Glass fibre reinforced thermoplastic polymer composition

Abstract

The present invention relates to a glass fibre reinforced thermoplastic polymer composition comprising a core and a thermoplastic polymer sheath surrounding said core, wherein the core comprises glass fibres and an impregnating agent and the sheath comprises a thermoplastic polymer and a carbon fiber. The invention further relates to a method for producing such compositions as well as structural parts made therefrom.

Description

[0001] 24POLYOQ24-WO-ORD 1

[0002] GLASS FIBRE REINFORCED THERMOPLASTIC POLYMER COMPOSITION

[0003] The present invention generally relates to a glass fibre reinforced thermoplastic polymer, and a method for producing the same. In particular, the present invention relates to a long glass fibre reinforced thermoplastic polymer such as a long glass fibre reinforced polypropylene. Such materials are used in applications requiring high stiffness, such as for example front-end module, tailgate, instrument panel carriers and other automotive parts.

[0004] Long glass fibre reinforced polypropylene materials are known per se and for example commercially available from SABIC under the brand name STAMAX™. These long glass fibre reinforced polypropylene materials are available as pellets comprising a core and a polypropylene sheath surrounding said core, wherein the core comprises glass fibres extending in a longitudinal direction of the pellet and an impregnating agent.

[0005] WO 2009 / 080281 discloses a method for the manufacture of said type of long glass fibre reinforced polypropylene materials. That method comprises the subsequent steps of:

[0006] a) unwinding from a package of at least one continuous glass multifilament strand comprising at most 2% by mass of a sizing composition;

[0007] b) applying from 0.5 to 20% by mass of an impregnating agent to said at least one continuous glass multifilament strand to form an impregnated continuous multifilament strand;

[0008] c) applying a sheath of thermoplastic polymer around the impregnated continuous multifilament strand to form a sheathed continuous multifilament strand; characterized in that the impregnating agent is non-volatile, has a melting point of at least 20°C below the melting point of the thermoplastic matrix, has a viscosity of from 2.5 to 100 cS at application temperature, and is compatible with the thermoplastic polymer to be reinforced.

[0009] Another process to manufacture long glass fibre reinforced polypropylene materials is based on what is known as a pultrusion process. In such a process, continuous glass multifibre strands are pulled through a molten resin in such a manner that the individual 24POLYOQ24-WO-ORD 2

[0010] filaments are fully dispersed into said resin. Examples of such processes are disclosed in EP1364760, NL1010646 and WO 2008 / 089963.

[0011] The term “multifilament strand” as used in W02009 / 080821 and the term “multifibre strand” as used should be regarded as synonyms and referring to the same type of material, which are often also referred to as roving.

[0012] An important difference between the pultrusion grade long glass fibre reinforced polypropylene materials and the long glass fibre reinforced thermoplastic polymer materials according to the present invention is that the glass fibres in the present invention are not dispersed in the thermoplastic polymer. This dispersion will only take place once the materials are moulded into finished or semi-finished parts in downstream conversion processes, such as for example injection moulding.

[0013] To allow a proper dispersion of the glass fibres in such downstream conversion processes the core of the pellets not only contains the glass fibres but also what is referred to as an impregnating agent. The impregnating agent facilitates a proper dispersion of the glass fibres during the moulding of the (semi) finished article. The impregnating agent is an important component of these long glass fibre reinforced thermoplastic polymer materials. In effect the impregnating agent has at least two key functions, the first one being to effectively couple the glass fibres to each other and to the thermoplastic polymer sheath in the pellet and the second one being to provide a sufficient dispersion of the glass fibres in downstream conversion processes.

[0014] Long glass fiber reinforced thermoplastic polymer is specifically used in many auto semi-structural and structural applications. Some examples are front-end carrier, door module, tailgate, instrument panel etc. However, the automotive industry is always looking for innovative lightweight material solution to further reduce part weight. In recent time, sustainability and lower CO2 footprint have become key drivers in the automotive industry.

[0015] Carbon fiber reinforced thermoplastic material are available in the market, which can provide higher mechanical property and lower weight but are not adopted extensively due to higher cost. 24POLYOQ24-WO-ORD 3

[0016] Thermoplastic material with hybrid reinforcements (glass fiber and carbon fiber) can provide improved specific performance of the material at acceptable cost. Further, recycled carbon fiber can be used in the hybrid filler system to improve CO2 footprint of this thermoplastic material. It is known in the field to impregnate hybrid fiber filaments comprising both glass fiber and recycled carbon fiber with a thermoplastic resin, such as polypropylene, to produce long fiber reinforced thermoplastic materials, as disclosed in for example CN114131784A, CN116041752A, US20170297274A1 , and

[0017] US20190337271 A1.

[0018] There is still a need in the field to provide long fiber reinforced thermoplastic materials with improved performance and reduced weight.

[0019] In one aspect, the present invention provides a glass fibre reinforced thermoplastic polymer composition comprising a core that extends in the longitudinal direction and a thermoplastic polymer sheath intimately surrounding said core, wherein the core comprises glass fibres and an impregnating agent, wherein the sheath comprises a thermoplastic polymer and a carbon fiber;

[0020] wherein the sheath is substantially free of the glass fiber and the core is substantively free of the carbon fiber; and

[0021] wherein the amount of the glass fiber and the amount of the carbon fiber is respectively 8-30 wt%, based on the total weight of the composition.

[0022] Thermoplastic polymer

[0023] The glass fiber-reinforced thermoplastic polymer composition of the present invention comprises a thermoplastic polymer sheath. The thermoplastic polymer sheath comprises at least one thermoplastic polymer.

[0024] In the thermoplastic polymer composition of the present invention, the core is substantially free of a thermoplastic polymer.

[0025] In one embodiment, the amount of the thermoplastic polymer is 45-85 wt%, preferably 50-80 wt%, more preferably 60-70 wt%, based on the total weight of the composition. 24POLYOQ24-WO-ORD 4

[0026] Suitable examples of the thermoplastic polymer include polyamides, such as polyamide 6, polyamide 66, or polyamide 46; polyolefins like polypropylenes and polyethylenes, including polyolefin homopolymer, copolymer or any blend thereof; polyesters, such as polyethylene terephthalate, polybutylene terephthalate; polycarbonates; polyphenylene ethers (PPE); polyphenylene sulphide (PPS); polyurethanes; also any type of polymer blends and compounds and any combinations thereon.

[0027] More particularly, polypropylene, polybutylene terephthalate and polyamide 6 may be used.

[0028] In some instances, the thermoplastic polymer is free of phthalates.

