Environmental issues top agenda at polyurethanes conference.
In their continuing effort to develop alternatives to CFCs, polyurethane producers are already looking beyond the chlorine chemistry that dominated the initial crop of replacements. Today, the leading hopes are that water-blown formulations and newer fluorinated blowing agents can provide a long-term solution to what many feel is the industry's most nagging problem. This month's Polyurethanes World Congress in Nice, France, cosponsored by SPI's Polyurethanes Div. and the European Isocyanates Producers Association, reflects the urethane industry's growing concern with environmental matters, as discussions of CFC replacement and recycling dominate the meeting's agenda.
The conference, scheduled for Sept. 24-26, is focusing pre-eminently on the scramble to optimize alternative formulations for both processability and performance, including toxicity, mechanical properties, insulation value and fire resistance.
RECYCLING METHODS EMERGE
This is also the first major conference in recent memory to devote a major part of its agenda to technologies for diverting some of the billions of pounds of annual polyurethane production from their ultimate destination in landfills. And techniques for recapturing blowing agents have joined the recycling discussions.
Earlier this year, Dow Plastics and Mobay Corp. announced processes for recycling of RIM auto parts (see PT, March '91, p. 38). New York in this field and some of the latest innovations are on tap at this year's polyurethanes meeting.
So far, glycolysis and the chopping and rebonding of scrap foam for carpet underlay have been the only commercially realized methods for recycling foam waste. Glycolysis has been limited mostly to in-plant scrap where production wastes are placed in a batch reactor and transformed into a polyol that is then used directly in the production of rigid foam. But as government and industry begin requiring the recovery of CFC-blown insulation foams from old refrigerators and other discarded products, a process to either recover or totally destroy the CFCs in the foam will have to be developed.
One process that has shown promise in recovering blowing agents from PUR foams has been developed by Du Pont Canada. Du Pont will present results from pilot programs in Canada where appliances were dismantled, the polyurethane foam removed and crushed in a solvent system, and the CFC blowing agent recovered.
New equipment to degas PUR insulation panels and recover CFC-11 from old refrigerators and freezers will be discussed by Adelmann GmbH of Germany. The CFC recovery unit shreds foam waste in a gas-tight system, and the shredded parts are then spiralfed into a high-pressure chamber. There, the foam waste is compressed, and the condensed water and pure CFC-11 produced are drained and recovered. A condenser liquifies the absorbed gas and the residual air is purified by activated charcoal filters, regenerated and released into the atmosphere. Adelmann says the system is 99% efficient.
Dr. Gunter Bauer of Aalen, Germany, is among a group of industry leaders who think alcoholysis, a process that degrades polyurethanes to simple, low-molecular-weight products, could provide an efficient answer to both polyurethane recycling and CFC recovery. Bauer has used an experimental alcoholysis process and continuous pilot plant in Germany to produce 2.2 lb/hr or polyol. Employing this system and waste from molding auto seats and RRIM parts at Ford AG in Cologne, Bauer was able to produce a polyol that was later combined with fresh polyol to produce rigid PU foams and RRIM material. According to Bauer, the recycled polyol had a water content of 0.1% and 0.5% aromatic amine content. Dr. Bauer says he made discontinuous slabstock with good properties, using a 50/50 combination of fresh primary polyol and recycled polyol and also with 100% recycled polyol at an isocyanate index of 200.
A technique that uses hot stamping or thermoforming to process recycled auto interior foams, is slated to be discussed by Phoenix AG of Hamburg, Germany. After the urethane-containing parts are dismantled and the foam is separated from the other components, it is granulated and pre-heated for 20 min at 302 F. This regrind is then molded at 374 F for 3 min. under 11,000 psi. The resulting parts have slightly reduced hardness and tear strength and a somewhat rough surface, Phoenix says. Also, Phoenix reports almost 90% reduction in ultimate elongation, limiting the potential applications to non-appearance auto parts such as wheel cases, splash guards, glove-box interiors and various housings.
