WO2020157301A1 - Composition de polyoléfine comprenant des structures carbonées à perte diélectrique réduite - Google Patents

Composition de polyoléfine comprenant des structures carbonées à perte diélectrique réduite Download PDF

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Publication number
WO2020157301A1
WO2020157301A1 PCT/EP2020/052472 EP2020052472W WO2020157301A1 WO 2020157301 A1 WO2020157301 A1 WO 2020157301A1 EP 2020052472 W EP2020052472 W EP 2020052472W WO 2020157301 A1 WO2020157301 A1 WO 2020157301A1
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polyolefin composition
structures
base resin
olefin polymer
tan
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PCT/EP2020/052472
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English (en)
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Thomas Gkourmpis
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Borealis Ag
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    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01B—CABLES; CONDUCTORS; INSULATORS; SELECTION OF MATERIALS FOR THEIR CONDUCTIVE, INSULATING OR DIELECTRIC PROPERTIES
    • H01B3/00—Insulators or insulating bodies characterised by the insulating materials; Selection of materials for their insulating or dielectric properties
    • H01B3/18—Insulators or insulating bodies characterised by the insulating materials; Selection of materials for their insulating or dielectric properties mainly consisting of organic substances
    • H01B3/30—Insulators or insulating bodies characterised by the insulating materials; Selection of materials for their insulating or dielectric properties mainly consisting of organic substances plastics; resins; waxes
    • H01B3/44—Insulators or insulating bodies characterised by the insulating materials; Selection of materials for their insulating or dielectric properties mainly consisting of organic substances plastics; resins; waxes vinyl resins; acrylic resins
    • H01B3/441—Insulators or insulating bodies characterised by the insulating materials; Selection of materials for their insulating or dielectric properties mainly consisting of organic substances plastics; resins; waxes vinyl resins; acrylic resins from alkenes
    • C—CHEMISTRY; METALLURGY
    • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
    • C08K—Use of inorganic or non-macromolecular organic substances as compounding ingredients
    • C08K3/00—Use of inorganic substances as compounding ingredients
    • C08K3/02—Elements
    • C08K3/04—Carbon
    • C08K3/042—Graphene or derivatives, e.g. graphene oxides
    • C—CHEMISTRY; METALLURGY
    • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
    • C08K—Use of inorganic or non-macromolecular organic substances as compounding ingredients
    • C08K3/00—Use of inorganic substances as compounding ingredients
    • C08K3/02—Elements
    • C08K3/04—Carbon
    • C08K3/043—Carbon nanocoils

Definitions

  • the present invention relates to a polyolefin composition comprising carbonaceous structures, wherein the polyolefin composition shows decreased dielectric losses. It also relates to the use of the polyolefin composition in a power cable. Further, the invention is also related to an article, preferably a power cable comprising at least one insulating layer comprising the polyolefin composition.
  • Polyolefins produced in a high pressure (HP) process are widely used in demanding polymer applications wherein the polymers must meet high mechanical and/or electrical requirements.
  • HP high pressure
  • the electrical properties of the polymer composition has a significant importance.
  • the requirement for the electrical properties may differ in different cable applications, as is the case between alternating current (AC) and direct current (DC) cable applications.
  • a typical power cable comprises a conductor surrounded, at least, by an inner semiconductive layer, an insulation layer and an outer semiconductive layer, in that order.
  • the tan (d) and thus the dielectric losses (which are linearly proportional to the tan (d)) shall be as low as possible for both technical and economical reasons:
  • Low losses means that low amount of transmitted electric energy is lost as thermal energy inside the cable insulation. These losses will mean economic losses for the power line operator. Low losses will reduce the risk for thermal runaway, i.e. an unstable situation where the temperature of the insulation will increase due to the tan d. When the temperature is increased, normally the tan (d) will also increase. This will further increase the dielectric losses, and thus the temperature. The results will be a dielectric failure of the cable that needs to be replaced. With regard to AC power cables, the problem of dielectric losses is particularly pronounced since the dielectric losses increase dramatically as the voltage increases.
  • US 9,595,374 is related to an alternating current (AC) power cable, comprising a conductor surrounded by at least an inner semiconductive layer comprising a first semiconductive composition, an insulation layer comprising a polymer composition, an outer semiconductive layer comprising a second semiconductive composition and optionally a jacketing layer comprising a jacketing composition, in that order.
  • the polymer composition of the insulation layer comprises a polyolefin and a crosslinking agent, and the polymer composition of the insulation layer has a dielectric loss expressed as tan d (50 Hz) of 12.0x10 -4 or less, when measured at 25 kV/mm and 130° C.
  • polyolefins have been mixed with carbonaceous structures, specifically carbonaceous structures derived from graphite and graphene, in order to alter the properties of the polyolefin including its electrical properties.
  • WO 03/024602 A1 discloses separated graphite nanostructures formed of thin graphite platelets having an aspect ratio of at least 1500: 1.
  • the graphite nanostructures are created from synthetic or natural graphite using a high- pressure mill.
  • the resulting graphite nanostructures can be added to polymeric materials to create polymer composites having increased mechanical characteristics, including an increased flexural modulus, heat deflection temperature, tensile strength, electrical conductivity, and notched impact strength.
  • the effects observed in this disclosure require filler loadings, if added to polypropylene, as high as 38 wt% or 53 wt%.
  • WO 2013/033603 A1 discloses a field grading material which is an insulation material used in electrical installation.
  • the composite material comprises a polymer material and reduced graphene oxide distributed within the polymer material.
  • the reduced graphene oxide supplies non-linear resistivity to the composite material.
  • the graphene nanoparticles may be formed of thin, independent graphite flakes or platelets.
  • the nanoparticles may also be shaped to have corners, or edges that meet to form points.
  • the platelets may be fully isolated from the original graphite particle, or may be partially attached to the original particle. Also, more complex secondary structures such as cones are also included, see for example Schniepp, Journal of Physical Chemistry B, 1 10 (2006) pp. 8535.
  • Graphene nanoplatelets are characterized in that the material is composed of one or several layers of two-dimensional hexagonal lattice of carbon atoms.
  • the platelets have a length parallel to the graphite plane, commonly referred to as lateral diameter, and a thickness orthogonal to the graphite plane, commonly referred to as thickness.
  • Another characteristic feature of GNPs is that the platelets are very thin yet have large lateral diameter, hence GNPs have a very large aspect ratio, i.e. ratio between the lateral diameter and the thickness.
  • Graphene nanoplatelets may also include graphene platelets that are somewhat wrinkled such as for example described in Stankovich et al, Nature 442, (2006), pp. 282. Additionally, graphene materials with wrinkles to another essentially flat geometry are included.
  • the GNPs can be functionalised to improve interaction with the base resins.
  • Non-limiting examples of surface modifications includes treatment with nitric acid; O2 plasma; UV/Ozone; amine; acrylamine such as disclosed in US2004/127621 A1 .
  • the graphene nanoparticles may be derived from treated graphite sheets, e.g. expanded graphite that can be exposed to high temperatures (e.g. in the range of from 600 to 1200 °C) so that the graphite sheets expand in dimension from 100 to 1000 or more times its original volume in an accordion-like fashion in the direction perpendicular to the crystalline planes of the graphite.
  • These agglomerates may assume an elongated shape with dimensions in the order of 1 to 100 pm.
  • AC alternating current
  • MVAC medium voltage alternating current
  • HVAC high voltage alternating current
  • EHVAC extra high voltage alternating current
  • the present invention is based on the surprising finding that all the above objects can be achieved by combining a polyolefin base resin with carbonaceous structures being reduced graphite oxide worm-like (rGOW) structures.
  • the present invention therefore provides an improved polyolefin composition comprising
  • the polyolefin composition is obtained by melt-mixing the olefin polymer base resin (a) with the carbonaceous structures (b).
  • the present invention further provides a power cable comprising an insulating layer which comprises the polyolefin composition according to the invention.
  • the present invention also provides the use of the polyolefin composition according to the invention in an insulating layer of a power cable.
  • the present invention has a number of surprising advantages. Specifically, the invention provides a plastomer-based system, i.e. a system based on an olefin polymer base resin, comprising carbonaceous structures which may exhibit a significant decrease in dielectric losses. It has been surprisingly found that despite the presence of carbonaceous structures, the dielectric losses of the polyolefin composition may be substantially the same or even lower than that of the pure olefin polymer base resin.
  • Fig. 1 a Schematic graphite configuration
  • Fig. 1 b Schematic structure of a rGOW structure
  • Fig. 2 Scanning electron microscopy SEM of an rGOW structure
  • Figs. 3a-c Three different embodiments of a graphite oxidation system
  • Fig. 4 Engineering diagram of one embodiment of a purification and concentration system
  • Fig. 5 Cross-sectional view of one embodiment of a high temperature spray dryer
  • Fig. 6 Flow chart showing the process of one embodiment of a method to produce rGOW particles
  • filler content in the context of the present description refers to the added amount of the carbonaceous structures (b) in weight percent (wt.%) in relation to the weight of the total polyolefin composition.
  • the carbonaceous structures (b) can thus also be labeled as“filler(s)”.
  • carbonaceous structure refers to partially dispersed clusters of a plurality of carbonaceous components, wherein each carbonaceous component is constituted by allotropes of carbon, in particular graphite and graphene.
  • the carbonaceous structures (b) of the present invention are reduced graphite oxide worm-like (rGOW) structures, or particles.
  • the rGOW structures may comprise any number of reduced oxidized graphene platelets, wherein at least some of the platelets are in a plane that is not parallel with that of an adjacent platelet, as shown in Fig. 1 b.
  • the rGOW platelets are referred to as planar, they are typically not as planar as, for example, graphene sheets, but rather include wrinkles and deformities that result from the oxidation/reduction processes by which the particles have been treated. As a result, the rGOW platelets are thicker than graphene sheets although they still retain a generally planar shape having a diameter that is several times greater than the thickness of the platelet. As can be seen in the photomicrograph of Fig. 2, these platelets include multiple sub-sections that are at distinct angles to each other. This unevenness contributes to the high surface area and low bulk density of the particles.
  • An adjacent platelet is defined as a platelet that is joined directly to the given platelet on either major side of the given platelet.
  • a platelet is not adjacent if it is joined to the given platelet via only a third platelet.
  • a platelet may be at an angle to a first adjacent platelet on one side and retain a parallel structure with a second adjacent platelet on the opposed side.
  • Many of the platelets in an rGOW structure can remain in a graphite configuration (see Fig. 1 a) in which they are parallel to each other and remain bound together by van der Waals forces. This is for example illustrated by stacks s1 and s2 in Fig. 1 b.
