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Flame Retardants.

Flame retardance--traditionally one of the weaker links in the chain of properties offered by plastics--continues to be strengthened, as pressures increase for enhanced fire safety, with products that lower heat release, smoke levels, and corrosivity.

Improved flame retardants now require less additive loading to satisfy test requirements, and consequently, they produce fewer negative effects on the physical properties of the base resins. Also, the push is on for greater synergism and performance/cost efficiency through a systems approach, rather than simply "brute force" additive loading to achieve flame retardance in the resins.

Another impetus is toward development of innovative reactive systems, in which resistance to fire would be integrated within the resin molecule or structure during polymerization, instead of by compounding. Although still only on the horizon, the reactive chemistry route, which would combine resin molecule and additive, could ultimately lead to even more effective flame retardance.

Less discoloration

Akzo Chemicals Group's enhanced Fyrol PBR brominated flame retardant features lower discoloration in flexible urethane foams. Now being commercially evaluated, the product offers higher-percentage water-blown foams instead of CFCs. The new product follows last year's introduction of a brominated lower-viscosity Fyrol PBR flame-retardant additive for flexible polyurethanes.

Bill Coble, business manager, Phosphorus Chemicals, North America, Akzo Chemicals Group, says the company is making a major effort to respond to increasing flame-retardant requirements of higher-temperature-processing engineering resins with phosphorus-based materials. Akzo's line of flame retardants includes the Fyrol phosphate esters for thermoplastics and thermosets (notably flexible and rigid urethanes), and phosphate plasticizers for PVC and other thermoplastics.

Fyroflex RDP, a new diphosphate flame retardant, is showing promise in applications requiring higher thermal stability and easy processing, in materials such as polycarbonate blends, polyesters, and nylons. Derivatives of the product, with further improved thermal stability and cost, are also expected.

New entries are expected next year from a development program for intumescent flame-retardant products. Fyrol MC and MP are now being used as synergists in intumescent coatings.

Effective without synergists

Albright & Wilson Americas' application of char-forming technology includes its Amgard NK and Amgard NP products for polyolefin flame retardance, based on alkyl amine phosphate salts. Mark Huggard, product development manager, says the products are effective without synergists and can compete on a cost/performance basis with established bromine chemicals.

The products are favorable relative to water sensitivity, blooming, and mold plate-out. Requiring only about 30% loading to achieve UL 94V-0 ratings at 1/16 inch, the NP grade provides cost-effective flame-retardant polypropylene with high impact strength and elongation for the molded goods market. Other uses that appear feasible, based on initial laboratory work, include ASTM E84-specified building panels and construction films.

Albright & Wilson's Antiblaze 1045 flame retardant is a high-molecular-weight organophosphorus compound designed for polyamides and polyesters. It has an amorphous, noncrystallizing structure and a high (21%) phosphorus content, permitting low loadings, which help retain elongation and impact resistance. Huggard says the flame retardants are suited for specialty extrusion and molding applications with unique performance requirements.

Scaling up

AmeriHaas is scaling up capacity for FR-1025 pentabromobenzyl polyacrylate, aimed at the nylon and PBT markets. Offering improved rheology and light stability, the melt-blendable powder also improves the "wetting-out" of glass-fiber reinforcements because of its acrylic backbone.

For flame-retardant styrenics (HIPS, ABS), the company offers several grades of low-molecular-weight brominated epoxies in its F-2000 series, with improved effect on impact strength, flow, and UV stability. F-2016 is for ABS; other low-molecular-weight brominated epoxies in the series are tailored for HIPS. For thermoplastic polyesters, nylons, and blends, the company markets several higher-molecular-weight products with improved flow, UV stability, and thermal aging. Through an arrangement with the Dead Sea Bromine Group and Dead Sea Periclase, AmeriHaas will offer commercial quantities of several grades of magnesium hydroxide (FR-20), which allows production of nonhalogen, low-smoke, flame-retarded thermoplastics without high filler loadings. Available in several coated versions and an uncoated version, FR-20 also provides improved flowability and color maintenance by keeping its crystal aspect ratios within a narrowly defined range.

