Title: Nanocomposites: mixing CNTs into polymers
1Nanocomposites mixing CNTs into polymers
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3Outline
- 1.Introduction
- 2. Composites of multiwalled carbon nanotubes
(MWNT) with polycarbonate (PC) produced by
masterbatch dilution technique - Electrical resistivity
- Dispersion and alignment
- Influence of processing parameters on
electrical resistivity - 3. Composites of MWNT and SWNT with PC produced
by direct incorporation - Percolation of different commercial MWNT in
PC - Percolation of SWNT in PC
- Stress-strain behaviour
- 4. Summary
4Benefits of CNTs to polymers
- Electrical conductivity
- Improvement of mechanical properties, especially
strength - Enhancement of thermal stability
- Enhancement of thermal conductivity
- Improvement of fire retardancy
- Enhancement of oxidation stability
- Effects at low CNT contents because of the very
high aspect ratio
5How to introduce CNTs into polymers
6Melt mixing of CNT with thermoplastic polymers
7Preparation of the PC-MWNT composites
- Masterbatch technology polycarbonate(PC) PC
based masterbatch (15 wt MWNT) - masterbatch (Hyperion Catalysis International,
Inc, Cambridge, USA) diluted with PC Iupilon
E2000 (PC1), PC Lexan 121 (PC2) or PC as used for
the masterbatch (PC3) - Haakeco-rotating, intermeshing twin screw
extruder with one kilogramm mixtures - DACA Micro Compounder, conical twin screw
extruder (4.5 cm3capacity) - Brabender PL-19 single screw extruder
8Characterization of the masterbatch (PC 15 wt
MWNT)
9Dispersion in PC-MWNT composites
10Alignment in PC-MWNT composites
11Comparison for different set of PC masterbatch
dilution
12Detection of percolation and influence of
processing conditions investigated by dielectric
spectroscopy
13Direct incorporation of different kinds of
commercial MWNT into PC
14Comparison of direct incorporation of CNT,
masterbatch dilution, and CB addition
15Direct incorporationof SWNT1 into PC
16Direct incorporation of SWNT1 into PC
17Direct incorporation of SWNT1 into PC
18Direct incorporationof SWNT2 into PC
19Direct incorporation of SWNT2 into PC
20Summary
- Melt mixing is a powerful method to disperse CNT
into polymers - Masterbatch dilution technique (based on a PC
masterbatch) - percolation in the range of 1.0 wt MWNT
- suitable processing conditions can shift
percolation to lower values (0.5wt) - effects of mixing equipment and PC viscosity on
percolation are small - Direct incorporation method
- percolation strongly depends on the kind of CNT,
production method (resulting in different sizes,
purity and defect levels), and the
purifying/modification steps - for commercial MWNT percolation occurs between
1.0 and 3.0 wt and is lower at lower MWNT
diameters and higher purity - HipCO-SWNT (CNI) percolation between 0.30 and
0.35 wt - stress-strain behavior of the composites modulus
and stress are - enhanced, elongation at break reduced
especially above percolation concentration
21Graphenepolymer composite
- Graphite oxide was prepared by the Hummers method
from SP-1 graphite (Bay Carbon), and dried for a
week over phosphorus pentoxide in a vacuum
desiccator. Dried graphite oxide (50 mg) was
suspended in anhydrous DMF (5 ml, Dow-Grubbs
solvent system), treated with phenyl isocyanate
(2 mmol, Sigma-Aldrich) for 24 h, and recovered
by filtration through a sintered glass funnel
(50 ml, medium porosity). Stable dispersions of
the resulting phenyl isocyanate-treated graphite
oxide materials were prepared by ultrasonic
exfoliation (Fisher Scientific FS60, 150 W, 1 h)
in DMF (1 mg ml-1). Polystyrene (Scientific
Polymer Products, approximate Mw 280 kD, PDI
3.0) was added to these dispersions and dissolved
with stirring (Fig. 1d, left). Reduction of the
dispersed material (Fig. 1d, right) was carried
out with dimethylhydrazine (0.1 ml in 10 ml of
DMF, Sigma-Aldrich) at 80 C for 24 h. Upon
completion, the coagulation of the polymer
composites was accomplished by adding the DMF
solutions dropwise into a large volume of
vigorously stirred methanol (101 with respect to
the volume of DMF used). The coagulated composite
powder (Fig. 1e) was isolated via filtration
washed with methanol (200 ml) dried at 130 C
under vacuum for 10 h to remove residual
solvent, anti-solvent, and moisture crushed into
a fine powder with a mortar and pestle, and then
pressed (Fig. 1f) in a hydraulic hot press (Model
0230C-X1, PHI-Tulip) at 18 kN with a temperature
of 210 C.
