Novel Surfactant Technology to Improve Polyurethane Spray Performance

Christian Eilbracht, Carsten Schiller Degussa AG Goldschmidt Polyurethane Additives

Goldschmidtstrasse 100 45127 Essen, Germany

Peter Hohl Degussa AG Goldschmidt Polyurethane Additives Goldschmidt Chemical Corp. 914 East Randolph Road

Hopewell, VA 23860

ABSTRACT Spray Polyurethane foam is a versatile construction product that can be easily applied to multiple types of surfaces with multiple types of contours. Due to this versatility, it has quickly become the product of choice for insulating new buildings and upgrading existing structures, both interior walls and existing roofs. Its ability to control both air and moisture penetration, while still providing high levels of R-value are truly unique when one considers its ease of application. The broad range of spray foam applications are rooted in the great versatility of the polyurethane chemistry. Formulations can be modified in order to achieve a desired set of final foam performance criteria. Recent changes in blowing agent technologies (HFCs - 245fa and 365mfc/227 blends, hydrocarbons and all water), polyol technologies (petroleum-based vs. vegetable based) and flame retardant technology have all had a great impact on how today’s formulators practice their art. This paper will discuss the growing role that surfactant technology plays in these “next-generation” spray systems. A series of experiments have been designed to illustrate how tailor made surfactants can improve foam quality and provide better blowing agent utilization. The resulting data clearly demonstrates how utilizing the correct surfactant molecule can provide solutions to a great range of challenges experienced by today’s formulators. Tailor made surfactants are a powerful tool in helping to meet the spray polyurethane foam manufacturers’ ongoing demand for balancing foam performance with lowest cost-in-use production. INTRODUCTION The Global market for polyurethane products is diverse and complex with a myriad of end-users. It has been growing at an average rate of over seven percent per annum for the last 15 years. The growth of polyurethane construction market segment has mainly been driven in the past 10 years by the penetration of polyurethanes into new construction fields.[1] One of the fastest growing segments is spray polyurethane foam, in particular, those systems designed for wall insulation. Spray polyurethane for wall applications has become popular for both its insulation and air barrier characteristics. Like other rigid polyurethane, the two main types of wall spray systems; 0.5 and 2.0 lb/ft3, are the result of a reaction between a resin blend, containing some combination of polyol, blowing agent (chemical and/or physical), catalyst, surfactant and methylene diphenyl diisocyanate (MDI). What makes these systems different from the more traditional types of polyurethane foam is that they are not manufactured in a controlled industrial environment such as metal panels or boardstock, but the foam is sprayed at a the construction job site. Due to the wide range in variables that can be encountered at a job site (temperature and humidity) formulators are required to develop formulations that not only produce good final foam physical properties (i.e. yield, adhesions, thermal properties…) but also that are robust enough to perform in the field under non-optimal conditions.[2,3,4] It has been shown in past work that surfactants play an integral part in the performance of polyurethane foam, both in the final performance as well as increasing a systems processing latitude. This has been found to be true for both flexible and rigid polyurethane foam applications, for both low and high density foam applications, for both fast and slow reacting systems and for all the various combinations of physical and chemical blowing agent to date.[5,6,7,8] It is in light of this historical perspective that Degussa Goldschmidt has looked to understand how significant an impact tailor made surfactants

can have on the performance of these types of wall insulation foams, both 0.5 and 2.0 pcf systems. This paper will discus results from a series of experiments that were designed to quantify the surfactant structure influence on three different wall spray formulations EXPERIMENTAL Spray Polyurethane foam can be considered unique when compared to traditional rigid foam applications. Due to its fast reactivity and distinctive processing, it became apparent that the underlining goal of this paper was to try and determine some of the fundamental structural characteristics of surfactant technology that have the greatest influence on those characteristics that are most important to the spray polyurethane foam market. Based on this premise, a series of experiments were conducted that looked to quantify the impact that surfactants can have on both 0.5 and 2.0 pcf wall spray systems. For this reason, three separate wall spray formulation were investigated. A nominal 2.0 pcf system (utilizing HFC 245fa), a 0.5 pcf system (all water) and a 0.5 pcf system (all water) that contains 25% renewable polyol source. To develop a baseline for this work, handmix studies were completed using Degussa Goldschmidt’s established stimulus-response techniques to identify surfactant structures that showed desirable foam characteristics in all three systems. [9] As expected, due to the base formulation differences all three systems identified multiple surfactant structures that warranted further investigation. Due to the basic research nature of this study and the desire to better understand the surfactant structure – foam performance relationship, all surfactants in this study were specifically designed to test specific structure – performance relationships within the parameters of each of the three spray formulations. Finally, as the systems were further investigated, a total of 21 experimental surfactants were screened on a Graco proportioning spray unit. All samples were sprayed onto a large sheet of drywall in a single pass. The resulting foams were tested for:

