Reactive Melt Extrusion for Polymer Deconstruction and Upcycling

Abstract

Global attention increasingly focuses on innovative recycling and upcycling strategies to advance polymer sustainability and reduce plastic waste. Reactive melt extrusion (RME) enables solvent-free polymer deconstruction and functionalization in the melt state, aligning with the principles of green chemistry: minimizing waste, avoiding solvents, and reducing energy consumption. RME leverages legacy polymer processing infrastructure, i.e., single- and twin-screw extruders, to empower rapid technology adaptation for research and industrial applications. This Perspective highlights the development of RME for rapid polymer deconstruction, emphasizing broad applicability for thermoplastics and thermosets that are derived from both chain-growth and step-growth polymerization processes. In addition, the RME platform offers rapid upcycling of plastic waste into vitrimers and other value-added materials with renewed service life, overall promoting polymer sustainability. Emerging in situ chemo-rheological characterization techniques deconvolute shear, temperature, and residence time effects during RME deconstruction/upcycling, unveiling key mechanistic insights into evolving rheological behavior during chemical and structural transformation. Finally, a perspective on emerging research directions aims to expand RME as a more versatile platform for polymer deconstruction, upcycling, and sustainability.

Reactive Melt Extrusion Platforms

Extrusion technologies form the foundation of modern polymer synthesis, processing, and engineering. Reactive melt extrusion (RME), in particular, leverages mechanical stress at relatively high temperatures to lower activation energy barriers and accelerate reaction rates in the melt state. Modular design, which employs customizable screw configurations (Figure ), precisely controls discrete zones within the extruder for melting, mixing, reacting, degassing, and pumping elements to engineer final polymer properties. For example, melt residence time and reaction rates can be controlled with modulation of throughput and temperature-controlled zones to target desired properties. This versatile, solvent-free RME platform enables polycondensation, free radical, ionic, and anionic polymerizations, as well as postpolymerization grafting and functionalization to synthesize diverse polymers, including poly­(ethylene terephthalate) (PET), polyurethanes (PUs), polyamides, and polystyrene-co-maleic acid copolymers. − For example, polypropylene grafting with maleic anhydride in the presence of peroxides (such as benzoyl or dicumyl peroxide) demonstrates the competition among grafting, chain scission, and branching efficiency, which depends on residence and mixing time scales as defined from extruder design and processing conditions. − PU reactive extrusion and reaction injection molding (RIM) similarly leverage fast isocyanate-polyol polycondensation reactions, short residence times, and efficient heat transfer to continuously produce elastomers and cross-linked microcellular foams. − RIM adapted to ring-opening metathesis polymerization (ROMP) enables high-throughput dicyclopentadiene (DCPD) manufacturing under comparably tight kinetic and mold-filling constraints. − Although RME polymerizes and functionalizes polymers through diverse reaction pathways, the structure–property–processing relationships established by these historical systems provide a critical framework for designing future RME technology. Figure traces the evolution of RMEs from thermoplastic shaping through synthesis to modern RME deconstruction and vitrimer upcycling (Figure , top), alongside parallel advances in in situ characterization techniques (Figure , bottom). These developments establish the structure–property-processing framework that positions RME to overcome solvent-based recycling limitations.

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TSE featuring modular screw design for discrete melting, mixing, reacting, and degassing, adapted with permission from ref . Copyright 2022 Wiley-VCH.

