Further Development of FEA-1100: a Low GWP Foam Expansion Agent

Transcription

1 Further Development of FEA-1100: a Low GWP Foam Expansion Agent GARY LOH, JOSEPH A. CREAZZO, MARK L. ROBIN, PHD DuPont Company 711 Chestnut Run Plaza, Wilmington, DE Tel: , Fax: ; gary.loh@usa.dupont.com ABSTRACT DuPont FEA-1100 is a nonflammable, stable liquid foam expansion agent for polyurethane foams, characterized by a zero ozone depletion potential (ODP), i.e. chlorine-free, and a low global warming potential (GWP), i.e., GWP<10. DuPont FEA exhibits good compatibility with commonly employed foam processing materials and provides excellent insulation performance in foams produced from a variety of polyols. This paper will discuss the results of further development of DuPont FEA-1100, including both laboratory studies and evaluations in commercial equipment and processes. INTRODUCTION Over the years, plastic foam insulation has evolved into one of the most efficient insulations in a number of industrial and consumer applications. Thermoset and thermoplastic insulation foams contribute to energy efficiency in applications such as commercial and residential construction, roofing, refrigerated transportation and distribution, heating and ventilation systems, home appliances, packaging, and so on. Integral to their high insulating performance are the gases used to foam the plastic and which remain trapped in the foam cells. Thirty years ago those gases were chlorofluorocarbons (CFCs). When replacement of the CFCs became necessary to address ozone depletion concerns, it kicked off a series of transitions that would not have been predicted at the time. Now, with current concerns about global climate change, a fourth generation of fluorinated gases is being developed for use in manufacturing these insulation foams. Besides fluorinated gases, other types of foam expansion agents (e.g., hydrocarbons, methyl formate, CO 2 ) came into use throughout these transitions, but there are applications where the safety and insulating value of the fluorinated gases continue to make them a more desirable option. With climate change concerns, the focus for the fourth generation of fluorinated foam expansion agents is minimal greenhouse gas impact while maintaining the historically desired attributes of safety and insulating performance. DEVELOPMENT OF HYDROFLUORO-OLEFIN (HFO) FOAM EXPANSION AGENTS With each subsequent generation, the industry has been challenged to continually improve the environmental performance of their foam expansion agents without sacrificing insulation properties and performance. The CFCs were relatively simple molecules, easy to make, easy to use, and provided excellent insulating performance. As the demands for reduced environmental impact grew, the foam expansion agents development progression took the industry from the relatively simple CFCs, to the larger, more complicated hydrochlorofluorocarbon (HCFC) and hydrofluorocarbon (HFC) molecules, and now to the hydrofluoro-olefin (HFO) family (see Figure 1). Over the past several years, there has been much discussion about this new HFO family as HCFC and HFC replacements in a number of industries, including their use as foam expansion agents. So, a brief background discussion on the nature of these molecules and how they are selected may be of value. Considering this paper addresses thermoset polyurethane foams, our background summary will focus on choices for that use. To reduce atmospheric lifetime, and consequently global warming potential, the HFO family is attractive because these molecules have an unsaturated double bond. And while this does reduce atmospheric lifetime, the potentially reactive double bond can cause problems with toxicity or stability. In fact, olefins tend to be a family of compounds that are recognized for such issues. The trick is to sort through what are literally hundreds of options to find the ones that still possess all the desired features of an excellent foam expansion agent. The work is further complicated by the fact that, as these molecules become

2 more complex, so do the processes for producing them. There have been quite a number of molecules studied, that for one reason or another, ended up not meeting the critical needs of the industry, but this is the nature of the current research with the fluoro-olefins. To cull potential candidates from such a large group of compounds requires establishing some filtering criteria. Consistent with the technology, the basic criteria set for selecting possible polyurethane foam expansion agents is as follows: Zero ODP Very low GWP High boiling point (liquid at room temperature) Low molecular weight Acceptable toxicity Nonflammable To help organize possible candidate molecules, we can group HFOs by the number of carbons in the molecule. Recall that in the fluorocarbon generic numbering convention, the first of the four digits from the left indicates the number of double bonds, in this case, one. The second digit from the left is one less than the number of carbons, so that a 1200 series molecule has one double bond and three carbons, a 1300 series molecule has one double bond and four carbons, a 1400 series molecule has one double bond and five carbons, and so on. Thus each higher series represents compounds of increasing molecular weight, an important consideration for a foam expansion agent. Two-carbon fluoro-olefins, like fluoroethylenes or chlorofluoroethylenes, bring stability and toxicity issues, minimizing the number of options. Moving to a higher number of carbons reduces these problems and affords some attractive possibilities. However, recognizing that molecular weight is an important criterion, moving too far up the series is not desirable. To illustrate, Table 1 shows a handful of the candidates evaluated as low-gwp replacements for HCFCs and HFCs. Some chlorinated candidates were considered, but were not selected because our belief is that even short-lived substances with ozone depleting potential would not be acceptable [1]. For the desired foam expansion agent boiling point, the trend tends to be toward the higher series. Once candidates were selected using the basic criteria above, potential process routes and cost were considered in prioritizing toxicity testing. Toxicity tests are continued until results are judged acceptable or a candidate fails, in which case, testing begins with the next one on the list. This is the process which identified Formacel FEA-1100 (HFO-1336mzz-Z, by the generic numbering convention) as one of the best balanced options in terms of environmental, toxicological, physical, processing, and insulating properties. HFO-1336mzz-Z meets the environmental criteria, its physical and performance properties are well matched and, in some cases better, than current foam expansion agents. Toxicity thus far has been judged acceptable, and it is nonflammable.

