U.S. patent application number 11/357644 was filed with the patent office on 2007-05-10 for nanotube/matrix composites and methods of production and use.
Invention is credited to Robert L. Shambaugh.
Application Number | 20070104947 11/357644 |
Document ID | / |
Family ID | 35810574 |
Filed Date | 2007-05-10 |
United States Patent
Application |
20070104947 |
Kind Code |
A1 |
Shambaugh; Robert L. |
May 10, 2007 |
Nanotube/matrix composites and methods of production and use
Abstract
A nanotube/matrix composite mixture, and a method of producing
it, which can be used to form a composite material such as a drawn
fiber having an increased strength over a drawn fiber formed from
the matrix material alone. Nanotubes are combined with a solvent
material to form a nanotube/solvent mixture. The nanotube/solvent
mixture is mixed, for example by sonication, such that the
nanotubes are uniformly dispersed in the nanotube/solvent mixture.
An amount of a matrix material (with or without a solvent) is then
combined with the nanotube/solvent mixture to form a
nanotube/solvent/matrix mixture. The matrix material is
polyethylene. The nanotube/solvent mixture and the matrix material
are mixed such that the nanotubes are maintained in uniformly
dispersed state in the nanotube/solvent/matrix mixture, for example
by continued sonication after the nanotubes and matrix material are
combined. The solvent material is then substantially removed from
the nanotube/solvent/matrix mixture to form the nanotube/matrix
composite mixture, which can then be used in a commercial process
to produce a composite material such as drawn fiber, as produced,
for example, by melt spinning.
Inventors: |
Shambaugh; Robert L.;
(Norman, OK) |
Correspondence
Address: |
DUNLAP, CODDING & ROGERS P.C.
PO BOX 16370
OKLAHOMA CITY
OK
73113
US
|
Family ID: |
35810574 |
Appl. No.: |
11/357644 |
Filed: |
February 17, 2006 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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10223559 |
Aug 16, 2002 |
7001556 |
|
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11357644 |
Feb 17, 2006 |
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60312980 |
Aug 16, 2001 |
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Current U.S.
Class: |
428/359 ;
264/210.6; 264/210.8; 264/211; 423/445B; 428/364 |
Current CPC
Class: |
B82Y 30/00 20130101;
Y10S 977/842 20130101; Y10T 428/2904 20150115; Y10T 428/2913
20150115; Y10S 977/753 20130101 |
Class at
Publication: |
428/359 ;
264/210.6; 264/210.8; 264/211; 423/445.00B; 428/364 |
International
Class: |
B82B 3/00 20060101
B82B003/00; D01F 1/10 20060101 D01F001/10; D01F 6/06 20060101
D01F006/06; D02G 3/00 20060101 D02G003/00 |
Claims
1. A method for forming a nanotube/matrix composite mixture,
comprising the steps of: a. combining an amount of single walled
carbon nanotubes with a solvent material to form a nanotube/solvent
mixture and mixing the nanotube/solvent mixture for a predetermined
mixing period such that the single walled carbon nanotubes are
uniformly dispersed in the nanotube/solvent mixture; b. combining
an amount of a matrix material with the single walled
nanotube/solvent mixture having the single walled carbon nanotubes
uniformly dispersed therein to form a nanotube/solvent/matrix
mixture and mixing the nanotube/solvent/matrix mixture for a
predetermined mixing period such that the single walled carbon
nanotubes are uniformly dispersed in the nanotube/solvent/matrix
mixture, the matrix material being polyethylene; and c. removing a
substantial amount of the solvent material from the
nanotube/solvent/matrix mixture to form a nanotube/matrix composite
mixture comprising less than about 5% by weight of the solvent
material.
2. The method of claim 1, wherein the solvent is decalin, toluene,
or a combination thereof.
3. The method of claim 1, wherein in step (a) the nanotube solvent
mixture further comprises a surfactant.
4. The method of claim 1, further comprising the steps of: d.
heating the nanotube/matrix composite mixture to a temperature
above the melting point of the matrix material; and e. passing the
heated nanotube/matrix composite mixture through an orifice to form
an extrudate.
5. The method of claim 4, further comprising the step of: f.
drawing the extrudate to form a drawn fiber.
6. The method of claim 5, wherein step (f) is further defined as
the steps of passing the extrudate through an oven and
simultaneously stretching the extrudate wherein the drawn fiber has
a diameter less than a diameter of the extrudate.
7. The nanotube/matrix composite mixture produced by the method of
claim 1.
8. The extrudate produced by the method of claim 4.
9. A composite material produced from the nanotube/matrix composite
mixture of claim 7.
