Biodegradable infill granule for use in an artificial turf system

Abstract

A granule for use as an infill for an artificial turf system, wherein said granule comprises substantially amorphous polyhydroxy alkanoate (PHA) and a pigment or pigment masterbatch.

Description

Technical field of the invention

[0001] The present invention is related to a granule for use in an artificial turf system, and to an artificial turf system using such granules.Background

[0002] Artificial turf systems seek to achieve the same characteristics as their natural counterparts although in certain areas these may have already been surpassed, at least in terms of predictability of behavior.

[0003] At present, typical turf systems comprise a backing layer with an upper surface comprising fibers extending substantially vertically, and an infill layer of soft granules disposed between the fibers. The backing layer may consist of a woven fabric in which artificial grass fibers are tufted to provide pile fibers oriented in an upward position and fixed to the woven fabric by a backing layer of latex or polyurethane. Installation of the turf system typically involves providing a layer of loose sand, strewn between the upstanding turf fibers, which by its weight holds the backing in place and supports the pile in upward position. Onto this sand layer and also between the artificial turf fibers, granules are strewn, forming a loose performance infill layer that provides the necessary sport performance. These performance characteristics will be dependent on the intended use but for most sports will include: rotational and linear grip, force reduction, vertical ball bounce; and rotational friction. This performance can be further supported by applying a shock pad layer directly under the backing layer.

[0004] Even if such artificial turfs have now been shown to have similar, or even better, properties than natural turfs, the plastic material used in such turfs is an environmental problem. The plastic material used in the artificial turfs spreads and is broken down into micro-plastics, which contaminates the environment.

[0005] Considering the above, there is a need for an environmentally friendly infill material for use in artificial turf systems, that provides similar or even better properties than natural turfs, and that biodegrades in nature leaving no microplastics behind and also has a lower global warming potential.

[0006] Examples of prior art can be found in documents EP3332067A2, DE102021113612A1, EP4047131A1 and EP3936665A1.Summary of the invention

[0007] In accordance with the present invention, there is provided a granule for use as an infill for an artificial turf system having the features of claim 1.

[0008] Further preferred embodiments are defined by the features of dependent claims 2-12.

[0009] The present invention relates to the environmental issue of persistent microplastic release from infill materials dispersed on artificial turf systems. In comparison to traditional infill materials, a relatively small amount of the present infill is required as infill, which in combination with its biodegradable properties prevents the release of persistent and harmful microplastics to the environment. It provides ideal playing surfaces for a wide range of outdoor and indoor sports such as football, paddle, lacrosse, basketball, and activities on playgrounds. PHA is fully biodegradable both in soil and in water meaning that if / when the granules leaves the artificial turf and end up in nature the granules will biodegrade relatively quickly, and therefore will not damage the environment with harmful microplastic.

[0010] Polyhydroxy alkanoates or PHAs are polyesters produced in nature by numerous microorganisms through bacterial fermentation of sugars or lipids. When produced by bacteria they serve as both a source of energy and as a carbon store. More than 150 different monomers can be combined within this family to give materials with extremely different properties. These plastics are biodegradable and are used in the production of bioplastics. They can be either thermoplastic or elastomeric materials, with melting points ranging from 40 to 180 °C.

[0011] The mechanical properties and biocompatibility of PHA can also be changed by blending, modifying the surface or combining PHA with other polymers, enzymes and inorganic materials, making it possible for a wider range of applications.

[0012] Certain strains of Bacillus subtilis bacteria can be used to produce polyhydroxy alkanoates.

[0013] To induce PHA production in a laboratory setting, a culture of a micro-organism such as Cupriavidus necator can be placed in a suitable medium and fed appropriate nutrients so that it multiplies rapidly. Once the population has reached a substantial level, the nutrient composition can be changed to force the micro-organism to synthesize PHA. The yield of PHA obtained from the intracellular granule inclusions can be as high as 80% of the organism's dry weight.

[0014] Polyesters are deposited in the form of highly refractive granules in the cells. Depending upon the microorganism and the cultivation conditions, homo- or copolyesters with different hydroxyalkanoic acids are generated. PHA granules are then recovered by disrupting the cells. Recombinant Bacillus subtilis str. pBE2C1 and Bacillus subtilis str. pBE2C1AB were used in production of polyhydroxyalkanoates (PHA) and it was shown that they could use malt waste as carbon source for lower cost of PHA production.

