ARTIFICIAL TURF FIBER WITH A CORE-CLADDING STRUCTURE COMPRISING AN AGED POLYMER

Abstract

 A method for producing an artificial turf fiber (710) from plastic waste (104), The method comprises :
- providing (402) an unaged polymer (102);
- providing (404) plastic waste (104) comprising one or more aged polymers, the one or more aged polymers comprising at least one aged polymer that is immiscible with the unaged polymer;
- melting and mixing (406) the plastic waste and the unaged polymer for preparing a liquid core polymer mixture (100, 200, 300, 350), the liquid core polymer mixture comprising a core polymer phase (106, 302, 902) and a thread polymer phase (108, 802), the thread polymer phase forming beads within the core polymer phase, the thread polymer phase comprising one or more of the aged polymers that are immiscible with the unaged polymer, the core polymer comprising the unaged polymer or comprising a blend of the unaged polymer and one or more further ones of the aged polymers that are miscible with the unaged polymer;
- coextruding (408) the liquid core polymer mixture with a liquid cladding polymer (904) into a monofilament (900, 950), the liquid core polymer mixture forming a cylindrical core, the liquid cladding polymer forming a cladding (904) encompassing the core; and
- providing (410) one or more of the monofilaments as the artificial turf fiber (710).

Description

Field of the invention

[0001] The invention relates to the production of synthetic fibers and, more specifically, of artificial turf fibers resembling grass blades. The invention further relates to producing artificial turf, which is also referred to as synthetic turf.

Background and related art

[0002] Artificial turfs are a class of polymer-based floor textiles that imitate natural grass in its visual appearance and physical properties. They are normally manufactured from synthetic fibers that are fixed to a synthetic carpet background. The synthetic fibers imitate natural grass blades and are formed from one or more extruded monofilaments. Mono- or bicomponent monofilaments are basic materials used for the production of state-of-the-art artificial turf fibers.

[0003] High-quality artificial turf fibers should offer a faithful reproduction of the qualitative behavior (e.g., visual appearance and wetting behavior) of natural grass. An important demand in this respect is resilience, the ability of the pile to recover from the compression that typically occurs during use of the artificial turf (e.g., after being trodden on). For this purpose, monocomponent artificial turf fibers are manufactured from polymers, such as polyamide, that provide sufficient mechanical stiffness and elasticity.

[0004] Today, more and more companies and sports clubs have become committed to sustainability. As a result, there have been several advances in using waste plastics for fabricating artificial turf fibers. For example, EP 2 161 374 B1 describes a method for producing artificial turf for sports fields, garden design, and golf courses, wherein the artificial turf fibers consist for the most part of polyethylene terephthalate (PET) and/or polybutylene terephthalate (PBT) from waste materials. The fibers are produced substantially as multicomponent fibers with a core-sheath configuration, whereby the plastic sheath consists substantially of PET or PBT (either virgin or from waste materials), and whereby the core also consists substantially of PET and/or PBT from waste materials.

[0005] A problem associated with many approaches to using plastic waste in the production of artificial turf fibers is that often the available plastic waste is a "postconsumer" waste (i.e., is a heterogeneous mixture of different types of plastics). Typically, the exact composition of postconsumer plastic waste is not known and varies over time. Hence, the mechanical and chemical properties of postconsumer plastic waste are typically not known, and they vary unpredictably. In many cases, this excludes the use of plastic waste to produce a new, high-quality artificial turf fiber. Sometimes, plastic waste is preprocessed in a complex manner (e.g., filtered, sorted, heated, or crystallized), in order to separate different types of polymers from each other.

[0006] However, this preprocessing of waste is often highly time-consuming and expensive. What's more, different plastic types frequently cannot be separated at all or cannot be separated into different polymer fractions that are sufficiently pure for use as an educt in an artificial turf fiber production process. Therefore, artificial turf fibers made from recycled plastic waste often require it to be postindustrial rather than postconsumer waste, or require complex preprocessing of the postconsumer waste in order to separate the plastic waste into the different types of polymers to be used for manufacturing a new artificial turf fiber.

Invention summary

[0007] The invention provides for a method of producing artificial turf fibers, a corresponding artificial turf fiber, and artificial turf comprising the fiber as specified in the independent claims. Embodiments of the invention are given in the dependent claims. Embodiments and examples described herein can freely be combined with one another as long as they are not mutually exclusive.

[0008] In one aspect, the invention relates to a method for producing an artificial turf fiber from plastic waste. The method comprises:

• providing an unaged polymer;
• providing plastic waste comprising one or more aged polymers, the one or more aged polymers comprising at least one aged polymer that is immiscible with the unaged polymer;
• melting and mixing the plastic waste and the unaged polymer for preparing a liquid core polymer mixture that comprises a core polymer phase and a thread polymer phase, where the thread polymer phase forms beads within the core polymer phase and comprises the at least one aged polymer that is immiscible with the unaged polymer, and where the core polymer phase comprises the unaged polymer or a blend of the unaged polymer and one or more further ones of the aged polymers that are miscible with the unaged polymer;
• coextruding the liquid core polymer mixture (which forms a cylindrical core) with a liquid cladding polymer (which forms a cladding encompassing the core) into a monofilament; and
• providing one or more of the monofilaments as the artificial turf fibers.

[0009] Said features may be advantages, because a high-quality artificial turf fiber made at least partially from plastic waste has a soft, elastic outer surface that faithfully reproduces the "look and feel" of natural grass blades, and that reduces the risk of injuries that may occur upon high-velocity body contact with the artificial turf fibers,. The "beadlike structures" composing the aged, non-immiscible polymer are transformed during the extrusion process into threadlike regions. The threadlike regions increase the resilience of the extruded monofilament and hence increase the ability of the resulting artificial turf fiber to re-erected after being trampled down.

[0010] In a further beneficial aspect, the artificial turf fiber is sufficiently rigid to be re-erected after being trampled down by a ball or a player. This may be achieved by creating the liquid core polymer mixture as an emulsion or suspension of beads accompanying a thread polymer phase within the liquid core polymer phase, such as polyethylene (PE). The thread polymer phase comprises one or more aged polymers, contained in the plastic waste, that are immiscible with the unaged polymer. Applicant has observed that aged polymers tend to be more rigid than newly generated polymer products. This may be at least partly because many plastic products comprise softeners (e.g., oils), which tend to migrate and leave a plastic product over many years of use. The reduced elasticity and flexibility of aged polymers and polymer blends is typically considered to be a negative, undesired feature, because the reduced flexibility increases the risk of injuries and skin burns, and may also increase the brittleness of the plastic product.

[0011] However, applicant has observed that the reduced flexibility of aged polymers may in fact represent a desired property, as it helps the fibers to be re-erected after being pushed down. The aged polymer is incorporated in a specific manner within a core polymer phase comprising an unaged polymer, thereby forming a core polymer mixture. The core polymer mixture is coextruded with a cladding polymer such that a core formed by the core polymer mixture is surrounded and wrapped by the cladding consisting of the cladding polymer. The cladding prevents any contact of the beadlike structures comprising the aged polymer with the surface of the monofilament, thereby protecting the skin from the inflexible aged polymer and protecting the aged polymer from damage by impacting forces. The cladding polymer has a dampening effect on any impacting forces, thereby shielding the comparatively brittle aged polymer (in the threadlike regions formed from the beadlike structures) from the skin of the players and vice versa.

[0012] Co-extrusion is a sophisticated manufacturing technology that may be used for generating extruded monofilaments with a core-cladding structure, where the materials for the core fiber and the elastic cladding are joined in a fluid phase. As high-impact mechanical forces and harsh environmental conditions act upon an artificial turf, a common downside of coextruded fibers that make up a core-cladding structure is the reduced cohesion between core and cladding and the risk that the cladding (or parts thereof) may get lost because of delamination or splicing. A coextrusion technology addressing this drawback has been proposed in DE 10307174 A1, where a multilayered monofilament is disclosed with a third polymer component interfacing the core and the cladding to increase cohesion.

[0013] According to some embodiments, the core polymer mixture - as a liquid multiphase system comprising a thread polymer phase that forms beads within a core polymer phase - is generated by mixing plastic waste with an unaged polymer. The plastic waste must comprise at least one polymer that is not miscible with the unaged polymer. This can be achieved comparatively easily.

[0014] For example, the unaged polymer may be an apolar polymer such as PE. In this case, a plastic waste can be chosen that contains a significant amount (at least 30%, or preferably at least 50%) of at least one polar polymer that is not miscible with the apolar polymer.

[0015] According to another example, an unaged polar polymer is added to the mixture. In this case, the plastic waste must contain at least one apolar polymer. The aged, apolar polymer will not mix with the unaged polar polymer when both polymer types are heated above their respective melting temperatures. Rather, the two polymers will form different phases.

[0016] In still other embodiments, the process conditions in the extruder - in particular, the temperature, pressure, speed of a stirrer, rheological additives, etc. - are chosen such that the fresh polymer and at least one aged polymer in the plastic waste cannot be mixed with each other for at least a certain period of time, so that two different phases are formed, one phase being embedded in the form of small droplets in the other. For example, the unaged polymer could have a comparatively low melting point (e.g., in the range of 240°C to 270°C), and the one or more aged polymers forming the thread polymer phase could have a significantly higher melting point (e.g., about 290°C to 320°C). At the moment of the mixing process when the fresh polymer already forms a thin-liquid phase (e.g., the core polymer mixture has been heated to above 280°C for at least 10 seconds), at least one aged polymer with a higher melting temperature may still be in a solid phase and may be suspended in the form of small, solid plastic waste granules comprising or basically consisting of this aged polymer within the low-viscous-liquid phase of the unaged polymer. Alternatively, at least one aged polymer may already be molten and may form small viscous droplets that are emulsified in said low-viscous-liquid phase of the unaged polymer.

[0017] This method for creation of multiphase polymer mixtures for fabricating a monofilament to be used as artificial turf fiber is known. For example, WO 2015/144223 A1 discloses a method of manufacturing artificial turf from a polymer mixture comprising two immiscible polymers and a compatibilizer. However, WO 2015/144223 A1 does not disclose that the multiphase-based fabrication of extruded monofilaments can also be used for manufacturing artificial turf fibers from plastic waste without reducing the quality of the fibers.