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RME developmental timeline. Top: RME and RME deconstruction/recycling development. − Bottom: In-line characterization development. −

Twin-screw extruders (TSEs), especially those with corotating configurations, outperform single-screw extruders (SSEs) and counter-rotating counterparts by offering larger capacity and better heat distribution, representing the ideal continuous RME platform. , Unlike batch-based ball milling, continuous RME is inherently more commercially scalable and energy efficient, which ensures the role of RME to advance polymer sustainability. , The International Union of Pure and Applied Chemistry (IUPAC) in 2019 recognized RME as one of the top ten emerging sustainable technologies, and RME aligns with the United Nations Sustainable Development Goals (UN SDGs) by reducing energy consumption, lowering CO₂ emissions, and minimizing dependence on volatile organic solvents. −

High temperature melt mixing in single- and twin-screw extruders enables thermoplastic reprocessing and recycling, as extensively reviewed elsewhere. − Unfortunately, thermo-mechanically induced chain scission decreases molecular weight during melt reprocessing, preventing continual reprocessing cycles without diminished mechanical performance. , In sharp contrast, RME leverages specific chemical reactions to alter polymer molecular weight or functionality and enables chemical recycling, which will serve as the focus of this Perspective.

RME for Polymer Deconstruction

Chemical recycling efforts focus on recovering valuable building blocks from postconsumer plastics at rapid time scales without energy-intensive separations. Reactive melt extrusion deconstruction (RMED), which is a subset of RME, expands the melt extrusion platform toward sustainability-driven deconstruction. Compatible with both thermoplastics and thermoset polymers, RMED utilizes a combination of mechanical stress and heat to significantly accelerate polymer deconstruction, simultaneously reducing molecular weight while introducing functionality during melt processing. ,,,, Adaptability across single- and twin-screw extrusion designs empowers efficient deconstruction of diverse polymer classes from polyester thermoplastics to engineering polyolefins, while real-time analysis provides fundamental understanding of mechanochemical transformations. ,,,,, Integrating the selectivity of chemical recycling with the speed, atom efficiency, and reduced CO₂ emissions of extrusion, RME bridges the gap between traditional polymer processing and sustainable materials. These benefits align RMED with the UN SDGs, fueling development of greener synthesis, deconstruction, and upcycling, which collectively benefit polymer waste management. ,

Although RMED decreases polymer molecular weight and deconstructs networks through covalent reactions, tailored approaches provide deconstructed polymers with tunable physical properties. One approach deconstructs the polymer to monomers/oligomers, enabling direct repolymerization into new polymers with conserved end-group functionality. This approach has been applied to many polyesters, such as PET RMED with ethylene glycol. Other groups leveraged ring-closing reactions to yield cyclic monomers capable of repolymerization, which was demonstrated for polycaprolactone soft segments in PU thermoplastics. An alternative approach, such as PU network RMED through carbamate exchange with carbamate-containing de-cross-linkers, yields deconstructed polymers chemically distinct from the original starting network. This approach simultaneously deconstructs and functionalizes the network structure by installing the decross-linkers as chain ends, thus producing branched oligomers with pendant functionality derived from the chemical structure of the de-cross-linker. Although this approach prevents direct PU network repolymerization from the de-cross-linked oligomers, functional de-cross-linkers install additional reactivity to the deconstructed polymer, such as photoactive methacrylate groups, thereby transforming the branched oligomeric product into a photoactive network-forming resin for 3D printing. These approaches are complementary and leverage RMED differently to tailor the properties of deconstructed polymers for targeted applications.

Considering the ubiquity of polyester products and the reactivity of the ester carbonyl toward various nucleophilic reactions, many groups have leveraged extrusion technology to deconstruct polyesters in the melt state. Haik and co-workers compared RMED with traditional solvent-based PET glycolysis, and their efforts involved melt deconstruction with ethylene glycol in a single screw extruder. Ethylene glycol concentration displayed the greatest influence on the depolymerization extent, while residence time, screw speed, and temperature played secondary roles. Differential scanning calorimetry (DSC) revealed that higher ethylene glycol concentrations decreased PET crystallinity and melting temperature by enhancing the segmental mobility. Furthermore, increased screw speed enhanced deconstruction by reducing crystallinity and increasing the mobile amorphous fraction. , Alternatively, polymers designed to deconstruct under proper mechanical stimuli, such as RMED or ultrasonic treatment, promote facile deconstruction and recovery of pure feedstocks for repolymerization. For example, ring-closing pendant hydroxyls enabled the RMED of a bicyclooctene-derived (BCOE) mechanophore (Figure ). Here, intramolecular transesterification and lactonization reduced polymer molecular weight to produce monomer. Similarly, Ellison and co-workers integrated a ring-closing depolymerization (RCD) process with RMED to recycle the polycaprolactone soft segments of PUs (Figure A). A custom vacuum attachment for a lab-scale TSE enabled reactive distillation, which recovered the volatile, ring-closed lactone monomer for subsequent polymerizations.

