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issue: January 2009 APPLIANCE Magazine

Appliance Engineer
Investigation of Low GWP Blowing Agents


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Ben Chen, Joseph Costa, Philippe Bonnet, Maher Elsheikh, and Laurent Abbas, Arkema Inc.

One company tests potential replacements for both gaseous and liquid hydrofluorocarbon (HFC) blowing agents used for rigid polyurethane foam insulation.

Since the phaseout of chlorofluorocarbon (CFC) in the mid-1990s, the rigid polyurethane foam industry in North America has faced an important period of change in the availability and use of different blowing agents. Regulations have imposed a significant cost burden on system suppliers and foam manufacturers to ensure that new blowing agents perform acceptably and products conform to building code requirements. However, these enforced changes have helped industry develop a greater understanding of the properties and performance attributes of the different blowing agents, giving rise to sophisticated combinations of liquid and low-boiling blowing agents.

For example, CFC 11 was a remarkable blowing agent until its phaseout due to its ozone-depletion potential (ODP). HCFC-141b was a good replacement, but its higher boiling point and its greater solubility in the polymer matrix led to some problems with dimensional stability and as a result, required an increase of the foam density. The inclusion of the low-boiling blowing agent, HCFC-22, permitted an improvement of dimensional stability and a reduction in overall density. However, both of these HCFCs still have an ODP, which led to the U.S. phaseout of HCFC-141b and HCFC-22 in 2003 and 2008, respectively, and the phaseout of HCFC-141b in Canada in 2008.

To fill the void created by these phaseouts, third-generation blowing agents HFC-134a and HFC-245fa were developed and commercialized. They have become widely used in many different rigid polyurethane foam applications, including appliances, pour-in-place, and spray.

However, the chemical industry is now facing an ever-increasing pressure to address climate changes by focusing on carbon footprint and, more specifically, on the global warming potential (GWP) of blowing agents. In Europe, the European Parliament has committed to adopting the Kyoto protocol, which aims to reduce emissions of greenhouse gas by 8% from 1990 levels.

Because of their high GWP values, HFCs are becoming regulated for some applications (e.g., HFC-134a has a GWP of 1300 and HFC-245fa 950). For example, the European MAC (mobile air conditioning) directive prohibits the use of HFC-134a in MAC systems for new platforms in 2011 and in all new cars as of 2017.

To address future market needs, Arkema investigated the development of fourth-generation blowing agents to replace HFC such as HFC-245fa and HFC-134a. To be fully environmentally acceptable, this next generation must have a zero ODP and a very low GWP while maintaining excellent general properties and, more specifically, insulation properties for rigid polyurethane foams.

Properties

The fourth-generation blowing agents (called the AFA series) include both liquid and gas versions and possess very low GWP (< 15) and negligible ozone-depletion effect. Due to skyrocketing energy costs and rising standards of energy efficiency, molecules that can provide better thermal insulation and meet strict environmental and safety standards are essential. Table I summarizes the properties of the fourth-generation blowing agent molecules and references other blowing agents such as cyclopentane, HFC-134a, HFC-245fa, and HCFC-141b.

Experiment

Gaseous blowing agents were evaluated using a specially designed dispensing system, while evaluation of the liquid blowing agents was accomplished using a typical hand-mix technique, employing an air-powered air mixer with a 2-in.-diam mix blade. The specially designed system for the gaseous blowing agents required a very low viscosity polyol blend (Formulation 1). To evaluate some of the new blowing agents in a less specialized formulation with a wider application, one of the liquid candidates was looked at in Formulation 2, which is a pour-in-place type system.

In both cases, all the ingredients of the B-side were premixed without the blowing agent. For the gaseous blowing agents, an amount of the premix was added to the dispensing unit, after which the necessary amount of blowing agent was added and mixed thoroughly. For the liquid blowing agents, an appropriate amount of blowing agent was added to the premix in a Nalgene bottle and mixed thoroughly. Tables II, III, and IV summarize the formulations of this study.

The blowing level/density and reactivity for Formulation 1 were set from the results obtained with HFC-134a: gel time around 50 seconds and free-rise density around 2.0 pcf. The blowing level/density and reactivity for the Formulation 2 evaluations were set from the results obtained using HCFC-141b: gel time around 50 seconds and free-rise density around 2.0 pcf.

A density and reactivity check was made on each system, prior to making larger samples for physical testing. For the gaseous blowing agents, after the dispensing unit was calibrated for the appropriate mix ratio, a small amount was placed into a 32-oz paper cup. Reactivity times were observed during the reaction and a free-rise density was measured on the cured foam. For the liquid blowing agents, a hand mix was performed using the 32-oz paper cup for mixing. Reactivity and density were measured in a similar fashion to the gaseous blowing agent foams.

