein said thickener is
present in said dispersion in an amount of from 0.05 to 5 percent
by weight based on a weight of said dispersion.
29. (canceled)
30. (canceled)
31. (canceled)
32. (canceled)
33. An article as set forth in any one of claims 21-28 wherein said
dispersion further comprises a condensation curable organic
compound.
34. An article as set forth in any of claims 21-28 wherein said
dispersion comprises from 20 to 80 parts by weight of said
condensation curable silicone rubber per 100 parts by weight of
said dispersion so long as a total amount of said dispersion does
not exceed 100 parts by weight.
35. An article as set forth in claim 34 wherein said dispersion
comprises from 20 to 80 parts by weight of said liquid per 100
parts by weight of said dispersion so long as a total amount of
said dispersion does not exceed 100 parts by weight.
36. An article as set forth in any one of claims 21-28 wherein said
liquid is further defined as water.
37. An article as set forth in claim 21 wherein said dispersion
comprises a dispersed phase comprising said condensation curable
silicone rubber and a continuous phase comprising said liquid, a
surfactant, and a thickener.
38. An article as set forth in claim 37 wherein said condensation
curable silicone rubber comprises a silicone elastomer present in
an amount of from 20 to 80 parts by weight per 100 parts by weight
of said dispersion, said liquid is further defined as water and is
present in an amount of from 20 to 80 parts by weight per 100 parts
by weight of the dispersion, said surfactant comprises
methylaminomethylpropanol present in an amount of from 0.5 to 5
parts by weight per 100 parts by weight of said dispersion, said
thickener is further defined as polyethylene oxide and is present
in an amount of from 0.05 to 5 parts by weight per 100 parts by
weight of said dispersion.
39. An article as set forth in any one of claims 21-28 that is
further defined as a non-woven mat.
40. A method of manufacturing an article comprising fibers formed
from a dispersion, said method comprising the steps of: A. forming
the dispersion comprising; (i) a liquid, and (ii) a condensation
curable silicone rubber, B. electrospinning the dispersion to form
the fibers; and C. curing the condensation curable silicone
rubber.
41. A method as set forth in claim 40 wherein the dispersion
further comprises a surfactant and a thickener.
42. A method as set forth in claim 41 wherein the surfactant is
present in the dispersion in an amount of from 0.5 to 5 percent by
weight based on a weight of the condensation curable silicone
rubber.
43. A method as set forth in claim 41 wherein the thickener is
further defined as polyethylene oxide.
44. A method as set forth in claim 41 wherein the thickener is
present in the dispersion in an amount of from 0.05 to 5 percent by
weight of the dispersion.
45. (canceled)
46. (canceled)
47. (canceled)
48. A method as set forth in any one of claims 40-44 wherein the
dispersion comprises from 20 to 80 parts by weight of the liquid
per 100 parts by weight of the dispersion so long as a total amount
of the dispersion does not exceed 100 parts by weight.
49. A method as set forth in any one of claims 40-44 wherein the
liquid is further defined as water.
50. A method as set forth in claim 49 wherein the condensation
curable silicone rubber.
Description
FIELD OF THE INVENTION
[0001] The present invention generally relates to an article and a
method of manufacturing the article. More specifically, the method
includes forming a dispersion including a liquid and a condensation
curable compound and electrospinning the dispersion to manufacture
the article.
DESCRIPTION OF THE RELATED ART
[0002] The development of fibers having micro- and nano-diameters
is currently the focus of much research and development in
industry, academia, and government. These types of fibers can be
formed from organic and inorganic materials such as polyaniline,
polypyrrole, polyvinylidene, polyacrylonitrile, polyvinyl chloride,
polymethylmethacrylate, polythiophene, and iodine-doped
polyacetylene. Fibers of this type have also been formed from
hydrophilic biopolymers such as proteins, polysaccharides,
collages, fibrinogens, silks, and hyaluronic acid, in addition to
polyethylene and synthetic hydrophilic polymers such as
polyethylene oxide.
[0003] Many of these types of fibers can be formed through a
process known in the art as electrospinning. Electrospinning is a
versatile method that includes use of an electrical charge to form
a mat of fibers. Typically, electrospinning includes loading a
solution into a syringe and driving the solution to a tip of the
syringe with a syringe pump to form a droplet at the tip.
Electrospinning also usually includes applying a voltage to the
needle to form an electrified jet of the solution. The jet is then
elongated and whipped continuously by electrostatic repulsion until
it is deposited on a grounded collector, thereby forming the mat of
fibers.
[0004] Fibers that are formed via electrospinning may be used in a
wide variety of industries including in medical and scientific
applications. More specifically, these types of fibers have been
used to reinforce certain composites. These fibers have also been
used to produce nanometer tubes used in medical dialysis, gas
separation, osmosis, and water treatment.
[0005] In some applications, fibers are formed from electrospinning
various types of two- and three-phased systems such as emulsions.
The electrospinning techniques that are used with these systems
typically produce fibers that exhibit undesirable mechanical
characteristics rendering the fibers brittle and fragile.
Accordingly, there remains an opportunity to form articles of
fibers that are formed from dispersions and that exhibit improved
stress and strain properties. There also remains an opportunity to
develop a method of forming such articles.
SUMMARY OF THE INVENTION AND ADVANTAGES
[0006] The present invention provides an article of fibers and a
method of manufacturing the article. The fibers include a cured
compound and are formed from electrospinning a dispersion. The
dispersion includes a liquid and a curable compound. The method
includes the steps of forming the dispersion and electrospinning
the dispersion. In one embodiment, the method includes the step of
curing the curable compound.
