Breaking Down Plastic Can Boost Recycling Effectiveness

Despite heightened awareness about the damaging impacts of plastic and the growing number of sustainable alternatives to it, change is disappointingly slow. Negotiations spearheaded by the UN Environment Program to reach a global agreement on plastic pollution are stalling, while polymers are being produced faster than we can get rid of them. In Switzerland, approximately 790,000 metric tons of plastic are used each year, yet only 9% of this is recycled - and that rate has barely improved in ten years, according to figures from the Federal Office for the Environment.

Switzerland has nevertheless set ambitious targets. The Swiss government's Dobler Motion, for example, aims to roll out the systematic collection and recycling of plastic waste across the country. Starting in January 2027, standardized recycling bags and collection points will be implemented nationwide. But logistical hurdles aren't the only reason why the recycling rate is so low - there are also challenges inherent in the material itself. Plastic comes in many different forms that are often mixed together, combined with dyes and additives and soiled during use, all of which makes it hard to turn plastic waste into a useful raw material. For some polymers, the recycling process requires so much energy or degrades the material to such an extent that it offers few environmental benefits versus incineration. That said, new methods are emerging that meet the stringent criteria of requiring relatively little energy and producing material good enough to replace virgin resin.

Tearing down to build back better

Today, plastic is usually recycled using mechanical methods based on grinding, melting and then remolding the material. Such methods are relatively cheap and simple and have proven to work well with PET and HDPE. However, they're less effective with plastic blends and with colored or contaminated plastic, as these processing steps lower the material's quality, damage its properties and result in a recycled product that's limited in its potential uses.

Scientists have been working since the 1970s to develop chemical recycling methods that are more effective. These methods involve recovering the core compounds in plastic: gases such as ethylene, hydrocarbon mixtures in an oily state, and monomers - the individual building blocks of polymers. The advantage is that these methods can be used to make new materials "from scratch," with no loss of quality. The drawback is they're still quite costly, complicated and financially unviable, meaning take-up has been marginal. Yet that hasn't discouraged research. EPFL spin-off DePoly - ranked the top Swiss startup in 2024 - has developed a system that can break down PET and polyester into their monomers, terephthalic acid and ethylene glycol, even if the initial plastic is soiled, blended or unsorted. These monomers can subsequently be used to produce PET with the same properties as virgin resin, but with a smaller carbon footprint since the process works at nearly ambient temperature. DePoly is currently building a pilot plant in Monthey with a 500 metric ton/year capacity. Meanwhile, Plastogaz, another EPFL startup, is exploring the use of catalytic hydrocracking to recycle more complicated forms of plastic. Its technology combines blended and soiled plastic with hydrogen and specific catalysts to create liquid hydrocarbon or methane. "Our process gives operators granular control over the chemical reactions and consumes around 40% less energy than conventional pyrolysis," says Felix Bobbink, the co-founder and CEO of Plastogaz. Up to 90% of the original material can be recovered and reintroduced into the production chain.

Going big by going small

Other scientists are investigating more radical approaches that employ natural processes or convert plastic into other materials. For example, a team at the Swiss Federal Institute for Forest, Snow and Landscape Research recently discovered microbes in the Graubünden Alps and the Arctic that can metabolize certain kinds of plastic at low temperature, including biodegradable polyurethane - used in sponges, mattresses and sneakers - and a polybutylene adipate terephthalate (PBAT)/polylactic acid (PLA) blend, which is a petroleum-based ingredient of biodegradable bags. This discovery - the result of fundamental research - paves the way for the use of enzymes to break down and recycle some of our plastic waste.

But what if we used plastic to make something other than just more plastic? That's the question being explored by Francesco Stellacci, the head of EPFL's Supramolecular Nano-Materials and Interfaces Laboratory. He came up with this idea after observing proteins, that are indeed natural plastics. Proteins consist of amino acid strings arranged in specific orders to form specific types of compounds.

Stellacci and his colleagues have shown that it is possible to copy Nature and split porteins into their constituent amino-acids and then rearranging them in completely new ways. "What's needed is a genuine paradigm shift, what if we could do this with synthetic polymers?" says Stellacci. He and his team see this as a step towards the ultimate form of upcycling, where a bunch of disparate items is transformed into a new material on a daily basis. While this may be a distant dream for now, it points to the bold prospect of moving beyond the concept of circularity by developing a material that's even more sustainable than the original.