[0015] PHA synthases are the key enzymes of PHA biosynthesis. They use the coenzyme A - thioester of (r)-hydroxy fatty acids as substrates. The two classes of PHA synthases differ in the specific use of hydroxy fatty acids of short or medium chain length.

[0016] The resulting PHA is of the two types: Poly (HA SCL) from hydroxy fatty acids with short chain lengths including three to five carbon atoms are synthesized by numerous bacteria, including Cupriavidus necator and Alcaligenes latus (PHB).

[0017] Poly (HA MCL) from hydroxy fatty acids with medium chain lengths including six to 14 carbon atoms, can be made for example, by Pseudomonas putida.

[0018] A few bacteria, including Aeromonas hydrophila and Thiococcus pfennigii, synthesize copolyester from the above two types of hydroxy fatty acids, or at least possess enzymes that are capable of part of this synthesis.

[0019] Another even larger scale synthesis can be done with the help of soil organisms. For lack of nitrogen and phosphorus they produce a kilogram of PHA per three kilograms of sugar.

[0020] The simplest and most commonly occurring form of PHA is the fermentative production of poly-beta-hydroxybutyrate [poly(3-hydroxybutyrate), P(3HB)], which consists of 1000 to 30000 hydroxy fatty acid monomers. Another PHA is poly(3-hydroxybutyrate-co-3-hydroxyvalerate), PHBV.

[0021] In the industrial production of PHA, the polyester is extracted and purified from the bacteria by optimizing the conditions of microbial fermentation of sugar, glucose, or vegetable oil.

[0022] As raw material for the fermentation, carbohydrates such as glucose and sucrose can be used, but also vegetable oil or glycerine from biodiesel production. PHAs are processed mainly via injection molding, extrusion and extrusion bubbles into films and hollow bodies.

[0023] PHA polymers are thermoplastic, can be processed on conventional processing equipment, and are, depending on their composition, ductile and more or less elastic. They differ in their properties according to their chemical composition (homo-or copolyester, contained hydroxy fatty acids). They are UV stable, in contrast to other bioplastics from polymers such as polylactic acid, partial ca. temperatures up to 180 °C, and show a low permeation of water. The crystallinity can lie in the range of a few to 70%. Processability, impact strength and flexibility improves with a higher percentage of valerate in the material. PHAs are soluble in halogenated solvents such chloroform, dichloromethane or dichloroethane.

[0024] PHB is similar in its material properties to polypropylene (PP), has a good resistance to moisture and aroma barrier properties. Polyhydroxybutyric acid synthesized from pure PHB is relatively brittle and stiff. PHB copolymers, which may include other fatty acids such as beta-hydroxyvaleric acid, may be elastic.

[0025] Today, 9 different PHA families are produced in the short, medium and long-chain length composition. They go from high-strength, hard and brittle to low-strength, soft and elastic. The chemical composition of PHAs can be formed and adjusted depending on which monomers are used and in which composition. PHAs have a potentially large design space and resulting application options as a wide variety of different polymers can be copolymerized and blended.

[0026] PHA is a group of polyesters that are biobased and completely biodegradable. The properties of the different PHAs can vary greatly, depending on the composition and it is therefore necessary to choose the right type of PHA for each application, whether the PHA should be a homopolymer or copolymer, and what type of monomer would be best suited and whether it is amorphous or crystalline. PHA is thermoplastic and fully biodegradable. It degrades fast both in soil and in water making it a suitable polymer for use as granules for artificial turfs where there is a high probability of granules ending up in nature.

[0027] PHA has a low global warming potential since it is biobased.

[0028] According to the present invention, PHA used in the granules is substantially amorphous, which offers the advantage of providing a soft and flexible material, such that the properties of the infill are improved. By the term "substantially amorphous" is understood as having no or negligible amount of long-range order.

[0029] In particular, the granules may comprise at least 10 wt%, preferably at least 50 wt%, more preferably at least 70 wt%, and most preferably at least 80 wt% substantially amorphous PHA.

[0030] The pigment forms a protecting surface around the granules that protects them from UV light and hence extends the product lifetime when used as an outdoor infill material. The pigment is preferably a dark pigment, such as having a color of dark green. The pigment may be provided in the form of a pigment masterbatch. A masterbatch is here referring to a solid or liquid additive for plastics comprising a concentrated mixture of pigments, encapsulated in a carrier, such as a resin made of polymer, wax or the like. The masterbatch may contain 20-65 wt% pigment.

