No one wants their bed, couch, chair, computer,
or TV to catch on fire. "If an ordinary upholstered chair in your home
gets ignited, it can essentially take your whole house down," says
Richard Gann, a senior research scientist at the U.S. National
Institute of Standards and Technology's (NIST) Building and Fire
Research Laboratory. The most flammable part of a mattress or couch is
its plastic polyurethane foam cushioning, he explains. Once a fire gets
through a chair or mattress's fabric covering and into this cushioning,
it can start a catastrophic reaction that quickly leads to "flashover,"
in which nearly everything combustible inside a room ignites
simultaneously.
Until very recently, brominated flame retardants,
especially polybrominated diphenyl ethers (PBDEs), were one of the main
materials used to reduce the speed with which the plastic components of
consumer goods including beds, couches, chairs, and electronics could
be consumed by fire. However, growing evidence shows that PBDE
compounds are escaping from the products they protect and making their
way into the products' users. Moreover, the chemicals may disrupt human
thyroid hormone functioning and cause other health effects, prompting
many nations to ban or suspend their use in new consumer goods. [For
more information on the health effects of PBDEs, see "Unwelcome Guest: PBDEs in Indoor Dust, p. A202 this issue.]
Although bromine- and chlorine-containing flame retardants are still
used in some products, the need for new alternatives is being driven by
a confluence of policy, standards, and pressure from environmental
groups. Europe banned the use of two formulations, PBDE pentaBDE and
octaBDE, in 2004, the same year they were withdrawn from the North
American market. A third compound, decaBDE, was banned 1 April 2008 by
the European Court of Justice. Stateside, Maine has banned the use of
decaBDE, the only PBDE still on the market in North America, in
mattresses and residential upholstered furniture produced and sold in
that state, and will extend the ban to electronics in 2010. Washington
prohibits the use of decaBDE in mattresses and sets a process for a
future ban in furniture and electronics if the state can identify a
safer and feasible alternative that meets fire safety standards. Asian
countries and other U.S. states have similar legislation in the works.
"Instead of adding new fire retardant chemicals that
ultimately may be shown to cause health problems, we should be asking
whether we need to use these chemicals or if there are other ways to
achieve equivalent fire safety," contends Arlene Blum, a biophysical
chemist and visiting scholar at the University of California, Berkeley.
"So many of the chemicals we have banned in the past were flame
retardants—think about asbestos, polychlorinated biphenyls,
polybrominated biphenyls, tris(2,3-dibromopropyl) phosphate,
PBDEs—[and] they all ended up in the environment and in people," she
points out. "We need to think carefully about adding these sorts of
chemicals to consumer products before there is adequate health
information."
Policy Drivers
Two new standards from the U.S. Consumer Product Safety Commission
(CPSC) are opening the door for innovative approaches for protecting
consumer goods containing polyurethane foam from fire. The first took
effect last year for mattresses. This standard is innovative in being
the first in the United States to focus on the rate of heat release,
which fire safety experts recognize is the main determinant of how
quickly a fire can spread out of control to the flashover point, Gann
says.
The mattress industry worked with NIST to develop the new standard
test method to meet the CPSC regulation, which stipulates that no
mattress may generate a peak heat release rate greater than 200
kilowatts when subjected to gas burners that mimic burning bedding. The
CPSC estimates the new standard will prevent as many as 270
fire-related deaths and 1,330 injuries every year. Since this is a
performance standard rather than a prescribed mattress design, it
allows manufacturers to choose how to fabricate mattresses that comply
with the regulation, Gann says.
One approach mattress manufacturers are using to meet the standard
is to employ what is known in the industry as a barrier material, says
Tom Ohlemiller, who was the project leader for the NIST team that
developed the mattress test method. The barrier materials themselves
may be inherently nonflammable, such as polyamides like Kevlar.
