Morphology, Thermal Expansion, and Electrical Conductivity of Multiwalled Carbon Nanotube/Epoxy Composites Alexandre S. dos Santos, 1 Thiago de O. N. Leite, 2 Clascı´dia A. Furtado, 2 Cezar Welter, 1 Luiz C. Pardini, 3 Glaura G. Silva 1 1 Departamento de Quı ´mica/Universidade Federal de Minas Gerais, Caixa Postal 702, 31270-901, Belo Horizonte, MG, Brazil 2 Centro de Desenvolvimento da Tecnologia Nuclear/Comissa ˜o Nacional de Energia Nuclear, Belo Horizonte, MG, Brazil 3 Centro Te ´cnico da Aerona ´utica/IAE, Sa ˜o Jose ´ dos Campos, SP, Brazil Received 16 April 2007; accepted 22 October 2007 DOI 10.1002/app.27614 Published online 18 January 2008 in Wiley InterScience (www.interscience.wiley.com). ABSTRACT: Multiwalled carbon nanotube/epoxy com- posites loaded with up to 0.5 wt % multiwalled carbon nanotubes were prepared and characterized. Infrared mi- croscopy, scanning electron microscopy, thermogravime- try, differential scanning calorimetry, thermomechanical analysis, and electrical conductivity measurements of the composites were performed. Infrared microscopy and scanning electron microscopy images showed that the debundled nanotubes were well dispersed. The thermal expansion coefficients, before and after the glass transition, remained approximately constant with the addition of nanotubes, whereas the electrical conductivity at room temperature increased approximately 5 orders of magni- tude. This result was attributed to the thermal expansion coefficients of the intertube gap on the carbon nanotube bundles, which were in the same range as that of the ep- oxy resin. Therefore, nanocomposites capable of electro- static dissipation can be processed as neat epoxy materials with respect to the volume changes with temper- ature. Ó 2008 Wiley Periodicals, Inc. J Appl Polym Sci 108: 979– 986, 2008 Key words: composites; morphology; nanocomposites; thermal properties INTRODUCTION Single-walled carbon nanotubes (SWNTs) and multi- walled carbon nanotubes (MWNTs) 1 present remark- able mechanical properties as carbon nanotubes (CNTs) can relax elastically when stress is released, whereas carbon fibers fracture easily under compres- sion. 2 A low CNT composite loading can be used to obtain high-performance levels suitable for specific applications in comparison with those of conven- tional fillers such as carbon black. 3 Although the CNT production cost is higher than that of conven- tional fillers, its low loading is advantageous because the effects on resin properties are minimal and the same processing equipment can be used with neat resins and nanocomposites. However, it has been frequently emphasized that the use of CNTs as structural reinforcements, specifically of polymer composites, depends on the ability to transfer the load from the matrix to the nanotubes. 4 Two factors are most critical for load transfer: (1) a homogeneous nanotube dispersion through the matrix and (2) strong CNT–polymer interfacial bonding. Epoxy-based composites are materials of high technological interest because of features such as their mechanical and thermal properties. A large number of recent works have dealt with CNT-rein- forced epoxy (e.g., refs. 3 and 5–17). Different proc- esses and controversial results were reported earlier concerning the improvement of their mechanical and thermal properties. However, recent works, 3,17 which show good CNT dispersion and improvements in interfacial adhesion by nanotube functionalization, have indicated significant enhancement of mechani- cal properties with low CNT loadings. Furthermore, there is agreement on the fact that these composites show a low percolation threshold (<0.5 wt %) and an increase of more than 6 orders of magnitude in electrical conductivity, reaching values close to 10 22 S/m. 12–15 The thermal expansion coefficient of SWNT bun- dles has been determined by X-ray diffraction stud- ies. 18 Three values have been obtained for the temperature range from 300 to 950 K: (20.15 6 0.20) 3 10 25 K 21 for the tube diameter, (0.75 6 0.25) 3 10 25 K 21 for the triangular lattice, and (4.2 6 1.4) 3 10 25 Correspondence to: G. G. Silva (glaura@qui.ufmg.br). Contract grant sponsor: Age ˆncia Espacial Brasileira (Pro- grama Uniespac ¸o). Contract grant sponsor: Instituto do Mile ˆnio de Nano- cie ˆncias/Programa de Apoio ao Desenvolvimento Cienti- fico e Tecnolo ´ gica/Conselho Nacional de Pesquisa/Min- iste ´rio de Cie ˆncia e. Journal of Applied Polymer Science, Vol. 108, 979–986 (2008) V V C 2008 Wiley Periodicals, Inc.