Carbon nanotubes as nanofillers

Layered silicate as nanofillers - Polymer-clay nanocomposites : melt blending vs.. Carbon nanotubes as nanofillers - Polymer-CNTs composites : production and properties - « Melt blending

I Polymer microcomposites filled with microparticles

I.1 Mechanical melt blendsI.2 Importance of « polymer/filler » interface (tension and adhesion) I.3 "Polymerization-filled composites" PFC's

II Polymer nanocomposites filled with nanoparticles

II.1 Layered silicate as nanofillers

- Polymer-clay nanocomposites : melt blending vs in situ polymerization

- Polyolefinic matrices : role of matrices and compatibility

- Polyester matrices : role of clays and organo-modificationII.2 Carbon nanotubes as nanofillers

- Polymer-CNTs composites : production and properties

- « Melt blending » technique, e.g., in elastomeric matrices

- in situ polymerization, e.g., in thermoplastic matrices III General conclusions et outlook

Chapter 3 :

Polymer nanocomposites filled with nanoparticles

Part II Carbon nanotubes as

nanofillers

Allotropic forms of Carbon

Curl, Kroto, Smalley 1985

Iijima 1991 graphene

(From R Smalley´s web image gallery)

- Single-wall nanotubes (SWNTs)

- Multi-wall nanotubes (MWNTs)

Carbon Nanotubes

~ 1-2 nm Few microns

TEM images of various MWNTs

~ 2 - 50 nm

Properties of CNT

• Electrical :

– High electric conductivity (higher than copper)

– Easy process for Conductive Semi-conductive

• Thermal :

– High thermal conductivity (higher than silicon)

– Stable at high temperature

• Physical :

– 100 times stronger than steel but very light

– Elastic behavior (Pressing CNT tip bend and recover to

its original state)

• Chemical :

– Rarely react with other compounds

– Chemically stable

(a) Conductive (b) Semiconductive (c) Diode

‘Kink CNT’: divide conductive and semi-conductive

Synthesis methods of CNT

• Arc discharge

– First CNT synthesis method used by Dr.Iijima

– Arc is formed in the gap between two

graphite electrodes

– Grow SWNT with catalyst (Co, Ni, Fe, Y, etc.),

while MWNT without catalyst metal

– For higher purity:

• Rotate cathode to uniform the arc

• High the temperature

• Use Hydrogen gas instead Helium gas

Synthesis methods of CNT (cont’)

• Laser vaporization

– First used Smalley Group in 1995

– Use He or Ar gas and maintain 500 torr

– Use laser, vaporize graphite

Synthesis methods of CNT (cont’)

CVD (Chemical vapor deposition)

– Advantages : temperature, the insert gas, pressure, gas flow, catalyst,

etc

– Insert hydrocarbon gas (C2H2, C2H4, CH4, etc) into

quartz tube and obtain Energy

 insert gas decomposed and CNT grow on a quartz boat surface

– Energy source categorizes CVD

: thermal CVD, Hot filament plasma CVD, Microwave plasma CVD, RF

plasma CVD, etc

Synthesis methods of CNT (cont’)

– Use mixture of Pd and Ni for substrate to maintain the high temperature condition

 can grow high purity CNT vertically under 600 o C

 Mechanic properties : high tenacity

 Electrical properties :

Electronic components, sensors,…

Tensile strength (GPa)

 Thermal properties : « stability » and flame retardant behavior

Interest of carbon nanotubes as nanofillers

Difficulty : Bundle-like aggregation of CNT’s

Bundle-like aggregation maintained upon melt blending within polymer matrix

500 nm

EVA + MWNT’s

Bundle-like aggregates

µm-size > thousands

bundle aggregates individual tubes

The Processing Challenge

Polymer

Proposed solution : CNT surface FUNCTIONALIZATION

Sun Y-P., Acc Chem Res., 35, 1096 (2002)

Easier dispersion in polymeric matrices…

Carbon nanotubes as nanofillers

Production of nanocomposites by « Melt

blending » technique :

Use of organo-clays to separate the

CNT’s

Commercial EVA : copolymer with 27 wt% VA

(ESCORENE UL00328 from Exxon)

CNT’s - produced by catalytic decomposition of acetylene on

50 nm

TEM image of MWNT’s

- Purification by dissolution of the catalytic support in boiling

concentrated NaOH (40wt%)

Collaboration with Prof

J.B.Nagy, FUNDP, Namur

(Belgium) and Nanocyl S.A.