New line

Anzon Inc. is marketing a full line of ammonium polyphosphate products for use in intumescent paints and coatings as well as resins such as polypropylene. AZ40, another new product, is a zinc-molybdenum-based smoke suppressant developed for PVC plenum applications, which, according to Carl A. Lance, product manager, may yield improved properties at lower cost. Anzon also is now offering a highly loaded concentrate form of its Pyrobloc SAP product for use in flame-retardant PET.

Nonhalogenated nylons

BASF Corp. Plastic Materials is now marketing nonhalogenated flame-retardant nylon molding resins. The FR Ultramid nylon 6/6 resins include A3X2G5 and A3X3G5, both 25% glass-fiber-reinforced; A3XZG5, 25% glass-fiber-reinforced and also containing an impact modifier; A3X2G7 and A3X3G7, both 35% glass-reinforced; A3X3G10, 50% glass-reinforced; and KR4205, unreinforced and available in select colors. The company says all the resins have excellent processing characteristics and are rated UL 94V-0 at 1/8-inch thickness.

In field trials

Elf Atochem North America, Inc.'s Pyronil 63, a 63% brominated phthalate ester, melt-processable, solid flame retardant now in field trials, is expected to be commercial next year, says Martin Martino, market manager, Flame Retardants.

The company's Pyronil 45 liquid flame retardant, used in PVC plenum wire and cable, polystyrene foam wallboard insulation, and thermoplastic polyesters for electronics, also acts as a plasticizer that boosts flow and processability.

Reduced risk

Saytex 8010 brominated flame retardant reduces risk of formation of brominated dibenzofurans or brominated dibenzodioxins, according to John M. McChesney, marketing communications manager, Ethyl Corp. The company markets more than a dozen Saytex flame retardants for polymers used in wire and cable, electronic equipment, building materials, and other applications. Saytex 8010 contains approximately 82 wt% bromine and features bloom and plate-out resistance, thermal stability, ignition resistance at low loading, and an intermediate level of UV stability. Flame retardance is similar to that of Saytex 102E (decabromodiphenyl oxide), 111 (octabromo diphenyloxide), RB-100 (tetrabromobisphenol-A), and BT-93 (ethylene bis tetrabromophthalimide) flame retardants.

McChesney sees flame-retarded HIPS as a growing market in electronics, including computers, TV and audio/video cabinets, and thermoformed sheets for small appliances, and refrigerator doors and liners.

Since 1987, Ethyl has invested more than $225 million in its brominated flame retardants business worldwide. Construction is nearing completion on a separate $20 million unit at the company's existing facilities in Magnolia, Ark., to produce Saytex 8010, and construction will soon begin on a $7 million expansion to the facility's existing capacity for tetrabromobisphenol-A.

Brominated polystyrene

Ferro Corp. continues to manufacture Pyro-Chek brominated polystyrene, differentiating the product line by bromine content, changes in molecular weight of the polystyrene chains, and physical form (powder or pellets). Fran Quinn, market manager, says the chemical structure of brominated polystyrene is perceived as producing less negative environmental impact than some other brominated additives. Ferro has been manufacturing brominated polystyrene at a facility near Marseilles, France, since 1992. The company has since initiated a 100% expansion, bringing it on line in the second quarter of this year. The plant now supplies growing markets in both the European Community and the Pacific Rim.

Ferro is continuing to further differentiate brominated polystyrene into additional customer products. Because the brominated polystyrene flame retardant is itself a thermoplastic polymer, it can be pelletized with a metal oxide synergist and other modifying additives. The masterbatches are now produced at a Ferro compounding plant in the European Community for sale to other compounders. About 60% of the total Pyro-Chek sold is in compacted form, rather than pelletized, and about 75% of the total is sold outside the U.S.

