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additives feature | Foaming agents


windows and the weak melt properties they usually have. For example, in the case of the newly developed PBT bead foams, a change of temperature by a factor of only 4°C could change the die pressure by almost 200 bar,” explains Fathi. University of Bayreuth researchers


Adidas is using BASF’s Infi nergy TPU particle foam in its Energy Boost running shoes


Adidas has


extended the use of TPU


particle foam midsoles to its latest snow-


boarding boots


are also looking at novel nucleating agents and their signifi cant role in tuning foam cell size. “For example, it was recently shown that very small amounts (0.5 wt.%) of graphene and carbon


nanotubes (CNTs) could signifi cantly reduce the cell size of extruded polystyrene foam (XPS),” says Fathi. One high-profi le example of how particle foams are being used in high performance applications can be found in the midsoles of the Energy Boost running shoes introduced by Adidas in 2013. They are made using BASF’s Infi nergy expand- ed thermoplastic polyurethane (E-TPU ) foam technology. The material is claimed to provide special spring and cushioning properties compared to the EVA foams typically used in such applica- tions.


“E-TPU is manufactured by foaming the starting


material, TPU granules,” explains Dr Uwe Keppeler, material and process developer at BASF. “After pre-treatment with pressure and heat, the individual granules measuring up to 5 mm each are blown up like popcorn.” In the process, its volume increases by a factor of 10. “These sealed air cells make the lightweight foam


beads very elastic and provide the desired rebound effect. The individual beads can be imagined as being like tiny footballs: The more air they contain, the better they bounce and rebound back,” adds BASF research


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scientist Dr Frank Prissok. Around 2,500 beads are used to produce each


midsole. They are treated with hot steam, which melts the outer layer of the beads slightly, causing them to bond into a stable shape. An Infi nergy midsole can be compressed to about half of its volume at a pressure of 2 bar. This helps it to absorb shock impact on the foot. Once the pressure subsides, the foam quickly returns to its original shape. Late last year, Adidas extended the use of TPU-E


particle foam midsoles to snowboarding boots, taking advantage of the fact that the material’s properties are retained at low temperatures.


More information


AMI is running two Polymer Foam conferences this year, one in America and the other in Europe. The fi rst takes place on 14-15 April 2015 in Newark, New Jersey, USA. For full details, visit: http://bit.ly/Foam15. The European version of the event is being held in Cologne, Germany, on 2-4 November 2015. For information on participating in the conference as a delegate, exhibitor, sponsor or speaker, please visit: http://bit.ly/FoamEU.


Click on the links for more information:  www.bergeninternational.comwww.mecaplast.com  www.polyfi lcorp.comwww.polyone.comwww.polymer-engineering.de (Bayreuth)  www.reedyintl.comwww.rowa-group.comwww.sumika.co.ukwww.tramaco.com


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