[0007] Electrospinning the dispersion allows the fibers that are
formed to exhibit characteristics typical of the cured compound and
exhibit improved stress and strain properties. This formation of
fibers allows for more efficient and accurate production of a
variety of materials to be used in medical, scientific, and
manufacturing industries. The use of the dispersion also allows for
a variety of types of condensation curable compounds to be utilized
to form products that can be manipulated based on desired physical
and chemical properties.
BRIEF DESCRIPTION OF THE DRAWING
[0008] Other advantages of the present invention will be readily
appreciated, as the same becomes better understood by reference to
the following detailed description when considered in connection
with the accompanying drawing wherein FIG. 1 is a scanning electron
microscope image of an article including fibers of the instant
invention including fiber-fiber junctions and spherical
defects.
DETAILED DESCRIPTION OF THE INVENTION
[0009] The present invention provides an article including fibers
(i.e., an article of fibers), as shown in FIG. 1. The present
invention also provides a method of manufacturing the article. The
method, which includes a step of electrospinning, is described in
greater detail below.
[0010] The article may include a single layer of fibers or multiple
layers of fibers. As such, the article may have a thickness of at
least 0.01 .mu.m. More typically, the article has a thickness of
from about 1 .mu.m to about 100 .mu.m and most typically has a
thickness of from about 25 .mu.m to about 100 .mu.m. The article is
not limited to any particular number of layers of fibers. The
article may be woven or non-woven, and may exhibit a microphase
separation. In one embodiment, the fibers and the article are
non-woven and the article is further defined as a mat. In another
embodiment, the fibers and the article are non-woven and the
article is further defined as a web. Alternatively, the article may
be a membrane. The fibers may also be uniform or non-uniform and
may have any surface roughness. The article may be waterproof,
water resistant, fire resistant, electrically conductive,
self-cleaning, water draining, drag reducing, and combinations
thereof. In one embodiment, the article is a coating. It is also
contemplated that the article may be a fabric, a breathable fabric,
a filter, or combinations thereof. Further, the article may be used
in a variety of industries such as in catalysts, filters, solar
cells, electrical components, transdermal patches, bandages, drug
delivery systems, and in antimicrobial applications. Another
potential application for the article may be use as a
superhydrophobic porous membrane for oil-water separation or for
use in biomedical devices, such as for blood vessel replacements
and uses in burn bandages to provide non-stick breathability.
[0011] The article may be a superhydrophobic fiber mat and may
exhibit a water contact angle of greater than about 150 degrees. In
various embodiments, the article exhibits water contact angles of
from 150 to 180, 155 to 175, 160 to 170, and 160 to 165, degrees.
The article may also exhibit a water contact angle hysteresis of
below 15 degrees. In various embodiments, the article exhibits
water contact angle hysteresis of from 0 to 15, 5 to 10, 8 to 13,
and 6 to 12. The article may also exhibit an isotropic or
non-isotropic nature of the water contact angle and/or the water
contact angle hysteresis. Alternatively, the article may include
domains that exhibit an isotropic nature and domains that exhibit a
non-isotropic nature.
[0012] The fibers may also be of any size and shape and are
typically cylindrical. Typically, the fibers have a diameter of
from 0.01 to 100, more typically of from 0.05 to 10, and most
typically of from 0.1 to 1, micrometers (.mu.m). In various
embodiments, the fibers have a diameter of from 1 nm to 30 microns,
from 1-500 nm, from 1-100 nm, from 100-300 nm, from 100-500 nm,
from 50-400 nm, from 300-600 nm, from 400-700 nm, from 500-800 nm,
from 500-1000 nm, from 1500-3000 nm, from 1000-5000 nm, from
2000-5000 nm, or from 3000-4000 nm. The fibers also typically have
a size of from of from 5 to 20 microns and more typically have a
size of from 10-15 microns. However, the fibers are not limited to
any particular size. The fibers are often referred to as "fine
fibers", which encompasses fibers having both micron-scale
diameters (i.e., fibers having a diameter of at least 1 micron) and
fibers having nanometer-scale diameters (i.e., fibers having a
diameter of less than 1 micron). The fibers may also have a glass
transition temperature (T.sub.g) of from 25.degree. C. to
500.degree. C.
[0013] The fibers may also be connected to each other by any means
known in the art. For example, the fibers may be fused together in
places where they overlap or may be physically separate such that
the fibers merely lay upon each other in the article. It is
contemplated that the fibers, when connected, may form a web or mat
having pore sizes of from 0.01 to 100 .mu.m. In various
embodiments, the pore sizes range in size from 0.1-100, 0.1-50,
0.1-10, 0.1-5. 0.1-2, or 0.1-1.5, microns. It is to be understood
that the pore sizes may be uniform or not uniform. That is, the
article may include differing domains with differing pore sizes in
each domain or between domains. Further, the fibers may have any
cross sectional profile including, but not limited to, a
ribbon-like cross-sectional profile, an oval cross-sectional
profile, a circular cross-sectional profile, and combinations
thereof. In some embodiments, "beading" of the fibers can be
observed, which may be acceptable for most applications. The
presence of beading, the cross-sectional profile of the fiber
(varying from circular to ribbonous), and the fiber diameter are
functions of the conditions of a method in which the fibers are
formed, to be described in further detail below.
