POLYMER NANOCOMPOSITE
Why PMN?
PMC- important commercial materials: Filled
elastomers for damping Electrical insulators Thermal conductor High performance composites in aircraft
Reach the limits of optimizing composites properties of micro-size fillers PMC usually involve compromises Overcome the limitations nanocomposites
Polymer Nanocomposites – Popular Nano-reinforcements Carbon Nanotube, Bukcyball
Clay
POSS
Building Blocks of the Nano Age
Graphite
Cellulose Other Synthetic Materials
Polymer Nanocomposites (PNC) Applications Heat-resistant materials Light weight and high strength structural materials Electrical package, conductive polymers. Barrier Properties Corrosion resistant, coating or structure Electro-magnetic field shielding Selective photo sensitivity, coatings, etc It is estimated that widespread use of PNCs by car manufacturers could save over 1.5 billion liters of gasoline annually and reduce CO2 emissions by nearly 10 billion pounds!
Polymer Nanocomposite Market 12.000
700
10.500
600
9.000
500
7.500
400
6.000 300
4.500
200
3.000
100
1.500 -
Brazil
Global Market
Projections - MM US$
2007
2009
2011
2013
2015
Global
1.322
1.830
3.660
6.508
11.355
Brazil
102
132
198
366
638
-
Source: Freedonia, International Rubber Study Group and Orbys analysis
29% per year estimate growth between 2005 and 2020
Orbys – 10% local and e 0,5% in global market 5
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Nanoparticles, 2015 - USA Demand – 39,900 ton Clays 18.1
Others 0.5
Carbon Black 12.7
Nanotubes 0.9
Minerals 7.7
Demand – 415 MM$ Minerals 60
Clays 115
Nanotubes 155
Others 35
Carbon Black 50
2020 – 164,200 ton - US$ 2,0 Bn Source: Freedonia, 2006
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Nanocomposites
Multiphase: 1 or more phases < 100nm
Properties unachievable with traditional materials
Types of nanocomposites: Nano-nanocomposites
Ceramic
nanocomposites Metal-Nanopolymer composites Polymer nanocomposites 7
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What is PMN?
Nanoscale filled polymer composites in which the filler is < 100 nm in at least one dimension
Causes in the Revolution of PMN
Unprecedented combinations of properties have been observed in some PMN.
Discovery of carbon nanotube in the early 1990s
0.04% mica-type silicates (MTS) in epoxy increase modulus below Tg by 58% and modulus in rubbery region by 450% Strength & electrical properties of CNT different from graphite offering possibilities for new composites
Significant development in the chemical processing of nanoparticles
In situ processing of nanocomposites led to unprecedented control over morphology of composites Create almost unlimited ability to control interface between matrix and filler
What is so unique to nanofillers?
Small size of the fillers Very small nanoparticles do not scatter light significantly- possible to make composites with altered electrical or mechanical properties that retain optical clarity Do not create large stress concentration – do not compromise the ductility of the polymer Lead to unique properties of the particles themselves – SWNTs are essentially molecules, free from defects, have modulus as high as 1 TPa, strength as high as 500 GPa.
What is so unique to nanofillers?
Leads to an exceptionally large interfacial area in composites Interface
controls the degree of interaction between fillers and polymers; control properties Greatest challenge: Learn to control the interface!
What is interfacial region?
Is the region beginning at the point in the fiber at which the properties differ from those of the bulk filler and ending at the point in the matrix at which the properties become equal to those of the matrix Can be a region of altered chemistry, altered polymer chain mobility, altered degree of cure & altered crystallinity Interface size- as small as 2 nm & as large as ~50 nm
Nanoscale fillers
Many shapes and sizes Into 3 categories Fiber or tube fillers- diameter < 100 nm and aspect ratio of at least 100; aspect ratio can be as high as 106 (CNT) Platelike nanofillers- layered materials typically with thickness on the order of 1 nm & aspect ratio in the other two dimensions of at least 25 Three dimensional (3D) nanofillers- relatively equiaxed particles < 100 nm in their largest dimension
Carbon Nanotubes
Structure of simple wall nanotubes (a, b, c) and multiple wall nanotube
14
Carbon Nanotube Properties Made out of graphite sheets rolled-up Extra high area (aspect ratio) Extra high tensile strength – 45 TPa Thermal stability – 750°C Inertness Tuning electrical properties: isolating ➜ conducting Electron emission
Carbon Nanotube Application Polymer nanocomposite
Ultra resistant, conductive – Automotive, Aeronautics
Nanofoams
Strong light weight materials Electrical energy storage
Future
Hydrogen storage Large Area Display
Carbon Nanotube Difficulties & Barriers High Price Precisely determinable structure (type, dimensions, properties, etc) Potential health risk (strong fibrous nature)
Single nanotubes, not bulk material Toxicity + Inertness
