"Everything was better in football in the past." Really? Yes, there was more sport and less business. But: What do the footballers say back then, how it was when they played football in the rain, for example my neighbor? "Such a wet ball hurt your forehead a lot! And it was heavy! I got wet on top of that." The "leather" used to be made of leather and soaked in water when it rained.
At least that's better today. The surface of a soccer ball is now made of plastic; it consists of several layers of - attention chemistry! - polyurethanes. Polyurethane is a polymer. Polymers are rather long chains, submicroscopic thin, very long threads. They are formed by chemical interlinking of a large number of smaller units. By the way, polyurethanes are also known from numerous other things in everyday life: foam mattresses, car seats, construction foam, paints, adhesives and many others 1.
On top of that, our football polyurethane is, more precisely, an elastomer. A material is elastic if it can be deformed by pressure or tension. However, it returns to its original shape when the pressure or tension ceases. And that is exactly what elastomer threads can do. Without pulling, they form a kind of ball (A). But if you pull the threads, they stretch in the direction of pull (B). When the tension slackens, they return to their original shape (A). The threads are linked to each other at the red points in the drawing below 2.
In modern soccer balls, several layers of such polyurethane elastomers are welded together. The innermost layer is a foam made up of tiny spheres; it is responsible for the restoring forces of the ball (in the figure from B to A). The next layer is a two-part polyurethane. It makes the ball surface elastic. The outermost cover layer is also made of polyurethane and prevents abrasion 3. The result: the ball is perfectly round (maximum deviation from the spherical shape is 0.1%!) And the "leather" does not absorb water, so it is equally heavy in all weathers. One example is the "Telstar 18" from the 2018 World Cup 4.
At Euro 2008 the "Europass" was presented 5, which for the first time had goose bumps 6. It made the ball more grippy and had special aerodynamic properties. This brings us to the flank, as "Banana King" Manfred Kaltz from HSV perfected it at the time. Original quote from Horst Hrubesch: "Manni Banane, I head, goal!" Chemistry and physics are perfectly intertwined on the surface of a football. In the language of physicists, the banana flank is a consequence of the Magnus Effect, but that's another story ... 7,8
Literature:
[1] Polyurethanes in Wikipedia.
[2] Source: "Thermoplastic Elastomers" in Chemgapedia®, Wiley Information Services GmbH.
[3] K. Kern, G. Hornung: Die Chemie des Fußballs, CHEMKON 2017, 24, 1-9
[4] Covestro press release: "Polyurethane materials for the perfect flight" 06/14/2018
[5] The Europass in Wikipedia
[6] Football in Wikipedia
[7] Banana flank on YouTube.
[8] A. Steinecke: The secret of the banana flank, Spiegel Online, January 31, 2006.
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last modified: 06.07.2021 19:59 H from MPM
