Third Day Poster Session, 17 June 2010 - NanoTR-VI

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Poster Session, Thursday, June 17
Theme F686 - N1123
Differential Scanning Calorimetry Investigation of Conductive Nanocomposites Based on EVA
Copolymer and Expanded Graphite
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UI. H. TavmanUP P*, K. SeverP P, Y. SekiP P, A. EzanP
PA. TurgutP
PI. Özdemir P P, I. KrupaP P, M. OmastovaP P, I. NovakP
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PMechanical Engineering Dept., Dokuz Eylul Univ., 35100 Bornova Izmir, Turkey
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PTDepartment of Chemistry, Dokuz Eylül University, Buca, 35160 zmir, Turkey
PFaculty of Engineering, Bartin University, Bartin, Turkey
PPolymer Institute, SAS, Dúbravská cesta 9, 842 36 Bratislava, Slovakia
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Abstract- Polymers which are normally insulating materials, may be made electrically and thermally conductive by the addition of
conductive fillers. In this study the nanocomposites consist of the ethylene- vinyl acetate copolymer (EVA) as base material, the conductive
fillers used are expanded graphite (EG) and untreated graphite (UG). Nanocomposites containing up to 50 weight % of filler material were
prepared by mixing them in a Brabender Plasticorder. A differential scanning calorimetry study reveals us a decrease in glass transition
temperature of the composite with increase in particle content.
During the last decade there has been an increasing
interest in the field of polymer nanocomposites since the
modification of polymer matrix with small amounts of
nanoparticles proved to be effective in enhancing the
mechanical, electrical, thermal, fire retardant, barrier and
optical properties of a variety of polymers. Polymergraphite
nanocomposites are interesting due to their
potential conductive properties. Graphite is found in nature
in the form of graphite flakes or powder of various particle
sizes. Graphite flakes, such as clays, are composed of
layers, normally smaller than 100 nm in thickness[1]. If
the appropriate process conditions are applied, graphite
nanocomposites offer the potential to produce materials
with excellent mechanical, electrical, and thermal
properties at reasonable cost, which opens up many new
applications[2]
In this study Ethylene- vinyl acetate copolymer (EVA)
containing 14 wt% of vinyl acetate (VA) was used as
matrix material. Its melt flow index is 9.8 g/10min
(190°C/2.16 kg). The filler materials were expanded
graphite (EG) and untreated graphite (UG). Ethylenevinyl
acetate copolymer (EVA) – graphite mixtures were
prepared in a Brabender Plasticorder PLE 331 internal
mixer at 150 °C for a total mixing time of 10 min, the
mixing chamber capacity being 30ml. The rotors turned at
35 rpm in a counter-rotating fashion with a speed ratio of
1.1. After 10 minutes, the mixing chamber of the
Brabender apparatus was opened and the resulting mixture
taken out. The resultant mixture was then put in a
comression moulding die and compressed in a
compression molding press at 120°C, under 40 kP pressure
for one minute to obtain samples in the form of sheets of
1mm in thickness. During the mixing process the
expanded graphite exfoliates. The exfoliation process
starts on the edges of EG grains and the exfoliated graphite
flakes have nano-sized dimensions with bigger surface
areas compared to micro-sized dimensions of the UG
pellets.
The glass transition (TRgR), melting(TRmR), crystallization
(TRcR) temperatures, as well as melting(hRmR) and
crystallization (hRcR) enthalpies for pure EVA and also
nanocomposites 6 and 15 weight % of EG; 6 and 15
weight % of UG were measured by DSC at a
heating/cooling rate of 10 °C /min. The results obtained
using Perkin-Elmer DSC were given in Table 1. There was
a decrease in glass transition temperature of the
nanocomposites with respect to pure EVA, the decrease is
slightly stronger for EG filled samples then UG filled
samples. The melting(TRmR) and crystallization (TRcR)
temperatures were practically unchanged for the
nanocomposites.
The EVA- EG nanocomposite showed a lower
percolation threshold of electrical conductivity which is
about 5% of volumetric filler content, compared to about
15% of volumetric filler content for EVA-UG composites.
Electrical conductivity of EVA- EG nanocomposites was
also higher than electrical conductivity of EVA-UG
composites filled with micro-sized filler at the same
concentrations.
Table 1. DSC analysis results of EVA/UG and EVA/EG nanocomposites
T g T hRm TR
c hRc
Sample Code o
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PC) (P PC) (j/g) (P PC) (j/g)
Pure Eva -28.2 87.71 89.53 72.71 -6.49
EVA-EG
94/6 -32.32 87.39 74.67 73.25 -8.01
EVA-UG
96/4 -30.58 88.23 76.14 73.25 -7.53
EVA-EG
85/15 -33.35 87.74 60.55 73.92 -2.75
EVA-UG
85/15 -31.39 87.55 67.11 73.41 -5.01
TRgR: Glass transition temperature
TRmR: Melting temperature
TRcR: Crystallization temperature
hRmR: Melting enthalpy
hRcR: Crystallization enthalpy
This research was supported by the Scientific Support of
the bilateral Project No. 107M227 of TUBITAK and SAS
and partly by the project VEGA No. 2/0063/09.
*Corresponding author: HTismail.tavman@deu.edu.trT
[1] Guterres, J-M, Basso, N.R.S, Galland, GB, 2010,
Polyethylene/Graphite Nanocomposites Obtained by In Situ
Polymerization, Fabiana De C. Fim, Journal of Polymer Science:
Part A: Polymer Chemistry, 48: 692–698.
[2] H. Fukushima,H. , Drzal, L-T., Rook, B. P. , Rich, M. J.,
2006, Thermal Conductivity of Exfoliated Graphite
Nanocomposites, Journal of Thermal Analysis and Calorimetry,
85(1): 235–238.
6th Nanoscience and Nanotechnology Conference, zmir, 2010 726