Process control for polypropylene degradation during reactive extrusion

This paper describes the development of process control schemes for the free radical initiated (reactive) degradation of polypropylene in an extruder (reactive extrusion). The objective of the work was to control the amount of degradation in order to produce polypropylene with a specified molecular weight. The die pressure drop was used as a measure of the amount of degradation (the measured variable) and the initiator concentration was used to control the amount of degradation (the manipulated variable). The reactive degradation process was modeled empirically to determine the dynamic relationship between the input degradation initiator concentration and the output die pressure drop. Several control schemes were evaluated for controlling the die pressure drop (amount of degradation) with emphasis placed on schemes designed to overcome the non‐linear process gain and dead time.