The finely ground version of Pyro-Chek is for applications having lower compounding temperatures where brominated polystyrene does not fuse and melt blend. Its use is growing rapidly in the Pacific Rim, because of a preference for the flame retardant's chemical structure. While no countries in that particular area are proposing regulation of brominated additives, these countries heavily export plastic products and react to protect their markets within the EC.

The short-chain brominated polystyrene, Pyro-Chek LM, which was commercialized in the U.S. in 1992, was introduced in both the Pacific area and the EC in the first quarter of this year. The short-chain structure facilitates solubilizing in certain plastic systems, as well as melt blending into other thermoplastics at comparatively low compounding temperatures.

Diminished concern

"While the perception of a problem about gaseous emissions during combustion of halogenated products still exists," says Russell C. Kidder, executive vice president of the Fire Retardant Chemicals Association, "the real concern seems to have subsided." Autopsy data appear to indicate that death from carbon monoxide occurs before it does from halogenated gases, thus making halogens essentially a noncontributor to mortality. R&D on nonhalogenated products goes on, however, in response to many end-users' continuing concerns, but performance/cost ratios are critical and must be satisfied before halogenated products are replaced.

Kidder adds that while toxicity questions about diphenyl ether products still exist in Germany and some other European countries, scientific research in the U.S. by the bromine industry has shown that the concerns have been vastly overstated. Where substitutes for brominated diphenyl ether flame retardants have been available, they have been replaced. However, performance/cost is a key criterion, and the Environmental Protection Agency has not considered regulating these bromine products.

Kidder says that the corrosive gases given off in a fire, which can damage wiring and expensive equipment, appear to be the biggest potential problem for halogenated products, although they can also be emitted by some nonhalogenated products. Several ASTM and ISO sub-committees are working on test method development, primarily for property damage control, to predict corrosivity for end-user specifications.


While flame inhibitors are usually based on either halogen or phosphorus, the FMC Corp.'s Process Additives Division has been pioneering in flame retardants containing both elements in the same molecule. In July, FMC announced commercialization of Reoflam PB-460, a brominated phosphate developed for use in engineering thermoplastics such as PC, PBT, PET, ABS, and PP, and blends such as PC/PET, PC/PBT, and PC/ABS. Joseph Green, principal scientist, says that in these polymers, PB-460 also acts as a processing aid, resulting in a significant increase in extrusion rates at reduced temperatures and in higher molding rates as a result of faster cooling.

In a paper to be delivered at the fall conference of the Fire Retardant Chemicals Association, to be held this month in Tucson, Ariz., Green shows data that bromine and phosphorus are synergistic in a 2/1 (by weight) PC/PET blend and that the synergy is further enhanced when both elements are in the same molecule. For example, achieving a UL 94V-0 rating for the blend requires 12% to 13% of the all-bromine or the all-phosphorus flame retardant, but a combined total of only 6% in PB-460. Green adds that the result is a resin with an excellent combination of mechanical properties and processability.

The PB-460 flame-retarded PC/PET resins show a "voluminous" char on combustion. Residues obtained during heating in thermogravimetric analysis apparatus, both in nitrogen and air, give chars of 30% to 55%. Char characterization, relative to its strength, hardness, crush resistance, and type of porosity, is currently in progress.

FMC expects to announce commercialization of a second brominated phosphate before the end of the year. PB-370 was developed for polypropylene molding resin and fibers/textiles. PB-370 and PB-460 disperse easily; are melt processable, non-pigmenting (remain transparent in the compound), nonblooming, and nonmutagenic; and can be stabilized to UV standards. Anticipated textile uses for PB-370 include office partitions, wall coverings, upholstery, blankets, automotive, and carpeting.


In spite of efforts in Europe to ban or restrict brominated flame retardants such as the brominated diphenyl oxides, no regulations to limit their use are currently in effect anywhere in the world. A move to ban brominated diphenyl oxides was rejected by the European Community in 1991, based on insufficient evidence that the particular brominated dioxins and furans generated in a fire were toxic; the absence of an adequate alternative for protection of furniture and textiles was also a mitigating factor. Notwithstanding German and Dutch proposals for restrictive legislation relative to brominated compounds, none has been implemented.