[0018] According to embodiments, the plastic waste and/or the one or more aged polymers contained therein are free of a plasticizer or comprise less than 0.5% of plasticizer by the weight of the plastic waste. This is typically the case for plastic products that were used for many years and/or that have been in a landfill for several years - in particular, when the use or the storage time at the landfill involved exposure to rain and sunlight. This may be beneficial, because the absence or low concentration of plasticizers increases the rigidity of the aged polymer, thereby increasing the ability of the extruded monofilament to be re-erected after being trampled down.

[0019] According to embodiments, the unaged polymer is an apolar polymer.

[0020] According to embodiments, the unaged polymer is polyethylene or polypropylene. Polyethylene and polypropylene are apolar polymers. In particular, the unaged polymer can be polyethylene (PE). This may be advantageous, because polyethylene is a soft, highly elastic polymer type that is able to efficiently protect the embedded, aged polymers in the thread polymer phase from the forces induced by impacting objects.

[0021] According to embodiments, the one or more aged polymers comprised in the thread polymer phase are polar polymers.

[0022] According to embodiments, one or more polar aged polymers included in the thread polymer phase are polyamide (PA) and/or polyethylene-terephthalate (PET).

[0023] This may be advantageous, because plastic waste composed of high portions of PA and/or PET is abundantly available. For example, PA is often used for producing some types of artificial turf fibers, and PET is commonly used for producing plastic bottles. Hence, large amounts of plastic waste comprising PA and/or PET are available and can be used for producing high-quality artificial turf fibers.

[0024] According to embodiments, the plastic waste is chosen such that at least 30%, and preferably at least 50%, of the weight of the plastic waste consists of one or more aged polymers.

[0025] According to embodiments, the plastic waste is chosen such that at least 80% of the weight of the plastic waste consists of the at least one aged polymer that is immiscible with the unaged polymer. It is also possible that the plastic waste basically consists of the at least one aged polymer that is immiscible with the unaged polymer. For example, the plastic waste could basically consist of PET or PA, and the unaged polymer could consist of PE. In general, plastic waste that comprises a large portion of the immiscible aged polymer of at least 50% is preferred, although plastic waste comprising a lower portion of the immiscible polymer may also be used. This is because the portions of the plastic waste that are miscible with the unaged polymer may intermix with it and form a core polymer blend whose physical and/or chemical properties are not well defined, given that the exact composition of plastic waste is typically not known and may vary depending on the source from which it is retrieved.

[0026] Therefore, it is generally preferable to use plastic waste with a high content of the immiscible aged polymer, which forms a separate phase that is emulsified and thereby finely dispersed within the core polymer phase. Many different types of aged polymers display increased rigidity due to the lack of plasticizers and other softneners and may therefore be able to fulfill their function of increasing the rigidity of the generated artificial turf fiber. The potential heterogeneity of the composition of the one or more aged polymers within the thread polymer phase will typically not have a significant impact on the property of the fiber core surface. Meanwhile, the potential heterogeneity of the composition of the one or more aged polymers that are miscible with the unaged polymer, and that may form a polymer blend together with the unaged polymer, may have an impact on the risk of delamination between the fiber core and the cladding of the resulting fiber. This is because the immiscible aged polymers may form a blend with the unaged polymer and hence may come into contact with the cladding polymer. If the core polymer blend cannot properly intermix with the cladding polymer during the coextrusion process (e.g., because of significant differences in the polarity or viscosity of the core polymer phase and the cladding polymer), there is a risk that the cladding may delaminate from the core after a while. Using plastic waste comprising a high portion of at least one polymer that is immiscible with the unaged polymer can ensure that the unaged polymer constitutes a large fraction (or preferably the largest fraction) of the core polymer phase; therefore, this also determines the physical and/or chemical properties of the core polymer phase. This may ensure that the quality and the physicochemical properties of the resulting, coextruded monofilament can repeatedly be reproduced in a manufacturing process even if different sources for the plastic waste are used.

[0027] In a further beneficial aspect, the fraction of aged polymers contained in plastic waste that are miscible with a particular unaged polymer can be easily determined. For example, if the unaged polymer to be used as the main component of the core polymer phase is PE, a simple test can be performed by mixing 100 parts of the unaged PE with 100 parts of the shredded plastic waste; heating the mixture until all polymer components of the mixture have melted and are in liquid phase; determining the volume of a first phase, comprising the unaged polymer as well as one or more aged polymers miscible with the unaged polymer, if any; and determining the volume of a second phase, comprising one or more aged polymers contained in the plastic waste that are not miscible with the unaged polymer. If the volume ratio of the first phase to the second phase is, for example, 120:80, it can easily be concluded that 80% by weight of the plastic waste consists of aged polymer(s) that are not miscible with the unaged polymer, whereby the volume percentage is used as an approximate measure for the weight percentage. This allows the performance of a quick check of whether a particular plastic waste lot is suited to being used for manufacturing high-quality artificial turf fibers.

[0028] According to embodiments, 3% to 40% by weight of the liquid core polymer mixture consists of the plastic waste (i.e., the one or more aged polymers contained in the plastic waste that are miscible with the unaged polymer). Often, 10% (or more) by weight of the liquid core polymer mixture consists of the plastic waste. This is because often, plastic waste - in particular, postconsumer plastic waste - is highly heterogeneous and comprises a mix of different polymer types.

[0029] According to some embodiments, the liquid core polymer mixture comprises 60% to 97% by weight of the unaged polymer.

[0030] According to embodiments, the cladding polymer is a polymer that is miscible with the unaged polymer.

[0031] This may be beneficial because the resulting coextruded monofilament offers a robust defense against delamination at the contact surface of core and cladding, given that the cladding polymer phase and the core polymer phase can intermix when coextruded together along a joining path (i.e., a path within an extrusion head of an extrusion machine where the core polymer mixture and the cladding polymer intermix by virtue of small-scale turbulences within two substantially laminar polymer mass flows).

[0032] According to embodiments, the cladding polymer is an apolar polymer - in particular, polyethylene or polypropylene or a mixture thereof.

[0033] According to embodiments, the method further comprises quenching the extruded monofilament; reheating the quenched monofilament; and stretching the reheated monofilament to deform the beads into threadlike regions, whereby the stretched monofilament is used for providing one or more monofilaments as the artificial turf fiber.

[0034] Said features may be advantageous because the stretching of the reheated monofilament will further elongate the threadlike regions. Long, threadlike regions prevent the fibers from buckling or make it easier for a fiber that has already been buckled to align itself again.

[0035] According to embodiments, the core polymer phase substantially consists either of the unaged polymer or of a blend of the unaged polymer with one or more of the aged polymers that are miscible with the unaged polymer.

[0036] According to embodiments, the plastic waste is a shredded, cut, crushed, minced, or ground plastic waste of heterogeneous origin - in particular, shredded postconsumer plastic waste.

[0037] According to embodiments, the plastic waste comprises used, aged artificial turf fibers - in particular, used and aged PA- or PET-based artificial turf fibers.

[0038] According to embodiments, the liquid core polymer mixture further comprises a compatibilizer. The compatibilizer is an amphiphilic substance adapted to emulsify the thread polymer phase within the core polymer phase such that the thread polymer phase forms the polymer beads surrounded by the compatibilizer within the core polymer phase.

[0039] This may be beneficial because the compatibilizer ensures that the extruded monofilament offers a robust defense against delamination at the contact zones of the thread polymer phase and the core polymer phase. In addition, in cases where a beadlike region comprising the thread polymer phase is located at the surface of the core polymer region and comes into contact with the cladding polymer, the compatibilizer may mediate adherence of the thread polymer phase and the cladding polymer, thereby preventing delamination at the regions within the fibers where the thread polymer phase and the cladding polymer phase may come into contact with each other.

[0040] According to embodiments, the compatibilizer is any one of the following: a maleic acid grafted onto polyethylene or polyamide; a maleic anhydride grafted onto free radical-initiated graft copolymer of polyethylene, SEBS (Styrene Ethylene Butylene Styrene Block Copolymer), EVA (Ethylene Vinylacetate), EPD, or polypropylene, with an unsaturated acid or its anhydride such as maleic acid, glycidyl methacrylate, ricinoloxazoline maleinate; a graft copolymer of SEBS with glycidyl methacrylate; a graft copolymer of EVA with mercaptoacetic acid and maleic anhydride; a graft copolymer of EPDM with maleic anhydride; a graft copolymer of polypropylene with maleic anhydride; a polyolefin-graft-polyamidepolyethylene or polyamide; and a polyacrylic acid type compatibilizer.

[0041] According to embodiments, the co-extrusion comprises extruding the core polymer mixture and the cladding polymer together such that the core polymer mixture is concentrically surrounded by the cladding polymer, and such that the two are in contact and intermix while being coextruded along a joining path. During the co-extrusion along the joining path, a contact layer forms between the core polymer mixture and the cladding polymer, and comprises a mixture of the core polymer mixture and the cladding polymer.

[0042] For example, the extrusion head used for performing the co-extrusion can comprise two separate, concentrically arranged ducts for the core polymer mixture and the cladding polymer, respectively. The dimensions of the ducts and other elements of the extrusion head are formed and shaped such that the core polymer mixture and the cladding polymer are transported in the direction of the opening of the extrusion head along the so-called joining path.

[0043] According to embodiments, the length of the joining path where the core polymer mixture and the cladding polymer are allowed to intermix is three to seven times the diameter of the liquid core polymer mixture at the upstream end of the joining path.

[0044] This may be beneficial because the abovementioned dimensions ensure that small-scale turbulences are formed at the contact surface of the core polymer mixture and the cladding polymer while being transported along the joining path. These turbulences cause the two different polymer masses to intermix, thereby forming a contact zone consisting of a blend of the core polymer mixture and the cladding polymer and ensuring that the core and the cladding of the resulting monofilament do not delaminate.

[0045] According to embodiments, the coextrusion is performed such that the liquid core polymer mixture enters the joining path at a different flow rate than the cladding polymer does. In particular, the liquid core polymer mixture enters the joining path at a greater flow rate than the cladding polymer does.

