How Clean is Dry Cleaning?

Last Updated (Monday, 21 February 2011 17:32) Written by Raymond Nakamura

My daughter's favourite pink down coat looked like something the cat dragged in after using it to catch sewer rats. Previously, our home washer and dryer left it looking lumpy. So I took it to the cleaners, and presto — it looked like new. What kind of magic was at work here?

Job Perc

Dry cleaning, it turns out, is not dry at all. Instead of water, it uses a liquid solvent, most commonly Perc, short for perchloroethylene, a chemical first concocted by the famous British scientist Michael Faraday in 1821. Some textiles shrink because the bonds between the molecules because heat and water alter them. Perc can separate oily soils from the fibres without changing the bonds in the fibres.

Out of Odour

I remember the distinctive perc smell of my uncle's dry cleaning business. But by the 1970s, scientists realized that was perc not good for people or the environment. If it's any consolation, my uncle lived into his nineties.

Problem Solvent

My local dry cleaner used to work for a different dry cleaner down the street, which was eventually torn down for redevelopment. The old equipment was too hazardous by today's standards, and a new system would cost her $200,000. So she actually uses another cleaner across town.

Water You Know

I spoke to another neighbourhood dry cleaner. Part of their environmentally friendly strategy is to apply more wet cleaning when possible, using soap and water with sophisticated cleaning machines and steam presses to control the drying process which affects shrinkage and fading. This is where they make everything look more professional than what you can do at home with an iron. Still, about a third of materials still require dry cleaning to look their best.

Coming Clean

They use a modern dry cleaning machine set up at the front of the shop, so customers can see how it works and smell that it leaves no scent. The machine combines washing and drying functions, to contain the perc more effectively than in the old days. They place the load in a perforated stainless steel basket. According to cleaner I spoke to, their machine could hold about 18 kilograms of material, about three times the capacity of a domestic washer. Modern systems use only distilled solvent to start each wash. The load gets doused in the solvent and runs for a certain amount of time depending on the material. The solvent gets spun out thanks to the wonders of centrifugal force. The machine heats up to so the remaining solvent evaporates. It then gets condensed over cooling coils and collected.

Separation Anxiety

The used solvent gets distilled in another compartment separate it from  the unwanted messes and residual water. Perc is about 75 percent denser than water, so water floats on top and can be removed. Some recent hydrocarbon solvents are closer in density to water, making it more difficult to separate. Licensed companies remove the sludge of unwanted messes and residual water. 

Is Your Dry Cleaning Ready?

Modern systems are better at containing perc than in the old days, and in recent years, Environment Canada has created more specific regulations and increased inspections regarding perc. But California is still outlawing perc by 2023. New systems using liquid carbon dioxide may be safer but also expensive to implement. Dry cleaning has come a long way since Jean Baptiste Jolly first noticed how spilled kerosene cleaned his table cloth in 1855, but it seems to be still searching for a sustainable solution that balances social, economic and environmental challenges. I wonder if I should keep that pink coat in its garment bag.

Speaking of environmental solutions, have you entered the BC Green Games?