Edition: U.S. / Global

Technology; Rethinking Plastics From the Ground Up

Published: September 11, 1994

FROM diapers to fast-food packaging, plastics have long been reviled by the environmentally conscious for their propensity to sit in landfills for decades without breaking down.

Yet some say the pollutants and waste created in the process of manufacturing plastics pose a greater environmental threat than what happens to them after they have been discarded.

The United States plastics industry generated 567 million pounds of toxic waste in 1992, according to the Environmental Protection Agency, which began recording the levels of industry waste in 1991. About one-quarter of the plastic industry's 1992 waste was released directly into the nation's land, air and water.

Now Joseph DeSimone -- an associate professor at the University of North Carolina in Chapel Hill who at 30 is a Wunderkind of chemical engineering -- has come up with an environmentally friendly way to make the polymers that are formed into plastics by using a form of carbon dioxide, the benign gas found in carbonated beverages ranging from beer to champagne.

The process, Professor DeSimone says, holds great potential for lessening the environmental burden, but perhaps just as important is the promise it offers for creating new materials "whose use we haven't yet imagined."

Professor DeSimone, who published a paper on the new process this summer in the journal Science, presented his research last month at the American Chemical Society's national meeting in Washington.

The work already has generated a lot of interest in the chemical industry. So far, four companies -- Du Pont, Hoechst Celanese, Air Products and Chemicals, and Eastman Chemical -- are participating in a consortium that is financing further research in Professor DeSimone's laboratory. Several other companies are expected to sign on to the consortium soon. In exchange for underwriting the research, the companies retain the option to license different aspects of the technology, which received its first patent in May.

For Professor DeSimone, success has come early. He received his doctorate only four years ago at Virginia Polytechnic Institute and State University in Blacksburg, and last year he was among 15 American scientists whom the White House named Presidential Faculty Fellows.

To continue his work with so-called supercritical carbon dioxide -- a pressurized form of the gas that has some unusual liquid-like properties -- this year Professor DeSimone received one of the first grants to be given out under the Environmentally Benign Chemical Synthesis and Processing program, a new effort jointly administered by the National Science Foundation, the main Federal financing agency for basic science research, and the E.P.A.

The first supercritical fluid was concocted more than 100 years ago, but supercritical fluids did not command attention until the 1970's, when they were widely touted as a way to reduce energy consumption by replacing chemical solvents, most of which are petroleum-based and take enormous amounts of energy to distill.

The unique properties of supercritical fluids can make them ideal solvents. By changing the amount of pressure or the temperature, a chemist can adjust the fluid's density -- that is, how closely its molecules are packed together -- and therefore how well it might dissolve a given substance. By contrast, the density of the liquid is fixed and cannot be manipulated.

Although the food industry has made use of supercritical carbon dioxide to decaffeinate coffee, purify spices and extract oils from hops to make beer, the supercritical bandwagon lost momentum by the early 1980's. By then the energy crisis had receded from memory and it had become abundantly clear that, given the expensive equipment needed to pressurize supercritical fluids, petroleum-based solvents were still the cheapest way to go.

BUT in the last couple of years, supercritical fluids, in particular carbon dioxide, have been resurrected, this time not as energy savers but as environmental saviors in an era when industry generally faces increased regulatory scrutiny on the production of hazardous byproducts.

"Supercritical carbon dioxide is an exciting area because it's nonpolluting," said Margaret A. Cavanaugh, a program director in the division of chemistry at the National Science Foundation. "If you can find a way for it to be used in a lot of chemical processes, it would be a major reduction in the use of petroleum solvents."

Currently, huge quantities of chemical solvents are used by the pharmaceutical, chemical and polymer industries to extract, separate and manufacture chemicals and to carry out or ease reactions.

In one example of the way supercritical carbon dioxide can be used in place of chemical solvents, Union Carbide now uses it as a thinner for industrial spray-painting. As a result, the company has reduced hazardous emissions associated with that process by as much as 80 percent.

Professor DeSimone, however, is pursuing what some consider a more difficult end: using supercritical carbon dioxide not just to dilute or extract, but to effect entirely new chemical reactions.