A new approach to analyzing residence time and mixing in a co-rotating twin screw extruder

A series of experiments was conducted to determine what correlations exist between an experimental parameter, percent drag flow, and other parameters such as head, tail and mean residence time. Experimentation was carried out on two polymer systems, a model system of near-Newtonian fluid and a visco elastic system of polyisoprene with several additives. To aid in the reside nce time analysis, data from three literature sources were cited and replot ted. A family of residence time curves for a partially filled system can be combined into one curve by plotting the number of screw revolutions carryi ng the tracer to the extruder exit versus the percent drag flow. This metho d of plotting the data for each screw configuration estimates the mean resi dence time for any throughput and screw speed once a few data points are ta ken. In all four sets of experiments, the number of screw revolutions carry ing the tracer to the exit decreases with increasing percent drag flow. The filled volume of the extruder was calculated from residence time data to s how that percent drag flow is linearly related to extruder filled volume. W hen percent drag flow increased in the viscoelastic system the following re sults were recorded: fraction of polymer residence time spent in conveying elements increased, fraction of residence time spent in mixing elements dec reased, polymer Mooney viscosity increased, number and weight average molec ular weights increased and polydispersivity increased.