Physical test samples were made in 6 × 6 × 6-in. open box pours. One box each was made for k-factor testing and dimensional stability at 70°C/97% relative humidity (RH). Due to the nature of the free-rise foams, especially with the gaseous blowing agents, the k-factor samples were cut such that the foam rise was parallel to the test face to minimize the effect of any defects running completely through the sample thickness. Also, since the k-factor samples were undersized (5 × 5 in.), each test piece was surrounded by like material. Dimensional stability test samples were cut such that the foam rise was perpendicular with the 4 × 4-in. test face.

Results and Discussion

The purpose of this investigation was to explore potential replacements for both gaseous and liquid HFC blowing agents currently used for rigid polyurethane foam insulation. Two criteria necessary for this area are processibility and performance, hence the investigation of the candidates’ blowing efficiency, dimensional stability, and insulation properties.

Gaseous Blowing Agent. After mixing the formulations listed in Table II, the containers with the fully blended B-side were allowed to stand at room temperature until the head space pressure had stabilized, prior to attachment of the dispensing gun and nitrogen. Table V contains the pressures of the B-sides compared with the vapor pressures of the neat blowing agents.

Previous work has shown the head space pressure to be an indication of solubility of the gaseous blowing agent in the polyol blend.1 This improved solubility was shown by AFA-G1 bottle pressure being lower than the neat blowing agent. This was confirmed by a better-quality foam than with either the AFA-G2 or HFC-134a.

Since the blowing level and percent water blowing were kept constant, AFA-G1 showed better blowing efficiency, as indicated by the lower free-rise density.

As shown in Table VI, the negative percent volume change for all the samples could indicate that a certain amount of cells ruptured during the testing, allowing the pressure to drop and the foams to shrink. Both the experimental blowing agents performed much better than the HFC-134a blown foam, indicating that the cell pressure was not high enough to rupture as many of the cells as with the HFC-134a system.

Table VII shows that the initial k-factor performance of AFA-G1 and AFA-G2 was comparable to HFC-134a over the test temperature range with the exception of the coldest temperature (17.6°F or –8°C), where AFA-G1 performance was worse than HFC-134a and AFA-G2.

Although AFA-G1 processed better, yielding a lower-density and better-quality foam than either HFC-134a or AFA-G2, the initial k-factor results were slightly poorer than HFC-134a and AFA-G2, especially at the colder application temperatures.

Liquid Blowing Agent. Table VIII contains the free-rise density and dimensional stability of the foams made with liquid blowing agents using Formulation 1. As previously mentioned, the foams using the liquid blowing agents were made by typical hand-mix technique whether using Formulation 1 or 2.

AFA-L1 and AFA-L2 showed similar blowing efficiency to HCFC-141b, HFC-245fa, and cyclo/isopentane, as indicated by a similar free-rise density with the same molar amount of blowing agent. Since the molecular weight of AFA-L1 and AFA-L2 are close to HFC-245fa, the same weight percentage of material would be needed in the formulation to obtain a similar density.

Because of this system’s lower-density and lower-functionality polyol, all foams showed a significant volume change. However, AFA-L1 showed 6–8% less change than HCFC-141b, HFC-245fa, and cyclo/isopentane; AFA-L2 showed the most dimensional change compared with the other examined blowing agents.

Table IX contains the initial k-factor results for the liquid blowing agents evaluated in Formulation 1. Both AFA-L1 and AFA-L2 exhibited significantly better k-factor than HCFC-141b, especially at the cold-to-room temperature test conditions. AFA-L1 exhibited significantly better k-factor than HFC-245fa over all test temperatures; AFA-L2 also performed better than HFC-245fa, but the gap was less, especially at the colder test temperatures. Both of the experimental liquid blowing agents performed much better than the cyclo/isopentane foam.

As with Formulation 1 foams, AFA-L1 showed similar blowing efficiency to HCFC-141b, HFC-245fa, and cyclo/isopentane (see Table X). AFA-L2 was not tested in this formulation. Due to the higher density and different polyol composition of this system versus Formulation 1, all of the tested blowing agents gave similar and acceptable dimensional stability performance.

As shown in Table XI, AFA-L1 exhibited similar k-factor performance to HCFC-141b over all the temperatures tested and performed slightly better than HFC-245fa. However, the differences were much less than with Formulation 1. Also, as with Formulation 1, AFA-L1 performed significantly better than the cyclo/isopentane foam.

In Formulation 1, both AFA-L1 and AFA-L2 gave much better initial k-factors than HCFC-141b, HFC-245fa, and cyclo/isopentane foams. However, AFA-L2 exhibited the poorest performance with regard to dimensional stability. Overall, in Formulation 2, AFA-L1 performed comparable with HCFC-141b and better than both the HFC-245fa and cyclo/isopentane foams.

