Alternatives+to+PBDE's


 * 3. Alternatives to the PBDE “Problem”**

Accompanying the discovery of the toxicity and persistence of PBDEs there has been a continual effort to design non-halogenated flame retardants. The lack of the presence of halogens typically means an alternate mechanism to fire retardation. A great deal of focus has involved the use of polymers which form a protective layer when burned, typically being composed of phosphorus containing compounds. Another substitute is the metal hydroxides which act through the mechanism of dilution.
 * 3.1 Alternate Chemicals**

It would be futile to attempt to delve into the vast pool of phosphorus containing compounds which serve as potentially viable flame retardants; however in general, phosphorus containing compounds work through the mechanism of polymerization into a protective char. Some compounds exhibit some dilution characteristics as some phosphorus will condense water when polymerizing. (Horrocks et al, 2001; Lui et al, 2002).

Metal Hydroxide compounds also provide a non halogenated alternative flame retardant. The metal constituent most commonly being aluminum or magnesium. Mg(OH)2 and Al(OH)3 do not actually contain water, but upon heating to between 220oC and 330oC will endothermically decompose to yield water along with a cooling effect on the surrounding area. Although the action of these compounds both cool and hydrate the flame it is also hypothesized that the anhydrous aluminum product can also aid in the acid catalyzed production of char. Also magnesia (MgO) is a good thermal insulator and it is hypothesized that it may be produced after the dehydration of the magnesium hydroxide (Horrocks et al, 2001).


 * 3.2 Substitutes to PBDEs: ring-brominated benzoates/phthalates and bisphenol A derivatives**

Decabromodiphenyl ether can be used as a preferred fire-retardant in a wide range of polymer applications including: polyolefins, polystyrene, acrylonitrile butadiene styrene (ABS), polyurethanes, unsaturated polyester, epoxy, and some thermoplastics (Chemtura 2006). It can also be used as an effective, but not-preferred fire-retardant for both rigid and flexible polyurethane, polycarbonate, and some thermoplastics (Stapleton et al., 2009). Historically speaking, PBDE's were often a preferred fire-retardant additive for rigid and flexible polyurethane foams due the favorable handling, effectiveness, and apparent high-quality of foam achieved. Much of the contemporary mass-produced upholstered furniture uses polyurethane foam for cushioning. Mass-produced upholstered furniture is ubiquitous in the developed world.

Considering that polyurethane foams remain the largest category of cellular polymer materials, the amount of PBDE used was very significant. Polyurethane foam offers a favorable balance of performance characteristics (elasticity, strength, aging, insulation, and chemical resistance) versus cost. Approximately half of the polyurethane foam produced is flexible, intended as cushioning material for upholstery, and rigid foam as intended for insulation in buildings and in refrigeration equipment (SRI consulting, 2010). The amount of PBDE used to impart flame-retardant properties varies with the foam and with the PBDE used, however the PBDE's were considered effective at dose-rates of 0.5% of total foam mass (Stapleton et al., 2009).

Additive rates for pentaBDE in upholstered items such as sofas and carpet could be considerably higher, up to 10% by mass to comply with comparatively strict California Open Flame Flammability Standard (bulletin 117), where polyurethane foam in furniture must withstand a 12 second exposure to an open flame. An estimated 20 000 lbs/year of pentaBDE was used in USA and Canada between years 1980 to 2004 to meet Californian standards. Other polymer products used to encase consumer electronics may require up to 20% of the finished polymer be composed of PBDE (Stapleton et al., 2009).

There is a wide-range of other fire-retardants available to substitute for the PBDE's. Ring-brominated benzoates are highly recommended substitutes intended for use in polyurethane foams, and somewhat recommended for polyurethane TPU, phenolics, and thermosets in the regulatory absence of PBDE's. A greater amount of a ring-brominated benzoate is required to impart effective fire-retardant properties to polyurethane foam, typically about 4.2 % or more by mass (Stapleton et al., 2009). At the time of writing, the retail price for ring-brominated benzoate from an American distributor was approximately $3.60 U.S.D. to $3.80 U.S.D. for a minimum purchase of 600 lbs before shipping, handling, customs and taxes (Myers, 2010). Due to continued large production volumes of polyurethane foams used today, any analysis of fire-retardants intended to replace PBDE's should give emphasis to the ring-brominated benzoates.

