CA Glue

Question: My new bottles of CA are in the fridge, and I add new glue from the big bottles to applicator bottles. After a length of time (weeks? months?) I noted that as I glued two pieces of balsa together, as I let go, the pieces fell apart. I glued again and held longer, and again the pieces fell apart. Finally, I applies a drop to my fingers and no stick. It was like water.

I have noted now that another bottle is getting slower to stick together. Logic says that CA must in time with that little air that gets in that hair size tube, cause it to loose its CA properties. Anyone ever read the tech stuff on CA as to this problem? I would appreciate the techno-nerd stuff on this to fill in that glaring hole in my knowledge of CA.

My guess is condensation is occuring in the application bottle when the cold CA is added or in the bigger bottles which are going in and out of the fridge numerous times. This water has diluted the CA.

If the problem gets worse when the storage bottle is nearly empty, then it's probably condensation in the storage bottles going in and out of the cold fridge and being opened repeatedly. Over time, it has contaminated the CA.

Edited Part - Moisture will trigger the curing mechanism in CA too.

This is a summary of stuff I've picked up regarding CyA glues from several sources, including at least one manufacturer. I can't find my folder of CyA info right now, but I believe all this is correct:

CyA glues have a "shelf life" of approximately 1 year - - From the date of manufacture (not the date of purchase). This can be extended considerably with refrigeration.

NEVER open a cold bottle of CyA; always let it come to room temperature before opening. If it's cold when opened, condensation will occur (even through that tiny opening) and the curing process will initiate.

Never put the cap back on an opened bottle of CyA; throw the !@#$ thing away as soon as you slice the nozzle! I don't remember the "why" of this, but it was convincing.

"Pure" CyA (water-thin) has a longer shelf life, and open life, than other formulations. Thick-set is considerably shorter. "Foam-Safe" has the shortest life of all.

Never use a pin to re-open the nozzle. Cut a little more off and insert a Teflon® tube. When that eventually plugs, pull it out and insert a new one.

Big bottles of CyA are much less expensive, per ounce, than small bottles. How much money do you save if you buy 4 oz. bottles and get to use 2 before the stuff starts to "act funny" (cure slow; not cure; not bond permanently; cure in the bottle)?

And how do you know when it is starting to "act funny"? Only after the fact! A good "Rule of Thumb" (and forefinger, for the unfortunates among us - I include myself) is to buy what you will use in 6 months. If you use a LOT of CyA, the 4 oz. bottles make sense. IF you build one plane a year, you'll save money and frustration by purchasing smaller quantities.

We all like to save $$$, but what percentage of the cost of a plane is glue? Even if you count only $$$, I'll bet it's under 1%. This is not the place to economize!

Over here, humidity is very high throughout the year. A opened bottle of CA left out will harden in a couple weeks. I keep all my unopened CA in the fridge, and my opened bottles get stored in a tupperware with a dehumidifier. I suppose silica gel would work, but much cheaper are the "Thirsty Hippo" type dehumidifiers with the calcium chloride in the plastic tubs. The CA still thickens over time, but it takes a good four months or so.

I put my polyurethane glues in with the Thirsty Hippo as well. So far, none of that annoying clogging/skinning over you usually get.

If you live in the southern U.S., you might want to try the same thing.

A couple of questions:

Does the fridge extend the life by much? I have always kept my CA "stash" in the Freezer (in a plastic baggie). I take it out the day before I need it so it can acclimate to the warm temp before using. (I use 1 oz. bottles)

Does leaving the cap off affect curing? My understanding is that CA is an anerobic reaction. I always thought that the eventual thickening was a slow chemical reaction. Has anyone left an unopened bottle on the shelf and had it harden?

The fridge does indeed extend life, as does the freezer, but probably not as much. I have some three or four year old CyA in the fridge that still works. What sets off the polymerization, I've been told, is water, i.e. moisture on the surface of the item being glued. Other things work, too (those fluorocarbons in the accelerator you get in the bottle, for instance). Moisture in the air is definitely bad for shelf life.

>A couple of questions:
>
> Does the fridge extend the life by much? I have always kept
>my CA "stash" in the Freezer (in a plastic baggie). I take
>it out the day before I need it so it can acclimate to the
>warm temp before using. (I use 1 oz. bottles)

Most chemical reaction rates are a function of temperature. Generally (but not all )rates increase with temperature. In the case of cyanoacrylates, this is true. So any reduction in temp. extends the life of CA. The colder the better!

>
> Does leaving the cap off affect curing? My understanding is
>that CA is an anerobic reaction. I always thought that the
>eventual thickening was a slow chemical reaction. Has anyone
>left an unopened bottle on the shelf and had it harden?

>George

Actually the reaction is not anerobic for our CA. In most cases, the moisture found on any surface will initiate the curing mechanism of the cyanoacrylate. This moisture, combined with the elements of the surface creates a possible activating pH level. The higher the acid level of the surface, the slower the cure. This is due to the fact that organic acids are used as stabilizers in the manufacturing of cyanoacrylates. These acidic stabilizers are a major facilitator in keeping the cyanoacrylate in its liquid form.

Even though CA is stabilzed, the crosslinking reation is occuring at some low rate..... so no matter what we do, CA has a finite shelf life.

While I agree in principle about the shelf life idea, I have personally had a large (6 oz.) bottle of thin CA in my freezer now for at least 4 years. When I need any, I use a blood pipette to extract some, and put the lid back on and back into the freezer it goes immediately.

That stuff is still working just fine. I think the secret is that the freezer is very dry, and the container is well sealed. By contrast, I've stored a medium CA bottle which had been opened, with its little snap on cap installed. After a period of (several) months, it had flashed and was completely solid. I think it wasn't sealed as well.

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"Good generally conquers evil. Unless, of course, good is stupid."

There is, incidentally, a strange phenomenon that happens once in a while. A bottle of superglue, usually the thin stuff, removed from a freezer and being allowed to warm up before opening, will once in a while "flash off" and become solid, releasing huge amounts of heat. It's never happened to me, but a couple of people on this BBS say it's happened to them.