Technical field

The present disclosure relates to a process for the preparation of polypropylene-based conductive injection-moulded articles, and the articles obtained and obtainable by said process.

Background

Polypropylene is today widely used in the industry. The main reasons are easy processing in different transformation techniques and a mix of good mechanical properties in the temperature range - 20°C to 100°C. Polymer materials, such as polypropylene (PP), are frequently used for preparing articles such as cups or tubs.

If conductive articles are required, the polypropylene can be then blended with carbon particles (CP) such as carbon nanotubes (CNT) to form a composite material. The production of such composite material is described for example in WO2016/142544.

Several methods can be used when producing such conductive articles, such as extrusion, compression-moulding or injection moulding. CNTs are affected by shear during the production process. There is no shear when the compression-moulding method is used. Some shear may appear when using an extrusion method. However, injection moulding implies high shear. The higher the shear, the higher is the content of CNT required to arrive at similar electrical properties.

In case the amount of CNT added to the composite material to arrive at an acceptable electrical resistance value in the final product is too high, the use of such a composite material is not economically viable. There is, therefore, a need to provide a composite material for the production of articles by injection moulding process having good electrical properties together with a content of CNT being as low as possible. There is also a need to provide a composite material for the production of articles by injection moulding process having homogeneous electrical properties.

Summary

It is, therefore, an object of the present disclosure to provide a process to produce an injection- moulded conductive article from a composite material having a low content of carbon particles (CP), such as carbon nanotubes (CNT) but good electrical properties. It is another object of the present disclosure to provide a process to produce an injection-moulded conductive article from a composite material having a low content of carbon particles (CP), such as a low content of carbon nanotubes (CNT), but good electrical properties and homogeneous electrical properties throughout their surface. It is also an object of the disclosure to provide injection- moulded articles having good and homogeneous electrical properties wherein the articles are made from a composite material having a low content of carbon particles (CP), such as a low content of carbon nanotubes (CNT).

According to a first aspect, the disclosure provides a process to produce an injection-moulded conductive article from a composite material; remarkable in that it comprises the steps of: a) providing a component A being a first polypropylene resin having a melt index MI2 ranging from 5 to 30 g /10 min as determined according to ISO 1133-2011 at 230 °C under a load of 2.16 kg; b) providing a component B being a CP-PP masterbatch, the component B comprising a blend of: at least 7.0 wt.% of carbon particles as determined according to ISO 11358-2014 and based on the total weight of said masterbatch wherein the carbon particles are selected from nanographene, nanographite, carbon nanotubes and any combination thereof; and a second polypropylene resin having an MI2 ranging from 60 to 300 g/10 min as determined according to ISO 1133-2011 at 230 °C under a load of 2.16 kg; c) providing metallic stearate; wherein the metallic stearate is provided by means of a polypropylene-based masterbatch comprising at least 2.5 wt.% of metallic stearate based on the total weight of the masterbatch; d) dry blending the components to obtain a composite material wherein the composite material comprises at least 0.7 wt.% of metallic stearate based on the total weight of the composite material, and from 2.0 wt.% to 8.0 wt.% of carbon particles based on the total weight of the composite material; and e) forming a conductive article by injection moulding of said composite material.

In a preferred embodiment, the disclosure provides a process to produce an injection-moulded conductive article from a composite material; characterized in that it comprises the steps of a) providing at least 50 wt.% of a component A based on the total weight of the composite material, the component A being a first polypropylene resin having a melt index MI2 ranging from 5 to 30 g/10 min as determined according to ISO 1133-2011 at 230 °C under a load of 2.16 kg; b) providing from 10 to 40 wt. % of a component B based on the total weight of the composite material, the component B being a CP-PP masterbatch, the component B comprising a blend of: at least 7.0 wt.% of carbon particles as determined according to ISO 11358-2014 and based on the total weight of said masterbatch wherein the carbon particles are selected from nanographene, nanographite, carbon nanotubes and any combination thereof; and a second polypropylene resin having an MI2 ranging from 60 to 300 g/10 min as determined according to ISO 1133-2011 at 230 °C under a load of 2.16 kg; c) providing metallic stearate; wherein the metallic stearate is provided by means of a polypropylene-based masterbatch comprising at least 2.5 wt.% of metallic stearate based on the total weight of the masterbatch; d) dry blending the components to obtain a composite material wherein the composite material comprises at least 0.7 wt.% of metallic stearate based on the total weight of the composite material, and from 2.0 wt.% to 8.0 wt.% of carbon particles based on the total weight of the composite material; and e) forming a conductive article by injection moulding of said composite material.

Surprisingly, it has been found that it was possible to achieve good and homogeneous electrical properties with the addition of at least 0.7 wt.% based on the total weight of the composite material, of metallic stearate within the composite material. The process according to the disclosure allows at similar CP content (such as similar CNT content), better electrical properties compared to articles produced without said the metallic stearate-containing masterbatch (i.e. the MeSt-containing masterbatch). The addition of metallic stearate allows reducing the content of carbon particles such as carbon nanotubes, within the composite material as compared to a composite material comprising processing aids or being devoid of any processing aids. It is, therefore, possible to achieve the targeted electrical properties, for example, an article, with a carbon particles content, such as a CNT content, as low as 3 wt.% based on the total weight of the composite material. The addition of the metallic stearate via a masterbatch allows achieving homogeneous electrical properties on the article.

The process comprises providing at least 50 wt.% based on the total weight of the composite material of a component A; preferably, at least 55 wt.%; more preferably, at least 60 wt.%. In an embodiment, the process comprises providing at most 90 wt.% based on the total weight of the composite material of a component A; preferably, at most 85 wt.%; more preferably, at most 80 wt.%; even more preferably, at most 75 wt.%.

With preference, one or more of the following embodiments can be used to further define component A:

The first polypropylene resin of component A is selected from a propylene homopolymer, a copolymer of propylene with one or more comonomer selected from ethylene and C4-C10 alpha-olefins, an heterophasic polypropylene and any mixture thereof.

The first polypropylene resin of component A is an heterophasic polypropylene resin consisting of: i. from 60 to 95 wt.% based on the total weight of the heterophasic polypropylene resin of a polypropylene-based matrix selected from a homopolymer and/or a copolymer of propylene with one or more comonomers selected from ethylene and C4-C10 alpha-olefins; and ii. from 40 to 5 wt.% based on the total weight of the heterophasic polypropylene resin of a dispersed ethylene-alpha-olefin copolymer; with preference, the alpha-olefin in the ethylene-alpha-olefin copolymer is selected from the group of alpha-olefins having from 3 to 8 carbon atoms and/or the alpha-olefin in the ethylene-alpha-olefin copolymer is in the range of 25 to 70 wt.% based on the total weight of the ethylene-alpha-olefin copolymer.

The first polypropylene resin of component A has a melt index MI2 ranging from 5 to 150 g/10 min as determined according to ISO 1133-2011 at 230 °C under a load of 2.16 kg; preferably, from 6 to 120 g/10 min; more preferably, from 7 to 100 g /10 min. The first polypropylene resin of component A is selected from virgin polypropylene resin, a polypropylene post-consumer resin and a blend of a virgin polypropylene resin and a polypropylene post-consumer resin

For example, the first polypropylene resin of component A: comprises from 10 to 99 wt.% of polypropylene post-consumer resin based on the total weight of the first polypropylene resin of component A; for example, from 20 to 90 wt.%; for example, from 40 to 80 wt.%; for example, from 50 to 70 wt.%; and/or is or comprises a post-consumer resin; wherein the polypropylene post-consumer resin has an MI2 ranging from 5 to 30 g/10 min as determined according to ISO 1133- 2011 at 230 °C under a load of 2.16 kg; for example, from 7 to 20 g/10 min; and/or is or comprises a post-consumer resin; wherein the polypropylene post-consumer resin is a blend of recycled polypropylene and recycled polyethylene, wherein the content of the recycled polyethylene is ranging from 2 to 15 wt.% relative to the total weight of the polypropylene post-consumer resin.

The process comprises providing from 10 to 40 wt. % based on the total weight of the composite material of a component B being a CP-PP masterbatch; preferably from 15 to 38 wt. %; more preferably, from 20 to 35 wt.%.

With preference, one or more of the following embodiments can be used to further define the component B:

The second polypropylene resin of component B is selected from a propylene homopolymer and/or a copolymer of propylene with one or more comonomers selected from ethylene and C4-C10 alpha-olefins; with preference, the second polypropylene resin is a copolymer of propylene and hexene.

The second polypropylene resin of component B has a melt index MI2 ranging from 60 to 300 g/10 min as determined according to ISO 1133-2011 at 230 °C under a load of 2.16 kg; preferably, from 70 to 200 g/10 min; more preferably, from 100 to 180 g /10 min.

At least 50 wt.% of the carbon particles in component B are carbon nanotubes which have an average length of 1.1 pm or more as determined by transmission electron microscopy before being blended with the second polypropylene resin; preferably, all the carbon particles are carbon nanotubes which have an average length of 1.1 pm or more as determined by transmission electron microscopy before being blended with the second polypropylene resin.

The CP-PP masterbatch is produced by blending a second polypropylene resin having a melting temperature Tm as measured according to ISO 3146-2000, carbon nanotubes, and optional processing aids, in an extruder comprising a transport zone and a melting zone, maintained at a temperature comprised between Tm + 1 °C and Tm + 50 °C, preferably, comprised between Tm + 5 °C and Tm + 30 °C.

The masterbatch further comprises from 0.01 to 4.0 wt.% of one or more processing aids as based on the total weight of the masterbatch, said one or more processing aids are selected from fluoroelastomers, waxes, tristearin, erucyl amide, oleic acid amide, ethylene-acrylic acid copolymer, ethylene-vinyl acetate copolymer, cetyl trimethyl ammonium bromide, polysiloxanes, oleamide, zinc stearate, stearamide, behenamide, oleyl palmitamide, ethylene bis-oleamide, ethylene bis (stearamide) (EBS), meta- cresol and any mixture thereof.

