stabmaster
Chemical
I am trying out all different sorts of bags to encapsulate a wax (ester) "pentaerythritol adipate stearate" which melts at around 135F. The bags are to store heat in the phase change region and over a temperature range of between 100F and perhaps as high as 190F. I have been having problems with different material compatabilties. A slight elasticity is preferred as there may be a volumetric expansion of 10%. Even when the bags are evacuated of gas, oxygen is entrained within the molecular matrices and will eventually escape, so there is potentially a volumetric expansion associated with that (boyle's law). The bags are underfilled so that even with the expansion there should not be enough pressure to cause a break;
however, the temperature may be a problem.
The requirements of the bag are that it must be relatively impermiable to water and air on the outside, and submersible in hot water which may fluctuate from 100 to 190F daily. Perhaps 20,000 cycles of expansion/contraction. The elasticity required is not known but the volumetric expansion of the entire bag must allow for a 10% change. The inside of the bag must be compatible with the same temperature fluctuations and it must be compatible with esters. Also the bag may contain copper wool. There is puncture resistance to consider.
Fluoropolymer film seems like an obvious homogenous choice. It seems too easy, but anything that is layered with aluminum (Mylar, etc.) either delaminates upon cycling volume or else the seal breaks at the temperatures in consideration.
Any help is appreciated!
Is there any advice?
however, the temperature may be a problem.
The requirements of the bag are that it must be relatively impermiable to water and air on the outside, and submersible in hot water which may fluctuate from 100 to 190F daily. Perhaps 20,000 cycles of expansion/contraction. The elasticity required is not known but the volumetric expansion of the entire bag must allow for a 10% change. The inside of the bag must be compatible with the same temperature fluctuations and it must be compatible with esters. Also the bag may contain copper wool. There is puncture resistance to consider.
Fluoropolymer film seems like an obvious homogenous choice. It seems too easy, but anything that is layered with aluminum (Mylar, etc.) either delaminates upon cycling volume or else the seal breaks at the temperatures in consideration.
Any help is appreciated!
Is there any advice?