Developing a polymer coating that could buy time and protection during a fire

The deaths of technicians, medical personnel and even graduate students who are burned in laboratory accidents might be prevented by a flame-resistant coating Texas A&M's Jaime Grunlan has developed.

Grunlan, an associate professor in the Department of Mechanical Engineering, works with polymer nanocomposites that have properties similar to those of metals and ceramics - conducting electricity, for instance - while maintaining properties of polymers, such as low density.

His development of a flame-resistant polymer coating has certainly gotten some attention. As the sole researcher in the use of this technique for flame retardancy, he has fielded calls from the United States military to the cotton industry to mattress manufacturers to the Federal Aviation Administration, and from companies around the world.

Grunlan's technology involves covering every microscopic fiber in a fabric with a thin composite coating of polymer and clay to enhance the flame-retardant properties of the fabric (and other forms of protection, too, including UV, thermal and abrasion resistance).

"It's like we're creating a nano-brick wall around each fiber. Anywhere you want to make fabric or foam anti-flammable, you can use this technology."

The thin films are about one-tenth of a micron thick, or about one-thousandth the thickness of a human hair, and are created with the layer-by- layer assembly technique in which the coating is deposited onto the surface of the fiber being coated. This layer-by-layer process allows Grunlan to control the thickness of the coating down to the nanometer level.

"It's like we're creating a nano-brick wall around each fiber," Grunlan says.

And the coating is so thin that it adds only 1 to 2 weight-percent to the fabric and does not negatively alter the fabric's color, texture or strength.

"A lot of anti-flammables degrade fabric and cause it to tear," Grunlan says.

But with Grunlan's technique, each thread can be individually coated and still remain soft and flexible. In fact, his coating could potentially strengthen fabric.
In tests, virgin cotton fabric is burned using an industry-standard UL94 test, also known as the vertical flame test. In the test, the treated and untreated fabrics are exposed to 12 seconds of flame. Grunlan and his students measure how long it takes for the fabric to catch fire and then how long the fire burns after the flame is extinguished.

After the vertical flame test, only wisps of untreated cotton fabric remain (top). By comparison, the fabric treated with Grunlan's polymer coating (bottom) shows less destruction and even retains some properties of fabric despite its layer of black soot.

The flame gets up to 700 degrees Celsius, and untreated cotton completely degrades at 600 degrees Celsius. But the fabric treated with Grunlan's coating still maintains the qualities of the fabric, remaining soft and flexible.

"This polymer coating buys time and protection," Grunlan says.

Grunlan says he expects the technology will be suitable for clothing, including children's clothing; lab coats; and medical clothing for both doctors and patients. It can even be used in military camps, where a fire in a single tent can wipe out an entire camp.

But the technology's applications go far beyond just clothing and fabric. The coating could be used in foams, such as those found in sofas, mattresses, theatre and auditorium seats, airplane seat cushions, and building insulation.

The nanocomposite clay-polymer mixture coats the interior walls of foam. The result is that when burned, the treated foam keeps its shape instead of puddling at high temperatures like untreated polyurethane foam does. This quality eliminates the melt-dripping effect that further spreads fires.

In fact, the technology is so promising that one company has funded the patent, which is filed in the United States and Europe, and several others have been in touch with Grunlan.

"Anywhere you want to make fabric or foam anti- flammable, you can use this technology," he says.