Processing of EPDM Polymers as Related to Structure and Rheology

Abstract We have shown that the rate of mixing oil and carbon black with EPDM polymers having the same Mooney viscosity is dependent on their molecular-weight distribution and degree of branching. Samples having broad molecular-weight distributions mix more slowly than samples with more narrow distributions, and branched samples mix more slowly than corresponding linear samples. The slower mixing of samples that are branched or broad in molecular-weight distribution is a consequence of their more elastic character. These samples tend to be more non-Newtonian in their flow characteristics and thus have high viscosities at low shear rate and low viscosities at high shear rate. They also drop more in viscosity on mixing with oil. These factors cause these polymers to wet the carbon black more slowly and to have lower shear stresses during the mixing, leading to slower mixing.