In May 2022, a German compost heap made it into the international media. Researchers at Leipzig University had found an enzyme with remarkable properties in a cemetery: PHL7 decomposes polyethylene terephthalate - commonly known as PET - in record time. After less than 24 hours, PHL7 completely decomposes a common plastic tray for food, which is used hundreds of times in supermarkets, into its two components, which in turn can be polymerised into new PET.
PHL7 is not only twice as fast as the previous record holder. It also only requires temperatures of 65 to 70 degrees Celsius for the reaction. And that is considerably less than the energy required by thermal processes that melt down plastic waste. In other words, the enzyme from the compost heap "is suitable for use in an environmentally friendly recycling process in which new plastic can be produced from the degradation products", according to the press release at the time.
A development that - if it proves to be scalable - could open a window into a new era of plastics recycling.
The PPWR: recycling plastic as a key step towards a circular economy
And time is of the essence. Not only because the environmental impact of plastic is becoming increasingly visible - see the alarming findings on microplastics, for example - but also because of the PPWR. When the European Packaging Regulation comes into force in 2026, it will focus on the recycling of plastic packaging. And it also clearly states the recycling targets to be achieved. "We have two players who are in demand here: the member states, who must set up a functioning infrastructure 'at scale' - in other words, not just theoretical recycling, as it often only exists on paper today. And the distributors, who then have to use packaging that is also recyclable. What happens if the Member State fails to achieve the target is not defined. But if the distributor fails to achieve recyclability, the product may not be marketed. However, our experience shows that the distributors have not yet dealt with the issue too intensively," says Pacoon Managing Director Peter Désilets.
Alongside the avoidance of unnecessary packaging, recycling is the second thrust of the Packaging and Packaging Waste Regulation (PPWR) on the way to a Europe-wide circular economy. It is logical that plastics are at the centre of this, because while cardboard, metals and glass already achieve high recycling rates and the reuse of recyclate is high, the situation for plastic packaging is pretty bleak: They are effectively in the single-digit to just under double-digit percentage range in terms of recycling volumes and only a proportion of this is also reused as recyclate - but not necessarily in packaging, if you disregard PET bottles. This also applies to countries such as Germany, whose recycling infrastructure is very good by comparison.
But the European Commission wants to see facts: The recyclate utilisation rates to be achieved are not theoretical figures based on sorting - it is about the actual proportions of recyclate in plastic packaging.
Targets that are currently a long way off and for which new approaches are needed.
Peter Désilets admits: "The quotas are ambitious, especially because the origin of the recyclates is also defined. It has to be PCR - post-consumer recyclate, i.e. recyclate from packaging that has already been used. And when it comes to food, cosmetics, baby and pet food or even pharmaceuticals, the quality requirements are very high, virtually at Virgin Material level. At the moment, there is still a lot of guesswork as to how this can be achieved. It will be difficult to achieve with our current mechanical recycling technology."
Household waste spoils the fun
As obvious as the idea of processing plastic packaging so that it can be turned into new packaging is, the restrictions are manifold. These are clearly greatest for post-consumer recyclate, which is obtained from packaging waste: the plastic accumulates at many small collection points, different types of plastic are mixed together and they are almost always contaminated.
Mechanical plastic recycling: one method is reaching its limits
The established technology for reprocessing plastics is mechanical (or mechanical recycling). In mechanical recycling, plastic waste is melted down and processed into granulate, which in turn is used as a secondary raw material in packaging or other products. This works well in principle, but encounters obstacles in practice.
This is because the material supplied for mechanical recycling must be unmixed and as free as possible from contamination or foreign matter. The less both of these are the case, the more promising the separation and cleaning processes can be in ensuring a high-quality recyclate. However, according to Peter Désilets, there are many opportunities to get lost on the way through these recycling processes: "Several parameters can significantly affect the quantity and quality of the recyclate. It starts with incorrect material combinations such as polyolefins with polyesters that cannot be separated, foamed polyesters that 'simulate' lighter polyolefins in the float-sink process and contaminate the recyclate, incorrect colours that outgas in the extruder and lead to grey and smelly recyclates, additives and adhesives to increase the functions that cannot be separated. The poorer the recyclate quality, the more difficult it is to create high-quality plastic applications with it.
Varietal purity: garbage in, garbage out
Varietal purity is an ongoing issue in recycling anyway. Analyses of collection points regularly show that the proportion of incorrect waste is alarmingly high. On the one hand, this is probably due to a lack of interest on the part of some consumers - but at the same time, the quality of the relevant information on the packaging could definitely be improved. Repeatedly changing specifications on what type of packaging should be collected and how, also do little to clarify the situation. "The EU also wants to strengthen and standardise separation and sorting instructions with the PPWR, and specific instructions have already been introduced in countries such as France and Italy. In Germany, too, the 'Waste separation works' initiative submitted proposals to standardise the instructions three years ago. However, with little implementation. Even digital information and video instructions have been integrated. In any case, manufacturers should integrate the instructions into the packaging design, as around a third of German private households do not collect waste at all," says Peter Désilets.
Mixtures of different plastics or with different additives and barriers can therefore rarely result in high-quality recyclates. This is also the reason why composite packaging is almost always sent for thermal utilisation - as incineration is so nicely called - because the energy is then recovered.
Purity: the battle for high-quality plastic waste
Another hurdle before polymers can be recovered is the requirement for cleanliness. Removing coarse dirt industrially is not a major problem. However, when it comes to recyclate that will later be used to package food, pet food or cosmetics, for example, the requirements are very high - the material must not impair either taste or odour, not to mention harmful residues.