The second polypropylene resin of component B is metallocene-catalyzed or Ziegler- Natta catalyzed; with preference, the second polypropylene resin of component B is Ziegler-Natta catalyzed.

The second polypropylene resin of component B is a metallocene-catalyzed polypropylene and has a molecular weight distribution ranging from 2.0 to 9.0 as determined by Size Exclusion Chromatography.

The second polypropylene resin of component B is selected from virgin polypropylene resin, a polypropylene post-consumer resin and a blend of a virgin polypropylene resin and a polypropylene post-consumer resin.

For example, the second polypropylene resin of component B: comprises from 10 to 99 wt.% of polypropylene post-consumer resin based on the total weight of the second polypropylene resin; for example, from 20 to 90 wt.%; for example, from 40 to 80 wt.%; for example, from 50 to 70 wt.%; and/or is or comprises a post-consumer resin; wherein the polypropylene post-consumer resin has an MI2 ranging from 60 to 300 g/10 min as determined according to ISO 1133- 2011 at 230 °C under a load of 2.16 kg; for example, from 70 to 200 g/10 min; and/or is or comprises a post-consumer resin; wherein the polypropylene post-consumer resin is a blend of recycled polypropylene and recycled polyethylene, wherein the content of the recycled polyethylene is ranging from 2 to 15 wt.% relative to the total weight of the polypropylene post-consumer resin.

For example, the polypropylene-based masterbatch comprising at least 2.5 wt.% of metallic stearate based on the total weight of the masterbatch is the masterbatch defined as the component B. In such a case, component B and the polypropylene-based masterbatch comprising at least 2.5 wt.% of metallic stearate based on the total weight of the masterbatch are the same. Therefore, component B is a CP-PP masterbatch comprising a blend of: at least 7.0 wt.% of carbon particles as determined according to ISO 11358-2014 and based on the total weight of said masterbatch wherein the carbon particles are selected from nanographene, nanographite, carbon nanotubes and any combination thereof; at least 2.5 wt.% of metallic stearate based on the total weight of the masterbatch; and a second polypropylene resin having an MI2 ranging from 60 to 300 g/10 min as determined according to ISO 1133-2011 at 230 °C under a load of 2.16 kg.

For example, component B comprises from 3.0 to 20.0 wt.% of metallic stearate based on the total weight of the masterbatch, preferably, from 3.5 to 15.0 wt.%, more preferably, from 4.0 to 10.0 wt.%, and even more preferably, from 4.5 to 8.0 wt.%. For example, the polypropylene-based masterbatch comprising at least 2.5 wt.% of metallic stearate based on the total weight of the masterbatch is a component C that is different from the component B. For example, one or more of the following is true:

The component C is a MeSt-PP masterbatch comprising at least 2.5 wt.% of metallic stearate based on the total weight of the MeSt-PP masterbatch that is different from component B.

The component C is a MeSt-PP masterbatch comprising a third polypropylene resin having a melt index MI2 ranging from 5 g/10 min to 300 g/10min as determined according to ISO 1133-2011 at 230°C under a load of 2.16 kg.

The component C is a MeSt-PP masterbatch comprising a blend of: i. at least 2.5 wt.% of metallic stearate based on the total weight of the MeSt-PP masterbatch; and ii. a third polypropylene resin having a melt index MI2 ranging from 5 g/10 min to 300 g/10 min as determined according to ISO 1133-2011 at 230 °C under a load of 2.16 kg.

The component C comprises from 3.0 to 20.0 wt.% of metallic stearate based on the total weight of the masterbatch; preferably, from 3.5 to 15.0 wt.%; more preferably, from 4.0 to 10.0 wt.%; and even more preferably, from 4.5 to 8.0 wt.%.

When component C comprises a third polypropylene resin, one or more of the following features advantageously define the third polypropylene resin of component C:

The third polypropylene resin of component C is preferably, selected from a propylene homopolymer, a copolymer of propylene with one or more comonomers selected from ethylene and C4-C10 alpha-olefins, an heterophasic polypropylene and any mixture thereof.

The third polypropylene resin of component C is an heterophasic polypropylene resin consisting of: i. from 60 to 95 wt.% based on the total weight of the heterophasic polypropylene resin of a polypropylene-based matrix selected from a homopolymer and/or a copolymer of propylene with one or more comonomer selected from ethylene and C4-C10 alpha-olefins; and ii. from 40 to 5 wt.% based on the total weight of the heterophasic polypropylene resin of a dispersed ethylene-alpha-olefin copolymer; with preference, the alpha-olefin in the ethylene-alpha-olefin copolymer is selected from the group of alpha-olefins having from 3 to 8 carbon atoms and/or the alpha-olefin in the ethylene-alpha-olefin copolymer is in the range of 25 to 70 wt.% based on the total weight of the ethylene-alpha-olefin copolymer.

The third polypropylene resin of component C has a melt index MI2 ranging from 5 to 300 g/10 min as determined according to ISO 1133-2011 at 230 °C under a load of 2.16 kg; preferably, from 6 to 200 g/10 min; more preferably, from 7 to 50 g /10 min. The third polypropylene resin is selected to be the same as the first polypropylene resin. The third polypropylene resin of component C is selected from virgin polypropylene resin, a polypropylene post-consumer resin and a blend of a virgin polypropylene resin and a polypropylene post-consumer resin.

The third polypropylene resin comprises from 10 to 99 wt.% of polypropylene post consumer resin based on the total weight of the third polypropylene resin; for example, from 20 to 90 wt.%; for example, from 40 to 80 wt.%; for example, from 50 to 70 wt.%; and/or

The third polypropylene resin is or comprises a post-consumer resin; wherein the polypropylene post-consumer resin has an MI2 ranging from 5 to 300 g/10 min as determined according to ISO 1133-2011 at 230 °C under a load of 2.16 kg; for example, from 7 to 200 g/10 min; and/or

The third polypropylene resin is or comprises a post-consumer resin; wherein the polypropylene post-consumer resin is a blend of recycled polypropylene and recycled polyethylene, wherein the content of the recycled polyethylene is ranging from 2 to 15 wt.% relative to the total weight of the polypropylene post-consumer resin.

Whatever is the embodiment chosen, (i.e. the metallic stearate being added by means of component B and/or component C) the metallic stearate is preferably selected from zinc stearate, calcium stearate, magnesium stearate or any mixture thereof; preferably, the metallic stearate is zinc stearate.

With preference one or more of the following embodiments can be used to further define the composite material:

The composite material comprises at least 50 wt.% based on the total weight of the composite material of component A; from 10 to 40 wt. % based on the total weight of the composite material of component B, and, optionally, from 2 to 10 wt.% based on the total weight of the composite material of component C.

The composite material comprises at least 50 wt.% based on the total weight of the composite material of component A; from 10 to 40 wt. % based on the total weight of the composite material of component B, and, optionally, from 2 to 10 wt.% based on the total weight of the composite material of component C, wherein component C is a MeSt-PP masterbatch comprising at least 2.5 wt.% of metallic stearate based on the total weight of the MeSt-PP masterbatch that is different from component B; and/or wherein component C is a MeSt-PP masterbatch comprising a third polypropylene resin having a melt index MI2 ranging from 5 g/10 min to 300 g/10min as determined according to ISO 1133-2011 at 230°C under a load of 2.16 kg; and/or wherein component C is a MeSt-PP masterbatch comprising a third polypropylene resin, and the third polypropylene resin is selected to be the same that the first polypropylene resin.

The composite material comprises from 15 to 38 wt. % based on the total weight of the composite material of component B; preferably, from 20 to 35 wt.%.

When component C is present, the composite material comprises from 2 to 10 wt. % based on the total weight of the composite material of component C; preferably, from 4 to 8 wt.%.

The composite material comprises at least 55 wt.% based on the total weight of the composite material of component A; preferably, at least 60 wt.%.

The total content of the first and the third polypropylene resin, based on the total weight of the composite material is at least 60 wt.%; preferably, at least 65 wt.%.

The composite material comprises at least 0.8 wt.% based on the total weight of the composite material of metallic stearate; preferably, at least 0.9 wt.%, more preferably, at least 1.0 wt.%.

The composite material comprises at most 4.0 wt.% based on the total weight of the composite material of metallic stearate; preferably, at most 3.0 wt.%, more preferably, at most 2.5 wt.%.

The composite material comprises from 2.2 to 5.5 wt.% of carbon particles based on the total weight of the composite material, and as determined according to ISO 11358- 2014; preferably, from 2.5 to 5.0 wt.% of carbon particles; more preferably, from 3.0 to 4.5 wt.% of carbon particles; even more preferably, from 3.2 wt.% to 3.9 wt.%.

The composite material comprises at least 2.2 wt.% of carbon particles based on the total weight of the composite material; preferably, at least 2.5 wt.%, more preferably, at least 2.8 wt.%, even more preferably, at least 3.0 wt.%, most preferably, at least 3.2 wt.%, and even most preferably, at least 3.4 wt.%.

The composite material comprises at most 5.5 wt.% of carbon particles based on the total weight of the composite material; preferably, at most 5.0 wt.%; more preferably, at most 4.5 wt.%; even more preferably, at most 4.2 wt.%; most preferably, at most 4.0 wt.%; and even most preferably, at most 3.9 wt.%.

The composite material comprises from 2.2 to 5.5 wt.% of carbon nanotubes based on the total weight of the composite material, and as determined according to ISO 11358- 2014; preferably, from 2.5 to 5.0 wt.% of carbon nanotubes; more preferably, from 3.0 to 4.5 wt.% of carbon nanotubes; even more preferably, from 3.2 wt.% to 3.9 wt.%. The composite material comprises at least 2.2 wt.% of carbon nanotubes based on the total weight of the composite material; preferably, at least 2.5 wt.%, more preferably, at least 2.8 wt.%, even more preferably, at least 3.0 wt.%, most preferably, at least 3.2 wt.%, and even most preferably, at least 3.4 wt.%.

