Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
~4
HOECHST AKTIENGESELLSCHAFT HOE 86/F 064 Dr.DA/DE
Flexible, electrically conductive composites, process
for their manufacture, and their use
It is known that heteroaromatics can be polymerized dur-
ing anodic oxidation under suitable conditions and in
doing so form electrically conducting polymers which are
of interest for electrical engineering, in semiconductor
components, sw;tches, screening materials, solar cells
and as electrode materials in electrochemical syntheses
and in reversible charge storage devices (cf., for ex-
ample, I~M J. Res. Develop. 27, 330 (1983)).
However, a considerable disadvantage of most of the pro-
ducts described is that they are produced as brittle
films or powders and as a consequence of their insolu-
bility and lack of thermal plasticity, cannot be conver-
ted to a processable form (cf., for example, J. Phys.
Chem. 1983, 2289~. An exception is formed by polypyr-
role, which under suitable conditions is produced as a
solid, to some extent flexible film (cf., for example,
German Offenlegungsschrift 3,226,278). Nevertheless,
even for this material, the subsequent shape is already
approximately determined during synthesis by the elec-
trode shape. In addition, it has virtually no internal
surface so that only the geometrical surface is avail-
able for the abovement;oned applications. The tensile
strength can be increased by incorporating carbon fibers
or fabrics made of carbon fibers in polypyrroles ~cf.
Japanese Offenlegungsschrift 83-89,639 The composites
obtained as a result have, however, little flexibility
and, ;n add;tion, have only a relatively low specif;c
surface. For applicat;ons of electr;cally conduct;ng
polymers, for example, as electrodes ;n electrochem;cal
processes or ;n storage cells, in addit;on to the mecha-
n;cal stabil;ty, the rapid charge transport and mass
transfer capab;lit;es, ;n part;cular, play an ;mportant
part. In th;s connect;on, a dec;s;ve cr;terion for
rapid exchange reactions is the spec;fic surface
1281784
-- 2
avai lable.
The ob ject of the present invention ~as therefore to
provide an electrically conductive composite comprising
carbon-fiber carriers and an electrically conducting
polymer, and also a process for the manufacture thereof.
Said composite should be sufficiently flexible and have
an increased specific surface, but the specific surface
of the carrier material itself should be within the
10 usual range.
To achieve said object the invention proposes an electri-
cally conductive composite comprising a carbon-fiber
carrier having a specific surface of Less than 100 m2/g
and an electically conductive Polymer, the specific sur-
face of the composite being greater than that of the
electrically conducting polymer, ~herein the form of the
composite is flexible and that of the carbon-fiber car-
rier is felt-like.
The invention also relates to a process for manufactur-
;ng said composites by applying an electrically conduc-
tive polymer to a carbon-fiber carrier having a specific
surface of less than 100 m2/g, ~herein a felt-like
carbon-fiber carrier is used.
The carrier material of the novel composite comprises
carbon, including graphite and should have a felt-like
structu~e. In this case this should be understood to
mean an arrangement of fiber-like constituents ~hich
presents as uniform a space filling as possible in all
three directions so that neither marked cavities nor
regions ~ith a build-up of fiber bundles are produced.
As examples of such carrier materials mention may be
made of carbon felts, in particular soft carbon felts,
graphite felts and carbon felts reinforced by carbon-
fiber fabrics.
. ~4
-- 3
An arrangement oriented in two dimensions having many
contact points and fibers arranged in parallel to form
bundles, such as is encountered in carbon-fiber fabrics,
results in uneven deposition of the conducting polymer
and also in the formation of sol;d blocks and, conse-
quently, in a reduction of the specific surface. In
addition, the flexibility is substantially lost under
these circumstances.
The felt-like carbon carrier material of the novel com-
posite has a specific surface of less than 100 m2/g, pre-
ferably of 0.01 to 10 m2/g and in particular, of 0.1 to
5 m2/g, determined by the BET method (for >0.5 m2/g) or
calculated using the formula specified further below.
As electrically conducting polymers, according to the
invention in principle all the products known for this
purpose are suitable, such as those described in IBM J.