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23Process flow of graphenepolymer composite
fabrication
- a, SEM and digital image (inset) of natural
graphite. b, A typical AFM non-contact-mode image
of graphite oxide sheets deposited onto a mica
substrate from an aqueous dispersion (inset) with
superimposed cross-section measurements taken
along the red line indicating a sheet thickness
of 1 nm. c, AFM image of phenyl
isocyanate-treated graphite oxide sheets on mica
and profile plot showing the 1 nm thickness. d,
Suspension of phenyl isocyanate-treated graphite
oxide (1 mg ml-1) and dissolved polystyrene in
DMF before (left) and after (right) reduction by
N,N-dimethylhydrazine. e, Composite powder as
obtained after coagulation in methanol. f,
Hot-pressed composite (0.12 vol. of graphene)
and pure polystyrene of the same 0.4-mm thickness
and processed in the same way. g, Low (top row)
and high (bottom row) magnification SEM images
obtained from a fracture surface of composite
samples of 0.48 vol. (left) and 2.4 vol.
(right) graphene in polystyrene.
24Advantages of Nanosized Additions
- The Nanocomposites 2000 conference has
revealed clearly the property advantages that
nanomaterial additives can provide in comparison
to both their conventional filler counterparts
and base polymer. Properties which have been
shown to undergo substantial improvements
include - Mechanical properties e.g. strength, modulus
and dimensional stability - Decreased permeability to gases, water and
hydrocarbons - Thermal stability and heat distortion
temperature - Flame retardancy and reduced smoke emissions
- Chemical resistance
- Surface appearance
- Electrical conductivity
- Optical clarity in comparison to
conventionally filled polymers
25Disadvantages of Nanosized Additions
- To date one of the few disadvantages associated
with nanoparticle incorporation has concerned
toughness and impact performance. Some of the
data presented has suggested that nanoclay
modification of polymers such as polyamides,
could reduce impact performance. Clearly this is
an issue which would require consideration for
applications where impact loading events are
likely. In addition, further research will be
necessary to, for example, develop a better
understanding of formulation/structure/property
relationships, better routes to platelet
exfoliation and dispersion etc.
26Examples of Mechanical Property gains due to
Nanoparticle Additions
- Data provided by Hartmut Fischer of TNO in the
Netherlands relating to polyamide
montmorillonite nanocomposites indicates tensile
strength improvements of approximately 40 and 20
at temperatures of 23ºC and 120ºC respectively
and modulus improvements of 70 and a very
impressive 220 at the same temperatures. In
addition Heat Distortion Temperature was shown to
increase from 65ºC for the unmodified polyamide
to 152ºC for the nanoclay-modified material, all
the above being achieved with just a 5 loading
of montmorillonite clay. Similar mechanical
property improvements were presented for
polymethyl methacrylate clay hybrids. - Further data provided by Akkepeddi of Honeywell
relating to polyamide-6 polymers confirms these
property trends. In addition, the further
benefits of short/long glass fibre incorporation,
together with nanoclay incorporation, are clearly
revealed.
27Area of Applications
- Such mechanical property improvements have
resulted in major interest in nanocomposite
materials in numerous automotive and
general/industrial applications. These include
potential for utilization as mirror housings on
various vehicle types, door handles, engine
covers and intake manifolds and timing belt
covers. More general applications currently being
considered include usage as impellers and blades
for vacuum cleaners, power tool housings, mower
hoods and covers for portable electronic
equipment such as mobile phones, pagers etc.
28Gas Barrier
- The gaseous barrier property improvement that can
result from incorporation of relatively small
quantities of nanoclay materials is shown to be
substantial. Data provided from various sources
indicates oxygen transmission rates for
polyamide-organoclay composites which are usually
less than half that of the unmodified polymer.
