Making sensible and efficient use of scrap tires
Every year, a waste volume of some 19.3 million metric tons of scrap tires is generated worldwide - including over 3.6 million metric tons in Europe alone. 20 years ago, over half of all scrap tires were incinerated to generate energy in Germany alone, while only every tenth scrap tire was processed into granulate. By now, the volume of the latter has caught up with energy-related processing.
Recycling scrap tires definitely makes environmental sense. "Reusing recycled tires secures valuable resources," says Thomas Engenhorst, sustainability strategy manager in the Resource Efficiency Segment of Evonik. "Tires are not classified as waste, but are considered a valuable material, which may not, for example, be disposed of in landfills. This use eliminates the disposal question: Instead of incinerating the tires, they have another life stage in road traffic - not as part of an engine-powered vehicle, but in the form of an elastomer or rubber powder in the road surface."
As part of a test track in the German town of Paderborn, the local road Detmolder Strasse was resurfaced in 2012 in compliance with the objectives of the EU Waste Directive. 50% of the new asphalt mixture consisted of milled material-asphalt granulate-from the old road. The new mixture formulation also included rubber powder and VESTENAMER®. For every 100 m of track, some 80 scrap tires were turned into an elastomer-modified road surface, along with recycling the old asphalt.
Fewer CO2 emissions
A study by the renowned Institute for Energy and Environmental Research in Heidelberg (ifeu) provides further information about the ecobalance: Each metric ton of recycled rubber powder saves some 2.7 metric tons of carbon dioxide, which would otherwise be generated during the incineration process. Accordingly, this material use significantly optimizes the carbon footprint.
The application of VESTENAMER® is a clean affair in many respects: The emissions of volatile and semi-volatile compounds, including hydrocarbons and sulfur compounds, are much lower in road surfaces containing rubber than in conventional, polymer-modified asphalt types.
Furthermore, Evonik's process additive reduces the migration of organic compounds that are washed out by rain and reach the groundwater. As a study conducted by FABES Forschungs-GmbH on behalf of Evonik has documented, the use of VESTENAMER® reduces the overall groundwater burden.
In the spring of 2013, the Road and Transportation Research Association added rubber-modified bitumen and asphalt types to German regulations for road construction.
VESTENAMER® was developed in the late 1970s as a processing aid for the rubber industry. Polyoctenamer, which is produced in the Marl Chemical Park, resolves a number of challenges associated with compounding and processing rubber. It is used to this day because of its positive characteristics in the interaction with other rubbers. In addition to the tire market, the product plays a part in the manufacture of rubber items such as hoses, clutch linings, roller coatings or molded parts. Since road transportation authorities have long been looking for an improved and more durable material, the High Performance Polymers Business Line of Evonik began to conduct extensive research in this area 10 years ago. Since then, VESTENAMER® has gradually become the unifying element of choice in rubber-modified asphalt.