[0031] The granules may further comprise 0-50 wt% of a compostable polymer. In particular, the granules may comprise 10-40 wt%, preferably 20-35 wt% of a compostable polymer. 20Such a compostable polymer may be selected from the group consisting of polyethylene furanoate (PEF), polylactic acid (PLA), polybutylene adipate terephthalate (PBAT), polybutylene succinate (PBS), poly(butylene succinate-co-butylene adipate) (PBSA), polycaprolactone (PCL), thermoplastic starch (TPS), crystalline and / or semi-crystalline PHA and combination thereof. Such compostable polymer may be included in order to adjust the hardness, flexibility, and other properties of the material.

[0032] PBAT is fully compostable and highly flexible, thus being sustainable. It has also been found to have very high-performance as infill distributed on artificial turf systems to provide ideal playing surfaces for a variety of outdoor and indoor applications, such as football. The granules comprising PBAT may be used to provide a fully compostable and highly flexible infill material for artificial turf systems. Such granules are extremely flexible and can be made by fully compostable plastic. The granules may e.g. be shaped as cylindrical granules, highly appropriate for applications such as infill for artificial turfs. The granules alleviate the release of long-lived microplastics to the surrounding environment and nearby watercourses. The new infill is in particular useful as an infill material on artificial turfs for football, where it fulfills the FIFA requirements for performance and quality. It is also suitable for racket sports such as padel and tennis. The outstanding properties are correlated to a high flexibility and softness of the material, giving rise to reduced requirement of infill (<8.5 kg / m 2< ). Used granules may furthermore be recycled as to move towards a circular chemical economy with no harmful impact on the environment.

[0033] The granules may further comprise a filler material. The filler material may be selected from a group consisting of chalk, talc, kaolin, wood fiber, bast fiber, lignocellulose, cellulose, hemicellulose, lignin, flax, hemp, and combinations thereof. Such a filler material may be added in order to improve other properties of the material, and to fulfil other conditions and requirements. Filler materials, such as chalk or the like, may e.g. be added for the purpose of reducing cost, increasing specific density or adjusting other characteristics of the granule(s). The amount of filler material(s) may be in the range of 0-50 wt%. The total amount of the filler material(s) is preferably less than 40 wt% and may in embodiments be less than 30 wt%, less than 20 wt%, less than 10 wt%, or less than 5 wt%. In embodiments, no filler material may be used. However, in other embodiments, the amount of filler material(s) may be at least 1 wt%, at least 5 wt%, at least 10 wt%, at least 20 wt% or at least 30 wt%. Thus, the amount of filler material(s) may be in the range of 0-40 wt%, and preferably in the range of 1-40 wt%, such as 1-30 wt%, 1-20 wt% or 1-10 wt%.

[0034] The granules may further comprise a plasticizer, such as vegetable oil, epoxidized oil, waxes and rosin. The amount of plasticizer may be in the range from 0 to 20 wt%. The plasticizer may be added in order to improve properties of the material, for example softness and flexibility.

[0035] The pigment may be a dark pigment, in particular a dark green pigment. Such an embodiment provides an improved aesthetic appearance to the artificial turf system since the artificial turf system closely resembles natural grass due to virtually invisible infill material.

[0036] The granules may comprise a flame retardant in order to provide nonflammable granules. Further, the granules may comprise a nucleating agent in order to improve heat resistance.

[0037] The granules may have a diameter size in the range of 0.1-7 mm. Preferably, the granules may have a diameter in the range from 0.5-5 mm, more preferably 1-5 mm, even more preferably 1.5-4 mm, and most preferably 1.5-3.5 mm. A length of each granule may be in the range of 1-15 mm, and preferably 1.5-10 mm, and most preferably 1.5-5 mm. Thus, the granule(s) may have a mean diameter size of 2.5 mm ± 1.0 mm and a length varying between 1-15 mm. Shorter lengths than 1 mm are also feasible, such as down to 0.5 mm or down to 0.1 mm. Thus, the length may alternatively be in the range 0.1-15 mm, 0.5-15 mm, 0.1-5 mm, 0.5-5 mm, 0.5-4 mm and the like.