10. The drawn fiber produced by the method of claim 5.
11. The drawn fiber of claim 10 having a stress-strain behavior at
least 50% greater than a stress-strain behavior of a drawn fiber
produced from the matrix material without nanotubes.
12. The drawn fiber produced by the method of claim 6.
13. The drawn fiber of claim 12 having a stress-strain behavior at
least 50% greater than a stress-strain behavior of a drawn fiber
produced from the matrix material without nanotubes.
14. The method of claim 1 wherein the nanotube/matrix composite
mixture formed in step (c) comprises from about 0.5% to 1.5% by
weight of single walled carbon nanotubes after step (d).
15. The method of claim 1 wherein in step (a) the solvent material
comprises more that one solvent.
16. The method of claim 1 wherein the predetermined mixing period
of step (a) is a length of time such that the single walled carbon
nanotubes remain substantially unbroken before step (b).
17. The method of claim 16 wherein the predetermined mixing period
of step (b) is a length of time such that the single walled carbon
nanotubes remain substantially unbroken before step (c).
18. A method for forming a nanotube/matrix composite mixture,
comprising the steps of: a. combining an amount of single walled
carbon nanotubes with a first solvent material to form a
nanotube/solvent mixture and mixing the nanotube/solvent mixture
for a predetermined mixing period such that the single walled
carbon nanotubes are uniformly dispersed in the nanotube/solvent
mixture; b. combining an amount of a matrix material with a second
solvent material to form a matrix/solvent mixture and mixing the
matrix material and the second solvent material in the
matrix/solvent mixture, the second solvent material being miscible
with the first solvent material, the matrix material being
polyethylene; c. combining the nanotube/solvent mixture with the
matrix/solvent mixture to form a nanotube/solvent/matrix mixture
and mixing the nanotube/solvent/matrix mixture for a predetermined
mixing period such that the single walled carbon nanotubes therein
are uniformly dispersed in the nanotube/solvent/matrix mixture; and
d. removing the first and second solvent materials from the
nanotube/solvent/matrix mixture to form a nanotube/matrix composite
mixture comprising less than about 5% by weight of the first and
second solvent materials.
19. The method of claim 18, wherein the first solvent material and
the second solvent material are selected from the group consisting
of decalin, toluene, and combinations thereof.
20. The method of claim 18, wherein step (a) further comprises
combining a surfactant material with the nanotube/solvent mixture
and/or step (b) further comprises combining a surfactant with the
matrix/solvent mixture.
21. The method of claim 18, further comprising the steps of: e.
heating the nanotube/matrix composite mixture to a temperature
above the melting point of the matrix material; and f. passing the
heated nanotube/matrix composite mixture through an orifice to form
an extrudate.
22. The method of claim 18, further comprising the steps of: g.
drawing the extrudate to form a drawn fiber.
23. The method of claim 22, wherein step (g) is further defined as
the steps of passing the extrudate through an oven and
simultaneously stretching the extrudate wherein the drawn fiber has
a diameter less than a diameter of the extrudate.
24. The nanotube/matrix composite mixture produced by the method of
claim 18.
25. A composite material produced from the nanotube/matrix
composite mixture of claim 24.
26. The extrudate produced by the method of claim 21.
27. The drawn fiber produced by the method of claim 22.
28. The drawn fiber of claim 27 having a stress-strain behavior at
least 50% greater than a stress-strain behavior of a drawn fiber
produced from the matrix material without nanotubes.
29. The drawn fiber produced by the method of claim 23.
30. The drawn fiber of claim 29 having a stress-strain behavior at
least 50% greater than a stress-strain behavior of a drawn fiber
produced from the matrix material without nanotubes.
31. The method of claim 18 wherein the nanotube/matrix composite
mixture formed in step (d) comprises from about 0.5% to 1.5% by
weight of single walled carbon nanotubes.
32. The method of claim 18 wherein in step a the solvent material
comprises more that one solvent.
33. The method of claim 18 wherein the predetermined mixing period
of step (a) is a length of time such that the single walled carbon
nanotubes remain substantially unbroken before step (b).
34. The method of claim 33 wherein the predetermined mixing period
of step (b) is a length of time such that the single walled carbon
nanotubes remain substantially unbroken before step (c).
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This application is a continuation of U.S. Ser. No.
10/223,559, filed Aug. 16, 2002, now U.S. Pat. No. 7,001,556, which
claims priority under 35 U.S.C. .sctn. 119(e) from U.S. Provisional
Application No. 60/312,980, filed Aug. 16, 2001, all of which are
hereby incorporated herein by reference in their entirety.
STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH AND
DEVELOPMENT
[0002] Not applicable.
BACKGROUND OF THE INVENTION
[0003] For sheets and films, a number of investigators have used
nanotubes as the reinforcement in a nanotube/polymer composite. For
example, Schadler et al. (1998) and Gong et al. (2000) produced
composites of nanotubes in epoxy. Shaffer and Windle (1999)
examined a nanotube/poly(vinyl alcohol) composite. Bower et al.
(1999) fabricated a composite with nanotubes in a
polyhydroxyaminoether. Unless sheets and films are unusually thin,
they can also be reinforced with more normally-sized (e.g.,
diameters of 100 microns or more) reinforcement. However,
nano-scale reinforcement is uniquely suited for strengthening
polymer fibers, since the fibers themselves are typically only 10
to 100 microns in diameter. Since nanotubes are orders of magnitude
smaller in diameter, a nanotube cannot occlude a high fraction of
the fiber cross-section.
[0004] Presently, fibers produced from "commodity" polymers (e.g.,
polyester, polypropylene, and nylon) have tensile strengths from
about 0.15 to 0.6 Gpa. More expensive "specialty" fibers (such as
Kevlar.RTM. and PAN carbon fiber) have strengths of about 2 to 5
Gpa. The recently discovered carbon nanotubes have a theoretical
strength of 200 Gpa (Schadler et al., 1998) --about 40 times higher
than existing materials. However, capitalizing on this potential
strength has thus far been problematic.
[0005] Several research teams have used single walled carbon
nanotubes (SWNTs) to enhance the strength of neat fibers. Andrews
et al. (1999) dispersed SWNTs in isotropic petroleum pitch. With a
5 wt % loading, the tensile strength and modulus were increased 90
and 150%, respectively. Haggenmueller et al. (2000) reinforced PMMA
(polymethyl methacrylate) with SWNTs. They found a 54% increase in
tensile strength and a 94% increase in modulus when an 8 wt %
loading of nanotubes was used.
[0006] Most multiwalled carbon nanotubes (MWNTs) are believed to
have the "Russian doll" structure where only weak van de Waal
forces bond one tube to another (Harris, 1999). Hence, the outer
layers of MWNTs could slide or telescope relative to each other
(Schadler et al., 1998; Shaffer and Windle, 1999). However, kinks
and defects could help prevent this sliding (Harris, 1999). Ruoff
and Lorents (1996) believe that SWNTs are preferable to MWNTs
because SWNTs are easier to bond than MWNTs. These researchers also
feel that the tensile strength of the modified SWNTs might be
affected by bonding. However, Garg and Sinnott (1998; also see
Harris, 1999) showed in theoretical calculations that covalent
attachments only decrease SWNT strength by about 15%.
[0007] Carbolex.RTM. AP Grade Nanotubes is a type of commercially
available nanotube material. Carbolex.RTM. AP Grade Nanotubes is an
"as prepared" nanotube material that contains about 70% SWNT and is
produced by a carbon arc process. Previous investigators have used
ultrasonic mixing (Schadler et al., 1998) or mechanical mixing and
a surfactant (Gong et al., 2000) in attempts to disperse material
of this type. However, both of these investigative teams reported
that dispersion was not uniform, and that further work was needed.
With the unique size range of nanotubes, the phase behavior of
nanotubes in polymers will probably affect their dispersion. For
submicron particles, phase separation processes occur which are not
observed in macroscopic (micron-scale) systems. In particular,
colloidal crystals are produced which depend on the form of
interparticle forces (Calvert, 1997; Milling et al., 1991; Vincent,
1987).
[0008] Melt spinning involves polymers that are melt processable
(thermoplastic). The polymer is melted, pressurized, and forced
through a fine capillary. The fiber can be drawn down with either a
mechanical roll (with speeds up to 10,000 m/min) or with air jets
(with speeds to 30,000 m/min). If the air jets are placed in the
melt die, this process is called melt blowing. The speeds possible
with melt spinning are orders of magnitude higher than the speeds
used in solution spinning. Hence, melt spinning is an inherently
less expensive process for producing fibers.
BRIEF DESCRIPTION OF THE DRAWINGS
[0009] FIG. 1 is a schematic representation of a process for
producing a composite mixture utilizing at least one solvent, in
accordance with the present invention.
[0010] FIG. 2 is a schematic representation of another process for
producing a composite mixture utilizing at least one solvent, in
accordance with the present invention.
[0011] FIG. 3 is a chart illustrating the increase in strength of
fibers produced in accordance with the present invention compared
to fibers produced by prior art methods.
