Electrically conductive polymeric compositions

Electrically conductive polymeric compositions suitable for fabricating devices for safely transporting volatile chemicals and fuels are disclosed. The electrically conductive polymeric compositions include at least one matrix polymer and an electrically conductive filler material incorporated in the matrix polymer in an amount sufficient to provide the conductive polymeric composition with an electrical conductivity of at least 10.sup.-10 S/cm. The electrically conductive filler material is intrinsically conductive polymer coated carbon black particles. The coating of intrinsically electrically conductive polymer provides a protective shield against loss of particle conductivity, contributes to the overall conductivity of the filler material and enhances the mechanical properties of the filled matrix polymer.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
The present invention relates generally to electrically conductive 
polymeric compositions. More particularly, the present invention involves 
a polymeric matrix material incorporating a filler of intrinsically 
conductive polymer coated carbon particles useful for fabricating devices 
capable of long term electrical charge dissipation. 
2. Description of Related Art 
Organic polymers are generally good insulators and have a high value of 
specific resistance. Materials having these insulating characteristics, 
such as plastic devices and polymeric films and powders, accumulate 
electrostatic charges which can produce sparks and potentially cause 
explosions and fires in certain environments. A particularly troublesome 
source of accumulated surface charge occurs as the result of friction 
created between moving surfaces. The static charge build-up can occur 
between moving fluids in contact with other materials, either liquids or 
solids. Thus, for example, when fuels or other volatile chemicals are 
transported through lines of insulating material, large surface voltages 
can build-up on the chemical and the insulating material. Under some 
circumstances, the material or fuel can discharge its energy to ground in 
a spark capable of igniting any volatile material in the surrounding 
environment. Additionally, the static potential can be high enough to 
actually cause a discharge through a chemical transport line, for example, 
a fuel line, creating a pinhole. Sparking caused by subsequent charging 
can ignite fuel or volatile material leaking through the pinhole with 
catastrophic results. 
Since it is not practical to prevent the friction which causes the charge 
generation, remedial measures for decreasing the possibility of fires and 
explosions are based on increasing the rate of charge dissipation or 
charge leakage so that charge build-up does not occur. Along these lines, 
one approach is to utilize inherently electrically conductive materials 
such as metals to fabricate fuel lines. However, due to weight, 
flexibility and cost considerations transport lines fabricated from 
polymeric materials are preferred. 
A more commonly utilized approach is to utilize polymers or polymeric 
compositions incorporating electrically conductive filler materials to 
fabricate chemical transport lines which are electrically conductive.. The 
incorporation of conductive filler material into polymer formulations 
increases the electrical conductivity of the whole polymeric material. The 
overall function of conductive filler material involves decreasing the 
rate of charge generation or increasing the rate of charge dissipation, or 
both mechanisms. Thus, the conductive nature of these polymers and 
polymeric compositions contributes to the prevention of possible 
catastrophic explosions and fires during the transport of volatile fuels 
and chemicals. 
Common electrically conductive filler materials utilized to impart 
electrical conductivity to polymers include carbon based particles. Carbon 
black in particular is widely utilized by polymer compounders to vary the 
electrical characteristics of polymers. By selecting suitable carbon black 
filler and carefully formulating the carbon black with an appropriate 
polymer, a wide range of conductive polymeric compositions can be 
fabricated. Typically, finished polymeric products can be made 
electrically conductive by effectively dispersing carbon filler into the 
polymer prior to fabricating the finished product. With respect to 
electrically conductive chemical transport lines, carbon black of varying 
graphitic structure is incorporated into a suitable polymer, for example 
nylon. Then, the resulting electrically conductive formulation is 
generally extruded into an appropriately sized conduit. 
One problem associated with carbon filled polymeric materials relates to 
the propensity of the surfaces of particles of carbon black to adsorb or 
otherwise react with their environment. When conductive carbon fillers are 
dispersed in polymeric chemical transport lines, the chemicals and 
additive components of the polymer interact with the surface of the carbon 
black filler particles. Once a sufficient amount of the chemical or 
additive adsorbs or reacts, the surface of the carbon filler becomes 
non-conductive. This in turn results in a non-conductive polymeric 
composition which is susceptible to failure and is potentially a serious 
safety hazard when used to transport chemicals. 
Another problem with carbon filler material involves the catalytic 
characteristics of carbon surfaces. In certain systems carbon surfaces may 
catalyze reactions between the surrounding polymer matrix and an adsorbed 
substance leading to mechanical weakening of the chemical transport line. 
Accordingly, it is an object of the present invention to provide 
electrically conductive polymeric compositions useful for fabricating 
devices having long term electrical conductivity characteristics. 
It is additionally an object of the present invention to provide an 
electrically conductive carbon filled polymeric composition which 
maintains its conductive properties and mechanical integrity after 
exposure to reactive and hostile environments. 
SUMMARY OF THE INVENTION 
The present invention accomplishes the above-described objectives by 
providing electrically conductive carbon filled polymeric compositions 
which maintain their conductivity and mechanical integrity in the presence 
of a variety of chemically reactive and hostile environmental conditions. 
Since the polymeric compositions of the present invention are able to 
retain their electrical conductivity and their long term ability to 
decrease static charge generation and increase charge dissipation in the 
presence of chemicals, they are particularly suitable for the fabrication 
of chemical transport devices including conduits, filters, and valving. 
Thus, the practice of the present invention provides methods and apparatus 
for significantly improving the safe handling and transport of volatile 
fuels and chemicals. 
More particularly, the present invention provides electrically conductive 
polymeric compositions which include at least one matrix polymer and an 
electrically conductive filler material incorporated in the matrix polymer 
in an amount sufficient to provide the organic polymeric composition with 
an electrical conductivity of at least 10.sup.-10 S/cm. The electrically 
conductive filler material is intrinsically electrically conductive 
polymer coated carbon black particles. For purposes of the present 
invention the term conductive polymer, as used herein, means polymers 
which are intrinsically electrically conductive. Preferred exemplary 
conductive polymeric compositions include conductive polyaniline coated 
carbon particles incorporated in a nylon matrix. These preferred 
compositions are particularly suitable for the fabrication of chemical 
transport lines as the coating of electrically conductive polymer protects 
the surface of the carbon black particles from the detrimental effects of 
exposure to chemicals and fuels. Additionally, the conductive polymer 
contributes to the overall conductivity of the polymeric composition by 
electrically interacting with the carbon black particles. 
The electrically conductive polymeric compositions of the present invention 
are prepared by first providing conductive polymer coated carbon black 
particles and then incorporating the coated carbon particles into a matrix 
polymer or prepolymer to provide a conductive polymeric composition. Those 
skilled in the art will appreciate that incorporating the coated carbon 
particles into the matrix polymer can be accomplished by any of a number 
of methods and depends upon the nature of the matrix polymer and the 
intended application of the conductive polymeric composition. In the case 
of preparing thermoset polymers, the conductive polymer coated carbon 
particles are generally incorporated in the matrix resin or prepolymer 
prior to finally curing the resin or prepolymer. Preparing conductive 
thermoplastic compositions typically involves blending coated carbon black 
particles into the thermoplastic polymer at blend temperatures to form a 
homogeneous coated carbon particle filled conductive thermoplastic 
polymeric composition which can be further heat processed. 
Conductive polymer coated carbon black particles can be prepared by forming 
a solution of the appropriate conductive polymer and then adding carbon 
black to the polymer solution. Adding water or other non-solvent to the 
mixture of carbon black and polymer solution causes the conductive polymer 
to precipitate onto the surface of the carbon black particles. An 
alternative method involves synthesizing the conductive polymer in a 
reaction mixture which incorporates the carbon black particles so that the 
polymer forms simultaneously with the coating process. 
Further objects, features and advantages of the conductive polymeric 
compositions of the present invention, as well as a better understanding 
thereof, will be afforded to those skilled in the art from a consideration 
of the following detailed explanation of preferred exemplary embodiments 
thereof.

DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS 
The polymeric compositions of the present invention have utility in 
applications in which conductive polymeric compositions are required or 
preferred due to their ability to conduct electricity. The nature of these 
applications varies widely and includes conductive polymeric adhesives 
used in the electronic industry, battery electrodes, and deterrents to 
static charge accumulation such as conductive polymeric fibers used in the 
textile industry. 
The conductive polymeric compositions of the present invention maintain 
their electrical conductivity even after long term exposure to hostile 
reactive environments. For this reason, they are particularly suitable for 
the fabrication of chemical transport lines and chemical transport filters 
where the electrically conductive nature of the polymeric compositions 
prevents potentially dangerous charge accumulation caused by friction 
between transported chemical fluids and the transport line. 
The present invention is based upon the discovery that carbon black 
particles which are widely used as electrically conductive filler material 
for polymers can be coated with a thin coating of intrinsically conductive 
polymer without losing their conductive characteristics. Moreover, unlike 
uncoated carbon black particles which are prone to conductive failure, the 
coated carbon particles utilized in the present invention can be exposed 
to chemicals and fuels without adversely affecting their ability to 
conduct electricity. It is believed that the conductive polymer coating 
electrically interacts with the carbon particle while providing a 
protective barrier to environmentally induced changes in the surface of 
the carbon particle. In the absence of the conductive polymeric coating, 
the surfaces of the carbon particles eventually lose their conductivity 
and cause the conductive failure of the conductive polymer composition. 
As a general rule the conductivity of carbon black particles increases with 
an increase in surface area corresponding to an increase in fine structure 
of the carbon particle. Thus highly structured carbon black particles are 
preferred for charge dissipation as they tend to be more highly 
conductive. Unfortunately increasing structure in carbon black particles 
tends to significantly increase the viscosity of resin matrices in which 
the particles are dispersed, often to such a degree that highly structured 
particles cannot be used as filler material at greater than minimal 
concentrations. 
As a feature of the present invention, intrinsically conductive polymer 
coated carbon black particles retain the finely structured dimensional 
properties and high surface areas of carbon black particles which make 
them effective filler material for a variety of polymers. As mentioned 
above, where their fine structure would normally lead to increased 
viscosities during the processing of carbon particle filled polymeric 
compositions, conductive polymer coated carbon black particles can be 
incorporated into polymeric matrix materials at higher than previously 
attainable loadings while maintaining advantageously low viscosities. 
Alternatively, the conductive polymeric compositions of the present 
invention can be fabricated with conventional amounts of filler material 
and polymer matrix with a resulting decrease in composition viscosity. 
This may be due to filling much of the spaces in the particle with 
conductive polymer such that the particle presents a smoother surface to 
the matrix resin while still retaining the fine structure of the carbon 
black particle. 
Accordingly, the present invention provides electrically conductive 
polymeric compositions which include at least one matrix polymer and 
incorporated in the matrix polymer electrically conductive filler material 
in an amount sufficient to provide the polymeric composition with an 
electrical conductivity of at least 10.sup.-10 S/cm. The electrically 
conductive filler material is intrinsically electrically conductive 
polymer coated carbon black particles, with the conductive polymer forming 
approximately 5 wt % to 50 wt % of the filler material. Exemplary 
conductive polymeric compositions include from about 0.5 wt % to about 60 
wt % conductive filler material. 
The carbon black particles utilized in the compositions of the present 
invention are preferably in the form of discrete uniformly sized particles 
each of which has a thin coating of conductive polymer. That is, 
aggregates of carbon black particulates are preferably minimized and the 
processes described herein for producing coated carbon particles provide 
relatively few numbers of coated aggregates of carbon particulates. 
However, it is expected that a certain number of coated carbon black 
particles will exist in the form of coated aggregates of carbon black 
particulates. Thus, for purposes of the present invention, coated 
aggregates of carbon particles in which more than one discrete carbon 
particulate forms an aggregate which itself has a thin coating of 
conductive polymer are within the definition of coated carbon black 
particles. 
Additionally, the conductive polymer coating is thin, which, as mentioned 
above, is preferably approximately 5 wt % to approximately 50 wt % of the 
weight of the filler material. The thin conductive polymer coating formed 
by the methods described herein allows the filler material to retain the 
bulk electrical characteristics of the uncoated carbon black particles. 
Thus, in accordance with the present invention, the conductive polymer 
coating serves largely as a protective electrical interconnection between 
the surrounding polymer matrix and the carbon black particle. 
Suitable forms of carbon particles include carbon black particles of 
varying graphitic content, size, morphology and shape. Such carbon black 
particles are widely available from commercial sources such as Degussa 
Corporation and Cabot. Particle sizes are generally in the sub-micron 
range and these particles have aspect ratios as high as 1 to 100. 
Additionally the surface areas of carbon black black particles having 
utility in the present invention are typically at least 200 m.sup.2 /gram 
and as high as 2000 m.sup.2 /gram. Those skilled in the art will 
appreciate that carbon black particles have physical and electrical 
conductivity properties which are primarily determined by the structure, 
particle size, morphology and surface chemistry of the particle. 
More particularly, carbon black particle structures can range from highly 
structured tree-like shapes to minimally structured rod-like shapes. 
Typically, the conductivity of carbon black particles increases with 
increases in the structure of the particle from low structure to fine 
structure. Associated with the increase in structure is an increase in 
surface area which also increases conductivity. Similarly, the 
conductivity of highly crystalline or highly graphitic particles is higher 
than the conductivity of the more amorphous particles. Generally speaking, 
any of the above-described forms of carbon black particles is suitable in 
the practice of the present invention and the particular choice of size, 
structure, and graphitic content depends upon the physical and 
conductivity requirements of the coated carbon black particle. 
It is contemplated as being within the scope of the present invention to 
provide carbon black particles having a coating of any of a large variety 
of intrinsically conductive polymers. Polymers having the capability of 
conducting electricity are documented in the literature, having been 
studied extensively during the past decade. A useful review article which 
discusses the synthesis and physical, electrical, and chemical 
characteristics of a number of conductive polymers is Conductive Polymers, 
Kanatzidis, M. G., C & E News, 36-54, Dec. 3, 1990. Some of the more 
useful classes of conductive polymers include unsaturated or aromatic 
hydrocarbons as well as nitrogen, sulfur, or oxygen containing compounds. 
The polymers include but are not limited to conductive forms of 
polyacetylene, polyphenylene, polyphenylenevinylene, polypyrrole, 
polyisothianaphthene, polyphenylene sulfide, polythiophene, 
poly(3-alkylthiophene), polyazulene, polyfuran, and polyaniline. For 
purposes of the present invention, conductive forms of polyaniline are 
preferred for forming the coating of conductive polymer. These conductive 
forms include self-doped, sulfonated polyaniline which is conductive 
without external doping. 
Polyaniline can occur in several general forms including a reduced form 
having the general formula 
##STR1## 
a partially oxidized form having the general formula 
##STR2## 
and the fully oxidized form having the general formula 
##STR3## 
Each of the above illustrated polyaniline oxidation states can exist in 
its base form or in its protonated form. Typically, protonated polyaniline 
is formed by treating the base form with protonic acids, such as mineral 
and/or organic acids. The electrical properties of polyaniline vary with 
the oxidation states and the degree of protonation, with the base forms 
being generally electrically insulating and the protonated form of 
polyaniline being conductive. Accordingly, by treating a partially 
oxidized base form of polyaniline, a polymer having an increased 
electrical conductivity of approximately 1-10 S/cm is formed. 
The preparation and properties of polyaniline, both its non-conductive or 
"free base" form and its conductive "acid" form, are well documented in 
the literature. For example, U.S. Pat. Nos. 5,008,041, 4,940,517, 
4,806,271, disclose methods for preparing polyaniline under a variety of 
conditions for obtaining different molecular weights and conductivities. 