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RMED enables BCOE intramolecular transesterification and lactonization, adapted with permission from ref . Copyright 2020 Springer Nature.

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(A) Polycaprolactone RCD, adapted with permission from ref . Copyright 2025 American Chemical Society; (B) Cross-linked PU RMED by carbamate exchange with low-molecular-weight, carbamate containing de-cross-linkers, adapted with permission from ref . Copyright 2024 American Chemical Society.

Jin, Long and co-workers developed a RMED process to rapidly deconstruct and convert cross-linked PUs into functional thermoplastics in the melt state (Figure B). Cross-linked PUs were simultaneously deconstructed and functionalized by reacting with carbamate-containing, functional small molecules, i.e., de-cross-linkers in the presence of Lewis acid catalysts. The catalyzed dissociative carbamate exchange reactions rapidly converted the PU networks into solvent-soluble thermoplastics bearing desired chain-end functionalities within 5 min of RMED at 165 °C, with reaction conditions such as temperature and de-cross-linker concentration controlling the viscosity of the deconstructed polymeric network. Specifically, photoactive methacrylate and anthracene-functionalized de-cross-linkers enabled postdeconstruction reactivity to transform PU waste into value-added products, with application toward other chain-growth or step-growth polymers capable of dynamic exchange reactions.

Chain-growth polymers are inherently more challenging to chemically recycle than step-growth polymers, as their backbones lack heteroatoms that often enable deconstruction reactions. Nonetheless, researchers used zeolite catalysts to induce chain scission and structural modification to depolymerize low density polyethylene (LDPE). This cracking-like RMED reaction decreased molecular weight and increased branching, providing a scalable process to depolymerized LDPE with tunable properties. Others explored polyolefin de-cross-linking through supercritical alcohols and subsequent peroxide-driven cross-linking in the melt state. Here, the radical-driven reaction improved thermal stability and tuned mechanical properties upon an increase in cross-link density (Figure ), however, limiting recycling potential. Together, these earlier studies highlight peroxide-enabled polyolefin RMED. ,

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Cross-linking mechanism PE blends in the presence of radical-forming dicumyl peroxide (DCP), adapted with permission from ref . Copyright 2024 Wiley-VCH.

Cross-linked rubbers, similar to many other commercial thermosets, remain difficult to recycle by conventional processes. RME enables rubber reprocessing through thermal-mechanical shear devulcanization. , Ex-situ infrared (IR) spectroscopy confirmed oxidative degradation as mono-, di- and poly-sulfide linkages cleaved to form various sulfur-containing compounds. Increasing screw speed and RME temperature decreased gel fraction and cross-link density. These parameters were tunable to achieve deconstructed polymers with properties tailored for diverse applications. Overall, these examples of RMED demonstrate the growing role of this platform in advancing polymer sustainability.

RME for Functional Upcycling

Postpolymerization modifications upcycle polymers by attaching functional groups through covalent and noncovalent interactions during either surface or bulk treatment. These modifications bridge mechanical recycling and chemical upcycling by converting polymeric waste into new materials for tailored applications. RME upcycling (RMEU) leverages several distinct mechanisms to extend the polymer service life by modifying the molecular architecture through additives. One pathway, termed RMEU chain extension (RMEU-CE), employs low concentrations of multifunctional chain extenders to covalently couple polymer chains to build molecular weight and increase branching. Alternatively, catalysts and other additives transform thermoplastics and thermosets into vitrimers, termed RMEU to vitrimers (RMEU-V), affording thermoplastic-like melt reprocessability through catalyzing dynamic bond exchange. Together, these approaches enable control over the molecular weight and architecture to advance polymer sustainability through RMEU.