[0046] For example, the feed rates of the core polymer mixture and the cladding polymer component may be controlled independently. The feed rates of the two polymers may be controlled precisely for controlling their velocity differences in the joining path and hence for controlling the size and location of the turbulences. The flow may get turbulent if the velocity difference exceeds a threshold that is characteristic for the particular viscosities and/or melt flow indexes of the two interacting fluids. Feeding the core polymer mixture at a greater feed rate than the cladding polymer component may thus maintain the flow at a stable, small-scale level of turbulence. This may result in the formation of a thin contact layer of constant thickness between core and cladding where the core polymer and the cladding polymer are intermixed. Eventually, the method may yield an artificial turf fiber with increased shear stability.

[0047] This may further stabilize the location of the small-scale turbulences along the contact surface and may ensure that the turbulences result in an intermixing of the two coextruded polymer masses at a contact zone of defined thickness.

[0048] According to embodiments, the liquid polymer mixture is a multiphase system comprising a thread polymer phase that is emulsified in the form of beadlike structures within a core polymer phase. An optional compatibilizer may form a further phase that constitutes an interface between the thread polymer phase and the core polymer phase.

[0049] According to embodiments, the cladding has a noncircular profile. For example, the cladding can have one or more protrusions in order to more faithfully reproduce the profile of natural grass fibers. As a further beneficial aspect, the protrusions increase the cladding-to-core ratio and may increase the softness of the fiber, because preferably a soft, elastic polymer like PE is used as the cladding polymer.

[0050] The noncircular profile of the cladding may increase the surface-to-mass ratio for each artificial turf fiber, compared to purely circular-cylindrical fibers, if a suitable noncircular geometry is selected. An artificial turf manufactured from these artificial turf fibers may thus feature an improved coverage per unit area, which would conventionally be achieved by manufacturing the artificial turf with a higher blade density. According to embodiments of the invention, the improved coverage can be achieved with lower polymer consumption, which may result in reduced manufacturing costs. According to embodiments, the finished bicomponent artificial turf fiber has a yarn weight between 1200 and 2300 dtex.

[0051] According to embodiments, the contact of the core polymer mixture with the cladding polymer comprises pressing the liquid core polymer mixture and the liquid cladding polymer mass concentrically along a joining path. The joining path is a path within an extrusion machine (e.g., within an extrusion head) along which the liquid core polymer mixture and the liquid cladding polymer component are allowed to mix, thereby forming the contact layer.

[0052] This may have the advantageous effect of maintaining the flow in the joining path at a stable, small-scale level of turbulence. This may support the formation of the thin contact layer at a constant thickness between core and cladding where the two are intermixed. Eventually, the configuration may provide a bicomponent polymer fiber with increased shear stability.

[0053] According to embodiments, the diameter of the liquid core polymer mixture at the upstream end of the joining path is between 0.5 and 1.5 mm, preferably 1.25 mm.

[0054] According to embodiments, the core of the coextruded monofilament has a diameter of 50 to 600 micrometers. The cladding has a minimum thickness of 25 to 300 micrometers in all directions, extending radially from the core. The cladding may optionally comprise one or more protrusions. Each protrusion can have a radial extension, measured from the perimeter of the core to the outer end of the protrusion, in the range of two to 10 times the radius of the core.

[0055] According to embodiments, the extrusion and the optional stretching of the fibers are performed such that the threadlike regions in the monofilament used for providing the artificial turf fiber have a diameter of less than 50 µm and/or a length of less than 2 mm. Said dimension may be beneficial, as the resulting artificial turf fiber may show a desirable degree of resilience. If the threadlike regions are manufactured with a diameter that is too large, an artificial turf manufactured with these fibers might have an inappropriately hard or stiff surface. Another parameter is the length of the threadlike regions: Although the thread polymer may be chosen to provide a high bending stiffness compared to the other polymers present in the artificial turf fibers, the fibers may become bendable with a large bending radius if they are too long. In an optimized design, the threadlike regions may be substantially shorter than an artificial turf blade and/or the full bending circle of a thread polymer cylinder of a given diameter, but still long enough that the low elasticity of the core polymer is not dominating.

[0056] According to embodiments, the core polymer mixture is prepared free of at least one of the following components contained in the cladding: a wax, a dulling agent, a UV stabilizer, a flame retardant, an antioxidant, a fungicide, a pigment, and combinations thereof.

[0057] According to embodiments, the unaged polymer in the core is high-density polyethylene (HDPE), and the cladding polymer is linear low-density polyethylene (LLDPE).

[0058] According to embodiments, the core polymer mixture comprises the thread polymer phase in an amount of 1% to 30% by weight of the core polymer mixture.

[0059] In addition, or alternatively, the core polymer mixture comprises the compatibilizer in an amount of 0% to 60% by weight of the core polymer mixture.

[0060] In addition, or alternatively, the monofilament comprises the cladding polymer in an amount of 50% to 80% by weight of the monofilament.

[0061] According to embodiments, the preparation of the liquid core polymer mixture comprises the following steps: The plastic waste is provided in the form of shredded and optionally agglomerated plastic waste particles; the plastic waste comprises one or more aged polymers, and the shredded plastic waste granulate is mixed with an aged polymer granulate (e.g., PE granulate) and optionally with a compatibilizer and/or one or more additives such as flame retardants, light stabilizers, rheological additives, and the like. The mixture is homogeneously mixed (e.g., by a screw of an extruder) and heated. The heating is performed such that preferably all polymers contained in the core polymer mixture melt. This allows the intermixing of those aged polymers with the unaged polymer and any of the optional components, and allows for the generation of small beadlike structures that are emulsified within the core polymer phase. The duration of the mixing and the temperature are chosen such that the different polymers contained in the plastic waste can separate into different phases depending on whether an aged polymer is miscible with the unaged polymer. Depending on the composition of the plastic waste, the resulting core polymer phase can substantially consist of the unaged polymer or can substantially consist of a blend of the unaged polymer with one or more aged polymers that are miscible with the unaged polymer.

[0062] According to embodiments, the coextruded monofilament can be further processed (e.g., stretched and/or textured) and can be used alone or in combination with other coextruded monofilaments in order to provide the artificial turf fiber. For example, one or more (optionally further processed) extruded monofilaments can be formed into a yarn (e.g., by weaving, spinning, twisting, rewinding, and/or bundling the stretched monofilament or a bundle of stretched monofilaments into the artificial turf fiber). The incorporation of the artificial turf fiber into the artificial turf backing could, for example, be performed as described in United States patent application US 2012/0125474 A1.

[0063] According to embodiments, the coextrusion is performed at temperatures between 180°C and 270°C. This may be a temperature range with beneficial rheologic properties for many polymers, such as polyethylene and/or polyamide, that are typically used for the production of artificial turf fibers. Said temperature range may be particularly beneficial for creating a stable, small-scale turbulence in a joining path where the core polymer mixture and the cladding polymer mass are brought into contact with each other, thus causing the two to mix in a thin contact layer interfacing core and cladding. Said temperature range may also be beneficial for allowing the melted cladding polymer mass to fill the whole noncircular profile of the coextruded artificial turf fiber, including narrow regions and/or boundary areas with a high flow resistance, completely and uniformly without edge instabilities caused by undesirable turbulence.

[0064] In a further aspect, the invention relates to a method of producing an artificial turf. The method comprises generating an artificial turf fiber by performing the method for producing an artificial turf fiber according to any of the embodiments and examples described herein, and incorporating the artificial turf fiber into an artificial turf backing.

[0065] According to embodiments, the method comprises cutting the artificial turf fiber into sections such that cut surfaces that expose the contact layer, are created. For example, when the artificial turf fibers are incorporated into the carrier by the tufting technique, the loops of the tufted fibers are typically cut. In some state-of-the-art systems, with some artificial turf fibers having a core-shell contact zone that is exposed to water and sun as a result of cutting the fibers, there is an increased risk of delamination of the cladding, because the water may penetrate any gap between the core and the claddings. The co-extrusion according to embodiments of the invention which comprises the formation of a contact layer where the core polymer mixture and the cladding polymer intermix may prevent the delamination of the core and the cladding even if the fibers are cut and the contact zone is exposed to rain and sun as a result of the cutting. In some embodiments, the artificial turf fiber is free of any protective coating. A protective coating may not be necessary, because the core polymer mixture and the cladding polymer are mechanically intermixed at the contact zone and because optionally a compatibilizer may ensure that also the thread polymer phase, if exposed to the cladding polymer, adheres to the cladding polymer at the contact zone.

[0066] According to embodiments, the co-extrusion is performed via an extrusion opening that is adapted to form the cladding into a noncircular shape comprising two protrusions that extend from the core in opposite directions.

[0067] In a further aspect, the invention relates to a method of manufacturing artificial turf. The method comprises incorporating a plurality of artificial turf fibers into a carrier. The incorporated artificial turf fibers have been manufactured according to a method of any one of the embodiments and examples described herein.

[0068] In a further aspect, the invention relates to an artificial turf fiber comprising one or more monofilaments. Each monofilament comprises a cylindrical core and a cladding. The core comprises a thread polymer mass. The cylindrical core comprises a core polymer mass. The core polymer mass comprises an unaged polymer or comprises a blend of the unaged polymer and one or more aged polymers that are miscible in liquid state with the unaged polymer. The thread polymer mass has the form of threadlike regions within the core polymer mass, and comprises one or more aged polymers that are immiscible with the unaged polymer. The cladding surrounds the core and comprises (or basically consists of) a cladding polymer.

[0069] According to embodiments, the monofilament further comprises a compatibilizer that surrounds the threadlike regions and embeds the thread polymer mass in the core polymer mass.

[0070] In a further aspect, the invention relates to an artificial turf comprising a textile carrier and an artificial turf fiber, as described herein for embodiments of the invention. The fiber is incorporated into the carrier.

[0071] In general, the core-cladding structure may offer the advantage that the core may be optimized to provide properties, such as a certain degree of elasticity or rigidity, that are desirable for each blade of artificial turf as a whole, while the cladding can be designed with specific surface properties such as softness and visual appearance. Particularly, the core may comprise a core polymer phase and a thread polymer phase, whereby one or more aged polymers in the thread polymer phase provide sufficient rigidity and resilience to the artificial turf fiber.

