U.S. patent application number 13/298259 was filed with the patent office on 2012-03-15 for cnt-infused fiber and method therefor.
This patent application is currently assigned to APPLIED NANOSTRUCTURED SOLUTIONS, LLC.. Invention is credited to Mark R. Alberding, Slade H. Gardner, Tushar K. SHAH.
Application Number | 20120065300 13/298259 |
Document ID | / |
Family ID | 39321521 |
Filed Date | 2012-03-15 |
United States Patent
Application |
20120065300 |
Kind Code |
A1 |
SHAH; Tushar K. ; et
al. |
March 15, 2012 |
CNT-INFUSED FIBER AND METHOD THEREFOR
Abstract
A carbon nanotube-infused fiber and a method for its production
are disclosed. Nanotubes are synthesized directly on a parent fiber
by first applying a catalyst to the fiber. The properties of the
carbon nanotube-infused fiber will be a combination of those of the
parent fiber as well as those of the infused carbon nanotubes.
Inventors: |
SHAH; Tushar K.; (Fulton,
MD) ; Gardner; Slade H.; (Palo Alto, CA) ;
Alberding; Mark R.; (Glen Arm, MD) |
Assignee: |
APPLIED NANOSTRUCTURED SOLUTIONS,
LLC.
Baltimore
MD
|
Family ID: |
39321521 |
Appl. No.: |
13/298259 |
Filed: |
November 16, 2011 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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11619327 |
Jan 3, 2007 |
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13298259 |
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Current U.S.
Class: |
523/468 ;
118/620; 423/414; 423/447.2; 427/177; 427/301; 427/450; 524/563;
524/599; 525/420; 536/56; 977/742; 977/840 |
Current CPC
Class: |
C01B 32/164 20170801;
C01B 32/162 20170801; B01J 23/755 20130101; B01J 23/74 20130101;
B01J 37/08 20130101; B82Y 30/00 20130101; B01J 23/745 20130101;
B01J 23/75 20130101; B82Y 40/00 20130101 |
Class at
Publication: |
523/468 ;
423/414; 423/447.2; 536/56; 525/420; 524/599; 524/563; 427/301;
427/177; 427/450; 118/620; 977/742; 977/840 |
International
Class: |
C08K 9/02 20060101
C08K009/02; C01B 31/04 20060101 C01B031/04; C08B 37/00 20060101
C08B037/00; C08G 69/48 20060101 C08G069/48; B05D 5/00 20060101
B05D005/00; C23C 4/04 20060101 C23C004/04; C23C 4/12 20060101
C23C004/12; C23C 4/02 20060101 C23C004/02; C01B 31/00 20060101
C01B031/00; B05D 3/10 20060101 B05D003/10 |
Claims
1. A method of infusing carbon nanotubes on a parent fiber, the
method comprising: applying a carbon nanotube-forming catalyst on a
surface of a parent fiber comprising a plurality of filaments,
thereby forming a catalyst-laden fiber; pre-heating the
catalyst-laden fiber to a temperature between about 500.degree. C.
and about 1000.degree. C. prior to synthesizing carbon nanotubes on
the catalyst-laden fiber; and while maintaining the catalyst-laden
fiber at a temperature ranging between about 500.degree. C. and
about 1000.degree. C., synthesizing carbon nanotubes on the
catalyst-laden fiber while the catalyst-laden fiber is being
transported, thereby forming a carbon nanotube-infused fiber.
2. The method of claim 1, further comprising: removing a sizing
material from the parent fiber prior to applying a carbon
nanotube-forming catalyst thereto.
3. The method of claim 1, further comprising: applying a resin to
the carbon nanotube-infused fiber.
4. The method of claim 3, further comprising: winding the carbon
nanotube-infused fiber about a mandrel after applying the
resin.
5. The method of claim 1, further comprising: spreading the
filaments of the parent fiber.
6. The method of claim 5, re-bundling the filaments of the spread
parent fiber.
7. The method of claim 1, wherein the carbon nanotube-forming
catalyst comprises a transition metal.
8. The method of claim 1, wherein the carbon nanotubes are
synthesized in a carbon plasma at atmospheric pressure.
9. The method of claim 1, wherein the parent fiber comprises a
fiber tow.
