WO2007096479A1

WO2007096479A1 - Novel compositions and methods for the production thereof

Info

Publication number: WO2007096479A1
Application number: PCT/FI2007/050100
Authority: WO
Inventors: Juha Hartikainen; Juha Repo; Kalle NÄTTINEN; Kirsi Immonen; Juha Sarlin
Original assignee: Panipol Oy; Valtion Teknillinen Tutkimuskeskus
Priority date: 2006-02-23
Filing date: 2007-02-23
Publication date: 2007-08-30
Also published as: FI20060186A0; FI20060186A

Abstract

A conductive composition and a method of producing such a composition. The composition comprises electrically conductive carbon based particles having a high aspect ratio, such as carbon nanotubes, the particles being present in an amount exceeding the percolation threshold of the composition, and at least one dispersing component selected from the group of substituted aromatic compounds capable of bonding to a polyaniline structure by non-covalent interaction. The dispersing component being present in an amount sufficient to provide a dispersed, conductive composition having an electrical conductivity better than 10-8 S/cm. Preferably, the particles are coated with an inherently conductive polymer. By means of the invention it is possible efficiently to melt-blend carbon nanotubes with thermoplastics to obtain highly conductive compositions with small concentrations of the nanotubes.

Description

NOVEL COMPOSITIONS AND METHODS FOR THE PRODUCTION THEREOF

Background of the Invention

Field of the Invention

The present invention relates to electrically conductive compositions. In particular, the present invention concerns compositions comprising electrically conductive carbon particles having a high aspect ratio, which are mixed with a dispersing agent to provide an electrically conductive composition. The present invention also concerns methods of producing such compositions and the use of the compositions in blends with thermoplastic polymers.

Description of Related Art

Carbon nanotubes are a new, third allotropic form of carbon in addition to graphite and diamond. In carbon nanotubes, graphite lattices are rolled into perfect cylinders with a diameter of a few nanometers or less. Due to their structure, carbon nanotubes have exceptional properties of stability both with respect to air and temperature variations and excellent mechanical, electronic and structural properties, which provides for their use in a plurality of engineering and scientific applications.

One interesting application comprises composites of nanotubes and thermoplastic polymers, in which the nanotube component provides a three-dimensional conductive network within a matrix formed by the thermoplastic polymer. To achieve this aim, the nanotubes should be evenly distributed and dispersed within the matrix.

Various strategies for dispersing carbon nanotubes are known in the art. Conventionally, nanotubes have been dispersed in a host polymer by either lengthy sonication in a polymer solution or by in situ polymerization in the presence of the nanotubes. Lengthy sonication can damage the nanotubes and the in situ polymerization is useful only for specific polymers.

An alternative way of proceeding is to employ dispersing agents. Thus, in one application of the latex technology, sodium dodecylsulphates or polysaccharides are used for dispersing the nanotubes which are then exfoliated in water. The supernatant of the aqueous dispersion is recovered and mixed with latex particles obtained by emulsion polymerization to provide a composite consisting of evenly dispersed nanotubes in a polymer matrix.

It is also known to functionalize single-wall carbon nanotubes in chloroform with poly(phenyleneethynylene)s along with vigorous shaking and/or short bath sonication.

As apparent, the known solutions are rather complicated and poorly applicable to industrial use.

Summary of the Invention

It is an aim of the present invention to eliminate at least some of the problems of the known art and to provide a novel way of dispersing carbon nanotubes into thermoplastic polymers.

According to a first object of the present invention, novel conductive compositions are provided which comprise a mixture of carbon nanotubes or similar conductive carbon based particles and monomeric dispersants.

It is a second aim of the invention to provide a novel thermoplastic composition comprising a dispersed phase of conductive carbon nanotubes in a matrix of a thermoplastic polymer.

According to a third aim of the invention, a novel method of producing a conductive composition comprising carbon nanotubes is provided.

The present invention is based on the finding that it is possible to efficiently disperse carbon nanotubes by mixing them with monomeric dispersants having an aromatic basic structure and capable of bonding to a polymeric structures comprising repeating units with aromatic structures. An example of such polymeric structures is polyaniline, and it has surprisingly been found that compounds capable of acting as molecular recognition compounds with respect to polyaniline are also capable of acting as dispersing agents for carbon nanotubes as such or for carbon nanotubes coated with polymeric structures of the above kind. When contacted with carbon nanotubes, the aromatic compounds of the above kind enter into non-covalent interaction which allows for their use as dispersing agents.

