Nanocomposites: mixing CNTs into polymers

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Nanocomposites mixing CNTs into polymers
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Outline

• 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

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Benefits 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

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How to introduce CNTs into polymers
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Melt mixing of CNT with thermoplastic polymers
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Preparation 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

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Characterization of the masterbatch (PC 15 wt
MWNT)
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Dispersion in PC-MWNT composites
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Alignment in PC-MWNT composites
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Comparison for different set of PC masterbatch
dilution
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Detection of percolation and influence of
processing conditions investigated by dielectric
spectroscopy
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Direct incorporation of different kinds of
commercial MWNT into PC
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Comparison of direct incorporation of CNT,
masterbatch dilution, and CB addition
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Direct incorporationof SWNT1 into PC
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Direct incorporation of SWNT1 into PC
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Direct incorporation of SWNT1 into PC
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Direct incorporationof SWNT2 into PC
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Direct incorporation of SWNT2 into PC
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Summary

• 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

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Graphenepolymer 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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Process 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.

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Advantages 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

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Disadvantages 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.

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Examples 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.

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Area 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.

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Gas 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.

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Fuel 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.

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Films

• 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.

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Environmental 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.

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Preparation 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.

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Preparation 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.

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Preparation 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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Polymers 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.

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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.

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Goal 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.

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Novel 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.

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Novel 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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