10. A system for producing carbon nanotube-infused fibers, the
system comprising: a carbon nanotube infusion station comprising,
in series, a catalyst application station, a heater, and a plasma
spray station; and a transport mechanism operable for conveying a
fiber comprising a plurality of filaments through the carbon
nanotube infusion station.
11. The system of claim 10, further comprising: a station for
spreading the fiber before the carbon nanotube infusion
station.
12. The system of claim 11, further comprising: a station for
re-bundling the spread fiber after the carbon nanotube infusion
station.
13. The system of claim 10, further comprising: a station for
removing a sizing material from the fiber before the carbon
nanotube infusion station.
14. The system of claim 13, wherein the station for removing a
sizing material comprises a heater.
15. The system of claim 10, wherein the plasma spray station
comprises a plurality of carbon plasma sprayers.
16. The system of claim 15, wherein the plasma spray station
further comprises heaters at the carbon plasma sprayers.
17. The system of claim 10, further comprising: a resin bath after
the carbon nanotube infusion station.
18. A composition comprising a carbon nanotube-infused fiber,
wherein the carbon nanotube-infused fiber comprises: a parent fiber
comprising a plurality of filaments; and a plurality of carbon
nanotubes covalently bonded to the parent fiber.
19. The composition of claim 18, further comprising a resin.
20. The composition of claim 18, wherein the parent fiber comprises
a fiber tow.
21. The composition of claim 18, wherein the carbon
nanotube-infused fiber is prepared by a process comprising:
applying a carbon nanotube-forming catalyst on a surface of a
parent fiber comprising a plurality of filaments, thereby forming a
catalyst-laden fiber; pre-heating the catalyst-laden fiber to a
temperature between about 500.degree. C. and about 1000.degree. C.
prior to synthesizing carbon nanotubes on the catalyst-laden fiber;
and while maintaining the catalyst-laden fiber at a temperature
ranging between about 500.degree. C. and about 1000.degree. C.,
synthesizing carbon nanotubes on the catalyst-laden fiber while the
catalyst-laden fiber is being transported.
22. The composition of claim 18, wherein the parent fiber comprises
a carbon fiber lacking a sizing material.
23. The composition of claim 18, wherein the electrical resistivity
of the carbon nanotube-infused fiber is lower than the electrical
resistivity of the parent fiber.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This application is a continuation of U.S. patent
application Ser. No. 11/619,327, filed on Jan. 3, 2007.
FIELD OF THE INVENTION
[0002] The present invention relates to carbon nanotubes and
fibers.
BACKGROUND OF THE INVENTION
[0003] Fibers are used for many different applications in a wide
variety of industries, such as the commercial aviation, recreation,
industrial and transportation industries. Commonly-used fibers for
these and other applications include cellulosic fiber (e.g.,
viscose rayon, cotton, etc.), glass fiber, carbon fiber, and aramid
fiber, to name just a few.
[0004] In many fiber-containing products, the fibers are present in
the form of a composite material (e.g., fiberglass, etc.). A
composite material is a heterogeneous combination of two or more
constituents that differ in form or composition on a macroscopic
scale. While the composite material exhibits characteristics that
neither constituent alone possesses, the constituents retain their
unique physical and chemical identities within the composite.
[0005] Two key constituents of a composite include a reinforcing
agent and a resin matrix. In a fiber-based composite, the fibers
are the reinforcing agent. The resin matrix keeps the fibers in a
desired location and orientation and also serves as a load-transfer
medium between fibers within the composite.
[0006] Fibers are characterized by certain properties, such as
mechanical strength, density, electrical resistivity, thermal
conductivity, etc. The fibers "lend" their characteristic
properties, in particular their strength-related properties, to the
composite. Fibers therefore play an important role in determining a
composite's suitability for a given application.
[0007] To realize the benefit of fiber properties in a composite,
there must be a good interface between the fibers and the matrix.
This is achieved through the use of a surface coating, typically
referred to as "sizing." The sizing provides an all important
physico-chemical link between fiber and the resin matrix and thus
has a significant impact on the mechanical and chemical properties
of the composite. The sizing is applied to fibers during their
manufacture.
