The recirculating screw mixer: A new small‐volume mixer for the polymer laboratory

The recirculating screw mixer (RSM), a new small‐volume intensive mixer for the polymer laboratory, is designed, built, modeled, and tested. This type of batch mixer is intended for the mixing of 1 to 30 cm³ of viscous material at high shear rates. A material element in the mixer experiences alternating screw pump and tubular flows with reorientation between these flows. A mixer with a 10 cm³ sample capacity is built for testing and evaluation. Flow visualization experiments are used to investigate the quality of the distributive mixing achieved. The flows in the mixer are modeled for the cases of a Newtonian fluid and a power law fluid. The Newtonian model accurately predicts the recirculation time for particles suspended in Newtonian silicone oils. The power law model accurately predicts the screw torque obtained with a polystyrene and polyethylene. A method for the measurement of fluid rheology from the operating conditions of the RSM is proposed and tested. The mixing achieved by the RSM is compared to that obtained by a batch mixer with roller blades. Both mixers are used to prepare blends of ethylene‐propylene rubber in polystyrene. The morphologies of the resultant blends are compared and differences in the mixing action are discussed. The mixers are also used to prepare composites of fumed silica in polyethylene. The quality of mixing obtained in the RSM compares quite favorably with that obtained in the batch mixer with roller blades for polystyrene/ethylene‐propylene rubber reactive blends and polyethylene/silica composites.