3 Figure 1 Development Progress for Fluorinated Foam Expansion Agents Table 1. Foam Expansion Agent Property Comparison

4 PREVIOUS APPLICATION STUDIES DEMONSTRATION OF INSULATION PERFORMANCE A major focus of recent research on FEA-1100 was the evaluation of its insulation performance compared to that of commercially available foam expansion agents (FEAs). In these studies FEA-1100 was evaluated in foam formulations containing the major types of polyols: Mannich base polyethers, sucrose-based polyethers, TDA based polyethers and aromatic polyesters. Equimolar quantities of FEA-1100 were dropped in to generic formulations without optimization to compare the relative insulation performance of FEA-1100 with commercially available FEAs (HCFCs, HFCs and hydrocarbons). All of the foams produced with FEA-1100 exhibited good cell structure and dimensional stability, and it was observed that the use of FEA-1100 provided superior initial and aged insulation performance (initial and aged R-value or k- factor) compared to HCFC-141b, HFC-245fa, HFC-365mfc, cyclopentane and isopentane [2, 3]. To verify the lab study, FEA-1100 samples were provided to several customers for larger scale testing in various applications. As in the lab, FEA was simply substituted for equal weights of HFC-245fa or HCFC-141b in existing formulations. In general, these unoptimized FEA-1100 foams showed better insulation performance with comparable dimensional stability and mechanical properties Improvements ranged from 1-2 percent in an HFC-245fa spray foam formulation to 6-7 percent in an HCFC-141b spray foam formulation. In that the equal weight substitutions were18%-29% less than equimolar substitution, the results suggest potential for further improvement in insulation performance with higher amounts of FEA FEA-1100 forms azeotropic mixtures with several currently employed FEAs. Performance testing demonstrated that foams produced with these azeotropic mixtures of FEA-1000 exhibited improved insulation performance compared to foams produced from the commercially available FEAs [2, 3]. Additional work involved the evaluation of FEA-1100 solubility and vapor pressure at 21 C and at 50 C in various polyols. FEA-1100 showed good solubility in commonly used polyols, with vapor pressures at 50 C well below the typical drum pressure rating [2, 3]. Good solubility and low vapor pressure allow higher FEA-1100 levels to be employed in formulations for superior insulation performance. Compatibility of FEA-1100 with materials used for foam processing and applications were also evaluated. FEA-1100 showed good compatibility with copper, brass, carbon steel, stainless steel and aluminum in sealed tube tests conducted at 100 C for 2 weeks. Tests with various elastomers and plastics at room temperature for 2 weeks also demonstrated good compatibility of FEA-1100 with commonly used elastomers and plastics, including ABS and HIPS which are widely used as refrigerator and freezer liners for appliance applications [2, 3]. CURRENT APPLICATION STUDIES - CUSTOMER TESTING SUPPORT Our recent work has focused on providing data for FEA-1100 customer testing. Additional FEA-1100 toxicity evaluations have been completed and the chemical stability of FEA-1100 during storage and during the foaming process was also evaluated. In addition, further investigations of FEA thermal properties and FEA efficiency of FEA-1100 were conducted. 1. Toxicity Assessment Toxicological testing performed to date indicates that FEA-1100 can be safely used in foam expansion applications: FEA is characterized by very low acute toxicity and low repeated inhalation toxicity as evidenced by the results of 90 day inhalation testing. Table 2 summarizes these toxicity assessments. Table 2. FEA-1100 Toxicological Assessments Test Results ALC and LC-50 Very low acute toxicity Skin Irritation Non-irritating Mutagencity-Ames Non-mutagenic Chromosomal Aberration No genetic material damage when tested in bacterial and mammalian cell cultures Cardiac Sensitization Favorable cardiac sensitization potential profile 28 day repeated inhalation Favorable repeated inhalation profile 90 day/developmental Favorable repeated inhalation profile consistent with 28-day test

