U.S. patent application number 12/255806 was filed with the patent office on 2009-04-23 for fiber formation by electrical-mechanical spinning.
This patent application is currently assigned to PPG Industries Ohio, Inc.. Invention is credited to Melanie S. Campbell, Stuart D. Hellring, Calum H. Munro.
Application Number | 20090102100 12/255806 |
Document ID | / |
Family ID | 40228078 |
Filed Date | 2009-04-23 |
United States Patent
Application |
20090102100 |
Kind Code |
A1 |
Hellring; Stuart D. ; et
al. |
April 23, 2009 |
FIBER FORMATION BY ELECTRICAL-MECHANICAL SPINNING
Abstract
A method of fiber formation by electrical-mechanical spinning is
disclosed. A liquid starting material is fed to a rotating annular
member such as a spinning cup. The liquid material is directed by
centrifugal force to the periphery of the annular member where it
is expelled in fibrous form. An electric charge is imposed on the
liquid while on the annular member or while immediately being
expelled from the annular member.
Inventors: |
Hellring; Stuart D.;
(Pittsburgh, PA) ; Campbell; Melanie S.; (Sarver,
PA) ; Munro; Calum H.; (Wexford, PA) |
Correspondence
Address: |
PPG INDUSTRIES INC;INTELLECTUAL PROPERTY DEPT
ONE PPG PLACE
PITTSBURGH
PA
15272
US
|
Assignee: |
PPG Industries Ohio, Inc.
Cleveland
OH
|
Family ID: |
40228078 |
Appl. No.: |
12/255806 |
Filed: |
October 22, 2008 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
60981848 |
Oct 23, 2007 |
|
|
|
Current U.S.
Class: |
264/454 ;
264/465 |
Current CPC
Class: |
D01D 5/0985 20130101;
D01D 5/18 20130101; D01F 6/18 20130101; D01D 5/0069 20130101 |
Class at
Publication: |
264/454 ;
264/465 |
International
Class: |
D01D 5/08 20060101
D01D005/08; D06M 10/00 20060101 D06M010/00 |
Claims
1. A method of fiber production from a liquid material comprising
a. feeding the liquid material to a rotating annular member having
an interior surface extending to an open end and a periphery around
the open end, b. directing the liquid material by centrifugal force
along the interior surface towards the periphery of the rotating
member, and c. expelling the liquid material from the periphery
towards a target in fibrous form; wherein the liquid material is
electrically charged and the target is grounded.
2. The method of claim 1 in which the rotating annular member has a
base or closed end and walls having the interior surface extending
from the base or closed end to an open end and a periphery around
the open end.
3. The method of claim 2 in which the liquid material is directed
by centrifugal force along the base and across the interior surface
of the walls toward the periphery of the rotating member.
4. The method of claim 1 in which the liquid material is in the
form of a polymer solution or a polymer melt.
5. The method of claim 4 in which the polymer solution or polymer
melt comprises an organic polymer, an inorganic polymer or a hybrid
organic/inorganic polymer.
6. The method of claim 1 in which the fibers have a diameter of 5
to 5,000 nanometers.
7. The method of claim 3 in which the fibers have a diameter of 50
to 1200 nanometers.
8. The method of claim 1 in which the nanofibers are twisted
together in the form of a twisted yarn.
9. The method of claim 3 in which the annular member is in the form
of a truncated cone.
10. The method of claim 3 in which the rotating member is
positioned in the front end of a hollow drive shaft that rotates
therewith.
11. The method of claim 10 in which a feed tube for the liquid
material extends through the hollow drive shaft and into the
central area of the rotating member for the supply of liquid
material to the rotating member.
12. The method of claim 3 in which the rotating member has spinning
points located on its periphery.
13. The method of claim 12 in which the spinning points are
V-shaped serrations.
14. The method of claim 13 in which the serrations extend outwardly
from the periphery of the rotating member and are substantially
parallel to the axis of rotation.
15. The method of claim 3, which further includes propelling an
airstream normally against the expelled fibers so as to shape the
fibers into a flow pattern concentric with the axis of rotation of
the rotating member and towards the target.
16. The method of claim 15 in which the air stream is generated at
a pressure of 1 to 60 PSIG
(6.9.times.10.sup.3-4.1.times.10.sup.5-Pascals).