Further data reveals the extent to which both the
amount of clay incorporated in the polymer, and
the aspect ratio of the filler contributes to
overall barrier performance. In particular,
aspect ratio is shown to have a major effect,
with high ratios (and hence tendencies towards
filler incorporation at the nano-level) quite
dramatically enhancing gaseous barrier
properties. Such excellent barrier
characteristics have resulted in considerable
interest in nanoclay composites in food packaging
applications, both flexible and rigid. Specific
examples include packaging for processed meats,
cheese, confectionery, cereals and
boil-in-the-bag foods, also extrusion-coating
applications in association with paperboard for
fruit juice and dairy products, together with
co-extrusion processes for the manufacture of
beer and carbonated drinks bottles. The use of
nanocomposite formulations would be expected to
enhance considerably the shelf life of many types
of food.
29Fuel Tanks
- The ability of nanoclay incorporation to reduce
solvent transmission through polymers such as
polyamides has been demonstrated. Data provided
by De Bievre and Nakamura of UBE Industries
reveals significant reductions in fuel
transmission through polyamide6/66 polymers by
incorporation of a nanoclay filler. As a result,
considerable interest is now being shown in these
materials as both fuel tank and fuel line
components for cars. Of further interest for this
type of application, the reduced fuel
transmission characteristics are accompanied by
significant material cost reductions.
30Films
- The presence of filler incorporation at
nano-levels has also been shown to have
significant effects on the transparency and haze
characteristics of films. In comparison to
conventionally filled polymers, nanoclay
incorporation has been shown to significantly
enhance transparency and reduce haze. With
polyamide based composites, this effect has been
shown to be due to modifications in the
crystallisation behaviour brought about by the
nanoclay particles spherilitic domain dimensions
being considerably smaller. Similarly,
nano-modified polymers have been shown, when
employed to coat polymeric transparency
materials, to enhance both toughness and hardness
of these materials without interfering with light
transmission characteristics. An ability to
resist high velocity impact combined with
substantially improved abrasion resistance was
demonstrated by Haghighat of Triton Systems.
31Environmental Protection
- Water laden atmospheres have long been regarded
as one of the most damaging environments which
polymeric materials can encounter. Thus an
ability to minimize the extent to which water is
absorbed can be a major advantage. Data provided
by Beall from Missouri Baptist College indicates
the significant extent to which nanoclay
incorporation can reduce the extent of water
absorption in a polymer. Similar effects have
been observed by van Es of DSM with polyamide
based nanocomposites. In addition, van Es noted a
significant effect of nanoclay aspect ratio on
water diffusion characteristics in a polyimide
nanocomposite. Specifically, increasing aspect
ratio was found to diminish substantially the
amount of water absorbed, thus indicating the
beneficial effects likely from nanoparticle
incorporation in comparison to conventional
microparticle loading. Hydrophobic enhancement
would clearly promote both improved nanocomposite
properties and diminish the extent to which water
would be transmitted through to an underlying
substrate. Thus, applications in which contact
with water or moist environments is likely could
clearly benefit from materials incorporating
nanoclay particles.
32Preparation and Characterization of Novel
Polymer/Silicate Nanocomposites
- Five categories cover the majority of composites
synthesized with more recent techniques being
modifications or combinations from this list. - Type I Organic polymer embedded in an inorganic
matrix without covalent bonding between the
components. - Type II Organic polymer embedded in an inorganic
matrix with sites of covalent bonding between the
components.
33Preparation and Characterization of Novel
Polymer/Silicate Nanocomposites
- Type III Co-formed interpenetrating networks of
inorganic and organic polymers without covalent
bonds between phases. - Type IV Co-formed interpenetrating networks of
inorganic and organic polymers with covalent
bonds between phases. - Type V Non-shrinking simultaneous polymerization
of inorganic and organic polymers.
34Preparation and Characterization of Novel
Polymer/Silicate Nanocomposites
- The great majority of nanocomposites incorporate
silica from tetraethoxysilane (TEOS). The
formation of the inorganic component involves two
steps, hydrolysis and condensation as seen in
Scheme 1.