Conclusion

This study presents a review of low-GWP blowing agents candidates versus currently used primary HFC blowing agents such as HFC-134a and HFC-245fa. It has been shown that AFA-G1, and to a lower extent AFA-G2, can potentially compete with F134a in terms of solubility in polyol, dimensional stability, and k-factor, although AFA-G1 seems to perform less at very cold temperatures.

Even more interesting results have been found for the low-GWP liquid blowing agents replacing HFC-245fa and hydrocarbons. AFA-L1 displayed a similar blowing efficiency and provided some improvement in dimensional stability and a significant advantage on k-factor versus HFC-245fa and hydrocarbons.

TABLES:

MW

BP(°C)

FP*(°C)

Lambda (mw/m-°K)

10°C 25°C

LFL/UFL**

ODP

GWP

AFA-G1

<120

<–15

11

12

9.9

0

<15

AFA-G2

<120

<–15

12

13

4.7

0

<15

AFA-L1

<134

<30 >10

None

9

10

None

0

<15

AFA-L2

<134

<30 >10

***

9

10

***

0

<15

cC5

70

49

–7

11

13

1.5

0

11

F 134a

102

–27

None

12

14

None

0

1300

F 245fa

134

15

None

13

13

None

0

950

F 141b

117

33

None

9

10

7.4/15.5

0.11

700

* Flash point ** Ambient temperature, with lower flammability limit (LFL) *** In progress

Table I. Properties of AFA molecules and references.

 


 

 

Formulation

HFC-134a

AFA-G1

AFA-G2

Jeffol SG-360

15.35

15.10

15.45

Jeffol R-425-X

4.39

4.31

4.41

Carpol TEAP-265

8.77

8.63

8.83

Diethylene Glycol

2.19

2.16

2.21

Jeffcat TD-33A

0.23

0.23

0.23

Jeffcat ZR-70

0.23

0.23

0.23

Tegostab B8465

0.90

0.90

0.90

Nonyl phenol 9.5

6.50

6.50

6.50

Water

0.42

0.42

0.42

HFC-134a

9.47

0

0

AFA-G1

0

10.57

0

AFA-G2

0

0

8.92

Rubinate M

51.6

51.0

51.9

Isocyanate Index

110

110

110

Total blowing, ml/g

26.0

26.0

26.0

% physical blowing

80

80

80

% water blowing

20

20

20

Table II. Gaseous blowing agent formulations—Formulation 1.

 


 

 

Formulation

HCFC-141b

HFC-245fa

Cyclo/Isopentane

AFA-L1

AFA-L2

Jeffol SG-360

15.04

14.70

15.99

14.77

14.77

Jeffol R-425-X

4.30

4.20

4.57

4.22

4.22

Carpol TEAP-265

8.60

8.40

9.14

8.44

8.44

Diethylene Glycol

2.15

2.10

2.28

2.11

2.11

Jeffcat TD-33A

0.23

0.23

0.23

0.23

0.23

Jeffcat ZR-70

0.23

0.23

0.23

0.23

0.23

Tegostab B8465

0.90

0.90

0.90

0.90

0.90

Nonyl phenol 9.5

6.50

6.50

6.50

6.50

6.50

Water

0.42

0.42

0.42

0.42

0.42

HCFC-141b

10.87

0

0

0

0

HFC-245fa

0

12.47

0

0

0

Cyclo/isopentane (80/20)

0

0

6.51

0

0

AFA-L1

0

0

0

12.11

0

AFA-L2

0

0

0

0

12.11

Rubinate M

50.8

49.9

53.2

50.1

50.1

Isocyanate Index

110

110

110

110

110

Total Blowing, ml/g

26.0

26.0

26.0

26.0

26.0

% physical blowing

80

80

80

80

80

% water blowing

20

20

20

20

20

Table III. Liquid blowing agent formulations—Formulation 1.


Formulation

HCFC-141b

HFC-245fa

Cyclo/Isopentane

AFA-L1

Voranol 490

18.27

18.05

18.85

18.09

Jeffol R-425-X

10.96

10.83

11.31

10.85

Stepanpol PS-2352

7.31

7.22

7.54

7.24

Polycat 5

0.07

0.07

0.07

0.07

Polycat 8

0.37

0.37

0.37

0.37

Tegostab B8465

0.71

0.71

0.71

0.71

TCPP

2.36

2.36

2.36

2.36

Water

0.64

0.64

0.64

0.64

Forane 141b

6.27

0

0

0

HFC-245fa

0

7.19

0

0

Cyclo/isopentane (80/20)

0

0

3.75

0

AFA-L1

0

0

0

7.00

Rubinate M

53.0

52.6

54.4

52.7

Isocyanate Index

115

115

115

115

Total blowing, ml/g

20.0

20.0

20.0

20.0

% physical blowing

60

60

60

60

% water blowing

40

40

40

40

Table IV. Liquid blowing agent formulations—Formulation 2.

