The effects of kneading block design and operating conditions on distributive mixing in twin screw extruders

A mixing limited interfacial reaction between polymer tracers was used to d irectly measure the distributive mixing performance of a co-rotating twin s crew extruder during melt-melt blending of polypropylene. The reaction betw een the polymer tracers, which are low molecular weight succinic anhydride and primary amine terminally functionalized polymer chains, was followed us ing Fourier-Transform Infrared Spectroscopy (FT-IR). Experiments were compl eted to determine the effects of flow rate, screw speed, and kneading block design on the distributive mixing performance and the residence time distr ibution (RTD). The only RTD variable that was significantly affected by the experimental factors was the average residence time. Distributive mixing w ith neutral and reverse kneading blocks was controlled by the average resid ence time, the fully filled volume, and the shear rate. Conversely, the mix ing performance of a forward kneading block did not follow the same trends.