Blowing agents: handicapping the CFC substitutes.

Which CFC alternatives look best for the long and short term in polyurethane and thermoplastic foams? Here's how it's shaking out so far.

Foam makers travel an increasingly uncertain path when it comes to picking a physical blowing agent for the long haul. With CFCs condemned to lame-duck status, suppliers have developed a short list of alternative blowing agents for both urethanes and thermoplastics, but that list threatens to become even shorter over the coming years.

Of the few replacement substances and technologies that have emerged as the most promising candidates, some are advocated as long-term solutions. Others, including some not even commercialized yet, seem best suited as interim steps in the transition away from CFCs. The HCFCs, for example, will ultimately face the same fate as their ozone-depleting forerunners. And an HCFC phaseout appears likely to come much sooner than the 2030 date suppliers counted on when they started developing CFC replacements (see PT, April '92, p. 115). "We're in the amazing position of developing substitutes for products that haven't even hit the market yet," says Frank Kerr, marketing manager for Allied-Signal.

A handful of companies already make CFC replacements. Elf Atochem produces 110 million lb/yr of HCFC-141b and 142b. It also plans to bring an HFC-134a plant on-stream in France by mid-year. Allied-Signal, meanwhile, began production of HCFC-141b and plans to build a facility to make HFC-134a. Du Pont manufactures HFC-134a and 152b, while ICI also makes 134a.

TRANSITION TIME FOR PUR

Dramatic reductions in CFC-11 use have already taken place in all segments of urethane foams. The Polyurethane Foam Association, Wayne, N.J., for instance, reports its members have reduced CFC use by 98% from 1986 levels in flexible foams. Rigid foams haven't seen as dramatic a decrease. Miles Inc. market manager Rick Stamper notes reformulations have enabled cuts of up to 50% from 1986 levels.

But reductions cannot do the trick for long, with CFC-11's career as a blowing agent now scheduled to halt by the end of 1995. Between now and then, the tax on using this CFC will escalate ferociously. For rigid foams, it will jump from its current 25|cents~/lb rate to a whopping $2.65/lb in 1994. Not surprisingly, urethane system suppliers such as Miles report that their customers desire an alternative before the tax kicks in. "They want to have something under their belt in '93," says Stamper.

Of those HCFCs under consideration to fill the gap CFC-11 will leave, a clearcut front runner has emerged as the best transitional substitute for the widest variety of applications. Though suppliers do not completely rule out HCFC-123 or -22 as CFC-replacement candidates, only HCFC-141b consistently gets the nod. "We're totally confident it's the clear choice," says Elf Atochem marketing manager Eugene Laughlin, voicing the supplier consensus. HCFC-141b is credited not only as being "friendlier" to the ozone layer than CFC-11, but also for its competitive cost and compatibility with existing foam processes.

As for HCFC-123, it ran into problems last year when preliminary results of a two-year toxicity test showed some benign tumor development in rats (PT, Sept. '91, p. 60). Du Pont had planned to market a blend of HCFC-123 and 141b. That product is now in limbo, pending results of further testing, says technical service engineer Joseph Creazzo. "It kind of gets a cool reception right now," he adds.

Until the completion of long-term toxicity tests at year's end, major suppliers say they will also keep HCFC-141b off the blowing-agent market. Once the tests wrap up, it should take only about a year for HCFC-141b to "ramp-in fully" in urethanes, estimates Allied-Signal's Kerr. At ICI Polyurethanes, commercial director Robert Reen says, "We're ready to go on HCFC-141b formulations as long as we don't get derailed by toxicity tests"--an eventuality he considers unlikely at this point.

Because HCFC-141b remains pre-commercial as a blowing agent, suppliers are reluctant to say precisely where its pricing will end up. Laughlin does note that HCFC-141b sells for roughly $1.31/lb right now in refrigeration uses, making it competitive with CFC-11 taxed at 25|cents~/lb. Once the tax hikes up to its full price, the balance clearly tilts even further toward 141b. Laughlin also points out that HCFC-141b, with its lower molecular weight, is more efficient than CFC-11, so you can use 10 to 15% less.

HCFC-141b suffers one drawback in insulation applications--16% higher thermal conductivity than CFC-11. But even this disadvantage can be offset with formulations that produce smaller and more numerous cells, says Donna Jernigan of Dow's technical service group.

As a liquid, HCFC-141b can be used in existing equipment with only "minor changes," says Miles applications development manager Joseph Sutej. By contrast, using a gas such as HCFC-22 requires some equipment revamping. Nonetheless, foam producers of all sorts (mainly in thermoplastics) currently use about 10 million lb/yr of HCFC-22 right now, according to Du Pont's Creazzo. Dow's Jernigan says HCFC-22 may have slightly less harmful effect on the ozone layer than 141b due to its slightly lower ODP.

