A Polymeric Solution For A Bromine Problem!


Manufacturers claim that brominated flame retardants are the most effective additives for slowing down the spread of flame on polymers that catch fire. Over the years, some of their products have come under regulatory scrutiny because of concerns over bioaccumulation and toxicity. One of these is hexabromocyclodo­decane (HBCD), long used to help polystyrene foam insulation meet fire-safety building codes.

The big three producers of brominated flame retardants—Albemarle, Chemtura, and ICL Industrial Products—say they have found viable alternatives to HBCD and other flame retardants. Brominated flame retardants built with long polymeric backbones can provide the flame-retarding benefits of bromine and decrease the possibility of toxicological side effects, they say. With molecular weights more than 1,000 daltons or so, the polymeric molecules are too big to penetrate cell walls and thus shouldn’t bioaccumulate or be toxic, they explain.

Efforts to develop a polymeric brominated flame retardant as a substitute for HBCD serve as a model of how regulators as well as users and makers of flame retardants ought to proceed, industry executives say. “It is a really good case study for taking one thing out of the market and bringing the next thing forward,” says Joel Tenney, director of advocacy for ICL’s industrial products segment.

Interestingly, the effort is not being led by a producer of brominated flame retardants. In 2004, Dow Chemical saw the writing on the wall for HBCD, the additive in what is perhaps Dow’s most recognizable brand: Styrofoam extruded polystyrene foam insulation.

HBCD had been under fire for a host of environmental and health reasons. The compound is fat-soluble, and according to studies cited by the Environmental Protection Agency, it bioaccumulates and is linked to toxicity in aquatic animals and to developmental problems in mammals.

In 2008, Norway proposed the listing of HBCD as a persistent organic pollutant under the Stockholm Convention. That same year, HBCD became a candidate for a Substance of Very High Concern designation under Europe’s Registration, Evaluation, Authorisation & Restriction of Chemical substances (REACH) regulation. In the U.S., EPA initiated an action plan for HBCD in 2010 and this year proposed rules that would require companies to notify EPA if they use HBCD on consumer textiles sold in the U.S. (see page 34).

“We saw there was pressure on brominated flame retardants building up over recent years, and even though we still believe that HBCD is safe to be used in foams, we started very early on to look into more sustainable solutions,” says Inken Beulich, senior R&D manager for Dow Building Solutions.

To find an alternative, Beulich says, Dow applied its polymer expertise as well as its competency in environment, health, and safety modeling. The firm’s goal was to come up with a new flame retardant that the entire polystyrene foam industry, not just Dow, could use.

The company explored bromine-free chemistry but eventually settled on a bromine-based approach. The key breakthrough, Beulich says, was finding the right polymer backbone: a styrene-butadiene block copolymer. The polystyrene block, she says, ensures good miscibility with the polystyrene foam matrix. The polybutadiene block gets brominated.

It stands to reason that Dow stuck with bromine, says James Innes, president of the consulting firm Flame Retardants Associates. Burning typically occurs when oxygen reacts with free radicals in the gas phase, he explains. Brominated flame retardants trap these free radicals, preventing them from reacting with the oxygen and thereby slowing down the burning process.

With polystyrene, the heat of the fire pyrolyzes the polymer and causes styrene monomers to break off. “A radical trap helps limit the combustion of the break-off products,” Innes says.

When Dow started working on its polymeric flame retardant, Albemarle, Chemtura, and ICL had been experimenting with their own candidates for HBCD replacement. Dow consulted with the three firms early in its development process, and the three quickly found that Dow’s new molecule outperformed their own.

The polymeric brominated flame retardant performs as well as HBCD in all important respects, Beulich says. It has equivalent flame-retarding ability, and it doesn’t hurt the mechanical, physical, and insulation properties of the foam.

Furthermore, ICL’s Tenney adds, the Dow technology works with both extruded and expandable polystyrene foam. “HBCD was a unique chemical because it satisfied both of these production approaches,” he says.

