Update on the Development of HFC-245fa as a Liquid HFC Blowing Agent

Abstract

Because of continuing environmental concerns about ozone depletion, regulatory mandates have been established that require the phaseout of compounds with any potential to deplete the ozone layer, including HCFC-141b. These regulations vary from country to country, but in the U.S., for example, HCFC-141b will be phased out in less than a decade. Although there are several potential options for replacement blowing agents, many applications will continue to require a liquid, non-flammable blowing agent designed to produce foams with low thermal conductivity using traditional processing techniques. The most promising class of materials to fill this need are liquid HFCs. AlliedSignal is committed to supplying a liquid HFC blowing agent to the foam industry.

At the 1994 Polyurethane World Congress, AlliedSignal announced that HFC-245fa (1,1,1,3,3-pentafluoropropane) was our primary candidate for a liquid HFC "third generation" blowing agent to replace HCFC-141b. This molecule was selected after a rigorous screening process in which several hundred candidates were ranked using physical properties, flammability characteristics, performance as a blowing agent, economics, environmental acceptability, and anticipated toxicity as selection criteria. HFC-245fa was found to offer the optimum combination of these attributes. In order to fully qualify this or any other material as a foam blowing agent, however, much more extensive work is required in all these areas. Additionally, customer validation and feedback is critical at every step in the process to ensure commercial viability and ultimate acceptance in the rigid foam market. This paper provides an update on the continuing HFC-245fa development program being conducted by AlliedSignal.

The physical, environmental, and flammability properties of HFC-245fa are reviewed. Of particular note is that the flammability of HFC-245fa has been extensively tested by several ASTM test methods and the product's non-flammability has been confirmed.

An update of the toxicity testing program for HFC-245fa is given. Results to date are very encouraging. The acute testing program is nearly complete and the results suggest that this material has a very low order of acute toxicity. This acute testing, however, does not provide a guarantee of success in full-scale toxicity tests. Full scale toxicity testing of HFC-245fa in several repeated dose studies is scheduled to begin soon.

An important property of any blowing agent is its stability, both thermal and chemical. HFC-245fa has previously been shown to exhibit excellent thermal stability up to 200°C neat and in the presence of water, aluminum, and/or stainless steel [1]. Further testing has been conducted to determine the thermal stability of HFC-245fa in the presence of cold rolled steel under a variety of conditions. HFC-245fa continues to show excellent thermal stability characteristics under a variety of conditions.

Three aspects of chemical stability are discussed. The first is the stability of the blowing agent in the presence of other common polyurethane foam raw materials and blends. Related to this is the stability of formulated "B" components after extended storage periods as measured by changes in system reactivity over time. The third is the stability of the blowing agent during the foaming reaction as determined by measuring levels of decomposition products, if any, in the foam's cells. The results of our preliminary investigations in these three areas are very encouraging.

A major difference between HFC-245fa and HCFC-141b is their boiling points, 59°F for HFC-245fa vs 89°F for HCFC-141b. The implications of the lower boiling point and correspondingly higher vapor pressure of HFC-245fa vs HCFC-141b in two important areas, storage/handling and foam properties have been previously discussed [1]. Although the higher vapor pressure of HFC-245fa may require some small modifications to the way the material is handled, the impact of this lower boiling point on low temperature dimensional stability and thermal conductivity appears to be very positive.

The acceptability of any blowing agent candidate will ultimately be based on performance. The results of both internal and customer evaluations involving machine and hand mix studies in a variety of formulations are presented. The viability of HFC-245fa as a foam blowing agent has been demonstrated. Work has begun to optimize both formulations and processing conditions to achieve optimum performance from HFC-245fa. It is anticipated that these data will provide a starting point from which foam formulators can begin their proprietary formulation development activities. In addition to producing foams with k-factors approaching those of HCFC-141b blown foams, our evaluations to date indicate that the intermediate boiling point of HFC-245fa (lower than a traditional liquid blowing agent but higher than a true gaseous blowing agent) results in foams that have the excellent uniformity and physical properties of traditional pour foams, but that also have the isotropic cell structure and excellent flow characteristics most often associated with froth foams. Results of an AHAM sponsored trial which evaluated the performance of HFC-245fa blown foam in a refrigerator cabinet are presented. The results are very positive. Foam processing was judged to be excellent and refrigerator energy consumption was nearly as good as that of refrigerator cabinets filled with HCFC-141b blown foams.

Data are provided on the k-factor aging characteristics of HFC-245fa blown appliance and boardstock foams. Thermal conductivity of HFC-245fa blown foams as a function of mean temperature is also discussed.

The paper concludes with a discussion of AlliedSignal's plans for the continuing development and commercialization of HFC-245fa as a blowing agent for rigid polyurethane and polyisocyanurate foams.