Optimizing Surfactant Technology for Blends of Blowing Agents in Next Generation Appliance Formulations

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1 Optimizing Surfactant Technology for Blends of Blowing Agents in Next Generation Appliance Formulations Robert Tauchen Dr. Christian Eilbracht, Comfort and Insulation Dr. Carsten Schiller Evonik Goldschmidt Corporation Comfort and Insulation 914 East Randolph Road Evonik Industries Hopewell, VA23860 Goldschmidtstrasse Essen, Germany ABSTRACT The impending energy and environmental regulations for refrigerators have led the appliance industry to examine improvements in mechanical components and polyurethane foam. Specifically the appliance polyurethane industry has investigated blowing agents with improved thermal gas conductivity compared to 245 fa or cyclopentane. These newer technologies also have lower global warming potential than standard HCFC or HFC blowing agents. Therefore, the industry and manufacturers may look to balance their cost/performance position through blends of high performance and cost effective blowing agents. The mixture of blowing agents presents a myriad of processing and formulation challenges due to differences in molecular weight, resin blend solubility, and vapor pressure. While changes in catalysts and polyols will be needed for proper formulations, improvements in the surfactant technology will be vital to completely alleviate processing challenges and realize the full believed benefit associated with blended blowing agents. In this paper, Evonik Industries investigates the essential surfactant characteristics to achieve optimum performance for blends of different blowing agents. Furthermore, Evonik Industries determine if the utilization of tailored surfactant technology allows for reduction in other blowing agents. INTRODUCTION With the recent need for improved insulation values to meet the demanding change in energy codes and the introduction of 4 th generation blowing agents, polyurethane appliance formulations continue to be more complex. This complexity has been further augmented by the potential to blend multiple blowing agents. The increased level of complexity puts extra stress on the system and surfactant leading to the need for research and new technology in this arena. We believe the greatest anticipated challenge for a surfactant in a co-blown formulation is the difference in boiling points between a 4 th generation blowing agent and cyclopentane. For well-established blowing agents such as 245 fa and cyclopentane, surfactant trends are well understood and industry workhorses have been established. However, with the future of blowing agents undetermined, and the need to understand proper surfactants for newer technology the first stages of development must be initiated to adapt surfactant technology to a dynamic market. 1

2 In order to develop a fundamental understanding of surfactant technology for the numerous blend potentials of different blowing agents the primary question to answer would be: does a coblown formulation require the surfactant characteristics of lower blowing agent technology, the characteristics of a liquid blowing agent, or do they fit into a whole new category of surfactant technology? EXPIERMENTAL Formulations For the initial development of surfactant structures for co-blown formulations, a simple 50:50 blend of cyclopentane and 4 th generation blowing agent by weight was selected. In addition, the best overall surfactant candidate from the co-blown analysis was compared to B 8462, a standard rigid surfactant, in an all cyclopentane blown formulation and an all 4 th generation blown formulation. The table below shows the formulations used: Table 1: Formulation Ingredient Weight % Co-blown Weight % Cyclopentane Weight % 4 th Generation Blowing agent Polyol Blend Surfactant Catalyst Package Water Cyclopentane th Generation Blowing Agent A/B Ratio This formulation targeted a gel time of seconds a tack free time of seconds. Structures A select number of standard Evonik surfactants were tested along with experimental candidates theoretically designed to balance the surfactant requirements for a high boiling CP (120 F) and a much lower boiling 4 th generation blowing agent (< 70 F). Typically, foams blown with cyclopentane require more emulsifying and stabilizing surfactants that better support foam formation associated with the higher boiling cyclopentane. These surfactants are typically higher molecular weight and have more emulsifying polyether pendants. On the other hand, surfactants for lower boiling blowing agents tend to be lower in molecular weight and higher in silicone content to better nucleate and encapsulate lower boiling blowing agents. To understand the trends needed for a blend of technologies a variety of surfactants were selected. In addition to 3 standard surfactant structures, a set of experimental candidates were designed to address the needs of a combination of high and low boiling blowing agents. To better classify the surfactant structures, they are compared by the nucleation potential of the silicone backbone and the emulsification capabilities of the polyether pendants. The nucleation 2

