The polyurethanes industry appears to have entered a new phase in its decade-long struggle to meet approaching deadlines for phasing out HCFC blowing agents in favor of “cleaner” alternatives for rigid foams. Now that technically effective substitutes have been identified, the focus seems to have shifted toward maximizing cost-effectiveness with these new alternatives. The latter was the overriding theme of the recent Polyurethanes 2000 conference in Boston, sponsored by the Alliance for the Polyurethanes Industry. Most notable were presentations of cost-effective foam formulations for construction and appliances based on HFC-245fa, the leading contender in the U.S.
Other highlights of the meeting include a new method for foaming sandwich insulation panels using vacuum-assisted injection and a new generation of insulation that can be sprayed onto a rotating pipe.
Also newsworthy are integral-skin foams made with HFC-245fa that match the performance of CFC-11 and new silicone surfactants for open-cell and semi-rigid foams in automotive applications like headliners. New PUR chemistry for flexible foams and elastomers also emerged.
The leading candidates
The Montreal Protocol specifies January 1, 2003 as the phase-out date for production of HCFC-141b, the leading blowing agent in North America for PUR insulation. The Protocol’s equivalent phase-out date for HCFCs 22 and 142b, which have lower ozone-depletion potential (ODP), is Jan.1, 2007. They have had much more limited use in rigid PUR foam, mostly as blends with HCFC-141b. But neither such blends nor HCFC-124, which has even lower ODP, have been approved by the EPA as substitutes for HCFC-141b in rigid PUR.
Although the Montreal Protocol permits PUR foamers to use existing stocks of HCFC-141b until Jan. 1, 2010, the U.S. EPA shocked industry on July 11 when it proposed to accelerate the termination date by five years. Strict limitations on foam uses of HCFC-22 and 142b would be implemented on the same date. EPA’s proposal is strongly contested by the PUR industry, claiming it wouldn’t allow sufficient time to find new blowing-agent alternatives for all applications. Nor would there be time to build sufficient manufacturing capacity or develop application know-how. In addition, industry petitions warn that a premature phase-out would impose staggering economic burdens on industry for little or no environmental benefit.
In North America, some market sectors are moving faster than others to adopt alternative blowing agents. This is particularly so for the appliance industry, which has been racing to meet new Dept. of Energy standards that require 25-35% better energy efficiency by July 2001. The leading candidates for refrigeration foams are liquid HFC-245fa and gaseous HFC-134a. The latter is already in use both here and in Europe, even though it costs almost twice as much as HCFC-141b, which sells for around $1/lb.
Some appliance makers have already signed up to use non-flammable HFC-245fa, which will sell for around three times the cost of HCFC-141b. In Europe, liquid HFC-365mfc, another HFC with limited flammability, appears to be one of the major candidates for rigid foam insulation, both alone and in blends with cyclopentane. Semi-commercial quantities are being produced by Belgium’s Solvay SA. The company is aiming for full commercial production by the end of 2002. Due to patent issues, it will not supply the product here.
Honeywell (formerly AlliedSignal) has licensed exclusive North American patent rights for both HFC-245fa and HFC-365mfc from Bayer AG in Germany. Honeywell plans to start commercial production of HFC-245fa at Geismar, La., by mid-2002. The company has no current plans to make 365mfc but it does not rule it out for the future.
Unlike in Europe, hydrocarbons (cyclopentane, isopentane, and n-pentane) have never been serious contenders for the North American appliance industry due to the flammability issue and associated costs.
The jury is still out regarding the winning candidate for the more cost-driven construction sector. Industry evaluations have shown HFC-245fa to produce rigid insulation foams with the best K-factor of any in the market, as well as better K-factor aging than foams made with HCFC-141b. Researchers are evaluating blends of HFC-245fa with CO2 or hydrocarbons in order to address two key concerns of this market—the higher cost and higher vapor pressure of HFC-245fa than HCFC-141b.