DETAILED DESCRIPTION OF THE INVENTION
[0012] The present invention is a method for producing single
walled carbon nanotube/matrix composite materials which preferably
have an anisotropic structure and which can be commercially
produced utilizing commercially available equipment. In general,
effective amounts of nanotubes, preferably single walled carbon
nanotubes, are mixed with a matrix material to form a composite
mixture, generally containing less than about 5 weight percent of
the nanotubes to about parts per billion of the nanotubes and
wherein the nanotubes are preferably generally randomly oriented in
the composite mixture. The composite mixture is then passed through
an orifice or a capillary (e.g., extruded) to form an extrudate or
composite material. Shear attenuation pressure is applied about the
extrudate, either as the extrudate passes through the orifice or
capillary, and/or after the extrudate passes through the orifice or
capillary, wherein the nanotubes are preferably substantially
aligned within the polymer with the longitudinal axis of the
extrudate. The shear attenuation pressure is preferably applied
through a melt blowing process, although, other processes could
also be utilized to provide the shear attenuation pressure to the
extrudate, such as a melt spinning process, or a gel spinning
process. Examples of such methods are shown in U.S. Pat. No.
6,299,812, the entire specification of which is hereby expressly
incorporated herein by reference.
[0013] The term "matrix material" as used herein, broadly refers to
any composition capable of functioning as the matrix constituent of
the materials produced by the present invention. Examples of
suitable matrix materials which can be employed in the practice of
the present invention, include, but are not limited to, metal,
glass, metal alloy, metal oxide glass or alloy thereof, polymer,
such as a thermoplastic resin, or any suitable blend thereof that
can be prepared to have a viscosity suitable for extruding,
stretching, shearing or otherwise deforming of the composite
mixture containing the matrix material and the nanotubes preferably
in a direction whereby an anisotropic structure, e.g., an enhanced
orientation/alignment of the fibers within the composite mixture is
created, in the direction the composite mixture has been pulled,
stretched, extruded, sheared, and combinations thereof or otherwise
deformed and which can be mixed with the nanotubes. Any polymer
capable of achieving the above described results can be utilized as
the matrix. Examples of matrix materials which will function as a
"matrix material" as used herein, are polyethylene,
poly(para-phenylenevinylene), polypyrrole, polypropylene, nylon-6,
polystyrene, polytrifluorochloroethylene and Resin Epon-812 and
combinations thereof. Further, the "matrix material" could be
organic/inorganic hybrid based.
[0014] A suitable viscosity of the nanotube/matrix composite
mixture can be adjusted so that the composite mixture can be
pulled, stretched, extruded, sheared, or otherwise deformed by any
suitable process, such as melting the composite mixture to form a
composite material.
[0015] For example, the transformation of the composite mixture
having the nanotubes into the nanotube/matrix composite material
having an anisotropic structure can be enhanced by increasing the
temperature of the composite mixture up to and above a temperature
where the matrix phase is considered a melted phase. By further
increasing the temperature of the composite mixture its viscosity
will decrease thus enhancing its fluid or fluid-like properties
thus further enhancing its ability to be stretched, pulled,
extruded, or combinations thereof or otherwise deformed in a
preferential direction.
[0016] As a further example, the transformation of the composite
mixture into a composite material having an anisotropic structure
may, in some instances, be enhanced by the addition of a solvent
that dissolves portions of some or all of the components considered
to compose the matrix material of the composite mixture as
described further below. The solvent dissolution of the matrix
material increases its fluid or fluid-like properties and by doing
so allows its deformation with less force and thus increases its
ability to be stretched, pulled, extruded, or otherwise deformed in
a preferential direction. Only those small volumes of solvents are
required that contribute to lower viscosity of the composite
mixture while simultaneously maintaining the self adhesive quality
of the matrix phase in such a way that it maintains its self
continuity and may be still stretched, pulled, extruded or
otherwise deformed.
[0017] Further, plastic deformation of materials including some
metals and metal alloys may be accomplished by the application of
significant pressures or forces. Likewise, the application of
pressure to the composite mixture can improve, create and/or
initiate the stretching, pulling, extruding, or deforming of the
composite mixture. Therefore, depending on the particular
properties of the composite mixture, low to extremely high
pressures can contribute to formation of the preferentially aligned
fibers within the composite mixture by aiding the composite mixture
in being deformed, stretched, extruded, pulled or otherwise
linearized into a fiber, tube, or rope-like form.
