Flame retardancy of polymers

Polyurethane (PU) foam is an extremely versatile material that commonly is used in bedding, upholstery and building insulation. However, PU foam is very flammable, often resulting in dripping of melted material that enhances flame spread through the formation of a pool fire under the burning object. Brominated flame retardant compounds (e.g. pentabromodiphenyl ether) have been used to reduce foam flammability but there is growing evidence that these chemicals are toxic to the environment and living organisms.

Replacing brominated flame retardants in polymer formulations with safer and more environmentally-friendly alternatives has also sparked the interest of nanoscientists. For instance, they have found that carbon nanotubes and clay can improve the flame retardancy of plastics. Their flame retarding mechanisms are different and their effect for improving the flame retardancy is limited when they are used alone. However, when they are used together, a significant synergism happens.

Another, more recent effort to create an environmentally-friendly flame retardant system involves the layer-by-layer assembly of thin films using materials obtained from completely renewable sources. 

“Our goal was to develop a truly ‘green’ film with flame-retardant and oxygen-barrier characteristics” Jaime C. Grunlan, Associate Professor and Gulf Oil/Thomas A. Dietz Development Professor in the Department of Mechanical Engineering at Texas A&M University, tells Nanowerk. “To our knowledge, this is the first study of a flame suppressing thin film consisting of completely renewable materials.” 

The general topic of safe flame retardant technologies is very timely, with many of the commonly used halogenated materials being restricted around the world. With legislation banning brominated compounds, there is a significant need for new anti flammable technologies that are not harmful to environment and do not degrade other important properties of a given object. 

“Our coating provides improvement to the flame retardancy of the foam but it does not alter its physical properties,” says Grunlan. “This is also the first demonstration of a high gas barrier thin film made from these same materials.” 

Grunlan and his team reported their findings in the February 16, 2012 online edition of Applied Materials & Interfaces (“Clay–Chitosan Nanobrick Walls: Completely Renewable Gas Barrier and Flame-Retardant Nanocoatings”), first-authored by Galina Laufer, a PhD student in Grunlan’s Polymer NanoComposites Group. (Source: Nanowerk)  

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