Note: Descriptions are shown in the official language in which they were submitted.
CA 02647727 2008-09-29
WO 2007/115162 PCT/US2007/065630
Carbon Nanotube-Reinforced Nanocomposites
This application claims priority to U.S. Provisional Application Serial Nos.
60/788,234
filed on March 31, 2006 and 60/810,394 filed on June 2, 2006.
BACKGROUND INFORMATION
Since their first observation by lijima in 1991 carbon nanotubes (CNTs) have
been the
focus of considerable research (S. lijima, `Helical microtubules of graphitic
carbon', Nature 354,
56 (1991)). Many investigators have reported the remarkable physical and
mechanical properties
of this new form of carbon. CNTs typically are 0.5-1.5 nm in diameter for
single wall CNTs
(SWNTs), 1-3 nm in diameter for double wall CNTs (DWNTs), and 5 nm to 100 nm
in diameter
for multi-wall CNTs (MWNTs). From unique electronic properties and a thermal
conductivity
higher than that of diamond to mechanical properties where the stiffness,
strength and resilience
exceeds that of any current material, CNTs offer tremendous opportunity for
the development of
fundamental new material systems. In particular, the exceptional mechanical
properties of CNTs
(E > 1.0 TPa and tensile strength of 50 GPa) combined with their low density
(1-2.0 g/cm3)
make them attractive for the development of CNT-reinforced composite materials
(Eric W.
Wong, Paul E. Sheehan, Charles M. Lieber, "Nanobeam Mechanics: Elasticity,
Strength, and
Toughness of Nanorods and Nanotubes", Science 277, 1971(1997)). CNTs are the
strongest
material known on earth. Compared with MWNTs, SWNTs and DWNTs have even more
promising as reinforcing materials for composites because of their higher
surface area and
higher aspect ratio. Table 1 lists surface area and aspect ratio of SWNTs,
DWNTs, and MWNTs.
Table 1
SWNTs DWNTs MWNTs
Surface area (m2/g) 300-600 300-400 40-300
Geometric aspect ratio -10,000 -5,000 100-1000
(length/diameter)
A problem is that both SWNTs and DWNTs are more expensive that MWNTs. The
price
of both purified SWNTs and DWNTs can be as high as $500/g while that of
purified MWNTs is
$1-10/g. Thus, the cost of MWNTs-reinforced nanocomposites is much lower than
that of either
SWNTs or DWNTs-reinforced nanocomposites.
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WO 2007/115162 PCT/US2007/065630
BRIEF DESCRIPTION OF THE DRAWINGS
Fig. 1 illustrates a process for manufacturing epoxy/CNT nanocomposites;
Fig. 2 illustrates a graph showing the flexural strength of epoxy
nanocomposites; and
Fig. 3 illustrates a graph showing the flexural modulus of epoxy
nanocomposites.
DETAILED DESCRIPTION
A combination of MWNTs (herein, MWNTs have more than 2 walls) and DWNTs
significantly improves the mechanical properties of polymer nanocomposites. A
small amount of
DWNTs reinforcment (<lwt.%) significantly improves the flexural strength of
epoxy matrix
nanocomposites. A same or similar amount of MWNTs reinforcement significantly
improves the
flexural modulus (stiffness) of epoxy matrix nanocomposites. Both flexural
strength and flexural
modulus of the MWNTs and DWNTs-coreinforced epoxy nanocomposites are further
improved
compared with same amount of either DWNTs or MWNTs-reinforced epoxy
nanocomposites. In
this epoxy/DWNTs/MWNTs nanocomposite system, SWNTs may also work instead of
DWNTs.
Besides epoxy, other thermoset polymers may also work.
In one embodiment of the present invention, a detailed example of this
embodiment is
given in an effort to better illustrate the invention.
Epoxy resin (bisphenol-A) was obtained from Arisawa Inc., Japan. The hardener
(dicyandiamide) was obtained from the same company which was used to cure the
epoxy
nanocomposites. Both DWNTs and MWNTs were obtained from Nanocyl, Inc.,
Belgium.
Those CNTs were functionalized with amino (-NH2) functional groups. Amino-
functionalized
CNTs may help to improve the bonding between the CNTs and epoxy molecular
chairs which
can further improve the mechanical properties of the nanocomposites. But,
pristine CNTs or
functionalized by other ways (such as carboxylic functional groups) may also
work (e.g., pellets
obtained from Arkema Co., Japan (product name: RILSAN BMV-P20 PAll). Clay was
provided by Southern Clay Products, U.S. (product name: Cloisite series 93A).
It is a natural
montmorillonite modified with a ternary ammonium salt. The elastomer was
styrene/ethylene
butylenes/styrene (SEBS) purchased from Kraton Inc., U.S. (product name:
G1657).
Figure 1 illustrates a schematic diagram of a process flow to make epoxy/CNT
nanocomposites. All ingredients were dried in a vacuum oven at 70 C for at
least 16 hours to fully
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WO 2007/115162 PCT/US2007/065630
eliminate moisture. CNTs were put in acetone 101 and dispersed by a micro-
fluidic machine is
step 102 (commercially available from Microfluidics Co.). The micro-fluidic
machine uses high-
pressure streams that collide at ultra-high velocities in precisely defined
micron-sized channels.
Its combined forces of shear and impact act upon products to create uniform
dispersions. The
CNT/acetone was then formed as a gel 103 resulting in the CNTs well dispersed
in the acetone
solvent. However, other methods, such as an ultrasonication process may also
work. A surfactant
may be also used to disperse CNTs in solution. Epoxy was then added in step
104 to the
CNT/acetone gel to create an epoxy/CNT/acetone solution 105, which was
followed by an
ultrasonication process in a bath at 70 C for 1 hour (step 106) to create an
epoxy/CNT/acetone
suspension 107. The CNTs were further dispersed in epoxy in step 108 using a
stirrer mixing
process at 70 C for half an hour at a speed of 1,400 rev/min. to create an
epoxy/CNT/acetone gel
109. A hardener was than added in step 110 to the epoxy/CNT/acetone gel 109 at
a ratio of 4.5
wt.% followed by stirring at 70 C for 1 hour. The resulting gel 111 was
degassed in step 112 in a
vacuum oven at 70 C for at least 48 hours. The material 113 was then poured
into a Teflon mold
and cured at 160 C for 2 hours. Mechanical properties (flexural strength and
flexural modulus) of
the specimens were characterized after a polishing process 115.
Table 2 shows the mechanical properties (flexural strength and flexural
modulus) of the
epoxies made using the process flow of Fig. 1 to make epoxy/CNT
nanocomposites. As shown in
Fig. 2, the flexural strength of epoxy/DWNTs is higher than that of
epoxy/MWNTs at the same
loading of CNTs, while the flexural modulus of epoxy/DWNTs is lower than that
of
epoxy/MWNTs at the same loading of CNTs, as shown in Fig. 3. Both the flexural
strength and
flexural modulus of epoxy/DWNTs (0.5wt.%)/MWNTs (0.5wt.%) are higher than
those of
epoxy/DWNTs (lwt.%).
Table 2
Epoxy material Flexural strength Flexural modulus
(MPa) (GPa)
Neat epoxy 116 3.18
Epoxy/MWNTs (0.5wt.%) 130.4 3.69
Epoxy/DWNTs (0.5wt.%) 138.9 3.26
Epoxy/DWNTs (lwt.%) 143.6 3.43
Epoxy/DWNTs(0.5wt.%)/MWNTs(0.5wt.%) 154.2 3.78
3