[0018] Examples of processes that transform bulk mixtures into
composite materials such as fibers, tubes or rope-like structures
are those processes known in the art as "wet spinning," "gel
spinning," "melt spinning," "melt blowing," or "extrusion." These
processes are well known in the art and a detailed discussion of
each of these processes is not deemed necessary to teach one of
ordinary skill in the relevant art to make and use the present
invention.
[0019] Referring now to the Figures, shown in FIG. 1 and designated
therein by the reference numeral 100, is a schematic representation
of a process for producing a nanotube/matrix composite mixture 102
utilizing at least one solvent, in accordance with the present
invention. The nanotube/matrix composite mixture 102 includes a
matrix material 104 having a uniform dispersion of nanotubes 106
contained therein. Preferably the nanotubes comprise 70-90% single
walled carbon nanotubes, more preferably 90-95% single walled
carbon nanotubes, and most preferably at least 98% single walled
carbon nanotubes.
[0020] In an example which will be discussed in more detail below,
the nanotube/matrix composite mixture 102 contains about 1% by
weight of nanotubes. The nanotube/matrix composite mixture 102 can
then be used to form a composite material such as a drawn fiber
having an increase in strength in excess of 50% over a drawn fiber
formed from the matrix material alone. This substantial and
unexpected increase in strength is believed to be due to the method
of mixing the nanotubes 106 and the matrix material 104, wherein
the nanotubes 106 are maintained in a uniformly dispersed state
prior to and during mixing of the nanotubes with the matrix
material.
[0021] To produce the nanotube/matrix composite mixture 102, an
amount of the nanotubes is first combined with a solvent material
108 to form a nanotube/solvent mixture 110. The nanotubes 106 and
the solvent material 108 are mixed together in the nanotube/solvent
mixture 110 such that the nanotubes 106 are uniformly dispersed in
the nanotube/solvent mixture 110.
[0022] Where used herein, the term "uniformly dispersed" means, in
one embodiment of the invention, that in a sampling of ten
one-milliliter samples randomly selected from the nanotube/solvent
mixture, or from the nanotube/solvent/matrix mixture, at least nine
of the ten one-ml samples differ from each other in the amount of
nanotubes contained therein by no more than 10% by weight of the
nanotubes. In a preferred version of the invention, the sampling
comprises ten 100-microliter samples. In a more preferred version
of the invention, the sampling comprises ten 10-microliter samples.
In an especially preferred version of the invention, the sampling
comprises ten 1-microliter samples.
[0023] The solvent material 108 is preferably a solvent material
which dissolves the matrix material 104 that is being used (e.g.,
decalin and toluene are known solvents capable of dissolving a
matrix material, such as polypropylene).
[0024] Other solvents contemplated for use in the present invention
include, but are not limited to tetralin and tetrachlorethane e.g.,
for polypropylene; acetone, e.g., for polystyrene; cyclohexanone,
methyl cyclohexanone, dimethyl foramide, nitrobenzene,
tetrahydrofuran, isophonone, mesityl oxide, dipropyl ketone, methyl
amyl ketone, methyl isobutyl ketone, acetonyl acetone, methyl ethyl
ketone, dioxone, and methylene chloride, e.g., for polyvinyl
chloride; and trichlorobenzene, e.g., for polyethylene. Other
examples of solvents for the thermoplastic resins used as matrix
materials herein will readily come to mind to persons of ordinary
skill in the art.
[0025] The nanotubes 106 and the solvent material 108 can be mixed
by any suitable method for any suitable period of time so as to
uniformly disperse the nanotubes 106 in the nanotube/solvent
mixture 110. For example, the nanotubes 106 and the solvent
material 108 can be mixed by mechanical mixing, shaking,
sonification, stirring, or the like. The most preferredly method is
sonication. Optionally, a surfactant 112 can be added to the
nanotube/solvent mixture 110 to enhance dispersion of the nanotubes
106.
[0026] Where used herein in reference to nanotubes or single walled
carbon nanotubes, the term "substantially unbroken" means that the
average length of a random sampling of the nanotubes in the mixture
after the predetermined mixing period is at least about 80% of the
average length of a random sampling of the nanotubes before the
mixing step was initiated.
[0027] In addition, the temperature of the nanotube/solvent mixture
110 can be increased or varied to enhance the uniform dispersion of
the nanotubes 106 in the nanotube/solvent mixture 110 as further
described below.
