Multiwall carbon nanotube elastomeric composites: A review

Nanostructured materials gained great importance in the past decade on account of their wide range of potential applications in many areas. A large interest is devoted to carbon nanotubes that exhibit exceptional electrical and mechanical properties and can therefore be used for the development of a new generation of composite materials. Nevertheless, poor dispersion and poor interfacial bonding limit the full utilization of carbon nanotubes for reinforcing polymeric media. In this paper, recent advances on carbon nanotubes and their composites will be presented through results of the author's research, essentially based on filled elastomeric networks. The intrinsic potential of carbon nanotubes as reinforcing filler in elastomeric materials will be demonstrated. It will be shown that, despite a poor dispersion, small filler loadings improve substantially the mechanical and electrical behaviors of the soft matrix. With the addition of 1 phr of multiwall carbon nanotubes in a styrene-butadiene copolymer, a 45% increase in modulus and a 70% increase in the tensile length are achieved. Straining effects investigated by atomic force microscopy and infrared and Raman spectroscopies, provide interesting results for the understanding of the mechanical behavior of these nanotube-based composites. All the experimental data lead to the belief that the orientation of the nanotubes plays a major role in the mechanical reinforcement. The strong restriction in equilibrium swelling in toluene with the MWNT content is not ascribed to filler-matrix interfacial interactions but to the occlusion of rubber into the aggregates. On the other hand, carbon nanotubes impart conductivity to the insulator matrix. Between 2 and 4 phr, the conductivity increases by five orders of magnitude reflecting the formation of a percolating network. Changes in resistivity under uniaxial extension completed by AFM observations of stretched composites bring new insights into the properties of these composites by highlighting the contribution of orientational effects. (c) 2007 Published by Elsevier Ltd.