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Let's get things straight

Bayer MaterialScience AG : 27 April, 2004  (Company News)
Outstanding robustness, low dead weight and a negligible effect on rigidity over a broad range of temperatures - these are some of the properties offered by thermoplastic polyurethanes (TPUs) such as Desmopan
'Till now, this material was mostly utilized for ski boots. But TPUs are not limited to ski equipment,' explains Bayer MaterialScience footwear expert Wolfgang Grimm. 'Quite the opposite, the robustness of these plastics makes them suitable for use in the outsoles of especially lightweight shoes.' And it is now possible to develop grades of Desmopan without any plasticizers at all, thereby making another massive contribution to increasing this material's spectrum of use, e.g. combination with ether-PU midsoles.

'One of the most significant trends on the footwear market in recent years has been the move toward increasingly lighter shoes. And thermoplastic polyurethanes such as Desmopan® could hold the key to producing extremely lightweight 'wellness' shoes,' says Grimm. For instance, these flexible materials are very abrasion-resistant, with values as little as a third of those of standard ester polyurethanes. This means that heard-wearing TPU soles, at approx. one millimeter thick, can be two to three times thinner than those made from 'traditional' polyurethanes, not to mention the fact that they are much lighter. The impression of lightness can also be accentuated in a fashionable way by giving TPUs a transparent or opaque look. Combining these materials with other sole materials also means that certain preparatory treatment stages, which are indispensable when utilizing rubber, become less complex or even unnecessary.

In the past, manufacturers aiming to get the best from their material by combining lightweight TPU soles with particularly light polyurethane midsole materials previously had to rely on polyester polyurethanes. 'The reason was that, under certain conditions, polyether polyurethanes were prone to absorbing plasticizer from the TPU outsole and swelling. As a result, dual-layer soles produced in this way could distort over time. In addition to the phthalate-free Desmopan grades (the phthalate-containing grades must be appropriately labeled as of April 1, 2004) being promoted in Europe, we have developed a version which does not require plasticizers at all,' says Grimm, summarizing the developments to date. So deformation of the polyurethane in ether midsoles is prevented from the very outset.

The new Desmopan® TP 6365 A and/or Desmopan® TP 5065 A thermoplastic is currently available with a Shore A hardness of 65 +3. And avoiding using plasticizers should even pay off when it comes to safety shoes, as brittleness resulting from the migration of this additive is prevented. Bayer also has plans to offer an anti-static variant for this particular market.

The new grades of Desmopan® were made possible by selectively altering key polymer properties, for example the molecule chain length distribution. 'Thanks to the plasticizer-free Desmopan grades, manufacturers who are experienced in processing polyether polyurethanes can now fully exploit the benefits of the lightweight combination of Desmopan outsoles and Bayflex® midsoles both for themselves and their customers.'
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