[0072] The miscibility of the core polymer and the cladding polymer may render unnecessary any additional interfacing materials for providing a sufficient amount of cohesion between core and cladding. During co-extrusion, the core polymer mixture and the cladding polymer may intermix, forming a contact zone between core and cladding that consists of a blend of the core polymer phase and the cladding polymer and that provides a mechanical stability and robustness against delamination that is comparable to monocomponent fibers.

[0073] Each coextruded monofilament can comprise a cylindrical core, where the term "cylindrical" denotes a general right cylinder (i.e., having its primary axis oriented perpendicular to its base plane or cross section). Specifically, the core can be a noncircular cylinder (i.e., having a noncircular cross section). Examples of a noncircular cross section include an ellipse or a polygon. It is understood that the cross sections of core and cladding may be selected independently, and that each may have a noncircular cross section. In a non-limiting example, an elliptical core is surrounded by a bean-shaped cladding. In another non-limiting example, the fiber has a circular core and a cladding with two protrusions extending away from the core with a length of at least the core diameter.

[0074] A "thread polymer phase" is understood here as any polymer phase that forms beadlike structures or regions within another polymer phase referred to herein as a "core polymer phase." The beadlike structures are transformed into threadlike regions in an extrusion process. Optionally, the monofilament can be stretched, and the threadlike regions can be further elongated in the stretching process. The threadlike regions consist of or comprise one or more aged polymers that typically are free of (or comprise only a very small concentration of) a plasticizer and that exhibit a high bending stiffness. The bending stiffness may be sufficiently high that no further means are needed to provide a desired level of resilience to an artificial turf fiber manufactured from the monofilament comprising threadlike regions derived from waste plastic. Often, the thread polymer phase will also have a higher density, because exposing polymers to UV light for many months or years will break polymer chains and lead to a more compact version of the unaged original polymer. Hence, in solid form, the threadlike regions may differ from the surrounding core polymer mass with regard to rigidity and/or density. At least one aged polymer that is contained in (and may constitute) the thread polymer phase is immiscible with the unaged polymer.

[0075] A "compatibilizer" as used herein is any substance that is capable of emulsifying a polymer that is immiscible with another polymer within said other polymer. For example, a compatibilizer can be an amphiphilic substance that comprises both a polar and an apolar portion and that can emulsify a polar polymer in the form of droplets or beads within an apolar base polymer phase, or can emulsify an apolar polymer in the form of droplets or beads within a polar base polymer phase. A "polymer" as used herein is preferably a polyolefin. An "amphiphilic substance" is a substance capable of connecting polar and nonpolar molecules. An amphiphilic compatibilizer may connect molecules of, for example, a nonpolar core polymer with molecules of a polar cladding polymer, and vice versa.

[0076] The term "plastic waste" as used herein is a type of waste that substantially consists of used and discharged plastic products. According to embodiments, the plastic waste used for providing the core polymer mixture has been exposed to sunlight and/or water for at least one year (e.g., plastic waste comprising outdoor products that have been in use for at least one year) or has been collected from the ocean, landfills, or other sources of waste. The plastic waste can, in particular, be postconsumer plastic waste.

[0077] The expression that one polymer is "immiscible" with another polymer here means that the one polymer and the other polymer form two separate phases when both polymers are heated above their respective melting temperatures and do not intermix at least during the time interval between melting and extruding the polymers. In some examples, the two polymers are permanently immiscible - for instance, because the one polymer is apolar and the other polymer is polar. In other examples, the two polymers are only temporarily immiscible during the abovementioned time interval and would intermix if the time interval between melting both polymers and extruding the liquid polymer mixture were significantly increased. In this example, the two polymers may temporarily form separated phases due to differences in the melting temperature, differences in the viscosity, and other factors. The time interval during which the two polymers are immiscible may depend on the respective polymer type used and on the temperature. For many embodiments, the time interval between melting all polymers contained in the core polymer mixture and performing the extrusion of the molten core polymer mixture is shorter than 5 minutes, preferably shorter than 2 minutes, and - in particular - shorter than 1 minute.

[0078] An "aged polymer" as used herein is a polymer or polymer mixture that was subject to an aging process. Preferably, an aged polymer is a polymer contained in and/or derived from "waste plastics." Typically, aged polymers are free of light stabilizers and/or plasticizers or comprise a significantly lower concentration of light stabilizers and/or plasticizers. For example, an unaged artificial turf fiber polymer may comprise at least 0.7% by weight a light stabilizer (e.g., HALS). After five years of being exposed to sun, rain, and mechanical wear, the same fiber may comprise less than 0.3% HALS, and after some additional years, the HALS content will typically fall below 0.1%. Likewise, a newly produced artificial turf fiber may exhibit a polymer mass that comprises 1% to 3% by weight of a plasticizer. After five years of exposing the fiber to sun, rain, and mechanical wear, the plasticizer may have disappeared completely or may be contained in the fiber in an amount of less than 0.2%. In addition, aged polymers are often strongly oxidized and/or have smaller main chain length and side chain length than the unaged polymers from which they derive. According to preferred embodiments, the aged polymer(s) used for creating the polymer mixture are not preprocessed for separating different types of aged polymers. Rather, the aged polymer(s) used for creating the core polymer mixture can be a heterogeneous mix of shredded and optionally aggregated plastic waste from different sources possibly comprising different types of postconsumer plastic waste.

[0079] An "unaged polymer" (or "newly synthesized polymer," "newly produced polymer," or "virgin polymer") as used herein is any polymer that has not been in use as a component of a product and has not been subject to an aging process. For example, an unaged polymer can be a polymer sold as a raw material to the polymer and plastic processing industry. In addition, or alternatively, the unaged polymer can be a polymer that was already processed by the polymer and plastic processing industry (e.g., by adding additional substances such as additives and pigments to the unaged polymer), but that was not yet in use as part of a product. Hence, the unaged polymer may in fact also be several years old, but - contrary to aged polymers - has not yet been exposed to sunlight, rain, or wear. According to embodiments, an unaged polymer is a polymer that was not exposed to sunlight for longer than a year. Preferably, an unaged polymer is a polymer that was not exposed to sunlight for longer than six months.

[0080] A "light stabilizer" as used herein is any substance that protects a plastic product from light-induced - in particular, UV-induced - decay.

[0081] The term "polymer bead" (or "beads") may refer to a localized piece, such as a droplet, of a polymer that is immiscible with another polymer. The polymer beads may in some instances be round, spherical, or oval-shaped, but they may also be irregularly shaped. In some instances, the polymer beads will typically have a diameter of approximately 0.1 to 3 micrometers, and preferably 1 to 2 micrometers. In other examples, the polymer beads will be larger. They may, for instance, have a diameter of a maximum of 50 micrometers.

[0082] The term "cladding polymer" is used here to refer to any polymer that can be used to surround a core strand formed by a core polymer and a thread polymer, to form a monofilament according to embodiments of the invention. The cladding polymer preferably is miscible with the core polymer phase in a fluid state. The cladding polymer is preferably chosen to exhibit soft and smooth haptic properties, as it is supposed to form the outer layer, or cladding, of an artificial turf fiber according to embodiments of the invention. Furthermore, a preferred cladding polymer is suitable for coextrusion with a second component formed by a mixture of core polymer and thread polymer. Preferably, the cladding polymer is an inexpensive polymer (e.g., PE), as it is supposed to form a major portion of the total mass or volume of a monofilament.

Short description of the figures

[0083] In the following, embodiments of the invention are explained in greater detail, by way of example only, making reference to the drawings in which:

Fig. 1

shows a solid polymer mixture used for creating a liquid core polymer mixture;

Fig. 2

shows another liquid core polymer mixture;

Fig. 3

shows two other liquid core polymer mixtures;

Fig. 4

is a flowchart of a method for producing an artificial turf fiber from waste plastic;

Fig. 5

is a flowchart of several processing steps for post-processing the extruded monofilament and for incorporating it into a carrier;

Fig. 6

illustrates the elongation of thread polymer phase beads during extrusion;

Fig. 7

shows the integration of artificial turf fibers in a carrier;

Fig. 8A

illustrates the effect of stretching the monofilament on the beads in the core;

Fig. 8B

shows an electron microscope picture of a cross section of a stretched core of a monofilament;

Fig. 9

shows three cross sections of artificial turf fibers having a core-cladding structure;

Fig. 10

shows a cross-sectional profile of a coextruded monofilament with protrusions comprising an undulated and a straight edge;

Fig. 11

shows a cross-sectional profile of a further coextruded monofilament with protrusions comprising an undulated and a concave edge; and

Fig. 12

shows a coextrusion device with a joining path for coextruding two polymer masses such that a contact zone with a polymer mixture is formed.

Detailed description

[0084] Like-numbered elements in these figures are either equivalent elements or perform the same function. Elements that have been discussed previously will not necessarily be discussed in later figures if the function is equivalent.

[0085] Figure 1 shows a solid polymer mixture 110 used for creating the liquid core polymer mixture 100.

[0086] The mixture 110 comprises shredded postconsumer plastic waste particles 104, granules 102 of an unaged polymer (e.g., newly synthesized PE), and optionally a compatibilizer and/or further additives such as light stabilizers, flame retardants, or pigments. The solid mixture 110 can be created within an extruder or another container connected with an extruder that can be heated. The container preferably comprises a stirring element (e.g., a screw or another stirring device adapted to homogeneously mix all components of the core polymer mixture). The solid mixture 110 is transformed into the liquid core polymer mixture by heating and mixing - e.g., stirring the components of the solid mixture 110. For example, the creation of the liquid core polymer mixture can be performed immediately before the actual co-extrusion of the core polymer mixture and a cladding polymer. The mixing duration and the temperature may depend on the particular composition of the mixture 110. Typically, the melting temperature is between 230°C and 280°C.