Harold L. James, market manager, Flame Retardants, Great Lakes Chemical Corp., says that the use of brominated flame retardants continues to expand with new products and applications. Contrary to many expectations--probably because of the general consensus that there are limited hazards associated with the brominated materials--the worldwide consumption of decabromodiphenyl oxide has increased significantly since the first toxicity concerns were raised nearly eight years ago. Great Lakes is marketing dibromostyrene (DBS) as a reactive monomer for end-product flame retardance and property modification. Derivative DBS products, featuring high-purity, low-corrosion properties, and thermal stability in excess of 360 |degrees~ C, include PDBS-10 and PDBS-80 homopolymers, with molecular weights of 10,000 and 80,000, respectively. The products are particularly suited to nylon, styrenics (HIPS, ABS), and thermoplastic polyesters (PET, PBT).

GPP-36 and GPP-39, polypropylene/DBS graft copolymers containing 36% and 39% bromine, respectively, can add flame retardance to fine denier polypropylene fibers, while maintaining fiber strength properties. GPP-39 is designed to provide UL 94V-0 in molded polypropylene without surface bloom. Great Lakes is devoting extensive R&D effort to the DBS derivatives because of their reduced effect on properties such as impact strength, melt flow, and strength, and expects to introduce additional products in the near future.

By the end of this year, the company anticipates market introduction of alkoxylated adducts of BA-59P tetrabromobisphenol-A as reactive flame retardants for thermosets and specialty thermoplastics. Also, for flexible urethanes, Great Lakes continues to make value-added adjustments to DE-60F Special, a proprietary pentabromodiphenyloxide blend, to meet changing customer performance requirements. Two products resulting from these efforts are DE-61 and DE-62.

Great Lakes is expanding its line of nonhalogen products for applications where corrosive gases must be avoided. NH-1511, which the company says exhibits lower water sensitivity, broadens the company's line of nitrogen- and phosphorus-based flame retardants used in polyolefins and thermoplastic polyesters; and NH-1197, also based on phosphorus, is for proprietary niche applications.


During the first quarter of this year, Himont USA took over the direct marketing in the U.S. of the Spinflam ammonium polyphosphate-based flame-retardant line originally invented by Himont in Italy and sold and expanded in Europe. The intumescent halogen-free Spinflam MF grades include 80/PU for polyurethane foams; 82/PP, for polypropylene and copolymers; 82/PP-1, for stabilized polypropylene and copolymers; 82/PE-2, for polyethylene and copolymers; 82/PE, for white pigmented polyethylene and copolymers; 82/PE-1, for crosslinkable polyethylene; 82/PU, for thermoplastic polyurethane; and 82/PA, for nylon 6.

The company also recently announced the availability of Spinflam MB 92 low-halogen flame retardant for polyolefins. Michael Goldin, director, Additive Concentrates, Functional Chemicals, Himont USA, says that product characteristics of flame-retarded polypropylenes, based on the Spinflam MB 92 low-halogen material, include low emissions during burning, easy processability, preservation of original polymer properties, colorability, low corrosivity, reduced smoke emission, good surface appearance, and wide melt flow range.


The addition to Hoechst Celanese's line of intumescent flame retardants, Hostaflam TP AP 750 for polyolefins (basically an upgrading of the company's Exolit IFR 23), features improved plate-out and reduced water pick-up. Expected to be commercially available in December, the intumescent flame retardant provides stability to 260 |degrees~ C and achieves a UL 94V-0 classification with 26% loading in a 1/16-inch-thick specimen.

One of the new flame retardant's key ingredients is high-molecular-weight Hostaflam AP 422, typically supplied for manufacture of intumescent coatings, flame-retarded polyurethane foams, roofing materials, adhesives, and other thermoset and thermoplastic polymers. The company also supplies, particularly for outdoor applications, Hostaflam AP 462, a micro-encapsulated ammonium polyphosphate with superior water resistance and reduced reactivity with other additives.

