We have a good example in our hands almost every day. Beverage bottles made of polyethylene terephthalate, or PET for short. They are extremely easy to recycle and are a prime example of the sensible recycling of plastic packaging. At the same time, however, they show why this is not enough to obtain good secondary material.
High recyclability is, of course, a key component in getting and keeping a raw material cycle going. What else is important? Here are the factors that determine the quality of recyclates.
Single-variety purity: when plastic makes material recycling of packaging more difficult
The purer the source material, the better the quality of the recyclate. Foreign plastics can even render the secondary material unusable in an emergency. PET bottles are a good example of this: the caps, for example, are often made of other materials such as PE or PP, which cannot be processed in the same way during recycling. However, the recycling industry has adapted to this so that the caps no longer pose a real problem.
Consumers cannot be expected to separate the different types of plastic in their waste. Not even from those who take their contribution to the cycle of recyclable materials particularly seriously. The ball is therefore in the court of the sorting and recycling companies. Manual pre-sorting makes sense here, but is also error-prone and very labour-intensive. In Germany and state-of-the-art sorting plants, this is done automatically, e.g. by NIR (Near InfraRed) scanning, i.e. the reflection of prismatic light through the packaging materials. Even in these systems, however, there is still manual re-sorting down to the last few metres.
It is therefore often a mix of technological processes that is intended to ensure pure sorting and reuse. The aforementioned infrared spectroscopy, for example, fluorescent pigments in the plastics are another method, as is the coding of the packaging or sorting using AI and image recognition. Density separation in the recycling process then selects the foreign materials from pre-sorted bales as far as possible. But they all have their specific limitations. In the search for greater accuracy, new ideas are constantly coming into play. So the search is on for the Holy Grail of packaging identification?
The Holy Grail 2.0
Since 2016, an initiative with the ambitious name "Holy Grail" has been looking for ways to improve the process. It identified digital watermarks as particularly worth pursuing, and "Holy Grail 2.0" is now dedicated to this topic: Sponsored by the European brand association AIM and supported by a considerable number of companies and organisations, HG2.0 is pursuing the idea of printing codes on packaging that are invisible to humans and function like a digital watermark. Special cameras in the waste recycling plant could read this information and sort the fractions accordingly.
AI controls the quality
Another promising approach is machine learning. The capacity of algorithms to process large amounts of data in a short space of time has been utilised in "Site Zero", a plastics recycling plant in Sweden, since 2023. The combination of state-of-the-art sensor technology and artificial intelligence allows the plant to prepare and process up to 200,000 tonnes of packaging waste per year. According to the operators, up to 95 per cent of the waste can be sorted for recycling. The rest is sent for chemical recycling or energy recovery with carbon capture and storage.
"If you ask the sorters and recyclers, there is a lot of discussion about the opportunities these new technologies offer. On the one hand, the new technologies are particularly geared towards better sorting, which essentially ends up in mechanical recycling. It is often argued that the added benefit is rather small and that mechanical recycling technology already delivers very good results. Therefore, the high investment in the last percentage of material sorting is not worthwhile. Or manufacturers incur costs if they have to apply codes to packs or feed the AI with new designs in order to sort them correctly," says Pacoon Managing Director Peter Désilets.
Contamination vs. sustainable recycling
It's not just foreign plastics and the remnants of the original contents: Many things can contaminate the original materials. Contamination from dirt, foreign bodies (especially metal particles, which can also come from the shredder itself) or labelling adhesives have a direct impact on the quality of the recyclate. Silicone is particularly "effective" in this context. Colours can also cause a special type of contamination. The usual nitrocellulose colours gasify in the recyclers' extruders. This not only produces an unattractive grey colour, but also an odour that now clings to the recyclate. Although there are other colour technologies on the market, such as PU inks, that can withstand the heat and produce transparent recyclates, the application is different and finishing on the outside is impaired or not possible at all. "But there are also new approaches to using NC inks and obtaining better recyclates, which is exactly what we will be demonstrating at FACHPACK 2025 in our SOLPACK 6.0 conference in Hall 3," says Désilets.
For example, the use of near-infrared spectroscopy (NIR) is widespread, which identifies both types of plastic and their colour very quickly and non-destructively. However, black or dark-coloured plastics are the end of the line: NIR cannot recognise them, or not sufficiently, which can lead to losses and lower quality secondary raw materials and therefore recycled products.
