U.S. patent application number 11/610726 was filed with the patent office on 2008-06-19 for electrospinning process.
This patent application is currently assigned to PPG Industries Ohio, Inc.. Invention is credited to Kenneth J. Balog, Stuart D. Hellring, Kaliappa G. Ragunathan.
Application Number | 20080145655 11/610726 |
Document ID | / |
Family ID | 39111761 |
Filed Date | 2008-06-19 |
United States Patent
Application |
20080145655 |
Kind Code |
A1 |
Hellring; Stuart D. ; et
al. |
June 19, 2008 |
Electrospinning Process
Abstract
A method for electrospinning polymer fibers and the resultant
electrospun fibers are disclosed. In the electrospinning method,
the polymer undergoes a crosslinking reaction prior to and during
the electrospinning process.
Inventors: |
Hellring; Stuart D.;
(Pittsburgh, PA) ; Ragunathan; Kaliappa G.;
(Gibsonia, PA) ; Balog; Kenneth J.; (Tarentum,
PA) |
Correspondence
Address: |
Diane R. Meyers;PPG Industries, Inc.
Law - Intellectual Property 39S, One PPG Place
Pittsburgh
PA
15272
US
|
Assignee: |
PPG Industries Ohio, Inc.
Cleveland
OH
|
Family ID: |
39111761 |
Appl. No.: |
11/610726 |
Filed: |
December 14, 2006 |
Current U.S.
Class: |
428/401 ;
264/465 |
Current CPC
Class: |
Y10T 428/298 20150115;
D01F 6/36 20130101; D01D 5/0038 20130101; D01D 5/38 20130101 |
Class at
Publication: |
428/401 ;
264/465 |
International
Class: |
D01F 1/09 20060101
D01F001/09; D02G 3/00 20060101 D02G003/00 |
Claims
1. A method for electrospinning a fiber from an electrically
conducting solution of polymer in the presence of an electric field
between a spinneret and a ground source, the polymer undergoing a
crosslinking reaction prior to and during electrospinning.
2. The method of claim 1 in which the polymer contains
crosslinkable groups along the polymer backbone.
3. The method of claim 2 in which the crosslinkable groups are
reactive with moisture.
4. The method of claim 3 in which the crosslinkable groups are
silane groups.
5. The method of claim 2 in which the polymer is a (meth)acrylic
polymer.
6. The method of claim 2 in which the polymer is a (meth)acrylic
polymer containing silane groups.
7. The method of claim 2 in which the polymer, besides containing
crosslinkable groups, also contains groups selected from carboxyl
and hydroxyl.
8. The method of claim 2 in which the polymer contains silane
groups, carboxyl groups, hydroxyl groups and nitrogen-containing
groups.
9. The method of claim 2 in which the silane groups are present in
the polymer in amounts of 0.2 to 20 percent by weight silicon based
on total polymer weight.
10. The method of claim 8 in which the polymer contains from: (a)
0.2 to 20 percent silane group measured as silicon, (b) 1 to 45
percent carboxyl groups, (c) 0.5 to 6.5 percent hydroxyl groups,
and (d) 0.2 to 5.0 percent nitrogen groups; the percentages by
weight being based on total polymer weight.
11. The method of claim 1 in which the solution contains a
thickener.
12. The method of claim 11 in which the thickener is polyvinyl
pyrrolidone.
13. The method of claim 12 in which the polyvinyl pyrrolidone is
present in amounts of no greater than 20 percent by weight based on
total weight of solution.
14. An electrospun fiber comprising a polymer that has been
crosslinked prior to and during the electrospinning process.
15. The electrospun fiber of claim 14 having a diameter of from 5
to 5,000 nanometers.
16. The electrospun fiber of claim 14 having --Si--O--Si--
crosslinks.
17. The electrospun fiber of claim 14 being a crosslinked
(meth)acrylic polymer.
18. The electrospun fiber of claim 14 being a (meth)acrylic polymer
with --Si--O--Si-- crosslinks.
Description
FIELD OF THE INVENTION
[0001] The present invention relates to an electrospinning process,
the resulting electrospun fiber and polymers used in the
electrospinning process.