Flammable barriers may be protected with proprietary fire retardant
treatments such as decaBDE. However, Ohlemiller says the standard does
not require such treatments for the polyurethane foam padding beneath
the barrier, which some scientists believe is the source of some of the
PBDE flame retardants that have escaped into people's homes. Over the
past year, scientists have reported detecting other flame retardants
used in polyurethane foam in household dust.
The second new standard, which affects upholstered furniture, is
still wending its way through the regulatory process. According to
Nancy Nord, acting chairman of the CPSC, the new rule will address
upholstered furniture fires without requiring the use of fire retardant
chemicals. Under the new proposal, furniture manufacturers could meet
the performance standard by using smolder-resistant cover fabrics or
interior fire-resistant barriers to protect the furniture's internal
filling material. The standard was put out for public comment in the
Federal Register on 4 March 2008 and is open for comment until May 19.
The furniture standard focuses on cigarettes as a source of fires
because they are responsible for 90% of the fires involving upholstery,
says Russell Batson, vice president of government affairs for the
American Home Furnishings Alliance, an industry group. "You can get
smolder resistance without relying on chemicals," he says. However,
Gann points out that "cigarette ignition resistance is going to be
improved significantly anyway" due to the passage over the past four
years of laws mandating that Canada and 24 U.S. states can sell only
"fire-safe" cigarettes, which self-extinguish if left unattended. These
laws affect nearly 60% of the North American population, according to
the nonprofit Coalition for Fire-Safe Cigarettes.
Additionally, Alexander Morgan, a group leader at the University of
Dayton Research Institute, says there is a lot of concern about
barriers failing against ignition sources stronger than a cigarette,
especially since smoking rates are declining in many developed nations,
according to the World Health Organization. He says candles, hot
electrical equipment, and short-circuiting laptops could easily
penetrate these protective barriers.
This is a fundamental weakness of the barrier approach in light of
several decades of fire safety data for furniture from the United
Kingdom, which Morgan says has the world's toughest flammability
standards for polyurethane foam. "Yes, they do use flame retardants,
but the level of fire safety of their products is very good and fire
losses in the UK due to furniture fires are quite low or non-existent.
When and if flashover occurs due to a furniture fire, the amount of
pollution and carcinogens released from this one fire far overwhelms
the production of potentially dangerous products from a flame retardant
foam," he says. Morgan argues that the solution may be to devise flame
retardants that are less likely to escape from the materials that they
protect, together with better product reclamation and recycling
programs for flame retardant products so that the chemicals don't end
up into the environment.
Despite such concerns, Batson says the proposed standard is
inspiring furniture manufacturers to investigate how barriers can be
used to insulate the interior cushioning materials inside upholstered
furniture. "Recent innovations in materials science, together with
concerns about flame retardant toxicity and ecotoxicity have convinced
people in the industry to try to design effective barrier materials for
the market," he says. The furniture industry is looking carefully at
how mattress manufacturers construct fire-blocking barrier layers of
fabric or "high-loft" materials such as batting rather than chemically
loading the outer fabric layer, he says. "That approach and some of the
technologies that are emerging in response to it is probably going to
be useful in the furniture [industry], as well," he says.
Nanomaterials
One promising approach is to incorporate flame retardants into the
materials themselves. A new company called G3 Technology Innovations (G3
i)
is pursuing that line of reasoning with its GreenShield FR™ treatment
for polyester fabrics. Such fabrics are the basis of 90% of the
products used in the contract textile industry—which produces all
furniture, floor coverings, wall coverings, and window treatments used
in commercial buildings and institutions—says Alex Qiao, G3
i's co-founder and president.
The technology, which G3
i co-founder and chief
operating officer Suresh Sunderrajan and his business partners
developed for different applications while previously employed at
Eastman Kodak, revolves around the ability to attach different
functional groups onto nanoparticles. "We are able to attach multiple
sets of these [functional molecules] onto the particles," he explains.
