Although HCFC-141b has been selected as the best replacement for the blowing agent CFC-11 used in refrigerator or freezer foams in North America, it is only an interim solution in the ongoing efforts to replace CFCs. Under investigation are hydrofluorocarbons (HFCs) which have zero ozone depletion potential (ODP). Papers have been presented at SPI conferences in 1991 and 1993 on one of these compounds, 1,1,1,4,4,4-hexafluorobutane or HFC-356mffm [1,2]. HFC-356mffm, like HCFC-141b, is a liquid with a low boiling point that offers low thermal conductivity in rigid polyurethane foams. It can be processed in existing processing equipment. It is nonflammable and does not form explosive mixtures with air. In addition, it offers good compatibility with appliance plastic food liners. Other potential zero ODP candidates are the isomers of HFC-245. The most promising of these is HFC-245fa. HFC-245fa is a liquid which boils at 150°C (59°F). It is highly miscible with many different polyols. It is reported to be nonflammable and produces foams with low thermal conductivity. Preliminary reports indicate it has shown good compatibility with plastic refrigerator liners, promising toxicity evaluation results, and feasibility of manufacture. The purpose of this paper is to present new information on foam formulations made with HFC-356mffm and one of the isomers of HFC-245. Our studies have shown that HFC-356mffm and HFC-245fa produce low thermal conductivity foams from masterbatches that do not separate upon aging. Information as to the processing of these systems in machinery will be presented. Results of these studies will be compared to a commercial HCFC-141b appliance foam system.

HCFC-141b blown rigid foams have now been used successfully for a couple of years in North America as insulation in refrigerated home appliances. Manufacturers have had time to adjust to the differences in processing between these systems and the CFC-11 systems that they replaced. Many appliance manufacturers have now focused their interest on foams that will provide lower cost without sacrificing properties or processing characteristics. Although there are a number of ways to reduce cost, one of the best ways is to reduce the density of the foam. Bayer Corporation has previously reported on low density HCFC-141b appliance foam which had similar densities to CFC-11 foams of around 1.9 to 2.0 pounds per cubic foot (pcf). These foams had somewhat higher k-factors but still were successful in replacing some of the CFC-11 foams commercially. Other HCFC-141b foam systems were developed that gave equivalent or lower k-factor foams but at somewhat higher densities. These systems replaced most of the commercial CFC-11 systems. Thermal conductivity of rigid polyurethane foams is to a large extent affected by the blowing agent, the closed cell content, cell size and the density. It has been reported that there exists a minimum thermal conductivity in the density range of around 2 to 3 pcf for CFC-11 blown foams. This appears to be true also for HCFC-141b foams, although the density range may be slightly different or narrower. It is not easy to reduce the density below 2 pcf without increasing the k-factor of the foam. Around or below 2 pcf, the increase in k-factor is caused not only by an increase in the radiation contribution to thermal conductivity due to coarser cells but to higher open cell content and possible convection currents within the cells. Since strength properties are also affected by density. There is a need by developers and manufacturers to evaluate long term dimensional stability of lower density foams. This paper will discuss the development of new low density HCFC-141b appliance foams which have similar k-factors compared to the majority of commercial appliance foam systems in the 2.1 to 2.2 pcf range. These new systems will also be shown to have substantially lower k-factors with only a slight increase in density compared to a commercial system in the 1.9 to 2.0 pcf range. In addition, physical properties and processing characteristics of these foams will be compared to commercial foams.

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.

The phaseout of HCFC-141b as a blowing agent for rigid foams is scheduled to begin in 2003 or sooner. The blowing agent to replace it should have low thermal conductivity, zero ozone depletion potential (ODP), low global warming potential (GWP) and be low in toxicity. In addition, other desirable characteristics include good compatibility with polyols, stability of the blowing agent by itself and in masterbatches, ease of handling, compatibility with plastic food liners, reasonable cost and feasibility of manufacture, good processing characteristics in machinery and no flammability. Finally, the blowing agent should produce foams having insulation properties which are comparable to or better than those made with HCFC-141b. Considerable effort is being directed to developing new appliance foam systems for North America which use blowing agents that have many or all of these characteristics. A number of candidates have been evaluated from which HFC-245fa meets the majority of these criteria if not all of them. Bayer Corporation reported data on HFC-245fa blown appliance foams which had most of these characteristics. Energy performance in cabinets was less than 1% poorer with the HFC-245fa foam versus an HCFC-141b commercial foam. For the future, energy standards in the United States will become 25 to 30% more stringent after July 1, 2001. Therefore, the insulation value of HFC-245fa foams will most likely have to be better than foams blown with HCFC-141b. This paper will discuss new developments with HFC-245fa blown appliance foams. Results of a design of experiments to study the effects of catalyst levels, the processing temperatures of the masterbatch and the isocyanate and the viscosity of the formulation on physical properties will be presented. Results will be compared to a previously reported HFC-245fa system and to an HCFC-141b commercial system.

The HCFC-141b blowing agent used in most appliance foams in the United States is scheduled for phase-out on January 1, 2003. The most promising replacement is HFC-245fa. It has met many of the requirements for a blowing agent such as zero ozone depletion potential (ODP), low toxicity, good miscibility with polyols, low vapor phase thermal conductivity, and a reasonable boiling point of 59.5°F (15.3°C). Also, because it is non-flammable, HFC-245fa will save manufacturers of household refrigerated appliances the costs associated with retrofitting their factories to safely handle flammable blowing agents.However, refrigerator manufacturers have concerns about higher product manufacturing costs. Foam insulation costs may rise. New processing equipment and procedures may need to be installed in factories for new blowing agents. Refrigerator producers want to know if their foam operation productivity and product quality will be affected. They are also concerned about staying compliant with the 2001 Energy Consumption Standards. This paper will report on work done at Bayer Corporation to address these concerns. We will show the effect of lowering the level of HFC-245fa on foam thermal conductivity, physical properties and demold characteristics. Thermal stability and pressure generation studies on HFC-245fa containing masterbatches are presented which provide insight into handling the new generation formulations. The information presented will assist household refrigerator producers in selecting the most cost-effective solution to their manufacturing concerns when replacing HCFC-141b with HFC-245fa.