  • Particles of rGOW structures do not typically have extensive graphitic structures and different embodiments of rGOW structures may be limited to parallel platelet composite structures containing fewer than 15, preferably fewer than 12, more preferably fewer than 1 1 adjacent parallel platelets.
  • rGOW structures exhibit a structure where any dimension of the particle, such as length L or diameter d, is greater than the sum of thicknesses w of all the graphene platelets in the particle. For example, if the thickness w of a single graphene platelet is about 1 nm, then an rGOW structure comprising 1 ,000 platelets would be greater than 1 mhp in both length L and diameter d.
  • rGOW structures also have an extension of at least 50 nm along each of the x, y and z axes as measured through at least one origin in the particle.
  • An rGOW structure is not a planar structure and has a morphology that distinguishes it from both graphite (stacks of graphene platelets) and individual graphene sheets. It is notable however, that rGOW structures can be exfoliated into single platelets, or stacks of platelets, that can have at least one extension along any of x, y and z axes that is less than 100 nm, preferably less than 50 nm, more preferably less than 10 nm, or even more preferably less than 5 nm.
  • the rGOW structures described herein can comprise a plurality of graphene platelets and in various embodiments may include greater than 10, preferably greater than 100, more preferably greater than 1000 graphene platelets.
  • the particles may be linear or serpentine, can take roughly spherical shapes, and in some cases may be cylindrical.
  • the structure of an rGOW structure can be described as accordion-like because of the way the particle expands longitudinally due to the alternating edges at which the platelets remain joined. For example, as shown in Fig.
  • At least some of the adjacent graphene planes are not parallel and are at angles to each other. As may be seen in Fig. 1 b, at least some of the adjacent graphene planes may be positioned at an angle a relatively each other, wherein the angle a may for example be about 25°.
  • Various embodiments may include one or more pairs of adjacent graphene platelets that are joined at angles of, for example, 10°, 25°, 35°, 45°, 60° or 90°. Different adjoining pairs of graphene platelets may remain joined at different edges or points, so the graphene platelets are not necessarily canted in the same direction. If the adjacent graphene platelets remain attached randomly to each other at platelet edges after expansion, the structure will extend in a substantially longitudinal direction.
  • the rGOW structure has a transverse extension, or diameter d, and a longitudinal extension being substantially perpendicular to the transverse extension, or length L. Further, each of the platelets in the rGOW structure has an extension in the longitudinal direction, or thickness w.
  • rGOW structures thus have elongated, expanded, worm-like structures that can have an aspect ratio, i.e. length L/diameter d, that can be preferably 1 : 1 or more, more preferably 2: 1 or more, still more preferably 3: 1 or more, even more preferably 5: 1 or more, or most preferably 10: 1 or more.
  • the aspect ratio is not more than 100: 1 or preferably 50: 1.
  • the length L of a rGOW structure is the longest line that passes through a central longitudinal core of the particle from one end to the other (Fig. 2).
  • This line may be curved or linear, or have portions that are curved or linear, depending on the specific particle.
  • the line runs substantially perpendicular to the average plane of the platelets in any particular portion along the line.
  • the length L of the carbonaceous structures (b) is preferably at least 1.0 pm, more preferably at least 2.0 pm, still more preferably at least 5.0 pm, even more preferably at least 10 pm, or even more preferably at least 100 pm.
  • the length L of the carbonaceous structures (b) is not more than 1000 pm.
  • the diameter d of the carbonaceous structures (b) is deemed to be the diameter of the smallest circle that can fit around the structure at its midpoint (Fig. 2).
  • the diameter d (diameter of the circle shown in Fig. 2) of the carbonaceous structures (b) is preferably equal to or less than 200 pm, more preferably equal to or less than 100 pm, still more preferably equal to or less than 50 pm, still more preferably equal to or less than 20 pm, still more preferably equal to or less than 10 pm, even more preferably equal to or less than 5 pm, even more preferably equal to or less than 2 pm or still more preferably equal to or less than 1 pm.
  • the diameter d is preferably equal to or greater than 50 nm, more preferably equal to or greater than 100 nm, still more preferably equal to or greater than 400 nm, and most preferably equal to or greater than 800 nm.
  • Preferred diameter ranges include 50 nm to 200 pm, 100 nm to 100 pm, 500 nm to 100 pm, 500 nm to 50 pm, 2.0 pm to 30 pm, 2.0 pm to 20 pm, 2.0 pm to 15 pm, 2.0 pm to 10 pm, 1 .0 pm to 5 pm, 100 nm to 5 pm, 100 nm to 2 pm, 100 nm to 1 pm.
  • the diameter d of the carbonaceous structures (b) along its length L need not be constant and can vary by a factor of greater than 2, greater than 3 or greater than 4 along the length L of the carbonaceous structures (b).
  • the carbonaceous structures (b) may contain carbon, oxygen and hydrogen and may be essentially void of other elements. A particle is essentially void of an element if the element is absent or is present only as an impurity. In specific embodiments, the carbonaceous structures (b) can comprise greater than 80%, greater than 90%, greater than 95% or greater than 99% carbon by weight. Some carbonaceous structures (b) may include oxygen, and particularly covalently bound oxygen, at concentrations by weight of greater than 0.1 %, greater than 0.5%, greater than 1 .0%, greater than 5.0%, greater than 10.0%, greater than 14.0%, less than 25%, less than 15%, less than 10%, less than 5.0%, less than 3%, less than 2% or less than 1 .0%.
  • Flydrogen content may be greater than 0.1 % or greater than 1 % by weight. Further, hydrogen content may be less than 1 %, less than 0.1 % or less than 0.01 % by weight. Heteroatoms such as nitrogen or sulfur may be present at amounts greater than 0.01 % or greater than 0.1 % by weight.
  • the carbonaceous structures (b) being reduced graphite oxide worm-like (rGOW) structures can exhibit a low density.
  • the carbonaceous structures (b) have a bulk density of less than 100 g/L, more preferably less than 50 g/L, still more preferably less than 30 g/L, still more preferably less than 20 g/L, even more preferably less than 10 g/L, and preferably greater than 5 g/L, more preferably greater than 10g/L or greater than 15 g/L when measured using ASTM D7481-09.
  • the rGOW structures are in the form of clusters, the density may be between 15 g/L and 100 g/L. In these preferred embodiments, the carbonaceous structures (b) have a density of between 15 and 100 g/L.
  • the rGOW structures are in the form of worms or densified worms.
  • the carbonaceous structures (b) have a density of between 5 and 15 g/L.
  • the carbonaceous structures (b) have a BET (Brunauer, Emmett and Teller, ASTM D6556-04) surface area of at least 200 m 2 /g, more preferably at least 300 m 2 /g, still more preferably at least 400 m 2 /g, still more preferably at least 500 m 2 /g, even more preferably at least 600 m 2 /g, and most preferably at least 650 m 2 /g.
  • the carbonaceous structures (b) have a BET surface area of not more than 10000 m 2 /g, measured according to ASTM D6556-04.
  • the carbonaceous structures (b) may also exhibit high structure, and when measured using oil absorption number (OAN) can exhibit structures of preferably greater than 500 mL/100 g, more preferably greater than 1000 mL/100 g, still more preferably greater than 1500 mL/100 g or most preferably greater than 2000 mL/100 g (ASTM D2414-16).
  • OAN oil absorption number
  • the carbonaceous structures (b) exhibit structures, measured using oil absorption number (OAN), of preferably smaller than 50000 mL/100 g, measured according to ASTM D2414-16.
  • the carbonaceous structures (b) have volatile content of less than 30 %, more preferably of less than 25 %, more preferably of less than 20 %, still more preferably of less than 15 %, even more preferably of less than 10 %, and most preferably of less than 7 %.
  • the carbonaceous structures (b) have volatile content of 0.01 %.
  • the carbonaceous structures (b) can have a volatile content, as measured by thermogravimetric analysis (TGA) from 125°C to 1000°C under inert gas, preferably of greater than 1 %, more preferably of greater than 1.5%, more preferably of greater than 2.0%, still more preferably of greater than 2.5%, and most preferably of greater than 5%. Further, the volatile content by the same technique is preferably less than 30%, more preferably less than 25%, still more preferably less than 20%, even more preferably less than 15%, and most preferably less than 10%.
  • TGA thermogravimetric analysis
  • the high oxygen content lowers the conductivity of the material and makes it insulating. Therefore, graphene oxide used as filler is reduced in order to lower the oxygen content.
  • the oxygen content of the rGOW structures when compared to the parent graphite oxide, can be reduced by at least 25%, at least 50% or at least 75%.
  • the energetic content of the structures (as measured by Differential Scanning Calorimetry, DSC) can be reduced by, for example, at least 25%, at least 50% or at least 75%.
  • the decomposition energy of the rGOW structures can be, for example, less than 150 J/g, less than 100 J/g, less than 50 J/g or less than 20 J/g.
  • the added amount of said carbonaceous structures (b) is in the range of from 0.05 to 0.40 wt.%, more preferably 0.10 to 0.35 wt.% and most preferably 0.15 to 0.30 wt.%, based on the total weight of the insulating polyolefin composition.
  • the graphitic structure of a rGOW structure can be investigated by Raman spectroscopy.
  • Pure graphite has a Raman spectrum with a strong G band (1580 cm 1 ) and non-existent D band (1350 cm 1 ).
  • Graphite oxide exhibits a strong D band as well as G band.
  • Reduced graphite oxide and rGOW structures have a strong D band that in many cases is stronger than the G band (FWHM).
  • the ratio of the D band to G band may be greater than 1 .0, greater than 1 .1 or greater than 1 .2.
  • rGOW structures can often be differentiated from graphite and similar materials due to differences in crystallinity.
  • Crystallinity of rGOW structures can be determined by Raman spectroscopy and in various embodiments the rGOW particles can exhibit crystallinity values of less than 40%, less than 30% or less than 20%.
  • X-ray diffraction can also be helpful in differentiating between graphite and materials such as graphite oxide and rGOW structures that exhibit different interlayer spacing than graphite.
  • Graphite has a strong XRD peak between 25° and 30°, while rGOW structures typically have no discernible peak in this range.
  • carbonaceous structures (b) according to the present invention does not include carbon nanotubes.
  • rGOW reduced graphene oxide worm
  • graphite oxide from graphite such as graphite particles
  • Graphite particles are combined with a mixture of mineral acids such as nitric acid and sulfuric acid.
  • This mixture is then reacted with a strong oxidizer such as chlorate ion, which can be provided via an aqueous chlorate salt solution.
  • the chlorate may be added to a reaction vessel at a constant rate. After a pre-determined amount of chlorate has been added, the system is allowed to purge for an extended period to complete the oxidation reaction and allow the resulting chlorine dioxide to vent from the reaction mixture.