[0038] The above-discussed diameters and lengths may be used for granule(s) having a cylindrical shape, having a circular cross-section. However, the same preferred diameter and lengths dimensions will apply also for granules forming cylinders with a non-circular cross-section, as well as for granules not in the form of cylinders. A diameter for non-circular cross-sections is consequently to be interpreted broadly and covers a mean cross-sectional dimension also for non-circular shapes. The diameter for such non-circular shapes may e.g. be calculated based on the perimeter of the non-circular shape, whereby the diameter d may be calculated as d = p / π.

[0039] In a preferred embodiment, the granule(s) are in the form of a cylinder. A cylinder has a uniform cross-section over its entire length. In one embodiment, the cross-section may be in the form of a circle, providing a circular cylinder. However, other cross-sectional shapes may also be used, such as shapes in the form of a triangle, a square, a rectangle, and other polygon shapes. The cross-sectional shape may also be an oval, or other, more complex shapes, such as the shape of a star, a crystal shape, a three- or four-leaf clover, etc.

[0040] In some embodiments, the granules may also be shaped in other 3-dimensional shapes than the one of a cylinder, such as in the form of a discus, a sphere or the like.

[0041] In some embodiments, the granules may be shaped as an ellipsoid. An ellipsoid has three pairwise perpendicular axes of symmetry which intersect at a center of symmetry, the center of the ellipsoid. The line segments that are delimited on the axes of symmetry by the ellipsoid may be referred to as the principal axes, or simply axes of the ellipsoid.

[0042] The granules may have the shape of an ellipsoid where the three axes have different lengths, whereby the ellipsoid may be referred to as a triaxial ellipsoid, and the axes are uniquely defined.

[0043] The granules may have the shape of an ellipsoid where two of the axes have the same length, whereas the third has a different length. In this case, the ellipsoid may be referred to as an ellipsoid of revolution, i.e. a biaxial ellipsoid or a spheroid. In this case, the ellipsoid is invariant under a rotation around the third axis.

[0044] The third axis may be shorter than the other two, whereby the ellipsoid forms an oblate spheroid. An oblate spheroid may be seen as an ellipse rotated about its minor axis, to form a flattened spheroid, shaped like a lentil.

[0045] Alternatively, the third axis may be longer than the other two, whereby the ellipsoid forms a prolate spheroid. A prolate spheroid may be seen as an ellipse rotated about its major axis, forming the shape of an American football or rugby ball.

[0046] The three axes may also have the same length, whereby the ellipsoid forms a sphere.

[0047] In order to further improve mechanical properties of the artificial turf system, a resilient layer comprising a shock-pad structure may be arranged beneath the substrate and an additional particulate layer between the shock-pad structure and the infill layer.

[0048] For production of the granules, the material is mixed into a master batch. The material may then be extruded, to form a strand, and be cut into granules using e.g. a strand pelletizer. In the process of strand pelletizing, the strand may be fed from the die of the extruder into a cooling water bath, and subsequently be cut and dried in the pelletizer. The result may be smooth green-grey extruded granules of cylindrical shape with a mean diameter size of 2.5 mm ± 1.0 mm and a length varying between 1.0-15 mm.

[0049] Production of non-cylindric shapes can be made in a similar way, and e.g. by use of an underwater pelletizing process in an underwater pelletizer.

[0050] After use, the granules are fully compostable. Specifically, preliminary tests indicate that the above-discussed granule(s) meets the requirements related to disintegration specified in the standard ISO 20200 (Disintegration test).

[0051] The granules may also be recycled by gathering the granules, separating them from dust, washing, drying, and re-processing them, to increase the bio-sustainability.

[0052] The artificial turf system may further comprise a resilient layer comprising a shock-pad structure beneath the substrate and an additional particulate layer between the shock-pad structure and the infill layer. The additional particulate layer may comprise particulates of at least one of: sand, grit, rubber, cork, wood, elastomer and plastic particulates, or combinations thereof. In a preferred embodiment, the additional particulate layer comprises sand.

[0053] These and other features and advantages of the present invention will in the following be further clarified with reference to the embodiments described hereinafter.Brief description of the drawings

[0054] For exemplifying purposes, the invention will be described in closer detail in the following with reference to embodiments thereof illustrated in the attached drawings, wherein: Fig. 1 is a schematic illustration of a granule for use as an infill for an artificial turf, in in accordance with an embodiment of the present invention; Fig. 2 is a schematic cross-sectional view illustrating an artificial turf in accordance with an embodiment of the present invention; Figs. 3a-g are schematic illustrations of cylindrical granules with other geometries, in accordance with other embodiments of the present invention; Figs. 4a-d are schematic illustrations of non-cylindrical granules with different geometries, in accordance with other embodiments of the present invention. Detailed description

[0055] In the following detailed description, preferred embodiments of the present invention will be described. However, it is to be understood that features of the different embodiments are exchangeable between the embodiments and may be combined in different ways, unless anything else is specifically indicated. Even though in the following description, numerous specific details are set forth to provide a more thorough understanding of the present invention, it will be apparent to one skilled in the art that the present invention may be practiced without these specific details. In other instances, well known constructions or functions are not described in detail, so as not to obscure the present invention.