Work with hydrocarbons alone remains primarily in rigid foam boardstock and sandwich panels. Pentanes have been shown to perform comparably to HCFC-141b and now appear to be serious candidates for these applications.
HFCs for construction
At the meeting, Honeywell reported on its latest trials with construction foams blown with HFC-245fa plus fairly high levels of water to generate CO2. This co-blowing technology was demonstrated in boardstock, metal-faced panels, and spray foams using standard equipment. The manufacturing advantage of HFC-245fa/CO2 formulations over hydrocarbons is non-flammability and a non-VOC classification from EPA.
Honeywell found that blending with water reduces the high vapor pressure of HFC-245fa, thus eliminating the need for a more costly type of container. The more water in the polyol blend, the lower the HFC vapor pressure. At 1.3 pbw water and 10 pbw HFC-245fa, the vapor pressure of a standard polyol blend is reportedly within industry-accepted levels for safe handling in a standard 16-gauge drum.
Boardstock laminate foams produced with various HFC-245fa/water blends were shown to have superior K-factor aging performance. Elevated levels of CO2 had no significant effect on initial K-factor, density, compressive strength, or dimensional stability. Work is under way to validate these findings at a commercial facility.
Honeywell also tested an HFC-245fa/CO2 foam system containing alpha-methyl styrene with metal-faced panels in a commercial-scale trial. The foam had better flow properties and resulted in less scrap and better K-factor than cyclopentane-blown foams. It also exhibited properties equal to or better than those of HCFC-141b foams. Resulting panels passed E-84 Class 1 burn specifications.
HFC-245fa/CO2 systems sprayed in commercial-scale roofing and wall trials were reported to produce foams with K-factors equivalent to those sprayed with HCFC-141b. Physical properties of the new foams were superior—similar to those seen in the past with the now-banned CFC-11.
Honeywell examined whether high levels of water can result in a large enough cost reduction to compensate for the higher price of HFC-245fa. Analysis of a roofing formulation indicates this technology is cost-equivalent to HCFC-141b technology at around 2-pbw water content. This comparison does not factor in any yield improvements that might be realized with the use of HFC 245fa.
Honeywell also reported on trials of an HFC-245fa/isopentane blend in a generic boardstock formulation. This blend is said to provide laminate-board makers a lower cost option with better K-factor than all-hydrocarbon-blown foams for applications where fire performance is not critical. Aged K-factor with the blends is similar to that of all-HFC-245fa foams.
Solvay reported similarly good results with HFC-365mfc blends. Most notable is a mix of HFC-365mfc and HFC-134a for spray and pour-in-place foams. It can be handled as a non-flammable product, and it yields foam properties similar to those with HCFC-141b, provided the polyol blend has been optimized for this blowing agent. Solvay also reported that blends of HFC-365mfc with hydrocarbons are an economically attractive way to improve the insulation value of foams for cost-driven markets and for plants that can handle highly flammable formulations safely.
New way to make panels
A new method for foaming high-quality sandwich insulation panels with vacuum-assisted injection was jointly developed in Italy by Cannon Group; MISA, a large panel maker; Manni, a press manufacturer; and Dow-Italy. The method is said to offer high productivity—over 300 panels/shift—along with excellent mechanical properties, including very uniform density distribution and enhanced compressive strength and adhesion.
The MVS (MISA Vacuum System) concept relies on controlled application of vacuum inside the foaming cavity of the press. The process reportedly allows use of blowing agents with a wider range of boiling points and also permits easy processing of polyisocyanurate foam.
The high manufacturing productivity achieved with MVS is linked to the use of shuttling platens for preparing the panels and to a very short demold time, thanks to the use of vacuum. An average 30-40% faster demold time over the conventional foaming method has been achieved across the entire range of thicknesses (60 to 130 mm). Occurrence of defects was less than 0.5% during the first three months, and sank to practically zero after some improvements in the preparation procedure. Excellent surface quality, free of bubbles or marks, is also reported.
