Remby

My Feedback: (3)

Have a issue with Epoxy. I had some fuse damage, and went for the epoxy, 5 minute type. Found the resin tube to be like a rock, the hardner looks good. So, went for the 30 minute, same story. These were purchased from Towers, their store brand, both flavors the 4 oz size in two tubes. The one was purchased in October of 04, and the 5 minute purchased Jan 05.

Now, I mark the tubes, to prevent switching the caps by mistake, so know it was not just a unwanted mix error.

I called towers, and they stated that this happens at around a year, and is normal. However, I have had other brands in larger amounts last much longer, and some other here that was over 5 years old was used ,and was fine. I don't wan't to fault tower here, just looking to see if anybody else had issues like this.

Again, it was the following..

item # LXPT45

$4.99

Tower Hobbies 6-Minute Epoxy 4 oz

And

Item # LXPT47


Tower Hobbies 30-Minute Epoxy 4 oz. Same Price..

So, anyone have any advise or comments?

Thanks!
Remby

Lomcevak Duck

My Feedback: (14)

I have had several brands of epoxy in various sizes and times go bad after a year or so. Usually I notice the troubles when the five minute epoxy starts to take 12 minutes to set, and then never sets as brick-solid as I would like. I usually don't keep epoxy more than two winters without it starting to go bad, so I cycle my supplies every so often.

Sneasle

Never used the tower stuff. I normally look around lowes and walmart and such and stock up on the epoxies that come in the dual plastic tubes that are side by side with the one big plunger. Never had a problem with this stuff. I also have a couple of tubes (about the size of the small JB Weld tubes) of epoxy. They are a little sticky on the outside, but are more then a few years old and still more then useable.

So ya, do't really know what the deal is with the tower stuff. I don't recall ever seeing that happen before to epoxy though. I have had it happen to a few bottles of CA, but not epoxy.

Lomcevak Duck

My Feedback: (14)

HA! I beat you by a second!

Remby

My Feedback: (3)

Well, I have bought these before, and it happened then as well. But, I thought it was me, putting the caps on wrong and mixing the two up. So, I bought another, and marked the caps before it was opened, and it still happened. Always just the one tube (resin), the hardener is fine.

I also noticed the formula looks different now, the picture on their site shows two colors in the tubes, these here looked clear and the same when new.

alpinestar

Same brand, same problem.... However the NHP adhesive epoxies and z-poxy finishing resins I've had for a while are all still good.

ptulmer

My Feedback: (5)

Ever so often I see the center of the bottles of epoxy starting to solidify. They haven't actually hardened, so I sit them in a sink of really hot water for a while. Keep rechecking the temp and after awhile it will go back to liquid form and stay that way for a while.

Remby

My Feedback: (3)

alpinestar;
Yes, I have used the NHP brand beforeas well, and never saw this happen.

ptulmer;
I will try to soak in hot water idea to see if it helps, it is thick and would need to be "spooned" out. About as thick as 40 W oil at 180 below.

Epoxys are all quite different then, like fuels and other items in the hobby.

Bipe Flyer

I've used a few brands and I like NHP the best. What I don't like is when he resin has already turned yellow/orange before you buy it. If it isn't clear and runny, I throw it out and buy new stuff. I'm not going to risk my work on an adhesive that may let go.

oparatomcat

I saw a post about a year ago about epoxy getting thick and looking crystalline. The cure one person suggested was to microwave the bottle for up to ten seconds. I tried it and have never tossed a bottle ever since. I microwave it in three second intervals, works every time. I use tower brands only.

scudrunner77

I have had good luck with the microwave too... works good when the epoxy is cold and won't come out of the bottle. Just a few seconds does the trick.

Deadstik

My Feedback: (8)

Epoxy varies from manufacturer to manufacturer and as such, you need to realize that epoxy resins and hardners have a SHELF LIFE. Yep, even if you didn't open the bottle and kept it inside your old refrigerator, it will one day cease to function like epoxy and may indeed turn to a rock.

I go thru at least 2 to 3 gallons of epoxy a month and so I really never have to worry about the shelf life... but each time I get in a shipment, I always mark in bright marker when the shelf life date expires...... To use old epoxy is taking a needless chance with your project to save a dollar or two and isn't worth it. In my case, it would lead to a bad fiberglass fuselage and not only a bad product but an unhappy customer... so....

If you do some research you'll find that epoxy varies in type/consistancy and use like motor oils so you just have to read the label. What you are looking for are properties such as exotherm/strength and useful temperatures....

I'm certainly not an epoxy expert.. but I do read a lot about the products I use and am somebody who uses a bunch of it where it counts... hope this helps...

Dan
Carolina Custom Aircraft..... aka Deadstik

Silvaire

My Feedback: (50)

I've noticed this phenomonon too, but I do not have any specific brands or time periods to cite. It seems to occur sooner in fast setting epoxies than in slower epoxies. I just figure that once it happens it is suspect for use in anything critical. I have some epoxy that is OVER 30 YEARS OLD though, and it still works just fine!

