Plastic Recycling : Swiss engineers have invented a new approach to recycling plastic

EPFL Stellacci Giaveri
© Alain Herzog 2021 EPFL

How to deal with the staggering amount of plastic discarded worldwide each year? How to solve the problem of used plastics and recycle it more effectively? Francesco Stellacci, a full professor and head of the Supramolecular Nanomaterials and Interfaces Laboratory at EPFL’s (École Polytechnique Fédérale de Lausanne) School of Engineering, and Prof. Sebastian J. Maerkl at the Bioengineering Institute at EPFL tried to find the answers to that questions. The they decided to co-advise a PhD student, Simone Giaveri, and the team has published its research in Advanced Materials.

The engineers decided to think up a completely new approach to recycling plastics. “When we use biodegradable plastics, the degradation process leaves residue that must be stockpiled or buried. The more land that is allocated for this means the less land available for farming, and there are environmental consequences to take into account as bio-degradation product necessarily change the area’s ecosystem,” says Stellacci.

Like a string of pearls

They focused on proteins, one of the main organic compounds of which the world is made of. They form part of the family of polymers, just like DNA. Proteins are basically long chains of molecules, or monomers, known as amino acids. “A protein is like a string of pearls, where each pearl is an amino acid", Giaveri explains. "Each pearl has a different colour, and the colour-sequence determines the string structure and consequently its properties. In nature, protein chains break up into the constituents amino acids and cells put such amino acids back together to form new proteins, that is they create new strings of pearls with a different colour sequence.” The scientist attempted to replicate this natural cycle outside living organisms in the lab.

A new mindset for plastic recycling

The connection to plastic recycling seemed obvious for them. They reckoned that because both compounds are polymers, the mechanisms naturally occurring in proteins could be applied to plastics as well. But: “It will require a radically different mindset. Polymers are strings of pearls, but synthetic polymers are made mostly of pearls all of the same colour and when the colour is different the sequence of colour rarely matters. Furthermore, we have no efficient way to assemble synthetic polymers from different colour pearls in a way that controls their sequence", Stellacci warns. On the other hand he points out that this new approach to plastic recycling, which they have called "nature-inspired circular-economy recycling", or NaCRe for short, appears to be the only one that truly adheres to the postulate of a circular economy. "In the future, sustainability will entail pushing upcycling to the extreme, throwing a lot of different objects together and recycling the mixture to produce every day a different new material. Nature already does this," he concludes.