Study of the effect of polyol and isocyanate viscosities upon the processing and properties of rigid polyisocyanurate foams blown with HCFC-141b

The mandated switch from CFC-11 (trichlorofluoromethane) to HCFC-141b (1,1-dichloro-1-fluoroethane) as a blowing agent for polyisocyanurate insulation foams has required producers of these foams to make numerous formulation changes. The changes have been warranted due to the differing physical properties of HCFC-141b versus CFC-11. These differences include higher boiling point, higher latent heat of vaporization, increased polymer solubility and decreased viscosity of the polyol and isocyanate blends which contain HCFC-141b compared to CFC-11. These differences have led to concerns with the ultimate physical properties of polyisocyanurate foams blown with HCFC-141b as compared to those with CFC-11 blown foams. In particular, the increased solubility of HCFC-141b in the foam's polymer matrix has led to a reduction in compressive strength and problems with dimensional stability. This paper deals with Dow's efforts at improving foam processing and dimensional stability of these foams with the use of high functional, low equivalent weight polyols and increased viscosity and higher functionality Polymeric MDI (PMDI).