With Tracer-Based-Sorting, purer sorting fractions become reality

Achieving a reliable and consistent level of purity and quality of mechanically recycled materials is a major challenge. Improved sorting technologies that enable a more efficient and accurate sorting process are the way forward, say Max Riedel and Jochen Moesslein, respectively of optical technology giant ZEISS and Polysecure, a manufacturer of tracer solutions. The two talked to Sustainable Plastics about the collaboration between their companies on a solution that is set to revolutionise the sorting process.

ZEISS is a well-established name in the industry. Polysecure, however, is a relatively young and far less well-known company. How did it get started? What does it do?

Polysecure started out in 2009 in Freiburg, Germany, with the aim of discovering, developing and marketing technology to mark materials and then authenticate the marked materials by measuring the marker. Such technology could serve as ‘In-Product-Marking’, which would be more robust than printing a security feature on a product or adhering a label onto a product. Both of these latter options can be easily detached or removed.

Building on this ‘start-up’ vision, we first developed and validated an X-ray fluorescence -XRF - authentication technology for ceramic marker particles. A bit later, we discovered that fluorescence offered a more robust technology to authenticate, then sort and then identify materials, and thus products. To take this further, we started a deep and strategic R&D relationship with Karlsruhe Institute of Technology, one of the largest R&D institutions in Germany.

This led to the development of a highly innovative technology platform that today features a range of marker materials and detection methods, allowing products and materials to be directly marked, practicably authenticated, tracked in a tamper-proof manner, and reliably sorted.

For the circular economy of the future, Polysecure, which has meanwhile grown into a company employing a staff of 36, has developed a disruptive sorting technology called Tracer-Based-Sorting (TBS). TBS makes it possible for packaging waste to be efficiently and reliably sorted into all desirable fractions.

What exactly is Tracer-Based Sorting technology? How does it work?

TBS is based on marking articles or materials with fluorescent tracers and then identifying articles and materials in the sorting process by the specific fluorescent properties of the fluorescent tracers. Sorting is done by moving articles or materials through a curtain with specific radiation which excites the tracers to fluoresce. One of the unique aspects of the technology is that the tracer fluorescence can be measured without background noise. This is an important advantage for sorting rapidly moving waste objects.

Another key advantage of TBS is that the fluorescent properties of tracers are independent of the composition of the materials to be sorted. Thus, the TBS sorting algorithm can be defined according to the needs of the circular economy. A tracer with an agreed emission characteristic could be associated with a particular plastic specification class (e.g. PET food tray, PET food bottles, PET non-food). This would allow, for the first time, packaging items, which should be processed and recycled together, to be efficiently sorted into one sorting fraction. Other packaging items would form other sorting fractions marked by other tracers.

The tracers can be applied to packaging products simply by adding them into a printing ink, by dispersing them into a label material or by homogenizing them at very low concentrations into the packaging plastic itself via compounding or via a masterbatch. In the latter case the tracers could be used for sorting, quality inspection and product tracking in many use cycles and until the “end” of the polymer. This solution has an outstanding efficiency potential.

What kind of marker materials are used?

Polysecure has developed several tracer materials. At present, Polysecure is pursuing the food contact approval for a crystalline inorganic material family with very good heat and chemical stability. All toxicological tests have been passed with very positive results. This material family will provide enough sorting codes to sort plastic packaging, plastic waste from automotive, E-waste and other waste streams. In general, the tracers should be seen as a functional additive.

You mentioned that ZEISS is ‘foundation-driven’: how is that important for the focus on sustainability and business?

Sustainability and business success are inextricably linked at ZEISS. The company is fully owned by the Carl ZEISS Foundation, one of the largest and oldest science-funding foundations in Germany.  This means that ZEISS can have a much more long-term business strategy than many stock-listed companies. A commitment to the common good and to finding solutions for key societal issues are part and parcel of the company’s ethos.

How did the collaboration between Polysecure and ZEISS come about? At whose initiative?

We met at a conference in Karlsruhe two years ago, shortly after the ZEISS Innovation Hub @ KIT had become operational. Polysecure afterwards reached out to ZEISS to help with a specific optical design problem and from this, the collaboration evolved into much more.

The circular economy is an important, sustainable trend that touches or will touch many companies. ZEISS was interested in further moving into this area of “green technologies”. The sorting technology of Polysecure requires innovative optical devices and optical physics processes. With the experience and excellence of ZEISS in this area, the synergies between Polysecure and ZEISS are obvious.

