Rubber-filler interactions and rheological properties in filled compounds

Filled rubber compounds are complex polymer systems that exhibit a number of singular flow properties markedly different from those of unfilled, molten polymers. In addition to usual hydrodynamics (or volume fraction) effects, reinforcing fillers such as carbon blacks or high-structure silica, impart modifications in flow properties whose origin is assigned to strong interactions arising between the elastomer and the filler particles. The report discusses the nature of rubber-filler interactions and their effects on rheological properties of uncured materials. The concept of rubber-filler mesophase is first introduced in order to underline the fundamental scaling problem that exists when attempting to relate phenomena occurring in the nanometer range to flow singularities, essentially observed in the macroscopic range. Then flow singularities exhibited by filled rubber compounds are briefly described, before interactions between fillers and elastomers are reviewed with respect to filler characteristics. Bound rubber is consequently considered, as a macroscopic result of rubber-filler interactions, and its importance is stressed as the obvious link towards flow singularities. Eventually dimensional aspects in filled rubber compounds are discussed in detail, since they offer the most likely key to understand the relationships between bound rubber and flow properties. (C) 2002 Elsevier Science Ltd. All rights reserved.