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★Mark us as a preferred sourceThe crisp packet, the cheese wrapper, the detergent pouch, the film bag your toilet paper came in. We throw them away by the dozen, and we know they are the “difficult case”. A Dutch–Belgian research team has now put numbers on exactly how difficult — and on the fact that the small amount of usable flexible mixed polyolefins our system recovers from them simply cannot satisfy two competing industrial demands at once. A choice has to be made. And the study has a very clear recommendation about which way to go — one that will surprise many.
Researchers from Maastricht University and Ghent University (Merel Molenbuur, Cris Garcia-Saravia Ortiz-de-Montellano, Steven De Meester, Yvonne van der Meer, Milad Golkaram and Kim Ragaert) published their analysis in Engineering. They project European material flows to 2030, then compare the two possible destinations using a newly proposed metric: the sustainability–circularity index (SCI). The work was partly funded by the Horizon Europe Syschemiq project.
What are flexible mixed polyolefins, and why are they such a hard case?
Polyolefins are the most widespread plastic family, covering polyethylene (PE) and polypropylene (PP). In Europe, 13.7 million tonnes of post-household plastic packaging waste per year falls into the “flexibles” category: films, pouches, lidding and wrappings. Most of it is polyolefin — 8.5 million tonnes of PE and 2.5 million tonnes of PP.
At the sorting plant this material ends up in several bale types. The best output is the film bale (code 310 in the German DSD system), relatively clean at around 74 per cent PE film content. But there is also a “mixed polyolefin” bale (DSD 323-2) in which only 35 per cent is PE film and 17 per cent PP film — two plastics that do not blend well, mixed together. And at the very end sits the “mixed plastics” bale (DSD 352), the leftover of sorting, which studies show still contains 30 to 60 per cent flexible polyolefins.
Those last two make up flexible mixed polyolefins, abbreviated fMPO. And here is the difficulty: these films are printed, contain adhesives, are often multilayer, and their barrier layers may include PET, polyamide or EVOH. PE and PP do not mix well in the melt — roughly like oil and water — so the commingled material cannot be turned back into film of the same quality it came from.
The CEFLEX industrial consortium did develop a better process (post-sorting, hot washing, improved extrusion, de-odorisation), but it is substantially more expensive, and in today’s market — with European recyclers going bankrupt one after another — industrial rollout has simply not happened.
Two possible destinations: melting down or breaking apart
Today, at best, this material goes to mechanical recycling. A float–sink step removes the heavier, non-polyolefin fraction, melt filtration follows, and the output goes into thick-walled products with wall thickness above 5 millimetres. The most iconic product of the genre is the park bench, replacing cast iron, wood or concrete. Based on Prodcom data and industry consultation, the researchers estimate the European market for such products at around one million tonnes a year, roughly half of which could be covered by flexible mixed polyolefins.
The other route is chemical recycling, specifically pyrolysis: the material is broken down in the absence of oxygen and the resulting oil goes back to the petrochemical plant to be cracked into ethylene and propylene. This route has one major advantage: the polymer it yields can be used in food-contact packaging, which mechanical recycling of the flexible mixed fraction cannot deliver. And this is exactly where regulation enters: the Packaging and Packaging Waste Regulation (PPWR, Regulation (EU) 2025/40) requires 10 per cent recycled content in contact-sensitive packaging from 2030.
So two entirely different industries — durable goods manufacturing and packaging — are bidding for the same waste stream.
There isn’t enough feedstock, whichever route we pick
The team built a material flow analysis covering the 27 EU member states plus Norway, Switzerland and the United Kingdom, projected to 2030. The result is sobering from the outset: 1,168 kilotonnes of material enters pre-treatment from the two relevant bale types, but only 717 kilotonnes emerges in a form actually suitable for recycling. The rest — more than 440 kilotonnes — is rejected and goes to residual treatment.
Two demands compete for those 717 kilotonnes:
- The thick-walled products market needs 580 kilotonnes of recyclate, which at 95 per cent yield means 611 kilotonnes of feedstock.
- The 10 per cent recycled content requirement for food-grade flexible PE packaging needs 360 kilotonnes of chemically recycled polymer.
The researchers ran three scenarios:
- Mechanical recycling first. The 611 kilotonnes goes to benches and similar products, leaving 107 kilotonnes for pyrolysis. At a 22 per cent polymer yield that gives barely 23 kilotonnes of polymer — a fraction of the 360 kilotonne demand.