Ring-saturated benzoates, particularly tetrabromobenzoate are produced from phthalic anhydrides and 2-ethylhexanol, as disclosed in U.S. Patent 5728760 (1995), by Great Lakes Chemical Corporation, (now Chemtura). Phthalate anhydride is a polymer component used to make phthalate compounds, and the solvent 2-ethylhexanol is a fatty-alcohol used as an alcohol solvent. This solvent is also used in the manufacture of bis (2-ethylhexyl) phthalate (DEHP), a plasticizer implicated as an endocrine-disruptor. Not all phthalate plasticizers exhibit endocrine-disrupting characteristics. It is recently alleged that di-isononyl phthalate (DINP) and di-isodecyl phthalate do not exhibit endocrine-disrupting effects6. The phthalate component of the tetrabromobenzoate should also be examined to determine if it also exhibits endocrine-disrupting characteristics or not, before leveling an allegation against tetrabromobenzoate.

The aryl bromide compound decabromophenylethane best replaces decabromodiphenyl ether for the polyolefins, styrenics, thermoplastic polyurethane (TPU), and thermosets such as unsaturated polyester and epoxy, and the thermoplastic polybutylene terephthalate (PBT).

Some brominated bisphenol derivatives are also useful to replace decabromodiphyenyl ether. For example, tetrabromobisphenol A bis (2,3-dibromopropyl ether)) is effective for some polyolefins (polypropylene and polyethylene) and polystyrene, while tetrabromobisphenol A is considered effective to replace PBDE's for polystyrene, ABS plastic, and thermosets, especially unsaturated polyester, and sometimes epoxy. The following three polybrominated phthalates: tetrabromophthalic anhydride, tetrabromophthalate diol, and tetrabromophthalate ester are also useful brominated fire-retardants. tetrabromophthalic anhydride is very useful with polyvinyl chloride, tetrabromophthalate diol is very effective for rigid foam polyurethane, and TPU, while tetrabromophthalate ester is very effective for epoxy thermoset. Both tetrabromophthalate diol and tetrabromophthalate ester are considered effective, but second-line treatments for flexible polyurethane foam cushioning.

Upholstered articles containing polyurethane foam treated with phthalate fire-retardants still wear and degrade with use and time, leading to possible debromination and exposure to bisphenol A or phthalate residues. It is apparent from the literature that bisphenol A is implicated as an endocrine-disrupting compound. Some, but not all pthalate compounds are also implicated as endocrine-disrupting compounds, so these fire-retardants that contain brominated phthalate compounds should also be very carefully scrutinized (Hallmark, 2010).

Rigid polymers can also be treated with simpler brominated molecules. Derivatives of dibromostyrene are recommended for thermoplastic polycarbonate and PBT. Bis (Tribromophenoxy) ethane is effective for some styrenics (high-impact polystyrene, ABS, and polycarbonate/ABS), polyurethane TPU, and unsaturated polyester.


 * Phosphate-containing fire-retardants:**

Triaryl phosphates isopropylated can effectively substitute for both rigid or flexible polyurethane foams, and epoxy or phenolic thermosets, but unlike PBDE's do not have useful fire-retardant properties with polyolefins or styrenics, yet are excellent with PVC.

Phosphate-containing resorcinol bis-(diphenyl phosphate) and bisphenol A bis-(diphenyl phosphate) are both excellent for styrenics: high impact polystyrene, and polycarbonate/ABS blends, and useful for most thermoplastics, but are not useful for polyolefins. The resorcinol bis-(diphenyl phosphate) derivative can find some application in thermoplastic polyurethane. Neither of these two phosphate-derivatives is considered a good choice for polyurethane foams, either rigid, or flexible, and hence cannot truly be considered equivalent replacements for PBDE's in carpet or upholstery.

