Freezing Catalysed Epoxy

[Rucksta]

I'm working on pieces that require multiple epoxy applications sealing laminating gluing filleting tabbing fairing.

Some work requires very small mixes e.g. second fair.

To reduce the cycle time between processes I'm freezing residual epoxy.

The cumulative working pot life is about the same as a single mix once the defrosting cycle is removed from the calculation.

The gel times of second & third generation mixes is reduced to and hour and the dry to sand is down to 4-6 hours.

Shelf life in the freezer is 36 hours.
After 36 hours any brew even with additional fresh resin gets lumpy.

Structural lamination is done with fresh mixes due to concerns with reducing the strength of the set resin.

I queried the manufacturer who had no data on the effect of freezing a catalysed mix.

Is there any data in the collective body of knowledge related to freezing epoxy?

[GordMay]

Wow! That's a good question.
Bump ...

[Bill O]

Originally Posted by Rucksta

I'm working on pieces that require multiple epoxy applications sealing laminating gluing filleting tabbing fairing.

Some work requires very small mixes e.g. second fair.

To reduce the cycle time between processes I'm freezing residual epoxy.

The cumulative working pot life is about the same as a single mix once the defrosting cycle is removed from the calculation.

The gel times of second & third generation mixes is reduced to and hour and the dry to sand is down to 4-6 hours.

Shelf life in the freezer is 36 hours.
After 36 hours any brew even with additional fresh resin gets lumpy.

Structural lamination is done with fresh mixes due to concerns with reducing the strength of the set resin.

I queried the manufacturer who had no data on the effect of freezing a catalysed mix.

Is there any data in the collective body of knowledge related to freezing epoxy?

Interesting observations on trying to store your catalyzed mixture. Doubt anyone has looked at trying to preserve the mixture for later use.

We usually only make as much as we need in a batch and have never tried storing it in the freezer. Your observations are interesting none the less.

Will agree there maybe some strength loss with continued freeze thaw of the mixture, but this is only conjecture w/no data to support the hypothesis. Would also think that different brands of epoxy may behave differently to freezing temps.

We use Progressive Epoxy (which may be Mas??) and Paul Oman the owner does like to experiment w/his epoxies. He may have some thoughts on freezing the catalyzed mixture. His web page has good info and products, but is difficult to navigate. He does respond to calls/emails promptly though. https://epoxyproducts.com/

[double u]

I seem to remember having read decades ago, that interrupting the hardening process will result in inferior strength.
(& please: "hardener", not "catalyst", thank you)

[Chotu]

It’s absolutely just fine. All you’re doing is slowing down the reaction. You are basically making your own pre-preg.

I’m not sure it’s as good to do multiple generations, but doing a fresh batch seems pretty reasonable.

[double u]

good point, Chotu. What's the storing temp of prepreg? Is it really "frozen"?

[Chotu]

Originally Posted by double u

good point, Chotu. What's the storing temp of prepreg? Is it really "frozen"?

Minimum is less than 40°F, which is standard refrigeration temperature. But it does best below freezing. It can last for up to a year below freezing. I think the reason the OP’s is not lasting is because he’s doing multiple generations and it’s partially catalyzing. Not good. He should just mix it up fresh, put it in there and apply when needed. Not returning any to the freezer.

[thinwater]

Originally Posted by double u

good point, Chotu. What's the storing temp of prepreg? Is it really "frozen"?

Yes.


Also, prepreg typically requires an oven heated cure, because it is a very slow set. My stiletto 27 was all Nomex prepreg.


The OP is going to need to do his own expereinments, since I know of nothing like that with fast cure epoxies. I have (and many have) chilled part a and part b to get longer pot life in the summer, but still get a fast cure (it warms the moment it hits the work). But you have to watch out for exotherm.

[Rucksta]

Originally Posted by double u

I seem to remember having read decades ago, that interrupting the hardening process will result in inferior strength.
(& please: "hardener", not "catalyst", thank you)

Yes Thank you.

I might have read a similar article.

The epoxy resins I'm using are way different from the ones I was using when I read that article.

The hardening process is more linear
Blush free low allergy resins 2:1 resin / hardener
Fully re-actable viscosity modifiers

Which is why I'm revisiting the the idea of freezing

The multi generation refreeze mix is dodgy.
It does allow laminate, glue & fill into a single day operation.
The fill layer would suffer most from any strength degradation as it is a two or more thaw.
I've reasoned if the mix flows smooth off the trowel it's OK.
Certainly don't want a lumpy fill layer

I'll work on better batch control.
Maybe a silicone ice cube tray filled with bogcicles.
Add dye at thaw to help identify sanding levels.


Good comment "making your own pre-preg"

This could be a solution for tabbing in finished panels without making a mess.

Wet out some lengths of tape.
Interleave with peel ply.
Package in Sarin Wrap
Freeze flat like Filo Pastry
Transport Thaw and apply at prepared work site.
Remove peel ply when dry.

Thanks for the idea

[ShoreFun]

I believe no one in this group can answer your question.

Here is why...

Talking to the owner of a paint company (used for car restoration) I was told that epoxy paint stops curing below a certain point and does not continue when the temp raises.

I have also read that some companies, not boat manufacturers, get their production epoxy pre-mixed and frozen. They thaw on the line and do production.

What is the answer???

I do not know.
Some thoughts as a smart person with no epoxy chemical knowledge, so take it with a grain of salt.

Maybe there are different epoxy formulations. Some can be frozen and the reaction restarted.

Maybe the production line epoxy did not need to be high strength and the frozen cure does the job.

Lots of questions. The ONLY answer I would accept is from the company that made the epoxy.
Anything else is not based on reality.

[Spot]

I like the spirit of this experiment Rucksta...but in practical terms... you are expending more energy to freeze and thaw and peel ply and transport, plus risking a performance downgrade by 'pregging' a non pre-preg system than it would be to make it 'hot and fresh'.

I have frozen and reused mixed epoxy for myself just to try it but I do not consider it a convenience. I would rather small batch mix part A and part B either by weight or by volume to suit the job at hand and either mix short and make a follow-up shot or have a 'standby' project that can take a few oz / grams overage. For me the standby project are the pock holes in my concrete garage floor.

I just did a 7.2 g mix taring out the container on a small digital scale (5 g part A 2.2 g part B by weight, 2:1 by volume system), consumed about 3g on the project, another 3g for the garage floor, and the rest left in the cup cured without any residue underneath so I am confident in the ratios and mixing.

I also agree that the vendor or the manufacturer would be the best first source for info followed by any testing done at the end-user level.

[Lake-Effect]

Last month I was fixing a few small areas on our boat. I couldn't organize the work to use up a decent amount (eg 2+ oz) of epoxy at once, so I made it easier to mix small batches as needed:

1. bought some clear disposable plastic shot-glasses at the dollar store
2. working with some measuring spoons and water, I calibrated one shot glass for a small batch of mixed epoxy (in my case using an epoxy with a 5:1 ratio, by volume) -
   • added 5x 1/2 teaspoon of water to a shotglass, then marked the level on the glass with a feltpen
   • added one more 1/2 teaspoon to that glass, and marked that level
3. I then transcribed those marks to a strip of plastic I stuck inside the glass. Now I can take any other of the same shotgasses, stick the ruler inside it, mark the glass to match the ruler, remove the ruler, and I'm set to add resin to the first mark, and top with hardener to the second mark... and I get a proper 5:1 mix. This has worked out well.

This idea could be done with any size cup you choose, and mixing up a new batch this way seems to be as fast or faster than thawing a frozen premixed batch.