[0087] The polymer mixture 100 comprises at least two different phases: a core polymer phase 106 that consists of or comprises the molten unaged polymer 102, and a thread polymer phase 108 comprising one or more aged polymers, originally contained in the plastic waste 104, that are immiscible with the unaged polymer but miscible with each other. The plastic waste can be postconsumer waste whose polymer composition and/or degree of oxidation and decay vary greatly between different aged polymer batches supplied. For example, the aged polymers contained in the plastic waste 104 may be a mixture of two or more different aged polymers like PE, PA, PP, PET, and/or PBT. In some embodiments, the plastic waste that is used for creating the liquid core polymer mixture 100 is derived from heterogeneous plastic waste. For example, the heterogeneous plastic waste can comprise or consist of aged PET bottles, aged artificial turf fibers, ocean plastic, plastic debris collected from biogas plants, or combinations thereof. Some of the different aged polymer types may be miscible with each other and with the unaged polymer 102 and form a core polymer phase 106 consisting of a polymer blend, as shown in figure 3. The mixture 100 depicted in figure 1 has a core polymer phase 106 that substantially consists of the unaged polymer 102.

[0088] As the unaged polymer 102 and one or more of the aged polymers contained in the plastic waste 104 are immiscible, the core polymer mixture comprises at least two different phases 106, 108. The mixture 100 is free of a compatibilizer, but the stirring conditions may ensure that the core polymer phase 106 is homogeneously distributed in the form of beadlike structures within the core polymer phase.

[0089] According to the example depicted in figure 1, the plastic waste 104 substantially consists of an aged polymer that is immiscible with the unaged polymer 102. The plastic waste 104 is basically free of any other type of polymer that is miscible with the unaged polymer. No compatibilizer is added to the solid mixture 110. As a consequence, the liquid core polymer mixture 100 comprises a core polymer phase that substantially consists of the unaged polymer 102 and of a thread polymer phase 108 that basically consists of one or more aged polymers contained in the plastic waste 104. This embodiment may be advantageous, because the physicochemical properties of the core are basically determined by the unaged polymer 102 which is a newly synthesized, pure polymer with known physicochemical properties. Typically, the mixture 100 is generated by using plastic waste that substantially consists of one or more aged polymers that share the feature that they are immiscible with the unaged polymer 102. For example, if the plastic waste substantially consists of aged, discarded polyamide fibers and if the unaged polymer 102 substantially consists of PE, the liquid core polymer mixture 100 can be generated.

[0090] Figure 2 shows a further example of a liquid core polymer mixture 200. The core polymer mixture 200 is a three-phase system - core polymer phase 106, compatibilizer 202, and thread polymer phase 108). The compatibilizer forms a third phase and prevents the separation of the core polymer phase and the thread polymer phase into two large separate volumes, by surrounding and embedding beadlike volumes of the thread polymer phase within the core polymer phase. This embedding of a small volume of one phase within another phase is referred to herein as "emulsification." The compatibilizer 202 emulsifies the thread polymer phase within the core polymer phase.

[0091] In cases where the thread polymer phase and the core polymer phase are separated into different phases only temporarily (e.g., because of different melting temperatures of the unaged polymer and the immiscible aged polymer), the thread polymer phase may also be a solid phase or a phase with a significantly higher viscosity than the core polymer phase, whereby the solid phase state or the difference in the viscosity at least temporarily stabilizes the emulsification (or "dispersion") of the thread polymer phase within the core polymer phase.

[0092] According to one example, the liquid core polymer mixture 200 depicted in figure 2 is created from plastic waste 104 that substantially consists of an aged polymer that is immiscible with the unaged polymer 102. The plastic waste 104 is basically free of any other type of polymer that is miscible with the unaged polymer. A compatibilizer is added to the solid mixture 110. As a consequence, the liquid core polymer mixture 200 comprises a core polymer phase that substantially consists of the unaged polymer 102, a thread polymer phase 108 that basically consists of one or more aged polymers contained in the plastic waste 104, and a compatibilizer 202 that wraps and embeds the beadlike structures of the thread polymer phase within the core polymer phase. This embodiment may offer the advantages described for the mixture 100 as shown in figure 1 and may offer a particularly robust defense against delamination.

[0093] Figure 3A shows a further example of a two-phase liquid core polymer mixture 300. The polymer mixture 300 comprises a core polymer phase 302 and a thread polymer phase 108. The core polymer phase consists of a blend of the unaged polymer 102 and one or more aged polymers contained in the plastic waste that are miscible with the unaged polymer. The thread polymer phase 108 substantially consists of one or more of the aged polymers contained in the plastic waste that are not miscible with the unaged polymer. The mixture is free of a compatibilizer, and the emulsion is created and stabilized mechanically.

[0094] According to one example, the liquid core polymer mixture 300 depicted in figure 3A is created from plastic waste 104 that substantially consists of a mixture of at least two different aged polymers, whereby a first aged polymer is miscible with the unaged polymer and forms a polymer blend constituting the core polymer phase 302, and whereby a second aged polymer is immiscible with the unaged polymer and forms, alone or in combination with other immiscible aged polymers, the thread polymer phase 108. The polymer mixture 300 is free of a compatibilizer. Because the core polymer phase is a blend of the unaged polymer with one or more aged polymers originally contained in the plastic waste, the physicochemical properties of the core polymer phase may be less predictable. However, this unpredictability may be compensated for by the cladding polymer, which wraps and shields the core polymer. In addition, the depicted embodiment can be used for recycling plastic waste that comprises a mixture of different types of polymers, which may or may not be miscible with the unaged polymer.

[0095] Figure 3B shows a further example of a liquid core polymer mixture 350. The mixture 350 differs from the liquid core polymer mixture 300 depicted in figure 3A only in that the mixture 350 also comprises a compatibilizer, which may provide additional protection against delamination at the contact area of the thread polymer phase and the core polymer phase.

[0096] Figure 4 is a flowchart of a method for producing an artificial turf fiber from waste plastic.

[0097] In step 402, an unaged polymer 102 is provided (e.g., in the form of a newly synthesized PE granulate). The PE granulate may comprise some additives such as flame retardants or antimicrobial agents.

[0098] In step 404, plastic waste 104 comprising at least one aged polymer that is immiscible with the unaged polymer is provided in the form of, for example, shredded polymer granules created by cutting or otherwise shredding postconsumer plastic waste, such as old, worn artificial turf fibers. Typically, the exact composition of the plastic waste is unknown, but at least a fraction of polar and apolar aged polymers can be determined easily in a preliminary test to ensure that the plastic waste comprises a desired minimum amount of an aged polymer that is immiscible with the unaged polymer.

[0099] Next, in step 406, a liquid core polymer mixture (100, 200, 300, 350) is created by mixing and heating the unaged polymer granules, the plastic waste, and optionally a compatibilizer and/or further additives to form a homogeneous mixture. For example, known pigments, UV and thermal stabilizers, process aids, and other substances can be added to the mixture. The mixing and melting of the components of the core polymer mixture can be performed in an extrusion machine immediately before the co-extrusion of the molten, liquid core polymer mixture and a cladding polymer.

[0100] As described (e.g., for the embodiments depicted in figures 1 to 3), a multiphase core polymer mixture is generated, wherein at least a core polymer phase and a thread polymer phase are temporarily or permanently formed. For example, differences in the melting temperature or viscosity can result in the formation of small beads of the thread polymer phase; this phase is mechanically dispersed within the liquid core polymer phase. This type of dispersion may be referred to as "temporal" phase separation because the phases might fuse into a single phase if the heating and/or mixing would be continued over a longer period of time. However, the liquid core polymer mixture is extruded before a fusion of the two different phases can happen. According to preferred embodiments, the thread polymer phase is permanently and stably dispersed within the liquid core polymer phase (e.g., because of polarity differences of the polymers contained in the respective phases). The separation of these two phases is more stable, because it depends on polymer-inherent physicochemical properties, and the mechanical mixing merely ensures a fine granular dispersion of the thread polymer phase within the core polymer phase.

[0101] During the mixing, any aged polymer that is contained in the plastic waste and that is miscible with the unaged polymer will intermix with the unaged polymer and form a blend that provides the core polymer mixture.

[0102] Typically, the unaged polymer is an apolar polymer such as PE. Preferably, the plastic waste is chosen such that the majority of polymer types contained in the plastic waste is polar. Hence, the largest portion of the plastic waste that provides the one or more aged polymers may form and be part of the thread polymer phase, and thus may be used for increasing the rigidity of the monofilament created in the co-extrusion process.

[0103] In some embodiments, the liquid core polymer mixture may comprise various compatibilizers that are used for emulsifying different types of aged polymers, thereby ensuring that any type of polymer that is immiscible with the unaged polymer forms polymer beads surrounded by the compatibilizer. The polymer beads may also be formed by additional polymers that are not miscible in the unaged polymer.

[0104] Next, in step 408, the core polymer mixture is coextruded with a cladding polymer (e.g., PE), into a monofilament 900, 950. The monofilament can be further processed (e.g.,quenched, reheated, and stretched). The melt temperature used during extrusions is dependent on the types of polymers and compatibilizer that are used. However, the melt temperature is typically between 230°C and 280°C. For example, the co-extrusion can be performed in an extruder depicted in greater detail in figure 12.

[0105] Next, in step 410, one or more of the extruded monofilaments are provided as artificial turf fibers.

[0106] Figure 5 is a flowchart of several processing steps for post-processing the extruded monofilament and for incorporating it into a carrier.

[0107] The coextruded monofilament, which can also be referred to as a "filament," is produced by feeding the core polymer mixture into a first duct system of an extruder of a fiber-producing extrusion line. In addition, a cladding polymer is set into a second duct system of the extruder. The two liquid polymer masses are pressed through the two different duct systems of the extrusion tool such that a concentric monofilament (composed of a core and a cladding) is formed.

[0108] In step 502, the extruded monofilament is quenched or cooled in a water spin bath, and is dried and optionally stretched by passing rotating heated godets with different rotational speeds and/or a heating oven.

[0109] Next, in step 504, the monofilament passes a heating oven and/or set of heated godets. This reheating step softens the coextruded monofilament and eases the stretching of the monofilament in preparation for the next step.

[0110] Next, in step 506, the beads or droplets of the IM polymer(s) surrounded by the compatibilizer are stretched longitudinally to form small, fiber-like, linear structures that stay completely embedded in the polymer matrix of the base polymer.