A method of recycling in-plant flexible microcellular scrap, such as trimmings from shoe soles, has been developed by Mobay. The process involves sorting and grinding the scrap, drying it for 2 hr at 200-220 F, and then compounding it with virgin thermoplastic polyurethane via extrusion and pelletizing. These pellets can then be injection molded into new products, Mobay says. The process can use as much as 90% regrind, Mobay says.
Ever since the Montreal Protocol was approved by 93 nations in June 1990, suppliers have been scrambling to meet its mandate of a complete phaseout of CFCs nin years from now. Recently Polyurethane Congresses have discussed this subject in great depth. The 1991 session is no exception, placing a major emphasis on this and closely related topics.
HCFCs appear to be the most promising replacements for CFCs in rigid PUR foams. Yet it is acknowledged by industry insiders that these present only a stop-gap measure and, because of their chlorine content and pending restrictions limiting their use, do not offer a long-term remedy to the depletion of the ozone layer. In an effort on develop more than a temporary solution, a number of different chemistries have been tried as alternatives to chlorine-based blowing agents.
BASF AG in Ludwigshafen, Germany, has developed a procedure to emulsify perfluoroalkanes such as perfluoro-pentane and perfluoro-hexane in polyols and produce foams by vaporizing the emulsified droplets. BASF says the foams have reaction kinetics similar to conventionally blown foams, very fine cells and low thermal conductivity.
Investigation into fluorine chemistry is also reflected in work done by the Polyurethane Div. of Bayer AG (parent of Mobay) in Leverkusen, Germany. Bayer has developed a chlorine-free hexafluorobutane blowing agent and insulation gas that is claimed to be non-ozone-depleting. The product reportedly has a short atmospheric lifetime, is nonflammable, has low gas-phase thermal conductivity, and is compatible with appliance inner-liner plastics.
THE COMPATIBILITY ISSUE
The last point is an important one, as finding a CFC-free foam/thermoplastic combination that works well in refrigerator liners is proving more than a bit difficult. This is a much-discussed topic at the 1991 Congress, with suppliers telling about their efforts to develop materials compatible with the new crop of alternative blowing agents.
HCFC-123 and HCFC-141b are considered by most industry insiders to be the closest "drop-in" substitutes for CFC-11 in refrigeration foams. Carbon dioxide (water-blown) has also been thought to be a possible CFC alternative. But all three have been found to be more aggressive than standard CFCs against thermoplastics like ABS and HIPS used in refrigerator liners. At their facilities in Belgium, Monsato Europe and ICI Polyurethanes have teamed up to find materials compatible with HCFC-123 and HCFC-141b, both known to cause stress-cracking of refrigerator liners.
Testing foams blown with HCFCs and with [CO.sub.2] in contact with HIPS, ABS and a high-acrylonitrile barrier resin, the companies found ABS to offer between three and four times better resistance to [CO.sub.2] than HIPS.
Using Monsanto's Lustran 723 ABS with HCFC-141b, researchers found the material's tensile properties remained unchanged after exposure to foam and thermocycling. Adding a coextruded layer of Lustran 732 ABS on the foam side of the liner offered even better protection from systems blown with 141b, the team says. HCFC-123, which has been found to cause more severe cracking in liners than HCFC-141b, was tested against a liner made from a co-extruded blend of 70% Lustran 723 and 30% Lustran 732, resulting in good stress-crack resistance and good foam adhesion, ICI and Monsanto report.
In similar work, Dow Europe in the Netherlands and Dow Plastics USA have found that either using a proprietary polyolefin film barrier laminated to the ABS liner material, or a foam made with the company's experimental X2-88061.0 polyol, completely eliminates cracking of the liner by contact with HCFC-123.
A joint effort between the Polyurethane and Polystyrene Divs. of Enichem Polimeri, Marghera, Italy, has devised a method that seems to overcome the problem of HCFCs 22 and 123 chemically attacking refrigerator liners. The process combines HIPS and polyolefins laminated or coextruded onto a polyethylene film barrier layer. Good adhesion of the materials to the foam insulation is accomplished by corona treatment, Enichem says.