BACKGROUND OF THE INVENTION
[0002] The process of electrospinning uses an electrical charge to
form fine fibers. The process consists of a spinneret with a
dispensing needle, a syringe pump, a power supply and a grounded
collection device. Polymers in solution or as melts are located in
the syringe and driven to the needle tip by the syringe pump where
they form a droplet. When voltage is applied to the needle, a
droplet is stretched to an electrified liquid jet. The jet is
elongated continuously until it is deposited on the collector as a
mat of fine fibers usually of nanometer-sized dimensions. The
resultant fibers are useful in a wide variety of applications such
as protective clothing, wound dressing and as supports or carriers
for catalyst. To form a fiber, the polymeric melt or solution must
have a sufficient viscosity otherwise a drop rather than a liquid
jet will form. Typically, thickeners are included in the polymer
solution or melt to provide the necessary viscosity. However,
thickeners can adversely affect the properties of the resultant
fibers and for this reason, their use should be minimized.
SUMMARY OF THE INVENTION
[0003] The present invention provides for a process of
electrospinning a fiber from an electrically conductive solution of
a polymer in the presence of an electric field between a spinneret
and a ground source. The polymer undergoes a crosslinking reaction
prior to and during the electrospinning process resulting in a
viscosity buildup of the polymer solution enabling fiber formation
and minimizing the use of thickeners.
[0004] The invention also provides for the resultant electrospun
fiber that contains silane, preferably carboxyl and hydroxyl groups
and optionally a nitrogen-containing group such as amine or amide
groups. The silane groups provide for crosslinking and viscosity
build-up. The carboxyl, hydroxyl, amine and amide groups provide
for a hydrogen bonding and viscosity build-up. The carboxyl group,
in the form of carboxylic acid, and the nitrogen-containing groups
are good electrical charge carrying groups.
BRIEF DESCRIPTION OF THE DRAWINGS
[0005] FIG. 1 depicts a basic electrospinning system.
[0006] FIG. 2 simulates a scanning electron microscopic (SCM) image
of a non-woven mat.
DETAILED DESCRIPTION OF THE INVENTION
[0007] For purposes of the following detailed description, it is to
be understood that the invention may assume various alternative
variations and step sequences, except where expressly specified to
the contrary. Moreover, other than in any operating examples, or
where otherwise indicated, all numbers expressing, for example,
quantities of ingredients used in the specification and claims are
to be understood as being modified in all instances by the term
"about". Accordingly, unless indicated to the contrary, the
numerical parameters set forth in the following specification and
attached claims are approximations that may vary depending upon the
desired properties to be obtained by the present invention. At the
very least, and not as an attempt to limit the application of the
doctrine of equivalents to the scope of the claims, each numerical
parameter should at least be construed in light of the number of
reported significant digits and by applying ordinary rounding
techniques. Notwithstanding that the numerical ranges and
parameters setting forth the broad scope of the invention are
approximations, the numerical values set forth in the specific
examples are reported as precisely as possible. Any numerical
value, however, inherently contains certain errors necessarily
resulting from the standard variation found in their respective
testing measurements.
[0008] Also, it should be understood that any numerical range
recited herein is intended to include all sub-ranges subsumed
therein. For example, a range of "1 to 10" is intended to include
all sub-ranges between (and including) the recited minimum value of
1 and the recited maximum value of 10, that is, having a minimum
value equal to or greater than 1 and a maximum value of equal to or
less than 10.
[0009] In this application, the use of the singular includes the
plural and plural encompasses singular, unless specifically stated
otherwise. In addition, in this application, the use of "or" means
"and/or" unless specifically stated otherwise, even though "and/or"
may be explicitly used in certain instances.
[0010] The term "polymer" is also meant to include copolymer and
oligiomer. The term "acrylic" is meant to include methacrylic and
is depicted by (meth)acrylic.
[0011] With reference to FIG. 1, the electrospinning system
consists of three major components, a power supply 1, a spinneret 3
and an electrically grounded collector 4. Direct current or
alternating current may be used in the electrospinning process. The
polymer solution 5 is contained in a syringe 7. A syringe pump 9
forces the solution through the spinneret 3 at a controlled rate. A
drop of the solution forms at the tip of the needle 11. Upon
application of a voltage, typically from 5 to 30 kilovolts (kV),
the drop becomes electrically charged. Consequently, the drop
experiences electrostatic repulsion between the surface charges and
the forces exerted by the external electric field. These electrical
forces will distort the drop and will eventually overcome the
surface tension of the polymer solution resulting in the ejection
of a liquid jet 13 from the tip of the needle 11. Because of its
charge, the jet is drawn downward to the grounded collector 4.
During its travel towards the collector 4, the jet 13 undergoes a
stretching action leading to the formation of a thin fiber. The
charged fiber is deposited on the collector 4 as a random oriented
non-woven mat as generally shown in FIG. 2.