Sprayed pipe insulation
Huntsman Polyurethanes announced a new generation of foam insulation that can be sprayed onto a rotating pipe and reportedly provides an optimal balance of high reactivity, good mechanical properties, and good heat resistance. These systems are based on aromatic amine co-initiated polyether polyols. In the past, such amine co-initiated polyols produced low foam heat resistance of 156 to 174 F. Huntsman’s new Daltofoam TE24205 and TE44208 polyols are said to produce foams that will withstand continuous service temperatures of 246 F or more for 30 years.
The new polyols were each reacted with Huntsman’s Suprasec 5005 polymeric MDI. TE24205 was used in an HCFC-141b blown system, while TE44208 was used in a fully water-blown spray system. Foam properties of both systems complied with the EN253 norm, according to the company. Similar good results were recently achieved in industrial-scale trials, Huntsman reports.
Huntsman also advocates continuous foam spraying instead of conventional discontinuous methods for insulating large-diameter pipes used for district heating and cooling systems and for transporting oil and chemicals. Besides the ability to produce pipes of any desired length, the continuous method is said to save money by reducing both foam density and the outer casing thickness.
HFC-245fa for appliances
Previous polyurethane conferences have heard evidence that refrigeration foams blown with HFC-245fa process well in existing machinery, produce K-factors comparable to HCFC-141b foams, and provide similar energy efficiency in fully assembled cabinets. This year, Bayer Corp. addressed the economic concerns of refrigerator makers regarding HFC-245fa—namely higher foam costs and higher overall manufacturing costs. Using the HFC-245fa appliance foam system it developed in 1997 for comparison, Bayer developed a less expensive foam system using 5 pbw less HFC-245fa and more water in the polyol blend. Density was very similar to the 1997 formulation, though average cell diameter was about 20% smaller. As a result, the foam’s thermal conductivity at 35 F and 75 F was 2-3% higher than its predecessor or an HCFC-141b foam.
Compared with commercial HCFC-141b systems, the new foam has comparable demold properties and densities, and slightly better compressive strength. Bayer says its data indicate that this foam will have similar or better aged K-factor, so that a refrigerator should have only about 2% or less reduction in energy efficiency vs. one insulated with a current HCFC-141b system.
News in automotive
HFC-245fa also appears to be very promising as a potential blowing agent for integral-skin foam automotive applications. HCFCs were banned in the U.S. from all such applications in 1996. CO2 (often in combination with HFC-134a) and hydrocarbons have been used with varying degrees of success. In Boston, Honeywell reported on the results of substituting HFC-245fa for CFC-11 in a commercial formulation.
Physical properties of the HFC-245fa foams were comparable to the CFC-11 foams in terms of skin quality, processing, and thickness. At the same weight percent of blowing agent in the polyol blend, free-rise density of HFC-245fa foams was about half that of the CFC-11 foams.
Honeywell also reported that HFC-245fa has better solubility in resin premixes than HFC-134a. At the same free-rise density, HFC-245fa provides a 25% to 50% thicker skin than HFC-134a, plus improved mechanical properties.
Turning from blowing agents to other additives, three new silicone surfactants for open-cell rigid and semi-rigid foam were presented by Goldschmidt. Although initial applications are in headliners, these products can also be used in energy-absorbing foams, packaging, and acoustic insulation. Open-cell content of foams can be controlled by varying the concentration of surfactant while maintaining a relatively fine cell structure.
One of the new products, Tegostab B8935 offers a balance of foam-stabilization and cell-opening properties. It is best suited for headliners, where a high proportion of open cells and a fine, uniform cell structure are desired. Tegostab B8871 is primarily a stabilizer with some cell-opening properties. It can be used alone or combined with the third product, Tegostab B8934, if more cell opening is needed. B8934 is primarily a cell opener with some contribution to stabilization. It is designed for use only in combination with a stabilizer such as B8871.
