Flow Visualization of the Motions of Elastomers and Molten Plastics in an Internal Mixer

Abstract A basic study of flow visualization of motions of elastomers in a model internal mixer with Banbury rotors has been presented. The behavior of butadienestyrene copolymers (SBR), cis-polybutadiene (BR), natural rubber (NR), and various molten plastics has been investigated. The SBR's and BR behave similarly, exhibiting tearing when stretched by the moving rotor tip away from the bridge in the mixer. This results in large stagnant regions between the bridge and ram in the mixer. The NR does not tear but stretches out when the rotor tip pulls it around the rotor circumference. At low fill factors, the NR bands about the rotors. Studies of molten plastics including low density, high density polyethylene and polystyrene are also reported. Longitudinal motions of rubber on the rotors have been investigated.