Extrusion technology for the production of artificial turf

• Artificial turf “yarn” made from tapes or monofilaments
• PA, PE and PP compete as possible raw materials
• PET bottle flakes can be recycled to artificial yarn

In the last few years, artificial turf has been used in an increasing number of applications. Apart from the rapidly growing sports and leisure time segment, artificial turf is more and more used in the hotel, home and landscaping area, especially in regions with little rainfall and restrictions on the watering of lawns.

Approved by FIFA since 2004

Currently, the market for sport applications in Europe is about 10,000 fields/year. This corresponds to a production of about 50,000 t/year of artificial turf. All in all, there are about 100,000 fields alone in Europe that will be modified in the next 10 years for reasons of cost. The fact that since February 2004, artificial turf has also been approved by FIFA further promotes this development.

Due to water shortage in the warmer Mediterranean countries, the landscaping sector will develop an even larger market than simply sport applications. Further benefits in both the sports and leisure sector and landscaping include a reduction in the cost of care and maintenance as compared to natural turf: this aspect is particularly advantageous for communities.

Artificial turf “yarn” made from tapes or monofilaments

The artificial turf “yarn” consists of tapes (=slit film) or of monofilaments (endlessly produced single fibres). Currently, the “yarn” which is “tufted” in a special weaving process is still dominating the market. Reifenhäuser states that in the years to come the monofilament will increasingly come to replace tape. One advantage of the monofilament over the tape is said to be its bending resistance which is identical in all directions and thus results in an“isotropic” ball behaviour. High-performance monofilament lines of Reimotec with an output of up to 500kg/h have contributed to replace tapes by monofilaments used in artificial grass production.

PA, PE and PP compete as possible raw materials

Different plastics used in the artificial turf “yarn” Polyamide (PA) is used in artificial turf “yarn” for hockey, landscaping, golf and American football. The advantage of PA is that by absorbing water, it springs back easily; however, its friction coefficient with skin is very poor. Polyethylene (PE) is used for football and American football. The friction coefficient of PE, especially linear low density polyethylene (LLDPE), with skin is very good; however, it does not spring back satisfactorily. Polypropylene (PP) is found in artificial turf “yarn” for football and American football. With regard to the friction coefficient, PP is slightly worse than LLDPE, however better than PA, and it also springs back better than PE, but much worse than PA. In landscaping, only PA is used, as PE and PP start to lose its stability already at 80°C. PA, however, can be used up to a temperature of 120°C.

With an increasing usage, the requirements on artificial turf, however, also increase, like antimycotic, antibiotic and flame-retardant characteristics. Another problem especially in the landscaping area in very hot regions is the heating of the artificial turf. With a temperature of 40°C in the shade, the artificial turf easily reaches temperatures of 70°C to 80°C, which are too high for applications in the leisure sector. An additional cooling effect by the layer set-up is therefore also desirable.

Tri-component technology

The production and/or the spinning of two-layer monofilaments and/or bi-component filaments of two different thermoplastic plastics are generally known. The disadvantage of many bi-component filaments is, however, that the two layers (core and jacket) do not adhere to each other suffi ciently and therefore delaminate in the stretching process. For this reason, Reimotec addresses the above disadvantages and limitations by using an adhesion-promoting layer and using a tri-component technology.

Consequently, completely new property profiles can be used (for example LLDPE in external layer for good sliding characteristics and PA core so that the “yarn” springs back easily). Environmentally friendly artificial turf systems New developments in the area artificial turf systems aim at eliminating the filling of the turf carpet with filling materials like plastic granulates or sand or at least at limiting it to a minimum. The reasons for this development include environmental aspects as in 2005, when the use of rubber tyre material for filling purposes and the related environmentally harmful aspects became publicly known.

PET bottle flakes can be recycled to artificial yarn

A new generation of grass yarn carpets consists of textured and plane monofilaments. The use of textured yarns offers the possibility to do without or minimise the quantity of infill materials like plastic granulate or sand. An economic and environmentally friendly solution is the production of an infill free artificial turf from recycled polyethylene terephthalate (RPET) for landscaping applications. With twin- screw technology 100% PET bottle flakes can be recycled to high performance artificial yarn: “Green solution – from bottle to yarn”.

Production of two coloured yarns in one stage

The monofilaments can be directly textured inline during the monofilament production or offline in a second stage. In the texturing, the turf yarn is permanently structured. This results in more volume in the turf and in a better longitudinal utilisation of the yarn. Current system concepts allow for the production of two coloured yarns in one stage. The direct two-colour extrusion of artificial grass filaments has become well accepted in the market due to specifically developed spin heads. They form the basis of this technology in which two colours are simultaneously fed using separate extruders. Sophisticated die geometries allow the production of “his artificial grass filament” in the desired shape. 3D CAD systems are used to develop these designs. The possibility of combining various colours, different monofilament cross-sections and filament thicknesses allows the production of turf carpets and fulfills the requirements that are made on the different artificial turf types for the following applications: venues, landscaping and gardening and wellness.