An EPA proposal to accelerate the phase-out of HCFCs puts added pressure on rigid foamers to adopt cost-effective alternatives.
Cannon helped develop a new method of foaming sandwich insulation panels with vacuum-assisted injection. It offers high productivity—over 300 panels per shift. (Photos: Cannon Group)
An Automatic Pressure Tracking Adiabatic Calorimeter (APTAC) was used by Bayer to measure thermal stability of a five-part appliance foam formulation with a reduced level of HFC-245fa. No sign of thermal decomposition was observed at temperatures up to 100 C.
Bayer’s five-part, reduced-HFC-245fa foam is shown to be only slightly poorer in insulation performance than either the commercial HCFC-141b appliance foam or the 1997 HFC-245fa system.
New Materials for Flexible Foams & Elastomers
New polyols, flexible foam systems, and TPUs were also introduced at the Boston conference:
Dow Polyurethanes developed low-resilience flexible foam formulations based on special silicone cell-opener additives. Open-celled LR foam was produced using CO2 blowing with a reduced amount of water. This allowed for an index as high as 105 while still obtaining the same hardness range as regular LR foam.
Bayer introduced Arcol I 9000, a new high-ethylene-oxide polyether polyol that can be used as a major polyol component or as an additive in flexible foams. It reportedly produces soft and ultrasoft foams with a unique “silky” feel for bedding and furniture.
Bayer also discussed initial trials with a reportedly unique polyol, called Experimental R-3083, which produces soft viscoelastic foams at 100 or higher index levels. This is said to eliminate processing inconsistencies associated with low-index foaming, and yields foams with superior shape conformance, memory, and compression-set resistance.
Dow Polyurethanes discussed a novel generation of polyether polyols, based on propylene oxide and/or ethylene oxide, for cast and sprayed elastomers. The new Vorastar systems reportedly offer up to tenfold improvement in abrasion resistance over standard polyester-based grades. Resulting elastomers are said to combine high hydrolytic stability with excellent wear resistance.
Huntsman described a new family of TPUs for footwear with hardness as low as 55 Shore A (until now, the softest available was 70A). Nonetheless, Avalon TPUs boast better abrasion resistance than conventional PUR elastomers or other rubbers.
Shell Chemical discussed TPUs made with a new type of polyol based on polycarbonate made from 1,3-propanediol. TPUs made with PTMC 2000 polyol boast good abrasion resistance and low compression set, plus excellent oil and solvent resistance. The polyol also can produce transparent elastomers.
Processing Considerations of
ALTERNATIVES TO HCFC-141b
Moderately low-boiling (B.P. = 59 F)
May experience frothing during pouring
Machine modifications needed:
- Possible temperature-control issues
- Seal materials must be compatible
- May require on-site blending
Low-Boiling Blowing Agents
(HCFC-22, HFC-134a, CO2)
Low-boiling and gaseous at room temperature (B.P. <32 F)
Will froth during pouring
Machine modifications needed:
- Component tanks must be rated for at least 150 psi
- Tank pressurizing circuit must be capable of maintaining pressure at all times
- Metering pumps must have higher pressure rating
- Seal materials must be compatible
- Flow meters must be used for calibration
- L-shaped mixheads may be required for efficient mixing and froth expansion control
- Larger heat exchangers may be needed to lower the chemical temperatures
- Isolation valves must be placed on inlet and outlet of pumps, filters, heat exchangers, etc.
- May require on-site blending
Pentanes and Blends of >1% Pentane
Boiling points similar to HCFC-141b
Machine modifications to accommodate a flammable liquid:
- Limit hazardous areas with multiple enclosures around specific machine components
- Primary and secondary ventilator system
- Atmospheric monitoring system
- Safety management and control system
- Leak detection and monitoring
- May require on-site blending
Source: Cannon U.S.A.