Yes the issue is the stability of the plastic at the temperature and pressures that sterilisation needs. I know that plastics have been developed for exactly this purpose but I don’t think they’re very widespread yet.
It appears from Wikipedia that normally you sterilize things at 121° in steam for 15–20 minutes? If that's the case, common plastics like nylon and polydimethylsiloxane should be okay, although poly(lactic acid), commonly used in FDM 3-D printing, and poly(ethylene terephthalate) won't be.
A lot of plastics will deform when autoclaving. There are enough lists for autoclave compatibility that I forget the answers, but this looks like a pretty complete chart.
This is a really comprehensive table! It lists PLA as "Poly(L-lactide)", giving it a surprisingly good "Fair" grade for autoclaving, and polydimethylsiloxane as "Silicones", rating them "Good". It also lists polycaprolactone, which melts around 70° and can be easily molded by hand while molten, as "Fair". Surprisingly, though (to me), it lists nylon (6 and 6-6) and teflon (polytetrafluoroethylene) as only "Fair", like PLA and PCL, even though at least teflon is totally insensitive to water and commonly used with service temperatures up to 260° (among other things, in FDM printer hotends).
So I wonder if this table might have some significant errors in it? Maybe someone interchanged some plastics without intending to. It can't possibly be correct to put PTFE and PCL in the same category, can it?
Anyway, common plastics it rates as "Good" for autoclaving include acetal (Delrin), polypropylene, silicones, and (for some definitions of "common") PEEK.
Surprisingly polyimide (Kapton), the favorite high-temperature chemically-inert plastic of aerospace and electronics, isn't in the table at all.
It is totally possible that different companies will have slightly different charts but usually they're about the same. The canonical way to know if to ask the manufacturer of the actual plastic you're using, these comprehensive tables are usually put out by distributors as general guidance.
I'm not surprised that some plastics may not be based on temperature only. For instance, nylon might crack if it's a thin piece due to thermal expansion. Or some may chemically react with steam.
I agree that it's weird that PCL would be okay while Teflon isn't, but it could be a molecular weight or thermal cycling thing. Teflon is very soft already so it might simply get deformed.
I'd trust such a table to point me in the right direction but find a second independent source if the answer seems weird.
Of course in practice you just try it and see if it survives and is functional. lots of plastics can survive a cycle or three but not five.
Note that it's 121˚C (and under pressure), not a tepid water bath.
Things like needle drivers and forceps hold up fine with some care, but things with delicate moving parts are not supposed to be autoclaved. Plastics depend on the material--some are fine, some deform.
Right, I didn't mean 121° Frankenstein, and I see now that my comment could be misinterpreted as meaning that all common plastics would be fine, when actually I only meant nylon, polydimethylsiloxane, and a few others — and even for nylon I should have been more specific.
I was just trying to emphasize that it's a fairly...aggressive process.
You can pasteurize eggs at ~135˚F and they're practically uncooked. The autoclave isn't like that at all--15-20 min at full temp/pressure plus the rampup/down times can do a number on things.
Thank you! The plastics compatibility chart linked above also listed it (even nylon 6-6, which it called nylon 66) as only "fair", which surprised me. Does it hydrolyze?
I have no idea what happens, maybe cracking or deformation. Most things I've read is that the max service temp of nylon is close to autoclaving temps (or just below) and its not suitable for use in boiling water either.
Given the temperature constraints, I can imagine exactly those plastics are fairly unlikely to be suited to the traditional extrusion heads on common-or-garden 3d printers.
Yes I would think moulding would be the way. One of my clients is a plastics company and I saw a presentation on it a little while back. The new plastic versions of things can be non-disposable but still much cheaper and lighter than metal versions.
