CA Glue Caps: On or Off?
Issue: Issue 303
Posted Date: 6/19/2012
One of our queries in last issue's Q&A dealt with the topic of keeping glue fresh. While the original question dealt with polyurethane glue, one of the Woodworker's Journal experts broadened his answer to include cyanoacrylate [CA] glue -- and it seems that therein lies some confusion. - Editor
"In your latest Woodworker’s Journal eZine, Tim Inman suggests storing CA glues uncapped and open to the atmosphere. According to this manufacturer’s information:
http://www.instantbond.com/storing-cyanoacrylate-glues/ and everything else I have read, he is quite mistaken. CA glues should be stored in the same manner as polyurethane glues: well-sealed and in a dry condition. They both cure by contact with atmospheric moisture. It is possible it works for him, if he lives in an arid area and/or has a very dry atmosphere in his shop." - Paul Taylor
"Now you have me confused. I think every article I have read about CA glue states that water vapor will harden it and that it needs a bit of moisture to set up. Therefore, they recommend not storing open bottles in the fridge or freezer as going from cold to warm will cause condensation. Some folks in Arizona may get by with never putting the cap back on, but, here, humid Florida, it's the trash can if you do. There are many other conflicting hints and tips about storing and using CA glue on the web. I would like to see a clear definitive description on the best way, in various climates. Hey, I remember it even gets humid in Minnesota in the summertime." - Earl Herman
"I have been building model (radio-controlled) airplanes for 20 years and use mainly CA (cyanoacrylate) glues. I have also found many uses for CA glue in my woodshop where I build things as small as pens and as large as furniture. I usually buy the largest sizes of CA and have found that the glue keeps for well over a year without any noticeable loss of strength by keeping it in the freezer between projects. I have one container of medium thick that has been in the freezer for over five years just to see how long before it gets hard. Thanks for all the info and tips that you have been passing on in your newsletters." - Marty Weigel
In an attempt to clear up some of this confusion, we went to the source, and asked a true glue expert for the definitive answer. Here's what Bob Behnke, a senior technical specialist from Franklin International
(makers of Titebond® glues) had to say. - Editor
"CA glue is made up of cyanoacrylate monomer and additives – specifically, inhibitors – to keep it from reacting in the bottle. Some products (such as Titebond Instant Bond Wood Adhesives) have high amounts of inhibitor to extend shelf life; some use lower amounts to give the adhesive an instantaneous bond. To cure or harden, the cyanoacrylate monomers must react with free radicals (electrons) to initiate polymerization (curing). These free radicals are usually generated from moisture in the air that reacts with a surface that is alkaline (high pH) in nature. The inhibitor is usually a type of acid (low pH) that interacts with the alkaline surface to prevent free radicals from forming and reacting with those already generated. Eventually, the moisture on the surface wins out, and the cyanoacrylate monomer polymerizes (solidifies). On some woods that have high tannic acids, the reaction will not occur unless a high pH additive, like Titebond Instant Bond Activator, is introduced to the surface of the substrate or adhesive.
"Leaving the cap off of the bottle does two things. One, it allows the cyanoacrylate monomer to evaporate from the bottle, leaving behind the inhibitor (as long as the inhibitor has a higher boiling point than the cyanoacrylate monomer) to keep the lower amount of monomer in the bottle from polymerizing. So in this case, leaving the cap off can help but allows loss of expensive monomer (an eye and nose irritant) to the atmosphere. Two, it also allows moisture to enter the bottle with the potential to initiate polymerization in the bottle. Eventually the inhibitor will be used up and polymerization will occur.
"I recommend using a similar strategy as with the one-component urethane products. Squeeze the bottle until all of the air is out of the bottle and then cap the bottle with a minimum of air space. This will eliminate loss of expensive adhesive and minimize the loss of inhibitor due to moisture, thereby increasing adhesive shelf life." - Bob Behnke, senior technical specialist, Franklin International