The composite material comprises at most 5.5 wt.% of carbon nanotubes based on the total weight of the composite material; preferably, at most 5.0 wt.%; more preferably, at most 4.5 wt.%; even more preferably, at most 4.2 wt.%; most preferably, at most 4.0 wt.%; and even most preferably, at most 3.9 wt.%.

With preference one or more of the following embodiments can be used to better define the inventive process:

Step d) of dry blending and step e) of forming a conductive article by injection moulding are performed together in a single step using a single injection moulding apparatus. Step e) of forming a conductive article by injection moulding of the said composite material is conducted at a temperature of at least 230°C, and/or of at most 260 °C. The injection moulding in step e) is selected from the group comprising regular injection moulding, injection blow moulding, injection stretch blow moulding, Preferably, the method is regular injection moulding.

According to a second aspect, the disclosure provides an injection-moulded conductive article made from a composite material produced by the process according to the first aspect.

In a preferred embodiment, the injection-moulded conductive article has a surface resistance of at most 5.10 ⁶ ohms as determined according to IEC 61340-4-1 with an SRM110 meter.

Wth preference, the article is selected from a bottle, a cup, a vessel, a vehicle panel, an interior trim, a container, a pipe, a pipe fitting, a box, a plate and a heating panel.

According to a third aspect, the disclosure relates to the use of a MeSt-PP masterbatch comprising at least 2.5 wt.% of metallic stearate based on the total weight of the MeSt-PP masterbatch and a third polypropylene resin having a melt index MI2 ranging from 5 g/10 min to 300 g/10 min as determined according to ISO 1133-2011 at 230 °C under a load of 2.16 kg, in a process to produce an injection moulded article made of a composite material comprising polypropylene and carbon nanotubes. Wth preference, the process is according to the first aspect and/or the injection moulded article is according to the second aspect.

The disclosure also relates to the use of a CP-PP masterbatch comprising a blend of at least 7.0 wt.% of carbon particles as determined according to ISO 11358-2014 and based on the total weight of said masterbatch wherein the carbon particles are selected from nanographene, nanographite, carbon nanotubes and any combination thereof; and at least 2.5 wt.% of metallic stearate based on the total weight of the masterbatch, and a second polypropylene resin having an MI2 ranging from 60 to 300 g/10 min as determined according to ISO 1133-2011 at 230 °C under a load of 2.16 kg; in a process to produce an injection moulded article made of a composite material comprising polypropylene and carbon particles; with preference, carbon nanotubes.

For example, the disclosure relates to the use in a process to produce an injection moulded article made of a composite material comprising polypropylene and carbon particles, of a polypropylene-based masterbatch comprising at least 2.5 wt.% of metallic stearate based on the total weight of the polypropylene-based masterbatch; with preference, the polypropylene- based masterbatch further comprises at least 7.0 wt.% of carbon particles as determined according to ISO 11358-2014 and based on the total weight of said masterbatch wherein the carbon particles are selected from nanographene, nanographite, carbon nanotubes and any combination thereof; and a second polypropylene resin having an MI2 ranging from 60 to 300 g/10 min as determined according to ISO 1133-2011 at 230 °C under a load of 2.16 kg.

Detailed description of the disclosure

For the disclosure the following definitions are given:

As used herein, a "polymer" is a polymeric compound prepared by polymerizing monomers, whether of the same or a different type. The generic term polymer thus embraces the term homopolymer, usually employed to refer to polymers prepared from only one type of monomer, and the terms copolymer and interpolymer as defined below.

As used herein, a "copolymer", "interpolymer" and like terms mean a polymer prepared by the polymerization of at least two different types of monomers. These generic terms include polymers prepared from two or more different types of monomers, e.g. terpolymers, tetrapolymers, etc.

As used herein, "blend", "polymer blend" and like terms refer to a composition of two or more compounds, for example, two or more polymers or one polymer with at least one other compound.

As used herein, the term “melt blending” involves the use of shear force, extensional force, compressive force, ultrasonic energy, electromagnetic energy, thermal energy or combinations comprising at least one of the foregoing forces or forms of energy and is conducted in processing equipment wherein the aforementioned forces are exerted by a single screw, multiple screws, intermeshing co-rotating or counter-rotating screws, non-intermeshing co rotating or counter-rotating screws, reciprocating screws, screws with pins, barrels with pins, rolls, rams, helical rotors, or combinations comprising at least one of the foregoing.

As used herein the terms “polypropylene” (PP) and “propylene polymer” may be used synonymously. The term “polypropylene” encompasses homopolypropylene as well as copolymers of propylene which can be derived from propylene and a comonomer such as one or more selected from ethylene or C4-C2oalpha-olefins. Suitable C4-C2oalpha-olefins are selected from the group comprising 1 -butene, 1-pentene, 4-methyl-1-pentene, 1 -hexene, 1- octene, 1-decene, 1-dodecene, 1-tetradecene, 1-hexadecene, 1-octadecene and 1-eicosene.

The term “polypropylene resin” as used herein refers to polypropylene fluff or powder that is extruded, and/or melted and/or pelletized and can be produced through compounding and homogenizing of the polypropylene resin as taught herein, for instance, with mixing and/or extruder equipment. As used herein, the term “polypropylene” may be used as a shorthand for “polypropylene resin”.

The term “fluff” or “powder” as used herein refers to polypropylene material with the hard catalyst particle at the core of each grain and is defined as the polymer material after it exits the polymerization reactor (or the final polymerization reactor in the case of multiple reactors connected in series).

Under normal production conditions in a plant, it is expected that the melt index (MI2, HLMI, MI5) will be different for the fluff than for the polypropylene resin. Unless otherwise indicated, the melt index for the polypropylene resin refers to the melt index as measured on the polypropylene resin as defined above.

The term “carbon nanotubes” excludes “carbon fibres”.

The terms "comprising", "comprises" and "comprised of as used herein are synonymous with "including", "includes" or "containing", "contains", and are inclusive or open-ended and do not exclude additional, non-recited members, elements or method steps. The terms "comprising", "comprises" and "comprised of" also include the term “consisting of”.

The recitation of numerical ranges by endpoints includes all integer numbers and, where appropriate, fractions subsumed within that range (e.g. 1 to 5 can include 1, 2, 3, 4, 5 when referring to, for example, a number of elements, and can also include 1.5, 2, 2.75 and 3.80, when referring to, for example, measurements). The recitation of endpoints also includes the recited endpoint values themselves (e.g. from 1.0 to 5.0 includes both 1.0 and 5.0). Any numerical range recited herein is intended to include all sub-ranges subsumed therein. As used herein, the term “masterbatch” refers to concentrates of active material (such as the carbon nanotubes (CNT) or metallic stearate) in a polymer, which is intended to be subsequently incorporated into another polymer miscible with the polymer already contained in the masterbatches.

The particular features, structures, characteristics or embodiments may be combined in any suitable manner, as would be apparent to a person skilled in the art from this disclosure, in one or more embodiments.

The process to produce the injection-moulded conductive articles

The disclosure provides a process to produce an injection-moulded conductive article from a composite material; remarkable in that it comprises the steps of: a) providing a component A being a first polypropylene resin having a melt index MI2 ranging from 5 to 30 g /10 min as determined according to ISO 1133-2011 at 230 °C under a load of 2.16 kg; b) providing a component B being a CP-PP masterbatch, the component B comprising a blend of: at least 7.0 wt.% of carbon particles as determined according to ISO 11358-2014 and based on the total weight of said masterbatch wherein the carbon particles are selected from nanographene, nanographite, carbon nanotubes and any combination thereof; and a second polypropylene resin having an MI2 ranging from 60 to 300 g/10 min as determined according to ISO 1133-2011 at 230 °C under a load of 2.16 kg; c) providing metallic stearate; wherein the metallic stearate is provided by means of a polypropylene-based masterbatch comprising at least 2.5 wt.% of metallic stearate based on the total weight of the masterbatch; d) dry blending the components to obtain a composite material wherein the composite material comprises at least 0.7 wt.% based on the total weight of the composite material of metallic stearate, and from 2.0 wt.% to 8.0 wt.% or from 2.0 wt.% to 6.0 wt.% based on the total weight of the composite material of carbon nanotubes; and e) forming a conductive article by injection moulding of said composite material.

In a preferred embodiment, the disclosure provides a process to produce an injection-moulded conductive article from a composite material; characterized in that it comprises the steps of a) providing at least 50 wt.% of a component A based on the total weight of the composite material, the component A being a first polypropylene resin having a melt index MI2 ranging from 5 to 30 g/10 min as determined according to ISO 1133-2011 at 230 °C under a load of 2.16 kg; b) providing from 10 to 40 wt. % of a component B based on the total weight of the composite material, the component B being a CP-PP masterbatch, the component B comprising a blend of: at least 7.0 wt.% of carbon particles as determined according to ISO 11358-2014 and based on the total weight of said masterbatch wherein the carbon particles are selected from nanographene, nanographite, carbon nanotubes and any combination thereof; and a second polypropylene resin having an MI2 ranging from 60 to 300 g/10 min as determined according to ISO 1133-2011 at 230 °C under a load of 2.16 kg; c) providing metallic stearate; wherein the metallic stearate is provided by means of a polypropylene-based masterbatch comprising at least 2.5 wt.% of metallic stearate based on the total weight of the masterbatch; d) dry blending the components to obtain a composite material wherein the composite material comprises at least 0.7 wt.% of metallic stearate based on the total weight of the composite material, and from 2.0 wt.% to 8.0 wt.% of carbon particles based on the total weight of the composite material; and e) forming a conductive article by injection moulding of said composite material.

It is understood that the step of providing a component to produce the composite material implies that the composite material, in return comprises said component. Thus, the step of providing at least 50 wt.% of a component A based on the total weight of the composite material, results in the composite material comprising at least 50 wt.% of a component A based on the total weight of the composite material. In the same way, the step of providing from 10 to 40 wt. % of a component B based on the total weight of the composite material results in the composite material comprising from 10 to 40 wt. % of a component B based on the total weight of the composite material.