- Chemical recycling first, strict mass balance. If recycled content can only be credited to the polymer actually produced, then hitting 360 kilotonnes of output requires 1,652 kilotonnes of feedstock. That does not exist: 934 kilotonnes would have to come from elsewhere.
- Chemical recycling first, fuel-exempt mass balance. If, as in the European Commission’s draft proposal, base chemicals can also carry the credit, 456 kilotonnes is enough to meet the packaging target. That leaves 262 kilotonnes for the mechanical route — yielding 248 kilotonnes of polymer against the 580 needed.
In none of the scenarios is there enough material for both demands. More importantly, the authors ran a sensitivity analysis: it still isn’t enough even if collection improves by 25 per cent and mass-balanced pyrolysis efficiency rises to 90 per cent. A prioritisation decision is unavoidable.
One further uncomfortable figure: demand for recycled content in non-food-contact flexible films reaches 3,130 kilotonnes by 2030, while mechanical recycling of clean PE film bales would supply 2,050 kilotonnes — and technically the gap cannot be filled from the flexible mixed fraction.
The bench that turned out not to be “downcycling” after all
If a choice must be made, it must be measured. The researchers compared the two routes at product level: on one side a park bench serving for thirty years, on the other one kilogram of food-grade LDPE packaging at varying recycled content (0, 10, 50 and 100 per cent). The bench was also benchmarked against cast iron, FSC-certified wood and virgin HDPE versions.
The life-cycle assessment result is clear: the bench made from flexible mixed polyolefins outperforms its rivals in 16 of the 18 impact categories examined. Wood leads on climate impact (14 kg CO₂ equivalent per functional unit, without counting biogenic carbon storage), and virgin HDPE on freshwater ecotoxicity. The cast iron bench, however, is dramatically worse: 32,000 kg 1,4-dichlorobenzene equivalent in terrestrial ecotoxicity and 170 kg copper equivalent in metal depletion.
Collapsing the impacts into a single figure (using CE Delft’s environmental pricing method) makes it starker still. The environmental cost of the flexible mixed polyolefin bench is EUR 24.02 — about the same as the wooden bench (EUR 21.40), less than the virgin HDPE bench (EUR 36.07), and trivial next to cast iron (EUR 582.75).
Why does packaging lose out?
Circularity was measured with the product circularity indicator (PCI), which runs from zero to one and accounts not only for material flows but also for product lifetime and use intensity. This is where the story gets genuinely interesting.
Among benches, cast iron scores highest (0.82) thanks to its durability and good recyclability, followed by the mechanically recycled polyolefin bench (0.75) and FSC wood (0.68). The virgin HDPE bench trails far behind (0.18).
Packaging plays in an entirely different league. Even 100 per cent chemically recycled LDPE packaging only reaches 0.25; at 50 per cent it is 0.16, and at 10 per cent — precisely what the PPWR requires by 2030 — just 0.08. Virgin LDPE scores 0.06.
The reason is simple, and it is not technological: packaging is short-lived. It serves for days or weeks, then becomes waste again. However good the material we put into it, the value stored in that material drains out of the system fast. A bench serves for thirty years — the same kilogram of plastic works far harder, and far longer.
A new metric: how much circularity per euro of environmental cost?
Hence the authors’ proposed sustainability–circularity index (SCI), simply the ratio of the circularity score to the environmental cost. In plain terms: how much circular value do we get for each “environmental euro” spent. To keep the comparison fair, both sides were standardised to the same 83 kilograms of material — exactly the amount of plastic in one bench.
The results:
- Mechanically recycled polyolefin bench and FSC wood bench: both around 0.031 EUR⁻¹ — the best scores.
- Virgin HDPE bench: around 0.005 EUR⁻¹.
- Cast iron bench: worst of all, because of the energy-intensive casting — despite having the highest circularity score.
- 100 per cent chemically recycled packaging: 0.013 EUR⁻¹.
- 50 per cent: 0.006 EUR⁻¹. 10 per cent: 0.0027 EUR⁻¹. Virgin LDPE: 0.002 EUR⁻¹.
The authors are careful here: the SCI does not claim a bench is a “better product” than a food pouch — they are not substitutes. It says that the same 83 kilograms of recycled material delivers several times the circular return in a long-lived product for the same environmental burden.
From which follows the study’s strongest claim, directly contradicting a widespread industry cliché: the narrative that turning flexible mixed polyolefins into benches is “downcycling” is flawed. On the contrary, the researchers argue — prioritising pyrolysis prematurely in order to feed packaging creates feedstock scarcity for durable goods manufacturers and pushes them towards materials with much higher environmental impacts, such as cast iron.