Torres-Giner and co-workers leveraged RMEU-CE to mitigate detrimental effects of melt reprocessing by increasing molecular weight and dispersity, thereby improving melt strength and mechanical performance. The process offers control over crystallinity and degree of branching, together providing tunable properties for diverse applications such as composites and filaments. Low concentrations of a poly­(styrene-co-glycidyl methacrylate) copolymer (PS-co-GMA) enabled PET RMEU-CE to enhance elongation at break and impact strength (Figure ). Here, the copolymer additive chain extended the PET following epoxy ring-opening, restoring properties during the reactive melt processing. Pastor and co-workers upcycled PET with additives that modified rheological properties while maintaining mechanical strength. Melt blending recycled with virgin PET controlled melt viscosity, while PET RME with 5-amino isophthalic acid introduced branching to lower viscosity and improve elastic modulus. Overall, the RMEU supports functional additives for tailored material properties to improve polymer sustainability.

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PET RMEU-CE by PS-co-GMA to increase molecular weight and improve mechanical properties, adapted with permission from ref . Copyright 2020 MDPI.

Vitrimers are emerging as a novel polymer class combining thermoplastic processability with traditional thermoset mechanical performance. ,− Often proposed as thermoset replacements, vitrimers rely on dynamic covalent bond exchange with neighboring functional groups under proper stimuli, enabling network rearrangement, stress relaxation, and thermoplastic-like reprocessing over multiple cycles. , RME’s high temperature and shear promote homogeneous catalyst mixing and dynamic bond exchange to upcycle thermoplastics and thermosets into vitrimers (RMEU-V). This approach enabled thermoplastic polyolefin RMEU-V. In this multistep process, thermoplastic polyolefins were first functionalized with maleic anhydride (Figure A, top) and then subsequently cross-linked with bisphenol A diglycidyl ether (DGEBA, Figure A, middle) to produce polyolefin vitrimers (Figure A, bottom) with rubbery elastic behavior above their melting temperature, enabled with dynamic bond exchange (Figure B). Nicolaÿ and co-workers leveraged RMEU-V to create high-performance materials from polyolefin blends using azidotriazine-based grafting agents that created phase-separated nanostructures at the polyethylene/polypropylene interface, enhancing ductility and thermal stability while imparting melt reprocessability. Others created similar polyolefin vitrimers by RMEU-V PE waste in the presence of peroxides and maleic anhydride. PET RMEU-V with DGEBA and other additives formed a PET vitrimer with improved mechanical properties and excellent reprocessability. Notably, Dichtel and colleagues advanced RMEU-V by creating a PU vitrimer capable of foam-to-foam reprocessing. , Here, zirconium­(IV) acetylacetonate catalyzed dynamic carbamate exchange while azodicarbonamide, a chemical blowing agent, decomposed into gas and formed pores. To create closed-cell PU foam (PUF), molten vitrimer filled a chamber connected to the TSE, and then the pressure was released to generate uniform closed-cell PUF with a consistent morphology. This hybrid RMEU-V/injection molding process offers continuous foam-to-foam reprocessing with consistent bulk density, cell density, pore size, and compression properties for injection molded applications. , Overall, RMEU-V establishes a powerful platform to upcycle traditional polymers into vitrimers, leveraging dynamic covalent chemistry to deliver high-performance materials for continuous reprocessing.

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(A) Polyolefin functionalization with maleic anhydride (top) with subsequent cross-linking upon addition of DGEBA (middle) to yield reprocessable polyolefin vitrimers (bottom). (B) Polyolefin vitrimer dynamic bond exchange through transesterification. Adapted with permission from ref . Copyright 2020 Royal Society of Chemistry.