The process according to the disclosure allows the production of injection-moulded conductive articles having a lower content of carbon particles, such as carbon nanotubes, than similar articles known from the prior art. As the filler content is lower, the articles have a better balance of electrical and mechanical properties. Moreover, the low content of carbon particles makes them less expensive. Also, as demonstrated by the examples, the electrical properties are homogeneous throughout the surface of the article. The article is preferably selected from a bottle, a cup, a vessel, a vehicle panel, an interior trim, a container, a pipe, a pipe fitting, a box, a plate and a heating panel; with preference, the article is selected from a pipe, a pipe fitting, a box, a plate and a heating panel; more preferably the article is a box or a plate.

In a preferred embodiment, the conductive article has a surface resistance lower than 5.10 ⁶ Ohm, preferably, lower than 1.10 ⁶ Ohm as measured according to I EC 61340-4-1 with an SRM110 meter.

Step a) of providing a component A

Component A is a first polypropylene resin having a melt index MI2 ranging from 5 to 30 g/10 min as determined according to ISO 1133-2011 at 230 °C under a load of 2.16 kg.

The process comprises providing at least 50 wt.% based on the total weight of the composite material of a component A; preferably, at least 55 wt.%; more preferably, at least 60 wt.%.

In an embodiment, the process comprises providing at most 90 wt.% based on the total weight of the composite material of a component A; preferably, at most 85 wt.%; more preferably, at most 80 wt.%; even more preferably, at most 75 wt.%.

The first polypropylene resin is preferably, selected from a propylene homopolymer, a copolymer of propylene with one or more comonomer selected from ethylene and C4-C10 alpha-olefins, an heterophasic polypropylene and any mixture thereof.

In a preferred embodiment of the disclosure, the first polypropylene resin is a homopolymer of propylene. A homopolymer according to this disclosure has less than 0.2 wt.%, preferably, less than 0.1 wt.%, more preferably, less than 0.05 wt.% and most preferably, less than 0.005 wt.%, of alpha-olefins other than propylene in the polymer. Most preferred, no other alpha-olefins are detectable. Accordingly, when the first polypropylene resin is a homopolymer of propylene, the comonomer content in the first polypropylene resin is less than 0.2 wt.%, more preferably, less than 0.1 wt.%, even more preferably, less than 0.05 wt.% and most preferably, less than 0.005 wt.% based on the total weight of the first polypropylene resin.

In case the first polypropylene resin is a random copolymer of propylene and at least one comonomer, it comprises at least 0.1 wt.% of comonomer(s), preferably, at least 1 wt.% as based on the total weight of the random copolymer of propylene and at least one comonomer. With preference, it comprises up to 10 wt.% of comonomer(s) and most preferably, up to 6 wt.%. Preferably, the random copolymers are copolymers of propylene and ethylene or hexene. In a preferred embodiment, the first polypropylene resin is a heterophasic propylene copolymer resin. The heterophasic propylene copolymers comprise a matrix propylene polymer phase and a dispersed phase of a rubber. With preference, the rubber is ethylene propylene rubber.

The heterophasic propylene copolymers of the present disclosure as defined above can be produced by sequential polymerization in a series of polymerization reactors in the presence of a catalyst system, wherein in a first polymerization stage the propylene polymer is produced, and in a second polymerization stage the rubber is produced by copolymerizing ethylene and at least one further olefin different from ethylene. The catalyst system is added to the first polymerization stage.

Thus, with preference, the first polypropylene resin is an heterophasic polypropylene resin consisting of: i. from 60 to 95 wt.% based on the total weight of the heterophasic polypropylene resin of a polypropylene-based matrix selected from a homopolymer and/or a copolymer of propylene with one or more comonomer selected from ethylene and C4-C10 alpha-olefins; and ii. from 40 to 5 wt.% based on the total weight of the heterophasic polypropylene resin of a dispersed ethylene-alpha-olefin copolymer; with preference, the alpha-olefin in the ethylene-alpha-olefin copolymer is selected from the group of alpha-olefins having from 3 to 8 carbon atoms and/or the alpha-olefin in the ethylene- alpha-olefin copolymer is in the range of 25 to 70 wt.% based on the total weight of the ethylene-alpha-olefin copolymer.

The first polypropylene resin can be produced by polymerizing propylene and one or more optional comonomers, in the presence of a catalyst being a metallocene catalyst or a Ziegler- Natta catalyst.

In a preferred embodiment, the catalyst system may comprise a Ziegler-Natta catalyst. The term "Ziegler-Natta catalysts" refers to catalysts of the general formula MXn, wherein M is a transition metal compound selected from group IV to VII, wherein X is a halogen, and wherein n is the valence of the metal. Preferably, the metal is titanium, chromium or vanadium. Most preferably, the metal is titanium.

The Ziegler-Natta catalyst system, under the disclosure, comprises a titanium compound having at least one titanium-halogen bond and an internal electron donor, both on a suitable support, an organoaluminium compound, and an optional external electron donor. Suitable support is, for example, a magnesium halide in an active form. A suitable external electron donor (ED) is, for example, phthalate or succinate or a diether compound. The organoaluminium compound used in the process of the present disclosure is triethyl aluminium (TEAL).

Advantageously, the triethyl aluminium has a hydride content, expressed as AIH ₃ , of less than 1.0 wt.% with respect to the triethyl aluminium. More preferably, the hydride content is less than 0.5 wt.%, and most preferably, the hydride content is less than 0.1 wt.%. It would not depart from the scope of the disclosure if the organoaluminium compound contains minor amounts of other compounds of the trialkyl aluminium family, such as triisobutyl aluminium, tri- n-butyl aluminium, and linear or cyclic alkyl aluminium compounds containing two or more Al atoms, provided they show polymerization behaviour comparable to that of TEAL.

In the process of the present disclosure, the molar ratio Al/Ti is not particularly specified. However, it is preferred that the molar ratio Al/Ti is at most 100. Al and Ti are measured by X- Ray fluorescence.

If an external electron donor is present, it is preferred that the molar ratio AI/ED, with ED denoting external electron donor, is at most 120, more preferably, it is within the range of 5 to 120, and most preferably, within the range of 10 to 80. Before being fed to the polymerization reactor, the catalytic system preferably undergoes a premix and/or a pre-polymerization step. In the premix step, the triethyl aluminium (TEAL) and the external electron donor (ED) - if present -, which have been pre-contacted, are mixed with the Ziegler-Natta catalyst at a temperature within the range of 0 °C to 30 °C, preferably, within the range of 5 °C to 20 °C, for up to 15 min. The mixture of TEAL, an external electron donor (if present) and Ziegler-Natta catalyst is pre-polymerized with propylene at a temperature within the range of 10 °C to 100 °C, preferably, within the range of 10 °C to 30 °C, for 1 to 30 min, preferably, for 2 to 20 min.

In the first stage, the polymerization of propylene and one or more optional comonomers can, for example, be carried out in liquid propylene as a reaction medium (bulk polymerization). It can also be carried out in diluents, such as hydrocarbon that is inert under polymerization conditions (slurry polymerization). It can also be carried out in the gas phase. Those processes are well known to one skilled in the art.

Diluents, which are suitable for being used per the present disclosure, may comprise but are not limited to hydrocarbon diluents such as aliphatic, cycloaliphatic and aromatic hydrocarbon solvents, or halogenated versions of such solvents. Non-limiting illustrative examples of solvents are butane, isobutane, pentane, hexane, heptane, cyclopentane, cyclohexane, cycloheptane, methyl cyclopentane, methyl cyclohexane, isooctane, benzene, toluene, xylene, chloroform, chlorobenzenes, tetrachloroethylene, dichloroethane and trichloroethane. For the present disclosure, the propylene polymers are preferably produced by polymerization in liquid propylene at temperatures within the range of 20 °C to 100 °C. Preferably, temperatures are within the range of 60 °C to 80 °C. The pressure can be atmospheric or higher. Preferably, the pressure is ranging between 2.5 and 5.0 MPa.

Hydrogen is used to control the chain lengths of the propylene polymers. For the production of a propylene polymer with higher MI2, i.e. with lower average molecular weight and shorter polymer chains, the concentration of hydrogen in the polymerization medium needs to be increased. Inversely, the hydrogen concentration in the polymerization medium has to be reduced to produce a propylene polymer with lower MI2, i.e. with higher average molecular weight and longer polymer chains.

In such a sequential arrangement of polymerization reactors, the propylene homopolymer withdrawn from one reactor is transferred to the one following in the series, where the polymerization is continued. To produce propylene homopolymer fractions of different melt indexes, the polymerization conditions in the respective polymerization reactors need to be different, for example in that the hydrogen concentration in the polymerization reactors differs.

The melt flow index (MI2) of the propylene polymer produced in the second reactor is calculated using the following equation (2):

Log (MI2finai) = WBI X (Log MI2 _B I) + w _B 2 x Log(MI2 _B2 ) (2) wherein MI2 _fjnai is the melt flow index of the total propylene polymer produced, MI2 _B I and MI2 _B2 are the respective melt flow index of the propylene polymers fractions produced in the first and the second polymerization loop reactors, and w _Bi and w _B 2 are the respective weight fractions of the propylene polymers produced in the first and the second polymerization loop reactors as expressed in weight per cent (wt.%) of the total propylene polymer produced in the two polymerization loop reactors. These weight fractions are also commonly described as the contribution by the respective loop.

The matrix propylene polymer, preferably, propylene homopolymer, can be made for example in loop reactors or in a gas phase reactor. The propylene polymer produced in this way, in a first polymerization stage, is transferred to a second polymerization stage, into one or more secondary reactors where ethylene and at least one further olefin different from ethylene are added to produce the rubber. For example, further olefin is propylene. Thus, the rubber produced is ethylene-propylene rubber (EPR). Preferably, this polymerization step is done in a gas phase reactor. The propylene copolymer can be prepared using a controlled morphology catalyst that produces rubber spherical domains dispersed in a polypropylene matrix. The amount and properties of the components are controlled by the process conditions. The average molecular weight of the rubber, for which the intrinsic viscosity is used as a measure, is controlled by the addition of hydrogen to the polymerization reactors of the second polymerization stage. The amount of hydrogen added is such that the rubber has an intrinsic viscosity of 2.0 dl/g, and of at most 5.5 dl/g, measured in tetralin at 135 °C following ISO 1628. The contribution of the second polymerization stage, i.e. the rubber content of the heterophasic propylene copolymer is from 5 to 50 wt.% relative to the total weight of the heterophasic propylene copolymer.

