Modeling of peroxide initiated controlled degradation of polypropylene in a twin screw extruder

In this work, experimental and theoretical studies of the free-radical init iated molecular weight degradation of polypropylene in a modular self-wipin g corotating twin screw extruder have been investigated. Our objective was to build a model that would be able to predict the evolution of the average molecular weight along the screws, in relation to the processing condition s and the geometry of the twin screw extruder. Modeling the process involve s resolving interactions occurring between the various flow conditions enco untered in the extruder, the kinetics of the reaction and the changes in vi scosity with changes in molecular weight. We have studied the influence of operating parameters such as the initial peroxide concentration, the feed r ate and the screw speed on the degradation reaction. Good agreement was fou nd between theoretical results and experimental values obtained by size exc lusion chromatography measurements.