The Exolit IFR 10, 15, and 23 ammonium polyphosphate-based intumescent series is a nonhalogenated system containing no chlorine, bromine, or antimony trioxide. When exposed to flame, a treated material swells into an insulative foam char that cuts off the oxygen supply, while emitting little smoke and corrosive gases and preventing the substrate from dripping.

Hoechst Celanese says the IFRs, thermally stable at processing temperatures of 240 |degrees~ C, achieve a UL 94V-0 rating in polyethylene, polypropylene, thermoplastic polyester elastomers, and ethylene-vinyl-acetate (EVA). At filler levels of 25% to 30%, the flame retardants reportedly do not affect tensile strength or toughness as adversely as formulations requiring twice the loading. Exolit IFR 10 and Exolit IFR 15 extend applications to thermoplastic urethanes, epoxy, and specialty thermoplastic blends.


Use of precipitated hydrates, as opposed to ground material, is increasing because of their improved uniformity and consistency, reports Roman Nykuforuk, marketing director, Lonza Inc. The company provides a series of precipitated hydrates, Martinal 104LE, Martinal 107LE, and Martinal 111LE, for a variety of applications, notably insulation and jacketing for wire and cable.

Specially coated aluminum trihydrates (ATH) that improve processability also are available for specific applications where water absorption must be minimized. Compounders are showing more interest in specific coatings that improve processing speeds and end-product appearance.

Lonza's Magnifin magnesium hydroxide is now formulated in polyethylene, polypropylene, and nylon 6 and 66 resins, providing V-0 flame retardance. The company's Magnifin H and HBV series, as well as the Martinal ATH products, conform to ISO 9001 specifications.


Monmouth Plastics Co., acquired in July by M.A. Hanna Co., and a producer of V-0- and V-2-rated polyolefin compounds, expects to continue producing its existing family of flame-retardant materials while adding capabilities to manufacture filled and glass-reinforced thermoplastics. "We are exploring developing compounds with higher loadings of additive packages, compounds based on nonhalogenated systems, and for new markets and processes," says Michael Braza, vice president of marketing. Monmouth traditionally has been active in injection molding for the appliance, automotive, and electrical/electronics industries. Braza adds that the strongly polyolefin-consuming wire and cable industry is a leading candidate for the company's expanding flame-retardant technology.


Morton International, Inc., markets nonhalogen flame retardants based on Elastocarb basic magnesium carbonate, where temperatures do not exceed 400 |degrees~ F, and on Versamag magnesium hydroxide, for processing temperatures up to about 500 |degrees~ F. Various grades of products are based on particle size and coating technology. Robert Stennick, product manager, says these product improvements have advanced performance by displaying minimal effect on polymer physical properties, even at high filler loadings. Morton expects to introduce additional Versamag products this year.


Advances in Dechlorane Plus technology from Occidental Chemical Co. include increased thermal stability in processing flame-retardant nylon 66 formulations by using a more stable zinc borate from the U.S. Borax & Chemical Corp. Ronald Markezich, technical manager, Flame Retardants, says a lower-cost formulation is 16% Dechlorane Plus with 2% antimony oxide and 4% zinc borate. The Firebrake 415 zinc borate gives a weight loss of 2% at 350 |degrees~ C, versus a weight loss of 8% using standard zinc borate. Antimony oxide alone, instead of the mixed antimony oxide/zinc borate system, yields a weight loss of 9%. The stability can be increased further by the addition of anatse titanium oxide.

In EVA, mixtures of magnesium hydroxide with Dechlorane Plus (a stable chlorinated cycloaliphatic flame retardant) are synergistic; alumina trihydrate in the same resin does not give the same effect. Markezich adds that the Dechlorane Plus/MgOH mixtures produce less smoke when burned in the NBS smoke chamber and also markedly decrease corrosivity.
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Author:Wigotsky, Victor
Publication:Plastics Engineering
Date:Oct 1, 1993
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