[0029] Polypropylene

[0030] In some instances, the thermoplastic polymer sheath of the present invention comprises at least one polypropylene polymer, which can be (a1) a propylene homopolymer, (a2) a random copolymer of propylene and at least one other olefin, (a3) a propylene impact copolymer, (a4) a modified- or functionalized-propylene homopolymer or copolymer, or mixtures thereof.

[0031] The polypropylene is preferably crystallizable. The term “crystallizable” generally means that the polymer has an isotactic structure, i.e. its isotacticity is high, for instance higher than 95% and preferably higher than 98%.

[0032] A random copolymer generally contains at most about 20 mol % of other olefins as comonomer, preferably at most 10 mol %, to retain crystalline character. The at least one other olefin may be for instance an alpha-olefin, in particular a 1 -alkene having for instance 2 or 4-20, preferably 4-12, carbon atoms or cyclic olefins, optionally containing more than one ring, having a double bond in the ring structure. Examples of suitable olefins include ethylene, butene, hexene, styrene, cyclopentene and norbornadiene. Preferably, the alpha-olefin is a 1 -alkene having 2, 4, 6 or 8 carbon atoms, more preferably, the alpha-olefin is ethylene.

[0033] Preferably, the polypropylene polymer is a propylene impact copolymer, because this results in a favorable combination of stiffness and toughness. Propylene impact 24POLY0024-WO-ORD 5

[0034] copolymers are also referred to as propylene block-copolymers or as heterophasic polypropylene copolymers. Such material basically has at least a two-phase structure, consisting of a crystalline propylene-based matrix and a dispersed elastomeric phase, typically an ethylene-olefin copolymer like an ethylene-propylene rubber (EPR). These polypropylenes are generally prepared in one or more reactors, by polymerization of propylene in the presence of a catalyst, and subsequent polymerization of an ethyleneolefin copolymer like an ethylene-propylene rubber (EPR), but may also be prepared by blending individual components, as is well known to a skilled person. The resulting polymeric materials are heterophasic, but their specific morphology usually depends on the preparation method and monomer types and ratios. In some instances, the thermoplastic polymer should have least one crystalline melting point (Tm) between 120 and 170C wherein the Tm has a heat capacity (dHm) of at least 10 J / g. Tm and dHm are determined by DSC as per ASTM D3418 with a heating rate of 20C / min.

[0035] Generally, the impact copolymer contains about 50-95 mass % of a crystalline propylene homo- or random-copolymer matrix, and about 50-5 mass % of dispersed copolymer of ethylene and at least one other olefin.

[0036] The amount of dispersed phase is preferably 10-35 mass %, more preferably 14-30 mass % of the total amount of heterophasic polymer, to arrive at a desired stiffnessimpact balance in the composition according to the invention.

[0037] The dispersed phase comprises a copolymer of ethylene and at least one other olefin, preferably a C3 to C10 alpha-olefin. Examples of suitable C3 to C10 alpha-olefins include 1-butene, 1-pentene, 4-methyl-1 -pentene, 1-hexene, 1-heptene and 1-octene. Preferably, an ethylene-propylene copolymer, known also as ethylene-propylene rubber (EPR) is used as the dispersed phase.

[0038] The amounts of the propylene-based matrix and the dispersed ethylene-olefin copolymer may be determined by NMR, as well known in the art.

[0039] Preferably, the propylene-based matrix is a propylene homopolymer. 24POLY0024-WO-ORD 6

[0040] Preferably, the melt flow index (MFI) of the propylene-based matrix (MFIPP) is at least 10 dg / min and at most 120 dg / min, measured according to ISO1133 (2.16 kg / 230°C). MFIPPmay be for example at least 40 dg / min, at least 45 dg / min, at least 50 dg / min, at least 55 dg / min or at least 60 dg / min, and / or for example at most 110 dg / min, at most 100 dg / min, at most 90 dg / min or at most 80 dg / min, measured according to ISO1133 (2.16 kg / 230°C).

[0041] The propylene-based matrix is preferably semi-crystalline, that is, it is not 100% amorphous, nor is it 100% crystalline. For example, the propylene-based matrix is at least 40% crystalline, for example at least 50%, for example at least 60% crystalline and / or for example at most 80% crystalline, for example at most 70% crystalline. For example, the propylene-based matrix has a crystallinity of 60 to 70%. For purpose of the present invention, the degree of crystallinity of the propylene-based matrix is measured using differential scanning calorimetry (DSC) according to ISO11357-1 and ISO11357-3 of 1997, using a scan rate of 10°C / min, a sample of 5mg and the second heating curve using as a theoretical standard fora 100% crystalline material 207.1 J / g.

[0042] The MFI of the dispersed ethylene-olefin copolymer (MFIEPR) may be for example at least 0.001 dg / min, at least 0.01 dg / min, at least 0.1 dg / min, at least 0.3 dg / min, at least 0.7 dg / min, at least 1 dg / min, and / or for example at most 30 dg / min, at most 20 dg / min, at most 15 dg / min, at most 10 dg / min, at most 5 dg / min, at most 3 dg / min, as measured according to ISO1133 (2.16 kg / 230°C).

[0043] The amount of ethylene in the ethylene-olefin copolymer is preferably in the range from 20 to 80 wt% based on the ethylene-olefin copolymer, more preferably, the amount of ethylene in the ethylene-olefin copolymer is from 25 to 65 wt%, more preferably from 35 to 55 wt%, more preferably from 40 to 50 wt%.

[0044] Preferably, the a-olefin in the ethylene-a-olefin copolymer is propylene.

[0045] The MFI of the polypropylene polymer is in the range from 10 to 100 dg / min, preferably in the range from 20 to 60 dg / min, more preferably in the range from 25 to 55 dg / min, even more preferably in the range from 28 to 40 dg / min as measured according to ISO1133 (2.16 kg / 230°C). 24POLYOQ24-WO-ORD 7

[0046] The xylene soluble part of the polypropylene polymer according to the invention is in the range from 5 to 40 wt%, preferably in the range from 10 to 35 wt%, more preferably in the range from 15 to 30 wt% as measured according to by ISO16152:2005.

[0047] The intrinsic viscosity of the xylene soluble part of the polypropylene is preferably in the range from 1.2 to 5.6 dl / g, preferably in the range from 1.8 to 4.0 dl / g, even more preferably in the range from 2.3 to 3.5 dl / g as measured according to IS01628-1:2009 in decalin at 135 °C.

[0048] The thermoplastic polymer sheath may also comprise a modified polypropylene; this generally improves properties by affecting glass fibers-polypropylene interactions. Examples of suitable modified polypropylenes are polypropylenes grafted with for instance an unsaturated organic compound, like a carboxylic acid, an anhydride, an ester, glycidyl esters or salts thereof. Suitable examples include maleic, fumaric, (meth)acrylic, itaconic or cinnamic acid or anhydride, ester or carboxylic acid salt thereof. Preferably, maleic anhydride is used. The amount of modified polypropylene may vary widely, but for economic reasons the amount normally will be rather low, for instance less than 5 mass %, preferably less than 4, 3, 2 or even 1 mass % (based on total composition).

