HFCs, pentanes, and blends are all in the running for next-generation rigid insulation foams. SPI's PUR Conference provided a status report.

As the deadline for phasing out ozone-depleting HCFCs draws nearer, the polyurethanes industry is stepping up efforts to develop and supply "cleaner" alternatives for rigid foams. This was a central theme of SPI's Polyurethanes Expo '99 in Orlando, Fla. Conference papers highlighted efforts to replace HCFC-141b, the leading blowing agent in North America for PUR thermal insulation.

The Montreal Protocol specifies a January 1, 2003 phase-out date for HCFC-141b. Industry has until 2007 to replace HCFCs 22 and 142, which have lower ODP (ozone depletion potential). However, these have limited application in rigid PUR foam and mostly in blends with 141b. HCFC-124, which has even lower ODP, can be used until 2010. HCFC-124 was brought forward as a candidate in the last year by AlliedSignal, which offers it commercially. However, it has not been approved by EPA as a blowing agent for rigid PUR foam and may not turn out to be a serious contender.

The presentations in Orlando indicated that the leading candidates to replace HCFC-141b currently include the liquid HFCs 245fa and 365mfc, gaseous HFC-134a, and hydrocarbons (cyclopentane, isopentane, and n-pentane). The latter, which are accepted as zero-ODP blowing agents overseas, have captured the interest of foamers here. Most of the current activity with hydrocarbons in the U.S. is in rigid foam laminations--both boardstock and sandwich panels. However, blends of HFC-245fa with CO2 and other agents are also very much under consideration for insulation uses.

The pressure is even greater on the appliance industry, which must meet new Dept. of Energy standards that require 25-35% better energy efficiency by July 2001. Extensive development efforts have centered on new rigid-foam systems for refrigeration. The leading candidates appear to be HFC-245fa, HFC-134a--a commercially available product that is already being used here and in Europe--and cyclopentane.

The conference also highlighted advances in PUR foam chemistry and equipment for automotive uses, particularly molded seating. They include a new cold-cure, low-density MDI foam technology; non-fugitive catalysts and low-fogging surfactants for flexible foam; and a low-BHT polymer polyol for cold-cure molding.

Making HFCs available

The key question a year ago was when would new HFCs become commercially available. Today, that question is getting some answers.

In mid-September, AlliedSignal Inc. received U.S. EPA approval of HFC-245fa for use in all foam-blowing end uses. The company has picked its Geismar, La., site for production of the new blowing agent. AlliedSignal plans to make the product commercially available by mid-2002. Capacity has yet to be finalized, as projected demand is still being determined. HFC-245fa's insulation performance has been shown to be superior to other non-ozone depleting products, including hydrocarbons and HFC-134a.

Meanwhile, ICI Klea plans to increase capacity for its Klea HFC-134a at St. Gabriel, La., and in the U.K. and Japan. Capacity at the three plants will be increased by 22 million lb/yr initially and by a total of 143 million lb/yr in 2001. A separate project includes plans to boost capacity at St. Gabriel by an additional 44 million lb/yr as required to meet market demand.

In September, Belgium's Solvay SA started up a pilot plant for HFC-365mfc. It has plans to start up commercial production sometime in 2002. HFC-365mfc has a higher boiling point than 245fa (104 F vs. 60 F), and Solvay is touting it as more suitable than 245fa for building insulation.

However, Solvay cannot supply the product in North America because of patent issues. AlliedSignal has licensed exclusive North American patent rights for both HFC-365mfc and HFC-245fa from Bayer AG. AlliedSignal has no plans to produce HFC-365mfc commercially. Company sources say HFC-245fa is the closest thing to a drop-in replacement for HCFC-141b as it requires only slight formulation changes, and it has been shown to be the best performer even for the more cost-sensitive construction market. In fact, within the last year AlliedSignal has come up with blends of 245fa and water that address both processing and cost limitations of using 245fa in spray foams.

What's new for appliances

In Orlando, Dow Chemical and Maytag-Galesburg Refrigerator Products, a div. of Maytag Corp. in Galesburg, Ill., discussed development of appliance foams using liquid and gaseous blowing agents. They reported that HFC-245fa, HFC-134a, and HCFC-124 reduce foam surface defects in contact with steel cabinets and plastic liners. This advantage is said to be due to their lower boiling points compared with HCFC-141b and cyclopentane.

Moreover, HFC-245fa and HCFC-124 have little or no effect on appliance manufacturing processes or DOE energy-efficiency ratings. In one study, the K-factor of an HFC-245fa-blown foam neared that of ones made with HCFC-141b. While HFC-245fa gave a higher K-factor at 75 F, its foams performed as well as or better than 141b foams at 30 F, where it counts. HCFC-124 performed even better. But Dow and Maytag sources feel that since EPA recently gave the green light to HFC-245fa, it is unlikely to do the same for an HCFC.