Arlen

treedog

This may be a silly question but the single plunger tubes i use 1 is thicker than the other so i try to block off the thin 1 to make it look like a 50/ 50 mix .Should i do this or will it mix ok anyway? I'm probly doing it wrong.
td

Bipe Flyer

You're doing the right thing.

treedog

Thx bipe wasn't sure about that for a long time now
Td

Remby

My Feedback: (3)

Thanks to all. Glad to see it was not just me seeing this trouble, if I can say it like that.

The Tower stuff works great, and the joint is just what you look for in a epoxy glue. Just don't get it and expect it to be usable after a couple of years. Again, not attacking Towers over this, and it sounds like other brands do this as well. However, some look to be free of this, and will go with other brands like NHP that never did this on me.

Great info guys, thanks!

I will give the nuke idea a shot to see what happens.

MJD

My Feedback: (1)

I think there are two situations being decribed in this thread.

One is crystallization of the epoxy resin, often seen when storage temperatures are low. Reconstituting it with some heat is effective, and if it reverts back to it's original appearance and viscosity then it is fine.

The other aging related thickening/hardening is where the epoxy resin crosslinks over time in storage. This is not reversible with heat. I am surprised however that this is occuring in such a short time to some systems. Depending on the quality of the base resin, what additives are incorporated into the formulation and their purity etc. (if it is indeed a formulated system versus repacked resin), I can see the aging stabilty varying widely.

Remby

My Feedback: (3)

MJD;
Your second description of the two is what I see here. I am just as surprised as you stated you were yourself. Any way to add something to the resin to re-liquefy it ? It is about as thick as say, between thick hair gel VS a super ball.

Could exposure to air cause this?

ptulmer

My Feedback: (5)

Remby, the easy way to tell which problem you are having is to heat up the bottle. I've used a heat gun on occasion, but make sure you don't burn through the bottle. It won't take but a few minutes and you can see a difference. (pretty handy when you need a little epoxy in a hurry and are face with this problem!)

There is a visual difference, too. Your analogy sounds like yours can be saved.

Remby

My Feedback: (3)

O.k.; I took the resin to the microwave, and gave it about 9 seconds, it came out partially fluid again, big lump of resin in center. Tried stirring with a stick , still a good sized chunk of material . So a bit more in the micro, 8 seconds, and it looks MUCH better. Still got a center lump. I push the cap secure, and start shaking for about a minute. Lookin good! Really not very warm, but is fluid , with no big masses. Some small specks of whitish material, but it is usable again. I will try and mix a batch to see how it gels and sets, but it looks good as far as the base two part glue should.

I think I will still change brands after these ones are used and gone, but nice to know of the fix.

The nod to the GA guy for the idea, and to all who offered help, Thanks! The 1/2 forum has another fix in the book, another troubling problem has been dropped from the sky!

MJD

My Feedback: (1)

No, there is nothing you can add to fix it. Once polymerization has occured, you cannot reverse it. The options for additives are:

1. More resin. Well, if you have good resin, then use that instead, right?
2. Reactive or non-reactive epoxy diluent. No point - these will reduce mechanical properties further, plus nobody has this around their workshop unless they formulate epoxy adhesives for a fun or a living. In which case they should already have some inventory of fresh resin to use instead.
3. Solvent. Don't use solvents in structural adhesives, except for specialized applications where you really know what you are doing.

Homopolymerization can cause epoxy resins to harden over time in storage and is a one-way street, as opposed to crystallizing which CAN be reversed with heat and agitation. With the amount of time most of us own epoxy (and the temperature in my workshop) crystallization is a more common problem, but old or crappy resins can indeed harden before their time.

Generally the cause of short storage life from homopolymerization is impurites in the resin, typically rogue metals (trace amounts of metals that act as polymerization catalysts). This relates directly to the quality of the base resin in the system - which in some cases is 100% of the A side in a non-formulated system. Resin that has polymerized notably will not deliver the same mechanical properties as fresh material - since some of the resin system has reacted already, the adhesion to the substrate will be reduced to some degree. In addition, the equivalent weight of the resin has changed meaning that mixing to original specified proportions will now result in a curative-rich mixture.

As to crystallization, that is indeed reversible, and usually about 120-125F is all that is needed. I typically sit the resin bottle in a hot water bath until it is up to temp, then stir. But I do use a microwave on occasion, but I pulse it for a few seconds, check/mix, then repeat to avoid local overheating. Crystallized resin recovered with moderate heat works just as well as it did before crystallization.

p.s. "formulated system" = an adhesive or laminating resin system involving more than simply downpacked resin (which is quite common), typically involving one or more of: epoxy resin, reactive or non-reactive diluents, rubber modifiers (tougheners), wetting agents, pigments, etc. Raw epoxy resins are not generally intended to be used as is for structural adhesive tasks, except in thin film applications (laminating) or composite layups where the reinforcing matrix takes care of the mechanical needs. But they are often marketed as such for economy (read: profit), and in many cases the mechanical properties of the unformuated adhesive exceed that of the substrate so it doesn't matter too much.