3 potential of the silicone backbone is determined by the number of organic modification per molecule. See Tables 2 and 3 below: Table 3: Degree of Silicone Backbone modification The polyether emulsification ranking is based on the molecular weight and number of moles of ethylene oxide in the polyether pendant. Meaning that a +++ generally could have a larger molecular weight, larger content of ethylene oxide, or both. Table 2: Surfactants Characterizations Surfactant B 8462 B 8465 B 8492 Experimental Candidate 1 Experimental Candidate 2 Experimental Candidate 3 Experimental Candidate 4 Experimental Candidate 5 Description Standard Evonik Rigid Surfactant Evonik Rigid Surfactant for high solubility CP formulations and gaseous blowing agents High Nucleation Surfactant for 245 fa formulations Degree of Silicone Backbone modification Polyether Emulsification High Pressure Machine Foaming All foams were made in Evonik Industries' Hopewell Virginia lab, using a Cannon model A-40 high pressure machine. In this machine, the polyol blend, catalyst, water and blowing agent were all added to the resin tank. The surfactant was added via 3 rd stream to the polyol blend before impingement mixing with the isocyanate. The total machine throughput was 40 lb/min, and both A and B chemicals were maintained at 70 F. 3

4 It is important to note that 3 rd stream addition of surfactants generally lowers the overall performance of the system. Generally using this method, min fill densities are slightly higher and insulation values are slightly poorer. However, relative trends generally translate very well. The foams were poured into a standard Brett mold (200 cm x 20 cm x 5 cm) heated to 120 F and orientated vertically. The material was injected near the bottom of flow and allowed to flow vertically. After a min fill density was determined for each surfactant, the samples were overpacked to 10% to for physical property testing. For each surfactant, 3 min fill panels were made for flow testing, 3-10% overpack foams were made for physical properties, and 1 10% overpack was saved for foam appearance. Physical Property Testing For physical property testing the Brett mold was divided into 9 different sections each 21 cm long. See figure 1 below: The very top 11 cm of the Brett mold is discarded. Figure 1: Brett Mold Diagram Two metrics were used to compare flow between surfactants. First, the min fill density (MFD) was investigated for overall flow performance. Second, a flow factor was determined by the formula below Flow Factor = MFD/Free Rise Core Density For each surfactant candidate, the following physical properties were measured: initial k-factor at 35 F mean temperature and 75 F mean temperature from sections 3 (3 samples per surfactant) and 7 (3 samples per surfactant) of the Brett Mold shown in figure 1. Core density was measured from sections 3 and 7, and compressive strengths were measured from section 4 and 8. Note: Reactivity and free rise core density were determined from large cup foams. Foam Appearance: The 10% overpack foams were evaluated for visual quality including top surface appearance, bottom surface appearance, and internal foam cell structure. The internal cell structure was also used to judge internal voids that could contribute to energy loss. 4

RESULTS AND DISCUSSION Solubility and B-side shelf life stability: Surfactant solubility was tested in all 3 formulations to determine if reduced cyclopentane content allowed for the use of higher

Table 4: Surfactant Solubility Surfactant Cyclopentane 4 th Gen/CP 4 th Gen B 8462 Clear Clear Clear B 8465 Clear Clear Clear B 8492 Hazy - Separation Hazy - Separation Hazy - Separation EC - 1 Clear

