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Polyurethanes: regulatory cost pressures spur foam formulators.

Polyurethane formulators are speeding up efforts to reduce costs of foam formulations that meet environmental or flammability standards. For rigid foams, the cost pressure comes from the industrywide conversion to "cleaner" blowing agents. For flexible slabstock and molded foams used in bedding and furniture, there is a move to optimize flame-retardant formulations, which is being driven by impending regulatory changes to industry flammability standards.

Finding effective approaches to compensate for these regulatory cost pressures was a focal point in several of the technical presentations at the recent Polyurethanes 2003 Conference and Expo in Orlando, Fla., sponsored by the Alliance for the Polyurethanes Industry (API). Other highlights included innovative PUR solutions for automotive interior applications.

Conversion update

The conversion to blowing agents with zero ozone-depletion potential (ODP) has been taking place in all major segments of rigid foam production. This year heralded the phase-out of HCFC-141b, which has been the leading blowing agent for PUR insulation since it replaced CFCs. Production of 141b ceased as of last Jan. 1, and its use as a blowing agent in PUR insulation is to be eliminated as of Jan. 1, 2005, as mandated by the U.S. EPA. The phase-out date for production of HCFC-22 and HCFC-142b, which have lower ODP but also very limited use in PUR insulation foam, is Jan. 1, 2007.

The two categories of preferred replacement blowing agents are the HFCs and the hydrocarbons. In North America, HFC-245fa and to a lesser extent HFC-134a are the two key contenders, while cyclopentane, n-pentane, isopentane, and blends of these are the most popular hydrocarbons.

HFC-245fa is the predominant choice in U.S. appliance applications, where non-flammability and high thermal insulation properties are needed to meet strict energy-efficiency requirements on the finished products. HFC-245fa is popular despite its higher cost--$4.50/lb vs. $1.20/lb for HCFC-141b, and 70 cents/lb for cyclopentane/isopentane blends.

While it costs about half as much as HFC-245fa, HFC-134a has the disadvantage that it is a gas at normal ambient conditions (boiling point is 15 F) and it results in foams with higher thermal conductivity than HFC-245fa (which boils at 59 F). I, contrast, HFC-245fa foams generally result in very little change in energy usage of refrigerators/freezers compared with HCFC-141b foams.

HFC-245fa has been sold in commercial quantities under the name Enovate 3000 for a year by the sole North American producer, Honeywell International. It's important to note that the first-generation HFC-245fa systems were based on simple drop-in replacement of the blowing agent at typical HCFC-141b levels, but the newer systems utilize higher water levels for co-blowing with CO2. Significant progress is being made in optimizing foam performance while reducing the cost of HFC-245fa foams.

HFC-245fa is also gaining ground in production of discontinuous metal panels used in applications such as walk-in coolers and refrigerated warehouses. It is also being evaluated in production of water heaters, although that market appears to be leaning toward pentane.

In the polyisocyanurate (PLR) board-stock market, where cost and the need for a liquid blowing agent system are more crucial, hydrocarbons and their blends are now the preferred choice.

In PUR spray foams for insulating walls, roofs, tanks, and spas, HFC-245fa blended with high levels of water is emerging as the preferred blowing system over pentane. This is driven by fire performance and processing safety considerations as well as insulation value.

In automotive integral-skin foams, skin-quality requirements are being met with CO2, HFC-134a, or hydrocarbons.

Cutting costs in appliances

Various approaches are being explored to reduce the cost of HFC-245fa appliance foams. For example, Huntsman Polyurethanes reported on two ways of minimizing foam cost. One way is to substitute water for equivalent reductions in HFC-245fa loading. A second is to ensure maximum retention of the HFC-245fa in the polyol blend.

Huntsman researchers showed that HFC-245fa appliance systems can use lower levels of the blowing agent than was the case with HCFC-141b. Huntsman evaluated a range of [CO.sub.2] levels and found very little change in thermal conductivity between 25% and 45% [CO.sub.2] blowing. Lower levels of

HFC-245fa are desirable not just because of cost but also to reduce the vapor pressure of this low-boiling agent. According to Huntsman, the thermal insulation of the higher-[CO.sub.2] systems is maintained because of improved density distribution and cell-size reduction in foams with higher water levels. Physical properties of the foam also were not negatively affected by the higher [CO.sub.2] levels.

For HCFC-141b-containing polyol systems, storage and day tanks are typically blanketed with about 10 psi of nitrogen or dry air. Huntsman's HFC-245fa polyol-blend retention study determined that when 45 to 50 psi blanket pressure was maintained, the amount of blowing-agent loss was kept in the low range of 1% to 1.5%

Researchers from Bayer Polymers reported at the conference on promising foam systems with reduced levels of HFC-245fa. A typical 245fa foam formulation uses a small amount of water and contains about 13% HFC245fa at the mix-head. A test foam formulation with 11% 245fa and high water level reduced the density of the foam by 5% with no negative effect on any physical properties except thermal conductivity. The additional water resulted in a slight increase in k-factor (0.134 Btu-in./hr-[ft.sup.2]-F[degrees]@75F vs. 0.130 for the control. However, a 5% decrease in cost/lb was achieved with the high-water formulation. When coupled with the density reduction, it translated to a 10% overall reduction in material cost/cu ft of foam.