Typically, polyaniline is prepared by polymerizing aniline in the presence 
of a protonic acid and an oxidizing agent resulting in the "acid" 
protonated conductive form of the polymer. 
Protonic acids having utility in the synthesis of polyaniline include acids 
selected from the group consisting of HX, H.sub.2 SO.sub.4, H.sub.3 
PO.sub.4, R(COOH).sub.n, R'(COOH).sub.n, R(SO.sub.3 H).sub.n, R(PO.sub.3 
H).sub.n, R'(SO.sub.3 H).sub.n, R'(PO.sub.3 H).sub.n, wherein X is a 
halogen, R is hydrogen or a substituted or unsubstituted alkyl moiety, R' 
is a substituted or unsubstituted aromatic moiety, and n is an integer 
.gtoreq.1. Exemplary acids include methane sulfonic acid, benzene sulfonic 
acid, toluene sulfonic acid, or acids having the formula HO.sub.3 
SR'--O--R"SO.sub.3 H wherein R' and R" are independently substituted or 
unsubstituted aromatic moieties. Substitutions for the aromatic moieties 
include halogen, alkyl, or alkoxy functionalities. 
As described in more detail below, in the practice of the present invention 
it may be preferable to prepare polyaniline with a protonic acid having 
the formula 
##STR4## 
wherein G and G' are independently hydrogen, lower alkyl, octyl, nonyl, or 
saturated or unsaturated linear or branched decyl, dodecyl, tetradecyl, 
hexadecyl, or octadecyl groups. Protonic acids belonging to this general 
class of compounds have surfactant properties which aid in dispersing and 
deaggregating carbon particles. Exemplary protonic acids having surfactant 
properties are, selected from the group consisting of decyl diphenylether 
disulfonic acid and decylphenylether disulfonic acid. 
Generally, the counter-ion of the protonated conductive polyaniline is 
supplied by the protonic acid utilized in the polymerization. Accordingly, 
the counterion can be selected from a large number of ions including the 
anions of the aforementioned protonic acids. The nonconductive form of 
polyaniline can be prepared by deprotonating the doped conductive form, 
for example, by dissolving or slurrying the polymer in ammonium hydroxide 
solution, to form non-conductive polyaniline free base. 
It is further contemplated as being within the scope of the present 
invention to utilize sulfonated polyaniline compositions having the 
following general formula: 
##STR5## 
wherein 0.ltoreq.y.ltoreq.1; R.sub.1, R.sub.2, R.sub.3, R.sub.4, R.sub.5, 
R.sub.6 are selected from the group consisting of H, --SO.sub.3.sup.-, 
--SO.sub.3 H, --R.sub.7 SO.sub.3.sup.-, --R.sub.7 SO.sub.3 H, --OCH.sub.3, 
--CH.sub.3, --C.sub.2 H.sub.5, --F, --Cl, --Br, --I, --NR.sub.7, 
--NHCOR.sub.7, --OH, --O.sup.-, --SR.sub.7, --OR.sub.7, --OCOR.sub.7, 
--NO.sub.2, --COOH, --COOR.sub.7, --COR.sub.7, --CHO, and --CN, wherein 
R.sub.7, is a C.sub.1 -C.sub.8 alkyl, aryl or arylalkyl group. 
Furthermore, the fraction of rings containing at least one R.sub.1, 
R.sub.2, R.sub.3, or R.sub.4 groups as --SO.sub.3.sup.-, --SO.sub.3 H--, 
R.sub.7 SO.sub.3.sup.-, or --R.sub.7 SO.sub.3 H can be varied from a few 
percent to one hundred percent. The solubility of the sulfonated 
polyaniline is varied by changing the degree of sulfonation. In fact the 
solubility of polyaniline is increased in basic aqueous solution by the 
presence of SO.sub.3 H groups on the phenyl rings. Also the oxidation 
state of the polymer and the degree of sulfonation can be independently 
varied. 
The synthesis of sulfonic acid ring-substituted polyaniline, or self-doped 
sulfonated polyaniline, is reported in an article entitled Synthesis of 
Self-Doped Conducting Polyaniline, Yue et al., J. Am. Chem. Soc, 
2800-2801, 1990 which is herein incorporated by reference. Briefly, 
sulfonated polyaniline is prepared by converting polyaniline to its more 
soluble nonconductive emeraldine base form and dissolving the base form in 
fuming sulfuric acid. Then, after 2 hours of constant stirring at room 
temperature, slowly adding the solution to methanol at a temperature of 
between 10 .degree. C. to 20 .degree. C. causes sulfonated polyaniline to 
precipitate. 
It is contemplated to be within the scope of the present invention to 
provide methods for preparing coated carbon black particles by forming 
conductive polymer in a reaction mixture which additionally includes 
carbon black particles. The amount of carbon black particles in the 
reaction mixture is sufficient to provide each of the carbon black 
particles with a coating of from approximately 5 wt % to 50 wt % 
conductive polymer. As previously mentioned, the carbon black particles 
are preferably in the form of discrete unaggregated particles. However, 
aggregates of carbon black particulates are fully within the definition of 
carbon black particles for purposes of the present invention. 
Conductive polymer coated carbon black particles can be prepared utilizing 
in situ methods by forming conductive polymer in a reaction mixture which 
incorporates carbon black particles in an amount sufficient to provide 
each of the carbon black particles with a coating of from approximately 5 
wt % to 50 wt % conductive polymer. Then separating the coated black 
carbon black particles from the reaction mixture provides an electrically 
conductive composition. When polyaniline is the selected conductive 
polymer the coating process is accomplished by forming a slurry of 
deaggregated and wetted carbon black particles in a reaction mixture of a 
solution of solvent, protonic acid, aniline, and other additives such as 
suitable oxidants. Preferably, the reaction mixture also includes 
dianiline in an amount sufficient to provide the desired polyaniline 
molecular weight according to known polyaniline synthetic methods. As 
conductive polyaniline forms it coats the surface of the carbon black 
particles, slowly growing a thin, adherent conductive coating. Typically 
the polymerization process occurs at temperatures between 
-10.degree.-80.degree. C. Once collected and washed the coated particles 
are suitable for incorporating into a suitable resin or matrix material as 
filler material, forming a conductive polymeric composition. 
A variety of protonic acids are suitable for forming acidic solutions 
and/or protonating polyaniline and include the aforementioned protonic 
acids useful in polyaniline synthesis and doping nonconductive polyaniline 
to form conductive polyaniline. Advantageously, protonic acids having 
surfactant properties are useful for prewetting and deaggregating carbon 
black. Thus, these surfactant protonic acids combine in their function as 
a surfactant and reactive acid in the above-described process. As 
previously mentioned, protonic acids belonging to this general class of 
compounds include decyl diphenylether disulfonic acid and decylphenylether 
disulfonic acid. Similarly, a variety of oxidants are suitable for 
incorporating into the reaction mixture and include ammonium persulfate, 
inorganic chlorates, inorganic chromates, and peroxides. 
Alternatively, carbon black particles can be coated with conductive polymer 
by first forming a mixture of deaggregated carbon black particles in a 
solution of polymer and then causing the polymer to precipitate onto the 
carbon black particle by adding water or other non-solvent for the polymer 
to the mixture. The coated carbon particles are then suitably collected, 
washed and dried. Typically, when polyaniline is the polymer of choice, 
the solution of polymer is a solution of free-base polyaniline in its 
undoped form. Accordingly, following the coating step the coated particles 
are converted to a conductive form by generating a coating of conductive 
polymer. This doping step is accomplished by forming a slurry of the 
coated carbon black particles and aqueous solution of dopant. Suitable 
dopants are those protonic acids already mentioned which are useful in the 
synthesis of polyaniline. 
