SO-CALLED ``biodegradable'' plastic got a bad rap in the late 1980s because the label was misleading at best. Some critics called it a snare and a delusion. Since then, scientists have found, and manufacturers are now making, new plastics that truly do biodegrade - break down into carbon and water in a short period of time. Already, a shampoo bottle in Germany completely degrades in as little time as six weeks after it is discarded, given ideal conditions. The plastic coating on paper cups used in one fast-food chain in Michigan begins to degrade about eight hours after they are used.
One new plastic, called polycaprolactone (PCL), is one of only a few petroleum-based plastics that are completely biodegradable. In tests, ``A piece of PCL, about as thick as a trash bag, was buried in garden soil in September. Within one month, it lost virtually all of its strength. Within three months, there was no evidence of the film,'' according to Joseph Rocky, marketing manager of Union Carbide, which makes the plastic. It is being used for shoe components, diaper backsheets, and other products that traditionally are made of the non-biodegradable plastic polyethylene.
In Canada, scientists at the National Research Council are using PCL to make polystyrene and polyethylene biodegradable. According to researcher Lin-Lin Zhou, ``We introduce a PCL unit into the backbone - the carbon components - of ethylene or styrene to form a new, biodegradable copolymer.'' The process Dr. Zhou uses is not simply a mixture of the two polymers. Instead, he actually changes the molecular structure of the plastic.
``When PCL made up 10 percent of the polyethylene, 20 percent of the material degraded within one month in a compost pile,'' Zhou says. This doesn't mean that the entire piece of plastic will degrade in five months, however. The PCL component of the copolymer degrades first because it has a lower molecular weight than the ethylene portion of the molecule. ``But,'' Zhou says, ``because we have introduced PCL, the entire molecule will degrade into carbon dioxide and water.''
In Japan, researchers have taken a different approach. They have blended PCL with starch, like adding eggs to flour to make a cake, to produce a strong, degradable material they have used to make plates.
Other scientists, in industry and in universities, are perfecting a ``natural'' plastic that is actually made by microbes. Known as PHA, it is a broad family of esters called polyhydroxyalkanoates. At thicknesses of one millimeter - about as thick as a plastic trash bag - sheets of PHA degrade in six weeks when they are placed in sewage that is exposed to air. In soil or sewage that was not exposed to air, PHA broke down within 75 weeks into water and carbon, according to reports from researchers R.C. Fuller and Robert W. Lenz at the University of Massachusetts at Amherst.
Microbes make and use this plastic themselves, ``much the same way bears store fat for winter,'' Dr. Fuller says. Generally, the microbes live on organic waste. When that food becomes scarce, they produce PHA within their cells and store it as granules. They can store up to about 95 percent of their weight, and digest it as needed.
To produce PHA or the similar plastic PHB commercially, any of dozens of species of microbes are fed, starved, and then gorged on whey or molasses. According to Fuller, it also is possible to feed the microbes with PHA that has been formed into products and discarded. The PHA can be removed by heating the microbes until they split open.
The Wella Corporation is beginning to use bottles made from PHA for one of its shampoos. Other possible uses include diapers, containers for fertilizers, implantable drug delivery systems, and wound dressings.
THE starch-based plastics that started much of the controversy also have improved dramatically since they were introduced. They have evolved from mixtures containing 6 percent starch to mixtures that are up to 95 percent starch. This means that up to 95 percent of the item will degrade. Although polymer chains remain, they are significantly fewer in number.
The Warner Lambert Company expects to market a plastic by 1992 that is 85 to 95 percent starch, according to E. Peter Wolf, media relations manager. Called Novon, the plastic is made from corn, potato, and rice starch and can be injected or extruded as are plastics used today. ``We're studying it to determine how long it takes to break down and what it breaks down into. Currently, it seems to degrade at the same rate as paper,'' Mr. Wolf says.
``Eventually, everything degrades,'' according to Ramani Narayan, at Michigan Biotechnology Institute. Normally, an item is considered biodegradable when it is metabolized by microbes into carbon and water.
One of the problems with biodegradable plastics is that the term has been used loosely. That usage is expected to tighten in January when the American Society for Testing and Materials releases the first of its standards for biodegradable plastics. Dr. Narayan, who chairs the society's biodegradable plastics committee, says that those new standards will define the term ``biodegradable'' for American industry and will identify tests to determine if a product is truly biodegradable. When released, these standards also will have been approved by the United States Environmental Protection Agency, the Federal Trade Commission, and the National Association of Attorneys General.
Once industry adheres to these standards, the challenge will be to adapt waste-disposal practices to take advantage of the biodegradability of these plastics. Until then, ``Degradation is a moot point,'' according to Bailey Condrey Jr. at the Committee for Solid Waste Solutions, a program of the Society of the Plastics Industry. ``Whatever is buried in a landfill is essentially put in a mummification chamber. Unless [organic] waste is going to a compost, biodegradable plastic won't do anything to reduce the waste.''
Composting of yard waste have long been effective for decomposing food and yard waste, and has been mandated in Iowa, Wisconsin, Michigan, and other states. Research under way at several US sites indicates it may be effective for plastics, too. According to Anthony Pometto III of Iowa State University, ``Lab studies showed that plastics containing 6 percent starch lost up to 60 percent of their molecular weight in four weeks when they were exposed to the bacteria, temperatures, and moisture they would encounter in compost piles.'' He is conducting studies at three municipal composts to determine what actually happens and expects results in about one year.
These advances seem to make little impression on environmental groups, however. According to Greenpeace, biodegradable plastics are `` ... designed to cash in on the American public's desire for environmental improvement.''
Jeanne Wirka, policy analyst for the Environmental Action Foundation, says, ``Biodegradable plastics are so expensive to produce they're not used for commodities. They're almost not worth talking about. The reason plastics are used is that they're cheap, so these are not a replacement for hydrocarbons.''
As an example of those costs, ICI Ltd., which manufactures PHB under the name Biopol, says the product currently costs about $15 per pound, compared with about 50 cents per pound for polyurethane, and about $1.10 per pound for PET - the plastic used for soft drink bottles. That cost is expected to drop to $2 to $3 per pound when ICI goes into larger scale production in about three years.
But even if price were not an issue, ``One of the difficulties with promoting biodegradable plastics is that it promotes a degradable ethic that runs counter to the conservation ethic,'' Ms. Wirka says. ``That's one of our major critiques. Without knowing the environmental impact of producing and then throwing away bottles, we still favor reusable materials.''
Sam Hartwell, a solid-waste specialist for the National Resources Defense Council, is more positive. ``It's encouraging to see research in this area, but it's too early to judge the effectiveness. What's really relevant is not what happens in the lab, but how these plastics perform in conditions where biodegradation is likely to happen - along roadsides, in landfills, and in compost piles. If they compete with recycling, biodegradable plastics are a step in the wrong direction. If they are used for common litter, like diaper liners, plastic plates, and cups, they could be a positive thing.''
There are no simple solutions to this issue, but Narayan and other scientists consider biodegradable plastics to be one part of a solution, coupled with recycling and waste reduction.