17. The method of claim 3 in which the fibers are collected on the
target.
18. The method of claim 17 distance from the periphery of the
rotating member to the target is from 2 to 30 inches (5-76 cm)
19. The method of claim 1 in which the fibers are collected on an
intermediate surface located between the target and the rotating
member.
20. The method of claim 1 in which the rotating member is rotating
at a speed of 1000 to 100,000 revolutions per minute.
21. The method of claim 1 in which the electrical potential between
the expelled liquid material and the grounded target is at least
5000 volts.
Description
FIELD OF THE INVENTION
[0001] The present invention relates to fiber formation,
particularly to fibers of nano dimensions.
BACKGROUND OF THE INVENTION
[0002] Fibers of nano dimensions can be produced by streaming an
electrostatically charged liquid such as a polymeric solution
through a jet or needle with a very small orifice. Scaling up this
process by using multiple needles suffers from the difficulty of
electrically isolating these needles from each other. Consequently,
needles typically must be at least one centimeter away from the
nearest neighbor. In addition, the need to draw a Tailor cone from
a single droplet on the end of each needle limits the maximum flow
rate per needle and increases the number of needles that are needed
to achieve large scale production.
[0003] Therefore, there is a need for a process to manufacture
fibers of nano dimensions with high throughput without the need for
multiple applicators. The present invention provides such a
process.
SUMMARY OF THE INVENTION
[0004] The present invention provides a method of fiber production
starting from a liquid material such as a polymer solution or a
polymer melt. The liquid material is fed to an annular rotating
member such as a disk or cup rotating around an axis concentric
therewith. The rotating member has a relatively smooth continuous
surface extending from the central area to a periphery. The liquid
material is directed by centrifugal force radially from the central
area to the periphery and is expelled from the periphery towards a
target. Liquid material is electrically charged either by the
rotating member or immediately after being expelled from the
periphery of the rotating member by passing through an electric
field. The target to which the fibers are directed is electrically
grounded. The difference in electrical potential between the
charged fibers and the target, the viscosity of the liquid material
and the size and speed of the annular member, the liquid delivery
rate and the optional use of shaping air are adjusted relative to
one another so that the liquid material is expelled in fibrous
form. Also adjusting these variables affects the quality and
quantity of the fibers.
DETAILED DESCRIPTION
[0005] Preferably, the continuous surface of the annular rotating
member is the interior surface of a substantially cylindrical
member such as a cup. The sides of the cup may be divergent such
that the cup is in the form of a truncated cone. The annular
spinning member rotates around an axis concentric therewith. The
rotating member may be electrically charged to impart an electrical
charge to the liquid material being fed to the rotating member.
Alternatively, an electrical charge can be imposed on the liquid
material as it is expelled from the rotating member in fibrous form
by passing the fibers through an electric field. As the rotating
member spins, the liquid material is centrifugally directed along
the interior surface towards the periphery of the rotating member.
Preferably, spinning points are located along the periphery of the
rotating member. Examples of such spinning points are V-shaped
serrations extending around the periphery, preferably extending
outwardly and substantially parallel to the axis of rotation of the
rotating member. The liquid material passes over the spin points
and is expelled from the rotating member towards the grounded
target. The rotating member may vary in size and geometry. The
rotating member may be as a disk or rotating bell. The diameter of
the rotating member may vary from 20 mm to 350 mm, such as 20 to
160, such as 30 to 80 mm. For fiber formation, the difference in
electrical potential between the charged fibers and the target is
preferably at least 5000 volts, such as within the range of 20,000
to 100,000 volts and 50,000 to 90,000 volts. If the electrical
potential is insufficient, droplets and not fibers may be
formed.
