Soy protein coated graphite nanoplatelets in polycarbonate
composite for improved static dissipation rate
Michelle Tsui1, Bin Li2, Jianying Ji2, Michael Robert Pierce2 and Wei-Hong Zhong2
1Department of Materials Science and Engineering, University of California-Berkeley
2School of Mechanical and Materials Engineering, Washington State University
Introduction
Dielectric properties\
Sample Preparation
SPI Treated GNP
Figure 1. Electrostatic discharging damage
to a circuit capacitor
Rate of static dissipation, τ:
 ESD protection requires quick
dissipation rate
 Want low electrical resistivity and
low relative permittivity
Surface
Treatment
• Stir on hotplate for 6 hours:
Denature SPI and let
denatured SPI coat GNP
1.E+01
1.E+00
1.E+03
Further
Dispersion
The Polymer Composite:
1.E+06
GNP Nanocomposite
GNP
Good Interface
1.E+06
PC
C. Untreated
Figure 5. SEM images of fractured
surface along thickness of composite.
 A. SPI treated specimen at X20,000good dispersion and many wellbonded interfaces of smaller
particles
 B. Untreated specimen at X20,000poor dispersion leading to
agglomerates (circled) and poor
interfacial interaction
 C. Large agglomerate of small GNP
particles in untreated specimen at
X50,000
Surface resistivity (Ohms/Sq)
no SPI
2E+12
8E+09
4E+07
2E+05
0
1
2
3
4
5
Concentration GNP (wt%)
Conclusions
6
Figure 2.
Direct current (DC) surface resistivity of SPI treated
and non-treated composites at different
concentrations of GNP.
C16H14O3
 SPI improves
dispersion, allowing
a conductive
network of GNP
(percolation
threshold) to form
at 0.05 wt%,
compared to
1
wt% without SPI
SPI
no SPI
2.E+15
8.E+12
4.E+10
0.05 wt% 1.0 wt%
1.E+06
0.0
1.0
2.0
3.0
4.0
Concentration of GNP (wt%)
GNP Agglomerate
Alternating Current
relative
permittivity
SPI
3E+14
Poor Interface
SEM imaging
Electrical Properties
Volume resistivity (ohm*cm)
1.E+05
B. Untreated
PC
Results
2.E+08
1.E+04
Frequency (Hz)
A. SPI Treated
1E+03
 Applications in
 Diameter of 25
 Applications
industry include:
micrometers
include: adhesives,
Electronic
 Width of 5-10
asphalts, cosmetics,
components,
micrometers
polyesters, textile
construction,
 Graphite also in pencils,
fibres
transportation,
superconductors,
 Food applications :
data storage (CDs,
batteries, lubricant
cereal, dietary
DVDs…)
supplement, pasta,
infant formulas
1.E+05
1.E+00
1.E+03
Scanning Electron Microscopy (SEM) Imaging
• Solution cast on glass panel
• 0.03-0.05 mm thickness for
testing
Direct current
surface resistivity
Soy Protein Isolate (SPI)
1.E+04
1.E+01
• Bath sonicate for 1 hour:
Ensure homogeneous
dispersion of GNP
Direct current
volume
resistivity
Exfoliated Graphite
Nanoplatelets (xGNP)
1%
Frequency (Hz)
Characterization Methods
Polycarbonate
(PC)
3%
1%
• Dissolve and mix PC with
suspension for 6 hours:
Compounding Achieve uniform composite
solution and thorough contact
between GNP and Polymer
Casting
 Polymers used in engineering applications for lightness, processability and
high specific strength, but are strong insulators and prone to ESD
 Conductive filler added to polymer decreases static dissipation rate.
Effectiveness depends strongly on:
• dispersion of particles in polymer
• interfacial bonding between filler and polymer
 Carbon nanoparticles are highly conductive and shape and size make them
attractive choice, but agglomeration occurs due to attractive forces (i.e.
Van Der Waals) between particles
 Surface treatment of filler improves dispersion and interfacial bonding.
 Surfactants usually toxic, but hypothesize soy protein isolate (SPI)— edible,
abundant, easily produced—is economical alternative with competitive
results
4.50%
1.E+02
3%
Relative Permittivity
Electrostatic discharging (ESD) occurs when an electrically charged object
attempts to neutralize through a sudden flow of electric charge, resulting in a
spark. Although most human encounters with ESD do not cause serious injury,
a spark can inflict latent and catastrophic damage to electronic parts as well as
cause fires or explosions.
GNP
Exfoliation
• Probe sonication for 1 hour:
Disperse aggregated graphite
platelets
1.E+02
Relative Permittivity
Electrostatic Discharging
Untreated GNP
4.5%
5.0
Figure 3.
DC volume resistivity of SPI treated and nontreated composites versus concentration of GNP.
 GNP reduces both volume and surface resistivities of PC, while SPI
further reduces resistivity of composite through improved dispersion
 SPI prevents permittivity from increasing with increasing GNP
concentration—a desirable property to static dissipation.
 Facile SPI surface treatment improves interfacial interaction between
GNP and PC
Future Work
 Investigate the effect of SPI concentration on dispersion and interfacial
interaction
 Probe sonication- effect of power, time, and temperature on GNP size during
sample preparation
Acknowledgements
This work was supported by the National Science
Foundation’s REU program under grant number DMR-1062898