  • the resulting graphite oxide slurry can then be neutralized and/or concentrated, for example by using the methods described herein.
  • the starting material graphite particles may be in any form such as powder, granules or flakes. Suitable graphite can be obtained from any available source, and in some cases natural graphite from Superior Graphite has been found to provide acceptable results. Other providers of graphite include Alfa Aesar and Asbury Carbons. In some embodiments, graphite particles may have a Dgo of less than 1 00 pm.
  • the acid solution that is to be combined with the graphite can be a mixture of mineral acids such as nitric and sulfuric acid. The graphite, nitric acid and sulfuric acid may be combined in any order, but in many embodiments the graphite is added after the nitric acid has been mixed with the sulfuric acid.
  • the embodiments described herein use 68-70 % nitric acid and 96-98% sulfuric acid.
  • the weight ratio of nitric acid (on an anhydrous basis, not including the weight attributable to the water content) to sulfuric acid can be, for example, between 0.2 and 0.4, more preferably between 0.25 and 0.35 or most preferably between 0.26 and 0.32.
  • the ratio of the weight of total acid to graphite can be less than 1 5: 1 , more preferably less than 20: 1 , more preferably less than 30: 1 , or most preferably less than 40: 1 .
  • Specific ranges include preferably between 1 0: 1 and 20: 1 , more preferably between 1 0: 1 and 30: 1 , and most preferably between 1 5: 1 and 25: 1 .
  • the weight ratio of total water to graphite can be less than 1 0.0: 1 , more preferably less than 9.0: 1 , more preferably less than 8.0: 1 , more preferably less than 7.0: 1 or most preferably less than 6.0: 1 .
  • One way of obtaining a lower acid to graphite ratio is to lower the total water to acid ratio.
  • total water is the sum of all sources of water that enter the reaction vessel, including water from the aqueous chlorate solution and water from the nitric acid.
  • the water to acid ratio is the total water compared to the total amount of acid added, on an anhydrous basis.
  • the total water to acid ratio is less than 0.43: 1 , more preferably less than 0.40: 1 , more preferably less than 0.35: 1 , more preferably less than 0.30: 1 or most preferably less than or equal to 0.26: 1 .
  • chlorate addition is started.
  • Chlorate ion (CIO3 ) can be delivered as an aqueous solution of a chlorate salt or as a dry powder.
  • Chlorate salts may be selected from those including an ammonium or alkali metal cation, such as potassium or sodium chlorate.
  • the chlorate salt concentration (including the cation) in aqueous solution can be, by weight, greater than or equal to 40%, more preferably greater than or equal to 50%, more preferably greater than 55% or most preferably greater than 60%.
  • the weight ratio of chlorate to water of the chlorate solution can be in the range of preferably 0.8:1 to 2:1 , more preferably 1 : 1 to 2: 1 or most preferably 1 : 1 to 1.5: 1.
  • the total amount of chlorate used is proportional to the amount of graphite being oxidized and the weight ratio of chlorate to graphite can be, for example, between 2:1 and 10:1 , more preferably between 2: 1 and 8:1 or most preferably between 3:1 and 6: 1.
  • the weight ratio of chlorate to water in the aqueous chlorate feed is greater than 1 : 1 and the ratio of chlorate to graphite is greater than 3:1.
  • Chlorate may be provided to the reaction mixture at a constant or varied rate during the course of the reaction. In some embodiments, it is provided at a constant rate of between 1 and 3 or between 1.5 and 2.5 grams of chlorate per hour per gram of graphite.
  • a flow of gas such as from a sparger
  • a flow of gas can be used to agitate the reaction mixture and/or aid in the removal of chlorine dioxide (CIO2) from the system.
  • gases and gas mixtures include nitrogen and air.
  • Chlorine dioxide is both toxic and reactive.
  • a constant flow of gas such as nitrogen or air, can serve as a diluent to keep the chlorine dioxide below unsafe levels.
  • the sparger gas flow can serve to carry the chlorine dioxide gas to a trap for safe destruction or disposal of the chlorine dioxide.
  • a flow of gas through the reaction medium can also accelerate the removal of chlorine dioxide from the medium, removing a product of reaction and thus accelerating the oxidation process.
  • a gas flow such as in a bubble column reactor can be used in the absence of any other agitation, such as stirring or shaking.
  • a flow of gas such as from a sparger, can be used to agitate the reaction mixture and/or aid in the removal of chlorine dioxide from the system.
  • gases and gas mixtures include nitrogen and air. Chlorine dioxide is both toxic and reactive. If the level of chlorine dioxide in the reaction medium reaches saturation, pure chlorine dioxide bubbles can develop with the potential to explosively decompose.
  • a constant flow of gas such as nitrogen or air
  • gas flow can serve as a diluent to keep the chlorine dioxide below unsafe levels.
  • the chlorine dioxide can be trapped and disposed of safely.
  • the gas flow can also be accompanied by stirring.
  • chlorine dioxide can be removed by sweeping the headspace of the reaction vessel.
  • the lower explosive limit (LEL) of chlorine dioxide is 1 0% by volume, so the target limit for chlorine dioxide levels in the headspace is typically below this level. Levels can be maintained below 1 0% by supplying sweeping gas at about 1 0 times the rate of chlorine dioxide production. If the reaction rate is faster, then the volume of gas should be increased proportionally.
  • the transfer of chlorine dioxide from the liquid medium to the headspace is dependent on the size of the gas/liquid interface. As the volume of a reaction vessel is increased, the ratio of the area of the gas/liquid interface to the volume of reaction medium decreases according to L 2 /L 3 where L is the characteristic length scale of the reaction vessel. As a result, as the size of the reaction vessel increases, the reaction time and purge time need to be increased to provide for the transfer of chlorine dioxide to the headspace. This leads to extended production times that are not tenable in a production scale operation.
  • gas flow through the reaction medium can be effective at removing chlorine dioxide during the chlorate addition reaction phase, after completion of chlorate addition during the purge phase, or during both phases.
  • Gas flow such as sparging, is particularly effective for larger, production scale systems because it is not dependent on the size of the surface area and headspace interface.
  • Fig. 3a One example of an oxidation system 21 0 is shown schematically in Fig. 3a.
  • System 21 0 uses mechanical impeller 212 for agitating the reaction medium 220.
  • Chlorine dioxide gas entering the headspace from reaction medium 220 is represented by arrow 214.
  • Sweeping gas such as nitrogen, is provided through gas inlet 216. Sweeping gas including chlorine dioxide is removed via gas exit 21 8 which leads to a trap or vent for disposal or reclamation.
  • Fig. 3b schematically represents an embodiment of a hybrid reaction system 230.
  • System 230 includes mechanical im peller 212 as in the embodiment of Fig. 3a.
  • system 230 also includes sparger 232 that is positioned at the bottom of the reaction vessel and is fed by sparging gas source 234.
  • the sparger is a ring with 12 to 16 holes drilled in the top to channel gas bubbles under the impeller 21 2.
  • the spinning impeller breaks down and disperses the gas bubbles to create a large gas/liquid interface. This large surface area of gas/liquid interface provides for efficient transfer of chlorine dioxide from the liquid to the gaseous phase.
  • the sparging gas then carries chlorine dioxide from the reaction medium 220 into the headspace.
  • the sparging gas can also dilute chlorine dioxide that is present in the headspace.
  • Gas exit 21 8 provides a pathway for the m ixture of sparging gas, water and chlorine dioxide to leave the reaction vessel.
  • a bubble column reactor can include a sparger but does not use a mechanical agitator.
  • Fig. 3c schematically depicts a bubble column system 250 that relies exclusively on sparging gas for agitation and chlorine dioxide removal.
  • the bubble column of system 250 has a large height to diameter ratio and a low surface interface area to volume ratio.
  • bubble column reactors can have height to diameter ratios of greater than 5: 1 , more preferably greater than 1 0: 1 or most preferably greater than 20: 1 . They can be made of any material that is resistant to low pH , including glass or PTFE lined steel.
  • the residence time of a gas bubble is extended due to the height of the column of reaction medium.
  • One specific embodiment includes a cylindrically shaped reaction vessels having a diameter of 6 inches and a height of 40 inches.
  • this reaction vessel can be charged up to the 25 inch level with graphite and acid, leaving about 1 5 inches for headspace and the addition of sodium chlorate solution.
  • the headspace of the bubble column reactor provides extra volume for expansion of the liquid phase that occurs as a result of the bubble volume contribution to the liquid reaction medium.
  • the absence of a stirring apparatus can free up space in the vessel and allows for attachment of accessories such as pressure inlets, gas exit vents, probes and pressure relief systems that might be difficult to include with reactor designs that include stirrers or other agitation devices.
  • Spargers used to provide sparging gas to bubble columns or alternative reaction vessels can be of any design that can provide an adequate supply of small bubbles capable of providing the desired amount of liquid/gas interface.
  • the sparger is in fluid communication with a gas supply, such as nitrogen or air.
  • Spargers can be made of materials that are resistant to the low pH conditions of the graphite oxidation reaction medium.
  • the spargers can be made from nickel alloys, polymers such as PTFE, or glass. Sparger shapes can be selected to maximize the distribution of bubbles across the cross-sectional area of the vessel.
  • the spargers can take the shape of a ring, a disk, a plate, a sphere, a cylinder or a spoked design where a plurality of perforated arms extend from a central axis.
  • Spargers can include a plurality of holes on either the upper surface, the lower surface, or both.
  • the sparger can be made from a porous material, such as sintered glass, that does not include readily defined holes or perforations.
  • multiple spargers can be used, and each sparger can be controlled independently to allow for tuning of the bubble pattern.
  • the graphite oxidation process is started by combining the nitric acid and sulfuric acid in the reaction vessel.
  • the graphite is then added to the mixture and agitation is started by sparging the mixture with nitrogen.
  • Sodium chlorate solution is fed to the reaction mixture at a constant rate of about 2 g/h chlorate per gram of graphite.
  • the addition process is ceased and the purging phase is started. Sparging is continued and the chlorine dioxide concentration in the reaction mixture is monitored.
  • the chlorine dioxide level drops below a threshold, for instance 1 000, 1 00, 10, 1 or 0.1 ppm by weight, the reaction is deemed complete and the graphite oxide product can be transferred to the concentration and purification stage described below.
  • a vacuum source such as a vacuum pump can be used to reduce the vapor pressure in the head space.
  • the low pressure in the reaction vessel causes bubbles of chlorine dioxide to form in the reaction medium.
  • the chlorine dioxide bubbles rise upward through the liquid into the headspace.
  • a trap or other chlorine dioxide removal device can be positioned between the reaction vessel and the vacuum source.
