Synergy in carbon black-filled natural rubber nanocomposites. Part I: Mechanical, dynamic mechanical properties, and morphology

Natural rubber (NR)/nanoclay and NR/carbon nanofiber (CNF) nanocomposites were consolidated with different loadings and grades of carbon blacks (CBs) to obtain ternary nanocomposites. It was observed that the mechanical and dynamic mechanical properties of these nanocomposites were much better compared with those of either NR/clay or NR/CNF nanocomposites or the NR/black control microcomposite. Thus, not only the grueling and at times conflicting property requirements of modern day applications were met, but also the tendency of saturation of property enhancements at high loadings could be mitigated. These nanocomposites exhibited 18% increment in tear strength, 40% in modulus at 300% elongation, and 326% in room temperature storage modulus, over the control microcomposite. Viscous loss properties were influenced favorably, as well. This indicated the presence of a much sought after synergy between CB and nanofillers. Transmission electron micrographs of the nanocomposites showed that CB formed “nano-blocks” of reinforcement—close association of nanofiller and black—driven by zeta potential differences between the black and the nanofillers. This unique ternary architectural base, with the space between nanofillers (clay/fiber) occupied by small CB aggregates forming networks or “nano-channels”, accounted for the synergistic improvements.