A New On-Line Technique for Morphology Analysis and Residence Time Measurement in a Twin-Screw Extruder

Abstract

A large number of blends are produced on twin-screw extruders. The typical screw profile usually consists of an initial melting or plastification section followed by transport through screw elements and subsequent mixing in a mixing section. It has been shown that blend morphology in an extruder does not change significantly after the initial softening stage in the melting zone. However, since the final morphology affects the properties of the blend, it is important to uncover the mechanisms of drop break-up and coalescence in the metering and discharge zone of an extruder. Very small changes in the blend morphology can cause drastic changes in the blend properties. It has been observed by a number of researchers that the morphology development takes place in the melting section and no subsequent large change in the final morphology occurs after the initial melting section. Most of this information is based on screw-pulling experiments or experiments with clam-shell or hinged-barrel machines. Another disadvantage of the traditional sampling techniques lies in the fact that the machine has to be stopped before a sample is taken, and while this is feasible on small machines only, the technique is obviously not optimal and cannot be used in a commercial environment. The new sampling plate can be used for on-line sampling along the twin-screw extruder. The technique uses two pistons to extract a sample from the flow chamber. This chapter describes both the morphology and residence time measurement techniques.