New Thermoset Plastic Is Remoldable, Repairable, and Recyclable

Chemists in France have reported a new lightweight plastic material that marries the desirable and eschews the unfavorable properties of thermoset plastics and silica glass into a new material. It can be remolded, repaired, and recycled using heat, while retaining its mechanical properties.

Thermoset plastics such as Bakelite are resistant to solvents and extreme temperatures. But because they are polymerized in a mold, they cannot be reshaped or recycled once set. Silica glass is fragile, yet can be reshaped, repaired, and recycled.

Lead researcher Ludwik Leibler of the School of Industrial Physics & Chemistry in Paris, part of France’s Centre National de la Recherche Scientifique (CNRS) described to James Urquhart of Chemistry World that possible applications for the new material range from coatings to propellers, and “more generally, any complex part in the fields where one wishes to combine lightness with mechanical and chemical resistance such as aviation, automotive, portable electronics.” Leibler suggested that reinforcing the new material with fibers might even make it competitive with metals in the most demanding applications.

Urquhart explains that the material was made by mixing a liquid resin, hardener, and catalyst, and then heating it between two hot plates. After complete curing, the material can be reshaped and remolded with sufficient heat source, such as an oven or heat gun.

The researchers have demonstrated that heat can repair scratches and small breaks in the material, and that the recycled material has the same properties as the original.

In Chemical & Engineering News, Bethany Halford describes the chemistry responsible for the material’s properties:

The key to the glassy behavior lies within the polymer’s molecular structure; it has an equal number of ester and alcohol groups. When the material is heated it transesterifies; that is, its ester cross-links transfer from one region of the polymer to another with the help of an embedded zinc catalyst. ‘You exchange links but you never diminish the chemical bonding’ that gives the polymer its strength, Leibler explains. ‘The number of chemical links always stays constant.’

Halford writes that Leibler’s team has patented the new material and wants to commercialize it, noting that chemical components are inexpensive and readily available.

Timothy F. Scott, a chemical engineering professor at the University of Michigan who studies polymers, expects this material will go far. He told Halford:

Given the tremendous potential for reversible covalent chemistries to generate dynamic, reconfigurable polymers, we’re certain to see more extraordinarily creative and exciting work in the field over the next several years.

Source: “A Plastic That Behaves Like Glass,” Chemical & Engineering News, 11/17/11
Source: “A thermoset plastic that bends like a thermoplastic,” Chemistry World, 11/17/11
Source: “A thermoset that behaves like thermoplastic,” YouTube

Rachel Petkewich is a freelance science writer and editor. She has worked as a research scientist in the chemical industry and spent eight years as a staff writer and editor at various science journals and magazines, including Chemical & Engineering News.