[0014] In some embodiments, the fibers may also be fire resistant,
as introduced above. Fire resistance of the fibers, particularly
the non-woven mat including the fibers, is tested using the
UL-94V-0 vertical burn test on swatches of the non-woven mat
deposited onto aluminum foil substrates. In this test, a strip of
the non-woven mat is held above a flame for about 10 seconds. The
flame is then removed for 10 seconds and reapplied for another 10
seconds. Samples are observed during this process for hot drippings
that spread the fire, the presence of afterflame and afterglow, and
the burn distance along the height of the sample. For non-woven
mats including the fibers in accordance with the instant invention,
intact fibers are typically observed beneath those that burn. The
incomplete combustion of the non-woven mats is evidence of
self-quenching, a typical behavior of fire-retardant materials and
is deemed excellent fire resistance. In many circumstances, the
non-woven mats may even achieve UL 94 V-0 classification. Without
intending to be bound by any particular theory, it is believed that
the fire resistance is typically attributable to a low ratio of
organic groups to silicon atoms in the fibers. The low ratio of
organic groups to silicon atoms is attributable to the absence of
organic polymers and organic copolymers in the fibers. However, it
is also contemplated that the fire resistance may be due to factors
other than the low ratio of organic groups to silicon atoms in the
fibers.
[0015] The fibers are formed from a dispersion. As is known in the
art, dispersions include one phase of matter that is immiscible
with, and dispersed in, another phase of matter, i.e., a dispersed
phase in a continuous phase. In the instant invention, the
dispersion includes a liquid and a curable compound, described in
greater detail below. In one embodiment, the liquid is a non-polar
liquid. In another embodiment, the liquid is a polar liquid such as
an alcohol, an ionic liquid, or water. Typically, the liquid is
water. The water may be tap water, well water, purified water,
deionized water, and combinations thereof and may be present in the
dispersion in varying amounts depending on the type of dispersion.
The liquid may be either the dispersed phase or the continuous
phase. In one embodiment, the dispersion includes solid particles
as the dispersed phase and the liquid as the continuous phase. In
another embodiment, the dispersion includes a non-polar liquid as
the dispersed phase and a polar liquid as the continuous phase. In
various embodiments, the liquid may be present in amounts of from
20 to 80, of from 30 to 70, of from 40 to 60, or in an amount of
about 50, parts by weight per 100 parts by weight of the
dispersion, so long as a total amount of the dispersion does not
exceed 100 parts by weight.
[0016] The dispersion may be further defined as a "colloid" or
"colloid dispersion," terminology which can be used
interchangeably. Typically, colloids include particles of less than
100 nanometers in size dispersed in the continuous phase. Colloids
may be classified in numerous ways. For purposes of the instant
invention, the colloid may also be classified as a gel (a liquid
dispersed phase and a solid continuous phase), an emulsion (a
liquid dispersed phase and a liquid continuous phase), and/or a
foam (a gas dispersed phase and a liquid continuous phase). The
colloid may be reversible (i.e., exist in more than one state) or
irreversible. Further, the colloid may be elastomeric or
viscoelastic.
[0017] In one embodiment, the dispersion is further defined as an
emulsion, as first introduced immediately above. Emulsions are
typically classified into one of four categories according to a
chemical nature of the dispersed and continuous phases. A first
category is an oil-in-water (O/W) emulsion. O/W emulsions typically
include a non-polar dispersed phase (e.g., oil) in an aqueous
continuous phase (e.g. water) which forms droplets, which are
typically referred to as emulsion particles. For purposes of the
instant invention, the terminology "oil" includes non-polar
molecules and may include the curable compound. A second category
of emulsion is a water-in-oil (W/O) emulsion. W/O emulsions
typically include a polar dispersed phase in a non-polar continuous
phase thereby forming an inverted emulsion. A third category is a
water-in-oil-in-water (W/O/W) emulsion. These types of emulsions
include a polar dispersed phase in a non-polar continuous phase
which is, in turn, dispersed in a polar continuous phase. For
example, W/O/W emulsions may include water droplets entrapped
within larger oil droplets that in turn are dispersed in a
continuous water phase. A fourth category is a water-in-water (W/W)
emulsion. These types of emulsions include aqueous solvated
molecules in a continuous aqueous solution wherein both the aqueous
solvated molecules and the continuous aqueous solution include
different molecules that are water-soluble. Without intending to be
bound by any particular theory, it is believed that the
aforementioned types of emulsions depend on hydrogen bonding, pi
stacking, and/or salt bridging of both the dispersed and continuous
phases. In this invention, the dispersion may be further defined as
any one of these four types of emulsions.
[0018] As is also known in the art, dispersions are, to a certain
degree, unstable. Typically, there are three types of dispersion
instability including (i) flocculation, where particles of the
dispersed phase form clumps in the continuous phase, (ii) creaming,
where the particles of the dispersed phase concentrate towards a
surface or bottom of the continuous phase, and (iii) breaking and
coalescence, where the particles of the dispersed phase coalesce
and form a layer of liquid in the continuous phase. The instant
dispersion may exhibit one or more of these types of
instability.
[0019] The dispersion of the instant invention may include
particles of varying sizes. In one embodiment, the dispersion
includes particles of from 1 nm to 10 .mu.m, more typically of from
1 nm to 1 .mu.m, and most typically of from 1 to 100 nm. In another
embodiment, the dispersion may be classified as a nanoemulsion. The
dispersion may include particles smaller or larger than the sizes
described immediately above, depending on the desire of those of
skill in the art.
