Polyurethanes: Foams Go 'Green' at Ever-Lower Cost

As the polyurethane foam industry converts to "cleaner" blowing agents required by environmental regulations, the focus is on minimizing cost and maximizing performance in areas such as mechanical properties, flammability, and thermal insulation value.

At the recent Polyurethanes Conference 2004 in Las Vegas, sponsored by the Alliance for the Polyurethanes Industry (API), a major share of the technical presentations addressed rigid PUR foams blown with HFC-245fa, HFC-134a, and pentane. Speakers unveiled new formulations to reduce levels of costly HFCs. They introduced polyols, isocyanates, surfactants, catalysts, flame retardants, and other additives that boost performance in non-ozone-depleting blown foams. A novel flexible isocyanurate HR foam offers a new approach to flame-resistant car seats. Equipment developments were also discussed, such as improved mixing heads, and use of thermoformed plastic sheet with PUR foam backing to make refrigerator doors and tractor hoods.

 

Regulatory update

Conference speakers from the U.S. Environmental Protection Agency (EPA) and Consumer Product Safety Commission (CPSC) addressed pending regulations. EPA environmental protection specialist Suzie Kocchi detailed the Final Rule (69 FR 58269) on the use of HCFC-141b in foams, published by EPA on Sept. 30. HCFC-141b has been the leading blowing agent for rigid foam insulation since it replaced CFCs. But EPA now states that as of Jan. 1, 2005, HCFC-141b will be unacceptable for use as a foam blowing agent with some minor exceptions for space vehicles and defense or nuclear applications. Formulated spray foam systems containing 141b that are already in inventory and on a certified list can be used by contractors until July 1.

Kocchi also addressed EPA's required phase-out of production and import of HCFC-22 and HCFC-142b, both of which have lower ozone-depletion potential (ODP) than HCFC-141b, but also have limited use in PUR insulation foam. She noted that EPA hopes to end use of HCFC-22 and 142b by 2010. 

Kocchi also ex plained the recent SNAP (Significant New Alternatives Policy) Notice 19 (69 FR 58903), published by the EPA on Oct. 1, which approved a new non-ozone-depleting alternative for use in spray foam. Developed by Foam Supplies, Inc., Ecomate is a patented blowing agent based on methyl formate. It is said to have zero ODP and zero global-warming potential (GWP) and is offered alone or blended into systems.

Meanwhile, the CPSC is very close to issuing a notice of proposed rulemaking addressing furniture fires ignited by cigarettes and small open flames. Although no details were revealed, CPSC project manager Dale Ray says the rule under consideration would apply to all residential upholstered furniture manufactured or imported for sale in the U.S.

 

HCFC conversion proceeds

All major rigid foam applications are well under way in converting to zero-ODP blowing agents. The primary contenders in North America are hydrofluorocarbons HFC-245fa and, to a lesser extent, HFC-134a (usually with high water levels for co-blowing with CO2), as well as the hydrocarbons cyclopentane, n-pentane, and isopentane. The newest contender is the methyl formate-based Ecomate.

HFC-245fa is dominant in appliance applications due to its non-flammability and higher thermal insulation properties, despite its price of $4/lb. That compares to $2/lb for HFC 134a and 50¢ to 90¢/lb for pentanes. HFC-245fa is also gaining ground in spray foams for insulating roofs, walls, tanks, and spas, as well as production of discontinuous metal panels. The sole North American producer is Honeywell International.

More cost-sensitive polyisocyanurate (PIR) boardstock insulation is moving toward hydrocarbons. The disadvantage of pentanes and pentane-extended polyols is that they are flammable. However, with proper safety measures, they have been used safely for a wide range of PUR foam products from refrigerators and freezers (primarily in Europe) to water heaters, construction panels and insulated pipes.

Pentane-blown foams have insulation K-factors comparable to those of foams with HFC-245fa and HFC-134a. Both HFCs have GWP values about 500 times higher than pentane's.

Gaseous HFC-134a is being used in automotive integral-skin foams and is also getting some play in appliances. It is a potential contender for building insulation when additives are used to reduce its very high vapor pressure.

Zero-ODP, zero-GWP Ecomate blowing agent is priced in the same range as pentanes. It has flammability characteristics similar to that of HCFC-141b. Because of its high solubility, low molecular weight, high blowing efficiency, and low volatility, it reportedly is effective at much lower levels than HCFC-141b or HFC-245fa. For example, a foam system using 15% HCFC-141b may only require 5% to 6% Ecomate to obtain the same density.

Ecomate has been used commercially within the last three years in PUR insulation foams for drink dispensers and large coolers and is being field tested for refrigerators, boardstock, and sprayed rigid foams.