[0049] The polypropylene polymer according to present invention can be produced using any conventional technique known to the skilled person, for example multistage process polymerization, such as bulk polymerization, gas phase polymerization, slurry polymerization, solution polymerization or any combinations thereof. Any conventional catalyst systems, for example, Ziegler-Natta or metallocene may be used. Such techniques and catalysts are described, for example, in W006 / 010414; Polypropylene and other Polyolefins, by Ser van der Ven, Studies in Polymer Science 7, Elsevier 1990; W006 / 010414; US4399054 and US4472524. Preferably, the polypropylene is made using Ziegler-Natta catalyst.

[0050] Recycled Polypropylene

[0051] In the present invention, preferably at least a part of the polypropylene used in the polymer sheath is a recycled material. In one embodiment, the thermoplastic polymer sheath comprises a virgin polypropylene and a recycled polypropylene, the amount of 24POLY0024-WO-ORD 8

[0052] the recycled polypropylene is in the range of 10-90wt%, for example, 20wt%, 30wt%, 40wt%, 50wt%, 60wt%, 70wt%, or 80wt%, based on the total amount of the polypropylene. In one embodiment, the weight ratio between the virgin polypropylene and the recycled polypropylene is in the range of 1:9-9: 1.

[0053] In one embodiment, the polymer sheath comprises 0-30 wt% of recycled thermoplastic polymer, based on the total weight of the composition.

[0054] Virgin plastic is new, direct resin produced using for example natural gas or crude oil and without any recycled materials. On the other hand, recycled plastic is a recycled resin that has gone through its lifecycle as a virgin plastic.

[0055] Recycled plastic is normally produced from mechanical recycling or chemical recycling. It can also be a bio-based material. The most common method for the recycling of plastic waste is mechanical recycling. This process typically includes collection, sorting, washing and grinding of the material. Steps may occur in a different order, multiple times or not at all, depending on the origins and composition of the waste.

[0056] The mechanically recycled polymer can be a post-consumer recycled (PCR) polymer or a post-industrial recycled (PIR) polymer.

[0057] A post-consumer recycled (PCR) material refers to material that is made from items recycled by consumers. Usually, recyclable items such as plastics, metals and cardboards / paper are collected by the local recycling program and transported to facilities for sorting based on material type. Recycled bales will then be purchased and sent to different recyclers to be used for a variety of finished products. Using PCR / PIR content, namely recycled materials, for new products results in environmental benefits of carbon savings and resource efficiency. Also, it reduces the demand for virgin raw materials and improves the end-of-life of the materials. The inclusion of PCR / PIR into production supports the development of a circular economy.

[0058] The PCR / PIR polypropylene can be a propylene homopolymer, a propylene copolymer including random copolymers and (multi)block copolymers or a heterophasic propylene copolymer, having propylene monomer units at an amount of at least 50 wt%, for 24POLY0024-WO-ORD 9

[0059] example at least 80 wt%. The PCR / PIR polypropylene can also be a mixture of at least two of the above polypropylenes.

[0060] Preferably, the PCR / PIR polypropylene has a melt flow index similar to that of the virgin polypropylene described above.

[0061] Preferably, the PCR / PIR polypropylene has an ash content, measured according to ISO 3451-1:2019 at 550°C, of 200-6000 ppm, preferably 300-4500 ppm, more preferably 500-3000 ppm. In comparison, a virgin polypropylene normally has an ash content that is substantively lower, such as lower than 100 ppm, preferably lower than 10 ppm, more preferably lower than 1 ppm, even more preferably 0 ppm, as measured according to ISO 3451-1:2019 at 550°C.

[0062] Glass Fibers

[0063] The glass fibre reinforced thermoplastic polymer composition of the present invention comprises a core, wherein the core comprises glass fibres.

[0064] In general, glass fiber is a glassy cylindrical substance where its length is significantly longer than the diameter of its cross section. It is known that adding glass fibers is able to improve the mechanical performance (e.g. strength and stiffness) of polymeric matrix. The level of performance improvement depends heavily on the properties of the glass fibers, e.g. diameter, length and surface property of the glass fiber.

[0065] In one embodiment, the composition of the present invention comprises 8-30 wt%, preferably 10-28 wt%, more preferably 15-25 wt%, even more preferably about 20 wt% of glass fiber, based on the total weight of the composition.

[0066] In one embodiment, the composition of the present invention comprises 10 to 30 wt% of the core, and 65 to 90 wt% of the thermoplastic polymer sheath.

[0067] In some instances, the glass fibers of the present invention have a length of 1-50 mm, preferably 10-25 mm, more preferably 10-20 mm. A composition containing glass fibers of length greater than 1 mm is generally referred to as a long glass fiber (LGF) reinforced composition, for example a LGF PP composition. 24POLYOQ24-WO-ORD 10

[0068] In contrast, short glass fiber compositions or compounds typically contain fibers of length below 1 mm. Such compounds are typically made by mixing chopped strands of pre-determined length with a thermoplastic polymer in an extruder, during which the glass fibers are dispersed in the molten thermoplastic. Because of fiber breakage occurring during this process the fiber length is decreased. Upon molding the composition into an article, the fibers are further reduced in size.

[0069] Long glass fiber-reinforced polymer compositions in the form of, for example, pellets or granules can be prepared from continuous lengths of fibers by a sheathing or wirecoating process, by crosshead extrusion or several pultrusion techniques. Using these technologies, fiber strands impregnated or coated with a polymer are formed; these may then be cut into lengths, and the pellets or granules thus obtained can be further processed, e.g. by injection molding or extrusion processes, into (semi)-finished articles.

[0070] In a pultrusion process, a bundle of continuous glass filaments is spread out into individual filaments and drawn through an impregnation die, into which molten thermoplastic is injected, aiming at entirely wetting and impregnating each filament with the molten thermoplastic. A strand of diameter of about 3 mm is drawn from the die and then cooled. Finally, the strand is chopped into segments of the desired length. The glass fibers are generally parallel to one another in the segment, with each fiber being individually surrounded by the thermoplastic.

