Impact of Extrusion Pretreatment on Polypropylene Waste Pyrolysis

Abstract

The present study investigates the influence of extrusion pretreatment on the pyrolysis of post-consumer polypropylene (PP), expanding upon previous findings related to the pyrolysis of polyethylene (PE, polymer engineering science, https://doi.org/10.1002/pen.27267). PP residues were extruded at 450°C for 2 min in a corotating twin-screw extruder prior to pyrolysis under different conditions (425°C–475°C; 15–45 min). Results showed that extrusion pretreatment can significantly affect the feedstock properties, reducing average molar masses and polydispersity, which in turn can affect the thermal decomposition dynamics. As shown experimentally, the yields obtained after extrusion pretreatment of PP samples were different from the ones obtained before pretreatment, as the apparent activation energy for total yields was reduced after the proposed extrusion pretreatment. However, at higher temperatures and conversions, overall product yields and compositions were similar between the original and extruded samples, as the reaction mechanism remains essentially the same and observed differences are related mainly to the heat transfer dynamics. This is similar to results reported previously for HDPE, but is different from results obtained with LLDPE, reinforcing that the existence of long and complex chain branches can increase the sensitivity of the degradation behavior to temperature trajectories.