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

Abstract

In this work, experimental and theoretical studies of the free‐radical initiated molecular weight degradation of polypropylene in a modular self‐wiping 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 conditions and the geometry of the twin screw extruder. Modeling the process involves resolving interactions occurring between the various flow conditions encountered in the extruder, the kinetics of the reaction and the changes in viscosity with changes in molecular weight. We have studied the influence of operating parameters such as the initial peroxide concentration, the feed rate and the screw speed on the degradation reaction. Good agreement was found between theoretical results and experimental values obtained by size exclusion chromatography measurements.

Evolution of the peroxide‐induced degradation of polypropylene along a twin‐screw extruder: Experimental data and theoretical predictions

“…For example, Tzoganakis and coworkers 9,10 and Pabedinskas et al 11 combined kinetic models of the peroxideinduced PP degradation reaction with flow in singlescrew extruders. Kim and White 12 and, more recently, Berzin et al 13 predicted MW changes along twin-screw extruders. In particular, these last authors considered the interactions occurring between flow in the extruder, reaction kinetics, and viscosity changes and their effect on the evolution of MW along the extruder.…”

“…Given the practical importance of the topic, this article aims at ascertaining the value of the predictions produced by Berzin et al 13 for the evolution of PP's MW along the axis of a corotating twin-screw extruder. For this purpose, we made use of sampling devices inserted along the extruder's barrel, 14 which provided the capacity of collecting 1-2 g of the polymer within 1-2 s. These samples were characterized in terms of their MW, MWD, and rheological behavior.…”

Evaluation of numerical simulation methods in reactive extrusion

“…There are various simulations focused on solid conveying, melting, pumping capacity and mixing, however, only few studies have been done in the modeling of reaction in twin-screw extruders. Furthermore, most of these simulations of reactive extrusion were based on a one-dimensional (1D) model, [2][3][4][5] in which the reaction progression, residence time, and temperature were assumed to have a uniform distribution in any axial cross section of the extruder. The main advantage of 1D model is that it makes the simulation simple and easy.…”

Scale up tools in reactive extrusion and compounding processes. Could 1D-computer modeling be helpful?

“…4) along the screws. Using Ludovic® software, on the basis of the study previously presented in [3], we can compute any known reaction kinetic.…”