The first polypropylene resin, according to the disclosure, may contain additives such as, by way of example, antioxidants, light stabilizers, acid scavengers, flame retardants, lubricants, antistatic additives, nucleating/clarifying agents, colourants. An overview of such additives may be found in Plastics Additives Handbook, ed. H. Zweifel, 5 ^th edition, 2001, Hanser Publishers.

The antioxidants used in the first polypropylene resin of the present disclosure, preferably, have anti-gas fading properties. The preferred antioxidants are selected from the group consisting of phosphites, hindered phenols, hindered amine stabilizers and hydroxylamines. An example of a suitable antioxidant additivation is a blend of Irgafos® 168 and Irganox® 3114. Alternatively, phenol-free antioxidant additivations are suitable as well, such as those based on hindered amine stabilizers, phosphites, hydroxylamines or any combination of these. In general, the antioxidants are added to the propylene homopolymer in an amount from 100 ppm to 2000 ppm with the exact amount depending upon the nature of the antioxidant, the processing conditions and other factors.

After the last polymerization reactor, the polymers are recovered as a powder and can then be pelletized or granulated.

With preference, the first polypropylene resin has a melt index MI2 ranging from 5 to 25 g/10 min as determined according to ISO 1133-2011 at 230 °C under a load of 2.16 kg; preferably, from 6 to 20 g/10 min; more preferably, from 7 to 15 g /10 min.

The first polypropylene resin has a monomodal molecular weight distribution or a bimodal molecular weight distribution.

In an embodiment, component A is selected from virgin polypropylene resin, a polypropylene post-consumer resin and a blend of a virgin polypropylene resin and a polypropylene post consumer resin.

For example, the first polypropylene resin of component A comprises from 10 to 99 wt.% of polypropylene post-consumer resin based on the total weight of the first polypropylene resin of component A; for example, from 20 to 90 wt.%; for example, from 40 to 80 wt.%; for example, from 50 to 70 wt.%. Wherein the first polypropylene resin of component A is or comprises a post-consumer resin; the polypropylene post-consumer resin has, for example, an MI2 ranging from 5 to 30 g/10 min as determined according to ISO 1133-2011 at 230 °C under a load of 2.16 kg; for example, from 7 to 20 g/10 min.

Wherein the first polypropylene resin of component A is or comprises a post-consumer resin; the polypropylene post-consumer resin is a blend of recycled polypropylene and recycled polyethylene, wherein the content of the recycled polyethylene is ranging from 2 to 15 wt.% relative to the total weight of the polypropylene post-consumer resin.

Polypropylene resins suitable for the disclosure as the first polypropylene resins of component A are commercially available from TOTAL®. A non-limitative example is TOTAL® PPC7760 with a melt index MI2 of 15.0 g/10 min as measured according to ISO 1133-2011 at 230 °C under a load of 2.16 kg. Another example is TOTAL® PPC 6742 with a melt index MI2 of 8 g/10 min as determined according to ISO 1133-2011 at 230 °C under a load of 2.16 kg.

Step b) of providing a component B

The process comprises providing from 10 to 40 wt. % based on the total weight of the composite material of a component B being a CP-PP masterbatch; preferably from 15 to 38 wt. %; more preferably, from 20 to 35 wt.%.

Component B is a CP-PP masterbatch, component B comprising a blend of: at least 50 wt.% of a second polypropylene resin based on the total weight of said masterbatch; wherein the second polypropylene resin has an MI2 ranging from 80 to 250 g/10 min as determined according to ISO 1133-2011 at 230 °C under a load of 2.16 kg; at least 7.0 wt.% of carbon particles, preferably carbon nanotubes as determined according to ISO 11358-2014 and based on the total weight of the said masterbatch.

The carbon particles are selected from nanographene, nanographite, carbon nanotubes and any combination thereof. In an embodiment, carbon particles are selected from nanographene and/or nanographite. In an embodiment, carbon particles are selected from nanographene and/or carbon nanotubes. In an embodiment, carbon particles are selected from nanographite and/or carbon nanotubes. In an embodiment, carbon particles are or comprise carbon nanotubes.

The second polypropylene resin of component B is selected from a propylene homopolymer and/or a copolymer of propylene with one or more comonomer selected from ethylene and C4- C10 alpha-olefins. The definition given for the homopolymer and the copolymer of the first polypropylene resin applies to the second polypropylene resin. With preference, the second polypropylene resin is a copolymer of propylene; more preferably, the comonomer is hexene. In a preferred embodiment, the second polypropylene resin is a metallocene-catalyzed polypropylene and has a molecular weight distribution of at least 2.0; preferably ranging from 2.0 to 9.0 or from 2.5 to 6.0 as determined by Size Exclusion Chromatography.

With preference, the second polypropylene resin of component B has a melt index MI2 ranging from 7 to 200 g/10 min as determined according to ISO 1133-2011 at 230 °C under a load of 2.16 kg; preferably, from 100 to 180 g/10 min; more preferably, from 120 to 160 g/10 min.

Preferably, the second polypropylene resin of component B has a melting temperature Tm comprised between 130 °C and 170 °C, as measured according to ISO 3146-2000, more preferably, of at least 145 °C.

Commercially available polypropylene resins suitable for use as second polypropylene resins are selected from TOTAL ^® . For example, the second polypropylene resin is selected from PPH12020 (a homopolymer with an MI2 of 60 g/10 min), MR60MC2 (a metallocene random copolymer with an MI2 of 60 g/10 min), MR110MC2 (a metallocene random copolymer with an MI2 of 110 g/10 min) or MH140CN0 (a metallocene random homopolymer with an MI2 of 140 g/10 min); with preference, the second polypropylene resin is, PPH12020 or MH140CN0.

Suitable carbon nanotubes used in the present disclosure can generally be characterized by having a size from 1 pm to 5 pm, this definition of size can be limited to two dimensions only, i.e. the third dimension may be outside of these limits. In a preferred embodiment, at least 50 wt.% of the carbon particles in component B are carbon nanotubes which have an average length of 1.1 pm or more as determined by transmission electron microscopy before being blended with the second polypropylene resin; preferably, all the carbon particles are carbon nanotubes which have an average length of 1.1 pm or more as determined by transmission electron microscopy before being blended with the second polypropylene resin.

Suitable carbon nanotubes also referred to as “nanotubes” herein, can be cylindrical in shape and structurally related to fullerenes, an example of which is Buckminsterfullerene (Obo). Suitable carbon nanotubes may be open or capped at their ends. The end cap may, for example, be a Buckminster-type fullerene hemisphere.

Suitable carbon nanotubes used in the present disclosure can comprise more than 80%, more preferably, more than 85%, more preferably, more than 90%, more preferably, more than 95%, even more preferably, more than 99%; and most preferably, more than 99.9% of their total weight in carbon. However, minor amounts of other atoms may also be present.

Carbon nanotubes can exist as single-walled nanotubes (SWNT) and multi-walled nanotubes (MWNT), i.e. carbon nanotubes having one single wall and nanotubes having more than one wall, respectively. In single-walled carbon nanotubes a one-atom thick sheet of atoms, for example, a one-atom thick sheet of graphite (also called graphene), is rolled seamlessly to form a cylinder. Multi-walled carbon nanotubes consist of a number of such cylinders arranged concentrically. The arrangement, in multi-walled carbon nanotubes, can be described by the so-called Russian doll model, wherein a larger doll opens to reveal a smaller doll.

In an embodiment, the carbon nanotubes are single-walled nanotubes characterized by an outer diameter of at least 0.5 nm, more preferably, of at least 1 nm, and most preferably, of at least 2 nm. Preferably, their outer diameter is at most 50 nm, more preferably, at most 30 nm and most preferably, at most 10 nm. Preferably, the length of single-walled nanotubes is at least 0.1 pm, more preferably, at least 1 pm, even more preferably, at least 10 pm. Preferably, their length is at most 50 pm, more preferably, at most 25 pm.

In an embodiment, the carbon nanotubes are single-walled, preferably, having an average L/D ratio (length/diameter ratio) of at least 1000.

In an embodiment, the carbon nanotubes are multi-walled, more preferably, multi-walled carbon nanotubes having on average from 5 to 15 walls.

Multi-walled carbon nanotubes are preferably characterized by an outer diameter of at least 1 nm, more preferably, of at least 2 nm, 4 nm, 6 nm or 8 nm, and most preferably, of at least 9 nm. The preferred outer diameter is at most 100 nm, more preferably, at most 80 nm, 60 nm or 40 nm, and most preferably, at most 20 nm. Most preferably, the outer diameter is in the range of from 10 nm to 20 nm. The preferred length of the multi-walled nanotubes is at least 50 nm, more preferably, at least 75 nm, and most preferably, at least 100 nm. In an embodiment, the multi-walled carbon nanotubes have an average outer diameter in the range from 10 nm to 20 nm or an average length in the range from 100 nm to 10 pm or both. In an embodiment, the average L/D ratio (length/diameter ratio) is at least 5, preferably, at least 10, preferably, at least 25, preferably, at least 50, preferably, at least 100, and more preferably, higher than 100.

Carbon nanotubes according to the disclosure have a transition metal oxide content of less than 3%, more preferably, less than 2%, and more preferably, less than 1% measured according to Inductively Coupled Plasma Mass Spectrometry (ICP-MS).

Suitable carbon nanotubes to be used in the present disclosure can be prepared by any method known in the art. Non-limiting examples of commercially available multi-walled carbon nanotubes are Graphistrength™ 100, available from Arkema, Nanocyl™ NC 7000 available from Nanocyl, FloTube™ 9000 available from CNano Technology.

