Mechanisms of Particulate Reinforcement of Rubber At Small Strains

Dynamic mechanical data collected at small strains within the linear viscoelastic region are presented for natural rubber filled with a range of carbon blacks and precipitated silicas of varying aggregate particle size. The surface energies and functionalities of the fillers are varied by thermal graphitisation of carbon black and silane surface modification of precipitated silica. Working at small strains allows for a simplified interpretation of elastic and viscous contributions to the loss tangent in terms of flocculated or dispersed filler structures and interfacial viscous dissipation. The viscous contribution is most readily interpreted, in this case, as interfacial slippage of polymer chains at the filler surface and is observed to be subject to a temperature and frequency dependence. In addition, data concerning the effects of different fillers on the matrix structure of natural rubber such as average crosslink densities and crosslink type are presented and demonstrated to have a significant, measurable effect on the bulk static and dynamic mechanical properties of the filled rubbers.