Filler effects on temperature shift factors in viscoelastic properties of carbon black filled rubbers

Abstract

Measurements of Relaxation modulus and/or differential dynamic modulus in linear and nonlinear viscoelasticity have been made on cured styrene-butadiene rubber (SBR) 1502 gum and cured SBR containing 20-60 phr carbon black (CB). Linear viscoelastometry has been made at temperatures ranged from -60 to 80°C and at frequencies ranged from 0.4 to 100 rad s-1. Nonlinear viscoelastometry has been made with small oscillations at dynamic strain of 0.005 and at frequency of 1.26 rad s-1 superposed on static strains of unity both for shear and extensional deformations. Cured SBR showed G'' peak temperatures of -48°C at 1.26 rad s-1. The mixing of CB filler showed no effect on the peak temperatures. It was found that all horizontal shift factors can be expressed by single WLF equation in linear viscoelasticity. The horizontal shift factors can be applied for the temperature dependent nonlinear viscoelasticity. Vertical shift factors in linear viscoelasticity depends on filler contents, showing change from entropic elasticity in gum rubber to energetic elasticity of enough filled rubber. Similar change has been found in large shear deformations, but entropic elasticity behaviors in vertical shift factors have been found irrespective of filler contents in large extension. The difference in behaviors of vertical shift factors between large shear and large extension can be understood with the change and recovery of filler network. It was concluded that the horizontal and the vertical shift factors of filled rubbers are governed by matrix polymer and filler network, respectively. © 2013 The Society of Rheology, Japan.