Self-healing plastic

Foto: Sam Rentmeester

Photo: Sam Rentmeester

Polymers that repair themselves after a crack has appeared. Sybrand van de Zwaag (AE) is developing ‘self-healing plastic’, which can be used for such purposes as repairing scratches in auto paint.

If you run your finger through hair gel, an opening appears in the gunk. It then becomes whole again. Self-healing polymers will work in about the same way.

Researchers in Delft are developing a method with which to influence polymers at the molecular level. ‘Suppose that a crack has appeared. It would close again, because the two halves would come back together following the application of slight pressure or a slightly higher temperature. This occurs due to reversible molecular bonds. Once these bonds have been reformed, the material would have the same conditions as before’, explains Sybrand van der Zwaag, a professor in the faculty of Aerospace Engineering and the director of the Dutch Polymer Institute and the Delft Centre for Materials.

One possible application would be in the automotive industry. An example could involve coating a car with the self-healing material. If it gets scratched or if cracks appear, it would have to be heated to 50 or 60 degrees. This could be accomplished with a blow dryer or by building in a small electronic warming mechanism. ‘But car paint also heats up on its own when it is exposed to sufficient sunlight. The coating would not melt, but the crack would close.’

The researchers are focusing their efforts primarily on creating a material that has the right mechanical properties. ‘It can’t simply repair, becoming gel-like in the process. That would make it impossible to use as a building material. It must be stiff and solid at the same time as well.’

Van der Zwaag shows a video of a PhD student and a cracked piece of polymer. She presses the two halves together and, within one minute, it becomes whole again. She then tries to pull it apart again, but does not succeed. It is a milestone in research on self-healing polymers. The process can repair cracks multiple times in the same place. ‘But we are not there yet. We are now making self-healing polymers on a small scale. We would also like to produce them on a larger scale, and we would like to make the pieces much larger.’ The research being conducted at TU Delft is part of a national programme that also includes the development of self-healing concrete, metals and composites.

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