5 2. Chemical Stability- Shelf Life Evaluation Low GWP molecules with short atmosphere lifetimes can in some cases exhibit high chemical reactivity; hence, the chemical stability of low GWP FEAs in B-side mixtures during storage requires investigation. The typical shelf-life for a B-side mixture is six months. FEA-1100 was tested in generic polyether and polyester B-side mixtures at 50 C. A polyether and polyester B-side system containing FEA-1100 was prepared and stored in aerosol containers. The aerosol containers were sealed to prevent the loss of FEA-1100 and stored in a 50 C oven for six months. The compositions of the B-side mixtures are shown in Tables 3 and 4. At regular intervals, one of the containers was removed from its storage environment and its contents analyzed for changes in appearance and acidity, and subjected to GC analysis. In addition, hand-mix foams were prepared to evaluate any changes in reaction profile (ratio of cream time and tack free time) or foam density following storage of the B-side mixtures at 50 C. Tables 5 and 6 provide a summary of the results, which demonstrate the high stability of the B-side mixtures examined. While these examples demonstrate the chemical stability of FEA-1100 in typical B-side formulations, verifying the compatibility of other B-side mixtures is advised as the B-side chemical stability can be affected by the ingredients employed in the formulation. Table 3. FEA-1100 B-Side System 1 Polyether Formulation B-side Ingredients Weight % (pbw) Polyether (TDA) 100 Silicon Type Surfactant 2.0 Amine-based Catalyst 3.0 Co-catalyst 1.0 Water 1.0 FEA Foam index 1.2 Table 4. FEA-1100 B-Side System 2 Polyester Formulation B-side Ingredients Weight% (pbw) Aromatic Polyester 100 Silicon Type Surfactant 6.2 Potassium Catalyst 2.8 Amine-based Catalyst 0.7 FEA Foam index 2.5 Table 5. Foam Reaction Profile and Density Polyether Formulation (6 Month Storage at 50 C) Days at 50 o Ratio C Cream time Tack free Foam (Tack free /Cream in Oven (seconds) (seconds) density (pcf) time)

6 Table 6. Foam Reaction Profile and Density Polyester Formulation (6 Month Storage at 50 C) Days at 50 o C in Oven Cream time (seconds) Tack free (seconds) Ratio (Tack free /Cream time) Foam density (pcf) 3. Thermal Stability: Accelerated Rate Calorimetry (ARC) During the foaming process, foam expansion agents can be exposed to elevated temperatures in the presence of formulation ingredients such as polyols, catalysts, surfactants and flame-retardants. To evaluate the thermal stability of FEA-1100 under such conditions, Accelerated Rate Calorimetry (ARC) tests were conducted at temperatures up to 100 C utilizing generic appliance and spray foam formulations (Tables 7 and 8). High levels of FEA-1100 were employed in these formulations to maximize the sensitivity of the tests. Appliance and spray foam formulations containing FEA-1100 were loaded into stainless steel bombs to approximately 90% full under 1 atmosphere of air. The bomb was then heated to 100 C using a heat-wait-search (HWS) cycle, i.e., the tests were conducted using a 10 C heat step followed by a 20 minute wait time and a 10 minute search time to identify temperature and pressure changes associated with chemical reactions or decomposition. Figures 2 and 3 show the temperature and pressure traces for the appliance and spray foam formulations during the heat-wait-search cycle. The stable temperatures and pressures observed during the wait and search period are consistent with a lack of chemical reaction. Figures 3 and 4 show the log (pressure) vs 1/T relationship for the formulations. The linear relationship indicates that there was no generation of gas from reaction. Therefore, it can be concluded that FEA-1100 is stable in these generic formulations. While these examples demonstrate the thermal stability of FEA-1100 in typical B-side formulations, verifying the stability of other B-side mixtures is advised as the B-side thermal stability can be affected by the ingredients employed in the formulation. Table 7. FEA-1100 Spray Foam Formulation for ARC Test Weight % Ingredients pbw Polyether (Mannich-base) Polyester Silicone surfactant 0.25 Additive 3.00 Flame retardant (TCPP) Tertiary amine catalyst 0.97 Potassium catalyst 0.25 Water 0.63 FEA