[0071] The process of sheathing or wire-coating is done without wetting fibers individually with thermoplastic, but by forming a continuous outer sheath, also called coating or skin, of a thermoplastic material around the continuous multifilament strand surface. The sheathed continuous strand is chopped into pellets or granules of desired length, e.g. for about 15 mm length, in which the fibers are generally parallel to one another and have the same length as the pellets or granules. The LGF pellets are further supplied to an injection molding or extrusion molding machine, and during this molding step the glass fibers are dispersed within the thermoplastic polymer and formed into molded (semi)-finished articles. Documents EP 0921919 B1 and EP 0994978 B1 describe a typical sheathing or wire-coating method. 24POLYOQ24-WO-ORD 11

[0072] The weight average length of the glass fibers in the standard ISO527 testing bar is preferably at least 2 mm, to result in higher strength and stiffness, more preferably at least 3, 4, 5 or even 6 mm. Too high a length may cause some problems, for example in processing or in surface appearance of the molded article, therefore the length of the glass fibers in the composition of the invention is preferably at most 40 mm, more preferably at most 30, 25, 20 or 15 mm.

[0073] The roving density of the continuous glass multifilament strand may vary within wide limits. Preferably, the continuous multifilament strand may have of from 500 to 10000 g / km and more preferably from 2000 to 5000 g / km, because of high throughput. The diameter of the glass filaments in the continuous multifilament strand may widely vary. Preferably, the diameter of the glass filaments ranges from 5 to 50 microns, more preferably from 10 to 30 microns and most preferably from 15 to 25 microns. Glass filaments diameters outside these ranges tend to result in a decrease of mechanical properties and / or enhanced abrasion of the equipment used.

[0074] Carbon Fiber

[0075] The glass fiber-reinforced thermoplastic polymer composition of the present invention comprises a thermoplastic polymer sheath. The thermoplastic polymer sheath comprises a carbon fiber, as a filler of the thermoplastic polymer.

[0076] In one embodiment, the sheath consists of the thermoplastic polymer and the carbon fiber.

[0077] Talc and short glass fiber are also commonly used fillers for the thermoplastic polymer sheath in the field, however, for the purpose of the present invention, the sheath comprises at most 10 wt%, preferably at most 5 wt%, more preferably at most 1 wt%, even more preferably 0 wt%, of talc and at most 10 wt%, preferably at most 5 wt%, more preferably at most 1 wt%, even more preferably 0 wt%, of short glass fiber with a length of at most 1 mm, based on the weight of the carbon fiber.

[0078] Carbon fibers or carbon fibres (alternatively CF, graphite fiber or graphite fibre) can be fibers of any suitable length, diameter, and aspect ratio. In some examples, the fibers 24POLYOQ24-WO-ORD 12

[0079] can be fibers of about 5 to about 10 micrometers in diameter and composed mostly of carbon atoms. The atomic structure of carbon fiber is typically similar to that of graphite, which includes sheets of carbon atoms arranged in a regular hexagonal pattern (graphene sheets), the difference between the two being the way these sheets interlock.

[0080] Depending upon the precursor to make the fiber, carbon fiber can be turbostatic or graphitic, or have a hybrid structure with both graphitic and turbostratic parts present. In turbostratic carbon fiber the sheets of carbon atoms are haphazardly folded, or "crumpled" together. For example, carbon fibers derived from polyacrylonitrile (PAN) are turbostratic, whereas carbon fibers derived from mesophase pitch are graphitic after heat treatment at temperatures exceeding 2200 °C. Turbostratic carbon fibers tend to have high tensile strength, whereas heat-treated mesophase-pitch-derived carbon fibers have high Young's modulus (i.e., high stiffness or resistance to extension under load) and high thermal conductivity.

[0081] In one embodiment, the composition of the present invention comprises 8-30 wt%, preferably 10-28 wt%, more preferably 15-25 wt%, even more preferably about 20 wt% of carbon fiber, based on the total weight of the composition.

[0082] In one embodiment, a weight ratio between the glass fiber and the carbon fiber is 1 :3-3:1, preferably 1:2-2: 1, more preferably about 1:1.

[0083] In one embodiment, a total amount of the glass fiber and the carbon fiber is 10-50 wt%, preferably 15-45 wt%, more preferably 20-40 wt%, based on the total weight of the composition.

[0084] In one embodiment, the length of the carbon fiber is between 0.1-3 mm, preferably 0.2-2 mm, more preferably between 0.2-1 mm.

[0085] In one embodiment, the carbon fiber used in the composition of the present invention is a recycled carbon fiber (rCF). Recycled carbon fiber helps in improving stiffness & strength of the hybrid material with density reduction while long glass fiber helps in providing toughness, impact performance and economical cost. Incorporation of 24POLY0024-WO-ORD 13

[0086] recycled carbon fiber material further helps in lowering CO2 footprint. As mentioned above, recycled polypropylene can also be used to further lower CO2 footprint.

[0087] The recycled carbon fiber can be produced from mechanical recycling or chemical recycling. The mechanically recycled carbon fiber can be a post-consumer recycled (PCR) carbon fiber or a post-industrial recycled (PIR) carbon fiber.

[0088] Examples of the recycled carbon fiber may include standard modulus recycled carbon fiber grades supplied by Vartega Inc., or similar recycled carbon fiber grades supplied by Procotex.

[0089] In one embodiment, the composition of the present invention comprises 8-30 wt%, preferably 10-28 wt%, more preferably 15-25 wt%, even more preferably about 20 wt% of recycled carbon fiber, based on the total weight of the composition.

[0090] In one embodiment, the weight ratio between the virgin carbon fiber and the recycled carbon fiber is in the range of 1 :9-9: 1.

[0091] In one embodiment, the recycled carbon fiber has an ash content between 200-6000 ppm, as measured according to ISO 3451-1:2019 at 550°C, preferably 300-4500 ppm, more preferably 500-3000 ppm. In comparison, a virgin carbon fiber normally has an ash content that is substantively lower, such as lower than 100 ppm, preferably lower than 10 ppm, more preferably lower than 1 ppm, even more preferably 0 ppm, as measured according to ISO 3451-1:2019 at 550°C.

[0092] For the purpose of the present invention, the carbon fiber can be used in two approaches. In one embodiment, a carbon fiber and polypropylene compound is produced on the compounding line, which is then introduced through hopper in the extruder and injected as sheath around the plurality of glass fiber filaments to form a sheathed bundle during cable wiring process to achieve hybrid systems. This approach can be called 2-step approach. Amount of glass fiber and carbon fiber can be easily controlled to achieve desired performance including mechanical, impact and lightweighting. Glass fiber length can vary from 10mm-25mm, while carbon fiber length can vary from 0.2-1 mm. 24POLYOQ24-WO-ORD 14

[0093] In another embodiment, the carbon fiber is introduced directly through the side feeder while polypropylene (PP) is introduced through the hopper, thus PP and CF are mixed in the extruder and injected as a sheath around the plurality of filaments to form a sheathed bundle during cable wiring process to achieve hybrid systems. This approach can be called 1-step approach or in-situ approach. Amount of glass fiber and carbon fiber can be easily controlled to achieve desired performance including mechanical, impact and light-weighting. Glass fiber length can vary from 10mm-25mm, while CF length can vary from 0.2-1 mm.

