A Plastic for Ecologists

The trouble with modern plastics is that they seem to be as immortal as they are useful. Plastic garbage bags litter Italy; Florida's discarded containers clog Bahama beaches. Each year one Kansas plant makes enough cellophane to wrap the earth with a 15-inch band 40 times; most of it becomes enduring garbage. Even getting rid of plastics can be dangerous. When polyvinyls like Saran Wrap are burned, they produce corrosive hydrochloric acid.

The obvious need, a plastic that decomposes naturally, may soon become a reality. An international team of scientists, led by University of Toronto Chemist James E. Guillet, has designed a plastic that Guillet claims will self-destruct when exposed to sunlight, but will remain intact if it is kept indoors.

Time Clock. Plastics contain tough carbon chains that are often 10.000 times longer than those found in ordinary molecules. Some scientists estimate that it may take a million years before microorganisms capable of attacking the man-made material can be produced in nature. Rather than wait, some chemists have infused plastics with chemical "time clocks": automatic decomposers. But there was no way of controlling the rate of decomposition, say weeks for cups, and years for auto taillights. Nor did manufacturers want a plastic that could disintegrate on the shelf or in a customer's hands.

Guillet's team got around such problems by finding a way to chemically bond groups of "sensitized" molecules directly into the plastic's carbon chain. When these "S" groups absorb ultraviolet light from direct sunlight, he says, their carbon "backbones" soon begin to be decomposed by microorganisms. But indoors--even in front of glass windows--they will not be affected. Guillet claims that the speed of the breakdown can be controlled by varying the number of "S" groups bonded into the plastic molecules. He also thinks that the process would raise the price of plastics by only a few cents per pound.

"I see first uses," says Guillet, "in wrappings and containers that get left behind outside, or are thrown overboard." The new plastics can also be used as a covering for some crops. Once ripped by weather, the film would be broken into even smaller particles by microorganisms--and so could be plowed back into the earth as fertilizer.

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