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With New Coating, ‘Cotton Doesn’t Burn’

Tuesday, May 8, 2012

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Materials scientists at Texas A&M University have unveiled an eco-friendly polymer coating that could keep everything from airplane seats to military tents from going up in flames.

“We can now make cotton fabric that doesn’t burn at all,” says Dr. Jaime Grunlan, an associate professor in the Department of Mechanical Engineering, who is leading the research.

Dr. Jaime Grunlan has developed an environmentally benign alternative to current flame retardant treatments.

Grunlan has been working on the coating for years. He announced an earlier version in 2010, drawing attention from the U.S. military and the Federal Aviation Administration, among others.

The newest iteration, however, is more effective than ever—and environmentally friendly to boot, Grunlan says.

Heating Up a Protective Coating

Grunlan works with polymer nanocomposites.

The new coating technology involves covering every microscopic fiber in a fabric with a thin composite coating of two polymers that exhibit an intumescent effect, producing a protective carbon foam coating when exposed to high temperatures, the university explains in an article.

The films are about one-tenth of a micron thick (about one-thousandth the thickness of a human hair) and are created with a layer-by-layer assembly technique that deposits the coating onto the fiber’s surface. The technique allows Grunlan to control the coating thickness down to the nanometer level.

Grunlan says the technology, reported in several science journals, will be suitable for a wide variety of clothing and fabrics, even those used in military camps, where a fire in a single tent can wipe out an entire camp.

Another Brick in the Foam Wall

It could also be used in foams, such as those found in seats, mattresses and building insulation.

In those applications, a coating of chitosan (a natural material extracted from shrimp and lobster shells) and clay is deposited on the polyurethane foam to eliminate the “melt dripping” effect that spreads fires.  The nanocomposite mixture coats the foam’s interior walls, enabling them to keep their shape when burned, rather than puddling like untreated foam.

Cotton shows minimal damage after Vertical Flame Testing (VFT).

“It’s like we’re building a nano-brick wall within each cell of the foam,” Grunlan says.

The ultra-thin coating adds only 4 to 5 weight-percent to the foam—a critical consideration in military and aviation applications—and does not alter its color, texture or flexibility.

“A lot of anti-flammables degrade fabric and foam properties,” Grunlan says.

But with the ability to coat individual threads of cotton, Grunlan’s technique may potentially strengthen fabric. The team is still looking at ways to make the coating softer and better able to withstand washing.

Green Alternative

By employing chitosan in his newest formulation, Grunlan’s coating also avoids the use of brominated compounds, which are currently used in flame-retardant materials but facing bans due to their potential toxicity.

“Based on initial results, I really think this is going to become a widely adopted, environmentally benign alternative to current flame retardant treatments,” says Grunlan.

“Anywhere you want to make fabric or foam anti-flammable, you can use this technology.”