  • gas bubble formation in the reaction medium can also agitate the medium and keep graphite oxide particles suspended in the fluid.
  • Graphite oxide produced as provided above can be purified and concentrated using techniques including filtration and centrifugation. It has been found that dead end filtration, such as with a Buchner funnel, is ineffective at purification and concentration of graphite oxide because the resulting filter cake becomes too impermeable for obtaining reasonable wash rates. As an alternative to dead end filtration, various tangential flow filtration techniques were attempted. Tangential flow filtration involves passing a slurry or suspension through a tubular membrane and collecting permeate through pores that pass through the walls of the tubular membrane. Tangential flow membranes can include ceramic tubular membranes as well as hollow fiber polymer membranes such as those made from polysulfone or polyvinylidene difluoride (PVDF).
  • PVDF polyvinylidene difluoride
  • Ceramic membranes typically have flow channels between 3 and 6 mm in diameter while hollow fiber polymer membranes have flow channels of about 0.7 to 1 .4 mm in diameter. Tangential flow rates for ceramic membranes are usually about 5 to 10 m/s but are typically lower for polymer membranes and can be, for example, about 1 or 2 m/s. As the graphite oxide slurry has a corrosive pH , ceramic membranes may be preferred over polymer membranes, although polymer membranes may be appropriate for some embodiments. In various embodiments using ceramic membranes, linear flow rates can be less than 7 m/s, less than 5 m/s, less than 4 m/s, less than 3 m/s or less than or equal to 2 m/s.
  • the linear flow rates can be greater than 1 m/s, greater than 2 m/s, greater than 4 m/s or greater than 6 m/s.
  • undesirable shear was realized due to the use of a backpressure valve in the recirculation loop that drives the pressure gradient across the membrane. This left a large pressure drop resulting in shear formation at the backpressure valve.
  • This shear inducing problem was solved by eliminating the backpressure valve and enclosing and pressurizing the entire retentate recirculation system, including the headspace above the retentate reservoir. In this manner, a pressure gradient across the filtration membrane can be maintained without the use of the backpressure valve in the recirculation loop.
  • the enclosed system can be limited to pressure differentials of, for example, no more than 1 5 psi, 10 psi or 5 psi.
  • shear conditions can be further reduced by limiting the fluid flow path to curves and elbows of less than 90°, for example, 45° or less.
  • Tangential flow membrane 31 0 can be a tangential flow membrane capable of filtering acidic aqueous suspensions.
  • ceramic membranes from Pall Corporation can be used.
  • useful membranes may have a pore exclusion size of 0.1 , 0.2, 0.65, 0.8 and 1 .4 pm and can have a membrane area of greater than 0.1 m 2 , greater than 0.2 m 2 or greater than 0.5 m 2 .
  • 7.5 liters of graphite oxide slurry, produced as described herein, are quenched with from 1 5 to 60 liters of deionized (D l) water.
  • the quenched slurry is then pumped from the quench tank to the retentate reservoir 320 using transfer pump 340.
  • Retentate reservoir 320 can be pressurized to, for example, greater than 2, greater than 5, or greater than 8 psi. This allows for the elimination of a backpressure valve that would conventionally be placed between the exit of the membrane 31 0 and retentate reservoir 320.
  • the quenched slurry is flowed into recirculation loop 330 that includes tangential flow membrane 31 0.
  • the graphite oxide slurry is diafiltered at a transmembrane pressure of 9 psi until the volume is reduced to about 5 liters.
  • This volume is then washed with 20 to 30 liters of D l water by continuing diafiltration and adding water via D l water conduit 350 to retentate reservoir 320 at the same rate at which the permeate is lost through permeate drain 360.
  • Pressure is maintained in retentate tank 320 by pressurizing the headspace in the tank with pressurized gas source 370.
  • the diafiltration process continues until impurities such as sulfate, nitrate and chlorate are reduced to acceptable levels, for example, ⁇ 1 000 ppm sulfate or ⁇ 300 ppm nitrate. These levels can be confirmed using, for example, ion chromatography, or can be monitored in line using conductivity detectors.
  • the resulting rGOW particles exhibited good morphology with a BET surface are of greater than 600 m 2 /g.
  • the particles were analyzed for metal content by ICP and were found to contain on average, by weight, ⁇ 30 ppm Fe, ⁇ 20 ppm K, ⁇ 1 000 ppm Na, less than 20 ppm Si, less than 20 ppm Ti and less than 5 ppm (below the detection limit) of each of Ag, Al, As, B, Ba, Ca, Co, Cr, Cu, Mg, Mn, Mo, N i, Pb, Pt, Sb, Te, TI, V, W, Zn and Zr.
  • the graphite oxide can be reduced by removing some or all of the bound oxygen groups from the graphite oxide. This process can also result in high inter-graphene platelet pressure that expands the graphite oxide to produce rGOW particles. This is different from some known reduction processes whereby individual graphene oxide sheets are exfoliated from a graphite oxide particle and subsequently reduced in a separate step. For example, in one known process, graphite oxide can be exfoliated in dilute solution and then chemically reduced or thermally reduced using, for example, a spray reduction process.
  • a high temperature spray drying and reduction process can be preferably used that allows for simultaneously drying and thermally reducing the graphite oxide particles to rGOW particles.
  • rGOW particles include a plurality of reduced graphene oxide sheets that are joined together, but in which at least some of the reduced graphene oxide sheets are positioned in non parallel planes.
  • the particles are exposed instantly to a temperature that exceeds the accelerated decomposition temperature threshold. Any additional energy released into the system by the decomposition reaction can be retained in the system and provides additional energy for maintaining temperature and for vaporizing the water fraction from the graphite oxide particles.
  • a controlled, continuous feed of slurry into the high temperature environment allows the exotherm to be controlled and exploited, in contrast to the batch heating of dried graphite oxide with its associated safety hazards.
  • High temperature chamber 410 is in fluid communication with spray nozzle 420 and electrical gas heater 440.
  • High temperature chamber 410 can be electrically heated, such as by resistance coils that are held in place around the chamber by clips 450.
  • Dry, reduced graphite oxide particles can be collected at outlet 460. Reduced particles can be cooled using cooling gas received via cooling gas inlet 470.
  • H igh temperature chamber 41 0 can be cylindrically shaped and is sized based on the desired rate of production.
  • Spray nozzle 420 is constructed and arranged to provide graphite to the interior of the high temperature chamber 41 0.
  • Nozzle 420 can be liquid cooled and can provide an atomized spray of a graphite oxide slurry to chamber 41 0.
  • the slurry can comprise a suspension of graphite oxide particles in water and the graphite oxide particles can have an average size, for example, of between 5 and 50 pm, and may fall into a size range having a D90 of less than 1 00, less than 50, less than 35 or less than 1 0 pm .
  • Spray nozzle 420 can provide an atomized flow of from about 300 to 1 000 ml_ per hour of a slurry containing between 7.5% and 1 5% graphite oxide by weight. Additional nozzle configurations can provide increased flow rates for larger systems and multiple nozzles may be used with a single high temperature chamber.
  • rGOW particles can exhibit useful properties such as high surface area and low density.
  • the multiple steps involved with producing rGOW particles such as oxidation, purification, concentration, drying and reduction can all affect the properties of the final rGOW particles.
  • a flow chart illustrating one embodiment of the production of rGOW particles from graphite is provided in Fig. 6.
  • Graphite particles are placed in mixture of nitric acid and sulfuric acid and sparging is started.
  • a supply of chlorate is provided to the graphite reaction mixture to oxidize the graphite to graphite oxide (GO).
  • the reaction is allowed to run to completion during a purging phase in which sparging is continued to remove chlorine dioxide gas.
  • the resulting slurry of GO is at a very low pH (less than .5) and is subsequently quenched with Dl water.
  • the quenched slurry is pumped to a tangential filtration system where it is purified and concentrated.
  • the concentrated slurry is further neutralized by the addition of a base.
  • the neutralized slurry is then fed to a high temperature spray dryer where it is simultaneously dried and chemically reduced to produce rGOWparticles.
  • the inventors have surprisingly found that carbonaceous structures (b) of the present invention dispersed in an olefin base resin may change their morphology during compounding step, assumingly due to the dedensification.
  • the final polyolefin composition of the present invention possesses new advanced and surprising properties, which enable new applications.
  • the carbonaceous structures (b) incorporated into the olefin polymer base resin (a) are intimately mixed in the compounding step and may change their morphology thereby.
  • clusters and/or stacks of carbonaceous structures (b) may be at least partly exfoliated in the compounding step to drastically increase BET surface area and decrease the diameter d of the carbonaceous structures.
  • the decrease of tan(b), and thus dielectric losses, of the polyolefin compositions of the present invention is surprisingly achieved.
  • the second value of tan (d) of the polyolefin composition is lower than or substantially the same as the first value of tan (d) of the olefin polymer base resin (a) at a given frequency (the‘first frequency’).
  • the second value of tan (d) of the polyolefin composition is lower than the first value of tan (d) of the olefin polymer base resin (a) at a given frequency (the ‘first frequency’).
  • the second value of tan (d) of the polyolefin composition is lower than the first value of tan (d) of the olefin polymer base resin (a)
  • the second value of tan (d) of the polyolefin composition is at least 0.05 x 10 4 , preferably at least 0.1 x 10 -4 , lower than the first value of tan (d) of the olefin polymer base resin (a) at a given frequency (the‘first frequency’).
  • tan (d) not only means that the second value of tan (d) of the polyolefin composition is the same as the first value of tan (d) of the olefin polymer base resin (a).“Substantially the same” also means that the second value of tan (d) of the polyolefin composition may be higher than the first value of tan (d) of the olefin polymer base resin (a) by 0.05 x 10 4 , preferably by 0.1 x 10 -4 , at a given frequency (the‘first frequency’).
  • the polyolefin composition of the present invention exhibits tan(5) values being lower or substantially the same compared to tan(5) of the olefin polymer base resin (a).
  • the polyolefin composition may preferably have tan(5) of below 10.
  • O x 10 -4 more preferably of below 6.
  • O x 10 -4 still more preferably of below 4.
  • O x 10 -4 even more preferably of below 2.
  • O x 10 -4 and most preferably of below 1.6-x 10 -4 , measured at 50 Hz and 22°C.
  • the tan(5) of the polyolefin composition is not less than O.
  • Tx 10 -7 preferably not less than 0.1 x 10 -6 , measured at 50 Hz and 22°C.
  • the tan(5) is measured as described below.
  • polyolefin or “olefin polymer” encompasses both an olefin homopolymer and a copolymer of an olefin with one or more comonomer(s).
  • “comonomer” refers to copolymerisable monomer units.