Also discussing "promising" barrier materials for refrigerators at the conference is BASF, though details were unavailable at press time.
Other nagging issues in refrigeration foams are thermal conductivity and foam physical properties. While many suppliers see [CO.sub.2] as the alternative that will ultimately receive the most widespread use in rigid foams, some feel it's probably not suited for use in refrigeration because of its detrimental effect on a foam's K-factor. But HCFCs 123 and 141b can also have a negative affect on K-value because they have higher vapor-phase thermal conductivities and increased solvent properties, leading to reduced thermal insulation capability and poorer strength and demolding characteristics than are provided by all-CFC systems.
In one approach to the problem, Air Product and Chemicals has developed a new, modified silicone surfactant for HCFC-123 and HCFC-141b blown rigid foam systems that reportedly enables the production of finer-celled foams with significantly improved K-values. Likewise, Union Carbide says it has identified selected silicone copolymer surfactants that yield finer foam cell structure to balance the higher thermal conductivity and plasticizing effect of HCFC-123.
Alternatively Mitsui Toatsu Chemicals of Japan tells of a new polyol that reportedly results in HCFC-blown refrigeration foam with thermal insulation and physical properties equivalent to those blown with CFC-11. Mitsui says the key is introduction of an aromatic ring ester group or amide group into the polyol. The result is a rigid polyurethane that is virtually incompatible with CFC substitutes and does not allow any penetration by the blowing agents. This formulation results in foams with higher compressive strength and elimination of the negative effect HCFCs have on thermal insulation properties and low-temperature dimensional stability.
Both Mobay and Dow Mitsubishi Kasei Ltd. of Japan say they have developed microcellular HCFC-blown appliance foams that reportedly provide demolding characteristics and thermal insulation properties equal to or better than those of commercial CFC-11 blown foams. Similar foams were introduced by Mobay at last year's urethanes conference in Orlando, Fla. Those foams suffered from high densities and extremely long demolding times due to their reduced strength caused by fewer urea groups and the HCFC's softening effect on the polymer. Newer foams from Mobay and Dow reportedly overcome those problems by combining new, proprietary polyols with tertiary amine catalysts and silicone surfactants, resulting in foams with low thermal conductivity and good demold properties.
NEW INSULATION SYSTEMS
A CFC-free technology for producing insulation panels has been developed by foam processor, Recticel NV of Wetteren, Belgium. The company's new foam is blown with what Recticel calls LBL 2, based on 2-chloropropane. LBL 2 has thermal conductivity 15 times higher than CFC-11 and 20 times higher than [CO.sub.2]. Its main advantage, though, is environmental - it reportedly has an atmospheric lifetime of only nine months, vs. 60 years for CFC-11, and its global warming potential is just 1% that of CFC-11, Recticel says. Extensive reformulation is required to substitute LBL 2 for CFC-11, the company says, but with LBL 2, 40% less blowing agent is required.
Seven low-viscosity, low-hydroxyl-value polyols for use in high-water, reduced-CFC rigid insulation foams are new from Rhone-Poulenc Canada. The new polyols - four neutral sucrose types, a sucrose amine, a 700-M.W. glycerine propoxylate and a propoxylated mannich adduct - were tested on three non-CFC formulations and compared to a 100% CFC-blown system. In each formulation, properties were almost identical to the all-CFC formulation, Rhone-Poulenc says. Adding a portion of the propoxylated mannich adduct to the formulation in place of 40% of the usual CFC reportedly contributed finer cell structure and improved surface quality. Addition of 30 pbw of the adduct plus a 3000-M.W. triol to the [CO.sub.2]-blown formulation increased cell formulation in the foam's softer segments and minimized demold time. This system also had 25% poorer thermal insulating performance than the all-CFC system.
Still-developmental polyols are also the key behind technology from Shell Chemical Co.'s Research Center in Belgium, designed to produce pipe insulation foams blown with systems combining water with HCFCs 141b and 142b. The developmental polyols provide slightly improved thermal conductivity over water-blown systems, Shell says.