5 RESULTS AND DISCUSSION Solubility and B-side shelf life stability: Surfactant solubility was tested in all 3 formulations to determine if reduced cyclopentane content allowed for the use of higher silicone content surfactants (see table 4). Table 4: Surfactant Solubility Surfactant Cyclopentane 4 th Gen/CP 4 th Gen B 8462 Clear Clear Clear B 8465 Clear Clear Clear B 8492 Hazy - Separation Hazy - Separation Hazy - Separation EC - 1 Clear Clear Clear EC - 2 Clear Clear Clear EC - 3 Clear Clear Clear EC - 4 Clear Clear Clear EC - 5 Hazy Hazy Hazy This formulation appears to have excellent solubility. Only, the very high silicone products resulted in haziness or separation. This must be monitored carefully for each formulation in order to ensure no separation. Due to the instability of the 4 th generation blowing agents, heat aging of the fully formulated B- side was also performed for each of the surfactant candidates. The B-side blends were tested at 122 F for 1 week and 2 weeks and the foam appearance was checked afterwards via hand- mix cup foams. The results are summarized in table 5. Table 5: Reactivity Stability 1 Week Week 2 Sample Images B 8462 Stable Foam Stable Foam B 8465 Stable Foam Stable Foam B 8492 Coarse Foam Coarse Foam B weeks 122 F EC - 1 Stable Foam Stable Foam EC - 2 Stable Foam Coarse Foam EC - 3 Stable Foam Stable Foam EC - 4 Stable Foam Stable Foam EC - 5 Stable Foam Stable Foam Experimental Candidate 4 2 weeks 122 F 5

6 For 2 weeks at 122 F, most surfactant candidates resulted in stable regular foam cell structure. This formulation does not appear to be sensitive to reactivity stability; however, this is an important consideration for all formulations containing 4 th generation blowing agents. Insulation value Insulation value performance of a blend of blowing agents is a key performance metric. Table 6 below shows the difference in insulation value at a mean temperature of 35 F and 75 F. The k- factor distribution along the brett is shown in figure 2 (35 F) and figure 3 (75 F). Table 6: Average k-factor Data for Section 3 and Section 7 Average k-factor 35 F Average k-factor 75 F B B B EC EC EC EC EC

7 Figure 2: k-factor Data Mean Temperature 35 F Figure 3: k-factor Data Mean Temperature 75 F 7

8 From the k-factor data, experimental candidate 4 provides the best insulation values at both 35 F and 75. It is important to note, that the k-factor performance for this formulation did not simply center on the nucleation potential of the surfactant, as B 8492 and experimental candidate 5 had the highest silicone content per molecule of the surfactants tested, but resulted in generally poorer insulation values. This indicates that the improved stabilization and emulsification of experimental candidate 4 significantly contributed to the improved insulation values. Flow Testing While the insulation value of the foam is the most important foam physical property, flow must also be considered in any surfactant evaluation (see table 7). Table 7: Flow Characteristics FRD Core (lb/ft^3) Min Fill Density (lb/ft^3) Flow Factor B B B EC EC EC EC EC From the foam flow evaluation, experimental candidate 1 appears to provide enhanced flow compared to the standard molecules. In addition, the two highest nucleation products, B 8492 and experimental candidate 5 resulted in the poorest flow, which is further indication that the foam requires a certain level of emulsification associated with cyclopentane. Compressive Strengths Table 8: Compressive Strengths Section 4 Compressive Str (psi) Core Density (lb/ft^3) Section 8 Compressive Str (psi) Core Density (lb/ft^3) B B B EC EC EC EC EC As compressive strengths are an important consideration for all formulations, the compressive strength for each surfactant was measured near the start of flow (Section 4) and towards the end 8

of flow (Section 8). Experimental candidate 4 provides the best compressive strengths of all the molecules tested which may allow for lower density and potentially higher performing foam formulation.

Specifically, the primary challenge for the surfactant would be balancing the need to reduce potential blowing agent eruption caused by the lower boiling point 4 th generation blowing agent, and the

9 of flow (Section 8). Experimental candidate 4 provides the best compressive strengths of all the molecules tested which may allow for lower density and potentially higher performing foam formulation. Foam Appearance As mentioned before, one of the anticipated challenges of handling two blowing agents with different boiling points is maintaining excellent foam aesthetics. Specifically, the primary challenge for the surfactant would be balancing the need to reduce potential blowing agent eruption caused by the lower boiling point 4 th generation blowing agent, and the need for enhanced stabilization and emulsification of the higher boiling cyclopentane. The results of the visual analysis are displayed in table 9 below, and pictures are provided in table 10. Table 9: Foam Aesthetics Top Surface Quality Bottom Surface Internal Cell Quality Structure/Voids B B B EC EC EC EC EC Table 10: Foam Cell Structure Quality Cell Structure Quality B 8462 Cell Structure Quality EC 4 9

Cell Structure Quality B 8492 Bottom Surface Quality B 8462/EC-4 For all the surfactants tested, the surface quality of the foams was generally good.