7 Temperature (C) Pressure (psia) Table 8. FEA-1100 Appliance Foam Formulation for ARC Test Weight% Ingredients (pbw) Polyether (sucrose) Polyether (TDA) Silicone surfactant 6.00 Tertiaty amine catalyst Tertiaty amine catalyst Co-catalyst 0.50 Water 1.70 FEA Figure 2. ARC Test for FEA-1100: Generic Spray Foam Formulation FEA-1100 in Generic Spray Foam System Temperature Pressure Time (minute)

8 Pressure (psia) Temperature (C) Pressure (psia) Figure 3- ARC Test for FEA-1100: Generic Appliance Formulation FEA-1100 in Generic Appliance System Temperature Pressure Time(minute) Figure 4- FEA-1100 Pressure vs Temperature Relationship: Appliance Formulation 10 3 Pressure vs. Temperature FEA-1100 in appliance formulation Temperature ( o C) [Plotted as -1/T]

9 Pressure (psia) Figure 5. FEA-1100 Pressure vs Temperature Relationship: Spray Foam Formulation 10 3 Pressure vs. Temperature FEA-1100 in spray foam formulation Temperature ( o C) [Plotted as -1/T] 4. Heat of Evaporation Polyurethane foam production is based on the reaction of a polyol with an isocyanate. The heat from this exothermic reaction is employed to vaporize a FEA within the developing polymer matrix, resulting in the formation of a cellular structure within the polyurethane. The heat required to vaporize a FEA is dependent upon the boiling point, liquid specific heat and latent heat of the FEA. Figures 6 and 7 compare the liquid specific heats and latent heats of FEA-1100, HCFC- 141b, HFC-245fa and cyclopentane. The total amounts of heat required to vaporize these FEAs from an initial temperature of 22 C (room temperature) are readily calculated. FEA-1100, HCFC-141b and cyclopentane are liquids at 22 C, and, therefore, vaporization of these FEAs is a two step process. In the first step, the FEA must be heated from 22 C to its boiling point; this is followed by a second step wherein the FEA, now a liquid at its boiling point, is vaporized into the gaseous state. HFC-245fa has a boiling point of 15 C and is thus dissolved in the foam system under pressure at 22 C; vaporization of HFC-245fa requires its transformation from a dissolved liquid state to a saturated vapor state at 22 C. The calculated results for the total amount of heat required to vaporize these FEAs from an initial temperature of 22 C are shown in Table 9. An analysis of Table 9 indicates that boiling point differences among these FEAs has only a small affect on the total amount of heat required for vaporization, i.e., the total amount of heat required for vaporization is primarily dependent upon the latent heat of the FEA. As a result, FEA-1100 can be used as a replacement for HCFC-141b, HFC-245fa or cyclopentane with minimum impact on reaction temperature profiles. The calculated results are in agreement with observations from FEA-1100 laboratory studies and customer testing.

10 Latent heat(btu/lb) Liquid heat capacity (Btu/lb-F) Figure 6 Liquid Heat Capacity Comparison Liquid Heat Capacity vs. Temperature Temperature ( o F) FEA-1100 HFC-245fa HCFC-141b Cylocpentane Figure 7 Latent Heat Comparison 200 Latent Heat vs. Temperature Temperature ( o F) FEA-1100 HFC-245fa HCFC-141b Cyclopentane

11 Vapor thermal conductivity (Btu/hr-ft-F) Table 9- Heat Required to Vaporize FEAs FEA-1100 HCFC- 141b HFC- 245fa Mass Basis: Boiling point ( C) Molecular Weight Cyclopentane Heat required to heat FEA from 22 C to its boiling point, (Btu/lb) Latent heat (Btu/lb) at FEA boiling point Total heat to vaporize FEA from 22 C, Btu/lb Relative heat requirement to vaporize Molar basis: Total heat to vaporize FEA from 22 C, Btu/mol 12,586 11,939 11, Relative heat requirement to vaporize FEA-1100 Vapor Thermal Conductivity Over Broader Temperature Range Figure 9 shows the vapor thermal conductivity of FEA-1100, HFC-245fa, HFCF-141b and cyclopentane from -50 F to 300 F. FEA-1100 has a low vapor thermal conductivity over a broad temperature range. FEA-1100 also shows the lowest thermal conductivity compared to the other FEAs at elevated temperatures. As a result, FEA-1100 can provide superior insulation performance over a broad range of temperatures. Figure 9. FEA Vapor Thermal Conductivity Vapor Thermal Conductivity vs Temperature FEA-1100 HFC-245fa HCFC-141b Cyclopentane Temperature ( o F) 6. Optimization of FEA Efficiency and Insulation Performance While FEA-1100 may be employed as a drop-in alternative for other liquid FEAs, optimization of formulations can provide improved insulation performance and FEA efficiency. Table 10 and Figure 10 show the impact on k- factors when changing the relative levels of FEA-1100 and water in a generic appliance formulation. In this example, reducing the FEA-1100 level from 0.21 moles to 0.14 moles while increasing the water level from 0.14 moles to 0.21 moles not only improves the k-factors at 32 F and 50 F, but also reduces the usage of FEA-1100 by 34%.

