I am alittle confused, though, about the blowing agent. My understanding from you is that they do not use Freon R11 and R12, and that the replacement is more ozone friendly. Still, you doubt that it is CO2. OK. Maybe they are using one of the soft-freons, the ones with a hydrogen attached. Is that what you mean?
Yes, HFC's, HCFC's and Hydrocarbons have replaced the the R11 & R12's. Some technology uses water as the sole blowing agent. This is sometimes refered to as CO2 blown because the water isocyante reaction releases CO2 which creates the foam during the reaction. If the replacement foam was a waterblown foam there could possibly have been a adhesion problem due to the poorer adhesion of water blown foams.
As I understand it the tanks are put on there side on a giant spindle and rotated. As they are rotated a Foam spray rig sprays foam on the rotating tank traversing the tank as it builds up the layers. As you can imagine the adhesion of the foam from layer to layer is very important.
extremely doubtful that the foam chunk was responsible totally for Columbia break-up, but, an ice laden foam piece, hitting precisely in the tile gap area (similar to grout on a tile floor) may have caused enough of an intrusion to slowly uncontest during the temperature variations upon re-entry. That may have caused the higher temp reading on the left wing and possible pilot manuver to kleep friction away from that side... what we do not know yet is if pilot made any manual adjustments or whether simtronics took over... given the state of the debris, no one will be able to tell without some flight manuver data
sad fact is though, they could have aborted flight BEFORE Columbia left atmosphere on Jan 16
let's start spending real money and get NASA into this century