PUR foams: 2003 deadline looms for HCFCs.

First CFCs got the axe, and soon it will be HCFCs' turn. Environmental acceptability is a moving target that keeps PUR foamers on the run.

Having taken less than a decade to make the transition to blowing agents with lower ozone-depletion potential (ODP), polyurethane foams are now racing toward zero ODP. For rigid PUR and polyisocyanurate (PIR) foams, the year 2003 is the deadline for phasing out use of HCFC-141b, the leading replacement for CFCs in the U.S. R&D on non-chlorinated blowing agents with zero ODP and low global-warming potential, such as liquid HFCs and water-blown foams, is progressing at a feverish pitch.

This sense of urgency permeated the 1997 Polyurethane World Congress held in Amsterdam last month under joint sponsorship by SPI's Polyurethane Div., the European Isocyanate Producers Association, and the organizers of the UTECH exhibitions and conferences. This report highlights the new developments presented in over 70 technical papers.

* For construction: Liquid HFC in commercial trials; progress in all-water-blown foams.

* For appliances: Foams based on HFC-245fa.

* For automotive: Novel C[O.sub.2]-blowing technology for integral-skin foams; high-performance TDI and low-density MDI seating; improved safety foams; new flame retardant for better flame lamination.

* For structural foams: Silicone surfactant with high stabilizing activity.

* For slabstock: All-MDI water-blown foams; new surfactants and FR agent.

HFCs FOR CONSTRUCTION

Liquid HFCs such as 245fa and 365mcf appear to be the leading contenders for replacing HCFC-141b in rigid foams in the U.S. They are expected to become available in small commercial quantities by 2000. Three companies gave papers on HFC-blown foams for building construction.

AlliedSignal described commercial-scale evaluations of its HFC-245fa in various construction applications within the last year:

* PIR boardstock: Good-quality HFC-245fa foams produced at multiple facilities reportedly show significantly better physical properties than board made with HCFC-141b. K-factor insulation values for the two foams are equivalent. Initial tests show the HFC foams to have acceptable burn properties.

* Spray and roofing foam: HFC-245fa foams have K-factors matching those of HCFC-141b foams but are stronger, with properties resembling CFC-11 foams and better aging performance than is obtained with HCFC-141b.

* Metal-face panels: HFC-245fa foams have better physical properties than HCFC-141b foams with high water levels. Initial K-factors were equivalent. Adhesion properties of the HFC foams were acceptable.

* Bunstock: Bunstock used to produce fabricated products made with HFC-245fa show initial K-factors similar to HCFC-141b foams but with superior compressive strength and dimensional stability.

Meanwhile, Bayer reported on recent evaluations of rigid foam laminations - both boardstock and sandwich panels - processed with HFC-245fa in comparison with HCFC-141b foams. Properties such as flow, compressive and tensile strength, and adhesion were improved with HFC-245fa, while K-factor and burn resistance were adversely affected.

Bayer also discussed preliminary evaluations of HFC-245fa in low-density rigid foams, where low thermal conductivity and good structural integrity are required. It appears to be a viable candidate for refrigerated transportation containers, structural components of entry doors, and appliance storage water heaters.

Solvay reported on its latest progress with both HFC-245fa and HFC-365mfc. With its low boiling point of 60 F, HCFC-245fa is viewed as a good option for refrigerators and freezers where its slight frothing effect is advantageous. HFC-365mfc has a boiling point of 104 F, making it a better option for building insulation, Solvay says.

ALL-WATER FOAMS FOR CONSTRUCTION

Two companies reported on C[O.sub.2]-blown PUR construction foams that reportedly overcome problems previously associated with water-blown foams.

Dow Europe reported on six years of successful use of special polyether polyols in metal-faced sandwich panels blown with water. Unlike some other water-blown foams, these products meet industry requirements for mechanical properties, adhesion, dimensional stability, and thermal conductivity. They also process readily on standard equipment without modification.

Nippon Polyurethane Industry Co. of Japan has developed a new all-waterblown PUR foam for insulation panels that features micro-cellular structure and enhanced strength. It employs a mixture of a high-functionality polyol for foam strength, a flowable polyol to reduce viscosity, and a low-viscosity polymeric MDI. Good dimensional stability, low thermal conductivity, low friability, and good adhesive strength are said to result. Foam density is similar to HCFC-blown foams.

HFCs IN APPLIANCE FOAMS

Reports on zero-ODP appliance foams and cabinets were presented by AlliedSignal, Bayer, and Dow. All three focused on use of HFC-245fa.

Recent studies by AlliedSignal showed HFC-245fa to produce appliance foams with physical properties comparable to those of HCFC-141b. In a freeze-stable density study, HFC-245fa foams were stable at lower overpacking than HCFC-141b at 1.5 php water, which indicates a potential reduction in foam cost per refrigerator.

Bayer compared new HFC-245fa foam systems for refrigerators and freezers to earlier HFC-245fa foams and HCFC-141b foams. Improvements were seen in K-factor and other properties with a new HFC-245fa system versus a 1995 version. The new system has properties comparable to HCFC-141b foams and has a slightly lower freeze-stable density at a lower packing level. K-factor suggests that similar or better energy performance can be obtained with the HFC245fa foam, Bayer says.