[0020] As first described above, the dispersion also includes the
curable compound. The curable compound may any organic or inorganic
compound known in the art that can be cured. Non-limiting examples
of suitable curable compounds include compounds that cure by
free-radical mechanisms, hydrosilylation, condensation, addition
reactions, ultraviolet light, microwaves, and heat. Examples of
such curable compounds include, but are not limited to, peroxides,
amides, acrylates, esters, ethers, imides, oxiranes, sulfones,
ureas, urethanes, compounds with ethylenically unsaturated bonds,
and combinations thereof. In one embodiment, the curable compound
is selected from the group of silanes, siloxanes, silazanes,
silicones, silicas, silenes, silsesquioxanes, and combinations
thereof. In this embodiment, the curable compound typically cures
via free radical, condensation, and/or hydrosilylation mechanisms.
In various embodiments, the curable compound may be present in
amounts of from 20 to 80, of from 30 to 70, of from 40 to 60, or in
an amount of about 50, parts by weight per 100 parts by weight of
the dispersion, so long as a total amount of the dispersion does
not exceed 100 parts by weight.
[0021] Alternatively, the curable compound may be further defined
as a condensation curable compound. As is known in the art,
condensation curable compounds cure via condensation reactions.
Condensation reactions are chemical reactions in which two
molecules combine to form a new single molecule, together with the
loss of a small molecule, such as water. When water is lost, the
condensation reaction may also be known as a dehydration reaction.
For descriptive purposes only, a general condensation (dehydration)
reaction scheme is set forth below:
##STR00001##
wherein R is an organic or inorganic moiety. The condensation
reaction is not limited to loss of water and instead may include a
loss of an organic or inorganic compound or a molecule of hydrogen.
The condensation reaction may also occur where one or more Si atoms
in the reaching scheme is replaced by a carbon (C) atom.
[0022] The condensation curable compound may include monomers,
dimers, oligomers, polymers, pre-polymers, co-polymers, block
polymers, star polymers, graft polymers, random co-polymers,
macromonomers, telechelic oligomers, nanoparticles, and
combinations thereof. The term "oligomer" as used herein includes
identifiable chemical groups, including dimers, trimers, tetramers
and/or pentamers, linked together through reactive moieties capable
of condensation. Examples of preferred organic reactive moieties
capable of condensation that may be included in the condensation
curable compound include, but are not limited to, hydrolyzable
moieties, hydroxyl moieties, hydrides, isocyanate moieties, amine
moieties, amide moieties, acid moieties, alcohol moieties, amine
moieties, acrylate moieties, carbonate moieties, epoxide moieties,
ester moieties, and combinations thereof. The condensation curable
compound may also include inorganic moieties including, but not
limited to, silicones, siloxanes, silanes, transition metal
compounds, and combinations thereof. In addition to the
condensation reactions, articles of the instant invention can also
be formed by various addition reactions such as free radical
additions, Michael reactions, hydrosilylation reactions, and/or
Diels Alder reactions. Ring opening polymerizations can also be
used.
[0023] In one embodiment, the condensation curable compound may be
any compound of U.S. Provisional Application No. 61/003,726 filed
on Nov. 20, 2007, which is expressly incorporated herein by
reference. In another embodiment, the condensation curable compound
may include organic and inorganic polymers such as polyesters,
polyamides, polyimides, polyureas, polyethers, polyamines,
polyurethanes, aramides, polycarbonates, carbonates, and
combinations thereof. Alternatively, the condensation curable
compound may cure to form a compound selected from the group of
polyesters, nylons, polyurethanes, aramides, carbonates, and
combinations thereof.
[0024] The (condensation) curable compound may be substantially
free of silicon (i.e., silicon atoms and/or compounds containing
silicon atoms). It is to be understood that the terminology
"substantially free" refers to a concentration of silicon of less
than 5,000, more typically of less than 900, and most typically of
less than 100, parts of compounds that include silicon atoms, per
one million parts of the condensation curable compound. It is also
contemplated that the (condensation) curable compound may be
totally free of silicon.
[0025] Alternatively, the (condensation) curable compound may
include a polymerization product of at least a silicon monomer and
an organic monomer. It is contemplated that the organic monomer
and/or silicon monomer may be present in the (condensation) curable
compound in any volume fraction. In various embodiments, the
organic monomer and/or silicon monomer are present in volume
fractions of from 0.05-0.9, 0.1-0.6, 0.3-0.5, 0.4-0.9, 0.1-0.9,
0.3-0.6, or 0.05-0.9.
[0026] The organic monomer may include any organic moiety described
above. The terminology "silicon monomer" includes any monomer that
includes at least one silicon (Si) atom such as silanes, siloxanes,
silazanes, silicones, silicas, silenes, silsesquioxanes, and
combinations thereof. It is to be understood that the silicon
monomer may include polymerized groups and remain a silicon monomer
so long as it retains an ability to be polymerized. In one
embodiment, the silicon monomer is selected from the group of
silanes, silsesquioxanes, siloxanes, and combinations thereof.
[0027] In an alternative embodiment, the (condensation) curable
compound is selected from the group of an organosilane, an
organopolysiloxane, and combinations thereof. In this embodiment,
the organopolysiloxane may be selected from the group of a silanol
terminated siloxane, an alkoxylsilyl-terminated siloxane, and
combinations thereof.
[0028] The (condensation) curable compound may be linear or
non-linear and may include hydroxyl and/or organosiloxy groups
(--SiOR) and may include hydroxyl terminated polydimethylsiloxane.
The (condensation) curable compound may include the general
structure:
##STR00002##
wherein each of R.sup.1 and R.sup.2 independently include one of a
hydrogen, a hydroxyl group, an alkyl group, a halogen substituted
alkyl group, an alkylenyl group, an aryl group, a halogen
substituted aryl group, an alkaryl group, an alkoxy group, an
acyloxy group, a ketoximate group, an amino group, an amido group,
an acid amido group, an amino-oxy group, a mercapto group, and an
alkenyloxy group, and n may be any integer.
