Enhanced Electrical and Mechanical Properties of Multiwall Carbon Nanotubes Rubber Composites

Enhanced electrical and mechanical properties of multiwall carbon nanotubes rubber composites  

Carbon black and silica have been used for a long time in the rubber industry to prepare composites with greatly improved properties such as strength, stiffness and wear resistance. These conventional fillers must be used at high loading levels to impart to the material the desired properties. The state of filler dispersion and orientation in the matrix, the size and aspect ratio of the particles as well as the interfacial interactions between the organic and inorganic phases have been shown to be crucial parameters in the extent of property improvement.

The unique properties of carbon nanotubes (CNTs) have generated intense research in the development of elastomeric composites, where they are expected to provide much higher reinforcement as well as electrical conductivity enhancement than conventional fillers. The high aspect ratio of CNTs is expected to yield a very large interfacial area and thus much greater interactions with the polymer if the nanotubes are uniformly dispersed in the host matrix. The high aspect ratio also influences the amount of conductive filler at which the electrical percolation threshold is observed. That makes CNTs particularly effective compared to conventional carbon blacks which have to be present in rubber matrices at contents as high as 10-50 wt% in order to achieve satisfactory electrical conductivity. In poly(dimethylsiloxane) (PDMS) for example, the electrically percolated network corresponding to the formation of a conductive path throughout the sample has been obtained at 0.05 phr of CNTs (phr = parts per hundred parts of rubber, by weight). 

This work presents a study on various elastomers filled with multiwall carbon nanotubes. The potential of carbon nanotubes as reinforcing fillers for rubbery materials will be demonstrated through the strain-strain curves of the composites that exhibit, with regard to the unfilled matrix, considerable improvements in stiffness with the nanotube loading. The state of nanotube dispersion, in the isotropic and uniaxially stretched states of the composite, is evaluated from electrical and rheological properties and from atomic force microscopy. Raman spectroscopy has also been used to determine the strength of the interface between the nanotubes and the matrix. The effect of excitation wavelength, nanotube loading and uniaxial deformation on the Raman bands will be discussed.