Flammability of thermoplastic carbon nanofiber nanocomposites

Five commodity thermoplastics (polyethylene, polypropylene, thermoplastic polyurethane, poly(butylene terephthalate), and poly(amide 6)) were melt compounded with vapor grown carbon nanofibers via twin screw extrusion. These materials were then analyzed for flammability behavior by cone calorimeter to determine how the nanofibers would reduce flammability of the polymers. It was found by cone calorimeter that the nanofibers greatly reduced peak heat release rate and improved many other flammability parameters of the samples. However, smoke release was increased in all samples, which may be one drawback of using these materials. Interestingly, the amount of flammability reduction was not uniform across all samples, with nanofiber reducing flammability the most in the thermoplastic polyurethane sample. The mechanism of flammability reduction in the polymers tested in this paper is shown again to be a mass loss rate reduction induced by the formation of thick tangled networks of carbon nanofibers during polymer decomposition. This mechanism was confirmed by studying the mass loss rate curves and electron microscopy analysis of the final chars collected from the cone calorimeter experiments. Copyright (C) 2010 John Wiley & Sons, Ltd.