Res. Develop. 27, 330 ff (1983) and in the IBM Research
Report (Electrochemical Synthesis of Conducting Polymers;
A.F. Diaz and J. Bargon, 23.11.1983). They should have
a spec;fic conductance at room temperature of at least
10 5 ohm 1 cm 1, preferably at least 1û 3 ohm 1 cm 1
and should be solid at room temperature. Preferably,
Z5 however, said polymers co0prise structural units which
are derived from the monomers of the general formulae
(I) and/or (II) specified further below. As examples
of such electrically conducting polymers mention may be
made here of: poly(pyrrole), poly(3-methylpyrrole),
poly(3,4-dimethylpyrrole), poly(N-methylpyrrole)~ poly-
(3-chloropyrrole), poly(thiophene), poly(3-methylthio-
phene), poly(3,4-dimethylthiophene), poly(thienothio-
phene), poly(thienoPyrrole), poly(carbazole), poly(1,2-
di(2-thienyl)ethene), poly(1,2-di(3-methylthien-2-yl)-
ethene), poly(1,2-di(2-furyl)ethene), poly(1-~2-
furanyL)-2-(2-thienyl)ethene), poly(1-(2-pyrrolyl)-2-
(2-thienyl)ethene), poly(1,4-di(2-thienyl)buta-1,3-diene),
poly(1,4-di(2-furyl)buta-1,3-diene), poly(1,4-di(2-
thienyl)benzene), poly(terthienyl(2,5-di(2-thienyl)thio-
.
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-- 4 --phene)), poly(2,5-d;(2-th;enyl)pyrrole) and poly(2,2'-
d;th;ophene).
Depending on the structure of the matrix material and
the density of the electrically conducting polymer, the
quantity of electrically conducting polymer which is
combined with the carbon-felt carrier is, as a rule, be-
tween 5% and 80%, in particular between 10% and 50%,
based on the total composite.
The Layer th;ckness of the electr;cally conducting poly-
mer on the carbon-felt carr;er ;s usually between 0.1
and 25 ~m, preferably between 1 and 6 ~m. In th;s man-
ner, a large geometrical surface of the composite is
produced when the novel carrier material ;s used, s;nce
the average d;stance between the individual fibers of
the felt is suff;ciently large and coalescence through
the polymer with the above Layer thicknesses does not
take place or does not take place to a substantial ex-
tent. On the contrary, ;n the nove~ compos;te, thepolymer coating on the carbon-felt fibers is fairly uni-
form.
~he novel comPOsite has an improved flexibility compared
with conventional composites comprising carbon fibers
and a conducting polymer. This is revealed by the fact
that ;t survives the bend test described further below
without fracture.
In addit;on, the specific surface of the novel composite
is in general a factor of 2 to 200 greater, preferably
5 to 100 greater and in particuLar, 10 to 50 greater
than the specific surface of the respective pure poly-
mer having the same surface area, so that a Larger part
of the conducting polymer is available when used as an
electrode in electrochemical syntheses and in storage
cells. Said specific surface is determined by calcula-
tion using the formula specified further below.
-- 5
Moreo~er, the nove~ compos;tes are notable for high sta-
bil;ty even when electrically conducting polymers are
used which under usual deposition conditions are produ-
ced only as powders or brittle films, and they have, in
addition, a fairly low specific resistance since an op-
timum charge transport can take place through the inter-
calated carbon skeleton in conjunction with the intimate
contact with the conducting polymer. The sPecific re-
sistance is usually therefore in the range from 0.1 to
100 ohm cm, preferabLy 1 to 10 ohm cm, and the specific
conductance is correspondingly 0 01 to 10 ohm 1 cm 1, pre-
ferably 0.1 to 1 ohm 1 cm 1.
The combination of these special properties, as a result
of which the novel composite differs from the kno~n com-
posites based on carbon fibers, makes it possible to use
said composite for applications which require, in addi-
tion to rapid charge transport and mass transfer, an un-
usual geometry (for example, extremely flat) with the
possibility of matching to specified structures. In
addition, however, they can be used also in all the
fields in which the eLectrically conducting polymers
hitherto known are of interest, for example as catalysts,
electrical switches, semiconductor components, screening
materials, solar cells, large-area heating conductors,
and aLso, in particular, as electrodes for electrosyn-
theses and in reversible charge storage devices ~batter-
ies).
The method of manufacturing the novel composite is to
app~y the electrically conducting polymer to the felt-
like carrier material using knoun polymerization methods.
Preferably, this is done by electrochemical polymeriza-
tion, in particular anodic oxidation of corresponding
~ 35 monomers, the felt-like carrier material acting as an
;~ anode, under conditions known per se for this purpose.
