U.S. patent application number 14/366323 was filed with the patent office on 2014-12-04 for melt electrospun fibers containing micro and nanolayers and method of manufacturing.
The applicant listed for this patent is Virginia Tech Intellectual Properties, Inc.. Invention is credited to Naresh Budhavaram, Eugene G. Joseph, Roop Mahajan.
Application Number | 20140357144 14/366323 |
Document ID | / |
Family ID | 48669373 |
Filed Date | 2014-12-04 |
United States Patent
Application |
20140357144 |
Kind Code |
A1 |
Joseph; Eugene G. ; et
al. |
December 4, 2014 |
Melt Electrospun Fibers Containing Micro and Nanolayers and Method
of Manufacturing
Abstract
Fibers having two or more alternating polymer layers are formed
by co-extrusion followed by electroprocessing. The fibers can be
used as a non-woven mat or other substrate for a variety of
applications. Delamination of the fibers using ultrasonication
yields separated, micro and nanolayer, fiber ribbons which may also
be used a non-woven mat or other substrate.
Inventors: |
Joseph; Eugene G.;
(Blacksburg, VA) ; Budhavaram; Naresh;
(Blacksburg, VA) ; Mahajan; Roop; (Blacksburg,
VA) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Virginia Tech Intellectual Properties, Inc. |
Blacksburg |
VA |
US |
|
|
Family ID: |
48669373 |
Appl. No.: |
14/366323 |
Filed: |
December 14, 2012 |
PCT Filed: |
December 14, 2012 |
PCT NO: |
PCT/US2012/069629 |
371 Date: |
June 18, 2014 |
Related U.S. Patent Documents
|
|
|
|
|
|
Application
Number |
Filing Date |
Patent Number |
|
|
61577241 |
Dec 19, 2011 |
|
|
|
Current U.S.
Class: |
442/60 ; 264/465;
428/373; 442/361 |
Current CPC
Class: |
D01D 5/423 20130101;
D01F 6/06 20130101; Y10T 442/2008 20150401; D01F 6/04 20130101;
D01D 5/0023 20130101; D04H 1/559 20130101; Y10T 428/2929 20150115;
D04H 1/4382 20130101; D01D 5/30 20130101; D04H 1/728 20130101; Y10T
442/637 20150401; D01F 6/625 20130101 |
Class at
Publication: |
442/60 ; 428/373;
442/361; 264/465 |
International
Class: |
D04H 1/728 20060101
D04H001/728; D04H 1/4382 20060101 D04H001/4382 |
Claims
1. A co-extruded, electroprocessed fiber containing a plurality of
alternating layers of two or more different polymers, wherein said
fiber has a diameter of 50 .mu.m or less and has at least 50
layers.
2. The co-extruded, electroprocessed fiber of claim 1 wherein said
fiber has a diameter of 10 .mu.m or less.
3. A fibrous substrate, comprising a plurality of co-extruded,
electroprocessed fibers containing a plurality of alternating
layers of two or more different polymers, wherein said fiber has a
diameter of 50 .mu.m or less and has at least 50 layers.
4. The fibrous substrate of claim 3 wherein said co-extruded,
electroprocessed fibers have a diameter of 10 .mu.m or less.
5. The fibrous substrate of claim 3 configured as a non-woven.
6. The fibrous substrate of claim 3 further comprising a bioactive
agent deposited on said substrate.
7. The fibrous substrate of claim 3 further comprising a catalytic
agent deposited on said substrate.
8. The fibrous substrate of claim 3 further comprising a fire or
flame retardant deposited on said substrate.
9. A fibrous substrate, produced by the process of: co-extruding
two or more polymers; electroprocessing the co-extruded polymers to
produce a fiber containing a plurality of alternating layers of two
or more different polymers, wherein said fiber has a diameter of 50
.mu.m or less; and delaminating the fiber to yield fiber ribbons of
individual polymers co-extruded in said co-extruding step.
10. The fibrous substrate of claim 9 wherein said delaminating step
is performed by sonication of said fiber.
11. The fibrous substrate of claim 9 configured as a non-woven.
12. The fibrous substrate of claim 9 further comprising a bioactive
agent deposited on said substrate.
13. The fibrous substrate of claim 9 further comprising a catalytic
agent deposited on said substrate.
14. The fibrous substrate of claim 9 further comprising a fire or
flame retardant deposited on said substrate.
15. A method of producing ribbon shaped fibers or a fibrous
substrate which includes ribbon shaped fibers, comprising the steps
of: co-extruding two or more polymers; electroprocessing the
co-extruded polymers to produce a fiber containing a plurality of
alternating layers of two or more different polymers, wherein said
fiber has a diameter of 50 .mu.m or less; and delaminating the
fiber to yield fiber ribbons of individual polymers co-extruded in
said co-extruding step.