[0008] Substantially all conventional sizing has lower interfacial
strength than the fibers to which it's applied. As a consequence,
the strength of the sizing and its ability to withstand interfacial
stress ultimately determines the strength of the overall composite.
In other words, using conventional sizing, the resulting composite
cannot have a strength that is equal to or greater than that of the
fiber.
SUMMARY OF THE INVENTION
[0009] The illustrative embodiment of the present invention is a
carbon nanotube-infused ("CNT-infused") fiber.
[0010] In CNT-infused fiber disclosed herein, the carbon nanotubes
are "infused" to the parent fiber. As used herein, the term
"infused" means physically or chemically bonded and "infusion"
means the process of physically or chemically bonding. The physical
bond between the carbon nanotubes and parent fiber is believed to
be due, at least in part, to van der Waals forces. The chemical
bond between the carbon nanotubes and the parent fiber is believed
to be a covalent bond.
[0011] Regardless of its true nature, the bond that is formed
between the carbon nanotubes and the parent fiber is quite robust
and is responsible for CNT-infused fiber being able to exhibit or
express carbon nanotube properties or characteristics. This is in
stark contrast to some prior-art processes, wherein nanotubes are
suspended/dispersed in a solvent solution and applied, by hand, to
fiber. Because of the strong van der Waals attraction between the
already-formed carbon nanotubes, it is extremely difficult to
separate them to apply them directly to the fiber. As a
consequence, the lumped nanotubes weakly adhere to the fiber and
their characteristic nanotube properties are weakly expressed, if
at all.
[0012] The infused carbon nanotubes disclosed herein effectively
function as a replacement for conventional "sizing." It has been
found that infused carbon nanotubes are far more robust molecularly
and from a physical properties perspective than conventional sizing
materials. Furthermore, the infused carbon nanotubes improve the
fiber-to-matrix interface in composite materials and, more
generally, improve fiber-to-fiber interfaces.
[0013] The CNT-infused fiber disclosed herein is itself similar to
a composite material in the sense that its properties will be a
combination of those of the parent fiber as well as those of the
infused carbon nanotubes. Consequently, embodiments of the present
invention provide a way to impart desired properties to a fiber
that otherwise lacks such properties or possesses them in
insufficient measure. Fibers can therefore be tailored or
engineered to meet the requirements of a specific application. In
this fashion, the utility and value of virtually any type of fiber
can be improved.
[0014] In accordance with the illustrative embodiment of a
CNT-infused fiber-forming process, nanotubes are synthesized in
place on the parent fiber itself. It is important that the carbon
nanotubes are synthesized on the parent fiber. If not, the carbon
nanotubes will become highly entangled and infusion does not occur.
As seen from the prior art, non-infused carbon nanotubes impart
little if any of their characteristic properties.
[0015] The parent fiber can be any of a variety of different types
of fibers, including, without limitation: carbon fiber, graphite
fiber, metallic fiber (e.g., steel, aluminum, etc.), ceramic fiber,
metallic-ceramic fiber, glass fiber, cellulosic fiber, aramid
fiber.
[0016] In the illustrative embodiment, nanotubes are synthesized on
the parent fiber by applying or infusing a nanotube-forming
catalyst, such as iron, nickel, cobalt, or a combination thereof,
to the fiber.
[0017] In some embodiments, operations of the CNT-infusion process
include: [0018] Removing sizing from the parent fiber; [0019]
Applying nanotube-forming catalyst to the parent fiber; [0020]
Heating the fiber to nanotube-synthesis temperature; and [0021]
Spraying carbon plasma onto the catalyst-laden parent fiber.
[0022] In some embodiments, the infused carbon nanotubes are
single-wall nanotubes. In some other embodiments, the infused
carbon nanotubes are multi-wall nanotubes. In some further
embodiments, the infused carbon nanotubes are a combination of
single-wall and multi-wall nanotubes. There are some differences in
the characteristic properties of single-wall and multi-wall
nanotubes that, for some end uses of the fiber, dictate the
synthesis of one or the other type of nanotube. For example,
single-walled nanotubes can be excellent conductors of electricity
while multi-walled nanotubes are not.
