Seeing the Light: New Process Breaks down Polymers with 98% Recovery

ETH Zurich scientists unveil a violet-light-triggered process that breaks commercial plastics into original monomers, significantly simplifying future recycling efforts worldwide.

• Researchers achieved over 98% depolymerisation in polymethacrylates
• No additional reagents or catalysts are required, only dichlorobenzene solvent and violet light
• Process is scalable, potentially transforming global plastic recycling practices

A newly published study in Science reveals a chemical process that could simplify polymer recycling by breaking down plastics into their original building blocks. Led by a team of materials scientists and engineers at ETH Zurich, the research addresses the growing concerns surrounding the global proliferation of plastic waste. Microplastics—tiny plastic fragments less than five millimetres long—have been found in marine life, food products, and even human blood. Strategies to handle plastic waste are therefore urgently needed, and chemical depolymerisation is increasingly viewed as one potential solution.

A Violet Light Reaction

The process in question revolves around dissolving plastic polymers in a dichlorobenzene solvent and then exposing the mixture to violet light at temperatures above 90°C. According to the researchers, “no reagents or other catalysts are needed,” which sets this method apart from existing chemical recycling techniques that typically require additional substances. The discovery was partly serendipitous, but the ETH Zurich team soon recognised its significance and sought to determine how it was able to depolymerise plastics so effectively.

Drawing on the study’s findings, dichlorobenzene forms chlorine radicals when exposed to violet light. These radicals “pulled hydrogen atoms from seemingly random parts of the polymer backbone, causing it to break,” notes the press release. Crucially, each cleavage event spawns a new radical, initiating a chain reaction that continues to dismantle the macromolecules. The editor’s summary in Science further explains that “the process appears to involve hydrogen abstraction from the backbone by small quantities of chlorine radicals liberated from the solvent.”

Polymethacrylates, including widely used materials such as plexiglass, were found to revert to monomers at yields above 98%. The researchers emphasise that this is possible regardless of polymer size, origin, or the presence of typical plastic additives. This universality may prove especially useful in real-world applications, where plastics often contain an array of dyes, stabilisers, and impurities that can interfere with standard recycling methods.

Wider Implications for Polymer Recycling

Chemical depolymerisation has long been an aspirational approach to tackling plastic pollution, precisely because it allows for the recovery of the pure monomers. “The reversion of vinyl polymers with carbon-carbon backbones to their monomers represents an ideal path to alleviate the growing plastic waste stream,” states the abstract. By restoring polymers to their original constituents, manufacturers can repolymerise them back into high-quality plastics with minimal loss of performance. This contrasts with traditional mechanical recycling, which tends to degrade material quality over multiple cycles.

Though the reaction described is slower than some existing approaches, its simplicity and high yield offer compelling advantages. The temperature threshold of 90°C is well within the range of industrial processes, and the absence of exotic reagents or precious-metal catalysts could reduce costs. As the authors point out, the method is also flexible enough to accommodate multigram-scale depolymerisations, suggesting it could be scaled up for more extensive commercial use.

Looking ahead, the researchers anticipate that this light-activated approach might be adapted to tackle other types of plastics. While no single technology is likely to solve the global plastic crisis on its own, innovations like this point towards new ways to transform what was previously considered waste into a valuable resource. With policymakers, industry leaders, and scientists prioritising sustainability, the ETH Zurich breakthrough could represent an important step in reconciling the massive production of plastics with environmental stewardship.