Instead of carbon nanotubes, other carbon based materials having high aspect ratios can be used as conductive components in the conductive compositions according to the invention. Said conductive components are present in amounts sufficient for exceeding the percolation threshold of the composition.

Thus, by the invention, conductive compositions of carbon based particles are provided which comprise as dispersing agents compounds selected from the group of substituted aromatic compounds capable of bonding to a polyaniline structure by non-covalent interaction, to provide a dispersed, conductive composition having an electrical conductivity better than 10^~8 S/cm.

The conductive compositions can be blended with thermoplastic polymers, such as polyolefins, polyesters, polyamides, polyimides, polyesterimides and polycarbonates to mention a few.

As mentioned above, by coating the conductive carbon based components with an inherently conductive polymer, such as polyaniline, conductivity of the composition can be further improved. The coating of the carbon is preferably carried out by polymerization of the polymer in situ, in the presence of the carbon components.

Based on the above, the present conductive compositions are characterized by what is stated in the characterizing part of claim 1.

The method according to the present invention for producing conductive compositions is characterized by what is stated in the characterizing part of claim 15 and the thermoplastic compositions according to the present invention by what is stated in the characterizing part of claim 20.

Considerable advantages are obtained by the present invention. Thus, the use of the present monomeric dispersants allows for efficient dispersion of carbon nanotubes which considerably facilitates their dispersion in a thermoplastic polymer, such as polypropylene. As the below examples show, the conductivity of the carbon nanotube and carbon fiber compositions are, as such, excellent and they are readily blended with thermoplastic polymers by conventional melt processing, for example in an extruder.

The production of the conductive composition is uncomplicated and requires merely a minimum of sonication, if any.

Brief Description of the Drawing

Figure 1 shows the percolation behaviour of Product 1 of the Examples with 20 % ethyl gallate in polypropylene.

Detailed Description of the Invention

As discussed above, the present invention provides novel conductive compositions of carbon based particles having high aspect ratio. In particular these particles comprise carbon nanotubes or carbon nanofibres. The present invention is applicable to both single- wall nanotubes and multi-wall nanotubes.

For the purpose of the present invention, "single-wall nanotubes" denote carbon nanotubes which consist of single layers of graphite lattice rolled into cylinders with a diameter in the range of, generally, about 0.1 to 5 nm, in particular about 0.5 to 3 nm, typically about 0.7 to 2 nm.

The definition "multi-wall nanotubes" denotes carbon nanotubes which consist of sets of concentric cylindrical shell, each of which meets the definition used above for "single-wall nanotubes".

For the purpose of dispersing the conductive carbon based particles substituted aromatic compounds capable of bonding to a polyaniline structure by non-covalent interaction are used. Such aromatic compounds can have, for example, the general formula (I)

A₁-B_j (I) wherein: i is an integer greater than 0; and j is an integer greater than 0, with the proviso that the sum of i and j is equal to or greater than 3;

A is a moiety selected from the group consisting of optionally substituted 3- to 7- membered rings, which rings may optionally include at least one nitrogen, sulfur or oxygen atom, and optionally substituted condensed ring systems thereof; and

B is a moiety capable of hydrogen bonding with NH-groups and is selected from the group consisting of -OH, -COOH, -OCOO-Q₁, -CO-Q₁, -SO-Q₁, -SO₂-Q₁, -

SO₂NH-Q₁, -OCOO-Q₁, -O Q₁, -SH, -S-Q₁, -P(O)(O-Q₁)(O-Q₂), -NO₂, -CN, - CONH-Q₁, -F, -Cl, -Br, and -I, wherein Q₁ and Q₂ are aliphatic or aromatic moieties.

The dispersing agent comprises an aromatic residue which is coupled to the conductive carbon based particles via functional groups or aromatic rings present on the aromatic residue.

The dispersing agents used comprise substituted aromatic compounds which are capable of bonding to the polyaniline structure by strong physical forces, in particular by forces that can be characterized as being "non-covalent" and leading up to the forming of bonding due to van der Waals forces or a similar non-covalent interaction (said interaction can also be called "molecular recognition"). It should be pointed out that this interaction will not interfere with the mechanism of electric conductivity of the carbon nanotubes or fibres.

Examples of compounds meeting the definition of formula I above are given in U.S. Patent No. 5, 783,111, the contents of which is herewith incorporated by reference. Generally, each A is independently selected from the group consisting of 5 or 6-membered aromatic rings, which rings may be optionally substituted and which may further include at least one nitrogen, sulfur or oxygen atom; and their substituted or unsubstituted condensed rings; and at least one B is -OH. A can be the same on each occurrence or different on at least two occurrences. Particularly preferred compounds for use as dispersing components are selected from the group of hydroxy- substituted benzoic acid derivatives, comprising 1 to 3 hydroxyl groups. Two or three hydroxyl groups are particularly preferred for compounds substituted with only hydroxy groups, and 1 to 3 hydroxyl groups are preferred for compounds which contain at least one other group B.

