Tuesday, 18 August 2009

Vacuum Degassing PU resin experiments 00-02

I have some Smooth On resins that are past their use by, including Task8 that's 15 months old and some other that are ~2 years old. They are supposed to be used within 12 months of manufacture, so they're a bit dodgy.

These resins are interesting materials with a lot of promise, so I did some experiments to get a feel for them.

I'm interesed in Reaction Injection Moulding (RIM), which can including injecting the resin under pressure into a mold under vacuum to reduce trapped air bubbles. This doesn't work with the resins I tried, because they seem to evolve a gas as they cure, after they gel, and vacuum causes them to foam hugely. This might be because my samples are old, but I suspect that it's a 'feature' of the material.

Experiment 00

Mixed ~180 ml
Put in in to degass after about 1:30 of mixing
degassing happened late in the cure
Result: cup full of hard cured coarse partly open foam

Experiment 01

Mixed ~240 ml
Put it in to degass after ~50s of mixing, in two cups:
~70ml on two layers of Biaxial glass fiber mat
~160ml on its own
Degass happened early in the cure, but post gel
Large cup overflowed.
Cured as solid, not foam, but surface of both very uneven. Partly clear amber which is interesting because this resin is supposed to cure opaque tan. Is the opacity a volatile reaction product that is causing foaming under vacuum?
Resin appears to wet out mat well.
Thin section was strong, but breakable by hand. Showed evidence of delamination, probably from part cured layers touching as the gelled foam colapsed.

Experiment 02

pre-degass 2 minute
mix 120ml
Vacuum half of it after 30s, keep under vaccum during cure
Vacuumed half overflowed cup and produced rubbery Clear amber mess with large bubbles in it
Unvacuumed half foamed very sightly and set to rubbery tan.

Experiment 03

same, but with 2 year old Smooth Cast 326
The half cured under vacuum had a totally clear and nearly colourless bottom part and a tall deck of hard coarse foam on top.
The half cured at room pressure had a bunch of pinhead bubbles.
I suspect that a little gas was evolved during cure.

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