1070-4272/03/7604-0603 $25.00 C 2003 MAIK [Nauka/Interperiodica]
Russian Journal of Applied Chemistry, Vol. 76, No. 4, 2003, pp. 603!606. Translated from Zhurnal Prikladnoi Khimii, Vol. 76, No. 4, 2003,
Original Russian Text Copyright + 2003 by Gorshenev, Bibikov, Novikov.
AND POLYMERIC MATERIALS
Conducting Materials Based on Thermally Expanded Graphite
V. N. Gorshenev, S. B. Bibikov, and Yu. N. Novikov
Emanuel’ Institute of Biochemical Physics, Moscow, Russia
Nesmeyanov Institute of Organoelemental Compounds, Russian Academy of Science, Moscow, Russia
Received August 2, 2002
Abstract-The electrical conductivity of composites produced from thermally expanded graphite, isoprene
rubber, and polyvinyl chloride plastisol was studied as influenced by the process conditions.
Preparation of conducting polymers (CPs) is a top-
ical task of modern materials science. Highly conduc-
tive polymers are extensively used to ensure reliable
operation of radio equipment in, particular, to shield
radioelectronic devices .
Low-resistance composites are known  to con-
tain, as a filler, expensive fine silver powders in
In this study, we prepared highly conductive poly-
meric composites containing thermally expanded
graphite (TEG) as filler and analyzed their properties
as influenced by the conditions of mixing of the filler
with a binder.
Thermally expanded graphite was prepared by the
hydrosulfate procedure  involving the follow-
ing three main steps: (1) stirring of low-ash GSM-1
graphite for 30 min in a mixture of concentrated ni-
tric and sulfuric acids to form an intercalation com-
pound (graphite hydrosulfate), (2) hydrolysis of the
graphite intercalation compound with water and dry-
ing of oxidized graphite to a friable state, and (3)
thermal expansion of oxidized graphite by rapid heat-
ing to 8003900oC to form TEG. The bulk density of
the TEG was r
. Elemental analysis
showed the presence of up to 0.5 wt% sulfur in the
TEG. As determined by scanning electron microscopy
with 100-nm resolution, graphite had pronounced lay-
ered structure .
Since TEG has the layered structure, it can be
rolled to give highly conductive sheets. A porous flat
132-cm-thick TEG sample prepared by compacting
a TEG powder was rolled on bench rolls with vari-
able gap to thickness of 0.730.3 mm. The rollers
were 10 cm in diameter (D), and their rotation rate
was n =5315 rpm. Dense sheets of TEG are formed
by compaction of the initial porous sample; in the
process, the gap between the rollers and the shearing
stress arising in the course of rolling were varied.
We used SKI-3 rubber and polyvinyl chloride
(PVC) plastisol as binders for prepating conducting
The conducting composites of TEG (50%) and
SKI-3 rubber were prepared by the following proce-
dure. A rubber solution in benzine (1 l, 15 g l
centration) was mixed with dicumyl peroxide (1 g)
and TEG (15 g). The solvent was removed on a rotary
evaporator at 50oC to give a loose powder. To ob-
tain samples for resistance measurements, the result-
ing formulation was pressed in a mold at 143oC and
a pressure of 20 MPa for 30 min.
The plastisol technology is frequently used to pro-
duce highly filled polymeric composites . This is
due to low viscosity of the plastisol, simple produc-
tion of the composite, and satisfactory physicomech-
anical properties of the plastigel.
The procedure for preparing PVC3TEG composites
included the following steps. An EP-66 PVC powder
was thoroughly mixed with dioctyl phthalate in the
weight ratio of 2 : 1 or 1 : 1. The mixture was plasti-
cized on a water bath at 90oC for 45 min. To inhibit
dehydrochlorination, 3wt % of calcium stearate was
added with vigorous stirring. Then, the conducting
filler, TEG, was added. The mixture was stirred until
a uniform composition was formed. The composites
was prepared by pressing in a mold at 0.230.5 MPa.
The resulting samples were rolled at 1203140oC with
the gap between the rollers slowly varied.