16. The method of claim 15 wherein said delaminating step is
performed by sonication of said fiber.
17. The method of claim 15 wherein said electroprocessing and
delaminating steps are performed under conditions which produce a
fibrous substrate configured as a non-woven.
18. The method of claim 15 further comprising depositing a
bioactive agent on said fiber ribbons.
19. The method of claim 15 further comprising depositing a
catalytic agent on said fiber ribbons.
20. The method of claim 15 further comprising depositing a fire or
flame retardant on said fiber ribbons.
21. The method of claim 15 wherein said fiber produced in said
electroprocessing step has a diameter of 10 .mu.m or less.
22. The method of claim 15 wherein said fiber produced in said
electroprocessing step has at least three layers.
23. The method of claim 15 wherein said fiber produced in said
electroprocessing step has at least 50 layers.
24. A method of producing fibers or a fibrous substrate which
includes said fibers, comprising the steps of: co-extruding two or
more polymers; and electroprocessing the co-extruded polymers to
produce a fiber containing a plurality of alternating layers of two
or more different polymers, wherein said fiber has a diameter of 50
.mu.m or less.
25. The method of claim 24 wherein said fiber produced in said
electroprocessing step has a diameter of 10 .mu.m or less.
26. The method of claim 24 wherein said fiber produced in said
electroprocessing step has at least three layers.
27. The method of claim 24 wherein said fiber produced in said
electroprocessing step has at least 50 layers.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This application claims priority to U.S. Provisional
Application 61/577,241 filed Dec. 19, 2011, and the complete
contents of that application is herein incorporated by
reference.
FIELD OF THE INVENTION
[0002] This invention pertains to electrospinning for the
production of nanofibers and nanofiber webs, and, more
particularly, the invention is focused on producing nanofibers and
nanofiber webs from a polymer melt.
BACKGROUND
[0003] Electrospinning is a process that is used to produce
nanofibers and nanofiber webs. The nanofibers and nanofiber webs
have been evaluated for use in a wide range of applications
including without limitation in filtration, protective clothing,
drug delivery, tissue engineering, and nanocomposites. Although
there is significant research interest in nanofiber development,
most of the current work is focused on electrospinning from
solutions. Solution electrospinning can pose a significant safety
problem during manufacture since most solvents used for synthetic
polymers are highly flammable, as well as toxic or carcinogenic.
The solvents employed in solution based electrospinning also pose
additional concerns such as solvent cost, solvent recovery, low
production rates, and limiting limited biomedical applications due
to residual toxic solvent. Hence, there is a strong interest in
developing solvent-free processes such as melt processes for the
manufacture of nanofibers.
SUMMARY
[0004] In an embodiment of the invention, co-extrusion technology
is combined with electroprocessing technology to produce nanofibers
containing multiple layers of materials.
[0005] In another embodiment of the invention, multilayered
nanofibers produced by electroprocessing are effectively
"delaminated" (i.e., the layers within the fibers are separated) by
sonication or other suitable energy application techniques.
[0006] According to an embodiment of the invention, a
"solvent-free" process is used to create fibrous materials that
have significantly higher surface areas than currently manufactured
nanofibers. Specifically, the process combines co-extrusion where
two polymer resins in the molten state are arranged to give
alternating layers via feed blocks or layer multipliers, with melt
electrospinning (or other suitable electroprocessing). By combining
the two technologies, nonwoven webs that have hundreds to over a
thousand layers within each microfiber can be created. These webs
can be subsequently exposed to ultrasonication to create
delamination of the layers which result in nanolayer melt
electrospun (NME) fibrous webs.
[0007] The multilayer electrospun fibers have been evaluated using
electron microscopy both before and after sonication. Experiments
have demonstrated that melt electrospun fibers produced according
to the invention with 257 alternating layers can be successfully
produced and delaminated by ultrasonication.
[0008] The invention includes melt electrospun fibers and matrices,
such as non-woven webs, of fibers that contain alternating layers,
and their method of production. In addition, the invention includes
nanolayer thick fibers (e.g., fiber ribbons) created by
delamination of melt electrospun fibers having alternating layers
of polymers. Also, the invention includes matrices of these
nanolayer thick fibers, in laminated or delaminated form. In some
applications, the inventive matrices can have substances of
interest deposited on them (e.g., bioactive agents, catalytic
agents, fire retardant chemicals, etc.).
