Injection molding of rubber compound with rheology affected by vulcanization .1. Material characterization

Rheological behavior of rubber is highly sensitive to the thermal history and cure kinetics. Rheological characterization for SBR compound is carried out using a capillary rheometer and modified Mooney viscometer. The viscosity function, which is not only temperature and shear-rate dependent but also cure-level dependent, is constructed. A modification of Cross model is proposed and verified to predict the rheological and chemorheological behaviors of SBR compounds. This rheological characterization is combined with vulcanization kinetic characterization. The parameters of vulcanization are obtained from DSC measurement under several nonisothermal conditions. The significance of correcting for temperature lag in the DSC measurements and the corresponding rate-of-vulcanization lag resulting from the nonisothermal DSC scan is illustrated. The proposed rheological function is further modified to incorporate the temperature- and state-of-cure-dependent yield behavior of rubber compounds at low shear rates. The proposed model is suitable for use in the simulation of processing operations.