Mechanical processes, solvents, enzymes and pyrolysis recover different things from plastic waste. Comparing usable output, contamination and energy across the full process reveals where each route can contribute to a circular economy.
A recycling reactor can convert most of its plastic feedstock and still return much less material to a new product. Sorting removes unsuitable items before treatment. Purification removes unwanted substances afterwards. Some outputs become fuels, while others need further chemical processing before they can replace virgin polymer. These distinctions determine what a recovery claim means.
For European industry, the choice is becoming more sophisticated than a contest between mechanical and chemical recycling. The practical challenge is to send each waste stream to a process that retains useful value at an acceptable environmental and economic cost. Recent research shows why success depends as much on the quality of incoming material and the requirements of its next customer as on reactor performance.
Mechanical recycling sets a demanding benchmark
A 2023 comparison led by Taylor Uekert assessed recycling routes for polyethylene, polypropylene and polyethylene terephthalate, or PET. Its process models estimated mechanical recycling energy use of 4.1–8.6 megajoules per kilogram and greenhouse gas emissions of 0.28–0.53 kilograms of carbon dioxide equivalent per kilogram. Mechanical recycling performed strongly on cost and environmental measures, while several solvent and depolymerisation routes produced higher quality material under the study’s assumptions.
Mechanical recycling generally preserves the polymer while sorting, cleaning, melting and reforming it. Avoiding the need to break molecules into smaller chemical building blocks and reconstruct them can save processing. Its difficulty is delivering consistent performance from materials whose composition and previous treatment vary.
That trade off has commercial consequences. A recycler selling material for a demanding application needs predictable properties, rather than simply a large volume of pellets. A process with a low environmental footprint still needs an outlet that uses its output effectively; a more intensive purification route needs to justify the additional quality it supplies.
More captured plastic can mean a harder feedstock
A June 2026 Nature study examined plastics from one material recovery facility, comparing separately collected packaging with material recovered from residual waste. Bales could contain similar percentages of the target polymer while differing substantially in moisture, dirt, volatile compounds, metals and halogens. Post sorting increased the opportunity to capture plastic, but also brought additional contamination that could complicate either mechanical or chemical recycling. The single facility comparison does not establish the performance of every collection system.
This exposes a weakness in describing feedstock only as, for example, polypropylene rich. Two loads with the same polymer percentage may require different washing, deodorisation or purification, and produce material suitable for different applications.
Increasing collection and maintaining quality therefore need to be developed together. A plant designed around unusually clean demonstration material may struggle when a municipality supplies a broader waste stream. Feedstock specifications, sampling and agreements over rejected loads are part of the technology’s operating conditions, rather than administrative details added after commissioning.
Dissolution tries to retain the polymer
Solvent based recycling can separate polymers without deliberately breaking their main chains. In the 2020 STRAP study, researchers used selective dissolution and precipitation to separate polyethylene, ethylene vinyl alcohol and PET from a commercial multilayer film with nearly complete material recovery. The accompanying economic analysis considered a plant processing 3,800 tonnes annually; it was a model, not evidence of commercial operating costs at that scale.
The attraction is clear for laminated products whose layers perform different functions in use but resist conventional separation afterwards. Recovering individual resins could preserve more of the original molecular work than converting the whole mixture into small molecules.
The separation system nevertheless has its own material flows. Solvent must be recovered, contaminants removed and the polymer dried sufficiently for its next application. A high polymer recovery percentage does not describe solvent losses or energy demand. Those quantities matter when moving from a carefully selected film to variable packaging collected after use.
Purification is a specific chemical problem
A study published in late 2025 examined dissolution recycling of polypropylene feedstocks representative of sorting centres. Its analytical work found that some lighter or more polar additives were removed more readily than high molecular weight antioxidants and long chain lubricants. Polyethylene contamination also persisted. One dissolution and precipitation cycle therefore did not create a universally purified material.
A separate 2025 experiment used membrane filtration to remove more than 90% of the flame retardant HBCD from tested virgin and post consumer polystyrene solutions. It exploited the size difference between polymer molecules and smaller contaminants. This was evidence for a particular separation, not proof that every additive in every plastic could be removed with the same membrane. The researchers also disclosed company and patent interests.
Together, the studies suggest a more useful development target than promising virgin quality in general. Researchers can specify the contamination that matters, demonstrate its removal and measure the resulting polymer properties. Manufacturers can then decide whether that improvement is relevant to the product they intend to make.
Depolymerisation changes the product being recovered
PET provides a different opportunity because its chemical bonds can be broken selectively to recover building blocks. A 2020 Nature study reported an engineered enzyme achieving at least 90% depolymerisation in ten hours under its tested conditions. The recovered material was used to make new PET, demonstrating a route from waste bottles back to suitable polymer. The result concerned prepared PET and an optimised enzyme process, rather than arbitrary mixed plastic waste.
Reaction conversion is only one stage in that route. Monomers must be separated and purified, and polymerisation must produce material with the required properties. Water, heat, enzyme production and preparation of the waste contribute to the process even when the reaction itself runs at comparatively modest temperature.
An enzyme’s selectivity can be both an advantage and a limit. It may target the desired polymer while leaving other material intact, but the remaining mixture still needs handling. The investment case depends on enough suitable PET reaching the plant consistently and on a buyer valuing the recovered building blocks.
Pyrolysis oil is an intermediate rather than a new bottle
Research published online in December 2024 and in a 2025 Energy and Fuels issue tested polyolefin enriched mixed plastic waste in a batch reactor. Dry washed material produced up to 78% oil by intake mass after an hour at 420°C under nitrogen. The investigators also measured its chemical composition, because a high liquid yield alone does not make an oil suitable for downstream petrochemical equipment.
That yield cannot be described as 78% of discarded plastic returning to new plastic. The feedstock had already undergone preparation, while upgrading, steam cracking and subsequent polymer production would add further transformations and losses. Burning a recovered oil uses its energy but does not preserve its carbon in another material cycle.
This distinction creates an opportunity for more informative demonstrations. Reporting the mass and composition of each output, together with the treatment needed before sale, allows a potential customer to judge compatibility. It also reveals whether the process is primarily a source of fuel, chemical feedstock or material for another polymer cycle.
The best route depends on the alternative
A Swiss material flow and life cycle study modelled a 2040 system that maximised environmentally beneficial mechanical recycling and directed suitable remaining waste to chemical or solvent routes. Compared with sending those residual streams to energy recovery, the additional routes reduced modelled system climate impacts by less than 10% to almost 40%, depending on process assumptions. Dissolution and depolymerisation generally offered greater benefits than more extensive conversion, while pyrolysis depended strongly on product substitution and efficient energy use.
The important industrial relationship is therefore complementary. A technology can be valuable for a difficult residual stream without being the preferred treatment for clean material that already has a productive mechanical route.
Europe’s next recycling capacity should be judged by the useful output it adds to that system. Following material through sorting, treatment and its next application makes the engineering challenge visible. It directs research towards the losses that actually restrict circularity and helps buyers distinguish a successful reaction from a dependable supply of secondary raw material.
