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Photo courtesy of Bradley at www.ecosalon.com

Perchloroethyene VS. Carbon Dioxide

Eco-Friendly Dry Cleaning
Evan Morgan
eka5@unh.edu
University of New Hampshire at Manchester



In a world quickly becoming more aware of the human environmental impact on our planet, virtually all commercial processes have been revisited in search of a greener method. Through this project, details about an environmentally friendly dry cleaning technique will come to light. The business predates the twentieth century when the main cleaning solvents included terpentine, camphor oils, and other volatile liquids like kerosene and even gasoline (State Coalition, 2007). Carbon tetrachloride was exported from Germany and sold as a spot-removing agent in the late nineteenth century and has remained the most popular reagent used in the dry cleaning business to this day.
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Photo courtesy of ClipArt

However, over the last twenty years researchers have identified carbon tetrachloride, more commonly known as perchloroethylene (or PERC), as a carcinogenous and harmful to the human body as well as the environment. A new method for application in a dry cleaning setting was founded by Professor Joseph DeSimone, who was awarded the Presidential Green Chemistry Award in 1997 involving supercritical Carbon Dioxide as the replacement for perchloroethylene (Chemistry for Changing Times). Since then, due to resultant reports on the detriments to PERC, the industry has slowly turned toward this greener alternative.





What exactly is dry cleaning?
Not particularly important in the grand scheme of chemistry, but to place it all in perspective, a background is important. First of all, dry cleaning isn't the type of dry the average person would understand. The specific reason it is so-named is because the process is absent of water, using a a chemical solvent instead without the aid of water. Using water leads to changes in the size of the fibers within the cloth, which can cause wrinkles and shrinking. Dry cleaning avoids these effects by using a nonpolar solvent that does not attach (wets), the cloth fibers. In regard to the removal of stains, the intermolecular rule or "like dissolves like" has a role to play. The nonpolar solvent, whether it is perchloroethylene or carbon dioxide requires the aid of detergents to remove polar stains. Detergents are long, tad-pole shaped molecules with a polar "head" and a non-polar "tail" which allow them to be both water and oil soluble (Greasy Stains, 2010). Dry cleaning has the added advantage that it can remove stains at lower temperatures than water, avoiding damage to the fabric that heat may produce.


When clothes are dropped off at the dry cleaner they go through a series of steps
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Photo created by Evan Morgan


Inspection - Identification is completed using small tags or labels to identify clothes so they don't get mixed up with others. Clothes are also examined for missing buttons, tears, etc. that the dry cleaner might get blamed for otherwise.
Pre-treatment - The cleaner searches for stains and treats them to make removal easier during the cycle phase.
Dry cleaning - The clothes are put in a machine and cleaned with a solvent.
Post-treatment- Any remaining stains are identified and removed.
Wrap-up - This includes pressing, folding, and packaging the clothing

For the purpose of this project we are focusing on step 3 when the clothes are cleaned with a solvent, most commonly PERC.

So when gasoline and other petroleum based solvents were being used in the dry cleaning industry, it was effective and did the job. But, obviously they are volatile liquids that risk explosion, not to mention dizziness and neurological problems if overexposed. So it's logical that when perchloroethylene came along it was considered revolutionary as it was not only safer, but also did a better job of restoring the clothes. The improvement of the business led to a massive propagation of dry cleaning stores and has been successful using PERC to this day.



Effects of Perchloroethylene exposure
In the last twenty years, however, research has found PERC to be a health hazard to humans. People exposed to high levels of PERC, regardless of length of time, may experience serious symptoms. including headaches, fatigue, nausea, as well as skin, lung, eye and mucous membrane irritation (Technology Transfer Network Air Toxics, 2007). Repeated exposure to high levels has also been found to cause liver damage and respiratory failure. Furthermore, studies in laboratory animals indicate that exposures to high levels of perc can produce effects on the developing fetus that include altered growth, birth defects, and death (Technology Transfer Network Air Toxics, 2007). Results from epidemiological studies of dry-cleaners workers exposed to tetrachloroethylene indicates increased risks for numerous types of cancer (Technology Transfer Network Air Toxics, 2007).

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Chemical Structure of Perchloroethylene (PERC). Created by Evan Morgan



Environmental effects
The enviromnent suffers as well, in the atmosphere, soil, and water. Most of the perc used by the dry cleaning industry escapes into the atmosphere by way of windows and vents. After a few weeks, the compound breaks down into other chemicals, some of which are toxic and some of which are suspected to deplete the ozone layer (Manning, 2006). Perchloroethylene is toxic to plants and can infiltrate the soil through spills by means of leaky pipes or machines and improperly handled waste (Manning, 2006). If burned, it may create even more severe problems as the "incineration of perc waste leads to the formation of dioxin, a potent carcinogen in humans" (Greenpeace, 2003).
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Created by Evan Morgan

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Perchloroethylene metal drum. Photo courtesy of gnuttibortolo.com

Water may be the most harmful medium for which pollution is created from perchloroethylene. When the dry cleaning process is finished, the cleaning fluid is isolated from the wastewater. Initially this waste was immediately poured into the floor drain but regulations have now required that the fluid is collected and removed by hazardous waste handlers, at least what hasn't already evaporated (Manning, 2006). Perc does not bind well with soil so it leads towards other liquids, potentially contaminating surface and groundwater. Even trace amounts of the compound can contaminate a larger body of water, leading to exposure by drinking or using the water (Manning, 2006).

Estimates from the environmental group, Greenpeace, state that "seventy percent of all of perc used ends up in the environment where it extensively contaminates both ground- and drinking water. At least 1.2 million Americans are exposed to perc in drinking water at levels that exceed safety limits" (Greenpeace, 2003).






This data is sufficient evidence to implement an alternative on a large scale. The answer has been proposed and it is in the form of liquid carbon dioxide.

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Works Cited
A Chronology of Historical Developments in Dry Cleaning.State Coaliton for Remediation of Dry Cleaning. November 2007. 28 November 2010.<http://www.drycleancoalition.org/download/drycleaning-historical_developments.pdf>
Chemistry for Changing Times. Hill, J.W; Kolb, D. K. Pearson/Prentice Hall. 2007; pp. 546-547.
Greasy Stains. Chemistry in your Cupboard!. Accessed December 6 2010. <http://www.chemistryinyourcupboard.org/vanish/9>
Greenpeace. 2003. "What's in, What's Out - A Rating of Dry Cleaning Methods Currently In Use in the U.S." December 03 2010.
Manning, Jennifer. Looking Good, Feeling Bad; or, What's the Problem with Perc (Percholorethylene). 07 March 2006. 04 December 2010. <http://environmentalchemistry.com/yogi/environmental/200603percholorethylene-pt2.html>
Tetrachloroethylene (Perchloroethylene). Technology Transfer Network Air Toxics Web Site. 06 November 2007. 04 December 2010. <http://epa.gov/ttn/atw/hlthef/tet-ethy.html>