Different carbon nanotubes

Nanotubes % impurities number of sheets Length Diameter

Ammonium cations used to modify the interlayer :

Montmorillonite : surface area : 750 m²/g ; thickness ~ 1 nm ; length ~ 500 nm

(US)

Nanofil 15 from Süd Chemie

R

N + R R R

H2O, T

Preparation of nanocomposites

By melt blending in a Brabender internal mixer

(at 45rpm) Total filler content : from 0.5 to 5 wt%

From Alexandre and Dubois,

Mater Sci Eng R., 28 (2000)

XRD of EVA organo-clay

nanocomposites

TEM of EVA organo-clay

50 nm

~1 nm

Binary and Ternary compositions

1) EVA + Cloisite 30B 2) EVA + CNT’s

Thermogravimetric Analysis:

The thermodegradation of ethylene vinyl acetate copolymer (EVA) takes place in 2 steps :

1° deacetylation with formation of acetic acid and

« c=c » double bonds along the backbone:

2° Thermo-oxidation of the unsaturated chains

CH3

+

Thermogravimetric Analysis of Binary Compositions :

More likely due to

gas barrier properties

(O2 and organic residues)

Zanetti and Camino, Polymer , 42, 2001, 4501

2 - 10wt%

1wt%

Thermogravimetric Analysis of Binary Compositions :

Thermogravimetric Analysis of Binary Compositions :

EVA + 3wt% various NTC’s

EVA

TGA under air flow at 20K/min

Crushed MWNT’s

MWNT’s

DWNT’s and Thin MWNT’s

0 1 2 3 4 5 6 7

« thermal stability » :

Length CNT’s

Thickness CNT’s

Unfilled EVA EVA + 3wt% long MWNT’s EVA + 3wt% crushed MWNT’s EVA + 3wt% thin MWNT’s EVA + 3wt% DWNT’s

Thermogravimetric Analysis of Ternary Compositions :

TGA under air flow at 20K/min

Thermogravimetric Analysis of Binary and

Ternary Compositions :

440 450 460 470 480 490 500

Temperature at max degradation rate for EVA

3 wt% Cloisite 30B + MWNT’s

TGA under air flow at 20K/min

0 5 10 15 20 25 30

Tensile properties

Crosshead speed : 50 mm/min

T : 20°C

0 1 2 3 4 5 6

Higher Young’s modulus : rigidity increase

Tensile Properties of Binary Compositions

Evolution of Young's Modulus for different binary systems

The Young’s modulus increases spectacularly with filler content

MWNT’s give similar results

to Cloisite 30B

Error : ±5%

Tensile properties:

ASTM D638 TYPE , 50mm/min, 20°C Ⅴ, 50mm/min, 20°C

Rigidity effect : Clay ~ MWNT’s

Ultimate Elongation ~ 900-1000%

Ultimate Stress ~ 20-22 MPa Close to EVA

MWNT’sCloisite 30B

Cloisite 30B + MWNT’s

Evolution of the Young's Modulus for different ternary systems containing purified CNT

10 12 14 16 18 20 22 24 26 28

Tensile Properties of Ternary Compositions

Ultimate Elongation ~ 900%

Ultimate Stress ~ 20-23 MPa Close to EVA

Tensile Properties of Binary and Ternary

ASTM D638 TYPE Ⅴ, 50mm/min, 20°C 50mm/min, 20°C

Effect of nanofiller nature

-Large increase of material rigidity while keeping high ductility

-Effect of CNT’s length on rigidity of binary composites :

long MWNT’s (50m) < thin MWNT’s (3-4m) < DWNT’s (2.2m) < crushed MWNT’s (300nm)

(more likely due to the extent of CNT’s dispersion)

-Ternary nanocomposites display comparable tensile performances (even for longer CNT’s)

Flame retardant properties are improved for all nanocomposites.

Organoclays and carbon nanotubes are effective in the reduction of PRHR

(Peak of Rate of Heat Release) , i.e, improved flame retardant behaviour

580 kW/m²

Flame retardant behaviour by

SYNERGISTIC EFFECT OF NANOFILLERS

Dubois, B.Nagy, Beyer, Comp Sci Tech (2004)

Morphology studied by XRD

0 200 400 600 800 1000 1200 1400 1600

EVA

EXFOLIATION

Morphology studied by TEM

Morphology studied by TEM

3wt% Cloisite 30B + 1wt% long MWNT’s

Longer CNT’s : higher degree of interconnectivity

(plus some remaining bundle-like aggregation)

Longer CNT’s are more difficult to disperse (even in the presence of organo-clays)

Ternary nanocompositions :

• Improved thermal stability

• Enhanced material stiffness while keeping performant ultimate properties

• Flame retardant performances

delaminated clay

Interconnectivity of longer CNT’s