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Tuesday, May 27, 2008

Dry Cleaning

Dry cleaning is any cleaning process for clothing and textiles using an organic solvent rather than water. The solvent used is typically tetrachloroethylene (perchloroethylene), abbreviated "perc" in the industry and "dry-cleaning fluid" by the public. Dry cleaning is necessary for cleaning items which would otherwise be damaged by water and soap or detergent. It may be used if hand washing— needed for some delicate fabrics — is excessively laborious.

Dry cleaning uses non-water-based solvents to remove soil and stains from clothes. The potential for using petroleum based solvents in this manner was discovered in the mid-19th century by French dye-works owner Jean Baptiste Jolly, who noticed that his tablecloth became cleaner after his maid spilled kerosene on it, and developed a service cleaning people's clothes in this manner, which he termed "nettoyage à sec," or "dry cleaning" in English.[1]
Early dry cleaners used petroleum-based solvents, such as gasoline and kerosene. Flammability concerns led William Joseph "Dixie" Stoddard, a dry cleaner from Atlanta, to develop Stoddard solvent as a slightly less flammable alternative to gasoline-based solvents. The use of highly flammable petroleum solvents caused many fires and explosions, resulting in government regulation of dry cleaners.
After World War I, dry cleaners began using chlorinated solvents. These solvents were much less flammable than petroleum solvents and had improved cleaning power. By the mid-1930s the dry cleaning industry had adopted tetrachloroethylene (perchloroethylene), colloquially called "perc," as the ideal solvent. It is stable, nonflammable, and has excellent cleaning power, and is gentle to most garments. However, perc was also the first chemical to be classified as a carcinogen by the Consumer Product Safety Commission (a classification later withdrawn). In 1993 the California Air Resources Board (CARB) adopted an airborne toxic control measure (ATCM) to reduce perc emissions from dry cleaning operations. The dry cleaning industry is now beginning to replace perc with other chemicals and/or methods.

Perchloroethylene — In use since the 1940s, perc is the most common solvent, the "standard" for cleaning performance, and most aggressive cleaner. It can cause color bleeding/loss, especially at higher temperatures, and may destroy special trims, buttons, and beads on some garments. Better for oil-based stains (which account for about 10% of stains) than more common water-soluble stains (coffee, wine, blood, etc). Known for leaving a characteristic chemical smell on garments. Nonflammable.
Hydrocarbon — This is most like standard dry cleaning, but the processes use hydrocarbon solvents such as Exxon-Mobil’s DF-2000 or Chevron Phillips' EcoSolv. These petroleum-based solvents are less aggressive than perc and require a longer cleaning cycle. While flammable, these solvents do not present a high risk of fire or explosion when used properly. Hydrocarbon also contains volatile organic compounds (VOCs) that contribute to smog.[3]
Liquid silicone(decamethylcyclopentasiloxane or D5) — gentler on garments than Perc and does not cause color loss. Requires a license be obtained to utilize the property of GreenEarth Cleaning. Degrades within days in the environment to silica and trace amounts of water and CO2. Produces nontoxic, nonhazardous waste. Toxicity tests by Dow Corning shows the solvent to increase the incidence of tumors in female rats (no effects were seen in male rats), but further research concluded that the effects observed in rats were not relevant to humans because the biological pathway that results in tumor formation is unique to rats.[7](170.6 °F/77 °C flash point)
Liquid CO2Consumer Reports rated this method superior to conventional methods, but the Drycleaning and Laundry Institute commented on its "fairly low cleaning ability" in a 2007 report.[8] Machinery is expensive--up to $90,000 more than a perc machine, making affordability difficult for small businesses. Most cleaners with these machines keep traditional machines on-site for the heavier soiled textiles. CO2 cleaning is also used for fire- and water-damage restoration due to its effectiveness in removing toxic residues, soot and associated odors of fire.
Modified hydrocarbon blends (Pure Dry)
Glycol ethers (dipropylene glycol tertiary-butyl ether) (Rynex) — not as effective as perchloroethylene.
Wet cleaning — Not a solvent, but a system that uses water and biodegradable soap. Computer-controlled dryers and stretching machines ensure that the fabric retains its natural size and shape. Wet cleaning is claimed to clean a majority of "dry clean only" garments safely, including leather, suede, most tailored woolens, silk and rayon. (Neckties seem to be the one exception.) Most perc cleaners use wet cleaning on some garments, but there are only about 20 exclusive wetcleaners in the U.S.

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