Acrylic Glass Recycling: Swiss Researchers Turn PMMA Back into Monomer at 230 °C Without Solvents

Acrylic glass recycling has long been a side story of the circular economy: acrylic glass (PMMA) is chemically well suited to being broken back down into its building block, yet in practice most of it still ends up in landfill or incineration. A research group at ETH Zurich led by Athina Anastasaki has now presented a process in Nature Chemistry that converts the polymer back into methyl methacrylate (MMA) monomer using a single inexpensive, commercially available additive – with no solvent and no light irradiation, at temperatures roughly 220–270 °C lower than conventional pyrolysis, and with lab yields of around or above 90 per cent, even on coloured commercial Plexiglas.

In short: A new Swiss method for acrylic glass recycling uses an N-hydroxyimide additive to break PMMA down into pure, colourless monomer at 180–230 °C without solvents, typically reaching about 90% conversion in the lab and 96–99% under optimised conditions. It also worked on coloured commercial Plexiglas and aluminium hydroxide-filled PMMA, but has so far only been demonstrated at gram scale, and industrial scale-up is still ahead.

Why acrylic glass is a special case

Poly(methyl methacrylate) – widely known by the brand name Plexiglas – replaces glass in windows and is found in car tail lights, furniture, signage, displays and, when filled with aluminium hydroxide, in many solid-surface kitchen worktops. Unlike most plastics, PMMA has a rare property: when heated, it tends to “unzip” back to its own monomer rather than to a mixed oil. In principle, that makes it one of the best candidates for chemical recycling.

The problem is temperature. Pyrolysis, the method in use today, runs at around 450 °C, which is not only energy-intensive but also causes side reactions and odorous by-products that contaminate the recovered monomer. According to ETH, monomer from pyrolysis can contain up to 3 per cent impurities – enough to affect the quality of the new plastic. Mechanical recycling is no real answer either: every remelting shortens the polymer chains and weakens the material, as we explained in our analysis The Illusion of Circularity: 12 Reasons Why Plastic Recycling is Failing Globally.

A single additive starts the breakdown

Anastasaki’s group has been working on lower-temperature depolymerisation of acrylic glass for years, but earlier solutions – theirs and their competitors’ – shared a common weakness. Either labile “weak link” end-groups had to be installed at the chain ends, a small amount of so-called sacrificial co-monomer had to be added during production, or a chlorinated solvent and visible light were needed at high dilution. The first two approaches only work on purpose-designed polymers and reduce the product’s thermal stability, so they do nothing for the acrylic waste already in circulation.

The new process, by contrast, breaks down finished commercial polymer. The key is an N-hydroxyimide compound mixed with the ground plastic. The researchers compared three related substances: N-hydroxysuccinimide (NHS), N-hydroxyphthalimide (NHPI) and its tetrachlorinated version (TCNHPI). On heating, the additive generates radicals that abstract a hydrogen atom from the polymer backbone. The resulting radical cleaves the chain in the middle, and the fragments then “unzip” into monomer. The team supported this mechanism with size exclusion chromatography, electron paramagnetic resonance (EPR) measurements and density functional theory calculations.

Part of the discovery was serendipitous: the original plan was to add a separate radical initiator alongside NHPI, but a control experiment showed that the additive alone triggered the breakdown – and a second additive actually made results slightly worse. Richard Whitfield, the study’s lead author, told ETH that the most exciting thing about the new approach is how simple it is.

The lab numbers in detail

Based on the data in the paper, the process performs as follows:

• Without additive, PMMA starts losing mass around 310 °C and needs 380 °C for 90% breakdown; at 230 °C almost nothing happens in two hours (about 3%).
• With TCNHPI, breakdown starts at 175 °C and 90% mass loss is reached at 250 °C; at 230 °C, 93% breaks down within two hours (63% with NHPI, 35% with NHS).
• Lower temperatures work too: 91% mass loss at 220 °C, 88% at 210 °C, 86% at 200 °C, and still 70% at 180 °C.
• Little additive is needed: the amount of TCNHPI can be cut from 0.05 to 0.004 equivalents per repeat unit without compromising the final yield – an important point for costs.
• Independent of production history: PMMA made by anionic, free radical and various controlled radical methods (ATRP, RAFT) reached 87–93% conversion.
• Works on giant molecules: PMMA with an average molar mass of 1.4 million daltons broke down by 96%, and a second dose of additive pushed this above 99%. The 25–1,400 kDa range comfortably covers commercial materials.

Nuclear magnetic resonance spectroscopy showed that the distilled product was pure, colourless methyl methacrylate. The researchers stress that this purity is a direct result of the low temperature. ETH’s press release cites a maximum monomer yield of 98%; the highest value in the paper is the conversion above 99% achieved with a second additive dose, while typical results lie between 90 and 96%.

Coloured Plexiglas and worktop material also qualify

Commercial products were the real test. Plexiglas sheets in various colours – which contain co-monomers, plasticisers, dyes and radical inhibitors – broke down with up to 90% conversion. In a larger 5.1-gram experiment, blue Plexiglas yielded 4.6 grams of colourless monomer after four hours of vacuum distillation at 230 °C, a 90% yield.

From a waste management perspective, aluminium hydroxide-filled PMMA may be even more important. This material is used in large quantities for kitchen worktops but cannot be handled by pyrolysis: at high temperatures aluminium hydroxide releases water, which reacts with the monomer and polymer to form large amounts of unwanted by-products. At 180 °C, however, the filler stays stable, and the researchers achieved roughly 70% depolymerisation with 10–50 wt% filler. According to the authors, this could open the way for a waste stream whose chemical recycling has not yet been achieved.