There are therefore many ways in which the contamination of plastic waste can lead to lower material quality in recyclates. Pacoon has been researching this for some time, says Peter Désilets: "As part of the KIOptiPack funding project, in which we are also a partner, we are therefore trying to improve recyclate quality through better sorting. This has already made it possible to produce better films that contain fewer 'specks' and thus minimise film tears or quality defects. It is important to realise that every bale of sorted HDPE and PP material always contains foreign matter, which can easily account for 10-12%. Shit in, shit out is the buzzword here - the better the input, the better the output."
However, Peter Désilets qualifies: "Even LDPE films are easy to sort and often have little to no printing - as a rule, the large film bags from textiles, electrical appliances or other bags are often sorted - but these film recyclates do not have a particularly high recyclate value and are often added to other plastic products. For some recyclates, recyclers even have to pay money to get rid of them. Perhaps the focus is on quota fulfilment."
Good design for high-quality recycling
Packaging made from materials with high recyclability often faces a massive obstacle: the packaging design. This is actually astonishing given the knowledge that has long been available in the world.
Design for recycling starts with the choice of materials. The reflexive call for mono-materials is in view of the restrictions is unfortunately often premature. This does not change the fact that materially homogeneous packaging can, of course, drastically facilitate processing.
One factor that could improve many things would be the elimination of certain additives or problematic components. Many plasticisers, dyes or stabilisers are not only harmful to health, but also impair sorting or contaminate the recyclate. The development of harmless substitutes, on the other hand, is an issue for the industry. For example, Fraunhofer CCPE is working together with a German company on new stabiliser systemsto counteract the ageing and thus the loss of quality of polymers.
"In some applications, such as injection moulding, the quality is therefore usually less impaired. The situation is quite different with films, where impurities can cause major production problems such as tears or rougher surfaces. This is not desirable, which is why the packaging industry prefers to use virgin material with known, easy-to-handle qualities," says Désilets.
Downcycling: at some point, the quality of the recyclates suffers
And there is another factor that limits the quality of the recyclate. The more frequently plastic is recycled, the more its quality deteriorates - recycling and downcycling are closely related. Heating and melting lead to the polymer chains being broken up and shortened, which affects the strength, elasticity and also the visual quality of the raw material obtained. There are recycling processes that counteract this effect, but they all reach their limits at some point.
"In addition to the fact that plastics can be recycled and reused, there is still a big question mark as to how often and in what quality the recycled polymers can be used at all? And then the recycled plastics are used for by-products rather than for high-quality but short-lived packaging solutions, which is where around half of the plastics come from," says Désilets.
At the end of the day, people like to talk about downcycling if the same high quality as for packaging is not achieved again. However, the negative connotation of the term is not always justified," says Désilets: "The more interesting aspect is that these 'poorer' recycled plastics also save new virgin material, usually from fossil sources."
For our bottles, this means that the production of new units from recycled PET (rPET) in the sense of a bottle-to-bottle system is entirely possible and will be practised for as long as possible. This should work up to ten to twelve times. But at some point, they will also end up as new products: They are reused as polyester fibres for carpets or as fence posts. The situation is worse, however, when these PET recyclates, which can be put to good use, are removed from the closed bottle stream and end up in textiles, films, other packaging or in the automotive sector. Although they sometimes remain there for several years, this means that the PET bottles have to obtain new virgin material. Or new packaging made from rPET can no longer be recycled well and then ends up in incineration for energy recovery. The cascade utilisation is therefore interrupted here too.
"Like all aspects of sustainable packaging design, recyclates must always be considered individually. Some approaches would be easy to implement, but are thwarted by the market. Or the legislation prevents it, such as with reusable to-go containers. Separate recycling and coding would enable high-quality sorting of the mostly PP material, but the law makes it more difficult to reuse the recyclate for new containers," criticises Désilett's regulations, which make no recognisable sustainable sense.
The industry as a whole is calling for the separate collection of high-quality - mostly rigid - packaging that could be used in a variety of ways. In theory, this would be very easy to achieve with labelling, and the successes can be seen with PET bottles. However, this would also require a significant increase in collection.
So why not just use reusable bottles instead of tedious recycling loops? Peter Désilets says: "The question is whether a reusable approach isn't more promising, because it would save a lot of energy, CO2 and generally also costs with just a few rounds. If I could invest money, I would invest it in reusable systems rather than in better sorting of disposable containers. This is because the return rates are at least as high as single-use containers with a deposit, the energy and CO2 balance is significantly better in the long term than single-use containers with a deposit and the conservation of resources has already been proven many times over with a factor of 10 to 30. In addition, reusable packaging still offers a lot of potential for optimisation, while many disposable solutions are already very much exhausted."
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