In particular, the dispersing component is selected from the group of hydroxyl-substituted benzoic acid derivatives containing a linear or branched alkyl chain having 1 to 24 carbon atoms. Examples of this kind of compounds are alkyl gallates, alkyl catechols and alkyl resorcinol, wherein each alkyl group is linear or branched and has 1 to 24 carbon atoms.

In each of the above, the alkyl groups may contain one or more substituents selected from the group of moieties B above.

According to one embodiment, the electrically conductive composition consists essentially of the conductive component and the dispersing component, which means that there are essentially only two components in the composition, viz. the conductive carbon nanotubes or nanofibres and the dispersing agent. The relative amounts are about 5 to 50 weight percent of the first component and about 95 to 50 of the other. Naturally, in such a composition, the dispersing component contacts directly with the conductive component, in particular with the surface of the component.

However, according to a preferred embodiment, the conductivity and electrical contact between the individual nanotubes or fibres is improved by coating them with a conductive polymer, preferably an inherently electrically conductive polymer, which can be doped to generate charge carriers. Preferably the inherently conductive polymer coats at least a majority, i.e. at least 50 %, in particular about 70 to 100 %, of the surface of the conductive component. In terms of weight of the composition, the proportion of conductive polymer can amount, for example, to about 7 - 50 %, in particular to about 10 - 35 %, depending on the thickness of the conductive coat.

Thus, in the preferred embodiment, the tubes or fibres are coated with a thin polyaniline layer and then the coated nanotubes or fibres are mixed with a thermoplastic polymer in an extrusion process or by another melt processing method. By the coating, an important advantage is reached: since there is a layer of polyaniline (or another inherently conductive polymer), it is possible to improve the dispersibility by using dispersants which interact with polyaniline. In addition, in some embodiments, reduction of surface resistivity may also take place, thus having positive impact on the electric conductivity of the nanotubes in some applications.

In the present invention, "Electrically conductive polymer" or "Conductive polymer" means inherently conductive polymers (ICP), which are "doped" (furnished, processed) in order to generate charge carriers (holes and electrons). Common to all electrically conductive polymers are the conjugated double bonds of the backbone chain (alternate single and double bonds, delocalized silicon electron system), which enable the movement of the charge carriers. Electrically conductive polymers have both ionic and electronic conductivity, which can be utilized in various applications. The conductivity of electrically conductive polymers can fluctuate and be regulated within the whole conductivity range, from an insulating material to a near- metallic conductor. Generally, a polymer is considered to be electrically conductive if its maximum surface resistance is 10¹¹ ohm.

An electrically conductive polymer can be bound in fibres both in an electrically conductive and in an electrically non-conductive form. Consequently, the term "electrically conductive polymer" in the claims presented below also means a polymer that is non- conductive at the time of reference, but which, however, can be brought to an electrically conductive state, for instance by using a suitable doping agent treatment.

Polyaniline, polypyrrole, polyacetylene, polyparaphenyl or polytiophene, or derivatives or mixtures of them are used as electrically conductive polymers. Among the derivatives, especially the alkyl and aryl derivatives and the chlorine and bromine- substituted derivatives of the polymers mentioned above, are worth mentioning.

Polyaniline is particularly preferred in the present invention. The monomer in the aniline polymer is aniline or its derivative, the nitrogen atom of which is in most cases bonded to the para-position carbon of the benzene ring of the next unit. The unsubstituted polyaniline can be in different forms, among which the emeraldine form, which is characterized by a clear, emerald-green colour, which stands for its name, is generally used for conductive polymer applications By doping, the electrically neutral polyaniline can be converted into a conductive polyaniline-complex. The doping agents used in the present invention can vary widely and they are generally employed when doping conjugated polymers into an electrically conductive or semiconductive form.

The dopant is selected from the group of inorganic acids and organic acids and derivatives thereof, including mineral acids, sulphonic acids, picric acid, n-nitrobenzene acid, dichloric acetic acid and polymer acids and mixtures thereof. And the salt of the dopant and the monomer is soluble in water.

Protonic acids are known doping agents in the field of inherently conductive polymers, as will appear from the references by J.-C. Chiang and Alan G. MacDiarmid and in the W. R. Salaneck citation: o Chiang et al., Synth. Metals (1986) 13:193-205 o MacDiarmid et al., Papers from the 6th European Physical Society Industrial

Workshop Eur. Phys. Soc. o Salaneck et al., Synth. Metals (1986) 13:291-297 No Month Available.