The Surfactants Effect on: • Improved Yield (Average Density) • Achieving dimensional stability • Maximizing K-factor value (in the case of 2.0 pcf foam) • Maximizing adhesion • Positively effecting resulting flame and smoke numbers • Ease of handling (spray pattern, edge)

Physical Testing Methods All samples were cured at least 24 hours before testing began.

Average Density Calculation The average of five core samples, at various locations, were taken, measured and recorded for each individual surfactant evaluation.

Dimensional Stability Determination Samples were aged in a humidity cabinet at 158oF and ~95% relative humidity for 72 hours.

Thermal Conductivity Determination To determine the thermal conductivity of the produced foams, three test samples were cut from the resulting sprayed panel. A Fox 300 Laser Comp was then used to measure the resulting thermal properties. The data shown in the tables are the average of the three samples.

Flame Spread and Smoke Generation Determination A series of burn testes were completed in a research tunnel developed and operated by the West

Development Group, located in LaGrange Ohio. This research burn tunnel is essentially a scaled down version of the Steiner Tunnel (ASTM E-84) test. The maximum flame spread and smoke index results have been demonstrated, through multiple testing, to correlate very well to E-84 results at UL.

RESULTS AND DISCUSSIONS Section 1: Surfactant Influence on 2.0 pcf Wall Spray System The intent of this experiment was to generate a “generic” formulation (see Table 1) that met the basic requirements of a commercially viable 2.0 pcf spray system using pentaflouropropane (HFC 245fa) as the main blowing agent. The spray portion of this experiment was conducted by the West Development Group. By employing expert applicators under a controlled environment, it is believed that an acceptable amount of consistency was achieved to give the following spray foam results validity (see Table 3).

As the goal of this paper was not to develop the “best in class” formulation, the results presented in Table 3 should be viewed solely in the context of the base formulation and to what extent a simple change in surfactant affected the resulting processing and final foam properties.

Table 1. System A: 2.0 pcf Wall Spray Formulation. Formulation % Process Conditions Polyester Polyol 40.0 Spray Unit Graco E-20 Mannich Based Polyether Polyol 20.0 Spray Gun Fusion Sucrose Initiated Polyether Polyol 5.0 Flame Retardants 17.0 Pressures (psi) Catalysts 4.5 A-Side 1300 - 1450 Surfactants 0.5 B-Side 1300 - 1450 Water 2.0 HFC 245fa 11.0 Temperature (oF) A-Side Hose 120 B-Side Hose 120 On reviewing the results presented in Table 3, a few very interesting effects are immediately observed. The first is a general observation. It is evident that even at relatively fast reaction rates, surfactants still significantly impact the resulting foam thermal conductivity. It had originally been theorized that, assuming reasonable foam was produced, at extremely fast gelling times the impact of a surfactant on cell nucleation and stabilization of the growing cells would be greatly marginalized. On inspection of results for samples A5 versus A1 or A8 one can see that this is not the case. One interesting aspect here is that all foams tested in this experiment, regardless of surfactant, had a high closed cell content. As mentioned earlier it is believed that the overall fast reactivity of the system is the major driver here but it was also assumed that closed cell count and K-factor would run more in parallel, i.e. high closed cell content equals the best K-factor. Under further investigation (see Table 5), it can be noted that those foams that gave good K-factor are also those, not surprisingly, that have the smallest and most uniform cell structure and not necessarily a higher closed cell content. A second important aspect worth noting is a surfactants effect of foam yield - - at least as one can relate it to average density. A simple calculation quickly reveals that a delta of ~8% can be seen between the surfactant with the lowest spray density (Surfactant A5) and that of the highest density (surfactant A1). The most surprising of all is the cumulative effect that the surfactant has on both the flame spread and smoke properties of the resulting sprayed foam. The fact that one could potentially achieve (Surfactant A4) or fail (Surfactant A3 or A5) a class 1 rating in the ASTM E84 trial with a simple surfactant change – - while all other physical properties appear to be equivalent - - clearly illustrates the significant influence that surface active compounds like surfactants have on optimizing a spray systems performance. More burn evaluations are already underway to better understand this phenomenon. Finally, the initial spray data (Tables 4 and 5) does appear to indicate that surfactant choice does influence polyurethane – substrate adhesion. Unfortunately at current time, only qualitative results can commented on.

