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Author Topic: Protic vs aprotic solvent for painted surface prep.  (Read 487 times)

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pcm81

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Protic vs aprotic solvent for painted surface prep.
« on: November 30, 2018, 05:39:46 PM »

CONTEXT:
This is a work related question, so forgive me for lack of details, don't want to give out any information that may be considered proprietary...

We bond things to bare metal surfaces, composite surfaces and painted metal surfaces. Our standard go to cleaners are MEK, Acetone and Isopropyl alcohol. So far we have a blanket policy that MEK is the best choice, acetone is second best and Isopropyl is last choice for cleaning the surface prior to bonding things to it.For bare metal surface we wipe off the leftover cleaner, for painted surface we let it evaporate. This policy was created long before my time.

I am trying to better understand the difference of chemical reactions that can take place with a painted surface in the case of protic solvent (acetone, MEK) vs aprotic solvent (Isopropyl alcohol). More specifically my concern is that if we leave MEK to evaporate off a painted surface it may dissolve the paint and weaken bond with adheisive, hence a less aggressive isopropyl alcohol or a faster evaporating acetone would be a better choice for painted surface.

All of my google-fu research about protic vs aprotic solvents takes me to organic chem courses explaining solvation for purposes of conducting a chemical reaction.

ACTUAL QUESTION
How do protic vs aprotic solvents functionally differ for cleaning off regular grease and dirt? In all the videos i watch online the solvents are suggested for a specific reaction, but i don't know what would be in the dirt covering the surface, so, not sure how to apply the SN1 vs SN2 based recommendations...
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wildfyr

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Re: Protic vs aprotic solvent for painted surface prep.
« Reply #1 on: November 30, 2018, 06:07:03 PM »

It's not a reaction, it's just solubility. MEK is indeed the best for grease, since it's the greasiest solvent of those 3. For dirt... Well it very much depends what that dirt is. Metal shavings? Human skin cells? Plant matter? Soapy water is a good choice for biological stuff.
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OrganicDan96

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Re: Protic vs aprotic solvent for painted surface prep.
« Reply #2 on: December 02, 2018, 04:56:36 AM »


 protic solvent (acetone, MEK) vs aprotic solvent (Isopropyl alcohol).
[/quote]
this is incorrect. alcohols are protic, acetone and MEK are aprotic
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