Carbon nanotubes as Raman sensors of vulcanization in natural rubber

A method has been developed to synthesize composites with cross-linked natural rubber (NR) and dispersed single-wall carbon nanotubes (SWNT). The mechanical response of the NR samples was observed to change as a function of the amount of sulfur used for cross-linking, based on the number density of cross-links resulting from the vulcanization process. The relationship between SWNTs D∗ wavenumber shift and the amount of sulfur have been obtained by means of Raman spectroscopy. The cross-link densities of the NR and SWNT/NR samples have been calculated from uniaxial stress–strain measurements, and plotted as the function of the amount of added sulfur. Comparison of the results from mechanical measurements and Raman spectroscopic measurements showed that SWNT Raman sensors are sensitive to the cross-link density in natural rubber and can be used to evaluate the cross-linking process of rubbery materials.