The electrochemical polymeri2ation of the monomers or
of the comonomer mixtures is accordingly performed in
'
~28~784
-- 6
one of the usual electrolyte solvent systems which is
sta~le under the conditions of the electrochemical poly-
merizat;on and wh;ch must have an adequate solubility
for the monomer and the conducting salt. Dipolar apro-
S t;c solvents such as acetonitrile, propylene carbonate,dimethylformamide, dimethyl sulfoxide and nitromethane,
are preferably used. Ho~ever, other solvents, such as
methylene chloride or tetrahydrofuran may also be used.
An addition of 1 to 5% water is beneficial in some cases.
In the case of monomers having a low oxidation potentia~,
such as, for example, pyrrole, it is even possible to
polymerize from aqueous dispersions, if necessary, with
dispersants added.
As a rule, the monomer concentration is 0.û01 to 5 mol,
preferably 0.01 to 1 mol of monomer per liter of electro-
lyte solvent.
As conducting salts, which serve, in particular, to
transport current during the electrochemical polymeriza-
tion, but which are also contained in the polymer pro-
duced and affect the properties thereof, use is made of
the usual conducting salts such as, are mentioned, for
example, in the German Offenlegungsschrift 3,2Z6,278.
Here mention may be made as examples of tetrafluorobor-
ates, hexafluoroarsenates, hexafLuoroantimonates, hexa-
fluorophosphates, hexachloroantimonates, perchlorates,
hydrogensulfates and sulfates. Aromatic and aliphatic
alkyl and arylsulfonates and perfluorinated alkylsulfon-
ates are also suitable. In addition to the alkalineearth metal cations and H(+~, in particular the alkali
metal cations are suitable as cations for the conducting
salts. Cations of the type R4N( ) or R4Pt ), in ~hich
the radicals R in each case denote, independently of
each other, hydrogen and/or lower alkyl radicals, cyclo-
al;phatic or aromatic radicals, prove to be particularly
beneficial. In some cases a mixture of R4N( ) and Ht+)
proves to be especially beneficial for the uniformity
and peel strength of the polymer deposit. The quantity
-- 7 --
of conducting salt ;s ;n general ;n the range from 0.001
to 1 mol, preferably 0.01 to 0.5 mol per liter of solvent.
An improvement in the uniformity and peel strength of
the polymer deposit can be achieved by adding acid to
the electrolyte This holds true, in particular, if
monomers according to the formula (II) below are used.
The acids on which the conducting salts described above
are based, in particular, perchloric acid, tetrafluoro-
boric acid, hexafLuorophosphoric acid, trifluoromethane-
sulfonic acid, toluenesulfonic acid and benzenesulfonic
acid are, for examPle, suitable.
The electrochemical polymerization may be Performed in
the usual cells or electrolysis apparatuses. Simple
electrolysis apparatuses comprising an undivided cell,
two or more electrodes and an external current source,
are, for example, quite suitable. However, it is also
possible to use divided cells with diaphragms or ion
exchange membranes or those having reference electrodes
for determining the potential precisely. Measurement of
the quantity of electricity is expedient, since the
quantity of polymer deposited and, for the same carrier
material, also the layer thickness is proportional
thereto. In this manner it is possible to contro~ the
thickness of the coating on the carbon fibers. An
electrolysis apparatus in which the cathode is of flat
construction at the bottom and the anode is passed through
the electrolyte in the form of a tape with a constant rate
of advance, makes it possible to conduct the process
continuously.
Under these circumstances, use is made~ as mentioned,
of the felt-like materials made of carbon, which act as
a carrier in the novel composite, as the anode. Carbon
felts, soft carbon felts or graphite felts of differing
flexibility which are obtainabLe commercially, eg.
(R) Sigratherm KFA, KFB, GFD or PF types, are, for
example, suitable for this Purpose~ Said anode material
;: '
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can be used in any desired shape, preferably, however,
a flat arrangement aligned parallel to the cathode is
chosen in order to achieve as uniform a sheathing of the
carbon fibers as possible. For this purpose the anode
material is clamped in a nonconducting frame which pre-
ferably comprises a plastic material which is inert to-
wards the electrolyte. The carbon-felt anode can be
gripped in the frame and/or screwed in using plastic-
material screws. The frame must ensure un;mpeded access
of the electro~yte to the anode and should therefore
only box in the anode or have a reticular structure.
Contact is made to the anode by one or more metal clips
which are either disposed outside the electrolyte or are
insu~ated excePt for the contacting surface.