[0012] The polymers of the present invention can be acrylic
polymers. As used herein, the term "acrylic" polymer refers to
those polymers that are well known to those skilled in the art
which results in the polymerization of one or more ethylenically
unsaturated polymerizable materials. (Meth)acrylic polymers
suitable for use in the present invention can be made by any of a
wide variety of methods as will be understood by those skilled in
the art. The (meth)acrylic polymers can be made by addition
polymerization of unsaturated polymerizable materials that contain
silane groups, carboxyl groups, hydroxyl groups and optionally a
nitrogen-containing group. Examples of silane groups include,
without limitation, groups that have the structure Si--X.sub.n
(wherein n is an integer having a value ranging from 1 to 3 and X
is selected from chlorine, alkoxy esters, and/or acyloxy esters).
Such groups hydrolyze in the presence of water including moisture
in the air to form silanol groups that condense to form
--Si--O--Si-- groups.
[0013] Examples of silane-containing ethylenically unsaturated
polymerizable materials, suitable for use in preparing such
(meth)acrylic polymers include, without limitation, ethylenically
unsaturated alkoxy silanes and ethylenically unsaturated acyloxy
silanes, more specific examples of which include vinyl silanes such
as vinyl trimethoxysilane, acrylatoalkoxysilanes, such as
gamma-acryloxypropyl trimethoxysilane and gamma-acryloxypropyl
triethoxysilane, and methacrylatoalkoxysilanes, such as
gamma-methacryloxypropyl trimethoxysilane, gamma-methacryloxypropyl
triethoxysilane and gamma-methacryloxypropyl tris-(2-methoxyethoxy)
silane; acyloxysilanes, including, for example, acrylato
acetoxysilanes, methacrylato acetoxysilanes and ethylenically
unsaturated acetoxysilanes, such as acrylatopropyl triacetoxysilane
and methacrylatopropyl triacetoxysilane. In certain embodiments, it
may be desirable to utilize monomers that, upon addition
polymerization, will result in a (meth)acrylic polymer in which the
Si atoms of the resulting hydrolyzable silyl groups are separated
by at least two atoms from the backbone of the polymer. Preferred
monomers are (meth)acryloxyalkylpolyalkoxy silane, particularly
(meth)acryloxyalkyltrialkoxy silane in which the alkyl group
contains from 2 to 3 carbon atoms and the alkoxy groups contain
from 1 to 2 carbon atoms.
[0014] In certain embodiments, the amount of the silane-containing
ethylenically unsaturated polymerizable material used in the total
monomer mixture is chosen so as to result in the production of a
(meth)acrylic polymer comprising silane groups that contain from
0.2 to 20, preferably 5 to 10 percent by weight, silicon, based on
the weight of the total monomer combination used in preparing the
(meth)acrylic polymer.
[0015] The (meth)acrylic polymer suitable for use in the present
invention can be the reaction product of one or more of the
aforementioned silane-containing ethylenically unsaturated
polymerizable materials and preferably an ethylenically unsaturated
polymerizable material that comprises carboxyl such as carboxylic
acid groups or an anhydride thereof. Examples of suitable
ethylenically unsaturated acids and/or anhydrides thereof include,
without limitation, acrylic acid, methacrylic acid, itaconic acid,
crotonic acid, maleic acid, maleic anhydride, citraconic anhydride,
itaconic anhydride, ethylenically unsaturated sulfonic acids and/or
anhydrides such as sulfoethyl methacrylate, and half esters of
maleic and fumaric acids, such as butyl hydrogen maleate and ethyl
hydrogen fumarate in which one carboxyl group is esterified with an
alcohol.
[0016] Examples of other polymerizable ethylenically unsaturated
monomers to introduce carboxyl functionality are alkyl including
cycloalkyl and aryl(meth)acrylates containing from 1 to 12 carbon
atoms in the alkyl group and from 6 to 12 carbon atoms in the aryl
group. Specific examples of such monomers include methyl
methacrylate, n-butyl methacrylate, n-butyl acrylate, 2-ethylhexyl
methacrylate, cyclohexyl methacrylate and phenyl methacrylate.
[0017] The amount of the polymerizable carboxyl-containing
ethylenically unsaturated monomers is preferably sufficient to
provide a carboxyl content of up to 55, preferably 15.0 to 45.0
percent by weight based on the weight of the total monomer
combination used to prepare the (meth)acrylic polymer. Preferably,
at least a portion of the carboxyl groups are derived from a
carboxylic acid such that the acid value of the polymer is within
the range of 20 to 80, preferably 30 to 70, on a 100% resin solids
basis.