In Situ RME Characterization Techniques

Emerging in situ characterization techniques are transforming extrusion-based technology by uncoupling the complex effects of chemical conversion, shear, and temperature during reactive extrusion. Traditional in situ process controls define motor torque, melt pressure, and melt temperature during RME. While traditionally viewed as a “black box” offering few opportunities for in-line characterization, advances in in-line FTIR, rheology, Raman, and X-ray diffraction (XRD) track evolving chemo-rheological profiles inside the extruder, whereas in situ molecular weight, composition, and morphological analyses remain challenging. Advances in computational modeling techniques enhance the understanding of these changes during RME and support AI-driven process optimization. , These techniques are fed data by melt stream sampling between the extruder and die, flush-mounted sensors, or specialized measurement sections. Initially developed for polymer synthesis and processing, RME’s modular nature inspires rapid adaptation to illuminate key structure–property–processing relationships during polymer deconstruction.

Technological advances to quantify chemical conversion enable pathways to characterize reaction mechanisms and monitor evolving chemical species. Spectroscopic probes for near-infrared (NIR), mid-infrared (MIR), and attenuated-total-reflection infrared (ATR-IR) spectroscopy are readily installable on the extruder barrel walls to monitor reaction progress. An in-line capillary bypass equipped with MIR and NIR spectroscopy monitored isocyanate conversion during PU synthesis on a lab scale TSE (Figure ), suggesting promise for industrial scale applications. Additionally, a NIR flow-through cell developed for extrusion-based 3D printing provided in situ chemical monitoring of reactive resins and is readily adapted to academic and commercial RME platforms to monitor polymer deconstruction. Other in situ techniques, such as Raman spectroscopy and XRD, offer structural and morphological insight during RME. Gugin and co-workers outfitted a commercial TSE with a Raman spectroscopy probe focused at the screw junction, providing real-time measurements without deadzones. Design modularity enabled sampling at multiple locations along the screw length to synthesize zeolitic imidazolate framework-8 (ZIF-8) in the melt. Additionally, time-resolved in situ (TRIS) XRD using energy-dispersive methods at a synchrotron facility provided insight on solid-state reactivity, kinetics, phase transitions, and crystalline size during RME. A motorized stage enabled movement along the screw axis to optimize process parameters and characterize the intermediate phases and evolving crystal sizes.

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Schematic cross section of lab-scale TSE equipped with a NIR probe, adapted with permission from ref . Copyright 2025 Elsevier.

Rheological measurements play a crucial role in characterizing real-time structural and morphological changes during RME. , Rheology bridges between process parameters including equipment design, shear rate, and reaction conditions (e.g., RME temperature) and material properties including molecular weight and dispersity. Melt viscosity often differs by 4–6 orders-of-magnitude between monomer and polymer forms, making viscosity essential to monitor during deconstruction reactions. Common in-process rheological measurement techniques include slit and capillary rheometry. Slit rheometry, the preferred in-line rheological characterization technique, calculates melt viscosity from the pressure drop and throughput through a slit die (Figure ). Fortunately, low viscosity melts display good agreement between online and off-line data, providing the ideal rheological characterization tool for RMED. Unfortunately, the slit die is incompatible with other die geometries connected in series, limiting application to research and development. Further, the slit die alters the thermomechanical history of the polymer melt, causing discrepancies between online and off-line rheological properties for highly viscous polymer melts. Otherwise, online capillary rheometry samples the polymer melt without interrupting the main flow channel (Figure A). Although oscillatory rheology characterizes complex multiphase systems, its application remains limited, since available instruments are not compatible with relevant polymer melt temperatures and viscosities (Figure B). In situ spectroscopy and rheological techniques offer real-time monitoring of RME reactions, necessary to further enable the platform for polymer deconstruction. ,

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(A) Slit die adapter to mount on the extruder. (B) Slit die. 1, 2: measurement and setup thermocouples, respectively; p_1–4: pressure transducers. Adapted with permission from ref . Copyright 2019 Wiley-VCH.