[0029] Alternatively, the (condensation) curable compound may
include hydrocarbylene and/or fluorocarbylene groups.
Hydrocarbylene groups include a divalent moiety including carbon
and hydrogen. Fluorocarbylene groups include a hydrocarbylene
moiety with at least one of the hydrogens replaced with at least
one fluorine atom. Typical fluorocarbylene groups include partially
or wholly fluorine substituted alkylene groups. The (condensation)
curable compound may also include olefinic moieties including
acrylate moieties, methacrylate moieties, vinyl moieties,
acetylenyl moieties, and combinations thereof.
[0030] If the (condensation) curable compound includes a hydroxyl
group, the (condensation) curable organopolysiloxane may include
siloxanes having at least one terminal silanol group or one
hydrogen atom bonded to silicon or a hydrolyzable group which, upon
exposure to moisture, forms silanol groups. Terminal or pendant
silanol groups, or their precursors, allow for condensation.
[0031] Alternatively, the (condensation) curable compound may be
further defined as an elastomer or as a curable elastomer. As is
known in the art, "elastomers" are compounds that exhibit
elasticity, i.e., an ability to deform under stress and return to
an approximately original shape. In the instant invention, the
terminology "elastomer" is not limited to polymer or monomers and
may include one or both. Additionally, the elastomer may include
any of the aforementioned (condensation) curable compounds. In one
embodiment, the curable elastomer is commercially available from
Dow Corning Corporation of Midland, Mich. under the trade name of
Dow Corning 84 Additive.
[0032] In one embodiment, the curable compound has a number average
molecular weight (M.sub.n) of greater than 5,000 g/mol and more
typically of greater than 10,000 g/mol. However, the curable
compound is not limited to such a number average molecular weight.
In another embodiment, the curable compound has a number average
molecular weight of greater than about 100,000 g/mol. In various
other embodiments, the curable compound has number average
molecules weights of from 100,000-5,000,000, from
100,000-1,000,000, from 100,000-500,000, from 200,000-300,000, of
higher than about 250,000, or of about 150,000, g/mol. In yet
another embodiment, the curable compound has a number average
molecular weight of greater than 50,000 g/mol, and more typically
of greater than 100,000 g/mol. In alternative embodiments, the
curable compound may have a number average molecular weight of at
least about 300 g/mol, of from about 1,000 to about 2,000 g/mol, or
of from about 2,000 g/mol to about 2,000,000 g/mol. In other
embodiments, the curable compound may have a number average
molecular weight of greater than 350 g/mol, of from about 5,000 to
about 4,000,000 g/mol, or of from about 500,000 to about 2,000,000
g/mol.
[0033] In addition to the curable compound, the dispersion may also
include one or more surfactants. In various embodiments, the
dispersion includes a (first) surfactant and a second surfactant or
multiple surfactants. The surfactant may be combined with the
liquid, with the curable compound, or with both the liquid and the
curable compound, prior to formation of the dispersion. Typically,
the surfactant is combined with the liquid before the dispersion is
formed. Surfactants are also known as surfactant active agents,
surface active solutes, emulsifiers, emulgents, and tensides.
Relative to this invention, the terminology "surface active agent",
"surface active solutes", "surfactants", "emulsifiers",
"emulgents", and "tensides" may be used interchangeably.
Surfactants reduce a surface tension of a liquid by adsorbing at a
liquid-gas interface. Surfactants also reduce interfacial tension
between polar and non-polar molecules by adsorbing at a
liquid-liquid interface. Without intending to be bound by any
particular theory, it is believed that surfactants act at these
interfaces and are dependent on various forces including, excluded
volume repulsion forces, electrostatic interaction forces, van der
waals forces, entropic forces, and steric forces. In the instant
invention, the surfactant may be chosen or manipulated based on one
or more of these forces.
[0034] The surfactant, first and second surfactants, or
first/second/and multiple surfactants may independently be selected
from the group of non-ionic surfactants, cationic surfactants,
anionic surfactants, amphoteric surfactants, and combinations
thereof. Suitable non-ionic surfactants include, but are not
limited to, alkylphenol alkoxylates, alcohol ethoxylates including
fatty alcohol ethoxylates, glycerol esters, sorbitan esters,
sucrose and glucose esters, including alkyl polyglucosides and
hydroxyalkyl polyglucosides, alkanolamides, N-alkylglucamides,
alkylene oxide block copolymers such as block copolymers of
ethylene oxide, propylene oxide and/or butylene oxide, polyhydroxy
and polyalkoxy fatty acid derivatives, amine oxides, siloxane based
polyethers, and combinations thereof.
