PEROXIDE-INDUCED AND THERMAL-DEGRADATION OF POLYPROPYLENE - EXPERIMENTAL STUDIES IN A BATCH REACTOR AND IN SINGLE AND INTERMESHING COUNTER-ROTATING TWIN-SCREW EXTRUDERS

An experimental study of the peroxide induced degradation of polypropylene is described. Experimental studies in a batch mixer, a single screw extruder and in a Leistritz modular counter-rotating twin screw extruder are presented. Three different screw configurations were used in the latter machine. When comparisons are made at the same temperature, peroxide level and residence time, the greatest extent of degradation is found in the twin screw extruder and the poorest in the single screw extruder. These differences seem associated with the rapid effective melting in the twin screw extruder and the slow melting and poor mixing in the single screw extruder. Of the three modular twin screw configurations, the configuration containing no intense shearing elements is most effective. Experiments based on removing the modular screw and following the reaction as a function of position suggests that Leistritz shearing elements cause rapid heating and reaction of the peroxide before it is mixed into the polypropylene matrix.