Elastic Plastic Could Be Endlessly Recycled
Manufacturing of a complex shape of a thermoset by local heating.
CREDIT: CNRS/ESPCI/Cyril FRESILLON
Virtually every manufactured plastic product gets squirted into a mold. Once the goop inside has cooled, that's it. There's no opportunity to change the shape. But now, chemists in France have designed a new plastic that stays durable in room temperature but gets progressively more elastic as it heats up. It could replace the process of using molds, with sculptors, and may prove especially useful in the aircraft industry.
You can work it like a glass and you get shapes you cannot get easily by molding, explains Ludwik Leibler, director of the soft matter and chemistry department at the École Supérieure de Physique et de Chimie Industrielles in Paris.
The polymers in use today fall into two categories: thermosets and thermoplastics. Glass is a thermoplastic. Even after it sets, glass can be reheated until the crystalline structure of the molecules breaks down, at which point it starts to flow like a liquid. However, glass is relatively brittle and can break. Bakelite, on the other hand, is a thermoset. When cast into a shape, the only way to change it is to destroy it. And that is hard to do.
Thermosets, because of their durability, are essential materials in many industries. But They can't be processed by heating and they cannot be recycled, said Leibler.
Leibler's team has designed an alternative that combines the stability of thermosets with the workability of thermoplastics.
The researchers made their novel plastic by combining a thermosetting epoxy with a chemical catalyst. The molecules in the material link up into a network of bonds, and breaking the bonds drastically changes the state of the material, as happens when glass melts. When the atoms in Leibler's plastic gets hot, bonds may break but they will immediately shift to another atom, keeping the number of bonds constant. They do this with the help of the catalyst.
Leibler compared it to a network of people holding hands, with each person having more than two hands so that they don't just form a chain. The catalysta free-moving cluster of hands among the networkfills the gap between any two people as they drop hands, then passes them on to a new set of hands.
The catalyst gives the whole network fluidity, letting it respond and adjust to areas of stress without losing its basic arrangement. But the catalyst works harder as the temperature rises, making Leibler's polymer more elastic as it heats up.
I think it will be especially useful for large objects, Leibler told InnovationNewsDaily. The chemists hope to attract some interest from the airplane manufacturers who now mostly use thermoplastics to shape their gargantuan parts.