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

Electromagnetic interference (EMI) hazards 2 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. www.hardwareinsight.com www.biotele.com

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

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

Typical curves of electrical conductivity and EMI SE versus filler concentration for CPCs

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

Experimental (Cont’d) Materials Masterbatch of multi-walled carbon nanotube (MWCNT) in Polystyrene, Hyperion (MB2020-00) 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

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):1455-64.

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.

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.

Conceptualization of the Effects of alignment on Real and Imaginary Permittivity

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.

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

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.

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.

Thanks For Your Attention marjmand@ucalgary.ca u.sundararaj@ucalgary.ca

Effects of MWCNT alignment on shieldings by reflection and absorption

Morphological Analysis Injection molding (EXP #1) Compression Molding