The origin of synergism between an organoclay and carbon black

Synergistic effects between a montmorillonite (Mt), modified with an organophilic ammonium as the compensating cation (OMt), and carbon black (CB) are reported in the literature. This work proposes the pronounced interaction between the organophilic ammonium cation and CB as a phenomenon at the origin of the synergism. A nanocomposite based on poly(1,4-cis-isoprene) containing both CB and OMt, formed in situ through the reaction between Mt and di(hydrogenated tallow)-dimethylammonium chloride (2HTCl), was prepared. Moreover, nanocomposites containing only CB in the presence and in the absence of 2HTCl were comparatively prepared and analysed. Synergism between OMt and CB was investigated by studying the filler networking process in the PI matrix through dynamic-mechanical tests and by assessing the nanocomposite structure by transmission electron microscopy analysis. It was found that 2HTCl promoted a pronounced enhancement of the non linear dynamic-mechanical behaviour of the nanocomposite material, with a much improved CB dispersion and a remarkable reduction of bound rubber. These effects were reduced in the presence of Mt, that involved the ammonium salt in the formation of OMt. The amount of 2HTCl required to achieve the largest non linear behaviour and the lowest bound rubber was calculated to correspond to a monolayer of the ammonium salt on the carbon black surface.