[0028] An amount of matrix material 104 is then combined with the
nanotube/solvent mixture 110 to form a nanotube/solvent/matrix
mixture 114. The amount of matrix material 104 combined with the
nanotube/solvent mixture 110 can vary depending on the particular
matrix material 104 selected, and the particular types of nanotubes
106 and solvent material 108 contained in the nanotube/solvent
mixture 110 and the desired properties of the composite material
formed from the nanotube/matrix composite mixture 102. For example,
the nanotube/solvent mixture 110 and the matrix material 104 in the
nanotube/solvent/matrix mixture 114 are mixed such that the
nanotubes 106 are maintained in a uniformly dispersed state in the
nanotube/solvent/matrix mixture 114, for example by continued
sonication after the nanotubes 106 and matrix material 104 are
combined. Optionally, a surfactant 116 can be added to the
nanotube/solvent/matrix mixture 114.
[0029] In addition, the temperature of the nanotube/solvent/matrix
mixture 114 can be increased or varied to enhance the uniform
dispersion of the nanotubes 106 and the matrix material 104 in the
nanotube/solvent/matrix mixture 114.
[0030] The solvent material 108 is then removed from the
nanotube/solvent/matrix mixture 114 to form the nanotube/matrix
composite mixture 102 preferably containing from about 0% by weight
to about 1% by weight to about 2% by weight to about 5% by weight
of the solvent material 108. The solvent material 108 can be
removed from the nanotube/solvent/matrix mixture 114 via any
suitable process known by persons of ordinary skill in the art. For
example, the solvent material 108 can be removed by evaporating the
solvent material 108 at room temperature and/or elevated
temperatures. Also, removal can be effected at atmospheric pressure
and/or reduced pressure (vacuum) in a manner well known in the
art.
[0031] For example, the nanotube/solvent/matrix mixture 114 can be
disposed in one or more drying surfaces 118. The drying surface 118
containing the nanotube/solvent/matrix mixture 114 can be placed in
a hood 120 to evaporate the solvent material 108 for a suitable
period of time of from hours to days.
[0032] The drying surface 118 can then be removed from the hood and
positioned in a vacuum oven 122 to further evaporate or remove the
solvent material 108 for a suitable period of time, and at a
suitable temperature and pressure to form the nanotube/matrix
composite mixture 102 containing preferably about 0% by weight to
about 1% by weight to about 2% by weight to about 5% by weight of
the solvent material 108.
[0033] In a preferred embodiment, the nanotube/matrix composite
mixture 102 will contain roughly 1% by weight of residual solvent
material 108 or less; the residual solvent material 108 thereby
acting as a plasticizer. Preferably all removed solvent material
108 will be recycled. Since removing and recycling solvent material
108 is expensive, the amount of solvent material 108 will be
minimized whenever possible.
[0034] After the solvent material 108 has been removed, the
nanotube/matrix composite mixture 102 can be crushed into a coarse
material (e.g., chunks having a diameter of 0.5 cm or less). The
crushed nanotube/matrix composite mixture 102 can then be further
processed into a composite material such as fibers, drawn fibers or
other products utilizing any suitable process, such as "wet
spinning," "gel spinning," "melt spinning," "melt blowing," or
"extrusion" as discussed above. These processes are well known in
the art and a detailed discussion of each of these processes is not
deemed necessary to teach one of ordinary skill in the relevant art
to make and use the present invention.
[0035] Referring now to FIG. 2, shown therein and designated by the
reference numeral 130 is a schematic representation of an alternate
process for producing the nanotube/matrix composite mixture 102
utilizing at least one solvent, in accordance with the present
invention. To produce the nanotube/matrix composite mixture 102, an
amount of the nanotubes 106 is combined with a first solvent
material 132 to form the nanotube/solvent mixture 110. The
nanotubes 106 and the first solvent material 132 are continuously
mixed in the nanotube/solvent mixture 110 wherein the nanotubes 106
are in a uniformly dispersed condition in the nanotube/solvent
mixture 110. The first solvent material 132 can be decalin, or any
other solvent in which nanotubes can be generally mixed and
uniformly dispersed.
[0036] The nanotubes 106 and the first solvent material 132 can be
mixed by any suitable method so as to uniformly disperse the
nanotubes 106 in the nanotube/solvent mixture 110. For example, the
nanotubes 106 and the first solvent material 132 can be mixed by
mechanical mixing, shaking, stirring, sonification, or the like. In
addition, to enhance the mixing and dispersion of the
nanotube/solvent mixture 110, a surfactant material 134, such as is
commonly known in the art and which is soluble in the first solvent
material 132 can be added to the nanotube/solvent mixture 110. In a
preferred embodiment, the nanotube/solvent mixture 110 is mixed for
about 1 hour prior to being mixed with the matrix material 104, the
nanotubes maintained in a uniformly dispersed condition before
being mixed with the matrix material.