Nanocyl™ NC 7000 available from Nanocyl are carbon nanotubes having an average L/D ratio of at most 500. The CP-PP masterbatch is produced by blending a second polypropylene resin having a melting temperature Tm as measured according to ISO 3146-2000, carbon particles, preferably carbon nanotubes, and optional processing aids, in an extruder comprising a transport zone and a melting zone maintained at a temperature comprised between Tm + 1 °C and Tm + 50 °C, preferably, comprised between Tm + 5 °C and Tm + 30 °C.

In an embodiment, the process for the preparation of the masterbatch according to the present disclosure comprises the steps of: i. providing carbon particles, preferably carbon nanotubes, ii. providing a second polypropylene resin having a melting temperature, Tm, measured according to ISO 3146-2000, and wherein said second polypropylene resin has a melt flow index ranging from 80 to 250 g/10 min as determined according to ISO 1133-2011 at 230 °C under a load of 2.16 kg, iii. blending said carbon particles, preferably carbon nanotubes, and said second polypropylene resin by extrusion in an extruder comprising a transport zone and a melting zone maintained at a temperature comprised between Tm + 1 °C and Tm + 50 °C, preferably, between Tm + 5 °C and Tm + 30 °C, and iv. forming a masterbatch through a die, said masterbatch,

• comprising at least 5 wt.% of carbon particles, preferably carbon nanotubes, based on the total weight of the masterbatch as determined according to ISO 11358-2014, and

• having a high load melt index, HLMI, of from 2 g/10 min to 1000 g/10 min, preferably, ranging from 10 to 1000 g/10 min, determined according to ISO 1133-2011 under a load of 21.6 kg.

In a preferred embodiment, the process further comprises the step of blending from 0.01 to 4.0 wt.%, preferably, from 0.1 to 2.0 wt.% of one or more processing aids based on the total weight of the masterbatch, with the second polypropylene resin and the carbon particles, preferably carbon nanotubes, in step iii).

Therefore, in an embodiment, the masterbatch further comprises from 0.01 to 4.0 wt.% of one or more processing aids as based on the total weight of the masterbatch, said one or more processing aids are selected from fluoroelastomers, waxes, tristearin, erucyl amide, oleic acid amide, ethylene-acrylic acid copolymer, ethylene-vinyl acetate copolymer, cetyl trimethyl ammonium bromide, polysiloxanes, oleamide, stearamide, behenamide, oleyl palmitamide, ethylene bis-oleamide, ethylene bis (stearamide) (EBS), meta-cresol and any mixture thereof.

In a preferred embodiment, step iii) is carried out on a co-rotating twin-screw extruder at a screw speed of at least 300 rpm, preferably, at least 500 rpm. In a preferred embodiment, the temperature of the masterbatch at the extruder’s outlet ranges from the crystallization temperature to the melting temperature of the masterbatch polymer.

The second polypropylene resin of component B is selected from virgin polypropylene resin, a polypropylene post-consumer resin and a blend of a virgin polypropylene resin and a polypropylene post-consumer resin.

For example, the second polypropylene resin of component B comprises from 10 to 99 wt.% of polypropylene post-consumer resin based on the total weight of the second polypropylene resin; for example, from 20 to 90 wt.%; for example, from 40 to 80 wt.%; for example, from 50 to 70 wt.%.

Wherein the second polypropylene resin of component B is or comprises a post-consumer resin; the polypropylene post-consumer resin has an MI2 ranging from 60 to 300 g/10 min as determined according to ISO 1133-2011 at 230 °C under a load of 2.16 kg; for example, from 70 to 200 g/10 min; and/or the polypropylene post-consumer resin is a blend of recycled polypropylene and recycled polyethylene, wherein the content of the recycled polyethylene is ranging from 2 to 15 wt.% relative to the total weight of the polypropylene post-consumer resin.

Step c) of providing metallic stearate

According to the disclosure, the metallic stearate is provided through a polypropylene-based masterbatch comprising at least 2.5 wt.% of metallic stearate based on the total weight of the masterbatch.

In an embodiment, the polypropylene-based masterbatch comprising at least 2.5 wt.% of metallic stearate based on the total weight of the masterbatch is the CP-PP masterbatch of component B. Therefore, component B is a CP-PP masterbatch comprising a blend of: at least 7.0 wt.% of carbon particles as determined according to ISO 11358-2014 and based on the total weight of said masterbatch wherein the carbon particles are selected from nanographene, nanographite, carbon nanotubes and any combination thereof; at least 2.5 wt.% of metallic stearate based on the total weight of the masterbatch; and a second polypropylene resin having an MI2 ranging from 60 to 300 g/10 min as determined according to ISO 1133-2011 at 230 °C under a load of 2.16 kg.

For example, component B comprises from 3.0 to 20.0 wt.% of metallic stearate based on the total weight of the masterbatch, preferably, from 3.5 to 15.0 wt.%, more preferably, from 4.0 to 10.0 wt.%, and even more preferably, from 4.5 to 8.0 wt.%.

In an embodiment, the polypropylene-based masterbatch comprising at least 2.5 wt.% of metallic stearate based on the total weight of the masterbatch is a component C that is different from the component B. For example, the component C is a MeSt-PP masterbatch comprising from 3.0 to 20.0 wt.% of metallic stearate based on the total weight of the masterbatch, preferably, from 3.5 to 15.0 wt.%, more preferably, from 4.0 to 10.0 wt.%, and even more preferably, from 4.5 to 8.0 wt.%.

In another embodiment, the metallic stearate is provided through both the CP-PP masterbatch of component B and the MeSt-PP masterbatch of component C.

Whatever is the embodiment chosen, the metallic stearate is preferably, selected from zinc stearate, calcium stearate, magnesium stearate or any mixture thereof; preferably, the metallic stearate is zinc stearate (CAS number 557-05-1).

When present, component C is a MeSt-PP masterbatch comprising a blend of: at least 2.5 wt.% of metallic stearate based on the total weight of the MeSt-PP masterbatch and, a third polypropylene resin having a melt index MI2 ranging from 5 g/10 min to 300 g/10 min as determined according to ISO 1133-2011 at 230 °C under a load of 2.16 kg.

The third polypropylene resin of component C is preferably, selected from a propylene homopolymer, a copolymer of propylene with one or more comonomer selected from ethylene and C4-C10 alpha-olefins, an heterophasic polypropylene and any mixture thereof. The third polypropylene resin is selected to be the same that the first polypropylene resin.

Therefore, in an embodiment the third polypropylene resin of component C is an heterophasic polypropylene resin consisting of: i. from 60 to 95 wt.% based on the total weight of the heterophasic polypropylene resin of a polypropylene-based matrix selected from a homopolymer and/or a copolymer of propylene with one or more comonomer selected from ethylene and C4-C10 alpha-olefins; and ii. from 40 to 5 wt.% based on the total weight of the heterophasic polypropylene resin of a dispersed ethylene-alpha-olefin copolymer; with preference, the alpha-olefin in the ethylene-alpha-olefin copolymer is selected from the group of alpha-olefins having from 3 to 8 carbon atoms and/or the alpha-olefin in the ethylene- alpha-olefin copolymer is in the range of 25 to 70 wt.% based on the total weight of the ethylene-alpha-olefin copolymer.

In a preferred embodiment, the third polypropylene resin of component C has a melt index MI2 ranging from 5 to 250 g/10 min as determined according to ISO 1133-2011 at 230 °C under a load of 2.16 kg; preferably, from 6 to 200 g/10 min; more preferably, from 7 to 50 g /10 min. More preferably, the component C further comprises from 0.1 to 4.0 wt.% based on the total weight of the masterbatch of one or more processing aids are selected from fluoroelastomers, waxes, tristearin, erucyl amide, oleic acid amide, ethylene-acrylic acid copolymer, ethylene- vinyl acetate copolymer, cetyltrimethylammonium bromide, polyethylene oxide, meta-cresol and any mixture thereof.

The third polypropylene resin of component C is selected from virgin polypropylene resin, a polypropylene post-consumer resin and a blend of a virgin polypropylene resin and a polypropylene post-consumer resin.

For example, the third polypropylene resin comprises from 10 to 99 wt.% of polypropylene post-consumer resin based on the total weight of the third polypropylene resin; for example, from 20 to 90 wt.%; for example, from 40 to 80 wt.%; for example, from 50 to 70 wt.%.

For example, the third polypropylene resin is or comprises a post-consumer resin; wherein the polypropylene post-consumer resin has an MI2 ranging from 5 to 300 g/10 min as determined according to ISO 1133-2011 at 230 °C under a load of 2.16 kg; for example, from 7 to 200 g/10 min.

For example, the third polypropylene resin is or comprises a post-consumer resin; wherein the polypropylene post-consumer resin is a blend of recycled polypropylene and recycled polyethylene, wherein the content of the recycled polyethylene is ranging from 2 to 15 wt.% relative to the total weight of the polypropylene post-consumer resin.

The MeSt-PP masterbatch is produced by blending the third polypropylene resin having a melting temperature Tm as measured according to ISO 3146-2000, metallic stearate and optional processing aids, in an extruder comprising a transport zone and a melting zone maintained at a temperature comprised between Tm + 1 °C and Tm + 50 °C, preferably, comprised between Tm + 5 °C and Tm + 30 °C.

With preference, the composite material comprises at least 0.50 wt.% of zinc stearate as based on the total weight of the composite material, preferably, at least 0.70 wt.%, more preferably, at least 0.85 wt.% and even more preferably, at least 0.90 wt.%.

In an embodiment, the composite material comprises at most 1.50 wt.% of zinc stearate as based on the total weight of the composite material, preferably, at most 1.20 wt.%.

Wth preference, the composite material comprises at least 0.05 wt.% of processing aids based on the total weight of the composite material; preferably, at least 0.10 wt.%, more preferably, at least 0.15 wt.% and even more preferably, at least 0.20 wt.%. In an embodiment, the composite material comprises at most 0.40 wt.% of processing aids based on the total weight of the composite material, preferably, at most 0.35 wt.%.

