1. PPS AMERICAS CONFERENCE
Comparative study of electromagnetic interference shielding properties of injection molded versus compression molded multi-walled carbon nanotube / polystyrene composites
M. Arjmand1, M. Mahmoodi2, S. Park2, U. Sundararaj1
1Department of Chemical and Petroleum Engineering, University of Calgary, Calgary, Canada
2Department of Mechanical and Manufacturing Engineering, University of Calgary, Calgary, Canada
PPS AMERICAS CONFERENCE
May 2012

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. Electromagnetic Interference (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

6. Motivation to compare the EMI shielding properties of injection molded samples versus compression molded samples
Flow-induced alignment of carbon nanotubes (CNTs) in injection molding process versus random distribution of CNTs in compression molding process
Lack of investigations discussing effects of CNT alignment on electrical conductivity, real permittivity and imaginary permittivity and their relationship with EMI SE

7. Experimental (Cont’d)
Materials
Masterbatch of multi-walled carbon nanotube (MWCNT) in Polystyrene, Hyperion (MB )
Neat Polystyrene (PS), Americas Styrenics LLC (Styron® 610)
Composite Preparation
Diluting the masterbatch with the neat PS using a Coperion ZSK co-rotating intermeshing twin-screw extruder with a residence time, melt temperature and extruder speed of 2 min, 200 °C and 150 rpm, respectively
Composite Molding
Compression Molding: Carver Plate Press: 210 oC, 38 MPa, 10 min

8. 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):

9. 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.

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. Conceptualization of the Effects of alignment on Real and Imaginary Permittivity

12. 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.

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
The EMI shielding properties of the compression molded samples of MWCNT/PS composites were superior to the injection molded samples.
Higher EMI SE in the compression molded samples was related to higher electrical conductivity, real permittivity and imaginary permittivity.
EMI shielding does not require filler connectivity; however, it increases with filler connectivity.
Due to better EMI shielding properties of the compression molded samples than the injection molded samples, it can be concluded that designing a mold for injection molding that achieves a random MWCNT distribution is crucial in order to attain high EMI shielding properties.

15. Acknowledgements
Natural Sciences and Engineering Research Council of Canada (NSERC).
Thomas Apperley and Dr. Michal Okoniewski, Electrical and Computer Engineering Department, University of Calgary, Calgary, Canada.
Dr. Tieqi Li and Ms. Jeri-Lynn Bellamy in Nova Chemicals®, Calgary, AB, Canada for the polymer extrusion/blending
Dr. Samaneh Abbasi of Ecole Polytechnique (Montreal, Canada) for assistance with Raman spectroscopy
Mr. Wei Xiang Dong and Dr. Tobias Fürstenhaupt for preparation of TEM specimens by ultramicrotoming.
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