Performance of Alternative Chlorofluorocarbons in Rigid Urethane Appliance Foams

Abstract

Two alternative chlorofluorocarbons, CFC-123 and CFC-141b, have been proposed as substitute blowing agents for CFC-11 in rigid urethane foams. Both of these have similar boiling points to CFC-11 but substantially reduced ozone depletion potentials. Mobay Corporation has evaluated both of these in a variety of systems to determine their potential use as blowing agents for rigid urethane foams in appliance applications. Due to the different molecular weights compared to CFC-11, there is theoretically 11 weight percent more CFC and 15 weight percent less CFC-141b required in foam formulation to obtain equivalent gas volumes. Using the same gas volumes as CFC- 11, CFC-123 and CFC-141b gave poorer flowability resulting in higher foam densi ties. With CFC-123, depending on the formulation, the nature of the isocyanate, the chemical structure and on the technique of foam preparation, there was a remarkable difference in densities and physical properties. The highest densities and the poorest physical properties were found in PMDI polyurethane foams because of a plasticiz ing effect of the CFC-123 in the polymer. However, in TDI polyurethane foams, densities and properties were more comparable to foams with CFC-11. CFC-123 also showed good performance in rigid polyisocyanurate foams. In all systems, CFC- 141b was closer to CFC-11 m overall properties. Both alternatives produced as theoretically expected, higher k-factor foams than CFC-11. In corresponding foam systems, we measured up to 15 percent higher ther mal conductivities. The k-value retention of foams made with CFC-123 and CFC- 141b appeared to be similar to CFC-11. The formulations tested were developed originally for use with CFC-11. To improve the performance of the alternatives as blowing agents in rigid polyure thane appliance foams, adjustments and optimization of the formulations will be nec essary.