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Nanocomposites: mixing CNTs into polymers

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2. Composites of multiwalled carbon nanotubes (MWNT) with polycarbonate (PC) ... [4] K. Chino, M. Ashiura, Macromolecules, 34, 9201 (2001) ... – PowerPoint PPT presentation

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Title: Nanocomposites: mixing CNTs into polymers


1
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

4

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

5
How to introduce CNTs into polymers
6
Melt mixing of CNT with thermoplastic polymers
7
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)
9
Dispersion in PC-MWNT composites
10
Alignment in PC-MWNT composites
11
Comparison for different set of PC masterbatch
dilution
12
Detection of percolation and influence of
processing conditions investigated by dielectric
spectroscopy
13
Direct incorporation of different kinds of
commercial MWNT into PC
14
Comparison of direct incorporation of CNT,
masterbatch dilution, and CB addition
15
Direct incorporationof SWNT1 into PC
16
Direct incorporation of SWNT1 into PC
17
Direct incorporation of SWNT1 into PC
18
Direct incorporationof SWNT2 into PC
19
Direct incorporation of SWNT2 into PC
20
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

21
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.

24
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.

26
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.

28
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.

29
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.

30
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.

31
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.

32
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.

33
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.

34
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.

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.

38
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.

39
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.

40
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.

41
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