Biodegradable plastic as strong as steel

A transparent plastic as strong as steel and as thin as a sheet of paper has been developed, according to a study published on Friday in Science magazine.

Made out of clay and non-toxic glue similar to that used in school classrooms, the composite plastic is biodegradable and requires very little energy to produce, according to lead researcher Nicholas Kotov.

"It's as green as you can imagine," he said, also mentioning the material is quite cheap to produce.

The plastic could be used to reduce the energy required to separate gases in chemical factories, improve microtechnology such as microchips or biomedical sensors and could soon produce lighter, stronger armour plating for the military.

Development has begun for practical applications for the composite plastic, which could become commercialised within a year or two.

"We're still at the exploratory stage but the machine is now being built in our lab to build pieces as big as one metre by one metre," he said.

Producing a composite material out of nano-sized building blocks that can maintain its strength at such large sizes has long confounded scientists.

Kotov managed to do it by mimicking the brick-and-mortar molecular structure found in seashells.

His engineering team at the University of Michigan built a robot which stacks the nanosheets like bricks in an alternating pattern and uses a glue-like polymer to create cooperative hydrogen bonds between the layers that can easily reform in another place if the bond is broken.

It takes a few hours to build up the 300 layers needed to make a thin sheet of the plastic as the robot's arm dips in an out of vials of glue and a dispersion of clay nanosheets.

"When you have a brick-and-mortar structure, any cracks are blunted by each interface," Kotov said. "We've demonstrated that one can achieve almost ideal transfer of stress between nanosheets and a polymer matrix."