[0018] The (meth)acrylic polymer used in the invention also
preferably contains hydroxyl functionality typically achieved by
using a hydroxyl functional ethylenically unsaturated polymerizable
monomer. Examples of such materials include hydroxyalkyl esters of
(meth)acrylic acids having from 2 to 4 carbon atoms in the
hydroxyalkyl group. Specific examples include
hydroxyethyl(meth)acrylate, hydroxypropyl(meth)acrylate and
4-hydroxybutyl (meth)acrylate. The amount of the hydroxy functional
ethylenically unsaturated monomer is sufficient to provide a
hydroxyl content of up to 6.5 such as 0.5 to 6.5, preferably 1 to 4
percent by weight based on the weight of the total monomer
combination used to prepare the (meth)acrylic polymer.
[0019] The (meth)acrylic polymer optionally contains nitrogen
functionality introduced from a nitrogen-containing ethylenically
unsaturated monomer. Examples of nitrogen functionality are amines,
amides, ureas, imidazoles and pyrrolidones. Examples of suitable
N-containing ethylenically unsaturated monomers are:
amino-functional ethylenically unsaturated polymerizable materials
that include, without limitation, p-dimethylamino ethyl styrene,
t-butylaminoethyl(meth)acrylate, dimethylaminoethyl(meth)acrylate,
diethylaminoethyl(meth)acrylate, dimethylaminopropyl(meth)acrylate
and dimethylaminopropyl(meth)acrylamide; amido-functional
ethylenically unsaturated materials that include acrylamide,
methacrylamide, n-methyl acrylamide and n-ethyl(meth)acrylamide;
urea functional ethylenically unsaturated monomers that include
methacrylamidoethylethylene urea.
[0020] If used, the amount of the nitrogen-containing ethylenically
unsaturated monomer is sufficient to provide nitrogen content of up
to 5 such as from 0.2 to 5.0, preferably from 0.4 to 2.5 percent by
weight based on weight of a total monomer combination used in
preparing the (meth)acrylic polymer.
[0021] Besides the polymerizable monomers mentioned above, other
polymerizable ethylenically unsaturated monomers that may be used
to prepare the (meth)acrylic polymer. Examples of such monomers
include poly(meth)acrylates such as ethylene glycol
di(meth)acrylate, trimethylolpropane tri(meth)acrylate,
ditrimethylolpropane tetraacrylate; aromatic vinyl monomers such as
styrene, vinyl toluene and alpha-methylstyrene; monoolefinic and
diolefinic hydrocarbons, unsaturated esters of organic and
inorganic acids and esters of unsaturated acids and nitrites.
Examples of such monomers include 1,3-butadiene, acrylonitrile,
vinyl butyrate, vinyl acetate, allyl chloride, divinyl benzene,
diallyl itaconate, triallyl cyanurate as well as mixtures thereof.
The polyfunctional monomers, such as the polyacrylates, if present,
are typically used in amounts up to 20 percent by weight. The
monfunctional monomers, if present, are used in amount up to 70
percent by weight; the percentage being based on weight of the
total monomer combination used to prepare the (meth)acrylic
polymer.
[0022] The (meth)acrylic polymer is typically formed by solution
polymerization of the ethylenically unsaturated polymerizable
monomers in the presence of a polymerization initiator such as azo
compounds, such as alpha, alpha'-azobis(isobutyronitrile),
2,2'-azobis(methylbutyronitrile) and
2,2'-azobis(2,4-dimethylvaleronitrile); peroxides, such as benzoyl
peroxide, cumene hydroperoxide and t-amylperoxy-2-ethylhexanoate;
tertiary butyl peracetate; tertiary butyl perbenzoate; isopropyl
percarbonate; butyl isopropyl peroxy carbonate; and similar
compounds. The quantity of initiator employed can be varied
considerably; however, in most instances, it is desirable to
utilize from 0.1 to 10 percent by weight of initiator based on the
total weight of copolymerizable monomers employed. A chain
modifying agent or chain transfer agent may be added to the
polymerization mixture. The mercaptans, such as dodecyl mercaptan,
tertiary dodecyl mercaptan, octyl mercaptan, hexyl mercaptan and
the mercaptoalkyl trialkoxysilanes such as 3-mercaptopropyl
trimethoxysilane may be used for this purpose as well as other
chain transfer agents such as cyclopentadiene, allyl acetate, allyl
carbamate, and mercaptoethanol.