Switching gears to CA adhesives, one common cause of short life in the workshop or field is proximity of the CA bottle to the catalyst container (kicker). Typical CA catalyst is a couple of percent of active material in a large percentage of solvent. Before awareness and action regarding fluorocarbons and the environment, Freon 113 was used as the solvent because it was pretty much inert, and would flash off in seconds. But of course it is not used anymore, and other solvents have replaced it in this application. BUT, the key point is that the catalysts themself have a fairly high vapor pressure, and free molecules of it tend to float around in an invisible cloud around the parts that have been spritzed, and the container itself. As these find their way onto the spout of your CA bottle and into the headspace above the adhesive, they begin to catalyze it and eventually you end up with blocked spouts, crusty chunks on the spout, and eventually premature curing of the CA itself. You can greatly extend the service life of your CA adhesives by keeping the CA bottle well away from the spritzer bottle, the spritzing job itself, and the spritzed parts. Now, I don't suggest you run into a different room to spritz parts then wait 5 minutes before returning, let's ne practical. But awareness of this tendency could help you avoid some headaches. I learned this on the job nearly two decades ago and once I became aware of the phenomenon, my CA started lasting longer and longer and I had a lot less trouble with clogged spouts and early curing in the bottle.

MJD

Remby

My Feedback: (3)

MJD;
Wow, lots of knowledge there, thanks!

You said "In addition, the equivalent weight of the resin has changed meaning that mixing to original specified proportions will now result in a curative-rich mixture. "

I take it then your saying to add a bit more resin to get the cure time correct again?

This is really interesting, glad I brought it into the "1/2a Air-Aces" forum and posts.

MJD

My Feedback: (1)

Well, don't think of epoxy hardeners as catalysts - those are a different animal. Catalysts do not take part in the final reaction, they only encourage it to happen much like you and I standing outside the ring and urging two boxers to go at it. Polyester resin for example is cured via addition of a catalyst, which is normally MEKP (methyl ethyl ketone peroxide). Cure time can be manipulated somewhat by varying the proportion of catalyst added - within reason.

Epoxy, like many other adhesive systems, cures through a polyaddition reaction - two chemicals with compatible reactive sites undergo a reaction whereby the reactive sites link together and join the molecules together to become one. Note that this is an exothermic reaction (otherwise there would be no tendency for it to happen). The number of reactive sites on the resin backbone are generally desired to match the number of reactive sites on the hardener for optimum properties. That is why measuring by weight is preferred. There is some tolerance for off ratio mixing without serious loss of properties, luckily, otherwise everyone would need to own an accurate scale. Volume is more convenient and sufficiently accurate for most purposes.

So no, you wouldn't add resin to change the cure time per se, but you would do so to ensure a complete cure without a bunch of unreacted hardener in the system which would reduce the mechanical properties. But, here's the problem - how are you going to know how much to add? Without the benefit if analytical chemistry you are shooting in the dark. Really, you are better off to start afresh, rather than try these sorts of party tricks. I really just made the statement above in an attempt to illustrate what is going on. If the resin has homopolymerized to a degree, then for a given mass of resin the number of reactive sites has reduced, therefore mixing it with the original amount of curative results in an off-ratio mix. How much off, you won't know though. Go buy some new stuff.

To manipulate cure time in epoxy systems, usually the curative is selected on the basis of it's reactivity. For example, there are many aliphatic amine curatives (just one possibility for curative chemistry) for a formulator to choose from, and they range in reactivity from very reactive to pretty slow. The formulator may select a slower curative as a baseline and backblend a more reactive curative in varying percentages to manipulate cure time. Heat speeds up the cure reaction of course, and this brings up the issue of the mass of material mixed versus cure time - as the cure reaction is exothermic, the amount you mix at one time plays an important role in potlife. Smaller masses of mixed adhesive will have a longer pot life than larger masses, due to the surface area to mass ratio. Larger masses have a harder time shedding heat, therefore they build up heat and as the temperature rises, so does the reaction rate, etc etc.. to the point where sufficiently large masses of mixed epoxy adhesives can get into thermal runaway and actually melt containers and catch fire. Epoxy resin data sheets often list a parameter known as peak exotherm temperature; this parameter is standardized via a specified mass of mixed adhesive and a particular curative - IIRC the parameters 500 grams of mixed material using DETA (diethylene triamine) curative; it's been a while since I dealt with this.

The term equivalent weight refers to the mass in grams of material that contains one mole of reactive sites. For epoxy resins the unit would be epoxide equivalent weight for example. Formulators use numbers like this to calculate the ratio of materials needed to react completely. As you can imagine, if a number of the reactive sites in a sample of resin have been used up in homopolymerization reactions during aging, then the equivalent weight would increase - meaning you would on average require a larger mass of material to find the same number of unused reactive sites. Therefore the ideal ratio of resin to curative would increase - as you surmised correctly. The reactive data for a material is generally provided in the lot analysis of the raw material from the manufacturer. Sometimes if the utmost precision is required, analysis is done in the recipient's lab to pin the numbers down more accurately for the material on hand.

Oops, time to stop babbling.. just trying to give you some stuff to think about.

MJD

Bipe Flyer

I told some guys in our club that this is what happens when you store your CA and kicker close to each other (one guy stores both in the same box), but they laughed at me.

Great post. Very valuable verbosity.