Such doping agents comprise organic acids, and their derivatives, among which sulphonic acids, picric acid, n-nitrobenzene acid, dichloric acetic acid and polymer acids are typical examples. If desired, more than one doping acid can be used.

Preferably, a functional acid is used for doping, such as sulphonic acid, particularly aromatic sulphonic acid, which comprises one aromatic ring, or two merged rings, in which case at least one ring may have a polar or a non-polar cyclic substituent, such as a functional group (for instance a hydroxyl group) or a hydrocarbon chain, such as an alkyl chain with 1-20 carbons. Examples of these are alkyl-benzene sulphonic acids and dialkylbenzene sulphonic acids (where the alkyl comprises 1-20 carbon atoms), other branched benzene sulphonic acids, aromatic diesters of phosphoric acid, etc.

The following can be particularly mentioned:

MSAs (methylsulphonic acids), Ethylsulphonic acids

BSAs (benzoic sulphonic acids)

TSAs (toluene sulphonic acids)

DBSAs (dodecylbenzene sulphonic acids) Ethylbenzene sulphonic acids

PSAs (phenol sulphonic acids or hydroxybenzene sulphonic acids)

CSAs (camphor sulphonic acids)

AMPSA (2-acrylamide-l-propanesulphonic acid)

Vinylsulphonic acids Isophthalic sulphonic acid and esters

PPA (phenyl phosphine acids)

Phosphone acetic acid,

DIOHP (bis(2-ethyl hexyl hydrogenphosphate))

Chlorobenzene sulphonic acids Pyridine sulphonic acids

Anisidine sulphonic acids

Aniline sulphonic acids

Quinoline sulphonic acids

Naphthalene sulphonic acids Sulphosalisylic acids

Phosphonic acids

Polymers which are functionalized at their ends by sulphonic acid [polystyrene (PSSA), polyolefins, polyethylene oxide, polyvinyls], as well as sulphonated polyparaphenylenes and sulphonated aromatic polyamides and alike substances, can be mentioned as examples of polymeric acids.

Preferred acids are dodecylbenzene sulpfonic acid (DBSA), camphor sulphonic acid, para- toluene sulphonic acid and phenol sulphonic acid.

The preparation of poly aniline complexes has been described in great detail in, e.g., EP Published Patent Applications Nos. 545 729 and 582 919 and in FI Patent Applications Nos. 932557, 932578 and 940626, the contents of which are herewith incorporated by reference. In the case of the inherently conductive polymer comprising polyaniline, which is doped with an inorganic or organic dopant, a component is provide having an electrical conductivity of the polymer of at least 10^~8 S/cm.

In the process according to the invention, the polymerization of the electrically conductive polymer is carried out "in situ" on the carbon nanotubes or fibres. This is achieved first by mixing both the monomer to be polymerized and a doping agent of the conductive polymer, allowing these to form a salt. Next, the nanotubes or fibres are added to this mixture. Thereafter, a catalyst or an oxidative agent enabling a polymerization reaction is added resulting in polymerization of the doped monomer inside the nanotubes or fibres and on the top of the tubes or fibres.

Oxidizing agents are generally used in polymerization of a monomeric compound into a corresponding electrically conductive polymer. Preferred oxidizing agents are polyatomic metallic salts such as iron(III) salts and per-compounds like peroxides, peracids, persulphates, perborates, permanganates, perchlorates and chlorates, nitrates and quinones. The amount of an oxidizing agent in relation to the monomer is generally from 10:1 to 1:1, most preferably from about 5:1 to 2:1 (parts by weight) or from 4:1 to 1:1 as mole fractions (oxidative/monomer).

Polyaniline is preferably coated on the nanotubes or fibres in electrically conductive form. Polyaniline has to be doped by a counter-ion for converting it into a conductive form. It is particularly preferred to coat with polyaniline in an electrically conductive form because it can be assumed that the binding of polyaniline happens, at least partially, with the aid of the doping agent.

The electrical resistivity of the coated nanotube or fibre composition built up in accordance with the invention, is generally about 10 - 10⁸ ohm.