[0111] Next, in step 508, one or more artificial turf fibers are incorporated into a carrier layer. The carrier layer can, in particular, be a carrier mesh (e.g., a synthetic mesh or a plant fiber mesh). In some embodiments, the incorporation of the fibers is performed in step 510 such that the first parts of a plurality of artificial turf fibers are exposed to the lower side of the carrier, and such that the second parts of the monofilaments are exposed to the top side of the carrier. For example, the artificial turf fibers can be tufted into the carrier such that the U-shaped parts of the fiber face the lower side of the carrier and such that other parts of the fiber that represent the synthetic grass fibers protrude to the upper side of the carrier as depicted in figure 7. Alternatively, the artificial turf fibers could be weaved into a carrier.

[0112] Next, in step 512, a fluid backing solution is added to the lower side of the carrier. The fluid backing solution can be, for example, a polyurethane reaction mixture or a latex mixture; it embeds and surrounds the portions of the fibers protruding from the lower side of the carrier. In step 514, the fluid backing solution is solidified into a film that surrounds and thereby mechanically fixes the embedded parts of the monofilaments, having been arranged within the carrier.

[0113] Figure 6 illustrates the elongation of thread polymer phase beads during the co-extrusion into threadlike regions. Within the core polymer mixture 200 there is a large number of beads consisting of the thread polymer phase that may be optionally surrounded by a compatibilizer. A first screw, piston, or other device is used to force the core polymer mixture 200 through a first duct 610. In addition, a second screw, piston, or other device is used to force a cladding polymer 604 through a second duct that concentrically surrounds the first duct. The first and second ducts are contained in an extrusion head of an extrusion machine parts 612 of which are depicted in figure 6. The two polymer masses 200, 604 are transported in the same direction and are allowed to intermix at their contact layer 906 while being transported along the so-called joining path, depicted in greater detail in figure 12. The core polymer mixture and the cladding polymer are coextruded into a monofilament. The co-extrusion process transforms the tread polymer phase beads into threadlike regions, as depicted by the elongated beadlike structure 608.

[0114] According to embodiments, the cladding is joined to the core by a contact layer 906 consisting of a blend or a mixture of the core polymer mass and the cladding polymer. Hence, core and cladding are connected by a substance-to-substance bond formed by a polymer mixture held together by intermolecular forces that may be stronger than purely adhesive forces acting across two different adjacent, but not intermixed, polymers. The two polymers are bonded together in a way that is similar to the intermolecular forces present in a monocomponent fiber. Shear stress occurring during use of an artificial turf manufactured from such fibers will therefore be less likely to delaminate the cladding from the core. An artificial turf according to embodiments of the invention may therefore feature an improved wear resistance and improved robustness against delamination. Moreover, no compatibilizing polymer is needed to bring core and cladding into cohesive contact. Embodiments of the invention may achieve an equal or stronger cohesion between core and cladding than three-component artificial turf fibers where the third component is a compatibilizer interfacing core and cladding. For this reason, the production of artificial turf fibers according to embodiments of the invention may also result in a simplified production setup, as only two components must be brought into contact. The aged polymer and its potentially undesirable physicochemical properties are thereby securely shielded and do not affect the physicochemical properties of the fiber surface.

[0115] In some examples, the core polymer phase is less viscous than the thread polymer phase. As a result, the beadlike structures formed by the thread polymer phase will tend to concentrate at the core of the extruded monofilament. This may lead to the creation of desirable properties for the final artificial turf fiber.

[0116] Figure 7 shows a cross section of an example of artificial turf 700 and shows the integration of artificial turf fibers 710 in a carrier 706. The artificial turf 700 comprises an artificial turf backing 708 that may, for example, be latex-based or PU-based. Artificial turf fiber 710 has been tufted into the carrier 706 - e.g., a textile carrier mesh. The backing 708 is on the lower side of the carrier and embeds U-shaped portions of the integrated fibers, thereby serving to bind or secure the artificial turf fiber 710 to the artificial turf carrier. The backing 708 may be optional. For example, the artificial turf fibers 710 may be alternatively woven into the carrier mesh. Various types of glues, coatings, or adhesives could be used for the backing 708. The artificial turf fibers 710 are shown as extending a distance 704 above the artificial turf carrier 706. The distance is essentially the height of the pile of the artificial turf fibers. The length of the threadlike regions within the artificial turf fibers is half the distance 704 or less.

[0117] Figures 8A and 8B illustrate the effect of stretching the monofilament on the beads in the core polymer mass.

[0118] Figure 8A is a cross section of a small segment 800 of the monofilament core that comprises threadlike regions of the thread polymer phase 802, which may optionally be wrapped by a compatibilizer. The threadlike regions are generated from beads (bead-shaped structures and droplets) that are emulsified within the liquid core polymer mixture and have been stretched in the extrusion and during an optional stretching operation. The optional stretching is performed along the length of the monofilament. Figure 8A illustrates that the polymer beads in figures 1 to 3 have been stretched into threadlike structures 802. The amount of deformation of the polymer beads would be dependent on the extrusion speed and on how much the monofilament has been stretched.

[0119] Figure 8B shows an electron microscope picture of a cross section of a stretched core of a monofilament. The horizontal white streaks within the stretched monofilament 606 are the threadlike regions 802. The threadlike structures 802 can be shown as forming small linear structures of the thread polymer phase within the core polymer phase.

[0120] The resultant monofilament, which has a core-cladding structure (the cladding is not shown), may have multiple advantages, namely softness combined with durability and long-term elasticity. In cases of different stiffness and bending properties of the polymers, the fiber can show increased resilience (i.e., once a fiber is stepped on, it will spring back). The threadlike structures of the comparatively stiff and rigid aged polymer(s) built into the core polymer matrix reinforce the artificial turf fiber.

[0121] In some embodiments, the thread polymer phase selectively comprises polar, aged polymers, and the core polymer phase selectively comprises an apolar, unaged polymer or a blend of said apolar, unaged polymers with one or more aged, apolar polymers originally contained in the plastic waste. For example, polar polymers can be PE, PET, or PBT, and the apolar polymer(s) can be PE or PP. The optional compatibilizer can be, for example, a maleic anhydride grafted onto polyethylene or polyamide.

[0122] Figures 9A, 9B, and 9C show three cross sections of artificial turf fibers having a core-cladding structure.

[0123] Figure 9A shows a cross section of an artificial turf fiber 900 created by concentric co-extrusion of a core polymer mass 902 and a cladding polymer mass 904. The monofilament 900 is created by extruding the core polymer mass and the cladding polymer mass together through a common extrusion path such that the core polymer mass is concentrically surrounded by the cladding polymer mass 904 and such that the two polymer masses are in contact - at a contact area 906 depicted in figures 9B and 9C)- while being coextruded through a common extrusion path. The core polymer mass 902 is the core polymer mixture 100, 200, 300, 350 created in a method according to any one of the embodiments and examples described herein. Preferably, the cladding polymer and the core polymer phase in the core polymer mass have the same polarity. In some examples, the cladding polymer 902 is identical to and miscible with the core polymer phase of the core polymer mixture 902.

[0124] This may be advantageous, as delamination of the cladding and the core at the contact zone 906 is prevented by the intermixing of the two polymer masses at the contact zone. Moreover, according to preferred embodiments, pigments, flame retardants, and/or light stabilizers are selectively added to the cladding polymer mass 904 that surrounds the core 903. This may allow for lower production costs without reducing the quality of the fiber.

[0125] The contact layer 906 constitutes a transition zone where the densities of the core polymer and cladding polymer form a gradient. This way, it is possible to obtain a bond strength between core and cladding that is based on a mechanical mixing of the two polymer masses and that is significantly higher than the adhesive forces achieved by coating a core with an additional cladding layer.

[0126] In a further beneficial aspect, using the concentric core-cladding structure as depicted in figures 9A to 9C may ensure that even in cases in which the mechanical properties of the core polymer mixture 100, 200, 300, 350 would be worsened by a large portion of an aged polymer that intermixes with the unaged polymer, the fibers 900, 950 do not have these worsened mechanical properties because they have a shell/cladding that is made completely of an unaged polymer (e.g., PE or PP).

[0127] Figures 9B and 9C show another embodiment of a fiber 950 with a core-cladding structure, whereby the core is made of a core polymer mixture described herein for embodiments of the invention and whereby the cladding is made of an unaged polymer that is identical to the base polymer of the core 903. The fiber 950 comprises two protrusions that consist of the cladding polymer and that increase the fiber's surface-to-mass ratio.

[0128] According to one example, the monofilaments 900, 950 formed by co-extrusion of the core polymer mass 902 with the cladding polymer mass 904 may already feature a robust bond between core and cladding. High elasticity offered by a rigid thread polymer may be reached by elongating and stretching the beads into threadlike regions whose elasticity follows the same principle as that of a leaf spring. As a result, an artificial turf fiber is formed, which may feature high resilience due to a highly elastic and resilient core, optimized surface properties as a result of an appropriate choice of the cladding polymer, and inherent protection from splicing or delamination thanks to a highly stable contact layer where the core polymer is mixed with the cladding polymer. The fiber can comprise high portions of plastic waste and nevertheless have the desired properties with respect to elasticity, resilience, rigidity, and smoothness of the surface.

[0129] According to embodiments, the core 903 of the fiber has a diameter of 50 to 600 micrometers, and the cladding is formed with a minimum thickness of 25 to 300 micrometers in all directions extending radially from the core. Each of the protrusions, if any, is formed with a radial extension pl in a range of two to 10 times the radius of the core. As explained in greater detail above, the mentioned ranges for the core diameter and the minimum cladding thickness may be beneficial for providing the desired degree of stiffness and a sufficient amount of cladding material surrounding the core to form the mechanically robust contact layer. Said ratio of the radial extension of the protrusions with respect to the core radius may be chosen so as to improve the biomimetic properties of the artificial turf and the surface-to-mass ratio of the artificial turf fibers.

[0130] According to embodiments, the unaged polymer 102 that is used for providing the core polymer phase is high-density polyethylene (HDPE), and the cladding polymer 904 is a linear low-density polyethylene (LLDPE). In liquefied form, this combination may feature high miscibility as well as rheological properties that are optimized for forming a firm bond between core and cladding by means of co-extrusion. When formed into a monofilament for producing an artificial turf fiber according to the embodiments of the invention, the two solidified polymers may provide further advantages: HDPE is denser and more rigid than LLDPE, which may add to the resilience of the artificial turf fiber, while LLDPE is soft and wear-resistant, which may provide a reduced risk of injury and enhanced durability.