Bisphenol A Bis-(Diphenyl Phosphate) can be suspected as an endocrine-disrupting agent due to the bisphenol A in the structure. Resorcinol (benzene 1, 3 diol) and derivatives are also often used a coupling component for oxidative dyes in 'permanent' hair-color. The 4-hexyl resorcinol derivative is a suspected in-vitro estrogen agonist (Am adasi et al. 2009).


 * Metallic flame-suppressants with adjunctive activities**

Microfine particles of antimony trioxide and/or are useful fire-suppressants for most polyolefins, most styrenics (except expanded and extruded polystyrenes), and most thermosets (exceptions of polyethylene terephthalate and polycarbonate), but not thermoplastics. The antimony trioxide fire-suppressants are noted to contain about 0.25% arsenic as a by-product. Antimony and arsenic are both noted as toxic, leading to contact dermatitis upon prolonged exposure to the dust. Dust exposure may result from direct contact or as released from vacuum-cleaning. Antimony trioxide is under review for possible ban by the next European RoHS directive, but not banned as of December 2009. Microfine particles are estimated to pose little risk when incorporated into molded plastic parts of electronics.

Microfine particles of zinc borate are effective adjunctive smoke-suppressants in polyolefins, most thermosets and thermoplastics. Microfine particles are sized in the micrometer range appear to function better as fire-retardants than larger particles, however particles of any description or composition will eventually be released as dust when the treated polymer degrades with age and use.

It is interesting to note that research continues towards developing new fire-retardants. A new series of fire-retardants is apparently due for release fourth quarter from Albemarle Corporation, likely to be named Earthwise GreenArmor as can also be indirectly substantiated by the large number of US patent applications held by that company. GreenArmor allegedly is a polymer-based material that will be easily separated from plastic to easily enable recycling (Albemarle, 2010). The company does not provide product formulation information now. It is not reasonable to comment upon the comparative effectiveness of products that are not commercially available. Yet another form of flame-retardants based on nanoclays and nanocomposites have been the subject of recent investor hyperbole, however few are available for sale. Those nanocomposites that have been sold to-date apparently cannot 'pass' UL 94 fire-safety ratings unless combined with other agents (Wiel and Levchik 2009).

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1 Cook, A. (1910). Phenyl ether and some of its derivatives. Journal of the American Chemical Society. 32: 1285-1294. 2 Chemtura product catalog, 2006 3 [] 4 Stapleton, H., Klosterhaus, S., Eagle, S., Fuh, J., Meeker, J., Blum, A., and Webster, T. Detection of Organophosphate Flame Retardants in Furniture Foam and U.S. House Dust. (2009). Environ. Sci. Technol. 43 (19): 7490–7495.Environ. Sci. Technol ., 2009, 43 (19), pp 7490–7495 5 Personal communication, July 38, 2010 with two American distributors for Chemtura Corporation: Meyers Chemicals, Inc. Buffalo NY meyerschemicals.com and Van Horn, Metz & Company, Inc. Conshohocken, PA vanhornmetz.com 6 Hallmark.pdf DINP and DIDP are not endocrine-disruptors Second Meeting of the Chronic Hazard Advisory Panel on Phthalates European Council for Plasticisers and Intermediates Nina Hallmark ECPI Technical Working Group U.S. Consumer Products Safety Commission July 26, 2010 [|www.ecpi.org] [|http://www.dnip-facts.com] ad [|http://www.didp-facts.com] 7 Am adasi, A., Mozzarelli, A., Meda, C., Maggi, A., and Pietro Cozzini. (2009). Identification of Xenoestrogens in Food Additives by an Integrated in Silico and in Vitro Approach. Chem. Res. Toxicol. 22 (1): 52-63. hem. Res. Toxicol. , 2009, 22 (1), pp 52–63 8 [] 9http://www.earthwiseinside.com/solutions/fire-safety-solutions-and-polymeric-materials-green-armor.htm 10 Wiel, E., and Levchik, S. (2009). Flame Retardants for Plastics and Textiles: Practical Applications. Hanser Verlag: 20.

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