The product can be produced by bringing the nanotubes or fibres into intimate contact with a monomer that forms an electrically conductive polymer, in a suitable medium, in particular in an aqueous medium. Organic, polar and nonpolar solvents can be used in addition to water and aqueous solutions. By "intimate contact" it is meant that the nanotubes or fibres and a monomeric precursor of polymer and/or a doping agent of polymer is mixed vigorously to have the monomer and/or doping agent efficiently distributed in the carbon material. Thus, "aqueous medium" stands for both water and water solutions in which nanotubes or fibres are slurried. Typically, the consistency of the aqueous slurry is from 0.1 to 50 % (weight/weight), preferably from about 0.5 to 30 %, and particularly from about 0.7 to 20 %. Thereafter, the counter-ion or the monomer of the electrically conductive agent to be polymerized, respectively, can be dissolved in the aqueous phase. The amount of the doping agent varies depending on the amount of a monomer. Generally, the amount of monomer is from about 0.1 to 200 % of the amount of carbon nanotubes or fibres, typically about 1 to 150 w-%, preferably about 5 to 120 w-%, and particularly about 10 to 100 w-%. Generally, the amount of a counter-ion can be equimolar with the amount of monomer but it can also be approximately the amount of moles of the monomer +30 %.

The temperature is generally above 0 ⁰C but below room temperature. Typically, the temperature is from about 1 to 18 ° C, preferably from about 2 to 15 ⁰C.

Generally, an acidic counter-ion is used and the pH of the aqueous phase, used in pairing of tubes or fibres and a polymer/monomer, is most suitably clearly acidic, preferably the pH is below 5 but above 1. Too high pH values can affect disadvantageously to the polymerization of the monomer and too low pH values can cause degradation of the conductive particles. This is why the preferred pH environment is from about 1 to 5 and, most suitably, from 1 to 3.

As stated above, in accordance with the invention, an aggregate (a complex or a salt) formed by the monomer and the doping agent is first introduced among the nanotubes or fibres and, thereafter, the monomer is polymerized in order to coat the polymer on the tubes or fibres in such a way that it is not washed out at demanding conditions.

The electrically conductive carbon particles are selected from the group consisting of carbon nanotubes and carbon nanofibres, having an aspect ratio of at least 100, preferably about 150 to 5000, in particular about 200 to 3000. They may comprise single- wall or multi-wall carbon nanotubes or carbon fibres having a purity of at least 85 %. In view of the above-explained conditions of the polymerization, it is required that the electrically conductive carbon particles are chemically stable at a pH below 4, in particular at pH of 1 or higher.

Based on the above, the preferred novel compositions comprise - 1 to 50 parts by weight of electrically conductive carbon particles,

- 1 to 50 parts by weight of dispersing component, and

- 0 to 50 parts by weight of an electrically conductive polymer.

Generally, the amount of dispersing agent (in parts per weight) is equal to or greater than the amount of the conductive material. Typically, the weight ratio between the dispersive agent and the conductive material is about 0.8 to 10, preferably about 1 to 5, in particular about 1.1 to 4. The "conductive material" includes the carbon based material which optionally is coated with an inherently conducting polymer.

Irrespective of the above, the conductive carbon based particles should always be present in an amount exceeding the percolation threshold to allow for the formation of a conductive pathway through the composition. Generally, this means that there should be at least 1 wt- % of the conductive particles, preferably at least 2 wt-% or even at least 5 wt-% of the total weight of the composition. An economically dictated upper limit can be set at about 50 % of the composition. By coating of the particles with inherently conductive polymers, the percolation threshold can be more readily exceeded with smaller concentrations of the particles, thus, typically the amount of the particles will be on the order of about 1 to 25 wt-%, in particular about 2 to 20 wt-%, e.g. about 3 to 18 wt-%.

As explained in the introductory portion, the composition according to the invention is mixed and/or blended with thermoplastic polymers to provide modified and conductive thermoplastic compositions. Such compositions typically contain about 1 to 30 % by weight of a composition described above and 70 to 99 % by weight of a thermoplastic polymer, although typically there is 1 to 20 wt-% of a conductive composition and 80 to 99 wt-% of the thermoplastic.

Although meltblended compositions are particularly interesting, it should be pointed out that the thermoplastic polymer can also constitute a carrier of a conductive composition of the above kind. Such a carrier can be present in an amount of 1 to 50 wt-% of the total composition. In a masterbatch product of the indicated kind, the carrier is used for binding together the composition.

The thermoplastic polymer is typically selected from the group of polyolefins, polyesters, polyethers, polyesterimides, polyamides, polycarbonates and mixtures thereof.

The thermoplastic polymer can also be a thermoplastic elastomer (TPE) or a mixture or a TPE and one or several of the above thermoplastics. The thermoplastic elastomer can be selected from the group consisting of styrene based block-copolymers, polyolefin based elastomers, polyurethane based elastomers and polyester based elastomers and mixtures thereof.