[0023] Methods and techniques for forming carbon nanotubes, as
disclosed in co-pending U.S. patent application Ser. No. 10/455,767
(now U.S. Pat. No. 7,261,779) and which is incorporated herein by
reference, can be adapted for use with the process described
herein. In the illustrative embodiment, acetylene gas is ionized to
create a jet of cold carbon plasma. The plasma is directed toward
the catalyst-bearing parent fiber.
[0024] As previously indicated, carbon nanotubes lend their
characteristic properties (e.g., exceptional mechanical strength,
low to moderate electrical resistivity, high thermal conductivity,
etc.) to the CNT-infused fiber. The extent to which the resulting
CNT-infused fiber expresses these characteristics is a function of
the extent and density of coverage of the parent fiber by the
carbon nanotubes.
[0025] In a variation of the illustrative embodiment, CNT infusion
is used to provide an improved filament winding process: In this
variation, carbon nanotubes are formed on fibers (e.g., graphite
tow, glass roving, etc.), as described above, and are then passed
through a resin bath to produce resin-impregnated, CNT-infused
fiber. After resin impregnation, the fiber is positioned on the
surface of a rotating mandrel by a delivery head. The fiber then
winds onto the mandrel in a precise geometric pattern in known
fashion.
[0026] The filament winding process described above provides pipes,
tubes, or other forms as are characteristically produced via a male
mold. But the forms made from the filament winding process
disclosed herein differ from those produced via conventional
filament winding processes. Specifically, in the process disclosed
herein, the forms are made from composite materials that include
CNT-infused fibers. Such forms will therefore benefit from enhanced
strength, etc., as provided by the CNT-infused fibers.
[0027] Any of a variety of different parent fibers can be used to
form CNT-infused fiber.
[0028] Of late, there has been a demand for carbon fiber forms that
are compatible with a broad range of resins and processes, and the
sizing material is an important determinant of this compatibility.
For example, sizing is critically important for providing an even
distribution of chopped carbon fiber in sheet molding compounds
("SMCs"), such as are used in some automotive body panels.
[0029] Notwithstanding this demand for carbon fiber and its
potentially broad applicability, carbon fiber has historically been
sized for compatibility with only epoxy resin. CNT-infused carbon
fiber, as produced according to the method disclosed herein,
addresses this problem by providing a fiber that is sized with
infused nanotubes, which provides the desired broad applicability
with a variety of resins and processes.
BRIEF DESCRIPTION OF THE DRAWINGS
[0030] FIG. 1 depicts a method for producing CNT-infused fiber in
accordance with the illustrative embodiment of the present
invention.
[0031] FIG. 2 depicts a system for implementing the illustrative
method for producing CNT-infused fiber.
[0032] FIG. 3 depicts a system for filament winding in accordance
with a variation of the illustrative embodiment.
DETAILED DESCRIPTION
[0033] The following terms are defined for use in this
Specification, including the appended claims: [0034] Carding--The
process by which the fibers are opened out into an even film.
[0035] Carded Fibers--Fibers that have been carded which opens them
up. [0036] Cloth--A reinforcement material made by weaving strands
of fiber yarns. [0037] Continuous Filament Strand--A fiber bundle
composed of many filaments. [0038] Also, when referring to gun
roving; a collection of string-like fiber or yarn, which is fed
through a chopper gun in a spray-up process. [0039] Continuous
Strand Roving--A bundle of filaments which are fed through a
chopper gun in a spray-up process. [0040] Fabric--A planar textile
structure produced by interlacing yarns, fibers, or filaments.
[0041] Fiber--A unit of matter, either natural, or manufactured,
which forms the basic element of fabrics and other textile
structures. [0042] Fiber orientation--Fiber alignment in a
non-woven or a mat laminate where the majority of fibers are in the
same direction, resulting in a higher strength in that direction.