[0131] The opening 602 of the extrusion head depicted in figure 12 can have a circular profile, resulting in a monofilament profile as depicted in figure 9A.

[0132] Alternatively, the opening 602 can have a noncircular profile. According to embodiments, the resulting monofilament profile comprises one or more protrusions that extend from the core in opposite directions, as depicted in figures 9B and 9C.

[0133] According to embodiments, the core 903 comprises 1% to 30% by its weight of the thread polymer phase. Particularly, the thread polymer phase can be 1% to 20% by weight of the core 903. More particularly, the core 903 may comprise 5% to 10% by its weight of the thread polymer phase. The core may, for instance, have a diameter of 50 to 600 micrometers in size. It may typically reach a yarn weight of 50 to 3000 dtex.

[0134] The threadlike regions may have a diameter of less than 50 micrometers. Particularly, the threadlike regions may have a diameter of less than 10 micrometers. More particularly, the threadlike regions may have a diameter between 1 and 3 micrometers.

[0135] The cladding completely surrounds the core with two circular sections on two opposite sides of the core and with two flat, thin, long protrusions on two other opposing sides of the core. The cladding is preferably formed by a polymer, such as polyethylene, that may provide a soft and smooth surface. The cladding may comprise additives that support its interfacing function to the environment and/or a user. Typical additives to the cladding may be, for example, pigments providing a specific color, a dulling agent, a UV stabilizer, flame retardant materials (such as aramid fibers or intumescent additives), an antioxidant, a fungicide, and/or waxes that increase the softness of the cladding. Providing the cladding with additives may offer the advantage that these can be left out from the core. This way, a smaller content of expensive additive material per mass unit is required. As an example, it is not necessary to add pigments to the core, because only the cladding is visible from the outside. By way of a more specific example, it may be beneficial to add a green pigment, a dying agent, and a wax to the cladding to gain a closer resemblance to natural grass blades.

[0136] The noncircular profile of the cladding may be symmetric or irregular; it could be polygonal, elliptic, lenticular, flat, pointed, or elongated. Preferably, the cladding resembles a blade of grass by encompassing the circular-cylindrical core with two convex segments extending in two opposite directions from the geometric center of the monofilament, and two flat protrusions extending in two further opposite directions from the geometric center of the monofilament, with the convex segments and the flat protrusions alternatingly joined by concave segments. The two flat protrusions may also add to the biomimetic properties of the monofilament and may increase the surface-to-mass ratio for each monofilament and, accordingly, may provide an improved surface coverage for an artificial turf manufactured from artificial turf fibers on the basis of such monofilaments.

[0137] According to embodiments, the quantities of the thread polymer phase are 5% to 10% by mass of the core polymer mixture, whereas the quantities of the compatibilizer (if any) are 5% to 10% by weight of the core polymer mixture. Preferably, the thread polymer phase amounts to not more than 30% by weight of the core, such that the cohesion provided by the contact layer 906 remains equal or stronger than in conventional three-component artificial turf fibers with a compatibilizing layer interfacing core and cladding, even if the thread polymer phase and the cladding polymer are not miscible.

[0138] According to embodiments, the contact layer 906, consisting of a mixture or a blend of the core polymer mixture and the cladding polymer, extends radially from the center of the core to 50% of the minimum thickness of the cladding in all directions.

[0139] According to preferred embodiments, the dimensions of the joining path are suitably chosen such that a stable contact layer of homogeneous thickness is formed.

[0140] According to embodiments, the contact layer has a radial thickness of between 10 and 150 micrometers.

[0141] According to preferred embodiments, the contact layer has a radial thickness of between 10% and 50% of the minimum thickness of the cladding in all directions extending radially from the core. A contact layer within the given dimensions may be beneficial for providing a firm connection between core and cladding, while sparing sufficient volumes of core and cladding so that their respective desired functions (e.g., resilience of the core and softness of the cladding) are not adversely affected.

[0142] Figure 10 shows a cross-sectional profile of a coextruded monofilament with protrusions comprising an undulated and a straight edge. Depicted is a cross-sectional profile of an undulated artificial turf fiber comprising a round bulge at the center and two protrusions with rounded tips. The profile extends over an overall thickness t between the front central bulge and the rear tip of the protrusions. The distance w between the two other tips is the overall width w of the fiber. Both protrusions have a profile with one straight side opposite one undulated side with four notches along a straight baseline. Taking into account the axial extension of the fiber, this profile corresponds to protrusions with one flat face and one grooved face.

[0143] The protrusions may include an angle between 100 and 180 degrees. In the non-limiting example shown, the protrusions enclose an angle of about 135 degrees toward the undulated side of the profile. Both protrusions have a radial extension of about three times the thickness of the bulge. For the purpose of demonstration only, assuming an exemplary overall profile width w = 1.35 mm and overall thickness t = 0.45 mm, the profile of figure 10 would have a cross-sectional area of 0.216 mm². At an exemplary average density of 0.92 g/mm², this corresponds to a yarn weight of about 2000 dtex.

[0144] The two protrusions of the cladding may give the artificial turf fiber a structure with a closer resemblance to blades of natural grass. This may result in a more natural appearance as well as characteristics for the artificial turf that imitate the physical characteristics of a natural lawn during usage more realistically.

[0145] According to embodiments, the profile of at least one of the protrusions comprises a concave side. Compared to protrusions with straight sides, this may reduce the cross-sectional area of the fiber while slightly increasing its perimeter. Therefore, protrusions comprising a concave side may increase the surface-to-mass ratio further, to the beneficial effects described before. Preferably, the curvature of the concave side is limited such that the thickness of at least one concavely tapered protrusion is smallest at the edge of the fiber (i.e., the protrusions should contain no "bottleneck" that might reduce mechanical stability of the fiber).

[0146] Protrusions with a single-sided undulation may contribute beneficially to the properties of an artificial turf manufactured with such fibers. In such artificial turf, a portion of the grooved face of each fiber may be distributed in a stochastic manner. This may give the turf a less homogeneous and matted appearance. In addition, using such turf (e.g., for athletic activities) may locally give the artificial grass blades a defined orientation, such that the oriented contact area becomes easily discernable from its stochastically oriented environment.

[0147] Figure 11 shows a cross-sectional profile of a further coextruded monofilament with protrusions comprising an undulated and a concave edge. In contrast to the profile depicted in figure 10, the profile depicted in figure 11 has two protrusions with a concave side instead of a straight side. The curvature has been designed such that the thickness of the protrusions (measured between the concave side and the baseline of the undulated side) is gradually declining toward their respective tips. For comparison with the non-limiting example above, with overall width w = 1.35 mm and overall thickness t = 0.45 mm as above, the profile of figure 11 would have a cross-sectional area of 0.180 mm². At the assumed average density of 0.92 g/mm², this corresponds to a yarn weight of about 1650 dtex. A fiber with the concave profile of figure 11 would thus have a weight reduction of about 17% compared to a fiber with the straight profile of figure 10. As the concave profile has a slightly larger perimeter than the straight profile does, a fiber with the concave profile would also have an increased surface-to-mass ratio compared to a fiber with the straight profile.

[0148] Figure 12 shows a coextrusion device with a coextrusion head 970 for coextruding two polymer masses 902, 904 such that a contact zone with a polymer mixture is formed when the two polymer masses come into contact with each other while being pressed in the direction of the extrusion opening 602 along a joining path 960. The extrusion device comprises two separate openings for the two different polymer masses - i.e., the core polymer mixture 902 and the cladding polymer 904 - that allow for a co-extrusion process that generates an artificial turf fiber monofilament 900, 950 with a core-shell structure.

[0149] The term "joining path," which may also be called a "common polymer path," is understood herein as a part (or element, section, region, or the like) of a capillary or channel system of a coextrusion spinneret adapted for producing bicomponent fibers of the core-cladding (core-sheath, skin-core) type. The joining path is a region of free channel space where two liquid polymer components, when fed through at least two inlet openings, are allowed to come into contact with no barrier in between. The joining path is typically located at the downstream end of the spinneret and may be immediately followed by the extrusion opening 602.

[0150] The mixing of polymer masses along the joining path is responsive to the flow characteristics downstream from the end of the inner channel 910. Process parameters, mainly temperature and feed rates, may be chosen such that a balance between laminar flow and turbulent flow is achieved during joining. A purely laminar flow could result in comparably weak adhesive bonding between core and cladding, as the molecules from both components would not mix significantly. On the other hand, a flow of more pronounced turbulence could cause instabilities that would destroy the core-cladding structure at least locally. The process parameters were preferably balanced such that a small-scale turbulence would be created where the core and cladding molecules could mix within a thin contact layer of nearly constant width around the core.

[0151] The core polymer mass 902, also referred to as a core polymer mixture, is fed through a first opening into a duct that is located at the center of the extrusion head. The cladding polymer mass 904 is fed through one or more further openings into a second duct that concentrically surrounds the first duct.

[0152] At first, the liquid cladding polymer 904 and the liquid core polymer mixture 902 are transported along their respective ducts toward the opening 602 of the extrusion head. The transportation of the polymer masses in their respective ducts is performed such that the two polymer masses are transported in a basically laminar flow. While the two polymer masses are transported in their respective ducts, an intermixing of the core and the cladding polymer mass is prohibited by the walls of the inner duct. The first duct, used for transporting the core polymer mass, is shorter than the second duct, used for transporting the cladding polymer mass. As a result, the two polymer masses come into contact with each other when the core polymer mass leaves the end of the inner duct. The portion where the core and the cladding polymer mass come into contact with each other and intermix, forming a contact area 906, is referred to herein as a "joining path" 960.

[0153] According to embodiments, the extrusion opening is located downstream of the joining path 960, where the core and cladding polymer masses 902, 904 are allowed to come into contact with each other while moving in parallel, with a laminar flow, toward the opening 602. The blend of the core and cladding polymer generated during the transportation of the polymer masses along the joining path provides the contact layer 906 - or "contact zone" - which prevents a delamination of the cladding from the core.

