Flammability of Polymer-Clay Nanocomposites:
TEM Analysis of Nanocomposite Structure Before and After Burning.
Alexander B. Morgan, Jeffrey W. Gilman, and Richard H. Harris
Materials Fire Research Group
Fire Science Division
Building and Fire Research Laboratory
Polymer-clay nanocomposites have generated a great deal of scientific interest due to their enhanced mechanical and barrier properties. It has also been shown that polymer-clay nanocomposites have reduced flammability when compared to polymers without nano-dispersed clay present. This is a significant finding, as most flame retardants reduce mechanical properties when used in a polymer. Organically treated clays actually improve mechanical properties while providing a flame retardant effect. We have analyzed a wide range of polymer-clay nanocomposites by cone calorimetry and by transmission electron microscopy (TEM). These two techniques not only characterize the nanocomposites, they also help shed light on the mechanism of the flame retardancy provided by organically treated clays. Further, the TEM analysis of these nanocomposites has shown a great deal of structure variability that was previously unknown.
TEM is a very powerful tool for analyzing the structure of polymer-clay nanocomposites. Wide angle X-ray diffraction (WAXS) is the technique typically used for analyzing these systems, but it has some drawbacks in that it cannot differentiate between certain types of clay dispersions found in polymers. In the case of burned polymer-clay nanocomposites, the resulting char may have disordered the clay sufficiently that no WAXS signal can be obtained. Again, TEM becomes a powerful tool for characterizing the dispersion of the clay when found in a char.
In this poster session, we will illustrate the advantages of TEM as a technique for analysis of polymer-clay nanocomposites. We will show its use in determining the mechanism of flammability for a polymer-clay nanocomposite before and after burning. Further, we will show how TEM can differentiate between all types of polymer-clay nanocomposites.