[0043] Fiber Pattern--Visible fibers on the surface of laminates or
moldings; the thread size and weave of glass cloth. [0044]
Filament--A single fiber of an indefinite or extreme length, either
natural (e.g., silk, etc.) or manufactured. Typically microns in
diameter, manufactured fibers are extruded into filaments that are
converted into filament yarn, staple, or tow. [0045] Filament
Winding--A process which involves winding a resin-saturated strand
of glass filament around a rotating mandrel. [0046] Filament
Yarn--A yarn composed of continuous filaments assembled with, or
without twist. [0047] Infuse--To form a chemical bond. [0048] Male
Mold--A convex mold where the concave surface of the part is
precisely defined by the mold surface. [0049] Matrix--The liquid
component of a composite or laminate. [0050] Mandrel--The core
around which paper-, fabric-, or resin-impregnated fiber is wound
to form pipes, tubes, or vessels; in extrusion, the central finger
of a pipe or tubing die. [0051] Pultrusion--Reversed "extrusion" of
resin-impregnated roving in the manufacture of rods, tubes and
structural shapes of a permanent cross-section. The roving, after
passing through the resin dip tank, is drawn through a die to form
the desired cross-section. [0052] Resin--A liquid polymer that,
when catalyzed, cures to a solid state. [0053] Roving--The soft
strand of carded fiber that has been twisted, attenuated, and freed
of foreign matter preparatory to spinning. [0054] Sizing--A surface
treatment that is applied to filaments immediately after their
formation for the purpose of promoting good adhesion between those
filaments and the matrix, to the extent the filaments are to be
used as the reinforcing agent in a composite material. [0055]
Spray-up--The process of spraying fibers, resin and catalyst
simultaneously into a mold using a chopper gun. [0056] Strands--A
primary bundle of continuous filaments (or slivers) combined in a
single compact unit without twist. These filaments (usually 51, 102
or 204) are gathered together in the forming operations. [0057]
Tape--A narrow-width reinforcing fabric or mat. [0058] Tow--A loose
strand of filaments without twist. [0059] Twist--A term that
applies to the number of turns and the direction that two yarns are
turned during the manufacturing process. [0060] Woven Roving
Fabric--Heavy fabrics woven from continuous filament in roving
form. Usually in weights between 18-30 oz. per square yard. [0061]
Yarn--A generic term for a continuous strand of textile fibers,
filaments, or material in a form suitable for knitting, weaving,
braiding, or otherwise intertwining to form a textile fabric.
[0062] As the definitions that are provided above indicate, terms
such as "fiber," "filament," "yarn," etc., have distinct meanings.
But for the purposes of the specification and the appended claims,
and unless otherwise indicated, the term "fiber" is used in this
specification as a generic term to refer to filament, yarn, tow,
roving, fabric, etc., as well as fiber itself. The phrase
"CNT-infused fiber" is therefore understood to encompass
"CNT-infused fiber," "CNT-infused filament," "CNT-infused tow,"
CNT-infused roving," etc.
[0063] FIG. 1 depicts a flow diagram of process 100 for producing.
CNT-infused fiber in accordance with the illustrative embodiment of
the present invention.
[0064] Process 100 includes the operations of: [0065] 102: Applying
nanotube-forming catalyst to the parent fiber. [0066] 104: Heating
the parent fiber to a temperature that is sufficient for carbon
nanotube synthesis. [0067] 106: Spraying carbon plasma onto the
catalyst-laden parent fiber.
[0068] To infuse carbon nanotubes into a parent fiber, the carbon
nanotubes are synthesized directly on the parent fiber. In the
illustrative embodiment, this is accomplished by disposing
nanotube-forming catalyst on the parent fiber, as per operation
102. Suitable catalysts for carbon nanotube formation include,
without limitation, transition metal catalysts (e.g., iron, nickel,
cobalt, combinations thereof, etc.).
[0069] As described further in conjunction with FIG. 2, the
catalyst is prepared as a liquid solution that contains nano-sized
particles of catalyst. The diameters of the synthesized nanotubes
are related to the size of the metal particles.
[0070] In the illustrative embodiment, carbon nanotube synthesis is
based on a plasma-enhanced chemical vapor deposition process and
occurs at elevated temperatures. The temperature is a function of
catalyst, but will typically be in a range of about 500 to
1000.degree. C. Accordingly, operation 104 requires heating the
parent fiber to a temperature in the aforementioned range to
support carbon nanotube synthesis.
[0071] In operation 106, carbon plasma is sprayed onto the
catalyst-laden parent fiber. The plasma can be generated, for
example, by passing a carbon containing gas (e.g., acetylene,
ethylene, ethanol, etc.) through an electric field that is capable
of ionizing the gas.
