An experimental study of polymer blend mixing in twin-screw extruders
The performance of a laboratory-scale, fully-intermeshing twin-screw extruder for the production of well-mixed (PSAN/PMMA) (polystyrene-acrylonitrile/polymethylmethacrylate) blends from commercial grade PSAN and PMMA pellets was investigated. We were interested in determining whether the composition of the extruded material reflected the composition of the mixture fed into the extruder as well as whether any polymer degradation occurred under the chosen operating conditions. This is of interest since twin-screw mixing is a popular and convenient technique for the production of blend samples for rheological analysis. Blends of PSAN and PMMA are of particular interest since, being partially miscible, they are useful in the study of the effect of flow on polymer blend thermodynamics. The uniformity of the extruded material was analyzed using infra-red spectrophotometry on samples taken at various locations along a strand extruded from a cylindrical die. We observed small fluctuations of local concentration around an average; this average coincides with the composition of the material fed to the extruder. The possibility of degradation was investigated through gel permeation chromatography, carried out on the same samples. The results indicated that under the chosen operating conditions no degradation was observed.