DETROIT PUTS BRAKES ON CFCs
Ford Motor Co.'s recently announced plan to eliminate 90% of CFC use from its seating and interior-trim production by the end of next year, and 100% elimination in 1993, is just one sign of the active development of non-CFC technologies for automotive use (see PT, June '91, p. 186).
A new way of producing low-density, MDI-based seating foams without CFC-11 has been devised by Dow Europe in the Netherlands. Density reduction was achieved by increasing water levels to 3.7 pbw and modifying the MDI component so the foams meets or exceed most automotive specifications for all-MDI foams. The substitution of water for CFC, however, affects the foam's reaction kinetics, morphology development and mechanical properties because water continues to react with the other components after the foam's cells open and the foam gets. By increasing the amount of 2,4-MMDI in the formulation, Dow has been able to delay cell opening, resulting in slower viscosity build-up and improved flowability around the mold, resulting in all-MDI foams that meet automotive standards requiring a molded density between 2.5 and 3.7 pcf, demold time of 3-4 min., elongation of 110-140%, and load-bearing potential of 0.3-1.45 psi. However, Dow warns, the higher 2,4-MMDI content also leads to a reduction in hardness.
Bayer in Germany discovered that adding small amounts of an inorganic salt to standard polyether polyol, together with a special TDI-based isocyanate, can reduce the hardness of hot-cure, all-water-blown seating foams to a level the company says could previously only be achieved in "supersoft" foams blown with a combination of CFC-11 and carbon dioxide.
In an attempt to overcome the problem of water-blown systems resulting in poor skin and inferior foam properties, Olin Corp., Stamford, Conn., has developed a series of polyether polyols with carboxylic acid groups directly grafted onto their chemical backbones. These polyols reportedly have a built-in blowing capability. The acid reacts slowly with the isocyanate. The acid reacts slowly with the isocyanate, causing the center of the foam to become hotter than the outside, Olin says. Therefore, less blowing occurs on the surface, resulting in the formation of a skin that, because of a cold mold and higher stream temperature, is of better quality than skins produced from water-blown systems. Initial applications for this technology have been in shoe soles, but Olin says it hopes to extend the technology to other integral-skin foam applications such as auto steering wheels, headrests and armrests.
More than one paper at the conference deals with innovations for steering-wheel production. One from Dow Italia presents technology for water-blown foams with strong physical properties, despite not having an integral skin.
Meanwhile, researchers at Enichem's Polyurethane Div. in Italy have found an unusual way to achieves economical demolding and cycle times for integral-skin foams blown without CFCs. Using rotational molding technology, Enichem has produced all-water-blown, low-density foams that would be suitable for complicated parts such as headrests and crashpads.
A non-CFC foam-in-fabric technology originally designed for seats has now been found to work well in headrests and armrests. Hyperlite foam is based on a polymer polyol from AC West Virginia Polyol Co., a new subsidiary of Arco Chemical Co. resulting from the company's acquisition of Union Carbide's urethane business. Hyperlite is TDI-based foam that reportedly offers advantages in potential density reduction and ability to produce parts with a wide firmness range. The foam-in-fabric system gels quickly to minimize penetration of foam into the fabric backing and allows rapid demolding.
NEW MATERIALS FOR RIM
As plastic auto exterior body panels get larger, supplier of PUR RIM materials have been working to increase the dimensional stability of their materials through the use of reinforcing fillers. A critical factor for these large parts is using a filler that does not adversely affect surface quality or "distinctness of image" (DOI). Sumitomo Bayer Urethane Co., Ltd. of Japan, a subsidiary of Bayer AG, reports that milled glass and classified mineral fibers 30-40 microns in length and less than 5 microns in diameter give outstanding surface quality while supplying sufficient reinforcement.
Research by BASF AG has shown that incorporating secondary polyether amines in a polyurea RIM system containing ketimines results in increased flowability of the system compared with polyurea/amide RIM and conventional polyurea systems. For automotive molders this means greater control over reactivity and product properties and the ability to mold larger exterior parts. BASF says these systems results in better elastomeric properties and tear resistance than polyurea/amide RIM materials, but still provide the superior heat resistance of the polyurea/amide RIM.