The following non-limiting examples illustrate the invention:

Examples

MATERIALS AND METHODS

1.1 Reaction materials and methods

Multiwalled carbon nanotubes (MWCNT, purity > 87 %) were supplied by Nanocyl S.A., carbon nanofibres (CNF) were obtained from Electrovac, carbon black Printex XE2 (CB) was obtained from Degussa, alkylphenolethoxylate, 2-ethylhexaneacid (dispersing agent), nanosized alumina powder (Disperal) were both supplied by Sasol, phenol sulphonic acid (PSA, 65 % water solution) by Synthetic Chemicals, ammonium persulphate (APS) by Degussa and, finally, aniline by Algol.

Aniline polymerisation was confirmed from a Fourier transform infrared (FTIR) spectra recorded with a Perkin Elmer Spectrum BX spectrophotometer using KBr pellets. Polyaniline formation on substrate surface was checked with a scanning electron microscope (SEM) JEOL Scanning Electron Microscope JSM-TlOO, the surface resistance of the product was measured from a 1 cm round 1 mm thick tablet by using a multimeter.

1.2 Polyaniline synthesis Carbon nanotube - PANi : Product 1 (MWCNT) Aniline was polymerized by chemical polymerisation in the presence of carbon nanotubes (MWCNT) in a 1 litre round bottle flask equipped with a semi-circular adjustable speed mixer and in an ice bath. In the first stage, 9 g of MWCNTs were dispersed in 200 g water containing 100 μl of dispersing agent and using ultrasonic for 20 minutes (mixture A). 8.63 g of PSA-solution was added to 400 g of deionised water and mixed for 30 minutes. 3 g of Aniline was added to the reaction mixture and mixed for 30 minutes. After that the reaction mixture was cooled to a 5⁰C and mixture A was added. Mixing was continued for 1 hour after which 7.4 g of APS in 20 w-% water solution was added and the reaction was mixed for 1 h in reaction temperature and 2 hours in room temperature. The product, black powder, was filtered with Bϋchner-filter and Whatman GF-A glass fibre filter. Washing was made on filter using 800 ml of water. The black product was dried in temperature below 4O⁰C and ground to fine powder.

The surface resistivity of Product 1 was 6 Ohms measured with multimeter.

Carbon black - PANi : Product 2

Aniline was polymerized by chemical polymerisation in the presence of carbon black (CB) in a 1 1 round bottle flask equipped with a semi-circular adjustable speed mixer and ice bath. In the first stage, 9 g of CB was dispersed in 500 ml water containing 100 μl of a dispersing agent and using ultrasonic for 20 minutes (mixture A) and overnight mixing. 8.63 g of PSA-solution was added to 350 ml of deionised water and mixed for 30 minutes. 3.0 g of Aniline was added to the reaction mixture and mixed for 30 minutes. After that the reaction mixture was cooled to 5⁰C and mixture A was added. Mixing was continued for 1 hour after which 7.4 g of APS in 20 w-% water solution was added and the reaction was mixed for 1 h in the reaction temperature and 2 hours in the room temperature. The product, black powder, was filtered with Bϋchner-filter and Whatman GF-A glass fibre filter. Washing was made on a filter using 1000 ml of water. The black product was dried at a temperature below 4O⁰C and ground to fine powder.

The surface resistivity of Product 3 was 5 Ohms measured with a multimeter. Nanosized alumina - PANi : Product 3

Aniline was polymerized by chemical polymerisation in the presence of nanosized alumina in a 3 1 round bottle flask equipped with a semi-circular adjustable speed mixer and ice bath. In the first stage, 35 g of dodecylbenzene sulphonic acid was dissolved in 2 1 of water and mixed for 30 minutes. 10 g of aniline was added to the reaction mixture and mixing was continued for 45 minutes while cooling the reaction mixture at the same time. 100 g of nanosized alumina was added to the mixture and it was cooled.

At a reaction temperature of 8⁰C, 24.5 g of APS in a 20 w-% aqueous solution was added during one hour. The reaction was allowed to proceeding under agitation at the reaction temperature for 1 h and overnight at room temperature. The product comprising dark green particles was washed three times with water using a centrifuge. The product was dried at temperature below 4O⁰C and ground to fine powder.

The surface resistivity of Product 4 was 200 kOhms measured with a multimeter.