  • copolymer refers to an olefin polymer made from at least two different monomers. It includes, for example, copolymers, terpolymers and tetrapolymers.
  • the polyolefin can be any polyolefin, such as a conventional polyolefin, which is suitable as a polymer in an insulating layer of a power cable, preferably of an AC power cable.
  • the olefin polymer base resin (a) is selected from the group consisting of a C2 to Cs olefin homo- or copolymer.
  • the olefin polymer base resin (a) is an olefin homopolymer or copolymer which contains one or more comonomer(s), more preferably an ethylene homo- or copolymer or a propylene homo- or copolymer, and most preferably a polyethylene, which can be made in a low pressure process or a high pressure process.
  • the olefin polymer base resin (a) may be a copolymer of ethylene with at least one comonomer selected from unsaturated esters or a heterophasic propylene copolymer.
  • the olefin polymer base resin (a) can e.g. be a commercially available polymer or can be prepared according to or analogously to known polymerization process described in the chemical literature.
  • the olefin polymer base resin (a), preferably polyethylene, is produced in a low pressure process, it is typically produced by a coordination catalyst, preferably selected from a Ziegler-Natta catalyst, a single site catalyst, which comprises a metallocene and/or non-metallocene catalyst, and/or a Cr catalyst, or any mixture thereof.
  • the catalyst may be supported, e.g. with conventional supports including silica, Al-containing supports and magnesium dichloride based supports.
  • the catalyst is a ZN catalyst, more preferably the catalyst is a non-silica supported ZN catalyst, and most preferably a MgCh- based ZN catalyst.
  • the Ziegler-Natta catalyst further preferably comprises a group 4 (group numbering according to new lUPAC system) metal compound, preferably titanium, magnesium dichloride and aluminium.
  • the polyethylene produced in a low pressure process can have any density, e.g. be a very low density linear polyethylene (VLDPE), a linear low density polyethylene (LLDPE) copolymer of ethylene with one or more comonomer(s), medium density polyethylene (MDPE) or high density polyethylene (HDPE).
  • VLDPE very low density linear polyethylene
  • LLDPE linear low density polyethylene copolymer of ethylene with one or more comonomer(s), medium density polyethylene (MDPE) or high density polyethylene (HDPE).
  • the olefin polymer base resin (a) can be unimodal or multimodal with respect to one or more of molecular weight distribution, comonomer distribution or density distribution.
  • Low pressure polyethylene may be multimodal with respect to molecular weight distribution.
  • Such a multimodal olefin polymer base resin (a) may have at least two polymer components which have different weight average molecular weight, preferably a lower weight average molecular weight (LMW) and a higher weight average molecular weight (HMW).
  • a unimodal olefin polymer base resin (a), preferably low pressure polyethylene, is typically prepared using a single stage polymerization, e.g. solution, slurry or gas phase polymerization, in a manner well-known in the art.
  • a multimodal e.g.
  • bimodal) olefin polymer base resin (a) for example a low pressure polyethylene can be produced by mechanically blending two or more, separately prepared polymer components or by in-situ blending in a multistage polymerization process during the preparation process of the polymer components. Both mechanical and in-situ blending is well-known in the field.
  • a multistage polymerization process may preferably be carried out in a series of reactors, such as a loop reactor, which may be a slurry reactor and/or one or more gas phase reactor(s). Preferably, a loop reactor and at least one gas phase reactor is used.
  • the polymerization may also be preceded by a pre-polymerization step.
  • a LDPE homopolymer or an LDPE copolymer of ethylene with one or more comonomers may be produced.
  • the LDPE homopolymer or copolymer may be unsaturated.
  • ethylene (co)polymers by high pressure radical polymerization reference can be made to the Encyclopedia of Polymer Science and Engineering, Vol. 6 (1986), pp 383-410 and Encyclopedia of Materials: Science and Technology, 2001 Elsevier Science Ltd.: “Polyethylene: High-pressure, R. KIimesch, D.Littmann and F.-O. Mahling pp. 7181 -7184.
  • the olefin polymer base resin (a) may include copolymers of ethylene and unsaturated ester with an ester content of up to 50 wt%, based on the weight of the copolymer.
  • unsaturated esters are vinyl esters, acrylic acid and methacrylic acid esters, typically produced by conventional high pressure processes.
  • the ester can have from 3 to about 20 carbon atoms, preferably 4 to 10 atoms.
  • Non-limiting examples of vinyl esters are: vinyl acetate, vinyl butyrate, and vinyl pivalate.
  • Non-limiting examples of acrylic and methacrylic acid esters are: methyl acrylate, ethyl acrylate, t-butyl acrylate, n- butyl acrylate, isopropyl acrylate, hexyl acrylate, decyl acrylate and lauryl acrylate.
  • the olefin polymer base resin (a) may be ethylene/a-olefin copolymers having an a-olefin content of from 15 wt%, preferably from 25 wt%, based on the weight of the copolymer. These copolymers typically have an a-olefin content of 50 wt% or less, preferably 40 wt% or less and most preferably 35 wt% or less, based on the weight of the copolymer.
  • the a-olefin content is measured by 13 C nuclear magnetic resonance (NMR) spectroscopy as described by Randall (Re. Macromolecular Chem. Phys. C29 (2&3)).
  • the a-olefin is preferably a C3-20 linear, branched or cyclic a-olefin.
  • C3-20 a-olefins include propene, 1 -butene, 4- methyl-1 -pentene, 1 -hexene, 1 -octene, 1 -decene, 1 -dodecene, 1 -tetradecene, 1 -hexadecene and 1 -octadecene.
  • the a-olefins can also contain a cyclic structure, such as cyclohexane or cyclopentane, resulting in an a-olefin such as 3-cyclohexyl-1 -propene and vinyl cyclohexane.
  • a-olefins in the classical sense of the term, for the purpose of this invention certain cyclic olefins such as norbornene and related olefins, particularly 5-ethylidene-2- norbornene, are encompassed by the term “a-olefins” and can be used as described above.
  • styrene and its related olefins e.g.
  • a- methylstyrene are a-olefins for the purpose of this invention.
  • Illustrative examples of copolymers in the sense of the present invention include ethylene/propylene, ethylene/butene, ethylene/1 -hexene, ethylene/1 -octene, ethylene/styrene and similar.
  • Illustrative examples of terpolymers include ethylene/propylene/1 -octene, ethylene/butene/1 -octene, ethylene/propylene/ diene monomer (EPDM) and ethylene/butene/styrene.
  • the copolymer can be random or blocky.
  • Copolymerization can be carried out in the presence of one or more further comonomers which are copolymerizable with ethylene and which, for example, may be selected from vinylcarboxylate esters such as vinyl acetate and vinyl pivalate; (meth)acrylates such as methyl(meth)-acrylate, ethyl(meth)acrylate and butyl(meth)acrylate; (meth)acrylic acid derivatives such as (meth)acrylonitrile and (meth)acrylamide; vinyl ethers, such as vinylmethyl ether and vinylphenyl ether; a-olefins such as propylene, 1 -butene, 1 -hexene, 1 -octene and 4-methyl-1 -pentene; olefinically unsaturated carboxylic acids, such as (meth)acrylic acid, maleic acid and fumaric acid; and aromatic vinyl compounds, such as styrene and alpha-methyl styrene.
  • Preferred comonomers are vinyl ethers of monocarboxylic acids having 1 -4 carbon atoms, such as vinyl acetate and (meth)acrylate of alcohols having 1 -8 carbon atoms, such as methyl(meth)acrylate.
  • the expression ’’(meth)acrylic acid” used herein is intended to include both acrylic acid and methacrylic acid.
  • the comonomer content in the polymer may be present in the amount of 40 wt% or less, preferably 0.5-35 wt%, more preferably 1 -25 wt%.
  • olefin polymers are: polypropylene, e.g. homopolypropylene, propylene copolymer; polybutene, butene copolymers; highly short chain branched a-olefins copolymers with an ethylene co-monomer content of 50 mole percent or less; polyisoprene; EPR (ethylene copolymerized with propylene); EPDM (ethylene copolymerized with propylene and a diene such as hexadiene, dicyclopentadiene, or ethylidene norbornene); copolymers of ethylene and an a-olefin having 3 to 20 carbon atoms such as ethylene/octene copolymers; terpolymers of ethylene, a-olefin and a diene; terpolymers of ethylene, a-olefin and an unsaturated ester; copolymers of ethylene and vinyl- tri-alky
  • the olefin polymer may comprise or may be a heterophasic olefin copolymer, e.g. a heterophasic propylene copolymer.
  • the heterophasic propylene copolymer may preferably be a heterophasic copolymer comprising a propylene random copolymer as matrix phase (RAHECO) or a heterophasic copolymer having a propylene homopolymer as matrix phase (HECO).
  • a random copolymer is a copolymer where the comonomer part is randomly distributed in the polymer chains and it also consists of alternating sequences of two monomeric units of random length (including single molecules).
  • the random propylene copolymer comprises at least one comonomer selected from the group consisting of ethylene and C 4 -C 8 alpha-olefins.
  • Preferred C 4 -C 8 a-olefins are 1 -butene, 1 -pentene, 4-methyl-1 -pentene, 1 - hexene, 1 -heptene or 1 -octene, more preferred 1 -butene.
  • a particularly preferred random propylene copolymer may comprise or consist of propylene and ethylene.
  • the comonomer content of the polypropylene matrix preferably is 0.5 to 10 wt%, more preferably 1 to 8 wt% and even more preferably 2 to 7 wt %.
  • the incorporation of the comonomer can be controlled in such a way that one component of the polypropylene contains more comonomer than the other. Suitable polypropylenes are described e.g. in WO 03/002652.
  • the olefin polymer base resin (a) can be e.g. a commercially available polymer or can be prepared according to or analogously to known polymerization process described in the chemical literature.
  • the olefin polymer base resin (a) is preferably a plastomer.
  • the olefin polymer base resin (a) of the present invention is an ethylene homo- or copolymer.
  • the olefin polymer base resin (a) is a polyethylene produced in a low pressure process, more preferably a high density polyethylene FIDPE produced in a low pressure process.
  • FIDPE polymer The meaning of FIDPE polymer is well known and documented in the literature. Although the term FIDPE is an abbreviation for high density polyethylene, the term is understood not to limit the density range, but covers the HDPE-like LP polyethylenes with low, medium and higher densities. The term FIDPE describes and distinguishes only the nature of LP polyethylene produced in the presence of an olefin polymerisation catalyst with typical features, such as different branching architecture, compared to the PE produced by high pressure radical polymerization.
