Sustainability: New Approaches to Plastics Recycling

For some time now, car manufacturers have been using recycled PET, for example from bottles, in the production of seat covers or cockpit parts. However, the possible applications are limited and safety-relevant or highly resilient components still must be manufactured using mineral oil as a resource. A pilot project of the Karlsruhe Institute of Technology (KIT) shows new opportunities.

Autohersteller setzen auf Kunststoff-Recycling. Radkappen oder Bezüge bestehen oft aus recycelten PET-Flaschen. Foto: Shutterstock - TRMK - Dumitrusphotography. Montage: ETM/Frieser

Car manufacturers rely on plastic recycling. Wheel caps or covers often consist of recycled PET bottles. Photo: Shutterstock – TRMK – Dumitrusphotography. Montage: ETM/Frieser

Highly specialized plastics have played an important role in automotive construction for years. In order to improve sustainability, manufacturers are already using recycled materials in many cases – at least for components where this doesn’t pose a problem. The focus lies on beverage bottles made of polyethylene terephthalate (PET). In the Adam compact car, for example, Opel has used recycled PET to make bumper mounts and headlight covers. In the BMW i3 and i8 or in the new electric version of the Fiat 500, some seat coverings are made from plastic threads obtained from shredded and melted plastic bottles. Ford, Mazda, Volvo, and other vehicle manufacturers also use recycled PET for individual parts and insulating materials in the interior or in mechanically non-critical components such as engine covers.

Nevertheless, the use of recycled plastics in vehicle construction quickly reaches its limits – namely for vehicle components that have to meet higher requirements in terms of stability, temperature resistance, and safety. Recycled materials almost inevitably present higher dispersion in the raw materials, which can lead to poorer characteristics in terms of quality, heat resistance, and tear resistance. Car body parts, airbag covers, and other highly stressed or safety-relevant parts are therefore still manufactured using mineral oil.

Another challenge arises during recycling: Plastic recycling requires starting materials that are as pure as possible – one reason why manufacturers like to use PET beverage bottles. If, on the other hand, a car is dismantled at the end of its service life, the resulting mixed plastic waste is hardly usable for established mechanical-thermal recycling methods.

Pilot project for chemical recycling

This is the starting point for a pilot project launched in the fall of 2020, in which the Industrial Resource Strategies Think Tank at the Karlsruhe Institute of Technology (KIT) is collaborating with Audi: The project relies on chemical recycling to return plastic mixtures to a resource-conserving cycle.

“Until now, recycling automotive plastics hasn’t been possible for many components, which is why we’re pioneering this work here with Audi,” says Professor Dieter Stapf, Head of the Institute of Technical Chemistry at KIT. “If we want to close these circles, we have to develop suitable processes to do so.” Chemical recycling makes it possible to convert mixed plastic waste back into virgin-quality products, thus forming an essential building block for comprehensive plastic recycling. “Closed material cycles like this save valuable resources because less source material is needed. This, in turn, saves energy and costs – and is good for the environment,” emphasizes Dr. Rebekka Volk from the KIT Institute of Industrial Management and Industrial Production.

In chemical recycling, plastic components that are no longer needed, such as fuel tanks, wheel trims, or radiator protection filters, are processed into so-called pyrolysis oil by means of a pyrolysis process, i.e. thermo-chemical conversion processes. This oil then serves as raw material for the production of new plastics and thus as a substitute for mineral oil.

Using pyrolysis oil from mixed waste, partners KIT and Audi want to enable the recycling of engineering plastics in automotive construction. (Photo: Markus Breig, KIT)

Using pyrolysis oil from mixed waste, partners KIT and Audi want to enable the recycling of engineering plastics in automotive construction. Photo: Markus Breig, KIT

This method can also play a role in end-of-life vehicle recycling

Audi is one of the first car manufacturers to test this recycling method in a pilot project. In this project, partners Audi and the KIT Think Tank want to test the technical feasibility of chemical recycling and evaluate the process for its economic efficiency and environmental impact. “If plastic components can be produced from pyrolysis oil instead of mineral oil without any loss of quality, it would be possible to significantly increase the proportion of sustainably produced parts in cars. In the long term, this process can also play a role in end-of-life vehicle recycling,” Marco Philippi, Head of Procurement Strategy at Audi, is convinced.

“These approaches sound promising,” agrees Karsten Zech, Head of the DEKRA Laboratory for Materials Technology and Failure Analysis in Saarbrücken. In this materials laboratory, DEKRA carries out mechanical-technological tests and analyses of a wide variety of materials – not just metals and composites but also plastics. For many industries, from sanitary and heating construction to sports equipment and automotive engineering, Karsten Zech and his staff for example carry out tests for tear and stress resistance and artificially age the materials in a UV chamber. Leak tests for hoses and connectors in automotive engineering are also typical. “The focus of our investigations often lies on how materials change over time or under certain loads, potentially leading to failures.” The new materials from chemical recycling will also have to face such aging and stress tests. “So far, we haven’t had such a material in our lab,” reports Karsten Zech. “But I’m already very excited about that first time a corresponding component finds its way to us.”

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