Nanoclay Properties Unique layered structure Rich intercalation chemistry High aspect ratio High in-plane strength and stiffness
Abundance in nature Availability at low cost Cost-effective and versatile raw material
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Processing of PMN
Key limitations in commercialization- processing Primary difficult: proper dispersion of the fillers Without
proper dispersion & distribution; The high surface area is compromised The aggregates can act as defects; limit the properties
Distribution- describes the homogeneity of nanofillers throughout samples Dispersion- describes the level of agglomeration
The schematic representation of mixing (top row, left to right): bad dispersion and distribution; bad dispersion, but good distribution; (bottom row, left to right): good dispersion, but bad distribution, and good dispersion and distribution
Nanotube/Polymer Composites Processing
Nanotube/Polymer Composites
The processing of nanotube/polymer composites is still in its infancy Although produced commercially; literature describing the process is limited Significant issues: Purification
Dispersion Bulk
processing
Most critical processing parameters
Ability to disperse SWNT and MWNT; Clumps or agglomerations of NT – create defect sites that will initiate failure & limit the efficiency of nanotubes to carry load CVD
grown MWNT- easily dispersed & less agglomerated increase modulus & strength of polystyrene without compromising strain-to-failure factor Not fully purified & not well dispersed arc-dischargegrown MWNT did not show the increase in toughness observed for well-dispersed
Methods of processing
Direct placing of resins onto NT thin film (Smallscale composites) Dispersion
is carried out; primarily by sonication- best solvent for SWNT are NMP, DMF, hexamethylphosphoramide, cyclopentane, tetramethylene sulfoxide and -caprolactone (all strong Lewis bases without hydrogen donors) Drying dispersion on a glass slide thin film of SWNT Placing resin directly onto thin film
Methods of processing
Direct mixing of NT and Polymers at TR Mixing of both NT and polymer in the presence of solvent; with help of a surfactant Eg.
SWNT dispersed in ethanol and then mixed with an epoxy resin Eg. CVD-grown MWNT dispersed in toluene with dissolved PS cast into film Eg. NT dispersed directly into liquid urethane acrylate polymer or methylmethacrylate monomer, or epoxy resin curing or polymerization
Methods of processing Direct melt-mixing of nanofibers (NF) in polymer st 1 stage-produce concentrated masterbatch (NF + solvent + surfactant + monomer of polymer) 2nd- mix the concentrated masterbatch and bulk polymer via melt-mixing in extruder/injection molding/internal mixer Eg. Melt-mixed NF with polyphenylene ether/polyamide matrices in twin screw extruder Has led to a commercial product in conductive plastics for electrostatic painting without loss of mechanical properties.
Layered Filler-Polymer Composite Processing
Polymer-Clay Nanocomposite
.
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Polymer-Clay Nanocomposites Application Automotive Components Packaging Materials Coatings and Pigments
Electro materials Drug Delivery Sensors and Medical Devices Building Materials
Polymer-Clay Nanocomposites Difficulties & Barriers Mechanical properties of individual silicate layers are not known
Processing in large scale
Lack of commercially available and thermally stable organoclays
Layered filler-polymer composite processing
1980s- clay/Nylon 6 composites were first commercialized Polymers
interact strongly with montmorillonite Clay surface can act as an initiator for polymerization
Steps in composites production: Open
clay galleries & match polarity of polymer Intercalation of organically modified clay XRD analysis- intercalation/exfoliation Processing of nanocomposites by traditional meltprocessing method
1. Open clay galleries & match polarity
Objective: to make sure polymers or monomers intercalate between clay layers Done by exchanging an organic cation for an inorganic cation Larger organic cations swell the layers and increase the hydrophobic properties of the clay Resulting in: organically modified clay or known as “organoclay”
2. Intercalation of Organoclay with polymer
By Solution Processing Dispersion of both organoclay and polymer in a common solution Highly polar polymers (Nylon & polyimides)- easily intercalated than nonpolar polymers (PP)
Polar polymers have higher affinity for the polar clay galleries
In-situ polymerization- intercalates monomer directly into organically modified clay galleries Monomer can either: Absorb onto the layer surface or Be anchored by free radical techniques
Fig. 10. Molecular Dynamics (MD) simulation scheme of intercalation process. Gray regions represent the polymer melt and striped regions represent the silicate particle: (a) reservoirs are equilibrated under constant pressure with slit closed, (b) slit is opened, and intercalation proceeds and (c) intercalation is complete [11]. Reproduced from Lee, Baljon and Loring by permission of American Institute of Physics.
