Technology Extending Lifecycle of Reusable PET Bottles Up for Prestigious German Award

What does it take to earn a spot in the winner’s circle of the circular plastics economy? According to IKV — the Institute for Plastics Processing at RWTH Aachen University in Aachen, Germany — a key attribute is that the product should retain its value as long as possible throughout its lifecycle.

Reusable PET bottles are a good example: After use, they can be washed with caustic soda solution and refilled. Compared to glass, however, PET is not gas-tight, which significantly reduces the shelf life of juices or carbonated beverages such as soft drinks or beer. Despite its many ecological advantages, the reusable PET content in fruit-juice packaging in Germany was no higher than 0.5% in 2018. This disadvantage of PET bottles can be reversed by applying a silicon oxide (SiOx) barrier coating via plasma technology.

PET bottle stock art from IKV
Image courtesy IKV — the Institute for Plastics Processing at RWTH Aachen University/congerdesign.

Conventional SiOx coatings are not resistant to the aggressive caustic soda used to wash returnable bottles, however, and IKV and KHS Corpoplast GmbH have developed a coating system using sodium hydroxide (NaOH), which is capable of withstanding the washing process. This paves the way for more frequent reuse without reducing the barrier properties of the container.

The PECVD gas barrier coating technology for reusable PET bottles has been nominated for the German Raw Materials Efficiency Prize by the Federal Ministry for Economic Affairs and Energy for outstanding products, processes, and research results.

The German deposit system for PET bottles distinguishes between single- and multi-use, or returnable bottles. Single-use PET bottles are, after collection, shredded and prepared for recycling. However, this does not represent a completely closed cycle, because only 30% of the processed PET is used for the production of new PET single-use bottles, said the announcement.

This is due, among other things, to the fact that PET can only be recycled a maximum of 10 times, as the molecule chains are shortened with each processing operation. In turn, this leads to a deterioration of the material’s properties. The remaining 70% is used for things such as textiles and can no longer be recycled into bottles. In 2018, 72% of all non-alcoholic beverages in Germany were sold in single-use PET bottles. This is the equivalent of 16.4 billion single-use PET bottles or 394,000 tonnes of newly produced PET in Germany per year, assuming that all the bottles are 0.5-liter PET bottles weighing 24 grams.

Reusable PET bottles, on the other hand, are cleaned after use in a washing process with a strong NaOH solution, sterilized, and subsequently refilled. At present, returnable PET bottles can pass through this cycle up to 20 times, which offers enormous potential for saving resources. “If we assume that a reusable PET bottle performs the work of 15 single-use PET bottles, it would be possible, in the event of a complete changeover to multi-use, to save around 260,000 tonnes of PET in Germany every year,” explained IKV.

Against the backdrop of current plastics packaging legislation, which targets a reusable quota of at least 70%, this research project devoted to coating returnable PET bottles can make a decisive contribution. The customary quality and storage life of the bottled content is preserved: In the same process step when the barrier coating is applied, a specially developed coating to protect against the aggressive caustic soda solution is applied by microwave-excited low-pressure plasma. As a result, beverage producers and bottling companies can now fill reusable PET bottles with any product without restriction, said IKV. This opens the way to fully exploiting the savings potential at the resource level.

IKV – the Institute for Plastics Processing at RWTH Aachen University is a European research and education institute engaged in the field of plastics processing. A staff of more than 300 are employed in finding solutions to problems connected with processing, materials technology, and part design in the plastics and rubber industries. IKV is divided into four specialist departments: Injection Molding, Extrusion and Rubber Technology, Part Design and Materials Technology, and Composites and Molding.

The winner of the German Raw Materials Efficiency Prize will be announced on October 21, 2020, in Berlin.

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