A preferred method for coating carbon black particles with polyaniline 
includes first deaggregating carbon black particles by stirring carbon 
particles in a suitable aqueous surfactant to form a slurry of carbon 
black particles. Suitable surfactants include any of a variety of ionic 
and nonionic surfactants as known in the art. Preferred surfactants are 
those which are additionally suitable in the polymer synthesis and as 
dopants for the conductive polymer. These preferred surfactants include 
long chain alkyl substituted sulfonic acids such as those protonic acids 
having the formula 
##STR6## 
wherein G and G' are independently hydrogen, lower alkyl, octyl, nonyl, or 
saturated or unsaturated linear or branched decyl, dodecyl, tetradecyl, 
hexadecyl, or octadecyl groups. Protonic acids belonging to this general 
class of compounds have surfactant properties which aid in dispersing and 
deaggregating carbon black particles. Exemplary protonic acids are 
selected from the group consisting of decyldiphenylether disulfonic acid 
and decylphenylether disulfonic acid. 
Subsequent process steps include pre-wetting carbon black particles in an 
aqueous solution of protonic acid, combining aniline and dianiline with 
the wetted carbon black particles, cooling the slurry and adding an 
appropriate oxidant. The polymer forms in the presence of the carbon black 
particles and the polymer material actually coats the carbon black as the 
polymer forms. During the work-up step the carbon particles are collected, 
washed, and dried resulting in coated carbon black particles having a 
coating of from about 5 wt % to about 50 wt % conductive polyaniline. 
An alternate method for coating carbon black particles with conductive 
polyaniline includes dissolving soluble free base polyaniline in a 
suitable solvent such as N-methyl pyrrolidinone, formamide, 
dimethylformamide or dimethylsulfoxide, forming a slurry of carbon black 
particles and then causing the dissolved polymer to precipitate onto the 
carbon particles. Typically water is added to the slurry to cause the 
precipitation. However, other non-solvents for the polymer are effective 
for precipitating the polymer. The coated carbon black particles are then 
dispersed in an aqueous solution of protonic acid as described above to 
produce the conductive acid-doped form of polyaniline. 
In accordance with the present invention, when self-doped sulfonated 
polyaniline is the conductive polymer of choice, the preferred method for 
preparing coated carbon black particles involves dissolving sulfonated 
polyaniline in an aqueous base to form a polymer solution, adding carbon 
black particles to form a slurry and then causing the polymer to 
precipitate onto the surface of the carbon particles. The preferred 
aqueous base is aqueous ammonia or ammonium hydroxide. However, other 
suitable aqueous bases include aqueous solutions of metal hydroxides 
having the formula: 
EQU M(OH).sub.n, 
wherein M is a metal having charge n, and n is an integer .gtoreq.1; 
compounds having the formula: 
EQU (NRR'R"R'")OH 
wherein R, R', R", R'" are independently H, alkyl, or aryl functionalities; 
and 
compounds having the formula: 
EQU NRR'R" 
wherein R, R', R" are independently H, alkyl, or aryl functionalities. 
Typically, precipitating the polymer is accomplished by changing the pH of 
the polymer solution. More particularly, the pH of the aqueous system is 
caused to decrease causing the polymer to precipitate. Those skilled in 
the art will appreciate that adding a protonic acid to the aqueous system 
will cause the sulfonated polyaniline to precipitate. When aqueous ammonia 
or a volatile amine is the aqueous base, a preferred method for changing 
the polymer solution pH includes heating the polymer solution. This causes 
the base to leave the solution with a resulting drop in pH. Exposing the 
polymer solution to a vacuum aids the pH lowering process by causing the 
volatile amine to be more completely removed from the system. 
Alternatively, carbon black particles having a coating of sulfonated 
polyaniline may be prepared using in situ methods similar to those 
discussed above. An exemplary method includes polymerizing amino-benzene 
sulfonic acid in 1M HCl in the presence of a suitable oxidant and carbon 
black. As the polymer chain develops the polymer grows on and/or 
precipitates from solution onto the surface of the carbon black particles, 
forming a thin coating of conductive polymer. 
In accordance with the present invention and independent of the method 
selected for preparing coated carbon black particles, the carbon particles 
are preferably dispersed and relatively free of aggregates. Alternatively, 
aggregates which are present are small enough to maintain the structural 
and conductive characteristics of particles. Those skilled in the art will 
appreciate that once provided with a thin coating of conductive polymer, 
carbon black particles having the least amount of aggregates are less 
likely to shear or break into a significant number of particles having 
exposed uncoated portions of carbon. The coating of conductive polymer 
protects the particle from conductive failure and provides other chemical 
and physical advantages. Accordingly, uncoated portions of aggregates or 
particles are preferably avoided. 
Suitable methods for deaggregating carbon black particles include 
mechanical and ultrasonic dispersion techniques which are typically 
performed with the carbon black dispersed in aqueous systems containing a 
surfactant. Thus, for example, carbon particles having a coating of 
conductive polyaniline can be prepared by dispersing carbon black 
particles in an aqueous solution of TRITON X-100 available from Rohm & 
Haas. Then, following the effective deaggregation of the carbon particles, 
a protonic acid, such as aqueous p-toluene sulfonic acid, aniline and/or 
dianiline and oxidant is charged into the dispersed carbon black mixture 
wherein the polymer forms on and/or precipitates onto the carbon black 
particles. 
In a preferred method for deaggregating and coating carbon black particles 
utilizing methods which involve in situ polymerization processes, a 
disulfonated alkyl diphenyl ether provides both the surfactant properties 
and the acidic medium for the polymerization. An exemplary surfactant in 
this class of compounds is n-decyldiphenyl ether disulfonic acid, 
available from PILOT Chemical Co. This compound has two sulfonic acid 
groups per molecule and at least one ten member hydrocarbon chain per 
molecule. 
In accordance with the present invention, when coated carbon black 
particles are prepared by polymerizing aniline in the presence of carbon 
black particles, the coated carbon particles generally have a greater 
conductivity than precipitating free-base polyaniline onto carbon black 
particles from a solution of the polymer and then re-doping the free-base 
polyaniline to form conductive polymer coated carbon black particles. 
Moreover, when free-base polyaniline is precipitated onto carbon black 
particles from a solution of polyaniline and then re-doped, the 
conductivity of the resulting coated carbon black particles is greater 
than the conductivity of material formed by merely combining neat 
conductive polyaniline and carbon black particles and pressing the 
combination into a pellet. This phenomenon indicates that the greatest 
interaction between the polymer and the carbon black particle occurs when 
the carbon is coated during the polymerization reaction. Similarly, a 
greater physical, chemical and electrical interaction between the 
conductive polymer and the carbon black particle occurs when the polymer 
is precipitated onto the surface of carbon as compared to merely mixing 
conductive polymer and carbon black particles. 
In view of the greater physical and chemical interactions which develop 
between the conductive polymer coating and carbon black particle formed by 
in situ polymerization techniques, in situ preparation methods are 
preferred. Additionally, when highly structured dendritic forms of carbon 
black are utilized, in situ polymerization techniques tend to preserve the 
fine tree-like structure in the final filler material. This is believed to 
occur because the polymer actually grows on the surface of the fine 
structure as opposed to being quickly adsorbed by precipitation 
techniques. The slow deposition of polymer during in situ polymerization 
coating methods results in a more orderly polymer. Since ordering in 
conductive polymers is directly related to increased conductivity, the in 
situ polymerization deposition results in a higher bulk conductivity of 
the carbon black particles. Furthermore, the in situ polymerization 
methods directly provide doped conductive polyaniline coating. This is in 
contrast to coatings formed during solvent precipitation methods which 
require further doping procedures in order to regenerate the conductive 
form. These final doping procedures frequently do not form fully doped 
polymer to provide maximum conductivity for the composition. 
