1. M. Arjmand1, M. Mahmoodi2, S. Park2, U. Sundararaj1.
An Investigation on Electrical and Electromagnetic Interference Shielding Properties of Flow-induced Oriented Carbon Nanotube in Polycarbonate
M. Arjmand1, M. Mahmoodi2, S. Park2, U. Sundararaj1.
1Department of Chemical and Petroleum Engineering, University of Calgary, Calgary, AB
2Department of Mechanical and Manufacturing Engineering, University of Calgary, Calgary, AB
PPS-27
May 2011

2. CPCs’ Structure
CPCs are made by adding a conductive filler into a polymer matrix.
Carbon nanotube (CNT) special characteristics:
Excellent Electrical Properties
Low Density
High Aspect Ratio
Corrosion Resistance

3. CPC Applications
The surface/volume Resistivity defines application: Anti-static Protection Ω.sq-1 Electrostatic Discharge Dissipation (ESD) Ω.sq-1 Electromagnetic Interference shielding < 10 Ω.sq-1

4. Polystyrene Masterbatch 20 wt% Blending with twin-screw extruder
Experimental
Injection Molding
Polystyrene Masterbatch 20 wt%
Blending with twin-screw extruder
Pure Polystyrene
Compression Molding

5. Designed Mold Employed in Injection Molding
Cavity 2
Cavity 1
Cavity 3

6. Experimental Design C1: Mold Temperature C2: Melt Temperature
C3: Injection/Holding Pressure
C4: Injection Velocity
Factors
Levels
C4(mm/sec)
C3 (bar)
( C°) C2
( C°) C1
240
100 60 + 24
215 25 _

7. Volume Resistivity of 5.0 wt% MWCNT/PS Composite in Thickness Direction
There is a direct relation between composite volume resistivity and MWCNT alignment.

8. Raman spectroscopy ratio parallel/perpendicular
Raman Spectrocopy
Raman spectroscopy ratio parallel/perpendicular
Dװ/D┴
G װ/G┴
Compression molding
1.01
PC #10
1.53
1.44
PC #12
1.35
1.27
PC #14
1.66
1.51

9. Compression Molded Percolation Curve
Percolation Concept
Nanocomposite
Structure
Compression Molded Percolation Curve
Percolation 1

10. Injection Molded Samples’ Percolation Curve
Current Dissipation
Flow Direction

11. Injection Molded Sample Compression Molded Sample
Illustration of the effect of nanotube alignment on the appearance of micrograph of CNT-aligned samples
Injection Molded Sample
Compression Molded Sample
Flow Direction
Parallel to the flow direction
Perpendicular to the flow direction
Adapted from Pötschke et al. Eur. Polym. J. 2004;40(1):

12. TEM Micrograph of 5.0 wt% MWCNT/PS Composite
Injection Molded Sample
(Parallel to the Flow)
Compression Molded Sample

13. Electromagnetic Interference (EMI) Shielding

14. Electromagnetic Interference (EMI) Shielding
Incident
EMI Shielding Mechanisms:
1- Reflection
2- Absorption
3- Multiple-Reflections EI
EI-R
Reflected ER
Transmitted ET
SE = 10 ·log (Pin/Pout)
Pin : Incident Energy Field
Pout: Transmitted Energy Field

15. The relation between conductivity and EMI SE
Many researchers believe that there is a direct relation between conductivity and EMI SE.
However, there is no scientific criterion to prove the mentioned claim since conductivity needs connectivity while EMI SE does not.

16. Volume Resistivity and EMI SE

17. The difference in connectivity of MWCNTs in compression molded and injection molded samples plays the key role in interpretation of the reflection and absorption mechanisms.

18. Shielding by Reflection and Volume Resistivity
The shielding by reflection is related to amount of mobile charge carriers on the shield’s surface and has nothing to do with composite’s conductivity.

19. Shielding by Absorption
There is a direct relation between shielding by absorption and MWCNT connectivity, however, the relation between absorption and composite’s conductivity is not always right.

20. Greater shielding by absorption in compression molded samples than injection molded ones can be related to higher imaginary permittivity (Electric loss), real permittivity (Electric dipole formation) and magnetic permeability (magnetic dipole formation) in compression molded (randomly distributed MWCNT) samples.

21. Conclusions
The conductive polymer composites showed lower electrical conductivity at greater MWCNT alignments which is ascribed to decrease in likelihood of MWCNT contacting each other at higher MWCNT alignments.
Increase in reflection by increase in MWCNT concentration is due to increase in amount of mobile charges and has nothing to do with CPCs’ electrical conductivity.
Absorption increases with decrease in MWCNT alignment which is due to higher real (electric dipole) and imaginary (electric loss) permittivity and magnetic permeability (magnetic dipole) at lower MWCNT alignments.
To achieve higher electrical properties, the injection molding process should be designed in such a way to approach the MWCNT random distribution.

22. Acknowledgements
Natural Sciences and Engineering Research Council of Canada (NSERC).
Thomas Apperley and Pr. Michal Okoniewski, Electrical Engineering Department, University of Calgary, Calgary, Canada for assistance with Electrical properties measurements.
Mr. Wei Xiang Dong and Dr. Tobias Fürstenhaupt for preparation of TEM specimens by ultramicrotoming.
Dr. Samaneh Abbasi of Ecole Polytechnique (Montreal, Canada) for assistance with Raman spectroscopy.
Polymer Processing Society PPS-26 Organizing Committee Graduate Travel Award.
SSAF Travel Grant from Schulich School of Engineering, University of Calgary.

23. Any Questions?