More About Blowing Agents
Note from Dyplast: This article is provided courtesy of Professional Roofing, a magazine of the NRDA. It is quite informative yet certain aspects are not applicable to Dyplast's polyiso. The LTTR, for example, is applicable to thin, laminated polyiso roofing sheets produced under a constrained-rise process, and is not applicable to Dyplast's free-rise polyiso bunstock.
A blowing agent update
Learn why the change to pentane was made and what it means for polyiso
by Lorraine Ross
With a predicted production of more than 5 billion board feet during 2005, polyisocyanurate roof insulation continues to be the dominant thermal insulation material used in the commercial roofing market. Currently, polyisocyanurate has improved environmental characteristics and is an important component in sustainable construction. Yet the past 20 years have presented a series of challenges largely driven by environmental regulations. The story of polyisocyanurate's survival is unusual given the typical demise of products whose raw materials have been targeted by environmental groups. Incredibly, the resultant product changes have led to an improved product and a closer cooperation between polyisocyanurate producers and roofing contractors, especially in improving the polyisocyanurate standard, ASTM C1289, "Standard Specification for Faced Rigid Cellular Polyisocyanurate Thermal Insulation Board." This article will provide an update about polyisocyanurate and a few observations of the product's future direction.
Polyisocyanurate insulation has three major components: MDI, polyol and a blowing agent. When these three components are mixed, along with small amounts of catalysts and surfactants, a heat-generating chemical reaction causes the liquid blowing agent to boil. The resultant blowing agent vapor expands the foam, creating gas-filled cells that provide polyisocyanurate's high thermal-resistance value. Currently, the polyisocyanurate industry uses a hydrocarbon blowing agent, pentane, which has zero ozone-depletion potential and negligible global-warming potential. However, the eventual use of pentane as a blowing agent was spurred by a series of environmental events that began in earnest in 1987 causing the polyisocyanurate industry to reformulate the product twice during a nine-year period.
From its introduction during the late 1970s, the polyisocyanurate industry was using CFC-11 as a blowing agent. Although the history of the connection between CFCs (chlorofluorocarbons) and ozone layer depletion is well-documented, a brief timeline of the issue and its implications for the polyisocyanurate industry follows:
1970's: Some scientists were alarmed at the apparent thinning of the ozone layer in certain parts of the world and suspected man-made chemicals were responsible.
1978: The United States banned CFCs in aerosol uses only, such as hairspray.
1980: Canada banned CFCs in aerosol uses only.
1987: The Vienna Convention for the Protection of the Ozone Layer became effective; it was the first international agreement that addressed the role of CFCs in the destruction of the ozone layer.
1989: The Montreal Protocol on Substances that Deplete the Ozone Layer became effective. It was the first international environmental treaty that spelled out a scheduled phase-out of ozone-depleting substances; Class I chemicals, including CFCs; and Class II chemicals, including HCFCs (hydrochlorofluorocarbons). Because Class I chemicals had high ozone-depletion potential, they were the first substances to be regulated.
1990: The U.S. Congress adopted a major revision of the Clean Air Act that regulates ozone-depleting chemicals in the United States. Subsequent U.S. Environmental Protection Agency (EPA) regulations set 1994 as the phase-out date for CFC-11 used by the polyisocyanurate industry and CFC-12 used by the extruded polystyrene industry. It also addressed the future of CFC substitutes.
1993: The polyisocyanurate industry completed its transition from CFC-11 to HCFC-141b one year ahead of schedule, earning the industry the EPA Stratospheric Ozone Protection Award. HCFC-141b was considered a significant improvement because it represented a 90 percent reduction in ozone-depletion potential compared with CFC-11 and possessed other desirable characteristics. However, it was permitted only as a temporary substitute as manufacturers sought a replacement that had zero ozone-depletion potential.
1993-95: The Antarctic ozone layer thinning worsened, and EPA announced an accelerated phase-out date for ozone-depleting substances. The phase-out date for the production and import of HCFC-141b production was set for Jan. 1, 2003. EPA also designated a phase-out date of 2010 for HCFC-142b used by the extruded polystyrene industry. The drive by polyisocyanurate insulation producers for a zero ozone-depletion potential blowing agent began.
1998-2002: The first polyisocyanurate insulation plant was converted to hydrocarbons in 1998, and members of the Polyisocyanurate Insulation Manufacturers Association (PIMA) completed plant conversions by the end of 2002.
Blowing Agent Selection
Because the blowing agent is one of the critical components needed to produce polyisocyanurate foam insulation, finding a substitute was no small task.
At the time of the first transition in 1993 from CFC-11 to HCFC-141b, a list of desirable blowing agent characteristics was developed; those characteristics follow:
- Low or zero ozone-depletion potential
- Low thermal conductivity to produce expected R-value
- Acceptable product for the roofing market
- Economically feasible
- Readily available
- Minimal plant modifications
- Meet fire test requirements
- Meet building code requirements
HCFC-141b was selected because it best fulfilled these necessary requirements. The "in-place" performance of polyisocyanurate using HCFC-141b as the blowing agent was assessed by a joint effort among NRCA, PIMA, Society of the Plastics Industry (SPI), EPA and U.S. Department of Energy (DOE). Conducted at Oak Ridge National Laboratory, this project was the first authorized by the Cooperative Research and Development Act. The act enables the formation of Cooperative Research and Development Agreements (CRADAs) between a private company and government agency to work together on a project. A CRADA allows the federal government and nonfederal partners to optimize their resources, share technical expertise in a protected environment, share intellectual property emerging from the effort and speed the commercialization of federally developed technology.