As mentioned above, the protonated conductive form of polyaniline 
incorporates a counter-ion which is typically supplied by the acid 
utilized in the polymerization process or by the protonic acid utilized 
for converting the free base polyaniline to the protonated polyaniline. 
Connected with the choice of counter-ion of the conductive acid form is an 
associated conductivity of the polyaniline. However, surprisingly, the 
conductivity of carbon particles having a coating of conductive 
polyaniline does not necessarily parallel the performance of the 
conductive polymer alone. For example, polyaniline mesylate has a 
conductivity of approximately 10-20 S/cm and polyaniline tosylate has a 
conductivity of approximately 3 S/cm. Conversely, carbon particles having 
a coating of approximately 20 wt % polyaniline tosylate formed in situ 
during the aniline polymerization in accordance with the present invention 
have a conductivity of about 30 S/cm. Carbon black particles having a 
coating of approximately 20 wt % polyaniline mesylate have a conductivity 
of about 24 S/cm. Thus, by selectively choosing the counter-ion associated 
with conductive polyaniline, it is possible to tailor the conductivity of 
the resulting coated carbon black particle. 
In accordance with the present invention the amount of conductive polymer 
formed on the surface of the carbon black particles is preferably the 
minimum amount necessary to provide a thin coating. Those skilled in the 
art will appreciate that less conductive polymer is necessary to provide a 
thin coating on each particle of a relatively low surface area conductive 
carbon black than the amount necessary to provide a thin coating on each 
particle of relatively high surface area carbon black. In fact, the weight 
percent of conductive polymer to the total weight of the coated particle 
can vary from perhaps 5% to 50% or even higher. However, excessively thick 
coatings may detract from the desirable properties of the carbon black. 
Thus, carbon black particles having a surface area of about 250 m.sup.2 
/gm (XC-72 from Degussa Corp.) demonstrate good physical properties when 
provided with a thin conductive polymer coating which is approximately 20% 
of the weight of the total particle. However, carbon black particles 
having a surface area of about 1000 m.sup.2 /gm (XE-2 from Degussa Corp.) 
are not well coated at this percentage because of their much higher 
surface area. In the case of carbon black particles having a surface area 
of 1000 m.sup.2 /gm a coating weight which is equivalent to the weight of 
the carbon particle provides adequate coverage. 
Molecular surface area calculations can be performed to estimate the amount 
of polymer required to cover carbon black particles having any given 
surface area. However, the results are only a guide due to the assumptions 
which go into the calculations. Another technique for measuring the 
quality of the polymer coating involves pressing a pellet of coated carbon 
black particles after heating the coated carbon particles to 160.degree. 
C. for 30 minutes. If a pellet forms by pressing at approximately 10,000 
psi and the pellet is not easily destroyed by handling, then the quality 
of the coating is indicated as good. Pure carbon is not pelletized under 
these conditions. 
The above-described evaluation technique is additionally useful for testing 
the conductive composition of the present invention for its heat 
stability. This is particularly important for compositions used as filler 
in polymers exposed to high temperature environments. For example XE-2 
carbon black particles having a surface area of about 1000 m.sup.2 /gm 
with a 20 wt % coating will form a pellet at room temperature. This pellet 
is stable to mechanical manipulation. However, if the coated carbon is 
heated to 160.degree. C. -200.degree. C. for 30 minutes and then pressed 
into a pellet, the pellet cracks easily and has little physical integrity. 
Apparently, the coating sinters at high temperatures and pools into carbon 
black particle pores, thus reducing the amount of polymer on the exterior 
surfaces of the particle. However when these high surface area carbon 
black particles are coated to a 50 wt % coating, the resulting conductive 
composition forms a strong pellet when subjected to the same conditions. 
It should be noted that even at these high coating levels the amount of 
conductive polymer in the composition is still substantially less than 
that typically used in a battery composition. 
Those skilled in the art will recognize that the above described 
conductivity properties of coated carbon black particles formed in 
accordance with the present invention indicate the presence of significant 
interactions between the conductive polymer and the carbon particles. That 
is, the overall conductivity of the electrically conductive compositions 
of the present invention is clearly a function of the combination of 
conductive polymer coating and the carbon black particles. If 
presynthesized conductive polyaniline tosylate is merely mixed with carbon 
black particles at a ratio of 20 wt % polymer and 80 wt % carbon black the 
conductivity is only about 13 S/cm. This is notably less than the 30 S/cm 
associated with carbon particles having a coating of polyaniline tosylate 
formed during the actual polymerization of aniline. This is further 
evidence of the interaction between the conductive polymer coating and the 
carbon black particles. 
Those skilled in the art will appreciate that in addition to being 
dependent upon the amount and type of conductive polymer coating on the 
surface of the carbon black particles, the conductivity of the 
compositions of the present invention is dependent upon the shape, size 
and morphology of the carbon black particles. As discussed above, more 
highly structured graphitic carbon black particles having dendritic shapes 
and high surface area are typically the most conductive forms. Similarly, 
coated carbon black particles prepared from the more conductive forms of 
carbon black are typically more highly conductive than filler prepared 
from particles having little structure and low graphitic content. 
Matrix polymers having utility in the conductive polymeric compositions of 
the present invention include any polymer or resin material which is 
benefitted by incorporating carbon particles in the polymer. Because 
filler material fabricated according to the present invention can be 
incorporated in polymers without acidic "out-gassing" or chemical 
interaction with the polymer and polymer additives, a variety of 
chemically diverse polymers has utility in the practice of the present 
invention. Exemplary embodiments include thermoset polymers such as 
epoxies and crosslinking insoluble polymers such as silicones. 
Particularly useful are thermoplastics such as polyethylene, ethylene 
vinylacetate, polystyrene, polypropylene, polyvinylchloride, 
polyetheramides, polyurethanes, acrylonitrile butadiene styrene and 
nylons. For purposes of providing electrically conductive polymeric 
compositions for forming chemical transport lines suitable matrix polymers 
include nylons, polyethylene, polypropylene, polyvinylchloride, 
polyetheramides, polyetherimides, polyethersulfones, polyetherketones, 
teflons, polyesters, acrylonitrile butadiene styrene, and polyurethanes. 
Filler material of conductive polymer coated carbon particles prepared 
according to the disclosure herein can be incorporated into selected 
polymers or prepolymers utilizing methods known within the industry. By 
combining a selected amount of prepared filler material with a selected 
amount of suitable matrix polymer, an electrically conductive polymeric 
composition is formed. Extruding or molding the electrically conductive 
polymeric composition into a final product provides a formed conductive 
article, which in the absence of the filler is non-conductive. The amount 
of filler material incorporated into the organic polymer or prepolymer is 
a function of the selected polymer, the desired conductivity of the final 
conductive polymeric composition and the preferred physical properties of 
the composition. 
More particularly, those skilled in the art will appreciate that for any 
given loading of carbon black particles compounded polymeric compositions 
based on different polymers will have different electrical properties. A 
variety of factors influence these properties including polymer rheology, 
the ability of the polymer to wet the carbon surface, polymer 
crystallinity, and the specific resistance of the polymer. Highly viscous 
and elastic polymers influence the ability of the filler material to 
disperse in the polymer. More crystalline polymers such as polypropylene 
tend to be more conductive and require less filler material than amorphous 
polymers such as polystyrene. 
In accordance with the present invention, the same basic principles apply 
to fabricating and formulating electrically conductive polymeric 
compositions of the present invention. However, unlike prior art carbon 
particle filled compositions, which typically have high viscosities at 
relatively low carbon particle content, the compositions of the present 
invention are capable of higher coated carbon particle content without a 
correspondingly large increase in the viscosity of the polymeric 
composition. This is attributed in part to the slightly greater apparent 
smoothness of the conductive polymer coated carbon black particles as 
compared to the uncoated particles. The coating of the particles may fill 
some of the minor surface features of the carbon black particles thus 
providing a smoother, less voidy filler material. 