[0094] Impregnating agent

[0095] The glass fibre reinforced thermoplastic polymer composition of the present invention comprises a core, wherein the core comprises an impregnating agent.

[0096] In one embodiment, the core consists of the glass fiber and the impregnating agent.

[0097] The amount of the impregnating agent applied to the thermoplastic composition depends on the amount of the glass fibers, on the thermoplastic polymer, on the size (diameter) of the glass fibers, and on the type of sizing that is on the surface of the fibers.

[0098] According to the present invention, the amount of impregnating agent applied to the thermoplastic composition should be at least 0.5% by mass, preferably it is at least 1% by mass, more preferably at least 1.5% by mass, such as at least 2.0%, at least 2.5%, at least 3.0%, or at least 3.5% by mass; but should be at most 20% by mass, preferably it is at most 10% by mass, more preferably at most 5.5% by mass, such as at most 5.0%, or at most 4.5% by mass, based on the total weight of the glass fibre reinforced thermoplastic composition. A suitable amount of impregnating agent is needed to assist homogeneous dispersion of glass fibers in the thermoplastic polymer matrix during moulding, but the amount should not be too high, because an excess of the agent may result in decrease of mechanical properties of the moulded articles.

[0099] It is found that the lower the viscosity of the thermoplastic polymer matrix is, the less impregnating agent can be applied. For instance, in case the thermoplastic polymer 24POLYOQ24-WO-ORD 15

[0100] matrix is polypropylene homopolymer with a melt index MFI of 25 to 65 g / 10 min (230°C / 2.16 kg) and the reinforcing long glass filaments have a diameter of 19 micron, the impregnating agent is preferably applied to the multifilament strand in an amount of from 2 to 10% by mass.

[0101] The impregnating agent used in the present invention is at least one compound that is compatible with the thermoplastic polymer matrix to be reinforced, enabling it to enhance dispersion of the glass fibers in the thermoplastic polymer matrix during the moulding process.

[0102] The viscosity of the impregnating agent should be at most 100 cS, preferably at most 75 cS and more preferably at most 25 cS at application temperature. The viscosity of the impregnating agent should be at least 2.5 cS, preferably at least 5 cS, and more preferably at least 7 cS at the application temperature. An impregnating agent having a viscosity higher than 100 cS is difficult to apply to the continuous glass multifilament strand. Low viscosity is needed to facilitate good wetting performance of the fibers, but an impregnating agent having a viscosity lower than 2.5 cS is difficult to handle, e.g., the amount to be applied is difficult to control; and the impregnating agent could become volatile. Without wishing to be bound to any theory, the inventors believe that the impregnation of the continuous glass multifilament strands, without separating or spreading of individual filaments, by the impregnating agent is driven mainly by capillary forces.

[0103] For purpose of the invention, unless otherwise stated, the viscosity of the impregnating agent is measured in accordance with ASTM D 3236-15 (standard test method for apparent viscosity of hot melt adhesives and coating materials, Brookfield viscometer Model RVDV 2, #27 spindle, 5 r / min) at 100° C.

[0104] The melting point of the impregnating agent is at least about 20°C below the melting point of the thermoplastic matrix. Without being wished to be bound to any theory, the inventors think this difference in melting points, and thus in solidification or crystallisation points, promotes fiber impregnation also after applying the thermoplastic sheath and cooling the sheathed strand, and fiber dispersion during subsequent moulding. Preferably, the impregnating agent has a melting point at least 25 or 30°C 24POLYOQ24-WO-ORD 16

[0105] below the melting point of the thermoplastic matrix. For instance, when the thermoplastic polymer matrix is polypropylene having a melting point of about 160°C, the melting point of the impregnating agent may be at most about 140°C.

[0106] The application temperature is chosen such that the desired viscosity range is obtained, and is preferably below the self-ignition temperature of the impregnating agent. For example, when the matrix is polypropylene, the application temperature of the impregnating agent can be from 150 to 240°C.

[0107] According to the present invention, the impregnating agent should be compatible with the thermoplastic polymer to be reinforced, and may even be soluble in said polymer.

[0108] According to the present invention, the impregnating agent is non-volatile, and substantially solvent-free. Being non-volatile means that the impregnating agent does not evaporate under the application and processing conditions applied; that is it has a boiling point or range higher than said processing temperatures. In the context of present application, “substantially solvent-free” means that impregnating agent contains less than 10% by mass of solvent, preferably less than 5% by mass solvent. Most preferably, the impregnating agent does not contain any organic solvent.

[0109] Examples of suitable impregnating agents are disclosed in WO 2009 / 080281 , WO2015062825A1, WO2016083327A1, and EP24152164.0.

[0110] Generally speaking, for the purpose of the present invention, the impregnating agent comprises a microcrystalline wax, and / or a hyper branched alpha olefin, and / or a synthetic hydrocarbon wax.

[0111] In one aspect of the present invention, the impregnating agent has one or more of the following properties,

[0112] a congealing point of from 55 to 95°C, preferably 60-90°C, as determined in accordance with ASTMD938, such as 65, 70, 75, 80 or 85°C,

[0113] a needle penetration at 110°F (43.3°C) of from 25 to 60, preferably 30-50, tenths of a mm as determined in accordance with ASTM D1321 , such as 35 or 40 tenths of a mm, 24POLY0024-WO-ORD 17

[0114] a dynamic viscosity at 100°C of from 5 to 45 cP, preferably 10-30 cP as determined in accordance with ASTM D3236, such as 15, 20 or 25 cP.

[0115] Polyolefin-based elastomer

[0116] In one aspect of the present invention, the thermoplastic polymer sheath further comprises a polyolefin-based elastomer. The polyolefin-based elastomer is mainly an ethylene-a-olefin copolymer, in which the a-olefin comonomer has 4 to 10 carbon atoms, preferably 4 to 8 carbon atoms, more preferably is an acyclic monoolefin such as 1-butene, 1- pentene, 1-hexene, 1-octene, or 4-methyl-1 -pentene.

[0117] The polyolefin-based elastomer is preferably selected from a group consisting of ethylene- 1-butene copolymer, ethylene-1-hexene copolymer, ethylene- 1-octene copolymer and mixtures thereof, more preferably, the elastomer is selected from ethylene- 1-octene copolymer. Most preferably, the elastomer is an ethylene- 1-octene copolymer.

