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Polymer, Heal Thyself—Over and Over

Wednesday, February 19, 2014

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Self-healing material technology is not new, but scientists at the University of Illinois have moved the field a significant step forward.

Their new polyurea-based polymer, made of off-the-shelf materials, heals itself repeatedly at low temperatures with no catalyst, the researchers say.

What looks like tiny dogbone-shaped gummies now could be the beginning of peel-off coatings and self-healing plastics, according to materials science and engineering professor Jianjun Cheng, graduate student Hanze Ying, and postdoctoral researcher Yanfeng Zhang.

Self-Healing Polymer Self-Healing Polymer
Photos, video: University of Illinois / Anne Lukeman

The plastic polymer was cut in two and allowed to heal overnight. Stretching the polymer did not break it.

Their paper, “Dynamic Urea Bond for the Design of Reversible and Self-Healing Polymers,” was recently published in the journal Nature Communications.

'Anybody Can Do This'

"We just buy commercial materials and mix them together, no fancy controls or special apparatus," said Cheng. "It's a very simple, low-cost, inexpensive process. Anybody can do this on any scale."

He adds: "The key advantage of using this material is that it's catalyst-free and low-temperature, and can be healed multiple times.

"These are very nice materials for internal cracks. This can heal the crack before it causes major problems by propagating."

Elastic polymers heal at the molecular level after they are cut in this University of Illinois demonstration.

Unlike other self-healing materials, the new product uses softer elastic materials made out of polyurea, one of the most common classes of polymers used in paints, coatings, elastics, plastics, and other consumer goods, the university reports.

Dynamic Chemistry

The polymer is made with commercially available ingredients. By tweaking the structure of the polymer's molecules, the team "can make the bonds between the molecules longer so that they can more easily pull apart and stick back together—the key for healing," the university says.

This molecular-level re-bonding, called dynamic chemistry, uses consumer materials and readily available ingredients, the team says.

When the polymer is cut or torn, the researchers press the two pieces back together and let the sample sit for about a day to heal. No chemicals or catalysts are required.

Furthermore, the team says, the materials can heal at room temperature, although curing at slightly higher temperatures (37 degrees Celsius, or about body temperature) does speed up the process.

HanzeYing

Graduate student Hanze Ying and colleagues at the University of Illinois developed the low-cost material, which requires no catalyst to self-heal.

The team says the mended polymer bonds "nearly as strongly as before it was cut."

In fact, the team adds, some healed samples tore in a new place when stretched, while the repaired area held.

What it Might Do

The researchers hope manufacturers can easily integrate the dynamic materials and are exploring how the polyurea could perform in different applications.

One possibility, they say, is a removable polyurethane coating or paint.

“In some areas, when it’s not necessary for the coating to be permanent and you want it to be removable, this chemistry may be applied to existing coating materials to make it reversible,” Cheng said.

“In general, polyurea and polyurethane are widely used. This chemistry could modify existing materials to make them more dynamic, healable.”

The research is supported by the National Science Foundation and the National Institutes of Health.

   

Tagged categories: Marine Coatings; Polymers; Polyurea; Polyurethane; Research; Self-healing

Comment from Gary Shapiro, (2/19/2014, 7:56 AM)

Very interesting. I would like to learn more.


Comment from Tom Schwerdt, (2/19/2014, 9:03 AM)

Interesting, though other soft materials such as wax tape have shown repeated self-healing ability for decades. If the material is sufficiently non-sticky, it could offer a nice benefit compared to waxes. Easy removability would be another nice benefit compared to waxes.


Comment from Nick Kaiser, (2/20/2014, 9:27 AM)

It seems that stable N=C=O and amine groups are formed upon chain scission, but the question is: how long after break is the isocyanate still reactive? If only sulfides smelled better!


Comment from Dudley Primeaux, (2/20/2014, 4:47 PM)

Yes, this is an interesting article, and work. It is a little missleading though as they do in fact use a catalyst in the system. They use dibutyltin diacetate, a known catalyst in urethane technology.


Comment from Dudley Primeaux, (2/20/2014, 4:49 PM)

Actually, this “concept” has been commercially practiced since about the mid 1990’s, though details were kept as a trade secret. But it does in fact work...


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