This pioneering project laid the groundwork for not only evaluating the physical properties of polyisocyanurate products with alternative blowing agents but also formed the basis for a method to determine the long-term thermal resistance (LTTR) of foam insulation.
The widespread introduction of polyisocyanurate containing HCFC-141b had some initial problems with isolated incidents of shrinkage. This experience set the stage for new evaluation methods when the time came to make the second transition to a zero ozone-depletion potential blowing agent.
In searching for a new blowing agent, polyisocyanurate insulation producers went back to the list of desirable blowing agent characteristics developed for the first transition from CFCs to HCFCs. They decided to add another attribute—a low global-warming potential. Recognizing the growing worldwide concern about climate change, polyisocyanurate insulation producers did not want to be in the position of successfully eliminating the use of a chemical that was tied to ozone layer depletion only to face new potential regulation of global-warming substances.
With the assistance of their chemical suppliers, polyisocyanurate producers looked to the use of hydrocarbons. Several European polyurethane producers had successfully used hydrocarbons, and the potential for their use in polyisocyanurate insulation was explored. Once formulation work began, extensive physical property and fire testing was conducted. The first test roof with hydrocarbon-blown polyisocyanurate was installed in 1995. Continued assessment confirmed pentane was the most suitable candidate as a replacement for HCFC-141b. Polyisocyanurate produced with hydrocarbons continue to have Class 1 Approval from FM for direct-to-steel deck applications. PIMA also reports there has been extensive use of hydrocarbon-blown polyisocyanurate in Europe during the same period with similar results.
After facing two blowing agent transitions in just nine years, the polyisocyanurate industry has reached its goal of producing a thermally efficient insulation that uses a blowing agent with zero ozone-depletion potential and negligible global-warming potential and has been well-received by roofing contractors. The industry does not expect to be subjected to new blowing regulations in the foreseeable future.
In terms of product acceptance, the transition to pentane has been smooth. This likely is the result of lessons learned during the move from CFC-11 to CFC-141b during the early 1990s. Confidence also was gained by the early placement of pentane-blown product in large test jobs. Although the switch to pentane was costly in terms of plant retrofit (up to $500,000 per plant), the polyisocyanurate industry has continued to invest in the future. This is confirmed by the announcement of new polyisocyanurate plants by several North American manufacturers.
Polyisocyanurate and LEED
With its improved environmental characteristics, polyisocyanurate insulation now can qualify as an important component of sustainable construction. During the early 1990s, the U.S. Green Building Council (USGBC) developed the Leadership in Energy and Environmental Design (LEED) Green Building Rating SystemÂ® as the standard for green buildings.
The LEED system establishes basic requirements for the various aspects of sustainable design: sustainable sites, water efficiency, energy and atmosphere, materials and resources, indoor environmental quality, and innovation and design process. Credits or points are earned for implementation of the technical requirements of the specific LEED rating category.
Using polyisocyanurate insulation may gain credits under three of LEED's six rating categories: energy and atmosphere, materials and resources, and innovation and design process.
For the past three years, improving the polyisocyanurate ASTM standard has been a major goal of the PIMA Technical Committee. Prompted in part by NRCA, the industry successfully completed a revision that allows roofing contractors to specify the exact product they require, including a choice of compressive strengths. Additional refinements to ASTM C1289 are planned, such as separating the Physical Property and Thermal Resistance Tables by application so roof insulation products will be clearly identified.
The polyisocyanurate industry's adoption of a method to determine the LTTR of permeable-faced products is found as a mandatory Appendix in ASTM C1289. It allows the prediction of a 15-year time-weighted R-value. The core concepts of LTTR came from CRADA supported by NRCA, PIMA, SPI, EPA and DOE formed in the early 1990s to assess the performance of polyisocyanurate with new blowing agents.
LTTR's many advantages include a technically supported descriptive measure of long-term thermal performance; application to all foam insulation products with blowing agents other than air; an additional assessment of sustainable construction; and basis on ASTM C1303, "Standard Test Method for Estimating the Long-Term Change in the Thermal Resistance of Unfaced Rigid Closed Cell Plastic Foams by Slicing and Scaling Under Controlled Laboratory Conditions," and CAN/ULC S770, "Standard Method of Test for Determination of Long Term Thermal Resistance of Closed-Cell Thermal Insulation Foams."
Recognizing the use of a new method to describe thermal performance might cause confusion, the polyisocyanurate industry then introduced the Quality Mark Program, which grants third-party certification of a polyisocyanurate manufacturer's claimed LTTR value. This is the only such program in place.
PIMA's Technical Committee will continue working on its core projects, such as product standards, building codes and product promotion support. Three technical bulletins are planned: Moisture Generated During Construction, Facers and Multiple Layers. A concentrated effort will be made in the area of sustainable construction, raising polyisocyanurate insulation's profile as an environmentally friendly product. For additional information about polyisocyanurate insulation, visit PIMA's Web site at www.pima.org.
Lorraine Ross is president of Intech Consulting Inc., a technical- and building code-focused company based in Gulfport, Fla.