acetone-resistant epoxy 1

[runcyclexcski]

Hi all,

Has anyone have across 2-part epoxy which would not swell/fail upon long-term (ovenright) exposure of acetone? Chlorofrom-resistance would be even better, but I doubt it. We assemble water-resistant cuvettes out of glass pieces using 5-min and a UV-curable NOA-61 epoxy, which allows us recycle the glass pieces by soaking overnight in acetone or (even better) chloroform. However, the glass holder that the pieces are held in needs to be resistant to the acetone, and the shape is intricate enough to make it problematic to machine it entirely out of glass. Can't use PTFE, either (too soft, not suitable mechanically). The piece is currently held together with JB Weld-cold-weld which resists acetone short-term, but long-term exposure (12 hours) causes it to swell. The bond seems OK, but the epoxy itself gets much weaker. I was hoping for there to be specialized epoxies even stronger than JBColdWeld.

 

[ScottyUK]

Something like MasterBond's EP62-1BF might be worth a look. Henkel-Loctite and MasterBond both have good technical support, why not ask their advice?

 

[epoxybot]

The JBColdWeld is I believe a paste(non-sag) formulation & 1:1 ratio which is nice but ScottyUK has the right idea. The more chemical resistant epoxies usually have very tight cross-linked networks. Talking to MasterBond about a non-sag equivalent to MasterBond's EP62-1BF is advisable. The Masterbond product requires relatively low heat curing which maximizes the amount of cross-linking.

You could even experiment with the JBColdWeld and a new casting by post-curing it for 24 hours at 140F to 160F. That would be, initial Room Temperature Cure followed by a 24hr elevated temperature Post-Cure. Depending on the formulation a post cure can modify the properties by 5 to 20% of a Room Temperature formula. Post Cure means tighter cross-linking but it may come at a price of greater brittleness.

Another candidate might be Loctite/Hysol 1C. It is high viscosity but still not quite non-sag. You can always thicken an epoxy with AEROSIL® fumed silica or similarly Cabosil® but it is better if the manufacturer can supply it as you want it. Link

 

[runcyclexcski]

Thank you epoxybot and ScottyUK. I will give the EP62-1BF product a try. I know MasterBond, it's just their products are not as 'of the shelf' as JB, but for this it's worth a try (and I do not need much epoxy, my optical mounts are only 2-3 inches in size).

Are you suggesting that using a silica-based filler reduces the tendency to absorb solvents b.c. silica is hydrophylic? Could that also create 'pores' into which solvents might diffuse? Is non-sag == non-shrinking? I believe non-shrinking epoxies are used in optics, and they even smell similar to the JB Cold weld.

I tend to be in a hurry, and 24 hr + 24 hr would be quite nerve-wrecking For prototyping, I often cure JB Cold Weld at 70C (150F) for 1 hr till I can manipulate the pieces, and this allows me to assemble pieces faster. But it does make sense that slow cure would allow more crosslinks to form. So I will go ahead and compare proper cure to my sloppy cure side by side.

 

[runcyclexcski]

Update: Epoxies etc recommend 20-3004 and "50-3182NC with Catalyst 30" for chemical resistance. Datasheets look quite impressive. The specs say they are resistant to conc H2SO4, conc NaOH, trichoroethane, and other solvents.

 

[epoxybot]

runcyclexcski - Products like AEROSIL® fumed silica are the standard thixotropic agent used to thicken epoxy formulas. They are in a manner specially manufactured by blowing air throw a stream of molten glass and creating angstrom level sized particles with a very high surface area. Obviously, being a pure form of glass, it has good chemical resistance but unless the particles are fully wetted during manufacturing/mixing, the filler introduces some porosity.

It is less desirable to add this material yourself because it is as light as smoke, requires a lot of mixing effort and when done with something like a tongue depressor on a small quantity, results in a great deal of air entertainment. And fumed silica ends up all over the place. Fumed silica is not to be confused with silica fume. That is why it is better to contact a manufacturer and find out if they have a paste formulation of a liquid formula.

Non-Sag, simply means paste-like. Shrinkage is different. The simpler the formula and the lower the heat of the chemical reaction can yield the least shrinkage. These formulas take far too long for your needs. While I can only guess, I don't think shrinkage is a property you can shoot for. Finding a product that has little or no non-reactive diluents would be advantageous but sometimes they are needed to accelerate the reaction. This is where a product that partly cures at room temperature followed by heat cure may offer some improvement. I can't speak to optical epoxies, I envision a cycloaliphatic UV cured epoxy as they offer the best UV resistance & clarity. Small percentages of Cycloaliphatic amines are blended with Aliphatic amines by the raw material manufactures to introduce unique qualities to the curing agent (where the epoxy is considered the resin) but on the whole, the greater difference in smell is between an Aliphatic amine and an Aromatic amine. Aromatic amines have more of a sulfur-like odor.

I would try doing your normal routine, followed by an overnight Post-Cure.

 

[runcyclexcski]

Great information, many thanks! It sounds like I am not ready to deal with aerosil, I will leave this to commercial manufacturers.

Regarding amines: I myself used aminated glass (APTES-treated) to improve epoxy bonding... found this by accident, actually. After soaking with chloroform, the epoxy is all gone, but you can clearly see the patches on the glass where it used to be, if the glass was pre-treated with amines. Trying to scratch amine-bonded epoxy off glass with a razor blade is fuhgeddaboudit, and I am talking 5-min Devcon epoxy, not some fancy stuff. So, perhaps, I could add amine-treated glass microparticles (not smoke-like), and mix in with any regular epoxy. However, this might also be the most expensive epoxy resin ever made, b.c. a gram of 5-micron silica spheres is $700

https://www.bangslabs.com/products/ordering/order/SA05000|SA05N|11885

I also wonder if anyone made an epoxy resin using fluorinated monomers to make the cured product more chemically inert? I suppose, the C-O-C bond is what holds the cured epoxy resin together, this is more vulnerable than C-F no matter how you put it.