[0006] As the liquid material is expelled from the rotating member
in fibrous form, the fibers are directed towards a grounded target
where the fibers are collected. Alternately, the grounded target
can be positioned behind a moving belt or conveyor where the fibers
can be collected and removed from the target area. The distance to
target can vary from 2 to 50 (5 to 130 cm), such as 2 to 30 inches
(5 to 76 cm) such as 10 to 20 inches (25-51 cm). Preferably, with a
rotating bell an air stream is propelled normally and concurrently
against the expelled fibers so as to shape the fibers into a flow
pattern concentric with the axis of rotation and towards the
target. Typically air exits the rotary applicator via ports that
surround the rotating member outside diameter. Air pressure
measured at the entrance of the rotating member can typically be
set at such as 1-80 PSIG (6.9.times.10.sup.3-5.5.times.10.sup.5
Pascals), such as 1-60 PSIG (6.9.times.10.sup.3-4.1.times.10.sup.5
Pascals) such as from 5 to 40 PSIG
(3.4.times.10.sup.4-2.8.times.10.sup.5 Pascals). With a rotating
disk, shaping air is usually not used.
[0007] The rotating member is connected to a drive means such as a
rotating drive shaft connected to a member such as an electrical
motor or air motor capable of spinning the rotary member at speeds
of at least 500 rpm, such as 1000 to 100,000, and 3000 to 50,000
rpms typically with speeds of 10,000 to 100,000 rpms. If the speed
of the rotating member is insufficient, fibers may not form and the
liquid may be expelled from the rotary member as sheets or globs.
If the speed of the rotating member is too high, droplets may form
or fibers may break off.
[0008] Typically, the liquid material is passed through the
interior of the drive shaft and fed to the rotating member. When
the rotating member is cup-shaped, such as a rotating bell, the
liquid material is fed through the closed end of the cup and in the
central or base area of the cup. Typically, the liquid enters the
closed end of the cup through a supply nozzle that may range in
size from 0.5 to 1.5 mm. The liquid can then travel through the
inside of the cup and exits on the surface of the cup through a
center orifice or series of orifices onto the cup face.
[0009] The flow rate of liquid material to the rotating member is
typically 1 ml/hour to 500 ml/minute, such as from 20 ml/hour to 50
ml/minute such as from 50 to 1000 ml/hour.
[0010] The liquid material that is spun into fibers in accordance
with the invention is typically a polymer solution or melt. The
polymers can be organic polymers such as polyesters, polyamides,
polymers of n-vinyl pyrrolidone polyacrylonitrile and acrylic
polymers such as are described in published application U.S.
2008/0145655A1. Alternately, the liquid can be an inorganic
polymer. Examples of inorganic polymers are polymeric metal oxides
that contain alkoxide groups and optionally hydroxyl groups.
Preferably, the alkoxide groups contains from 1 to 4 carbon atoms
such as methoxide and ethoxide. Examples of such polymeric metal
oxides are polyalkylsilicates such as those of the following
structure:
##STR00001##
where R is alkyl containing from 1 to 4, preferably from 1 to 2
carbon atoms, and n is 3 to 10.
[0011] Also, hybrid organic/inorganic polymers such as acrylic
polymers and polymeric metal oxides can be employed. Examples of
such organic/inorganic hybrid polymers are described in published
application U.S. 2008/0207798A1. Also, inorganic materials such as
inorganic oxides or inorganic nitrides or carbon or ceramic
precursors, such as silica, aluminia, Titania, or mixed metal
oxides can be used
[0012] The electrical conductivity of the liquid material can vary
and should be sufficiently electrically conductive such that it can
accept a charge build up but not to the point that electrical
shorting occurs. With indirect charging, the electrical
conductivity can be high since shorting is not a problem. The
electrical conductivity can be adjusted by using appropriate
amounts of salts such as ammonium salts and electrically conductive
solvents such as alcohol-water mixtures.
[0013] The surface tension of the liquid material can vary. If the
surface tension is too high, atomization and droplets rather than
fibers may be formed.
[0014] The liquid preferably thickens as polymer concentration
increases or polymer crosslinking occurs. In the case of a polymer
solution, the viscosity of the solution can be controlled by
controlling the molecular weight of the polymer, the concentration
of the polymer in the solution, the presence of crosslinking of the
polymer in solution, or by adding a thickening agent to the polymer
solution such as polyvinyl pyrrolidone, polyvinyl alcohol,
polyvinyl acetate, polyamides and a cellulosic thickener. If the
viscosity of the solution is too high, i.e., at its gel point or
above, it behaves more like a solid material and may not form a
fiber and may build up as solid polymer on the surface of the
rotating member. If the viscosity of the liquid is too low,
atomization and not fiber formation may result.
