### Zero Ozone Depleting Blowing Agents for Use in Polyurethane Based Foam Insulations

E. Blevins and J. Sharpe Martin Marietta Manned Space Systems Marshall Space FlightCenter, Alabama
A. Fine and B. Kopko Global Change Division U.S. Environmental Protection Agency



### Abstract
Due to environmental concerns, the polyurethane insulation industry is tasked with replacing CFC-l1. Any teplacewent blowing agent must meet the dual challenge ofbeing environmentally friendly, andretaining the properties that have made CFC-ll so desirable. These desirable physicalproperties include: solubilityin both the isocyanate'andpolyol components ofpolyurethane based foams, aboiling pointjust above 23°C at ambient pressure, molecular weight around 130 grams per mole, and a low thermal conductivity. The blowing agents reportedin this paperare neardrop-in replacements for CFC-ll. The two fluorinated ethers reported are soluble in polyurethane foam components; have boiling points of29 to 30°C; have molecularweights similarto thatofCFC-ll; andproduce foam 'insulations with good mechanical and thermal properties. This paperreports the physical properties ofthese ethers, and themechanical strength, flammability, and thermal conductivity ofa rigid, polyurethane based, thermally stable, cryogenic insulation foamed with these ethers. 

### Introduction
Thermal Prptection Systems (TPS) ofthe National Aernautics and SpaceAdministration (NASA) Space Shuttle's External Tank (ET) 

### include polyurethane andpolyisocyanurate foam insulations. These insulations serve to maintain cryogenic propellant quality. mainWn structural temperature limits, arid minimize the formation ofice andfrost that could potentially damage the fragile insulation ofthe space shuttle orbiter. The TPS must pass cryogenic flexure and substrateadhesion tests at -253°C, aerothermal and radiant -heating rates ofup to approximately 12 British Thermal Units per square foot per second, and thermal conductivity**tests~** 

### Currently, ET foams are blown with CFC-l1,and HCFC141b is scheduled for use in production by 1995. Realizing thatHCFC's are an interinl blowing agent, several third generationblowing agents are under evaluation foruse in ET insulations. This paperreports data onJwo fluorinated ethers under investigation as blowing agents for thermal protection systems ofthe Space ShuttleExternal Tank.
The fluorinated ethers E245 and E263, produced in limited quantities by Halocarbon Products ofNorth Augusta, South Carolina, have proven to 

### be_excellentblowing agents of polyurethane based foam insulations. Dataindicates that these third generation blowing agents with zero ozone depletion potential (GDP) may serve as near drop-in replacements for chlorofluorocarbon (CFC) and hydrochlorofluorocarbon (HCFC) blowing agents. 

### Experimental Developmentofthese blowing agents was initiated by evaluating the physical properties of the fluorinated ethers, followed by a study of their solubility in'polyurethane foam components. Studies were then performed to determine the effects of**the~e** 

### blowing agents 

### 0!l the foaming reaction and the final properties ofthe insulations producedPhysical Properties ofthe fluorinated Ethers Physicalpropenies ofthese ethers are presentedin Table 1. A review ofthis dataindicates thafthese fluorinated ethers can be expected to serve as foaming agents with a blowing efficienCy similarto that ofCFC-ll**~use** oftheir similarmolecularweights and boiling points. The shorter atmospheric lifetime andprojected lowercost ofE263 are positive traits that must be weighed againstits low flash ,pOint and flammability concerns. Another advantage is demonstrated in Figure 

### 1, which shows E263 has a slightly lowervaporphase therrilalconductivity than E245 at temperatures below 32°C.' Both E245 andE263 were carried forward 

### in experimentation asfoam blowing agents. The initial work was to detemUne solubility ofthe ethers in the isocyanate and polyol components of the urethane insulation. As presented inTable 

### 1, E245 and E263 are sufficiently soluble in these urethaile components to make processing possible with existing polyurethane industry equipment

.

Table 1. Properties or E245 and E263
E245 E263 CFC-11 HCFC-141b mCH20CHF2 CF3CH20CH3 CFClJ CH3W2E 'MolecularWeight 150 114 137

. 111 Speci¥c Gravity 1.14 1.16 1.49 1.24 Boiling point (0C) 29 30 24 32**Ozon~** Depletion Potential 0 0 1 0.15 Atmospheric Lifetime 1 6 years 2 months 70 years 12 years Global Warming Potential 2 0.15 0 1 0.09 Flashpoint 3 none -16°C none none Flammability 4 non flam. 4.5-14.3% non flam. 7.6-17.7% Isocyanate Solubility 5 13% by weight 20% >50% >50% Polyol Solubility 5 infmite >26% >50% >50% Toxicity 6 limited data limited data non-toxic limiteddata
1 Initially there was a concern that these ethers may fO,rm peroxides with aging and exposure to air. The manufacturerhas worked with National Institute for Standards and Technology (NIS1) to evaluate the chances ofthis occurence in E245. The long atmospheric lifetime ofthis prOductprecludes the formation ofperoxides. Nevertheless, the manufacturerattempted to form peroxides by oxygenating the material, but