The type and design of the cathode is not critical, it
being possible to use one or more cathodes. The cathode
comprises one of the usual electrode materials, such as,
for example, graphite, preferably, however, stainless
steel or platinum. It is generally arranged parallel
to the anode; if two cathodes are used, these are situ-
ated at the same distance in front of and behind the
anode. This parallel arrangement of two cathodes
favors the uniformity of the polymer deposit. If only
one cathode is used, repeatedly turning the anode has
the same effect.
The process is normally performed at room temperature,
but the temperature may also vary uithin a wide range,
uhich is limited in the downward direction by the solidi-
fication temperature and in the upper direction by the
boiling point of the electrolyte/solvent system, and is
usually between -50 and 8ûC, preferably -10 and 4ûC.
Any DC source which supplies a sufficiently high electri-
cal vo~tage is suitable as a current source for operat-
ing the electrolytic ce~l in which the process is per-
formed. Usually the electrochemical polymerization is
conducted ~ith a voltage of 0.1 to 100 V, preferably in
;:::
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.'784
the range from 1.5 to 30 V. Values for the current den-
sity in the range from 0.01 to 100 mA/cm2, in particular
in the range from 0.1 to 10 mA/cm2, have proved benefi-
cial and advantageous.
The duration of electrolysis depends, inter alia, on the
electrolyte system used, the particular electrolysis
conditions, and also, in particular, on the desired
coating thickness. Usually the duration of electrolysis
is 1 to 12 hours, preferably 2 to 8 hours
To remove adhering conducting salt, the co~posite
obtained in the electrolysis is washed with solvents,
preferably with the electrolyte solvent, and dried at
temperatures in the range 20 - 150C, optionally under
vacuum. Electrically conducting polymer which only
loosly adheres to the composite can be removed
mechanically, for example by carefully brushing off, by
blowing off, for example, with compressed air, or by
treatment with ultra-sound in an inert liquid.
As monomers of the conducting po~ymers to be deposited
on the carrier material, the aromatics and heteroaroma-
tics known for this purpose are suitable. Preferably,
howeYer, compounds of the general formula (I)
R2 R~
~y ~ (I)
R1 R4
are suitable for this purpose. Here the radicals R2 and
R3 are in each case, independently of each other, hydro-
gen, halogen, (C1-C4)-alkyl, aryl, preferably phenyl
or thienyl, or form an aromatic ring uith each other,
preferably a benzene, thiophene or pyrrole ring. The
radicals R1 and R4 are in each case, independently of
each other, either hydrogen or form with R2 or R3 an aro-
matic ring, preferab(y a benzene, thiophene or pyr~ole
ring. X corresponds to 0, S, NH, N-alkyl, preferably
~:
....
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- 10 -
N-(C1-C4)alkyl, or N-aryl, preferably N-phenyl. In parti-
cular, pyrrole, 3-chloropyrrole, 3-methylpyrrole, 3,4-
dimethylpyrrole, N-methylpyrrole, thiophene, 3-methyl-
thiophene, 3,4-dimethylthiophene, thienothiophene, thieno-
pyrrole and carbazole are suitable.
Compounds of the general formula (II)
R5 ,R R ,R
H~}K~H (II)
can also be used as monomers. The radicals R5, R6, R7
and R8 are in each case, independently of each other,
hydrogen, (C1-C4)alkyl or aryl, preferably phenyl or
thienyl. Y and Z correspond, independently of each
other, to 0, S, NH, N-alkyl, preferably N-(C1-C4)alkyl,
or N-aryl, preferably N-phenyl. K represents aryl, pre-
ferably phenyl, heteroaryl, preferably thienyl, furanyl,
pyrrolyl or a conjugated system of the formula (III)
~CH = CH~n (III)
with n = 0 to 3.
In particular, 1,2-di(2-thienyl)ethene, 1,2-di(3-methyl-
thien-2-yl)ethene, 1,2-di(2-furyl)ethene, 1-(2-furyl)-
2-(2-thienyl)ethene, 1-(2-pyrrolyl)-2-(2-thienyl)ethene,
1,4-di(2-thienyl)buta-1,3-diene, 1,4-di(2-furyl)buta-
1,3-diene, 1,4-di(2-thienyl)benzene, terthienyl(2,5-
di(2-thienyl)thiophene), 2,5-di(2-thienyl)pyrrole and
2,2'-dithiophene are suitable.