 


 

 

Blowing agent

Vapor pressure (psig)

B-side headspace pressure (psig)

Free-rise density (pcf)

Forane 134a

71

82

1.98

AFA-G1

53

44

1.79

AFA-G2

74

133

2.03

Table V. Processing and density.


Blowing agent

Free-rise density (pcf)

% Volume change

HFC-134a

1.98

-17.3

AFA-G1

1.79

-5.0

AFA-G2

2.03

-6.4

Table VI. Free-rise density and dimensional stability—14 days at 70°C/97% RH.

 

 

Mean
temperature, °F

HFC-134a

AFA-G1

AFA-G2

18

0.129

0.134

0.127

32

0.134

0.137

0.132

50

0.142

0.143

0.140

75

0.154

0.154

0.152

104

0.167

0.168

0.166

Table VII. Initial k-factor for gaseous blowing agents (BTU.in/ft2.h.°F).

 

 

Blowing agent

Free rise density (pcf)

% Volume change

HCFC-141b

1.69

25.4

HFC-245fa

1.66

26.8

Cyclo/isopentane (80/20)

1.68

24.3

AFA-L1

1.68

18.6

AFA-L2

1.69

41.8

Table VIII. Free-rise density and dimensional stability—14 days at 70°C/97% RH.

 

 

Mean
temperature (°F)

HCFC-141b

HFC-245fa

Cyclo/isopentane (80/20)

AFA-L1

AFA-L2

18

0.139

0.125

0.143

0.120

0.123

32

0.145

0.129

0.145

0.123

0.126

50

0.146

0.137

0.148

0.131

0.133

75

0.152

0.150

0.155

0.143

0.145

104

0.164

0.166

0.172

0.158

0.159

Table IX. Initial k-factor for liquid blowing agents (BTU.in/ft2.h.°F)—Formulation 1.

 

 

Blowing agent

Free-rise density (pcf)

% Volume change

HCFC-141b

2.07

5.2

HFC-245fa

1.99

5.4

Cyclo/isopentane (80/20)

2.04

4.4

AFA-L1

2.07

4.0

Table X. Free-rise density and dimensional stability—14 days at 70°C/97% RH.

 

 

Mean
Temperature (°F)

HCFC-141b

HFC-245fa

Cyclo/isopentane (80/20)

AFA-L1

18

0.124

0.124

0.137

0.122

32

0.126

0.129

0.140

0.127

50

0.132

0.138

0.144

0.134

75

0.144

0.150

0.155

0.146

104

0.159

0.166

0.172

0.162

Table XI. Initial k-factor for liquid blowing agents (BTU.in/ft2.h.°F)—Formulation 2.

 
 

Reference

1. Ian Wheeler and Michael Cartmell, “HFC-134a Blended with Transcend Additive Technology as a Replacement for HCFC-22 in Pour-in-Place Rigid Polyurethane Foams,” API 2006 Conference Proceedings (Salt Lake City, UT, U.S., September 25–27, 2006), 572–579.

This is an edited version of a paper presented at the Polyurethanes 2008 Technical Conference in San Antonio, TX, U.S.

Ben Chen is a research scientist of fluorochemicals at Arkema’s Technical Center in King of Prussia, PA, U.S. He received a PhD in chemical engineering from the University of Pittsburgh, and a BS from East China University of Science and Technology in Shanghai.

Joseph Costa is a senior tech service engineer at Arkema’s Technical Center. He received a BS in psychology from the University of Miami (FL) and an MS in chemistry from the University of Scranton (PA).

Philippe Bonnet is R&D director for fluorochemicals at Arkema’s Technical Center. He graduated from École Supérieure de Chimie Industrielle de Lyon (France), earned a PhD from Lyon University at the Institut de Recherches sur la Catalyse, and has an MBA from the Management School at Écully (France).

Maher Elsheikh received his BS and MS from Alexandria University in Egypt and a PhD from Warwick University of England. He has been with Arkema since 1984. He is the inventor and coinventor of 47 patents, including 36 U.S. patents.

Laurent Abbas received a PhD in polymer science from the Université Louis Pasteur in Strasbourg, France. After being a postdoctoral fellow in the microelectronics industry, he joined Arkema France in 2007 as a technical development manager of fluorinated blowing agents. If you wish to contact the authors,
e-mail lisa.bonnema@cancom.com.

 

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