Dry Cleaned Clothes and Evaporation of Solvents

November 17, 2014, by Debra Lynn Dadd

Question from Stacey

Hi Debra,

I have some dry-cleaned clothes still in the plastic that have been in my closet for about 6 years. Would these be safe by now to wear, or would you dispose of them?

Thank you!

Debra's Answer

The dry cleaning solvent perchorethylene is very volatile and will evaporate completely. I can't tell you exactly the evaporation rate because it depends on the conditions. (Just so you get how complex this is, take a look at this paper on how to calculate evaporation rate).

So if you brought you dry-cleaned clothes home from the cleaners 6 years ago and had removed the plastic and hung them outdoors so the perc could freely evaporate, I would say in a day or so. Certainly 3 days or 7 days there would be nothing left. The plastic, however, slows evaporation. At 6 years I don't know what it would be. But you could simply take the clothing out of the closet, remove the plastic, put them outdoors, and within several days the perc would evaporate completely.

As long as we are talking about evaporation, there is a toxicological factor of solvents called the "evaporation rate." Each solvent has it's own evaporation rate. These rates are established by supposing the evaporation rate of ether (or some other substance) = 1 and by indicating other slower drying solvents as multiples of the evaporation rate of substance it is being related to.

As an example, here is a chart of the evaporation rates of solvents used in printing inks, using ether=1.

But this still doesn't tell us how long it would take for your perc to evaporate.

The MSDS definition of evaporation rate is "the rate at which a material will vaporize (evaporate, change from liquid to vapor) compared to the rate of vaporization of a specific known material. This quantity is a ratio, therefore it is unitless." (MSDS HyperGlossary: Evaporation Rate)

In general usage we think of it as the amount of material that evaporates from a surface per unit of time. So there are three variables
* amount of evaporated material
* per space
* per time

Here is a chart where butyl acetate=1.

The problem is that you need to start with the evaporation rate of butyl acetate, which is unknown because the number would depend on a number of variables, such as temperature, atmospheric pressure, humidity, air flow, viscosity, and, as in the case of your dry cleaning, whether or not it was covered.

But here's something you can glean from this chart. The evaporation rate of water is classified at 0.3. Heat the water and it will evaporate faster as we can observe as steam. Freeze it and it won't evaporate at all. That's true for solvents too—heat speeds evaporation. But if you know water is classified as 0.3 on the butyl alcohol scale, and you know that is slow evaporation, then you can tell that acetone (nail polish) at 5.6 is five times faster.

There is a line on the MSDS for "volatility" in Section 9: Physical and Chemical Properties, but there is no data on the MSDS for perc.

Well, there's the science lesson for today. I wish it were simpler. I just try to think in terms of is it going to evaporate fast or slower. Formaldehyde, for example, evaportates pretty quickly from an open bottle, and very slowly when bound up in a resin in particleboard.