CFCs AND FLAME RETARDANCY
Reducing CFC levels in rigid foam insulation reportedly has caused manufacturers some difficulty in meeting flammability requirements, and only the most efficient flame retardants seem to work well enough to be considered. One such flame retardant is dimethyl-methylphosphonate (DMMP), says Albright & Wilson. However, as long as even a small portion of CFC is retained in the formulation, questions have arisen regarding the side reactions between DMMP and CFCs.
Albright & Wilson will discuss the benefits of its new Amgard V490, an 18.6%-phosphorus, halogen-free liquid said to provide the same properties as DMMP, and which is mixable with polyols, MDI and organic solvents. The company says the new flame retardant is nonreactive with CFC and remains stable when used in both one- and two-component systems, eliminating formation of undesirable methylated byproducts. In reduced-CFC systems, Amgard V490 reportedly provides a marked viscosity reduction.
Standard regulating flammability of flexible furniture foams have become more stringent over the past few years, leading to more complex formulations with, in some cases, attendant processing complications. In Nice, Olin Corp. will report on what's said to be a novel, easier-to-process polyol system for flame-resistant flexible foams. The system is based on an undisclosed, conventional polyol of 3000 M.W. The new system, which reportedly meets the most stringent fire standards, can be used with as little as 20 phr of melamine along with a liquid chlorinated monophosphate or diphosphate ester, Olin says. Conventional silicone surfactants and other catalysts can be used, and Olin says physical properties of the resulting foams are improved. Compression sets reportedly are lower and tensile and tear strength higher than in other flame-resistant HR foams.
Halogenated phosphate esters and aromatic hydrocarbons such as pentabromodiphenyloxide are probably the most widely used flame retardants in flexible polyurethane foam, experts say. But these products are not without their faults, frequently having negative effects on processing and the final physical properties of the foams produced. Hardness is reduced, compression set soars, and in many cases high fogging occurs. Th. Goldschmidt AG in Germany has developed a proprietary flame-retardant additive for flexible foams said to limit the adverse affects on processing, mechanical properties and fogging that can be observed with common FR agents such as phosphate esters and halogenated aromatics like pentabromodiphenyloxide. The new additive, which Goldschmidt will not identify, reportedly allows 15-35% reduction in the use of these other additives in conventional foam systems with little or no other adjustments to the formulation.
Reduced levels of FR additives in flexible polyester slabstock are said to be possible with a new generation of silicone surfactants from Union Carbide. The surfactants reportedly provide improved foam processability, reduced emission of volatile compounds during manufacturing and fine, open foam without pinholes and with minimum property gradients in flat and round block operation.
NEW CATALYSTS FOR FLEXIBLES
In the same presentation, Carbide is expected to talk about new low-odor amine catalysts with processing characteristics as good as the current crop of highly volatile compounds. They are highly catalytic, so they can be used at low levels, and have low vapor pressure.
A separate research effort at Union Carbide has produced a new blocked amine catalyst that reportedly has a high degree of delayed activity in free-rise and molded flexible foams. The proprietary blocker used in the catalyst is designed to react into the foam matrix, eliminating any volatility. The catalyst is reportedly noncorrosive in most applications further limiting its volatility, the company says.
PHOTO : Realizing HCFCs represent only a short-term solution to their CFC problem, polyurethane researchers are exploring a variety of alternative chemistries.
PHOTO : The trend in Detroit is toward larger exterior auto parts made with polyurea RIM systems. Additives such as ketimines and secondary polyether amines can increase these systems' flowability while giving processors greater control over reactivity and product properties.
PHOTO : Urethane suppliers are finding that systems blown with HCFCs or water can achieve nearly the same thermal insulation values as CFC-blown foams.
PHOTO : NOT STAMPING PROCESS FOR PROCESSING RECYCLED POLYURETHANES
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|Title Annotation:||includes related article; chlorofluorocarbons, recycling; Polyurethanes World Congress|
|Date:||Sep 1, 1991|
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