[0009] In any exemplary embodiment, two extruders deliver different
polymers to a 3 layer feedblock where layering of the melt occurs
and this 3 layer melt stream is fed to a single orifice die. A high
voltage is applied to a flat plate collector placed at a suitable
distance from the die and electrospun fibers are formed and
collected on the flat plate. In another exemplary embodiment of
this invention, the 3 layer melt stream is fed to a layer
multiplying unit where the melt layers are multiplied (multiplying
depends on the number of multipliers used). A melt stream with 257
layers, when 7 multipliers are used, is fed to the single orifice
die. A high voltage is applied to a flat plate collector placed at
a suitable distance and electrospun fibers are collected on the
flat plate. In yet another embodiment of the invention, melt
electrospun webs that have about 257 alternating layer fibers are
exposed to ultrasonication (or other energy application or chemical
application) to create nanolayer thick fibers due to delamination
of the layers. Delamination can be achieved by other mechanisms
such as exposure to chemicals such as chloroform.
DESCRIPTION OF THE DRAWINGS
[0010] FIG. 1(a) is a schematic of the layer multiplying process
that occurs when using two layers as input to the layer multiplying
process.
[0011] FIG. 1(b) is a schematic of the cross-section of a fiber
with multiple layers of two different polymers.
[0012] FIGS. 2A-C are, respectively, schematic drawings of a system
for producing multilayer electrospun fibers according to the
invention with a flat plate collector (FIG. 2A), a rotary drum
collector (FIG. 2B), and a wide width die in combination with a
rotary drum collector (FIG. 2C).
[0013] FIG. 3 illustrates a simplified process for delaminating
fibers in a fibrous mat formed by melt electroprocessing multiple
polymers according to the invention.
[0014] FIG. 4 is a scanning electron micrograph (SEM) of a melt
electrospun fiber described in Example 1 that has 257 alternating
layers of polycaopactone (PCL) and polyethylene (PE).
[0015] FIG. 5 is a SEM image of a melt electrospun fiber described
in Example 2 that has 257 alternating layers of PCL and PE.
[0016] FIG. 6 is a SEM image of a melt electrospun fiber web
described in Example 7 that has 257 alternating layers of PCL and
PE after ultarsonication which shows delamination of the layers
after sonication.
[0017] FIG. 7 is an SEM image of a melt electrospun fiber web
described in Example 8 where PCL and PP layers in the fibers are
delaminated by exposure to chloroform with slight agitation.
[0018] FIG. 8 is an SEM image of a melt electrospun fiber web
described in Example 9 where PCL and PE layers in the fibers are
delaminated by exposure to chloroform with slight agitation.
DETAILED DESCRIPTION
[0019] "Co-extrusion" in the context of the present invention is a
process by which two polymer resins in the molten state are
arranged via feed blocks or layer multipliers to give alternating
layers. The number of layers in the final extruded form (e.g., film
or microfiber) can be as low as two or in the hundreds (up to and
exceeding a thousand). While feedblock technology is typically used
to produce films with approximately 3 to 7 layers,
layer-multiplying technology is used to produce hundreds to
thousands of layers within 25-50 micron thick films. The layer
multiplying process is shown schematically in FIGS. 1a and 1b.
[0020] With reference to FIG. 1a there is shown a two component
(AB) co-extrusion system which could include, for example, two
single screw extruders each connected by a melt pump to a
co-extrusion feedblock. The feedblock combines polymeric material
(a) and polymeric material (h) in an (AB) layer configuration (see
leftmost portion of FIG. 1a). Melt pumps (not shown) control the
two melt streams that are combined in the feedblock as two parallel
layers. By adjusting the melt pump speed, the relative layer
thickness, that is, the ratio of A to B can be varied (as shown,
the ratio of the top layer to the bottom layer). From the
feedblock, the melt goes through a series of multiplying elements.
As shown in FIG. 1a a multiplying element first slices the AB
structure vertically, and subsequently spreads the melt
horizontally. The flowing streams recombine, doubling the number of
layers. An assembly of n multiplier elements produces an extrudate
with the layer sequence (AB), where x is equal to (2).sup.n and n
is the number of multiplying elements to form a multilayer stack
(as depicted in the right most portion of FIG. 1a). FIG. 1b is a
cross-sectional view of a fiber with multiple layers produced by
co-extrusion (it being recognized that the layers in a co-extruded
fiber may not be flat as depicted in FIG. 1b; rather, the
individual layers may be curved or have other configurations, but
will form distinct regions in the fiber).
[0021] Co-extrusion with the use of feedblocks and multipliers is a
well understood technique in chemical engineering (see, for
example, U.S. Pat. No. 7,936,802, U.S. Pat. No. 7,141,297, U.S.
Pat. No. 7,255,928, U.S. Pat. No. 7,052,762, U.S. Pat. No.