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(A) Online capillary rheometer featuring (1) the TSE, (2) extruder barrel, (3) rheometer shaft, (4) piston, (5) die, and (6) extruded polymer, adapted with permission from ref . Copyright 2000 Elsevier. (B) Oscillatory rheometer attachment with (1) extruder barrel, (2) rheometer body, (3) TSE port to rheometer, (4) top geometry, (5) bottom geometry, (6) cleaning ring, and (7) linear variable differential transformer, adapted with permission from ref . Copyright 2008 Elsevier.

Summary and Outlook

RME emerges as a viable solution to the longstanding challenges associated with solvent-based polymer deconstruction; that is, adaptability and adherence to green practices drive translational success with rapid melt deconstruction and opportunities for upcycling. Leveraging high shear rates and modest temperatures to accelerate deconstruction reaction rates, RMED employs the precision of traditional solvolytic chemical recycling with the speed, atom-efficiency, and reduced CO₂ emissions of melt extrusion. RME, particularly RMEU-CE and RMEU-V, reduces plastic waste and detrimental environmental impacts by elongating product lifetimes. ,,,,,,− Emerging in situ characterization techniques provide real-time analytics to ensure acceptable evolving properties while advances in computational modeling techniques deepen understanding of chemo-rheological changes during RME. , General advances in heat management, specifically to combat increased heat gradients during process scale-up, motivate RME adoption. Collectively, these features advance the UN SDGs with the promotion of more environmentally friendly synthetic methods, more efficient manufacturing, and enhanced overall polymer sustainability. This area of research focus is rapidly expanding, and this Perspective provides new research directions for RME toward polymer deconstruction and upcycling.

While solvent effects appear extensively in the literature, their comprehensive removal reshapes reactions in ways that remain poorly resolved. , Traditional radical polymerizations tolerate solvent variations without altering core mechanisms, where measured rate laws shift through changes in the local concentration, solvation, and diffusion. For example, atom transfer radical polymerization (ATRP) kinetics respond acutely to solvent choice, where solvents tune redox equilibria and dictate catalyst diffusion, thus altering apparent kinetics while preserving reaction steps. Solvent-free RME introduces shear and mechanical stress that further transform relative reaction rates and product distributions beyond solvent-based precedents. Mechanical energy under solvent-free conditions can produce three distinct outcomes relative to solvated synthesis:

• Solvent-optional reactions yield equivalent products, though selectivity may vary.

• Solvent-dependent reactions: solvation may stabilize critical intermediates (e.g., coordinated water enables quantitative yields from hydrated monomers, whereas anhydrous conditions fail). , Mechanical energy with small amounts of liquid (e.g., liquid-assisted grinding or solvate-assisted grinding) or halide salts unlock otherwise inaccessible pathways. These phenomena are poorly understood and require mechanistic clarification.

• Solid-state exclusive reactions generate novel products undiscovered in solution, potentially driven by absent solvation. ,

Reaction rate and outcome preservation thus demand case-specific evaluation, underscoring the need to elucidate RME-specific chemo-mechanical effects.

RMED modular design drives increased adoption for advancing polymer sustainability. At the laboratory scale, state-of-the-art processes utilize devolatilization zones to selectively recover valuable monomers during melt deconstruction, offering a blueprint for repurposing similar technology at manufacturing scales to efficiently extract high-purity building blocks for future polymerizations. Other modular designs will support polymer deconstruction, leveraging specific mechanical force-responsive functionality to efficiently convert polymer to monomer following RMED. Complementary strategies require the addition of low-molecular-weight de-cross-linkers to concurrently deconstruct a covalent network while introducing chemical functionality specifically engineered for next generation products. Future RMED processes will leverage rapid exchange kinetics to deconstruct networks in the melt state, with promising applicability toward postconsumer PUF waste and other networks capable of dynamic bond exchange. Next generation RMED processes will take advantage of shear-induced thermal-mechanical devulcanization to transform rubber into a versatile feedstock for future applications. Collectively, these advances position RMED as a versatile platform that enables scalable, sustainable, and circular lifecycles for polymers across diverse applications; waste polymeric products will become more versatile as valuable feedstocks for the design of novel products.