Mixtures of the monomers may also be used, in particular
also mixtures of monomers of the formula (I) with those
of the formula (II), and also, if necessary, also mix-
tures with other compounds copolymerizable therewith.
The invention is explained in more detail by the following
examples. The parts and percentages specified ;n the
examples are based, unless otherw;se noted, on the weight.
The m;nimum specific surface was calculated using the
following formula, the quantities R, D and Z being de-
termined from SEM photographs:
A = 2 ~( R+D ~ Z
G
A: specific surface ~m2/g],
R: radius of a carbon fiber [m],
D: mean thickness of the Polymer layer [m],
Z: mean number of fibers in the composite,
G: weight of the composite Cg].
The specific conductance of the composites was determined
by means of four-point measurement at various points so
that, as a result of chance variations in the microsco-
pic structure at the particular test point, a range of
conductances was obtained. The flexibility was deter-
mined from a bend test ;n which the composite was rolledround a cylinder of a certain diameter and examined for
any fracture. The flexibility criterion is cons;dered
to be fulfilled if the quotient obtained by d;viding the
thickness of the composite by the diameter of the cylin-
der around which the composite can be rolled withoutfracture is equal to or greater than 10 2, preferably
equal to or greater than 5 x 10 2 This was the case for
the composites of the novel Examples 1 to 9.
Example 1
3.7 parts of tri(n-butyl)amine, 7.6 parts of p-toluene-
sulfonic acid hydrate, 1.34 parts of pyrrole and 200
parts of acetonitriLe were introduced into an undivided
electrolysis celL. The cathode comprised optionally
platinum or V2A steel. As anode, a carbon felt (specific
surface (BET) = approx. 0.5 m2/g, Sigratherm KFB 2, made
by Sigri Elektrographit GmbH) was mounted parallel to the
cathode using a spacer. With an anodic current dens;ty
28~.'78~
of 0 8 mA/cm2 (anode surface on both s;des) and a cell
voltage of 2.5 V a flex;ble compos;te having a specific
surface of approx. 0.18 m2/g and a specif;c conductance
of 0.2 - 1 ohm 1 cm 1 and comprising 66 parts of carbon
S and 34 parts of polypyrrole was obtained after an electroly-
sis period of 4 hours. The thickness of the polypyrro~e
coating was 2 - 4 ~m.
Example 2
4.34 parts of tetraethylammonium tetrafluoroborate, 1.34
parts of pyrrole and 30û parts of acetonitrile were in-
troduced into an undivided electrolysis cell. Under the
electrolysis conditions as in Example 1, a flexible com-
posite having a specific surface of approx. 0.18 m2/gand a specific conductance of 0.2 - 1 ohm 1 cm 1 and com-
prising 69 parts of carbon and 31 parts of polypyr-
role was obtained after an electrolysis period of 4
hours. The thickness of the polypyrrole coating was 2 -
4 ~m.
Example 3
4.34 parts of tetraethylammonium tetrafluoroborate, 1.34
parts of pyrrole and 350 parts of acetonitrile ~ere in-
troduced into an undivided electrolysis cell. A carbon
felt (specific surface (BET) = 0.3 - 0.4 m2/g) ("Sigra-
therm 6FD") was used as anode. One V2A cathode in each
case was arranged on both sides of the anode at the same
distance. ~ith an anodic current density of 0.5 mA/cm2
(anode surface on both sides) and a cell voltage of 25 V,
a flexible composite having a specific surface of approx.
0.21 mZ/g and a specific conductance of 0.2 - 1 ohm 1
cm 1 and comprising 57 parts of carbon and 43 parts of
polypyrrole was obtained after an electrolysis period
ot 4 hours and subsequent cleaning. The polypyrrole
"
coating was 4 - 6 ~m thick.
~:
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~2~784
- 13 -
Example 4
4.34 parts of tetraethylammonium tetrafluoroborate, 0.98
parts of 3-methylthiophene and 200 parts of acetonitrile
were electroly2ed in an und;vided cell under the condi-
tions as in Example 1. A flexible composite, which com-
prised 75X carbon and 25% poly(3-methylthiophene), was
obtained. Its specific surface was approx. 0.16 m2/g and
its specific conductance was 0.2 - 1 ohm 1 cm 1. The
polymer coating was 1 - 2 ~m thick.