[0015] The fibers that are formed in accordance with the invention
typically have diameters of up to 5,000 nanometers, such as 5 to
5,000 nanometers or within the range of 50 to 1200 nanometers such
as 50 to 700 nanometers. Fibers can also have ribbon or flat face
configuration and in this case the diameter is intended to mean the
largest dimension of the fiber. Typically, the width of
ribbon-shaped fibers is up to 5,000, such as 500 to 5,000
nanometers, and the thickness is up to 200, such as 5 to 200
nanometers.
[0016] In certain instances the nanofibers can be twisted around
each other in a yarn-like structure.
BRIEF DESCRIPTION OF THE DRAWINGS
[0017] FIG. 1 is a schematic vertical cross-section through a
centrifugal spinning apparatus in which the process of the
invention may be practiced.
[0018] FIG. 2 is a bottom elevation of a spinning member in
accordance with the process of the invention.
[0019] FIG. 3 is a section along line III-III of FIG. 2.
[0020] FIG. 4 shows photomicrographs at various magnifications of
nanofibers prepared in accordance with Example 1.
[0021] FIG. 4a (comparative) shows photomicrographs at various
magnifications of droplets prepared in accordance with Example 1a
(comparative).
[0022] FIG. 5 is a chart showing how the variables of rotating
member speed, shaping air and liquid flow effect fiber formation
for the polymer solutions of Examples 1 and 1a (comparative).
[0023] FIG. 6 shows photomicrographs at various magnifications of
nanofibers prepared in accordance with Example 2.
[0024] FIG. 6a (comparative) shows photomicrographs at various
magnifications of droplets prepared in accordance with Example 2a
(comparative).
[0025] FIG. 7 is a chart showing how the variables of rotating
member speed, shaping air and liquid flow effect fiber formation
for the polymer solutions of Examples 2 and 2a (comparative).
[0026] FIG. 8 shows photomicrographs at various magnifications of
nanofibers prepared in accordance with Example 3.
[0027] FIG. 8a (comparative) shows photomicrographs at various
magnifications of droplets prepared in accordance with Example 3a
(comparative).
[0028] FIG. 9 shows photomicrographs at various magnifications of
nanofibers in the form of a twisted yarn prepared in accordance
with Example 4.
[0029] FIG. 10 shows photomicrographs at various magnifications of
nanofibers prepared in accordance with Example 5.
[0030] With reference to FIG. 1, the apparatus 1 contains a
cup-shaped rotating member 5 and an air plenum arrangement 7
through which air is directed to shape the fibrous stream 9 as it
is directed towards the target 11. Positioned before the target is
a conveyor 12 for removing the fibrous product from the apparatus
1. A container 13 for the liquid material 15 includes a suitable
feed mechanism (not shown) for feeding the liquid material to the
rotating cup 5 via a feed supply line 17 mounted concentrically
with the axis 3. The supply line 17 has an exit in the rotating cup
5 adjacent to closed end. Preferably, the feed supply line is
located within a rotating drive shaft for rotating the cup-shaped
rotary member 5. As shown in FIG. 1, a voltage is imposed on the
rotating cup to impart a charge on the liquid material and the
fibers that are expelled from the rotating cup.
[0031] With references to FIGS. 2 and 3, the rotating member 5 is
cup-shaped having a planar base or closed end 21 and divergent
walls 23 extending from the base 21. The base 21 has a central
aperture 25 through which the feed supply line extends and fixing
elements 27 by which the rotating cup S is mounted on the drive
means for rotation around the axis 3. The interior surface 29 of
the wall 23 is relatively smooth over the region extending from the
base 21 to the edge 31 of the cup 5. The edge of the cup 5 is
serrated such that there are spinning points 33 defined by V-shaped
serrations 35 on the external periphery of the cup 5. V-shaped
serrations 35 lie in a plane parallel to the base of the cup 5, In
using apparatus 1, the cup 5 is spun at the desired rate and the
liquid is fed to the rotating cup in the central area of the base
of the cup and is directed to the periphery of the base 21 and
across the interior surface 29 by centrifugal force. The liquid
that is electrically charged flows across the interior surface 29
of the rotating cup through the spinning points 33 from which the
liquid is expelled in fibrous form towards the grounded target
11.