AlliedSignal's update on HFC-245fa emphasized that the product is non-flammable and has a low order of toxicity. Studies have shown the product to be less aggressive than HCFC-141b to HIPS liner material used in refrigerator cabinets and therefore the barrier layer can be eliminated.

In addition, compared with HCFC-141b, HFC-245fa appears to provide equal energy efficiency, while refrigerators foamed with HFC-134a and cyclopentane use 14% and 11% more energy, respectively. HFC-245fa is expected to be about 9% more expensive to use than HCFC-141b. HFC-134a and cyclopentane would be about 38% and 30% more expensive, respectively.

Nonetheless, work continues on optimizing use of the two currently available 141b replacements, HFC-134a and cyclopentane. A blend of the two was shown to offer a good compromise between the better insulation value of cyclopentane and the better dimensional stability obtained with 134a. Such a blowing combo is not expected to need a barrier liner over the foam.

Bayer Corp. reported at the conference that high-purity cyclopentane produces better K-factors than blends of cyclo- and isopentane. The latter produced neither lower densities nor higher compressive strengths as had been expected. Bayer researchers also noted that increasing the foam's water level reduced the amount of catalyst needed to obtain a given gel time and reduced the foam density obtained with a given amount of auxiliary blowing agent. Bayer says those two factors can reduce costs. Foam with higher water levels also had lower K-factor due to improved foam cell structure.

New foams for construction

Huntsman Polyurethanes (formerly ICI Polyurethanes) reported on the first phase of its work on replacing HCFC-141b in rigid spray foams for roofing with water or water/HFC-134a blends. Both formulations reportedly met specifications for density, compressive strength, and dimensional stability, while adhesion and appearance were judged to be acceptable. When a small amount of HFC-134a was added to a water-blown foam, all aspects of dimensional stability improved. This is because the heavier blowing agent molecule does not diffuse from the cells as rapidly as CO2 does. Thermal performance with various foams was in line with what can be expected for water-blown foams. Initial K-factors ranged from 0.18 to 0.21 Btu-in./hr-ft2-¡F, with the variation attributed to processing variables affecting cell size and orientation. Huntsman researchers believe these parameters could be manipulated to keep the K-factor at the low end of the range.

Solvay reported on its lab-scale development of formulations based on HFC-365mfc and blends. A key drawback of HFC-365mfc is its low solubility in standard polyols, compared with HCFC-141b. Trials with a non-flammable blend of 93% HFC-365mfc and 7% HFC-134a showed it can be used in applications ranging from discontinuous panel production to spray foams without major problems, once the polyol systems have been optimized for solubility of 365mfc. In addition, field trials showed that the losses of HFC-134a during foam production are very limited, even in spray foam.

Trials with a blend of HFC-365mfc and n-pentane in industrial PIR laminate foaming plants showed that it can achieve better insulation value than foams with hydrocarbons.

Better automotive foams

At the meeting, there were several papers on flexible-foam developments for car seats and mats for sound insulation. The issue of foams' contribution to VOCs and windshield fogging was addressed in two reports.

Air Products & Chemicals unveiled a family of proprietary, non-fugitive, cell-opening blowing catalysts. These experimental catalysts chemically bind to the foam matrix, rendering them incapable of migrating afterward. As a result, the new catalysts are said to provide significant improvements in fogging and vinyl staining. They are also said to provide good physical properties (dimensional stability, airflow, compression set, and crushability) equal to or better than industry standards.

Goldschmidt AG reported on three new low-fogging (LF) silicone surfactants--Tegostab B 4113 LF, 8715 LF, and 8729 LF--designed to replace currently used products without sacrificing performance in foams based on MDI, TDI, and blends. The new LF products were shown to perform as well as established surfactants in terms of foam structure, density, and other physical properties.

Bayer reported on a cold-cure, low-density, MDI-based flexible-foam technology for automotive seating that boasts excellent elongation and tear properties, along with good humid-aged and wet-set performance. The secret is said to be a careful balance of polyol functionality and isocyanate composition and functionality at the elevated water level necessary to reach the lower densities. Core densities below 2.5 pcf can be achieved while maintaining good foam performance, Bayer says. In addition to molded seating, the technology is suitable for foam-in-cover seating, headrests, and sound-deadening carpet underlay.

Shell unveiled Caradol MD32-04, a new "BHT-lean" polymer polyol that is said to produce intermediate-hardness, high-resilience, TDI-based foams for auto seating. It reportedly also exhibits a wide processing latitude. This new type of polymer polyol, made with Shell's POSTech technology, contains stably dispersed polystyrene particles. Mechanical properties of foams made with the new polyol include superior tear strengths, leading to shorter demold times, as well as excellent foam durability, which enhances both static and dynamic seating comfort.