 

Economical appliance foam

A great deal of effort and a variety of approaches are being directed toward improving the cost and performance of HFC-245fa appliance foams. For example, Bayer MaterialsScience reported on ways to make foams more economical by using less 245fa and increasing water levels to generate more CO2. Bayer researchers showed that HFC-245fa can be reduced by 68%—from 12.5% to 4%—while the average K-factor increases by only 11%. Another strategy to reduce foam cost is supplementing reduced levels of HFC-245fa with HFC-134a.

The researchers indicate that for very low K-factors of 0.123 to about 0.129, using HFC-245fa and water is the best choice. For K-factors between 0.130 and 0.136, a foam co-blown with HFC-134a and 245fa may be more cost-effective, though these systems may require special equipment to handle the gaseous HFC-134a. For applications that can use K-factors above about 0.137, HFC-134a or cyclopentane can be the sole blowing agent.

Dow Chemical Co. has developed a novel polyol technology that allows appliance foams to use less HFC-245fa while enhancing post-demold foam expansion and maintaining K-factor.

Dow has designed a predictive model to assist in customizing foam systems with 245fa and the new polyol. The model can specify a foam system that meets customer requirements and predicts its reactivity, density, blowing-agent level, insulation performance, and demold expansion.

Degussa (which acquired surfactant supplier Goldschmidt Chemical) reported that new silicone surfactants can improve foam quality and provide more efficient utilization of HFC-245fa in appliance foams. Using an optimized surfactant significantly reduces freeze-stable density and minimum fill density while improving K-factor in "next-generation" HFC-245fa systems, including ones with low and high water contents or co-blown with HFC-134a.

In a system using a low level of HFC-245fa with HFC-134a, developmental surfactant EP13 improves flow by 3.4% and K-factor by 2.7%, compared with workhorse Tegostab B8465. Smaller but still significant improvements can be achieved in a high-245fa/low-water system with new Tegostab B8481, which improves flow by 0.5% and K-factor by 2.2%.

In another 245fa/water system, developmental EP3 surfactant reportedly improves K-factor and freeze-stable density (FSD) 1.5% and 2%, respectively. In the same system, developmental EP8 and EP9 surfactants both reduce FSD by 3.2% without loss of thermal performance, Degussa reports.

 

FR building insulation

Albemarle has developed a new series of Saytex low-viscosity brominated flame retardants that provide greater formulation flexibility in HFC-245fa foams as well as some pentane-blown PUR and PIR systems for lamination boardstock, pour-in-place, and sprayed foams. Albemarle researchers say a Class I fire rating can be achieved in pour-in-place PUR blown with either HFC-245fa or cyclopentane. In 245fa foams, Saytex XP-7272 provided the best flame rating (27.8) and smoke results (248). Best results in pentane-blown foams were obtained with Saytex RB-7001, which gave a flame spread of 29.4 and smoke density of 415.

PIR open-pour foam blown with HFC-245fa can also achieve Class I, although smoke levels are relatively high. Saytex retardant XP-7353 was the best performer for PIR, with a flame spread of 24.5 and 411 smoke density.

Saytex XP-7353 makes a Class I, 245fa PUR spray foam with a flame spread of 27.4 and 276 smoke.

Tosoh Corp. came out with new Toycat trimerization catalyst systems that significantly improve adhesion and hydrolysis resistance of PIR foams containing polyester polyols and zero-ODP blowing agents. For example, in HFC-245fa foams, new TR20/D10 or TRX/D10 reportedly provide high adhesive strength. In n-pentane foams, TRX20/ACK/DT and TRX/DT provide high adhesive strength. In water-blown PIR foam, DM70 and D60 provide the highest adhesive strength, while a TRX/DM70/TMF package exhibits significantly improved system stability.

Arkema Inc. (the new name of Atofina Chemicals) has previously demonstrated that its zero-ODP and very low-GWP additive, trans-1,2-dichloroethylene (TDCE), can significantly improve the fire-performance of HFC-245fa foams. Researchers have since found that TDCE also allows lower HFC-134a levels, which significantly reduces the blowing agent's vapor pressure, making the blowing agent more user-friendly in PUR insulation. TDCE also dramatically reduces the viscosity of polyols and improves foam processing.

Bayer MaterialScience has developed a rigid PUR spray foam blown with cyclopentane for insulating high-temperature (above 250 F) fluid pipes in chemical plants. The new formulation utilizes a phthalic-based polyester polyol with a polyether polyol, polymeric MDI, and a combination of amine and metal-based catalysts. Recently evaluated at a commercial insulated-pipe manufacturer, the system reportedly processed very well and foam properties were comparable to or better than an existing system certified to the European EN 253 standard.

