Clay-Catalyzed Cracking Leads to Suppressed Flammability in Clay-Polyolefin Nanocomposites

Organoclay–polyolefin nanocomposites have been shown to exhibit slightly increased thermal stability and decreased flammability, compared to unfilled polyolefins. In contrast, we find that when the clay has not been organically modified, the resulting polyolefin nanocomposites are less thermally stable and, unexpectedly, also much less flammable. In this contribution, we investigate the mechanistic origins of these effects. Clay–polyolefin nanocomposites were prepared by in situ polymerization of ethylene or propylene, using a catalyst adsorbed onto the clay. Decreased thermal stability is attributed to clay‐catalyzed polymer decomposition, while decreased flammability arises in part from clay‐catalyzed formation of a polyaromatic char from olefins trapped in the material by the dispersed nanofiller. Acid‐treated montmorillonite suppresses the flammability of polyolefins by a combination of chemical effects (clay‐catalyzed reactions) and physical effects (mass and energy diffusion barriers). The overall flammability depends strongly on the extent of clay dispersion. A polyethylene melt‐blend and a nanocomposite, both containing 10wt.% clay, exhibit slower combustion and self‐extinguishing behavior, respectively, in a vertical burn test.