Monday, January 17, 2011

More on Cyanoacrylates

Another thought occurred to me regarding cyanoacrylate adhesives that is nowhere near as widely known as it should be. The polymerization of this adhesive is catalyzed by hydroxide ions or other bases. It is often stated that water is the catalyst (the Wikipedia article tiptoes along this line) but this is definitely not true. You can prove it for yourself by adding water to the monomers and watching nothing occur. Instead, it is the hydroxide ion that always exist in water that catalyzes the polymerization, and what a pretty powerful catalyst it is! Neutral water has a hydroxide ion concentration of 10-7 moles/l, and with moisture making up about a few percent of the air, you can knock that number down further by a couple orders of magnitude, call it 10-9 moles/l. Truly a catalyst!

That the polymerization is catalyzed by a component of moisture is easy to confirm here in Minnesota. In the summers, we have high humidity. Dewpoints are often in the 60's or 70's and our superglues work just wonderfully. But then comes winter, when dewpoints become frostpoints and the air inside most buildings is dryer than in the lab's desiccators. Just getting a cyanoacrylate to work is then quite challenging. I've found that exhaling a big breath of warm humid air right before I jam the two pieces together helps, although even that is not guaranteed.

8 comments:

Eric F. Brown said...

John--if I recall correctly, the standard 'super glue' is not to be used on plastics. However, there is a product sold that is 'superglue for plastics.' Do you know what ingredient is required so that cyanoacrylate bonds to polymers?

John said...

Sorry Eric, I really don't know. It could be a silance of some sort or some other coupling agent.

John said...

Opps, make that "silane", not "silance".

agiantamongmolecules said...

John,

Maybe I have no understanding of the mechanism of cyanoacrylate propagation, but I would assume that hydroxide is an initiator for the anionic polymerization of cyanoacrylate,not a catalyst. This would account for the low concentration of hydroxide ion needed to kick off the reaction.

John said...

Sorry AGAM, that is my industrial experience slipping into high gear. The terms "catalyst" and "initiator" can often be interchanged with certain systems, mostly in free-radical reactions. I usually try and stick to the more academic options as I think they are clearer, but I do fail at times.

Such confusion however, is quite rare in industry. For example, we all agree on what "resin" means :)

Anonymous said...

Hi! I could have sworn I’ve been to this web site just before but soon after searching by way of a number of the publish I recognized it is new to me. Anyways, I’m certainly delighted I discovered it and I’ll be book-marking and checking back again usually!

jang geun gulk said...

May I want to know how to use Cyanoacrylate Adhesive?

Janardhan Reddy said...

This post was really helpful....Super Glue or Cyanoacrylate.