BASF claims world first with expanded TPU
01/07/2013
BASF has said it will bring the E-TPU to market under the brand name Infinergy, but the first product making use of the new, closed-cell particle foam has already come onto the market, the new Energy Boost running shoe from adidas, developed “in close partnership” with BASF, the chemical company has said.
To produce Infinergy, an established BASF thermoplastic polyurethane, Elastollan, is expanded using a new procedure in which the benefits of thermoplastic polyurethane (TPU) are retained and added to by the typical properties of foams. In keeping with all particle foam materials, Infinergy has a low bulk weight, with a density of about 110 kilos per cubic-metre, and, after processing on standard moulding machines, a moulded part weight of between 200 and 320 kilos per cubic-metre.
This puts the new foam somewhere between the generally lighter expanded polystyrene (EPS) or polypropylene (EPP), and the heavier elastomeric polyurethane foams.
Thanks to its closed-cell structure, Infinergy also absorbs little water, less than 2% by volume in 24 hours, BASF has said. Like the TPU on which it is based, it is also characterised by high breaking elongation (between 100% and 150% depending on the density), high tensile strength (approximately 600 kilopascals) and good abrasion resistance, combined with good chemical resistance.
According to BASF, one of the main features of Infinergy is its recovery behaviour which is due partly to the closed-cell structure of the foam. The company has gone as far as to say this makes it “the most elastic particle foam currently available on the market”. Tests of the resilience elasticity under ISO 8307 (the ball rebound test) and under DIN 53512 (using a pre-set pendulum hammer) show that the rebound height for E-TPU can be as much as about 55%, higher than other particle foams like EPS (less than 20%) or EPP (30%).
Infinergy does not lose its resilience even when under a continuous load: during a high-frequency fatigue test using dynamic loads at five cycles per second and a constant pressure of 250 kilopascals, the material performed about 75% better than EPE. After 40,000 load cycles, the thickness of the test piece of E-TPU was still 37 millimetres (compared to a starting figure of 40 millimetres), whereas the EPE remained permanently compressed and the thickness of the test piece was reduced to about nine millimetres. This means that Infinergy returns almost all the energy that is applied to it.
Furthermore, Infinergy also remains elastic and soft over a wide temperature range, BASF has reported. Dynamic mechanical analysis has shown that, even in extremely low temperatures of minus-20 degrees Celsius, Infinergy is still very soft and stretchy and does not go stiff.
With the help of crack-splitting and pressure-filling, Infinergy can be processed on the same moulding machines as expanded polypropylene (EPP). In a number of stages, the pre-foamed particles are pressed together under hot steam and bonded together. In addition, because polyurethane binders adhere well to Infinergy, other processing techniques are possible such as gluing and foam sealing of the particles. This procedure will enable large-scale processing, BASF said.
“Infinergy can be used anywhere where customers require a combination of low weight, excellent mechanical properties and good durability across a wide temperature range,” the company added. “Infinergy could replace rubber as a cushioning element, anywhere where a low-weight material is needed.”
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