Characterization of polyisocyanurate foams: The effect of blowing agents and exposure conditions on physical, chemical, and microstructural properties

The effects of blowing agents and exposure conditions on the physical, chemical, and microstructural properties were determined for rigid, polyisocyanurate (PIR) foams. At the onset of this project, the two most promising alternatives to CFC-11 as a blowing agent were HCFC-141b and HCFC-123. Since that time, HCFC-123 has been removed from the market and the advent of coblowing has arrived. The thermal properties of foams produced using these new materials and methods have been investigated extensively, but the role of the alternative blowing agents on the mechanical properties of the foams has not been studied. Additionally, the changes which occur in the foams as they age are not well understood. Therefore, this project had the following objectives, to characterize the independent or associated roles that blowing agent and aging have in determining mechanical properties of PIR foams.; The foams tested had three different blowing agents combined in various fashions to produce six formulations.; The foams were exposed to three environments, a field exposure on a roof at Oak Ridge National Laboratory for 16 months, 75{dollar}spcirc{dollar}C/10%RH for 1, 5, and 25 weeks, or 60{dollar}spcirc{dollar}C/75%RH for 1, 5, and 25 weeks.; The microstructural results for the foams were consistent regardless of blowing agent or exposure condition. The cell size increased for the foams with increased exposure while the cell wall thickness declined.; The chemical analysis of the foams again showed no differences between the blowing agents. Each of the test methods, differential scanning calorimetry (DSC), thermogravimetric analysis (TGA), and Fourier transform infrared (FTIR) spectroscopy, showed a decrease in blowing agent, a decrease in unreacted isocyanate (NCO), or an increase in polyurethane or polyisocyanurate components.; The physical properties (including mechanical) were determined for the foams using a number of methods. Again, no difference could be discerned in the behavior of the foam based on the blowing agent used. The density of the foams decreased with increasing exposure. This was in agreement with the increase in the cell size and decrease in cell wall thickness observed earlier. The ultrasonic moduli, Young's and shear, increased with exposure as did the compressive modulus. This result was the opposite of the expected behavior since mechanical properties in foams are believed to vary in the same fashion as the density. The explanation offered is that the crosslinking which occurred led to a higher modulus which more than compensated for the decrease in density.