xxiii πανελληνιο ÏƒÏ Î½ÎµÎ´ÏÎ¹Î¿ Ï†Ï ÏƒÎ¹ÎºÎ·Ï‚ στερεας καταστασης & επιστημης ...

Thermal and Electrical Properties of Polymer / Multi-Walled
Carbon Nanotubes Nanocomposites
E. Logakis 1* , Ch. Pandis 1 , P. Pissis 1 , J. Pionteck 2 , P. Pötschke 2 , M. Mičušík 3 and M. Omastová 3
1 National Technical University of Athens, Zografou Campus, 15780, Athens, Greece
2 Leibniz Institute of Polymer Research Dresden, 01069 Dresden, Germany
3 Polymer Institute, Slovak Academy of Sciences, 842 36 Bratislava, Slovakia
*E-mail: logmanos@central.ntua.gr
Tel.: (+30) 210 772 2974, Fax: (+30) 210 772 2932
Carbon nanotubes (CNTs) have attracted special interest as new materials for mixing with polymers due to their
exceptional electrical, mechanical and thermal properties. Polymer/CNTs nanocomposites are promising materials with
potential applications as electromagnetic shielding coatings, electrostatically dissipative materials, aerospace structural
materials and active elements in sensors.
Several processing methods are available for the production of polymer / CNT composites. Melt-mixing of CNT into
thermoplastic polymers using conventional processing techniques are particularly desirable, because of the speed, simplicity,
and availability in the plastic industry. This method is also beneficial because is free of solvents and contaminants, which are
present in solution processing methods and in-situ polymerization.
In the present study, the nanocomposites were prepared by melt mixing a starting masterbatch (Hyperion Catalysis, USA)
of polyamide 6 (PA6) or polypropylene (PP) containing 20 wt% multi-walled carbon nanotubes (MWCNTs) with the pure
polymers in a Plasti-corder kneading machine PLE 331 (Brabender, Germany), followed by compression moulding using a
laboratory hydraulic press SRA 100 in order to obtain different concentrations in CNTs.
The purpose of this work is to examine the thermal, electrical and dielectric properties of multi-walled carbon nanotubes
(MWCNT) filled PA6 or PP nanocomposites formed by melt-mixing. To that aim differential scanning calorimetry and
dielectric relaxation spectroscopy were employed. The influence of CNT on the thermal transitions (glass transition
temperature, melting, crystallization) of the pure polymers is investigated. The results are discussed in terms of nucleating
action of CNT and interfacial polymer-filler interactions. Special attention is paid to percolation aspects by both ac and dc
conductivity measurements for the samples which are above the percolation threshold (p c ). Percolation threshold is the
critical concentration of the filler where conducting pathways are formed by CNT and consequently a transition from the
insulating to the conducting phase is observed. p c is usually determined through dc conductivity measurements. In this work
ac measurements were performed, as apart from the determination of dc conductivity, the opportunity to study in detail the
frequency dependence of conductivity is provided by defining the critical frequency (f c ), where the transition from dc to ac
conductivity is observed. Furthermore, the actual aspect ratio (length-to-diameter ratio) of the inclusions in the
nanocomposites is calculated using two different theoretical models (E. J. Garboczi et al. and I. Balberg et al. model) and the
exported values are correlated with the percolation threshold values. It is already known that CNT have the tendency to form
bundles due to van der Waals interactions and the final aspect ratio of CNT in the nanocomposites is much lower, comparing
with the value of an individual nanotube. This fact leads to increased p c values. Besides, the conductivity mechanism is
examined through the temperature dependence of conductivity. Finally, the influence of CNT on the study of dielectric
relaxation mechanisms of PA6 is investigated, to look for effects of CNT on molecular mobility of the polymer matrix, which
may arise from polymer-filler interactions.
Acknowledgement
"This work has been funded by the project PENED 2003. The project is cofinanced 75% of public expenditure through EC -
European Social Fund, 25% of public expenditure through Ministry of Development - General Secretariat of Research and
Technology and through private sector, under measure 8.3 of OPERATIONAL PROGRAMME "COMPETITIVENESS" in
the 3rd Community Support Programme."
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