I understand the physical (chemical) differences between Styrofoam (polystyrene?) and Polyurethane.
I have used Styrofoam in various densities from 2 to 6 lb/cub ft - the higher density stuff appears to be mechanically as strong (or stronger) than PolyU when used as a composite core material - is this correct? This may be a naïve question as I have not seen (touched) the stuff you call Lastofoam (Divinicel?). Maybe this is a mechanically stronger polyU, but the stuff locally available is very fragile - I can poke my finger all the way into it without much effort and the surface readily crumbles almost to a dust when rubbed - not an ideal surface to glue anything to. My wife uses it for flower arrangements. Styrofoam has its own draw backs in that Vinyl Ester resins (and most solvents /avgas) will attack it. I need to appreciate the structural qualities /suitability for use in the KR type construction. In a perfect world (and the US) a large variety of core materials can be purchased without any trouble - in fact, someone will deliver whatever you desire to your front door. This is not the case for me in Africa. I can however source good quality (not re-cycled) white Styrofoam in many densities from South Africa. The stuff is easy to "slice" into sheets of any thickness with a hot wire. It does not sand as well as polyU, but the higher density stuff is not too bad - it can be done. I am looking to do Mark L style sandwich wing skins - glass on both sides of the skin core. The logistics of shaping the material aside - can Styrofoam be used to the same good effect? The theory says that the strength of a composite sandwich increases almost exponentially with thickness. I cannot see that polyU will outperform Styrofoam in compressive or tensile strength - maybe the shear capability is the issue? I will appreciate any informed advice Regards Steve J