Preferably, the zinc stearate and the one or more processing aids form an additive mixture, and the content of zinc stearate in the additive mixture is ranging from 50 wt.% to 99 wt.% as based on the total weight of the additive mixture, more preferably, from 60 wt.% to 90 wt.%, most preferably, from 65 wt.% to 85 wt.%.

In all embodiments of the disclosure, the composite material may further comprise one or more additives different from the listed processing aids, the one or more additives being selected from the group comprising an antioxidant, an antiacid, a UV-absorber, an antistatic agent, a light stabilizing agent, an acid scavenger, a lubricant, a nucleating/clarifying agent, a colorant or a peroxide. An overview of suitable additives may be found in Plastics Additives Handbook, ed. H. Zweifel, 5 ^th edition, 2001, Hanser Publishers, which is hereby incorporated by reference in its entirety.

In all embodiments of the disclosure, the composite material may comprise from 0% to 45% by weight of one or more fillers based on the total weight of the composite material, preferably, from 1% to 35 % by weight. The one or more fillers being selected from the group consisting of talc, calcium carbonate, calcium hydroxide, barium sulphate, mica, calcium silicate, clay, kaolin, silica, alumina, wollastonite, magnesium carbonate, magnesium hydroxide, titanium oxide, zinc oxide, zinc sulphate, natural fibres, glass fibres. With preference, the filler is talc.

The disclosure also encompasses an article as described herein wherein the composite material comprises from 0% to 10% by weight of at least one additive such as antioxidant, based on the total weight of the composite material. In a preferred embodiment, said composite material comprises less than 5% by weight of an additive, based on the total weight of the composite material, for example from 0.1 to 3% by weight of the additive, based on the total weight of the composite material.

In an embodiment, the composite material comprises an antioxidant. Suitable antioxidants include, for example, phenolic antioxidants such as pentaerythritol tetrakis[3-(3',5'-di-tert-butyl- 4'-hydroxyphenyl)propionate] (herein referred to as Irganox® 1010), tris(2,4-ditert-butylphenyl) phosphite (herein referred to as Irgafos® 168), 3DL-alpha-tocopherol, 2,6-di-tert-butyl-4- methylphenol, dibutylhydroxyphenylpropionic acid stearyl ester, 3,5-di-tert-butyl-4- hydroxyhydrocinnamic acid, 2,2'-methylenebis(6-tert-butyl-4-methyl-phenol), hexamethylene bis[3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate], benzenepropanamide,N,N’-1,6- hexanediyl bis[3,5-bis(1,1-dimethylethyl)-4-hydroxy] (Antioxidant 1098), Diethyl 3.5-Di-Tert- Butyl-4-Hydroxybenzyl Phosphonate, Calcium bis[monoethyl(3,5-di-tert-butyl-4- hydroxylbenzyl)phosphonate], Triethylene glycol bis(3-tert-butyl-4-hydroxy-5- ethylphenyl)propionate (Antioxidant 245), 6,6'-di-tert-butyl-4,4'-butylidenedi-m-cresol, 3,9- bis(2-(3-(3-tert-butyl-4-hydroxy-5-methylphenyl)propionyloxy -1 , 1 -dimethylethyl)-2,4,8, 10- tetraoxaspiro[5.5]undecane, 1 ,3,5-trimethyl-2,4,6-tris(3,5-di-tert-butyl-4- hydroxybenzyl)benzene, 1 , 1 ,3-tris(2-methyl-4-hydroxy-5-tert-butylphenyl)butane, (2,4,6- trioxo-1,3,5-triazine-1 ,3,5(2H,4H,6H)-triyl)triethylene tris[3-(3,5-di-tert-butyl-4- hydroxyphenyl)propionate], tris(3,5-di-tert-butyl-4-hydroxybenzyl) isocyanurate, Tris(4-tert- butyl-3-hydroxy-2,6-dimethylbenzyl) isocyanurate, ethylene bis[3,3-bis(3-tert-butyl-4- hydroxyphenyl)butyrate], and 2,6-bis[[3-(1,1-dimethylethyl)-2-hydroxy-5-methylphenyl] octahydro-4,7- ethano-1 H-indenyl]-4- ethyl-phenol. Suitable antioxidants also include, for example, phenolic antioxidants with dual functionality such 4,4'-Thio-bis(6-tert-butyl-m-methyl phenol) (Antioxidant 300), 2,2'-Sulfanediylbis(6-tert-butyl-4-methylphenol) (Antioxidant 2246- S), 2-Methyl-4,6-bis(octylsulfanylmethyl)phenol, thiodiethylene bis[3-(3,5-di-tert-butyl-4- hydroxyphenyl)propionate], 2,6-di-tert-butyl-4-(4,6-bis(octylthio)-1,3,5-triazin-2- ylamino)phenol, N-(4-hydroxyphenyl)stearamide, bis(1 ,2,2,6,6-pentamethyl-4-piperidyl) [[3,5- bis(1 ,1-dimethylethyl)-4-hydroxyphenyl]methyl]butylmalonate, 2,4-di-tert-butylphenyl 3,5-di- tert-butyl-4-hydroxybenzoate, hexadecyl 3,5-di-tert-butyl-4-hydroxy-benzoate, 2-(1 , 1 - dimethylethyl)-6-[[3-(1,1-dimethylethyl)-2-hydroxy-5-methylp henyl] methyl]-4-methylphenyl acrylate, and CAS 128961-68-2 (Sumilizer® GS). Suitable antioxidants also include, for example, aminic antioxidants such as N-phenyl-2-naphthylamine, poly(1,2-dihydro-2, 2,4- trimethyl-quinoline), N-isopropyl-N'-phenyl-p-phenylenediamine, N-Phenyl-1-naphthylamine, CAS 68411-46-1 (Antioxidant 5057), and 4,4-bis(alpha,alpha-dimethylbenzyl)diphenylamine (Antioxidant KY 405). Preferably, the antioxidant is selected from pentaerythritol tetrakis[3- (3',5'-di-tert-butyl-4'-hydroxyphenyl) propionate] (herein referred to as Irganox® 1010), tris(2,4- ditert-butylphenyl) phosphite (herein referred to as Irgafos® 168), or a mixture thereof.

Step d) of dry blending

In a preferred embodiment, the step of dry blending the components is performed to obtain a composite material wherein the composite material comprises at least 50 wt.% based on the total weight of the composite material of component A; from 10 to 40 wt. % based on the total weight of the composite material of component B, and, optionally, from 2 to 10 wt.% based on the total weight of the composite material of component C.

For example, the composite material comprises at least 50 wt.% based on the total weight of the composite material of component A; from 10 to 40 wt. % based on the total weight of the composite material of component B, and, optionally, from 2 to 10 wt.% based on the total weight of the composite material of component C, wherein component C is a MeSt-PP masterbatch comprising at least 2.5 wt.% of metallic stearate based on the total weight of the MeSt-PP masterbatch that is different from component B; and/or wherein component C is a MeSt-PP masterbatch comprising a third polypropylene resin having a melt index MI2 ranging from 5 g/10 min to 300 g/10min as determined according to ISO 1133-2011 at 230°C under a load of 2.16 kg; and/or wherein component C is a MeSt-PP masterbatch comprising a third polypropylene resin, and the third polypropylene resin is selected to be the same that the first polypropylene resin.

In an embodiment, the composite material comprises from 15 to 38 wt. % based on the total weight of the composite material of component B; preferably, from 20 to 35 wt.%.

When component C is present, the composite material comprises from 2 to 10 wt. % based on the total weight of the composite material of component C; preferably, from 4 to 8 wt.%.

With preference, the composite material comprises at least 55 wt.% based on the total weight of the composite material of component A; preferably, at least 60 wt.%.

With preference, the total content of the first and the third polypropylene resin, based on the total weight of the composite material is at least 60 wt.%; preferably, at least 65 wt.%.

With preference, the composite material comprises at least 0.8 wt.% based on the total weight of the composite material of metallic stearate; preferably, at least 0.9 wt.%, more preferably, at least 1.0 wt.%.

With preference, the composite material comprises at most 4.0 wt.% based on the total weight of the composite material of metallic stearate; preferably, at most 3.0 wt.%, more preferably, at most 2.5 wt.%.

In some embodiments, the composite material comprises from 2.2 to 5.5 wt.% of carbon particles based on the total weight of the composite material, and as determined according to ISO 11358-2014; preferably, from 2.5 to 5.0 wt.% of carbon particles, more preferably, from 3.0 to 4.5 wt.% of carbon particles; even more preferably, from 3.2 wt.% to 3.9 wt.%.

With preference, the composite material comprises at least 2.2 wt.% of carbon particles based on the total weight of the composite material; preferably, at least 2.5 wt.%, more preferably, at least 2.8 wt.%, even more preferably, at least 3.0 wt.%, most preferably, at least 3.2 wt.%, and even most preferably, at least 3.4 wt.%.

With preference, the composite material comprises at most 5.5 wt.% of carbon particles based on the total weight of the composite material; preferably, at most 5.0 wt.%; more preferably, at most 4.5 wt.%; even more preferably, at most 4.2 wt.%; most preferably, at most 4.0 wt.%; and even most preferably, at most 3.9 wt.%.

With preference, the composite material comprises from 2.2 to 5.5 wt.% of carbon nanotubes based on the total weight of the composite material, and as determined according to ISO 11358-2014; preferably, from 2.5 to 5.0 wt.% of carbon nanotubes; more preferably, from 3.0 to 4.5 wt.% of carbon nanotubes; even more preferably, from 3.2 wt.% to 3.9 wt.%.

Wth preference, the composite material comprises at least 2.2 wt.% of carbon nanotubes based on the total weight of the composite material; preferably, at least 2.5 wt.%, more preferably, at least 2.8 wt.%, even more preferably, at least 3.0 wt.%, most preferably, at least 3.2 wt.%, and even most preferably, at least 3.4 wt.%.