PET beverage bottles are basically ideal for this. They provide high-quality recyclate that is also food-safe due to its previous use. Because it is virtually the only PET that is recycled, other industries are also very interested in the material. The valuable PET recyclate is increasingly being removed from the cycle and used in textiles, car seats, films and packaging other than beverage bottles, and the beverage sector then generally has to resort to fossil raw materials. "We have been trying to educate the industry for years that this is basically greenwashing and harmful. We are slowly hearing more and more that this is not the right way to go. It's nice to advertise the 'use of recycled material', but in theory it should read 'polyester recyclate that has been removed from the bottle cycle and for which new fossil raw materials have to be used'. But of course that sounds very unattractive. That's why the organisations are pushing for other sectors such as the textile and automotive industries to close their own polyester cycles and not 'use other people's cycles'," says Désilets.
Classic recycling with new technologies
There is something new here, especially in sorting. Exciting automation technologies have emerged in recent years, and artificial intelligence is increasingly becoming a factor when it comes to better identifying the individual fractions and separating them more cleanly.
"In mechanical recycling, the technologies are pretty much exhausted; it's essentially about fine-tuning. Finer sorting of different packs could also lead to better recyclates, but this makes the sorting process significantly more expensive. In this case, small cattle also make a lot of muck: better colours that do not outgas during extrusion would produce much better recyclate. But the colours are more expensive and the application is less flexible. This is why the industry generally uses nitrocellulose inks, which produce soot and turn the recyclate grey. Additives can also have such undesirable effects. Monomaterials without many foreign substances also lead to purer recyclates. There are many ways of adjusting this, but there is often a lack of knowledge in the industry," Désilets points out.
In view of the high standards set by the PPWR, however, it is unlikely that technological developments or further optimisation of the collection infrastructure will be enough. This means that the focus is turning to other recycling technologies such as chemical recycling.
Chemical recycling: new products with a footprint
Chemical recycling of plastics (or raw material recycling) involves the depolymerisation of plastics into their individual components - into other polymers or monomers. The different methods therefore change the chemical structure of the starting materials. A wide variety of new plastics can be produced from the products, the quality of which corresponds to that of the original materials.
When the various methods of chemical recycling emerged (pyrolysis in particular has become established), they aroused great hopes. They are now often viewed more critically. The high energy consumption in the recycling process is particularly noticeable, and the processes leave a considerableCO2 footprint. In addition, only between 20 and 50 per cent of material output is achieved - the rest is waste. And last but not least, the processes are not yet very scalable.
The proponents of mechanical recycling criticise another point. Chemical recycling fishes in the same pond: it is in direct competition for valuable plastics such as polyolefins, but achieves a significantly lower output at higher costs.
Another method is 'oiling', which works at much lower temperatures and is currently being trialled. In theory, contaminated plastics can also be used for this, but development is currently still working with post-industrial waste that is pure and clearly defined.
"The hope of the industry is that these processes will provide clean recyclates by the time the PPWR recyclate utilisation quotas are reached in 2030. However, it is questionable whether the processes will be industrially scaled by then, whether investors will be found to develop the processes and whether the quantities will be sufficient to fulfil all quotas. Whether these hopes will be realised is questionable, especially as the recyclates will certainly be significantly more expensive. And the industry is already unwilling to pay the additional price for mechanical recyclates. Instead of developing alternative packaging concepts, the industry is largely hoping for a miracle," says Désilets.
Enzymatic recycling: recycling plastics with finds from landfill sites
Enzymes are bio-catalysts, in most cases proteins that trigger specific chemical reactions. The special thing about them is that catalysts leave the reaction unchanged, i.e. they are not consumed. Properties that can also be utilised for plastics recycling.
While enzymatic recycling (or biorecycling) is still in the prototyping phase in the case of the aforementioned PHL7, there are already more concrete implementations. One of the major players in this field is the French company Carbios.
The biotech company's researchers rummaged through landfill sites and waste in search of bacteria that break down plastics, and they found what they were looking for. They discovered a suitable candidate and specifically mutated the enzyme. The result: bacterial enzymes that break down PET packaging into its monomers at high speed. This means, among other things, that different coloured substances in the plastic waste become secondary raw materials that can be converted into colourless PET.
Carbios is cooperating with well-known brand owners and aims to have a corresponding plant up and running by 2025 that will be able to process tens of thousands of tonnes of PET material. How sustainable the approach is will depend, among other things, on the scalability factor.
"The process has many advantages over chemical recycling, it is cheaper, does not have toxic by-products as things stand today and consumes much less energy. In addition, development has already progressed further than pyrolysis. However, enzymes cannot be scaled up so easily and behave differently in a test tube than in a swimming pool. But the process harbours great potential," hopes Peter Désilets.
It therefore remains exciting to see how recycling will develop and whether the hoped-for quantities of recyclate will be available by 2030. AI will also be used to find out how recyclates from mechanical recycling can be better utilised. One current research project is KIOptiPack, in which 40 companies and institutes are involved in finding out about better recyclate and consumer acceptance. The project will run until July 2025 and the consortium is eager to see whether the breakthrough will be achieved. At the same time, however, there are already solutions that go beyond plastic solutions or with optimised mixtures that meet the PPWR requirements.
Désilets: "Our credo for PPWR compliance is therefore: it is not enough to simply reuse the material and utilise recyclates; new solutions must also be considered. Rethinking instead of just embellishing!"