10 Cell Structure Quality B 8492 Bottom Surface Quality B 8462/EC-4 For all the surfactants tested, the surface quality of the foams was generally good. However, when examining the internal cell structure it appears that this formulation requires the enhanced stability and emulsification seen with typical cyclopentane surfactants as the standard surfactant and the high nucleating B 8492 lead to a larger number of internal voids. Theoretically, this indicates that even at 8.6% of the formulation, which is significantly below the industry standard of 12 to 14%, cyclopentane may begin to dominate this formulation. While these internal voids may not be seen in k-factor testing, they will affect the overall energy performance and potentially foam stability. 100% 4 th Generation and 100% Cyclopentane Testing With regards to every performance metric except flow, experimental candidate 4 appears to offer the best performance in this formulation. To further understand the performance of this theoretically designed product and standard surfactant technology, B 8462 and experimental candidate 4 were both screened in a 100% 4 th generation blown formulation and a 100% cyclopentane blown formulation. This would further help characterize the formulation as cyclopentane dominated or 4 th generation blowing agent dominated. Finally, Evonik Industries wanted to determine if the new surfactant structure was interesting for single blowing agent formulations as well. Insulation value comparison Table 11 and figure 4 compare B 8462 and experimental candidate 4 in a 100% 4 th generation blown formulation, the 50:50 by weight blown formulation, and the 100% cyclopentane blown formulation. 10

11 Table 11: k-factor Analysis at Different Blowing Agent Levels Surfactant/ Temperature 100 % 4th Generation 50:50 4th Generation Cyclopentane Differential (Blend 4 th Gen) 100% Cyclopentane Differential (CP Blend) B F EC F B F EC F Figure 4: k-factor Analysis at Different Blowing Agent Levels The results above demonstrate that experimental candidate 4 offers no improvement in this 100 % blown 4 th generation formulation but offers improvement in the 100% cyclopentane blown formulation. From this, it could be further speculated that this blended formulation behaves most similarly to a cyclopentane blown formulation. This cyclopentane like performance could be connected to the difference in molecular weight between the 4 th generation blowing agent and cyclopentane. Another interesting result was that replacing 3.9% cyclopentane with 8.6% 4 th generation blowing agent offered a k-factor improvement of at 35 F and at75 F. However, by further replacing the remaining 8.6% cyclopentane with 17.4 % 4 th generation blowing agent an additional improvement of only at 35 F and at 75 is achievable. It appears that there is a significant impact of adding even a small percentage of 4 th generation blowing agent. 11

12 Other Physical Properties Table 12: Physical Property Analysis at Different Blowing Agent Levels Surfactant/ Core Compressive Compressive MFD Flow Blowing FRD Str Section 4 Str Section 8 (lb/ft^3) Factor agent (lb/ft^3) (psi) (psi) B th Generation EC - 4 4th Generation Core Density (lb/ft^3) Core Density (lb/ft^3) B 8462 CP EC - 4 CP In the physical property testing it appears that B 8462 and experimental candidate 4 offer similar physical properties in the 100% 4 th generation blown formulation. However, experimental candidate 4 offers improved physical properties in the cyclopentane blown formulation. Foam Appearance Table 13: Foam Appearance at Different Blowing Agent Levels Surface Bottom Surfactant Cell Structure/Void Quality Quality B th Generation EC - 4 4th Generation B 8462 CP EC - 4 CP Similar to the insulation values and physical property testing, experimental candidate 4 offered improved foam aesthetics in the 100% cyclopentane blown formulation but not in the 100% 4 th generation blown formulation. CONCLUSIONS From this research, Evonik Industries was able to draw two conclusions and take the first steps to understanding and optimizing surfactant technology for appliance formulations with blended blowing agent technology. First, blends of blowing agents do benefit from tailored surfactant technology to address the intricate needs of this technology package. Second, blended blowing agent technology offers another tool to formulators to balance formulation and foam performance. While the surfactant development in this paper was performed on a generic appliance formulation, it is evident to Evonik that blends of 4 th generation blowing agents and cyclopentane do benefit from surfactant modifications. For this specific formulation, it appears that surfactant technology benefits from a balanced silicone backbone and emulsifying polyethers in order to stabilize plus retain the less compatible cyclopentane and encapsulate the 12