Wth preference, the composite material comprises at most 5.5 wt.% of carbon nanotubes based on the total weight of the composite material; preferably, at most 5.0 wt.%; more preferably, at most 4.5 wt.%; even more preferably, at most 4.2 wt.%; most preferably, at most 4.0 wt.%; and even most preferably, at most 3.9 wt.%.

Wth preference, in all embodiments, step d) of dry blending and step e) of forming a conductive article by injection moulding are performed together in a single step using a single injection moulding apparatus. Thus, the different components of the composite material are dry blended together and directly provided to the injection moulding apparatus. The different components of the composite material are not melted nor blended nor chopped into pellets before the injection moulding step.

Conducting the dry blending and the shaping of the article by injection moulding in a single step allows to achieve better electrical properties. Indeed, the fact that the composite material is not chopped into pellets before being injection moulded allows reducing the percentage of carbon particles, preferably carbon nanotubes, being damaged under shear so their length is reduced.

Step e) of forming an article

The injection moulding in step e) is preferably selected from the group comprising regular injection moulding, injection blow moulding, injection stretch blow moulding. Preferably, the method is regular injection moulding.

The regular injection moulding process comprises the steps of:

• melting the propylene polymer of the present disclosure, and

• injecting the molten propylene polymer from step (a) into an injection mould to form an injection-moulded article. The injection moulding is performed using methods and equipment well known to the person skilled in the art. In a preferred embodiment, step e) of forming a conductive article by injection moulding of the said composite material is conducted at a temperature of at least 230°C and/or of at most 260 °C. The injection moulding temperature influences the electrical properties obtained. The best electrical properties are obtained at a temperature above 250°C, such as 260°C for example. Test methods

The melt flow index (MI2 _PP ) of the polypropylene is determined according to ISO 1133-2011 at 230 °C under a load of 2.16 kg.

The high load melt flow index (HLMI) of the polypropylene is determined according to ISO 1133-2011 at 230 °C under a load of 21.6 kg. Molecular weights are determined by Size Exclusion Chromatography (SEC) and in particular by IR-detected gel permeation chromatography (GPC) at high temperature (145 °C). A 10 mg polypropylene sample is dissolved at 160 °C in 10 ml_ of trichlorobenzene (technical grade) for 1 hour. Analytical conditions for the GPC-IR from Polymer Char are:

Injection volume: +/- 0.4 ml_; - Automatic sample preparation and injector temperature: 160 °C;

Column temperature: 145 °C;

Detector temperature: 160 °C;

Column set: 2 Shodex AT-806MS and 1 Styragel HT6E;

Flow rate: 1 mL/min; - Mobile Phase: trich!orobenzene stabilized with 1000 ppm of butylhydroxytoluene (BHT) filtered through a 045 pm PTFE filter;

Detector: IR5 Infrared detector (2800-3000 cm ^-1 );

Calibration: Narrow standards of polystyrene (commercially available);

Calculation for polypropylene: Based on Mark-Houwink relation (logio(Mpp) = logio(Mps) - 0.25323); cut off on the low molecular weight end at MPP = 1000;

The molecular weight averages used in establishing molecular weight/property relationships are the number average (M _n ), weight average (M _w ) and z average (M _z ) molecular weight. These averages are defined by the following expressions and are determined from the calculated M,:

Here N, and W, are the number and weight, respectively, of molecules having molecular weight Mi. The third representation in each case (farthest right) defines how one obtains these averages from SEC chromatograms h, is the height (from baseline) of the SEC curve at the i _th elution fraction and M, is the molecular weight of species eluting at this increment. The molecular weight distribution (MWD) is then calculated as Mw/Mn.

The ¹³ C-NMR analysis is performed using a 400 MHz or 500 MHz Bruker NMR spectrometer under conditions such that the signal intensity in the spectrum is directly proportional to the total number of contributing carbon atoms in the sample. Such conditions are well known to the skilled person and include for example sufficient relaxation time etc. In practice, the intensity of a signal is obtained from its integral, i.e. the corresponding area. The data are acquired using proton decoupling, 2000 to 4000 scans per spectrum with 10 mm room temperature through or 240 scans per spectrum with a 10 mm cryoprobe, a pulse repetition delay of 11 seconds and a spectral width of 25000 Hz (+/- 3000 Hz). The sample is prepared by dissolving a sufficient amount of polymer in 1 ,2,4-trichlorobenzene (TCB, 99%, spectroscopic grade) at 130 °C and occasional agitation to homogenize the sample, followed by the addition of hexadeuterobenzene (CeD ₆ , spectroscopic grade) and a minor amount of hexamethyldisiloxane (HMDS, 99.5+ %), with HMDS serving as the internal standard. To give an example, about 200 mg to 600 mg of the polymer is dissolved in 2.0 ml. of TCB, followed by the addition of 0.5 ml. of CeD ₆ and 2 to 3 drops of HMDS. Following data acquisition, the chemical shifts are referenced to the signal of the internal standard HMDS, which is assigned a value of 2.03 ppm. The comonomer content of polypropylene is determined by ¹³ C-NMR analysis of pellets according to the method described by G.J. Ray et al. in Macromolecules, vol. 10, n° 4, 1977, p. 773-778.

Melting temperatures Tm were determined according to ISO 3146-2000 on a DSC Q2000 instrument by TA Instruments. To erase the thermal history the samples are first heated to 200 °C and kept at 200 °C for 3 minutes. The reported melting temperatures Tm are then determined with heating and cooling rates of 20 °C/min.

The content of carbon nanotubes in percentage by weight in blends (%CNT) can be determined by thermal gravimetric analysis (TGA) according to ISO 11358-2014, using a Mettler Toledo STAR TGA/DSC 1 apparatus. Before the determination of the content of carbon nanotubes in % by weight in blends (%CNT), the carbon content of the carbon nanotubes in % by weight (%C-CNT) was determined as follows: 2 to 3 milligrams of carbon nanotubes were placed into a TGA. The material was heated at a rate of 20 °C/min from 30 °C to 600 °C in nitrogen (100 ml/min). At 600 °C, the gas was switched to air (100 ml/min), and the carbon oxidized, yielding the carbon content of the carbon nanotubes in % by weight (%C-CNT). The %C-CNT value was the average of 3 measurements. For the content of carbon nanotubes % by weight in blends (%CNT), 10 to 20 milligrams of the sample were placed into a TGA. The material was heated at a rate of 20 °C/min from 30 °C to 600 °C in nitrogen (100 ml/min). At 600 °C, the gas was switched to air (100 ml/min), and the carbon oxidized, yielding to the carbon content of carbon nanotubes in the sample (%C-sample). The %C-sample value was the average of 3 measurements. The content of carbon nanotubes in % by weight in the sample (%CNT) was then determined by dividing the carbon content of carbon nanotubes in % by weight in samples (%C-sample) by the carbon content of the carbon nanotubes in % by weight (%C-CNT) and multiplying by 100.

%CNT = %C-sample / %C-CNT * 100

The same method applies to the determination of the content of carbon particles.

The surface resistance (SR) (Ohm) was measured according to I EC 61340-4-1 with an SRM110 meter. The SRM110 is a surface resistance tester. Its internal parallel electrodes comply with DIN EN 100 015/1. IEC electrodes were externally connected for tests according to IEC 61340-4-1.

The following non-limiting examples illustrate the disclosure.

Examples:

Example 1: Preparation of a masterbatch comprising carbon nanotubes The carbon nanotubes used were multi-walled carbon nanotubes Nanocyl™ NC 7000, commercially available from Nanocyl. These CNTs have a surface area of 250-300 m ² /g (measured by the BET method), a carbon purity of carbon of about 90 % by weight (measured by thermal gravimetric analysis), an average diameter of 9.5 nm and an average length of 1.5 pm (as measured by transmission electron microscopy).

The second polypropylene resin used is polypropylene PP2 with a melt flow index of 140 g/10 min as measured according to ISO 1133-2011 (230 °C-2.16kg) and a Tm of 150 °C (ISO 3146-2000).

The masterbatch MB1 was prepared by blending polypropylene PP2 and carbon nanotubes, using a classical twin-screw extrusion process. Carbon nanotubes powder and polypropylene were introduced into the extruder such as to obtain a CNT content of about 10 % by weight based on the total weight of the masterbatch. The masterbatch MB1 was blended on Leitstriz co-rotating twin-screw extruder with an L/D ratio of 52 (D=60), the barrel temperature was set at 180°C The properties of the polypropylene-based masterbatches are provided in below table 1. Table 1 - Properties of the PP masterbatch

Example 2: Production of bars

The masterbatch MB1 dry blended with a first polypropylene resin PP1 and injected to form a bar. Injection trials were conducted on an injection press sold by DR BOY. The melt temperature was either 240 or 260 °C, the injection speed was 25 mm/s. The Mold temperature was 40 °C; after introduction in the mold, a pressure of 35 bars is maintained on the polymer during 40 s.

The first polypropylene resin used was polypropylene PP1 commercially available from Total under the tradename PPC 6742. PP1 has an MI2 of 8 g/10 min as measured according to ISO 1133-2011 (230 °C- 2.16 kg) and a melting point of 165 °C as measured according to ISO 3146-2000.

In bars 1 to 5, no zinc stearate was added.

In bars 6 and 7, zinc stearate was added in powder in parallel to the masterbatch. In bars 8 and 9, zinc stearate was added via a ZnSt-PP masterbatch containing 5 wt.% of Zn St based on the total weight of the masterbatch. The polypropylene used in the ZnSt-PP masterbatch was PP1.

The surface resistance was determined at several points of the bar (at least 2 points; with preference, more than 2 points), the difference between the maximum and the minimum value measured is an indication of the homogeneity of the product, the lower the difference, the better the homogeneity.

The properties of the bars are displayed in table 2. The results showed an influence of the barrel temperature on the surface resistance and the homogeneity achieved. It can be seen that a good homogeneity is obtained for the bars wherein zinc stearate is added with a ZnSt- PP masterbatch.

Table 2 - Properties of the bars

(1)

⁽²⁾ added via ZnSt- PP Masterbatch