Modelling of the Peroxide Degradation of Polypropylene

Abstract A fully-predictive mathematical model has been developed for the peroxide promoted degradation of polypropylene in a plasticating single-screw extruder. The model is based on a free radical kinetic mechanism for the degradation reaction and on conventional plasticating extrusion theory. Solids conveying, melting, melt pumping and reaction phenomena have been combined and the interactions between flow pattern, mass and heat transfer fields via residence time distribution and the chemorheology of the reactive melt have been considered. Given the geometrical configuration of the screw, the operating conditions and the physical properties of the starting polymer, the model can predict: flow rate, pressure, temperature and molecular weight profiles in the extruder channel and in the die, and the residence time distribution in the system. Finally, model predictions are compared with experimental data from runs on a 38mm, 24:1 L/D single-screw extruder using various peroxide concentrations and rotational screw speeds.