[0056] An embodiment of a granule for use as an infill for an artificial turf system is schematically illustrated in Fig. 1. Here, the granule has a cylindrical shape with a circular cross-section, i.e. a circular cylinder. The diameter size may be in the range of 0.1-5 mm, and preferably 0.5-5 mm, and more preferably 1-5 mm, and more preferably 1-4 mm, and most preferably 1.5-3.5 mm, and the length may be in the range of 1-15 mm, and preferably 1-10 mm, and most preferably 1-5 mm.

[0057] The above-discussed diameters and lengths may be used also for granule(s) having a cylindrical shape with non-circular cross-sections, as well as for non-cylindrical granule(s), as will be exemplified in more detail in the following. In such cases, a diameter for non-circular cross-sections relates to is a mean cross-sectional dimension. The diameter for such non-circular shapes may e.g. be calculated based on the perimeter of the non-circular shape, whereby the diameter d may be calculated as d = p / π.

[0058] However, the granule may also be in the form of other cylindrical shapes, having other cross-sections. Such alternative shapes are schematically illustrated in Figs. 3a-i. For example, the cylinder may have a cross-sectional shape in the form of a crystal, as shown in Fig. 3a. Here, the crystal shape is generally in the shape of two overlaid squares, 45 degrees rotated in relation to each other. However, other crystal shapes are also feasible. The cross-section may also be in the form of a triangle, as shown in Fig. 3b, a square, as shown in Fig. 3d, and a rectangle, as shown in Fig. 3e. However, other polygon shapes are also feasible, such as in the form of a star, as illustrated in Fig. 3c. The star here has five radiating points, but may also have fewer radiating points, such as 3 or 4, or more radiating points, such as 6 or 7. The polygon may have relatively sharp corners, as in the example of Fig. 3d, or rounded corners, as in the example of Fig. 3e. The cross-sectional shape may also be an oval or the like. The cross-sectional shape may also be a more complex shape, such as the shape of a three- or four-leaf clover, as illustrated in Fig. 3f, etc.

[0059] The cylinder may have a length which is greater than the diameter, as in the illustrative example of Fig. 1. However, the cylinder may also have a diameter which is essentially the same as the length. The cylinder may also have a diameter which is greater than the length, as in the illustrative example of Fig. 3g.

[0060] In some embodiments, the granules may also be shaped in other 3-dimensional shapes than the one of a cylinder, such as in the form of a sphere, as schematically illustrated in Fig. 4a, in the form of a discus, as schematically illustrated in Fig. 4b, or the like. The discus shape is here generally a flat cylinder but with curved, convex base surfaces.

[0061] In some embodiments, the granules may be shaped as an ellipsoid. An ellipsoid has three pairwise perpendicular axes of symmetry which intersect at a center of symmetry, the center of the ellipsoid. The line segments that are delimited on the axes of symmetry by the ellipsoid may be referred to as the principal axes, or simply axes of the ellipsoid.

[0062] The granules may have the shape of an ellipsoid where the three axes have different lengths, whereby the ellipsoid may be referred to as a triaxial ellipsoid, and the axes are uniquely defined.

[0063] The granules may, as illustrated in Figs. 4c and 4d, have the shape of an ellipsoid where two of the axes x and y have the same length a, whereas the third axis z has a different length c. In this case, the ellipsoid may be referred to as an ellipsoid of revolution, i.e. a biaxial ellipsoid or a spheroid. In this case, the ellipsoid is invariant under a rotation around the third axis.

[0064] The third axis z, i.e. the length c, may be shorter than the other two axes, i.e. the radius a, whereby the ellipsoid forms an oblate spheroid, as illustrated in Fig. 4c. An oblate spheroid may be seen as an ellipse rotated about its minor axis, to form a flattened spheroid, shaped like a lentil. Here, the length of the granule is c, and the diameter is 2*a, and c < a.