[0154] The length, diameter, and feeding rate of both polymer masses are chosen such that the core polymer mass and the cladding polymer mass come into contact with each other, and such that a contact layer 906 - comprising a mixture of the core polymer mass and the cladding polymer mass - is formed between the two. The forming of the contact layer 906 may be achieved by controlling the flow characteristics (streaming pattern, velocity distribution, viscosities, shear moduli, temperature, melt flow indices, etc.) during the joining, such that a stable, small-scale turbulence is created, which causes the two polymer masses to intermix in a thin region 906, interfacing the core polymer mixture and the cladding polymer mass.

[0155] According to embodiments, the core polymer mass and the cladding polymer mass are pressed concentrically along the joining path 960, whereby the two are allowed to mix along the joining path to form the contact layer 906.

[0156] According to preferred embodiments, the joining path has a length of three to seven times the diameter of the inner duct (used for transporting the core polymer mass) at the upstream end of the joining path 960. According to embodiments, the diameter of the core polymer mixture at the upstream end of the joining path (i.e., the lower end of the inner duct) is between 0.5 and 1.5 mm, preferably 1.25 mm. These dimensions may ensure that the flow in the joining path is maintained at a stable, small-scale level of turbulence. If the joining path is too long, turbulence may be suppressed by feedback of increased wall-polymer interaction. On the other hand, a joining path that is too short may destroy the stability of the turbulence such that the contact layer becomes variable (e.g., in thickness and position). A fiber produced with a joining region that is too short may show no beneficial surface properties anymore, because the aged polymer within the core may reach the surface of the cladding if the turbulences are too large, and the resilience of the fiber may be reduced because the threadlike regions may also be destroyed by the turbulences.

[0157] In the coextrusion device depicted in figure 12, the joining path 960 is located upstream of a coextrusion opening 602. The setup comprises a cavity that receives a free end of a capillary tube 905. Opposite the inserted capillary tube 905, the cavity ends in a coextrusion opening 602. A clearance between the capillary tube 905 and the walls of the cavity 906 hydraulically connects the cavity to a second channel system, used for transporting the cladding polymer mass 904. The capillary tube 905 is hydraulically connected to a first channel system adapted for transporting the core polymer mass 902 and is not fully inserted into the cavity 906, such that a section 960 of the cavity 906 is hydraulically connected both to the first channel system and the second channel system. This section 960 is the "joining path" of the depicted coextrusion setup. The joining path 960 extends from the capillary inner tube 905 to the beginning of the extrusion opening 602, as is indicated by dotted horizontal lines.

[0158] During the coextrusion operation, the capillary tube 905 receives a molten core polymer mass from the first channel system, and the cavity 906 receives a molten cladding polymer mass from the second channel system. The respective transport directions of the polymer components are indicated by arrows. The two polymer masses flow separately from each other until they come into contact with each other in the joining path 960. The two joined polymer masses pass the joining path 960, which narrows to the cross section of the coextrusion opening 602, and exit the end of the opening as a bicomponent monofilament.

[0159] When the coextruded polymer masses are pressed through the extrusion opening 602, it generates a monofilament in the form of the contour of the opening. The contour corresponds to and defines the perimeter of the artificial turf fiber monofilament to be produced. Preferably, the extrusion opening comprises two circular or ellipsoidal sections that are located on two opposite sides from the center and that are connected to each other via two long, narrow protrusion gaps located on two further opposite sides from the center. Hence, the center of the joined strand pressed through the opening may comprise the core surrounded by circular or ellipsoidal sections of the cladding, while the protrusion gaps would be filled by the cladding polymer component only. The described opening geometry may therefore yield a monofilament that resembles a blade of natural grass more closely than, for example, a circular-cylindrical monofilament would.

LIST OF REFERENCE NUMERALS

[0160] 

100

liquid core polymer mixture

102

solid granules of unaged polymer

104

solid granules of plastic waste comprising aged polymers

106

liquid core polymer phase comprising the unaged polymer

108

liquid thread polymer phase comprising the aged polymer

110

solid polymer granulate mixture for fiber core

200

liquid core polymer mixture

202

compatibilizer

300

liquid core polymer mixture

302

liquid core polymer phase

350

liquid core polymer mixture

402-412

steps

502-514

steps

602

extrusion opening

604

cladding

608

elongated beadlike structure

610

duct for the core polymer

612

extrusion machine part

700

artificial turf

702

cutting tufted fibers

704

fiber portions protruding from the carrier

706

carrier

708

backing

710

artificial turf fibers

800

section of a monofilament

802

threadlike regions

900

monofilament

902

core polymer mass

903

core made of core polymer mass

904

cladding made of cladding polymer mass

906

contact surface where core and cladding intermix

950

monofilament

960

joining path

970

extrusion head of coextruder

Claims

1. A method for producing an artificial turf fiber (710) from plastic waste (104), the method comprising:

- providing (402) an unaged polymer (102);

- providing (404) plastic waste (104) comprising one or more aged polymers, the one or more aged polymers comprising at least one aged polymer that is immiscible with the unaged polymer;

- melting and mixing (406) the plastic waste and the unaged polymer for preparing a liquid core polymer mixture (100, 200, 300, 350), the liquid core polymer mixture comprising a core polymer phase (106, 302, 902) and a thread polymer phase (108, 802), the thread polymer phase forming beads within the core polymer phase, the thread polymer phase comprising the at least one aged polymer that is immiscible with the unaged polymer, the core polymer phase comprising the unaged polymer or comprising a blend of the unaged polymer and one or more further ones of the aged polymers that are miscible with the unaged polymer;

- coextruding (408) the liquid core polymer mixture with a liquid cladding polymer (904) into a monofilament (900, 950), the liquid core polymer mixture forming a cylindrical core (903), the liquid cladding polymer forming a cladding (904) encompassing the core; and

- providing (410) one or more of the monofilaments as the artificial turf fiber (710).

2. The method of claim 1, wherein the unaged polymer is an apolar polymer.

3. The method of any one of the previous claims, wherein the unaged polymer is polyethylene or polypropylene.

4. The method of any one of the previous claims, wherein the one or more aged polymers comprised in the thread polymer phase are polar polymers.

5. The method of any one of the previous claims, wherein the one or more aged polymers comprised in the thread polymer phase are polyamide and/or polyethylene-terephthalate or a blend thereof.

6. The method of any one of the previous claims, wherein the plastic waste is chosen such that at least 30% - preferably at least 50% - of the weight of the plastic waste consists of the at least one aged polymer that is immiscible with the unaged polymer.

7. The method of claim 6, wherein the plastic waste is chosen such that at least 80% of the weight of the plastic waste consists of the at least one aged polymer that is immiscible with the unaged polymer.

8. The method of any one of the preceding claims,

- wherein 3% to 40% by weight of the liquid core polymer mixture consists of the plastic waste; and/or

- wherein 60% to 97% by weight of the liquid core polymer mixture consists of the unaged polymer.

9. The method of any one of the previous claims, wherein the cladding polymer is a polymer that is miscible with the unaged polymer.

10. The method of any one of the previous claims, further comprising:

- quenching the extruded monofilament;

- reheating the quenched monofilament; and

- stretching the reheated monofilament to deform the beads into threadlike regions, whereby the stretched monofilament is used for providing the one or more monofilaments as the artificial turf fiber.

11. The method of any one of the previous claims, wherein the core polymer phase consists of the unaged polymer or of a blend of the unaged polymer with one or more of the aged polymers that are miscible with the unaged polymer.

12. The method of any one of the preceding claims, wherein the plastic waste is a shredded, cut, crushed, minced, or ground plastic waste of heterogeneous origin - in particular, shredded postconsumer plastic waste.

13. The method of any one of the previous claims, wherein the liquid core polymer mixture further comprises a compatibilizer (202), wherein the compatibilizer is an amphiphilic substance adapted to emulsify the thread polymer phase within the core polymer phase, such that the thread polymer phase forms the polymer beads surrounded by the compatibilizer within the core polymer phase.

14. The method of claim 13, wherein the compatibilizer is any one of the following: a maleic acid grafted on polyethylene or polyamide; a maleic anhydride grafted on free radical-initiated graft copolymer of polyethylene, SEBS, EVA, EPD, or polypropylene, with an unsaturated acid or its anhydride such as maleic acid, glycidyl methacrylate, ricinoloxazoline maleinate; a graft copolymer of SEBS with glycidyl methacrylate; a graft copolymer of EVA with mercaptoacetic acid and maleic anhydride; a graft copolymer of EPDM with maleic anhydride; a graft copolymer of polypropylene with maleic anhydride; a polyolefin-graft-polyamidepolyethylene or polyamide; and a polyacrylic acid type compatibilizer.

15. The method of any one of the previous claims, the co-extrusion comprising:

- extruding the core polymer mixture and the cladding polymer together such that the core polymer mixture is concentrically surrounded by the cladding polymer, and such that the core polymer mixture and the cladding polymer are in contact and intermix with each other while being coextruded along a joining path (960), thereby forming a contact layer (906) between the core polymer mixture and the cladding polymer, the contact layer comprising a mixture of the core polymer mixture and the cladding polymer.

16. The method of claim 15, the length of the joining path where the core polymer mixture and the cladding polymer are allowed to intermix being three to seven times the diameter of the liquid core polymer mixture at the upstream end of the joining path.

17. The method of claim 15 or 16, the coextrusion being performed such that the liquid core polymer mixture enters the joining path at a different flow rate - in particular, a greater flow rate - than the cladding polymer does.

18. An artificial turf fiber (710) comprising at least one monofilament, wherein each of the at least one monofilament comprises:

- a cylindrical core (903) comprising:

∘ a core polymer mass (100, 200, 300, 350) comprising an unaged polymer (106) or comprising a blend (302) of the unaged polymer and one or more aged polymers that are miscible with the unaged polymer, and

∘ a thread polymer mass (108, 802), the thread polymer mass having the form of threadlike regions within the core polymer mass, the thread polymer mass comprising one or more aged polymers that are immiscible with the unaged polymer;

- a cladding (904) surrounding the core, the cladding comprising a cladding polymer.

19. An artificial turf (700) comprising a textile carrier (706) and an artificial turf fiber (710) according to claim 18, the fiber being incorporated into the carrier.

Drawing