The Chemistry Behind Dry Cleaning

“[Dry cleaning] cleans all sorts of....fabrics...in such a manner that nobody would ever think they had been wetted...it neither changes nor alters color, but it takes the dirt, oil, and grease out of silks, cotton, and wool assisted by labor.”

History And an Overview

In “Dry Cleaning, Part 1. The Process and History: From Starch to Finish,” author Eugene Garfield noted the early history of dry cleaning. It has been studied that the Mycenaean civilization, which was in existence from 1600 - 1100 B.C., employed a basic dry cleaning process. An Oxford Classicist by the name of C.M. Bowra had demonstrated that the profession known as “dry cleaner” could be found in the clay tablets of the civilization. (Garfield, 218) Thus, Garfield says, this early Greek civilization may have used grease-absorbent materials as solvents to remove dirt from garments. Now, to this day, dry cleaning is done with solvents that are not necessarily “dry” in the sense that one usually understands it, as in “a dry desert,” but rather, solvents are dry in that they do not need water to be effective. In other words, these solvents used today are non-aqueous.

In Drycleaning: Technology and Theory, authors Martin and Fulton define dry cleaning as “the cleansing of textiles in an organic solvent.” (Martin and Fulton, 1) The authors note that the process birthed in the middle of the 19th century in Paris, France, when camphene, an oil used for lamps, was spilled onto a gown accidentally. Consequently, the gown seemed cleaner. Now, the fact that the process originated in France gives rise to the process being referred to as “French cleaning. Other sources, however, describe the legend differently. Jean-Baptiste Jolly was the Frenchman who accidentally discovered, in the mid-19th century, that camphene made a garment cleaner. And it was not a gown that the oil was spilled on; he actually spilled the oil onto a table cloth. Perhaps the origin of dry cleaning is legend after all, because it seems that no one source can agree to the exact details of what happened. It makes one wonder how many inventions were the result of accident and not careful planning!

Now, Garfield continued his article by mentioning the process that pre-dry cleaning industry workers used to clean garments. It seems that workers had to dismantle garments and clean them in hot water, a process that was very time consuming and costly. Remember that garments were not always cleaned often in those days. Indeed, the birth of the dry-cleaning industry abolished the dismantling process and the expensive costs. The “modern” process itself, again, involves solvents that are used as cleaning substances which remove stains one would find difficult to remove with water alone. The immediate advantages of using solvents with the absence of water is that they do not cause wrinkling, shrinkage, piling, or other consequences one sees when cleaning clothes with water. Martin and Fulton note that dry cleaning's greatest advantage concerns the final step of the process, namely pressing, which often proves difficult when one uses water to wash garments.

The popularity of other solvents grew following the discovery of the efficacy of camphene; benzene, benzol, and turpentine were three such solvents among many. In the United States, in the early 20th century, gasoline was the most widely used solvent in dry cleaning. Its nature as a fire hazard was obviously a concern, and thus another solvent was quickly found as a substitute. Indeed, Congress passed what is known as a “Standard” in 1928, which promoted the use of a “solvent from petroleum with a minimum flash point (i.e., flammability) of 100Ð'oF.” (Martin and Fulton, 2) This standard, though revised over the years (the flash point has risen to 140Ð'oF), has given rise to one of the most popular solvents used today, Stoddard solvent. Another kind of popular solvent used today include chlorinated hydrocarbons, the main advantage of which is that they are nonflammable.

What are some other solvents that have been used over the years? Carbon tetrachloride, CCl4, which was also discovered to be nonflammable, had been in use as early as 1897, though it has its several disadvantages: it is a health hazard, a carcinogen, to those in contact with it and it corrodes machinery. It had other uses, however, as a refrigerant and in fire extinguishers. Its use had since been deemphasized with the Montreal Protocol of 1995. Trichloroethylene, C2HCl3, was used in Europe as early as 1918 before its introduction to the U.S. In 1930. While nonflammable like CCl4, it too was a health hazard, capable of affecting the central nervous system, the symptoms of which can be likened to drunkenness. As far as it being a solvent is concerned, Martin and Fulton note that it had one major disadvantage, in that “it clauses bleeding of some acetate dyes, especially when it became warmer than 75Ð'oF.” (Martin and Fulton, 3) Nevertheless, it too had other uses, as it could extract oils from vegetables, could be used as a degreaser, and could decaffeinate coffee. One other known solvent was tetrachloroethylene, the introduction of which was in 1934. It is perhaps known better as perchloroethylene, or C2Cl4. It was found to be less of a health hazard and did not bleed dyes as the two former solvents, while keeping its nonflammable nature. Furthermore, of all the solvents mentioned thus far, Stoddard solvent and perchloroethylene (henceforth will be shortened as “perc”), have emerged as the two most popular solvents in the United States today.

Now, as befitting of its cost-effective nature, the solvents that are used in dry cleaning are not discarded; rather, as Martin and Fulton puts it, they are “reclaimed.” The process of reclamation has evolved, from simply allowing the insoluble soils to settle, to using centrifuges, to using filters. One should remember, however, that these dry cleaning fluids in of themselves are meant to dissolve soils that are oily or greasy, and thus they are known as solvents. Oils and greases, because they are soluble in the dry cleaning fluids, are by nature not removed by filtration alone. That is why detergents are often used in combination with the solvents in the process. The disadvantage of detergents, however, is that they too are at least somewhat soluble in the dry cleaning fluids, and only makes the solvent in reclamation even more impure. So what exactly are the consequences of allowing the impurities to remain in the process? Odors and unwanted color may accompany the dry cleaned garments.