12 K-factor Table 10 Impact of FEA-1100 and Water Levels in Appliance Formulations FEA-1100 (0.21 moles) FEA-1100 (0.14 moles) FEA-1100 (0.07 moles) Ingredients pbw pbw pbw Susrose polyol) TDA Surfactant Catalyst Catalyst Co-catalyst Moles of H2O Moles of FEA Total moles of FEA-1100+H2O Isocyanate Foam index Initial foam properties Density(pcf) K-factor 35 o F K-factor 50 o F K-factor 75 o F FEA-1100 pbw change 0% -34% -67% Figure 10. FEA and Water Levels for Optimal K-factor and FEA Efficiency Effect of FEA-1100 (Generic Appliance Formulation) Moles of FEA-1100 K-factor (35F) K-factor (50F) K-factor (75F)

13 K-factor Table 11 and Figure 11 show the impact on the k-factor of varying the weight of FEA-1100 in FEA-1100/cyclopentane mixtures. In these tests, equimolar quantities of FEA-1100/cyclopentane mixtures were added to the foam formulation shown in Table 11. As seen from Figure 11, the relationship between the weight percent FEA-1100 in FEA- 1100/cyclopentane mixtures and the k-factor is not linear. As seen from Table 11 and Figure 11, the addition of cyclopentane to FEA-1100 can increase the FEA efficiency of FEA-1100: an 85/15 by weight mixture of FEA-1100 and cyclopentane provides a k factor slightly lower than that provided by pure FEA FEA-1100 can also be used by hydrocarbon users to improve the insulation performance: an 85/15 by weight mixture of FEA-1100 and cyclopentane provides a significant improvement in k-factor compared to pure cyclopentane. The relative levels of cyclopentane and FEA-1100 can be optimized for the best FEA-1100 efficiency and insulation performance, Table 11. Impact of FEA-1100 and Cyclopentane Levels 100 wt% FEA wt % FEA-1100/ 15 wt% cyclopentane 50 wt % FEA-1100/ 50 wt% cyclopentane 100 wt% cyclopentane pbw pbw pbw pbw TDA based polyol Surfactant Catalyst Co-catalyst FEA(moles) Water(moles) Isocyanate foam index Density (PCF) K-factor (Btu.in/ft2.h. o 75 o F Figure 11. FEA and Cyclopentane Levels for Optimal K-factor and FEA Efficiency Effect of FEA-1100 Level (Generic PIP Formulation) % 20% 40% 60% 80% 100% Weight% of FEA-1100 in cyclopentane

14 CONCLUSIONS FEA-1100 is a zero ODP, low GWP and non-flammable FEA. It is characterized by good compatibility and chemical stability in generic foam systems and foam processing materials. The initial drop-in customer tests reported here not only demonstrate superior insulation performance, but also demonstrate the achievement of good FEA efficiencies. Laboratory and customer test results indicate that FEA-1100 may be employed as a drop-in replacement for HFCF-141b, HFC-245fa, HFC365mfc, cyclopentane, or pentane, providing superior insulation performance at low conversion costs. REFERENCES 1. Executive Summary: Scientific Assessment of Ozone Deletion: 2006, 19 pp. World Meteorological Organization, Geneva, Switzerland, [Reprinted from Scientific Assessment of Ozone Depletion: 2006, Global Ozone Research and Monitoring Project-Report No. 50, 572 pp., World Meteorological Organization, Geneva, Switzerland, 2007.] 2. Loh, G., Creazzo J., Robin, M., Development Program Update for a low GWP Foam Expansion Agent, PU Magazine (2010), Vol. 7, No. 2 (April/May), p Loh, G., Creazzo J., Robin, M., Further Development of Low GWP Foam Expansion Agent with Improved Insulating Performance vs Commercially Available Options Today, Proceedings of 12th Blowing Agents and Foaming Process, DISCLAIMER The information set forth herein is furnished free of charge and based on technical data that DuPont believes to be reliable. It is intended for use by persons having technical skill, at their own risk. Since conditions of use are outside our control, we make no warranties, expressed or implied and assume no liability in connection with any use of this information. Nothing herein is to be taken as a license to operate under, or a recommendation to infringe any patents or patent applications.