3,565,985, and U.S. Pat. No. 3,051,453, each of which are herein
incorporated by reference). Layered melt blown fibers made using
feed block technology are described in U.S. Pat. No. 5,176,952 and
U.S. Pat. No. 5,207,970, both of which are herein incorporated by
reference.
[0022] The Examples below show the combination of polyethylene (PE)
and polycaprolactone (PCL) being combined as multiple layers in
electroprocessed fibers according to the present invention.
However, many different polymers can be employed in the practice of
the invention including without limitation polyolefins (e.g.,
polyethylene, polypropylene, etc.), poly(urethanes),
poly(siloxanes), poly(vinyl pyrolidone), poly(-hydroxy ethyl
methacrylate), poly(N-vinyl pyrrolidone), poly(methyl
methacrylate), poly(vinyl alcohol), poly(acrylic acid),
polyacrylamide, poly(ethylene-co-vinyl acetate), poly(ethylene
glycol), poly(methacrylic acid), polylactides (PLA), polyplycolides
(PGA), poly(lactide-co-glycolides) (PLGA), polyanhydrides,
polyorthoesters, styrene-diene block copolymers, and block
copolymers with tackifiers. In addition, thermally stable and melt
processable natural polymers (e.g., those occurring naturally in a
plant or animal) can be employed in the practice of the invention
including without limitation plasticized cellulose acetate.
[0023] In the context of the present invention, "electroprocessing"
or "electrodeposition" broadly include all methods of
electrospinning, electrospraying, electroaerosoling, and
electrosputtering of materials, including combinations of two or
more of such methods, as well as any other method wherein materials
are streamed, sprayed, sputtered, or dripped across an electric
field toward a target. A material can be electroprocessed from one
or more grounded reservoirs in the direction of a charged substrate
or from charged reservoirs toward a grounded target.
Electroprocessing can be performed using one or a plurality of
nozzles, and, in the case of using multiple nozzles, each nozzle
can be connected to a single reservoir or each can be connected to
a different reservoir where each reservoir contains the same or a
different melt. The size of the nozzles can be varied to provide
for increased or decreased flow out of the nozzles, and a pump or a
plurality of pumps can be used to control flow from the
reservoir(s). Electrospinning is generally defined as a process by
which fibers are formed from melt by streaming the melt through an
orifice. In an embodiment of this invention, elecrospinning is
achieved by applying a voltage to a collector and the melt is
streamed from through the orifice to the collector. Other
configurations are possible. Electroaerosoling is generally defined
as a process by which droplets are formed from a melt by streaming
an electrically charged solution or melt through an orifice.
[0024] Electroprocessing techniques are well known in the art. See,
for example, U.S. Pat. No. 7,759,082, U.S. Pat. No. 7,615,373, U.S.
Pat. No. 7,374,774, U.S. Pat. No. 6,787,357, U.S. Pat. No.
8,282,712, U.S. Pat. No. 6,592,623, U.S. Pat. No. 8,282,712, U.S.
Pat. No. 8,277,712, U.S. Pat. No. 8,277,711, U.S. Pat. No.
8,277,706, U.S. Pat. No. 8,262,958, U.S. Pat. No. 8,257,628, U.S.
Pat. No. 8,247,335, U.S. Pat. No. 8,246,730, U.S. Pat. No.
8,241,729, U.S. Pat. No. 8,178,199, U.S. Pat. No. 8,240,174, U.S.
Pat. No. 8,206,484, U.S. Pat. No. 8,178,199, U.S. Pat. No.
8,178,029, U.S. Pat. No. 8,173,559, U.S. Pat. No. 8,172,092, U.S.
Pat. No. 8,168,550, U.S. Pat. No. 8,163,350, U.S. Pat. No.
8,052,407, U.S. Pat. No. 7,757,811, U.S. Pat. 7,754,123, U.S. Pat.
No. 7,717,975, U.S. Pat. No. 7,691,168, U.S. Pat. No. 7,662,332,
U.S. Pat. No. 7,628,941, U.S. Pat. No. 7,618,579, U.S. Pat. No.
7,601,262, U.S. Pat. No. 7,452,835, U.S. Pat. No. 7,291,300, U.S.
Pat. No. 7,134,857, U.S. Pat. No. 7,070,640, and U.S. Pat. No.
6,838,005, each of which are herein incorporated by reference. As
discussed in these patents, natural fibers (e.g., collagen, fibrin,
etc.), and synthetic fibers, and combinations thereof can be
produced from solutions by electroprocessing.
[0025] The invention contemplates a co-extruded stream of two or
more polymer melts (e.g., polymer blend streams), which can be
multiplied or not multiplied, being subject to electroprocessing to
produce fibers with a plurality of layers therein. The fibers will
have at least two layers (Examples below show co-extruded,
electroprocessed fibers with three layers, and show the order of
the layers does not impact the ability to form fibers), and
possibly 50 to 100 or more layers (Examples below show co-extruded,
electroprocessed fibers with 247 layers).
