Nanocomposites from styrene-butadiene rubber (SBR) and multiwall carbon nanotubes (MWCNT) part 2: Mechanical propertiesby Peddini, SK (Peddini, S. K.); Bosnyak, C (Bosnyak, C. P.); Henderson, NM (Henderson, N. M.); Ellison, CJ (Ellison, C. J.); Paul, DR (Paul, D. R.)
Due to their high aspect ratio, strength, and modulus, multiwall carbon nanotubes (MWCNT) have attracted interest as a reinforcing filler in the automotive tire industry. In part 1 of this study, we demonstrated that styrene–butadiene rubber (SBR) composites containing up to 15 wt. % of well-dispersed, discreet MWCNTs can be prepared using MWCNTs with a specific surface modification and controlled aspect ratios. The melt rheology of the composites with discreet MWCNT was best described in terms of an effective aspect ratio and by considering the discrete MWCNT to be flexible rather than rigid rods. In this work, the effect of tensile strains, up to values of 6, for cured SBR composites containing discreet MWCNT concentrations up to 12% by weight were investigated. The deformation behavior indicates good adhesion between these MWCNT and the SBR. Mooney–Rivlin plots derived from the composite tensile stress–strain data displayed a dramatic change in mechanical behavior as the MWCNT loading exceeded about 5 wt. % attributed to a combined reinforcing effect of tubes on SBR plus overlap of curved or coiled MWCNT. Beyond tensile strains of about 1.7, strain hardening increases dramatically at MWCNT loading greater than 5 wt. % that is attributed straightening of the initially curved nanotubes such that they behave as rigid rods or fibers. Mechanical hysteresis and swelling in toluene on cured composites samples revealed that MWCNTs are in fact well bonded to the SBR. Studies with SBR and a combination of carbon black and discreet MWCNT demonstrate dramatically improved resistance to fracture by tearing.