[0035] Suitable cationic surfactants include, but are not limited
to, interface-active compounds including ammonium groups such as
alkyldimethylammonium halides and compounds having the chemical
formula RR'R''R'''N.sup.+X.sup.- wherein R, R', R'', and R''' are
independently selected from the group of alkyl groups, aryl groups,
alkylalkoxy groups, arylalkoxy groups, hydroxyalkyl(alkoxy) groups,
and hydroxyaryl(alkoxy) groups and wherein X is an anion. Suitable
anionic surfactants include, but are not limited to, fatty alcohol
sulfates. Further non-limiting examples of suitable anionic
surfactants include alkanesulfonates, linear
alkylbenzenesulfonates, and linear alkyltoluenesulfonates. Still
further, the anionic surfactant may include olefinsulfonates and
di-sulfonates, mixtures of alkene- and hydroxyalkane-sulfonates or
di-sulfonates, alkyl ester sulfonates, sulfonated polycarboxylic
acids, alkyl glyceryl sulfonates, fatty acid glycerol ester
sulfonates, alkylphenol polyglycol ether sulfates, olefin
sulfonates, paraffinsulfonates, alkyl phosphates, acyl
isothionates, acyl taurates, acyl methyl taurates, alkylsuccinic
acids, sulfosuccinates, alkenylsuccinic acids and corresponding
esters and amides thereof, alkylsulfosuccinic acids and
corresponding amides, mono- and di-esters of sulfosuccinic acids,
acyl sarcosinates, sulfated alkyl polyglucosides, alkyl polyglycol
carboxylates, hydroxyalkyl sarcosinates, and combinations thereof.
Suitable amphoteric surfactants include, but are not limited to,
aliphatic derivatives of secondary and/or tertiary amines which
include an anionic group, betaines, and combinations thereof.
[0036] Additionally, the surfactant and/or first and second
surfactants may independently include aliphatic and/or aromatic
alkoxylated alcohols, LAS (linear alkyl benzene sulfonates),
paraffin sulfonates, FAS (fatty alcohol sulfates), FAES (fatty
alcohol ethersulfates), alkylene glycols, trimethylolpropane
ethoxylates, glycerol ethoxylates, pentaerythritol ethoxylates,
alkoxylates of bisphenol A, and alkoxylates of 4-methylhexanol and
5-methyl-2-propylheptanol, and combinations thereof. Typically, the
surfactant is present in an amount of from 0.1 to 100, more
typically of from 0.01 to 5, even more typically of from 0.5 to 5,
and most typically of from 1.5 to 5, parts by weight per 100 parts
by weight of the dispersion.
[0037] The dispersion may also include a thickener. As is known in
the art, thickeners increase a viscosity of the dispersion at low
shear rates while maintaining flow properties of the dispersion at
higher shear rates. Suitable thickeners for use in the instant
invention include, but are not limited to, polyalkylene oxides such
as polyethylene oxide, polypropylene oxide, polybutylene oxide, and
combinations thereof. In one embodiment, the thickener is selected
from the group of algenic acid and its derivatives, polyethylene
oxide, polyvinyl alcohol, methyl cellulose, hydroxypropylmethyl
cellulose, alkyl and hydroxyalkyl cellulose, carboxymethyl
cellulose, hydroxyethyl cellulose, guar gum, gum arabic, gum
ghatic, polyvinylpyrrolidone, starch, modified starch, tamarind
gum, xanthan gum, polyacrylamide, polyacrylic acid, and
combinations thereof. The thickener may also include a nanoparticle
such as titanium dioxide and/or a nanoclay such as betonite. The
thickener may also be conductive, semi-conductive, insulating,
magnetic, or light-emitting. Alternatively, the thickener may
include a conductive polymer such as polypyrrole, polyaniline,
and/or polyacetylene. The thickener may also include biological
components such as proteins or DNA.
[0038] The thickener may be combined with the liquid, with the
curable compound, or with both the liquid and the curable compound
before the dispersion is formed. Typically, the thickener is
combined with the liquid before the dispersion is formed. The
thickener is typically present in an amount of from 0.001 to 25,
more typically of from 0.05 to 5, and most typically of from 0.1 to
5, parts by weight per 100 parts by weight of the dispersion.
[0039] As is also known in the art, dispersions typically have two
different types of viscosities, a total viscosity and a viscosity
of the dispersed phase. The dispersion of the instant invention
typically has a total viscosity of at least 20 centistokes at a
temperature of 25.degree. C. In various embodiments, the dispersion
has a viscosity of at least 20 centistokes, more typically from
about 30 to about 100 centistokes, most typically from about 40 to
about 75 centistokes at a temperature of 25.degree. C. using a
Brookfield rotating disc viscometer equipped with a thermal cell
and an SC4-31 spindle operated at a constant temperature of
25.degree. C. and a rotational speed of 5 rpm. The viscosity of the
dispersed phase is not limited and is not believed to affect the
total viscosity. In one embodiment, the dispersed phase is solid
and has an infinite viscosity.
[0040] The dispersion may also have a zero shear rate viscosity of
from 0.1 to 10, from 0.5 to 10, from 1 to 10, from 5 to 8, or about
6, PaS. Further, the dispersion may have a conductivity of from
0.01-25 mS/m. In various embodiments, the conductivity of the
dispersion ranges from 0.1-10, from 0.1-5, from 0.1-1, from
0.1-0.5, or is about 0.3, mS/m. The dispersion may also have a
surface tension of from 10-100 mN/m. In different embodiments, the
surface tension ranges from 20-80, or from 20-50, mN/m. In one
embodiment, the surface tension of the dispersion is about 30 mN/m.
The dispersion may also have a dielectric constant of from 1-100.
In various embodiments, the dielectric constant is between 5-50,
10-70, or 1-20. In one embodiment, the dielectric constant of the
dispersion is about 10.
