When everyday plastics become high-performance, reusable materials

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Windmills, cars, tubing, robotics and electronics call for lighter and more resistant materials, which are cheap and reusable. Can ordinary plastics become such a high-performance material? Yes! According to Ludwik Leibler, Renaud Nicolaÿ, and colleagues from the Soft Matter and Chemistry Laboratory (MMC, CNRS, ESPCI, Paris). A targeted chemical reaction transforms plastics into dynamic molecular networks, vitrimers. With a unique combination of properties vitrimers could lead to a revolution in plastic and composite materials, while retaining conventional production and processing methods. Promisingly, this approach opens the way to recycling mixed plastics without sorting, by transforming them into a vitrimer alloy. This work is published in Science, on 7 april, 2017.

The need for plastic materials is continuously increasing, with higher and higher requirements for performance and recyclability. Commodity plastics suffer from limits and cannot satisfy all requirements. A solution is coming from vitrimers, a new class of organic materials invented in recent years by Ludwik Leibler and collaborators. Vitrimers exhibit a rich combination of mechanical and thermal resistance together with chemical stability. The idea of vitrimers has inspired scientists and companies to invent functional materials and composites, such as liquid crystal and shape-memory materials. However, in order for vitrimers to become the plastic of the future two questions remain unanswered:

Is it possible to produce vitrimers from the same ingredients as common plastics? Could vitrimers be processed using the same tools and at the same rate as commodity plastics?

Scientists from ESPCI, Paris have taken up the challenge. They have invented a metathesis reaction which exchanges atoms between molecules without breaking chemical bonds. Since this reaction is very efficient, it becomes easy to transform into a vitrimer any polymer with a carbon backbone (75% of the plastics market). Remarkably, the reaction does not need a catalyst, which is an economic and ecological advantage. It is also easy to adjust the composition and the processing conditions to use standard transformation methods (injection or compression moulding, extrusion blowing, thermal forming). Vitrimers formed from polystyrene, acrylics, polyethylene, have better mechanical and thermal resistance than the original product, without compromising the possibility of repair, welding and recycling.

Dynamic chemistry brings more thermal and solvant resistance to everyday plastics, without compromising their easy processing or recylabilty (from left to right vitrimers from poly(methyl methacrylate), polystyrene and polyethylene)

Another, less well known aspect, is that a quarter of failures of plastic and composite parts is due to contact with liquids. Vitrimers are far less sensitive to such attacks, and are an excellent alternative, for example, for protective coatings, pipes, glue, liquid containers, organic glasses, medical devices and car components.

Surprisingly, the metathesis reaction works at surfaces. It brings strong adhesion between vitrimers made from completely incompatible plastics. This opens perspectives in fields ranging from packaging to tires. As for recycling plastics, today it requires sorting according to chemical identity. The metathesis reaction allows the reuse of plastics without sorting, and should even allow alloys with properties which are improved compared to those of the original components (rigidity, impact and tearing resistance, impermeability to solvents).

This vitrimer technology has been patented by ESPCI, Paris

* Max Röttger, Trystan Domenech, Rob van der Weegen, Antoine Breuillac, Renaud Nicolaÿ, Ludwik Leibler, Science 07 Apr 2017, Vol. 356, Issue 6333,
pp. 62-65 - (DOI: 10.1126/science.aah5281)

** Damien Montarnal, Mathieu Capelot, François Tournilhac, Ludwik Leibler, Science 334, 965 (2011) - (DOI: 10.1126/science.1212648)

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