Filler Network Change and Nonlinear Viscoelasticity of Rubbers

Abstract

Uncured, filled rubbers show remarkable nonlinear viscoelasticity as well as cured, filled rubbers. The nonlinearity may come from change in entanglement and filler network structures. Many people use dynamic modulus to characterize rubber materials. However, dynamic modulus cannot be defined at large strain. Hence we must study a viscoelastic function to be defined at large strain. In addition, we need other information to separate the effects of the change in entanglement and filler network structures on nonlinear viscoelasticity. In this work, we have measured simultaneously relaxation modulus G(γ,t) and electrical resistivity ρ(γ,t) for carbon black (CB)-filled, uncured styrene-butadiene copolymers (SBRs) at wide range of strains. Electrical resistivity at equilibrium, ρ(0,t), showed step-like change at the CB loading between 20 and 35 phr, indicating threshold for filler network formation should exist in the range of values in CB loading. Both G(γ,t) and ρ(γ,t) for the samples having CB loading to be higher than the threshold showed nonlinearity at the strain larger than shear strain γ=0.1, indicating rupture in filler network at large strain.

Controlling the Performance of Filled Rubbers

“…Filler particles may agglomerate to form secondary aggregates, which threedimensionally connect to form a filler network [18][19][20] that increases the tensile strength and modulus. However, the filler network 21,22) is easily broken into small aggregates after deformation because the filler-filler interaction is too weak to maintain the network structure. The Peyne effect 23) and Mullins effect 24) are shown in Figures 6 and 7, respectively.…”

The nonlinear stress relaxation behavior after a step shear of star‐shaped styrene‐butadiene rubber filled with precipitated silica: Experiment and simulation

“…Several researchers have investigated the relaxation behavior of uncured rubber compounds filled with carbon black and silica. Relaxation after a step shear strain has been investigated 16–28 . Stress relaxation tests have also been conducted in extension, 29,30 compression, 29 and after cessation of steady shear flow 17,28,31,32 .…”