[0023] The polymerization reaction for the mixture of monomers to
prepare the acrylic polymer can be carried out in an organic
solvent medium utilizing conventional solution polymerization
procedures which are well known in the addition polymer art as
illustrated with particularity in, for example, U.S. Pat. Nos.
2,978,437; 3,079,434 and 3,307,963. Organic solvents that may be
utilized in the polymerization of the monomers include virtually
any of the organic solvents often employed in preparing acrylic or
vinyl polymers such as, for example, alcohols, ketones, aromatic
hydrocarbons or mixtures thereof. Illustrative of organic solvents
of the above type which may be employed are alcohols such as lower
alkanols containing 2 to 4 carbon atoms including ethanol,
propanol, isopropanol, and butanol; ether alcohols such as ethylene
glycol monoethyl ether, ethylene glycol monobutyl ether, propylene
glycol monomethyl ether, and dipropylene glycol monoethyl ether;
ketones such as methyl ethyl ketone, methyl N-butyl ketone, and
methyl isobutyl ketone; esters such as butyl acetate; and aromatic
hydrocarbons such as xylene, toluene, and naphtha.
[0024] In certain embodiments, the polymerization of the
ethylenically unsaturated components is conducted at from 0.degree.
C. to 150.degree. C., such as from 50.degree. C. to 150.degree. C.,
or, in some cases, from 80.degree. C. to 120.degree. C.
[0025] The polymer prepared as described above is usually dissolved
in solvent and typically has a resin solids content of about 15 to
80, preferably 20 to 60 percent by weight based on total solution
weight. The molecular weight of the polymer typically ranges
between 3,000 to 1,000,000, preferably 5,000 to 100,000 as
determined by gel permeation chromatography using a polystyrene
standard.
[0026] For the electrospinning application, the polymer solution
such as described above can be mixed with water to initiate the
crosslinking reaction and to build viscosity necessary for fiber
formation. Typically about 5 to 20, preferably 10 to 15 percent by
weight water is added to the polymer solution with the percentage
by weight being based on total weight of the polymer solution and
the water. Preferably a base such as a water-soluble organic amine
is added to the water-polymer solution to catalyze the crosslinking
reaction. Optionally a thickener such as polyvinyl pyrrolidone,
polyvinyl alcohol, polyvinyl acetate, polyamides and/or a
cellulosic thickener can be added to the electrospinning
formulation to better control its viscoelastic behavior. If used,
the thickener is present in amounts no greater than 20 percent by
weight, typically from 1 to 6 percent by weight based on weight of
the polymer solution.
[0027] The electrospinning formulation prepared as described above
is then stored to permit the viscosity to build to the crosslinking
reaction. When the viscosity is sufficiently high but short of
gelation, the formulation is subjected to the electrospinning
process as described above.
[0028] Typically, the viscosity is at least 5 and less than 2,000,
usually less than 1,000, such as preferably within the range of 50
to 250 centistokes for the electrospinning process. A Bubble
Viscometer according to ASTM D-1544 determines the viscosity. The
time for storing the electrospinning formulation will depend on a
number of factors such as temperature, crosslinking functionality
and catalyst. Typically, the electrospinning formulation will be
stored for as low as one minute up to two hours.
[0029] When subject to the electrospinning process, the
formulations described above typically produce fibers having a
diameter of up to 5,000, such as from 5 to 5,000 nanometers, more
typically within the range of 50 to 1,200 nanometers, such as 50 to
700 nanometers. The fibers also can have a ribbon configuration and
in this case diameter is intended to mean the largest dimension of
the fiber. Typically the width of the ribbon shaped fibers is up to
5000 such as 500 to 5000 nanometers and the thickness up to 200
such as 5 to 200 nanometers.
[0030] The following examples are presented to demonstrate the
general principles of the invention. However, the invention should
not be considered as limited to the specific examples presented.
All parts are by weight unless otherwise indicated.
EXAMPLES A, B and C
Synthesis of Acrylic Silane Polymers
[0031] For each of Examples A to C in Table 1 below, a reaction
flask was equipped with a stirrer, thermocouple, nitrogen inlet and
a condenser. Charge A was then added and stirred with heat to
reflux temperature (75.degree. C.-80.degree. C.) under nitrogen
atmosphere. To the refluxing ethanol, charge B and charge C were
simultaneously added over three hours. The reaction mixture was
held at reflux condition for two hours. Charge D was then added
over a period of 30 minutes. The reaction mixture was held at
reflux condition for two hours and subsequently cooled to
30.degree. C.