Commodity polymers such as polyolefins and polystyrene (PS) lack main-chain reactive, typically electrophilic, functionality, i.e., a carbon–carbon backbone. Most vitrimers rely on main-chain reactive sites to enable dynamic covalent chemistries (DCCs) through esters, urethanes, disulfides, and other reactive functional groups. ,− The strength of these carbon–carbon backbones relegates commodity polymers primarily to mechanical reprocessing. Recent advances demonstrate solvent-free deconstruction to monomer: ball milling cleaves PS and methacrylate derivatives, while cracking and hydrogenation deconstruct polyethylene into low-molecular-weight species rather than ethylene monomer. − RME promises to build directly on these insights through melt deconstruction of polymers with C–C backbones to monomers under continuous shear, thereby revolutionizing sustainability for the most abundant plastic waste streams.

Future research will increasingly employ RME upcycling to extend the service life of commodity polymers. For certain systems, such as PET chain extension with epoxy-containing oligomers, RMEU-CE may offer distinct advantages over RMED by enabling tailored application spaces. The transition toward vitrimers as sustainable alternatives to traditional thermosets will similarly depend on RME-enabled melt processing to achieve closed-loop recyclability. Furthermore, high shear mixing that is intrinsic to RME presents a practical route for converting existing thermoplastics and thermosets into vitrimers through uniform dispersion of exchange-enabling catalysts and other additives. Recent extensions of RMEU-V to include PU foam-to-foam reprocessing exemplify the potential for RME to redefine recyclability for cross-linked polymers historically viewed as irrecoverable; this signals a paradigm shift toward more circular polymer technologies.

Emerging RME characterization techniques will reveal their potential and address key obstacles in modern extrusion technologies. While in situ methods like FTIR, Raman spectroscopy, and more were originally developed for polymer synthesis and processing, their modular design nature enables adaptation toward polymer deconstruction processes. Advances in rheological measurements aim to characterize evolving melt properties during RME without perturbing the main melt flow, ensuring analytical consistency between online and off-line measurements. Future research will focus on in situ molecular weight characterization to provide real-time measurements. Initially developed for extrusion-based 3D printing, machine vision combined with AI-guided feedback and image correlation techniques enable in situ defect detection and real-time optimization. Ultimately, AI will integrate with in situ characterization tools to predict evolving polymer properties during RMED, enabling structure–property–processing relationships. Together, these advances in characterization with integrated AI will provide real-time tuning of RMED processes that deliver unprecedented control over the deconstructed polymer structure and performance.

General advances in RME technology (beyond RMED) motivate adoption and scale-up as innovations in design and process intensification lower cost per unit volume, a key barrier to competing economically with traditional solvent-based processes for polymer deconstruction. Advances in heat management are necessary during process scale-up to combat increased heat gradients and local overheating, especially for highly exothermic or endothermic reactions. These heat gradients are caused by diminished surface area to volume ratios between the polymer melt and screw/barrel surfaces, which are often exacerbated by shear-induced viscous dissipation that promotes side reactions for high-viscosity polymers. ,, In all, future researchers will seek to mitigate these process design bottlenecks at the laboratory scale before implementation on production-scale equipment to fully leverage the sustainability potential of future RME technologies.

Jared Nettles: conceptualization, writing, reviewing and editing; Timothy E. Long: conceptualization, funding acquisition, supervision, writing, review and editing; Kailong Jin: conceptualization, funding acquisition, supervision, writing, review and editing. All authors have given approval to the final version of the manuscript.

The authors declare no competing financial interest.