[0041] The dispersion may also include an additive. The additive
may include, but is not limited to, conductivity-enhancing
additives, salts, dyes, colorants, labeling agents, and
combinations thereof. Conductivity-enhancing additives may
contribute to excellent fiber formation, and may further enable
diameters of the fibers to be minimized, especially when the fibers
are formed through electrospinning. In one embodiment, the
conductivity-enhancing additive includes an ionic compound. In
another embodiment, the conductivity-enhancing additives are
generally selected from the group of amines, organic salts and
inorganic salts, and mixtures thereof. Typical
conductivity-enhancing additives include amines, quaternary
ammonium salts, quaternary phosphonium salts, ternary sulfonium
salts, and mixtures of inorganic salts with organic ligands. More
typical conductivity-enhancing additives include quaternary
ammonium-based organic salts including, but not limited to,
tetrabutylammonium chloride, tetrabutylammonium bromide,
tetrabutylammonium iodide, phenyltrimethylammonium chloride,
phenyltriethylammonium chloride, phenyltrimethylammonium bromide,
phenyltrimethylammonium iodide, dodecyltrimethylammonium chloride,
dodecyltrimethylammonium bromide, dodecyltrimethylammonium iodide,
tetradecyltrimethylammonium chloride, tetradecyltrimethylammonium
bromide, tetradecyltrimethylammonium iodide,
hexadecyltrimethylammonium chloride, hexadecyltrimethylammonium
bromide, and hexadecyltrimethylammonium iodide. The additive may be
present in either the continuous or dispersed phase of the
dispersion in any amount selected by one of skill in the art so
long as the amount of the additive allows the curing of the curable
compound to occur. In various embodiments, the amount of the
additive is typically of from about 0.0001 to about 25%, more
typically from about 0.001 to about 10%, and more typically from
about 0.01 to about 1% based on the total weight of the fibers. In
one embodiment, the additive includes
methylaminomethylpropanol.
[0042] Referring now to the method of manufacturing the article,
the method includes the step of forming the dispersion, described
above. The dispersion may be formed by adding the curable compound
and the liquid together and mixing. In one embodiment, the method
includes the step of adding the condensation curable compound and
the liquid together and mixing. The step of mixing may include
mechanical mixing using ribbon mixers, plow mixers, fluidizing
paddle mixers, sigma blade mixers, tumble blenders, vortex mixers,
feed mixers, vertical mixers, horizontal mixers, rotor-stator
mixers, sonicators, Speedmixers.RTM., and combinations thereof.
[0043] The instant invention is not limited to any particular order
of addition. In one embodiment, the dispersion is formed by
combining the thickener and water to form a mixture and adding the
mixture to the curable compound. Alternatively, the dispersion may
be formed by any method known in the art.
[0044] The method also includes the step of electrospinning the
dispersion. In one embodiment, this step reduces a content of the
liquid (e.g. water) such that the condensation curable compound
cures. Without intending to be bound by any particular theory, it
is believed that electrospinning causes at least partial
evaporation of the liquid, such as water, such that the
condensation curable compound cures. Loss of solvent may allow the
curable compounds to blend, i.e. come into intimate contact,
allowing for cure. Without intending to be limited by any
particular theory, it is believed that the force of an electric
field, used in electrospinning, may align functional groups such
that they are more readily in contact. The step of electrospinning
may be conducted by any method known in the art. A typical
electrospinning process includes use of an electrical charge to
form the fibers. Typically, the dispersion used to form the fibers
is loaded into a syringe, the dispersion is driven to a tip of the
syringe with a syringe pump, and a droplet is formed at the tip of
the syringe. The pump enables control of flow rate of the
dispersion used to form the fibers to the spinning head. Flow rate
of the dispersion used to form the fibers through the tip of the
syringe may have an effect on formation of the fibers. The flow
rate of the dispersion through the tip of the syringe may be from
about 0.005 ml/min to about 0.5 ml/min, typically from about 0.005
ml/min to about 0.1 ml/min, more typically from about 0.01 ml/min
to about 0.1 ml/min, and most typically from about 0.02 ml/min to
about 0.1 ml/min. In one specific embodiment, the flow rate of the
dispersion through the tip of the syringe may be about 0.05
ml/min.
[0045] The droplet is then typically exposed to a high-voltage
electric field. In the absence of the high-voltage electrical
field, the droplet exits the tip of the syringe in a
quasi-spherical shape, which is the result of surface tension in
the droplet. Application of the electric field results in the
distortion of the spherical shape into that of a cone. The
generally accepted explanation for this distortion in droplet shape
is that the surface tension forces within the droplet are
neutralized by the electrical forces. Narrow diameter jets of the
dispersion emanate from the tip of the cone. Under certain process
conditions, the jet of the dispersion undergoes the phenomenon of
"whipping" instability. This whipping instability results in the
repeated bifurcation of the jet, yielding a network of fibers. The
fibers are ultimately collected on a collector plate. The liquid,
such as water, is believed to rapidly evaporate from the dispersion
during the electrospinning process, leaving behind the solids
portion of the dispersion to form the fibers and cure the curable
compound. The collector plate is typically formed from a solid
conductive material such as, but not limited to, aluminum, steel,
nickel alloys, silicon wafers, Nylon.RTM. fabric, and cellulose
(e.g., paper). The collector plate acts as a ground source for the
electron flow through the fibers during electrospinning of the
dispersion. As time passes the number of fibers collected on the
collector plate increases and the non-woven fiber mat is formed on
the collector plate. Alternatively, instead of using the collection
plate, the fibers may be collected on the surface of a liquid that
is not part of the dispersion, thereby achieving a free-standing
non-woven mat. One example of liquid that can be used to collect
the fibers is water.
[0046] In various embodiments, the step of electrospinning
comprises supplying electricity from a DC generator having
generating capability of from about 10 to about 100 kilovolts (KV).