2. BLENDING EXPERIMENT DETAILS

2.1 Blending materials and methods

Method A

A 6.00 g blend of electrically conductive PANI-Nanoparticle-hybrid, selected substituted aromatic compound, and polypropylene (PP Domolen 2600 M, MFI 7.5) was mixed in a miniature, co-rotating conical twin-screw extruder at a temperature of 200 ⁰C for 1 minute at a screw rotation speed of 100 rpm. The resulting blend was discharged in a miniature injection moulding machine and further moulded into rectangular 1 x 10 x 60 mm samples at 220 ⁰C with a mould temperature of 40 ⁰C, injection pressure 350 bar (3 seconds), and post pressure of 160 bar (5 seconds). The electrical conductivity of the resulting samples was measured with a four-point probe method according to ISO 3915 which was adapted to suit the sample dimensions.

EXAMPLE 1 A blend was prepared from 0.60 g Product 1, 1.2O g ethyl gallate (Sigma- Aldrich) and 4.20 g polypropylene (Domolen 2600M) according to Method A. The electrical conductivity was determined to be 26 S/cm.

Comparative example I

By contrast, 0.60 g Product 1 in 5.40 g polypropylene (Domolen 2600M) resulted in a bblleenndd wwiitthh aa ccoonndduuccttiivviittyy ooff 1100^""1122 SS//ccmm.. TThhiiss uunnddeerrlliinnees the efficiency of the gallate plasticiser in increasing the conductivity of the blends.

EXAMPLE 2

Example 1 was repeated; blends were prepared according to Method A of Products 1 - 3, multiwall carbon nanotubes and carbon nanofibres, selected substituted aromatic compounds and polypropylene. The aromatic compounds are selected from those mentioned in U.S. Patent No. 5,783,111. The blend compositions, and conductivities are collected in Table 1.

Table 1 Electrical conductivities of blends of PANI-hybnds, various substituted aromatic compounds and polypropene.

Conductive material Conductive Subst aromatic Subst aromatic Polypropene Conductivity / Example material / % compound compound / % / % S/cm

Product 1 10 Ethyl gallate 10 80 10 " Comparative

Product 1 10 Ethyl gallate ₂0 70 ₂6 1

Product 1 10 Ethyl gallate 30 60 15 2

Product 1 10 Lauryl gallate 10 80 26 x 10² 2

Product 1 10 Lauryl gallate ₂0 70 I x IO ¹ 2

Product 1 10 Lauryl gallate 30 60 3 7 x 10² 2

Product 1 10 Catechol ₂0 70 1 5 x 10⁴ 2

Product 1 10 Octadecyl catechol ₂0 70 1 7 x 10¹ 2

Product 1 10 Hexylresorsinol ₂0 70 _{2 2} χ l0³ 2

Product 2 10 Ethyl gallate ₂0 70 10 " Comparative

Product 3 10 Ethyl gallate ₂0 70 10 ¹⁰ Comparative

Product 1 10 - - 90 10 ⁿ Comparative

MWCNT 10 - - 90 10 ¹⁰ Comparative

MWCNT 10 Ethyl gallate 10 80 8 0 x 10² 2

CNF 10 Ethyl gallate ₂0 70 O ₂ X lO ¹ 2

The results illustrate the efficiency of the substituted aromatic compounds in plasticising the PANI-hybrids in the blends. The percolation behaviour of the blend with Product 1 and ethyl gallate is shown in Figure 1.

Claims

1. A conductive composition comprising

- electrically conductive carbon based particles having a high aspect ratio, said particles being present in an amount exceeding the percolation threshold of the composition, and

- at least one dispersing component selected from the group of substituted aromatic compounds capable of bonding to a polyaniline structure by non-covalent interaction, said dispersing component being present in an amount sufficient to provide a dispersed, conductive composition having an electrical conductivity better than 10^~8 S/cm.

2. The composition according to claim 1, wherein the substituted aromatic compounds have the general formula (I)

A₁-B_j (I)

wherein: i is an integer greater than 0; and j is an integer greater than 0, with the proviso that the sum of i and j is equal to or greater than 3;

A is a moiety selected from the group consisting of optionally substituted 3- to 7- membered rings, which rings may optionally include at least one nitrogen, sulfur or oxygen atom, and optionally substituted condensed ring systems thereof; and B is a moiety capable of hydrogen bonding with NH-groups and is selected from the group consisting of -OH, -COOH, -OCOO-Q₁, -CO-Q₁, -SO-Q₁, -SO₂-Q₁, - SO₂NH-Q₁, -OCOO-Q₁, -O Q₁, -SH, -S-Q₁, -P(O)(O-Q₁)(O-Q₂), -NO₂, -CN, - CONH-Q₁, -F, -Cl, -Br, and -I, wherein Q₁ and Q₂ are aliphatic or aromatic moieties.