The promise of a better toxicological profile, the makers of flame retardants say, was every bit as attractive as good performance. “We at Albemarle were not able to develop a polymeric solution; everything we came up with that had promise was a small molecule,” acknowledges David Clary, Albemarle’s chief sustainability officer. “So when Dow’s technology became available for license, we decided to go that way instead. Especially from a health, safety, and environment standpoint, it was a superior offering.”

The scale-up of the Dow technology will depend on local regulations to restrict HBCD, as well as the ability of foam and flame retardants companies to adopt the new technology. All three major makers of brominated flame retardants have taken licenses from Dow and are in various stages of commercializing the product.

Chemtura is already producing the flame retardant commercially under the Emerald Innovation 3000 name. Albemarle is building a plant to make it, under the GreenCrest name, at its Orangeburg, S.C., site. ICL says it is selling small quantities of the flame retardant so customers can start transitioning to the new technology.

It will take Dow some time to switch its close to 20 Styrofoam plants to the new technology, Beulich says. The firm will first use the new flame retardants in Japan, followed by Europe and North America, and then the rest of the world. BASF is also planning to use the Dow technology with its polystyrene foam product line.

Long before Dow orchestrated the transition from HBCD, makers of brominated flame retardants had decided that their industry’s future lies with polymeric materials. “We had already committed that was the direction we wanted to go, and that’s the target we have set ourselves for new flame retardants that are bromine-based,” Clary says. “We really want them to be polymeric.”

In fact, polymeric flame retardants have been available for a while. Brominated polystyrene has been used for the past decade in applications such as electronic connectors made from polybutylene terephthalate and high-temperature nylon.

Today, makers of flame retardants are busy introducing polymeric alternatives to decabromodiphenyl ether (decaBDE), a workhorse flame retardant that’s used in electronics housing and a host of other applications. In 2009, EPA expressed concern about the environmental impact of decaBDE and its potential link to cancer and diminished brain function. The agency obtained commitments from the three makers of flame retardants to phase out the chemical for most uses by the end of this year.

Albemarle’s GreenArmor product was specifically designed to substitute for deca­BDE. Clary won’t disclose details about the molecule other than to say it is a brominated “cousin” of polystyrene. Chemtura and ICL both offer polymeric substitutes to decaBDE as well.

A draft report EPA issued this summer on alternatives to decaBDE noted that polymers have relatively low bioaccumulation and toxicity. The report did point out that the molecules, much like the plastics to which they are added, have a tendency to persist in the environment. If polymeric flame retardants become widely used, EPA cautioned, further study of their degradation might be needed.

Chemtura is looking to plunge even further into polymeric flame retardants with its Greener Innovation Grant program, through which it sought grant proposals from academia on sustainable flame retardants.

“We encouraged proposals that would look at sustainable brominated flame-retardant systems because of the benefits that halogenated flame retardants have in their versatility, efficiency, and effectiveness,” says Marshall Moore, director of technology, advocacy, and marketing at Chemtura’s Great Lakes Solutions unit. The company is awarding four grants to yet-to-be-disclosed university researchers.

Although they do want to introduce polymeric flame retardants whenever they can, companies producing flame retardants are quick to point out that the shift is no admission of guilt about their current product lines. Chemtura’s Moore characterizes the strategy more as a reaction to market demand and “a response to regulations and restrictions that are being put in place that are sometimes a legislative process, not a scientific risk assessment process.”

Albemarle’s Clary hopes polymeric flame retardants foster public confidence. Small-molecule products have been painted with a broad brush, he says. Decabromodiphenyl ethane, for example, is a decaDBE replacement that actually has an excellent toxicological profile, he adds.

The public, Clary suggests, may have an easier time understanding polymers. “People get intuitively that these polymers are not going to be absorbable in the human body,” he says. “You have an extra level of comfort, of assurance that there isn’t going to be an unexpected health impact.” (source: C&EN)

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