New family of recyclable plastics created 'by accident'

Gel The second group of new plastics are elastic, self-healing gels

Researchers have developed a collection of new plastics that are recyclable and adaptable - and the discovery began with a laboratory mistake.

They include strong, stiff plastics and flexible gels that can mend themselves if torn.

The findings, reported in the journal Science, could lead to cheaper and greener cars, planes and electronics.

It is the first time that durable "thermoset" plastic has been produced in a recyclable form.

Dr Jeanette Garcia, from IBM's Almaden Research Center in San Jose, stumbled upon the first new class of thermosets in many years when she accidentally left one of three components out of a reaction.

"I had this chunk of plastic, and I had to figure out what it was," Dr Garcia told the BBC. "I had to smash my round-bottomed flask with a hammer."

That chunk of plastic, produced from unexpectedly simple ingredients, proved to be tremendously hard and stable. Crucially, it could be digested in acid, reverting to its original components.

This digestion reaction allows the chemical building blocks, or monomers, to be reused.

Bakelite telephone All previous "thermosets", like the Bakelite found in old telephones and radios, were not recyclable

"It was definitely fortuitous," Dr Garcia said. "The first thing I did, of course, was to hit the literature, to try and see if it'd been done before. I just assumed that it had been - it's such a simple reaction."

But her search turned up nothing. This was new.

Once she understood what she had created, Dr Garcia set about repeating her finding. "We wasted a lot of flasks," she said.

Because they are strong and light-weight, thermosets are used throughout modern cars and aircraft, often mixed with carbon fibres to form composites. Some 50% of the new Airbus A350 jet, for example, will be made from composites.

Yet until now, none of this thermoset plastic could be recycled.

"The potential impact here is phenomenal," said Dr Charl Faul, a materials chemist at the University of Bristol. He says the study offers a "very simple, elegant answer to a very old problem".

Microchips The new plastics could reduce waste from aircraft materials

Dr James Hedrick, who was in charge of the research at IBM, is excited by the possiblities. When a large or expensive component is damaged or reaches the end of its useful life, he explained, it could be repaired or recycled instead of thrown away.

"The ability to rework saves a tremendous amount of money and mitigates waste."

Beyond replacing thermoset-based composites in current technology, Dr Hedrick sees the potential for many more innovative applications. "We're at the discovery phase," he said. "Every time you discover a new polymer-forming reaction it leads to all sorts of new materials."

As well as very hard and durable plastics, the researchers adapted their procedure to a different monomer and produced flexible, self-healing gels. These could be useful in anything from cosmetics, to paint, to the design of drug capsules, because of their particular solubility properties.

"Applications are running like water," Dr Hedrick said. "We don't even know where to go with this yet."

Composite of new thermaset with carbon nanotubes The researchers have already used one of the tough new plastics to create a composite further strengthened with carbon nanotubes, seen here at the fractured edge of a thin sheet

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