ABSTRACT
Chlorofluorocarbon (CFC) compounds have historically been used to achieve superior thermal performance in closed-cell polymeric foams. Changes in thermal performance which take place quite slowly occur as the gaseous components from the atmosphere and the insulating gases are rearranged. Thin-slicing of closed-cell core material and aging at room temperature has achieved meaningful reductions in the time required to evaluate the foam properties which define the time-scale for aging.
In a previous paper, changes in apparent thermal conductivity of stacks of thin-sliced foam were used to determine the effective diffusivity of the blowing agent (CFC-11) in the second region of polyisocyanurate (PIR) foam aging. There are two other methods for monitoring this time-dependent phenomena which are more directly connected to the diffusion process than thermal conductivity.
As specimens of PIR foam for the ORNL/Industry Aging Study were stored at 75 °F and 50 % RH, one set of thin-slices was intermittently subjected to thermal conductivity measurement while a second set of thin-slices were weighed. These two sets of data have been processed and each set was used to evaluate the effective diffusivity of CFC-11. Using 0.254 cm specimens, the effective diffusivity of CFC-11 in a closed-cell PIR foam of 29.2 kg/m3 bulk density was found to be 0.9 × 10−10 cm2/s by gravimetric monitoring compared to 1.33 × 10−11 cm2/s determined by thermal conductivity.