TABLE-US-00001 TABLE 1 Example A Example B Example C Charge A
(weight in grams) Ethanol SDA 40B.sup.1 360.1 752.8 1440.2 Charge B
(weight in grams) Methyl Methacrylate 12.8 41.8 137.9 Acrylic acid
8.7 18.1 34.6 Silquest A-174.sup.2 101.4 211.9 405.4
2-hydroxylethylmethacrylate 14.5 0.3 0.64 n-Butyl acrylate 0.2 0.3
0.64 Acrylamide 7.2 -- -- Sartomer SR 355.sup.3 -- 30.3 -- Ethanol
SDA 40B 155.7 325.5 622.6 Charge C (weight in grams) Vazo 67.sup.4
6.1 12.8 24.5 Ethanol SDA 40B 76.7 160.4 306.8 Charge D (weight in
grams) Vazo 67 1.5 2.1 6.1 Ethanol SDA 40B 9.1 18.9 36.2 % Solids
17.9 19.5 19.1 Acid value 51.96 45.64 45.03 (100% resin solids) Mn
-- 3021.sup.5 5810 .sup.1Denatured ethyl alcohol, 200 proof,
available from Archer Daniel Midland Co.
.sup.2gamma-methacryloxypropyltrimethoxysilane, available from GE
silicones. .sup.3Di-trimethylolpropane tetraacrylate, available
from Sartomer Company Inc. .sup.42,2'-azo bis(2-methyl
butyronitrile), available from E.I. duPont de Nemours & Co.,
Inc. .sup.5Mn of soluble portion; the polymer is not completely
soluble in tetrahydrofuran.
EXAMPLES 1, 2 AND 3
Acrylic-Silane Nanofibers
Example 1
[0032] The acrylic-silane resin solution from Example C (8.5 grams)
was blended with polyvinylpyrrolidone (0.2 grams) and water (1.5
grams). The formulation was stored at room temperature for 215
minutes. A portion of the resulting formulation was loaded into a
10 ml syringe and delivered via a syringe pump at a rate of 1.6
milliliters per hour to a spinneret (stainless steel tube 1/16-inch
outer diameter and 0.010-inch internal diameter). This tube was
connected to a grounding aluminum collector via a high voltage
source to which about 21 kV potential was applied. The delivery
tube and collector were encased in a box that allowed nitrogen
purging to maintain a relative humidity of less than 25%. Ribbon
shaped nanofibers having a thickness of about 100-200 nanometers
and a width of 500-700 nanometers were collected on the grounded
aluminum panels and were characterized by optical microscopy and
scanning electron microscopy.
Example 2
[0033] The acrylic-silane resin solution from Example B (8.5 grams)
was blended with polyvinylpyrrolidone (0.1 grams) and water (1.5
grams). The formulation was stored at room temperature for 210
minutes. A portion of the resulting solution was loaded into a 10
ml syringe and delivered via a syringe pump at a rate of 0.2
milliliters per hour to the spinneret of Example 1. The conditions
for electrospinning were as described in Example 1. Ribbon shaped
nanofibers having a thickness of 100-200 nanometers and a width of
900-1200 nanometers were collected on grounded aluminum foil and
were characterized by optical microscopy and scanning electron
microscopy.
Example 3
[0034] The acrylic-silane resin from Example A (8.5 grams) was
blended with polyvinylpyrrolidone (0.1 grams) and water (1.5
grams). The formulation was stored at room temperature for 225
minutes. A portion of the resulting solution was loaded into a 10
ml syringe and delivered via a syringe pump at a rate of 1.6
milliliters per hour to the spinneret as described in Example 1.
The conditions for electrospinning were as described in Example 1.
Ribbon shaped nanofibers having a thickness of 100-200 nanometers
and a width of 1200-5000 nanometers were collected on grounded
aluminum foil and were characterized by optical microscopy and
scanning electron microscopy. A sample of the nanofibers was dried
in an oven at 110.degree. C. for two hours. No measurable weight
loss was observed. This indicates the nanofibers were completely
crosslinked.
[0035] Whereas particular embodiments of this invention have been
described above for purposes of illustration, it will be evident to
those skilled in the art that numerous variations of the details of
the present invention may be made without departing from the
invention as defined in the appended claims.
* * * * *