In accordance with the present invention, the amount of filler material 
incorporated in a suitable matrix polymer can be varied to provide the 
resulting electrically conductive polymeric compositions with a 
conductivity ranging from 10.sup.-10 S/cm to 10 S/cm and preferably from 
10.sup.-10 S/cm to 10.sup.-4 S/cm. The amount of filler material 
incorporated in these conductive polymeric compositions can range from 
about 0.5 wt % to about 60 wt % of the weight of the conductive polymeric 
compositions and is dependent upon the final use of the article fabricated 
of the composition. More typically, the amount of filler material 
incorporated in the conductive polymeric compositions is from 3 wt % to 15 
wt % of the total composition weight. For example, when the compositions 
of the present invention are utilized to fabricate low static floor mats 
for use in electronic assembly areas, the compositions will typically 
incorporate from 3 wt % to 4 wt % filler material of conductive polymer 
coated carbon black particles. Electrically conductive compositions useful 
in the fabrication of housings for computers and other electronic 
equipment preferably incorporate from 15 wt % to 20 wt % conductive 
polymer coated carbon particles. For purposes of preparing chemical 
transport lines in accordance with the present invention, the electrically 
conductive polymeric compositions preferably include from 4 wt % to 6 wt % 
conductive polymer coated carbon black particles and have conductivities 
ranging from about 10.sup.-5 -10.sup.-4 S/cm when measured by a standard 
four point surface conductivity probe. 
Typically, combining thermoplastic polymers with filler material prepared 
according to the present invention is performed at elevated temperatures 
which are near or at the thermoplastic polymer softening temperature. 
Typically the formulation procedure includes sufficient agitation to 
provide an homogeneous mixture of filler material and thermoplastic 
polymer. Once combined the homogeneous mixture can be pelletized into 
small cylindrically shaped pellets for processing into final formed 
product. 
When the conductive polymeric compositions of the present invention include 
thermoset matrix polymers the prepolymer, resinous material, or monomers 
can be combined with conductive filler material in a similar manner. This 
results in a mixture of resin prepolymer or monomer and carbon black 
particles having a coating of conductive polymer. Since the resinous or 
prepolymer material is generally liquid or a very high viscosity 
semi-solid, the filler material can be incorporated often into the resin 
with suitable agitation without adding heat, to form a homogeneous 
mixture. The formulated mixture can then be cast or molded into the shape 
of a final product and polymerized. Depending upon the type of thermoset 
polymer utilized to form the electrically conductive apparatus, the final 
polymerization may require the addition of heat. 
As discussed above, preferred exemplary embodiments of the present 
invention include electrically conductive polymeric compositions useful 
for the fabrication of chemical transport devices. More particularly, 
nylon compositions incorporating filler material of polyaniline tosylate 
or polyaniline n-decyldiphenylether disulfonate coated carbon black 
particles are suitable for fabricating fuel lines or similar conduits for 
transporting volatile and flammable chemicals. Electrically conductive 
nylon compositions of the present invention utilized in these applications 
include nylon 12 incorporating from approximately 1 wt % to approximately 
10 wt % filler material of conductive polyaniline n-decyldiphenylether 
disulfonate coated carbon black particles. Preferably the compositions 
incorporate from 4 wt % to 6 wt % conductive polyaniline coated carbon 
black particles. Exemplary conductivities of these electrically conductive 
nylon compositions range from approximately 10.sup.-10 S/cm to 
approximately 10.sup.-1 S/cm with the preferred conductivity being about 
10.sup.-8 to 10.sup.-5 S/cm. 
An exemplary procedure for preparing electrically conductive nylon 12 fuel 
lines can be described as follows. Six pounds of conductive polyaniline 
coated carbon black particles prepared according to the in situ 
preparation procedures described herein are transferred to a high 
intensity mixer. While mixing, 94 pounds of compounded nylon 12 is added 
to the coated carbon black particles in the high intensity mixer. The 
combination of nylon 12 and conductive polyaniline coated carbon black 
particles is mixed in the high speed mixer near the melting temperature of 
the nylon 12 until homogeneous. The homogeneous mixture is then cooled and 
transferred to the hopper of a 11/2" extruder with vented barrel and screw 
and a multi hole die assembly. The homogeneous mixture is then heated to a 
temperature sufficient to melt the nylon and extrude it through a die into 
a water bath. The extrudate is then pelletized into pellets sized about 
1/8" diameter and 3/16" long. 
To extrude tubing suitable for forming fuel lines the pellets are pre-dried 
at 212.degree. F. for 12 hours in a vacuum oven and then placed in the 
hopper of a suitably sized extruder. The injection speed, pressure, screw 
speed and temperature profile are dependent upon the desired tubing outer 
diameter and inner diameter. The resulting fuel line has a conductive 
filler material content of 6 wt % and a conductivity of about 10.sup.-6 
S/cm. 
The chemical transport devices are typically lines or transportation 
conduits which vary in length from a few inches to many feet. However, it 
is also contemplated as being within the scope of the present invention to 
provide additional parts of chemical transport devices such as filters and 
valves formed of conductive polymeric compositions of the present 
invention. When utilized in connection with the transport and storage of 
chemicals, especially fuels and other volatile substances, the 
electrically conductive chemical transport devices of the present 
invention reduce the risk of catastrophic explosions and fires caused by 
electrical charge build-up and subsequent sparking. Moreover, the filler 
material which forms the basis of the conductive properties of the 
chemical transport devices is not susceptible to diminished or lost 
conductivity caused by the adsorption or reaction of the carbon black 
particle surface with substances in the environment. In fact, when 
subjected to standard sour gas evaluation procedures designed by the 
automotive industry to determine the chemical and principal stability of 
materials in harsh environments, the compositions of the present invention 
have greater stability than polymeric compositions incorporating uncoated 
carbon black particles. These improved mechanical and conductivity 
properties are attributed to the coating of conductive polymer formed on 
the surface of the carbon black particles. 
Furthermore, the thin conductive polymer coating actually improves the 
ability of the carbon black particle filled polymeric composition to 
dissipate static charge. The basis for this improved capability is an 
increased interaction between the carbon black particles themselves as a 
result of the thin coating. Since the conductive polymeric coating is 
softer than the relatively hard uncoated carbon black particles, the 
contact points between coated carbon black particles have increased 
malleability. This increased malleability results in increased surface 
area at the contact points, and thus an overall increase in the physical 
interaction between coated carbon black particles and an increase in the 
conductivity of the chemical transport device. 
The organic matrix polymers utilized in the chemical and fuel transport 
devices of the present invention are preferably nylons having a 
substantial degree of resistance to attack by the chemicals and fuels 
coming into contact with the matrix polymer. However, it is contemplated 
as being within the scope of the present invention to utilize any of a 
wide variety of polymers having physical and chemical properties suitable 
for exposure to selected fuels and chemicals including those 
thermoplastics and thermosets mentioned above. 
Thus for example chemical transport devices including but not limited to 
fuel filters, fuel line valves, and generally tubular conduits are 
suitably fabricated according to the present invention by incorporating 
conductive polyaniline coated carbon black particles into a matrix polymer 
selected from the group consisting of nylon, polyethylene, polypropylene, 
polyetheramides, teflon, epoxies, polyesters, acrylonitrile butadiene 
styrene, polyurethanes and polystyrene. 
It is further contemplated as being within the scope of the present 
invention to provide processes for transporting fuels and chemicals. 
Typically, transporting processes involve moving fuels from one holding 
area to another over distances which vary from a few feet to miles. 
Processes for transporting fuels and chemicals include the steps of 
providing a chemical transport line formed of an electrically conductive 
polymeric composition of the present invention and causing the chemicals 
and fuels to flow through the chemical transport line. Advantageously, 
when transporting volatile chemicals and fuels according to the present 
invention, the risk of catastrophic explosions and fires caused by static 
discharge is eliminated or substantially reduced. 