[0037] In addition, the temperature of the nanotube/solvent mixture
110 can be increased or varied to enhance the uniform dispersion of
the nanotubes 106 in the nanotube/solvent mixture 110.
[0038] An amount of matrix material 104 is combined with a second
solvent material 136 (which may be the same or different from first
solvent material 32) to form a matrix/solvent mixture 138. The
matrix material 104 and the second solvent material 136 are mixed
in the matrix/solvent mixture 138 such that the matrix material 104
is dissolved in the matrix/solvent mixture 138. To enhance the
mixing of the matrix/solvent mixture 138, a surfactant material
139, such as a non-polar surfactant, can be added to the
matrix/solvent mixture 138. The second solvent material 136 is
preferably miscible with the first solvent material 132 to optimize
mixing. The second solvent material 136 can be any solvent able to
dissolve the matrix material 104 as discussed elsewhere herein and
which is miscible with the first solvent material 132.
[0039] An amount of the matrix/solvent mixture 138 is then combined
with the nanotube/solvent mixture 110 to form the
nanotube/solvent/matrix mixture 114. The amount and ratio of
matrix/solvent mixture 138 combined with the nanotube/solvent
mixture 110 can vary depending on the particular matrix material
104 selected, and the particular type of nanotubes 106, and the
first and second solvent materials 132 and 136. The
nanotube/solvent mixture 110 and the matrix/solvent mixture 138 in
the nanotube/solvent/matrix mixture 114 are mixed such that the
nanotubes 106 are uniformly dispersed in the
nanotube/solvent/matrix mixture 114.
[0040] The nanotube/solvent mixture 110 and the matrix material 104
can be mixed by any suitable method for any suitable period of time
so as to about uniformly disperse the nanotubes 106 and the matrix
material 104 in the nanotube/solvent/matrix mixture 114, as
discussed previously above. Optionally, a surfactant 140 can be
added to improve mixing.
[0041] In addition, the temperature of the nanotube/solvent/matrix
mixture 114 can be increased or varied to enhance the dispersion of
the nanotubes 106 and the matrix material 104 in the
nanotube/solvent/matrix mixture 114.
[0042] The first and second solvent materials 132 and 136 are then
removed from the nanotube/solvent/matrix mixture 114 to form the
nanotube/matrix composite mixture 102 preferably containing about
0% by weight to about 1% by weight to about 2% by weight to about
5% by weight of the first and second solvent materials 132 and 136.
The first and second solvent materials 132 and 136 can be removed
from the nanotube/solvent/matrix mixture 114 via any suitable
process as previously described. For example, the first and second
solvent materials 132 and 136 can be removed by evaporating the
first and second solvent materials 132 and 136 at room temperature
and/or elevated temperatures. Also, removal can be effected at
atmospheric pressure and/or reduced pressure (vacuum) as previously
discussed.
[0043] Preferably, the nanotube/matrix composite mixture 102 will
contain roughly 0% to 1% to 2% to 5% by weight of the first and
second solvent materials 132 and 136 and preferably less than 1% by
weight. The residual first and second solvent materials 132 and 136
can act as a plasticizer. Preferably all removed first and second
solvent materials 132 and 136 will be recycled.
[0044] While the invention will now be described in connection with
certain preferred embodiments in the following examples so that
aspects thereof may be more fully understood and appreciated, it is
not intended to limit the invention to these particular
embodiments. On the contrary, it is intended to cover all
alternatives, modifications and equivalents as may be included
within the scope of the invention as defined by the appended
claims. Thus, the following examples, which include preferred
embodiments will serve to illustrate the practice of this
invention, it being understood that the particulars shown are by
way of example and for purposes of illustrative discussion of
preferred embodiments of the present invention only and are
presented in the cause of providing what is believed to be the most
useful and readily understood description of formulation procedures
as well as of the principles and conceptual aspects of the
invention.
EXAMPLE 1
[0045] In this example, commercial carbon nanotubes (nanotubes 106)
were combined with commercially available polypropylene (matrix
material 104). More specifically, 150 ml of decalin (solvent
material 108) was placed in a 400-ml container. Next, 0.200 g of AP
grade CARBOLEX carbon nanotubes were added to the decalin forming a
nanotube/solvent mixture. Then, the mixture was sonicated with a
Fisher Scientific Model 550 Ultrasonic Generator. The sonification
was conducted for 60 minutes at a power setting of "4".
[0046] During the sonification, the temperature of the
nanotube/solvent mixture gradually rose due to the effects of
sonification. After 60 minutes, the temperature of the
nanotube/solvent mixture reached about 100.degree. C. and the
nanotubes were uniformly dispersed within the decalin. Then, 20 g
of polypropylene pellets (matrix material 106) were added to the
nanotube/solvent mixture having the nanotubes uniformly dispersed
therein. Heat was applied to bring the temperature to 135.degree.
