Extruding the yarn
Formerly made of nylon, elements imitating blades of grass are now often made of polypropylene or coloured polypropylene, or more rarely polyamide or polyester, in the form of monofilament or fibrillated tape. They are made to look like a mowed lawn or a new, dense, unmowed lawn. Polymer granules, melted at high temperature, are extruded to form artificial blades of grass. There are two techniques; the first is extrusion spinning, which consists of continuously pushing the polymers through a die. The profile of the long fibres of artificial turf created in this way is determined at this stage using capillary tubing. After stretching and cooling, the fibre is both flexible and strong. The other technique is to extrude a film then cut it into thin strips to the desired widths.
An important parameter for the yarn is the density of its strands. Decitex (dTEx) is used, which specifies the weight in grams of 10,000 m of thread. The width of the monofilament fibre is often 0.8 to 1.2 mm, while the fibrillated tape may be 5 to 12 mm. Fibre thickness is between 50 and 150 microns.
Manufacturing artificial turf
Creating sections of actual artificial grass uses the ‘tufting’ technology widely used in the field of carpet manufacture: on the same principle as the sewing machine, loops of yarn are formed through a woven or non-woven backing material, depending on the desired parameters (height, number of points etc.). To achieve the final look of blades of grass, the loops are cut off at the top by a special machine and the fibres stand up. The fabric is then coated with complex compounds (latex, polyurethane) to firmly anchor the blade to its backing material: this step is crucial for the life of the product, especially on sports grounds where this ‘grass’ will be subjected to sliding, boot studs, knocks and blows. Draining holes are made to allow rainwater to seep away.
It can then be inspected, rolled, packaged and shipped.