Last month KIJK Magazine published an article about artificial turf in top soccer leagues and artificial turf developments in general. Edel Grass and Ten Cate Grass were interviewed to give their perspective on innovations to be expected in the near future. For infilled fields as well as non-infill soccer fields, both Edel Grass and Ten Cate are in the lead to develop the next generation in artificial soccer systems, which are likely to also be adapted by the soccer top league clubs.

KIJK Magazine is a well respected and 50 year old scientific magazine for younger readers and focusses on well educated minds.

Read and download the article (in dutch) here:
Kijk Magazine september 2018

A copy of the printed magazine can be bought online here:
KIJK Magazine September 2018

Text by Mike van Damme, sports journalist and writer. For this article he consulted the research findings from ‘Artificial grass: additional risk of football injuries?’ by professor Frank J.G. Backx (2016) and ‘Ideal Fields’ by KNVB, Jan Verbeek and Thijs Velema (2016).

The english translation of the contents are available below:

Technological ingenuity has to deal with prejudices about artificial grass

Artificial turf for premier soccer competitions

Dutch professional football players are often heard to complain about the artificial grass used in the Dutch premier league: it plays entirely differently from natural grass and is a hazard to players’ limbs. Is it really not possible in this era of technical progress to create artificial grass that feels and responds like the real thing? We explore the (future) world of artificial grass.

The Dutch premier league football season starts again this month, and six clubs currently feature artificial grass in their stadiums. And the truth is, many Dutch footballers simply dislike the stuff. They are convinced they get injured more easily and that the ball responds differently than it does on natural grass. This seems to be mostly a gut feeling, as scientific research does not actually reveal such extreme differences between artificial and natural grass.

In 2016 Frank J.G. Backx, lecturer in sports medicine at Utrecht University, researched the risks of injury for the two different surfaces. He concluded that the risk of injury is more or less the same for both. However the type of injury differs. For example, there is a greater risk of ankle injuries on artificial grass as this surface tends to be stiffer, presenting increased resistance when turning. On the other hand, artificial grass has fewer holes and bumps, reducing the number of lower leg injuries.

Clubs with natural grass in their own stadium feel that clubs using artificial grass have a home advantage. The KNVB, the Royal Dutch Football Association, examined this perceived advantage. They concluded that visiting teams with natural grass at home achieve pretty much the same result on artificial grass over an entire season as they would have if they had played these matches on natural grass. However, over an entire season, on artificial grass they score one less goal and also concede one more. No perceivable difference was noted in the number of fouls, duels or shorter and longer passes.

In this respect, the players’ intuition and science are diametrically opposed. Still, manufacturers of artificial grass investigate ways to improve their product. And these improvements are on their way, as was demonstrated by a visit to the two largest Dutch manufacturers of artificial grass, Edel Grass and TenCate Grass.

An artificial grass system consists of various layers, only two of which are visible: the grass fibres (110,000 to 140,000 per square meter) and the elastic granule infill that springs up when players slide or the ball bounces. Below this is a layer of smooth grains of sand, less abrasive to the fibres and players’ legs than the sand familiar to us from the beach or sand box. The sand layer is supported by first a shock pad (an elastic layer to absorb shocks), then a fabric layer to prevent holes and tracks forming and finally a foundation layer.

Research at Edel Grass and TenCate Grass concentrates on the grass fibres and the infill. Victor Neuteboom, manager of research and development at Edel Grass, is direct: The material and form of the grass fibre have more or less reached the end of their development. The fibres are made of polyethylene (also used for packaging, plastic bottles and containers among other things), a soft and flexible alternative to the stiff nylon of early artificial grass.

As for the shape, few further developments are anticipated there either. There are fibres that look like a V, W, U or C, or a lozenge when viewed in cross-section. “The C and the lozenge shapes are most favoured for football fields these days,” explains Neuteboom. “It seems that these have the greatest capacity for staying upright. And that’s important in football, as the player needs to be able to get his foot under the ball. Something not as easily achievable with flat fibres.”

According to the researcher, developments involving the so-called infill are more likely. These elastic granules ensure the playing action feels as natural as possible: they provide grip for football boot studs, and also assist in making turns on the field. The granules also help keep the artificial grass fibres upright.

For a long time the infill consisted of shredded rubber, usually recycled from old car tyres. These rubber granules came in for some poor press in a 2016 Zembla broadcast. The programme’s researchers stated that there were health issues surrounding the rubber granules and that this required serious further investigation. A decisive answer has yet to be found on this.