Bayer researchers also showed that foam cost reduction can be achieved by improving foam properties. Using a specially modified polyol, Bayer produced two test foams with elevated water levels and 12% or 10% 245fa. Although the higher water levels drove up the k-factor slightly, overall material cost reductions per cubic foot of foam were 5% and 10%, respectively.

Air Products and Chemicals, Inc. reported on new Dabco PM200, a blowing-agent-enhancing (BAE) additive designed specifically for HFC-245fa blown appliance foams. This novel additive has inherent surfactant properties and reportedly eliminates the need for a conventional silicone surfactant in the polyol blend. Furthermore, it produces a significant reduction in viscosity of the blend and allows 10% to 20% lower use levels of HFC-245fa--or reduced density at the same levels--while maintaining thermal and mechanical properties. PM200 reportedly shows good potential for use in other HFC applications such as spray foam.

Better building insulation

Great Lakes Chemical reported on flammability evaluations of novel flame retardants in PIR boardstock insulation blown with hydrocarbons. Great Lakes said the switch to hydrocarbons has reduced the ability of the standard hot-plate test to predict flammability performance of PIR roofing boards in the Factory Mutual Calorimeter test (FM 4450). PIR roofing board that now passes the standard hot-plate test generally fails the calorimeter test in constructions without a cover board. Great Lakes has focused on developing a new small-scale predictive test so that PIR roofing board without a cover board can meet FM requirements.

Great Lakes researchers tried two new hot-plate procedures, both of which indicate that new brominated flame retardants outperform the two chlorinated phosphate esters (TCEP and TCPP) currently used in virtually all PIR roofing boards. Both phosphates are under review by the European Risk Assessment (EURA) board, and concerns about human toxicity have been raised.

To compensate for the higher flammability of the blowing agent, the isocyanate index of hydrocarbon-blown PIR foam is typically raised to about 300, vs. 265 for HCFC-141b foam. Recent industry efforts are centered on reducing the index of hydrocarbon-blown foam to reduce costs. Great Lakes researchers identified CN-2837 as the best-performing of the experimental flame retardants with the new predictive test in foams with a range of iso indexes. At the lowest index (250), there was less shrinkage during the burn test. Also, the low-index foam expanded to a greater extent during the charring process.

Bayer Polymers reported on a Class I HFC-245fa rigid PUR foam system for discontinuous metal panels used in walk-in coolers and refrigerated warehouses. This system met Class I requirements at 3.5-in. thickness and will next be tested at 6-in. thickness to expand its market potential. This system reportedly processed well, and panels demolded after 30 min. The foam quality was said to be very good, although the panels were initially not as firm as HCFC-141b panels. Bayer researchers are working to improve the firmness of the foam system at demolding and to further optimize its physical and processing properties.

Honeywell discussed results of a foam aging study that compared k-factor performance of PIR boardstock produced with HCFC-141b, n-pentane, cyclopentane, and Enovate 3000 HFC-245fa. When tested at the standard mean temperature of 75 F (average of hot and cold sides of the sample), all the foams performed similarly, though Enovate 3000 showed slightly better performance, Honeywell said. When tested at lower mean temperatures (more representative of winter conditions), Enovate 3000 foams reportedly outperformed all others, particularly those blown with hydrocarbons because pentane condenses in the cold foam cells, resulting in an abrupt drop in insulation performance.

Burn testing flexible foams

In early 2002, the State of California proposed a change to the CAL TB 117 flammability test, which has been the de facto industry standard for furniture foam in the U.S. since 1975. Although the revision is stiff in draft form, optimization of foam formulations to meet the new flame-retardant specs will be a key technical issue facing all foamers supplying the U.S. furniture industry.

At the conference, Degussa Gold schmidt Chemical discussed the impact of silicone surfactants on flammability of flexible slabstock foam, specifically comparing the new CAL TB 117/draft 2002 with established flammability tests. The evaluation determined that the right selection of surfactant can reduce the consumption of flame retardant. In comparison with conventional surfactants, some of Goldschmidt's developmental silicone types reportedly can allow up to 30% reduction in the FR level. Goldschmidt's research also determined that the new CAL TB 117/draff 2002 is not necessarily more severe than the old CAL TB 117. Rather, any difference in foam performance in the two tests depends on the FR package used and the foam density.

Goldschmidt researchers concluded that for the optimal choice of silicone surfactant, a laboratory screening is absolutely essential once the new furniture test is established and the optimum FR package is selected. The company is equipped to perform all types of' burn tests at its new Polyurethanes Competence Center in Hopewell, Va.

Flammability wasn't the only aspect of flexible-foam performance discussed at the conference. BASF reported on a new all-MDI slabstock foam technology that is said to offer superior processing, excellent physical properties and durability, and the ability to fine-tune the "feel" and performance of the foam with minor adjustments. This Pluracel viscoelastic, "slow-recovery" foam technology is initially targeted for mattresses.