[0032] 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
Example A
[0033] An acrylic-silane polymer was prepared as follows.
[0034] With reference to 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 Charge A (weight in grams) Ethanol
SDA 40B.sup.1 477.5 Charge B (weight in grams) Methyl Methacrylate
0.2 Acrylic acid 11.5 Silquest A-174.sup.2 134.4
2-hydroxylethylmethacrylate 45.8 n-Butyl acrylate 0.2 Acrylamide
7.2 Ethanol SDA 40B 206.5 Charge C (weight in grams) Vazo 67.sup.3
8.1 Ethanol SDA 40B 101.7 Charge D (weight in grams) Vazo 67 2.0
Ethanol SDA 40B 12.0 % Solids 21.3 Acid value (solution) 10.5
.sup.1Denatured ethyl alcohol, 200 proof, available from Archer
Daniel Midland Co. .sup.2gamma-methacryloxypropyltrimethoxysilane,
available from GE silicones. .sup.32,2'-azo bis(2-methyl
butyronitrile), available from E.I. duPont de Nemours & Co.,
Inc.
[0035] A hybrid organic-inorganic polymer was prepared as
follows:
[0036] The ethanol solution of acrylic-silane polymer solution,
prepared as described above, 200 grams, was poured into a jar, and
deionized water (30 grams) was added. An ethanol solution of ethyl
polylsilicate (Silbond 40, Akzo Chemical, Inc) was added to the
polymer solution along with polyvinylpyrrolidone (4 grams, Aldrich,
Catalog 437190, CAS [9003-39-8], and MW 1,300,000). While warming
the jar with hot tap water, the mixture was hand shaken, and hand
stirred with a spatula until a homogeneous solution was obtained.
After this solution was allowed to stand at room temperature for
about 3.5 hours, its viscosity of was determined to be C.sup.+ by
the method of ASTM-D1545.
Example B
[0037] An acrylic-silane polymer was prepared as follows.
[0038] With reference to Table 2 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-00002 TABLE 2 Example A Charge A (weight in grams) Ethanol
SDA 40B.sup.1 288.0 Charge B (weight in grams) Methyl Methacrylate
16.0 Acrylic acid 6.9 Silquest A-174.sup.2 81.1
2-hydroxylethylmethacrylate 0.1 n-Butyl acrylate 0.1 Glycidyl
Methacrylate 11.6 Ethanol SDA 40B 124.5 Charge C (weight in grams)
Vazo 67.sup.3 49.0 Ethanol SDA 40B 61.1 Charge D (weight in grams)
Vazo 67 1.2 Ethanol SDA 40B 7.2 % Solids 18.5 Acid value (solution)
8.9 .sup.1Denatured ethyl alcohol, 200 proof, available from Archer
Daniel Midland Co. .sup.2gamma-methacryloxypropyltrimethoxysilane,
available from GE silicones. .sup.32,2'-azo bis(2-methyl
butyronitrile), available from E.I. duPont de Nemours & Co.,
Inc.
[0039] Deionized water (30 grams) was pored into a jar, and
polyvinylpyrrolidone (4 grams, Aldrich, Catalog 437190, CAS
[9003-39-8], and MW 1,300,000) was added. The mixture was warmed on
a hotplate to promote dissolution, and the resulting solution was
allowed to stand at room temperature. The acrylic-silane polymer
solution, 170 grams, was added to this aqueous polyvinylpyrrolidone
solution. While heating the contents of the jar with warm water on
a hot plate, the mixture was hand shaken until a homogeneous
solution was obtained. This organic polymer solution was allowed to
stand at room temperature to cool before use.
Example C
[0040] An inorganic sol gel polymer was prepared as follows.
[0041] Deionized water (36 grams) was placed in a jar, and
polyvinyl alcohol (4 grams, Aldrich, Catalog 36311, CAS
[9002-89-5], 96% hydrolyzed, and MW 85,000-100,000) was added to
the water while stirring magnetically. This mixture was warmed to
80.degree. C. in a hot water bath to affect dissolution. More
deionized water (40 grams) was added to this warm aqueous polyvinyl
alcohol solution while continuing to stir. To this warm, diluted
aqueous polyvinyl alcohol solution was added colloidal silica
dispersion (120 grams, MT-ST Silica, Nissan Chemical Industries,
LTD., about 30% silica in methanol) while continuing to stir.