[0118] Preferably the density of the polyolefin-based elastomer is in the range from 0.840 to 0.890 g / cm3, preferably in the range from 0.848 to 0.865 g / cm3, more preferably in the range from 0.853 to 0.860 g / cm3 as measured according to ASTM D792-13.

[0119] Preferably the MFI of the polyolefin-based elastomer is in the range from 0.5 to 18.0, preferably in the range from 0.8 to 14.2 dg / min as measured according to ASTM D1238-13, 190°C, 2.16kg.

[0120] The shore A hardness of the polyolefin-based elastomer is preferably in the range from 35 to 90, preferably in the range from 42 to 69, more preferably in the range from 47 to 60 as measured according to ASTM D2240-15, 1s.

[0121] The polyolefin-based elastomers which are suitable for use in the current invention are commercially available for example under the trademark EXACT™ available from Exxon Chemical Company of Houston, Texas, or under the trademark ENGAGE™ polymers, a line of metallocene catalyzed elastomers available from Dow Chemical Company of Midland, Michigan, or under the trademark TAFMER™ available from 24POLYOQ24-WO-ORD 18

[0122] MITSUI Chemicals Group of Minato Tokyo, or under the trademark Fortify™ and Cohere™ available from SABIC.

[0123] The polyolefin-based elastomers may be prepared using methods known in the art, for example by using a single site catalyst, i.e., a catalyst the transition metal components of which is an organometallic compound and at least one ligand of which has a cyclopentadienyl anion structure through which such ligand bondingly coordinates to the transition metal cation. This type of catalyst is also known as "metallocene" catalyst. Metallocene catalysts are for example described in U.S. Patent Nos.

[0124] 5,017,714 and 5,324,820. The elastomer s may also be prepared using traditional types of heterogeneous multi-sited Ziegler-Natta catalysts.

[0125] Preferably, the amount of ethylene incorporated into the polyolefin-based elastomer is at least 45 wt%. More preferably, the amount of ethylene incorporated into the polyolefin-based elastomer is at least 48 wt%, for example at least 50 wt%. The amount of ethylene incorporated into the polyolefin-based elastomer may typically be at most 95 wt%, for example at most 85 wt%, for example at most 75 wt%, for example at most 65 wt%, for example at most 60 wt%, for example at most 58 wt%.

[0126] The amount of the polyolefin-based elastomer is preferably in the range from 5 to 20 wt%, more preferably in the range from 7 to 15 wt% based on the total amount of the thermoplastic composition.

[0127] Flame-retardant agent

[0128] In one aspect of the present invention, the thermoplastic polymer sheath further comprises a non-halogen flame-retardant agent.

[0129] The non-halogen flame retardant agent comprises at least one non-halogen flame retardant compound. Examples of the non-halogen flame retardant compound include ammonium phosphate, ammonium polyphosphate; melamine orthophosphate, melamine pyrophosphate, melamine polyphosphate, and melamine phosphate; piperazine orthophosphate, piperazine phosphate, piperazine polyphosphate, and piperazine pyrophosphate. 24POLYOQ24-WO-ORD 19

[0130] Further examples of the non-halogen flame retardant compound include phosphinates of the following phosphinic acids: dimethylphosphinic acid, ethylmethylphosphinic acid, diethylphosphinic acid, methyl-n-propylphosphinic acid, methanedi(methylphosphinic acid), benzene-1,4-(dimethylphosphinic acid), methylphenylphosphinic acid and diphenylphosphinic acid. Examples also include metal salts of the above dialkyl or diaryl or arylalkyl phosphinic acid, where metal is an alkali metal, Li, Na, K and Cs and the like or alkaline earth metal, Be, Ca, Mg, Ba, Sr and the like or a transition metal, Zn, Ti and the like or other main group elements such as Al, Sn, Sb and the like, such as aluminum diethyl phosphinate.

[0131] In one embodiment, the non-halogen flame retardant agent comprises a melamine polyphosphate and an aluminum diethyl phosphinate. In an embodiment, the nonhalogen flame retardant agent consists of a melamine polyphosphate and an aluminum diethyl phosphinate in a weight ratio of 0.5-2, such as 1.

[0132] In one embodiment, the non-halogen flame retardant agent comprises an organic phosphate compound, an organic phosphoric acid compound and zinc oxide.

[0133] Preferably, the weight ratio of organic phosphate compound to organic phosphoric acid compound is 1:0.01 to 1:2, more preferably, the weight ratio is from 1:1 to 1:2.

[0134] The organic phosphate compound includes piperazine pyrophosphate, piperazine polyphosphate or combinations thereof.

[0135] The organic phosphoric acid compound includes melamine pyrophosphate, melamine polyphosphates, melamine phosphate or combinations thereof. It is preferred that the phosphoric acid compound is melamine phosphate.

[0136] The zinc oxide is used in an amount of from 2 - 10 wt.%, more preferably from 3 - 6 wt.% based on the weight of the flame-retardant agent.

[0137] A similar flame-retardant agent is described in WO2016102278A1.

[0138] The amount of flame-retardant agent is from 2-40, preferably 10-30 wt.% based on the weight of the glass fibre reinforced thermoplastic polymer composition. Higher 24POLYOQ24-WO-ORD 20

[0139] amounts, such as from 20 - 35 wt.% may be required for applications that need to be compliant with a UL-945V rating. For ULS-94 VO ratings, lower amounts may suffice.

[0140] Other additives

[0141] The material of the sheath may further contain additives and / or stabilizers like antioxidants, UV stabilizers, pigments, dyes, adhesion promoters like modified polypropylene, in particular maleic anhydride-modified polypropylene, antistatic agents, mold release agents, slip agents, nucleating agents and the like.

[0142] Method for production

[0143] The present invention further provides a method for producing a glass fibre reinforced thermoplastic polymer composition comprising a core that extends in the longitudinal direction and a thermoplastic polymer sheath intimately surrounding said core, wherein the core comprises glass fibres and an impregnating agent, wherein, the method comprising the steps of

[0144] a) providing at least one continuous glass multifibre strand,

[0145] b) applying the impregnating agent to said at least one continuous multifibre strand,

[0146] c) applying a sheath comprising a thermoplastic polymer and a carbon fiber around the strand obtained in step b) so as to form a sheathed continuous multifibre strand, and

[0147] d) cutting the sheathed continuous multifibre strand so as to form pellets; wherein the amount of the glass fiber and the amount of the carbon fiber is respectively 8-30 wt%, based on the total weight of the composition.