, no Peroxides were detected. The degradation ofE263 has notbeeIttested, butaccording to NIST**repres~ntatives,** the long cham ethers that typically form peroxides have an atmospheric lifetime ofonly

several hours, where E263 h3$ an atmospheric lifetime of2 months. 2 Estimates only. £263 may be classified as a volatile organic compound. ·3 E245 & E263 tested by ASTM D 92. CFC-ll & HCFC-141b tested by ASTM D 1310 and D 56. 4 A blend ofE245 and E263 was proposed as a meanstoreduce the flammability ofE263. By calculation using the ASTM E 681 equation to estimate Lower Flammability Limit (LFL), 79.7 molar % E245 is required to raise the LFL ofan E2451E263 blend to that ofHCF<:'-141b (7% in air). The manufacturer determined empirically that 75% E245 was required to raise the LFL according to the Cleveland Open Cup Test Method (ASTM D 92). 5 Solubility tested in proprietary foam formulation containing polymeric methylene diisocyanate and polyester polyols. 6 Limited toxicity testing has been conducted. Fourhourrate exposure tests were run on E245, and in those conditions the material was considered to be safe. A general waiverfor materials used forresearch purposes exists. Commercial production would requireEPA approval and would almost certainly require additional toxicity testing.

### Figure 1. Vapor Phase Thermal Conductivity 1S ..,.....-------------------,

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Foam Preparation InitiallY,J50 isocyanate index, rigid isocyai1Urate foams were produced with a free rise density ofapproximately 3.6 pounds per cubic foot (pet). More recently, foams have been produced with a lowerqensity ofapproximately 2.3 pef. Testing ofthe lowerdensity foams iscurrently in progress. Table 2 shows that E245 and E263 do not hinder the foaming reaction, and produce foams with similar

### free rise densities when substituted on a molecularweight basis.

Table 2. Reactivity and Free Rise Density or Foams Blown with E24S, E263, CFC11, and HCFC·141b
£245 £263 CFC·ll HCFC-141b High Density Gel Time (sec) 57 53 52 49 Density (pet) 3.43 3.65 3.66 3.85

... Low Density Gel Time(sec) 61 48 46 54 Density (pet) 2.20 2.27 2.34 2.30
Hand mix reactivity tests with 70±2°Pcomponent temperatures.
J Foam Properties

- Mechanical, Flammability, and Thermal Conductivity
Testpanels ofthese foam insulations were hand mixed and molded at component and mold temperatures of25°C. In some Gases, the density ofthe molded pans varied ±OApounds percubic foot; actual density is reported 

### in all tables. Mechanical tests run on these molded panels included: friability (ASTM C 421), compressive strength (ASTM D 1621), bond adhesion at 21°C, 149°C, and -253°C (ASTM 01623), cohesive strength at

# room tempe.rature (ASTM D 1623) and cryogenic strain compatibility 

### in a gradient cryofJexure test at -253°C (Martin Marietta Corporation in':'house test). Datafrom mechanical tests are presented in Taole 3. The data establishes foams produced with the fluorinated ethers had properties similar to the foams produced with CFC-l1.... Data not yet available. Elected to evaluate E245, with no flashpoint, first 1 Adhesion to epoxy primed 2219 aluminum 2 AlUininum substrate with 1 inch ofinsulation is mechanically stressed to 30 ksi, while a thermal stress is applied by a-253°Cbackface temperature.

Limitefi flammability test;i.ng has been completed to date, but available-data is presented in Table 4. Since E245 and E263 are ethers, there was an initial concern that they would increase the flammability offoams produced. In a proprietary isocyanurate foam system, this was not the case. Limiting Oxygen Index (LOr

- ASTM D 2863) is the percentoxygen required to sustain a flame. The foams based on E245 and E263, despite the slightly lower density, have LOr values of2K6 and 27.7**r~spectively,** and are comparable to foams

. produced with CFC and HCFC blowing agents. Flammability by NHB 8060.1B is a test developed by NASA to quantify flammability ofmaterials in airor in oxygen rich environments. Results are reported as inches burned, and a value of3.5 to 4.5 inches in

.air is excellent. Data for foam recession 

### in aradiant heat/vacuum environment and in an aerothermal environment are not yet a,vailable. Scheduled tests will 

### berun at heating rates from 7 to 15 British Thermal Units per square foot per second.

... Data not yet available. 

