dissolving PU foam?

[cristofa]

We make the carbon parts on the ROCAT rowing catamaran by wrapping rigid PU foam blanks in carbon, and infusing them in epoxy in closed moulds.

After it has performed its internal tooling fiunction, the PU foam is a heavy waste of space ... does anybody know of anything which will dissolve PU foam so we can get rid of it?

atb ... Christopher

www.rocat.co.uk

[SailDesign]

The simple answer is "No".
From the "Polyurethane foam FAQ (http://www.shopmaninc.com/faq_foam.html)

"15. Can I dissolve this foam once it has fully cured?

No. This foam is designed to be completely solvent resistant once cured. Gasoline and acetone will not cause any destruction of this foam. Please prepare ahead of time by covering any objects/areas that you do not want to come in contact with this highly adhesive product. If you do happen to spill some foam and it cures you will have to either sand or scrape the product away."

[cristofa]

ta for the prompt response, even if it's not what I want to hear ...

Interesting that they can produce something that isn't attacked by anything.

atb ... Christopher

www.rocat.co.uk

[ondarvr]

There is water soluble foam that may work, it can be purchased in sheet and rope form. The problem is I don't the contact information right now. Try google, you may find it, I'll look for it too.

[cristofa]

Water soluble would be great, but I've got to be able to cast the shape - in fact, if I can easily get it out, it doesn't have to be foam. There's some stuff called 'aquapour' which would be ideal, but it's 'one use' and extremely expensive.

atb ... Christopher

www.rocat.co.uk

[marshmat]

9 mol/L aqueous hydrogen fluoride will dissolve the PU foam. Trouble is, it'll also dissolve your hull and your employees if you're not careful. These are really good foams in that they're very stable; the few things that will attack them will also attack everything else in the boat. You might look at a less robust foam, such as polystyrene or the water-soluble one ondarvr mentions, for this application.

[cristofa]

Matt ... WOW, I'd not heard of that stuff before, nor read such a long health hazard document ... seriously not nice! So we probably won't use that, but thanks for bringing it to my attention.

Down the line, we could possibly use polystyrene but, whereas we can cast the PU in the workshop, I understand polystyrene demands high temperature and pressure, and we don't have the resources.

And, so far as I can understand, it's not possible to cast the water soluble
foam on site.

[marshmat]

LOL
My point was, PU foam is so stable that the few chemicals that can dissolve it, are far too dangerous to use in a boat shop. HF (aq) is one of the most potent commercially available acids and will eat through darn near anything.
One castable option you might consider is Dow Corning's Silastic J. It's a silicone rubber and is fairly easy to cast. You could cast the hull in this (not solid, just a few inches) and cut it into manageable pieces, then assemble them on a metal frame. When the boat's done, you could unbolt the metal parts and the Silastic forms would be flexible enough to peel away and re-use. I've never used it for anything bigger than about 24" though, so this is all theoretical.

[georgelewisray]

If you are using epoxy resins, why not make your blank out of a foam that can be desolved by a common solvent. Blue DOW styrofoam is workable in the same manner as yellow PU foam and it is epoxy friendy and MOST IMPORTANTLY, acetone (etc etc) will make it disappear.