Compressed Foam....for what it's worth

I did a rather mad experiment this morning of compressing ordinary Dow blue XPS foam, which I believe to be about 1.3 pounds per cubic foot, using heat. polystyrene begins to soften at about 100C, and becomes liquid at about 200-240C. I was unable to devise a really accurate way to heat the foam the way I wanted to. The idea was to heat from the outside, not allowing the piece to "normalize" all the way through. To do this, I simply dropped as square of foam and two pieces of 1" board I was going to place on either side in the pressure cooker, and bringing the temp up to the point that it would begin to vent, then immediately bleeding the pressure off, opening the cooker as soon as possible..(zero pressure). I immediately removed the foam and boards, and clamped them in a vice, compressing to about 2/3 it's original thickness, and allowing the works to slowly cool.
The foam distorted a bit in the cooker, as I expected it would, but not enough to be a problem.

The result was nothing short of amazing. The foam had completely different character. The original foam would dent permanently with hard finger pressure, and would snap at the slightest excuse. The compressed foam has tremendous spring back. Hard finger pressure will create a dent, and wrinkles will form in the skin, but it will immediately rebound. It takes a lot of concentrated point load to fail the surface. The foam also is very flexible, It will snap, but I can bend it into a radius I would estimate to be under 2" without it failing. Wrinkles will form on the inside skin, and they will come out as it recovers it's original shape. It has definite "memory"

Density at this point is about 2 pcf, as compared to Divinicell at 5pcf. The foam would need to be compressed to about 1/4 it's original thickness to equal Divinicell.

Much of the resilience is probably due to increased internal gas pressure.

I just tried a repeat, leaving the foam in the pressure cooker longer, and squeezing it to about 25%. Unfortunately the foam distorted badly enough that it didn't work correctly. Clearly it needs to be confined on all sides, and heating and compression should take place at the same time. The center of the piece was very soft, and the outer edges extremely solid, hard and brittle. Obviously not what I was looking for.
To accomplish this successfully would probably require a press made specially to contain the foam, with flanges all the way around, and hollow platens that would heat the foam to the desired temp with hot oil, and then cool it with cold oil. Not very practical......

I worked in a plywood mill many years ago running the hot press that was about 30' tall and had a stack of steam heated platens. Each sheet was fed between two platens, and the press was closed for a specific period of time.

An interesting experiment for what it's worth. It would be interesting to be able to do it more scientifically and see what the properties were at different levels of compression and temps.

H.W.

 

Why?

 

It sounds like the outside of the panel is being fused, and the interior remains much as it was, because of the insulation property of the foam, I'm guessing if you kept compressing it under heat, it would come out like a thin sheet of plastic. Essentially, it isn't going to acquire more strength than the material inherently has. You just give it a skin.

 

For what purpose?
Active pressurisation, with heat, under load?
Why?

 

To make a higher density foam, you must pour a very specific amount into a very rigid closed mold.
Compressing foam under heat not likely to strengthen it at all, weaker would be my guess.
Sheet foam is available in higher densities than your blue HD stuff, and is proportionally expensive, but we’re discussing boatbuilding, right, so you need to use the right materials for obvious reasons.

 

Agreed

you have the power of foam sandwich but with plastic

It would be cool if the OP stumbled on a way to "Pressure treat" foam.

OP you should get it tested at a credible lab but my guess is Mr E has it figured out

 

Agreed. Please use the right materials for your boat. You are not only putting yourself at risk but ruining your purchase as well. Nothing wrong with experimentation but boat materials have been tested out for years if not decades before being released to the public. At the very least, they are well tested before you and I get a hold of them. Just be careful bud.