Viscosity of this polyvinyl alcohol, silica solution was determined
to be A.sup.- by the method of ASTM-D1545.
Example D
[0042] A solution of polyacrylonitrile was prepared by dissolving
12 weight percent of polyacrylonitrile resin (Aldrich, Catalog
181315, CAS [25014-41-9], MW 150,000) in dimethylformaldehyde
solvent while warming on a hot plate.
Example 1
[0043] The polyacrylonitrile resin solution of Example D was loaded
into a 300 ml positive pressure fluid delivery system. A rate of
300 milliliters per hour was fed through a 3/8 inch (9.5 mm)
outside diameter teflon tube system to a rotary spray applicator
via a 1.1 mm diameter fluid nozzle. The outlet of the nozzle was
connected to a rotary bell cup 55 mm in diameter. The fluid nozzle
inserts to the back of the bell cup where approximately 80-100% of
the fluid exits through a circular slit of approximately 40 mm
diameter. The fluid then forms a thin sheet across the bell cup and
spins off the edge of the rotary bell cup to form fibers. This
rotary bell was set to spin at a rate of 12,000 rpms. The bell cup
edge geometry is configured with straight serrations. The
perpendicular distance from the circular slit to the edge of the
bell cup is approximately 7.85 cm. The bell cup referred to in this
experiment is a Durr Behr Eco bell cup model N16010037 type. The
bell shaping air was set at 25 psig (1.72.times.10.sup.5 Pascals)
at the back of the bell via a 1/2 inch (12.7 mm) outside diameter
nylon tube. The rotary applicator was connected to a high voltage
source with a 75,000 Volt indirect charge applied potential. The
entire delivery tube, rotary applicator and collector were in a
booth that allowed the environmental condition to maintain a
relative humidity of approximately 55% to 60% at a room temperature
of 70.degree. F. to 72.degree. F. (21.degree. C.-22.degree. C.).
Nanofibers were collected on the grounded target onto aluminum
panels set at a target/collection distance of 15 inches (38 cm)
from the rotary bell and were characterized by optical microscopy
and scanning electron microscopy. The nanofibers were essentially
cylindrical and had diameters of 600 to 1800 nanometers (nm). Some
large diameter fibers were observed that appear to be assemblies of
the smaller diameter fibers. The scanning electron micrograph is
shown in FIG. 4 and shows many fibers with little or no drops.
[0044] A Design Analysis was completed for the solution of Example
1 to determine application factors with respect to this solution.
The application factors studied for this work were bell speed from
12K rpms to 28K rpms, target distance from 10 inches to 20 inches
(25.4-50.8 cm), voltage from 60 KV to 90 KV, fluid delivery rate
from 100 ml/hour to 300 ml/hour and bell shaping air from 15 psig
to 35 psig (1.03.times.10.sup.5-2.41.times.10.sup.5 Pascals). The
results reported in FIG. 5 showed that fluid delivery rate, shaping
air, and bell speed were the most influential application factors
followed by target distance and KV.
[0045] In FIG. 5 "BS" refers to Bell Speed". "SA" refers to Shaping
Air. "FF" refers to Fluid Delivery Rate.
[0046] The values of the vertical axis are the product of the
thickness of the nanofiber mat that is formed multiplied by the
ratio of nanofiber to drops. The thickness of the mat is given a
subjective value of 1 to 10 and the ratio of nanofibers to drops is
given a subjective value of 1 to 6.
[0047] The higher the number of the value on the vertical axis,
more volume of good fibers is generated.
Example 1A (Comparative)
[0048] In this example, the procedure of Example 1 was repeated
with the following differences:
TABLE-US-00003 Bell Speed 28,000 rpms Target collector distance 10
inches (25.4 cm) Fluid delivery rate 200 ml/hour
[0049] Nanofibers were attempted to be collected on the grounded
aluminum target onto aluminum panels set at a part/collection and
were characterized by scanning electron microscopy as shown in FIG.
4a. The electron microscopy shows very little fiber formation and
many wet drops.