3. The composition according to claim 2, wherein the dispersing agent comprises an aromatic residue which is coupled to the conductive carbon based particles via functional groups present on the aromatic residue.

4. The composition according to claim 2 or 3, wherein the dispersing component is selected from the group of hydroxy- substituted benzoic acid derivatives, comprising 1 to 3 hydroxyl groups.

5. The composition according to claim 4, wherein the dispersing component is selected from the group of hydroxyl- substituted benzoic acid derivatives containing a linear or branched alkyl chain having 1 to 24 carbon atoms.

6. The composition according to claim 5, wherein the dispersing component is selected from the group of alkyl gallates, alkyl catechols and alkyl resorcinol.

7. The composition according to any of the preceding claims, wherein the electrically conductive composition consists essentially of the conductive component and the dispersing component.

8. The composition according to any of claims 1 to 7, wherein the dispersing component contacts with the conductive component.

9. The composition according to claim 1 to 6, wherein the electrically conductive polymer comprises an inherently electrically conductive polymer, which can be doped to generate charge carriers.

10. The composition according to claim 9, wherein the electrically conductive polymer is polyaniline, polypyrrole or polytiophene.

11. The composition according to claim 9 or 10, wherein the inherently conductive polymer coats at least a majority of the surface of the conductive component.

12. The composition according to any of claims 9 to 11, wherein the inherently conductive polymer comprises polyaniline, which is doped with an inorganic or organic dopant to provide an electrical conductivity of the polymer of at least 10^"8 S/cm.

13. The composition according to claim 12, wherein the dopant is selected from the group of inorganic acid and organic acids and derivatives thereof, including mineral acids, sulphonic acids, picric acid, n-nitrobenzene acid, dichloric acetic acid and polymer acids and mixtures thereof.

14. The composition according to claim 13, wherein the salt of the dopant is soluble in water.

15. The composition according to any of the preceding claims, wherein the electrically conductive carbon particles are selected from the group consisting of carbon nanotubes and carbon nanofibres, having an aspect ratio of at least 100, preferably about 150 to 5000, in particular about 200 to 3000.

16. The composition according to any of the preceding claims, wherein the electrically conductive carbon particles comprise single-wall or multi-wall carbon nanotubes.

17. The composition according to any of the preceding claims, wherein the electrically conductive carbon particles are chemically stable at a pH below 4, in particular at pH of 1 or higher.

18. The composition according to any of the preceding claims, comprising - 1 to 50 parts by weight of electrically conductive carbon particles,

- 1 to 50 parts by weight of dispersing component, and

- 0 to 50 parts by weight of an electrically conductive polymer.

19. A thermoplastic composition comprising a composition according to any of claims 1 to 18 mixed or blended with a thermoplastic polymer.

20. The thermoplastic composition according to claim 19, comprising 1 to 20 % by weight of a composition according to any of claims 1 to 17 and 80 to 99 % by weight of a thermoplastic polymer.

21. The thermoplastic composition according to claim 19 or 20, comprising a thermoplastic polymer selected from the group of polyolefins, polyesters, polyethers, polyesterimides, polyamides, polycarbonates and mixtures thereof.

22. The thermoplastic composition according to claim 19 or 20, comprising a thermoplastic polymer selected from the group of thermoplastic elastomers.

23. The thermoplastic composition according to claim 22, wherein the thermoplastic elastomer is selected from the group consisting of styrene based block-copolymers, polyolefin based elastomers, polyurethane based elastomers and polyester based elastomers and mixtures thereof.

24. A method of producing an electrically conductive composition comprising the steps of mixing together

- at least one dispersing component selected from the group of substituted aromatic compounds capable of bonding to a polyaniline structure by non-covalent interaction, said dispersing component being used in an amount sufficient to provide a dispersed, conductive composition having an electrical conductivity better than 10^"8 S/cm.

25. The method according to claim 24, wherein the electrically conductive carbon based particles are coated with an inherently conductive polymer.

26. The method according to claim 25, wherein the inherently conductive polymer is polymerized in situ in the presence of the electrically conductive particles.

27. The method according to claim 26, wherein the polymer is polymerized in aqueous phase and the polymer is doped with a dopant which is soluble in water.

28. The method according to any of claims 24 to 27, comprising mixing together - 1 to 50 parts by weight of electrically conductive carbon particles,

- 1 to 50 parts by weight of dispersing component, and

- 0 to 50 parts by weight of an electrically conductive polymer.

29. The method according to any of claims 24 to 28, comprising the step of further mixing or blending with a thermoplastic polymer.