  • the FIDPE as said olefin polymer base resin (a) means a high density homopolymer of ethylene (referred herein as FIDPE homopolymer) or a Ihigh density copolymer of ethylene with one or more comonomer(s) (referred herein as FIDPE copolymer).
  • the one or more comonomers of FIDPE copolymer are preferably selected from the polar comonomer(s), non-polar comonomer(s) or from a mixture of the polar comonomer(s) and non-polar comonomer(s), as defined above or below.
  • said HDPE homopolymer or HDPE copolymer as said olefin polymer base resin (a) may optionally be unsaturated.
  • a polar comonomer for the HDPE copolymer as said olefin polymer base resin (a), comonomer(s) containing hydroxyl group(s), alkoxy group(s), carbonyl group(s), carboxyl group(s), ether group(s) or ester group(s), or a mixture thereof, can be used. More preferably, comonomer(s) containing carboxyl and/or ester group(s) are used as said polar comonomer. Still more preferably, the polar comonomer(s) of HDPE copolymer is selected from the groups of acrylate(s), methacrylate(s) or acetate(s), or any mixtures thereof.
  • the polar comonomer(s) is preferably selected from the group of alkyl acrylates, alkyl methacrylates or vinyl acetate, or a mixture thereof. Further preferably, said polar comonomers are selected from C1 - to C6-alkyl acrylates, C1 - to C6-alkyl methacrylates or vinyl acetate. Still more preferably, said polar HDPE copolymer is a copolymer of ethylene with C1 - to C4-alkyl acrylate, such as methyl, ethyl, propyl or butyl acrylate, or vinyl acetate, or any mixture thereof.
  • non-polar comonomer(s) for the HDPE copolymer as said olefin polymer base resin (a) comonomer(s) other than the above defined polar comonomers can be used.
  • the non-polar comonomers are other than comonomer(s) containing hydroxyl group(s), alkoxy group(s), carbonyl group(s), carboxyl group(s), ether group(s) or ester group(s).
  • the polyunsaturated comonomer(s) are further described below in relation to unsaturated HDPE copolymers.
  • the HDPE polymer is a copolymer, it preferably comprises 0.001 to 50 wt.-%, more preferably 0.05 to 40 wt.-%, still more preferably less than 35 wt.-%, still more preferably less than 30 wt.-%, more preferably less than 25 wt.-%, of one or more comonomer(s).
  • the HDPE polymer as said olefin polymer base resin (a) is a copolymer of ethylene with C3 to C10 alpha- olefin ⁇ ), such as propylene, 1 -butene, 1 -hexene, 4-methyl-1 -pentene, styrene, 1 -octene, 1 -nonene, or any mixture thereof.
  • the polyolefin composition preferably the olefin polymer base resin (a) thereof, more preferably the HDPE polymer, may optionally be unsaturated, i.e. the polyolefin composition, preferably the olefin polymer base resin (a), more preferably the HDPE polymer, may comprise vinyl groups.
  • unsaturated means herein that the polyolefin composition, preferably the olefin polymer base resin (a), more preferably the HDPE polymer, contains vinyl groups/1000 carbon atoms in a total amount of at least 0.04/1000 carbon atoms.
  • the unsaturation can be provided to the polyolefin composition i.a. by means of the olefin polymer base resin (a), a low molecular weight (Mw) compound(s), such as crosslinking booster(s) or scorch retarder additive(s), or any combinations thereof.
  • a olefin polymer base resin
  • Mw low molecular weight compound(s)
  • crosslinking booster(s) or scorch retarder additive(s) such as crosslinking booster(s) or scorch retarder additive(s), or any combinations thereof.
  • the total amount of vinyl groups in the polyolefin composition means the sum of the vinyl groups present in the vinyl group sources.
  • the content of the vinyl groups is determined according to“Determination of the content of double bonds” as described below in the section“Measurement methods and procedures”.
  • the unsaturation originates at least from an unsaturated olefin polymer base resin (a). More preferably, the unsaturated olefin polymer base resin (a) is an unsaturated polyethylene, more preferably an unsaturated HDPE polymer, even more preferably an unsaturated HDPE homopolymer or an unsaturated HDPE copolymer.
  • the HDPE polymer is an unsaturated HDPE copolymer.
  • an HDPE homopolymer is unsaturated
  • the unsaturation can be provided e.g. by a chain transfer agent (CTA), such as propylene, and/or by polymerization conditions.
  • CTA chain transfer agent
  • the unsaturation can be provided by one or more of the following means: by a chain transfer agent (CTA), by one or more polyunsaturated comonomer(s) or by polymerisation conditions. It is well known that selected polymerisation conditions such as peak temperatures and pressure, can have an influence on the unsaturation level.
  • an unsaturated HDPE copolymer it is preferably an unsaturated HDPE copolymer of ethylene with at least one polyunsaturated comonomer, and optionally with other comonomer(s), such as polar comonomer(s) which is preferably selected from acrylate or acetate comonomer(s).
  • the polyunsaturated comonomers suitable for the unsaturated olefin polymer base resin (a) preferably consist of a straight carbon chain with at least 8 carbon atoms and at least 4 carbons between the non-conjugated double bonds, of which at least one is terminal, more preferably, said polyunsaturated comonomer is a diene, preferably a diene which comprises at least eight carbon atoms, the first carbon-carbon double bond being terminal and the second carbon-carbon double bond being non-conjugated to the first one.
  • Preferred dienes are selected from C8 to C14 non-conjugated dienes or mixtures thereof, more preferably selected from 1 ,7-octadiene, 1 ,9-decadiene, 1 , 1 1 -dodecadiene, 1 , 13-tetradecadiene, 7-methyl-1 ,6-octadiene, 9-methyl-1 ,8- decadiene, or mixtures thereof. Even more preferably, the diene is selected from 1 ,7-octadiene, 1 ,9-decadiene, 1 , 1 1 -dodecadiene, 1 , 13-tetradecadiene, or any mixture thereof, however, without limiting to above dienes.
  • propylene can be used as a comonomer or as a chain transfer agent (CTA), or both, whereby it can contribute to the total amount of the C— C double bonds, preferably to the total amount of the vinyl groups.
  • CTA chain transfer agent
  • a compound which can also act as comonomer, such as propylene is used as CTA for providing double bonds, then said copolymerisable comonomer is not calculated to the comonomer content.
  • the total amount of vinyl groups is preferably higher than 0.05/1000 carbon atoms, more preferably higher than 0.08/1000 carbon atoms, still more preferably of higher than 0.1 1 /1000 carbon atoms and most preferably of higher than 0.15/1000 carbon atoms.
  • the total amount of vinyl groups is of lower than 4.0/1000 carbon atoms.
  • the olefin polymer base resin (a), prior to crosslinking contains preferably vinyl groups in total amount of more than 0.20/1000 carbon atoms, more preferably more than 0.25/1000 carbon atoms, still more preferably of more than 0.30/1000 carbon atoms.
  • the higher vinyl group amounts are preferably provided by an unsaturated HDPE copolymer of ethylene with at least one polyunsaturated comonomer.
  • the preferred olefin polymer base resin (a) for use in the polyolefin composition is a saturated HDPE homopolymer or a saturated HDPE copolymer of ethylene with one or more comonomer(s) or an unsaturated HDPE polymer, which is selected from an unsaturated HDPE homopolymer or an unsaturated HDPE copolymer of ethylene with one or more comonomer(s), preferably with at least one polyunsaturated comonomer.
  • the density of the olefin polymer base resin (a), preferably of the HDPE polymer is higher than 900 kg/m 3 .
  • the density of the olefin polymer base resin (a), preferably of the HDPE polymer, i.e. of the high density ethylene homo- or copolymer is not higher than 980 kg/m 3 , and preferably is from 930 to 975 kg/m 3 , more preferably from 940 to 970 kg/m 3 .
  • the MFR2 (2.16 kg, 190° C) of the olefin polymer base resin (a), preferably of the HDPE polymer, is preferably from 0.1 to 50 g/10 min, more preferably from 0.5 to 25 g/10 min, and most preferably is from 1 .0 to 20 g/10 min.
  • the present invention further provides a power cable comprising an insulating layer which comprises the inventive polyolefin composition.
  • All embodiments of the polyolefin composition described above are also preferred embodiments of the power cable according to the invention.
  • the polyolefin composition of the invention is very suitable for AC power cables, especially for power cables operating at voltages between 6 kV and 36 kV (medium voltage (MV) cables) and at voltages higher than 36 kV, known as high voltage (HV) cables and extra high voltage (EHV) cables, which EHV cables operate, as well known, at very high voltages.
  • the terms have well known meanings and indicate the operating level of such cables.
  • the polymer composition with advantageous low dielectric losses properties is highly suitable HV or EHV AC power cable which operates at voltages higher than 36 kV, preferably at voltages of 40 kV or higher, even at voltages of 50 kV or higher.
  • EHV AC power cables operate at very high voltage ranges e.g as high as up to 800 kV, however without limiting thereto.
  • the power cable of the present invention is preferably a MVAC power cable, a HVAC power cable or an EHVAC power cable.
  • the invention also provides a process for producing an alternating current (AC) power cable, preferably a HV or EHV AC power cable, as defined above, wherein the process comprises the steps of:
  • an inner semiconductive layer comprising a first semiconductive composition, an insulation layer comprising the inventive polyolefin composition, an outer semiconductive layer comprising a second semiconductive composition, and optionally, and preferably, a jacketing layer comprising a jacketing composition, and
  • crosslinking at least the olefin polymer base resin (a) of the polymer composition of the insulation layer, optionally, and preferably, the first semiconductive composition of the inner semiconductive layer, optionally the second semiconductive composition of the outer semiconductive layer and optionally the jacketing composition of the optional jacketing layer, in the presence of a crosslinking agent and at crosslinking conditions.
  • the process comprises the steps of: (a) providing and mixing, preferably meltmixing in an extruder, an optionally crosslinkable first semiconductive composition comprising a polyolefin, a conductive filler, preferably carbon black, and optionally further component(s) for the inner semiconductive layer, providing and mixing, preferably meltmixing in an extruder, the polyolefin composition of the invention for the insulation layer, providing and mixing, preferably meltmixing in an extruder, an optionally crosslinkable second semiconductive composition which comprises a polyolefin, a conductive filler, preferably carbon black, and optionally further component(s) for the outer semiconductive layer, providing and mixing, preferably meltmixing in an extruder, an optionally crosslinkable jacketing composition which comprises a polyolefin and optionally further component(s) for the outer semiconductive layer,
  • step (b) applying on a conductor, preferably by coextrusion, a meltmix of the first semiconductive composition obtained from step (a) to form the inner semiconductive layer, a meltmix of polyolefin composition of the invention obtained from step (a) to form the insulation layer, a meltmix of the second semiconductive composition obtained from step (a) to form the outer semiconductive layer, a meltmix of the jacketing composition obtained from step (a) to form the shield jacketing layer, and
  • Melt mixing means mixing above the melting point of at least the major polymer component(s) of the obtained mixture and is typically carried out in a temperature of at least 10-15°C above the melting or softening point of polymer component(s).
