1. Electromagnetic Interference Shielding Properties of Injection Molded and Compression Molded Multi-walled Carbon Nanotube/Polystyrene Composites
M. Arjmand1, T. Apperley2, M. Okoniewski2, U. Sundararaj1*
1Department of Chemical and Petroleum Engineering, University of Calgary, Calgary, Canada
2Department of Electrical and Computer Engineering, University of Calgary, Calgary, Canada
PPS – 28
Dec 11-15, thailand

2. electromagnetic interference (emi) hazards2 1
Thermographic image of the head: (a) with no exposure to harmful cell phone radiation; (b) after a 15-min phone-call. Yellow and red areas indicate thermal (heating) effects.

3. conductive filler / polymer composites (CPCs) as EMI shields
CPCs have many advantages over metals in terms of:
Processability
Light Weight
Resistance to Corrosion
Low Cost

4. EMI SHIELDING MECHANISMS
Incident Power PI
EMI Shielding Mechanisms:
1- Reflection
2- Absorption
3- Multiple-Reflections
PI-R
Reflected Power PR
Transmitted Power PT
SE = 10 · log (PI/PT)
Expressed in dB

5. Typical curves of electrical conductivity and EMI SE versus filler concentration for CPCs
1Arjmand M, Apperley T, Okoniewski M, and Sundararaj U. Carbon 2012; 50:

6. incentives to investigate effects of carbon nanotube alignment on EMI shielding mechanisms
Unavoidable flow-induced alignment of carbon nanotubes (CNTs) in injection molding process
The importance of the knowledge of EMI shielding mechanisms in the design of CPCs as EMI shields

7. Experimental (Cont’d)
Injection Molding
BOY 12A
Polystyrene Masterbatch 20 wt%
(MB )
Blending with Twin-Screw Extruder
“Coperion ZSK”
Compression Molding
Pure Polystyrene
(Styron® 610)

8. Experimental Composite Molding
Compression Molding: Carver Plate Press: 210 oC, 38 MPa, 10 min
Injection Molding
EXP #
Mold Temp. (°C)
Melt Temp. (°C)
Injection Press. (bar)
Injection Vel. (mm.s-1) 1 60
215
100
240 2 3 24

9. Raman spectroscopy ratios parallel/perpendicular
┴/DװD
┴/GװG
Compression Molding
1.01
EXP #1
1.66
1.51
EXP #2
1.53
1.44
EXP #3
1.35
1.27
The order of the Raman intensity ratios, and consequently MWCNT alignment, from the highest to the lowest is EXP #1 > EXP #2 > EXP #3 > compression molded samples.

10. effects of mwcnt alignment on dc conductivity and emi se
The order of electrical conductivity and EMI SE from the highest to the lowest is compression molded samples > EXP #3 > EXP #2 > EXP #1.
EMI shielding does not require filler connectivity; however, it increases with filler connectivity.

11. EFFECTS OF MWCNT ALIGNMENT ON REAL PERMITTIVITY AND IMAGINARY PERMITTIVITY
The order of real permittivity and imaginary permittivity from the highest to the lowest is compression molded samples > EXP #3 > EXP #2 > EXP #1.

12. conceptualization of the effects of alignment on real and imaginary permittivities+ + - + + + + - + +

13. hierarchy of random distribution of MWCNTs and higher EMI SE
Greater Probability of MWCNT Contacts
Greater Electrons’ Mean Free Path
Higher Imaginary Permittivity and Ohmic loss
Higher EMI SE
Higher Applied Electric Field Between MWCNTs
Higher Real Permittivity and Polarization loss

14. Conclusions
MWCNT alignment has an adverse effect on electrical properties.
EMI shielding does not require filler connectivity; however, it increases with filler connectivity.
Measuring electrical conductivity and real and imaginary permittivities can give an idea about EMI SE.
In order to achieve conductive composites with high EMI shielding performance, designing the mold and processing conditions in injection molding process should be performed as to achieve random distribution of conductive filler.

15. Acknowledgements
Natural Sciences and Engineering Research Council of Canada (NSERC).
Dr. Tieqi Li and Ms. Jeri-Lynn Bellamy in Nova Chemicals®, Calgary, AB, Canada for the polymer extrusion/blending
Mr. Mehdi Mahmoodi and Dr. Simon Park, Department of Mechanical and Manufacturing Engineering, University of Calgary for assistance with the mold design and manufacturing
Dr. Samaneh Abbasi of Ecole Polytechnique (Montreal, Canada) for assistance with Raman spectroscopy
Americas Styrenics LLC, for Providing Pure Polystyrene.

16. THANKS FOR YOUR ATTENTION!

17. Effects of MWCNT alignment on shieldings by reflection and absorption

18. Morphological Analysis
Injection molding (EXP #1)
Compression Molding

19. Injection Molding vs Compression Molding: Length Distribution

20. Experimental Injection Molding
Our previous study showed that the melt temperature had the greatest impact on MWCNT alignment followed by the injection velocity, while the impacts of mold temperature and injection/holding pressure were insignificant.1
Levels (set points) of the processing parameters used in the injection molding experiments (EXPs). The processing parameters are mold temperature (C1), melt temperature (C2), injection/holding pressure (C3) and injection velocity (C4).
EXP #
C1 (°C)
C2 (°C)
C3 (bar)
C4 (mm.s-1) 1 60
215
100
240 2 3 24
Parameter
Value (mm) a
22.86 b
10.16
c, d 1 e 2 f 10
1 Mahmoodi M, Arjmand M, Sundararaj U, Park S. Carbon 2012; 50(4):

21. Raman spectroscopy ratios parallel/perpendicular
Two significant characteristics in the Raman spectra of the MWCNT/polymer composites are the D band (disorder band), and the G band (graphite band).
The Dװ/D ┴and Gװ/G ┴ parallel/perpendicular to the flow direction were used to determine the degree of MWCNT alignment.
Raman spectroscopy ratios parallel/perpendicular
┴/DװD
┴/GװG
Compression Molding
1.01
EXP #1
1.66
1.51
EXP #2
1.53
1.44
EXP #3
1.35
1.27
The order of the Raman intensity ratios, and consequently MWCNT alignment, from the highest to the lowest is EXP #1 > EXP #2 > EXP #3 > compression molded samples.