Styrofoam that dissolves in water

[Pengyou]

I have seen styrofoam peanuts that dissolve in water. Do they make that in sheets? It might be useful us use as a mold when making parts.

 

[JamesG123]

They aren't "styrofoam" which is made of styrene plastic, but if I remember right, starch and cellulose. I don't think its made in sheet form because the practicality of an insulation that degrades in humidity and is digestible by pests isn't very high.

Depending on your resin, you can use acetone or other solvent (like gasoline) to dissolve plain ol' styrofoam. This was how composite tanks and ducts were/are sometimes made before the advent of low temp melting machineable plastics (lost "wax").

 

[Mr Efficiency]

Something as flexible as sheet polystyrene foam would not be much good as a mould, anyway.

 

[Dejay]

Depending of how big a part you're talking about you can also 3D print in PVA that dissolves in water. Or 3D print in clay. Rough surface though

 

[rxcomposite]

Water soluble mandrels are used. PVA and sand mixture. Sometimes coated with breakout plaster. Sodium silicate is commercially available and is blended with sand for casting.

 

[rxcomposite]

Depending on your resin, you can use acetone or other solvent (like gasoline) to dissolve plain ol' styrofoam. This was how composite tanks and ducts were/are sometimes made before the advent of low temp melting machineable plastics (lost "wax").

We used that before. Styrofoam mold and epoxy resin. After laying up the outside part and curing, we pour acetone into the cavity to dissolve the foam.

 

[upchurchmr]

Styrofoam will collapse to a very small solid when heated to 160F or so.
Aviation guy Burt Rutan would make a mandrel of styrofoam, wrap glass or graphite and epoxy over it, let it cure, then heat in an oven.
At the end you could reach in and pick out a little hardened "sausage" looking left over, without having to separate it from the laminate.
His way of reducing the weight of an aircraft part.

Watched it with my own eyes.