C. After another 60 minutes of sonification at power level "4", the
polypropylene was totally dissolved to create a
nanotube/solvent/matrix mixture with the nanotubes uniformly
dispersed therein.
[0047] The container of the nanotube/solvent/matrix mixture was
placed in a vacuum oven at a temperature of 70.degree. C. and an
absolute pressure of 10.1 kPa for two days. The resultant dried
nanotube/matrix composite mixture was a coarse powder (the chunks
were all 0.5 cm size and less). The final weight of the
nanotube/matrix composite mixture was 20.13 g, which indicated that
about 0.4 ml (about 0.65% by weight) of the composite mixture was
decalin and about 1% was nanotubes.
[0048] For forming into a composite material, the nanotube/matrix
composite mixture was placed in the barrel of a ram extruder and
was then heated to 190.degree. C. The nanotube/matrix composite
mixture was extruded out at a mass rate of 0.50 g/min. A 15.2 cm
diameter mechanical roll was placed at a distance of 1.35 meters
below the spinneret. The roll was run at a surface speed of 519
m/min forming a fiber (the composite material) which was collected
on the roll.
[0049] The collected nanotube/matrix composite material was then
post drawn by passing the fiber through an oven set at 118.degree.
C. The oven length was 38 cm, the feed roll (6.5 cm diameter) was
run at a surface speed of 1.5 m/min, and the takeup roll (also 6.5
cm diameter) was run at a surface speed of 9 m/min (for a draw
ratio of 6x).
[0050] The drawn fiber was tested with an Instron tensile test
machine at a strain rate of 2.54 cm/min. The results of four
replicate tests are given in FIG. 6. Also shown in the graph of
FIG. 3 are four replicate tests of the stress-strain behavior of a
blank (polypropylene matrix with no nanotubes) subjected to the
same processing conditions. As will be understood in the art, the
drawn fibers produced in accordance with the present invention had
a common stress-strain behavior of 13.1 grams/denier. This
surprising and unexpected result represents over a 50% increase of
the stress-strain behavior of blank polypropylene matrix (without
nanotubes).
[0051] The nanotubes utilized in the example discussed above are
provided as an "as prepared" nanotube material ("CARBOLEX") that
contains about 70% single wall nanotubes produced commercially by a
carbon arc process. The nanotubes were not treated or cleaned
before being mixed with the decalin solvent. The strength of the
drawn fibers produced in accordance with the present invention can
be increased by using more highly purified or "clean" nanotubes
before the nanotubes are added to the solvent material 108.
[0052] For example, in one method, single walled carbon nanotubes
may be provided in combination with catalyst particles and silica
support due to the process used for producing the nanotubes. To
purify the nanotubes, a caustic treatment could be used to remove
any silica and then an acid treatment could be used to remove any
catalyst material for example, as shown in U.S. Pat. No. 6,413,487,
the entire specification of which is hereby expressly incorporated
herein by reference.
EXAMPLE 2
[0053] In an alternative embodiment the nanotubes were dispersed in
toluene, rather than decalin, before addition of polypropylene and
the process was followed as previously described in Example 1.
Notably, it was found that sonicating carbon nanotubes in toluene
for a relatively short time (e.g., 30 minutes) provided a uniformly
dispersed suspension of the carbon nanotube material that was
stable for several days, unlike carbon nanotubes mixed in decalin,
which settled out of suspension soon after ultrasonic mixing was
ceased. Additionally, mixtures of solvents such as toluene and
decalin, for example at concentrations of 20, 40, 50, 60, and 80
vol. % (prior to mixing) were used, as described below, and in
Example 1.
[0054] In the present embodiment of the method, carbon nanotube
material was combined with toluene to form a nanotube/solvent
mixture which was sonicated for 30 minutes. In a separate
container, polypropylene was heated and dissolved in decalin to
form a matrix/solvent mixture. After ultrasonic mixing, the
nanotube/solvent mixture was combined with the matrix/solvent
mixture which was further mixed by sonication, forming a
nanotube/solvent/matrix mixture. The nanotube/solvent/matrix
mixture was sonicated for additional 35 minutes, after which the
mixture was removed from the heat and allowed to dry as before to
form the nanotube/matrix composite mixture for further
processing.
[0055] Changes may be made in the combinations, operations, and
arrangements of the various components, elements and processes
described herein without departing from the spirit and scope of the
invention as defined in the following claims.
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