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36Polymers considered PEO, PEO/PPO, PVAc, PVA,
PAN, MEEP
- A general synthesis for a base, acid, or salt
catalyzed polyphosphazene, polyethylene oxide
(PEO), and polyethylene oxide/polypropylene oxide
(PPO/PEO) block nanocomposite is as follows 300
mg of polymer is dissolved into 10 mL of a 50/50
by volume tetrahydrofuran (THF)/ethanol mixed
solvent in a capped vial. To this solution is
added TEOS (336 mg). A catalyst is then
introduced as an aqueous solution (150 µl) and
the mixture is capped and sonicated at 50oC for
30 minutes. The solution is aged from hours to
days depending upon the catalyst used in a sealed
vial and poured into a Teflon mold and loosely
covered at room temperature. The nanocomposite
self assembles as the volatile solvent slowly
escapes during the condensation process. - The synthesis of polyvinyl acetate
(PVAc)/silicate nanocomposites requires a
different approach from the other nanocomposites.
PVAc (300 mg) is dissolved into an 50/50 by
volume acetic acid/methanol (10 mL) mixed solvent
in a capped vial. To this solution is added TEOS
(373 mg). The solution is then sonicated for 5
minutes in a sealed vial at room temperature and
poured into a Teflon mould and loosely covered at
room temperature. The nanocomposite self
assembles during the curing process, which
typically lasts up to 24 hours. Additional
heating at 100 C for 30 minutes aids in removing
lingering acetic acid from the nanocomposite.
37 Applications
- One of the most interesting of these applications
is as solid polymer electrolytes (SPE) for
lithium batteries. The polyphosphazene MEEP is a
well-known SPE with very high room temperature
conductivity, however it lacks the mechanical
stability to be used in a practical device (12).
Traditional stabilization methods, such as deep
UV or electron beam crosslinking methods do
improve the physical stability of SPEs, however
this crosslinking lowers ionic conductivity
tests performed in our laboratory revealed this
to be a factor of 30-45 for MEEP-like phosphazene
polymers. This reduction is due to the additional
covalent linkages formed during the crosslinking
process that inhibit chain segmental motion and
ion transfer. Since the nanocomposites formed by
the ceramic condensation process do not form
bonds to the polymer component, (Type I
nanocomposites) mechanical stabilization is
achieved without a great loss of ionic
conductivity (13). However, these nanocomposites
have the highest tensile strength of any of the
catalyst types studied yet they were also found
to be glassy and brittle.
38Goal for Type I Nanocomposites
- The goal in the process is to form a completely
interpenetrating network (IPN) of both inorganic
and organic phases. Homogeneous nanocomposites
with good IPNs are often stronger, more
resilient, and optically transparent, whereas
heterogeneous composites are often mechanically
weaker and opaque.
39Novel Rubber Nanocomposites with Adaptable
Mechanical Properties
- Silica particles have become more important in
tire applications since the introduction of the
Green Tire by Michelin. As a filler, silica has
greater reinforcing power, such as improving tear
strength, abrasion resistance, age resistance and
adhesion properties than carbon black 6-8.
However, due to the strong inter-particle
hydrogen bonds between hydroxyl groups, the
agglomeration nature of silica is generally
believed to be responsible for the significant
Payne effect which brings about considerable
rolling resistance for tire applications. In
order to reduce the filler-filler interaction
and/or to enhance the mechanical properties of
silica filled composites, researchers have been
working for many years on different strategies to
improve silica-rubber interaction and, in turn,
to reduce the rolling resistance. Among these
strategies, chemical modifications of rubbers by
attaching functional groups interacting with
silica 9-22 and surface treatments of silica by
reducing surface polarity with different silane
coupling agents 22-36 are the most popular
techniques. -
40Novel Rubber Nanocomposites with Adaptable
Mechanical Properties
- However, these techniques admittedly have quite a
few drawbacks. For the former technique, the
chemical modification reaction of rubber was
usually not applicable to commercial production
and its degree of modification was usually very
low 9,11,14,18,22. Additionally, the chemical
modification was limited to rubber chain ends
12,17,20, meaning that the final silica
composite was unsatisfactory in terms of reducing
silica agglomeration. For the latter, the used
coupling agents are expensive and it could
possibly lower the crosslinking density by
reacting with the chemical ingredients for
vulcanization. This technique would lead to lower
overall cure rates 34,35, and at the same time
it degraded the mechanical performance of such
silica filled material for tire applications. In
summary, due to these flaws none of the methods
mentioned above could simultaneously ensure both
the ability in reducing the silica agglomeration
and improving the material performance.
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