HFCs FOR THE LONG-HAUL?

In anticipation of the ultimate phaseout of HCFCs like 141b, suppliers have begun to look for the next wave of replacements--ones with absolutely no ozone-depletion potential (ODP). All suppliers acknowledge that HFCs are the most promising. Du Pont, for one, has both HFC-134a and 152a under evaluation as blowing agents for urethanes, Creazzo says. As gases, they would require both formulation and equipment changes. Kerr of Allied-Signal considers HFC-134a "one potential candidate among many others," noting that its low toxicity has already been established and it essentially has zero ODP.

Other hopes center around HFC-356, an experimental liquid from Miles' German parent company, Bayer AG. As a liquid, it would drop into existing systems more readily, says Sutej.

For some applications, another alternative that presents negligible environmental concerns already exists. Both Miles and ICI Polyurethanes advocate water-blown systems for applications where insulation values are not critical. Miles' Sutej says the water-blown systems' higher K-factors can mean as much as 40% lower insulation values than with CFC-11. ICI's water-blown rigid system has been commercialized for two years with customers that include a major manufacturer of soft-drink vending machines.

THE STYRENE SCENE

Foamed PS producers embraced CFC alternatives even faster than did urethane foamers, in response to the barrage of unfavorable publicity their product attracted a few years ago. In place of CFC-12, alternative systems based on HCFCs have gone into use, while the traditional hydrocarbon technologies also remain on the scene.

Du Pont senior technical-service engineer Robert York notes that HCFC-22 showed the most promise for reasons of cost and performance when PS foam packaging makers converted from CFC-12 five years ago. More recently, HCFC-142b has also taken hold, says Allied-Signal's Frank Kerr.

But with the HCFC window of opportunity likely to close as early as 1994 for PS packaging, manufacturers are now searching for blowing agents with zero ODP. According to York, Du Pont has settled on HFC-152a as the most promising candidate for both PS food packaging and a variety of polyethylene foam applications. Aside from zero ODP, it has the least impact on global warming of any HFC and causes less of a problem with VOC regulations than do hydrocarbons, he says.

But York cites economic factors as the primary incentive. HFC-152a sells for the relatively low price of $1.81/lb and its molecular-weight advantage makes it 20-25% more efficient than HCFC-22. By contrast HFC-134a costs roughly $8/lb, making it unattractive for food-packaging use. Still, York says HFC-134a shows promise as a replacement for HCFC-142b in PS foam building insulation. And because it behaves more like CFC-12 in areas like post-expansion, he considers it "a better blowing agent than 152a."

Allied-Signal, meanwhile, continues to look at a range of HFCs, including 134a. "It's premature to pinpoint one that we're targeting," Kerr says. Elf Atochem also reports R&D efforts with a range of HFCs, especially 134a.

INERT GAS 

Moving away from a fluorocarbon approach, Dow Plastics now offers PS foaming technology that uses 100% carbon dioxide as the blowing agent. Since the system's introduction in April '91, the company has sold four licenses in North America. Three will come on line at undisclosed locations in the U.S. over the next few months.

Currently, C|O.sub.2~ technology is limited to PS foams with densities between 2 and 10 lb/cu ft and thicknesses up to a quarter inch. Those limitations may pretty well restrict this technology to food packaging for now, but Gary Welsh of Dow's Styrenics technical-service group notes that Dow is hard at work to apply the technology to other areas.

Comparing the C|O.sub.2~ system with hydrocarbons and HCFCs, Welsh says the inert gas produces food-packaging foams with comparable densities and surface quality. But from an environmental angle, it doesn't face a coming phaseout like the HCFCs or VOC restrictions like the hydrocarbons. He adds that C|O.sub.2~ already comes in food grades due to its use in the beverage industry. Dow also downplays any global-warming liability, because the gas is produced as a byproduct of existing manufacturing processes. "So there are no net increase," Welsh asserts.

Dow offers a complete technology package for all-C|O.sub.2~ foam with its licensing agreements. "Everything from gas storage to shipping the product out the door is covered," says Welsh, He cites gas handling and injection method, die and mandrel type, and thermoforming equipment as a few of the things Dow helps specify. Welsh characterizes the retrofit as relatively simple for tandem foam extrusion systems. "Its not so complex that processors have to abandon existing capital equipment," he says. Welsh predicts "some cost savings" over HCFC-22 but says it's premature to judge the long-term economics of the C|O.sub.2~ system.

Another inert-gas solution may also be on the horizon. Du Pont's York envisions nitrogen foaming systems for PS in the future. "It's the only completely benign gas out there."