[0072] Nanotubes grow at the sites of the metal catalyst. The
presence of the strong plasma-creating electric field can affect
nanotube growth. That is, the growth tends to follow the direction
of the electric field. By properly adjusting the geometry of the
plasma spray and electric field, vertically-aligned carbon
nanotubes (i.e., perpendicular to the fiber) are synthesized. Under
certain conditions, even in the absence of a plasma, closely-spaced
nanotubes will maintain a vertical growth direction resulting in a
dense array of tubes resembling a carpet or forest.
[0073] FIG. 2 depicts system 200 for producing CNT-infused fiber in
accordance with the illustrative embodiment of the present
invention. System 200 includes fiber payout and tensioner station
202, fiber spreader station 208, sizing removal station 210,
CNT-infusion station 212, fiber bundler station 222, and fiber
uptake bobbin 224, interrelated as shown.
[0074] Payout and tension station 202 includes payout bobbin 204
and tensioner 206. The payout bobbin delivers fiber 201 to the
process; the fiber is tensioned via tensioner 206.
[0075] Fiber 201 is delivered to fiber spreader station 208. The
fiber spreader separates the individual elements of the fiber.
Various techniques and apparatuses can be used to spread fiber,
such as pulling the fiber over and under flat, uniform-diameter
bars, or over and under variable-diameter bars, or over bars with
radially-expanding grooves and a kneading roller, over a vibratory
bar, etc. Spreading the fiber enhances the effectiveness of
downstream operations, such as catalyst application and plasma
application, by exposing more fiber surface area.
[0076] Payout and tension station 202 and fiber spreader station
208 are routinely used in the fiber industry; those skilled in the
art will be familiar with their design and use.
[0077] Fiber 201 then travels to sizing removal station 210. At
this station, any "sizing" that is on fiber 201 is removed.
Typically, removal is accomplished by burning the sizing off of the
fiber.
[0078] Any of a variety of heating means can be used for this
purpose, including, without limitation, an infrared heater, a
muffle furnace, etc. Generally, non-contact heating methods are
preferred. In some alternative embodiments, sizing removal is
accomplished chemically.
[0079] The temperature and time required for burning off the sizing
vary as a function of (1) the sizing material (e.g., silane, etc.);
and (2) the identity of parent fiber 201 (e.g., glass, cellulosic,
carbon, etc.). Typically, the burn-off temperature is a minimum of
about 650.degree. C. At this temperature, it can take as long as 15
minutes to ensure a complete burn off of the sizing. Increasing the
temperature above a minimum burn temperature should reduce burn-off
time. Thermogravimetric analysis can be used to determine minimum
burn-off temperature for sizing.
[0080] In any case, sizing removal is the slow step in the overall
CNT-infusion process. For this reason, in some embodiments, a
sizing removal station is not included in the CNT-infusion process
proper; rather, removal is performed separately (e.g., in parallel,
etc.). In this way, an inventory of sizing-free fiber can be
accumulated and spooled for use in a CNT-infused fiber production
line that does not include a fiber removal station). In such
embodiments, sizing-free fiber is spooled in payout and tension
station 202. This production line can be operated at higher speed
than one that includes sizing removal.
[0081] Sizing-free fiber 205 is delivered to CNT-infusion station
212, which is the "heart" of the process and system depicted in
FIG. 2. Station 212 includes catalyst application station 214,
fiber pre-heater station 216, plasma spray station 218, and fiber
heaters 220.
[0082] As depicted in FIG. 2, sizing-free fiber 205 proceeds first
to catalyst application station 214. In some embodiments, fiber 205
is cooled prior to catalyst application.
[0083] In some embodiments, the nanotube-forming catalyst is a
liquid solution of nanometer-sized particles (e.g., 10 nanometers
in diameter, etc.) of a transition metal. Typical transition metals
for use in synthesizing nanotubes include, without limitation,
iron, iron oxide, cobalt, nickel, or combinations thereof. These
transition metal catalysts are readily commercially available from
a variety of suppliers, including Ferrotech of Nashua, N.H. The
liquid is a solvent such as toluene, etc.
