Effect of carbon nanotubes and montmorillonite on the flammability of epoxy nanocomposites

Addition of just 0.0025 mass fraction of highly aligned multiwall carbon nanotubes (MWCNTs) showed a 45% reduction in the peak mass loss rate (PMLR) during gasification of epoxy/MWCNT composites; this 45% decrease in PMLR at such a low loading (0.0025mass fraction) of MWCNTs, is much better than that reported previously with either MWCNTs (0.02 mass fraction) or SWCNTs (0.005 mass fraction). We attribute this effect to the use of highly aligned MWCNTs which easily exfoliate, or debundle, using high shear mixing. In addition, 0.005 mass fraction MWCNTs showed significant reduction in the initial mass loss rate as compared to other epoxy/MWCNT, epoxy montmorillonite (MMT) and pure epoxy samples. Reduced PMLR was also observed for epoxy/MMT nanocomposites, but required much higher MMT content. The epoxy/MWCNTs composites residue/char integrity (no visible cracks on the char surface of MWCNTs/epoxy samples) appeared to be superior to that for epoxy/MMT samples. The rheological characterization of the epoxy composites was carried out in order to study the effect of nanoparticle network formation on the rheological properties and flammability. Significant increase in thermal conductivity (k) was observed for epoxy/MWCNTs composite with high loadings of MWCNTs. This gasification mass loss behavior of the nanocomposites was investigated using a model that combines a continuum description of the transport of thermal energy with Ahrrenius kinetics for the decomposition of the polymer. The enhanced thermal conductivity for the epoxy/MWCNT composites appears to be responsible for the initial mass loss reduction. (C) 2010 Published by Elsevier Ltd.