Enhancement of mechanical reinforcement due to hybrid filler networking promoted by an organoclay in hydrocarbon-based nanocomposites

This work investigated the ability of a nano-filler, such as an organically modified montmorillonite (OMt) to create filler networks in a hydrocarbon polymer matrix, both when OMt was the only filler and when it was in the presence of a suitable amount of a nanostructured filler such as carbon black (CB). Montmorillonite (Mt) was modified with di(hydrogenated tallow)-dimethylammonium as the organophilic cation and poly-(1,4-cis-isoprene) was used as the polymer matrix. The study of the morphology, as well as the static and dynamic mechanical behaviour of the nanocomposites, was performed. The OMt was found, through X-ray analysis, to be prevailingly delaminated with a minor presence of stacks, without polymer chains intercalated between two consecutive layers. Moreover, in transmission electron microscopy pictures, OMt was observed to form a filler network when it was the only filler and to take part to a hybrid filler network in the presence of CB. The OMt concentration required for the formation of OMt based filler networks was investigated by determining the material initial modulus and the dependence of both shear storage and loss moduli on strain amplitude. OMt was found to form a filler network at a much lower content (about 6 parts per hundred parts of the polymer) with respect to a traditional nanostructured filler. The affinity between OMt and CB led to a clear enhancement of filler networking, with the formation of a hybrid OMt /CB filler network at a lower OMt content with respect to non-hybrid filler systems. Two regimes were observed for the dependence of the excess of initial modulus on OMt content, below and above a critical OMt concentration. Moreover, OMt was found to promote a higher reinforcement of the nanocomposite material when it was in the presence of CB. This work demonstrates that an OMt and CB are able to develop a cooperative interaction, beneficial for the enhancement of mechanical properties of a hydrocarbon material and proposes the filler networking promoted by the nano-filler as the key for the rationalization of the experimental findings.