[0026] The fibers produced by co-extrusion and electroprocessing
according to the invention are multilayered and have a diameter of
100 .mu.m or less. As shown in the Examples below, fibers of 50
.mu.m or less have been produced, and some multilayer fibers having
diameters as small as 5-10 .mu.m have been produced. Furthermore,
on delamination of the multilayer fibers, ribbon shaped fibers
which have thicknesses on the order of nanometers have been
produced.
[0027] In a preferred embodiment, the electroprocessed materials
form a "matrix". Matrices are comprised of multilayer fibers, or
blends of multilayer fibers and droplets of any size or shape.
Matrices can be single structures or groups of structures, and can
be formed through one or more electroprocessing methods using a
plurality of materials. Matrices can be engineered to possess
specific porosities.
[0028] Substances of interest can be deposited within, anchored to,
or placed on matrices. Exemplary substances of interest can include
bioactive agents (e.g., proteins, nucleic acids, antibodies,
anesthetics, hypnotics, sedatives, sleep inducers, antipsychotics,
antidepressants, antiallergics, antianginals, antiarthritics, anti
asthmatics, antidiabetics, antidiarrheal drugs, anticonvulsants,
antigout drugs, antihistamines, antipruritics, emetics,
antiemetics, antispasmondics, appetite suppressants, neuroactive
substances, neurotransmitter agonists, antagonists, receptor
blockers, reuptake modulators, beta-adrenergic blockers, calcium
channel blockers, disulfarim, muscle relaxants, analgesics,
antipyretics, stimulants, anticholinesterase agents,
parasympathomimetic agents, hormones, anticoagulants,
antithrombotics, thrombolytics, immunoglobulins,
immunosuppressants, hormone agonists, hormone antagonists,
vitamins, antimicrobial agents, antineoplastics, antacids,
digestants, laxatives, cathartics, antiseptics, diuretics,
disinfectants, fungicides, ectoparasiticides, antiparasitics, heavy
metals, heavy metal antagonists, chelating agents, alkaloids,
salts, ions, autacoids, digitalis, cardiac glycosides,
antiarrhythmics, antihypertensives, vasodilators, vasoconstrictors,
antimuscarinics, ganglionic stimulating agents, ganglionic blocking
agents, neuromuscular blocking agents, adrenergic nerve inhibitors,
anti-oxidants, anti-inflammatories, wound care products,
antithrombogenic agents, antitumoral agents, antithrombogenic
agents, antiangiogenic agents, antigenic agents, wound healing
agents, plant extracts, growth factors, growth hormones, cytokines,
immunoglobulins, osteoblasts, myoblasts, neuroblasts, fibroblasts,
glioblasts; germ cells, hepatocytes, chondrocytes, keratinocytes,
smooth muscle cells, cardiac muscle cells, connective tissue cells,
epithelial cells, endothelial cells, hormone-secreting cells,
neurons, emollients, humectants, anti-rejection drugs, spermicides,
conditioners, antibacterial agents, antifungal agents, antiviral
agents, antibiotics, tranquilizers, cholesterol-reducing drugs,
antitussives, histamine-blocking drugs and monoamine oxidase
inhibitors), catalysts (e.g., metals and metal alloys, such as
platinum, gold, ruthenium, rhodium, iridium, transition metals and
transition metal complexes, nanomaterial catalysts, zeolites,
alumina etc.), flame retarding agents, and carbon black
[0029] FIGS. 2A-C shows schematic drawings of an exemplary
electroprocessing configuration where a voltage controller 10 is
used to charge a target 12 or 12'. In FIG. 2A, the target 12 is a
flat panel. In FIGS. 2B and 2C, the target 12' is a mandrel or
rotary drum. In FIGS. 2B and 2C, the target 12 may be rotated
during electroprocessing in order to take up thicker non-woven mats
of multilayer fibers. The Target 12 or 12' can be of many different
shapes and sizes to suit the needs of the application.