In the meantime, sufficient cleaner alternatives have emerged; synthetic rubbers such as EPDM (used for cables and roofing) and TPE (used for window sealing and soft grips for tools and pens). Neuteboom: “EPDM is usually produced in blocks then shredded. The result is tiny square blocks, similar to the rubber granulate recycled from old car tyres. TPE however can be manufactured in any shape imaginable.”

And this is really where the opportunities for the future lie. Edel Grass is currently looking into which shape of infill would provide the most optimal, consistent dampening and grip. A bit of trial and error really, according to Neuteboom. One type of infill the researcher believes we will be seeing more of in the near future is ring-shaped. Long strands of hollow ‘spaghetti’ are made from TPE and then cut into pieces. The hollowness of the infill provides additional dampening. Neuteboom: “First, the granules’ resistance against compression ensures a dampening effect. Once both sides do press together, the material’s elasticity kicks in, improving the dampening even further.”

Are there other shapes that could work? Neuteboom is considering star-shaped granules. “Due to their projections, the granules tend to hook together more and therefore spring up less easily. This prevents spots in the field where the infill has ‘jumped’ clear, leaving an excessively hard underlay in these areas. As the granules cannot lie as tightly against each other as the square ones, more air is retained between the granules. Something which also improves dampening. Well, that’s the theory at least. We will need to do some R&D first.”

At TenCate Grass they are even considering going a step further. A new system is currently being tested in their sports lab in Nijverdal, without elastic granules. In other words, a non-fill surface. Rather than using infill, they have increased the density of the grass fibres: curled fibres are placed between the upright fibres to improve the grip.

Niels Kolkman, head of the development department, explains: “The crimped fibres are 20 millimetres long and form a dense underlay that can bear the player and withstand the boots’ studs well. This provides outstanding grip. The longer fibres sticking up through it give the field the perfect characteristic football look and ensure correct ball-rolling behaviour. The fibre’s bending moment and the material’s stiffness exert a resistance on the ball comparable to natural grass.”

The upright grass fibres used in this field do not have a C or lozenge shape, but rather an asymmetrical structure. This is to increase flexibility and durability. Kolkman: “A fibre is burdened in constantly differing ways, from being trodden on, players sliding over it and the ball bouncing and rolling across it. Due to its asymmetric structure the fibre responds differently to each type of load, not always affecting the same spot, but many different areas at a lower level instead. This makes the fibre less prone to wear and tear.”

Because granules move – for example during heavy rain or when the field is swept clear after snowfall – players experience variations in the hardness on a field with infill. Kolkman: “In a non-fill field, the conditions are the same across the entire surface, because unlike fields with infill, the additional fibres cannot move. This also eliminates the discussion on whether or not the infill is hazardous to health or the environment.”

The non-fill field has another challenge to meet concerning ‘sliding-friendliness’, Kolkman acknowledges. “To facilitate proper sliding, the field must currently be slightly damp. You solve this by spraying it down right before the match. In future we want to solve this within the artificial grass system itself, so without the need for spraying. For example, we could use a somewhat ‘smoother’ fibre. We have the knowledge, but the challenge lies in finding the right balance between grip and comfortable sliding.”

And then the real challenge starts: changing the footballers’ gut feelings.

Rigorous demands for artificial grass systems

Every field is different. In professional football, this applies equally to natural grass fields and the artificial grass systems. However, what the latter do have in common is: they have all been approved by the FIFA world football association. A system used in professional football must comply with an extensive list of demands drawn up by FIFA. For example, the ball must not bounce too high or too low, not roll too long or too briefly, nor veer off-course after a shot. Also, the player must not experience too much resistance to turns and the field must not be too hard (shock absorption) or sink down too easily (deformation). Only once all of these demands have been satisfied will FIFA approve a field.

The history of artificial grass

First generation of artificial grass:
Artificial grass emerged in the seventies for sports such as American football and baseball. Fibres were stiff nylon or polypropylene.

Second generation of artificial grass:
A new type of field scattered with sand, mainly used for hockey, appeared at the end of the seventies.

Third generation of artificial grass:
In 1981 the English Queens Park Rangers were the first footballers with artificial grass, using supple, longer (polyethylene) fibres.

Hybrid grass:
Hybrid grass is currently popular in professional football. This is mainly natural grass, with a maximum of 10% artificial fibres.

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