  • (co)extrusion means herein that in case of two or more layers, said layers can be extruded in separate steps, or at least two or all of said layers can be coextruded in a same extrusion step, as well known in the art.
  • (co)extrusion” means herein also that all or part of the layer(s) are formed simultaneously using one or more extrusion heads. For instance triple extrusion can be used for forming three cable layers.
  • the polyolefin composition of the invention and the first and second semiconductive compositions and the optional, and preferable, jacketing composition can be produced before or during the cable production process.
  • the polyolefin composition of the insulation layer, the first and second semiconductive compositions and the optional, and preferable, jacketing composition can each independently comprise part or all of the component(s) thereof before introducing to the (melt) mixing step a) of the cable production process.
  • part or all of the polyolefin composition preferably at least the olefin polymer base resin (a) is in form of powder, grain or pellets, when provided to the cable production process.
  • Pellets can be of any size and shape and can be produced by any conventional pelletising device, such as a pelletising extruder.
  • the polyolefin composition comprises said optional further component(s).
  • the carbonaceous structures (b) and part or all of said further component(s) may e.g. be added 1 ) by meltmixing to the olefin polymer base resin (a), which may be in a form as obtained from a polymerisation process, and then the obtained meltmix is pelletised, and/or
  • part or all of the further component(s) can be meltmixed together with the pellets and then the obtained meltmix is pelletised; and/or part or all of the further components can be impregnated to the solid pellets.
  • the polyolefin composition may be prepared in connection with the cable production line e.g. by providing the olefin polymer base resin (a), preferably in form of pellets, which may optionally comprise part of the carbonaceous structures (b) and/or part of the further component(s), and combined with all or rest of the carbonaceous structures (b) and/or all or rest of the further component(s) in the mixing step a) to provide a (melt) mix for the step b) of the process of the invention.
  • the pellets of the olefin polymer base resin (a) contain part of the carbonaceous structures (b) and/or the further component(s)
  • the pellets may be prepared as described in the above first embodiment.
  • the further component(s) is preferably selected at least from one or more additive(s), preferably at least from free radical generating agent(s), more preferably from peroxide(s), optionally, and preferably, from antioxidant(s) and optionally from scorch retardant(s) as mentioned above.
  • the mixing step a) of the provided polyolefin composition, the first and second semiconductive compositions and the optional, and preferable, jacketing composition is preferably carried out in the cable extruder.
  • the step a) may optionally comprise a separate mixing step, e.g. in a mixer, preceding the cable extruder. Mixing in the preceding separate mixer can be carried out by mixing with or without external heating (heating with an external source) of the component(s). Any further component(s) of the polyolefin composition or the first and second semiconductive composition and the optional, and preferable, jacketing composition, if present and added during the cable production process, can be added at any stage and any point(s) in to the cable extruder, or to the optional separate mixer preceding the cable extruder.
  • the addition of additives can be made simultaneously or separately as such, preferably in liquid form, or in a well known master batch, and at any stage during the mixing step (a).
  • the (melt) mix of the polyolefin composition obtained from (melt) mixing step (a) consists of the olefin polymer base resin (a) of the invention as the sole polymer component and of the carbonaceous structures (b).
  • the optional, and preferable, additive(s) can be added to polyolefin composition as such or as a mixture with a carrier polymer, i.e. in a form of so- called master batch.
  • the mixture of the polyolefin composition of the insulation layer and the mixture of each of the first and second semiconductive compositions and the optional, and preferable, jacketing composition obtained from step (a) is a meltmix produced at least in an extruder.
  • At least the polyolefin composition of the insulation layer of the invention is provided to the cable production process in a form of premade pellets.
  • a crosslinked MV, HV or EHV AC power cable is produced, which comprises a conductor surrounded by an inner semiconductive layer comprising, preferably consisting of, a first semiconductive composition, an insulation layer comprising, preferably consisting of, a crosslinkable polyolefin composition of the invention comprising a olefin polymer base resin (a), carbonaceous structures (b) and a crosslinking agent, preferably peroxide, as defined below, an outer semiconductive layer comprising, preferably consisting of, a second semiconductive composition, and the optional, and preferable, jacketing layer comprising, preferably consisting of, the jacketing composition, wherein at least the polyolefin composition of the insulation layer is crosslinked in the presence of said crosslinking agent, more preferably, wherein at least the first semiconductive composition of the inner semiconductive layer and the polyolefin composition of the insulation layer are crosslinked.
  • the crosslinking agent(s) can already be present in the first and second semiconductive composition before introducing to the crosslinking step (c) or introduced during the crosslinking step (c).
  • Peroxide is the preferred crosslinking agent for said first and second semiconductive compositions and for the optional, and preferable, jacketing composition in case any of said layer(s) are crosslinked, and is then preferably included to the pellets of semiconductive compositions and the pellets of the jacketing composition before the composition is used in the cable production process as described above.
  • Crosslinking can be carried out at increased temperature which is chosen, as well known, depending on the type of crosslinking agent. For instance temperatures above 150° C. are typical, however without limiting thereto.
  • the polyolefin composition of the present invention may be crosslinkable.
  • Crosslinkable means that when the polyolefin composition is used in cable applications, the cable layer can be crosslinked before the use in the end application thereof.
  • interpolymer crosslinks bridges
  • Crosslinking can be initiated by free radical reaction using irradiation or preferably using a crosslinking agent, which is typically a free radical generating agent, or by the incorporation of crosslinkable groups into polymer component(s), as known in the art.
  • the crosslinking step of the semiconductive composition is typically carried out after the formation of the cable.
  • the peroxide can be any suitable peroxide conventionally used in the field.
  • Crosslinking may also be achieved by incorporation of crosslinkable groups, preferably hydrolysable silane groups, into the olefin polymer base resin (a) of the polyolefin composition.
  • the hydrolysable silane groups may be introduced into the olefin polymer base resin (a) by copolymerisation of e.g. ethylene monomers with silane group containing comonomers or by grafting with silane groups containing compounds, i.e. by chemical modification of the polymer by addition of silane groups mostly in a free radical grafting process.
  • silane groups containing comonomers and compounds are well-known in the field and are commercially available.
  • the hydrolysable silane groups are typically then crosslinked by hydrolysis and subsequent condensation in the presence of a silanol-condensation catalyst and water trace in a manner known in the art. Also, silane crosslinking technique is well-known in the art.
  • the crosslinkable polyolefin composition of the insulation layer comprises crosslinking agent(s), preferably free radical generating agent(s), more preferably peroxide.
  • crosslinking agent(s) preferably free radical generating agent(s)
  • the crosslinking of at least the insulation layer, and optionally, and preferably, of the at least one semiconductive layer is preferably carried out by free radical reaction using one or more free radical generating agents, preferably peroxide(s).
  • the crosslinking agent is preferably used in an amount of less than 10 wt%, more preferably in an amount of between 0.05 to 8 wt%, still more preferably in an amount of 0.2 to 3 wt% and even more preferably in an amount of 0.3 to 2.5 wt% with respect to the total weight of the composition to be crosslinked.
  • peroxidic crosslinking agents are organic peroxides, such as di-ferf-amylperoxide, 2,5-di(ferf-butylperoxy)-2,5-dimethyl-3-hexyne, 2,5-di(ferf-butylperoxy)-2,5-dimethylhexane, ferf-butylcumylperoxide, di (tert- butyl)peroxide, dicumylperoxide, butyl-4, 4-bis(ferf-butylperoxy)-valerate, 1 , 1 - bis(ferf-butylperoxy)-3,3,5-trimethylcyclohexane, ferf-butylperoxybenzoate, dibenzoylperoxide, bis(ferf butylperoxyisopropyl)benzene, 2,5-dimethyl-2,5- di(benzoylperoxy)hexane, 1 , 1 -di(ferf-
  • the peroxide is selected from 2,5-di(ferf-butylperoxy)-2,5-dimethylhexane, di (tert- butylperoxyisopropyl)benzene, dicumylperoxide, ferf-butylcumylperoxide, di(ferf-butyl)peroxide, or mixtures thereof.
  • Insulating layers for MV, HV or EHV, preferably for HV or EHV, AC power cables generally have a thickness of at least 2 mm, typically of at least 2.3 mm, when measured from a cross section of the insulation layer of the cable, and the thickness increases with increasing voltage the cable is designed for.
  • the polyolefin composition can preferably comprise further additive(s), such as antioxidant(s), stabiliser(s), water tree retardant additive(s), processing aid(s), scorch retarder(s), filler(s), metal deactivator(s), free radical generating agent(s), crosslinking booster(s), flame retardant additive(s), acid or ion scavenger(s), additional inorganic filler(s), voltage stabilizer(s) or any mixtures thereof.
  • additives such as antioxidant(s), stabiliser(s), water tree retardant additive(s), processing aid(s), scorch retarder(s), filler(s), metal deactivator(s), free radical generating agent(s), crosslinking booster(s), flame retardant additive(s), acid or ion scavenger(s), additional inorganic filler(s), voltage stabilizer(s) or any mixtures thereof.
  • additives such as antioxidant(s), stabiliser(s), water tree retardant additive(s), processing aid(s), scorch retarder(s), fill
  • Non-limiting examples of antioxidants are sterically hindered or semi-hindered phenols, aromatic amines, aliphatic sterically hindered amines, organic phosphites or phosphonites, thio compounds, and mixtures thereof.
  • the antioxidant is selected from the group of diphenyl amines and diphenyl sulfides.
  • the phenyl substituents of these compounds may be substituted with further groups such as alkyl, alkylaryl, arylalkyl or hydroxy groups.
  • the phenyl groups of diphenyl amines and diphenyl sulfides are substituted with ferf-butyl groups, preferably in meta or para position, which may bear further substituents such as phenyl groups.
  • the antioxidant is selected from the group of 4,4'- bis(1 , Tdimethylbenzyl)diphenylamine, para-oriented styrenated diphenylamines, 6,6'-di-ferf-butyl-2,2'-thiodi-p-cresol, tris(2-ferf-butyl-4-thio-(2'- methyl-4'hydroxy-5'-ferf-butyl)phenyl-5-methyl)phenylphosphite, polymerized 2,2,4-trimethyl-1 ,2-dihydroquinoline, or derivatives thereof.
