Thermal and Flammability Properties of Polypropylene/Carbon Nanotube Nanocomposites

Published

May 1, 2004

Author(s)

Takashi Kashiwagi, E A. Grulke, J N. Hilding, Richard H. Harris Jr., John R. Shields, Kathryn M. Butler, K M. Groth, S B. Kharchenko, Jack F. Douglas

Abstract

The thermal and flammability properties of polypropylene/multi-walled carbon nanotube, (PP/MWNT) nanocomposites were measured with the MWNT content varied from 0.5 % to 4 % by mass. Dispersion of MWNTs in these nanocomposites was characterized by SEM and optical microscopy. Flammability properties were measured with a cone calorimeter in air and a gasification device in a nitrogen atmosphere. A significant reduction in the peak heat release rate was observed; the greatest reduction was obtained with a MWNT content of 1 % by mass. Since the addition of carbon black powder to PP did not reduce the heat release rate as much as with the PP/MWNT nanocomposites, the size and shape of carbon particles appear to be important for effectively reducing the flammability of PP. It was noted that, however, the radiative ignition delay time of a nanocomposite having less than 2 % by mass of MWNT was shorter than that of PP due to an increase in the radiation in-depth absorption coefficient by the addition of carbon nanotubes. The effects of residual iron particles and of defects in the MWNTs did not significantly affect the heat release rate of the nanocomposite. The flame retardant performance was achieved through the formation of a relatively uniform network-structured floccule layer covering the entire sample surface without any cracks or gaps. This layer re-emitted much of the incident radiation back into the gas phase from its hot surface and thus reduced the transmitted flux to the receding PP layers below it, slowing the PP pyrolysis rate. To give insight into this phenomena, thermal conductivities of the nanocomposites were measured as a function of temperature and their effects on the gasification process of the nanocomposites were examined by numerically calculated results. The thermal conductivity of the nanocomposite increases with an increase in MWNT content in particular above 160 C, but does not increase nearly as dramatically as the increase in electric conductivity.

Citation

Polymer

Volume

45

Issue

No. 12

Pub Type

Journals

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Keywords

carbon nanotube, flammability, nanocomposite, polypropylene, thermal conductivity

Citation

Kashiwagi, T. , Grulke, E. , Hilding, J. , Harris, R. , Shields, J. , Butler, K. , Groth, K. , Kharchenko, S. and Douglas, J. (2004), Thermal and Flammability Properties of Polypropylene/Carbon Nanotube Nanocomposites, Polymer, [online], https://tsapps.nist.gov/publication/get_pdf.cfm?pub_id=861275 (Accessed October 11, 2025)