The following examples are offered as being illustrative of the principles 
of the present invention and not by way of limitation. 
EXAMPLE 1 
Carbon black was dispersed, deaggregated and coated using in situ 
polymerization techniques and a dispersing surfactant which is also a 
suitable dopant for polyaniline. The dispersing and coating procedure was 
as follows. A solution of 0.73 grams of dianiline in 10.6 mL acetic acid 
was charged into a 2L reaction flask. Then 64 grams of XE-2 carbon black 
was wetted with 16 mL acetic acid followed by the addition of 370 mL of 
water. 
After the carbon black was wetted by the acetic acid/water solution it was 
combined with 10.7 grams aniline and 270 mL of 1N decyldiphenylether 
disulfonic acid (CALFAX 10LA - 40 from PILOT Chemical Co.) and charged 
into the 2L reaction flask. The mixture was agitated for 1 hour and a 
first sample was taken for particle size analysis. After 1.5 hours of 
agitation a second sample was taken. Then an ultrasonic probe was immersed 
in the mixture. Samples were intermittently taken for particle size 
analysis over a 4.5 hour period of time. During this time the average 
particle size remained between 0.13-0.15 microns. 
Following the above described dispersing step, 25.4 grams of ammonium 
persulfate was added to the flask over a 20 minute period while 
maintaining the temperature of the flask contents at 5.degree. C. After 20 
minutes of stirring 5 grams of sodium sulfite in 25 mL of water was added 
to the flask. A particle size analysis of the coated carbon black before 
filtering the coated particles indicated that the particles had an average 
size of 0.41 microns. The coated particles were then collected by both 
filtration and centrifugation and washed with acetone on a buchner funnel. 
The above procedure illustrated the successful preparation of carbon 
particles which were dispersed and coated using the same disulfonic acid. 
EXAMPLE 2 
Conductive polyaniline coated carbon particles were prepared according to 
the following procedure. XE-2 carbon filler material was pre-wet by adding 
640 grams of the carbon particles to 159 mL of acetic acid followed by the 
addition of 8.7L of deionized water. The slurry of carbon particles, 
acetic acid and water was stirred until the carbon particles were well 
dispersed and wet. 
In a separate reaction container equipped with an ice bath, nitrogen inlet, 
solids addition funnel and condenser/outlet bubbler, 7.30 grams of 
dianiline was dissolved in 106 mL of acetic acid. Then 2.7L of 1N 
p-toluene sulfonic acid monohydrate and 106.62 grams of aniline were added 
to the dianiline solution. Finally the slurry of acetic acid, water, and 
carbon was added to the dianiline, aniline and p-toluene sulfonic acid 
monohydrate solution while rinsing the slurry container with deionized 
water. This reaction mixture was cooled to 5.degree. C. by maintaining an 
external dry ice bath between -5.degree. C. and -10.degree. C. 
Then a total of 253.78 grams of ammonium persulfate was added gradually to 
the cooled reaction mixture while maintaining the reaction mixture at 
5.degree. C.-10.degree. C. Once all the oxidant was added the reaction 
mixture was stirred for 20 minutes at 5.degree. C.-10.degree. C. After the 
20 minute stirring period, a solution of 50.28 grams of sodium sulfite 
(Na.sub.2 SO.sub.3) in 250 mL of deionized water was added to the reaction 
mixture and stirred for 10 minutes. 
To work up and recover the conductive polyaniline coated carbon particles, 
the solids were retrieved from the reaction mixture by filtering the 
product on a buchner funnel using #2 filter paper. The resulting filter 
cake was rinsed with 2L of aqueous 1.0N p-toluene sulfonic acid solution, 
2L of deionized water, 2L of isopropyl alcohol, and 43L of acetone. The 
rinsed solid product was then dried in a vacuum oven under full vacuum at 
50.degree. C. 
EXAMPLE 3 
A thin coating of self-doped sulfonated polyaniline was formed onto the 
surface of highly dendritic carbon black particles according to the 
following procedure. First, 0.30 grams of sulfonated polyaniline were 
stirred in 3.0 mL of concentrated (28%) aqueous ammonia. After the 
sulfonated polyaniline was completely dissolved in the ammonia, 1.2 grams 
of XE-2 carbon black and 30 mL of aqueous ammonia were added to the 
ammonia and sulfonated polyaniline solution and stirred until the carbon 
black was well dispersed. 
Heat was added to the carbon black, ammonia and sulfonated polyaniline 
system until the temperature reached 60.degree. C.-70.degree. C. and a 
vacuum was applied to the system. Thus, the ammonia was driven from the 
water, reducing the pH and causing the sulfonated polyaniline to 
precipitate onto the surface of the carbon black particles. The pH dropped 
to between 7 and 8. 
Finally, the coated carbon black particles were collected by filtering and 
then washed with water, isopropyl alcohol, and acetone. The final coated 
carbon black was heated and oven dried to provide carbon particles having 
a coating of sulfonated polyaniline. A pellet weighing 0.152 grams and 
having a thickness of 1442 microns was prepared and its conductivity 
determined using a standard 4 point probe conductivity measuring 
technique. The measured conductivity was 23.4 S/cm. 
EXAMPLE 4 
In order to test the thermal stability and physical integrity of a 
composition of the present invention, a sample of VULCAN XC-72 carbon from 
Cabot Corp. was coated with conductive polyaniline according to the method 
described in Example 1. Then a pellet was pressed from 0.2425 grams of the 
coated carbon in a pellet press at 9000 psi to give a disk having a 
thickness of 2054 microns. The conductivity of the pellet was determined 
to be 12.4 S/cm using a Loresta 4-point probe conductivity/resistance 
meter. A gram of the conductive coated carbon particles from the same 
batch was then heated to 160.degree. C. in air in an oven for 30 minutes. 
A pellet having a thickness of 2333 microns was pressed from 0.2881 grams 
of this material. This pellet had good mechanical integrity and a 
conductivity of 12.0 S/cm as determined by the Loresta conductivity meter 
which corrects internally for variations in sample geometry. A third gram 
of the coated XC-72 carbon particles from the same batch was exposed to 
180.degree. C. for 30 minutes and then pressed to a pellet. This pellet 
had good mechanical integrity and a conductivity of 12.0 S/cm. A final 
gram of the above described conductive composition was exposed to 
200.degree. C. for 30 minutes and then pressed to a pellet at 9000 psi. 
This pellet had good mechanical integrity and a conductivity of 11.7 S/cm. 
This example demonstrates both the quality of the coating of an XC-72 
particle at 20 weight percent polymer and the excellent thermal stability 
of the polyaniline decyldiphenylether disulfonate coated composition. 
EXAMPLE 5 
XE-2 carbon particles, having a surface area of 1000 m.sup.2 /gm were 
coated with conductive polyaniline according to the method of Example 1. 
The resulting composition was pressed at 9000 psi to form a pellet. The 
conductivity of the pellet was determined to be 24.0 S/cm using a Loresta 
4-point probe conductivity/resistance meter. A portion of the above 
described composition was heated to 160.degree. C. in air in an oven for 
30 minutes. A pellet was pressed from a portion of this material after it 
had cooled to room temperature. The pellet had a conductivity of 21.5 S/cm 
but cracked during testing of the conductivity. Portions of the same 
coated carbon particles treated at 180.degree. C. and 200.degree. C., 
which were pressed into pellets behaved similarly. 
EXAMPLE 6 
XE-2 carbon particles from Degussa Corporation having a surface area of 
1000 m.sup.2 /gm were coated with conductive polyaniline according to the 
method of Example 1. However, the coating process differed from that of 
Example 1 in that the conductive polymer coating represented 50 weight 
percent of the composition. The resulting conductive composition was then 
treated according to the procedures outlined in Example 5. The pellet, 
which was formed without a heat treatment had a conductivity of 8.1 S/cm. 