In particular, the syringe is electrically connected to the
generator. The step of exposing the droplet to the high-voltage
electric field typically includes applying a voltage and an
electric current to the syringe. The applied voltage may be from
about 5 KV to about 100 KV, typically from about 10 KV to about 40
KV, more typically from about 15 KV to about 35 KV, most typically
from about 20 KV to about 30 KV. In one specific example, the
applied voltage may be about 30 KV. The applied electric current
may be from about 0.01 nA to about 100,000 nA, typically from about
10 nA to about 1000 nA, more typically from about 50 nA to about
500 nA, most typically from about 75 nA to about 100 nA. In one
specific embodiment, the electric current is about 85 nA.
Typically, when electrospinning, the dispersion is at a temperature
within 60.degree. C. of ambient temperature. More typically, when
electrospinning, the dispersion is at a temperature within
60.degree. C. of a processing temperature.
[0047] The step of electrospinning is believed to at least
partially cure the condensation curable compound. In one
embodiment, the step of electrospinning completely cures the
condensation curable compound. In other embodiments, the step of
electrospinning does not completely cure, or even partially cure,
the curable compound such that an additional curing step is needed.
The method may include the step of drying to more completely cure
the curable compound. When the curable compound is further defined
as the condensation curable compound, it is hypothesized that the
step of drying removes the liquid (e.g. water) and drives the
condensation reaction to the right, i.e., towards completion.
[0048] The method may also include the step of curing the curable
compound, as first introduced above. The step of curing may be
implemented independent of, or in combination with, the step of
electrospinning. This step may include any curing step known in the
art including, but not limited to, those related to free-radical
curing, hydrosilylation curing, condensation curing, UV light
curing, microwave curing, heat curing, and combinations
thereof.
[0049] The method may also include the step of annealing the
fibers. This step may be completed by any method known in the art.
In one embodiment, the step of annealing may be used to enhance the
hydrophobicity of the fibers. In another embodiment, the step of
annealing may enhance a regularity of microphases of the fibers.
The step of annealing may include heating the article. Typically,
to carry out the step of annealing, the article is heated to a
temperature above ambient temperature of about 20.degree. C. More
typically, the article is heated to a temperature of from about
40.degree. C. to about 400.degree. C., most typically from about
40.degree. C. to about 200.degree. C. Heating of the article may
result in increased fusion of fiber junctions within the article,
creation of chemical or physical bonds within the fibers (generally
termed "cross-linking"), volatilization of one or more components
of the fiber, and/or a change in surface morphology of the
fibers.
EXAMPLES
[0050] A series of fibers and a non-woven mat (i.e., the article of
the instant invention) are formed according to the present method.
The non-woven mat includes the fibers formed from the dispersion
including a silicone elastomer as a condensation curable
compound.
[0051] More specifically, 2 g of 2.5% polyethylene oxide (2,000,000
number average molecular weight) solution in water is added to 10 g
of a dispersion including 63% by weight of Dow Corning 84 Additive
in water. Dow Corning Additive 84 includes a mix of silica and
cross-linked silicone rubber including functional groups that can
undergo a condensation cure. The polyethylene oxide and the
dispersion are stirred to form a translucent white dispersion. The
dispersion is then delivered by a syringe/syringe pump to a
stainless steel tube with inner diameter of 0.040 inches in
preparation for electrospinning. An electric field is applied
between the stainless steel tube and a piece of grounded aluminum
foil. As the electric field is applied, a droplet at a tip of the
stainless steel tube is electrospun into thin white fibers which
are deposited onto the grounded aluminum foil. The step of
electrospinning is performed at a plate gap of 30 cm, a tip
protrusion of 3 cm, an applied voltage of 22 kV, and a flow rate of
1 mL/hr. The electrospinning is performed for one hour. The
resultant fibers are one to five microns in diameter and tend to
have fiber-fiber junctions. Spherical defects are present within
the fibers, as shown in FIG. 1.
[0052] After electrospinning for one hour, the fibers form an
opaque white membrane with a thickness of approximately 200
microns. After 24 hours, the membrane is peeled off the aluminum
foil and tested to determine tensile properties (stress/strain) at
a breaking point using an Alliance RT/5 Tensile Tester commercially
available from RTS. More specifically, a "dog-bone" shaped sample
of the membrane having a width of 0.1 inches is tested in a 10 N
maximum load cell at a pull rate of 100 mm/min. A stress-strain
curve is also generated. The peak stress measurement of the fibers
is approximately 19 psi and the strain measurement is approximately
120 percent. Additionally, the stress-strain curve is approximately
linear suggesting that the fibers are elastomeric at the breaking
point.
[0053] The fibers formed in the aforementioned Example evidence
that electrospinning a dispersion allows fibers to be formed that
exhibit characteristics of the dispersed phase, i.e., the
condensation curable compound, as opposed to the continuous phase.
The fibers formed in this Example exhibit elastomeric stress and
strain properties and an elastomeric stress-strain curve. The
formation of these types of fibers allows for more efficient and
accurate production of a variety of materials to be used in
medical, scientific, and manufacturing industries. The use of the
dispersion also allows for a variety of types of curable compounds
to be utilized thus forming new products. The use of, for example,
a dispersion in which a continuous phase is water, allows for an
electrospinning process to be done through evaporation of a
non-hazardous volatile liquid. The use of an active material, for
example a bacteria, in the continuous phase, may allow for the
creation of biologically functionalized fibers that are curable in
a one-step process.
[0054] The invention has been described in an illustrative manner,
and it is to be understood that the terminology which has been used
is intended to be in the nature of words of description rather than
of limitation. Obviously, many modifications and variations of the
present invention are possible in light of the above teachings, and
the invention may be practiced otherwise than as specifically
described.
* * * * *