Fig. 26. Snapshot at 1000 ps of octadecyltrimethyl–clay. Clay platelets are represented by a stick model and each surfactant chain is represented by a ball model with a different color for better visualization and includes nitrogen (large ball), united carbon (small ball) of hydrocarbon chain, and oxygen (medium ball) [105]. Reproduced from Paul, Zeng, Yu and Lu by permission of Elsevier Science Ltd.
Fig. 27. Snapshot of the 350,840-atom supercell after 0.5 ns of MD simulation showing a perspective view of the rectilinear supercell, the clay sheets exhibiting gentle undulations. The color scheme is C gray, H white, O red, N blue, Si orange, Al green, Mg magenta and Na brown [107]. Reproduced from Greenwell, Harvey, Boulet, Bowden, Coveney and Whiting by permission of American Chemical Society.
Fig. 19. Representative models of nanoparticle-reinforced polymer systems: (a) one spherical nanoparticle in polymer [84]. Reproduced from Starr, Schroder and Glotzer by permission of American Chemical Society; (b) one silica nanoparticle in polyimide [86]. Reproduced from Odegard, Clancy and Gates by permission of Elsevier Science Ltd.; (c) multiple nanoparticles in polymer [15]. Reproduced from Vacatello by permission of Wiley-VCH; and (d) polymer intercalated nanocomposite [87]. Reproduced from Hackett, Manias and Giannelis by permission of American Chemical Society.
Intercalation of Organoclay with polymer
By Melt Intercalation Mixing of clay and polymer melt with or without shear Higher success rate- gallery spacing is only about 2 nm and radius of gyration of polymer is significantly larger. Speed of intercalation is faster than self diffusion of polymers, but inversely proportionate with molecular weight of polymers The stronger the clay/polymer interaction, the slower the intercalation rate. “Kink” model of melt intercalation:
When accelerating an object it is necessary to consider inertia, the tendency of a body to remain at rest, or in uniform motion, unless acted upon by an external force. Moment of inertia, a measure of a body's resistance to angular/rotation acceleration, equals the product of the body's mass and the square of its distance from the axis of rotation,
Intercalation of Organoclay with polymer
“Kink” model of melt intercalation Layer flexibility control the mechanism of intercalation Sufficient force causes kink to form in clay sheet (a form of compression failure) Then, polymer can penetrate into new space between the layers Kink can propagate along the layer more polymer intercalated Fast intercalation rate:
Enhance by space created by kinking Depend on layers flexibility (Low modulus layers, kink more easily)
3. X-Ray Diffraction Analysis
To monitor the increase of layer spacing Intense peaks between 3 and 9- indicates an intercalated composites If peaks extremely broad or disappear completely- indicates complete exfoliation
4. Processing of Nanocomposites by Traditional Melt-processing
Final processing-important in determining the final properties Mixing facilities- nanoscale dispersion; lead to clay and/or polymer chain alignment Degree of shear during molding determines: Degree of clay layer alignment Degree of crystalline alignment
Eg. Extruded Nylon sheet with a draw ratio of 4:1Had higher modulus than sheet processed by injection molding May be due to higher degree of platelet and crystallite allignment
draw ratio: distance the plastic sheet is stretched vertically divided by the distance it is stretched horizontally.
Figure 2-1. Types of polymer/clay composites: (a) conventional miscible, (b) partially intercalated and exfoliated, (c) fully intercalated and dispersed and (d) fully exfoliated and dispersed
Figure 2-3. (a) TEM micrograph showing exfoliated/intercalated clay particles in Dow DER331/732 epoxy resin, (b) TEM micrograph revealing well intercalated clay layers
Processing of Nanocomposites by Traditional Melt-processing
Other studies; Crystallinity increases (36-38%) compared to 31% for unfilled Nylon Crystallinity remains constant with filler content Decreases in crystallinity -increasing pressure during processing to 0.1-0.6 GPa favors the phase Clay platelets can enhance alignment of Nylon 6 chains and the crystallite (the effect is lower than degree of shear)
Type of final structures
Intercalated nanocomposites Is
a tactoid with expanded interlayer spacing Clay galleries have a fixed interlayer spacing
Exfoliated nanocomposites Formed
when individual clay layers break off the
tactoid Either randomly dispersed in the polymer (a disordered nanocomposite) or left in an ordered array)
Partially exfoliated
Type of matrices
Polyamide: Nylon-6; Nylon-12 Polyimide Nonpolar polymers: Polypropylene and polyethylene Liquid-crystal matrices Polymetylmethacrylate/polystyrene Epoxy and polyurethane Polyelectrolyte Rubber Others
Orbys Technology What is it?
Nanocomposites obtained through colloidal construction Prepared by mixture, by adding to exfoliated clay and natural or synthetic latex.
