The role of surface activity of silica on viscoelastic behavior of elastomeric vulcanizates

Incorporating reinforcing fillers into elastomers followed by vulcanization is a well known technology in the development of engineered elastomeric materials. Numerous theories have been proposed to describe the enhancement in the mechanical properties of these materials. Of these, the hydrodynamic theory has utilized the strain amplification effect in the elastomer matrix to describe increasing reinforcement with filler addition. However, the hydrodynamic effect cannot describe the nonlinear viscoelastic behavior of the vulcanizate containing highly reinforcing fillers which change the vulcanizate characteristics via strong filler-elastomer interactions.; Silicas containing different concentration of mercaptan on their surface were prepared in order to study the effect of filler-rubber interaction on the viscoelastic behavior of the filled rubber. The filler-elastomer interaction is introduced by formation of the covalent bond between the filler surface and the elastomer chains via mercaptan functional groups. These surface modified silicas are hydrophobic in nature and have the same concentration of organosilanes on their surface in addition to having the same surface area and structure. The experiments were conducted to measure (1) the tensile stress-strain behavior, (2) the ultimate tensile properties, (3) the stress relaxation, (4) the hysteresis and (5) the dynamic viscoelastic properties.; The experimental findings listed below show the effect of the filler elastomer interaction on the viscoelastic behavior of the silica filled rubber. The morphological effect of the filler is the controlling mechanism at small strains. The initial Young's modulus can be predicted using the Guth-Gold equation in conjunction with Medalia's concept of occluded volume and agrees with experiment for vulcanizates having 30 phr of hydrophobic silica. The tensile stress increases more rapidly with strain as the filler reactivity increases. A non-linear strain function is introduced to describe the tensile stress-strain behavior. The formation of filler-elastomer bonds increases primarily the elastic properties of the vulcanizate.