What this means for acrylic glass recycling in industry

The process’s biggest practical advantage is that it is purely thermal: no light source, solvent or metal catalyst is required, so according to the authors it may even be compatible with existing pyrolysis infrastructure. Anastasaki told ETH that their earlier methods never reached industry because companies would have had to modify their processes and equipment – too expensive for most. ETH Zurich has filed a patent application, is seeking licensees, and according to the press release the chemical industry has already shown interest.

Industrial success stories in chemical recycling have so far mostly involved PET and polyolefins – for example the partnership between PepsiCo and Eastman, which breaks hard-to-recycle polyester waste down to the molecular level. Our report on ARA’s 100 million euro investment programme also showed that food-grade purity can today almost only be guaranteed through expensive chemical processes, and our analysis of PET tray recycling explained why monomer-recovering depolymerisation belongs in a different category from pyrolysis or gasification. The Swiss result stands out because it promises clean, repolymerisable feedstock for a smaller-volume but valuable plastic, with lower energy demand than pyrolysis.

As next steps, the researchers plan to scale up the method and understand the reaction mechanism in more detail, and they intend to try the same principle on polystyrene, one of the most widely produced plastics in the world.

Where enthusiasm needs a brake

ETH’s press release headline says the new method makes acrylic glass recycling “economically viable”. For now, that is a promise rather than a proven fact. The paper itself is more cautious: the experiments consist of milligram-scale thermogravimetric measurements and a single 5-gram distillation, and the authors explicitly state that the feasibility of scale-up still has to be assessed. The paper contains no cost analysis or life-cycle assessment.

Several technical questions also remain open:

• Chlorine content. The most effective additive, TCNHPI, contains four chlorine atoms, and its thermal decomposition produces tetrachlorophthalimide and tetrachlorophthalic anhydride. At industrial scale, the fate of these residues, the handling of distillation bottoms and the effect on equipment need separate investigation. Encouragingly, a chlorine-free dimeric NHPI derivative also achieved monomer recoveries above 90%.
• Low-molecular-weight material. For 25 kDa PMMA the yield dropped to 66%, rising to 87% only with more additive.
• A narrow polymer family. The process works for polymethacrylates; with polyacrylates the chain does break, but no monomer is regenerated.
• Input material. The method works with homogeneous, ground PMMA. As our coverage of flexible mixed polyolefins shows, contamination and input variability in real waste streams rarely appear with full weight in the lab.

The same caution applies to other promising chemical recycling claims, such as the projections in the PPI report on US chemical recycling: the chemistry works, the industrial chain is not yet in place.

A waste manager’s view: collection is the bottleneck

However elegant the chemistry, the circularity of acrylic glass will be decided by collection. Acrylic sheet is not packaging, so it does not show up in separate packaging collection systems but appears scattered and mixed with other materials. The cleanest and most accessible source is production waste: offcuts from sign and display makers, cutting waste from worktop fabricators, and light units from end-of-life vehicle dismantlers. Industrial deployment of such a technology is most realistic where PMMA is available in bulk and of known composition.

The ETH result is therefore not tomorrow’s industrial solution, but a well-founded, simple and inexpensive chemical route that – if scale-up succeeds – could lift acrylic glass into the ranks of genuinely circular plastics.

Acrylic Glass Recycling – Frequently Asked Questions

How does the new Swiss method for acrylic glass recycling work?

It uses a single additive and heat. ETH Zurich researchers mix an N-hydroxyimide compound – with the best results from tetrachloro-N-hydroxyphthalimide – into ground acrylic glass and heat it to 180–230 °C. The resulting radicals abstract hydrogen atoms from the polymer chain, the chain breaks in the middle, and the fragments unzip into monomer. No solvent, metal catalyst or light is needed.

How much monomer can be recovered from acrylic glass?

Typically around or above 90 per cent in the lab. Coloured commercial Plexiglas samples reached up to 90% conversion, and a 5.1-gram blue sample yielded 4.6 grams of pure, colourless methyl methacrylate after distillation. PMMA with a molar mass of 1.4 million daltons broke down by 96%, and a second dose of additive pushed conversion above 99%.

How is the new process better than pyrolysis?

It delivers purer monomer at much lower temperatures. Pyrolysis runs at around 450 °C, with side reactions and odorous by-products that contaminate the recovered monomer. The new process works at 180–230 °C, so aluminium hydroxide-filled PMMA – the material of many kitchen worktops – can also be processed, which pyrolysis cannot handle because the filler releases water when heated strongly.

When could the ETH Zurich method reach industry?

There is no date yet. The process has only been demonstrated at laboratory scale, on quantities of a few grams at most, and the authors themselves note that scale-up still has to be assessed. ETH Zurich has filed a patent application and is seeking licensees; the chemical industry is interested because the process may be compatible with existing infrastructure.

Does the process work on other plastics?

For now, only on polymethacrylates, so primarily on acrylic glass. With polyacrylates the polymer chain does break, but no monomer is regenerated, which the researchers attribute to the lower stability of the backbone radical. As a next step, the group plans to try the same principle on polystyrene, one of the most widely produced plastics in the world.

🔗 Official sources and references: 👉

• Whitfield, R., Lohmann, V., Agrachev, M., Kim, H., Wang, H. S., De Alwis Watuthanthrige, N., Truong, N. P., Choi, T.-L., Jeschke, G., Anastasaki, A.: Lower-temperature bulk depolymerization of commercial polymethacrylates. Nature Chemistry (2026). https://doi.org/10.1038/s41557-026-02232-4
• ETH Zurich: New method makes acrylic glass recycling economically viable (19 October 2026). https://ethz.ch/en/news-and-events/eth-news/news/2026/10/new-method-makes-acrylic-glass-recycling-economically-viable.html

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