Experimental methods in chemical engineering: Reactive extrusion

Abstract

AbstractReactive extrusion (REX) is a manufacturing technique that combines traditional melt extrusion with chemical reactions, including polymerization, polymer functionalization, and depolymerization (chemical recycling). Single screw, counter‐rotating, and co‐rotating twin‐screw extruders (TSE) are possible configurations, but the TSE is most effective for viscous media with better mixing capability, temperature and residence time distribution control, and self‐wiping (cleaning) performance. Compared to traditional polymer processing where monomers react in tanks, followed by compounding and pelletizing, REX can operate solvent‐free in a single step. This simplifies the downstream separation and saves equipment and operational costs. However, the short residence times (on the order of seconds to minutes) of extruders limit their applications to fast reactions. For longer reactions, a sequential design and string extruders with a batch reactor extend residence times. Furthermore, the surface‐to‐volume ratio decreases with increasing scale, which introduces design complexity to remove the heat of reaction. Here, we review REX working principles, apparatuses and their elements, applications and reactions, simulation/modelling and scale‐up considerations, as well as limitations and recommendations. Web of Science indexed 579 articles that mention REX between 2017 and 2021. A bibliometric analysis of these articles identified five research clusters: composite, nano‐composite, and thermal properties; degradation, crosslinking, rheology, and acid; crystallization, polypropylene, maleic anhydride, and rheological properties; morphology, compatibilization, and copolymer; and oxidative stress and mechanisms.