For example, he says one set of the molecules might encompass the
particles needed to allow the molecules to attach themselves to a
fabric's fibers, a second set might provide water and stain repellency,
and a third set could involve flame retardancy. "All of this is built
onto a [silica-based] backbone which is inherently nonflammable," he
explains. The GreenShield FR treatment "goes into the [polyester] fiber
and becomes a permanent part of it," Qiao says.
The company has also worked with a textile finisher called
Preferred Finishing to develop new barrier materials that Qiao says can
become integral parts of the fabric they protect because both are made
of polyester resin. This confers an additional advantage of avoiding
the use of melamine–formaldehyde resin, which is often used to bind
other barriers to decorative fabrics, Sunderrajan points out. When the
resin degrades, he explains, it releases formaldehyde, which the
International Agency for Research on Cancer classifies as a known human
carcinogen. The company says all of its technologies are based upon
commercially available materials that have been tested individually for
toxicity. Several furniture makers are now testing the G3
i products.
Nanoclays are another material that could change the way consumer
products are protected from combustion. Flame retardants made with
naturally occurring clay called montmorillonite are poised to have a
huge influence on future fire safety, Gann says. Scientists at NIST and
Cornell University have been investigating how this clay can help
reduce the amount of energy released during fires for more than a
decade, says Jeffrey Gilman, a research chemist at NIST.
"When things burn, contrary to how it looks, it is not the solid
that is burning. The solid breaks down to give you small fragments of
molecules. These vaporize and mix with the air, and they burn there,"
Gann explains. "The 'nano-network' formed by the nanoclays impedes this
from happening," he says. "If the [nanoclay] particles are
appropriately spread out and dispersed through the host [material],
they form sort of a gauze inside the material. It slows down
significantly or even prevents the breakdown of material and the
release of gas-phase combustible molecules," he says.
The potential of nanoclays isn't just theoretical. A company called
Nanocor sells nanoclay-based flame retardants that are used in
electronics, wires, cables, and decorative wallpapers, says Tie Lan,
general manager for the company's U.S. operations. "The fundamental
nature of the nanoclay will make the material burn slower [and] lower
the temperature of the flame," he says, adding that the same clays are
also used in nonclumping kitty litters.
Both Nanocor and Albemarle Corporation, one of the major flame
retardant makers, sell flame retardants combining nanoclays with
another major class of flame retardants based on metal hydroxides. The
nanoclays synergistically improve how the metal hydroxide retardants
perform, Gilman says. Combining the two flame retardants also improves
how the plastics are processed, as well as their material properties.
Nanoclays are appealing to plastics manufacturers because they can be
added in relatively small amounts, on the order of a few percent by
weight. This means both that they are unlikely to negatively affect the
functionality of the plastic material to which they are added and that
they are relatively inexpensive, Gann says.
More recently, the NIST researchers have also begun to look at
other nanomaterials, including carbon nanotubes, layered hydroxides,
and polyhedral oligomeric silsesquioxane nanocomposites that also
contain silicon, says Gilman. Some nanomaterials, especially carbon
nanofibers, appear to have promise for use in polyurethane foam, says
Mauro Zammarano, a guest researcher from Italy evaluating these
materials at NIST. Testing at NIST suggests carbon nanofibers are able
to reduce the rate at which heat is released when polyurethane foam is
burned.
However, Andrew Maynard, chief science advisor of the Project on
Emerging Nanotechnologies, a nonprofit group associated with the
Woodrow Wilson International Center for Scholars, cautions that the
same properties that make the nanoparticles effective could also make
them toxic. "With any sort of nanotechnology . . . [the] potential for
harm is associated with the size and shape of the particles, as well as
what they're made of. That applies whether you're looking at sunscreen,
impregnated fabrics, or flame retardants," he says. Scientists need to
look carefully to determine if there is any way the nanomaterial-based
flame retardants escape from the fabric or material in which they're
used and enter the environment, and whether people could be exposed to
the nanoparticles, he says.
