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Our company uses acetone and isopropanol in our manufacturing process to clean our product. Our operators get the chemicals from a large container and put it into small containers like this (http://www.soscleanroom.com/product/facilities/8-oz-esd-safe-solvent-dispenser-standard-pump/?gclid=CILep_rTzc0CFdBZhgodSWsEiA) to keep at their station.

Some times our operators say that it was more difficult to clean the product today and equate that to mean the chemicals were weaker that day. Recently our operators stated that the chemicals seemed weak again but the next day they used the same chemicals and said they were fine now. This leads me to believe that the chemicals are fine and that there is a different problem leading to harder cleaning.

How fast does acetone or isopropanol absorb water from the air? How long will it take for the chemicals to be noticeably weaker if stored in the containers mentioned above? Should we be dumping the chemicals everyday or would weekly dumping be fine?

The temperature and humidity is relatively constant at our factory.

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    $\begingroup$ Unless you buy dry acetone or unless you are in a very humid environment, water takeup from the atmosphere can be neglected. $\endgroup$ – Jan Jun 29 '16 at 16:47
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    $\begingroup$ I don't believe in that water thing either. If left in the open, acetone itself would evaporate completely too fast to take any significant amount of water. That being said, why wouldn't you check it with some indicator paper prior to further action? Chemistry is an experimental science, they say. $\endgroup$ – Ivan Neretin Jun 29 '16 at 18:29
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    $\begingroup$ I think that the method of cleaning is the issue. Perhaps the item being cleaned soaked for a few minutes sometime and the soaking factor is not given attention. Or perhaps the items being cleaned have been sitting for a variable length time (allowing dirt/stuff to get stuck like glue). Something along those lines makes too much sense. But if moisture is truly the issue, you could add a drying agent (like anhydrous magnesium sulfate) to the jar of acetone. Otherwise there are far too many untold variables to answer the question, how fast does acetone to absorb moisture. The answer is, test it. $\endgroup$ – Ben Welborn Jun 29 '16 at 19:52
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For Acetone or IPA we are more than happy to keep it in normal squeeze bottles which are not air tight so the bottle you've got should be fine. I believe you're more likely to see it evaporate first than to see it get 'noticeably weaker' (I assume you're using technical grade acetone since it's just for cleaning). There should be no need to dump the acetone/IPA in the bottles on a weekly basis - although acetone is cheap its unnecessary to waste money like that!

Along the lines of trying to figure out what could be the cause of the experience of your staff, I doubt it has anything to do with the acetone itself because you say that they can use the same chemical on two different days and have two different experiences. So it's either they're imagining it (let's assume they are not), or it is the dirt that has to be cleaned that is the issue.

I've experienced it in the lab before that sometimes it does seem more difficult to wash out and clean glassware despite using the same chemicals - and this usually has something to do with how long the 'dirt' has been sitting in my flask or how it got there in the first place (slow precipitation/crystallization, crashed out, solvent dried out and left overnight, etc.). Without knowing what your product is and what it is you're trying to clean out, I can't offer much else other than checking out the consistency of the incoming product that needs to be cleaned. It could be a sign that the manufacturer's process is contaminated on some days.

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I agree that the solvent isn't getting weaker. Have you considered the environmental conditions and how they might impact evaporation rate to see if this correlates?

The solvent evaporation rate will be affected by the room's temperature, humidity, and barometric pressure. Warm dry air can hold much more vapor than cold damp air. Higher barometric pressures will resist the vapor pressure of the solvent. It will likewise be affected by the temperature of the solvent and the surface temperature of the part being cleaned. The temperature of the solvent determines its vapor pressure. As solvent evaporates, the remaining solvent and part surface becomes cooler. Warm solvent has a higher vapor pressure and evaporates faster. Air turnover also has an impact (consider your HVAC system's behavior on a day-to-day basis, as its duty cycle can impact ambient air velocity in a room). A room with static air will allow the solvent to shield itself with a localized cloud of solvent vapor that will resist further evaporation.

When cleaning with solvent on a day favorable to fast evaporation (warm, dry), my experience has been that the quick evaporation makes it easier to clean with because each swipe is over a drier surface. You're wiping a denser dirt concentration from the surface each time.

Likewise, if the operator is cleaning a warm part right off the production line, I would expect it to clean easier than a cooled part that has been sitting overnight. This would also be due to the dirt/oil that you are attempting to clean. A warm film of oil dissolves easier than a cool firm of oil.

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