Washington, Oct 5 : Composite plastic that’s as strong as steel, but light and transparent at the same time is now a reality.

University of Michigan researchers have mimicked a brick and mortar molecular structure found in seashells to create such a type of plastic. It is made up of layers of clay nanosheets and a water-soluble polymer that shares chemistry with white glue.

Engineering professor Nicholas Kotov has dubbed it “plastic steel,” although the new material isn't quite stretchy enough.
The researchers created this new composite plastic with a machine they developed that builds materials one nanoscale layer after another.

The robotic machine consists of an arm that hovers over a wheel of vials of different liquids. In this case, the arm held a piece of glass about the size of a stick of gum on which it built the new material.

The arm dipped the glass into the glue-like polymer solution and then into a liquid that was a dispersion of clay nanosheets. After the layers dried, the process was repeated. It took 300 layers of each the glue-like polymer and the clay nanosheets to create a piece of material as thick as a piece of plastic wrap.

Prof. Kotov described the process as somewhat similar to pearl growth in mussel and oyster shells.

He said the glue-like polymer used in this experiment, which is polyvinyl alcohol, was as important as the layer-by-layer assembly process. The structure of the “nanoglue” and the clay nanosheets allowed the layers to form cooperative hydrogen bonds, which gave rise to “the Velcro effect”.

Such bonds, if broken, can reform easily in a new place. The Velcro effect is one reason the material is so strong. Another is the arrangement of the nanosheets. They're stacked like bricks, in an alternating pattern, said Prof. Kotov.

“When you have a brick-and-mortar structure, any cracks are blunted by each interface. It's hard to replicate with nanoscale building blocks on a large scale, but that's what we've achieved,” he said.

Prof. Kotov said further development could lead to lighter, stronger armour for soldiers, police and their vehicles. It could also be used in unmanned aircraft, microelectromechanical devices, microfluidics, and biomedical sensors and valves, he said.

Prof. Kotov and the U-M research team report their study in the Oct 5 issue of Science. (ANI)