Table 2. System A Surfactants Surfactant A1 A2 A3 A4 A5 A6 A7 A8 Cloud Point High High High High Medium Medium Low n.a. Silicone Content High Medium Medium Low High Low Low High Molecular Weight Low Medium Low Low Medium High Medium High

Table 3. System A: 2.0 pcf Wall Spray Formulation. - - Results Surfactant A1 A2 A3 A4 A5 A6 A7 A8 Reactivity (sec) Cream 2 2 2 2 2 2 2 2 End of Rise 12 12 12 11 12 12 11 13 Average Core Density (pcf) 2.03 1.99 1.98 1.97 1.88 1.92 1.90 1.96 Aged K-Factor 0.1677 0.1563 0.1563 0.1545 0.1523 0.1527 0.1543 0.1855 Open Cell Content (%) 13 14 12 14 18 12 13 11 Dimensional Stability @ < 3 < 4 < 3 < 13 < 4 < 3 < 3 < 3

72 hrs (% change) Texture Coarse Coarse Coarse Coarse Minor Minor Coarse Smooth Coarse Coarse Edge Good Orange Orange Orange Good Good Very Good

Peel Peel Peel Good

Spray Pattern Good Good Good Good Good Hard to Very Good Handle Good Max Flame Spread 42 44 42 32 42 42 44 40 Smoke Index 549 500 539 365 824 547 582 845

Table 4. System A: 2.0 pcf Wall Spray Formulation. - -Surface Texture

A4

A7A6A5

A1 A3A2

A8

A4A4

A7A7A6A6A5A5

A1A1 A3A3A2A2

A8A8

Table 4. System A: 2.0 pcf Wall Spray Formulation. - - Cell Structure

A1 A2 A3

A5 A6 A7

A4

A8

A1 A2 A3

A5 A6 A7

A4

A8

Section 2: Surfactant Influence on 0.5 pcf Wall Spray System Due to the unanticipated results found when investigating the 2.0 pcf wall spray system, it was decided to further investigate a surfactants effect on the even more unique 0.5 pcf system. As with the previously discussed 2.0 pcf spray foam system, the intent in these set of experiments was to generate a “generic” formulation (see Table 6) that met the basic requirements of a commercially viable 0.5 pcf spray system, were water was used as the sole chemical blowing agent. The spray portion of this experiment was again conducted by the West Development Group (WDG) located in LaGrange, Ohio. Once more by employing expert applicators under a controlled environment, it is believed that an acceptable amount of consistency was achieved to give the following spray foam results validity (see Table 8). As the goal of this paper was not to develop the “best in class” formulation, the results presented in Table 8 should be viewed solely in the context of the base formulation and to what extent a simple change in surfactant affected the resulting processing and final foam properties.

