<p>Screw extrusion technology in waste plastic recycling</p>

<p>Screw extrusion stands as a cornerstone technology in the mechanical recycling of waste</p><p>plastics, a critical endeavor in addressing the global plastic pollution crisis.</p><p>This review provides a comprehensive analysis of the multifaceted role of screw</p><p>extrusion in this domain. It begins by elucidating the fundamental principles of</p><p>extruder design and operation, specifically comparing single-screw and twin-screw</p><p>systems and their respective suitabilities for processing diverse plastic recyclates.</p><p>A significant portion is dedicated to polymer-specific degradation phenomena - thermal,</p><p>thermo-mechanical, and thermo-oxidative - that occur during extrusion, detailing</p><p>their impact on common polymers such as polyethylene terephthalate (PET), polyolefin</p><p>(polyethylene and polypropylene), polyvinyl chloride (PVC), and polystyrene (PS,</p><p>HIPS). Subsequently, the review explores a wide array of quality improvement strategies</p><p>essential for enhancing the properties and value of extruded recyclates. These include</p><p>pre-extrusion feedstock preparation, in-process melt filtration and devolatilization,</p><p>and post-extrusion modifications through additive incorporation (antioxidants, acid</p><p>scavengers, light stabilizers) and reactive extrusion (chain extension, compatibilization,</p><p>and filler addition). The report also critically examines the industrial challenges</p><p>inherent in the screw extrusion of waste plastics, including feedstock variability</p><p>and contamination, process control intricacies, economic viability concerns, and</p><p>energy efficiency. Finally, an outlook on future trends is presented, covering advancements</p><p>in extrusion technology, the importance of Design for Recycling, the evolving interface</p><p>between mechanical and chemical recycling, and innovations in additives for upcycling.</p><p>The review synthesizes current knowledge to provide an expert-level understanding,</p><p>aiming to inform research, industrial practices, and policy development toward more</p><p>effective and sustainable plastic recycling.</p>