Mohammad Arjmand, Mehdi Mahmoodi, Simon Park, Genaro Gelves, .... Mr. Wei Xiang Dong and Dr. Tobias Fürstenhaupt for preparation of TEM specimens.
Theme 3 - (A5) Injection molded multi-walled carbon nanotube/polystyrene composites: Effect of alignment on electromagnetic interference (EMI) shielding properties Mohammad Arjmand, Mehdi Mahmoodi, Simon Park, Genaro Gelves, Uttandaraman Sundararaj* Schulich School of Engineering
HQP Scientific Network Conference École Polytechnique de Montréal November 14 – 15, 2011
University of Calgary
Introduction
Composite Molding
The Polymer Processing Group develops strategic studies of conductive polymer composites using different nanofillers like carbon nanotubes, carbon nanofibers, metal nanowires, and graphene. Different strategies for preparation of nanocomposites with relevant industrial interest and characterization of the electrical behavior and performance are subject of current studies in the group. The rapid growth in portable electronics market has accelerated the demand for light-weight enclosures that can reduce electromagnetic interferences (EMI) pollution. EMI shielding compounds provide "immunity" for sensitive components from incoming EMI and/or prevent excessive emissions of EMI to other susceptible equipment.
•Injection Molding As there is a direct relation between the MWCNT alignment and volume resistivity,3 three experiments showing the greatest variation in the volume resistivity were selected as the representatives of different MWCNT alignments for the injection molding of the composites at different MWCNT concentrations. EXP #
C1 (°C)
C2 (°C)
C3 (bar)
C4 (mm.s-1)
A
60
215
100
240
B
60
240
100
240
C
60
240
100
24
Schematic view of the designed mold used in the injection molding process and filling simulation of the cavities employing mold flowTM software.
•Compression Molding Carver Plate Press: 210 oC, 5500 psi, 10 min
TEM Micrographs Compression molded sample (Randomly distributed MWCNT )
• Materials’ Resistivity and its relevant application
• Percolation Curve
Results
Injection molded sample (Aligned MWCNT)
•EMI shielding effectiveness (EMI SE) is the ability of a material to attenuate an incident electromagnetic wave. EMI SE is expressed in dB and defined as following: EMI SE= 10·log(EI/ET) where EI is the incident energy field and ET is the transmitted energy field.
Raman spectroscopy The Raman spectrum of MWCNT/polymer composites shows two characteristic peaks, i.e. D band and G band, which are sensitive to MWCNT alignment. The Dװ/D┴ and Gװ/G┴ (parallel/perpendicular) to the flow direction), achieved from applied polarized laser beam, were used to determine the degree of alignment. Raman spectroscopy ratios parallel/perpendicular
Ref. 1
Experimental Materials •Masterbatch of multi-walled carbon nanotube (MWCNT) in Polystyrene, Hyperion (MB2020-00) •Neat polystyrene, Americas Styrenics LLC (Styron* 610) Composite Preparation •Diluting the masterbatch with neat polystyrene using a Coperion co-rotating twin-screw extruder with a residence time, melt temperature and extruder speed of 2 min, 200 °C and 150 rpm, respectively
Experimental Design
EXP #
A series of experiments, denoted as "EXP", were carried out on a 5.0 wt% MWCNT/polystyrene composite using a two-level, four-factor factorial design employing an injection molding machine to study the impact of four processing parameters, i.e. mold temperature (C1), melt temperature (C2), injection/holding pressure (C3) and injection velocity (C4) on the volume resistivity of the molded samples.2 Level
High level (+) Low level (-)
Factors C1 (°C)
C2 (°C)
C3 (bar)
C4 (mm.s-1)
60
240
100
240
25
215
60
24
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15
c1 + + + + + + +
c2 + + + + + + + + -
Factors c3 + + + + + + + + -
16
+
-
-
c4 + + + + + + + +
-
Dװ/D┴
Gװ/G┴
Compression Molding
1.01
1.01
EXP #A
1.66
1.51
EXP #B
1.53
1.44
EXP #C
1.35
1.27
According to the Raman spectroscopy results, the order of the Raman intensity ratios, and consequently MWCNT alignment, from the highest to the lowest is EXP #A > EXP #B > EXP #C > compression molded samples.
Effect of MWCNT alignment and concentration on volume resistivity and EMI SE
Conclusions Alignment decreases the likelihood of MWCNTs contacting each other leading to higher volume resistivity and percolation threshold. EMI SE is highly sensitive to MWCNT alignment. EMI SE of compression molded samples is significantly higher than that of injection molded samples. The molds and processing conditions in industrial injection molding process should be designed in such a way as to approach the random distribution of MWCNTs in order to get better electrical properties.
Acknowledgements a) Minitab main effect plot of the volume resistivity mean of the molded samples and b) interaction plot for electrical resistivity of the nanocomposites.
1. RTP company, www.rtpcompany.com. 2. Mahmoodi M, Arjmand M, Sundararaj U, Park S. In: Proceedings of ANTEC Conference. Boston, May, 2011. p. 525-530. 3. Arjmand M, Mahmoodi M, Gelves GA, Park S, Sundararaj U. Carbon 2011;49:3430-3440.
• NSERC for funding • Mr. Thomas Apperley and Dr. Michal Okoniewski for assistance with the EMI SE measurements • Dr. Tieqi Li and Ms. Jeri-Lynn Bellamy in Nova Chemicals®, Calgary for polymer blending • Mr. Wei Xiang Dong and Dr. Tobias Fürstenhaupt for preparation of TEM specimens • Dr. Samaneh Abbasi of Ecole Polytechnique (Montreal) for assistance with Raman Spectroscopy • Americas Styrenics LLC, for providing neat polystyrene