[0065] Alternatively, the third axis z, i.e. the length c, may be longer than the other two axes, i.e. the radius a, whereby the ellipsoid forms a prolate spheroid, as illustrated in Fig. 4d. A prolate spheroid may be seen as an ellipse rotated about its major axis, forming the shape of an American football or rugby ball. Here, the length of the granule is c, and the diameter is 2*a, and c > a.

[0066] The three axes may also have the same length, whereby the ellipsoid forms a sphere, as in the illustrative example of Fig. 4a.

[0067] The above-discussed shapes, and in particular the cylindrical shapes and the spheroid shapes, provides granules that immediately reach a packed structure when placed as an infill layer in an artificial turf system. This packed structure is reached directly after installation and is stable during time because it cannot compact more than this. However, the particles are loose enough to move under influence of force. This results in a structure of the infill layer, which is responsible for a natural turf character.

[0068] The granules may be used as an infill for an artificial turf system. Such an artificial turf system is schematically illustrated in Fig. 2. The artificial turf system here comprises an artificial grass layer comprising a substrate 21 and pile fibers 22 upstanding from the substrate. The substrate 21 functions as a backing sheet and may comprise a sheet of plastic material such as, for example, a non-woven fabric, which is impregnated with for instance latex, such as for example SBR latex. Extending upwardly from the upper surface of the substrate there is a large number of upstanding fibers 22. The length of the fibers is selected depending upon the depth of the infill material and the desired resilience of the completed artificial turf structure. The depth of the infill layer is less than the length of the fibers. The length of the fibers is for example below 50 mm. Preferably the length of the fibers is below 45 mm.

[0069] The fibers may be synthetic fibers composed of polyethylene, polypropylene or nylon. The fibers are for example single fibers or multiple fibers but also a mixture of multiple fibers and single fibers may be used. The thickness of the fibers may vary. However also a mix of thick and thin fibers is possible. The general criteria for making the backing sheet and the fibers are known in the art, and hence do not require a detailed description.

[0070] The infill layer 25, comprising the above-discussed granules, is placed above the substrate 21. The infill layer 25 may have granules provided in the range of 5-12 kg / m 2< , preferably 6-10 kg / m 2< , and most preferably 7-8.5 kg / m 2< , such as about 8 kg / m 2< or about 8.5 kg / m 2< . The weight of the infill layer is preferably less than 8.5 kg / m 2< .

[0071] The infill layer can be present at a depth that is sufficient to adequately support the pile fibers over a substantial portion of their length and may depend on the length of these fibers and the desired free pile. In a preferred embodiment, the infill layer has a depth of at least 10 mm. In other embodiments, the infill layer may be present to a depth of at least 20 mm or even to a depth of greater than 30 mm. It will be understood that the final depth will also depend upon whether the infill layer is the only layer on the substrate supporting the pile fibers and if a shock pad or other form of resilient layer is applied. In a preferred embodiment, the infill layer has a depth in the range of 10-25 mm, and preferably 15-20 mm, such as about 17 mm. Depending on the nature of the sport, the pile fibers may extend at least 10 mm or at least 15 mm or even more than 20 mm above the level of the infill.

[0072] The system may also comprise one or more additional particulate layers disposed on the substrate beneath the infill layer. The additional particulate layers may have various functions, including shock absorption, pile stabilization, drainage, filling and the like and may be selected from the group comprising: sand, grit, rubber particles, elastomer particles, thermoplastic particles and any other particles that do not meet the definition of the infill granules. In the illustrative example, the additional particulate layer 24 comprises sand, such as silica sand.

[0073] The additional particulate layer 24, here of sand, may have a weight of 10-20 kg / m 2< , and preferably 12-17 kg / m 2< , such as about 15 kg / m 2< . The additional particulate layer may have a depth of 5-15 mm, such as about 10 mm.

[0074] Beneath the substrate 21 a resilient layer 23 comprising a shock-pad structure may be provided. The shock-pad may e.g. be made of PE closed-cell foam. The shock-pad may have a thickness in the range 8-15 mm, and preferably 10-13 mm, such as 12 mm, and may have a density of 25-75 kg / m 3< , such as 50 kg / m 3< .

[0075] The granules are preferably made of a homogeneous material. The material comprises substantially amorphous polyhydroxy alkanoate (PHA) and a pigment or pigment masterbatch. The pigment is preferably dark, such as a dark green pigment. The pigment protects the granules from degradation due to UV radiation, and also makes the granules more heat absorbing.

