Technical elastomer products (TEPs), also referred to as rubber, are already known to be used in profiles, sealing rings and rubber mats. For some time now, the developments in TEP recycling have been the focus of both scientists and users. The topic of recycling of rubber residues is increasingly gaining in importance, in particular against the background of severely increased energy and raw material prices. However, holistic utilization approaches and processes to develop high quality materials from rubber residues have been missing to date. The objective of the research work was to systematically analyze elastomers in powder and granulate form to optimize the recycling of rubber residues, because the elastomers in powder and granulate form can be used as functional additives, i.e., they provide plastics compounds with the desired properties such as haptics, hardness or elasticity. They can also be used to modify paints, coatings and powder coatings. In addition, new, high quality applications can also be developed with them.

By adding elastomeric powder, Fraunhofer UMSICHT has now developed high quality plastics compounds, elastomeric powder modified thermoplastics (EPMT®). The materials are already undergoing application tests at industry customers. A broad range of areas of use is possible. For this, Fraunhofer UMSICHT analyzes possible substitutions together with the customer, e.g. the application in the area of wheels (lawnmower etc.) or in the vehicle area (splash guard, mudguards).

Scale-up to the industrial process

The researchers pursue a holistic utilization approach in the development to sustainably record and utilize the residues. Fraunhofer UMSICHT has knowledge of the complete value added chain from collecting, comminuting and processing the elastomer residues to the development of suitable formulations to the manufacturing of marketable products at a technical shop scale and the subsequent analytics. It is not just the individual aspects of the recycling of elastomers that are taken into consideration due to its comprehensive expertise regarding the whole recycling chain. Starting from the laboratory systems, a scale-up to the industrial process is performed at the technical shop systems. This makes it possible to inspect elastomer residues of any quality for their recyclability and to flexibly adjust the material properties based on the customers' requirements.

The new plastics compounds obtain the desired property through the elastomer powder and are processed into granulates in the compounder system, together with thermoplastics and
additives. These in return can be melted. The comminution process that turns rubber residues into elastomer powder is, among other things, responsible for the desired mechanical properties of the compounds. In case of the EPMT®, important functions such as impact absorption, e.g. for engine mounts, or transfer of friction, e.g. for tire materials, can be adjusted.

New market perspectives through recycling

The recycling of elastomers increases the added value and opens up new market perspectives. Production waste, e.g. from rubber processors, no longer has to be disposed of but rather can be recycled. As such, elastomer residues remain in the production cycle much longer. At present, 60 to 80 percent of elastomeric powder by mass can be worked into the thermoplastic matrixes. EPMT® can be used cost-effectively, are easily processed in injection molding or extrusion machines, and are themselves also recyclable.

Processors of thermoplastic elastomers can now, on the one hand, obtain EPMT® and further process it into products, whereby they lower the raw material costs since recycled EPMT® is cheaper than new material. But industry customers who incur elastomer residues can recycle these, too, by manufacturing EPMT® from them, integrating it into products and thereby closing materials cycles.

Funding note
Financed by the German Federal Ministry for Economics and Technology (BMWi) as part of the EXIST research transfer program