Analysis of Dispersed Structure of Carbon Black and Silica in Natural Rubber

Abstract

Synopsis: Use of transmission electron microscopy (TEM) combined with computerized tomography (abbreviated as 3D-TEM in this review, which is sometimes called electron tomography) enabled us to reconstruct three-dimensional (3D) images of nano-filler aggregates, agglomerates and network in rubbery matrix. The 3D-TEM results on dispersion of carbon black (CB) and silica in natural rubber (NR) were presented in this review. The network structure formed by agglomeration of CB aggregates was elucidated by combining the 3D images and physical properties of the vulcanizates. On the other hand, the relationship between optical transparency and filler loading was found to differ markedly between hydrophobic silicafilled and hydrophilic silica-filled peroxide cross-linked NR. The optical transparency of the former NR showed virtually no change when the hydrophobic silica filler loading was increased. In contrast, the latter NR exhibited an optical anomaly in which optical transparency initially decreased with increasing hydrophilic silica filler loading and then began to increase again. Then, the observed silica networks were analyzed using 3D-TEM. As a result, a light scattering equation was formulated using the product of the density and squared length of the isolated chains, and the equation was used to reveal the differences in optical transparency between the two types of silica-filled NR samples.