Abstract
Polyurethane materials have been known for decades. More recently thermoplastic polyurethanes (TPUs) have been introduced. These materials represent an alternative to either conventional thermoplastics or rubber, depending on the hardness. TPUs have a substantially higher tear propagation resistance and abrasion resistance than rubber, but for a long time they remained very vulnerable to hydrolysis and had poor compression set. Recent developments by raw material manufacturers have significantly improved the hydrolysis resistance. However, as sealing applications also require very good compression set values, the greatest improvements in this area have been achieved by the major seal manufacturers who synthesise their own polyurethane. TPUs are clearly the sealing material of choice for applications in hydraulics systems and are increasingly taking over from rubber. Recent developments have succeeded in obtaining excellent low-temperature flexibility combined with good compression set at high temperatures. For special sealing applications in the food sector, however, good hydrolysis resistance is no longer sufficient in itself. A new range of materials developed for this sector offers resistance to CIP/SIP media that is even better than that of many conventional elastomers.
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