  • the antioxidants is selected from the group of 4,4'- bis(1 , Tdimethylbenzyl)diphenylamine, para-oriented styrenated diphenylamines, 6,6'-di-ferf-butyl-2,2'-thiodi-p-cresol, tris(2-ferf-butyl-4-thio-(2'- methyl-4'hydroxy-5'
  • the amount of an antioxidant is preferably from 0.005 to 2.5 wt%, based on the total weight of the polyolefin composition, more preferably from 0.005 to 2 wt%, still more preferably from 0.01 to 1.5 wt%, and even more preferably from 0.04 to 1 .2 wt%, based on the total weight of the polyolefin composition.
  • the scorch retarder is a well-known additive type in the field and can i.e. prevent premature crosslinking. As also known the SR may also contribute to the unsaturation level of the polymer composition.
  • scorch retarders are allyl compounds, such as dimers of aromatic alpha-methyl alkenyl monomers, preferably 2,4-di-phenyl-4-methyl-1 -pentene, substituted or unsubstituted diphenylethylenes, quinone derivatives, hydroquinone derivatives, monofunctional vinyl containing esters and ethers, monocyclic hydrocarbons having at least two or more double bonds, or mixtures thereof.
  • the amount of a scorch retarder is within the range of 0.005 to 2.0 wt%, more preferably within the range of 0.005 to 1.5 wt%, based on the total weight of the polyolefin composition. Further preferred ranges are e.g. from 0.01 to 0.8 wt%, 0.03 to 0.75 wt%, 0.03 to 0.70 wt%, or 0.04 to 0.60 wt%, based on the total weight of the polyolefin composition.
  • One preferred SR added to the semiconductive composition is 2,4-diphenyl-4-methyl-1 -pentene.
  • processing aids include metal salts of carboxylic acids such as zinc stearate or calcium stearate; fatty acids; fatty amids; polyethylene wax; copolymers of ethylene oxide and propylene oxide; petroleum waxes; non-ionic surfactants and polysiloxanes.
  • Non-limiting examples of additional fillers are clays precipitated silica and silicates; fumed silica calcium carbonate.
  • compounding embraces mixing of the material according to standard methods to those skilled in the art.
  • Non-limiting examples of compounding equipments are continuous single or twin screw mixers such as FarellTM, Werner and PfleidererTM , Kobelco BollingTM and BussTM, or internal batch mixers, such as BrabenderTM or BanburyTM.
  • Any suitable process known in the art may be used for the preparation of the polyolefin compositions of the present invention such as dry-mixing, solution mixing, solution shear mixing, melt mixing, extrusion, etc. It is however preferred to prepare the polyolefin composition by melt-mixing said olefin polymer base resin (a) with carbonaceous structures (b) in an extruder, such as a Brabender compounder.
  • the present invention is also directed to a process for producing the preferred inventive polyolefin composition, which may comprise pre-mixing of the carbonaceous structures (b).
  • Pre-mixing as used herein shall indicate that the mixing occurs before the resulting mixture is contacted and mixed with the olefin polymer base resin (a).
  • the premixing may be conducted in a dispersant such as isopropanol.
  • the olefin polymer base resin (a) is subsequently added to the dispersed carbonaceous structures (b) and/or filler mixture, before the complete mixture is introduced into a compounder, preferably an extruder, such as a Brabender compounder, as will be described in greater detail below.
  • the present invention is concerned with a polyolefin composition obtainable by such a process.
  • the present invention also provides a polyolefin composition obtained by melt-mixing the olefin polymer base resin (a) with carbonaceous structures (b).
  • melt-mixing is performed in an extruder.
  • the temperature for melt-mixing mainly depends on the type of olefin polymer base resin (a) employed.
  • melt-mixing is carried out at a temperature in the range of 125 °C to 230 °C, more preferably 135 °C to 220 °C.
  • the carbonaceous structures (b) are pre-mixed as defined above.
  • All embodiments of the polyolefin composition described above are also preferred embodiments of the polyolefin composition obtained by melt-mixing the olefin polymer base resin (a) with carbonaceous structures (b). That is, the polyolefin composition obtained by melt-mixing the olefin polymer base resin (a) with carbonaceous structures (b) has a second value of tan (d) at a first frequency which is lower than or substantially the same as a first value of tan (d) at the first frequency of the olefin polymer base resin (a).
  • the present invention also relates to the use of the polyolefin composition in an insulating layer of a power cable, preferably an AC power cable as described above. All embodiments of the polyolefin composition described above and all embodiments of the power cable described above are also preferred embodiments of the use according to the invention.
  • the present invention further provides the use of carbonaceous structures being reduced graphite oxide worm-like (rGOW) structures (b) for reducing the dielectric loss of a polyolefin composition comprising an olefin polymer base resin (a).
  • Said polyolefin composition hence comprises said carbonaceous structures, preferably in the amounts as described herein. All preferred embodiments of the carbonaceous structures being reduced graphite oxide worm-like (rGOW) structures (b) and of the polyolefin composition described above are also preferred embodiments of the use of the carbonaceous structures being reduced graphite oxide worm-like (rGOW) structures (b).
  • PE1 A cross-linkable polyethylene, which is prepared by high pressure polymerization process and which has a density of 922 kg/m 3 and an MFR2 (2.16 kg, 190 °C) of 2 g/10 min, is used as olefin polymer base resin for preparing the composition of comparative example 1 (CE1 ).
  • Said olefin polymer base resin is in the form of pellets which contains dicumyl peroxide as a cross-linking agent.
  • PE1 is commercially available from Borealis AG.
  • PE2 A unimodal high density copolymer of ethylene and 1 -butene (comonomer content of 0.8 mol%) (HDPE), which is prepared by a low pressure polymerization process in a gas phase reactor and which has a density of 962 kg/m3 and an MFR2 (2.16kg, 190 °C) of 12 g/10min, is used as olefin polymer base resin for preparing the compositions of comparative examples 2 (CE2 to CE6) and of the inventive example (IE1 ).
  • PE2 is commercially available from Borealis AG
  • GNP M-25 was obtained from XG Sciences, Lansing, Ml USA. It consists of carbonaceous structures having a BET surface area of 120 to 150 m 2 /g, a particle size distribution of 5 to 25 pm, and a content of volatiles of lower than 1 wt%.
  • CS are carbonaceous structures which form worm-like structures and are obtained from Cabot Corporation, Boston, MA, USA. CS can be obtained by the process as described herein.
  • the MFR2 was measured with 2.16 kg load at 190°C for polyethylene and at 230°C for polypropylene according to ISO 1 133.
  • the MFR21 was measured with 21.6 kg load at 190°C for polyethylene and at 230°C for polypropylene according to ISO 1 133.
  • T m Melt temperature
  • DSC Differential Scanning Calorimetry
  • the procedure for the determination of the amount of double bonds/1000 C- atoms is based upon the ASTM D3124-72 method. In that method, a detailed description for the determination of vinylidene groups/1000 C-atoms is given based on 2, 3-dimethyl-1 ,3-butadiene. This sample preparation procedure has also been applied for the determination of vinyl groups/1000 C-atoms, vinylidene groups/1000 C-atoms and trans-v inylene groups/1000 C-atoms in the present invention.
  • Thin films were pressed with a thickness of 0.5-1 .0 mm. The actual thickness was measured.
  • FT-IR analysis was performed on a Perkin Elmer 2000. Four scans were recorded with a resolution of 4 cm 1 .
  • a base line was drawn from 980 cm -1 to around 840 cm 1 .
  • the peak heights were determined at around 888 cm -1 for vinylidene, around 910 cm -1 for vinyl and around 965 cm -1 for trans-v inylene.
  • Densities are determined using a method similar to ASTM D7481 - 09, i.e. weighing a specified volume of material after at least three taps. (f) BET surface area
  • Particle size distribution is determined by scanning electron microscopy without statistical analysis.
  • the powder sample was sprinkled onto an aluminum stub affixed with conductive carbon sticker for SEM imaging.
  • the SEM micrograph was taken using a Zeiss Ultraplus field emission SEM using the InLens secondary electron detector. An acceleration voltage of 10kV, aperture of 7 pm and a working distance of 2.6 mm were used to acquire this image.
  • Measurements were performed using a Novocontrol Alpha spectrometer in the frequency range of 10 2 to 10 7 Hz, at different temperatures in the range 20- 130°C with an error of ⁇ 0.1 °C, at atmospheric pressure and under nitrogen atmosphere.
  • the sample cell consisted of two stainless steel electrodes 40 mm in diameter and the sample with a thickness of 0.1 mm. Each measurement was carried out six times, and average values were recorded.
  • the plaques were moulded at 180°C for 300 s without pressure. Thereafter, the pressure was increased to 367 N/cm 2 while temperature was kept constant for additional 300 s. Finally, the temperature was decreased using the cooling rate 15 °C/min until room temperature was reached when the pressure was released. The plaque thickness was determined immediately after the compression moulding. The final plaques had a thickness of 0.1 mm and a round sample of the same thickness and of a diameter of 40 mm was cut out.
  • Sample preparation for CE1 Plaques were compression moulded from pellets of the test polymer composition. Mylar foils were put between the pellets and the lower and upper metal plates. The plaques were moulded at 120°C for 60 s at 40 N/cm 2 . Thereafter, the pressure was increased to 392 N/cm 2 and the temperature increased at a rate of 18°C/min to 180°C. The temperature was kept constant at 180°C for 480 s during which the plaque became fully crosslinked by means of the peroxide present in the test polymer composition. Finally, the temperature was decreased using the cooling rate 15 °C/min until room temperature was reached when the pressure was released. The plaque thickness was determined immediately after the compression moulding. The final plaques had a thickness of 0.1 mm and a round sample of the same thickness and of a diameter of 40 mm was cut out.
  • Filled polyolefin compositions having incorporated carbonaceous structures were prepared as follows:

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Abstract

La présente invention concerne une composition de polyoléfine comprenant (a) une résine de base de polymère d'oléfine ayant une première valeur de tan (δ) à une première fréquence, et (b) des structures carbonées étant des structures de type vis sans fin d'oxyde de graphite réduit (rGOW), la composition de polyoléfine ayant une seconde valeur de tan (δ) à ladite première fréquence, et ladite seconde valeur de tan (δ) à une première fréquence est inférieure ou sensiblement égale à la première valeur de tan (δ) à ladite première fréquence. En outre, l'invention concerne un câble d'alimentation comprenant une couche isolante qui comprend la composition de polyoléfine et l'utilisation de la composition de polyoléfine dans une couche isolante d'un câble d'alimentation.
PCT/EP2020/052472 2019-01-31 2020-01-31 Composition de polyoléfine comprenant des structures carbonées à perte diélectrique réduite WO2020157301A1 (fr)

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