http://www.abc.net.au/science/articles/2010/07/05/2944850.htm?topic=



Plastic bags may become new energy source

Monday, 5 July 2010 Jessica Marshall
Discovery News


Why should a plastic bag languish in a landfill when it could be powering your computer.

Rather than languishing in landfills or littering roadsides, plastic bags could make their way into useful products like toner, lubricants, or rechargeable Cell Phone or laptop batteries.

Plastic recycling is limited by the fact that different types of plastic cannot be mixed. The quality of the resulting recycled plastic may also be poor. "That's why recycling is not very successful," says study author Vilas Pol of Argonne National Laboratory in Illinois.

"I was thinking why not go beyond this," he says. "Take it and degrade it. You can take the different kinds of plastics together."

In a process that is as simple as throwing bits of plastic in a chamber and heating it up, Pol can turn the plastic into tiny spheres of pure carbon just a few microns across.

These spheres, which conduct heat and electricity, could be used in a long list of applications from tyres to batteries to lubricants.

Adding the spheres to tyres, for instance, could dissipate the heat generated from friction against the road, protecting the rubber from melting.

"They are also working very well as an anode for a lithium ion rechargeable battery," says Pol. These are the types of batteries used in mobile phones and laptops, for instance.

Pol is also investigating carbon nanotubes made from plastic bags via a similar process for several applications including rechargeable batteries.

Carbon microspheres are also useful in lubricants, toner, paint and filters, he says.
Plastic gas

Rather than just melting the waste plastic and re-extruding it, Pol's process continues to heat plastic bags or other plastic waste past the point of melting. He holds the material in a sealed container that builds up pressure as the material gets hotter and hotter and becomes a gas.

At high temperatures and pressures in the chamber, the plastic decomposes into its elements. If the chamber is filled with inert gas instead of air, the hydrogen in the plastic becomes hydrogen gas, which can be collected and used as hydrogen fuel.

The carbon in the plastic forms spheres or egg-shapes depending on the type of waste plastic used in the reactor. The uniform size and shape make the spheres particularly useful for certain applications, like filtration, where packing tightly together is useful.

"Microspheres are expensive to make using the current technology," says Nishkamraj Deshpande of the United Space Alliance, a NASA contractor.

"Not only are the resulting spheres cheaper than today's sources, they take care of plastic waste," says Deshpande.

It is helpful that the potential applications for the spheres have huge markets to match the huge amount of plastic waste. "It makes sense to replace a mass level of waste with something that has a mass level of usage," he says.

Pol is receiving many inquiries about his work and is working to develop a larger scale reactor to move the process from the laboratory to something that could be commercialised.

"With this process, we don't have to invest new petroleum gases to make carbon spheres or nanotubes," he says. "It's cost effective. It is reproducible."

And, for now, it's a product made from something many people want to get rid of. "I've had three plastic companies saying, 'We will bring plastic to you,'" says Pol.