[0076] The granule(s) preferably comprises at least 10 wt%, preferably at least 50 wt%, more preferably at least 70 wt%, and most preferably at least 80 wt% substantially amorphous PHA.

[0077] The granules may further comprise a filler material, wherein the filler material comprises at least one of: chalk, wood fiber, lignocellulose, cellulose, hemicellulose, lignin, bast-fiber, flax and hemp, and combinations thereof. The total amount of the filler material(s) is preferably less than 40 wt% and may in embodiments be less than 30 wt%, less than 20 wt%, less than 10 wt%, or less than 5 wt%. In embodiments, no filler material may be used. However, in other embodiments, the amount of filler material(s) may be at least 1 wt%, at least 5 wt%, at least 10 wt%, at least 20 wt% or at least 30 wt%. Thus, the amount of filler material(s) may be in the range of 0-40 wt%, and preferably in the range of 1-40 wt%, such as 1-30 wt%, 1-20 wt% or 1-10 wt%.

[0078] For production of the granules, the material is mixed into a master batch. The material may then be extruded, to form a strand, and be cut into granules using e.g. a strand pelletizer. In the process of strand pelletizing, the strand may be fed from the die of the extruder into a cooling water bath, and subsequently be cut and dried in the pelletizer. The result may be smooth green-grey extruded granules of cylindrical shape with a mean diameter size of 2.5 mm ± 1.0 mm and a length varying between 1.0-15 mm.

[0079] For production of non-cylindrical shapes, such as spheres or spheroids, pelletizing with die-face cutters may be used, where the melt is cut directly at the die opening, before a cooling medium, usually air or more often water, transports the freshly cut particles away, cooling them in process. In particular, it is possible to use underwater pelletizing for formation of such granules.

[0080] After use, the granules are fully compostable. Specifically, the granules are believed to meet the requirements related to disintegration specified in the standard ISO 20200 (Disintegration test).

[0081] The granules may also be recycled after use by gathering the granules, separating them from dust, washing, drying, and re-processing them, to increase the bio-sustainability.

[0082] The invention has now been described with reference to specific embodiments. It should be noted that the above-mentioned embodiments illustrate rather than limit the invention, and that those skilled in the art will be able to design many alternative embodiments without departing from the scope of the appended claims.

Claims

1. A granule for use as an infill for an artificial turf system, wherein said granule comprises substantially amorphous polyhydroxy alkanoate (PHA) and a pigment or pigment masterbatch.

2. The granule according to claim 1, wherein said granule comprises at least 10 wt%, preferably least 50 wt%, more preferably at least 70 wt%, and most preferably at least 80 wt% substantially amorphous PHA.

3. The granule according to claim 1 or 2, wherein said granule further comprises up to 50 wt% of a compostable polymer.

4. The granule according to claim 3, wherein said compostable polymer is selected from the group consisting of polyethylene furanoate (PEF), polylactic acid (PLA), polybutylene adipate terephthalate (PBAT), polybutylene succinate (PBS), poly(butylene succinate-co-butylene adipate) (PBSA), polycaprolactone (PCL), thermoplastic starch (TPS), crystalline and / or semi-crystalline PHA and combination thereof.

5. The granule of any one of the preceding claims, wherein the granule further comprises up to 50% of a filler material.

6. The granule according to claim 5, wherein said filler material is selected from a group consisting of chalk, talc, kaolin, wood fiber, bast fiber, lignocellulose, cellulose, hemicellulose, lignin, flax, and hemp, and combinations thereof.

7. The granule according to any one of the preceding claims, wherein said granule further comprises a plasticizer.

8. The granule of any one of the preceding claims, wherein the pigment is a dark green pigment.

9. The granule of any one of the preceding claims, wherein the granule has a diameter size in the range of 0.1-7 mm.

10. The granule according to any one of the preceding claims, wherein said granule has cylindrical or non-cylindrical shape.

11. An artificial turf system, comprising: an artificial grass layer comprising a substrate (21) and pile fibers (22) upstanding from the substrate; an infill layer (25), disposed on the substrate and interspersed between the pile fibers, the infill layer comprising granules according to any one of claims 1-10.

12. The artificial turf system according to claim 11, wherein said artificial turf system further comprises a resilient layer (23) comprising a shock-pad structure beneath the substrate and an additional particulate layer (24) between the shock-pad structure and the infill layer.

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