The pellet which was formed following a 160.degree. C. heat treatment had 
a conductivity of 4.5 S/cm and good mechanical integrity. Finally, pellets 
which were formed following 180.degree. C. and 200.degree. C. treatments 
had good mechanical integrity and conductivities of 4.8 S/cm and 5.3 S/cm 
respectively. From the foregoing description it is clear that carbon 
particles having surface areas in the range of 1000 m.sup.2 /gm are 
sufficiently coated with 50 wt % conductive polymer. 
EXAMPLE 7 
High surface area carbon particles (XE-2) were coated with conductive 
polyaniline according to the procedure of Example 1 except that toluene 
sulfonic acid was utilized instead of decyldiphenylether disulfonic acid. 
The resulting conductive composition had a carbon particle coating weight 
of 20 wt % conductive polymer. Samples of this composition were treated 
and formed into pellets as described in Example 5. The pellet which was 
formed without heat treatment had a conductivity of 19.23 S/cm. Pellets 
prepared from the conductive composition after exposure for 30 minutes at 
160.degree. C., 180.degree. C., and 200.degree. C. showed conductivities 
of 24.3 S/cm, 18.8 S/cm, and 22.3 S/cm respectively. However, all of the 
pellets prepared from the heat aged samples cracked readily. The results 
of these experiments demonstrate that high surface area carbon particles 
should be coated with greater than 20 wt % polyaniline tosylate in order 
to have optimum properties for use at high temperatures. 
EXAMPLE 8 
The following example demonstrates the utility of an acidic dopant which 
can also serve as a surfactant for dispersing and deaggregating carbon 
particles. The carbon particle deaggregation step includes preparing a 
solution of 0.73 grams of p-dianiline in 10.6 mL of glacial acetic acid 
and charging this solution into a 2000 mL round bottom flask equipped with 
a teflon paddle mechanical stirrer, a thermometer, and N.sub.2 atmosphere. 
This was followed by adding 270 mL of an aqueous 1.0N n-decyldiphenylether 
disulfonic acid solution to the round bottom flask. Then 10.7 grams of 
aniline were added to this solution. Then 64 grams of carbon (Black Pearl 
2000, Cabot corporation) were wetted with 16 mL of acetic acid followed by 
slowly adding 870 mL of water to form an aqueous carbon black slurry. This 
slurry was added to the 2000 mL reaction flask and rinsed in with 100 mL 
of deionized water. Agitation was continued under a N.sub.2 blanket. After 
5 days of agitation the aggregates of carbon particles had broken down to 
a median particle size of 0.15 microns as measured by a sedimentation type 
particle size analyzer. 
EXAMPLE 9 
The procedure of example 8 was repeated except that a 1.0N solution of 
p-toluene sulfonic acid was used instead of the 1.0 N solution of n 
-decyldiphenylether disulfonic acid. This mixture was agitated for 14 
days. After 14 days aggregates of carbon were still visible to the naked 
eye indicating poor dispersing ability of the p-toluene sulfonic acid as 
compared to the n-decyldiphenylether disulfonic acid described in Example 
8. This experiment demonstrates the superior ability of 
n-decyldiphenylether disulfonic acid to disperse and deaggregate carbon 
particles. 
EXAMPLE 10 
An electrically conductive composition of carbon particles having a coating 
of sulfonated polyaniline was prepared by dissolving 0.30 grams of 
sulfonated polyaniline in 3 mL of 30% aqueous ammonia to give a dark blue 
solution. This solution was added to 1.2 grams of deaggregated XE-2 carbon 
particles slurried in 30 mL of 30% aqueous ammonia. This mixture was 
heated at 60.degree.-70.degree. C. for 3 hours under approximately 28 
inches of vacuum. The resulting slurry of carbon particles having a 
coating of sulfonated polyaniline was then filtered and washed with water. 
The water wash was slightly brown. This was followed by washes with 
isopropyl alcohol and acetone. These washes were clear. The carbon powder 
was dried overnight under vacuum at 50.degree. C. A pellet pressed from 
0.1518 grams of the powder had good mechanical integrity and a 
conductivity of 23.4 S/cm. 
EXAMPLE 11 
Conductive polyaniline coated carbon particles were prepared by causing 
presynthesized polyaniline to precipitate onto the surface of carbon 
particles according to the following procedure. A solution of 1.07 grams 
of polyaniline free-base in 10 mL of N-methylpyrrolidinone was prepared, 
followed by the addition of 5.35 grams of XE-2 carbon black, forming a 
paste. 75 mL of N-methylpyrrolidinone was added to the paste and the 
resulting slurry was stirred until the carbon was wetted. Then 50 mL of 
methanol was added dropwise to the slurry followed by 100 mL of water 
which was also added dropwise. At this point a small sample of the slurry 
was collected and allowed to settle. The supernatant was colorless 
indicating that the polymer had been adsorbed onto the surface of the 
carbon. The coated carbon particles were then filtered on a buchner 
funnel. The filter cake was then dispersed in 400 mL of aqueous 1.0N 
p-toluene sulfonic acid with vigorous stirring for 30 minutes. This slurry 
was then filtered and the filter cake was washed with 1.0N p-toluene 
sulfonic acid, isopropyl alcohol, and finally with acetone. The filtrate 
was colorless. The filter cake was broken-up, placed in a vacuum oven and 
dried overnight at full vacuum and 50.degree. C. A pellet pressed from 
this coated powder had a conductivity of 19.7 S/cm. 
Typically, as the loading of polymeric matrices with carbon black increases 
a degradation in mechanical properties is observed. However, the use of 
conductive polymer coated carbon black as a filler in accordance with the 
present invention improves the mechanical properties of the filled 
polymeric matrices so that sufficient loading to achieve the desired 
conductivities can be utilized Without adversely affecting the mechanical 
properties. The following Example illustrates the effect on mechanical 
properties of various fillers. 
EXAMPLE 12 
Nylon 12 (L-2124 Vestimid Nylon 12 available from HULS) samples, carbon 
black (VULCAN XC-72 carbon black available from Cabot Corp.) filled Nylon 
12 samples, and conductive polyaniline coated carbon black filled Nylon 12 
samples using polyaniline coated carbon black particles prepared in 
accordance with Example 4 were tested in the form of injection molded 
dogbone shaped tensile bars for elongation following exposure to peroxide 
enriched gasoline at 60.degree. C. for 30 days. Testing was conducted at 
room temperature using an Instron tensile measuring system at a rate of 50 
mm/min. The elongation was recorded at the point at which microcracking 
was first observed. 
The results are shown in Table 1. 
TABLE 1 
______________________________________ 
% ELONGATION vs. 
SAMPLE % ELONGATION PURE NYLON 12 
______________________________________ 
Pure Nylon 12 
315.0 100 
4% of carbon 
266.7 84.66 
black added to 
Nylon 12 
5% of carbon 
271.7 86.24 
black added to 
Nylon 12 
6% of carbon 
265.0 84.13 
black added to 
Nylon 12 
7% of carbon 
283.0 89.84 
black coated with 
conductive 
polymer added to 
Nylon 12.sup.1 
7% of XC-72R 
289.0 91.75 
coated with 
polyaniline con- 
ductive polymer 
added to 
Nylon 12.sup.2 
______________________________________ 
.sup.1 Average temperature of compounding Nylon 12 with conductive polyme 
coated carbon black, 228.degree. C., screw speed 300 rpm. 
.sup.2 Average temperature of compounding Nylon 12 with conductive polyme 
coated carbon black, 235.degree. C., screw speed 303 rpm. 
The results given in Table 1 show that the mechanical strength of filled 
polymeric matrices is enhanced appreciably by use of conductive polymer 
coated carbon black fillers, even at substantially elevated loadings. 
The foregoing detailed description is to be clearly understood as given by 
way of illustration and example only, the spirit and scope of this 
invention being limited solely by the appended claims.