NIST has begun to work with the CPSC and Scripps Institution of
Oceanography to evaluate whether any of these nanomaterial-based fire
retardants are toxic, Gilman says. Dimitri Deheyn, a marine biologist
at Scripps' Marine Biology Division, is conducting some of this testing
using brittle stars, which Deheyn says have nervous systems that
function very similarly to mammals, including humans. He says the
testing he has conducted to date suggests the surfactants used to
ensure the nanomaterials disperse throughout the materials to which
they are added may be more toxic than the nanomaterials themselves.
Halogen-Free Electronics
The electronics industry is under pressure from environmental
groups to remove potentially toxic compounds from their products,
including the brominated flame retardants that were once widely used in
electronics housings and cases and are still used extensively in
printed circuit boards. At least nine leading electronics companies
have pledged to remove brominated and/or halogenated flame retardants
from some or all of their products, according to the Environmental
Working Group.
The main way that companies are doing this is by using
phosphorus-based flame retardants for casings and circuit boards, and
using minerals such as nanoclays in combination with aluminum and
magnesium hydroxide for the machinery's wiring and cabling, says
Morgan. However, he points out that companies and environmental
watchdogs are scrutinizing some of these phosphorus-based retardants
for potential health problems of their own; for example, some are
suspected to be neurotoxicants when they break down in the environment,
he points out. He says his experience testing how well different
nonhalogenated flame retardants work suggests that reactive
phosphorus-based retardants appear to be the best nonhalogenated flame
retardants for printed circuit boards at this time, in terms of their
effectiveness, long-term durability, sustainability, and environmental
impact.
Trying to find halogen-free alternatives for electronic circuit
boards involves significant trade-offs, stresses Fern Abrams, the
director of government relations and environmental policy for IPC, an
electronics industry association for manufacturers of printed circuit
boards and other electronics components. She says the "holy grail"
would be to develop materials for building and housing electronics that
are inherently flame-resistant.
Morgan agrees. He says the aerospace industry currently uses some
inherently nonflammable plastics, but they are too expensive for
commodity-type applications such as electronics housings, given the
industry's profit margins. More recently, scientists have begun trying
to develop plastic polymers that are inherently nontoxic and
nonflammable.
One team involved in this effort is at the University of
Massachusetts Amherst, where researchers have developed a new plastic
polymer based on bishydroxydeoxybenzoin (BHDB) that releases water
vapor rather than hazardous gases when it breaks down in a fire. "The
great thing about BHDB is that . . . it is extremely fire-safe and does
not contain halogenated additives," says Bryan Coughlin of the
university's Polymer Science and Engineering Department, one of the new
material's co-inventors.
The Amherst researchers believe BHDB may prove to be cost-effective
for use in some consumer products, including home furnishings and
electronics. "We are currently trying to determine how well BHDB works
in a variety of plastics formulations . . . including polyurethane
foam," says Todd Emrick, another co-inventor at the University of
Massachusetts Amherst Polymer Science and Engineering Department. The
fire safety experts at NIST say that they believe the material has a
great deal of promise. But the biggest challenge, as Morgan points out,
may be finding a company willing to make the investment needed to bring
such an innovative technology to the marketplace.
Kellyn S. Betts
Suggested Reading
Kashiwagi T. 2007. Flame retardant mechanism of the nanotubes-based
nanocomposites. Final report. NIST GCR 07-912. Gaithersburg, MD:
National Institute of Standards and Technology.
Morgan AB, Wilkie CA, eds. 2007. Flame retardant polymer nanocomposites. Hoboken, NJ: John Wiley & Sons.
Nelson GL, Wilkie CA, eds. 2001. Fire and polymers: materials solutions
for hazard prevention. ACS Symposium Series #797. Washington, DC:
American Chemical Society.
U.S. EPA. 2005. Environmental profiles of chemical flame-retardant
alternatives for low-density polyurethane foam, volume 2: chemical
hazard reviews. EPA 742-R-05-002B. Washington, DC: U.S. Environmental
Protection Agency.
originally published at http://www.ehponline.org/members/2008/116-5/innovations.html