[0030] Each of FIGS. 2A-2C, show a source 13 having a feedblock 14
and multiplier section 15 that allow combining a plurality of
polymers from polymer sources 16a-16n. The multiplier section 15
can have zero to a plurality of multipliers (e.g., 2, 3, 7, 10, 20,
etc.) depending on the application. With zero multipliers, the
feedblock 14 will be used to introduce a layered polymer melt for
electroprocessing. However, in some applications, it will be
advantageous to have 50 or 100 or more layers in each fiber (the
Examples below show formation of fibers with 247 layers). In the
present invention, the fibers produced will have at least two
different layers of two different polymers (the Examples below show
some fibers produced with three different layers having two
different polymers, wherein in one Example the outer layers are PE
and the inner layer is PCL and in another Example the inner layer
is PE and the outer layer is PCL). While the Examples below show
combining two polymers into one multilayered fiber, it will be
recognized that a plurality of the polymers can be combined by
co-extrusion. Thus, fibers having layers of three different
polymers, four different polymers, five different polymers, etc.
can be made according to the present invention. Thus, FIGS. 2A-C
are depicted with polymer sources 16A-16N, where N equals the
number of polymers being combined. Further, the polymers in the
polymer sources 16A-16N may themselves be polymer blends.
[0031] For simplicity, FIGS. 2A-2C show a single source 13.
However, it should be recognized that in the practice of the
present invention there can be a plurality of sources interacting
with a single target 12 or 12' during electroprocessing, and that
the polymers provided by each of the sources can be the same or
different. Furthermore, different operational designs can be used
for each of the sources to achieve the formation of multilayer
fibers of different diameter as well as mixtures of multilayer
fibers and multilayer droplets. In the context of the invention,
what is required is that the polymers provided by source 13 have at
least two different layers of two different polymers. The thickness
of each of the layers of polymers in the fiber can be varied by a
variety of means including by control of pumps (not shown) from the
polymer sources 16A-16N.
[0032] In FIGS. 2A-2C, the stream of polymer 18 emanating from the
nozzles or "tips" 20 or 20' directed towards the target 12 or 12'
can be controlled. For example, source 13 could supply a stream 18
of multilayer fibers or a mixture of multilayer fibers and droplets
towards target 12, or source 13 could supply a stream 22 of
multilayer fiber which may include branching. Control of the
streams can be achieved by a variety of mechanisms including
controlling polymer supply pumps, regulating the nozzle 20 or 20'
sizes in the sources 13, regulating the charge on the polymer
and/or target 12 or 12', etc. Ultimately, the target 12 or 12' will
receive a mass of multilayer fibers generally configured as a
non-woven mat. The multilayer fibers can have some crosslinking
with the polymers in adjacent fibers, and can contain multilayer
droplets interspersed with the multilayer fibers. The bottom of
FIG. 2C shows a plan view of the tip 20' where there are multiple
orifices for emitting multiple streams of polymer during
electroprocessing. With this design a thick mat can be created over
a wide area in a short term.
[0033] FIG. 3 illustrates the process of converting the multilayer
fibers created by coextrusion/electroprocessing to ribbon shaped
fibers, as shown by Example 7 below. The fibrous mat 50 from the
electrospinning target is placed in a delaminating device 52 such
as a sonicating bath. The sonicating bath 50 can contain any
suitable fluid (e.g., water, solvents, etc.) for permitting
ultrasonic energy to interact with the fibers such as, for example,
a mixture of isopropanol and water. Alternatively, delamination may
be achieved chemically by, for example, exposure to chloroform,
ethyl acetate, or other solvent. Further, chemical and physical
techniques may be used in combination, for example, by exposure to
chloroform or ethyl acetate which promotes delamination (e.g., by a
rinse) in combination with exposure to energy (e.g., sonication).
Delamination can be achieved fairly quickly. For example,
sonication of a multilayered polyethylene/polycaprolactone fiber of
less than 100 .mu.m in diameter achieved delamination in
approximately 30 seconds. FIG. 3 shows the delaminated fibers 54
can be retrieved as a mat from the delaminator (sonicating bath)
52. The delaminated fibers 54 are comprised of a plurality of
ribbon shaped fibers, typically on the order of nanometers in
thickness where each individual ribbon is of one distinct material.
FIG. 3 also shows that active agents 56 (such as biological active
agents, catalytic agents, etc.) can be deposited on the delaminated
fibers 54. This can be accomplished by spraying the active agent
onto the mat, dipping the mat into a pool of active agents,
electroplating the active agent onto the mat, and by many other
means recognized by those of skill in the art. In addition, while
FIG. 3 shows application of the active agent 56 to the delaminated
fibers 54, in some applications, active agents could simply be
applied to the mat of multilayer fibers 50.
[0034] The fibrous mats produced according to the invention can be
used in a wide variety of applications including without limitation
filtration, protective clothing, drug delivery, tissue engineering,
and nanocomposites. The fibrous materials have significantly higher
surface areas than currently manufactured nanofibers, which can
provide superior properties in many applications. In addition, the
fibrous materials are manufactured in a "solvent free" manner which
avoids many of the manufacturing risks and costs encountered in
current electrospinning processes.