Example 2
[0050] The hybrid organic--inorganic polymer solution of Example A
was spun into nanofibers in accordance with the procedure of
Example 1, but using a Dur Behr Eco bell cup model N16010033. The
nanofibers were characterized by optical microscopy and scanning
electron microscopy. The nanofibers were somewhat flat-faced with
cross-sectional dimensions that ranged from 700 nanometers (nm) to
5000 nm. The scanning electron micrograph is shown in FIG. 6 and
shows many fibers with little or no wet drops.
Example 2A (Comparative)
[0051] In this example, the procedure of Example 2 was generally
followed with the following differences:
TABLE-US-00004 Bell Speed 28,000 rpms Target/collector distance 10
inches (25.4 cm) Fluid delivery rate 200 ml/hour
Nanofibers were attempted to be collected on the grounded aluminum
panel target and were characterized by scanning electron microscopy
as shown in FIG. 6A. This electron microscopy shows very little
fiber formation and many wet drops.
[0052] A Design Analysis as described in Example 1 was completed
for the solution of Example 2. The application factors studied for
this work were bell speed from 12K rpms to 28K rpms, target
distance from 10 inches to 20 inches (25.4-38.1 cm), voltage from
60 KV to 90 KV, fluid delivery rate from 100 ml/hour to 300 ml/hour
and bell shaping air from 15 psig to 35 psig
(1.03.times.10.sup.5-2.41.times.10.sup.5 Pascals). The results
reported in FIG. 7 showed that fluid delivery rate, shaping air,
bell speed and target distance were the most influential followed
by KV. FIG. 7 uses the same terminology as used in FIG. 5.
Example 3
[0053] The inorganic sol gel polymer solution of Example C was spun
into nanofibers in accordance with the procedure of Example 2 using
a fluid delivery rate of 100 milliliters per hour, a spin rate of
28,000 rpms, a voltage of 90,000 volts and a target collector
distance of 20 inches (50.8 cm). The bell shaping air was set at 15
psig (1.03.times.10.sup.5 Pascals) at the back of the bell.
Nanofibers were collected on the grounded aluminum panel target and
were characterized by optical microscopy and scanning electron
microscopy.
[0054] The nanofibers were essentially cylindrical and had
diameters of 100 to 700 nm. Some of the fibers appeared to have
small beads along the linear axis that had not drawn into a fiber.
The scanning electron micrograph is shown in FIG. 8 and shows many
small fibers with little drop formation.
Example 3A (Comparative)
[0055] In this example, the procedure of Example 3 was repeated
with the following differences:
TABLE-US-00005 Bell Speed 12,000 rpms Fluid flow rate of 300
ml/hour Target collector distance 10 inches (25.4 cm) Shaping air
35 psig (2.4 .times. 10.sup.5 Pascals)
[0056] Nanofibers were attempted to be collected on the grounded
aluminum target and were characterized by scanning electron
microscopy as shown in FIG. 8A. The electron microscopy shows
little fibers with wet drops.
Example 4
[0057] The polyacrylonitrile resin solution of Example D was spun
into fiber in accordance with the procedure of Example 1 using a
voltage 86,000. Fibers were collected on the grounded aluminum
panel target and were characterized by optical microscopy and
scanning electron microscopy. Large fibers collected on the panel.
One large fiber was removed from the panel and was evaluated
microscopically as shown in FIG. 9. A low resolution optical image
(left-most image) indicated that the large fiber might be an
assembly of smaller fibers. Scanning electron microscopy (center
image) revealed that these large fibers are a twisted yarn 100
microns in diameter comprised of several much smaller fibers. The
yarn is formed as the smaller fibers rotate from the spinning bell
cup. Higher magnification (right-most image) revealed that these
smaller fibers are nano-scale in diameter within the yarn.
Example 5
[0058] The organic polymer solution of Example B was spun into
fibers in accordance with the procedure of Example 1 with the
following differences:
TABLE-US-00006 Fluid flow rate 200 ml/hour Shaping air 35 psig
(2.41 .times. 10.sup.5 Pascals) Target collector distance 20 inches
(50.8 cm)
The nanofibers were somewhat flat-faced with cross-sectional
dimensions and had diameters of 300 to 700 nm. The scanning
electromicrograph is shown in FIG. 10. The micrograph shows many
small fibers with little drop formation.
[0059] The invention is now set forth in the following claims.
* * * * *