Cure Kinetics for Silane Coupled Silica Filled SBR Compounds

Vulcanization kinetics for silane-modified, silica-filled SBR has been investigated using the cure meter and swelling measurements to determine the crosslink density. The silane modifier was Si-69, bis(3-triethoxy-silylpropyl)tetrasulfane. To simulate the induction and curing periods as a function of temperature and compounding recipe, a three component kinetic model for curing was developed. The kinetic model consists of (a) curing in the bulk elastomer phase, (b) curing at the silica surface and (c) cross-phase curing between the bulk components and the silica surface. In order to describe the partitioning of reagents between the bulk and surface domains, the parameter reactive surface thickness,θ, was introduced into the kinetic model. An average value of 24.7 nm for θ was calculated from the kinetic data and the silica particle surface area. Physically significant model kinetic parameters were extracted from the experimental data using a cure meter at different temperatures for (a) bulk curing (no filler) using the model of Ding and Leonov; (b) curing at the silica surface with Si-69 (no sulfur); and (c) whole compound recipe. Crosslink density values determined from the shear modulus were in good agreement with results from equilibrium swelling measurements. Using experimental data from the cure meter studies at 160 and 180 °C, it was possible to calculate (predict) the cure meter data at 140 °C for several different recipes.