[0148] This method is typically known as a wire-coating process. Wire-coating is done by passing the continuous glass multifibre strand (roving) through a wire-coating die. Said die is attached to an extruder, which supplies molten thermoplastic polymer through an opening substantially perpendicular to the direction of the glass multifibre strand through the die. As such, the thermoplastic polymer basically sheaths or encapsulates the glass multifibre strand which is the “wire” to be “coated”. Such a process is also disclosed in WO 99 / 00543, the essential difference being that WO 99 / 00543 does not require the application of impregnating agent prior to the sheathing with the thermoplastic polymer. 24POLYOQ24-WO-ORD 21

[0149] The skilled person will understand that the core of the pellet comprising the glass fibres and the impregnating agent will only be surrounded by the thermoplastic polymer sheath in the longitudinal direction. Hence, the core of the pellet is exposed to the surrounding at the two cutting planes, or cross-sectional surfaces corresponding to the positions where the pellet was cut. It is for this reason that upon insufficient coupling of the glass fibres to the thermoplastic polymer sheath the glass fibres may separate from the pellet resulting in free glass as explained above.

[0150] In one embodiment, the pellets have a length of from 1 to 40 mm, such as from 5 to 20 and preferably from 10 to 18 mm.

[0151] In one embodiment, the glass fibre reinforced thermoplastic polymer composition according to the present invention and / or the pellet according to the present invention has a density of at most 1.300 g / cm3, preferably at most 1.200 g / cm3, more preferably at most 1.195 g / cm3, even more preferably at most 1.190 g / cm3, for example in a range of 1.000 to 1.180 g / cm3, as measured according to ASTM D792-13.

[0152] The glass fibre reinforced thermoplastic polymer composition according to the present invention may be used for the manufacture of articles or structural parts by known down-stream processing techniques. Such techniques include injection moulding, extrusion moulding, compression moulding and the like.

[0153] Typical applications of the composition of the present invention are (semi-)structural parts requiring a high stiffness.

[0154] For example, the composition of the present invention can be used for the manufacture of automotive parts, like a bumper, instrument panel carriers, door modules, tailgates, front-end modules, central console, gas pedal boxes, headlamp bracket, airbag housing, air conduits, sun-roof structures, battery-tray-holder, cross car beam, dash panel, seating structure and the like. 24POLYOQ24-WO-ORD 22

[0155] Alternatively, the composition of the present invention can be used for the manufacture of rods, sheets, or pipes forming the basic building blocks for any structural application either as automotive or non-automotive.

[0156] In addition, the composition of the present invention may be used for the manufacture of domestic appliances like washing machines, wash dryers, electrical appliances like coffeemakers, toasters, refrigerators, vacuum cleaners and the like.

[0157] In the context of the present invention, the term "mass" and "weight" are used interchangeably. The term “mass%” has the same meaning as the term “weight%” or simply “wt%”.

[0158] In the context of the present invention, an amount / content of a specific component in a percentage (“%”) is on weight basis, unless clearly specified otherwise.

[0159] In the context of the present invention, the term “degree Celsius” or “°C” is sometimes simplified as “C”. For example, “190C” means “190°C”, as is known to a skilled person in the field.

[0160] In the context of the present invention, the singular forms “a”, “an” and “the” are intended to include the plural forms as well, unless the context clearly indicates otherwise.

[0161] In the context of the present invention, the term “comprise” or “include” also includes the meanings of “comprised of’, “essentially comprised of’, “consist of” or “essentially consist of’.

[0162] In the context of the present invention, any numerical values describing a same aspect / feature of the present invention throughout the disclosure can be combined together to form a new range. For example, when it is described in the context that an amount of a certain component is at least 1wt%, preferably at least 2wt%, and at most 5%, preferably at most 4wt%, being in one example specifically 3wt%, then the amount ranges of 1-2wt%, 2-3wt%, 3-4wt%, 4-5wt%, 1-5wt%, 2-4wt% etc., are all inherently disclosed, as if they were explicitly described in the present invention. For example, 24POLY0024-WO-ORD 23

[0163] when it is described in the context that an amount of a certain component is in the range of 1-5wt%, preferably 2-4wt%, being in one example specifically 3wt%, then the amount ranges of 1-2wt%, 2-3wt%, 3-4wt%, 4-5wt%, etc., are all inherently disclosed, as if they were explicitly described in the present invention.

[0164] The present invention will now be further explained by figures and the following examples, which should not be considered as limiting the present invention in anyway. Fig. 1 plots Isotropic Elastic Modulus of the compositions of comparative examples 1-9 and inventive examples 1-4 against Density thereof.

[0165] Fig. 2 shows the effect of weight reduction of a tailgate made from the composition of Inventive example 1 compared with traditional STAMAX comprising 30wt% or 40wt% of long glass fiber.

[0166] Examples

[0167] Glass fibre reinforced thermoplastic polymer compositions in the form of pellets were manufactured in accordance with the method disclosed in WO 2009 / 080281. Such pellets comprise a core extending in the longitudinal direction and a sheath intimately surrounding said core, wherein the core comprises glass fibres and the sheath comprises a thermoplastic polymer and a filler.

[0168] Comparative examples

[0169] Examples 11-13 and 16 of EP3041648B1 are respectively considered as Comparative Examples (CE) 1-4, in which the fillers are ultrafine talc and short glass fiber (SGF). Examples 1-5 of EP3554786B1 are respectively considered as Comparative Examples 5-9, in which the fillers are glass bubble alone or together with nanoclay.

[0170] Composition and performance of the pellets of comparative examples 1-9 are reported in tables 1-2.

[0171] Table 1.

[0172]

[0173] 24POLY0024-WO-ORD 24

[0174]

[0175] Table 2.

[0176]

[0177] Inventive examples

[0178] Glass fibre reinforced thermoplastic polymer compositions in the form of pellets were manufactured in accordance with the method disclosed in WO 2009 / 080281.

[0179] The thermoplastic polymer is SABIC PP595A polypropylene (PP), available from SABIC and having a melt flow as determined according to ISO 1133 (2.16kg, 230 °C) of 47 g / 10min.

[0180] The glass multifibre strand (roving) is NEG Tufrov 9000 with a diameter of about 19 micrometer and a density of about 3000 tex, which can be calculated to correspond to approximately 4000 fibres per multifibre strand.

[0181] A recycled carbon fiber is used as the filler in the sheath. The recycled carbon fiber is a standard modulus recycled carbon fiber with a nominal chop length of 6 mm supplied by Vartega Inc.

[0182] An additive package, comprising 0.2 wt% of anti-oxidant, 0.06wt% of UV stabilizer, 1.8wt% of Bondyram 1010MP, which is a maleic anhydride modified polypropylene, 24POLY0024-WO-ORD 25

[0183] and 0.3wt% of color master batch, all relative to the whole glass fibre reinforced PP composition, is used in the manufacturing process.