### ** Fl;unmability perNASA test procedure NHB 8060.lB Flammability tests are run in controlled environments and should not be construed to determine the potentialhazards ofthese materials in fIres. Thermal conductivity (ASTM C 177) data is presented 

### in Table 5. One test was run for each test temperature. Neither foam was consistently betterthan the otherat 

### all test temperatures. The values presented show that despite the higher thermal conductivity of the E245 blowing agent in the vaporphase, the thermal conductivity ofthe high density. molded foams produced with these blowing**ag~nts** is comparable to foams produced with CFC-IL The limited solubility ofthese blowing agents is perhaps one reason for the lower overall foam conductivity. The lower solubility ofthe blowing agent makes it more. likely to have many gas nucleation sites. Thisgreater number ofnucleation sites translates into more numerous, smallerbubbles producing a foamed structure with finer cells. Figures 2 through 5 show that the cellular structure ofthe foams produced with E245 and E263 is finer than with CFC-ll orHCFC-141b. The foams have a wide distribution of

### Figure 2.

. Cellular Structure of Polyisocyanurate Foam Produced with E245 

### Blowing Agent

Figure 3. CelhIlar Structure of Polyisocyanurate Foam Produced with E263 

### Blowing Agent

..**~.**

### Figure 4. Cellular Structure of Polyisocyanurate Foam Produced _!!,!_tb CFC.l!

..**J31owi~g** 

### .**:~gent** 

### _

Figure S. Celluiar Structure of Polyisocyanurate Foam Produced with HCFC-141b Blowing Agent

.cell sizes because they were hand mixed, but foams produced with the fluorinated ethers have more small cells. This fine cellular structure plays a majorrole in the thermal conductivity ofthe foams, and compensates for the highervaporphase thermal conductivity ofthe fluorinated ethers. Although data is not yet available, one would expect that the insulations produced with these fluorinated ethers would have less drift 

### in thermal conductivity with aging. The larger, less soluble molecules shouldremain in the insulation longer than the smaller

### CFC-ll molecules. "

Table S. Thermal Conductivity or Foams Produced with E24S and CFC-ll, Thennal Conductivity (W/m°K)
Test Temperature (OC) -130 

### o 52 200 :Density (PCt) E245 0.0220 0.0249 0.0326 0.0502 4.86 

### CfC-ll 0.0209 0.0253 0.0272 0.0523 4.45
Data for the low density foams is not yetavailable


### Co"nchisions

-The data presented warrants further evaluation ofthese fluorinated ethers as blowing agents for urethane basedfoam insulations. The major issue associated with these blowing agents is**~e** fact that these fluorinated**eth~rs** are notcommercially available. Toxicity tests must still berun,**ai1~** the handling ofE263 with the 4.5 to 14.3% flammability limits in air must be addressed. Users and manufacturers must work togetherto initiate and fund the toxicity

"testing so these materials with zero ozone depletion potential may be made available to industry.



### Acknowledgements
This work was funded by the Space Shuttle External TankProject ofthe National

_Aeronautics and SpaceAdministration undercontractNAS8-36200. Efforts were "

coordinated with the Global Change Division ofthe U.S. Environmental Protection Agency. Flainmability testing ofE263 wa.s performed by N. Dean Smith ofthe Airand

- Energy Engineering Research Laboratory atEPA in Research Triangle Park, North

catolina. Vapor phase**the~** conductivity testing ofE245 and£263 was completedby Rich Perkins 

### in the Thermophysics Division at NIST in Bolder, Colorado.

### References

Adcock. "Fluorinated**Eth~:** A New Family ofHalons", International CFC and Halon Alr.ematives Conference, Baltimore, MD, 1991,342-50. Adcock, "Fluorinated Ethers: A New Series ofCFC Substitutes", International CFC andHalon Alternatives Conference, Baltimore, MD, 1991,.386-95.
Allied Signal Literature Bare, "CompressorCalorimeterTesting ofFluorinatedEthers and Fluorinated Propanes", International CFC and Halon Alternatives Conference, Baltimore, MD, 1991,418-27.

. Benning, Calvin J. Plastic Foams, Volume 

### n, Structure, Properties, and Applications, Wiley Interseience, 1969 Robbins, "Preliminary Studies ofthe Anesthetic Activity ofFluorinated Hydrocarbons",Journal of Phar:macology, 1945. Speers, Szur, Terrell, Treadwell, and Ucciardi, "General Anesthetics. 2. Halogenated Methyl Isopropyl Ethers", Journal of Medicinal Chemistry, 14,593. ". Terrell, Speers,**~zur.** Treadwell, and Ucciardi, "General Anesthetics. 1. Halogenated Methyl Ethyl Ethers as Anesthetic Agents", Journal of Medicinal Chemistry, 14, 517. Terrell, Speers, SzUr, Uccardi, and Viteha, "General Anesthetics. 3. Fluriitated Methyl EthylEthers as Anesthetic Agents", Journal of Medicinal Chemistry, IS, 604-608.