PTFE, PVC ... polymers fill stadiums

PTFE covers, polypropylene seats, PVC roof... plastics are very useful for designing and building football stadiums. Without them, the stadiums would be much less functional and eco-friendly.

Artificial turf improved with plastics

As is the case with the ball, a stadium’s turf is often the subject of much discussion. And rightly so, as it is one of the centrepieces of the stadium for the players. It must be flat, smooth and wet enough to allow sliding. In this area, as is the tradition, the English had, for a long time, the greenest thumbs. So much so that, much like their players, the best groundsmen were also traded at top prices. However, not all clubs can afford to acquire such talent, let alone change their turf every year. The turf alone accounts for around 1% of the cost of a stadium!
Some stadiums therefore opted for artificial turf, which first appeared in the 1960s. At the time, it was made up of thin strips of polyamide anchored into a latex and polyurethane fabric. Although satisfactory, these first turfs would soon be improved upon. Polyamide was replaced with polypropylene and polyethylene, stronger polymers whose strands were coated with silicone and planted into a mixture of expanded polypropylene and synthetic rubber granules generally derived from old tires. The latter gives the pitch elasticity and promotes drainage. It is effective, gives the ball a better bounce, speeds up the game but players can get burnt in the event of a fall or a slide. The rubber granules have recently been the subject of much discussion. The current trend involves replacing the crushed tires by small pellets of EPDM (ethylene propylene diene monomer), an inert polymer whose white colouring limits the sun’s infrared rays and therefore prevents the pitch from overheating.

Thanks to synthetic microfibres, artificial turf has improved considerably over the past years.

During the World Cup, all of the pitches will be made from natural turf because of the amount of money invested. However, the choice of turf is important, particularly in Qatar where temperatures regularly exceed 40° C. There is a solution, and once again brought by polymers. The concept involves simply strengthening the blades of grass. To do this, the natural turf is planted in a substrate composed of cork, fine sand and synthetic microfibres in which the grass takes root by wrapping around the fibres. What is the nature of that polymer? Impossible to know for the time being, as manufacturers refuse to reveal their secrets.

The PVC roof of the Munich Olympic Stadium: the forerunner of football stadium roofs

Plastics pull the covers over to their side Covering a stadium to shelter the players and spectators has been mastered for several decades. It seems trivial today, but it would have been difficult to achieve without polymers. Although we talk of roofs, they are obviously transparent or at least transparent surfaces. There are such things as glass roofs, but they do not cover large areas such as stadiums simply because of their weight. As for concrete, although nothing is technically impossible, it is not used for obvious reasons relating to luminosity. In the late 1960s, brothers Günter Behnisch and Frei Otto, the architects of Munich’s Olympic Stadium, turned to polymers.

They wanted to create more than a simple stadium and wanted a monument that would become emblematic of the city. Their goal was to reproduce the draped aspect and rhythm of a mountain range in the Alps. They decided to erect masts and drape hundreds of metres of a PVC-coated polyester fabric, a waterproof textile that was flexible enough to withstand the wind, over the masts. In total, 74,000 m2 of that fabric were used. A technological feat for the time as everything had the be invented; at the inauguration, the technical aspect was all the press could talk about.

The road had thus been paved for polymers, and they were not about to wait patiently for their superiority to be discovered. Since then, most covered stadiums are covered either with polycarbonate, a lightweight and transparent material, or and mainly with PTFE (poly-tetrafluoroethylene), better known under its trade name of Teflon®. However, although the term is commonly used, a PTFE membrane is actually a fabric of fibreglass coated with PTFE. This translucent fabric has all fine qualities: it can withstand extreme temperatures (from -70° C to +230° C), a few drops of rain suffice to clean it off, and it has a lifetime of close to thirty years. Better yet, it reflects over 73% of solar energy. This will be important in Qatar, where the 2022 World Cup will be held. In fact, almost all Qatari stadiums currently under construction will be covered with PTFE. Finally, it would be unfair to leave out ETFE (ethylene-tetrafluoroethylene), a transparent and very lightweight polymer. This material was used to coat the external walls of Munich’s Allianz Arena that hosted various games during the 2006 World Cup. Its transparency could make it a favourite among architects, but it is deemed weaker than PTFE and therefore costlier over time as it requires more maintenance.

PTFE, ETFE, two of architects’ favourite polymers because of the elegant touch they bring to football stadiums. Lightweight and easy to stretch, they can take on any shape to cover any of a football stadium’s surfaces.

It would have been more difficult to build the new stands at the Ekaterinburg stadium without the help of polypropylene seats.

Making the impossible possible If it was looking for a way to make the news, it certainly achieved its goal. FIFA judged the World Cup stadium in Ekaterinburg, Russia, to be too small. Re-building a stadium was unthinkable, for budgetary reasons in particular. The organisers therefore built temporary stands outside the stadium after literally cutting it open. The result is impressive, albeit slightly scary. The stands are in fact scaffolding made up of thousands of metal tubes holding up 9,000 seats. A polymer was selected to create the seats, most likely polypropylene, a material that is sufficiently lightweight to enable its creators to dare build such a structure.

A little sun to cool down

One of the great questions relating to the 2022 World Cup in Qatar is the following: is it possible to play football for ninety minutes under a blazing sun? And what about the spectators? The stadiums will obviously be covered, which will provide some shade, but there are no guarantees that that will suffice to bring the temperature down to an acceptable level. The Qataris have solved the problem by installing air conditioning in their stadiums. However, is this not counterintuitive at a time when most nations wish to curtail global warming? Theoretically not, as the energy to power the air conditioning systems is to be provided by the sun. Given that the stadiums are under construction, it is difficult to ascertain which technology will be used. However, a similar experiment has been carried out in various stadiums around the world. The most famous of these was that carried out at Kaohsiung stadium in Taiwan, which was covered with close to 9,000 solar panels made up polymer cells specifically designed for it. The progress made each year in this area of technology led us to believe that the performance of these types of cells will have further improved by 2022. Qatar may yet come out triumphant in this regard; in addition, by opting for polymers, the future organising country is already placing itself firmly on the side of the builders of ecological stadiums, as manufacturing those cells requires less energy than silicon cells.

Hundreds of thousands of polymer photovoltaic cells now cover certain football stadiums. They can produce enough energy to light, and even cool the stadium.