The Smart “Fortwo” has become the first series-manufactured automobile to use body panels entirely of polypropylene (PP). To make the parts, Smart's supplier Plastal (Kungälv / Sweden; www.plastal.com) uses the newly developed thermoplastic polyolefin composite (TPO) "Daplen ED230HP" from Borealis (Vienna / Austria; www.borealisgroup.com). A slightly different version of the composite is already being used in the tailgate of the Renault Modus and in the tailgate lining of the Citroën “C2”.

Daplen ED230HP is an injection mouldable PP containing 20% by weight of mineral filler and additionally modified with an elastomer component. In the Smart, it replaces the PC/PBT blend used up to now in exterior body panels, tailgates and hoods. The Daplen material, unlike PC/PBT, is an in-mass coloured compound, which means that the colours are blended into the material. As a result, post-assembly painting steps are reduced and only a clear coat has to be applied. In addition, the material’s low thermal expansion imparts dimensional stability over a wide temperature range and allows zero gap tolerance between the parts. In the Smart, replacing PC/PBT has reduced overall vehicle weight by 15%, says Borealis.

The use of TPOs in the automotive industry has increased significantly over the past ten years. Because of their superior properties, these are increasingly substituting other plastics. In 1995, for example, only 9% of bumpers were made of TPOs, but by 2005, the figure had risen to 67%. Over the same period, consumption of PC/PBT for this application dropped from 18% to 4%.