Modeling and characterization of a plasticating extruder with a compact mixing screw

This study presents the pilot-scale implementation of a compact extruder designed to process post-consumer recycled plastics using chaotic mixing theories. The system features a novel mixing screw with an exceptionally short 8:1 length-to-diameter ratio and counter-rotating mixing slots cut into double flights of variable pitch. These features induce chaotic advection to enhance dispersive and distributive mixing by disrupting solid bed formation, improving thermal and compositional homogeneity in the extrudate through the baker’s transformation. A model-based screw design methodology using non-isothermal, non-Newtonian computational fluid dynamic (CFD) simulations was developed to optimize geometry for energy efficiency and throughput. Significant experimental validation employed a custom-built extruder with a 31 mm screw and an instrumented nozzle equipped with melt pressure and temperature sensors. Throughput and melt temperature were characterized as functions of screw speed, barrel temperature, nozzle geometry, and extruder orientation. Multiple regression models for simulated and experimental data showed high fidelity (R² ≈ 0.99) and strong correlation (r ≈ 0.95). Discrepancies in mass output were attributed to lower packing density of pelletized feedstock relative to the continuum assumption in simulations. The extruder demonstrated near-linear control of melt temperature (1.1 °C per unit setpoint) and mass flow rate (0.84 g min⁻¹ per RPM) with minimal cross-effects. A specific energy consumption of 0.254 kWh kg⁻¹ at 200 °C and 60 RPM corresponded to 76% efficiency, representing a 26% improvement over a previous design. The system offers reduced energy use, short residence times, and enhanced processing of recycled and bio-based polymers, advancing sustainable manufacturing in polymer processing and additive manufacturing.