Honeywell has conducted studies of its Enovate 3000 (HFC-245fa) in spray foams for roofing and walls in comparison with HCFC-141b foams. Honeywell's aim is to provide spray foam applicators with recommendations on spray gun selection and operating conditions that can improve foam quality and application yields in specific foam application environments.

Foams based on Dow Chemical's Voracor CY 3019 spray formulation with Enovate 3000 had equivalent or superior performance and a wider application window than the commercial HCFC-141b system. Voracor CY 3019 sprayed roof foams boasted smoother surfaces, which can reduce the roof assembly's installed cost since it requires less coating. HFC-245fa also caused a dramatic reduction in "wall creep"—the lateral movement of foam after the rate of rise slows. This would eliminate a problem for applicators doing detail work around roofing penetrations such as drains. There was no creep with the Voracor CY 3019/245fa foams versus substantial creep with HCFC 141b foams.

 

Automotive developments

BASF's Elastogran subsidiary and Swiss equipment supplier Isotherm AG together developed a process to help the automotive industry overcome difficulties in back-foaming leather-covered interior upholstery. The new rear-foaming process is being introduced to the U.S. by Linden Industries. Fabrics can also be back-foamed with this process.

The method is said to eliminate adhesion problems and orange peel defects caused by exposing the leather directly to urethane chemicals. It also eliminates the need for seam sealing. Going from six to three processing steps also reduces cycle time and labor, making it cost-effective for large components such as instrument panels.

The key is to mold the foam backing separately, allowing it to cure just enough to remain tacky. Then it is pressed into the preformed leather covering in a mold, where it reportedly forms a good bond.

Bayer researchers have developed novel high-resilience foams that boast greatly reduced flammability for auto seating and premium furniture. The secret is building isocyanurate structures into the foam chemistry. This is done by preparing a reactive isocyanurate that can be added to the formulation. Foam properties are said to be much better than "one-shot" flexible isocyanurate foams. Bayer's new foams are said to be the first that both pass open-flame burn tests such as MVSS-302 and maintain foam comfort, durability, and stability without altering processability.

Foam flammability is reduced because PIR is the most thermally stable reaction product of isocyanates. Because no other flame retardant is needed, according to the researchers, this new class of flexible isocyanurates can achieve new levels of density reduction and foam performance.

 

New mixhead technology

Three new technologies for high-pressure PUR mixheads from Linden Industries are geared to open-pour or multi-density applications. First, LaserSite is a retrofittable device designed to cut the margin of error in open-pour applications by assisting operators in orienting the exact pour point in the mold. Whether pouring is manual or robot-assisted, there is always potential error in aiming where the material will end up in the mold. The device makes pouring more accurate by projecting three dots onto the surface of the tool to indicate where the shot is aimed.

Second, Linden introduced an L-style mixhead for multiple-density foams like those in car seats requiring a soft center and firm sides. It uses two hydraulic cylinders to create consecutive mixing chambers. Software signals a change in the orifice to adjust the pressure at the different ratios.

Third, for processors who cannot afford computer-controlled servo orifices, Linden has developed an hydraulic variable orifice that can be set for two fixed needle positions, one for high throughput and one for low. It can be adjusted to achieve optimum impingement pressure. The needle position is operated by the existing mixhead hydraulics. The two-position orifices can easily be added to existing machines that have variable-frequency drives to automatically change throughput. The modification involves reprogramming the machine to use alternate settings.

 

Backfoaming formed sheet

Cannon has come up with new applications for its InterWet technology that mixes fillers and reinforcements with PUR chemicals inside the mixhead. It was designed for structural interior and exterior vehicle components, using chopped glass fibers as an alternative to glass mat. More recently, the technology has been used for backfoaming thermoformed plastic sheets. InterWet was used by GMP SpA of Oderzo, Italy, to replace the typical foam-filled steel refrigerator door with an all-plastic version. Its patented Foiled PUR Technology (FPT) uses the InterWet process to deposit filled foam directly onto the backside of preformed sheet in an open mold. The sheet provides an aesthetic surface in a variety of colors and decorative effects while eliminating the costly painting step. Thermoforming also offers greater freedom of shapes—such as undercuts for hand grips—than does stamping sheet metal.

GMP SpA took this approach a step further by using InterWet with PUR and glass fibers on the back of thermoformed sheets. This Foiled FiberPur Technology (FFT) has been used with PVC or PETG sheets to make large exterior parts like hoods, bumpers, and tool carrier panels for agricultural and construction equipment.