What this means in practice
The study is built on European material flows, but its conclusions apply directly to national systems too.
First, the quality of household film collection determines whether the material ends up in the better or the worse bale category in the first place. The cleaner, drier and more food-residue-free the film that goes in, the greater the chance it lands in the higher-value film bale rather than the mixed residue. This is the one point where households directly influence the material’s onward path.
Second, national waste management systems have to decide where they direct the flexible mixed fraction. The study warns that the political and investment momentum towards chemical recycling — driven by the PPWR’s food-grade recycled content requirement — diverts material from a segment that already works and already has a market: street furniture, fence panels, pallets, planks and marker posts.
Third, on the authors’ own numbers, the biggest loss does not occur at the technology choice but before it. Of 1,168 kilotonnes, 717 survive — the rest is lost in sorting and pre-treatment. Whichever route we pick, the largest potential gain lies in the precision of collection and sorting, and in design for recycling.
What the study itself lists as limitations
The authors write unusually candidly about uncertainty, and that deserves to be passed on honestly.
They used two different pyrolysis yields: 79 per cent in the material flow analysis (under fuel-exempt mass balance), but a more conservative 62 per cent from an earlier, well-cited study in the environmental calculations. This puts the chemical route in a worse light — a deliberate choice in favour of the more conservative figure.
At the same time, the mechanical route also got unfavourable assumptions: every recycled polyolefin bench is assumed to be incinerated at end of life, while the virgin HDPE bench is assumed to be recycled. Second and third life cycles were not modelled. The food-grade suitability of pyrolysis was taken as given, with contamination limits not examined. Only pyrolysis was analysed on the chemical side — gasification, hydrogenolysis and solvent-based processes were not.
The bottom line
The study is not an argument against chemical recycling. It argues that a technology cannot be assessed in isolation from the product its output ends up in. The same kilogram of material is worth more in a bench used for thirty years than in a pouch used for three days — and as long as there isn’t enough feedstock for both, that consideration cannot be left out of the decision.
Or more simply: a park bench made from crisp packets is nothing to be ashamed of. Right now, it is the best our system can get out of them.
Frequently asked questions about flexible mixed polyolefins
What are flexible mixed polyolefins and where do they come from?
Flexible mixed polyolefins are the film and pouch waste left after sorting, in which polyethylene and polypropylene are commingled. They come from two bale types: the mixed polyolefin bale and the mixed plastics bale. The material is printed, contains adhesives, is often multilayer, and its barrier layers may include other polymers.
Why can’t flexible mixed polyolefins be turned back into film?
Polyethylene and polypropylene do not blend well in the melt, roughly like oil and water, so the commingled material never matches the mechanical properties of the original. Printing inks, adhesives and multilayer structures compound the problem, leaving output unsuitable for demanding film applications without expensive additional treatment.
Is there enough feedstock for both mechanical and chemical recycling?
No. The study finds that in 2030, 1,168 kilotonnes enters pre-treatment from the two bale types but only 717 kilotonnes emerges usable. In all three scenarios examined, that is too little to satisfy the 580 kilotonne demand for thick-walled products and the 360 kilotonne packaging demand simultaneously.
Which recycling route does the study recommend?
Purely from a sustainability and circularity standpoint, mechanical recycling into thick-walled products. That route delivers lower environmental impacts and higher circularity scores. Chemical recycling brings only modest benefits, particularly at low recycled content levels between 10 and 50 per cent, and because packaging lifetimes are inherently short.
Why is a park bench made from film waste not downcycling?
Because a bench serving thirty years returns several times more circular value from the same material than packaging used for a few days. The study puts the bench’s environmental cost at EUR 24.02 and its circularity score at 0.75 — both better than the virgin plastic or cast iron alternatives.
What can households do to improve the outcome?
Collection quality determines whether material lands in the higher-value film bale or the mixed residue. Clean, dry film free of food residue starts from a better position. The study notes that the largest loss occurs not at the technology choice but before it, during sorting and pre-treatment.
Source:
Merel Molenbuur, Cris Garcia-Saravia Ortiz-de-Montellano, Steven De Meester, Yvonne van der Meer, Milad Golkaram, Kim Ragaert: Should Flexible Mixed Polyolefins Be Sent to Mechanical or Chemical Recycling? A Technology-Agnostic Analysis Based on a Sustainability–Circularity Index. Engineering (2026). DOI: 10.1016/j.eng.2025.12.044 — accepted manuscript, in press.
