Artificial Grass Pile Fibers

Artificial grass pile fibers are normally made of Polyethylene (PE), Polypropylene (PP) and Polyamide (PA). Two types of fake grass yarns are to be distinguished: fibrillated fibers and monofilaments.

• For production of artificial grass fibrillated fibers thin films (slit film) are extruded which contain parallel splits or “points of fracture by design”. The final properties are created by subsequent treatment such as stretching and heat (curled structure). Up to 12 such fibers are combined to form the individual carpet tufts.
• The characteristic of faux grass fibrillated fibers is their softness which severely limits skin burn injuries that occur when sliding over the fake grass surface with uncovered/ unprotected skin (sliding skin burns, rug burns). This is especially true for the artificial grass fibers known as LSR fibers (LSR = low sliding resistance). However, fibrillated fibers still experience issues with the longevity of the elastic behavior and their form stability (splitting and felting). A further consequence of this design is that these faux grass fibers snap off right above the pile infill after a rather short time which negatively changes the ball and sliding behavior. The LSR technique is also applied to monofilament fibers.
• Today, artificial turf surfaces are mainly manufactured with monofilament fibers which are extruded as individual fibers. This allows the design of the cross section and thickness of the fibers (bent, imprinted with grooves, profiled) to be specified. Their thickness varies between 90 and 200 μm (0.200mm) and they can be manufactured from stiffer or softer material which allows for more or less flexibility according to the type of cross section. Monofilaments are also subject to subsequent treatment, especially to produce a curled structure.

Today, fake grass fibrillated fibers are used mainly in combination with fake grass monofilament fibers only.

The stabilization of the artificial turf and synthetic pile fibers against UV light and heat is crucial to the aging behavior. Since the stabilization is costly special attention must be paid to it. Unfortunately, the effect of the stabilization cannot be measured with simple and immediate tests and visually it is not detectable as all artificial turf and synthetic carpets are green when new. Therefore, a diligent process of quality determination is vital (identity of the fake grass fiber, manufacturer of the fake grass fiber; reference installations, certificates of long-term ageing). The fake grass pile fibers are tufted into a primary backing fabric. Several pile fibers are combined per tuft. The distance of the tufts varies both parallel and across the axis of the carpet rolls.

Experience has shown that the tips of the fake grass pile fibers must stand above the infill by about 15 to 20mm in order to control the ball roll behavior according to the requirements of the sport of Football (Soccer). This exposed fiber also creates the look of natural grass that is desired.

The pile fibers can be a problem for the player even if the technical requirements have been met. For example, when non-filled surfaces exhibit a relatively thick pile layer made of relatively stiff pile fibers, the resilience is initially caused by the fibers laying over instead of vertically compressing which is the desired action (i.e. the foot is constantly deflected to the side by up to 25mm; uncertain footing). More important is the fact that this is connected with increased abrasiveness.

Another problem exists with (mainly) non-filled surfaces in the form of electrostatic charges. This is especially true with surfaces on top of PE or EPP foam elastic layers. This phenomenon is observed on dry surfaces only. A solution to this problem has been found by adding conductive fibers to the pile layer. However, the charge must also be conducted through the elastic layer into the substrate (design task).

Abrasiveness is not limited to unfilled pile layers, it can also be a problem with filled surfaces. Essentially it is caused by the density of the pile layer (number of pile fibers
and tufts per m2), structure, shape and hardness/stiffness of the (monofilament) fibers. Abrasiveness manifests itself with skin burn injuries and abrasions when players slide over the surface with uncovered/unprotected skin. Abrasiveness is especially
noted with Polyamide fibers. Therefore, these fibers are used as supporting fibers only. In this application they are very effective because they exhibit – different from PE fibers – very good deformation recovery. Instead of the Nylon 6.6 fibers which were used in the beginning, only Nylon6 fibers are used today.

In order to avoid the problem of abrasiveness, non-filled artificial turf surfaces should always be installed with a sprinkler system. Different from irrigation of natural grass pitches, in this case irrigation serves to moisten the pile layer only (therefore less water consumption). It is important to use water which does not have too much carbonate, manganese or iron since these elements can accelerate weathering and hence discolor the fibers or form a crust on the pile.