A first target in the strategic collaboration between the two companies is the development of a new multi-modal optical detector that can combine several measurements for each waste object: tracer detection, a NIR (near infrared) measurement, colour measurement and image recognition (artificial intelligence), as well as the detection of a watermark, if necessary.

How far along are you with the development of this new detector technology and when do you plan to commercialise this?

Polysecure and ZEISS are already working on the new detector, and it will be a core part of the new industrial TBS sorting line at Polysecure in Freiburg. The collaboration partners are striving to have the line ready for industrial sorting trials by the end of 2022. The technology has already been discussed with stakeholders and the first potential pilot customers. In-house recycling and post-production recycling projects are being focussed on as the first phase of commercialisation. Thus, in certain respects, commercialisation can be said to have already started.

What will a sorting line equipped with the new technology look like? Will it take up more space? Is more automation needed?

The new sorting technology will look a lot like the picture shown on this page. It will require more or less the same amount of space and level of automation as the current state-of-the-art sorting technology, which requires at least 19 sorting steps to sort a waste stream into 20 sorting fractions, because only one fraction can be blown out at each sorting step. By contrast, our new sorting technology will measure each article only once, but more completely, and then, based on a single line sorting concept, precisely steer each item to its correct destination and sorting fraction, respectively. Besides TBS and the new detector, this handling and sorting process is the third aspect of our innovative waste sorting concept.

You say your system will not lead to additional costs – why not, how is this possible?

As explained, the conventional setup requires many sorting stages and significantly more conveyor belts and handling equipment than single sorting, since waste articles have to pass several sorting stages before being sorted to their final fraction. With our new sorting process, detection and sorting are both done at one stage only. This saves significantly on the amount of measurement equipment, conveyor belts and material handling needed, and compensates the additional singularisation. Furthermore, in many regions worldwide labour costs are at a level that makes manual singularisation viable. Thus, many sustainable jobs could be created while improving the recycling quality substantially.

Furthermore, TBS complete – where the current sorting technology is replaced by a one-step TBS sorting technology -  enables better specified and purer sorting fractions, which reduces the process costs at the recyclers and increases quality and price of the derived recyclates.

The bottom line, according to our calculations, is that a TBS installation should at least achieve the same financial viability as the conventional sorting technology available today.

Does your technology differ - or perhaps complement -  the Holy Grail 2.0 watermarks project?

Watermarks are small changes in the printed artwork or surface of packaging items. Thus, detection requires a precise optical picture recognition, which is influenced by the deformation, movement, dust and dirt in the packaging waste stream. Looking at Tracer-Based-Sorting, the sorting signal is emitted from each tracer particle in a radially symmetric manner. Thus, detection is much less influenced by “waste stream” aspects. And relevant for practical application, TBS works for any packaging, also for flexible films, small packaging and packaging with little or no print. Importantly, circular plastic strategies rather look for less print than more.

Regarding the combination of different detection technologies: Indeed, our new sorting process explicitly combines multiple measurements for each waste object. Therefore sorting does not require having to decide on a detection technology yet. From a physics point of view, TBS is probably the best general technology for plastic waste sorting. But it is not a standard yet. In this phase an integrative detection approach as pushed by Polysecure and ZEISS is an ideal solution for plastic waste sorting worldwide.

After this technology has been commercialized, can we look forward to further developments arising from this strategic partnership?

Our sorting technology approach is quite comprehensive. We therefore expect a rather broad and longer-term commercialisation strategy addressing several waste markets worldwide. We anticipate further innovations which will support and integrate our technology and product strategy. One interesting aspect is the inline detection of our fluorescence-based particle fingerprint technology by which every product unit could be tracked individually. This robust and forgery proof marking technology could be the ideal physical code for a product pass or digital twin.

Your system is a timely development in view of the increasingly stringent recycling targets for packaging being set by the EU, wouldn’t you say?

Yes, the link to the EU overall situation is interesting: According to a study by the Circular Plastic Alliance, around 21 million tons of plastic waste are collected in Europe each year, of which only 9.2 million tons are sorted and processed in recycling plants to produce around 5.2 million tons of recyclate. On the other hand, the European Plastics Strategy sets a target for the EU to use 10 million tonnes of recycled plastic by the year 2025. These goals create an urgent need to at least double the volume and increase the quality of sorted plastic waste if this 10-million-tonne target is to be met. Therefore, we definitely need better sorting technologies!