Example 5
4.34 parts of tetraethylammonium tetrafluoroborate, 1.76
parts of 50X aqueous tetrafluoroboric acid, 1.67 parts
of carbazole and 200 parts of acetonitrile were electro-
lyzed in an undivided cell as in Example 1. With an
anodic current density of û.3 mA/cm2 (anode surface on
both sides) and a cell voltage of 25 V, a flexible com-
posite having a specific surface of approx. 0.18 m2/g anda specific conductance of 0.2 - 1 ohm 1 cm 1 and compri-
sing 60 parts of carbon and 40 parts of polycarbazole
was obtained after an electrolysis period of 8 hours.
The thickness of the polycarbazole coating vas 2 - 5 ~m.
Example 6
4.34 parts of tetraethylammonium tetrafluoroborate, 0.88
parts of SOX a~ueous tetrafluoroboric acid, 0.96 parts
of ~E)-1,2-di(2-thienyl)ethene and 200 parts of aceto-
nitrile uere electrolyzed as in Example 5. A flexible
composite having a specific surface of approx. 0.15 m2/g
and a specific conductance of 0.2 - 1 ohm 1 cm 1 compri-
sing 64 parts of carbon and 36 parts of poly~1,2-di(2-
,
thienyl)ethene) ~as obtained after an electrolysis peri-
od of 6 hours. The coating of conducting polymer under
these circumstances uas 1 - 3 ~m thick.
~; ~'','
,~. .~."
'-`` ` 12
- 14 -
Examp~e 7
-
4.34 parts of tetraethylammonium tetrafluoroborate, 0.88
parts of 50% aqueous tetrafluoroboric acid, 0.80 parts
of (E)-1,2-di(2-furyl)ethene and 200 parts of aceto-
nitrile were electrolyzed as in Example 5. A composite
comprising 68 parts of carbon and 32 parts of poly(1,2-
di(2-furyl)ethene) was obtained after an electrolysis
period of 7 hours. The flexible composite had a speci-
fic surface of 0.13 m2/g and a specific conductance of0.2 - 1 ohm 1 cm 1 for a polymer layer thickness of 1 -
2 ~m.
Example 8
4.34 parts of tetraethylammonium tetrafluoroborate, 0.88
parts of 50% aqueous tetrafluoroboric acid, 0.85 parts of
(E,E)-1,4-di(2-thienyl~buta-1,3-diene and 200 parts of
acetonitrile ~ere electrolyzed as in Example 5. A
composite comprising 77 parts of carbon and 23 parts of
poly(1,4-di(2-thienyl)butadiene) was obtained after an
electroLysis period of S hours. The f~exible composite
had a specific surface of approx. 0.10 m2/g and a
sPecific conductance of 0.2 - 1 ohm 1 cm 1 for a polymer
layer thickness of 1 - 2 ~m.
Example 9
4.34 parts of tetraethylammonium tetrafluoroborate, 0.88
parts of 50~ aqueous tetrafluoroboric acid, 0.96 parts
of 1,4-di(2-thienyl)benzene and 200 parts of acetonit-
rile were electrolyzed as in Example S. A flexible com-
posite comPrising 66 parts of carbon and 34 parts of
poly(1,4-di(2-thienyl)benzene) was obtained after an
electro~ysis period of 7 hours. The composite had a
specific surface of approx. 0.15 m2~g and a specitic con-
ductance of 0.2 - 1 ohm 1 c- 1 for a polymer layer thick-
~;~ ness of 2 - 4 ~m.
: ~ :
', ' :
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~4
- 15 -
Comparison experiment
~ 3.01 parts of tetraethylammonium p-toluenesulfonate,
0.97 parts of N-methylpyrrole, 1 part of water and 200
parts of acetonitrile were ;ntroduced ;nto an und;vided
electrolysis cell A platinum sheet was used as cathode,
and a cloth-like flat fabric comprising carbon fibers
(7 - 8 ,um diameter) having a length of 25 mm and a width
of 20 mm was used as anode. The electropolymerization
was carried out at a current density of 4 mA and a cell
voltage of 2 - 2.5 V. A composite comprising 80 parts
of carbon and 20 parts of poly(N-methylpyrrole) was ob-
tained after 6 hours. The polymer layer thickness on
detached carbon fibers was 1 - 2 um and the spec;f;c
conductance 0.2 - 1 ohm 1 cm 1
Despite a coat;ng th;ckness of 2 ,um maximum, it was not
poss;ble to calculate the spec;fic surface of the compo-
site obtained using the above formula since large re-
gions of the fiber bundles had coalesced.
The flexibility of the composite was insufficient topass the bend test described further above.
