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SYNOPSISIt has been found that appreciable carbon black flocculation can occur in filled rubber stocks during storage or vulcanization in the absence of shear. The kinetics of this flocculation process were studied by means of low strain dynamic mechanical property and electrical conductivity measurements. The results showed the rate of flocculation to be governed by the type and concentration of carbon black, polymer macrostructure, mixing history, and annealing temperature. A mechanism responsible for the formation of this carbon black network structure was proposed and the resulting changes in the physical properties of vulcanizates prepared from these rubber compounds were elucidated.

A single polymer pair (BR and EPDM) was used to confirm experimentally rheology-morphology relationships that have been previously gleaned from comparison of a variety of blend systems. The relative importance of the primary factors which govern blend morphology (composition and relative mixing viscosity of the components) was determined over the range of practical interest. In addition, correlation of mixing rheology with more accurate and complete shear modulus data allowed (a) molecular interpretation of rheological behavior in terms of network parameters, such as physical entanglements, and (b) estimation of the elastic and loss components of the shear modulus during mixing. An attempt was made at explaining the dependence of blend morphology on the viscoelastic properties of the components in terms of a fracture or tearing mechanism.

Filler flocculation was followed for silica filled compounds containing various alkoxy silanes and non-silane type polar additives. The methodology employed in this paper permitted a quantitative characterization of filler flocculation and polymer-filler interactions after heating the compound under conditions that simulated vulcanization. With the addition of trialkoxy silanes, the reduction of filler flocculation and the degree of polymer-filler interactions were found to depend on the type and the concentration of silane added, and on the mixing drop temperature (Td) used. Greater polymer-filler interactions and flocculation suppression were obtained with a compound containing a tetrasulfane when compared to that containing either a disulfane or a monofunctional-silane. Polar additives such as an amine compound and a sugar alcohol did not reduce the silica flocculation during simulated vulcanization because they were dewetted from the silica surface upon heating. The filler flocculation process was monitored by following the change of dynamic storage moduli using an on-line rheometer. The flocculation process order and process constant were extracted from the non-linear regression analysis of the kinetic data. These kinetic parameters were used to quantify the suppression of filler flocculation by the additives used. Filler flocculation was found not to be affected by the vulcanization process because it occurred prior to the onset of cure.