Table 6. System B: 0.5 pcf Wall Spray Formulation. Formulation % Process Conditions Polyester Polyol 25.0 Spray Unit Graco E-20 Mannich Based Polyether Polyol 10.0 Spray Gun Fusion Sucrose Initiated Polyether Polyol 5.0 Flame Retardants 30.0 Pressures (psi) Catalysts 8.5 A-Side 1450 - 1550 Surfactants 2.5 B-Side 1450 - 1550 Water 19.0 Temperature (oF) A-Side Hose 135 B-Side Hose 135 Results found in tables 8, 9 and 10 clearly highlight those surfactants that achieve acceptable yield (Surfactants B1, B4 and B5) versus those that do not perform well (Surfactants B2, B3 and B6). But of equal importance, from the stance of the developer, is that two other results, or process performance, seem to go hand-in-hand with achieving that targeted density. They are the surface texture and spray pattern. It is important to note that when reviewing Table 8 along with the images in Table 9 and Table 10, it becomes very apparent that, because by the nature of being all water blown and forced to gel in a very short period of time, these systems are under the regime of strong chemical and physical stress. Stressed to remain compatible, stressed to expand under such a severe catalytic environment and stressed to be applied by spraying. All these conditions can be to a great extent managed by employing a surface active component, i.e. the surfactant, that aids in the emulsification of incompatible raw materials and that can stabilize the rapidly expanding polymer cell structure.

Table 7. System B Surfactants

Surfactant B1 B2 B3 B4 B5 B6 Cloud Point Medium Medium High Low n.a. Low Silicone Content Low High Medium High n.a. Low Molecular Weight High Medium High High High High

Table 9. System B: 0.5 pcf Wall Spray Formulation - - Results Surfactant B1 B2 B3 B4 B5 B6 Reactivity (sec) Cream 4 4 4 5 4 4 End of Rise 13 13 13 13 13 11 Average Core Density (pcf) 0.69 1.49 1.17 0.70 0.56 1.16 Open Cell Content (%) 96 93 96 94 94 90 Dimensional Stability @ < 5 < 4 < 5 < 5 < 3 < 3 72 hrs (% change) Texture Minor Popcorn Large Minor Excellent Large Popcorn Popcorn Irregularities Popcorn Edge Good Blistering Good Excellent Good Heavy

Spray Pattern Excellent Good Good Excellent Excellent Good Max Flame Spread 42 42 36 42 42 36 Smoke Index 517 434 588 620 484 557

Table 10. System B: 0.5 pcf Wall Spray Formulation - - Surface Texture

B3

B5B4

B1 B2

B6

B3B3

B5B5B4B4

B1B1 B2B2

B6B6

Table 11. System B: 0.5 pcf Wall Spray Formulation - - Cell Structure

B3

B5B4

B1 B2

B6

B3

B5B4

B1 B2

B6

Section 3: Surfactant Influence on 0.5 pcf Wall Spray System – Employing a Renewable Polyol In order to better understand a surfactants influence on “next generation” wall spray formulations it was necessary to investigate renewable polyol technologies. Due to the increased interest in renewable polyol resources in 0.5 pcf spray systems it was decided to again target a commercially acceptable 0.5 pcf system that would replaced 25% of its polyol with that of a renewable source. As with the previously discussed 0.5 pcf spray foam system, the intent in these set of experiments was to create a formulation (see Table 11) that met the basic requirements of a commercially viable 0.5 pcf spray system, were water was used as the sole chemical blowing agent. The spray portion of this experiment was again conducted by the West Development Group (WDG) located in LaGrange, Ohio. Once more by employing expert applicators under a controlled environment, it is believed that an acceptable amount of consistency was achieved to give the following spray foam results validity (see Table 13).

As stated previously, the goal of this paper was not to develop the “best in class” formulation, the results presented in Table 13, 14 and 15 should be viewed solely in the context of the base formulation and to what extent a simple change in surfactant affected the resulting processing and final foam properties.

Table 12. System C: 0.5 pcf Wall Spray Formulation with Renewable Polyol Technology Formulation % Process Conditions Renewable-type Polyol 25.0 Polyester Polyol 7.5 Spray Unit Graco E-20 Mannich Based Polyether Polyol 7.0 Spray Gun Fusion Flame Retardants 30.0 Pressures (psi) Catalysts 8.5 A-Side 1450 - 1550 Surfactants 3.0 B-Side 1450 - 1550 Water 19.0 Temperature (oF) A-Side Hose 135 B-Side Hose 135 A review of the results from Tables 13, 14 and 15 reveal that, similar to what was observed when reviewing the data from the more traditional 0.5 pcf system (Formulation B), surfactants do indeed play a major role in the foam performance. In particularly, foam yield and the surface texture of the resulting foam are areas that one can see macro changes in performance with just small changes in surfactant structures. Reviewing the data more thoroughly, Table 13 clearly identifies that only four of the seven surfactants achieve even remotely acceptable polymer yield (Surfactants C1, C2, C4 and C7). And unlike the previous 0.5 pcf formulation, those surfactants that performed poorly (C3 and C5) performed very poorly. That is they produced foams that were showed significant signs of localized cell and foam collapse. At the time of this paper it is not understood if the use of a renewable polyol was the major factor in causing this failure or just one part of the puzzle. Finally, one further observation should be commented on here. It appears that Formulation 3 is much more sensitive, with respect to surfactant choice, in terms of smoke index. The values, ranging from a low of 548 to a high of 1159, produce a delta much greater than seen with either of the two systems (Formulation A and B) tested previously. One would naturally assume that by reviewing the flame spread and chare results would indicate that some foam samples burned hotter and longer than others thus producing a reasonable correlation between flame spread and smoke generation. Unfortunately this does not appear to be true in this formulation. Further investigations are planned to better understand this phenomenon.

