Bean bag

BIODEGRADABLE plastic bags made from soya beans would be Food for the environment. They don't take up landfill space, and because they degrade quickly they are less likely to strangle or suffocate wild animals that encounter them. There Is only one problem: the plastic bags are so biodegradable that they almost dissolve in the rain

But Joshua Otaigbe, a materials scientist at Iowa State University in Ames, has found that mixing the soya-bean protein with polyphosphate fillers and silane produces a more durable and Waterresistant plastic.

"The polyphosphate fillers increase the stiffness and strength of soya-protein plastic," he says. "They are also able to reduce the water absorbency." The silane retards water absorbency as well, and helps the polyphosphate to bind with the soya-protein plastic.

In laboratory tests, the modified plastics have survived more than a year underwater. The unmodified plastic dissolved in a few hours.

Otaigbe is now testing the soya-based plastics in soil to see how well they degrade. He expects the materials to be useful in a variety of roles, from food packaging to medical sutures. They may even turn up on the golf course as tees. "After you finish your round of golf you can throw them away to biodegrade in the environment," he says.

The plastics will be relatively cheap, Otaigbe says, because soya beans are a renewable resource. The crop is grown extensively in Iowa and neighbouring states in the Midwest. Harvey Black