13 lower boiling 4 th generation blowing agent. The improvements in k-factors seen with this surfactant technology allow for appliance formulators to continue improving energy numbers to meet the demands of new regulations. Finally, if insulation values are already met by the standard surfactant candidates, this surfactant may allow the formulator to adjust the blowing agent ratio to fit the formulator s needs. As discussed in the results section the improved performance of experimental candidate 4 was seen in the blend blown formulation and in the 100% blown cyclopentane formulation, but not in the 100% 4 th generation blown formulation. This demonstrates that the formulation performs more like a cyclopentane blown formulation. However, if the blend ratio is increased to be closer to a 100% 4 th generation blown form, surfactant properties will have to be further optimized to address the higher levels of 4 th generation blowing agents. Finally, the development could be continued to attempt to combine the improved flow of experimental candidate 1 and the better k- factor and compressive strengths of experimental candidate 4. REFERNCES: 1. Schilling S. Comparison of Gaseous and Liquid Low-GWP Blowing Agents with HFC 134a and HFC 245fa in Rigid Polyurethane Insulating Foams, Proceedings of the CPI Expo Abbas L.; Bonnet P.; Costa J.; Chen B.; A Continued Investigation of AFA-L1, a New Low GWP Blowing Agent Proceedings of the CPI Expo Ling J.; Lu B.; Qin R.; Pan R.; Continued Evaluation of Blowing Agent Solutions in Pour-in-place Panel Applications With Less Environmental Impact Proceedings of the CPI Expo

BIOGRAPHIES Christian Eilbracht Dr. Christian Eilbracht received his Ph.D. in Chemistry with an emphasis on solid state chemistry at the University of Dortmund in 1997.

He joined the Degussa Goldschmidt PU Additive business line in 2001. As a technical director he is globally responsible for product development and technical service. Carsten Schiller Dr.

He changed to the University of Essen and continued his research activities in the department of Inorganic Chemistry.

14 BIOGRAPHIES Christian Eilbracht Dr. Christian Eilbracht received his Ph.D. in Chemistry with an emphasis on solid state chemistry at the University of Dortmund in 1997.He then worked for the Clariant Pigment and Additive Division and was in charge of the R&D activities on flame retardants for flexible polyurethane foams. He joined the Degussa Goldschmidt PU Additive business line in As a technical director he is globally responsible for product development and technical service. Carsten Schiller Dr. Carsten Schiller received his Ph.D. in Chemistry at the University of Bochum with a thesis on biomaterials for bone substitution in He changed to the University of Essen and continued his research activities in the department of Inorganic Chemistry. In early of 2005 he joined Evonik Goldschmidt and is currently responsible for development of additives for rigid foam applications. Robert Tauchen Robert Tauchen received his BS in Chemical Engineering from Virginia Tech in In June 2010, he joined the Evonik Rigid Technical Team and is responsible for technical service and development of additives for rigid foam applications in North America. 14

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AFA-L1, a Low Global Warming Potential Blowing Agent for Cold Chain Applications

AFA-L1, a Low Global Warming Potential Blowing Agent for Cold Chain Applications JOSEPH COSTA BEN CHEN LAURENT ABBAS SRI SESHADRI Arkema, Inc. 900 First Avenue King of Prussia, PA 19406 ABSTRACT The requirements