Dow and Maytag-Galesburg Refrigerator Products reported jointly on recent blowing-agent evaluations in a top freezer cabinet. HFC245fa, HFC-236ea, and cyclopentane were compared with HCFC-141b. The HFC-245fa foam showed the lowest K-factor at 75 F and a lower percent overpack than the HCFC-141b foam. Its cabinet energy performance was essentially equivalent to the HCFC-141b foam.

INTEGRAL SKINS WITH C[O.sub.2]

New C[O.sub.2]-blown foam technology for producing PUR semi-rigid integral-skin (SRIS) automotive components was the topic of reports from Dow Europe and by Bayer jointly with Otto-Bock Kunststoffe and Sumitomo Bayer Urethane.

Dow discussed a novel liquid-C[O.sub.2] blowing technology for SRIS steering wheels, said to overcome the key draw-back - absence of skin formation - or conventional SRIS water-blown foams. Dow's new technology reportedly can achieve a better SRIS foam density gradient with increased skin densification. Key properties like abrasion and "touch feel" (ratio between compression load deflection and hardness) of such foams are said to closely approach those of CFC-11 SRIS foams. Also claimed are good processability and faster demolding: Steering wheels of 5-25 pcf can be demolded in just 70 sec.

Bayer reported on new C[O.sub.2] blowing systems that contain neither water nor added free C[O.sub.2]. Instead the foams are produced by reaction of isocyanate with special amine chain extenders. These systems reportedly can be processed on existing equipment with demold times down to 60 sec for production of SRIS auto-interior products having a high level of mechanical properties. An additional benefit is that these systems can use polymeric MDI instead of the more expensive monomeric MDI required by other C[O.sub.2] systems. Otto Bock is now producing patented integral-skin foams with these compounds in the U.S. and Canada.

MORE AUTOMOTIVE PUR NEWS

New developments in improving flexible molded PUR foams for automotive seating were addressed by ICI and Bayer. And Arco Chemical reported on advancements in safety foams for auto interiors and exteriors.

ICI discussed a versatile foam technology based on MDI that reportedly can be tailored to meet car makers' requirements - from durable, low-density foams for North America, to high-density comfort foams for thinner seat cushions in Europe, and high-resilience foams specified in Japan. Currently being evaluated by several U.S. auto seating foam makers, this technology reportedly permits production of thinner seat cushions without compromising durability.

Bayer reported on a new family of high-performance isocyanates (TDIHP) produced with a newly developed modification process that allows for production of low-density, high-resilience, cold-cure molded foams with high hardness. Such foams have the property profile of MDI-based foams but with lower density and improved flow. They require much lower levels of copolymer polyol to adjust foam hardness.

Arco Chemical reported on its Flexure PUR systems for automotive energy-management interior and exterior foams ranging from bumpers to head-impact protection. Flexure uses a polymeric MDI and blends of two polymer polyols that are adjusted to vary foam properties such as compressive strength and recovery. Water and catalyst are adjusted to vary density.

Dynamic impact data show these systems can be formulated to match or exceed the energy-management properties of EPP bead foam of equal density.

MDI WATER-BLOWN HR SLAB

BASF reported on the introduction of all-MDI, water-blown HR slabstock technology for furniture and bedding. Based on a new MDI prepolymer and standard polyether, polyester, or polymer polyols, this technology runs on existing production lines with C[O.sub.2] as the sole blowing agent. Short cure time and minimal density gradient within the foam bun are said to result. Fast cure is said to overcome the block deformation sometimes observed in TDI foams, and final foam properties are said to be achieved faster. Numerous dynamic fatigue tests show the new foams to offer high resilience and excellent durability. BASF says a wide range of density and hardness can be achieved by changing the water level or isocyanate index or by addition of polymer polyols.

NEWS IN ADDITIVES

Witco OrganoSilicones Group discussed new silicone surfactants designed to optimize foam quality and processability with liquid-C[O.sub.2] processes like Cannon's CarDio, Hennecke's NovaFlex, and Beamech's CO-2 (see PT, Sept. '97, p. 40).

Witco's Niag SC-154 and L-5770 reportedly can be used on all equipment types to achieve acceptable cell structure and cell-size uniformity. Niax SC-155 is viewed as best in the case of Planiblock-type machines, as it achieves a finer cell structure and a very narrow density distribution throughout the block. Niax L-5770 and L-603, part of a new family of high-efficiency silicone cell stabilizers, are said to impart good flame-retardancy to foams. Although the high levels of flame retardant required by California Bulletin 117 make it difficult to achieve fine cell structure, both these products reportedly allow production of fine-celled foams.

Goldschmidt presented a new silicone surfactant for low-density, water-blown rigid polyether or polyester foams for non-insulating applications where some structural support is needed (e.g., packaging and crash pads). Tegostab B8870 reportedly produces foam densities as low as 0.44 pcf with high-water formulations. Such foams are said to have a fine and regular cell structure with a minimum of defects, especially on the surface.

Great Lakes Chemical has a new aromatic-bromine flame retardant not based on diphenyl oxide that's said to enhance flame lamination of polyether and polyester flexible foams for automotive, packaging, and furniture uses. CN-2065 is said to have excellent thermal and hydrolytic stability, which suits it to applications that require resistance to degradation in humid conditions. It reportedly increases adhesion of flame-laminated foams without detriment to foam physical properties or appearance. It is also scorch resistant, anti-fogging, and produces HR foams without center softening.