Pluracel foam formulations require no tin catalyst, exhibit fast cure, and are sufficiently open-celled that they do not require crushing. They also retain much of their slow recovery after fatigue. The fine cell structure is said to provide a soft, luxurious feel. Moreover, Pluracel foam reportedly passes the CAL TB 117 flammability test without any flame retardant. All of these desirable properties can be achieved over an extremely wide density range of 2.3 to 13 pcf. The technology is under development for molded foam used in high-end furniture cushions.

Auto interior innovations

Cannon gave an update on its "RIM skin" technology for soft-feel skins of interior components like door and instrument panels. Cannon says the RIM skin process produces less waste than spraying PUR skins in the mold. Cannon also says the RIM skin process will enable manufacturers to make car interior components that consist of just two layers--skin and rigid substrate--made of the same material. Compared with typical three-component (skin, foam, substrate) systems involving three materials, the all-PUR approach is said to offer easier recycling and superior design flexibility for incorporating airbags. The technology also has potential for seats and furniture.

Cannon reported that a major European auto-interior component supplier recently installed a plant to make door panels with an RRIM substrate containing 15% to 20% chopped glass and 7% recycled PUR. Initial production utilizes a PVC door skin, but prototype RIM skins are being tested. The complete plant includes two turntables with clamps and RRIM molds, two Cannon HE cylinder-type metering machines, and a recycling system to grind and reuse PUR from doors and bumpers.

Bayer's Hennecke Machinery division reported on its own SkinRIM technology for door and instrument panels. This closed-mold pouring process produces PUR cast skins that reportedly reduce or eliminate "grain washout," a common problem when PVC skins are thermoformed into complex contours. SkinRIM reportedly produces PUR skins of 0.5 to 3 mm using Hennecke's standard HK series metering units and MQ mixhead. Like Cannon, Hennecke advocates producing an all-PUR instrument panel by pouring or spraying a PUR skin and then pouring onto it a rigid PUR composite substrate that can be as thin as 1.5 mm. The latter can be produced with Hennecke's FipurTec Plus process using glass rovings or its NafpurTec variant using natural fibers.

An innovative application for Cannon's Foam-in-Place (FIP) gasket technology was described by company researchers. FIP gasketing, which utilizes a low-pressure dispensing mixhead, typically has been limited to electrical enclosures, lighting, filters, and drum lids. The new application is encapsulating an automotive rear quarter window. FIP has the advantage of curing at room temperature and provides a continuous seal with no seams that could cause leakage.

Cannon has supplied two turnkey systems in Europe for this new application. One is used to dispense a PUR gasket on an EPDM encapsulated window for a new automobile. Utilizing a Cannon shuttle table, 10 windows are being foamed on one platen while an equal number of parts on a second platen are being unloaded and loaded up for the next batch. The process includes plasma surface pretreatment of parts on the shuttle table before foaming. Total cycle is less than 40 sec per window, which is said to result in estimated production capacity of 1 million parts/yr.

At the second installation, the window glass is loaded on a Cannon Technos Shuttle Bed Clamp and indexed into a Cannon-Sandretto injection molding machine, which encapsulates the window with EPDM material. After demolding, the parts are placed on a conveyor and transferred to the FIP gasketing station.

Hennecke reported on a significant upgrade to its WKH oval conveyor for foaming car seats. WKH now incorporates the newly patented, automatic QCD (Quick Connect/Disconnect) station for mold carriers. A typical mold carrier can accommodate up to three bucket-seat molds, two 60/40 molds, or a single bench-seat mold. With QCD technology, carriers for production of various seat models can enter and exit the oval conveyor system "on the fly" and at full conveyor speed. This allows for off-line mold set-up, preparation, and maintenance without halting production.

NEED TO KNOW MORE?

Air Products and Chemicals, Allentown, Pa. (800) 345-3148, www.airproducts.com

Bayer Polymers LLC, Pittsburgh (412) 777-2000, www.bayer.com

BASF Corp., Urethanes, Wyandotte, Mich. (734) 324-6292, www.pu.basf.com

Cannon USA, Cranberry Township, Pa. (724) 772-5600, www.cannonusa.com

Degussa Goldschmidt Chemical Corp., Hopewell, NJ. (804) 541-8658, www.goldschmidt.com

Great Lakes Chemical Corp., Indianapolis (765) 497-6100, www.greatlakes.com

Hennecke Machinery Div., Bayer Polymers LLC, Pittsburgh (412) 777-2000, www.henneckemachinery.com

Honeywell International Inc., Fluorine Products Div., Morristown, NJ. (973) 455-3187, www.honeywell.com

Huntsman Polyurethanes, West Deptford, NJ. (800) 257-5547, www.huntsman.com/pu
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Author:Sherman, Lilli Manolis
Publication:Plastics Technology
Date:Dec 1, 2003
Words:2592
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