Macromol. Rapid Commun. 2002, 23, 761–765 761 Thermal Degradation and Flammability Properties of Poly(propylene)/Carbon Nanotube Composites Takashi Kashiwagi,* 1 Eric Grulke, 2 Jenny Hilding, 2 Richard Harris, 1 Walid Awad, 1 Jack Douglas 3 1 Fire Science Division, Building and Fire Research Laboratory, National Institute of Standards and Technology, Gaithersburg, MD 20899-8665, U.S.A. E-mail: takashi.kashiwagi@nist.gov 2 Advanced Carbon Materials Center, University of Kentucky, Lexington, KY 40506, U.S.A. 3 Polymers Division, Materials Science and Engineering Laboratory, NIST, Gaithersburg, MD 20899, U.S.A. Keywords: carbon nanotubes; flame retardant; nanocomposites; poly(propylene); Introduction There is a high level of interest in using nanoscale rein- forcing fillers for making polymeric nanocomposite materials with exceptional properties. [1, 2] (Nanocompo- sites are particle-filled polymers where at least one dimension of the dispersed particle is on the nanometer scale.) An improvement in flammability properties of polymers has been obtained with nanoscale additives and these filled systems provide an alternative to conven- tional flame retardants. It is important to explore how the asymmetry (aspect ratio) and other geometrical effects of nanoparticle additives influence the flammability proper- ties of polymer nanocomposites. At present, the most common approach is the use of layered silicates having large aspect ratios; the flame retardant (FR) effectiveness of clay/polymer nanocomposites with various resins has been demonstrated. [1–6] The FR effectiveness in poly- (methyl methacrylate) (PMMA) of nanoscale silica parti- cles (average diameter of 12 nm) has also been demon- strated. [7] Carbon nanotubes provide another candidate as an FR additive because of their highly elongated shape, but we are aware of only one study concerned with an ethylene vinyl acetate (EVA)/carbon nanotube nanocom- posites. [8] Polyolefins are quite flammable and it is diffi- cult to reduce their heat release rates with environmen- tally friendly flame retardants. Thus, we have investi- gated the effects of the addition of a small quantity of car- bon nanotubes on the flame retardant behavior of poly- (propylene) (PP). Characteristics of carbon nanotubes and of some nanotube-based polymer composites are well summarized in a previous publication. [9] Moreover, nano- tube-based composites can be made with various resins. [10–12] Multi-wall carbon nanotubes (MWNTs) are used due to their cost advantage over single wall carbon nanotubes. There are two practical advantages for dispersing carbon nanotubes in PP compared with dispersing clay or silica into polyolefins. Since clay and silica are hydrophilic, they often require (i) an organic treatment on their sur- faces and/or (ii) a compatibilizing polymer modifier, e. g. PP grafted with maleic anhydride (PP-g-MA). [13] How- Communication: Nanocomposites based on poly(prop- ylene) and multi-wall carbon nanotubes (up to 2 vol.-%) were melt blended, yielding a good dispersion of nano- tubes without using any organic treatment or additional additives. Carbon nanotubes are found to significantly enhance the thermal stability of poly(propylene) in nitro- gen at high temperatures. Specifically, the nanotube addi- tive greatly reduced the heat release rate of poly(prop- ylene). They are found to be at least as effective a flame- retardant as clay/poly(propylene) nanocomposites. Macromol. Rapid Commun. 2002, 23, No. 13 i 2002 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim 1022-1336/2002/1309–0761$17.50+.50/0 SEM photomicrograph of MWNT dispersion in the poly- (propylene) composite after solvent removal.