[0184] Composition and performance of the pellets of inventive examples (IE) 1-4 are reported in table 3.

[0185] Table 3.

[0186]

[0187] Density is measured according to ASTM D792-13.

[0188] Isotropic Elastic Modulus is measured according to ISO 527 / 1 A at temperature of 23°C. Isotropic Tensile Strength and Isotropic Elongation at break are measured according to ISO 527 / 1 A at temperature of 23°C.

[0189] Notched Impact strength is measured according to IS0179 / 1 eA.

[0190] As can be seen from tables 1-3, the hybrid fibre reinforced thermoplastic polymer compositions of the present invention are substantively lower in density and higher in modulus, in other words, a higher ratio between modulus and density, compared with the similar compositions in the comparative examples, as can also be seen in fig.

[0191] 1.

[0192] Also with lower CO2 footprint of rCF (2.0 kg CCheq / kg), the hybrid material of the present invention offers lower CO2 footprint and lower specific CO2 footprint.

[0193] The hybrid fibre reinforced thermoplastic polymer compositions of the present invention in the form of pellets can be used in injection molding production for automotive applications. Tailgate is one such application where injected molded thermoplastic 24POLYOQ24-WO-ORD 26

[0194] composite technology is increasingly used for lightweighting, design flexibility and functional integration.

[0195] Considering a tailgate made from the hybrid fibre reinforced thermoplastic polymer compositions of the Inventive example 1 as a baseline, a tailgate made from traditional STAMAX, comprising 30wt% or 40wt% of long glass fiber in the core part without any filler in the sheath part, with similar performance with regard to stiffness, has obviously higher weight, as shown in fig. 2. Although 40wt% LGF STAMAX has a higher density than 30wt% LGF STAMAX, it needs lower thickness to achieve the same level of stiffness, thus the overall weight consumption is lowered, and the weight to achieve the same level of stiffness for the hybrid fibre reinforced thermoplastic polymer compositions of the Inventive example 1 is even lower. The hybrid fibre reinforced thermoplastic polymer composition of the present invention thus provides substantive weight reduction in the application of automotive parts.

Claims

24POLYOQ24-WO-ORD 27C LA I M S1. A glass fibre reinforced thermoplastic polymer composition comprising a core that extends in the longitudinal direction and a thermoplastic polymer sheath intimately surrounding said core, wherein the core comprises glass fibres and an impregnating agent, wherein the sheath comprises a thermoplastic polymer and a carbon fiber;wherein the sheath is substantially free of the glass fiber and the core is substantively free of the carbon fiber; andwherein the amount of the glass fiber and the amount of the carbon fiber is respectively 8-30 wt%, based on the total weight of the composition.

2. The composition according to claim 1 wherein the core is substantially free of a thermoplastic polymer.

3. The composition according to any of the preceding claims wherein the sheath comprises at most 10 wt%, preferably 0 wt%, of talc and at most 10 wt%, preferably 0 wt%, of short glass fiber with a length of at most 1 mm, based on the weight of the carbon fiber.

4. The composition according to any one of the preceding claims, wherein the length of the glass fiber is between 10-50mm, preferably between 10-25 mm, more preferably between 10-20 mm; and the length of the carbon fiber is between 0.1-3 mm, preferably 0.2-2 mm, more preferably between 0.2-1 mm.

5. The composition according to any of the preceding claims wherein a weight ratio between the glass fiber and the carbon fiber is 1 :3-3: 1 , preferably 1:2-2: 1, more preferably about 1:1.

6. The composition according to any one of the preceding claims, wherein a total amount of the glass fiber and the carbon fiber is 10-50 wt%, preferably 15-45 wt%, more preferably 20-40 wt%, based on the total weight of the composition.

7. The composition according to any one of the preceding claims, wherein the carbon fiber is a recycled carbon fiber with an ash content between 200-6000 ppm, as measured according to ISO 3451-1:2019 at 550°C.

8. The composition according to any one of the preceding claims, wherein the amount of the thermoplastic polymer is 45-85 wt%, based on the total weight of the composition.24POLYOQ24-WO-ORD 289. The composition according to any one of the preceding claims, wherein the composition comprises 0-30 wt% of recycled thermoplastic polymer, based on the total weight of the composition.

10. The composition according to any of the preceding claims wherein the thermoplastic polymer is a polypropylene with a melt flow index of 10-100 dg / min, tested according to ISO 1133 at 230 °C and 2.16 kg.

11. The composition according to any of the preceding claims wherein the thermoplastic polymer comprises a virgin polypropylene and a recycled polypropylene with a weight ratio in the range of 1 :9-9: 1 , wherein the virgin polypropylene has an ash content below 100 ppm, and the recycled polypropylene has an ash content between 200-6000 ppm, as measured according to ISO 3451- 1:2019 at 550°C.

12. The composition according to any of the preceding claims wherein the thermoplastic polymer sheath comprises 0.1-20 wt% of additional additives, based on the total weight of the composition, such as a fl a me- retard a nt agent, a polyolefin-based elastomer.

13. The composition according to any of the preceding claims comprising from 0.5 to 10 wt%, preferably from 1 to 5 wt% of the impregnating agent based on the total weight of the composition.

14. The composition according to any of the preceding claims having a density of at most 1.200 g / cm3, preferably at most 1.195 g / cm3, more preferably at most 1.190 g / cm3, for example in a range of 1.000 to 1.180 g / cm3, as measured according to ASTM D792-13.

15. The composition according to any of the preceding claims wherein the composition is in the form of one or more pellets which have a length of from 1 to 40 mm such as from 5 to 20 and preferably from 10 to 18 mm.

16. Method for producing the composition according to any of the preceding claims comprising the steps of:a) providing at least one continuous glass multifibre strand,b) applying the impregnating agent to said at least one continuous multifibre strand,c) applying a sheath comprising a thermoplastic polymer and a carbon fiber around the strand obtained in step b) so as to form a sheathed continuous multifibre strand, and24POLYOQ24-WO-ORD 29d) cutting the sheathed continuous multifibre strand so as to form pellets; wherein the amount of the glass fiber and the amount of the carbon fiber is respectively 8-30 wt%, based on the total weight of the composition.

17. A structural part obtainable by moulding the composition of one or more of claims 1-15 or the pellets obtainable by the method of claim 16.

18. The structural part of claim 17 wherein said structural part is an automotive part, such as a bumper, instrument panel carrier, door module, tailgate, front-end module, gas-pedal box, airbag house, air conduit, sun-roof structure, battery-tray- holder, cross car beam, dash panel, seating structure or wherein said structural part is comprised in domestic appliances, such as coffee makers, vacuum cleaners, washing machines, wash dryers.

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