A new way of converting stubborn plastic waste into high-value chemicals using only water and oxygen, has been developed by an international team of scientists.
The researchers from Zhejiang University, in collaboration with Cardiff University, the University of Tokyo and others, successfully transformed a wide range of everyday plastic waste including polyethylene, polypropylene, and even rubber tyres into value-added organic acids.
These acids are essential chemical building blocks widely used in medicines, food additives, and the manufacturing of biodegradable materials.
Recycling processes of this kind are usually kick-started by expensive and sometimes toxic catalytic technology, according to the team.
Their study, published in the journal Nature, instead offers a simple, economically viable and catalyst-free recycling strategy to one of the world's most pressing environmental challenges.
Professor Yong Wang, the study's lead author from the Zhejiang Provincial Key Laboratory of Low-carbon Synthesis of High-value Chemicals at Zhejiang University, said: "By eliminating the need for expensive or toxic catalysts entirely, we have removed one of the major economic and environmental barriers to the industrial adoption of chemical plastic recycling."
The team's innovation is powered by tiny water droplets.
By simply melting and stirring the plastic in water, the polymer disperses into microscopic droplets.
This process creates a dynamic water-oil interface where highly reactive hydroxyl radicals are generated spontaneously.
These natural radicals act as "chemical scissors," neatly cleaving the tough bonds of the polymer chain.
Using polyethylene as a model, the team achieved near-complete plastic conversion with a 69% yield of short-chain diacids under mild conditions, leaving no microplastic residues behind.
Professor Graham Hutchings, one of the study's co-authors and Regius Professor of Chemistry at Cardiff University's Cardiff Catalysis Institute, added: "We are awash with plastic waste, and we need viable solutions for its effective recycle. Our discovery shows the way, demonstrating that water and oxygen alone – under the right microdroplet conditions – are powerful enough to drive the selective oxidation of some of the most chemically inert and durable materials on Earth."
While the unique chemical properties of microdroplet interfaces have fascinated scientists for years, this study marks the first time the phenomenon has been harnessed at a practically relevant scale.
The researchers successfully scaled up the process to a 300g batch in the lab, demonstrating its commercial viability.
Crucially, the method is robust enough to tolerate commercial additives and mixed waste streams that would typically poison and deactivate conventional catalysts. Furthermore, it works perfectly using both tap water and seawater.
The paper, 'Catalyst-free, microdroplet-mediated waste plastic conversion to diacids', is published in Nature.