Table 13. System C: 0.5 pcf Wall Spray Formulation with Renewable Polyol Technology - - Results Surfactant B1 B2 B3 B4 B5 B6 B7 Reactivity (sec) Cream 4 4 4 4 4 3 4 End of Rise 10 9 8 9 17 9 9 Average Core Density (pcf) 0.67 0.60 2.27 0.64 1.75 0.97 0.78 Open Cell Content (%) 94 97 88 98 94 94 97 Dimensional Stability @ < 4 < 4 < 1 < 5 < 2 < 4 < 5 72 hrs (% change) Texture Popcorn Popcorn Minor Excellent Good Heavy Good I rregularities Popcorn Edge Good Good Poor Excellent Poor Heavy Good

Yield Yield Popcorn

Spray Pattern Good Good Good Good Good Good Good Max Flame Spread 42 40 46 40 54 36 44 Smoke Index 1159 654 964 548 758 874 653

Table 14. System C: 0.5 pcf Wall Spray Formulation with Renewable Polyol Technology - - Surface Texture

C1 C2 C3

C4 C5 C6 C7

C1 C2 C3

C4 C5 C6 C7

Table 15. System C: 0.5 pcf Wall Spray Formulation with Renewable Polyol Technology - - Cell Structure

C1 C2 C3

C4 C5 C6 C7

C1 C2 C3

C4 C5 C6 C7

CONCLUSION

The original premise of this paper was to determine to what extent, if any, surfactants have on the performance of spray formulations. Through a series of formulations, it is clear that surfactants do play a major role in optimizing formulations. In the 2.0 pcf wall system, the major impact was both K-factor and burn properties. The significance of surfactant on flame spread and smoke generation is very amazing when one considers that only ~0.25% of surfactant could have such an impact. Summarizing the results from the 0.5 pcf systems also is quit revealing. It appears that surfactant technology has even a greater influence on these types of stressed system, in particular on foam yield. It also has become evident that one surfactant structure does not work for all 0.5 pcf systems, and that tailored solutions are the key to successfully produce the desired product. Finally, as this market is expected to continue to grow, as more stringent legislation will come into effect both in the European Union and the United States regarding building efficiency, formulators will be pressed more and more to achieve improved foam quality and increase the process window for the contractor. In light of these technical challenges, it will become even more critical for today’s formulators to optimize their spray foam systems. Consequently, it is clear through this work that the use of a tailored surfactant, specifically designed to optimize the chemical and physical environment of an individual spray system, will play an integral part in meeting the needs of tomorrows spray polyurethane foam formulations. REFERENCES

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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 2001. He is currently the global technical director of this polyurethane Business Line within Degussa. 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 2003. He changed to the University of Essen and continued his research activities in the department of Inorganic Chemistry. Since the beginning of 2005 he joined Degussa – Goldschmidt Polyurethane Additives and is currently responsible for development of additives for rigid foam applications. Peter Hohl Mr. Hohl received a BS in Chemistry from Gettysburg College and a MS in Polymer Science and Engineering from Lehigh University. He joined Air Products and Chemicals in 1993 and gained invaluable experience working in the field of polyurethane additives development. In 2002, he joined Degussa – Goldschmidt Polyurethane Additives and is currently the North American group leader supporting rigid foam applications.