[0084] In the illustrative embodiment, the catalyst solution is
sprayed, such as by air sprayer 214, onto fiber 205. In some other
embodiments, the transition metal catalyst is deposited on the
parent fiber using evaporation techniques, electrolytic deposition
techniques, suspension dipping techniques and other methods known
to those skilled in the art. In some further embodiments, the
transition metal catalyst is added to the plasma feedstock gas as a
metal organic, metal salt or other composition promoting gas phase
transport. The catalyst can be applied at room temperature in the
ambient environment (neither vacuum nor an inert atmosphere is
required).
[0085] Catalyst-laden fiber 207 is then heated at fiber preheater
station 216. For the infusion process, the fiber should be heated
until it softens. Generally, a good estimate of the softening
temperature for any particular fiber is readily obtained from
reference sources, as is known to those skilled in the art. To the
extent that this temperature is not a priori known for a particular
fiber, it can be readily determined by experimentation. The fiber
is typically heated to a temperature that is in the range of about
500 to 1000.degree. C. Any of a variety of heating elements can be
used as the fiber preheater, such as, without limitation, infrared
heaters, a muffle furnace, and the like.
[0086] After preheating, fiber 207 is finally advanced to plasma
spray station having spray nozzles 218. A carbon plasma is
generated, for example, by passing a carbon containing gas (e.g.,
acetylene, ethylene, ethanol, etc.) through an electric field that
is capable of ionizing the gas. This cold carbon plasma is
directed, via spray nozzles 218, to fiber 207. The fiber is
disposed within about 1 centimeter of the spray nozzles to receive
the plasma. In some embodiments, heaters 220 are disposed above
fiber 207 at the plasma sprayers to maintain the elevated
temperature of the fiber.
[0087] After CNT-infusion, CNT-infused fiber 209 is re-bundled at
fiber bundler 222. This operation recombines the individual strands
of the fiber, effectively reversing the spreading operation that
was conducted at station 208.
[0088] The bundled, CNT-infused fiber 209 is wound about uptake
fiber bobbin 224 for storage. CNT-infused fiber 209 is then ready
for use in any of a variety of applications, including, without
limitation, for use as the reinforcing material in composite
materials.
[0089] It is noteworthy that some of the operations described above
should be conducted under inert atmosphere or vacuum, such that
environmental isolation is required. For example, if sizing is
being burned off of the fiber, the fiber must be environmentally
isolated to contain off-gassing and prevent oxidation. Furthermore,
the infusion process should be conducted under an inert atmosphere
(e.g., nitrogen, argon, etc.) to prevent oxidation of the carbon.
For convenience, in some embodiments of system 200, environmental
isolation is provided for all operations, with the exception of
fiber payout and tensioning (at the beginning of the production
line) and fiber uptake (at the end of the production line).
[0090] FIG. 3 depicts a further embodiment of the invention wherein
CNT-infused fiber is created as a sub-operation of a filament
winding process being conducted via filament winding system
300.
[0091] System 300 comprises fiber creel 302, carbon nanotube
infusion section 226, resin bath 328, and filament winding mandrel
332, interrelated as shown. The various elements of system 300,
with the exception of carbon nanotube infusion section 226, are
present in conventional filament winding processes. Again, the
"heart" of the process and system depicted in FIG. 3 is the carbon
nanotube infusion section 226, which includes fiber spreader
station 208, (optional) sizing-removal station 210, and
CNT-infusion station 212.
[0092] Fiber creel 302 includes plural spools 204 of parent fiber
201A through 201H. The untwisted group of fibers 201A through 201H
is referred to collectively as "tow 303." Note that the term "tow"
generally refers to a group of graphite fibers and the term
"roving" usually refers to glass fibers. Here, the term "tow" is
meant to refer, generically, to any type of fiber.
[0093] In the illustrative embodiment, creel 302 holds spools 204
in a horizontal orientation. The fiber from each spool 206 moves
through small, appropriately situated rollers/tensioners 206 that
change the direction of the fibers as they move out of creel 302
and toward carbon nanotube infusion section 226.
[0094] It is understood that in some alternative embodiments, the
spooled fiber that is used in system 300 is CNT-infused fiber
(i.e., produced via system 200). In such embodiments, system 300 is
operated without nanotube infusion section 226.