EXAMPLES
[0035] In the Examples below, the polymeric components are melted
in a single screw extruder and transported via gear pumps to a 3
layer feedblock, where the two polymers are formed into a single
flow stream of 3 alternating layers. This 3 layer melt stream is
delivered to a layer multiplier that has seven multipliers where
the 3 layer stream is cut and stacked seven times to have final
melt stream that has 257 alternating layers. This melt stream is
delivered to a single orifice die and electrospun into fibers by
the application of a high voltage to a flat plate collector which
is positioned at a suitable distance across from the die.
[0036] The size and structure of the electrospun fibers were
obtained using a LEO (Zeiss) 1550 field emission scanning electron
microscope (FE-SEM) in the secondary electron mode. Scanning
electron microscopy images were obtained at different
magnifications and the fiber diameters were measured using image
analysis software.
[0037] For delamination, the melt electrospun fibers and webs were
immersed in a water/isopropanol (w/w 80/20) mix and exposed to
sonication using a Tekmar Sonic Disruptor at different intensities
and time periods. These materials were viewed in the SEM to
determine if delamination of the layers occurred and to what extent
it occurred.
Example 1
[0038] A melt electrospun fiber and web of the present invention
was made using polycaprolactone (PCL) resin (CAPA 6250 available
from Persorp UK Ltd) and polyethylene (PE) resin (Epolene C-10
available from Westlake Chemical Corporation). The polymer pellets
were fed to two extruders connected to gear pumps to control the
flow, which fed the melt streams to a 3 layer feedblock. Both
extruders and the feedblock were maintained at about 356.degree. F.
The feedblock split the two melt streams and arranged them in an
alternating fashion into a 3 layer melt stream on exiting the
feedblock, with the outer layers being PCL. The PCL PE ratio was
maintained at a 50:50 ratio by adjusting the gear pumps and the
flow rate of both gear pumps were maintained at 1 revolution per
minute (RPM). The layered melt stream was fed to a layer multiplier
that had 7 multipliers, which cut and stacked the layered stream
7.times. and resulted in a melt stream that had 257 layers upon
exiting the layer multiplier. The layer multiplier was maintained
at about 356.degree. F. This stream with 257 alternating layers was
fed to a single orifice die which was maintained at about
356.degree. F., and a voltage of 58 kV was applied to a flat plate
collector placed 6 inches away from the die to electrospin a
fibrous web. The resulting web had each fiber comprised of 258
alternating PCL/PE layers.
[0039] A scanning electron micrograph (SEM) of the electrospun
fiber produced according to this Example 1 is presented in FIG. 4.
The diameter of the fiber is approximately 5-10 .mu.m.
Example 2
[0040] A melt electrospun fiber and web, comprising 257 layer
fibers was prepared according to the procedure described in Example
1, except the voltage applied was 42 kV.
[0041] An SEM of the electrospun fibers is presented in FIG. 5. The
fiber diameters are approximately in the 25 to 30 .mu.m range.
Example 3
[0042] A melt electrospun fiber and web, comprising 257 layer
fibers was prepared according to the procedure described in Example
1, except the flow rate of both gear pumps were maintained at 2
RPM's, the voltage was 60 kV and the flat plate collector was
placed 4 inches away from the die.
Example 4
[0043] A melt electrospun fiber and web of the present invention
was made using polycaprolactone (PCL) resin (CAPA 6250 available
from Persorp UK Ltd) and polyethylene (PE) resin (Epolene C-10
available from Westlake Chemical Corporation). The polymer pellets
were fed to two extruders connected to gear pumps to control the
flow, which fed the melt streams to a 3 layer feedblock. Both
extruders and the feedblock were maintained at about 320.degree. F.
The feedblock split the two melt streams and arranged them in an
alternating fashion into a 3 layer melt stream on exiting the
feedblock, with the outer layers being PCL. The PCL:PE ratio was
maintained at a 50:50 ratio by adjusting the gear pumps and the
flow rate of both gear pumps were maintained at 0.5 RPM's. This
stream with 3 alternating layers was fed to a single orifice die
which was maintained at about 320.degree. F., and a voltage of 60
kV was applied to a flat plate collector placed 4 inches away from
the die to electrospin a fibrous web. The resulting web had each
fiber comprised of 3 alternating PCL/PE layers.
Example 5
[0044] A melt electrospun fiber and web of the present invention
was made using polyethylene (Epolene C-10 available from Westlake
Chemical Corporation) and polypropylene (PP) resin (PP 3746G
available from Exxon-Mobile Corporation). The polymer pellets and
granules were fed to two extruders connected to gear pumps to
control the flow, which fed the melt streams to a 3 layer
feedblock. Both extruders and the feedblock were maintained at
about 392.degree. F. The feedblock split the two melt streams and
arranged them in an alternating fashion into a 3 layer melt stream
on exiting the feedblock, with the outer layers being PE. The PE:PP
ratio was maintained at a 50:50 ratio by adjusting the gear pumps
and the flow rate of both gear pumps were maintained at 0.5 RPM.
