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A New Spin on Dry-Cleaning


Dry-cleaning is one of the great misnomers of modern life.

It isn't a dry process: Liquid solvents such as perchloroethylene and petroleum are used as substitutes for water. Nor is it clean, as far as the environment is concerned: The Environmental Protection Agency identifies "perc" as a cancer-causing agent, and the petroleum used to scrub threads releases smog-producing compounds and is flammable at high temperatures.

Now dry-cleaners are poised to wash their hands of perc, petroleum and other harmful chemicals in favor of a new process that relies on a clean, reusable solvent: liquid carbon dioxide. For the nation's 30,000 dry-cleaning shops, their landlords and many of their customers, the new technology promises nothing less than a revolution.

"Carbon dioxide is a benign, inert, inexhaustible resource," said Jack Alquist, who owns three dry-cleaning stores in Northern California and is chairman of the International Fabricare Institute, the industry's major trade group. "If the process does what the scientific papers say it will, it should be gentler to fabrics and have better cleaning capabilities."

Liquid carbon dioxide has long been seen as a promising alternative to current dry-cleaning solvents. But scientists were stumped on how to design a detergent that would clean effectively in a liquid CO2 solution.

Researchers at Hughes Environmental Systems in El Segundo and at the University of North Carolina at Chapel Hill independently--and quite accidentally--hit upon key methods that make dry-cleaning with liquid carbon dioxide feasible. Those innovations have spawned a pair of companies that are commercializing the technology and plan to make it available to consumers as early as the first quarter of next year.

Dry-cleaners typically wash wool, silk and other garments that can be damaged by water. The clothes are submerged in perc or petroleum and mixed with specially formulated detergents that pull dirt particles away from cloth. Then the clothes must be heated at high temperatures so the solvents will evaporate and the clothes will dry. The dirt particles are disposed of with the used solvent.

Washing with liquid carbon dioxide is a quicker and cleaner process. The CO2, which is a gas at room temperature, must be liquefied in high-pressure storage containers and washing machines. Liquefied CO2 is commonly delivered to restaurants and used to carbonate soda, and dry-cleaners would be able to buy it from the same sources.

The key discovery came when chemists created a detergent that, when added to liquid carbon dioxide, breaks up into spheres called micelles that attract CO2 on the outside and water on the inside. Dirt and stains that are water-soluble--such as grass stains--are drawn away from clothes and into the micelles. The detergent itself does not adhere to the clothing.

When the clothes are removed from the high-pressure washer, the carbon dioxide reverts to its gaseous state; it can be captured and reconverted into liquid for use in another cycle. The garments dry as soon as the liquid evaporates from the cloth. The dirt particles trapped in the micelles don't evaporate, and they are easily collected as a residue for disposal.

At Hughes, chemists had been looking for an environmentally friendly solvent to clean metals, circuit boards and other aerospace electronics hardware. In 1990, they commercialized a cleaning method that uses supercritical carbon dioxide, which is still a gas but has the density of a fluid because of its high pressure. Four years later, they adapted the process for dry-cleaning.

"We said, since this can remove organics and dirt from hardware, we can't see any reason why it can't work for clothing," said Sid Chao, president of Hughes Environmental Systems.

The Hughes system uses liquid CO2 and special washing machines that move clothes around with jets instead of moving parts, which make it more difficult to maintain high pressure inside the machine, Chao said.

Meanwhile, chemists at the University of North Carolina were studying ways of manufacturing plastics without using organic solvents that pollute the air, such as chlorofluorocarbons, or CFCs. By 1992, they had made some kinds of plastics with carbon dioxide instead of CFCs.

Joseph DeSimone, a chemistry professor at UNC, realized that the method could also be used to make detergents for use with liquid carbon dioxide, and it took his group a few more years to figure out exactly how to do it.

Last year, DeSimone raised $5 million in venture capital and started Micell Technologies to commercialize the technology. The Raleigh, N.C., firm will sell the MiCare Garment Cleaning Fluid System--which includes liquid carbon dioxide, machines manufactured by American Dryer Corp., detergent and technical support--starting early next year. Micell Technologies President Brad Lienhart expects to have 100 customers by the end of 1998 and 500 by the end of 1999.

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