Kinetic Monte Carlo residence time distributions and kinetics in view of extrusion-based polymer modification and recycling

Abstract

Reactive extrusion (REX) is an important processing technique for polymer modification and mechanical/chemical recycling. In the present work, for the first time, a stochastic coupled macro–micro scale modeling framework is applied to jointly calculate the variation of the residence time distribution (RTD) and average polymer characteristics, selecting free radical induced grafting (FRIG) of polyethylene by maleic anhydride as REX case study. The convective macro-scale mass transfers are captured by a cascade of compartments defining a set of numerical parameters, capable (i) to benchmark with RTD's from limiting (ideal) cases of a continuous stirred tank reactor and a plug flow reactor and (ii) to span a broad range of expected extrusion RTD's displaying various degrees of mixing efficiencies. The micro-scale is embedded via recently developed coupled matrix-based kinetic Monte Carlo (CMMC) simulations, allowing to track per compartment the residence time and compositional/topological information per individual molecule, and upon coupling with the macro-scale to grasp the mixing of individual molecules between compartments. A successful model validation to literature extrusion RTD data is additionally included, delivering a process-driven correlation to obtain the macro-scale numerical parameters. The construction of such correlations opens the pathway to in silico design of REX for detailed (de)polymerization chemistries via stochastic solvers. It is shown that for the REX FRIG case study the RTD is rather broad and the grafting highly selective.