Clay Nanocomposite Dispersion
Latex
Other routes: melt intercalation & in situ polymerization 46
apresentacoes/orbys_sitep_2007 _v1.ppt
Nanoparticle/Polymer Composites Processing
Nanoparticle/Polymer Composites Processing
3 general ways: Direct mixing of polymer and nanoparticles either as discrete phases or in solution In-situ polymerization in the presence of nanoparticles Both in-situ formation of nanoparticles and in-situ polymerization- results in hybrid nanocomposites due to intimate mixing of two particles
Direct Mixing
Two roll mill
Twin-screw extruder
PP and nanoscale silica- samples with more than 20wt% filler could not be drawn Nanoscale silica/PP composites-successful dispersion after modification of silica interface to increase compatibility with the matrix
Brabender high-shear mixer- successfully used to mix nanoscale alumina with PET, LDPE Thermal spraying-successful in processing nanoparticlesfilled Nylon Traditional melt-mixing:
Adv: the fastest method for producing new products (traditional methods available) Disadv: for some polymers, viscosity increases rapidly with the addition of significant volume fraction of nanofiller (can limit the practicality of the processing method)
Solution Mixing
Limitations of melt-mixing can be overcome if both polymers and nanoparticles are dissolved or dispersed in solution Allows modification of particle surface without drying, reduce particle agglomeration The nanoparticle/polymer solution can be; Cast
into a solid nanoparticle/polymer can be isolated from solution by solvent evaporation or precipitation
Further processing- by conventional techniques
In-situ polymerization
Nanoscale particles are dispersed in the monomer or monomer solution Resulting mixture is polymerized by standard polymerization methods Potential to graft the polymer onto the particle surface Eg. of nanocomposites via this process;
Silica/Nylon6 Silica/poly 2-hydroxyethylmethacrylate Alumina/polymethylmethacrylate Titania/PMMA CaCO3/PMMA
Key to in-situ polymerization- appropriate dispersion of filler in the monomer Often requires modification of the particle surface Dispersion is easier since it is in liquid rather than in a viscous melt Settling process is more rapid
In-Situ Particle ProcessingCeramic/Polymer Composites
In-situ sol-gel processing of the particles inside the polymer Successfully to produce polymer nanocomposites with silica & titania in a range of matrices Overall reaction for silica from tetrathylorthosilicate (TEOS) : Si(OC2H5)4 + excess H2 SiO2 + 4C2H5OH Few approach to form composites
Polymer Nanocomposites – Surface Modification, Dispersion
Ion exchange for clays Addition reaction on CNTs (fullerenes) Acidification, fluorination, etc. in order to attach different functional groups onto nano reinforcement surface to improve dispersion as well as reactivity with the matrix structure morphology change & tailoring of interface
Focus : Carbon Nanotube Functionalization Azomethine Ylides M. Prato, A. Hirsch et al., 2001 DMF, 130 oC 120 h R1NHCH2C(=O)OH + R2CH=O
- H2O, CO2
S R1 SWNTs W R2 N N H2C CH _ + T
N R1 R2
R1 = -CH2(CH2)6CH3, -CH2CH2OCH2CH2OCH2CH2OCH3
R2 = H,
SWNTs
R
Fluorination J. L. Margrave et al., 1998
+
-
F2/H2 R
(CH3)2CHCH2CH2ONO
SWNTs, -1 V
N2 BF4
- N2
SWNT [>NC(=O)OR]x
R = tert-Butyl, Ethyl, oligoether groups
Aryl Diazonium Salts, J. Tour et al., 2001
CH3CN + Bu4N BF4
160 oC ODCB
x
ROC(=O)N3 + SWNT
OCH3,
SWNT
Nitrenes A. Hirsch et al., 2001, 2003
R x
ODCB / CH3CN, 2:1 65 oC
R = tert-Butyl, halogen, COOH,NO2, COOH, CO2CH3 etc.
NH2
SWNTs
heat
[F]x-SWNTs
Acyl Peroxides V.N.Khabashesku et al., 2002 heat SWNTs + RC(=O)OO(=O)CR - CO2
[R]x-SWNTs
R = C11H23, C6H5, CH2CH2COOH
Polymer Nanocomposites – Network Formation
POSS
Carbon Nanotubes
Controlling Factors Properties of the Matrix Properties of the Nanoreinforcement Interface Properties of the Nanocomposites Interaction between Reinforcement and Matrix during Loading (Thermal, Mechanical, Electronical, etc.)
Conflicting Property Reports Conflicts Result from Differences in Matrix Polymer Repeating Unit Relative Mobility of Nano-reinforcement Compared with Matrix Degree of Crosslinking
Polymerization Mechanism Nano-reinforcement Surface Treatment
De-convolution
Degree of Dispersion
Simple Model System
etc.
Experimental Condition
Raw Materials Selection Molecular Dynamics
the Future …
Properties Design
Microscopic Morphology Control Optimum Interface Design Mechanosynthesis of Polymer Chains
