Anyone who has seen an old piece of EPS which has been exposed to water and possibly ice for a long time would never use it. It becomes just a mushy mess with absolutely no strength and very heavy.
We can even see it from your report. If it takes up 5% of its volume in water it has already increased more than 100% in weight!
That would add 50g/dm3. while the initial weight was something like 40g/dm3 or less.
And thats with a piece which has large volume compared to it's surface area. So that's not all to it. The result looks even worse if we look at what the surface can absorb. They used samples which where 2x2x0.5 dm, which has a volume of 2dm3 and and area of 12dm². The difference in absorption between different cutting methods weren't huge, so we can assume water was absorbed pretty uniform over the surface area. The sample absorbed 2dm3 * 50g/dm3 = 100g, and 100g / 12dm² = 8.3g/dm², which is 833 g/m²!
If we assume that the core will absorb the same volume per surface area during an infusion. it will be even heavier, since epoxy is heavier than water. Density is around 1.2g/dm3, so the core would absorb about 1000g per side of a square meter of foam. That would add 2kg/m² of epoxy to the weight and cost of the double sided laminate! This should be compared to H80 which Rob says absorbs 0.2kg per side, so 0.4kg/m². If we run the numbers for XPS, they absorbed about 1/10th of the EPS. Then that means about 0.1kg/side, so 0.2kg/m² of a double sided laminate.
On Wed, Jul 4, 2018 at 3:43 PM, '.' eruttan@yahoo.com [harryproa] <harryproa@yahoogroups.com.au> wrote:
I found this. Not sure it is relevant.
https://www.sciencedirect.com/science/article/pii/ S2214509514000060
Its freely downloadable.
It is hard to say how useful this is. It is interesting that XPS absorbed far more water than expected. But looking at the knife vs circular saw cuts, and its effects, one might assume that could be responsible for most all of the water gain.
If 5p/sf EPS exists, it might be mostly immune or greatly reduce the water absorption. Also i imagine the higher densities of XPS we are considering might also mitigate.
This all being said, i still think EPS may work just fine, assume a vacable density of material and some sort of shaping. i.e. 3d core
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