This stream with 3 alternating layers was fed to a single orifice
die which was maintained at about 392.degree. F., and a voltage of
60 kV was applied to a flat plate collector placed 3 inches away
from the die to electrospin a fibrous web. The resulting web had
each fiber comprised of 3 alternating PE/PP layers.
Example 6
[0045] A melt electrospun fiber and web, comprising 3 layer fibers
was prepared according to the procedure described in Example 5,
except that PCL was substituted for PE, the PCL extruder
temperature was maintained at 356.degree. F., the PP extruder and
feedblock temperatures were maintained at 428.degree. F., the die
temperature was maintained at 536.degree. F., the voltage was 62 kV
and the flat plate collector was placed 10 inches away from the
die.
Example 7
[0046] A melt electrospun fiber web described in Example 1 was
immersed in a water/isopropanol (w/w 90/10) mix and exposed to
sonication using a Tekmar Sonic Disruptor at a setting of 3 for 30
minutes. FIG. 6 shows an SEM of the resulting material. Thick,
ribbon shaped fibers are observed due to delamination of the
layers.
Example 8
[0047] A melt electrospun fiber and web of the present invention
was made using polycaprolactone (PCL) resin (CAPA 6250 available
from Persorp UK Ltd) and polypropylene (PP) resin (PP 3746G
available from Exxon-Mobile Corporation). The polymer pellets and
granules were fed to two extruders connected to gear pumps to
control the flow, which fed the melt streams to a 3 layer
feedblock. Both extruders and the feedblock were maintained at
about 356.degree. F. The feedblock split the two melt streams and
arranged them in an alternating fashion into a 3 layer melt stream
on exiting the feedblock, with the outer layers being PCL. The
PCL:PP ratio was maintained at a 50:50 ratio by adjusting the gear
pumps and the flow rate of both gear pumps were maintained at 1
revolution per minute (RPM). The layered melt stream was fed to a
layer multiplier that had 7 multipliers, which cut and stacked the
layered stream 7.times. and resulted in a melt stream that had 257
layers upon exiting the layer multiplier. The layer multiplier was
maintained at about 356.degree. F. This stream with 257 alternating
layers was fed to a single orifice die which was maintained at
about 356.degree. F., and a voltage of 63 kV was applied to a flat
plate collector placed 10 inches away from the die to electrospin a
fibrous web. The resulting web had each fiber comprised of 257
alternating PCL/PP layers.
[0048] A melt electrospun fiber web described in this Example 8 was
immersed in a beaker of chloroform with a magnetic stirrer and
exposed to gentle agitation for 30 minutes. FIG. 7 shows an SEM of
the fibrous material where at least a portion of the layers of the
multilayer melt electrospun fibers have been delaiminated.
Example 9
[0049] A melt electrospun fiber and web of the present invention
was made using polycaprolactone (PCL) resin (CAPA 6250 available
from Persorp UK Ltd) and polyethylene (PE) resin (Epolene C-10
available from Westlake Chemical Corporation). The polymer pellets
were fed to two extruders connected to gear pumps to control the
flow, which fed the melt streams to a 3 layer feedblock. Both
extruders and the feedblock were maintained at about 356.degree. F.
The feedblock split the two melt streams and arranged them in an
alternating fashion into a 3 layer melt stream on exiting the
feedblock, with the outer layers being PCL. The PCL:PE ratio was
maintained at a 1:2 ratio by adjusting the gear pumps and the flow
rate of both gear pumps were maintained at 0.5 and 1.0 revolution
per minute (RPM) respectively. The layered melt stream was fed to a
layer multiplier that had 7 multipliers, which cut and stacked the
layered stream 7.times. and resulted in a melt stream that had 257
layers upon exiting the layer multiplier. The layer multiplier was
maintained at about 356.degree. F. This stream with 257 alternating
layers was fed to a single orifice die which was maintained at
about 356.degree. F., and a voltage of 65 kV was applied to a flat
plate collector placed 10 inches away from the die to electrospin a
fibrous web. The resulting web had each fiber comprised of 257
alternating PCL/PE layers.
[0050] A melt electrospun fiber web produced as described in this
Example 9 was immersed in a beaker of chloroform with a magnetic
stirrer and exposed to gentle agitation for 30 minutes. FIG. 8
shows an SEM of the fibrous material with delamination of at least
a portion of the layers.
* * * * *