[0095] In carbon nanotube infusion section 226, tow 303 is spread,
sizing is removed, nanotube-forming catalyst is applied, the tow is
heated, and carbon plasma is sprayed on the fiber, as described in
conjunction with FIG. 2.
[0096] After passing through nanotube infusion section 226,
CNT-infused tow 307 is delivered to resin bath 328. The resin bath
contains resin for the production of a composite material
comprising the CNT-infused fiber and the resin. Some important
commercially-available resin-matrix families include general
purpose polyester (e.g., orthophthalic polyesters, etc.), improved
polyester (e.g., isophthalic polyesters, etc.), epoxy, and vinyl
ester.
[0097] Resin bath can be implemented in a variety of ways, two of
which are described below. In the illustrative embodiment, resin
bath 328 is implemented as a doctor blade roller bath wherein a
polished rotating cylinder (e.g., cylinder 330) that is disposed in
the bath picks up resin as it turns. The doctor bar (not depicted
in FIG. 3) presses against the cylinder to obtain a precise resin
film thickness on cylinder 330 and pushes excess resin back into
the bath. As fiber tow 307 is pulled over the top of cylinder 330,
it contacts the resin film and wets out. In some other embodiments,
resin bath 328 is realized as an immersion bath wherein fiber tow
307 is simply submerged into resin and then pulled through a set of
wipers or roller that remove excess resin.
[0098] After leaving resin bath 328, resin-wetted, CNT-infused
fiber tows 309 is passed through various rings, eyelets and,
typically, a multi-pin "comb" (not depicted) that is disposed
behind a delivery head (not depicted). The comb keeps the fiber
tows 309 separate until they are brought together in a single
combined band on rotating mandrel 332.
Example
[0099] A CNT-infused carbon fiber was formed in accordance with the
illustrative embodiment. A current was passed through carbon fiber
(the parent fiber) to heat it to approximately 800.degree. C. to
remove epoxy sizing material. The fiber was then cooled to room
temperature and left clamped between electrodes. A ferro-fluid
catalyst was applied to the fiber using an aerosol spray technique.
The fiber was allowed to dry and the chamber was closed, evacuated
and filled with argon. A current was passed through the carbon
fiber again to heat it to approximately 800.degree. C. for carbon
nanotube synthesis. A carbon plasma was generated from acetylene
precursor using 13.56 MHz microwave energy using an atmospheric
pressure plasma jet. The carrier gas in the plasma jet was helium
at 20 standard liters per minute (slm) and the argon was provided
at 1.2 slm. The plasma jet was fixtured to a robotic motion control
system allowing the plasma jet to move over the length of the fiber
at a speed between 6 and 12 inches per minute. The CNT-infused
fiber was then cooled to room temperature and removed from the
chamber. Scanning Electron Microscopy showed carbon nanotube
formation on the surface of the parent carbon fiber.
[0100] It is to be understood that the above-described embodiments
are merely illustrative of the present invention and that many
variations of the above-described embodiments can be devised by
those skilled in the art without departing from the scope of the
invention. For example, in this Specification, numerous specific
details are provided in order to provide a thorough description and
understanding of the illustrative embodiments of the present
invention. Those skilled in the art will recognize, however, that
the invention can be practiced without one or more of those
details, or with other methods, materials, components, etc.
[0101] Furthermore, in some instances, well-known structures,
materials, or operations are not shown or described in detail to
avoid obscuring aspects of the illustrative embodiments. It is
understood that the various embodiments shown in the Figures are
illustrative, and are not necessarily drawn to scale. Reference
throughout the specification to "one embodiment" or "an embodiment"
or "some embodiments" means that a particular feature, structure,
material, or characteristic described in connection with the
embodiment(s) is included in at least one embodiment of the present
invention, but not necessarily all embodiments. Consequently, the
appearances of the phrase "in one embodiment," "in an embodiment,"
or "in some embodiments" in various places throughout the
Specification are not necessarily all referring to the same
embodiment. Furthermore, the particular features, structures,
materials, or characteristics can be combined in any suitable
manner in one or more embodiments. It is therefore intended that
such variations be included within the scope of the following
claims and their equivalents.
* * * * *