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<electronic_eel>
azonenberg: about the epoxy shelf life problem you mentioned on twitter: i suspect it has to do with the container and how permeable it is
<electronic_eel>
if it is some plastic syringe or similar, moisture from the air can slowly come in and parts of the epoxy slowly evaporate
<electronic_eel>
the original jb weld came in metal tubes. it had a very long shelf life of several years. i think the metal tubes are the main reason for that
<azonenberg>
It's a heat sealed plastic pouch with two premeasured components in a 5 or 10 gram total mass
<azonenberg>
that you squeeze to mix
<azonenberg>
If it's components offgassing then chilling to reduce the vapor pressure should work
<azonenberg>
if it's stuff getting in, inerting should fix that
<azonenberg>
and so that's what i want to figure out
<azonenberg>
is the problem things getting in, out, or both?
<azonenberg>
and what "things" are getting in specifically that i need to keep out?
<azonenberg>
e.g. is n2 purging enough or should i have a desiccant or oxygen absorber in the chamber too?
<azonenberg>
they also have plastic jars with a 1 year shelf life
<azonenberg>
the pouches have the 3 month shelf life and i want to extend that
<electronic_eel>
are the two containers for the two components next to each other or are they in separate containers?
<electronic_eel>
so can you put the two different pouches in separate n2 filled containers?
<electronic_eel>
then it could also be that some gaseous parts mix prematurely through the plastic
<azonenberg>
That is possible but i think less likely
<azonenberg>
the resin does not appear to change consistency or appearance
<azonenberg>
only the hardener
<azonenberg>
my leading suspect right now is ethyleneamines in the hardener reacting with co2, o2, or water vapor in the atmosphere (all of which they react with)
<azonenberg>
which would be eliminated by inerting the environment around the pouch
<electronic_eel>
so you think the reaction takes part in the hardener that is in the pouch
<electronic_eel>
and not that something outgasses from the hardener and is now missing to make a proper curing
<electronic_eel>
i played with some cheap chinese epoxies a few years ago. the still closed packages were very smelly, so i suspect some strong outgassing. the effect significantly lessened after about 3 or 4 months. also the quality of the bonds when i used them after this time. so it could have been that something important from the hardener evaporated and was then missing
<azonenberg>
Just got off the phone with the manufacturer
<azonenberg>
Good and bad news
<azonenberg>
Bad news: the F110 epoxy is the *one product* they sell whose shelf life cannot be improved by freezing lol
<azonenberg>
i guess something degrades if you freeze it
<azonenberg>
Good news: F113 has very similar properties, slightly higher viscosity but not by too big a margin, and has a six month shelf life at ambient
<azonenberg>
So i'm probably going to switch to it
<electronic_eel>
you could also try to store it in a n2 atmosphere
<electronic_eel>
do you have a big n2 cylinder in your lab?
<azonenberg>
I have a 20 cubic foot one. so i could inert but it would use a good chunk of my gas each purge
<azonenberg>
The manufacturer says they have not tested inerting, only freezing. But they don't think it would work as some of the degradation is a reaction between the hardener and the plastic pouch itself
<azonenberg>
which chilling slows down
<electronic_eel>
oh, reaction between the hardener and the pouch material. i didn't think of that
<azonenberg>
yeah me neither
<azonenberg>
i assumed the pouch was chosen to be chemically inert
<azonenberg>
and that the reaction involved constituents or atmosphere diffusing in or out
<azonenberg>
apparently it's kinda inert but on a months long time scale not so much
<azonenberg>
lol
<electronic_eel>
why don't they use metal tubes like the original jb weld? i guess you aren't using the cheapest epoxy here. the material costs for the tubes shouldn't matter that much
<azonenberg>
yeah the processing/labor cost for the packaging is nontrivial i imagine
<azonenberg>
as the cost per gram is way more than the bigger packages
<azonenberg>
but not the plastic
<electronic_eel>
i think it is more that they don't want a too long shelf life, because it will often expire and the customers will buy new packs then
<azonenberg>
Lol, yes that is probably part of it :p but the big jars are longer inherently
<azonenberg>
maybe just different polymer or something
<azonenberg>
polypropylene vs polyester i think
<azonenberg>
in other news, new print of the differential probe mechanical enclosure is coming shortly
<azonenberg>
with a few small tweaks for manufacturability and second alignment pin
<azonenberg>
out for delivery now, still waiting on next pcb rev to ship
<electronic_eel>
i want to have different types of glues available in my workshop. i think i only use like 25% of what i buy, the rest i have to throw away because they degraded too much. i would really like to improve that ratio
<azonenberg>
Yeah same here
<azonenberg>
i burn through a lot
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<Bird|otherbox>
yeah, adhesive shelf life is a pain in the butt :/
<Bird|otherbox>
learned that the *hard* way when my tube of neutral cure silicone became useless the second time I needed it (having bought it originally because I needed a dab of silicone for a project several years back and the smallest tube I could easily get at the time was a 5oz or so)