Researchers Develop Plastic as Strong as Steel

Researchers at the University of Michigan have devised a way to bond nanosheets and create a composite plastic that is as durable as steel. The researchers copied the molecular structure of the inner lining of oyster and mussel shells called Mother of Pearl which contributed to the strength of the composite plastic. The new plastic material is made up of layers of clay nanosheets and polyvinyl alcohol that has the same chemistry as white glue, though not quite as stretchable so researchers had to scrap the name "plastic steel" for their composite plastic.

Nicholas Kotov, an engineering professor at the University of Michigan and other researchers were able to make the composite plastic by hurdling a problem that has confused engineers and scientists for decades: how to bond nano-size building blocks. Nano-size building blocks such as nanotubes, nanosheets and nanorods are very strong by themselves, however, when a larger product is made out of these nano-sized building blocks, they become weaker.

Kotov says that when scientist tried to build something out of the nano-sized blocks that they can hold, they have difficulties in transferring the strength of each individual nanosheets to the entire material. The researchers however, were able to achieve an ideal transfer of stress between nanosheets and a polymer matrix using a machine that they have developed that can build materials one nanoscale layer after another.

The researchers' machine was able to build the composite plastic using its robotic arms that hold a piece of glass where it builds the new material. The robot's arm dips the glass into the glue-like polymer solution and into a liquid that was a dispersion of clay nanosheets and then the layers are dried; the process is repeated until about 300 layers are made. The 300 layers of glue-like polymer and clay nanosheets are used to create the material as thick as a piece of plastic wrap. The glue-like polymer substance and the clay nanosheets created a cooperative hydrogen bond which if broken, can reform easily in a new place. Kotov calls this bond, "the Velcro effect." The Velcro effect contributes to why the plastic material is so strong and so did the arrangement of the nanosheets which the researchers patterned after the brick and mortar molecular structure found in seashells. The lining of the seashells is one of the toughest natural mineral-based materials. Kotov explained that the brick and mortar structure blunts any cracks.

Kotov said that with further development, the plastic could be used to develop stronger and lighter armors to be used by the military.

SOURCE:

University of Michigan