Bordeaux and Marseille chemists have succeeded in transforming two of the most widely used but also most difficult plastics to chemically recycle: polystyrene and polyethylene. Using gentle, metal-free, and low-energy processes, they are paving the way for a new era in plastic waste recycling and valorization.
Plastics made from petroleum have the drawbacks of their advantages: designed to be resistant and recalcitrant to degradation, they remain very difficult to recycle (less than 10% are recycled), causing significant soil and ocean pollution problems and threatening ecosystem health. For polystyrene (PS), widely used in food packaging and insulation, less than 5% is recycled in France. Every year, hundreds of thousands of tons end up in our waste bins.
Pixabay illustration image
To change the situation, scientists from the Laboratoire de chimie des polymères organiques (CNRS/Bordeaux INP/Université de Bordeaux) and the Biodiversité et biotechnologies fongiques laboratory (INRAE/Aix Marseille Université) have devised a simple and robust solution: using enzymes from fungi to degrade it.
Their trick? Putting this polymer in the form of stable nanoparticles in water using a surfactant and in the presence of oxygen. The polystyrene formulated in this way becomes more accessible to enzymes which cut the long polymer chains into smaller fragments, until obtaining value-added molecules, such as benzoic acid and benzaldehyde.
These molecules are already used in daily life: benzoic acid for its antifungal and antibacterial properties, benzaldehyde for its almond scent. But their production methods remain very energy-intensive. Producing them directly from plastic waste using enzymes would therefore be a major advance for the environment and the circular economy. The process, still under development, suggests a fascinating future where used yogurt pots could be transformed into medicines or flavorings.
In a second study in collaboration with the Institut des sciences moléculaires (CNRS/Bordeaux INP/Université de Bordeaux), the team tackles polyethylene (PE), the most produced plastic in the world (over 150 million tons annually). This time, the aim is not to break it down but to chemically transform it into a new high-value-added material.
Valorization of polyethylene-based plastic waste by upcycling via grafting oxime or ketone functions onto the polymer chain.
© Yannick Landais et Daniel Taton
For this, the scientists use a simple and inexpensive oxidant: tert-butyl nitrite. Activated by visible light, it generates radicals, highly reactive species capable of removing a hydrogen atom from the polyethylene chain and replacing it with new chemical functions, oximes (C=N-OH) or ketone (C=0), without using metal catalysts.
The Bordeaux teams have shown that this chemical modification can also be performed thermally in an extruder for the treatment of PE waste on scales compatible with the recycling industry. The grafted functions constitute "entry points" on the polymer chain which then allow the material to be transformed, its rigidity, mechanical behavior, or polarity to be modified to make it more compatible with other plastics or solvents.
The study thus offers a dual perspective: recycling PE-based plastics more effectively and accessing innovative polymers with tunable properties and higher added value. In the long term, these advances could even enable the design of "intelligent" plastics, conceived from their manufacture to be transformed, repaired, or recycled more cleanly.
These two studies, published in
Angewandte Chemie International Edition, illustrate a paradigm shift in plastic chemistry and their circularity.
Editor: AVR