Honeywell has introduced two new blowing agents that could dramatically reduce the global warming potential (GWP) of a variety of foam insulation types. Marketed under the brand name Solstice, they are designed to be “drop-in” substitutes for blowing agents currently used to manufacture insulation for both buildings and appliances, including extruded polystyrene and closed-cell polyurethane foams.
Both chemicals have zero ozone-depletion potential and a GWP of 7, meaning that when they are released into the atmosphere their potency is seven times that of CO 2 . While that may sound high, the chemicals they replace can have a GWP of hundreds or thousands. Since insulation reduces fossil fuel use, a GWP of 7 results in a very short global-warming payback time (see EBN June 2010).
The gaseous Solstice blowing agent (HFO-1234ze) has been in use in Europe for extruded polystyrene insulation for a few years, but the liquid blowing agent for polystyrene and polyurethanes (HFO-1233zd) is new, and both are now being introduced worldwide. “We expect this to be a global solution replacing all types of blowing agents,” said Sanjeev Rastogi, structural enclosures director at Honeywell Fluorine Products.
The new blowing agents—along with a refrigerant also being marketed under the name Solstice (HFO-1234yf)—are hydrofluoroolefins, or HFOs. This class of chemical is a “fourth-generation” family of compounds, developed to replace a long line of similar substances that had high ozone-depletion potential or GWP. The first-generation chemicals, CFCs, had GWP as high as 10,900; use of these chemicals has long since been phased out through the Montreal Protocol, which also called for the phase-out of transitional second-generation blowing agents, hydrochlorofluorocarbons (HCFCs). HCFCs were duly succeeded by the third generation, hydrofluorocarbons (HFCs), which are now also being phased out—this time due to high GWP.
The chemical structure of HFOs means they break down quickly, resulting in an atmospheric lifetime of weeks rather than years or decades.
Honeywell has reported thermal performance improvements of 2%–5% (both initial and aged) of rigid and spray polyurethane foam manufactured with HFO-1233zd when compared with polyurethanes manufactured with HFC-245fa. According to Rastogi, thermal performance exceeds that of cyclopentane by 6%–10% as well. “The blowing agent has a significant impact on thermal insulation value,” he said, “and we are still in the process of optimizing the formulations. We look at these numbers as the lower bound.”
While low GWP is a huge and welcome breakthrough—and better thermal performance is a nice bonus—any use of fluorinated chemicals raises safety questions. Many halogenated compounds (those containing elements such as fluorine, bromine, and chlorine) break down into persistent chemicals, many of which are both bioaccumulative and toxic (PBTs). HFOs are relatively new, and their long-term environmental effects are unknown. However, like HFCs, they produce trifluoroacetic acid (TFA), which has “no known environmental degradation mechanisms,” according to Scott Mabury, Ph.D., professor of environmental chemistry at the University of Toronto. Mabury told EBN that, despite its persistence, “TFA has not been shown to be biologically very problematic, even at very high concentrations,” adding that “global warming is a bigger item than TFA’s going to be.”
According to Tom Lent, policy director at the Healthy Building Network, however, not everyone is so confident, and “with something as persistent as this, we can’t afford to be wrong.” From what we know right now, however, the new HFOs do not appear to be more problematic than the HFCs they replace.
“We’re looking forward to it as an industry,” said Rick Duncan, Ph.D., P.E., technical director at the Spray Polyurethane Foam Alliance. “While 245fa-based spray foams have excellent R-values, the molecule’s high GWP has been viewed by some as a limiting factor in selection of closed-cell SPF products.”
Although he characterized the transition to a new blowing agent as a major project that takes about a year, Duncan believes that when manufacturers see results of life-cycle assessments recently completed by his organization, “several will take the opportunity to look at newer blowing agents and promote these more environmentally friendly products.” Duncan estimated that we could start seeing fourth-generation blowing agents in closed-cell spray polyurethane foam products as early as mid-2013, adding that DuPont and Arkema had also recently announced the impending launch of their own low-GWP blowing agents.
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New Chemical to Reduce Climate Impact of Foam Insulation